Preparation method of carbon-coated lithium iron phosphate positive electrode material doped with double heterogeneous atoms

Abstract

The present invention discloses a method for preparing a carbon-coated lithium iron phosphate positive electrode material alternately doped with double heterogeneous atoms, which is to first obtain a sulfur-doped carbon film on the surface of the lithium iron phosphate material by unbalanced magnetron sputtering of a graphite target under an argon and hydrogen sulfide atmosphere; obtain a phosphorus-doped carbon film on the surface of the material under an argon and phosphine atmosphere, and alternately dope the carbon film with sulfur and phosphorus to stabilize the structure of the material, enhance the conductivity of the material, ensure a high doping amount, solve the problem of low intrinsic electronic and ionic conductivity of the lithium iron phosphate positive electrode material, effectively improve the electronic conductivity and ion diffusion rate of the lithium iron phosphate electrode material, and the preparation process does not involve liquid phase and high temperature processes, effectively avoid the introduction of impurities and grain growth, and the experimental process is highly controllable, efficient, and less polluting. After the carbon-coated lithium iron phosphate positive electrode material prepared by the present invention is prepared into a lithium ion half-cell, it shows good rate performance and stability.

Description

Technical Field

[0001] The invention relates to a lithium iron phosphate positive electrode material, and in particular to a method for preparing a double heterogeneous atom alternately doped carbon-coated lithium iron phosphate positive electrode material, belonging to the field of composite materials and battery material technology. Background Art

[0002] The widespread use of fossil energy has made environmental pollution and energy crisis the two major global problems. The development of new energy devices based on electrochemistry is of great significance to reducing environmental pollution and solving the energy crisis. 4 It is proposed as the current mainstream lithium-ion battery positive electrode material due to its low cost, excellent cycle life and thermal stability. Compared with lithium transition metal oxides, LiFePO 4 This type of cathode has good long-term cycling stability and low reactivity with the electrolyte. However, LiFePO 4 The main difficulty lies in their low intrinsic electronic conductivity and ion diffusion rate.

[0003] At present, the surface of lithium iron phosphate electrode materials is coated with heterogeneous atoms doped with carbon to promote the transmission of electrons, reduce the charge transfer resistance, thereby increasing the ion diffusion rate and improving its electrochemical performance. CN115241462A discloses a polymer-coated lithium iron phosphate positive electrode material and a preparation method and application thereof, wherein iron salt, lithium salt, phosphate and high molecular organic polymer are first mixed in a solvent, and then the temperature is raised to different temperatures at a specific heating rate in sequence for reaction, and after the reaction is completed, the mixture is reacted with hexadecyltrimethylammonium halide and soluble iron salt in an acidic aqueous solution at low temperature for 2 to 4 hours, and the solid-liquid is separated to obtain a polymer-coated lithium iron phosphate positive electrode material; CN115133010A discloses a nitrogen-doped carbon-modified lithium iron phosphate positive electrode material, wherein boron-doped carbon nanotubes are prepared by doping carbon nanotubes with B, and then the boron-doped carbon nanotubes are compositely doped with N, Na and Fe by sodium ferric diethylenetriamine pentaacetate to obtain functionalized carbon nanotubes doped with B and N and uniformly loaded with Na and Fe on the surface; finally, the functionalized carbon nanotubes are modified to form a LiFePO 4 The material is in-situ coated and modified to obtain the nitrogen-doped carbon-modified lithium iron phosphate positive electrode material. However, in the above scheme, there are liquid phase reaction conditions in the formation of the film and the doping process of heterogeneous atoms, which is easy to introduce impurities; furthermore, the high temperature process is easy to cause phase change and grain growth of the electrode material, destroying the original structure, and the process is relatively complicated and poor in controllability. Therefore, it is very necessary to develop a preparation method for double heterogeneous atom alternating doped carbon-coated lithium iron phosphate positive electrode material without liquid phase participation. Summary of the invention

[0004] In response to the above technical problems, the present invention proposes a method for preparing a carbon-coated lithium iron phosphate positive electrode material with double heterogeneous atoms alternately doped, so as to improve the binding force of the carbon film, while improving the electronic conductivity and ion diffusion rate of the lithium iron phosphate electrode material, thereby effectively improving the electrochemical properties of the lithium iron phosphate electrode material.

[0005] The method for preparing the carbon-coated lithium iron phosphate positive electrode material doped with double heterogeneous atoms in an alternating manner of the present invention comprises the following steps:

[0006] (1) After drying the lithium iron phosphate powder, place it on the rotating frame of the vacuum coating chamber of the magnetron sputtering device, adjust the target spacing and evacuate to 10 -4 Pa, turn on the rotating rack and graphite target, and make the graphite target and the rack rotate at a constant speed in the opposite direction. The drying is carried out in an oven at 110°C under vacuum conditions for 120 min;

[0007] (2) Argon and hydrogen sulfide gases were introduced, and the gas flow ratio of argon and hydrogen sulfide gases was controlled to be 5:1~2:1; the chamber working pressure was adjusted to be maintained at 1Pa, and a sulfur-doped carbon film was deposited on the surface of lithium iron phosphate powder using unbalanced magnetron sputtering technology; the current of the graphite target was 0.8A, the output power was 600W, and the thickness of the sulfur-doped carbon film was 3nm;

[0008] (3) Stop the introduction of hydrogen sulfide gas, introduce phosphine gas, adjust the gas flow ratio of argon gas to phosphine gas to 10:1~6:1, adjust the chamber pressure to 1Pa, and use unbalanced magnetron sputtering technology to deposit phosphorus-doped carbon film. The current of the graphite target is 1A, the output power is 600W, and the thickness of the phosphorus-doped carbon film is 2nm;

[0009] (4) Repeating steps (2) and (3) alternately until the film reaches a target thickness of 15 nm, stopping the reaction, and obtaining a carbon-coated lithium iron phosphate positive electrode material alternately doped with double heterogeneous atoms.

[0010] Figure 1 The schematic diagram of the structure of the carbon-coated lithium iron phosphate positive electrode material with double heterogeneous atoms alternately doped prepared by the present invention. The present invention first obtains a sulfur-doped carbon film on the surface of the lithium iron phosphate material by unbalanced magnetron sputtering of a graphite target in an argon and hydrogen sulfide atmosphere. Sulfur doping can adjust the electronic structure of the deposited carbon film and increase active sites to facilitate the transmission of lithium ions; in an argon and phosphine atmosphere, a phosphorus-doped carbon film is obtained on the surface of the material by unbalanced magnetron sputtering of a graphite target. Phosphorus doping can promote the conversion of Sp3 carbon to Sp2 carbon, so the phosphorus-doped carbon film can provide the material with extremely high electrical conductivity. Alternating doping can improve the bonding force of the carbon film, stabilize the structure of the material, and ensure a high doping amount.

[0011] The prepared double heterogeneous atom alternately doped carbon-coated lithium iron phosphate cathode material was prepared into a lithium-ion half-cell. In the secondary electrolyte (1.0M LiPF6 in EC:DEC:EMC=1:1:1 Vol%), the first charge and discharge specific capacity can reach 92.5mA hg at a current density of 0.2C. -1 , showing good rate performance and stability.

[0012] In summary, the present invention has the following advantages over the prior art:

[0013] 1. The doped carbon film is deposited on the surface of the lithium iron phosphate positive electrode material by alternating doping of two heterogeneous atoms, which stabilizes the structure of the material, enhances the conductivity of the material, ensures a high doping amount, solves the problem of low intrinsic electron and ion conductivity of the lithium iron phosphate positive electrode material, and effectively improves the electronic conductivity and ion diffusion rate of the lithium iron phosphate electrode material; at the same time, it reduces the preparation cost; after being prepared into a lithium ion half-cell, it shows good rate performance and stability;

[0014] 2. The preparation process does not involve liquid phase or high temperature process, which effectively avoids the introduction of impurities and grain growth. The experimental process is highly controllable, efficient, and has little pollution, and has broad market application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a schematic structural diagram of the double heterogeneous atom alternately doped carbon-coated lithium iron phosphate positive electrode material prepared by the present invention. DETAILED DESCRIPTION

[0016] The preparation and performance of the double heterogeneous atom alternately doped carbon-coated lithium iron phosphate positive electrode material of the present invention are described in detail below with reference to specific examples.

[0017] Example 1

[0018] (1) Experimental conditions for thin film deposition: Weigh 150 g of lithium iron phosphate raw material dried in vacuum at 110°C, place it on a rotating rack, put it on the rotating rack of the vacuum coating chamber of the magnetron sputtering device, and evacuate to 10 -4 Pa, turn on the rotating device to make the graphite target and the work stand rotate at a constant speed in the opposite direction;

[0019] (2) Preparation of sulfur-doped carbon film: Argon and hydrogen sulfide gas (gas flow ratio of 5:1) were introduced, the chamber working pressure was maintained at 1 Pa, and the sulfur-doped carbon film was sputtered and deposited using unbalanced magnetron sputtering technology: the current of the graphite target was 0.8 A, the output power was 600 W, and the film thickness was 3 nm;

[0020] (3) Preparation of phosphorus-doped carbon film: Stop the introduction of hydrogen sulfide gas, introduce phosphine gas, adjust the flow rate of argon gas and phosphine gas (gas flow ratio is 10:1), maintain the chamber pressure at 1 Pa, and use unbalanced magnetron sputtering technology to sputter and deposit phosphorus-doped carbon film: the current of the graphite target is 1A, the output power is 600W, and the film thickness is 2 nm;

[0021] (4) Repeating steps (2) and (3) alternately until the film thickness reaches 15 nm, stopping the reaction, and obtaining a carbon-coated lithium iron phosphate positive electrode material alternately doped with double heterogeneous atoms;

[0022] (5) The prepared double heterogeneous atom alternately doped carbon-coated lithium iron phosphate material was prepared into a lithium ion half-cell. In the secondary electrolyte (1.0M LiPF6 in EC:DEC:EMC=1:1:1 Vol%), the first charge and discharge specific capacity was 92.5 mA h g at a current density of 0.2C. -1 .

[0023] Example 2

[0024] (1) Experimental conditions for thin film deposition: Weigh 150 g of lithium iron phosphate raw material dried in vacuum at 110°C, place it on a rotating rack, put it on the rotating rack of the vacuum coating chamber of the magnetron sputtering device, and evacuate to 10 -4 Pa, turn on the rotating device to make the graphite target and the work stand rotate at a constant speed in the opposite direction;

[0025] (2) Preparation of sulfur-doped carbon film: Argon and hydrogen sulfide gas (gas flow ratio of 2:1) were introduced, the chamber working pressure was maintained at 1 Pa, and the sulfur-doped carbon film was deposited by unbalanced magnetron sputtering technology: the current of the graphite target was 0.8 A, the output power was 600 W, and the film thickness was 3 nm;

[0026] (3) Preparation of phosphorus-doped carbon film: Stop the introduction of hydrogen sulfide gas, introduce phosphine gas, adjust the flow rate of argon gas and phosphine gas (gas flow ratio is 6:1), maintain the chamber pressure at 1 Pa, and use unbalanced magnetron sputtering technology to deposit phosphorus-doped carbon film: the current of the graphite target is 1A, the output power is 600W, and the film thickness is 2 nm;

[0027] (4) Repeating steps (2) and (3) alternately until the film thickness reaches 15 nm, stopping the reaction, and obtaining a carbon-coated lithium iron phosphate positive electrode material alternately doped with double heterogeneous atoms;

[0028] (5) The prepared double heterogeneous atom alternately doped carbon-coated lithium iron phosphate material was prepared into a lithium ion half-cell. In the secondary electrolyte (1.0M LiPF6 in EC:DEC:EMC=1:1:1 Vol%), the first charge and discharge specific capacity was 89.5 mA h g at a current density of 0.2C. -1 .

[0029] Example 3

[0030] (1) Experimental conditions for thin film deposition: Weigh 150 g of lithium iron phosphate raw material dried in vacuum at 110°C, place it on a rotating rack, put it on the rotating rack of the vacuum coating chamber of the magnetron sputtering device, and evacuate to 10 -4 Pa, turn on the rotating device to make the graphite target and the work stand rotate at a constant speed in the opposite direction;

[0031] (2) Preparation of sulfur-doped carbon film: Argon and hydrogen sulfide gas (gas flow ratio of 4:1) were introduced, the chamber working pressure was maintained at 1 Pa, and the sulfur-doped carbon film was deposited by unbalanced magnetron sputtering technology: the current of the graphite target was 0.8 A, the output power was 600 W, and the film thickness was 3 nm;

[0032] (3) Preparation of phosphorus-doped carbon film: Stop the introduction of hydrogen sulfide gas, introduce phosphine gas, adjust the flow rate of argon gas and phosphine gas (gas flow ratio is 8:1), maintain the chamber pressure at 1 Pa, and use unbalanced magnetron sputtering technology to deposit phosphorus-doped carbon film: the current of the graphite target is 1A, the output power is 600W, and the film thickness is 2 nm;

[0033] (4) Repeating steps (2) and (3) alternately until the film thickness reaches 15 nm, stopping the reaction, and obtaining a carbon-coated lithium iron phosphate positive electrode material alternately doped with double heterogeneous atoms;

[0034] (5) The prepared double heterogeneous atom alternately doped carbon-coated lithium iron phosphate material was prepared into a lithium ion half-cell. In the secondary electrolyte (1.0M LiPF6 in EC:DEC:EMC=1:1:1 Vol%), the first charge and discharge specific capacity was 90.5 mA h g at a current density of 0.2C. -1 .

[0035] Comparative Example: The lithium iron phosphate cathode material without surface coating was prepared into a lithium ion half-cell. In the secondary electrolyte (1.0M LiPF6 in EC:DEC:EMC=1:1:1 Vol%), the first charge and discharge specific capacity was 80.1mA hg at a current density of 0.2C. -1 .

Claims

1. A method for preparing a carbon-coated lithium iron phosphate positive electrode material with double heterogeneous atoms alternately doped, The following steps are involved: (1) After drying the lithium iron phosphate powder, place it on the rotating frame of the vacuum coating chamber of the magnetron sputtering device, adjust the target spacing and evacuate to 10 -4 Pa, turn on the rotating workbench and graphite target, so that the graphite target and the workbench rotate at a constant speed in the opposite direction; (2) introducing argon gas and hydrogen sulfide gas, and adjusting the chamber working pressure to maintain at 1 Pa, and using unbalanced magnetron sputtering technology to deposit a sulfur-doped carbon film on the surface of lithium iron phosphate powder; the gas flow ratio of argon gas to hydrogen sulfide gas is 5:1 to 2:1; the thickness of the sulfur-doped carbon film is 3 nm; (3) Stop the introduction of hydrogen sulfide gas, introduce phosphine gas, adjust the gas flow ratio of argon gas to phosphine gas to 10:1~6:1, and adjust the chamber pressure to 1Pa, and use unbalanced magnetron sputtering technology to deposit a phosphorus-doped carbon film; the phosphorus-doped carbon film has a thickness of 2nm; the current of the graphite target is 1A, and the output power is 600W; (4) Repeating steps (2) and (3) alternately until the target film thickness reaches 15 nm; stopping the reaction to obtain a carbon-coated lithium iron phosphate positive electrode material alternately doped with double heterogeneous atoms.

2. A method for preparing a double heterogeneous atom alternately doped carbon-coated lithium iron phosphate positive electrode material as claimed in claim 1, Features: In step (1), the drying is carried out in an oven at 110° C. under vacuum conditions for 120 min.

3. A method for preparing a double heterogeneous atom alternately doped carbon-coated lithium iron phosphate positive electrode material as claimed in claim 1, Features: In step (2), the current of the graphite target is 0.8A and the output power is 600W.

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