Negative electrode material and preparation method thereof, and lithium ion battery

Abstract

The present application relates to a negative electrode material and a preparation method thereof, and a lithium-ion battery, belonging to the technical field of energy storage materials. The negative electrode material comprises a first skeleton and a second skeleton intertwined with each other, and nano-silicon. The first skeleton is a Li-ion battery with a network structure. x M y SiO4 material, the second skeleton is a carbon material with a network structure; among them, Li x M y Nano-silicon is distributed within the SiO4 matrix and / or on the surface. The values of x and y are chosen to maintain charge balance, and M includes a metal element other than Li that can reduce silicon oxide. This negative electrode material has excellent conductivity, a more stable structure, low volume expansion, high conductivity, initial efficiency, and excellent rate performance.

Description

Technical Field

[0001] The present application relates to the technical field of energy storage materials, and in particular to a negative electrode material and a preparation method thereof, and a lithium-ion battery. Background Art

[0002] Currently, graphite is the most widely used anode material for lithium batteries, but due to its low theoretical capacity (372 mAh / g), it cannot meet the demand for high energy density. Silicon, with its higher theoretical capacity (4200 mAh / g), is considered a next-generation anode material for lithium batteries and has attracted widespread attention and research within the industry.

[0003] However, silicon also has obvious disadvantages, such as: silicon has low electrical conductivity; in addition, the volume expansion of silicon changes greatly during the cycle, which is prone to pulverization, loss of electrical contact between the active material and the current collector, and even further fall off from the current collector, ultimately causing serious degradation of the cycle performance; in addition, the expansion causes the formed SEI film to rupture, exposing a new interface and continuing to form a new SEI film, resulting in the SEI film on the outer layer of the silicon particles becoming thicker and thicker after the cycle, ultimately blocking the embedding of lithium ions.

[0004] How to more effectively alleviate the volume expansion of silicon, ensure the cycle stability of silicon negative electrodes, and obtain silicon negative electrode materials with lower volume expansion, higher initial efficiency, and long cycle life is a technical hotspot that needs to be urgently addressed in the current lithium battery field.

[0005] Composite graphite and silicon can solve the above problems to a certain extent. However, existing silicon-carbon composite materials usually have silicon coated in a carbon layer, which reduces the initial effect of the silicon-carbon composite material. Summary of the Invention

[0006] The embodiments of the present application include providing a negative electrode material and a preparation method thereof, and a lithium-ion battery, which can improve the volume expansion of the negative electrode material while improving its initial efficiency and cycle performance.

[0007] In the first aspect, the embodiment of the present application provides a negative electrode material, which includes a first skeleton and a second skeleton intertwined with each other, and nano-silicon, wherein the first skeleton is a network structure of Li x M y SiO4 material, the second skeleton is a carbon material with a network structure; among them, Li x M y Nano-silicon is distributed in the SiO4 material matrix or / and on the surface, the values of x and y are in accordance with charge balance, and M includes metal elements other than Li that can reduce silicon oxide.

[0008] In combination with the first aspect, in some embodiments of the present application, the carbon material is also distributed in the Li x M yA carbon coating is formed on the outer surface of the SiO4 material;

[0009] or / and, the thickness of the coating carbon layer is 5nm-80nm;

[0010] Or / and, the negative electrode material satisfies at least one of the following conditions (1)-(8):

[0011] (1)Li x M y In SiO4 materials, 2≤x≤3.4, 0.4≤y≤1;

[0012] (2) M includes Mg and / or Al;

[0013] (3) The particle size of nano-silicon is 5nm-200nm;

[0014] (4) The carbon material includes one or a combination of soft carbon and hard carbon;

[0015] (5) The specific surface area of the negative electrode material is 1m 2 / g-3m 2 / g;

[0016] (6) The shape of the negative electrode material is spherical particles, and the average particle size D50 of the negative electrode material is 5 μm-30 μm;

[0017] (7) The skeleton diameter of the carbon material is 10nm-500nm;

[0018] (8)Li x M y The skeleton diameter of SiO4 material is 10nm-400nm;

[0019] (9)Li x M y The mass percentage of SiO4 material in the negative electrode material is 5%-30%;

[0020] (10) The mass percentage of nano-silicon in the negative electrode material is 30%-60%;

[0021] (11) The mass percentage of carbon material in the negative electrode material is 10%-65%.

[0022] In the second aspect, the embodiment of the present application provides a negative electrode material, the negative electrode material includes Li x M y SiO4 materials, carbon materials and nano-silicon, Li x M y SiO4 material has a porous structure, Li x M y The pores of SiO4 material are filled with carbon material; among them, Li x My Nano-silicon is distributed in the SiO4 material matrix or / and on the surface, the values of x and y are in accordance with charge balance, and M includes metals other than Li that can reduce silicon oxide.

[0023] In conjunction with the second aspect, in some embodiments of the present application, the carbon material is also distributed in the Li x M y A carbon coating is formed on the outer surface of the SiO4 material;

[0024] or / and, the thickness of the coating carbon layer is 5nm-80nm;

[0025] Or / and, the negative electrode material satisfies at least one of the following conditions (12)-(21):

[0026] (12)Li x M y In SiO4 materials, 2≤x≤3.4, 0.4≤y≤1;

[0027] (13) M includes Mg and / or Al;

[0028] (14) The particle size of nano-silicon is 5nm-200nm;

[0029] (15) The carbon material includes one or a combination of soft carbon and hard carbon;

[0030] (16) The specific surface area of the negative electrode material is 1m 2 / g-3m 2 / g;

[0031] (17) The shape of the negative electrode material is spherical particles, and the average particle size D50 of the negative electrode material is 5 μm-30 μm;

[0032] (18)Li x M y The porosity of SiO4 material is 30%-46%;

[0033] (19)Li x M y The mass percentage of SiO4 material in the negative electrode material is 5%-30%;

[0034] (20) The mass percentage of nano-silicon in the negative electrode material is 30%-60%;

[0035] (21) The mass percentage of carbon material in the negative electrode material is 10%-65%.

[0036] In a third aspect, an embodiment of the present application provides a lithium-ion battery, comprising the negative electrode material provided in the first aspect or the second aspect.

[0037] In a fourth aspect, an embodiment of the present application provides a method for preparing a negative electrode material, comprising:

[0038] Lithium ions formed from silicon oxides on the surface of nano-silicon to form porous or network structures x M y SiO4 material, in Li x M y The negative electrode material is obtained by filling the pores of the porous structure of the SiO4 material or the gaps in the network structure with carbon material, wherein M includes a metal element other than Li that can reduce silicon oxide.

[0039] In conjunction with the fourth aspect, in some embodiments of the present application, the preparation method includes:

[0040] The network structure or porous structure skeleton material is mixed with lithium salt and then calcined to obtain Li x M y SiO4 material, wherein the skeleton material includes nano-silicon, silicon oxide and metal oxide on the surface of nano-silicon; and in Li x M y Carbon material is formed in the pores or gaps of SiO4 material to obtain negative electrode material;

[0041] Alternatively, a network structure or porous structure skeleton material, a lithium salt and an organic carbon source are mixed and then heat treated to obtain a negative electrode material, wherein the skeleton material includes nano-silicon, silicon oxide on the surface of nano-silicon and metal oxide.

[0042] In conjunction with the fourth aspect, in some embodiments of the present application, in Li x M y The steps of forming carbon material in the pores or gaps of SiO4 material to obtain negative electrode material include: x M y SiO4 material is mixed with an organic carbon source and calcined to carbonize the organic carbon source to form a carbon material; or a ... x M y Carbon material is formed in the pores or gaps of the SiO4 material;

[0043] Alternatively, the step of mixing the skeleton material with a network structure or a porous structure, a lithium salt and an organic carbon source comprises: mixing the skeleton material with a network structure or a porous structure with the lithium salt, and then mixing with the organic carbon source.

[0044] In conjunction with the fourth aspect, in some embodiments of the present application, the method for preparing the skeleton includes:

[0045] The silicon oxide and the binder are mixed and granulated to obtain a precursor 1;

[0046] Precursor 1, metal M powder and molten salt are mixed and subjected to a thermal reaction so that at least a portion of the silicon oxide is reduced to nano-silicon to obtain precursor 2;

[0047] The second precursor is acid-washed to remove part of the metal oxide to form a skeleton material with a porous structure or a network structure.

[0048] In conjunction with the fourth aspect, in some embodiments of the present application, the preparation method satisfies at least one of the following conditions (22)-(26):

[0049] (22) dispersing silicon oxide and a binder in a solution and spray granulating the solution to obtain a precursor 1;

[0050] (23) The mass ratio of silicon oxide to binder is (40-100):1;

[0051] (24) The mass ratios of precursor 1, molten salt, and metal M powder are 1:(3-8):(0.5-1.5);

[0052] (25) Metal M powder includes one or more combinations of Mg powder, Al powder and MgAl alloy powder;

[0053] (26) The skeleton material, soluble lithium salt and water are mixed, stirred evenly and then dried.

[0054] Compared with the prior art, the advantages of this application include:

[0055] For negative electrode materials: Li x M y The addition of SiO4 material (M includes metal elements other than Li that can reduce silicon oxide) can supplement lithium to the negative electrode material to improve its initial efficiency, and Li x M y SiO4 material has good lithium ion and electron conductivity, which can improve the conductivity of the material; the network structure of Li x M y The SiO4 material and the network structure carbon material are intertwined with each other, and the network structure carbon material is basically distributed throughout the negative electrode material, which can make the negative electrode material more conductive; at the same time, due to the Li x M y Nano-silicon is distributed in the SiO4 material matrix or / and on the surface. The addition of nano-silicon can increase the capacity of the material, and the particle size of nano-silicon is small and the distribution is more uniform. Although the volume of nano-silicon will expand during the charge and discharge process, due to the intertwined network structure of Li x M yThe SiO4 material and the network-structured carbon material can limit the expansion of nano-silicon and, to a certain extent, prevent the structural collapse caused by the volume expansion of nano-silicon. This can improve the conductivity of the negative electrode material, make the structure more stable, and have low volume expansion, high conductivity, initial efficiency, and excellent rate performance.

[0056] For the preparation method of negative electrode materials: Li-ion battery based on silicon oxide on the surface of nano-silicon to form a porous structure or network structure x M y SiO4 material, nano-silicon and Li x M y The distribution of SiO4 materials is relatively uniform, and nano-silicon is located in the Li x M y The SiO4 material is in the matrix and / or on the surface; after being compounded with the carbon material, the obtained negative electrode material has better conductivity, more stable structure, lower volume expansion, higher conductivity, first efficiency and excellent rate performance.

[0057] For lithium-ion batteries: the lithium-ion battery uses the negative electrode material provided by this application, which can make the battery have lower volume expansion, higher initial efficiency and excellent rate performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0059] Figure 1 A schematic cross-sectional view of the negative electrode material provided in an embodiment of the present application;

[0060] Figure 2 A process flow chart of a method for preparing a negative electrode material provided in an embodiment of the present application;

[0061] Figure 3 The scanning electron microscope image and EDS image of the precursor 5 in Example 1;

[0062] Figure 4 XRD pattern of the negative electrode material provided in Example 1 of the present application;

[0063] Figure 5 This is a scanning electron microscope image of the negative electrode material provided in Example 1 of the present application;

[0064] Icon: 110-Li x M ySiO4 material; 120-carbon material; 130-nanosilicon. DETAILED DESCRIPTION

[0065] In order to make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions of the present application are clearly and completely described below.

[0066] The inventors found that silicon can increase the capacity of the negative electrode material, but it is easy to cause volume expansion, and the oxide layer on the surface of silicon will cause the first efficiency of the battery to decrease; carbon can improve the conductivity of the negative electrode material, but its capacity is low; Li x M y SiO4 can supplement lithium to the negative electrode material to improve the initial efficiency, and Li x M y SiO4 has good lithium ion and electron conductivity, which can improve the material's electrical conductivity. Therefore, the inventors provide a negative electrode material that combines the three elements to achieve a negative electrode material with low volume expansion, high conductivity, initial efficiency, and excellent rate performance.

[0067] Figure 1 This is a cross-sectional diagram of the negative electrode material provided in the embodiment of the present application. Figure 1 , Figure 1 In the figure, the black part is Li x M y SiO 4 material 110 , the white part is nano-silicon 130 , and the gray part is carbon material 120 .

[0068] Please continue reading Figure 1 The negative electrode material includes a first skeleton and a second skeleton intertwined with each other, and nano-silicon 130, the first skeleton is a network structure of Li x M y SiO4 material 110, the second skeleton is a carbon material 120 with a network structure; wherein Li x M y Nano-silicon 130 is distributed in the matrix and / or on the surface of the SiO 4 material 110 . The values of x and y are in accordance with charge balance. M includes metal elements other than Li that can reduce silicon oxide.

[0069] The first skeleton and the second skeleton are intertwined to form a composite skeleton. The network structure of Li x M y The SiO4 material 110 is intertwined with the carbon material 120, and the carbon material 120 of the network structure is intertwined with the Li x M y The SiO4 material 110 can make the structure of the negative electrode material more stable; at the same time, the carbon material 120 is basically evenly distributed throughout the negative electrode material, which can make the material more conductive.

[0070] Li x M y The addition of SiO4 material 110 (M includes metal elements other than Li that can reduce silicon oxide) can supplement lithium to the negative electrode material to improve its initial efficiency. Nano-silicon 130 is distributed in the Li x M y The SiO4 material 110 matrix or / and surface can increase the capacity of the negative electrode material; although the nano-silicon 130 will expand in volume during the charge and discharge process, due to the intertwined network structure of Li x M y The SiO4 material 110 and the network-structured carbon material 120 can limit the expansion of the nano-silicon 130 and, to a certain extent, prevent the structural collapse caused by the volume expansion of the nano-silicon 130. This can improve the conductivity of the negative electrode material, make it more stable, and have low volume expansion, high conductivity, initial efficiency, and excellent rate performance.

[0071] It should be noted that the network structure here does not refer to the structure of an intangible computer network, but rather to the network structure of tangible matter, which is equivalent to a solid structure. For example, if a spherical material has no internal voids, consistent with the surface structure of the spherical material, it is called a solid structure; if it has a large internal void, it is called a hollow structure; if it has many internal voids, which may be partially conductive, it is called a network structure.

[0072] For example, if a material is called a metal mesh, its usual structure is a metal mesh with multiple metal wires woven together to form a metal mesh with multiple hole structures. The network structure in this application is somewhat different from this. The network structure in this application has a basic three-dimensional structure (for example, a spherical structure, a cube structure, a rectangular parallelepiped structure, and other irregular three-dimensional structures) with many pores inside and on the surface (for example, similar to a three-dimensional foam metal structure, but the material is different and the pore structure may also be different), thereby forming a network structure.

[0073] Therefore, the network structure in this application refers to the three-dimensional Li x M y The SiO4 material 110 and the carbon material 120 have many voids inside and on their surfaces, thereby forming a structure in which the voids and materials of the two are intertwined. The voids in the network structure are not limited to uniformly distributed voids. The voids may be larger in some areas and smaller in others, or may be irregular.

[0074] Nano-Si 130 is distributed in Li x M ySiO4 material 110 matrix or / and surface, refers to Li x M y The surface of SiO4 material 110 is distributed with nano-silicon 130; or Li x M y Nano-silicon 130 is distributed in the matrix of SiO4 material 110; or Li x M y Nano-silicon 130 is distributed on the surface and in the matrix of the SiO 4 material 110 .

[0075] Nano-silicon 130 mainly refers to silicon materials with nano-scale particle size. The particle size of the silicon material of this particle size is small. Under the condition of the same silicon content, the nano-silicon 130 with a smaller particle size is easier to be evenly distributed on the Li x M y On the SiO4 material 110.

[0076] Although the present application records that the nano-silicon 130 is distributed on the Li x M y The SiO4 material 110 matrix and / or surface, however, does not limit the Li x M y The mass of SiO4 material 110 is greater than that of nano-silicon 130. x M y The mass of SiO4 material 110 can be greater than the mass of nano-silicon 130, and the mass of nano-silicon 130 can also be greater than the mass of Li x M y The mass of SiO4 material 110, Li x M y The quality of the SiO 4 material 110 may be comparable to that of the nano-silicon 130 .

[0077] Please continue reading Figure 1 , the negative electrode material includes Li x M y SiO4 material 110, carbon material 120 and nano-silicon 130, Li x M y The SiO4 material 110 is a porous structure. x M y The pores of SiO4 material 110 are filled with carbon material 120; wherein, Li x M y Nano-silicon 130 is distributed in the matrix and / or on the surface of the SiO 4 material 110 . The values of x and y are in accordance with charge balance. M includes metals other than Li that can reduce silicon oxide.

[0078] Porous Li x M yThe pores of the SiO4 material 110 are filled with carbon material 120, which can make the structure of the negative electrode material more stable; at the same time, the carbon material 120 is basically evenly distributed throughout the negative electrode material, which can make the material more conductive. x M y The addition of SiO4 material 110 (M includes metal elements other than Li that can reduce silicon oxide) can supplement lithium to the negative electrode material to improve its initial efficiency. Nano-silicon 130 is distributed in the Li x M y The SiO4 material 110 matrix or / and surface can increase the capacity of the negative electrode material; although the volume of the nano-silicon 130 will expand during the charge and discharge process, the Li x M y The SiO4 material 110 and the porous carbon material 120 can limit the expansion of the nano-silicon 130 and, to a certain extent, prevent the structural collapse caused by the volume expansion of the nano-silicon 130. This can improve the conductivity of the negative electrode material, make it more stable, and have low volume expansion, high conductivity, initial efficiency, and excellent rate performance.

[0079] As an example, the porous structure of Li x M y The porosity of the SiO4 material 110 is 30%-46%, such as 30%, 32%, 35%, 40%, 43%, 46%, etc., that is, to ensure that the Li x M y SiO4 material has sufficient volume to fill carbon material, which improves the conductivity of the composite negative electrode material, reduces the expansion rate of the composite negative electrode material, and ensures that the capacity is not too low.

[0080] It should be noted that the carbon material 120 can also be regarded as a porous structure, and the porous structure here refers to: Li x M y The SiO4 material 110 and the carbon material 120 are essentially three-dimensional structures, having numerous pores within and / or on their surfaces. These pores may be partially connected or partially disconnected, allowing the two materials to intersperse. The pores of the porous structure are not limited to uniformly distributed pores or pores of uniform pore diameter. The pores may be larger in some areas and smaller in others, or may be irregular.

[0081] Regardless of whether it is a porous structure or a network structure, optionally, the skeleton diameter of the carbon material 120 is 10nm-500nm; Li x M y The skeleton diameter of the SiO4 material 110 is 10nm-400nm; it is not limited to the carbon material 120 and Li x My The diameters of all the skeletons of the SiO4 material 110 are within the above range. Generally, the diameters of more than 70% of the skeletons are within the above range, which makes it easy to realize Li x M y The SiO4 material 110 and the carbon material 120 are filled or intertwined with each other. At the same time, it is not limited to the same diameter of the skeleton at different parts. The diameters of different parts of the skeleton of the same particle can be different.

[0082] As an example, the skeleton diameter of the carbon material 120 is 10 nm to 100 nm, and Li x M y The skeleton diameter of the SiO4 material 110 is 10nm-90nm; or the skeleton diameter of the carbon material 120 is 100nm-300nm, Li x M y The skeleton diameter of the SiO4 material 110 is 90nm-200nm; or the skeleton diameter of the carbon material 120 is 300nm-500nm, Li x M y The skeleton diameter of the SiO4 material 110 is 200 nm to 400 nm, which can be observed by a scanning electron microscope.

[0083] Please continue reading Figure 1 , Li x M y The carbon material filled in the pores of SiO4 material is also distributed in the Li x M y A carbon coating forms on the outer surface of the SiO4 material. This coating improves the conductivity of the negative electrode material, limits the volume expansion of the nano-silicon 130, and protects the internal structure, making the overall material more stable.

[0084] The following is an explanation of the carbon coating, for example: Figure 1 As shown, the porous structure of Li x M y The diameter of SiO4 material 110 is D1 (Li x M y Although the SiO4 material 110 is a porous structure or a network structure, its basic outer contour is spherical, and the diameter of the spherical outer contour is D1). x M y The diameter of the carbon filling in the SiO4 material is also D1 (the carbon filling is also a porous structure, but the basic outer contour is spherical, and the diameter of the spherical outer contour is D1). The particle size of the negative electrode material is D2, so the carbon coating layer is Figure 1The area of the sphere where D2 is located minus the area of the sphere where D1 is located. The carbon coating layer refers to the area covered on the Li x M y The carbon layer structure other than SiO4 material 110 is basically not x M y The SiO 4 materials 110 are intertwined or filled with each other.

[0085] Optionally, the thickness of the coated carbon layer is 5nm-80nm. The thickness of the coated carbon layer here means that there is substantially no Li x M y The thickness of the outermost layer of the SiO4 material 110 is, for example: Figure 1 The value of D is (D2-D1) / 2. A carbon coating of this thickness stabilizes the material structure, effectively limits silicon volume expansion, and optimizes the mass ratio of nano-silicon 130 and LixMySiO4 material 110, thereby optimizing the overall performance of the negative electrode material.

[0086] As an example, the thickness of the carbon coating layer may be 5nm-20nm; or the thickness of the carbon coating layer may be 20nm-40nm; or the thickness of the carbon coating layer may be 40nm-60nm; or the thickness of the carbon coating layer may be 60nm-80nm. Figure 1 As shown, the coated carbon layer is approximately a spherical layered structure, and the thickness of different positions of the sphere can be the same or different, which is not limited in this application.

[0087] It should be noted that Figure 1 In the case of Li, whether it is a network structure or a porous structure x M y The outer contour of the SiO4 material 110 is a spherical structure, or the outer contour of the granular negative electrode material is a spherical structure. It is only an exemplary shape or structure and is not limited to a spherical structure. Its spherical structure or the solution that can form a granular shape are all within the scope of protection of this application.

[0088] Optionally, Li x M y In the SiO 4 material 110 , 2≤x≤3.4, 0.4≤y≤1, and the values of x and y meet the charge balance.

[0089] In some possible embodiments, M includes Mg and / or Al, which can easily react with silicon oxide and metal oxide to obtain Li x M ySiO4 material 110; on the other hand, its source is wider and easier to obtain; on the other hand, its pre-lithiation effect is better, and the performance of the negative electrode material is better.

[0090] Optionally, Li x M y SiO4 material 110 may be lithium magnesium silicate; or Li x M y The SiO4 material 110 may be lithium aluminum silicate; or Li x M y The SiO 4 material 110 may be a mixture of lithium magnesium silicate and lithium aluminum silicate.

[0091] In other embodiments, M may further include Ca and / or Zn.

[0092] In some possible embodiments, the particle size of the nano-silicon 130 is 5 nm to 200 nm; the nano-silicon 130 is more easily evenly distributed on the Li x M y On the SiO4 material 110, the nano-silicon 130 of this particle size can be directly obtained by reducing silicon oxide, and the preparation is more convenient.

[0093] Li x M y A plurality of nano-silicon particles 130 are distributed on the SiO4 material 110. The particle size of each nano-silicon particle 130 is not necessarily uniform. Generally, the particle size of the nano-silicon particles 130 is generally within a certain range, and the particle distribution of the nano-silicon particles 130 is relatively uniform. For example, the particle size of the nano-silicon particles 130 is 5 nm to 50 nm; or 50 nm to 100 nm; or 100 nm to 150 nm; or 150 nm to 200 nm.

[0094] In some possible implementations, the carbon material 120 includes hard carbon, soft carbon, or a combination thereof.

[0095] In some possible embodiments, the specific surface area of the negative electrode material is 1 m 2 / g-3m 2 / g. The negative electrode material has a small specific surface area and has basically no pores or a small amount of pores, making the structure of the entire negative electrode material more stable.

[0096] For example: the specific surface area of the negative electrode material is 1m 2 / g, 1.5m 2 / g, 2m 2 / g, 2.5m 2 / g or 3m 2 / g.

[0097] Optionally, the negative electrode material is in the form of spherical particles, and the average particle size D50 of the negative electrode material is 5 μm-30 μm. The spherical particles herein are not limited to regular spheres, and may be irregular spherical particles, for example, having a small number of concave portions on the surface and an overall ellipsoidal structure. The average particle size herein may refer to the average particle size of different particles, or may refer to the average particle size of the same particle in different directions, which is not limited here.

[0098] The average particle size D50 of the spherical particles of the negative electrode material is within the range of 5 μm to 30 μm, which can make the size of the negative electrode material more uniform, thereby improving its capacity retention rate and performance. As an example, the average particle size D50 of the negative electrode material is 5 μm to 10 μm; or the average particle size D50 of the negative electrode material is 10 μm to 20 μm; or the average particle size D50 of the negative electrode material is 20 μm to 30 μm.

[0099] For example, the average particle size D50 of the spherical particles of the negative electrode material is 5 μm, 8 μm, 10 μm, 15 μm, 20 μm, 25 μm or 30 μm.

[0100] In some possible embodiments, Li x M y The mass percentage of SiO4 material 110 in the negative electrode material is 5%-30%, the mass percentage of nano-silicon 130 in the negative electrode material is 30%-60%, and the mass percentage of carbon material 120 in the negative electrode material is 10%-65%. x M y The contents of the SiO 4 material 110 , the nano-silicon 130 , and the carbon material 120 are limited to the above ranges, which can make the composition of the negative electrode material more reasonable and improve the overall performance of the negative electrode material.

[0101] In one embodiment, Li x M y The mass percentage of SiO4 material 110 in the negative electrode material is 5%-10%, the mass percentage of nano-silicon 130 in the negative electrode material is 30%-40%, and the mass percentage of carbon material 120 in the negative electrode material is 50%-65%. x M y The content of SiO4 material 110 is relatively small, while the content of nano-silicon 130 and carbon material 120 is relatively large, which can effectively improve the initial efficiency of the negative electrode material; at the same time, the addition of more carbon material 120 can effectively limit the expansion of nano-silicon 130 during the charging and discharging process, and the performance of the negative electrode material is better.

[0102] In another embodiment, Li x M yThe mass percentage of SiO4 material 110 in the negative electrode material is 10%-20%, the mass percentage of nano-silicon 130 in the negative electrode material is 30%-40%, and the mass percentage of carbon material 120 in the negative electrode material is 50%-60%.

[0103] In another embodiment, Li x M y The mass percentage of SiO4 material 110 in the negative electrode material is 20%-30%, the mass percentage of nano-silicon 130 in the negative electrode material is 40%-60%, and the mass percentage of carbon material 120 in the negative electrode material is 10%-30%.

[0104] For example: Li x M y The mass percentage of SiO4 material 110 in the negative electrode material is 5%, the mass percentage of nano-silicon 130 in the negative electrode material is 60%, and the mass percentage of carbon material 120 in the negative electrode material is 35%; or, Li x M y The mass percentage of SiO4 material 110 in the negative electrode material is 10%, the mass percentage of nano-silicon 130 in the negative electrode material is 50%, and the mass percentage of carbon material 120 in the negative electrode material is 40%; or, Li x M y The mass percentage of SiO4 material 110 in the negative electrode material is 20%, the mass percentage of nano-silicon 130 in the negative electrode material is 45%, and the mass percentage of carbon material 120 in the negative electrode material is 35%; or, Li x M y The mass percentage of the SiO4 material 110 in the negative electrode material is 30%, the mass percentage of the nano-silicon 130 in the negative electrode material is 30%, and the mass percentage of the carbon material 120 in the negative electrode material is 40%.

[0105] The above-mentioned negative electrode material can be used to prepare lithium-ion batteries. The prepared lithium-ion batteries have low volume expansion, high initial efficiency and excellent rate performance.

[0106] The lithium-ion battery can be used to provide electrical energy to electrical devices, and has a better endurance.

[0107] After introducing the negative electrode materials and their applications, the following is an introduction to their preparation methods. The method includes: forming a porous structure or a network structure of Li based on silicon oxide on the surface of nano-silicon. x M y SiO4 material, in Li x M yThe negative electrode material is obtained by filling the pores of the porous structure of the SiO4 material or the gaps in the network structure with carbon material, wherein M includes a metal element other than Li that can reduce silicon oxide.

[0108] Lithium ions with porous or network structures are formed based on silicon oxide on the surface of nano-silicon. x M y SiO4 material, nano-silicon and Li x M y The distribution of SiO4 materials is relatively uniform, and nano-silicon is located in the Li x M y The SiO4 material is in the matrix and / or on the surface; after being compounded with the carbon material, the obtained negative electrode material has better conductivity, more stable structure, lower volume expansion, higher conductivity, first efficiency and excellent rate performance.

[0109] The preparation method is described in detail below. Figure 2 For a process flow chart of the preparation method of the negative electrode material provided in the embodiment of the present application, please refer to Figure 2 , the preparation method comprises:

[0110] S110 mixes silicon oxide and a binder and then granulates them to obtain a precursor 1. Granulation by adding a binder can make the particles more uniform and can also facilitate the subsequent formation of a skeleton with a porous structure or a network structure.

[0111] Alternatively, silicon oxide and a binder are dispersed in a solution and spray granulated to obtain precursor 1. This can make the silicon oxide and the binder disperse more uniformly, thereby obtaining particles with more uniform particle sizes.

[0112] In some possible embodiments, the mass ratio of silicon oxide to binder is (40-100):1. The content of silicon oxide is much higher than that of the binder. After granulation, the main component of the precursor 1 is silicon oxide, and the binder is only used as a bonding material to facilitate granulation.

[0113] As an example, the mass ratio of silicon oxide to binder is (40-60):1; or the mass ratio of silicon oxide to binder is (60-80):1; or the mass ratio of silicon oxide to binder is (80-100):1. For example, the mass ratio of silicon oxide to binder is 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, or 100:1.

[0114] In some possible embodiments, the silicon oxide is one or more combinations of SiO, SiO2, and Si2O6. For example, the silicon oxide is silicon dioxide, which is relatively stable and has a wider source.

[0115] In some possible embodiments, the binder is one or more combinations of epoxy resin, phenolic resin, furfural resin, urea-formaldehyde resin, polyvinyl alcohol, polyvinyl chloride, polyethylene glycol, polyethylene oxide, polyvinylidene fluoride, glucose, sucrose, asphalt, polystyrene, polypyrrole, polyaniline, sodium carboxymethyl cellulose, and polyvinyl pyrrolidone.

[0116] Optionally, silicon oxide is dispersed in an aqueous solution, stirred evenly, and then a binder is added to the solution, with the mass ratio of silicon oxide to binder being (40-60):1. After further stirring evenly, the solution is spray-granulated to obtain a precursor 1.

[0117] S120 mixes the precursor 1, the metal M powder and the molten salt, and performs a thermal reaction so that at least part of the silicon oxide is reduced to nano-silicon, thereby obtaining the precursor 2. Wherein, M includes a metal element other than Li that can reduce silicon oxide. During the thermal reaction, the silicon oxide is reduced to nano-silicon by the metal M, and the metal M is converted into metal oxide. The formed particles basically have a structure in which the inner shell is nano-silicon and the surface layer is metal oxide, and molten salt is distributed between the particles.

[0118] It should be noted that: this does not limit all silicon oxides to being reduced, nor does it limit the surface of nano-silicon to being entirely attached with metal oxides; in the actual production process, most of the silicon oxides are reduced, and the metal oxides on the nano-silicon generally cover part of the surface of the nano-silicon, and part of the surface of the nano-silicon may be exposed.

[0119] At the same time, not all nano-silicon particles (particles with nano-silicon inside and metal oxide on the surface) are distributed with molten salt. Molten salt can be distributed between some nano-silicon particles, or some nano-silicon particles can be combined with nano-silicon particles.

[0120] The addition of molten salt can control the reaction conditions of the thermal reaction and avoid the violent reaction to a certain extent; at the same time, it can also avoid the adhesion or agglomeration between particles, so as to finally form a negative electrode material with more uniform particles, and the reaction is also easier to control; after the subsequent removal of the molten salt, it is also conducive to the formation of a porous structure.

[0121] In some possible embodiments, the mass ratio of Precursor 1, molten salt, and Metal M powder is 1:(3-8):(0.5-1) in that order. The molten salt content is relatively high, and it essentially does not participate in the reaction. After the molten salt is subsequently removed, a porous structure or network structure can be formed, facilitating the preparation of the negative electrode material. The mass ratio of Precursor 1 to Metal M powder is within the above range to allow for the reduction of more silicon oxide and the production of nano-silicon.

[0122] As an example, the mass ratio of precursor 1, molten salt and metal M powder is 1:(3-5):(0.8-1); or the mass ratio of precursor 1, molten salt and metal M powder is 1:(5-8):(0.5-0.8); or the mass ratio of precursor 1, molten salt and metal M powder is 1:(3-6):(0.5-0.7).

[0123] For example, the mass ratios of precursor 1, molten salt and metal M powder are 1:3:0.8, 1:4:0.8, 1:5:0.8, 1:6:0.8, 1:7:0.8, 1:8:0.8, 1:3:0.9, 1:4:0.9, 1:5:0.9, 1:6:0.9, 1:7:0.9, 1:8:0.9, 1:3:1, 1:4:1, 1:5:1, 1:6:1, 1:7:1 or 1:8:1.

[0124] In some possible embodiments, the metal M powder includes one or more combinations of Mg powder, Al powder, and MgAl alloy powder. Due to the redox reaction occurring during the thermal reaction, the metal M powder contacts the silicon oxide, and the resulting metal oxide is mostly formed on the surface of the nano-silicon. However, this is not limited to the entire metal oxide forming on the surface of the nano-silicon. Some metal oxide may not form on the surface of the nano-silicon, which is not a limitation here.

[0125] In other embodiments, the metal M powder may further include calcium powder, zinc powder, etc.

[0126] In some possible embodiments, the molten salt is one or more combinations of magnesium chloride, sodium chloride, potassium chloride, calcium chloride, copper chloride, sodium sulfate, calcium sulfate, barium sulfate, aluminum sulfate, sodium nitrate, potassium nitrate, ammonium nitrate, calcium nitrate, lead nitrate, cerium nitrate, sodium fluoride, potassium fluoride, and calcium fluoride.

[0127] Optionally, the thermal reaction is carried out in an inert gas atmosphere at a temperature of 400°C to 800°C for 1 to 10 hours. In an inert gas atmosphere, the metal M powder is substantially not oxidized by oxygen, but instead undergoes a redox reaction with silicon oxide, thereby converting the silicon oxide into nano-silicon. Thermal reaction temperature and time within the aforementioned ranges can achieve a better reduction effect on the silicon oxide.

[0128] Illustratively, the conditions for the thermal reaction are: in a nitrogen atmosphere, the reaction is carried out at a temperature of 400°C-500°C for 8h-10h; or, in a nitrogen atmosphere, the reaction is carried out at a temperature of 500°C-600°C for 6h-8h; or, in a nitrogen atmosphere, the reaction is carried out at a temperature of 600-700°C for 1h-6h; or, in a nitrogen atmosphere, the reaction is carried out at a temperature of 700°C-800°C for 1h-6h.

[0129] Optionally, precursor one, metal M powder and molten salt are mixed, and the mass ratio of precursor one, molten salt and metal M powder is 1:(3-8):(0.5-1.5) respectively; after mixing, they are placed in a nitrogen atmosphere and reacted at a temperature of 400℃-800℃ for 1h-10h to obtain precursor two.

[0130] S130 acid-washes the precursor 2 to remove part of the metal oxide to form the precursor 3. The acid washing step is carried out in an acid solution. After the precursor 2 is mixed with the acid solution, part of the metal oxide on the surface of the nano-silicon dissolves in the acid solution; the molten salt dissolves in the acid solution to form a collection of nano-silicon with a porous structure or a network structure. A part of the surface of the nano-silicon may be attached by the metal oxide, and a part is exposed. The precursor 3 is a skeleton material with a network structure or a porous structure. The skeleton material includes nano-silicon, silicon oxide on the surface of nano-silicon, and metal oxide. Among them, the silicon oxide can be unreduced silicon oxide, or it can be silicon oxide naturally formed on the surface after the nano-silicon is exposed.

[0131] In some possible implementations, the acid solution is one or more combinations of nitric acid solution, hydrochloric acid solution, and sulfuric acid solution.

[0132] Optionally, the mass concentration of the nitric acid solution is 5%-15%; the mass concentration of the hydrochloric acid solution is 5%-15%; and the mass concentration of the sulfuric acid solution is 5%-15%.

[0133] Optionally, the amount of the acid solution added is 10%-120% of the mass of the precursor 2. As an example, the amount of the acid solution added is 10%-30% of the mass of the precursor 2; or, the amount of the acid solution added is 30%-50% of the mass of the precursor 2; or, the amount of the acid solution added is 50%-80% of the mass of the precursor 2; or, the amount of the acid solution added is 80%-120% of the mass of the precursor 2.

[0134] For example, the amount of acid solution added is 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, 110% or 120% of the mass of the precursor 2.

[0135] Optionally, the precursor 2 is mixed with a hydrochloric acid solution with a mass concentration of 5%-15% and immersed for 0.3-1h. By adjusting the concentration of the acid solution and the immersion time, part of the metal oxide can be removed, and then the impurities are removed after washing with water and solid-liquid separation (wherein, the solid-liquid separation method can be centrifugation, filtration, suction filtration, etc.), and dried to obtain a skeleton material with a porous structure or a network structure, wherein the skeleton material includes nanosilicon, silicon oxide on the surface of nanosilicon, and metal oxide.

[0136] It should be noted that steps S110 to S130 may or may not be implemented, and a skeleton material with a porous structure or a network structure may also be obtained by using other methods.

[0137] S140 mixes the precursor 3 with the lithium salt and sintered to obtain a porous structure or a network structure of Li x M y SiO4 material. Among them, Li x M y Nano-silicon is distributed in the SiO4 material matrix and / or on the surface, and the values of x and y are consistent with charge balance.

[0138] By soaking the precursor 2 in an acid solution of a certain concentration for a certain period of time, part of the metal oxide in the precursor 2 can be removed, more nano-silicon is exposed, and a pore structure (a skeleton of a porous structure or a network structure) is formed; after the lithium salt is mixed with the precursor 3, the lithium salt will come into contact with the nano-silicon, the metal oxide, and the silicon oxide (the silicon oxide can be unreduced silicon oxide or silicon oxide naturally formed on the surface after the nano-silicon is exposed). During sintering, part of the silicon oxide and the metal oxide react with the lithium salt to obtain a porous structure or a network structure of Li x M y SiO4 material; at this time, Li x M y Nano-silicon is distributed in the matrix and / or on the surface of the SiO4 material.

[0139] In some possible embodiments, the lithium salt is one or more combinations of lithium acetate, lithium oxalate, lithium carbonate, lithium hydroxide, lithium formate, lithium benzoate, lithium chloride, lithium sulfate, and lithium nitrate.

[0140] Optionally, the calcination conditions are: calcination at a temperature of 600°C-1200°C in an inert gas atmosphere for 1-10 hours. As an example, the calcination conditions are: reaction at a temperature of 600°C-800°C in a nitrogen atmosphere for 8-10 hours; or, reaction at a temperature of 800°C-1000°C in a nitrogen atmosphere for 5-8 hours; or, reaction at a temperature of 1000°C-1200°C in a nitrogen atmosphere for 1-5 hours.

[0141] Alternatively, the precursor 3, a soluble lithium salt and water are mixed, stirred evenly and then dried; calcined at a temperature of 600°C-1200°C in an inert gas atmosphere for 1h-10h to obtain Li x M y SiO4 material.

[0142] Mixing soluble lithium salt with precursor three in water can make the surface of precursor three evenly adsorb a layer of soluble lithium salt. After drying, the lithium salt is adsorbed on the surface of precursor three, which is convenient for controlling Li x M y The amount of SiO4 material can also make the nano-silicon evenly distributed in the Li x M y On SiO4 material.

[0143] S150 in Li x M y Carbon material is formed in the pores of SiO4 material to obtain negative electrode material. x M y SiO4 material is a porous structure or network structure, and Li x M y Nano-silicon is distributed in the SiO4 material matrix or / and on the surface, Li x M y There are many pores inside the SiO4 material, and the carbon material is formed on the Li x M y In the pores of SiO4 material, Li x M y The SiO4 materials are filled or intertwined with each other to obtain the negative electrode material. If the mass of the carbon material is large, a carbon coating layer can be formed on the surface to obtain a negative electrode material with better performance.

[0144] In one embodiment, Li x M y SiO4 material is mixed with an organic carbon source and calcined to carbonize the organic carbon source to form a carbon material. x M y After SiO4 material is mixed with organic carbon source, part of the organic carbon source will enter Li x M y In the pores of SiO4 material, part of the organic carbon source is coated on Li x M y The surface of SiO4 material can form Li x M y SiO4 materials are filled with carbon materials and form a coating carbon layer on the surface.

[0145] Among them, the organic carbon source is one or more combinations of polymers, sugars, organic acids, asphalt and high molecular materials; for example: the organic carbon source is polyvinyl chloride, polyvinyl butyral, sucrose, glucose, citric acid, asphalt, furfural resin, epoxy resin, phenolic resin, polyacrylic acid, etc.

[0146] Optionally, Li xM y The mixing method of SiO4 material and organic carbon source can be hot pressing coating method. x M y After the SiO4 material and the organic carbon source are evenly mixed, they are placed in a sintering furnace and calcined for 1h-10h in an inert gas atmosphere at a pressure of 5Mpa-20Mpa and a temperature of 700℃-1200℃ to carbonize the organic carbon source.

[0147] By hot pressing, the organic carbon source can be hot pressed into the porous Li x M y The pores or gaps of SiO4 materials allow the subsequent carbonization of organic carbon sources in the porous structure of Li x M y The pores or gaps of the SiO4 material are filled with carbon material.

[0148] As an example, the conditions for carbonization of the organic carbon source are: reacting at a temperature of 700°C-800°C in a nitrogen atmosphere for 8h-10h; or, reacting at a temperature of 800°C-1000°C in a nitrogen atmosphere for 5h-8h; or, reacting at a temperature of 1000°C-1200°C in a nitrogen atmosphere for 1h-5h.

[0149] The pressure of the hot pressing furnace is 5Mpa-20Mpa. The pressure is relatively high. During the calcination process, the volume of the organic carbon source will decrease after carbonization. Therefore, the carbon material can be hot pressed to a porous structure of Li while calcining. x M y In order to form a porous structure of carbon material and a porous structure of Li within the SiO4 material x M y The SiO4 materials are more closely intertwined and filled, and the performance of the negative electrode material is better.

[0150] As an example, the conditions for carbonization of the organic carbon source are: reaction in an inert gas atmosphere at a pressure of 5 MPa-10 MPa and a temperature of 700°C-800°C for 8h-10h; or, reaction in an inert gas atmosphere at a pressure of 10 MPa-15 MPa and a temperature of 800°C-1000°C for 5h-8h; or, reaction in an inert gas atmosphere at a pressure of 15 MPa-20 MPa and a temperature of 1000°C-1200°C for 1h-5h.

[0151] In another embodiment, Li x M y SiO4 material is placed in a chemical vapor deposition furnace and deposited on Li x M yCarbon material is formed in the pores and surface of SiO4 material. Carbon material is formed by chemical vapor deposition and filled in Li x M y The filling effect of SiO4 material is good, even if the pores are small, the gas source can enter the porous structure of Li x M y In the SiO4 material, the carbon material with a porous structure and the Li x M y SiO4 material.

[0152] Optionally, the chemical vapor deposition method is carried out under the following conditions: using acetylene, methane or acetone as a carbon source, using argon or nitrogen as a protective gas, and vapor deposition at 750° C.-1200° C.

[0153] It should be noted that the aforementioned step S140 and step S150 are performed twice separately by firing and calcining, but the present application does not limit them to being performed twice, and they can also be prepared by a single heat treatment.

[0154] Optionally, the precursor three is mixed with a lithium salt and an organic carbon source, and then heat-treated to obtain a negative electrode material, wherein the precursor three is a skeleton material with a porous structure or a network structure, and the skeleton material includes nanosilicon, silicon oxide on the surface of nanosilicon, and metal oxide.

[0155] During the heat treatment, some nano-silicon, silicon oxide, metal oxide and lithium salt can react to obtain porous or network structured Li x M y SiO4 material; at the same time, it can carbonize the organic carbon source, so that the carbonized carbon material can react with Li x M y The SiO4 materials are filled or intertwined with each other.

[0156] Alternatively, the precursor 3 is mixed with a lithium salt, and then mixed with an organic carbon source and then heat-treated to obtain a negative electrode material. For example, the precursor 3, a soluble lithium salt and water are mixed, stirred evenly and then dried; then the organic carbon source is coated on the surface and inside of the precursor, and heat-treated in an inert gas atmosphere at a temperature of 700°C-1200°C for 1h-10h to carbonize the organic carbon source to form a carbon material. At the same time, the lithium salt reacts to obtain Li x M y SiO4 material.

[0157] The negative electrode material prepared by the above method includes Li x M y SiO4 materials and carbon materials, and Li x M yNano-silicon is distributed in the SiO4 material matrix and / or on the surface, which can make the structure of the negative electrode material more stable, and have lower volume expansion, higher conductivity, first efficiency and excellent rate performance.

[0158] To make the purpose, technical solutions and advantages of the examples of the present application clearer, the technical solutions in the examples of the present application will be described clearly and completely below. Where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0159] Example 1

[0160] A method for preparing a negative electrode material comprises the following steps:

[0161] (1) 500 g of nano-silica was dispersed in 10 kg of aqueous solution, stirred evenly, and then 10 g of sodium carboxymethyl cellulose was added thereto. After stirring evenly, the mixture was spray-granulated to obtain a precursor 1.

[0162] (2) Precursor 1 was mixed with molten sodium chloride and magnesium powder, and the mass ratio of precursor 1, sodium chloride and magnesium powder was 1:5:0.8 respectively. After mixing evenly, the mixture was placed in a nitrogen atmosphere at 700°C for 5 hours to obtain precursor 2.

[0163] (3) Precursor 2 is placed in an aqueous solution with a ratio of precursor 2 to water of 1:4. After stirring evenly, an industrial hydrochloric acid solution with a weight ratio of 1:1 to precursor 2 is added thereto. After reacting for 0.5 hours, the mixture is centrifuged and washed with water to remove impurities to obtain precursor 3.

[0164] (4) Precursor 3 is dispersed in an aqueous solution with a ratio of the skeleton material to water of 1:5, lithium carbonate is added thereto at a weight ratio of lithium carbonate to the skeleton material of 10:1, and the solvent is evaporated under stirring to obtain precursor 4.

[0165] (5) Precursor 4 is placed in a rotary kiln and sintered at 1100°C for 3 h under inert gas conditions to obtain precursor 5.

[0166] (6) After the precursor 5 is mixed with asphalt, it is placed in a hot pressing furnace and calcined at 800°C for 3 hours under a pressure of 10 MPa. The calcined material is crushed and sieved to obtain the negative electrode material.

[0167] Figure 3 This is a scanning electron microscope image of the precursor 5 in Example 1 ( Figure 3 left figure) and EDS figure ( Figure 3 (right picture in the middle), from Figure 3 It can be seen that the precursor five has a porous structure and contains lithium magnesium silicate material and nano-silicon, and the nano-silicon is uniformly dispersed in the lithium magnesium silicate matrix.

[0168] Figure 4 The XRD pattern of the negative electrode material provided in Example 1 is as follows: Figure 4 It can be seen that the negative electrode material provided in Example 1 contains Li x Mg y SiO4 materials, carbon materials and nano-silicon.

[0169] Figure 5 The scanning electron microscope image of the negative electrode material provided in Example 1 is Figure 5 It can be seen that the negative electrode material is relatively uniform and its surface is coated with a carbon layer.

[0170] Combined with the above-mentioned figures and method analysis, it can be seen that the negative electrode material obtained in this embodiment includes a first skeleton, a second skeleton and nano-silicon intertwined with each other, the first skeleton is a lithium magnesium silicate material with a network structure, and the second skeleton is a carbon material with a network structure; wherein nano-silicon is distributed in the matrix and on the surface of the lithium magnesium silicate material.

[0171] Combined with the above-mentioned figures and method analysis, it can be seen that the negative electrode material obtained in this embodiment includes lithium magnesium silicate material, carbon material and nano-silicon. The lithium magnesium silicate material has a porous structure, and the pores of the lithium magnesium silicate material are filled with carbon material; wherein nano-silicon is distributed in the matrix and on the surface of the lithium magnesium silicate material.

[0172] Example 2

[0173] The method steps of this embodiment are basically the same as those of Example 1, except that: Step (5) and Step (6) are combined into: After the precursor 4 is mixed with the asphalt, it is placed in a hot pressing furnace and heat-treated at 800°C for 3 hours under a pressure of 10 MPa. The heat-treated material is crushed and sieved to obtain the negative electrode material.

[0174] Combining the scanning electron microscope images, EDS images and XRD images, as well as the content analysis of the method steps, it can be seen that through a single heat treatment, lithium carbonate can be reacted to obtain lithium magnesium silicate material, and asphalt can be carbonized to obtain carbon material, and the two can be made into an intertwined or mutually filled structure.

[0175] The negative electrode material obtained in this embodiment includes a first skeleton, a second skeleton and nano-silicon intertwined with each other, the first skeleton is a lithium magnesium silicate material with a network structure, and the second skeleton is a carbon material with a network structure; wherein nano-silicon is distributed in the matrix and on the surface of the lithium magnesium silicate material.

[0176] The negative electrode material obtained in this embodiment includes lithium magnesium silicate material, carbon material and nano-silicon. The lithium magnesium silicate material has a porous structure, and the carbon material is filled in the pores of the lithium magnesium silicate material. Among them, nano-silicon is distributed in the matrix and on the surface of the lithium magnesium silicate material.

[0177] Example 3

[0178] The method steps of this embodiment are basically the same as those of embodiment 1, except that in step (6), the precursor 5 is mixed with asphalt, placed in a sintering furnace, and calcined at 800°C for 3 hours. The calcined material is crushed and sieved to obtain the negative electrode material.

[0179] Combined with the scanning electron microscope images, EDS images and XRD images, as well as the content analysis of the method steps, it can be seen that during the calcination process, even without hot pressing treatment, the asphalt can be carbonized by calcination to obtain carbon material, and the carbon material can be filled in the pores of the lithium magnesium silicate material.

[0180] The negative electrode material obtained in this embodiment includes a first skeleton, a second skeleton and nano-silicon intertwined with each other, the first skeleton is a lithium magnesium silicate material with a network structure, and the second skeleton is a carbon material with a network structure; wherein nano-silicon is distributed in the matrix and on the surface of the lithium magnesium silicate material.

[0181] The negative electrode material obtained in this embodiment includes lithium magnesium silicate material, carbon material and nano-silicon. The lithium magnesium silicate material has a porous structure, and the carbon material is filled in the pores of the lithium magnesium silicate material. Among them, nano-silicon is distributed in the matrix and on the surface of the lithium magnesium silicate material.

[0182] Example 4

[0183] The method steps of this embodiment are basically the same as those of embodiment 1, except that in step (6), the precursor 5 is placed in a chemical vapor deposition furnace, methane is introduced, and deposition is carried out at 800°C for 3 hours. The deposited material is crushed and sieved to obtain the negative electrode material.

[0184] Combining the scanning electron microscope images, EDS images and XRD images, as well as the content analysis of the method steps, it can be seen that carbon materials can also be formed in the pores or gaps of the lithium magnesium silicate material by chemical vapor deposition.

[0185] The negative electrode material obtained in this embodiment includes a first skeleton, a second skeleton and nano-silicon intertwined with each other, the first skeleton is a lithium magnesium silicate material with a network structure, and the second skeleton is a carbon material with a network structure; wherein nano-silicon is distributed in the matrix and on the surface of the lithium magnesium silicate material.

[0186] The negative electrode material obtained in this embodiment includes lithium magnesium silicate material, carbon material and nano-silicon. The lithium magnesium silicate material has a porous structure, and the carbon material is filled in the pores of the lithium magnesium silicate material. Among them, nano-silicon is distributed in the matrix and on the surface of the lithium magnesium silicate material.

[0187] Example 5

[0188] The method steps of this embodiment are basically the same as those of Example 1, except that: in step (2), the precursor one is mixed with sodium chloride and aluminum powder, and the mass ratio of the precursor one, sodium chloride and aluminum powder is 1:5:0.9 respectively. After being mixed evenly, the mixture is placed in a nitrogen atmosphere at 700°C for 5 hours to obtain the precursor two.

[0189] Combining the scanning electron microscope images, EDS images and XRD images, as well as the content analysis of the method steps, it can be seen that this method uses aluminum powder to reduce silicon dioxide and finally forms lithium aluminum silicate material.

[0190] The negative electrode material obtained in this embodiment includes a first skeleton, a second skeleton and nano-silicon intertwined with each other, the first skeleton is a lithium aluminum silicate material with a network structure, and the second skeleton is a carbon material with a network structure; wherein nano-silicon is distributed in the matrix and on the surface of the lithium aluminum silicate material.

[0191] The negative electrode material obtained in this embodiment includes lithium aluminum silicate material, carbon material and nano-silicon. The lithium magnesium silicate material has a porous structure, and the pores of the lithium aluminum silicate material are filled with carbon material. Among them, nano-silicon is distributed in the matrix and on the surface of the lithium magnesium silicate material.

[0192] Example 6

[0193] The method steps of this embodiment are basically the same as those of Example 1, except that: in step (2), the precursor one is mixed with sodium chloride, magnesium powder, and aluminum powder, and the mass ratio of the precursor one, sodium chloride, magnesium powder, and aluminum powder is 1:5:0.45:0.4 respectively. After mixing evenly, the mixture is placed in a nitrogen atmosphere at 700°C for 5 hours to obtain the precursor two.

[0194] Combining the scanning electron microscope images, EDS images and XRD images, as well as the content analysis of the method steps, it can be seen that the method uses aluminum powder and magnesium powder to simultaneously reduce silicon dioxide, and finally forms lithium aluminum silicate material and lithium magnesium silicate material.

[0195] The negative electrode material obtained in this embodiment includes a first skeleton, a second skeleton and nano-silicon intertwined with each other, the first skeleton is a mixed material of lithium aluminum silicate and lithium magnesium silicate with a network structure, and the second skeleton is a carbon material with a network structure; wherein nano-silicon is distributed in the matrix and on the surface of the mixed material of lithium aluminum silicate and lithium magnesium silicate.

[0196] The negative electrode material obtained in this embodiment includes a mixed material of lithium aluminum silicate and lithium magnesium silicate, a carbon material and nano-silicon. The mixed material of lithium magnesium silicate and lithium magnesium silicate has a porous structure, and the pores of the lithium aluminum silicate material are filled with carbon material; wherein nano-silicon is distributed in the matrix and on the surface of the mixed material of lithium magnesium silicate and lithium magnesium silicate.

[0197] Table 1 Negative electrode materials provided in Examples 1-6

[0198]

[0199] It should be noted that: Li x M y The sum of the mass percentage of SiO4 material, the mass percentage of nano-silicon and the mass percentage of carbon material is close to and less than 100%. The reason is that when preparing the negative electrode material, it is very likely to contain one or more impurities, such as one or more impurities in incompletely reacted SiO, MgO, by-product MgSiO4, etc.

[0200] The thickness of the coated carbon layer is tested by SEM test of the cross section.

[0201] The test method for the specific surface area of the negative electrode material is: Micrometer specific surface analyzer;

[0202] The D50 test method of the negative electrode material is: Malvern Laser Particle Sizer 3000;

[0203] Li x M y The test method for the mass percentage of SiO4 material is: total dissolution component analysis method;

[0204] The test method for the mass percentage of nano-silicon is: X-ray fluorescence analysis;

[0205] The test method for the mass percentage of carbon materials is: infrared carbon and sulfur analyzer;

[0206] The porosity test method is as follows: Porosity is measured by mercury intrusion method. The porosity is measured at least three times, and the arithmetic average of at least three times is used as the measurement result;

[0207] Testing method for the distribution range of skeleton diameter: different points in a fixed area are selected by scanning electron microscopy to measure the skeleton diameter and obtain the distribution range of the skeleton diameter.

[0208] Comparative Example 1

[0209] The method steps of this comparative example are basically the same as those of Example 1, except that step (4) is not performed, and ultimately no lithium magnesium silicate material is formed.

[0210] Comparative Example 2

[0211] The method steps of this comparative example are basically the same as those of Example 1, except that step (4) and step (6) are not performed, and ultimately no lithium magnesium silicate material and carbon material are formed.

[0212] Comparative Example 3

[0213] The method steps of this comparative example are basically the same as those of Example 1, except that in step (2), molten sodium chloride is not added, and a porous structure or a network structure skeleton is not formed.

[0214] Comparative Example 4

[0215] The method steps of this comparative example are basically the same as those of Example 1, except that the hydrochloric acid cleaning reaction in step (3) is not performed, and a porous lithium magnesium silicate material is not formed.

[0216] The performance of the negative electrode materials provided in Examples 1 to 6 and Comparative Examples 1 to 4 is shown in Table 2.

[0217] The composite negative electrode materials of Examples 1-6 and Comparative Examples 1-4 were mixed with a conductive agent and a binder in a solvent at a mass ratio of 93:2:5. The resulting mixed slurry was coated on a copper foil current collector and vacuum dried to produce a negative electrode sheet. A 1 mol / L LiPF6 / EC+DMC+EMC (v / v = 1:1:1) electrolyte, an SK (12 μm) separator, and a housing were then assembled using conventional processes to form a CR2016 button cell. The electrochemical performance was tested at a current density of 1C equal to 1000 mA h / g. The material capacity and initial efficiency were tested at 0.1C, and the retention rate and volume expansion rate after 100 charge-discharge cycles were tested at 1C.

[0218] Table 2 Performance of negative electrode materials

[0219]

[0220] It can be seen from the preparation method of the negative electrode material, Table 1 and Table 2 that the negative electrode material provided in the embodiment of the present application has a high first efficiency, a high cycle retention rate, and a small volume expansion coefficient.

[0221] Among them, by comparing Example 1 with Comparative Example 1, it can be seen that in Comparative Example 1, no lithium carbonate was added to prepare the lithium magnesium silicate material, and its first efficiency was low and the cycle retention rate was low. At the same time, due to the lack of restrictions on the lithium magnesium silicate material, the volume expansion coefficient of the negative electrode material is high.

[0222] From the comparison between Example 1 and Comparative Example 2, it can be seen that in Comparative Example 2, no lithium carbonate was added to prepare the lithium magnesium silicate material, and no carbon coating was performed. Although the obtained negative electrode material has a high capacity, its volume expansion coefficient is very high, the cycle retention rate is very small, and the first efficiency is also low.

[0223] From the comparison between Example 1 and Comparative Example 3, it can be seen that no molten salt was added in Comparative Example 3. When preparing the lithium magnesium silicate material, almost no pores were formed, and it was not easy to form a structure in which the carbon material and the lithium magnesium silicate material were intertwined. The cycle retention rate of the obtained product was low.

[0224] By comparing Example 1 and Comparative Example 4, it can be seen that in Comparative Example 4, molten salt was added but hydrochloric acid pickling was not performed. The obtained negative electrode material contained more molten salt, and it was not easy to form a porous structure of lithium magnesium silicate material. Its capacity, first efficiency and cycle retention rate were very low, and its volume expansion coefficient was also high.

[0225] Comparison between Example 1 and Example 2 shows that in Example 1, the lithium magnesium silicate material is first sintered to obtain the lithium magnesium silicate material, and then calcined to obtain the carbon material; in Example 2, lithium magnesium silicate and the carbon material are formed by a single heat treatment, and the performance of the obtained negative electrode materials is not much different, indicating that the performance of the obtained negative electrode material can be better whether it is prepared by sintering and calcining in stages or by a single heat treatment.

[0226] Comparison between Example 1 and Example 3 shows that Example 1 is pressure coated, while Example 3 is normal pressure coated, and the performance of the negative electrode material obtained by pressure coating is relatively more excellent.

[0227] Comparison between Example 1 and Example 4 shows that in Example 1, the carbon material was prepared by asphalt coating, and in Example 4, the carbon material was prepared by chemical vapor deposition, and the performance of the obtained negative electrode materials is comparable.

[0228] Comparison of Example 1, Example 5 and Example 6 shows that the Li x M y The M metal in SiO4 is magnesium, the M metal in Example 5 is aluminum, and the M metal in Example 6 is a mixture of magnesium and aluminum. The performance of the negative electrode materials finally obtained is comparable.

[0229] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

Claims

1. A negative electrode material, characterized in that The negative electrode material includes a first skeleton and a second skeleton intertwined with each other, and nano-silicon, wherein the first skeleton is a Li x M y SiO4 material, the second skeleton is a carbon material with a network structure; wherein the Li x M y The nano-silicon is distributed in the SiO4 material matrix or / and on the surface, the values of x and y are consistent with charge balance, and M includes metal elements other than Li that can reduce silicon oxide; Wherein, the skeleton diameter of the carbon material is 10nm-500nm, and the Li x M y The skeleton diameter of SiO4 material is 10nm-400nm.

2. The negative electrode material according to claim 1, characterized in that The carbon material is also distributed in the Li x M y A carbon coating is formed on the outer surface of the SiO4 material; Or / and, the thickness of the coating carbon layer is 5nm-80nm; Or / and, the negative electrode material satisfies at least one of the following conditions (1)-(9): (1)Li x M y In SiO4 materials, 2≤x≤3.4, 0.4≤y≤1; (2) M includes Mg and / or Al; (3) The particle size of the nano-silicon is 5nm-200nm; (4) The carbon material comprises one or a combination of soft carbon and hard carbon; (5) The specific surface area of the negative electrode material is 1m 2 / g-3m 2 / g; (6) The negative electrode material is in the form of spherical particles, and the average particle size D50 of the negative electrode material is 5 μm-30 μm; (7) Li x M y The mass percentage of SiO4 material in the negative electrode material is 5%-30%; (8) The mass percentage of the nano-silicon in the negative electrode material is 30%-60%; (9) The mass percentage of the carbon material to the negative electrode material is 10%-65%.

3. A negative electrode material, characterized in that The negative electrode material includes Li x M y SiO4 material, carbon material and nano-silicon, the Li x M y SiO4 material has a porous structure, and the Li x M y The pores of the SiO4 material are filled with the carbon material; wherein the Li x M y The nano-silicon is distributed in the SiO4 material matrix or / and on the surface, the values of x and y are consistent with charge balance, and M is a metal other than Li that can reduce silicon oxide; Wherein, the skeleton diameter of the carbon material is 10nm-500nm, and the Li x M y The skeleton diameter of SiO4 material is 10nm-400nm.

4. The negative electrode material according to claim 3, characterized in that The carbon material is also distributed in the Li x M y A carbon coating is formed on the outer surface of the SiO4 material; Or / and, the thickness of the coating carbon layer is 5nm-80nm; Or / and, the negative electrode material satisfies at least one of the following conditions (12)-(21): (12)Li x M y In SiO4 materials, 2≤x≤3.4, 0.4≤y≤1; (13) M includes Mg and / or Al; (14) The particle size of the nano-silicon is 5nm-200nm; (15) The carbon material comprises one or a combination of soft carbon and hard carbon; (16) The specific surface area of the negative electrode material is 1m 2 / g-3m 2 / g; (17) The negative electrode material is in the form of spherical particles, and the average particle size D50 of the negative electrode material is 5 μm-30 μm; (18) Li x M y The porosity of SiO4 material is 30%-46%; (19) Li x M y The mass percentage of SiO4 material in the negative electrode material is 5%-30%; (20) The mass percentage of the nano-silicon in the negative electrode material is 30%-60%; (21) The mass percentage of the carbon material to the negative electrode material is 10%-65%.

5. A lithium-ion battery, characterized in that: The negative electrode material comprises the negative electrode material according to any one of claims 1 to 4.

6. A method for preparing a negative electrode material according to claim 1 or 3, characterized in that: include: Lithium ions formed from silicon oxides on the surface of nano-silicon to form porous or network structures x M y SiO4 material, in the Li x M y The negative electrode material is obtained by filling the pores of the porous structure of the SiO4 material or the gaps in the network structure with carbon material, wherein M includes a metal element other than Li that can reduce silicon oxide.

7. The preparation method according to claim 6, characterized in that The preparation method comprises: The network structure or porous structure skeleton material is mixed with lithium salt and then calcined to obtain the Li x M y SiO4 material, wherein the skeleton material includes nano-silicon, silicon oxide and metal oxide on the surface of nano-silicon; and in the Li x M y The carbon material is formed in the pores or gaps of the SiO4 material to obtain the negative electrode material; Alternatively, a network structure or porous structure skeleton material, a lithium salt and an organic carbon source are mixed and then heat treated to obtain the negative electrode material, wherein the skeleton material includes nano-silicon, silicon oxide on the surface of nano-silicon and metal oxide.

8. The preparation method according to claim 7, characterized in that In the Li x M y The step of forming the carbon material in the pores or gaps of the SiO4 material to obtain the negative electrode material comprises: x M y SiO4 material is mixed with an organic carbon source and calcined to carbonize the organic carbon source to form the carbon material; or ... form the carbon material; or SiO4 material is mixed with an organic carbon source and calcined to form the carbon material; or SiO4 material is mixed with an organic carbon source and calcined to form the carbon material x M y The carbon material is formed in the pores or gaps of the SiO4 material; Alternatively, the step of mixing the framework material with a network structure or a porous structure, a lithium salt and an organic carbon source comprises: mixing the framework material with a network structure or a porous structure with the lithium salt, and then mixing with the organic carbon source.

9. The preparation method according to claim 7 or 8, characterized in that The method for preparing the skeleton comprises: The silicon oxide and the binder are mixed and granulated to obtain a precursor 1; Mixing the precursor 1, metal M powder and molten salt, and performing a thermal reaction so that at least a portion of the silicon oxide is reduced to nano-silicon, thereby obtaining the precursor 2; The second precursor is acid-washed to remove part of the metal oxide to form the skeleton material with a porous structure or a network structure.

10. The preparation method according to claim 9, characterized in that The preparation method satisfies at least one of the following conditions (22)-(26): (22) dispersing silicon oxide and a binder in a solution and spray granulating the solution to obtain a precursor 1; (23) The mass ratio of the silicon oxide to the binder is (40-100):1; (24) The mass ratio of the precursor 1, the molten salt and the metal M powder is 1:(3-8):(0.5-1.5) in sequence; (25) The metal M powder includes one or more combinations of Mg powder, Al powder and MgAl alloy powder; (26) The skeleton material, soluble lithium salt and water are mixed, stirred evenly and then dried.

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