Method for removing copper and aluminum from an electrode material, and process for recycling electrode material from waste lithium-ion batteries

Abstract

The present invention provides a method for removing copper and aluminum from an electrode material and a process for recycling electrode material from waste lithium-ion batteries. The method for removing copper and aluminum from the electrode material comprises: subjecting the electrode material containing electrode active material, copper and aluminum to reaction with an aqueous solution, wherein the aqueous solution has a pH value of higher than 10, and comprises base, oxidizing agent and complexing agent. The process for recycling electrode material from waste lithium-ion batteries comprises: a) harvesting an electrode material containing electrode active material, copper and aluminum from waste lithium-ion batteries; b) removing copper and aluminum from the electrode material according to the foresaid method; and c) further purifying and regenerating the electrode active material for reuse in new lithium-ion batteries. The present invention thus provides a practical and efficient method for recycling active materials from waste lithium-ion batteries.

Claims

1. A method for removing copper and aluminum from an electrode material, comprising: subjecting the electrode material containing electrode active material, copper, and aluminum, to reaction with an aqueous solution, wherein the aqueous solution has a pH value higher than 10, and comprises base, oxidizing agent and complexing agent.

2. The method of claim 1, in which the base in the aqueous solution is one or more selected from the group consisting of inorganic bases with a pKb less than <1.

3. The method of claim 2, in which the base in the aqueous solution is one or more selected from the group consisting of lithium hydroxide (LiOH), sodium hydroxide (NaOH), and potassium hydroxide (KOH).

4. The method of claim 1, in which the pH value of the aqueous solution is higher than 11.

5. The method of claim 1, in which the oxidizing agent is dissolved oxygen.

6. The method of claim 5, in which the dissolved oxygen is provided by aerating oxygen gas into the aqueous solution.

7. The method of claim 1, in which the complexing agent is ammonium hydroxide (NH.sub.4OH).

8. The method of claim 1, in which the concentration of the complexing agent is between 1 mol/L to 10 mol/L.

9. The method of claim 1, in which the reaction temperature is between 20 C. to 90 C., and the reaction time is between 0.5 hour and 100 hours.

10. The method of claim 1, in which the electrode active material is one or more selected from the group consisting of LiCoO.sub.2, LiMn.sub.2O.sub.4, LiNiO.sub.2, LiNiCoO.sub.2, Li(LiNiCoMn)O.sub.2, LiNiCoMnO.sub.2, and LiFePO.sub.4.

11. The method of claim 1, in which the electrode material is powder or slurry.

12. The method of claim 1, in which the electrode material is derived from waste lithium-ion batteries.

13. A process for recycling electrode material from waste lithium-ion batteries, comprising: a) harvesting an electrode material containing electrode active material, and which may contain copper and aluminum, from waste lithium-ion batteries; b) removing copper and aluminum from the electrode material according to the method of claim 1; and c) further purifying and regenerating the electrode active material obtained in operation b) for reuse in new lithium-ion batteries.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a SEM image with X-ray elemental mapping of a LiCoO.sub.2 cathode laminate, containing particles of aluminum and copper, before treatment.

(2) FIG. 2 is an X-ray EDS elemental spectrum of the LiCoO.sub.2 cathode laminate of FIG. 1.

(3) FIG. 3 is a SEM image with X-ray elemental mapping of the LiCoO.sub.2 cathode laminate of FIG. 1, after treatment.

(4) FIG. 4 is an X-ray EDS elemental spectrum of the LiCoO.sub.2 cathode laminate of FIG. 3.

(5) FIG. 5 shows voltage curves for the first 10 cycles of a LiCoO.sub.2 cathode after treatment.

DETAILED DESCRIPTION

(6) In the method for removing copper and aluminum from an electrode material of the present invention, an aqueous solution is used to react with copper and aluminum contained in the electrode material, such that said copper and aluminum are dissolved in the aqueous solution. The aqueous solution comprises base, oxidizing agent and complexing agent. The base is used to dissolve aluminum. The oxidizing agent is used to dissolve copper. And the complexing agent is used to prevent copper hydroxide precipitation. In addition, the pH value of the aqueous solution should be maintained at a relatively high level, and the high enough value (such as higher than 10, and preferably higher than 11) can prevent aluminum hydroxide precipitation.

(7) In the present invention, the electrode material may be harvested from anode or cathode in waste lithium-ion secondary batteries. The electrode material may be used in its conventional harvested form, such as a powder or slurry. The electrode material may be pulverized to a fine particle size (for example, by a hammer mill), and then can be introduced to the solution bath in either a batch or continuous process. The solution is stirred and allowed to react until all of the copper and aluminum is dissolved.

(8) In the present invention, the electrode active material contained in the electrode material may be any kind of conventional electrode active material which includes but is not limited to LiCoO.sub.2, LiMn.sub.2O.sub.4, LiNiO.sub.2, LiNiCoO.sub.2, Li(LiNiCoMn)O.sub.2, LiNiCoMnO.sub.2, and LiFePO.sub.4.

(9) In the present invention, the aqueous solution may be made basic using an inorganic base with a pKb<1, such as lithium hydroxide (EOM, sodium hydroxide (NaOH), potassium hydroxide (KOH), or calcium hydroxide (Ca(OH).sub.2).

(10) In the present invention, the oxidizing agent may be dissolved oxygen. In one embodiment, the aqueous solution is aerated with oxygen gas (O.sub.2) in order to maintain a strongly oxidizing environment, while purging the solution of other undesired dissolved gasses, such as carbon dioxide. Preferably, the dissolved oxygen concentration is maintained near or above ambient levels.

(11) In the present invention, the complexing agent may be any kind of conventional complexing agent that can form a complex compound with Cu.sup.2+. In the most preferred embodiment, the complexing agent is ammonium hydroxide (NH.sub.4OH), and the concentration of NH.sub.4OH in the aqueous solution is maintained between 1 mol/L and 10 mol/L.

(12) In the present invention, the reaction of the electrode material with the aqueous solution is carried out under a condition that the reaction temperature is 20 C. to 90 C., and the reaction time is between 0.5 hour to 100 hours, and preferably 5 hours to 20 hours.

(13) In the present invention, the dissolved aluminum and copper can be re-precipitated either chemically or electrochemically in order to be collected and recycled.

(14) In one preferred embodiment, the method for removing copper and aluminum from an electrode material comprises the following steps:

(15) (1) formulating an aqueous solution comprising base, oxidizing agent and complexing agent that is corrosive to both aluminum and copper, the usage of the base is to maintain the pH value of the aqueous solution at higher than 10, the amount of the oxidizing agent is maintained by aerating with oxygen gas (O.sub.2);
(2) introducing electrode material harvested from waste lithium-ion secondary batteries into the aqueous solution obtained in step (1) for a sufficient time as to dissolve any aluminum and copper initially present in the electrode material; and
(3) filtering, rinsing, and collecting the purified electrode active materials.

(16) In the above preferred embodiment, when the complexing agent is NH.sub.4OH, the reaction mechanisms are as follows:

(17) Aluminum dissolution begins as a localized corrosion process:
Al(s).fwdarw.Al.sup.3++3e.sup.(anodic reaction)
2H.sub.2O+2e.sup..fwdarw.2OH.sup.+H.sub.2(g)(cathodic reaction)

(18) Followed by:
Al.sup.3+(aq)+3OH.sup.(aq).fwdarw.Al(OH).sub.3(s)
Al(OH).sub.3(s)+OH.sup.(aq).fwdarw.Al(OH).sub.4.sup.(aq)

(19) Where the rate of dissolution of Al(OH).sub.3 is dependant on the basicity (pH) of the solution, or amount of OH.sup. present in the solution.

(20) Localized corrosion of copper proceeds according to:
Cu(s).fwdarw.Cu.sup.2+(aq)+2e.sup.(anodic reaction)
O.sub.2+H.sub.2O+2e.sup..fwdarw.2OH.sup.(cathodic reaction)

(21) Where the rate of copper dissolution is dependent on the amount of dissolved oxygen in the solution,

(22) Followed by:
Cu.sup.2+(aq)+4NH.sub.3(aq).fwdarw.Cu(NH.sub.3).sub.4.sup.2+(aq)

(23) Hereinafter, the present invention will be described by way of examples. However, it will be recognized by those skilled in the art that these examples are provided for the purpose of illustration rather than limitation to the range of the present invention.

EXAMPLES

Example 1

(24) A slurry consisting of 90 wt. % ground LiCoO.sub.2 cathode laminate, 5 wt. % aluminum powder, and 5 wt. % copper powder was mixed with polyvinylidene fluoride (PVDF) binder, and coated and dried as a thin film onto a stainless steel substrate. FIG. 1 shows an electron micrograph of a selected area of the electrode film before treatment, and X-ray elemental mapping showing the distribution of cobalt, aluminum and copper particles for the electrode film before treatment. FIG. 2 shows a spectrum of the X-ray elemental composition for the area shown in FIG. 1.

(25) After the area had been mapped, the sample was placed in an aqueous solution comprising 5 mol/L NH.sub.4OH and 1 mol/L LiOH in deionized water, with the dissolved oxygen content maintained by aerating with oxygen gas, and having a pH value above 13. The sample was stirred and allowed to soak in the aqueous solution at room temperature for a period of 12 hours, and then was rinsed with deionized water and dried. The sample was again analyzed in the electron microscope, and the same region was mapped for cobalt, aluminum, and copper. As can be seen in FIGS. 3 and 4, the cobalt particles remained virtually intact within the coated film, while the aluminum and copper particles observed before treatment were completely dissolved away. Furthermore, the solution had adopted a pale blue color, indicating the presence of Cu(NH.sub.3).sub.4.sup.2+ complex ion.

Example 2

(26) To a beaker containing 10 g of aqueous 5 mol/L NH.sub.4OH and 1 mol/L LiOH in deionized water was added 0.2 g of a powder consisting of 90 wt. % ground LiCoO.sub.2 cathode laminate, 5 wt. % aluminum and 5 wt. % copper. The mixture was stirred at room temperature for 12 hours, then the solids were filtered and rinsed with deionized water and dried in a vacuum oven at 90 C. to remove any residual water. The obtained powder was mixed with acetylene black and PVDF to form a slurry, then coated onto aluminum foil to form a new cathode laminate. A coin cell was made comprising the cathode laminate, electrolyte, separator, and a lithium metal anode, and the coin cell was charged to 4.3V then discharged to 3.0V at a current of 0.15 mA. FIG. 5 shows the voltage curves for the first 10 cycles. And the result shows that the cycling performance of the recycled LiCoO.sub.2 is consistent with untreated LiCoO.sub.2. As can be seen from this example, the performance of the recycled electrode active material can be preserved according to the method of the present invention.