Negative electrode material and battery

Abstract

The application provides a negative electrode material and a battery, the negative electrode material comprising an inner core and a carbon layer 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, the mass percentage of the doping element being less than or equal to 1%; the doping element comprises P and O; the negative electrode material is tested by X-ray photoelectron spectroscopy analysis, and the negative electrode material has P-C chemical bonds and P-O chemical bonds; wherein the area ratio of the characteristic peaks of the P-C chemical bonds and the P-O chemical bonds is A, A=(25-65):(75-35). The negative electrode material provided by the application can comprehensively improve the reversible capacity, thermal stability and cycle performance of the negative electrode material.

Description

Technical Field

[0001] This application relates to the field of negative electrode material technology, specifically to negative electrode materials and batteries. Background Technology

[0002] 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.

[0003] 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 effect on improving the thermal stability and cycle performance of graphite. Summary of the Invention

[0004] 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.

[0005] 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; 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).

[0006] In some embodiments, the mass percentage of P element in the negative electrode material is 10 ppm to 2000 ppm.

[0007] In some embodiments, the total pore volume of the negative electrode material is V cm. 3 / g, 0.0035<V≤0.006.

[0008] In some embodiments, the area ratio of the characteristic peaks of the PC chemical bond to the PO chemical bond is (30~60):(70~40).

[0009] In some embodiments, the graphite includes at least one of artificial graphite and natural graphite.

[0010] In some embodiments, the graphite comprises spherical natural graphite.

[0011] In some embodiments, the graphite has a fixed carbon content of ≥98%.

[0012] In some embodiments, the median particle size of the graphite is 5 μm to 25 μm.

[0013] In some embodiments, the carbon layer in the negative electrode material has a mass percentage content of 1% to 30%.

[0014] In some embodiments, the thickness of the carbon layer is 5 nm to 200 nm.

[0015] In some embodiments, the median particle size of the negative electrode material is 5 μm to 30 μm.

[0016] In some embodiments, the negative electrode material has a powder conductivity of 140 S / cm to 180 S / cm under a pressure of 4 kN.

[0017] In some embodiments, the specific surface area of ​​the negative electrode material is 1.5 m². 2 / g~2.0m 2 / g.

[0018] In some embodiments, the tap density of the negative electrode material is 0.8 g / cm³. 3 ~1.1g / cm 3 .

[0019] In some embodiments, the carbon content in the negative electrode material is ≥95% by mass.

[0020] This application provides a battery comprising the aforementioned negative electrode material.

[0021] The technical solution of this application has at least the following beneficial effects: 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 high-temperature storage, and reduces capacity decay. In addition, due to the high electronegativity of oxygen atoms, they can form PO chemical bonds with phosphorus atoms, which are highly polar and relatively chemically weak. PO chemical bonds can remain relatively stable during repeated charging and discharging and high-temperature storage. PO chemical bonds are not easily broken and P atoms are not easily dissolved, thereby enhancing the thermal and chemical stability of the anode material.

[0022] This application controls the total mass percentage of doping elements (P and O) to be below 1%, and simultaneously controls the area ratio A of the characteristic peaks of PC chemical bonds to PO chemical bonds to be (25~65):(75~35), that is, controls the content ratio of PC chemical bonds to PO chemical bonds to be within the above range. Some phosphorus atoms form PO chemical bonds with oxygen atoms, which have relatively weak chemical activity, thereby reducing the dissolution of phosphorus atoms; other phosphorus atoms combine with carbon atoms to form PC chemical bonds with higher chemical activity, which can improve the adsorption capacity of the anode material for active lithium ions. Under the synergistic effect of the above characteristics, the specific capacity, high-temperature cycle stability and high-temperature storage stability of the anode material can be comprehensively improved. Attached Figure Description

[0023] Figure 1 A schematic diagram of the discharge state of a battery provided in an embodiment of this application; Figure 2 This is a SEM image of the negative electrode material prepared in Example 1 of this application; Figure 3 This is a schematic diagram of the XPS negative electrode material prepared in Example 1 of this application; Figure 4 This is a schematic diagram of the capacity-voltage curve of the negative electrode material prepared in Example 1 of this application. Detailed Implementation

[0024] 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.

[0025] Based on this, 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; 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).

[0026] 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 high-temperature storage, and reduces capacity decay. Furthermore, due to the high electronegativity of oxygen atoms, they can form PO chemical bonds with phosphorus atoms, which are highly polar but relatively less chemically reactive. PO chemical bonds remain relatively stable during repeated charge-discharge cycles and high-temperature storage, and are not easily broken, thus preventing the dissolution of P atoms. This enhances the thermal and chemical stability of the anode material. This application controls the total mass percentage of doping elements (P and O) to be 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 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 cycling stability, and high-temperature storage stability of the anode material are comprehensively improved.

[0027] In some embodiments, the area ratio of the characteristic peaks of the PC chemical bond to the PO chemical bond 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 of course, other values ​​within the above range are also possible, which are not limited here. Preferably, the area ratio of the characteristic peaks of the PC chemical bond to the PO chemical bond is (30~60):(70~40).

[0028] In some embodiments, the mass percentage of the doped element in the negative electrode material is ≤1%, 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., and of course it can also be other values ​​within the above range, which are not limited here.

[0029] In some embodiments, the mass percentage of phosphorus (P) in the negative electrode material is 10 ppm to 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 negative electrode 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 negative electrode material. When the mass percentage of P in the negative electrode material is too low, the lithium-ion transport rate at the solid-liquid interface of the negative electrode material slows down, which is detrimental to the capacity utilization of the negative electrode material.

[0030] 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 0.0035 / 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.

[0031] In some embodiments, the graphite includes at least one of artificial graphite and natural graphite.

[0032] 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.

[0033] 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.

[0034] In some embodiments, the median particle size of the 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 the graphite within the above range is beneficial for the graphite to balance processing performance, capacity, and rate performance. Preferably, the median particle size of the graphite is 8 μm to 18 μm.

[0035] In some embodiments, the fixed carbon content of the 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 are also applicable. Preferably, the mass content of carbon in the graphite is ≥99.95%.

[0036] In some embodiments, the carbon layer in the negative electrode 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 negative electrode material achieves both high capacity and rate performance.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] In some embodiments, the specific surface area of ​​the negative electrode material is 1.5 m². 2 / g~2.0m 2 / g; specifically, it can be 1.5m 2 / g, 1.6m 2 / g, 1.7m 2 / g, 1.8m 2 / g, 1.9m 2 / g or 2.0m 2 / g, etc., can also be other numbers within the above range, and are not limited here. 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 first coulombic efficiency of the negative electrode material.

[0043] In some embodiments, the tap density of the composite negative electrode material is 0.8 g / cm³. 3 ~1.1g / cm 3 Specifically, it could be 0.8 g / cm³. 3 0.85g / cm 3 0.9g / cm 3 0.95g / cm 3 1.0g / cm 3 1.05g / cm 3 Or 1.1g / cm 3 This applies to, but is not limited to, the listed values; other unlisted values ​​within this range also apply.

[0044] 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.

[0045] Secondly, this application provides a method for preparing a negative electrode material, comprising the following steps: Step S10: The mixture containing graphite, coating agent and doped phosphorus source is subjected to polymerization treatment to obtain a precursor, wherein the mass ratio of coating agent to doped phosphorus source is (1~99):1.

[0046] Step S20: The precursor is carbonized to obtain the negative electrode material.

[0047] 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.

[0048] The preparation method of this application is explained in detail below with reference to the embodiments: Before step S10, the method may further include: shaping natural flake graphite to obtain spherical graphite.

[0049] 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.

[0050] In some embodiments, the shaping includes at least one of crushing, spheroidizing, or grading.

[0051] 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.

[0052] 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.

[0053] In some implementations, artificial graphite may also be used.

[0054] 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.

[0055] 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.

[0056] Step S10: The mixture containing graphite, coating agent and doped phosphorus source is subjected to polymerization treatment to obtain a precursor, wherein the mass ratio of coating agent to doped phosphorus source is (1~99):1.

[0057] 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.

[0058] 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℃.

[0059] 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.

[0060] In some embodiments, the doped phosphorus 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 doped phosphorus 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.

[0061] In some embodiments, the mass ratio of graphite to coating agent 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.

[0062] 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.

[0063] In some embodiments, the graphite, coating agent, and phosphorus source 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, 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.

[0064] 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.

[0065] In some embodiments, the polymerization treatment is carried out at a temperature of 150°C to 700°C for a time of 0.5 h to 5 h. Controlling the temperature and time of the polymerization treatment can adjust the degree of asphalt polymerization.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] Step S20: The precursor is carbonized to obtain the negative electrode material.

[0070] In some embodiments, the carbonization reaction temperature is 600℃~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℃.

[0071] In some embodiments, the holding time for the carbonization treatment 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 the carbonization treatment is 1 hour to 3 hours. 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. Other unlisted values ​​within this range are also applicable.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] In some implementations, the pulverization method is any one of a mechanical pulverizer, an air jet mill, and a cryogenic pulverizer.

[0076] In some implementations, the screening method is any one of 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.

[0077] 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.

[0078] Thirdly, embodiments of the present invention also provide a battery. Figure 1 This is a schematic diagram of the discharge state of the battery provided in the embodiments of this application, such as... Figure 1As shown, 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.

[0079] 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.

[0080] In some embodiments, the positive electrode 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 electrode active layer 102 contains a positive electrode active material, which includes compounds that can reversibly insert and deintercalate metal ions.

[0081] 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.

[0082] 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).

[0083] 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.

[0084] 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.

[0085] 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.

[0086] The embodiments of the present invention will be further described below with reference to several examples.

[0087] The embodiments in this patent are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. 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 embodiments and features of the embodiments 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 embodiments are only a part of the embodiments of this application, and not all of them. The embodiments of this application are further described below with reference to several examples.

[0088] Example 1 (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. (2) The precursor is carbonized in a carbonization furnace 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.

[0089] 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 This is a SEM image of the negative electrode material prepared in Example 1 of this application. Figure 3 This is a schematic diagram of the XPS anode material prepared in Example 1 of this application, as shown. Figure 3 As shown, 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 This is a schematic diagram of the capacity-voltage curve of the negative electrode material prepared in Example 1 of this application.

[0090] Following the preparation steps of Example 1, Examples 2-12 (abbreviated as S1-S12) were prepared. The specific process parameters for each example are shown in Table 1. Comparative Example 1 (1) Spherical graphite (D50=16.5μm) 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. (2) The precursor is carbonized in a carbonization furnace 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.

[0091] Comparative Example 2 (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. (2) The precursor was carbonized in a carbonization kiln without any protective atmosphere. The carbonization temperature was 1400℃ and the treatment time was 4h. After cooling to room temperature, the negative electrode material was obtained.

[0092] Comparative Example 3 (1) Spherical graphite (D50=16.5μm) 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; (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.

[0093] Comparative Example 4 (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. (2) The precursor is carbonized in a carbonization furnace 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.

[0094] In Tables 1 to 3 below, S1 to S12 represent Examples 1 to 12, and D1 to D4 represent Comparative Examples 1 to 4.

[0095] Table 1. Preparation process parameters of negative electrode materials

[0096] Test methods (1) Test methods for doping elements and their content in negative electrode materials: 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 and detect the carbon layer, and the presence of each chemical bond was determined by the peak position. The Avantage software was used to perform peak fitting, and the content of each chemical bond was calculated by fitting the peak area, and the peak area ratio was calculated.

[0097] (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, such as the Mastersizer 3000 laser particle size analyzer from Malvern Industries Ltd. in the UK.

[0098] (3) Test method for tap density of negative electrode material: The specific surface area of ​​the material is tested using a McMurray tap tester. Place the negative electrode material in the sample chamber of the tap density tester, vibrate it 1000 times and record the sample volume at this time. The tap density can be calculated according to the mass-volume ratio.

[0099] (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 McMeter specific meter. The sample is loaded into the 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 into the corresponding analysis station for testing. Under constant temperature and low temperature, the amount of gas adsorbed on the solid surface at different relative pressures is measured. Based on the Brown-Nauer-Etter-Taylor adsorption theory and its formula (BET formula), the amount of monolayer adsorption of the sample is obtained, thereby calculating the specific surface area and pore volume of the material.

[0100] (5) Test methods for surface morphology and carbon layer 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 the sample that was not firmly fixed was blown away with a rubber bulb. The sample was then placed in the scanning electron microscope chamber for testing. The test steps for cross section and coating layer 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 it. 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 rubber bulb. The sample stage was placed on the sample holder, the sample position was adjusted, and the airflow was adjusted to the maximum ion beam current. The polishing time was set for sample processing. After completion, the cross section and carbon layer of the negative electrode material surface were observed using a HITACHI-S4800 scanning electron microscope.

[0101] (6) Test method for the mass content of carbon in negative electrode materials: Thermogravimetric analysis was used to determine the mass content of carbon in the negative electrode material.

[0102] (7) 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, Celgard C2400 was used as the separator, and 1.3M LiPF6 electrolyte was used, 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 coin cell was assembled in an argon-filled glove box. Charge and discharge tests were performed at a current density of 0.1C, with a charge and discharge range of 0.01-1.5V. Cyclic charge and discharge were performed to obtain the first reversible specific capacity, the first charge capacity, and the first discharge capacity. The first coulombic efficiency = first discharge capacity / first charge capacity.

[0103] (8) High-temperature storage performance test: Large single-crystal lithium nickel cobalt manganese oxide (NCM523) was mixed with conductive carbon black and PVDF at a mass ratio of 94:3.0:3.0 and dissolved in N-methylpyrrolidone, with the solid content controlled at 50%, to obtain a positive electrode slurry. The positive electrode slurry was coated onto an aluminum foil current collector, and after vacuum drying at 95°C, rolling and pressing, a positive electrode sheet was obtained. 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. 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) + EMC (volume ratio 1:0.3:1:1), and the separator is a PP / PE / PP three-layer composite separator.

[0104] 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 55°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.

[0105] The remaining capacity retention rate and recovered 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.

[0106] 100% SOC high-temperature storage recovery capacity retention rate = C2 / C0 × 100%.

[0107] Table 2. Summary of Performance Test Results of Anode Materials

[0108] Table 3. Summary of Battery Performance Test Results

[0109] As shown in Table 1, the natural graphite anode materials provided in Examples 1-10 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, 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.

[0110] 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 relatively small. During the high-temperature carbonization process, this phosphorus source evaporated, leading to a decrease in porosity. 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.

[0111] 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.

[0112] 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.

[0113] The graphite raw material used in Comparative Example 2 is oxidized spherical graphite, which increases the mass content of PO bonds in the anode 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 anode material. However, the high-temperature cycling capacity retention rate of the anode material can still be maintained at a relatively high level.

[0114] 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.

[0115] 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.

[0116] Although this application discloses preferred embodiments as described above, it is not intended to limit the claims. Any person skilled in the art can make several possible changes and modifications without departing from the concept of this application. Therefore, the scope of protection of this application should be determined by the scope defined in the claims of this application.

Claims

1. A negative electrode material, characterized in that, The negative electrode material includes a core and 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).

2. The negative electrode material according to claim 1, characterized in that, The mass percentage of P element in the negative electrode material is 10 ppm to 2000 ppm.

3. The negative electrode material according to claim 1, characterized in that, The total pore volume of the negative electrode material is V cm⁻¹ 3 / g, 0.0035<V≤0.

006.

4. The negative electrode material according to claim 1, 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).

5. The negative electrode material according to claim 1, 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 5μm~25μm.

6. The negative electrode material according to claim 1, characterized in that, The carbon layer in the negative electrode material has a mass percentage content of 1% to 30%.

7. The negative electrode material according to claim 1, characterized in that, The thickness of the carbon layer is 5 nm to 200 nm.

8. The negative electrode material according to claim 1, characterized in that, The negative electrode material has a powder conductivity of 140 S / cm ~ 180 S / cm under a pressure of 4 kN.

9. The negative electrode material according to any one of claims 1 to 8, 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 1.5 m². 2 / g~2.0m 2 / g; (3) The tap density of the negative electrode material is 0.8 g / cm³. 3 ~1.1g / cm 3 ; (4) The mass content of carbon in the negative electrode material is ≥95%.

10. A battery, characterized in that, The battery includes the negative electrode material as described in any one of claims 1-9.

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