Silicon-oxygen composite material, method for manufacturing the same, secondary battery, and electric device

Abstract

The application provides a silicon-oxygen composite material, which comprises a silicon-oxygen material matrix and a first doped element distributed in the silicon-oxygen material matrix, at least part of the first doped element exists in the silicon-oxygen material matrix in a crystal form, and the grain size of the crystal is ≤9 nm, wherein the first doped element satisfies: the lithium ion diffusion coefficient of the elemental substance of the first doped element at 25 ℃ is greater than the lithium ion diffusion coefficient of the elemental substance of silicon at 25 ℃.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a silicon-oxygen composite material, a preparation method thereof, a secondary battery and an electric device. BACKGROUND

[0002] Secondary batteries have the characteristics of high capacity and long service life, and are therefore widely used in electronic devices such as mobile phones, notebook computers, electric vehicles, electric cars, electric planes, electric ships, electric toy cars, electric toy ships, electric toy planes and electric tools. Due to the great progress made in secondary batteries, higher requirements are placed on the performance of secondary batteries. In order to improve the energy density of secondary batteries, the industry is currently considering using silicon-based negative electrode active materials, but the large expansion and poor conductivity of the silicon-based negative electrode active materials seriously affect the cycle performance and rate performance of the battery, greatly limiting the further application of the silicon-based negative electrode active materials. SUMMARY

[0003] The present application is made in view of the above problems, and aims to provide a silicon-oxygen composite material that, as a negative electrode active material, can prolong the discharge time of a battery, improve the rate performance of the battery, prolong the cycle life of the battery and improve the cycle performance of the battery.

[0004] In a first aspect, the present application provides a silicon-oxygen composite material, which comprises a silicon-oxygen material matrix and a first doping element distributed in the silicon-oxygen material matrix, at least part of the first doping element exists in the silicon-oxygen material matrix in the form of a crystal, and the grain size of the first doping element is ≤9 nm, wherein the first doping element satisfies: the lithium ion diffusion coefficient of the elemental substance of the first doping element at 25°C is greater than the lithium ion diffusion coefficient of the elemental silicon at 25°C.

[0005] The first doping element is distributed in the form of a crystal inside the silicon-oxygen material matrix, and the grain size is ≤9 nm, indicating that the first doping element is uniformly dispersed at the atomic scale inside the silicon-oxygen material matrix, which can effectively reduce the migration energy barrier of lithium ions, improve the lithium ion diffusion coefficient, improve the lithium ion migration kinetics, prolong the discharge time of the battery, improve the rate performance of the battery, in addition, the crystals formed by the first doping element are dispersed around the silicon grains, which can alleviate the growth of silicon clusters, effectively inhibit the expansion and pulverization effect of the silicon-oxygen composite material, enhance the structural integrity and volume stability of the silicon-oxygen composite material during the process of lithium intercalation / deintercalation, and improve the cycle performance of the battery, in addition, the first doping element exists in the form of a small-grain-size crystal, which will not cause large changes in the crystal structure of the silicon-oxygen material matrix and will not cause large changes in the phase characteristics of the material, can well maintain the structural stability of the material, is not easy to pulverize during charging and discharging, prolongs the cycle life of the battery and improves the cycle performance of the battery.

[0006] In any embodiment, the lithium ion diffusion coefficient of the single element of the first doping element at 25°C is greater than 10 - 14 cm 2 / S, optionally greater than 10 -14 cm 2 / S and less than or equal to 10 -13 cm 2 / S.

[0007] In any embodiment, the lithium ion diffusion coefficient of the single element of silicon at 25°C is less than 10 -14 cm 2 / S, optionally greater than 10 -15 cm 2 / S and less than 10 -14 cm 2 / S.

[0008] In any embodiment, the first doping element comprises at least one of Sn, Ge, Sb, Bi, and Sr.

[0009] The first doping element described above has an excellent lithium ion diffusion coefficient, is abundant and easy to obtain, is suitable for use in various batteries, and has excellent application prospects.

[0010] In any embodiment, the grain size of the first doping element is ≤7 nm.

[0011] Controlling the grain size of the first doping element within a suitable range can further prolong the discharge time of the battery, further improve the rate performance and cycle performance of the battery, and prolong the cycle life of the battery.

[0012] In any embodiment, the XRD diffraction pattern of the silicon-oxygen composite material further comprises a diffraction peak of silicon grains, and the silicon-oxygen composite material satisfies at least one of the following relationships (1)-(2):

[0013] (1) 0.35≤Y / 2X≤4, optionally 0.7≤Y / 2X≤4;

[0014] (2) -5≤5Xsin2θ-Y≤15, optionally -5≤5Xsin2θ-Y≤10;

[0015] wherein Y is the grain size of the first doping element, X is the grain size of the silicon grains, X and Y are both in nm, and 2θ is the XRD diffraction angle of the crystal.

[0016] The battery has excellent cycle performance and rate performance, and the battery has a long cycle life.

[0017] In any embodiment, the XRD diffraction pattern of the silicon-oxygen composite material contains a diffraction peak of the first doped element crystal, the diffraction peak half-width of the crystal is 3-7°, and / or the intensity of the diffraction peak of the crystal is 600 counts -1 -1200 counts -1 .

[0018] In any embodiment, the mass fraction of the first doped element is less than or equal to 12%, and is optionally 1-10%, based on the total mass of the silicon-oxygen composite material.

[0019] Controlling the mass content of the first doped element within a suitable range, the battery has excellent cycle performance and rate performance, and the battery has a long cycle life.

[0020] In any embodiment, the silicon-oxygen composite material further comprises a second doped element, the second doped element comprises at least one of a non-metallic element, an alkali metal element, and an alkaline earth metal element, the non-metallic element comprises at least one of B, N, F, Cl, and S;

[0021] Optionally, the non-metallic element comprises at least one of B, N, F, Cl, and S;

[0022] Optionally, the alkali metal element comprises at least one of Li, Na, and K;

[0023] Optionally, the alkaline earth metal element comprises at least one of Mg, Ca, Be, and Sr;

[0024] The silicon-oxygen composite material contains the second doped element, which can improve the discharge capacity retention rate of the battery at low temperature or / and improve the energy density of the battery.

[0025] In any embodiment, the mass fraction of the second doped element is less than or equal to 7%, and is optionally 1-5%, based on the total mass of the silicon-oxygen composite material.

[0026] Controlling the mass fraction of the second doped element within a suitable range, the battery has excellent cycle performance and rate performance, and the battery has a long cycle life.

[0027] In any embodiment, the silicon-oxygen composite material further comprises a carbon layer covering at least part of the surface of the silicon-oxygen material matrix, and the thickness of the carbon layer is optionally 1-4 nm.

[0028] The silicon-oxygen composite material is coated with a carbon layer on at least part of the surface, so that the battery has excellent cycle performance and rate performance, and the battery has a long cycle life.

[0029] In any embodiment, the volume distribution particle size Dv50 of the silicon-oxygen composite material is 3-8 μm, and optionally 4-6 μm.

[0030] The volume distribution particle size Dv50 of the silicon-oxygen composite material is within a suitable range, the battery has excellent cycle performance and rate performance, and the battery has a long cycle life.

[0031] In a second aspect of the present application, a preparation method of a silicon-oxygen composite material is provided, and the preparation method comprises:

[0032] A first vapor containing silicon and silicon dioxide is subjected to first vapor deposition to obtain a silicon-oxygen material matrix;

[0033] A second vapor containing a first doping element is subjected to second vapor deposition with the silicon-oxygen material matrix to obtain a silicon-oxygen composite material, at least part of the first doping element exists in the silicon-oxygen material matrix in the form of a crystal, and the grain size of the first doping element crystal is ≤9 nm, wherein the first doping element satisfies: the lithium ion diffusion coefficient of the elemental substance of the first doping element at 25°C is greater than the lithium ion diffusion coefficient of the elemental silicon at 25°C.

[0034] The silicon-oxygen composite material is obtained by vapor deposition, and the bulk doping causes the first doping element to be uniformly and dispersedly distributed in the silicon-oxygen material matrix at an atomic scale, causes the first doping element to be distributed in the silicon-oxygen material matrix in the form of a crystal, and the grain size of the crystal is less than or equal to 9 nm, indicating that the first doping element is uniformly and dispersedly distributed in the silicon-oxygen material matrix at an atomic scale, can effectively reduce the migration energy barrier of lithium ions, improve the lithium ion diffusion coefficient, improve the lithium ion migration kinetics, prolong the discharge time of the battery, improve the rate performance of the battery, in addition, the crystal formed by the first doping element is dispersed around the silicon grains, can alleviate the growth of silicon clusters, effectively inhibit the expansion and pulverization effect of the silicon-oxygen composite material, enhance the structural integrity and volume stability of the silicon-oxygen composite material during the embedding and de-embedding of lithium, improve the cycle performance of the battery, in addition, the first doping element exists in the form of a crystal with a small grain size, will not cause large changes in the crystal structure of the silicon-oxygen material matrix, will not cause large changes in the phase characteristics of the material, can well maintain the structural stability of the material, is not easy to pulverize during charging and discharging, improves the cycle performance of the battery, and prolongs the cycle life of the battery.

[0035] In any embodiment, the temperature of the first vapor deposition is 1000°C-1300°C, and optionally 1100°C-1250°C; and / or, the time of the first vapor deposition is 6h-12h, and optionally 8h-10h.

[0036] Controlling the temperature and / or time of the first vapor deposition within a suitable range can obtain a silicon-oxygen material matrix with excellent structural parameters and facilitate the subsequent doping process of the elements.

[0037] In any embodiment, the temperature of the second vapor deposition is 800-900°C, which can be 820-880°C; and / or, the time of the second vapor deposition is 4-10h, which can be 6-8h.

[0038] Controlling the temperature and / or time of the second vapor deposition within a suitable range can achieve the bulk doping distribution of the first doping element while ensuring the existence of the first doping element in the form of small-sized crystals in the silicon-oxygen material matrix, thereby improving the conductivity of the material and the rate performance and cycle performance of the battery.

[0039] In any embodiment, the method for preparing the silicon-oxygen composite material comprises:

[0040] The second vapor containing the first doping element and the second doping element is subjected to the second vapor deposition with the silicon-oxygen material matrix to obtain the silicon-oxygen composite material, and the second doping element comprises at least one of a non-metallic element, an alkali metal element, and an alkaline earth metal element;

[0041] Optionally, the non-metallic element comprises at least one of B, N, F, Cl, and S;

[0042] Optionally, the alkali metal element comprises at least one of Li, Na, and K;

[0043] Optionally, the alkaline earth metal element comprises at least one of Mg, Ca, Be, and Sr.

[0044] Doping the second doping element in the form of vapor can achieve the uniform bulk doping of the second doping element and improve the discharge capacity retention rate of the battery at low temperature and / or the energy density of the battery.

[0045] In any embodiment, the method for preparing the silicon-oxygen composite material further comprises:

[0046] Performing carbon coating treatment on the surface of the silicon-oxygen composite material;

[0047] Optionally, the temperature of the carbon coating treatment is 500-750°C, which can be 660-720°C;

[0048] Optionally, the time of the carbon coating treatment is 2-10h, which can be 6-8h.

[0049] Suitable carbon coating treatment temperature and / or time, on the one hand, forms a carbon layer structure with uniform distribution and suitable thickness on the surface of the silicon-oxygen composite material, which can buffer the volume change of the silicon-oxygen composite material during lithium extraction, and at the same time improve the electronic conductivity of the material surface, improve the cycle performance and rate performance of the battery, on the other hand, can effectively control the grain size of the first doped element and the silicon grain size within a suitable range, so that the silicon-oxygen material has excellent structure parameters, thereby prolonging the discharge time of the battery, improving the rate performance of the battery, improving the cycle performance of the battery, and prolonging the cycle life of the battery.

[0050] The third aspect of the present application provides a secondary battery comprising a negative electrode sheet, wherein the negative electrode sheet comprises the silicon-oxygen composite material of the first aspect or the silicon-oxygen composite material prepared by the preparation method of the second aspect.

[0051] The fourth aspect of the present application provides an electric device comprising the secondary battery of the third aspect. BRIEF DESCRIPTION OF DRAWINGS

[0052] Figure 1 is an XRD pattern of the silicon-oxygen composite material of Example 1 of the present application;

[0053] Figure 2 is a scanning electron microscope image of the silicon-oxygen composite material of Example 1 of the present application;

[0054] Figure 3 is a schematic diagram of a secondary battery of an embodiment of the present application;

[0055] Figure 4 is Figure 3 is an exploded view of the secondary battery of an embodiment of the present application shown in FIG. 5;

[0056] Figure 5 is a schematic diagram of a battery module of an embodiment of the present application;

[0057] Figure 6 is a schematic diagram of a battery pack of an embodiment of the present application;

[0058] Figure 7 is Figure 6 is an exploded view of the battery pack of an embodiment of the present application shown in FIG. 9;

[0059] Figure 8 is a schematic diagram of an electric device using the secondary battery of an embodiment of the present application as a power source.

[0060] REFERENCE SIGNS:

[0061] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 cover plate. DETAILED DESCRIPTION

[0062] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the adhesive, preparation method, electrode, battery, and power device of this application. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of essentially identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0063] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this application; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0064] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0065] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0066] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0067] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0068] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0069] In the field of novel rechargeable battery anode active materials, silicon-based anode materials have attracted widespread attention due to their ultra-high lithium storage capacity and low voltage platform, making them ideal next-generation rechargeable anode active materials. However, silicon-based materials have several problems during the charging and discharging process of lithium-ion insertion and extraction: huge volume changes, with the volume of silicon-based materials expanding to 300% of its original size during lithium-ion insertion and then shrinking sharply during lithium-ion extraction, resulting in the breakage of active material particles and the shedding and pulverization of electrode sheets, leading to a sharp decline in cycle life; large irreversible capacity, with low initial coulombic efficiency of silicon-based materials, especially silicon-oxygen materials, which contain inactive components that can consume lithium ions, generating a large amount of irreversible capacity during the first charge and discharge process, making cathode matching difficult, resulting in low full-cell efficiency and short cycle life; in addition, silicon itself is a semiconductor with poor conductivity, which is not conducive to the rapid transfer of electrons, thus affecting the rate performance of silicon-oxygen materials.

[0070] [Silicon-oxygen composite materials]

[0071] Based on this, this application proposes a silicon-oxygen composite material comprising a silicon-oxygen material matrix and a first dopant element distributed in the silicon-oxygen material matrix, wherein at least a portion of the first dopant element exists in crystalline form in the silicon-oxygen material matrix, and the grain size of the first dopant element is ≤9nm, wherein the first dopant element satisfies the following: the lithium-ion diffusion coefficient of the elemental form of the first dopant element at 25°C is greater than the lithium-ion diffusion coefficient of silicon elemental form at 25°C.

[0072] The first dopant element is distributed in crystalline form within the silicon-oxygen matrix, with a crystal grain size of less than or equal to 9 nm. This indicates that the first dopant element is uniformly dispersed at the atomic scale within the silicon-oxygen matrix, effectively reducing the lithium-ion migration barrier, increasing the lithium-ion diffusion coefficient, improving lithium-ion migration kinetics, enhancing the material's conductivity, extending battery discharge time, and improving battery rate performance. Furthermore, the crystals formed by the first dopant element, dispersed around the silicon grains, can alleviate silicon cluster growth, effectively suppressing the expansion and pulverization effect of the silicon-oxygen composite material, enhancing the structural integrity and volume stability of the silicon-oxygen composite material during lithium insertion / extraction, and improving battery cycle performance. Additionally, the presence of the first dopant element in a small-grain-size crystalline form does not cause significant changes to the crystal structure of the silicon-oxygen matrix, nor does it lead to major alterations in the material's phase properties. This maintains the material's structural stability well, making it less prone to pulverization during charge and discharge, thus improving battery cycle performance and extending battery cycle life.

[0073] Compared to the first dopant element existing in an amorphous form, the first dopant element existing in a crystalline form has superior electrical conductivity and ion conductivity, which can effectively improve the lithium-ion diffusion coefficient and improve the rate performance of the battery.

[0074] In summary, the silicon-oxygen composite material of this application, as a negative electrode active material, can extend the discharge time of the battery, improve the rate performance of the battery, extend the cycle life of the battery, and improve the cycle performance of the battery.

[0075] In this application, the grain size of the first dopant element has a meaning known in the art and can be determined using instruments and methods known in the art. As an example, the XRD pattern of the silicon-oxygen composite material can be tested according to the JIS / K0131-1996 testing standard. Based on the XRD pattern of the silicon-oxygen composite material, the full width at half maximum (FWHM) β and the diffraction angle θ of the (101) crystal plane diffraction peak of the first dopant element are taken and substituted into the Debye-Scherrer formula to calculate the crystal grain size. The Debye-Scherrer formula is as follows: Dhkl=kλ / (βcosθ), where Dhkl represents the crystal grain size in nm; k represents the Scherrer constant, 0.89; λ represents the incident X-ray wavelength, 0.15406 nm; β represents the FWHM of the diffraction peak in rad; and θ represents the diffraction angle in degrees.

[0076] In some embodiments, the grain size of the first dopant element may be less than or equal to 4 nm, less than or equal to 5 nm, less than or equal to 6 nm, less than or equal to 7 nm, less than or equal to 8 nm, or less than or equal to 9 nm.

[0077] In some embodiments, the first dopant element includes at least two or more elements, and the grain size of the first dopant element is the average of the grain sizes of the multiple first dopant elements.

[0078] In this application, "lithium-ion diffusion coefficient" refers to an important parameter used to characterize the kinetic behavior of materials. The larger the diffusion coefficient of a material, the better its high-current discharge capability, the higher its power density, and the better its high-rate performance.

[0079] In this application, the "first doping element" refers to a class of elements whose elemental form has a lithium-ion diffusion coefficient greater than that of elemental silicon.

[0080] The lithium-ion diffusion coefficient of a material has a meaning known in the art and can be tested using methods known in the art. As an example, this application uses the constant current intermittent titration (GITT) method to determine the lithium-ion diffusion coefficient of a single-element material composed of doped elements.

[0081] In this application, the term "crystal" refers to a substance formed by the regular, periodic repetition of matter's particles (molecules, atoms, ions) in three-dimensional space.

[0082] In some embodiments, the elemental form of the first dopant has a lithium-ion diffusion coefficient greater than 10 at 25°C. - 14 cm 2 / S, can be greater than 10 -14 cm 2 / S and less than or equal to 10-13 cm 2 / S, the lithium-ion diffusion coefficient of elemental silicon at 25°C is less than 10. -14 cm 2 / S, can be greater than 10 -15 cm 2 / S and less than 10 -14 cm 2 / S.

[0083] In some embodiments, the lithium-ion diffusion coefficient of the first dopant element at 25°C can be selected as 2 × 10⁻⁶. -14 cm 2 / S、3×10 -14 cm 2 / S、4×10 -14 cm 2 / S、5×10 -14 cm 2 / S、6×10 -14 cm 2 / S、7×10 -14 cm 2 / S、8×10 -14 cm 2 / S、9×10 -

[0084] 14 cm 2 / S、10 -13 cm 2 Any value in / S or a range consisting of any two of its values.

[0085] In some embodiments, the lithium-ion diffusion coefficient of elemental silicon at 25°C is greater than 10. -15 cm 2 / S and less than 10 -14 cm 2 / S. In some embodiments, the lithium-ion diffusion coefficient of elemental silicon at 25°C can be selected as 2 × 10⁻⁶. -15 cm 2 / S、3×10 -15 cm 2 / S、4×10 -15 cm 2 / S、5×10 -15 cm 2 / S、6×10 -15 cm 2 / S、7×10 -15 cm 2 / S、8×10 -

[0086] 15 cm2 / S、9×10 -15 cm 2 Any value in / S or a range consisting of any two of its values.

[0087] In some embodiments, the first dopant element includes at least one of Sn, Ge, Sb, Bi, and Sr.

[0088] In some implementations, the first dopant element includes at least two of Sn, Ge, Sb, Bi, and Sr. For example, the first dopant element may include Ge and Sb, or the dopant element may include Sn and Bi.

[0089] The aforementioned first doping element possesses an excellent lithium-ion diffusion coefficient, which can effectively improve the conductivity of the silicon-oxygen matrix and enhance the rate performance of the battery. Furthermore, the raw material is abundant and readily available, making it suitable for various batteries and demonstrating excellent application prospects.

[0090] In some implementations, the first dopant element includes Sn.

[0091] Existing batteries exhibit greater polarization, particularly concentration polarization, at low SOC levels, limiting their further applications. The Sn-doped silicon-oxygen composite material of this application possesses an excellent lithium-ion diffusion coefficient, which can improve electrode conductivity, reduce electrode polarization, enhance rate performance, and extend discharge time at low SOC levels, thus meeting the needs of novel application scenarios.

[0092] In the application, the term "battery polarization" refers to the phenomenon that an electrode deviates from its equilibrium electrode potential when current passes through it. The equilibrium electrode potential is the electrode potential when no current passes through the battery, and includes ohmic polarization, electrochemical polarization, and concentration polarization.

[0093] In the application, the term "concentration polarization" refers to polarization caused by the diffusion rate of lithium ions participating in the reaction in the solid phase being less than the electrochemical reaction rate.

[0094] In some implementations, the grain size of the first dopant element is ≤7nm.

[0095] In some implementations, the grain size of the first dopant element is less than or equal to 4 nm, less than or equal to 5 nm, less than or equal to 6 nm, or less than or equal to 7 nm.

[0096] By controlling the grain size of the first dopant element within a suitable range, the discharge time of the battery can be further extended, the rate performance and cycle performance of the battery can be further improved, and the cycle life of the battery can be extended.

[0097] In some embodiments, the XRD diffraction pattern of the silicon-oxygen composite material also includes diffraction peaks of silicon grains, and the silicon-oxygen composite material exhibits at least one of the following relationships (1)-(2):

[0098] (1) 0.35≤Y / 2X≤4, optionally, 0.7≤Y / 2X≤4;

[0099] (2) -5≤5Xsin2θ-Y≤15, optionally, -5≤5Xsin2θ-Y≤10;

[0100] Where Y is the grain size of the first dopant element, X is the grain size of the silicon grain, and the units of X and Y are both nm, and 2θ is the XRD diffraction angle of the crystal.

[0101] In some embodiments, the silicon-oxygen composite material has the following relationship: 0.35≤Y / 2X≤4, where Y is the grain size of the first dopant element and X is the grain size of the silicon grain.

[0102] In some embodiments, the silicon-oxygen composite material exhibits any of the following relationships: 0.35≤Y / 2X≤1, 0.35≤Y / 2X≤0.7, 0.35≤Y / 2X≤1, 0.35≤Y / 2X≤2, 0.35≤Y / 2X≤3, 0.35≤Y / 2X≤4, 0.7≤Y / 2X≤1, 0.7≤Y / 2X≤2, 0.7≤Y / 2X≤3, 0.35≤Y / 2X≤4, 1≤Y / 2X≤2, 1≤Y / 2X≤3, 1≤Y / 2X≤4, 2≤Y / 2X≤3, 2≤Y / 2X≤3, 2≤Y / 2X≤4, 3≤Y / 2X≤4.

[0103] In this paper, the grain size of silicon is a term known in the art and can be tested using methods known in the art. As an example, the XRD pattern of silicon-oxygen composites can be tested according to the JIS / K0131-1996 testing standard. Based on the XRD pattern of the silicon-oxygen composites, the full width at half maximum (FWHM) β and the diffraction angle θ of the Si(111) crystal plane diffraction peak are taken and substituted into the Debye-Scherrer formula to calculate the grain size of silicon. The Debye-Scherrer formula is as follows: Dhkl=kλ / (βcosθ), where Dhkl represents the grain size of silicon in nm; k represents the Scherrer constant, 0.89; λ represents the incident X-ray wavelength, 0.15406 nm; β represents the FWHM of the diffraction peak in rad; and θ represents the diffraction angle in degrees.

[0104] Having appropriately sized silicon grains can reduce the volume expansion of the silicon-oxygen matrix during charging and discharging, thus reducing the likelihood of material pulverization. Furthermore, appropriately sized silicon grains can effectively shorten the distance lithium ions travel during charging and discharging, which is beneficial for improving the rate performance of silicon-oxygen composite materials.

[0105] The crystals formed by the first dopant element are dispersed around the silicon grains, which can alleviate the growth of silicon clusters. Both the crystal grain size and the silicon grain size affect the size of the silicon clusters, and the formation of large-sized silicon clusters will deteriorate the rate performance and cycle performance of the battery. Therefore, by controlling the crystal grain size Y nm and the silicon grain size X nm within the range of 0.35 ≤ Y / 2X ≤ 4, the possibility of forming large-sized silicon clusters can be effectively reduced through the synergistic cooperation of the crystal grain size and the silicon grain size. The battery exhibits excellent cycle performance and rate performance, and has a long cycle life.

[0106] In some embodiments, the silicon-oxygen composite material has the following relationship: 0.7≤Y / 2X≤4, where Y nm is the grain size of the crystal and X nm is the grain size of the silicon grain in the silicon-oxygen composite material.

[0107] In some embodiments, the silicon-oxygen composite material exhibits any of the following relationships: 0.7≤Y / 2X≤1, 0.7≤Y / 2X≤0.7, 0.7≤Y / 2X≤1, 0.7≤Y / 2X≤2, 0.7≤Y / 2X≤3, 0.7≤Y / 2X≤4, 1≤Y / 2X≤2, 1≤Y / 2X≤3, 1≤Y / 2X≤4, 2≤Y / 2X≤3, 2≤Y / 2X≤3, 2≤Y / 2X≤4, 3≤Y / 2X≤4.

[0108] By controlling the crystal grain size Y nm and the silicon grain size X nm within the range of 0.7 ≤ Y / 2X ≤ 4, the possibility of generating large-grain-size silicon clusters can be effectively reduced through the synergistic cooperation between the crystal grain size and the silicon grain size, thereby further improving the cycle performance of the battery.

[0109] In some embodiments, the XRD diffraction pattern of the silicon-oxygen composite material also includes diffraction peaks of silicon grains, and the silicon-oxygen composite material exhibits the following relationship: -5≤5Xsin2θ-Y≤15.

[0110] Where Y is the grain size of the first dopant element, X is the grain size of the silicon grain, and the units of X and Y are both nm, and 2θ is the XRD diffraction angle of the crystal.

[0111] In some embodiments, the silicon-oxygen composite material exhibits any of the following relationships:

[0112] -5≤5Xsin2θ-Y≤0, -5≤5Xsin2θ-Y≤5, -5≤5Xsin2θ-Y≤10

[0113] -5≤5Xsin2θ-Y≤15, 0≤5Xsin2θ-Y≤5, 0≤5Xsin2θ-Y≤10

[0114] 0≤5Xsin2θ-Y≤15、5≤5Xsin2θ-Y≤10、5≤5Xsin2θ-Y≤15、

[0115] 10≤5Xsin2θ-Y≤15.

[0116] In some implementations, the first dopant element comprises two or three elements, then 2θ is the average value of the two or three dopant elements.

[0117] The crystals formed by the first dopant element are dispersed around the silicon grains, which can alleviate the growth of silicon clusters. Both the crystal grain size and the silicon grain size affect the size of the silicon clusters, and the formation of large-sized silicon clusters will deteriorate the rate performance and cycle performance of the battery. In addition, different first dopant elements have different degrees of influence on the rate performance and cycle performance of the material. Therefore, by controlling the crystal grain size Y nm, the silicon grain size, and the XRD diffraction angle of the crystal within the range of -5 ≤ 5Xsin2θ-Y ≤ 15, the battery exhibits excellent cycle performance and rate performance, and a long cycle life.

[0118] In some embodiments, the XRD diffraction pattern of the silicon-oxygen composite material also includes diffraction peaks of silicon grains, and the silicon-oxygen composite material exhibits the following relationship: -5≤5Xsin2θ-Y≤10.

[0119] Where Y is the grain size of the first dopant element, X is the grain size of the silicon grain, and the units of X and Y are both nm, and 2θ is the XRD diffraction angle of the crystal.

[0120] In some embodiments, the silicon-oxygen composite material exhibits any of the following relationships:

[0121] -5≤5Xsin2θ-Y≤0, -5≤5Xsin2θ-Y≤5, -5≤5Xsin2θ-Y≤10

[0122] 0≤5Xsin2θ-Y≤5、0≤5Xsin2θ-Y≤10、5≤5Xsin2θ-Y≤10.

[0123] By controlling the crystal grain size Y nm, the silicon grain size, and the crystal XRD diffraction angle within the range of -5≤5Xsin2θ-Y≤10, the cycle life of the battery can be further improved.

[0124] In some embodiments, the XRD diffraction pattern of the silicon-oxygen composite material includes diffraction peaks of the crystal, with a full width at half maximum (FWHM) of 3°-7°.

[0125] In some embodiments, the diffraction peak intensity of the crystal is 600S. -1 -1200S -1 .

[0126] In some embodiments, the full width at half maximum (FWHM) of the diffraction peaks of the crystal is any value of 3°, 4°, 5°, 6°, or 7°, or a range consisting of any two of these values.

[0127] In some embodiments, the diffraction peak intensity of the crystal is 600S. -1 700S -1 800S -1 900S -1 1000S -1 1100S -1 1200S -1 Any value in or a range consisting of any two values ​​in it.

[0128] In some embodiments, the first dopant element comprises two or more elements, and the diffraction peak intensity and half-width at half-maximum (WHM) of the crystal are the average of the diffraction peak intensity and WHM of the two or more first dopant elements.

[0129] The full width at half maximum (FWHM) and intensity of diffraction peaks in crystals are well-known in the art and can be measured using methods known in the art. As an example, the XRD pattern of a silicon-oxygen composite material can be tested according to the JIS / K0131-1996 testing standard, and the FWHM and intensity of the diffraction peaks of the crystal can be obtained from the XRD pattern of the silicon-oxygen composite material.

[0130] When the diffraction peak half-width of the crystal is within a suitable range, the crystal has a suitable grain size, the battery has excellent cycle performance and rate performance, and the battery has a long cycle life.

[0131] When the diffraction peak intensity of a crystal is within a suitable range, it indicates that the crystal has a high degree of crystallinity, which can effectively reduce the migration barrier of lithium ions, increase the lithium ion diffusion coefficient, improve lithium ion migration kinetics, and give the battery excellent cycle performance and rate performance, as well as a long cycle life.

[0132] In some embodiments, based on the total mass of the silicon-oxygen composite material, the mass fraction of the first dopant element is less than or equal to 12%. In some embodiments, based on the total mass of the silicon-oxygen composite material, the mass fraction of the first dopant element can be selected from any one of less than or equal to 1%, less than or equal to 2%, less than or equal to 3%, less than or equal to 4%, less than or equal to 5%, less than or equal to 6%, less than or equal to 7%, less than or equal to 8%, less than or equal to 9%, less than or equal to 10%, less than or equal to 11%, and less than or equal to 12%.

[0133] The mass content of the first dopant element in the silicon-oxygen composite material can be tested using methods and equipment known in the art, such as the determination according to EPA 6010D-2014 standard. Specifically, ICP-OES (elemental analysis-inductively coupled plasma atomic emission spectrometry) can be used. The sample to be tested is first dissolved into a liquid with a strong acid, and then the liquid is introduced into the ICP light source by atomization. The gaseous atoms to be tested are further ionized and excited in a strong magnetic field, and then recover from the excited state to the ground state. In the above process, energy is released and recorded as different characteristic spectral lines for elemental quantitative analysis.

[0134] The first dopant element, when present in an appropriate mass concentration, can improve the electrical conductivity of silicon-oxygen composite materials, enhance the lithium-ion transport capacity of the material, and improve the cycle performance and rate performance of the battery. At the same time, the first dopant element, when present in an appropriate mass concentration, will not alter the internal structure and crystal phase of the material, thus improving the cycle performance of the battery.

[0135] In some embodiments, based on the total mass of the silicon-oxygen composite material, the mass fraction of the first dopant element is 1%-10%. In some embodiments, based on the total mass of the silicon-oxygen composite material, the mass fraction of the first dopant element can be selected from any one of 1%-9%, 1%-8%, 1%-7%, 1%-6%, 1%-5%, 1%-4%, 1%-3%, 2%-10%, 2%-9%, 2%-8%, 2%-7%, 2%-6%, 2%-5%, 2%-4%, 3%-10%, 3%-9%, 3%-8%, 3%-7%, 3%-6%, 3%-5%, 4%-10%, 4%-9%, 4%-8%, 4%-7%, etc.

[0136] Controlling the mass content of the first dopant element within a suitable range can further improve the conductivity of silicon-oxygen composite materials, extend the discharge time of the battery, and improve the rate performance of the battery.

[0137] In some embodiments, the silicon-oxygen composite material further includes a second doping element, which includes at least one of a nonmetallic element, an alkali metal element, and an alkaline earth metal element.

[0138] In some embodiments, the nonmetallic element includes at least one of B, N, F, Cl, and S.

[0139] In some embodiments, the alkali metal element includes at least one of Li, Na, and K.

[0140] In some embodiments, the alkaline earth metal element includes at least one of Mg, Ca, Be, and Sr.

[0141] In some implementations, the second dopant element includes a nonmetallic element.

[0142] At low temperatures, the diffusion capacity of active ions within silicon-oxygen composite materials decreases, and the charge transfer impedance increases significantly. By adding non-metallic elements, the charge transfer impedance can be reduced, the discharge capacity retention rate of the battery at low temperatures can be improved, and the battery's performance at low temperatures can be enhanced.

[0143] In some embodiments, the second dopant includes at least one of alkali metals and alkaline earth metals.

[0144] Alkali metals and alkaline earth metals are reactive to lithium, which can improve the specific capacity of silicon-oxygen composite materials and increase the energy density of batteries.

[0145] In some embodiments, based on the total mass of the silicon-oxygen composite material, the mass fraction of the second dopant element is less than or equal to 7%. In some embodiments, based on the total mass of the silicon-oxygen composite material, the mass fraction of the second dopant element can be selected as any one of less than or equal to 1%, less than or equal to 2%, less than or equal to 3%, less than or equal to 4%, less than or equal to 5%, less than or equal to 6%, or less than or equal to 7%.

[0146] The mass content of the second dopant element in the silicon-oxygen composite material can be tested using methods and equipment known in the art, such as referring to the EPA 6010D-2014 standard. Specifically, ICP-OES (elemental analysis-inductively coupled plasma atomic emission spectrometry) can be used. First, the sample to be tested is dissolved into a liquid with a strong acid. Then, the liquid is introduced into the ICP light source by atomization. The gaseous atoms to be tested are further ionized and excited in a strong magnetic field, and then recover from the excited state to the ground state. During the above process, energy is released and recorded as different characteristic spectral lines for elemental quantitative analysis.

[0147] By controlling the mass fraction of the second dopant element within a suitable range, the battery exhibits excellent cycle performance and rate performance, and has a long cycle life.

[0148] In some embodiments, based on the total mass of the silicon-oxygen composite material, the mass fraction of the second dopant element is 1%-5%. In some embodiments, based on the total mass of the silicon-oxygen composite material, the mass fraction of the second dopant element can be selected from any one of 1%-2%, 1%-3%, 1%-4%, 1%-5%, 2%-3%, 2%-4%, 2%-5%, 3%-4%, 3%-5%, and 4%-5%.

[0149] Controlling the mass fraction of the second dopant element within a suitable range can further extend the battery's discharge time, improve its cycle performance and rate performance, and extend its cycle life.

[0150] In some embodiments, the silicon-oxygen composite material further includes a carbon layer that at least partially covers the surface of the silicon-oxygen material matrix.

[0151] Forming a carbon layer on the surface of a silicon-oxygen material matrix can effectively suppress particle breakage and pulverization during charge-discharge cycles, alleviate volume expansion, and ensure structural stability. After carbon coating, the silicon-oxygen composite material exhibits better conductivity and stability, improving battery cycle stability and rate performance.

[0152] In some implementations, the thickness of the carbon layer is 1-4 nm.

[0153] The thickness of the carbon layer is a well-known concept in the art and can be measured using methods known in the art. As an example, a silicon-oxygen composite material is embedded and cured with epoxy resin, and then complete particles are cut using an ultrathin sectioning method to prepare samples. High-magnification transmission electron microscopy is used to observe cross-sections of the particle samples, observing the long-range, regularly arranged, ordered regions, i.e., the silicon-oxygen matrix. The amorphous regions (lacking long-range, regularly arranged lamellar layers, with disordered lamellar arrangement) covering the surface of the silicon-oxygen matrix are the carbon layer regions. The average thickness of the carbon layer is measured multiple times.

[0154] In some embodiments, the volumetric particle size distribution (Dv50) of the silicon-oxygen composite material is 3-8 μm.

[0155] In some embodiments, the volumetric particle size Dv50 of the silicon-oxygen composite material can be selected from any one of 3-4μm, 3-5μm, 3-6μm, 3-7μm, 3-8μm, 4-5μm, 4-6μm, 4-7μm, 4-8μm, 5-6μm, 5-7μm, 5-8μm, 6-7μm, 7-8μm, and 6-8μm.

[0156] The volume distribution particle size Dv50 of silicon-oxygen composite materials has a well-known meaning in the art and can be tested using methods known in the art. As an example, the Dv50 of silicon-oxygen composite material samples can be determined according to the standard GB / T19077-2016 / ISO 13320:2009, and the testing equipment can be a laser particle size analyzer (such as Malvern Master Size 3000).

[0157] By controlling the volume distribution particle size Dv50 of the silicon-oxygen composite material within a suitable range, the silicon-oxygen composite material structure becomes relatively stable and its kinetic performance becomes relatively good, which is beneficial to improving the cycle performance and rate performance of the battery.

[0158] In some embodiments, the volumetric particle size distribution Dv50 of the silicon-oxygen composite material is 4-6 μm.

[0159] In some embodiments, the volume distribution particle size Dv50 of the silicon-oxygen composite material can be selected as any one of 4-6μm, 4-7μm, 4-8μm, and 5-6μm.

[0160] Controlling the volume distribution particle size Dv50 of silicon-oxygen composite materials within a suitable range can further improve lithium-ion transport speed, enhance the conductivity of the material, extend the battery discharge time, improve the battery cycle performance and rate performance, and extend the battery cycle life.

[0161] In some embodiments, a method for preparing a silicon-oxygen composite material is provided, the method comprising:

[0162] A silicon-oxygen material matrix is ​​obtained by first vapor deposition of a first vapor containing elemental silicon and silicon dioxide.

[0163] A second vapor containing the first dopant element is subjected to a second vapor deposition with a silicon-oxygen material matrix to obtain a silicon-oxygen composite material. At least a portion of the first dopant element exists in the silicon-oxygen material matrix in crystalline form, and the grain size of the first dopant element crystal is ≤9nm. The first dopant element satisfies the following: the lithium-ion diffusion coefficient of the elemental first dopant element at 25°C is greater than that of elemental silicon at 25°C.

[0164] In this application, the term "vapor deposition" refers to the process of generating solid deposits by reacting gaseous or vaporous substances at the gas phase or gas-solid interface.

[0165] Bulk-doped silicon-oxygen composite materials were obtained through vapor deposition. Bulk doping resulted in the first dopant element being uniformly dispersed at the atomic scale within the silicon-oxygen matrix, forming crystals with a grain size of less than or equal to 9 nm. This indicates that the uniform atomic-scale dispersion of the first dopant element within the silicon-oxygen matrix effectively reduces the lithium-ion migration barrier, increases the lithium-ion diffusion coefficient, improves lithium-ion migration kinetics, extends battery discharge time, and improves battery rate performance. Furthermore, the crystals formed by the first dopant element, dispersed around the silicon grains, can alleviate the growth of silicon clusters, effectively suppressing the expansion and pulverization effect of the silicon-oxygen composite material. This enhances the structural integrity and volume stability of the silicon-oxygen composite material during lithium insertion / extraction, improving battery cycle performance. Additionally, the small-grain-size crystals of the first dopant element do not significantly alter the crystal structure of the silicon-oxygen matrix, thus maintaining the material's structural stability and preventing pulverization during charge / discharge, further improving battery cycle performance and extending battery cycle life.

[0166] In some implementations, the temperature of the first vapor deposition is 1000°C-1300°C.

[0167] In some implementations, the temperature of the first vapor deposition is 1100°C-1250°C.

[0168] In some embodiments, the temperature of the first vapor deposition is any value or a range of any two of 1000°C, 1100°C, 1200°C, 1250°C, and 1300°C.

[0169] In some implementations, the first vapor deposition takes 6-12 hours.

[0170] In some implementations, the first vapor deposition takes 8-10 hours.

[0171] In some implementations, the time for the first vapor deposition is any value or a range of any two of the following: 6h, 7h, 8h, 9h, 10h, 11h, and 12h.

[0172] By controlling the temperature and / or time of the first vapor deposition within a suitable range, a silicon-oxygen material matrix with excellent performance and structural parameters can be obtained, which is beneficial for subsequent element doping processes.

[0173] In some embodiments, the silicon dioxide grain size is 1-4 nm. In some embodiments, the silicon dioxide grain size can be selected from any one of 1-2 nm, 1-3 nm, 1-4 nm, 2-3 nm, 2-4 nm, and 3-4 nm.

[0174] Controlling the grain size of the raw material silicon dioxide within a suitable range ensures that the grain size of silicon grains in the silicon-oxygen composite material is within a suitable range, avoiding the formation of silicon clusters with large grain sizes. This can effectively suppress the expansion and pulverization effect of the silicon-oxygen composite material and improve the cycle stability of the battery.

[0175] In some implementations, the temperature of the second vapor deposition is 800°C-900°C.

[0176] In some implementations, the temperature for the second vapor deposition is 820°C-880°C.

[0177] In some embodiments, the temperature of the second vapor deposition is any value of 800°C, 820°C, 880°C, 900°C, or a range of any two of these values.

[0178] In some implementations, the second vapor deposition takes 4-10 hours.

[0179] In some implementations, the second vapor deposition takes 6-8 hours.

[0180] In some implementations, the time for the second vapor deposition is any value of 4h, 5h, 6h, 7h, 8h, 9h, 10h, or a range of any two of these values.

[0181] By controlling the temperature and / or time of the second vapor deposition within a suitable range, the bulk doping distribution of the first dopant element can be achieved, while ensuring that the first dopant element exists in the silicon-oxygen material matrix as small-grain-size crystals, thereby improving the conductivity of the material, avoiding the formation of large crystals, and improving the rate performance and cycle performance of the battery.

[0182] In some embodiments, the preparation method of the silicon-oxygen composite material includes:

[0183] A second vapor containing a first doping element and a second doping element is subjected to a second vapor phase deposition with a silicon-oxygen material matrix to obtain a silicon-oxygen composite material. The second doping element includes at least one of a non-metallic element, an alkali metal element, and an alkaline earth metal element.

[0184] In some embodiments, the nonmetallic element includes at least one of B, N, F, Cl, and S;

[0185] In some embodiments, the alkali metal element includes at least one of Li, Na, and K;

[0186] In some embodiments, the alkaline earth metal element includes at least one of Mg, Ca, Be, and Sr.

[0187] Doping the second dopant element in the form of vapor can achieve uniform bulk doping of the second dopant element, which can improve the discharge capacity retention rate of the battery at low temperature and / or improve the energy density of the battery.

[0188] In some embodiments, the preparation method further includes:

[0189] Carbon coating treatment is applied to the surface of the silicon-oxygen composite material.

[0190] In some embodiments, the carbon coating treatment temperature is 500°C-750°C.

[0191] In some embodiments, the carbon coating treatment temperature is 660°C-720°C.

[0192] In some embodiments, the carbon coating temperature is any value or a range of any two of 500°C, 550°C, 600°C, 660°C, 720°C, and 750°C.

[0193] In some implementations, the carbon coating treatment time is 2h-10h.

[0194] In some implementations, the carbon coating treatment takes 6-8 hours.

[0195] In some implementations, the carbon coating treatment time is any value from 2h, 4h, 6h, 8h, 10h, or a range of any two of these values.

[0196] Appropriate carbon coating temperature and / or time can, on the one hand, form a uniformly distributed carbon layer structure of suitable thickness on the surface of silicon-oxygen composite materials, which can buffer the volume change of silicon-oxygen composite materials during lithium insertion / extraction, while improving the electronic conductivity of the material surface and improving the cycle performance and rate performance of the battery. On the other hand, it can effectively control the grain size of the first dopant element and the silicon grain size within a suitable range, so that the silicon-oxygen material has excellent structural parameters, thereby extending the discharge time of the battery, improving the rate performance of the battery, improving the cycle performance of the battery, and extending the cycle life of the battery.

[0197] [Negative electrode plate]

[0198] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0199] In some embodiments, a negative electrode sheet is provided, including a negative electrode active material, which includes a silicon-oxygen composite material as described in some embodiments or a silicon-oxygen composite material prepared by the preparation method described in some embodiments.

[0200] This electrode exhibits excellent conductivity and cycle stability, and has a high specific capacity.

[0201] In some embodiments, the mass content of the silicon-oxygen composite material is greater than or equal to 20% based on the total mass of the negative electrode active material. In some embodiments, the mass content of the silicon-oxygen composite material can be selected from any one of greater than or equal to 20%, greater than or equal to 30%, greater than or equal to 40%, greater than or equal to 50%, greater than or equal to 60%, greater than or equal to 70%, greater than or equal to 80%, or greater than or equal to 90% based on the total mass of the negative electrode active material.

[0202] When the mass content of silicon-oxygen composite material is within a suitable range, the silicon-oxygen composite material has a high theoretical specific capacity. In addition, the appropriate content of silicon-oxygen composite material gives the material good conductivity, and the battery has excellent rate performance.

[0203] In some embodiments, the mass content of the silicon-oxygen composite material is 25%-90% based on the total mass of the negative electrode active material. In some embodiments, the mass content of the silicon-oxygen composite material can be selected as 25%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or a value within a range consisting of any two of the above, based on the total mass of the negative electrode active material.

[0204] By controlling the silicon-oxygen composite material within a suitable range, both the energy density and cycle life of the battery can be balanced, thus comprehensively improving the battery's electrochemical performance.

[0205] In some embodiments, this application also proposes a secondary battery, which includes the negative electrode sheet in any embodiment.

[0206] In some implementations, the energy density of the secondary battery is 400-500 Wh / kg.

[0207] At 25℃, the secondary battery was left to stand for 2 hours. It was then charged at 0.1C to the charging cutoff voltage, and continued to be charged at this cutoff voltage under constant voltage until the current reached 0.05C, at which point charging was stopped (where C represents the rated capacity of a single battery cell). The secondary battery was then left to stand at 25℃ for 1 hour. It was then discharged at 0.1C to the discharge cutoff voltage, and the total discharge capacity C0 and total discharge energy E0 were recorded.

[0208] Secondary battery mass measurement: Place the secondary battery on an electronic balance until its mass stabilizes, and read the mass value M0 of the secondary battery.

[0209] The mass energy density of a secondary battery = E0 / M0.

[0210] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0211] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0212] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0213] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0214] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0215] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0216] In some embodiments, the negative electrode sheet of a full cell can be prepared by dispersing the components used to prepare the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then drying, cold pressing and other processes to obtain the negative electrode sheet of the full cell.

[0217] [Positive electrode plate]

[0218] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0219] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0220] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0221] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0222] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0223] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0224] [Electrolytes]

[0225] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0226] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0227] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0228] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0229] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0230] [Isolation membrane]

[0231] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0232] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0233] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0234] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0235] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0236] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 3 This is an example of a square-structured secondary battery 5.

[0237] In some implementations, refer to Figure 4 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0238] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0239] Figure 5 This is battery module 4, used as an example. (See reference...) Figure 5 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0240] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0241] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0242] Figure 6 and Figure 7 This is battery pack 1 as an example. (See reference...) Figure 6 and Figure 7The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0243] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0244] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0245] Figure 8 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0246] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0247] The lithium-ion diffusion coefficient data for the first doping element and the elemental silicon used in the following embodiments are as follows:

[0248] The lithium-ion diffusion coefficient of elemental Sn at 25℃ is 1×10⁻⁶. -13 cm 2 / S;

[0249] The lithium-ion diffusion coefficient of elemental Ge at 25°C is 5 × 10⁻⁶. -14 cm 2 / S;

[0250] The lithium-ion diffusion coefficient of elemental Sb at 25°C is 7 × 10⁻⁶. -14 cm 2 / S;

[0251] The lithium-ion diffusion coefficient of elemental Bi at 25℃ is 4 × 10⁻⁶. -13 cm 2 / S;

[0252] The lithium-ion diffusion coefficient of elemental Sr at 25°C is 6 × 10⁻⁶. -13 cm 2 / S;

[0253] The lithium-ion diffusion coefficient of element B at 25°C is 10. -16 cm 2 / S;

[0254] The lithium-ion diffusion coefficient of elemental silicon at 25°C is 2 × 10⁻⁶. -15 cm 2 / S.

[0255] Example

[0256] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0257] Example 1

[0258] (1) Preparation of positive electrode sheet

[0259] LiNi 0.98 Co 0.01 Mn 0.01 O2, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) are added to solvent N-methylpyrrolidone in a mass ratio of 97%:1%:2% and mixed and stirred evenly to obtain a positive electrode slurry. Then, it is uniformly coated on the positive electrode current collector, dried, cold-pressed, and slit to obtain the positive electrode sheet.

[0260] (2) Preparation of negative electrode sheet

[0261] 1) Preparation of silicon-oxygen composite materials

[0262] 900g of Si powder and 1200g of SiO2 powder were mixed to obtain a silicon source, which was then added to the heating chamber 1 of a vacuum furnace. The vacuum was evacuated to below 1 Pa and heating was started. After heating to 1300℃, the material was placed into the deposition system and deposited at 1200℃ for 6.6h to obtain a silicon-oxygen material matrix. 30g of tin metal was added to the heating chamber 2, and the vacuum was evacuated to below 10 Pa and heating was started. After heating to 1100℃, the material was placed into the deposition system and deposited at 830℃ for 6.2h. After naturally cooling to room temperature, a block-shaped deposited material was obtained.

[0263] The obtained deposition material was crushed into particles with a median particle size of 5 μm by air jet milling and added to a CVD vapor deposition furnace for carbon coating treatment. Acetylene gas was introduced at a mass flow rate of 700 sccm and deposited at 680℃ for 5 h. The coated material was then placed under nitrogen protection and heated to 800℃ at a heating rate of 5℃ / min and held for 1 h. After natural cooling, a silicon-oxygen composite material was obtained.

[0264] 2) Preparation of negative electrode sheet: Artificial graphite and the silicon-oxygen composite material prepared above are mixed at a mass ratio of 3:7 to obtain negative electrode active material. Negative electrode active material, conductive agent carbon black, carbon nanotubes (CNT), binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are added to deionized water at a weight ratio of 94.5%:1%:0.375%:2.8%:1.325% and mixed evenly to obtain negative electrode slurry. This slurry is coated on negative electrode current collector, and after drying, cold pressing, and slitting, negative electrode sheet is obtained.

[0265] (3) Separating membrane

[0266] Polypropylene film is used as the separator.

[0267] (4) Preparation of electrolyte

[0268] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate, methyl ethyl carbonate, diethyl carbonate, and fluoroethylene carbonate (FEC) were mixed uniformly in a volume ratio of 1:1:1:1. LiPF6 was then added and dissolved in the organic solvent to make the electrolyte concentration 1 mol / L, thus obtaining the electrolyte of Example 1.

[0269] (5) Preparation of secondary batteries

[0270] The positive electrode, separator, and negative electrode of Example 1 are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The cells are then wound to obtain a battery cell, tabs are welded to the battery cell, and the battery cell is installed in an aluminum shell. Electrolyte is then injected and the shell is sealed. After processes such as settling, cold pressing, formation, shaping, and capacity testing, a lithium-ion secondary battery is obtained.

[0271] The preparation parameters in Examples 2-5 are basically the same as those in Example 1, except that the first doped metal element is different. Specific parameters are shown in Table 1.

[0272] Example 2:

[0273] 900g of Si powder was mixed with 1200g of SiO2 powder with a grain size of 3nm to obtain a silicon source. The source was added to the heating chamber 1 of a vacuum furnace, and the vacuum was evacuated to below 1Pa before heating began. After heating to 1300℃, the source was placed in the deposition system and deposited at 1160℃ for 6.7h to obtain a silicon-oxygen material matrix. 30g of germanium metal was added to the heating chamber 2, and the vacuum was evacuated to below 12Pa before heating began. After heating to 1100℃, the source was placed in the deposition system and deposited at 828℃ for 6.4h. After natural cooling to room temperature, a blocky deposited material was obtained.

[0274] Example 3:

[0275] 900g of Si powder was mixed with 1200g of SiO2 powder with a grain size of 2nm to obtain a silicon source. The source was added to the heating chamber 1 of a vacuum furnace, and the vacuum was evacuated to below 1Pa before heating began. After heating, the source was placed in the deposition system and deposited at 1170℃ for 6.5h to obtain a silicon-oxygen material matrix. 30g of antimony metal was added to the heating chamber 2, and the vacuum was evacuated to below 10Pa before heating began. After heating to 1100℃, the source was placed in the deposition system and deposited at 827℃ for 6.9h. After natural cooling to room temperature, a block-shaped deposited material was obtained.

[0276] Example 4:

[0277] 900g of Si powder was mixed with 1200g of SiO2 powder with a grain size of 2nm to obtain a silicon source. The source was added to the heating chamber 1 of a vacuum furnace, and the vacuum was evacuated to below 1Pa before heating began. After heating, the source was placed in the deposition system and deposited at 1180℃ for 6.4h to obtain a silicon-oxygen material matrix. 30g of bismuth metal was added to the heating chamber 2, and the vacuum was evacuated to below 10Pa before heating began. After heating to 1250℃, the source was placed in the deposition system and deposited at 826℃ for 6.8h. After natural cooling to room temperature, a blocky deposited material was obtained.

[0278] Example 5:

[0279] A silicon source was obtained by mixing 900g of Si powder with 1200g of SiO2 powder with a grain size of 2nm. This mixture was then added to heating chamber 1 of a vacuum furnace, and the vacuum was evacuated to below 1Pa before heating began. After heating to 1300℃, the mixture was transferred to the deposition system and deposited at 1190℃ for 6.8 hours to obtain a silicon-oxygen material matrix. 15g of tin metal was added to heating chamber 2, and the vacuum was evacuated to below 10Pa before heating began to 1100℃. 15g of germanium metal was added to heating chamber 3, and the vacuum was evacuated to below 12Pa before heating began to 1100℃. Vapor from heating chambers 2 and 3 was transferred to the deposition system, and deposition was carried out at 825℃ for 6.7 hours. After natural cooling to room temperature, a bulk deposition material was obtained.

[0280] Examples 6-11

[0281] The preparation parameters for Examples 6-11 are basically the same as those for Example 1, except that the temperature and time of the first vapor deposition, the temperature and time of the second vapor deposition, and the carbon coating treatment temperature are different. Specific parameters are shown in Table 1.

[0282] Examples 12-16

[0283] The preparation parameters for Examples 12-16 are basically the same as those for Example 1, except that the temperature and time of the first vapor deposition, the temperature and time of the second vapor deposition, and the treatment temperature of carbon coating are different. In addition, the mass of tin metal is adjusted to 15g, 45g, 150g, 7.5g, and 180g respectively, thereby adjusting the mass content of tin. The specific parameters are shown in Table 1.

[0284] Examples 17-18

[0285] The preparation parameters for Examples 17-18 are basically the same as those for Example 1, except that a second doping element, boron or lithium, is also included. Specifically,

[0286] Example 17

[0287] 900g of Si powder was mixed with 1200g of SiO2 powder with a grain size of 2nm to obtain a silicon source. This source was added to heating chamber 1 of a vacuum furnace, and the vacuum was evacuated to below 1Pa before heating began. After heating to 1300℃, the material entered the deposition system and was deposited at 1175℃ for 7.6 hours to obtain a silicon-oxygen material matrix. Simultaneously, 30g of tin metal was added to heating chamber 2, and the vacuum was evacuated to below 10Pa before heating began to 1100℃. 30g of boron was added to heating chamber 3, and the vacuum was evacuated to below 10Pa before heating began to 1180℃. Vapor from heating chambers 2 and 3 entered the deposition system, and deposition was carried out at 850℃ for 6.9 hours. After natural cooling to room temperature, a block-shaped deposited material was obtained.

[0288] Example 18

[0289] 900g of Si powder was mixed with 1200g of SiO2 powder with a grain size of 2nm to obtain a silicon source. This source was added to heating chamber 1 of a vacuum furnace, and the vacuum was evacuated to below 1Pa before heating began. After heating to 1300℃, the material entered the deposition system and was deposited at 1175℃ for 7.5 hours to obtain a silicon-oxygen material matrix. Simultaneously, 30g of tin metal was added to heating chamber 2, and the vacuum was evacuated to below 10Pa before heating began to 1100℃. 30g of lithium was added to heating chamber 3, and the vacuum was evacuated to below 10Pa before heating began to 900℃. Vapor from heating chambers 2 and 3 entered the deposition system, and deposition was carried out at 855℃ for 7 hours. After natural cooling to room temperature, a block-shaped deposited material was obtained.

[0290] The preparation parameters in Comparative Examples 1-3 are basically the same as those in Example 1. Specific parameters are shown in Table 1.

[0291] Comparative Example 1

[0292] 900g of Si powder was mixed with 1200g of SiO2 powder with a grain size of 2nm to obtain a silicon source. The source was added to the heating chamber 1 of a vacuum furnace, and the vacuum was evacuated to below 1Pa to start heating. The temperature was raised to 1300℃. The vapor in the heating chamber 1 entered the deposition zone of the deposition system. The temperature of the deposition zone was controlled to be maintained at 1170℃. The deposition time was 7.3h. After natural cooling to room temperature, a blocky deposition material was obtained.

[0293] Comparative Example 2

[0294] 900g of Si powder was mixed with 1200g of SiO2 powder with a grain size of 2nm to obtain a silicon source. The source was added to the heating chamber 1 of a vacuum furnace, and the vacuum was evacuated to below 1Pa before heating began. After heating to 1300℃, the source was placed in the deposition system and deposited at 1170℃ for 7.6h to obtain a silicon-oxygen material matrix. At the same time, 30g of boron was added to the heating chamber 2, and the vacuum was evacuated to below 10Pa before heating began. After heating to 1100℃, the source was placed in the deposition system and deposited at 800℃ for 7.4h. After natural cooling to room temperature, a block-shaped deposited material was obtained.

[0295] The obtained deposition material was crushed into particles with a median particle size of 5 μm by air jet milling and added to a CVD vapor deposition furnace for carbon coating treatment. Acetylene gas was introduced at a mass flow rate of 700 sccm and deposited at 680℃ for 5 h. The coated material was then placed under nitrogen protection and heated to 800℃ at a heating rate of 5℃ / min and held for 1 h. After natural cooling, a silicon-oxygen composite material was obtained.

[0296] Comparative Example 3

[0297] 900g of Si powder was mixed with 1200g of SiO2 powder with a grain size of 2nm to obtain a silicon source. The source was added to the heating chamber 1 of a vacuum furnace, and the vacuum was evacuated to below 1Pa before heating began. After heating to 1300℃, the source was placed in the deposition system and deposited at 1180℃ for 7.5h to obtain a silicon-oxygen material matrix. 30g of tin metal was added to the heating chamber 2, and the vacuum was evacuated to below 10Pa before heating began. After heating to 1100℃, the source was placed in the deposition system and deposited at 800℃ for 7.5h. After natural cooling to room temperature, a block-shaped deposited material was obtained.

[0298] The obtained deposition material was crushed into particles with a median particle size of 5 μm by air jet milling and added to a CVD vapor deposition furnace for carbon coating treatment. Acetylene gas was introduced at a mass flow rate of 700 sccm and deposited at 800℃ for 5 h. The coated material was then placed under nitrogen protection and heated to 800℃ at a heating rate of 5℃ / min and held for 1 h. After natural cooling, a silicon-oxygen composite material was obtained.

[0299] II. Testing Methods

[0300] 1. Lithium-ion diffusion coefficients of each element

[0301] (1) Preparation of button cell: The elemental materials formed by various doping elements or silicon, binder, and conductive agent are mixed in a ratio of 8:1:1 and added to deionized water. The mixture is stirred evenly to obtain a negative electrode slurry. This slurry is coated on one surface of the negative electrode current collector copper foil, dried, cold-pressed, and slit to obtain a negative electrode sheet. A certain area (153.86 mm²) is obtained using a stamping die. 2 The negative electrode is a small circular disc. A lithium metal sheet is used as the counter electrode, a PP film is used as the separator, and the electrolyte formula is as follows: ethylene carbonate, methyl ethyl carbonate, diethyl carbonate, and FEC are mixed in a volume ratio of 1:1:1:1 to form a solvent. LiPF6 is used as the lithium salt and dissolved in the above solvent to prepare a solution with a concentration of 1 mol / L. The CR2032 type coin cell is assembled in an argon-protected glove box.

[0302] (2) The lithium-ion diffusion coefficient of the doped element or silicon element is calculated according to the following formula: D Li =1 / (1000×S×Z) iq ),

[0303] Where: D Li Z is the lithium-ion diffusion coefficient; S is the area of ​​the small disc in the coin cell prepared above; Z iq The specific capacity of a single-element material;

[0304] Among them, Z iq The following steps can be used for testing: At 25℃, the prepared coin cell is charged at a constant current of 0.1C until the battery voltage is less than 0.05V, and then left to stand for 120 minutes; then, the prepared coin cell is discharged at a constant current of 0.1C until the battery voltage is greater than 1.5V, and the specific capacity of the coin cell at this time is measured and recorded as Z. iq .

[0305] 2. Confirm the form in which the first dopant element exists.

[0306] The presence of the first dopant element was confirmed by X-ray diffraction (XRD): The silicon-oxygen composite material was tested using an X-ray powder diffractometer (XRD, instrument model: Bruker D8 ADVANCE) with Cu Kα as the target material; the voltage and current were 40 kV / 40 mA, the scanning angle range was 5° to 80°, the scanning step size was 0.00836°, and the time of each step was 0.3 s. The morphology of the diffraction peaks in the obtained spectrum confirmed that the first dopant element existed in crystalline form.

[0307] 3. The first doping element is uniformly doped.

[0308] Conductive adhesive was applied to the sample stage. Powdered samples of the silicon-oxygen composite materials from each example and comparative example were spread evenly on the conductive adhesive. Unattached powder was blown away with a syringe, gold was sprayed, and the particles of the powdered sample were cross-sectionally cut using argon plasma. Scanning electron microscope images of the powdered samples were obtained using the EDS of a Philips XL-30 field emission scanning electron microscope at an accelerating voltage of 10 kV and an emission current of 10 mA.

[0309] 4. Crystal grain size formed by the first doping element

[0310] The XRD pattern of the silicon-oxygen composite material was tested according to the JIS / K0131-1996 testing standard. Based on the XRD pattern of the silicon-oxygen composite material, the full width at half maximum (FWHM) β and the diffraction angle θ of the (101) crystal plane diffraction peak of the first dopant element were taken and substituted into the Debye-Scherrer formula to calculate the crystal grain size. The Debye-Scherrer formula is as follows: Dhkl=kλ / (βcosθ), where Dhkl represents the crystal grain size in nm; k represents the Scherrer constant, 0.89; λ represents the incident X-ray wavelength, 0.15406nm; β represents the FWHM of the diffraction peak in rad; and θ represents the diffraction angle in degrees.

[0311] 5. Silicon grain size

[0312] The XRD pattern of the silicon-oxygen composite material was tested according to the JIS / K0131-1996 testing standard. Based on the XRD pattern of the silicon-oxygen composite material, the full width at half maximum (FWHM) β and the diffraction angle θ of the Si(111) crystal plane diffraction peak were taken and substituted into the Debye-Scherrer formula to calculate the grain size of the silicon grain. The Debye-Scherrer formula is as follows: Dhkl=kλ / (βcosθ), where Dhkl represents the grain size of the silicon grain in nm; k represents the Scherrer constant, 0.89; λ represents the incident X-ray wavelength, 0.15406 nm; β represents the FWHM of the diffraction peak in rad; and θ represents the diffraction angle in degrees.

[0313] 6. Mass content of the first and second doping elements

[0314] The determination is performed in accordance with EPA 6010D-2014 standards. Specifically, ICP-OES (Inductively Coupled Plasma Emission Spectrometry) can be used. The sample to be tested is first dissolved into a liquid with a strong acid, and then the liquid is introduced into the ICP light source by atomization. The gaseous atoms to be tested are further ionized and excited in a strong magnetic field, and then recover from the excited state to the ground state. During the above process, energy is released and recorded as different characteristic spectral lines, and quantitative analysis of the first dopant element and the second dopant element is performed.

[0315] 7. Battery 25℃ Cycle Performance Test

[0316] The secondary batteries prepared in each embodiment and comparative example were charged at a constant current rate of 0.5C to the charging cutoff voltage of 4.25V, then charged at a constant voltage until the current ≤0.05C, allowed to stand for 5 minutes, and then discharged at a constant current rate of 0.33C to the discharge cutoff voltage of 2V, allowed to stand for 5 minutes. This constitutes one charge-discharge cycle. The batteries were subjected to cyclic charge-discharge tests according to this method until the battery capacity decreased to 80%. The number of cycles at this point is the cycle life of the battery at 25°C.

[0317] 8. Battery energy density

[0318] At 25°C, the secondary batteries prepared in each embodiment and comparative example were allowed to stand for 2 hours. They were then charged at 0.1C to the charging cutoff voltage, and then continued to be charged at this voltage under constant voltage until the current reached 0.05C, at which point charging was stopped (where C represents the rated capacity of a single battery cell). The secondary batteries were then allowed to stand at 25°C for 1 hour. They were then discharged at 0.1C to the discharge cutoff voltage, and the total discharge capacity C0 and total discharge energy E0 were recorded.

[0319] Secondary battery mass measurement: Place the secondary battery on an electronic balance until its mass stabilizes, and read the mass value M0 of the secondary battery.

[0320] The mass energy density of a secondary battery = E0 / M0.

[0321] 9. Battery discharge time at 40% SOC

[0322] The secondary batteries prepared in the examples and comparative examples were discharged at a constant current of 0.33C to 2.8V and allowed to stand for 30 minutes; charged at a constant current of 0.33C to 4.25V and then charged at a constant voltage of 0.05C until the voltage stabilized, and allowed to stand for 30 minutes; discharged at a constant current of 0.33C to 2.8V, at which point the initial capacity C0 was read, and allowed to stand for 30 minutes; charged at a constant current of 0.33C to 4.25V and then charged at a constant voltage of 0.05C until the voltage stabilized, and allowed to stand for 30 minutes; discharged at a constant current of 0.33C to 0.4C0Ah (40%) SOC and allowed to stand for 60 minutes; discharged at a constant current of 4.5C to 2.8V, and the discharge time was recorded.

[0323] 10. Battery low-temperature discharge capacity retention rate

[0324] At -20°C, the secondary batteries prepared in the above examples and comparative examples were charged at a constant current of 0.33C to a voltage of 4.25V, then charged at a constant voltage of 4.25V until the current ≤0.05C. The batteries were then discharged at a constant current of 0.33C to a voltage of 2.5V. This constitutes one charge-discharge cycle, and the discharge capacity C1 of the first cycle was recorded. This charge-discharge cycle was repeated, and the discharge capacity C2 after 500 cycles was recorded.

[0325] The capacity retention rate of the battery after 500 cycles = C2 / C1 × 100%.

[0326] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0327] The silicon-oxygen composite materials, negative electrode sheets, and batteries of each embodiment and comparative example were prepared according to the above method, and various parameters were measured. The results are shown in Tables 1, 2, 3, and 4 below.

[0328] Table 1

[0329]

[0330] Table 2

[0331]

[0332] Table 3

[0333]

[0334] Table 4

[0335]

[0336] Figure 1 The image shows the XRD pattern of the silicon-oxygen composite material from Example 1. Figure 1 The XRD pattern shows a peak at a position of 33° 2θ, indicating that the tin in Example 1 exists in the silicon-oxygen matrix in crystalline form.

[0337] Figure 2 The image shows a scanning electron microscope (SEM) image of a silicon-oxygen composite material. It can be seen from the image that the first dopant element, tin, is uniformly distributed in the silicon-oxygen matrix.

[0338] The silicon-oxygen composite materials in Examples 1-18 comprise a silicon-oxygen matrix and a first dopant element selected from Sn, Ge, Sb, and Bi distributed in the silicon-oxygen matrix. The lithium-ion diffusion coefficients of Sn, Ge, Sb, and Bi at 25°C are greater than those of silicon at 25°C. At least a portion of Sn, Ge, Sb, or Bi exists in crystalline form in the silicon-oxygen matrix, and the grain size of the first dopant element is ≤9 nm.

[0339] As can be seen from the comparison between Examples 1-18 and Comparative Example 1, the silicon-oxygen composite material containing the first doping element Sn, Ge, Sb or Bi can extend the discharge time of the battery, improve the rate performance of the battery, improve the cycle performance of the battery, and extend the cycle life of the battery.

[0340] As can be seen from the comparison between Examples 1-18 and Comparative Example 2, the lithium-ion diffusion coefficient of the first dopant element in the silicon-oxygen composite material is greater than that of the elemental silicon, which can extend the battery discharge time, improve the battery rate performance, improve the battery cycle performance, and extend the battery cycle life.

[0341] As can be seen from the comparison between Examples 1-16 and Comparative Example 3, the crystal grain size formed by the first doping element in the silicon-oxygen composite material is ≤9nm, which can extend the discharge time of the battery, improve the rate performance of the battery, improve the cycle performance of the battery, and extend the cycle life of the battery.

[0342] A comparison of Examples 1 and 6 with Example 7 shows that the crystal grain size formed by the first doping element is ≤7nm, which can further extend the discharge time of the battery, further improve the rate performance and cycle performance of the battery, and extend the cycle life of the battery.

[0343] As can be seen from Examples 1-16, the grain size Y nm of the crystal in the silicon-oxygen composite material and the grain size X nm of the silicon grain satisfy at least one of the following relationships: 0.35≤Y / 2X≤4 or -5≤5Xsin2θ-Y≤15, where 2θ is the XRD diffraction angle of the crystal formed by the doping element. The battery has excellent cycle performance and rate performance, and the battery has a long cycle life.

[0344] A comparison of Examples 1-4, 6-8, 10-11 with Example 9 shows that the grain size of the crystals in the silicon-oxygen composite material and the grain size X nm of the silicon grains satisfy the following relationship: 0.7≤Y / 2X≤4, which can further improve the cycle performance of the battery.

[0345] A comparison of Examples 1-4, 6-8, 10-11 with Example 9 shows that the grain size of the crystals in the silicon-oxygen composite material and the grain size X nm of the silicon grains satisfy the following relationship: -5≤5Xsin2θ-Y≤10, where 2θ is the XRD diffraction angle of the tin crystal, which can further improve the cycle performance of the battery.

[0346] As can be seen from Examples 1-16, the XRD diffraction patterns of the silicon-oxygen composite material contain diffraction peaks of the first doped element crystal. The full width at half maximum (FWHM) of the diffraction peaks of the first doped element crystal is 3°-7°, and the peak intensity is 600 S. -1 -1200S -1 The battery has excellent cycle performance and rate performance, and a long cycle life.

[0347] As can be seen from Examples 1-16, based on the total mass of the silicon-oxygen composite material, when the mass fraction of the first dopant element is less than or equal to 12%, the battery exhibits excellent cycle performance and rate performance, and a long cycle life. A comparison of Examples 1, 12-14 with Examples 15-16 shows that, based on the total mass of the silicon-oxygen composite material, when the mass fraction of the first dopant element is 1%-10%, the battery discharge time can be further extended, and the rate performance of the battery can be further improved.

[0348] The silicon-oxygen composite materials of Examples 17 and 18 further include a second doping element, B or Li. A comparison between Example 17 and Example 1 shows that doping with the second element B can improve the discharge capacity retention rate of the battery at low temperatures, thus improving the battery's performance at low temperatures. A comparison between Example 18 and Example 1 shows that doping with the second element Li can improve the energy density of the battery, meeting the requirements of new battery technologies.

[0349] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A silicon-oxygen composite material, characterized in that, The invention comprises a silicon-oxygen material matrix and a first dopant element distributed in the silicon-oxygen material matrix, wherein at least a portion of the first dopant element exists in the silicon-oxygen material matrix in crystalline form, and the grain size of the first dopant element is ≤9nm, wherein the first dopant element satisfies the following: the lithium-ion diffusion coefficient of the elemental form of the first dopant element at 25°C is greater than the lithium-ion diffusion coefficient of elemental silicon at 25°C. The first doping element includes at least one of Sn, Ge, Sb, Bi, and Sr; The silicon-oxygen composite material further includes a second doping element, which includes at least one of alkali metal elements and alkaline earth metal elements.

2. The silicon-oxygen composite material according to claim 1, characterized in that, The elemental form of the first dopant has a lithium-ion diffusion coefficient greater than 10 at 25°C. -14 cm 2 / S; and / or, the lithium-ion diffusion coefficient of the silicon at 25°C is less than 10. -14 cm 2 / S.

3. The silicon-oxygen composite material according to claim 2, characterized in that, The lithium-ion diffusion coefficient of the first doped element at 25°C is greater than 10. -14 cm 2 / S and less than or equal to 10 -13 cm 2 / S; and / or, the lithium-ion diffusion coefficient of the silicon at 25°C is greater than 10. -15 cm 2 / S and less than 10 -14 cm 2 / S.

4. The silicon-oxygen composite material according to any one of claims 1 to 3, characterized in that, The grain size of the first dopant element is ≤7nm.

5. The silicon-oxygen composite material according to any one of claims 1 to 4, characterized in that, The XRD diffraction pattern of the silicon-oxygen composite material also contains diffraction peaks of silicon grains, and the silicon-oxygen composite material has at least one of the following relationships (1)-(2): (1) 0.35≤Y / 2X≤4; (2) -5≤5Xsin2θ-Y≤15; Where Y is the grain size of the first doped element, X is the grain size of the silicon grain, the units of X and Y are both nm, and 2θ is the XRD diffraction angle of the crystal.

6. The silicon-oxygen composite material according to claim 5, characterized in that, The XRD diffraction pattern of the silicon-oxygen composite material also contains diffraction peaks of silicon grains, and the silicon-oxygen composite material has at least one of the following relationships (1)-(2): (1) 0.7 ≤ Y / 2X ≤ 4; (2) -5≤5Xsin2θ-Y≤10.

7. The silicon-oxygen composite material according to any one of claims 1 to 6, characterized in that, The XRD diffraction pattern of the silicon-oxygen composite material includes diffraction peaks of the first doped element crystal, wherein the full width at half maximum (FWHM) of the diffraction peaks of the first doped element crystal is 3°-7°; and / or, the diffraction peak intensity of the crystal is 600 S. -1 -1200 S -1 .

8. The silicon-oxygen composite material according to any one of claims 1 to 7, characterized in that, Based on the total mass of the silicon-oxygen composite material, the mass fraction of the first dopant element is less than or equal to 12%.

9. The silicon-oxygen composite material according to claim 8, characterized in that, Based on the total mass of the silicon-oxygen composite material, the mass fraction of the first dopant element is 1%-10%.

10. The silicon-oxygen composite material according to any one of claims 1 to 9, characterized in that, The second doping element also includes non-metallic elements.

11. The silicon-oxygen composite material according to claim 10, characterized in that, The nonmetallic element includes at least one of B, N, F, Cl, and S.

12. The silicon-oxygen composite material according to any one of claims 1 to 11, characterized in that, The alkali metal element includes at least one of Li, Na, and K.

13. The silicon-oxygen composite material according to any one of claims 1 to 12, characterized in that, The alkaline earth metal element includes at least one of Mg, Ca, Be, and Sr.

14. The silicon-oxygen composite material according to any one of claims 1 to 13, characterized in that, Based on the total mass of the silicon-oxygen composite material, the mass fraction of the second dopant element is less than or equal to 7%.

15. The silicon-oxygen composite material according to claim 14, characterized in that, Based on the total mass of the silicon-oxygen composite material, the mass fraction of the second dopant element is 1%-5%.

16. The silicon-oxygen composite material according to any one of claims 1 to 15, characterized in that, The silicon-oxygen composite material also includes a carbon layer that at least partially covers the surface of the silicon-oxygen material matrix.

17. The silicon-oxygen composite material according to claim 16, characterized in that, The thickness of the carbon layer is 1-4 nm.

18. The silicon-oxygen composite material according to any one of claims 1 to 17, characterized in that, The volumetric particle size distribution (Dv50) of the silicon-oxygen composite material is 3 μm-8 μm.

19. The silicon-oxygen composite material according to claim 18, characterized in that, The volumetric particle size distribution (Dv50) of the silicon-oxygen composite material is 4 μm-6 μm.

20. A method for preparing a silicon-oxygen composite material, characterized in that, The preparation method includes: A silicon-oxygen material matrix is ​​obtained by first vapor deposition of a first vapor containing elemental silicon and silicon dioxide. A second vapor containing a first dopant element and a second dopant element is subjected to a second vapor deposition with the silicon-oxygen material matrix to obtain the silicon-oxygen composite material. At least a portion of the first dopant element exists in the silicon-oxygen material matrix in crystalline form, and the grain size of the first dopant element crystal is ≤9nm. The first dopant element satisfies the following condition: the lithium-ion diffusion coefficient of the elemental first dopant element at 25°C is greater than that of elemental silicon at 25°C. The first doping element includes at least one of Sn, Ge, Sb, Bi, and Sr; The second doping element includes at least one of alkali metal elements and alkaline earth metal elements.

21. The preparation method according to claim 20, characterized in that, The temperature of the first vapor deposition is 1000℃-1300℃; and / or the time of the first vapor deposition is 6h-12h.

22. The preparation method according to claim 21, characterized in that, The temperature of the first vapor deposition is 1100℃-1250℃; and / or the time of the first vapor deposition is 8h-10h.

23. The preparation method according to any one of claims 20 to 22, characterized in that, The temperature of the second vapor deposition is 800℃-900℃; and / or the time of the second vapor deposition is 4h-10h.

24. The preparation method according to claim 23, characterized in that, The temperature of the second vapor deposition is 820℃-880℃; and / or the time of the second vapor deposition is 6h-8h.

25. The preparation method according to any one of claims 20 to 24, characterized in that, The preparation method includes: The silicon-oxygen composite material is obtained by a second vapor deposition of a second vapor containing a first dopant element and a second dopant element with the silicon-oxygen material matrix. The second dopant element also includes a non-metallic element.

26. The preparation method according to claim 25, characterized in that, The nonmetallic element includes at least one of B, N, F, Cl, and S.

27. The preparation method according to any one of claims 20 to 26, characterized in that, The alkali metal element includes at least one of Li, Na, and K.

28. The preparation method according to any one of claims 20 to 27, characterized in that, The alkaline earth metal element includes at least one of Mg, Ca, Be, and Sr.

29. The preparation method according to any one of claims 20 to 28, characterized in that, The preparation method further includes: performing carbon coating treatment on the surface of the silicon-oxygen composite material.

30. The preparation method according to claim 29, characterized in that, The carbon coating treatment temperature is 500℃-750℃.

31. The preparation method according to claim 30, characterized in that, The carbon coating treatment temperature is 660℃-720℃.

32. The preparation method according to any one of claims 29 to 31, characterized in that, The carbon coating treatment time is 2h-10h.

33. The preparation method according to claim 32, characterized in that, The carbon coating treatment time is 6-8 hours.

34. A secondary battery, comprising a negative electrode, characterized in that, The negative electrode sheet includes a negative electrode active material, which includes a silicon-oxygen composite material as described in any one of claims 1 to 19 or a silicon-oxygen composite material prepared by the preparation method according to any one of claims 20 to 33.

35. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 34.

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