Negative electrode material and preparation method therefor, and lithium-ion battery

Abstract

A negative electrode material and a preparation method therefor, and a lithium-ion battery containing the negative electrode material. By observing an SEM image, the negative electrode material comprises carbonaceous particles having pores, and the length-diameter ratio of at least some of the pores is greater than 3; and by randomly observing 100 pores in total, the number of pores having a pore size of 0.1 μm-0.5 μm accounts for 60% or more of the total number of pores, and the maximum pore size of the pores is less than or equal to 3 μm. The negative electrode material has elongated pores and most of the pores have a small pore size, indicating that the pores inside the carbonaceous particles have small volume and the number of macropores is small, so that the carbonaceous particles have excellent compactness, thereby improving the capacity performance, expansion performance, and cycle performance of the negative electrode material.

Description

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

[0001] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office on June 30, 2023, with application number 202310798360X and application name “Negative electrode material and preparation method thereof, lithium-ion battery”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of negative electrode materials, and in particular to negative electrode materials and preparation methods thereof, and lithium-ion batteries. Background Art

[0003] As global warming intensifies, controlling CO2 emissions has become a major and urgent challenge for human society. Against the backdrop of national goals for carbon neutrality and carbon peak, the development of new energy vehicles is an inevitable trend. Governments around the world have introduced various preferential policies and subsidies to promote the development of new energy vehicles. Driven by these policies, electric vehicles powered by lithium-ion batteries have seen rapid growth. Anode materials are a crucial component of lithium-ion batteries, directly determining their performance and price.

[0004] Currently, graphite remains the dominant negative electrode material. Depending on its source, graphite can be divided into artificial graphite and natural graphite. Artificial graphite, with its excellent cycle stability, dominates the power battery market. However, its production requires a costly graphitization process, and the continued rise in raw material prices means its price is unlikely to fall and will instead continue to rise. To further reduce negative electrode material costs, researchers are turning their attention to natural graphite. Natural graphite's greatest advantage is that it doesn't undergo a graphitization process during its preparation, resulting in a low price. However, its cycle stability and expansion performance are poor in power batteries.

[0005] Therefore, how to improve the expansion performance and cycle stability of natural graphite has become an important research topic in the field of negative electrode materials. Natural graphite negative electrode materials are usually made from natural flake graphite raw materials through spheroidization and modification processes. During the production process of natural graphite negative electrode materials, the spheroidization process inevitably leads to the formation of pores inside the particles. Usually, the pores inside spherical natural graphite particles are large, mostly on the micron level. The presence of these internal pores leads to the problems of large expansion and poor cycle stability of natural graphite negative electrode materials. Usually, the expansion performance and cycle performance of the material are improved by reducing the size of the internal pores. However, in the actual production process, it is difficult to reduce the pores inside the graphite particles through the spheroidization process. Instead, the internal pores of the particles are reduced in the back-end process of the spheroidization. Moreover, since some of the pores in the spherical natural graphite particles are closed pores, the conventional filling process is not easy to control the density of the pores inside the particles. In addition, the filled graphite particles introduce a phase different from the original natural flake graphite material crystal structure, resulting in an increase in grain boundaries and a decrease in kinetic performance, which cannot improve the electrochemical performance of the natural graphite negative electrode material as a whole.

[0006] Summary of the Invention

[0007] The present application provides a negative electrode material and a preparation method thereof, and a lithium-ion battery, which can improve the capacity performance, expansion performance and cycle performance of the negative electrode material.

[0008] In the first aspect, an embodiment of the present application provides a negative electrode material. By observing the SEM image, the negative electrode material includes carbonaceous particles with pores, and the aspect ratio of at least some of the pores is greater than 3. The total number of randomly observed pores is 100, and the number of pores with a pore diameter of 0.1μm to 0.5μm accounts for greater than or equal to 60% of the total number of pores.

[0009] In some embodiments, the maximum pore size of the pores is less than or equal to 3 μm.

[0010] In some embodiments, the carbonaceous particulates include natural graphite.

[0011] In some embodiments, the natural graphite includes at least one of flake graphite and microcrystalline graphite.

[0012] In some embodiments, the carbonaceous particles have a median particle size of 5 μm to 25 μm.

[0013] In some embodiments, the negative electrode material further includes a coating layer covering at least a portion of the surface of the carbonaceous particles.

[0014] In some embodiments, the coating layer is made of a carbon material.

[0015] In some embodiments, the carbon material includes at least one of soft carbon, crystalline carbon, amorphous carbon, and hard carbon.

[0016] In some embodiments, the median particle size D50 of the negative electrode material satisfies: 5 μm <D50<25μm。

[0017] In some embodiments, the sphericity Sh(10%) of the negative electrode material is ≥0.75.

[0018] In some embodiments, the sphericity Sh(50%) of the negative electrode material is ≥0.83.

[0019] In some embodiments, the sphericity Sh(90%) of the negative electrode material is ≥0.88.

[0020] In some embodiments, the pore volume of the negative electrode material is 0.05 mL / g to 0.11 mL / g.

[0021] In some embodiments, the specific surface area of ​​the negative electrode material is 0.5 m 2 / g~3.5m 2 / g.

[0022] In a second aspect, an embodiment of the present application provides a method for preparing a negative electrode material, comprising the following steps:

[0023] Providing a natural graphite precursor, wherein the median particle size of the natural graphite precursor is 5 μm to 25 μm, the sphericity Sh (10%) of the natural graphite precursor is ≥ 0.75, the sphericity Sh (50%) of the natural graphite precursor is ≥ 0.83, and the sphericity Sh (90%) of the natural graphite precursor is ≥ 0.88;

[0024] The natural graphite precursor is densified so that the obtained negative electrode material includes carbonaceous particles with pores, at least some of the pores have an aspect ratio greater than 3, and when a total number of randomly observed pores is 100, the number of pores with a pore diameter of 0.1 μm to 0.5 μm accounts for greater than or equal to 60% of the total number of pores.

[0025] In some embodiments, the natural graphite precursor is prepared by the following method: subjecting natural graphite to a shaping treatment.

[0026] In some embodiments, the natural graphite includes at least one of flake graphite and microcrystalline graphite.

[0027] In some embodiments, the densification process comprises at least one of cold isostatic pressing, hot isostatic pressing, molding, and hot pressing.

[0028] In some embodiments, the pressure of the densification treatment is 20 MPa to 200 MPa.

[0029] In some embodiments, the densification treatment lasts for 1 min to 200 min.

[0030] In some embodiments, the temperature of the densification treatment is 25°C to 1500°C.

[0031] In some embodiments, before the natural graphite precursor is subjected to densification treatment, the process further includes: mixing a coating material with the natural graphite precursor, and then densifying the mixture, wherein the coating material includes at least one of a polymer, a resin, coal tar, petroleum asphalt, mesophase asphalt, coal tar and heavy oil.

[0032] In some embodiments, after obtaining the negative electrode material, the method further includes: mixing the negative electrode material and a coating material and then performing heat treatment.

[0033] In some embodiments, the coating material includes at least one of a high molecular weight polymer, a resin, coal pitch, petroleum pitch, mesophase pitch, coal tar, and heavy oil.

[0034] In some embodiments, the mass ratio of the negative electrode material to the coating material is 100:(2-100).

[0035] In some embodiments, the heat treatment temperature is 800°C to 3000°C.

[0036] In some embodiments, the heat treatment is performed in a protective gas atmosphere, and the protective gas includes at least one of helium, neon, argon, nitrogen, and krypton.

[0037] In some embodiments, the heat treatment time is 1 hour to 24 hours.

[0038] In a third aspect, an embodiment of the present application provides a lithium-ion battery, wherein the lithium-ion battery comprises the negative electrode material described in the first aspect or the negative electrode material prepared by the preparation method described in the second aspect.

[0039] The technical solution of the present application has at least the following beneficial effects: the negative electrode material of the present application includes carbonaceous particles with pores, and the aspect ratio of at least some of the pores is greater than 3, indicating that the shape of the pores in the carbonaceous particles of the present application is elongated. The presence of elongated pores indicates that the material inside the carbonaceous particles is arranged in order, and the scaly graphite layers inside the particles are in close contact, which is beneficial to improving the capacity performance of the negative electrode material; the present application further limits the number of pores with a pore diameter of 0.1μm to 0.5μm to a ratio greater than or equal to 60% of the total number of pores, indicating that the carbonaceous particles with pores in the present application have fine pores, and the porosity of the carbonaceous particles is low, indicating that the carbonaceous particles have a densified structure, so that the negative electrode material can produce less expansion during the charging and discharging process. The negative electrode material of the present application has elongated pores and most of the pores have a small pore diameter, indicating that the internal pore volume of the carbonaceous particles of the present application is small and the number of large pores is small, so that the carbonaceous particles have excellent density, thereby improving the capacity performance, expansion performance and cycle performance of the negative electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The present application is further described below with reference to the accompanying drawings and examples.

[0041] FIG1 is a flow chart of the preparation of the negative electrode material of the present application;

[0042] FIG2 is a SEM image of the negative electrode material prepared in Example 1 of the present application;

[0043] FIG3 is a SEM image of the negative electrode material prepared in Example 2 of the present application;

[0044] FIG4 is a SEM image of the negative electrode material prepared in Example 3 of the present application;

[0045] FIG5 is a SEM image of the negative electrode material prepared in Example 4 of the present application;

[0046] FIG6 is a SEM image of the negative electrode material prepared in Comparative Example 1 of the present application;

[0047] FIG7 is a SEM image of the negative electrode material prepared in Comparative Example 2 of the present application;

[0048] FIG8 is a SEM image of the negative electrode material prepared in Comparative Example 3 of the present application. DETAILED DESCRIPTION

[0049] In order to better understand the technical solutions of this specification, the embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0050] It should be clear that the embodiments described are only part of the embodiments of this specification, not all of the embodiments. Based on the embodiments in this specification, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this specification.

[0051] The terms used in the examples of this application are for the purpose of describing specific embodiments only and are not intended to limit this specification. The singular forms "a," "an," "the," and "the" used in the examples of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0052] It should be understood that the term "and / or" used in this application merely describes an association relationship between associated objects, indicating that three possible relationships exist. For example, ΔJ and / or B can represent the existence of ΔJ alone, the existence of both ΔJ and B, and the existence of B alone. Furthermore, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0053] In the field of anode materials, natural graphite primarily refers to spherical natural graphite obtained by processing flake graphite. The main reason for the poor cycling performance of this type of material is that during the lithium insertion process, organic molecules in the electrolyte co-intercalate into the spherical natural graphite, causing structural damage to the graphite material. As a result, natural graphite anode materials have a shorter cycle life than artificial graphite and also experience a greater expansion rate during cycling. Currently, a surface coating method is commonly used to coat the natural graphite with a layer of amorphous carbon to isolate the electrolyte and natural graphite, thereby improving its performance.

[0054] At present, the main method used for surface coating of natural graphite is solid-phase coating. The solid-phase coating method is: first, natural graphite and a coating modifier are mixed by physical mixing, and then, during the carbonization process, the coating modifier undergoes a liquefaction process, and the liquefied coating modifier can flow for self-coating. This method is simple to operate and low in cost, and is widely used in the modification of natural graphite negative electrode materials. However, due to the continuous volatilization of small molecules in the modifier during this process, the liquefaction process is short and the time cannot be controlled. The liquid coating agent has no way to completely cover the outer surface of natural graphite, especially the surface of flake graphite inside spherical graphite. As a result, during the cycle, the electrolyte will gradually penetrate into these uncoated natural graphite surfaces, continuously generate SEI film and the electrolyte is continuously embedded in the natural graphite layer structure, consuming a large amount of active lithium and destroying the natural graphite structure, resulting in continuous capacity decay.

[0055] In view of this, the present application provides a negative electrode material, please refer to Figures 1 to 4. By observing the SEM image of the cross-section of the negative electrode material, the negative electrode material includes carbonaceous particles with pores, the aspect ratio of the pores in the negative electrode material is greater than 3, and the total number of randomly observed pores is 100. The proportion of pores with a pore diameter of 0.1μm to 0.5μm accounts for greater than or equal to 60% of the total number of pores.

[0056] In the above scheme, the negative electrode material of the present application includes carbonaceous particles with pores, and the aspect ratio of the pores is greater than 3, indicating that the shape of the pores in the carbonaceous particles of the present application is elongated. The presence of elongated pores indicates that the material inside the carbonaceous particles is arranged in order, and the scaly graphite layers inside the particles are in close contact, which is beneficial to improving the capacity performance of the negative electrode material; the present application further limits the number of pores with a pore diameter of 0.1μm to 0.5μm to a ratio of greater than or equal to 60% of the total number of pores, indicating that the carbonaceous particles with pores in the present application have fine pores, and the porosity of the carbonaceous particles is low, indicating that the carbonaceous particles have a densified structure, so that the negative electrode material can produce less expansion during the charge and discharge process. The negative electrode material of the present application has elongated pores and most of the pores have a small pore diameter, indicating that the internal pore volume of the carbonaceous particles of the present application is small, and the number of large pores is small, so that the carbonaceous particles have good density, thereby improving the capacity performance, expansion performance and cycle performance of the negative electrode material.

[0057] In this application, the pore diameter and pore length are measured by scanning electron microscopy. The pore shape of the carbonaceous particles described in this application is elongated, which means that the pores are regular linear and the ratio of the pore length to the diameter is greater than 3.

[0058] In some embodiments, the number of pores with a pore size of 0.1 μm to 0.5 μm accounts for more than or equal to 60% of the total number of pores, and can specifically be 60%, 65%, 70%, 75%, 80%, 85% or 90%, etc., and of course it can also be other values ​​within the above range, which is not limited by the present application. Within the above-mentioned limited range, it is shown that the carbonaceous particles of the present application have relatively small pores, and the diameters of most of the pores are in the range of 0.1 μm to 0.5 μm, indicating that the carbonaceous particles have a densified structure and a low porosity, which enables the negative electrode material to produce less expansion during the charge and discharge process, which is beneficial to improving the expansion performance and cycle performance of the negative electrode material. If the number of pores with a pore size of 0.1 μm to 0.5 μm accounts for less than 60% of the total number of pores, there are more pores with larger pores in the carbonaceous particles, resulting in poor expansion performance of the negative electrode material.

[0059] In some embodiments, the maximum pore diameter is less than or equal to 3 μm, and specifically can be 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, or 3 μm, etc., and can also be other values ​​within the above range, which is not limited by this application. If the maximum pore diameter is greater than 3 μm, it means that the contact between the materials within the carbonaceous particles is relatively loose, the compaction effect is poor, and the expansion performance and cycle performance of the negative electrode material are poor.

[0060] In some embodiments, the median particle size of the carbonaceous particles is 5 μm to 25 μm, specifically, it can be 5 μm, 8 μm, 10 μm, 13 μm, 15 μm, 18 μm, 20 μm, 23 μm or 25 μm. Of course, it can also be other values within the above range, and the present application does not limit this here.

[0061] In some embodiments, the carbonaceous particles include natural graphite. Compared with artificial graphite, natural graphite has a lower cost and excellent specific capacity.

[0062] In some embodiments, the natural graphite includes at least one of flake graphite and microcrystalline graphite.

[0063] In some embodiments, the negative electrode material further includes a coating layer covering at least a part of the surface of the carbonaceous particles. By arranging the coating layer on the surface of the carbonaceous particles, on the one hand, it can reduce the side reactions caused by the electrolyte entering the interior of the negative electrode material, resulting in a decrease in the first efficiency and capacity. On the other hand, it can alleviate the volume expansion of the carbonaceous particles, reduce the volume expansion of the entire negative electrode material, and reduce the swelling of the electrode sheet.

[0064] In some embodiments, the material of the coating layer includes a carbon material.

[0065] In some embodiments, the carbon material includes at least one of soft carbon, crystalline carbon, amorphous carbon and hard carbon.

[0066] In some embodiments, the median particle size D50 of the negative electrode material satisfies: 5 μm < D50 < 25 μm. Specifically, the median particle size D50 of the negative electrode material can be 6 μm, 8 μm, 10 μm, 13 μm, 15 μm, 18 μm, 20 μm, 22 μm or 24 μm, etc. Of course, it can also be other values within the above range, and the present application does not limit this here.

[0067] In some embodiments, the sphericity Sh(10%) of the negative electrode material is ≥ 0.75, specifically, it can be 0.75, 0.75, 0.78, 0.80, 0.83, 0.85, 0.88, 0.90 or 0.95, etc. Of course, it can also be other values within the above range, and the present application does not limit this here. The sphericity Sh(%) is the sphericity corresponding to when the particle size distribution number reaches 10%. Its physical meaning is that the particles with a sphericity less than (or greater than) it account for 10%.

[0068] In some embodiments, the sphericity Sh(50%) of the negative electrode material is ≥ 0.83, and can specifically be 0.83, 0.85, 0.88, 0.90, or 0.95, etc., and can of course be other values ​​within the above range, which are not limited in this application. The sphericity Sh(10%) refers to the sphericity corresponding to the particle size distribution number reaching 50%. Its physical meaning is that particles with a sphericity less than (or greater than) this value account for 50%.

[0069] In some embodiments, the sphericity Sh(90%) of the negative electrode material is ≥ 0.88, and can specifically be 0.88, 0.90, or 0.95, etc., and can of course be other values ​​within the above range, which are not limited in this application. The sphericity Sh(90%) refers to the sphericity corresponding to the 90th percentile of the particle size distribution. Its physical meaning is that 90% of the particles have a sphericity less than (or greater than) this value.

[0070] The negative electrode material of the present application has a high sphericity and a narrow sphericity distribution, and the internal materials in the natural graphite particle negative electrode material are arranged in an orderly manner, and the flake graphite layers inside the particles are in close contact, so that the negative electrode material of the present application has a small specific surface area and a large tap density, which is beneficial to inhibiting the expansion of the negative electrode material and improving the expansion performance and cycle stability of the negative electrode material.

[0071] In some embodiments, the pore volume of the negative electrode material is 0.05 mL / g to 0.11 mL / g, specifically 0.05 mL / g, 0.06 mL / g, 0.07 mL / g, 0.08 mL / g, 0.09 mL / g, 0.10 mL / g, or 0.11 mL / g, etc., and of course other values ​​within the above range are also possible, and this application is not limited thereto. The small pore volume of the negative electrode material of the present application indicates that the internal contact of the negative electrode material is relatively close, which is conducive to improving the expansion performance of the negative electrode material.

[0072] In some embodiments, the specific surface area of ​​the negative electrode material is 0.5 m 2 / g~3.5m 2 / g, specifically 0.5m 2 / g, 0.7m 2 / g, 1.0m 2 / g, 1.3m 2 / g, 1.5m 2 / g, 1.8m 2 / g, 2.3m 2 / g, 2.8m 2 / g, 3.0m 2 / g or 3.5m 2 / g, etc., and of course, it can also be other values ​​within the above range, which is not limited in this application.

[0073] The present application also provides a method for preparing the above-mentioned negative electrode material, as shown in FIG1 , which is a flow chart for preparing the negative electrode material of the present application, including the following steps:

[0074] Providing a natural graphite precursor, wherein the natural graphite precursor meets the following requirements: the median particle size of the natural graphite precursor is 5 μm to 25 μm, the sphericity Sh (10%) of the natural graphite precursor is ≥ 0.75, the sphericity Sh (50%) is ≥ 0.83, and the sphericity Sh (90%) is ≥ 0.88;

[0075] The natural graphite precursor is densified so that the obtained negative electrode material includes carbonaceous particles with pores, at least some of the pores have an aspect ratio greater than 3, and the number of pores with a diameter of 0.1μm to 0.5μm accounts for more than or equal to 60% of the total number of pores.

[0076] In the above scheme, the present application adopts a natural graphite precursor with a specific particle size and morphology, and then densifies the natural graphite precursor so that the negative electrode material of the present application has elongated pores and the pore size of most of the pores is small, indicating that the carbonaceous particles prepared by the present application have higher compactness, and because the natural graphite precursor of the present application has a higher sphericity, the densification process has little effect on the morphology of the material (i.e., the sphericity is almost the same before and after the densification process), so that the negative electrode material prepared by the present application has high sphericity while having elongated pores inside and smaller pore size, thereby improving the capacity performance, expansion performance and cycle performance of the negative electrode material. The preparation process of the present application is simple. By using high-sphericity natural graphite raw materials and coordinating specific process conditions, the pores of the natural graphite particles are not filled or filled in small amounts while reducing the internal pores to a specified level, thereby being able to solve the problems of large expansion and poor cycle performance of natural graphite negative electrode materials in the prior art.

[0077] If the sphericity of the natural graphite precursor is smaller than the specified range of this application, the pores inside the natural graphite precursor particles will be compressed in the subsequent densification process, resulting in a smaller sphericity and a worse morphology. Although the pores inside the material are small and the scaly graphite layers inside the particles are in close contact, it is impossible to obtain a negative electrode material with excellent expansion performance and cycle performance.

[0078] The preparation method of the present application is described in detail below with reference to the examples:

[0079] Step S100: providing a natural graphite precursor.

[0080] Specifically, the natural graphite precursor is prepared by the following method: natural graphite is subjected to shaping treatment to obtain the natural graphite precursor.

[0081] In some embodiments, the natural graphite includes at least one of flake graphite and microcrystalline graphite.

[0082] In some embodiments, the shaping equipment includes at least one of a mechanical pulverizer, a jet mill, and a crusher.

[0083] In some embodiments, the particle size of the natural graphite precursor is 5 μm to 25 μm, specifically 5 μm, 8 μm, 10 μm, 13 μm, 15 μm, 18 μm, 20 μm, 23 μm or 25 μm. Of course, it can also be other values ​​within the above range, which is not limited in this application.

[0084] In some embodiments, the sphericity Sh (10%) of the natural graphite precursor is ≥ 0.75, and specifically can be 0.75, 0.75, 0.78, 0.80, 0.83, 0.85, 0.88, 0.90 or 0.95, etc., and of course can also be other values ​​within the above range, which is not limited in this application.

[0085] In some embodiments, the sphericity Sh(50%) of the natural graphite precursor is ≥0.83, specifically 0.83, 0.85, 0.88, 0.90 or 0.95, etc. Of course, it can also be other values ​​within the above range, which is not limited in this application.

[0086] In some embodiments, the sphericity Sh (90%) of the natural graphite precursor is ≥ 0.88, specifically 0.88, 0.90, or 0.95, etc., and certainly other values ​​within the above range, which is not limited in this application.

[0087] The natural graphite precursor of the present application has a high sphericity, which is beneficial to suppressing the expansion of the negative electrode material and improving the expansion performance of the negative electrode material.

[0088] Step S200, densifying the natural graphite precursor so that the obtained negative electrode material includes carbonaceous particles with pores, at least some of the pores have an aspect ratio greater than 3, and the total number of randomly observed pores is 100, the proportion of pores with a pore diameter of 0.1 μm to 0.5 μm in the total number of pores is greater than or equal to 60%, and the maximum pore diameter is less than or equal to 3 μm.

[0089] The present application densifies graphite within a specific sphericity range to transform a natural graphite precursor into carbonaceous particles in which the flake graphite layers inside the particles are in close contact, the particles have elongated pores, and most of the pores have small pore sizes. This indicates that the carbonaceous particles of the present application have a small internal pore volume and a small number of large pores, so that the carbonaceous particles have excellent density, thereby improving the capacity performance, expansion performance and cycle performance of the negative electrode material.

[0090] In some embodiments, the densification process comprises at least one of cold isostatic pressing, warm isostatic pressing, hot isostatic pressing, compression molding, and hot press forming.

[0091] In some embodiments, the pressure of the cold isostatic pressing densification treatment is 60 MPa to 200 MPa, specifically 60 MPa, 80 MPa, 100 MPa, 120 MPa, 150 MPa, 180 MPa or 200 MPa, etc. Of course, it can also be other values ​​within the above range, and this application does not limit it here.

[0092] In some embodiments, the pressure for densification without cold isostatic pressing is 20 MPa to 200 MPa, specifically 20 MPa, 60 MPa, 80 MPa, 100 MPa, 120 MPa, 150 MPa, 180 MPa, or 200 MPa, etc., and other values ​​within the above range are also possible, and this application is not limited thereto. That is, the densification pressure for warm isostatic pressing, hot isostatic pressing, molding, and hot pressing is 20 MPa to 200 MPa.

[0093] In some embodiments, the time for the densification treatment is 1 min to 200 min, specifically 1 min, 10 min, 50 min, 100 min, 150 min or 200 min, etc. Of course, it can also be other values ​​within the above range, and this application does not limit it here.

[0094] In some embodiments, the temperature of the densification treatment is 25°C to 1500°C, specifically 25°C, 50°C, 100°C, 300°C, 500°C, 800°C, 1000°C, 1200°C or 1500°C, etc. Of course, it can also be other values ​​within the above range, and this application does not limit it here.

[0095] By adopting the above-mentioned densification process, the internal pores of a suitable natural graphite precursor can be squeezed and reduced under the action of pressure, so that a negative electrode material can be obtained in which the pore aspect ratio is greater than 3, the proportion of pores with a pore diameter of 0.1μm to 0.5μm in the total number of pores is greater than or equal to 60%, and the maximum pore diameter is less than or equal to 3μm.

[0096] In some embodiments, the densification process further includes a step of crushing the obtained material.

[0097] In some embodiments, the median particle size of the densified material after crushing is 5 μm to 25 μm. It can be understood that the densification treatment only has a greater impact on the pores inside the natural graphite precursor, but has little effect on the particle size of the material. Therefore, the median particle size of the crushed material is also controlled to be 5 μm to 25 μm.

[0098] In some embodiments, before the natural graphite precursor is subjected to densification treatment, the process further includes: a step of mixing the coating material with the natural graphite precursor, and then subjecting the above-mentioned mixture to densification treatment, that is, before the densification treatment, the coating material is first covered on at least part of the surface of the natural graphite precursor, and then subjected to densification treatment, or, while the natural graphite precursor is subjected to densification treatment, a coating layer is formed on the surface of the natural graphite precursor, or, the natural graphite precursor is first subjected to densification treatment, and then a coating layer is formed on the surface of the natural graphite precursor. The order of the above steps can be adjusted according to actual conditions and is not specifically limited thereto.

[0099] In some embodiments, the coating material includes a carbon material. Preferably, the carbon material includes a carbon material having a softening point of 20°C to 300°C.

[0100] In some embodiments, the coating material includes at least one of a high molecular weight polymer, a resin, coal pitch, petroleum pitch, mesophase pitch, coal tar, and heavy oil.

[0101] In some embodiments, the mass ratio of the natural graphite precursor to the coating material is 100:(2-100), specifically 100:2, 100:10, 100:20, 100:50, 100:80 or 100:100, etc. Of course, it can also be other values ​​within the above range, and this application is not limited thereto.

[0102] Step S300: mixing the negative electrode material and the coating material obtained in step S200 and then performing heat treatment.

[0103] It is understandable that after the natural graphite precursor and the coating material are mixed and then subjected to densification treatment in step S200, step S300 can be omitted.

[0104] In some embodiments, the coating material includes a carbon material. Preferably, the carbon material includes a carbon material having a softening point of 20°C to 300°C.

[0105] In some embodiments, the coating material includes at least one of a high molecular weight polymer, a resin, coal pitch, petroleum pitch, mesophase pitch, coal tar, and heavy oil.

[0106] In some embodiments, the mass ratio of the negative electrode material to the coating material is 100:(2-100), specifically 100:2, 100:10, 100:20, 100:50, 100:80 or 100:100, etc. Of course, it can also be other values ​​within the above range, and this application is not limited here.

[0107] In some embodiments, the heat treatment temperature is 800°C to 3000°C, specifically 800°C, 1000°C, 1200°C, 1500°C, 1800°C, 2000°C, 2500°C, 2800°C or 3000°C, etc. Of course, it can also be other values ​​within the above range, and this application does not limit it here.

[0108] In some embodiments, the heat treatment is performed in a protective gas atmosphere, and the protective gas includes at least one of helium, neon, argon, nitrogen, and krypton.

[0109] In some embodiments, the heat treatment time is 1 h to 24 h, specifically 1 h, 5 h, 12 h, 15 h, 18 h or 24 h, etc. Of course, it can also be other values ​​within the above range, and this application does not limit it here.

[0110] In some embodiments, after the heat treatment, the obtained material is further subjected to the steps of breaking up, screening and demagnetizing.

[0111] In some embodiments, the mesh size of the screening is 100 mesh to 500 mesh, specifically 100 mesh, 200 mesh, 300 mesh, 400 mesh or 500 mesh, etc. Of course, it can also be other values ​​within the above range, and this application does not limit it here.

[0112] In a third aspect, the present application further provides a lithium-ion battery, which includes the above-mentioned negative electrode material, or includes the negative electrode material prepared by the above-mentioned preparation method.

[0113] The present application will be further described below through specific examples.

[0114] Example 1

[0115] (1) Natural flake graphite is crushed and shaped to obtain spherical natural graphite with an average particle size of 17 μm, and the sphericity of the spherical natural graphite satisfies Sh(10%)≥0.75, Sh(50%)≥0.83, and Sh(90%)≥0.88.

[0116] (2) The spherical natural graphite obtained in step (1) is densified in a cold isostatic press at a working pressure of 100 MPa, a time of 30 minutes, and a temperature of 30° C. to obtain block graphite. The block graphite is crushed to obtain densified natural graphite having a median particle size of 17 μm.

[0117] (3) The densified natural graphite obtained in step (2) is solid-phase mixed with petroleum asphalt in a mass ratio of 90:10, and the mixture is then carbonized in a kiln in an inert atmosphere at a carbonization temperature of 1000° C. After carbonization, the material is dispersed, sieved, and demagnetized to obtain a negative electrode material.

[0118] The SEM image of the cross section of the negative electrode material prepared in this embodiment is shown in FIG2 . In FIG2 , it can be observed that the natural graphite has elongated pores inside.

[0119] Example 2

[0120] (1) Natural flake graphite is crushed and shaped to obtain spherical natural graphite with an average particle size of 17 μm, and the sphericity of the spherical natural graphite satisfies Sh(10%)≥0.75, Sh(50%)≥0.83, and Sh(90%)≥0.88.

[0121] (2) The spherical natural graphite obtained in step (1) was mixed with petroleum asphalt in a ratio of 90:10, and the mixture was then processed using a hot press at a heating temperature of 1000° C., a pressure of 25 MPa, and a time of 30 minutes. The processed material was block graphite. The block graphite was crushed and pulverized to obtain a negative electrode material with a median particle size of 17 μm.

[0122] The SEM image of the cross section of the negative electrode material prepared in this embodiment is shown in FIG3 . In FIG3 , it can be observed that the natural graphite has elongated pores inside and on the surface.

[0123] Example 3

[0124] (1) Natural flake graphite is crushed and shaped to obtain spherical natural graphite with an average particle size of 17 μm, and the sphericity of the spherical natural graphite satisfies Sh(10%)≥0.75, Sh(50%)≥0.83, and Sh(90%)≥0.88.

[0125] (2) The spherical natural graphite obtained in step (1) is mixed with petroleum asphalt in a ratio of 80:20, and the mixture is pretreated in a heating mixer protected by an inert atmosphere at a temperature of 300° C. and a mixing time of 5 hours. The treated material is block graphite.

[0126] (3) The block graphite obtained in step (2) was processed using a die press at a pressure of 25 MPa for 30 min. After the processing, a densified natural graphite block was obtained. The densified natural graphite block was then crushed to obtain a negative electrode material having a median particle size of 17 μm.

[0127] The SEM image of the cross section of the negative electrode material prepared in this embodiment is shown in FIG4 . In FIG4 , it can be observed that the natural graphite has elongated pores inside.

[0128] Example 4

[0129] (1) Natural flake graphite is crushed and shaped to obtain spherical natural graphite with an average particle size of 5 μm, and the sphericity of the spherical natural graphite satisfies Sh(10%)≥0.75, Sh(50%)≥0.83, and Sh(90%)≥0.88.

[0130] (2) The spherical natural graphite obtained in step (1) is densified in a cold isostatic press at a working pressure of 100 MPa, a time of 30 minutes, and a temperature of 30° C. to obtain block graphite. The block graphite is crushed to obtain densified natural graphite having a median particle size of 5 μm.

[0131] (3) The densified natural graphite obtained in step (2) is solid-phase mixed with petroleum asphalt in a mass ratio of 90:10, and the mixture is then carbonized in a kiln in an inert atmosphere at a carbonization temperature of 1000° C. After carbonization, the material is dispersed, sieved, and demagnetized to obtain a negative electrode material.

[0132] The SEM image of the cross section of the negative electrode material prepared in this embodiment is shown in FIG5 . In FIG5 , it can be observed that the natural graphite has elongated pores inside and on the surface.

[0133] Example 5

[0134] (1) Natural flake graphite is crushed and shaped to obtain spherical natural graphite with an average particle size of 11 μm, and the sphericity of the spherical natural graphite satisfies Sh(10%)≥0.75, Sh(50%)≥0.83, and Sh(90%)≥0.88.

[0135] (2) The spherical natural graphite obtained in step (1) is densified in a cold isostatic press at a working pressure of 100 MPa, a time of 30 minutes, and a temperature of 30° C. to obtain block graphite. The block graphite is crushed to obtain densified natural graphite having a median particle size of 11 μm.

[0136] (3) The densified natural graphite obtained in step (2) is solid-phase mixed with petroleum asphalt in a mass ratio of 90:10, and the mixture is then carbonized in a kiln in an inert atmosphere at a carbonization temperature of 1000° C. After carbonization, the material is dispersed, sieved, and demagnetized to obtain a negative electrode material.

[0137] Example 6

[0138] (1) Natural flake graphite is crushed and shaped to obtain spherical natural graphite with an average particle size of 25 μm, and the sphericity of the spherical natural graphite satisfies Sh(10%)≥0.75, Sh(50%)≥0.83, and Sh(90%)≥0.88.

[0139] (2) The spherical natural graphite obtained in step (1) is densified in a cold isostatic press at a working pressure of 100 MPa, a time of 30 minutes, and a temperature of 30° C. to obtain block graphite. The block graphite is crushed to obtain densified natural graphite having a median particle size of 25 μm.

[0140] (3) The densified natural graphite obtained in step (2) is solid-phase mixed with petroleum asphalt in a mass ratio of 90:10, and the mixture is then carbonized in a kiln in an inert atmosphere at a carbonization temperature of 1000° C. After carbonization, the material is dispersed, sieved, and demagnetized to obtain a negative electrode material.

[0141] Example 7

[0142] (1) Natural flake graphite is crushed and shaped to obtain spherical natural graphite with an average particle size of 17 μm, and the sphericity of the spherical natural graphite satisfies Sh(10%)≥0.75, Sh(50%)≥0.83, and Sh(90%)≥0.88.

[0143] (2) The spherical natural graphite obtained in step (1) is densified in a cold isostatic press at a working pressure of 60 MPa, a time of 30 minutes, and a temperature of 30° C. to obtain block graphite. The block graphite is crushed to obtain densified natural graphite having a median particle size of 17 μm.

[0144] (3) The densified natural graphite obtained in step (2) is solid-phase mixed with petroleum asphalt in a mass ratio of 90:10, and the mixture is then carbonized in a kiln in an inert atmosphere at a carbonization temperature of 1000° C. After carbonization, the material is dispersed, sieved, and demagnetized to obtain a negative electrode material.

[0145] Example 8

[0146] (1) Natural flake graphite is crushed and shaped to obtain spherical natural graphite with an average particle size of 17 μm, and the sphericity of the spherical natural graphite satisfies Sh(10%)≥0.75, Sh(50%)≥0.83, and Sh(90%)≥0.88.

[0147] (2) The spherical natural graphite obtained in step (1) is densified in a cold isostatic press at a working pressure of 200 MPa, a time of 30 minutes, and a temperature of 30° C. to obtain block graphite. The block graphite is crushed to obtain densified natural graphite having a median particle size of 17 μm.

[0148] (3) The densified natural graphite obtained in step (2) is solid-phase mixed with petroleum asphalt in a mass ratio of 90:10, and the mixture is then carbonized in a kiln in an inert atmosphere at a carbonization temperature of 1000° C. After carbonization, the material is dispersed, sieved, and demagnetized to obtain a negative electrode material.

[0149] Example 9

[0150] (1) Natural flake graphite is crushed and shaped to obtain spherical natural graphite with an average particle size of 17 μm, and the sphericity of the spherical natural graphite satisfies Sh(10%)≥0.75, Sh(50%)≥0.83, and Sh(90%)≥0.88.

[0151] (2) The spherical natural graphite obtained in step (1) is densified in a cold isostatic press at a working pressure of 250 MPa, a time of 30 minutes, and a temperature of 30° C. to obtain block graphite. The block graphite is crushed to obtain densified natural graphite having a median particle size of 17 μm.

[0152] (3) The densified natural graphite obtained in step (2) is solid-phase mixed with petroleum asphalt in a mass ratio of 90:10, and the mixture is then carbonized in a kiln in an inert atmosphere at a carbonization temperature of 1000° C. After carbonization, the material is dispersed, sieved, and demagnetized to obtain a negative electrode material.

[0153] Example 10

[0154] Different from Example 1, step (3) is not performed.

[0155] Comparative Example 1

[0156] (1) Natural flake graphite is crushed and shaped to obtain spherical natural graphite with an average particle size of 17 μm, and the sphericity of the spherical natural graphite satisfies Sh(10%)≥0.75, Sh(50%)≥0.83, and Sh(90%)≥0.88.

[0157] (2) The spherical natural graphite obtained in step (1) is solid-phase mixed with asphalt in a mass ratio of 90:10, and then the mixture is carbonized in a kiln in an inert atmosphere at a carbonization temperature of 1000° C. After carbonization, the material is broken up, sieved and demagnetized to obtain a negative electrode material.

[0158] The SEM image of the cross section of the negative electrode material prepared in this comparative example is shown in FIG6 . In FIG6 , it can be observed that the natural graphite has elongated pores inside and on the surface.

[0159] Comparative Example 2

[0160] (1) Natural flake graphite is crushed and shaped to obtain spherical natural graphite with an average particle size of 17 μm, and the sphericity of the spherical natural graphite satisfies Sh(10%)≥0.75, Sh(50%)≥0.83, and Sh(90%)≥0.88.

[0161] (2) The spherical natural graphite obtained in step (1) is subjected to a densification treatment, wherein the densification is carried out in a cold isostatic press with a working pressure set to 50 MPa to obtain block graphite, and the block graphite is crushed and pulverized to obtain a densified natural graphite with a median particle size of 17 μm.

[0162] (3) The densified natural graphite prepared in step (2) is solid-phase mixed with asphalt in a mass ratio of 90:10, and the mixture is carbonized in a kiln in an inert atmosphere at a carbonization temperature of 1000° C. After carbonization, the material is broken up, sieved, and demagnetized to obtain a negative electrode material.

[0163] The SEM image of the cross section of the negative electrode material prepared in this comparative example is shown in FIG7 . In FIG7 , it can be observed that the natural graphite has pores, and the number of pores is large and the shapes are irregular.

[0164] Comparative Example 3

[0165] (1) Natural flake graphite is crushed and shaped to obtain spherical natural graphite with an average particle size of 17 μm. The sphericity of the spherical natural graphite is Sh(10%)=0.72, Sh(50%)=0.79, and Sh(90%)=0.87.

[0166] (2) The spherical natural graphite obtained in step (1) is densified in a cold isostatic press at a working pressure of 100 MPa, a time of 30 minutes, and a temperature of 30° C. to obtain block graphite. The block graphite is crushed to obtain densified natural graphite having a median particle size of 17 μm.

[0167] (3) The densified natural graphite obtained in step (2) is solid-phase mixed with petroleum asphalt in a mass ratio of 90:10, and the mixture is then carbonized in a kiln in an inert atmosphere at a carbonization temperature of 1000° C. After carbonization, the material is dispersed, sieved, and demagnetized to obtain a negative electrode material.

[0168] The SEM image of the cross section of the negative electrode material prepared in this comparative example is shown in FIG8 . In FIG8 , it can be observed that the natural graphite has pores, and the number of pores is large and the shapes are irregular.

[0169] Comparative Example 4

[0170] (1) Natural flake graphite is crushed and shaped to obtain spherical natural graphite with an average particle size of 30 μm, and the sphericity of the spherical natural graphite satisfies Sh(10%)≥0.75, Sh(50%)≥0.83, and Sh(90%)≥0.88.

[0171] (2) The spherical natural graphite obtained in step (1) is densified in a cold isostatic press at a working pressure of 100 MPa, a time of 30 minutes, and a temperature of 30° C. to obtain block graphite. The block graphite is crushed to obtain densified natural graphite having a median particle size of 30 μm.

[0172] (3) The densified natural graphite obtained in step (2) is solid-phase mixed with petroleum asphalt in a mass ratio of 90:10, and the mixture is then carbonized in a kiln in an inert atmosphere at a carbonization temperature of 1000° C. After carbonization, the material is dispersed, sieved, and demagnetized to obtain a negative electrode material.

[0173] Performance Testing

[0174] (1) The median particle size D50 of the negative electrode material was measured using a Malvern laser particle size analyzer MS 2000;

[0175] (2) The sphericity of the material Sh(10%), Sh(50%) and Sh(90%) was tested using SYMPATEC's QICPIC dynamic particle image analyzer.

[0176] (3) The specific surface area of ​​the negative electrode material was tested using Micromeritics' Tristar equipment.

[0177] (4) The pore volume of the material was tested using a mercury intrusion instrument, Micromeritics AutoPore IV 9500, to measure the pore volume within the pore diameter range of 3 nm to 1000 nm.

[0178] (5) The electrode expansion rate test uses the test device and system disclosed in patent CN201920973729.5 to test the electrode expansion rate for 20 cycles.

[0179] (6) The particle sample was milled using an ion mill (HITACHI E3500) to observe the cross section of the particle. The sample was then placed under a high-power electron microscope (HITACHI S4800) to obtain internal information of the particle. The pore width in the selected area was measured and counted using a ruler. A total of 100 pores were randomly observed. The number of pores less than 0.1 μm, 0.1-0.5 μm, and greater than 0.5 μm were counted and their proportions were calculated. Pores less than 0.1 μm, 0.1-0.5 μm, and greater than 0.5 μm were defined as small pores, medium pores, and large pores, respectively. The number of these three types of pores was counted and their proportions were calculated. The aspect ratio of the pores refers to the ratio of the length and width of the pores in the selected area measured using a ruler to obtain internal information of the particle under a high-power electron microscope (HITACHI S4800).

[0180] (7) The negative electrode material, conductive agent, and binder were dissolved in a solvent in a mass ratio of 94:1:5, and the solid content was controlled to 50%. The mixture was coated on a copper foil current collector and vacuum dried to obtain a negative electrode. Then, the ternary positive electrode prepared by a conventional mature process, a 1 mol / L LiPF6 / EC+DMC+EMC (v / v=1:1:1) electrolyte, a Celgard2400 separator, and a shell were assembled into an 18650 cylindrical single cell using a conventional production process. The charge and discharge test of the cylindrical battery was carried out on the LAND battery test system of Wuhan Jinnuo Electronics Co., Ltd. at room temperature, with a constant current of 0.2C and a charge and discharge voltage limited to 2.75~4.2V. The first reversible capacity, first cycle charge capacity, and first cycle discharge capacity were obtained. The first coulomb efficiency = first cycle discharge capacity / first cycle charge capacity.

[0181] Repeat the cycle for 50 cycles and record the discharge capacity as the remaining capacity of the lithium-ion battery; capacity retention rate = remaining capacity / initial capacity*100%.

[0182] 20-week electrode expansion rate (%) determination: The negative electrode material, conductive agent and binder are dissolved in a solvent at a mass percentage of 94:1:5, and the solid content is controlled at 50%. The mixture is coated on a copper foil current collector and vacuum dried to obtain a negative electrode. The negative electrode material loading on the electrode is controlled to be 7.0 mg / cm 2 After rolling, the electrode sheet compaction density was 1.60 g / cm3. The electrode sheet thickness d1 was measured, and then the battery was assembled into a button cell for testing. After 20 cycles, the battery was disassembled and the electrode sheet thickness d2 was measured again. The electrode sheet expansion rate = (d2-d1) / d1*100%.

[0183] The test results are shown in Tables 1 and 2.

[0184] Table 1. Parameter test results of negative electrode materials of various embodiments and comparative examples

[0185] It can be understood that the pore morphology described in Comparative Examples 2 and 3 is irregular. Irregular means that the pores on the natural graphite are not elongated, that is, the pores are not arranged linearly, and / or the aspect ratio of the pores is less than or equal to 3.

[0186] Table 2. Performance test data of various embodiments and comparative examples

[0187] As shown in Tables 1 and 2, the negative electrode materials prepared in Examples 1 to 10 of the present application include carbonaceous particles with pores, and the shape of the pores of the carbonaceous particles is an elongated structure, indicating that the material inside the carbonaceous particles is arranged in order and the scaly graphite layers inside the particles are in close contact, which is beneficial to improving the capacity performance of the negative electrode material; the present application further limits the pores with a pore size of 0.1 μm to 0.5 μm to a ratio of greater than or equal to 60% of the total number of pores, indicating that the carbonaceous particles with pores in the present application have fine pores, and the porosity of the carbonaceous particles is low, indicating that the carbonaceous particles have a densified structure, so that the negative electrode material can produce less expansion during the charge and discharge process. The negative electrode material of the present application has elongated pores and most of the pores have a small pore size, indicating that the internal pore volume of the carbonaceous particles of the present application is small and the number of large pores is small, so that the carbonaceous particles have excellent density, thereby improving the capacity performance, expansion performance and cycle performance of the negative electrode material.

[0188] The negative electrode material prepared in Comparative Example 1 was not subjected to densification treatment, resulting in a larger pore volume and a higher porosity of the negative electrode material prepared in Comparative Example 1, which resulted in poor expansion performance and cycle performance of the negative electrode material prepared in Comparative Example 1.

[0189] The working pressure of the cold isostatic press in Comparative Example 2 is not within the limit of this application, resulting in irregular pores in the negative electrode material prepared in Comparative Example 2 and a high pore volume. Its capacity and initial efficiency are lower than those in Example 1.

[0190] The sphericity of the graphite raw material in Comparative Example 3 is not within the scope specified in this application. The sphericity of the prepared negative electrode material is poor, resulting in high material expansion. Although the material has elongated pores inside, the expansion performance of the material is still poor.

[0191] The particle size of the graphite raw material in Comparative Example 4 is not within the range specified in this application, resulting in poor densification effect of the prepared negative electrode material. Although there are a considerable number of slender small pores inside the material, there are still a small number of large pores, resulting in high expansion and poor cycle performance of the final prepared negative electrode material.

[0192] The above description is merely a preferred embodiment of the present application and is not intended to limit the present application. Various modifications and variations are possible for those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A negative electrode material, characterized in that: The negative electrode material includes carbonaceous particles with pores. By observing the SEM image, at least the aspect ratio of the pores is greater than 3. When a total number of 100 pores are randomly observed, the number of pores with a pore diameter of 0.1 μm to 0.5 μm accounts for more than or equal to 60% of the total number of pores.

2. The negative electrode material according to claim 1, characterized in that The maximum pore diameter of the pores is less than or equal to 3 μm.

3. The negative electrode material according to claim 1, characterized in that The negative electrode material includes at least one of the following features (1) to (3): (1) The carbonaceous particles include graphite; (2) The carbonaceous particles include natural graphite, and the natural graphite includes at least one of flake graphite and microcrystalline graphite; (3) The median particle size of the carbonaceous particles is 5 μm to 25 μm.

4. The negative electrode material according to claim 1, characterized in that The negative electrode material further includes a coating layer coated on at least a portion of the surface of the carbonaceous particles, and the negative electrode material includes at least one of the following features (1) to (2): (1) The material of the coating layer includes carbon material; (2) The material of the coating layer includes a carbon material, and the carbon material includes at least one of soft carbon, crystalline carbon, amorphous carbon and hard carbon.

5. The negative electrode material according to claim 1, characterized in that The negative electrode material includes at least one of the following features (1) to (6): (1) The median particle size D50 of the negative electrode material satisfies: 5 μm <D50<25μm; (2) The sphericity Sh (10%) of the negative electrode material is ≥ 0.75; (3) The sphericity Sh (50%) of the negative electrode material is ≥ 0.83; (4) The sphericity Sh (90%) of the negative electrode material is ≥ 0.88; (5) The pore volume of the negative electrode material is 0.05 mL / g to 0.11 mL / g; (6) The specific surface area of ​​the negative electrode material is 0.5 m 2 / g~3.5m 2 / g.

6. A method for preparing a negative electrode material, characterized in that: The steps include: Providing a natural graphite precursor, wherein the median particle size of the natural graphite precursor is 5 μm to 25 μm, the sphericity Sh (10%) of the natural graphite precursor is ≥ 0.75, the sphericity Sh (50%) of the natural graphite precursor is ≥ 0.83, and the sphericity Sh (90%) of the natural graphite precursor is ≥ 0.88; The natural graphite precursor is densified so that the obtained negative electrode material includes carbonaceous particles with pores, at least some of the pores have an aspect ratio greater than 3, and the total number of randomly observed pores is 100, and the number of pores with a pore diameter of 0.1μm to 0.5μm accounts for more than or equal to 60% of the total number of pores.

7. The preparation method according to claim 6, characterized in that: The preparation method comprises at least one of the following features (1) to (2): (1) The natural graphite precursor is prepared by the following method: shaping natural graphite; (2) The natural graphite precursor is prepared by the following method: natural graphite is subjected to shaping treatment, and the natural graphite includes at least one of flake graphite and microcrystalline graphite.

8. The preparation method according to claim 6, characterized in that: The preparation method comprises at least one of the following features (1) to (4): (1) The densification treatment includes at least one of cold isostatic pressing, hot isostatic pressing, molding and hot pressing; (2) The pressure of the densification treatment is 20MPa to 200MPa; (3) The densification treatment time is 1 min to 200 min; (4) The temperature of the densification treatment is 25°C to 1500°C.

9. The preparation method according to claim 6, characterized in that: Before the natural graphite precursor is subjected to densification treatment, the method also includes: mixing a coating material with the natural graphite precursor, and then subjecting the mixture to densification treatment, wherein the coating material includes at least one of a high molecular polymer, a resin, coal tar, petroleum asphalt, mesophase asphalt, coal tar and heavy oil.

10. The preparation method according to claim 6, characterized in that: After obtaining the negative electrode material, the method further includes: mixing the negative electrode material and the coating material and then performing heat treatment. The preparation method includes at least one of the following features (1) to (5): (1) The coating material comprises at least one of a polymer, a resin, coal tar, petroleum tar, mesophase tar, coal tar and heavy oil; (2) The mass ratio of the negative electrode material to the coating material is 100:(2-100); (3) The temperature of the heat treatment is 800° C. to 3000° C.; (4) The heat treatment is carried out in a protective gas atmosphere, wherein the protective gas comprises at least one of helium, neon, argon, nitrogen and krypton; (5) The heat treatment time is 1 h to 24 h.

11. A lithium ion battery, characterized in that: The lithium-ion battery comprises the negative electrode material according to any one of claims 1 to 5, or comprises the negative electrode material prepared by the preparation method according to any one of claims 6 to 10.

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