Negative electrode material and battery

Abstract

Provided in the present application are a negative electrode material and a battery. The negative electrode material comprises an inner core and amorphous carbon located on at least part of the surface of the inner core, wherein the inner core comprises natural graphite. There are pores inside particles of the negative electrode material. In a sectional SEM image of the negative electrode material, 20 pores in the SEM image are randomly selected for measurement, the measured average width of the pores is D, the average length of the pores is L, and the average aspect ratio L / D of the pores is greater than or equal to 2.5. 20 particles in the SEM image are randomly selected for measurement, the area of all the pores on the section and the total section area of each particle are measured, and the calculated average area proportion value of the pores in the total section area is 5-15%. The negative electrode material provided in the present application has a relatively small expansion effect and a long cycle life.

Description

Anode materials and batteries

[0001] This application claims priority to Chinese patent application 202510008817.1, filed on January 2, 2025. The entire contents of the aforementioned Chinese patent application are incorporated herein by reference. Technical Field

[0002] This application relates to the field of negative electrode material technology, specifically to negative electrode materials, negative electrode sheets, and batteries. Background Technology

[0003] Anode materials can be broadly classified into two categories: artificial graphite and natural graphite. Natural graphite anode materials offer advantages over artificial graphite anode materials, including higher capacity and better processability. In recent years, natural graphite has received increasing attention due to its low carbon emissions. However, natural graphite also suffers from high expansion and short cycle life. The poor cycle performance of natural graphite is mainly due to the co-intercalation of organic molecules in the electrolyte during lithium intercalation, leading to structural damage to the anode material. Furthermore, the numerous pores within natural graphite particles exacerbate expansion and contraction during charge and discharge, further degrading cycle performance. Currently, conventional coating methods offer limited improvement to the cycle performance of graphite anode materials. Therefore, further reducing the expansion effect and improving the cycle performance of anode materials remains a crucial problem to be solved. Summary of the Invention

[0004] In view of this, this application provides a negative electrode material and a battery, wherein the expansion effect of the negative electrode material is reduced, thereby improving the cycle performance of the negative electrode material.

[0005] In a first aspect, this application provides a negative electrode material, which includes a core and amorphous carbon located on at least a portion of the surface of the core, the core including natural graphite, and the particles of the negative electrode material having pores inside;

[0006] In the cross-sectional SEM image of the negative electrode material, 20 pores were randomly selected for measurement. The average width of the pores was D, the average length of the pores was L, and the average aspect ratio of the pores was L / D≥2.5.

[0007] Twenty particles were randomly selected from the SEM images for measurement. The area of ​​all pores on the cross-section of each particle and the total cross-sectional area were measured. The average area ratio of pores in the total cross-sectional area was calculated to be 5% to 15%.

[0008] Secondly, this application provides a battery comprising the aforementioned negative electrode material.

[0009] The technical solution of this application has at least the following beneficial effects:

[0010] The negative electrode material provided in this application includes graphite. The particles of the negative electrode material have internal pores, with the pore area accounting for an average of 5% to 15% of the total cross-sectional area. Simultaneously, the average aspect ratio of the pores is controlled to be greater than or equal to 2.5. This synergistic effect allows the negative electrode material to maintain a low porosity and a relatively dense particle structure, reducing side reactions between the negative electrode material and the electrolyte, and enabling the negative electrode material to undergo minimal expansion during charge and discharge. Furthermore, by controlling the shape of the pores to be elongated, it increases the lithium-ion transport channels, improving lithium-ion transport efficiency, while also making the particles denser, thereby improving the capacity performance, expansion performance, and cycle performance of the negative electrode material. Moreover, the amorphous carbon on the core surface of the negative electrode material can act as a spatial barrier to the co-intercalation of solvent molecules in the electrolyte, preventing the electrolyte from penetrating into the graphite core during battery cycling, thus improving cycle performance. Therefore, the negative electrode material provided in this application possesses both high reversible capacity and excellent cycle performance. Attached Figure Description

[0011] Figure 1 is a schematic diagram of the discharge state of the battery provided in an embodiment of this application.

[0012] Figure 2 is a SEM image of the negative electrode material provided in Embodiment 3 of this application.

[0013] Figure 3 is a schematic diagram of the pore length and width measurement in the SEM image of the negative electrode material provided in this application.

[0014] Figure 4 is a schematic diagram of the pore distribution of the negative electrode material provided in Embodiment 3 of this application;

[0015] Figure 5 is a SEM image of the negative electrode material provided in Comparative Example 1 of this application.

[0016] The above figures contain the following reference numerals: 1. Positive electrode sheet; 2. Negative electrode sheet; 3. Separator membrane; 101. Positive current collector; 102. Positive active layer; 201. Negative current collector; 202. Negative active material layer; 4. Non-porous; 5. Pore. Detailed Implementation

[0017] To better illustrate this application and facilitate understanding of its technical solutions, the following detailed description is provided. However, the following embodiments are merely simplified examples and do not represent or limit the scope of protection of this application. The scope of protection of this application is determined by the claims.

[0018] In a first aspect, this application provides a negative electrode material, which includes a core and amorphous carbon located on at least a portion of the surface of the core. The core includes natural graphite, and the particles of the negative electrode material have pores inside.

[0019] In the cross-sectional SEM image of the negative electrode material, 20 pores were randomly selected for measurement. The average width of the pores was D, the average length of the pores was L, and the average aspect ratio of the pores was L / D≥2.5.

[0020] Twenty particles were randomly selected from the SEM images for measurement. The area of ​​all pores on the cross-section of each particle and the total cross-sectional area were measured. The average area ratio of pores in the total cross-sectional area was calculated to be 5% to 15%.

[0021] The anode material provided in this application comprises natural graphite in its core. The particles of the anode material have pores, with the pore area accounting for an average of 5% to 15% of the total cross-sectional area. Simultaneously, the average aspect ratio of the pores is controlled to be greater than or equal to 2.5. This synergistic effect allows the anode material to maintain a low porosity and a relatively dense particle structure, reducing side reactions between the anode material and the electrolyte, resulting in less expansion during charge and discharge. Furthermore, by controlling the shape of the pores to be elongated, it increases the lithium-ion transport channels, improving lithium-ion transport efficiency, and simultaneously making the particles denser, thereby improving the capacity, expansion, and cycle performance of the anode material. Moreover, the amorphous carbon on the surface of the anode material's core can act as a spatial barrier to the co-intercalation of solvent molecules in the electrolyte, preventing electrolyte penetration into the graphite core during battery cycling and improving cycle performance. Therefore, the anode material provided in this application possesses both high reversible capacity and excellent cycle performance. Furthermore, the average area ratio of pores in the total cross-sectional area is 5% to 10%, and the average length-to-width ratio of the pores is L / D ≥ 7.5.

[0022] In some embodiments, the average pore width is D, where D takes the value of 0.1 μm to 1.0 μm, or 0.24 μm to 0.31 μm; or 0.1 μm to 0.31 μm; or, specifically, D can be 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, or any value within the range of any two of the above values, and is not limited herein. Controlling the average pore width within the above range is beneficial for increasing the density of the negative electrode material and reducing the probability of solvent molecules embedding into the core.

[0023] In some embodiments, the average length of the pores is L, where L is 0.5 μm to 3.5 μm, or 2.2 μm to 2.5 μm; or 1.1 μm to 2.7 μm; or L can specifically be 0.5 μm, 0.8 μm, 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, 2.8 μm, 3.0 μm, 3.2 μm, 3.5 μm, or any value within the range of any two of the above values, and is not limited herein. Controlling the average length of the pores within the above range is beneficial for improving the lithium-ion transport efficiency and enhancing the capacity and rate performance of the anode material.

[0024] In some embodiments, the average aspect ratio of the pores, L / D, is ≥ 2.5; or, L / D ≥ 7.5; or, 2.5 ≤ L / D ≤ ​​20; or, 7.5 ≤ L / D ≤ ​​9.3; or, L / D can specifically be 2.5, 3, 4, 5, 6, 8, 10, 12, 15, 20, or any value within the range of any two of the above values, without limitation. When L / D is less than 2.5, the average width of the pores is larger, leading to an increase in side reactions between the negative electrode material and the electrolyte, resulting in a significant decrease in the specific capacity of the negative electrode material. This application controls the average aspect ratio of the pores within the above range, making the internal structure of the negative electrode material particles more compact. The elongated pores are beneficial for lithium-ion transport and can also alleviate the volume expansion of graphite, which is beneficial for improving the specific capacity and cycle performance of the negative electrode material.

[0025] In some embodiments, the average area ratio of pores in the total cross-sectional area is 5% to 15%; or, the average area ratio of pores in the total cross-sectional area is 5% to 10%; or, the average area ratio of pores in the total cross-sectional area is 5% to 9.6%; or, the average area ratio of pores in the total cross-sectional area can specifically be 5%, 6%, 7%, 8%, 10%, 11%, 12%, 13%, 14%, 15%, or any value within the range of any two of the above values, and is not limited herein. If the average area ratio of pores is too small, the porosity of the negative electrode material is too low, which is not conducive to the electrolyte fully wetting the negative electrode material, reduces the lithium-ion transport channels of the negative electrode material, leading to a decrease in the capacity of the negative electrode material, and further exacerbates the expansion effect of the negative electrode material during cycling, thus reducing the capacity retention rate. If the average area ratio of pores is too large, the side reactions between the negative electrode material and the electrolyte are intensified, leading to a significant decrease in the capacity retention rate of the negative electrode material. Controlling the average area ratio of pores within the above range is beneficial for the electrolyte to fully wet the negative electrode material, increase the lithium ion transport channels in the negative electrode material, and thus improve the capacity of the negative electrode material. In addition, it also helps to alleviate the expansion effect of the negative electrode material during cycling and increase the cycle life of the negative electrode material.

[0026] In some embodiments, the pore volume of the negative electrode material is measured by mercury porosimetry as V1 mL / g, and by BET method as V2 mL / g, where 0.04 ≤ V1 - V2 ≤ 0.14; or 0.04 ≤ V1 - V2 ≤ 0.08; or 0.06 ≤ V1 - V2 ≤ 0.10; or, V1 - V2 can specifically be 0.04, 0.05, 0.06, 0.08, 0.10, 0.12, 0.13, 0.14, or any value within the range of any two of the above values, and is not limited here. Since the mercury porosimetry and BET methods differ in pore volume for different pore size ranges, controlling V1-V2 within the aforementioned range indicates a moderate number of mesopores with pore sizes greater than 2 nm in the anode material. This prevents excessive consumption of active lithium ions and is beneficial for improving the cycle performance of the anode material. Furthermore, controlling V1-V2 within the aforementioned range also indicates a moderate number of micropores or closed pores with pore sizes within 2 nm, resulting in good electrolyte wetting performance and excellent lithium ion intercalation ability between graphite layers. This is beneficial for improving the initial coulombic efficiency of batteries made with this anode material. This application controls the value of V1-V2 within the aforementioned range, ensuring that the anode material has a reasonable number of lithium ion transport channels, alleviating the expansion stress caused by lithium intercalation / deintercalation in graphite particles; it also balances the side reactions between the anode material and the electrolyte, reducing irreversible loss of active lithium ions and improving the capacity and initial coulombic efficiency of the anode material.

[0027] In some embodiments, the pore volume of the negative electrode material, measured by mercury porosimetry, is V1 mL / g, where 0.05 ≤ V1 ≤ 0.12. Specifically, it can be 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, or any value within the range of any two of the above values, and is not limited here. Controlling the pore volume of the negative electrode material measured by mercury porosimetry to be within the above range indicates that the negative electrode material has an appropriate amount of porosity. The presence of porosity can provide more lithium-ion diffusion channels and electrochemical reaction interfaces, promote the diffusion of lithium ions at the solid-liquid interface and within the solid phase, reduce concentration polarization, and is beneficial to improving the reversible capacity and rate performance of the negative electrode material.

[0028] In some embodiments, the pore volume of the negative electrode material tested by the BET method is V² mL / g, where 0.004 ≤ V² ≤ 0.02. Specifically, it can be 0.004, 0.005, 0.006, 0.008, 0.01, 0.015, 0.018, 0.019, 0.02, or any value within the range of any two of the above values, and is not limited herein. Understandably, the BET method measures the pore volume based on the principle of physical adsorption. Controlling the pore volume of the negative electrode material measured by the BET method within the above range also indicates the presence of an appropriate amount of porosity in the negative electrode material. This is beneficial for improving the capacity and rate performance of the negative electrode material, and also for maintaining its stability.

[0029] In some embodiments, the oil absorption value of the negative electrode material is 38 mL / 100g to 55 mL / 100g, specifically 38 mL / 100g, 39 mL / 100g, 40 mL / 100g, 42 mL / 100g, 43 mL / 100g, 45 mL / 100g, 48 mL / 100g, 50 mL / 100g, 52 mL / 100g, 55 mL / 100g, or any value within the range of any two of the above values, without limitation. Controlling the oil absorption value of the negative electrode material within the above range helps to weaken the side reactions between the negative electrode material and the electrolyte, resulting in a higher capacity retention rate; it also helps the electrolyte to fully wet the negative electrode material, reducing lithium-ion transport resistance and improving the rate performance of the negative electrode material; and it also helps to improve the tap density of the negative electrode material.

[0030] In some embodiments, the volumetric particle size distribution width of the negative electrode material satisfies: 0.90 ≤ (D 90 -D 10 ) / D 50 The value ≤1.20 can specifically be 0.90, 0.98, 1.02, 1.05, 1.1, 1.13, 1.15, 1.18, 1.2, or any value within the range of any two of the above values; no specific limitation is imposed here. A volumetric particle size distribution of the negative electrode material satisfying the above range is beneficial for increasing the compaction density and energy density of the negative electrode material.

[0031] In some embodiments, natural graphite includes at least one of flake graphite and microcrystalline graphite. Natural graphite is typically formed from sedimentary rocks rich in organic matter or carbon through regional metamorphism.

[0032] In some embodiments, the negative electrode material also includes amorphous carbon located on at least part of the surface of the core. By using amorphous carbon on the surface of natural graphite particles, on the one hand, the probability of the electrolyte entering the interior of the negative electrode material and causing side reactions can be reduced, ensuring that the negative electrode material has a high initial coulombic efficiency and capacity. On the other hand, it can alleviate the volume expansion of carbon particles, reduce the volume expansion rate of the entire negative electrode material, and reduce the swelling of the electrode sheet.

[0033] In some embodiments, natural graphite includes spherical natural graphite. Spherical natural graphite can be obtained by spheroidizing natural flake graphite.

[0034] In some embodiments, the median particle size of graphite is 5 μm to 18 μm, more specifically, it can be 5 μm, 5.5 μm, 6 μm, 6.5 μm, 8 μm, 9 μm, 10 μm, 12 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, or any value within the range of any two of the above values, and is not limited herein. Multiple experiments have shown that controlling the median particle size of graphite within the above range is beneficial for balancing the processing performance, capacity, and rate performance of the anode material.

[0035] In some embodiments, the mass percentage of amorphous carbon in the negative electrode material is 1% to 20%. Specifically, it can be 1%, 5%, 8%, 10%, 12%, 15%, 20%, or any value within the range of any two of the above values, and is not limited here.

[0036] In some implementations, the specific surface area of ​​the negative electrode material is 0.5 m². 2 / g~4.0m 2 / g; specifically, it can be 0.5m 2 / g, 0.8m 2 / g, 0.9m 2 / g, 1.0m 2 / g, 1.5m 2 / g, 1.8m 2 / g, 2.0m 2 / g, 3.0m 2 / g, 4.0m 2 / g or any value within the range of any two of the above values, without limitation. Controlling the specific surface area of ​​the negative electrode material within the above range is beneficial to improving the initial coulombic efficiency and cycle performance of lithium batteries made from this negative electrode material.

[0037] In some embodiments, the tap density of the negative electrode material is 0.85 g / cm³. 3 ~1.20g / cm 3 Specifically, it could be 0.85 g / cm³. 3 0.95g / cm3 1.0g / cm 3 1.05g / cm 3 1.09 g / cm 3 1.1g / cm 3 1.12 g / cm 3 1.15g / cm 3 1.18 g / cm 3 1.2g / cm 3 Or any value within the range of any two of the above values, without limitation.

[0038] In some embodiments, the median particle size of the negative electrode material is 8μm to 20μm. Specifically, it can be 8μm, 9μm, 10μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm or 20μm, etc., and is not limited here.

[0039] Secondly, this application provides a method for preparing a negative electrode material, comprising the following steps:

[0040] S10 involves shaping natural graphite to obtain spherical natural graphite.

[0041] S20, the first mixture containing spherical natural graphite and modifier is pressed to obtain a precursor, wherein the average area ratio of pores in the precursor to the total area of ​​particles is 8% to 20%.

[0042] S30, the second mixture containing the precursor and the coating agent is carbonized to obtain the negative electrode material.

[0043] In the above scheme, the first mixture obtained by mixing spherical natural graphite with a modifier is first pressed. During the pressing process, some of the modifier can penetrate into the pores of the natural graphite, thereby reducing the porosity of the natural graphite. Then, the precursor is further filled with a coating agent, so that most of the pores in the natural graphite are filled, improving the density of the negative electrode material. This can reduce the side reactions between the negative electrode material and the electrolyte. Furthermore, the reduction of pores between the graphite layers of natural graphite during the pressing process creates elongated pores that can increase the lithium ion transport channels and improve lithium ion transport efficiency, thereby improving the capacity performance, expansion performance, and cycle performance of the negative electrode material.

[0044] The preparation method of this application is described in detail below with reference to the embodiments:

[0045] Step S10: Shape the natural graphite to obtain spherical natural graphite.

[0046] In some embodiments, natural graphite includes at least one of flake graphite and microcrystalline graphite.

[0047] In some embodiments, the equipment for shaping includes at least one of a mechanical pulverizer, an air jet mill, and a crusher.

[0048] In some embodiments, the particle size of the spherical natural graphite is 5μm to 25μm, specifically 5μm, 8μm, 10μm, 13μm, 15μm, 18μm, 20μm, 23μm or 25μm, and of course other values ​​within the above range are also possible, which are not limited herein.

[0049] In some implementations, spherical natural graphite helps to suppress the expansion of the negative electrode material and improve its expansion performance.

[0050] Step S20: The first mixture containing spherical natural graphite and modifier is pressed to obtain a precursor. The average area ratio of pores in the precursor to the total area of ​​the particles is 8% to 20%.

[0051] In some embodiments, the modifier includes one or more of triglycerides, gum arabic, fatty alcohol polyoxyethylene ether, polyoxyethylene sorbitan fatty acid ester, phenolic resin, epoxy resin, polymethylcellulose, sucrose, starch, and polyacryl alcohol.

[0052] In some embodiments, the modifier includes at least one of fatty alcohol polyoxyethylene ether and polyoxyethylene sorbitan fatty acid ester. Because fatty alcohol polyoxyethylene ether and polyoxyethylene sorbitan fatty acid ester have excellent emulsifying and dispersing abilities, they can more easily fill the pores of spherical natural graphite during the pressing process. Furthermore, since these substances first enter the spherical natural graphite particles, it facilitates the effective filling of pores by subsequent coating agents, thereby improving the density of the negative electrode material and reducing its porosity.

[0053] In some embodiments, the mass ratio of spherical natural graphite to modifier is 100:(1 to 10), specifically 100:1, 100:2, 100:5, 100:8, 100:10 or any value within the range of any two of the above values, without limitation.

[0054] In some embodiments, the pressing process includes at least one of cold isostatic pressing, hot isostatic pressing, molding, and hot pressing.

[0055] In some embodiments, the pressure used for cold isostatic pressing is 60 MPa to 200 MPa, specifically 60 MPa, 80 MPa, 100 MPa, 120 MPa, 150 MPa, 180 MPa or 200 MPa, etc., and of course other values ​​within the above range are also possible, which are not limited in this application.

[0056] In some embodiments, the densification pressure of warm isostatic pressing, hot isostatic pressing, molding, and hot 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. Of course, other values ​​within the above range are also possible, and this application does not limit them.

[0057] In some embodiments, the pressing time is 1 min to 200 min, specifically 1 min, 10 min, 50 min, 100 min, 150 min or 200 min, etc., and of course other values ​​within the above range are also possible, which are not limited here.

[0058] In some embodiments, the pressing temperature 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., and of course, other values ​​within the above range are also possible, which are not limited here.

[0059] S30, the second mixture containing the precursor and the coating agent is carbonized to obtain the negative electrode material.

[0060] In some embodiments, the coating agent includes a carbon source material with a softening point of 20°C to 300°C.

[0061] In some embodiments, the carbon source material includes at least one of polymer, resin, coal tar pitch, petroleum pitch, mesophase pitch, coal tar, and heavy oil.

[0062] In some embodiments, the mass ratio of the precursor to the coating agent is 100:(2-30), specifically 100:2, 100:5, 100:10, 100:15, 100:20 or 100:30, etc. Of course, other values ​​within the above range are also possible, and this application does not limit them.

[0063] In some embodiments, the carbonization temperature is 800℃ to 3000℃, specifically 800℃, 1000℃, 1200℃, 1500℃, 1800℃, 2000℃, 2500℃, 2800℃ or 3000℃, etc., and of course other values ​​within the above range are also possible, which are not limited in this application.

[0064] In some embodiments, the carbonization process is carried out in a protective gas atmosphere, the protective gas including at least one of helium, neon, argon, nitrogen and krypton.

[0065] In some embodiments, the carbonization treatment time is 1 hour to 24 hours, specifically 1 hour, 5 hours, 12 hours, 15 hours, 18 hours or 24 hours, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0066] In some embodiments, the carbonization process is followed by steps of breaking up, sieving, and demagnetizing the resulting material.

[0067] In some embodiments, the mesh size of the sieve is 100 to 500 mesh, specifically 100 mesh, 200 mesh, 300 mesh, 400 mesh or 500 mesh, etc., and of course other values ​​within the above range are also possible. This application does not limit this.

[0068] Thirdly, this application provides a negative electrode sheet, which includes a negative electrode current collector and a negative electrode active material layer located on at least one side of the negative electrode current collector. The negative electrode active material layer includes a negative electrode material prepared by the method of preparing the negative electrode material of the first aspect or the negative electrode material of the second aspect.

[0069] Fourthly, this application provides a battery, which includes a negative electrode material according to the first aspect, a negative electrode material prepared by the method for preparing the negative electrode material according to the second aspect, or a negative electrode sheet according to the third aspect.

[0070] The battery provided in this application can be a secondary battery (such as a lithium-ion battery, sodium-ion battery, etc.), including a casing, electrode assembly, and electrolyte. Both the electrode assembly and electrolyte are located inside the casing. The casing can be a packaging bag sealed with an encapsulation film (such as an aluminum-plastic film), such as a soft-pack battery for the secondary battery. In other embodiments, the secondary battery can also be a steel-cased battery, an aluminum-cased battery, etc. Figure 1 is a schematic diagram of the discharge state of the battery provided in an embodiment of this application. As shown in Figure 1, the battery includes a casing and an electrode assembly. The electrode assembly includes a positive electrode 1, a negative electrode 2, and a separator 3, with the separator 3 disposed between the positive electrode 1 and the negative electrode 2. The electrode assembly can be a stacked structure, formed by alternately stacking the positive electrode 1, the separator 3, and the negative electrode 2. In other embodiments, the electrode assembly can also be a wound structure, formed by sequentially stacking and winding the positive electrode, the separator, and the negative electrode.

[0071] In some embodiments, the positive electrode 1 includes a positive current collector 101 and a positive active layer 102 disposed on at least one surface of the positive current collector 101.

[0072] In some embodiments, the positive current collector 101 may be made of aluminum foil or nickel foil, or any composite current collector disclosed in the prior art, such as, but not limited to, current collectors formed by combining the aforementioned conductive foil (aluminum foil or nickel foil, etc.) with a polymer substrate. The positive active layer 102 comprises a positive active material, which includes compounds that reversibly insert and deintercalate metal ions.

[0073] In some embodiments, the positive electrode active material may include lithium transition metal composite oxides, sodium transition metal composite oxides, etc. The lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese, and nickel.

[0074] In some embodiments, the positive electrode active material may include, but is not limited to, lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary materials (NCM), lithium manganese oxide (LiMn2O4), and lithium nickel manganese oxide (LiNi). 0.5 Mn 1.5 At least one of lithium iron phosphate (LiFePO4) or lithium iron phosphate (LiFePO4).

[0075] In some embodiments, the negative electrode 2 includes a negative electrode current collector 201 and a negative electrode active material layer 202 disposed on at least one surface of the negative electrode current collector.

[0076] In some embodiments, the negative electrode current collector 201 can be at least one of copper foil, nickel foil, stainless steel foil, titanium foil, or carbon-based current collector, or any composite current collector disclosed in the prior art, such as, but not limited to, current collectors formed by combining the aforementioned conductive foil and polymer substrate. The negative electrode active material layer 202 includes a negative electrode material, which is the negative electrode material described in the first aspect or the negative electrode material prepared by the aforementioned preparation method. The battery provided in this application embodiment has the advantages of high capacity, high initial coulombic efficiency, long cycle life, excellent rate performance, and low expansion. The battery can be a lithium-ion battery, a sodium-ion battery, a solid electrolyte battery, etc., and is not limited thereto.

[0077] The embodiments of the present invention will be further described below with reference to several examples. However, the embodiments of the present invention are not limited to the specific embodiments described below. Appropriate modifications can be made within the scope of the original claims.

[0078] Example 1

[0079] The method for preparing the negative electrode material in this embodiment includes the following steps:

[0080] (1) Natural flake graphite was crushed and shaped to obtain spherical natural graphite with an average particle size of 16μm.

[0081] (2) Spherical natural graphite and modifier (fatty alcohol polyoxyethylene ether AEO-9) were mixed at a mass ratio of 100:5 to obtain a first mixture. The first mixture was placed in an isostatic press for isostatic pressing treatment. The working pressure was set to 90 MPa, the time was 80 min, and the temperature was 80 °C to obtain block graphite. The block graphite was crushed and pulverized to obtain a precursor with a median particle size of 16 μm.

[0082] (3) The precursor and asphalt are mixed in a solid phase at a mass ratio of 85:15 to obtain a second mixture. The second mixture is then carbonized in an inert atmosphere kiln at a carbonization temperature of 1200℃ for 10 hours. After carbonization, the material is broken up, screened and demagnetized to obtain the negative electrode material.

[0083] Figure 2 shows the SEM image of the cross-section of the negative electrode material prepared in this embodiment. Figure 2 shows that the natural graphite has long and thin pores inside.

[0084] Examples 2 to 16 and comparative examples were prepared according to the preparation process of Example 1. The differences in process parameters between the other examples and Example 1 are detailed in Table 1.

[0085] Table 1. Preparation process parameters of negative electrode materials

[0086] Test methods

[0087] (1) Test method for particle size distribution of negative electrode material: The particle size test method refers to GB / T 19077-2016. The particle size distribution range of the negative electrode material was tested using a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK. The cumulative particle size distribution based on volume was determined by laser diffraction. D10 represents the particle size corresponding to a cumulative volume distribution percentage of 10%, D50 represents the particle size corresponding to a cumulative volume distribution percentage of 50%, and D90 represents the particle size corresponding to a cumulative volume distribution percentage of 90%. Volume particle size distribution width = (D 90 -D 10 ) / D 50 .

[0088] (2) The pore size distribution of the anode material was tested using a Micromeritics TriStar 3020 instrument. Referring to GB / T 24533-2019 "Graphite Anode Materials for Lithium-ion Batteries", the amount of nitrogen gas adsorbed on the solid surface at different relative pressures was measured under constant temperature and low temperature. Based on the Brown-Nauer-Etter-Taylor adsorption theory and its formula (BET formula), the amount of monolayer adsorption of the sample was calculated, and the specific surface area of ​​the material was calculated.

[0089] (3) Test method for tap density of negative electrode material: Refer to GB / T 24533-2019 "Graphite Anode Materials for Lithium-ion Batteries" for testing. Place the negative electrode material in the sample chamber of the tap density meter, vibrate it 1000 times and record the sample volume at this time. The tap density can be calculated according to the mass-volume ratio.

[0090] (4) Test method for oil absorption value of negative electrode material: The oil absorption value Q is tested by ASAHI S-500 oil absorption value tester of ASAHISOUKEN Japan. The oil absorption value Q is the amount of linseed oil added when the torque generated by the change of viscosity characteristics reaches 70% of the maximum torque. The unit is mL / 100g.

[0091] (5) The particle sample was milled using an ion milling machine (HITACHI E3500) to allow observation of the particle cross-section, and the sample was then placed under a high-power electron microscope (HITACHI S4800) to obtain information about the particle's interior. The aspect ratio of the pore refers to the information obtained from observing the particle's interior under the high-power electron microscope (HITACHI S4800). Twenty pores were randomly selected from the cross-section of the SEM image for measurement, as shown in Figure 3. The length and width of the pores were measured using a ruler. The longest diameter of the pore was defined as L, and the widest point perpendicular to the longest diameter was defined as D. The average length L and average width D of the 20 pores were calculated to obtain the average aspect ratio L / D of the pores.

[0092] Average area ratio of pores: Twenty particles were randomly selected from the SEM image for measurement. ImageJ software was used to analyze the cross-section of the spherical graphite particles in the cross-sectional SEM image. The color depth of non-pore 4 and pore 5 were distinguished by the color depth (as shown in Figure 4). The ratio of the pixel area of ​​all pores inside the particle to the total pixel area of ​​the cross-section was calculated, which is the area ratio of pores in the total area of ​​the cross-section. Then, the average area ratio of pores in the total area of ​​the cross-section of the 20 particles was calculated, which is the average area ratio of pores in the total area of ​​the cross-section.

[0093] (6) Pore volume test of negative electrode material:

[0094] 6.1 The pore volume of the material was tested using a Micromeritics AutoPore IV 9500 mercury porosimeter. The pore volume within the pore size range of 3 nm to 1000 nm was determined, and the pore volume was V = 1 mL / g. The mercury porosimeter method mainly displays the total volume of mesopores and macropores.

[0095] 6.2 The pore size distribution of the negative electrode material was tested using a Micromeritics TriStar 3020 instrument. At a constant low temperature, the adsorption amount of gas (nitrogen) on the solid material at different partial pressures was measured to obtain adsorption-desorption isotherms. Based on the Kelvin equation, there is a correlation between the pressure at which gas undergoes capillary condensation within the pores and its pore size; the lower the pressure, the smaller the pore size at which condensation occurs. By analyzing the desorption curves and using an appropriate mathematical model (BJH method), the pore volume V² mL / g can be calculated. The pore volume obtained by this method mainly includes the mesopore volume above 2 nm and the micropore volume below 2 nm on the particle surface.

[0096] (7) Test of the mass percentage of amorphous carbon in the negative electrode material: XRD was used to test the negative electrode material. A sample was prepared by adding 30% by mass of crystalline silicon powder as an internal standard, and the mixture was thoroughly mixed to form the test sample. During testing, a step scan was used with a step size of 0.02°, a time constant of 15s, and a scan range of 20°–40° (2Φ). Then, the Retive method was used for fitting and refinement calculations. The proportion of the crystalline silicon phase was fixed at 30%, and the proportion of the graphite phase was calculated, requiring a fitting factor Rwp less than 5. The remainder of the sum of the crystalline silicon phase and the graphite phase is the content of the amorphous carbon phase.

[0097] (8) The electrode expansion rate was tested using the testing device and system disclosed in patent CN201920973729.5 after 20 cycles. The negative electrode material, dispersant CMC, conductive agent SP, and binder SBR were mixed at a mass ratio of 95:1.5:1:2.5, with the solid content controlled at 50%. The mixture was then coated onto a copper foil current collector with a thickness of d0, vacuum dried, and the negative electrode sheet was obtained. The loading of the negative electrode material on the negative electrode sheet was controlled at 7.0 mg / cm². 2 The compacted density of the electrode sheet after roller pressing is 1.60 g / cm³. 3 The thickness d1 of the electrode was tested. Then, an LCO positive electrode prepared by a traditional mature process, a 1 mol / L LiPF6 / EC+DMC+EMC (v / v = 1:1:1) electrolyte, and a Celgard 2400 separator were assembled into a mold battery (testing device disclosed in patent CN201920973729.5) for testing. Under room temperature conditions, constant current charge and discharge was performed at 0.2C for the first week, and at 0.5C for the second week and thereafter, with the voltage limited to 2.75V~4.2V. After 20 cycles, the battery was disassembled, and the electrode thickness d2 was tested again. The electrode expansion rate = (d2-d1) / (d1-d0)*100%.

[0098] (9) The negative electrode material, conductive agent SP, and binder SBR were mixed at a mass percentage of 95:1:2.5, with the solid content controlled at 50%, and coated onto a copper foil current collector. The mixture was then vacuum dried to obtain the negative electrode sheet. Then, the LCO positive electrode sheet (lithium cobalt oxide model HVC-15D, slurry prepared at a mass ratio of positive electrode:SP:PVDF = 97.5:1.5:1, coated onto aluminum foil), 1 mol / L LiPF6 / EC+DMC+EMC (v / v = 1:1:1) electrolyte, Celgard 2400 separator, and casing were assembled into 18650 cylindrical cells using conventional manufacturing processes. The charge / discharge tests of the cylindrical cells were conducted on the LAND battery testing system of Wuhan Jinno Electronics Co., Ltd., under normal temperature conditions, with a constant current charge / discharge of 0.2C and a charge / discharge voltage limited to 2.75V–4.2V. The first charge capacity and first discharge capacity were obtained. First coulombic efficiency = first discharge capacity / first charge capacity.

[0099] 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 / first charge capacity * 100%.

[0100] The negative electrode materials prepared in the examples and comparative examples were subjected to various tests. The results are shown in Tables 2 and 3, where S1 to S16 represent Examples 1 to 16, and D1 to D5 represent Comparative Examples 1 to 5.

[0101] Table 2. Parameter test results of the negative electrode materials in each embodiment and comparative example

[0102] In Comparative Examples 2 and 3, the pore morphology of the negative electrode materials is non-elongated, meaning the pores are not linearly arranged, and the average aspect ratio of the pores is <2.5.

[0103] Table 3. Performance test data of each embodiment and comparative example

[0104] According to the data in Tables 2 and 3, the average area ratio of pores in the negative electrode materials prepared in Examples 1-16 is 5%-15% of the total cross-sectional area. This indicates low porosity and a relatively dense particle structure, allowing for minimal expansion during charging and discharging. Furthermore, controlling the average aspect ratio (L / D) of the pores to be greater than or equal to 2.5, with most pores being elongated and slender, further densifies the particles. By synergistically controlling the area ratio and average aspect ratio of the pores, the porosity of the negative electrode material can be controlled, reducing side reactions between the negative electrode material and the electrolyte. An appropriate amount of elongated pores can increase lithium-ion transport channels, improve lithium-ion transport efficiency, and thus improve the capacity, expansion, and cycle performance of the negative electrode material.

[0105] Furthermore, based on the data from Examples 16 and 1-15, it can be seen that Examples 1-15, in addition to satisfying that the average area ratio of pores in the total cross-sectional area of ​​the negative electrode material is 5% to 15% and the average aspect ratio L / D is greater than or equal to 2.5, also satisfy 0.04≤V1-V2≤0.14. This not only ensures that the negative electrode material has a reasonable number of lithium-ion transport channels and alleviates the expansion stress caused by lithium insertion / extraction of graphite particles, but also further improves the capacity and first coulombic efficiency of the negative electrode material.

[0106] Figure 5 is a SEM image of the negative electrode material provided in Comparative Example 1 of this application. As shown in Figures 2 and 5, the average pore area ratio of the negative electrode material prepared in Comparative Example 1 is larger than that of the negative electrode material in Example 3, and exceeds the upper limit of 15%. The pore filling efficiency in the spherical natural graphite decreases, the side reactions between the negative electrode material and the electrolyte increase, resulting in a decrease in the capacity and initial coulombic efficiency of the negative electrode material, and a significant decrease in the capacity retention rate after 50 cycles, leading to a deterioration in electrical performance.

[0107] According to the data from Comparative Example 2 and Example 3, the average pore area ratio of the negative electrode material prepared in Comparative Example 2 increased significantly to 24.8%, and the average aspect ratio L / D of the pores was only 1.9, which led to a significant increase in the pore size, an increase in side reactions between the negative electrode material and the electrolyte, a slight decrease in the capacity and initial coulombic efficiency of the negative electrode material, and a significant decrease in the capacity retention rate after 50 cycles.

[0108] According to the data from Comparative Example 3 and Example 3, the average pore area ratio of the negative electrode material prepared in Comparative Example 3 increased significantly to 19.4%, and the average length-to-width ratio (L / D) of the pores was 2.2. Some pores could not be effectively filled, resulting in a significant increase in the pore diameter. This led to an increase in side reactions between the negative electrode material and the electrolyte, resulting in a decrease in the capacity and initial coulombic efficiency of the negative electrode material, and a significant decrease in the capacity retention rate after 50 cycles.

[0109] According to the data from Comparative Example 4 and Example 3, the average area ratio of the pores in the negative electrode material prepared in Comparative Example 4 is only 4.8%. The average area ratio of the pores is too small, and the porosity of the negative electrode material is too low. This is not conducive to the electrolyte fully wetting the negative electrode material, and the lithium-ion transport channels of the negative electrode material are reduced, resulting in a decrease in the specific capacity of the negative electrode material. Furthermore, during cycling, the expansion effect of the negative electrode material is aggravated, and the capacity retention rate will also decrease.

[0110] According to the data from Comparative Example 5 and Example 3, although the average pore area ratio of the negative electrode material prepared in Comparative Example 5 is 13.2%, the pore aspect ratio is 1.6. The average aspect ratio of the pores is too small and the average width of the pores is too large, which leads to an increase in side reactions between the negative electrode material and the electrolyte, resulting in a significant decrease in the specific capacity of the negative electrode material.

[0111] Although this application discloses preferred embodiments as described above, it is not intended to limit the claims. Any person skilled in the art can make several possible changes and modifications without departing from the concept of this application. Therefore, the scope of protection of this application should be determined by the scope defined in the claims of this application.

Claims

1. A negative electrode material, characterized in that, The negative electrode material includes a core and amorphous carbon located on at least a portion of the surface of the core, the core including natural graphite, and the particles of the negative electrode material have pores inside; In the cross-sectional SEM image of the negative electrode material, 20 pores were randomly selected for measurement. The average width of the pores was measured as D, the average length of the pores was measured as L, and the average aspect ratio of the pores was L / D≥2.

5. Twenty particles were randomly selected from the SEM images for measurement. The area of ​​all pores on the cross-section of each particle and the total cross-sectional area were measured. The average area ratio of pores in the total cross-sectional area was calculated to be 5% to 15%.

2. The negative electrode material according to claim 1, characterized in that, The average aspect ratio L / D of the pores is ≥7.5; or, The average aspect ratio L / D of the pores satisfies: 2.5 ≤ L / D ≤ ​​20; or, The average aspect ratio L / D of the pores satisfies: 7.5 ≤ L / D ≤ ​​9.3; or, The average aspect ratio L / D of the pore is 2.5, 3, 4, 5, 6, 8, 10, 12, 15, 20 or any value within the range of any two of the above values.

3. The negative electrode material according to claim 1, characterized in that, The average area ratio of the pores in the total cross-sectional area is 5% to 10%; or, The average area ratio of the pores in the total cross-sectional area is 5% to 9.6%; or, The average percentage of the area of ​​the pores in the total cross-sectional area is 5%, 6%, 7%, 8%, 10%, 11%, 12%, 13%, 14%, 15%, or any value within the range of any two of the above values.

4. The negative electrode material according to claim 1, characterized in that, The D is 0.1 μm to 1.0 μm; and / or the L is 0.5 μm to 3.5 μm.

5. The negative electrode material according to claim 4, characterized in that, The value of D is 0.24 μm to 1.0 μm; or, The value of D is 0.24 μm to 0.31 μm; or, The value of D is 0.1 μm to 0.31 μm; or, The value of D is 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1.0μm, or any value within the range of any two of the above values; or The value of L is 2.2 μm to 2.5 μm; or, The value of L is 1.1 μm to 2.7 μm; or, The value of L is 0.5μm, 0.8μm, 1.0μm, 1.5μm, 2.0μm, 2.5μm, 2.8μm, 3.0μm, 3.2μm, 3.5μm, or any value within the range of any two of the above values.

6. The negative electrode material according to claim 1, characterized in that, The pore volume of the negative electrode material was determined by mercury porosimetry to be V1 mL / g, and by BET method to be V2 mL / g, with 0.04 ≤ V1 - V2 ≤ 0.

14.

7. The negative electrode material according to claim 6, characterized in that, 0.06≤V1-V2≤0.0725; or, 0.04≤V1-V2≤0.08; or 0.06≤V1-V2≤0.10; or V1-V2 is 0.04, 0.05, 0.06, 0.08, 0.10, 0.12, 0.13, 0.14, or any value within the range of any two of the above values.

8. The negative electrode material according to claim 6, characterized in that, 0.05≤V1≤0.12。 9. The negative electrode material according to claim 6, characterized in that, 0.004≤V2≤0.02。 10. The negative electrode material according to any one of claims 1 to 9, characterized in that, The oil absorption value of the negative electrode material is 38mL / 100g to 55mL / 100g.

11. The negative electrode material according to any one of claims 1 to 9, characterized in that, The volumetric particle size distribution width of the negative electrode material satisfies: 0.90 ≤ (D 90 -D 10 ) / D 50 ≤1.

20.

12. The negative electrode material according to any one of claims 1 to 9, characterized in that, The negative electrode material satisfies at least one of the following characteristics: (1) The natural graphite includes spherical natural graphite; (2) The median particle size of the natural graphite is 5 μm to 18 μm.

13. The negative electrode material according to any one of claims 1 to 9, characterized in that, The amorphous carbon content in the negative electrode material is 1% to 20% by mass.

14. The negative electrode material according to any one of claims 1 to 9, characterized in that, The negative electrode material satisfies at least one of the following characteristics: (1) The median particle size of the negative electrode material is 8 μm to 20 μm; (2) The specific surface area of ​​the negative electrode material is 0.5 m². 2 / g~4.0m 2 / g; (3) The tap density of the negative electrode material is 0.85 g / cm³. 3 ~1.20g / cm 3 .

15. A battery, characterized in that, The battery comprises the negative electrode material according to any one of claims 1 to 14.

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