Method for recovering lithium iron phosphate from waste batteries

Abstract

The embodiment of the application discloses a waste battery lithium iron phosphate recovery method, comprising the following steps: dissolving black powder recovered from waste batteries by using a mixed organic acid solution to obtain a first dissolving solution; detecting the actual element proportion of lithium, iron and phosphorus in the first dissolving solution; adding lithium source, iron source, phosphorus source and dispersant into the dissolving solution according to the required element proportion of a precursor and the actual element proportion to obtain a second dissolving solution; performing sand grinding mixing on the second dissolving solution and drying to obtain a solid-phase precursor; sintering the precursor to obtain a to-be-screened crystal; and crushing and screening the to-be-screened crystal to obtain lithium iron phosphate. The energy consumption of the sand grinder is reduced, the sand grinding efficiency is improved, and the particle size after grinding is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of battery recycling, in particular to a waste battery lithium iron phosphate recycling method. BACKGROUND

[0002] In recent years, the overall sales of new energy vehicles in China have shown a growing trend, and the expansion of the battery new energy industry chain has been in full swing. Perfecting the waste recycling network, realizing the recycling of renewable resources, promoting the recycling of retired power batteries and other emerging industrial waste. The lithium resources contained in the positive materials of waste lithium ion batteries are strategic metals for the country, and also a scarce resource in China. It is of great significance to realize the clean recovery of lithium in the positive material. Moreover, the recycling and reuse of LiFePO4 waste batteries not only can reduce environmental pollution, but also has certain economic benefits, and has a great promoting effect on the sustainable development of the battery industry.

[0003] Lithium iron phosphate has stable structure, and although it has obvious lithium deficiency after multiple cycles, it can still maintain the olivine structure. Therefore, by regenerating the recycled lithium iron phosphate, regenerated lithium iron phosphate with performance not inferior to new lithium iron phosphate can be obtained.

[0004] In the process of regenerating and recycling lithium iron phosphate, water is used as a medium for sanding ferroferric oxide, and the minimum particle size can reach 1-3 microns. Continuing to sand ferroferric oxide particles will cause agglomeration and coarsening, and cannot meet the demand for nanoscale.

[0005] At present, there is no effective solution to the problems in the prior art. SUMMARY

[0006] To solve the above problems, the present application provides a waste battery lithium iron phosphate recycling method, which adds a dispersing agent to the dissolution solution before sanding to reduce the particle size of ferroferric oxide to nanoscale to solve the problems in the prior art.

[0007] To achieve the above purpose, the present application provides a waste battery lithium iron phosphate recycling method, which comprises: dissolving the black powder recovered from waste batteries with a mixed organic acid solution to obtain a first dissolution solution; detecting the actual element ratio of lithium, iron and phosphorus elements in the first dissolution solution, and adding lithium source, iron source, phosphorus source and dispersing agent to the dissolution solution according to the required element ratio of the precursor and the actual element ratio to obtain a second dissolution solution; sanding and mixing the second dissolution solution, drying to obtain a solid precursor; sintering the precursor to obtain a to-be-screened crystal; crushing and screening the to-be-screened crystal to obtain lithium iron phosphate.

[0008] Further, the iron source is diiron trioxide; the lithium source is lithium carbonate; the phosphorus source is phosphoric acid; the adding of the lithium source, the iron source, the phosphorus source and the dispersant in the dissolving solution according to the required element proportion and the actual element proportion of the precursor to obtain the second dissolving solution comprises: determining the element proportion to be added according to the required element proportion and the actual element proportion; weighing the lithium carbonate, the diiron trioxide and the phosphoric acid according to the element proportion to be added and adding them into the first dissolving solution; adding the dispersant into the first dissolving solution to obtain the second dissolving solution.

[0009] Further, the dispersant comprises an alumina dispersant and xanthan gum; the adding amount of the alumina dispersant is 0.2% of the first dissolving solution, and the adding amount of the xanthan gum is 0.5% of the first dissolving solution.

[0010] Further, the sanding mixing of the second dissolving solution comprises: adding the second dissolving solution into a dissolving tank of a sanding machine; gradually increasing the rotating speed of the sanding machine from 200 rpm to 900 rpm; detecting the current element proportion of lithium element, iron element and phosphorus element in the second dissolving solution after sanding for 4 hours; adding the lithium source, the iron source and the phosphorus source according to the current element proportion and the required element proportion; and continuing to grind the second dissolving solution until the slurry is uniformly dispersed and does not settle within 2 hours.

[0011] Further, the diameter of the zirconium beads of the sanding machine is 0.3-0.4 mm.

[0012] The above technical solution has the following beneficial effects: the diiron trioxide is effectively sanded, the suitable dispersant is selected, the sanding machine loss and energy consumption are reduced, the sanding efficiency is improved, the particle size index of the diiron trioxide is met under low energy consumption and high efficiency, the scrapped lithium iron phosphate is converted into high-performance lithium iron phosphate through the resynthesis process, and the technical added value of the scrapped lithium iron phosphate is improved. BRIEF DESCRIPTION OF DRAWINGS

[0013] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creating laborious work.

[0014] Figure 1 is a flow chart of the waste battery lithium iron phosphate recycling method provided by the embodiments of the present application;

[0015] Figure 2 is a flow chart of the dissolving solution adjusting method provided by the embodiments of the present application;

[0016] Figure 3is a flow chart of the dissolving solution sanding method provided by the embodiment of the present application. DETAILED DESCRIPTION

[0017] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present application.

[0018] To solve the problem that the particle size cannot be effectively reduced when sanding ferric oxide in the prior art, the embodiment of the present application provides a waste battery lithium iron phosphate recovery method, Figure 1 is a flow chart of the waste battery lithium iron phosphate recovery method provided by the embodiment of the present application, as shown in the figure, the method comprises: Figure 1

[0019] S1, using a mixed organic acid solution to dissolve the black powder recovered from the waste battery to obtain a first dissolving solution;

[0020] The mixed organic acid system can well dissolve the lithium iron phosphate recovered from the retired power battery, and the active substances in the black powder of the waste battery are introduced into the mixed acid to obtain the first dissolving solution.

[0021] S2, detecting the actual element ratio of lithium element, iron element and phosphorus element in the first dissolving solution, and adding lithium source, iron source, phosphorus source and dispersant in the dissolving solution according to the required element ratio of the precursor and the actual element ratio to obtain a second dissolving solution;

[0022] By detecting the phosphorus element, lithium element and iron element in the first dissolving solution, the actual element ratio of the lithium element, the iron element and the phosphorus element in the first dissolving solution is determined, and different amounts of lithium source, iron source, phosphorus source and dispersant are added in the first solution according to the required element ratio of the precursor, so as to meet the demand of synthesizing lithium iron phosphate material, to obtain the second dissolving solution. In this process, it should be ensured that each element in the dissolving solution maintains ionic state. The required element ratio is P: Fe: Li (mol) = 1: 1: 1.

[0023] The dispersant is an interfacial active agent with both lipophilicity and hydrophilicity in the molecule, which can uniformly disperse inorganic and organic solid and liquid particles that are difficult to dissolve in liquid, and can improve and improve the dispersing performance of the object material. It helps to crush particles and prevent the agglomeration of crushed particles to maintain dispersion stability, and can also prevent the settlement and agglomeration of particles to form a stable suspension required by the two amphiphilic reagents.

[0024] ​The dispersant required in the embodiment has good dispersing performance, can prevent mutual aggregation of particles, has proper compatibility with the solvent, has good stability in acid and certain temperature, and does not affect the performance of the synthetic material and is non-toxic.

[0025] As an optional implementation, the dispersant can be one or more of polyethylene glycol, polypropylene glycol, alumina dispersant, polyvinyl alcohol and xanthan gum.

[0026] S3, sanding and mixing the second dissolving solution, and drying to obtain a solid-phase precursor;

[0027] After adjusting the components of the dissolving solution, a uniform dispersion system is formed by sanding and mixing. Then, the adjusted slurry needs to be dehydrated to form a solid-phase precursor. The adjusted slurry is converted into the precursor by drying, and it is required that the phosphorus source, the iron source and the lithium source in the precursor are uniformly distributed and mixed at the smallest scale as much as possible, thereby providing favorable conditions for the subsequent sintering process.

[0028] S4, sintering the precursor to obtain a to-be-screened crystal;

[0029] Sintering is generally performed in a sintering furnace during preparation, inert gas is protected in the furnace, and the reaction is performed to obtain lithium iron phosphate with higher density. In the embodiment, the inert gas is preferably nitrogen. The precursor is obtained by heat treatment to obtain the lithium iron phosphate material. In the sintering process, the temperature needs to be controlled by programming, the organic matter is decomposed at a low temperature first, and then the lithium iron phosphate is crystallized at a high temperature stage, and finally the carbon-coated lithium iron phosphate is obtained.

[0030] S5, crushing and screening the to-be-screened crystal to obtain lithium iron phosphate.

[0031] Lithium iron phosphate with reasonable particle size distribution is obtained by crushing and screening. Reducing the particle size can improve the bulk density and thus the battery energy density, effectively shorten the migration path of Li+ in the particles, improve the electronic conductivity and ionic conductivity, and significantly improve the rate performance and low-temperature discharge capacity of the lithium iron phosphate battery.

[0032] As an optional implementation, the iron source is diiron trioxide, the lithium source is lithium carbonate, and the phosphorus source is phosphoric acid.

[0033] Figure 2 The flowchart of the dissolving solution adjusting method provided in the embodiment is shown in FIG. 1. Figure 2 As shown in FIG. 1, the lithium source, the iron source, the phosphorus source and the dispersant are added in the dissolving solution according to the required element ratio and the actual element ratio of the precursor to obtain the second dissolving solution, including:

[0034] S201, determining the element ratio to be added according to the required element ratio and the actual element ratio.

[0035] S202, weighing lithium carbonate, diiron trioxide and phosphoric acid according to the proportion of elements to be added, and adding into the first dissolving solution;

[0036] S203, adding a dispersant into the first dissolving solution to obtain a second dissolving solution.

[0037] The proportion of elements to be added is determined according to the proportion of required elements and the actual proportion of elements, and the adding amount of lithium carbonate, diiron trioxide and phosphoric acid is determined in combination with the proportion of elements to be added and the lithium carbonate, diiron trioxide and phosphoric acid, the corresponding substances are weighed and added into the adjusting tank according to the adding amount, and a certain amount of dispersant is added thereinto, and stirred for 1 h.

[0038] As an optional embodiment, the dispersant includes an alumina dispersant and xanthan gum; the adding amount of the alumina dispersant is 0.2% of the first dissolving solution, and the adding amount of the xanthan gum is 0.5% of the first dissolving solution.

[0039] The alumina dispersant is preferably AD8030.

[0040] As an optional embodiment, Figure 3 is a flow chart of the dissolving solution sanding method provided by the embodiment of the present application, as shown in Figure 3 the second dissolving solution is sanding mixed, including:

[0041] S301, adding the second dissolving solution into a dissolving tank of a sanding machine;

[0042] S302, gradually increasing the rotating speed of the sanding machine from 200 rpm to 900 rpm, detecting the current proportion of elements of lithium element, iron element and phosphorus element in the second dissolving solution after sanding for 4 h, and adding lithium source, iron source and phosphorus source according to the current proportion of elements and the proportion of required elements;

[0043] S303, continuing to grind the second dissolving solution until the slurry is uniformly dispersed and does not settle within 2 h.

[0044] The second dissolving solution in the adjusting tank is poured into the dissolving tank of the sanding machine, and sanding is started, after gradually increasing the adjusting rotating speed from 200 rpm to 900 rpm, the iron content, the phosphorus content, the lithium content and the content of other impurity metal ions are detected by sampling analysis after sanding for 4 h, and the amount of various metals is continuously supplemented according to the results to make the final P: Fe: Li (mol) reach 1: 1: 1. The grinding condition is observed until the slurry is uniformly dispersed and does not settle within 2 h, and then the adjusted slurry enters the next process.

[0045] The sand mill is mainly used for grinding the solid-liquid slurry of the lithium iron phosphate positive material in the lithium iron phosphate recovery equipment configuration in the dissolution and adjustment process. A full ceramic rod pin type nano sand mill is usually used. The parts of the equipment in contact with the material are all resistant to corrosion by acids such as oxalic acid and citric acid. The main body of the machine box is made of high-strength carbon steel, and the surface is painted. The legs are shock-absorbing pads. The grinding cavity volume is 10L, including a blast-proof motor, a digital display variable frequency speed regulator, a pneumatic diaphragm pump for the feeding system, which is resistant to corrosion by oxalic acid and citric acid. The discharge system is a large-area static discharge, which does not block the material and does not jam the grinding beads, with a gap of ≤0.3mm. The rod pins are made of wear-resistant and heat-resistant zirconia ceramic material, the cylinder is made of silicon carbide ceramic material, the double-end mechanical seal is resistant to 0.4Mpa pressure, and the independent cooling system is provided. The automatic shutdown protection is provided for the conditions of material temperature being too high, cylinder pressure being too high, seal liquid level being too low, motor being overloaded, air inlet pressure being too low, and cooling water pressure being too low. The operation column, electric box, pressure gauge, temperature gauge, and electromagnetic valve of the electric control system are safe and durable in the field explosion-proof control box, and the control panel is a PLC automatic control system. 95% zirconia beads of 0.3-0.4mm, 300L ceramic double-layer stirring tank controllable speed stirring, explosion-proof equipment link management, and PVC pipe linking between the stirring tank and the sand mill.

[0046] As an optional implementation, the diameter of the zirconia beads of the sand mill is 0.3-0.4mm.

[0047] Under the diameter of the zirconia beads, tests of various dispersants are carried out, and the following conditions should be reached after sand milling:

[0048] (1) The color of the diiron trioxide remains dark red;

[0049] (2) The particle size of the slurry does not become coarse during the sand milling process;

[0050] (3) The particle size distribution of the sand-milled diiron trioxide reaches the following indexes:

[0051]

[0052] In the adjustment liquid containing nitric acid, citric acid, phosphoric acid, metal ion iron with a concentration of 0.2-0.5mol / L, metal ion 0.2-2ol / L, and a small amount of metal ions copper, aluminum, and magnesium 0.001-0.01mol / L, the PH is kept at 0.5-4, and the temperature is 20-80C. Take 150L of the same batch of dissolution liquid, use polyethylene glycol as a dispersant to carry out tests, and obtain the particle size data as shown in Table 1:

[0053]

[0054] Table 1

[0055] From Table 1, it can be seen that polyethylene glycol as dispersant has no significant effect on reducing the particle size of ferric oxide in the acidic system, and the slurry is settled after 30 minutes, so the particle size cannot be guaranteed to be uniformly dispersed, which affects the uniformity of material combination in the next process.

[0056] Using polypropylene glycol as dispersant, 150L of the same batch of dissolving solution was tested, and the particle size data obtained are shown in Table 2:

[0057]

[0058] Table 2

[0059] From Table 2, it can be seen that polypropylene glycol as dispersant has no significant effect on reducing the particle size of ferric oxide in the acidic system, and the slurry is settled after 30 minutes, so the particle size cannot be guaranteed to be uniformly dispersed, which affects the uniformity of material combination in the next process.

[0060] Using AD8030 as dispersant, 150L of the same batch of dissolving solution was tested, and the particle size data obtained are shown in Table 3:

[0061]

[0062] Table 3

[0063] From Table 3, it can be seen that AD8030 as dispersant has significant effect on reducing the particle size of ferric oxide in the acidic system, and when the addition amount is 0.1%-0.5%, sand grinding for 1h can meet the process requirements, but the slurry is settled after 30 minutes, so the particle size cannot be guaranteed to be uniformly dispersed, which affects the uniformity of material combination in the next process.

[0064] Using polyethylene glycol as dispersant, 150L of the same batch of dissolving solution was tested, and the particle size data obtained are shown in Table 4:

[0065]

[0066] Table 4

[0067] From Table 4, it can be seen that polyethylene glycol as dispersant has no significant effect on reducing the particle size of ferric oxide in the acidic system, and the slurry is settled after 30 minutes, so the particle size cannot be guaranteed to be uniformly dispersed, which affects the uniformity of material combination in the next process.

[0068] Using xanthan gum as dispersant, 150L of the same batch of dissolving solution was tested, and the particle size data obtained are shown in Table 5:

[0069]

[0070] Table 5

[0071] As shown in Table 5, xanthan gum is used as a dispersant, which has a significant effect on reducing the particle size of the ferric oxide in the acidic system, but still fails to meet the index requirements. During the test, when the xanthan gum addition amount is 0.2%, the slurry has some settlement after 24 hours, and when the addition amount is 0.5%, the slurry has no obvious settlement after 24 hours.

[0072] Take 150L of the same batch of dissolved solution, and use xanthan gum and AD8030 as dispersants to perform the test, and the obtained particle size data is shown in Table 6:

[0073]

[0074] Table 6

[0075] As shown in Table 6, the addition amount of AD8030 is 0.1%-0.5%, the addition amount of xanthan gum is 0.3-1%, and the sand milling time is 1h, which can ensure the dispersion effect and prevent settlement, and AD8030 and xanthan gum can be decomposed in the subsequent high-temperature sintering process, which does not affect the performance of the lithium iron phosphate.

[0076] The above technical scheme has the following beneficial effects: effective sand milling of ferric oxide, selection of a suitable dispersant, reduction of sand mill wear and energy consumption, improvement of sand milling efficiency, meeting of the particle size index of ferric oxide under low energy consumption and high efficiency, conversion of scrap lithium iron phosphate into high-performance lithium iron phosphate through a re-synthesis process, and improvement of the technical added value of the scrap lithium iron phosphate.

[0077] The above detailed description of the embodiments of the present application further illustrates the purposes, technical solutions and beneficial effects of the present application. It should be understood that the above content is only a specific embodiment of the present application, and is not used to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A method for recovering spent battery lithium iron phosphate, characterized in that, The application relates to a preparation method of a lithium iron phosphate precursor. The black powder recovered from waste batteries is dissolved by using a mixed organic acid solution to obtain a first dissolving solution; The actual element proportion of lithium, iron and phosphorus in the first dissolving solution is detected, lithium source, iron source, phosphorus source and dispersant are added into the dissolving solution according to the required element proportion of the precursor and the actual element proportion, and a second dissolving solution is obtained; wherein the dispersant comprises an alumina dispersant and xanthan gum; the adding amount of the alumina dispersant is 0.2% of the first dissolving solution, and the adding amount of the xanthan gum is 0.5% of the first dissolving solution; wherein the iron source is diiron trioxide; the alumina dispersant is AD8030; The second dissolving solution is subjected to sand mill mixing and drying to obtain a solid-phase precursor; wherein the sand mill mixing of the second dissolving solution comprises: the second dissolving solution is put into a dissolving tank of a sand mill for sand mill mixing; the zirconium bead diameter of the sand mill is 0.3-0.4 mm; The precursor is sintered to obtain a to-be-screened crystal; The to-be-screened crystal is crushed and screened to obtain lithium iron phosphate.

2. The method according to claim 1, wherein, The lithium source is lithium carbonate; and the phosphorus source is phosphoric acid; The adding of the lithium source, the iron source, the phosphorus source and the dispersant into the dissolving solution according to the required element proportion of the precursor and the actual element proportion to obtain the second dissolving solution comprises: The required element proportion and the actual element proportion are used to determine the element proportion that should be added; Lithium carbonate, diiron trioxide and phosphoric acid are weighed according to the element proportion that should be added and are added into the first dissolving solution; The dispersant is added into the first dissolving solution to obtain the second dissolving solution.

3. The method according to claim 1, wherein: The sand mill mixing of the second dissolving solution comprises: The rotating speed of the sand mill is gradually increased from 200 rpm to 900 rpm, the current element proportion of lithium, iron and phosphorus in the second dissolving solution is detected after sand mill mixing for 4 hours, and the lithium source, the iron source and the phosphorus source are added according to the current element proportion and the required element proportion; The second dissolving solution is continuously ground until the slurry is uniformly dispersed and does not settle within 2 hours.

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