CN114956193B - Preparation method and application of positive electrode active material - Google Patents

Preparation method and application of positive electrode active material Download PDF

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CN114956193B
CN114956193B CN202210757692.9A CN202210757692A CN114956193B CN 114956193 B CN114956193 B CN 114956193B CN 202210757692 A CN202210757692 A CN 202210757692A CN 114956193 B CN114956193 B CN 114956193B
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precursor
active material
positive electrode
mixed solution
electrode active
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CN114956193A (en
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王雀乐
李长东
阮丁山
刘伟健
缪建麟
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Hunan Brunp Recycling Technology Co Ltd
Guangdong Brunp Recycling Technology Co Ltd
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Hunan Brunp Recycling Technology Co Ltd
Guangdong Brunp Recycling Technology Co Ltd
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Abstract

The invention discloses a preparation method and application of a positive electrode active material, wherein a dispersing agent, a conductive carbon source, ferric nitrate, an accelerator and water are mixed to prepare an acidic mixed solution, the mixed solution is heated to induce self-propagating reaction, a precursor is obtained after the reaction is finished, the precursor is mixed with a lithium source, sintering is carried out under a micro-oxygen atmosphere, a sintering material is crushed, and the obtained crushed material is subjected to vacuum vapor deposition cladding by hydrocarbon gas, so that the positive electrode active material is obtained. According to the invention, the nano-scale precursor is synthesized through self-propagating reaction of the oxidizing substance and the reducing substance, and a high-content carbon source substance is introduced in the precursor synthesis stage, so that the growth of material particles can be effectively inhibited during the synthesis of the material, and the conductivity of the material is improved; by the synthesis process, the cathode active material with fine and uniform particles and high capacity can be synthesized.

Description

Preparation method and application of positive electrode active material
Technical Field
The invention belongs to the technical field of lithium ion battery materials, and particularly relates to a preparation method and application of a positive electrode active material.
Background
At present, the market demand of new energy automobiles is rapidly developed, the productivity is continuously expanded, and the sales of lithium batteries is also continuously expanded. At present, the more critical index circulation capacity density requirement of the market on lithium batteries isThe higher the charge and discharge efficiency of the lithium ion battery is, the lower the cycle capacity of the lithium ion battery is, the more the lithium ion battery is lost due to the formation of SEI film and low charge and discharge efficiency, and in order to solve the problem, the active material is usually added into the positive electrode material to improve the lithium ion battery, and Li is 5 FeO 4 Has the advantages of low charging voltage platform and high theoretical capacity, is an excellent electrochemical active substance, but synthesizes Li conventionally 5 FeO 4 The method still has some problems, and the common preparation method is to prepare an iron source by a hydrothermal method and synthesize Li by a high-temperature solid-phase sintering method 5 FeO 4 Or directly synthesizing the lithium hydroxide by directly utilizing the micron-sized ferric oxide and the lithium hydroxide through direct high-temperature solid-phase sintering, wherein the two methods have the defects of higher energy consumption, lower productivity or large primary particles of a synthetic material, so that the lithium ion migration path is long, the capacity is relatively low, the stability is poor, and further the production cost is higher. In addition, li 5 FeO 4 Materials also commonly suffer from poor electrical conductivity.
Disclosure of Invention
The present invention aims to solve at least one of the technical problems in the prior art described above. Therefore, the invention provides a preparation method and application of the positive electrode active material, the process is simple, the energy is relatively saved, and the prepared product has the advantages of good conductivity and high capacity.
According to an aspect of the present invention, there is provided a method for preparing a positive electrode active material, comprising the steps of:
s1: mixing a dispersing agent, a conductive carbon source, ferric nitrate, an accelerator and water to prepare an acidic mixed solution, wherein the accelerator is a reducing organic matter;
s2: heating the mixed solution to induce self-propagating reaction, and obtaining a precursor after the reaction is finished;
s3: mixing the precursor with a lithium source, and sintering in a micro-oxygen atmosphere to obtain a sintered material;
s4: pulverizing the sintered material, and vacuum vapor deposition coating the pulverized material with hydrocarbon gas to obtain positive electrode active material Li 5 FeO 4 。
The reactions involved in the above processes are mainly:
(1) Step S2, generation of a precursor: 2Fe 3+ +Fe 2+ +4O 2- →Fe 3 O 4 Wherein the ferrous ions are derived from the reduction of excess accelerator.
(2) Step S3 sintering process (for example lithium hydroxide monohydrate): (1) fe (Fe) 3 O 4 →3FeO+0.5O 2 ；②2FeO+0.5O 2 →Fe 2 O 3 ；③Fe 2 O 3 +10LiOH·H 2 O→2Li 5 FeO 4 +15H 2 O. In the sintering process, the ferroferric oxide has poor stability under the condition of moisture (the precursor contains a small amount of water, the lithium hydroxide is high in lithium content, the lithium hydroxide contains bound water, and the hydroxyl group can be dehydrated at high temperature), so that the ferroferric oxide is easy to decompose into ferrous oxide and oxygen at high temperature, the ferrous oxide is also unstable, and the ferrous oxide can be immediately oxidized into ferric oxide when encountering oxygen.
It should be noted that the temperature of the self-propagating reaction in step S2 is about 200-300 ℃, and the temperature does not cause oxidation of the carbon source.
In some embodiments of the invention, in step S1, the pH of the mixture is 1-5.
In some embodiments of the invention, in step S1, the dispersant is at least one of polyethylene glycol, polyvinyl alcohol, or polyethylene oxide.
In some embodiments of the invention, in step S1, the dispersant is added in an amount of 1 to 20% by mass of the conductive carbon source.
In some embodiments of the present invention, in step S1, the conductive carbon source is at least one of carbon nanotubes, graphite powder, glucose, or conductive carbon black. Preferably, the conductive carbon source has a particle diameter Dv50 of 80nm to 200nm.
In some embodiments of the present invention, in step S1, the conductive carbon source is added in an amount that is the final theoretical yield of Li 5 FeO 4 2-10% by weight. Preferably, the addition amount of the conductive carbon source is Li which is finally theoretically produced 5 FeO 4 4-8% by weight.
In some embodiments of the invention, in step S1, the promoter is at least one of acetaldehyde, ethyl acetate, formic acid, or ethylene glycol.
In some embodiments of the invention, in step S1, the molar ratio of the promoter to nitrate ions in the mixed liquor is 1.1-1.3.
In some embodiments of the present invention, in step S1, the specific preparation process of the mixed solution is: adding a dispersing agent and a conductive carbon source into an acidic ferric nitrate solution to obtain a dispersing liquid, mixing an accelerator with water to obtain an accelerator solution, and mixing the dispersing liquid and the accelerator solution to obtain the mixed liquid.
In some embodiments of the invention, in step S1, the acidic ferric nitrate solution has a concentration of 0.1 to 5mol/L.
In some embodiments of the invention, in step S1, the pH of the acidic ferric nitrate solution is < 5.0.
In some embodiments of the invention, in step S1, the concentration of the accelerator solution is from 0.2 to 10mol/L.
In some embodiments of the invention, in step S2, heating to above 50 ℃ may induce the self-propagating reaction.
In some embodiments of the invention, in step S2, the precursor has a particle size Dv50 of 100-500nm.
In some embodiments of the invention, in step S2, the water content of the precursor is 0.3-0.8wt%.
In some embodiments of the invention, in step S3, the micro-oxygen atmosphere is composed of inert gas and oxygen, wherein the oxygen content is 0.3-1.3%. Preferably, the oxygen content in the micro-oxygen atmosphere is 0.3-1.3%. The purpose of the inert gas protection is to prevent the oxidation of the carbon source due to the excessive oxygen content.
In some embodiments of the invention, in step S3, the lithium source is at least one of lithium hydroxide monohydrate, lithium oxide, or lithium hydroxide anhydrous. Preferably, the lithium source is lithium hydroxide monohydrate.
In some embodiments of the invention, in step S3, the molar ratio of Li in the lithium source to Fe in the precursor is 5.0-5.8.
In some embodiments of the invention, in step S3, the sintering temperature is 480-700 ℃.
In some embodiments of the invention, in step S3, the sintering time is 6-20h.
In some embodiments of the invention, in step S4, the hydrocarbon gas is selected from at least one of methane, acetylene, or ethylene.
In some embodiments of the present invention, in step S4, the positive electrode active material Li 5 FeO 4 The particle diameter Dv50 of (2) is 3-6 μm.
In some embodiments of the invention, in step S4, the vacuum vapor deposition coating is performed at 250-700 ℃. Further, the treatment time of the vacuum vapor deposition coating is 2-8h.
In some embodiments of the invention, in step S4, the vacuum vapor deposition coating pressure is-20 to 5kpa.
The invention also provides application of the preparation method in preparation of the lithium ion battery.
According to a preferred embodiment of the invention, there is at least the following advantageous effect:
1. according to the invention, the nano-scale precursor is synthesized through self-propagating reaction of the oxidizing substance and the reducing substance, and a high-content carbon source substance is introduced in the precursor synthesis stage, so that the growth of material particles can be effectively inhibited during the synthesis of the material, and the conductivity of the material is improved; through the synthesis process, the cathode active material Li with fine and uniform particles and higher capacity can be synthesized 5 FeO 4 。
2. The method adopts specific raw materials to induce severe self-propagating reaction under a certain heating condition, emits a large amount of heat, evaporates the solvent into gas, and evaporates the material while reacting to dryness to obtain the precursor with fine and uniform particles.
Drawings
The invention is further described with reference to the accompanying drawings and examples, in which:
FIG. 1 is a schematic diagram of the synthesis process of the present invention;
FIG. 2 is an SEM image of a precursor synthesized according to example 1 of the present invention;
FIG. 3 is a diagram of Li synthesized in example 1 of the present invention 5 FeO 4 SEM images of (a);
FIG. 4 is a diagram of Li synthesized in example 1 of the present invention 5 FeO 4 Is a charge-discharge curve of (2);
FIG. 5 is a diagram of Li synthesized in example 2 of the present invention 5 FeO 4 SEM images of (a);
FIG. 6 is a diagram of Li synthesized in example 2 of the present invention 5 FeO 4 Is a charge-discharge curve of (2);
FIG. 7 is Li synthesized in comparative example 1 5 FeO 4 SEM images of (a);
FIG. 8 is Li synthesized in comparative example 1 5 FeO 4 Is a charge-discharge curve of (a).
Detailed Description
The conception and the technical effects produced by the present invention will be clearly and completely described in conjunction with the embodiments below to fully understand the objects, features and effects of the present invention. It is apparent that the described embodiments are only some embodiments of the present invention, but not all embodiments, and that other embodiments obtained by those skilled in the art without inventive effort are within the scope of the present invention based on the embodiments of the present invention.
Example 1
This example prepares a lithium ion battery positive electrode active material Li 5 FeO 4 Referring to fig. 1, the specific process is:
(1) Preparing 10L of acid ferric nitrate solution with concentration of 1mol/L, slowly adding concentrated nitric acid with concentration of 95%, regulating pH to 2.5 by using a pH meter, and adding a dispersing agent and a conductive carbon source in a certain proportion into the solution, wherein the dispersing agent adopts polyethylene glycolAlcohol, the addition amount of which is 15 percent of the weight of the conductive carbon source, the conductive carbon source is selected from carbon nano-tubes with Dv50 of 80nm, and the addition amount of which is Li finally synthesized 5 FeO 4 5% of the theoretical weight of the material;
(2) Preparing a promoter solution with the concentration of 2mol/L, wherein the active substance is acetaldehyde, and the dosage of the acetaldehyde is 1.15 times of the molar quantity of nitrate ions in the acidic ferric nitrate solution;
(3) Adding the accelerator solution prepared in the step (2) into the acidic ferric nitrate solution prepared in the step (1), fully stirring to obtain a mixed solution with pH of 3.5, heating the mixed solution to enable the temperature in a solution system to be higher than 50 ℃, at the moment, initiating self-propagating reaction, releasing a large amount of heat, and evaporating a solvent to obtain a precursor Fe with the particle size Dv50 of 200nm and the water content of 0.5wt% 3 O 4 See fig. 2;
(4) Fe obtained 3 O 4 Mixing with lithium hydroxide monohydrate, wherein the molar ratio of Li/Fe is 5.3, the mixing equipment is a high-speed mixer, the mixing rotating speed is 600rpm, wherein the mixed materials are sintered in nitrogen atmosphere (oxygen content is 0.7%), the sintering temperature is 700 ℃, the sintering time is 18h, and Li can be obtained 5 FeO 4 A block material;
(5) The obtained Li 5 FeO 4 Crushing the blocky materials in a nitrogen atmosphere, controlling the Dv50 of the blocky materials to be 4-6 mu m, and carrying out vacuum vapor deposition coating on the crushed materials, wherein the molar ratio of the used gases is 4:1, wherein the coating temperature is 400 ℃, the time is 8 hours, the pressure is-20 kpa, and after the coating is finished, the anode active material Li with good performance can be obtained 5 FeO 4 。
Characterization test: li prepared by the synthesis method 5 FeO 4 Referring to FIG. 3, the particles formed were relatively small, and had a carbon content of 4.7% and a particle diameter Dv50 of 5.2. Mu.m, as measured by a carbon-sulfur meter.
Example 2
This example prepares a lithium ion battery positive electrode active material Li 5 FeO 4 The specific process is as follows:
(1) Preparing 10L of acidic ferric nitrate solution with concentration of 2mol/LSlowly adding concentrated nitric acid with the concentration of 95%, regulating the pH value of the solution to 3 by using a pH meter, and adding a dispersing agent and a conductive carbon source in a certain proportion into the solution, wherein the dispersing agent adopts polyvinyl alcohol, the adding amount of the dispersing agent is 15% of the weight of the conductive carbon source, the conductive carbon source adopts graphite powder with the Dv50 of 120nm, and the adding amount of the conductive carbon source is finally synthesized Li 5 FeO 4 5% of the theoretical weight of the material;
(2) Preparing a formic acid solution with the concentration of 15mol/L as an accelerator solution, wherein the dosage of the formic acid is 1.15 times of the molar quantity of nitrate ions in the acidic ferric nitrate solution;
(3) Adding the accelerator solution prepared in the step (2) into the acidic ferric nitrate solution prepared in the step (1), fully stirring to obtain a mixed solution with pH of 4.0, heating the mixed solution to enable the temperature in a solution system to be higher than 50 ℃, at the moment, initiating self-propagating reaction, releasing a large amount of heat, and evaporating a solvent to obtain a precursor Fe with Dv50 of 250nm and water content of 0.6wt% 3 O 4 ；
(4) Fe obtained 3 O 4 Mixing with lithium hydroxide monohydrate, wherein the molar ratio of Li/Fe is 5.2, the mixing equipment is a high-speed mixer, the mixing rotating speed is 600rpm, wherein the mixed materials are sintered in nitrogen atmosphere (oxygen content is 1.0%), the sintering temperature is 670 ℃, the sintering time is 18h, and Li can be obtained 5 FeO 4 A block material;
(5) The obtained Li 5 FeO 4 Crushing the blocky materials in a nitrogen atmosphere, controlling the Dv50 of the blocky materials to be 4-6 mu m, and carrying out vacuum vapor deposition coating on the crushed materials, wherein the molar ratio of the used gases is 4:1, wherein the coating temperature is 400 ℃, the time is 8 hours, the pressure is-20 kpa, and after the coating is finished, the anode active material Li with good performance can be obtained 5 FeO 4 。
Characterization test: li prepared by the synthesis method 5 FeO 4 Referring to fig. 5, the resulting material had good overall uniformity, a carbon content of 4.1% as measured by a carbon sulfur meter, and a particle size Dv50 of 5.8 μm.
Comparative example 1
The comparative example uses a conventional high temperature solid phaseThe method prepares a lithium ion battery anode active material Li 5 FeO 4 Conventional existing iron oxide (Dv 50 of 3 μm, BET of 25m was used 2 And/g) is an iron source, the carbon nano tube is a carbon source, and the specific process is as follows:
mixing lithium hydroxide and ferric oxide at a high speed according to a mole ratio of Li/Fe of 5.3, wherein the adding amount of the carbon nano tube is 8% of the mass of the ferric oxide, a coulter type mixer is used as equipment, the mixing rotating speed is 650rpm, the mixing time is 30min, the mixed materials are subjected to heat preservation and sintering at a sintering temperature of 200 ℃ for 5h, then sintered at 740 ℃ for 16h, and the Li is obtained after crushing 5 FeO 4 。
Characterization test: li obtained by the synthesis method 5 FeO 4 The carbon content was measured by a carbon-sulfur meter and found to be 4.2% and the particle diameter Dv50 was 18 μm. Referring to fig. 7, the particles formed are very large, mainly due to the large size of the iron source particles used.
Test examples
Li synthesized in examples 1 and 2 and comparative example 1 5 FeO 4 The button cell is manufactured respectively, and the preparation, coating, drying, tabletting, assembly, cabinet loading test and other steps of the sizing agent are needed: (1) preparing slurry, weighing 10g of material, mixing with a conductive agent and a binder, wherein the material is as follows: conductive agent: the mass ratio of the binder is 8:1:1, the binder is PVDF, the solvent is N-methyl pyrrolidone, and the conductive agent is conductive carbon; (2) coating, namely coating the aluminum foil by using a scraper; the coating thickness is controlled to be 200 mu m plus or minus 30 mu m, (3) drying is carried out, the coated pole piece is dried in a vacuum drying oven, the drying temperature is 120 ℃, and the drying time is 2 hours; (4) tabletting, namely tabletting the dried pole piece by using a pair roller; (5) and assembling battery parts such as a positive pole piece, a negative pole piece, a diaphragm, electrolyte and the like into the button battery. Specific capacity was tested at a charging voltage of 4.25V and a charging rate of 0.1C.
FIG. 4 is Li synthesized in example 1 5 FeO 4 The charge-discharge curve of (2) shows that the capacity can reach 625mAh/g.
FIG. 6 is Li synthesized in example 2 5 FeO 4 Is visible from the graphThe capacity can reach 648mAh/g.
FIG. 8 is Li synthesized in comparative example 1 5 FeO 4 The charge-discharge curve of (2) shows that the capacity can reach 512mAh/g.
The embodiments of the present invention have been described in detail with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge of one of ordinary skill in the art without departing from the spirit of the present invention. Furthermore, embodiments of the invention and features of the embodiments may be combined with each other without conflict.

Claims (5)

1. A method for preparing a positive electrode active material, comprising the steps of:
s1: mixing a dispersing agent, a conductive carbon source, ferric nitrate, an accelerator and water to prepare an acidic mixed solution, wherein the accelerator is a reducing organic matter; the promoter is at least one of acetaldehyde, ethyl acetate, formic acid or ethylene glycol; in the mixed solution, the mol ratio of the accelerator to nitrate ions is 1.1-1.3;
s2: heating the mixed solution to above 50 ℃ to induce self-propagating reaction, and obtaining a precursor after the reaction is finished; the particle diameter Dv50 of the precursor is 100-500nm; the temperature of the self-propagating reaction is 200-300 ℃;
s3: mixing the precursor with a lithium source, and sintering in a micro-oxygen atmosphere to obtain a sintered material; the sintering temperature is 480-700 ℃; the micro-oxygen atmosphere consists of inert gas and oxygen, wherein the oxygen content is 0.3-1.3%;
s4: pulverizing the sintered material, and vacuum vapor deposition coating the pulverized material with hydrocarbon gas to obtain positive electrode active material Li 5 FeO 4 。
2. The method according to claim 1, wherein in step S1, the pH of the mixed solution is 1 to 5.
3. The method according to claim 1, wherein in step S1, the dispersant is at least one of polyethylene glycol, polyvinyl alcohol or polyethylene oxide.
4. The method according to claim 1, wherein in step S1, the conductive carbon source is at least one of carbon nanotubes, graphite powder, or conductive carbon black.
5. Use of the preparation method according to any one of claims 1 to 4 for the preparation of a lithium ion battery.
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