Sodium-ion battery positive electrode material, preparation method thereof, positive electrode sheet, sodium-ion battery and application thereof

Abstract

This invention relates to a sodium-ion battery cathode material, its preparation method, cathode sheet, sodium-ion battery, and its applications. The preparation method includes: mixing a polycrystalline layered oxide matrix with an organic carbon source, followed by melt infiltration and carbonization under pressure to obtain the sodium-ion battery cathode material. The organic carbon source has a melting point below 200°C and a viscosity of 50-300 mPa·s during melting. In the melt infiltration step, the organic carbon source can penetrate to the grain boundaries of the polycrystalline layered oxide matrix through capillary action. After carbonization, a continuous carbon network distributed along the grain boundaries and a carbon layer coating the polycrystalline layered oxide matrix can be formed. Simultaneously, during carbonization, the reducing gas generated by the decomposition of the organic carbon source can reduce the surface of the polycrystalline layered oxide matrix, forming oxygen vacancies. Therefore, the sodium-ion battery cathode material obtained by this preparation method exhibits excellent rate performance and cycle stability.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to sodium-ion battery cathode materials and their preparation methods, cathode sheets, sodium-ion batteries and their applications. Background Technology

[0002] Driven by global demand for clean energy, sodium-ion batteries are considered a key candidate technology to replace lithium-ion batteries due to their abundant resources, low cost, and environmental friendliness. However, current sodium-ion battery cathode materials mainly focus on layered oxides and polyanionic materials. The poor conductivity of polyanionic materials results in poor rate performance, i.e., rapid charge and discharge capability, requiring coating processes, which are costly and complex. Layered oxides can be further divided into monocrystalline and polycrystalline types. Monocrystalline materials have no grain boundary structure, good particle integrity, and can significantly suppress crack propagation, exhibiting excellent cycle stability. However, monocrystalline materials have a single sodium ion diffusion path. Polycrystalline materials have abundant grain boundaries and pores, providing more sodium ion transport channels, and their cost is much lower than that of monocrystalline materials. However, polycrystalline materials have high grain boundary resistance and poor electronic conductivity, leading to poor rate performance, especially severe capacity decay and intensified polarization at high rates. Furthermore, polycrystalline materials have poor cycle stability. Summary of the Invention

[0003] Therefore, it is necessary to address the above problems by providing a sodium-ion battery cathode material, its preparation method, cathode sheet, sodium-ion battery, and its application. The sodium-ion battery cathode material obtained by the preparation method has excellent rate performance and cycle stability.

[0004] A method for preparing a sodium-ion battery cathode material includes: mixing a polycrystalline layered oxide matrix with an organic carbon source, and then performing melt infiltration and carbonization treatment under pressure to obtain the sodium-ion battery cathode material; wherein the organic carbon source has a melting point of less than or equal to 200°C and a viscosity of 50 mPa·s-300 mPa·s when melted.

[0005] In one embodiment, the organic carbon source is selected from at least one of the following: a mixture of choline salts and polyols, a mixture of citric acid and / or malic acid and urea, alicyclic epoxy resins, and ionic liquid oligomers with a molecular weight of 500 g / mol to 3000 g / mol.

[0006] In one embodiment, the choline salt is selected from at least one of choline chloride and choline bicarbonate, and the polyol is selected from at least one of glycerol, butanediol, and ethylene glycol;

[0007] And / or, the alicyclic epoxy resin is selected from at least one of dicyclopentadiene dioxide epoxy resin and 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate epoxy resin.

[0008] And / or, the ionic liquid oligomer is selected from at least one of imidazole-type ionic liquid oligomers and pyrrolidine-onium-type ionic liquid oligomers.

[0009] In one embodiment, in the step of mixing the polycrystalline layered oxide matrix with an organic carbon source, the mass of the organic carbon source is 2%-10% of the mass of the polycrystalline layered oxide matrix.

[0010] In one embodiment, during the melt infiltration step, the temperature is higher than the melting point of the organic carbon source, the pressure is 0.5 MPa-20 MPa, and the time is 0.5 h-2 h.

[0011] And / or, in the carbonization process, the temperature is 600℃-800℃, the pressure is 0.5MPa-2MPa, and the time is 2h-5h.

[0012] In one embodiment, the melt infiltration step is performed at a temperature of 200°C-400°C, a pressure of 0.5MPa-2MPa, and a time of 0.5h-2h.

[0013] A sodium-ion battery cathode material prepared by the aforementioned method.

[0014] A positive electrode sheet prepared using the aforementioned sodium-ion battery positive electrode material.

[0015] A sodium-ion battery, wherein the sodium-ion battery uses the aforementioned positive electrode.

[0016] An application of the sodium-ion battery described above in a battery module or battery pack.

[0017] In the preparation method of the sodium-ion battery cathode material of this invention, an organic carbon source with a melting point below 200°C and a viscosity in the range of 50 mPa·s to 300 mPa·s during melting can penetrate to the grain boundaries of the polycrystalline layered oxide matrix through capillary action during the melt infiltration step. After carbonization, a continuous carbon network distributed along the grain boundaries and a carbon layer covering the polycrystalline layered oxide matrix can be formed, thereby constructing a three-dimensional conductive pathway of "grain boundary-surface layer", significantly reducing grain boundary resistance and enhancing conductivity. At the same time, during the carbonization process, the reducing gas generated by the decomposition of the organic carbon source can reduce the surface of the polycrystalline layered oxide matrix, forming oxygen vacancies, thereby enhancing the interfacial electron transport of the carbon layer / polycrystalline layered oxide matrix. Therefore, the sodium-ion battery cathode material obtained by the above preparation method has excellent rate performance and cycle stability. Detailed Implementation

[0018] To facilitate understanding of the present invention, it will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. Rather, these embodiments or examples are provided to make the disclosure of the present invention more thorough and complete.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments or examples only and is not intended to limit the invention. The optional scope of the term "and / or" as used herein includes any one of two or more of the related listed items, as well as any and all combinations of the related listed items, including any two related listed items, any more related listed items, or a combination of all related listed items.

[0020] In this invention, numerical ranges are involved. Unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe features or characteristics, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are included.

[0021] The method for preparing sodium-ion battery cathode material provided by the present invention includes: mixing a polycrystalline layered oxide matrix with an organic carbon source, and then performing melt infiltration and carbonization treatment under pressure to obtain sodium-ion battery cathode material, wherein the melting point of the organic carbon source is less than or equal to 200°C, and the viscosity at melting point is 50 mPa·s-300 mPa·s.

[0022] It is understood that this invention does not impose any requirements on the selection of the polycrystalline layered oxide matrix, such as Na. 0.6 Ni 0.3 Fe 0.2 Mn 0.5 O2, NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, Na 2 / 3 Ni 1 / 3 Mn 2 / 3 O2, Na 2 / 3 Ni 1 / 3 Mn 1 / 3 Co 1 / 3O2, etc. Furthermore, a polycrystalline layered oxide precursor can be synthesized first via a co-precipitation method, and then the polycrystalline layered oxide precursor can be ball-milled and mixed with a sodium source before being calcined at high temperature to obtain the polycrystalline layered oxide matrix.

[0023] In the preparation method of the sodium-ion battery cathode material of this invention, during the melt infiltration step under pressure, an organic carbon source with a melting point below 200°C and a viscosity in the range of 50 mPa·s to 300 mPa·s during melting can penetrate to the grain boundaries of the polycrystalline layered oxide matrix through capillary action. After carbonization, the organic carbon source can form a continuous carbon network distributed along the grain boundaries and a carbon layer coating the polycrystalline layered oxide matrix, thereby constructing a three-dimensional conductive pathway of "grain boundary-surface" within the polycrystalline layered oxide matrix, significantly reducing grain boundary resistance and enhancing conductivity. Simultaneously, during carbonization, the reducing gas generated by the decomposition of the organic carbon source can also reduce the surface of the polycrystalline layered oxide matrix, forming oxygen vacancies, thereby enhancing interfacial electron transport between the carbon layer and the polycrystalline layered oxide matrix. Therefore, the sodium-ion battery cathode material obtained by the above preparation method exhibits excellent rate performance and cycle stability.

[0024] In some embodiments, the organic carbon source is selected from a mixture of choline salts and polyols, wherein the quaternary ammonium cation ([Ch]) in the choline salt is... + The choline salt can form strong hydrogen bonds with the hydroxyl groups (-OH) of polyols, disrupting the original ionic lattice structure and significantly lowering the melting point and viscosity of the mixture. This facilitates efficient and rapid penetration to grain boundaries. The choline salt is selected from at least one of choline chloride and choline bicarbonate, and the polyol is selected from at least one of glycerol, butanediol, and ethylene glycol, such as mixtures of choline chloride and glycerol, choline chloride and butanediol, choline bicarbonate and glycerol, or choline bicarbonate and ethylene glycol. To achieve optimal melting point and viscosity characteristics, the molar ratio of the choline salt to the polyol is preferably 1:2 to 1:5.

[0025] In some embodiments, the organic carbon source is selected from mixtures of citric acid and / or malic acid with urea, such as mixtures of citric acid and urea, mixtures of malic acid and urea, or mixtures of citric acid, malic acid, and urea. Urea (containing -NH2 and C=O groups) can bind with organic acids (containing -COOH or -OH groups) through hydrogen bonds, disrupting the original crystal arrangement, forming a eutectic solvent, lowering the melting point and viscosity, and thus efficiently and rapidly penetrating to grain boundaries. To achieve optimal melting point and viscosity characteristics, the mass fraction of urea in the mixture is preferably 20%-50%.

[0026] In some embodiments, the organic carbon source is selected from alicyclic epoxy resins, whose fluidity allows them to penetrate well into the grain boundaries of the polycrystalline layered oxide matrix. Optionally, the alicyclic epoxy resin is selected from at least one of dicyclopentadiene dioxide epoxy resin and 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate epoxy resin.

[0027] In some embodiments, the organic carbon source is selected from ionic liquid oligomers with a molecular weight of 500 g / mol to 3000 g / mol. The small molecular size of these ionic liquid oligomers allows them to penetrate well into the grain boundaries of the polycrystalline layered oxide matrix. Optionally, the ionic liquid oligomer is selected from at least one of imidazole-type ionic liquid oligomers, such as 1-vinyl-3-ethylimidazolium bromide, and pyrrolidine-onium-type ionic liquid oligomers, such as 1-amino-1-methylpyrrolidineonium bis(trifluoromethanesulfonyl)imide.

[0028] In order to enable the organic carbon source to fully penetrate into the grain boundaries, so that after carbonization there is an amorphous carbon distribution at the grain boundaries, thereby forming a continuous carbon network distributed along the grain boundaries and a carbon layer covering the polycrystalline layered oxide matrix, a three-dimensional conductive path of "grain boundary-surface" is constructed in the polycrystalline layered oxide matrix. In the step of mixing the polycrystalline layered oxide matrix with the organic carbon source, the mass of the organic carbon source is preferably 2%-10% of the mass of the polycrystalline layered oxide matrix.

[0029] Similarly, in order to enable the organic carbon source to fully penetrate to the grain boundaries, in the melt penetration step, the temperature is higher than the melting point of the organic carbon source. More preferably, the temperature is 200℃-400℃, the pressure is 0.5MPa-20MPa, more preferably 0.5MPa-2MPa, and the time is 0.5h-2h.

[0030] Optionally, in the carbonization process, the temperature is preferably 600℃-800℃, the pressure is preferably 0.5MPa-2MPa, and the time is preferably 2h-5h, so that the organic carbon source can be carbonized into amorphous carbon. At the same time, the reducing gas generated by the decomposition of the organic carbon source during the carbonization process can fully reduce the surface of the polycrystalline layered oxide matrix to form oxygen vacancies.

[0031] It should be noted that the melt infiltration step and the carbonization step of the present invention are preferably carried out under an inert atmosphere such as nitrogen or argon.

[0032] Furthermore, the present invention also provides a sodium-ion battery cathode material obtained by the preparation method described above. The sodium-ion battery cathode material includes a polycrystalline layered oxide matrix and amorphous carbon. The amorphous carbon coats the polycrystalline layered oxide matrix to form a carbon layer and extends into the grain boundaries of the polycrystalline layered oxide matrix.

[0033] Furthermore, the present invention also provides a positive electrode sheet prepared using the aforementioned sodium-ion battery positive electrode material.

[0034] It is understood that the positive electrode sheet includes sodium-ion battery positive electrode material, conductive agent, and binder, etc. The present invention does not have special requirements on the mass ratio of sodium-ion battery positive electrode material, conductive agent, and binder in the positive electrode sheet. Conventional selection and control are sufficient. There are also no special requirements on the selection of conductive agent and binder. For example, the conductive agent is selected from carbon nanotubes (CNT), conductive carbon black (Super P), acetylene black, Ketjen black, and conductive graphite, etc., and the binder is selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), sodium alginate, styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), etc. The present invention will not elaborate further here.

[0035] Furthermore, the present invention also provides a sodium-ion battery, wherein the sodium-ion battery uses the aforementioned positive electrode sheet.

[0036] It is understood that sodium-ion batteries also include negative electrode sheets, separators, and electrolytes. This invention does not have special requirements for the negative electrode sheets, separators, and electrolytes of sodium-ion batteries; conventional designs are sufficient. For example, the active material of the negative electrode sheet is selected from hard carbon materials, soft carbon materials, graphite, etc.; the conductive agent is selected from carbon nanotubes (CNT), conductive carbon black (Super P), acetylene black, Ketjen black, and conductive graphite, etc.; the binder is selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), sodium alginate, styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), etc.; the separator is selected from polypropylene separators (PP), polyimide separators (PI), polyethylene separators (PE), ceramic-coated separators, etc.; the electrolyte contains sodium salts and organic solvents, wherein the sodium salt is selected from NaPF6, etc., and the organic solvent is selected from ethylene carbonate (EC), dimethyl carbonate (DMC), etc., which will not be elaborated further in this invention.

[0037] This invention does not impose any requirements on the shape of the sodium-ion battery; it can be a cylindrical battery, a square battery, etc.

[0038] The present invention also provides an application of sodium-ion batteries in battery modules or battery packs, thereby providing battery modules or battery packs using the sodium-ion batteries of the present invention with excellent charge and discharge performance and longer service life.

[0039] The technical solution of the present invention will be further described below through specific embodiments. However, those skilled in the art will understand that the following embodiments are only for illustrating the present invention and should not be regarded as limiting the scope of the present invention. Unless otherwise specified, specific conditions in the embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used without specified manufacturers are all commercially available conventional products.

[0040] Example 1

[0041] Will Na 0.6 Ni 0.3 Fe 0.2 Mn 0.5 O2 is mixed with an organic carbon source, wherein the mass of the organic carbon source is Na. 0.6 Ni 0.3 Fe 0.2 Mn 0.5 The composition of the sodium-ion battery cathode material is 5% by mass of O2, and the organic carbon source includes choline chloride and glycerol (melting point 35℃, viscosity 105 mPa·s) in a molar ratio of 1:2. Under argon protection, the temperature is increased to 100℃ at 2℃ / min and the pressure is 1 MPa, and the temperature and pressure are maintained for 2 hours. Then, the temperature is increased to 600℃ and the pressure is 1 MPa, and the temperature and pressure are maintained for 5 hours. Finally, the temperature is reduced to room temperature to obtain the cathode material.

[0042] The sodium-ion battery cathode material, Super P, MWCNT, and PVDF prepared above were added to NMP solvent at a mass ratio of 96:2:1:1. The mixture was first ultrasonically dispersed at 500W for 30 minutes, and then mechanically stirred at 800rpm for 2 hours to form a cathode slurry. The cathode slurry was then uniformly coated onto aluminum foil using a coating machine. The coated electrode sheet was then rolled, slit, and sheeted to obtain the cathode sheet.

[0043] Hard carbon material, Super P, and CMC are mixed in a mass ratio of 97:1.5:1.5 to form a negative electrode slurry. Then, the negative electrode slurry is uniformly coated onto copper foil using a coating machine, and the coated electrode is rolled, slit, and sheeted to obtain the negative electrode sheet.

[0044] A ceramic-coated diaphragm was obtained by coating a 3μm thick Al2O3@BN composite ceramic coating on a 9μm thick PE base film, wherein the mass fraction of BN in the composite ceramic coating was 30wt%.

[0045] NaPF6 was used as the sodium salt. NaPF6 was dissolved in a mixed solvent of EC / DMC with a volume ratio of 4:6. Then, 1 wt% of fluoroethylene carbonate (FEC) was added as a film-forming additive to obtain the electrolyte. The concentration of sodium salt in the electrolyte was 1.0 mol / L, and the conductivity of the electrolyte was 12 mS / cm (25℃).

[0046] The battery adopts a full tab design, with positive electrode, negative electrode and separator stacked alternately in the order of "positive electrode-separator-negative electrode" and wound into a bare cell; after flattening and shaping the end face, the current collector end face is laser welded to bring out the full tab; then it is put into the casing, injected with electrolyte and sealed, and finally made into a 32700 cylindrical battery.

[0047] Example 2

[0048] Will Na 0.6 Ni 0.3 Fe 0.2 Mn 0.5 O2 is mixed with an organic carbon source, wherein the mass of the organic carbon source is Na. 0.6 Ni 0.3 Fe 0.2 Mn 0.5 The oxygen content is 5% by mass, and the organic carbon source includes citric acid and urea (melting point 80℃, viscosity 150 mPa·s at 80℃) in a mass ratio of 2:1. Under argon protection, the temperature is increased to 150℃ at 2℃ / min and the pressure is 2MPa, and the temperature and pressure are maintained for 2 hours. Then, the temperature is increased to 700℃ and the pressure is 2MPa, and the temperature and pressure are maintained for 5 hours. Finally, the temperature is reduced to room temperature to obtain the sodium-ion battery cathode material.

[0049] The sodium-ion battery cathode material, Super P, MWCNT, and PVDF prepared above were added to NMP solvent at a mass ratio of 96:2:1:1. The mixture was first ultrasonically dispersed at 500W for 30 minutes, and then mechanically stirred at 800rpm for 2 hours to form a cathode slurry. The cathode slurry was then uniformly coated onto aluminum foil using a coating machine. The coated electrode sheet was then rolled, slit, and sheeted to obtain the cathode sheet.

[0050] Hard carbon material, Super P, and CMC are mixed in a mass ratio of 97:1.5:1.5 to form a negative electrode slurry. Then, the negative electrode slurry is uniformly coated onto copper foil using a coating machine, and the coated electrode is rolled, slit, and sheeted to obtain the negative electrode sheet.

[0051] A ceramic-coated diaphragm was obtained by coating a 3μm thick Al2O3@BN composite ceramic coating on a 9μm thick PE base film, wherein the mass fraction of BN in the composite ceramic coating was 30wt%.

[0052] NaPF6 was used as the sodium salt. NaPF6 was dissolved in a mixed solvent of EC / DMC with a volume ratio of 4:6. Then, 1 wt% of fluoroethylene carbonate (FEC) was added as a film-forming additive to obtain the electrolyte. The concentration of sodium salt in the electrolyte was 1.0 mol / L, and the conductivity of the electrolyte was 12 mS / cm (25℃).

[0053] The battery adopts a full tab design, with positive electrode, negative electrode and separator stacked alternately in the order of "positive electrode-separator-negative electrode" and wound into a bare cell; after flattening and shaping the end face, the current collector end face is laser welded to bring out the full tab; then it is put into the casing, injected with electrolyte and sealed, and finally made into a 32700 cylindrical battery.

[0054] Example 3

[0055] Will Na 0.6 Ni 0.3 Fe 0.2 Mn 0.5 O2 is mixed with dicyclopentadiene dioxide epoxy resin (melting point 180℃, viscosity 200 mPa·s at 180℃), wherein the mass of dicyclopentadiene dioxide epoxy resin is Na. 0.6 Ni 0.3 Fe 0.2 Mn 0.5 5% of the mass of O2. Under argon protection, the temperature is increased to 200℃ at 2℃ / min and the pressure is 2MPa, and the temperature and pressure are maintained for 2h. Then the temperature is increased to 800℃ and the pressure is 1MPa, and the temperature and pressure are maintained for 5h. Finally, the temperature is reduced to room temperature to obtain the sodium-ion battery cathode material.

[0056] The sodium-ion battery cathode material, Super P, MWCNT, and PVDF prepared above were added to NMP solvent at a mass ratio of 96:2:1:1. The mixture was first ultrasonically dispersed at 500W for 30 minutes, and then mechanically stirred at 800rpm for 2 hours to form a cathode slurry. The cathode slurry was then uniformly coated onto aluminum foil using a coating machine. The coated electrode sheet was then rolled, slit, and sheeted to obtain the cathode sheet.

[0057] Hard carbon material, Super P, and CMC are mixed in a mass ratio of 97:1.5:1.5 to form a negative electrode slurry. Then, the negative electrode slurry is uniformly coated onto copper foil using a coating machine, and the coated electrode is rolled, slit, and sheeted to obtain the negative electrode sheet.

[0058] A ceramic-coated diaphragm was obtained by coating a 3μm thick Al2O3@BN composite ceramic coating on a 9μm thick PE base film, wherein the mass fraction of BN in the composite ceramic coating was 30wt%.

[0059] NaPF6 was used as the sodium salt. NaPF6 was dissolved in a mixed solvent of EC / DMC with a volume ratio of 4:6. Then, 1 wt% of fluoroethylene carbonate (FEC) was added as a film-forming additive to obtain the electrolyte. The concentration of sodium salt in the electrolyte was 1.0 mol / L, and the conductivity of the electrolyte was 12 mS / cm (25℃).

[0060] The battery adopts a full tab design, with positive electrode, negative electrode and separator stacked alternately in the order of "positive electrode-separator-negative electrode" and wound into a bare cell; after flattening and shaping the end face, the current collector end face is laser welded to bring out the full tab; then it is put into the casing, injected with electrolyte and sealed, and finally made into a 32700 cylindrical battery.

[0061] Example 4

[0062] Will Na 0.6 Ni 0.3 Fe 0.2 Mn 0.5 O2 is mixed with 1-vinyl-3-ethylimidazolium bromide oligomers with an average molecular weight of 500 (melting point 130℃, viscosity 80 mPa·s at 130℃), wherein the mass of the 1-vinyl-3-ethylimidazolium bromide oligomer is Na. 0.6 Ni 0.3 Fe 0.2 Mn 0.5 The mass of O2 was 10%. Under argon protection, the temperature was increased to 180℃ at 2℃ / min and the pressure was 0.5MPa, and the temperature and pressure were maintained for 2h. Then the temperature was increased to 600℃ and the pressure was 1MPa, and the temperature and pressure were maintained for 5h. Finally, the temperature was reduced to room temperature to obtain the sodium-ion battery cathode material.

[0063] The sodium-ion battery cathode material, Super P, MWCNT, and PVDF prepared above were added to NMP solvent at a mass ratio of 96:2:1:1. The mixture was first ultrasonically dispersed at 500W for 30 minutes, and then mechanically stirred at 800rpm for 2 hours to form a cathode slurry. The cathode slurry was then uniformly coated onto aluminum foil using a coating machine. The coated electrode sheet was then rolled, slit, and sheeted to obtain the cathode sheet.

[0064] Hard carbon material, Super P, and CMC are mixed in a mass ratio of 97:1.5:1.5 to form a negative electrode slurry. Then, the negative electrode slurry is uniformly coated onto copper foil using a coating machine, and the coated electrode is rolled, slit, and sheeted to obtain the negative electrode sheet.

[0065] A ceramic-coated diaphragm was obtained by coating a 3μm thick Al2O3@BN composite ceramic coating on a 9μm thick PE base film, wherein the mass fraction of BN in the composite ceramic coating was 30wt%.

[0066] NaPF6 was used as the sodium salt. NaPF6 was dissolved in a mixed solvent of EC / DMC with a volume ratio of 4:6. Then, 1 wt% of fluoroethylene carbonate (FEC) was added as a film-forming additive to obtain the electrolyte. The concentration of sodium salt in the electrolyte was 1.0 mol / L, and the conductivity of the electrolyte was 12 mS / cm (25℃).

[0067] The battery adopts a full tab design, with positive electrode, negative electrode and separator stacked alternately in the order of "positive electrode-separator-negative electrode" and wound into a bare cell; after flattening and shaping the end face, the current collector end face is laser welded to bring out the full tab; then it is put into the casing, injected with electrolyte and sealed, and finally made into a 32700 cylindrical battery.

[0068] Comparative Example 1

[0069] The only difference between Comparative Example 1 and Example 1 is that Na was directly added. 0.6 Ni 0.3 Fe 0.2 Mn 0.5 O2, Super P, MWCNT, and PVDF are added to NMP solvent in a mass ratio of 96:2:1:1. The mixture is first ultrasonically dispersed at 500W for 30 minutes, and then mechanically stirred at 800rpm for 2 hours to form a positive electrode slurry. The positive electrode slurry is then uniformly coated onto aluminum foil using a coating machine. The coated electrode is then rolled, slit, and sheeted to obtain the positive electrode sheet.

[0070] Comparative Example 2

[0071] The only difference between Comparative Example 2 and Example 1 is that Na is used... 0.6 Ni 0.3 Fe 0.2 Mn 0.5 O2 is mixed with phenolic resin, wherein the mass of phenolic resin is Na. 0.6 Ni 0.3 Fe 0.2 Mn 0.5 The mass of O2 is 10%. Under argon protection, the temperature is increased to 700℃ at 2℃ / min and the pressure is 1MPa. The temperature and pressure are maintained for 5 hours, and finally cooled to room temperature to obtain the sodium-ion battery cathode material.

[0072] Comparative Example 3

[0073] The only difference between Comparative Example 3 and Example 1 is that Na is used... 0.6 Ni 0.3 Fe 0.2 Mn 0.5 O2 is mixed with glucose (melting point 150℃, viscosity >1000 mPa·s at 150℃), wherein the mass of glucose is Na. 0.6 Ni 0.3 Fe 0.2 Mn 0.5 The mass of O2 is 10%. Under argon protection, the temperature is increased to 200℃ at 2℃ / min and the pressure is 1MPa. The temperature and pressure are maintained for 2h. Then the temperature is increased to 700℃ and the pressure is 2MPa. The temperature and pressure are maintained for 5h. Finally, the temperature is reduced to room temperature to obtain the sodium-ion battery cathode material.

[0074] Comparative Example 4

[0075] The only difference between Comparative Example 4 and Example 1 is that Na is used... 0.6 Ni 0.3 Fe 0.2 Mn 0.5 O2 is mixed with sucrose (melting point 190℃, viscosity >1000 mPa·s at 190℃), wherein the mass of sucrose is Na. 0.6 Ni 0.3 Fe 0.2 Mn 0.5 O2 mass 5%. Under argon protection, the temperature is increased to 200℃ at 2℃ / min and the pressure is 1MPa, and the temperature and pressure are maintained for 2h. Then the temperature is increased to 700℃ and held for 5h. Finally, the temperature is reduced to room temperature to obtain sodium-ion battery cathode material.

[0076] Comparative Example 5

[0077] The only difference between Comparative Example 5 and Example 3 is that Na is used... 0.6 Ni 0.3 Fe 0.2 Mn 0.5 O2 is mixed with dicyclopentadiene dioxide epoxy resin (melting point 180℃, viscosity 200 mPa·s at 180℃), wherein the mass of dicyclopentadiene dioxide epoxy resin is Na. 0.6 Ni 0.3 Fe 0.2 Mn 0.5 O2 is 5% of its mass. Under argon protection, the temperature is increased to 200℃ at 2℃ / min and held for 2h, then increased to 800℃ and held for 5h, and finally cooled to room temperature to obtain the sodium-ion battery cathode material.

[0078] The sodium-ion batteries of Examples 1-4 and Comparative Examples 1-5 were subjected to rate performance tests. The test standards were as follows: constant current discharge: 0.2C to 2.75V; rest for 5 min; constant current and constant voltage charging: 0.2C to 4.45V, cutoff current: 0.05C; rest for 5 min; cycled 3 times; then the discharge and charge rates were changed to 0.5C, 1C, 5C, 10C, 30C, 35C and 40C respectively. The results are shown in Table 1.

[0079] Table 1. Rate performance test results of sodium-ion batteries

[0080]

[0081] As shown in Table 1, the sodium-ion battery cathode material prepared by the method of the present invention has excellent rate performance and cycle stability.

[0082] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0083] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing a sodium-ion battery cathode material, characterized in that, include: A polycrystalline layered oxide matrix is ​​mixed with an organic carbon source, and then melt-infiltrated and carbonized under pressure to obtain a sodium-ion battery cathode material. The organic carbon source has a melting point of less than or equal to 200°C and a viscosity of 50 mPa·s-300 mPa·s when melted. The organic carbon source is selected from at least one of the following: a mixture of choline salts and polyols, a mixture of citric acid and / or malic acid and urea, alicyclic epoxy resin, and an ionic liquid oligomer with a molecular weight of 500 g / mol-3000 g / mol.

2. The method for preparing the sodium-ion battery cathode material according to claim 1, characterized in that, The choline salts are selected from at least one of choline chloride and choline bicarbonate, and the polyols are selected from at least one of glycerol, butanediol, and ethylene glycol. And / or, the alicyclic epoxy resin is selected from at least one of dicyclopentadiene dioxide epoxy resin and 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate epoxy resin. And / or, the ionic liquid oligomer is selected from at least one of imidazole-type ionic liquid oligomers and pyrrolidine-onium-type ionic liquid oligomers.

3. The method for preparing the sodium-ion battery cathode material according to claim 1, characterized in that, In the step of mixing the polycrystalline layered oxide matrix with an organic carbon source, the mass of the organic carbon source is 2%-10% of the mass of the polycrystalline layered oxide matrix.

4. The method for preparing the sodium-ion battery cathode material according to claim 1, characterized in that, In the melt infiltration step, the temperature is higher than the melting point of the organic carbon source, the pressure is 0.5 MPa-20 MPa, and the time is 0.5 h-2 h. And / or, in the carbonization process, the temperature is 600℃-800℃, the pressure is 0.5MPa-2MPa, and the time is 2h-5h.

5. The method for preparing the sodium-ion battery cathode material according to claim 4, characterized in that, In the melt infiltration step, the temperature is 200℃-400℃, the pressure is 0.5MPa-2MPa, and the time is 0.5h-2h.

6. A sodium-ion battery cathode material prepared by any one of claims 1 to 5.

7. A positive electrode sheet prepared using the sodium-ion battery positive electrode material as described in claim 6.

8. A sodium-ion battery, characterized in that, The sodium-ion battery uses the positive electrode as described in claim 7.

9. The application of the sodium-ion battery as described in claim 8 in a battery module or battery pack.

Images