A sodium ion battery positive electrode material and its preparation method and application

Abstract

The present invention relates to the technical field of sodium ion batteries, and in particular to a sodium ion battery positive electrode material, a preparation method thereof, and an application thereof. The sodium ion battery positive electrode material comprises a layered metal oxide and a modified polyanionic compound coated on the surface of the layered metal oxide: the chemical formula of the layered metal oxide is Na x Ni a Fe b Mn c M 1‑a‑b‑c O2; the chemical formula of the modified polyanionic compound is NaFe(PO4) (3‑y) / 3 F y @C; M is a doping element substituted into a transition metal element, including one or more of Cu, Mg, Zr, Ti, Al, Zn, or W; 0.8 < x ≤ 1, 0 < a ≤ 0.5, 0 < b ≤ 0.5, 0 < c ≤ 0.5; 0 < y ≤ 0.2. This sodium-ion battery cathode material has high operating voltage and capacity, high air stability, low moisture absorption, high safety, and long cycle life.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a sodium ion battery positive electrode material, a preparation method thereof, and applications thereof. Background Art

[0002] Currently, due to the continuous rise in the price of lithium salts, the progress of sodium-ion battery technology has been significant, making sodium-ion batteries a research hotspot. The industrialization process is also advancing rapidly, and it can be quickly applied in the fields of energy storage and small power. The positive electrode material is a very important component of sodium-ion batteries. At present, there are three main technical routes for sodium-ion positive electrode materials: layered oxides, Prussian blue, and polyanions. Among them, layered oxides are the most promising for rapid industrialization because they have high energy density and compaction density, and have a similar synthesis route to lithium-ion ternary materials. However, sodium-ion layered oxide positive electrode materials have many defects. Currently, the main defects are poor air stability, easy hygroscopicity, and sodium is more active than lithium, which leads to more serious residual alkali on the surface of sodium-ion layered oxides than in lithium batteries.

[0003] In view of this, the present invention is proposed. Summary of the Invention

[0004] One aspect of the present invention relates to a positive electrode material for a sodium ion battery, comprising a layered metal oxide and a modified polyanionic compound coated on the surface of the layered metal oxide:

[0005] The chemical formula of the layered metal oxide is Na x Ni a Fe b Mn c M 1-a-b-c O2; the chemical formula of the modified polyanionic compound is NaFe(PO4) (3-y) / 3 F y @C;

[0006] Wherein, M is a doping element in a transition metal element, including one or more of Cu, Mg, Zr, Ti, Al, Zn or W; 0.8<x≤1, 0<a≤0.5, 0<b≤0.5, 0<c≤0.5; 0<y≤0.2.

[0007] The sodium ion battery positive electrode material has high operating voltage and capacity, high air stability, is not easy to absorb moisture, is highly safe, and has a long cycle life.

[0008] Another aspect of the present invention also relates to a method for preparing the positive electrode material for a sodium ion battery, comprising the following steps:

[0009] The layered metal oxide is mixed with a sodium source, an iron source, a carbon source, a phosphate and a fluorine source, and then ball milled and calcined.

[0010] The method for preparing the positive electrode material for a sodium ion battery adopts solid-phase sintering, has a simple process, is conducive to industrial large-scale production, and the prepared positive electrode material for a sodium ion battery has excellent performance.

[0011] Another aspect of the present invention also relates to a positive electrode plate, comprising the above-mentioned sodium ion battery positive electrode material.

[0012] Another aspect of the present invention also relates to a sodium ion battery, including a sodium ion battery positive electrode plate.

[0013] Compared with the prior art, the present invention has the following beneficial effects:

[0014] (1) The sodium ion battery positive electrode material provided by the present invention has high operating voltage and capacity, high air stability, low moisture absorption, high safety and long cycle life; the modified polyanionic compound is coated on the surface of the layered metal oxide to enhance the stability of the layered metal oxide interface; different from the method of using a passivation layer to coat to achieve interface stability in the prior art, the present invention coats another type of sodium battery positive electrode material NaFePO4 on the surface of the layered metal oxide. This type of material has good thermal stability, safety and cycle life, ensuring the electrochemical activity of the surface, and in order to address the problem of poor conductivity of the coated NaFePO4, carbon coating is also performed to improve its rate performance. In addition, F doping is used to improve the operating voltage and capacity, and fluorine doping can stabilize the interface layer and improve the rate performance. Without sacrificing capacity, the high residual alkali problem on the surface of the layered oxide is greatly improved.

[0015] (2) The preparation method of the positive electrode material of the sodium ion battery provided by the present invention does not adopt a wet method in the coating process, but directly adopts solid-phase sintering. The process is simple and is conducive to industrial large-scale production. The prepared positive electrode material of the sodium ion battery has excellent performance. DETAILED DESCRIPTION

[0016] The technical scheme of the present invention will be clearly and completely described below in conjunction with specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work premise belong to the scope of protection of the present invention. Those who do not specify specific conditions in the embodiments are carried out according to normal conditions or the conditions recommended by the manufacturer. Those whose reagents or instruments are not specified by the manufacturer are conventional products that can be purchased commercially.

[0017] One aspect of the present invention relates to a sodium ion battery positive electrode material, comprising a layered metal oxide and a modified polyanionic compound coated on the surface of the layered metal oxide:

[0018] The chemical formula of the layered metal oxide is Na x Ni a Fe b Mn c M 1-a-b-c O2; the chemical formula of the modified polyanionic compound is NaFe(PO4) (3-y) / 3 F y @C;

[0019] Wherein, M is a doping element in a transition metal element, including one or more of Cu, Mg, Zr, Ti, Al, Zn, or W; 0.8 < x ≤ 1, 0 < a ≤ 0.5, 0 < b ≤ 0.5, 0 < c ≤ 0.5; and 0 < y ≤ 0.2. The values ​​of x, a, b, and c satisfy the charge balance of the chemical formula.

[0020] The invention effectively improves the problem of high residual alkali in layered metal oxides and enhances their stability in air. The present invention coats the layered metal oxides to give them a higher capacity, and the coated material is a carbon-coated fluorine-doped sodium iron phosphate material, which ensures the electrochemical activity of the surface. The carbon coating helps to improve the electrical conductivity, while the fluorine doping can stabilize the interface layer and improve the rate performance.

[0021] Layered metal oxides have a high capacity and are expected to be the first to be industrialized. However, the interface is extremely unstable and a high residual alkali is generated on the surface. In the present invention, a coating technology is used to enhance its interface stability. Unlike the existing methods of coating with a passivation layer (such as metal oxides such as Al2O3 or ordinary phosphates) to achieve interface stability, the present invention coats another type of sodium cathode material NaFePO4 on the surface of the layered transition metal oxide. This type of material has good thermal stability, safety and cycle life. In addition, carbon coating is performed to improve the rate performance of the coated NaFePO4 to address the problem of poor conductivity. In addition, F doping is used to increase the operating voltage and capacity. Without sacrificing capacity, the high residual alkali problem on the surface of the layered oxide is greatly improved.

[0022] Preferably, in the modified polyanionic compound, the mass of C is 0.01 wt% to 2 wt% (e.g., 0.01 wt%, 0.05 wt%, 0.1 wt%, 0.3 wt%, 0.5 wt%, 0.7 wt%, 0.9 wt%, 1.3 wt%, 1.5 wt%, 1.7 wt%, 1.9 wt% or 2 wt%) of the modified polyanionic compound.

[0023] Preferably, the mass of the modified polyanionic compound is 1 wt% to 10 wt% (e.g., 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt% or 10 wt%) of the sodium ion battery positive electrode material.

[0024] Another aspect of the present invention also relates to a method for preparing the positive electrode material for a sodium ion battery, comprising the following steps:

[0025] The layered metal oxide is mixed with a sodium source, an iron source, a carbon source, a phosphate and a fluorine source, and then ball milled and calcined.

[0026] Preferably, the ball mill has a rotation speed of 200 to 500 rpm / min (e.g., 200 rpm / min, 220 rpm / min, 240 rpm / min, 260 rpm / min, 280 rpm / min, 300 rpm / min, 320 rpm / min, 340 rpm / min, 360 rpm / min, 380 rpm / min, 400 rpm / min, 420 rpm / min, 440 rpm / min, 460 rpm / min, 480 rpm / min or 500 rpm / min).

[0027] Preferably, the ball milling time is 2 to 8 h (eg, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h or 8 h).

[0028] Preferably, the calcination temperature is 500-900°C (e.g., 500°C, 520°C, 540°C, 560°C, 580°C, 600°C, 620°C, 640°C, 660°C, 680°C, 700°C, 720°C, 740°C, 760°C, 780°C, 800°C, 820°C, 840°C, 860°C, 880°C or 900°C).

[0029] Preferably, the calcination time is 6 to 12 hours (eg, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours or 12 hours).

[0030] Preferably, the sintering atmosphere of the calcination includes nitrogen.

[0031] Preferably, the sodium source includes at least one of sodium carbonate, sodium bicarbonate, sodium hydroxide or sodium sulfate.

[0032] Preferably, the iron source includes at least one of ferrous oxalate dihydrate (FeC2O4·H2O), ferrous phosphate (FePO4) or ferrous sulfate.

[0033] Preferably, the carbon source comprises at least one of glucose, sucrose or fructose.

[0034] Preferably, the phosphate includes at least one of ammonium dihydrogen phosphate (NH4H2PO4), diammonium hydrogen phosphate ((NH4)2HPO4) or ammonium phosphate ((NH4)3PO4).

[0035] Preferably, the fluorine source includes at least one of sodium fluoride, ferric fluoride or ferrous fluoride.

[0036] Another aspect of the present invention also relates to a positive electrode plate, comprising the above-mentioned sodium ion battery positive electrode material.

[0037] Another aspect of the present invention also relates to a sodium ion battery, comprising the sodium ion battery positive electrode sheet.

[0038] The embodiments of the present invention will be described in detail below with reference to specific examples and comparative examples.

[0039] Example 1

[0040] The sodium ion battery cathode material provided in this embodiment has a structure with a layered metal oxide as a core, a carbon coating and a fluorine-doped sodium iron phosphate material as a shell, and its expression is NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2@NaFe(PO4) 0.96 F 0.1 @C;

[0041] The mass percentage of the sodium iron phosphate shell structure oxide in the layered metal oxide is 5%.

[0042] In this embodiment, the layered metal oxide is sodium nickel iron manganate (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2);

[0043] The sodium source is sodium carbonate;

[0044] The iron source was ferrous oxalate dihydrate;

[0045] The phosphate is ammonium dihydrogen phosphate;

[0046] The fluoride source is sodium fluoride;

[0047] The carbon source is glucose;

[0048] The specific preparation method is:

[0049] 1. Take 10g of NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3O2 positive electrode material, then weigh and mix 0.16g sodium carbonate, 0.35g ammonium dihydrogen phosphate, 0.5g ferrous oxalate dihydrate, 0.012g sodium fluoride and 0.25g glucose;

[0050] 2. After mixing evenly, ball mill at a speed of 300 rpm / min for 5 hours;

[0051] 3. Then transfer it to a nitrogen atmosphere and calcine it at 700°C for 8 hours to obtain a coated modified sodium ion battery positive electrode material.

[0052] Example 2

[0053] The sodium ion battery cathode material provided in this embodiment has a structure with a layered oxide material as a core, a carbon-coated and fluorine-doped sodium iron phosphate material as a shell, and its expression is NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2@NaFe(PO4) 0.96 F 0.1 @C;

[0054] Among them, the mass percentage of sodium iron phosphate shell structure oxide in the layered metal oxide is 1%;

[0055] In this embodiment, the layered metal oxide is sodium nickel iron manganate (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2);

[0056] The sodium source is sodium carbonate;

[0057] The iron source was ferrous oxalate dihydrate;

[0058] The phosphate is ammonium dihydrogen phosphate;

[0059] The fluoride source is sodium fluoride;

[0060] The carbon source is glucose;

[0061] The specific preparation method is:

[0062] 1. Take 10g of NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 positive electrode material, then weigh and mix 0.032g sodium carbonate, 0.07g ammonium dihydrogen phosphate, 0.1g ferrous oxalate dihydrate, 0.0024g sodium fluoride and 0.25g glucose;

[0063] 2. After mixing evenly, ball mill at a speed of 300 rpm / min for 5 hours;

[0064] 3. Then transfer it to a nitrogen atmosphere and calcine it at 700°C for 8 hours to obtain a coated and modified sodium ion battery positive electrode material.

[0065] Example 3

[0066] The sodium ion battery cathode material provided in this embodiment has a structure with a layered oxide material as a core, a carbon-coated and fluorine-doped sodium iron phosphate material as a shell, and its expression is NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2@NaFe(PO4) 0.96 F 0.1 @C;

[0067] The mass percentage of the sodium iron phosphate shell structure oxide in the layered transition metal oxide is 10%;

[0068] In this embodiment, the layered oxide is sodium nickel iron manganate (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2);

[0069] The sodium source is sodium carbonate;

[0070] The iron source was ferrous oxalate dihydrate;

[0071] The phosphate is ammonium dihydrogen phosphate;

[0072] The fluoride source is sodium fluoride;

[0073] The carbon source is glucose;

[0074] The specific preparation method is:

[0075] 1. Take 10g of NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 positive electrode material, then weigh and mix 0.064g sodium carbonate, 0.7g ammonium dihydrogen phosphate, 1.0g ferrous oxalate dihydrate, 0.024g sodium fluoride and 0.25g glucose;

[0076] 2. After mixing evenly, ball mill at a speed of 300 rpm / min for 5 hours;

[0077] 3. Then transfer it to a nitrogen atmosphere and calcine it at 700°C for 8 hours to obtain a coated and modified sodium ion battery positive electrode material.

[0078] Example 4

[0079] The sodium ion battery cathode material provided in this embodiment has a structure with a layered metal oxide as a core, a carbon coating and a fluorine-doped sodium iron phosphate material as a shell, and its expression is NaNi 1 / 3 Fe1 / 3 Mn 1 / 3 O2@NaFe(PO4) 0.96 F 0.1 @C;

[0080] The mass percentage of the sodium iron phosphate shell structure oxide in the layered metal oxide is 5%.

[0081] In this embodiment, the layered metal oxide is sodium nickel iron manganate (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2);

[0082] The sodium source is sodium carbonate;

[0083] The iron source was ferrous oxalate dihydrate;

[0084] The phosphate is ammonium dihydrogen phosphate;

[0085] The fluoride source is sodium fluoride;

[0086] The carbon source is glucose;

[0087] The specific preparation method is:

[0088] 1. Take 10g of NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 positive electrode material, then weigh and mix 0.16g sodium carbonate, 0.35g ammonium dihydrogen phosphate, 0.5g ferrous oxalate dihydrate, 0.012g sodium fluoride and 0.25g glucose;

[0089] 2. After mixing evenly, ball mill at a speed of 200 rpm / min for 8 hours;

[0090] 3. Then transfer it to a nitrogen atmosphere and calcine it at 900°C for 6 hours to obtain a coated modified sodium ion battery positive electrode material.

[0091] Example 5

[0092] The sodium ion battery cathode material provided in this embodiment has a structure with a layered metal oxide as a core, a carbon coating and a fluorine-doped sodium iron phosphate material as a shell, and its expression is NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2@NaFe(PO4) 0.96 F 0.1 @C;

[0093] The mass percentage of the sodium iron phosphate shell structure oxide in the layered metal oxide is 5%.

[0094] In this embodiment, the layered metal oxide is sodium nickel iron manganate (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2);

[0095] The sodium source is sodium carbonate;

[0096] The iron source was ferrous oxalate dihydrate;

[0097] The phosphate is ammonium dihydrogen phosphate;

[0098] The fluoride source is sodium fluoride;

[0099] The carbon source is glucose;

[0100] The specific preparation method is:

[0101] 1. Take 10g of NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 positive electrode material, then weigh and mix 0.16g sodium carbonate, 0.35g ammonium dihydrogen phosphate, 0.5g ferrous oxalate dihydrate, 0.012g sodium fluoride and 0.25g glucose;

[0102] 2. After mixing evenly, ball mill at a speed of 500 rpm / min for 2 hours;

[0103] 3. Then transfer it to a nitrogen atmosphere and calcine it at 500°C for 12 hours to obtain a coated modified sodium ion battery positive electrode material.

[0104] Comparative Example 1

[0105] The preparation method of the sodium ion battery positive electrode material provided in this comparative example comprises the following steps:

[0106] 1. Take 10g of NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 positive electrode material, then weigh and mix 0.16g sodium carbonate, 0.35g ammonium dihydrogen phosphate, 0.5g ferrous oxalate dihydrate and 0.25g glucose;

[0107] 2. After mixing evenly, ball mill at a speed of 300 rpm / min for 5 hours;

[0108] 3. Then transfer it to a nitrogen atmosphere and calcine it at 700°C for 8 hours to obtain a coated and modified sodium ion battery positive electrode material.

[0109] Comparative Example 2

[0110] The method for preparing the positive electrode material for a sodium ion battery provided in this comparative example comprises the following steps:

[0111] 1. Take 10g of NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 positive electrode material, then weigh and mix 0.16g sodium carbonate, 0.35g ammonium dihydrogen phosphate, 0.5g ferrous oxalate dihydrate and 0.012g sodium fluoride;

[0112] 2. After mixing evenly, ball mill at a speed of 300 rpm / min for 5 hours;

[0113] 3. Then transfer it to a nitrogen atmosphere and calcine it at 700°C for 8 hours to obtain a coated modified sodium ion battery positive electrode material.

[0114] Comparative Example 3

[0115] Sodium nickel iron manganese oxide (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2).

[0116] Comparative Example 4

[0117] The only difference between this comparative example and Example 1 is that the rotation speed of the ball mill is 600 rpm / min.

[0118] Comparative Example 5

[0119] The only difference between this comparative example and Example 1 is that the calcination temperature is 450°C.

[0120] Experimental example

[0121] The prepared materials were placed in a 20% humidity environment for 5 hours and then tested for moisture and residual alkali to assess their stability. Coin cells were assembled using the fresh cathode materials and charged and discharged at 0.1C in the 2.0V to 4.0V range to compare their electrochemical performance. The results are shown in Table 1.

[0122] Table 1

[0123] Experiment number Moisture ppm Residual alkali% Discharge capacity mAh / g Example 1 386 0.83 135.6 Example 2 670 1.07 136.9 Example 3 359 0.80 125.8 Example 4 851 1.36 133.7 Example 5 613 0.98 134.4 Comparative Example 1 1335 4.29 133.2 Comparative Example 2 348 0.95 134.9 Comparative Example 3 2470 6.32 137.5 Comparative Example 4 385 0.90 134.8 Comparative Example 5 840 2.17 137.4

[0124] As shown in the table above, by comparing Example 1, Example 2, Example 3 and Comparative Example 3, it is found that the coating modification can effectively improve the stability of the sodium-based layered oxide cathode material in the air, inhibit the surface moisture absorption, and reduce the content of residual alkali on the surface; by comparing Example 1 with Comparative Example 1, it is found that the doping of F can effectively stabilize the interface and improve some of the capacity; by comparing Examples 1, 4, 5 and Comparative Examples 4 and 5, the suitable coating temperature is 700°C. Too high or too low a temperature will weaken the performance, and a ball milling speed of 300rpm can achieve a better dispersion effect. By comparing the experimental data, Example 1 has better air stability, relatively low moisture and residual alkali, and after coating modification, the gram capacity is not lost much compared to the uncoated material of Comparative Example 3, so it has better comprehensive performance.

[0125] Although the present invention has been illustrated and described using specific embodiments, it should be appreciated that the above embodiments are merely intended to illustrate the technical solutions of the present invention rather than to limit them. Those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents, without departing from the spirit and scope of the present invention. However, these modifications or replacements do not deviate from the essence of the corresponding technical solutions within the scope of the technical solutions of the embodiments of the present invention. Therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A sodium ion battery cathode material, characterized in that It comprises a layered metal oxide and a modified polyanionic compound coated on the surface of the layered metal oxide: The chemical formula of the layered metal oxide is Na x Ni a Fe b Mn c M 1-a-b-c O2; the chemical formula of the modified polyanionic compound is NaFe(PO4) (3-y) / 3 F y @C; Wherein, M is a doping element in a transition metal element, including one or more of Cu, Mg, Zr, Ti, Al, Zn or W; 0.8<x≤1, 0<a≤0.5, 0<b≤0.5, 0<c≤0.5; 0<y≤0.2; The mass of C is 0.01 wt% to 2 wt% of the modified polyanionic compound; the mass of the modified polyanionic compound is 1 wt% to 10 wt% of the sodium ion battery positive electrode material.

2. The method for preparing a positive electrode material for a sodium ion battery according to claim 1, wherein: The following steps are involved: The layered metal oxide is mixed with a sodium source, an iron source, a carbon source, a phosphate and a fluorine source, and then ball milled and calcined.

3. The method for preparing a positive electrode material for a sodium ion battery according to claim 2, wherein: The ball milling speed is 200-500 rpm / min; The ball milling time is 2 to 8 hours.

4. The method for preparing a positive electrode material for a sodium ion battery according to claim 2, wherein: The calcination temperature is 500-900°C; The calcination time is 6 to 12 hours.

5. The method for preparing a positive electrode material for a sodium ion battery according to claim 2, wherein: The sintering atmosphere of the calcination includes nitrogen.

6. The method for preparing a positive electrode material for a sodium ion battery according to claim 2, wherein: The sodium source includes at least one of sodium carbonate, sodium bicarbonate, sodium hydroxide or sodium sulfate.

7. The method for preparing a positive electrode material for a sodium ion battery according to claim 2, wherein: The iron source includes at least one of ferrous oxalate dihydrate, ferrous phosphate or ferrous sulfate.

8. The method for preparing a positive electrode material for a sodium ion battery according to claim 2, wherein: The carbon source includes at least one of glucose, sucrose or fructose.

9. The method for preparing a positive electrode material for a sodium ion battery according to claim 2, wherein: The phosphate includes at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate or ammonium phosphate.

10. The method for preparing a positive electrode material for a sodium ion battery according to claim 2, wherein: The fluorine source includes at least one of sodium fluoride, ferric fluoride or ferrous fluoride.

11. A positive electrode plate, characterized in that: The invention comprises the sodium ion battery positive electrode material according to claim 1.

12. A sodium ion battery, characterized in that: Including the positive electrode sheet according to claim 11.