Negative electrode material, preparation method, negative electrode sheet and battery

Abstract

The present invention discloses a negative electrode material, a preparation method, a negative electrode plate, and a battery. The negative electrode material comprises: a carbon material core; a coating layer, wherein the coating layer covers at least a portion of the outer surface of the carbon material core, and the coating layer comprises a first material, wherein the first material is an inorganic mesoporous material having mesoporous channels, and the electrical conductivity of the first material is σ, 1×10 ‑18 S / m<σ≤1×10 2 The negative electrode material of the present invention adopts an inorganic mesoporous material having mesoporous channels as the first material and limits the electrical conductivity of the first material, which is not only conducive to changing the surface defect structure of the carbon material core and improving the dispersibility of the carbon material core during the preparation of the negative electrode material, but also can improve the liquid absorption and retention capacity of the carbon material core in the electrolyte.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and more specifically, to a negative electrode material, a preparation method, a negative electrode plate, and a battery. Background Art

[0002] Graphite is a common negative electrode material for lithium-ion batteries. To improve the dynamic performance of graphite, the surface of the graphite is coated. The coating material used is typically asphalt, resin, or heavy oil. After high-temperature carbonization, a carbon layer forms on the graphite surface, thereby improving the dynamic performance of the graphite.

[0003] The current carbon coating of graphite not only has limited ability to diffuse and retain electrolytes, but the amorphous carbon layer also tends to increase surface defects in the graphite, which increases electrolyte consumption and thus reduces the battery's initial charge and discharge efficiency and cycle life. Summary of the Invention

[0004] One object of the present invention is to provide a negative electrode material that can solve at least one of the problems of the prior art amorphous carbon-coated graphite, such as the tendency to increase graphite surface defects, increase electrolyte consumption, and affect battery performance.

[0005] Another object of the present invention is to provide a method for preparing a negative electrode material.

[0006] Another object of the present invention is to provide a negative electrode plate, which includes a negative electrode material.

[0007] Another object of the present invention is to provide a battery comprising the above-mentioned negative electrode plate.

[0008] In order to achieve the above objectives, the present invention provides the following technical solutions.

[0009] According to the first embodiment of the present invention, the negative electrode material comprises: a carbon material core; a coating layer, wherein the coating layer covers at least a portion of the outer surface of the carbon material core, and the coating layer comprises a first material, wherein the first material is an inorganic mesoporous material having mesoporous channels, and the electrical conductivity of the first material is σ, 1×10 -18 S / m<σ≤1×10 2 S / m.

[0010] Alternatively, 1×10 -18 S / m<σ≤1×10 -4 S / m.

[0011] Optionally, the coating layer further comprises: a second material, wherein the electrical conductivity of the second material is greater than the electrical conductivity of the first material.

[0012] Optionally, the second material is an amorphous carbon material, and the second material and the first material are mixed with each other.

[0013] Optionally, the inorganic mesoporous material is a combination of one or more of mesoporous silica, mesoporous titania, mesoporous alumina and mesoporous ceramics; and / or, the carbon material core is graphite; the graphite includes at least one of artificial graphite or natural graphite.

[0014] Optionally, the mass proportion of the coating layer in the negative electrode material is not higher than 5%; and / or the mass proportion of the first material in the coating layer is not higher than 80% and not lower than 10%; and / or the D50 of the first material is 10nm~1000nm; and / or the coating layer covers the entire outer surface of the carbon material core, and the thickness of the coating layer is 10nm~2μm.

[0015] According to the second aspect of the present invention, the method for preparing the negative electrode material of the embodiment comprises the following steps: forming a coating layer on at least a portion of the outer surface of the carbon material core, wherein the carbon material core and the coating layer constitute the negative electrode material, and the coating layer comprises a first material, wherein the first material is an inorganic mesoporous material having mesoporous channels, wherein the electrical conductivity of the first material is σ, which is 1×10 -18 S / m<σ≤1×10 2 S / m.

[0016] Optionally, the step of forming a coating layer on at least a portion of the outer surface of the carbon material core includes: mixing a first component and a second component to obtain a coating additive, wherein the first component contains a first material or a first material precursor, and the second component contains an amorphous carbon material or an amorphous carbon material precursor; and mixing the coating additive with the carbon material core.

[0017] Optionally, the method for preparing the negative electrode material further comprises the following step: depolymerizing the negative electrode material through a depolymerization device to regulate the particle size distribution of the negative electrode material.

[0018] According to the third aspect of the present invention, the negative electrode plate includes: a current collector; a negative electrode material, wherein the negative electrode material is coated on the outer surface of the current collector, and the negative electrode material is any of the negative electrode materials described above, or is the negative electrode material prepared by any of the methods for preparing the negative electrode materials described above.

[0019] A battery according to an embodiment of the third aspect of the present invention includes any of the above-mentioned negative electrode plates.

[0020] The carbon material according to the embodiment of the present invention utilizes a first material having mesoporous channels, which not only facilitates changing the surface defect structure of the carbon material core and improving the dispersibility of the carbon material core during the preparation of the negative electrode material, but also improves battery performance. The mesopore size distribution is concentrated, and the degree of dispersion in water is high, thereby improving the dispersibility of the carbon material core. At the same time, by limiting the range of the electrical conductivity σ of the first material, the ability of the carbon material core to absorb and retain liquid in the electrolyte can be improved. In lithium-ion batteries, it can partially replace the conductive agent as an electrolyte buffer, optimize the void structure of the negative electrode plate, increase the porosity of the negative electrode plate, improve the ion diffusion capacity, and reduce battery polarization.

[0021] Further features and advantages of the present invention will become apparent from the following detailed description of exemplary embodiments of the present invention with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

[0023] Figure 1 is a flow chart of a method for preparing a negative electrode material according to one embodiment of the present invention;

[0024] Figure 2 The figure is a flow chart of a method for preparing a negative electrode material according to another embodiment of the present invention. DETAILED DESCRIPTION

[0025] Various exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that unless otherwise specifically stated, the relative arrangement of components and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present invention.

[0026] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses.

[0027] Technologies, methods, and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and equipment should be considered part of the specification.

[0028] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0029] It should be noted that like reference numerals and letters refer to like items in the following figures, and therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0030] The negative electrode material according to the embodiment of the present invention is described in detail below with reference to the accompanying drawings.

[0031] The negative electrode material according to an embodiment of the present invention includes a carbon material core and a coating layer.

[0032] Specifically, the coating layer covers at least a portion of the outer surface of the carbon material core, and the coating layer comprises a first material, which is an inorganic mesoporous material having mesoporous channels, and the electrical conductivity of the first material is σ, which is 1×10 -18 S / m<σ≤1×10 2 S / m.

[0033] In other words, the negative electrode material according to an embodiment of the present invention is mainly composed of a carbon material core and a coating layer, wherein the coating layer covers at least a portion of the outer surface of the carbon material core. That is, in this embodiment, the coating layer may cover a portion of the outer surface of the carbon material core, or the coating layer may cover the entire outer surface of the carbon material core.

[0034] Furthermore, the first material is an inorganic mesoporous material having mesoporous channels. According to the IUPAC definition, the pore size of the mesoporous channels is between 2 nm and 50 nm, and a porous material with a pore size between 2 nm and 50 nm can be called a mesoporous material. For example, in this embodiment, the first material is a material with a low dielectric constant, such as alumina or silica. Optionally, the pore size of the inorganic mesoporous material is preferably K∈[2 nm, 40 nm], and more preferably K∈[2 nm, 30 nm], which can improve the uniformity of the pore size distribution.

[0035] Among them, the inorganic mesoporous material with mesoporous channels used as the first material has the following properties:

[0036] First, the first material is a mesoporous material. By using the mesoporous material, the absorption / saturation of the electrolyte can be increased.

[0037] Second, the first material is a mesoporous material, which has a relatively uniform pore structure, so that the first material is highly dispersed in water, thereby improving the dispersion of the carbon material core during the batching process. It should be noted that carbon materials (such as graphite materials) are inherently hydrophobic materials and easily agglomerate in water, making them difficult to disperse. In this embodiment, by coating the surface of the carbon material with an inorganic mesoporous material, the surface of the carbon material is transformed from a hydrophobic state to a hydrophilic state, making it easier to disperse in aqueous ingredients.

[0038] Third, the first material is a mesoporous material, which has rigid properties. Therefore, it can effectively reduce the physical rebound of the carbon material after rolling and reduce the physical rebound during the electrochemical process; thereby improving the energy density of the battery and the cycle life of the battery.

[0039] Fourth, the first material is a mesoporous material with mesoporous channels on its surface. This reduces the surface-to-surface contact between adjacent negative electrode material particles in existing technologies and increases the number of point-to-point contacts, thereby facilitating electrolyte diffusion into the negative electrode material. In other words, using carbon materials as negative electrode sheets optimizes the internal gaps within the negative electrode sheet, improving the negative electrode's ability to diffuse and retain electrolytes. This also increases the migration rate of lithium ions, thereby enhancing the battery's rate performance.

[0040] Fifth, the surface of the carbon material core particle has a defect structure, and by coating at least a portion of the surface of the graphite particle with the first material, the defect structure on the surface of the carbon material core particle can be changed.

[0041] It should be noted that organic mesoporous materials are commonly used in existing technologies. However, because they contain organic components, they swell when immersed in the electrolyte, which can easily cause the coating to fall off. In contrast, in this embodiment, inorganic mesoporous materials are used, which do not swell after being immersed in the electrode solution. This improves structural stability and bonding strength.

[0042] In this embodiment, the electrolyte is adsorbed through the mesoporous channels of the coating material (coating layer), thereby increasing the saturation of the negative electrode material, thereby reducing the ion diffusion path around the carbon material core (such as graphite), and thereby increasing the rate performance of the negative electrode material; at the same time, the dielectric constant of the mesoporous material is low, and during charging and discharging, there are fewer side reactions with the electrolyte, thereby reducing the consumption of the electrolyte and increasing the cyclability; at the same time, fewer side reactions can also increase the first effect.

[0043] In addition, the electrical conductivity of the first material is σ, which is 1×10 -18 S / m<σ≤1×10 2 S / m. For example, σ is 1×10 -17 S / m, 1×10 -16 S / m, 1×10 -15 S / m, 1×10 -14 S / m, 1×10 -13 S / m, 1×10 -12 S / m, 1×10 -11 S / m, 1×10 -10 S / m, 1×10 -9 S / m, 1×10 -8 S / m, 1×10 -5 S / m, 1×10 -1 S / m, 1×10S / m or 1×10 2 S / m, etc. It can be seen that in this embodiment, the first material has low electrical conductivity, is difficult to react with the electrolyte, and has a strong ability to absorb and retain liquid.

[0044] The conductivity test method of the embodiment of the present invention can be tested using the four-probe method. The specific test method is as follows: the sample is spread flat in the test chamber of the resistance meter, the test probe is allowed to contact the sample surface, and the test is performed. The resistivity ρ of the sample is read from the instrument computer, and the conductivity of the sample is obtained according to the formula σ = 1 / ρ.

[0045] Therefore, the carbon material according to the embodiment of the present invention, by adopting a first material having mesoporous channels, is not only conducive to changing the surface defect structure of the carbon material core and improving the dispersibility of the carbon material core during the preparation of the negative electrode material, but also can improve the performance of the battery; the mesopore pore size distribution is concentrated, the degree of dispersion in water is high, and the dispersibility of the carbon material core is improved. At the same time, by limiting the range of the electrical conductivity σ of the first material, the ability of the carbon material core to absorb and retain liquid in the electrolyte can be improved. In lithium-ion batteries, it can partially replace the conductive agent as an electrolyte buffer, optimize the void structure of the negative electrode plate, increase the porosity of the negative electrode plate, improve the ion diffusion capacity, and reduce battery polarization.

[0046] According to one embodiment of the present invention, 1×10 -18 S / m<σ≤1×10 -4 S / m, that is, preferably, 1×10 -18 S / m<σ≤1×10 -4 S / m, using the first material with conductivity within this range can further ensure the liquid absorption and retention ability of the carbon material core in the electrolyte.

[0047] In some specific embodiments of the present invention, the coating layer further comprises a second material having a greater electrical conductivity than the first material. In this embodiment, since the inorganic mesoporous material itself has a low electrical conductivity, the combination of the second material with a higher electrical conductivity with the first material ensures that the electrical conductivity of the carbon material core itself is not easily reduced. Thus, in this embodiment, the use of a conductive second material helps ensure that the prepared negative electrode material has a certain electrical conductivity.

[0048] According to one embodiment of the present invention, the second material is an amorphous carbon material, and the second material is mixed with the first material. The electrical conductivity of the amorphous carbon material is 10 2 S / m~10 4 S / m. That is to say, the coating layer contains not only the first material but also the second material, and the two are combined in the form of a mixture. For example, the coating layer contains not only an amorphous carbon material but also an inorganic mesoporous material, that is, it can be prepared by mixing an amorphous carbon material and an inorganic mesoporous material, thereby ensuring that the prepared negative electrode material has a certain electrical conductivity; and can reduce the consumption of the electrolyte, thereby improving the initial efficiency and life of the battery.

[0049] In this embodiment, inorganic mesoporous material is used to partially replace amorphous carbon material, and the inorganic mesoporous material and amorphous carbon material are uniformly coated on the surface of the carbon material core particles. Compared with the coating structure in the prior art that is entirely prepared with amorphous carbon material, the coating layer of the embodiment of the present invention partially replaces the amorphous carbon material with inorganic mesoporous material, so that the surface of the carbon material core is coated with a mixture of amorphous carbon material and inorganic mesoporous material, thereby reducing the negative impact of amorphous carbon on the battery cell.

[0050] According to one embodiment of the present invention, the inorganic mesoporous material is a combination of one or more of mesoporous silica, mesoporous titania, mesoporous alumina and mesoporous ceramics; and / or the core of the carbon material is graphite; the graphite includes at least one of artificial graphite or natural graphite.

[0051] Among them, when the inorganic mesoporous material is one or a combination of mesoporous silica, mesoporous titania, mesoporous alumina and mesoporous ceramics, that is, the above-mentioned materials with lower dielectric constants can be used as inorganic mesoporous materials, which is conducive to ensuring that the inorganic mesoporous material has low electrical conductivity, is difficult to react with the electrolyte, and has strong liquid absorption and retention capabilities.

[0052] When the core of the carbon material is graphite, and the graphite includes at least one of artificial graphite and natural graphite, the core of the carbon material is graphite, which has the advantages of wide sources and easy use. Among them, when the coating structure prepared by all amorphous carbon materials in the prior art is inspected, for example, the coating layer of the traditional graphite material is all amorphous carbon, and the main element of the graphite surface is detected under the EDS spectrometer. In comparison, in the embodiment of the present invention, the amorphous carbon material is partially replaced by a mesoporous material, which is coated on the surface of the graphite particles to change the defect structure of the graphite particle surface, reduce the negative impact on the amorphous carbon material, and the corresponding mesoporous material elements can be detected on the graphite surface under the EDS spectrometer.

[0053] Furthermore, the graphite core particles can be artificial graphite or natural graphite, or a combination thereof; the graphite core material can be primary particles or secondary particles, or a combination thereof. When the graphite material is artificial graphite, the raw material coke used is not specifically limited.

[0054] It should be noted that during production, specific materials can be selected as inorganic mesoporous materials and carbon material cores according to specific needs, which has the advantage of high flexibility.

[0055] In some specific embodiments of the present invention, the mass proportion of the coating layer in the negative electrode material is not higher than 5%; and / or the mass proportion of the first material in the coating layer is not higher than 80% and not lower than 10%; and / or the D50 of the first material is 10nm~1000nm; and / or the coating layer covers the entire outer surface of the carbon material core, and the thickness of the coating layer is 10nm~2μm.

[0056] First, when the mass proportion of the coating layer in the negative electrode material is not higher than 5%, that is, 0% < the mass proportion of the coating layer in the negative electrode material ≤ 5%. For example, the mass proportion of the coating layer in the negative electrode material is 5%, 3%, 2% or 1%, etc. It should be noted that if the mass proportion of the coating layer in the negative electrode material is higher than 5%, it is easy to cause the charge ratio and discharge ratio of the negative electrode material to be low. It can be seen that in this embodiment, by limiting the mass proportion of the coating layer in the negative electrode material to no more than 5%, it is beneficial to ensure low production costs of the coating layer, achieve fast charging and discharging, and improve the fast charging performance of the battery.

[0057] Second, when the mass proportion of the first material in the coating layer is not higher than 80% and not lower than 10%, that is, 10% ≤ the mass proportion of the first material in the coating layer ≤ 80%, for example, the mass proportion of the first material in the coating layer is 10%, 20%, 30%, 40%, 50%, 60%, 70% or 80%, etc. It should be noted that if the mass proportion of the first material in the coating layer is higher than 90%, it is easy to affect the overall conductivity of the negative electrode material; if the mass proportion of the first material in the coating layer is lower than 10%, it is difficult to reduce the consumption of the electrolyte and improve the first efficiency and life of the battery. That is to say, if the mass proportion of the first material in the coating layer is less than 10%, it is easy for the inorganic mesoporous material to fail to reduce the consumption of the electrolyte; if it is higher than 80%, it is easy to cause the internal resistance of the battery to be too large, affecting the fast charging performance of the battery. It can be seen that in this embodiment, by limiting the mass proportion of the first material in the coating layer to no more than 80% and no less than 10%, it is beneficial to reduce electrolyte consumption and ensure low internal resistance of the battery.

[0058] Preferably, the inorganic mesoporous material content X satisfies 30%≤X≤70%, and more preferably, the inorganic mesoporous material content X satisfies 40%≤X≤60%. Within this range, the negative electrode's liquid absorption and retention capacity can be improved, thereby improving the battery's initial efficiency and further reducing its impact on the battery's internal resistance.

[0059] It should be noted that, in this embodiment, the calculation formula for the mass proportion of the inorganic mesoporous material in the coating layer is: mass of inorganic mesoporous material / (carbon material + mass of inorganic mesoporous material), and the proportion X of the inorganic mesoporous material satisfies 10%≤X≤80%.

[0060] The calculation method is as follows:

[0061] By sintering at a high temperature of 2000°C, the quality difference of the samples before and after sintering was compared. In the embodiment of the present invention, due to the small amount of amorphous carbon added (≤4.5% of the mass proportion of the negative electrode active material), it will oxidize during the sintering process, and the sample mass will be reduced. After sintering, inorganic mesoporous elements can still be detected on the surface of the sample by EDS and other methods.

[0062] Third, when the D50 of the first material is between 10 nm and 1000 nm, for example, 10 nm, 20 nm, 100 nm, 500 nm, 800 nm, or 1000 nm, the first material is a nanomaterial. When an inorganic mesoporous material is used as a nanomaterial, it is an excellent flow promoter. Coating the inorganic mesoporous material on the surface of the carbon material core can improve the powder flowability of the carbon material core, increase the accumulation of negative electrode material particles in the negative electrode, and thus enhance the peel strength of the negative electrode sheet.

[0063] Fourth, when the coating layer covers the entire outer surface of the carbon material core and the thickness of the coating layer is 10nm to 2μm, that is, 10nm≤the thickness of the coating layer≤2μm, for example, the thickness of the coating layer is 10nm, 20nm, 50nm, 100nm, 500nm, 800nm, 1μm or 2μm, etc. It should be noted that if the thickness of the coating layer is less than 10nm, it is easy to break and increase the preparation cost; if the thickness of the coating layer is greater than 2μm, it is easy to cause the particles of the negative electrode material to be larger, or affect the volume of the carbon material core based on a certain volume. It can be seen that in this embodiment, by limiting the coating layer to cover the entire outer surface of the carbon material core, it is beneficial to increase the coverage of the coating layer; by limiting the thickness of the coating layer to 10nm to 2μm, it is beneficial to ensure the stability of the capacitance and liquid retention capacity of the negative electrode material.

[0064] In addition, regarding the four characteristics of the mass proportion of the coating layer in the negative electrode material, the mass proportion of the first material in the coating layer, the D50 of the first material, and the thickness of the coating layer, users can make flexible choices according to their needs. They can meet one or two of the conditions separately, or all three conditions at the same time, or all four conditions at the same time, so as to achieve the production of negative electrode materials with different characteristics.

[0065] like Figure 1 and Figure 2 As shown, the present invention also provides a method for preparing a negative electrode material, which can be used to prepare the negative electrode material of any of the above embodiments. The preparation method may include the following steps:

[0066] A coating layer is formed on at least a portion of the outer surface of the carbon material core. The carbon material core and the coating layer constitute the negative electrode material. The coating layer comprises a first material, which is an inorganic mesoporous material having mesoporous channels. The electrical conductivity of the first material is σ, which is 1×10 -18 S / m<σ≤1×10 2 S / m.

[0067] It should be noted that mesoporous materials have advantages such as regular pore structure, concentrated pore size distribution, and high degree of dispersion in water. In the preparation method of the negative electrode material of this embodiment, the surface coating layer of the carbon material core contains a mesoporous material, which can improve the dispersibility of the carbon material core during the batching process. In addition, the carbon material core and the coating layer constitute the negative electrode material, which does not mean that only the carbon material core and the coating layer can exist in the negative electrode material.

[0068] In this embodiment, by forming a coating layer on the outer surface of the carbon material core, a negative electrode material having both a carbon material core and a coating layer is prepared. This can fully utilize the characteristics of the mesoporous material with mesoporous channels in the coating layer, which is not only conducive to improving the surface defect structure of the carbon material core, but also improving the dispersibility of the negative electrode material during the slurrying process, thereby obtaining a negative electrode sheet with a more uniform distribution of the negative electrode material, thereby improving the performance of the battery. In addition, the conductivity of the first material is σ, which is 1×10 -18 S / m<σ≤1×10 2 S / m, the first material has low electrical conductivity, is difficult to react with the electrolyte, and has strong liquid absorption and retention capabilities, which is conducive to achieving the negative electrode material prepared by the preparation method of the embodiment of the present invention having good fast charging capabilities when used in batteries, which will not be elaborated here.

[0069] In some specific embodiments of the present invention, the amorphous carbon material precursor is one or a combination of pitch, resin or heavy oil, etc., and the amorphous carbon material can be prepared from the above hard carbon materials.

[0070] According to one embodiment of the present invention, the step of forming a coating layer on at least a portion of the outer surface of the carbon material core includes:

[0071] Mixing a first component and a second component to obtain a coating additive, wherein the first component comprises a first material or a first material precursor, and the second component comprises an amorphous carbon material or an amorphous carbon material precursor;

[0072] The coating additive is mixed with the carbon material core. If the amorphous carbon precursor is solid, it needs to be heated and stirred to soften it; if the amorphous carbon precursor is fluid, no heating is required during the stirring process.

[0073] For example, an inorganic mesoporous material and an amorphous carbon material precursor are mixed to obtain a coating additive. The coating additive is then added to a carbon material core and stirred to mix. When the coating additive coats the outer surface of the carbon material core particle, the inorganic mesoporous material and the amorphous carbon material precursor are coated together on the outer surface of the carbon material core particle, thereby obtaining a mixed material.

[0074] Alternatively, the mixed material can be carbonized at high temperature in a carbonization device to carbonize the amorphous carbon precursor to obtain an amorphous carbon structure, and the inorganic mesoporous material having mesoporous channels and the amorphous carbon can be coated on the surface of the graphite particles. For example, the mixture can be carbonized and sintered at a temperature of 1000°C to 1200°C.

[0075] Optionally, the temperature during the carbonization process is 1000°C to 1200°C. If the temperature is less than 1000°C, the amorphous carbon precursor is difficult to sinter fully, which will increase the specific surface area of ​​the product, increase the side reactions in the battery cell, and reduce the initial efficiency of the battery; if the temperature is higher than 1200°C, this temperature will increase the cost, and if the temperature continues to increase above 2000°C, the amorphous carbon in the coating will begin to graphitize, reducing the active sites on the surface of the finished reaction product and reducing the rate performance. It can be seen that in this embodiment, by limiting the temperature during the carbonization process to 1000°C to 1200°C, for example, the temperature during the carbonization process is 1000°C, 1050°C, 1100°C, or 1200°C, etc., it can be ensured that the negative electrode material has good electrical properties when applied to the battery.

[0076] According to one embodiment of the present invention, the method for preparing a negative electrode material further includes the following steps: depolymerizing the negative electrode material through a depolymerization device to regulate the particle size distribution of the negative electrode material. For example, the obtained graphite-coated product is depolymerized through a depolymerization device to obtain graphite particles that meet the particle size distribution requirements according to actual needs. The obtained graphite particles include graphite core particles and their coating layers. For another example, after carbonization and sintering are completed, depolymerization is carried out according to actual needs to obtain a negative electrode material whose surface is coated with mesoporous material and amorphous carbon.

[0077] It should be noted that there are no specific requirements for the models of the stirring device, carbonization equipment, and depolymerization equipment in the embodiments of the present invention.

[0078] The preparation process of the negative electrode material is described below using inorganic mesoporous materials, amorphous carbon material precursors and graphite core particles as examples.

[0079] First, the inorganic mesoporous material and the amorphous carbon material precursor are stirred and mixed in a stirring tank at a certain ratio (the mass proportion of the mesoporous material is 10% to 80%) as required to obtain a mixture of the mesoporous material and the amorphous carbon material precursor as a coating additive.

[0080] Then, add the coating additive to the graphite core particles to be coated (the amount added is based on the formula: the mass of the coating agent after sintering / (the mass of the coating agent after sintering + the negative electrode material) ≤ 5%), and stir and mix. If the amorphous carbon precursor is solid, it needs to be heated and stirred (stirring temperature 100°C ~ 300°C) to soften it; if the amorphous carbon precursor is fluid, no heating is required during the stirring process.

[0081] Subsequently, the uniformly stirred mixture is carbonized at a heating temperature of 1000°C to 1200°C. After sintering, it is depolymerized according to actual needs to obtain a negative electrode material with an inorganic mesoporous material and amorphous carbon coated on the surface.

[0082] The present invention also provides a negative electrode plate, comprising a current collector and a negative electrode material, the negative electrode material being coated on the outer surface of the current collector. The negative electrode material is any of the negative electrode materials described above, or is a negative electrode material prepared according to any of the preparation methods described above. Because the negative electrode materials of the embodiments of the present invention have advantages such as improved battery performance, the negative electrode plates of the embodiments of the present invention also have the same advantages, which will not be described in detail here.

[0083] In addition, the negative electrode plate may include a negative electrode active material coating and a current collector. The negative electrode active material coating may be provided on one or both surfaces of the current collector. The current collector may be any material. Preferably, the current collector is copper foil, and more preferably, the current collector is carbon-coated copper foil.

[0084] Optionally, the negative electrode active material may be a graphite material, which may be one or a combination of artificial graphite and natural graphite. The negative electrode active material coating may include a graphite particle coating, a binder, and a conductive agent; the graphite particle coating may include graphite and a composite coating layer wrapped around the surface;

[0085] The present invention further provides a battery comprising the negative electrode sheet of any of the above embodiments, wherein the battery may further comprise a positive electrode sheet, a separator and an electrolyte.

[0086] Among them, the positive electrode plate may include a positive electrode active material coating and a current collector. The positive electrode active material coating may be arranged on one surface or both surfaces of the current collector; the current collector is not limited. Preferably, the current collector is aluminum foil, and further preferably, the current collector is carbon-coated aluminum foil.

[0087] The positive electrode active material can be one or a combination of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, olivine structure lithium phosphate, etc.

[0088] In addition, the separator may include, but is not limited to, one or a composite membrane of polyethylene, polypropylene, polyvinylidene fluoride, etc. The electrolyte may not be limited and may be selected according to actual conditions.

[0089] The present invention is described in further detail below by taking specific implementation modes as examples.

[0090] The specific implementation methods used in the following embodiments are as follows:

[0091] Example 1

[0092] Silica (D50 is 300 nm) and asphalt are stirred and mixed in a stirring tank according to the formula: silica mass: (asphalt mass × coking value) = 5:5 to obtain a mixture of silica and asphalt as a coating additive;

[0093] The coating additive is added to the artificial graphite according to the ratio of silica, asphalt and artificial graphite: (silica mass + asphalt mass × coking value) / (silica mass + asphalt mass × coking value + artificial graphite) = 4%, and the mixture is softened by heating and stirring (stirring temperature 200°C).

[0094] The uniformly stirred mixture was heated at 1600°C for carbonization. After carbonization, it was depolymerized according to actual needs to obtain a negative electrode material with a surface coated with silicon dioxide and amorphous carbon, which was marked as N1. The specific parameters are shown in Table 1.

[0095] Battery preparation: The negative electrode material N1 obtained above was mixed evenly with a conductive agent (superP), a thickener (CMC), and a binder (SBR) in a ratio of 96:0.3:0.7:1:2 with deionized water to form a slurry. The slurry was coated on both sides of the copper foil using a coater to prepare the negative electrode sheet A1.

[0096] The positive electrode active material lithium iron phosphate (LiFePO4), conductive agent (EP), and binder (PVDF) were evenly mixed with NMP in a ratio of 96:1:3. An integrated positive electrode sheet was prepared on aluminum foil using a coater. The positive electrode sheet, separator, and negative electrode sheet were stacked in this order, and an appropriate amount of electrolyte was injected to prepare a 2Ah battery, marked as B1. The battery performance was tested, and the test results are shown in Table 2.

[0097] Example 2

[0098] The difference from Example 1 is that the inorganic mesoporous material used is mesoporous aluminum oxide (D50 is 600 nm), and the rest of the process is the same as Example 1. The obtained negative electrode material is marked as N2, the negative electrode sheet is A2, and the battery is B2.

[0099] Example 3

[0100] The difference from Example 1 is that the amount of silica and asphalt follows the formula: silica mass: (asphalt mass × coking value) = 1:9; the other steps are the same as Example 1. The resulting negative electrode material is labeled N3, the negative electrode sheet is A3, and the battery is B3.

[0101] Example 4

[0102] The difference from Example 1 is that the amount of silica and asphalt follows the formula: silica mass: (asphalt mass × coking value) = 8:2; the other steps are the same as Example 1. The resulting negative electrode material is labeled N4, the negative electrode sheet is A4, and the battery is B4.

[0103] Example 5

[0104] The difference from Example 1 is that silica, asphalt, and artificial graphite are mixed in a ratio of (silica mass + asphalt mass × coking value) / (silica mass + asphalt mass × coking value + artificial graphite) = 2%. The other steps are the same as in Example 1. The resulting negative electrode material is labeled N5, the negative electrode sheet is labeled A5, and the battery is labeled B5.

[0105] Example 6

[0106] The difference from Example 1 is that the silica, asphalt, and artificial graphite are mixed in a ratio of (mass of silica + mass of asphalt × coking value) / (mass of silica + mass of asphalt × coking value + artificial graphite) = 6%. The other steps are the same as in Example 1. The resulting negative electrode material is labeled N6, the negative electrode sheet is labeled A6, and the battery is labeled B6.

[0107] Example 7

[0108] The difference from Example 1 is that natural graphite is used as the carbon material core, and the other steps are the same as Example 1. The obtained negative electrode material is marked as N7, the negative electrode sheet is marked as A7, and the battery is marked as B7.

[0109] Example 8

[0110] The negative electrode materials prepared in Example 1 and Example 7 were mixed evenly with a conductive agent (superP), a thickener (CMC), and a binder (SBR) in a ratio of 48:48:0.3:0.7:1:2 with deionized water to form a slurry. The slurry was coated on both sides of a copper foil using a coating machine to prepare a negative electrode sheet A8, and the battery was B8.

[0111] Example 9

[0112] The difference from Example 1 is that silicon dioxide and artificial graphite are directly mixed in a ratio of silicon dioxide mass / (silicon dioxide mass + artificial graphite) = 4%. The other steps are the same as in Example 1. The resulting negative electrode material is labeled N9, the negative electrode sheet is labeled A9, and the battery is labeled B9.

[0113] Comparative Example 1

[0114] The difference from Example 1 is that the artificial graphite is not coated. Specifically, the artificial graphite is carbonized using the same steps as in Example 1. The resulting negative electrode material is labeled DN1, the negative electrode sheet is DA1, and the battery is DB1.

[0115] Comparative Example 2

[0116] The difference from Example 1 is that only the graphite coated with an amorphous carbon layer is used. Specifically, asphalt and artificial graphite are mixed in a ratio of (asphalt mass × coking value) / (asphalt mass × coking value + artificial graphite) = 4%. The other steps are the same as in Example 1. The resulting negative electrode material is labeled DN2, the negative electrode sheet is DA2, and the battery is DB2.

[0117] Comparative Example 3

[0118] The difference from Example 1 is that the inorganic mesoporous material is mesoporous carbon (conductivity of about 2×10 5 S / m, D50 is 300nm). The mesoporous carbon and pitch usage follows the formula: mesoporous carbon mass: asphalt mass × coking value = 5:5; the mesoporous carbon, asphalt and natural graphite usage ratio follows the formula: (mesoporous carbon + asphalt mass × coking value) / (mesoporous carbon + asphalt mass × coking value + artificial graphite) = 4%. The other steps are the same as in Example 1. The resulting negative electrode material is labeled DN3, the negative electrode sheet is DA3, and the battery is DB3.

[0119] Comparative Example 4

[0120] The difference from Example 7 is that silicon dioxide is replaced by mesoporous carbon, and the other steps are the same as Example 7. The obtained negative electrode material is marked as DN4, the negative electrode sheet is marked as DA4, and the battery is marked as DB4.

[0121] Comparative Example 5

[0122] The difference from Example 8 is that the negative electrode materials prepared in Comparative Examples 1 and 4 are mixed evenly with a conductive agent (superP), a thickener (CMC), and a binder (SBR) in a ratio of 48:48:0.3:0.7:1:2 with deionized water to form a slurry, and the slurry is coated on both sides of a copper foil using a coating machine to prepare a negative electrode sheet DA5, and the battery is DB8.

[0123] Table 1 Summary of negative electrode material parameters

[0124]

[0125] The performance of the negative electrode sheets A1-A9 and DA1-DA5 obtained in Examples 1-8 and Comparative Examples 1-5 were tested as follows:

[0126] First, use a contact angle meter to test the liquid absorption rate of the negative electrode: lay the negative electrode flat on the test platform, fix the amount of electrolyte droplets, drop the electrolyte on the surface of the negative electrode, and start timing. Observe the electrolyte droplets through the display lens until they disappear, record the time taken for the disappearance process, and calculate the liquid absorption rate. Liquid absorption rate = liquid droplet amount / droplet disappearance time.

[0127] Second, use an electronic balance to test the liquid absorption capacity of the negative electrode: place the electrode at 120°C for 12 hours, record the weight of the negative electrode after baking, and then immerse the baked electrode in electrolyte at 25°C for 24 hours, remove it, and record the weight of the electrode after immersion in electrolyte. Calculate the electrode's liquid retention capacity: Liquid retention capacity = (weight of the electrode after immersion - weight of the electrode after baking) / weight of the electrode coating.

[0128] Third, the first charge and discharge efficiency test: In an environment with a temperature of 25°C, charge the battery at a constant current and constant voltage of 0.1C to 100% SOC state, age it at 45°C for 24 hours, and discharge it at a constant current of 0.1C to 0% SOC state. Record the charge capacity and discharge capacity, and calculate the first charge and discharge efficiency. The first charge and discharge efficiency = discharge capacity / charge capacity * 100%

[0129] Fourth, the rate charge and discharge test conditions are as follows: in an environment with a temperature of 25°C, the battery is charged to 100% SOC at 0.1C, left for 30 minutes, and then discharged to 0% SOC at 4C. The discharge efficiency is calculated as follows: discharge ratio = discharge capacity at 4C rate / discharge capacity at 0.1C rate.

[0130] In an environment with a temperature of 25°C, the battery was charged to 100% SOC at 4C and left for 30 minutes. The charging efficiency was calculated as follows: charging ratio = charging capacity at 3C rate / charging capacity at 0.1C.

[0131] Fifth, the cycle test conditions are: in an environment with a temperature of 25°C, charge and discharge at 1C, calculate the capacity retention rate, capacity retention rate = current cycle discharge capacity / first cycle discharge capacity, compare the battery capacity retention rate under the same number of cycles.

[0132] Sixth, record the battery thickness d1 at 0% SOC before cycling and the battery thickness d2 at 0% SOC after cycling, and calculate the thickness growth rate of the battery: thickness growth rate = (d2-d1) / d1

[0133] The negative electrode sheets of the remaining embodiments and comparative examples were tested under the same test conditions as in Example 1. The test method is as shown in Example 1. The test results are shown in Table 2 below.

[0134] Table 2 Test results of negative electrode and battery

[0135]

[0136] In conjunction with Table 1 and Table 2, Example 1 is compared with Example 6. In Example 1, silica and asphalt are mixed with artificial graphite in a ratio of (mass of silica + mass of asphalt × coking value) / (mass of silica + mass of asphalt × coking value + artificial graphite) = 4%; in Example 6, silica and asphalt are mixed with artificial graphite in a ratio of (mass of silica + mass of asphalt × coking value) / (mass of silica + mass of asphalt × coking value + artificial graphite) = 6%. In other words, the mass percentage of the coating layer in Example 1 is 4%, and the mass percentage of the coating layer in Example 6 is 6%. It can be seen from Table 2 that the discharge ratio and charge ratio of Example 1 are both better than those of Example 6. Therefore, by preferably making the coating layer account for no more than 5% of the mass of the negative electrode material, it is beneficial to improve the fast charging performance of the battery.

[0137] Comparing Comparative Example 1 with Example 1, in conjunction with Tables 1 and 2, reveals that Comparative Example 1 uses artificial graphite without a coating layer. The corresponding liquid absorption rate of the negative electrode material of Comparative Example 1 is lower than that of Example 1, and the corresponding liquid retention capacity of the negative electrode material of Comparative Example 1 is also lower than that of Example 1. The initial efficiency, capacity retention rate, discharge ratio, and charge ratio of Comparative Example 1 are all lower than those of Example 1, and the increase in battery thickness of Comparative Example 1 is greater than that of Example 1. Therefore, the battery product of Comparative Example 1 has poor performance, is thicker, and occupies a large space.

[0138] In conjunction with Table 1 and Table 2, Comparative Example 2 is compared with Example 1. It can be seen that Comparative Example 2 contains graphite that is only coated with an amorphous carbon layer and does not contain inorganic mesoporous materials. Among them, the liquid absorption rate corresponding to the negative electrode material of Comparative Example 2 is lower than the liquid absorption rate corresponding to Example 1, and the liquid retention capacity corresponding to the negative electrode material of Comparative Example 2 is also lower than the liquid retention capacity corresponding to Example 1. The first effect, capacity retention rate, discharge ratio and charging ratio of Comparative Example 2 are all lower than those of Example 1, and the degree of increase in battery thickness of Comparative Example 2 is greater than that of Example 1. It can be seen that the battery product of Comparative Example 2 has poor performance, a large thickness, and occupies a large space. In other words, Comparative Example 2 does not add inorganic mesoporous materials. On the basis of the same carbon material core and the same amorphous carbon material, the liquid absorption rate and liquid retention rate of Example 1 are better than those of Comparative Example 2, which is beneficial to improving the fast charging performance of the battery.

[0139] Combined with Table 1 and Table 2, Comparative Example 3 is compared with Example 1. In Comparative Example 3, mesoporous carbon (conductivity of about 2×10 3 S / m, D50 is 300nm. Among them, the liquid absorption rate corresponding to the negative electrode material of Comparative Example 3 is lower than the liquid absorption rate corresponding to Example 1, and the liquid retention capacity corresponding to the negative electrode material of Comparative Example 3 is also lower than the liquid retention capacity corresponding to Example 1. The first effect, capacity retention rate, discharge ratio and charging ratio of Comparative Example 3 are all lower than those of Example 1, and the thickness growth degree of the battery of Comparative Example 3 is greater than that of Example 1. It can be seen that the battery product of Comparative Example 3 has poor performance, large thickness and large space occupation. In other words, the conductivity of mesoporous carbon is 10 2 S / m~10 4 S / m, comparative example 3 uses mesoporous carbon to replace inorganic mesoporous materials, and the conductivity of the mesoporous carbon in comparative example 3 is 2×10 3 S / m, based on the same carbon material core and the same amorphous carbon material, the liquid absorption rate and liquid retention rate of Example 1 are better than those of Comparative Example 3.

[0140] Combining Table 1 and Table 2, Comparative Example 4 and Example 7 are compared. In Comparative Example 4, silicon dioxide is replaced with mesoporous carbon. Among them, the liquid absorption rate corresponding to the negative electrode material of Comparative Example 4 is lower than the liquid absorption rate corresponding to Example 7, and the liquid retention capacity corresponding to the negative electrode material of Comparative Example 4 is also lower than the liquid retention capacity corresponding to Example 7. The first efficiency, capacity retention rate, discharge ratio, and charge ratio of Comparative Example 4 are all lower than those of Example 7, and the increase in battery thickness of Comparative Example 4 is greater than that of Example 7. It can be seen that the battery product of Comparative Example 4 has poor performance, is thicker, and occupies a large space.

[0141] Combined with Table 1 and Table 2, Comparative Example 5 is compared with Example 8. In Comparative Example 5, the negative electrode materials prepared in Comparative Example 1 and Comparative Example 4 are mixed evenly with a conductive agent (superP), a thickener (CMC), and a binder (SBR) in a ratio of 48:48:0.3:0.7:1:2 and deionized water to form a slurry, and the slurry is coated on both sides of the copper foil using a coating machine. Among them, the liquid absorption rate corresponding to the negative electrode material of Comparative Example 5 is lower than the liquid absorption rate corresponding to Example 8, and the liquid retention capacity corresponding to the negative electrode material of Comparative Example 5 is also lower than the liquid retention capacity corresponding to Example 8. The first effect, capacity retention rate, discharge ratio and charging ratio of Comparative Example 5 are all lower than those of Example 8, and the degree of increase in battery thickness of Comparative Example 5 is greater than that of Example 8. It can be seen that the battery product of Comparative Example 5 has poor performance, a large thickness, and occupies a large space.

[0142] In summary, the negative electrode material according to the embodiment of the present invention adopts an inorganic mesoporous material with mesoporous channels as the first material, which is beneficial to changing the surface defect structure of the carbon material core and improving the dispersibility of the carbon material core during the preparation of the negative electrode material; and 1×10 -18 S / m<σ≤1×10 2 S / m, the first material has low electrical conductivity and strong liquid absorption and retention capabilities, which is beneficial to improving battery performance.

[0143] Although some specific embodiments of the present invention have been described in detail by way of examples, it should be understood by those skilled in the art that the above examples are for illustration only and are not intended to limit the scope of the present invention. It should be understood by those skilled in the art that modifications may be made to the above embodiments without departing from the scope and spirit of the present invention. The scope of the present invention is defined by the appended claims.

Claims

1. A negative electrode material, characterized in that Include: Carbon material core; The coating layer covers at least a portion of the outer surface of the carbon material core, and the coating layer comprises a first material, the first material is an inorganic mesoporous material with mesoporous channels, and the electrical conductivity of the first material is σ, 1×10 -18 S / m<σ≤1×10 2 S / m; The inorganic mesoporous material is a combination of one or more of mesoporous silica, mesoporous titania and mesoporous alumina.

2. The negative electrode material according to claim 1, characterized in that 1×10 -18 S / m<σ≤1×10 -4 S / m。 3. The negative electrode material according to claim 1, characterized in that The coating layer further comprises: A second material having an electrical conductivity greater than that of the first material.

4. The negative electrode material according to claim 3, characterized in that The second material is an amorphous carbon material, and the second material and the first material are mixed with each other.

5. The negative electrode material according to claim 1, characterized in that The carbon material core is graphite; the graphite includes at least one of artificial graphite and natural graphite.

6. The negative electrode material according to claim 1, characterized in that The coating layer accounts for no more than 5% by mass of the negative electrode material; and / or, The mass proportion of the first material in the coating layer is not higher than 80% and not lower than 10%; and / or, The D50 of the first material is 10 nm to 1000 nm; and / or, The coating layer covers the entire outer surface of the carbon material core, and the thickness of the coating layer is 10 nm to 2 μm.

7. A method for preparing a negative electrode material, characterized in that: The following steps are involved: A coating layer is formed on at least a portion of the outer surface of the carbon material core, wherein the carbon material core and the coating layer constitute the negative electrode material, and the coating layer comprises a first material, wherein the first material is an inorganic mesoporous material having mesoporous channels, wherein the electrical conductivity of the first material is σ, which is 1×10 -18 S / m<σ≤1×10 2 S / m; The inorganic mesoporous material is a combination of one or more of mesoporous silica, mesoporous titania and mesoporous alumina.

8. The method for preparing the negative electrode material according to claim 7, wherein: The step of forming a coating layer on at least a portion of the outer surface of the carbon material core comprises: Mixing a first component and a second component to obtain a coating additive, wherein the first component comprises a first material or a first material precursor, and the second component comprises an amorphous carbon material or an amorphous carbon material precursor; The coating additive is mixed with the carbon material core.

9. The method for preparing the negative electrode material according to claim 7 or 8, characterized in that: The following steps are also included: The negative electrode material is depolymerized by a depolymerization device to regulate the particle size distribution of the negative electrode material.

10. A negative electrode plate, characterized in that: include: current collector; A negative electrode material is coated on the outer surface of the current collector, and the negative electrode material is the negative electrode material according to any one of claims 1 to 6, or the negative electrode material prepared by the method for preparing the negative electrode material according to any one of claims 7 to 9.

11. A battery, characterized in that: Including the negative electrode sheet according to claim 10.

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