Lithium iron phosphate composite precursor and preparation method therefor

Abstract

The present invention relates to a lithium iron phosphate composite precursor, which comprises an Li3Fe2(PO4)3 component and an Fe2O3 component, wherein the molar ratio of the main elements of the precursor satisfies the equation: Li:Fe:P=(0.95-1.05):(0.95-1):1. The present invention further relates to a preparation method for the lithium iron phosphate composite precursor. The preparation method comprises the following steps: (1) solution preparation, involving: preparing an aqueous raw material solution having an Fe content of 60-210 g / L according to the molar ratio of Li:Fe:P＝(0.95-1.05):(0.95-1):1; and (2) spray pyrolysis, involving: subjecting the aqueous raw material solution to spray pyrolysis in an aerobic environment at 400-800ºC, so as to obtain the lithium iron phosphate composite precursor.

Description

Lithium iron phosphate composite precursor and preparation method thereof

[0001] This application claims priority to Chinese patent application No. 202311586655.7 filed with the State Intellectual Property Office of China on November 24, 2023. The contents of the above-mentioned Chinese patent application disclosure are hereby incorporated by reference in their entirety as part of this application. Technical Field

[0002] The present invention relates to the field of lithium-ion battery positive electrode materials, and in particular to a lithium iron phosphate composite precursor and a preparation method thereof. Background Art

[0003] Lithium iron phosphate (LIFP) is an important cathode material for lithium-ion batteries, typically prepared using iron phosphate as a precursor. However, when using an iron phosphate precursor to prepare LFP cathode materials, a certain amount of lithium must be added. Due to the high price of lithium, this leads to high costs in cathode material manufacturing. While the use of a lithium-containing iron phosphate precursor can reduce cathode material manufacturing costs, from an overall cost perspective, lithium-containing iron phosphate precursors must also offer cost advantages to be practical.

[0004] On the other hand, with the increasing market share and scrap volume of lithium iron phosphate power batteries, earlier-entered lithium iron phosphate batteries have begun to be scrapped, and the recycling and reuse of electrode materials in spent lithium iron phosphate batteries has become increasingly prominent. Therefore, there is a need for environmentally friendly and cost-effective methods to recycle and reuse the lithium iron phosphate materials in spent lithium iron phosphate batteries.

[0005] Since waste lithium iron phosphate materials contain lithium, if they can be recycled to make lithium-containing iron phosphate precursor materials, it will help reduce the overall manufacturing cost of lithium-ion battery positive electrode materials and also help reduce pollution to the environment.

[0006] As a result, people began to consider using waste lithium iron phosphate batteries to manufacture lithium-containing iron phosphate precursor materials. On the one hand, this can achieve resource recycling and reduce the overall manufacturing cost of lithium-ion battery positive electrode materials. On the other hand, it can also improve the performance of the precursor by improving the composition and morphology of the precursor, thereby improving the performance of the positive electrode material and lithium battery. On the other hand, there is no need to further separate lithium from the recycled raw materials, thereby reducing the recycling cost. However, it is well known that the composition of waste lithium iron phosphate battery powder is relatively complex. In addition to positive and negative electrode powders, it often contains binders, copper and aluminum chips generated during the crushing process of the current collector, and other impurities, which also brings corresponding difficulties to recycling.

[0007] CN113526482 discloses a method for preparing lithium iron phosphate by recycling waste batteries. The method pre-treats waste lithium iron phosphate power batteries to obtain pure lithium iron phosphate waste, then supplements the proportions of various elements and prepares lithium iron phosphate products by spray pyrolysis. This patent removes aluminum by soaking in a certain concentration of liquid caustic soda. Although this method can remove aluminum from lithium iron phosphate powder materials to a certain extent, the resulting metaaluminate must be neutralized with acid to prepare aluminum hydroxide, etc., which makes the process more complicated and produces a large amount of wastewater. At the same time, since waste lithium iron phosphate powder generally contains a certain amount of carbon powder, it will absorb aluminum in the solution, resulting in a low aluminum impurity removal rate of the method, and it is also unable to remove impurities such as titanium and copper, resulting in poor performance of the lithium iron phosphate finally prepared. The first discharge specific capacity of the lithium iron phosphate product prepared in Example 1 is only about 131mAh / g.

[0008] CN116216684A discloses a method for recovering and separating lithium iron phosphate materials from lithium iron phosphate batteries. The method comprises leaching crushed positive and negative electrode powders with sulfuric acid; adding iron powder to remove copper; using a sodium sulfite solution and simultaneously adding an alkaline solution to adjust the pH to remove aluminum as aluminum phosphate precipitate; adding an H3PO4-H2O2 mixed solution for reaction; adding a NaOH solution to neutralize the residual acid and adjust the pH to obtain a high-concentration lithium dihydrogen phosphate solution and a mixture of FePO4·2H2O and carbon powder; then adding a NaOH solution to convert the lithium dihydrogen phosphate into lithium phosphate; supplementing with lithium and iron sources, adding the powder to an ethanol solution for ball milling and drying; and calcining the powder under inert gas protection to obtain the lithium iron phosphate product. This process is complex, generates a large amount of wastewater, and introduces new impurities such as sulfur and sodium into the final lithium iron phosphate material. Furthermore, since the lithium and iron sources are supplemented after obtaining the precursor, the distribution of lithium and iron elements is uneven, which affects the performance of the final product.

[0009] CN115744857A discloses a method for producing lithium iron phosphate cathode material from waste lithium iron phosphate batteries in a directional cycle, comprising: (1) alkali-leaching the waste lithium iron phosphate battery black powder, followed by solid-liquid separation to obtain a solid residue, mixing the solid residue with an acid and an oxidant, soaking the solid residue, adding a reducing agent, and then performing solid-liquid separation to obtain a filtrate; (2) adding phosphoric acid to the filtrate and pyrolyzing it to obtain a dry material, which is then mixed with a lithium source, a ferrous source, and a carbon source to obtain a mixed material; (3) adding the mixed material to ammonia water for hydrothermal reaction, then evaporating ammonia to obtain solid particles, and then roasting the solid particles in an inert gas to obtain the lithium iron phosphate cathode material. This method requires the use of multiple reagents and requires pyrolysis and hydrothermal reaction, resulting in a complex process, a large amount of wastewater, and high cost.

[0010] However, the above existing technologies all have their own technical problems, making it difficult to obtain ideal lithium iron phosphate precursor materials. In addition, generally speaking, the iron in the lithium iron phosphate precursor material is divalent iron, which also leads to many limitations on the performance of the existing lithium iron phosphate precursor / lithium iron phosphate material.

[0011] Therefore, there is a need in the art for a lithium iron phosphate composite precursor with excellent performance and a preparation method thereof that is simple to prepare, environmentally friendly and low-cost. Summary of the Invention

[0012] The present invention is made in view of the above problems existing in the prior art.

[0013] In a first aspect, the present invention provides a lithium iron phosphate composite precursor comprising a Li3Fe2(PO4)3 component and a Fe2O3 component, wherein the main element molar ratio of the precursor is Li:Fe:P=(0.95-1.05):(0.95-1):1.

[0014] In a second aspect, the present invention provides a method for preparing a lithium iron phosphate composite precursor, comprising the following steps:

[0015] (1) Solution preparation: Prepare a raw material aqueous solution with an Fe content of 60-210 g / L according to a molar ratio of Li:Fe:P=(0.95-1.05):(0.95-1):1;

[0016] (2) Spray pyrolysis: spray pyrolysis the raw material aqueous solution in an aerobic environment at 400-800° C. to obtain the lithium iron phosphate composite precursor.

[0017] The lithium iron phosphate composite precursor may be the precursor of the first aspect of the present invention.

[0018] The present invention also relates to a product obtainable by the process of the second aspect of the invention.

[0019] Specifically, the present invention is achieved as follows.

[0020] A lithium iron phosphate composite precursor comprises a Li3Fe2(PO4)3 component and a Fe2O3 component, wherein the main element molar ratio of the precursor is Li:Fe:P=(0.95-1.05):(0.95-1):1.

[0021] Furthermore, the Li3Fe2(PO4)3 component belongs to the P21 / n space group.

[0022] Preferably, the Li3Fe2(PO4)3 component is a monoclinic crystal system, and / or the Fe2O3 component is a hematite phase.

[0023] Preferably, the lattice parameters of the monoclinic crystal system are a=0.8566 nm, b=1.2053 nm, and c=0.8596 nm.

[0024] Preferably, the primary particles of the lithium iron phosphate composite precursor are fragment structures formed by hollow spheres, the diameter of the fragments is 50-500 nm, and the thickness of the fragments is 20-300 nm.

[0025] Furthermore, the primary particles agglomerate to form secondary particles, the diameter of the secondary particles is 200 nm-50 μm, and the thickness of the secondary particles is 50-1000 nm.

[0026] Preferably, the specific surface area of ​​the lithium iron phosphate composite precursor is 4.0-30.0 m 2 / g.

[0027] Preferably, the tap density of the lithium iron phosphate composite precursor is 0.3-1.5 g / cm 3 .

[0028] Preferably, the sulfur content of the lithium iron phosphate composite precursor is at most 200 ppm.

[0029] A method for preparing a lithium iron phosphate composite precursor comprises the following steps:

[0030] (1) Solution preparation: Prepare a raw material aqueous solution with an Fe content of 60-210 g / L according to a molar ratio of Li:Fe:P=(0.95-1.05):(0.95-1):1;

[0031] (2) Spray pyrolysis: spray pyrolysis the raw material aqueous solution in an aerobic environment at 400-800° C. to obtain the lithium iron phosphate composite precursor.

[0032] Furthermore, step (1) includes:

[0033] 1.1) Discharging, disassembling, and separating the used lithium iron phosphate batteries in sequence to obtain a solid material to be processed containing lithium iron phosphate powder;

[0034] 1.2) Leaching the obtained solid material with an acid solution to obtain a first treatment solution containing Li, Fe, and P;

[0035] 1.3) removing copper ions from the first treatment solution and reducing the ferric ions to ferrous ions to obtain a third treatment solution;

[0036] 1.4) adding a pH adjuster to the third treatment solution in the presence of a reducing agent for trivalent iron ions to adjust the pH to 2.8-4.0, and then separating and removing the formed precipitate to obtain a fourth treatment solution;

[0037] 1.5) adjusting the pH of the fourth treatment solution to 0.2-0.8, adjusting the molar ratio of Li, Fe, and P in the fourth treatment solution to Li:Fe:P=(0.95-1.05):(0.95-1):1 using at least one of a lithium source, an iron source, or a phosphorus source, and adjusting the Fe content to 60-210 g / L to obtain the raw aqueous solution.

[0038] Preferably, the acid used in the leaching treatment in step 1.2) is hydrochloric acid, and preferably the concentration of the hydrochloric acid is 20-37% by weight.

[0039] Furthermore, step 1.3) is performed as follows:

[0040] 1.3-1) treating the first treatment liquid with a copper removal agent, and performing solid-liquid separation to obtain a second treatment liquid; and

[0041] 1.3-2) Treating the second treatment liquid with a reducing agent to obtain the third treatment liquid.

[0042] Preferably, the copper removing agent is iron powder, and the reducing agent is iron powder.

[0043] Preferably, the pH regulator in step 1.4) is at least one selected from lithium carbonate, lithium hydroxide, lithium bicarbonate, lithium oxalate, ferric hydroxide, iron powder, lithium phosphate, ferrous phosphate, and ferrous dihydrogen phosphate.

[0044] Preferably, the lithium source in step 1.5) is selected from at least one of lithium carbonate, lithium hydroxide, lithium bicarbonate, lithium oxalate, lithium phosphate, lithium monohydrogen phosphate, and lithium dihydrogen phosphate; the iron source is selected from at least one of ferrous hydroxide, iron powder, iron oxide, ferric oxide, ferric hydroxide, ferric carbonate, and ferric phosphate; and the phosphorus source is selected from at least one of phosphoric acid, lithium phosphate, and ferric phosphate.

[0045] Preferably, the pH adjustment in step 1.5) is performed using the same acid as that used in the leaching process in step 1.2). Alternatively or additionally, it is performed using an acid solution recovered from an excess acid solution used in the leaching process in step 1.2).

[0046] This application achieves the following beneficial effects:

[0047] (1) The lithium iron phosphate composite precursor component obtained according to the first aspect of the present invention or the method according to the second aspect of the present invention is completely different from the precursor component used to prepare lithium iron phosphate materials in the prior art. On the one hand, the precursor used to prepare lithium iron phosphate in the prior art is usually a mixture of lithium source particles, iron source particles and phosphorus source particles, or a mixture of particles of a precursor (such as iron phosphate) formed by two elements among the lithium source, iron source and phosphorus source and particles of the precursor of the remaining element (such as lithium carbonate). The mixture is a mixture at the particle level, so it is difficult to achieve a uniform distribution of lithium, iron and phosphorus elements at the molecular level in the lithium iron phosphate product manufactured therefrom; while the elemental composition of the lithium iron phosphate composite precursor in the present invention corresponds to the elemental composition of the final lithium iron phosphate product, so when manufacturing the lithium iron phosphate material therefrom, there is no need to add a lithium source, an iron source and / or a phosphorus source, and it is a uniform mixture (at the molecular level) of two independent main components, namely Li3Fe2(PO4)3 and Fe2O3, thereby ensuring the composition uniformity of the lithium iron phosphate material prepared therefrom, achieving a uniform distribution of lithium, iron and phosphorus elements at the molecular level, and being conducive to achieving better electrochemical properties of the lithium iron phosphate material.

[0048] (2) On the other hand, since the precursor has a specific composition and a stable crystal structure, the crystal structure, orientation and morphology of lithium iron phosphate can be more easily controlled in the subsequent process of synthesizing lithium iron phosphate positive electrode materials from it, and the crystal structure of the obtained positive electrode material is more complete and more stable, which is conducive to achieving better electrochemical performance of lithium iron phosphate materials.

[0049] (3) On the other hand, since Li3Fe2(PO4)3 has been uniformly mixed with the Fe2O3 component, in the process of preparing lithium iron phosphate positive electrode material from the precursor of the present invention or the precursor prepared by the method of the present invention, the slurry feeding step can be reduced in the slurrying step, and the equipment of the ingredient slurrying process can be simplified, thereby achieving labor and cost savings. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the aspects, embodiments, features, and advantages of the present invention, the present invention will be described below in conjunction with the accompanying drawings. It should be understood that these drawings are only provided to facilitate technicians to more easily understand the present invention and are not intended to limit the scope of the present invention.

[0051] FIG1 is a flow chart illustrating an exemplary embodiment of the method according to the present invention.

[0052] 2A-2B illustrate the results of X-ray diffraction (XRD) analysis of the lithium iron phosphate composite precursor prepared in Preparation Example 1. FIG.

[0053] 3A-3B illustrate the results of scanning electron microscopy (SEM) analysis of the lithium iron phosphate precursor prepared in Preparation Example 1. FIG.

[0054] Figures 4(a)-4(d) illustrate the results of energy dispersive X-ray spectroscopy (EDS) analysis of the lithium iron phosphate precursor prepared in Preparation Example 1, where (a) represents the overall morphology of the precursor, (b) represents the O element distribution, (c) represents the P element distribution, and (d) represents the Fe element distribution. DETAILED DESCRIPTION

[0055] In order to make the invention objectives, technical solutions and beneficial technical effects of this application clearer, this application will be described in detail below. It should be noted that the various aspects, features, implementation methods, and advantages described in this application may be compatible and / or combinable.

[0056] Unless otherwise specified, the meanings of the technical terms in this specification are the same as those generally understood by those skilled in the art.

[0057] In this application, unless otherwise stated, the term "substantially" means at least 90%, such as at least 95%, such as at least 98%, such as at least 99%, such as at least 99.5%, such as at least 99.8%, such as at least 99.9% of the stated value or object.

[0058] In this application, unless otherwise specified, the term "mainly" means at least 50%, such as at least 55%, such as at least 60%, such as at least 65%, such as at least 70%, such as at least 75%, such as at least 80%, such as at least 90%, such as at least 95%, such as at least 98%, such as at least 99%, such as at least 99.5%, such as at least 99.8%, such as at least 99.9% of the stated value or object.

[0059] In this application, unless otherwise specified, the term "about" means 90%-110%, for example, 95%-105% of the stated value, and includes the stated value. In this application, even if a numerical value is not modified by the term "about", it should be understood that it should also be understood as having been modified by "about", that is, the stated numerical value includes the numerical value itself and the above deviation around the numerical value.

[0060] In this application, unless otherwise stated, process steps were carried out at room temperature (25° C.) and atmospheric pressure (1 atm).

[0061] The invention relates to a lithium iron phosphate composite precursor and a preparation method thereof.

[0062] The present invention will be described in detail below.

[0063] Lithium iron phosphate composite precursor

[0064] In a first aspect of the present invention, the present invention relates to a lithium iron phosphate composite precursor comprising a Li3Fe2(PO4)3 component and a Fe2O3 component, wherein the main element molar ratio of the precursor is Li:Fe:P=(0.95-1.05):(0.95-1):1.

[0065] In this application, the term "lithium iron phosphate composite precursor" refers to a precursor composite or mixture used to synthesize lithium iron phosphate positive electrode materials.

[0066] In this application, the term "main element" means an element other than the element O and an element at an impurity (content) level. In other words, except for the impurity elements, the lithium iron phosphate composite precursor is essentially composed of lithium, iron, phosphorus and oxygen elements, or is composed of lithium, iron, phosphorus and oxygen elements.

[0067] In an embodiment, the Li3Fe2(PO4)3 and Fe2O3 components are present in the precursor as a homogeneous mixture thereof. Here, the term "homogeneous mixture" refers to a mixture that is homogeneous at the molecular level. In other words, the distribution of each of the lithium, iron, phosphorus, and oxygen elements in the precursor is uniform. For the purposes of this application, a mixture obtained by mixing particles with each other is not considered a "homogeneous mixture."

[0068] In an embodiment, the precursor includes a Li3Fe2(PO4)3 component and a Fe2O3 component, for example, mainly includes a Li3Fe2(PO4)3 component and a Fe2O3 component, basically consists of a Li3Fe2(PO4)3 component and a Fe2O3 component, or consists of a Li3Fe2(PO4)3 component and a Fe2O3 component.

[0069] For example, the sum of the weights of the Li3Fe2(PO4)3 and Fe2O3 components relative to the total weight of the precursor may be at least 50.0, 50.5, 51.0, 51.5, 52.0, 52.5, 53.0, 53.5, 54.0, 54.5, 55.0, 56.0, 56.5, 57.0, 57.5, 58.0, 58.5, 59.0, 59.0, 59.5 ...5, 59.0, 59.5, 59.5, 59.5, 59.5, 59.5, 59.5, 59.5, 59.5, 59.5, 59.5, 59.5, 59.5, 59.5, 59.5, 59.5 .5, 60.0, 60.5, 61.0, 61.5, 62.0, 62.5, 63.0, 63.5, 64.0, 64.5, 65.0, 66.0, 66.5, 67.0, 67.5, 68.0, 68.5, 69.0, 69.5, 70.0, 70.5, 71.0, 71.5, 72.0, 72.5, 73.0, 73.5, 74.0, 74.5, 75.0, 76.0, 76.5, 77.0, 77.5, 78.0, 78.5, 79.0, 79.5, 80.0, 80.5, 81.0, 81.5, 82.0, 82.5, 83.0, 83.5, 84.0, 84.5, 85.0, 86.0, 86.5, 87.0, 87.5, 88.0, 88. 5, 89.0, 89.5, 90.0, 90.5, 91.0, 91.5, 92.0, 92.5, 93.0, 93.5, 94.0, 94.5, 95.0, 96.0, 96.5, 97.0, 97.5, 98.0, 98.5, 99.0, 99.5, 99.8, 99.9, 100% by weight, or a range limited by any two thereof.

[0070] In the precursor, the P element exists in the form of phosphate.

[0071] The molar ratio of Li, Fe and P in the precursor is (0.95-1.05):(0.95-1):1.

[0072] For example, in the precursor, the content of Li element is 0.95-1.05 mol, such as 0.95, 0.96, 0.97, 0.98, 0.99, 1.00, 1.01, 1.02, 1.03, 1.04, 1.05 mol, or within the range defined by any two thereof, relative to 1 mol of P element.

[0073] For example, in the precursor, the content of the iron element is 0.95-1.00 mol, such as 0.95, 0.96, 0.97, 0.98, 0.99, 1.00 mol, or within the range defined by any two thereof, relative to 1 mol of the P element.

[0074] Since the molar ratio of Li, Fe, and P in the precursor of the present invention corresponds to the molar ratio of Li, Fe, and P in the final lithium iron phosphate material, there is no need to add additional Li, Fe, and P source compounds in the subsequent synthesis of lithium iron phosphate, thereby avoiding the use of raw materials such as lithium carbonate, and eliminating the process and energy required for the decomposition of raw materials such as lithium carbonate. As a result, the sintering time for synthesizing lithium iron phosphate can be reduced relative to the precursor of the prior art, thereby reducing the synthesis cost. In addition, since the precursor has a specific composition (Li3Fe2(PO4)3 component and Fe2O3 component), the crystal structure, orientation, and morphology of the lithium iron phosphate can be more easily controlled in the subsequent process of synthesizing the lithium iron phosphate positive electrode material therefrom, and the crystal structure of the resulting positive electrode material is more complete and more stable, thereby facilitating better electrochemical performance of the lithium iron phosphate material. In addition, since the Li3Fe2(PO4)3 component and the Fe2O3 component are evenly mixed (at the molecular level), the composition uniformity of the lithium iron phosphate material prepared therefrom is ensured, and the uniform distribution of lithium, iron and phosphorus elements at the molecular level is achieved, which is conducive to achieving better electrochemical properties of the lithium iron phosphate material.

[0075] In embodiments, the Li3Fe2(PO4)3 component may be primarily, substantially, or monoclinic.

[0076] In an embodiment, the Fe2O3 component may be primarily, substantially, or in the hematite phase.

[0077] In an embodiment, the precursor may include a monoclinic Li3Fe2(PO4)3 component and a hematite phase Fe2O3 component, for example, mainly including a monoclinic Li3Fe2(PO4)3 component and a hematite phase Fe2O3 component, basically consisting of a monoclinic Li3Fe2(PO4)3 component and a hematite phase Fe2O3 component, or consisting of a monoclinic Li3Fe2(PO4)3 component and a hematite phase Fe2O3 component.

[0078] For example, the sum of the weights of the monoclinic Li3Fe2(PO4)3 and hematite phase Fe2O3 components relative to the total weight of the precursor may be at least 50.0, 50.5, 51.0, 51.5, 52.0, 52.5, 53.0, 53.5, 54.0, 54.5, 55.0, 56.0, 56.5, 57.0, 57.5, 58.0, 58.5, 59. 9.0, 59.5, 60.0, 60.5, 61.0, 61.5, 62.0, 62.5, 63.0, 63.5, 64.0, 64.5, 65.0, 66.0, 66.5, 67.0, 67.5, 68.0, 68.5, 69.0, 69.5, 70.0, 70.5, 71.0, 71.5, 72.0, 72.5, 73.0, 7 3.5, 74.0, 74.5, 75.0, 76.0, 76.5, 77.0, 77.5, 78.0, 78.5, 79.0, 79.5, 80.0, 80.5, 81.0, 81.5, 82.0, 82.5, 83.0, 83.5, 84.0, 84.5, 85.0, 86.0, 86.5, 87.0, 87.5, 88.0, 8 8.5, 89.0, 89.5, 90.0, 90.5, 91.0, 91.5, 92.0, 92.5, 93.0, 93.5, 94.0, 94.5, 95.0, 96.0, 96.5, 97.0, 97.5, 98.0, 98.5, 99.0, 99.5, 99.8, 99.9, 100% by weight, or a range limited by any two thereof.

[0079] When the precursor has the above-mentioned specific crystal structure, the crystal structure, orientation and morphology of lithium iron phosphate can be more easily and better controlled in the subsequent process of synthesizing lithium iron phosphate positive electrode material therefrom, and the crystal structure of the obtained positive electrode material is more complete and more stable, which is conducive to achieving better electrochemical performance of lithium iron phosphate material.

[0080] In an embodiment, the lattice parameters of the monoclinic crystal system may be a=0.8566 nm, b=1.2053 nm, and c=0.8596 nm.

[0081] In an embodiment, the Li3Fe2(PO4)3 component may belong to the P21 / n space group.

[0082] In addition to Li, Fe, P, and O, the precursor contains very low levels of impurity elements such as Na, K, Ca, Cu, Ni, Cr, and Zn. For example, the precursor may satisfy one or more, or all, of the following conditions (1) to (10):

[0083] (1) the Na content of the precursor is at most 100 ppm, at most 95 ppm, at most 90 ppm, at most 85 ppm, at most 80 ppm, at most 75 ppm, at most 70 ppm, at most 65 ppm or less, or a range limited by any two thereof; and / or

[0084] (2) the K content in the precursor is at most 20 ppm, at most 15 ppm, or at most 10 ppm or less, or a range defined by any two thereof; and / or

[0085] (3) the Ca content in the precursor is at most 100 ppm, at most 95 ppm, or at most 90 ppm, at most 85 ppm, at most 80 ppm, at most 75 ppm, at most 70 ppm, or at most 65 ppm, at most 60 ppm, at most 55 ppm, at most 50 ppm, at most 45 ppm or less, or a range limited by any two thereof; and / or

[0086] (4) the Cu content in the precursor is at most 10 ppm, at most 8 ppm, at most 6 ppm, at most 5 ppm or less, or a range limited by any two thereof; and / or

[0087] (5) the Ni content in the precursor is at most 50 ppm, at most 45 ppm, at most 40 ppm, at most 35 ppm, at most 30 ppm, at most 25 ppm, at most 20 ppm, at most 15 ppm, at most 10 ppm or less, or a range limited by any two thereof; and / or

[0088] (6) the Cr content in the precursor is at most 70 ppm, at most 65 ppm, at most 60 ppm, at most 55 ppm, at most 50 ppm, at most 45 ppm, at most 40 ppm, at most 35 ppm, at most 30 ppm, at most 25 ppm or less, or a range limited by any two thereof; and / or

[0089] (7) The Zn content of the precursor is at most 50 ppm, at most 45 ppm, at most 40 ppm, at most 35 ppm, at most 30 ppm, at most 25 ppm, at most 20 ppm or less, or a range limited by any two thereof; and / or

[0090] (8) The Mg content of the precursor is at most 50 ppm, at most 45 ppm, at most 40 ppm, at most 35 ppm, at most 30 ppm, at most 25 ppm, at most 20 ppm, at most 15 ppm or less, or a range limited by any two thereof; and / or

[0091] (9) The Al content of the precursor is at most 50 ppm, at most 45 ppm, at most 40 ppm, at most 35 ppm, at most 30 ppm, at most 25 ppm, at most 20 ppm or less, or a range limited by any two thereof; and / or

[0092] (10) The sulfur content of the precursor is at least 200 ppm, for example, at most 195, 190, 185, 180, 175, 170, 165, 160, 155, 150, 145, 140, 135, 130, 125, 120, 115, 110, 105, 100, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25 ppm or less, or a range bounded by any two thereof.

[0093] When the precursor has the impurity content defined above, the adverse effects of the impurities on the performance of the lithium iron phosphate material prepared therefrom can be significantly reduced, thereby improving the electrochemical performance of the lithium iron phosphate material.

[0094] The precursor can be in the form of non-agglomerated primary particles, secondary particles formed by agglomeration of primary particles, or any combination thereof, wherein the primary particles can be solid spheres, solid sphere fragments, hollow spheres, hollow sphere fragments, or a combination thereof in any proportion, preferably hollow spheres, hollow sphere fragments, or a combination thereof in any proportion, more preferably substantially in the form of hollow sphere fragments.

[0095] The particle size of each of the solid sphere and the hollow sphere is not particularly limited and can be 1 μm-2000 μm, for example, can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 7 μm, 8 μm, 9 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 150 μm, 200 μm, 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, 800 μm, 1000 μm (1 mm), 1200 μm, 1500 μm, 2000 μm or the range limited by any two thereof. The particle size can be measured by any suitable method known in the art, for example, by (laser) particle size analyzer or electron microscope photo analysis. Unless otherwise specified, particle size refers to the volume average particle size (also known as median particle size D 50 ).

[0096] The wall thickness of the hollow sphere can be 50-500 nm, for example, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 450, 500 nm, or a range bounded by any two thereof. The wall thickness can be measured by any suitable method known in the art, such as electron microscopic analysis. Unless otherwise specified, wall thickness refers to average wall thickness.

[0097] The particle size (primary particle size) of the primary particles can be 100-800 nm, for example 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800 nm or a range limited by any two thereof. The particle size can be measured by any suitable method known in the art, for example, by electron micrograph analysis of a precursor. If not otherwise specified, the particle size refers to the (volume average) average particle size (also referred to as median particle size D 50 ).

[0098] The particle diameter of the secondary particles can be 200nm-50μm, for example, can be 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, 600nm, 650nm, 700nm, 750nm, 800nm, 900nm, 1000nm, 1μm, 2μm, 3μm, 4μm, 5μm, 7μm, 8μm, 9μm, 10μm, 20μm, 30μm, 40μm, 50μm or the range limited by any two thereof. The particle diameter can be measured by any suitable method known in the art, for example, by laser scattering analysis of precursor, sieving, or electron micrograph analysis. If not otherwise specified, the particle diameter refers to (volume average) average particle diameter (also referred to as median particle diameter D 50 ).

[0099] In one embodiment, the primary particles of the precursor are hollow sphere fragments (fragment structures formed by hollow spheres), and the thickness of the fragments is 20-300 nm, for example, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230, 240, 250, 260, 270, 280, 290, 300 nm, or a range limited by any two thereof; the diameter of the fragments is 50-500 nm. 400, 410, 420, 430, 440, 450, 460, 470, 480, 490, 500 nm, or a range defined by any two of them.

[0100] In one embodiment, the primary particles agglomerate to form secondary particles, and the diameter of the secondary particles is 200nm-50μm, for example, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, 600nm, 650nm, 700nm, 750nm, 800nm, 900nm, 1000nm, 1μm, 2μm, 3μm, 4μm, 5μm, 7μm, 8μm, 9μm, 10μm, 20μm, 30μm, 40μm, 50μm, or the range limited by any two of them; the thickness of the secondary particles is 50-1000nm, for example, it can be 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 900, 1000nm, or the range limited by any two of them.

[0101] In this application, the "path length" of a particle (primary particles and secondary particles) refers to the maximum dimension in a direction perpendicular (or substantially perpendicular) to the "thickness" direction of the particle. In this application, "path length" and "length" have the same meaning and are used interchangeably. "Path length" and "thickness" can be measured, for example, by electron microscopy analysis.

[0102] In one embodiment, the specific surface area of ​​the precursor particles is 4.0-30.0 m 2 / g, for example, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, 10.0, 10.5, 11.0, 11.5, 12.0, 12.5, 13.0, 13.5, 14.0, 14.5, 15.0, 15.5, 16.0, 16.5 ,17.0,17.5,18.0,18.5,19.0,19.5,20.0,20.5,21.0,21.5,22.0,22.5,23 .0, 24.5, 25.0, 25.5, 26.0, 26.5, 27.0, 27.5, 28.0, 28.5, 29.0, 29.5, 30.0m 2 The specific surface area can be measured by, for example, the BET method.

[0103] In one embodiment, the tap density of the precursor is 0.3-1.5 g / cm 3 , for example, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5 g / cm 3 , or the range defined by any two of them.

[0104] When the precursor has the above-defined size or particle size (primary particle size and / or secondary particle size) and / or BET and / or tap density, it is beneficial to improve the compaction density of the lithium iron phosphate positive electrode material prepared therefrom, thereby obtaining a higher energy density.

[0105] Preparation method of lithium iron phosphate composite precursor

[0106] In a second aspect, the present invention relates to a method for preparing a lithium iron phosphate composite precursor, comprising the following steps:

[0107] (1) Solution preparation: Prepare a raw material aqueous solution with an Fe content of 60-210 g / L according to a molar ratio of Li:Fe:P=(0.95-1.05):(0.95-1):1;

[0108] (2) Spray pyrolysis: spray pyrolysis the raw material aqueous solution in an aerobic environment at 400-800° C. to obtain the lithium iron phosphate composite precursor.

[0109] FIG1 shows an exemplary embodiment of the method of the present invention. The method will be described in detail below with reference to FIG1 .

[0110] Step (1)

[0111] In step (1), a solution is prepared, wherein a raw material aqueous solution having an Fe element content of 60-210 g / L is prepared according to a molar ratio of Li:Fe:P=(0.95-1.05):(0.95-1):1.

[0112] In an embodiment, in the raw aqueous solution, the P element exists in the form of phosphate.

[0113] The raw aqueous solution can be prepared by dissolving a lithium source, an iron source, and a phosphorus source in water, optionally in the presence of an acid. The acid can be as described below.

[0114] In the prepared raw water solution, the Li:Fe:P element ratio is (0.95-1.05):(0.95-1):1. For example, in the prepared raw water solution, the Li element is 0.95-1.05 moles relative to 1 mole of the P element, such as 0.95, 0.96, 0.97, 0.98, 0.99, 1.00, 1.01, 1.02, 1.03, 1.04, 1.05 moles, or within the range defined by any two thereof. For example, in the prepared raw water solution, the iron element is 0.95-1.00 moles relative to 1 mole of the P element, such as 0.95, 0.96, 0.97, 0.98, 0.99, 1.00 moles, or within the range defined by any two thereof.

[0115] In the prepared raw material aqueous solution, the iron content can be 60-210g / L, for example 150-200g / L. For example, the iron content can be 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180, 185, 190, 195, 200, 205, 210g / L, or within the range defined by any two thereof. By controlling the content of the iron element within the range, on the one hand, the energy consumption during spray sintering can be reduced, and on the other hand, the particle size of the particles obtained by spray sintering can be controlled, which is conducive to reducing the sintering time of subsequent synthesis of lithium iron phosphate and reducing the synthesis cost.

[0116] The iron concentration in the solution can be determined or confirmed by any suitable method known in the art. For example, it can be determined by the amount of each element used and the amount of water. The concentration can also be measured or confirmed by inductively coupled plasma optical emission spectroscopy (ICP).

[0117] In one embodiment, the solution preparation step (1) may include or be performed as follows:

[0118] 1.1) Discharging, disassembling, and separating the used lithium iron phosphate batteries in sequence to obtain a solid material to be processed containing lithium iron phosphate powder;

[0119] 1.2) Leaching the obtained solid material with an acid solution to obtain a first treatment solution containing Li, Fe, and P;

[0120] 1.3) removing copper ions from the first treatment solution and reducing the ferric ions to ferrous ions to obtain a third treatment solution;

[0121] 1.4) adding a pH adjuster to the third treated solution in the presence of a reducing agent for ferric ions to adjust the pH to 2.8-4.0, and then separating and removing the formed precipitate to obtain a fourth treated solution;

[0122] 1.5) adjusting the pH of the fourth treatment solution to 0.2-0.8, adjusting the molar ratio of Li, Fe, and P in the fourth treatment solution to Li:Fe:P=(0.95-1.05):(0.95-1):1 using at least one of a lithium source, an iron source, or a phosphorus source; and adjusting the Fe element content to 60-210 g / L to obtain a fifth treatment solution as the raw aqueous solution.

[0123] Step 1.1)

[0124] In step 1.1), the waste lithium iron phosphate batteries are discharged, disassembled, and separated in sequence ("discharge, disassembly, separation" in Figure 1) to obtain a solid material to be treated containing lithium iron phosphate powder ("lithium iron phosphate battery powder" in Figure 1).

[0125] In this step, the used lithium iron phosphate battery is first discharged. The discharge can be performed by any method known in the art. For example, the discharge can be performed using a charge-discharge device. Alternatively, the discharge can be performed by immersing the battery in salt water. The discharge is typically complete, which can be reflected by the battery voltage. For example, when the battery voltage is below 2V, such as 1-2V, the discharge can be considered complete.

[0126] After the discharge is completed, the battery is disassembled and separated to obtain a solid material to be processed containing lithium iron phosphate powder.

[0127] The disassembly is performed by mechanically destroying the battery casing, disassembling the negative electrode / diaphragm / positive electrode, and then separating them to remove the battery casing, diaphragm, negative electrode, electrolyte, etc., thereby obtaining the positive electrode sheet. Those skilled in the art will understand that some of the diaphragm, negative electrode (negative electrode active material, negative electrode current collector (copper)) and other materials may remain in the obtained positive electrode sheet material; after disassembling to obtain the positive electrode sheet, the positive electrode sheet is crushed and sieved to remove the aluminum foil (positive electrode current collector), thereby separating the solid material to be processed containing lithium iron phosphate powder.

[0128] The pulverization can be performed by any means known in the art, such as using a pulverizer.

[0129] Screening can be performed by any means known in the art, such as screening, vibrating screening, for example, using a disc vibrating screen.

[0130] Therefore, in a specific embodiment, in step 1.1), the waste lithium iron phosphate battery is discharged and then disassembled to obtain the positive electrode sheet, the positive electrode sheet is crushed, and the aluminum foil is sieved to obtain a solid material to be processed containing lithium iron phosphate powder.

[0131] Step 1.2)

[0132] In step 1.2), the solid material to be treated obtained in step 1.1) is leached with an acid solution ("leaching" in FIG. 1 ) to obtain a first treatment solution containing Li, Fe, and P ("first treatment solution" in FIG. 1 ).

[0133] The acid solution is used to dissolve lithium iron phosphate, copper oxide, Al and other substances, so that elements such as Li, Fe, P, Cu, Al, etc. enter the solution. The acid solution can be hydrochloric acid, sulfuric acid or nitric acid solution, preferably hydrochloric acid.

[0134] When hydrochloric acid is used, the mass ratio of HCl to the solid to be treated can be 0.10-0.30:1, preferably 0.13-0.26:1, or even more preferably 0.14-0.20:1, based on the mass of HCl used in the leaching process and the mass of the solid to be treated. For example, the amount of HCl used can be 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, or 0.30 parts by mass per 1 part by mass of the solid to be treated, or within a range defined by any two of these. A mass ratio of 0.10-0.30:1 can ensure sufficient and rapid dissolution of substances such as lithium iron phosphate, copper oxide, and Al. Higher mass ratios can also be used. However, this is not preferred from an economic and environmental perspective.

[0135] Preferably, the leaching process is carried out under stirring.

[0136] The leaching process can be carried out for at least 4 hours, for example 6-48 hours or longer. For example, the leaching process can be carried out for 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48 hours, or within the range defined by any two thereof. It will be understood by those skilled in the art that the leaching process time refers to the time from the time the solid to be treated begins to contact with the hydrochloric acid solution.

[0137] The leaching process may be performed at a liquid-to-solid mass ratio of 3.0-50.0:1, for example, 3.0-35.0. For example, the liquid-to-solid ratio may be 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, 10.0, 10.5, 11.0, 11.5, 12.0, 12.5, 13.0, 13.5, 14.0, 14.5, 15.0, 15.5, 16.0, 16.5, 17.0, 17.5, 18.0, 18.5, 19.0, 19.5, 20.0, 20.5, 21.0, 21.5, 12.0, 22.5, 23.0, 23.5, 24.0, 24.5, 25.0, 25.5, 26.0, 26.5, 27.0, 27.5 .5, 28.0, 28.5, 29.0, 29.5, 30.0, 30.5, 31.0, 31.5, 32.0, 32.5, 33.0, 33.5, 34.0, 34.5, 35.0, 35.5, 36.0, 36.5, 37.0, 37.5, 38.0, 38.5, 39.0, 39.5, 40.0, 40.5, 41.0, 41.5, 42.0, 42.5, 43.0, 43.5, 44.0, 44.5, 45.0, 45.5, 46.0, 46.5, 47.0, 47.5, 48.0, 48.5, 49.0, 49.5, 50.0, or in a range defined by any two thereof.

[0138] The leaching treatment can be carried out at a suitable temperature, for example, within a temperature range of 20-60°C, such as 20, 25, 30, 35, 40, 45, 50, 55, 60°C, or a temperature range bounded by any two thereof.

[0139] The leaching treatment may be performed as follows: (i) mixing the solid matter to be treated with a hydrochloric acid solution and stirring.

[0140] Alternatively, the leaching treatment may be performed by: (i') mixing the solid matter to be treated with water and stirring to prepare a slurry; and then (ii') adding a hydrochloric acid solution to the obtained slurry and stirring.

[0141] In step (i'), the solid matter to be treated may be mixed with water at a liquid-solid mass ratio of 2.5-49.5:1, for example, 3.0-35.0. The liquid-to-solid mass ratio can be, for example, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, 10.0, 10.5, 11.0, 11.5, 12.0, 12.5, 13.0, 13.5, 14.0, 14.5, 15.0, 15.5, 16.0, 16.5, 17.0, 17.5, 18.0, 18.5, 19.0, 19.5, 20.0, 20.5, 21.0, 21.5, 12.0, 22.5, 23.0, 23.5, 24.0, 24.5, 25.0, 25.5, 26.0, 26.5, 27. .0, 27.5, 28.0, 28.5, 29.0, 29.5, 30.0, 30.5, 31.0, 31.5, 32.0, 32.5, 33.0, 33.5, 34.0, 34.5, 35.0, 35.5, 36.0, 36.5, 37.0, 37.5, 38.0, 38.5, 39.0, 39.5, 40.0, 40.5, 41.0, 41.5, 42.0, 42.5, 43.0, 43.5, 44.0, 44.5, 45.0, 45.5, 46.0, 46.5, 47.0, 47.5, 48.0, 48.5, 49.0, 49.5, or in a range defined by any two thereof.

[0142] In step (i'), the stirring time can be 1-24 hours, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24 hours, or within the range defined by any two thereof.

[0143] In step (ii'), the mass ratio of HCl to the solid to be treated can be 0.10-0.30:1, preferably 0.13-0.26:1, or preferably 0.14-0.20:1, based on the mass of HCl in the added hydrochloric acid solution and the mass of the solid to be treated. For example, the amount of HCl used can be 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21, 0.22, 0.23, 0.24, 0.25, 0.26, 0.27, 0.28, 0.29, or 0.30 parts by mass relative to 1 part by mass of the solid to be treated, or within the range defined by any two of them. As described above, when the mass ratio is 0.10-0.30:1, sufficient and rapid dissolution of substances such as lithium iron phosphate, copper oxide, and Al can be ensured. Higher mass ratios can also be used. However, this is not preferred from an economic and environmental perspective.

[0144] The concentration of the hydrochloric acid solution added in step (ii') can be 15-37% by mass, for example 20-37% by mass, for example, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37% by mass, or within the range defined by any two of them.

[0145] Steps (i), (i') and (ii') can each be independently carried out at a suitable temperature, for example, at a temperature of 20-60°C, such as 20, 25, 30, 35, 40, 45, 50, 55, 60°C, or a temperature range defined by any two thereof.

[0146] The mass ratio of the hydrochloric acid solution added in step (ii') to the solid to be treated can be 0.45-1.50: 1, for example, 0.60-0.80: 1. For example, in step (ii'), the mass of the hydrochloric acid solution added relative to 1 part by mass of the solid to be treated can be 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, 1.00, 1.05, 1.10, 1.15, 1.20, 1.25, 1.30, 1.35, 1.40, 1.45, 1.50, or within the range defined by any two thereof.

[0147] 45, 46, 47, 48 hours, or within the range defined by any two thereof.

[0148] Other acids such as sulfuric acid or nitric acid can also be used. When other acids such as sulfuric acid or nitric acid are used, the amount used can be the amount obtained by converting the amount described above for HCl to the same number of H atoms. In other words, the amount of hydrogen ions calculated based on the amount of HCl is also applicable when other acids such as nitric acid and sulfuric acid are used. That is, when nitric acid is used, the amount used can be the amount of HCl described herein, and the amount of sulfuric acid can be half the amount of HCl.

[0149] By treating the solid material to be treated containing lithium iron phosphate powder with an acid solution, the lithium iron phosphate powder, copper oxide, and aluminum components contained in the solid material to be treated can be dissolved, the Li, Fe, and P elements can be mixed at the molecular level, and the subsequent removal of copper and aluminum elements can be facilitated.

[0150] When using acid such as HCl for leaching, conductive agents such as carbon black and binders such as polyvinylidene fluoride from batteries such as positive electrodes do not dissolve, so that after the leaching treatment, the resulting mixture will contain carbon residue (solid matter mainly or essentially formed of carbon black).

[0151] Thus, after the leaching treatment, solids are optionally removed from the resulting mixture (not shown in FIG. 1 ), thereby obtaining a first treatment solution.

[0152] In one embodiment, after the acid leaching treatment, solids (carbon residue) (not shown in FIG. 1 ) are removed from the resulting mixture to obtain a first treatment solution.

[0153] The first treatment liquid contains Li ions, iron ions, and phosphate ions, and further contains copper ions, aluminum ions, and other impurity ions.

[0154] Step 1.3)

[0155] In step 1.3), copper ions are removed from the first treatment solution and ferric ions are reduced to ferrous ions ("copper removal" and "reduction" in FIG. 1 ), obtaining a third treatment solution ("third treatment solution" in FIG. 1 ).

[0156] This step can be performed as follows:

[0157] 1.3-1) treating the first treatment liquid with a copper removal agent that selectively converts divalent copper ions into solid precipitates, and optionally separating and removing the solids to obtain a second treatment liquid ("second treatment liquid" in FIG. 1 ); and

[0158] 1.3-2) The second treatment liquid is treated with a reducing agent capable of reducing ferric ions to ferrous ions under an inert atmosphere to obtain a third treatment liquid ("third treatment liquid" in FIG1 ).

[0159] The term "selectively" herein means that the copper remover is capable of converting divalent copper ions into solid precipitates, while not or substantially not converting iron ions, lithium ions, or phosphate ions in the solution into solid precipitates.

[0160] In one embodiment, the copper removal agent can be a reducing agent that reduces divalent copper ions to copper, such as metallic iron, such as iron powder. Alternatively, the copper removal agent can also be a non-reducing agent that converts divalent copper ions into solid precipitates via a double decomposition reaction, such as one or more of sodium sulfide or lithium sulfide.

[0161] In one embodiment, the copper removal agent can be a combination reagent. For example, in addition to the above-mentioned reducing agent such as iron powder, it can also include at least one of the above-mentioned non-reducing reagents such as sodium sulfide or lithium sulfide, preferably lithium sulfide. The non-reducing reagent such as sodium sulfide or lithium sulfide can be added together with the reducing agent such as iron powder. In this case, the non-reducing reagent such as sodium sulfide or lithium sulfide can be added all at once together with the reducing agent such as iron powder, or can be added in steps to achieve multiple copper removals. The non-reducing reagent such as sodium sulfide or lithium sulfide can also be added after the reducing agent such as iron powder to play a secondary copper removal role, so that the copper ion content in the copper removal solution is lower, thereby obtaining a higher quality product; in this case, the reducing agent can be added once or multiple times, and the non-reducing reagent can also be added once or multiple times. By adopting a copper removal agent, substantially all of the copper elements in the solution can be removed, thereby avoiding an excessively high copper impurity content in the final precursor, which helps to improve the performance of the lithium iron phosphate material prepared therefrom.

[0162] Preferably, the copper removal agent is metallic iron (having reducing properties), such as iron powder. When metallic iron is used as a reducing agent, copper ions can be effectively reduced. Furthermore, since iron is a constituent element of lithium iron phosphate, no additional elements are introduced, thereby helping to reduce the introduction of impurities into the lithium iron phosphate prepared from the precursor, avoiding adverse effects on the performance of the lithium iron phosphate material and improving the performance of the manufactured lithium iron phosphate material.

[0163] The copper removal treatment may be performed by mixing the first treatment liquid with the copper removal agent and stirring the mixture.

[0164] In one embodiment, in step 1.3-1), the copper removal agent is used in an excess amount relative to the copper ions contained in the first treatment solution. For example, the amount of the copper removal agent used can be 1.01-2.0 mol, such as 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.10, 1.15, 1.20, 1.25, 1.30, 1.35, 1.40, 1.45, 1.50, 1.55, 1.60, 1.65, 1.70, 1.75, 1.80, 1.85, 1.90, 1.95, 2.00, or a range bounded by any two thereof, relative to 1 mol of the copper ions contained in the first treatment solution.

[0165] Alternatively, for convenience of calculation, the amount of copper remover can also be considered in step 1.1) in the treated solids to be processed and relative to the quality of the treated solids in step 1.1) to be measured, condition is that described copper remover is relative to being contained in step 1.2) in the treated solids or the copper ion excessive use in the first treatment liquid.For example, relative to the step 1.1) in 1 mass part) in the treated solids, the amount of copper remover (for example iron powder, or lithium sulfide or sodium sulfide) can be 0.01-0.10 mass parts, preferred 0.02-0.05 mass parts, for example, can be 0.01,0.02,0.03,0.04,0.05,0.06,0.07,0.08,0.09,0.10 mass parts or by its any two limited ranges.Within the above amount range, can ensure that the copper ion in the solution is all removed substantially, do not increase too high cost simultaneously.Also can adopt the copper remover of higher consumption, but from economic and environmental protection angle, this is not preferred.

[0166] The treatment may be carried out at a suitable temperature, for example, within a temperature range of 20-60°C, such as 20, 25, 30, 35, 40, 45, 50, 55, 60°C, or a temperature range bounded by any two thereof.

[0167] After the copper ions are removed, the solids (including the solid precipitate formed (e.g., sponge copper, or copper sulfide) and any excess solid copper removal agent such as iron powder) may then be optionally removed to obtain a second treatment solution. The removal may be performed by any means known in the art, such as filtering, centrifuging, and / or pouring.

[0168] In step 1.3-2), the second treatment liquid is treated under an inert atmosphere with an excess reducing agent capable of reducing ferric ions to ferrous ions to obtain a third treatment liquid.

[0169] In one embodiment, the inert atmosphere can be any non-oxidizing atmosphere, such as nitrogen, helium, argon, etc. From the perspective of availability and cost, nitrogen is preferably used.

[0170] In one embodiment, an inert gas may be introduced into the second treatment liquid.

[0171] In one embodiment, the reducing agent is metallic iron, preferably iron powder. When metallic iron is used as the reducing agent, on the one hand, it can effectively reduce trivalent iron ions to divalent iron ions. On the other hand, since iron is a constituent element of lithium iron phosphate, it supplements iron without introducing any additional elements, thereby helping to reduce the introduction of impurities into the final prepared lithium iron phosphate, avoiding adverse effects on the performance of the final manufactured lithium iron phosphate material, and improving the performance of the manufactured lithium iron phosphate material.

[0172] The treatment may be performed by mixing the second treatment liquid with the reducing agent and stirring.

[0173] The treatment may be carried out at any suitable temperature, for example, within a temperature range of 20-60°C, such as 20, 25, 30, 35, 40, 45, 50, 55, 60°C, or a temperature range bounded by any two thereof.

[0174] In one embodiment, in step 1.3-2), the reducing agent is used in an excess amount relative to the iron ions contained in the second treatment liquid. For example, the amount of the reducing agent used can be 1.01-2.0 moles per 1 mole of the iron ions contained in the second treatment liquid, for example, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.10, 1.15, 1.20, 1.25, 1.30, 1.35, 1.40, 1.45, 1.50, 1.55, 1.60, 1.65, 1.70, 1.75, 1.80, 1.85, 1.90, 1.95, 2.00, or a range bounded by any two thereof.

[0175] Alternatively, for ease of calculation, the amount of the reducing agent can also be measured relative to the mass of the solid material to be treated in step 1.1), taking into account the total content of copper and iron elements in the solid material to be treated in step 1.1), provided that the reducing agent is used in excess relative to the iron ions contained in the second treatment solution in step 1.3-2). For example, the amount of the reducing agent (e.g., iron powder) relative to 1 part by mass of the solid material to be treated in step 1.1) can be 0.01-0.20 parts by mass, preferably 0.02-0.05 parts by mass, for example, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20 parts by mass, or a range defined by any two of these. Within the above amount range, it is possible to ensure that substantially all of the ferric ions in the solution are reduced to ferrous ions without increasing excessive costs. Higher amounts of reducing agent may also be used, but this is not preferred from an economic and environmental perspective.

[0176] After the reaction is completed, it is preferred not to separate the remaining solid reducing agent (excess iron powder) from the liquid, but to leave the excess iron powder in the solution so that the iron in the solution remains in a divalent state and is not oxidized.

[0177] The Ksp of aluminum phosphate is about 5.8*10 -19 , the Ksp of iron phosphate is about 1.3*10 -22 , the two are very close, so ferric iron and aluminum ions are very easy to co-precipitate. By reducing ferric ions to ferrous ions, the loss of Fe due to subsequent co-precipitation with Al is avoided.

[0178] Considering that divalent iron ions are easily oxidized to trivalent iron ions in an air atmosphere, step 1.3) (or step 1.3-1) and step 1.3-2)), or at least step 1.3-2) is performed in an inert atmosphere.

[0179] As mentioned above, metallic iron such as iron powder can produce copper precipitation with copper ion generation replacement reaction and realize copper removal purpose, and iron powder can also be used as reducing agent on the other hand, and the ferric iron present in the solution is reduced to ferrous iron, and new impurity can not be introduced.Therefore, in a preferred embodiment, step 1.3-1) can be carried out by using metallic iron such as iron powder (copper ion is reduced to metallic copper), and step 1.3-2) can also be carried out by using metallic iron such as iron powder (ferric ion is reduced to ferrous ion).In this case, step 1.3-1) and step 1.3-2) can be carried out separately (i.e. as mentioned above, first add metallic iron such as iron powder to the first treatment solution and carry out copper removal, then after optionally removing formed metallic copper, then add metallic iron such as iron powder to the second treatment solution obtained and ferric ion is reduced to ferrous ion, obtain the 3rd treatment solution), also can merge and carry out (that is, add metallic iron such as iron powder to the first treatment solution and carry out copper removal and ferric ion is reduced to ferrous ion, obtain the 3rd treatment solution).

[0180] Preferably, the third treatment solution is obtained by removing copper ions from the first treatment solution using metallic Fe such as iron powder and reducing the ferric ions to ferrous ions. In this case, the metallic Fe such as iron powder is used in excess relative to the copper ions and iron ions present in the first treatment solution. For example, the amount of metallic iron, such as iron powder, can be 1.01-2.0 mol, for example, 1.01, 1.02, 1.03, 1.04, 1.05, 1.06, 1.07, 1.08, 1.09, 1.10, 1.15, 1.20, 1.25, 1.30, 1.35, 1.40, 1.45, 1.50, 1.55, 1.60, 1.65, 1.70, 1.75, 1.80, 1.85, 1.90, 1.95, 2.00, or a range limited by any two of them, relative to 1 mol of the total amount of copper ions and iron ions contained in the first treatment solution.

[0181] Alternatively, for ease of calculation, the amount of metallic Fe, such as iron powder, can also be measured relative to the mass of the solid material to be treated in step 1.1), taking into account the total content of copper and iron in the solid material to be treated in step 1.1), provided that it is used in excess relative to the total amount of copper ions and ferric ions in the first treatment solution in step 1.1). For example, the amount of metallic Fe, such as iron powder, relative to 1 part by mass of the solid material to be treated in step 1.1) can be 0.01-0.20 parts by mass, preferably 0.02-0.10 parts by mass, for example, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.20 parts by mass, or a range defined by any two of them. Within the above amount range, it can be ensured that substantially all of the copper ions in the solution are removed and substantially all of the ferric ions are reduced to ferrous ions without increasing excessive costs.

[0182] Step 1.4)

[0183] In step 1.4), a pH adjuster is added to the third treatment liquid in the presence of a reducing agent for trivalent iron ions to adjust the pH value to 2.8-4.0, and then the formed precipitate is removed ("pH adjustment and aluminum removal" in Figure 1) to obtain a fourth treatment liquid ("fourth treatment liquid" in Figure 1).

[0184] The reducing agent is, for example, the reducing agent used in step 1.3-2) described above, for example, metallic iron such as iron powder.

[0185] The pH regulator includes but is not limited to at least one of the following: alkaline lithium-containing substances such as lithium carbonate, lithium hydroxide, lithium bicarbonate, lithium oxalate, lithium phosphate, iron-containing substances (such as alkaline iron-containing substances) such as ferrous hydroxide, ferric hydroxide, ferric oxide, ferric oxide, ferric carbonate, ferric phosphate, iron powder, and phosphorus sources such as phosphoric acid, lithium phosphate, and lithium phosphate. When the above-mentioned reagents containing lithium, iron, and phosphorus are used as pH regulators, compared with traditional pH regulators such as liquid caustic soda, ammonia water, calcium oxide, sodium carbonate, etc., it is possible to avoid introducing new impurity elements into the system and avoid the subsequent use of a large amount of pure water to wash the finished lithium iron phosphate product to remove impurity elements such as sodium and sulfur. In addition, the ratio between lithium, iron, and phosphorus can be effectively adjusted, reducing the introduction of other subsequent reagents, simplifying the process, and saving costs.

[0186] In this step, the pH value is adjusted to 2.8-4.0, preferably 3.5-4.0, for example, the pH value can be adjusted to 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4.0, or within the range defined by any two thereof.

[0187] When the pH is adjusted to the above range, for example, the preferred range, impurity elements such as Al and Ti contained in the solution will precipitate out as phosphates. By removing these precipitates, impurities such as Al and Ti in the solution can be substantially removed.

[0188] This step 1.4) can be performed under an air atmosphere or under an inert atmosphere, preferably under an inert atmosphere.

[0189] Step 1.5)

[0190] In step 1.5), the pH value of the fourth treatment liquid is adjusted to 0.2-0.8, and the molar ratio of Li, Fe, and P in the fourth treatment liquid is adjusted to Li:Fe:P=0.95-1.05:0.95-1:1; and the Fe element content is adjusted to 60-210 g / L ("Adjusting element ratio, Fe concentration" in Figure 1) to obtain a fifth treatment liquid as the raw aqueous solution ("Raw aqueous solution" in Figure 1).

[0191] The pH value adjustment in step 1.5) can be performed using the same acid as that used in the leaching process in step 1.2).

[0192] Preferably, the pH value adjustment in step 1.5) is performed using the same acid solution as that used in the leaching process in step 1.2).

[0193] Alternatively or additionally, it can be carried out using an acid solution recovered from the acid solution used in excess during the leaching process described in step 1.2).

[0194] Therefore, the above description of the acid used in step 1.2) also applies here and will not be repeated here.

[0195] The molar ratio of Li, Fe, and P can be adjusted by adding at least one of a lithium source, an iron source, or a phosphorus source.

[0196] The Li source, Fe source, and P source are preferably sources that do not introduce other impurities into the final precursor. The Li source, Fe source, and P source can be provided as separate sources (i.e., a source compound only provides one of Li, Fe, and P elements), or as a combined source of the two (i.e., a source compound simultaneously provides two of Li, Fe, and P elements, such as lithium phosphate and iron phosphate). Preferably, when (needed) a lithium source is used, the lithium source is lithium carbonate, lithium hydroxide, lithium bicarbonate, lithium oxalate, lithium phosphate, lithium monohydrogen phosphate, lithium dihydrogen phosphate, or any combination thereof. Preferably, when (needed) a Fe source is used, the Fe source is ferrous hydroxide, iron powder, iron oxide, ferric oxide, ferric hydroxide, ferric carbonate, iron phosphate, or any combination thereof. Preferably, when (needed) a P source is used, the P source is phosphoric acid, lithium phosphate, iron phosphate, or any combination thereof. The lithium source, Fe source, and P source can be the same or different from each other.

[0197] The molar ratio of Li, Fe, and P in the fourth treatment solution can be adjusted to 0.95-1.05:0.95-1:1.

[0198] For example, the molar ratio of Li, Fe, and P in the fourth treatment liquid can be adjusted so that in the fifth treatment liquid, the Li element is 0.95-1.05 moles per 1 mole of P element, for example, 0.95, 0.96, 0.97, 0.98, 0.99, 1.00, 1.01, 1.02, 1.03, 1.04, 1.05 moles, or within the range limited by any two of them.

[0199] For example, the molar ratio of Li, Fe, and P in the fourth treatment liquid can be adjusted so that in the fifth treatment liquid, the iron element is 0.95-1.00 moles per 1 mole of P element, for example, 0.95, 0.96, 0.97, 0.98, 0.99, 1.00 moles, or within the range limited by any two of them.

[0200] The molar ratio of Li, Fe, and P can be obtained by measuring the respective contents of Li, Fe, and P and then calculating the ratio therebetween. The contents of Li, Fe, and P can be measured by any suitable method known in the art, such as inductively coupled plasma atomic emission spectrometry (ICP).

[0201] By adjusting the molar ratio of Li, Fe, and P in the fourth treatment solution to 0.95-1.05:0.95-1:1, the molar ratio of Li, Fe, and P in the precursor produced in the subsequent process can be controlled, thereby controlling the molar ratio of Li, Fe, and P in the final lithium iron phosphate product. Moreover, because the molar ratio of Li, Fe, and P is adjusted in solution, the Li, Fe, and P elements can be mixed at the molecular level, resulting in a uniform distribution of Li, Fe, and P in the final lithium iron phosphate material, thereby achieving excellent performance.

[0202] Step 1.5) further includes adjusting the Fe content of the solution to 60-210 g / L after adjusting the molar ratio of Li, Fe, and P. This adjustment can be performed, for example, by any means known in the art (e.g., concentration by distillation, evaporation, etc.). Those skilled in the art will appreciate that if the Fe content of the solution is already 60-210 g / L after adjusting the molar ratio of Li, Fe, and P, concentration may not be performed.

[0203] When adjusting (concentrating), the adjustment (concentrating) is carried out to the iron content of the fourth treatment liquid being processed, which is 60-210g / L, for example, 150-200g / L. For example, the iron content can be 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180, 185, 190, 195, 200, 205, 210g / L or within the range defined by any two thereof. By controlling the content of the iron element, on the one hand, the energy consumption during spray sintering can be reduced, and on the other hand, the particle size of the particles obtained by spray sintering can be controlled, which is conducive to reducing the sintering time of synthetic lithium iron phosphate and reducing synthesis cost.

[0204] The concentration of iron in the solution can be determined by any suitable method known in the art. For example, it can be measured by inductively coupled plasma emission spectroscopy (ICP). Alternatively, it can be calculated based on the concentration of iron measured in step (6), the volume of solution entering step (6), and the volume of solution remaining in step (7).

[0205] The conditioning (concentration) is preferably performed at a temperature of 60-110° C. For example, the temperature may be 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110 or within the range defined by any two thereof.

[0206] The heat used for the adjustment (concentration) can be provided by any type of heat source. In a preferred embodiment, the heat used for the concentration is provided at least in part by the sintering exhaust gas produced by the spray pyrolysis in step (2). In a preferred embodiment, under steady-state conditions, the heat is provided entirely by the sintering exhaust gas produced by the spray pyrolysis in step (2).

[0207] When the raw material aqueous solution is prepared from waste lithium iron phosphate batteries by the method of the present invention to prepare the lithium iron phosphate composite precursor (i.e., step (1) is carried out through steps 1.1)-1.5), on the one hand, since the molar ratio of Li, Fe, and P in the precursor synthesized by the present invention corresponds to the molar ratio of Li, Fe, and P in the final lithium iron phosphate material, the demand for Li and Fe sources, especially the demand for expensive Li sources, is reduced in the subsequent preparation of lithium iron phosphate. There is no need to purchase lithium materials to prepare the lithium iron phosphate composite precursor, thereby reducing the manufacturing cost of the lithium iron phosphate material, and eliminating the process and energy required for the decomposition of raw materials such as lithium carbonate. Therefore, compared with the methods and precursors of the prior art, the sintering time for synthesizing lithium iron phosphate can be reduced, and the synthesis cost can be reduced. At the same time, there is no need to further separate the lithium in the waste lithium iron phosphate battery material, and it can be directly utilized, reducing the recycling cost, shortening the element circulation cycle, and improving the element utilization efficiency. On the other hand, when lithium iron phosphate products are manufactured using precursors synthesized from waste lithium iron phosphate batteries through the method of the present invention, the resulting lithium iron phosphate products have a low impurity content, reducing the adverse effects of impurities on product performance; during the preparation process, Li, Fe, and P elements are mixed at the molecular level, thereby ensuring the compositional uniformity of the lithium iron phosphate material prepared therefrom, and achieving a uniform distribution of lithium, iron, and phosphorus elements at the molecular level, which is beneficial to controlling the crystal structure, orientation, and morphology of the lithium iron phosphate material prepared therefrom, thereby facilitating the realization of better electrochemical properties of the lithium iron phosphate material: the lithium iron phosphate material finally prepared has excellent electrochemical properties, which can achieve performance comparable to or even better than that of the fresh lithium iron phosphate material used in the initial manufacturing process of the waste lithium iron phosphate battery as a raw material, such as the first cycle efficiency, the first discharge capacity, etc.

[0208] Step (2)

[0209] In step (2), the raw material aqueous solution prepared in step (1) or the fifth treatment liquid obtained in step 1.5) is spray pyrolyzed in an aerobic environment at 400-800°C ("spray pyrolysis" in Figure 1) to obtain the lithium iron phosphate composite precursor ("lithium iron phosphate composite precursor" in Figure 1). The spray pyrolysis (or spray sintering) can be carried out at a temperature of 400-800°C, preferably 650-750°C. For example, the temperature can be 400, 450, 500, 550, 600, 650, 700, 750, 800°C, or a range limited by any two thereof.

[0210] The spray pyrolysis is carried out in an aerobic environment, which may be, for example, an air environment.

[0211] By carrying out spray pyrolysis within the temperature range and in an aerobic environment, the previously reduced divalent iron is fully oxidized to trivalent iron, effectively ensuring the composition and morphological characteristics of the obtained lithium iron phosphate composite precursor, which is further conducive to controlling the crystal structure, orientation and morphology of the lithium iron phosphate material prepared therefrom. Therefore, the lithium iron phosphate material finally prepared has excellent electrochemical properties, which can achieve comparable or even better performance than the fresh lithium iron phosphate material used as a raw material in the initial manufacturing process of the waste lithium iron phosphate battery, such as the first cycle efficiency and the first discharge capacity. At the same time, the divalent iron is directly oxidized by the oxygen in the spray pyrolysis environment (which can be oxygen in the air), eliminating the need for the addition of an oxidant in solution oxidation and saving oxidation costs. In the prior art, most spray pyrolysis is carried out in an oxygen-free protective atmosphere to ensure the presence of divalent iron in the product, and the cost of the protective gas is much higher than that of free air.

[0212] When the fifth treatment liquid obtained in the above step 1.5) is used for spray pyrolysis, a second effluent containing water vapor and HCl is also generated as a combustion tail gas (corresponding to "HCl recovery" in FIG1 ).

[0213] For example, the spray sintering is performed in a synthesis furnace, wherein the synthesis furnace is an oxidizing atmosphere, preferably an air atmosphere, and the temperature is 400-800° C., preferably 650-750° C. For example, the temperature can be 400, 450, 500, 550, 600, 650, 700, 750, 800° C., or a range bounded by any two thereof.

[0214] The temperature / heat of the synthesis furnace can be provided by any form of heat source. In one embodiment, it is provided by the combustion of natural gas.

[0215] The spray sintering is performed by spraying the raw material aqueous solution from above downward and then sintering.

[0216] For example, in spray sintering, a raw aqueous solution is pumped into a synthesis furnace, where it is atomized by an atomizer at the top of the furnace, forming droplets. These droplets then sinter from top to bottom under the influence of gravity, synthesizing a lithium-containing precursor. The synthesized precursor then settles to the bottom of the furnace due to gravity, where it cools and is discharged as the finished precursor.

[0217] In a preferred embodiment, the second effluent (burning tail gas) is fed (e.g., fed under negative pressure) to the concentrator used for the concentration treatment in step (7), so that the second effluent serves as a heat source for the concentrator to heat the fifth process liquid. Thus, the heat of the burning tail gas can be utilized to evaporate water and HCl.

[0218] The tail gas (third effluent) from the second effluent and coming out of the concentrator contains (a small amount of) heat, water vapor and (a large amount of) HCl. In one embodiment, the tail gas (third effluent and / or first effluent) leaving the concentrator is sent to an absorption tower for heat recovery and absorption of HCl.

[0219] In one embodiment, circulating cooling water is provided in the absorption tower to absorb heat.

[0220] In a preferred embodiment, spray water is provided at the top of the absorption tower to absorb HCl in the tail gas.

[0221] In a preferred embodiment, the hydrochloric acid formed by absorption in the absorption tower is collected in a regenerated acid storage tank.

[0222] In a preferred embodiment, the recovered hydrochloric acid is transferred to the dissolution zone for reuse.

[0223] In a preferred embodiment, the tail gas leaving the absorption tower is discharged from the top of the absorption tower.

[0224] In a preferred embodiment, the tail gas leaving the absorption tower, for example, the tail gas discharged from the top of the absorption tower, is passed into the scrubbing tower.

[0225] In a preferred embodiment, pure water is sprayed on the upper part of the scrubbing tower to absorb the residual HCl in the tail gas.

[0226] In a preferred embodiment, the spray water after absorbing HCl is allowed to enter the washing water storage tank from the bottom of the washing tower.

[0227] In a preferred embodiment, the wash water is transferred to the absorption tower as absorption tower spray water.

[0228] In a preferred embodiment, the washed tail gas is discharged from the top of the washing tower.

[0229] The process of the present invention facilitates the treatment of calcination exhaust gases (e.g., energy and material recovery), thereby improving the process's energy efficiency. HCl and water are effectively recovered, significantly reducing wastewater generation and, in turn, the need for and cost of further wastewater treatment. Furthermore, the wastewater, primarily consisting of HCl and water, can be conveniently recycled, reducing environmental pollution and lowering the need for externally added HCl, further reducing process costs.

[0230] The product prepared by the method according to the second aspect of the present invention is the lithium iron phosphate composite precursor described in the first aspect of the present invention. Therefore, all the descriptions of the "lithium iron phosphate composite precursor" in the first aspect above are applicable here.

[0231] Therefore, in one aspect, the present invention also relates to a lithium iron phosphate composite precursor obtained by the method of the second aspect of the present invention.

[0232] The lithium iron phosphate composite precursor of the present invention or prepared by the method of the present invention has more excellent performance due to the improvement of components, and makes the comprehensive cost of the lithium iron phosphate battery positive electrode material prepared therefrom lower; by improving the preparation method of the lithium iron phosphate composite precursor, the characteristics of the product are effectively guaranteed, and the efficient, low-cost and green recycling of waste lithium iron phosphate batteries is realized, which has broad industrial application prospects.

[0233] Example

[0234] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0235] Preparation Example 1: Preparation of lithium iron phosphate composite precursor

[0236] The waste lithium iron phosphate batteries are discharged, disassembled and sieved in sequence to obtain positive electrode sheets. The positive electrode sheets are crushed and sieved through a disc vibrating screen. The upper aluminum foil is removed to obtain a solid to be processed containing lithium iron phosphate powder.

[0237] 3000 g of water was added to 100 g of the disassembled solid material to be treated, and the mixture was stirred for 4 h. Then, 70 g of a 20 wt% hydrochloric acid solution was added, and hydrochloric acid leaching was continued for 8 h under stirring. The mixture was then filtered to obtain a mixed solution containing Li, Fe, and P after leaching.

[0238] 2 g of iron powder was added to the above mixed solution and stirred for 1 h, after which the solid (except copper) was removed by filtration.

[0239] Then, 2 g of iron powder was added with stirring while nitrogen was bubbled into the solution.

[0240] After 2 hours, lithium hydroxide solution (calculated at a lithium element concentration of 20 g / l) was added to adjust the pH value to 3.5, and the formed solid precipitate was removed by filtration to obtain a mixed solution containing Li, Fe, and P.

[0241] Then, the pH value of the mixed solution was adjusted to 0.2 using a 20 wt % hydrochloric acid solution, and 3.5 g of 85 wt % phosphoric acid was added to make the molar ratio of Li, Fe, and P 1:1:1 (detected by ICP).

[0242] The resulting solution is transferred to a synthesis furnace. This furnace includes a concentration section and a spray drying section. Natural gas combustion generates heat to heat the entire furnace. The furnace is first heated to 700°C. During the heating process, the negative pressure system is activated, and the concentrator cycle is started. After the internal temperature of the synthesis furnace reaches 700°C, the prepared fifth treatment liquid is introduced into the concentrator. After the iron content in the raw materials in the concentrator reaches a concentration of 180g / L, the concentrated solution is pumped into the synthesis furnace and atomized through the atomization device at the top of the synthesis furnace to form small droplets. The small droplets sinter from top to bottom under the action of gravity. The synthesis furnace is filled with air and the sintering temperature is 700°C. The sintering combines to form a lithium-containing precursor. The synthesized precursor is deposited at the bottom of the furnace due to gravity. After cooling at the bottom of the furnace, the material is discharged as the finished precursor.

[0243] Preparation Example 2-3: Preparation of lithium iron phosphate composite precursor

[0244] A lithium iron phosphate composite precursor was prepared in the same manner as in Preparation Example 1, except that the process conditions were changed as shown in Table 1 below.

[0245] Table 1

[0246] Example 1: Preparation of lithium iron phosphate

[0247] Weigh 2198g of the lithium iron phosphate composite precursor of Preparation Example 1, 160g of anhydrous glucose (Xiwang Group, GB / T20880), and 60g of PEG 1500 (Sinopharm Chemical Reagent Co., Ltd., Q / CYDZ2317-2009), mix them together and add them into 3500g of pure water, stirring and mixing for 30 minutes until all the raw materials are evenly mixed and form a slurry. The slurry is then spray-dried at 180°C, and the resulting dry powder is placed in an atmosphere furnace and sintered under nitrogen atmosphere. The temperature is uniformly raised from room temperature to 750°C over 4 hours, sintered for 8 hours, and cooled to room temperature under nitrogen atmosphere to obtain carbon-coated lithium iron phosphate. The obtained carbon-coated lithium iron phosphate is crushed with a jet mill, and the crushed material is lithium iron phosphate.

[0248] Example 2-3: Preparation of lithium iron phosphate

[0249] Lithium iron phosphate was prepared in the same manner as in Example 1, except that the lithium iron phosphate composite precursors of Preparation Examples 2-3 were used instead of the lithium iron phosphate composite precursor of Preparation Example 1, respectively.

[0250] Evaluation Examples

[0251] Evaluation Example 1: X-ray Diffraction (XRD)

[0252] The precursor prepared in Example 1 was subjected to X-ray diffraction (XRD) analysis under the following conditions: using Japan Rigaku UItima IV as the test instrument, Cu target, wavelength Accelerating voltage: 40 kV, accelerating current: 40 mA, scanning range: 10-80°, scanning speed: 5° / min, step size: 0.002°.

[0253] The results are shown in Figures 2A-2B. As can be seen from Figures 2A-2B, the XRD diffraction peaks of the resulting precursor fully match those of Li3Fe2(PO4)3 and Fe2O3. The Li3Fe2(PO4)3 in the sample agrees well with the standard chart PDF#47-0107, belonging to the monoclinic system, space group P21 / n, with lattice parameters a=0.8566nm, b=1.2053nm, and c=0.8596nm, respectively. The sample also contains diffraction peaks of Fe2O3, a hematite phase, which agree well with the standard chart PDF#85-0987 and belong to the hematite phase. The peak at 2θ=20.7° is characteristic of Li3Fe2(PO4)3, and the peak at 2θ=35.7° is characteristic of Fe2O3, indicating that the resulting precursor is composed of both Li3Fe2(PO4)3 and Fe2O3.

[0254] Evaluation Example 2: Scanning Electron Microscopy

[0255] The precursor prepared in Preparation Example 1 was subjected to scanning electron microscopy (SEM) analysis under the following conditions: using a tungsten filament scanning electron microscope VEGA LMS from TESCAN, an accelerating voltage of 10 keV, and magnifications of 1000 times and 30000 times, respectively.

[0256] The results are shown in Figures 3A-3B. As can be seen from Figures 3A-3B, the precursor prepared in Preparation Example 1 is mainly in the form of flake aggregates of fragments formed by crushing hollow spheres.

[0257] Evaluation Example 3: Energy Dispersive X-ray Spectroscopy (EDS) Analysis

[0258] The precursor prepared in Preparation Example 1 was subjected to EDS analysis using an XFlash Detector 630M instrument produced by Bruker, Germany, under the following conditions: acceleration voltage: 15 keV, conductive adhesive: double-sided carbon conductive adhesive, working distance: 15 mm.

[0259] The results are shown in Figures 4(a)-4(d). As can be seen from Figures 4(a)-4(d), the Fe, O, and P elements are evenly distributed in the precursor.

[0260] Evaluation Example 4: Element Content Analysis

[0261] For the lithium iron phosphate composite precursor prepared in Preparation Example 1-3 and the lithium iron phosphate prepared in Example 1-3, the contents of elements other than C were measured using inductively coupled plasma atomic emission spectrometry (ICP) as follows.

[0262] First, prepare the lithium iron phosphate composite precursor sample solution and the lithium iron phosphate sample solution: accurately weigh 0.3500g of sample, add 6mL of hydrochloric acid and 2mL of water, place it on a hot plate and heat at 200℃ for 30min, cool to room temperature, and filter out the impurity elements to be tested.

[0263] The content of Li, Fe, and P in each sample was determined by the standard curve method. Before the test, the concentrations of the mixed standard curve were as follows: Li: 1.00, 2.00, 3.00, 4.00, 5.00 μg / mL; Fe: 10.00, 20.00, 30.00, 40.00, 50.00 μg / mL; P: 5.00, 10.00, 15.00, 20.00, 25.00 μg / mL. After cooling and filtration according to the digestion method, the sample was diluted 100 times to measure the content of the above main elements.

[0264] For elements such as Na, K, Ca, Cu, Ni, Cr, Zn, Mg, Al, S, Ni, and Cr in the sample, the standard addition method was used for measurement. Before the sample solution was fixed to volume, the mixed standard solution was added to four parallel digested sample solutions of the same sample in sequence. After the addition, the volume was fixed to 25 mL and the solution was thoroughly shaken on an oscillator. The concentrations of the element standard solution added to the sample after the fixed volume were: 0 μg / mL, 0.2 μg / mL, 0.4 μg / mL, and 0.8 μg / mL. The solution was mixed and then tested.

[0265] The specific settings of the injection system are as follows.

[0266] A standard working curve is made based on the standard sample test, and then the sample to be tested is tested. According to the test value of the sample to be tested, the corresponding content is obtained from the standard curve.

[0267] The C content, magnetic substances, and H2O content in the lithium iron phosphate composite precursor and lithium iron phosphate material are measured according to GB / T 33822-2017.

[0268] The results are shown in Tables 2 and 3. As can be seen from Tables 2-3, the lithium iron phosphate composite precursor material prepared in Preparation Examples 1-3 and the lithium iron phosphate material prepared in Example 1-3 have very low impurity content.

[0269] Evaluation Example 5: Particle size, specific surface area, compacted density, tapped density, and pH measurement

[0270] For the lithium iron phosphate composite precursor material prepared in Preparation Example 1-3 and the lithium iron phosphate material prepared in Example 1-3, the compacted density was measured according to GBT30835-2014, and the particle size, specific surface area, compacted density, tapped density, and pH were measured according to GB / T 33822-2017.

[0271] The results are shown in Table 2 below.

[0272] Table 2: Properties of lithium iron phosphate composite precursors

[0273] Evaluation Example 6: Evaluation of the electrochemical properties of lithium iron phosphate materials

[0274] The lithium iron phosphate, PVDF (HSV900, Arkema, France) and conductive carbon black (Super P) prepared in Examples 1-3 were mixed in a solvent (NMP) at a mass ratio of 90:5:5 and stirred to obtain a slurry. The slurry was then coated on aluminum foil, dried at 100°C for 1.5 hours, and rolled to obtain a positive electrode sheet, wherein the surface density of the electrode sheet was 10 mg / cm 2 , the compacted density of the electrode is 2.1g / cm 3 , and then punched it into positive electrode discs with a diameter of 14 mm. After weighing, it was placed in a vacuum drying oven and dried at 0.1 MPa and 85°C for 8 h to obtain positive electrode discs.

[0275] In an argon glove box, an LIR2016 button cell was assembled using the positive electrode disc, a lithium disc as a counter electrode, a PP-PE-PP composite membrane as a separator, and an electrolyte (TC-E sample K of Tianci Materials).

[0276] Charge and discharge test procedure: The assembled button cell was tested at room temperature with the following initial charge and discharge procedures: 0.1C charge, 0.1C discharge; 0.2C charge, 0.2C discharge; 0.2C charge, 0.5C discharge; 0.2C charge, 1.0C discharge. The charge and discharge cut-off voltages were all 2.0-3.95V.

[0277] The electrochemical properties of the prepared lithium iron phosphate material are shown in Table 3 below.

[0278] Table 3: Performance comparison of unused lithium iron phosphate material before recycling and lithium iron phosphate material of Examples 1-3

[0279] As can be seen from Tables 2-3 above, the precursors prepared in Preparation Examples 1-3 have very low impurity content, so that the lithium iron phosphate materials of Examples 1-3 prepared therefrom are very similar to the unused (fresh) lithium iron phosphate battery materials before recycling in terms of impurity element content, and have comparable or slightly higher first coulombic efficiency, 0.1C and 0.2C first discharge capacities, and the same 1.0C first discharge capacity. Without being bound by theory, this excellent electrochemical performance is believed to be attributed to the uniform element distribution and specific composition of the precursors, resulting in uniform distribution of Li, Fe, and P elements in the final lithium iron phosphate material, as well as better control of the crystal structure, orientation, and morphology.

[0280] The lithium iron phosphate precursor prepared using waste lithium iron phosphate batteries as raw materials using the method of the present invention has excellent performance, which is comparable to or even slightly better than the lithium iron phosphate material synthesized by conventional methods. In addition, since waste lithium iron phosphate batteries are used as raw materials, the preparation of the product has cost advantages and is suitable for mass production, while also enabling the recycling of lithium-ion battery materials. In addition, using the method of the present invention, the HCl and water produced during the synthesis process can be easily recycled, reducing wastewater, and thus being more environmentally friendly. In addition, since the process of preparing lithium iron phosphate does not involve energy-consuming processes such as the decomposition of lithium carbonate, the sintering time for synthesizing lithium iron phosphate is reduced, thereby reducing the synthesis cost.

[0281] The above description is merely an exemplary embodiment of the present invention. It should be noted that, for those skilled in the art, improvements can be made to the present invention without departing from the inventive concept of the present invention, and these improvements all fall within the scope of protection of the present invention.

Claims

1. A lithium iron phosphate composite precursor, characterized in that: It includes Li3Fe2(PO4)3 components and Fe2O3 components, wherein the main element molar ratio of the precursor is Li:Fe:P=(0.95-1.05):(0.95-1):

1.

2. The lithium iron phosphate composite precursor according to claim 1, characterized in that: The Li3Fe2(PO4)3 component belongs to the P21 / n space group.

3. The lithium iron phosphate composite precursor according to claim 1, characterized in that: The Li3Fe2(PO4)3 component is a monoclinic crystal system, and / or the Fe2O3 component is a hematite phase.

4. The lithium iron phosphate composite precursor according to claim 3, characterized in that: The lattice parameters of the monoclinic system are a=0.8566 nm, b=1.2053 nm, and c=0.8596 nm.

5. The lithium iron phosphate composite precursor according to claim 1, characterized in that: The primary particles of the lithium iron phosphate composite precursor are fragment structures formed by hollow spheres, the diameter of the fragments is 50-500nm, and the thickness of the fragments is 20-300nm.

6. The lithium iron phosphate composite precursor according to claim 5, characterized in that: The primary particles agglomerate to form secondary particles, the diameter of the secondary particles is 200nm-50μm, and the thickness of the secondary particles is 50-1000nm.

7. The lithium iron phosphate composite precursor according to claim 1, characterized in that: The specific surface area of ​​the lithium iron phosphate composite precursor is 4.0-30.0 m 2 / g.

8. The lithium iron phosphate composite precursor according to claim 1, characterized in that: The tap density of the lithium iron phosphate composite precursor is 0.3-1.5 g / cm 3 .

9. The lithium iron phosphate composite precursor according to claim 1, characterized in that: The sulfur content of the lithium iron phosphate composite precursor is at most 200 ppm.

10. A method for preparing a lithium iron phosphate composite precursor, characterized in that: The steps include: (1) Solution preparation: Prepare a raw material aqueous solution with a Fe content of 60-210 g / L according to a molar ratio of Li:Fe:P=(0.95-1.05):(0.95-1):1; (2) Spray pyrolysis: spray pyrolysis the raw material aqueous solution in an aerobic environment at 400-800° C. to obtain the lithium iron phosphate composite precursor.

11. The method according to claim 10, characterized in that Step (1) comprises: 1.1) Discharging, disassembling and separating the waste lithium iron phosphate batteries in sequence to obtain a solid material to be treated containing lithium iron phosphate powder; 1.2) Leaching the obtained solid matter to be treated with an acid solution to obtain a first treatment solution containing Li, Fe and P; 1.3) removing copper ions from the first treatment solution and reducing trivalent iron ions to divalent iron ions to obtain a third treatment solution; 1.4) adding a pH adjuster to the third treatment solution in the presence of a reducing agent for trivalent iron ions to adjust the pH value to 2.8-4.0, and then separating and removing the formed precipitate to obtain a fourth treatment solution; 1.5) adjusting the pH value of the fourth treatment solution to 0.2-0.8, using at least one of a lithium source, an iron source or a phosphorus source to adjust the molar ratio of Li, Fe and P in the fourth treatment solution to Li:Fe:P=(0.95-1.05):(0.95-1):1, and adjusting the Fe element content to 60-210 g / L to obtain the raw aqueous solution.

12. The method according to claim 11, characterized in that: The acid used in the leaching treatment in step 1.2) is hydrochloric acid, and preferably the concentration of the hydrochloric acid is 20-37% by weight.

13. The method according to claim 11, characterized in that: Step 1.3) is performed as follows: 1.3-1) treating the first treatment liquid with a copper removal agent, and performing solid-liquid separation to obtain a second treatment liquid; and 1.3-2) treating the second treatment liquid with a reducing agent to obtain the third treatment liquid.

14. The method according to claim 13, characterized in that: The copper removing agent is iron powder, and the reducing agent is iron powder.

15. The method according to claim 11, wherein the pH adjusting agent in step 1.4) is at least one selected from the group consisting of lithium carbonate, lithium hydroxide, lithium bicarbonate, lithium oxalate, ferric hydroxide, iron powder, lithium phosphate, ferrous phosphate, and ferrous dihydrogen phosphate.

16. The method of claim 11, wherein the lithium source in step 1.5) is selected from at least one of lithium carbonate, lithium hydroxide, lithium bicarbonate, lithium oxalate, lithium phosphate, lithium monohydrogen phosphate, and lithium dihydrogen phosphate; the iron source is selected from at least one of ferrous hydroxide, iron powder, iron oxide, ferric oxide, ferric hydroxide, ferric carbonate, and ferric phosphate; and the phosphorus source is selected from at least one of phosphoric acid, lithium phosphate, and ferric phosphate.

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