WO2012072619A1

WO2012072619A1 - Process for the recovery of lithium and iron from lfp batteries

Info

Publication number: WO2012072619A1
Application number: PCT/EP2011/071249
Authority: WO
Inventors: Maarten Schurmans; Ben Thijs
Original assignee: Umicore NV SA
Current assignee: Umicore NV SA
Priority date: 2010-11-29
Filing date: 2011-11-29
Publication date: 2012-06-07
Anticipated expiration: 2013-05-29

Abstract

Lithium iron phosphate (LFP) batteries are expected to become widespread in electrical vehicles. The need for recovery of the contained metals, and of lithium in particular, from end-of-live LFP batteries will therefore become pressing in the future. The proposed process allows for the selective leaching and recovery of lithium from lithium iron phosphate. It comprises the steps of: - contacting the phase with an acidic solution in presence of an oxidizing agent, thereby precipitating iron phosphate and solubilizing lithium; - separating the iron phosphate from the lithium-bearing solution by solid/liquid separation; and, - separating the lithium from the solution by precipitation as a salt. This process is particularly ecological with minimal acid consumption as only lithium is leached.

Description

Process for the recovery of lithium and iron from LFP batteries

A lithium iron phosphate (LiFeP0₄) battery, also called LFP battery, is a type of rechargeable battery, specifically a lithium ion battery, which uses LiFeP0₄ as cathode material.

A key advantage of LiFeP0₄ when compared to the typical current consumer products based on LiCo0₂ is the higher current or peak-power rating. Such LFP batteries are therefore particularly suitable for use in electrical vehicles or in hybrid electrical vehicles. Consequently, considerable quantities of such batteries are expected on the scrap market, being production refuses or end-of-live batteries. The need for recycling of the valuable metals in these batteries will arise with the expected popularity of electrical vehicles.

The recovery of the metals in this kind of materials can be performed according to either pyrometallurgical or hydrometallurgical routes. When lithium recycling is envisaged, hydrometallurgical processes may be advantageous.

Such a process is described in EP- 1733451. This document mainly concerns cobalt- bearing batteries, but the divulgation extends to the recovery of iron and lithium from LFP batteries. The batteries are shredded under inert gas, the shreds being physically separated into 4 different phases. One of these phases is a fine fraction, enriched in metal oxides and carbon. When dealing with LFP batteries, this fraction contains the major part of the LiFeP0₄. It is washed and leached in sulfuric acid, thereby solubilizing both lithium and iron. The iron is then precipitated as goethite at a pH of 3.85 under addition of H2O2, and separated. The lithium is precipitated from the solution as phosphate.

According to the above process, both the iron and the lithium are dissolved. This involves a relatively high acid consumption. Excess acid has moreover to be provided during the leaching step, which needs to be neutralized. To cope with this problem of high acid consumption, a selective leaching process is divulged, specifically adapted for the recovery of lithium from the LiFeP0₄ contained in LFP batteries. Starting from battery packs, batteries, or cells, preliminary mechanical processing steps such as shredding or crushing can be used to release the powdery LiFeP0₄ cathode material, thereby rendering it accessible to the leaching media. The preliminary mechanical processing steps may be followed by physical separation steps using sieves as well as magnetic or densitometric means. As one of the phases, a fine fraction is obtained, which typically contains the major part of the LiFeP0₄. This fraction generally also contains most of the anode material, which may be a carbon-based powder also containing some lithium.

In a first embodiment, lithium and iron are recovered from this fine LiFeP0₄-bearing fraction in a process comprising the steps of: contacting this fraction with an acidic solution in presence of an oxidizing agent, thereby precipitating iron phosphate and solubilizing lithium; separating the iron phosphate from the lithium-bearing solution by solid/liquid separation; and, separating the lithium from the solution by its precipitation as a salt.

The acidic solution can be based on sulfuric acid, whereby the contacting step is performed at a pH lower than 3. It is useful to add the oxidizing agent so as to maintain a redox potential of at least 200 mV vs. Ag/AgCl, and preferably of at least 300 mV, so as to maximally suppress the leaching of iron.

When using oxygen as oxidizing agent, a sufficient oxidizing effect can be obtained by contacting the reaction mixture with a gas phase having an oxygen partial pressure of at least 1 hPa. In another embodiment, the reactor is a pressure reactor, allowing for a process temperature of more than 100 °C.

Once the lithium-bearing solution is obtained by solid/liquid separation, lithium can be precipitated as a salt, in particular as a carbonate.

In a final embodiment, lithium and iron are recovered from LFP batteries in a process comprising the steps of: shredding the LFP batteries; separating the shreds into fractions by physical methods, thereby obtaining a LiFeP0₄-bearing phase as a fine fraction; and, said LiFeP0₄-bearing phase being further processed according to any one of the above- described processes.

The separation of fine and coarse fractions can be made by conventional means such as by dry or wet sieving. A cutoff at about 25 μηι is appropriate, although the optimal value depends upon the particle size distribution of the LiFeP0₄ powder used in the batteries.

According to the invention, and assuming oxygen as the oxidizing agent, the selective leaching of lithium can be represented by the reaction:

4 LiFeP0₄ + 2 H₂S0₄ + 0₂→ 2 Li₂S0₄ + 4 FeP0₄ j + 2 H₂0 (1)

This contrasts with the known non-selective leaching, which is represented as:

2 LiFeP0₄ + 3 H₂S0₄→ Li₂S0₄ + 2 FeS0₄ + 2 H₃P0₄ (2)

In this latter case, an additional step is needed to precipitate iron, e.g. as goethite according to:

2 FeS0₄ + 2 H₂0 + H₂0₂→ 2 FeOOH j + 2 H₂S0₄ (2')

From this, it is readily apparent that the acid consumption in (1) is only 0.5 mole per mole of LiFeP0₄, whereas in (2), it is 1.5 mole per mole of LiFeP0₄. The acid generated in (2') cannot be recycled as it has to be continuously neutralized to maintain a pH of about 3 to 4, which is needed to ensure the formation of goethite.

The batteries may be partially or fully discharged before shredding, to lower the risk of fire. The lithium is then mainly present in the cathode material, which is LiFeP0₄. Conversely, partially or fully charged batteries have a significant part of the lithium under metallic form, in the anode, e.g. as LiC₆. Anode material typically also is collected in the fine fraction after shredding. The contained lithium readily reacts and dissolves in the acidic medium used to leach the LiFeP0₄.

The acidity of the solution in reaction (1) has to be chosen so as to avoid the formation of L13PO4, a species that precipitates at pH values above 3. This determines the minimum pH to ensure Li vs. Fe selectivity. Also in reaction (1), the need for the oxidation of Fe to Fe imposes a minimal oxidation power to the reaction medium. This is most adequately achieved using oxygen, with a partial pressure of at least 1 hPa. This can be realized e.g. by bubbling pure oxygen at atmospheric pressure through the reaction mixture, or by using a pressure reactor with an oxygen-bearing atmosphere. The use of a pressure vessel has the advantage of faster kinetics as reaction temperatures of more than 100 °C will typically be used. In addition, pressure leaching allows for a higher p0₂, ensuring a more selective leaching of lithium.

Other oxidizing agents are also suitable, such as mixtures of 0₂, O3, and H₂0₂. The Li-rich liquor can be further processed for the precipitation of Li, e.g. as a carbonate by addition of Na₂CC>3, leading to the formation of Li₂CC>3, an insoluble species that can be separated by filtration.

The FeP0₄ can be reused in agriculture or gardening, or even as a precursor for the manufacture of cathode material for new lithium battery. Examples

The following Examples illustrate the selectivity of the leaching process when using 0₂ or H2O2 as an oxidizing agent, and H2SO4 as acid.

Either an open reactor or a pressure reactor is used. A solids load of about 100 g/1 is chosen, although higher loads of e.g. 400 g/1 could easily be achieved. The reaction conditions are maintained for about 2 h. When using an open reactor, thus working at atmospheric pressure, oxygen (Examples 1, 3, 6, 8 and 10) or air (comparative Example 7) is continuously injected directly into the solution at a rate of 50 1/h. This ensures a pC of 1 hPa in the solution with pure oxygen, and of only 0.21 hPa with air. The redox potential vs. Ag/AgCl amounts to 300 to 550 mV using pure oxygen, and to only 120 mV using air.

In Examples 9 and 11 , the oxidation is performed with H2O2. This is continuously added so as to maintain a redox potential of about 500 mV vs. Ag/AgCl.

The pH is kept sufficiently acidic by continuous addition of H₂SO₄ 9N. Alternatively, it is allowed to start the reaction with an excess of acid, this excess being determined by the expected consumption and by the desire to arrive at a pH below 3 when the reaction terminates.

When using a pressurized reactor, thus working under pressure (Examples 2, 4 and 5), oxygen is added to the gas phase of the reactor at a constant inlet pressure being the sum of the pH₂0 (about 2 hPa at 120 °C and 0.5 hPa at 80 °C) and the desired p0₂ of at least 1 hPa. Obviously, the oxygen could also in this case be injected directly into the solution, as this would tend to further increase the oxidizing potential. Example 6 is comparative, showing a marginally low lithium yield because the leaching solution has a marginally low acidity. A pH of less than 3 (such as 2.5 or 2) is therefore recommended. Example 7 is also comparative, showing an undesirably high iron leaching yield, and thus an unsatisfactory selectivity with respect to lithium. This is due to the lack of oxidizing power of air at atmospheric pressure. When using oxygen as oxidizing agent, a partial pressure of 1 hPa or more is recommended. When using H₂SO₄ as leaching acid, satisfactory results are obtained when the pH is less than 3; using oxygen as an oxidizing agent, satisfactory results are obtained when its partial pressure is 1 hPa or more. This is illustrated in Table 1.

Table 1 : Oxidative leaching of LiFeP0₄

The selective leaching process is further illustrated on a 75:25 mixture of LiFeP0₄ and graphite, which is the typical composition of the fine fraction after shredding LFP batteries. Graphite is quantitatively recovered in the iron phosphate residue. Any lithium in the anode material (as LiC₆) is extracted with excellent yields. This is illustrated in Table 2.

Table 2: Oxidative leaching of a 75:25 mixture of LiFeP0₄ and graphite

Some LFP batteries contain titanium-based anodes, such as Li₄Ti50i₂ instead of graphite. In this case, the Li is selectively leached with respect to both Fe and Ti. Titanium is quantitatively recovered in the iron phosphate, presumably as Ti0₂. Any lithium in the anode material (as L1₄T1₅O ) is extracted with excellent yields. This is illustrated in Table

Table 3 : Oxidative leaching of a 75:25 mixture of LiFeP0₄ and Li₄TisOi₂

Example Acidity Oxidizing Temperature Leaching Leaching agent (°C) yield Li (%) yield Fe (%)

10 lO g/1 0₂, 1 hPa 80 89 5

11 pH 2 H₂0₂ 80 84 1

Claims

1. Process for the recovery of lithium and iron from a LiFePCVbearing phase, comprising the steps of:

- contacting the phase with an acidic solution in presence of an oxidizing agent, thereby precipitating iron phosphate and solubilizing lithium;

separating the iron phosphate from the lithium-bearing solution by solid/liquid separation; and,

separating the lithium from the solution by its precipitation as a salt.

2. Process according to claim 1, wherein the acidic solution comprises sulfuric acid and wherein the contacting step is performed at a pH lower than 3.

3. Process according to claims 1 or 2, wherein the oxidizing agent is added in such a quantity as to maintain a redox potential of at least 300 mV vs. Ag/AgCl.

4. Process according to any one of claims 1 to 3, wherein the oxidizing agent is oxygen and wherein the contacting step is performed at a p0₂ of at least 1 hPa.

5. Process according to any one of claims 1 to 4, wherein the contacting step is performed in a pressurized reactor at a temperature of more than 100 °C.

6 Process any one of claims 1 to 5, wherein lithium is precipitated as a carbonate salt by addition of carbonate anions.

7. Process for the recovery of lithium and iron from LFP batteries, comprising the steps of:

shredding the LFP batteries;

separating the shreds into fractions by physical methods, thereby obtaining a LiFeP0₄- bearing phase as a fine fraction; and,

said LiFeP0₄-bearing phase being further processed according to any one of claims 1 to 6.