Composite positive electrode material, preparation method, positive electrode sheet and sodium ion battery

Abstract

The application discloses a kind of composite positive electrode materials, including layered oxide and cladding layer, cladding layer is coated outside layered oxide, layered oxide general formula is NaMeO2, wherein, Me is one or several of Ni, Fe, Mn, Co and the combination of Cu, cladding layer is sulfur-doped carbon-coated Cu-Sn alloy, and S-Sn chemical bond exists in cladding layer.The application also discloses its preparation method, which is to mix and grind layered oxide, Cu powder, Sn powder, organic carbon source solid powder and sulfur source solid powder, and then sinter at 500-600 DEG C for 2-3 hours in a protective atmosphere.The application also discloses a positive plate and a sodium-ion battery with the composite positive electrode material.The application enhances the bonding force between the cladding layer and the layered oxide substrate, and the S-Sn bond effectively inhibits the interlayer peeling of the cladding layer material during the cycle process, thereby improving the battery capacity retention rate.

Description

Technical Field

[0001] This invention belongs to the field of battery technology and relates to a composite cathode material, preparation method, cathode sheet and sodium-ion battery. Background Technology

[0002] Layered oxide cathode materials, as a typical type of cathode material for sodium-ion batteries, have advantages such as high reversible capacity, stable structure, and simple preparation, making them highly promising candidate cathode materials for sodium-ion batteries.

[0003] However, layered oxides still have the following key problems in practical applications: the intrinsic electronic conductivity of the material is low, and transition metal ions are easily dissolved during cycling, which leads to structural decay and rapid capacity decay; the electrode / electrolyte interface stability is poor, and side reactions are significant, affecting the battery cycle life and safety; while conventional carbon coating and oxide coating cannot simultaneously achieve high conductivity, strong interface bonding and long-term stable protection. Summary of the Invention

[0004] To address the shortcomings of the prior art, the present invention aims to provide a composite cathode material and its preparation method, solving the problems of low conductivity and large capacity decay during cycling. Another objective of the present invention is to provide a cathode sheet and a sodium-ion battery.

[0005] The technical solution of the present invention is as follows: a composite cathode material, comprising a layered oxide and a coating layer, wherein the coating layer covers the layered oxide, the layered oxide having the general formula NaMeO2, wherein Me is one or more of Ni, Fe, Mn, and Co combined with Cu, the coating layer being a sulfur-doped carbon-coated Cu-Sn alloy, and the coating layer having S-Sn chemical bonds.

[0006] Furthermore, sulfur accounts for 1% to 3% of the mass of the composite cathode material, and carbon accounts for 2% to 5% of the mass of the composite cathode material. For example, the proportion of sulfur is 1%, 2%, or 3%, and the proportion of carbon is 2%, 3%, 4%, or 5%.

[0007] Furthermore, the Cu-Sn alloy accounts for 1% to 3% of the mass of the composite cathode material, for example, 1%, 2% or 3%.

[0008] Furthermore, the mass percentage of Sn in the Cu-Sn alloy is 7% to 10%, for example, 7%, 8%, 9% or 10%.

[0009] Another technical solution of the present invention is: a method for preparing a composite cathode material, comprising the following steps: mixing and grinding layered oxide, Cu powder, Sn powder, organic carbon source solid powder and sulfur source solid powder, and then sintering at 500-600°C for 2-3 hours in a protective atmosphere.

[0010] Furthermore, during the mixing and grinding process, anhydrous ethanol is added and the mixture is ground for 1 to 2 hours before drying.

[0011] Furthermore, the Cu powder and Sn powder are first ball-milled and passed through a 300-mesh sieve, and then mixed and ground with layered oxides, organic carbon source solid powder and sulfur source solid powder.

[0012] Furthermore, the organic carbon source solid powder is glucose, and the sulfur source solid powder is thiourea.

[0013] Another technical solution of the present invention is: a positive electrode sheet, comprising a positive electrode current collector, wherein the surface of the positive electrode current collector is coated with a positive electrode slurry layer containing the aforementioned composite positive electrode material.

[0014] Another technical solution of the present invention is: a sodium-ion battery, comprising a negative electrode, an electrolyte, a separator, and the aforementioned positive electrode sheet.

[0015] Compared with the prior art, the present invention has the following significant advantages:

[0016] Cu-Sn alloys possess excellent metallic conductivity. When combined with sulfur-doped carbon (SC), they form a continuous and highly efficient conductive network, which improves the low intrinsic electronic conductivity of layered oxide cathodes and enhances battery rate performance and charge / discharge efficiency.

[0017] Both the layered oxide matrix and the Cu-Sn alloy coating contain Cu, exhibiting good interfacial chemical compatibility and extremely low lattice mismatch. Simultaneously, S and Sn in the coating form stable S-Sn chemical bonds, further strengthening the bonding force between the coating and the matrix, as well as within the coating itself, effectively suppressing interlayer delamination during cycling. Furthermore, by leveraging the adsorption properties of porous carbon, the Cu-Sn alloy achieves tight adhesion and uniform coating with the layered oxide matrix, overcoming the problems of weak bonding and easy detachment in conventional coating technologies, and improving capacity retention.

[0018] The dense and stable composite coating layer can prevent the electrode from directly contacting the electrolyte, build a stable solid-phase interface layer, significantly reduce interfacial side reactions, and inhibit the dissolution of transition metal ions, thereby improving the battery cycle life and safety. Attached Figure Description

[0019] Figure 1 NaCu used in the embodiments and comparative examples of this invention 1 / 3 Fe 1 / 3 Mn 1 / 3 XRD pattern of O2.

[0020] Figure 2 This is a SEM image of the composite cathode material prepared in Example 1 of the present invention.

[0021] Figure 3 This is a transmission electron microscope (TEM) image of the composite cathode material prepared in Example 1 of the present invention.

[0022] Figure 4 This is an XPS fitting image of the S2p orbital of the composite cathode material prepared in Example 1 of the present invention.

[0023] Figure 5 This is an XPS fitting image of the Sn3d orbitals of the composite cathode material prepared in Example 1 of the present invention. Detailed Implementation

[0024] The present invention will be further described below with reference to the embodiments and accompanying drawings. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. After reading this description, any modifications of this description in various equivalent forms by those skilled in the art will fall within the scope defined by the appended claims.

[0025] Example 1

[0026] The preparation process of the composite cathode material in this embodiment is as follows:

[0027] 1) Preparation of Cu-Sn alloy: Cu powder (purity ≥99.95wt.%) and Sn powder (purity ≥99.5wt.%) were ball-milled in a planetary ball mill at a mass ratio of Cu to Sn of 93:7 for 3 hours at a speed of 400 r / min. The mixture was then passed through a 300-mesh sieve to obtain nano-Cu-Sn precursor powder.

[0028] 2) Using a planetary ball mill (Focucy F-P4000), 2g of Cu-Sn precursor powder, 5.23g of thiourea powder, 11.69g of glucose, and 91g of NaCu were collected. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 was mixed and ground in anhydrous ethanol for 1 hour, then dried in an oven at 70°C. The mixture was then placed directly in a reaction vessel, purged with nitrogen, and sintered at 550°C for 2 hours at a rate of 5°C / min. After natural cooling to room temperature, the mixture was crushed, demagnetized, sieved, and washed 2-3 times with deionized water and anhydrous ethanol to obtain the final product, NaCu. 1 / 3 Fe 1 / 3 Mn 1 / 3 The O2 is coated with a sulfur-doped carbon-coated Cu-Sn alloy layer, in which sulfur accounts for about 2% of the mass of the composite cathode material, carbon accounts for about 5% of the mass of the composite cathode material, and Cu-Sn alloy accounts for about 2% of the mass of the composite cathode material (approximately 1.1 times the amount is used considering the high-temperature loss of thiourea and glucose).

[0029] Among them, NaCu 1 / 3 Fe1 / 3 Mn 1 / 3 O2 was synthesized using a solid-state method. The raw materials were weighed according to a stoichiometric ratio, with Na2CO3 in 5% excess (i.e., 1.05 times the amount): Na2CO3:CuO:Fe2O3:Mn2O3 = 1.5:1:0.5:0.5. The raw materials were placed in an alumina ball mill jar and wet-milled at 1400 rpm for 2 hours with acetone as the solvent until homogeneous. The resulting slurry was dried in an oven at 80℃ for 2 hours to obtain the precursor powder. The precursor powder was placed in a muffle furnace and heated to 900℃ at a rate of 5℃ / min under air atmosphere, and sintered at this temperature for 12 hours. It was then cooled to room temperature (20~25℃) with the furnace to obtain the layered oxide NaCu. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, the XRD pattern of this material is as follows Figure 1 As shown, the O3 phase is consistent with the card in the PDF-04-005-8593 standard, proving that a pure O3 phase material has been synthesized. This material was used in all subsequent examples and comparative examples.

[0030] The SEM image of the composite cathode material in this embodiment is as follows: Figure 2 As shown, the transmission electron microscope image is as follows: Figure 3 As shown, a coating layer can be observed on the surface. XPS fitting plots for the S2p and Sn3d orbitals are shown below. Figure 4 and Figure 5 As shown, the chemical environment of the elements can be clearly seen: Sn+2 valence (Sn-S bond) and Sn0 valence (alloy).

[0031] Example 2

[0032] The preparation process of the composite cathode material in this embodiment is as follows:

[0033] 1) Preparation of Cu-Sn alloy: Cu powder (purity ≥99.95wt.%) and Sn powder (purity ≥99.5wt.%) were ball-milled in a planetary ball mill at a mass ratio of Cu to Sn of 93:7 for 3 hours at a speed of 400 r / min. The mixture was then passed through a 300-mesh sieve to obtain nano-Cu-Sn precursor powder.

[0034] 2) Using a planetary ball mill (Focucy F-P4000), take 2g of Cu-Sn precursor powder, 2.61g of thiourea powder, 4.51g of glucose, and 95g of NaCu. 1 / 3 Fe 1 / 3 Mn 1 / 3O2 was mixed and ground in anhydrous ethanol for 1 hour, then dried in an oven at 70°C. The mixture was then placed directly in a reaction vessel, purged with nitrogen, and sintered at 550°C for 2 hours at a rate of 5°C / min. After natural cooling to room temperature, the mixture was crushed, demagnetized, sieved, and washed 2-3 times with deionized water and anhydrous ethanol to obtain the final product, NaCu. 1 / 3 Fe 1 / 3 Mn 1 / 3 The composite cathode material is coated with a sulfur-doped carbon-coated Cu-Sn alloy layer with O2, wherein the sulfur element accounts for about 1% of the mass of the composite cathode material, the carbon element accounts for about 2% of the mass of the composite cathode material, and the Cu-Sn alloy accounts for about 2% of the mass of the composite cathode material.

[0035] Example 3

[0036] The preparation process of the composite cathode material in this embodiment is as follows:

[0037] 1) Preparation of Cu-Sn alloy: Cu powder (purity ≥99.95wt.%) and Sn powder (purity ≥99.5wt.%) were ball-milled in a planetary ball mill at a mass ratio of Cu to Sn of 90:10 for 3 hours at a speed of 400 r / min. The mixture was then passed through a 300-mesh sieve to obtain nano-Cu-Sn precursor powder.

[0038] 2) Using a planetary ball mill (Focucy F-P4000), take 3g of Cu-Sn precursor powder, 5.61g of polythiophene powder, 5.24g of sucrose, and 90g of NaCu. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 was mixed and ground in anhydrous ethanol for 1 hour, then dried in an oven at 70°C. The mixture was then placed directly in a reaction vessel, purged with nitrogen, and sintered at 580°C for 3 hours at a rate of 5°C / min. After natural cooling to room temperature, the mixture was crushed, demagnetized, sieved, and washed 2-3 times with deionized water and anhydrous ethanol to obtain the final product, NaCu. 1 / 3 Fe 1 / 3 Mn 1 / 3 The composite cathode material is coated with a sulfur-doped carbon Cu-Sn alloy layer with O2 coating. The sulfur element accounts for about 2% of the mass of the composite cathode material, the carbon element accounts for about 5% of the mass of the composite cathode material, and the Cu-Sn alloy accounts for about 3% of the mass of the composite cathode material.

[0039] Comparative Example 1

[0040] The preparation process of the composite cathode material in this comparative example is as follows:

[0041] 1) Preparation of Cu-Sn alloy: Cu powder (purity ≥99.95wt.%) and Sn powder (purity ≥99.5wt.%) were ball-milled in a planetary ball mill at a mass ratio of Cu to Sn of 93:7 for 3 hours at a speed of 400 r / min. The mixture was then passed through a 300-mesh sieve to obtain nano-Cu-Sn precursor powder.

[0042] 2) Using a planetary ball mill (Focucy F-P4000), 2g of Cu-Sn precursor powder, 11.69g of glucose, and 91g of NaCu were taken. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 was mixed and ground in anhydrous ethanol for 1 hour, then dried in an oven at 70°C. The mixture was then placed directly in a reaction vessel, purged with nitrogen, and sintered at 550°C for 2 hours at a rate of 5°C / min. After natural cooling to room temperature, the mixture was crushed, demagnetized, sieved, and washed 2-3 times with deionized water and anhydrous ethanol to obtain the final product.

[0043] Comparative Example 2

[0044] The preparation process of the composite cathode material in this comparative example is as follows:

[0045] 5.23g of thiourea powder, 11.69g of glucose, and 91g of NaCu were obtained using a planetary ball mill (Focucy F-P4000). 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 was mixed and ground in anhydrous ethanol for 1 hour, then dried in an oven at 70°C. The mixture was then placed directly in a reaction vessel, purged with nitrogen, and sintered at 550°C for 2 hours at a rate of 5°C / min. After natural cooling to room temperature, the mixture was crushed, demagnetized, sieved, and washed 2-3 times with deionized water and anhydrous ethanol to obtain the final product.

[0046] Comparative Example 3

[0047] 1) Preparation of Cu-Sn alloy: Cu powder (purity ≥99.95wt.%) and Sn powder (purity ≥99.5wt.%) were ball-milled in a planetary ball mill at a mass ratio of Cu to Sn of 93:7 for 3 hours at a speed of 400 r / min. The mixture was then passed through a 300-mesh sieve to obtain nano-Cu-Sn precursor powder.

[0048] 2) Using a planetary ball mill (Focucy F-P4000), take 2g of Cu-Sn precursor powder, 5.23g of thiourea powder, and 91g of NaCu. 1 / 3 Fe 1 / 3 Mn 1 / 3O2 was mixed and ground in anhydrous ethanol for 1 hour, then dried in an oven at 70°C. The mixture was then placed directly in a reaction vessel, purged with nitrogen, and sintered at 550°C for 2 hours at a rate of 5°C / min. After natural cooling to room temperature, the mixture was crushed, demagnetized, sieved, and washed 2-3 times with deionized water and anhydrous ethanol to obtain the final product.

[0049] Comparative Example 4

[0050] 1) Preparation of Cu-Sn alloy: Cu powder (purity ≥99.95wt.%) and Sn powder (purity ≥99.5wt.%) were ball-milled in a planetary ball mill at a mass ratio of Cu to Sn of 93:7 for 3 hours at a speed of 400 r / min. The mixture was then passed through a 300-mesh sieve to obtain nano-Cu-Sn precursor powder.

[0051] 2) Using a planetary ball mill (Focucy F-P4000), 2g of Cu-Sn precursor powder, 9.75g of thiourea powder, 11.69g of glucose, and 91g of NaCu were taken. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 was mixed and ground in anhydrous ethanol for 1 hour, then dried in an oven at 70°C. The mixture was then placed directly in a reaction vessel, purged with nitrogen, and sintered at 550°C for 2 hours at a rate of 5°C / min. After natural cooling to room temperature, the mixture was crushed, demagnetized, sieved, and washed 2-3 times with deionized water and anhydrous ethanol to obtain the final product.

[0052] The composite cathode materials obtained in each embodiment and comparative example were made into cathode sheets according to the following method: PVDF binder was added to NMP at a mass ratio of 1:8 and stirred to obtain a slurry. Then, the composite cathode material, conductive agent acetylene black, and slurry were mixed at a mass ratio of 97:1:2 and stirred under vacuum until the system was homogeneous to obtain cathode slurry. The cathode slurry was uniformly coated on the cathode current collector (13μm carbon-coated aluminum foil), dried at room temperature, and then transferred to an oven for further drying. After cold pressing, the cathode sheets were obtained by cutting according to the required specifications. The prepared positive electrode sheet is then used to manufacture the battery: The negative electrode active material graphite, conductive agent acetylene black, thickener CMC, and binder SBR are mixed in a mass ratio of 96.2:0.8:1.2:1.8. Deionized water is then added to the mixture, and the mixture is stirred under vacuum until homogeneous, yielding a negative electrode slurry. This slurry is uniformly coated onto a negative electrode current collector (13μm carbon-coated aluminum foil), air-dried at room temperature, and then transferred to an oven for further drying. After cold pressing, the slurry is cut to the required specifications to obtain the negative electrode sheet. The positive electrode sheet, separator (Shenzhen Xingyuan Material Technology Co., Ltd., 12+4μm ceramic wet-process separator), and negative electrode sheet are stacked in sequence, and after assembly, a battery cell is obtained. The battery cell assembly is placed into the inner cavity of the battery casing. After drying, an electrolyte is injected into the inner cavity of the battery casing. The electrolyte solvent is ethylene carbonate, and the solute is sodium hexafluorophosphate (1 mol / L). After sealing, settling, formation, and capacity testing, a square sodium-ion battery is obtained. This square battery has a capacity of 20 Ah, a thickness of 15 mm, a width of 119 mm, and a height of 208 mm.

[0053] test:

[0054] 1) The composite cathode materials obtained in Examples 1-3 and the composite materials obtained in Comparative Examples 1-4 were subjected to electronic conductivity tests. The electronic conductivity was tested using a conductivity meter, and the results are shown in the table below.

[0055]

[0056] 2) Cyclic performance test:

[0057] Sodium-ion batteries were charged at 25°C with a constant current and constant voltage of 0.5C to a cutoff voltage of 4.0V, a cutoff current of 0.05C, and allowed to rest for 10 minutes. They were then discharged at 0.5C to a cutoff voltage of 2.0V and allowed to rest for 10 minutes. This cycle was repeated 800 times, and the capacity retention rate (%) after 800 cycles was calculated. The upper limit of the charging voltage was 4.0V. The test results are shown in the table below.

[0058]

[0059] It can be seen that the composite cathode material of the present invention significantly improves the cycle performance of sodium-ion batteries compared with the embodiments.

[0060] Compared with Example 1, Comparative Example 1 did not have sulfur doping in the coating layer, and its cycling performance was worse. The possible reason is that the doping of sulfur into the carbon skeleton increases the electronic conductivity of the carbon layer, forms Sn-S bonds with the alloy to enhance the interfacial bonding force between the coating layers, builds a stable surface interface phase, suppresses side reactions and metal ion dissolution, and improves cycling stability and safety.

[0061] Compared with Example 1, Comparative Example 2 did not have Cu-Sn alloy in the coating layer, so the electronic conductivity and cycling performance of the material deteriorated. The possible reason is that the alloy has ultra-high electronic conductivity and moderate Sn-S interface bonding ability, which can effectively suppress the dissolution of transition metals and electrolyte decomposition, and significantly improve cycling stability and rate performance.

[0062] Compared with Example 1, Comparative Example 3 did not have carbon material bonded to the coating layer, resulting in poorer electronic conductivity and cycle performance. The possible reasons are: the lack of carbon material buffering reduces the bonding force between coating layers, and the lack of carbon material conductivity affects the conductivity of the material and the cycle performance of the battery.

[0063] Compared with Example 1, Comparative Example 4 showed a significant increase in the sulfur content in the coating layer, resulting in poorer battery cycle performance. The possible reason is that excessive sulfur can generate impurities, which may cause surface cracks, affect the structural stability of the material, hinder Li⁺ diffusion, and thus affect the cycle.

Claims

1. A composite cathode material, comprising a layered oxide and a coating layer, wherein the coating layer covers the outside of the layered oxide, characterized in that, The layered oxide has the general formula NaMeO2, wherein Me is one or more of Ni, Fe, Mn, and Co combined with Cu. The coating layer is a sulfur-doped carbon-coated Cu-Sn alloy, and the coating layer contains S-Sn chemical bonds. The mass ratio of sulfur to the composite cathode material is 1% to 3%, the mass ratio of carbon to the composite cathode material is 2% to 5%, the mass ratio of Cu-Sn alloy to the composite cathode material is 1% to 3%, and the mass ratio of Sn in the Cu-Sn alloy is 7% to 10%.

2. A method for preparing the composite cathode material as described in claim 1, characterized in that, The process includes the following steps: mixing and grinding layered oxides, Cu powder, Sn powder, organic carbon source solid powder and sulfur source solid powder, and then sintering them at 500-600°C for 2-3 hours in a protective atmosphere.

3. The method for preparing the composite cathode material according to claim 2, characterized in that, During the mixing and grinding process, anhydrous ethanol is added and the mixture is ground for 1 to 2 hours before drying.

4. The method for preparing the composite cathode material according to claim 3, characterized in that, The Cu powder and Sn powder are first ball-milled and passed through a 300-mesh sieve, and then mixed and ground with layered oxides, organic carbon source solid powder and sulfur source solid powder.

5. The method for preparing the composite cathode material according to claim 2, characterized in that, The organic carbon source solid powder is glucose or sucrose, and the sulfur source solid powder is thiourea or polythiophene.

6. A positive electrode plate, comprising a positive current collector, characterized in that, The surface of the positive electrode current collector is coated with a positive electrode slurry layer containing the composite positive electrode material as described in claim 1.

7. A sodium-ion battery, comprising a negative electrode, an electrolyte, a separator, and the positive electrode as described in claim 6.

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