Negative active material and method of manufacturing, negative electrode, and battery and electric device

Abstract

The application relates to the field of batteries, in particular to a negative electrode active material and a preparation method thereof, a negative electrode, a battery and an electric device. The negative electrode active material comprises graphite particles and a carbon layer coating the graphite particles; the graphite particles have holes in the interior and / or surface, and the holes are filled with fillers; the fillers comprise graphite powder and optional amorphous carbon. The negative electrode active material provided by the application is mainly composed of graphite particles which are densified by graphite powder and optional amorphous carbon; the electrochemical expansion of the graphite particles is low during the battery cycle process; the expansion problem of the graphite negative electrode is solved; the battery has better rate performance and a longer cycle life; compared with a negative electrode active material in which amorphous carbon is completely used as the filler of the graphite holes, the charge-discharge efficiency under the condition of 25 DEG C and 3C rate can be increased to more than 80%, and the capacity retention rate after 1000 cycles under the condition of 25 DEG C and 1C charge-discharge can be increased to more than 86%.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of batteries, in particular to a negative electrode active material, a preparation method thereof, a negative electrode, a battery and an electric device. BACKGROUND

[0002] In the battery negative electrode material, the graphitization degree of natural graphite is high, the specific capacity is high, and the price is low compared with artificial graphite. However, due to the large grain size of natural graphite, there are many pores in the particle, which causes the large rate capacity of natural graphite to be low. In addition, in the battery cycle process, due to the existence of pores in the natural graphite particle, the natural graphite will swell outwardly while also swelling inwardly, resulting in a large electrochemical expansion, which causes the natural graphite particle to continuously expose new reaction interfaces, resulting in a short battery cycle life. Reducing the internal pores of the natural graphite particle can effectively improve the defects of the natural graphite in electrochemical expansion and cycle life.

[0003] At present, the filler used to fill the internal pores of natural graphite is amorphous carbon formed by carbonizing pitch or resin. In the long-term cycle process of the battery, due to repeated expansion, the pores will inevitably reopen, exposing the filled amorphous carbon interface. Amorphous carbon has a large specific surface area, which will bring more side reactions, causing the electrolyte to increase in digestion, and to some extent, reducing the battery life. In addition, using amorphous carbon as the pore filler of natural graphite, the compactness is usually not high, which will affect the rate performance of the battery to some extent.

[0004] Therefore, it is urgent to improve the filling technology of the internal pores of natural graphite. SUMMARY

[0005] The present application provides a negative electrode active material, a preparation method thereof, a negative electrode, a battery and an electric device, aiming at the problem that the existing technology of natural graphite negative electrode material is prone to large volume expansion in the battery cycle process, which affects the cycle life and rate performance of the battery.

[0006] In order to achieve the above-mentioned purpose, the first aspect of the present application provides a negative electrode active material, which comprises: graphite particles, and a carbon layer covering the graphite particles.

[0007] Among them, the internal pores of the graphite particles exist, and the pores are filled with fillers.

[0008] The fillers include graphite powder and optional amorphous carbon.

[0009] The second aspect of the present application provides a preparation method of a negative electrode active material, comprising:

[0010] (1) Granulating natural graphite raw materials and fillers together to obtain graphite particles;

[0011] (2) mixing the graphite particles with an organic carbon source to obtain graphite particles coated with the organic carbon source;

[0012] (3) carbonizing the graphite particles coated with the organic carbon source to obtain the negative electrode active material;

[0013] The internal pores of the graphite particles are filled with the filler;

[0014] The filler comprises graphite powder, optionally pitch, and optionally resin.

[0015] The third aspect of the present application provides the negative electrode active material prepared by the method of the second aspect.

[0016] The fourth aspect of the present application provides a negative electrode comprising a negative electrode current collector and an active material layer disposed on the negative electrode current collector;

[0017] The active material layer contains the negative electrode active material of the first aspect or the third aspect.

[0018] The fifth aspect of the present application provides a battery comprising the negative electrode of the fourth aspect.

[0019] The sixth aspect of the present application provides an electric device comprising the battery of the fifth aspect.

[0020] Through the above technical solution, the present application uses graphite powder and optional amorphous carbon as the pore filler of the graphite particles to densify the graphite particles, and obtains the negative electrode active material based on this, which can achieve the following beneficial effects:

[0021] (1) The negative electrode active material provided by the present application, wherein the internal pores of the graphite particles are filled to achieve densification, which greatly reduces the electrochemical expansion space of the graphite particles during the cycle process, thereby effectively reducing the expansion phenomenon, solving the expansion problem of the graphite negative electrode, and prolonging the cycle life of the battery;

[0022] (2) The negative electrode active material provided by the present application uses graphite powder as the main filler of the pores of the graphite particles. Compared with the filler amorphous carbon of the prior art, the graphite powder has a smaller specific surface area, produces fewer side reactions during the operation of the battery, can reduce the consumption of electrolyte, improve the cycle life of the battery, and improve the rate performance of the battery;

[0023] (3) The negative active material provided by the present application adopts graphite powder as the main filler, which can be graphite powder byproduct, for example, fine powder of artificial graphite obtained in the screening process of the preparation process of artificial graphite, so that the byproduct of artificial graphite can be reused, the crushing process of pitch or resin required in the prior art technical solution using amorphous carbon as the main filler can be avoided, and the cost of subsequent graphitization can be reduced;

[0024] (4) The negative active material provided by the present application has a carbon coating layer on the surface, which is beneficial to improving the cycle life and the first charge-discharge efficiency of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0025] The accompanying drawings are included to provide a further understanding of the present application, and constitute a part of the specification, and together with the specific embodiments below, serve to explain the present application, but do not constitute a limitation on the present application. In the drawings:

[0026] Figure 1 SEM test diagram of the negative active material P1 prepared for the embodiment 1 of the present application after ion cutting.

[0027] Figure 2 SEM test diagram of the negative active material DP1 prepared for the comparative example 1 of the present application after ion cutting. DETAILED DESCRIPTION

[0028] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The ranges or values should be construed to be approximations that allow for significant variation. Various ranges of values that are explicitly delineated in the specification as supplied herein constitute new and nonobvious ranges of values that are specifically disclosed.

[0029] The first aspect of the present application provides a negative active material, which comprises: graphite particles, and a carbon layer covering the graphite particles.

[0030] The graphite particles have holes in the interior, and the holes are filled with fillers.

[0031] The fillers comprise graphite powder and optional amorphous carbon.

[0032] The negative active material provided by the present application is mainly composed of graphite particles, the internal holes of the graphite particles are filled with specific fillers, and the surface of the graphite particles is coated with a carbon layer. At the micro level, the negative active material is in the form of particles, preferably, the particle shape of the negative active material is spherical or ellipsoidal.

[0033] According to the present application, in the negative active material, the graphite particles are prepared from natural graphite as raw material. Preferably, the graphite particles are particles of spheroidal graphite.

[0034] In the present application, the natural graphite is preferably natural flake graphite.

[0035] In the present application, the spheroidal graphite should be understood according to the definition of "spheroidal graphite" known to those skilled in the art of graphite materials and batteries.

[0036] According to the present application, in the negative active material, the average particle size of the graphite particles is 8-35 μm. If the average particle size of the graphite particles is too large, the ion migration path during battery cycling will be too long, which is not conducive to the kinetic performance of the battery. If the average particle size of the graphite particles is too small, the specific surface area of the graphite particles will increase, leading to increased consumption of electrolyte, and thus reducing the first charge-discharge efficiency and cycle life of the battery. Preferably, the average particle size of the graphite particles is 10-30 μm.

[0037] In the present application, the average particle size refers to the median diameter (D50), which can be measured by a laser particle size analyzer.

[0038] According to the present application, in the negative active material, the carbon layer is coated on the surface of the graphite particles, which can reduce the specific surface area of the graphite particles, increase the active sites, and be conducive to improving the first charge-discharge efficiency and cycle life of the battery. In the present application, the carbon layer should not be too thick, because a too large thickness will lead to the formation of a thicker SEI film, and thus reducing the first charge-discharge efficiency of the battery. Preferably, the thickness of the carbon layer is 1-100 nm.

[0039] In the present application, the thickness of the carbon layer can be measured by a transmission electron microscope (TEM).

[0040] According to the present application, in the negative active material, the internal pores of the graphite particles are filled with graphite powder and optional amorphous carbon. The use of this specific filler for the densification of the graphite particles can greatly reduce the electrochemical expansion space of the graphite particles during battery cycling, and thus effectively inhibit the expansion of the graphite negative electrode, and prolong the cycle life of the battery. Preferably, based on the total weight of the negative active material, the content of the filler in the negative active material is 5-15 wt%, and further preferably 7-10 wt%.

[0041] According to the application, in one embodiment, the filler can be all graphite powder, using graphite powder as the filler can compact the internal pores of the graphite particles, reduce the irreversible expansion of the graphite particles caused by multiple cycles, inhibit and significantly delay the reopening of the pores, and when the pores of the graphite particles open to expose the filler interface, due to the less reaction of the filled graphite powder with the electrolyte, compared with the method mainly using amorphous carbon as the filler, the consumption of the electrolyte can be reduced, thereby improving the cycle life of the battery.

[0042] In another embodiment, the filler can be a mixture of graphite powder and amorphous carbon, and an appropriate amount of amorphous carbon can provide more ion diffusion paths, thereby improving the migration rate of ions in graphite, but when the proportion of amorphous carbon in the filler is too high, it will cause the electrolyte to be consumed more rapidly, thereby reducing the cycle life of the battery. Preferably, the content of the graphite powder in the filler is 90-100 wt%, and further preferably 95-100 wt%, based on the total weight of the filler.

[0043] According to the application, the average particle size of the filler is 0.5-3 μm, and preferably 1-2 μm.

[0044] According to the application, preferably, the graphitization degree of the graphite powder is ≥ 94%, which can enable the battery to obtain higher initial charge-discharge efficiency and capacity.

[0045] In the present application, graphite powder meeting the above-mentioned defined conditions can be used as the filler in the negative electrode active material. In a preferred embodiment of the present application, the graphite powder can be the fine powder of artificial graphite obtained in the powder screening process during the preparation of artificial graphite. The fine powder of artificial graphite is a by-product in the preparation process of artificial graphite, and it is already a fine particle graphite product. Directly using the fine powder of artificial graphite as the filler can avoid the need for a crushing process of pitch or resin (as a precursor of the filler) in the prior art in which amorphous carbon is mainly used as the filler.

[0046] The negative electrode active material provided by the present application is mainly composed of graphite particles densified by using a specific filler (graphite powder and optional amorphous carbon). Compared with graphite particles densified mainly by using amorphous carbon, the former has significantly reduced electrochemical expansion during battery cycling and produces fewer side reactions, which can enable the battery to have a longer cycle life and better rate performance. Specifically, the charge-discharge efficiency under the condition of 25℃ and 3C rate can be increased to 80% or more, and the capacity retention rate after 1000 cycles under the condition of 25℃ and 1C charge-discharge can be increased to 86% or more.

[0047] The second aspect of the present application provides a preparation method of a negative electrode active material, comprising:

[0048] (1) granulating the natural graphite raw material together with the filler to obtain graphite particles;

[0049] (2) mixing the graphite particles with an organic carbon source to obtain graphite particles coated with the organic carbon source;

[0050] (3) carbonizing the graphite particles coated with the organic carbon source to obtain a negative electrode active material;

[0051] wherein the internal pores of the graphite particles are filled with the filler;

[0052] The filler comprises graphite powder, optionally pitch, and optionally resin.

[0053] According to the present application, in step (1), during the granulation process, the natural graphite raw material wraps the filler, and after granulation molding, the graphite particles with the internal pores filled with the filler are formed.

[0054] According to the present application, in step (1), the granulation process is preferably a spheroidization process of the natural graphite raw material. Preferably, the granulation process comprises:

[0055] The natural graphite raw material is subjected to spheroidization treatment, and the filler is added during the spheroidization process, so that the natural graphite raw material wraps the filler to obtain graphite particles.

[0056] According to the present application, in the above preferred granulation process, by adding the filler during the spheroidization process, the natural graphite raw material is fully mixed with the filler, and under the impact, friction and shearing action of the spheroidization device on the natural graphite raw material, the filler is wrapped into the natural graphite raw material to obtain spherical graphite particles filled with graphite powder, optional pitch and optional resin.

[0057] According to the present application, in step (1), the natural graphite raw material is a conventional raw material for preparing spherical graphite, and is preferably natural flake graphite.

[0058] According to the present application, in step (1), preferably, the weight ratio of the filler to the natural graphite raw material (the filler + the natural graphite raw material) is (10-30):100, preferably (15-20):100. In the case of satisfying the above ratio, it is beneficial to obtain graphite particles with better densification effect.

[0059] According to the present application, in one embodiment, the filler can be all graphite powder, graphite powder is used as the hole filler of the graphite particles, after subsequent carbonization treatment, the graphite structure of the graphite powder remains unchanged, and the filler is filled in the holes in the form of graphite, which can improve the capacity of natural graphite, reduce the irreversible expansion of the graphite particles caused by multiple cycles, inhibit and significantly delay the reopening of the holes, and when the holes of the graphite particles are opened to expose the filler interface, the consumption of the electrolyte can be reduced due to the less reaction of the filled graphite powder with the electrolyte, thereby improving the cycle life of the battery.

[0060] In another embodiment, the filler can also be a mixture of graphite powder, pitch and / or resin, and this mixture is used as the hole filler of the graphite particles, after subsequent carbonization treatment, the graphite structure of the graphite powder remains unchanged, and the pitch and / or resin are converted into amorphous carbon, i.e. a mixture of graphite powder and amorphous carbon is formed as the filler filled in the holes. The appropriate amount of amorphous carbon can provide more ion diffusion paths, thereby improving the migration rate of ions in graphite, but when the proportion of amorphous carbon in the filler is too high, it will cause the electrolyte to be consumed more rapidly, thereby reducing the cycle life of the battery.

[0061] According to the present application, in step (1), the content of the graphite powder in the filler is 90-100 wt%, preferably 95-100 wt%. In the present application, for the case where the filler contains pitch and / or resin, the amount of pitch and / or resin other than graphite powder in the above proportion is the weight of the amorphous carbon converted after subsequent carbonization.

[0062] According to the present application, for the case where the filler contains pitch and / or resin in step (1), it is preferred to heat and soften the pitch and / or resin before granulation.

[0063] According to the present application, the average particle size of the filler is 0.5-3 μm, preferably 1-2 μm. If the average particle size of the filler is too large, the flowability of the filler will be poor, and it will be difficult to be fully wrapped by the natural graphite raw material, thereby causing the internal holes of the graphite particles obtained by granulation to remain. If the average particle size of the filler is too small, the filler will fly during the granulation process, and it will also be difficult to be fully wrapped by the natural graphite raw material, thereby reducing the densification effect of the graphite particles obtained by granulation.

[0064] According to the present application, preferably, the graphitization degree of the graphite powder is ≥94%, which can enable the battery to obtain higher initial charge-discharge efficiency and capacity.

[0065] According to the present application, graphite powder meeting the above-mentioned defined condition can be used as the filler. In a preferred embodiment of the present application, the graphite powder can be fine artificial graphite powder obtained in a screening process in the preparation process of artificial graphite. In the present application, the raw materials (e.g. oil-based coke, coal-based coke, etc.), the processes and parameters in the artificial graphite preparation process known to those skilled in the art in the field of graphite materials and the field of batteries can be generally used, and the process generally mainly includes sequentially performed crushing process, shaping process, graphitization process and screening process, wherein the fine artificial graphite powder obtained in the screening process is usually in an average particle size of 1-3 μm and has no good use, and the present application directly uses the fine artificial graphite powder as the pore filler of the graphite particles, which can avoid the crushing process (the bitumen and / or resin are crushed to have a suitable particle size) required in the prior art using bitumen and / or resin as the main filler, and can reduce the process and cost of graphitizing the bitumen and / or resin filler after the pore filling, and realize the improvement of the utilization rate of the artificial graphite by-product.

[0066] According to the present application, in the filler, the average particle size of the bitumen and / or resin is 0.5-3 μm.

[0067] According to the present application, in the filler, the selection range of the bitumen is wide, and the filler bitumen commonly used in the prior art using amorphous carbon as the main filler can be selected.

[0068] According to the present application, in the filler, the selection range of the resin is also wide, and the filler resin commonly used in the prior art using amorphous carbon as the main filler can be selected. For example, phenolic resin, furfural resin and epoxy resin, etc.

[0069] According to the present application, in step (2), the organic carbon source can be selected from bitumen and / or resin. In the present application, for the bitumen and / or resin as the organic carbon source, the substance selection can be the same as the bitumen and / or resin as the filler in step (1) above.

[0070] According to the present application, in step (2), preferably, the weight ratio of the organic carbon source: (the graphite particles + the organic carbon source) is (0.5-5): 100.

[0071] According to the present application, in step (2), the carbonization treatment condition includes: the temperature is 1100-1200 ℃, and the oxygen content in the carbonization atmosphere is less than 400 ppm.

[0072] The preparation method of the negative electrode active material provided by the application adopts graphite powder, optional pitch and optional resin as fillers, preferably implements filling in the spheroidization process of natural graphite raw materials, and realizes densification of graphite particles by graphite powder and optional amorphous carbon after the graphite particles containing fillers are coated with an organic carbon source and carbonized, so that the negative electrode active material obtained thereby has significantly reduced electrochemical expansion in the battery cycle process, fewer side reactions, and can make the battery have longer cycle life and better rate performance.

[0073] The third aspect of the application provides the negative electrode active material prepared by the method of the second aspect.

[0074] According to the application, the structure, composition and performance of the negative electrode active material prepared by the method of the second aspect are the same as those of the negative electrode active material described in the first aspect of the application, and will not be repeated here.

[0075] The fourth aspect of the application provides a negative electrode, which comprises a negative electrode current collector and an active material layer arranged on the negative electrode current collector.

[0076] The active material layer contains the negative electrode active material of the first aspect or the third aspect.

[0077] According to the application, in some embodiments, the active material layer in the negative electrode can also contain other negative electrode active materials in addition to the negative electrode active material provided by the application, including but not limited to at least one of carbon materials other than graphite, silicon-based materials, tin-based materials and lithium-containing composite materials. The carbon materials other than graphite can include but are not limited to at least one of carbon fibers, soft carbon, hard carbon, mesocarbon microbeads and graphene; the silicon-based materials can include but are not limited to at least one of elemental silicon, silicon oxide, silicon alloy and composite silicon; and the tin-based materials can include but are not limited to tin oxide and / or tin alloy.

[0078] According to the application, the negative electrode current collector in the negative electrode can be various conventional negative electrode current collectors for batteries, and the application does not particularly limit the material selection and specification parameters thereof. For example, the negative electrode current collector can be a copper foil, preferably a carbon-coated copper foil.

[0079] Compared with conventional negative electrodes, the negative electrode provided by the application has the advantage of low expansion, has low thickness change rate in the cycle process of the battery, has fewer side reactions with electrolyte, and can make the battery have longer cycle life and better rate performance.

[0080] The fifth aspect of the application provides a battery comprising the negative electrode of the fourth aspect.

[0081] In the application, further, the battery is preferably a lithium ion battery or a sodium ion battery.

[0082] The sixth aspect of the present application provides a power consuming device comprising the battery of the fifth aspect described above.

[0083] The present application will be described in detail below by way of examples. In the following examples and comparative examples, the reagents used are all commercially available unless otherwise specified.

[0084] Artificial graphite fine powder-1 (filler): obtained from a sieving process in the production of artificial graphite (based on petroleum green coke raw material), having an average particle size (D50) of 1.2 μm and a graphitization degree of 95%.

[0085] Artificial graphite fine powder-2 (filler): obtained from a sieving process in the production of artificial graphite (based on petroleum green coke raw material) (the production raw material, production process and production parameters are the same as those of the above graphite powder-1), having an average particle size (D50) of 2.5 μm and a graphitization degree of 95%.

[0086] Pitch: high temperature pitch (softening point of 200°C), having an average particle size of 0.5 μm.

[0087] Phenolic resin: having an average particle size of 3 μm.

[0088] Natural flake graphite: having a carbon content of 97%, an average particle size (D50) of 70 μm for large flakes and an average particle size (D50) of 37 μm for small flakes.

[0089] Example 1

[0090] This example is used to illustrate the preparation of a negative electrode active material

[0091] (1-1) Natural flake graphite was added to a mixer and mixed with filler (artificial graphite fine powder-1), and the resulting mixture was then added to a spheroidization device for spheroidization treatment. Under the impact, friction and shearing action of the spheroidization wheel on the natural flake graphite, the filler was wrapped in the natural flake graphite to obtain spheroidized graphite particles (D50 of 18 μm) with compact filler; wherein the weight ratio of filler : (filler + natural flake graphite) was 20:100.

[0092] (1-2) The spheroidized graphite particles obtained in step (1-1) were mixed with pitch (temperature of pitch was 200°C) to obtain pitch-coated graphite particles; wherein the weight ratio of pitch : (pitch + spheroidized graphite particles) was 2.5:100.

[0093] (2) The pitch-coated graphite particles obtained in step (1-2) were subjected to carbonization treatment (carbonization temperature was 1150°C, oxygen content in the carbonization atmosphere was <150 ppm) to obtain a negative electrode active material (denoted as P1).

[0094] P1 is an ellipsoidal shape, which contains graphite particles (D50 of graphite particles is 18 μm) densified with fillers (graphite powder, D50 is 1.2 μm), and the outer surface of the graphite particles is coated with a carbon layer (the average thickness of the carbon layer is 40 nm); the content of fillers in the graphite particles is 9.8% by weight based on the total weight of P1; the content of graphite powder in the fillers is 100% by weight.

[0095] P1 was ion cut, and then SEM test was performed, and the results are shown in Figure 1 , where Figure 1 no obvious holes are visible in the graphite particles in P1, indicating that artificial graphite fine powder-1 is wrapped into the interior of the graphite particles and realizes the densification of the graphite particles.

[0096] Example 2

[0097] (1-1) Add natural flake graphite into a mixer, and add fillers (artificial graphite fine powder-1) for mixing, and then add the obtained mixture into a spheroidization device for spheroidization treatment. Under the action of collision, friction and shearing of the spheroidization wheel on the natural flake graphite, the fillers are wrapped into the natural flake graphite, to obtain spheroidal graphite particles (D50 is 18 μm) densified with fillers; wherein the weight ratio of fillers to (fillers + natural flake graphite) is 15:100;

[0098] (1-2) Mix the spheroidal graphite particles obtained in step (1-1) with pitch (the temperature of the pitch is 200°C) to obtain pitch-coated graphite particles; wherein the weight ratio of pitch to (pitch + spheroidal graphite particles) is 2.5:100;

[0099] (2) Carbonize the pitch-coated graphite particles obtained in step (1-2) (carbonization temperature is 1150°C, oxygen content in carbonization atmosphere is <150 ppm) to obtain a negative electrode active material (denoted as P2).

[0100] P2 is an ellipsoidal shape, which contains graphite particles (D50 of graphite particles is 18 μm) densified with fillers (graphite powder, D50 is 1.2 μm), and the outer surface of the graphite particles is coated with a carbon layer (the average thickness of the carbon layer is 40 nm); the content of fillers in the graphite particles is 7.8% by weight based on the total weight of P2; the content of graphite powder in the fillers is 100% by weight.

[0101] Example 3

[0102] (1-1) The natural flake graphite was added to a mixer, and a filler (artificial graphite fine powder-1) was added for mixing. Then, the obtained mixture was added to a spheroidization device for spheroidization treatment. Under the impact, friction and shearing action of the spheroidization wheel on the natural flake graphite, the filler was wrapped in the natural flake graphite, obtaining spheroidized graphite particles (D50 of 18 μm) with compacted fillers; wherein the weight ratio of the filler to (filler + natural flake graphite) was 10:100;

[0103] (1-2) The spheroidized graphite particles obtained in step (1-1) were mixed with pitch (temperature of the pitch was 200°C) to obtain pitch-coated graphite particles; wherein the weight ratio of the pitch to (pitch + spheroidized graphite particles) was 2.5:100.

[0104] (2) The pitch-coated graphite particles obtained in step (1-2) were subjected to carbonization treatment (carbonization temperature was 1150°C, oxygen content in the carbonization atmosphere was <150 ppm) to obtain a negative electrode active material (denoted as P3).

[0105] P3 had an ellipsoidal appearance, and contained graphite particles (D50 of 18 μm) with compacted fillers (graphite powder, D50 of 1.2 μm). The outer surface of the graphite particles was coated with a carbon layer (average thickness of 40 nm). The content of the fillers in the graphite particles was 5.5% by weight based on the total weight of P3. The content of the graphite powder in the fillers was 100% by weight.

[0106] Example 4

[0107] (1-1) The natural flake graphite was added to a mixer, and a filler (artificial graphite fine powder-1) was added for mixing. Then, the obtained mixture was added to a spheroidization device for spheroidization treatment. Under the impact, friction and shearing action of the spheroidization wheel on the natural flake graphite, the filler was wrapped in the natural flake graphite, obtaining spheroidized graphite particles (D50 of 18 μm) with compacted fillers; wherein the weight ratio of the filler to (filler + natural flake graphite) was 10:100;

[0108] (1-2) The spheroidized graphite particles obtained in step (1-1) were mixed with pitch (temperature of the pitch was 200°C) to obtain pitch-coated graphite particles; wherein the weight ratio of the pitch to (pitch + spheroidized graphite particles) was 2.5:100.

[0109] (2) The pitch-coated graphite particles obtained in step (1-2) were subjected to carbonization treatment (carbonization temperature was 1150°C, oxygen content in the carbonization atmosphere was <150 ppm) to obtain a negative electrode active material (denoted as P3).

[0110] P4 has an ellipsoidal appearance, and contains graphite particles (D50 of the graphite particles is 18 μm) in which fillers (graphite powder, D50 is 2.5 μm) are densified, and the outer surface of the graphite particles is coated with a carbon layer (average thickness of the carbon layer is 40 nm); the content of the fillers in the graphite particles is 5.5% by weight based on the total weight of P4; the content of the graphite powder in the fillers is 100% by weight.

[0111] Example 5

[0112] (1-1) The natural flake graphite is added into a mixer, and fillers (artificial graphite fine powder-1 and pitch at 200°C in a weight ratio of 99:1) are added for mixing, and then the obtained mixture is added into a spheroidization device for spheroidization treatment. Under the collision, friction and shearing action of the natural flake graphite on the spheroidization wheel, the fillers are wrapped into the natural flake graphite, to obtain spheroidized graphite particles (D50 is 18 μm) in which the fillers are densified; wherein the weight ratio of the fillers to (the fillers + the natural flake graphite) is 10:100; the weight of the pitch in step (1-1) is calculated based on the weight of the amorphous carbon converted after subsequent carbonization;

[0113] (1-2) The spheroidized graphite particles obtained in step (1-1) are mixed with pitch (temperature of the pitch is 200°C) to obtain pitch-coated graphite particles; wherein the weight ratio of the pitch to (the pitch + the spheroidized graphite particles) is 2.5:100;

[0114] (2) The mixture obtained in step (1-2) is subjected to carbonization treatment (carbonization temperature is 1150°C, oxygen content in the carbonization atmosphere is <150 ppm) to obtain a negative electrode active material (denoted as P5).

[0115] P5 has an ellipsoidal appearance, and contains graphite particles (D50 of the graphite particles is 18 μm) in which fillers (graphite powder, D50 is 1.2 μm; amorphous carbon, D50 is 3 μm) are densified, and the outer surface of the graphite particles is coated with a carbon layer (average thickness of the carbon layer is 40 nm); the content of the fillers in the graphite particles is 5.5% by weight based on the total weight of P5; the content of the graphite powder in the fillers is 99% by weight.

[0116] Example 6

[0117] (1-1) natural flake graphite is added to a mixer, and a filler (artificial graphite fine powder-1 and 200°C asphalt in a weight ratio of 89:11) is added and mixed, and then the resulting mixture is added to a spheroidization device for spheroidization treatment. Under the collision, friction and shearing action of the spheroidization wheel on the natural flake graphite, the filler is wrapped into the natural flake graphite to obtain spherical graphite particles (D50 is 18μm) with a filler densification; wherein the weight ratio of filler: (filler + natural flake graphite) is 10:100; the weight of the asphalt in step (1-1) is based on the weight of amorphous carbon converted after subsequent carbonization;

[0118] (1-2) mixing the spherical graphite particles obtained in step (1-1) with asphalt (the temperature of the asphalt is 200° C.) to obtain asphalt-coated graphite particles; wherein the weight ratio of asphalt to (asphalt + spherical graphite particles) is 2.5:100;

[0119] (2) The pitch-coated graphite particles obtained in step (1-2) were carbonized (carbonization temperature was 1150° C., and the oxygen content in the carbonization atmosphere was less than 150 ppm) to obtain a negative electrode active material (denoted as P6).

[0120] P6 has an ellipsoidal appearance and contains graphite particles (D50 of graphite particles is 18 μm) densified with fillers (graphite powder, D50 is 1.2 μm; amorphous carbon, D50 is 3 μm). The surface of the graphite particles is covered with a carbon layer (the average thickness of the carbon layer is 40 nm). Based on the total weight of P6, the content of filler in the graphite particles is 5.5 wt%; the content of graphite powder in the filler is 89 wt%.

[0121] Comparative Example 1

[0122] The method of Example 1 was followed, except that no filler was added during the spheroidization of the natural flake graphite in step (1-1). Unfilled spherical graphite particles were obtained in step (1-1), and steps (1-2) and (2) were sequentially performed on the unfilled spherical graphite particles. Other operating procedures and parameters were the same as in Example 1, yielding a negative electrode active material (denoted as DP1).

[0123] DP1 has an ellipsoidal appearance and contains spherical graphite particles (D50 of graphite particles is 18μm. DP1 was ion cut and then SEM tested. The results are as follows Figure 2 As shown, in Figure 2 As can be seen in the figure, there is no filler in the pores inside the graphite particles in DP1), and the surface of the graphite particles is covered with a carbon layer (the average thickness of the carbon layer is 40 nm).

[0124] Comparative Example 2

[0125] (1-1) Add natural flake graphite into a mixer, and add filler (phenolic resin) for mixing, then add the obtained mixture into a spheroidization device for spheroidization treatment. Under the collision, friction and shearing action of the spheroidization wheel on the natural flake graphite, the filler is wrapped into the natural flake graphite, to obtain spheroidized graphite particles (D50 is 18 μm) with compact filler; wherein the weight ratio of the filler to (filler + natural flake graphite) is 20:100; the weight of the phenolic resin in step (1-1) is based on the weight of the amorphous carbon converted after subsequent carbonization;

[0126] (1-2) Mix the spheroidized graphite particles obtained in step (1-1) with pitch (the temperature of the pitch is 200 ℃) to obtain pitch-coated graphite particles; wherein the weight ratio of the pitch to (pitch + spheroidized graphite particles) is 2.5:100;

[0127] (2) Carbonize the pitch-coated graphite particles obtained in step (1-2) (carbonization temperature is 1150 ℃, oxygen content in carbonization atmosphere is <150 ppm) to obtain a negative electrode active material (denoted as DP2).

[0128] DP2 has an ellipsoidal appearance, which contains graphite particles (D50 of the graphite particles is 18 μm) with compact filler (amorphous carbon, D50 is 3 μm), and the outer surface of the graphite particles is coated with a carbon layer (the average thickness of the carbon layer is 40 nm); the content of the filler in the graphite particles is 9.8% by weight based on the total weight of DP2; the content of amorphous carbon in the filler is 100% by weight.

[0129] Comparative Example 3

[0130] According to the method of Example 1, the difference is that no filler is added during the spheroidization process of the natural flake graphite in step (1-1), and the spheroidized graphite particles without filler are obtained, and the spheroidized graphite particles without filler are mixed with pitch (the temperature of the pitch is 200 ℃) in a mixer (wherein the weight ratio of the pitch to (pitch + spheroidized graphite particles without filler) is 2.5:100), then the mixture is placed in an elastic rubber tank for isostatic pressing, and finally the isostatic pressing product is subjected to step (2). Other operation processes and parameters are the same as those of Example 1, to obtain a negative electrode active material (denoted as DP3).

[0131] DP3 has an ellipsoidal appearance, which contains spheroidized graphite particles (the average particle size of the graphite particles is 18 μm, which has no filler inside and the pores have been compacted after isostatic pressing), and the outer surface of the graphite particles is coated with a carbon layer (the average thickness of the carbon layer is 40 nm).

[0132] Test Example

[0133] The negative electrode active materials P1-P6 and DP1-DP3 prepared by the above Examples 1-6 and Comparative Examples 1-3, respectively, were used to prepare negative electrodes, which were then used to prepare batteries, and the high-rate charge-discharge performance, cycle performance, and expansion degree of the batteries were tested.

[0134] Preparation of the negative electrode: The negative electrode active materials P1-P6 and DP1-DP3 were mixed with a conductive agent (ketjen black), a thickening agent (sodium carboxymethyl cellulose), a binder (styrene-butadiene rubber), and the like in a weight ratio of 96:1:1:2 to obtain a mixed powder, and then the mixed powder was stirred with deionized water by a vacuum stirrer to prepare a negative electrode slurry and uniformly coated on a carbon-coated copper foil. After baking and rolling, the negative electrode (N1-N6, DN1-DN3, respectively) was prepared.

[0135] Preparation of the positive electrode: Lithium iron phosphate (LiFePO4), a conductive agent (ketjen black), and a binder (polyvinylidene fluoride) were mixed in a weight ratio of 96:1.5:2.5 to obtain a mixed powder, and then the mixed powder was stirred with N-methyl pyrrolidone (NMP) by a vacuum stirrer to prepare a positive electrode slurry and uniformly coated on an aluminum foil. After baking and rolling, the positive electrode was prepared.

[0136] Preparation of the electrolyte: Ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to prepare the electrolyte.

[0137] The above positive electrode, negative electrode (N1-N6, DN1-DN3), electrolyte, and polypropylene separator were used to prepare 1.5 Ah laminated lithium batteries (B1-B6, DB1-DB3, respectively), and the batteries were subjected to high-rate charge-discharge tests and cycle performance tests, wherein,

[0138] Conditions for the high-rate charge-discharge test:

[0139] (1) The battery capacity was calibrated at 25°C by charging and discharging at 0.1C.

[0140] (2) The discharge efficiency of the battery was calculated by charging at 0.1C to full state and then discharging at 3C.

[0141] (3) The charge efficiency of the battery was calculated by charging at 3C to full state and then discharging at 0.1C.

[0142] Conditions for the cycle performance test:

[0143] The battery was installed on a displacement sensor to measure the thickness, and the capacity retention rate of the battery was calculated by charging and discharging at 1C at 25°C for 1000 cycles. After the above cycle, the displacement sensor data was recorded, and the thickness change rate of the battery was calculated based on the initial thickness and the thickness after the cycle.

[0144] The test results are shown in Table 1.

[0145] Table 1

[0146]

[0147] As can be seen from Table 1, the negative active material provided by the application uses graphite powder as the main filler of the pores of the graphite particles, which can effectively inhibit the expansion of the negative electrode during the battery cycle process. The thickness change rate of the battery after 1000 cycles under the above test conditions is less than 0.8%, which is significantly lower than that of DB1-DB3. Due to the effective solution of the expansion problem of the natural graphite negative electrode, B1-B6 shows higher cycle life, the capacity retention rate after 1000 cycles under the condition of 25℃ and 1C charge-discharge is higher than 86%, and has excellent rate performance, the charge-discharge efficiency under the condition of 25℃ and 3C rate is higher than 80%.

[0148] The above describes the preferred embodiments of the application, but the application is not limited thereto. Within the technical concept of the application, various simple modifications can be made to the technical solutions of the application, including the combination of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as disclosed by the application and fall within the protection scope of the application.

Claims

1. A negative electrode active material, characterized in that The negative electrode active material includes: graphite particles, and a carbon layer covering the graphite particles; There are pores inside the graphite particles, and the pores are filled with fillers; The filler comprises graphite powder and optionally amorphous carbon; In the filler, the content of the graphite powder is 90-100% by weight.

2. The negative electrode active material according to claim 1, wherein The particle shape of the negative electrode active material is spherical or ellipsoidal.

3. The negative electrode active material according to claim 2, wherein The graphite particles are spherical graphite particles.

4. The negative electrode active material according to any one of claims 1 to 3, wherein The average particle size of the graphite particles is 8-35 μm.

5. The negative electrode active material according to claim 4, wherein The average particle size of the graphite particles is 10-30 μm.

6. The negative electrode active material according to any one of claims 1 to 3, wherein The thickness of the carbon layer is 1-100 nm.

7. The negative electrode active material according to any one of claims 1 to 3, wherein The filler may be present in the negative electrode active material in an amount of 5-15 wt % based on the total weight of the negative electrode active material.

8. The negative electrode active material according to claim 7, wherein The filler may be present in the negative electrode active material in an amount of 7-10 wt % based on the total weight of the negative electrode active material.

9. The negative electrode active material according to any one of claims 1 to 3, wherein The content of the graphite powder in the filler is 95-100 wt % based on the total weight of the filler.

10. The negative electrode active material according to any one of claims 1 to 3, wherein The average particle size of the filler is 0.5-3 μm; and / or, the graphitization degree of the graphite powder is ≥94%; And / or, the graphite powder is artificial graphite fine powder obtained in a powder screening process during the preparation of artificial graphite.

11. The negative electrode active material according to claim 10, wherein The average particle size of the filler is 1-2 μm.

12. A method for preparing a negative electrode active material, characterized in that: include: (1) Granulating natural graphite raw materials and fillers together to obtain graphite particles; (2) mixing the graphite particles with an organic carbon source to obtain graphite particles coated with an organic carbon source; (3) carbonizing the graphite particles coated with the organic carbon source to obtain a negative electrode active material; Wherein, the internal pores of the graphite particles are filled with the filler; The filler comprises graphite powder, optional asphalt and optional resin; In the filler, the content of the graphite powder is 90-100% by weight.

13. The preparation method according to claim 12, wherein The granulation process includes: The natural graphite raw material is spheroidized, and the filler is added during the spheroidization process so that the natural graphite raw material wraps the filler to obtain graphite particles.

14. The preparation method according to claim 12 or 13, wherein The natural graphite raw material is natural flake graphite; And / or, the weight ratio of the filler: (the filler + the natural graphite raw material) is (10-30):100; And / or, the organic carbon source is selected from asphalt and / or resin.

15. The preparation method according to claim 12 or 13, wherein In the filler, the content of the graphite powder is 95-100% by weight; and / or, the average particle size of the filler is 0.5-3 μm; and / or, the graphitization degree of the graphite powder is ≥94%; And / or, the graphite powder is artificial graphite fine powder obtained in a powder screening process during the preparation of artificial graphite.

16. The preparation method according to claim 15, wherein The average particle size of the filler is 1-2 μm.

17. The preparation method according to claim 12 or 13, wherein The weight ratio of the organic carbon source: (the graphite particles + the organic carbon source) is (0.5-5):100; And / or, the carbonization treatment conditions include: a temperature of 1100-1200° C., and an oxygen content in the carbonization atmosphere less than 400 ppm.

18. A negative electrode active material prepared by the method according to any one of claims 12 to 17.

19. A negative electrode comprising a negative electrode current collector and an active material layer disposed on the negative electrode current collector; in, The active material layer contains the negative electrode active material according to any one of claims 1 to 11 and 18.

20. A battery comprising the negative electrode according to claim 19.

21. The battery according to claim 20, wherein The battery is a lithium ion battery or a sodium ion battery.

22. An electrical device comprising the battery according to claim 20 or 21.

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