Negative electrode material and secondary battery

Abstract

The invention provides a negative electrode material and a secondary battery, the negative electrode material comprises a plurality of particles, each particle comprises an inner core and a carbon material, the inner core comprises a silicon-based material and a doping element, one part of the carbon material exists in the inner core, the other part of the carbon material coats the surface of the inner core, and the silicon-based material is doped with the doping element. The compactness index alpha of the negative electrode material is greater than or equal to 0.1 and less than or equal to 1.5, and the compactness index alpha is measured by the following test method: performing section energy spectrum analysis processing on the negative electrode material; a two-dimensional preset area is randomly selected from the cross section of the range from the center of the n particles to 80% of the radius of the outer surface of each particle for scanning analysis, the obtained mass content values of the carbon elements in the preset areas of the n particles are k1, k2, k3,... kn-1 and kn respectively and are the average value of the mass content of the carbon elements in the preset areas of the n particles, and the average value of the mass content of the carbon elements in the preset areas of the n particles is the average value of the mass content of the carbon elements in the preset areas of the n particles. N is a natural number greater than 5;

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a negative electrode material and a secondary battery. Background Technology

[0002] Silicon oxide anode materials are currently the most mature high-capacity anode materials in terms of application technology. Compared with graphite anode materials, their specific capacity is as high as 2100mAh / g. Compared with crystalline silicon anode materials, they overcome the problem of large volume expansion and greatly improve the cycle life of the material.

[0003] Existing technology discloses a method for vacuum co-evaporation and condensation of a mixture of silicon and silicon dioxide with metal M. The negative electrode material prepared by this method achieves an initial efficiency of over 83%, greatly improving the effective utilization rate of lithium ions in the positive electrode material of secondary batteries. However, because the reaction of the silicon and silicon dioxide mixture to generate silicon oxide vapor under heating conditions is a solid-solid interface reaction, the contact surface between silicon and silicon dioxide gradually deteriorates as the reaction proceeds, resulting in a gradual decrease in the reaction rate and a gradual reduction in Mg diffusion capacity. The density of the negative electrode material varies greatly from the outside to the center due to the different pore channel effects formed by the Mg vapor diffusion reaction. Furthermore, the nano-silicon domains generated by the magnesothermic reaction vary greatly, which can easily lead to the formation of lithium dendrites that pierce the separator during subsequent lithium intercalation / deintercalation, causing safety problems such as fires and explosions. Summary of the Invention

[0004] This application provides a negative electrode material with uniform density and high safety, and a secondary battery.

[0005] In a first aspect, this application provides a negative electrode material comprising a plurality of particles, each particle comprising a core and a carbon material. The core comprises a silicon-based material and a dopant element. A portion of the carbon material is present within the core, and another portion coats the surface of the core. The density index α of the negative electrode material satisfies: 0.1 ≤ α ≤ 1.5, wherein the density index α is measured by the following test method:

[0006] The negative electrode material was subjected to cross-sectional energy dispersive spectroscopy (EDS). A two-dimensional preset region was arbitrarily selected within a cross-section extending from the center of each of the n particles to 80% of the particle's outer surface for scanning analysis. The mass content values ​​of carbon in each preset region of the n particles were obtained as k1, k2, k3, ... k n-1 k n , Let be the average mass content of carbon in a preset region of n particles, where n is a natural number greater than 5.

[0007]

[0008] Secondly, this application provides a secondary battery comprising the aforementioned negative electrode material.

[0009] The anode material provided in this application exhibits a high degree of density uniformity or small variation between particles when the density index meets the requirement of 0.1 ≤ α ≤ 1.5. This not only buffers the volume change of the anode material during lithium insertion / extraction but also allows for the formation of a good conductive network through the carbon material in the core. Furthermore, it reduces the resistance to lithium ion transport within the particles, increases the migration speed of lithium ions, and enhances the lithium storage channel, thereby effectively improving the fast charging / discharging capability and cycle performance of the anode material. Additionally, it effectively improves the low-temperature performance of the anode material. Attached Figure Description

[0010] Figure 1 This is a flowchart illustrating the manufacturing process of the negative electrode material according to one embodiment of this application.

[0011] Figure 2 This is a schematic diagram of the discharge state of a secondary battery according to an embodiment of this application.

[0012] Figure 3 Selected area diagrams of electron microscopy and energy dispersive spectroscopy analysis of the negative electrode material of Example 2 of this application. Detailed Implementation

[0013] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0014] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0015] In the description of the embodiments of this application, the technical terms "inner" and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0016] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0017] The first aspect of this application provides a negative electrode material comprising multiple particles, each particle including a core and a carbon material. The core includes a silicon-based material and doping elements. A portion of the carbon material is located inside the core, and another portion is coated on the surface of the core. The density index α of the negative electrode material satisfies: 0.1 ≤ α ≤ 1.5, wherein the density index α is measured by the following test method:

[0018] Cross-sectional energy dispersive spectroscopy (EDS) was performed on the negative electrode material. A pre-defined two-dimensional region was arbitrarily selected within an 80% radius radius of the outer surface of each of the n particles for scanning analysis. The mass content values ​​of carbon in each of the n particles within their respective pre-defined regions were obtained as k1, k2, k3, ... k n-1 k n , Let be the average mass content of carbon in a preset region of n particles, where n is a natural number greater than 5.

[0019]

[0020] It should be noted that the two-dimensional region mentioned above is selected individually for a cross-section extending from the center of each particle to 80% of the radius of the particle's outer surface, with the carbon element mass content values ​​k1, k2, k3, ... k n-1 k n The carbon content is calculated based on the element content within each preset region being 100%. The density index reflects the consistency or difference in density among multiple particles of the anode material. When the density index of the anode material satisfies 0.1≤α≤1.5, it indicates that the density consistency among multiple particles of the anode material is high or the difference is small. This can buffer the volume change of the anode material during lithium insertion and extraction, and can also form a good conductive network with the help of carbon materials inside the particles (e.g., amorphous carbon materials described later). It can also reduce the resistance to lithium ion transport inside the particles, increase the migration speed of lithium ions, and improve the lithium storage channel, thereby effectively improving the fast charging and discharging capability and cycle performance of the anode material. In addition, it can effectively improve the low-temperature performance of the anode material.

[0021] When the density index α of the negative electrode material is less than 0.1, it indicates two things: firstly, the doping amount of the dopant element is low, and the internal structure of the particles is too dense, leaving no space for volume expansion. This makes the particles prone to breakage and electrochemical deactivation due to volume changes during lithium insertion / extraction. Secondly, excessive density results in a higher impedance of the negative electrode material, which is not conducive to maintaining stable battery voltage. On the other hand, excessively loose internal structure of the particles leads to a larger surface area of ​​the negative electrode material, which can cause rapid electrolyte consumption and cycling failure when applied to batteries.

[0022] When the density index α of the negative electrode material is greater than 1.5, it indicates that the density difference between particles is too large, which will cause uneven lithium insertion and extraction between and inside the material particles. Uneven lithium insertion and extraction will lead to uneven stress distribution inside the negative electrode particles, thereby causing safety problems such as particle structural breakage and lithium plating.

[0023] In some embodiments, the silicon-based material includes silicon oxide, the chemical formula of which is SiO. x Where 0 < x ≤ 2, and x can take values ​​of 0.1, 0.3, 0.5, 0.8, 1.0, 1.2, 1.5, 1.8, 1.95, 2, or any value between them. Preferably, 0 < x < 1. The silicon oxide can be a material formed by dispersing silicon particles in SiO2, or it can be a material with tetrahedral structural units, where silicon atoms are located at the center of the tetrahedral structural units, and silicon atoms and / or oxygen atoms are located at the four vertices of the tetrahedral structural units.

[0024] In some embodiments, the silicon oxide comprises the mass of silicon and the mass of oxygen, wherein the atomic ratio of the mass of silicon to the mass of oxygen is 0 to 2, excluding 0. Specifically, the atomic ratio of the mass of silicon to the mass of oxygen can be 0.05, 0.11, 0.21, 0.26, 0.31, 0.41, 0.51, 0.59, 0.61, 0.69, 0.71, 0.74, 0.76, 0.79, 0.89, 0.99, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, and 2, etc., and is not limited herein. Preferably, the atomic ratio of the mass of silicon to the mass of oxygen is 0 to 1, excluding 0.

[0025] In some embodiments, the particle density of the negative electrode material satisfies 2.30 g / cc ≤ ρg ≤ 2.60 g / cc, which is beneficial to improving the low-temperature performance of the negative electrode material. For example, the particle density of the negative electrode material can specifically be 2.30 g / cc, 2.35 g / cc, 2.40 g / cc, 2.45 g / cc, 2.5 g / cc, 2.55 g / cc, 2.60 g / cc, or any value between them.

[0026] In some embodiments, the powder conductivity σ of the negative electrode material under a pressure of 20 kN is ≥ 0.3 S / cm, for example, it can be 0.3 S / cm, 0.4 S / cm, 0.5 S / cm, 0.6 S / cm, etc.

[0027] In some embodiments, in the negative electrode material, D10 > 2.0 μm, 4 μm < D50 < 10 μm, and 8 μm < D90 < 15 μm. For example, the D10 of the negative electrode material can specifically be 2.1 μm, 2.5 μm, 3.0 μm, 3.5 μm, 4.0 μm, 4.5 μm, 5.0 μm, 5.5 μm, 6.0 μm, or any value between them; the D50 can specifically be 4.5 μm, 5.0 μm, 6.0 μm, 7.0 μm, 8.0 μm, 9.9 μm, or any value between them; and the D90 can specifically be 8.2 μm, 9.0 μm, 11.0 μm, 12.0 μm, 14.0 μm, 14.9 μm, or any value between them. It is understandable that selecting the particle size of the negative electrode material within the above range is beneficial to reducing side reactions, reducing the consumption of active lithium on the surface of the negative electrode material and the consumption of electrolyte, and improving the cycle performance of the negative electrode material.

[0028] In some embodiments, the particle size distribution of the negative electrode material satisfies: 0.9 ≤ (D90 - D10) / D50 ≤ 2.3. For example, it can be 0.9, 1.2, 1.5, 1.8, or 2.3. It is understood that when the particle size distribution of the negative electrode material is within the above range, the larger particles and smaller particles of the negative electrode material can cooperate with each other, with the smaller particles filling the pores between the larger particles, which can improve the tap density of the negative electrode material.

[0029] It should be noted that the cumulative particle size distribution measured by laser diffraction method represents the particle size corresponding to a cumulative particle size distribution percentage of 10%, D50 represents the particle size corresponding to a cumulative particle size distribution percentage of 50%, and D90 represents the particle size corresponding to a cumulative particle size distribution percentage of 90%.

[0030] In some embodiments, the specific surface area of ​​the negative electrode material is 1.5 m². 2 / g-15m 2 / g, for example, specifically 1.5m 2 / g、3m 2 / g, 4.5m 2 / g、6m 2 / g、8m 2 / g, 10m 2 / g、12m 2 / g, 15m 2 / g or any value between them. Understandably, a specific surface area distribution of the negative electrode material within the above range is beneficial for reducing side reactions, reducing the consumption of active lithium on the surface of the negative electrode material and the consumption of electrolyte, and improving the cycle performance of the negative electrode material.

[0031] In some embodiments, the doping element is selected from at least one metallic element from Groups IA, IIA, and IIIA.

[0032] Furthermore, in some embodiments, the uniformity parameter β of the dopant element distribution satisfies: β ≤ 0.5, and β is measured by the following test method:

[0033] Cross-sectional energy dispersive spectroscopy (EDS) was performed on the negative electrode material. A pre-defined two-dimensional region was arbitrarily selected within an 80% radius radius from the center of each of the N particles to their surface for scanning analysis. The mass content values ​​of the doped elements in each of the N particles in the pre-defined region were obtained as K1, K2, K3, ... K. N-1 K N , Let N be the average mass content of doped elements within a preset region of N particles, where N is a natural number greater than 5.

[0034]

[0035] It should be noted that, in this application, the aforementioned two-dimensional region is selected individually within a cross-section of 80% radius from the center of each particle to its outer surface, and the mass content values ​​of the doping elements are K1, K2, K3, ... K. N-1 K N The proportion of doped elements is calculated with the element content in each preset region as 100%. Uniformity β refers to the difference in the distribution of doped elements among the N particles of the negative electrode material. When β≤0.5, it indicates that the difference in the distribution of doped elements among the particles is small, and the grain difference of silicon particles is small, which can effectively avoid the problem of large electrode expansion caused by excessive grain size and excessive grain difference.

[0036] Furthermore, in some embodiments, the mass percentage of the doping element is 3%-20% based on the mass of the negative electrode material, specifically 3%, 6%, 10%, 12%, 15%, 18%, 20%, or any value between them. Selecting this range is beneficial for improving initial efficiency when applied to a battery and for facilitating control of the battery's chemical performance.

[0037] Furthermore, in some embodiments, when the mass percentage of the dopant element is greater than or equal to 3% and less than or equal to 13%, the anode material includes MgSiO3 (i.e., MgO·SiO2). Based on the mass of the anode material, the mass percentage of MgSiO3 ranges from 8% to 65%, for example, it can be 8%, 10%, 20%, 30%, 40%, 50%, 60%, 65%, or any value between them. When the dopant element is selected within this range, the resulting silicate is mainly MgSiO2. 3， Furthermore, the doping elements are well-distributed and the MgSiO3 is also uniformly distributed and relatively thin, which is beneficial for lithium-ion conduction.

[0038] In some embodiments, when the mass of the dopant element is greater than or equal to 15% and less than or equal to 20%, the anode material includes Mg2SiO4 (i.e., 2MgO·SiO2). Based on the mass of the anode material, the mass percentage of Mg2SiO4 ranges from 20% to 60%, for example, it can be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or any value between them. Within this range, due to the excess of the dopant element, the generated product is mainly Mg2SiO4, and β≤0.5, the dopant element distribution is uniform, the distribution of Mg2SiO4 is also uniform, and its impedance increase is relatively small.

[0039] In some embodiments, the carbon material of the negative electrode material includes amorphous carbon. By selecting a carbon source including hydrocarbon gases that can be cracked to form amorphous carbon, the carbon material can smoothly enter the active material, effectively increasing the electron transport path and speed between particles, improving the stability of the SEI film structure in subsequent electrochemical processes, enhancing the low-temperature performance of the negative electrode material, and reducing the cycling drop phenomenon caused by excessive electrolyte consumption.

[0040] In some embodiments, the carbon content of the negative electrode material is 3%-8% based on the mass of the negative electrode material. For example, it can be 3%, 5%, 6%, 7%, 8%, or any value between them. If the carbon content is too low, the conductivity of the negative electrode material will be poor, and the carbon layer formed by the carbon material will be too thin. During subsequent charge and discharge processes, the carbon layer formed by the carbon material on the surface of the negative electrode material cannot fully restrain the volume change of the particles, which will make the carbon layer on the surface of the negative electrode material prone to cracking, leading to additional side reactions and thus deteriorating the cycle performance. If the carbon content is too high, small-particle floating carbon will easily form. This floating carbon will result in low particle capacity and large specific surface area, which will affect the capacity of the battery and accelerate the consumption of electrolyte.

[0041] In some embodiments, at least a portion of the carbon material is formed on the surface of the active material to form a carbon layer, the thickness of which ranges from 50 nm to 500 nm. Specifically, it can be 50 nm, 100 nm, 150 nm, 200 nm, 350 nm, 400 nm, 450 nm, 500 nm, or any value between these. By selecting a carbon layer within the above range, it is beneficial to improve the conductivity of the negative electrode material and the capacity of the secondary battery.

[0042] like Figure 1 As shown, the second aspect of this application provides a method for preparing a negative electrode material, which includes the following steps:

[0043] Step S1: The silicon source vapor and the vapor containing doped elements are mixed and condensed in a vacuum system to obtain the precursor material. The flow rate of the condensation medium is controlled by gradient during the condensation process.

[0044] In some embodiments, step S1 further includes the following steps:

[0045] The silicon oxide source material and the doped source material are placed in the first and second chambers of the same vacuum heating system for heating and evaporation, respectively, to obtain silicon source vapor and doped element vapor.

[0046] Silicon source vapor and doped element vapor are mixed in the third chamber of the same vacuum system, and then condensed and deposited in the fourth chamber of the same vacuum system to obtain the precursor material. In one embodiment, the silicon oxide source material can be obtained commercially or prepared by the following method: Si and SiO2 powders are mixed uniformly at a molar ratio of 0.4-1.25 and placed in a vacuum reactor at 1260℃-1390℃. The mixture is then condensed and collected in a condensation chamber under the same vacuum system, with the condensation deposition thickness controlled to be ≤6cm. After removing the deposit, it is coarsely crushed, and silicon oxide blocks with a side length of 2-6cm are selected as the silicon oxide source material.

[0047] In some embodiments, the silicon oxide source material comprises bulk silicon oxide.

[0048] In one embodiment, the silicon oxide source material includes at least one of amorphous silicon oxide and disproportionated silicon oxide.

[0049] In some embodiments, the dopant element vapor includes at least one selected from lithium vapor, magnesium vapor, potassium vapor, calcium vapor, and aluminum vapor. It is understood that the dopant source material includes at least one selected from lithium source material, magnesium source material, potassium source material, calcium source material, and aluminum source material, thereby obtaining the corresponding vapor.

[0050] In some embodiments, the dopant source material includes an elemental metal, a metal oxide, or a mixture of a metal salt and a reducing agent.

[0051] It should be noted that when the doping source material is a metallic element, the mass ratio of the doping element to the silicon oxide source material is 3-20%; when the doping source material is a metal oxide or a mixture of metal salt and reducing agent, the mass ratio of the doping element to the silicon oxide source material is calculated based on the mass of the reduced metallic element M.

[0052] It is understandable that by using doping elements to react with silicon oxide source materials in a redox reaction, a portion of the active oxygen elements are consumed in advance to generate elemental silicon and silicates, which can improve the first efficiency of the material. Furthermore, the generated silicates can be used as a buffer carrier to improve the structural stability of the anode material.

[0053] In some embodiments, when the dopant element is magnesium, the magnesium source material includes at least one of magnesium powder, magnesium ingots, magnesium granules, a mixture of magnesium oxides and reducing substances, and a mixture of magnesium salts and reducing substances.

[0054] In some embodiments, the size of the silicon oxide bulk material ranges from 2 to 6 cm, and the dopant source material is placed in a space with a fixed cross-sectional area of ​​X m. 2 In the crucible, the value of X ranges from 0.1 to 0.5, specifically 0.1, 0.2, 0.3, 0.4, 0.5, or any value between them. It can be understood that by controlling the size of the bulk silicon oxide source material and the evaporation area of ​​the dopant source material, the relative evaporation rate can be effectively controlled to achieve stable doping of the dopant element.

[0055] In some embodiments, the heating and evaporation process of the silicon oxide source material and the doped source material is carried out in a vacuum or inert atmosphere.

[0056] In some embodiments, the first chamber is used to place the silicon oxide source material, and the evaporation temperature in the first chamber is in the range of 1100°C to 1600°C, for example, it can be 1100°C, 1200°C, 1300°C, 1400°C, 1500°C, 1600°C or any value between them.

[0057] In some embodiments, the second chamber is used to place the doped source material, and the evaporation temperature in the second chamber is in the range of 600°C to 1400°C, for example, it can be 600°C, 700°C, 800°C, 900°C, 1000°C, 1100°C, 1200°C, 1300°C, 1400°C, 1500°C, 1600°C or any value between them.

[0058] In some embodiments, the temperature range of the third chamber is 1200°C-1300°C, specifically 1200°C, 1220°C, 1240°C, 1260°C, 1280°C, 1300°C, or any value between them. The temperature of the third chamber is controlled to stabilize the gas flow of silicon source vapor and doped element vapor, and to mix these two phases of vapor.

[0059] In some embodiments, the temperature range within the fourth chamber is 450°C to 750°C, specifically 450°C, 500°C, 600°C, 650°C, 700°C, 750°C, or any value between them.

[0060] It should be noted that the temperature in the fourth chamber can be used as the initial temperature of the condensation interface, that is, the initial temperature at which deposition begins.

[0061] It is understandable that as steam is continuously generated and condensed, the thickness of the deposited product gradually increases, resulting in poor thermal conductivity. Furthermore, the heat released by the redox reaction during deposition increases the temperature difference at the steam-condensation interface, leading to changes or even reversals in the steam-condensation interface gradient. This, in turn, causes microstructural problems in the product due to changes / reversals in the condensation temperature gradient. Additionally, the microstructure of the deposited product from vacuum evaporation and condensation, such as its pore structure, is highly dependent on the temperature gradient at the condensation interface. In this application, the flow rate of the condensing medium is externally controlled to increase in a gradient, thereby enhancing the cooling capacity of the condensing medium, reducing the temperature difference at the steam-condensation interface, and resulting in high uniformity or low variation in the density of the negative electrode material particles. Furthermore, the flow rate of the condensing medium is automatically controlled based on the detection of the condensing medium outlet temperature, and the outlet temperature of the condensing medium decreases in a gradient. The cooling rate can range from 0.5℃ / h to 2℃ / h, specifically 0.5℃ / h, 1℃ / h, 1.5℃ / h, 2℃ / h, or any value between them.

[0062] In some embodiments, the initial temperature of the condenser is 450-750°C, which allows the temperature of the condenser-product interface to remain relatively constant and the deposited product in the initial stage to remain in a stable state with low activity.

[0063] In some embodiments, the silicon source vapor and the doped element vapor are mixed under vacuum conditions of 0-100 Pa, such as 1 Pa, 20 Pa, 40 Pa, 60 Pa, 80 Pa, 100 Pa, or any value between them. In some embodiments, the condensation method includes at least one of water cooling and air cooling.

[0064] In some embodiments, the condensing medium includes one of water, air, brine, and oil. In this embodiment, a condensing space (not shown) for the flow of the condensing medium is provided between the inner chamber (not shown) forming the fourth chamber, i.e., the condensation collection zone, and the equipment casing (not shown). Heat in the fourth chamber is conducted to the condensing medium, and then the heated condensing medium is pumped to a radiator (not shown) to dissipate heat through the flow of external air / water. Finally, the cooled condensing medium is transferred back to the condensing space to receive the heat generated again. This allows for temperature control within the fourth chamber during the deposition process, achieving condensation cooling. Preferably, pure water can be used as the condensing medium.

[0065] In some embodiments, the initial temperature of the condensing medium, i.e., the temperature range when the condensing medium enters the condensation space between the fourth chamber and the device housing, is 80°C-90°C. It should be noted that the temperature of the condensing medium is adjusted in real time via an external heat sink as the reaction proceeds to control the temperature of the condensation interface.

[0066] In some embodiments, after condensation and collection, the process further includes: introducing a constant amount of nitrogen or oxygen to solidify the active material, collecting the condensed precursor material, and pulverizing the precursor to obtain the core material. In some embodiments, the flow rate of nitrogen or oxygen is 0.03 L / min to 0.05 L / min, for example, specifically 0.03 L / min, 0.04 L / min, 0.05 L / min, or any value between them, and the solidification time is 1 h to 3 h, for example, specifically 1 h, 2 h, 3 h, or any value between them.

[0067] It is understandable that after cooling to T1℃, nitrogen or oxygen is introduced to solidify the precursor material. Among them, 250℃ < T1 < 450℃. During the condensation process, a small amount of elemental metal M may not have completely reacted. Introducing nitrogen or oxygen allows the nitrogen or oxygen to react with the remaining elemental metal M. After solidifying the precursor material, it is cooled to room temperature, removed, and powdered. This avoids the rapid oxidation of the active substances in the precursor caused by the exothermic oxidation of elemental metal M after exposure to air, thus maintaining the high capacity and high first-efficiency characteristics of the product.

[0068] In some embodiments, the two-phase vapors, namely silicon source vapor and doped element vapor, are mixed in the third chamber and then enter the fourth chamber for condensation deposition. The deposition thickness of the product is controlled to be 1 cm-5 cm by controlling the reaction time. For example, it can be 1 cm, 1.5 cm, 2 cm, 2.5 cm, 3 cm, 3.5 cm, 4 cm, 4.5 cm, 5 cm, or any value between them. It should be noted that as the deposition product thickness gradually increases, the thermal conductivity of the deposited product becomes poor, and the heat released by the redox reaction during product deposition will cause the temperature difference at the vapor condensation interface to increase. By controlling the deposition thickness of the product to be 1 cm-5 cm, excessive temperature differences at the vapor condensation interface can be effectively avoided.

[0069] Step S2: Powder the above precursor material and carbon-coat it to obtain the negative electrode material.

[0070] In some embodiments, the powdering method includes mechanical grinding, ball milling, or air jet milling.

[0071] In some embodiments, the particle size of the pulverized negative electrode material is D10 > 2.0 μm, 4 μm < D50 < 10 μm, and 8 μm < D90 < 15 μm. In this step, the particle size range of the negative electrode material can be slightly wider than the standard particle size range of the negative electrode material. If the particle size of the pulverized negative electrode material is too small, there will be too many side reactions and low initial capacity efficiency; if the particle size of the pulverized negative electrode material is too large, the local lithium insertion / extraction expansion of the negative electrode sheet will be too large, and the lithium-ion transport path impedance will increase, resulting in poor battery cycle performance.

[0072] In some embodiments, the carbon coating amount is 1-20%. Specifically, it can be 1%, 5%, 10%, 15%, 20%, or any value between them.

[0073] In some embodiments, the preferred carbon coating amount is 3-10%.

[0074] It should be noted that selecting the carbon coating amount within the above-mentioned range is beneficial to improving the mechanical properties, conductivity, capacity, and first-time efficiency of the anode material. If the carbon coating amount is too low, the carbon layer structure is thin, resulting in poor mechanical properties. The particles are prone to cracking and losing electrical contact due to lithium insertion / extraction expansion. Furthermore, too low a carbon coating amount leads to poor conductivity and cycle performance of the anode material. Conversely, too high a carbon coating amount results in low capacity of the anode material, and excessively high carbon coating can easily form floating carbon, further reducing the capacity and first-time efficiency of the anode material.

[0075] In some embodiments, carbon coating includes at least one of gas phase coating, solid phase coating, and liquid phase coating.

[0076] The temperature of the gas phase coating is 600℃-1050℃, and the carbon source gas for the gas phase coating includes at least one of methane, ethane, propane, butane, ethylene, propylene, and acetylene. The protective gas for the gas phase coating can be at least one of nitrogen and argon, or a mixture of at least one of the above gases and hydrogen.

[0077] In some embodiments, the gas encapsulated in the gas phase may also include hydrogen.

[0078] In some embodiments, the gas encapsulated in the gas phase includes a carbon source gas and a carrier gas.

[0079] In some embodiments, the protective gas for gas phase coating may be at least one of nitrogen and argon, or a mixture of nitrogen or argon and hydrogen.

[0080] In the manufacturing method of the anode material of this application, silicon oxide source material and doped source material are placed in a vacuum system and evaporated in a first chamber at 1100℃-1600℃ and a second chamber at 600-1400℃, respectively, and stably mixed in a third chamber at 1200℃-1300℃. Finally, they are condensed and deposited in a fourth chamber at an initial temperature of 450℃-750℃ to form a precursor material with a fixed thickness range. After cooling to T1℃, nitrogen or oxygen is introduced to solidify the precursor material. After cooling to room temperature, it is taken out and finally powdered and carbon-coated to obtain an amorphous carbon-coated silicon-based anode material with certain density and particle density.

[0081] In the manufacturing method of the negative electrode material of this application, the temperature of the condensing medium is controlled by gradient control during the mixing and condensation process of two-phase vapors with different boiling points / condensation points. The flow rate of the condensing medium is increased by gradient control by external control to enhance the cooling capacity of the condensing medium and reduce the temperature difference at the vapor condensation interface. This results in the anode material having a density index α that satisfies: 0.1≤α≤1.5. The anode material exhibits high consistency or small difference in density between particles, and the particle density of the anode material meets the requirement of 2.30g / cc≤ρg≤2.60g / cc. This solves the problem of uneven material reaction caused by segregation of two-phase vapors with different boiling points / condensation points during the mixing and condensation process, which leads to inconsistent defect structures and mechanical properties. Furthermore, materials within this density index α range or particle density range can provide a buffer space for the volume expansion generated during the lithium insertion / extraction process of the active material in the subsequent anode material, maintaining structural integrity. In addition, materials that meet the corresponding particle density range can form a good conductive network when filled with amorphous carbon materials inside the anode material, reducing the resistance to lithium ion transport within the particles, thereby increasing the migration speed of lithium ions, improving the lithium storage channel, reducing electrical contact failure caused by volume changes and polarization caused by poor conductivity, and ultimately synergistically and effectively improving the fast charging / discharging capability and cycle performance of the anode material.

[0082] Furthermore, it can effectively improve the problem of poor SEI film stability in anode materials. Anode materials that meet the above-mentioned density index can also effectively increase the electron transport path and speed between particles, improve the stability of the SEI film structure in subsequent electrochemical processes, improve the low-temperature performance of anode materials, and reduce the phenomenon of cycle drop caused by excessive consumption of electrolyte.

[0083] Thirdly, one embodiment of this application provides a secondary battery (such as a lithium-ion battery, sodium-ion battery, etc.), including a casing, an electrode assembly, and an electrolyte / electrolyte. Both the electrode assembly and the electrolyte / electrolyte are located within the casing.

[0084] The outer casing can be a packaging bag sealed with an encapsulating film (such as aluminum-plastic film), for example, a pouch battery for a secondary battery. In other embodiments, the secondary battery can also be a steel-cased battery, an aluminum-cased battery, etc.

[0085] Figure 2 This diagram shows a battery in a discharged state, i.e., during operation. Figure 2As shown, the electrode assembly includes a positive electrode 110, a negative electrode 120, and a separator 130, with the separator disposed between the positive and negative electrode sheets. The electrode assembly can be a stacked structure, formed by alternating layers of the positive electrode, separator, and negative electrode. In other embodiments, the electrode assembly can also be a wound structure, formed by winding the positive electrode, separator, and negative electrode after they have been stacked sequentially.

[0086] Positive electrode film

[0087] The positive electrode 110 includes a positive current collector 111 and a positive active layer 112 disposed on at least one surface of the positive current collector. The positive current collector can be aluminum foil or nickel foil, or any composite current collector disclosed in the prior art, such as, but not limited to, current collectors formed by combining the aforementioned conductive foil and polymer substrate. The positive active layer contains a positive active material, which includes compounds capable of reversibly intercalating and deintercalating metal ions. In some embodiments, the positive active material may include lithium transition metal composite oxides, sodium transition metal composite oxides, etc. The lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel.

[0088] In some embodiments, the positive electrode active material may include, but is not limited to, lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary materials (NCM), lithium manganese oxide (LiMn2O4), and lithium nickel manganese oxide (LiNi). 0.5 Mn 1.5 At least one of lithium iron phosphate (LiFePO4) or lithium iron phosphate (LiFePO4).

[0089] negative electrode sheet

[0090] The negative electrode 120 includes a negative electrode current collector 121 and a negative electrode active material layer 122 disposed on at least one surface of the negative electrode current collector. The negative electrode current collector can be at least one of copper foil, nickel foil, stainless steel foil, titanium foil, or carbon-based current collectors, or any composite current collector disclosed in the prior art, such as, but not limited to, current collectors formed by combining the aforementioned conductive foil and polymer substrate. The negative electrode active material layer includes a negative electrode material.

[0091] During battery operation, i.e. when the battery is in a discharge state, metal ions 140 (e.g., lithium ions) in the negative electrode are released from the lattice of the negative electrode material, pass through the electrolyte / electrolyte through the separator 130, and are embedded in the lattice of the positive electrode material.

[0092] Conversely, when the battery is charged by applying an external circuit, the oxidation of the positive electrode material causes metal ions (such as lithium ions) in the positive electrode to be released from the lattice of the positive electrode material, pass through the electrolyte / electrolyte through the separator, and move to the negative electrode; at the same time, the negative electrode material undergoes a reduction reaction, causing metal ions to be embedded in the lattice of the negative electrode material.

[0093] As metal ions move back and forth between the positive and negative electrodes, the battery can achieve the discharge and charge process in thousands of cycles.

[0094] The implementation schemes of this application will be described in detail below with reference to specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating this application and should not be regarded as limiting the scope of this application. Unless otherwise specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments used without specified manufacturers are all conventional products that can be purchased commercially.

[0095] Example 1

[0096] (1) Select silicon oxide blocks with a side length of about 3cm as silicon oxide vapor sources;

[0097] (2) Metallic Mg melts in a medium with a cross-sectional area of ​​0.5 m³. 2 It is condensed inside a cylindrical crucible;

[0098] (3) Silicon oxide and metallic Mg are placed in the same vacuum system at a mass ratio of 12:1; the silicon oxide block is placed in the first chamber at 1380°C, and the crucible described in (2) is placed in the second chamber at 800°C.

[0099] (4) The temperature of the third chamber with a stable steam flow is 1250℃;

[0100] (5) The initial temperature of the fourth chamber is set to 570℃. Its cooling capacity is enhanced by increasing the flow rate of the condensate gradient controlled externally. The flow rate is automatically controlled based on the detection of the outlet temperature of the condensate medium. The cooling rate of the outlet temperature of the condensate medium is set to 2.5℃ / h, the condensation collection cycle is 16h, and the product deposition thickness is 3cm. When the temperature drops to 400℃, nitrogen gas at 0.03L / min is introduced to solidify and stabilize the product to room temperature.

[0101] (6) The product is collected and pulverized, and then coated with gaseous carbon in a rotary kiln at 1000℃.

[0102] (7) Product detection results: carbon content was 5.0%, Mg content was 6.5%, cross-sectional energy dispersive spectroscopy analysis showed a density index of 0.10, Mg elemental uniformity index was 0.19, particle density was 2.41 g / cc, and specific surface area was 1.63 m². 2 / g, powder conductivity is 1.73S / cm, button half-cell tested capacity is 1420.5mAh / g, first efficiency is 82.99%, finished battery tested 1000 cycles capacity retention rate is 84%, rate charge and discharge ratio is 54.7% and 88.5% respectively.

[0103] Example 2

[0104] (1) Select silicon oxide blocks with a side length of about 3cm as silicon oxide vapor sources;

[0105] (2) Metallic Mg melts in a medium with a cross-sectional area of ​​0.5 m³. 2 It is condensed inside a cylindrical crucible;

[0106] (3) Silicon oxide and metallic Mg are placed in the same vacuum system at a mass ratio of 10:1; the silicon oxide block is placed in the first chamber at 1380°C, and the crucible described in (2) is placed in the second chamber at 800°C.

[0107] (4) The temperature of the third chamber with a stable steam flow is 1250℃;

[0108] (5) The initial temperature of the fourth chamber is set to 570℃. Its cooling capacity is enhanced by increasing the flow rate of the condensate gradient controlled externally. The flow rate is automatically controlled based on the detection of the outlet temperature of the condensate medium. The cooling rate of the outlet temperature of the condensate medium is set to 2.5℃ / h, the condensation collection cycle is 16h, and the product deposition thickness is 3cm. When the temperature drops to 400℃, nitrogen gas at 0.03L / min is introduced to solidify and stabilize the product to room temperature.

[0109] (6) The product is collected and pulverized, and then coated with gaseous carbon in a rotary kiln at 1000℃.

[0110] (7) Product detection results: carbon content was 5.2%, Mg content was 8.2%, cross-sectional energy dispersive spectroscopy analysis showed a density index of 0.23, Mg elemental uniformity index was 0.23, particle density was 2.45 g / cc, and specific surface area was 1.60 m². 2 / g, powder conductivity is 1.59S / cm, button half-cell tested capacity is 1403.8mAh / g, first efficiency is 83.37%, finished battery tested 1000 cycles capacity retention rate is 85%, rate charge and discharge ratio is 65.1% and 92.8% respectively.

[0111] A schematic diagram of the cross-sectional structure of the negative electrode material in Example 2 is shown below. Figure 3 As shown.

[0112] Example 3

[0113] (1) Select silicon oxide blocks with a side length of about 4cm as silicon oxide vapor sources;

[0114] (2) Metallic Ca melts in a medium with a cross-sectional area of ​​0.25 m³. 2 It is condensed inside a cylindrical crucible;

[0115] (3) Silicon oxide and metal Ca are placed in the same chamber at a mass ratio of 12:1. The silicon oxide block is placed in the first chamber at 1300°C, and the metal Ca source described in (2) is placed in the second chamber at 1100°C.

[0116] (4) The temperature of the third chamber with a stable steam flow is 1210℃;

[0117] (5) The initial temperature of the fourth chamber is set to 680℃. Its cooling capacity is enhanced by increasing the flow rate of the condensate gradient controlled externally. The flow rate is automatically controlled based on the detection of the outlet temperature of the condensate medium. The cooling rate of the outlet temperature of the condensate medium is set to 1.0℃ / h, the condensation collection cycle is 24h, and the product deposition thickness is 4cm. When the temperature drops to 350℃, nitrogen gas at 0.03L / min is introduced to solidify and stabilize the product to room temperature.

[0118] (6) The product is collected and pulverized, and then coated with gaseous carbon in a rotary kiln at 1050°C.

[0119] (7) Product detection results: carbon content was 4.5%, Mg content was 6.1%, cross-sectional energy dispersive spectroscopy analysis showed a density index of 0.75, Mg elemental uniformity index was 0.15, particle density was 2.48 g / cc, and specific surface area was 4.76 m². 2 / g, powder conductivity is 1.23S / cm, button half-cell tested capacity is 1371.9mAh / g, first efficiency is 83.91%, finished battery tested 1000 cycles capacity retention rate is 81%, rate charge and discharge ratio is 61.2% and 91.5% respectively.

[0120] Example 4

[0121] (1) Select silicon oxide blocks with a side length of about 5cm as silicon oxide vapor sources;

[0122] (2) Metallic Mg melts in a medium with a cross-sectional area of ​​0.25m³. 2 It is condensed inside a cylindrical crucible;

[0123] (3) Silicon oxide and metallic Mg are placed in the same vacuum system at a mass ratio of 12:1; the silicon oxide block is placed in the first chamber at 1380°C, and the crucible described in (2) is placed in the second chamber at 800°C.

[0124] (4) The temperature of the third chamber with a stable steam flow is 1290℃;

[0125] (5) The initial temperature of the fourth chamber is set to 550℃. Its cooling capacity is enhanced by increasing the flow rate of the condensate gradient controlled externally. The flow rate is automatically controlled based on the detection of the outlet temperature of the condensate medium. The cooling rate of the outlet temperature of the condensate medium is set to 1℃ / h, the condensation collection cycle is 16h, and the product deposition thickness is 5cm. When the temperature drops to 350℃, nitrogen gas is introduced at 0.02L / min to solidify and stabilize the product to room temperature.

[0126] (6) The product is collected and pulverized, and then coated with gaseous carbon in a rotary kiln at 1050°C.

[0127] (7) Product detection results: carbon content was 5.9%, Mg content was 7.7%, cross-sectional energy dispersive spectroscopy analysis showed a density index of 1.2, Mg elemental uniformity index was 0.34, particle density was 2.41 g / cc, and specific surface area was 6.07 m². 2 / g, powder conductivity is 0.87S / cm, button half-cell tested capacity is 1397.2mAh / g, first efficiency is 83.17%, finished battery tested after 1000 cycles capacity retention is 80%, and rate charge / discharge ratio is 53.5% and 93.8%, respectively.

[0128] Example 5

[0129] (1) Select silicon oxide blocks with a side length of about 6cm as silicon oxide vapor sources;

[0130] (2) Metallic Mg melts in a medium with a cross-sectional area of ​​0.15m³. 2 It is condensed inside a cylindrical crucible;

[0131] (3) Silicon oxide and metallic Mg are placed in the same vacuum system at a mass ratio of 6:1; the silicon oxide block is placed in the first chamber at 1380°C, and the crucible described in (2) is placed in the second chamber at 800°C.

[0132] (4) The temperature of the third chamber with a stable steam flow is 1290℃;

[0133] (5) The initial temperature of the fourth chamber is set to 710℃. Its cooling capacity is enhanced by increasing the flow rate of the condensate gradient through external control. The flow rate is automatically controlled based on the detection of the outlet temperature of the condensate medium. The cooling rate of the outlet temperature of the condensate medium is set to 2℃ / h. The condensation collection cycle is 18h and the product deposition thickness is 5cm. When the temperature drops to 350℃, air is introduced at 0.015L / min to solidify and stabilize the product to room temperature.

[0134] (6) The product is collected and pulverized, and then coated with gaseous carbon in a rotary kiln at 980°C.

[0135] (7) Product detection results: carbon content was 6.1%, Mg content was 7.5%, cross-sectional energy dispersive spectroscopy (EDS) analysis showed a density index of 0.5, Mg elemental uniformity index was 0.27, particle density was 2.44 g / cc, and specific surface area was 7.46 m². 2 / g, powder conductivity is 0.70S / cm, button half-cell tested capacity is 1390.1mAh / g, first efficiency is 83.05%, finished battery tested after 1000 cycles capacity retention is 83%, and rate charge / discharge ratio is 57.3% and 89.9%, respectively.

[0136] Example 6

[0137] (1) Select silicon oxide blocks with a side length of about 5cm as silicon oxide vapor sources;

[0138] (2) Metallic Mg melts in a medium with a cross-sectional area of ​​0.25m³. 2 It is condensed inside a cylindrical crucible;

[0139] (3) Silicon oxide and metallic Mg are placed in the same vacuum system at a mass ratio of 10:1; the silicon oxide block is placed in the first chamber at 1380°C, and the crucible described in (2) is placed in the second chamber at 800°C.

[0140] (4) The temperature of the third chamber with a stable steam flow is 1290℃;

[0141] (5) The initial temperature of the fourth chamber is set to 350℃. Its cooling capacity is enhanced by increasing the flow rate of the condensate gradient controlled externally. The flow rate is automatically controlled based on the detection of the outlet temperature of the condensate medium. The cooling rate of the outlet temperature of the condensate medium is set to 3℃ / h, the condensation collection cycle is 16h, and the product deposition thickness is 5cm. When the temperature drops to 250℃, nitrogen gas at 0.02L / min is introduced to solidify and stabilize the product to room temperature.

[0142] (6) The product is collected and pulverized, and then coated with gaseous carbon in a rotary kiln at 1050°C.

[0143] (7) Product detection results: carbon content was 3.9%, Mg content was 7.0%, cross-sectional energy dispersive spectroscopy analysis showed a density index of 1.35, Mg elemental uniformity index was 0.60, particle density was 2.43 g / cc, and specific surface area was 8.75 m². 2 / g, powder conductivity is 1.35S / cm, button half-cell tested capacity is 1397.2mAh / g, first efficiency is 82.05%, finished battery tested after 1000 cycles capacity retention is 69%, and rate charge / discharge ratio is 50.0% and 88.1% respectively.

[0144] Example 7

[0145] (1) Compared with Example 6, the mass ratio of silicon oxide and metallic Mg was changed to 15:1.

[0146] (2) Product detection results: carbon content was 4.5%, Mg content was 4.7%, cross-sectional energy dispersive spectroscopy analysis showed a density index of 0.46, Mg elemental uniformity index was 0.22, particle density was 2.36 g / cc, and specific surface area was 6.51 m². 2 / g, powder conductivity is 0.99S / cm, button half-cell tested capacity is 1445.2mAh / g, first efficiency is 81.79%, finished battery tested after 1000 cycles capacity retention is 83%, and rate charge / discharge ratio is 63.5% and 90.1%, respectively.

[0147] Example 8

[0148] (1) Compared with Example 6, the mass ratio of silicon oxide and Mg metal was changed to 4:1, and the cooling rate of the condensing medium outlet temperature was set to 2℃ / h.

[0149] (2) Product detection results: carbon content was 5%, Mg content was 16.1%, cross-sectional energy dispersive spectroscopy (EDS) analysis showed a density index of 1.5, Mg elemental uniformity index was 0.45, particle density was 2.56 g / cc, and specific surface area was 3.65 m². 2 / g, powder conductivity is 1.57S / cm, button half-cell tested capacity is 1275.0mAh / g, first efficiency is 89.97%, finished battery tested after 1000 cycles capacity retention is 70%, and the rate charge / discharge ratio is 52.3% and 87.4%, respectively.

[0150] Comparative Example 1

[0151] (1) Select silicon oxide blocks with a side length of about 3cm as silicon oxide vapor sources;

[0152] (2) Metallic Mg melts in a medium with a cross-sectional area of ​​0.5 m³. 2 It is condensed inside a cylindrical crucible;

[0153] (3) Silicon oxide and metallic Mg are placed in the same vacuum system at a mass ratio of 10:1; the silicon oxide block is placed in the first chamber at 1380°C, and the crucible described in (2) is placed in the second chamber at 800°C.

[0154] (4) The temperature of the third chamber with a stable steam flow is 1250℃;

[0155] (5) The initial temperature of the fourth chamber is set to 570℃. The outlet temperature of the condensing medium is not monitored or adjusted. The condensation collection cycle is 18h and the product deposition thickness is 4cm. When the temperature drops to 400℃, nitrogen gas is introduced at 0.03L / min to solidify and stabilize the product to room temperature.

[0156] (6) The product is collected and pulverized, and then coated with gaseous carbon in a rotary kiln at 1000℃.

[0157] (7) Product detection results: carbon content was 6.5%, Mg content was 7.1%, cross-sectional energy dispersive spectroscopy (EDS) analysis showed a density index of 2.35, Mg elemental uniformity index was 0.66, particle density was 2.35 g / cc, and specific surface area was 30.94 m². 2 / g, powder conductivity is 0.17S / cm, button half-cell tested capacity is 1271.5mAh / g, first efficiency is 79.95%, finished battery tested after 1000 cycles capacity retention is 55%, and the rate charge / discharge ratio is 16.9% and 23.2%, respectively.

[0158] Comparative Example 2

[0159] (1) Select silicon oxide blocks with a side length of about 6cm as silicon oxide vapor sources;

[0160] (2) Metallic Mg melts in a medium with a cross-sectional area of ​​0.25m³. 2 It is condensed inside a cylindrical crucible;

[0161] (3) Silicon oxide and metallic Mg are placed in the same vacuum system at a mass ratio of 10:1; the silicon oxide block is placed in the first chamber at 1380°C, and the crucible described in (2) is placed in the second chamber at 600°C.

[0162] (4) The temperature of the third chamber with a stable steam flow is 1250℃;

[0163] (5) The initial temperature of the fourth chamber is set to 450℃. Its cooling capacity is enhanced by increasing the flow rate of the condensate gradient through external control. The flow rate is automatically controlled based on the detection of the outlet temperature of the condensate medium. The cooling rate of the outlet temperature of the condensate medium is set to 5℃ / h, the condensation collection cycle is 12h, and the product deposition thickness is 2cm. When the temperature drops to 400℃, nitrogen gas at 0.03L / min is introduced to solidify and stabilize the product to room temperature.

[0164] (6) The product is collected and pulverized, and then coated with gaseous carbon in a rotary kiln at 1000℃.

[0165] (7) Product detection results: carbon content was 4.3%, Mg content was 3.9%, cross-sectional energy dispersive spectroscopy analysis showed a density index of 0.08, Mg elemental uniformity index was 0.49, particle density was 2.33 g / cc, and specific surface area was 3.10 m². 2 / g, powder conductivity is 1.57S / cm, button half-cell tested capacity is 1485.3mAh / g, first efficiency is 80.17%, finished battery tested after 1000 cycles capacity retention is 65%, and the rate charge-discharge ratio is 48.1% and 73.7%, respectively.

[0166] Comparative Example 3

[0167] (1) Compared with Example 6, the mass ratio of silicon oxide to Mg metal was changed to 16.5:1.

[0168] (2) Product detection results: carbon content was 4.5%, Mg content was 2.3%, cross-sectional energy dispersive spectroscopy analysis showed a density index of 0.05, Mg elemental uniformity index was 0.08, particle density was 2.29 g / cc, and specific surface area was 2.86 m². 2 / g, powder conductivity 1.23S / cm, button half-cell tested capacity 1480.1mAh / g, first efficiency 78.04%, finished battery tested 1000 cycles capacity retention 69%, rate charge and discharge ratios 43.5% and 73.8% respectively.

[0169] Comparative Example 4

[0170] (1) Compared with Example 1, the cooling rate of the condensing medium outlet temperature was set to 0.25℃ / h, and the carbon coating temperature was adjusted to 600℃.

[0171] (2) Product detection results: carbon content was 0.9%, Mg content was 6.5%, cross-sectional energy dispersive spectroscopy analysis showed a density index of 1.83, Mg elemental uniformity index was 0.17, particle density was 2.41 g / cc, and specific surface area was 13.52 m². 2 / g, powder conductivity is 0.01S / cm, button half-cell tested capacity is 1279.9mAh / g, first efficiency is 70.36%, finished battery tested after 1000 cycles capacity retention is 33%, and the rate charge-discharge ratio is 40.1% and 62.3%, respectively.

[0172] Performance testing methods:

[0173] I. Tightness Testing Method

[0174] The above-mentioned negative electrode material was subjected to cross-sectional energy dispersive spectroscopy (EDS). A predetermined region was arbitrarily selected within a two-dimensional cross-section of 80% radius from the center of each of the n particles to the particle surface for scanning analysis. The mass content values ​​of carbon in each predetermined region of the n particles were obtained as k1, k2, k3, ... k n-1 k n , Let be the average mass content of carbon in a preset region of n particles, where n is a natural number greater than 5.

[0175]

[0176] α is the density index of the negative electrode material, and n is a natural number greater than 5. Specific testing methods for energy dispersive spectroscopy (EDS): Multiple particles were cut using a Hitachi E-3500 ion mill, and their cross-sectional morphology was observed using a Hitachi S-4800 cold field emission scanning electron microscope. The elemental composition and distribution were then observed using an Oxford energy dispersive spectrometer (EDS).

[0177] II. Test method for uniform distribution of doped elements

[0178] The negative electrode material was subjected to cross-sectional energy dispersive spectroscopy (EDS). A predetermined region was randomly selected within a two-dimensional cross-section of 80% radius from the center of each of the N particles to the particle surface for scanning analysis. The mass content values ​​of the doped elements in the predetermined regions of the N particles were obtained as K1, K2, K3, ... K N-1 K N , Let N be the average mass content of doped elements within a preset region of N particles, where N is a natural number greater than 5.

[0179]

[0180] β is the uniformity parameter of the dopant element distribution, and N is a natural number greater than 5. Specific testing methods for energy dispersive spectroscopy (EDS): Multiple particles were cut using a Hitachi E-3500 ion mill, and the morphology of their cross-sections was observed using a Hitachi S-4800 cold field emission scanning electron microscope. The elemental composition and distribution were then observed using an Oxford energy dispersive spectrometer (EDS).

[0181] III. Carbon Content Testing Method

[0182] Infrared absorption method

[0183] Test method: The sample is burned in an oxygen stream to produce CO2. Under a certain pressure, the energy of CO2 absorbing infrared radiation is proportional to its concentration. Therefore, by measuring the energy change of CO2 gas before and after passing through the infrared absorber, the carbon content can be calculated.

[0184] IV. Test Methods for Doping Element Content

[0185] 0.100g of the negative electrode material was placed in a clean platinum crucible and then calcined in a muffle furnace under air atmosphere at 750°C for 4 hours until the carbon elements were completely burned off. The cooled residue was then reacted thoroughly with a mixture of 4mL HNO3 and 6mL HF. The platinum crucible containing this solution was then placed on a 350°C hot plate until the hydrofluoric acid evaporated without emitting white smoke. 6mL of concentrated HCl was then added, and the mixture was heated until the residue was completely dissolved and diluted to a 100mL plastic volumetric flask. Finally, the total dopant content of the material was determined using an ICP spectrometer (Agilent 5800V DVICP-OES).

[0186] V. Particle density testing method

[0187] Helium replacement method

[0188] The particle density of the negative electrode material was obtained by gas adsorption expansion method using a true density meter (AccuPyc II) from the United States.

[0189] Test Method: Particle density testing typically employs the gas expansion displacement method. This method utilizes Boyle's law (PV = nRT) for small-molecule inert gases under specific conditions. The volume of the sample (including the volume of closed pores within the particles) is accurately determined by measuring the change in gas volume within the test chamber caused by the insertion of the sample, thus obtaining its particle density.

[0190] VI. Test methods for D10, D50, and D90

[0191] Measurements were taken in accordance with GB / T 19077.1-2008 "Particle size analysis by laser diffraction - Part 1: General rules" or the equipment manual. A laser particle size analyzer (Malvin Panaco MS3000) was used. D10, D50, and D90 in this application refer to the cumulative volume distribution particle size.

[0192] VII. Methods for testing specific surface area

[0193] The measurement was performed according to GB / T 19587-2004 "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method" or the equipment manual. A specific surface area and pore size analyzer (McTriStar II 3020) was used. The adsorbed gas was N2.

[0194] VIII. Methods for testing the thickness of the carbon layer

[0195] The negative electrode material was cross-sectioned using an ion mill, and the average thickness of the carbon coating layer on the material surface was measured using SEM.

[0196] Electrical performance testing methods:

[0197] I. Capacity and First-Effect Test Methods

[0198] The battery sample fabrication process was as follows: the specific capacity and initial charge-discharge coulombic efficiency of the negative electrode material were determined according to the equipment and methods outlined in BTRTC / ZY / 01-020 "Button Battery Method Operating Instruction": a button battery was assembled. The counter electrode used a lithium metal sheet, and the separator was a PP-PE-PP composite membrane with a diameter of 19.2 mm. The electrolyte composition ratio was EC / EMC / DMC = 1:1:1, and the lithium salt (LiPF6) concentration was 1.05 mol / L.

[0199] Using a button cell battery charging and discharging device, charge at a constant current of 0.1C to 10mV, then switch to a constant current of 0.02C to 5mV, and discharge at a constant current of 0.1C to 1.5V (cutoff).

[0200] II. Cyclic Performance and Rate Charge-Discharge Performance Test Methods

[0201] The following methods were used to test the electrochemical cycling performance and rate charge / discharge performance:

[0202] The negative electrode sheet was prepared according to a silicon-graphite composite: binder: conductive agent ratio of 95.1:3.4:1.5. The positive electrode was prepared using high-nickel NMC product M2-C2 (manufactured by BTR) with a binder: conductive agent ratio of 96.6:1.4:2.0. The positive and negative electrode sheets were then wound into 18650 cylindrical cells. After aging, electrolyte injection, formation, and capacity testing, the cells formed a cylindrical battery. The battery design parameters were: positive electrode compaction 3.4 g / cc, negative electrode compaction 1.65 g / cc, and negative electrode areal density 200 g / m³. 2 The N / P ratio was designed to be 8.2%. The cells were then subjected to cycle performance and rate performance tests after capacity grading.

[0203] Cyclic performance test conditions are: 25℃, 0.5C charging / 1C discharging, voltage range 2.75-4.2V;

[0204] The rate performance test conditions are: 25℃, 0.2C charging / 3C discharging and 3C charging / 0.2C discharging, with a voltage range of 2.75-4.2V.

[0205] III. Test Methods for Powder Conductivity

[0206] Using a powder conductivity meter (MCP-PD51) from Mitsubishi Chemical (Japan), the resistivity of circular block materials under different pressures was measured using the dynamic four-probe method. This allows for accurate calculation of the resistivity and conductivity of powder samples under varying pressures, and also provides a curve showing the relationship between pressure and conductivity. Powder conductivity values ​​under a 20 kN pressure condition were then compared.

[0207] After the above tests, the negative electrode materials prepared in Examples 1-8 and Comparative Examples 1-4 are sample numbers S1-S8 and R1-R4, respectively; the relevant parameters of the negative electrode materials are shown in Table 1.

[0208] Table 1: Relevant parameters of the negative electrode materials of Examples 1-8 and Comparative Examples 1-4

[0209]

[0210] Table 2: Electrochemical performance characterization of the negative electrode materials of Examples 1-8 and Comparative Examples 1-4

[0211]

[0212]

[0213] The results in Tables 1 and 2 illustrate that Embodiments 1 to 8 of this application control the temperature of the condensation interface by gradient control of the condensation medium temperature, and in conjunction with... Figure 3 It can be seen that the doping elements of the particles obtained in Example 2 are evenly distributed and have good density, which enables the negative electrode material to have high capacity, first efficiency and cycle retention when applied to the battery, and the battery has better chemical performance.

[0214] In contrast, in Comparative Example 1, the temperature of the condensation interface was not controlled by gradient control of the condensation medium temperature. The reaction between the dopant elements and the silicon oxide matrix was too vigorous in the later stages of deposition, resulting in a high density index. Furthermore, the secondary evaporation of a large number of exothermic dopant elements led to a high dopant element distribution uniformity parameter, i.e., a large β. The test results show that, compared to Examples 1-8, the battery capacity, initial efficiency, and cycle retention rate are all lower.

[0215] Furthermore, by comparing Examples 1-8 and Comparative Example 1, controlling the temperature of the condensation interface and reducing the temperature difference at the condensation interface during condensation can result in higher battery capacity, initial efficiency, and rate performance. In Comparative Example 2, although the temperature of the fourth chamber was controlled by gradient cooling, the large cooling gradient of the condensation medium led to severe separation of the two phases during vapor mixing and condensation. This resulted in ineffective doping of the negative electrode material with dopant elements, leading to a low dopant content and a density index α of 0.08, lower than 0.1. Additionally, the dopant element distribution uniformity parameter β was relatively large, approaching the upper limit. The test results show that, compared to Examples 1-4, the battery's initial efficiency, rate performance, and rate capability—that is, its chemical performance—are inferior.

[0216] In Example 6, although the temperature of the fourth chamber was controlled by gradient cooling, the dopant could be effectively doped because the cooling gradient of the condensing medium was slightly small. However, the initial temperature of the condensation interface was low, meaning the initial temperature of the fourth chamber was low, and the set temperature of the cooling gradient was higher than that of Examples 1-4. Due to the temperature effect, the condensation rates of the two-phase vapors were significantly different, resulting in uneven doping of the dopant and a large dopant distribution uniformity parameter β. In addition, when the dopant was unevenly doped, the redox reaction between the dopant and silicon oxide was also uneven, resulting in localized looseness and localized density. Therefore, when carbon was subsequently coated, the density index α was close to the upper limit of 1.35. Combined with the test results, it can be seen that compared with Examples 1-4, the battery's first efficiency, 1000-cycle cycle retention rate, rate performance, and overall chemical performance were slightly worse.

[0217] In Examples 7 and 8, the dopant element was Mg, and the mass content of Mg and the values ​​of α and β were all within the preferred range. The first efficiency, 1000-cycle retention rate, and rate charge / discharge ratio were all relatively high. In Comparative Examples 3 and 4, the mass content of the dopant element and the values ​​of α and β were not within the preferred range. Compared with Examples 7 and 8, the first efficiency, 1000-cycle retention rate, and rate charge / discharge ratio were all relatively low. It can be seen that if the dopant element content is too small or too large, it will directly affect the dopant element distribution uniformity parameters, and thus affect the chemical performance of the battery, such as the first efficiency, 1000-cycle retention rate, and rate charge / discharge ratio.

[0218] Furthermore, those skilled in the art should recognize that the above embodiments are merely illustrative of this application and are not intended to limit this application. Any appropriate changes and variations made to the above embodiments within the essential spirit and scope of this application fall within the scope of this application's disclosure.

Claims

1. A negative electrode material, characterized in that, It comprises multiple particles, each particle including a core and carbon material. The core includes silicon-based material and doping elements. A portion of the carbon material exists within the core, and another portion coats the surface of the core. The density index α of the negative electrode material satisfies: 0.1 ≤ α ≤ 1.5, wherein the density index α is measured by the following test method: The negative electrode material was subjected to cross-sectional energy dispersive spectroscopy (EDS). A two-dimensional preset region was arbitrarily selected within a cross-section extending from the center of each of the n particles to 80% of the particle's outer surface for scanning analysis. The mass content values ​​of carbon in each preset region of the n particles were obtained as k1, k2, k3, ... k n-1 k n , Let be the average mass content of carbon in a preset region of n particles, where n is a natural number greater than 5.

2. The negative electrode material according to claim 1, characterized in that, The negative electrode material satisfies at least one of the following conditions. (1) The doping element is selected from at least one element in Group IA, IIA, and IIIA; (2) The doping element is selected from at least one element in Groups IA, IIA, and IIIA, and the distribution uniformity parameter β of the doping element satisfies: β≤0.5, and β is measured by the following test method. The negative electrode material was subjected to cross-sectional energy dispersive spectroscopy (EDS). A two-dimensional preset region was arbitrarily selected within an 80% radius radius from the center of each of the N particles to the particle surface for scanning analysis. The mass content values ​​of the doped elements in the preset regions of each of the N particles were obtained as K1, K2, K3, ... K N-1 K N , Let N be the average mass content of doped elements within a preset region of N particles, where N is a natural number greater than 5. (3) The doping element is selected from at least one element in Group IA, IIA, or IIIA, and the mass percentage of the doping element is 3%-20% based on the mass of the negative electrode material.

3. The negative electrode material according to claim 1, characterized in that, The doping element is magnesium. When the mass percentage of the doping element is greater than or equal to 3% and less than or equal to 13%, the negative electrode material includes MgSiO3, and the mass percentage of MgSiO3 is 8-65% based on the mass of the negative electrode material. When the mass percentage of the doping element is greater than or equal to 15% and less than or equal to 20%, the anode material includes Mg2SiO4, and the mass percentage of Mg2SiO4 is 20-60% based on the mass of the anode material.

4. The negative electrode material according to claim 1, characterized in that, The negative electrode material satisfies at least one of the following conditions. (1) The silicon-based material includes silicon oxide, the chemical formula of which is SiO2. x where 0 < x ≤ 2; (2) The silicon-based material includes silicon oxide, the chemical formula of which is SiO₂. x where 0 < x < 1; (3) The silicon-based material includes silicon oxide, which includes the mass of silicon and the mass of oxygen, and the atomic ratio of the mass of silicon to the mass of oxygen is 0 to 2, excluding 0; (4) The silicon-based material includes silicon oxide, which includes the mass of silicon and the mass of oxygen, and the atomic ratio of the mass of silicon to the mass of oxygen is 0 to 1, excluding 0.

5. The negative electrode material according to claim 1, characterized in that, The carbon material covering the surface of the core forms a carbon layer with a thickness ranging from 50 nm to 500 nm.

6. The negative electrode material according to claim 1, characterized in that, The negative electrode material satisfies at least one of the following conditions. (1) Based on the mass of the negative electrode material, the mass percentage of the carbon material is 1%-20%; and (2) The carbon material includes amorphous carbon.

7. The negative electrode material according to claim 1, characterized in that, The negative electrode material satisfies at least one of the following conditions. (1) The particle density of the negative electrode material satisfies 2.30 g / cc ≤ ρg ≤ 2.60 g / cc; (2) The powder conductivity σ of the negative electrode material under 20KN pressure is ≥0.3S / cm; (3) The specific surface area of ​​the negative electrode material is 1.5-15m². 2 / g.

8. The negative electrode material according to claim 1, characterized in that, The negative electrode material satisfies at least one of the following conditions. (1) In the negative electrode material, D10 > 2.0 μm; (2) In the negative electrode material, 4μm < D50 < 10μm; (3) In the negative electrode material, 8μm < D90 < 15μm.

9. The negative electrode material according to claim 1, characterized in that, The particle size distribution of the negative electrode material satisfies: 0.9≤(D90-D10) / D50≤2.

3.

10. A secondary battery, characterized in that, It includes the negative electrode material according to any one of claims 1 to 9.

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