A copper fluoride / polymer double-coated chromium oxide positive electrode material and its preparation method and application

Abstract

A copper fluoride / polymer double-coated chromium oxide positive electrode material and its preparation method and application belong to the field of lithium-ion battery technology. The specific scheme is as follows: the positive electrode material includes a core, an inner coating layer coated on the core, and an outer coating layer coated on the inner coating layer; the core is chromium oxide, the inner coating layer is a copper fluoride coating layer, and the outer coating layer is a mixed coating layer of polymer and highly conductive material. The present invention uses a chemical precipitation method to introduce a copper fluoride coating layer with a high voltage window and high discharge capacity on the surface of the chromium oxide, and constructs a mixed coating layer of conductive material and polymer on the outer surface of the material. The double coating layer isolates the self-discharge phenomenon between the chromium oxide and the electrolyte, improves the discharge platform of the material, and the polymer layer constructed by in-situ polymerization enables the material to have excellent ion and electron transport properties, effectively improving the discharge specific capacity, rate performance and storage performance of the chromium oxide.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and in particular relates to a copper fluoride / polymer double-coated chromium oxide positive electrode material, a preparation method thereof, and an application thereof. Background Art

[0002] With the continuous expansion of the demand for energy storage batteries in civilian portable electronic devices and the defense field, the development of new battery systems with high energy efficiency and strong safety has become the current focus. As the main component of the battery, the positive electrode largely determines the energy density and power characteristics of the battery. At present, commercial batteries mainly use lithium-containing oxides (such as LiFePO4, LiCoO2, NCM, NCA, etc.) with intercalation reactions as the positive electrode, and graphite, silicon oxide or a mixture of the two as the negative electrode. Its energy density is difficult to exceed 400Wh / Kg. The lithium-free positive electrode (metal oxide, metal phosphide and metal fluoride) based on the conversion reaction has the advantages of high specific energy, low price and easy synthesis. Compared with the lithium-containing positive electrode, it has huge potential research value in many fields. As a lithium-free positive electrode material, the chromium oxide positive electrode (mainly Cr8O 21 ) has the advantages of extremely high theoretical specific capacity (642mAh / g), actual energy density (1210Wh / Kg) and low raw material cost, and is a very promising type of positive electrode material.

[0003] However, Cr8O 21 The actual capacity of the material is far lower than the theoretical capacity, and the rate performance is relatively poor. In addition, the material is generally prepared by high-temperature solid-phase calcination and contains trace amounts of CrO3 that are difficult to remove. The strong oxidizing properties of CrO3 cause it to easily react with the electrolyte, releasing a large amount of heat while also generating by-products, thereby affecting the safety and storage performance of the battery. This also limits the application of chromium oxide positive electrodes.

[0004] Patent publication number CN112968176 A describes the preparation of a positive electrode material composed of chromium oxide and carbon nanotubes, improving the material's initial discharge capacity and rate capability. However, the high-temperature solid-phase method makes it difficult to obtain a uniform and dense coating on the material surface. This allows the chromium oxide to remain in contact with the electrolyte, resulting in side reactions that affect the battery's safety and storage performance.

[0005] Patent application CN116759569A discloses a chromium oxide cathode material containing boron and other metal elements, improving its electrical conductivity, high-temperature performance, and rate capability. However, the metal source is an organic salt, and the doping process utilizes a high-temperature solid-phase method, resulting in poor material consistency. Furthermore, the initial discharge capacity of 351.7 mAh / g is not very high, failing to meet current performance requirements for primary batteries.

[0006] Patent CN112194182A prepares chromium oxide containing lithiated polyacrylonitrile (PSN), improving the material's initial coulombic efficiency, reversibility, and conductivity. However, the material loses some capacity after storage in the PSN, resulting in an initial discharge capacity of only 326.5 mAh / g, leaving significant room for performance improvement.

[0007] In summary, the current conventional modification mainly focuses on sintered Cr8O 21 It is difficult to form a uniform and stable coating layer by doping or coating, which can simultaneously improve the ionic and electronic conductivity of the chromium oxide material. Therefore, the improvement effect of the discharge capacity, rate performance and storage performance of the modified material is difficult to achieve the expected effect. Summary of the Invention

[0008] In order to solve the problems of low discharge specific capacity, poor rate performance and storage performance of chromium oxide positive electrode materials, the present invention provides a copper fluoride / polymer double-coated chromium oxide positive electrode material and a preparation method and application thereof.

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] A copper fluoride / polymer double-coated chromium oxide positive electrode material, comprising an inner core, an inner coating layer coated on the inner core, and an outer coating layer coated on the inner coating layer; the inner core is chromium oxide, the inner coating layer is a copper fluoride coating layer, and the outer coating layer is a mixed coating layer of polymer and conductive material.

[0011] Furthermore, the chromium oxide is Cr8O 21 .

[0012] Furthermore, the thickness of the inner cladding layer and the outer cladding layer is 3-10 nm.

[0013] A method for preparing the copper fluoride / polymer double-coated chromium oxide positive electrode material comprises the following steps:

[0014] S1: CrO3 is calcined at high temperature in an oxygen atmosphere to prepare Cr8O 21 ;

[0015] S2: Cr8O 21 , Cu(NO3)2·3H2O and dispersant were added to solvent I, and Cr8O 21 Evenly disperse and dissolve Cu(NO3)2·3H2O to obtain solution I;

[0016] S3: slowly adding the ammonium fluoride solution dropwise to solution I with vigorous stirring during the addition process. After the addition is complete, stirring is performed to allow the material to fully react. The sample is then separated, washed, and dried. The sample is then placed in a tube furnace and calcined under an inert atmosphere to obtain a copper fluoride-coated chromium oxide material.

[0017] S4: dissolving the lithium salt in a sulfone monomer solvent and adding an initiator to obtain a precursor solution;

[0018] S5: Dissolve the precursor solution, conductive material and chromium oxide coated with copper fluoride in sufficient acetonitrile, heat and stir to polymerize and solidify the sulfone monomer, and vacuum dry to obtain a chromium oxide positive electrode material with a copper fluoride / polymer double coating layer.

[0019] Furthermore, in S1, the high-temperature calcination temperature is 270-330°C, the time is 6-24 hours, and the heating rate is 1-10°C / min. Preferably, after the CrO3 is calcined at high temperature in an oxygen atmosphere, it is crushed and then subjected to a second re-firing to ensure a more complete reaction of the CrO3. The crushing method is ball milling at a ball milling speed of 350-500 rpm and a ball milling time of 2-8 hours.

[0020] Furthermore, in S2, the dispersant includes a combination of one or more of oleic acid, linoleic acid, oleyl alcohol, alkylphenol polyoxyethylene ether, polyoxyethylene oleyl alcohol ether, and polyvinyl pyrrolidone, and the solvent I includes anhydrous ethanol.

[0021] Furthermore, in S2, the Cr8O 21 The dispersion concentration is 1-50g / L, and the concentration of Cu(NO3)2·3H2O is 0.01-0.03mol / L.

[0022] Furthermore, in S3, the concentration of the ammonium fluoride solution is 0.04-0.12 mol / L (twice the theoretical ratio of the Cu source); the precipitate is separated by centrifugation, and after obtaining the precipitate, it needs to be centrifuged and washed three times with ethanol to remove residual unreacted raw materials. After centrifugation, the precipitate is vacuum dried to completely dry the precipitate; the temperature of the calcination process is 200-300°C, the calcination time is 5-10h, and the heating rate is 1-10°C / min.

[0023] Furthermore, in S4, the sulfone monomer includes one or more of arylene ether sulfone, methyl vinyl sulfone, aromatic ether ether sulfone, sulfone ether, 3-acryloyl cyclopentane sulfone, tetramethylene sulfone, sulfonated ether ketone sulfone, and phenyl sulfone; the lithium salt includes one or more of LiPF6, LiBF4, LiTFSI, LiFSI, LiDFOB, LiBOB, etc.; the initiator includes azobisisobutyronitrile; the concentration of the lithium salt in the precursor solution is 0.1-4 mol / L; the mass fraction of the initiator in the precursor solution is 1 wt.%.

[0024] Furthermore, in S5, the mass ratio of the copper fluoride-coated chromium oxide, the precursor solution and the conductive material is 100:5-20:0.1-1; the conductive material includes one of carbon nanotubes, carbon black, silver powder and graphene; the heating and stirring temperature is 60°C and the time is 12 hours; the vacuum drying temperature is 60°C and the time is 12-24 hours.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) The present invention forms a uniform and dense coating layer of CuF2 on the surface of chromium oxide by chemical precipitation, and utilizes the high voltage platform of CuF2 (3.55V, vs Li / Li + ) and high discharge specific capacity (528mAh / g), which significantly improved the discharge platform and first-cycle discharge specific capacity of chromium oxide.

[0027] (2) The present invention further coats a mixed coating layer of polymer and conductive material on the surface of the chromium oxide material coated with copper fluoride. The uniform dispersion of the conductive material improves the conductivity of the chromium oxide and CuF2. At the same time, the presence of the polymer layer constructs a good transmission path for the lithium ion insertion and extraction in the active material, which can greatly improve the kinetics and electrochemical properties of the electrode material.

[0028] (3) The inner coating layer and the outer coating layer of the present invention isolate the contact between the chromium oxide and the electrolyte, inhibit the self-discharge reaction between the highly oxidizing chromium oxide material and the electrolyte, and improve the storage performance of the material.

[0029] (4) The chemical precipitation method for coating CuF2 and the polymer coating method of the present invention are universal and can be extended to other lithium-ion battery systems for electrode material modification. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the chromium oxide positive electrode material with a copper fluoride / polymer double coating layer of the present invention;

[0031] Figure 2 The unmodified chromium oxide positive electrode Cr8O in Comparative Example 1 21 Electrochemical performance diagram of

[0032] Figure 3 : This is the room temperature impedance diagram of the polysulfone polymer electrolyte obtained after polymerization of the precursor solution prepared in Example 1;

[0033] Figure 4 Graph showing the electrochemical performance of the CuF2 and polymer-coated chromium oxide positive electrodes in Example 1;

[0034] Figure 5This is a comparison chart of the impedance of the modified chromium oxide positive electrode in Example 1 and the unmodified chromium oxide positive electrode in Comparative Example 1;

[0035] Figure 6 1 and 2 are discharge curves of the battery with the modified chromium oxide positive electrode in Example 1 and the battery with the unmodified original chromium oxide positive electrode in Comparative Example 1 after storage at 55° C. for 7 days. DETAILED DESCRIPTION

[0036] The technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and embodiments. Obviously, the described embodiments are only part of the embodiments of the invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0037] Example 1

[0038] A method for preparing a copper fluoride / polymer double-coated chromium oxide positive electrode material comprises the following steps:

[0039] (1) 4 g of chromium trioxide powder was placed in a tube furnace, high-purity oxygen was introduced into the tube furnace, and the tube furnace program was set to heat up to 270 ° C at 5 ° C / min, calcined at high temperature for 12 hours, and then taken out after cooling to room temperature. The product was ground and washed with water to remove unreacted chromium trioxide. After vacuum drying at 60 ° C for 24 hours, the product was calcined again according to the above steps, ground again, sieved and washed with water to obtain a high-valent chromium oxide active material (Cr8O 21 ).

[0040] (2) Take 2g of Cr8O 21 , 1 mmol of Cu(NO3)2·3H2O was added to a beaker containing 40 ml of anhydrous ethanol, oleic acid was added dropwise as a dispersant, and ultrasonication was performed for 30 min to uniformly disperse the chromium oxide in the anhydrous ethanol and promote the complete dissolution of the Cu(NO3)2·3H2O particles to obtain solution I; another 4 mmol of ammonium fluoride was dissolved in 40 ml of deionized water to obtain an ammonium fluoride solution, and then the ammonium fluoride solution was slowly dripped into solution I with vigorous stirring during the process. After the addition was complete, stirring was continued for 5 h to allow the material to fully react. Then the solution and the precipitate were transferred to a centrifuge tube, the centrifuge speed was set to 5000 rpm, the centrifugation time was 10 min, the precipitate was centrifuged out, and then ethanol was added to the precipitate. The precipitate was centrifuged and washed three times under the same parameters to remove the unreacted copper source and fluorine source. The washed precipitate was dried in a vacuum oven at 60°C for 24 h. Finally, the dried powder was ground into fine powder in an argon-filled glove box, and then placed in an argon-filled tube furnace and heated to 250°C at a heating rate of 5°C / min and calcined for 8 hours to obtain a CuF2-coated chromium oxide material.

[0041] (3) LiPF6 was dissolved in an arylene ether sulfone polymerization monomer solvent, and azobisisobutyronitrile was added as an initiator. The precursor solution was obtained by magnetic stirring for 15 minutes. The concentration of LiPF6 in the precursor solution was 1 mol / L, and the mass fraction of azobisisobutyronitrile in the precursor solution was 1 wt%. The chromium oxide coated with CuF2, a trace amount of carbon black, and the precursor solution were mixed and dissolved in a sufficient amount of acetonitrile. The arylene ether sulfone polymerization monomer was polymerized by heating at 60°C and magnetic stirring for 12 hours. The mass ratio of the chromium oxide coated with CuF2, the precursor solution, and the carbon black was 100:5:0.1. The polymerized lithium storage material was dried in a vacuum oven at 60°C for 12 hours, and the acetonitrile solvent was removed to obtain a chromium oxide positive electrode material having a copper fluoride / polymer double coating layer.

[0042] (4) The chromium oxide positive electrode material with a copper fluoride / polymer double coating layer was dissolved in NMP with Super P and PVDF at a mass ratio of 8:1:1 and stirred for 12 hours. The slurry was coated on aluminum foil with a coater and placed in a vacuum oven and heated at 60°C for 12 hours to obtain a modified chromium oxide electrode sheet. The above-mentioned electrode sheet was used as the positive electrode, 1M LiPF6+EC / DMC (volume ratio of 3:7)+FEC (mass fraction of 5%) was used as the electrolyte, and a lithium metal negative electrode and Celgard-2400 commercial polypropylene separator were assembled into a CR2025 button cell, and the electrochemical performance was tested. The voltage test range was: 1.5V~4.5V.

[0043] Comparative Example 1

[0044] Cr8O 21 As the positive electrode material, it was dissolved in NMP with Super P and PVDF in a mass ratio of 8:1:1 and stirred for 12 hours. The slurry was coated onto aluminum foil with a coater and placed in a vacuum oven and heated at 60°C for 12 hours to obtain an unmodified chromium oxide electrode sheet. The above electrode sheet was used as the positive electrode, 1M LiPF6+EC / DMC (volume ratio of 3:7)+FEC (mass fraction of 5%) was used as the electrolyte, the lithium metal negative electrode and Celgard-2400 commercial polypropylene separator were assembled into a CR2025 button cell, and the electrochemical performance was tested. The voltage test range was: 1.5V to 4.5V.

[0045] Figure 1 Schematic diagram of the structure of the chromium oxide positive electrode material with copper fluoride / polymer double coating layer in Example 1. Figure 2 This is the first-cycle discharge curve of the unmodified chromium oxide positive electrode in Comparative Example 1, and its first-cycle discharge capacity at a current density of 30 mA / g is 372 mAh / g. Figure 3 The room temperature impedance spectrum of the polysulfone polymer electrolyte obtained after polymerization of the precursor solution prepared in Example 1 is shown. The room temperature ionic conductivity is calculated to be 3.5×10-4 S / cm, demonstrating that the polysulfone polymer coating can promote the rapid transport of lithium ions. Figure 4 The first-cycle discharge capacity of the modified chromium oxide positive electrode in Example 1 is 442 mAh / g at a current density of 30 mA / g, which is significantly improved compared with the unmodified chromium oxide positive electrode in Comparative Example 1. Figure 5 The impedance comparison of the modified chromium oxide positive electrode in Example 1 and the unmodified chromium oxide positive electrode in Comparative Example 1 is shown. The impedances of Comparative Example 1 and Example 1 are 168Ω and 97Ω, respectively. Figure 6 The discharge curves for the battery with the modified chromium oxide positive electrode and the battery with the unmodified chromium oxide positive electrode in Example 1 after 7 days of storage at 55°C are shown. The storage capacities of Comparative Example 1 and Example 1 were 314 mAh / g and 420 mAh / g, respectively, representing capacity losses of 15.6% and 5%, respectively. This demonstrates that the dual-coating strategy not only increases the discharge capacity of the chromium oxide but also mitigates self-reactions at the electrode / electrolyte interface, significantly improving the material's storage performance.

[0046] Example 2

[0047] A method for preparing a copper fluoride / polymer double-coated chromium oxide positive electrode material comprises the following steps:

[0048] (1) Same as step (1) in Example 1.

[0049] (2) Take 2g of Cr8O 21 , 0.4 mmol of Cu(NO3)2·3H2O was added to a beaker containing 40 ml of anhydrous ethanol, oleic acid was added dropwise as a dispersant, and ultrasonication was performed for 30 min to uniformly disperse the chromium oxide in the anhydrous ethanol and promote the complete dissolution of the Cu(NO3)2·3H2O particles to obtain solution I; another 1.6 mmol of ammonium fluoride was dissolved in 40 ml of deionized water to obtain an ammonium fluoride solution, and then the ammonium fluoride solution was slowly dripped into solution I with vigorous stirring during the process. After the addition was complete, stirring was continued for 5 h to allow the material to fully react. Then the solution and the precipitate were transferred to a centrifuge tube, the centrifuge speed was set to 5000 rpm, the centrifugation time was 10 min, the precipitate was centrifuged out, and then ethanol was added to the precipitate. The precipitate was centrifuged and washed three times under the same parameters to remove the unreacted copper source and fluorine source. The washed precipitate was dried in a vacuum oven at 60°C for 24 h. Finally, the dried powder was ground into fine powder in an argon-filled glove box, and then placed in an argon-filled tube furnace and heated to 270°C at a heating rate of 3°C / min and calcined for 6 hours to obtain a CuF2-coated chromium oxide material.

[0050] (3) Same as step (3) in Example 1.

[0051] (4) Same as step (4) in Example 1.

[0052] Example 3

[0053] A method for preparing a copper fluoride / polymer double-coated chromium oxide positive electrode material comprises the following steps:

[0054] (1) Same as step (1) in Example 1.

[0055] (2) Same as step (2) in Example 1.

[0056] (3) 1 mol / L LiPF6 was dissolved in a methyl vinyl sulfone polymerization monomer solvent, 1 wt% azobisisobutyronitrile was added as an initiator, and magnetic stirring was performed for 15 minutes to obtain a precursor solution. The chromium oxide coated with CuF2, a trace amount of carbon black, and the precursor solution were mixed and dissolved in a sufficient amount of acetonitrile, and heated at 60°C and magnetic stirring for 12 hours to polymerize the methyl vinyl sulfone polymerization monomer, wherein the mass ratio of the chromium oxide coated with CuF2, the precursor solution, and the carbon black was 100:10:1. The polymerized lithium storage material was dried in a vacuum oven at 60°C for 12 hours, and the acetonitrile solvent was removed to obtain a chromium oxide positive electrode material with a copper fluoride / polymer double coating layer.

[0057] (4) Same as step (4) in Example 1.

[0058] Example 4

[0059] A method for preparing a copper fluoride / polymer double-coated chromium oxide positive electrode material comprises the following steps:

[0060] (1) Same as step (1) in Example 1.

[0061] (2) Same as step (2) in Example 1.

[0062] (3) 1 mol / L LiFSI was dissolved in a methyl vinyl sulfone polymerization monomer solvent, 1 wt% of azobisisobutyronitrile was added as an initiator, and magnetic stirring was performed for 15 minutes to obtain a precursor solution. The chromium oxide coated with CuF2, a trace amount of graphene, and the precursor solution were mixed and dissolved in a sufficient amount of acetonitrile, and heated at 60°C and magnetically stirred for 12 hours to polymerize the methyl vinyl sulfone polymerization monomer, wherein the mass ratio of the chromium oxide coated with CuF2, the precursor solution, and the carbon black was 100:10:1. The polymerized lithium storage material was dried in a vacuum oven at 60°C for 12 hours, and the acetonitrile solvent was removed to obtain a chromium oxide positive electrode material with a copper fluoride / polymer double coating layer.

[0063] (4) Same as step (4) in Example 1.

[0064] The present invention uses a chemical precipitation method to introduce a copper fluoride coating with a high voltage window and high discharge capacity on the surface of the chromium oxide, and constructs a mixed coating layer of a conductive material and a polymer on the outer surface of the material. The double coating isolates the self-discharge phenomenon between the chromium oxide and the electrolyte, improving the discharge platform of the material. The polymer layer constructed by in-situ polymerization gives the material excellent ion and electron transport properties, effectively improving the discharge specific capacity, rate performance and storage performance of the chromium oxide.

[0065] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A copper fluoride / polymer double-coated chromium oxide positive electrode material, characterized by: The positive electrode material comprises a core, an inner coating layer coated on the core, and an outer coating layer coated on the inner coating layer; the core is chromium oxide, the inner coating layer is a copper fluoride coating layer, and the outer coating layer is a mixed coating layer of polymer and conductive material; the chromium oxide is Cr8O 21 ; The thickness of the inner coating layer and the outer coating layer is 3-10nm.

2. A method for preparing the copper fluoride / polymer double-coated chromium oxide positive electrode material according to claim 1, characterized in that: The following steps are involved: S1: CrO3 is calcined at high temperature in an oxygen atmosphere to prepare Cr8O 21 ; S2: Cr8O 21 , Cu(NO3)2·3H2O and dispersant are added into solvent I, dispersed and dissolved uniformly to obtain solution I; S3: adding the ammonium fluoride solution dropwise to solution I with vigorous stirring, stirring after the addition is complete to allow the material to fully react, then separating, washing, and drying the sample, and then calcining under an inert atmosphere to obtain a copper fluoride-coated chromium oxide material; S4: dissolving the lithium salt in a sulfone monomer solvent and adding an initiator to obtain a precursor solution; S5: Dissolve the precursor solution, conductive material and chromium oxide coated with copper fluoride in acetonitrile, heat and stir to polymerize and solidify the sulfone monomer, and vacuum dry to obtain a chromium oxide positive electrode material with a copper fluoride / polymer double coating layer.

3. The preparation method according to claim 2, wherein: In S1, the high-temperature calcination temperature is 270-330° C., the time is 6-24 hours, and the heating rate is 1-10° C. / min.

4. The preparation method according to claim 2, wherein: In S2, the dispersant includes one or more of oleic acid, linoleic acid, oleyl alcohol, alkylphenol polyoxyethylene ether, polyoxyethylene oleyl alcohol ether, and polyvinyl pyrrolidone, and the solvent I includes anhydrous ethanol.

5. The preparation method according to claim 2, wherein: In S2, the Cr8O 21 The dispersion concentration is 1-50g / L, and the concentration of Cu(NO3)2·3H2O is 0.01-0.03mol / L.

6. The preparation method according to claim 2, wherein: In S3, the concentration of the ammonium fluoride solution is 0.04-0.12 mol / L; the temperature of the calcination process is 200-300° C., the calcination time is 5-10 h, and the heating rate is 1-10° C. / min.

7. The preparation method according to claim 2, characterized in that: In S4, the sulfone monomer includes one or more of arylene ether sulfone, methyl vinyl sulfone, aryl ether sulfone, 3-acryloyl cyclopentane sulfone, tetramethylene sulfone, sulfonated ether ketone sulfone, and phenyl sulfone; the lithium salt includes one or more of LiPF6, LiBF4, LiTFSI, LiFSI, LiDFOB, LiBOB, etc.; the initiator includes azobisisobutyronitrile; the concentration of the lithium salt in the precursor solution is 0.1-4 mol / L; the mass fraction of the initiator in the precursor solution is 1 wt.%.

8. The preparation method according to claim 2, wherein: In S5, the mass ratio of the copper fluoride-coated chromium oxide, the precursor solution, and the conductive material is 100:5-20:0.1-1; and the conductive material comprises one of carbon nanotubes, carbon black, silver powder, and graphene.

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