Anode strips, electrochemical and electronic devices

Abstract

The present invention provides a negative electrode piece, an electrochemical device, and an electronic device, the negative electrode piece comprising a negative electrode active material layer, the negative electrode active material layer comprising a negative electrode active material, the negative electrode active material comprising a carbon-doped silicon oxygen composite material and graphite, the carbon-doped silicon oxygen composite material comprising carbon, silicon, and oxygen, the carbon content in the surface region (12) of the carbon-doped silicon oxygen composite particle (10) being greater than the carbon content in the inner region (13) of the carbon-doped silicon oxygen composite particle, the mass percentage of carbon in the carbon-doped silicon oxygen composite material being 2% to 10% based on the total mass of carbon, silicon, and oxygen. The carbon-doped silicon oxygen composite material in the negative electrode piece has good expansion performance and is resistant to powdering, and the negative electrode piece has good electrical conductivity, which is advantageous for improving the cycle performance and expansion performance of the electrochemical device.

Description

[Technical Field]

[0001] The present invention relates to the electrochemical technology field, and more particularly to negative electrode strips, electrochemical devices and electronic devices. [Background technology]

[0002] Lithium-ion batteries have the characteristics of high operating voltage, high energy density, long cycle life, and a wide operating temperature range, etc. Due to these excellent properties, lithium-ion batteries are widely used in three areas: consumer electronics, power batteries, and energy storage.

[0003] Silicon materials have a high theoretical gram capacity and are therefore expected to be widely used in lithium-ion batteries. However, during charge-discharge cycles, silicon materials undergo a volume expansion of 120% to 300% as they absorb and release lithium ions. This causes the silicon material to pulverize and detach from the negative electrode current collector, resulting in poor conductivity of the negative electrode and affecting the cycle performance of lithium-ion batteries. Summary of the Invention

[0004] The present invention aims to provide an electrochemical device and an electronic device for improving the cycle performance of the electrochemical device. Specific technical solutions are as follows:

[0005] A first aspect of the present invention provides an anode piece, the anode piece comprising an anode active material layer, the anode active material layer comprising an anode active material, the anode active material comprising a carbon-doped silicon oxygen composite material and graphite, the carbon-doped silicon oxygen composite material comprising elemental carbon, elemental silicon, and elemental oxygen, the carbon content in the surface region of a particle of the carbon-doped silicon oxygen composite material being greater than the carbon content in the internal region of the particle of the carbon-doped silicon oxygen composite material, the surface region being a region extending from the surface of the particle to a depth of 500 nm, the internal region being a region of the particle excluding the surface region, and the mass percentage of the carbon in the carbon-doped silicon oxygen composite material being 2% to 10% based on the total mass of the elemental carbon, elemental silicon, and elemental oxygen in the carbon-doped silicon oxygen composite material. The carbon-doped silicon oxygen composite material in the negative electrode piece provided by the present invention introduces carbon element, and the carbon element content in the surface region of the carbon-doped silicon oxygen composite particle is greater than the carbon element content in the inner region of the carbon-doped silicon oxygen composite particle. By controlling the mass percentage of carbon element in the carbon-doped silicon oxygen composite material within the above range, the carbon-doped silicon oxygen composite material in the negative electrode piece has good expansion performance and is not easily powdered. The negative electrode piece has good electrical conductivity, which is beneficial to improving the cycle performance and expansion performance of the electrochemical device.

[0006] In some embodiments of the present invention, the mass percentage of the carbon element in the surface region is 0.5% to 8% based on the total mass of the carbon, silicon, and oxygen elements in the carbon-doped silicon oxygen composite material. By controlling the mass percentage of the carbon element in the surface region of the carbon-doped silicon oxygen composite material within this range, the carbon-doped silicon oxygen composite material in the negative electrode piece has good expansion performance and is less likely to powder, and the negative electrode piece has good electrical conductivity, which is advantageous for improving the cycle performance and expansion performance of the electrochemical device.

[0007] In some embodiments of the present invention, the mass percentage of the silicon in the carbon-doped silicon-oxygen composite material is 40% to 60% based on the total mass of the carbon, silicon, and oxygen elements in the carbon-doped silicon-oxygen composite material. By controlling the mass percentage of the silicon in the carbon-doped silicon-oxygen composite material within the above range, the resulting electrochemical device has good cycle performance and expansion performance, as well as a relatively high energy density.

[0008] In some embodiments of the present invention, the carbon-doped silicon oxygen composite material has a particle size distribution in the range of 0.2 μm to 20 μm, a Dv50 of 4 μm to 10 μm, and a Dv99 of 13 μm to 20 μm. Controlling the particle size distribution range, Dv50, and Dv99 of the carbon-doped silicon oxygen composite material within the above ranges is advantageous for improving the cycle performance of electrochemical devices.

[0009] In some embodiments of the present invention, the carbon-doped silicon oxygen composite material has a powder electrical conductivity of 0.03 S / cm to 8 S / cm, which is advantageous for improving the cycle performance of electrochemical devices.

[0010] In some embodiments of the present invention, the particles of the carbon-doped silicon oxygen composite material form Si-C bonds in the interior region and Si-O-C bonds in the surface region, which are advantageous for improving the cycling and expansion performance of electrochemical devices.

[0011] In some embodiments of the present invention, the mass content of carbon element in the surface region of the carbon-doped silicon oxygen composite particles is 10% to 80% of the mass content of carbon element in the carbon-doped silicon oxygen composite material. Controlling the mass content of carbon element in the surface region to the mass content of carbon element in the carbon-doped silicon oxygen composite material within the above range is advantageous for improving the cycle performance and expansion performance of the electrochemical device.

[0012] In some embodiments of the present invention, the distribution of silicon and oxygen elements in the particles of the carbon-doped silicon oxygen composite material is uniform, which is beneficial to improving the cycle performance and expansion performance of electrochemical devices.

[0013] In some embodiments of the present invention, the graphite includes at least one of natural graphite, artificial graphite, mesocarbon microbeads, etc. The selection of the above graphite is advantageous for improving the cycle performance of the electrochemical device.

[0014] In some embodiments of the present invention, the mass ratio of the carbon-doped silicon oxygen composite material to the graphite is (3 to 20):(80 to 97). Controlling the mass ratio of the carbon-doped silicon oxygen composite material to the graphite within the above range is advantageous for improving the cycle performance of the electrochemical device.

[0015] In some embodiments of the present invention, the negative electrode active material layer further comprises a binder, which may include at least one of polyacrylate, polyimide, polyamide, polyamideimide, polyvinylidene fluoride, polystyrene-butadiene copolymer, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethylcellulose, potassium carboxymethylcellulose, sodium hydroxymethylcellulose, and potassium hydroxymethylcellulose. By selecting such a binder, the resulting negative electrode active material layer has good structural stability, which is advantageous for improving the cycle performance of the electrochemical device.

[0016] A second aspect of the present invention provides an electrochemical device comprising the negative electrode piece according to any one of the above embodiments, so that the electrochemical device provided by the present invention has good cycle performance and expansion performance.

[0017] A third aspect of the present invention provides an electronic device comprising the electrochemical device according to any one of the above embodiments, so that the electronic device provided by the present invention has good performance in use.

[0018] The present invention provides a negative electrode piece, an electrochemical device, and an electronic device, wherein the negative electrode piece comprises a negative electrode active material layer, the negative electrode active material layer comprising a negative electrode active material, the negative electrode active material comprising a carbon-doped silicon oxygen composite material and graphite, the carbon-doped silicon oxygen composite material comprising elemental carbon, elemental silicon, and elemental oxygen, the carbon content in the surface region of a particle of the carbon-doped silicon oxygen composite material is greater than the carbon content in the internal region of the particle of the carbon-doped silicon oxygen composite material, the surface region is a region from the surface to the interior of the particle to a depth of 500 nm, and the internal region is a region of the particle excluding the surface region, and the mass percentage of the carbon element in the carbon-doped silicon oxygen composite material is 2% to 10% based on the total mass of elemental carbon, elemental silicon, and elemental oxygen. The carbon-doped silicon oxygen composite material in the negative electrode piece is introduced with carbon element, and the carbon element content in the surface region of the carbon-doped silicon oxygen composite particle is greater than the carbon element content in the inner region of the carbon-doped silicon oxygen composite particle, forming Si-C bonds in the inner region of the particle and Si-O-C bonds in the surface region, and the synergistic effect of Si-C bonds restricts the growth of silicon crystal grains during cycling, reduces the risk of pulverization of the negative electrode active material, improves the expansion performance of the negative electrode active material, and improves the surface stability of the particles, reducing the risk of etching by the electrolyte, thereby improving the cycle performance of the electrochemical device.Therefore, the negative electrode piece provided by the present invention has good electrical conductivity, and when applied to an electrochemical device, it can improve the cycle performance and expansion performance of the electrochemical device. [Brief explanation of the drawings]

[0019] In order to more clearly explain the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings that need to be used in the embodiments. It is obvious that the drawings in the following description are only some embodiments of the present invention, and those skilled in the art can also obtain other drawings based on the drawings without any creative efforts. [Figure 1] FIG. 1 is a schematic diagram of the structure of a particle of a carbon-doped silicon oxygen composite material in some embodiments of the present invention. [Figure 2] FIG. 2 is an image of the carbon-doped silicon-oxygen composite material in Example 1-1 taken by an energy dispersive X-ray analyzer (EDS). [Figure 3] FIG. 3 shows the distribution image of oxygen element in the carbon-doped silicon-oxygen composite material, corresponding to the EDS layer image in FIG. [Figure 4] FIG. 4 is a distribution image of silicon element in a carbon-doped silicon-oxygen composite material, corresponding to the EDS layered image in FIG. [Figure 5] FIG. 5 is a distribution image of carbon element in a carbon-doped silicon-oxygen composite material, corresponding to the EDS layered image in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0020] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be described in more detail below with reference to the drawings and examples. Obviously, the described examples are not all examples, but only a part of the examples of the present invention. Based on the examples described in the present invention, all other examples that a person skilled in the art can obtain without creative work also fall within the scope of the protection claims of the present invention.

[0021] In the following, the present invention will be described using a lithium ion battery as an example of an electrochemical device, but the electrochemical device of the present invention is not limited to a lithium ion battery. Specific technical solutions are as follows:

[0022] In a first aspect of the present invention, there is provided an anode piece, the anode piece comprising an anode active material layer, the anode active material layer comprising an anode active material, the anode active material comprising a carbon-doped silicon oxygen composite material and graphite, the carbon-doped silicon oxygen composite material comprising elemental carbon, elemental silicon, and elemental oxygen, the carbon content in the surface region of a particle of the carbon-doped silicon oxygen composite material being greater than the carbon content in the internal region of the particle of the carbon-doped silicon oxygen composite material, the surface region being a region extending from the surface of the particle to a depth of 500 nm, and the internal region being a region of the particle excluding the surface region, and the mass percentage of the carbon in the carbon-doped silicon oxygen composite material being 2% to 10% based on the total mass of elemental carbon, elemental silicon, and elemental oxygen in the carbon-doped silicon oxygen composite material. For example, Figure 1 shows a schematic diagram of the structure of a particle 10 of a carbon-doped silicon oxygen composite material in some embodiments of the present invention, in which the particle 10 includes a surface region 12 and an internal region 13, the direction indicated by the arrow inside the particle 10 is the direction extending from the surface 11 of the particle 10 to the interior of the particle 10, the distance d shown in the figure is the depth extending from the surface 11 of the particle 10 to the interior of the particle 10, the surface region 12 is a region with a depth d of 500 nm from the surface 11 of the particle 10 to the interior, and the internal region 13 is the region of the particle 10 excluding the surface region 12.

[0023] The carbon-doped silicon oxygen composite material in the negative electrode piece is introduced with carbon, and the carbon content in the surface region of the carbon-doped silicon oxygen composite particle is greater than the carbon content in the inner region of the carbon-doped silicon oxygen composite particle, forming Si-C bonds in the inner region of the particle and Si-O-C bonds in the surface region. The synergistic effect of the Si-C bonds and Si-O-C bonds restricts the growth of silicon crystal grains in the particle interior during cycling, reduces the risk of powdering of the negative electrode active material, improves the expansion performance of the negative electrode active material, and improves the stability of the particle surface, reducing the risk of etching by the electrolyte, thereby improving the cycle performance of the electrochemical device. As a result, the carbon-doped silicon oxygen composite material in the negative electrode piece provided by the present invention is less likely to powder during cycling, and the negative electrode piece has good electrical conductivity. The carbon-doped silicon oxygen composite material in the negative electrode piece has good expansion performance and is less likely to powder, so that the application of the negative electrode piece provided by the present invention to an electrochemical device can improve the cycle performance and expansion performance of the electrochemical device.

[0024] Specifically, the mass percentage of carbon in the carbon-doped silicon oxygen composite material can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range consisting of any two of the above values. If the mass percentage of carbon in the carbon-doped silicon oxygen composite material is too low, for example, less than 2%, the Si-C bonds formed inside the particles of the carbon-doped silicon oxygen composite material and the Si-O-C bonds formed on the surface region of the particles are relatively few, so the growth of silicon crystal grains during cycling cannot be effectively restricted, the stability of the particle surface is not significantly improved, the particles are easily pulverized during charging and discharging cycles, and the particle expansion performance and the conductivity of the negative electrode strips are affected. If the mass percentage of carbon in the carbon-doped silicon oxygen composite material is too high, for example, more than 10%, the gram capacity and initial coulombic efficiency of the carbon-doped silicon oxygen composite material will be affected, and the energy density of the electrochemical device will be affected. By controlling the mass percentage of carbon element in the carbon-doped silicon oxygen composite material within the above range, the carbon-doped silicon oxygen composite material in the negative electrode piece has good expansion performance and is not easily powdered. The negative electrode piece has good electrical conductivity, which allows the electrochemical device to have a relatively high energy density and is also advantageous in improving the cycle performance and expansion performance of the electrochemical device.

[0025] In general, the carbon-doped silicon oxygen composite material in the negative electrode piece provided by the present invention incorporates carbon element, and the carbon element content in the surface region of the carbon-doped silicon oxygen composite particle is greater than the carbon element content in the inner region of the carbon-doped silicon oxygen composite particle. By controlling the mass percentage of carbon element in the carbon-doped silicon oxygen composite material within the above range, the carbon-doped silicon oxygen composite material in the negative electrode piece has good expansion performance and is not easily powdered. The negative electrode piece has good electrical conductivity, which is beneficial to improving the cycle performance and expansion performance of the electrochemical device.

[0026] In some embodiments of the present invention, the mass percentage of carbon in the surface region is 0.5% to 8% based on the total mass of carbon, silicon, and oxygen in the carbon-doped silicon oxygen composite material. For example, the mass percentage of carbon in the surface region may be 0.5%, 2%, 4%, 6%, 8%, or a range consisting of any two of the above values. By controlling the mass percentage of carbon in the surface region of the carbon-doped silicon oxygen composite material within the above range, the carbon-doped silicon oxygen composite material in the negative electrode piece has good expansion performance and is less likely to pulverize. The negative electrode piece has good electrical conductivity, which is advantageous for improving the cycle performance and expansion performance of the electrochemical device.

[0027] In some embodiments of the present invention, the mass percentage of silicon in the carbon-doped silicon oxygen composite material is 40% to 60% based on the total mass of carbon, silicon, and oxygen in the carbon-doped silicon oxygen composite material. For example, the mass percentage of silicon in the carbon-doped silicon oxygen composite material may be 40%, 45%, 50%, 55%, 60%, or a range consisting of any two of the above values. By controlling the mass percentage of silicon in the carbon-doped silicon oxygen composite material within the above range, the high capacity characteristics of silicon materials can be exhibited, and the carbon-doped silicon oxygen composite material in the negative electrode piece has good expansion performance and is less likely to pulverize. The negative electrode piece has good conductivity, so the resulting electrochemical device has good cycle performance and expansion performance, as well as a relatively high energy density.

[0028] In the present invention, the mass percentage of oxygen in the carbon-doped silicon oxygen composite material is 100%-(mass percentage of silicon+mass percentage of carbon) based on the total mass of carbon, silicon, and oxygen in the carbon-doped silicon oxygen composite material. Note that the carbon-doped silicon oxygen composite material usually contains some impurity elements with a relatively low content (for example, a mass percentage of 0.1% or less), and the present invention does not take these impurity elements into account when calculating the mass percentages of carbon, silicon, and oxygen.

[0029] In the present invention, there are no particular limitations on the mass percentages of elemental silicon and elemental oxygen in the surface region, as long as the object of the present invention can be achieved. For example, based on the total mass of elemental carbon, elemental silicon, and elemental oxygen in the carbon-doped silicon-oxygen composite material, the mass percentage of elemental silicon in the surface region may be 0.5% to 8%, and the mass percentage of elemental oxygen in the surface region may be 20% to 40%.

[0030] In some embodiments of the present invention, the carbon-doped silicon oxygen composite material has a particle size distribution in the range of 0.2 μm to 20 μm, a Dv50 of 4 μm to 10 μm, and a Dv99 of 13 μm to 20 μm. For example, the particle size distribution may be any one of the ranges of 0.2 μm to 20 μm, 0.3 μm to 20 μm, 0.4 μm to 20 μm, 0.5 μm to 20 μm, and 0.6 μm to 20 μm; Dv50 may be 4 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 9 μm, 10 μm, or a range consisting of any two of the above values; and Dv99 may be 13 μm, 14 μm, 15 μm, 17 μm, 17 μm, 18 μm, 19 μm, 20 μm, or a range consisting of any two of the above values. By controlling the particle size distribution range, Dv50 and Dv99 of the carbon-doped silicon oxygen composite material within the above ranges, the side reaction between the carbon-doped silicon oxygen composite material and the electrolyte can be reduced, thereby mitigating the volume change of the carbon-doped silicon oxygen composite material, improving the pressure resistance strength of the carbon-doped silicon oxygen composite material, and enhancing the structural stability of the negative electrode piece, which is beneficial to improving the cycle performance of the electrochemical device.

[0031] In the present invention, Dv50 refers to the particle size at which the cumulative volume reaches 50% from the smallest diameter side in the volume-based particle size distribution of a material, and Dv99 refers to the particle size at which the cumulative volume reaches 99% from the smallest diameter side in the volume-based particle size distribution of a material.

[0032] In some embodiments of the present invention, the powder electrical conductivity of the carbon-doped silicon oxygen composite material is 0.03 S / cm to 8 S / cm. For example, the powder electrical conductivity of the carbon-doped silicon oxygen composite material may be 0.03 S / cm, 0.05 S / cm, 0.1 S / cm, 0.5 S / cm, 1 S / cm, 1.5 S / cm, 2 S / cm, 3 S / cm, 4 S / cm, 5 S / cm, 6 S / cm, 7 S / cm, 8 S / cm, or a range consisting of any two of the above values. By having a powder electrical conductivity within this range, the carbon-doped silicon oxygen composite material can effectively control the current density at the interface between the negative electrode piece and the electrolyte, thereby reducing the occurrence of lithium deposition in the negative electrode piece, which is advantageous for improving the cycle performance of the electrochemical device.

[0033] In some embodiments of the present invention, the mass content of carbon element in the surface region of the carbon-doped silicon / oxygen composite particles accounts for 10% to 80% of the mass content of carbon element in the carbon-doped silicon / oxygen composite. For example, the mass content of carbon element in the surface region of the carbon-doped silicon / oxygen composite particles may be 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or a range consisting of any two of the above values. Controlling this ratio within the above range limits the growth of silicon crystal grains within the particles during cycling, reduces the risk of powdering of the negative electrode active material, improves the expansion performance of the negative electrode active material, and further improves the stability of the particle surface, reducing the risk of etching by the electrolyte, thereby improving the cycle performance of the electrochemical device. As a result, the carbon-doped silicon oxygen composite material in the negative electrode piece provided by the present invention is less likely to powder during cycling, the negative electrode piece has good electrical conductivity, and the carbon-doped silicon oxygen composite material in the negative electrode piece has good expansion performance and is less likely to powder. Therefore, by applying the negative electrode piece provided by the present invention to an electrochemical device, the cycle performance and expansion performance of the electrochemical device can be improved.

[0034] In some embodiments of the present invention, the uniform distribution of silicon and oxygen elements in the particles of the carbon-doped silicon oxygen composite material is advantageous for improving the cycle performance and expansion performance of the electrochemical device.

[0035] In some embodiments of the present invention, the graphite includes at least one of natural graphite, artificial graphite, mesocarbon microbeads, etc. The selection of the above graphite material is advantageous for improving the cycle performance of the electrochemical device.

[0036] In some embodiments of the present invention, the mass ratio of the carbon-doped silicon oxygen composite to graphite is (3-20):(80-97). For example, the mass ratio of the carbon-doped silicon oxygen composite to graphite may be 20:80, 18:82, 15:85, 12:88, 10:90, 7:93, 6:94, 5:95, 4:96, 3:97, or a range consisting of any two of the above ratios. Controlling the mass ratio of the carbon-doped silicon oxygen composite to graphite within the above range allows the negative electrode active material layer to maintain a high gram capacity while reducing the probability of direct contact between the silicon and the electrolyte, thereby reducing side reactions between the silicon and the electrolyte and the formation of a solid electrolyte interface (SEI) film and mitigating volume expansion of the silicon. Furthermore, graphite can increase the conductivity of the negative electrode pieces, resulting in a synergistic improvement in the cycle performance of the electrochemical device.

[0037] In some embodiments of the present invention, the negative electrode active material layer further comprises a binder. The binder may include 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. By selecting the above binder, the resulting negative electrode active material layer has good structural stability, which is advantageous for improving the cycle performance of the electrochemical device.

[0038] In the present invention, the negative electrode active material layer may further include a conductive agent. The conductive agent is not particularly limited in the present invention, as long as it achieves the objectives of the present invention. For example, the conductive agent may include at least one of 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 active material, conductive agent, and binder in the negative electrode active material layer is not particularly limited, and those skilled in the art can select it as needed, as long as it achieves the objectives of the present invention.

[0039] The negative electrode piece of the present invention includes a negative electrode current collector, and a negative electrode active material layer is disposed on at least one surface of the negative electrode current collector. The phrase "the negative electrode active material layer is disposed on at least one surface of the negative electrode current collector" means that the negative electrode active material layer may be disposed on one surface of the negative electrode current collector along its thickness direction, or on both surfaces of the negative electrode current collector along its thickness direction. The term "surface" here refers to the entire area of ​​the negative electrode current collector or a partial area of ​​the negative electrode current collector, and is not particularly limited in the present invention, as long as the objective of the present invention is achieved. The negative electrode current collector is not particularly limited in the present invention, as long as the objective of the present invention is achieved. The negative electrode current collector may be, 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.). The thickness of the negative electrode current collector and the negative electrode active material layer is not particularly limited in the present invention, as long as the objective of the present invention is achieved. For example, the thickness of the negative electrode current collector is 6 μm to 12 μm, and the thickness of the negative electrode active material layer is 30 μm to 120 μm. In the present invention, there is no particular limitation on the thickness of the negative electrode piece, as long as the object of the present invention can be achieved. For example, the thickness of the negative electrode piece is 50 μm to 150 μm.

[0040] The negative electrode piece may optionally further include a conductive layer located between the negative electrode current collector and the negative electrode active material layer. In the present invention, the composition of the conductive layer is not particularly limited and may be a conductive layer commonly used in this field. For example, the conductive layer may include a conductive agent and a binder. In the present invention, the conductive agent and binder in the conductive layer are not particularly limited and may be, for example, at least one of the above-mentioned conductive agents and binders.

[0041] In the present invention, there are no particular limitations on the method for preparing a carbon-doped silicon oxygen composite material. For example, the method for preparing a carbon-doped silicon oxygen composite material may include, but is not limited to, the steps of uniformly mixing a carbon-doped silicon oxygen material with a silicone solution, drying the mixture, and then heat-treating the mixture in an inert atmosphere to obtain the carbon-doped silicon oxygen composite material. Here, the drying temperature is 80°C to 120°C, the heat-treatment temperature is 600°C to 1000°C, the heat-treatment temperature is 1°C / min to 10°C / min, and the heat-treatment temperature retention time is 1 hour to 6 hours. The silicone solution contains a silicone and a solvent. The silicone may include, but is not limited to, at least one of tetramethyl-tetravinyl-cyclotetrasiloxane and methylhydrogenpolysiloxane. The solvent may include, but is not limited to, ethanol. The mass ratio of the silicone to the solvent may be 1:(2 to 6). The inert atmosphere may be argon gas and / or nitrogen gas.

[0042] Usually, the mass percentages of carbon, silicon and oxygen in the carbon-doped silicon-oxygen composite material can be controlled by changing the temperature, heating rate and heat-up time of heat treatment.For example, when the heat treatment temperature is increased, the mass percentage of carbon, the mass percentage of silicon and the mass percentage of oxygen in the carbon-doped silicon-oxygen composite material increase, while when the heat treatment temperature is decreased, the mass percentage of carbon, the mass percentage of silicon and the mass percentage of oxygen in the carbon-doped silicon-oxygen composite material decrease, while when the heat treatment temperature is decreased, the mass percentage of carbon, the mass percentage of silicon and the mass percentage of oxygen in the carbon-doped silicon-oxygen composite material decrease, while when the heating rate is increased, the mass percentage of carbon, the mass percentage of silicon and the mass percentage of oxygen in the carbon-doped silicon-oxygen composite material increase, while when the heating rate is decreased, the mass percentage of carbon, the mass percentage of silicon and the mass percentage of oxygen in the carbon-doped silicon-oxygen composite material increase, while when the heating rate is decreased, the mass percentage of carbon, the mass percentage of silicon and the mass percentage of oxygen in the carbon-doped silicon-oxygen composite material increase. When the heat-treatment temperature retention time is extended, the mass percentage of carbon element, the mass percentage of silicon element, and the mass percentage of oxygen element in the carbon-doped silicon-oxygen composite material increases, while when the heat-treatment temperature retention time is shortened, the mass percentage of carbon element, the mass percentage of silicon element, and the mass percentage of oxygen element in the carbon-doped silicon-oxygen composite material decreases.

[0043] The mass percentages of carbon, silicon, and oxygen in the surface region can also be controlled by changing the temperature, heating rate, and temperature retention time of the heat treatment.For example, when the heat treatment temperature is increased, the mass percentage of carbon, silicon, and oxygen in the surface region increases, while when the heat treatment temperature is decreased, the mass percentage of carbon, silicon, and oxygen in the surface region decreases.When the heating rate is increased, the mass percentage of carbon, silicon, and oxygen in the surface region decreases, while when the heating rate is decreased, the mass percentage of carbon, silicon, and oxygen in the surface region increases. When the heat-holding time of the heat treatment is extended, the mass percentage of carbon element in the surface region increases, the mass percentage of silicon element increases, and the mass percentage of oxygen element decreases, whereas when the heat-holding time of the heat treatment is shortened, the mass percentage of carbon element in the surface region decreases, the mass percentage of silicon element decreases, and the mass percentage of oxygen element increases.

[0044] The particle size distribution range, Dv50, and Dv99 of the carbon-doped silicon oxygen composite material can be controlled by changing the heat treatment temperature, heating rate, and heating time. For example, increasing the heat treatment temperature broadens the particle size distribution range of the carbon-doped silicon oxygen composite material, increasing Dv50 and Dv99. However, decreasing the heat treatment temperature narrows the particle size distribution range of the carbon-doped silicon oxygen composite material, decreasing Dv50 and Dv99. Increasing the heating rate narrows the particle size distribution range of the carbon-doped silicon oxygen composite material, decreasing Dv50 and Dv99. However, decreasing the heating rate widens the particle size distribution range of the carbon-doped silicon oxygen composite material, increasing Dv50 and Dv99. When the heat treatment time is extended, the particle size distribution range of the carbon-doped silicon oxygen composite material becomes wider, Dv50 increases, and Dv99 increases, but when the heat treatment time is shortened, the particle size distribution range of the carbon-doped silicon oxygen composite material becomes narrower, Dv50 decreases, and Dv99 decreases.

[0045] In the present invention, the method for preparing the carbon-doped silicon-oxygen material is not particularly limited as long as the object of the present invention can be achieved. For example, the method for preparing the carbon-doped silicon-oxygen material may include, but is not limited to, the steps of uniformly mixing silicon and silica, placing the mixture in a vacuum deposition furnace, controlling the temperature to 1300°C to 1350°C and the vacuum to 1 Pa to 100 Pa, and then aerating an appropriate amount of carbon source gas (e.g., methane, acetylene, ethylene, etc.) to obtain the carbon-doped silicon-oxygen material. The contents of carbon, silicon, and oxygen in the carbon-doped silicon-oxygen material can be controlled by the mixing ratio of silicon and silica and the content of the aerated carbon source gas. For example, increasing the mixing ratio of silicon and silica increases the silicon content and decreases the oxygen content, whereas decreasing the mixing ratio of silicon and silica decreases the silicon content and increases the oxygen content. When the amount of carbon source gas aerated increases, the carbon element content increases, whereas when the amount of carbon source gas aerated decreases, the carbon element content decreases.

[0046] For example, in the present invention, based on the total mass of the carbon-doped silicon / oxygen material, the mass percentage of carbon element is 2% to 10%, the mass percentage of silicon element is 40% to 60%, and the mass percentage of oxygen element is 30% to 50%. Note that the carbon-doped silicon / oxygen material usually contains some impurity elements with a relatively low content (e.g., a mass percentage of 0.1% or less). In the present invention, when calculating the mass percentages of carbon element, silicon element, and oxygen element in the carbon-doped silicon / oxygen material, "based on the total mass of the carbon-doped silicon / oxygen material" refers to the total mass excluding the above impurity elements, and the mass percentages of carbon element, silicon element, and oxygen element are further obtained.

[0047] The present invention allows carbon-doped silicon and oxygen materials with different particle size distributions to be obtained by particle size classification. The particle size classification method is not particularly limited as long as a material satisfying the particle size requirements of the present invention can be obtained. For example, carbon-doped silicon and oxygen composite materials with different particle size distributions can be obtained by sieving the particle size through polishing.

[0048] In the present invention, there is no particular limitation on the method for controlling the powder electrical conductivity of the carbon-doped silicon-oxygen composite material, as long as the object of the present invention can be achieved. For example, the electrical conductivity of the carbon-doped silicon-oxygen composite material can be controlled by controlling the mass percentage of carbon element. Typically, the powder electrical conductivity of the carbon-doped silicon-oxygen composite material increases with an increase in the mass percentage of carbon element in the carbon-doped silicon-oxygen composite material, and decreases with a decrease in the mass percentage of carbon element in the carbon-doped silicon-oxygen composite material.

[0049] A second aspect of the present invention provides an electrochemical device comprising the negative electrode piece according to any one of the above embodiments, so that the electrochemical device provided by the present invention has good cycle performance and expansion performance.

[0050] In the present invention, the electrochemical device further includes a positive electrode piece, which includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. The "positive electrode active material layer disposed on at least one surface of the positive electrode current collector" refers to the positive electrode active material layer being disposed on one surface of the positive electrode current collector along its thickness direction, or on both surfaces of the positive electrode current collector along its thickness direction. The "surface" here may refer to the entire area of ​​the positive electrode current collector or a partial area of ​​the positive electrode current collector, and is not particularly limited in the present invention as long as the objective of the present invention is achieved. In the present invention, there are no particular limitations on the positive electrode current collector, and it is sufficient that the objective of the present invention is achieved. The positive electrode current collector can include, for example, aluminum foil, aluminum alloy foil, or a composite current collector (e.g., an aluminum-carbon composite current collector). The positive electrode active material layer includes a positive electrode active material. In the present invention, there are no particular limitations on the positive electrode active material, and it is sufficient that the objective of the present invention is achieved. For example, the positive electrode active material may include at least one of lithium nickel cobalt manganese oxide (e.g., conventional 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 iron manganese phosphate, and lithium titanate. The positive electrode active material layer further includes a conductive agent and a binder. In the present invention, the type of conductive agent and binder are not particularly limited as long as the objectives of the present invention are achieved. For example, at least one of the above-mentioned conductive agents and binders may be used. In the present invention, the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode active material layer is not particularly limited, and those skilled in the art can select the appropriate ratio as long as the objectives of the present invention are achieved. In the present invention, the thicknesses of the positive electrode current collector and the positive electrode active material layer are not particularly limited as long as the objectives of the present invention are achieved. For example, the thickness of the positive electrode current collector is 6 μm to 12 μm, and the thickness of the positive electrode active material layer is 30 μm to 120 μm. In the present invention, there is no particular limitation on the thickness of the positive electrode piece, as long as the object of the present invention can be achieved. For example, the thickness of the positive electrode piece is 50 μm to 150 μm.

[0051] The positive electrode piece may optionally further include a conductive layer located between the positive electrode current collector and the positive electrode active material layer. The composition of the conductive layer is not particularly limited and may be a conductive layer commonly used in this field. The conductive layer includes a conductive agent and a binder. In the present invention, the conductive agent and binder in the conductive layer are not particularly limited. For example, the conductive layer may be at least one of the above-mentioned conductive agents and binders.

[0052] In the present invention, the electrochemical device further includes a separator that separates the positive and negative electrode pieces to prevent short circuits within the electrochemical device, 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) such as 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, calendered film, and spun film.

[0053] 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. The material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven 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 may be a layer formed by mixing a polymer and an inorganic material.

[0054] For example, the inorganic layer includes inorganic particles and a binder. The inorganic particles are not particularly limited and may include, for example, 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, and barium sulfate. The binder is not particularly limited and may be, for example, at least one of the binders listed above. The polymer layer includes a polymer. The polymer material may include at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0055] In the present invention, the electrochemical device further includes an electrolyte solution, which 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(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 is 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 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. The non-aqueous solvent can include, but is not limited to, at least one of a carbonate compound, a carboxylic acid ester compound, an ether compound, and other organic solvents. The carbonate compound can include, but is not limited to, at least one of a chain carbonate compound, a cyclic carbonate compound, and a fluorocarbonate compound. The chain carbonate compound can include, but is not limited to, 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). The cyclic carbonate compound can include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and vinyl ethylene carbonate (VEC).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, pentanolactone, 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, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, and trioctyl phosphate. The mass percentage of the nonaqueous solvent in the electrolyte may be 15% to 80%. For example, it may be 15%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or any range therebetween.

[0056] The electrochemical device 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 electrochemical devices. The present invention does not limit the above-mentioned other components. In the present invention, there is no particular limitation on the packaging bag, and any packaging bag known in the art may be used as long as the object of the present invention can be achieved.

[0057] The electrochemical device of the present invention is not particularly limited and may include any device that generates an electrochemical reaction. In some embodiments, the electrochemical device 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.

[0058] The process for preparing an electrochemical device of the present invention is well known to those skilled in the art and is not particularly limited thereto. For example, the process may include, but is not limited to, stacking positive electrode pieces, separators, and negative electrode pieces in this order, and optionally winding or folding them 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 an electrochemical device; or stacking positive electrode pieces, separators, and negative electrode pieces in this order, fixing 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 an electrochemical device. Furthermore, to prevent an increase in pressure inside the electrochemical device and overcharging and discharging, an overcurrent protection element and a guide plate may be placed in the packaging bag as needed.

[0059] A third aspect of the present invention provides an electronic device comprising the electrochemical device according to any one of the above embodiments, so that the electronic device provided by the present invention has good performance in use.

[0060] The electronic device of the present invention is not particularly limited and may be any known electronic device used in the prior art. In some embodiments, the electronic device may include, but is not limited to, a notebook computer, a pen-input 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 auxiliary 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. [Example]

[0061] Hereinafter, the embodiments of the present invention will be described in more detail with reference to examples and comparative examples. Each test and evaluation was carried out according to the following methods. Unless otherwise specified, "parts" and "%" are by mass. Measurement methods and equipment

[0062] Measurement of element distribution and content A conductive adhesive was attached to a sample stage, and a powder sample of the carbon-doped silicon-oxygen composite material in each example or a powder sample of the negative electrode active material other than graphite in each comparative example was taken and laid flat on the conductive adhesive. Unattached powder was blown off with an earwashing ball, and then gold sprayed. The element distribution and mass percentage were measured by mapping using an EDS attached to a Philips XL-30 field emission scanning electron microscope at an acceleration voltage of 10 kV and an emission current of 10 mA.

[0063] Measurement of the mass percentage of elemental carbon in the surface region A conductive adhesive was applied to a sample stage, and a powder sample of the carbon-doped silicon-oxygen composite material in each example or a powder sample of the negative electrode active material other than graphite in each comparative example was placed flat on the conductive adhesive. The remaining powder was blown off with an earwashing ball, gold sprayed, and cross-sectioned using argon gas plasma. Using an EDS attached to a Philips XL-30 field emission scanning electron microscope, particles with a particle diameter of 4 μm to 10 μm were selected under conditions of an acceleration voltage of 10 kV and an emission current of 10 mA. The mass percentage of elements in the surface region of the particles was measured, and the mass percentage of carbon element in the surface region was obtained.

[0064] Powder Electrical Conductivity Measurement Five grams of powder sample of the carbon-doped silicon-oxygen composite material in each example or the negative electrode active material other than graphite in each comparative example was taken, and a constant pressure of 5000 kg was applied in an electronic press and maintained for 20 seconds to obtain a sample sheet. The area of ​​the sample sheet at this time was S = 3.14 cm. 2 After measuring the height h of the sample sheet, the area S is 3.14 cm 2 The sample sheet was placed between the electrodes of a resistance measuring instrument (Suzhou Crystal Electronics ST-2255A), a voltage U was applied across the sample sheet, and the current I was measured to obtain the resistance R of the sample sheet according to the formula R = U / I. The powder electrical conductivity (unit: S / cm) was calculated according to the formula δ = h / (S × R) / 1000.

[0065] Particle size distribution, Dv50 and Dv99 measurements 0.02 g of a powder sample of the carbon-doped silicon-oxygen composite material in each Example or the negative electrode active material other than graphite in each Comparative Example was placed in a clean 50 ml beaker, 20 ml of deionized water was added, and five drops of a surfactant with a concentration of 1% were then added to completely disperse the powder sample in the water. The dispersion was then subjected to ultrasonic treatment for 5 minutes in a 120 W ultrasonic cleaner, and the particle size distribution, Dv50, and Dv99 were measured using a MasterSizer 2000 laser scattering particle size analyzer.

[0066] Gram capacity measurement The negative electrode active material, conductive carbon black (a conductive agent), and polyethyl acrylate (a PAA adhesive) were mixed in a mass ratio of 8:1:1, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solids content of 45 wt%. The slurry was then uniformly coated on copper foil and dried to obtain negative electrode pieces. A lithium sheet was then used as the counter electrode. The negative electrode pieces, lithium sheet, separator, and electrolyte were assembled into a button cell and measured. The measurement procedure was as follows: Specifically, the battery was charged at a constant current of 0.05 C to 5 mV, then further charged at a constant current of 10 μA to 5 mV. The initial charge capacity was recorded, and then the battery was allowed to stand for 5 minutes. The battery was then discharged at 0.05 C to 2 V, and the initial discharge capacity was recorded. The gram capacity = initial discharge capacity / mass of negative electrode active material. The negative electrode active material was a carbon-doped silicon-oxygen composite material in each example, or a negative electrode active material other than graphite in the comparative example. The separator and electrolyte were the same as in Example 1-1.

[0067] Measurement of cycle capacity retention rate At 25°C, the lithium-ion battery was charged at a constant current of 0.5C to 4.45V, then charged at a constant voltage of 0.025C from 4.45V, allowed to stand for 5 minutes, discharged at a constant current of 0.5C to 3.0V, allowed to stand for 5 minutes, and the discharge capacity of the first cycle was recorded. The battery was then charged and discharged 500 times using the same procedure, and the discharge capacity of the lithium-ion battery after the 500th cycle was recorded. Lithium-ion battery cycle capacity retention rate (%) = (discharge capacity at 500th cycle / discharge capacity at first cycle) x 100%.

[0068] Cyclic expansion rate measurement The thickness of the lithium-ion battery at 50% state of charge (SOC) was measured using a screw micrometer at a measurement temperature of 25°C and designated as H0. Then, after 500 cycles according to the charge / discharge steps in "Measurement of Cycle Capacity Retention Rate," the thickness of the lithium-ion battery at 100% SOC was measured and designated as H1. The cycle expansion rate was calculated as (H1 - H0) / H0 x 100%.

[0069] Example 1-1 <Preparation of carbon-doped silicon-oxygen composite materials> Tetramethyl-tetravinyl-cyclotetrasiloxane, methylhydrogenpolysiloxane, and ethanol were mixed in a mass ratio of 1:1:8 and stirred to obtain a silicone solution. The carbon-doped silicon-oxygen material and silicone solution were mixed in a mass ratio of 63:50 and stirred to obtain a silicone solution. The mixture was then dried at 80°C. The mixture was then heat-treated at 800°C, with a heating rate of 3°C / min and a holding time of 3 hours to obtain a carbon-doped silicon-oxygen composite material. The carbon-doped silicon-oxygen material contained 2% by mass carbon, 59% by mass silicon, and 39% by mass oxygen.

[0070] <Preparation of negative electrode pieces> The carbon-doped silicon-oxygen composite material, graphite, conductive carbon black, and styrene-butadiene rubber prepared above were mixed in a mass ratio of 5:92:1.8:1.2, and deionized water was added as a solvent to prepare a slurry with a solids content of 45 wt%. This slurry was then uniformly mixed using a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry was then uniformly coated onto one surface of a 10 μm-thick copper foil current collector and dried at 90°C to obtain a negative electrode piece coated with a 100 μm-thick negative electrode active material layer on one side. The above steps were then repeated on the other surface of the copper foil to obtain a negative electrode piece coated with a double-sided negative electrode active material layer. After drying at 90°C, the negative electrode piece was cold-pressed, cut, and tabs were welded to obtain a 78 mm x 875 mm negative electrode piece, which was then subjected to the next step.

[0071] <Preparation of positive electrode piece> The positive electrode active material, lithium cobalt oxide (LiCoO), conductive carbon black, and polyvinylidene fluoride (PVDF), were mixed in a mass ratio of 97.5:1.0:1.5, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solids content of 75 wt%. The slurry was then uniformly mixed. The slurry was then uniformly coated onto one surface of a 10 μm-thick aluminum foil current collector and dried at 90°C to obtain a positive electrode piece coated with a 100 μm-thick layer of positive electrode active material on one side. The above steps were then repeated on the other surface of the aluminum foil to obtain a positive electrode piece coated with positive electrode active material on both sides. After drying at 90°C, the piece was cold-pressed, cut, and tabs were welded to obtain a positive electrode piece measuring 74 mm x 867 mm, which was then subjected to the next step.

[0072] <Preparation of electrolyte> In a dry argon atmosphere glove box, the organic solvents EC, PC, DEC, and EP were mixed in a mass ratio of 3:1:3:3, and then lithium hexafluorophosphate (LiPF6) was added to the organic solvent and dissolved, followed by homogeneous mixing to obtain an electrolyte solution with a lithium salt concentration of 12.5 wt%.

[0073] <separator> A 7 μm thick porous polyethylene film (provided by Celgard) was used.

[0074] <Preparation of lithium-ion batteries> The positive electrode pieces, separator, and negative electrode pieces prepared above were stacked in this order, with the separator interposed between the positive and negative electrode pieces to act as insulators, and then wound up to obtain an electrode assembly. The electrode assembly was placed in an aluminum plastic film packaging bag, and moisture was removed at 80°C. The prepared electrolyte was then injected, and the assembly was subjected to processes such as vacuum packaging, standing, formation, degassing, and trimming to obtain a lithium-ion battery.

[0075] Examples 1-2 to 1-12 In <Preparation of carbon-doped silicon-oxygen composite material>, the same as in Example 1-1 was carried out, except that the relevant preparation parameters were adjusted according to Table 1.

[0076] Example 2-1 to Example 2-2 <Preparation of negative electrode pieces> was the same as in Example 1-1, except that the total mass of the carbon-doped silicon-oxygen composite material and graphite was not changed and the mass ratio of the carbon-doped silicon-oxygen composite material to graphite was adjusted according to Table 3.

[0077] Comparative Example 1 A negative electrode active material was prepared according to the following steps, which was the same as Example 1-1, except that the carbon-doped silicon oxygen composite material in <Preparation of negative electrode pieces> was replaced with the negative electrode active material prepared below.

[0078] <Preparation of negative electrode active material> The carbon-doped silicon-oxygen material was heat-treated at 800°C, with a heating rate of 3°C / min and a heat-holding time of 3 hours to obtain a negative electrode active material. Here, the carbon-doped silicon-oxygen material had a mass percentage of 2% carbon, 59% silicon, and 39% oxygen.

[0079] Comparative Example 2 The same as Example 1-1, except that the relevant preparation parameters were adjusted according to Table 1.

[0080] Comparative Example 3 The procedure was the same as in Example 1-1, except that the carbon-doped silicon-oxygen composite material in the <Preparation of negative electrode pieces> was replaced with a silicon-oxygen material as the negative electrode active material. In the silicon-oxygen material, the mass percentage of silicon element was 62% and the mass percentage of oxygen element was 38%. The silicon-oxygen material may be a commercially available material as long as it satisfies the above elemental contents.

[0081] Tables 1 to 3 show the preparation parameters and performance parameters of each example and comparative example.

[0082] [Table 1] Note: In Table 1, "element content" refers to the mass percentage of the corresponding element; "negative electrode active material" refers to the carbon-doped silicon oxygen composite material in each example or the negative electrode active material other than graphite in each comparative example; "proportion" refers to the mass content of carbon element in the surface region of the carbon-doped silicon oxygen composite particle as a percentage of the mass content of carbon element in the carbon-doped silicon oxygen composite material; and " / " indicates that the corresponding parameter or substance does not exist.

[0083] [Table 2] Note: In Table 2, "element content" refers to the mass percentage of the corresponding element, "negative electrode active material" refers to the carbon-doped silicon-oxygen composite material in each example or the negative electrode active material other than graphite in each comparative example, " / " indicates that the corresponding parameter or material does not exist, and in Example 1-1 as an example, "0.2-20" indicates that the particle size distribution of the negative electrode active material is 0.2 μm to 20 μm, and the same applies to the other examples and comparative examples.

[0084] As can be seen from Examples 1-1 to 1-12 and Comparative Examples 1 to 3, all of the examples use the anode pieces provided by the present invention. The mass percentage of carbon in the carbon-doped silicon oxygen composite material in the anode pieces is within the range of the present invention, and the carbon content in the surface region of the carbon-doped silicon oxygen composite particles is higher than the carbon content in the inner region of the carbon-doped silicon oxygen composite particles. However, there is no carbon on the surface of the anode active material prepared in Comparative Example 1, the carbon content in the surface region of the carbon-doped silicon oxygen composite particles is lower than the carbon content in the inner region of the particles in Comparative Example 2, and the silicon oxygen material in Comparative Example 3 is carbon-free. The lithium-ion batteries obtained in the examples have higher cycle capacity retention rates and lower expansion rates, thereby demonstrating that the use of the anode pieces provided by the present invention can effectively improve the cycle performance and expansion performance of lithium-ion batteries. The anode active materials in Comparative Examples 1 and 3 have relatively high gram capacities, but the cycle performance and expansion performance of the lithium-ion batteries are significantly inferior to those of the examples. The gram capacity of the carbon-doped silicon oxygen composite material in the Example was substantially equal to or higher than that of Comparative Example 2, but the cycle performance and expansion performance of the lithium ion battery in Comparative Example 2 were also clearly inferior to those of the Example. Therefore, while the Examples of the present invention can achieve both a gram capacity of the negative electrode active material and lithium ion battery performance, Comparative Examples 1 to 3 demonstrate that it is difficult to achieve both a gram capacity of the negative electrode active material and lithium ion battery performance.

[0085] Specifically, Figure 2 is an EDS hierarchical image of the carbon-doped silicon oxygen composite material in Example 1-1, and Figures 3 to 5 are distribution images of oxygen, silicon, and carbon elements in the carbon-doped silicon oxygen composite material, respectively, corresponding to the EDS hierarchical image in Figure 1. As can be seen from Figures 2 to 5, the carbon-doped silicon oxygen composite material contains oxygen, silicon, and carbon elements, and the distribution of oxygen and silicon elements in the carbon-doped silicon oxygen composite material is relatively uniform, with carbon element being distributed mainly in the surface region of the particles of the carbon-doped silicon oxygen composite material.

[0086] The mass percentage of carbon element in the surface region of the particles of the carbon-doped silicon oxygen composite material usually affects the cycle performance and expansion performance of the lithium ion battery. However, as can be seen from Examples 1-1 to 1-12, when the mass percentage of carbon element in the surface region of the particles of the carbon-doped silicon oxygen composite material is within the range of the present invention, the resulting lithium ion battery has a relatively high cycle capacity and a relatively low cycle expansion rate, thereby indicating that the lithium ion battery has good cycle performance and expansion performance.

[0087] The mass percentage of silicon in the carbon-doped silicon oxygen composite material generally affects the cycle performance and expansion performance of the lithium ion battery. However, as can be seen from Examples 1-1 to 1-12, when the mass percentage of silicon in the carbon-doped silicon oxygen composite material is within the range of the present invention, the resulting lithium ion battery has a relatively high cycle capacity and a relatively low cycle expansion rate, thereby indicating that the lithium ion battery has good cycle performance and expansion performance.

[0088] The particle size distribution ranges, Dv50 and Dv99, of the carbon-doped silicon oxygen composite material generally affect the cycle performance and expansion performance of the lithium-ion battery. However, as can be seen from Examples 1-1 to 1-12, when the particle size distribution ranges, Dv50 and Dv99, of the carbon-doped silicon oxygen composite material are within the ranges of the present invention, the resulting lithium-ion battery has a relatively high cycle capacity and a relatively low cycle expansion rate, thereby demonstrating that the lithium-ion battery has good cycle performance and expansion performance.

[0089] The powder electrical conductivity of the carbon-doped silicon oxygen composite material generally affects the cycle performance and expansion performance of the lithium ion battery. However, as can be seen from Examples 1-1 to 1-11, when the powder electrical conductivity of the carbon-doped silicon oxygen composite material is within the range of the present invention, the resulting lithium ion battery has a relatively high cycle capacity and a relatively low cycle expansion rate, thereby indicating that the lithium ion battery has good cycle performance and expansion performance.

[0090] [Table 3]

[0091] The mass ratio of the carbon-doped silicon oxygen composite material to graphite generally affects the cycle performance and expansion performance of a lithium ion battery. However, as can be seen from Examples 1-1, 2-1 and 2-2, when the mass ratio of the carbon-doped silicon oxygen composite material to graphite is within the range of the present invention, the resulting lithium ion battery has a relatively high cycle capacity and a relatively low cycle expansion rate, thereby indicating that the lithium ion battery has good cycle performance and expansion performance.

[0092] 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 piece, The negative electrode piece includes a negative electrode active material layer, the negative electrode active material layer contains a negative electrode active material, the negative electrode active material includes a carbon-doped silicon-oxygen composite material and graphite; The carbon-doped silicon oxygen composite material comprises carbon, silicon and oxygen elements; the carbon content in the surface region of the particle of the carbon-doped silicon oxygen composite material is greater than the carbon content in the internal region of the particle of the carbon-doped silicon oxygen composite material, the surface region is a region having a depth of 500 nm from the surface to the interior of the particle, and the internal region is a region of the particle excluding the surface region; The negative electrode piece, based on the total mass of the carbon, silicon and oxygen elements, the mass percentage of the carbon element in the carbon-doped silicon-oxygen composite material is 2% to 10%.

2. 2. The anode piece of claim 1, wherein the mass percentage of the carbon element in the surface region is 0.5% to 8% based on the total mass of the carbon element, the silicon element, and the oxygen element.

3. 2. The negative electrode piece according to claim 1, wherein the mass percentage of the silicon element in the carbon-doped silicon-oxygen composite material is 40% to 60% based on the total mass of the carbon element, the silicon element, and the oxygen element.

4. 2. The anode piece of claim 1, wherein the carbon-doped silicon oxygen composite material has a particle size distribution in the range of 0.2 μm to 20 μm, a Dv50 of 4 μm to 10 μm, and a Dv99 of 13 μm to 20 μm.

5. 2. The negative electrode piece of claim 1, wherein the carbon-doped silicon-oxygen composite material has a powder electrical conductivity of 0.03 S / cm to 8 S / cm.

6. 2. The anode piece of claim 1, wherein the particles of the carbon-doped silicon oxygen composite material form Si--C bonds in the interior region and Si--O--C bonds in the surface region.

7. 2. The negative electrode piece according to claim 1, wherein the mass content of carbon element in the surface region of the particles of the carbon-doped silicon oxygen composite material accounts for 10% to 80% of the mass content of carbon element in the carbon-doped silicon oxygen composite material.

8. 10. The anode piece of claim 1, wherein the distribution of silicon and oxygen elements in the particles of the carbon-doped silicon-oxygen composite material is uniform.

9. 10. The anode piece of claim 1, wherein the graphite comprises at least one of natural graphite, synthetic graphite, and mesocarbon microbeads.

10. 2. The anode piece of claim 1, wherein the mass ratio of the carbon-doped silicon oxygen composite material to the graphite is (3-20):(80-97).

11. the negative electrode active material layer further contains a binder, 10. The anode piece of claim 1, wherein the binder comprises at least one of polyacrylate, polyimide, polyamide, polyamideimide, polyvinylidene fluoride, polystyrene butadiene copolymer, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethylcellulose, potassium carboxymethylcellulose, sodium hydroxymethylcellulose, and potassium hydroxymethylcellulose.

12. An electrochemical device comprising the negative electrode piece according to any one of claims 1 to 11.

13. An electronic device comprising the electrochemical device of claim 12.

Images