Method for quickly upgrading and regenerating lithium iron manganese phosphate from lithium iron phosphate waste powder

Abstract

The invention belongs to the technical field of recycling of positive electrode materials of waste lithium ion batteries, and particularly discloses a method for quickly upgrading and regenerating lithium iron manganese phosphate by utilizing waste lithium iron phosphate powder. According to the method, the inherent characteristics of a leaching agent and an oxidizing agent are utilized, mechanical activation is combined with high-temperature sintering, and the waste lithium iron phosphate positive electrode active material is quickly regenerated into the lithium iron manganese phosphate material. Solid-liquid separation and impurity removal are not needed in the whole process, the obtained precursor can be directly used for preparing lithium manganese iron phosphate, compared with existing recycling, economic benefits can be improved to the maximum extent, influences on the environment can be reduced, and the additional value of recycled products is effectively improved.

Description

Technical Field

[0001] The invention relates to the technical field of recycling waste lithium-ion battery positive electrode materials, and in particular to a method for rapidly upgrading and regenerating lithium iron manganese phosphate by utilizing waste lithium iron phosphate powder. Background Art

[0002] As an excellent energy storage material, lithium iron phosphate (LiFePO4, LFP) plays a vital role in human society. Its advantages such as excellent safety, low cost, low toxicity and no dependence on nickel and cobalt have attracted extensive attention, research and application. At the same time, due to the limited lifespan caused by degradation, the widespread use of lithium iron phosphate batteries will produce a large number of waste batteries, which will cause environmental pollution and waste of resources if not properly disposed. Therefore, from the perspective of reducing pollution, saving resources and economic benefits, their recycling is imperative.

[0003] Since lithium iron phosphate contains almost no other valuable metals besides lithium, traditional leaching to recover waste lithium iron phosphate has no economic advantage. For this reason, the leaching recovery process has begun to develop in the direction of highly selective leaching. Under certain acidic conditions, the positive electrode active material is leached with the assistance of an oxidant to extract valuable metals, and then the iron and lithium elements are separated by precipitation, separation and other methods, and then used to prepare new lithium iron phosphate positive electrode materials, such as CN108390120A and CN108470952A. However, this process engineering process is still relatively lengthy and the operation process is complicated. In particular, in order to fully extract the lithium element, it is often necessary to far exceed the theoretical chemical dose, and secondary pollution caused is inevitable.

[0004] At present, although lithium iron phosphate batteries are the mainstream power batteries, their energy density has reached a bottleneck. 1-x Fe x PO4, LMFP) is considered to be an ideal upgrade of lithium iron phosphate in the future. It has a similar crystal structure to lithium iron phosphate and has the characteristics of stable chemical properties and excellent safety performance. At the same time, the manganese element doped with lithium manganese iron phosphate can increase the voltage platform of the material to 4.1 V, further improving the theoretical energy density of lithium manganese iron phosphate batteries, which helps to break through the bottleneck of lithium iron phosphate energy density. In addition, lithium manganese iron phosphate has a low degree of dependence on rare metals and can be produced on the same line as lithium iron phosphate, with obvious cost advantages. Summary of the invention

[0005] In view of the deficiencies of the prior art, the purpose of the present invention is to provide a mechanochemical process that integrates lithium iron phosphate recovery and preparation to drive the rapid upgrading and regeneration of lithium manganese iron phosphate. This method benefits from the inherent characteristics of the additives, and gives full play to the multiple roles of the leaching agent and the oxidant as grinding aids. In addition to its own oxidizing properties, the oxidant can also be used as a dispersant to provide a solution medium to ensure full contact between the reactants; while the leaching agent provides hydrogen ions, its organic ligands chelate with lithium ions to ensure effective leaching of lithium and directional enrichment of iron phosphate. There is no impurity to be removed in the entire process. The obtained precursor is upgraded and regenerated into lithium manganese iron phosphate by adding phosphorus source, manganese source and lithium source according to the molar ratio of each element in the preparation of lithium manganese iron phosphate, so there is no need to consider the degree of lithium deficiency in the lithium iron phosphate.

[0006] In order to achieve the above object, the specific technical scheme adopted by the present invention is as follows: (1) Discharge the waste lithium iron phosphate batteries, disassemble them, and sort out the positive electrode sheets, negative electrode sheets, separators, etc., soak the waste lithium iron phosphate positive electrode sheets in N-methylpyrrolidone to dissolve the binder PVDF therein, filter, wash, and dry to obtain lithium iron phosphate waste powder, and recycle the N-methylpyrrolidone solvent by rotary evaporation; (2) Take the waste lithium iron phosphate powder and mix it with the leaching agent, add it into a ball mill filled with zirconium oxide beads, and add an oxidant to the mixture. After ball milling for a period of time, obtain part of the raw material of regenerated lithium manganese iron phosphate; Inductively coupled plasma optical emission spectroscopy (ICP-OES) was used to determine the contents of phosphorus, iron and lithium in some raw materials of ball mill.

[0007] (3) Based on the lithium iron manganese phosphate LiMn to be prepared 1-x Fe x The molar ratio of each element in PO4 is adjusted, and appropriate amounts of phosphorus source, manganese source and lithium source are added to the ball mill. The mixture is then placed in the ball mill for secondary ball milling, and the obtained mixed powder is dried.

[0008] (4) The solid powder obtained after drying is transferred into an atmosphere furnace for high-temperature sintering, and an inert gas such as nitrogen or argon is introduced for protection to obtain upgraded and regenerated lithium manganese iron phosphate.

[0009] In the above preparation method, in step (2), the leaching agent is at least one of formic acid, citric acid, acetic acid, malic acid, and tartaric acid, and the molar ratio of the leaching agent to the waste lithium iron phosphate powder is 0.2:1 to 1:1; the oxidant is at least one of hydrogen peroxide and peracetic acid, and the solid-liquid ratio of the waste lithium iron phosphate powder to the oxidant is 10 to 50 g L -1 ; In the above preparation method, in step (2), the ball milling time is 0.5 to 3 h; the ball milling speed is 100 to 500 rpm; In the above preparation method, in step (3), the manganese source is at least one of manganese carbonate and manganese hydroxide; the lithium source is at least one of lithium carbonate and lithium hydroxide; the phosphorus source is at least one of ammonium hydrogen phosphate or ammonium dihydrogen phosphate; wherein the molecular formula LiMn 1-x Fe x PO4, Li: (Fe+Mn): P = (1~1.05): (0.96~1): 1, 0.2≤ x ≤0.7; In the above preparation method, in step (3), the secondary ball milling rate is 100 to 600 rpm; the ball milling time is 0.5 to 6 hours; In the above preparation method, in step (4), the mixed solid powder is placed in an inert atmosphere, pre-sintered at 350-450°C for 1-4 h, then heated to 550-750°C, kept warm for 6-12 h, and the heating rate is 2-10°C min -1 .

[0010] Compared with the prior art, the present invention has the following beneficial effects: The invention discloses a method for rapidly upgrading and regenerating lithium iron manganese phosphate by utilizing waste lithium iron phosphate powder, which gives full play to the multiple functions of additives and coordinated mechanical forces, accelerates the dissociation of lithium iron phosphate crystal phase, and realizes selective leaching of lithium and directional enrichment of iron and phosphorus while maintaining the olivine structure.

[0011] The present invention is based on a mechanochemical process that combines lithium iron phosphate recovery and preparation. By adjusting different feed ratios and combining high-temperature roasting, lithium manganese iron phosphate is directly upgraded and regenerated. The entire recovery process does not require solid-liquid separation and impurity removal, which effectively shortens the process flow and reduces the difficulty of operation, greatly improving the economic efficiency of recycling.

[0012] The present invention upgrades waste lithium iron phosphate into lithium iron manganese phosphate with a simple process, which is similar to the subsequent process in the existing lithium iron phosphate solid phase synthesis process, is completely consistent with the equipment used, reduces construction costs, and is easy to realize industrial large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is a process flow chart of the present invention; Figure 2 The XRD diagrams of the leached product iron phosphate and the upgraded regenerated lithium manganese iron phosphate obtained in Example 1 of the present invention; Figure 3 The graphs are the cycle performance and rate performance of the lithium manganese iron phosphate prepared in Example 1 of the present invention, wherein (a) is the cycle performance and (b) is the rate performance graph. DETAILED DESCRIPTION

[0014] Many specific details are set forth in the following description to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways than those described herein, and those skilled in the art can make similar modifications without violating the connotation of the present invention, so the present invention is not limited to the specific implementation disclosed below.

[0015] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0016] Example 1 (1) After discharging and disassembling the waste lithium iron phosphate battery, the required positive electrode sheet is obtained, and after simple pretreatment to remove the PVDF binder, the waste lithium iron phosphate active material is obtained, and after drying, the waste lithium iron phosphate powder is obtained; (2) Weigh the required lithium iron phosphate waste powder and oxalic acid, mix them in a ball mill filled with zirconium oxide beads, and place them in a molar ratio of 1:0.4. Then, add 30% vol. of oxidant hydrogen peroxide to the mixture, with a solid-liquid ratio of 25 g L -1 and ball-milled at 300 rpm for 0.5 h to obtain the precursor of regenerated lithium manganese iron phosphate; (3) The lithium content leached from the precursor and the amount of lithium iron phosphate waste powder were measured by ICP. 1.03 Mn 0.6 Fe 0.4 PO4 is added with lithium hydroxide, ammonium dihydrogen phosphate and manganese carbonate to mix, and the mixed materials in the ball mill are subjected to secondary ball milling at a ball milling rate of 400 rpm for 6 h, and a mixed powder is obtained after drying; (4) Place the dried mixture into a tube furnace, introduce argon gas, and heat at 2 °C min -1 The temperature was raised to 350 °C, pre-sintered for 1 h, and then further raised to 650 °C and kept for 10 h. After natural cooling, the regenerated lithium manganese iron phosphate positive electrode material was obtained.

[0017] Figure 2 The XRD diagram of the upgraded regenerated lithium manganese iron phosphate in this example is consistent with the characteristic diffraction peaks of the standard card JCPDS: 74-0375 LiMnPO4, indicating that the final prepared material is a pure phase olivine structure. The peak of the sample is sharp, indicating that the material has a high degree of crystallinity. Compared with the diffraction peak of pure phase LiMnPO4, the diffraction peak of the sample is obviously shifted towards the high angle direction to a certain extent. This is because the Fe 2+Doping leads to Fe 2+ The ionic radius is smaller than that of Mn 2+ Ionic radius, Fe 2+ Partially replace Mn 2+ This will reduce the crystal cell parameters and cause the diffraction peak to shift toward higher angles.

[0018] Figure 3 The cycle (a) and rate (b) performance diagrams of the regenerated lithium manganese iron phosphate according to the embodiment of the present invention are shown in the figure. It can be seen from the figure that the discharge specific capacity can reach 121 mA h g at 1C, 2C and 5C rates respectively. -1 , 108 mA hg -1 and 87mA hg -1 , which is significantly higher than the discharge capacity of waste lithium iron phosphate (111 mA h g -1 , 102 mA hg -1 and 71 mA hg -1 , and the capacity retention rate is close to 95.8% after 100 cycles at 1 C, which has good rate capability and cycle stability.

[0019] Example 2 (1) After discharging and disassembling the waste lithium iron phosphate battery, the positive electrode sheet is obtained, and after simple pretreatment to remove the PVDF binder, the waste lithium iron phosphate active material is obtained, and after drying, the waste lithium iron phosphate powder is obtained; (2) Weigh the required lithium iron phosphate waste powder and citric acid, mix them in a ball mill filled with zirconium oxide beads, and place them in a molar ratio of 1:0.2. Then, add 30% vol. of oxidant hydrogen peroxide to the mixture, with a solid-liquid ratio of 10 g L -1 and ball milled at 200 rpm for 1 h to obtain the precursor of regenerated lithium manganese iron phosphate; (3) The lithium content leached from the precursor and the amount of lithium iron phosphate waste powder were measured by ICP. 1.05 Mn 0.8 Fe 0.2 PO4 is added with lithium carbonate, ammonium hydrogen phosphate and manganese carbonate to mix, and the mixed materials in the ball mill are subjected to secondary ball milling at a ball milling rate of 400 rpm for 6 h, and a mixed powder is obtained after drying; (4) Place the dried mixture into a tube furnace, introduce nitrogen, and heat at 2 °C min -1 The temperature was raised to 350 °C, pre-sintered for 2 h, and then further raised to 750 °C and kept for 10 h. After natural cooling, the regenerated lithium manganese iron phosphate positive electrode material was obtained, and its electrochemical properties were tested.

Claims

1. A method for rapidly upgrading and regenerating lithium iron manganese phosphate from lithium iron phosphate waste powder, characterized in that: The steps include: (1) The waste lithium iron phosphate battery is discharged and disassembled, and the obtained positive electrode is soaked in N-methylpyrrolidone and dried to obtain lithium iron phosphate positive electrode powder. The solvent N-methylpyrrolidone can be reused by rotary evaporation; (2) mixing the lithium iron phosphate powder obtained in step (1) with a leaching agent, dispersing the mixture in a ball mill, adding an oxidant, and ball milling the mixture at a certain speed to obtain a leaching slurry; (3) Lithium, iron and phosphorus content of the leached slurry according to step (2) and re-preparation of LiMn 1-x Fe x The molar ratio of lithium, manganese, iron and phosphorus in the PO4 product is adjusted by adding appropriate amounts of phosphorus source, manganese source and lithium source for batching, and the mixture is placed in a ball mill for secondary ball milling and mixing, and then dried to obtain a mixed batch; (4) The mixed ingredients obtained by the secondary ball milling in step (3) are transferred into an inert gas atmosphere for two-stage high-temperature sintering to obtain upgraded regenerated lithium manganese iron phosphate.

2. The method for rapidly upgrading and regenerating lithium iron manganese phosphate using waste lithium iron phosphate powder according to claim 1, characterized in that In step (2), the leaching agent is at least one of malic acid, formic acid, citric acid, tartaric acid, and acetic acid, and the molar ratio of the leaching agent to the lithium iron phosphate waste powder is 0.2:1 to 1:1; the oxidant is at least one of hydrogen peroxide and peracetic acid, and the liquid-to-solid ratio is controlled at 10 to 50 g / L.

3. The method for rapidly upgrading and regenerating lithium iron manganese phosphate using waste lithium iron phosphate powder according to claim 1, characterized in that In step (2), the ball milling rate is 100 to 500 rpm, and the ball milling time is 0.5 to 3 h.

4. The method for rapidly upgrading and regenerating lithium iron manganese phosphate using waste lithium iron phosphate powder according to claim 1, characterized in that In step (3), the manganese source is at least one of manganese carbonate and manganese hydroxide; the lithium source is at least one of lithium carbonate and lithium hydroxide; the phosphorus source is at least one of ammonium hydrogen phosphate and ammonium dihydrogen phosphate; the molecular formula LiMn 1-x Fe x PO4, Li: (Fe+Mn): P = (1~1.05): (0.96~1): 1, 0.2≤ x ≤0.

7.

5. The method for rapidly upgrading and regenerating lithium iron manganese phosphate using waste lithium iron phosphate powder according to claim 1, characterized in that In step (3), the secondary ball milling rate is 100 to 600 rpm, and the ball milling time is 0.5 to 6 h.

6. The method for rapidly upgrading and regenerating lithium iron manganese phosphate using waste lithium iron phosphate powder according to claim 1, characterized in that In step (4), two-stage high-temperature sintering is performed, the pre-sintering temperature is 350-450°C, and the pre-sintering time is 1-4 h; the temperature is increased to the second-stage sintering temperature of 550-750°C, the holding time is 6-12 h, and the heating rate is 2-10°C / min.

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