CN115394973A - High-first-efficiency high-energy-density cathode material and preparation method thereof - Google Patents

Abstract

The invention discloses a high-efficiency high-energy-density cathode material and a preparation method thereof. The preparation method comprises the steps of adding aluminum propoxide, an aluminate coupling agent and a carbon nano tube conductive solution into deionized water to prepare a 1-10% solution, then adding graphite, uniformly dispersing, carrying out hydrothermal reaction, carrying out freeze drying to obtain the porous alumina coated graphite composite material, and then depositing a silicon-based material on the surface or in the pores by using oxygen plasma carrier gas. The cathode material prepared by the invention has better high-temperature storage performance, energy density and power performance.

Description

High-first-efficiency high-energy-density cathode material and preparation method thereof

Technical Field

The invention belongs to the field of preparation of lithium ion battery materials, particularly relates to a high-first-efficiency high-energy-density cathode material, and also relates to a preparation method of the high-first-efficiency high-energy-density cathode material.

Background

With the improvement of the requirement of the lithium ion battery on the energy density of the negative electrode, the negative electrode material is required to have high specific capacity, the first efficiency of the material is also improved, the gram capacity of the positive electrode of the full battery is improved, and the energy density of the full battery is improved. The current marketable negative electrode material mainly uses artificial graphite as a main material, the surface coating material is soft carbon/hard carbon material, the first efficiency of the artificial graphite is between 91-94%, especially for a positive electrode LFP system (the first efficiency is more than 96%), the first efficiency of the whole battery is low, and the energy density is influenced because the soft carbon or the hard carbon coated on the surface of the artificial graphite has low specific capacity and low first efficiency (300 mAh/g, 80%), and one of the measures for improving the first efficiency of the material is to coat the carbon-based/non-carbon-based material with high first efficiency and good dynamics on the surface of the graphite, and the energy density of the material is not reduced. The porous metal oxide improves the dynamic performance by the porous structure, the oxide has the inertia to the electrolyte, reduces the lithium ions consumed by forming an SEI film, improves the first efficiency, and is doped with a high-capacity silicon-based material to improve the energy density. For example, chinese patent publication No. CN110828811 a discloses a silicon oxide-graphite composite anode material for a lithium ion battery and a preparation method thereof, wherein the preparation method comprises the following steps: the preparation method comprises the steps of ball-milling and mixing the silica slurry, the graphite slurry, the asphalt, the aluminum isopropoxide and other organic carbon sources in a ball-milling tank, spray-drying, and sintering at high temperature to obtain the silica-graphite composite negative electrode material, wherein the silica is coated on the surface of graphite by a chemical method, so that the uniformity is poor, the thickness is uneven, and the first efficiency and the cycle performance of the silica-graphite composite negative electrode material are influenced. The patent application number 201711489355.1 is that aluminum fluoride coated lithium manganate is obtained by liquid phase coating of aluminum isopropoxide and fluoride solution on the surface of lithium manganate material and sintering, and the specific surface area of aluminum fluoride on the surface of the material is small, so that the material dynamic performance is reduced.

Disclosure of Invention

The invention aims to overcome the defects and provide a high-efficiency high-energy-density cathode material with better high-temperature storage performance, energy density and functional performance.

The invention also aims to provide a preparation method of the high-first-efficiency high-energy-density negative electrode material.

The invention relates to a high-efficiency high-energy-density cathode material which is composed of an inner core made of graphite, amorphous carbon/porous alumina coated on the surface of the inner core and a silicon-based material.

The invention relates to a preparation method of a high-efficiency high-energy-density cathode material, which comprises the following steps:

(1) Weighing aluminum propoxide, an aluminate coupling agent and a carbon nano tube conductive liquid according to the mass ratio of 100-5:1-5, adding the aluminum propoxide, the aluminate coupling agent and the carbon nano tube conductive liquid into deionized water to prepare a 1-10% mixed solution, adding graphite into the mixed solution, ultrasonically dispersing uniformly, carrying out hydrothermal reaction at the temperature of 120 ℃ and the pressure of 2Mpa for 3 hours, and carrying out freeze drying at the temperature of-40 ℃ for 6 hours to obtain the porous alumina coated graphite composite material;

wherein, the aluminum propoxide: graphite mass ratio =1 to 5;

(2) Transferring the porous alumina coated graphite composite material into a reaction chamber of a vacuum chamber to be used as a substrate, adjusting the silicon-based target material to be 1-3mm away from the substrate, and keeping the vacuum degree at 1 multiplied by 10^-4 ～1×10^-5 Heating to 200-500 ℃, then starting a pulse laser, introducing an optical introduction system, introducing oxygen into a vacuum chamber, ionizing the gas in the vacuum chamber to generate oxygen under the high pressure of 100-1000V, and depositing the silicon-based material in an oxygen plasma auxiliary atmosphere for 10-120 minutes to obtain the silicon-based doped porous alumina coated graphite composite material.

The mass concentration of the carbon nano tube conductive solution in the step (1) is 1-5 wt%.

The silicon-based material in the step (2) is nano silicon and silicon oxide (SiO)_X 2 > X > 0) or silicon carbon.

Compared with the prior art, the invention has obvious beneficial effects, and the technical scheme can show that: according to the invention, the porous alumina obtained by adopting the organic aluminum compound (aluminum propoxide) and the aluminum-based coupling agent thereof through a hydrothermal method has the advantages of mild reaction conditions, good uniformity and stable coating structure compared with inorganic porous alumina, and the porous network structure is obtained and is compounded with the carbon nano tube with high electronic conductivity to improve the electronic conductivity. Meanwhile, the specific capacity and the power performance of the material are improved by depositing a high-capacity silicon-based material on the outer layer of the material through an oxygen plasma technology, the material has the advantages of high reaction speed, controllable process, high density and free oxygen generated by oxygen plasma in the reaction process, and the silicon-based material can be obtained to improve the cycle performance. Tests show that the specific capacity of the cathode material is more than or equal to 370mAh/g, and the first efficiency is more than or equal to 96%.

Drawings

Fig. 1 is an SEM image of the silicon-based doped porous alumina-coated graphite composite prepared in example 1.

Detailed Description

Example 1

A preparation method of a high-efficiency high-energy-density negative electrode material comprises the following steps:

(1) Weighing 100g of aluminum propoxide, 3g of an aluminate coupling agent, 100ml of a carbon nanotube conductive solution with the concentration of 3% and adding the mixture into 2020ml of deionized water to prepare a 5% mixed solution, adding 3333g of artificial graphite into the mixed solution, ultrasonically dispersing the mixture uniformly, performing hydrothermal reaction (120 ℃,2Mpa and 3h), filtering, and freeze-drying filter residues at (-40 ℃,6 h) to obtain the porous alumina coated graphite composite material;

(2) Transferring 100g of porous alumina-coated graphite composite material into a reaction chamber of a vacuum chamber as a substrate, adjusting the nano silicon target material to be 2mm away from the substrate by adopting an oxygen plasma technology, and keeping the vacuum degree at 5 multiplied by 10^-5 Heating to 300 ℃, starting a pulse laser, introducing an optical introduction system, introducing oxygen into a vacuum chamber, ionizing gas in the vacuum chamber at the oxygen partial pressure of 20pa under the high pressure of 500V to generate oxygen, and depositing the nano-silicon in the oxygen plasma auxiliary atmosphere for 60 minutes to obtain the silicon-doped porous alumina-coated graphite composite material.

Example 2

A preparation method of a high-efficiency high-energy-density negative electrode material comprises the following steps:

(1) Weighing 100g of aluminum propoxide, 1g of an aluminate coupling agent, 100ml of a carbon nanotube conductive solution with the concentration of 1% and adding the mixture into 10100ml of deionized water to prepare a 1% mixed solution, adding 10000g of artificial graphite into the mixed solution, uniformly dispersing by using ultrasonic waves, carrying out hydrothermal reaction (120 ℃,2Mpa and 3h), filtering, and freeze-drying filter residues at (-40 ℃,6 h) to obtain the porous alumina coated graphite composite material;

(2) Transferring 100g of porous alumina-coated graphite composite material into a reaction chamber as a substrate, adjusting the SiO target to be 1mm away from the substrate by adopting an oxygen plasma technology, and keeping the vacuum degree at 1 multiplied by 10^-4 Heating to 500 ℃, starting a pulse laser, introducing an optical introduction system, introducing oxygen into a vacuum chamber, ionizing gas in the vacuum chamber to generate oxygen at the oxygen partial pressure of 1pa under the high pressure of 100V, and depositing the SiO material in the oxygen plasma auxiliary atmosphere for 10 minutes to obtain the silicon-doped porous alumina-coated graphite composite material.

Example 3

A preparation method of a high-first-efficiency high-energy-density cathode material comprises the following steps:

(1) Weighing 100g of aluminum propoxide, 5g of an aluminate coupling agent, 100ml of a 5% carbon nanotube conductive solution, adding the mixture into 1000ml of deionized water to prepare a 10% mixed solution, adding 2000g of artificial graphite into the mixed solution, performing uniform ultrasonic dispersion, performing hydrothermal reaction (120 ℃,2Mpa and 3h), filtering, and freeze-drying filter residues (-40 ℃,6 h) to obtain the porous alumina-coated graphite composite material;

(2) Transferring 100g of porous alumina-coated graphite composite material into a reaction chamber as a substrate, adjusting the SiC target to be 3mm away from the substrate by adopting an oxygen plasma technology, and keeping the vacuum degree at 1 multiplied by 10^-5 Heating to 200 ℃, then starting a pulse laser, introducing an optical introduction system, introducing oxygen into a vacuum chamber, ionizing gas in the vacuum chamber to generate oxygen at the oxygen partial pressure of 50pa under the high pressure of 1000V, and depositing the SiC material in the oxygen plasma-assisted atmosphere for 120 minutes to obtain the silicon-based doped porous alumina-coated graphite composite material.

Comparative example 1

A preparation method of a silicon amorphous carbon coated graphite composite material comprises the following steps:

weighing 100g of the porous alumina-coated graphite composite material, 10g of asphalt and 1g of silicon oxide in the step (1) in the example 1, adding the materials into a ball mill, uniformly mixing, heating to 250 ℃ in an argon atmosphere to soften for 1h, heating to 800 ℃ to carbonize for 3h, and naturally cooling to room temperature to obtain the silicon amorphous carbon-coated graphite composite material.

Comparative example 2

A preparation method of a silicon-doped artificial graphite composite material comprises the following steps:

transferring 100g of artificial graphite composite material into a reaction chamber as a substrate, adjusting the nano silicon target material to be 2mm away from the substrate by adopting an oxygen plasma technology, and keeping the vacuum degree at 5 multiplied by 10^-5 Heating to 300 ℃, starting a pulse laser, introducing an optical introduction system, introducing oxygen into a vacuum chamber, ionizing gas in the vacuum chamber at the oxygen partial pressure of 20pa under the high pressure of 500V to generate oxygen, and depositing the nano-silicon in the atmosphere assisted by oxygen plasma for 60 minutes to obtain the silicon-doped artificial graphite composite material.

Comparative example 3

A preparation method of a silicon-doped graphite composite material comprises the following steps:

(1) Weighing 10g of phenolic resin, adding the phenolic resin into 200ml of cyclohexane to prepare a 5% mixed solution, adding 100g of artificial graphite into the mixed solution, performing ultrasonic dispersion uniformly, performing hydrothermal reaction (120 ℃,2Mpa and 3h), filtering, and performing freeze drying (40 ℃ below zero and 6 h) to obtain an amorphous carbon coated graphite composite material;

(2) Transferring 100g of amorphous carbon-coated graphite composite material into a reaction chamber as a substrate, adjusting the nano silicon target material to be 2mm away from the substrate by adopting an oxygen plasma technology, and keeping the vacuum degree at 5 multiplied by 10^-5 Heating to 300 deg.C, starting pulse laser, introducing optical introduction system, introducing oxygen into vacuum chamber at oxygen partial pressure of 20pa, ionizing gas in vacuum chamber at 500V to generate oxygen, depositing nano-silicon in oxygen plasma-assisted atmosphere, and depositingThe time is 60 minutes, and the silicon-doped graphite composite material is obtained.

Test example:

performance testing

(1) SEM test

FIG. 1 is an SEM image of the silicon-based doped porous alumina-coated graphite composite material prepared in example 1, and it can be seen that the material has a granular structure, a particle size of 10-15 μm and a uniform size.

(2) Physical and chemical property test

The graphite composite materials prepared in examples 1 to 3 and comparative examples 1 to 3 were tested for oil absorption to characterize the ability of the materials to absorb electrolyte. The specific surface area and the tap density of the composite material and the content of the metal substance aluminum in the composite material through EDS are tested according to the method in GB/T7046-2003 'determination of absorption value of pigment carbon black dibutyl phthalate', and meanwhile, GB/T243358-2019 'graphite cathode material for lithium ion batteries'.

TABLE 1 comparison of physicochemical Properties of examples 1-3 with comparative examples

As can be seen from Table 1, the tap density of the composite material prepared by the invention is obviously higher than that of comparative examples 1-3, and the reason is that oxygen plasma can be adopted to uniformly and compactly coat porous alumina on the surface of graphite; meanwhile, the porous alumina has the characteristic of high density and improves the tap density. Meanwhile, the porous alumina has high specific surface area, and the specific surface area of the graphite composite material is improved.

(2) Measurement of Charge and discharge Properties

The assembly method of the composite materials of examples 1-3 and comparative example into button cell batteries respectively comprises the following steps: and adding a binder and a solvent into the composite material, stirring and pulping, coating the mixture on a copper foil, and drying and rolling to obtain the pole piece. Wherein, the used binder is PVDF binder, the solvent is NMP, and the dosage ratio is graphene: PVDF: NMP = 80g; the electrolyte is LiPF₆ EC + DEC (EC, DEC bodies)Product ratio 1, liPF₆ The concentration is 1.3 mol/L), a metal lithium sheet is a counter electrode, a diaphragm adopts a polyethylene propylene (PEP) composite membrane, and the assembly is carried out in an argon-filled glove box.

The electrochemical performance is carried out on a Wuhan blue electricity 5V/10mA type battery tester, the charge-discharge voltage range is 0.005V-2.0V, and the charge-discharge multiplying power is 0.1C. Simultaneously testing the multiplying power and the cycle performance of the material, wherein the discharge multiplying power is 0.1C/0.2C/0.5C/1C/2C/3C respectively, and calculating the 2C/0.1C retention rate; meanwhile, the test method tests the cycle performance of the charging at 0.2C/0.2C, 0.005V-2V and 25 +/-3 ℃.

And testing the normal-temperature DCR of the material through electricity deduction.

The test results are shown in table 2.

TABLE 2 comparison of electrochemical Performance test results of examples and comparative examples

As can be seen from Table 2, the discharge capacity and efficiency of the batteries using the composites obtained in examples 1 to 3 were significantly higher than those of the comparative examples. The porous alumina coated in the composite material has the characteristic of insolubility with electrolyte, so that lithium ions consumed by SEI film formation in the charge-discharge process are reduced, and the first efficiency of the material is improved; meanwhile, the porous structure and the high specific surface area of the material improve the liquid retention performance and the cycle performance of the material.

The above are only preferred examples and experimental examples of the present invention, and do not limit the scope of the present invention. It will be apparent to those skilled in the art that various changes and modifications may be made in the invention as embodied and described. Any modification, replacement (equivalent), improvement and the like made within the spirit of the present invention should be included in the scope of protection of the present invention.

Claims (4)

1. A high-efficiency high-energy-density cathode material is composed of a core made of graphite, amorphous carbon/porous alumina coated on the surface of the core, and a silicon-based material.

2. A preparation method of a high-efficiency high-energy-density negative electrode material comprises the following steps:

(1) Weighing aluminum propoxide, an aluminate coupling agent and a carbon nano tube conductive liquid according to the mass ratio of 100-5:1-5, adding the aluminum propoxide, the aluminate coupling agent and the carbon nano tube conductive liquid into deionized water to prepare a 1-10% mixed solution, adding graphite into the mixed solution, performing ultrasonic dispersion uniformly, performing hydrothermal reaction at 120 ℃ and 2Mpa for 3 hours, and performing freeze drying at-40 ℃ for 6 hours to obtain the porous alumina coated graphite composite material;

wherein, the aluminum propoxide: graphite mass ratio =1 to 5;

(2) Transferring the porous alumina coated graphite composite material into a reaction chamber of a vacuum chamber as a substrate, adjusting the silicon-based target material to be 1-3mm away from the substrate, and keeping the vacuum degree at 1 multiplied by 10^-4 ～1×10^-5 Heating to 200-500 ℃, then starting a pulse laser, introducing an optical introduction system, introducing oxygen into a vacuum chamber, ionizing the gas in the vacuum chamber to generate oxygen under the high pressure of 100-1000V, and depositing the silicon-based material in an oxygen plasma auxiliary atmosphere for 10-120 minutes to obtain the silicon-based doped porous alumina coated graphite composite material.

3. The method for preparing a high-efficiency high-energy-density anode material according to claim 2, wherein: the mass concentration of the carbon nano tube conductive solution in the step (1) is 1-5 wt%.

4. The method for preparing a high-efficiency high-energy-density cathode material as claimed in claim 2, wherein the silicon-based material in the step (2) is nano silicon, silicon oxygen (SiO)_X 2 > X > 0) or silicon carbon.

Images