Facility for producing electrodes for batteries

Abstract

The present invention relates to a facility for producing electrodes for lithium-ion batteries, the facility comprising a station for coating cathodes with active materials in a solvent consisting of NMP, and a station for coating anodes with active materials in an aqueous solvent, the facility comprising a system (500) for condensing and recovering NMP in the cathode dryer (100), characterised in that the stream handled by the system (500) for condensing and recovering NMP consists of a portion that is made up of between 15 et 90% of the stream from the cathode dryer (100) and is calculated as precisely as possible according to the amount of NMP to be evaporated.

Description

PLANT FOR THE PRODUCTION OF ELECTRODES FOR BATTERIES Field of invention

[0001] The present invention relates to the field of recovery of NMP (N-methyl-2-pyrrolidone) or any other solvent serving as an intermediate product for the manufacture of anodes and cathodes and installations for the recovery of the NMP or solvent in question.

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

[0003] For the production of lithium-ion batteries, aluminum or copper foils coated with active ingredients are diluted in the organic solvent NMP to bind the lithium ions to the carrier foils. The coated foils 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 and are also rapidly flammable. Furthermore, they lead to significant consumption of NMP if it is not recovered and recycled.

[0004] Steam recovery in a recovery tower is known to reduce environmental and economic problems. The processes usually involve adding water to this steam, which acts as an NMP absorbent. In the container, the hot NMP steam mixes with cold water, the NMP concentration in the air decreases, and the concentration in the water increases. The NMP changes its aggregation state and becomes a liquid and is no longer highly flammable. The water becomes warm. Existing technology for the recovery and purification of liquid NMP waste mainly involves recovering NMP through 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 prone to oxidation in the presence of air, producing acidic substances, especially under the combined action of water, air and high temperatures. State of the art

[0007] Known in the prior art is Chinese patent CN110152338 describing a solution for recycling NMP vapor condensates in lithium battery production, comprising the following steps: diverting 80% of the NMP vapors from the baking plant by a fan and returning the recycling to the coating machine of 20% exhaust gasDischarging 20% ​​of the exhaust vapors through the waste heat recuperator, the water condenser and the water-cooled condenser of the cooling water machine, for cooling the vapor and the NMP vapor, condensation in the exhaust gas. This is an efficient treatment process that discharges the exhaust gas in the present invention in the production of lithium batteries, which performs closed circulation condensation recovery. Disadvantages of the prior art

[0008] The solution proposed in the prior art has the disadvantage of a fixed sampling of 20% of the NMP vapors from the cathode dryer. This sampling rate is empirical and is not generally appropriate. Indeed, the size of the dryer and the operating conditions vary greatly from one installation to another, and the NMP content in the drying chamber is critical. If it exceeds a threshold value, the atmosphere in the dryer becomes flammable and explosive. Solution provided by the invention

[0009] To address this drawback, the invention proposes introducing into the NMP recovery circuit a valve controlling the suction flow rate to adjust the rate to a non-fixed value set by the operator according to the configuration of the installation and the current production, in a variable manner according to changes in production. The invention also proposes reheating the injected air to prevent the formation of condensation.

[0010] the present invention relates, in its most general sense, to an installation for the production of electrodes for lithium-ion batteries having the characteristics set out in claim 1.

[0011] The typical installation comprises 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 system for condensing and recovering NMP in the cathode dryer, characterized in that the flow treated by said system for condensing and recovering NMP consists of a portion of between 15 and 90% of the flow from said cathode dryer.

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

[0013] According to one variant, said air-water heat exchanger is supplied by a heat transfer fluid coming from an air-water exchanger arranged on the downstream conduit 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 comprises an air-water heat exchanger arranged on the downstream duct for sucking in hot air from the anode dryer, said air-water exchanger being connected by a heat transfer fluid circuit to a second air-water exchanger arranged on the upstream duct for injecting hot air into 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 flow partially or totally treated by said system (500) for condensation and recovery of NMP.

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

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

[0020] describes a schematic view of an installation in accordance with the invention

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

[0022] The installation described as an example is illustrated by the schematic diagram. It includes

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

[0024] - an anode coating line equipped with a drying tunnel (200) intended for the evaporation of the solvent used during the anode coating step. The cathode coating step, upstream of the invention, consists of depositing on current collectors, for example aluminum sheets, a composite ink containing lithium ions. The components are dissolved in a solvent, NMP (N-methyl-2-pyrrolidone) using tools such as deflocculators and other homogenizers and dispersers allowing 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 rule in order to obtain the target 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 approximately 50 m, a section of the order of 0.5 m and a temperature of the order of 80°C to 130°C, which the electrode passes through in approximately one minute.

[0026] This drying tunnel (100) releases air loaded with NMP, the aim of the invention being to purify this air to avoid releasing toxic effluents and to recover the NMP with a view to reusing it for a new process for preparing an induction ink. To this end, the air loaded 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). The air coming from the drying tunnel (100) is sucked into the downstream duct (110) with a flow rate slightly higher than the reinjection flow rate of purified air by the upstream duct (120), for example a flow rate of 80000 m 3 per hour for suction in the downstream duct (110) of air containing approximately 8240 mg / m 3 of NMP, at a temperature of around 97°C.

[0027] The purified air is reinjected through the upstream duct (120) with a start of 78200 m 3 / h, at a temperature of 70°C and with an NMP rate lower than 5990 mg / m 3 .

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

[0029] A downstream conduit (110) has, for example, a suction duct ensuring the recycling of vapors from the drying of the cathodes. A valve (130) makes it possible to control the suction flow rate.

[0030] The downstream duct (120) comprises a hot pure air injection duct associated with a fan (125) providing a depression of 4000 Pa.

[0031] The downstream duct (120) comprises a first valve (121) for controlling the flow rate of introduction of fresh outside air, and a second valve (122) for controlling the arrival of recycled hot air, as well as a third valve (123) for the discharge of air to the outside. These valves serve as a safety device by injecting outside air if the NMP concentration is too high, in order to limit the risks of explosion of NMP vapors in the dryer.

[0032] Presentation of the NMP recycling facility

[0033] The hot air loaded with NMP from the downstream duct (110) is divided into two flows by a bypass (130) directing a part of the flow to a condenser (500) and the rest of the flow directly to the upstream duct (120). The proportion of air passing through the condenser is calculated on the basis of the quantity of NMP to be condensed (customer data)

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

[0035] For example, the flow rate through the condenser (500) is approximately 21450 m 3 / h, and the flow rate transmitted directly to the upstream conduit (120) of approximately 56700 m 3 / 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 comprising a valve (530). This washing tower (520) also optionally receives gases from a suction hood (150) placed above the electrode coating chamber.

[0038] The washing tower (520) releases into the atmosphere air containing less than 1 to 2 mg / m 3 of NMP, according to applicable local regulations.

[0039] Presentation of the anode drying tunnel air treatment plant

[0040] The air treatment of the anode drying tunnel (200) is simpler because the solvent used for coating the anodes is generally pure water. It therefore simply comprises a downstream suction duct (210) sucking in humid air at a temperature of approximately 97°C and a water vapor content with a given flow rate and an upstream air injection duct (220) with a slightly lower flow rate. The pressure differential guarantees a depression inside the anode dryer (200) avoiding untimely 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 is drawn in by a fan (243) with filtering by two filters (241, 242). The air is also filtered by a filter (243) before injection 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 treating effluents from drying cathodes and anodes.

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

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

[0046] Finally, a heat recovery unit (1) is connected to the circuit to remove excess 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 conduit (220) opening into the anode dryer (200) provides, in a particular embodiment, an energy saving of approximately 343 kW, and the air-water exchanger (501) arranged on said NMP condensation and recovery system (500) provides an energy saving of approximately 184 kW.

[0048] A second energy recovery unit is placed on the air loop of the anode dryer. It comprises an air-water exchanger (31) arranged on the downstream duct (210) for sucking in hot air from the anode dryer (200). This air-water exchanger (31) is connected by a heat transfer fluid circuit to a second air-water exchanger (32) arranged on the upstream duct (220) arranged on the upstream duct (220) for reinjecting 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 shutdown. Energy recovery in the condenser

[0050] Schematically illustrates the condenser intended for the recovery of NMP. The air loaded with NMP 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 batteries (520 to 523) in which a low-temperature heat transfer fluid from a cold source (540) at -2°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 loaded 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 respectively as it passes through the successive condensation cells (520 to 523). The condensed NMP is recovered in each condensation cell (520 to 523) and transferred to a reservoir (550).

[0053] A heat recovery system is composed of an air-water exchanger (502) located at the outlet of the condenser, crossed by the purified air at a temperature of approximately 3°C and emerging at a temperature of approximately 35°C to 55°C. The cooled heat fluid circulates in a transfer circuit (560) thanks to a pump (565) to cool an upstream heat exchanger (501) placed between the supply of contained air of the NMP (520) and the first cell (520), and ensures primary cooling of the air to bring it to a temperature of approximately 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 anode drying tunnel (200) comprises the same equipment as the air recycling circuit from the cathode drying tunnel (100), and in particular a condenser (500) with a heat recovery circuit as described above.

Claims

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 system (500) for condensing and recovering NMP in the cathode dryer (100) characterized in that the flow treated by said system (500) for condensing and recovering NMP consists of a variable part of between 15 and 90% of the flow from said cathode dryer (100), the suction flow rate of this flow treated by the system (500) for recovering NMP is calculated as accurately as possible according to the quantity of NMP to be evaporated and is controlled by a bypass valve (130) and in that it comprises an air-water heat exchanger (20) ensuring the heating of the air injected into the upstream conduit (220) opening in the anode dryer (200). 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 coming from an air-water exchanger (10) arranged on the downstream conduit (110) of the cathode dryer (100). 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. 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). 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) arranged on the downstream duct (210) for sucking in hot air from the anode dryer (200), said air-water exchanger (31) being connected by a heat transfer fluid circuit to a second air-water exchanger (32) arranged on the upstream duct (220) for injecting hot air into the anode dryer (200). 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 flow partially or totally treated by said system (500) for condensation and recovery of NMP.

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