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

Abstract

The invention relates to a sodium-ion battery positive electrode material and a preparation method thereof, a positive plate, a sodium-ion battery and application thereof, the preparation method comprises the following steps: mixing a polycrystalline layered oxide matrix with an organic carbon source, and then carrying out melt permeation and carbonization treatment under a pressurization condition to obtain the sodium-ion battery positive electrode material, wherein the melting point of the organic carbon source is below 200 DEG C, and the viscosity during melting is 50-300 mPa.s. The organic carbon source can permeate into the grain boundary of the polycrystalline layered oxide matrix through the capillary action in the melt permeation step, and after carbonization, a continuous carbon network distributed along the grain boundary and a carbon layer wrapping the polycrystalline layered oxide matrix can be formed; meanwhile, in the carbonization process, reducing gas generated by decomposition of the organic carbon source can reduce the surface of the polycrystalline layered oxide matrix, and oxygen vacancies are formed. Therefore, the sodium-ion battery positive electrode material obtained by the preparation method has excellent rate capability and cycling stability.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular to a sodium ion battery positive electrode material and a preparation method thereof, a positive electrode sheet, a sodium ion battery and applications thereof. Background Art

[0002] Driven by global demand for clean energy, sodium-ion batteries (SIBs) are considered an important candidate technology to replace lithium-ion batteries due to their abundant resources, low cost, and environmental friendliness. However, the cathode materials of existing SIBs are mainly layered oxides and polyanion materials. The poor conductivity of polyanions prevents them from having excellent rate performance, i.e., fast charge and discharge capabilities. They rely on coating processes, which are costly and complex. Layered oxides can be divided into single crystal and polycrystalline. Single crystal materials have no grain boundary structure and good particle integrity, which can significantly inhibit crack propagation and have excellent cycling stability. However, single crystal materials have a single sodium ion diffusion path. Polycrystalline materials have abundant grain boundaries and pores, which can provide more sodium ion transmission channels and are much cheaper than single crystal materials. However, polycrystalline materials have high grain boundary resistance and poor electronic conductivity, resulting in poor rate performance. In particular, at high rates, the capacity decay is severe, polarization is aggravated, and the cycling stability of polycrystalline materials is poor. Summary of the Invention

[0003] Based on this, it is necessary to provide a sodium ion battery positive electrode material and its preparation method, a positive electrode sheet, a sodium ion battery and its application to address the above problems. The sodium ion battery positive electrode material obtained by the preparation method has excellent rate performance and cycle stability.

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

[0005] In one embodiment, the organic carbon source is selected from at least one of a mixture of choline salts and polyols, a mixture of citric acid and / or malic acid and urea, an alicyclic epoxy resin, and an ionic liquid oligomer with a molecular weight of 500 g / mol-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, butylene glycol, and ethylene glycol;

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

[0008] And / or, the ionic liquid oligomer is at least one selected from imidazolium-type ionic liquid oligomers and pyrrolidinium-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, in the melt infiltration step, the temperature is greater 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 step, the temperature is 600° C.-800° C., the pressure is 0.5 MPa-2 MPa, and the time is 2 h-5 h.

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

[0013] A sodium ion battery positive electrode material obtained by adopting the preparation method.

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

[0015] A sodium ion battery using the positive electrode sheet.

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

[0017] In the preparation method of the sodium ion battery positive electrode material of the present invention, the organic carbon source with a melting point below 200°C and a viscosity in the range of 50mPa.s-300mPa.s when melted can penetrate into the grain boundaries of the polycrystalline layered oxide matrix by 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 path of "grain boundary-surface layer", significantly reducing the grain boundary resistance and enhancing the 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 interface electron transport of the carbon layer / polycrystalline layered oxide matrix. Therefore, the sodium ion battery positive electrode material obtained by the preparation method has excellent rate performance and cycle stability. DETAILED DESCRIPTION

[0018] To facilitate understanding of the present invention, the present invention 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. On the contrary, the purpose of providing these embodiments or examples is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the technical field of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific embodiments or embodiments and are not intended to limit the present invention. The optional scope of the term "and / or" used herein includes any one of two or more related listed items, and also includes any and all combinations of related listed items, including any two related listed items, any more related listed items, or the combination of all related listed items.

[0020] In the present invention, when referring to numerical ranges, 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 such minimum and maximum values. Furthermore, when a range refers to an integer, every integer between the minimum and maximum values of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges subsumed therein.

[0021] The present invention provides a method for preparing a sodium ion battery positive electrode material, comprising: 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 positive electrode material, wherein the melting point of the organic carbon source is less than or equal to 200°C and the viscosity when melted is 50mPa.s-300mPa.s.

[0022] It is understood that the present invention does not impose any requirements on the selection of 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 by a coprecipitation method, and then the polycrystalline layered oxide precursor is mixed with a sodium source by ball milling and then calcined at a high temperature to obtain the polycrystalline layered oxide matrix.

[0023] In the preparation method of the sodium ion battery positive electrode material of the present invention, in the step of melt infiltration under pressurized conditions, an organic carbon source with a melting point below 200°C and a viscosity in the range of 50mPa.s-300mPa.s when melted can penetrate into the grain boundaries of the polycrystalline layered oxide matrix by capillary action, so that after carbonization treatment, the organic carbon source can be carbonized in situ to 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 path of "grain boundary-surface layer" in the polycrystalline layered oxide matrix, significantly reducing the grain boundary resistance and enhancing the conductivity. At the same time, during the carbonization process, the reducing gas generated by the decomposition of the organic carbon source can also reduce the surface of the polycrystalline layered oxide matrix to form oxygen vacancies, thereby enhancing the interfacial electron transport between the carbon layer and the polycrystalline layered oxide matrix. Therefore, the sodium ion battery positive electrode material obtained by the preparation method has 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] + ) can form strong hydrogen bonds with the hydroxyl groups (-OH) of the polyol, disrupting the original ionic lattice structure, significantly lowering the melting point and viscosity of the mixture, which facilitates efficient and rapid penetration into 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, butylene glycol, and ethylene glycol, such as mixtures of choline chloride and glycerol, choline chloride and butylene glycol, choline chloride, glycerol, and butylene glycol, choline bicarbonate and glycerol, and 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 1:2-1:5.

[0025] In some embodiments, the organic carbon source is selected from a mixture of citric acid and / or malic acid with urea, such as a mixture of citric acid and urea, a mixture of malic acid and urea, or a mixture of citric acid, malic acid, and urea. Urea (containing -NH2 and C=O groups) can hydrogen bond with organic acids (containing -COOH or -OH groups), disrupting the original crystal arrangement to form a deep eutectic solvent, lowering the melting point and viscosity, and allowing efficient and rapid penetration into 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 a cycloaliphatic epoxy resin. The fluidity of the cycloaliphatic epoxy resin enables it to penetrate well into the grain boundaries of the polycrystalline layered oxide matrix. Optionally, the cycloaliphatic 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 an ionic liquid oligomer having a molecular weight of 500 g / mol to 3000 g / mol. Ionic liquid oligomers have a small molecular size and can penetrate well into the grain boundaries of the polycrystalline layered oxide matrix. Alternatively, the ionic liquid oligomer is selected from at least one of an imidazolium-type ionic liquid oligomer such as 1-vinyl-3-ethylimidazolium bromide oligomer, and a pyrrolidinium-type ionic liquid oligomer such as 1-amino-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide salt.

[0028] In order to enable the organic carbon source to fully penetrate into the grain boundaries, so that amorphous carbon is distributed at the grain boundaries after carbonization, and then form 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 allow the organic carbon source to fully penetrate into the grain boundaries, in the melt infiltration step, the temperature is greater than the melting point of the organic carbon source. Furthermore, the temperature is preferably 200°C-400°C, the pressure is preferably 0.5MPa-20MPa, further preferably 0.5MPa-2MPa, and the time is preferably 0.5h-2h.

[0030] Optionally, in the carbonization treatment step, the temperature is preferably 600°C-800°C, 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 treatment 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 positive electrode material obtained by the preparation method, wherein the sodium ion battery positive electrode material includes a polycrystalline layered oxide matrix and amorphous carbon, wherein 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 above-mentioned sodium ion battery positive electrode material.

[0034] It can be understood that the positive electrode sheet includes a sodium ion battery positive electrode material, a conductive agent and a binder, etc. The present invention has no special requirements for the mass ratio of the sodium ion battery positive electrode material, the conductive agent and the binder in the positive electrode sheet, and can be selected and controlled according to conventional methods. There are no special requirements for the selection of the conductive agent and the 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 be repeated here.

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

[0036] It is understood that sodium-ion batteries also include a negative electrode sheet, a separator, and an electrolyte. The present invention does not have any special requirements for the negative electrode sheet, separator, and electrolyte of the sodium-ion battery, and conventional designs can be used. 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 (CNTs), 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 separator (PP), polyimide separator (PI), polyethylene separator (PE), ceramic coated separator, etc. The electrolyte contains a sodium salt and an organic solvent, wherein the sodium salt is selected from NaPF6, etc., and the organic solvent is selected from ethylene carbonate (EC), dimethyl carbonate (DMC), etc. The present invention will not be repeated here.

[0037] The present invention does not impose any requirements on the shape of the sodium ion battery, which can be a cylindrical battery, a square battery, etc.

[0038] The present invention also provides an application of a sodium ion battery in a battery module or a battery pack, so that the battery module or battery pack using the sodium ion battery of the present invention has excellent charge and discharge performance and a longer service life.

[0039] Below, the technical solution of the present invention will be further described by the following specific examples. However, it will be understood by those skilled in the art that the following examples are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. Where specific conditions are not specified in the examples, the procedures were carried out according to conventional conditions or the conditions recommended by the manufacturer. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be obtained commercially.

[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, where the mass of the organic carbon source is Na 0.6 Ni 0.3 Fe 0.2 Mn 0.5 The reaction mixture contained 5% of the mass of O2, and the organic carbon source included choline chloride and glycerol (melting point 35°C, viscosity 105 mPa.s at 35°C) in a 1:2 molar ratio. Under argon protection, the temperature was raised to 100°C at a rate of 2°C / min and a pressure of 1 MPa. This was maintained for 2 hours. The temperature was then raised to 600°C and a pressure of 1 MPa. This was maintained for 5 hours before being cooled to room temperature to produce the positive electrode material for a sodium-ion battery.

[0042] The sodium-ion battery cathode material prepared above, Super P, MWCNT, and PVDF were added to NMP solvent at a mass ratio of 96:2:1:1. The mixture was first dispersed with 500W ultrasonic waves for 30 minutes, followed by mechanical stirring at 800 rpm for 2 hours to form a cathode slurry. The cathode slurry was then evenly coated onto aluminum foil using a coater. 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. The negative electrode slurry is then evenly coated on copper foil using a coater. The coated electrode sheet is then rolled, slit, and sheeted to obtain the negative electrode sheet.

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

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

[0046] Using a full-tab design, the positive electrode sheet, negative electrode sheet and separator are alternately stacked in the order of "positive electrode-separator-negative electrode" and wound into a bare battery cell; after the end face is flattened and shaped, the end face of the current collector is laser welded to lead out the full-tab; then it is placed in a shell, the electrolyte is injected and the battery is sealed to finally make 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, where the mass of the organic carbon source is Na 0.6 Ni 0.3 Fe 0.2 Mn 0.5 The reaction mixture was heated to 150°C at a rate of 2°C / min and maintained at a pressure of 2 MPa for 2 hours. The reaction mixture was then heated to 700°C and maintained at a pressure of 2 MPa for 5 hours before being cooled to room temperature to produce the positive electrode material for a sodium-ion battery.

[0049] The sodium-ion battery cathode material prepared above, Super P, MWCNT, and PVDF were added to NMP solvent at a mass ratio of 96:2:1:1. The mixture was first dispersed with 500W ultrasonic waves for 30 minutes, followed by mechanical stirring at 800 rpm for 2 hours to form a cathode slurry. The cathode slurry was then evenly coated onto aluminum foil using a coater. 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. The negative electrode slurry is then evenly coated on copper foil using a coater. The coated electrode sheet is then rolled, slit, and sheeted to obtain the negative electrode sheet.

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

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

[0053] Using a full-tab design, the positive electrode sheet, negative electrode sheet and separator are alternately stacked in the order of "positive electrode-separator-negative electrode" and wound into a bare battery cell; after the end face is flattened and shaped, the end face of the current collector is laser welded to lead out the full-tab; then it is placed in a shell, the electrolyte is injected and the battery is sealed to finally make 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 is 180℃, viscosity is 200mPa.s at 180℃), where the mass of dicyclopentadiene dioxide epoxy resin is Na 0.6 Ni 0.3 Fe 0.2 Mn 0.5 Under argon protection, the temperature was raised to 200°C at a rate of 2°C / min and a pressure of 2 MPa, and the temperature was maintained at this temperature for 2 hours. The temperature was then raised to 800°C and the pressure was 1 MPa, and the temperature was maintained at this temperature for 5 hours. Finally, the temperature was lowered to room temperature to obtain the positive electrode material for sodium ion batteries.

[0056] The sodium-ion battery cathode material prepared above, Super P, MWCNT, and PVDF were added to NMP solvent at a mass ratio of 96:2:1:1. The mixture was first dispersed with 500W ultrasonic waves for 30 minutes, followed by mechanical stirring at 800 rpm for 2 hours to form a cathode slurry. The cathode slurry was then evenly coated onto aluminum foil using a coater. 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. The negative electrode slurry is then evenly coated on copper foil using a coater. The coated electrode sheet is then rolled, slit, and sheeted to obtain the negative electrode sheet.

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

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

[0060] Using a full-tab design, the positive electrode sheet, negative electrode sheet and separator are alternately stacked in the order of "positive electrode-separator-negative electrode" and wound into a bare battery cell; after the end face is flattened and shaped, the end face of the current collector is laser welded to lead out the full-tab; then it is placed in a shell, the electrolyte is injected and the battery is sealed to finally make 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 oligomer with an average molecular weight of 500 (melting point of 130℃, viscosity of 80mPa.s at 130℃), wherein the mass of 1-vinyl-3-ethylimidazolium bromide oligomer is Na 0.6 Ni 0.3 Fe 0.2 Mn 0.5 Under argon protection, the temperature was raised to 180°C at a rate of 2°C / min and a pressure of 0.5 MPa, and the temperature was maintained at this temperature for 2 hours. The temperature was then raised to 600°C and the pressure was 1 MPa, and the temperature was maintained at this temperature for 5 hours. Finally, the temperature was lowered to room temperature to obtain the positive electrode material for sodium ion batteries.

[0063] The sodium-ion battery cathode material prepared above, Super P, MWCNT, and PVDF were added to NMP solvent at a mass ratio of 96:2:1:1. The mixture was first dispersed with 500W ultrasonic waves for 30 minutes, followed by mechanical stirring at 800 rpm for 2 hours to form a cathode slurry. The cathode slurry was then evenly coated onto aluminum foil using a coater. 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. The negative electrode slurry is then evenly coated on copper foil using a coater. The coated electrode sheet is then rolled, slit, and sheeted to obtain the negative electrode sheet.

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

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

[0067] Using a full-tab design, the positive electrode sheet, negative electrode sheet and separator are alternately stacked in the order of "positive electrode-separator-negative electrode" and wound into a bare battery cell; after the end face is flattened and shaped, the end face of the current collector is laser welded to lead out the full-tab; then it is placed in a shell, the electrolyte is injected and the battery is sealed to finally make a 32700 cylindrical battery.

[0068] Comparative Example 1

[0069] The difference between Comparative Example 1 and Example 1 is that Na 0.6 Ni 0.3 Fe 0.2 Mn 0.5 O2, Super P, MWCNT, and PVDF were added to NMP solvent at a mass ratio of 96:2:1:1. The mixture was first dispersed with 500W ultrasonic waves for 30 minutes, followed by mechanical stirring at 800rpm for 2 hours to form a positive electrode slurry. The positive electrode slurry was then evenly coated onto aluminum foil using a coater. The coated electrode sheet was then rolled, slit, and sheeted to obtain the positive electrode sheet.

[0070] Comparative Example 2

[0071] The difference between Comparative Example 2 and Example 1 is that Na 0.6 Ni 0.3 Fe 0.2 Mn 0.5 O2 is mixed with phenolic resin, where the mass of phenolic resin is Na 0.6 Ni 0.3 Fe 0.2 Mn 0.5 Under argon protection, the temperature was raised to 700°C at a rate of 2°C / min and a pressure of 1 MPa, maintained at this temperature for 5 hours, and finally cooled to room temperature to obtain a sodium ion battery positive electrode material.

[0072] Comparative Example 3

[0073] The difference between Comparative Example 3 and Example 1 is that Na 0.6 Ni 0.3 Fe 0.2 Mn 0.5 O2 is mixed with glucose (melting point is 150℃, viscosity is >1000mPa.s at 150℃), where the mass of glucose is Na 0.6 Ni 0.3 Fe 0.2 Mn 0.5 Under argon protection, the temperature was raised to 200°C at a rate of 2°C / min and a pressure of 1 MPa, and the temperature was maintained at this temperature for 2 hours. The temperature was then raised to 700°C and the pressure was 2 MPa, and the temperature was maintained at this temperature for 5 hours. Finally, the temperature was lowered to room temperature to obtain a positive electrode material for a sodium ion battery.

[0074] Comparative Example 4

[0075] The difference between Comparative Example 4 and Example 1 is that Na 0.6 Ni 0.3 Fe 0.2 Mn 0.5 O2 is mixed with sucrose (melting point is 190℃, viscosity is >1000mPa.s at 190℃), where the mass of sucrose is Na 0.6 Ni 0.3 Fe 0.2 Mn 0.5 Under argon protection, the temperature was raised to 200°C at a rate of 2°C / min and a pressure of 1 MPa, and the temperature was maintained for 2 hours. The temperature was then raised to 700°C and maintained for 5 hours, and finally the temperature was lowered to room temperature to obtain the positive electrode material for sodium ion batteries.

[0076] Comparative Example 5

[0077] The difference between Comparative Example 5 and Example 3 is that Na 0.6 Ni 0.3 Fe 0.2 Mn 0.5 O2 is mixed with dicyclopentadiene dioxide epoxy resin (melting point is 180℃, viscosity is 200mPa.s at 180℃), where the mass of dicyclopentadiene dioxide epoxy resin is Na 0.6 Ni 0.3 Fe 0.2 Mn 0.5 Under argon protection, the temperature was raised to 200°C at a rate of 2°C / min, maintained for 2 hours, then raised to 800°C, maintained for 5 hours, and finally cooled to room temperature to obtain the positive electrode material for sodium ion batteries.

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

[0079] Table 1 Sodium ion battery rate performance test results

[0080]

[0081] As can be seen from Table 1, the sodium ion battery positive electrode material obtained by the preparation method of the present invention has excellent rate performance and cycle stability.

[0082] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned 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 above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A method for preparing a positive electrode material for a sodium ion battery, characterized in that: include: A polycrystalline layered oxide matrix is mixed with an organic carbon source, and then melt infiltration and carbonization are performed under pressure to obtain a sodium ion battery positive electrode material; wherein the melting point of the organic carbon source is less than or equal to 200°C and the viscosity when melted is 50mPa.s-300mPa.s.

2. The method for preparing a positive electrode material for a sodium ion battery according to claim 1, wherein The organic carbon source is selected from at least one of a mixture of choline salts and polyols, a mixture of citric acid and / or malic acid and urea, an alicyclic epoxy resin, and an ionic liquid oligomer with a molecular weight of 500 g / mol-3000 g / mol.

3. The method for preparing a positive electrode material for a sodium ion battery according to claim 2, wherein: 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, butylene glycol, and ethylene glycol; And / or, the alicyclic epoxy resin is at least one selected from dicyclopentadiene dioxide epoxy resin and 3,4-epoxycyclohexylmethyl-3',4'-epoxycyclohexanecarboxylate epoxy resin; And / or, the ionic liquid oligomer is at least one selected from imidazolium-type ionic liquid oligomers and pyrrolidinium-type ionic liquid oligomers.

4. The method for preparing a positive electrode material for a sodium ion battery according to claim 1, wherein 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.

5. The method for preparing a positive electrode material for a sodium ion battery according to claim 1, wherein: In the melt infiltration step, the temperature is greater 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 step, the temperature is 600° C.-800° C., the pressure is 0.5 MPa-2 MPa, and the time is 2 h-5 h.

6. The method for preparing a positive electrode material for a sodium ion battery according to claim 5, wherein: In the melt infiltration step, the temperature is 200° C.-400° C., the pressure is 0.5 MPa-2 MPa, and the time is 0.5 h-2 h.

7. A sodium ion battery positive electrode material obtained by the preparation method according to any one of claims 1 to 6.

8. A positive electrode sheet prepared using the sodium ion battery positive electrode material according to claim 7.

9. A sodium ion battery, characterized in that: The sodium ion battery uses the positive electrode sheet as claimed in claim 8.

10. Use of the sodium ion battery according to claim 9 in a battery module or a battery pack.

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