Negative electrode material and battery

Abstract

The present application provides a negative electrode material and a battery. The negative electrode material comprises an inner core and a carbon layer located on at least part of the surface of the inner core, wherein the inner core comprises graphite. The negative electrode material comprises a doping element, wherein the mass percentage content of the doping element is less than or equal to 1%, and the doping element comprises P and O. The negative electrode material is tested by means of X-ray photoelectron energy spectrum analysis, and the negative electrode material has a P-C chemical bond and a P-O chemical bond, wherein the area ratio of the characteristic peak of the P-C chemical bond to the characteristic peak of the P-O chemical bond is A, and A=(25-65):(75-35). By means of the negative electrode material provided in the present application, the reversible capacity, thermal stability and cycle performance of a negative electrode material can be comprehensively improved.

Description

Anode materials and batteries

[0001] This application claims priority to Chinese patent application No. 202411783440.9, filed with the State Intellectual Property Office of China on December 5, 2024, entitled "Anode Material and Battery", and Chinese patent application No. 202411913792.1, filed with the State Intellectual Property Office of China on December 20, 2024, entitled "Anode Material and Battery", the contents of which are incorporated herein by reference. Technical Field

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

[0003] The rapid development of lithium-ion batteries has brought about tremendous changes to human life. As one of the core components of lithium-ion batteries, the anode material has a significant impact on their electrochemical performance. Therefore, developing cost-effective anode materials is of great importance in lithium-ion battery research. Natural graphite, due to its stable structure and high theoretical specific capacity (372 mAh / g), is widely used as an anode material for lithium-ion batteries. However, with the pursuit of higher energy density batteries, the theoretical capacity of graphite anode materials has approached its limit, making it difficult to meet the needs of future battery development. To further improve the specific capacity and other related properties of anode materials, element doping technology has emerged.

[0004] Currently, in order to improve the specific capacity of graphite anode materials, doping treatment (such as nitrogen doping) is performed on graphite anode materials, which increases the specific capacity of graphite anode materials, but has limited improvement on the thermal stability and cycle performance of graphite.

[0005] Application content

[0006] In view of this, this application provides a negative electrode material and a battery that can comprehensively improve the reversible capacity, thermal stability and cycle performance of the negative electrode material.

[0007] In a first aspect, this application provides a negative electrode material, the negative electrode material comprising a core and a carbon layer located on at least a portion of the surface of the core, the core comprising graphite;

[0008] The negative electrode material contains doping elements, and the mass percentage of the doping elements is ≤1%; the doping elements include P and O elements.

[0009] The negative electrode material was tested by X-ray photoelectron spectroscopy, and the negative electrode material has PC chemical bonds and PO chemical bonds; wherein, the area ratio of the characteristic peaks of the PC chemical bonds to the PO chemical bonds is A, A = (25~65):(75~35).

[0010] The technical solution of this application has at least the following beneficial effects:

[0011] Firstly, the negative electrode material provided in this application includes a core and a carbon layer on the surface of the core. The negative electrode material is doped with phosphorus (P) and oxygen (O), resulting in PC (polyphosphate) and PO (polyoxygenate) chemical bonds. The PC chemical bonds improve the conductivity and lithium intercalation sites of the negative electrode material, increasing its lithium storage capacity. However, because the PC chemical bonds have higher electrochemical activity than the PO chemical bonds, some phosphorus atoms react with and dissolve in the electrolyte during charge-discharge cycles, especially at high temperatures, leading to a decrease in the thermal stability and high-temperature storage performance of the negative electrode material. Therefore, this application controls the mass percentage of P and O elements in the negative electrode material to be less than or equal to 1%, which can reduce the dissolution of phosphorus atoms, reduce electrolyte decomposition, ensure the capacity retention rate of the negative electrode material during high-temperature cycling and high-temperature storage, and reduce capacity decay. Furthermore, due to the high electronegativity of oxygen atoms, they can form highly polar and relatively less chemically reactive PO chemical bonds with phosphorus atoms. These PO chemical bonds remain relatively stable during repeated charge-discharge cycles and high-temperature storage, making them less prone to breakage and phosphorus atoms less likely to dissolve, thus enhancing the thermal and chemical stability of the anode material. This application controls the total mass percentage of doping elements (P and O) to below 1%, and simultaneously controls the area ratio A of the characteristic peaks of PC and PO chemical bonds to be (25–65):(75–35), meaning the ratio of PC to PO chemical bonds is controlled within the aforementioned range. Some phosphorus atoms combine with oxygen atoms to form relatively less chemically reactive PO chemical bonds, reducing phosphorus atom dissolution; other phosphorus atoms combine with carbon atoms to form more chemically reactive PC chemical bonds, enhancing the anode material's adsorption capacity for active lithium ions. Under the synergistic effect of these characteristics, the specific capacity, high-temperature cycle stability, and high-temperature storage stability of the anode material can be comprehensively improved.

[0012] In a second aspect, this application provides a negative electrode material, the negative electrode material comprising a core and a carbon layer located on at least a portion of the surface of the core, the core comprising graphite;

[0013] The total pore volume of the negative electrode material is 0.003 cm³. 3 / g~0.015cm 3 / g, wherein the volume of pores with a pore size of 3nm to 5nm accounts for 6% to 13% of the total pore volume;

[0014] The negative electrode material contains doping elements, including P and O elements; X-ray photoelectron spectroscopy analysis shows that the negative electrode material has PC and PO chemical bonds; wherein the area ratio of the characteristic peaks of the PC chemical bonds to the PO chemical bonds is A, 0.1≤A≤1.5.

[0015] The technical solution of this application has at least the following beneficial effects:

[0016] Secondly, the negative electrode material provided in this application includes a core and a carbon layer located on at least a portion of the surface of the core. The negative electrode material possesses PC and PO chemical bonds. These PC and PO chemical bonds effectively improve the stability of the SEI film and 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 and improving cycle performance. Furthermore, by controlling the area ratio A of the characteristic peaks of the PC and PO chemical bonds to be between 0.1 and 1.5, some phosphorus atoms form relatively weak PO chemical bonds with oxygen atoms, which can reduce phosphorus atom dissolution, reduce electrolyte decomposition, and ensure the capacity retention rate of the negative electrode material during cycling. Moreover, an appropriate amount of PC and PO chemical bonds can improve the active sites for lithium intercalation and the lithium storage capacity of the negative electrode material, thereby increasing the reversible capacity of the negative electrode material. Simultaneously, the total pore volume of the negative electrode material is controlled to be 0.003 cm³. 3 / g~0.015cm 3 The volume fraction of Li⁻ is 6%–13% with pores having a diameter of 3 nm–5 nm, and the presence of these pores can also increase the Li⁻ content. + The diffusion channels also provide more lithium storage active sites, promoting the diffusion of lithium ions at the solid-liquid interface and within the solid phase, which is beneficial for improving the reversible capacity and rate performance of the anode material. The anode material of this application synergistically controls the A value and the total pore volume to 0.003 cm³. 3 / g~0.015cm 3 The volume percentage of pores with a diameter of 3nm to 5nm is 6% to 13%, which means that the anode material has more lithium storage active sites, can also enhance the stabilizer of the SEI film, reduce electrolyte decomposition, and enable the anode material to have higher reversible capacity and excellent cycle stability.

[0017] This application provides a battery comprising the aforementioned negative electrode material. Attached Figure Description

[0018] Figure 1 is a schematic diagram of the discharge state of the battery provided in an embodiment of this application;

[0019] Figure 2 is a SEM image of the negative electrode material prepared in Example 1 of this application;

[0020] Figure 3 is a schematic diagram of the XPS negative electrode material prepared in Example 1 of this application;

[0021] Figure 4 is a schematic diagram of the capacity-voltage curve of the negative electrode material prepared in Example 1 of this application;

[0022] Figure 5 is a schematic diagram of the pore size distribution of the negative electrode materials prepared in Example 20 and Comparative Example 20 of this application;

[0023] Figure 6 is a schematic diagram of the XPS negative electrode material prepared in Example 20 of this application;

[0024] Figure 7 is a schematic diagram of the capacity-voltage curve of the negative electrode material prepared in Example 20 of this application;

[0025] Figure 8 is a comparison of the cycle performance of the negative electrode materials prepared in Example 23 and Comparative Example 20 of this application. Detailed Implementation

[0026] 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.

[0027] Based on this, in a first aspect, this application provides a negative electrode material, the negative electrode material including a core and a carbon layer located on at least a portion of the surface of the core, the core including graphite;

[0028] The negative electrode material contains doped elements, with a mass percentage of doped elements ≤1%; the doped elements include P and O elements;

[0029] The negative electrode material was tested by X-ray photoelectron spectroscopy and found to have PC and PO chemical bonds. The area ratio of the characteristic peaks of the PC chemical bonds to those of the PO chemical bonds is A, where A = (25-65): (75-35).

[0030] The negative electrode material provided in this application includes a core and a carbon layer on the surface of the core. The negative electrode material is doped with phosphorus (P) and oxygen (O), resulting in PC (polyphosphate) and PO (polyoxygenate) chemical bonds. The PC chemical bonds improve the conductivity and lithium intercalation sites of the negative electrode material, increasing its lithium storage capacity. However, because the PC chemical bonds have higher electrochemical activity than the PO chemical bonds, some phosphorus atoms react with and dissolve in the electrolyte during charge-discharge cycles, especially at high temperatures, leading to a decrease in the thermal stability and high-temperature storage performance of the negative electrode material. Therefore, this application controls the mass percentage of P and O elements in the negative electrode material to be less than or equal to 1%, which reduces phosphorus atom dissolution, reduces electrolyte decomposition, ensures the capacity retention of the negative electrode material during high-temperature cycling and storage, and reduces capacity decay. Furthermore, due to the high electronegativity of oxygen atoms, they can form highly polar and relatively less chemically reactive PO chemical bonds with phosphorus atoms. These PO chemical bonds remain relatively stable during repeated charge-discharge cycles and high-temperature storage, making them less prone to breakage and phosphorus atoms less likely to dissolve, thus enhancing the thermal and chemical stability of the anode material. This application controls the total mass percentage of doping elements (P and O) to below 1%, and simultaneously controls the area ratio A of the characteristic peaks of PC and PO chemical bonds to be (25–65):(75–35), meaning the ratio of PC to PO chemical bonds is controlled within the aforementioned range. Some phosphorus atoms combine with oxygen atoms to form relatively less chemically reactive PO chemical bonds, reducing phosphorus atom dissolution; other phosphorus atoms combine with carbon atoms to form more chemically reactive PC chemical bonds, enhancing the anode material's adsorption capacity for active lithium ions. Under the synergistic effect of these characteristics, the specific capacity, high-temperature cycle stability, and high-temperature storage stability of the anode material can be comprehensively improved.

[0031] In some embodiments, the area ratio of the characteristic peaks of PC chemical bonds to PO chemical bonds is (25-65):(75-35), specifically 25:75, 30:70, 35:65, 40:60, 45:55, 50:50, 55:45, 60:40, 65:35, etc., and other values ​​within the above range are also possible, without limitation. Preferably, the area ratio of the characteristic peaks of PC chemical bonds to PO chemical bonds is (30-60):(70-40).

[0032] In some embodiments, the mass percentage of doped elements is ≤1% based on the mass of the negative electrode material as 100%. Specifically, it can be 1%, 0.8%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, 0.1%, 0.05%, or 0.01%, etc. Of course, it can also be other values ​​within the above range, which are not limited here.

[0033] In some embodiments, the mass percentage of phosphorus (P) in the anode material is between 10 ppm and 2000 ppm. Specifically, it can be 10 ppm, 20 ppm, 50 ppm, 60 ppm, 80 ppm, 100 ppm, 150 ppm, 200 ppm, 300 ppm, 500 ppm, 800 ppm, 1000 ppm, 1500 ppm, or 2000 ppm, or other values ​​within the above range, which are not limited here. When the mass percentage of P in the anode material is greater than 2000 ppm, excessive phosphorus atoms dissolve, leading to partial electrolyte decomposition, especially at high temperatures, resulting in decreased thermal stability and high-temperature storage performance of the anode material. When the mass percentage of P in the anode material is too low, the lithium-ion transport rate at the solid-liquid interface of the anode material slows down, which is detrimental to the capacity utilization of the anode material.

[0034] In some embodiments, the total pore volume of the negative electrode material is V cm. 3 / g, 0.0035<V≤0.006, specifically it can be 0.00351cm 3 / g, 0.0036cm 3 / g, 0.0037cm 3 / g, 0.0038cm 3 / g, 0.004cm 3 / g, 0.0045cm 3 / g, 0.005cm 3 / g, 0.0055cm 3 / g or 0.006cm 3 / g, etc., are not limited here. Controlling the total pore volume of the negative electrode material within the above range allows for more lithium-ion diffusion channels and electrochemical reaction interfaces during electrochemical reactions, promoting lithium-ion diffusion at the solid-liquid interface and within the solid phase, and reducing concentration polarization. However, excessive pores can exacerbate side reactions between the electrolyte and PC chemical bonds, leading to the dissolution of some phosphorus atoms and the decomposition of part of the electrolyte, thus reducing the electrochemical performance of the battery made from the negative electrode material. Therefore, controlling the total pore volume of the negative electrode material within the above range in this application can both promote lithium-ion transport and reduce side reactions at the solid-liquid interface between the electrolyte and the negative electrode material, which is beneficial for improving the reversible capacity and rate performance of the negative electrode material.

[0035] In some embodiments, graphite includes at least one of synthetic graphite and natural graphite.

[0036] Natural graphite is flake graphite, a natural crystalline graphite with a fish-scale-like shape. It belongs to the hexagonal crystal system and has a layered structure, possessing excellent properties such as high temperature resistance, electrical conductivity, thermal conductivity, lubrication, plasticity, and resistance to acids and alkalis. Artificial graphite is a graphite material obtained by carbonizing organic matter and then undergoing a high-temperature graphitization process.

[0037] In some embodiments, the graphite includes spherical graphite, which is natural graphite. Specifically, spherical graphite can be obtained by shaping graded material during the spheroidization process of natural flake graphite. Spherical natural graphite has high isotropy, and the lithium-ion transport paths are similar, which can help to comprehensively improve the lithium-ion transport efficiency of the anode material.

[0038] In some embodiments, the median particle size of graphite is 5 μm to 25 μm, more specifically, it can be 5 μm, 6 μm, 8 μm, 9 μm, 10 μm, 11.5 μm, 12 μm, 15 μm, 16 μm, 20 μm, 22 μm, 23 μm, or 25 μm, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. Multiple experiments have shown that controlling the median particle size of graphite within the above range is beneficial for achieving a balance between processing performance, capacity, and rate performance. Preferably, the median particle size of graphite is 8 μm to 18 μm.

[0039] In some embodiments, the fixed carbon content of graphite is ≥98%, specifically 98%, 98.5%, 99%, 99.5%, 99.8%, or 99.9%, etc., but not limited to the listed values; other unlisted values ​​within this range also apply. Preferably, the mass content of carbon in graphite is ≥99.95%.

[0040] In some embodiments, the carbon layer in the anode material has a mass percentage of 1% to 30%; specifically, it can be 1%, 3%, 5%, 8%, 10%, 15%, 18%, 20%, 25%, 28%, or 30%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. An appropriate amount of carbon layer on the core surface can ensure that the anode material achieves both high capacity and rate performance.

[0041] In some embodiments, the thickness of the carbon layer is 5nm to 200nm. Specifically, it can be 5nm, 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 100nm, 150nm or 200nm, etc., and is not limited here.

[0042] In some embodiments, the carbon layer comprises amorphous carbon containing doped elements. The carbon layer is formed by reacting a phosphorus-containing compound with a coating agent, and the doping elements mainly include oxygen and phosphorus, with the phosphorus uniformly distributed in the carbon layer.

[0043] In some embodiments, the amorphous carbon in the carbon layer may be derived from at least one of petroleum-based bitumen and coal-based bitumen. The bitumen may be solid bitumen or liquid bitumen. Preferably, the amorphous carbon in the carbon layer is derived from petroleum bitumen.

[0044] In some embodiments, the median particle size of the negative electrode material is 5μm to 30μm. Specifically, it can be 5μm, 8μm, 9μm, 10μm, 11μm, 12μm, 14μm, 15μm, 16μm, 20μm, 25μm or 30μm, etc., and is not limited here.

[0045] In some embodiments, the carbon content in the negative electrode material is ≥95%, specifically it can be 95%, 95.2%, 95.5%, 96%, 96.5%, 96.8%, 97%, 97.5%, 98%, 99%, 99.5% or 100%, etc., and is not limited here.

[0046] In some implementations, the specific surface area of ​​the negative electrode material is 1m². 2 / g~5m 2 / g; specifically, it can be 1.0m 2 / g, 1.8m 2 / g, 2.0m 2 / g, 2.5m 2 / g, 3.3m 2 / g, 4.0m 2 / g, 4.8m 2 / g、5m 2 / g or any value within the range of any two of the above values, without limitation. Preferably, the specific surface area of ​​the negative electrode material is 1.5m². 2 / g~2.0m 2 / g. By controlling the specific surface area of ​​the negative electrode material within the above range, the side reactions between the negative electrode material and the electrolyte are reduced, which is beneficial to improving the initial coulombic efficiency of the negative electrode material.

[0047] In some embodiments, the tap density of the negative electrode material is 0.6 g / cm³. 3 ~1.5g / cm 3 Specifically, it could be 0.6 g / cm³. 3 0.7g / cm 3 0.75g / cm 3 0.8g / cm 3 0.85g / cm 3 0.9g / cm 3 0.95g / cm 3 1.0g / cm 3 1.2g / cm 3 1.5g / cm3 Or any value within the range of any two of the above values, without limitation herein. Preferably, the tap density of the negative electrode material is 0.8 g / cm³. 3 ~1.1g / cm 3 .

[0048] In some embodiments, the powder conductivity of the negative electrode material under a pressure of 4 kN is 140 S / cm to 180 S / cm, more specifically, it can be 140 S / cm, 145 S / cm, 150 S / cm, 155 S / cm, 160 S / cm, 170 S / cm, or 180 S / cm, etc., but is not limited to the listed values; other unlisted values ​​within this range are also applicable. In this application, the conductivity of the negative electrode material is improved because appropriate amounts of P and O elements are doped at the solid-liquid reaction interface.

[0049] In a second aspect, this application provides a negative electrode material, which includes a core and a carbon layer located on at least a portion of the surface of the core, wherein the core includes graphite;

[0050] The total pore volume of the negative electrode material is 0.003 cm³. 3 / g~0.015cm 3 / g, of which the pore volume of pores with a pore size of 3nm to 5nm accounts for 6% to 13% of the total pore volume;

[0051] The anode material contains doping elements, including P and O elements. X-ray photoelectron spectroscopy analysis shows that the anode material has PC and PO chemical bonds. The area ratio of the characteristic peaks of the PC and PO chemical bonds is A, where 0.1 ≤ A ≤ 1.5.

[0052] The negative electrode material provided in this application includes a core and a carbon layer located on at least a portion of the surface of the core. The negative electrode material has PC and PO chemical bonds, which effectively improve the stability of the SEI film and 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. Furthermore, by controlling the area ratio A of the characteristic peaks of PC and PO chemical bonds to be between 0.1 and 1.5, some phosphorus atoms form relatively weak PO chemical bonds with oxygen atoms, reducing phosphorus atom dissolution and electrolyte decomposition, thus ensuring the capacity retention of the negative electrode material during cycling. Additionally, an appropriate amount of PC and PO chemical bonds can improve the active sites for lithium intercalation and the lithium storage capacity of the negative electrode material, thereby increasing its reversible capacity. Simultaneously, the total pore volume of the negative electrode material is controlled to be 0.003 cm³. 3 / g~0.015cm 3The volume fraction of Li⁻ is 6%–13% with pores having a diameter of 3 nm–5 nm, and the presence of these pores can also increase the Li⁻ content. + The diffusion channels also provide more lithium storage active sites, promoting the diffusion of lithium ions at the solid-liquid interface and within the solid phase, which is beneficial for improving the reversible capacity and rate performance of the anode material. The anode material of this application synergistically controls the A value and the total pore volume to 0.003 cm³. 3 / g~0.015cm 3 The volume percentage of pores with a diameter of 3nm to 5nm is 6% to 13%, which means that the anode material has more lithium storage active sites, can also enhance the stabilizer of the SEI film, reduce electrolyte decomposition, and enable the anode material to have higher reversible capacity and excellent cycle stability.

[0053] In some embodiments, the area ratio of the characteristic peaks of the PC chemical bond to the PO chemical bond is A, where 0.1 ≤ A ≤ 1.5. A can specifically be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, or 1.5, or any other value within the above range or any value within the range of any two of the above values; no limitation is made here. When the value of A is too large, the reversible capacity of the negative electrode material increases. During charge-discharge cycles, some phosphorus atoms react with the electrolyte and dissolve in the electrolyte, especially at high temperatures, leading to a decrease in the thermal stability and high-temperature storage performance of the negative electrode material. When the value of A is too small, the cycle performance of the negative electrode material improves, but the reversible capacity of the negative electrode material decreases. Preferably, 0.3 ≤ A ≤ 1.2.

[0054] In some embodiments, the total pore volume of the negative electrode material is 0.003 cm³. 3 / g~0.015cm 3 / g, specifically 0.003cm 3 / g, 0.004cm 3 / g, 0.005cm 3 / g, 0.006cm 3 / g, 0.007cm 3 / g, 0.008cm 3 / g, 0.009cm 3 / g, 0.01cm 3 / g, 0.011cm 3 / g, 0.012cm 3 / g, 0.013cm 3 / g, 0.014cm 3 / g or 0.015cm 3 / g, or any value within the range of any two of the above values, is not limited here. When the total pore volume of the negative electrode material is controlled within the above range, the pores create more lithium-ion diffusion channels and electrochemical reaction interfaces for the negative electrode material during electrochemical reactions. This promotes the diffusion of lithium ions at the solid-liquid interface and within the solid phase, reduces concentration polarization, and is beneficial for improving the reversible capacity and rate performance of the negative electrode material.

[0055] In some embodiments, the pore size distribution of the negative electrode material is in the range of 0.2nm to 250nm, specifically 0.2nm, 1nm, 2nm, 5nm, 8nm, 10nm, 20nm, 30nm, 50nm, 100nm, 150nm, 200nm, 250nm, or any value within the range of any two of the above values, without limitation.

[0056] In some embodiments, the volume percentage of pores with a diameter of 3 nm to 5 nm in the total pore volume is 6% to 13%; specifically, it can be 6%, 7%, 8%, 9%, 10%, 12%, or 13%, etc., or other values ​​within the above range, or any value within the range formed by any two of the above values, and is not limited herein. In this application, controlling the volume percentage of pores with a diameter in the range of 3 nm to 5 nm in the total pore volume is beneficial because the presence of these pores can increase the lithium storage active sites, thereby improving the capacity and rate performance of the anode material. Preferably, the volume percentage of pores with a diameter of 3 nm to 5 nm in the total pore volume is 8% to 11%.

[0057] In some embodiments, the volume ratio of pores with a diameter of 5 nm or more in the total pore volume is 75% to 88%, specifically 75%, 78%, 80%, 83%, 85%, 86%, or 88%, or any value within the range of any two of the above values, without limitation.

[0058] In some embodiments, the mass percentage of phosphorus (P) in the anode material is between 10 ppm and 2000 ppm. Specifically, it can be 10 ppm, 20 ppm, 50 ppm, 60 ppm, 80 ppm, 100 ppm, 150 ppm, 200 ppm, 300 ppm, 500 ppm, 800 ppm, 1000 ppm, 1500 ppm, 2000 ppm, or any value within the range of any two of the above values; no limitation is made here. When the mass percentage of P in the anode material is greater than 2000 ppm, excessive phosphorus atoms dissolve, leading to partial electrolyte decomposition, especially at high temperatures, resulting in decreased thermal stability and high-temperature storage performance of the anode material. When the mass percentage of P in the anode material is too low, the number of PC and PO chemical bonds formed by P doping decreases, reducing the anode material's adsorption capacity for lithium ions and decreasing the number of lithium ion storage active sites, which is detrimental to the capacity utilization of the anode material.

[0059] In some embodiments, graphite includes at least one of synthetic graphite and natural graphite.

[0060] Natural graphite is flake graphite, a natural crystalline graphite with a fish-scale-like shape. It belongs to the hexagonal crystal system and has a layered structure, possessing excellent properties such as high temperature resistance, electrical conductivity, thermal conductivity, lubrication, plasticity, and resistance to acids and alkalis. Artificial graphite is a graphite material obtained by carbonizing organic matter and then undergoing a high-temperature graphitization process.

[0061] In some embodiments, the graphite includes spherical graphite, which is natural graphite. Specifically, spherical graphite can be obtained by shaping graded material during the spheroidization process of natural flake graphite. Spherical natural graphite has high isotropy, and the lithium-ion transport paths are similar, which can help to comprehensively improve the lithium-ion transport efficiency of the anode material.

[0062] In some embodiments, the fixed carbon content of graphite is ≥98%, specifically it can be 98%, 98.5%, 99%, 99.5%, 99.8%, 99.9%, or any value within the range of any two of the above values, and is not limited herein. Preferably, the mass content of carbon in graphite is ≥99.95%.

[0063] In some embodiments, the thickness of the carbon layer is 5 nm to 200 nm. Specifically, it can be 5 nm, 10 nm, 20 nm, 50 nm, 80 nm, 110 nm, 140 nm, 170 nm, 200 nm, or any value within the range of any two of the above values, and is not limited herein. Preferably, the thickness of the carbon layer is 40 nm to 100 nm.

[0064] In some embodiments, the carbon layer comprises amorphous carbon containing doped elements. The carbon layer is formed by reacting a phosphorus-containing compound with a coating agent, and the doping elements mainly include oxygen and phosphorus, with the phosphorus uniformly distributed in the carbon layer.

[0065] In some embodiments, the carbon layer in the anode material has a mass percentage of 1% to 30%; specifically, it can be 1%, 3%, 5%, 8%, 10%, 15%, 18%, 20%, 25%, 28%, or 30%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. An appropriate amount of carbon layer on the core surface can ensure that the anode material achieves both high capacity and rate performance.

[0066] In some embodiments, the particle sphericity Sh(90%) corresponding to a cumulative volume distribution percentage of 90% in the negative electrode material is 0.8 to 0.94. Specifically, Sh(90%) can be 0.8, 0.85, 0.86, 0.89, 0.90, 0.92, 0.94, or any value within the range of any two of the above values, and is not limited here. Preferably, the sphericity Sh(90%) is 0.9 to 0.94. The sphericity of the negative electrode material is mainly affected by the sphericity of the core graphite. The higher the sphericity of the negative electrode material, the higher its orientation. During cycling, due to the continuous insertion and extraction of lithium ions between graphite layers, the resulting expansion stress can be released in multiple directions, reducing particle breakage caused by excessive local expansion stress in the negative electrode material particles, improving the expansion effect of the negative electrode material, and effectively enhancing the cycling performance of the negative electrode material.

[0067] In some embodiments, in the Raman spectrum of the negative electrode material, the negative electrode material at 1300 cm⁻¹ -1 -1400cm -1 It has a D peak at 1550 cm⁻¹ -1 -1600cm -1 The ratio of the Raman intensity of the D peak to the G peak is 0.25 ≤ I. D / I G ≤0.5. I D / I G Specifically, it can be 0.25, 0.30, 0.33, 0.35, 0.37, 0.38, 0.42, 0.46, 0.48, 0.5, or any value within the range of any two of the above values, without any limitation here.

[0068] In some embodiments, the oil absorption value of the negative electrode material is 37mL / 100g to 48mL / 100g, specifically it can be 37mL / 100g, 38mL / 100g, 40mL / 100g, 42mL / 100g, 44mL / 100g, 45mL / 100g, 46mL / 100g, 47mL / 100g, 48mL / 100g, or any value within the range of any two of the above values, and is not limited here.

[0069] In some embodiments, the median particle size of the negative electrode material is 5 μm to 25 μm. Specifically, it can be 5 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 14 μm, 15 μm, 16 μm, 20 μm, 25 μm, or any value within the range of any two of the above values, and is not limited here.

[0070] In some implementations, the specific surface area of ​​the negative electrode material is 1m². 2 / g~5m 2 / g; specifically, it can be 1.0m 2 / g, 1.8m 2 / g, 2.0m 2 / g, 2.5m 2 / g, 3.3m 2 / g, 4.0m 2 / g, 4.8m 2 / g、5m 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 reduces side reactions between the negative electrode material and the electrolyte, which is beneficial to improving the initial coulombic efficiency of the negative electrode material.

[0071] In some embodiments, the tap density of the negative electrode material is 0.6 g / cm³. 3 ~1.5g / cm 3 Specifically, it could be 0.6 g / cm³. 3 0.7g / cm 3 0.75g / cm 3 0.8g / cm 3 0.85g / cm 3 0.9g / cm 3 0.95g / cm 3 1.0g / cm 3 1.2g / cm 3 1.5g / cm 3 Or any value within the range of any two of the above values, without limitation.

[0072] In some embodiments, the powder conductivity of the negative electrode material under a pressure of 4 kN is 110 S / cm to 175 S / cm. More specifically, it can be 110 S / cm, 115 S / cm, 120 S / cm, 130 S / cm, 140 S / cm, 150 S / cm, 160 S / cm, 175 S / cm, or any value within the range of any two of the above values, and is not limited herein. The negative electrode material of this application improves conductivity and effectively enhances powder conductivity by incorporating appropriate amounts of doping elements within the carbon layer.

[0073] This application provides a method for preparing a negative electrode material, comprising the following steps:

[0074] Step S10: The mixture containing graphite, coating agent and phosphorus doping source is subjected to polymerization treatment to obtain a precursor, wherein the mass ratio of coating agent to phosphorus doping source is (1-99):1.

[0075] Step S20: The precursor is carbonized to obtain the negative electrode material.

[0076] The method for preparing the anode material provided in this application involves polymerizing a mixture containing graphite, a coating agent, and a phosphorus-doped source, followed by carbonization. During carbonization, the phosphorus-doped source decomposes to produce gases such as H2O and CO2, which are then released. Simultaneously, elemental doping occurs in the carbon layer, increasing the number of lithium-storage active sites and improving the migration rate of lithium ions. By controlling the amount of phosphorus-doped source added, the area ratio A of the characteristic peaks of PC and PO chemical bonds in the anode material is controlled to be within the aforementioned range. Phosphorus has high electronegativity and can combine with the carbon material formed by the coating agent to form PC chemical bonds, which can improve the conductivity of the anode material, increase the number of active sites, and enhance its lithium-storage capacity. A portion of the phosphorus atoms form relatively weak PO chemical bonds with oxygen atoms. The presence of PO chemical bonds can reduce the dissolution of phosphorus atoms and enhance the structural stability and high-temperature storage stability of the anode material. The synergistic effect of PC and PO chemical bonds comprehensively improves the specific capacity, high-temperature cycle stability, and high-temperature storage stability of the anode material.

[0077] The preparation method of this application is explained in detail below with reference to the embodiments:

[0078] Before step S10, the method may further include: shaping natural flake graphite to obtain spherical graphite.

[0079] Natural flake graphite is a type of natural crystalline graphite. It resembles fish scales, belongs to the hexagonal crystal system, and has a layered structure. It possesses excellent properties such as high temperature resistance, electrical conductivity, thermal conductivity, lubrication, plasticity, and acid and alkali resistance.

[0080] In some embodiments, shaping includes at least one of crushing, spheroidizing, or grading.

[0081] Natural graphite can be shaped by spheroidization, with the spheroidization rate controlled at 500 r / min to 5000 r / min and the spheroidization time at 0.2 to 10 h.

[0082] The median particle size of the graphite obtained after shaping is 5μm to 25μm. More specifically, it can be 5μm, 8μm, 9μm, 10μm, 11μm, 12μm, 14μm, 15μm, 16μm, 20μm, or 25μm, but it is not limited to the listed values; other unlisted values ​​within this range are also applicable. Multiple experiments have shown that controlling the median particle size of graphite within the above range is beneficial for balancing processing performance, capacity, and rate performance.

[0083] In some implementations, artificial graphite may also be used.

[0084] In some embodiments, the carbon content in the graphite is ≥95% by mass, specifically 95%, 96%, 97%, 97.5%, 98.3%, 98.8%, or 99%, etc., but not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0085] In other embodiments, graphite materials that directly meet the requirements can be purchased to perform the following steps S10 to S20, which are not limited here.

[0086] Step S10: The mixture containing graphite, coating agent and phosphorus doping source is subjected to polymerization treatment to obtain a precursor, wherein the mass ratio of coating agent to phosphorus doping source is (1-99):1.

[0087] In some embodiments, the coating agent includes at least one of petroleum-based liquid asphalt and coal-based liquid asphalt. Specifically, the petroleum-based liquid asphalt can be petroleum asphalt, modified asphalt, or mesophase asphalt, etc.

[0088] In some embodiments, the softening point of the coating agent is 100℃ to 400℃; specifically, it can be 100℃, 150℃, 200℃, 250℃, 300℃, 350℃, or 400℃, or other values ​​within the above range, which are not limited here. Controlling the softening point of the coating agent within this range allows it to soften sufficiently during the thermal polymerization process, facilitating thorough mixing between the coating agent and graphite. Part of the coating agent fills into the pore structure of the graphite, increasing the compaction density of the negative electrode material. Preferably, the coating agent comprises petroleum asphalt, and the softening point of the petroleum asphalt is 100℃ to 200℃.

[0089] In some embodiments, the residual carbon value of the coating agent is 10% to 80%, specifically 10%, 20%, 30%, 40%, 50%, 60%, 70% or 80%, etc., and of course, other values ​​within the above range are also possible, which are not limited here.

[0090] In some embodiments, the phosphorus doping source includes at least one selected from phosphoric acid, lithium phosphate, phosphorus pentoxide, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphazene, pentafluorocyclotriphosphazene, ethoxy(pentafluoro)cyclotriphosphazene, hexachlorocyclotriphosphazene, phosphate ester, triphenylphosphine, ammonium phosphate, and ammonium polyphosphate. In this application, during the polymerization process, the P and O elements in the phosphorus doping source can be used to dope the coating agent, effectively improving the conductivity of the carbon layer and thus enhancing the high-temperature storage stability and high-temperature cycling stability of the anode material.

[0091] In some embodiments, the mass ratio of graphite to coating agent is (1 to 99):1, specifically 1:1, 2:1, 5:1, 10:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1 or 99:1, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0092] In some embodiments, the mass ratio of the coating agent to the doped phosphorus source is (1–99):1, specifically 1:1, 2:1, 5:1, 10:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, or 99:1, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. It should be noted that as the amount of doped phosphorus source added increases, the mass percentage of phosphorus in the anode material first gradually increases, and then, after reaching a certain level, the increase in the mass percentage of phosphorus in the anode material slows down and reaches a peak.

[0093] In some embodiments, graphite, coating agent, and phosphorus dopant are thoroughly mixed to form a mixture, and the mixing method includes at least one of mechanical stirring and ultrasonic dispersion. When mechanical stirring is used for mixing, a propeller stirrer, turbine stirrer, or flatbed stirrer can be used, and the order of addition of the components is not limited, as long as the components are thoroughly and uniformly mixed.

[0094] Stirring can be carried out at room temperature or under preheating conditions. Preferably, the stirring temperature can be controlled between 25°C and 80°C. Understandably, proper preheating is beneficial for the graphite, coating agent, and doped phosphorus source to fully mix and form a homogeneous liquid slurry.

[0095] In some embodiments, the polymerization treatment temperature is 150°C to 700°C, and the time is 0.5 h to 5 h. By controlling the temperature and time of the polymerization treatment, the degree of asphalt polymerization can be adjusted.

[0096] In some embodiments, the polymerization temperature can be 150°C, 180°C, 200°C, 220°C, 250°C, 300°C, 350°C, 400°C, 450°C, 500°C, 550°C, or 700°C, etc., and the polymerization time can be 0.5h, 1h, 2h, 2.5h, 3h, 3.5h, 4h, or 5h, etc., but is not limited to the listed values; other unlisted values ​​within this range are also applicable. Preferably, the polymerization temperature is 300°C to 550°C.

[0097] In some embodiments, the heating rate of the polymerization process is 1℃ / min to 10℃ / min, specifically 1℃ / min, 2℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 8℃ / min, 9℃ / min or 10℃ / min, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0098] In some embodiments, the polymerization process is carried out under a protective atmosphere, including at least one of nitrogen, helium, neon, argon, krypton, and xenon. In other embodiments, the polymerization process may also be carried out in an air environment.

[0099] Step S20: The precursor is carbonized to obtain the negative electrode material.

[0100] In some embodiments, the carbonization reaction temperature is 600℃ to 1500℃, specifically, it can be 600℃, 650℃, 670℃, 700℃, 800℃, 950℃, 1080℃, 1300℃, 1400℃, or 1500℃, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. Understandably, a suitable carbonization temperature allows the amorphous carbon in the graphite core surface bonding layer and the carbon layer to possess suitable Ig. D / I G The temperature is set to ensure that the composite anode material maintains both high initial efficiency and rate performance. Preferably, the carbonization temperature is 800℃~1300℃.

[0101] In some embodiments, the holding time for carbonization is 1 hour to 10 hours. Specifically, it can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, or 10 hours, but it is not limited to the listed values; other unlisted values ​​within this range are also applicable. Preferably, the holding time for carbonization is 1 hour to 3 hours.

[0102] In some embodiments, the heating rate of the carbonization process is 1℃ / min to 10℃ / min, specifically 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 8℃ / min or 10℃ / min, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0103] In some embodiments, the carbonization process is carried out under a protective atmosphere, which includes at least one of nitrogen, helium, neon, argon, krypton, and xenon.

[0104] In some embodiments, the gas flow rate of the protective atmosphere is 2 mL / s to 100 mL / s, specifically 2 mL / s, 5 mL / s, 10 mL / s, 15 mL / s, 20 mL / s, 30 mL / s, 50 mL / s, 60 mL / s, 70 mL / s, 89 mL / s, or 100 mL / s, etc., and is not limited here.

[0105] In some embodiments, after carbonization, at least one of crushing, sieving, and demagnetizing is performed; preferably, after carbonization, crushing, demagnetizing, and sieving are performed in sequence.

[0106] In some implementations, the pulverization method is any one of a mechanical pulverizer, an air jet mill, and a cryogenic pulverizer.

[0107] In some implementations, the screening method is any one of a fixed screen, drum screen, resonant screen, roller screen, vibrating screen, and chain screen, and the screening mesh is 200 to 500 mesh, specifically 200 mesh, 300 mesh, 400 mesh, or 500 mesh, etc. Controlling the particle size of the negative electrode material within the above range is beneficial to improving the processing performance of the negative electrode material.

[0108] In some implementations, the demagnetizing equipment is any one of a permanent magnet drum magnetic separator, an electromagnetic iron remover, and a pulsed high-gradient magnetic separator. Demagnetization is used to control the magnetic content of the negative electrode material, prevent magnetic materials from affecting the charging and discharging of the lithium-ion battery, and ensure the safety of the battery during use.

[0109] This application provides a method for preparing a negative electrode material in a second aspect, comprising the following steps:

[0110] Step S01: Shape the natural flake graphite to obtain spherical graphite.

[0111] Natural flake graphite is a type of natural crystalline graphite. It resembles fish scales, belongs to the hexagonal crystal system, and has a layered structure. It possesses excellent properties such as high temperature resistance, electrical conductivity, thermal conductivity, lubrication, plasticity, and acid and alkali resistance.

[0112] In some embodiments, shaping includes at least one of crushing, spheroidizing, or grading.

[0113] Natural graphite can be shaped by spheroidization, with the spheroidization rate controlled at 500 r / min to 5000 r / min and the spheroidization time at 0.2 to 10 h.

[0114] The median particle size of the graphite obtained after shaping is 5μm to 25μm. More specifically, it can be 5μm, 8μm, 9μm, 10μm, 11μm, 12μm, 14μm, 15μm, 16μm, 20μm, or 25μm, but it is not limited to the listed values; other unlisted values ​​within this range are also applicable. Multiple experiments have shown that controlling the median particle size of graphite within the above range is beneficial for balancing processing performance, capacity, and rate performance.

[0115] The sphericity Sh (90%) of the shaped graphite is ≥0.8, specifically it can be 0.8, 0.82, 0.85, 0.87, 0.9, 0.92, 0.95, 0.98, 0.99, etc., and is not limited here. Preferably, the sphericity of the shaped graphite is ≥0.9. The higher the sphericity, the higher the orientation of the graphite. During the cycling process, due to the continuous insertion and extraction of lithium ions between the graphite layers, the resulting expansion stress can be released in multiple directions, reducing particle breakage caused by excessive local expansion stress of the anode material particles, improving the expansion effect of the anode material, and effectively improving the cycling performance of the anode material.

[0116] In some implementations, artificial graphite may also be used.

[0117] In some embodiments, the carbon content in the graphite is ≥99.5% by mass.

[0118] In other embodiments, graphite materials that directly meet the requirements can be purchased to perform the following steps S20 to S30, which are not limited here.

[0119] Step S10': The graphite material is subjected to pre-oxidation treatment at 400℃~700℃ for 0.5h~5h in an oxygen-containing atmosphere to obtain pre-oxidized graphite.

[0120] In some embodiments, the temperature of the pre-oxidation treatment is 400°C to 700°C, specifically 400°C, 420°C, 450°C, 470°C, 500°C, 550°C, 600°C, 650°C or 700°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0121] In some embodiments, the pre-oxidation treatment time is 0.5h to 5h, specifically 0.5h, 1h, 2h, 2.5h, 3h, 3.5h, 4h or 5h, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0122] In some embodiments, the heating rate of the pre-oxidation treatment is 1℃ / min to 10℃ / min, specifically 1℃ / min, 2℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 8℃ / min, 9℃ / min or 10℃ / min, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0123] In some embodiments, the rotation speed of the pre-oxidation treatment equipment is 2 to 20 r / min, specifically 2 r / min, 3 r / min, 5 r / min, 8 r / min, 10 r / min, 13 r / min, 15 r / min or 20 r / min, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0124] In some embodiments, the oxygen-containing atmosphere includes at least one of oxygen or air.

[0125] In some embodiments, the oxygen-containing atmosphere is air, and the air flow rate is 3 mL / min to 30 mL / min. Specifically, it can be 3 mL / min, 5 mL / min, 10 mL / min, 15 mL / min, 20 mL / min, 25 mL / min, or 30 mL / min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0126] In this application, by controlling parameters such as temperature, time, and air flow rate of the pre-oxidation treatment, the surface defects of graphite materials can be repaired, the defects on the graphite surface can be reduced, and more oxygen-containing functional groups can be formed on the surface of graphite particles, which is conducive to the formation of a more stable solid-liquid reaction interface with the carbon layer and improves the cycle performance of the negative electrode material.

[0127] In step S20', the mixture containing pre-oxidized graphite, coating agent and doped phosphorus source is carbonized to obtain the negative electrode material.

[0128] In some embodiments, the mass ratio of the coating agent to the doped phosphorus source is (1 to 99):1, specifically 1:1, 10:1, 20:1, 30:1, 50:1, 70:1, 80:1, 90:1 or 99:1, etc., and of course, other values ​​within the above range are also possible, which are not limited here.

[0129] In some embodiments, the coating agent includes at least one of asphalt, modified asphalt, tar, pitch coke, coal coke, resin, oil, alkanes, olefins, alkynes, and aromatics.

[0130] In some embodiments, the residual carbon value of the coating agent is 10% to 80%, specifically 10%, 20%, 30%, 40%, 50%, 60%, 70% or 80%, etc., and of course, other values ​​within the above range are also possible, which are not limited here.

[0131] In some embodiments, the phosphorus doping source includes at least one of phosphoric acid, phosphorous acid, hypophosphoric acid, ammonium phosphate, phosphorus pentoxide, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium hexafluorophosphate, phosphorus chloride, phosphorus oxychloride, pentafluorocyclotriphosphazene, ethoxy(pentafluoro)cyclotriphosphazene, hexachlorocyclotriphosphazene, phosphate ester, triphenylphosphine, and ammonium polyphosphate.

[0132] In some embodiments, the mass ratio of graphite to coating agent is (1 to 99):1, specifically 1:1, 2:1, 5:1, 10:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1 or 99:1, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0133] In some embodiments, the mass ratio of the coating agent to the doped phosphorus source is (1 to 99):1, specifically 1:1, 2:1, 5:1, 10:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1 or 99:1, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0134] In some embodiments, graphite, coating agent, and phosphorus dopant are thoroughly mixed to form a mixture. The mixing method includes at least one of physical ball milling, mechanical fusion, mechanical stirring, water-soluble stirring, and spray drying. When mechanical stirring is used, a propeller agitator, turbine agitator, or flat paddle agitator can be used, and the order of addition of the components is not limited, as long as the components are thoroughly and uniformly mixed.

[0135] Stirring can be carried out at room temperature or under preheating conditions. Preferably, the stirring temperature can be controlled between 25°C and 80°C. Understandably, proper preheating is beneficial for the graphite, coating agent, and doped phosphorus source to fully mix and form a homogeneous liquid slurry.

[0136] In some embodiments, the carbonization reaction temperature is 800℃ to 1100℃, specifically, it can be 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃, or 1100℃, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. Understandably, a suitable carbonization temperature allows the amorphous carbon in the graphite core surface bonding layer and the carbon layer to possess suitable Ig. D / I G This ensures that the composite anode material maintains both high initial efficiency and rate performance.

[0137] In some embodiments, the holding time for carbonization is 1 hour to 10 hours. Specifically, it can be 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, or 10 hours, but it is not limited to the listed values; other unlisted values ​​within this range are also applicable. Preferably, the holding time for carbonization is 1 hour to 3 hours.

[0138] In some embodiments, the heating rate of the carbonization process is 1℃ / min to 10℃ / min, specifically 1℃ / min, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 8℃ / min or 10℃ / min, etc., but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0139] In some embodiments, the carbonization process is carried out under a protective atmosphere, which includes at least one of nitrogen, helium, neon, argon, krypton, and xenon.

[0140] In some embodiments, the gas flow rate of the protective atmosphere is 2 mL / s to 100 mL / s, specifically 2 mL / s, 5 mL / s, 10 mL / s, 15 mL / s, 20 mL / s, 30 mL / s, 50 mL / s, 60 mL / s, 70 mL / s, 89 mL / s, or 100 mL / s, etc., and is not limited here.

[0141] In some embodiments, after carbonization, at least one of crushing, sieving, and demagnetizing is performed; preferably, after carbonization, crushing, demagnetizing, and sieving are performed in sequence.

[0142] In some implementations, the pulverization method is any one of a mechanical pulverizer, an air jet mill, and a cryogenic pulverizer.

[0143] In some implementations, the screening method is any one of a fixed screen, drum screen, resonant screen, roller screen, vibrating screen, and chain screen, and the screening mesh is 200 to 500 mesh, specifically 200 mesh, 300 mesh, 400 mesh, or 500 mesh, etc. Controlling the particle size of the negative electrode material within the above range is beneficial to improving the processing performance of the negative electrode material.

[0144] In some implementations, the demagnetizing equipment is any one of a permanent magnet drum magnetic separator, an electromagnetic iron remover, and a pulsed high-gradient magnetic separator. Demagnetization is used to control the magnetic content of the negative electrode material, prevent magnetic materials from affecting the charging and discharging of the lithium-ion battery, and ensure the safety of the battery during use.

[0145] This application provides a method for preparing a negative electrode material in the second aspect. By pre-oxidizing graphite, more oxygen-containing functional groups are generated on the surface of the graphite particles. These oxygen-containing functional groups can react with the doped phosphorus source and coating agent during carbonization. The doped phosphorus source and coating agent decompose to produce gases such as H2O and CO2, which are then released. Furthermore, the doped phosphorus source tends to undergo condensation reactions with oxygen-containing functional groups with lower bond energy, releasing some reaction gases. This results in the formation of more pores (3nm-5nm) in the carbon layer. Simultaneously, elemental doping is performed in the carbon layer to form appropriate amounts of PC and PO chemical bonds. These chemical bonds and appropriate porosity increase the number of lithium storage active sites, improve the migration rate of lithium ions, and enhance the capacity of the negative electrode material, leading to a specific capacity exceeding the theoretical capacity of 375mAh / g. Moreover, the PC and PO bonds in the carbon layer effectively improve the stability of the SEI film, preventing electrolyte penetration into the graphite core during battery cycling and improving cycle performance.

[0146] Thirdly, this application also provides a battery. Figure 1 is a schematic diagram of the discharge state of the battery provided in this application embodiment. 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.

[0147] 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.

[0148] 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.

[0149] 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.

[0150] 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).

[0151] 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.

[0152] In some embodiments, the negative electrode current collector 201 may 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.

[0153] The battery provided in this application has the advantages of high capacity, high initial efficiency, long cycle life, excellent rate performance, and low expansion. The battery can be a lithium-ion battery, a sodium-ion battery, a solid-state electrolyte battery, etc., and is not limited thereto.

[0154] The embodiments of this application will be further described below through multiple examples.

[0155] The embodiments in this patent are exemplary and are only used to explain this application, and should not be construed as limiting this application. It should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. Where there is no conflict, the implementation methods and features of the implementation methods of this application can be combined with each other. Many specific details are set forth in the following description to provide a thorough understanding of this application; the described implementation methods are only a part of the implementation methods of this application, and not all of them. The embodiments of this application are further described below with reference to several examples.

[0156] The following embodiments were prepared according to the method for preparing the negative electrode material described in the first aspect:

[0157] Example 1

[0158] (1) Spherical graphite (D 50 =16.5μm) and coating agent (petroleum asphalt, softening point 120℃, residual carbon content 33%) were mixed at a mass ratio of 90:10, and coating agent and doped phosphorus source (ammonium polyphosphate) were mixed at a mass ratio of 10:2.5. After mixing, the mixture was subjected to low-temperature thermal polymerization treatment in a box furnace at a thermal polymerization temperature of 500℃ for 2 hours. After cooling to room temperature, the mixture was taken out to obtain the precursor.

[0159] (2) The precursor is carbonized in a carbonization kiln under a nitrogen atmosphere. The gas flow rate is 20 mL / s, the carbonization temperature is 1400℃, and the treatment time is 4 h. After cooling to room temperature, the negative electrode material is obtained.

[0160] The negative electrode material prepared in Example 1 of this application includes a core and a carbon layer located on at least a portion of the surface of the core, wherein the core includes graphite. Figure 2 is a SEM image of the negative electrode material prepared in Example 1 of this application, and Figure 3 is a schematic XPS image of the negative electrode material prepared in Example 1 of this application. As shown in Figure 3, the area ratio of the characteristic peaks of the PC chemical bond to the PO chemical bond is A = 43.25:56.75. Figure 4 is a schematic capacity-voltage curve of the negative electrode material prepared in Example 1 of this application.

[0161] Following the preparation steps of Example 1, Examples 2 to 12 (abbreviated as S1 to S12) were prepared. The specific process parameters for each example are shown in Table 1.

[0162] Comparative Example 1

[0163] (1) Spherical graphite (D50 = 16.5 μm) and coating agent (petroleum asphalt, softening point 120℃, residual carbon content 33%) were mixed at a mass ratio of 90:10 without adding any doped phosphorus source. After mixing, the mixture was subjected to low-temperature thermal polymerization in a box furnace without any protective atmosphere. The thermal polymerization temperature was 500℃ and the treatment time was 2h. After cooling to room temperature, the precursor was obtained.

[0164] (2) The precursor is carbonized in a carbonization kiln under a nitrogen atmosphere. The gas flow rate is 20 mL / s, the carbonization temperature is 1400℃, and the treatment time is 4 h. After cooling to room temperature, the negative electrode material is obtained.

[0165] Comparative Example 2

[0166] (1) Spherical graphite (D50=16.5μm) was first heated to 300℃ for oxidation treatment to obtain oxidized spherical graphite. Then it was mixed with coating agent (petroleum asphalt, softening point 120℃, residual carbon content 33%) at a mass ratio of 90:10. The coating agent was mixed with doped phosphorus source (ammonium polyphosphate) at a mass ratio of 10:2.5. After mixing, it was subjected to low-temperature thermal polymerization treatment in a box furnace without any protective atmosphere. The thermal polymerization temperature was 500℃ and the treatment time was 2h. After cooling to room temperature, it was taken out to obtain the precursor.

[0167] (2) The precursor is carbonized in a carbonization kiln without any protective atmosphere. The carbonization temperature is 1400℃ and the treatment time is 4h. After cooling to room temperature, the negative electrode material is obtained.

[0168] Comparative Example 3

[0169] (1) Spherical graphite (D50 = 16.5 μm) and coating agent (petroleum asphalt, softening point 120℃, residual carbon content 33%) were mixed at a mass ratio of 90:10, and the coating agent and doped phosphorus source (ammonium polyphosphate) were mixed at a mass ratio of 10:1.1 to obtain the precursor;

[0170] (2) The precursor was carbonized in a CVD vapor deposition furnace under a nitrogen atmosphere. The gas flow rate was 20 mL / s, the carbonization temperature was 1400℃, and the treatment time was 4 h. After cooling to room temperature, the negative electrode material was obtained.

[0171] Comparative Example 4

[0172] (1) Spherical graphite (D 50=16.5μm) and coating agent (petroleum asphalt, softening point 120℃, residual carbon content 33%) were mixed at a mass ratio of 90:10, and coating agent and doped phosphorus source (ammonium polyphosphate) were mixed at a mass ratio of 10:15. After mixing, the mixture was subjected to low-temperature thermal polymerization treatment in a box furnace at a thermal polymerization temperature of 500℃ for 2 hours. After cooling to room temperature, the mixture was taken out to obtain the precursor.

[0173] (2) The precursor is carbonized in a carbonization kiln under a nitrogen atmosphere. The gas flow rate is 20 mL / s, the carbonization temperature is 1500℃, and the treatment time is 4 h. After cooling to room temperature, the negative electrode material is obtained.

[0174] In Tables 1 to 3 below, S1 to S12 represent Examples 1 to 12, and D1 to D4 represent Comparative Examples 1 to 4.

[0175] Table 1. Preparation process parameters of negative electrode materials

[0176] Test Method 1

[0177] (1) Test methods for doping elements and their content in negative electrode materials:

[0178] X-ray photoelectron spectroscopy (XPS) was performed using a Thermo Scientific K-Alpha instrument from the United States. The X-ray source was Al Ka, and the vacuum level was approximately 10. -9 Torr. XPS was used to analyze the carbon layer, determining the presence of each chemical bond by peak position. Avantage software was then used to perform peak fitting on the P2p energy spectrum (with PC bonds around 130 eV and PO bonds around 133 eV), fitting the peak areas and calculating the ratio of each peak area. The specific steps are as follows:

[0179] a) Import the data to be analyzed into Avantage software;

[0180] b) Perform background subtraction and smoothing on the data;

[0181] c) Select the fitting region and set the peak shape parameter (Gaussian-Lorentz mixture function);

[0182] d) Set the two peaks of the PC bond (around 130 eV, P2p3 / 2, main peak; P2p1 / 2, companion peak) and the two peaks of the PO bond (around 133 eV, P2p3 / 2, main peak; P2p1 / 2, companion peak);

[0183] e) Use Avantage software to perform peak fitting, clicking the "Fit" button at least 5 times;

[0184] f) Obtain the total mass content of the doped elements and the area of ​​each peak. Calculate the area ratio A.

[0185] (2) Test method for particle size distribution of negative electrode material: The particle size test method refers to GB / T 19077-2016. It can be conveniently determined by a laser particle size analyzer, specifically the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK. This application is for cumulative volumetric particle size distribution.

[0186] (3) Test method for tap density of negative electrode material: The specific surface area of ​​the material is tested using a McMurray tap tester. The negative electrode material is placed in the sample chamber of the tap density tester and vibrated 1000 times. The volume of the sample at this time is recorded, and the tap density can be calculated according to the mass-volume ratio.

[0187] (4) Test method for specific surface area and pore volume of negative electrode material: The specific surface area of ​​the material is tested using a McMurray specific meter. The sample is loaded into a sample tube, and an isothermal jacket is used on the sample tube. The filler rod is placed into the bubble tube, and the retaining ring and O-ring are installed on the bubble tube. The assembled sample bubble tube is then placed in the corresponding analysis station for testing. Under constant temperature and low temperature, the amount of nitrogen gas adsorbed on the solid surface at different relative pressures is measured. Based on the Brunauer-Emmett-Teller adsorption theory and its formula (Brunauer-Emmett-Teller, BET formula), the amount of monolayer adsorption of the sample is obtained, thereby calculating the specific surface area and pore volume of the material.

[0188] (5) Test method for surface morphology of negative electrode material particles: The microstructure of the negative electrode material surface was observed using a HITACHI-S4800 scanning electron microscope. The steps are as follows: The conductive adhesive was attached to the sample cup, the sample was evenly coated on the conductive adhesive, and any loose sample was blown away with a bulb syringe. The sample was then placed in the scanning electron microscope chamber for testing. The section test steps are as follows: First, the graphite particles were polished using a HITACHI-E3500 ion milling machine. A small amount of carbon conductive adhesive was applied to the edge of the sample stage, and the graphite sample was evenly sprinkled on top. The sample was then gently pressed with a glass slide. After the conductive adhesive dried for 2 minutes, the excess sample was blown away with a bulb syringe. The sample stage was placed on the sample holder, and the sample position was adjusted. After this, the airflow was adjusted to the maximum ion beam current, and the polishing time was set for sample processing. After completion, the section of the negative electrode material was observed using a HITACHI-S4800 scanning electron microscope.

[0189] (6) Test method for the thickness of the particle coating layer of negative electrode material:

[0190] Add appropriate amounts of the negative electrode material powder and ethanol to a mortar and pestle, grind manually for 5 minutes, and then sonicate for 20 minutes. Take an appropriate amount of the homogeneous mixture of powder and ethanol and drop 2 to 3 drops of this mixture onto a microgrid. Observe the morphology of the sample coating layer using a Talos F200S electron microscope with an accelerating voltage of 200 kV. Under the TEM field of view, select an area where the surface coating layer can be clearly observed (graphite cores show clearly ordered lattice fringes, while carbon coating layers are disordered), measure the thickness of the coating layer, and perform at least 5 tests at different locations, taking the average value. Take corresponding images at an appropriate magnification (the electron microscope scale is 5 nm to 20 nm at this time).

[0191] (7) Test method for the mass content of carbon in negative electrode materials:

[0192] a) Spread the sample evenly in a clean crucible and dry it in an oven at 105°C to constant weight (the difference between two weighings should not exceed 0.3 mg).

[0193] b) Turn on the instrument.

[0194] c) Place two clean porcelain crucibles in a muffle furnace at 950°C and calcine for 1 hour. Cool them in air for 2 minutes. Then place the porcelain crucibles in a desiccator to cool to room temperature and weigh them to an accuracy of 0.1 mg. Continue calcining for half an hour, cool them, and weigh them again until the difference between two consecutive weighings does not exceed 0.3 mg. Record the mass of the two crucibles as m1.

[0195] d) Weigh 1g of the dried sample into two porcelain crucibles respectively, perform parallel tests, and weigh to the nearest 0.1mg, and record it as m2;

[0196] e) Place the two porcelain crucibles containing the sample into a muffle furnace at 950°C and ignite for 1.5 hours. Then remove the porcelain crucibles, cool them in air for 2 minutes, place them in a desiccator to cool for 30 minutes, and weigh them after cooling to room temperature, accurate to 0.1 mg.

[0197] f) Continue calcining the porcelain crucible for 30 minutes, cool it, and weigh it until the difference between two consecutive weighings does not exceed 0.3 mg. Record the mass of the last weighing as m4.

[0198] Calculate the mass content of fixed carbon elements using the formula:

[0199] The mass content of carbon element = (m2-m4) / (m2-m1)*100%

[0200] (8) Testing of pore size distribution and total pore volume of negative electrode material:

[0201] The pore size distribution of the sample was tested using a BSD-660M A6B6M instrument. The adsorbate was nitrogen gas, and the degassing conditions were 300℃ for 300 min. The pore size distribution was determined using a static method, also known as the static volumetric method. This method involves injecting a certain amount of gas into the sample chamber and then measuring the adsorption process of the gas by the sample to calculate the pore size distribution and total pore volume.

[0202] (9) Test of P element content in negative electrode material:

[0203] Weigh 0.3-0.5g of sample, add 6mL of hydrochloric acid and 2mL of nitric acid, heat on a graphite digester for about 30 minutes to completely digest the trace elements in the sample, filter and adjust the volume, and use an Agilent OPTIMA 8000 inductively coupled plasma (ICP) spectrometer to test the content of P element doped in the negative electrode material.

[0204] (10) Powder conductivity

[0205] The powder conductivity was tested using an MCP-PD51 powder conductivity testing system. The conductivity of the sample was tested at five pressure points of 4, 8, 12, 16, and 20 kN using the 4-probe method. The powder conductivity corresponding to the 4 kN pressure was taken.

[0206] (11) Electrochemical performance testing method: The negative electrode materials prepared in the examples and comparative examples were mixed with N-methylpyrrolidone in a mass ratio of 92:5:3 to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated on a copper foil current collector and dried under vacuum at 120°C to obtain a negative electrode sheet. A lithium metal sheet was used as the counter electrode, the separator was Celgard C2400, and the electrolyte concentration was 1.3 mol / L LiPF6 electrolyte, in which the solvent was a solution of ethylene carbonate (EC), polycarbonate (PC), and diethyl carbonate (DEC) in a volume ratio of 3:1:6. The cells were assembled into coin cells in an argon-filled glove box. Charge-discharge tests were performed at a current density of 0.1C, with a charge-discharge range of 0.01-1.5V. Cyclic charge-discharge was performed to obtain the first reversible specific capacity.

[0207] (12) High-temperature storage performance test:

[0208] Large single-crystal lithium nickel cobalt manganese oxide (NCM523 cathode material produced by BTR Corporation) was mixed with conductive carbon black and polyvinylidene fluoride (PVDF) in a mass ratio of 94:3.0:3.0 and dissolved in N-methylpyrrolidone, with the solid content controlled at 50%, to obtain a cathode slurry. The cathode slurry was coated onto an aluminum foil current collector, and after vacuum drying at 95°C, rolling, and pressing, a cathode sheet was obtained.

[0209] The graphite anode material, carboxymethyl cellulose, styrene-butadiene rubber, and conductive carbon black of the examples and comparative examples were dissolved in N-methylpyrrolidone at a mass ratio of 95:1.5:2.1:1.2, respectively, and the solid content was controlled at 50% to obtain anode slurry. The anode slurry was coated on a copper foil current collector, and after vacuum drying at 95°C, rolling and pressing, anode sheet was obtained.

[0210] The positive electrode, separator, and negative electrode are assembled into a lithium-ion battery, and an electrolyte is injected to obtain a soft-pack battery with a capacity of about 40mAh. The electrolyte is 1mol / L LiPF6 / ethylene carbonate (EC) + propylene carbonate (PC) + diethyl carbonate (DEC) + methyl ethyl carbonate (EMC) (volume ratio 1:0.3:1:1), and the separator is a polypropylene / polyethylene / polypropylene three-layer composite separator.

[0211] Two sets of battery samples were placed in a 25℃ constant temperature chamber and left to stand for 30 minutes to calibrate the battery capacity. Then, the batteries were charged at a 1C rate and discharged at a 0.2C rate at 45℃ to perform a full charge and discharge cycle test until the battery reached 400 cycles. The discharge capacity was then recorded and the capacity retention rate after 400 cycles was calculated.

[0212] Two groups of battery samples were placed sequentially in a 25°C constant temperature chamber and allowed to stand for 30 minutes to allow the lithium-ion batteries to reach a constant temperature of 25°C. They were then charged at a constant current and constant voltage of 1C to 4.2V, and then discharged at a constant current of 1C to 2.75V. The discharge capacity of each group was recorded as the initial capacity, and the average value C0 was taken. Afterward, the samples were charged at a constant current and constant voltage of 0.5C to 4.2V, and then transferred to a 60°C constant temperature chamber for storage for 15 days. The samples were then transferred to a 25°C constant temperature chamber and allowed to stand for 60 minutes. They were then discharged at a constant current of 1C to 2.75V, and the discharge capacity of each group was recorded as the remaining capacity, and the average value C1 was taken. This cycle was repeated 2-3 weeks, charging at a constant current and constant voltage of 1C to 4.2V and then discharging at a constant current of 1C to 2.75V. The highest discharge capacity of each group was recorded as the recovery capacity, and the average value C2 was taken.

[0213] The remaining capacity retention rate and storage capacity retention rate of lithium-ion batteries in the two groups of samples are calculated according to the following formula, and used as indicators to evaluate the high-temperature storage performance of lithium-ion batteries at 100% SOC.

[0214] 100% SOC high-temperature storage capacity retention rate = C2 / C0 × 100%.

[0215] Table 2. Summary of Performance Test Results of Anode Materials

[0216] Table 3. Summary of Battery Performance Test Results

[0217] As can be seen from Tables 1 to 3, the natural graphite anode materials provided in Examples 1 to 10 and Comparative Examples 2 and 3, by controlling the mass percentage of P and O elements in the anode material to be less than or equal to 1%, can reduce the dissolution of phosphorus atoms while allowing the doped phosphorus source to react with the coating agent, embedding P-containing chemical groups in the carbon layer through chemical bonding. Due to the high theoretical specific capacity of P itself, the reversible capacity of the material can be effectively improved. Among them, PC chemical bonds can mainly improve the specific capacity of the anode material, while the presence of PO chemical bonds can better improve the capacity retention rate of the material during high-temperature storage. Therefore, by controlling the content of doped elements and controlling the area ratio A of the characteristic peaks of PC chemical bonds to PO chemical bonds to be in the range of (25-65):(75-35), the specific capacity, high-temperature cycling stability, and high-temperature storage stability of the anode material can be comprehensively improved.

[0218] Based on the test data from Examples 11 and 1-10, it is known that the amount of phosphorus source added during the preparation process in Example 11 was insufficient. During the high-temperature carbonization process, this phosphorus source evaporated, leading to a decrease in porosity. Consequently, the mass percentage of phosphorus in the anode material decreased to 9 ppm (less than 10 ppm), resulting in a slower lithium-ion transport rate and a slight decrease in the capacity of the anode material compared to Examples 1-10. Preferably, the mass percentage of phosphorus is between 10 ppm and 2000 ppm.

[0219] Based on the test data from Examples 12 and 1-10, it is known that Example 12 added too much phosphorus source during the preparation process. This resulted in more evaporation and pore formation during the high-temperature carbonization process. Although the high-temperature storage performance of the negative electrode material was ensured, the increased pores exacerbated the side reactions between the electrolyte and the PC chemical bonds, leading to a slight decrease in the capacity retention of the negative electrode material in Example 12. Preferably, the total pore volume of the negative electrode material is V cm³. 3 / g, 0.0035<V≤0.006.

[0220] Comparative Example 1 did not add a phosphorus source and did not modify the carbon layer. The reversible capacity and high-temperature storage capacity retention of the anode material were lower than those of the anode materials in Examples 1-10.

[0221] The graphite raw material used in Comparative Example 2 is oxidized spherical graphite, which increases the mass content of PO bonds in the negative electrode material, resulting in a significant decrease in the content of PC chemical bonds. It does not meet the requirement that the area ratio A of the characteristic peaks of PC chemical bonds and PO chemical bonds is (25-65):(75-35), which leads to a significant decrease in the reversible capacity of the negative electrode material. However, the high-temperature cycling capacity retention rate of the negative electrode material can still be maintained at a relatively high level.

[0222] The main difference between Comparative Example 3 and Example 1 is that Comparative Example 3 was prepared using a large CVD vapor deposition furnace, and most of the P was discharged from the furnace with the gas. Therefore, the content of PC chemical bonds formed was too high, which did not meet the requirement that the area ratio A of the characteristic peaks of PC chemical bonds and PO chemical bonds be (25-65): (75-35). Furthermore, since the PC bonds are mainly located on the surface of the negative electrode material, some phosphorus atoms will react with the electrolyte and dissolve in the electrolyte when the SEI film is formed, resulting in a significant decrease in the high-temperature storage stability and high-temperature cycling capacity retention of the negative electrode material.

[0223] The test data from Comparative Example 4 and Example 1 show that the amount of phosphorus source added in Comparative Example 4 was excessive. Although the A value range was met, the total mass content of doped elements in the negative electrode material (1.16%) increased significantly, and the mass percentage of P element also increased substantially. Excessive P element reacts with and dissolves in the electrolyte, resulting in a decrease in high-temperature storage performance and high-temperature cycle capacity retention compared to Example 1. In addition, the porosity formed during the carbonization process of these phosphorus sources also increased, resulting in an excessively large total pore volume in the negative electrode material. More P element was exposed, further aggravating the side reactions between the negative electrode material and the electrolyte, leading to excessive consumption of active lithium ions and a decrease in the specific capacity of the negative electrode material.

[0224] The following examples were prepared according to the method for preparing the negative electrode material in the second aspect:

[0225] Example 20

[0226] (1) Natural spherical graphite with an intermediate particle size of D50 = 16.5 μm and a sphericity Sh (90%) = 0.9 was selected. The spherical graphite was pre-oxidized in a rotary kiln with an air flow rate of 3 mL / min, a heating rate of 10℃ / min, and a pre-oxidation treatment at 400℃ for 0.5 h. The rotary kiln rotation speed during the pre-oxidation process was 20 rad / min, and pre-oxidized graphite was obtained.

[0227] (2) The pre-oxidized graphite and the coating agent pitch (60% residual carbon) are mixed evenly at a mass ratio of 90%:5%, and the coating agent and the doped phosphorus source (ammonium dihydrogen phosphate) are mixed evenly at a mass ratio of 70%:30%. The mixture is then carbonized in a box furnace at 1000°C in a nitrogen atmosphere for 5 hours. After cooling to room temperature, the material is removed to obtain the negative electrode material.

[0228] According to the preparation steps of Example 20, Examples 21 to 29 were prepared. The specific process parameters of each example (abbreviated as S20 to S29) are shown in Table 4:

[0229] Table 4. Preparation process parameters of negative electrode materials

[0230] Test Method Two

[0231] (1) Test methods for the formation of chemical bonds and their content of doping elements in negative electrode materials:

[0232] Same as test item (1) in test method one.

[0233] (2) Test method for particle size distribution of negative electrode material:

[0234] Same as test item (2) in test method one.

[0235] (3) Test method for tap density of negative electrode material:

[0236] Same as test item (3) in test method one.

[0237] (4) Method for testing the specific surface area of ​​negative electrode materials:

[0238] Same as test item (4) in test method one.

[0239] (5) Test methods for surface morphology and coating thickness of negative electrode material particles:

[0240] Same as test items (5) and (6) in test method one.

[0241] (6) Testing of pore size distribution and total pore volume of negative electrode material:

[0242] The pore size distribution of the sample was tested using a BSD-660M A6B6M instrument. The adsorbate was nitrogen gas, and the degassing conditions were 300℃ for 300 min. The pore size distribution was determined using a static method, also known as the static volumetric method. This method involves injecting a certain amount of gas into the sample chamber and then measuring the adsorption process of the gas by the sample to calculate the pore size distribution and total pore volume.

[0243] (7) Test of P element content in the negative electrode material:

[0244] Weigh 0.3-0.5g of sample, add 6mL of hydrochloric acid and 2mL of nitric acid, heat on a graphite digester for about 30 minutes to completely digest the trace elements in the sample, filter and adjust the volume, and use an Agilent OPTIMA 8000 inductively coupled plasma (ICP) spectrometer to test the content of P element doped in the negative electrode material.

[0245] (8) Sphericity test:

[0246] The sphericity Sh (90%) of natural spherical graphite was tested and analyzed using the QICPIC dynamic particle image spectrometer from Newpatek, Germany.

[0247] (9) Powder conductivity

[0248] The powder conductivity was tested using an MCP-PD51 powder conductivity testing system. The conductivity of the sample was tested at five pressure points of 4, 8, 12, 16, and 20 kN using the 4-probe method. The powder conductivity corresponding to the 4 kN pressure was taken.

[0249] (10) Raman testing of negative electrode materials:

[0250] Raman scattering spectra were measured using a HORIBA-XPLORA laser confocal Raman spectrometer with a laser wavelength of 532 nm. Data were collected at 30 points on the surface of the negative electrode material particles. The scattering spectra obtained at each point were then subjected to peak fitting to obtain the peaks at 1300 cm⁻¹. -1 -1400cm -1 The peak area of ​​the D characteristic peak within the range and located at 1550 cm⁻¹ -1 ~1600cm -1 The intensity ratio of the G characteristic peak within the range is I D / I G .

[0251] (11) Electrochemical performance testing methods:

[0252] Half-cell test: Using the negative electrode materials prepared in the examples and comparative examples, the negative electrode materials, carboxymethyl cellulose, and styrene-butadiene rubber were mixed uniformly in N-methylpyrrolidone at a mass ratio of 96.5:1.5:1, with the solid content controlled at 50%. The mixture was coated onto a copper foil current collector, vacuum dried, rolled, and stamped to obtain the negative electrode sheet. A lithium metal sheet was used as the counter electrode, and the cells were assembled into coin cells for testing in an argon-filled glove box. The test steps were as follows: stand for 2 hours, discharge at 0.1C to 0.005V, and discharge the 0.09C and 0.08C cells to 0.001V; stand for 15 minutes, charge at 0.1C to 1.5V, and stand for 15 minutes to obtain the first reversible specific capacity. The test results are shown in Table 6.

[0253] Full cell testing: The cycle performance of the raw materials in the examples and comparative examples was tested using the full cell testing method. The negative electrode materials prepared in the examples and comparative examples were mixed with an appropriate amount of deionized water in the ratio of SP:SBR (50% solid content):CMC = 94:2.5:1.5:2 (weight ratio) to form a paste. The paste was then coated onto copper foil and dried under vacuum at 90°C.

[0254] A positive electrode slurry (70wt% solid content) was prepared by mixing a large single-crystal lithium nickel cobalt manganese oxide (NCM523 positive electrode material produced by BTR Corporation), a conductive agent Super P, a binder polyvinylidene fluoride (PVDF), and N-methylpyrrolidone (NMP) in a mass ratio of 96.8:2:1.2. The slurry was coated on aluminum foil current collector and dried at 100°C. The dried positive and negative electrode sheets were then rolled, cut, wound, injected with liquid, sealed, and formed to assemble a 554065 soft-pack full battery (nominal capacity of 1.6mAh). The slurry was made of 1mol / L LiPF6 / ethylene carbonate (EC) + diethyl carbonate (DEC) + dimethyl carbonate (DMC) (volume ratio 1:1:1.5), and the separator was polypropylene Celgard2400.

[0255] The battery was tested for cycle performance using a battery testing device. The battery capacity was calibrated at 25°C. Then, the battery was charged and discharged at 1C rate at 25°C for a full charge and discharge cycle test until the battery reached 1000 cycles. The discharge capacity was recorded and the capacity retention rate after 1000 cycles was calculated. The test results are shown in Table 6.

[0256] Table 5. Summary of Performance Test Results of Anode Materials

[0257] Table 6. Summary of Battery Performance Test Results

[0258] As can be seen from Tables 5 and 6, the total pore volume of the negative electrode materials provided in Examples 20-29 and the comparative examples is controlled to be 0.003 cm³. 3 / g~0.015cm 3 The volume of pores with a diameter of 3 nm to 5 nm accounts for 6% to 13% of the total pore volume. The presence of pores can also increase the Li content. + The diffusion channels also provide more lithium storage active sites, promoting the diffusion of lithium ions at the solid-liquid interface and within the solid phase, which is beneficial for improving the reversible capacity and rate performance of the anode material. Simultaneously, by synergistically controlling the area ratio (A value) of the characteristic peaks of the PC chemical bond and the PO chemical bond to be within the range of 0.1–1.5, the anode material has more lithium storage active sites, which also enhances the stabilizer effect of the SEI film, reduces electrolyte decomposition, and enables the anode material to have higher reversible capacity and excellent cycle stability.

[0259] Figure 5 is a schematic diagram of the pore size distribution of the negative electrode materials prepared in Example 20 and Comparative Example 20 of this application. As shown in Figure 5, the volume ratio of pores with a pore size of 3nm to 5nm in the negative electrode material prepared in Example 20 is significantly increased.

[0260] Figure 6 is a schematic diagram of the XPS negative electrode material prepared in Example 20 of this application. As shown in Figure 6, the negative electrode material of Example 20 has PC chemical bonds and PO chemical bonds, and the area ratio of the characteristic peaks of PC chemical bonds to PO chemical bonds is A = 0.93. According to the test data of Example 20 and Example 21, in the preparation process of Example 21, due to the larger amount of asphalt added, more PC bonds were produced in the reaction. On the other hand, due to the slightly lower pre-oxidation temperature compared to Example 20, the degree of oxidation on the graphite surface decreased, and the number of oxygen-containing functional groups decreased, resulting in a decrease in PO bonds. This increased the ratio A of PC to PO bonds, thus improving the reversible capacity of the negative electrode material. During charge-discharge cycling, a small number of phosphorus atoms reacted with the electrolyte and dissolved in the electrolyte, resulting in a slight decrease in the cycle capacity retention rate of the negative electrode material.

[0261] Figure 7 is a schematic diagram of the capacity-voltage curve of the negative electrode material prepared in Example 20 of this application. As shown in Figure 7, the negative electrode material of Example 20 has excellent reversible capacity.

[0262] Based on the test data from Examples 20 and 22, it can be seen that in Example 22, due to the higher oxidation temperature during the preparation process, more O-containing functional groups are formed on the graphite surface, and the P doping process generates more PO bonds, resulting in a decrease in the A value. The cycle performance of the anode material is improved, but the reversible capacity of the anode material is slightly lower than that of Example 20.

[0263] The main difference between Example 26 and Comparative Example 20 is that Comparative Example 20 did not undergo phosphorus doping treatment, and the prepared anode material did not contain PC or PO bonds. Furthermore, the pore volume ratio of 3-5 nm pore size in the anode material was significantly reduced, resulting in lower reversible capacity and cycle performance of Comparative Example 20 compared to the Example.

[0264] Figure 8 is a comparison of the cycle performance of the negative electrode materials prepared in Example 23 and Comparative Example 20 of this application. The cycle performance of the negative electrode material in Example 23 of this application is better than that in Comparative Example 20.

[0265] The main difference between Example 23 and Comparative Example 21 is that the graphite core surface of Comparative Example 21 has a higher degree of oxidation, and the phosphorus doping forms more PO bonds, resulting in a lower PC to PO bond ratio, which leads to a significant decrease in the capacity and cycle performance of the anode material.

[0266] The main difference between Example 26 and Comparative Example 22 is that Comparative Example 22 did not undergo pre-oxidation treatment, resulting in a significantly increased PC to PO bond ratio. The PC to PO bond ratio A in the negative electrode material of Example 26 is smaller than that of the negative electrode material of Comparative Example 22. While PO bonds are beneficial for improving cycle performance, PC bonds are more conducive to improving reversible capacity. Although the reversible capacity of the negative electrode material of Comparative Example 22 increased slightly, its cycle performance was significantly lower than that of Example 26, resulting in poorer overall electrical performance.

[0267] 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

A negative electrode material, characterized in that, The negative electrode material includes a core and a carbon layer located on at least a portion of the surface of the core, wherein the core includes graphite; The negative electrode material contains doping elements, and the mass percentage of the doping elements is ≤1%; the doping elements include P and O elements. The negative electrode material was tested by X-ray photoelectron spectroscopy, and the negative electrode material has PC chemical bonds and PO chemical bonds; wherein, the area ratio of the characteristic peaks of the PC chemical bonds to the PO chemical bonds is A, A = (25~65):(75~35). The negative electrode material according to claim 1 is characterized in that, A is 25:75, 30:70, 35:65, 40:60, 45:55, 50:50, 55:45, 60:40, 65:35, or any value within the range of any two of the above values. The negative electrode material according to claim 1 is characterized in that, The total pore volume of the negative electrode material is V cm⁻¹ 3 / g, 0.0035<V≤0.

006. The negative electrode material according to claim 1 is characterized in that, The area ratio of the characteristic peaks of the PC chemical bond to that of the PO chemical bond is (30-60):(70-40). A negative electrode material, characterized in that, The negative electrode material includes a core and a carbon layer located on at least a portion of the surface of the core, wherein the core includes graphite; The total pore volume of the negative electrode material is 0.003 cm³. 3 / g~0.015cm 3 / g, wherein the volume of pores with a pore size of 3nm to 5nm accounts for 6% to 13% of the total pore volume; The negative electrode material contains doping elements, including P and O elements; X-ray photoelectron spectroscopy analysis shows that the negative electrode material has PC and PO chemical bonds; wherein the area ratio of the characteristic peaks of the PC chemical bonds to the PO chemical bonds is A, 0.1≤A≤1.

5. The negative electrode material according to claim 5 is characterized in that, The negative electrode material satisfies at least one of the following characteristics: (1) A is 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5 or any value within the range of any two of the above values; (2)0.3≤A≤1.2。 The negative electrode material according to claim 1 or 5 is characterized in that, Pores with a diameter of 5 nm or larger account for 75% to 88% of the total pore volume. The negative electrode material according to claim 1 or 5 is characterized in that, The mass percentage of P element in the negative electrode material is 10 ppm to 2000 ppm. The negative electrode material according to claim 5 is characterized in that, The oil absorption value of the negative electrode material is 37mL / 100g to 48mL / 100g. The negative electrode material according to claim 5 is characterized in that, In the Raman spectrum of the negative electrode material, the negative electrode material at 1300 cm⁻¹ -1 -1400cm -1 It has a D peak at 1550 cm⁻¹ -1 -1600cm -1 The ratio of the Raman intensity of the D peak to the G peak is 0.25 ≤ I. D / I G ≤0.

5. The negative electrode material according to claim 5 is characterized in that, In anode materials, the particle sphericity Sh(90%) corresponding to a cumulative volume distribution percentage of 90% is 0.8 to 0.

94. The negative electrode material according to claim 1 or 5 is characterized in that, The negative electrode material satisfies at least one of the following characteristics: (1) The graphite includes at least one of artificial graphite and natural graphite; (2) The graphite includes spherical natural graphite; (3) The fixed carbon content of the graphite is ≥98%; (4) The median particle size of the graphite is 5 μm to 25 μm; (5) The carbon layer includes amorphous carbon containing the doping element. The negative electrode material according to claim 1 or 5 is characterized in that, The carbon layer in the negative electrode material has a mass percentage content of 1% to 30%; and / or the thickness of the carbon layer is 5 nm to 200 nm. The negative electrode material according to claim 1 is characterized in that, The negative electrode material has a powder conductivity of 140 S / cm to 180 S / cm under a pressure of 4 kN. The negative electrode material according to claim 5 is characterized in that, The negative electrode material has a powder conductivity of 110 S / cm to 175 S / cm under a pressure of 4 kN. The negative electrode material according to any one of claims 1 to 11 is 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 5 μm to 30 μm; (2) The specific surface area of ​​the negative electrode material is 1m². 2 / g~5.0m 2 / g; (3) The tap density of the negative electrode material is 0.6 g / cm³. 3 ~1.5g / cm 3 ; (4) The carbon content in the negative electrode material is ≥95% by mass. A battery characterized in that, The battery includes the negative electrode material as described in any one of claims 1-16.

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