Method for preparing mixed phosphate sodium ion positive electrode material through chelating agent assisted transition metal salt

Abstract

The invention belongs to the technical field of sodium ion battery materials, and particularly relates to a method for preparing a mixed type phosphate sodium ion positive electrode material by using a chelating agent to assist transition metal salt. The preparation method comprises the following steps: preparing a phosphorus source, a sodium source and transition metal oxalate according to the stoichiometric ratio of a P element, a sodium element and an M element in Na4Mx (PO4) 2P2O7, then adding the phosphorus source, the sodium source and the transition metal oxalate together with a carbon source and a chelating agent into deionized water, uniformly mixing, grinding, collecting precursor powder, and sintering to obtain the mixed phosphate sodium ion positive electrode material. The transition metal oxalate is adopted, no impurity phase is introduced in the preparation process, the chelating agent is used for auxiliary preparation, the problem of non-uniform mixing of the raw materials is solved, the obtained mixed phosphate sodium ion positive electrode material has excellent cycle stability, and support is provided for industrial preparation of the sodium ion battery mixed phosphate positive electrode material.

Description

Technical Field

[0001] The invention belongs to the technical field of sodium ion battery materials, and in particular relates to a method for preparing a mixed phosphate sodium ion positive electrode material by using a chelating agent to assist a transition metal salt. Background Art

[0002] With the rapid growth of demand for sustainable energy in recent years, large-scale energy storage technology has attracted great attention in recent years. As the battery industry continues to expand, the cost of lithium-ion batteries, which are the representative of energy storage systems, has increased significantly due to their extremely uneven distribution around the world and their rapid and large-scale consumption, which has greatly limited the use of lithium-ion batteries in large-scale energy storage. At the same time, sodium-ion batteries have attracted widespread attention due to their abundant raw material resources, uniform distribution, and low price.

[0003] At present, the cathode materials of sodium ion batteries mainly include layered transition metal oxides, polyanion compounds and Prussian blue analogs. Mixed phosphate sodium ion cathode material is a kind of polyanion cathode material with excellent performance. It has the advantages of sodium iron phosphate and sodium iron pyrophosphate, and shows high redox potential and excellent cycle stability in application. 4 Fe 3 (PO 4 ) 2 P 2 O 7 The positive electrode material has low cost, good cycle performance, low volume expansion (<4%), high thermal stability, and is not easily affected by the environment. It has a high theoretical capacity (129mAhg -1 ) advantages. However, it still has problems such as low electronic conductivity and uneven mixing of raw materials. NaFePO is easily generated during the preparation process. 4 、Na 2 FeP 2 O 7 Such impurities seriously affect the reversible specific capacity and cycle stability of the material.

[0004] Currently reported Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 7 Preparation methods mostly use Fe(NO 3 ) 3 9H 2 O and FePO 4 As an iron source, Na 4 Fe 3 (PO 4 )2 P 2 O 7 The product inevitably contains NaFePO 4 、Na 2 FeP 2 O 7 The main reason is that Fe(NO 3 ) 3 9H 2 O is easily decomposed into FeO at low temperature, and FeO is easily reacted with NaH 2 PO 4 Formation of NaFePO 4 Impurity phase; FePO 4 Then it is easy to 2 PO 4 Formation of NaFePO 4 、Na 2 FeP 2 O 7 impurity phase; at the same time, the crystallization water introduced by the raw materials during the sintering process and the high and low temperature heat treatment process are not fully controlled and optimized, and the carbon coating effect needs to be improved.

[0005] Therefore, it is necessary to provide an improved method for preparing a mixed sodium phosphate positive electrode material to solve the above problems. Summary of the invention

[0006] The purpose of the present invention is to provide a method for preparing a mixed phosphate sodium ion positive electrode material by using a chelating agent to assist a transition metal salt, using a transition metal oxalate as a raw material, reducing the generation of impurity phases by regulating the carbon source and the chelating agent, thereby improving the cycle stability of the material.

[0007] To achieve the above object, the present invention provides a method for preparing a mixed sodium phosphate positive electrode material by using a chelating agent to assist a transition metal salt, comprising: 4 M x (PO 4 ) 2 P 2 O 7 A phosphorus source, a sodium source and a transition metal oxalate containing the M element are prepared in a stoichiometric ratio of the P element, the sodium element and the M element, the transition metal oxalate, the sodium source, the phosphorus source, the carbon source and the chelating agent are added to deionized water, mixed evenly and then ground, the precursor powder is collected, and then sintered to obtain a mixed phosphate sodium ion positive electrode material;

[0008] The amount of the chelating agent is 0.2 to 3 times the molar amount of the transition metal M, the amount of the carbon source is 1 to 2 times the molar amount of the transition metal M; the amount of the transition metal oxalate, the sodium source and the phosphorus source meets the requirement of Na 4 M x (PO 4 ) 2 P 2 O 7 The stoichiometric ratio, where M represents a transition metal and x satisfies Na 4 M x (PO 4 ) 2 P 2 O 7 The positive and negative valences are balanced, and the average value of the valence of the transition metal M is recorded as y, then y×x=6.

[0009] Further, the chelating agent is one or more of ethylenediaminetetraacetic acid, tetrasodium ethylenediaminetetraacetate, and disodium ethylenediaminetetraacetate;

[0010] The carbon source includes one or more of glucose, ascorbic acid, formaldehyde, acetaldehyde, n-butyraldehyde, lactic acid, citric acid, malic acid, oxalic acid, adipic acid, soluble starch and sucrose.

[0011] Furthermore, the sintering process adopts a staged heating method, first heating to 200-350°C, keeping the temperature for 2-12 hours, then heating to 460-560°C, keeping the temperature for 3-20 hours. The carbon coating is improved by staged sintering.

[0012] Furthermore, the gas atmosphere of the sintering treatment is argon, nitrogen, argon-hydrogen mixed gas or nitrogen-hydrogen mixed gas.

[0013] Furthermore, the transition metal oxalate is selected from one or more of iron oxalate, manganese oxalate, cobalt oxalate, nickel oxalate, copper oxalate, and zinc oxalate.

[0014] Furthermore, the sodium source includes one or more of sodium nitrate, sodium carbonate, sodium bicarbonate, sodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium formate, sodium acetate, sodium citrate, and sodium hydroxide; the phosphorus source includes one or more of sodium dihydrogen phosphate, sodium phosphate, sodium monohydrogen phosphate, phosphoric acid, ammonium dihydrogen phosphate, triammonium phosphate, pyrophosphoric acid, sodium pyrophosphate, and sodium dihydrogen pyrophosphate.

[0015] Furthermore, the precursor powder is obtained by dielectric heating, spray drying, forced air drying, vacuum drying, or freeze drying, preferably spray drying, wherein the inlet air temperature of the spray drying is 120-140°C, and the outlet air temperature is 80-90°C.

[0016] Furthermore, the grinding is sand milling or ball milling, and the parameters of the sand milling are: rotation speed 1000-1600rpm, time 1-24h; the parameters of the ball milling are: rotation speed 200-1800rpm, time 3-30h.

[0017] The present invention also provides a mixed sodium phosphate positive electrode material, which is obtained by using any of the preparation methods described above.

[0018] The present invention also provides an application of a mixed sodium phosphate positive electrode material in a sodium ion battery.

[0019] In general, the above technical solution conceived by the present invention has the following technical advantages compared with the prior art:

[0020] 1. The invention provides a method for preparing a mixed sodium phosphate positive electrode material by chelating agent-assisted transition metal salts. The method uses transition metal oxalate as a raw material, and promotes the dissolution of transition metal oxalate by regulating the carbon source and the chelating agent, reduces the generation of impurity phases, and obtains a uniformly mixed precursor after adding the Na source, carbon source and P source. The problem of uneven multiphase mixing of raw materials in the prior art is solved, and the effect of carbon-coated sodium phosphate is improved. The obtained carbon-coated mixed phosphate positive electrode material has high crystallinity and almost no NaMPO. 4 、Na 2 MP 2 O 7 The phase purity is significantly improved, and the electrochemical performance is also improved to a certain extent, especially the cycle stability is better.

[0021] 2. Furthermore, the present invention further improves the formation of a homogeneous phase of the raw material mixture and reduces the impurity phase by optimizing the type of chelating agent, thereby improving the cycle stability of the mixed sodium phosphate positive electrode material.

[0022] 3. The entire preparation process of the present invention is simple, green and environmentally friendly, and does not emit three wastes. It can realize mass production and is applicable to the preparation of various transition metal sodium ion positive electrode materials. The prepared material has a small particle size, good coating performance, high electrical conductivity, and excellent cycle performance, providing technical support for the industrial preparation of mixed phosphate sodium ion positive electrode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a SEM image of the mixed sodium phosphate cathode material prepared in Example 1 of the present invention;

[0024] Figure 2 This is a SEM image of the mixed sodium phosphate cathode material prepared in Example 2 of the present invention;

[0025] Figure 3 This is the XRD pattern of the mixed sodium phosphate positive electrode material prepared in Example 3 of the present invention;

[0026] Figure 4 This is the XRD pattern of the mixed sodium phosphate positive electrode material prepared in Example 4 of the present invention;

[0027] Figure 5 This is the XRD diagram of the mixed sodium phosphate positive electrode material prepared in Comparative Example 2 of the present invention;

[0028] Figure 6 The charge and discharge curves of the mixed phosphate sodium ion positive electrode material prepared in Example 1 of the present invention at a rate of 0.1C after being assembled into a button cell as a positive electrode material for a sodium ion battery;

[0029] Figure 7 This is a cycle performance diagram of the mixed phosphate sodium ion positive electrode material prepared in Example 1 of the present invention as a sodium ion battery positive electrode material assembled into a button cell at a 1C rate current density;

[0030] Figure 8 The mixed phosphate sodium ion positive electrode material prepared in Comparative Example 1 of the present invention is used as a positive electrode material for a sodium ion battery and assembled into a button cell at a charge and discharge rate of 0.1C;

[0031] Fig. 9 This is a cycling performance diagram of the mixed phosphate sodium ion positive electrode material prepared in Comparative Example 1 of the present invention, which is assembled into a button cell as a sodium ion battery positive electrode material at a 1C rate current density. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0033] The present invention provides a method for preparing a mixed sodium phosphate positive electrode material by using a chelating agent to assist a transition metal salt, comprising the following steps:

[0034] Step S1: adding transition metal oxalate and chelating agent into deionized water, and mixing and stirring thoroughly;

[0035] Step S2: Mix the Na source, carbon source, and P source according to Na 4 Fe 3 (PO 4 ) 2 P 2 O7 Add the stoichiometric ratio into S1, and stir and mix thoroughly again to obtain a suspension;

[0036] Step S3: grinding the suspension obtained in step S2 to refine the particle size, and then drying it to obtain a light yellow precursor;

[0037] Step S4: performing a staged sintering treatment on the precursor powder in an oxygen-free atmosphere to finally obtain a mixed sodium phosphate positive electrode material coated with a carbon layer.

[0038] The present invention uses transition metal oxalate, which does not introduce impurities during the preparation process, and the obtained material has high purity. In addition, the chelating agent is used to assist in the preparation, which solves the problem of uneven mixing of raw materials in the process of preparing mixed phosphate sodium ions from transition metal salts. At the same time, the carbon formed during the calcination process can more evenly coat the Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 Moreover, the entire preparation process is simple, easy to operate and easy to control. The obtained mixed phosphate sodium ion positive electrode material has the characteristics of good coating performance and stable structure, and shows excellent cycle stability, providing support for the industrial preparation of mixed phosphate positive electrode materials for sodium ion batteries.

[0039] Example 1

[0040] A method for preparing a mixed phosphate sodium ion positive electrode material by chelating agent-assisted transition metal salt: FeC 2 O 4 as an iron source, glucose as a carbon source, sodium dihydrogen phosphate as a phosphorus and sodium source, and ethylenediaminetetraacetic acid as a chelating agent;

[0041] 4.496 g FeC 2 O 4 , 8.767g ethylenediaminetetraacetic acid, 4.799g sodium dihydrogen phosphate and 7.206g glucose were added to 100mL deionized water respectively, magnetically stirred at room temperature for 20h, mixed and stirred for 2h, and then sand milled at a speed of 1500rpm for 3h. The suspension was spray dried, the inlet air temperature was set to 130℃, the outlet air temperature was 85℃, and the precursor powder was collected. The precursor was sintered in stages under a nitrogen gas protection atmosphere. The temperature of the first stage was 250℃, and the heat preservation was 6h. The temperature of the second stage was 550℃, and the heat preservation was 15h. After cooling with the furnace, Na 4 Fe 3 (PO 4 ) 2 P 2O 7 Powder, such as Figure 1 Assemble the button cell in the glove box.

[0042] Comparative Example 1

[0043] The method of this comparative example is the same as the preparation method of Example 2, except that ethylenediaminetetraacetic acid as a chelating agent is not added, as follows;

[0044] 4.496gFeC 2 O 4 , 4.799g sodium dihydrogen phosphate and 7.206g glucose were added to 100mL deionized water, stirred magnetically for 20h at room temperature, mixed and stirred for 2h, and then sand milled at a speed of 1500rpm for 3h. The suspension was spray dried, the inlet temperature was set to 130℃, the outlet temperature was 85℃, and the precursor powder was collected. The precursor was sintered in stages under a nitrogen gas protection atmosphere. The first stage temperature was 250℃, kept warm for 6h, and the second stage temperature was 550℃, kept warm for 15h. After cooling with the furnace, Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 Powder. Assembling button cells in a glove box.

[0045] Example 2

[0046] A method for preparing a mixed phosphate sodium ion positive electrode material by chelating agent-assisted transition metal salt: using manganese oxalate dihydrate as a manganese source, glucose as a carbon source, ammonium dihydrogen phosphate as a phosphorus source, and tetrasodium ethylenediaminetetraacetic acid as a chelating agent and a sodium source;

[0047] Add 21.8038g of manganese oxalate dihydrate and 20.81g of tetrasodium ethylenediaminetetraacetate to 300mL of deionized water, and stir magnetically at room temperature for 18h. Add 23.006g of ammonium dihydrogen phosphate and 42.028g of glucose to 50mL of deionized water, stir magnetically at room temperature for 5h, and then mix and stir for 2h, followed by sand milling at a speed of 1500rpm for 3h. The suspension was spray dried with the inlet air temperature set to 130℃ and the outlet air temperature set to 85℃, and the precursor powder was collected. The precursor was sintered in stages under a nitrogen gas protection atmosphere. The first stage temperature was 250℃, and the temperature was kept at 6h. The second stage temperature was 550℃, and the temperature was kept at 15h. After cooling with the furnace, Na 4 Mn 3 (PO 4 ) 2 P 2 O 7 Powder, such as Figure 2 Assemble the button cell in the glove box.

[0048] Comparative Example 2

[0049] The method of this comparative example is the same as the preparation method of Example 2, except that the tetrasodium ethylenediaminetetraacetate as a chelating agent is replaced by sodium carbonate, as follows;

[0050] Add 21.8038g of manganese oxalate dihydrate and 5.80g of sodium carbonate to 300mL of deionized water, and stir magnetically at room temperature for 18h. Add 23.006g of ammonium dihydrogen phosphate and 42.028g of glucose to 50mL of deionized water, stir magnetically at room temperature for 5h, and then mix and stir for 2h. Then sand grind at a speed of 1500rpm for 3h. Spray dry the suspension, set the inlet temperature to 130℃, the outlet temperature to 85℃, and collect the precursor powder. Sinter the precursor in stages under a nitrogen gas protection atmosphere. The first stage temperature is 250℃, and the temperature is kept for 6h. The second stage temperature is 550℃, and the temperature is kept for 15h. After cooling with the furnace, Na 4 Mn 3 (PO 4 ) 2 P 2 O 7 Powder. Assembling button cells in a glove box.

[0051] Example 3

[0052] A method for preparing a mixed phosphate sodium ion positive electrode material by chelating agent-assisted transition metal salt: FeC 2 O 4 as an iron source, ammonium dihydrogen phosphate as a supplemental phosphorus source, sodium acetate trihydrate as a sodium source, and citric acid monohydrate as a carbon source and chelating agent;

[0053] 22.1705g FeC 2 O 4 42.028g of citric acid monohydrate, 6.2692g of ammonium dihydrogen phosphate and 27.216g of sodium acetate trihydrate were added to 200mL of deionized water respectively, and magnetically stirred at room temperature for 12h. After mixing, the mixture was fully stirred for 2h and then sand-milled at a speed of 1300rpm for 2h. The obtained suspension was heated in a water bath and stirred dry at a heating temperature of 80°C, and the precursor was obtained in a collection tank. The precursor was sintered under inert gas conditions, with the first stage temperature at 300°C for 4h and the second stage temperature at 480°C for 10h. After cooling with the furnace, Na 4 Fe 3 (PO 4 ) 2 P 2O 7 Powder. Assembling button cells in a glove box.

[0054] Example 4

[0055] A method for preparing a mixed phosphate sodium ion positive electrode material by chelating agent-assisted transition metal salt: using ferrous oxalate dihydrate as an iron source, citric acid as a carbon source, sodium dihydrogen phosphate as a phosphorus source and a sodium source, and ethylenediaminetetraacetic acid as a chelating agent;

[0056] Add 10.9018g of ferrous oxalate dihydrate and 14.612g of ethylenediaminetetraacetic acid to 200mL of deionized water, stir magnetically at room temperature for 20h, add 11.503g of ammonium dihydrogen phosphate and 21.014g of citric acid to 50mL of deionized water, stir magnetically at room temperature for 16h, mix and stir for 1.5h, then sand grind at a speed of 1500rpm for 2h. Spray dry the suspension, set the inlet temperature to 135℃ and the outlet temperature to 85℃, and collect the precursor powder. Sinter the precursor in stages under a nitrogen gas protection atmosphere, with the first stage temperature at 310℃ for 4h, and the second stage temperature at 580℃ for 12h. After cooling in the furnace, Na 4 Fe 3 (PO 4 ) 2 P 2 O 7 Powder. Assembling button cells in a glove box.

[0057] from Figure 3-5 It can be seen that when the chelating agent is replaced with sodium carbonate in Comparative Example 2, the product has impurity phases of sodium manganese pyrophosphate and sodium manganese phosphate at 10.8° and 33°. This shows that the present invention can promote the transition metal oxalate to form a homogeneous solution through a specific chelating agent, thereby reducing the generation of impurity phases. The cyclic stability of Comparative Example 2 is also lower than that of Example 2.

[0058] from Figure 6-8 It can be seen that the mixed phosphate sodium ion positive electrode material obtained in Example 1 of the present invention is assembled into a button-type battery as a positive electrode material for a sodium ion battery, and has a higher specific capacity than that of Comparative Example 1, and has excellent cycle stability. However, the specific capacity of Comparative Example 1 decreases after 150 cycles, indicating that the type and amount of the chelating agent have an important influence on the electrical properties of the material.

[0059] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a mixed sodium phosphate positive electrode material by chelating a transition metal salt, characterized in that: include: By Na4M x The stoichiometric ratio of P element, sodium element and M element in (PO4)2P2O7 is to prepare a phosphorus source, a sodium source and a transition metal oxalate containing the M element, add the transition metal oxalate, the sodium source, the phosphorus source, the carbon source and the chelating agent into deionized water, mix them evenly and grind them, collect the precursor powder, and then perform a sintering treatment to obtain a mixed phosphate sodium ion positive electrode material; The amount of the chelating agent is 0.2 to 3 times the molar amount of the transition metal M, and the amount of the carbon source is 1 to 2 times the molar amount of the transition metal M; wherein M represents a transition metal, and x satisfies such that Na4M x The positive and negative valence balance of (PO4)2P2O7.

2. The method for preparing a mixed phosphate sodium ion positive electrode material by chelating agent-assisted transition metal salt according to claim 1, characterized in that: The chelating agent is one or more of ethylenediaminetetraacetic acid, tetrasodium ethylenediaminetetraacetate, and disodium ethylenediaminetetraacetate; The carbon source includes one or more of glucose, ascorbic acid, formaldehyde, acetaldehyde, n-butyraldehyde, lactic acid, citric acid, malic acid, oxalic acid, adipic acid, soluble starch and sucrose.

3. The method for preparing a mixed phosphate sodium ion positive electrode material by chelating agent-assisted transition metal salt according to claim 1, characterized in that: The sintering treatment adopts a staged heating method, first heating to 200-350° C., keeping the temperature for 2-12 hours, then heating to 460-560° C., keeping the temperature for 3-20 hours.

4. The method for preparing a mixed phosphate sodium ion positive electrode material by chelating agent-assisted transition metal salt according to claim 3, characterized in that: The gas atmosphere for the sintering process is argon, nitrogen, argon-hydrogen mixed gas or nitrogen-hydrogen mixed gas.

5. The method for preparing a mixed phosphate sodium ion positive electrode material by chelating agent-assisted transition metal salt according to claim 1, characterized in that: The transition metal oxalate is selected from one or more of iron oxalate, manganese oxalate, cobalt oxalate, nickel oxalate, copper oxalate and zinc oxalate.

6. The method for preparing a mixed phosphate sodium ion positive electrode material by chelating agent-assisted transition metal salt according to claim 1, characterized in that: The sodium source includes one or more of sodium nitrate, sodium carbonate, sodium bicarbonate, sodium phosphate, sodium dihydrogen phosphate, disodium hydrogen phosphate, sodium formate, sodium acetate, sodium citrate, and sodium hydroxide; The phosphorus source includes one or more of sodium dihydrogen phosphate, sodium phosphate, sodium monohydrogen phosphate, phosphoric acid, ammonium dihydrogen phosphate, triammonium phosphate, pyrophosphoric acid, sodium pyrophosphate, and sodium dihydrogen pyrophosphate.

7. The method for preparing a mixed phosphate sodium ion positive electrode material by chelating agent-assisted transition metal salt according to claim 1, characterized in that: The precursor powder is collected by spray drying, wherein the inlet air temperature of the spray drying is 120-140°C, and the outlet air temperature is 80-90°C.

8. The method for preparing a mixed phosphate sodium ion positive electrode material by chelating agent-assisted transition metal salt according to claim 1, characterized in that: The grinding is sand milling or ball milling. The parameters of the sand milling are: rotation speed 1000-1600rpm, time 1-24h; the parameters of the ball milling are: rotation speed 200-1800rpm, time 3-30h.

9. A mixed sodium phosphate positive electrode material, characterized in that: The method is obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the mixed phosphate sodium ion positive electrode material according to claim 9 in a sodium ion battery.

Images