A lithium iron phosphate positive electrode material for lithium extraction from salt lakes by electrochemical deintercalation method, preparation method and application thereof

Abstract

The present disclosure belongs to the technical field of lithium extraction from salt lakes, and specifically relates to a lithium iron phosphate positive electrode material for lithium extraction from salt lakes by electrochemical deintercalation, its preparation method and application. Lithium iron phosphate is sintered to form a coating by using aluminum oxide, and the sintered material obtained after sintering is heat-treated in the presence of chlorine. The aluminum oxide coated on the surface of the material reacts with carbon when exposed to chlorine, and the generated aluminum chloride sublimates, thereby forming an uneven coating layer on the surface of the material. At the same time, the gas generated by the reaction can cause the coating layer to form a loose and porous structure. Compared with a smooth and uniform coating layer, a rough coating layer can accelerate the infiltration process of brine inside the material and further diffuse it to the surface of the particles. When the porous lithium iron phosphate material prepared by this method is used for lithium extraction, the internal dendritic channels can promote the brine to enter the interior of the material and provide more active sites for reaction, thereby improving the mass transfer rate and lithium extraction efficiency.

Description

Technical Field

[0001] The present disclosure belongs to the technical field of lithium extraction from salt lakes, and specifically relates to a lithium iron phosphate positive electrode material for lithium extraction from salt lakes by an electrochemical deintercalation method, a preparation method thereof, and applications. Background Art

[0002] In recent years, lithium extraction from salt lakes has gradually become the mainstream of lithium extraction. Among them, various processes such as evaporation, electrodialysis, membrane separation, solvent extraction, and ion sieve adsorption are commonly used. However, due to the complex composition of salt lakes, evaporation can easily cause significant lithium losses. Electrodialysis and membrane separation require large amounts of water to dilute the brine and are generally suitable for processing high-quality old brine. However, the evaporation process to obtain the old brine also faces significant lithium losses. Solvent extraction is prone to emulsification when treating brine, and the organic extractant has a certain solubility in the brine, which can potentially pollute the environment. The current mainstream ion sieve adsorption method is aluminum ion sieve, but its adsorption capacity is low, and the adsorption and desorption processes often require elevated temperatures. Other ion sieves, such as manganese and titanium, have high adsorption capacities, but the material loss during acid desorption is prominent.

[0003] To address the challenges of lithium extraction from salt lakes, existing technologies have disclosed an electrochemical deintercalation method. Using LiFePO4 / FePO4 or LiMn2O4 / MnO2 as electrode pairs, lithium ions are extracted by intercalation into the cathode electrode material upon application of power. Simultaneously, lithium from the anode is released into a clean solution, enabling lithium recovery and enrichment. This method offers numerous advantages, including high selectivity and environmental friendliness.

[0004] However, due to the poor conductivity and hydrophilicity of the electrodes used, the current density during actual operation is low, resulting in low production efficiency. In addition, because salt lake brine is located in high-altitude and cold areas, and the brine has high viscosity, mass transfer within the electrode is difficult, resulting in the electrode material's performance being difficult to achieve. Some researchers have improved mass transfer and conductivity, such as by coating with carbon or metal to increase conductivity, but this dense and uniform coating will narrow the mass transfer channel, thereby limiting further improvement in lithium extraction efficiency.

[0005] Therefore, developing an electrode material with higher lithium extraction efficiency is a technical problem that needs to be solved urgently. Summary of the Invention

[0006] The purpose of the present disclosure includes providing a lithium iron phosphate positive electrode material for lithium extraction from salt lakes by electrochemical deintercalation method, its preparation method and application, aiming to improve the efficiency of electrochemical lithium extraction.

[0007] In order to achieve the above-mentioned purpose of the present disclosure, the following technical solutions can be adopted:

[0008] In a first aspect, the solution provided by the present disclosure includes providing a method for preparing a lithium iron phosphate positive electrode material for lithium extraction from salt lakes by an electrochemical deintercalation method, comprising:

[0009] Sintering a mixture of carbon-containing lithium iron phosphate and a coating agent to obtain a sintered material, and heat-treating the sintered material in the presence of chlorine;

[0010] The coating agent includes a first coating agent, and the first coating agent is aluminum oxide.

[0011] In some embodiments of the present disclosure, the coating agent further includes a second coating agent, and the second coating agent contains at least one of the elements aluminum, zirconium, titanium, and iron.

[0012] In some embodiments of the present disclosure, the second coating agent is selected from at least one of aluminum fluoride, zirconium oxide, titanium dioxide, and ferrosoferric oxide.

[0013] In some embodiments of the present disclosure, the mass ratio of the first coating agent to the second coating agent is 0.5-2:1.

[0014] In some embodiments of the present disclosure, the mass ratio of the first coating agent to the second coating agent is 1-2:1.

[0015] In some embodiments of the present disclosure, the mass ratio of the total metal content in the coating agent to the total amount of the mixture is 1-5:100.

[0016] In some embodiments of the present disclosure, the mass ratio of the total metal content in the coating agent to the total amount of the mixture is 2-4:100.

[0017] In some embodiments of the present disclosure, lithium iron phosphate, a carbon source, and a coating agent are mixed and sintered.

[0018] In some embodiments of the present disclosure, the heat treatment is performed at 100° C. to 300° C. for 0.5 h to 4 h.

[0019] In some embodiments of the present disclosure, the heat treatment is performed at 200° C.-300° C. for 2 h-3 h.

[0020] In some embodiments of the present disclosure, during the heat treatment, the introduction rate of chlorine gas is controlled to be 0.5 L / min-1.0 L / min.

[0021] In some embodiments of the present disclosure, during the preparation of the sintering material, the sintering temperature is controlled to be 600° C.-800° C., and the sintering time is controlled to be 5 h-12 h.

[0022] In some embodiments of the present disclosure, during the preparation of the sintering material, the sintering temperature is controlled to be 700° C.-800° C., and the sintering time is controlled to be 6 h-10 h.

[0023] In some embodiments of the present disclosure, sintering is performed in an inert atmosphere.

[0024] In some embodiments of the present disclosure, the inert atmosphere is nitrogen.

[0025] In some embodiments of the present disclosure, the mixture is prepared by ball milling.

[0026] In some embodiments of the present disclosure, the preparation process of the mixture includes: firstly dry-milling the raw materials to be mixed, and then wet-milling them.

[0027] In some embodiments of the present disclosure, wet ball milling is to mix the dry ball milled material with a solvent and an emulsifier for ball milling.

[0028] In some embodiments of the present disclosure, the mass ratio of the dry ball-milled material to the solvent and the emulsifier is 100:(50-120):(0.1-5).

[0029] In some embodiments of the present disclosure, the solvent is selected from at least one of water and ethanol.

[0030] In some embodiments of the present disclosure, the emulsifier is selected from at least one of polyethylene glycol, glycerol fatty acid ester, sucrose fatty acid ester and polyoxyethylene ether.

[0031] In some embodiments of the present disclosure, during the dry ball milling process, the ball milling speed is 300 rpm-500 rpm, and the ball milling time is 1 h-10 h.

[0032] In some embodiments of the present disclosure, during the wet ball milling process, the ball milling speed is 300 rpm-600 rpm, and the ball milling time is 3 h-12 h.

[0033] In some embodiments of the present disclosure, the carbon content of the carbon-containing lithium iron phosphate is 1%-10% by mass.

[0034] In some embodiments of the present disclosure, the preparation process of carbon-containing lithium iron phosphate includes: mixing an iron source, a phosphorus source, a lithium source, and a carbon source and calcining the mixture.

[0035] In some embodiments of the present disclosure, the calcination temperature is 600° C.-800° C., and the calcination time is 5 h-12 h.

[0036] In some embodiments of the present disclosure, the amounts of the iron source, phosphorus source, and lithium source are such that the molar ratio of iron, phosphorus, and lithium is controlled to be 1-1.2:1-1.1:1-1.2.

[0037] In some embodiments of the present disclosure, the iron source is selected from at least one of ferric oxide, ferrous oxalate, ferric carbonate, and ferric phosphate.

[0038] In some embodiments of the present disclosure, the phosphorus source is selected from at least one of phosphoric acid, lithium dihydrogen phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, iron phosphate, and manganese phosphate.

[0039] In some embodiments of the present disclosure, the lithium source is selected from at least one of lithium carbonate, lithium hydroxide, lithium acetate, and lithium dihydrogen phosphate.

[0040] In some embodiments of the present disclosure, the carbon source used in the preparation process is selected from at least one of acetylene black, graphene, carbon nanotubes, sucrose, fructose and glucose.

[0041] In a second aspect, the solution provided by the present disclosure also includes a lithium iron phosphate positive electrode material for extracting lithium from salt lakes by the electrochemical deintercalation method, which is prepared by the preparation method in the above embodiment.

[0042] In a third aspect, the solution provided by the present disclosure also includes a lithium iron phosphate electrode, which is prepared from the lithium iron phosphate positive electrode material in the above embodiment.

[0043] In a fourth aspect, the solution provided by the present disclosure also includes a lithium battery, including the lithium iron phosphate electrode in the above embodiment.

[0044] In a fifth aspect, the lithium iron phosphate electrode in the above embodiment is used in the electrochemical deintercalation method for lithium extraction.

[0045] Alumina and lithium iron phosphate are sintered to form an alumina coating. The sintered material obtained after sintering is heat-treated in the presence of chlorine. The alumina coated on the surface of the material reacts with carbon when exposed to chlorine, and the generated aluminum chloride sublimates, thereby forming an uneven coating on the surface of the material. At the same time, the gas produced by the reaction can form a loose and porous structure in the coating. Compared with a smooth and uniform coating, the uneven coating can accelerate the infiltration process of brine inside the material and further diffuse it to the surface of the particles. When the porous lithium iron phosphate material prepared by this method is used for lithium extraction, the internal dendritic channels can promote the entry of brine into the material and provide more active sites for reaction, thereby improving the mass transfer rate and lithium extraction efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present disclosure and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0047] Figure 1 This is the SEM image of the positive electrode material prepared in Example 1;

[0048] Figure 2 This is a graph showing the change in lithium ion concentration in the anode solution with electrolysis time. DETAILED DESCRIPTION

[0049] The embodiments of the present disclosure will be described in detail below with reference to the examples. However, those skilled in the art will appreciate that the following examples are intended only to illustrate the present disclosure and should not be construed as limiting the scope of the present disclosure. Where specific conditions are not specified in the examples, the experiments were performed under conventional conditions or the conditions recommended by the manufacturer. Where the manufacturer of the reagents or instruments is not specified, all are commercially available conventional products.

[0050] The endpoints of the ranges and any values ​​disclosed in this disclosure are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be considered to be specifically disclosed herein.

[0051] The present disclosure provides a method for preparing a lithium iron phosphate cathode material for extracting lithium from salt lakes by an electrochemical deintercalation method, comprising the following steps:

[0052] S1. Preparation of lithium iron phosphate

[0053] An iron source, a phosphorus source, a lithium source and a carbon source are mixed and calcined to prepare carbon-doped lithium iron phosphate, the carbon content of which is 1%-10%, such as 1%, 3%, 5%, 8%, 10%, etc.

[0054] In some embodiments, the iron source is selected from at least one of ferrous oxide, ferrous oxalate, ferric carbonate, and ferric phosphate, and may be any one or more of the above. The phosphorus source is selected from at least one of phosphoric acid, lithium dihydrogen phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ferric phosphate, and manganese phosphate, and may be any one or more of the above. The lithium source is selected from at least one of lithium carbonate, lithium hydroxide, lithium acetate, and lithium dihydrogen phosphate, and may be any one or more of the above. The carbon source is selected from at least one of acetylene black, graphene, carbon nanotubes, sucrose, fructose, and glucose, and may be any one or more of the above.

[0055] In actual operation, the iron source, phosphorus source, lithium source and carbon source can be mixed evenly by grinding, and then the obtained slurry is calcined under an inert atmosphere. The amount of iron source, phosphorus source and lithium source is to control the elemental molar ratio of iron, phosphorus and lithium to be 1-1.2:1-1.1:1-1.2, and the amount of raw materials can be adjusted according to the element ratio in the target product. The amount of carbon source is not limited and can be within the conventional amount range. Specifically, the elemental molar ratio of iron, phosphorus and lithium can be 1:1:1, 1.1:1.05:1.1, 1.1:1.07:1.15, 1.2:1.1:1.2, etc.

[0056] In some embodiments, the type of inert atmosphere is not limited and may be high-purity nitrogen or high-purity helium.

[0057] In some embodiments, the calcination temperature is controlled to be 600° C.-800° C. and the calcination time is controlled to be 5 h-12 h to obtain uniform lithium iron phosphate with a particle size range of 0.3 μm-1 μm. Specifically, the calcination temperature can be 600° C., 650° C., 700° C., 750° C., 800° C., etc., and the calcination time can be 5 h, 8 h, 10 h, 12 h, etc.

[0058] S2. Sintering

[0059] The lithium iron phosphate and coating agent are mixed and then sintered to obtain a sintered material. The coating agent includes a first coating agent and a second coating agent. The first coating agent is alumina, and the second coating agent contains at least one of aluminum, zirconium, titanium, and iron, which may be one or more of the elements. Coating with multiple metal elements is beneficial for improving the electrochemical performance of the resulting positive electrode material.

[0060] In some embodiments, the second coating agent is selected from at least one of aluminum fluoride, zirconium oxide, titanium dioxide, and ferrosoferric oxide, and can be any one or more of the above raw materials.

[0061] In some embodiments, the mass ratio of the total metal content in the coating agent to the total amount of the mixture is 1-5:100, preferably 2-4:100; the mass ratio of the first coating agent to the second coating agent is 0.5-2:1, preferably 1-2:1. By controlling the amount of lithium iron phosphate, carbon source, first coating agent and second coating agent, it is beneficial to further improve the electrochemical properties of the prepared positive electrode material.

[0062] Specifically, the mass ratio of the total metal content in the coating agent to the total amount of the mixture can be 1:100, 2:100, 3:100, 4:100, 5:100, etc., where the total amount of the mixture refers to the sum of the amounts of lithium iron phosphate, carbon source, and coating agent. The mass ratio of the first coating agent to the second coating agent can be 0.5:1, 1.0:1, 1.5:1, 2.0:1, etc.

[0063] In some embodiments, a carbon source may be added during the sintering process. The amount of the carbon source is not limited and may be adjusted as needed.

[0064] In some embodiments, sintering is carried out under an inert atmosphere at a sintering temperature of 600°C-800°C and a sintering time of 5h-12h. Preferably, the sintering temperature is controlled to be 700°C-800°C and the sintering time is 6h-10h to obtain a uniformly coated positive electrode material. The type of inert atmosphere is not limited and can be high-purity nitrogen or high-purity helium. Specifically, the sintering temperature can be 600°C, 650°C, 700°C, 750°C, 800°C, etc., and the sintering time can be 5h, 8h, 10h, 12h, etc.

[0065] The method of mixing the lithium iron phosphate, the carbon source and the coating agent is not limited, and existing methods such as stirring mixing and ball milling mixing can be used.

[0066] In some embodiments, dry ball milling and wet ball milling can be used to improve mixing uniformity. In actual operation, the mixing process includes: dry ball milling the lithium iron phosphate, carbon source, and coating agent, and then mixing the dry ball milled materials with a solvent and an emulsifier for wet ball milling.

[0067] Furthermore, during the dry ball milling process, the ball milling speed is 300 rpm-500 rpm and the ball milling time is 1 hour-10 hours to further improve the uniformity of the mixture. Specifically, during the dry ball milling process, the ball milling speed can be controlled to be 300 rpm, 400 rpm, 500 rpm, etc., and the ball milling time can be 1 hour, 3 hours, 5 hours, 8 hours, 10 hours, etc.

[0068] Furthermore, the mass ratio of the dry-milled material to the solvent and emulsifier is 100:(50-120):(0.1-5). The solvent is selected from at least one of water and ethanol, and may be any one or more of the above. The emulsifier is selected from at least one of polyethylene glycol, glycerol fatty acid ester, sucrose fatty acid ester, and polyoxyethylene ether, and may be any one or more of the above. Specifically, the mass ratio of the material to the solvent and emulsifier can be 100:50:0.1, 100:70:2, 100:90:3, 100:120:5, etc.

[0069] Furthermore, the ball milling speed of the wet ball milling is 300 rpm-600 rpm, and the ball milling time is 3 h-12 h to further improve the uniformity of the mixture. Specifically, the ball milling speed during the wet ball milling process can be controlled to be 300 rpm, 400 rpm, 500 rpm, 600 rpm, etc., and the ball milling time can be 3 h, 5 h, 8 h, 10 h, 12 h, etc.

[0070] S3. Heat treatment

[0071] The sintered material is heat treated in the presence of chlorine. The aluminum oxide coated on the surface of the material reacts with the carbon when exposed to chlorine. The generated aluminum chloride sublimates immediately, forming an uneven coating layer on the surface of the material. At the same time, the gas produced by the reaction can make the coating form a loose and porous structure.

[0072] In some embodiments, the heat treatment is performed at 100°C-300°C for 0.5-4 hours, with the chlorine gas introduction rate controlled at 0.5 L / min-1.0 L / min. The total amount of chlorine gas used can be close to the theoretical amount. The reaction does not need to proceed fully, and a portion of the metal coating layer can be retained to improve conductivity. By further controlling the heat treatment conditions, the reaction can be fully carried out to form a loose and porous structure.

[0073] Specifically, the temperature of the heat treatment may be 100°C, 150°C, 200°C, 250°C, 300°C, etc., preferably 200°C-300°C.

[0074] Specifically, the heat treatment time can be 0.5h, 1.0h, 1.5h, 2.0h, 2.5h, 3.0h, 3.5h, 4.0h, etc., preferably 2h-3h.

[0075] Specifically, the introduction rate of chlorine gas can be 0.5 L / min, 0.6 L / min, 0.7 L / min, 0.8 L / min, 0.9 L / min, 1.0 L / min, etc.

[0076] The present invention also provides a lithium iron phosphate cathode material for electrochemical deintercalation lithium extraction from salt lakes. The material is prepared using the aforementioned method. The coating layer has a loose, porous structure, making it suitable for electrochemical deintercalation lithium extraction. Compared to a smooth, uniform coating layer, the porous material accelerates the infiltration of brine into the material and further diffuses onto the particle surface. When used for lithium extraction, the resulting porous lithium iron phosphate material has dendritic channels that facilitate brine entry and provide more reactive active sites, thereby improving mass transfer rates and lithium extraction efficiency.

[0077] An embodiment of the present invention further provides a lithium iron phosphate electrode, which is prepared from the above-mentioned lithium iron phosphate positive electrode material. Existing electrode preparation methods can be used and are not limited here.

[0078] In some embodiments, the preparation process of the lithium iron phosphate electrode includes: mixing LiFePO4, PVDF and conductive carbon black in a mass ratio of 8:1:1, and using N-methylpyrrolidone as a solvent, fully grinding and slurrying, and then evenly coating it on the current collector, and then drying it in a vacuum drying oven. The drying temperature can be about 90°C and the drying time can be about 12 hours.

[0079] An embodiment of the present invention further provides a lithium battery, comprising the above-mentioned lithium iron phosphate electrode, and may further comprise a negative electrode and an electrolyte, and the types of the negative electrode and the electrolyte are not limited.

[0080] An embodiment of the present invention also provides an application of the above-mentioned lithium iron phosphate electrode in lithium extraction by electrochemical deintercalation. When the porous lithium iron phosphate material prepared by the embodiment of the present invention is used for lithium extraction, the internal dendritic channels can promote the entry of brine into the material and provide more active sites for reaction, thereby improving the mass transfer rate and lithium extraction efficiency.

[0081] In the actual operation process, the lithium-deficient state Li can be formed first. 1-x FePO4 electrode material, and then place the prepared lithium iron phosphate electrode and the delithiated lithium iron phosphate electrode in the anode chamber and cathode chamber respectively, inject the brine to be treated into the cathode chamber, inject the electrolyte into the anode, and apply voltage to carry out the electrochemical lithium extraction process.

[0082] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0083] Example 1

[0084] This embodiment provides a method for preparing a lithium iron phosphate positive electrode material for extracting lithium from salt lakes by an electrochemical deintercalation method, comprising the following steps:

[0085] (1) Weigh 151.85 g of iron phosphate, 37.45 g of lithium carbonate, and 12.98 g of glucose, mix and grind them. Sinter the uniformly ground slurry under high-purity nitrogen with a purity of more than 99% at a temperature of 700° C. for 8 h to obtain lithium iron phosphate.

[0086] (2) Add 180g of the prepared lithium iron phosphate, 1.55g of aluminum oxide, and 3.10g of aluminum fluoride to a ball mill and perform dry ball milling at a speed of 400rpm / min for 5h. Add 200g of deionized water and 2.5g of polyethylene glycol PEG-6000 and perform high-energy wet ball milling at a speed of 600rpm / min for 5h. Load the mixed slurry into a tubular electric furnace feed tube, place the feed tube in the tubular electric furnace and calcine it under high-purity nitrogen protection at a temperature of 750℃ for 8h.

[0087] (3) After the calcination is completed, the material is allowed to cool to 250°C, and chlorine gas is slowly introduced into it at a rate of 0.5 L / min. The reaction is carried out at 250°C for 3 hours. Aluminum oxide reacts to form aluminum chloride and sublimates to obtain a lithium iron phosphate material with a rough surface.

[0088] Example 2

[0089] This embodiment provides a method for preparing a lithium iron phosphate positive electrode material for extracting lithium from salt lakes by an electrochemical deintercalation method, comprising the following steps:

[0090] (1) Weigh 151.85 g of iron phosphate, 37.45 g of lithium carbonate, and 12.98 g of glucose, mix and grind them. Sinter the uniformly ground slurry under high-purity nitrogen with a purity of more than 99% at a temperature of 600° C. for 12 h to obtain lithium iron phosphate.

[0091] (2) Add 180g of the prepared lithium iron phosphate, 1.55g of aluminum oxide, and 3.10g of aluminum fluoride to a ball mill and perform dry ball milling at a speed of 300rpm / min for 10h. Add 300g of deionized water and 2.5g of polyethylene glycol PEG-6000 and perform high-energy wet ball milling at a speed of 300rpm / min for 12h. Load the mixed slurry into a tubular electric furnace feed tube, place the feed tube in the tubular electric furnace and calcine it under high-purity nitrogen protection at a temperature of 600℃ for 12h.

[0092] (3) After the calcination is completed, the material is allowed to cool to 100°C, and chlorine gas is slowly introduced into it at a rate of 0.5 L / min. The reaction is carried out at 100°C for 2 hours. The aluminum oxide reacts to form aluminum chloride and sublimes to obtain a lithium iron phosphate material with a rough surface.

[0093] Example 3

[0094] This embodiment provides a method for preparing a lithium iron phosphate positive electrode material for extracting lithium from salt lakes by an electrochemical deintercalation method, comprising the following steps:

[0095] (1) Weigh 151.85 g of iron phosphate, 37.45 g of lithium carbonate, and 12.98 g of glucose, mix and grind them. Sinter the mixed slurry under high-purity nitrogen with a purity of more than 99% at a temperature of 800° C. for 5 h to obtain lithium iron phosphate.

[0096] (2) Add 180g of the prepared lithium iron phosphate, 1.55g of aluminum oxide, and 0.775g of aluminum fluoride to a ball mill and perform dry ball milling at a speed of 500rpm / min for 1h. Add 300g of deionized water and 2.5g of polyethylene glycol PEG-6000 and perform high-energy wet ball milling at a speed of 600rpm / min for 3h. Load the mixed slurry into a tubular electric furnace feed tube, place the feed tube in the tubular electric furnace and calcine it under high-purity nitrogen protection at a temperature of 800℃ for 5h.

[0097] (3) After the calcination is completed, the material is allowed to cool to 300°C, and chlorine gas is slowly introduced into it at a rate of 1.0 L / min. The reaction is carried out at 300°C for 2 hours. The aluminum oxide reacts to form aluminum chloride and sublimes to obtain a lithium iron phosphate material with a rough surface.

[0098] Example 4

[0099] The only difference from Example 1 is that the amounts of aluminum oxide and aluminum fluoride are different, the mass ratio of aluminum oxide to aluminum fluoride is 1:1, and the total amount of aluminum added remains unchanged.

[0100] Example 5

[0101] The only difference from Example 1 is that the amounts of aluminum oxide and aluminum fluoride are different, the mass ratio of aluminum oxide to aluminum fluoride is 2:1, and the total amount of aluminum added remains unchanged.

[0102] Comparative Example 1

[0103] The only difference from Example 1 is that in step (2), aluminum oxide is not added, aluminum oxide is replaced by aluminum fluoride, and step (3) is not performed. The specific steps are as follows:

[0104] (1) Weigh 151.85 g of iron phosphate, 37.45 g of lithium carbonate, and 12.98 g of glucose, mix and grind them. Sinter the uniformly ground slurry under high-purity nitrogen with a purity of more than 99% at a temperature of 700° C. for 8 h to obtain lithium iron phosphate.

[0105] (2) The prepared lithium iron phosphate and 4.10 g of aluminum fluoride were added to a ball mill and dry-milled at a speed of 400 rpm / min for 5 h. 200 g of deionized water and 2.5 g of polyethylene glycol PEG-6000 were added and wet-milled at a speed of 600 rpm / min for 5 h. The mixed slurry was loaded into a tubular electric furnace feed tube, and the feed tube was placed in the tubular electric furnace for calcination under high-purity nitrogen protection at a temperature of 750°C for 8 h.

[0106] Comparative Example 2

[0107] The only difference from Example 1 is that no metal coating agent is added. The specific steps are as follows:

[0108] 151.85g of iron phosphate, 37.45g of lithium carbonate, and 12.98g of glucose were weighed and dry-milled in a ball mill at 400 rpm for 5 hours. 200g of deionized water and 2.5g of polyethylene glycol (PEG-6000) were then added and wet-milled at 600 rpm for 5 hours. The resulting slurry was then loaded into a tubular furnace feed tube and calcined in the furnace under high-purity nitrogen at 750°C for 8 hours to yield the lithium iron phosphate material.

[0109] Comparative Example 3

[0110] The only difference from Example 1 is that the heat treatment temperature is 350°C.

[0111] (1) Weigh 151.85 g of iron phosphate, 37.45 g of lithium carbonate, and 12.98 g of glucose, mix and grind them. Sinter the uniformly ground slurry under high-purity nitrogen with a purity of more than 99% at a temperature of 700° C. for 8 h to obtain lithium iron phosphate.

[0112] (2) Add 180g of the prepared lithium iron phosphate, 1.55g of aluminum oxide, and 3.10g of aluminum fluoride to a ball mill and perform dry ball milling at a speed of 400rpm / min for 5h. Add 200g of deionized water and 2.5g of polyethylene glycol PEG-6000 and perform high-energy wet ball milling at a speed of 600rpm / min for 5h. Load the mixed slurry into a tubular electric furnace feed tube, place the feed tube in the tubular electric furnace and calcine it under high-purity nitrogen protection at a temperature of 750℃ for 8h.

[0113] (3) After the calcination is completed, the material is allowed to cool to 350°C, and chlorine gas is slowly introduced into it at a rate of 0.5 L / min. The reaction is carried out at 350°C for 3 hours. The aluminum oxide reacts to form aluminum chloride and sublimates to obtain a lithium iron phosphate material with a rough surface.

[0114] Comparative Example 4

[0115] The only difference from Example 1 is that the heat treatment time is 4 hours.

[0116] (1) Weigh 151.85 g of iron phosphate, 37.45 g of lithium carbonate, and 12.98 g of glucose, mix and grind them. Sinter the uniformly ground slurry under high-purity nitrogen with a purity of more than 99% at a temperature of 700° C. for 8 h to obtain lithium iron phosphate.

[0117] (2) Add 180g of the prepared lithium iron phosphate, 1.55g of aluminum oxide, and 3.10g of aluminum fluoride to a ball mill and perform dry ball milling at a speed of 400rpm / min for 5h. Add 200g of deionized water and 2.5g of polyethylene glycol PEG-6000 and perform high-energy wet ball milling at a speed of 600rpm / min for 5h. Load the mixed slurry into a tubular electric furnace feed tube, place the feed tube in the tubular electric furnace and calcine it under high-purity nitrogen protection at a temperature of 750℃ for 8h.

[0118] (3) After the calcination is completed, the material is allowed to cool to 250°C, and chlorine gas is slowly introduced into it at a rate of 0.5 L / min. The reaction is carried out at 250°C for 4 hours. The aluminum oxide reacts to form aluminum chloride and sublimates to obtain a lithium iron phosphate material with a rough surface.

[0119] Test Example 1

[0120] The SEM image of the lithium iron phosphate material prepared in Test Example 1 is as follows: Figure 1 shown.

[0121] Test Example 2

[0122] The electrochemical properties of the lithium iron phosphate materials prepared in the examples and comparative examples were tested, and the results are shown in Table 1.

[0123] Electrochemical performance testing method: The prepared lithium manganese iron phosphate cathode material was dispersed with SP and PVDF in the solvent NMP at a ratio of 80:10:10. After ball milling, the mixture was coated on aluminum foil and vacuum dried to produce a positive electrode sheet. The electrolyte was 1 mol / L LiPF6, the separator was Celgard polypropylene film, and the negative electrode was a metal lithium sheet. The battery was assembled. The battery was subjected to charge and discharge cycle performance testing. The 0.1C and 1C discharge specific capacities were tested within the cut-off voltage range of 2.2 to 4.3V. The test results are shown in Table 1:

[0124] Table 1 Electrochemical properties of lithium iron phosphate materials prepared in Examples and Comparative Examples

[0125] Group 0.1C discharge capacity mAh / g 1C discharge capacity mAh / g Example 1 160.8 145.1 Comparative Example 1 162.9 146.2 Comparative Example 2 151.8 138.5 Comparative Example 3 153.2 139.8 Comparative Example 4 153.8 139.1

[0126] Test Example 2

[0127] The performance of the lithium iron phosphate materials prepared in the examples and comparative examples was verified through lithium extraction experiments. The results are shown in Table 2.

[0128] Test method:

[0129] (1) The prepared LiFePO4 material was mixed with PVDF and conductive carbon black in a mass ratio of 8:1:1, and N-methylpyrrolidone was used as a solvent. After being fully ground and slurried, it was evenly coated on the current collector, and then kept at 90°C in a vacuum drying oven for 12 hours. The prepared LiFePO4 electrode was used as the anode, nickel foam was used as the cathode, and 1.0 mol / L NaCl was used as the supporting electrolyte. Lithium was electrolytically removed at a DC voltage of 1.0 V until the current was less than 0.5 A / m 2 , obtaining lithium-deficient Li 1-x FePO4 electrode material.

[0130] (2) The electrolysis apparatus was separated into a cathode chamber and an anode chamber using an anion membrane. The prepared lithium iron phosphate electrode and the delithiated lithium iron phosphate electrode were placed in the anode chamber and the cathode chamber, respectively. 15 L of brine to be treated was injected into the cathode chamber, and 2 L of a 5 g / L NaCl solution was injected into the anode chamber as a supporting electrolyte. A voltage of 0.3 V was applied to the anode and cathode, and electrolysis was performed at 20°C for 4 hours.

[0131] The compositions of brine and anode lithium-rich solution before and after lithium extraction are shown in Table 2. Figure 2 is the change of lithium ion concentration in the anolyte with electrolysis time.

[0132] Table 2 Lithium extraction performance of lithium iron phosphate materials prepared in Example

[0133] Concentration (g / L) Li Na Mg K <![CDATA[SO4 2- ]]> brine 0.64 52.70 51.40 4.01 10.54 Brine after lithium extraction 0.11 52.55 51.15 3.97 10.50 Anode lithium-rich solution 3.46 3.07 0.89 0.06 0.19

[0134] In Example 1, the lithium concentration in the brine decreased from 0.64 g / L to 0.11 g / L, while the lithium concentration in the anode lithium-rich solution increased to 3.46 g / L. After the electrolysis, the adsorption capacity of the electrode was 30.5 mg (Li) / g (LiFePO4).

[0135] In Comparative Example 1, the lithium concentration in the brine decreased from 0.66 g / L to 0.27 g / L, while the lithium concentration in the anode lithium-rich solution increased to 2.59 g / L. After the electrolysis, the electrode's adsorption capacity was 26.8 mg (Li) / g (LiFePO4), a significant decrease compared to Example 1.

[0136] In Comparative Example 2, the lithium concentration in the brine decreased from 0.63 g / L to 0.31 g / L, while the lithium concentration in the anode lithium-rich solution increased to 2.10 g / L. After the electrolysis, the electrode's adsorption capacity was 22.5 mg (Li) / g (LiFePO4), a significant decrease compared to Example 1.

[0137] In Comparative Example 3, the lithium concentration in the brine decreased from 0.64 g / L to 0.30 g / L, while the lithium concentration in the anode lithium-rich solution increased to 2.28 g / L. After the electrolysis, the electrode's adsorption capacity was 25.2 mg (Li) / g (LiFePO4), a significant decrease compared to Example 1.

[0138] In Comparative Example 4, the lithium concentration in the brine decreased from 0.62 g / L to 0.29 g / L, while the lithium concentration in the anode lithium-rich solution increased to 2.30 g / L. After the electrolysis, the electrode's adsorption capacity was 25.8 mg (Li) / g (LiFePO4), a significant decrease compared to Example 1.

[0139] The preferred embodiments of the present disclosure are described in detail above, but the present disclosure is not limited thereto. Within the technical concept of the present disclosure, various simple variations of the technical solution of the present disclosure may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed by the present disclosure and fall within the scope of protection of the present disclosure.

[0140] Industrial Applicability

[0141] The present invention uses aluminum oxide to sinter lithium iron phosphate to form a coating, and the sintered material obtained after sintering is heat-treated in the presence of chlorine. The aluminum oxide coated on the surface of the material reacts with carbon when exposed to chlorine, and the generated aluminum chloride sublimes, thereby forming an uneven coating layer on the surface of the material. At the same time, the gas generated by the reaction can cause the coating layer to form a loose and porous structure. Compared with a smooth and uniform coating layer, a rough coating layer can accelerate the infiltration process of brine inside the material and further diffuse to the surface of the particles. When the porous lithium iron phosphate material prepared by this method is used for lithium extraction, the internal dendritic channels can promote the brine to enter the interior of the material and provide more active sites for reaction, thereby improving the mass transfer rate and lithium extraction efficiency. The technical solution provided by the present invention introduces a coating agent during the sintering process to increase the step of heat treatment under chlorine conditions, which is easy to implement and has good industrial applicability.

Claims

1. A method for preparing a lithium iron phosphate cathode material for extracting lithium from salt lakes by electrochemical deintercalation, characterized in that: include: Sintering a mixture of carbon-containing lithium iron phosphate and a coating agent to obtain a sintered material, and heat-treating the sintered material in the presence of chlorine; Wherein, the coating agent includes a first coating agent, and the first coating agent is aluminum oxide; The coating agent further includes a second coating agent, wherein the second coating agent contains at least one of the elements aluminum, zirconium, titanium and iron; The mass ratio of the first coating agent to the second coating agent is 0.5-2:1; the mass ratio of the total metal content in the coating agent to the total amount of the mixture is 1-5:100; The heat treatment is carried out at 100° C.-300° C. for 0.5 h-4 h.

2. The preparation method according to claim 1, characterized in that The second coating agent is selected from at least one of aluminum fluoride, zirconium oxide, titanium dioxide and ferrosoferric oxide.

3. The preparation method according to claim 1, characterized in that The mass ratio of the first coating agent to the second coating agent is 1-2:

1.

4. The preparation method according to claim 1, characterized in that The mass ratio of the total metal content in the coating agent to the total amount of the mixture is 2-4:

100.

5. The preparation method according to claim 1, characterized in that The lithium iron phosphate, the carbon source and the coating agent are mixed and sintered.

6. The preparation method according to claim 1, characterized in that The heat treatment is carried out at 200° C.-300° C. for 2 h-3 h.

7. The preparation method according to claim 1, characterized in that During the heat treatment, the introduction rate of chlorine gas is controlled to be 0.5 L / min-1.0 L / min.

8. The preparation method according to claim 1, characterized in that During the preparation of the sintering material, the sintering temperature is controlled to be 600° C.-800° C., and the sintering time is controlled to be 5 h-12 h.

9. The preparation method according to claim 8, characterized in that During the preparation of the sintering material, the sintering temperature is controlled to be 700° C.-800° C., and the sintering time is controlled to be 6 h-10 h.

10. The preparation method according to claim 8, characterized in that Sintering is carried out in an inert atmosphere.

11. The preparation method according to claim 10, characterized in that: The inert atmosphere is nitrogen.

12. The preparation method according to claim 1, characterized in that The mixture is prepared by ball milling.

13. The preparation method according to claim 12, characterized in that The preparation process of the mixture comprises: firstly performing dry ball milling on the raw materials to be mixed, and then performing wet ball milling.

14. The preparation method according to claim 13, characterized in that The wet ball milling is to mix the dry ball milled material with a solvent and an emulsifier and then ball mill the mixture.

15. The preparation method according to claim 14, characterized in that The mass ratio of the dry ball-milled material to the solvent and the emulsifier is 100:(50-120):(0.1-5).

16. The preparation method according to claim 14 or 15, characterized in that: The solvent is selected from at least one of water and ethanol.

17. The preparation method according to claim 14, characterized in that The emulsifier is selected from at least one of polyethylene glycol, glycerol fatty acid ester, sucrose fatty acid ester and polyoxyethylene ether.

18. The preparation method according to claim 13, characterized in that During the dry ball milling process, the ball milling speed is 300 rpm-500 rpm, and the ball milling time is 1 h-10 h.

19. The preparation method according to claim 13, characterized in that During the wet ball milling process, the ball milling speed is 300 rpm-600 rpm, and the ball milling time is 3 h-12 h.

20. The preparation method according to claim 1, characterized in that Calculated by mass fraction, the carbon content of the carbon-containing lithium iron phosphate is 1%-10%.

21. The preparation method according to claim 20, characterized in that The preparation process of the carbon-containing lithium iron phosphate comprises: mixing an iron source, a phosphorus source, a lithium source and a carbon source and calcining them.

22. The preparation method according to claim 21, characterized in that The calcination temperature is 600°C-800°C, and the calcination time is 5h-12h.

23. The preparation method according to claim 21, characterized in that The amounts of the iron source, the phosphorus source and the lithium source are controlled so that the molar ratio of iron, phosphorus and lithium is 1-1.2:1-1.1:1-1.

2.

24. The preparation method according to claim 21, characterized in that The iron source is selected from at least one of ferric oxide, ferrous oxalate, ferric carbonate and ferric phosphate.

25. The preparation method according to claim 21, characterized in that The phosphorus source is selected from at least one of phosphoric acid, lithium dihydrogen phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, iron phosphate and manganese phosphate.

26. The preparation method according to claim 21, characterized in that The lithium source is selected from at least one of lithium carbonate, lithium hydroxide, lithium acetate and lithium dihydrogen phosphate.

27. The preparation method according to claim 21, characterized in that The carbon sources used in the preparation process are all selected from at least one of acetylene black, graphene, carbon nanotubes, sucrose, fructose and glucose.

28. A lithium iron phosphate cathode material for extracting lithium from salt lakes by electrochemical deintercalation, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 27.

29. A lithium iron phosphate electrode, characterized in that Prepared from the lithium iron phosphate positive electrode material according to claim 28.

30. A lithium battery, characterized in that: Including the lithium iron phosphate electrode as described in claim 29.

31. Use of the lithium iron phosphate electrode according to claim 30 in lithium extraction by electrochemical deintercalation.

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