A composite cathode material, its preparation method and application

Abstract

The application provides a composite positive electrode material and a preparation method and application thereof. The composite positive electrode material comprises a polyanionic phosphate and a layered oxide; the polyanionic phosphate comprises vanadium elements and / or manganese elements. In the application, the polyanionic phosphate material containing vanadium elements and / or manganese elements can realize partial V 4+ / V 5+ and / or Mn 3+ / Mn 4+ redox potential activation, has a higher average voltage, and the layered oxide material has a higher specific capacity. Therefore, the composite positive electrode material prepared by mixing the two in a certain proportion can improve the average working voltage of sodium ion deintercalation, thereby improving the overall energy density of the material and making the sodium ion battery positive electrode material have stronger competitiveness and cost performance. This provides a new idea for the practical application of the sodium ion battery positive electrode material and is conducive to the commercial development of the sodium ion battery in the future.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion batteries, specifically relating to a composite cathode material, its preparation method, and its application. Background Technology

[0002] Since its initial commercialization in 1991, lithium-ion batteries have been widely used in electric vehicles and electronic devices due to their high energy density, long cycle life, and wide operating temperature range. However, lithium resources comprise only 0.0017 wt% of the Earth's crust, and their geographical distribution is highly uneven. In contrast, sodium resources are abundant on Earth, making sodium-ion batteries a promising complement to lithium-ion batteries. Furthermore, sodium and lithium belong to the same group of elements, share similar chemical and physical properties, and have similar energy storage mechanisms. Therefore, the development of sodium-ion batteries can draw upon the mature experience of lithium-ion batteries.

[0003] Sodium superionic conductor (NASICON) is a typical vanadium-based phosphate cathode material. Na3V2(PO4)3 is a typical representative of the NASICON series compounds, with a rhombic crystal structure in the R-3c space group. VO6 octahedra and PO4 tetrahedra are connected by sharing angles, forming a three-dimensional [V2P3O] structure. 12 The network skeleton is Na. + Two different storage sites (Na1 and Na2) are provided. Studies have shown that only the two Na atoms located at the Na2 site can be extracted from the structure, achieving 2 mol of V. 3+ / V 4+ The reversible redox reaction occurs, and the remaining inert Na at the Na1 position does not participate in the insertion / extraction reaction. The theoretical capacity is only 117.6 mAh / g, with a voltage plateau of approximately 3.3 V. Furthermore, studies have shown that in Na3V2(PO4)3, V... 4+ / V 5+ The activation of redox couples is of great significance because V 4+ / V 5+ The high redox potential of the electrode couple, coupled with its ability to provide additional capacity, can enhance the energy density of this cathode material. Theoretical calculations show that in Na3V2(PO4)3, V 4+ / V 5+ The redox plateau is 4.78V, which clearly exceeds the stable voltage range for normal operation of the electrolyte. Jian Zhang et al. prepared Na by replacing V with Mn. 3.5 Mn 0.5 V 1.5 (PO4)3 cathode material, achieving partial V... 4+ / V 5+The activation of the redox potential has a voltage plateau of around 3.9V, with a higher average voltage, but its electrochemical performance still has a lot of room for improvement.

[0004] Therefore, designing a sodium-ion battery cathode material with higher energy density to make it more competitive and cost-effective is a technical challenge that urgently needs to be solved. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a composite cathode material, its preparation method, and its applications. The present invention prepares a composite cathode material by mixing a polyanionic phosphate containing vanadium and / or manganese with a layered oxide. The polyanionic phosphate material containing vanadium and / or manganese can achieve partial Vo... 4+ / V 5+ and / or Mn 3+ / Mn 4+ The redox potential of sodium ions is activated, resulting in a high average voltage, while layered oxide materials have a high specific capacity. Therefore, mixing the two in a certain proportion to prepare composite cathode materials can improve the average working voltage of sodium ion insertion / extraction, thereby increasing the overall energy density of the material. This makes sodium ion battery cathode materials more competitive and cost-effective, providing a new approach for the practical application of sodium ion battery cathode materials and contributing to the future commercial development of sodium ion batteries.

[0006] To achieve this objective, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a composite cathode material, the composite cathode material comprising polyanionic phosphate and layered oxide;

[0008] The polyanionic phosphate includes vanadium and / or manganese.

[0009] This invention prepares a composite cathode material by mixing a polyanionic phosphate containing vanadium and / or manganese with a layered oxide. The polyanionic phosphate material containing vanadium and / or manganese can achieve partial V... 4+ / V 5+ and / or Mn 3+ / Mn 4+Activated by the redox potential, it has a relatively high average voltage, and its charging cut-off range is required to be 4.2 - 4.5V. The layered oxide material has a relatively high specific capacity, and its charging cut-off range is also required to be 4.2 - 4.5V. Therefore, mixing the two in a certain proportion to prepare a composite cathode material can not only improve the tap density, but also increase the average working voltage of sodium ion insertion and extraction, thereby enabling the overall energy density of the material to be improved, making the cathode material of sodium ion batteries more competitive and cost-effective. This provides a new idea for the practical application of cathode materials for sodium ion batteries and is conducive to the future commercial development of sodium ion batteries.

[0010] As a preferred technical solution of the present invention, the molecular formula of the polyanionic phosphate is Na 9-(3x+2y+nz) V x Mn y M n+ z (PO4)3, where 0 ≤ x < 2, 0 ≤ y < 2, 0 ≤ z < 2, x + y + z = 2, and x, y, and z cannot be 0 at the same time, n is an integer greater than or equal to 1, and M is a doped metal.

[0011] In the present invention, 0 ≤ x < 2, for example, it can be 0, 0.5, 1, 1.5, or 1.8, etc.

[0012] In the present invention, 0 ≤ y < 2, for example, it can be 0, 0.5, 1, 1.5, or 1.8, etc.

[0013] In the present invention, 0 ≤ z < 2, for example, it can be 0, 0.5, 1, 1.5, or 1.8, etc.

[0014] Preferably, the M includes any one or a combination of at least two of Fe, Ti, Li, K, Mg, Ca, Sr, Zn, Co, Ni, Cu, Cr, Ga, Al, Y, La, Zr, Sn, Nb, or W, preferably any one of the combinations of Li and K, K and Mg, Mg and Ca, Ca and Zn, Co and Ni, Cu and Cr, or Al, Ga, and La.

[0015] Preferably, the molecular formula of the layered oxide is Na m NO2, where 0.6 < m ≤ 1.0, and N includes any one or a combination of at least two of Fe, Cu, Co, Ni, Mn, Cr, or Ti.

[0016] In the present invention, 0.6 < m ≤ 1.0, for example, it can be 0.65, 0.7, 0.8, 0.9, 0.98, or 1.0, etc.

[0017] Preferably, the mass ratio of the polyanionic phosphate to the layered oxide is (1-9):(9-1), wherein the polyanionic phosphate is selected from the range "1-9", for example, 1, 2, 3, 4, 5, 6, 7, 8 or 9, and the layered oxide is selected from the range "9-1", for example, 1, 2, 3, 4, 5, 6, 7, 8 or 9.

[0018] In this invention, if the mass ratio of polyanionic phosphate to layered oxide is too small, the effect of improving the voltage plateau of the layered oxide will not be obvious; if the mass ratio of polyanionic phosphate to layered oxide is too large, the capacity of the composite cathode material will be reduced because the capacity of polyanionic phosphate itself is lower than that of layered oxide. Therefore, it is necessary to determine the optimal ratio based on the balance of mutual influences on the overall performance.

[0019] As a preferred embodiment of the present invention, the surface of the polyanionic phosphate is provided with a carbon coating layer.

[0020] In this invention, loading polyanionic phosphates into a carbon framework helps to further improve the electronic conductivity of the material.

[0021] Preferably, the thickness of the carbon coating layer is 2-5 nm, for example, it can be 2 nm, 3 nm, 4 nm or 5 nm.

[0022] In a second aspect, the present invention provides a method for preparing the composite cathode material as described in the first aspect, the method comprising the following steps:

[0023] The composite cathode material is obtained by mixing polyanionic phosphate material and layered oxide raw material.

[0024] In a preferred embodiment of the present invention, the mass ratio of the polyanionic phosphate material to the layered oxide raw material is (1-9):(9-1), wherein the polyanionic phosphate material is selected from a range of "1-9", for example, 1, 2, 3, 4, 5, 6, 7, 8, or 9, and the layered oxide material is selected from a range of "9-1", for example, 1, 2, 3, 4, 5, 6, 7, 8, or 9.

[0025] As a preferred technical solution of the present invention, the preparation method of the polyanionic phosphate material includes any one of the following: solid phase method, spray drying method, coprecipitation method or sol-gel method.

[0026] Preferably, the preparation method of the polyanionic phosphate material includes the following steps:

[0027] Sodium source, vanadium source, manganese source, phosphorus source, M source and solvent are mixed to obtain a precursor. The precursor is dried and sintered to obtain the polyanionic phosphate material.

[0028] Preferably, the sodium source includes any one or a combination of at least two of sodium bicarbonate, sodium carbonate, sodium acetate, sodium nitrate, sodium hydroxide, or sodium oxalate, and is preferably any one of the following combinations: sodium bicarbonate and sodium carbonate, sodium carbonate and sodium acetate, sodium acetate and sodium nitrate, sodium nitrate and sodium hydroxide, or sodium hydroxide and sodium oxalate.

[0029] Preferably, the vanadium source includes any one or a combination of at least two of vanadium pentoxide, vanadium tetroxide, vanadium trioxide, vanadium oxide, ammonium metavanadate, ammonium vanadate, vanadium acetylacetonate, or vanadium acetylacetonate. More preferably, it includes any one of the following combinations: vanadium pentoxide and vanadium tetroxide, vanadium tetroxide and vanadium trioxide, vanadium trioxide and vanadium oxide, vanadium oxide and ammonium metavanadate, ammonium metavanadate and ammonium vanadate, ammonium vanadate and vanadium acetylacetonate, or vanadium acetylacetonate and vanadium acetylacetonate.

[0030] Preferably, the manganese source includes any one or a combination of at least two of manganese tetroxide, manganese trioxide, manganese dioxide, manganese monoxide, manganese carbonate, manganese acetate, manganese carbonyl, or manganese acetylacetonate. More preferably, it is any one of the following combinations: manganese tetroxide and manganese trioxide, manganese dioxide and manganese monoxide, manganese carbonate and manganese acetate, or manganese carbonyl and manganese acetylacetonate.

[0031] Preferably, the phosphorus source includes any one or a combination of at least two of phosphoric acid, ammonium dihydrogen phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, or sodium phosphate, preferably any one of the following combinations: phosphoric acid and ammonium dihydrogen phosphate, sodium dihydrogen phosphate and ammonium dihydrogen phosphate, ammonium dihydrogen phosphate and diammonium hydrogen phosphate, disodium hydrogen phosphate and diammonium hydrogen phosphate, or ammonium phosphate and sodium phosphate.

[0032] Preferably, the M source includes any one or a combination of at least two of the following: an M-containing oxide, an M-containing acid, an M-containing base, an M-containing nitrate, an M-containing carbonate, an M-containing acetate, an M-containing sodium salt, or an M-containing ammonium salt. More preferably, it includes any one of the following combinations: a Li-containing base and a K-containing acid, a K-containing acid and a Mg-containing base, a Mg-containing sodium salt and a Ca-containing ammonium salt, a Ca-containing acid and a Zn-containing base, a Co-containing sodium salt and a Ni-containing base, or a Cu-containing ammonium salt and a Cr-containing acid.

[0033] Preferably, the solvent includes any one or a combination of at least two of deionized water, ethanol, or acetone, and more preferably any one of a combination of deionized water and ethanol, a combination of deionized water and acetone, or a combination of ethanol and acetone.

[0034] As a preferred embodiment of the present invention, the drying temperature is 50-150℃, for example, it can be 50℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃ or 150℃, preferably 90-120℃.

[0035] Preferably, the drying time is 8-24 hours, for example, 8 hours, 12 hours, 16 hours, 20 hours or 24 hours.

[0036] Preferably, the sintering atmosphere includes an inert atmosphere and / or a reducing atmosphere.

[0037] Preferably, the gas in the inert atmosphere includes argon and / or nitrogen.

[0038] Preferably, the gas in the reducing atmosphere includes carbon monoxide and / or hydrogen.

[0039] Preferably, the sintering temperature is 500-900℃, for example, it can be 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃ or 900℃, etc., and the time is 2-20h, for example, it can be 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h or 20h, etc.

[0040] In this invention, if the sintering temperature is too low, the crystallinity of the material will be poor; if the sintering temperature is too high, the active elements will be easily deactivated, reducing the activity of the material.

[0041] Preferably, after drying, the material is first ground and then sintered.

[0042] Preferably, the grinding time is 1 min to 48 h, for example, it can be 1 min, 5 min, 10 min, 20 min, 30 min, 40 min, 50 min, 1 h, 5 h, 10 h, 15 h, 20 h, 25 h, 30 h, 35 h, 40 h, 45 h or 48 h, etc., and preferably 0.5 to 2 h.

[0043] As a preferred embodiment of the present invention, a reducing agent is also added during the mixing process of the sodium source, vanadium source, manganese source, phosphorus source, M source and solvent.

[0044] In this invention, the purpose of adding a reducing agent is to keep the transition metal ions in the molecular formula in a low valence state so that an oxidation reaction can occur during charging, accompanied by a sodium removal process.

[0045] Preferably, the molar ratio of the reducing agent to the M source is (0.5-3):1, for example, it can be 0.5:1, 1:1, 1.5:1, 2:1, 2.5:1 or 3:1, etc.

[0046] Preferably, the reducing agent comprises any one or a combination of at least two of oxalic acid, ascorbic acid, sucrose, glucose, hydroxylamine hydrochloride, ethanol, polyethylene glycol, dopamine hydrochloride, citric acid, malic acid, or ethylenediaminetetraacetic acid, preferably any one of the following combinations: sucrose and glucose, oxalic acid and ethanol, ascorbic acid and hydroxylamine hydrochloride, citric acid and oxalic acid, dopamine hydrochloride and glucose, malic acid and ascorbic acid, oxalic acid and ethylenediaminetetraacetic acid, or hydroxylamine hydrochloride and oxalic acid.

[0047] Preferably, a carbon source is also added during the mixing process of the sodium source, vanadium source, manganese source, phosphorus source, M source and solvent.

[0048] Preferably, the carbon source includes any one or a combination of at least two of citric acid, oleic acid, polyvinylpyrrolidone, polyethylene glycol, glucose, ascorbic acid, sucrose, starch, graphene, carbon nanotubes, or Ketjen black, preferably any one of the following combinations: glucose and citric acid, sucrose and oleic acid, polyvinylpyrrolidone and polyethylene glycol, polyethylene glycol and glucose, ascorbic acid and sucrose, glucose and starch, or carbon nanotubes and Ketjen black.

[0049] Preferably, the molar ratio of the carbon source to the M source is (0-10):1, for example, it can be 0, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1 or 10:1, etc., and preferably (0-3):1.

[0050] In this invention, if the molar ratio of carbon source to M source is too large, the coated carbon layer will be too thick and the proportion of active material will be too low, ultimately affecting the energy density of the battery.

[0051] As a preferred technical solution of the present invention, the preparation method includes the following steps:

[0052] (1) Sodium source, vanadium source, manganese source, phosphorus source, M source, reducing agent, carbon source and solvent are mixed to obtain a precursor. The precursor is dried and ground, and then sintered under an inert atmosphere and / or a reducing atmosphere to obtain a polyanionic phosphate material.

[0053] The drying temperature is 50-150℃ and the time is 8-24h; the grinding time is 1min-48h; the sintering temperature is 500-900℃ and the time is 2-20h; the molar ratio of carbon source to M source is (0-10):1.

[0054] (2) The polyanionic phosphate material and the layered oxide raw material are mixed to obtain the composite cathode material;

[0055] The mass ratio of polyanionic phosphate material to layered oxide material is (1-9):(9-1).

[0056] Thirdly, the present invention provides a sodium-ion battery, the sodium-ion battery comprising the composite cathode material as described in the first aspect.

[0057] Fourthly, the present invention provides an energy storage device, the energy storage device comprising the sodium-ion battery described in the third aspect.

[0058] It should be noted that the energy storage device described in this invention is not limited. For example, it may be an energy storage device used in low-speed electric vehicles, solar power generation, wind power generation, smart grid peak shaving, distributed power stations, backup power supplies, or communication base stations.

[0059] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0060] Compared with the prior art, the present invention has the following beneficial effects:

[0061] (1) This invention prepares a composite cathode material by mixing a polyanionic phosphate containing vanadium and / or manganese with a layered oxide, wherein the polyanionic phosphate material containing vanadium and / or manganese can achieve partial V 4+ / V 5+ and / or Mn 3+ / Mn 4+ The redox potential of sodium ions is activated, resulting in a high average voltage, while layered oxide materials have a high specific capacity. Therefore, mixing the two in a certain proportion to prepare composite cathode materials can improve the average working voltage of sodium ion insertion / extraction, thereby increasing the overall energy density of the material. This makes sodium ion battery cathode materials more competitive and cost-effective, providing a new approach for the practical application of sodium ion battery cathode materials and contributing to the future commercial development of sodium ion batteries.

[0062] (2) The vanadium- and / or manganese-containing polyanionic phosphates used in this invention have a discharge specific capacity of 110-130 mAh / g at 0.2C when charged to 4.2-4.5V, and an average discharge voltage of 3.5-3.7V, exhibiting the advantage of high voltage. The layered oxides used have a discharge specific capacity of 140-170 mAh / g at 0.2C when charged to 4.2-4.5V, and an average discharge voltage of 3.1V, exhibiting the advantage of high discharge capacity. The composite cathode material prepared in this invention has a discharge specific capacity of 130-150 mAh / g at 0.2C when charged to 4.2-4.5V, and an average voltage plateau of 3.3-3.5V, exhibiting higher energy density compared to single materials. Attached Figure Description

[0063] Figure 1 This is the XRD pattern of the vanadium manganese-based phosphate material used in Example 1 of this invention;

[0064] Figure 2 This is a scanning electron microscope image of the vanadium manganese-based phosphate material used in Example 1 of this invention;

[0065] Figure 3 This is the XRD pattern of the layered oxide material used in Example 1 of this invention;

[0066] Figure 4 This is a scanning electron microscope image of the layered oxide material used in Embodiment 1 of the present invention;

[0067] Figure 5 This is a charge-discharge curve of the composite cathode material prepared in Example 1 of the present invention at 0.2C.

[0068] Figure 6 This is a schematic diagram of the cycling curve of the composite cathode material prepared in Example 1 of the present invention after 100 cycles at 1C;

[0069] Figure 7 This is a comparison of the first charge-discharge curves of the composite cathode material prepared in Example 1, the cathode material prepared in Comparative Example 1, and the cathode material prepared in Comparative Example 2 at 0.2C. Detailed Implementation

[0070] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0071] Example 1

[0072] This embodiment provides a composite cathode material, which includes polyanionic phosphate and layered oxide;

[0073] The molecular formula of the polyanionic phosphate is Na. 3.4 V 1.5 Mn 0.4 M 3+ 0.1 (PO4)3, M is Fe, and the molecular formula of the layered oxide is Na. 1.0 NO2, where N is Ni 0.33 Fe 0.33 Mn 0.33 The mass ratio of the polyanionic phosphate to the layered oxide is 2:6;

[0074] The surface of the polyanionic phosphate is provided with a carbon coating layer, the thickness of which is 3 nm.

[0075] This embodiment also provides a method for preparing the above-mentioned composite cathode material, the method comprising the following steps:

[0076] (1) 3 mmol sodium dihydrogen phosphate, 0.4 mmol sodium acetate, 1.5 mmol vanadium sulfate, 0.4 mmol manganese carbonate, 0.1 mmol ferric nitrate, oxalic acid, sucrose and solvent ethanol were added to a ball mill jar and mixed. After sealing, the mixture was centrifuged and ball milled for 24 h to obtain a precursor. The precursor was dried at 90 °C for 15 h and ground for 24 h. Then, it was sintered at 650 °C for 10 h in a tube furnace under nitrogen atmosphere to obtain carbon-coated polyanionic phosphate material.

[0077] The molar ratio of sucrose to ferric nitrate is 3:1, and the molar ratio of reducing agent oxalic acid to ferric nitrate is 1:1.

[0078] (2) The polyanionic phosphate material and the layered oxide material are mixed to obtain the composite cathode material;

[0079] The mass ratio of polyanionic phosphate material to layered oxide material is 2:6.

[0080] Figure 1 and Figure 2 The XRD pattern and scanning electron microscope image of the vanadium manganese-based phosphate material used in this embodiment are shown respectively. As can be seen from the figure, the prepared vanadium manganese-based phosphate is a pure phase, and the particles are a mixture of primary and secondary particles with small size.

[0081] Figure 3 and Figure 4 The XRD pattern and scanning electron microscope image of the layered oxide material used in this embodiment are shown respectively. As can be seen from the figure, the layered oxide is a pure phase and the particles are larger secondary particles formed by the aggregation of primary particles.

[0082] Figure 5The figure shows the first charge-discharge curve of the composite cathode material prepared in this embodiment at 0.2C. As can be seen from the figure, the average working voltage of the composite cathode material is 3.35V and the first-cycle capacity is 140mAh / g.

[0083] Figure 6 The figure shows a schematic diagram of the cycling curve of the composite cathode material prepared in this embodiment after 100 cycles at 1C. As can be seen from the figure, the capacity retention rate of the composite cathode material is 84% ​​after 100 cycles at 1C.

[0084] Example 2

[0085] This embodiment provides a composite cathode material, which includes polyanionic phosphate and layered oxide;

[0086] The molecular formula of the polyanionic phosphate is Na. 3.3 V 1.5 Mn 0.3 M 3+ 0.2 (PO4)3, M is Cr, and the molecular formula of the layered oxide is Na. m NO2, where N is Cu 0.4 Fe 0.3 Mn 0.4 The mass ratio of the polyanionic phosphate to the layered oxide is 1:1;

[0087] The surface of the polyanionic phosphate is provided with a carbon coating layer, the thickness of which is 2 nm.

[0088] This embodiment also provides a method for preparing the above-mentioned composite cathode material, the method comprising the following steps:

[0089] (1) 3 mmol of phosphoric acid, 3.3 mmol of sodium acetate, 1.5 mmol of vanadium acetylacetonate, 0.3 mmol of manganese acetate, 0.2 mmol of chromium acetate, ascorbic acid and citric acid were added to the solvent ethanol. The resulting mixed solution was then placed in a water bath and magnetically stirred at 80°C until the ethanol was completely evaporated to obtain a precursor. The precursor was then dried at 110°C for 12 h and ground for 24 h. Finally, it was sintered at 800°C for 12 h in a tube furnace under a nitrogen atmosphere to obtain carbon-coated polyanionic phosphate material.

[0090] The molar ratio of carbon source to chromium acetate is 2:1, and the molar ratio of reducing agent ascorbic acid to chromium acetate is 0.5:1.

[0091] (2) The polyanionic phosphate material and the layered oxide material are mixed to obtain the composite cathode material;

[0092] The mass ratio of polyanionic phosphate material to layered oxide material is 1:1.

[0093] Example 3

[0094] This embodiment provides a composite cathode material, which includes polyanionic phosphate and layered oxide;

[0095] The molecular formula of the polyanionic phosphate is Na. 3.4 V 1.6 Mn 0.3 N + 0.1 (PO4)3, M is Mg, and the molecular formula of the layered oxide is Na. m NO2, where N is Ni 0.3 Fe 0.2 Mn 0.2 Cu 0.1 Ti 0.2 The mass ratio of the polyanionic phosphate to the layered oxide is 1:7;

[0096] The surface of the polyanionic phosphate is provided with a carbon coating layer, the thickness of which is 4 nm.

[0097] This embodiment also provides a method for preparing the above-mentioned composite cathode material, the method comprising the following steps:

[0098] (1) 3 mmol sodium dihydrogen phosphate, 0.2 mmol sodium carbonate, 1.6 mmol ammonium metavanadate, 0.3 mmol manganese carbonate, 0.1 mmol magnesium carbonate, hydroxylamine hydrochloride, citric acid and solvent acetone were added to a ball mill jar and mixed. After sealing, the mixture was centrifuged and ball milled for 20 h to obtain a precursor. The precursor was dried at 100 °C for 24 h and ground for 24 h. Then it was sintered at 700 °C for 12 h in a tube furnace under nitrogen atmosphere to obtain carbon-coated polyanionic phosphate material.

[0099] The molar ratio of citric acid to magnesium carbonate is 5:1, and the molar ratio of the reducing agent hydroxylamine hydrochloride to magnesium carbonate is 0.5:1.

[0100] (2) The polyanionic phosphate material and the layered oxide material are mixed to obtain the composite cathode material;

[0101] The mass ratio of polyanionic phosphate material to layered oxide material is 1:7.

[0102] Example 4

[0103] This embodiment provides a composite cathode material, which includes polyanionic phosphate and layered oxide;

[0104] The molecular formula of the polyanionic phosphate is Na. 3.3 V 1.5 Mn 0.3 M 3+ 0.2 (PO4)3, M is Ga, and the molecular formula of the layered oxide is Na. m NO2, N includes Ni 0.4 Fe 0.2 Mn 0.4 The mass ratio of the polyanionic phosphate to the layered oxide is 9:1;

[0105] The surface of the polyanionic phosphate is provided with a carbon coating layer, the thickness of which is 5 nm.

[0106] This embodiment also provides a method for preparing the above-mentioned composite cathode material, the method comprising the following steps:

[0107] (1) 3 mmol of phosphoric acid, 3 mmol of sodium acetate, 0.15 mmol of sodium carbonate, 0.75 mmol of vanadium trioxide, 0.3 mmol of manganese acetate, 0.1 mmol of gallium oxide, oxalic acid and citric acid were added to the solvent acetone. The resulting mixed solution was then placed in a water bath and magnetically stirred at 100°C until the acetone was completely evaporated to obtain a precursor. The precursor was then dried at 120°C for 10 h and ground for 24 h. Finally, it was sintered at 650°C for 18 h in a tube furnace under a nitrogen atmosphere to obtain a carbon-coated polyanionic phosphate material.

[0108] The molar ratio of citric acid to gallium oxide is 10:1, and the molar ratio of the reducing agent oxalic acid to gallium oxide is 3:1.

[0109] (2) The polyanionic phosphate material and the layered oxide material are mixed to obtain the composite cathode material;

[0110] The mass ratio of polyanionic phosphate material to layered oxide material is 9:1.

[0111] Example 5

[0112] This embodiment provides a composite cathode material, which includes polyanionic phosphate and layered oxide;

[0113] The molecular formula of the polyanionic phosphate is Na. 3.2 Mn 1.2 M 3+ 0.8 (PO4)3, M is Ti, and the molecular formula of the layered oxide is Na. m NO2, N includes Ni 0.4 Fe0.2 Mn 0.4 The mass ratio of the polyanionic phosphate to the layered oxide is 1:9;

[0114] The surface of the polyanionic phosphate is provided with a carbon coating layer, the thickness of which is 4 nm.

[0115] This embodiment also provides a method for preparing the above-mentioned composite cathode material, the method comprising the following steps:

[0116] (1) 3 mmol of phosphoric acid, 3.2 mmol of sodium acetate, 1.2 mmol of manganese carbonate, 0.8 mmol of titanic acid, reducing agent sucrose, glucose and solvent deionized water were added to a ball mill jar and mixed. After sealing, the mixture was centrifuged and ball milled for 18 h to obtain a precursor. The precursor was dried at 120 °C for h and ground for 1 min-48 h. Then it was sintered at 750 °C for 10 h in a tube furnace under nitrogen atmosphere to obtain carbon-coated polyanionic phosphate material.

[0117] The molar ratio of glucose to titanic acid is 5:1, and the molar ratio of sucrose to titanic acid is 0.5:1.

[0118] (2) The polyanionic phosphate material and the layered oxide material are mixed to obtain the composite cathode material;

[0119] The mass ratio of polyanionic phosphate material to layered oxide material is 1:9.

[0120] Example 6

[0121] The difference between this embodiment and embodiment 1 is that the mass ratio of polyanionic phosphate material to layered oxide material in step (2) is 1:10.

[0122] The remaining preparation methods and parameters are consistent with those in Example 1.

[0123] Example 7

[0124] The difference between this embodiment and embodiment 1 is that the mass ratio of polyanionic phosphate material to layered oxide material in step (2) is 10:1.

[0125] The remaining preparation methods and parameters are consistent with those in Example 1.

[0126] Example 8

[0127] The difference between this embodiment and Embodiment 1 is that the surface of the polyanionic phosphate is not coated with a carbon layer, that is, sucrose is not added in step (1).

[0128] The remaining preparation methods and parameters are consistent with those in Example 1.

[0129] Example 9

[0130] The difference between this embodiment and embodiment 1 is that the sintering temperature in step (1) is 400°C.

[0131] The remaining preparation methods and parameters are consistent with those in Example 1.

[0132] Example 10

[0133] The difference between this embodiment and embodiment 1 is that the sintering temperature in step (1) is 1000℃.

[0134] The remaining preparation methods and parameters are consistent with those in Example 1.

[0135] Example 11

[0136] The difference between this embodiment and embodiment 1 is that the reducing agent oxalic acid is not added in step (1).

[0137] The remaining preparation methods and parameters are consistent with those in Example 1.

[0138] Comparative Example 1

[0139] The difference between this comparative example and Example 1 is that the composite cathode material does not contain layered oxides, i.e., step (2) is not performed.

[0140] The remaining preparation methods and parameters are consistent with those in Example 1.

[0141] Comparative Example 2

[0142] The difference between this comparative example and Example 1 is that the composite cathode material contains only layered oxides, i.e., steps (1) and (2) are not performed.

[0143] The remaining preparation methods and parameters are consistent with those in Example 1.

[0144] Figure 7 The figure shows a comparison of the first charge-discharge curves of the composite cathode material prepared in Example 1, the cathode material prepared in Comparative Example 1, and the cathode material prepared in Comparative Example 2 at 0.2C. As can be seen from the figure, the average working voltage of the composite cathode material prepared in Example 1 is significantly improved compared to the layered oxide, and the discharge capacity does not decrease with the addition of the polyanionic compound with lower capacity. Therefore, the final composite cathode material exhibits a higher energy density.

[0145] Performance testing

[0146] The composite cathode materials prepared in the above embodiments and comparative examples were made into cathode sheets and assembled into 2032 type button cells.

[0147] The preparation method of the positive electrode sheet includes: grinding and mixing the above-mentioned composite positive electrode material, conductive carbon black and binder polytetrafluoroethylene in a mass ratio of 8:1:1 until uniform, then rolling it thoroughly with a roller mill to form a film of uniform thickness, drying it in a vacuum drying oven at 120℃ for 12 hours, cutting the obtained positive electrode film into square positive electrode sheets with a side length of about 6mm, accurately weighing its mass, and calculating the mass of active material in the positive electrode sheet according to the formula composition.

[0148] Battery assembly: The square positive electrode sheet, 16 mm diameter separator, 15 mm diameter sodium sheet, spring sheet and gasket obtained above are assembled into a 2032 type button cell in a glove box (oxygen content less than 0.01 ppm, water content less than 0.01 ppm).

[0149] The electrochemical performance of the assembled batteries was tested using the Wuhan Landian high-performance battery testing system.

[0150] The test results are shown in Table 1.

[0151] Table 1

[0152]

[0153]

[0154] analyze:

[0155] As shown in the table above, the composite cathode material prepared in this invention, compared with a single oxide cathode, not only has a higher average operating voltage for sodium ion insertion / extraction but also maintains a higher discharge capacity. Compared with a single phosphate cathode, the discharge specific capacity is significantly improved, thus achieving a higher energy density. Therefore, this composite cathode material combines the high voltage advantage of vanadium manganese-based phosphate with the high capacity advantage of oxide materials, providing a new approach for the practical application of sodium-ion battery cathodes and contributing to the future commercial development of sodium-ion batteries.

[0156] As can be seen from Examples 1 and 6-7, if the mass ratio of polyanionic phosphate material to layered oxide material is too small, the effect of improving the voltage platform of layered oxide is not obvious, and the capacity of composite cathode material is reduced; if the mass ratio of polyanionic phosphate material to layered oxide material is too large, since the capacity of polyanionic phosphate itself is lower than that of layered oxide, it will reduce the capacity of composite cathode material.

[0157] As can be seen from Examples 1 and 8, if the surface of the polyanionic phosphate is not coated with a carbon layer, it is difficult to further improve the electronic conductivity of the material.

[0158] As can be seen from Examples 1 and 9-10, if the sintering temperature is too low, the crystallinity of the material will be poor, which will lead to a deterioration in the capacity performance of the composite cathode material; if the sintering temperature is too high, the active elements will be easily deactivated, reducing the activity of the material, which will lead to a deterioration in the capacity performance of the composite cathode material.

[0159] As can be seen from Examples 1 and 11, adding the reducing agent oxalic acid can keep the transition metal ions in the molecular formula in a low valence state, so that oxidation reaction can occur during charging, accompanied by sodium removal process, effectively improving the capacity performance of the composite cathode material.

[0160] As can be seen from Example 1 and Comparative Example 1, the 0.2C first discharge specific capacity of Example 1 is 20% higher than that of Comparative Example 1.

[0161] As can be seen from Example 1 and Comparative Example 2, the average voltage of the first discharge at 0.2C in Example 1 is 5.2% higher than that in Comparative Example 2.

[0162] The applicant declares that the present invention is illustrated by the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A composite cathode material, characterized in that, The composite positive electrode material comprises a polyanionic phosphate and a layered oxide; The polyanionic phosphate comprises vanadium and / or manganese; The molecular formula of the polyanionic phosphate is Na 9-(3x+2y+nz) V x Mn y M n+ z (PO4)3, wherein 0≤x<2, 0≤y<2, 0≤z<2, x+y+z=2, and x, y, and z cannot be 0 at the same time, n is an integer greater than or equal to 1, and M is a doping metal. The M comprises any one or a combination of two or more of Fe, Ti, Li, K, Mg, Ca, Sr, Zn, Co, Ni, Cu, Cr, Ga, Al, Y, La, Zr, Sn, Nb or W; The molecular formula of the layered oxide is Na m NO2, wherein 0.6 < m < 1.0, N includes any one or a combination of at least two of Fe, Cu, Co, Ni, Mn, Cr, or Ti.

2. The composite cathode material of claim 1, wherein, The M is any one of a combination of Li and K, a combination of K and Mg, a combination of Mg and Ca, a combination of Ca and Zn, a combination of Co and Ni, a combination of Cu and Cr, or a combination of Al, Ga and La.

3. The composite cathode material of claim 1, wherein, The mass ratio of the polyanionic phosphate and the layered oxide is (1-9):(9-1).

4. The composite cathode material of claim 1, wherein, The polyanionic phosphate is provided with a carbon coating layer on the surface; The thickness of the carbon coating layer is 2-5 nm.

5. A method of producing the composite cathode material as claimed in any one of claims 1 to 4, characterized in that, The preparation method comprises the following steps: Mixing a polyanionic phosphate material and a layered oxide material to obtain the composite positive electrode material.

6. The production method according to claim 5, wherein The mass ratio of the polyanionic phosphate material and the layered oxide material is (1-9):(9-1).

7. The preparation method according to claim 5, characterized in that, The preparation method of the polyanionic phosphate material comprises any one of a solid phase method, a spray drying method, a coprecipitation method or a sol-gel method.

8. The preparation method according to claim 7, characterized in that, The preparation method of the polyanionic phosphate material comprises the following steps: Mixing a sodium source, a vanadium source, a manganese source, a phosphorus source, an M source and a solvent to obtain a precursor, drying the precursor, and sintering to obtain the polyanionic phosphate material; The sodium source comprises any one or a combination of two or more of sodium bicarbonate, sodium carbonate, sodium acetate, sodium nitrate, sodium hydroxide or sodium oxalate; The vanadium source comprises any one or a combination of two or more of vanadium pentoxide, vanadium tetroxide, vanadium trioxide, vanadium oxide, ammonium metavanadate, ammonium vanadate, vanadyl acetylacetonate or vanadium acetylacetonate; The manganese source comprises any one or a combination of two or more of trimanganese tetroxide, dimanganese trioxide, manganese dioxide, manganese monoxide, manganese carbonate, manganese acetate, carbonyl manganese or manganese acetylacetonate; The phosphorus source comprises any one or a combination of two or more of phosphoric acid, ammonium dihydrogen phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate or sodium phosphate; The M source comprises any one or a combination of two or more of an oxide containing M, an acid containing M, a base containing M, a nitrate containing M, a carbonate containing M, an acetate containing M, a sodium salt containing M or an ammonium salt containing M; The solvent comprises any one or a combination of two or more of deionized water, ethanol or acetone.

9. The production method according to claim 8, characterized by, The sodium source is any one of a combination of sodium bicarbonate and sodium carbonate, a combination of sodium carbonate and sodium acetate, a combination of sodium acetate and sodium nitrate, a combination of sodium nitrate and sodium hydroxide, or a combination of sodium hydroxide and sodium oxalate; The vanadium source is any one of a combination of vanadium pentoxide and vanadium tetroxide, a combination of vanadium tetroxide and vanadium trioxide, a combination of vanadium trioxide and vanadium oxide, a combination of vanadium oxide and ammonium metavanadate, a combination of ammonium metavanadate and ammonium vanadate, a combination of ammonium vanadate and vanadyl acetylacetonate, or a combination of vanadyl acetylacetonate and vanadium acetylacetonate. The manganese source is any one of a combination of trimanganese tetraoxide and dimanganese trioxide, a combination of manganese dioxide and manganese monoxide, a combination of manganese carbonate and manganese acetate, or a combination of manganese carbonyl and manganese acetylacetonate; The phosphorus source is any one of a combination of phosphoric acid and ammonium dihydrogen phosphate, a combination of sodium dihydrogen phosphate and ammonium dihydrogen phosphate, a combination of ammonium dihydrogen phosphate and diammonium hydrogen phosphate, a combination of sodium hydrogen phosphate and diammonium hydrogen phosphate, or a combination of ammonium phosphate and sodium phosphate; The M source is any one of a combination of a Li-containing base and a K-containing acid, a combination of a K-containing acid and a Mg-containing base, a combination of a Mg-containing sodium salt and a Ca-containing ammonium salt, a combination of a Ca-containing acid and a Zn-containing base, a combination of a Co-containing sodium salt and a Ni-containing base, or a combination of a Cu-containing ammonium salt and a Cr-containing acid; The solvent is any one of a combination of deionized water and ethanol, a combination of deionized water and acetone, or a combination of ethanol and acetone.

10. The method of claim 8, wherein, The drying temperature is 50-150℃.

11. The method of claim 10, wherein, The drying temperature is 90-120℃.

12. The method of claim 8, wherein, The drying time is 8-24h.

13. The preparation method according to claim 8, characterized in that, The sintering atmosphere includes an inert atmosphere and / or a reducing atmosphere; The gas in the inert atmosphere includes argon and / or nitrogen; The gas in the reducing atmosphere includes carbon monoxide and / or hydrogen; The sintering temperature is 500-900℃, and the time is 2-20h; The drying is followed by a grinding process, and then sintering; The grinding time is 1min-48h.

14. The method of claim 13, wherein, The grinding time is 0.5-2h.

15. The method of claim 8, wherein the method further comprises, A reducing agent is added during the mixing of the sodium source, the vanadium source, the manganese source, the phosphorus source, the M source, and the solvent; The reducing agent includes any one or a combination of at least two of oxalic acid, ascorbic acid, sucrose, glucose, hydroxylamine hydrochloride, ethanol, polyethylene glycol, dopamine hydrochloride, citric acid, malic acid, or ethylenediaminetetraacetic acid; The molar ratio of the reducing agent to the M source is (0.5-3):

1.

16. The method of claim 15, wherein, The reducing agent is any one of a combination of sucrose and glucose, a combination of oxalic acid and ethanol, a combination of ascorbic acid and hydroxylamine hydrochloride, a combination of citric acid and oxalic acid, a combination of dopamine hydrochloride and glucose, a combination of malic acid and ascorbic acid, a combination of oxalic acid and ethylenediaminetetraacetic acid, or a combination of hydroxylamine hydrochloride and oxalic acid.

17. The method of claim 8, wherein the method further comprises, A carbon source is added during the mixing of the sodium source, the vanadium source, the manganese source, the phosphorus source, the M source, and the solvent; The carbon source includes any one or a combination of at least two of citric acid, oleic acid, polyvinylpyrrolidone, polyethylene glycol, glucose, ascorbic acid, sucrose, starch, graphene, carbon nanotubes, or Ketjen black; The molar ratio of the carbon source to the M source is (0-10):

1.

18. The method of claim 17, wherein, The carbon source is any one of a combination of glucose and citric acid, a combination of sucrose and oleic acid, a combination of polyvinylpyrrolidone and polyethylene glycol, a combination of polyethylene glycol and glucose, a combination of ascorbic acid and sucrose, a combination of glucose and starch, or a combination of carbon nanotubes and Ketjen black.

19. The preparation method according to claim 17, characterized in that, The molar ratio of the carbon source to the M source is (0-3):

1.

20. The method of claim 5, wherein, The preparation method includes the following steps: (1) mixing a sodium source, a vanadium source, a manganese source, a phosphorus source, an M source, a reducing agent, a carbon source and a solvent to obtain a precursor, drying and grinding the precursor, and then sintering the precursor under an inert atmosphere and / or a reducing atmosphere to obtain a polyanionic phosphate material; wherein the temperature for drying is 50-150 DEG C, the time is 8-24 h; the time for grinding is 1 min-48 h; the temperature for sintering is 500-900 DEG C, the time is 2-20 h; the molar ratio of the carbon source to the M source is (0-10):1; (2) mixing the polyanionic phosphate material and a layered oxide material to obtain the composite cathode material; wherein the mass ratio of the polyanionic phosphate material to the layered oxide material is (1-9):(9-1).

21. A sodium-ion battery, characterized in that, The sodium ion battery comprises the composite cathode material according to any one of claims 1-4.

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