Processes for the purification and regeneration of active materials of battery electrodes

Abstract

The invention relates to a method for purifying an active material of a battery electrode comprising the following steps: a) providing an active material to be purified, the active material to be purified comprising a metal oxide, aluminum impurities and copper impurities, b) dissolving the aluminum impurities by immersing the active material to be purified in a sodium hydroxide solution at a concentration chosen at an effective value to obtain dissolution of the aluminum impurities, and c) dissolving the copper impurities by immersing the active material to be purified in an ammonia solution having an effective value to obtain dissolution of the copper impurities, whereby a purified active material is obtained. The invention also relates to a method for regenerating a used active material of a battery electrode implementing this purification method. Figure for abstract: Figure 2A .

Description

Title of the invention: Methods for purifying and regenerating active materials of battery electrodes Technical field

[0001] The present invention relates to the general field of recycling accumulators or batteries, in particular Li-ion accumulators or batteries.

[0002] The invention relates to a method for purifying and / or regenerating the active materials of mixed metal oxide type of such devices.

[0003] The invention is particularly interesting since it makes it possible to obtain an active material free from impurities and having an intact crystallographic structure. The material can be directly reused. STATE OF THE PRIOR ART

[0004] The market for accumulators (or batteries), particularly of the Li-ion type, is currently experiencing strong growth, particularly with the development of mobile applications ("smartphones", portable power tools, etc.) and with the emergence of electric and hybrid vehicles.

[0005] Lithium-ion batteries comprise a negative electrode, a positive electrode, a separator, an electrolyte and a casing which may be a polymer pouch, or a metal package. The negative electrode generally comprises graphite, mixed with a binder of the carboxymethylcellulose (CMC) or polyvinylidene fluoride (PVDF) type, and deposited on a copper foil acting as a current collector. The positive electrode is a lithium ion insertion material, typically a lithium mixed oxide (for example, LiCoO2, LiMnO2, Li3NiMnCoO6, LiFePO4), mixed with a binder of the polyvinylidene fluoride type, and deposited on an aluminum foil acting as a current collector.The electrolyte consists of lithium salts (LiPF6, LiBF4, LiCF3SO3, LiC104) solubilized in an organic base consisting of mixtures of binary or ternary solvents based on cyclic carbonates (ethylene carbonate, propylene carbonate, butylene carbonate), linear or branched (dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dimethoxyethane) in various proportions.

[0006] The operation is as follows: during charging, the lithium is deintercalated from the active material of the positive electrode and inserted into the active material of the negative electrode. During discharge, the process is reversed.

[0007] Given the environmental, economic and strategic challenges in the supply of certain metals present in batteries, it is necessary to recycle at least 50% of the materials contained in Li-ion batteries and accumulators. (Directive 2006 / 66 / EC). Indeed, end-of-life batteries represent a significant source of materials of interest (Co, Ni, Li, etc.) commonly referred to as urban mining. These elements are mainly present in the electrodes and more particularly in the positive electrode materials of Li-ion batteries.

[0008] Currently, there are a wide variety of approaches to recycling battery contents. Manufacturers generally use a combination of physical, thermal and chemical methods to separately recover the valuable elements.

[0009] Physical methods include, in particular, dismantling, crushing and screening the batteries.

[0010] Thermal methods are based on pyrometallurgical processes consisting of heating the residues to high temperatures to separate the metals in the form of slag or alloys. These processes are energy-intensive, requiring temperatures of up to 1400 °C. Although they are very effective in separating cobalt, nickel and copper, it is difficult to recover manganese and lithium.

[0011] The implementation of chemical processes is then necessary to recover the valuable elements in a pure form. Chemical processes are hydrometallurgical processes that rely on the use of liquid-phase reagents to dissolve or precipitate metals. Traditional leaching generally uses strong acids. Then, various methods and different chemical reagents can be used for the separation of the different elements, the objective being to individually separate the elements present so that they can then be recycled.

[0012] The various elements and materials recovered must have a high degree of purity, and therefore be free of contaminating metals. Contaminants can be aluminum and copper from the current collectors as well as iron which can come from the casing when it is made of steel or from pollution resulting from the recycling processes. Indeed, if these elements are not eliminated, they will have a negative impact on the cycling performance and the energy density of the recycled product.

[0013] Iron can be easily removed by exploiting its magnetic properties.

[0014] Concerning aluminum and copper, the most effective way to isolate these elements from metal oxides (NMC, LFP, etc.) is to dissolve them selectively with respect to these metal oxides, it being understood that all of the steps must be carried out while maintaining the crystallographic structure of the active material.

[0015] For example, US patent 10,103,413 B2 describes a method for removing copper and aluminum from an electrode material originating from used lithium-ion batteries. The method comprises a step during which the electrode active material comprising copper and aluminum to be removed is brought into contact with an aqueous solution containing a base (of the LiOH, NaOH, KOH or Ca(OH)2 type), an agent oxidant of the dioxygen type (O2), and a complexing agent (of the NH4OH type at a concentration ranging from 1 to 10 mol.L *)• The solution is at a pH greater than 10 and preferably greater than 11.

[0016] However, on the one hand, the treatment time is very long (12 hours in the examples) and, on the other hand, the aluminum and the copper are dissolved simultaneously, which requires subsequent separation steps to individually recover these elements and therefore impacts the costs of the process.

[0017] International application WO 2021 / 161316 A1 describes a hydrometallurgical process for recovering lithium and transition metals contained in a positive electrode of Li-ion batteries. The process comprises a phase of dissolving the lithium present in the electrode material by means of an alkaline solution (with NaOH and NH40H) at a pH greater than 12.

[0018] However, under such conditions, aluminum also dissolves. A pretreatment step is therefore implemented. This pretreatment step consists of contacting the electrode material with an acid solution (hydrochloric acid) in order to make the lithium more easily accessible.

[0019] The examples show the absence of dissolution of Co, Mn and Ni. However, this document does not mention the presence of copper impurities, nor the crystallographic structure of the active material obtained. Statement of the invention

[0020] An aim of the present invention is to propose a method for recycling active materials (metal oxide type) from battery or accumulator electrodes, in particular Li-ion type batteries or accumulators, and in particular a method for removing metal impurities (Al, Cu) from these materials, without dissolution or structural damage to the mixed oxides.

[0021] For this, the present invention proposes a method for purifying an active battery electrode material comprising the following steps:

[0022] a) providing an active material to be purified comprising a metal oxide, aluminum impurities and copper impurities,

[0023] b) dissolving the aluminium impurities by immersing the active material to be purified in a sodium hydroxide solution at a concentration chosen at an effective value to obtain dissolution of the aluminium impurities, whereby an active material free of aluminium impurities is obtained, and

[0024] c) dissolving the copper impurities by immersing the active material to be purified in an ammonia solution at a pH having a value effective for achieving dissolution of the copper impurities, whereby an active material free of copper impurities is obtained, whereby a purified active material is obtained.

[0025] Steps b) and c) can be carried out in the order b) then c) or in the order c) then b).

[0026] The purification process according to the invention may, in addition, comprise an additional rinsing step between steps b) and c) or between steps c) and b) and / or an additional rinsing step at the end of step c) or at the end of step b).

[0027] The invention is fundamentally distinguished from the prior art, not only by the implementation of two distinct stages of selective dissolution of the impurities originating essentially from the current collectors, but also by the nature of the chemistry and the operating conditions implemented during these stages.

[0028] With such a process, the metallic impurities of aluminum and copper are dissolved in ionic and soluble form while the metal oxide is not dissolved or crystallographically modified.

[0029] The active material, in solid form, free of aluminum impurities and free of copper impurities, is thus easily recovered.

[0030] The active material thus purified can then be reused in a new battery or a new accumulator.

[0031] The active material subjected to the purification process according to the invention may be an active material, i.e. an active material from a used battery electrode. This active material may also come from waste ("scrap") or from a new material considered as scrap.

[0032] In an advantageous variant, and in particular when the active material is an active material of a used battery electrode, in particular of the lithium-ion type and, for example, a lithiated metal oxide, the purification method according to the invention comprises, after the implementation of steps b) then c), or c) then b), a step d) of relithiation of the purified active material by heating it in the presence of a lithium source, whereby a regenerated active material is obtained.

[0033] Such an active material thus regenerated has good electrochemical properties, comparable to those of a new material.

[0034] Advantageously, during step b), the sodium hydroxide solution has a concentration of between 1 and 4 mol / L.

[0035] Advantageously, during step b), the solid / liquid ratio, which corresponds to the ratio between the mass of active material to be purified (kg) and the volume of sodium hydroxide solution (L), is between 5 and 30%, preferably between 10 and 20%.

[0036] Advantageously, during step b), the temperature is between 20 and 80°C, preferably between 40 and 60°C.

[0037] Advantageously, step c) is carried out at a pH between 8.5 and 9.9, advantageously between 9 and 9.7, preferably between 9 and 9.5.

[0038] Advantageously, the ammonia solution is buffered with carbonates, preferably ammonium carbonates. Carbonates are stable in the pH range of step c).

[0039] Advantageously, during step c), the solid / liquid ratio is between 5 and 30%, preferably between 10 and 20%. The solid / liquid ratio corresponds to the ratio between the mass of treated material (kg) and the volume of ammonia solution (L).

[0040] Advantageously, hydrogen peroxide is added to the ammonia solution.

[0041] The method makes it possible to recycle one or more active materials of the battery electrodes, preferably the active materials of the Li-ion batteries. Preferably, these are positive electrode active materials. According to another variant, they could be negative electrode active materials.

[0042] The active material(s) are metal oxides which may be lithiated metal oxides, such as lithiated metal oxides selected from LiFePO4 (LFP), LiCoO2 (lithium cobalt oxide (LCO)), LiMnO2, LiNiO2, LiNiCoAlO2 (nickel-cobalt-aluminium (NCA)) and LiNixMnyCozO2 (NMC (nickel-manganese-cobalt)). The NMC material may have different ratios of nickel, cobalt and manganese. For example, the ratio may be 1 / 1 / 1, 5 / 3 / 2, 6 / 2 / 2, 8 / 1 / 1 or 9 / 0.5 / 0.5.

[0043] Advantageously, the metal oxide is chosen from NMC, LFP and NCA.

[0044] As indicated above, the invention also relates to a method for regenerating an active material of a used battery electrode.

[0045] According to the invention, this regeneration method comprises the following steps (1) and (2):

[0046] (1) the purification of the active material by the process as defined above, and

[0047] (2) relithiating the purified active material in step (1), whereby a material regenerated asset is obtained.

[0048] Step (2) of relithiation corresponds to step d) mentioned above and typically comprises one or more heat treatments, at least one of the heat treatments being carried out in the presence of a lithium source.

[0049] The purification and regeneration processes according to the invention have numerous advantages:

[0050] - have a low processing cost,

[0051] - have a low environmental impact (because a very low volume of effluent is shape),

[0052] - avoid the formation of metallic salts,

[0053] - obtain a selective dissolution of copper (absence of co-element such as aluminum): copper is thus recovered in a pure form with high added value,

[0054] - rapid kinetics of dissolution of copper at room temperature with suitable pH and oxidizing conditions,

[0055] - use a buffer solution with good stability, which avoids putting in implements pH control, thus facilitating the implementation of such a process in an industrial environment,

[0056] - easily obtain, without additional treatment, active materials having a high purity and the desired crystallographic structure, allowing subsequent regeneration as a battery material.

[0057] Other characteristics and advantages of the invention will emerge from the additional description which follows.

[0058] It goes without saying that this additional description is given only as an illustration of the subject of the invention and must in no case be interpreted as a limitation of this subject. Brief description of the drawings

[0059] The present invention will be better understood upon reading the description of exemplary embodiments given purely for informational purposes and in no way limiting, with reference to the appended drawings in which:

[0060] - [Fig.l] is a graph representing the atomic percentage of elements Mn, Co, Ni and Al as a function of the distance from the external surface of a cathode particle of type NMC 8 / 1 / 1 (shown in the image in the inset of [Fig.l]); the values ​​are obtained by energy dispersive X-ray microanalysis with a scanning transmission electron microscope (STEM-EDX),

[0061] - [Fig.2A] represents a photograph obtained with a transmission electron microscope at scanning of an NMC 8 / 1 / 1 particle after treatment,

[0062] - [Fig.2B], [Fig.2C] and [Fig.2D] are elementary analyses, respectively of the elements Ni, Mn, and Co, carried out on the particle of [Fig.2A] and obtained by dark field annular imaging obtained.

[0063] DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS

[0064] We will now describe in more detail the method of purifying an active material of a battery electrode.

[0065] Although the description particularly refers to a Li-ion battery, the method could also be used to purify an active material from a Na-ion battery electrode.

[0066] The term battery is used, it being understood that this term can be replaced by electrochemical generator, accumulator or cell.

[0067] The active material to be purified is preferably a cathode (positive electrode) active material.

[0068] For a Li-ion accumulator, it is a lithium ion insertion material. It can more specifically, a lithiated metal oxide, such as a lamellar oxide of the LiMO2 type, a LiMPO4 phosphate of olivine structure or a spinel compound LiMn2O4, with M representing a transition metal. For example, we will choose a positive electrode made of LiCoO2, LiMnO2, LiNiO2, LiNiCoAlO2jLi3 NiMnCoO6, LiNixCO|XC)2(avcc 0 <x<l) ou LiFePO4.

[0069] In the case of a Na-ion accumulator, it could be a sodium ion insertion material. It could be a sodium oxide type material comprising at least one transition metal element, a sodium phosphate or sulfate type material comprising at least one transition metal element or a sodium fluoride type material.

[0070] The current collector of a positive electrode is made of aluminum, for example aluminum foil.

[0071] The active material could be an anode active material (negative electrode). It can also be a lithium mixed oxide such as lithium titanate Li4Ti50i2 (LTO) for a Li-ion battery or a sodium mixed oxide such as sodium titanate for a Na-ion battery. Conventionally, the current collector of the negative electrodes is made of copper (a copper foil for example).

[0072] The active material contains copper impurities and aluminum impurities. The active material may contain graphite impurities in addition to the aluminum and copper impurities. These graphite impurities, like those of PVDF, can be removed by carrying out a heat treatment, such as that envisaged in the regeneration method according to the invention.

[0073] In the purification process, it is possible to treat a single active material or a mixture of several other active materials. It is possible to treat a mixture of positive electrode active materials and / or negative electrode active materials.

[0074] The active material may come from a used battery, scrap or even a new material considered as waste. The material may be a ground material, i.e. a material in particulate form.

[0075] The ground lithium-ion batteries or battery elements can be obtained, for example, according to the following steps:

[0076] - securing and dismantling batteries or battery elements,

[0077] - crushing of batteries or battery elements.

[0078] Preferably, before implementing the purification process, a step is implemented to obtain a concentrate of metal oxides. Thus, a fraction rich in active material (at least 50% by mass) is obtained.

[0079] The purification process comprises a step of selective dissolution of the aluminum and then a step of selective dissolution of the copper (or vice versa). These two steps ensure the dissolution of the impurity elements (Al and Cu). preferably, all impurities are put into solution.

[0080] We will describe in more detail a process implementing an aluminum dissolution step and then a copper dissolution step. As mentioned previously, the order of the steps could be reversed.

[0081] During the step of selective dissolution of the aluminum, the material is treated in a sodium hydroxide solution at a concentration, for example, between 1 and 4 mol / L, preferably 2M. The solid to liquid ratio is, for example, between 5 and 30% and preferably between 20 and 10%. The reaction time can be between 30 minutes and 6 hours. The temperature can be between 20 and 80°C, preferably between 40 and 60°C. The solution is advantageously stirred. Stirring can be carried out by means of a turbine, for example a turbine with 4 inclined blades equipped with a scraper. The speed can be between 50 and 2000 revolutions / min (rpm) and preferably between 100 and 400 revolutions / min (rpm). The reactor can be equipped with counter-blades, for example, made of polytetrafluoroethylene (PTFE), in order to increase turbulence.

[0082] After dissolving the aluminum, the solution is filtered. An aluminum-rich filtrate is thus recovered.

[0083] A solid of metal oxides still containing copper impurities is obtained at the end of this first step.

[0084] The step of selective dissolution of the copper is then carried out, if necessary, after a step of rinsing the solid of metal oxides as obtained at the end of this first step. The active material to be purified is treated in an ammonia solution. The concentration is, for example, 0.5 mol / L.

[0085] The pH of the solution is advantageously between 8.5 and 9.9 and preferably between 9 and 9.7 and more preferably between 9 and 9.5.

[0086] The solution may be buffered with carbonates. Preferably, this is ammonium carbonate. For illustration purposes, a pH of 9.6 corresponds to a concentration of 0.5 mol / L of ammonium carbonates. The use of another ammonium salt is possible (ammonium hydrogen carbonate, ammonium sulfate).

[0087] The solid / liquid ratio is between 5% and 30% and preferably between 10% and 20%.

[0088] Hydrogen peroxide may be added to the solution. For example, a ratio of 1% by volume relative to the total volume of the solution may be chosen when the solid / liquid ratio is 10%. The amount of hydrogen peroxide is chosen based on the amount of solid to be treated per unit volume.

[0089] The duration of this step is, for example, between 5 minutes and 1 hour. Preferably, it is carried out at room temperature (typically between 20 and 25°C).

[0090] Preferably, the solution is stirred during this step.

[0091] Rapid dissolution of copper is obtained and a soluble and stable ammoniacal complex is formed.

[0092] The mixture is then advantageously filtered. A copper-rich filtrate is recovered. The filtrate can be recycled. A solid rich in metal oxides, free of aluminum and copper impurities, is also obtained. After implementing an optional rinsing step, the solid can be reused, in particular in the battery field.

[0093] Illustrative and non-limiting examples of an embodiment

[0094] In this example, the crushed lithium-ion batteries or battery elements are obtained after securing and dismantling used batteries, then implementing different physical separation steps (such as crushing, screening, etc.).

[0095] The method is carried out on different NMC type cathode materials in mixture. The mixture comprises:

[0096] - polycrystalline 8 / 1 / 1 NMC particles,

[0097] - NMC 5 / 3 / 2 monolithic particles.

[0098] The particles are spherical.

[0099] The atomic composition of an NMC particle with an atomic ratio of 8 / 1 / 1 has been characterized ([Fig.l]). Such particles contain aluminum at about 2 at%. The aluminum is distributed homogeneously between the outer surface and the core of the particle. The particles do not have a surface coating. The aluminum acts as a dopant here. Such doping is common in the field of Li-ion batteries. The presence of aluminum as a component of the structure is a fundamental element that must be taken into account in the analysis of the chemical treatment. This aluminum as a dopant is not an impurity unlike the aluminum from the current collector.

[0100] The following table lists the mass composition of Li-ion battery waste.

[0101] [Tables 1] Composition (% by mass) Li Ni Mn Co Al Cu Fe 5.699 44.308 4.534 7.239 0.856 1.760 0.071

[0102] The aluminum (0.856% by mass) comes from the aluminum collectors (0.685% by mass) and doping (the remainder, i.e., 0.171% by mass). The aluminum from the aluminum collectors must be selectively removed from the metal oxide.

[0103] The purification process is carried out on this mixture of metal oxides comprising aluminum impurities and copper impurities.

[0104] The method comprises the steps in the following order:

[0105] - selective dissolution of aluminum,

[0106] - selective dissolution of copper.

[0107] It is understood that the purification process does not aim to remove the aluminum constituting the structure of the cathode material (doping aluminum), but only to remove the aluminum impurities coming from the collectors (0.685% by mass of aluminum).

[0108] The material is treated in a 2 mol / L sodium hydroxide solution, with a solid / liquid ratio of 10% by mass. The reaction takes place for 1 h, at a temperature of 50°C, with stirring at 400 rpm. Stirring is carried out using a turbine with 4 inclined blades equipped with a PTFE scraper. The reactor is equipped with PTFE counter-blades to increase turbulence.

[0109] After treatment, the mixture is vacuum filtered through a sintered glass support and a 5-13 pm porosity filter paper. Chemical analysis by inductively coupled plasma (ICP) spectrometry of the leaching solution confirms the complete dissolution of the aluminum from the collectors; i.e., 100% of the aluminum impurities have been removed. The resulting solid is recovered.

[0110] To remove the copper, the material recovered in the previous step is treated in an ammonia solution at a concentration of 0.5 mol / L, buffered with ammonium carbonates also at 0.5 mol / L. The solution is at a pH of 9.6. The solid / liquid ratio is 10%. Hydrogen peroxide at 30% by volume is added in a ratio of 1% by volume, which leads to the formation of a soluble and stable ammoniacal copper complex. The stirring is 400 rpm. The stirring is obtained using a turbine with 4 inclined blades equipped with a PTFE scraper. The reactor is equipped with PTFE counter-blades to increase turbulence. The reaction is very rapid (a few minutes) at room temperature.

[0111] ICP chemical analysis of the leaching solution reveals an efficient and almost complete dissolution of the copper from the collectors. A quantity of copper less than 0.2 atomic % was observed, which corresponds to a few residual atoms. This quantity may come from the limit of the chemical analysis and / or the presence of a few copper atoms within the NMC structure which may have migrated during the battery usage phase.

[0112] At the end of the purification process, the material is therefore free of aluminum impurities and copper impurities from the collectors. Figures 2B, 2C and 2D also confirm that the treated material corresponds to an NMC type material: the spherical particles have a homogeneous chemical composition of nickel, cobalt and manganese.

Claims

Claims

1. A method for purifying a battery electrode active material comprising the following steps: a) providing an active material to be purified comprising a metal oxide, aluminum impurities and copper impurities, b) dissolving the aluminum impurities by immersing the active material to be purified in a sodium hydroxide solution at a concentration selected at a value effective to achieve dissolution of the aluminum impurities, and c) dissolving the copper impurities by immersing the active material to be purified in an ammonia solution at a pH having a value effective to achieve dissolution of the copper impurities, whereby a purified active material is obtained.

2. Purification process according to claim 1, characterized in that, during step b), the sodium hydroxide solution has a concentration of between 1 and 4 mol / L.

3. Purification process according to claim 1 or 2, characterized in that step c) is carried out at a pH between 8.5 and 9.9, advantageously between 9 and 9.7 and, preferably, between 9 and Q 5

4. A purification process according to any one of claims 1 to 3, characterized in that the ammonia solution is buffered with carbonates, preferably ammonium carbonates.

5. Purification process according to any one of the preceding claims, characterized in that, during step c), the solid / liquid ratio is between 5 and 30%, preferably between 10 and 20%.

6. A purification method according to any one of the preceding claims, characterized in that hydrogen peroxide is added to the ammonia solution.

7. Purification process according to any one of the preceding claims, characterized in that during step b), the solid / liquid ratio is between 5 and 30%, preferably between 10 and 20%.

8. Purification process according to any one of the preceding claims, characterized in that during step b), the temperature is between 20 and 80°C, preferably between 40 and 60°C.

9. Purification process according to any one of the preceding claims, characterized in that the metal oxide is chosen from NMC, LFP and NCA.

10. Purification process according to any one of claims 1 to 9, characterized in that steps b) and c) are carried out in the order b) then c) or c) then b).

11. A method of regenerating a used battery electrode active material, said method comprising the following steps (1) and (2): (1) purifying the active material by the method according to any one of claims 1 to 10, and (2) relithiating the active material purified in step (1), whereby a regenerated active material is obtained.

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