Apparatus and method for manufacturing slab from cathode active material of rechargeable battery

Abstract

The invention relates to a device (1) for producing a slab (2) from powdered raw material. The powdered raw material is a cathode active material for a rechargeable battery. The apparatus (1) comprises: a lower mold (3) defining a molding cavity (4); and the upper die (6) is provided with an upper punch (601). The upper die (6) and the lower die (3) are movable relative to each other along a vertical direction (V) between an open position and a pressing position. The upper die (6) and the lower die (3) are also displaceable to a pre-pressing position in which the molding cavity (4) is closed by the upper punch (601) but in air communication with the ambient air volume. The apparatus (1) further comprises a vacuum system for drawing air from the molding cavity (4) when in the pre-pressing position and maintaining a negative pressure within the molding cavity when in the pressing position.

Description

Technical Field

[0001] The present invention relates to an apparatus and method for manufacturing slabs from cathode active materials of rechargeable batteries. Background Art

[0002] Driven by the increasing demand for batteries in many fields, battery production is growing at an increasing rate.

[0003] Generally, batteries are divided into two major categories: primary batteries, i.e., batteries that cannot be recharged and are discarded at the end of their life cycle; and secondary batteries, i.e., rechargeable batteries.

[0004] Rechargeable batteries include a set of electrodes integrated in a sealed housing for charging and discharging electrical energy. Generally, the set of electrodes has an anode material layer, a separator, and a cathode material layer, which are rolled up or stacked to form a single body, and the single body is inserted into the sealed housing to form a battery cell. In addition, the battery cell is filled with an electrolyte to carry positively charged lithium ions from the anode through the separator to the cathode and vice versa.

[0005] Among different types of secondary batteries, lithium-ion batteries are currently the most popular worldwide due to their high capacity and low self-discharge. In addition, cathode active materials are one of the most important components for manufacturing lithium-ion batteries because they determine the efficiency, reliability, cost, life, and size of the batteries, and thus determine their applications.

[0006] More specifically, cathode active materials are high-purity chemicals. More specifically, cathode active materials undergo a calcination process (high-temperature treatment) to remove impurities and volatile substances. Cathode materials are usually composed of cobalt, nickel, and manganese in a crystal structure to form a multi-metal oxide material, and lithium is added to the material to form a powdery mixture. During the calcination process, the powdery mixture is placed in a container (such as a firing box) and is usually fired in a kiln.

[0007] However, this method has some disadvantages. For example, in this method, the efficiency of the calcination process is low because the powdery mixture is kept inside the firing box, so the heat and mass transfer coefficients are low, and thus the mixture has to be kept in the kiln for a long time, making the calcination process longer. In addition, the time required to cool the firing box when it comes out of the kiln further increases the process downtime. Moreover, due to continuous heating and cooling, the firing box usually has to be replaced after only a few weeks of use, increasing the cost of the process.

[0008] Therefore, there is a need to perform the calcination process without using any container to improve the efficiency of the process.

[0009] Against this background, patent document JP2019175697A provides a method for manufacturing a cathode active material. More specifically, this document describes a method in which a molded object is obtained by pressing a powdery cathode active material (i.e., in powder form); then the molded object is subjected to a calcination process. Therefore, there is a need to provide an apparatus and method for manufacturing a slab from powdery raw materials. Against this background, patent document US3657917A provides methods and systems for obtaining high-quality molded objects by compressing powdery raw materials. In this solution, the powdery material is placed in a mold cavity, then the gas is evacuated, and the powdery material is pre-compressed by a double piston hammer assembly. Additionally, the piston mass body is impacted at high speed to apply a high-energy pulse through a stamping die, thereby firmly binding the particles of the powdery material together under high vacuum, so that the product precisely conforms to the mold configuration.

[0010] In addition, patent document US2011113924A1 discloses an apparatus and method for manufacturing a slab from powder, particularly from silicon. Specifically, in this document, the powder is fed into a feeding device to transfer the powder to be compacted from a loading position to a cavity where the powder is compacted. The cavity is bounded laterally by a press table and from below by a lower die, and a molding chamber is formed. On the inner side facing the molding chamber, the press table has a gas-permeable filter insert made of ceramic material, and an evacuation mechanism is connected to this filter insert. Additionally, an upper die with a punch is provided, and the molding chamber is hermetically closed by the punch at its upper end. Specifically, the upper die is vertically movable. Then the molding chamber is loaded with a vacuum through the evacuation mechanism; thus the pressure in the molding chamber is reduced.

[0011] Then a pressure is generated by a pressure generating mechanism on the upper die with the punch to axially compact the powder in the molding chamber.

[0012] Specifically, the upper die is guided downward along the longitudinal axis until the punch hermetically closes the molding chamber at the upper end.

[0013] Then a negative pressure is introduced into the molding chamber via the evacuation mechanism.

[0014] However, in this field, there is an increasing demand for an apparatus and method that can more efficiently produce slabs from powdery cathode active materials. Summary of the Invention

[0015] The object of the present disclosure is to provide an apparatus and method for manufacturing a slab from a cathode active material of a rechargeable battery to overcome the above-mentioned drawbacks of the prior art.

[0016] This object is fully achieved by the apparatus and method of the present disclosure characterized in the appended claims.

[0017] According to one aspect of the present disclosure, the present disclosure provides an apparatus for manufacturing a slab from a powdered raw material. In one example, the powdered raw material is a cathode active material of a rechargeable battery. The apparatus may also produce slabs from other materials. The term "powdered" is used to describe a material consisting of very fine dry particles obtained by grinding, crushing or disintegrating a solid substance. In one example, the slab is preferably rectangular. In other examples, the slab may have other geometries. The apparatus includes a lower die. The lower die defines a molding cavity. It should be noted that the molding cavity may have different geometries. The apparatus includes a feeding device. The feeding device is configured to receive a charge of the powdered raw material and feed the charge of the powdered raw material into the molding cavity. The term "charge" is used to denote a measured quantity of raw material placed into the molding cavity for manufacturing the slab. The apparatus further includes an upper die. The upper die is provided with an upper punch. The upper die is movable relative to the lower die along a vertical direction. More specifically, the upper die and the lower die are movable along the vertical direction between an open position and a pressing position. In the open position, the upper punch is spaced apart from the lower die to allow the charge to be loaded into the molding cavity. Further, in the pressing position, the upper punch is inserted into the molding cavity to compress the charge to form a slab. In one example, the upper die and the lower die are also displaceable to a pre-pressing position. The pre-pressing position is vertically between the open position and the pressing position. More specifically, in the pre-pressing position, the molding cavity is closed by the upper punch to prevent the charge from moving out of the molding cavity. However, in the pre-pressing position, the molding cavity is in air communication with the surrounding air volume.

[0018] The apparatus may further include a sealing device. The sealing device is configured to keep the molding cavity and the surrounding air volume airtight. More specifically, the sealing device is configured to keep the molding cavity and the surrounding air volume airtight at the pre-pressing position and the pressing position of the upper die and the lower die.

[0019] According to one aspect of the present specification, the apparatus includes a vacuum system. The vacuum system is configured to suck air from the molding cavity. In one example, the vacuum system is configured to suck air from the molding cavity at the pre-pressing position of the upper die and the lower die. Further, the vacuum system is configured to maintain a negative pressure inside the molding cavity at the pressing position of the upper die. Thus, according to one aspect of the present disclosure, when the cavity is closed by the upper die but before the upper die compresses the powdered raw material inside the cavity, the vacuum system removes the air inside the molding cavity. Further, the negative pressure inside the molding cavity can be maintained during compression to prevent air from entering the cavity during this period.

[0020] It should be noted that degassing during compression of the powdered raw material inside the cavity is typically accomplished by a pulsating movement of the upper punch. During the degassing step, the movement performed by the upper punch is a movement away from the powder and then towards the powder and into contact with the powder, which was previously compressed (pulsating cycle). In this way, excess air in the mold can be discharged from the inside to the outside.

[0021] This degassing process can take a long time because the molding cavity usually requires several degassing cycles. Using a vacuum system allows the air in the molding cavity to be removed without having to perform the above degassing process. This enables a device that can compress the powdered material faster and in a particularly efficient manner without losing material, thereby obtaining a higher quality slab.

[0022] In one example, the lower die includes a bottom wall. The lower die also has side walls. More specifically, the side walls cooperate with the bottom wall to define a molding cavity. In one example, the bottom wall and the side walls move relative to each other along the vertical direction. In this way, the bottom wall and the side walls can move relative to each other to load the charge into the molding cavity and / or remove the formed slab from the molding cavity.

[0023] In one example, the lower die includes a lower punch. More specifically, the lower punch defines the bottom wall of the lower die. In one example, the lower die also includes a lower block. The lower block defines the side walls. The lower block also has a top surface. In one example, the top surface extends along a horizontal plane perpendicular to the vertical direction. The lower punch and the lower block can move relative to each other along the vertical direction so as to be displaceable between an aligned position and an offset position. More specifically, in the aligned position, the bottom wall is flush with the top surface such that the bottom wall and the top surface are in the same feed plane. In the offset position, the bottom wall is located below the top surface to define a molding cavity.

[0024] In one example, the device includes a feed surface. The feed surface extends along a feed plane. In one example, the feeding device defines a vertically oriented channel. In addition, the feeding device can move in the working direction. The working direction is parallel to the feed surface. In one example, the feeding device can also move in sliding contact with the feed surface. More specifically, the feeding device can move between a loading position and an unloading position. In the loading position, the feeding device receives a charge of powdered raw material. In the unloading position, the channel is vertically aligned with the bottom wall. More specifically, in the unloading position, the channel is vertically aligned with the bottom wall such that the charge is received in the volume defined by the channel and the bottom wall.

[0025] Thus, according to one aspect of the present disclosure, when the feeding device reaches the loading position as it moves, the charge is loaded without stopping, and the charge is conveyed in direct contact with the feed surface. Further, when the feeding device is in the unloading position, the bottom wall and the top surface are aligned and form a feed plane; since the feed surface extends along the feed plane, the feeding device can easily move along the feed plane to unload the charge onto the bottom wall. In this way, feeding the charge into the molding cavity is made more efficient.

[0026] The device includes an outlet. In particular, the formed slab is provided to the outlet. In one example, the device includes a pick-up device. The pick-up device can move along the working direction. The pick-up device can move between a pick-up position and a delivery position. At the pick-up position, the pick-up device grabs the formed slab. At the delivery position, the pick-up device delivers the slab to the outlet.

[0027] In one example, the device includes a carriage. The carriage is configured to move backward and forward along the working direction. In one example, the pick-up device and the feeding device are connected to the carriage. Furthermore, the pick-up device is positioned upstream of the feeding device in the forward direction. More specifically, the forward direction is defined as from the loading position towards the outlet of the device. In one example, at the pick-up position of the pick-up device, the feeding device is located at the loading position. In one example, at the delivery position of the pick-up device, the feeding device is located at the unloading position. Thus, the process is particularly fast because the feeding device and the pick-up device move simultaneously between two positions, where, at the first position, the formed slab is picked up while the feeding device feeds the charge, and at the second position, the formed slab is delivered to the outlet while the molding cavity is loaded and can continue to form the next slab. In another example, the feeding device and the pick-up device can also be displaced to a third position downstream of the unloading position. More specifically, at the third position, both the feeding device and the pick-up device are downstream of the molding cavity and at the outlet of the device in the forward direction. In this example, during the movement in the backward direction (defined from the outlet to the loading position), the feeding device scrapes the charge when the lower block and the lower punch are in the offset position, so that the charge in the molding cavity is leveled by the feeding device.

[0028] In one example, at the pick-up position of the pick-up device ( Figure 1 ), the bottom wall is configured to move upward along the vertical direction V. Also at the pick-up position of the pick-up device, the side wall is configured to displace downward along the vertical axis. When the pick-up device is in the pick-up position, the bottom wall can move upward to the alignment position, while at the same time, the side wall moves downward. This solution is particularly beneficial for removing the formed slab from the molding cavity without damaging the slab.

[0029] In one example, the device includes a pair of sliding rods. In one example, the sliding rods extend longitudinally. The sliding rods are spaced apart from each other along a first horizontal axis. Each sliding rod has a first end and a second end. More specifically, the first horizontal axis is orthogonal to a second horizontal axis extending along the working direction. The carriage can be configured to slide on the sliding rods. More specifically, the carriage slides backward and forward along the working direction on the sliding rods. In one example, the device includes a plurality of longitudinal wheels. The longitudinal wheels are distributed on each sliding rod. The longitudinal wheels are distributed along the working direction. The longitudinal wheels are configured to support the weight of the carriage along the sliding rods. The longitudinal wheels allow the carriage to move backward and forward along the working direction. The device may also include transverse wheels. The transverse wheels are located on each sliding rod. The transverse wheels are arranged to rotate 90 degrees relative to the longitudinal wheels. The transverse wheels are adapted to keep the carriage aligned with the working direction along which the carriage moves. In one example, the longitudinal wheels and the transverse wheels are made of materials that do not pose a risk of contaminating the cathode material processed in the press.

[0030] For example, the longitudinal wheels can be made of steel, preferably case-hardened steel. Steel is advantageous because it reduces the wear rate of the longitudinal wheels that have to bear the weight of the sliding carriage.

[0031] Regarding the transverse wheels, they can be made of rubber, for example, or they can be rubber-coated, for example, by a vulcanization process.

[0032] The transverse wheels can be located at the first end and the second end of each sliding rod.

[0033] In one example, the bottom wall can move vertically relative to the side walls. The device includes an inlet for receiving powdered raw material. In one example, the device includes a particle suction system. The particle suction system is configured to remove particles floating in the air. In one example, the particle suction system has a first hood and a second hood. In one example, the first hood and the second hood are connected to the upper die. More specifically, the first hood can be located upstream of the molding cavity in the forward direction. The forward direction is defined as from the inlet towards the outlet. The first hood is configured to remove particles floating in the air from the surroundings of the molding cavity. In addition, the second hood is located downstream of the molding cavity in the forward direction. The second hood is configured to remove particles floating in the air from the surroundings of the outlet.

[0034] In one example, the lower die includes a plurality of molding cavities. The molding cavities among the plurality of molding cavities can be arranged to form an array of molding cavities. In addition, the upper die can include a plurality of upper punches. More specifically, each upper punch is configured to cooperate with a corresponding molding cavity to form a respective slab among a plurality of slabs. Thus, the productivity of the device can be increased.

[0035] In one example, the device includes a heating system. The heating system is connected to the lower die and the upper die to maintain them at a predetermined temperature.

[0036] The heating die allows for easier removal of the formed slab from the molding cavity and generally prevents the powdery raw material from adhering to the molding cavity or the upper punch.

[0037] In one example, the bottom wall, side walls, and upper punch are made of stainless steel. Thus, according to one aspect of the present disclosure, all parts of the die that come into direct contact with the powdery raw material are made of a material that does not react with the powdery raw material; this solution prevents the powdery material from being contaminated in any way.

[0038] In addition, the steel can withstand the pressure exerted by the powder (powdery raw material) pressed against the side walls.

[0039] In one example, the upper punch has a first layer and a second layer. The lower punch may also have a first layer and a second layer. The second layer comes into contact with the powdery raw material. The second layer is removably connected to the first layer. More specifically, the second layers of the upper punch and the lower punch are made of stainless steel. Thus, the upper punch and the lower punch can be manufactured in such a way that the parts in contact with the powdery raw material are made of stainless steel. Therefore, the device can be made more cost-effective.

[0040] In one example, the step of sucking air from the molding cavity starts when the upper die and the lower die are in the pre-pressing position and continues during the downward movement of the upper die along the vertical direction between the pre-pressing position and the position where the upper punch contacts the powder in the cavity. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] These and other features will become more apparent from the following description of the preferred embodiments shown by way of non-limiting examples in the drawings, in which:

[0042] - Figure 1 shows a device for manufacturing a slab from a powdery cathode active material according to the present disclosure, where the feeding device is in the loading position;

[0043] - Figure 2 shows the picking position of the picking device;

[0044] - Figure 3 shows the device with the picking device in the delivery position;

[0045] - Figure 4 shows the pre-pressing position of the lower die and the upper die;

[0046] - Figure 5 shows the pressing position of the lower die and the upper die;

[0047] - Figure 6 and Figure 8 shows the lower die and the upper die;

[0048] - Figure 7The device is shown in an axonometric view from different angles;

[0049] - Figure 9 is a side view of the device;

[0050] - Figure 10 shows the scraping element,

[0051] - Figure 11 shows details of the sliding rod,

[0052] - Figure 12 shows the hydraulic system,

[0053] - Figure 13A and Figure 13B shows details of the vacuum system. Detailed Description of the Invention

[0054] Referring to the accompanying drawings, numeral 1 denotes a device for manufacturing a slab 2 from a powdered raw material. In one example, the powdered raw material is a cathode active material of a rechargeable battery. The device (i.e., device 1) for manufacturing a slab 2 from a powdered raw material includes a lower die 3. The lower die 3 defines a molding cavity 4. The molding cavity receives the powdered raw material to be compressed to form a slab. More specifically, the lower die 3 includes a bottom wall 301. The lower die 3 further includes side walls 302. The side walls 302 cooperate with the bottom wall to define the molding cavity 4. In one example, the shape of the molding cavity is rectangular. In this example, the side walls 302 include four walls surrounding the bottom wall 301. In one example, the lower die 3 includes a plurality of molding cavities. The molding cavities in the plurality of molding cavities may be arranged to form an array of molding cavities. Each molding cavity has a corresponding bottom wall 301 and side walls 302.

[0055] The bottom wall 301 and the side walls 302 move relative to each other along the vertical direction V. In one example, the bottom wall 301 is vertically movable relative to the side walls 302.

[0056] The lower die 3 may include a lower punch 303. More specifically, the lower punch 303 defines the bottom wall 301.

[0057] In one example, the lower punch 303 includes a first layer L1 and a second layer L2. The second layer contacts the powdered raw material.

[0058] In one example, the second layer is removably connected to the first layer.

[0059] In one example, the lower die 3 includes a plurality of magnets M. In this example, the first layer L1 of the lower punch 303 is magnetized. Thus, the first layer can be connected to the lower punch 303 via the magnets M. In one example, the first layer L1 is made of soft iron. In one example, the first layer L1 also has a plurality of through-holes. The second layer L2 includes a plurality of blind holes. The first layer can be connected to the second layer by a plurality of screws that connect the first layer to the second layer via the through-holes and the blind holes. In one example, the second layer is made of stainless steel. Preferably, the second layer L2 of the lower punch 303 is made of high hardenability martensitic stainless steel. The stainless steel can contain carbon. The stainless steel can contain silicon. The stainless steel can contain manganese. The stainless steel can contain chromium. The stainless steel can contain vanadium. More specifically, the stainless steel has high polishability and resistance to corrosion and thermal oxidation.

[0060] In addition, the stainless steel can undergo one or more heat treatments.

[0061] In one example, the stainless steel is annealed to have a hardness less than or equal to 240. Preferably, the stainless steel is annealed at 750 °C - 800 °C. The stainless steel can be annealed for at least 3 hours under steady-state conditions. Then the steel is cooled. It can also undergo a relaxation process. The relaxation process is carried out after the processing process. The relaxation process is carried out before the final heat treatment. During the relaxation process, the steel is heated to 600 - 650 °C. During the relaxation process, the steel is heated for 2 hours. There can also be a step of tempering the stainless steel. During the tempering step, the steel is heated to 600 - 700 °C. The tempering step also includes a step of austenitizing at 990 - 1040 °C. Then the steel is cooled. In one example, the steel can be cooled in oil. The steel can undergo a hot bath at 500 - 550 °C and then an oil bath, and the steel is cooled in the oil bath according to the shape and size of the steel. In one example, the hardness of the steel after tempering is 52 - 56 HRC.

[0062] In one example, the second layer is thinner than the first layer. Thus, the portion in direct contact with the powdered raw material is made of the steel as described above. It should be noted that connecting the second layer to the first layer (through the blind holes) as described above results in a structure where no material other than the stainless steel contacts the powdered raw material. As described above, the cathode active material has a very high value and must be very pure to obtain high-quality electrodes. Therefore, the powdered raw material must only be in contact with materials that do not cause any unwanted reactions or contamination. In addition, this structure enables the use of the smallest amount of the said stainless steel to provide the thin layer (second layer) in contact with the raw material, thereby improving the efficiency in terms of process cost.

[0063] In addition, in one example, the sidewall 302 is made of two layers. The first layer of the sidewall 302 is made of the stainless steel. In one example, the first layer of the sidewall is connected to the second layer of the sidewall by a plurality of screws. In this example, both the second layer and the first layer of the sidewall 302 include a plurality of through holes, and the plurality of screws pass through these through holes. In one example, the through holes of the sidewall are formed in the bottoms of the first layer and the second layer of the sidewall, such that the through holes are located at a height below the bottom wall along the vertical direction V. In this way, the plurality of screws and the through holes do not contact the powdered raw material.

[0064] The lower die 3 may further include a lower block 304. The lower block 304 defines the sidewall 302. The lower block also has a top surface 3041. The top surface 3041 extends along a horizontal plane perpendicular to the vertical direction V. In one example, the lower punch 303 and the lower block 304 can move relative to each other along the vertical direction V. The lower punch 303 and the lower block 304 can move relative to each other along the vertical direction to be displaced between an alignment position and an offset position. In the alignment position, the bottom wall 301 is flush with the top surface 3041. More specifically, in the alignment position, the bottom wall 301 is flush with the top surface 3041, such that the bottom wall 301 and the top surface 3041 are located in the same feed plane. In addition, in the offset position, the bottom wall 301 is located below the top surface 3041 to define the molding cavity 4. In other words, in the offset position, the bottom wall 301 is located at a height lower than the top surface 3041 along the vertical direction.

[0065] More specifically, the lower punch 303 moves along the vertical direction V by an actuator. In one example, the actuator is a hydraulic system. The hydraulic system has a cylinder and a piston that moves along the vertical direction V in the cylinder. More specifically, the lower punch 303 moves along the vertical direction by the piston.

[0066] The apparatus 1 further includes an upper die 6. The upper die 6 is provided with an upper punch 601. In the case where the lower die 3 includes a plurality of molding cavities, the upper die 6 includes a plurality of upper punches 601. More specifically, each upper punch is configured to cooperate with a corresponding molding cavity 4 to form a corresponding slab 2 in the plurality of slabs 2. In one example, the upper punch 6 includes a first layer L1 and a second layer L2. In one example, the second layer L2 of the upper punch 601 contacts the powdered raw material.

[0067] In one example, the second layer L2 of the upper punch 601 is removably connected to the first layer.

[0068] In one example, the upper die 6 includes a plurality of magnets M. In this example, the first layer L1 of the upper punch 601 is magnetized. Thus, the first layer of the upper punch 601 can be connected to the second layer of the upper punch 601 via the magnets M of the upper punch. In one example, the first layer L1 of the upper punch 601 is made of soft iron. In one example, the first layer L1 of the upper punch 601 also has a plurality of through holes. The second layer L2 of the upper punch 601 includes a plurality of blind holes. The first layer of the upper punch 601 can be connected to the second layer of the upper punch 601 by a plurality of screws, and the plurality of screws connect the first layer of the upper punch 601 to the second layer of the upper punch 601 via the through holes and the blind holes. In one example, the second layer of the upper punch 601 is made of stainless steel. In one example, the lower punch 303 and the second layer of the upper punch 601 are corrugated. Thus, in one example, the top surface and the lower surface of the slab 2 are corrugated.

[0069] The device further includes a feeding device 5. The feeding device is configured to receive a charge of powdered raw material and feed the charge of powdered raw material into the molding cavity 4. The feeding device receives the charge of powdered raw material from the hopper 13.

[0070] The upper die 6 can move relative to the lower die 3 along the vertical direction V. More specifically, the upper die 6 can move relative to the lower die along the vertical direction between an open position and a pressing position. In one example, the upper die 6 moves vertically to move between the open position and the pressing position. In another example, the upper die can remain stationary while the lower die moves between the open position and the pressing position. Alternatively, both the lower die and the upper die move together between the open position and the pressing position.

[0071] In the open position, the upper punch 601 is spaced apart from the lower die 3 to allow the charge to be loaded into the molding cavity 4. In the pressing position, the upper punch 601 is inserted into the molding cavity 4 to compress the charge to form the slab 2. More specifically, in the pressing position, the upper punch 601 defines the upper wall of the molding cavity 4. In one example, the upper die 6 and the lower die 3 can also be displaced to a pre-pressing position. The pre-pressing position is vertically between the open position and the pressing position. More specifically, in the pre-pressing position, the molding cavity 4 is closed by the upper punch 601 to prevent the charge from moving out of the molding cavity 4. In addition, the molding cavity is in air communication with the surrounding air volume.

[0072] The device 1 includes a feeding surface 9. The feeding surface extends along a feeding plane. In one example, the feeding device 5 defines a channel 501. The channel 501 is vertically oriented. In one example, the feeding device 5 can move in a working direction WD. The working direction is parallel to the feeding surface 9. In one example, the feeding device 5 can move in sliding contact with the feeding surface 9. The feeding device can move between a loading position and an unloading position.

[0073] In one example, the lower block 304 is fixed. Accordingly, the top surface 3041 is fixed and horizontally aligned with the feed surface. In one example, the lower block 304 has a fixed part and a movable part. More specifically, the fixed part is defined by the top surface 3041, and the movable part is defined by the side wall 302 of the lower die 3.

[0074] It should be noted that the block 304 can be fixed or movable. If the block 304 is movable, it moves synchronously with the top surface 3041 and the wall 302 (which are integral or can be integral). The movement of the block 304 can assist in removing the object from the molding cavity. If the block 304 is fixed, the removal of the object is accomplished (only) by the upward movement of the lower punch 303.

[0075] The side wall 302 of the lower die can move along the vertical direction V. In one example, at the alignment position, the side wall is at the same height as the top surface to form a feed plane together with the bottom wall.

[0076] At the loading position, the feeding device 5 receives a charge of powdered raw material. At the unloading position, the channel 501 is vertically aligned with the bottom wall 301 of the lower die 3. More specifically, at the unloading position, the channel is vertically aligned with the bottom wall such that, at the unloading position, the charge is received in the volume defined by the channel 501 and the bottom wall 301.

[0077] In one example, the feeding device 5 includes a plurality of blades 502 that are horizontally arranged orthogonally to the working direction WD and spaced apart from each other. The blades are equidistant from each other. More specifically, when the feeding device moves between the loading position and the unloading position, the blades remain in sliding contact with the feed surface 9. In this way, the powdered raw material is evenly conveyed on the feed surface 9. In one example, the blades 502 can be provided with a plurality of grooves. The grooves are formed along the bottom of each blade, where the blade makes sliding contact with the feed surface 9. In the case where the lower die 3 includes a plurality of molding cavities, the feeding device 5 is divided into different sections. Each section is defined by a plurality of rods that are spaced apart from each other and arranged orthogonally to the blades 502. These sections are separated from each other. Each section corresponds to a respective molding cavity 4.

[0078] The apparatus 1 further includes a sealing device 7. The sealing device is configured to keep the molding cavity and the surrounding air volume airtight at the pre-pressing position and the pressing position of the upper die and the lower die. The sealing device is connected to the upper die 6. More specifically, the sealing device surrounds the upper die 601 to keep the molding cavity and the surrounding air volume airtight at the pre-pressing position and the pressing position of the upper die and the lower die. In addition, when the upper die and the lower die are in the pre-pressing position, the sealing device rests on the top surface 3041. In addition, when the dies 3, 6 are in the pressing position, the sealing device is compressed.

[0079] According to one aspect of the present disclosure, the device further includes a vacuum system. The vacuum system sucks air from the molding cavity 4. In one example, at the pre-pressing position of the upper mold and the lower mold, the vacuum system sucks air from the molding cavity 4. Alternatively, the vacuum system can operate when the mold is in other positions.

[0080] Specifically, during vacuuming, air is sucked in from above (upward) and below (downward) of the cavity. Suction guide grooves are provided in the lower mold and the upper mold for sucking air from the molding cavity, such that air is sucked from above and below the molding cavity. Specifically, the air sucked in from above is sucked in through an upper guide groove (in the gap separating the side wall and the sealing device) located between the side wall of the molding cavity and the sealing device. The bottom wall is provided with suction holes for sucking air from below. In one example, the lower mold is provided with a hole F, and the hole F allows air to be sucked from below the cavity during suction. In addition, a lower guide groove can be provided in the lower mold and connected to the hole, such that the sucked-in air is guided into the guide groove and sucked out through the hole. In addition, the upper mold and the lower mold are equipped with suction pipes 20, 21, and suction is performed through the suction pipes 20, 21.

[0081] The vacuum system is further configured to maintain a negative pressure in the molding cavity. In one example, the vacuum system is configured to maintain a negative pressure in the molding cavity at the pressing position of the upper mold and the lower mold. The vacuum system includes a vacuum pump. The vacuum system includes one or more vacuum tubes. In one example, the vacuum tubes include a first tube VT1 and a second tube VT2 respectively connected to the upper mold 6 and the lower mold 3.

[0082] The device includes an inlet I. The inlet I is configured to receive powdered raw materials. A hopper 13 is located at the inlet I of the device 1. The device 1 includes an outlet O. The formed slab 2 is provided at the outlet. In one example, the device 1 includes a picking device 11. The picking device 11 can move along the working direction WD. The picking device 11 can move between a picking position and a delivery position. At the picking position, the picking device grabs the formed slab 2. At the delivery position, the picking device 11 delivers the slab to the outlet O. In one example, the picking device includes a plurality of fingers 111 (or grippers). The fingers are spaced apart from each other to receive the slab. In this case, the lower mold 3 includes a plurality of molding cavities 4. The number of fingers corresponds to the number of molding cavities, such that each pair of fingers grabs a slab 2.

[0083] In one example, the side wall 302 moves vertically to the picking position of the picking device. Thus, when the picking device 11 is at the picking position, the bottom wall moves vertically upward to transport the slab to the height of the feeding surface 9, at which height the picking device receives the slab. In one example, the side wall moves downward simultaneously. In one example, only the side wall moves downward.

[0084] The upper punch 601 moves vertically up and down via the hydraulic system 19. This hydraulic system is different from the hydraulic system that moves the lower die.

[0085] The hydraulic system includes a tank 190. The tank holds oil (activating oil). The hydraulic system includes an activating element 191. The activating element includes a fixed part 191A and a movable part 191B. The movable part of the activating element can move vertically. The movable part of the activating element can move vertically between an open position and a closed position. In the closed position, the movable part approaches the fixed part.

[0086] In the open position of the activating element, the movable part is away from the fixed part and is located at a height lower than the fixed part.

[0087] The activating element is placed inside the tank and is thus surrounded by oil. The hydraulic system includes a first lowering conduit 192 and a first lifting conduit 193. The activating element is in communication with the first lifting conduit and the first lowering conduit.

[0088] In particular, oil passages are provided between the movable part and the fixed part. These oil passages are in communication with the first lifting conduit and the first lowering conduit and form a closed oil chamber with a variable volume (these chambers are separated from the oil in the tank) between the movable part and the fixed part. The volume of the said oil chamber changes with the movement of the movable part. In particular, when the movable part moves towards the open position of the activating element and the distance between the movable part and the fixed part increases, this volume increases. When oil is supplied to the first lowering conduit, the movable part of the actuating element moves vertically towards the open position of the actuating element (and the volume of the oil chamber connected to the first lowering conduit increases). The movable part moves downwards until it reaches a predetermined end position. When the movable part is in the open position (end position), the movable part no longer moves downwards even if oil continues to be supplied to the first lowering conduit. When oil is supplied to the first lifting conduit, the movable part moves vertically upwards towards the closed position. The hydraulic system also includes a displacement element 194. The displacement element is connected to the upper punch 601 on one side and to the tank on the other side. In particular, the displacement element is in oil communication with the tank. When the movable part is in the open position of the activating element, an oil chamber is created between the displacement element and the movable part at the lower part of the tank. Thus, when the movable part is in the open position of the activating element, the displacement element is only in oil communication with a part of the oil in the tank, and it is closed between the moving part and the displacement element. In addition, the displacement element is connected to a second lowering conduit 195 and a second lifting conduit 196. In particular, the displacement element includes an upper part 194A and a lower part 194B.

[0089] The upper part of the displacement element is in fluid communication with the tank and is connected to the second lowering conduit. The lower part of the displacement element is attached to the upper punch and is in communication with the second lifting conduit. The upper and lower parts are joined together. In particular, fluid communication is provided between the lower and upper parts of the displacement element. There is a capillary channel C for oil between the lower and upper parts.

[0090] When oil is supplied to the second lowering conduit (and the movable part is in the open position), the oil pushes the upper part of the displacement element, so that the displacement element and thus the upper punch move downward (thus the punch moves towards the pressing position). In one example, the tank also moves vertically. When oil is supplied to the second lifting conduit, the movable part is in the closed position, so that the displacement element is in fluid communication with the oil of the entire tank. In this case, the oil enters the capillary channel C and pushes the part of the displacement element between the lower and upper parts, and lifts the displacement element, thus lifting the upper punch.

[0091] The hydraulic system also includes a hydraulic circuit HC in communication with the hydraulic system, and this hydraulic circuit HC allows the oil to circulate in the system. To avoid complication, Figure 11 the hydraulic circuit is shown by two boxes in this figure. The circuit includes valves (such as solenoid valves) and other elements known in hydraulic circuits.

[0092] In addition, the device includes a control unit. The control unit automatically manages the hydraulic system.

[0093] It can be provided that when the top punch moves downward, the movement of the top punch is regulated via the hydraulic system, for example, by regulating the throttle valve between the position where the upper punch starts to interact with the side wall to close the cavity and is in the pre-pressing position (powder cannot come out of the cavity but air can) and the position where the upper punch contacts the powder (but no pressure is applied yet).

[0094] Preferably, when the cavity is closed by the upper punch, the suction (via the vacuum system) is activated. Thus, when the suction is activated, dust does not come out of the cavity. It can be expected that the suction continues even after the cavity is closed by the upper punch (pre-pressing is generated). Therefore, when reaching the pre-pressing position of the lower die and the upper die, the suction is activated. In one example, when the lower die and the upper die are in the pre-pressing position, the vertical movement of the upper die (and the punch) stops, and the vacuum is activated while the lower die and the upper die are in the pre-pressing position. It can be provided that when a predetermined decompression threshold is reached, the vacuum is deactivated. Then the vertical movement of the upper die downward continues until the upper die and the lower die are in the pressing position. In another example, it is envisaged that the suction continues even during the movement of the upper die from the pre-pressing position to the pressing position. Therefore, in this example, the suction starts when the lower die and the upper die are in the pre-pressing position, and continues as the upper die moves towards the pressing position until it reaches the point where the upper punch contacts the powder but does not press the powder in the cavity.

[0095] Suction can be managed in feedback control. In particular, it can be stipulated that a vacuum signal representing the cavity suction value is obtained; when a predetermined (desired) decompression threshold is reached, the vacuum is deactivated.

[0096] The hydraulic system can be configured to generate a damping effect for the upper die during vertical downward movement.

[0097] It can be stipulated that when suction continues while the upper punch is in contact with the powder in the cavity (but pressure has not yet been applied), the hydraulic system continues to generate a damping effect to relieve the upper die, which has a significant weight and may apply excessive pressure on the powder in the cavity.

[0098] In particular, since the closing of the cavity starts through the upper punch, the vacuum can be started while the upper punch moves downward and suction continues; at a certain point, the upper punch comes into contact with the powder and can remain in this state (without pressing the dust), and the vacuum can continue in this configuration. In this configuration, the upper punch (via the hydraulic system, for example, via a regulating valve) remains in a balanced state.

[0099] After suction is completed, the upper die and the upper punch in contact with the powder are pressed downward to compress the powder.

[0100] The pressing (compression) of the powder can be carried out in feedback control based on the setpoint value of the pressure applied to the powder and / or the position of the upper punch. Once the compression is completed, the upper die (and the upper punch) moves upward to the open position. In particular, the upper die moves upward and downward via this hydraulic system. Two different branches (including separate pipes and valves) can be provided in the hydraulic circuit for moving the upper die between the open position, the pre-pressing position, and the position where the upper die is in contact with the powder in the cavity but the powder is not compressed by the upper punch, and for pressing the upper die downward to compress the powder when the upper die is in contact with the powder.

[0101] The device can include an interface that allows the operator to adjust a series of working parameters to adapt the pressing process to the material and product to be molded. For example, a database can be provided that includes adjustment parameters identified and set by the operator for different types of materials.

[0102] In one example, the device 1 includes a carriage 12. The carriage 12 is configured to move backward and forward along the working direction WD. In one example, the picking device 11 and the feeding device 5 are connected to the carriage 12. In one example, the picking device 11 is positioned upstream of the feeding device 5 in the forward direction. The forward direction is defined as from the loading position towards the outlet O. Additionally, at the picking position of the picking device 11, the feeding device 5 is located at the loading position. At the delivery position of the picking device, the feeding device 5 is located at the unloading position. In one example, the carriage extends on the feeding surface 9.

[0103] In one example, the apparatus 1 includes a pair of sliding rods 14. The sliding rods 14 extend longitudinally. The sliding rods 14 are spaced apart from each other along a first horizontal axis H1. Further, each sliding rod has a first end 14A and a second end 14B. The first horizontal axis is orthogonal to a second horizontal axis H2. The second horizontal axis H2 extends along a working direction WD. The carriage 12 is configured to extend backward and forward along the working direction on the sliding rods.

[0104] The apparatus further includes a plurality of longitudinal bearings. The apparatus also includes a plurality of longitudinal wheels 15. The longitudinal wheels are distributed along the working direction WD on each sliding rod 14. The longitudinal wheels are configured to support the weight of the carriage 12 along the sliding rods. The longitudinal bearings rotatably support the respective longitudinal wheels 15 associated with the carriage 12 to allow the carriage 14 to extend along the sliding rods 14. In one example, the apparatus includes a pair of wiper elements 18 which are located upstream and downstream of the wheels with respect to the moving direction along the sliding direction of the wheels. The wiper elements 18 are in sliding contact with the sliding rods 14 on which the respective wheels roll; the wiper elements 18 have the function of keeping the surfaces of the sliding rods 14 on which the wheels roll clean. Preferably, the wiper elements or at least the portions of the wiper elements that slide on the sliding rods 14 are made of plastic. This has the advantage of preventing contamination.

[0105] The apparatus further includes transverse wheels 16. The apparatus also includes a plurality of transverse bearings. The transverse bearings rotatably support the corresponding transverse wheels 16, and the function of the transverse wheels 16 is to keep the carriage 12 aligned with the working direction WD along which the carriage 12 moves. The transverse wheels are located, for example, at the first end 14A and the second end 14B of each sliding rod 14. The transverse wheels are arranged to rotate 90 degrees relative to the longitudinal wheels 15.

[0106] Preferably, the transverse wheels 16 are made of vulcanized rubber (or coated with vulcanized rubber), and the longitudinal wheels 15 are made of (carburized) steel. This has the advantage of preventing the generation of dust or particles that may contaminate the product to be processed (i.e., the cathode powder to be compacted in the press); although the longitudinal wheels support the weight of the carriage, the carburized steel also ensures a long working life.

[0107] In this case, as described above for the longitudinal wheels, one or more (or all) of the transverse wheels 16 are also provided with corresponding pairs of wiper elements 18. The wipers of the transverse wheels have the function of keeping the guides on which the transverse wheels roll clean. Thus, in this case, the fact that the wiper elements or at least the portions of the wiper elements that slide on the respective guides are preferably made of plastic also has the advantage of preventing the generation of possible contaminants.

[0108] In one example, at the pick-up position of the pick-up device 11, the bottom wall 301 moves upward along a vertical axis V. Further, when the pick-up device 11 reaches the pick-up position, the side walls 302 have moved downward along the vertical axis V.

[0109] Thus, the carriage moves between different positions. In the initial position, the feeding device 5 is in the loading position. In this position, the channel 501 of the feeding device 5 is vertically aligned with the hopper to receive the charge. In this position, the picking device is located upstream of the molding cavity 4. Further, in the initial position, the lower die and the upper die are in the pressing position. In the pressing position, the lower punch 303 is lowered to form the molding cavity 4, and the upper punch is inserted into the molding cavity and compresses the raw material. Thus, when a slab 2 is being formed in the molding cavity 4, the feeding device 5 is in the loading position to receive the charge to be compressed to form a slab in the next cycle. When the slab is formed, the lower die and the upper die move to the open position ( Figure 1 ). Additionally, the lower punch 303 moves upward along the vertical direction V to bring the formed slab to the height of the feeding surface 9. In one example, the sidewall 302 moves downward at the delivery position of the picking device. More specifically, the downward movement of the sidewall occurs simultaneously with the upward movement of the bottom wall. In this position, the carriage moves forward in the working direction WD, and the picking device is in the picking position ( Figure 2 ). In the case where the carriage 12 moves along the working direction, the powdered raw material is conveyed along the feeding surface 9 towards the molding cavity 4. Next, the carriage moves forward in the working direction. The slab grasped by the picking device 11 moves towards the outlet. When the picking device is at the outlet O, the feeding device 5 is in the unloading position. In this position, the lower punch 303 and the top surface 3041 are in the aligned position and the channel 501 of the feeding device 5 is vertically aligned with the bottom wall 301. In one example, after unloading the charge onto the bottom wall, the carriage 12 moves forward in the working direction WD. In this position, both the feeding device and the picking device are at the outlet ( Figure 3 ). In this position, the mold is still in the open position. Then, the carriage moves backward to return to the initial position. When the carriage 12 moves backward along the working direction, the mold is still in the open position, and the feeding device 5 skims over the powdered raw material in the molding cavity.

[0110] At this time, the lower die and the upper die move to the pre - pressing position ( Figure 4 ). In one example, in this position, the vacuum system is activated. As the carriage moves back, the feeding device 5 skims over the charge. Next, the mold moves to the pressing position to form a slab ( Figure 5 ).

[0111] The device includes a particle suction system. The particle suction system removes particles floating in the air. More specifically, the particle suction system has a first hood 17A and a second hood 17B. The first hood and the second hood are connected to the upper mold 6. The first hood is located upstream of the molding cavity 4 in the forward direction AD. The forward direction AD is defined as from the inlet I towards the outlet O. The first hood removes particles floating in the air in the surroundings of the molding cavity 4. The second hood is located downstream of the molding cavity 4 in the forward direction. The second hood removes particles floating in the air in the surroundings of the outlet. In one example, the second hood can move vertically. The second hood can also move horizontally. In one example, the second hood is activated when the mold is in the pressing position.

[0112] In one example, the device includes a heating system. The heating system is connected to the lower mold 3. The heating system is also connected to the upper mold. The heating system maintains the mold at a predetermined temperature. The heating system can be a resistance heating system.

Claims

1. An apparatus (1) for manufacturing a slab (2) from a powdery raw material, which is a cathode active material of a rechargeable battery, the apparatus comprising: - A lower die (3) defining a molding cavity (4); - A feeding device (5) configured to receive a charge of the powdery raw material and feed the charge of the powdery raw material into the molding cavity (4); - An upper die (6) provided with an upper punch (601) and movable relative to the lower die (3) along a vertical direction (V) between an open position and a pressing position. In the open position, the upper punch (601) is spaced apart from the lower die (3) to allow the charge to be loaded into the molding cavity (4). In the pressing position, the upper punch (601) is inserted into the molding cavity (4) to compress the charge to form the slab (2), wherein the upper die (6) and the lower die (3) can also be displaced to a pre-pressing position vertically between the open position and the pressing position. In the pre-pressing position, the molding cavity (4) is closed by the upper punch (601) to prevent the charge from moving out of the molding cavity (4), but at the same time the molding cavity (4) is in air communication with the surrounding air volume; - A sealing device (7) configured to keep the molding cavity (4) and the surrounding air volume airtight in the pre-pressing position and the pressing position of the upper die (6) and the lower die (3); - A vacuum system configured to suck air from the molding cavity in the pre-pressing position of the upper die and the lower die, and maintain a negative pressure in the molding cavity in the pressing position of the upper die and the lower die.

2. The apparatus (1) according to claim 1, wherein the lower die (3) comprises a bottom wall (301) and side walls (302) cooperating with the bottom wall to define the molding cavity (4), and the bottom wall and the side walls are movable relative to each other along the vertical direction (V).

3. The apparatus (1) according to claim 2, wherein the lower die (3) comprises a lower punch (303) defining the bottom wall (301) and a lower block (304) defining the side walls (302) and having a top surface (3041) extending along a horizontal plane perpendicular to the vertical direction (V), wherein the lower punch (303) and the lower block (304) are movable relative to each other along the vertical direction (V) to be displaceable between an alignment position and an offset position. In the alignment position, the bottom wall (301) is flush with the top surface (3041) such that the bottom wall (301) and the top surface (3041) are in the same feeding plane (8). In the offset position, the bottom wall (301) is located below the top surface (3041) to define the molding cavity (4).

4. The device (1) according to claim 3, comprising a feed surface (9) extending along the feed plane (8), wherein the feed device (5) defines a vertically oriented channel (501) and is capable of moving between a loading position and an unloading position in sliding contact with the feed surface (9) in a working direction (WD) parallel to the feed surface (9), in the loading position, the feed device (5) receives the charge of the powdered raw material, and in the unloading position, the channel (501) is vertically aligned with the bottom wall (301) such that in the unloading position, the charge is received in a volume defined by the channel and the bottom wall.

5. The device (1) according to claim 4, further comprising: - an outlet (O) where the formed slab (2) is provided; - a pick-up device (11) capable of moving between a pick-up position and a delivery position along the working direction (WD), in the pick-up position, the pick-up device (11) grasps the formed slab, and in the delivery position, the pick-up device (11) delivers the slab to the outlet (O).

6. The device (1) according to claim 5, comprising a carriage (12) configured to move backwards and forwards along the working direction (WD), wherein the pick-up device (11) and the feed device (5) are connected to the carriage (12), wherein the pick-up device is positioned upstream of the feed device in a forward direction defined from the loading position towards the outlet (O), and wherein, In the pick-up position of the pick-up device, the feed device is in the loading position, and in the delivery position of the pick-up device, the feed device is in the unloading position.

7. The device according to claim 5 or 6, wherein in the pick-up position of the pick-up device (11), the bottom wall (301) is configured to move upward along the vertical direction (V), and the side wall (302) is configured to be displaced downward along the vertical axis.

8. The device (1) according to claim 6 or 7, further comprising: - a pair of sliding rods (14) longitudinally extending and spaced apart from each other along a first horizontal axis (H1), each sliding rod having a first end (14A) and a second end (14B), the first horizontal axis being orthogonal to a second horizontal axis (H2) along the working direction (WD), wherein the carriage (12) is configured to slide backward and forward along the working direction (WD) on the sliding rods; - a plurality of longitudinal wheels (15) distributed along the working direction (WD) on each of the sliding rods (14) and configured to support the weight of the carriage (12) along the sliding rods and allow the carriage to move backward and forward along the working direction (WD); - a plurality of transverse wheels (16) located at both ends of each sliding rod (14) and arranged to rotate 90 degrees relative to the longitudinal wheels (15) to keep the carriage (12) aligned with the working direction (WD) along which the carriage (12) moves, wherein the longitudinal wheels and the transverse wheels are made of rubber.

9. The device (1) according to any one of the preceding claims 2 to 8, wherein the bottom wall (301) is capable of moving vertically relative to the side wall (302).

10. The device (1) according to any one of the preceding claims, having an inlet (I) for receiving the powdered raw material and an outlet (O) for receiving the formed slabs, the device further comprising a particle suction system configured to remove particles floating in the air, the particle suction system having a first hood (17A) and a second hood (17B) connected to the upper die (6), wherein the first hood is located upstream of the molding cavity (4) in the forward direction (AD) defined from the inlet (I) towards the outlet (O) and is configured to remove particles floating in the air in the surroundings of the molding cavity (4), and wherein the second hood is located downstream of the molding cavity (4) in the forward direction (AD) and is configured to remove particles floating in the air in the surroundings of the outlet (O).

11. The device (1) according to any one of the preceding claims, wherein the lower die (3) comprises a plurality of molding cavities (4) arranged to form an array of molding cavities, and wherein the upper die (6) comprises a plurality of upper punches (601), each upper punch being configured to cooperate with a corresponding molding cavity to form a respective slab (2) among a plurality of slabs.

12. The device (1) according to any one of the preceding claims, comprising a heating system connected to the lower die (3) and the upper die (6) to maintain them at a predetermined temperature.

13. The device (1) according to any one of the preceding claims, wherein the lower die (3) comprises a bottom wall (301) and side walls (302) cooperating with the bottom wall to define the molding cavity, wherein the bottom wall (301), the side walls (302) and the upper punch (601) are made of stainless steel.

14. The device (1) according to claim 12, wherein the upper punch (601) and the lower punch (303) have a first layer (L1) and a second layer (L2) removably connected to the first layer, the second layer being in contact with the powdered raw material, wherein the second layer of the upper punch and the lower punch is made of stainless steel.

15. A method for manufacturing slabs (2) from a powdered raw material, which is a cathode active material of a rechargeable battery, the method comprising the following steps: - providing a lower die (3) defining a molding cavity (4); - providing an upper die (6) having upper punches (601); - moving the upper die (6) and the lower die (3) relative to each other along a vertical direction (V) between an open position and a pressing position to compress a charge of the powdered raw material to form the slab (2); - feeding the charge of the powdered raw material into the molding cavity by a feeding device (5) when the upper die (6) and the lower die (3) are in the open position; - Move the upper die (6) and the lower die (3) to an intermediate configuration between the open position and the pressing position such that the upper die and the lower die are in a pre-pressing position, wherein, in the pre-pressing position, the molding cavity (4) is closed by the upper punch (601) to prevent the charge from moving out of the molding cavity (4), but at the same time the molding cavity (4) is in air communication with the surrounding air volume; - Keep the molding cavity (4) and the surrounding air volume airtight when the upper die (6) is in the pre-pressing position and the pressing position; - When the upper die and the lower die are in the pre-pressing position, suck air from the molding cavity, and maintain a negative pressure in the molding cavity when pressing the charge.

16. The method according to claim 15, comprising the steps of: - Provide the lower die (3) having a bottom wall (301) and side walls (302) cooperating with the bottom wall to define the molding cavity (4); - Move the bottom wall (301) and the side walls (302) relative to each other along the vertical direction (V); - Provide a lower punch (303) and a lower block (304) for the lower die (3), the lower punch (303) defining the bottom wall (301), the lower block (304) defining the side walls (302) and having a top surface (3041) extending in a horizontal plane perpendicular to the vertical direction (V), wherein the side walls (302) cooperate with the bottom wall (301) to define the molding cavity (4); - Move the lower punch (303) and the lower block (304) relative to each other along the vertical direction (V) between an alignment position and a displacement position, in the alignment position, the bottom wall (301) is flush with the top surface (3041) such that the bottom wall (301) and the top surface (3041) are in the same feed plane (8), in the displacement position, the bottom wall (301) is located below the top surface (3041) to define the molding cavity (4), - Move the bottom wall (301) vertically relative to the side walls (302).

17. The method according to claim 16, comprising the steps of: - Provide a vertically oriented channel (501) for the feeding device (5); - Move the feeding device (5) in sliding contact with the feed surface (9) and move between a loading position and an unloading position in a working direction (WD) parallel to the feed surface, wherein the feed surface extends along the feed plane (8); - Load the feeding device (5) with the charge at the loading position; - At the unloading position, vertically align the channel (501) with the bottom wall (301) such that, at the unloading position, the charge is received in the volume defined by the channel and the bottom wall.

18. The method according to claim 17, comprising the steps of: - Provide a picking device (11); - Move the picking device along the working direction (WD) between a picking position and a delivery position; - At the pick-up position, a slab (2) formed is grasped by the pick-up device (11); - At the delivery position, the slab is provided to the outlet (O) by the pick-up device. - Connect the pick-up device (11) and the feed device (5) to the carriage (12); - Move the carriage (12) backward and forward along the working direction (WD); - Position the pick-up device (11) upstream of the feed device (5) in the forward direction defined from the loading position towards the outlet; - When the pick-up device (11) is in the pick-up position, position the feed device (5) at the loading position; - When the pick-up device (11) is in the unloading position, position the feed device (5) at the unloading position.

19. The method according to any one of the preceding claims 15 to 18, wherein, The step of sucking air from the molding cavity starts when the upper mold and the lower mold are in the pre-pressing position and continues during the downward movement of the upper mold along the vertical direction between the pre-pressing position and the position where the upper punch contacts the powder in the cavity.

20. The method according to any one of the preceding claims 15 to 19, wherein suction guide grooves are provided in the lower mold and the upper mold for sucking air from the molding cavity such that air is sucked from above and below the molding cavity.

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