INSTALLATION FOR THE PRODUCTION OF ELECTRODES FOR BATTERIES

Abstract

The present invention relates to an installation for the production of electrodes for lithium-ion batteries, comprising a cathode coating station for active materials in a solvent consisting of NMP, and an anode coating station for active materials in an aqueous solvent. The installation includes a system (500) for condensing and recovering NMP from the cathode dryer (100), characterized in that the stream treated by said system (500) for condensing and recovering NMP consists of a portion between 15 and 90% of the stream from said cathode dryer (100). Abstract figure: Figure 1

Description

Title of the invention: INSTALLATION FOR THE PRODUCTION OF ELECTRODES FOR BATTERIES Scope of the invention

[0001] The present invention relates to the field of NMP (N-methyl-2-pyrrolidone) recovery and NMP recovery facilities.

[0002] NMP is a polar solvent with high selectivity and stability, widely used in the electronics and battery industries. It is a colorless, transparent, oily liquid with a slight amine odor. NMP exhibits low volatility, good thermal and chemical stability, and evaporates with water vapor. It is light-sensitive and has a boiling point of 202°C at atmospheric pressure. It is readily soluble in water, ethanol, ether, acetone, ethyl acetate, chloroform, and benzene, and can dissolve most organic and inorganic compounds, polar gases, and natural and synthetic polymer compounds. NMP is notably used in industries such as the manufacture of cathode electrodes for lithium batteries, pharmaceuticals, pesticides, pigments, cleaning agents, and insulating materials.

[0003] For the production of lithium-ion batteries, aluminum or copper sheets are coated with active materials diluted in the organic solvent NMP to bind lithium ions to the substrate sheets. The coated sheets are then placed in a dryer to evaporate the NMP. This results in polluting vapors formed from a mixture of air and NMP. These vapors are hazardous to the environment and health, are also highly flammable, and lead to significant NMP consumption if it is not recovered and recycled.

[0004] It is known to recover steam in a recovery tower to reduce environmental and economic problems. The processes usually consist of adding water, which acts as an absorbent for NMP, to this steam. In the container, the hot NMP steam mixes with the cold water, the concentration of NMP in the air decreases and the concentration in the water increases. The NMP changes its aggregation state and becomes liquid and is no longer highly flammable. The water becomes lukewarm. Existing technology for the recovery and purification of liquid NMP waste mainly processes NMP by vacuum distillation. In addition to the objective of removing water and solids, the finished NMP product can be recycled.

[0005] With the development of lithium-ion battery technology, recycling this solvent is a major challenge for saving production resources and protecting the environment.

[0006] NMP presents difficult recycling procedures because NMP is subject to oxidation in the presence of air, producing acidic substances, particularly under the combined action of water, air and high temperatures. State of the art

[0007] Prior art is known Chinese patent CN107626186B describing a process for recovering N-methylpyrrolidone waste gas from lithium-ion battery production by a membrane separation process, in particular a process for coupling N-methylpyrrolidone by coupling a ceramic filter membrane and a pervaporation membrane. This patent proposes a solution consisting of extracting NMP from the absorption liquid at a higher concentration by using the NMP exhaust gases from the lithium-ion battery electrode production process, and then filtering through the ceramic membrane under low-temperature conditions. Macromolecular impurities such as powders and particles are trapped there, and the ceramic membrane filtrate is sent to the pervaporation membrane for dehydration. This prior art membrane separation process comprises the following steps: - A first step, where the polar part of the lithium battery coated with the slurry containing the NMP solvent is dried; - A second stage, where the exhaust gases are sent to the absorption tower and diluted in water used as the absorption solvent, so that the NMP concentration in the absorption liquid at the bottom of the tower is increased to at least 65% by weight; the temperature of the absorption liquid is 5 to 60°C, typically 20 to 50°C, and the NMP concentration in the absorption liquid at the bottom of the column is 75% or even 80% by weight - A third stage involves sending the bottom absorption liquid to a porous ceramic membrane for filtration in a cross-flow filtration mode; the average pore diameter of the porous ceramic membrane is 2 to 50 nm, more preferably 5 to 20 nm; and the operating temperature is 5 to 50°C, more preferably 15 to 45°C, more preferably 20 to 40°C; filtration pressure 0.1 to 1 MPa - A fourth step involves sending this filtrate to a permeation membrane for dehydration in order to recover NMP. This is a permeation-type permeation membrane, preferably an inorganic permeation membrane, and more preferably a NaA zeolite membrane. In this fourth step, the filtrate enters The permeate membrane is in the liquid phase, and the permeate process has an operating temperature of 50 to 100°C, more preferably 65 to 95°C, and even more preferably 80 to 90°C; and a permeate membrane. The permeate-side pressure is an absolute pressure of less than 3000 Pa.

[0008] Utility model CN215587012U is also known, proposing an alternative NMP condensation and recovery system for a lithium-ion battery cathodic coating machine. It comprises a heat exchange unit connected to the electrode coating dryer and a condensation recovery unit, with heat exchange between the exhaust air discharged from the dryer and the purified air outlet of the low-condensation recovery unit. It also includes a condensation recovery unit and an exhaust gas scrubbing unit, so that the purified air is heated to the specified temperature and then re-enters the coating dryer.A condensing recovery unit cools the exhaust air pre-cooled by the heat exchange unit, so that some of the N-methylpyrrolidone present in the exhaust air is condensed and separated into droplets. The purified air is then returned to the coating dryer, while the separating N-methylpyrrolidone condensate is collected. A waste gas scrubbing unit uses water or an aqueous solution as an absorbent to scrub some of the exhaust air cooled by the heat exchange unit, reducing the N-methylpyrrolidone content in the exhaust air to a specified range before discharge. Disadvantages of prior art

[0009] Prior art solutions are not entirely satisfactory because the NMP recovery cycle involves processing, including the production of chilled water and high temperatures for hot air production in the drying chamber, resulting in high energy consumption. The overall economics of the installation, taking into account the additional cost of using NMP as a solvent rather than water, and the energy expenditure incurred by reprocessing the evaporation effluents in the dryer, may lead to rejecting this technology because the cost of electrode preparation is no longer competitive.

[0010] Nor do they guarantee the total absence of NMP release into the atmosphere. Solution provided by the invention

[0011] In order to overcome these drawbacks, the present invention, in its most general sense, relates to an installation for the production of electrodes for lithium-ion batteries comprising a station for coating active materials on cathodes in a solvent consisting of NMP, and a station for coating active materials on anodes in an aqueous solvent, said installation comprising a condensation and recovery system of NMP at the cathode dryer characterized in that the stream treated by said condensation and recovery system of NMP consists of a part between 15 and 90% of the stream from said cathode dryer.

[0012] Advantageously, the installation includes an air-to-water heat exchanger ensuring the heating of the air injected into the upstream duct leading into the anode dryer.

[0013] According to one variant, said air-to-water heat exchanger is supplied by a heat transfer fluid from an air-to-water exchanger disposed on the downstream duct of the cathode dryer.

[0014] According to one variant, said NMP condensation system comprises an upstream air-water exchanger and a downstream air-water exchanger, connected by a circulation of a heat transfer fluid.

[0015] According to one variant, the installation includes an energy recovery unit placed on the air loop of the anode dryer.

[0016] Advantageously, said energy recovery unit includes an air-to-water heat exchanger disposed on the downstream hot air intake duct from the anode dryer, said air-to-water heat exchanger (being connected by a heat transfer fluid circuit to a second air-to-water heat exchanger disposed on the upstream hot air injection duct in the anode dryer.

[0017] According to another variant the solvent of the anode coating station also contains NMP, and in that said anode dryer generates a second stream treated partially or totally by said system (500) of condensation and recovery of NMP.

[0018] Detailed description of a non-limiting example of embodiment

[0019] The present invention will be better understood upon reading the following description, concerning a non-limiting example of an embodiment illustrated by the accompanying drawings where:

[0020] [Fig-1] [Fig.1] describes a schematic view of an installation conforming to the invention

[0021] [Fig.2] [Fig.2] describes a schematic cross-sectional view of a condenser operated in an installation according to the invention. Presentation of the cathode coating line

[0022] The installation described by way of example is illustrated by [Fig. 1] representing the schematic diagram. It comprises

[0023] - a cathode coating line equipped with a drying tunnel (100) intended to the evaporation of the solvent used during the cathode coating step, and

[0024] - an anode coating line equipped with a drying tunnel (200) intended to the evaporation of the solvent used during the anode coating step. The cathode coating step, upstream of the invention, consists of depositing onto Current collectors, for example aluminum foils, and a composite ink containing lithium ions are used. The components are dissolved in a solvent, NMP (N-methyl-2-pyrrolidone), using tools such as deflocculators and other homogenizers and dispersers to ensure good homogeneity of the inks produced.

[0025] This ink is deposited on the current collectors using a coating table by adjusting the height of the coating ruler in order to obtain the desired basis weight (quantity of material per unit area in mg.cm-2), then the coated electrodes are heated to evaporate the solvent in a dryer (100) typically having a length of about 50 m, a cross-section of about 0.5m and a temperature of about 80°C to 130°C, which the electrode passes through in about one minute.

[0026] This drying tunnel (100) releases air laden with NMP, the object of the invention being to purify this air to avoid the discharge of toxic effluents and to recover the NMP for reuse in a new process for preparing an induction ink. To this end, the air laden with NMP is extracted from the drying tunnel (100) by a downstream duct (110), and the recycled air is reinjected into the drying tunnel (100) by an upstream duct (120). Air from the drying tunnel (100) is drawn into the downstream duct (110) with a flow rate slightly higher than the flow rate of reinjection of purified air through the upstream duct (120), for example a flow rate of 80000 m3 per hour for the aspiration into the downstream duct (110) of air containing approximately 8240 mg / m3 of NMP, at a temperature of around 97°C.

[0027] The purified air is reinjected through the upstream duct (120) with a starting flow rate of 78200 m3 / h, at a temperature of 70°C and with an NMP level of less than 5990 mg / m3.

[0028] The pressure differential guarantees a vacuum inside the cathode dryer (100) preventing untimely releases of stale air into the atmosphere of the coating room.

[0029] A downstream conduit (110) has, for example, a suction duct with a cross-section of 1800 mm² ensuring the recycling of vapors from the drying of the cathodes. A valve (130) allows the suction flow rate to be controlled.

[0030] The downstream conduit (120) includes a hot pure air injection conduit with a cross-section of 1000 mm associated with a fan (125) ensuring a nominal flow rate of 78200 m3 / h with a depression of 4000 Pa.

[0031] The downstream duct (120) includes a first valve (121) to control the flow rate of fresh outside air, and a second valve (122) to control the intake of recirculated hot air, as well as a third valve (123) for the exhaust of air to the outside. These valves serve as a safety measure by injecting outside air if the The concentration of NMP is too high, in order to limit the risk of explosion of NMP vapors in the dryer

[0032] Presentation of the NMP recycling plant

[0033] The hot air charged with NMP from the downstream duct (110) is divided into two streams by a bypass (130) directing about a quarter of the stream to a condenser (500) and three quarters of the stream directly to the upstream duct (120).

[0034] The NMP condenser is of a known type, but unlike prior art solutions, it only treats a part of the outlet flow from the drying tunnel (100).

[0035] By way of example, the flow rate through the condenser (500) is approximately 21450 m3 / h, and the flow rate transmitted directly to the upstream conduit (120) is approximately 56700 m3 / h.

[0036] The NMP is recovered in a tank (550) with a flow rate of approximately 3 kg per minute, at a temperature of 3°C.

[0037] The outlet of the condenser (500) is connected to a washing tower (520) by a controlled circuit including a valve (530). This washing tower (520) also optionally receives gases from an extraction hood (150) placed above the electrode coating chamber.

[0038] The washing tower (520) releases into the atmosphere air containing less than 1 mg / m3 of NMP.

[0039] Presentation of the air treatment system for the anode drying tunnel

[0040] The air treatment of the anode drying tunnel (200) is simpler because the solvent used for coating the anodes is generally water. It therefore simply comprises a downstream suction duct (210) drawing in humid air at a temperature of approximately 97°C and a water vapor content of 5.5 kg / min with a flow rate of approximately 81,800 m³ / h, and an upstream air injection duct (220) with a flow rate of 80,000 m³ / h and a temperature of approximately 70°C. The pressure differential ensures a negative pressure inside the anode dryer (200), preventing unwanted releases of stale air into the atmosphere of the coating rooms.

[0041] A valve controls the discharge of air to the outside via a fan (230). Fresh air at an ambient temperature between -10°C and +30°C is drawn in by a fan (243) and filtered by two filters (241, 242). The air is also filtered by a filter (243) before being injected into the dryer via the upstream duct (220).

[0042] Energy recovery between the anode dryer and the cathode dryer

[0043] The invention relates more particularly to the energy optimization of the installation for the treatment of drying effluents from cathodes and anodes.

[0044] For this purpose, the installation includes an air-water heat exchanger (20) ensuring the heating of the air injected into the upstream duct (220) leading into the anode dryer (200).

[0045] This heat exchanger (20) is supplied by a heat transfer fluid from a first air-water exchanger (10) located on the downstream duct (110) of the cathode dryer (100).

[0046] Finally, a heat recovery unit (1) is connected to the circuit to remove heat from the heat transfer fluid when the anode dryer (200) is not in operation.

[0047] The air-water heat exchanger (20) ensuring the heating of the air injected into the upstream duct (220) leading into the anode dryer (200) provides, in a particular embodiment, an energy gain of about 343 kW, and the air-water heat exchanger (501) disposed on said NMP condensation and recovery system (500) provides an energy gain of about 184 kW.

[0048] A second energy recovery unit is placed on the air loop of the anode dryer. It includes an air-to-water heat exchanger (31) located on the downstream intake duct (210) of hot air from the anode dryer (200). This air-to-water heat exchanger (31) is connected by a heat transfer fluid circuit to a second air-to-water heat exchanger (32) located on the upstream intake duct (220) of hot air from the anode dryer (200).

[0049] Two isolation valves (225, 226) allow the installation to be isolated from the outside in the event of a stoppage of operation. Energy recovery in the condenser

[0050] Figure 2 schematically illustrates the condenser for NMP recovery. NMP-laden air from the cathode drying tunnel (100) enters the condenser enclosure at a temperature of 68 to 85°C through an upstream end (520) and passes through a series of condensation coils (520 to 523) in which a low-temperature heat transfer fluid from a cold source (540) at -5°C circulates.

[0051]

[0052] Typically, the fluid enters the cell (520 to 523) at a temperature of -2°C and exits at a temperature of +3°C. The air laden with NMP cools as it passes through each condensation cell (520 to 523), and its temperature decreases, for example, to 30°C, 20°C, 12°C, and then 3°C as it passes through successive condensation cells (520 to 523). The condensed NMP is collected in each condensation cell (520 to 523) and transferred to a reservoir (550).

[0053] A heat recovery system comprises an air-to-water heat exchanger (502) located at the condenser outlet, through which purified air passes at a temperature of approximately 3°C and exits at a temperature of approximately 35°C to 55°C. The cooled heat transfer fluid circulates in a transfer circuit (560) via a pump (565) to cools an upstream heat exchanger (501) placed between the contained air supply of the NMP (520) and the first cell (520), and provides primary cooling of the air to bring it to a temperature of about 50 °C. Variant

[0054] Optionally, the coating of the anodes also uses a solvent containing NMP. In this case, the air recycling circuit from the drying tunnel (200) of the anodes includes the same equipment as the air recycling circuit from the drying tunnel (100) of the cathodes, and in particular a condenser (500) with a heat recovery circuit as described above.

Claims

Demands

1. - An installation for the production of electrodes for lithium-ion batteries comprising a cathode coating station with active materials in a solvent consisting of NMP, and an anode coating station with active materials in an aqueous solvent, said installation comprising an NMP condensation and recovery system (500) at the cathode dryer (100) characterized in that the stream treated by said NMP condensation and recovery system (500) consists of a variable portion between 15 and 90% of the stream from said cathode dryer (100), the suction flow rate of this stream treated by the NMP recovery system (500) being controlled by a bypass valve (130), and in that it comprises an air-to-water heat exchanger (20) providing heating for the air injected into the upstream duct (220) leading to the anode dryer (200).

2. - Installation for the production of electrodes for lithium-ion batteries according to the preceding claim characterized in that said air-water heat exchanger (20) is supplied by a heat transfer fluid from an air-water exchanger (10) disposed on the downstream duct (110) of the cathode dryer (100).

3. - Installation for the production of electrodes for lithium-ion batteries according to claim 1 or 2 characterized in that said NMP condensation system (500) comprises an upstream air-water exchanger (501) and a downstream air-water exchanger (502), connected by a circulation of a heat transfer fluid.

4. - Installation for the production of electrodes for lithium-ion batteries according to claim 1 characterized in that it comprises an energy recovery unit placed on the air loop of the anode dryer (200).

5. - Installation for the production of electrodes for lithium-ion batteries according to the preceding claim characterized in that said energy recovery unit comprises an air-water heat exchanger (31) disposed on the downstream duct (210) for the intake of hot air from the anode dryer (200), said air-water heat exchanger (31) being connected by a heat transfer fluid circuit to a second air-water heat exchanger (32) disposed on the upstream duct (220) for the injection of hot air into the anode dryer (200).

6. - Installation for the production of electrodes for lithium-ion batteries according to claim 1 characterized in that the solvent of the anode coating station also contains NMP, and in that said anode dryer (200) generates a second stream treated partially or totally by said NMP condensation and recovery system (500).

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