A preparation method of a phosphate cathode material

Abstract

The present invention provides a method for preparing a phosphate cathode material, comprising the following steps: mixing at least one of a lithium source, a sodium source, and a potassium source, a phosphate, a reducing agent, and water for reaction to obtain a phosphate cathode material product. The present invention can carry out the reaction under relatively low temperature and pressure conditions, even at normal temperature and pressure, with a short reaction time, simple, safe, and low-energy-consuming process, effectively reducing carbon emissions.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and particularly relates to a preparation method of a phosphate cathode material. Background Art

[0002] Phosphate cathode materials are widely used in electric vehicles and large-scale energy storage facilities due to their high capacity, long cycle life, good thermal stability, environmental friendliness, low cost, etc., accounting for one-third of the entire lithium-ion battery market. Currently, the main methods for preparing phosphate cathode materials are the hydrothermal method and the solid-phase sintering method. Among them, the hydrothermal method requires reactions under high-pressure environments, has high requirements for equipment, has potential safety hazards of excessive pressure, and generates a large amount of wastewater with complex processes; while the high-temperature solid-phase method requires reactions above 500 °C, requires high-temperature resistant equipment, consumes a large amount of energy, and has a long reaction time. In order to reduce energy consumption and carbon emissions, it is urgent to develop a low-carbon, environmentally friendly and safe preparation method for phosphate cathode materials. Summary of the Invention

[0003] In view of this, the technical problem to be solved by the present invention is to provide a preparation method of a phosphate cathode material. The preparation method of the phosphate cathode material provided by the present invention can be carried out under lower temperature and pressure conditions, reducing energy consumption and carbon emissions.

[0004] The present invention provides a preparation method of a phosphate cathode material, comprising the following steps:

[0005] Mix at least one of a lithium source, a sodium source, and a potassium source, a phosphate, a reducing agent, and water for reaction to obtain a phosphate cathode material;

[0006] The phosphate has an olivine structure and is M x N y PO4, where M is one or more of Li, Na, K, Ca, Al, Mg, Cu, F, B, Ni, Co, Mn, Ti, Nb, Sn, Mo, W, N is one or more of Fe, Mn, Co, Ni, 0 ≤ x ≤ 0.1, 0.9 ≤ y ≤ 1;

[0007] The phosphate cathode material is Q 1-z M a N b PO4, where Q is one or more of Li, Na, K, M is one or more of Li, Na, K, Ca, Al, Mg, Cu, F, B, Ni, Co, Mn, Ti, Nb, Sn, Mo, W, N is one or more of Fe, Mn, Co, Ni, -0.1 ≤ z ≤ 0.1, 0 ≤ a ≤ 0.1, 0.9 ≤ b ≤ 1.

[0008] Preferably, the temperature of the reaction is ≤50 °C, and the pressure of the reaction is ≤0.5 MPa.

[0009] Preferably, the lithium source is selected from one or more of lithium hydroxide, lithium acetate, lithium nitrate, lithium oxalate, lithium sulfate, lithium chloride, lithium carbonate, lithium bicarbonate, lithium formate, and lithium tetraborate;

[0010] The sodium source is selected from one or more of sodium hydroxide, sodium acetate, sodium nitrate, sodium oxalate, sodium sulfate, sodium chloride, sodium carbonate, sodium bicarbonate, sodium iodide, sodium sulfite, and sodium bisulfite.

[0011] The potassium source is selected from one or more of potassium hydroxide, potassium nitrate, potassium sulfate, potassium chloride, potassium iodide, potassium sulfite, and potassium bisulfite.

[0012] Preferably, the reducing agent is selected from one or more of sodium sulfite, sodium bisulfite, hydrogen sulfide, sulfur dioxide, oxalate, iodide, formaldehyde, sodium borohydride, ascorbic acid, and sodium sulfide.

[0013] Preferably, the molar ratio of at least one of lithium in the lithium source, sodium in the sodium source, and potassium in the potassium source to the phosphate is (1 - 5):1;

[0014] The molar ratio of the reducing agent to the phosphate is (0.1 - 5):1.

[0015] Preferably, the phosphate is prepared by the following method:

[0016] Mix the alkali metal compound of phosphate, oxidant, acid, and water and react to obtain the phosphate.

[0017] Preferably, the oxidant is selected from one or more of hydrogen peroxide, oxygen, ozone, sodium peroxide, hypochlorous acid, hypoiodous acid, and peracetic acid;

[0018] The acid is selected from one or more of sulfuric acid, hydrochloric acid, nitric acid, carbonic acid, and oxalic acid;

[0019] The temperature for mixing the alkali metal compound of phosphate, oxidant, acid, and water and reacting is 0 - 100 °C, and the time is 0.1 - 10 h.

[0020] Preferably, the temperature for mixing at least one of the lithium source, sodium source, and potassium source, phosphate, reducing agent, and water and reacting is 0 - 50 °C, the pressure is 0.08 - 0.5 MPa, and the time is 0.1 - 10 hours.

[0021] Preferably, mixing at least one of the lithium source, sodium source, and potassium source, phosphate, reducing agent, and water and reacting can be under normal temperature and pressure conditions.

[0022] Preferably, after mixing at least one of a lithium source, a sodium source, and a potassium source, a phosphate, a reducing agent, and water for reaction, a solid-liquid mixture is obtained;

[0023] The solid-liquid mixture is successively filtered, washed with water, and dried to obtain a phosphate cathode material.

[0024] Compared with the prior art, the present invention provides a method for preparing a phosphate cathode material, comprising the following steps: mixing at least one of a lithium source, a sodium source, and a potassium source, a phosphate, a reducing agent, and water for reaction to obtain a phosphate cathode material; the phosphate has an olivine structure and is M x N y PO4, M is one or more of Li, Na, K, Ca, Al, Mg, Cu, F, B, Ni, Co, Mn, Ti, Nb, Sn, Mo, W, N is one or more of Fe, Mn, Co, Ni, 0 ≤ x ≤ 0.1, 0.9 ≤ y ≤ 1. The phosphate cathode material is Q 1-z M a N b PO4, Q is one or more of Li, Na, K, M is one or more of Li, Na, K, Ca, Al, Mg, Cu, F, B, Ni, Co, Mn, Ti, Nb, Sn, Mo, W, N is one or more of Fe, Mn, Co, Ni, -0.1 ≤ z ≤ 0.1, 0 ≤ a ≤ 0.1, 0.9 ≤ b ≤ 1. The present invention can carry out the reaction under relatively low temperature and pressure conditions, even under normal temperature and pressure conditions, with a short reaction time, simple, safe, and low-energy-consuming process, effectively reducing carbon emissions and having great cost advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 XRD pattern of the lithium iron phosphate material prepared in Example 1 of the present invention;

[0026] Figure 2 Charge-discharge curve of the lithium iron phosphate material prepared in Example 1 of the present invention;

[0027] Figure 3 XRD pattern of the iron phosphate material prepared in the present invention;

[0028] Figure 4 XRD pattern of the commercially available iron phosphate material;

[0029] Figure 5 XRD comparison chart of the iron phosphate prepared in the present invention and the commercially available iron phosphate;

[0030] Figure 6 Comparison of the XRD crystal forms of the solid before and after the reaction in Comparative Example 2;

[0031] Figure 7 XRD pattern of Al-doped iron phosphate prepared for this invention;

[0032] Figure 8 XRD pattern of sodium iron phosphate material prepared in Example 6 of this invention. Detailed implementation mode

[0033] This invention provides a preparation method of a phosphate cathode material, comprising the following steps:

[0034] Mix at least one of a lithium source, a sodium source and a potassium source, a phosphate, a reducing agent and water for reaction to obtain a phosphate cathode material;

[0035] The phosphate has an olivine structure and is M x N y PO4, where M is one or more of Li, Na, K, Ca, Al, Mg, Cu, F, B, Ni, Co, Mn, Ti, Nb, Sn, Mo, W, N is one or more of Fe, Mn, Co, Ni, 0 ≤ x ≤ 0.1, 0.9 ≤ y ≤ 1.

[0036] The phosphate cathode material is Q 1-z M a N b PO4, where Q is one or more of Li, Na, K, M is one or more of Li, Na, K, Ca, Al, Mg, Cu, F, B, Ni, Co, Mn, Ti, Nb, Sn, Mo, W, N is one or more of Fe, Mn, Co, Ni, -0.1 ≤ z ≤ 0.1, 0 ≤ a ≤ 0.1, 0.9 ≤ b ≤ 1.

[0037] This invention first dissolves at least one of a lithium source, a sodium source and a potassium source in water to obtain a solution containing lithium ions and / or sodium ions and / or potassium ions,

[0038] wherein, the lithium source is selected from one or more of lithium hydroxide, lithium acetate, lithium nitrate, lithium oxalate, lithium sulfate, lithium chloride, lithium carbonate, lithium bicarbonate, lithium formate and lithium tetraborate. The sodium source is selected from one or more of sodium hydroxide, sodium acetate, sodium nitrate, sodium oxalate, sodium sulfate, sodium chloride, sodium carbonate, sodium bicarbonate, sodium iodide, sodium sulfite and sodium bisulfite. The potassium source is selected from one or more of potassium hydroxide, potassium nitrate, potassium sulfate, potassium chloride, potassium iodide, potassium sulfite and potassium bisulfite. There is no special requirement for the water used, and it can be a conventional choice in the art.

[0039] Then, phosphate is added to the solution containing lithium ions and / or sodium ions and / or potassium ions and stirred. The stirring time is 0.1 to 5 h, preferably 0.5, 1, 2, 3, 4, 5, or any value between 0.1 and 5 h. The molar ratio of at least one of lithium in the lithium source, sodium in the sodium source, and potassium in the potassium source to the phosphate is (1 to 5):1, preferably 1:1, 2:1, 3:1, 4:1, 5:1, or any value between (1 to 5):1.

[0040] Among them, the phosphate has an olivine structure and is M x N y PO4, where M is one or more of Li, Na, K, Ca, Al, Mg, Cu, F, B, Ni, Co, Mn, Ti, Nb, Sn, Mo, W, N is one or more of Fe, Mn, Co, Ni, 0 ≤ x ≤ 0.1, 0.9 ≤ y ≤ 1;

[0041] In the present invention, the phosphate with an olivine structure is preferably prepared according to the following method:

[0042] A phosphate is obtained by mixing an alkali metal compound of phosphate, an oxidant, an acid, and water and reacting them.

[0043] Among them, the alkali metal compound of phosphate is an alkali metal compound of olivine-type phosphate. The alkali metal in the alkali metal compound of phosphate is selected from one or more of lithium, sodium, and potassium.

[0044] The alkali metal compound of phosphate is A f D c E d PO4, where A is one or more of Li, Na, K, D is one or more of Li, Na, K, Ca, Al, Mg, Cu, F, B, Ni, Co, Mn, Ti, Nb, Sn, Mo, W, E is one or more of Fe, Mn, Co, Ni, 0.5 ≤ f ≤ 1.05, 0 ≤ c ≤ 0.1, 0.9 ≤ d ≤ 1.

[0045] The oxidant is selected from one or more of hydrogen peroxide, oxygen, ozone, sodium peroxide, hypochlorous acid, hypoiodous acid, and peracetic acid.

[0046] The acid is selected from one or more of sulfuric acid, hydrochloric acid, nitric acid, carbonic acid, and oxalic acid.

[0047] The molar ratio of the alkali metal compound of phosphate, the oxidant, and the acid is 1:(1 to 5):(1 to 5), preferably 1:(2 to 4):(2 to 4).

[0048] The temperature for the reaction by mixing an alkali metal compound of phosphate, an oxidizing agent, an acid and water is 0 to 100 °C, preferably 0, 5, 10, 20, 25, 30, 40, 50, 60, 70, 80, 90, 100, or any value between 0 and 100 °C, preferably under normal temperature conditions, and the time is 0.1 to 10 h, preferably 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or any value between 0.1 and 10 h.

[0049] During the process of adding phosphate and stirring as described above, a reducing agent is added and stirring is continued to obtain a solid-liquid mixture. The time for the continued stirring is 0.1 to 10 h, preferably 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or any value between 0.1 and 10 h.

[0050] The reducing agent is selected from one or more of sodium sulfite, sodium bisulfite, hydrogen sulfide, sulfur dioxide, oxalate, iodide, formaldehyde, sodium borohydride, ascorbic acid and sodium sulfide. The molar ratio of the reducing agent to the phosphate is (0.1 to 5):1, preferably 0.1:1, 1:1, 2:1, 3:1, 4:1, 5:1, or any value between (0.1 and 5):1.

[0051] Among them, the temperature of the reaction ≤ 50 °C, the pressure of the reaction ≤ 0.5 MPa; in some specific embodiments of the present invention, the temperature of the reaction is 0 to 50 °C, preferably 0, 5, 15, 20, 25, 30, 50, or any value between 0 and 50 °C, the pressure is 0.08 to 0.5 MPa, preferably 0.08, 0.1, 0.15, 0.2, or any value between 0.08 and 0.5 MPa; in some specific embodiments of the present invention, the temperature can be normal temperature and the pressure can be normal pressure.

[0052] After obtaining the solid-liquid mixture, the solid-liquid mixture is successively filtered, washed with water and dried to obtain a phosphate cathode material.

[0053] The phosphate cathode material is Q 1-z M a N b PO4, Q is one or more of Li, Na, K, M is one or more of Li, Na, K, Ca, Al, Mg, Cu, F, B, Ni, Co, Mn, Ti, Nb, Sn, Mo, W, N is one or more of Fe, Mn, Co, Ni, -0.1 ≤ z ≤ 0.1, 0 ≤ a ≤ 0.1, 0.9 ≤ b ≤ 1.

[0054] There are no special requirements for the equipment used for the filtration, washing with water and drying in the present invention, and it can be a conventional choice in the art.

[0055] The method described in the present invention uses inexpensive phosphates as raw materials, combined with corresponding lithium sources, sodium sources, and potassium sources, and can react under relatively low temperature and pressure conditions, even at normal temperature and pressure. The reaction time is short, the process is simple, safe, and energy-consuming is low, effectively reducing carbon emissions and having great cost advantages.

[0056] To further understand the present invention, the preparation method of the phosphate cathode material provided by the present invention will be described below in conjunction with embodiments, and the protection scope of the present invention is not limited by the following embodiments.

[0057] In the following embodiments, the phosphates with olivine structure are prepared according to the following method:

[0058] The iron phosphates in Examples 1 to 4 are prepared according to the following method:

[0059] Under normal temperature conditions, 60 g of concentrated sulfuric acid, 60 g of hydrogen peroxide, and 150 g of lithium iron phosphate are added to an aqueous solution and stirred for 3 h to obtain 142 g of iron phosphate and a lithium-containing solution;

[0060] See Figure 3 , Figure 3 which is the XRD pattern of the iron phosphate material prepared by the present invention.

[0061] The aluminum-doped iron phosphate in Example 5 is prepared according to the following method:

[0062] Under normal temperature conditions, 30 g of concentrated sulfuric acid, 30 g of hydrogen peroxide, and 70 g of aluminum-doped lithium iron phosphate are added to an aqueous solution and stirred for 3 h to obtain 62 g of aluminum-doped iron phosphate and a lithium-containing solution;

[0063] See Figure 7 , Figure 7 which is the XRD pattern of the aluminum-doped iron phosphate material prepared by the present invention.

[0064] The iron phosphates in Examples 6 and 7 are prepared according to the following method:

[0065] Under normal temperature conditions, 60 g of concentrated sulfuric acid, 60 g of hydrogen peroxide, and 150 g of sodium iron phosphate are added to an aqueous solution and stirred for 4 h to obtain 135 g of iron phosphate and a sodium-containing solution;

[0066] The manganese phosphate in Example 8 is prepared according to the following method:

[0067] Under normal temperature conditions, 50 g of concentrated sulfuric acid, 50 g of hydrogen peroxide, and 120 g of lithium manganese phosphate are added to an aqueous solution and stirred for 5 h to obtain 109 g of manganese phosphate and a lithium-containing solution.

[0068] The lithium iron manganese phosphate of Example 9 was prepared according to the following method:

[0069] At room temperature, 80 g of hydrochloric acid, 60 g of hydrogen peroxide and 100 g of lithium iron manganese phosphate were added to an aqueous solution and stirred for 2 h to obtain 82 g of lithium iron manganese phosphate and a lithium-containing solution.

[0070] The cobalt iron phosphate of Example 10 was prepared according to the following method:

[0071] At room temperature, hydrochloric acid, oxygen and lithium cobalt iron phosphate were added to an aqueous solution and stirred for 8 h to obtain cobalt iron phosphate and a lithium-containing solution.

[0072] The nickel iron phosphate of Example 11 was prepared according to the following method:

[0073] At room temperature, hydrochloric acid, oxygen and lithium nickel iron phosphate were added to an aqueous solution and stirred for 8 h to obtain nickel iron phosphate and a lithium-containing solution.

[0074] The iron phosphate of Example 12 was prepared according to the following method:

[0075] At room temperature, hydrochloric acid, oxygen and lithium iron phosphate were added to an aqueous solution and stirred for 4 h to obtain iron phosphate and a lithium-containing solution.

[0076] Example 1

[0077] (1) At 25 °C and 0.1 MPa, 24 g of lithium hydroxide was dissolved in 10 L of deionized water to obtain a solution containing lithium ions;

[0078] (2) 70 g of iron phosphate was added to the solution obtained in step (1), and then stirred with a stirrer at a speed of 360 revolutions per minute for 0.5 h;

[0079] (3) 70 g of ascorbic acid was added during the stirring in step (2), and stirring was continued for 5 h to obtain a solid-liquid mixture;

[0080] (4) The solid-liquid mixture obtained in step (3) was filtered with a filter, and then the filter residue was washed 5 times with deionized water. Finally, the washed filter residue was placed in a blast drying oven and dried for 10 h to obtain the lithium iron phosphate material, Li 0.99 FePO4.

[0081] Example 2

[0082] (1) At 25 °C and 0.1 MPa, 50 g of lithium sulfate was dissolved in 15 L of deionized water to obtain a solution containing lithium ions;

[0083] (2) 60 g of iron phosphate was added to the solution obtained in step (1), and then stirred with a stirrer at a speed of 360 revolutions per minute for 0.5 h;

[0084] (3) During the stirring process in step (2), add 80 g of sodium oxalate and continue stirring for 6 h to obtain a solid-liquid mixture;

[0085] (4) Filter the solid-liquid mixture obtained in step (3) using a filter, then wash the filter residue with deionized water 5 times, and finally place the washed filter residue in a blast drying oven and dry it for 10 h to obtain the lithium iron phosphate material, Li 1.00 FePO4.

[0086] Example 3

[0087] (1) At 25 °C and 0.1 MPa, dissolve 40 g of lithium chloride in 5 L of deionized water to obtain a solution containing lithium ions;

[0088] (2) Add 60 g of iron phosphate to the solution obtained in step (1), and then stir it with a stirrer at a speed of 360 revolutions per minute for 0.2 h;

[0089] (3) During the stirring process in step (2), add 100 g of potassium oxalate and continue stirring for 5 h to obtain a solid-liquid mixture;

[0090] (4) Filter the solid-liquid mixture obtained in step (3) using a filter, then wash the filter residue with deionized water 5 times, and finally place the washed filter residue in a blast drying oven and dry it for 10 h to obtain the lithium iron phosphate material, Li 0.99 FePO4.

[0091] Example 4

[0092] (1) Dissolve 24 g of lithium hydroxide in 10 L of deionized water to obtain a solution containing lithium ions;

[0093] (2) Add 70 g of iron phosphate to the solution obtained in step (1), and then stir it with a stirrer at a speed of 360 revolutions per minute for 0.2 h;

[0094] (3) During the stirring process in step (2), add 70 g of ascorbic acid and continue stirring at 50 °C and 0.5 MPa for 3 h to obtain a solid-liquid mixture;

[0095] (4) Filter the solid-liquid mixture obtained in step (3) using a filter, then wash the filter residue with deionized water 5 times, and finally place the washed filter residue in a blast drying oven and dry it for 10 h to obtain the lithium iron phosphate material, Li 1.01 FePO4.

[0096] Example 5

[0097] (1) At 25 °C and 0.1 MPa, 24 g of lithium hydroxide is dissolved in 10 L of deionized water to obtain a solution containing lithium ions;

[0098] (2) 70 g of Al-doped iron phosphate is added to the solution obtained in step (1), and then stirred with a stirrer at a speed of 360 revolutions per minute for 0.5 h;

[0099] (3) 70 g of ascorbic acid is added during the stirring process of step (2), and stirring is continued for 4 h to obtain a solid-liquid mixture;

[0100] (4) The solid-liquid mixture obtained in step (3) is filtered with a filter, and then the filter residue is washed 5 times with deionized water. Finally, the washed filter residue is placed in a blast drying oven and dried for 10 h to obtain an Al-doped lithium iron phosphate material, Li 0.99 Al 0.01 Fe 0.99 PO4.

[0101] Example 6

[0102] (1) At 25 °C and 0.1 MPa, 40 g of sodium hydroxide is dissolved in 10 L of deionized water to obtain a solution containing sodium ions;

[0103] (2) 70 g of iron phosphate is added to the solution obtained in step (1), and then stirred with a stirrer at a speed of 360 revolutions per minute for 0.5 h;

[0104] (3) 70 g of ascorbic acid is added during the stirring process of step (2), and stirring is continued for 5 h to obtain a solid-liquid mixture;

[0105] (4) The solid-liquid mixture obtained in step (3) is filtered with a filter, and then the filter residue is washed 5 times with deionized water. Finally, the washed filter residue is placed in a blast drying oven and dried for 10 h to obtain a sodium iron phosphate material, Na 0.97 FePO4. See Figure 8 , Figure 8 which is the XRD pattern of the sodium iron phosphate material prepared in Example 6 of the present invention.

[0106] Example 7

[0107] (1) At 25 °C and 0.1 MPa, 40 g of sodium hydroxide and 24 g of lithium hydroxide are dissolved in 10 L of deionized water to obtain a solution containing lithium ions and sodium ions;

[0108] (2) 70 g of iron phosphate is added to the solution obtained in step (1), and then stirred with a stirrer at a speed of 360 revolutions per minute for 0.5 h;

[0109] (3) During the stirring process in step (2), add 70 g of ascorbic acid and continue stirring for 5 h to obtain a solid-liquid mixture;

[0110] (4) Filter the solid-liquid mixture obtained in step (3) using a filter, then wash the filter residue with deionized water 5 times, and finally place the washed filter residue in a blast drying oven and dry it for 10 h to obtain lithium sodium iron phosphate material, Li 0.73 Na 0.26 FePO4.

[0111] Example 8

[0112] (1) At 25 °C and 0.1 MPa, dissolve 70 g of lithium chloride in 10 L of deionized water to obtain a solution containing lithium ions;

[0113] (2) Add 70 g of manganese phosphate to the solution obtained in step (1), and then stir with a stirrer at a speed of 360 revolutions per minute for 0.5 h;

[0114] (3) During the stirring process in step (2), add 70 g of ascorbic acid and continue stirring for 5 h to obtain a solid-liquid mixture;

[0115] (4) Filter the solid-liquid mixture obtained in step (3) using a filter, then wash the filter residue with deionized water 5 times, and finally place the washed filter residue in a blast drying oven and dry it for 10 h to obtain lithium manganese phosphate material, Li 0.98 MnPO4.

[0116] Example 9

[0117] (1) At 25 °C and 0.1 MPa, dissolve 50 g of lithium oxalate in 20 L of deionized water to obtain a solution containing lithium ions;

[0118] (2) Add 50 g of manganese iron phosphate to the solution obtained in step (1), and then stir with a stirrer at a speed of 360 revolutions per minute for 0.5 h;

[0119] (3) During the stirring process in step (2), add 70 g of ascorbic acid and continue stirring for 4 h to obtain a solid-liquid mixture;

[0120] (4) Filter the solid-liquid mixture obtained in step (3) using a filter, then wash the filter residue with deionized water 5 times, and finally place the washed filter residue in a blast drying oven and dry it for 10 h to obtain lithium manganese iron phosphate material, Li 1.0 Fe 0.63 Mn 0.37 PO4.

[0121] Example 10

[0122] (1) At 25 °C and 0.1 MPa, dissolve 50 g of lithium chloride in 20 L of deionized water to obtain a solution containing lithium ions;

[0123] (2) Add 60 g of cobalt iron phosphate to the solution obtained in step (1), and then stir with a stirrer at a speed of 360 revolutions per minute for 0.5 h;

[0124] (3) Add 50 g of ascorbic acid and 20 g of ammonium oxalate during the stirring process in step (2), and continue stirring for 4 h to obtain a solid-liquid mixture;

[0125] (4) Filter the solid-liquid mixture obtained in step (3) with a filter, then wash the filter residue with deionized water 5 times, and finally place the washed filter residue in a forced-air drying oven and dry for 10 h to obtain lithium cobalt iron phosphate material, Li 0.97 Fe 0.58 Co 0.41 PO4.

[0126] Example 11

[0127] (1) At 25 °C and 0.1 MPa, dissolve 50 g of lithium chloride in 20 L of deionized water to obtain a solution containing lithium ions;

[0128] (2) Add 60 g of nickel iron phosphate to the solution obtained in step (1), and then stir with a stirrer at a speed of 360 revolutions per minute for 0.5 h;

[0129] (3) Add 50 g of ascorbic acid and 30 g of ammonium iodide during the stirring process in step (2), and continue stirring for 4 h to obtain a solid-liquid mixture;

[0130] (4) Filter the solid-liquid mixture obtained in step (3) with a filter, then wash the filter residue with deionized water 5 times, and finally place the washed filter residue in a forced-air drying oven and dry for 10 h to obtain lithium nickel iron phosphate material, Li 0.99 Fe 0.48 Ni 0.51 PO4.

[0131] Example 12

[0132] (1) At 25 °C and 0.1 MPa, dissolve 40 g of potassium chloride and 40 g of sodium chloride in 10 L of deionized water to obtain a solution containing potassium ions and sodium ions;

[0133] (2) Add 70 g of iron phosphate to the solution obtained in step (1), and then stir with a stirrer at a speed of 360 revolutions per minute for 0.5 h;

[0134] (3) Add 70 g of ascorbic acid during the stirring process in step (2), and continue stirring for 5 h to obtain a solid-liquid mixture;

[0135] (4) Filter the solid-liquid mixture obtained in step (3) using a filter, then wash the filter residue with deionized water 5 times, and finally place the filter residue washed clean in a blast drying oven and dry it for 10 h to obtain K 0.21 Na 0.78 FePO4.

[0136] Comparative Example 1

[0137] (1) At 25 °C and 0.1 MPa, dissolve 24 g of lithium hydroxide in 10 L of deionized water to obtain a solution containing lithium ions;

[0138] (2) Add 70 g of commercially available iron phosphate to the solution obtained in step (1), and then stir with a stirrer at a speed of 360 revolutions per minute for 0.5 h. See Figure 4 , Figure 4 which is the XRD pattern of commercially available iron phosphate;

[0139] See Figure 5 , Figure 5 which is the XRD comparison chart of the iron phosphate prepared in the present invention and commercially available iron phosphate.

[0140] (3) During the stirring in step (2), add 70 g of ascorbic acid and continue stirring for 5 h to obtain a solid-liquid mixture;

[0141] (4) Filter the solid-liquid mixture obtained in step (3) using a filter, then wash the filter residue with deionized water 5 times, and finally place the filter residue washed clean in a blast drying oven and dry it for 10 h, and it is impossible to obtain the lithium iron phosphate material.

[0142] Comparative Example 2

[0143] (1) At 80 °C and 0.1 MPa, dissolve 24 g of lithium hydroxide in 10 L of deionized water to obtain a solution containing lithium ions;

[0144] (2) Add 70 g of commercially available iron phosphate to the solution obtained in step (1), and then stir with a stirrer at a speed of 360 revolutions per minute for 0.5 h;

[0145] (3) During the stirring in step (2), add 70 g of ascorbic acid and continue stirring for 5 h to obtain a solid-liquid mixture;

[0146] (4) Filter the solid-liquid mixture obtained in step (3) using a filter, then wash the filter residue with deionized water 5 times, and finally place the filter residue washed clean in a blast drying oven and dry it for 10 h, and perform XRD detection on the filter residue. The results are shown in Figure 6 , Figure 6 which is the comparison of the XRD crystal forms of the solid before and after the reaction. From Figure 6It can be seen that the XRD crystal form of the solid remains unchanged before and after the reaction, that is, no lithium iron phosphate material is obtained (the solid before the reaction is iron phosphate, and the solid after the reaction is the dried filter residue).

[0147] Comparative Example 3

[0148] (1) Add 2.3 g of ammonium dihydrogen phosphate, 0.85 g of lithium hydroxide monohydrate, and 3.04 g of ferrous sulfate into the inner lining of a hydrothermal autoclave with a volume of 100 ml, and then add 80 ml of deionized water;

[0149] (2) Place the hydrothermal autoclave in step (1) in a forced-air drying oven at 180 °C and heat for 24 h to obtain a solid-liquid mixture;

[0150] (3) Filter the solid-liquid mixture obtained in step (2) with a filter, then wash the filter residue with deionized water 5 times, and finally place the washed filter residue in a forced-air drying oven and dry for 10 h to obtain the lithium iron phosphate material.

[0151] (4) Perform electrochemical performance tests on the lithium iron phosphate material prepared in step (3) according to the method described in Test Example 1. The discharge capacity at a 0.5C rate is 147.6 mAh / g, and the first efficiency at 0.5C is 97%.

[0152] Test Example 1

[0153] Perform XRD tests on the lithium iron phosphate material prepared in Example 1. The obtained XRD results are as Figure 1 shown. Comparing the XRD pattern of the lithium iron phosphate material prepared in Example 1 with the lithium iron phosphate standard card, the characteristic peaks are obvious and there are no extra impurity peaks. The material shows a good crystal structure, indicating that the lithium iron phosphate material was successfully prepared in Example 1.

[0154] The electrochemical performance test is carried out according to the following method: Weigh 2 g of the lithium iron phosphate material prepared in Example 1 and compound it with PVDF (polyvinylidene fluoride) and Super P carbon in a mass ratio of 80:10:10. Use NMP (N-methylpyrrolidone) as a dispersant to make a slurry, coat it on a flat aluminum foil, dry it in a forced-air dryer for 12 h, roll it and punch it into a positive electrode sheet with a diameter of 14 mm. In an inert glove box, use a lithium metal sheet as the negative electrode material, use a Celgard 2400 membrane as the separator, and use a solution containing 1 mol / L lithium hexafluorophosphate in a mixed solution of EC (ethylene carbonate):DMC (dimethyl carbonate) = 3:7 (volume ratio) as the electrolyte to assemble a button cell. Control the test voltage range between 2.5 and 4.2 V to perform button cell tests.

[0155] The electrochemical performance test results are as Figure 2As shown, the electrochemical performance of the lithium iron phosphate cathode material prepared by the present invention has a discharge capacity of 152.1 mAh / g at a rate of 0.5C, and the first efficiency at 0.5C is 98%, indicating that the lithium iron phosphate material prepared by the present invention has good electrical performance. In addition, the process for preparing the lithium iron phosphate material of the present invention can be carried out under normal temperature and pressure conditions, with low energy consumption and less carbon emissions, without the need for high-pressure and high-temperature resistant equipment, being safe and controllable, and having great cost advantages.

[0156] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a phosphate cathode material, characterized in that, It includes the following steps: Mix at least one of a lithium source, a sodium source, and a potassium source, a phosphate, a reducing agent, and water for reaction to obtain a phosphate cathode material; The temperature of the reaction is normal temperature, the pressure is normal pressure, and the time is 0.1 to 6 hours; The phosphate has an olivine structure and is M x N y PO4, where M is one or more of Li, Na, K, Ca, Al, Mg, Cu, F, B, Ni, Co, Mn, Ti, Nb, Sn, Mo, W; N is one or more of Fe, Mn, Co, Ni; 0 ≤ x ≤ 0.1; 0.9 ≤ y ≤ 1; The phosphate cathode material is Q 1-z M a N b PO4, where Q is one or more of Li, Na, and K; M is one or more of Li, Na, K, Ca, Al, Mg, Cu, F, B, Ni, Co, Mn, Ti, Nb, Sn, Mo, and W; N is one or more of Fe, Mn, Co, and Ni; -0.1 ≤ z ≤ 0.1, 0 ≤ a ≤ 0.1, and 0.9 ≤ b ≤ 1; The reducing agent is selected from one or more of oxalate and ascorbic acid.

2. The preparation method according to claim 1, characterized in that, The lithium source is selected from one or more of lithium hydroxide, lithium acetate, lithium nitrate, lithium oxalate, lithium sulfate, lithium chloride, lithium carbonate, lithium bicarbonate, lithium formate, and lithium tetraborate; The sodium source is selected from one or more of sodium hydroxide, sodium acetate, sodium nitrate, sodium oxalate, sodium sulfate, sodium chloride, sodium carbonate, sodium bicarbonate, sodium iodide, sodium sulfite, and sodium bisulfite; The potassium source is selected from one or more of potassium hydroxide, potassium nitrate, potassium sulfate, potassium chloride, potassium iodide, potassium sulfite, and potassium bisulfite.

3. The preparation method according to claim 1, wherein, The molar ratio of at least one of lithium in the lithium source, sodium in the sodium source, and potassium in the potassium source to the phosphate is (1 to 5):1; The molar ratio of the reducing agent to the phosphate is (0.1 to 5):

1.

4. The preparation method according to claim 1, characterized in that, The phosphate is prepared according to the following method: Mix a phosphate alkali metal compound, an oxidizing agent, an acid, and water for reaction to obtain a phosphate.

5. The preparation method according to claim 4, characterized in that, The oxidizing agent is selected from one or more of hydrogen peroxide, oxygen, ozone, sodium peroxide, hypochlorous acid, hypoiodous acid, and peracetic acid; The acid is selected from one or more of sulfuric acid, hydrochloric acid, nitric acid, carbonic acid, and oxalic acid; The temperature for mixing the phosphate alkali metal compound, the oxidizing agent, the acid, and water for reaction is 0 to 100 °C, and the time is 0.1 to 10 h.

6. The preparation method according to claim 1, characterized in that, After mixing at least one of a lithium source, a sodium source, and a potassium source, a phosphate, a reducing agent, and water for reaction, a solid-liquid mixture is obtained; Filter, wash with water, and dry the solid-liquid mixture in sequence to obtain a phosphate cathode material.

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