Method for recycling cathode material in a battery

Abstract

This invention provides a method for recycling positive electrode materials in batteries, comprising the following steps: separating the positive electrode sheet to obtain a positive electrode current collector and positive electrode active layer powder, wherein the positive electrode active layer powder includes lithium iron phosphate and lithium lanthanum zirconium oxide electrolyte; performing lithium-ion leaching treatment on the positive electrode active layer powder using citric acid to obtain a lithium-containing solution and positive electrode active layer residue; performing iron-phosphorus leaching treatment on the positive electrode active layer residue using sulfuric acid to obtain an iron-phosphorus mixed solution and lanthanum zirconate residue; subjecting the iron-phosphorus mixed solution to a hydrothermal reaction to obtain iron(III) oxide; and performing alkaline dissolution treatment on the lanthanum zirconate residue with sodium hydroxide to obtain NaLaO2 and Na2ZrO3. The recycling method of this invention can efficiently recover lithium, iron, phosphorus, zirconium, and lanthanum elements from the positive electrode material in batteries, and has the characteristics of low cost and environmental friendliness.

Description

Technical Field

[0001] This invention relates to the field of battery recycling, and in particular to a method for recycling positive electrode materials in batteries. Background Technology

[0002] With the rapid development of new energy vehicles and the energy storage industry, lithium iron phosphate (LFP) batteries have become one of the mainstream power batteries due to their high safety, long cycle life, and low cost. In recent years, lithium lanthanum zirconium oxide (LLZO) (Li7La3Zr2O) has also seen significant development. 12 Due to its high ionic conductivity (10 at room temperature) -4 ~10 -3 With its high efficiency (S / cm), wide voltage window (0~5V), and thermal stability, LLZO has become the mainstream electrolyte for batteries. Using LLZO and LFP together as cathode materials not only enables batteries to achieve energy densities of 300~360Wh / kg, but also balances safety and cost. However, with the arrival of the peak battery retirement period, how to efficiently and environmentally recycle the cathode materials from batteries has become an industry challenge.

[0003] The recycling of positive electrode materials for batteries mainly focuses on recovering valuable metals. Among battery positive electrode materials, LLZO has a high melting point (>1500℃). Current technologies use strong acids such as sulfuric acid and hydrochloric acid to impregnate LLZO, but LLZO is difficult to dissolve and requires additional high-temperature and high-pressure treatment. This makes it difficult to recover valuable metals such as lithium (Li), lanthanum (La), and zirconium (Zr) from LLZO. Furthermore, LFP and LLZO residues are easily mixed during the recycling process, affecting the electrochemical performance of the recycled valuable metals. At the same time, the acid leaching method can only generate a profit of 200-500 yuan per ton of LFP, which is economically inefficient. On the other hand, recycling LLZO requires the use of strong alkalis or ionic liquids to destroy its crystal lattice, with energy consumption reaching 3000-6000 kWh / ton, resulting in high costs.

[0004] Existing technologies also use pyrometallurgy to recover the positive electrode material of batteries. However, pyrometallurgy requires high-temperature roasting (900~1600℃) of the positive electrode material of the battery, which consumes a lot of energy and also releases harmful gases (such as fluorides).

[0005] It can be seen that the existing technology for recycling battery cathode materials has a low recycling rate and suffers from high cost, low economic benefits, and environmental unfriendliness. Therefore, it is necessary to provide a method for recycling battery cathode materials to achieve efficient recovery of lithium, lanthanum, zirconium, iron, and phosphorus in battery cathode materials, while also being economical and environmentally friendly. Summary of the Invention

[0006] This invention provides a method for recycling positive electrode materials in batteries. This method can improve the recovery rate of lithium, lanthanum, zirconium, iron and phosphorus elements in battery positive electrode materials, and is both economical and environmentally friendly.

[0007] This invention provides a method for recycling positive electrode material in a battery, comprising the following steps:

[0008] The positive electrode sheet is separated to obtain a positive electrode current collector and a positive electrode active layer powder, wherein the positive electrode active layer powder includes lithium iron phosphate and lithium lanthanum zirconium oxygen electrolyte.

[0009] The positive electrode active layer powder was subjected to lithium ion leaching treatment with citric acid to obtain a lithium-containing solution and positive electrode active layer residue.

[0010] The positive electrode active layer residue was subjected to iron-phosphorus leaching treatment with sulfuric acid to obtain an iron-phosphorus mixed solution and lanthanum zirconate residue.

[0011] The iron-phosphorus mixture was subjected to a hydrothermal reaction to obtain iron(III) oxide.

[0012] The lanthanum zirconate residue was subjected to alkaline dissolution treatment with sodium hydroxide to obtain NaLaO2 and Na2ZrO3.

[0013] In the recovery method described above, the lithium-ion leaching treatment is performed at a temperature of 30-60°C for 2-3 hours and a pH of 1.5-3.0; and / or,

[0014] In the iron-phosphorus leaching treatment, the concentration of sulfuric acid is 0.5~1.0 mol / L, the temperature is 80~90℃, and the time is 2~4 h; and / or,

[0015] In the hydrothermal reaction, the pH is 11-13, the temperature is 145-155℃, and the time is 10-12 hours; and / or,

[0016] In the alkaline dissolution treatment, the temperature is 490~510℃ and the time is 2~3h.

[0017] The recycling method described above, wherein the separation process includes:

[0018] A positive electrode fragment solution is obtained by alternately subjecting the solution containing the positive electrode sheet to a first ultrasonic treatment and a second ultrasonic treatment.

[0019] The positive electrode fragment solution is sieved to obtain the positive electrode current collector and the positive electrode active slurry.

[0020] The positive electrode active slurry is calcined to obtain the positive electrode active layer powder;

[0021] The temperature of the first ultrasonic treatment is 60~80℃, and the temperature of the second ultrasonic treatment is -10~0℃.

[0022] In the recovery method described above, the first ultrasonic treatment and / or the second ultrasonic treatment have a time of 30-45 minutes, a frequency of 20-40 kHz, and a power density of 0.5-2 W / cm². 2 ; and / or,

[0023] The roasting process is carried out at a temperature of 300-500℃ for 1-2 hours.

[0024] The recovery method described above further includes electrolyzing the lithium-containing solution in the H-type electrolytic cell to obtain a lithium-rich solution.

[0025] In the recycling method described above, the H-type electrolytic cell includes a cathode cell, a proton exchange membrane, and an anode cell connected in sequence.

[0026] The anode cell contains the lithium-containing solution, the cathode cell contains the lithium replenishment solution, the volume ratio of the lithium-containing solution to the lithium replenishment solution is 1:(1.5~2.0), and the electrolysis temperature is 30~60℃.

[0027] The recovery method described above further includes, prior to the hydrothermal reaction:

[0028] The iron-phosphorus mixture was extracted with tributyl phosphate to remove zirconium ions, followed by treatment to remove heavy metal ions, aluminum, calcium and organic residues.

[0029] The pH of the extraction process is 1.5 to 3.0.

[0030] The recovery method described above further includes, prior to the alkaline dissolution treatment, washing the lanthanum zirconate residue with oxalic acid.

[0031] The concentration of oxalic acid is 0.1~0.2 mol / L.

[0032] The recovery method described above further includes a post-treatment process following the hydrothermal reaction, the post-treatment comprising:

[0033] The products obtained from the hydrothermal reaction were magnetically separated to yield ferric oxide and a phosphate solution.

[0034] The pH of the phosphate solution is adjusted to obtain phosphate.

[0035] The recovery method described above, wherein the citric acid is prepared by a method comprising the following steps:

[0036] Heat treatment of lemons yields a gaseous acidic substance;

[0037] The gaseous acidic substance is condensed to obtain crude citric acid.

[0038] The crude citric acid was subjected to distillation and adsorption treatments in sequence to obtain the citric acid.

[0039] In the heat treatment, the temperature is 100~150℃ and the time is 6~12h; and / or,

[0040] In the adsorption treatment, the temperature is 95~105℃ and the time is 15~30min.

[0041] The recycling method of the present invention includes separating the positive electrode sheet to obtain a positive electrode current collector and a positive electrode active layer powder, wherein the positive electrode active layer powder includes lithium iron phosphate and lithium lanthanum zirconium oxide electrolyte; performing lithium ion leaching treatment on the positive electrode active layer powder using citric acid to obtain a lithium-containing solution and a positive electrode active layer residue; performing iron-phosphorus leaching treatment on the positive electrode active layer residue using sulfuric acid to obtain an iron-phosphorus mixture and a lanthanum zirconate residue; subjecting the iron-phosphorus mixture to a hydrothermal reaction to obtain iron(III) oxide; and performing alkaline dissolution treatment on the lanthanum zirconate residue with sodium hydroxide to obtain NaLaO2 and Na2ZrO3. In the recycling method of this invention, citric acid can gently leach lithium from the positive electrode active layer powder without leaching iron and phosphorus, resulting in a higher lithium ion content in the lithium-containing solution and improving the lithium recovery rate. Furthermore, citric acid is biodegradable, enhancing the environmental friendliness of the battery positive electrode material recycling process. Subsequently, iron, phosphorus, lanthanum, and zirconium are recovered stepwise from the positive electrode active layer residue, further improving the recovery rates of these elements. The recycling method of this invention has low cost, and the recovered lithium-containing solution can be recycled and reused. Iron(III) oxide can be used in battery or chemical production, and NaLaO2 and Na2ZrO3 can be used to resynthesize lithium lanthanum zirconium oxide electrolyte, reducing battery production costs. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0043] Existing technologies for recovering lithium, iron, phosphorus, lanthanum, and zirconium from battery cathode materials suffer from problems such as low recovery rates, high costs, and environmental pollution. The inventors discovered in their research that by selectively leaching lithium from battery cathode materials using citric acid, and then gradually recovering iron, phosphorus, zirconium, and lanthanum, cross-contamination between lithium and these elements can be avoided. Furthermore, the recovery rates of lithium, iron, phosphorus, lanthanum, and zirconium are high, the cost is low, and the process is environmentally friendly.

[0044] This invention provides a method for recycling positive electrode materials in a battery, comprising the following steps:

[0045] The positive electrode sheet is separated to obtain a positive electrode current collector and a positive electrode active layer powder, which includes lithium iron phosphate and lithium lanthanum zirconium oxygen electrolyte.

[0046] Citric acid was used to leach lithium ions from the positive electrode active layer powder to obtain a lithium-containing solution and positive electrode active layer residue.

[0047] The residue of the positive electrode active layer was subjected to iron-phosphorus leaching treatment with sulfuric acid to obtain an iron-phosphorus mixed solution and lanthanum zirconate residue.

[0048] The iron-phosphorus mixture was subjected to a hydrothermal reaction to obtain iron(III) oxide;

[0049] Lanthanum zirconate residue was subjected to alkaline dissolution with sodium hydroxide to obtain NaLaO2 and Na2ZrO3.

[0050] Specifically, the positive electrode sheet is separated to obtain a positive current collector and a positive electrode active layer powder. Then, citric acid is used to perform lithium ion leaching treatment on the positive electrode active layer. Citric acid can gently dissolve lithium elements in lithium iron phosphate and lithium lanthanum zirconium oxide electrolyte, selectively leaching lithium ions to obtain a lithium-containing solution and positive electrode active layer residue, which includes iron phosphate and lanthanum zirconate. Next, sulfuric acid is used to perform iron-phosphorus leaching treatment on the positive electrode active layer residue. The sulfuric acid reacts with the iron phosphate in the positive electrode active layer to obtain an iron-phosphorus mixture including iron sulfate and phosphoric acid and lanthanum zirconate residue. Then, the iron-phosphorus mixture is subjected to a hydrothermal reaction. During the hydrothermal reaction, iron ions are converted into iron(III) oxide. During the alkaline dissolution treatment of the lanthanum zirconate residue with sodium hydroxide, sodium hydroxide can destroy the lanthanum zirconate lattice, causing the zirconium ions in lanthanum zirconate to react with sodium hydroxide to form Na2ZrO3, and the lanthanate ions to react with sodium hydroxide to form NaLaO2.

[0051] This invention uses citric acid to selectively leach lithium from the positive electrode active layer powder, while retaining iron and phosphorus in the positive electrode active layer residue. This increases the concentration of lithium ions in the lithium-containing solution, thereby improving the recovery rate of lithium in the battery positive electrode material. Compared to existing technologies that use strong acids to treat battery positive electrode materials, the citric acid used in this invention is biodegradable, highly safe, and reduces environmental pollution. Simultaneously, the stepwise recovery of iron, phosphorus, zirconium, and lanthanum can improve their recovery rates. Furthermore, the lithium-containing solution recovered by this invention can be recycled and reused, iron(III) oxide can be used in battery or chemical production, and Na2ZrO3 and NaLaO2 can be used to synthesize lithium lanthanum zirconium oxide electrolyte, reducing battery production costs. Therefore, the method for recovering positive electrode materials in batteries according to this invention is both environmentally friendly and economical.

[0052] In some implementations, the recovery rate of iron in the battery cathode material is greater than 94%, the recovery rate of lanthanum is greater than 95%, and the recovery rate of zirconium is greater than 95%.

[0053] In some embodiments, the method for recycling the positive electrode material in the battery of the present invention can reduce costs by 35% and energy consumption by 40% compared to the conventional hydrometallurgical method for recycling the positive electrode material in the battery.

[0054] This invention does not specifically limit the battery; the battery can be any common battery in the art, including lithium iron phosphate and lithium lanthanum zirconium oxygen electrolyte. For example, the battery can be a used battery.

[0055] This invention does not impose any particular limitation on the positive electrode sheet, which can be obtained from the dismantling of waste batteries;

[0056] Understandably, before recycling the positive electrode material in the battery, the battery needs to be pre-treated. Pre-treatment includes discharging and disassembling the battery, and separating it according to the positive electrode, negative electrode, separator, aluminum-plastic film (aluminum shell), and electrolyte.

[0057] In some embodiments of the present invention, during the lithium ion leaching treatment, when the temperature is 30~60℃, the time is 2~3h, and the pH is 1.5~3.0, the carboxyl groups in citric acid form soluble complexes with the lithium ions in lithium iron phosphate, while the iron ions and phosphate ions are inhibited from dissolving due to the acidic environment, which allows for more rapid selective leaching of lithium ions.

[0058] In some embodiments, when using citric acid to perform lithium-ion leaching treatment on the positive electrode active layer powder, hydrogen peroxide solution is also used. The hydrogen peroxide solution can remove Fe from the lithium iron phosphate. 2+ Oxidized to Fe 3+ This promotes the release of lithium ions from lithium iron phosphate.

[0059] In some embodiments of the present invention, during the iron-phosphorus leaching treatment, when the concentration of sulfuric acid is 0.5~1.0 mol / L, the temperature is 80~90℃, and the time is 2~4h, the iron phosphate in the positive electrode active residue can react more quickly with sulfuric acid and be completely converted into an iron-phosphorus mixture while saving costs, and lanthanum zirconate is retained due to its acid resistance; in some embodiments, the solid-liquid ratio of sulfuric acid to positive electrode active residue is 1 (g): 10 (mL);

[0060] In some embodiments of the present invention, when the pH is 11-13, the temperature is 145-155°C, and the time is 10-12 hours during the hydrothermal reaction, the iron ions in the iron-phosphorus mixture can be completely converted into iron(III) oxide while saving energy, thereby improving the recovery rate of iron.

[0061] In some embodiments of the present invention, during the alkali dissolution treatment, when the temperature is 490~510℃ and the time is 2~3h, the lanthanum zirconate lattice in the lanthanum zirconate residue can be destroyed while saving energy, so that zirconium ions and lanthanate ions can react more quickly with sodium hydroxide to generate Na2ZrO3 and NaLaO2.

[0062] In some embodiments, alkali dissolution treatment can be performed using sodium hydroxide solution and lanthanum zirconate residue, wherein the sodium hydroxide solution contains 40% sodium hydroxide by mass.

[0063] In some embodiments, during the alkali dissolution treatment, the mass ratio of sodium hydroxide solution to lanthanum zirconate residue is 2:1.

[0064] In some embodiments of the present invention, the separation process includes:

[0065] A positive electrode fragment solution was obtained by alternately subjecting the solution containing the positive electrode sheet to a first ultrasonic treatment and a second ultrasonic treatment.

[0066] The positive electrode fragment solution is sieved to obtain the positive electrode current collector and the positive electrode active slurry;

[0067] The positive electrode active slurry was calcined to obtain positive electrode active layer powder;

[0068] The temperature of the first ultrasonic treatment is 60~80℃, and the temperature of the second ultrasonic treatment is -10~0℃.

[0069] Typically, a positive electrode sheet includes a positive current collector, a positive active material, a binder, and a conductive agent. Specifically, the solution containing the positive electrode sheet is first subjected to a first ultrasonic treatment at 60~80℃, followed by a second ultrasonic treatment at -10~0℃. This first and second ultrasonic treatments are repeated multiple times. The alternating hot and cold ultrasonic treatment can break down the adhesiveness of the binder in the positive electrode sheet. The high temperature of the first ultrasonic treatment and the low temperature of the second ultrasonic treatment create a stress difference between the positive active material and the positive current collector, causing them to separate and obtain a positive electrode fragment solution. The positive electrode fragment solution is then sieved to obtain a positive current collector and a positive active slurry. The positive active slurry contains the positive active material and a small amount of conductive agent and binder. The positive active slurry is then calcined to remove residual conductive agent and binder, resulting in a positive active layer powder.

[0070] This invention employs a method of alternating hot and cold ultrasonic treatment of the positive electrode sheet. On the one hand, it can efficiently separate the positive electrode current collector and the positive electrode active material in the positive electrode sheet, reducing the damage to the positive electrode sheet caused by mechanical processing in existing technologies and improving the recovery rate of the positive electrode current collector. On the other hand, it can inhibit the agglomeration of the positive electrode active material, ensuring the leaching efficiency of lithium ions in the subsequent lithium ion leaching process. Calcination of the positive electrode active slurry can remove residual conductive agents and binders in the positive electrode active slurry, thereby improving the purity of lithium iron phosphate and lithium lanthanum zirconium oxide electrolyte in the positive electrode active layer powder.

[0071] In some embodiments, the solution including the positive electrode can be subjected to the first ultrasonic treatment and the second ultrasonic treatment 3 to 5 times.

[0072] The present invention does not impose any particular limitation on the conductive agent. The conductive agent can be any conductive agent commonly used in the art. For example, the conductive agent can be Super P Li.

[0073] The present invention does not impose any particular limitation on the adhesive, which can be any adhesive commonly used in the art. For example, the adhesive can be polyvinylidene fluoride (PVDF).

[0074] The present invention does not impose any particular limitation on the positive electrode current collector. The positive electrode current collector can be any positive electrode current collector commonly used in the art. For example, the positive electrode current collector can be aluminum foil.

[0075] In some implementations, when the positive current collector is aluminum foil, the separation rate of the aluminum foil can be ≥98.5%.

[0076] In some embodiments, when the positive current collector is aluminum foil, the separation process of the positive electrode sheet of the present invention may include the following steps:

[0077] Cut the positive electrode sheet into 5×5cm fragments, or mechanically crush it into positive electrode sheet particles with a size of 1~3cm; put the positive electrode sheet fragments into a hot water bath at 60~80℃, introduce compressed air for bubbling, and turn on the ultrasonic generator for the first ultrasonic treatment. Then switch to a cold water bath at -10~0℃ and repeat the above steps for the second ultrasonic treatment, alternating 3~5 times to obtain a positive electrode fragment solution.

[0078] The positive electrode fragment solution is separated by sieve to obtain a positive electrode current collector and a positive electrode active slurry; the positive electrode current collector is directly dried and then recovered; the positive electrode active slurry is dehydrated by centrifugation or pressure filtration and then calcined to obtain positive electrode active layer powder;

[0079] In the hot water tank, the solid-liquid ratio of the positive electrode fragments to the water is 1 (g): 10 (mL);

[0080] The positive electrode active material in the positive electrode active slurry is in particulate form with a particle size of 1~10μm.

[0081] In some embodiments of the present invention, the first ultrasonic treatment and / or the second ultrasonic treatment last for 30 to 45 minutes, the frequency is 20 to 40 kHz, and the power density is 0.5 to 2 W / cm². 2 At this time, the adhesiveness of the binder can be completely destroyed, allowing the positive electrode active material to separate from the positive electrode current collector more quickly;

[0082] In some embodiments of the present invention, during the calcination process, when the temperature is 300~500℃ and the time is 1~2h, the conductive agent and binder in the positive electrode active material can be completely removed, resulting in higher purity of lithium iron phosphate and lithium lanthanum zirconium oxygen electrolyte in the positive electrode active layer powder.

[0083] Since only ions are allowed to communicate within the H-type electrolytic cell, in some embodiments of the present invention, when a lithium-containing solution is electrolyzed in an H-type electrolytic cell, a lithium-rich solution can be obtained, further improving the lithium recovery rate.

[0084] In some embodiments of the present invention, the H-type electrolytic cell includes a cathode cell, a proton exchange membrane, and an anode cell connected in sequence; the anode cell contains a lithium-containing solution, and the cathode cell contains a lithium replenishment solution. Because the proton exchange membrane has selective permeability, during electrolysis, an electrolytic reaction occurs in the anode cell, releasing oxygen, and the Li in the anode cell... + Under the influence of an electric field, the protons migrate through the proton exchange membrane to the cathode cell, where they combine with the hydroxide ions generated by reduction in the cathode cell to form LiOH. Simultaneously, the Li in the cathode cell... + The concentration is kept stable to achieve efficient enrichment of lithium ions, resulting in a lithium-rich solution; furthermore, the lithium-rich solution in the cathode cell can be recrystallized for recycling and reuse.

[0085] In some embodiments of the present invention, the volume ratio of lithium-containing solution to lithium replenishment solution is 1:(1.5~2.0), and the electrolysis temperature is 30~60°C, which can increase the rate of electrolysis of lithium-containing solution, so that lithium ions in the anode cell can quickly migrate to the cathode cell.

[0086] In some embodiments, the lithium replenishment solution may be a LiOH solution and / or a LiCl solution, and the concentration of the LiOH solution and / or LiCl solution may be 0.1 mol / L.

[0087] In some embodiments of the present invention, the process further includes:

[0088] The iron-phosphorus mixture was extracted with tributyl phosphate (TBP) to remove zirconium ions, followed by treatment to remove heavy metal ions, aluminum, calcium, and organic residues; the pH of the extraction treatment was 1.5~3.0.

[0089] In some embodiments, when sulfuric acid is used to leach iron and phosphorus from the positive electrode active layer residue, a small amount of lanthanum zirconate in the residue reacts with sulfuric acid, resulting in a small amount of zirconium ions (Zr) remaining in the iron-phosphorus mixture. 4+ Specifically, TBP, as a neutral extractant, reacts with Zr under acidic conditions. 4+ A hydrophobic complex is formed, followed by extraction to remove Zr-containing compounds. 4+ Hydrophobic complexes.

[0090] During the extraction process, an acidic environment with a pH of 1.5 to 3.0 can inhibit the hydrolysis of iron ions in the iron-phosphorus mixture, resulting in higher purity of the iron(III) oxide obtained in the subsequent hydrothermal treatment. In some embodiments, the iron-phosphorus mixture also contains small amounts of heavy metal ions, aluminum ions, calcium ions, and organic residues. Removing zirconium ions, heavy metal ions, aluminum ions, calcium ions, and organic residues can improve the purity of the iron-phosphorus mixture and further enhance the recovery rate of iron and phosphorus elements.

[0091] In some implementations, sodium sulfide precipitation can be used to remove heavy metal ions, ammonium fluoride complexation precipitation can be used to remove aluminum and calcium ions, and activated carbon adsorption can be used to remove organic residues.

[0092] In some embodiments, after extraction treatment, the residual zirconium ions in the iron-phosphorus mixture can be <50 ppm.

[0093] In some embodiments of the present invention, the process further includes washing the lanthanum zirconate residue with oxalic acid before the alkali dissolution treatment; the concentration of oxalic acid is 0.1~0.2 mol / L.

[0094] Specifically, a small amount of iron ions are present in the lanthanum zirconate residue. When the lanthanum zirconate residue is washed with oxalic acid, the carboxyl groups in the oxalic acid can form stable complexes with the iron ions.

[0095] Washing with oxalic acid at a concentration of 0.1~0.2 mol / L can effectively remove iron ions adhering to the surface of lanthanum zirconate residue, improve the purity of lanthanum zirconate, and reduce the interference of iron ions on alkaline dissolution treatment.

[0096] In some embodiments, after washing the lanthanum zirconate residue with oxalic acid, the mass percentage of iron in the lanthanum zirconate residue can be <0.01%.

[0097] In some embodiments of the present invention, a post-processing is further included after the hydrothermal reaction, which includes: magnetic separation of the product obtained from the hydrothermal reaction to obtain ferric oxide and phosphate solution.

[0098] Phosphate is obtained by adjusting the pH of the phosphate solution.

[0099] Iron(III) oxide is magnetic, and magnetic separation can quickly and efficiently separate it from phosphate solution, improving the purity of the phosphate solution. After adjusting the pH of the phosphate solution to crystallize it into phosphate, it can be directly used as a raw material in the phosphate chemical industry.

[0100] In some embodiments, the phosphate solution can be a sodium phosphate solution, and the phosphate can be sodium phosphate dodecahydrate;

[0101] In some implementations, the pH of the phosphate solution can be 10.

[0102] In some embodiments, the recycling of the positive electrode material in the battery of the present invention may include the following steps:

[0103] First, the positive electrode sheet is separated to obtain the positive electrode current collector and the positive electrode active layer powder;

[0104] Next, the positive electrode active material powder, citric acid and hydrogen peroxide solution are placed in a warm water bath in a certain weight ratio and stirred thoroughly to carry out lithium ion leaching treatment, resulting in a first mixture including a lithium-containing solution and positive electrode active layer residue. The first mixture is filtered to obtain a lithium-containing solution and positive electrode active layer residue. The positive electrode active layer residue is washed with deionized water 2-3 times and then placed in an 80°C oven for drying.

[0105] The lithium-containing solution was then electrolyzed using an H-type electrolytic cell to obtain a lithium-rich solution in the cathode cell. The lithium-rich solution can be recrystallized and recycled.

[0106] The positive electrode active layer residue was baked at 500℃ for 2-3 hours, then crushed into positive electrode active layer particles to initially dissociate the iron phosphate and lanthanum zirconate in the residue. Next, under stirring, sulfuric acid was used to leach the positive electrode active layer particles with iron and phosphorus, yielding a second mixture comprising an iron-phosphorus mixture and lanthanum zirconate residue. This second mixture was filtered to obtain the iron-phosphorus mixture and lanthanum zirconate residue. Tributyl phosphate was then added to the iron-phosphorus mixture for extraction.

[0107] Then, the iron-phosphorus mixture is subjected to treatment to remove heavy metal ions, aluminum, calcium and organic residues to obtain a purified iron-phosphorus mixture.

[0108] The pH of the purified iron-phosphorus mixture was adjusted to 11 using sodium hydroxide solution to obtain an alkaline iron-phosphorus mixture. The alkaline iron-phosphorus mixture was placed in a high-pressure reactor for hydrothermal reaction to obtain iron oxide particles and sodium phosphate solution. The iron oxide was separated by magnetic separation using a magnet, and the pH of the sodium phosphate solution was adjusted. The sodium phosphate solution crystallized into sodium phosphate dodecahydrate.

[0109] Finally, the lanthanum zirconate residue was washed with oxalic acid, then washed 2-3 times with deionized water. After drying, sodium hydroxide solution was added to the lanthanum zirconate residue and it was ground to mix the sodium hydroxide solution with the lanthanum zirconate residue evenly, resulting in alkaline lanthanum zirconate residue. The alkaline lanthanum zirconate residue was then subjected to alkali dissolution treatment to obtain NaLaO2 and Na2ZrO3.

[0110] The concentration of citric acid is 1 mol / L, and the mass percentage of hydrogen peroxide in the hydrogen peroxide solution is 30%.

[0111] The mass ratio of the positive electrode active material powder, citric acid, and hydrogen peroxide solution is 1:3:0.2.

[0112] The particle size of the positive electrode active layer particles is 100~200 mesh (150~75μm).

[0113] Sodium hydroxide solution can be obtained by electrolysis using the H-type electrolytic cell described above. Specifically, sodium chloride solution is placed in both the anode and cathode cells of the H-type electrolytic cell, and then electrolysis is carried out to obtain sodium hydroxide solution in the anode cell.

[0114] The sodium hydroxide solution contains 40% sodium hydroxide by mass.

[0115] In some embodiments of the present invention, citric acid is prepared by a method comprising the following steps:

[0116] Heat treatment of lemons yields a gaseous acidic substance;

[0117] Crude citric acid is obtained by condensing gaseous acidic substances.

[0118] Crude citric acid was subjected to distillation and adsorption treatments to obtain citric acid.

[0119] Specifically, the lemons are first heat-treated, causing the acidic components, such as citric acid, in the lemons to volatilize or decompose into gaseous acidic substances. Then, the gaseous acidic substances are condensed to obtain crude liquid natural citric acid. Finally, the crude citric acid is distilled to remove impurities with different boiling points, and then adsorption treatment is used to remove odors and impurities, ultimately yielding pure citric acid.

[0120] This method for preparing citric acid utilizes the natural citric acid in lemon fruit. High-purity citric acid is obtained through pyrolysis, condensation, and purification processes. Citric acid is biodegradable, and its use in place of traditional chemical acids (such as sulfuric acid and hydrochloric acid) can reduce hazardous waste emissions.

[0121] In some embodiments of the present invention, when the heat treatment is carried out at a temperature of 100~150°C for 6~12 hours, citric acid can be extracted from lemons under mild conditions, and the yield of citric acid is improved.

[0122] In some embodiments of the present invention, during the adsorption treatment, when the temperature is 95~105℃ and the time is 15~30min, impurities and odors in the crude citric acid can be completely removed, thereby improving the purity of citric acid; in some embodiments, activated carbon can be used for adsorption treatment.

[0123] In some embodiments, the citric acid of the present invention can be prepared by a method comprising the following steps:

[0124] Waste lemons or green lemons are sliced, dried, chopped or crushed into granules, and placed in a three-way flask. An appropriate amount of water is added, and the temperature is gradually increased to produce a gaseous acidic substance. The gaseous acidic substance is then passed through a pipe into a condenser, and after multi-stage cooling, crude liquid citric acid is obtained. The crude citric acid is then distilled and adsorbed by activated carbon to finally obtain citric acid, which is then concentrated to obtain citric acid with a concentration of 1 mol / L.

[0125] The solid-liquid ratio of lemon to water is 5 (g): 1 (mL).

[0126] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0127] Example 1

[0128] The battery in this embodiment is a spent semi-solid lithium iron phosphate battery, and the recycling of the positive electrode material includes the following steps:

[0129] (1) Pretreatment

[0130] Waste semi-solid lithium iron phosphate batteries are discharged and disassembled, and then separated into positive electrode plates, negative electrode plates, separators, aluminum-plastic films (aluminum shells), and electrolytes.

[0131] (2) Positive electrode current collector separation

[0132] The positive current collector of the positive electrode is aluminum foil. The positive electrode is mechanically crushed into particles with a size of 1-3 cm. The particles are then placed in a hot water bath at 80°C to obtain a solution containing the positive electrode. In the hot water bath, the solid-liquid ratio of the positive electrode particles to water is 1 (g):10 (mL), and the solution is prepared at a concentration of 0.5 m... 3 Compressed air is bubbled into the hot water tank at a rate of / h, and the ultrasonic generator is turned on, with the frequency set to 30kHz and the power density to 2W / cm². 2 The solution containing the positive electrode was subjected to a first ultrasonic treatment for 30 minutes; subsequently, a cold water bath at -10°C was used to obtain a solution containing the positive electrode. In the cold water bath, the solid-liquid ratio of the positive electrode particles to water was 1 (g):10 (mL), and the solution was prepared at a concentration of 0.5 m... 3 Compressed air is bubbled into the hot water tank at a rate of / h, and the ultrasonic generator is turned on, with the frequency set to 30kHz and the power density to 2W / cm². 2 The process takes 30 minutes. The solution containing the positive electrode is subjected to a second ultrasonic treatment. The steps of the first and second ultrasonic treatments are repeated and alternated 3 times to obtain a positive electrode fragment solution.

[0133] The positive electrode fragment solution was separated using a 200-mesh sieve to obtain aluminum foil and positive electrode active slurry. The aluminum foil was dried and then recycled. The positive electrode active slurry was centrifuged and then calcined at 350℃ for 2 hours to obtain positive electrode active layer powder. The main components of the positive electrode active layer powder are lithium iron phosphate and lithium lanthanum zirconium oxide electrolyte.

[0134] (3) Selective leaching of lithium

[0135] a) After slicing and drying lemons, crush them into granules and place them in a three-way flask. Add water to the three-way flask at a solid-liquid ratio of lemon to water of 5 (g): 1 (mL). Then heat the three-way flask at 120℃ for 12 hours to produce a gaseous acidic substance. Pass the gaseous acidic substance through a pipe into a condenser and after multi-stage cooling, obtain crude liquid citric acid. Distill the crude liquid citric acid and perform activated carbon adsorption treatment at 100℃ for 30 minutes to obtain citric acid. After concentration treatment, obtain citric acid with a concentration of 1 mol / L.

[0136] b) The positive electrode active layer powder, citric acid (concentration of 1 mol / L) and hydrogen peroxide solution (mass percentage of hydrogen peroxide of 30%) were mixed and subjected to lithium ion leaching treatment. The mass ratio of positive electrode active layer powder:citric acid:hydrogen peroxide solution was 1:3:0.2. The lithium ion leaching treatment temperature was 60℃ and the time was 3h. The mixture was stirred thoroughly to obtain a first mixture including lithium-containing solution and positive electrode active layer residue. The first mixture was filtered to obtain lithium-containing solution and positive electrode active layer residue. The positive electrode active layer residue was washed three times with deionized water and then placed in an oven at 80℃ for drying treatment. The main components of the positive electrode active layer residue were FePO4 and lanthanum zirconate.

[0137] c) The lithium-containing solution was electrolyzed using an H-type electrolytic cell. In the H-type electrolytic cell, a proton exchange membrane was used to separate the anode and cathode cells. The lithium-containing solution was placed in the anode cell, and the cathode cell contained a 0.1 mol / L LiOH solution. The volume ratio of the liquids in the anode cell to the cathode cell was 1:1.5. The H-type electrolytic cell was placed in a 60°C warm water bath to electrolyze the lithium-containing solution. Finally, a lithium-rich solution was obtained in the cathode cell.

[0138] (4) Separation of iron, phosphorus, lanthanum and zirconium elements

[0139] a) The positive electrode active layer residue was baked at 500℃ for 2 hours. The baked positive electrode active layer residue was crushed into positive electrode active layer particles of 150 mesh. Then, the positive electrode active layer particles were subjected to iron-phosphorus leaching treatment with 0.5 mol / L sulfuric acid under stirring. The solid-liquid ratio of positive electrode active layer particles to sulfuric acid was 1 (g):10 (mL). The iron-phosphorus leaching treatment temperature was 80℃ and the time was 4 hours. A second mixture including iron-phosphorus mixture and lanthanum zirconate residue was obtained. The second mixture was filtered to obtain iron-phosphorus mixture and lanthanum zirconate residue.

[0140] b) Adjust the pH of the iron-phosphorus mixture to 1.5, add tributyl phosphate (TBP) to the iron-phosphorus mixture to extract zirconium ions, then use sodium sulfide precipitation to remove heavy metal ions from the iron-phosphorus mixture, use ammonium fluoride complexation precipitation to remove residual aluminum and calcium ions from the solution, and use activated carbon to adsorb organic residues from the solution to obtain a purified iron-phosphorus mixture.

[0141] c) The pH of the purified iron-phosphorus mixture was adjusted to 11 using sodium hydroxide to obtain an alkaline iron-phosphorus mixture. The alkaline iron-phosphorus mixture was placed in a high-pressure reactor for hydrothermal reaction at 150°C for 10 hours to obtain Fe3O4 particles and Na3PO4 solution. The Fe3O4 particles were separated using a magnet. The pH of the Na3PO4 solution was adjusted to 10 and then crystallized to obtain Na3PO4·12H2O.

[0142] d) The lanthanum zirconate residue was washed with 0.1 mol / L oxalic acid, and then washed 2-3 times with deionized water. After drying, the residue was added to NaOH solution and ground. The mass ratio of lanthanum zirconate residue to NaOH solution was 1:2, and the mass percentage of NaOH in the NaOH solution was 40%. Alkaline lanthanum zirconate residue was obtained. The alkaline lanthanum zirconate residue was then subjected to alkaline dissolution treatment at 500℃ for 2 hours to obtain NaLaO2 and Na2ZrO3.

[0143] Comparative Example 1

[0144] The battery used in this comparative example is a spent semi-solid lithium iron phosphate battery, and the recycling of the positive electrode material includes the following steps:

[0145] (1) Pretreatment

[0146] Waste semi-solid lithium iron phosphate batteries are discharged and disassembled, and then separated into positive electrode plates, negative electrode plates, separators, aluminum-plastic films (aluminum shells), and electrolytes.

[0147] (2) Positive electrode breakage

[0148] The positive current collector of the positive electrode is aluminum foil. The positive electrode is mechanically crushed into positive electrode particles with a size of 1~3cm, without the aluminum foil separation step.

[0149] (3) Strong acid leaching treatment

[0150] The positive electrode particles were added to a sulfuric acid solution with a concentration of 2 mol / L and stirred for leaching treatment. The solid-liquid ratio of the positive electrode particles to the sulfuric acid solution was 1 (g): 8 (mL). The leaching treatment temperature was 90℃ and the time was 4h. A first mixture including lithium ions, iron ions, phosphate ions and lanthanum zirconate was obtained. The first mixture was filtered to obtain a first liquid including lithium ions, iron ions and phosphate ions and lanthanum zirconate residue.

[0151] (4) Treatment of Lanthanum Zirconate Residue

[0152] The lanthanum zirconate residue was washed with 0.1 mol / L oxalic acid, then washed 2-3 times with deionized water. After drying, the residue was added to NaOH solution and ground. The mass ratio of lanthanum zirconate residue to NaOH solution was 1:2, and the mass percentage of NaOH in the NaOH solution was 40%. This yielded alkaline lanthanum zirconate residue. The alkaline lanthanum zirconate residue was then subjected to alkaline dissolution treatment at 500℃ for 2 hours to obtain NaLaO2 and Na2ZrO3.

[0153] (5) Separation of lithium, iron and phosphorus elements

[0154] Add the first liquid in (3) and P204 extractant in a volume ratio of 1:1 into the separatory funnel, tighten the stopcock of the separatory funnel, place the separatory funnel into a constant temperature water bath shaker, set the temperature to 2±2℃, the shaking frequency to 200r / min, shake for 30min, after shaking is finished, take out the separatory funnel, let it stand to separate into layers, the separation time is 30min, slowly open the stopcock of the separatory funnel, first release the lower layer liquid, and then pour out the upper layer liquid, in which the lower layer liquid contains lithium ions and phosphate ions, and the upper layer liquid contains iron ions;

[0155] Slowly add 1 mol / L sodium carbonate solution to the lower layer until the pH of the upper layer reaches 8.0. After the addition is complete, let it stand at room temperature for 2 hours to obtain a second mixture containing sodium phosphate and lithium carbonate precipitate. Filter the second mixture to obtain a second liquid containing sodium phosphate and crude lithium carbonate. Wash and dry the crude lithium carbonate to obtain lithium carbonate.

[0156] Add 1 mol / L hydrochloric acid dropwise to the second liquid to adjust the pH to 5.0, then slowly add 2 mol / L calcium chloride solution. After the addition is complete, let it stand at room temperature for 2 hours to obtain a third mixture including waste liquid and calcium phosphate precipitate. Filter the third mixture to obtain crude calcium phosphate. Collect the waste liquid in a waste liquid tank, wash and dry the crude calcium phosphate to obtain calcium phosphate.

[0157] Performance testing

[0158] Recovery rate test of lithium, iron, phosphorus, lanthanum and zirconium elements

[0159] In Example 1, the contents of lithium in the lithium-rich solution, iron in Fe3O4, phosphorus in Na3PO4·12H2O, lanthanum in NaLaO2, and zirconium in Na2ZrO3 were determined using ICP. In Comparative Example 1, the contents of lanthanum in NaLaO2, zirconium in Na2ZrO3, iron in the upper layer, lithium in lithium carbonate, and phosphorus in calcium phosphate were determined using ICP. The recovery rate of an element is calculated as (content of the element after recovery ÷ content of the element before recovery) × 100%. The test results are shown in Table 1.

[0160] Table 1

[0161]

[0162] As can be seen from Table 1, in Example 1, the recovery rates of lithium, iron, phosphorus, lanthanum, and zirconium in the battery cathode material are all higher than those in Comparative Example 1. This indicates that the recovery method of the present invention can efficiently recover lithium, iron, phosphorus, lanthanum, and zirconium in the battery cathode material. The reason is that the present invention first uses citric acid to selectively leach lithium from the battery cathode material under mild conditions, and then recovers iron, phosphorus, lanthanum, and zirconium stepwise, avoiding cross-contamination of lithium with other elements. Furthermore, the citric acid used in the recovery method of the present invention is a biomass acid that can be degraded and recycled. Therefore, the recovery method of the present invention also has certain economic and environmental benefits.

[0163] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and various modifications and changes may be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A method for recycling positive electrode material in a battery, characterized in that, Includes the following steps: The positive electrode sheet is separated to obtain a positive electrode current collector and a positive electrode active layer powder, wherein the positive electrode active layer powder includes lithium iron phosphate and lithium lanthanum zirconium oxygen electrolyte. The positive electrode active layer powder was subjected to lithium ion leaching treatment with citric acid to obtain a lithium-containing solution and positive electrode active layer residue. The positive electrode active layer residue was subjected to iron-phosphorus leaching treatment with sulfuric acid to obtain an iron-phosphorus mixed solution and lanthanum zirconate residue. The iron-phosphorus mixture was subjected to a hydrothermal reaction to obtain iron(III) oxide. The lanthanum zirconate residue was subjected to alkaline dissolution treatment with sodium hydroxide to obtain NaLaO2 and Na2ZrO3.

2. The recycling method according to claim 1, characterized in that, In the lithium-ion leaching treatment, the temperature is 30~60℃, the time is 2~3h, and the pH is 1.5~3.0; and / or, In the iron-phosphorus leaching treatment, the concentration of sulfuric acid is 0.5~1.0 mol / L, the temperature is 80~90℃, and the time is 2~4 h; and / or, In the hydrothermal reaction, the pH is 11-13, the temperature is 145-155℃, and the time is 10-12 hours; and / or, In the alkaline dissolution treatment, the temperature is 490~510℃ and the time is 2~3h.

3. The recycling method according to claim 1 or 2, characterized in that, The separation process includes: A positive electrode fragment solution is obtained by alternately subjecting the solution containing the positive electrode sheet to a first ultrasonic treatment and a second ultrasonic treatment. The positive electrode fragment solution is sieved to obtain the positive electrode current collector and the positive electrode active slurry; The positive electrode active slurry is calcined to obtain the positive electrode active layer powder; The temperature of the first ultrasonic treatment is 60~80℃, and the temperature of the second ultrasonic treatment is -10~0℃.

4. The recycling method according to claim 3, characterized in that, In the first and / or second ultrasonic treatments, the time is 30-45 minutes, the frequency is 20-40 kHz, and the power density is 0.5-2 W / cm². 2 ; and / or, The roasting process is carried out at a temperature of 300-500℃ for 1-2 hours.

5. The recycling method according to claim 1, characterized in that, It also includes electrolyzing the lithium-containing solution in an H-type electrolytic cell to obtain a lithium-rich solution.

6. The recycling method according to claim 5, characterized in that, The H-type electrolytic cell includes a cathode cell, a proton exchange membrane, and an anode cell connected in sequence. The anode cell contains the lithium-containing solution, the cathode cell contains the lithium replenishment solution, the volume ratio of the lithium-containing solution to the lithium replenishment solution is 1:(1.5~2.0), and the electrolysis temperature is 30~60℃.

7. The recycling method according to claim 1, characterized in that, The process also includes the following steps prior to the hydrothermal reaction: The iron-phosphorus mixture was extracted with tributyl phosphate to remove zirconium ions, followed by treatment to remove heavy metal ions, aluminum, calcium and organic residues. The pH of the extraction process is 1.5 to 3.

0.

8. The recycling method according to claim 1, characterized in that, Prior to the alkaline dissolution treatment, the process further includes washing the lanthanum zirconate residue with oxalic acid. The concentration of oxalic acid is 0.1~0.2 mol / L.

9. The recycling method according to claim 1, characterized in that, The hydrothermal reaction is followed by a post-processing step, which includes: The products obtained from the hydrothermal reaction were magnetically separated to yield ferric oxide and a phosphate solution. The pH of the phosphate solution is adjusted to obtain phosphate.

10. The recycling method according to claim 1, characterized in that, The citric acid is prepared by a method comprising the following steps: Heat treatment of lemons yields a gaseous acidic substance; The gaseous acidic substance is condensed to obtain crude citric acid. The crude citric acid was subjected to distillation and adsorption treatments in sequence to obtain the citric acid. In the heat treatment, the temperature is 100~150℃ and the time is 6~12h; and / or, In the adsorption treatment, the temperature is 95~105℃ and the time is 15~30min.

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