A P2 / O3 composite layered oxide composite material, its preparation method and application

Abstract

The present invention discloses a P2 / O3 composite layered oxide and its preparation method and application, belonging to the field of sodium ion batteries. The molecular formula of the composite material is Na x Ni 0.2 Mn 0.55 Cu y Ti z Zn δ O2, where 0.67

Description

Technical Field

[0001] The present invention relates to the field of sodium-ion batteries, and particularly to a P2 / O3 composite layered oxide, a preparation method thereof, and an application thereof. Background Art

[0002] Currently, lithium-ion batteries have the advantages of high energy density and being reusable, becoming one of the main clean energies and being widely used in the fields of mobile electronic devices and new energy vehicles. However, lithium is not an element with rich reserves, and the recycling of lithium is also a major problem; with the popularity of lithium-ion batteries, the price of lithium ore has continued to rise, and the cost of lithium-ion batteries has continued to increase. Sodium-ion batteries have a storage principle similar to that of lithium-ion batteries and similar storage performance. Due to the abundance of sodium, they are undoubtedly a cheaper alternative.

[0003] The general formula of layered transition metal oxides is generally Na x MO 2 , which can be divided into two types, P-type and O-type, according to different sodium ion coordination environments. In the P-type structure, sodium ions occupy the trigonal prism position, while in the O-type structure, sodium ions are in the octahedral position. The number represents the stacking layer number of the oxygen layer in the minimum repeating unit. Currently, the two most concerned structures are the P2 and O3 structures, and each has its own advantages and disadvantages in different performance aspects. For example, in the P2-type structure, there is an open channel for Na + , which can enhance the diffusion of Na + and provide high capacity. However, the initial Na content of the P2-type electrode is usually lower than that of the O3-type electrode, which limits the initial Coulomb efficiency and is prone to P2→O2 phase transformation, affecting the cycle stability. Compared with P2-type materials, in O3-type materials, the diffusion of sodium from one octahedral position to another occurs through the face-sharing interstitial tetrahedral position, and the diffusion rate is relatively slow, resulting in poor rate performance and cycle performance. Moreover, when the O3-type layered oxide is exposed to air, sodium will be spontaneously extracted and form sodium residues (such as sodium carbonate, sodium hydroxide, etc.) on the interface, thereby reducing the active material and interface ionic conductivity and greatly increasing the material storage and battery manufacturing costs.

[0004] Therefore, it is particularly important to develop a layered metal oxide with high specific capacity, excellent cycle stability and rate performance as the positive electrode material of sodium-ion batteries. Summary of the Invention

[0005] Aiming at the deficiencies of the above-mentioned existing technologies, one of the purposes of the present invention is to provide a P2 / O3 composite layered oxide composite material, which has a P2 / O3 composite structure, has the stability of the P2 structure and the high capacity of the O3 structure, and has a high specific capacity as a cathode material for sodium-ion batteries, excellent cycle stability and rate performance, and is particularly suitable for applications on cathode materials for high-rate sodium-ion batteries.

[0006] The above object of the present invention is achieved by the following technical solutions:

[0007] A P2 / O3 composite layered oxide composite material, the molecular formula of the composite material is Na x Ni 0.2 Mn 0.55 Cu y Ti z Zn δ O 2 , where 0.67 < x < 1, y = 2z, y + z + δ = 0.25, 0.02 < δ < 0.05;

[0008] The composite material has a P2 structure and an O3 structure, where the P2 structure is concentrated on the periphery of the composite material, and the O3 structure is concentrated inside the composite material.

[0009] The layered metal oxide of the present invention has a P2 / O3 composite structure. The outer P2 structure not only provides a sodium ion diffusion channel, accelerates the migration power of ions and electrons, but also alleviates the problem that the O3-type material is prone to failure when exposed to air. The internal O3 structure provides sufficient sodium content for the whole, and there is also a certain intercalation pseudocapacitance effect at the interface between P2 and O3, which can provide a certain capacity. At the same time, there are certain dislocations in the composite structure, which is beneficial to improving the stability of the composite material and alleviating the volume expansion during charge and discharge. This composite material exhibits high capacity, high rate performance and excellent cycle stability as a cathode material for sodium-ion batteries.

[0010] The present invention uses specific proportions of copper, titanium, and zinc to replace nickel. On the one hand, it can reduce costs. On the other hand, the introduction of several transition metal ions all has a certain impact on the performance of the composite material. For example, the introduction of copper ions can inhibit phase transformation and enhance the stability of the composite material in air; titanium ions can make the charge and discharge curves smooth, solve the problem of oxygen evolution at high voltages, and effectively improve the sodium ion diffusion coefficient; the introduction of zinc ions can play a pillar role and alleviate the electrostatic repulsion effect between sodium layers.

[0011] Preferably, the composite material includes a hexagonal crystal structure and a rhombohedral crystal structure.

[0012] Another object of the present invention is to provide a method for preparing the P2 / O3 composite layered oxide composite material, which specifically includes the following steps:

[0013] S1. According to the stoichiometric ratio of metal elements in the composite material, dissolve the sodium source, manganese source, nickel source, zinc source and copper source in deionized water, stir evenly at 70-90 °C, then add citric acid in an amount 1-2 times the molar ratio of metal ions to obtain a green transparent solution; then add a mixed solution of tetrabutyl titanate and ethanol, continuously stir at 80-90 °C, and the solvent evaporates to form a sol. After drying the obtained sol, a light green precursor powder is obtained;

[0014] S2. Grind the precursor powder obtained in step S1, then place it at 500-700 °C for heat preservation for 4-6 h, and then raise the temperature to 850-950 °C for heat preservation for 10-14 h to obtain the P2 / O3 composite layered oxide composite material.

[0015] In the preparation method of the present invention, a wet gel is first synthesized by the sol-gel method, and then a layered oxide Na x Ni 0.2 Mn 0.55 Cu y Ti z Zn δ O 2 is obtained through high-temperature annealing; this method has the advantages of simple preparation process, low cost, environmental protection and non-toxicity.

[0016] Preferably, in step S1, the volume ratio of tetrabutyl titanate to ethanol is (2-4):50.

[0017] Preferably, in step S1, the drying temperature is 110-120 °C and the time is 12 h.

[0018] Preferably, in step S2, the temperature of the solvothermal reaction is 140-160 °C and the reaction time is 8-16 h.

[0019] Preferably, in step S2, the precursor powder is ground to obtain a white powder, then the white powder is placed at 500 °C for heat preservation for 5 h, and then heated to 900 °C at a rate of 8 °C / min for heat preservation for 12 h.

[0020] Preferably, the sodium source is at least one of sodium carbonate, sodium nitrate, and sodium acetate; the manganese source includes at least one of manganese acetate, manganese nitrate, manganese sulfate, and manganese chloride; the nickel source includes at least one of nickel acetate, nickel nitrate, nickel sulfate, and nickel chloride.

[0021] Preferably, the zinc source is zinc acetate or zinc chloride; the copper source is copper acetate or copper chloride.

[0022] Another object of the present invention is to provide an application of the P2 / O3 composite layered oxide composite material prepared by the preparation method in the preparation of a positive electrode material for a sodium ion battery.

[0023] Compared with the prior art, the present invention is beneficial in that:

[0024] (1) The layered metal oxide of the present invention has a P2 / O3 composite structure. The peripheral P2 structure not only provides a sodium ion diffusion channel and accelerates the migration power of ions and electrons, but also alleviates the problem that the O3 type material is easily ineffective when exposed to air. The internal O3 structure provides sufficient sodium content for the whole, and there is also a certain intercalation pseudocapacitance effect at the interface between P2 and O3, which can provide a certain capacity. At the same time, there are certain dislocations in the composite structure, which is beneficial to improve the stability of the composite material and alleviate the volume expansion during the charge and discharge process. The composite material exhibits high capacity, high rate performance and excellent cycle stability as a positive electrode material for sodium ion batteries.

[0025] (2) The present invention uses copper, titanium and zinc in specific proportions to replace nickel, which can reduce costs on the one hand, and on the other hand, the introduction of several transition metal ions has a certain effect on the performance of the composite material. For example, the introduction of copper ions can inhibit phase change and enhance the stability of the material in the air; titanium ions can make the charge and discharge curve smooth, solve the problem of oxygen evolution under high voltage, and effectively improve the diffusion coefficient of sodium ions; the introduction of zinc ions can play a supporting role and alleviate the electrostatic repulsion effect between sodium layers.

[0026] (3) The layered oxide composite material of the present invention is used as a positive electrode material for sodium ion batteries at 0.01 A·g -1 The current density can reach 133.9 mAh g -1 The reversible capacity at 1A·g -1 At high current density, it can reach 82.8mAh·g -1 , it can maintain 65.4mAh·g after 500 cycles -1 capacity. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 HR-TEM image and SEAD image of the composite material prepared in Example 1;

[0028] Figure 2 for Figure 1 (a) A partial enlarged view;

[0029] Figure 3 The SEM images of the composite materials prepared in Examples 1-2 and Comparative Example 1;

[0030] Figure 4XRD patterns of the composite materials prepared in Examples 1-2 and Comparative Example 1;

[0031] Figure 5 Cycling performance graphs of the composite materials prepared in Examples 1-2 and Comparative Example 1 at a current density of 1 A·g -1 ;

[0032] Figure 6 Rate performance graph of the composite material prepared in Example 1;

[0033] Figure 7 Cycling performance graph of the composite material prepared in Example 4 at a current density of 0.1 A·g -1 ; Detailed implementation manners

[0034] The technical solutions of the present invention will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the protection scope of the present invention.

[0035] Example 1

[0036] A preparation method of a P2 / O3 composite layered oxide composite material specifically includes the following steps:

[0037] S1. Dissolve 0.45 mmol of sodium carbonate, 0.55 mmol of manganese acetate tetrahydrate, 0.2 mmol of nickel acetate tetrahydrate, 0.14 mmol of copper acetate monohydrate, and 0.04 mmol of zinc acetate dihydrate in 200 mL of deionized water in sequence, then mix, stir at 80°C to obtain a uniform metal solution, add citric acid in an amount 1.5 times the molar ratio of the total metal ions, and the turbid solution becomes a green transparent solution; then add a mixed solution of tetrabutyl titanate and ethanol (tetrabutyl titanate is 0.07 mmol in the mixed solution, and the volume ratio of tetrabutyl titanate to ethanol is 3:50), continuously stir at 80°C, the solvent evaporates to form a sol, and finally dry the obtained sol at 120°C for 12 h to obtain a light green precursor powder;

[0038] S2. Grind the precursor powder obtained in step S1 to obtain a white powder, then put the white powder into a crucible, place the crucible in a muffle furnace, keep it at 500°C for 5 h, and then heat it to 900°C at a rate of 8°C / min and keep it for 12 h to obtain the P2 / O3 composite layered oxide composite material Na 0.9 Ni 0.2 Mn 0.55 Cu 0.14 Ti 0.07 Zn 0.04 O2 。

[0039] Figure 1 (a) and Figure 2 Na 0.9 Ni 0.2 Mn 0.55 Cu 0.14 Ti 0.07 Zn 0.04 O 2 HR-TEM image of the composite material, Figure 2 SEAD pattern of the composite material. It can be seen that the measurement of its interplanar spacing shows that the edge part is the P2 phase and the inner part is the O3 phase. The (001) interplanar spacing of the P2 phase is 0.249 nm, and the (012) interplanar spacing of the O3 phase is 0.244 nm. The SEAD pattern shows polycrystalline diffraction rings, including planes such as (002) and (103) belonging to P2, and planes such as (012) and (015) belonging to O3. Figure 2 The composite material prepared in Example 1 contains a hexagonal crystal structure and a rhombohedral crystal structure.

[0040] Example 2

[0041] The preparation method of the P2 / O3 composite layered oxide material in this example is basically the same as that in Example 1, except that the amount of sodium carbonate used is 0.35 mmol, and the amount of citric acid is the same as the amount of total metal ions; the molecular formula of the prepared composite material is Na

[0042] 0.7 Ni 0.2 Mn 0.55 Cu 0.14 Ti 0.07 Zn 0.04 2 O 2 。

[0043] Example 3

[0044] A preparation method of a P2 / O3 composite layered oxide material specifically includes the following steps:

[0045] S1. Dissolve 0.8 mmol of sodium acetate, 0.55 mmol of manganese nitrate, 0.2 mmol of nickel nitrate, 0.14 mmol of copper chloride and 0.04 mmol of zinc chloride in 200 mL of deionized water in sequence, then mix them, stir at 90 °C to obtain a homogeneous metal solution, add citric acid with a molar ratio of 1.5 times the total metal ions, and the turbid solution turns into a green transparent solution; then add a mixed solution of tetrabutyl titanate and ethanol (in the mixed solution, tetrabutyl titanate is 0.07 mmol, and the volume ratio of tetrabutyl titanate to ethanol is 4:50), continuously stir at 90 °C, the solvent evaporates to form a sol, and finally dry the obtained sol at 110 °C for 12 h to obtain a light green precursor powder;

[0046] S2. Grind the precursor powder obtained in step S1 to obtain a white powder, then put the white powder into a crucible, place the crucible in a muffle furnace, keep it at 700 °C for 4 h, then heat it to 850 °C at a rate of 8 °C / min and keep it for 14 h to obtain the P2 / O3 composite layered oxide composite material Na 0.8 Ni 0.2 Mn 0.55 Cu 0.14 Ti 0.07 Zn 0.04 O 2 .

[0047] Example 4

[0048] The preparation method of the P2 / O3 composite layered oxide composite material in this example is basically the same as that in Example 1, except that the dosage of sodium carbonate is 0.35 mmol, the dosage of copper acetate monohydrate is 0.15 mmol, the dosage of zinc acetate dihydrate is 0.025 mmol, and the dosage of tetrabutyl titanate is 0.075 mmol; the molecular formula of the prepared composite material is Na 0.7 Ni 0.2 Mn 0.55 Cu 0.15 Ti 0.075 Zn 0.025 O 2 .

[0049] Comparative Example 1

[0050] The preparation method of the P2 / O3 composite layered oxide composite material in this comparative example is basically the same as that in Example 1, except that the dosage of sodium carbonate is 0.5 mmol; the molecular formula of the prepared composite material is

[0051] NaNi 0.2 Mn 0.55 Cu 0.14 Ti 0.07 Zn 0.04 O2 .

[0052] Comparative Example 2

[0053] The preparation method of the P2 / O3 composite layered oxide composite material in this comparative example is basically the same as that in Example 1. The difference is that no zinc source is added, and the proportions of copper source and titanium source are increased synchronously. 0.45 mmol of sodium carbonate, 0.5 mmol of manganese acetate tetrahydrate, 0.2 mmol of nickel acetate tetrahydrate, and 0.2 mmol of copper acetate monohydrate are successively dissolved in 200 mL of deionized water, and then a mixed solution of tetrabutyl titanate and ethanol (in the mixed solution, tetrabutyl titanate is 0.1 mmol, and the volume ratio of tetrabutyl titanate to ethanol is 3:50) is added. The remaining operations are the same as those in Example 1; the molecular formula of the prepared composite material is Na 0.9 Ni 0.2 Mn 0.5 Cu 0.2 Ti 0.1 O 2 .

[0054] Figure 3 FIG. is the SEM image of the composite material. Among them, (a), (b), and (c) are the SEM images of the composite materials prepared in Example 1, Example 2, and Comparative Example 1 respectively. It can be seen from the figure that the surface morphology of the material is relatively smooth and has a layered structure, which is beneficial to the infiltration of the electrolyte.

[0055] Figure 4 FIG. is the XRD pattern of the composite materials prepared in Example 1, Example 2, and Comparative Example 1. It can be seen from the figure that all the peaks in the XRD pattern of the composite material in Example 1 can well correspond to the standard card peaks of O3-(PDF#54-0887) and P2-(PDF#0894), having both P2 structure and O3 structure. While the composite material in Comparative Example 1 lacks some characteristic peaks of the P2 structure.

[0056] Application Example

[0057] The composite materials prepared in Examples 1 to 4 and Comparative Examples 1 to 2, a conductive agent (acetylene black), and a binder (polyvinylidene fluoride) were mixed according to a mass ratio of 7:2:1, an appropriate amount of N-methylpyrrolidone was added, and after ultrasonic dispersion, a slurry was formed. The slurry was coated on an aluminum foil and vacuum dried for 12 h and then pressed into a positive electrode sheet. Using the prepared composite material as the positive electrode, a sodium sheet as the negative electrode, a glass fiber as the separator, and NaClO 4 as the electrolyte, a button battery (CR2032) was assembled and its electrochemical performance was tested.

[0058] Using a Blue Power battery test system at 1 A·g -1At a current density of, the electrochemical performance of the composite materials of Examples 1 to 2 and Comparative Example 1 was tested by constant current charge and discharge technology, and the test results are as follows Figure 5 shown; from Figure 5 it can be seen that at a current density of 1 A·g -1 , the initial discharge specific capacity of the composite material of Example 1 was 82.8 mAh / g, the discharge specific capacity after 500 cycles was 65.4 mAh / g, and the capacity retention rate was 78.9%; the initial discharge specific capacity of the composite material of Example 2 was 86.6 mAh / g, and the discharge specific capacity after 500 cycles was 67 mAh / g; it shows that the P2 / O3 composite layered composite material of the present invention has excellent cycle stability. The initial discharge specific capacity of the composite material of Comparative Example 1 was 86.3 mAh / g, the discharge specific capacity after 500 cycles was 51.5 mAh / g, and the capacity retention rate was only 59.7%. The initial discharge specific capacity of Comparative Example 2 was only 67.7 mAh / g, and the discharge specific capacity after 500 cycles was 59.2 mAh / g.

[0059] Figure 6 Figure of the rate performance of the composite material of Example 1, from Figure 6 it can be seen that at a current density of 0.01 A·g -1 , a reversible capacity of 133.9 mAh·g -1 can be achieved, and at a large current of 1 A·g -1 , there is still a reversible capacity of more than 80 mAh·g -1 , and when restored to a small current, the capacity is not lost; it shows that the composite material of the present invention has excellent rate performance.

[0060] The R of the composite material of Example 1 as a positive electrode material for sodium ion batteries ct is 280 Ω to 360 Ω, and the sodium ion diffusion coefficient is 1.552×10 -11 cm 2 ·s -1 ~2.382×10 -10 cm 2 ·s -1 .

[0061] Using a blue battery test system at a current density of 0.1 A·g -1 , the electrochemical performance of the composite material of Example 4 was tested by constant current charge and discharge technology, and the test results are as follows Figure 7 shown, from Figure 7 it can be seen that at a current density of 0.1 A·g -1 , the initial discharge specific capacity of the composite material of Example 4 was 103.9 mAh / g, and the discharge specific capacity after 100 cycles was 91 mAh / g.

[0062] Although embodiments of the present invention have been shown and described, those of ordinary skill in the art will understand that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A P2 / O3 composite layered oxide composite material, characterized in that, The molecular formula of the composite material is Na x Ni 0.2 Mn 0.55 Cu y Ti z Zn δ O 2 , where 0.67 < x < 1, y = 2z, y + z + δ = 0.25, 0.02 < δ < 0.05; the composite material has a P2 structure and an O3 structure, wherein the P2 structure is concentrated on the periphery of the composite material, and the O3 structure is concentrated inside the composite material.

2. The P2 / O3 composite layered oxide composite material according to claim 1, characterized in that, the composite material comprises a hexagonal crystal structure and a rhombohedral crystal structure.

3. A method for preparing the P2 / O3 composite layered oxide composite material according to any one of claims 1 to 2, characterized in that, it includes the following steps: S1. According to the stoichiometric ratio of metal elements in the composite material, dissolve the sodium source, manganese source, nickel source, zinc source and copper source in deionized water, stir evenly at 70-90 °C, then add citric acid with a molar ratio of metal ions of 1-2 times to obtain a green transparent solution; then add a mixed solution of tetrabutyl titanate and ethanol, continuously stir at 80-90 °C, the solvent evaporates to form a sol, and the obtained sol is dried to obtain a light green precursor powder; S2. Grind the precursor powder obtained in step S1, then place it at 500-700 °C for heat preservation for 4-6 h, and then raise the temperature to 850-950 °C for heat preservation for 10-14 h to obtain the P2 / O3 composite layered oxide composite material.

4. The method for preparing the P2 / O3 composite layered oxide composite material according to claim 3, characterized in that, in step S1, the volume ratio of the tetrabutyl titanate to the ethanol is (2-4):

50.

5. The method for preparing the P2 / O3 composite layered oxide composite material according to claim 3, characterized in that, in step S1, the drying temperature is 110-120 °C and the time is 12 h.

6. The method for preparing the P2 / O3 composite layered oxide composite material according to claim 3, characterized in that, in step S2, the precursor powder is ground to obtain a white powder, then the white powder is placed at 500 °C for heat preservation for 5 h, and then heated to 900 °C at a rate of 8 °C / min for heat preservation for 12 h.

7. The method for preparing the P2 / O3 composite layered oxide composite material according to claim 3, characterized in that, the sodium source is at least one of sodium carbonate, sodium nitrate, and sodium acetate; the manganese source includes at least one of manganese acetate, manganese nitrate, manganese sulfate, and manganese chloride; the nickel source includes at least one of nickel acetate, nickel nitrate, nickel sulfate, and nickel chloride.

8. The method for preparing the P2 / O3 composite layered oxide composite material according to claim 3, characterized in that, the zinc source is zinc acetate or zinc chloride; the copper source is copper acetate or copper chloride.

9. Application of the P2 / O3 composite layered oxide composite material prepared by the preparation method according to any one of claims 3 to 8 in the preparation of a positive electrode material for a sodium ion battery.

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