A FeP2 / C composite anode material with LiF interface modification and its preparation method

Abstract

The application discloses a kind of FeP2 / C / CNTs / LiF composite negative materials containing LiF interface modification and preparation method thereof, for the problems of low specific capacity of existing graphite negative electrode, poor conductivity of FeP2-based material, large volume expansion and unstable SEI film, the application adopts two-step dry ball milling process: first step, mix reduced iron powder, red phosphorus powder and expanded graphite treated by 900-1100 DEG C argon heat treatment, under inert atmosphere, with 30:1-70:1 ball-to-material ratio, 1100-1300 rpm high-speed ball milling for 7.5-8.5 hours, to obtain FeP2 / C composite powder (molar ratio of iron powder to red phosphorus 1:2-1:4);Second step, mix it with 5% mass fraction of CNTs, 10%-20% mass fraction of LiF, with 30:1-70:1 ball-to-material ratio, 300-500 rpm low-speed ball milling for 10-30 hours, to form quaternary composite material.The method is solvent-free pollution, easy industrialization, LiF can induce the formation of stable SEI film, so that the first circle coulomb efficiency of the material reaches 79.71%-83.15%, significantly improves the charge-discharge performance and cycle stability, suitable for high energy density lithium ion battery negative electrode.

Description

Technical Field

[0001] This invention relates to the field of alloy materials and lithium-ion battery anode materials, specifically to a FeP2 / C composite anode material with LiF interface modification and its preparation method. Background Technology

[0002] Driven by the rapid development of electric vehicles and large-scale energy storage systems, lithium-ion batteries are facing unprecedented pressure to improve their energy density. Currently widely used graphite anodes, limited by their inherently low specific capacity, have very limited room for performance improvement and cannot support the design requirements of next-generation high-energy-density batteries. Developing new anode materials has become a consensus in the industry.

[0003] Among the many promising new anode materials, iron diphosphide (FeP2) stands out due to its comprehensive advantages, including high lithium storage capacity, abundant resources, and environmental friendliness. However, FeP2 faces three significant obstacles in practical applications: First, its inherent semiconductor properties and low electronic conductivity severely limit the charge and discharge rates; second, during lithium insertion and extraction, the crystal structure undergoes significant volume expansion and contraction, easily leading to electrode material breakage and failure, resulting in poor cycle stability; and finally, under repeated volume changes, the solid electrolyte interphase (SEI) film on the electrode surface is difficult to stabilize, leading to continuous consumption of active lithium and electrolyte, and a rapid decline in battery coulombic efficiency and lifespan.

[0004] To address these challenges, existing modification strategies mainly focus on two aspects: "nano-sizing" and "carbon coating" (e.g., combining FeP2 with carbon nanotubes or graphene). While these strategies can construct conductive networks to improve conductivity and partially buffer volume effects, the problems of "interfacial side reactions" and "repeated SEI film rupture" still exist. During repeated volume breathing, the SEI film on the surface of FeP2 will continuously rupture and regenerate, leading to the continuous consumption of active lithium, ultimately resulting in low battery coulombic efficiency and rapid cycle life decay.

[0005] Therefore, it is urgent to introduce components that can stabilize the interface and induce the formation of LiF-SEI films on the basis of FeP2 / C composite materials. Lithium fluoride (LiF) has attracted attention as a key functional interface component. It can induce the formation of a mechanically strong and chemically stable SEI film on the electrode surface, significantly suppressing the occurrence of side reactions. More importantly, LiF itself has good lithium-ion conductivity, which can effectively reduce interfacial impedance and improve ion migration efficiency. Although lithium fluoride (LiF) is an ideal interface modifier, its high melting point and insolubility in common organic solvents make it difficult to uniformly introduce it through wet coating.

[0006] Current technologies lack a dry, uniform composite process for high-hardness FeP2, carbon matrix, CNTs, and ionic crystal LiF that does not damage the nanostructure of the materials and is simple and easily scalable. Therefore, developing a new method for controllable composite of LiF as a key component is of vital importance for advancing the practical application of high-performance FeP2-based anode materials. Summary of the Invention

[0007] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a FeP2 / C composite anode material with LiF interface modification and its preparation method. This method has advantages such as simple operation and strong controllability in preparing nano-FeP2 / C / CNTs / LiF composite materials, and solves the technical problems of poor interface stability and low first-cycle coulombic efficiency of existing FeP2-based anode materials.

[0008] (II) Technical Solution To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a nano-FeP2 / C / CNTs / LiF composite material for lithium-ion batteries includes the following steps: (1) Reduced iron powder, red phosphorus powder and pretreated expanded graphite are mixed in a set ratio and ball-milled at high speed in an inert gas environment to make the iron and phosphorus components undergo an alloying reaction and the carbon matrix undergo preliminary composite to obtain FeP2 / C composite powder.

[0009] (2) The FeP2 / C composite powder obtained in the above process is mixed with carbon nanotubes (CNTs) and lithium fluoride (LiF) powder in a specific ratio, and homogenized by low-speed ball milling in an inert atmosphere to finally obtain nanoscale FeP2 / C / CNTs / LiF quaternary composite material.

[0010] Furthermore, the expanded graphite used in process (1) is obtained by heat treatment of expandable graphite in an argon atmosphere at high temperature, with a treatment temperature range of 900 to 1100°C and a holding time of 5 to 30 minutes.

[0011] Furthermore, in step (1), the molar ratio of reduced iron powder to red phosphorus powder is controlled between 1:2 and 1:4; more preferably, the molar ratio ranges from 1:2.5 to 1:3.5.

[0012] Furthermore, in step (1), the amount of expanded graphite added accounts for 8% to 30% of the total mass of the initial mixed powder; preferably, its mass fraction is 10% to 20%.

[0013] Furthermore, in step (1), the weight ratio of the ball milling media to the material (ball-to-material ratio) is 30:1 to 70:1; preferably, the ball-to-material ratio is 40:1 to 60:1.

[0014] Furthermore, the ball milling duration in step (1) is set to 7.5 to 8.5 hours; preferably, the ball milling time is 7.8 to 8.2 hours.

[0015] Furthermore, the ball mill speed in process (1) is controlled at 1100 to 1300 rpm; preferably, the speed range is 1150 to 1250 rpm.

[0016] Furthermore, in process (2), the proportions of the three components FeP2 / C composite powder, CNTs and LiF by mass percentage must meet the following requirements: the CNTs content is 5%, the amount of LiF added can be selected from three gradients of 10%, 15% or 20%, and the content of FeP2 / C composite powder is adjusted to 85%, 80% or 75% respectively.

[0017] Furthermore, the ball-to-material ratio in process (2) is maintained at 30:1 to 70:1; preferably, the ball-to-material ratio is 40:1 to 60:1.

[0018] Furthermore, the composite ball milling time in process (2) is controlled at 10 to 30 hours; preferably, the time is 18 to 25 hours.

[0019] Furthermore, the ball milling speed in process (2) is set to 300-500 rpm; preferably, the speed range is 350-450 rpm.

[0020] (III) Beneficial Effects Compared with the prior art, the present invention provides a FeP2 / C composite anode material with LiF interface modification and its preparation method, which has the following beneficial effects: 1. This FeP2 / C composite anode material with LiF interface modification and its preparation method innovatively employ a two-step ball milling method. First, the FeP2 / C core is synthesized in high-speed ball milling, and then CNTs conductive network and LiF interface modifier are simultaneously introduced in the low-speed ball milling stage. The addition of LiF component is the core improvement of this scheme, which can induce the formation of a robust and stable interface protective layer on the surface of electrode material particles, effectively improving the initial charge-discharge efficiency and significantly enhancing the structural integrity of the material during long-term cycling.

[0021] 2. The FeP2 / C composite anode material with LiF interface modification and its preparation method are all dry physical processes, which do not require the use of solvents. The process is simple, the energy consumption is relatively low, the production safety is good, and the batch consistency of the products is strong, making it particularly suitable for large-scale industrial production applications. Attached Figure Description

[0022] Figure 1 The cycling performance diagram is shown for the 85wt% (FeP2 / 10wt% C) / 5wt% CNTs / 10wt% LiF material prepared in Example 1. Figure 2 The cycling performance diagram is shown for the 80wt% (FeP2 / 10wt% C) / 5wt% CNTs / 15wt% LiF material prepared in Example 1. Figure 3 The cycling performance diagram is shown for the 75wt% (FeP2 / 10wt% C) / 5wt% CNTs / 20wt% LiF material prepared in Example 1. Figure 4 SEM image of the 85wt% (FeP2 / C) / 5wt% CNTs / 10wt% LiF material prepared in Example 2; Figure 5 SEM image of the 80wt% (FeP2 / C) / 5wt% CNTs / 15wt% LiF material prepared in Example 2; Figure 6 SEM image of the 75wt% (FeP2 / C) / 5wt% CNTs / 20wt% LiF material prepared in Example 2; Figure 7 The XRD pattern of the 85wt% (FeP2 / C) / 5wt% CNTs / 10wt% LiF material prepared in Example 2; Figure 8 The image shows the XRD pattern of the 80wt% (FeP2 / C) / 5wt% CNTs / 15wt% LiF material prepared in Example 2.

[0023] Figure 9 This describes the overall process from preparation to use of the present invention. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] Battery assembly and testing conditions: Using deionized water as solvent, the prepared nano-FeP2 / C / CNTs / LiF composite material, conductive agent Super P Li, and binder carboxymethyl cellulose (CMC) were mixed in a mass ratio of 8:1:1 to form a slurry, which was then uniformly coated onto copper foil to prepare the electrode. A CR2016 coin cell was assembled using the prepared electrode sheet as the working electrode and a lithium metal sheet as the counter and reference electrodes. The electrolyte was a 1M LiPF6 solution of ethylene carbonate (EC) / diethyl carbonate (DEC) (volume ratio 1:2), with 10% fluoroethylene carbonate (FEC) added as a film-forming additive. All batteries were electrochemically tested at room temperature.

[0026] Example 1 Preparation and properties of 85wt%(FeP2 / 10wt%C) / 5wt%CNTs / 10wt%LiF composite material 1) Preparation of FeP2 / C composite material: Reduced iron powder, red phosphorus and expanded graphite (10% by mass) were mixed. Under argon protection, the mixture was ball-milled at high speed for 7.5 to 8.5 h at a ball-to-material ratio of 30:1 to 70:1 and a rotation speed of 1100 to 1300 rpm to obtain FeP2 / 10wt%C composite material.

[0027] 2) Introduction of CNTs and LiF: The above FeP2 / 10wt%C composite material was accurately weighed and mixed with CNTs and LiF at a mass ratio of 85:5:10. The mixture was then ball-milled at low speed for 18–25 h in an argon atmosphere, maintaining a ball-to-material ratio of 30:1–70:1 and a rotation speed of 300–500 rpm, to obtain the final product 85wt%(FeP2 / 10wt%C) / 5wt%CNTs / 10wt%LiF.

[0028] Example 2 Preparation and properties of 85wt%(FeP2 / 10wt%C) / 5wt%CNTs / 10wt%LiF composite material 1) The preparation steps and conditions of the FeP2 / C composite material are the same as in Example 1.

[0029] 2) The FeP2 / 10wt%C composite material was mixed with CNTs and LiF at a mass ratio of 80:5:15 and compounded using the same low-speed ball milling process to obtain the final product 80wt%(FeP2 / 10wt%C) / 5wt%CNTs / 15wt%LiF.

[0030] Example 3 Preparation and properties of 75wt%(FeP2 / 10wt%C) / 5wt%CNTs / 20wt%LiF composite material 1) The preparation steps and conditions of the FeP2 / C composite material are the same as in Example 1.

[0031] 2) The FeP2 / 10wt%C composite material was mixed with CNTs and LiF at a mass ratio of 75:5:20 and compounded using the same low-speed ball milling process. The final product was 75wt%(FeP2 / 10wt%C) / 5wt%CNTs / 20wt%LiF.

[0032] Under the above battery assembly and testing conditions, an 85wt% (FeP2 / 10wt%C) / 5wt%CNTs / 10wt%LiF electrode was subjected to 100mA g -1 The first discharge and charge specific capacities at current density are 996 mA hg, respectively. -1 and 1213mAhg -1 The initial coulombic efficiency was 82.11% for an 80wt% (FeP2 / 10wt%C) / 5wt% CNTs / 15wt% LiF electrode at 100mA g. -1 The specific capacity of the first discharge and charge under the current density is 960.4 mA hg. -1 and 1204.8mA hg -1 The initial coulombic efficiency was 79.71%. A 75wt% (FeP2 / 10wt%C) / 5wt%CNTs / 20wt%LiF electrode was used at 100 mA g. -1 The specific capacity of the first discharge and charge under the current density is 896.5 mA hg. -1 and 1078.2 mA hg -1 The initial Coulomb efficiency was 83.15%.

[0033] All three methods show significant improvements over the electrode material without added LiF, reflected in improved initial coulombic efficiency, improved initial charge-discharge specific capacity, and improved overall efficiency at 2A g. -1 Capacity retention at current density has been improved.

[0034] Three ratio battery cycle performance such as Figure 1 , Figure 2 , Figure 3 As shown. SEM images of the three composite material samples are as follows. Figure 4 , Figure 5 , Figure 6As shown, the material maintains a good overall nanoparticle morphology, with carbon nanotubes interwoven into a network. LiF modifies the particle surface to some extent, gradually becoming blurred as it is co-coated with carbon. The XRD patterns of the two composite materials, 85wt%(FeP2 / 10wt%C) / 5wt%CNTs / 10wt%LiF and 80wt%(FeP2 / 10wt%C) / 5wt%CNTs / 15wt%LiF, are shown below. Figure 7 , Figure 8 The characteristic diffraction peaks of the FeP2 crystalline phase were clearly visible in the spectrum, and the intensity of the characteristic diffraction peaks of the LiF crystals showed a regular increase. This indicates that the high-speed ball milling successfully synthesized the well-crystallized FeP2 main phase, and the content of LiF was precisely controlled, proving the success and controllability of the composite.

[0035] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a nano-FeP2 / C / CNTs / LiF composite material for lithium-ion batteries, characterized in that, Includes the following steps: (1) Reduced iron powder, red phosphorus powder and expanded graphite are mixed and ball-milled at high speed under inert gas protection to obtain FeP2 / C composite powder; (2) The FeP2 / C composite powder obtained in step (1) is mixed with carbon nanotubes (CNTs) and lithium fluoride (LiF) powder, and then ball-milled at low speed under an inert atmosphere to obtain the nano FeP2 / C / CNTs / LiF composite material.

2. The method for preparing a nano-FeP2 / C / CNTs / LiF composite material for lithium-ion batteries according to claim 1, characterized in that, The expanded graphite in step (1) is prepared by heat treatment of expandable graphite at 900-1100℃ for 5-30 minutes in an argon atmosphere.

3. The method for preparing a nano-FeP2 / C / CNTs / LiF composite material for lithium-ion batteries according to claim 1, characterized in that, The molar ratio of reduced iron powder to red phosphorus powder in step (1) is 1:2 to 1:

4.

4. The method for preparing a nano-FeP2 / C / CNTs / LiF composite material for lithium-ion batteries according to claim 1, characterized in that, The molar ratio of reduced iron powder to red phosphorus powder is 1:2.5 to 1:3.

5.

5. The method for preparing a nano-FeP2 / C / CNTs / LiF composite material for lithium-ion batteries according to claim 1, characterized in that, The amount of expanded graphite added in step (1) accounts for 8% to 30% of the total mass of the initial mixed powder.

6. The method for preparing a nano-FeP2 / C / CNTs / LiF composite material for lithium-ion batteries according to claim 1, characterized in that, In step (1), the ball-to-material ratio of the high-speed ball mill is 30:1 to 70:1, the milling time is 7.5 to 8.5 hours, and the rotation speed is 1100 to 1300 rpm.

7. The method for preparing a nano-FeP2 / C / CNTs / LiF composite material for lithium-ion batteries according to claim 1, characterized in that, The mass percentages of FeP2 / C composite powder, carbon nanotubes (CNTs) and lithium fluoride (LiF) in step (2) are as follows: FeP2 / C composite powder 75%–85%, carbon nanotubes (CNTs) 5%, and lithium fluoride (LiF) 10%–20%.

8. The method for preparing a nano-FeP2 / C / CNTs / LiF composite material for lithium-ion batteries according to claim 1, characterized in that, In step (2), the ball-to-material ratio of the low-speed ball mill is 30:1 to 70:1, the ball milling time is 10 to 30 hours, and the rotation speed is 300 to 500 rpm.

9. A nano-FeP2 / C / CNTs / LiF composite material prepared by the method according to any one of claims 1-8.

10. The application of the nano-FeP2 / C / CNTs / LiF composite material according to claim 9 in the negative electrode of a lithium-ion battery.

Images