A sodium-ion battery positive electrode material and a preparation method and a pole piece, a battery

Abstract

The application relates to the field of batteries, and specifically discloses a sodium-ion battery positive electrode material, a preparation method, a pole piece and a battery. The battery positive electrode material comprises a parent phase formed by a sodium electricity layer material, and a coating layer formed by a lithium electricity lithium cobalt oxide material and coated on the surface of the parent phase, wherein a specific ion co-doped high-entropy transition layer is formed between the coating layer and the parent phase through secondary sintering of the sodium electricity layer material and the lithium electricity lithium cobalt oxide material; the lithium electricity lithium cobalt oxide material is composed of Li x Co y M z O2, wherein 0

Description

TECHNICAL FIELD

[0001] The present application relates to the field of batteries, more particularly, it relates to a sodium-ion battery positive electrode material, a preparation method and a pole piece and a battery. BACKGROUND

[0002] With the continuous progress of new energy storage technology, lithium-ion batteries have encountered significant challenges in large-scale energy storage applications due to the scarcity of lithium resources and the continuous rise in price. In contrast, sodium-ion batteries have similar operating mechanisms to lithium-ion batteries, but exhibit better performance in safety and cycle durability, making them more suitable for the needs of the energy storage field. In addition, from a global resource distribution perspective, sodium resources are abundant and widely distributed, with higher overall cost efficiency. Given these factors, sodium-ion batteries have received widespread attention from many new energy companies and are considered an ideal option for the next generation of large-scale energy storage technology.

[0003] Sodium-ion batteries have similar working principles to lithium-ion batteries. Sodium-ion battery systems can be divided into three types according to the type of positive electrode material: layered oxides, polyanions, and Prussian blue. Among them, layered oxide materials and lithium battery ternary materials have similar two-dimensional layered structures, and the charging and discharging of the battery is achieved through the deintercalation process of Na + ions between the layers. Sodium battery layered oxide materials and lithium battery ternary layered materials not only have similar crystal structure types, but also have very similar processing techniques to lithium-ion batteries in actual production, with excellent compatibility. Therefore, among the three major systems of sodium-ion batteries, the industrialization of layered oxides is more rapid.

[0004] The standard molecular formula of layered oxide materials is Na x MeO2, where x is the content of Na in the molecular formula, and Me is a metal ion, typically Ni, Fe, Mn, and other transition metals. However, layered oxide materials have high surface residual alkali and poor electronic conductivity in actual use. The high surface residual alkali is mainly because the interlayer spacing of sodium battery layered materials is large, and the sodium ions in the layer are easily replaced by water molecules in the air. The escaped sodium ions on the material surface form residual alkali, which not only reduces the capacity of the material, but also makes the processing performance worse and the surface impedance of the material higher. The poor electronic conductivity is mainly because the powder resistance of sodium battery layered materials is significantly higher than that of lithium battery layered materials, which not only increases the impedance and heat production, but also affects the rate performance. In view of this, the present application proposes a sodium-ion battery positive electrode material that can effectively improve the above problems. SUMMARY

[0005] In order to solve the problems of high residual alkali on the surface and poor electronic conductivity of the existing layered oxide material as the positive electrode material of the sodium ion battery in the actual application process, the application provides a sodium ion battery positive electrode material and a preparation method and a pole piece and a battery, and the sodium ion battery positive electrode material has the characteristics of low residual alkali, no interlayer cleavage, low powder resistance, high capacity, excellent cycle performance and better thermal stability.

[0006] The application adopts the following technical solutions:

[0007] In a first aspect, the application provides a sodium ion battery positive electrode material, which comprises a parent phase formed by a sodium electric layered material, and a coating layer formed by a lithium cobalt lithium material coated on the surface of the parent phase, and the coating layer and the parent phase are a high-entropy transition layer formed by the sodium electric layered material and the lithium cobalt lithium material through secondary sintering;

[0008] The composition of the sodium electric layered material is Na a A b Ni c B d O2, wherein 0

[0009] The composition of the lithium cobalt lithium material is Li x Co y M z O2, wherein 0

[0010] Further, the coating layer is 0.2-3 wt% of the mass of the parent phase.

[0011] Further, the above-mentioned M is at least one of Zr, Nb and Ti.

[0012] Further, the above-mentioned B includes Fe elements and a combination formed with at least one of Mn, Zr and Sn.

[0013] Further, in the lithium cobalt lithium material, the value range of z is 0

[0014] Preferably, the composition of the above-mentioned lithium cobalt lithium material is Li x Co y M zO2, wherein 0.94≤x≤0.96, y+z=1, 0.96≤y≤0.98, M is Zr or Nb alone, or Nb+Ti, or Nb+Zr.

[0015] Preferably, the sodium electric layered material has a composition of Na a A b Ni c B d O2, wherein 0<a+b≤1, c+d=1; wherein, 0.94≤a≤0.97, A is one or more of Li, Ca, La; 0.33≤c≤0.40, B is Fe+Mn elements, or B is a combination of Fe and Mn elements with at least one of Zr, Sn.

[0016] In a second aspect, the application provides a preparation method of the above-mentioned sodium ion battery cathode material, comprising:

[0017] (1) mixing a precursor powder of a sodium electric layered material, a sodium source and an additive, and then performing first sintering to obtain a parent phase;

[0018] (2) mixing the parent phase with a solution containing a cobalt salt and a sodium source, and then performing a precipitation reaction to obtain a composite material coated with cobalt on the surface; and then uniformly mixing the composite material with a lithium source and a doping additive containing an M element according to a stoichiometric ratio, and then performing second sintering to obtain the sodium ion battery cathode material.

[0019] Preferably, the precursor powder in step (1) is obtained by co-precipitation reaction of a metal sulfate solution, a precipitant and a complexing agent according to a stoichiometric ratio, and then aging, filtering, washing and drying.

[0020] Preferably, the sulfate in the metal sulfate solution is selected from one or more of nickel sulfate, aluminum sulfate, magnesium sulfate, titanyl sulfate, manganese sulfate, ferrous sulfate, cobalt sulfate, copper sulfate and zinc sulfate. The precipitant is an alkaline sodium source solution, which can be one or more of sodium carbonate, sodium bicarbonate and sodium hydroxide. The complexing agent is ammonia water or other alkaline solution.

[0021] Preferably, the additive in step (1) is a doping additive, which includes one or more of lithium carbonate, lithium hydroxide monohydrate, vanadium pentoxide, chromium sesquioxide, gallium sesquioxide, tin dioxide, zirconium dioxide, niobium pentoxide and tantalum pentoxide.

[0022] Further, the cobalt salt in step (2) is selected from one or more of cobalt nitrate, cobalt sulfate and cobalt chloride; the alkaline sodium source is one or more of sodium carbonate, sodium bicarbonate and sodium hydroxide; and the lithium source is one or more of lithium carbonate, lithium hydroxide monohydrate and lithium bicarbonate.

[0023] Further, the doping additive containing M element is one or more of lanthanum trioxide, titanium dioxide, silicon dioxide, zirconium dioxide, niobium pentoxide and tantalum pentoxide.

[0024] Further, the sintering temperature of the first sintering and the second sintering is 800-1000℃, and the sintering time is 6-18h.

[0025] Preferably, the sintering temperature is 850-950℃, and the sintering time is 6-14h.

[0026] More preferably, the sintering temperature of the first sintering is 870-950℃, and the sintering time is 10-12h; the sintering temperature of the second sintering is 820-870℃, and the sintering time is 6-12h.

[0027] In a third aspect, the application provides a positive electrode tab, wherein the positive electrode active paste of the positive electrode tab comprises the sodium ion battery positive electrode material.

[0028] In a fourth aspect, the application provides a sodium ion battery comprising the positive electrode tab.

[0029] In summary, the application has the following beneficial effects:

[0030] The sodium ion battery positive electrode material provided by the application has a parent phase and a coating layer. Compared with the coating technology commonly used in battery materials, the coating layer material of the application is Li x Co y M z O2, which is a lithium cobaltate material similar to the lithium battery positive electrode, also has a layered structure, is similar to the crystal material of the parent phase, has better lattice matching, and has better interface bonding and compatibility with the parent phase. In the long cycle process, the parent phase material can always maintain good coating effect, effectively inhibit the volume strain and interlayer cleavage phenomenon, and ensure better capacity retention and cycle life. At the same time, as a coating layer material, the lithium cobaltate material for lithium battery has excellent electronic conductivity, while the electronic conductivity of the parent phase sodium battery layered positive electrode material itself is poor, and the powder resistance is high. The use of lithium cobaltate for surface coating can effectively improve the powder resistance of the parent phase material.

[0031] The sodium ion battery positive electrode material provided in the application is mixed with a lithium source and a doping additive containing an M element to perform secondary sintering in the preparation process. In the second sintering process, residual alkali on the surface can enter the parent phase material or be combined with the surface coating material, effectively reducing the amount of residual alkali. At the same time, the lithium source in the coating layer material has a lower melting point, and in the high-temperature reaction process of secondary sintering, the sharp edges and corners on the surface of the parent phase layer material are effectively reduced, and the overall particle becomes more rounded, so that the compaction density of the powder is further improved.

[0032] In the preferred embodiments of the application, by selecting specific metals for doping in the coating layer and the parent phase, the replacement of Na+ ions with water molecules in the air can be effectively blocked, effectively improving the moisture stability of the material. At the same time, the parent phase material and the coating material are both combined and doped, and in the high-temperature reaction process of secondary sintering, a local mixed transition region is formed at the interface between the parent phase and the coating layer, effectively reducing the activity of free lattice oxygen, and the thermal stability of the obtained material is significantly improved. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 FIG. 1 is a structural schematic diagram of the sodium electric layered positive electrode material with a coating layer provided by the application.

[0034] Figure 2 FIG. 2 is a scanning electron microscope micro-morphology picture of the coated sodium electric layered positive electrode material prepared in Example 1 of the application and the uncoated parent phase positive electrode material sample prepared in Comparative Example 1.

[0035] Figure 3 FIG. 3 is a scanning electron microscope micro-morphology picture of the coated sodium electric layered positive electrode material prepared in Example 1 of the application and the uncoated parent phase positive electrode material sample prepared in Comparative Example 1 after 50 cycles of discharging.

[0036] Figure 4 FIG. 4 is a comparison of the cycle curves of the coated sodium electric layered positive electrode material prepared in Example 1 of the application and the uncoated parent phase positive electrode material sample prepared in Comparative Example 1, measured in the voltage range of 2-4V at 0.5C discharging and 1C charging. DETAILED DESCRIPTION

[0037] The embodiments of the application will be described in detail below with reference to the examples, but those skilled in the art will understand that the following examples are only for illustration of the application and should not be regarded as limiting the scope of the application. The specific conditions not mentioned in the examples are carried out according to the conventional conditions or the conditions recommended by the manufacturer, and the reagents or instruments not mentioned by the manufacturer are conventional products that can be purchased on the market.

[0038] The specific embodiments of the present application are described in detail below. It should be understood that the specific embodiments described herein are merely illustrative and explanatory in nature and are not intended to limit the application.

[0039] Example 1

[0040] The present embodiment provides a sodium ion battery cathode material, Figure 1 is a structural schematic diagram, and the compositions of the parent phase and the coating layer are respectively:

[0041] Parent phase: Na 0.97 La 0.01 (Ni 0.33 Fe 0.33 Mn 0.32 Sn 0.01 )O2,

[0042] Coating layer: Li 0.96 Co 0.96 Zr 0.04 O2;

[0043] The preparation method is as follows:

[0044] (1) Preparation of parent phase layered oxide

[0045] Nickel sulfate, ferrous sulfate and manganese sulfate are weighed according to a molar ratio of 0.33:0.33:0.32, and then dissolved in deionized water to prepare a 2 mol / L soluble metal salt solution. NaOH is configured into a 5 mol / L solution as a precipitating agent, and ammonia water is configured into a 5 mol / L solution as a complexing agent. The metal salt solution, the precipitating agent and the complexing agent are respectively added to the precipitation reactor at a certain flow rate, and after complete reaction, the mixture is aged and left for 12 hours. Then, the mixture is filtered, washed and dried to obtain a hydroxide precursor powder. The precursor powder is weighed together with sodium carbonate, lanthanum oxide and tin dioxide ultrafine powder according to a molar ratio of Na:La:Ni:Fe:Mn:Sn=0.97:0.01:0.33:0.33:0.32:0.01, and then uniformly mixed at high speed. The mixture is sintered at 900°C for 12 hours in an air atmosphere, and then cooled to obtain a parent phase cathode material.

[0046] (2) Preparation of surface coating layer

[0047] The design of the coating layer quality is 1.5wt% of the quality of the parent phase positive electrode material. 100g of the parent phase positive electrode material is weighed and added into ethanol for stirring and dispersion. 2.3026g of cobalt sulfate is weighed and added into a certain amount of deionized water to prepare a 2mol / L cobalt sulfate solution. The cobalt sulfate solution is added into the ethanol solution of the parent phase material under stirring to disperse uniformly. A 5mol / L sodium hydroxide aqueous solution is added at a certain flow rate to carry out a precipitation reaction. After the reaction is completed, the cobalt hydroxide coated positive electrode material is obtained through filtration, washing and drying. 100g of the cobalt hydroxide coated positive electrode material is weighed, and 0.5388g of superfine lithium carbonate and 0.0749g of superfine zirconium dioxide are weighed and mixed uniformly at a high speed. Then, the coated sodium battery layered positive electrode material is obtained by sintering at 850℃ for 8h in an air atmosphere and cooling.

[0048] Example 2

[0049] The present embodiment provides a sodium ion battery positive electrode material, and the compositions of the parent phase and the coating layer are respectively:

[0050] Parent phase: Na 0.94 Ca 0.03 (Ni 0.33 Fe 0.26 Mn 0.39 Zr 0.01 )O2,

[0051] Coating layer: Li 0.96 Co 0.98 Nb 0.02 O2;

[0052] The preparation method is as follows:

[0053] (1) Preparation of parent phase layered oxide

[0054] Nickel sulfate, ferrous sulfate and manganese sulfate are weighed according to a molar ratio of 0.33:0.26:0.39, and then dissolved in deionized water to prepare a 2mol / L soluble metal salt solution. NaOH is configured into a 5mol / L solution as a precipitant, and ammonia water is configured into a 5mol / L solution as a complexing agent. The metal salt solution, the precipitant and the complexing agent are respectively added into a precipitation reactor at a certain flow rate. After complete reaction, the mixture is aged for 12h, and then the hydroxide precursor powder is obtained through filtration, washing and drying. The above precursor powder, sodium carbonate, calcium carbonate and zirconium dioxide superfine powder are weighed according to a molar ratio of Na:Ca:Ni:Fe:Mn:Zr=0.94:0.03:0.33:0.26:0.39:0.01, and then mixed uniformly at a high speed. The parent phase positive electrode material is obtained by sintering at 950℃ for 12h in an air atmosphere and cooling.

[0055] (2) Preparation of surface coating layer

[0056] The design of the coating layer quality is 1wt% of the quality of the parent phase cathode material. 100g of the parent phase cathode material is weighed and added to ethanol for stirring and dispersion, 100g of the parent phase cathode material is weighed and added to ethanol for stirring and dispersion, 1.5677g of cobalt sulfate is weighed and a certain amount of deionized water is added to prepare a 2mol / L cobalt sulfate solution, and the cobalt sulfate solution is added to the ethanol solution of the parent phase material under stirring to disperse uniformly. A 5mol / L sodium hydroxide aqueous solution is added at a certain flow rate to carry out a precipitation reaction. After the reaction is completed, the cobalt hydroxide coated cathode material is obtained after filtration, washing and drying. 100g of the cobalt hydroxide coated cathode material is weighed, and 0.3607g of superfine lithium carbonate, 0.0271g of superfine niobium pentoxide are weighed and mixed uniformly at high speed, and then sintered at 870℃ for 6h in an air atmosphere, and after cooling, the coated sodium battery layered cathode material is obtained.

[0057] Example 3

[0058] The present embodiment provides a sodium ion battery cathode material, the composition of the parent phase and the coating layer is respectively:

[0059] Parent phase: Na 0.94 La 0.02 (Ni 0.33 Fe 0.33 Mn 0.32 Zr 0.005 Sn 0.005 )O2,

[0060] Coating layer: Li 0.94 Co 0.96 Ti 0.02 Nb 0.02 O2;

[0061] The preparation method is as follows:

[0062] (1) Preparation of parent phase layered oxide

[0063] Nickel sulfate, ferrous sulfate, manganese sulfate were weighed according to the molar ratio of 0.33:0.33:0.32, and then dissolved in deionized water to prepare a 2 mol / L soluble metal salt solution. NaOH was prepared into a 5 mol / L solution as a precipitant, and ammonia water was prepared into a 5 mol / L solution as a complexing agent. The metal salt solution, precipitant, and complexing agent were added to the precipitation reactor at a certain flow rate, respectively. After complete reaction, the mixture was aged for 12 h, and then filtered, washed, and dried to obtain hydroxide precursor powder. The above precursor powder, sodium carbonate, lanthanum oxide, zirconium dioxide, and tin dioxide ultrafine powder were weighed according to the molar ratio of Na:La:Ni:Fe:Mn:Zr:Sn=0.94:0.02:0.33:0.33:0.32:0.005:0.005, and then uniformly mixed at high speed. After sintering at 930°C in an air atmosphere for 10 h, the cooled product was a parent phase positive electrode material.

[0064] (2) Preparation of surface coating layer

[0065] The mass of the coating layer was designed to be 3wt% of the mass of the parent phase positive electrode material. 100 g of the parent phase positive electrode material was added to ethanol for stirring and dispersion. 4.6072 g of cobalt sulfate was weighed and dissolved in a certain amount of deionized water to prepare a 2 mol / L cobalt sulfate solution. The cobalt sulfate solution was added to the ethanol solution of the parent phase material under stirring to disperse uniformly. A 5 mol / L sodium hydroxide solution was added at a certain flow rate to carry out a precipitation reaction. After the reaction was completed, the mixture was filtered, washed, and dried to obtain a positive electrode material coated with cobalt hydroxide. 100 g of the positive electrode material coated with cobalt hydroxide was mixed with 1.0411 g of ultrafine lithium carbonate, 0.0479 g of ultrafine titanium dioxide, and 0.0797 g of ultrafine niobium pentoxide powder at high speed. Then, the mixture was sintered at 820°C in an air atmosphere for 10 h, and the cooled product was a coated sodium battery layered positive electrode material.

[0066] Example 4

[0067] The present embodiment provides a sodium ion battery positive electrode material, and the compositions of the parent phase and the coating layer are as follows:

[0068] Parent phase: Na 0.95 Li 0.03 Ca 0.01 (Ni 0.40 Fe 0.20 Mn 0.40 )O2,

[0069] Coating layer: Li 0.95 Co 0.97 Zr 0.01 Nb 0.02 O2;

[0070] (1) Preparation of parent phase layered oxide

[0071] Nickel sulfate, ferrous sulfate, and manganese sulfate were weighed according to a molar ratio of 0.40:0.20:0.40, and then dissolved in deionized water to prepare a 2 mol / L soluble metal salt solution. NaOH was prepared into a 5 mol / L solution as a precipitant, and ammonia water was prepared into a 5 mol / L solution as a complexing agent. The metal salt solution, the precipitant, and the complexing agent were added into a precipitation reactor at a certain flow rate, respectively. After complete reaction, the mixture was aged and left standing for 12 h, and then filtered, washed, and dried to obtain a hydroxide precursor powder. The precursor powder was weighed together with ultrafine sodium carbonate, lithium carbonate, and calcium carbonate powders according to a molar ratio of Na:Li:Ca:Ni:Fe:Mn = 0.95:0.03:0.01:0.40:0.20:0.40, and then uniformly mixed at high speed. The mixture was sintered at 870°C for 12 h in an air atmosphere, and then cooled to obtain a parent-phase cathode material.

[0072] (2) Preparation of the surface coating layer

[0073] The mass of the coating layer was designed to be 2 wt% of the mass of the parent-phase cathode material. 100 g of the parent-phase cathode material was added into ethanol for stirring and dispersion. 3.1035 g of cobalt sulfate was weighed and added into a certain amount of deionized water to prepare a 2 mol / L cobalt sulfate solution. The cobalt sulfate solution was added into the ethanol solution of the parent-phase material under stirring to uniformly disperse. A 5 mol / L sodium hydroxide aqueous solution was added at a certain flow rate to perform a precipitation reaction. After the reaction was completed, the mixture was filtered, washed, and dried to obtain a cobalt hydroxide-coated cathode material. 100 g of the cobalt hydroxide-coated cathode material was weighed, and 0.7076 g of ultrafine lithium carbonate, 0.0248 g of ultrafine zirconium dioxide, and 0.0536 g of ultrafine niobium pentoxide powder were weighed and uniformly mixed at high speed. Then, the mixture was sintered at 830°C for 12 h in an air atmosphere, and then cooled to obtain a coated sodium battery layered cathode material.

[0074] Example 5

[0075] The present embodiment provides a sodium-ion battery cathode material, the compositions of the parent phase and the coating layer thereof are respectively:

[0076] Parent phase: Na 0.95 K 0.03 La 0.01 (Ni 0.33 Fe 0.33 Mn 0.32 V 0.005 Ga 0.005 )O2,

[0077] Coating layer: Li 0.95 Co 0.97 Si 0.01 Ta 0.02 O2;

[0078] (1) Preparation of a parent phase layered oxide

[0079] Nickel sulfate, ferrous sulfate, and manganese sulfate were weighed according to a molar ratio of 0.33:0.33:0.32, and then dissolved in deionized water to prepare a 2 mol / L soluble metal salt solution. NaOH was prepared into a 5 mol / L solution as a precipitant, and ammonia water was prepared into a 5 mol / L solution as a complexing agent. The metal salt solution, the precipitant, and the complexing agent were respectively added into a precipitation reactor at a certain flow rate, and after complete reaction, the mixture was aged and left to stand for 12 h. Then, the mixture was filtered, washed, and dried to obtain a hydroxide precursor powder. The precursor powder was weighed together with superfine sodium carbonate, lithium carbonate, and calcium carbonate powders according to a molar ratio of Na:K:La:Ni:Fe:Mn:V:Ga=0.95:0.03:0.01:0.33:0.33:0.32:0.005:0.005, and then uniformly mixed at high speed. The mixture was sintered at 870°C for 12 h in an air atmosphere, and after cooling, a parent phase positive electrode material was obtained.

[0080] (2) Preparation of a surface coating layer

[0081] The mass of the coating layer was designed to be 2 wt% of the mass of the parent phase positive electrode material. 100 g of the parent phase positive electrode material was added into ethanol for stirring and dispersion. 3.1035 g of cobalt sulfate was weighed and added into a certain amount of deionized water to prepare a 2 mol / L cobalt sulfate solution. The cobalt sulfate solution was added into the ethanol solution of the parent phase material under stirring to uniformly disperse. A 5 mol / L sodium hydroxide aqueous solution was added at a certain flow rate to perform a precipitation reaction. After the reaction was completed, the mixture was filtered, washed, and dried to obtain a positive electrode material coated with cobalt hydroxide. 100 g of the positive electrode material coated with cobalt hydroxide was weighed, and superfine lithium carbonate, superfine tantalum pentoxide powder, and superfine silicon dioxide powder were weighed according to a molar ratio and uniformly mixed at high speed. Then, the mixture was sintered at 800°C for 18 h in an air atmosphere, and after cooling, a coated sodium layered positive electrode material was obtained.

[0082] Example 6

[0083] The present example provides a sodium ion battery positive electrode material, the compositions of the parent phase and the coating layer thereof are respectively:

[0084] Parent phase: Na 0.97 La 0.01 (Ni 0.33 Fe 0.32 Mn 0.32 Co 0.01 Ta 0.01 )O2,

[0085] Coating layer: Li 0.95 Co 0.97 Zr 0.01Nb 0.02 O2;

[0086] (1) Preparation of parent phase layered oxide

[0087] Nickel sulfate, ferrous sulfate, and manganese sulfate were weighed according to a molar ratio of 0.33:0.32:0.32, and then dissolved in deionized water to prepare a 2 mol / L soluble metal salt solution. NaOH was prepared into a 5 mol / L solution as a precipitant, and ammonia water was prepared into a 5 mol / L solution as a complexing agent. The metal salt solution, the precipitant, and the complexing agent were respectively added into a precipitation reactor at a certain flow rate, and after complete reaction, the mixture was aged and left standing for 12 h, and then filtered, washed, and dried to obtain a hydroxide precursor powder. The precursor powder was weighed together with superfine sodium carbonate, lithium carbonate, and calcium carbonate powders according to a molar ratio of Na:La:Ni:Fe:Mn:Co:Ta = 0.97:0.01:0.33:0.32:0.32:0.01:0.01, and then uniformly mixed at high speed, and sintered at 1000°C for 6 h in an air atmosphere, and after cooling, a parent phase positive electrode material was obtained.

[0088] (2) Preparation of surface coating layer

[0089] The mass of the coating layer was designed to be 0.25wt% of the mass of the parent phase positive electrode material. 100 g of the parent phase positive electrode material was added into ethanol for stirring and dispersion, 3.1035 g of cobalt sulfate was weighed and added into a certain amount of deionized water to prepare a 2 mol / L cobalt sulfate solution, and the cobalt sulfate solution was added into the ethanol solution of the parent phase material under stirring to uniformly disperse. A 5 mol / L sodium hydroxide aqueous solution was added at a certain flow rate to perform a precipitation reaction. After the reaction was completed, the mixture was filtered, washed, and dried to obtain a positive electrode material coated with cobalt hydroxide. 100 g of the positive electrode material coated with cobalt hydroxide was weighed, and 0.7076 g of superfine lithium carbonate, 0.0248 g of superfine zirconium dioxide, and 0.0536 g of superfine niobium pentoxide powder were weighed and uniformly mixed at high speed, and then sintered at 830°C for 12 h in an air atmosphere, and after cooling, a coated sodium battery layered positive electrode material was obtained.

[0090] Example 7

[0091] The present embodiment provides a sodium ion battery positive electrode sheet, and a preparation method thereof includes:

[0092] The coated sodium battery layered positive electrode material prepared by any one of Examples 1-6 was mixed with an adhesive and conductive carbon black according to a mass ratio of 94:3:3, dissolved in N-methyl pyrrolidone, and after sufficient stirring and defoaming, the mixture was filtered to obtain a positive electrode slurry.

[0093] The positive electrode slurry is coated on the surface of the current collector aluminum foil by an automatic coating machine, and then the coated electrode sheet is dried at 105°C for more than 12 hours under air blowing and vacuum conditions respectively, and after rolling, a sodium ion battery positive electrode sheet is obtained.

[0094] Example 8

[0095] The present embodiment provides a sodium ion battery, and a preparation method thereof comprises:

[0096] The positive electrode sheet provided in Example 7 is punched into a circular sheet with a diameter of 12 mm, the negative electrode counter electrode is a metal sodium sheet, the glass fiber membrane is used as a separator, and the electrolyte is 1 mol / L NaPF6 dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate (EC:DEC=1:1). A sodium ion battery is assembled in an argon glove box with a water and oxygen content of less than 1 ppm.

[0097] Comparative Example 1

[0098] The present comparative example prepares a sodium battery layered positive electrode material without coating, and the composition is Na 0.97 La 0.01 (Ni 0.33 Fe 0.33 Mn 0.32 Sn 0.01 )O2, and the preparation method is the same as that of Example 1.

[0099] Comparative Example 2

[0100] The present comparative example prepares a sodium battery layered positive electrode material without coating, and the composition is Na 0.94 Ca 0.03 (Ni 0.33 Fe 0.26 Mn 0.39 Zr 0.01 )O2, and the preparation method is the same as that of Example 2.

[0101] Comparative Example 3

[0102] The present comparative example prepares a sodium battery layered positive electrode material without coating, and the composition is Na(Ni 0.33 Fe 0.33 Mn 0.33 )O2, and the preparation method is as follows:

[0103] Nickel sulfate, ferrous sulfate, manganese sulfate were weighed according to the molar ratio of 0.33:0.33:0.33, and then dissolved in deionized water to prepare a 2 mol / L soluble metal salt solution. NaOH was prepared into a 5 mol / L solution as a precipitant, and ammonia water was prepared into a 5 mol / L solution as a complexing agent. The metal salt solution, precipitant and complexing agent were added into the precipitation reactor at a certain flow rate, respectively. After complete reaction, the mixture was aged for 12 h, and then filtered, washed and dried to obtain hydroxide precursor powder. The above precursor powder and sodium carbonate ultrafine powder were weighed according to the molar ratio of Na:Ni:Fe:Mn=1:0.33:0.33:0.33, and then uniformly mixed at high speed. After sintering at 930 ℃ in air atmosphere for 10 h, the mother phase positive electrode material was obtained after cooling.

[0104] Comparative Example 4

[0105] The sodium-ion battery positive electrode material of the present comparative example is not coated, and its composition is Na(Ni 0.4 Fe 0.2 Mn 0.4 )O2. The preparation method is as follows:

[0106] Nickel sulfate, ferrous sulfate, manganese sulfate were weighed according to the molar ratio of 0.40:0.20:0.40, and then dissolved in deionized water to prepare a 2 mol / L soluble metal salt solution. NaOH was prepared into a 5 mol / L solution as a precipitant, and ammonia water was prepared into a 5 mol / L solution as a complexing agent. The metal salt solution, precipitant and complexing agent were added into the precipitation reactor at a certain flow rate, respectively. After complete reaction, the mixture was aged for 12 h, and then filtered, washed and dried to obtain hydroxide precursor powder. The above precursor powder and sodium carbonate ultrafine powder were weighed according to the molar ratio of Na:Ni:Fe:Mn:Zr=1:0.40:0.20:0.40, and then uniformly mixed at high speed. After sintering at 870 ℃ in air atmosphere for 12 h, the mother phase positive electrode material was obtained after cooling.

[0107] Comparative Example 5

[0108] The sodium-ion battery positive electrode material of the present comparative example is not coated, and its composition is Na(Ni

[0109] Mother phase: Na 0.97 La 0.01 (Ni 0.33 Fe 0.33 Mn 0.32 Sn 0.01 )O2,

[0110] Coating layer: Li 0.96 Co 1.00 O2;

[0111] Its preparation methods include:

[0112] The parent phase layered oxide was prepared in the same manner as in Example 1.

[0113] Preparation of surface coating layer:

[0114] The designed coating layer mass is 1.5 wt% of the parent phase cathode material. 100 g of the parent phase cathode material was weighed and added to ethanol for dispersion. 2.3026 g of cobalt sulfate was weighed and added to a certain amount of deionized water to prepare a 2 mol / L cobalt sulfate solution. The cobalt sulfate solution was added to the ethanol solution of the parent phase material under stirring and dispersed evenly. A 5 mol / L sodium hydroxide aqueous solution was added at a certain flow rate to initiate a precipitation reaction. After the reaction was complete, the cathode material was obtained by filtration, washing, and drying. 100 g of the cobalt hydroxide-coated cathode material was weighed and simultaneously mixed with ultrafine lithium carbonate at high speed until homogeneous. The mixture was then sintered at 850 °C for 8 h in air. After cooling, the coated sodium-ion layered cathode material was obtained.

[0115] Comparative Example 6

[0116] This comparative example provides a sodium-ion battery cathode material, wherein the compositions of the matrix phase and the coating layer are as follows:

[0117] Mother phase: Na 0.97 La 0.01 (Ni 0.33 Fe 0.33 Mn 0.32 Sn 0.01 O2,

[0118] Coating: Cr 0.96 P 0.04 O2;

[0119] Its preparation methods include:

[0120] The parent phase layered oxide was prepared in the same manner as in Example 1.

[0121] Preparation of surface coating: Prepared according to existing methods.

[0122] Comparative Example 7

[0123] This comparative example provides a sodium-ion battery cathode material, wherein the compositions of the matrix phase and the coating layer are as follows:

[0124] Mother phase: Na 0.98 (Ni 0.33 Fe 0.33 Mn 0.32 Sn 0.01 O2,

[0125] Coating: Li 0.96 Co0.96 Zr 0.04 O2;

[0126] The preparation method is as follows:

[0127] (1) Preparation of a parent phase layered oxide

[0128] Nickel sulfate, ferrous sulfate, and manganese sulfate are weighed according to a molar ratio of 0.33:0.33:0.32, and then dissolved in deionized water to prepare a 2 mol / L soluble metal salt solution. NaOH is prepared into a 5 mol / L solution as a precipitant, and ammonia water is prepared into a 5 mol / L solution as a complexing agent. The metal salt solution, the precipitant, and the complexing agent are respectively added into a precipitation reactor at a certain flow rate, and after complete reaction, the mixture is aged and left standing for 12 h, and then filtered, washed, and dried to obtain a hydroxide precursor powder. The precursor powder is weighed together with sodium carbonate, lanthanum oxide, and tin dioxide ultrafine powder according to a molar ratio of Na:Ni:Fe:Mn:Sn=0.98:0.33:0.33:0.32:0.01, and then uniformly mixed at high speed, and sintered at 900°C for 12 h in an air atmosphere, and after cooling, a parent phase positive electrode material is obtained.

[0129] (2) Preparation of a surface coating layer: same as Example 1.

[0130] Performance detection test

[0131] Detection method

[0132] 1. Scanning electron microscope: the materials provided in the examples and the comparative examples are subjected to scanning electron microscope observation to observe the material morphology.

[0133] 2. Button cell production: the positive electrode material, the adhesive PVDF, and the conductive carbon black (Super P) are mixed according to 94:3:3, and then dissolved in a solvent NMP, and after sufficient stirring and defoaming, the mixture is filtered to obtain a slurry. The obtained slurry is coated on the surface of a current collector aluminum foil using an automatic coating machine, and the coated electrode piece is dried at 105°C for 12 hours or more under air blowing and vacuum conditions, and after rolling, a positive electrode piece is obtained. The positive electrode piece is punched into a round piece with a diameter of 12 mm, the negative electrode counter electrode is a metal sodium piece, the glass fiber membrane is used as a separator, and the electrolyte is 1 mol / L NaPF6 dissolved in an organic solution of EC:DEC=1:1, and a CR2032 button cell is assembled in an argon glove box with a water and oxygen content of 1 ppm or less. The battery is charged and discharged at a current of 120 mA / g, and the cycle curve is detected in a voltage range of 2-4 V.

[0134] 3. Powder resistance test: a certain amount of powder sample is weighed and placed in a cylindrical mold, and the powder is pressed into a dense round piece under a pressure of 1T, and the maximum pressure is maintained for a certain time to read the resistance value.

[0135] 4. Compaction density test: a certain amount of powder sample is weighed and placed in a cylindrical mold, and the powder is compressed into a disc under pressure. After holding the pressure for a certain time under 3T pressure, the volume of the compressed material is read, and the compaction density of the powder is obtained by the mass-to-volume ratio.

[0136] 5. Thermal stability test: the discharged battery is disassembled, the positive electrode sheet is removed and soaked with solvent, and the powder on the surface of the electrode sheet is scraped and placed in a thermal gravimetric-differential thermal analysis linkage device. The DSC exothermic curve is tested by heating to 550℃ in a nitrogen atmosphere.

[0137] 6. Air exposure test: a certain amount of powder is weighed and placed in a self-sealing bag, and exposed to normal air for 72 hours. The difference in water content before and after placement is tested.

[0138] (II) Test results

[0139] As shown in Table 1 and Figures 2-4 :

[0140] As can be seen from Figure 2 , the left picture of the uncoated one-burn (Comparative Example 1) shows that the particles are flaky and angular; the right picture of the coated two-burn (Example 1) shows that the particle morphology is relatively round. This shows that the sodium battery layered positive electrode material provided by the present application, with surface coating and high-temperature secondary sintering, makes the matrix material more round, the particles grow again, and the overall compaction density is improved.

[0141] As can be seen from Figure 3 , the left picture of the uncoated one-burn (Comparative Example 1) shows that the particles are flaky and angular; the right picture of the coated two-burn (Example 1) shows that the particle morphology is relatively round. This shows that the sodium battery layered positive electrode material provided by the present application, with surface coating and high-temperature secondary sintering, makes the matrix material more round, the particles grow again, and the overall compaction density is improved.

[0142] As can be seen from Figure 4 , under the condition of 0.5C discharge and 1C charge, the cycle capacity retention rate of the sample coated and modified (Example 1) is significantly higher than that of the sample uncoated and modified (Comparative Example 1) as the number of cycles increases.

[0143] As can be seen from Figure 3 , Figure 4 , it can be seen that the surface coating layer of the sodium battery layered positive electrode material provided by the present application can effectively inhibit the stress release during the cycle process, weaken the interlayer cleavage of the particles, stabilize the interface film on the surface of the active material in the battery, and improve the cycle performance.

[0144] The test results of the materials obtained in Examples 1-6 and Comparative Examples 1-7 of the present application are shown in Table 1:

[0145]

[0146] In combination with Embodiments 1-2 and Comparative Examples 1-2, it can be seen that the excellent electronic conductivity of the lithium cobaltate coated on the surface of the parent phase layered oxide reduces the powder resistance of the overall material; and after the secondary sintering at high temperature in the process of preparing the coating layer, the intermediate transition layer formed at the interface junction has multiple atoms coexisting, thus forming a local high-entropy region at the interface, which on the one hand hinders the replacement of sodium ions with water molecules in the air, thereby improving the moisture absorption stability of the material, and on the other hand inhibits the activity of free lattice oxygen, thereby improving the thermal stability of the material; at the same time, the cycle performance of the battery is also greatly improved.

[0147] In combination with Comparative Examples 1-2 and Comparative Examples 3-4, it can be seen that even without coating, due to the fact that Comparative Example 1-2 is doped with other elements (La+Sn; or Ca+Zr) on the basis of Na(Ni 0.33 Fe 0.33 Mn 0.33 )O2 or Na(Ni 0.4 Fe 0.2 Mn 0.4 )O2, the moisture absorption performance of the obtained sodium battery layered positive electrode material is obviously improved. This indicates that the parent phase formed by the sodium battery layered material itself has excellent moisture absorption stability.

[0148] In combination with Embodiments 1 and Comparative Examples 5-6, it can be seen that under the condition of both being coated, due to the difference in the material of the coating layer, the obtained positive electrode material also exhibits great difference. Compared with Comparative Examples 5-6, the present application uses lithium cobaltate with a similar structure as the coating layer and is doped, which not only ensures better interface bonding with the parent phase material, but also further enhances the thermal stability, moisture absorption stability and cycle performance of the material. When the coating layer is undoped lithium cobaltate, as shown in Comparative Example 5, the structure and thermal stability of the coating layer itself are relatively poor, resulting in poor cycle performance and insufficient thermal stability of the final material. When the coating layer is other substances, as shown in Comparative Example 6, the capacity of the final material is low, the powder resistance is high, and the cycle performance is relatively poor.

[0149] In combination with Embodiments 1 and Comparative Example 7, it can be seen that under the condition of both being coated, since the sodium ion position of the parent phase material is not doped and modified, the sodium ions of the sodium layer are relatively more prone to moisture absorption and replacement with water molecules, and the corresponding material is severely exposed to water, and the cycle performance is also poor.

[0150] This specific embodiment is merely an explanation of the present application, and is not a limitation of the present application. Those skilled in the art can make modifications to this embodiment without creative contribution after reading the present specification, but as long as the modifications are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A sodium-ion battery cathode material, characterized in that, The positive electrode material includes: The parent phase formed by the sodium-ion layered material, and the composition of the sodium-ion layered material is Na a A b Ni c BdO2, where 0 < a + b ≤ 1, c + d = 1; A is one or more of Li, K, Ca, La, and B is one or more of V, Cr, Mn, Fe, Co, Ga, Sn, Zr, Nb, Ta; A coating layer formed of lithium cobalt oxide material, which covers the surface of the parent phase, wherein the lithium cobalt oxide material has a composition of Li... x Co y MzO2, where M is one or more of La, Si, Zr, Nb, Ta, and Ti; A transition layer located between the matrix phase and the coating layer, and the transition layer is a high-entropy transition layer with coexistence of multiple ions formed by the second sintering of the sodium-based layered material and the lithium cobaltate material; Among them, in the lithium cobaltate material, the value range of z is 0 < z < 0.05; in the sodium-based layered material, the value range of b is 0 < b < 0.05, and the value range of c is 0 < c < 0.

8.

2. The sodium-ion battery cathode material according to claim 1, characterized in that, The M is at least one of Zr, Nb, and Ti.

3. The sodium-ion battery cathode material according to claim 1, characterized in that, The B includes an Fe element and a combination formed with at least one of Mn, Zr, and Sn.

4. A method for preparing a sodium-ion battery cathode material according to any one of claims 1-3, characterized in that, It includes: After mixing the precursor powder of the sodium-based layered material, a sodium source, and an additive, perform the first sintering to obtain a matrix phase; Mix the matrix phase with a solution containing a cobalt salt and a sodium source, and obtain a composite material with a cobalt-coated surface after a precipitation reaction; Then, uniformly mix the composite material with a lithium source and a doping additive containing an M element according to a stoichiometric ratio, and perform the second sintering to obtain the positive electrode material for the sodium-ion battery.

5. The method for preparing the sodium-ion battery cathode material according to claim 4, characterized in that, The doping additive containing an M element is one or more of lanthanum sesquioxide, titanium dioxide, silicon dioxide, zirconium dioxide, niobium pentoxide, and tantalum pentoxide.

6. The method for preparing the sodium-ion battery cathode material according to claim 4, characterized in that, The sintering temperature of the first sintering and the second sintering is 800 - 1000 °C, and the sintering time is 6 - 18 h.

7. A positive electrode sheet, characterized in that, The positive electrode active paste in the positive electrode sheet includes the positive electrode material for the sodium-ion battery according to any one of claims 1 - 3.

8. A sodium-ion battery, characterized in that, It includes the positive electrode sheet according to claim 7.

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