CN110838576A - A kind of doped coated sodium ion battery cathode material and preparation method and use thereof - Google Patents

Abstract

The invention discloses a doped coated sodium ion battery positive electrode material and a preparation method and use thereof. The preparation method comprises: weighing a sodium source, an M1 source and an M2 source according to a required stoichiometric ratio and uniformly mixing them; Heat treatment in an air atmosphere of 700℃～1000℃ for 2～24 hours to prepare a composite oxide core material Na _x M1 _a M2 _b O ₂ of O3 phase; disperse the composite oxide core material into a dispersant, and heat the composite oxide core material in a dispersant at 25 ℃ Stir at ~200°C, add the doping coating precursor during the stirring process, evaporate the dispersant to dryness, and then dry the obtained material in an oven at 80°C to 200°C to obtain a coating material; the coating material is subjected to secondary or multiple times of sintering, the sintering temperature is 400°C to 900°C, and the sintering time is 3 to 25 hours. After sintering, a coating product with a doped coating layer is obtained; Grinding to obtain a doped coated sodium ion battery positive electrode material.

Description

A kind of doped coated sodium ion battery cathode material and preparation method and use thereof

technical field

The invention relates to the technical field of materials, in particular to a doped coated sodium ion battery positive electrode material and a preparation method and application thereof.

Background technique

The problem of the depletion of fossil energy has aroused widespread concern in the society, and the large-scale utilization of renewable and clean energy such as solar and wind energy cannot be delayed. The rapid development of energy storage devices, especially electrochemical energy storage, is very important due to the intermittent characteristics of such clean energy sources that are difficult to directly connect to the grid. In electrochemical energy storage, lithium-ion batteries are widely used in people's lives due to their high voltage, high capacity, and long cycle life. However, due to the limited and uneven distribution of lithium resources, with the gradual consumption of limited lithium resources, the cost of lithium gradually increases, and its use as a large-scale energy storage lithium-ion battery is bound to be limited. Especially in recent years, the cost of lithium-ion batteries has increased due to the wide application in the 3C field and electric vehicles, which cannot meet the low-cost demand of the large-scale energy storage market.

Therefore, in the field of energy storage, it is necessary to find a secondary battery system that supplements or even replaces lithium-ion batteries. The element sodium and lithium in the same main group have very similar physical and chemical properties, and the abundance of sodium on the earth is higher than that of lithium, and the cost is lower, so the development of sodium-ion secondary batteries as a large-scale energy storage device has become a A better choice.

SUMMARY OF THE INVENTION

The invention discloses a doped coated sodium ion battery positive electrode material and a preparation method and application thereof. The doped type coated sodium ion battery positive electrode material of the invention has excellent cycle performance, good rate performance, good stability to electrolyte, simple preparation method, and improves the comprehensive performance and application potential of the material. The sodium ion secondary battery using the cathode material of the present invention has excellent cycle performance, excellent rate performance and good safety performance, and can be used for large-scale storage of solar power generation, wind power generation, smart grid peak regulation, distributed power station, backup power supply or communication base station. capable equipment.

In a first aspect, the embodiment of the present invention provides a preparation method of a doped coated sodium ion battery cathode material, the preparation method comprising:

The sodium source, M1 source and M2 source are weighed and uniformly mixed according to the required stoichiometric ratio, and heat treated in an air atmosphere of 700 ℃ to 1000 ℃ for 2 to 24 hours to prepare the composite oxide core material Na _x of the O3 phase. M1 _a M2 _b O ₂ ; the sodium source includes one or more of sodium carbonate, sodium bicarbonate and sodium hydroxide; the M1 source and the M2 source are oxides, carbonates, One or more of hydroxides; wherein, 0.8≤x≤1.0, a+b=1 and the material is electrically neutral; M1 is one or more transition metal elements; M2 is a non-transition metal element one or more of them;

Disperse the composite oxide core material into a dispersant, stir at 25°C to 200°C, add a required dose of doping coating precursor during the stirring process, evaporate the dispersant to dryness, and place the obtained material in an oven Drying at 80°C to 200°C to obtain a coating material; the doping coating precursors include Al, Mg, Ti, Zn or La nitrates and their hydrates, sulfates and their hydrates, and organic salts one or more of;

The coating material is sintered twice or multiple times, the sintering temperature is 400°C-900°C, and the sintering time is 3-25 hours, and a coating product with a doped coating layer is obtained after sintering;

The coating product with the doped coating layer is ground to obtain the doped coated sodium ion battery positive electrode material.

Preferably, the dispersing agent includes one or more of water, absolute ethanol, N-methylpyrrolidone, and acetone.

In a second aspect, an embodiment of the present invention provides a doped coated sodium-ion battery positive electrode material prepared by the preparation method described in the first aspect above, the positive electrode material includes: a core material composed of a composite oxide and a part of A doped cladding layer doped in the core material and partially covering the core material;

The core material is Na _x M1 _a M2 _b O ₂ in O3 phase, and the space group is R-3m, where 0.8≤x≤1.0, a+b=1, and the material is electrically neutral; M1 is a transition metal element , including one or more of Ti, Mn, Fe, Ni, Cu, Zn; M2 is a non-transition metal element, including one or more of Li, B, Mg, Al, Si, Ca;

The doped coating layer is Na _y M3 _d M4 _e O ₂ of O3 phase, 0≤y≤1.0, d+e=1, and the material is electrically neutral; M3 is a non-transition metal element, including Li, B , one or more of Mg, Al, Si, Ca, M4 is a transition metal element, including one or more of Ti, Mn, Fe, Ni, Cu, Zn, Zr, La.

Preferably, in the doped coated sodium ion battery cathode material, the mass percentage of the doped coated layer is 0.05%-20%.

Preferably, the doped coating layer is formed by reacting a doped coating precursor with the core material or surface impurities of the core material after liquid phase dispersion treatment and sintering; wherein, the doped coating precursor Including one or more of Al, Mg, Ti, Zn or La nitrates and their hydrates, sulfates and their hydrates, and organic salts.

In a third aspect, an embodiment of the present invention provides a sodium-ion secondary battery including the doped-type coated sodium-ion battery cathode material described in the second aspect.

In a fourth aspect, an embodiment of the present invention provides the use of the ion secondary battery described in the third aspect above, wherein the sodium ion secondary battery is used for solar power generation, wind power generation, smart grid peak regulation, distributed power station, backup power supply or Large-scale energy storage equipment for communication base stations.

The doped cladding layer obtained by the doped cladding in the present invention can provide protection for the core material while reducing the reaction between the raw material and the electrolyte, thereby reducing the accumulation of by-products such as metal fluorides on the surface, ensuring that the sodium ions are in The effective transport at the interface ultimately improves the cycle stability of the material; the preparation process is simple, the coating is uniform, and the obtained material has better comprehensive properties and application prospects, including better rate performance, cycle performance, and stability to electrolytes, etc. , has great practical value.

Description of drawings

The technical solutions of the embodiments of the present invention will be described in further detail below through the accompanying drawings and embodiments.

1 is a flowchart of a method for preparing a doped coated sodium-ion battery cathode material provided in an embodiment of the present invention;

Fig. 2 is the X-ray diffraction (XRD) pattern of core 1 provided in Example 1 of the present invention;

3 is a scanning electron microscope (SEM) image of the core 1 provided in Example 1 of the present invention;

Fig. 4 is the XRD pattern of the coating product 1 provided in Example 1 of the present invention;

Fig. 5 is the SEM image of coating product 1 provided in Example 1 of the present invention;

6 is a first-week charge-discharge curve diagram of the core 1 provided in Embodiment 1 of the present invention;

FIG. 7 is a cycle stability performance diagram of the core 1 provided in Example 1 of the present invention at a rate of 0.5C;

8 is a first-week charge-discharge curve diagram of the coated product 1 provided in Example 1 of the present invention;

Fig. 9 is the cycle stability performance diagram of coating product 1 provided in Example 1 of the present invention at a rate of 0.5C;

Fig. 10 is the XRD pattern of coating product 2 provided by Example 2 of the present invention;

Fig. 11 is the SEM image of coating product 2 provided in Example 2 of the present invention;

Fig. 12 is the distribution diagram of Ti element under the energy dispersive X-ray spectrometer (EDX) of the coating product 2 section provided in Example 2 of the present invention;

13 is a graph of the cycle stability performance of the core 1 provided in Example 2 of the present invention at a 2C rate;

14 is a first-week charge-discharge curve diagram of the coated product 2 provided in Example 2 of the present invention;

Fig. 15 is the cycle stability performance diagram of coating product 2 provided by Example 2 of the present invention at a rate of 0.5C;

Fig. 16 is the cycle stability performance diagram of coating product 2 provided in Example 2 of the present invention at 2C rate;

17 is the analysis result of F 1s under X-ray photoelectron spectroscopy (XPS) before the nuclear 1 cycle provided in Example 2 of the present invention;

Figure 18 is the analysis result of F 1s under XPS before 2 cycles of the coating product provided in Example 2 of the present invention;

Figure 19 is the analysis result of F 1s under XPS after 5 weeks of nuclear 1 cycle provided in Example 2 of the present invention;

Figure 20 is the analysis result of F 1s under XPS after 2 cycles of the coating product provided in Example 2 of the present invention;

Figure 21 is the XRD pattern of the core 2 provided in Example 3 of the present invention;

Figure 22 is the SEM image of the core 2 provided in Example 3 of the present invention;

Fig. 23 is the XRD pattern of coating product 3 provided by Example 3 of the present invention;

Figure 24 is the SEM image of the coating product 3 provided in Example 3 of the present invention;

Figure 25 is a Ti element distribution diagram under EDX for the section of coating product 3 provided in Example 3 of the present invention;

FIG. 26 is a first-week charge-discharge curve diagram of the core 2 provided in Embodiment 3 of the present invention;

Figure 27 is a cycle stability performance diagram of the core 2 provided in Example 3 of the present invention at a rate of 0.5C;

FIG. 28 is a first-week charge-discharge curve diagram of the coated product 3 provided in Example 3 of the present invention;

Figure 29 is a cycle stability performance diagram of the coating product 3 provided in Example 3 of the present invention at a rate of 0.5C;

Figure 30 is the XRD pattern of the core 3 provided in Example 4 of the present invention;

Figure 31 is the SEM image of the core 3 provided in Example 4 of the present invention;

Figure 32 is the XRD pattern of the coating product 4 provided by Example 4 of the present invention;

Fig. 33 is the SEM image of coating product 4 provided by Example 4 of the present invention;

34 is a Ti element distribution diagram under EDX for the section of the coating product 4 provided in Example 4 of the present invention;

35 is a first-week charge-discharge curve diagram of the core 3 provided in Example 4 of the present invention;

Figure 36 is a cycle stability performance diagram of the core 3 provided in Example 4 of the present invention at a rate of 0.5C;

37 is a first-week charge-discharge curve diagram of the coated product 4 provided in Example 4 of the present invention;

FIG. 38 is a cycle stability performance diagram of the coated product 4 provided in Example 4 of the present invention at a rate of 0.5C.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

An embodiment of the present invention provides a doped coated sodium-ion battery cathode material, comprising: a core material composed of a composite oxide and a dopant partially doped in the core material and partially coated outside the core material Cladding layer; wherein, the core material is Na _x M1 _a M2 _b O ₂ of O3 phase, the space group is R-3m, 0.8≤x≤1.0, a+b=1, and the material is electrically neutral; M1 is transition Metal elements, including one or more of Ti, Mn, Fe, Ni, Cu, Zn; M2 is a non-transition metal element, including one or more of Li, B, Mg, Al, Si, Ca;

The doped coating layer is formed by the reaction between the doped coating precursor and the above-mentioned core material or the surface impurities of the core material after liquid phase dispersion treatment and sintering; the doped coating precursor includes Al, Mg, Ti, Zn or La One or more of nitrates and their hydrates, sulfates and their hydrates, and organic salts. The doping cladding layer is specifically Na _y M3 _d M4 _e O ₂ of O3 phase, 0≤y≤1.0, d+e=1, and the material satisfies electrical neutrality; M3 is a non-transition metal element, including Li, B, One or more of Mg, Al, Si, Ca, M4 is a transition metal element, including one or more of Ti, Mn, Fe, Ni, Cu, Zn, Zr, La.

In the doped type coated sodium ion battery cathode material, the mass percentage of the doped coating layer is 0.05%-20%.

The above-mentioned materials can be prepared by the following methods, and the specific process steps can be shown in Figure 1:

In step 110, the sodium source, the M1 source and the M2 source are weighed according to the required stoichiometric ratio and uniformly mixed, and heat treated in an air atmosphere of 700° C. to 1000° C. for 2 to 24 hours to prepare a composite oxide core of the O3 phase. Material Na _x M1 _a M2 _b O ₂ ;

Wherein, the sodium source includes one or more of sodium carbonate, sodium bicarbonate and sodium hydroxide; M1 source and M2 source are one or more of oxides, carbonates and hydroxides of M1 and M2 respectively Among them, 0.8≤x≤1.0, a+b=1 and the material satisfies electrical neutrality; M1 is one or more transition metal elements; M2 is one or more non-transition metal elements;

Step 120: Disperse the composite oxide core material into a dispersant, stir at 25°C to 200°C, add a required dose of doping coating precursor during the stirring process, evaporate the dispersant to dryness, and place the obtained material in an oven. drying at 80℃～200℃ to obtain the coating material;

Wherein, the doping and coating precursors include one or more of Al, Mg, Ti, Zn or La nitrates and their hydrates, sulfates and their hydrates, and organic salts; One or more of water ethanol, N-methylpyrrolidone and acetone.

Step 130, sintering the coating material for two or more times, the sintering temperature is 400°C-900°C, and the sintering time is 3-25 hours, and a coating product with a doped coating layer is obtained after sintering;

In step 140, the coating product with the doped coating layer is ground to obtain the positive electrode material of the doped coated sodium ion battery.

The doped cladding layer obtained by the preparation method is formed by reacting the doped cladding precursor and the inner core material within a certain depth at high temperature, that is to say, on the basis of the traditional cladding, through the reaction A new cladding layer is formed, and we call this method "doped cladding". In the doped coating process, the impurities on the surface of the raw material (ie the composite oxide core material) or the raw material within a certain depth and the doping coating precursor infiltrate, dope and react with each other, forming a different form of the raw material and the coating. New cladding on the front body.

The doped coated sodium ion battery positive electrode material prepared by the invention can be used for sodium ion secondary battery, has the characteristics of excellent cycle performance, excellent rate performance and good safety performance, and can be used for solar power generation, wind power generation and smart grid. Large-scale energy storage equipment for peak shaving, distributed power stations, backup power supplies or communication base stations.

The preparation process, material characteristics, performance, etc. of the doped coated sodium-ion battery cathode material of the present invention will be described in detail below with some specific examples.

Example 1

First, weigh sodium carbonate, nickel monoxide, copper oxide, ferric oxide and manganese dioxide according to the required stoichiometric ratio, grind them uniformly with a mortar and place them in a muffle furnace, and sinter them into NaCu at 900°C for 24 hours. _1/9 Ni _2/9 Fe _1/3 Mn _1/3 O ₂ . It is marked as core 1, and its XRD pattern is shown in Figure 2. The results show that it is a typical O3 phase structure with a small amount of CuO impurities. The morphology under SEM is shown in Figure 3, the particle size is 1-10 microns, and there are fine particles on the surface.

Then, take 10 g of the ground core 1 and disperse it into 50 mL of absolute ethanol, stir under the heating condition of the oil bath, add 3.679 g of aluminum nitrate nonahydrate crystals (corresponding to the coating amount of 8%) during the stirring process, and the heating temperature is 90 ℃, adjust the stirring speed to 200 r/min, evaporate to dry the anhydrous ethanol, and dry the obtained solid in an oven at 120 ℃.

Pour the dried solid into a crucible and place it in a muffle furnace at 800 °C for 12 h for secondary sintering to obtain a coated product, which is labeled as coated product 1, and its XRD pattern is shown in Figure 4. The results showed that the O3 phase structure was not changed, and NaAlO ₂ was produced. The SEM photo is shown in Figure 5, the particle size is 1-10 microns, and the surface forms a uniform island-like coating. Based on the results of XRD and SEM, it can be inferred that the coating layer is NaAlO ₂ , which is the product of the reaction between the precursor aluminum nitrate nonahydrate and the core 1 within a certain depth at high temperature.

The core 1 and the coating product 1 prepared above are respectively used as the active material of the positive electrode material of the sodium ion battery for the preparation of the sodium ion battery. The specific steps are as follows: mix the prepared active material of the positive electrode material of the sodium ion battery with the conductive carbon black and the binder polyvinylidene fluoride (PVDF) according to the mass ratio of 7:2:1, add an appropriate amount of N-methylpyrrolidone ( NMP) solution was ground in a dry environment at room temperature to form a slurry, and then the slurry was evenly coated on the current collector aluminum foil, dried, and cut into a circular pole piece with a diameter of 12 mm. The circular pole pieces were dried under vacuum at 120°C for 12 hours, and then transferred to a glove box for later use. The assembly of the simulated cells was carried out in a glove box under Ar atmosphere, with metallic sodium as the counter electrode, glass fiber as the separator, and 1 mol/L NaPF ₆ in ethylene carbonate (EC)/dimethyl carbonate (DMC) (volume ratio). 1:1) solution as electrolyte, assembled into CR2032 button battery. The charge-discharge test was performed at a current density of 0.5C using the constant-current charge-discharge mode. The test conditions are: the discharge cut-off voltage is 2.0V, and the charge cut-off voltage is 4.0V.

The first-cycle charge-discharge curve of the battery prepared by core 1 is shown in Figure 6, the first-cycle discharge capacity at 0.5C rate is 110 mA h/g; the cycle performance at 0.5C rate is shown in Figure 7, and the capacity is maintained after 200 cycles The rate was 82.4%.

Figure 8 shows the first cycle charge-discharge curve of the battery prepared with doped coating product 1. The first cycle discharge capacity at 0.5C rate is 111mA·h/g; the cycle performance at 0.5C rate is as follows As shown in Figure 9, the capacity retention rate after 200 weeks was 86.6%.

Compared with the uncoated structure, it can be seen that the cycle performance of the coated material has been improved to a certain extent.

Example 2

Take 10 g of the ground core 1 in Example 1 and disperse it into 50 mL of N-methylpyrrolidone, stir in an air atmosphere and under the heating condition of an oil bath, add 2.13 mL of tetrabutyl titanate liquid dropwise during the stirring process, and heat The temperature was 60° C., the stirring speed was adjusted to 200 r/min, the N-methylpyrrolidone was evaporated to dryness in about 24 hours, and the obtained solid was dried in an oven at 120° C. overnight.

Pour the dried solid into a crucible and place it in a muffle furnace at 900 °C for 12 h for secondary sintering to obtain a coated product, which is labeled as coated product 2. Its XRD pattern is shown in Figure 10. The results show that the O3 phase structure has not changed. The SEM photo is shown in Figure 11, the particle size is 1-10 microns, and the surface forms a uniform island-like coating. Figure 12 shows the Ti element distribution of its cross-section under EDX. Combining the results of XRD, SEM and EDX, it can be inferred that Ti is distributed in a certain depth, and the coating layer is the product of the reaction between the precursor tetrabutyl titanate and a certain depth of core 1. The coating layer is O3 phase. Not shown in the XRD pattern.

The core 1 and the coating product 2 prepared above were respectively used as the active material of the positive electrode material of the sodium ion battery according to the steps described in Example 1, and assembled into a CR2032 button battery. The charge-discharge test was performed at a current density of 0.5C using the constant-current charge-discharge mode. The test conditions are: the discharge cut-off voltage is 2.0V, and the charge cut-off voltage is 4.0V.

The cycle performance of the battery prepared by core 1 at 2C rate is shown in Fig. 13, and the capacity retention rate is 82.3% after 250 cycles.

Figure 14 shows the first cycle charge-discharge curve of the battery prepared with the doped coating product 2, the first cycle discharge capacity at 0.5C rate is 111mA h/g; the cycle performance at 0.5C rate is as follows As shown in Fig. 15, the capacity retention rate after 200 cycles is 82.9%; the cycle performance at 2C rate is shown in Fig. 16, and the capacity retention rate after 250 cycles is 88.1%.

XPS was used to analyze the pole pieces of core 1 and coating product 2 before and after the charge-discharge test. First, soak the uncirculated pole piece in the electrolyte for 3 hours in the glove box, then suck the electrolyte away, rinse the surface of the positive pole piece with DMC several times, let it stand for 10 minutes, and then suck the liquid away. Repeat this step three times to ensure that NaPF ₆ has no residue, and the test will be conducted after the DMC has completely evaporated. The battery after the cycle is disassembled to take out the pole piece, and the test is carried out after the above-mentioned washing operation. Analysis of fluorine element, the results of core 1 before cycling are shown in Figure 17, and the results of coating product 2 are shown in Figure 18; the results of core 1 after five weeks of cycling are shown in Figure 19, and the results of coating product 2 are shown in Figure 19 As shown in Figure 20. From the XPS results, it can be seen that the accumulation of metal fluoride in the pole pieces of core 1 and coating product 2 is roughly the same before the cycle, but after only 5 weeks of cycling, there is a large amount of metal fluoride on the surface of the pole piece of core 1 (mainly The accumulation of sodium fluoride) has caused a certain obstacle to the conduction of sodium ions; in contrast, the surface of the coated product 2 pole piece has less accumulation, and a dense metal fluoride film is formed from the very beginning, which has a negative impact on the internal material. Protection, weakening the further reaction between the internal material and the electrolyte, preventing the damage of the material structure and ensuring the conduction of sodium ions.

Compared with the uncoated structure, it can be seen that the cycle performance of the coated material has been improved to a certain extent, and it has a good performance even at a higher magnification; the formed coating layer will affect the internal material. The protective effect and the safeguarding effect on sodium ion conduction are combined into one.

Example 3

First, weigh sodium carbonate, copper oxide, ferric oxide and manganese dioxide according to the required stoichiometric ratio, grind them uniformly with a mortar and place them in a muffle furnace, and sinter them into Na _0.92 Cu _0.22 Fe at 900 ° C for 24 hours _0.33 Mn _0.45 O ₂ . It is marked as core 2, and its XRD is shown in Figure 21. The results show that it is a typical O3 phase structure with a small amount of CuO impurities. The SEM is shown in Figure 22, the particle size is 1-10 microns, and there are fine particles on the surface.

Take 10g of the ground core 2 and disperse it into 50mL of N-methylpyrrolidone, stir in an air atmosphere and under the heating condition of an oil bath, and add 1.06mL of tetrabutyl titanate liquid (corresponding to a coating amount of 10) dropwise during the stirring process. %), the heating temperature was 60 °C, the stirring speed was adjusted to 200 r/min, the N-methylpyrrolidone was evaporated to dryness in about 24 h, and the obtained solid was dried in a 120 °C oven overnight.

Pour the dried solid into a crucible and place it in a muffle furnace at 900 °C for 12 h for secondary sintering to obtain a coated product, which is labeled as coated product 3, and its XRD pattern is shown in Figure 23. The results show that the O3 phase structure has not changed. The SEM photo is shown in Figure 24, the particle size is 1-10 microns, and the surface forms a uniform island-like coating. Figure 25 shows the Ti element distribution of its cross-section under EDX. Based on the results of XRD, SEM and EDX, it can be inferred that Ti is distributed in a certain depth, and the coating layer is the product of the reaction between the precursor tetrabutyl titanate and the inner core 2 at a certain depth. The coating layer is O3 phase. Not shown in the XRD pattern.

The core 2 and the coating product 3 prepared above were respectively used as the active material of the positive electrode material of the sodium ion battery according to the steps described in Example 1, and assembled into a CR2032 button battery. The charge-discharge test was performed at a current density of 0.5C using the constant-current charge-discharge mode. The test conditions are: the discharge cut-off voltage is 2.0V, and the charge cut-off voltage is 4.0V.

The first cycle charge-discharge curve of the battery prepared with core 2 is shown in Figure 26. The first cycle specific capacity at 0.5C rate is 107.1mA·h/g. The cycle performance at 0.5C rate is shown in Figure 27, and the capacity after 100 cycles is shown in Figure 27. The retention rate was 80.7%.

Figure 28 shows the first cycle charge-discharge curve of the battery prepared with the coated product 3 after doped coating, the first cycle discharge capacity at 0.5C rate is 118.1mA h/g; the cycle performance at 0.5C rate As shown in Figure 29, the capacity retention rate after 100 weeks was 86.0%.

Compared with the uncoated structure, it can be seen that the cycle performance of the coated material has been greatly improved.

Example 4

Weigh sodium carbonate, nickel oxide, ferric oxide and manganese dioxide according to the required stoichiometric ratio, grind them uniformly with a mortar and place them in a muffle furnace, and sinter them into NaNi _1/3 Fe _{1/ 3} Mn _1/3 O ₂ . It is labeled as core 3, and its XRD is shown in Fig. 30, and the results show that it is a typical O3 phase structure. The SEM is shown in Figure 31, the particle size is 1-10 microns, and the surface is relatively smooth.

Take 10g of the ground core 3 and disperse it into 50mL of N-methylpyrrolidone, stir in an air atmosphere and under the heating condition of an oil bath, and add 0.53mL of tetrabutyl titanate liquid (corresponding to a coating amount of 5) dropwise during the stirring process. %), the heating temperature was 70 °C, the stirring speed was adjusted to 200 r/min, the N-methylpyrrolidone was evaporated to dryness for about 12 h, and the obtained solid was dried in an oven at 120 °C overnight.

Pour the dried solid into a crucible and place it in a muffle furnace at 800 °C for 12 h for secondary sintering to obtain a coated product, which is marked as coated product 4, and its XRD pattern is shown in Figure 32. The results show that the O3 phase structure has not changed. The SEM photo is shown in Figure 33, the particle size is 1-10 microns, and the surface forms a uniform island-like coating. Figure 34 shows the Ti element distribution of its cross-section under EDX. Based on the results of XRD, SEM and EDX, it can be inferred that Ti is distributed in a certain depth, and the coating layer is the product of the reaction between the precursor tetrabutyl titanate and the inner core 3 at a certain depth. The coating layer is O3 phase. Not shown in the XRD pattern.

The core 3 and the coating product 4 prepared above were respectively used as the active material of the positive electrode material of the sodium ion battery according to the steps described in Example 1, and assembled into a CR2032 button battery. The charge-discharge test was performed at a current density of 0.5C using the constant-current charge-discharge mode. The test conditions are: the discharge cut-off voltage is 2.0V, and the charge cut-off voltage is 4.0V.

The first-cycle charge-discharge curve of the battery prepared with core 3 is shown in Figure 35. The first-cycle discharge specific capacity at 0.5C rate is 121.8mA·h/g. The cycle performance at 0.5C rate is shown in Figure 36. The capacity after 200 cycles is shown in Figure 36. The retention rate was 61.2%.

Figure 37 shows the first cycle charge-discharge curve of the battery prepared with the doped coating product 4, the first cycle discharge capacity at 0.5C rate is 118.1mA·h/g; the cycle performance at 0.5C rate As shown in Figure 38, the capacity retention rate after 200 weeks was 74.6%.

Compared with the uncoated structure, it can be seen that the cycle performance of the coated material has been greatly improved.

The doped coated sodium ion battery cathode material provided by the present invention improves the cycle stability of the raw material, and the doped coated layer obtained by the method is a precursor and a raw material within a certain depth that penetrate each other at high temperature and react with each other. The product protects the internal material while ensuring the conduction of sodium ions, and achieves the effect of improving the cycle stability under the dual action of the two, which has high practical value.

The specific embodiments described above further describe the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention, and are not intended to limit the scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (7)

1. A preparation method of a doped coated sodium-ion battery positive electrode material is characterized by comprising the following steps:

weighing and uniformly mixing a sodium source, an M1 source and an M2 source according to a required stoichiometric ratio, and performing heat treatment for 2-24 hours in an air atmosphere at 700-1000 ℃ to prepare an O3-phase composite oxide core material Na_xM1_aM2_bO₂(ii) a The sodium source comprises one or more of sodium carbonate, sodium bicarbonate and sodium hydroxide; the M1 source and the M2 source are respectively one or more of oxides, carbonates and hydroxides of M1 and M2; wherein x is 0.8-1.0, a + b is 1, and the material satisfies electroneutrality; m1 is transition metal element, including one or more of Ti, Mn, Fe, Ni, Cu, Zn; m2 isNon-transition metal elements including one or more of Li, B, Mg, Al, Si and Ca;

dispersing the composite oxide core material into a dispersing agent, stirring at 25-200 ℃, adding a required dosage of doped coating precursor in the stirring process, drying the dispersing agent by distillation, and drying the obtained material in an oven at 80-200 ℃ to obtain a coating material; the doped coating precursor comprises one or more of nitrates and hydrates of Al, Mg, Ti, Zn or La, sulfates and hydrates thereof, and organic salts;

sintering the coating material for two or more times at the sintering temperature of 400-900 ℃ for 3-25 hours to obtain a coating product with a doped coating layer;

and grinding the coating product with the doped coating layer to obtain the doped coated sodium ion battery anode material.

2. The preparation method of claim 1, wherein the dispersant comprises one or more of water, absolute ethanol, N-methyl pyrrolidone and acetone.

3. A doped coated sodium-ion battery positive electrode material prepared by the preparation method of claim 1 or 2, wherein the positive electrode material comprises: the composite oxide comprises a core material and a doped coating layer, wherein the core material is formed by a composite oxide, and the doped coating layer is doped in the core material and partially coated outside the core material;

the core material is Na of O3 phase_xM1_aM2_bO₂The space group is R-3m, wherein x is more than or equal to 0.8 and less than or equal to 1.0, a + b is 1, and the material satisfies the condition of electric neutrality; m1 is transition metal element, including one or more of Ti, Mn, Fe, Ni, Cu, Zn; m2 is non-transition metal element, including one or more of Li, B, Mg, Al, Si, Ca;

the doped coating layer is O3-phase Na_yM3_dM4_eO₂Y is more than or equal to 0 and less than or equal to 1.0, d + e is 1, and the material satisfies the condition of electric neutrality; m3 is notTransition metal elements including one or more of Li, B, Mg, Al, Si and Ca, and M4 is transition metal elements including one or more of Ti, Mn, Fe, Ni, Cu, Zn, Zr and La.

4. The doped coated sodium-ion battery positive electrode material according to claim 3, wherein the doped coating layer is 0.05-20% by mass of the doped coated sodium-ion battery positive electrode material.

5. The doped coated sodium-ion battery positive electrode material according to claim 3, wherein the doped coating layer is generated by a reaction between a doped coating precursor and the core material or surface impurities of the core material after liquid phase dispersion treatment and sintering; wherein the doped coating precursor comprises one or more of nitrates and hydrates of Al, Mg, Ti, Zn or La, sulfates and hydrates thereof, and organic salts.

6. A sodium ion secondary battery comprising the doped coated sodium ion battery positive electrode material according to any one of claims 3 to 5.

7. Use of the sodium ion secondary battery according to claim 6 for solar power generation, wind power generation, smart grid peak shaving, distributed power plants, backup power sources or large-scale energy storage devices of communication base stations.

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