FR3157003A1 - Processes for the purification and regeneration of active materials of battery electrodes - Google Patents

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 selected to be effective in dissolving the aluminum impurities, and c) dissolving the copper impurities by immersing the active material to be purified in an ammonia solution having a concentration effective in dissolving the copper impurities, whereby a purified active material is obtained. The invention also relates to a method for regenerating a used battery electrode active material using this purification method. Figure 2A for abstract.

Description

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

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

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

The invention is particularly interesting because it makes it possible to obtain an active material free of impurities and with an intact crystallographic structure. The material can be directly reused.

STATE OF THE PRIOR ART

The market for accumulators (or batteries), particularly Li-ion batteries, 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.

Lithium-ion batteries comprise a negative electrode, a positive electrode, a separator, an electrolyte and a casing which can be a polymer pouch, or a metal wrapper. 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 (e.g., LiCoO ₂ , LiMnO ₂ , Li ₃ NiMnCoO ₆ , LiFePO ₄ ), 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 (LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiClO ₄ ) 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.

The way it works is as follows: when charging, the lithium deintercalates from the active material of the positive electrode and inserts itself into the active material of the negative electrode. When discharging, the process is reversed.

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 called urban mining. These elements are mainly present in the electrodes and more particularly in the positive electrode materials of Li-ion batteries.

Currently, there are a wide variety of approaches for recycling battery contents. Manufacturers typically use a combination of physical, thermal, and chemical methods to separately recover valuable components.

Physical methods include dismantling, crushing and screening batteries.

Thermal methods are based on pyrometallurgical processes that involve heating residues to high temperatures to separate metals in the form of slag or alloys. These processes are energy-intensive, requiring temperatures as high as 1400°C. While they are highly effective at separating cobalt, nickel, and copper, it is difficult to recover manganese and lithium.

Chemical processes are then required 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 typically uses strong acids. Various methods and chemical reagents can then be used to separate the various elements, with the goal of individually separating the elements present for subsequent recycling.

The various elements and materials recovered must have a high degree of purity, and therefore be free of contaminating metals. Contaminants can include aluminum and copper from current collectors, as well as iron from the steel casing or pollution resulting from recycling processes. If these elements are not eliminated, they will have a negative impact on the recycling performance and energy density of the recycled product.

Iron can be easily removed by exploiting its magnetic properties.

Concerning aluminum and copper, the most efficient 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 the steps must be carried out while maintaining the crystallographic structure of the active material.

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 active electrode 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 oxidizing agent of the dioxygen (O ₂ ) type, and a complexing agent (of the NH ₄ OH type at a concentration ranging from 1 to 10 mol.L ^-1 ). The solution is at a pH greater than 10 and preferably greater than 11.

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

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 NH ₄ OH) at a pH greater than 12.

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

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.

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.

For this, the present invention provides a method for purifying an active battery electrode 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 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

(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.

Steps b) and c) can be performed in the order b) then c) or in the order c) then b).

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).

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

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.

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

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

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 waste.

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.

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

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

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%.

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

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.

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

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).

Advantageously, hydrogen peroxide is added to the ammonia solution.

The method allows recycling one or more active materials from battery electrodes, preferably active materials from Li-ion batteries. Preferably, these are positive electrode active materials. Alternatively, they could be negative electrode active materials.

The active material(s) are metal oxides which may be lithiated metal oxides, such as lithiated metal oxides selected from LiFePO ₄ (LFP), LiCoO ₂ (lithium cobalt oxide (LCO)), LiMnO ₂ , LiNiO ₂ , LiNiCoAlO ₂ (nickel-cobalt-aluminium (NCA)) and LiNi _x Mn _y Co _z O ₂ (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.

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

As indicated above, the invention also relates to a method for regenerating a used battery electrode active material.

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

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

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

Relithiation step (2) 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.

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

- have a low processing cost,

- have a low environmental impact (because a very low volume of effluent is formed),

- avoid the formation of metallic salts,

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

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

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

- easily obtain active materials with high purity and the desired crystallographic structure without additional processing, allowing subsequent regeneration as battery material.

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

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.

The present invention will be better understood by reading the description of exemplary embodiments given for purely indicative and non-limiting purposes with reference to the appended drawings in which:

- there FIG. 1 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 (represented on the picture in the inset of the FIG. 1 ); values are obtained by energy dispersive X-ray microanalysis with a scanning transmission electron microscope (STEM-EDX),

- there FIG. 2 represents a snapshot obtained using a scanning transmission electron microscope of an NMC 8/1/1 particle after treatment,

- THE FIG. 2 , FIG. 2 And FIG. 2 are elemental analyses, respectively of the elements Ni, Mn, and Co, carried out on the particle of the FIG. 2 and obtained by dark field annular imaging obtained.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

We will now describe in more detail the process of purifying an active material from a battery electrode.

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

The term battery is used, with the understanding that this term can be replaced by electrochemical generator, accumulator or cell.

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

For a Li-ion battery, this is a material for inserting lithium ions. More specifically, it can be a lithiated metal oxide, such as a lamellar oxide of the LiMO ₂ type, a LiMPO ₄ phosphate with an olivine structure or a spinel compound LiMn ₂ O ₄ , with M representing a transition metal. For example, a positive electrode made of LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , LiNiCoAlO _{2 ,} Li ₃ NiMnCoO ₆ , LiNi _x Co _1-x O ₂ (with 0 < x < 1) or LiFePO ₄ will be chosen.

In the case of a Na-ion battery, this could be a sodium ion insertion material. This 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.

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

The active material could be an anode (negative electrode) active material. It can also be a lithium mixed oxide such as lithium titanate Li ₄ Ti ₅ O ₁₂ (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 electrode is made of copper (a copper foil for example).

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 implementing a heat treatment, such as that envisaged in the regeneration method according to the invention.

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.

The active material can come from a used battery, scrap, or a new material considered waste. The material can be a shredded material, that is, a material in particulate form.

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

- securing and dismantling of batteries or battery elements,

- crushing of batteries or battery elements.

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

The purification process includes a step of selective dissolution of aluminum and then a step of selective dissolution of copper (or vice versa). These two steps ensure the dissolution of the impurity elements (Al and Cu). Preferably, all impurities are dissolved.

We will describe in more detail a process involving an aluminum dissolution step followed by a copper dissolution step. As mentioned earlier, the order of the steps could be reversed.

During the step of selective dissolution of 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.

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

A solid of metal oxides still containing copper impurities is obtained at the end of this first stage.

The step of selective dissolution of copper is then implemented, 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.

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.

The solution can 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).

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

Hydrogen peroxide can be added to the solution. For example, a ratio of 1% by volume to the total volume of the solution can 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.

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

Preferably, the solution is stirred during this step.

Rapid dissolution of copper is achieved and a soluble and stable ammoniacal complex is formed.

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, particularly in the battery sector.

Illustrative and non-limiting examples of ' an embodiment

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

The process is carried out on different NMC type cathode materials in mixture. The mixture includes:

- polycrystalline NMC 8/1/1 particles,

- NMC 5/3/2 monolithic particles.

The particles are spherical.

The atomic composition of an NMC particle with an atomic ratio of 8/1/1 has been characterized ( FIG. 1 ). Such particles contain about 2 at% aluminum. The aluminum is distributed evenly 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 structural component is a fundamental element that must be taken into account in the analysis of the chemical processing. This aluminum as a dopant is not an impurity unlike the aluminum from the current collector.

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

Composition (% by mass) Li Neither Mn Co Al Cu Fe 5,699 44,308 4,534 7,239 0.856 1,760 0.071

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

The purification process is carried out on this mixture of metal oxides including aluminum impurities and copper impurities.

The process includes the steps in the following order:

- selective dissolution of aluminum,

- selective dissolution of copper.

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 from the collectors (0.685% by mass of aluminum).

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 4-blade inclined turbine equipped with a PTFE scraper. The reactor is equipped with PTFE counter-blades to increase turbulence.

After treatment, the mixture is vacuum filtered through a sintered glass support and a 5-13 µm 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; that is, 100% of the aluminum impurities have been removed. The resulting solid is recovered.

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 has 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. Stirring is 400 rpm. Stirring is achieved using a 4-blade inclined turbine 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.

ICP chemical analysis of the leaching solution revealed efficient and almost complete dissolution of copper from the collectors. A copper content of less than 0.2 atomic percent was observed, which corresponds to a few residual atoms. This amount may be due to the limitation of the chemical analysis and/or the presence of a few copper atoms within the NMC structure that may have migrated during the battery usage phase.

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 (11)

A method of 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 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, 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 obtain dissolution of the copper impurities, whereby a purified active material is obtained. 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. 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 9.5. Purification process according to any one of claims 1 to 3, characterized in that the ammonia solution is buffered with carbonates, preferably ammonium carbonates. 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%. Purification process according to any one of the preceding claims, characterized in that hydrogen peroxide is added to the ammonia solution. 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%. 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. Purification process according to any one of the preceding claims, characterized in that the metal oxide is chosen from NMC, LFP and NCA. 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). A method for regenerating a used battery electrode active material, said method comprising the following steps (1) and (2):
(1) purification of 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.