Process for the preparation of precursor compounds for lithium battery cathodes

Abstract

The present disclosure concerns the production of precursor compounds for lithium battery cathodes. Batteries or their scrap are smelted in reducing conditions, thereby forming an alloy suitable for further hydrometallurgical refining, and a slag. The alloy is leached in acidic conditions, producing a Ni- and Co-bearing solution, which is refined. The refining steps are greatly simplified as most elements susceptible to interfere with the refining steps concentrate in the slag. Metals such as Co, Ni and Mn are then precipitated from the solution, forming a suitable starting product for the synthesis of new battery precursor compounds.

Claims

1. A process for the preparation of a precursor compound for the synthesis of cathode material for rechargeable lithium batteries, comprising the steps of: reducing smelting of a metallurgical charge comprising spent rechargeable lithium batteries or their scrap containing Ni, Co, Al, Li, F, either one or both of Cu and Fe, and fluxing agents, thereby producing an alloy comprising the major part of the Ni, Co, and Cu, at least part of the Fe, and depleted in Al, Li and F; leaching the alloy in a mineral acid, thereby obtaining a Ni- and Co-bearing solution also containing either one or both of Cu and Fe; refining the Ni- and Co-bearing solution, by removing the therein contained Cu and Fe, thereby obtaining a purified Ni- and Co-bearing solution; and simultaneous precipitation of Ni and Co from the purified Ni- and Co-bearing solution as hydroxides or salts, by heat treatment, crystallization, or addition of hydroxide or carbonate, thereby obtaining a solid suitable for the synthesis of cathode material for rechargeable lithium batteries.

2. The process according to claim 1, wherein the process is free from a solvent extraction or ion exchange step in which Ni and/or Co are extracted from the Ni- and Co-bearing solution.

3. The process according to claim 1, wherein the alloy is granulated, atomized or comminuted before the leaching step.

4. The process according to claim 1, wherein the mineral acid is H.sub.2SO.sub.4.

5. The process according to claim 1, wherein the step of leaching is performed under oxidizing conditions.

6. The process according to claim 5, wherein the step of leaching is performed under oxidizing conditions using O.sub.2 or H.sub.2O.sub.2 as oxidizing agent.

7. The process according to claim 5, wherein the removal of Cu in the refining step is performed by precipitation.

8. The process according to claim 7, wherein the removal of Cu in the refining step is performed by precipitation using cementation with the alloy.

9. The process according to claim 1, wherein, in the step of leaching, Co is leached selectively versus Cu by control of pH and redox potential during leaching.

10. The process according to claim 1, wherein the removal of Fe in the refining step is performed under oxidizing conditions leading to the precipitation of a Fe.sup.3+ compound.

11. The process according to claim 10, wherein the removal of Fe in the refining step is performed under oxidizing conditions leading to the precipitation of a Fe.sup.3+ compound using O.sub.2 or H.sub.2O.sub.2 as oxidizing agent.

12. The process according to claim 1, wherein, between the steps of leaching and precipitation, the ratio of the elements Ni to Co to Mn in the purified Ni- and Co-bearing solution is adjusted to a preset value by addition of any one of these elements as a soluble compound.

13. The process according to claim 1, wherein said precursor compound is a solid Ni- and Co-containing product and said solid suitable for the synthesis of cathode material for rechargeable lithium batteries is the same solid Ni- and Co-containing product.

14. The process according to claim 13, wherein the Ni- and Co-containing product also contains Mn, wherein, during the simultaneous precipitation of Ni and Co from the purified Ni- and Co-bearing solution, also a Mn-oxide and/or Mn-hydroxide and/or a Mn-salt is precipitated, by heat treatment, crystallization, or addition of a source of hydroxide ions or carbonate ions, thereby obtaining said Ni- and Co-containing product also containing Mn.

Description

(1) The following example illustrates the invention.

(2) End of life batteries with a composition given Table 1 are recycled in a 60-liter alumina crucible. A starting slag is melted to a temperature of 1450° C. using an induction furnace. Once this temperature is reached, a mixture of end of life batteries and fluxes is gradually added to the liquid slag over a period of 2 hours. Over this time, 50 kg of batteries are added together with 10 kg of limestone and 5 kg of sand to ensure the slag composition with a suitable composition. O.sub.2 is blown at a rate of 220 L/h above the bath during the loading of the feed to combust any metallic Al and carbon in the batteries. Once the final addition is made, CO is blow through the bath at a rate of 300 L/h for 1 hour to obtain the desired reduction degree. Samples are taken from the slag and the alloy and the phases are separated after cooling. The composition of the resulting phases is shown in Table 2.

(3) TABLE-US-00001 TABLE 1 Composition in wt. % of end of life batteries Al Fe Mn Co Cu Ni Li C 10 2 4 4 9 13 2.5 25

(4) TABLE-US-00002 TABLE 2 Detailed material balance of the smelting operation with compositions in wt. % Mass Input (kg) Al Si Ca Fe Mn Co Cu Ni Li C Starting slag 20 20 13 19   — 3 0.2 0.1 4 Batteries 50 10 — — 2 4 4 9 13 2.5 25 Limestone 10 — 2.2 38.0 — — — — — — 11.7 Sand 5 — 46.7 — — — — — — — — Mass Output (kg) Al Si Ca Fe Mn Co Cu Ni Li Alloy 15 0.0 0.0 0.0 6.6 5.8 13.6 30.0 43.5 0.0 Slag 43 19.8 11.8 17.6 0.1 4.0 0.2 0.0 0.1 3.0 Yield Al Si Ca Fe Mn Co Cu Ni Li Alloy 0.0 0.0 0.0 92.0 33.3 95.9 99.1 99.1 0.0 Slag 100.0 100.0 100.0 8.0 66.7 4.1 0.9 0.9 100.0

(5) Part of the alloy phase from the smelting operation is re-melted under inert atmosphere and atomized in a water jet. This yields a powder fraction that is sufficiently fine for leaching and subsequent hydrometallurgical processing.

(6) 600 g of atomized powder is added to a glass beaker filled with 5 L of water. An agitator is used for suspending the powder and for the distribution of oxygen gas that is injected at the bottom of the beaker. The oxygen acts as an oxidizing agent during leaching. The mixture is heated and maintained at 80° C. Concentrated sulfuric acid is slowly supplied to dissolve the powder. The acid flow is controlled to maintain a pH above 1. After adding a near-stoichiometric amount of acid, pH 1 can be maintained without supplying addition acid. This is the end point of the leaching step, at which stage essentially all metal is dissolved. The beaker is cooled, and the content is filtered. The composition of the solution is shown in Table 3.

(7) TABLE-US-00003 TABLE 3 Composition in g/L of the solution after leaching Fe Mn Co Cu Ni 8 7 17 37 54

(8) Next, Cu is selectively removed from this solution by cementation with Ni powder. This is performed by slowly pumping the leach solution into another heated and agitated beaker while simultaneously adding a stoichiometric excess amount of Ni powder to the same beaker. During this process, Ni exchanges with Cu in solution. After filtration, a mixed Cu—Ni cement, and a de-coppered solution is obtained.

(9) In a next step, Fe is removed by hydrolysis. This is performed by reheating the de-coppered solution to 80° C. Oxygen gas is injected in the agitated beaker and a Na.sub.2CO.sub.3 solution is slowly added until a pH of 4 is reached. Under these conditions, iron is precipitated. After filtration, an iron cake and a filtrate are obtained. The composition of the filtrate is shown in Table 4.

(10) TABLE-US-00004 TABLE 4 Composition in g/L of the solution after refining Fe Mn Co Cu Ni <0.01 5 12 <0.01 65

(11) The Co, Mn and Ni concentrations are then corrected to achieve the desired Ni to Co to Mn ratio before final precipitation of the NMC hydroxide product. In this example we aim for a molar ratio of Ni:Co:Mn of 6:2:2. This is achieved by reheating the solution in an agitated beaker at 80° C., adding suitable amounts of cobalt sulfate and manganese sulfate crystals. Also some water is added in this step to obtain the concentrations shown in Table 5.

(12) TABLE-US-00005 TABLE 5 Composition in g/L of the solution after adjusting the Ni:Co:Mn ratio Fe Mn Co Cu Ni <0.01 17 18 <0.01 55

(13) Finally, the NMC metals are precipitated by slowly adding a concentrated NaOH solution until a pH of 10 is reached. After cooling, the NMC hydroxide product is be separated by filtration and washed. Table 6 shows the composition of the final product on dry basis, which is suitable for the synthesis of new battery precursor compounds.

(14) TABLE-US-00006 TABLE 6 Composition in wt. % (on dry) of the solids after precipitation Fe Mn Co Cu Ni 0 12 13 0 38