Method for recycling lithium iron phosphate into sodium battery cathode material

Abstract

The application provides a method for recycling and regenerating lithium iron phosphate into a sodium battery positive electrode material, and comprises the following steps: S1, after ball milling and activating waste lithium iron phosphate material, a phosphorus source and an iron source, sintering is performed to obtain a precursor Li x Fe3(PO4)2(P2O7), wherein 0.8<=x<=1; S2, after uniformly mixing a sodium source with the precursor, low-temperature sintering is performed under a reducing atmosphere to realize Li + / Na + ion exchange and reduction reaction to obtain a block material; S3, the block material is washed to remove impurity ions, and then solid-liquid separation, drying and low-temperature heat treatment are performed to obtain a sodium battery positive electrode material Na 4‑a Li a Fe3(PO4)2(P2O7), wherein the value of a is 0-0.3. The method regenerates a pure-phase sodium battery positive electrode material with high structural stability and cycle stability, solves the problems of long recycling process and high cost of a conventional lithium iron phosphate battery, and also solves the problem that a material prepared by a conventional preparation process is prone to generating impurities.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of battery material recycling, and particularly relates to a method for preparing a sodium battery positive electrode material with high structural stability and cycle stability from waste lithium iron phosphate material. BACKGROUND

[0002] The development of new energy vehicles and other industries has driven the rapid growth of demand for lithium / sodium ion batteries, which has led to the problem of recycling a large number of waste lithium / sodium ion batteries. Waste lithium / sodium ion batteries contain valuable metal elements such as lithium, nickel, cobalt, manganese, aluminum and copper, and also contain organic electrolyte and plastic components that seriously threaten the safety of the ecological environment. Therefore, the recycling of waste lithium / sodium ion batteries has considerable economic and environmental benefits.

[0003] At present, the recycling methods of lithium battery lithium iron phosphate positive electrode materials include solid phase method, inorganic acid leaching and precipitation. The solid phase method repairs and supplements lithium by adding a lithium source to waste lithium iron phosphate material and calcining. However, the composition of the recycled battery material is uneven, and the difference in raw materials leads to poor consistency of the recycled battery material. Inorganic acid leaching obtains iron-containing phosphorus filter residue through liquid phase leaching and filtration, and finally obtains iron phosphate by adjusting the pH. However, this method uses a large amount of inorganic acid in the leaching process, which causes difficulties in subsequent impurity removal when excessive acid ions are introduced, and does not recycle lithium ions, resulting in waste of lithium ions and increasing the difficulty of subsequent wastewater treatment. Therefore, how to efficiently recycle lithium battery lithium iron phosphate positive electrode materials is a major challenge for those skilled in the art.

[0004] CN115259125A discloses a recycling and regeneration method of lithium iron phosphate recycling material, which obtains lithium iron phosphate material by pretreatment with hydrogen peroxide and subsequent lithium supplementing calcination. However, the problem of large fluctuations in lithium content in lithium iron phosphate recycling material has not been solved.

[0005] CN115312897A reports a repair method for waste lithium iron phosphate and the obtained lithium iron phosphate material. The waste lithium iron phosphate is subjected to degumming treatment to obtain lithium iron phosphate recycling material. The lithium iron phosphate recycling material is mixed with a reducing agent, a lithium source is added, and the mixture is placed in a fluidized bed reactor to react so that the lithium iron phosphate and the lithium source are fully mixed and contacted to achieve sufficient lithium supplementing effect. A carbon source is sprayed in the high-temperature filtration in the second stage to form a carbon-coated structure on the surface of the lithium iron phosphate, so that the repaired lithium iron phosphate is separated from the excess lithium source. However, this method is complicated and requires strict equipment, which cannot be applied on a large scale. SUMMARY

[0006] To solve the above technical problems, the application provides a method for regenerating waste lithium iron phosphate material into a sodium battery positive electrode material.

[0007] To achieve the above object, the present application proposes the following solutions:

[0008] In a first aspect, a method for recycling and regenerating a lithium iron phosphate material into a sodium battery positive electrode material is provided, comprising:

[0009] S1, activating the waste lithium iron phosphate material with a phosphorus source and an iron source by ball milling, and then sintering to obtain a precursor Li x Fe3(PO4)2(P2O7), wherein 0.8≤x≤1;

[0010] S2, mixing the sodium source with the precursor uniformly, and then sintering at low temperature in a reducing atmosphere to realize Li + / Na + ion exchange and reduction reaction to obtain a blocky material;

[0011] S3, washing the blocky material to remove impurity ions, and then performing solid-liquid separation, drying and low-temperature heat treatment to obtain a sodium battery positive electrode material Na 4-a Li a Fe3(PO4)2(P2O7), wherein the value of a is 0-0.3.

[0012] In a second aspect, a sodium battery positive electrode material is provided, having a chemical formula of Na 4-a Li a Fe3(PO4)2(P2O7), wherein the value of a is 0-0.3, and the material is prepared by the above method.

[0013] In a third aspect, a sodium ion battery is provided, comprising the above sodium battery positive electrode material.

[0014] Compared with the prior art, one or more of the above technical solutions can achieve at least one of the following beneficial effects:

[0015] The waste lithium iron phosphate positive electrode material is activated by ball milling, crystal transformation, reduction, Li + / Na + exchange, low-temperature heat treatment, and is regenerated into a sodium battery positive electrode material Na 4-a Li a Fe3(PO4)2(P2O7) with high structural stability and cycle stability, solving the problems of long recycling process and high cost of conventional lithium iron phosphate batteries, and also solving the problem that the Na 4- a Li a Fe3(PO4)2(P2O7) material prepared by conventional preparation process is prone to produce impurities.

[0016] The recycling method can prepare a sodium battery positive electrode material free of impurities or having low impurity content, high ionic conductivity and good morphology, and improves the rate performance and long cycle stability of the battery.

[0017] The recycling method is low in cost and has been widely applied. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0019] Figure 1 The process flow diagram of recycling lithium iron phosphate to sodium battery positive electrode material in the present application.

[0020] Figure 2 The SEM diagram of lithium iron phosphate material obtained in Example 1.

[0021] Figure 3 The XRD detection result of sodium battery positive electrode material obtained in Example 1.

[0022] Figure 4 The electrochemical cycle data diagram of the battery assembled by the sodium battery positive electrode material obtained in Example 1.

[0023] Figure 5 The electrochemical rate data diagram of the battery assembled by the sodium battery positive electrode material obtained in Example 1.

[0024] Figure 6 The electrochemical cycle data diagram of the battery assembled by the sodium battery positive electrode material obtained in Example 2.

[0025] Figure 7 The electrochemical rate data diagram of the battery assembled by the sodium battery positive electrode material obtained in Example 2.

[0026] Figure 8 The XRD detection result of sodium battery positive electrode material obtained in Comparative Example 1.

[0027] Figure 9 The local enlarged diagram of the XRD detection result of sodium battery positive electrode material obtained in Example 1.

[0028] Figure 10 The local enlarged diagram of the XRD detection result of sodium battery positive electrode material obtained in Comparative Example 1.

[0029] Figure 11 The electrochemical cycle data diagram of the battery assembled by the sodium battery positive electrode material obtained in Comparative Example 1.

[0030] Figure 12 Electrochemical rate data plot of a battery assembled with the sodium battery cathode material obtained from Comparative Example 1.

[0031] Figure 13 Electrochemical cycle data plot of a battery assembled with the sodium battery cathode material obtained from Example 3.

[0032] Figure 14 Electrochemical rate data plot of a battery assembled with the sodium battery cathode material obtained from Example 3.

[0033] Figure 15 Electrochemical cycle data plot of a battery assembled with the sodium battery cathode material obtained from Example 4.

[0034] Figure 16 Electrochemical rate data plot of a battery assembled with the sodium battery cathode material obtained from Example 4. DETAILED DESCRIPTION

[0035] The present application provides a method for recycling lithium iron phosphate to sodium battery cathode material, comprising:

[0036] S1, after ball milling activation of waste lithium iron phosphate material with phosphorus source and iron source, sintering to obtain precursor Li x Fe3(PO4)2(P2O7), wherein 0.8≤x≤1;

[0037] S2, after mixing the sodium source with the precursor uniformly, low temperature sintering under reducing atmosphere to realize Li + / Na + ion exchange and reduction reaction, to obtain blocky material;

[0038] S3, washing the blocky material to remove impurity ions, then solid-liquid separation, drying and low temperature heat treatment to obtain sodium battery cathode material Na 4-a Li a Fe3(PO4)2(P2O7), wherein the value of a is 0~0.3, further preferably 0~0.25, for example 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, etc.

[0039] In some preferred embodiments, in step S1, the rotation speed of the ball milling activation is 100~200rpm, for example 100rpm, 125rpm, 150rpm, 175rpm, 200rpm, etc.

[0040] In some preferred embodiments, in step S1, the time for the ball milling activation is 0.5-3h, such as 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, etc.

[0041] In some preferred embodiments, in step S1, the sintering temperature is 300-550℃, such as 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, etc.; and the sintering time is 5-12h, such as 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, etc.

[0042] In some preferred embodiments, the phosphorus source is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, lithium dihydrogen phosphate, sodium pyrophosphate, ammonium pyrophosphate.

[0043] In some preferred embodiments, the iron source is one or more of ferric nitrate and its hydrate, diiron trioxide, ferric phosphate, ferrous oxide, iron hydroxide, ferric pyrophosphate.

[0044] In some preferred embodiments, the waste and old lithium iron phosphate material is lithium iron phosphate black powder.

[0045] In some preferred embodiments, the waste and old lithium iron phosphate material, the phosphorus source and the iron source are proportioned according to the molar ratio of Li contained to total Fe contained and total P contained as 0.8-1:3:4, such as 0.8:3:4, 0.82:3:4, 0.85:3:4, 0.88:3:4, 0.9:3:4, 0.92:3:4, 0.95:3:4, 1:3:4, etc.

[0046] In some preferred embodiments, in step S2, the low-temperature sintering temperature is 300-550℃, which is higher than the melting point of the sodium source, such as 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, etc.; and the low-temperature sintering time is 1-15h, such as 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, etc.

[0047] In some preferred embodiments, in step S2, the reducing atmosphere is a mixed atmosphere of argon and hydrogen.

[0048] In some preferred embodiments, the ratio of the molar amount of Na contained in the sodium source to the molar amount of the precursor is 5-10:1, such as 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, etc.

[0049] In some preferred embodiments, the sodium source is one or more of sodium acetate and hydrates thereof, sodium nitrate and hydrates thereof, sodium carbonate, and sodium hydroxide. Preferably, the sodium source is a mixed sodium salt, which can lower the melting point and thus the temperature of low-temperature sintering. For example, a mixed sodium salt of sodium nitrate, sodium chloride, and sodium carbonate can be used, which can be in a molar ratio of 0.92:0.064:0.016, or other ratios.

[0050] In some preferred embodiments, in step S3, the temperature of the low-temperature heat treatment is 300-550℃, such as 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, etc.; the time of the low-temperature heat treatment is 5-12h, such as 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, etc.; and the atmosphere of the low-temperature heat treatment is a protective gas atmosphere.

[0051] In some preferred embodiments, in step S2, the mixing is grinding mixing; the grinding mixing is mechanical grinding or manual grinding; the time of the manual grinding is 0.5-2h, and the manual grinding is performed in a vacuum or a protective atmosphere; and the mechanical grinding is grinding for 0.5-2h after adding a dispersant.

[0052] The present application also provides a sodium battery cathode material, which has a chemical formula of Na 4-a Li a Fe3(PO4)2(P2O7), where a is 0-0.3, further preferably 0-0.25, such as 0.01, 0.03, 0.05, 0.08, 0.10, 0.12, 0.15, 0.18, 0.20, 0.22, 0.25, etc., and is prepared by the aforementioned preparation method.

[0053] The present application also provides a sodium ion battery comprising the aforementioned sodium battery cathode material.

[0054] In order to facilitate understanding of the present application, the present application will be described in more detail below in conjunction with the accompanying drawings and preferred embodiments, but the scope of protection of the present application is not limited to the following specific embodiments.

[0055] Example 1

[0056] The process flow of the method for recycling and regenerating lithium iron phosphate into a sodium battery cathode material is shown in Figure 1 and comprises the following steps:

[0057] (1) Take 1.6 g of LiFePO4 black powder material and 3.45 g of ammonium dihydrogen phosphate, 8.08 g of iron nitrate nonahydrate (the molar ratio of lithium, iron and phosphorus in the raw material is 0.98:3:4), and perform ball milling activation in a ball milling tank at a speed of 200 rpm for 0.5 h. Then the mixed powder is sintered in a tube furnace in an air atmosphere to obtain a black powder precursor Li x Fe3(PO4)2(P2O7), the sintering temperature is 400°C, and the time is 5 h.

[0058] (2) According to the molar ratio of sodium to precursor of 6:1, weigh the sodium source and the black powder precursor, and put them into a mortar. Manual grinding is performed in an argon-filled glove box for 1 h. The sodium source is a mixed sodium salt of sodium nitrate, sodium chloride and sodium carbonate (the molar ratio of NaNO3:NaCl:Na2CO3 is 0.92:0.064:0.016); the uniformly mixed material is placed in an argon-hydrogen furnace, Ar / H2 mixed gas is introduced, and the temperature is raised to 350°C at a speed of 5°C / min and sintered for 8 h, and then cooled in the furnace.

[0059] (3) The obtained blocky material is dissolved in deionized water and stirred for 20 min, then centrifuged at a speed of 5000 r / min, each time for 7 min, a total of 4 times, then placed in a blast drying oven and dried, the drying temperature is 80°C, and the drying time is 15 h, to obtain a powder material.

[0060] (4) The powder material is heat treated in an argon atmosphere furnace at a temperature of 300°C for 5 h to obtain a sodium battery positive electrode material. The SEM image of the obtained sodium battery positive electrode material is shown in Figure 2 . Figure 2 It is shown that the material is a blocky primary particle agglomerated into a spherical secondary particle, and the secondary particle still maintains a spherical shape. The optimization of the morphology can reduce the formation of microcracks in the material, reduce the invasion of the electrolyte during the material cycle, reduce the generation of microcracks, and improve the cycle performance and service life of the material. The XRD pattern of the obtained sodium battery positive electrode material is shown in Figure 3 . The XRD pattern shows that the generated sodium battery positive electrode material phase is Na4Fe3(PO4)2(P2O7) phase.

[0061] Table 1 is the ICP detection result of the Na4Fe3(PO4)2(P2O7) phase material obtained in Example 1, and the data shows that after Li + / Na + exchange and heat treatment, the material contains only about 0.21wt.% of Li + , and the material contains 14.05wt.% of Na + , which proves that the target material Na 4-a Li aFe3(PO4)2(P2O7).

[0062] Table 1

[0063]

[0064] The sodium positive electrode material obtained in this example is assembled into a button cell, and the specific steps are as follows:

[0065] According to the mass ratio (active material: conductive agent: binder = 8: 1: 1), 0.08 g of the positive electrode material is weighed, and 0.01 g of acetylene black is weighed as a conductive agent and 0.01 g of polyvinylidene fluoride is weighed as a binder, which is placed in a mortar and mixed. After mixing evenly, N-methyl pyrrolidone is added as a dispersant, and then mixed again and coated on an aluminum foil to make a positive electrode sheet. In an inert protective atmosphere glove box, lithium metal is used as the negative electrode to assemble a CR2032 button cell.

[0066] Figure 4 Na 4-a Li a The electrochemical cycle data graph of the battery assembled by the Fe3(PO4)2(P2O7) material shows that the battery still has a discharge specific capacity of 89 mAh / g after 300 cycles, and the cycle retention rate is as high as 98%.

[0067] Figure 5 Na 4-a Li a The electrochemical rate data graph of the battery assembled by the Fe3(PO4)2(P2O7) material shows that the battery still has a discharge specific capacity of 78 mAh / g at an ultra-high rate of 5C, which shows extremely high potential in the field of fast charging and discharging.

[0068] Example 2

[0069] This example includes the following steps:

[0070] (1) Take 1.6 g of LiFePO4 black powder material and 3.45 g of ammonium dihydrogen phosphate, 8.484 g of iron nitrate nonahydrate (the molar ratio of lithium, iron and phosphorus in the raw material is 0.98:3.1:4), and ball mill in a ball mill jar at a speed of 200 rpm for 0.5 h. Then the mixed powder is sintered in a tube furnace to obtain a black powder precursor, and the sintering temperature is 400℃ and the time is 5h.

[0071] (2) Sodium source and black powder precursor were weighed according to the molar ratio of sodium to precursor of 8:1, and were put into a mortar and ground manually for 1 h in an argon-filled glove box. The sodium source was a mixed sodium salt of sodium nitrate, sodium chloride and sodium carbonate (molar ratio of NaNO3:NaCl:Na2CO3was 0.92:0.064:0.016). The mixed material was placed in an argon-hydrogen furnace, and Ar / H2mixed gas was introduced, and the temperature was increased to 400°C at a rate of 5°C / min, and sintered for 8 h, and the furnace was cooled down.

[0072] (3) The blocky material was dissolved in deionized water and stirred for 20 min, and then centrifuged at a speed of 5000 r / min for 7 min each time, and a total of 4 times. Then it was placed in a blast drying oven and dried at a temperature of 80°C for 15 h to obtain a powder material.

[0073] (4) The powder material was heat-treated in an argon furnace at a temperature of 300°C for 5 h to obtain a positive electrode material.

[0074] The positive electrode material obtained was assembled into a button cell according to the method of assembling a battery in Example 1, and electrochemical performance test was carried out.

[0075] Figure 6 The electrochemical cycle data graph of the button cell assembled by the positive electrode material obtained in Example 2 showed that after 300 cycles, the battery only had a discharge specific capacity of 76 mAh / g, and the cycle retention rate was only 93%.

[0076] Figure 7 The electrochemical rate data graph of the button cell assembled by the positive electrode material obtained in Example 2 showed that at an ultra-high rate of 5C, the battery only had a discharge specific capacity of 67 mAh / g.

[0077] Comparative Example 1

[0078] (1) 1.212 g of LiFePO4black powder material and 1.2 g of sodium persulfate were added to 70 ml of deionized water, and heated in a water bath for 2 h at a temperature of 80°C for oxidative delithiation.

[0079] (2) The above solution was centrifuged at a speed of 5000 r / min for 7 min each time, and a total of 4 times. Then it was placed in a blast drying oven and dried to obtain a black powder (the test result was that the molar ratio of Li:Fe:P was about 0.072:0.976:1), and the temperature was 80°C, and the drying time was 15 h.

[0080] (3) Take 0.9048 g of the black powder obtained in (2), 0.2254 g of ammonium dihydrogen phosphate, 0.424 g of sodium carbonate and 0.3568 g of glucose, and perform ball milling activation in a ball milling tank at a rotation speed of 200 rpm for 0.5 h to obtain a powder material.

[0081] (4) Perform heat treatment on the powder material in an argon-hydrogen furnace by passing Ar / H2mixed gas at a temperature of 550°C for 10 h, and cool down with the furnace to obtain a sodium battery positive electrode material.

[0082] The XRD pattern of the obtained sodium battery positive electrode material is shown in FIG. 3. It can be seen from the XRD pattern that the obtained sodium battery positive electrode material contains the phase Na4Fe3(PO4)2(P2O7), but the diffraction peaks also show the presence of impurity peaks. In order to further compare the sodium battery positive electrode material obtained in Example 1 and the sodium battery positive electrode material obtained in Comparative Example 1, the partial enlargements of Figure 8 and Figure 3 are performed, as shown in FIG. 4 and FIG. 5, respectively. It can be seen from the comparison of Figure 8 and Figure 9 that 10 and Figure 9 show obvious impurity phase peaks at 33° and 35°. This indicates that the Na4Fe3(PO4)2(P2O7) obtained by first oxidizing and delithiating lithium iron phosphate and then sintering with a sodium source and a phosphorus source according to the corresponding ratio contains an impurity phase of sodium iron phosphate. Figure 10 Figure 10 The obtained positive electrode material is assembled into a button cell according to the method of assembling a battery in Example 1, and electrochemical performance test is performed.

[0083] The electrochemical cycle data graph of the button cell assembled by the positive electrode material obtained in Comparative Example 1 is shown in FIG. 6. The data shows that after 300 cycles, the battery has only a discharge specific capacity of 68 mAh / g, and the cycle retention rate is only 84%.

[0084] Figure 11 The electrochemical rate data graph of the button cell assembled by the positive electrode material obtained in Comparative Example 1 is shown in FIG. 7. The data shows that at an ultra-high rate of 5C, the battery has only a discharge specific capacity of 62 mAh / g.

[0085] Figure 12 Example 3

[0086] The method for recycling lithium iron phosphate into a sodium battery positive electrode material is shown in FIG. 8, which comprises the following steps:

[0087] The method for recycling lithium iron phosphate into a sodium battery positive electrode material is shown in FIG. 8, which comprises the following steps: Figure 1

[0088] ​​(1) Take 1.6 g of LiFePO4 black powder material and 3.45 g of ammonium dihydrogen phosphate, 8.08 g of iron nitrate nonahydrate (lithium-iron-phosphorus molar ratio is 0.98:3:4), and perform ball milling activation in a ball milling jar at a speed of 200 rpm for 0.5 h. Then the mixed powder is sintered in a tube furnace in an air atmosphere to obtain a black powder precursor, the sintering temperature is 450°C, and the time is 5 h.

[0089] (2) The sodium source and the black powder precursor with a sodium-lithium molar ratio of 6:1 are weighed and placed in a mortar and manually ground in an argon-filled glove box for 1 h. The sodium source is a mixed sodium salt of sodium nitrate, sodium chloride, and sodium carbonate (molar ratio of NaNO3:NaCl:Na2CO3 is 0.92:0.064:0.016). The uniformly mixed material is placed in an argon-hydrogen furnace and is heated to 400°C at a rate of 5°C / min and sintered for 8 h, and then cooled in the furnace.

[0090] (3) The block material is dissolved in deionized water and stirred for 20 min, then centrifuged at a speed of 5000 r / min for 7 min each time, a total of 4 times. Then it is placed in a forced air drying oven and dried at a temperature of 80°C for 15 h to obtain a powder material.

[0091] (4) The powder material is heat treated in an argon furnace at a temperature of 300°C for 5 h to obtain a sodium battery positive electrode material.

[0092] Table 2 is the ICP detection results of the material obtained in Example 3, the data shows that after the Li + / Na + exchange and heat treatment, the material contains only about 0.19wt.% of Li + , and 14.07wt.% of Na + in the material, proving that the target material is successfully synthesized.

[0093] Table 2

[0094]

[0095] The obtained positive electrode material is assembled into a button cell according to the method of assembling a battery in Example 1, and electrochemical performance test is carried out.

[0096] Figure 13 is the electrochemical cycle data graph of the button cell assembled by the Na 4-a Li a Fe3(PO4)2(P2O7) material obtained in Example 3, the data shows that after 300 cycles, the battery still has a discharge specific capacity of 84.5 mAh / g, and the cycle retention rate is as high as 97.8%.

[0097] Figure 14 Na obtained from Example 3 4-a Li a The electrochemical rate data graph of the button cell assembled by the Fe3(PO4)2(P2O7) material group shows that the battery still has a discharge specific capacity of 72 mAh / g at an ultra-high rate of 5C, which exhibits extremely high potential in the field of fast charging and discharging.

[0098] Example 4

[0099] The method for recycling and regenerating lithium iron phosphate into a sodium battery positive electrode material has a process flow as shown in Figure 1 The method comprises the following steps:

[0100] (1) Take 1.6 g of LiFePO4 black powder material, 3.45 g of ammonium dihydrogen phosphate, and 8.08 g of iron nitrate nonahydrate (the molar ratio of iron to phosphorus is 0.98:3:4) and perform ball milling activation in a ball milling jar at a speed of 200 rpm for 0.5 h. Then, the mixed powder is sintered in a tube furnace in an air atmosphere to obtain a black powder precursor, and the sintering temperature is 500°C and the time is 5h.

[0101] (2) Take a sodium source and the black powder precursor with a sodium-lithium molar ratio of 10:1, and place them in a mortar. Manually grind them in an argon glove box for 1 h. The sodium source is a mixed sodium salt of sodium nitrate, sodium chloride, and sodium carbonate (NaNO3:NaCl:Na2CO3 molar ratio is 0.92:0.064:0.016). Place the uniformly mixed material in an argon-hydrogen furnace and sinter at a rate of 5°C / min to 400°C for 8h, and cool down with the furnace.

[0102] (3) Dissolve the blocky material in deionized water and stir for 20 min, then centrifuge at a speed of 5000 r / min for 7 min each time, a total of 4 times. Then place it in a blast drying oven and dry at a temperature of 80°C for 15h to obtain a powder material.

[0103] (4) Heat treat the powder material in an argon furnace at a temperature of 400°C for 5h to obtain a sodium battery positive electrode material.

[0104] Table 3 shows the ICP detection results of the material obtained in Example 4, which shows that after Li + / Na + exchange and heat treatment, the material contains only about 0.21wt.% of Li + , and the material contains 14.05wt.% of Na + , proving that the target material has been successfully synthesized.

[0105] Table 3

[0106]

[0107] The obtained positive electrode material was assembled into a button cell according to the method of assembling a battery in Example 1, and electrochemical performance test was conducted.

[0108] Figure 15 Na 4-a Li a The electrochemical cycle data of the button cell assembled by the Fe3(PO4)2(P2O7) material showed that the battery still had a discharge specific capacity of 84.3 mAh / g after 300 cycles, and the cycle retention rate was as high as 97.7%.

[0109] Figure 16 Na 4-a Li a The electrochemical rate data of the button cell assembled by the Fe3(PO4)2(P2O7) material showed that the battery still had a discharge specific capacity of 72.3 mAh / g at an ultra-high rate of 5C, and exhibited extremely high potential in the field of fast charging and discharging.

[0110] The above only describes the preferred embodiments of the present application, and it should be noted that for those skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements should also be considered within the scope of protection of the present application.

Claims

1. A method for recycling lithium iron phosphate to sodium electric positive electrode material, characterized in that, The preparation method comprises the following steps: S1, after ball-milling activation of waste lithium iron phosphate material with phosphorus source and iron source, sintering is carried out to obtain precursor Li x Fe3(PO4)2(P2O7), wherein 0.8≤x≤1; S2, after mixing the sodium source and the precursor uniformly, low-temperature sintering is performed under a reducing atmosphere to obtain a block material; S3, washing the blocky material to remove impurity ions, then performing solid-liquid separation, drying and low-temperature heat treatment to obtain a sodium battery positive electrode material Na 4-a Li a Fe3(PO4)2(P2O7), wherein the value of a is 0-0.

3.

2. The method of claim 1, wherein the lithium iron phosphate is recovered and regenerated as a sodium electric cathode material. In step S1, the rotation speed of the ball milling activation is 100-200 rpm. In step S1, the time of the ball milling activation is 0.5-3 h.

3. The method of claim 1, wherein the lithium iron phosphate is recovered and regenerated as a sodium electric cathode material. In step S1, the sintering temperature is 300-550 ℃, and the sintering time is 5-12 h.

4. The method of claim 1, wherein the lithium iron phosphate is recovered and regenerated as a sodium electric cathode material. The phosphorus source is one or more of ammonium dihydrogen phosphate, ammonium phosphate, lithium dihydrogen phosphate, sodium pyrophosphate, ammonium pyrophosphate and phosphoric acid; The iron source is one or more of ferric nitrate and its hydrate, diiron trioxide, ferric phosphate, ferrous oxide, iron hydroxide and ferric pyrophosphate; The waste and old lithium iron phosphate material, the phosphorus source and the iron source are matched according to a molar ratio of Li contained to total Fe contained and total P contained of 0.8-1:3:4; The waste and old lithium iron phosphate material is lithium iron phosphate black powder.

5. The method of claim 1, wherein the lithium iron phosphate is recovered and regenerated as a sodium electric cathode material. In step S2, the low-temperature sintering temperature is 300-550 ℃, and the low-temperature sintering time is 1-15 h; in step S2, the reducing atmosphere is a mixed atmosphere of argon and hydrogen.

6. The method of claim 1, wherein the lithium iron phosphate is recovered and regenerated as a sodium electric cathode material. The molar amount of Na contained in the sodium source is 5-10 times the molar amount of the precursor. The sodium source is one or more of sodium acetate and its hydrate, sodium nitrate and its hydrate, sodium carbonate and sodium hydroxide.

7. The method of claim 1, wherein the lithium iron phosphate is recovered and regenerated as a sodium electric cathode material. In step S3, the low-temperature heat treatment temperature is 300-550 ℃, the low-temperature heat treatment time is 5-12 h, and the low-temperature heat treatment atmosphere is a protective gas atmosphere.

8. The method of claim 1, wherein the lithium iron phosphate is recovered and regenerated as a sodium electric cathode material. In step S2, the mixing is grinding mixing; the grinding mixing is mechanical grinding or manual grinding; the manual grinding time is 0.5-2 h, and the manual grinding is performed under vacuum or a protective atmosphere; the mechanical grinding is grinding for 0.5-2 h after adding a dispersant.

9. A sodium battery cathode material, the sodium battery cathode material having a chemical formula of Na 4-a Li a Fe3(PO4)2(P2O7), where a has a value of 0 to 0.3, characterized in that, The sodium electric positive electrode material is prepared by using the preparation method.

10. A sodium-ion battery, characterized in that, The sodium electric positive electrode material comprises the sodium electric positive electrode material.

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