CN115101742B - Composite positive electrode material, preparation method thereof, positive plate and sodium ion battery - Google Patents

Composite positive electrode material, preparation method thereof, positive plate and sodium ion battery Download PDF

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CN115101742B
CN115101742B CN202211022427.2A CN202211022427A CN115101742B CN 115101742 B CN115101742 B CN 115101742B CN 202211022427 A CN202211022427 A CN 202211022427A CN 115101742 B CN115101742 B CN 115101742B
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prussian blue
fluorophosphate
sodium
metal oxide
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CN115101742A (en
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赵成龙
陈梦婷
谈亚军
李芳芳
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Phylion Battery Co Ltd
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Abstract

The invention discloses a composite cathode material, a preparation method thereof, a cathode plate and a sodium-ion battery, and relates to the technical field of batteries; the composite anode material comprises a fluorophosphate compound, ternary sodium, a Prussian blue compound and a metal oxide, wherein the fluorophosphate compound is of a hollow structure, and the Prussian blue compound is a spherical compound; and the ternary sodium and the metal oxide are wrapped on the outer side of the Prussian blue compound to form an intermediate compound, the intermediate compound is filled in a hollow structure of the fluorophosphate compound, and the working voltage of the fluorophosphate compound is 3.5-5.0V. On one hand, the composite cathode material can fully utilize the advantages of high safety of ternary sodium, high energy density of Prussian blue compounds, high mechanical stability of metal oxides and high voltage platform of fluorophosphate compounds to improve the cycle performance and energy density of the battery; on the other hand, the safety performance of the battery can be improved by utilizing the characteristics of high safety of ternary sodium and fluorophosphate.

Description

Composite positive electrode material, preparation method thereof, positive plate and sodium ion battery
Technical Field
The invention relates to the technical field of batteries, in particular to a composite cathode material, a preparation method of the composite cathode material, a cathode plate and a sodium-ion battery.
Background
The sodium ion battery has a wide application prospect in the field of energy storage due to the cost advantage, the working principle of the sodium ion battery is similar to that of the lithium ion battery, and the reversible embedding and releasing of sodium ions between a positive electrode and a negative electrode are utilized to realize the storage and the release of energy.
However, there is currently no sodium ion battery having high safety performance, long cycle performance and high energy density. In view of this, the invention is particularly proposed.
Disclosure of Invention
The invention aims to provide a composite cathode material and a preparation method thereof, and the composite cathode material can be used for preparing a sodium ion battery with high safety performance, long cycle performance and high energy density.
The invention also aims to provide a positive plate which comprises the composite positive electrode material. Therefore, the sodium ion battery prepared from the positive plate also has the advantages of high safety performance, long cycle performance and high energy density.
The invention also aims to provide a sodium ion battery which is prepared from the positive plate. Therefore, it has advantages of high safety performance, long cycle performance and high energy density.
The embodiment of the invention is realized by the following steps:
in a first aspect, the present invention provides a composite positive electrode material comprising:
the metal oxide-containing composite material comprises a fluorophosphate compound, ternary sodium, a Prussian blue compound and a metal oxide, wherein the fluorophosphate compound is of a hollow structure, and the Prussian blue compound is a spherical compound; and the ternary sodium and the metal oxide are wrapped on the outer side of the Prussian blue compound, an intermediate compound formed by wrapping the ternary sodium and the metal oxide on the outer side of the Prussian blue compound is filled in the hollow structure of the fluorophosphate compound, and the working voltage of the fluorophosphate compound is 3.5-5.0V.
In an alternative embodiment, the mass ratio of the ternary sodium, the prussian blue compound, the fluorophosphate compound and the metal oxide is (10-60): 10-50): 3-15.
In an alternative embodiment, the pore diameter of the hollow structure of the fluorophosphate compound is 6-8 μm, and the size of the intermediate compound formed after the prussian blue compound is wrapped by the ternary sodium and the metal oxide is 2-7 μm.
In an alternative embodiment, the size of the metal oxide is smaller than the size of the tribasic sodium, the size of the tribasic sodium is smaller than the size of the prussian blue-like compound, and the size of the prussian blue-like compound is smaller than the size of the fluorophosphate compound.
In an alternative embodiment, the metal oxide is 0.1-0.5 μm in size, the tribasic sodium is 0.5-1 μm in size, the prussian blue-based compound is 1-5 μm in size, and the fluorophosphate compound is 10-30 μm in size.
In an alternative embodiment, the fluorophosphate compound has the formula Na r C1 s (P u O w ) t F i ，r>0，s>0，u>0，w>0,t is more than or equal to 1, i is more than or equal to 1; and the values of r, s, u, w, t and i satisfy the charge balance of the chemical formula, and C1 is one of transition metal elements of Ti, V, cr, mn, fe, co, ni and Cu; and/or the chemical general formula of the prussian blue compound is Na j C2 k (CN) 6 ，j>0，k>0; and the values of j and k satisfy the charge balance of the chemical formula; c2 is one of transition metal elements Mn, fe, co, ni and Cu; and/or, the general formula of the ternary sodium is Na a Ni b Co v Mn q O 2 ，a>0，b>0，v>0，q>0; and the values of a, b, v and q satisfy the charge balance of the chemical formula; the metal oxide is one of alumina, boehmite, titania, magnesia, or zirconia.
In a second aspect, the present invention provides a preparation method of the composite cathode material, including:
mixing ternary sodium, metal oxide and ethanol solution, and spraying the mixture to the outer side of the Prussian blue compound by a spray drying method to form an intermediate compound;
the intermediate compound and the fluorophosphate compound are mixed and then subjected to solid-phase sintering, so that the intermediate compound is filled in the fluorophosphate compound which is a hollow structure.
In an optional embodiment, the temperature of the spray drying step is 100 to 250 ℃, and the gas-liquid ratio is 0.2 to 0.5; the temperature of the solid phase sintering step is 800-1000 ℃, the heating rate is 5-10 ℃/min, and the sintering heat preservation time is 10-24h.
In a third aspect, the present invention provides a positive electrode sheet, including:
the positive electrode paste is prepared by mixing the composite positive electrode material, the conductive agent, the binder and the solvent in any one of the previous embodiments.
In a fourth aspect, the present invention provides a sodium ion battery comprising:
the battery comprises a shell, a positive plate, a diaphragm, a negative plate and electrolyte, wherein the positive plate, the diaphragm and the negative plate are laminated or wound to obtain a pole group, the pole group is arranged in the shell, and the electrolyte is filled in the shell.
Embodiments of the invention have at least the following advantages or benefits:
the embodiment of the invention provides a composite cathode material, which comprises a fluorophosphate compound, ternary sodium, a prussian blue compound and a metal oxide, wherein the fluorophosphate compound is of a hollow structure, and the prussian blue compound is a spherical compound; and the ternary sodium and the metal oxide are coated on the outer side of the Prussian blue compound, an intermediate compound formed after the ternary sodium and the metal oxide are coated on the outer side of the Prussian blue compound is filled in a hollow structure of the fluorophosphate compound, and the working voltage of the fluorophosphate compound is 3.5-5.0V.
On one hand, the combination of the four materials can fully utilize the advantages of high safety of ternary sodium, high energy density of the Prussian blue compound, high mechanical stability of metal oxides and high voltage platform of the fluorophosphate compound, so that the defects existing when the three materials are used independently can be overcome, and the cycle performance and the energy density of the battery are obviously improved; on the other hand, the composite cathode material is arranged in a manner that the intermediate compound formed by wrapping the ternary sodium and the metal oxide on the outer side of the Prussian blue compound is filled in the fluorophosphate compound to form a hollow structure, so that when the battery is subjected to safety tests such as short circuit, acupuncture and the like, a short circuit point acts on the ternary sodium, the metal oxide and the fluorophosphate compound particles firstly, the high safety of the ternary sodium, the metal oxide and the fluorophosphate compound can be fully utilized, the characteristic of larger short circuit resistance is realized, the short circuit current is buffered and weakened, and the purpose of obviously improving the safety performance of the sodium-ion battery is realized by the safety protection effect.
On the other hand, when the battery assembled by the composite cathode material is punctured by a foreign object, due to the high extensibility and the electronic insulation property of the metal oxide, the Prussian blue compound can be wrapped, so that the internal short circuit can be greatly reduced or even avoided, and the needling safety of the battery is improved.
The embodiment of the invention also provides a positive plate which comprises the composite positive electrode material. Therefore, the sodium ion battery prepared from the positive plate also has the advantages of high safety performance, long cycle performance and high energy density.
The embodiment of the invention also provides a sodium ion battery which is prepared from the positive plate. Therefore, the sodium ion battery also has the advantages of high safety performance, long cycle performance and high energy density.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and those skilled in the art can also obtain other related drawings based on the drawings without inventive efforts.
FIG. 1 is an SEM topography of the composite cathode material of the present invention;
FIG. 2 is an SEM topography of an intermediate compound of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
The features and properties of the present invention are described in further detail below with reference to examples.
FIG. 1 is an SEM topography of the composite positive electrode material of the present invention; FIG. 2 is an SEM topography of an intermediate compound of the present invention. Referring to fig. 1 and 2, an embodiment of the present invention provides a composite positive electrode material, which includes a fluorophosphate compound, ternary sodium, a prussian blue compound and a metal oxide, wherein the fluorophosphate compound is a hollow structure, and the prussian blue compound is a spherical compound; and the ternary sodium and the metal oxide are wrapped on the outer side of the Prussian blue compound, an intermediate compound (shown in figure 2) formed by wrapping the ternary sodium and the metal oxide on the outer side of the Prussian blue compound is filled in the hollow structure of the fluorophosphate compound, and the working voltage of the fluorophosphate compound is 3.5-5.0V.
The positive electrode materials currently used for sodium ion batteries mainly comprise three types, namely transition metal oxide systems, polyanion compounds and prussian blue systems. Polyanionic compounds can be further classified into phosphate systems, fluorophosphate systems, NASICON structures, etc. The fluorophosphate compound has the general formula of Na r C1 s (P u O w ) t F i ，r>0，s>0，u>0，w>0,t is more than or equal to 1, i is more than or equal to 1; and the values of r, s, u, w, t and i satisfy the charge balance of the chemical formula, and C1 is one of transition metal elements of Ti, V, cr, mn, fe, co, ni and Cu. The fluorophosphate system is formed by introducing fluorinions with larger electronegativity value into a polyanion compound, and when the working voltage of the fluorophosphate compound is 3.5-5.0V, the fluorophosphate compound can improve the working voltage of the material, so that the energy density is improved, and the fluorophosphate compound has better thermal stability and higher safety, but has the defects of low electronic conductivity, incapability of charging and discharging under large current and lower theoretical capacity.
The ternary sodium in the transition metal oxide system refers to an oxide containing nickel, cobalt and manganese metal ions, and has stable structure and high safety. The general formula of the ternary sodium is Na a Ni b Co v Mn q O 2 ，a>0，b>0，v>0，q>0; and the values of a, b, v and q satisfy the charge balance of the chemical formula.
The chemical general formula of the Prussian blue compounds is Na j C2 k (CN) 6 ，j>0，k>0; and the value of j, k satisfies the charge balance of the chemical formula; c2 is one of transition metal elements of Mn, fe, co, ni and Cu. The Prussian blue compound has a large sodium storage site and an ion de-intercalation channel due to a unique open frame and a three-dimensional macroporous structure, is very suitable for storing sodium ions with large ionic radius, has high effective sodium storage amount and high theoretical capacity, but crystal water in a material system is difficult to remove, and the material has structural collapse in the charging and discharging processes, so that the circulating stability of the material is influenced, the safety is poor, and potential safety hazards exist;
the metal oxide is one of aluminum oxide, boehmite, titanium oxide, magnesium oxide or zirconium oxide, and the metal oxide has stable property, does not participate in reaction, improves the stability of an electrode/electrolyte interface, and can improve the cycle performance and safety of the electrode.
Therefore, the embodiment of the invention combines the four materials, can fully utilize the high safety of the ternary sodium, the high energy density of the prussian blue compound and the high voltage platform of the fluorophosphate compound, and the mechanical stability of the metal oxide, can overcome the defects existing when the three materials are independently utilized, and obviously improves the cycle performance and the energy density of the battery.
In addition, the ternary sodium and the metal oxide are wrapped on the outer side of the Prussian blue compound, and an intermediate compound formed by wrapping the ternary sodium and the metal oxide on the outer side of the Prussian blue compound is filled in the hollow fluorophosphate compound. The metal oxide has high mechanical strength, can improve the stability of an electrode/electrolyte interface, can improve the cycle performance and safety of an electrode, can fully utilize the characteristics of high safety and large short-circuit resistance of ternary sodium and fluorophosphate compounds when the battery is subjected to safety tests such as thermal runaway, short circuit, acupuncture and the like, can buffer and weaken short-circuit current, and can wrap Prussian blue compounds due to the high extensibility and the electronic insulation property of the metal oxide, thereby greatly reducing or even avoiding internal short circuit and obviously improving the safety performance of the sodium-ion battery.
In this example, in the preparation of the composite positive electrode material, the mass ratio of the ternary sodium, the prussian blue compound, the fluorophosphate compound, and the metal oxide was (10 to 60) to (10 to 50) in the following manner: (3-15). By limiting the proportion of each component, the sodium ion battery prepared by the composite cathode material can simultaneously meet the requirements of high safety performance, long cycle performance and high energy density.
It should be noted that, in this embodiment, in order to ensure that the intermediate compound formed by wrapping the prussian blue compound with the ternary sodium is filled in the hollow structure of the fluorophosphate compound, in this embodiment, the pore diameter of the hollow structure of the fluorophosphate compound is 6 to 8 μm, and the size of the intermediate compound formed by wrapping the prussian blue compound with the ternary sodium is 2 to 7 μm. The aperture and the size are limited, so that the stability and the reliability of a structure formed by compounding the three materials can be fully ensured, and the safety, the cycle performance and the energy density of the sodium-ion battery can be ensured.
In addition, it should be noted that in the present example, the size of the metal oxide is smaller than that of the tribasic sodium, the size of the tribasic sodium is smaller than that of the prussian blue-based compound, and the size of the prussian blue-based compound is smaller than that of the fluorophosphate compound. The sizes of the ternary sodium and the metal oxide are set to be smaller than that of the Prussian blue compound, so that the ternary sodium can be tightly wrapped on the outer side of the Prussian blue compound, and therefore when thermal runaway or acupuncture and other tests occur, the ternary sodium and the metal oxide which are positioned on the outer side and have higher safety can protect the safety of the Prussian blue compound positioned on the inner side, and the safety performance of the sodium-ion battery is further improved. And because the particle size of the metal oxide is smaller than that of the ternary sodium, when the battery is out of control due to heat, the structure of the composite material collapses, the metal oxide with the minimum particle size optimally comes out of the hollow structure, and the metal oxide is an electrical poor conductor, so that the thermal runaway can be prevented from further expanding, and the safety performance of the battery can be further improved.
Illustratively, in the embodiments of the present invention, the size of the metal oxide is 0.1 to 0.5 μm, the size of the tribasic sodium is 0.5 to 1 μm, the size of the prussian blue-based compound is 1 to 5 μm, and the size of the fluorophosphate compound is 10 to 30 μm. By the definite limitation of the size, the safety, the cycle performance and the energy density of the sodium-ion battery can be fully ensured and improved.
The embodiment of the invention also provides a preparation method of the composite cathode material, which comprises the steps of mixing ternary sodium, metal oxide and ethanol solution, and spraying the mixture to the outer side of a prussian blue compound by a spray drying method to form an intermediate compound; the intermediate compound and the fluorophosphate compound are mixed and then subjected to solid-phase sintering, so that the intermediate compound is filled in the fluorophosphate compound which is a hollow structure.
On one hand, ternary sodium and metal oxide can be uniformly coated on the outer side of the prussian blue compound by a spray drying method, so that an intermediate compound can be formed. Meanwhile, the intermediate compound can be filled in the fluorophosphate compound which is a hollow structure by a solid-phase sintering method. Therefore, the composite cathode material can be rapidly prepared, so that the sodium ion battery prepared from the composite cathode material has the advantages of high safety performance, long cycle performance and high energy density.
In the embodiment of the invention, the temperature in the spray drying step is 100 to 250 ℃, and the gas-liquid ratio is 0.2 to 0.5; the temperature of the solid phase sintering step is 800-1000 ℃, the heating speed is 5-10 ℃/min, and the sintering heat preservation time is 10-24h. The selection of parameters can be adjusted as required to ensure that the composite cathode material has the structural characteristics, and the embodiment of the invention is not limited.
In the examples of the present invention, the spray pressure during spray drying may be appropriately increased in order to ensure that the ternary sodium and the metal oxide are stably attached to the outer side of the prussian blue-based compound after spray drying. Of course, in other embodiments, a binder may be mixed into the solution to improve the binding performance, and the embodiments of the present invention are not limited.
In addition, if conditions allow, the method for wrapping the external side of the prussian blue-based compound with the ternary sodium and the metal oxide may be selected from electrodeposition or vapor deposition, and the method for filling the intermediate compound formed by wrapping the external side of the prussian blue-based compound with the ternary sodium and the metal oxide into the hollow structure of the fluorophosphate compound may also be spraying or coating, and the like, so that the prussian blue-based compound can be formed to have the structural characteristics described above, and the embodiment of the present invention is not limited as well.
The embodiment of the invention also provides a positive plate which comprises an aluminum foil current collector and positive slurry coated on the aluminum foil current collector, wherein the positive slurry is obtained by mixing the composite positive material, the conductive agent, the binder and the solvent in any one of the above embodiments. The conductive agent is any one of conductive carbon black, conductive graphite, vapor-grown carbon fiber, carbon nanotube and graphene, the binder is polyvinylidene fluoride (PVDF), and the solvent is N-methylpyrrolidone (NMP). Because the positive plate is prepared from the composite positive electrode material, the sodium ion battery prepared from the positive plate also has the advantages of high safety performance, long cycle performance and high energy density.
The embodiment of the invention also provides a sodium ion battery, which comprises a shell, the positive plate, the diaphragm, the negative plate and the electrolyte, wherein the positive plate, the diaphragm and the negative plate are laminated or wound to obtain a pole group, the pole group is arranged in the shell, and the electrolyte is filled in the shell. The diaphragm can be selected as a PE film or a PP film, the negative plate can be obtained by coating negative slurry on a copper foil current collector, the negative slurry comprises a negative material, a conductive agent, a binder and a solvent, wherein the negative material can be selected from soft carbon, hard carbon or composite carbon, the conductive agent can be selected from any one of conductive carbon black, conductive graphite, vapor-grown carbon fiber, a carbon nanotube and graphene, the binder can be selected from styrene-butadiene rubber, and the solvent can be selected from N-methylpyrrolidone (NMP). The sodium ion battery is prepared by the positive plate. Therefore, the sodium ion battery also has the advantages of high safety performance, long cycle performance and high energy density.
The preparation process of the sodium ion battery and its performance are described in detail by the following specific examples:
example 1
The embodiment provides a sodium ion battery, which is prepared by the following method:
s1: mixing ternary sodium, aluminum oxide and an ethanol solution, spraying the mixture to the outer side of a Prussian blue compound by a spray drying method to form an intermediate compound, mixing the intermediate compound and a fluorophosphate compound, and performing solid-phase sintering to fill the intermediate compound into the fluorophosphate compound to form a hollow structure to form a composite anode material; uniformly mixing a composite positive electrode material, acetylene black and polyvinylidene fluoride (PVDF) according to a ratio of 94;
wherein the temperature of the spray drying step is 100 ℃, and the gas-liquid ratio is 0.2; the temperature of the solid phase sintering step is 800 ℃, the heating rate is 5 ℃/min, and the sintering heat preservation time is 24h; the mass ratio of the ternary sodium, the Prussian blue compound, the fluorophosphate compound and the alumina in the composite cathode material is 20; the size of the alumina is 0.1 mu m, the size of the tribasic sodium is 0.5 mu m, the size of the prussian blue compound is 1 mu m, and the size of the fluorophosphate compound is 10 mu m; the aperture of the hollow structure of the fluorophosphate compound is 6 mu m, and the size of an intermediate compound formed by wrapping the prussian blue compound with ternary sodium and alumina is 2 mu m;
s2: uniformly mixing hard carbon, acetylene black and styrene-butadiene rubber according to the proportion of 90;
s3: laminating the positive plate, the negative plate and the diaphragm to prepare a pole group, and then performing shell entering, assembly, welding, drying and liquid injection;
s4: and standing, pre-charging, exhausting waste gas, sealing and grading the battery after liquid injection to prepare the sodium ion battery.
Example 2
This example provides a sodium ion battery, which is prepared by a method different from that of example 1 in that:
in step S1: the temperature in the spray drying step is 150 ℃, and the gas-liquid ratio is 0.3; the temperature of the solid phase sintering step is 900 ℃, the heating rate is 8 ℃/min, and the sintering heat preservation time is 20h; the mass ratio of the ternary sodium to the Prussian blue compound to the fluorophosphate compound to the alumina in the composite anode material is 50; the size of the alumina is 0.2 mu m, the size of the tribasic sodium is 0.6 mu m, the size of the prussian blue compound is 3 mu m, and the size of the fluorophosphate compound is 20 mu m; the aperture of the hollow structure of the fluorophosphate compound is 7 mu m, and the size of the intermediate compound formed by wrapping the prussian blue compound by the ternary sodium is 3.5 mu m.
Example 3
This example provides a sodium ion battery, which is prepared by a method different from that of example 1:
in step S1: the temperature in the spray drying step is 200 ℃, and the gas-liquid ratio is 0.4; the temperature of the solid phase sintering step is 950 ℃, the heating rate is 9 ℃/min, and the sintering heat preservation time is 18h; the mass ratio of the ternary sodium to the Prussian blue compound to the fluorophosphate compound to the alumina in the composite anode material is 60; the size of the alumina is 0.4 μm, the size of the tribasic sodium is 0.8 μm, the size of the prussian blue compound is 3 μm, and the size of the fluorophosphate compound is 25 μm; the aperture of the hollow structure of the fluorophosphate compound is 7 mu m, and the size of the intermediate compound formed by wrapping the prussian blue compound by the ternary sodium is 4.5 mu m.
Example 4
This example provides a sodium ion battery, which is prepared by a method different from that of example 1:
in step S1: the temperature in the spray drying step is 250 ℃, and the gas-liquid ratio is 0.5; the temperature of the solid phase sintering step is 1000 ℃, the temperature rise speed is 10 ℃/min, and the sintering heat preservation time is 10h; the mass ratio of the ternary sodium, the Prussian blue compound, the fluorophosphate compound and the alumina in the composite cathode material is 30; the size of the alumina is 0.5 mu m, the size of the tribasic sodium is 1 mu m, the size of the prussian blue compound is 4.5 mu m, and the size of the fluorophosphate compound is 30 mu m; the aperture of the hollow structure of the fluorophosphate compound is 8 mu m, and the size of the intermediate compound formed by wrapping the prussian blue compound by the ternary sodium is 5 mu m.
Comparative example 1
Comparative example 1 provides a sodium ion battery, which is manufactured by a method different from that of example 1 in that:
in step S1, ternary sodium is selected as the positive electrode material.
Comparative example 2
Comparative example 2 provides a sodium ion battery, which is manufactured by a method different from that of example 1 in that:
in step S1, a prussian blue compound is selected as the positive electrode material.
Comparative example 3
Comparative example 3 provides a sodium ion battery, which is manufactured by a method different from that of example 1 in that:
in step S1, the positive electrode material is selected to be a fluorophosphate compound.
Comparative example 4
Comparative example 4 provides a sodium ion battery, which is manufactured by a method different from that of example 1 in that:
in step S1, the positive electrode material is selected as a mixture of ternary sodium, a prussian blue-based compound, and a fluorophosphate compound.
Experimental example 1
The energy density test was performed on the sodium ion batteries prepared in examples 1 to 4 and comparative examples 1 to 4, and the test results are shown in table 1. In the energy density test, the energy density ED = U × C0/(L × W × H) of the battery, where U is an average voltage of the battery during discharge from full power to a lower limit voltage, C0 is an actual capacity, L is a battery length, W is a battery width, and H is a battery height. Meanwhile, the actual capacity C0 is measured by fully charging at a rate of 0.5C, then discharging at a rate of 0.5C to a cut-off voltage (the voltage range used here is 5.0V to 3.0V), and taking the discharge capacity as the actual capacity C0 of the lithium ion battery.
TABLE 1 test results
Composite positive electrode material Energy Density (Wh/kg) The number of circulating turns is @85%
Example 1 Tribasic sodium + prussian blue + fluorophosphate + metal oxide 128 4320
Example 2 Tribasic sodium + prussian blue + fluorophosphate + metal oxide 128 4333
Example 3 Tribasic sodium + prussian blue + fluorophosphate + metal oxide 129 4332
Example 4 Tribasic sodium + prussian blue + fluorophosphate + goldMetal oxides 127 4333
Comparative example 1 Ternary sodium salt 116 3600
Comparative example 2 Prussian blue 144 2700
Comparative example 3 Fluorophosphate salts 120 3150
Comparative example 4 Tribasic sodium + prussian blue + fluorophosphate 136 3600
As can be seen from comparison between examples 1 to 4 and comparative examples 1 to 4 in table 1, the sodium ion battery prepared by using the composite cathode material obtained by compositing ternary sodium + prussian blue + fluorophosphate + metal oxide in the examples of the present invention has a higher energy density and a relatively higher cycle performance. Meanwhile, as can be seen from the comparative effects of examples 1 to 4 and comparative example 4, the addition of the metal oxide is effective in improving the cycle performance.
Experimental example 2
The sodium ion batteries provided in examples 1 to 4 and comparative examples 1 to 4 were subjected to overcharge, external short circuit and needle prick tests, wherein the overcharge test was carried out by preparing the cell as specified, charging the cell with a constant current of 12A and a voltage limited of 5V for 90min or until the cell explodes and fires, and stopping the charging when the above conditions were satisfied, and then left to stand for 6h. The external short circuit test is to prepare the single battery according to the specification, and then externally short circuit the positive electrode and the negative electrode of the battery for 10min, wherein the resistance of an external line is less than 5m omega. The needling test is that after the single cell is prepared according to the specification, a high temperature resistant steel needle (the conical angle of the needle point is 45-60 degrees, the surface of the needle is smooth and clean, and is free of rust, oxidation layer and oil stain) with the diameter of 5-8 mm penetrates through the single cell at the speed of (25 +/-5) mm/s from the direction vertical to the polar plate of the storage battery, the penetrating position is close to the geometric center of the needling surface, and the steel needle stays in the storage battery; observe for 1h. The results of the overcharge, external short circuit and needle prick tests are shown in table 2:
TABLE 2 electrochemical test results
Item Whether or not to catch fire Whether or not to explode Overcharge (qualification times/total times) External short circuit (qualification times/Total times) Acupuncture test (pass/total times)
Example 1 Whether or not Whether or not 10/10 10/10 10/10
Example 2 Whether or not Whether or not 10/10 10/10 10/10
Example 3 Whether or not Whether or not 10/10 10/10 10/10
Example 4 Whether or not Whether or not 10/10 10/10 10/10
Comparative example 1 Whether or not Whether or not 10/10 10/10 9/10
Comparative example 2 Is that Is that 8/10 8/10 7/10
Comparative example 3 Is that Whether or not 10/10 9/10 9/10
Comparative example 4 Whether or not Whether or not 10/10 10/10 9/10
As can be seen from the comparison between examples 1 to 4 in tables 1 and 2 and comparative example 4, energy density of the composite positive electrode material added with the metal oxide is reduced compared with that of comparative example 4, (2) cycle of the examples is better compared with that of comparative example 4 due to mechanical stability of the metal oxide, and (3) the electronic poor conductor of the metal oxide makes the examples have better safety compared with that of comparative example 4.
As can be seen from tables 1 and 2, in comparison with comparative example 1, comparative example 4 shows that ternary sodium is selected as the positive electrode material in comparative example 1, and has the advantages of stable structure, high safety, low energy density, general cyclicity, high safety, excellent safety passing test, and difficulty in completely passing the needle puncture test.
As can be seen from tables 1 and 2, when the positive electrode material of comparative example 2 is prussian blue, which is a pure material, compared with comparative example 2, comparative example 4 has high energy density, but the structure is unstable, collapse is likely to occur, and due to the existence of crystal water, thermal stability is poor, and safety tests such as needle punching are not likely to pass.
As can be seen from tables 1 and 2, when comparing example 4 with comparative example 3, the positive electrode material of comparative example 3 is a pure fluorophosphate, which has a high voltage plateau, but has a low energy density, is poor in cycle, and is difficult to completely pass safety tests such as needle punching.
In summary of the examples and comparative examples, the following conclusions can be drawn: 1) Comparative example 4 compared to comparative examples 1, 2 and 3: the comprehensive performance of energy density, circulation and safety embodied by the mixed use of the three materials is better than that of the materials when the materials are used independently; 2) Compared with comparative example 4, the metal oxide is added into the composite cathode material, partial energy density is lost, but the cycle performance and the safety performance are better, and the composite cathode material can pass safety tests such as needle punching 100%.
In summary, embodiments of the present invention provide a composite positive electrode material, a positive electrode sheet, and a sodium ion battery having high safety performance, long cycle performance, and high energy density at the same time.
The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes will occur to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. A composite positive electrode material, characterized by comprising:
the special compound comprises a fluorophosphate compound, ternary sodium, a prussian blue compound and a metal oxide, wherein the fluorophosphate compound is of a hollow structure, and the prussian blue compound is a spherical compound; the ternary sodium and the metal oxide are wrapped on the outer side of the Prussian blue compound, an intermediate compound formed after the ternary sodium and the metal oxide are wrapped on the outer side of the Prussian blue compound is filled in a hollow structure of the fluorophosphate compound, and the working voltage of the fluorophosphate compound is 3.5-5.0V;
wherein the general formula of the fluorophosphate compound is Na r C1 s (P u O w ) t F i ，r>0，s>0，u>0，w>0,t is more than or equal to 1, i is more than or equal to 1; and r, s, u, w, t, i satisfy the charge balance of the chemical formula, and C1 is a transition metal element TiV, cr, mn, fe, co, ni, cu; the general formula of the ternary sodium is Na a Ni b Co v Mn q O 2 ，a>0，b>0，v>0，q>0; and the values of a, b, v and q satisfy the charge balance of the chemical formula; the metal oxide is one of alumina, boehmite, titania, magnesia, or zirconia.
2. The composite positive electrode material according to claim 1, characterized in that:
the mass ratio of the ternary sodium to the Prussian blue compound to the fluorophosphate compound to the metal oxide is (10-60) to (10-50) to (3-15).
3. The composite positive electrode material according to claim 1, characterized in that:
the pore diameter of the hollow structure of the fluorophosphate compound is 6-8 mu m, and the size of an intermediate compound formed by wrapping the prussian blue compound by the ternary sodium and the metal oxide is 2-7 mu m.
4. The composite positive electrode material according to claim 1, characterized in that:
the size of the metal oxide is smaller than that of the ternary sodium, the size of the ternary sodium is smaller than that of the prussian blue-like compound, and the size of the prussian blue-like compound is smaller than that of the fluorophosphate compound.
5. The composite positive electrode material according to claim 4, characterized in that:
the size of the metal oxide is 0.1-0.5 mu m, the size of the tribasic sodium is 0.5-1 mu m, the size of the prussian blue compound is 1-5 mu m, and the size of the fluorophosphate compound is 10-30 mu m.
6. The composite positive electrode material according to claim 1, characterized in that:
the chemical general formula of the prussian blue compound is Na j C2 k (CN) 6 ，j>0，k>0; and the value of j, k satisfies the charge balance of the chemical formula; c2 is one of transition metal elements of Mn, fe, co, ni and Cu.
7. A method for producing the composite positive electrode material according to any one of claims 1 to 6, characterized by comprising:
mixing the ternary sodium, the metal oxide and an ethanol solution, and spraying the mixture to the outer side of the Prussian blue compound by a spray drying method to form the intermediate compound;
and mixing the intermediate compound and the fluorophosphate compound, and then carrying out solid-phase sintering to fill the intermediate compound into the hollow fluorophosphate compound.
8. The method for producing a composite positive electrode material according to claim 7, characterized in that:
the temperature of the spray drying step is 100 to 250 ℃, and the gas-liquid ratio is 0.2 to 0.5;
the temperature of the solid phase sintering step is 800-1000 ℃, the heating rate is 5-10 ℃/min, and the sintering heat preservation time is 10-24h.
9. A positive electrode sheet, comprising:
an aluminum foil current collector and a positive electrode slurry coated on the aluminum foil current collector, wherein the positive electrode slurry is obtained by mixing the composite positive electrode material, the conductive agent, the binder and the solvent according to any one of claims 1 to 8.
10. A sodium ion battery, comprising:
the positive plate, the diaphragm, the negative plate and the electrolyte are laminated or wound to obtain a pole group, the pole group is arranged in the shell, and the electrolyte is filled in the shell.
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