Method for preparing lithium-rich lithium iron oxide from waste lithium iron phosphate, lithium-rich lithium iron oxide, lithium supplement material and modified lithium ion battery positive electrode material

Abstract

This invention belongs to the technical field of waste lithium iron phosphate recycling, and discloses a method for preparing lithium-rich lithium ferrite from waste lithium iron phosphate, as well as lithium-rich lithium ferrite, lithium replenishment materials, and modified lithium-ion battery cathode materials. The preparation method of lithium-rich lithium ferrite includes sequentially subjecting waste lithium iron phosphate to impurity removal, hydrochloric acid solution purification, mixed extractant extraction, organic phase washing and back-extraction, lithium iron precipitation, drying and calcination, and sintering. The mixed extractant comprises 50-80 wt% tributyl phosphate, 10-40 wt% light petroleum, and 1-10 wt% calcium chloride solution. Through the synergistic effect of each processing step, effective separation of lithium, iron, and lithium elements is achieved from waste lithium iron phosphate, yielding high-purity lithium-rich lithium ferrite. This lithium-rich lithium ferrite has high irreversible capacity, is an excellent lithium replenishment material, has high added value, and has broad application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of recycling waste lithium iron phosphate, and in particular relates to a method for preparing lithium-rich lithium iron oxide from waste lithium iron phosphate, lithium-rich lithium iron oxide, lithium supplement material and modified lithium ion battery positive electrode material. Background Art

[0002] With the adjustment of my country's industrialization and energy structure, and with the support of multiple policies, the new energy field of lithium-ion batteries has entered a stage of rapid development. However, with the rapid development of the industry, a large amount of lithium-ion battery solid waste has caused a great impact on the environment. Therefore, recycling and reprocessing of waste lithium iron phosphate and lithium iron-containing waste is one of the important directions in the development of lithium-ion battery technology.

[0003] The research and development of recycling technology for solid waste of lithium-ion batteries has been carried out for nearly 20 years. Among them, the research on recycling solid waste of lithium-ion batteries for the preparation of lithium supplement additives has been a hot topic in the field of lithium batteries in recent years. In the existing technology, there is a method of adding a certain amount of sodium carbonate auxiliary material and lithium carbonate to supplement the volatilization of high-temperature lithium to the powder of the positive electrode material of waste lithium iron phosphate batteries, and recovering lithium iron phosphate through ball milling, solid phase sintering, pulping filtration and product collection, so that all iron is precipitated in the form of iron phosphate and lithium is dissolved in the leachate in the form of lithium dihydrogen phosphate to achieve the recovery of lithium iron phosphate; there is also a method of using a highly selective extractant of iron ions and aluminum ions to remove impurities to obtain a phosphoric acid solution, and additionally adding an iron source to recover the iron phosphate precipitate.

[0004] However, the products recovered by the methods in the prior art have low purity, low reversible capacity, low added value, and narrow application areas. It is impossible to continuously form a complete industrial chain for waste recycling and high-value product sales. The scale is small, which is not conducive to the sustainable development of lithium-ion battery solid waste recycling. Summary of the invention

[0005] In order to achieve effective treatment of lithium iron phosphate-containing solid waste and obtain high-purity lithium ferrite with high irreversible capacity as a lithium supplement material, the present invention provides a method for preparing lithium-rich lithium ferrite from waste lithium iron phosphate, lithium-rich lithium ferrite, lithium supplement material and modified lithium-ion battery positive electrode material.

[0006] In a first aspect, the present invention provides a method for preparing lithium-rich lithium iron oxide from waste lithium iron phosphate, the method comprising the following steps:

[0007] S1. removing impurities from waste lithium iron phosphate to obtain black material whose main component is lithium iron phosphorus;

[0008] S2, dissolving the black material with hydrochloric acid solution and then separating the solid and liquid, determining the contents of lithium and iron in the liquid phase and adding a lithium source and / or an iron source to adjust the lithium-iron molar ratio in the solution to obtain a lithium-iron solution;

[0009] S3, extracting the lithium iron solution with a mixed extractant to separate an organic phase and an aqueous phase; the mixed extractant comprises 50-80wt% of tributyl phosphate, 10-40wt% of light petroleum and 1-10wt% of calcium chloride solution;

[0010] S4, washing and stripping the organic phase to prepare a stripping solution containing lithium iron;

[0011] S5, determining the contents of lithium and iron in the stripping solution, and adding a lithium source and an alkaline carbonate to adjust the lithium-iron molar ratio and pH value in the stripping solution to precipitate the lithium compound and the iron compound to obtain a turbid solution;

[0012] S6, performing solid-liquid separation on the turbid liquid, and then drying, calcining and sintering the obtained solid phase product to obtain the lithium-rich lithium ferrite.

[0013] In some specific embodiments, in step S1, the waste lithium iron phosphate is selected from one or more of lithium iron phosphorus-containing minerals, waste generated during the production of lithium iron phosphate positive electrodes, waste lithium iron phosphate pole pieces generated during battery processing, and waste lithium iron phosphate batteries.

[0014] In some specific embodiments, in step S2, the concentration of the hydrochloric acid solution is 9-12 mol / L; the lithium source is selected from one or more of lithium chloride, lithium carbonate, lithium hydroxide, lithium nitrate and lithium oxide; the iron source is selected from one or more of ferric chloride, ferric oxide, ferrous oxide, ferric dioxide, ferric oxide and ferric oxide.

[0015] In some specific embodiments, in step S2, the molar ratio of lithium to iron in the lithium-iron solution is (0.5-1.5):1.

[0016] In some specific embodiments, in step S3, the light petroleum is selected from one or more of kerosene, diesel and gasoline.

[0017] In some specific embodiments, in step S3, the concentration of the calcium chloride solution is 5 to 8 mol / L.

[0018] In some specific embodiments, in step S3, the extraction temperature is 20-55° C., the extraction is a multi-stage extraction, and the number of extraction stages of the multi-stage extraction is 3-20.

[0019] In some specific embodiments, in step S4, the washing solution used for the washing includes 0.4-2 mol / L HCl and 2.0-5 mol / L CaCl2.

[0020] In some specific embodiments, in step S4, the stripping solution used in the stripping is a 0.5-5 mol / L ammonia solution.

[0021] In some specific embodiments, in step S5, the lithium source is selected from one or more of lithium chloride, lithium carbonate, lithium hydroxide, lithium nitrate and lithium oxide; the alkaline carbonate is selected from one or more of sodium carbonate, potassium carbonate and lithium carbonate; the molar ratio of lithium to iron in the turbid solution is (5.0-5.5):1.

[0022] In some specific embodiments, in step S6, the drying and calcining is carried out at a temperature of 200 to 400° C. and for a time of 5 to 20 hours.

[0023] In some specific embodiments, in step S6, the sintering is performed under the protection of an inert gas, and the sintering temperature is 500 to 900° C., and the sintering time is 5 to 20 hours.

[0024] In a second aspect, the present invention further provides a lithium-rich lithium iron oxide, wherein the lithium-rich lithium iron oxide is prepared by the above-mentioned method for preparing lithium-rich lithium iron oxide from waste lithium iron phosphate.

[0025] In a third aspect, the present invention further provides a lithium supplement material, wherein the lithium supplement material at least comprises lithium-rich lithium iron oxide prepared by the above method for preparing lithium-rich lithium iron oxide from waste lithium iron phosphate.

[0026] In a fourth aspect, the present invention further provides a modified lithium-ion battery positive electrode material, wherein the modified lithium-ion battery positive electrode material comprises a positive electrode material and the above-mentioned lithium supplement material.

[0027] Beneficial effects of the present invention:

[0028] The key to the present invention is to sequentially remove impurities from waste lithium iron phosphate, purify with hydrochloric acid solution, extract with mixed extractant, wash and reverse extract the organic phase, precipitate lithium iron, dry, calcine and sinter, wherein the extraction process uses a mixed extractant containing tributyl phosphate, light petroleum and calcium chloride solution, so that the phosphorus element enters the aqueous phase in the form of phosphate and is removed, thereby achieving effective separation of lithium, iron and phosphorus elements. The organic combination of the above steps makes the final lithium-rich lithium iron oxide high in purity and has a high irreversible capacity. It is an excellent lithium-rich lithium iron oxide lithium battery lithium supplement material with high added value. While achieving effective treatment of waste lithium iron phosphate products, it can also bring certain economic benefits and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A schematic diagram of the process for preparing lithium-rich lithium iron oxide provided in Example 1 of the present invention. DETAILED DESCRIPTION

[0030] Based on a deep understanding of the recycling technology of lithium battery solid waste, the inventors of this application, after in-depth and extensive research, creatively used tributyl phosphate, light petroleum and calcium chloride solution as a mixed extractant to extract the lithium iron solution, thereby achieving effective separation of lithium, iron and phosphorus elements, and obtaining high-purity lithium iron-rich lithium ferrate. Its irreversible capacity for the first charge and discharge reaches more than 437.1 mAh / g. It is a lithium-supplementing material with excellent performance, which realizes the effective recycling of lithium iron phosphate-containing solid waste and has good application prospects.

[0031] The present application provides a method for preparing lithium-rich lithium iron oxide from waste lithium iron phosphate, the method specifically comprising the following steps:

[0032] S1. removing impurities from waste lithium iron phosphate to obtain black material whose main component is lithium iron phosphorus;

[0033] S2, dissolving the black material with a hydrochloric acid solution and then separating the solid and the liquid, determining the contents of lithium and iron in the liquid phase, and adding a lithium source and / or an iron source to adjust the lithium-iron molar ratio in the solution to obtain a lithium-iron solution;

[0034] S3, extracting the lithium iron solution with a mixed extractant to separate an organic phase and an aqueous phase; the mixed extractant comprises 50-80wt% of tributyl phosphate, 10-40wt% of light petroleum and 1-10wt% of calcium chloride solution;

[0035] S4, washing and stripping the organic phase to obtain a stripping solution containing lithium iron;

[0036] S5, determining the contents of lithium and iron in the stripping solution, and adding a lithium source and an alkaline carbonate to adjust the lithium-iron molar ratio and pH value in the stripping solution to precipitate the lithium compound and the iron compound to obtain a turbid solution;

[0037] S6, performing solid-liquid separation on the turbid liquid, and then drying, calcining and sintering the obtained solid phase product to obtain the lithium-rich lithium ferrite.

[0038] In the present invention, waste lithium iron phosphate may be, but is not limited to, one or more of minerals containing lithium iron phosphorus, waste generated in the production process of lithium iron phosphate positive electrodes, waste lithium iron phosphate pole pieces generated in the battery processing process, and waste lithium iron phosphate batteries. Among them, waste lithium iron phosphate batteries may specifically be, but are not limited to, one or more of test batteries or waste lithium iron phosphate batteries discarded after use in the 3C, automotive, and energy storage fields. The use of the above-mentioned waste lithium iron phosphate as a raw material to prepare lithium-rich lithium iron oxide can achieve resource utilization of solid waste and achieve good economic benefits while solving environmental pollution problems.

[0039] In step S1, before impurities are removed, the solid waste containing lithium iron phosphate can be mechanically crushed by extrusion crushing, impact crushing, grinding crushing, splitting crushing, bending crushing and other methods, thereby increasing the specific surface area of ​​the solid waste, which is conducive to the subsequent impurity removal and achieves good results. Generally, the D50 particle size of the waste lithium iron phosphate after mechanical crushing is 0.05-2 μm.

[0040] In some specific embodiments, in step S1, the impurity removal method may be high-temperature sintering, specifically: in an air atmosphere, the waste lithium iron phosphate is sintered at 600-800° C. for 8-12 hours to remove impurities such as electrolyte, adhesive and conductive agent.

[0041] In step S2, a high concentration of hydrochloric acid solution is used to dissolve the lithium iron phosphorus and other components in the black material, and a small amount of insoluble matter is removed by solid-liquid separation methods such as filtration and centrifugation. In some specific embodiments, the concentration of the hydrochloric acid solution used is 9 to 12 mol / L, and more specifically, the concentration of the hydrochloric acid solution can be 9 mol / L, 9.5 mol / L, 10 mol / L, 10.5 mol / L, 11 mol / L, 11.5 mol / L, 12 mol / L or any value therebetween.

[0042] In step S2, by additionally adding a lithium source and / or an iron source, the molar ratio of lithium and iron in the liquid phase is adjusted to (0.5-1.5):1, which is conducive to the effective separation of lithium iron and phosphorus during the extraction process, and finally a high-purity lithium-rich ferrite can be prepared as an excellent lithium supplement material. In some specific embodiments, the lithium-iron molar ratio in the lithium-iron solution can be 0.5:1, 0.8:1, 1:1, 1.2:1, 1.4:1, 1.5:1 or any value therebetween. Preferably, when the lithium-iron molar ratio in the lithium-iron solution is (0.8-1.0):1, the separation effect of lithium iron and phosphorus during the extraction process is more ideal, and finally a higher purity lithium-rich ferrite can be prepared.

[0043] In some specific embodiments, in step S2, the lithium source may be, but is not limited to, one or more of lithium chloride, lithium carbonate, lithium hydroxide, lithium nitrate, and lithium oxide. The iron source may be, but is not limited to, one or more of ferric chloride, ferric oxide, ferrous oxide, ferric dioxide, ferric oxide, and ferric oxide.

[0044] In step S3, the mixed extractant used includes tributyl phosphate, light petroleum and calcium chloride solution. Wherein, the content of tributyl phosphate is 50-80wt%, specifically 50wt%, 53wt%, 55wt%, 60wt%, 68wt%, 70wt%, 72wt%, 76wt%, 80wt% or any value therebetween. Light petroleum can be selected as one or more of gasoline, diesel and kerosene. The content of light petroleum is 10-40wt%, specifically 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt% or any value therebetween. The use of calcium chloride solution can significantly improve the recovery rate of lithium and iron metal elements and the removal rate of phosphorus, thereby achieving effective separation of lithium, iron and phosphorus. The content of calcium chloride solution is 1-10wt%, specifically 1wt%, 2wt%, 4wt%, 6wt%, 8wt%, 10wt% or any value therebetween. The concentration of the calcium chloride solution can be 9-12 mol / L, specifically 9 mol / L, 9.5 mol / L, 10 mol / L, 10.3 mol / L, 10.5 mol / L, 11 mol / L, 11.5 mol / L, 12 mol / L or any value therebetween.

[0045] The mixed extractant provided by the present invention has an ideal extraction effect on the lithium iron solution, and can realize the effective separation of lithium, iron and phosphorus. It is worth noting that when the components and proportions in the mixed extractant exceed the range disclosed by the present invention, the effective separation of lithium, iron and phosphorus cannot be realized, so that the finally prepared lithium-rich lithium iron oxide still contains a large amount of impurities, and the product has low added value.

[0046] When the light petroleum in the mixed extractant is selected as kerosene and the concentration of the calcium chloride solution is 5 to 8 mol, the components in the mixed extractant work synergistically to achieve a perfect extraction effect. The Li recovery rate, Fe recovery rate and P removal rate of multi-stage extraction using the mixed extractant can be as high as 93.5%, 93.8% and 99.5%.

[0047] In the present invention, the extraction temperature in step S3 is preferably controlled at 20-55°C, so that the lithium- and iron-containing substances have good solubility in the organic phase, and the phosphorus-containing substances have extremely low solubility in the organic phase, which can achieve effective separation of lithium, iron and phosphorus elements. In some specific embodiments, the extraction temperature can be 20°C, 23°C, 25°C, 27°C, 30°C, 32°C, 41°C, 45°C, 50°C, 55°C or any value therebetween.

[0048] In some specific embodiments, the extraction is a multi-stage extraction, which can improve the recovery rate of lithium and iron. In some specific embodiments, the number of multi-stage extractions is 3 to 20. In each extraction, the mixed extractant is added to the aqueous phase obtained by each extraction and separation of the lithium iron solution, and the mixture is shaken and stirred vigorously for 25 to 50 minutes and then allowed to stand to separate the organic phase and the aqueous phase, collect the organic phase, and extract the aqueous phase for the next time; more specifically, the number of multi-stage extractions can be 3, 4, 5, 8, 10, 12, 15, 18, 20, or any integer therebetween.

[0049] In step S4, the organic phase collected in the extraction is washed with a washing liquid. The washing liquid used in the present invention is prepared from a hydrochloric acid solution and a calcium chloride solution, and the concentration of HCl contained in the washing liquid is preferably 0.4-2 mol / L, and the concentration of CaCl2 is preferably 2.0-5 mol / L. In some specific embodiments, the concentration of HCl in the washing liquid can be specifically 0.40 mol / L, 0.50 mol / L, 0.60 mol / L, 0.1 mol / L, 0.12 mol / L, 0.15 mol / L, 0.18 mol / L, 0.2 mol / Lmol / L or any value therebetween. In some specific embodiments, the concentration of CaCl2 in the washing solution can be 2.0mol / L, 2.4mol / L, 2.6mol / L, 2.8mol / L, 3.0mol / L, 3.2mol / L, 3.4mol / L, 3.6mol / L, 3.8mol / L, 4.0mol / L, 4.2mol / L, 4.4mol / L, 4.6mol / L, 4.8mol / L, 5.0mol / L or any value therebetween.

[0050] In the present invention, after washing the organic phase collected in the extraction with a washing liquid, it is necessary to use a stripping solution for stripping, and the substances containing lithium and iron elements are transferred to the aqueous phase, and the phosphorus-containing substances can be further removed, so that the prepared lithium-rich lithium ferrate has a higher purity and better electrical properties. Specifically, the stripping solution can be selected as an ammonia solution with a concentration of 0.5 to 5 mol / L. In some specific embodiments, the concentration of the stripping solution can be 0.5 mol / L, 0.8 mol / L, 1.0 mol / L, 1.4 mol / L, 1.8 mol / L, 2.0 mol / L, 2.7 mol / L, 3.0 mol / L, 3.5 mol / L, 4.0 mol / L, 4.8 mol / L, 5.0 mol / L or any value therebetween.

[0051] In addition, the organic phase separated in the back extraction of step S4 can be used as the mixed extractant in step S3, which can improve the recovery rate of Li and Fe while realizing the recycling of reagents.

[0052] In step S5, a lithium source and an alkaline carbonate are added to the stripping solution to adjust the lithium-iron molar ratio in the stripping solution to (5.0-5.5):1, and the pH value is adjusted to 11.5-13, so that the iron compound and the lithium compound are precipitated from the solution in the form of a precipitate. At this time, the precipitate contains few impurities. After drying, calcining and sintering, a high-purity lithium iron-rich lithium with a high irreversible capacity can be prepared. In some specific embodiments, the lithium-iron molar ratio in the solution after the stripping solution is added with a lithium source can be specifically 5.0:1, 5.1:1, 5.2:1, 5.3:1, 5.4:1, 5.5:1 or any value therebetween. In addition, specific examples of the lithium source include, but are not limited to, one or more of lithium chloride, lithium carbonate, lithium hydroxide, lithium nitrate and lithium oxide, preferably lithium carbonate and / or lithium hydroxide, and most preferably lithium hydroxide. Specific examples of the alkaline carbonate include, but are not limited to, one or more of sodium carbonate, potassium carbonate and lithium carbonate, preferably sodium carbonate.

[0053] In step S6, the solid phase product obtained by solid-liquid separation of the turbid liquid is placed at a temperature of 200-400°C for drying and calcining for 5-20 hours to remove moisture in the solid phase product and form a preliminary structure; then, in an atmosphere of an inert gas such as helium, neon, argon and / or nitrogen, the dried and calcined solid phase product is placed at a temperature of 500-900°C for sintering for 5-20 hours to prepare lithium-rich iron phosphate with a good crystal structure. The lithium-rich iron phosphate can be used as a lithium supplement material for lithium-rich iron phosphate lithium batteries, has a high irreversible capacity, is a lithium supplement material with excellent performance, and has extremely high product added value.

[0054] The present application also provides a lithium-rich lithium iron oxide, which is prepared by the above-mentioned method for preparing lithium-rich lithium iron oxide from waste lithium iron phosphate.

[0055] The present application also provides a lithium supplement material, which at least includes lithium-rich lithium iron oxide prepared by the above method for preparing lithium-rich lithium iron oxide from waste lithium iron phosphate.

[0056] The present application also provides a modified lithium-ion battery positive electrode material, which comprises a positive electrode material and the above-mentioned lithium supplement material.

[0057] Embodiments of the present invention are described in detail below, and the examples of the embodiments are intended to be used to explain the present invention, but should not be construed as limiting the present invention. In the embodiments, if specific techniques or conditions are not specified, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not specified for reagents or instruments used, they are all conventional products that can be obtained commercially.

[0058] Example 1.

[0059] This embodiment provides a method for preparing lithium-rich lithium iron oxide, which uses waste lithium iron phosphate (waste generated in the production process of lithium iron phosphate positive electrode) as raw material, and prepares lithium-rich lithium iron oxide with good performance through mechanical crushing, impurity removal, hydrochloric acid solution purification, multi-stage extraction, stripping, lithium iron precipitation, drying, calcination and sintering. Figure 1 The preparation method of lithium-rich lithium iron oxide specifically includes the following steps.

[0060] S1, mechanically crushing the waste lithium iron phosphate to a particle size D50 of 1 μm, and then sintering the mechanically crushed waste lithium iron phosphate at 700° C. for 10 hours in an air atmosphere to remove impurities in the waste lithium iron phosphate to obtain a black material whose main component is lithium iron phosphorus;

[0061] S2, using 10mol / L hydrochloric acid solution to dissolve the black material, filtering to remove a small amount of insoluble matter, and determining the contents of lithium and iron in the filtrate, adding an appropriate amount of lithium carbonate or ferric dioxide according to the contents of lithium and iron in the filtrate, and adjusting the lithium-iron molar ratio of the filtrate to 0.8:1 to prepare a lithium-iron solution;

[0062] S3, adding a mixed extractant to the lithium iron solution at 35°C, shaking and stirring for 30 minutes and letting it stand, then separating to obtain an organic phase and an aqueous phase, adding the mixed extractant to the aqueous phase for multi-stage extraction, and collecting the organic phase separated in the multi-stage extraction;

[0063] S4, all organic phases were combined, the organic phase was washed 3 times with a washing solution, and then the organic phase was stripped with a 3 mol / L ammonia solution, and the stripping solution containing lithium iron was obtained by filtering;

[0064] S5, measuring the content of lithium and iron in the stripping solution, and adding appropriate amounts of lithium hydroxide and sodium carbonate according to the content of lithium and iron, adjusting the lithium-iron molar ratio in the stripping solution to 5.15:1, and adjusting the pH value to 12, so that the lithium compound and the iron compound are precipitated as a precipitate to obtain a turbid solution;

[0065] S6. Filter the turbid liquid to obtain a solid phase product, dry and calcine the solid phase product at 300° C. for 10 hours, and then sinter it at 700° C. for 15 hours in an Ar atmosphere to obtain lithium-rich lithium ferrite.

[0066] The mixed extractant used in this embodiment includes 70wt% of tributyl phosphate (TBP), 25wt% of kerosene and 5wt% of 6mol / L calcium chloride solution, the number of multi-stage extraction stages is 10, and the washing liquid is prepared by mixing 1mol / L hydrochloric acid and 5mol / L calcium chloride solution in equal volumes.

[0067] Examples 2 to 8.

[0068] Examples 2 to 8 prepare lithium iron-rich lithium oxide according to the method provided in Example 1, except that the molar ratio of lithium to iron in the lithium-iron solution is different, the mixed extractant used in step S3 and the conditions of multi-stage extraction are different, and the other conditions are the same as those in Example 1. The specific differences are shown in Table 1, wherein X represents the molar ratio of lithium to iron in the lithium-iron solution.

[0069] Table 1. Conditions for preparing lithium-rich lithium iron oxide in Examples 2 to 8

[0070]

[0071] Comparative Example 1.

[0072] In this comparative example, lithium-rich lithium ferrate is prepared according to the method provided in Example 4, except that the mixed extractant used in step S3 includes 70wt% of tributyl phosphate and 30wt% of kerosene, and does not include calcium chloride solution. Other conditions are the same as those in Example 8.

[0073] Comparative Example 2.

[0074] In this comparative example, lithium-rich lithium ferrate is prepared according to the method provided in Example 4, except that the mixed extractant used in step S3 includes 65wt% of tributyl phosphate, 15wt% of kerosene and 20wt% of a 6mol / L calcium chloride solution, that is, the mass fraction of the calcium chloride solution in the mixed extractant is greater than the scope of the present invention, and the other conditions are the same as those in Example 8.

[0075] Comparative Example 3.

[0076] In this comparative example, lithium-rich lithium ferrate is prepared according to the method provided in Example 4, except that the mixed extractant used in step S3 includes 68wt% of di(2-ethylhexyl) phosphate (P204), 23wt% of kerosene and 9wt% of 6mol / L calcium chloride solution, and the other conditions are the same as those in Example 8.

[0077] Comparative Example 4.

[0078] In this comparative example, lithium-rich lithium ferrate is prepared according to the method provided in Example 4, except that the mixed extractant used in step S3 includes 68wt% of 2-ethylhexyl mono-2-ethylhexyl phosphate (P507), 23wt% of kerosene and 9wt% of a 6mol / L calcium chloride solution, and the other conditions are the same as those in Example 8.

[0079] Test example 1.

[0080] In the process of preparing lithium-rich lithium ferrate in Examples 1 to 8 and Comparative Examples 1 to 4, the iron, lithium and phosphorus contents in the filtrate and the stripping solution of step S2 were detected, and the amounts of lithium source and iron source additionally added during the preparation process were subtracted to calculate the iron and lithium recovery rates and the phosphorus removal rates. The results are shown in Table 2.

[0081] Table 2. Separation effect of lithium, iron and phosphorus elements in lithium iron phosphate solid waste

[0082]

[0083]

[0084] As can be seen from Table 2, compared with the low P removal rate of Comparative Examples 1 to 4, the P removal rate in Examples 1 to 8 of the present invention is as high as 88.0 to 99.5%, indicating that only by using the mixed extractant provided by the present invention can the lithium, iron and phosphorus elements in the waste products containing lithium iron phosphate be effectively separated, thereby preparing high-purity lithium-rich lithium iron acid, which is a high-quality lithium-rich lithium iron acid lithium battery lithium supplement material with high added value. Among them, in the preparation method provided by Example 8, multiple factors such as the lithium-iron molar ratio in the lithium-iron solution, the components in the mixed extractant, and the extraction temperature work together to achieve the most ideal separation effect of lithium, iron and phosphorus elements in the waste products containing lithium iron phosphate, and have a high P removal rate while also having a high Li and Fe recovery rate.

[0085] Examples 9 to 15.

[0086] Examples 9 to 15 prepare lithium-rich lithium iron oxide according to the method provided in Example 8, except that the lithium-iron molar ratio of the stripping solution after the lithium source is added in step S5 is different, the sintering temperature and time in step S6 are different, the mixed extractant used and the conditions of multi-stage extraction are different, and other conditions are the same, as shown in Table 3, wherein Y represents the lithium-iron molar ratio of the stripping solution after the lithium source is added in step S5.

[0087] Table 3. Conditions for preparing lithium-rich lithium ferrate in Examples 9 to 15

[0088]

[0089] Test example 2.

[0090] The lithium-rich lithium ferrite provided in Examples 1 to 15 and Comparative Examples 1 and 4 was used as the positive electrode material, mixed with a conductive agent and a binder and pressed to obtain a positive electrode, and a lithium metal sheet was used as the negative electrode. A button battery was prepared using the preparation method of a laboratory button battery CR2032 and the electrochemical performance was tested. During the test, the operating voltage range was set to 2.5 to 4.6 V, CC was 0.05 C / 0.02 C and DC was 0.05 C. The test results are shown in Table 4.

[0091] Table 4. Electrical properties of lithium-rich lithium iron oxide

[0092]

[0093]

[0094] From the test results, it can be seen that compared with comparative examples 1 to 4, the first charge and discharge irreversible capacity of the lithium-rich lithium iron oxide provided by embodiments 1 to 15 of the present invention is 437.1 to 649.9 mAh / g, which is an excellent lithium-rich lithium iron oxide lithium battery lithium supplement material with extremely high product added value and huge application prospects.

[0095] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention.

Claims

1. A method for preparing lithium-rich lithium iron oxide from waste lithium iron phosphate, characterized in that: The method comprises the following steps: S1. removing impurities from waste lithium iron phosphate to obtain black material whose main component is lithium iron phosphorus; S2, dissolving the black material with hydrochloric acid solution and then separating the solid and liquid, measuring the contents of lithium and iron in the liquid phase and adding a lithium source and / or an iron source to adjust the lithium-iron molar ratio in the solution to obtain a lithium-iron solution, wherein the lithium-iron molar ratio in the lithium-iron solution is (0.5-1.5):1; S3, extracting the lithium iron solution with a mixed extractant to separate an organic phase and an aqueous phase; the mixed extractant comprises 50-80wt% of tributyl phosphate, 10-40wt% of light petroleum and 1-10wt% of calcium chloride solution; S4, washing and stripping the organic phase to obtain a stripping solution containing lithium iron, wherein the washing solution used in the washing comprises 0.4-2 mol / L HCl and 2.0-5 mol / L CaCl2, and the stripping solution used in the stripping is 0.5-5 mol / L ammonia solution; S5, determining the contents of lithium and iron in the stripping solution, and adding a lithium source and an alkaline carbonate to adjust the lithium-iron molar ratio and pH value in the stripping solution so that the lithium compound and the iron compound are precipitated to obtain a turbid solution; S6, performing solid-liquid separation on the turbid liquid, and then drying and sintering the obtained solid phase product to obtain the lithium-rich lithium ferrite.

2. The method for preparing lithium-rich lithium iron oxide from waste lithium iron phosphate according to claim 1, characterized in that: In step S1, the waste lithium iron phosphate is selected from one or more of minerals containing lithium iron phosphorus, waste materials generated in the production process of lithium iron phosphate positive electrodes, waste lithium iron phosphate pole pieces generated in the battery processing process, and waste lithium iron phosphate batteries.

3. The method for preparing lithium-rich lithium iron oxide from waste lithium iron phosphate according to claim 1, characterized in that: In step S2, the concentration of the hydrochloric acid solution is 9-12 mol / L; the lithium source is selected from one or more of lithium chloride, lithium carbonate, lithium hydroxide, lithium nitrate and lithium oxide; the iron source is selected from one or more of ferric chloride, ferric oxide, ferrous oxide, ferric dioxide, ferric oxide and ferric oxide.

4. The method for preparing lithium-rich lithium iron oxide from waste lithium iron phosphate according to claim 1, characterized in that: In step S3, the light petroleum is selected from one or more of kerosene, diesel and gasoline; and the concentration of the calcium chloride solution is 5-8 mol / L.

5. The method for preparing lithium-rich lithium iron oxide from waste lithium iron phosphate according to claim 1, characterized in that: In step S3, the extraction temperature is 20-55° C.; the extraction is a multi-stage extraction; and the number of extraction stages of the multi-stage extraction is 3-20.

6. The method for preparing lithium-rich lithium iron oxide from waste lithium iron phosphate according to claim 1, characterized in that: In step S5, the lithium source is selected from one or more of lithium chloride, lithium carbonate, lithium hydroxide, lithium nitrate and lithium oxide; the alkaline carbonate is selected from one or more of sodium carbonate, potassium carbonate and lithium carbonate; the molar ratio of lithium to iron in the turbid solution is (5.0~5.5):

1.

7. The method for preparing lithium-rich lithium iron oxide from waste lithium iron phosphate according to claim 1, characterized in that: In step S6, the drying temperature is 200-400°C, and the time is 5-20 hours; in step S6, the sintering is carried out under the protection of an inert gas, and the sintering temperature is 500-900°C, and the time is 5-20 hours.

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