FR3117271A1 - Process for inerting electrochemical batteries, in particular metal-ion batteries, by initial immersion in a solution of sodium nitrite then in a solution of sodium chloride. - Google Patents

Abstract

"Process for inerting electrochemical accumulators, in particular metal-ion, by initial immersion in a solution of sodium nitrite then in a solution of sodium chloride. The invention relates to a process for inerting electrochemical accumulators (A), in particular metal-ion, comprising the following steps: i/ immersion of a batch of accumulators in a solution of previously determined concentration of sodium nitrite ( NaNO2), so as to determine, within the batch, the number X of accumulators whose electrochemistry is active, ii/ once step i/ has been completed, immersion in a solution of sodium chloride (NaCl) of at least a part of the X electrochemically active accumulators. Figure 2A.

Description

Process for inerting electrochemical batteries, in particular metal-ion batteries, by initial immersion in a solution of sodium nitrite then in a solution of sodium chloride.

The present invention relates to the field of electrochemical accumulators, and more particularly metal-ion accumulators or other chemistries (lead, etc.).

The invention aims firstly to guarantee the electric discharge of accumulators before their recycling, by immersion in an NaCl solution, while controlling the quantity of dihydrogen released during their immersion.

Although described with reference to a lithium-ion battery, the invention applies to any metal-ion electrochemical battery, that is to say also sodium-ion, magnesium-ion, aluminum-ion, or even others. chemicals (Lead..)…

With the very significant development of consumer electric vehicles using lithium-ion batteries, the production of these has increased considerably.

Among lithium-ion battery end-of-life strategies, recycling used batteries is a solution to achieve sustainable development and minimal environmental pollution.

The inerting of lithium-ion batteries is an essential step prior to the recycling process as such to ensure the safety of people and the environment during their recycling. Indeed, one of the stages of recycling consists in carrying out the grinding of the accumulators.

During this grinding, if an accumulator is not completely discharged, there is a risk of short-circuiting which causes the accumulator to overheat and which can lead to its thermal runaway. In this case, there is a physical risk due to possible explosions and the outbreak of fire, but also a chemical risk due to the toxic fumes that can be produced during runaway.

A process that allows rapid and secure discharge of a large quantity of accumulators so that they can be recycled afterwards consists of immersing the accumulators, previously separated from each other, in a tank containing an NaCl solution of given concentration.

There schematically represents an installation implementing such a process: the accumulators A1, A2, ..Ax whose electrochemistry is still active are immersed in a tank 1 containing a solution of NaCl introduced by a supply conduit 2. The solution of NaCl can be extracted through outlet pipe 3.

The voltage U between the output terminals of an accumulator A1, A2,..Ax being greater than 1.23V, the hydrolysis of salt water can take place according to the reaction equations:

• to the negative terminal: H ₂ O = 1/2O ₂ +2H ⁺ +2e ^-
• to the positive terminal: 2H ⁺ +2e ^- = H ₂ .

Consequently, each accumulator with active electrochemistry discharges electrically gradually. The flow of hydrogen that can be released by hydrolysis can be significant. For example, for an immersion of a number equal to 8000 18650 format batteries in a NaCl solution concentrated at 5% by mass, it could be measured at 103.7 l/s.

There are publications in the literature dealing with the influence of the salt concentration on the discharge of lithium ion batteries.

Publication [1] focuses on a Li-ion accumulator in 18650 format, the positive electrode material of which is LiNiCoO ₂ , is immersed in a bath containing 30mL of a NaCl solution for a period of 24 hours. The evolution of the voltage for a 10% mass NaCl solution is shown in figure numbered 2 of this publication.

Figure numbered seven from a similar publication [2] shows the discharge efficiency as a function of time of different solutions, including pure water and different mass % concentrations of NaCl, in which a Li-ion battery is immersed by comparison with a self-discharge of the accumulator.

Another publication [3] also details the discharge of accumulators by immersion in solutes. In this publication, a single accumulator, electrically charged, beforehand at 100% is immersed in 1L baths. These baths consist of solutions with various solutes concentrated at 5% by weight, including NaCl. This publication details the influence of the nature of the solute on the discharge rate and on the corrosion of the accumulator. Thus, the figure numbered three of this publication shows the evolution of the voltage for the different solutes as a function of time.

All these publications are content to carry out discharge tests only on a single accumulator and therefore do not highlight the effectiveness of this technique of direct and simultaneous immersion, in a solution of NaCl, of a large quantity of 'Accumulators.

Furthermore, none of them details or quantifies the quantity of dihydrogen generated by hydrolysis. However, this quantity is all the higher as the number of accumulators is large, and thereby increases the risks of explosive atmospheres (ATEX). Ventilation equipment surrounding the discharge solution (NaCl) must be able to manage hydrogen evolution while remaining within acceptable limits. This influences their sizing, and also the quantity of accumulators that can be discharged simultaneously, which depends on their residual electrochemical activity.

There is therefore a need to offer a reliable solution to limit the ATEX risks associated with the release of dihydrogen when immersing a large quantity of accumulators in an NaCl solution.

The object of the invention is to meet this need at least in part.

To do this, the invention relates, in one of its aspects, to a process for inerting electrochemical accumulators (A), in particular metal-ion batteries, comprising the following steps:

i/ immersion of a batch of accumulators in a solution of previously determined concentration of sodium nitrite (NaNO ₂ ), so as to determine, within the batch, the number X of accumulators whose electrochemistry is active,

ii/ once step i/ is completed, immersion in a sodium chloride (NaCl) solution of at least some of the X electrochemically active accumulators.

According to a first alternative, steps i/ and ii/ are carried out one after the other in the same tank filled successively with the NaNO ₂ solution then with that of NaCl. Stage ii/ is preferably carried out by immersing the entire batch from stage i/.

According to a second alternative, step i/ is carried out in a tank separate from that in which step ii/ is carried out.

According to this second alternative, several advantageous variants can be implemented.

According to a first variant, stage ii/ is carried out by immersing the entire batch from stage i/.

According to a second variant, the method comprises, between step i/ and step ii/, a step of subdividing the batch into sub-batches, step ii/ being carried out for each sub-batch. Thus, if at the end of step i/ the calculated release of hydrogen from the X accumulators is above a fixed threshold, for example taking into account the performance of the aeration equipment(s) in place, then carry out a step ii/ with sub-batches makes it possible to ensure that H ₂ is released within acceptable limits.

According to a third variant, the method comprises prior to step ii/, the reiteration of step i/ for several batches, step ii/ being carried out for the grouping of at least part of the several batches. The fact of grouping together several batches from step i/, on condition that the cumulative release of H ₂ from the X accumulators authorizes it, for the implementation of a single step ii/ for the electric discharge allows to optimize the process both in terms of cost and time.

Advantageously, step i/ is carried out for a period (t) of between 1 min and 30 min, preferably less than 5 min.

According to an advantageous embodiment, the concentration of the NaCl solution in step ii/ is determined so that with the number X of accumulators, each with a voltage (U) of the order of 4.2 V and an internal resistance (Rint) of the order of 10 mOhm, the hydrogen content of the atmosphere during step ii/ being kept below 4% vol, preferably below 3% vol.

Preferably, the concentration of the NaCl solution in step ii/ is between 0.5% and 20% by weight.

Also preferably, the concentration of the NaNO ₂ solution in step i/ is between 0.1% and 20% by mass, in particular between 0.1% and 10% by mass.

The invention also relates to an accumulator electrically discharged according to the method described above.

Each battery can be a Li-ion battery in which:

• the material of the negative electrode(s) is chosen from the group comprising graphite, lithium, titanate oxide Li ₄ TiO ₅ O _12;
• the material of the positive electrode(s) is chosen from the group comprising LiFePO ₄ , LiCoO ₂ , LiNi _0.33 Mn _0.33 Co _0.33 O ₂ .

The invention also relates to a method for recycling electrochemical accumulators, comprising a step of grinding accumulators resulting from the method described above.

Thus, the invention essentially consists in adding a step, prior to the immersion of electrochemical accumulators in a solution of NaCl for their inerting, which consists of immersion in a solution of NaNO ₂ .

This preliminary step makes it possible to determine upstream the exact parameters of the electrochemical activity of the accumulators, in order to size the inerting to generate a controlled flow of dihydrogen during immersion in the NaCl solution.

Indeed, the concentration, the composition of the bath containing the solution as well as the nature and the number X of submerged and still electrochemically active accumulators give a direct indication of the maximum flow rate of dihydrogen generated by the discharge solution. This flow can be calculated according to the following equation 1:

[Eq 1]

in which :

D(H ₂ ) represents the dihydrogen flow rate in mol/s;

U the accumulator voltage in V;

X the number of electrochemically active accumulators;

Rint the internal resistance of an accumulator here equal to 10mohm;

k a coefficient corresponding to the exchange surface of an accumulator here equal to 1 cm²;

l the ionic path in cm;

F the Faraday number in mol^-1 ;

λ the molar conductivity in S.cm².mol ^-1 and

[NaCl] the concentration of the NaCl solution in mol/litre.

The inventors therefore analyzed that, in order to have control over the quantity of dihydrogen generated during immersion in the NaCl solution by modulating its concentration, it was necessary to determine beforehand the number X of electrochemically active accumulators.

To do this, the number X is determined using a solution of NaNO₂ whose reduction half-reaction competes with the formation of dihydrogen, according to the following equation 2:

[Eq 2]

Thus, a large number of mixed accumulators comprising a number X of active accumulators, the other accumulators being electrochemically inactive, is initially immersed in a bath containing a solution of known NaNO ₂ concentration.

The measurement of the variation in NaNO ₂ concentration over a period of time subsequently makes it possible to determine the number X, in the batch of accumulators, without having produced dihydrogen.

To optimize the process, it is possible to divide the initial batch, or on the contrary to combine several batches at the end of stage i/, before implementing stage ii/.

The invention brings numerous advantages, among which we can cite:

• a precise prediction of the dihydrogen released during the immersion of electrochemical accumulators with a view to their electrical discharge, and thereby a control of the ATEX risks linked to this release of H ₂ .
• optimization of the inerting process in terms of time and safety with a guarantee of electrical discharge of all batches of accumulators before their actual recycling.

Other advantages and characteristics of the invention will emerge better on reading the detailed description of examples of implementation of the invention given by way of illustration and not limitation with reference to the following figures.

there is a schematic view of an installation according to the state of the art, for inerting lithium-ion batteries by immersion in an NaCl solution.

there is a schematic view of an installation according to the invention for inerting lithium-ion batteries implementing a first step by immersion in a solution of NaNO2.

there is a schematic view of an installation according to the invention for inerting lithium-ion batteries implementing a second step by immersion in an NaCl solution.

detailed description

There relates to an installation implementing direct inerting of a plurality of Li-ion accumulators according to the state of the art. This has already been commented on in the preamble and is therefore not commented on further below.

For the sake of clarity, the same references designating the same elements according to the state of the art and according to the invention are used for all FIGS. 1 to 2B.

A process for inerting Li-ion batteries according to the invention is now described.

Step i/: immersed in a tank 1 filled with a solution of NaNO₂at a given concentration, a batch consisting of a plurality of Li-ion batteries A1, A2, A3 separated from each other ( ).

A hydrolysis reaction then takes place with NaNO ₂ .

The NaNO2 salt is thus consumed to form N ₂ O gas. The gas flow formed can be determined from the final NaNO ₂ concentration of the solution according to the following equation 3:

[Eq 3]

in which

D(N ₂ O) represents the N ₂ O flow rate in mol/s;

[NO^- ₂]^initiatethe initial concentration of NO nitrite ions^- ₂ in mol/litre;

[NO^- ₂]^finalthe final concentration of NO nitrite ions^- ₂ in mol/litre;

V the volume of the bath of the NaNO ₂ solution _;

t the period of immersion of the accumulators in the NaNO ₂ solution.

However, the flow of N ₂ O can also be determined by the parameters of the accumulators according to the following equation 4:

[Eq 4]

D(N ₂ O) represents the N ₂ 0 flow rate in mol/s;

U the accumulator voltage in V;

X the number of electrochemically active accumulators within the batch;

Rint the internal resistance of an accumulator here equal to 10 mohm;

k a coefficient corresponding to the exchange surface of an accumulator here equal to 1 cm²;

l the ionic path in cm;

F the Faraday number in mol ^-1 ;

λ the molar conductivity in S.cm².mol ^-1 and

[NO^- ₂]^initiatethe initial concentration of NO nitrite ions^- ₂ in mol/litre;

Thus, it is possible to determine the number X of electrochemically active accumulators according to equation 5:

[Eq 5]

Thus, this step i/ makes it possible to determine the number X, without producing dihydrogen.

This makes it possible to predict the quantity of dihydrogen which would be released if this same batch were discharged directly into an NaCl solution. Thus, the compatibility of this clearance with the capacity of the equipment to manage this quantity is provided.

The number X being known within the batch, the individual in charge of the inerting process can determine the quantity of dihydrogen which will be released during stage ii/ of discharging X accumulators according to the NaCl concentration , which will have been chosen by the aforementioned equation 1:

[Eq 1]

Typically, the hydrogen concentration in the air should not approach 4% vol, and preferably be less than 3% vol. Indeed, there is a risk of explosion when the H2 concentration is between 4%vol and 75%vol. This concentration of hydrogen in the air is largely influenced by the capacity of the means of ventilation and air extraction to dilute the release of hydrogen during the discharge in the NaCl solution.

If the planned hydrogen flow rate is too high for the discharge installation, this hydrogen flow rate can be reduced by adapting one and/or the other of the various process parameters as follows:

• the concentration of NaCl to be implemented for the second discharge stage of the process, the reduction of the concentration reducing the emissions of dihydrogen;
• in the case where the value of X is such that the concentrations of NaCl available for the process do not allow discharge of the entire batch of accumulators, including the X accumulators still electrochemically active at once while remaining within the constraints of maximum flow rates of dihydrogen, the possible subdivision of this batch into several sub-batches which will be unloaded each in turn.

In the latter case, each sub-batch can be evaluated again according to the process described above, in order to evaluate its characteristics in relation to the discharge process. Alternatively, the accumulators can be mixed, in order to ensure a homogeneous distribution of the X active accumulators within the initial batch, and the sub-batches formed on a single quantitative and statistical basis.

Similarly, different batches evaluated according to step i/ can be grouped together so that step ii/ below is carried out with this grouping, provided that the sum of the number of active accumulators present in the different batches is compatible with the dihydrogen evacuation capacity generated during step ii/. This allows a significant saving in time in the electrical discharge steps which are then pooled for several batches.

Stage ii/: Once the process parameters have been chosen, including the concentration of NaCl and the content of the (potential) batch(es) to be treated at the end of stage i/, the process is then immersed in a tank 1 filled of a NaCl solution at a given concentration, the batch(es) consisting of a plurality of Li-ion accumulators A1, A2, A3 separated from each other ( ), and comprising the X active accumulators, in order to discharge them electrically.

Thus, this step ii/ allows a complete electrical discharge in one or more times of all the X active accumulators in the NaCl solution, in complete safety since the flow rate of dihydrogen released can be perfectly quantified and therefore controlled.

The invention is not limited to the examples which have just been described; it is in particular possible to combine together characteristics of the examples illustrated within variants not illustrated.

Other variants and improvements can be considered without departing from the scope of the invention.

List of cited references:

[1] M. Lu, H. Zhang, B. Wang, X. Zheng, C. Dai, “ The re-synthesis of Li-CoO2 from spent lithium ion batteries separated by vacuum-assisted heat-treating method ,” Int. J. Electrochem. Science. 8 (6) (2013).

[2] J. Li, G. Wang, Z. Xu “ Generation and detection of metal ions and volatile organic compounds (VOCs) emissions from the pretreatment processes for recycling spent lithium-ion batteries ” , Waste Management, Volume 52, June 2016 , Pages 221-227.

[3] Shaw-Stewart et al., “ Aqueous solution discharge of cylindrical lithium-ion cells ” Sustain. Mater. Technol., vol. 22, no. November, p. e00110, 2019.

Claims (14)

Process for inerting electrochemical accumulators (A), in particular metal-ion, comprising the following steps:
i/ immersion of a batch of accumulators in a solution of previously determined concentration of sodium nitrite (NaNO ₂ ), so as to determine, within the batch, the number X of accumulators whose electrochemistry is active,
ii/ once step i/ has been completed, immersion in a solution of sodium chloride (NaCl) of at least some of the X electrochemically active accumulators. Process according to claim 1, stages i/ and ii/ being carried out one after the other in the same tank filled successively with the NaNO ₂ solution then with that of NaCl. Process according to claim 2, stage ii/ being carried out by immersing the entire batch from stage i/. Process according to claim 1, stage i/ being carried out in a tank separate from that in which stage ii/ is carried out. Process according to claim 4, stage ii/ being carried out by immersing the entire batch from stage i/. Process according to claim 2 or 4, comprising, between step i/ and step ii/, a step of subdividing the batch into sub-batches, step ii/ being carried out for each sub-batch. Process according to claim 4, comprising, prior to step ii/, repeating step i/ for several batches, step ii/ being carried out for the grouping of at least part of the several batches. Method according to one of the preceding claims, step i/ being carried out for a period (t) of between 1 min and 30 min, preferably less than 5 min. Method according to one of the preceding claims, the concentration of the NaCl solution in step ii/ being determined so that with the number X of accumulators, each with a voltage (U) of the order of 4 .2 V and an internal resistance (R _int ) of the order of 10 mOhm, the hydrogen content of the atmosphere during stage ii/ being kept below 4% vol, preferably below 3% vol. . Process according to one of the preceding claims, the concentration of the NaCl solution in stage ii/ being between 0.5% and 20% by mass. Process according to one of the preceding claims, the concentration of the NaNO ₂ solution in stage i/ being between 0.1% and 20% by mass, in particular between 0.1% and 10% by mass. Electrochemical accumulator electrically discharged according to the method according to one of the preceding claims. Accumulator according to Claim 12 constituting a Li-ion accumulator in which:
- the negative electrode material(s) is selected from the group comprising graphite, lithium, titanate oxide Li ₄ TiO ₅ O _12;
- the positive electrode material(s) is chosen from the group comprising LiFePO ₄ , LiCoO ₂ , LiNi _0.33 Mn _0.33 Co _0.33 O ₂ . Process for recycling electrochemical accumulators, comprising a step of grinding accumulators resulting from the process according to one of Claims 1 to 11.