Calcium ion doped modified sodium ion positive electrode material and preparation method thereof, positive electrode plate and half cell

Abstract

The invention belongs to the technical field of sodium ion batteries, and particularly relates to a calcium ion doped modified sodium ion positive electrode material and a preparation method thereof, a positive electrode plate and a half battery. The calcium ion doped modified sodium ion positive electrode material comprises a sodium source, a doping source and a precursor, and is characterized in that the chemical general formula of the positive electrode material is Na < 1-x > M < x > Ni Fe Mn < c > O < 2 >, the value range of the doping sources M and x is x < = 0.05, a + b + c = 1, and all elements in the chemical formula meet charge balance. Sodium sites in a layered structure are replaced by calcium ion doping, so that interlayer spacing is enlarged, sodium ion transmission kinetics is enhanced, and adverse phase change is inhibited. The sodium ion positive electrode material shows high specific capacity and excellent cycle stability, the capacity retention ratio is 93.03% after 100 times of cycle charge and discharge at 1C, and the sodium ion positive electrode material has the characteristics of simple preparation, low cost, high specific capacity and excellent cycle performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries and relates to a calcium ion-doped modified sodium ion positive electrode material and a preparation method thereof, a positive electrode sheet and a half-battery. Background Art

[0002] In recent years, with the large-scale application of electric vehicles, the demand for lithium resources has increased dramatically. However, the reserves of lithium resources in the earth's crust are very small, and there is an uneven distribution problem in the region, which leads to rising costs year by year, limiting its application in the field of large-scale power storage. Sodium-ion batteries have a similar charging and discharging mechanism to lithium-ion batteries, and sodium ions and lithium ions have very similar physical and chemical properties. The most important thing is that sodium resources are very abundant and widely distributed, so the development of sodium-ion battery technology has a positive significance for large-scale power storage systems. While reducing costs, sodium-ion batteries also have high specific energy density, excellent energy conversion efficiency and long charge and discharge cycle life, which provides an opportunity to gradually replace the use of lead-acid batteries.

[0003] Transition metal oxides in sodium ion layered oxides (Na x MO2), which has been widely studied due to the low cost and environmental friendliness of Mn and Fe and the attractive sodium ion embedding behavior. It is mainly divided into two types, P2 type and O3 type, of which O3 type has the advantage of accommodating a higher amount of Na ions into the layered structure and shows a higher charge / discharge capacity, but has poor stability. This is because some complex phase transition processes during the charge and discharge process cause the P2 type material to undergo an irreversible P2→O2 phase transition at high potential, while the phase transition of the O3 type material is more complicated, which leads to reduced cycle performance.

[0004] The Chinese patent application with application number CN 117996069A discloses a method of effectively solving the problems of poor cycle stability and poor rate performance of the positive electrode material system by co-doping with Cu, Mg and Ti, which is beneficial to maintain the structural stability of the electrode material during the sodium ion insertion and extraction process. However, this method involves co-doping of three elements, and the material cost and process cost are too high, which is not conducive to industrial large-scale production. Summary of the invention

[0005] In view of the problems existing in the prior art, the purpose of the present invention is to focus on the advantages of low cost of sodium ion batteries, and propose a preparation method and application of a calcium ion-doped modified sodium ion positive electrode material from the comprehensive perspectives of single element doping, low energy consumption, and high electrical performance. Specifically, calcium ions are introduced to replace part of the sodium sites to expand the interlayer spacing and improve the sodium ion diffusion capacity; at the same time, calcium ion doping can inhibit the complex phase change during the charge and discharge process and promote highly reversible phase change, thereby improving the cycle stability and specific capacity of the battery.

[0006] In order to achieve the above invention objectives, the present invention is implemented by the following technical solutions: A calcium ion-doped modified sodium ion positive electrode material has a layered structure. The positive electrode material is prepared by doping calcium ions into the crystal interior of the sodium ion positive electrode material and the interlayer spacing becomes larger, but the crystal structure does not change.

[0007] The general formula of the modified sodium ion positive electrode material doped with calcium ions is Na 1-2x M x Ni a Fe b Mn c O2.

[0008] Preferably, the value range of the doping source M is x ≤ 0.05, and a+b+c=1, and the charge balance between the elements in the chemical formula is satisfied. 0.9 Ca 0.05 Ni 0.3334 Fe 0.3332 Mn 0.3334 O2.

[0009] Preferably, the present invention also provides a method for preparing the above-mentioned calcium ion-doped modified sodium ion positive electrode material, the preparation method being a ball milling method and a high-temperature solid phase method; the preparation method comprising the following steps: (1) Weigh the corresponding metal elements such as sodium source, doping source and precursor according to the molar ratio of the chemical formula in the positive electrode material; (2) placing the sodium source, doping source and precursor weighed in step (1) into a premix container, then premixing at high speed, and then transferring to a horizontal ball mill for high-speed ball milling to obtain a mixture powder; (3) The mixed powder obtained in step (2) is placed in a crucible, and after special pretreatment, the crucible is transferred to a muffle furnace, and high-temperature calcination is performed at a certain heating rate, calcination time, calcination temperature and protective atmosphere. A two-step calcination method is used to obtain a sodium ion battery positive electrode material with low cost, high specific capacity and excellent cycle performance.

[0010] According to a specific embodiment of the present invention, in step (1), the sodium source has an excess of 1% to 5% (molar percentage) of sodium element to compensate for the loss of sodium source during the high-temperature calcination process.

[0011] According to a specific embodiment of the present invention, in step (1), the sodium source is provided by a sodium salt, preferably, the sodium salt is selected from at least one of sodium nitrate, sodium peroxide, sodium oxalate, sodium hydroxide, and sodium carbonate. The doping source is provided by a calcium salt, preferably, the calcium salt is selected from at least one of calcium oxide, calcium carbonate, calcium nitrate, and calcium acetate. The precursor is provided by a nickel-iron-manganese precursor, preferably, the nickel-iron-manganese precursor is selected from at least one of nickel-iron-manganese carbonate, nickel-iron-manganese hydroxide, and nickel-iron-manganese oxide.

[0012] According to a specific embodiment of the present invention, in step (2), the rotation speed of the horizontal ball mill is 300-600 rpm, preferably 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm, 550 rpm, 600 rpm or a range between any two of the above values. Preferably, the ball milling time is 0.5 h to 3 h.

[0013] According to a specific embodiment of the present invention, in the step (3), the parameters of high temperature calcination are: the first calcination temperature (T1) is 500-700°C, the heating rate is 2-5°C / min, and the calcination time is 3-6 h. Preferably, the first calcination temperature is 500°C, 550°C, 600°C, 650°C, 700°C or a range between any two of the above values. The secondary calcination temperature (T2) is 800-1000°C, and the calcination time is 9-14 h. Preferably, the secondary calcination temperature is 800°C, 850°C, 900°C, 950°C, 1000°C or a range between any two of the above values. Preferably, the calcination is carried out in an atmosphere muffle furnace, and the protective atmosphere includes but is not limited to argon atmosphere, oxygen atmosphere, and air atmosphere.

[0014] The present invention also protects the use of the above-mentioned calcium ion-doped modified sodium ion positive electrode material, preferably as a positive electrode material for a sodium ion battery.

[0015] The present invention also provides a sodium ion positive electrode plate, preferably containing the positive electrode material of the sodium ion battery mentioned above.

[0016] The present invention also provides a sodium ion half-cell, preferably, the working electrode contains the above sodium ion positive electrode sheet, and the commercial sodium sheet is used as the counter electrode and the reference electrode. Preferably, the diaphragm is made of at least one of polyethylene, polypropylene and ceramic.

[0017] The present invention also provides an application of the above-mentioned sodium ion battery in large-scale energy storage devices such as electric two-wheeled vehicles, A00-class new energy vehicles, start-stop power supplies, portable household energy storage or photovoltaic power stations.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (i) The present invention adopts a modification method of calcium ion doping to dope calcium ions into the crystal structure of the sodium ion layered oxide positive electrode material to replace part of the sodium ions, thereby increasing the interlayer spacing of the layered structure and enhancing the transport kinetics of the sodium ions; (ii) At the same time, calcium ion doping can inhibit the Mn 4+ To Mn 3+ The Jiang-Taylor effect is effectively improved, thereby effectively improving the battery life and cycle stability.

[0019] (III) The preparation method of the calcium ion-doped modified sodium ion positive electrode material proposed in the present invention is simple, highly operable, low-cost and has good repeatability. It has the advantages of high specific capacity, high energy density and excellent cycle stability in electrical properties and has good commercialization potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 0.1 C first cycle charge and discharge curves of Example 1, Example 2 and Comparative Example 1; Figure 2 0.1 C first cycle charge and discharge curves of Example 3, Example 4 and Comparative Example 2; Figure 3 The discharge specific capacity curves of Example 3, Example 4 and Comparative Example 2 after 100 cycles of 1 C are shown in FIG. DETAILED DESCRIPTION The present invention is further described below in conjunction with embodiments, which are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, other embodiments obtained by ordinary technicians in the field without creative work are all within the scope of protection of the present invention.

[0021] In the present application, % not specifically indicated indicates the mass percentage, i.e., wt%; the reagents or instruments used without indicating the manufacturer are conventional products that can be purchased commercially.

[0022] Embodiment 1: Preparation of Na 0.9 Ca 0.05 Ni 0.3328 Fe 0.3326 Mn 0.3346 O2 calcium ion doped modified sodium ion cathode material: According to the above chemical formula, 135.78 g of nickel-iron-manganese precursor Ni 0.3328 Fe 0.3326 Mn 0.3346(OH)2, 74.08 g sodium carbonate (Na2CO3), and 6.02 g calcium carbonate (CaCO3) were milled in a horizontal ball mill at 400 rpm for 3 h to obtain a mixed powder, which was placed in an atmosphere muffle furnace after treatment. The first sintering was completed by heating to 600 °C at 5 °C / min and keeping it for 4 h, and then the second sintering was completed by heating to 1050 °C at 5 °C / min and keeping it for 10 h. The modified sodium ion positive electrode material Ca-1 doped with calcium ions was obtained by cooling to room temperature with the furnace.

[0023] Example 2 Preparation of Na 0.94 Ca 0.03 Ni 0.3328 Fe 0.3326 Mn 0.3346 O2 calcium ion doped modified sodium ion cathode material: According to the above chemical formula, 135.78 g of nickel-iron-manganese precursor Ni 0.3328 Fe 0.3326 Mn 0.3346 (OH)2, 77.27 g sodium carbonate (Na2CO3), 7.52 g calcium carbonate (CaCO3), use a horizontal ball mill at 400 rpm for 3 h to obtain a mixed powder, which is placed in an atmosphere muffle furnace after treatment. The first sintering is completed by heating to 600 ℃ at 5 ℃ / min and keeping it for 4 h, and then the second sintering is completed by heating to 1050 ℃ at 5 ℃ / min and keeping it for 10 h. The modified sodium ion positive electrode material Ca-2 doped with calcium ions is obtained by cooling to room temperature with the furnace.

[0024] Example 3 Preparation of Na 0.9 Ca 0.05 Ni 0.3328 Fe 0.3326 Mn 0.3346 O2 calcium ion doped modified sodium ion cathode material: According to the above chemical formula, 135.78 g of nickel-iron-manganese precursor Ni 0.3328 Fe 0.3326 Mn 0.3346 (OH)2, 74.08 g sodium carbonate (Na2CO3), and 7.52 g calcium carbonate (CaCO3) were milled in a horizontal ball mill at 400 rpm for 3 h to obtain a mixed powder, which was placed in an atmosphere muffle furnace after treatment. The first sintering was completed by heating to 570 ℃ at 5 ℃ / min and keeping it for 4 h, and then the second sintering was completed by heating to 800 ℃ at 5 ℃ / min and keeping it for 10 h. The modified sodium ion positive electrode material Ca-3 doped with calcium ions was obtained by cooling to room temperature with the furnace.

[0025] Example 4 Preparation of Na 0.94 Ca 0.03 Ni 0.3328 Fe 0.3326 Mn 0.3346 O2 calcium ion doped modified sodium ion cathode material: According to the above chemical formula, 135.78 g of nickel-iron-manganese precursor Ni 0.3328 Fe 0.3326 Mn 0.3346 (OH)2, 77.27 g sodium carbonate (Na2CO3), 7.52 g calcium carbonate (CaCO3), use a horizontal ball mill at 400 rpm for 3 h to obtain a mixed powder, which is placed in an atmosphere muffle furnace after treatment. The first sintering is completed by heating to 570 ℃ at 5 ℃ / min and keeping it for 4 h, and then the second sintering is completed by heating to 800 ℃ at 5 ℃ / min and keeping it for 10 h. The modified sodium ion positive electrode material Ca-4 doped with calcium ions is obtained by cooling to room temperature with the furnace.

[0026] Comparative Example 1 Weigh 135.78 g of nickel-iron-manganese precursor Ni 0.3328 Fe 0.3326 Mn 0.3346 (OH)2, 82.05 g sodium carbonate (Na2CO3), use a horizontal ball mill at 400 rpm for 3 h to obtain a mixed powder, which is placed in an atmosphere muffle furnace after treatment. The first sintering is completed by heating to 600 ℃ at 5 ℃ / min and keeping it for 4 h, and then the second sintering is completed by heating to 1050 ℃ at 5 ℃ / min and keeping it for 10 h. The sodium ion positive electrode material NFM-1 is obtained by cooling to room temperature with the furnace.

[0027] Comparative Example 2 Weigh 135.78 g of nickel-iron-manganese precursor Ni 0.3328 Fe 0.3326 Mn 0.3346 (OH)2, 82.05 g sodium carbonate (Na2CO3), use a horizontal ball mill at 400 rpm for 3 h to obtain a mixed powder, which is placed in an atmosphere muffle furnace after treatment. The first sintering is completed by heating to 570 ℃ at 5 ℃ / min and keeping it for 4 h, and then the second sintering is completed by heating to 800 ℃ at 5 ℃ / min and keeping it for 12 h. The sodium ion positive electrode material NFM-2 is obtained by cooling to room temperature with the furnace.

[0028] Performance Testing: (1) Preparation of button cells: The sodium ion positive electrode materials prepared in the examples and comparative examples were made into button cells to test their electrical properties. First, the positive electrode slurry was homogenized and coated in the ratio of active material: Super-P: PVDF = 94:3:3 to obtain a sodium ion positive electrode material electrode. The negative electrode battery shell, spring sheet, gasket, negative electrode, diaphragm, electrolyte, sodium ion positive electrode material and positive electrode battery shell were assembled in the order of argon gas in a glove box, wherein the negative electrode used a commercial sodium metal sheet and the diaphragm used a polypropylene isolation film coated with single-sided ceramic.

[0029] (2) First cycle charge and discharge curve test Test conditions: voltage range 2-4 V, current 0.1 C.

[0030] Figure 1 The 0.1 C first cycle charge and discharge curves of Example 1, Example 2 and Comparative Example 1, where the discharge specific capacity of NFM-1 is 123.1 mAh / g. The discharge specific capacities of the modified sodium ion positive electrode materials Ca-1 and Ca-2 doped with calcium ions are both higher than that of NFM-1, which are 124.61 mAh / g and 125.93 mAh / g, respectively. The results show that the modified sodium ion material doped with calcium ions prepared by this method can improve the discharge specific capacity of the raw materials.

[0031] Figure 2 The 0.1 C first cycle charge and discharge curves of Example 3, Example 4 and Comparative Example 2, among which the discharge specific capacity of NFM-2 is 128.03 mAh / g. The discharge specific capacity of the modified sodium ion positive electrode materials Ca-3 and Ca-4 doped with calcium ions is still higher than that of NFM-2, which are 135.95 mAh / g and 137.42 mAh / g, respectively. The results further show that calcium ion doping significantly improves the specific capacity of the raw materials. At the same time, compared with Examples 1, 2 and Comparative Example 1, it is found that reducing the secondary calcination temperature to 800 ° C not only greatly reduces energy consumption and process costs, but also improves battery capacity and life. Because excessively high calcination temperatures can cause secondary crystallization of the material, the particle size of the material becomes larger, the specific surface area is reduced, which is not conducive to the embedding and extraction of sodium ions, thereby reducing its capacity.

[0032] (3) Battery cycle performance test Test conditions: voltage range 2-4 V, 1 C cycle 100 times after activation.

[0033] Figure 3The discharge capacity curves of Example 3, Example 4 and Comparative Example 2 after 100 cycles at 1 C are shown in the figure. As shown in the figure, Ca-4 shows the highest discharge capacity and capacity retention rate, where the discharge capacity drops from 128.57 mAh / g to 119.62 mAh / g, and the capacity retention rate is as high as 93.03%; after Ca-3 cycles at 1 C for 100 cycles, its discharge capacity drops from 125.16 mAh / g to 114.25 mAh / g, and the capacity retention rate is 91.28%. After NFM-2 cycles at 1 C for 100 cycles, the discharge capacity drops from 104.31 mAh / g to 88.37 mAh / g, and the capacity retention rate is 84.72%. The results show that the calcium ion-doped modified sodium ion cathode material prepared by this method not only improves the battery capacity, but also greatly enhances the cycle stability of the battery. This is because calcium ion doping can replace part of the sodium sites in the raw materials, increase the interlayer spacing, and thus improve the transport kinetics of sodium ions; at the same time, calcium ion doping can inhibit the Mn 4+ To Mn 3+ adverse phase transition, thereby improving battery stability.

[0034] The above basic examples of the present invention and their further selected examples can be freely combined to form multiple embodiments, all of which are embodiments that can be adopted and claimed by the present invention. In the scheme of the present invention, each selected example can be arbitrarily combined with any other basic example and selected example. Those skilled in the art will know that there are many combinations.

[0035] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A calcium ion-doped modified sodium ion positive electrode material, comprising a sodium source, a doping source and a precursor, characterized in that: The chemical formula of the positive electrode material is Na 1-x M x Ni a Fe b Mn c O2; The value range of the doping source M, x is x ≤ 0.05, and a+b+c=1, and the charge balance between the elements in the chemical formula is satisfied.

2. The calcium ion-doped modified sodium ion positive electrode material according to claim 1, characterized in that: The doping source is selected from calcium ions.

3. The method for preparing a calcium ion-doped modified sodium ion positive electrode material according to claim 1, comprising a ball milling method and a high temperature solid phase method, characterized in that Follow these steps: (1) Weigh the corresponding sodium source, doping source and metal elements required by the precursor according to the molar ratio of the chemical formula in the positive electrode material; (2) placing all the materials weighed in step (1) into a premix container, then premixing them at high speed, and then transferring them to a horizontal ball mill for high-speed ball milling to obtain a mixture powder; (3) placing the mixture powder obtained in step (2) in a crucible, and then transferring the crucible to a muffle furnace, and performing high-temperature calcination at a certain heating rate, calcination time, calcination temperature and protective atmosphere, and adopting a two-step calcination method to obtain a calcium ion-doped modified sodium ion battery positive electrode material with low cost, high specific capacity and excellent cycle performance.

4. The preparation method according to claim 3, characterized in that: In the step (1), the sodium source has an excess of 1% to 5% of sodium element to compensate for the loss of sodium source during the high-temperature calcination process.

5. The preparation method according to claim 3, characterized in that: In the step (1), the sodium source is provided by a sodium salt; the sodium salt is selected from at least one of sodium nitrate, sodium peroxide, sodium oxalate, sodium hydroxide, and sodium carbonate; the doping source is provided by a calcium salt, and the calcium salt is selected from at least one of calcium oxide, calcium carbonate, calcium nitrate, and calcium acetate; the precursor is provided by a nickel-iron-manganese precursor, and the nickel-iron-manganese precursor is selected from at least one of nickel-iron-manganese carbonate, nickel-iron-manganese hydroxide, and nickel-iron-manganese oxide.

6. The preparation method according to claim 3, characterized in that: In the step (2), the rotation speed of the horizontal ball mill is 300 to 600 rpm; and the ball milling time is 0.5 h to 3 h.

7. The preparation method according to claim 3, characterized in that: In the step (3), the parameters of high temperature calcination are: the first calcination temperature is 500 ~ 700 ° C, the heating rate is 2 ~ 5 ° C / min, and the calcination time is 3 ~ 6 h; the second calcination temperature is 800 ~ 1000 ° C, and the calcination time is 9 ~ 14 h; the calcination is carried out in an atmosphere muffle furnace, and the protective atmosphere includes argon atmosphere, oxygen atmosphere, and air atmosphere.

8. The calcium ion-doped modified sodium ion positive electrode material according to claim 1 or the calcium ion-doped modified sodium ion positive electrode material prepared by the method according to any one of claims 3 to 7, characterized in that: Calcium ion doped modified sodium ion positive electrode materials are used in sodium ion battery positive electrode materials.

9. A sodium ion positive electrode plate, characterized in that: The positive electrode plate includes the calcium ion-doped modified sodium ion positive electrode material according to claim 8.

10. A sodium ion half-cell, characterized in that: The working electrode is the sodium ion positive electrode sheet as described in claim 9, and the commercial sodium sheet is used as the counter electrode and the reference electrode; the diaphragm is made of at least one of polyethylene, polypropylene and ceramic.

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