CN113929069B - A kind of manganese-rich phosphate cathode material and its preparation method and application - Google Patents

Abstract

The invention provides a cathode material. The cathode material is a Mn-rich phosphate cathode material containing V and Ti. The chemical formula of the cathode material is Na _{3+δ+(4‑n)x+2y} Ti _{1‑δ ‑x‑y} M ⁿ⁺ _x V _δ Mn _1+y (PO ₄ ) ₃ ; wherein, the M ⁿ⁺ includes Li ⁺ , K ⁺ , Mg ²⁺ , Ca ²⁺ , Sr ²⁺ , Zn ²⁺ , Co ^{2 +} , Ni ²⁺ , Cu ²⁺ , Al ³⁺ , Cr ³⁺ , Fe ³⁺ , Y ³⁺ , La ³⁺ , Ga ³⁺ , Zr ⁴⁺ , Sn ⁴⁺ , Nb ⁵⁺ or W ⁶⁺ Any one or a combination of at least two of them; the 0≤x≤0.5; the 0<δ≤0.5; the n≥1; the 0≤y≤0.5. The positive electrode material prepared by the present invention can obtain a higher effective specific capacity, suppress the voltage hysteresis phenomenon of the manganese-rich phosphate positive electrode, suppress the Jiang Taylor structural distortion of manganese ions and the dissolution of manganese ions, and exhibit good dynamic performance and rate performance, further improving the electrochemical performance of the material.

Description

A kind of manganese-rich phosphate cathode material and its preparation method and application

Technical field

The invention relates to the field of sodium ion batteries, and relates to a new type of manganese-rich phosphate cathode material and its preparation method and application.

Background technique

Against this background, advanced technologies such as clean energy (solar energy, wind energy, tidal energy, etc.) and smart grids have achieved unprecedented development. Therefore, higher requirements are also put forward for energy storage devices. As an energy storage device, secondary rechargeable lithium-ion batteries have been widely studied because of their high conversion efficiency and energy density. However, problems such as the scarcity and uneven distribution of lithium resources limit its future development. With the rise of large-scale energy storage and considering the high abundance and low price of sodium resources in the earth's crust, sodium-ion batteries have become an important supplement to lithium-ion batteries. Phosphate cathode materials, which are sodium superion conductors, have three-dimensional ion channels and have been extensively studied. Among them, sodium vanadium phosphate cathode, because vanadium ions can provide a stable and flat voltage platform, sodium vanadium phosphate exhibits excellent rate performance and cycle performance. However, because vanadium resources are relatively expensive, the industrial application of sodium vanadium phosphate is greatly limited. Although the iron-based phosphate cathode with a sodium superion conductor structure has a cost advantage, the Fe ²⁺ /Fe ³⁺ voltage platform is too low, only about 2.5V, and has no practical application value. For the same green and low-cost manganese-based phosphate cathode materials, such as sodium vanadium manganese phosphate, although there are two reaction pairs, the amount of vanadium is still high, making the cost of the material still high and difficult to industrialize; for non-containing Vanadium manganese titanium phosphate material is cheap, and positive tetravalent titanium ions can activate two reaction pairs, Mn ²⁺ /Mn ³⁺ and Mn ³⁺ /Mn ⁴⁺ . Their voltage platforms are at 3.6V and 4.1V respectively. It is even higher than the voltage platform of V ³⁺ /V ⁴⁺ (3.4V). However, the mutual occupation of Na and Mn in the material is serious, resulting in serious attenuation of the material during the sodium deintercalation process, and it has no practical application value.

In manganese-based phosphates, since the radii of manganese ions and sodium ions are similar, the manganese ions in the crystal structure can easily occupy the active site of sodium (Na1 position), resulting in a mixed arrangement of sodium and manganese, resulting in the inability to effectively exert the capacity of the material. During the charging process, divalent manganese ions are oxidized to form smaller trivalent manganese ions (or tetravalent manganese ions), which then migrate to a thermodynamically stable state. This migration process of manganese ions causes serious voltage hysteresis in the charge-discharge curve, which not only reduces the output voltage of the material, but also affects the capacity release of the material in the effective voltage window. Moreover, the Jahn-Teller effect of Mn ³⁺ and the dissolution of Mn ²⁺ in the organic electrolyte will reduce the structural stability of the material and worsen the dynamic properties of the material. Therefore, it is urgent to develop new low-priced Mn-rich phosphate cathodes to overcome the above shortcomings of the manganese-rich phosphate structure and obtain better rate performance and cycle performance, which is of great significance for the future industrial application of manganese-rich phosphate cathodes. .

CN106981641A discloses a method for preparing carbon-coated sodium titanium manganese phosphate cathode material. Organic compounds are used as reducing agents and carbon sources, and phosphorus sources, manganese sources, sodium sources and titanium sources are mixed and ball milled. After high-temperature sintering, that is, Carbon-coated sodium titanium manganese phosphate cathode material is available. Although the introduction of carbon coating can improve the overall conductivity of the cathode material, problems such as sodium and manganese mixing in the sodium titanium manganese phosphate structure, the Ginger Taylor effect of trivalent manganese ions, and the dissolution of manganese ions have still not been effectively solved. The above-mentioned sodium titanium manganese phosphate cathode material has a low discharge specific capacity and poor cycleability, making it difficult to achieve industrial-level mass production.

CN111092220A discloses a M element bulk-doped modified tunnel-type sodium-ion battery manganese-based cathode material and its preparation method. The precursor is prepared by solid-phase ball milling and high-temperature solid-phase sintering reaction to prepare a rod-shaped structure of M element bulk-doped material. Complex manganese-based materials for tunnel-type sodium-ion batteries. The bulk doping of M element effectively improves the electronic conductivity of the electrode material, improves the structural stability of the material, and is beneficial to improving its rate performance and cycle stability. Among them, the M element includes any one or a combination of at least two of Al ³⁺ , Co ³⁺ , Ni ²⁺ , Mg ²⁺ and Fe ³⁺ . Although M element bulk doping improves the conductivity of the material, it has limitations in improving the conductivity of the cathode material, and also has limitations in improving the material's cycle performance and rate performance.

CN112563484A discloses a sodium-ion battery cathode material and a preparation method thereof, as well as a sodium-ion battery. The chemical formula of the sodium-ion battery cathode material is Na _x Ni _y M _1-y O ₂ , where, 0.5<x<1, 0.1<y <0.5, M is selected from at least one of Mn, Fe, Co, V, Cu, Cr and Ti; the sodium ion battery cathode material is spherical-like particles, and the sodium ion battery cathode material has a layered structure. Although the cycle performance of the battery cathode material is improved, it does not have a beneficial effect on improving the battery conductivity.

How to improve the electrochemical performance of sodium-ion batteries is an important research direction in this field.

Contents of the invention

The purpose of the present invention is to provide a Mn-rich phosphate cathode material containing V and Ti, which can obtain more effective specific capacity, suppress the voltage hysteresis of the Mn-rich phosphate cathode, and exhibit good kinetic performance and rate It can inhibit the structural distortion of the manganese ions and the dissolution of manganese ions, further improving the electrochemical performance of the material.

In order to achieve the purpose of this invention, the present invention adopts the following technical solutions:

One of the objects of the present invention is to provide a cathode material. The cathode material is a Mn-rich phosphate cathode material containing V and Ti. The chemical formula of the cathode material is Na _{3+δ+(4-n)x+ 2y} Ti _1-δ-xy M ⁿ⁺ _x V _δ Mn _1+y (PO ₄ ) ₃ .

Wherein, the M ⁿ⁺ includes Li ⁺ , K ⁺ , Mg ²⁺ , Ca ²⁺ , Sr ²⁺ , Zn ²⁺ , Co ²⁺ , Ni ²⁺ , Cu ²⁺ , Al ³⁺ , Cr ³⁺ , Fe Any one or a combination of at least two of ³⁺ , Y ³⁺ , La ³⁺ , Ga ³⁺ , Zr ⁴⁺ , Sn ⁴⁺ , Nb ⁵⁺ or W ⁶⁺ , the combination is typical but not limiting Examples are: the combination of Li ⁺ and K ⁺ , the combination of K ⁺ and Mg ²⁺ , the combination of Mg ²⁺ and Ca ²⁺ , the combination of Ca ²⁺ and Zn ²⁺ , the combination of Co ²⁺ and Ni ²⁺ , The combination of Cu ²⁺ and Al ³⁺ , the combination of Cr ³⁺ and Y ³⁺ and La ³⁺ , the combination of Sr ²⁺ and Fe ³⁺ and Sn ⁴⁺ , the combination of Ga ³⁺ and Zr ⁴⁺ or Nb ^{5 +} and W ⁶⁺ combinations, etc.

Said 0≤x≤0.5, wherein the value of x may be 0, 0.1, 0.2, 0.3, 0.4 or 0.5, etc., but is not limited to the listed values, and other unlisted values within this range of values are also applicable.

The 0<δ≤0.5, wherein the value of δ can be 0.1, 0.2, 0.3, 0.4 or 0.5, etc., but is not limited to the listed values, and other unlisted values within this range of values are also applicable.

Said n≥1, wherein the value of said n can be 1, 2, 3, 4, 5, 6 or 7, etc., but is not limited to the listed values, and other unlisted values within this numerical range are also applicable.

Said 0≤y≤0.5, wherein the value of y can be 0, 0.1, 0.2, 0.3, 0.4 or 0.5, etc., but is not limited to the listed values, and other unlisted values within this range of values are also applicable.

Compared with many reported Mn- and Ti-containing phosphate cathode materials, the Mn-rich phosphate cathode material of the present invention can obtain more effective specific capacity due to the doping of trivalent vanadium ions. More sodium content can reduce the degree of sodium and manganese mixing, thereby suppressing the voltage hysteresis of the manganese-rich phosphate cathode; V ³⁺ , Ti ⁴⁺ and Mn ²⁺ have good solid solubility and synergistic effects, showing good Dynamic performance and rate performance; other Mn ⁺ ions in the material can inhibit the Jiang Taylor structural distortion of manganese ions and the dissolution of manganese ions, further improving the electrochemical performance of the material.

In the present invention, V ³⁺ , Ti ⁴⁺ and Mn ²⁺ have good solid solubility. In order to reduce the cost of raw materials, a small amount of active V ³⁺ is used to form a new type of Mn-rich phosphate with Ti ⁴⁺ and Mn ²⁺ . By adjusting the values of Mn ⁺ , δ, x and y, more sodium ions are introduced to occupy the lattice sites, which reduces the degree of sodium-manganese mixing and reduces the migration of trivalent or tetravalent manganese ions during the electrochemical reaction. Thereby suppressing the voltage hysteresis of the material. Since V ³⁺ , Ti ⁴⁺ and Mn ²⁺ have good solid solubility, they are conducive to the formation of a pure phase, which has a synergistic effect in the electrochemical reaction process and exhibits good kinetic performance and rate performance. Introducing Mn ⁺ ions with typical stabilizing effects can obtain a more stable framework structure, suppress the structural distortion of the manganese ions and the dissolution of manganese ions, and improve the cycle stability of the material.

The second object of the present invention is to provide a method for preparing the cathode material as described in the first aspect. The preparation method includes:

The raw materials of the cathode material are mixed with a solvent to obtain a precursor, which is dried and then sintered to obtain the cathode material.

The method for synthesizing the cathode material in the present invention includes any one of solid phase method, spray drying method and sol-gel method.

As a preferred technical solution of the present invention, the raw materials include sodium source, manganese source, titanium source, vanadium source, phosphorus source and metal ion source.

As a preferred technical solution of the present invention, 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. The combination is typical but not limited to Limiting examples are: the combination of sodium bicarbonate and sodium carbonate, the combination of sodium carbonate and sodium acetate, the combination of sodium acetate and sodium nitrate, the combination of sodium nitrate and sodium hydroxide or the combination of sodium hydroxide and sodium oxalate, etc.

Preferably, the manganese source includes manganese acetate, manganese nitrate, manganese acetylacetonate, manganese oxalate, manganese carbonate, manganese monoxide, manganese dioxide, manganese trioxide, manganese tetroxide, manganous anhydride, manganese anhydride or high Any one or a combination of at least two manganese anhydrides. Typical but non-limiting examples of the combinations are: the combination of manganese acetate and manganese nitrate, the combination of manganese acetylacetonate and manganese oxalate, the combination of manganese oxalate and manganese carbonate, The combination of manganese monoxide and manganese dioxide, the combination of manganese trioxide and manganese tetroxide, the combination of manganese tetroxide and manganous anhydride, the combination of manganous anhydride and manganese anhydride or the combination of manganese anhydride and permanganese anhydride wait.

Preferably, the titanium source includes any one or a combination of at least two of titanium dioxide, titanium trioxide, sodium titanate, titanium acetylacetonate, titanium acetylacetonate or tetrabutyl titanate, and the combination is typically Non-limiting examples are: the combination of titanium dioxide and titanium trioxide, the combination of titanium trioxide and sodium titanate, the combination of sodium titanate and titanium acetylacetonate, the combination of titanium acetylacetonate and titanium acetylacetonate or titanium acetylacetonate. The combination of titanium and tetrabutyl titanate, etc.

Preferably, the vanadium source includes any one of various types of vanadium pentoxide, vanadium tetroxide, vanadium trioxide, vanadium oxide, sodium ammonium metavanadate, ammonium vanadate, vanadium acetylacetonate or vanadium acetylacetonate. One or a combination of at least two. Typical but non-limiting examples of the combination include: the combination of vanadium pentoxide and vanadium tetroxide, the combination of vanadium tetroxide and vanadium trioxide, vanadium trioxide and vanadium oxide. The combination of vanadium oxide and sodium ammonium metavanadate, the combination of sodium ammonium metavanadate and ammonium vanadate, the combination of ammonium vanadate and vanadyl acetylacetonate or the combination of vanadyl acetylacetonate and vanadium acetylacetonate, etc.

Preferably, the phosphorus source includes any one or a combination of at least two of phosphoric acid, sodium ammonium dihydrogen phosphate, ammonium dihydrogen phosphate, sodium diammonium hydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate or sodium ammonium phosphate, Typical but non-limiting examples of the combinations include: the combination of phosphoric acid and sodium ammonium dihydrogen phosphate, the combination of sodium ammonium dihydrogen phosphate and ammonium dihydrogen phosphate, the combination of ammonium dihydrogen phosphate and sodium diammonium hydrogen phosphate, dihydrogen dihydrogen phosphate. The combination of sodium ammonium and diammonium hydrogen phosphate or the combination of ammonium phosphate and sodium ammonium phosphate, etc.

Preferably, the metal ion source includes Li ⁺ , K ⁺ , Mg ²⁺ , Ca ²⁺ , Sr ²⁺ , Zn ²⁺ , Co ²⁺ , Ni ²⁺ , Cu ²⁺ , Al ³⁺ , Cr ^{3 +} , Fe ³⁺ , Y ³⁺ , La ³⁺ , Ga ^{3+ ,} Zr ⁴⁺ , Sn ⁴⁺ , Nb ⁵⁺ or any one of the corresponding acids, bases, sodium salts or ammonium salts or at least Two combinations, typical but non-limiting examples of the combinations include: the combination of the base corresponding to Li ⁺ and the acid corresponding to K ⁺ , the combination of the acid corresponding to K ⁺ and the base corresponding to Mg ²⁺ , the combination of the base corresponding to Mg ²⁺ The combination of sodium salt and the ammonium salt corresponding to Ca ²⁺ , the combination of the acid corresponding to Ca ²⁺ and the alkali corresponding to Zn ²⁺ , the combination of the sodium salt corresponding to Co ²⁺ and the alkali corresponding to Ni ²⁺ , the combination of Cu ²⁺ The combination of the ammonium salt and the acid corresponding to Al ³⁺ , the combination of the base corresponding to Cr ³⁺ and the base corresponding to Y ³⁺ and the base corresponding to La ³⁺ , the acid corresponding to Ga ³⁺ and the base corresponding to Zr ⁴⁺ Combination or combination of sodium salt corresponding to Nb ⁵⁺ and acid corresponding to W ⁶⁺ , etc.

As a preferred technical solution of the present invention, the raw material further includes a carbon source.

Preferably, the carbon source includes sodium citrate, citric acid, sodium oleate, oleic acid, polyvinylpyrrolidone, polyethylene glycol, glucose, ascorbic acid, sucrose, dopamine hydrochloride, starch, graphene oxide, reduced graphene, Any one or a combination of at least two of carbon nanotubes or Ketjen Black. Typical but non-limiting examples of the combination are: the combination of sodium citrate and citric acid, the combination of citric acid and sodium oleate, oleic acid The combination of sodium and oleic acid, the combination of oleic acid and polyvinylpyrrolidone, the combination of polyvinylpyrrolidone and polyethylene glycol, the combination of polyethylene glycol and glucose, the combination of ascorbic acid and sucrose, the combination of dopamine hydrochloride and starch, graphite oxide The combination of ene and reduced graphene or the combination of carbon nanotubes and Ketjen Black, etc.

Preferably, the molar ratio of the carbon source and the metal ion source is 0 to 10:1, wherein the molar ratio 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., but are not limited to the listed values. Other unlisted values within this range are also applicable, and more preferably 0 to 3: 1.

As a preferred technical solution of the present invention, the solvent includes any one or a combination of at least two of deionized water, ethanol or acetone. Typical but non-limiting examples of the combination include: a combination of deionized water and ethanol, The combination of deionized water and acetone or the combination of ethanol and acetone, etc.

As a preferred technical solution of the present invention, grinding is performed after the drying.

Preferably, the drying temperature is 60-150°C, and the temperature can be 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C ℃, 115 ℃, 120 ℃, 125 ℃, 130 ℃, 135 ℃, 140 ℃, 145 ℃ or 150 ℃, etc., but are not limited to the listed values. Other unlisted values within this range of values are also applicable, and further preferably 90～120℃;

Preferably, the time of the grinding treatment is 1 min to 48 h, wherein the time may 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, 40h, 45h or 48h, etc., but not limited to the listed values, other unlisted values within this range are also applicable. More preferably, it is 30 min to 2 hours.

As a preferred technical solution of the present invention, the sintering atmosphere includes an inert atmosphere and/or a reducing atmosphere.

Preferably, the reducing atmosphere includes carbon monoxide and/or hydrogen.

Preferably, the inert atmosphere includes argon and/or nitrogen.

As a preferred technical solution of the present invention, the sintering temperature is 500-900°C, where the temperature can be 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C or 900°C ℃, etc., but are not limited to the listed values, other unlisted values within this range are also applicable.

Preferably, the sintering time is 2 to 20h, wherein the time can be 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h , 18h, 19h or 20h, etc., but not limited to the listed values, other unlisted values within this range are also applicable.

The third object of the present invention is to provide an application of the cathode material as described in the first aspect, which is characterized in that the cathode material is used in a sodium-ion battery.

The sodium ion battery in the present invention is used for large-scale energy storage equipment in solar power generation, wind power generation, smart grid peak shaving, distributed power stations, backup power supplies or communication base stations.

Compared with the existing technology, the present invention has the following beneficial effects:

(1) The Mn-rich phosphate cathode material containing V and Ti prepared in the present invention greatly reduces the cost due to the small amount of V used.

(2) The Mn-rich phosphate cathode material containing V and Ti prepared by the present invention has good electrochemical properties. When charged and discharged at 0.1C, its first discharge gram specific capacity reached more than 110mAh/g, and the discharge medium voltage was 3.5 V or above; more than 80mAh/g can be obtained at 10C; the capacity retention rate after 1000 cycles at 2C is more than 90%.

Description of the drawings

Figure 1 is an XRD pattern of the Mn-rich phosphate cathode material containing V and Ti prepared in Example 1 of the present invention.

Figure 2 is a scanning electron microscope image of the Mn-rich phosphate cathode material containing V and Ti prepared in Example 1 of the present invention.

Figure 3 is a rate charge-discharge curve of the Mn-rich Mn-based phosphate cathode material containing V and Ti prepared in Example 1 of the present invention.

Figure 4 is a cycle performance diagram at 2C of the Mn-rich Mn-based phosphate cathode material containing V and Ti prepared in Example 1 of the present invention.

Figure 5 is a charge-discharge curve of the phosphate cathode prepared in Example 1-2 and Comparative Example 1-2.

Detailed ways

The technical solution of the present invention will be further described below through specific implementations. Those skilled in the art should understand that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

Example 1

This embodiment provides a method for preparing a Mn-rich phosphate cathode material containing V and Ti:

Add manganese acetate, titanium dioxide, ammonium metavanadate, magnesium acetate, sodium acetate and phosphoric acid with a composition ratio of 1:0.80:0.15:0.05:3.25:3 to an ethanol solution containing citric acid, in which carbon and transition metal substances The volume ratio is 1.5:1. The mixed solution was then placed in a water bath at 70 degrees Celsius and stirred magnetically until the ethanol evaporated completely. The obtained precursor is dried at 100 degrees Celsius, ground to a powder state, and sintered in a tube furnace at 700 degrees Celsius for 10 hours in an argon atmosphere to obtain Na _3.25 Ti _0.8 V _0.15 Mg _0.05 Mn(PO ₄ ) ₃ @C cathode material.

The structure of the cathode material in this example was analyzed, and an X-ray instrument was used to conduct XRD analysis on the Mn-rich phosphate cathode material prepared in this example. The test results are shown in Figure 1. It can be seen from the figure that the crystallinity of the material is good. , and has high phase purity.

A scanning electron microscope was used to analyze the surface morphology of the phosphate cathode prepared in this example. The test results are shown in Figure 2. It can be seen from the figure that the prepared material is composed of random primary particles stacked. This agglomeration phenomenon is caused by the particles being embedded in the carbon layer and showing a cross-linked state.

The phosphate cathode prepared in this example is used to assemble a 2032-type testable button battery, and the rate charge and discharge curve is shown in Figure 3. The cycle performance at 2C is shown in Figure 4.

Example 2

This embodiment provides a method for preparing a Mn-rich phosphate cathode material containing V and Ti:

Add manganese carbonate, titanium dioxide, vanadium trioxide, aluminum trioxide, sodium hydroxide, ammonium dihydrogen phosphate and oleic acid with a composition ratio of 1.2:0.65:0.075:0.025:3.55:3 into the aqueous solution, in which carbon and transition The molar ratio of metallic substances is 3:1. Then put the mixture into a ball mill and mix evenly. The obtained precursor is dried at 110 degrees Celsius, ground to a powder state, and sintered in a tube furnace at 750 degrees Celsius for 20 hours in an argon atmosphere to obtain Na _3.55 Ti _0.65 V _0.10 Al _0.05 Mn _1.2 (PO ₄ ) ₃ @C cathode material.

Example 3

This embodiment provides a method for preparing a Mn-rich phosphate cathode material containing V and Ti:

Add manganese acetate, tetrabutyl titanate, ammonium metavanadate, ammonium tungstate, sodium acetate and phosphoric acid with a composition ratio of 1:0.74:0.25:0.01:3.19:3 to an acetone solution containing ascorbic acid, in which carbon and transition The molar ratio of metallic substances is 1:1. The mixed solution was then placed in a water bath with magnetic stirring at 80 degrees Celsius until the acetone evaporated completely. The obtained precursor is dried at 110 degrees Celsius, ground to a powder state, and sintered in a tube furnace at 650 degrees Celsius for 12 hours in an argon atmosphere to obtain Na _3.19 Ti _0.74 V _0.25 W _0.01 Mn(PO ₄ ) ₃ @C cathode material.

Example 4

This embodiment provides a method for preparing a Mn-rich phosphate cathode material containing V and Ti:

Add manganese carbonate, titanium dioxide, vanadium trioxide, zirconium dioxide, sodium carbonate, ammonium dihydrogen phosphate and glucose with a composition ratio of 1.15:0.7:0.05:0.05:1.775:3 into the aqueous solution, in which carbon and transition metal substances The quantity ratio is 1.25:1. Then put the mixture into a ball mill and mix evenly. The obtained precursor is dried at 120 degrees Celsius, ground to a powder state, and sintered in a tube furnace at 800 degrees Celsius for 10 hours in an argon atmosphere to obtain Na _3.4 Ti _0.7 V _0.10 Zr _0.05 Mn _1.15 (PO ₄ ) ₃ @C cathode material.

Example 5

This embodiment provides a method for preparing a Mn-rich phosphate cathode material containing V and Ti:

Add manganese acetate, tetrabutyl titanate, vanadium acetylacetonate, sodium acetate and phosphoric acid with a composition ratio of 1:0.75:0.25:3.25:3 into the ethanol solution, in which the amount of carbon and transition metal substances is 1.25:1 . Then put the mixture into a ball mill and mix evenly. The obtained precursor is dried at 120 degrees Celsius, ground to a powder state, and sintered in a tube furnace at 800 degrees Celsius for 10 hours in an argon atmosphere to obtain Na _3.4 Ti _0.7 V _0.10 Zr _0.05 Mn _1.15 (PO ₄ ) ₃ @C cathode material.

Example 6

In this example, manganese acetate, titanium dioxide, ammonium metavanadate, magnesium acetate, sodium acetate and phosphoric acid with a composition ratio of 1:0.80:0.15:0.05:3.25:3 are added to an ethanol solution containing citric acid, in which carbon and transition metals The amount ratio of the substances is 1.5:1, replace it with the composition ratio of 1:0.80:0.15:0.05:3.25:3 of manganese acetate, titanium dioxide, ammonium metavanadate, magnesium acetate, sodium acetate and phosphoric acid, add more citric acid In the ethanol solution, the amount ratio of carbon and transition metal substances was 10:1, and other conditions were the same as in Example 1.

Example 7

In this example, manganese acetate, titanium dioxide, ammonium metavanadate, magnesium acetate, sodium acetate and phosphoric acid with a composition ratio of 1:0.80:0.15:0.05:3.25:3 are added to an ethanol solution containing citric acid, in which carbon and transition metals The mass ratio of the substances is 1.5:1, replaced by the composition ratio of 1:0.80:0.15:0.05:3.25:3. Manganese acetate, titanium dioxide, ammonium metavanadate, magnesium acetate, sodium acetate and phosphoric acid are added to the ethanol solution, in which carbon and The substance ratio of the transition metal is 0, and other conditions are the same as in Example 1.

Comparative example 1

This comparative example provides a method for preparing a phosphate cathode material containing only Ti and Mn:

The preparation steps are as follows:

Manganese acetate, tetrabutyl titanate, sodium acetate and phosphoric acid with a composition ratio of 1:1:3:3 were added to the ethanol solution containing citric acid, in which the amount ratio of carbon and transition metal substances was 1.5:1. The mixed solution was then placed in a water bath with magnetic stirring at 80 degrees Celsius until the ethanol evaporated completely. The obtained precursor is dried at 100 degrees Celsius, ground to a powder state, and sintered in a tube furnace in an argon atmosphere at 700 degrees Celsius for 10 hours to obtain the Na ₃ TiMn(PO ₄ ) ₃ @C cathode material.

Comparative example 2

This comparative example provides a method for preparing a phosphate cathode material that only contains Ti and Mn and has more Mn content:

Manganese carbonate, titanium dioxide, sodium carbonate, ammonium dihydrogen phosphate and glucose with a composition ratio of 1.2:0.8:1.5:3 were added to the aqueous solution, in which the amount ratio of carbon and transition metal substances was 2:1. Then put the mixture into a ball mill and mix evenly. The obtained precursor is dried at 120 degrees Celsius, ground to a powder state, and sintered in a tube furnace at 800 degrees Celsius for 15 hours in an argon atmosphere to obtain the Na _3.4 Ti _0.8 Mn _1.2 (PO ₄ ) ₃ @C cathode. Material.

Comparative example 3

This comparative example provides a method for preparing a phosphate cathode material containing only V and Mn:

Add manganese carbonate, vanadium trioxide, sodium carbonate, ammonium dihydrogen phosphate and glucose with a composition ratio of 1.2:0.8:1.5:3 into the aqueous solution, in which the amount ratio of carbon to transition metal is 2:1. Then put the mixture into a ball mill and mix evenly. The obtained precursor is dried at 120 degrees Celsius, ground to a powder state, and sintered in a tube furnace at 800 degrees Celsius for 15 hours in an argon atmosphere to obtain the Na _3.4 Ti _0.8 Mn _1.2 (PO ₄ ) ₃ @C cathode. Material.

Conduct electrochemical performance analysis on the cathode materials prepared in Examples 1-5 and Comparative Examples 1-3,

Among them, the electrochemical performance analysis is as follows:

1. Battery preparation

(1) Preparation of battery cathode sheet: Grind and mix the prepared phosphate cathode material, Ketjen Black, and polytetrafluoroethylene binder in a mass ratio of 7:2:1, and then fully roll them with a pair of rollers to form Film of uniform thickness. After drying in a vacuum drying oven at 120°C for 5 hours, the positive electrode film was cut into square electrode pieces with a side length of about 6 mm. After accurately weighing its mass, the mass of the active material in the positive electrode piece was calculated based on the formula composition.

(2)Battery assembly:

Assemble the square positive electrode piece, the diaphragm with a diameter of 16mm, the sodium piece with a diameter of 15mm, the shrapnel and the gasket obtained above in a glove box (oxygen content is less than 0.01ppm, water content is less than 0.01ppm) to form a testable 2032 type. Button cell battery.

2. Electrochemical performance testing method:

The assembled batteries were charged and discharged at various rates using the Wuhan Blue Power high-performance battery testing system. The results are shown in Table 1. The charge and discharge curves of the phosphate positive electrodes prepared in Example 1, Example 2, Comparative Example 1, and Comparative Example 2 are shown in Figure 5.

Table 1

By comparing the above Examples 1-5 and Comparative Examples 1-3, it can be seen that the Ti element can activate the two voltage platforms related to manganese-rich phosphate cathode and manganese; the introduction of V can obtain more effective specific capacity, At the same time, the voltage hysteresis of the manganese-rich phosphate cathode is suppressed, and the three elements V, Ti and Mn have good solid solution properties and synergistic effects, showing good kinetic properties and rate performance. The introduction of stable metal ions Mn+ can effectively suppress the structural distortion of the Jiang Taylor structure of manganese ions and the dissolution of manganese ions, further improving the electrochemical performance of the material. Comparing Example 1 and Example 7, it can be seen that without carbon coating, the electrochemical performance will be worse due to poor electronic conductivity; Comparing Example 1 and Example 6, it can be seen that too much carbon coating will It increases the interface resistance of the cathode material and causes more side reactions, which is also detrimental to the electrochemical performance of the material.

The applicant declares that the above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the technical field should understand that any person skilled in the technical field will not use the invention disclosed in the present invention. Within the technical scope, changes or substitutions that can be easily imagined fall within the protection scope and disclosure scope of the present invention.

Claims (17)

1. A positive electrode material, characterized in that the positive electrode material is a Mn-rich phosphate positive electrode material containing V and Ti, and the chemical formula of the positive electrode material is Na _{3+δ+(4-n)x+2y} Ti _1-δ-xy M ⁿ⁺ _x V _δ Mn _1+y (PO ₄ ) ₃ ; Wherein, the M ⁿ⁺ includes Mg ²⁺ , Ca ²⁺ , Sr ²⁺ , Zn ²⁺ , Co ²⁺ , Ni ²⁺ , Cu ²⁺ , Al ³⁺ , Cr ³⁺ , Fe ³⁺ , Y ³⁺ , La ³⁺ , Ga ³⁺ , Zr ^{4 +} , Sn ⁴⁺ , Nb ⁵⁺ or W ⁶⁺ any one or a combination of at least two; The 0<x≤0.05; The 0<δ≤0.25; The n≥2; Said 0<y<0.15. 2. A method for preparing the cathode material according to claim 1, characterized in that the preparation method includes: The raw materials of the positive electrode material are mixed with a solvent to obtain a precursor, the precursor is dried and then sintered to obtain the positive electrode material, and grinding is performed after the drying, and the sintering atmosphere includes an inert atmosphere and/or a reducing atmosphere, so The sintering temperature is 500~900 ℃, and the sintering time is 2~20 h; The raw materials include sodium source, manganese source, titanium source, vanadium source, phosphorus source and metal ion source. The metal ion source includes Mg ²⁺ , Ca ²⁺ , Sr ²⁺ , Zn ²⁺ , Co ²⁺ , Ni ²⁺ , Cu ²⁺ , Al ³⁺ , Cr ³⁺ , Fe ³⁺ , Y ³⁺ , La ³⁺ , Ga ³⁺ , Zr ⁴⁺ , Sn ⁴⁺ , Nb ⁵⁺ or W ⁶⁺ corresponding acid, Any one or a combination of at least two of alkali, sodium salt or ammonium salt; The raw material also includes a carbon source, and the molar ratio of the carbon source and the metal ion source is 0 to 10:1. 3. The preparation method according to claim 2, wherein the sodium source includes any one or at least two of sodium bicarbonate, sodium carbonate, sodium acetate, sodium nitrate, sodium hydroxide or sodium oxalate. combination. 4. The preparation method according to claim 2, wherein the manganese source includes manganese acetate, manganese nitrate, manganese acetylacetonate, manganese oxalate, manganese carbonate, manganese monoxide, manganese dioxide, manganese trioxide, Any one or a combination of at least two of manganese tetroxide, manganous anhydride, manganese anhydride or permanganic anhydride. 5. The preparation method according to claim 2, wherein the titanium source includes any one of titanium dioxide, titanium trioxide, sodium titanate, titanium acetylacetonate, titanium acetylacetonate or tetrabutyl titanate. or a combination of at least two. 6. The preparation method according to claim 2, wherein the vanadium source includes various types of vanadium pentoxide, vanadium tetroxide, vanadium trioxide, vanadium oxide, sodium ammonium metavanadate, and ammonium vanadate. , any one or a combination of at least two of vanadium acetylacetonate or vanadium acetylacetonate. 7. The preparation method according to claim 2, wherein the phosphorus source includes phosphoric acid, sodium ammonium dihydrogen phosphate, ammonium dihydrogen phosphate, sodium diammonium hydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate or ammonium phosphate. Any one or a combination of at least two of sodium. 8. The preparation method according to claim 2, wherein the carbon source includes sodium citrate, citric acid, sodium oleate, oleic acid, polyvinylpyrrolidone, polyethylene glycol, glucose, ascorbic acid, sucrose, Any one or a combination of at least two of dopamine hydrochloride, starch, graphene oxide, reduced graphene, carbon nanotubes or Ketjen black. 9. The preparation method according to claim 2, characterized in that the molar ratio of the carbon source and the metal ion source is 0~3:1. 10. The preparation method according to claim 2, wherein the solvent includes any one or a combination of at least two of deionized water, ethanol or acetone. 11. The preparation method according to claim 2, characterized in that the drying temperature is 60~150°C. 12. The preparation method according to claim 11, characterized in that the drying temperature is 90~120°C. 13. The preparation method according to claim 2, characterized in that the time of the grinding treatment is 1 min~48h. 14. The preparation method according to claim 13, characterized in that the time of the grinding treatment is 30 min~2h. 15. The preparation method according to claim 2, characterized in that the reducing atmosphere includes carbon monoxide and/or hydrogen. 16. The preparation method according to claim 2, characterized in that the inert atmosphere includes argon and/or nitrogen. 17. An application of the cathode material according to claim 1, characterized in that the cathode material is used in sodium ion batteries.