METHOD FOR THE HIGH EFFICIENCY RECYCLING OF LITHIUM IRON PHOSPHATE BATTERIES FOR CLOSED LOOP BATTERY PRODUCTION

Abstract

This method recycles lithium iron phosphate batteries to extract cathode active materials, anode active materials, current collector metals, electrolyte, and separator materials in a highly pure state. The process involves the discharging and subsequent disassembly of used batteries into individual componentsanode and cathode electrodes, electrolyte, separator, tape, and tabs, achieved via a brine bath, a dimethyl carbonate bath, and physical dismounting. Anode and cathode materials are then separated from their respective current collectors using specific solvent-cosolvent combinations, followed by purification procedures involving washing, heat treatment, and additional purification steps for the cathode. The process results in the extraction of highly pure battery materials including active anode and cathode materials, current collector metals, electrolyte, and separators. This approach obtains and purifies battery materials rather than base elemental compounds, thereby using few chemicals and having high reclamation efficiency, leading to enhanced recovery rates and high purity of resulting materials.

Claims

1. A method for the recycling of lithium iron phosphate batteries, characterized by the following steps, whereby step (a) is performed first but step (b) and step (c) may be performed in either order or concurrently: (a) the preparation and disassembly of a LFP battery into its components; the components of which include the anode electrode, cathode electrode, electrolyte, and separator and may also include high temperature tape, battery tabs, or other structural components of the battery, including casings, packings, safety valves, circuit devices, and spacers; the preparation and disassembly of which includes discharging the battery, followed by disassembly of the battery's shell, followed by bathing the battery's core in dimethyl carbonate solution, followed by a drying and physical dismounting step to obtain the separated components; (b) the separation of the anode electrode into its component current collector and anode active material mix, followed by the purification of the anode active material mix; whereby the separation of the anode electrode is conducted by immersing the anode electrode in a stripping solution that is composed of a solvent and a cosolvent, and then filtering the solution to extract the separated anode active material mix and the separated current collector; the solvent of which is municipal water, pure water, distilled water, hydrochloric acid, or a combination thereof; the cosolvent of which is either an inorganic solvent or an organic solvent; whereby the purification of the anode active material mix is conducted by having the anode active material mix, that is obtained after the separation, undergo a washing step and a heat treatment step; (c) the separation of the cathode electrode into its component current collector and cathode active material mix, followed by the purification of the cathode active material mix; whereby the separation of the cathode electrode is conducted by immersing the cathode electrode in a stripping solution that is composed of a solvent and a cosolvent, and then filtering the solution to extract the separated cathode active material mix and the separated current collector; the solvent of which is N-methyl pyrrolidone; the cosolvent of which is acetone, tetrahydrofuran, methyl ethyl acetone, methyl ethyl butyl ketone, dimethylformamide, dimethylacetamide, tetramethylurea, dimethyl sulfoxide, trimethyl phosphate, or a combination thereof; whereby the purification of the cathode active material mix is conducted by having the cathode active material mix, that is obtained after the separation, undergo a washing step, the addition of cathode active material mix compounds step, a milling step, and a heat treatment step; whereby the addition of cathode active material mix compounds step of which involves adding lithium and carbon compounds to the cathode active material mix.

2. The method for the recycling of lithium iron phosphate batteries of claim 1, in which, during step (a), dimethyl carbonate is replaced with propylene carbonate, methyl carbonate, ethylene carbonate, ethyl methyl carbonate, acrylonitrile, dimethyl carbonate, or a combination thereof.

3. The method for the recycling of lithium iron phosphate batteries of claim 2, in which, during step (a), during the bathing the battery's core step, nitrogen is bubbled into the solution.

4. The method for the recycling of lithium iron phosphate batteries of claim 1, in which, during step (b), the cosolvent is sulfuric acid, nitric acid, carbonic acid, acetic acid, oxalic acid, citric acid, hypochlorous acid, perchlorate, sodium pyrophosphate, sodium tripolyphosphate, sodium hexametaphosphate, or a combination thereof.

5. The method for the recycling of lithium iron phosphate batteries of claim 1, in which, during step (b), the cosolvent is benzene, toluene, xylene, pentane, hexane, octane, cyclohexane, cyclohexanone, toluene cyclohexanone, chlorobenzene, dichlorobenzene, methylene chloride, methanol, ethanol, propyl alcohol, epoxy propane, methyl acetate, ethyl acetate, propyl acetate, acetone, methyl ethyl ketone, methyl isobutyl ketone, glycol monomethyl ether, ethylene glycol monoethyl ether, glycol monobutyl ether, or a combination thereof.

6. The method for the recycling of lithium iron phosphate batteries of claim 1, in which, during step (b), during immersion, pH is maintained at 6-8.

7. The method for the recycling of lithium iron phosphate batteries of claim 1, in which, during step (b) and step (c) or during step (b) or step (c), the weight ratio of the solvent to the cosolvent is from 99.95:0.05-0.05:99.95.

8. The method for the recycling of lithium iron phosphate batteries of claim 1, in which, during step (b) and step (c) or during step (b) or step (c), immersion is carried out under rapid stirring at 40-98 C. for 0.5-3 h.

9. The method for the recycling of lithium iron phosphate batteries of claim 1, in which, during step (b) and step (c) or during step (b) or step (c), after immersing the electrode in stripping solution, but prior to the purification of the active material mix, the separated current collector and active material mix are dried at 80-200 C.

10. The method for the recycling of lithium iron phosphate batteries of claim 1, in which, during step (c), the lithium compound added is lithium acetate dihydrate (CH.sub.3COOLi.Math.H.sub.2O), lithium hydroxide monohydrate (LiOH.Math.H.sub.2O), lithium hydroxide (LiOH), lithium oxalate (Li.sub.2C.sub.2O.sub.4), lithium carbonate (Li.sub.2CO.sub.3) or a combination thereof, and the carbon compound added is glucose, sucrose, cellulose, dextrose monohydrate, polyethlyene glycol, polyvinyl alcohol, soluble starch, monocrystal/polycrystal crystal sugar, fructose, vinyl pyrrolidone, poly(sugar alcohol), polymethacrylate, or a combination thereof.

11. The method for the recycling of lithium iron phosphate batteries of claim 1, in which, during step (c), during the addition of cathode active material mix compounds step, the ratio of lithium:iron:phosphate ions of the cathode active material mix is initially measured using Inductively Coupled Plasma Atomic Emission Spectroscopy analysis or Inductively Coupled Plasma Mass Spectrometry analysis, and the amount of lithium compound added to the cathode active material mix is an amount that achieves a ratio of lithium:iron:phosphate ions of 1.03-1.05:1:1 within the cathode active material mix.

12. The method for the recycling of lithium iron phosphate batteries of claim 1, in which, during step (c), the mass of carbon added is 0.03-3% the mass of the cathode active material mix.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] FIG. 1 presents a flow chart that illustrates the steps for the recovery of battery components in an embodiment according to the invention.

[0043] FIG. 2 illustrates the discharge capacity and capacity retention % of a lithium iron phosphate battery manufactured using materials recycled according to an embodiment of the present invention. These measurements are compared to those of a lithium iron phosphate battery manufactured using non-recycled materials.

DETAILED DESCRIPTION OF THE INVENTION

[0044] In order to promote the understanding of the present disclosure, the disclosure will be described below in detail, with reference to the preferred embodiment. It should be understood that the embodiment is merely illustrative, and is not intended to limit the scope of the present disclosure. Any changes, modifications and replacements made by those skilled in the art without departing from the spirit of the disclosure should fall within the scope of the disclosure defined by the claims.

Assembly of Pouch-Type LFP Battery

Assembling Positive Electrode

[0045] The positive electrode was prepared by mixing 96.5 wt. % LFP material (99.5% purity), 1.5 wt. % carbon black as a conductive agent, and 3 wt. % polyvinylidene fluoride as a binder, which were dispersed in N-methyl pyrrolidone to form a slurry with a solid content of 55 wt. %. The slurry was then uniformly spread onto aluminum foil as a current collector, roll-pressed, and dried at 110 C. for 12 h to obtain a cathode sheet.

Assembling Negative Electrode

[0046] The negative electrode was prepared by mixing 95.8 wt. % of graphite, 2 wt. % styrene-butadiene rubber and 1.2 wt. % carboxymethyl cellulose as a binder, and 1 wt. % carbon black as a conductive agent. The slurry was then uniformly spread onto copper foil as a current collector, roll-pressed and dried at 100 C. for 12 h to obtain an anode sheet.

Assembling Pouch-Type Battery

[0047] After drying, the resulting cathode sheet and anode sheet were cut into rectangular pieces of size 2.5 cm14.7 cm. The cathode and anode sheets were stacked in an alternating manner and separated by porous polyethylene separators having a thickness of 25 m. The electrolyte was a solution of 1M lithium hexafluorophosphate (LiPF.sub.6) in a mixture of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a volume ratio of 1:1:1. The cells were assembled in an atmosphere with a dew point <45 C.

[0048] The assembled batteries were then subjected to repeated charge and discharge cycles at a constant current rate of 1 C between 2.0V and 3.65V to mimic real-life usage patterns. During these cycles, the battery's discharge capacity and capacity retention percentages were measured. Their nominal capacity fell below 80% of its initial rated capacity after 1200 cycles.

Recycling of Battery

[0049] A 13 Ah used lithium-ion battery was fully discharged by soaking in 1 L of 1M sodium chloride (NaCl) solution for 12 h. After discharging, the lithium-ion battery was disassembled and its cell core was extracted. The cell core was immersed into 1 L dimethyl carbonate at 20 C. within an nitrogen atmosphere, during which nitrogen was constantly bubbled. After filtration, the electrolyte was distilled and collected. The cell core was dried at 80 C. for 2 h and subsequently disassembled into its separator, high temperature tape, metal battery tabs, anode electrode, and cathode electrode. The separator, high temperature tape, and metal battery tabs were collected.

[0050] The anode was immersed in 1 L of a 98:2 wt. % water to hydrochloric acid solution under rapid stirring for 1 h at 50 C. After drying at 80 C. for 1 h, the copper current collector was reclaimed and the resulting anode mixture was heat treated at 700 C. for 7 h in a high purity nitrogen atmosphere. The resulting powder was subsequently sifted and collected.

[0051] The cathode was immersed in 1 L of a 90:10 wt. % N-methyl pyrrolidone to acetone solution under rapid stirring for 1 h at 35 C. After drying at 100 C. for 1 h, the aluminum current collector was reclaimed and the resulting cathode mixture was subjected to ICP-AES analysis, determining the ratio of lithium:iron:phosphate ions to be 0.78:1:1. To compensate, lithium carbonate (Li.sub.2CO.sub.3) was uniformly mixed into the powder to achieve a ratio of lithium:iron:phosphate ions to be 1.02:1:1. A3:1 wt. % mixture of glucose to polyethylene glycol equal to 0.5% of the mass of the lithium iron phosphate was mixed uniformly with the powder as well. The resulting mixture was immersed in water such that the solid weight was 32% and the whole solution was milled to a particle size of 300 nm (D50). The resulting wet powder was heat treated at 700 C. for 7 h in a high purity nitrogen atmosphere. The resulting powder was subsequently sifted and collected.

[0052] The recorded yields for the separator (98%), high temperature tape (96%), metal battery tabs (95%), aluminum current collector (97%), copper current collector (98%), anode active material (98%), and the cathode active material (97%) are indicated.

[0053] Multiple pouch type LFP batteries were constructed and recycled in the manner described in the example. The recycled material was then used to construct multiple pouch type LFP batteries in a similar manner to the method used to create the original pouch type LFP batteries. These batteries' discharge capacities and capacity retention percentages were measured and averaged. These results are compared to the average capacities and capacity retention percentages of the original pouch type LFP batteries and can be seen in FIG. 2. Evidently, the performance of a LFP battery manufactured using materials recycled according to an embodiment of the present invention has excellent capacity and cycling stability.