A polyanionic sodium-ion battery cathode material, and a preparation method and application thereof

Abstract

The application relates to a polyanionic sodium ion battery positive electrode material and a preparation method and application thereof, and the material has a chemical formula of Na4Mn a Fe b M c M' d (PO4)2P2O7 / C, wherein M is selected from one or more of Mg, Ni, Al, Cu, Zn and Zr, M' is selected from one or more of Cr, Ti, La, Ce, Sn, Mo, Nb and V, Y, and 0 The method adopts a coprecipitation combined with a high-temperature solid-phase sintering method. Compared with the prior art, the electrode material prepared by the application has good electrochemical performance, the preparation process is simple, raw materials are easy to obtain, the cost is low, the application has obvious industrial application value, and large-scale production is easy.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of secondary batteries, and relates to a polyanionic sodium ion battery positive electrode material and a preparation method and application thereof. BACKGROUND

[0002] With the rapid popularization of electric vehicles and the growth of large-scale energy storage demand, lithium ion battery technology has developed rapidly in the past decade and has become the mainstream energy storage battery system today. However, the content of lithium element in the earth's crust is low and unevenly distributed, resulting in significant fluctuations in the prices of basic raw materials lithium carbonate and lithium hydroxide. Sodium ion batteries have similar working principles to lithium ion batteries, and the content of sodium element is abundant, the raw materials are widely available, and the price is cheap, so they are considered as an important supplement to lithium ion batteries and are expected to occupy a place in the market in the future.

[0003] Sodium ion battery positive electrode materials mainly include three categories of layered oxides, polyanionic compounds and prussian blue analogues. Among them, iron-based polyanionic compound Na4Fe3(PO4)2P2O7 (theoretical specific capacity 129 mAh / g) has been widely concerned by researchers because of its excellent cycle stability, low raw material cost, non-toxic elements and good air stability. Na4Mn3(PO4)2P2O7 material with similar structure and theoretical specific capacity to Na4Fe3(PO4)2P2O7 has a higher working voltage (about 3.6V on average) than Na4Fe3(PO4)2P2O7 (3.0V on average), showing higher specific energy and potential application prospects. However, due to the Jahn-Teller effect of manganese and the poor intrinsic conductivity of the material, the actual prepared Na4Mn3(PO4)2P2O7 / C material has poor electrochemical performance. By doping iron elements to improve the electronic conductivity and sodium ion diffusion capacity of the material and inhibit the Jahn-Teller effect of manganese, Na4Mn x Fe 3-x (PO4)2P2O7 / C positive electrode material with high average working voltage and high specific capacity can be obtained, improving the practical application performance of the material.

[0004] Currently, there are few reports on manganese iron sodium pyrophosphate phosphate materials. CN114613998A discloses a carbon-coated sodium ion battery positive electrode material Na4Fe 3-x M xThe preparation method of the (PO4)2P2O7 / C material directly adopts a solid-phase sintering method, sodium source, iron source, M (Ni / Co / Mn) source, and phosphorus source materials are mixed through wet ball milling, the mixture obtained after drying is mixed with a carbon source and is calcined at high temperature to obtain a carbon-coated product, typically, sodium pyrophosphate, iron oxalate, manganese oxalate, and ammonium dihydrogen phosphate are used as raw materials to prepare Na4Fe 1.5 Mn 1.5 The (PO4)2P2O7 / C material has a first-cycle discharge capacity of 75 mAh / g at a 0.5C rate, and in the patent, the metal salt raw materials are directly mixed in a solid phase, which cannot achieve uniform molecular-level mixing between metal ions, affecting the performance of the material. SUMMARY

[0005] The purpose of the present application is to overcome the defects of the prior art and provide a kind of polyanionic sodium ion battery positive material and its preparation method and application, which can ensure the uniform molecular mixing of transition metal elements in the material. The electrode material prepared by the present application shows good electrochemical performance, and the preparation process is simple, the raw materials are easy to obtain, the cost is low, and it has significant industrial application value and is easy to mass production.

[0006] The purpose of the present application can be achieved by the following technical solutions:

[0007] One of the technical solutions of the present application is to provide a kind of polyanionic sodium ion battery positive material, the chemical formula of the material is: Na4Mn a Fe b M c M’ d (PO4)2P2O7 / C, wherein M is selected from one or more of Mg, Ni, Al, Cu, Zn, Zr, M' is selected from one or more of Cr, Ti, La, Ce, Sn, Mo, Nb, V, Y, and 0

[0008] Because the iron element is introduced into the sodium manganese pyrophosphate in order to significantly improve the Jahn-Teller effect of manganese, and at the same time improve the electronic conductivity and ion diffusion coefficient of the material, and the iron element acts through the-Fe-O-Mn- bond, so in the material preparation process, the iron and manganese elements are highly uniformly mixed at a molecular scale. In order to achieve this purpose, the present application proposes to use a coprecipitation method to first prepare a manganese-iron element coprecipitation precursor, so as to ensure that the iron and manganese elements can be mixed uniformly at a molecular scale, and then the precursor is mixed with sodium dihydrogen phosphate to prepare a sodium ion battery positive electrode material. The introduction of doping elements M or M' can stabilize the material lattice structure during charging and discharging, and the substitution of part of high-valence, large-radius ions at the Mn site can expand the lattice parameter and produce transition metal ion hole sites, which is beneficial to improve the diffusion ability of sodium ions, thereby improving the charging and discharging performance of the material.

[0009] One of the technical solutions of the present application is to provide a preparation method of a polyanionic sodium ion battery positive electrode material, which adopts a coprecipitation combined with high-temperature solid-phase sintering method, comprising the following steps:

[0010] (1) Dissolve soluble manganese salt, iron salt and doping element M source in water according to a suitable ratio to configure a mixed solution, and add the mixed solution to a reactor protected by an inert atmosphere under the condition of water bath heating, and under the condition of rapid stirring, a coprecipitation reaction occurs to obtain a metal element coprecipitation product;

[0011] (2) After the coprecipitation product is washed and dried, it is mixed with sodium dihydrogen phosphate, doping element M' source and carbon source according to a suitable ratio by mechanical mixing to obtain a precursor powder;

[0012] (3) The precursor powder is placed in an atmosphere furnace under the protection of an inert atmosphere, and is first subjected to pre-sintering treatment, and then is subjected to high-temperature sintering, and after cooling, is crushed and sieved to obtain the final product.

[0013] Further, in step (1), the manganese salt, iron salt and doping element M source are selected from at least one of sulfate, chloride and acetate or nitrate, and the total concentration of the manganese salt, iron salt and doping element M source is 0.1-2.5 mol / L.

[0014] In step (2), the doping element M' source is selected from one of oxide, oxalate, acetate, citrate or carbonate.

[0015] Further, in step (1), the combination of the precipitating agent / adjusting agent is sodium hydroxide / ammonia, sodium oxalate / sulfuric acid, ammonium oxalate / sulfuric acid or oxalic acid / sodium hydroxide, and the molar ratio of the salts, precipitating agent and adjusting agent in the mixed solution is 1:(1-2):(0-1).

[0016] Further, the reaction temperature in step (1) is 40-70 DEG C, and the time is 1-24h.

[0017] As a preferred technical solution, the stirring speed in step (1) is 250-700 rpm.

[0018] Further, the inert atmosphere in step (1) is nitrogen or argon, and the inert atmosphere in step (3) is nitrogen or argon.

[0019] Further, the drying temperature in step (2) is 60-120 DEG C, and the time is 5-18h, and the mechanical mixing includes one of mechanical stirring mixing, ball milling mixing, and wet sand milling mixing combined with spray drying.

[0020] Further, the carbon source in step (2) is selected from at least one of sucrose, glucose, citric acid, cellulose, water-soluble starch, dextrin or polyethylene glycol, and the carbon content of the final product is 1-10%.

[0021] Further, the pre-sintering temperature in step (3) is 250-350 DEG C, and the time is 2-8h, and the high-temperature sintering temperature is 500-700 DEG C, and the time is 5-12h.

[0022] One of the technical solutions of the application is to provide an application of a polyanionic sodium ion battery positive electrode material.

[0023] Compared with the prior art, the application has the following advantages:

[0024] (1) The application effectively inhibits the Jahn-Teller effect of manganese by partially replacing manganese elements with iron elements, reduces the dissolution of manganese elements during the cycle process; at the same time, the introduction of iron can reduce the band gap of the material, significantly improve the electronic conductivity of the material; in addition, by doping other elements, the structural stability and conductivity of the material are further improved, and good electrochemical performance is shown;

[0025] (2) The application realizes the mixing of manganese, iron and other elements on a molecular scale by a simple co-precipitation method, ensures the beneficial effect of iron element mixing on the manganese-containing polyanion material, and effectively reduces the generation of impurity phases in the sintering process, and obtains a product with excellent electrochemical performance;

[0026] (3) The raw materials used in the application are all cheap and easily available bulk chemicals, and the co-precipitation-solid phase sintering combined method is used for material preparation, the process method is simple, the process parameters are easy to control, and large-scale production is easy. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1The polyanionic sodium-ion battery cathode material Na4MnFeNi(PO4)2P2O7 / C prepared by the embodiment 3 of the present application 1.8 Fe 1.2 The charge-discharge curve of the assembled battery of the polyanionic sodium-ion battery cathode material Na4MnFeNi(PO4)2P2O7 / C at 0.1C rate.

[0028] Figure 2 The polyanionic sodium-ion battery cathode material Na4MnFeNi(PO4)2P2O7 / C prepared by the embodiment 3 of the present application 2.15 Fe 0.85 The charge-discharge curve of the assembled battery of the polyanionic sodium-ion battery cathode material Na4MnFeNi(PO4)2P2O7 / C at 0.1C rate.

[0029] Figure 3 The polyanionic sodium-ion battery cathode material Na4MnFeNi(PO4)2P2O7 / C prepared by the embodiment 3 of the present application

[0030] Figure 4 The polyanionic sodium-ion battery cathode material Na4MnFeNi(PO4)2P2O7 / C prepared by the embodiment 3 of the present application 1.8 Fe 1.2 The charge-discharge curve of the assembled battery of the polyanionic sodium-ion battery cathode material Na4MnFeNi(PO4)2P2O7 / C at 0.1C rate. DETAILED DESCRIPTION

[0031] The present application will be described in detail below with specific examples. The present embodiment is implemented on the premise of the technical solution of the present application, and detailed implementation and specific operation process are given, but the protection scope of the present application is not limited to the following examples.

[0032] The equipment used in the following examples is conventional in the art unless otherwise specified; the reagents used are commercially available or prepared by conventional methods in the art unless otherwise specified, and those not described in detail in the following examples can be achieved by conventional experimental means in the art.

[0033] Example 1

[0034] A mixed solution of 150 mL of 1.2 mol / L manganese sulfate (MnSO4) and 0.8 mol / L ferrous sulfate (FeSO4) and 150 mL of 2 mol / L oxalic acid solution and 150 mL of 0.9 mol / L sodium hydroxide solution were prepared, and the three solutions were added to a four-necked flask containing 50 mL of deionized water bottom liquid by peristaltic pump. The co-precipitation reaction was carried out at 40°C water bath heating and 400 rpm stirring for 2.5 h. After the precipitation was completed, the co-precipitation product was aged for 12 h, washed with deionized water and alcohol three times respectively, and then placed in a vacuum oven at 60°C for drying for 6 h to obtain Mn 0.6 Fe0.4 C2O4·2H2O. The obtained manganese ferrous oxalate precipitate of 25.000 g was mixed with 22.992 g of sodium dihydrogen phosphate and 8.711 g of sucrose by ball milling for 3 h, and finally the ball-milled precursor powder was pre-sintered at 350 °C for 3 h and then sintered at 650 °C for 8 h under nitrogen atmosphere to obtain 29.865 g of the final product Na4Mn 1.8 Fe 1.2 (PO4)2P2O7 / C.

[0035] The material prepared in this example was prepared into a positive electrode sheet according to the mass ratio of active material, acetylene black and polyvinylidene fluoride (PVDF) of 8:1:1, and a metal sodium sheet was used as the negative electrode. A semi-battery was assembled using a propylene carbonate and methyl ethyl carbonate electrolyte (NaPF6 / PC+EMC) with a volume ratio of 3:2 of 1M sodium hexafluorophosphate, and the charge-discharge test was performed.

[0036] As shown in Figure 1 , the material has a reversible discharge specific capacity of 100.3 mAh / g at a rate of 0.1C in the voltage range of 1.7-4.5V, and the average working voltage is greater than 3.1V.

[0037] Example 2:

[0038] A mixed solution of 2L of 1.43 mol / L manganese sulfate and 0.57 mol / L ferrous sulfate and 2L of 2 mol / L oxalic acid and 2L of 0.9 mol / L sodium hydroxide solution were prepared, respectively. The three solutions were added to a reaction kettle containing 1L of base solution by peristaltic pump, and the co-precipitation reaction was carried out under the conditions of 40 °C water bath heating and 360 rpm stirring for 8 h. After the precipitation was completed, the co-precipitation product was aged for 12 h, washed with deionized water three times, and then placed in a vacuum oven at 80 °C for drying for 12 h to obtain Mn 0.717 Fe 0.283 C2O4·2H2O. The obtained manganese ferrous oxalate precipitate of 25.000 g was mixed with 22.992 g of sodium dihydrogen phosphate and 8.711 g of sucrose by ball milling for 3 h, and finally the ball-milled precursor powder was pre-sintered at 350 °C for 3 h and then sintered at 650 °C for 8 h under nitrogen atmosphere to obtain 29.865 g of the final product Na4Mn 2.15 Fe 0.85 (PO4)2P2O7 / C.

[0039] The electrode material prepared in this example was prepared into a battery according to the same method as in Example 1 and subjected to charge-discharge test. As shown in Figure 2As shown, the material has a reversible discharge specific capacity of 90.8 mAh / g at 0.1C rate in the voltage range of 1.7-4.3V, and the average working voltage is greater than 3.2V.

[0040] Example 3:

[0041] A mixed solution of 0.5 mol / L manganese sulfate, 0.5 mol / L ferrous sulfate and 0.5 mol / L nickel sulfate (NiSO4) 90 mL, and a 3 mol / L sodium hydroxide solution 90 mL, a 0.5 mol / L ammonia solution 90 mL were prepared respectively, and the above three solutions were added to a four-necked flask containing 40 mL of base solution by peristaltic pump, and the co-precipitation reaction occurred under the condition of 60°C water bath heating and 500 rpm stirring for 1.5 h. After the precipitation was completed, the co-precipitation product was aged for 12 h, washed with deionized water and alcohol three times respectively, and then placed in a vacuum oven at 80°C for drying for 12 h, to obtain Mn 1 / 3 Fe 1 / 3 Ni 1 / 3 (OH)2. 23.000 g of the obtained hydroxide precipitate was mixed with 40.667 g of sodium dihydrogen phosphate and 15.407 g of sucrose by ball milling for 3 h, and finally the ball-milled precursor powder was pre-fired at 350°C for 3 h and then high-temperature sintered at 700°C for 7 h in a nitrogen atmosphere, to obtain 52.823 g of the final product Na4MnFeNi(PO4)2P2O7 / C.

[0042] The electrode material prepared in this example was used to prepare a battery according to the same method as in Example 1 for charge and discharge test. As shown, the material has a reversible discharge specific capacity of 116.0 mAh / g at 0.1C rate in the voltage range of 1.7-4.5V, and the average working voltage is greater than 3.3V. Figure 3

[0043] Example 4:

[0044] A mixed solution of 0.75 mol / L manganese sulfate, 0.745 mol / L ferrous sulfate and 0.005 mol / L magnesium sulfate (MgSO4) 180 mL, and a 3 mol / L sodium hydroxide solution 180 mL, a 0.45 mol / L ammonia solution 180 mL were prepared respectively, and the above three solutions were added to a four-necked flask containing 60 mL of base solution by peristaltic pump, and the co-precipitation reaction occurred under the condition of 70°C water bath heating and 450 rpm stirring for 3 h. After the precipitation was completed, the co-precipitation product was aged for 12 h, washed with deionized water and alcohol three times respectively, and then placed in a vacuum oven at 80°C for drying for 12 h, to obtain Mn 0.5 Fe 0.497 Mg 0.003 ​(OH)2. The obtained hydroxide precipitate was mixed with 28.292 g of sodium dihydrogen phosphate and 10.718 g of glucose by high-speed stirring, and finally the mixed precursor powder was pre-fired at 350°C for 3 h and then sintered at 660°C for 10 h in a nitrogen atmosphere to obtain 36.748 g of the final product Na4(Mn 0.5 Fe 0.497 ) 2.99 Mg 0.01 (PO4)2P2O7 / C.

[0045] The electrode material prepared in this example was used to prepare a battery which was subjected to charge and discharge tests in the same manner as in Example 1. The material had a reversible discharge specific capacity of 103.2 mAh / g at a rate of 0.1C in the voltage range of 1.7-4.3 V.

[0046] Example 5:

[0047] A mixed solution of 0.5 mol / L manganese sulfate and 1 mol / L ferrous sulfate was prepared in a volume of 120 mL, as well as a 3 mol / L sodium hydroxide solution in a volume of 120 mL and a 0.5 mol / L aqueous ammonia solution in a volume of 120 mL. The three solutions were added to a four-necked flask containing 50 mL of a base solution by using a peristaltic pump, and a coprecipitation reaction was allowed to occur under the conditions of heating in a 60°C water bath and stirring at 450 rpm for 2 h. After the completion of the precipitation, the coprecipitation product was aged for 12 h, washed three times with deionized water and alcohol respectively, and then dried in a vacuum oven at 100°C for 12 h to obtain 10.000 g of Mn 1 / 3 Fe 2 / 3 (OH)2. The obtained hydroxide precipitate was mixed with 28.292 g of sodium dihydrogen phosphate and 10.718 g of glucose by high-speed stirring, and finally the mixed precursor powder was pre-fired at 350°C for 3 h and then sintered at 660°C for 10 h in a nitrogen atmosphere to obtain 36.748 g of the final product Na4(Mn 1 / 3 Fe 2 / 3 ) 2.98 Ti 0.01 (PO4)2P2O7 / C.

[0048] The electrode material prepared in this example was used to prepare a battery which was subjected to charge and discharge tests in the same manner as in Example 1. The material had a reversible discharge specific capacity of 103.2 mAh / g at a rate of 0.1C in the voltage range of 1.7-4.3 V.

[0049] Comparative Example:

[0050] Manganese oxalate 10.412 g, ferrous oxalate 5.236 g and sodium dihydrogen phosphate 13.833 g were mixed with 5.241 g sucrose as carbon source by ball milling for 3 h, and then the ball-milled precursor powder was pre-fired at 350 °C for 3 h and sintered at 650 °C for 8 h in nitrogen atmosphere to obtain 17.968 g of final product Na4Mn 1.8 Fe 1.2 (PO4)2P2O7 / C.

[0051] The electrode material prepared in this example was used to prepare a battery which was subjected to charge-discharge test in the same manner as example 1. As shown in Table 1, the material has a reversible discharge specific capacity of 85.8 mAh / g at 0.1 C rate in the voltage range of 1.7-4.5 V, which is significantly lower than the Na4Mn Figure 4 1.8 Fe 1.2 (PO4)2P2O7 / C material prepared by co-precipitation-solid sintering combined method in example 1. The example using the method of the present application obtained a material with excellent electrochemical performance.

[0052] The above description of the examples is for the purpose of enabling one of ordinary skill in the art to understand and use the present application. It will be apparent to those skilled in the art that various modifications and variations can be made to the examples without departing from the spirit or scope of the application. Thus, it is intended that the present application cover modifications and variations of this application provided they come within the scope of the appended claims and their equivalents.​

Claims

1. A polyanionic sodium-ion battery cathode material, characterized in that, The chemical formula of this material is: Na₄Mn a Fe b M c M' d (PO4)2P2O7 / C, wherein M is selected from one or more of Mg, Ni, Al, Cu, Zn, Zr, and M' is selected from one or more of Cr, Ti, La, Ce, Sn, Mo, Nb, V, Y, and 0 < a, b ≤ 3, 0 ≤ c + d ≤ 1, a + b + c + d ≤ 3, and the element ratio in the chemical formula satisfies charge balance; The preparation method of the polyanionic sodium-ion battery cathode material adopts a co-precipitation combined with high-temperature solid-state sintering method, including the following steps: (1) Dissolve manganese salt, iron salt and dopant element M source in water to prepare a mixed solution. Add the mixed solution, precipitant and regulator to a reactor protected by an inert atmosphere. Coprecipitation reaction occurs under stirring to obtain coprecipitation product. The precipitant / regulator combination is sodium hydroxide / ammonia, sodium oxalate / sulfuric acid, ammonium oxalate / sulfuric acid or oxalic acid / sodium hydroxide. (2) After washing and drying, the coprecipitated product is mixed with sodium dihydrogen phosphate, dopant element M' source and carbon source by mechanical mixing to obtain precursor powder; (3) The precursor powder is pre-calcined under an inert atmosphere and then heated to a high temperature for sintering to obtain the cathode material.

2. The polyanionic sodium-ion battery cathode material according to claim 1, characterized in that, In step (1), the manganese salt, iron salt and dopant element M source are selected from at least one of sulfate, chloride, acetate or nitrate, and in step (2), the dopant element M' source is selected from one of oxide, oxalate, acetate, citrate or carbonate.

3. The polyanionic sodium-ion battery cathode material according to claim 1, characterized in that, In step (1), the molar ratio of salt, precipitant and regulator in the mixed solution is 1:(1-2):(0-1).

4. The polyanionic sodium-ion battery cathode material according to claim 1, characterized in that, In step (1), the reaction temperature is 40-70℃ and the time is 1-24h.

5. The polyanionic sodium-ion battery cathode material according to claim 1, characterized in that, In step (1), the inert atmosphere is nitrogen or argon, and in step (3), the inert atmosphere is nitrogen or argon.

6. The polyanionic sodium-ion battery cathode material according to claim 1, characterized in that, In step (2), the drying temperature is 60-120℃ and the time is 5-18h. Mechanical mixing includes one of mechanical stirring mixing, ball milling mixing, and wet sand milling mixing combined with spray drying.

7. The polyanionic sodium-ion battery cathode material according to claim 1, characterized in that, In step (2), the carbon source is selected from at least one of sucrose, glucose, citric acid, cellulose, water-soluble starch, dextrin or polyethylene glycol, and the final product contains 1 to 10% carbon by mass.

8. The polyanionic sodium-ion battery cathode material according to claim 1, characterized in that, In step (3), the pre-firing temperature is 250-350℃ and the time is 2-8h, and the high-temperature sintering temperature is 500-700℃ and the time is 5-12h.

9. An application of the polyanionic sodium-ion battery cathode material as described in claim 1, characterized in that, This material is used in sodium-ion battery electrode sheets.

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