Lithium ferrite composite material as well as preparation method and application thereof

Abstract

The invention discloses a lithium ferrite composite material as well as a preparation method and application thereof, and the preparation method of the lithium ferrite composite material comprises the following steps: uniformly mixing lithium ferrite and carbon nanotubes, pressing, and sintering to obtain carbon nanotube compounded lithium ferrite; mixing the carbon nanotube compounded lithium ferrite with an MXene dispersion liquid, and carrying out hydrothermal treatment to obtain a transition product; and sintering the transition product to obtain the lithium ferrite composite material. The lithium ferrite composite material prepared by the preparation method of the lithium ferrite composite material is not easy to deliquesce, and when the lithium ferrite composite material is used for preparing a battery, the cycling stability and long-term performance of the battery can be improved.

Description

Technical Field

[0001] This invention belongs to the field of battery materials, specifically relating to a lithium ferrite composite material, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries are rechargeable batteries that work by moving lithium ions between the positive and negative electrodes. During charging, lithium ions move from the positive electrode to the negative electrode and store energy; during discharging, lithium ions move from the negative electrode to the positive electrode and release energy. Due to their high energy density, long cycle life, and relatively low self-discharge rate, these batteries are widely used in various devices such as mobile phones, laptops, electric vehicles, and renewable energy storage systems.

[0003] Pre-lithiation is a technology used to improve the performance of lithium-ion batteries. Positive electrode pre-lithiation is achieved by adding lithium-replenishing additives to the positive electrode. Because these additives have high theoretical capacity and exhibit irreversible reactions, they can compensate for the lithium lost during the initial SEI film formation. Pre-lithiation technology is also an important means of improving lithium-ion battery performance, not only increasing battery capacity but also helping to stabilize battery cycle performance. Overall, pre-lithiation technology plays a crucial role in improving lithium-ion battery performance, especially for battery systems using novel high-capacity anode materials. This technology can significantly improve the overall battery performance, including capacity, cycle life, and charge / discharge efficiency, thereby meeting the requirements of modern electronic devices for high-performance batteries.

[0004] However, lithium supplementation additives for cathode pre-lithiation still present many problems, with lithium ferrite being a commonly used additive. First, untreated lithium ferrite, due to its inherently low conductivity, exhibits slow lithium-ion diffusion during pre-lithiation. This significantly slows down battery formation, leading to higher costs in industrial production. In battery manufacturing, increasing formation speed is crucial for cost reduction and efficiency improvement. Second, the low conductivity of lithium ferrite also affects the battery's rate performance, i.e., its performance under high-current charge-discharge conditions. This limits its use in applications requiring rapid charge-discharge, such as electric vehicles and certain electronic devices. Pre-lithiation additives are typically added during the slurry mixing process in electrode preparation. Untreated lithium ferrite is susceptible to moisture in air, exhibiting poor stability and undergoing deliquescence. The resulting alkaline substances may cause gelation of the slurry, affecting the uniformity and quality of the electrode slurry. This sensitivity makes storage and handling difficult, increasing manufacturing and maintenance costs. Finally, direct pre-lithiation of lithium ferrite produces iron oxide (Fe2O3) as a byproduct. These byproducts can negatively impact battery performance, particularly affecting long-term cycle stability and capacity.

[0005] The information disclosed in this background section is intended only to enhance the understanding of the overall background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing lithium ferrite composite material, which is not easily deliquescent and can improve the cycle stability and long-term performance of batteries when used in battery manufacturing.

[0007] To achieve the above objectives, a specific example of the present invention provides a method for preparing a lithium ferrite composite material, comprising the following steps:

[0008] Lithium ferrite and carbon nanotubes are mixed evenly, pressed and sintered to obtain lithium ferrite composite with carbon nanotubes.

[0009] A carbon nanotube composite lithium ferrite and MXene dispersion were mixed and subjected to hydrothermal treatment to obtain a transition product.

[0010] The transition products were sintered to obtain lithium ferrite composite materials.

[0011] In one or more embodiments of the present invention, the temperature of the hydrothermal treatment is 160-220°C, the heating rate is 3-5°C / min, and the hydrothermal treatment time is 4-10h.

[0012] In one or more embodiments of the present invention, the preparation process of the lithium ferrite includes:

[0013] After the lithium source and iron source are mixed evenly, they are ball-milled, sintered in a protective atmosphere, and cooled to obtain lithium ferrite.

[0014] In one or more embodiments of the present invention, the lithium source is at least one selected from lithium oxide and lithium carbonate; and / or,

[0015] The iron source is at least one of ferric oxide and magnetite; and / or,

[0016] The molar ratio of lithium in the lithium source to iron in the iron source is (4.8–5.25):1.

[0017] In one or more embodiments of the present invention, the ball mill rotation speed is 380–520 rpm, and the ball milling time is 4–6 h; and / or,

[0018] The sintering step in the preparation of lithium ferrite includes:

[0019] Sinter at 500–600℃ for 8–12 hours, with a heating rate of 2–6℃ / min;

[0020] Sinter at 850–900℃ for 12–18 h, with a heating rate of 2–6℃ / min.

[0021] In one or more embodiments of the present invention, in the steps of uniformly mixing lithium ferrite and carbon nanotubes, pressing, and sintering, the sintering temperature is 300–450°C, the heating rate is 2–6°C / min, and the sintering time is 12–18 h; and / or,

[0022] In the step of sintering the transition product, the sintering temperature is 300-500℃, the heating rate is 2-6℃ / min, and the sintering time is 8-12h.

[0023] In one or more embodiments of the present invention, the molar ratio of lithium ferrite to carbon nanotubes is (2-15):1.

[0024] In one or more embodiments of the present invention, the MXene is Ti3C2T. x Or Ti3AlC2; and / or,

[0025] The concentration of MXene in the MXene dispersion is 3–8 mg / mL; and / or,

[0026] The MXene dispersion is an NMP dispersion of MXene, and the mass ratio of the carbon nanotube composite lithium ferrite to the MXene NMP dispersion is (3-5):1.

[0027] A specific example of the present invention provides a lithium ferrite composite material, wherein the lithium ferrite composite material has a core-shell structure, the shell layer of the core-shell structure is MXene, and the core layer of the core-shell structure is lithium ferrite composite with carbon nanotubes.

[0028] This invention provides a specific example of the application of a lithium ferrite composite material as described above, or a lithium ferrite composite material prepared by the method described above, in the field of lithium-ion batteries.

[0029] A specific example of the present invention provides a positive electrode sheet, the raw materials of which include the lithium ferrite composite material as described above or the lithium ferrite composite material prepared by the method described above for preparing the lithium ferrite composite material.

[0030] In one or more embodiments of the present invention, the raw material of the positive electrode sheet further includes a positive electrode material, and the mass of the lithium ferrite composite material is less than or equal to 5% of the mass of the positive electrode material.

[0031] A specific example of the present invention provides a lithium-ion battery, which includes a positive electrode, an electrolyte, and a negative electrode, wherein the positive electrode is as described above.

[0032] Compared with the prior art, the beneficial effects of the lithium ferrite composite material, its preparation method, and its application of the present invention are as follows:

[0033] (1) Improved formation speed and reduced production cost: Due to the high conductivity of MXene, this material can significantly improve the conductivity of lithium ferrite, thereby accelerating the formation speed of the battery, directly reducing the manufacturing cost of the battery and improving production efficiency.

[0034] (2) Improved battery rate performance: The combination of MXene and carbon nanotubes not only improves the conductivity of lithium ferrite composite materials, but also enhances the performance of the battery under high rate charge and discharge conditions, making the battery more suitable for applications that require fast charge and discharge, such as electric vehicles.

[0035] (3) Reduce gelation: The improved design of lithium ferrite composite material helps to reduce gelation caused by the deliquescence of lithium ferrite during the stirring process in the preparation of positive electrode; it ensures the uniformity and quality of electrode material, which is crucial for improving the overall performance of battery.

[0036] (4) Improved storage stability: The core-shell structure provides better protection and reduces the possibility of lithium ferrite coming into contact with air, thereby reducing the risk of moisture absorption and improving the storage stability of the material;

[0037] (5) Reduce the impact of pre-lithiation byproducts: MXene and carbon nanotubes can mitigate the generation of Fe2O3 during the pre-lithiation of lithium ferrite, thereby improving the cycle stability and long-term performance of the battery. Attached Figure Description

[0038] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] Figure 1 This is a flowchart of a method for preparing lithium ferrite composite material in one embodiment of the present invention;

[0040] Figure 2 This is a schematic diagram of a method for preparing lithium ferrite composite material in one embodiment of the present invention;

[0041] Figure 3 This is a SEM image of the lithium ferrite composite material in Example 1 of the present invention;

[0042] Figure 4 The image shown is the XRD pattern of the lithium ferrite composite material in Example 1 of this invention.

[0043] Figure 5 This is a charge-discharge curve of the lithium ferrite material electrode prepared in Comparative Example 1 of the present invention at different rates;

[0044] Figure 6 The above are charge-discharge curves of the lithium ferrite composite material electrode prepared in Example 1 of this invention at different rates.

[0045] Figure 7 The electrochemical impedance spectroscopy of the batteries prepared from lithium ferrite composite material in Example 1 of the present invention, the batteries prepared from lithium ferrite material in Comparative Example 1, and the batteries prepared from the blank group are shown.

[0046] Figure 8 This is a graph showing the first three charge-discharge curves of the battery made from the lithium ferrite composite material in Example 1 of this invention.

[0047] Figure 9 This is a graph showing the first three charge-discharge curves of the battery prepared as a blank group in this invention;

[0048] Figure 10 The images show the long-cycle curves of the lithium ferrite composite material battery prepared in Example 1 of this invention and the blank group battery prepared in the same invention. Detailed Implementation

[0049] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0050] like Figure 1 and combined Figure 2 As shown, a method for preparing a lithium ferrite composite material in an example of the present invention includes the following steps:

[0051] S1. Lithium ferrite and carbon nanotubes are mixed evenly, pressed and sintered to obtain lithium ferrite composite with carbon nanotubes.

[0052] S2. The carbon nanotube composite lithium ferrite and MXene dispersion are mixed and subjected to hydrothermal treatment to obtain the transition product.

[0053] S3. The transition product is sintered to obtain a lithium ferrite composite material.

[0054] It should be noted that the lithium ferrite composite material prepared by the preparation method of the present invention has a core-shell structure, wherein the shell layer of the core-shell structure is MXene, and the core layer of the core-shell structure is lithium ferrite composite with carbon nanotubes.

[0055] Compared with the prior art, the beneficial effects of the lithium ferrite composite material, its preparation method, and its application of the present invention are as follows:

[0056] (1) Improved formation speed and reduced production cost: Due to the high conductivity of MXene, this material can significantly improve the conductivity of lithium ferrite, thereby accelerating the formation speed of the battery, directly reducing the manufacturing cost of the battery and improving production efficiency.

[0057] (2) Improved battery rate performance: The combination of MXene and carbon nanotubes not only improves the conductivity of lithium ferrite composite materials, but also enhances the performance of the battery under high-rate charge and discharge conditions, making the battery more suitable for applications that require fast charge and discharge, such as electric vehicles.

[0058] (3) Reduce gelation: The improved design of lithium ferrite composite material helps to reduce gelation caused by the deliquescence of lithium ferrite during the stirring process in the preparation of positive electrode; it ensures the uniformity and quality of electrode material, which is crucial for improving the overall performance of battery.

[0059] (4) Improved storage stability: The core-shell structure provides better protection and reduces the possibility of lithium ferrite coming into contact with air, thereby reducing the risk of moisture absorption and improving the storage stability of the material.

[0060] (5) Reduce the impact of pre-lithiation byproducts: MXene and carbon nanotubes can mitigate the generation of Fe2O3 during the pre-lithiation of lithium ferrite, thereby improving the cycle stability and long-term performance of the battery.

[0061] In this invention, lithium ferrite products can be purchased directly, or lithium ferrite can be prepared according to requirements. For example, the preparation process of lithium ferrite includes:

[0062] After the lithium source and iron source are mixed evenly, they are ball-milled, sintered in a protective atmosphere, and cooled to obtain lithium ferrite.

[0063] Wherein, the lithium source is at least one of lithium oxide and lithium carbonate; the average particle size of the lithium source is 3-5 μm; the average particle size of the lithium ferrite is 1-2 μm; the iron source is at least one of ferric oxide and iron tetroxide; the molar ratio of lithium in the lithium source to iron in the iron source is (4.8-5.25):1.

[0064] Specifically, the iron source can have a particle size in the nanometer range, resulting in higher activity. Lithium ferrite (LFO) particles can have a particle size in the micrometer range.

[0065] In the preparation of lithium ferrite, the ball mill rotation speed is 380–520 rpm, and the milling time is 4–6 hours. Specifically, a planetary ball mill can be used for milling; dry milling is used, the milling media are agate balls, and the material ratio is 1:(20–30).

[0066] Preferably, the sintering step in the preparation of lithium ferrite may include two stages:

[0067] First stage: Sintering at 500-600℃ for 8-12 hours, with a heating rate of 2-6℃ / min;

[0068] Second stage: Sintering at 800-900℃ for 12-18 hours, with a heating rate of 2-6℃ / min.

[0069] In step S1 of the present invention, the sintering temperature is 300-450°C, the heating rate is 2-6°C / min, and the sintering time is 12-18h.

[0070] In all steps of this invention, the sintering step can be carried out in a protective atmosphere. The protective gas can be nitrogen or an inert gas, etc.

[0071] Specifically, the carbon nanotubes are single-walled or multi-walled carbon nanotubes with a length of 30-60 μm; the molar ratio of lithium ferrite to carbon nanotubes is (2-15):1.

[0072] MXene (also written as Mxene) is a two-dimensional material with the following properties:

[0073] Composition: Composed of transition metal carbides, nitrides, or carbonitrides, with the chemical formula (Mn+1XnT) x ), where (M) represents transition metal elements (such as Sc, Ti, V, etc.), (X) represents C and / or N elements, (T) represents transition metal elements (such as Sc, Ti, V, etc.), (X) represents C and / or N elements, and (T) represents transition metal elements (such as Sc, Ti, V, etc.). x ) represents surface end groups (such as -O, -OH, -F, etc.).

[0074] Structure: MXene is a novel two-dimensional nanomaterial obtained by etching away the a element from the layered ceramic material MAX phase, and has a graphene-like two-dimensional sheet structure.

[0075] In step S2, MXene is preferably Ti3C2T. x Alternatively, Ti3AlC2. The preferred concentration of MXene in the MXene dispersion is 3–8 mg / mL; the MXene dispersion is an NMP dispersion of MXene, and the mass ratio of the carbon nanotube composite lithium ferrite (which can be simply referred to as LFO-CNT) to the NMP dispersion of MXene is (3–5):1. Among them, Ti3C2Tx The NMP (N-methylpyrrolidone) dispersion can be obtained by treating a 20 mL aqueous solution of Ti3C2 (concentration of 5 mg / mL) for Shandong Xiyan MXene New Materials Co., Ltd., to obtain Ti3C2T. x NMP (N-methylpyrrolidone) dispersion.

[0076] The processing procedure can be as follows: 5 mg / mL of Ti3C2T from Shandong Xiyan MXene new material. x The aqueous solution (total volume 20 mL) was poured into a heat-resistant glass beaker and then placed on a heating plate set to 150°C. During heating, the solution was continuously stirred with a stirring rod to ensure uniform and rapid evaporation of the water. When the aqueous solution had completely evaporated, only dry Ti3C2T remained. x After turning off the heating stage and allowing the material to cool naturally to room temperature, slowly add NMP (N-methylpyrrolidone) solvent dropwise to the cooled Ti3C2T material using a dropper. x For the material, simultaneously stir with a stirring rod to gradually disperse it in NMP. Continue stirring until a homogeneous Ti3C2T is obtained. x The NMP dispersion (concentration 5 mg / mL) was prepared. Finally, the dispersion was transferred to a suitable container, sealed, and stored for later use.

[0077] Furthermore, in step S2, the hydrothermal treatment temperature is 160–220℃, the heating rate is 3–5℃ / min, and the hydrothermal treatment time is 4–10 hours. If the hydrothermal treatment temperature is below 120℃, the carbon nanotube composite lithium ferrite will have virtually no MXene coating. If the hydrothermal treatment temperature is 120–160℃, the carbon nanotube composite lithium ferrite will be partially coated with MXene, resulting in a deterioration in the performance of the lithium ferrite composite material. If the hydrothermal treatment temperature is above 220℃, the pressure during the hydrothermal treatment process will be excessive, posing a high risk of explosion and potentially causing the lithium ferrite composite material (which can be simply referred to as MXene@LFO-CNT) to break.

[0078] In step S3 of the present invention, the sintering temperature is 300-500°C, the heating rate is 2-6°C / min, and the sintering time is 8-12h.

[0079] A specific example of the present invention provides a lithium ferrite composite material, wherein the lithium ferrite composite material has a core-shell structure, the shell layer of the core-shell structure is MXene, and the core layer of the core-shell structure is lithium ferrite composite with carbon nanotubes.

[0080] The lithium ferrite composite material of the present invention can be prepared by the above-described method for preparing lithium ferrite composite materials, or by other methods.

[0081] This invention provides a specific example of the application of a lithium ferrite composite material as described above, or a lithium ferrite composite material prepared by the method described above, in the field of lithium-ion batteries.

[0082] That is, the lithium ferrite composite material of the present invention can be used as a positive electrode lithium replenishing agent (also known as a positive electrode pre-lithiation additive, lithium replenishing additive, etc.) in the field of lithium-ion batteries.

[0083] A specific example of the present invention provides a positive electrode sheet, the raw materials of which include the lithium ferrite composite material as described above or the lithium ferrite composite material prepared by the method described above for preparing the lithium ferrite composite material.

[0084] In one or more embodiments of the present invention, the raw materials of the positive electrode sheet further include a positive electrode material, and the mass of the lithium ferrite composite material is less than or equal to 5% of the mass of the positive electrode material, that is, in the raw materials of the positive electrode sheet, the mass of the lithium ferrite composite material is less than or equal to 5% of the mass of the positive electrode material.

[0085] Specifically, the cathode material can be at least one of lithium cobalt oxide, lithium manganese oxide, and ternary materials. Among them, ternary materials (NCM) refer to materials composed of three metal elements, nickel, cobalt, and manganese (aluminum), used to prepare the cathode of lithium-ion batteries, such as NCM523, NCM811, etc.

[0086] Furthermore, the raw materials for the positive electrode sheet can also include conductive agents and binders. Conductive agents and binders are common raw materials used in positive electrode sheets on the market. For example, conductive agents can be carbon black, carbon nanotubes, etc.; binders can be polyvinylidene fluoride (PVDF) binders, etc.

[0087] This invention provides a specific example of a lithium-ion battery, which includes a positive electrode, an electrolyte, and a negative electrode. The positive electrode is as described above. It is understood that the lithium-ion battery may also include structures such as a separator. The electrolyte can also be considered as a liquid electrolyte solution.

[0088] The lithium ferrite composite material of the present invention, its preparation method and its application will be described in detail below with reference to specific embodiments and comparative examples.

[0089] Example 1

[0090] Lithium carbonate and nanoscale Fe2O3 were mixed in a molar ratio of 5.25:1 and subjected to two-stage sintering: first, held at 500 °C for 10 h, and then sintered at 850 °C for 15 h, both at a heating rate of 4 °C / min, to obtain lithium ferrite with an average particle size of 3 μm. Lithium ferrite and multi-walled carbon nanotubes with an average length of 50 μm were mixed in a mass ratio of 10:1, and this mixture was dry milled in a planetary ball mill at a speed of 500 rpm for 5 h, using agate balls as the ball milling medium, and the ball-to-material ratio was 1:25. The milled mixture was sintered at 350 °C for 15 h, with a heating rate of 4 °C / min, and carried out in a nitrogen atmosphere to ensure the stability and purity of the material. The obtained carbon nanotube-composite lithium ferrite was mixed with a NMP dispersion of few-layer Ti3C2 T x with a mass concentration of 5 mg / mL (prepared from 20 mL of an aqueous solution of Ti3C2 (concentration of 5 mg / mL) from Shandong Xiyan MXene New Materials by the above method) in a mass ratio of 3:1, and then hydrothermally treated at 200 °C for 4 h. Finally, this composite material was sintered at 400 °C in a nitrogen atmosphere for 8 h to obtain the lithium ferrite composite material of the present invention.

[0091] Refer Figure 3 Shown is the SEM image of the lithium ferrite composite material in this embodiment. It can be seen that the lithium ferrite composite material is oval-shaped, with an average particle size of 3 - 5 μm. Refer Figure 4 Shown is the XRD pattern of the lithium ferrite composite material in this embodiment. It can be seen that the synthesized material has the corresponding peak positions of carbon nanotubes, lithium ferrite, and carbon nanotubes.

[0092] Example 2

[0093] Lithium carbonate and nanoscale Fe2O3 were mixed in a molar ratio of 5.2:1 and subjected to two-stage sintering: first, held at 600 °C for 10 h, and then sintered at 900 °C for 14 h, both at a heating rate of 4 °C / min, to obtain lithium ferrite with an average particle size of 3.5 μm. Lithium ferrite and multi-walled carbon nanotubes with an average length of 50 μm were mixed in a mass ratio of 8:1, and this mixture was dry milled in a planetary ball mill at a speed of 450 rpm for 5 h, using agate balls as the ball milling medium, and the ball-to-material ratio was 1:28. The milled mixture was sintered at 400 °C for 15 h, with a heating rate of 5 °C / min, and carried out in a nitrogen atmosphere to ensure the stability and purity of the material. The obtained carbon nanotube-composite lithium ferrite was mixed with a NMP dispersion of few-layer Ti3C2 T x with a mass concentration of 5 mg / mL in a mass ratio of 4:1, and then hydrothermally treated at 220 °C for 4 h. Finally, this composite material was sintered at 420 °C in a nitrogen atmosphere for 8 h to obtain the lithium ferrite composite material of the present invention.

[0094] Example 3

[0095] Lithium carbonate and nano-sized Fe₂O₃ were mixed in a 5:1 molar ratio and sintered in two stages: first at 550℃ for 12 h, then at 880℃ for 16 h, both at a heating rate of 4℃ / min, to obtain lithium ferrite with an average particle size of 4 μm. Lithium ferrite and 50 μm (average) long multi-walled carbon nanotubes were mixed in a 6:1 mass ratio and dry-milled in a planetary ball mill at 400 rpm for 5 h, using agate balls as the milling medium at a ball-to-material ratio of 1:26. The milled mixture was then sintered at 400℃ for 15 h at a heating rate of 5℃ / min under a nitrogen atmosphere to ensure material stability and purity. The resulting carbon nanotube-composite lithium ferrite was then mixed with 5 mg / mL of few-layer Ti₃C₂T₂. x The NMP dispersion was mixed at a mass ratio of 3.5:1 and then subjected to hydrothermal treatment at 160°C for 5 hours. Finally, the composite material was sintered at 300°C in a nitrogen atmosphere for 8 hours to obtain the lithium ferrite composite material of the present invention.

[0096] Example 4

[0097] Lithium carbonate and nano-sized Fe₂O₃ were mixed at a molar ratio of 4.8:1 and sintered in two stages: first at 560℃ for 10 h, followed by sintering at 890℃ for 15 h, both at a heating rate of 3℃ / min, to obtain lithium ferrite with an average particle size of 5 μm. Lithium ferrite and 50 μm (average) long multi-walled carbon nanotubes were mixed at a mass ratio of 9:1 and dry-milled in a planetary ball mill at 420 rpm for 6 h, using agate balls as the milling medium at a ball-to-material ratio of 1:27. The milled mixture was then sintered at 440℃ for 13 h at a heating rate of 5℃ / min under a nitrogen atmosphere to ensure material stability and purity. The resulting carbon nanotube-composite lithium ferrite was then mixed with 5 mg / mL of few-layer Ti₃C₂T₂. x The NMP dispersion was mixed at a mass ratio of 3.8:1 and then subjected to hydrothermal treatment at 190°C for 6 hours. Finally, the composite material was sintered at 360°C in a nitrogen atmosphere for 8 hours to obtain the lithium ferrite composite material of the present invention.

[0098] Comparative Example 1

[0099] Lithium ferrite (LFO), which is available on the market, was selected as the lithium ferrite material.

[0100] Comparative Example 2

[0101] Lithium carbonate and nano-sized Fe₂O₃ were mixed at a molar ratio of 5.25:1 and sintered in two stages: first at 500℃ for 10 h, followed by sintering at 850℃ for 15 h, both at a heating rate of 4℃ / min, yielding lithium ferrite with an average particle size of 3 μm. Lithium ferrite and 50 μm (average) long multi-walled carbon nanotubes were mixed at a mass ratio of 10:1. This mixture was then dry-milled in a planetary ball mill at 500 rpm for 5 h, using agate balls as the milling medium, with a ball-to-material ratio of 1:25. The milled mixture was then sintered at 350℃ for 15 h at a heating rate of 4℃ / min under a nitrogen atmosphere to ensure material stability and purity. The resulting carbon nanotube composite lithium ferrite material is the final lithium ferrite material.

[0102] Comparative Example 3

[0103] Lithium carbonate and nano-sized Fe₂O₃ were mixed at a molar ratio of 5.25:1 and subjected to a two-stage sintering process: first, sintering at 500℃ for 10 h, followed by sintering at 850℃ for 15 h, both at a heating rate of 4℃ / min, to obtain lithium ferrite with an average particle size of 3 μm. The lithium ferrite was then reacted with 5 mg / mL of few-layer Ti₃C₂T₂. x The NMP dispersion (prepared from 20 mL of Ti3C2 (concentration 5 mg / mL) aqueous solution from Shandong Xiyan MXene New Material Co., Ltd. using the above method) was mixed at a mass ratio of 3:1, and then subjected to hydrothermal treatment at 200℃ for 4 h. Finally, this composite material was sintered at 400℃ in a nitrogen atmosphere for 8 h to obtain MXene-coated lithium ferrite, which is the lithium ferrite material.

[0104] The lithium ferrite composite materials prepared in Examples 1-4 and the lithium ferrite composite materials in Comparative Examples 1-3 were subjected to the following performance tests:

[0105] (1) A composite electrode, consisting of a lithium ferrite composite material (lithium ferrite material), conductive agent carbon black, and PVDF binder (polyvinylidene fluoride) uniformly mixed at a ratio of 8:1:1 (mass ratio), was used as the working electrode. A lithium metal sheet was used as the counter electrode, and a 1 mol / L LiPF6 solution (ED:DMC:EMC = 1:1:1 (volume ratio)) was used as the electrolyte to assemble a lithium-ion battery. Charge-discharge tests were then conducted between 2.5 and 4.5 V. The test results are shown in Table 1 and as shown in... Figure 5 and Figure 6 The charge / discharge curves.

[0106] (2) The degradation time of the lithium ferrite composite materials prepared in Examples 1 to 4 and the lithium ferrite materials in Comparative Examples 1 to 3 under different air humidity conditions was compared to obtain the data shown in Table 3.

[0107] The lithium ferrite composite material prepared in Example 1 and the lithium ferrite (LFO) composite material in Comparative Example 1 were subjected to the following performance tests:

[0108] A composite electrode was prepared by uniformly mixing lithium iron phosphate, lithium ferrite composite material (lithium ferrite material), conductive agent carbon black, and binder polyvinylidene fluoride in a mass ratio of 75:5:10:10. Graphite was used as the counter electrode, with an N / P ratio of 1.1. A lithium-ion battery was assembled using a 1 mol / L LiPF6 solution (ED:DMC:EMC = 1:1:1 (volume ratio)) as the electrolyte. Electrochemical impedance spectroscopy (EIS) was performed (a blank group was added, i.e., the working electrode of the lithium-ion battery in the blank group did not contain the lithium ferrite composite material). The results were as follows: Figure 7 The electrochemical impedance spectroscopy is shown below. (Through...) Figure 7 It can be seen that the battery in Comparative Example 1 has a larger electrochemical impedance, while the electrochemical impedance data of the battery in Example 1 and the blank group are similar.

[0109] The lithium ferrite composite material prepared in Example 1, and the lithium ferrite materials of Comparative Examples 1 to 3 were subjected to the following performance tests:

[0110] A composite electrode was prepared by uniformly mixing lithium iron phosphate, lithium ferrite composite material (lithium ferrite material), conductive agent carbon black, and binder polyvinylidene fluoride at a mass ratio of 75:X:10:10. Graphite was used as the counter electrode, with N / P = 1.1. A 1 mol / L LiPF6 solution (ED:DMC:EMC = 1:1:1 (volume ratio)) was used as the electrolyte to assemble lithium-ion batteries (a blank group was added, in which the working electrode of the lithium-ion battery did not contain the lithium ferrite composite material). The first cycle charge-discharge test was conducted between 2.7-4.5V, and the subsequent cycle test was conducted between 2.8-3.65V. The test results are shown in Table 2. Figure 10 The data chart.

[0111] In Example 1, the working electrode contained a lithium iron phosphate / lithium ferrite composite material with a conductive agent (carbon black) and a binder (polyvinylidene fluoride) ratio of 75:5:10:10. The charge-discharge curves of the battery for the first three cycles are shown below. Figure 8 As shown, the first charge capacity is 192mAh / g, and the discharge capacity is 174mAh / g. Figure 9 The first three charge / discharge curves of the blank group battery are shown. The specific capacity of the first charge cycle is 176mAh / g, and the specific capacity of the first discharge cycle is 162mAh / g.

[0112] Table 1

[0113]

[0114] Through Table 1 and Figure 5 and Figure 6 As can be seen from the data of Example 1 and Comparative Example 1, the lithium ferrite composite material of the present invention has a higher irreversible capacity and a better lithium replenishment effect, regardless of whether it is at a low rate or a high rate.

[0115] Table 2

[0116]

[0117]

[0118] Through Table 2 and Figure 10 The data shows that adding lithium ferrite composite material (also known as lithium replenisher or pre-lithiation agent) can effectively improve the capacity retention rate of the battery. Furthermore, with the same number of positive electrode materials, the battery with the lithium ferrite composite material of this invention exhibits a significantly better capacity retention rate than the batteries with lithium ferrite materials added in Comparative Examples 1 to 3.

[0119] Table 3

[0120]

[0121] As can be seen from the data in Table 3, the stability of the lithium ferrite composite material of the present invention is superior to that of conventional lithium ferrite materials under both low and high humidity conditions.

[0122] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0123] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing a lithium ferrite composite material, characterized in that, Includes the following steps: Lithium ferrite and carbon nanotubes are mixed evenly, pressed and sintered to obtain lithium ferrite composite with carbon nanotubes. A carbon nanotube composite lithium ferrite and MXene dispersion were mixed and subjected to hydrothermal treatment to obtain a transition product. The transition products were sintered to obtain lithium ferrite composite materials.

2. The method for preparing the lithium ferrite composite material according to claim 1, characterized in that, The hydrothermal treatment temperature is 160–220℃, the heating rate is 3–5℃ / min, and the hydrothermal treatment time is 4–10h.

3. The method for preparing the lithium ferrite composite material according to claim 1, characterized in that, The preparation process of the lithium ferrite includes: After the lithium source and iron source are mixed evenly, they are ball-milled, sintered in a protective atmosphere, and cooled to obtain lithium ferrite.

4. The method for preparing the lithium ferrite composite material according to claim 3, characterized in that, The lithium source is at least one of lithium oxide and lithium carbonate; and / or, The iron source is at least one of ferric oxide and magnetite; and / or, The molar ratio of lithium in the lithium source to iron in the iron source is (4.8–5.25):

1.

5. The method for preparing the lithium ferrite composite material according to claim 3, characterized in that, The ball mill rotation speed is 380–520 rpm, and the ball milling time is 4–6 hours; and / or, The sintering step in the preparation of lithium ferrite includes: Sinter at 500–600℃ for 8–12 hours, with a heating rate of 2–6℃ / min; Sinter at 850–900℃ for 12–18 h, with a heating rate of 2–6℃ / min.

6. The method for preparing the lithium ferrite composite material according to claim 1, characterized in that, In the step of uniformly mixing lithium ferrite and carbon nanotubes, pressing, and sintering, the sintering temperature is 300–450℃, the heating rate is 2–6℃ / min, and the sintering time is 12–18 h; and / or, In the step of sintering the transition product, the sintering temperature is 300-500℃, the heating rate is 2-6℃ / min, and the sintering time is 8-12h.

7. The method for preparing the lithium ferrite composite material according to claim 1, characterized in that, The molar ratio of lithium ferrite to carbon nanotubes is (2-15):

1.

8. The method for preparing the lithium ferrite composite material according to claim 1, characterized in that, The MXene is Ti3C2T x Or Ti3AlC2; and / or, The concentration of MXene in the MXene dispersion is 3–8 mg / mL; and / or, The MXene dispersion is an NMP dispersion of MXene, and the mass ratio of the carbon nanotube composite lithium ferrite to the MXene NMP dispersion is (3-5):

1.

9. A lithium ferrite composite material, characterized in that, The lithium ferrite composite material has a core-shell structure, with the shell layer being MXene and the core layer being lithium ferrite composite made of carbon nanotubes.

10. The application of a lithium ferrite composite material as described in claim 9 or a lithium ferrite composite material prepared by any one of the preparation methods of lithium ferrite composite materials as described in claims 1 to 8 in the field of lithium-ion batteries.

11. A positive electrode plate, characterized in that, Its raw materials include lithium ferrite composite material as described in claim 9 or lithium ferrite composite material prepared by the preparation method of lithium ferrite composite material as described in any one of claims 1 to 8.

12. The positive electrode sheet according to claim 11, characterized in that, The raw materials for the positive electrode sheet also include positive electrode material, and the mass of the lithium ferrite composite material is less than or equal to 5% of the mass of the positive electrode material.

13. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode, an electrolyte, and a negative electrode, wherein the positive electrode is the positive electrode as described in claim 11 or 12.

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