Method for acid dissolution of LiCoO2 contained in spent lithium-ion batteries

Abstract

A method for the acid dissolution of LiCoO.sub.2 contained in the cathode of lithium ion batteries, using acetic or tartaric acid as leaching agent, the method being characterized in that it comprises a first stage and a second stage, wherein said first stage comprises the step of separating the cathode components, while said second stage comprises the step of dissolving the pure LiCoO.sub.2 with at least one acid. The method allows achieving an economically viable complete recycling process with low environmental impact.

Claims

1. A method for acid dissolution of LiCoO.sub.2 contained in a Li-ion battery cathode, the method comprising a first stage and a second stage, wherein the first stage comprises a step of separating the cathode components by one or more steps of removal of adhesives used to adhere the LiCoO.sub.2 to an aluminum foil in the Li-ion battery, wherein such removal of adhesives is effected by means of one diluted acid selected from the group consisting of H.sub.4C.sub.2O.sub.2, H.sub.6C.sub.4O.sub.6, H.sub.8C.sub.6O.sub.7, and H.sub.2SO.sub.4, and thus obtaining an aluminum foil as a recycling material, an effluent containing a remainder of the acid used in the first stage, and LiCoO.sub.2 without impurities, and wherein the second stage comprises the step of dissolving LiCoO.sub.2 from the first stage with acetic acid or tartaric acid as a leaching agent and hydrogen peroxide as a reducing agent.

2. The method according to claim 1, wherein the removal of adhesives by means of one diluted acid comprises several reuse stages of H.sub.4C.sub.2O.sub.2, H.sub.6C.sub.4O.sub.6, H.sub.8C.sub.6O.sub.7, or H.sub.2SO.sub.4.

3. The method according to claim 2, wherein after removal of adhesives with H.sub.2SO.sub.4, the effluent generated therefrom is dried at low temperature and obtained residues are treated by a waste operator.

4. The method according to claim 1, further comprising a step of recycling the effluent generated after one or more steps of removal of adhesives with one diluted acid selected from H.sub.4C.sub.2O.sub.2, H.sub.6C.sub.4O.sub.6, or H.sub.8C.sub.6O.sub.7 into the second stage, for dissolution of LiCoO.sub.2.

5. The method according to claim 1, wherein the second stage starts from a solid without impurities, which is dissolved with acetic or tartaric acids at a concentration lower than 15% v/v or lower than 5% w/v, using a reaction time of less than 60 minutes and a temperature of 75 C., achieving complete dissolution of LiCoO.sub.2.

6. The method according to claim 1, further comprising a step of subjecting the LiCoO.sub.2 dissolved in the second stage to a sol-gel synthesis method for re-synthesizing LiCoO.sub.2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) For better clarity and understanding of the object of the present invention, it has been illustrated in several figures, in which one of the preferred embodiments has been represented as an example, wherein:

(2) FIGS. 1a and 1b are graphs showing the characterization of LiCoO.sub.2 by (a) XRD and (b) SEM;

(3) FIG. 2 is a graph showing the effect of the relation H.sub.2O.sub.2H.sub.4C.sub.2O.sub.2.

(4) FIG. 3 is a graph showing the effect of the concentration of H.sub.4C.sub.2O.sub.2.

(5) FIG. 4 is a graph showing the effect of reaction time.

(6) FIG. 5 is a graph showing the effect of temperature.

(7) FIG. 6 is a graph showing the effect of the solid/liquid ratio.

(8) FIG. 7 is a graph showing the effect of agitation speed.

(9) FIGS. 8a and 8b show the characterization of residues by (a) XRD and (b) SEM.

DETAILED DESCRIPTION OF THE INVENTION

(10) The invention will now be described in detail with reference to the drawings which illustrate a preferred embodiment by way of example only, which is non-limiting to the scope of the invention.

(11) The method which is an object of the present invention comprises a first stage, relating to the separation of the cathode components. In this stage, the separation of the aluminum foil from the mixed oxide of lithium and cobalt (LiCoO.sub.2) using diluted aqueous solutions of acetic or tartaric or citric or nitric or sulfuric acid at concentrations and times lower than 2% v/v and 15 respectively was carried out at room temperature. With this treatment, any of the adhesives used to adhere the LiCoO.sub.2 to the aluminum foil are dissolved. As a result of this process, the clean aluminum foil (free of glue and LiCoO.sub.2) on the one hand and on the other hand the LiCoO.sub.2 (free of glue and Al) are obtained, after a stage of filtering and washing with distilled water.

(12) At this point, it should be noted that there are several works in the literature regarding the joint treatment of the main components of the cathode and anode (cathode: aluminum+glue+LiCoO2, and anode: copper+carbon+glue+etc.). In most of them, organic solvents or mixtures thereof are used in order to dissolve the glue from both electrodes jointly, and as a result the sample obtained after the above-mentioned treatment contains, in addition to the components of the cathode, the ones from the anode, which pass to the solution in the leaching stage. Since they are leached together, several separation stages prior to dissolution or separation and/or purification treatments after leaching might be needed in order to obtain pure compounds. In addition, the organic solvents employed have the disadvantage of being expensive, flammable, of difficult handling and recycling, and hazardous to health. In a few works, grinding of the entire cathode is carried out, thus obtaining a solid containing, besides LiCoO.sub.2, adhesives and aluminum remains; all of these components will be dissolved in the dissolution stage. In this case, the precipitation stage of Co is difficult due to the presence of aluminum; this has been partially solved by the authors by using specific organic solvents for cobalt, which adds one more separation stage involving an additional solvent, with the problems the latter entails.

(13) Considering the drawbacks described in the present invention, at this stage, diluted H.sub.4C.sub.2O.sub.2, H.sub.6C.sub.4O.sub.6, H.sub.8C.sub.6O.sub.7, HNO.sub.3 or H.sub.2SO.sub.4 acids are used to dissolve the glue and obtain, on one hand, the aluminum foil (material for recycling) and on the other the LiCoO.sub.2 without impurities to be treated in the next stage (2nd stage). The effluent generated after various stages of acids reuse may be appropriately treated, for example in the case of the use of carboxylic acids, these effluents can be incorporated into the LiCoO.sub.2 dissolution step; or by using calcium hydroxide in the case of the effluent containing H.sub.2SO.sub.4, where the remainder is precipitated to yield calcium sulfate (gypsum). After filtration of this product, the remaining liquid is dried at low temperatures and the remainders obtained are treated by a waste operator. It is noteworthy that the amount of glue contained in the cathode of each battery is of about 50 mg depending on the size of said device. In short: the separation stage uses inexpensive and reusable acids, at low concentrations and for a short period of time; the generated effluents are recycled almost completely and in addition the separation of the component to be used in the subsequent dissolution stage (LiCoO.sub.2) is effectively achieved without the need for further treatment stages and/or processes. Considering the above, in this stage, the procedure significantly improves the procedures of the prior art, being for these reason advantageous.

(14) Subsequently, the method of the present invention has a second stage which comprises dissolving the pure LiCoO.sub.2 with different acids to those found in the literature, such as acetic and tartaric. This stage starts from a solid without impurities, which is dissolved with acetic or tartaric acid at low acid concentrations (<15% v/v or <5% w/v) using short reaction times (<60 min) and a temperature of 75 C., thus achieving high dissolutions of the mixed oxide. In this stage a solution containing only Li, Co and acetic or tartaric acid free from impurities is obtained, which allows obtaining: By chemical precipitation, pure lithium and cobalt compounds separately. Known chemical agents are used, such as: with sodium hydroxide, sodium mixed cobalt oxide (CoOCo.sub.2O.sub.3) is obtained and, with oxalic acid, cobalt oxalate (CoC.sub.2O.sub.4) is obtained. Then, the remaining solution is concentrated by evaporation and treated with Na.sub.2CO.sub.3 (traditional method) or CO.sub.2 (new method for this system) to obtain Li.sub.2CO.sub.3. Using the sol-gel synthesis method directly on any of the obtained solutions without the addition of a binder the LiCoO.sub.2 is again obtained (re-synthesized).

(15) It is herein emphasized that, although there are several processes in the literature for dissolution of the cathode, cathode and anode together, and complete battery prior to the freezing or calcination and grinding thereof, these all lead to dissolving all of the sample components, making multistage separation and purification stages necessary to obtain high purity compounds. Other important issues have been described in a part of the second paragraph in the previous item.

(16) Therefore, at this stage, the inventive step lies in the use of leaching agents tartaric or acetic acid not used in any previous works for the dissolution of spent lithium ion batteries cathodes. Obviously, it is clear that the use of acetic acid greatly reduces costs since, as is public knowledge, it is universally available and its commercial price is minimal, besides it being an environmentally friendly and, logically, non-polluting acid. On the other hand, from a purely technical standpoint, as the process starts with of LiCoO.sub.2 without impurities, solutions containing only Li and Co and with high performances in the dissolution of said metals are obtained. The solutions may be thus treated directly in order to obtain compounds of these metals with high purity, avoiding several separation stages; or to re-synthesize good quality LiCoO.sub.2 without need of purifying the solution and also without the need to add a binder. Thus, the method of the invention has advantages over the prior art, making it a simple procedure, in a limited number of stages, while being environmentally friendly and economically favorable.

Exemplary Embodiments

(17) In the following exemplary embodiments of the method of the invention and in the analysis of the results, a sample of 500 spent lithium ion batteries from cell phones of different brands and models were used. These batteries were discharged and dismantled then selecting the cathodes, from which the LiCoO.sub.2 is obtained by dissolving the glue using any of the acids H.sub.4C.sub.2O.sub.2, H.sub.6C.sub.4O.sub.6, H.sub.8C.sub.6O.sub.7, HNO.sub.3 or H.sub.2SO.sub.4. The LiCoO.sub.2 sample was then dried, ground and sieved. The remaining parts of the batteries were stored for future studies.

(18) Materials and Reactants:

(19) The agents used were glacial acetic acid and hydrogen peroxide both of analytical quality, Biopack brand.

(20) Leaching Experiments and Characterization Techniques:

(21) Experiments were conducted in a PVC batch (closed) reactor with a capacity of 500 mL, provided with a heating and agitation system, mounted on a control unit. The characterization of reactants and products was carried out by X-ray diffraction (XRD) on a Rigaku D-Max III C, operated at 35 kV and 30 mA, using K radiation of Cu and Ni filter and, =0.15418 nm. The morphological analysis of the solids was performed by scanning electron microscopy (SEM) and X-ray detection (EDS) on a LEO 1450VP microscope.

(22) Analysis of Results

(23) Sample Characterization

(24) FIG. 1 shows the sample characterization by (a) SEM and (b) XRD. From FIG. 1 (a) it can be seen that the sample is composed of LiCoO.sub.2 (ICDD 01-075-0532). The diffractogram in FIG. 1(a) indicates that only one crystal structure exists in the sample, corresponding to LiCoO.sub.2 (ICDD 01-075-0532). In FIG. 1(b) it can be seen that LiCoO.sub.2 particles have irregular sizes and shapes with rounded edges.

(25) The dissolution efficiency was monitored by the following expression:
X%=[(mimf)/mi]100

(26) where X %, is the dissolution efficiency percentage, mi, is the initial simple mass and mf, is the final mass of the residue after leaching.

(27) Evaluation of the Operating Parameters.

(28) Effect of H.sub.2O.sub.2H.sub.4C.sub.2O.sub.2 Ratio

(29) The effect of the H.sub.2O.sub.2H.sub.4C.sub.2O.sub.2 ratio was studied by working with H.sub.2O.sub.2 in concentrations of 0, 2, 4, 6, 8 and 10% v/v and with H.sub.4C.sub.2O.sub.2 in a concentration of 15% v/v. Experiments were performed at 75 C. for 60 min with a agitation speed of 330 rpm and a solid/liquid ratio of 0.8% w/v. The chemical bond between Co and O in LiCoO.sub.2 is extremely strong and, therefore, dissolution of LiCoO.sub.2 with a weak acid is difficult. When H.sub.2O.sub.2 is added to the reaction system, the oxygen resulting from peroxide decomposition reduces Co (III) to Co (II), favoring the dissolution. Since Co and Li are main components of LiCoO.sub.2, the dissolution of one promotes dissolution of the other [2]. In FIG. 2 it can be seen that by increasing the concentration of H.sub.2O.sub.2, the dissolution rate increases until reaching a concentration of 6% v/v. After such concentration is reached the extraction value remains constant, which may be due to all Co (III) present being reduced. Results showed that the H.sub.2O.sub.2H.sub.4C.sub.2O.sub.2 ratio of 6% v/v-15% v/v, respectively, gave the greatest value for LiCoO.sub.2 dissolution.

(30) Effect of H.sub.4C.sub.2O.sub.2 Concentration

(31) 0-15 2-15 4-15 6-15 8-15 10-15 0 20 40 60 80 100 X (%) H.sub.2O.sub.2/acetic acid ratio (% v/v) 2.5 5.0 7.5 10.0 12.5 15.0 0 20 40 60 80 100 X (%) Concentration of leaching agent (% (v/v)

(32) The study of this variable was performed at 75 C. for 60 minutes, with an agitation speed of 330 rpm, with a H.sub.2O.sub.2 concentration of 6% v/v and a solid/liquid ratio of 0.8%. H.sub.4C.sub.2O.sub.2 in concentrations of 1.25; 2.5; 5; 7.5; 15 and 25% v/v were used.

(33) From FIG. 3 it can be inferred that the increase in the concentration of H.sub.4C.sub.2O.sub.2 has a marked influence on the dissolution. In addition, it is noted that the dissolution percentage decreases after reaching a concentration of 15% v/v, which may be due to that, when reaching this concentration, the system is saturated in protons. The results showed that the best dissolution percentage was obtained by working at a H.sub.4C.sub.2O.sub.2 concentration of 15% v/v.

(34) Effect of Reaction Time

(35) The dissolution with H.sub.4C.sub.2O.sub.2 may be influenced by reaction time. To study the effect of this variable, experiments were conducted at 75 C., with an agitation speed of 330 rpm, a solid/liquid ratio of 0.8% w/v, and a H.sub.2O.sub.2H.sub.4C.sub.2O.sub.2 ratio of 6% v/v-15% v/v. The reaction times studied were 15, 30, 60, 120, 180 and 300 min. In FIG. 4 (a) it can be observed that with increasing reaction time, the percentage of dissolved oxide increases. This behavior may be due to an increased contact time between the leaching agent, the reducing agent and the oxide [7]. Results showed that the optimal reaction time is 300 min.

(36) Effect of Reaction Temperature

(37) The influence of temperature on the oxide dissolution was studied by working with a range of temperatures between 15 C. and 90 C., at 15 C. intervals. Experiments were performed for 60 min with an agitation speed of 330 rpm, a solid/liquid ratio of 0.8% w/v and a H.sub.2O.sub.2H.sub.4C.sub.2O.sub.2 ratio of 6% v/v-15% v/v. FIG. 5 shows the dependence of the reaction system with temperature, the dissolution percentage increases when increasing this variable. The reaction rate and the ion transfer rate are strongly influenced by the temperature so that, at low temperatures, the dissolution rate is governed by the speed at which the chemical reaction occurs. Increasing the temperature increases the reaction rate and, therefore, the ion transfer rate governs the dissolution rate [7]. 0 30 60 90 120 150 180 210 240 270 300 330 0 20 40 60 80 100 X (%) Time (min.) 0.4 0.8 1.2 1.6 2.0 0 20 40 60 80 100 X (%) solid/liquid ratio (/v) 15 30 45 60 75 90 0 20 40 60 80 100 X (%) Temperature ( C.) 0 100 200 300 400 500 0 20 40 60 80 100 X (%) Agitation speed (rpm)

(38) Effect of Solid/Liquid Ratio

(39) The effect of solid/liquid ratio on the dissolving power of the acid system was studied working at 75 C. for 60 min, with an agitation speed of 330 rpm and a H.sub.2O.sub.2H.sub.4C.sub.2O.sub.2 ratio of 6-15% v/v, respectively. The values of solid/liquid ratio studied were: 0.4; 0.8; 1.2; 1.6 and 2% w/v. From FIG. 6 it can be inferred that the solid/liquid ratio has a significant influence on the dissolution process. It is observed that by increasing the solid/liquid ratio, the dissolution percentage decreases because there is more oxide in contact with H.sub.2O.sub.2H.sub.4C.sub.2O.sub.2. The obtained results showed that, working with a ratio of 0.2% w/v, the best dissolution percentages are obtained.

(40) Effect of Agitation Speed

(41) FIG. 7 shows the results of the effect of agitation speed on the dissolution of LiCoO.sub.2. Experiments to study this variable were carried out at 0, 110, 330, 400 and 430 rpm, working for 60 min at 75 C., with a solid/liquid ratio of 0.8% w/v and a H.sub.2O.sub.2H.sub.4C.sub.2O.sub.2 ratio of 6% v/v-15% v/v, respectively. FIG. 7 shows that the system does not have a strong dependence on the agitation speed, but a noticeable difference in working with and without agitation is observed. Agitation caused a decrease in the boundary layer, increasing the amount of leaching reagent going through said layer, which leads to an increase in dissolution percentage [7]. The results showed that the best leaching percentage was obtained working at 330 rpm.

(42) Characterization of Residues

(43) FIG. 8 shows the SEM and XRD of the residues of LiCoO.sub.2 dissolution with 10 20 30 40 50 60 70 500 1000 H.sub.4C.sub.2O.sub.2.

(44) In FIG. 8(a) diffraction lines corresponding to undissolved LiCoO.sub.2 (ICCD 01-075-0532) were identified, the formation of solid products was not detected. In FIG. 8 (b), attacked particles (laminar) and non-attacked particles (rounded) can be observed

(45) Therefore, it can be said that spent lithium ion batteries are an alternative source for the recovery of metals, including Li and Co, and their recycling not only brings economic but also environmental benefits. The operating parameters for optimum acid dissolution of LiCoO.sub.2 with H.sub.4C.sub.2O.sub.2 are: 90 C., a solid/liquid ratio of 0.8% w/v, an agitation speed of 330 rpm and a H.sub.2O.sub.2H.sub.4C.sub.2O.sub.2 ratio of 6% v/v-15% v/v, yielding dissolution values close to 90%.

REFERENCES CITED IN THE PRESENT SPECIFICATION

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