Negative electrode material, secondary battery and electronic device

Abstract

The present application provides a negative electrode material, a secondary battery, and an electronic device. The secondary battery includes a negative electrode plate, the negative electrode plate includes a negative electrode material, and the negative electrode material includes a composite material. The composite material particles include elemental silicon and carbon material. The composite material has a first-cycle delithiation curve dQ / dV main peak intensity to secondary peak intensity ratio of 1.15 to 1.65. The composite material in the secondary battery provided in the present application meets the above-mentioned characteristics, enabling the secondary battery to have a high specific capacity while also having excellent cycling performance and expansion performance.

Description

Technical Field

[0001] The present application relates to the field of electrochemical technology, and in particular to a negative electrode material, a secondary battery, and an electronic device. Background Art

[0002] Secondary batteries, such as lithium-ion batteries, are widely used in all aspects of life today due to their advantages such as no memory effect, small size, light weight, and environmental friendliness. In recent years, secondary batteries have seen rapid development in new energy vehicles and large-scale energy storage.

[0003] However, among the negative electrode materials of traditional commercial secondary batteries, taking lithium-ion batteries as an example, carbon-based materials such as graphite have a low capacity, resulting in a low energy density of the secondary batteries; while silicon-based materials are easy to expand, resulting in poor cycle performance of the secondary batteries, which greatly limits their large-scale application in secondary batteries. Summary of the Invention

[0004] The purpose of this application is to provide a negative electrode material, a secondary battery, and an electronic device, which enable the secondary battery to have a high specific capacity while also having excellent cycle performance and expansion performance. The specific technical solution is as follows:

[0005] In a first aspect, the present application provides a negative electrode material comprising a composite material, wherein particles of the composite material include elemental silicon and carbon material, wherein the ratio of the dQ / dV main peak intensity to the secondary peak intensity of the first-cycle delithiation curve of the composite material is 1.15 to 1.65, wherein the dQ / dV main peak refers to a characteristic peak located between 0.25V and 0.3V, and the dQ / dV secondary peak refers to a characteristic peak located between 0.4V and 0.45V. The composite material in the negative electrode material provided herein satisfies the above-mentioned characteristics, and the secondary battery exhibits significantly improved cycle performance and expansion performance while maintaining a high specific capacity.

[0006] In some embodiments of the present application, the elemental silicon includes at least one of silicon nanoparticles or silicon submicron particles, which is beneficial to improving the cycle performance and expansion performance of the secondary battery.

[0007] In some embodiments of the present application, based on the total mass of the composite material, the carbon material content a of the composite material is 40 wt% to 90 wt%, and the elemental silicon content b is 10 wt% to 60 wt%. When the carbon material content a and the elemental silicon content b of the composite material are within the above ranges, the cycling performance and expansion performance of the secondary battery are improved.

[0008] In some embodiments of the present application, the carbon material content a of the composite material is 55 wt % to 70 wt %, and the elemental silicon content 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, the cycling performance and expansion performance of the secondary battery are improved.

[0009] In some embodiments of the present application, the ratio of a to b is 1 to 3. When the ratio of a to b is within the above range, it is beneficial to improve the cycle performance and expansion performance of the secondary battery.

[0010] In some embodiments of the present application, 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 material particles satisfy the relationship: c>d>e, the region I is the region of 0.5μm to 1.5μm in the radial direction, the region II is the region of 2.5μm to 3.5μm in the radial direction, and the region III is the region of 4.5μm to 5.5μm in the radial direction, which is beneficial to improving the cycle performance and expansion performance of the secondary battery.

[0011] In some embodiments of the present application, the particle size D of the composite material V 50 is 5μm to 10μm, D V By regulating the particle sizes Dv50 and Dv99 of the composite material within the above range, the cycle performance and expansion performance of the secondary battery are improved.

[0012] In some embodiments of the present application, the specific surface area of ​​the composite material is 1 m 2 / g to 50m 2 The composite material has a specific surface area within the above range, which is beneficial to improving the cycle performance and expansion performance of the secondary battery.

[0013] In some embodiments of the present application, the X-ray diffraction pattern of the composite material does not contain a silicon crystallization peak, which is beneficial to improving the cycle performance and expansion performance of the secondary battery.

[0014] In some embodiments of the present application, in the Raman spectrum of the composite material, the region at 521 cm -1 and 480cm -1 The intensity ratio of the peak at I 521 / I 480 The value of 0.6 to 1 is beneficial to improving the cycle performance and expansion performance of the secondary battery.

[0015] In some embodiments of the present application, the composite material has an oxygen content of 1 wt % to 5 wt % based on the total weight of the composite material. When the oxygen content of the composite material is within the above range, it is beneficial to improve the cycle performance and expansion performance of the secondary battery.

[0016] In some embodiments of the present application, the composite material has a first delithiation specific capacity of 500 mAh / g to 2500 mAh / g. The composite material has a first delithiation specific capacity within the above range, which is beneficial for improving the cycle performance and expansion performance of the secondary battery.

[0017] The second aspect of the present application provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte, wherein the negative electrode sheet comprises the negative electrode material of any of the aforementioned embodiments. Therefore, the secondary battery provided by the present application has good cycle performance and expansion performance.

[0018] In some embodiments of the present application, the secondary battery is cycled for 100 cycles at 25°C using a 1C charge, 0.5C discharge, and 0.025C cutoff cycle profile. The oxygen content of the composite material in the negative electrode plate is 5 wt% to 15 wt% based on the total mass of the composite material in the negative electrode plate. By regulating the oxygen content of the composite material in the negative electrode plate within this range, the cycling performance of the secondary battery is improved.

[0019] The third aspect of the present application provides an electronic device, which includes the secondary battery in any of the aforementioned embodiments. Therefore, the electronic device provided by the present application has good performance.

[0020] Beneficial effects of this application:

[0021] The present application provides a negative electrode material, a secondary battery, and an electronic device. The secondary battery includes a negative electrode plate, the negative electrode plate includes a negative electrode material, and the negative electrode material includes a composite material. The composite material particles include elemental silicon and carbon material. The composite material has a first-cycle delithiation curve dQ / dV main peak intensity to secondary peak intensity ratio of 1.15 to 1.65. The composite material in the secondary battery provided in the present application meets the above-mentioned characteristics, enabling the secondary battery to have a high specific capacity while also having excellent cycling performance and expansion performance.

[0022] Of course, it is not necessary to achieve all the advantages described above at the same time when implementing any product or method of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other embodiments can also be obtained based on these drawings.

[0024] Figure 1 This is the first cycle charge and discharge curve of the composite material in Example 1;

[0025] Figure 2 This is the differential capacity curve of the composite material in Example 1 during the first cycle of lithium removal;

[0026] Figure 3 is a scanning electron microscope (SEM) image of a cross section of the composite material particle in Example 1;

[0027] Figure 4 Schematic diagram of a selected area of ​​a cross section of a composite material particle in Example 1;

[0028] Figure 5 is the X-ray diffraction pattern of the composite material in Example 1. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field based on this application are within the scope of protection of this application.

[0030] It should be noted that in the following description, lithium-ion batteries are used as an example of secondary batteries to explain this application, but the secondary batteries of this application are not limited to lithium-ion batteries. The specific technical solutions are as follows:

[0031] The first aspect of the present application provides a negative electrode material, which includes a composite material. The particles of the composite material include elemental silicon and carbon material. The ratio of the dQ / dV main peak intensity to the secondary peak intensity of the first-cycle delithiation curve of the composite material is 1.15 to 1.65, the dQ / dV main peak refers to a characteristic peak located at 0.25V to 0.3V, and the dQ / dV secondary peak refers to a characteristic peak located at 0.4V to 0.45V.

[0032] The inventors have found that the first cycle charge and discharge curve of the composite material can be obtained by taking the first cycle charge and discharge capacity of the composite material as the horizontal axis and the voltage as the vertical axis. For example, Figure 1The first cycle charge and discharge curve of the composite material in Example 1 is shown. Then, the first-order derivative of the first cycle lithium removal capacity Q of the composite material is calculated against the voltage V, and then the voltage V is plotted to obtain the differential capacity curve. For example, Figure 2 The differential capacity curve of the composite material in Example 1 during the first cycle of lithium removal is shown. The differential capacity curve reflects the capacity of the composite material within a unit voltage range. If the capacity at a certain voltage platform is high, it means that a lot of capacity will be contributed within a very small voltage fluctuation range, and a characteristic peak will appear on the curve. Each characteristic peak represents an electrochemical reaction. The characteristic peak at 0.25V to 0.3V represents the amorphous Li x The characteristic peak of Si delithiation reaction at 0.4V to 0.45V represents the crystalline Li 15 The delithiation reaction of Si4. The stronger the peak intensity of the characteristic peak between 0.4V and 0.45V, the more crystalline Li 15 The more Si4, the more Li 15 The delithiation reaction of Si4 accounts for a high proportion, which in turn deteriorates the cycling performance and expansion performance of the composite material. When the ratio of the dQ / dV main peak intensity to the secondary peak intensity of the first cycle delithiation curve is between 1.15 and 1.65, the secondary battery has a higher specific capacity and improves the cycling performance and expansion performance of the secondary battery.

[0033] Specifically, the ratio of the dQ / dV main peak intensity to the secondary peak intensity of the first-cycle delithiation curve of the composite material can 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 range consisting of any two of the above values. Preferably, the ratio of the dQ / dV main peak intensity to the secondary peak intensity of the first-cycle delithiation curve of the composite material is 1.25 to 1.55. When the ratio of the dQ / dV main peak intensity to the secondary peak intensity of the first-cycle delithiation curve of the composite material is too low (for example, lower than 1.15), the crystalline Li 15 The delithiation reaction of Si4 accounts for a high proportion, which will affect the cycle performance and expansion performance of the composite material. When the ratio of the dQ / dV main peak intensity to the secondary peak intensity of the first cycle delithiation curve of the composite material is too high (for example, higher than 1.65), the amorphous Li x A high proportion of Si delithiation reactions affects the specific capacity and energy density of the composite material. By regulating the ratio of the primary and secondary peak intensities of the composite material's first-cycle delithiation curve within the above range, the secondary battery can maintain a high specific capacity while also improving its cycling and expansion performance.

[0034] In general, the negative electrode material provided in the present application comprises a composite material whose particles include elemental silicon and carbon material, and the ratio of the dQ / dV main peak intensity to the secondary peak intensity of the first-cycle delithiation curve of the composite material is 1.15 to 1.65, and the obtained secondary battery has good cycle performance and expansion performance.

[0035] In some embodiments of the present application, elemental silicon includes at least one of silicon nanoparticles or silicon submicron particles. The use of the above-mentioned elemental silicon is beneficial to alleviate the breakage and pulverization of silicon particles, increase the transmission rate of active ions such as lithium ions, and improve the cycle performance and expansion performance of the secondary battery. For example, Figure 3 A scanning electron microscope (SEM) image of a cross section of the composite material particle in Example 1 is shown.

[0036] In some embodiments of the present application, based on the total mass of the composite material, the content a of the carbon material of the composite material is 40wt% to 90wt%, and the content b of elemental silicon is 10wt% to 60wt%. Preferably, the content a of the carbon material of the composite material is 55wt% to 70wt%, and the content b of elemental silicon is 30wt% to 45wt%. For example, a can be 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, 85wt%, 90wt% or a range consisting of any two of the above values, and b can be 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt% or a range consisting of any two of the above values. By regulating the values ​​of a and b in the above range, it is possible to take into account the gram capacity of the composite material as well as the cycle performance and expansion performance.

[0037] In some embodiments of the present application, the ratio of a to b is 1 to 3. For example, the ratio of a to b can be 1, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, 2.8, 3, or a range consisting of any two of the above values. By regulating the ratio of a to b within the above range, the composite material can have a smaller volume effect, reduce the particle expansion rate, and improve the cycle performance and expansion performance of the secondary battery.

[0038] In some embodiments of the present application, 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 material particle satisfy the relationship: c>d>e. Wherein, region I is the region of 0.5 μm to 1.5 μm in the radial direction, region II is the region of 2.5 μm to 3.5 μm in the radial direction, and region III is the region of 4.5 μm to 5.5 μm in the radial direction. For example, Figure 4A schematic diagram of a selected region of the cross-section of the composite material particles in Example 1 is shown. By regulating the silicon content c in region I, d in region II, and e in region III of the composite material particle cross-section to satisfy the above relationship, the composite material can exhibit a certain silicon concentration gradient, which facilitates stress release in the overall material, significantly reduces the expansion rate of the silicon material, and improves the cycling performance and expansion performance of the secondary battery.

[0039] In some embodiments of the present application, the particle size D of the composite material V 50 is 5μm to 10μm, D V 99 is 15μm to 25μm. For example, the particle size D V 50 can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm or a range consisting of any two of the above values, D V 99 can be 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm, 24μm, 25μm, or a range consisting of any two of the above values. By regulating the particle size Dv50 and Dv99 of the composite material within the above range, the dispersion uniformity of the slurry can be improved, the transport of active ions can be improved, and thus the cycling performance and expansion performance of the secondary battery can be improved.

[0040] In this application, Dv50 represents the particle size at which the volume accumulation reaches 50% in the volume-based particle size distribution of the material, and Dv99 represents the particle size at which the volume accumulation reaches 99% in the volume-based particle size distribution of the material, starting from the small particle size.

[0041] In some embodiments of the present application, the specific surface area of ​​the composite material is 1 m 2 / g to 50m 2 / g. For example, the specific surface area of ​​the composite material can be 1m 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 The composite material has a specific surface area within the above range, which can reduce side reactions between the composite material and the electrolyte, and is beneficial to improving the cycle performance and expansion performance of the secondary battery.

[0042] In some embodiments of the present application, the X-ray diffraction pattern of the composite material does not contain any crystalline peak of silicon. That is, the silicon in the composite material exists in an amorphous form. For example, Figure 5 The X-ray diffraction pattern of the composite material in Example 1 is shown. The silicon in the composite material meets the above requirements and can have a large space within the silicon material, thereby absorbing the volume expansion of silicon when lithium is inserted, which is beneficial to improving the cycle performance and expansion performance of the secondary battery.

[0043] In some embodiments of the present application, the Raman spectrum of the composite material is located at 521 cm -1 and 480cm -1 The intensity ratio of the peak at I 521 / I 480 For example, at 521cm -1 and 480cm -1 The intensity ratio of the peak at I 521 / I 480 The value may be 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1 or a range consisting of any two of the above values. -1 and 480cm -1 The intensity ratio of the peak at I 521 / I 480 When the above range is met, a relatively higher amorphous silicon content can be achieved, which is beneficial for improving the cycle performance and expansion performance of the secondary battery.

[0044] In some embodiments of the present application, the oxygen content of the composite material is 1 wt% to 5 wt% based on the total weight of the composite material. For example, the oxygen content of the composite material can 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 range consisting of any two of the foregoing values. When the oxygen content of the composite material is within the foregoing range, the Li2O generated during the initial lithium insertion process can serve as a buffer, which is beneficial for improving the cycle performance and expansion performance of the secondary battery.

[0045] In some embodiments of the present application, the composite material has an initial delithiation specific capacity of 500 mAh / g to 2500 mAh / g. For example, the initial delithiation specific capacity of the composite material can 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 range consisting of any two of the above values. When the initial delithiation specific capacity of the composite material is within the above range, it can take into account the gram capacity of the composite material as well as the cycle performance and expansion performance.

[0046] The present application does not particularly limit the preparation method of the composite material. For example, the preparation method of the composite material may include but is not limited to the following steps: placing a porous carbon material in a reaction apparatus, introducing a silicon-containing gas, causing the silicon-containing gas to pyrolyze and deposit into elemental silicon in the pores of the carbon material, and then introducing a carbon source gas, causing the carbon source gas to pyrolyze and deposit into amorphous carbon, thereby obtaining 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, or 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, or butane.

[0047] Generally, the ratio of the dQ / dV main peak intensity to the secondary peak intensity of the composite material's first-cycle delithiation curve can be controlled by changing the pyrolysis temperature, gas flow rate, and the time of introducing the silicon-containing gas. For example, increasing the pyrolysis temperature decreases the ratio of the dQ / dV main peak intensity to the secondary peak intensity; decreasing the pyrolysis temperature increases the ratio of the dQ / dV main peak intensity to the secondary peak intensity; increasing the gas flow rate decreases the ratio of the dQ / dV main peak intensity to the secondary peak intensity; decreasing the gas flow rate increases the ratio of the dQ / dV main peak intensity to the secondary peak intensity; extending the time of introducing the silicon-containing gas decreases the ratio of the dQ / dV main peak intensity to the secondary peak intensity; and shortening the time of introducing the silicon-containing gas increases the ratio of the dQ / dV main peak intensity to the secondary peak intensity. Technicians can adjust the pyrolysis temperature of the silicon-containing gas or carbon source gas, the gas flow rate of the silicon-containing gas or carbon source gas, and the introduction time of the silicon-containing gas or carbon source gas as needed. For example, the pyrolysis temperature of the silicon-containing gas or carbon source gas is 400°C to 800°C, the gas flow rate of the silicon-containing gas or carbon source gas is 50sccm to 500sccm, the time for introducing the silicon-containing gas is 1h to 20h, and the time for introducing the carbon source gas is 1h to 20h.

[0048] The second aspect of the present application provides a secondary battery comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte, wherein the negative electrode sheet comprises the negative electrode material of any of the aforementioned embodiments. Therefore, the secondary battery provided by the present application has good cycle performance and expansion performance.

[0049] In some embodiments of the present application, the secondary battery is cycled for 100 cycles at 25°C with a cycle regime of 1C charge, 0.5C discharge, and 0.025C cutoff. The oxygen content of the composite material in the negative electrode sheet is 5wt% to 15wt% based on the total mass of the composite material in the negative electrode sheet. For example, the oxygen content of the composite material in the negative electrode sheet can be 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt% or a range consisting of any two of the above values. By regulating the oxygen content of the composite material in the negative electrode sheet for 100 cycles within the above range, the structural deformation of the composite material during the charge and discharge process can be suppressed, which is beneficial to improving the cycle performance of the secondary battery.

[0050] The negative electrode plate of the present application may also include a binder. The present application does not particularly limit the binder, as long as it can achieve the purpose of the present application. For example, the binder may include but is not limited to at least one of polyacrylate, polyimide, polyamide, polyamide-imide, polyvinylidene fluoride, polystyrene butadiene copolymer (styrene-butadiene rubber), sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, sodium hydroxymethyl cellulose, or potassium hydroxymethyl cellulose. By selecting the above binder, the obtained negative electrode plate has good structural stability, which is conducive to improving the cycle performance of the secondary battery.

[0051] The negative electrode sheet of the present application may also include a conductive agent. This application does not specifically limit the conductive agent, as long as it can achieve the purpose of this application. For example, the conductive agent may include at least one of acetylene black, conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fiber, flake graphite, Ketjen black, or graphene. This application does not specifically limit the mass ratio of the negative electrode material, conductive agent, and binder. Those skilled in the art can select according to actual needs, as long as it can achieve the purpose of this application.

[0052] The negative electrode sheet of the present application includes a negative electrode current collector. The present application has no particular restrictions on the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, it can include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam or composite current collector (such as carbon copper composite current collector, nickel copper composite current collector, titanium copper composite current collector, etc.). The present application has no particular restrictions on the thickness of the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, the thickness of the negative electrode current collector is 6μm to 12μm. The present application has no particular restrictions on the thickness of the negative electrode sheet, as long as the purpose of the present application can be achieved. For example, the thickness of the negative electrode sheet is 50μm to 150μm.

[0053] In the present application, the secondary battery also includes a positive electrode plate, and the positive electrode plate includes a positive electrode current collector and a positive electrode material layer arranged on at least one surface of the positive electrode current collector. The above-mentioned "positive electrode material layer arranged on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be arranged on one surface of the positive electrode current collector along the thickness direction of itself, or can be arranged on two surfaces of the positive electrode current collector along the thickness direction of itself. It should be noted that the "surface" here can be the entire area of ​​the positive electrode current collector or a partial area of ​​the positive electrode current collector. This application has no special restrictions, as long as the purpose of this application can be achieved. This application has no special restrictions on the positive electrode current collector, as long as the purpose of this application can be achieved. For example, it can include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector). The positive electrode material layer includes a positive electrode active material. This application has no particular restrictions on the positive electrode active material, as long as the purpose of this application can be achieved. For example, the positive electrode active material may include lithium nickel cobalt manganese oxide (such as common NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganate, lithium iron manganese phosphate or lithium titanate. The positive electrode material layer also includes a conductive agent and a binder. This application has no particular restrictions on the types of conductive agents and binders, as long as the purpose of this application can be achieved. For example, it can be at least one of the above-mentioned conductive agents and binders. This application has no particular restrictions on the mass ratio of the positive electrode active material, conductive agent and binder in the positive electrode material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved. This application has no particular restrictions on the thickness of the positive current collector and the positive electrode material layer, as long as the purpose of this application 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. The application does not specifically limit the thickness of the positive electrode sheet, as long as it can achieve the purpose of this application. For example, the thickness of the positive electrode sheet is 50 μm to 150 μm.

[0054] In the present application, the secondary battery also includes a separator to separate the positive electrode plate and the negative electrode plate, prevent internal short circuit of the secondary battery, allow electrolyte ions to pass freely, and do not affect the electrochemical charge and discharge process. The present application has no special restrictions on the separator, as long as the purpose of the present application can be achieved. For example, the material of the separator may include but is not limited to polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyester (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or aramid at least one; the type of separator may include at least one of a woven membrane, a non-woven membrane, a microporous membrane, a composite membrane, a rolled membrane or a spun membrane.

[0055] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven fabric, film, or composite film having a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixed 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, for example, include at least one of aluminum oxide, 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, or barium sulfate. The binder is not particularly limited and may, for example, be at least one of the above binders. The polymer layer contains polymers, 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).

[0056] In the present application, the secondary battery also includes an electrolyte, and the electrolyte includes a lithium salt and a non-aqueous 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(oxalatoborate) (LiBOB) or lithium difluoroborate. The present application does not particularly limit the concentration of the lithium salt in the electrolyte, as long as the purpose of the present application can be achieved. For example, the concentration of the lithium salt in the electrolyte is 0.9mol / L to 1.5mol / L. Exemplarily, the concentration of the lithium salt in the electrolyte can be 0.9mol / L, 1.0mol / L, 1.1mol / L, 1.3mol / L, 1.5mol / L or a range consisting of any two of the above values. The application has no particular restrictions on non-aqueous solvents, as long as the purpose of the application can be achieved, for example, can include but not limited to at least one of carbonate compounds, carboxylate compounds, ether compounds or other organic solvents. Above-mentioned carbonate compounds can include but not limited to at least one of linear carbonate compounds, cyclic carbonate compounds or fluorinated carbonate compounds. Above-mentioned linear carbonate compounds can include but not limited to at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC) or methyl ethyl carbonate (MEC). Above-mentioned cyclic carbonate can include but not limited to at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) or vinyl ethylene carbonate (VEC). The fluorinated carbonate 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, or trifluoromethylethylene carbonate. The above-mentioned carboxylate compound may include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerolactone, or caprolactone. The ether compound may include, but is not limited to, at least one of dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran.The above-mentioned other organic solvents may include but are not limited to at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate.

[0057] The secondary battery of this application also includes a packaging bag for containing the positive electrode sheet, separator, negative electrode sheet, and electrolyte, as well as other components of the secondary battery known in the art. This application does not limit these other components. This application does not specifically limit the packaging bag and can be any packaging bag known in the art, as long as it can achieve the purpose of this application.

[0058] The secondary battery of the present application is not particularly 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.

[0059] The preparation process of the secondary battery of the present application is well known to those skilled in the art and is not particularly limited in the present application. For example, it may include but is not limited to the following steps: stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and winding, folding and other operations as needed to obtain an electrode assembly with a wound structure, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain a secondary battery; or stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and then fixing the four corners of the entire stacked structure with tape to obtain an electrode assembly with a stacked structure, placing the electrode assembly in a packaging bag, injecting the electrolyte into the packaging bag and sealing it to obtain a secondary battery. In addition, as needed, overcurrent protection elements, guide plates, etc. can also be placed in the packaging bag to prevent pressure rise and overcharge and discharge inside the secondary battery.

[0060] The third aspect of the present application provides an electronic device, which includes the secondary battery in any of the aforementioned embodiments. Therefore, the electronic device provided by the present application has good performance.

[0061] The electronic device of the present application is not particularly limited and can be any electronic device known in the art. In some embodiments, the electronic device may include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0062] Example

[0063] The following examples and comparative examples are provided to more specifically illustrate the embodiments of the present invention. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0064] Test methods and equipment:

[0065] Test of elemental silicon content:

[0066] The content of elemental silicon in the composite material can be tested with the help of inductively coupled plasma spectrometer (ICP) characterization.

[0067] Test of silicon content in regions I, II and III in the cross section of composite particles:

[0068] Conductive adhesive was applied to the sample stage. A powdered sample of the composite material from each example was spread flat on the adhesive. Unattached powder was blown off with an ear bulb. The sample was then sprayed with gold. The powdered sample particles were cross-sectioned using argon plasma. Scanning electron micrographs of the powdered sample were obtained using a Philips XL-30 field-emission scanning electron microscope equipped with energy dispersive X-ray spectroscopy (EDS) at an accelerating voltage of 10 kV and an emission current of 10 mA. The silicon mass percentage of the particles was then measured in regions I, II, and III of the SEM images.

[0069] Specific capacity test:

[0070] Preparation of the negative electrode sheet: The composite material described in this application is 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 is 70:20:10. The negative electrode active material, acetylene black, and sodium alginate aqueous solution are thoroughly mixed to form a slurry. The slurry is evenly coated on copper foil and dried to form the negative electrode sheet.

[0071] Preparation of the positive electrode sheet: Super P is used as the conductive agent and PVDF is used as the binder. The mass ratio of the positive electrode active material (LiFePO4), Super P, and PVDF is 70:20:10. The positive electrode active material, Super P, and 10wt% PVDF solution are thoroughly mixed to form a slurry. The mixture is evenly coated on aluminum foil and dried to form the positive electrode sheet.

[0072] A mixture of ethylene carbonate / dimethyl carbonate (EC / DMC, volume ratio of 1:1) dissolved in 1 mol / L LiPF6 and 5 vol% fluoroethylene carbonate (FEC) was used as the electrolyte, a Celgard 2400 separator was used, and a lithium sheet was used as the counter electrode to assemble a button-type half-cell in a glove box, and a positive electrode sheet was used as the counter electrode to assemble a button-type full cell in a glove box.

[0073] On the LAND CT2001A battery test system, half-cell and full-cell charge and discharge tests were performed separately. Among them, the half-cell test adopts an operating voltage range of 0.01V to 2V, discharges at a constant current of 0.1C to 0.01V, stands for 5min, then discharges at a constant current of 50μA to 0.01V, stands for 5min, charges at a constant current of 0.1C to 2.0V, stands for 5min, and records the first charge capacity of the half-cell as the first delithiation specific capacity; the full-cell test adopts an operating voltage range of 2.4V to 3.8V, charges at a constant current of 0.1C to 3.8V, then charges at a constant voltage of 3.8V to 50μA cutoff, stands for 5min, discharges at a constant current of 0.1C to 2.4V, stands for 5min, and records the first discharge capacity of the full-cell. The first discharge specific capacity of the full-cell = the first discharge capacity of the full-cell / the mass of the positive electrode active material.

[0074] Test of oxygen content in the composite material of the negative electrode after 100 cycles:

[0075] The secondary battery that had been cycled 100 times was disassembled, and the negative electrode was obtained. It was placed in a glove box to dry naturally, and then the powder was carefully scraped off with a knife. Finally, the oxygen content was tested using a German Elementar elemental analyzer.

[0076] Test of thickness expansion rate of negative electrode sheet:

[0077] The secondary battery was disassembled before and after 100 cycles, and the negative electrode sheets were obtained. The thickness of the sheet was measured 12 times with a vernier caliper and the average value was taken. If the copper foil thickness is a, the sheet thickness before 100 cycles is b, and the sheet thickness after 100 cycles is c, then the thickness expansion rate k of the negative electrode sheet after 100 cycles is: k = (cb) / (ba) × 100%.

[0078] Cycle capacity retention test:

[0079] At 25°C, discharge the half-cell at a constant current of 0.5C to 0.01V, let it rest for 5 minutes, then discharge it at a constant current of 50μA to 0.01V, let it rest for 5 minutes, and charge it at a constant current of 0.5C to 2.0V, let it rest for 5 minutes. Record the discharge capacity of the first cycle. Then, perform 50 charge and discharge cycles using the same procedure, and record the discharge capacity at the 50th cycle.

[0080] Capacity retention rate of half-cell after 50 cycles (%) = (discharge capacity at the 50th cycle / discharge capacity at the first cycle) × 100%.

[0081] In a 25°C environment, charge the battery at a constant current of 0.5C to 3.8V, then charge it at a constant voltage of 3.8V to a cutoff of 50μA. Let it rest for 5 minutes. Discharge it at a constant current of 0.5C to 2.4V, let it rest for 5 minutes, and record the discharge capacity of the first cycle. Then, perform 100 cycles of charge and discharge using the same steps, and record the discharge capacity of the 100th cycle.

[0082] Full battery 100-cycle capacity retention rate (%) = (discharge capacity at the 100th cycle / discharge capacity at the first cycle) × 100%.

[0083] Example 1

[0084] <Preparation of Composite Materials>

[0085] 25 g of porous carbon material was placed in a reaction instrument, and monosilane was introduced at 500°C and a flow rate of 200 sccm for 10 hours to cause the monosilane to be thermally decomposed and deposited into elemental silicon in the pores of the porous carbon material. Then, acetylene was introduced at 500°C and a flow rate of 200 sccm for 5 hours to cause the acetylene to be thermally decomposed and deposited into amorphous carbon, thereby obtaining a composite material.

[0086] <Preparation of negative electrode sheet>

[0087] The composite material in this application is 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 is 70:20:10. The negative electrode active material and acetylene black are fully mixed in proportion and then ground evenly. Sodium alginate aqueous solution is added in proportion and stirred for 4 hours. The mixture slurry is then evenly coated on copper foil and vacuum dried at 70°C for 12 hours. It is then punched into a circular electrode sheet with a diameter of 10 mm. The loading amount of the negative electrode active material is 1.0 mg cm -2 .

[0088] <Preparation of positive electrode sheet>

[0089] Super P was used as a conductive agent and PVDF as a binder. The mass ratio of the positive electrode active material (LiFePO4), Super P, and PVDF was 70:20:10. The positive electrode active material and Super P were thoroughly mixed and ground uniformly. A 10 wt% PVDF solution was added and stirred for 4 hours. The mixture was then evenly coated on aluminum foil and vacuum-dried at 70°C for 12 hours. The resulting circular electrode sheets were punched out with a diameter of 10 mm. The positive electrode active material loading was 7.0 mg cm -2 .

[0090] <Preparation of Electrolyte>

[0091] In a dry argon atmosphere glove box, a mixture of ethylene carbonate / dimethyl carbonate (EC / DMC, volume ratio of 1:1) containing 1 mol / L of LiPF6 and a mixture containing 5 vol% of fluoroethylene carbonate (FEC) were mixed to obtain an electrolyte.

[0092] <Preparation of Separator>

[0093] A porous polyethylene film with a thickness of 20 μm (supplied by Celgard) was used.

[0094] <Preparation of lithium-ion batteries>

[0095] The negative electrode sheet is used as the counter electrode with the lithium sheet and the positive electrode sheet as the counter electrode, and button half-cells and full batteries are assembled in a glove box in the order of negative electrode sheet, isolation membrane, lithium sheet or positive electrode sheet.

[0096] Example 2 to Example 8

[0097] Except that the relevant preparation parameters in <Preparation of composite material> were adjusted according to Table 1, the rest were the same as in Example 1.

[0098] Comparative Examples 1 to 4

[0099] Except that the relevant preparation parameters in <Preparation of composite material> were adjusted according to Table 1, the rest were the same as in Example 1.

[0100] Comparative Example 5

[0101] Except for preparing the negative electrode active material according to the following steps, the rest is the same as Example 1.

[0102] <Preparation of Composite Materials>

[0103] First, fumed silica (fumed silica) with an average particle size of 0.05 μm is used as silica powder, and metallic silicon with an average particle size of 5 μm that has been crushed using a jet mill is used as metallic silicon powder, and the mixture is mixed at a molar ratio of metallic silicon powder to silica powder = 1.01. The obtained mixed powder is loaded into a reaction apparatus and heated at a temperature of 1420°C at 40 Pa under reduced pressure to generate silicon monoxide gas. The generated silicon monoxide gas is precipitated on the surface of a stainless steel precipitation substrate, thereby obtaining a silicon oxide block. The obtained silicon oxide is crushed using a ball mill, thereby obtaining a block with an average particle size of 5 μm and a specific surface area of ​​4.8 m 2 / g of silicon oxide powder (SiO x ∶x=1.02). Next, 200g of the obtained silicon oxide powder was placed in a silicon nitride tray and allowed to stand in a treatment furnace capable of maintaining a stable atmosphere. Argon gas was then introduced to replace the interior of the treatment furnace with argon. A methane-argon mixture was then introduced at 2 NL / min. The temperature was raised at a rate of 300°C / hour, and the temperature was maintained at 600°C to 1000°C for 3 to 10 hours. After the temperature was maintained at room temperature, the temperature was lowered and the powder was recovered.

[0104] The preparation parameters, powder performance parameters and electrical performance parameters of each embodiment and comparative example are shown in Table 1, Table 2 and Table 3.

[0105] Table 1

[0106]

[0107] Table 2

[0108]

[0109]

[0110] Table 3

[0111]

[0112] Referring to Tables 1, 2, and 3, it can be seen from Examples 1 to 8 and Comparative Examples 1 to 4 that the ratio of the dQ / dV main peak intensity to the secondary peak intensity of the first-cycle delithiation curve of the composite material is too small (e.g., Comparative Examples 1 to 3). Although the lithium-ion battery has a high specific capacity, its cycle performance and expansion performance are significantly reduced. The ratio of the dQ / dV main peak intensity to the secondary peak intensity of the first-cycle delithiation curve of the composite material is too large (e.g., Comparative Example 4). Although the lithium-ion battery has relatively good cycle performance and expansion performance, the specific capacity is significantly reduced. By regulating the ratio of the dQ / dV main peak intensity to the secondary peak intensity of the first-cycle delithiation curve of the composite material within the scope of this application, the lithium-ion battery can have a high specific capacity while also having excellent cycle performance and expansion performance.

[0113] It can be seen from Examples 1 to 8 and Comparative Example 5 that, compared with existing composite materials, the composite material of the present application has higher specific capacity and more excellent cycle performance and expansion performance, thereby showing more outstanding lithium storage performance.

[0114] It can also be seen from Examples 1, 3, 4, 5, 6 and 7 that by regulating the ratio of the dQ / dV main peak intensity to the secondary peak intensity of the first-cycle delithiation curve to be within the range of 1.25 to 1.55, it is beneficial to further balance the specific capacity, cycle performance and expansion performance of the lithium-ion battery, thereby improving the overall performance of the lithium-ion battery.

[0115] After cycling a lithium-ion battery, the oxygen content of the composite material in the negative electrode sheet also affects the cycling performance of the lithium-ion battery. As can be seen from Examples 1 to 7 and Example 8, regulating the oxygen content of the composite material in the negative electrode sheet after cycling within the scope of this application can 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.

[0116] Composite material D V 50. D V 99. The specific surface area and the ratio of carbon material to elemental silicon usually also affect the performance of lithium-ion batteries. From Examples 1 to 8, it can be seen that by controlling the D V 50. D V 99.D V 50 / D V 99. The ratio of carbon material to elemental silicon is within the range of this application, which is conducive to obtaining a lithium-ion battery with excellent specific capacity, cycle performance and expansion performance.

[0117] The above description is only a preferred embodiment of the present application and is not intended to limit the scope of protection of the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application are included in the scope of protection of the present application.

Claims

1. A negative electrode material, comprising a composite material, wherein particles of the composite material include elemental silicon and carbon material, wherein a ratio of a dQ / dV main peak intensity to a secondary peak intensity of a first-cycle delithiation curve of the composite material is 1.15 to 1.65, wherein the dQ / dV main peak is a characteristic peak located between 0.25V and 0.3V, and the dQ / dV secondary peak is a characteristic peak located between 0.4V and 0.45V; Based on the total mass of the composite material, the carbon material content a of the composite material is 40wt% to 90wt%, the elemental silicon content b is 10wt% to 60wt%, and the ratio of a to b is 1 to 3; 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 material particle satisfy the relationship: c>d>e, the region I is the region of 0.5 μm to 1.5 μm in the radial direction, the region II is the region of 2.5 μm to 3.5 μm in the radial direction, and the region III is the region of 4.5 μm to 5.5 μm in the radial direction; The particle size D of the composite material V 50 is 5μm to 10μm, D V 99 is 15μm to 25μm.

2. The negative electrode material according to claim 1, wherein The elemental silicon includes at least one of silicon nanoparticles or silicon submicron particles.

3. The negative electrode material according to claim 1, wherein The carbon material content a of the composite material is 55 wt % to 70 wt %, and the elemental silicon content b is 30 wt % to 45 wt %.

4. The negative electrode material according to claim 1, wherein The composite material satisfies at least one of the following conditions: (1) The specific surface area of ​​the composite material is 1m 2 / g to 50m 2 / g; (2) The X-ray diffraction pattern of the composite material does not contain a silicon crystallization peak; (3) In the Raman spectrum of the composite material, the -1 and 480cm -1 The intensity ratio of the peak at I 521 / I 480 0.6 to 1; (4) Based on the total mass of the composite material, the oxygen content of the composite material is 1 wt% to 5 wt%; (5) The initial delithiation specific capacity of the composite material is 500 mAh / g to 2500 mAh / g. 5 . A secondary battery comprising a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the negative electrode sheet comprises the negative electrode material according to claim 1 .

6. The secondary battery according to claim 5, wherein The secondary battery is cycled for 100 cycles at 25° C. with a cycle regime of 1C charge, 0.5C discharge, and 0.025C cutoff. Based on the total mass of the composite material in the negative electrode plate, the oxygen content of the composite material in the negative electrode plate is 5 wt % to 15 wt %. 7 . An electronic device comprising the secondary battery according to claim 5 .

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