Negative electrode composite, method for producing the same, and use thereof

Abstract

This application provides a negative electrode composite material, its preparation method, and its application. The aforementioned negative electrode composite material includes a carbon material and a coating layer disposed on its surface; the carbon material is doped with P, O, and N elements, and the coating layer is made of titanium dioxide and / or aluminum oxide. This negative electrode composite material not only has a high specific capacity but also a long cycle life and superior rate performance.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to negative electrode composite materials, their preparation methods, and applications. Background Technology

[0002] Currently, the energy density of lithium-ion batteries is limited, partly due to the low specific capacity of graphite, a commonly used anode material in lithium-ion batteries. To improve anode capacity, the industry has adopted hard carbon as a substitute for graphite as the active material for the anode, but the capacity of unmodified hard carbon still cannot meet the ever-increasing demand for energy density. Summary of the Invention

[0003] Therefore, embodiments of this application provide a negative electrode composite material, its preparation method, and its application. This negative electrode composite material not only has a high specific capacity but also a long cycle life and superior rate performance.

[0004] The first aspect of this application provides a negative electrode composite material, including a carbon material and a coating layer disposed on its surface; wherein the carbon material is doped with P, O and N elements, and the coating layer is made of titanium dioxide and / or aluminum oxide.

[0005] Phosphorus, oxygen, and nitrogen co-doping can effectively improve the specific capacity and electronic conductivity of carbon materials. Furthermore, the coating layer formed by titanium dioxide and / or aluminum oxide can effectively suppress the expansion of carbon materials during charge-discharge cycles, thereby extending the cycle life of the anode composite material. Therefore, the aforementioned anode composite material can possess both high specific capacity, long cycle life, and superior rate performance.

[0006] In some embodiments of this application, the carbon material is an amorphous carbon nanoribbon co-doped with P, O and N elements.

[0007] In some embodiments of this application, the thickness of the coating layer is 5nm-30nm.

[0008] In some embodiments of this application, based on the mass of the negative electrode composite material, the mass percentage of the carbon material is 28%-40%, the mass percentage of the P element is 4%-5%, the mass percentage of the O element is 36%-45%, the mass percentage of the N element is 4%-5%, and the mass percentage of the Ti element is 14%-19%.

[0009] In some embodiments of this application, the radial dimension of the negative electrode composite material is 300nm-2000nm.

[0010] The second aspect of this application provides a method for preparing a negative electrode composite material, comprising:

[0011] Phosphorus and a nitrogen-containing carbon source were mixed under a protective atmosphere to prepare a carbon material precursor.

[0012] The coating layer is formed on the surface of the carbon material precursor to obtain a composite material precursor.

[0013] The composite material precursor is heated under a protective atmosphere to obtain the negative electrode composite material.

[0014] The above preparation method has simple steps, strong process controllability, and high production efficiency, making it suitable for large-scale industrial production.

[0015] In some embodiments of this application, the preparation of the carbon material precursor includes:

[0016] The mixture of the phosphorus and the nitrogen-containing carbon source is spun to obtain a nanofiber-like carbon material precursor; the spinning process includes electrospinning.

[0017] In some embodiments of this application, the phosphorus element includes red phosphorus with a particle size of 200nm-2000nm, and the nitrogen-containing carbon source includes polyacrylonitrile and / or polyacrylamide.

[0018] In some embodiments of this application, the mass ratio of the elemental phosphorus to the carbon source is 1:(5-15).

[0019] In some embodiments of this application, forming a coating layer on the surface of the nanofibers includes:

[0020] Titanium dioxide and / or aluminum oxide are deposited on the surface of the nanofiber-like carbon material precursor, the deposition process including atomic layer deposition.

[0021] In some embodiments of this application, the heating includes: heating to 400℃-500℃ at a heating rate of 5℃ / min-10℃ / min and holding at that temperature for 2h-6h.

[0022] A third aspect of this application provides a negative electrode, comprising the negative electrode composite material provided in the first aspect of this application. By employing the negative electrode composite material provided in this application, the aforementioned negative electrode can be used to provide a secondary battery that combines superior rate performance, superior cycle performance, and high energy density.

[0023] A fourth aspect of this application provides a secondary battery, including the negative electrode provided in the third aspect of this application. By employing the negative electrode provided in this application, the secondary battery can possess superior rate performance, superior cycle performance, and higher energy density.

[0024] The fifth aspect of this application provides an electrical device, including the secondary battery provided in the fourth aspect of this application. Because it can be powered by the secondary battery provided in this application, the electrical device has a long battery life and a certain degree of fast charging capability, indicating a promising market prospect. Attached Figure Description

[0025] Figure 1 This is a Scanning Electron Microscope (SEM) image of the composite material precursor obtained in Example 2 of this application.

[0026] Figure 2A and Figure 2B The images shown are SEM images and transmission electron microscope (TEM) images of the negative electrode composite material prepared in Example 2 of this application, respectively.

[0027] Figure 3 This is a rate performance diagram of the button cell in Embodiment 2 of this application;

[0028] Figure 4 The graph shows the cycling performance of the coin cell of Example 2 of this application at a current density of 0.1 A / g.

[0029] Figure 5 This is a graph showing the cycle performance of the coin cell of Example 2 of this application at a current density of 0.5 A / g. Detailed Implementation

[0030] This application provides a negative electrode composite material, including a carbon material and a coating layer disposed on its surface; wherein the carbon material is doped with P, O, and N elements, and the coating layer is made of titanium dioxide and / or aluminum oxide. In this application embodiment, the carbon material in the negative electrode active material has the ability to de-intercalate / de-intercalate metal ions (e.g., lithium ions). In this application embodiment, the presence of the aforementioned P, O, and N elements can be characterized using X-ray photoelectron spectroscopy (XPS).

[0031] Phosphorus, oxygen, and nitrogen co-doping can expose more active sites in the anode composite material without compromising the adsorption activity of the carbon material, while simultaneously increasing the specific surface area of ​​the anode composite material. This enhances the adsorption capacity of the anode composite material for metal ions, thereby effectively improving the specific capacity and electronic conductivity of the carbon material. Furthermore, the coating layer formed by titanium dioxide and / or alumina can effectively suppress the expansion of the carbon material during charge-discharge cycles, thus extending the cycle life of the anode composite material. Therefore, the aforementioned anode composite material can possess both high specific capacity, long cycle life, and superior rate performance.

[0032] In some embodiments of this application, the coating layer is made of titanium dioxide. Titanium dioxide has good permeability of active ions (e.g., lithium ions), which is more conducive to the de-intercalation / de-intercalation of active ions in the negative electrode composite material.

[0033] In some embodiments of this application, the coating layer is made of alumina. The coating layer formed with alumina has a higher density, which is more conducive to limiting the volume expansion of the carbon material during charge-discharge cycles.

[0034] In some embodiments of this application, the carbon material is amorphous carbon nanoribbons co-doped with P, O, and N elements. That is, the carbon material is amorphous carbon co-doped with P, O, and N elements, and its morphology is nanoribbon-like; amorphous carbon refers to carbon materials that lack long-range order. This makes the negative electrode composite material easier to prepare; it also increases the specific surface area of ​​the negative electrode composite material, improves the lithium intercalation kinetics of the negative electrode composite material, and thus reduces the risk of lithium plating at the negative electrode during battery charging and discharging.

[0035] In some embodiments of this application, the thickness of the coating layer is 5nm-30nm. Controlling the coating layer thickness within this range provides sufficient binding force to better suppress the expansion of the internal carbon material during charge-discharge cycles, and also facilitates the penetration of active ions, that is, facilitates the de-intercalation / de-intercalation of active ions in the negative electrode composite material. Specifically, the thickness of the coating layer can be, but is not limited to, 5nm, 8nm, 10nm, 12nm, 15nm, 18nm, 20nm, 22nm, 25nm, 28nm, 30nm, etc.

[0036] In some embodiments of this application, based on the mass of the negative electrode composite material, the mass percentage content of carbon material is 28%-40%, the mass percentage content of phosphorus (P) is 4%-5%, the mass percentage content of oxygen (O) is 36%-45%, the mass percentage content of nitrogen (N) is 4%-5%, and the mass percentage content of titanium (Ti) is 14%-19%. By controlling the content of each element within the above ranges, the specific capacity and electronic conductivity of the negative electrode composite material can be maintained at a relatively high level. In the embodiments of this application, XPS (X-ray Photoelectron Spectroscopy) can be used to test the mass percentage of each element in the carbon material. In this embodiment, the mass percentage of carbon material in the negative electrode composite material can be, for example, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, etc.; the mass percentage of phosphorus (P) in the negative electrode composite material can be, for example, 4%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5.0%, etc.; and the mass percentage of oxygen (O) in the negative electrode composite material can be, for example, 36%, 37%, etc. 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, etc.; the mass percentage of N element in the negative electrode composite material can be, for example, 4%, 4.1%, 4.2%, 4.3%, 4.4%, 4.5%, 4.6%, 4.7%, 4.8%, 4.9%, 5.0%, etc.; the mass percentage of Ti element in the negative electrode composite material can be, for example, 14%, 14.5%, 15%, 15.5%, 16%, 16.5%, 17%, 17.5%, 18%, 18.5%, 19%, etc.

[0037] In some embodiments of this application, the negative electrode composite material is in the form of nanoribbons, with a radial dimension of 300 nm to 2000 nm. Controlling the size of the negative electrode active material within this range allows for shorter insertion / extraction paths for active ions, thereby improving the rate performance of the negative electrode composite material. Specifically, the radial dimension of the negative electrode composite material can be, for example, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, 1100 nm, 1200 nm, 1300 nm, 1400 nm, 1500 nm, 1600 nm, 1700 nm, 1800 nm, 1900 nm, 200 nm, etc.

[0038] This application also provides a method for preparing a negative electrode composite material, which can be used to prepare the negative electrode composite material provided in this application. The preparation method includes:

[0039] S01. Mix elemental phosphorus and a nitrogen-containing carbon source under a protective atmosphere to prepare a carbon material precursor;

[0040] S02. The coating layer is formed on the surface of the carbon material precursor to obtain a composite material precursor;

[0041] S03. The composite material precursor is heated under a protective atmosphere to obtain the negative electrode composite material. Under the heating conditions of step S03, the carbon source undergoes a carbonization reaction, and elemental phosphorus reacts and is doped into the carbon material. In addition, titanium dioxide or alumina in the coating layer can provide an oxygen source, thereby obtaining a phosphorus, oxygen, and nitrogen co-doped carbon material. In the embodiments of this application, the protective atmosphere in step S03 can be nitrogen or argon.

[0042] The above preparation method has simple steps, strong process controllability, and high production efficiency, making it suitable for large-scale industrial production.

[0043] In some embodiments of this application, step S01 involves preparing a carbon material precursor via a spinning process, specifically including:

[0044] Phosphorus is mixed with a nitrogen-containing carbon source, and the resulting mixture is spun to obtain a nanofiber-like carbon material precursor. The spinning process includes electrospinning. In some specific embodiments, in order to obtain a mixture with a suitable viscosity to improve spinnability, a solvent is added when mixing phosphorus and the nitrogen-containing carbon source, and the solid content of the mixture is controlled within the range of 4%-12%.

[0045] In some embodiments of this application, the elemental phosphorus includes red phosphorus with a particle size of 200 nm to 500 nm. Using red phosphorus facilitates the preparation of phosphorus-doped carbon materials; controlling the particle size of red phosphorus within the aforementioned range promotes its uniform dispersion in the mixture, reduces the risk of agglomeration, and provides a larger specific surface area, which is beneficial for doping. Specifically, the particle size of the elemental phosphorus is not limited to 200 nm, 300 nm, 400 nm, 500 nm, etc. In the embodiments of this application, a laser particle size analyzer can be used to test the particle size of the elemental phosphorus.

[0046] In some embodiments of this application, commercial red phosphorus can be taken and pretreated to obtain red phosphorus with the target particle size. The pretreatment includes: pulverizing the commercial red phosphorus, centrifuging the pulverized particles, specifically using a speed of 2000 rpm for the first centrifugation, taking the supernatant, increasing the speed to 8000 rpm, taking the precipitate, and then vacuum drying to obtain red phosphorus with a particle size of 50 nm-500 nm.

[0047] In some embodiments of this application, the nitrogen-containing carbon source includes, but is not limited to, one or more of polyacrylonitrile (PAN) and / or polyacrylamide.

[0048] In some embodiments of this application, step S01, mixing elemental phosphorus and a nitrogen-containing carbon source under a protective atmosphere, includes:

[0049] A nitrogen-containing carbon source is dispersed in a solvent to obtain a carbon source solution. Then, under a protective atmosphere, elemental phosphorus is dispersed in the carbon source solution and stirred thoroughly to obtain a mixture. Specifically, to reduce the viscosity of the carbon source solution and accelerate the dispersion of elemental phosphorus, the stirring can be carried out at 20℃-60℃ for 6-12 hours until a homogeneous mixture is obtained. In the embodiments of this application, the solvent for the carbon source solution can be a commonly used organic solvent in the field, such as dimethylacetamide (DMF), depending on the actual production situation.

[0050] In some embodiments of this application, the mass ratio of elemental phosphorus to a nitrogen-containing carbon source is 1:10. By controlling the mass ratio within the above range, the final doping amount of elemental phosphorus can be kept within a suitable range.

[0051] In this embodiment, in step S01, the equipment and process parameters used for electrospinning can be those known to those skilled in the art and can be adjusted according to actual production conditions. In some embodiments, the voltage range used during electrospinning is 12kV-20kV, the fiber output speed is 1mL / min-3mL / min, and the distance from the spinning nozzle to the take-up device is 25cm-35cm. The take-up device can be a commonly used take-up device in the industry, such as a roller. In some embodiments of this application, the spinning time is 2h-5h. The amount of fiber spun can be controlled by controlling the spinning time.

[0052] In some embodiments of this application, step S02, forming a coating layer on the surface of the carbon material precursor, includes depositing titanium dioxide and / or aluminum oxide on the surface of the nanofiber-like carbon material precursor. The deposition can be any chemical deposition method familiar to those skilled in the art. In some specific embodiments, the deposition process is atomic layer deposition (ALD). ALD allows for atomic-level thickness control, offering high flexibility. Since the thickness of the coating layer hardly changes in step S03, in some specific embodiments of this application, the thickness of the coating layer in step S02 can be controlled within the range of 5 nm to 30 nm. Specifically, the deposition raw material for titanium dioxide can be, for example, Ti(N(CH3)2)4, and the deposition raw material for aluminum oxide can be, for example, Al2O3. Those skilled in the art can determine the deposition raw materials and deposition conditions according to actual production conditions and control the thickness of the coating layer by the number of deposition passes.

[0053] In some embodiments of this application, the heating in step S03 includes: heating to 400℃-500℃ at a heating rate of 5℃ / min-10℃ / min and holding at that temperature for 2h-6h. That is, the composite material precursor is placed in a protective atmosphere and heated to 400℃-500℃ at a heating rate of 5℃ / min-10℃ / min and held at that temperature for 2h-6h. Specifically, the holding temperature for the heat treatment can be, but is not limited to, 400℃, 410℃, 420℃, 430℃, 440℃, 450℃, 460℃, 470℃, 480℃, 490℃, 500℃, etc. Controlling the holding temperature within the above range can both carbonize the nitrogen-containing carbon source to form carbon materials, effectively prevent phosphorus atoms, oxygen atoms, and nitrogen atoms from escaping from the system and allow phosphorus atoms, oxygen atoms, and nitrogen atoms to be doped into the carbon materials, and also prevent the reaction and deterioration of the coating layer material. In this embodiment, the heat preservation time can be, but is not limited to, 2h, 3h, 4h, 5h, 6h, etc. Controlling the heat preservation time within the above range allows for complete carbonization of the nitrogen-containing carbon source and results in higher production efficiency. This embodiment also provides a negative electrode, including the negative electrode composite material provided in this embodiment. Due to the inclusion of the negative electrode composite material provided in this embodiment, the negative electrode can be used to provide a secondary battery with high energy density, superior cycle performance, and good rate performance.

[0054] In some embodiments of this application, the negative electrode includes a negative electrode current collector and a negative electrode material layer disposed on at least one side surface of the negative electrode current collector, wherein the negative electrode material layer includes the negative electrode composite material provided in the embodiments of this application.

[0055] In this embodiment, the negative electrode active material in the negative electrode material layer can be entirely composed of the negative electrode composite material provided in this embodiment; it may also include other negative electrode active materials known to those skilled in the art, such as silicon-based negative electrode materials, phosphorus-based negative electrode materials (e.g., red phosphorus), etc. The aforementioned negative electrode active material refers to a substance capable of deintercalating / intercalating active ions.

[0056] In some embodiments of this application, the aforementioned negative electrode material layer may further include a conductive agent and a binder. The conductive agent and binder may be materials suitable for negative electrodes that are well-known to those skilled in the art. No limitations are placed on the mass ratio of the negative electrode active material, the negative electrode composite material, the conductive agent, and the binder; those skilled in the art can adjust these ratios according to actual application needs.

[0057] In this embodiment of the application, the aforementioned negative electrode current collector is used to support the negative electrode material layer, and it can be any negative electrode current collector well known to those skilled in the art, such as copper foil.

[0058] In the embodiments of this application, the negative electrode can be prepared using any process known in the art, and this application does not impose any restrictions on it. Specifically, taking a wet process as an example:

[0059] The negative electrode composite material provided in this application embodiment can be dispersed in a solvent with a conductive agent and a binder, and after stirring evenly, a negative electrode slurry can be obtained. The negative electrode slurry is coated on the surface of the negative electrode current collector, and after drying, rolling, and slitting, a negative electrode is obtained.

[0060] This application also provides a secondary battery, including the negative electrode provided in this application embodiment. Due to the use of the negative electrode provided in this application embodiment, the secondary battery can simultaneously possess superior rate performance, longer service life, and higher energy density.

[0061] In this embodiment of the application, the secondary battery may be a lithium-ion battery or the like.

[0062] In this embodiment of the application, the secondary battery can be a liquid battery using a liquid electrolyte, a solid battery using a solid electrolyte, or a semi-solid battery.

[0063] In some embodiments of this application, the secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte located between the positive and negative electrodes. In the embodiments of this application, the positive electrode can be any positive electrode known in the art. The separator can be any separator known in the art.

[0064] This application also provides an electrical device, including the secondary battery provided in this application embodiment. Since it can be powered by the secondary battery provided in this application embodiment, the electrical device has a long battery life and a certain degree of fast charging capability, showing good market prospects.

[0065] In some embodiments of this application, the aforementioned electrical equipment includes, but is not limited to, vehicles and consumer electronics. Among these, the aforementioned vehicles include, but are not limited to, new energy vehicles and electric bicycles.

[0066] The technical solutions of the embodiments of this application are further described below through multiple examples.

[0067] Example 1

[0068] (1) Red phosphorus with a particle size of 50-500 nm was added to a DMF solution of carbon source (specifically polyacrylonitrile) and stirred at 60 °C for 12 h to obtain a mixture; the mass ratio of red phosphorus to polyacrylonitrile in the mixture was 1:10.

[0069] (2) The mixture was transferred to a syringe and connected to an electrospinning machine for electrospinning. The voltage was 16 kV and the fiber output speed was 1 mL / min. The distance from the spinning nozzle to the fiber take-up device was 25 cm, and the spinning time was 4 h, resulting in a nanofiber-like carbon material precursor.

[0070] (3) A titanium dioxide coating layer is deposited on the surface of the carbon material precursor prepared above using an atomic deposition process. The thickness of the coating layer is 15 nm, thus obtaining the composite material precursor.

[0071] (4) The composite material precursor was placed in a tube furnace and heated to 450°C at 10°C / min under a nitrogen atmosphere and held for 4 hours to obtain the negative electrode composite material.

[0072] Example 2

[0073] The difference from Example 1 is that: (2) the mixture is transferred to a syringe and connected to an electrospinning machine for electrospinning at a voltage of 16kV and a fiber output speed of 1.5mL / min. The distance from the spinning nozzle to the fiber take-up device is 25cm, and the spinning time is 4h, resulting in a nanofiber-like carbon material precursor.

[0074] (3) A titanium dioxide coating layer is deposited on the surface of the carbon material precursor prepared above using an atomic deposition process. The thickness of the coating layer is 15 nm, thus obtaining the composite material precursor.

[0075] (4) The composite material precursor was placed in a tube furnace and heated to 400°C at 10°C / min under a nitrogen atmosphere and held for 0.6h to obtain the negative electrode composite material.

[0076] Example 3

[0077] The difference from Example 1 is that: (2) the mixture is transferred to a syringe and connected to an electrospinning machine for electrospinning at a voltage of 16kV and a fiber output speed of 1.5mL / min. The distance from the spinning nozzle to the fiber take-up device is 25cm, and the spinning time is 4h, resulting in a nanofiber-like carbon material precursor.

[0078] (3) A titanium dioxide coating layer is deposited on the surface of the carbon material precursor prepared above using an atomic deposition process. The thickness of the coating layer is 25 nm, thus obtaining the composite material precursor.

[0079] (4) The composite material precursor was placed in a tube furnace and heated to 450°C at 10°C / min under a nitrogen atmosphere and held for 0.6h to obtain the negative electrode composite material.

[0080] Example 4

[0081] (1) Red phosphorus with a particle size of 50-500 nm was added to a DMF solution of carbon source (specifically polyacrylonitrile) and stirred at 60 °C for 12 h to obtain a mixture; the mass ratio of red phosphorus to polyacrylonitrile in the mixture was 1:10.

[0082] (2) The mixture was transferred to a syringe and connected to an electrospinning machine for electrospinning. The voltage was 16 kV and the fiber output speed was 1 mL / min. The distance from the spinning nozzle to the fiber take-up device was 25 cm, and the spinning time was 4 h, resulting in a nanofiber-like carbon material precursor.

[0083] (3) An aluminum oxide coating layer is deposited on the surface of the carbon material precursor prepared above using an atomic deposition process. The thickness of the coating layer is 15 nm, thus obtaining the composite material precursor.

[0084] (4) The composite material precursor was placed in a tube furnace and heated to 450°C at 10°C / min under a nitrogen atmosphere and held for 4 hours to obtain the negative electrode composite material.

[0085] Comparative Example 1

[0086] (1) Red phosphorus with a particle size of 50-500 nm was added to a DMF solution of carbon source (specifically polyacrylonitrile) and stirred at 60 °C for 12 h to obtain a mixture; the mass ratio of red phosphorus to polyacrylonitrile in the mixture was 1:10.

[0087] (2) The mixture was transferred to a syringe and connected to an electrospinning machine for electrospinning. The voltage was 16 kV and the fiber output speed was 1 mL / min. The distance from the spinning nozzle to the fiber take-up device was 25 cm, and the spinning time was 4 h, resulting in a nanofiber-like carbon material precursor.

[0088] (3) The carbon material precursor is placed in a tube furnace and heated to 400°C at 10°C / min under a nitrogen atmosphere and held for 0.6h to obtain the negative electrode composite material.

[0089] Comparative Example 2

[0090] (1) Stir the carbon source (specifically polyacrylonitrile) in a DMF solution at 60°C for 12 hours to obtain a mixture; the mass ratio of red phosphorus to polyacrylonitrile in the mixture is 1:10.

[0091] (2) The mixture was transferred to a syringe and connected to an electrospinning machine for electrospinning. The voltage was 16 kV and the fiber output speed was 1 mL / min. The distance from the spinning nozzle to the fiber take-up device was 25 cm, and the spinning time was 4 h, resulting in a nanofiber-like carbon material precursor.

[0092] (3) A titanium dioxide coating layer is deposited on the surface of the carbon material precursor prepared above using an atomic deposition process. The thickness of the coating layer is 15 nm, thus obtaining the composite material precursor.

[0093] (4) The composite material precursor was placed in a tube furnace and heated to 450°C at 10°C / min under a nitrogen atmosphere and held for 4 hours to obtain the negative electrode composite material.

[0094] Performance testing

[0095] (1) Morphology Test: The morphology of the composite precursors prepared in each example and comparative example was observed under SEM, and the negative electrode composites prepared in each example and comparative example were observed under SEM and TEM, respectively. The SEM image of the composite precursor prepared in Example 2 is shown below. Figure 1 As shown, the SEM and TEM images of the prepared negative electrode composite material are as follows: Figure 2A and Figure 2B As shown; observations revealed that the negative electrode composite materials prepared in each embodiment were nanoribbon-shaped, and their radial dimensions were all distributed in the range of 300nm-2000nm.

[0096] (2) Elemental analysis test: XPS test was performed on the negative electrode composite materials prepared in each embodiment and comparative example, and the results are summarized in Table 1.

[0097] (3) Electrochemical performance testing

[0098] ① Preparation of the test battery: The negative electrode active material, conductive agent (multi-walled carbon nanotubes) and binder (carboxymethyl cellulose solution with a concentration of 2 wt.%) prepared in each example and comparative example were dispersed in a solvent (specifically deionized water) at a mass ratio of 7:2:1 and stirred evenly to obtain a negative electrode slurry; the negative electrode slurry was coated on the surface of copper foil using a 50 μm doctor blade, dried at 100°C for 12 h, and then cut into circular pieces to obtain the negative electrode; the above negative electrode and counter electrode (lithium metal sheet) were assembled into a 2032 coin cell in a glove box (filled with argon gas, with water and oxygen below 0.05 ppm) and injected with a commercial 1M LiPF6 ethylene carbonate and diethyl carbonate (1:1) electrolyte.

[0099] ② Initial discharge capacity test: At a constant temperature of 25℃, the coin cells of each embodiment and comparative example were discharged at 0.1Ag. -1 The current is constant and discharged to 0.005V, then discharged at 0.1Ag. -1 Charge the battery to 1.5V with constant current and record the first discharge capacity.

[0100] ③ Cyclic performance test: At a constant temperature of 25℃, with 0.1Ag -1 The current is constant and discharged to 0.005V, then discharged at 0.1Ag. -1 Charge the battery to 1.5V using a constant current; let it rest for 10 minutes; then discharge it to 0.005V using a constant current at 0.1C, which constitutes one cycle. Repeat this process to test the battery capacity and capacity retention rate after 80 cycles. The capacity retention rate (%) is calculated as: discharge capacity of the nth cycle / discharge capacity of the first cycle × 100%. The results are summarized in Table 2.

[0101] ④ Rate performance test: At a constant temperature of 25℃, with a concentration of 0.1A g... -1 Constant current discharge to 0.005V, constant current charge to 1.5V cutoff; at 0.2A g -1 Constant current discharge to 0.005V, constant current charge to 1.5V cutoff; at 0.5A g -1 Constant current discharge to 0.005V, constant current charge to 1.5V cutoff; at 1A g -1 Constant current discharge to 0.005V, constant current charge to 1.5V cutoff.

[0102] Figure 3 The rate performance diagram of the button cell in Example 2 is shown. Figure 4 The graph shows the cycling performance of the coin cell in Example 2 at a current density of 0.1 A / g. Figure 5 The graph shows the cycling performance of the coin cell in Example 2 at a current density of 0.5 A / g.

[0103] Table 1

[0104] Case C Ti O N P Example 1 39.60％ 14.55％ 36.83％ 4.62％ 4.40％ Example 2 38.42％ 15.10％ 37.56％ 4.53％ 4.39％ Example 3 28.63％ 18.3％ 44.70％ 4.24％ 4.13％ Example 4 37.63％ 15.20％ 38.14％ 4.71％ 4.32％ Comparative Example 1 77.26％ 0％ 8.54％ 7.23％ 6.97％ Comparative Example 2 41.39％ 15.67％ 37.92％ 5.02％ 0％

[0105] Table 2

[0106]

[0107]

[0108] As can be seen from the data in Tables 1 and 2, the negative electrode composite material provided in this application embodiment can simultaneously improve the cycle performance and rate performance of the secondary battery, while also maintaining the battery's first discharge capacity at a high level.

[0109] The above description is an exemplary embodiment of this application. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principles of this application, and these improvements and modifications are also considered to be within the scope of protection of this application.

Claims

1. A negative electrode composite material, characterized in that, This includes carbon materials and a coating layer disposed on their surface; The carbon material is doped with P, O and N elements, and the coating layer is made of titanium dioxide and / or aluminum oxide.

2. The negative electrode composite material according to claim 1, characterized in that, The carbon material is an amorphous carbon nanoribbon co-doped with P, O and N elements.

3. The negative electrode composite material according to claim 1, characterized in that, The thickness of the coating layer is 5nm-30nm.

4. The negative electrode composite material according to any one of claims 1-3, characterized in that, Based on the mass of the negative electrode composite material, the mass percentage of carbon material is 28%-40%, the mass percentage of P element is 4%-5%, the mass percentage of O element is 36%-45%, the mass percentage of N element is 4%-5%, and the mass percentage of Ti element is 14%-19%.

5. The negative electrode composite material according to claim 2, characterized in that, The radial dimension of the negative electrode composite material is 300nm-2000nm.

6. The method for preparing the negative electrode composite material according to any one of claims 1-5, characterized in that, include: Phosphorus and a nitrogen-containing carbon source were mixed under a protective atmosphere to prepare a carbon material precursor. The coating layer is formed on the surface of the carbon material precursor to obtain a composite material precursor. The composite material precursor is heated under a protective atmosphere to obtain the negative electrode composite material.

7. The preparation method according to claim 6, characterized in that, The carbon material precursor includes: The mixture of the phosphorus and the nitrogen-containing carbon source is spun to obtain a nanofiber-like carbon material precursor; the spinning process includes electrospinning.

8. The preparation method according to claim 6 or 7, characterized in that, The phosphorus element includes red phosphorus with a particle size of 200nm-2000nm, and the nitrogen-containing carbon source includes polyacrylonitrile and / or polyacrylamide.

9. The preparation method according to any one of claims 6-8, characterized in that, The mass ratio of the phosphorus element to the carbon source is 1:(5-15).

10. The preparation method according to any one of claims 6-9, characterized in that, The formation of the coating layer on the surface of the nanofibers includes: Titanium dioxide and / or aluminum oxide are deposited on the surface of the nanofiber-like carbon material precursor, the deposition process including atomic layer deposition.

11. The preparation method according to any one of claims 6-10, characterized in that, The heating process includes: heating to 400℃-500℃ at a heating rate of 5℃ / min-10℃ / min and holding at that temperature for 2h-6h.

12. A negative electrode, characterized in that, Including the negative electrode composite material as described in any one of claims 1-5.

13. A secondary battery, characterized in that, Includes the negative electrode as described in claim 12.

14. An electrical appliance, characterized in that, Includes the secondary battery as described in claim 13.

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