Cathode current collector assembly for an aluminum electrolysis cell

Abstract

The invention relates to a cathode current collector assembly for an aluminum electrolysis cell, a kit-of-parts for manufacturing a cathode current collector assembly and an aluminum electrolysis cell comprising a cathode current collector assembly.

Description

[0001] Cathode current collector assembly for an aluminum electrolysis cell

[0002] FIELD OF THE INVENTION

[0003] The invention relates to a cathode current collector assembly for an aluminum electrolysis cell, a kit-of-parts for manufacturing a cathode current collector assembly and an aluminum elec- trolysis cell comprising a cathode current collector assembly.

[0004] BACKGROUND OF THE INVENTION

[0005] Aluminium is produced by the Hall-Héroult process, by electrolysis of alumina dissolved in cryolite based electrolytes at temperature up to 1000°C. Atypical Hall-Heroult ceil is composed of a steel shell, an insulating lining of refractory materials and a carbon cathode holding the liquid metal. The cathode is composed of a number of cathode blocks in which collector bars are embedded at their bottom to extract the current flowing through the ceil.

[0006] A number of patent publications have proposed different approaches for minimizing the voltage drop between the liquid metal to the end of the collector bars. WO 2008 / 062318 discloses the use of a high conductive material in complement to the existing steel collector bar and gives reference to WO 02 / 42525, WO 01 / 63014, WO 01 / 27353, WO 2004 / 031452 and WO 2005 / 098093 that disclose solutions using copper inserts inside collector steel bars. US patent 4,795,540 splits the cathode in sections as well as the collector bars. WO 2001 / 27353 and WO 2001 / 063014 use high conductive materials inside the collector bars. US 2006 / 0151333 covers the use of different electrical conductivities in the collector bars. WO 2007 / 118510 proposes to increase the section of the collector bar when moving towards the centre of the cell for changing the current distribution at the surface of the cathode. US 5,976,333 and US 6,231 ,745 present the use of a copper insert inside the steel collector bar. EP 2 133 446 A1 describes cathode block arrangements to modify the surface geometry of the cathode in order to stabilize the waves at the surface of the metal pad and hence to minimize the ACD (anode to cathode distance). WO 2011 / 148347 describes a carbon cathode of an aluminium production cell that comprises highly electrically conductive inserts sealed in enclosures within the carbon cathode. These inserts alter the conductivity of the cathode body but do not participate in current collection and extraction by the collector bars. The electrical conductivity of molten cryolite is relatively low and the ACD cannot be decreased much due to the formation of magneto-hydrodynamic instabilities leading to waves at the metal-bath (metal - cryolite electrolyte) interface. The existence of waves leads to a loss of current efficiency of the process and does not allow decreasing the energy consumption under a critical value. On average in the aluminium industry, the current density is such that the voltage drop in the ACD is a minimum at 0.3 V / cm. As the ACD is 3 to 5 cm, the voltage drop in the ACD is typically 1 .0 V to 1 .5 V. The magnetic field inside the liquid metal is the result of the currents flowing in the external busbars and the internal currents. The internal local current density inside the liquid metal is mostly defined by the cathode geometry and its local electrical conductivity. The mag - netic field and current density produce the Lorentz force field which itself generates the metal surface contour, the metal velocity field and defines the basic environment for the magneto - hydrodynamic cell stability. The cell stability can be expressed as the ability of lowering the ACD without generating unstable waves at the surface of the metal pad. The level of stability depends on the current density and induction of magnetic fields but also on the shape of the liquid metal pool. The shape of the pool depends on the surface of the cathode and the ledge shape. The prior art solutions respond to a given level to the required magneto-hydrodynamic status to satisfy good cell stability (low ACD) but the solutions using copper inserts often need sophisticated machining processes.

[0007] Therefore, in recent years there has been a trend of substituting steel collector bars equipped with copper inserts, with pure copper collector bars. Regularly, the copper collector bars com- prise a central part located under a central part of the carbon cathode, usually directly located into a cathode slot or through-hole, this central part of the copper collector bar having at least its upper outer surface in direct electrical contact with the carbon cathode or in contact with the carbon cathode through an electrically conductive interface formed by an electrically conduc- tive glue and / or an electrically conductive flexible foil or sheet applied over the surface of the copper collector bar. The copper collector bar comprises one or two outer parts located adja- cent to and on one side or on both sides of the central part and a terminal end part or parts extending outwardly from said outer part(s). These terminal end part(s) of the copper collector bar is / are electrically connected in series each to a steel conductor bar of greater cross-sec- tional area than the copper collector bar, said steel conductor bar(s) extending outwardly for connection to an external current supply busbar.

[0008] Usually, the carbonaceous blocks with collector bar are placed on a solid support of refractory material. Since it is very difficult within the time constraints involved in lining a cathode in order to level it enough for supporting the blocks evenly, a powdered bedding layer is often provided on top of the solid support. Both components of the lining, the solid support and the powder bed, regularly consist of refractory materials of similar nature and prevent alloying and con- tamination of the (pure) bar material with aluminium and impurities, which penetrate through voids of the cell components and reach the bar material from below.

[0009] However, in particular in case of a copper collector bar, deleterious effects caused by the dif- fusion of aluminum and other products produced during operation of the cell are nevertheless still observed. This impacts the performance and the long-term stability of the electrolysis cell. Aluminum and other metals, such as Na, diffusing to the copper bar do not only result in an alloying process deteriorating the cell performance, but they also impede recuperation after the end of the lifecycle of the cell.

[0010] For additional protection of the copper current collector bar, it is known to increase the groove height, arrange the current collector bar within the groove and fill the remaining void with car- bonaceous ramming paste or a steal beam so that the groove flushes with the surface of the carbonaceous cathode. However, introducing this additional protection layer decreases the effective height of the carbonaceous cathode and consequently results in a decreased cell lifetime as well as higher operating voltages. In case of ramming paste a layer of minimum 35 mm height is necessary to obtain a sufficient protection. The use of a steal beam on the other hand, can lead to cracking when the cell is heated up, due to the different coefficients of ther- mal expansion.

[0011] OBJECT OF THE INVENTION

[0012] Hence, it is an object of the present invention to provide a cathode current collector assembly for an aluminum electrolysis cell, which has a higher and more stable performance, in particular throughout the whole life cycle of the cell, a decreased energy consumption as well as a max- imized current efficiency and which enables operating the electrolysis cell at lower voltages and over a longer period of time. Another object is the facilitation of current collector system recycling.

[0013] DESCRIPTION OF THE INVENTION

[0014] The above problems are solved by a cathode current collector assembly for being placed on the lining of an aluminum electrolysis cell comprising a) a copper or copper alloy current collector system, b) a carbonaceous cathode with a groove for receiving a first portion of the current col- lector system, wherein the first portion of the current collector system is arranged in the groove of the carbo- naceous cathode, and wherein the cathode current collector assembly further comprises c) a cover element, which at least partially covers the groove with the first portion of current collector system arranged therein, and d) a filling material selected from carbonaceous and / or carbide-based materials, ar- ranged in between cover element and the first portion of the copper or copper alloy current collector system.

[0015] A cathode current collector assembly comprises a carbonaceous cathode with a groove re- cessed in one of its surfaces, in which a current collector system is at least partially arranged. Electrical contact between carbonaceous cathode and current collector system can be achieved over the whole embedded area. The electrical current flows from the carbon cathode into the copper collector system, which must itself be connected - for example via additional transition elements such as a steel conductor element (e.g. steel conductor bar)- to an external current supply busbar to lead the current to the next cell.

[0016] The groove as well as the corresponding (“negative”) current collector system can have differ- ent shapes. Regularly, the current collector system is bar shaped, in particular rectangular bar shaped, however, also elliptical or rounded forms are possible. Preferably, the carbonaceous cathode has a rectangular shape and the current collector system (preferably also rectangular bar shaped) is arranged in a groove extending in a longitudinal surface of the carbonaceous cathode.

[0017] The current collector system can consist of one or more elements, in particular bar shaped elements. Preferably, the current collector system comprises at least two longitudinal, rectan- gular bar elements.

[0018] According to the invention the term "carbonaceous" means all types of materials based on anthracite and / or graphite and / or coke, regardless whether these cathodes are baked or graphitized.

[0019] In a preferred embodiment of the invention, the cathode current collector and connector as- sembly comprises a conductor element, being preferably arranged at the terminal end parts of the current collector system, i.e. is interconnected between current collector system and a connecting point to the external supply busbar. The optional conductor element preferably comprises a recess, wherein a second portion of the current collector system is arranged in this recess.

[0020] According to the invention a “carbide material” is a hard chemical compound of ceramic or refractory nature consisting of a metal or half metal, and carbon.

[0021] According to the invention the term "carbide-based materials" encompasses any kind of ma- terial or combination of materials containing more than 50%, preferably more than 80% of carbide materials. Particularly preferred is that the carbide-based materials consist of carbide material(s).

[0022] According to the invention the term "filling material” is any material capable of filling the gap between current collector system and cover element.

[0023] The combination of a separate cover element and a carbonaceous and / or carbide-based filling material enables an improved protection against aluminum and / or impurity diffusion while sim- ultaneously avoiding cracking of the carbonaceous cathode during the heating up of the cell. By effectively impeding diffusion and alloying of the copper collector system with metals such as aluminum the positive effects associated with the use of copper as collector system material - inter aliaan optimized current distribution in the liquid metal and / or inside the carbon cathode allowing for operating the cell at lower voltages - can be maximized and achieved over the whole life time of the cell.

[0024] With the inventive combination of cover element and carbonaceous or carbide-based filling material, in cathode current collector assemblies with a ramming paste layer covering the cur- rent collector system the height of protecting ramming paste layer can be reduced from a min- imum of 45 mm down to values of ~ 10 mm, while simultaneously obtaining the same or even a better protection. As a consequence, the cathode collector bar position can be lowered (ref- erence: cross-sectional view in operational position), which results in more wearable material between liquid Al and collector bar, i.e. an increased effective height of the carbonaceous cathode. As a consequence, a longer life time of the cathode current collector assembly can be obtained.

[0025] In a preferred embodiment of the invention, the cover element is formed by at least one, i.e. one or more plate, which is at least partially, preferably fully arranged within the groove, so that the current collector system and the filling material are arranged between cathode and the at least one plate.

[0026] Preferably, the cover element, e.g. in form of a plate, is arranged within the groove in a way, that it flushes with the surface of the carbonaceous cathode, in which the groove is recessed. In case the cover element is connected to the cathode by fastening means, also these fas- tening means preferably flush with the surface of the carbonaceous cathode, in which the groove is recessed. This simplifies arranging the cathode current collector assembly on the lining.

[0027] In another preferred embodiment the cover element is formed by at least one plate, which is at least partially, preferably fully arranged on the surface of the cathode, in which the groove with the current collector system therein is recessed, i.e. the at least one plate is in direct contact with the surface of the cathode.

[0028] In case the cover element is at least one plate, the thickness of the plate(s) is preferably in the range of 0.5 to 10 mm, more preferred in the range of 1 to 8 mm and most preferred in the range of 2 to 6 mm.

[0029] Preferably the carbonaceous cathode has a block form and the cover element is arranged parallel to the horizontal surfaces of the block, thereby covering the groove, recessed in a horizontal surface.

[0030] Preferably, the cover element covers at least 50 % of the groove, more preferred at least 70 %, even more preferred at least 80 %, and most preferred at least 90 %. In a particularly preferred embodiment the cover element completely covers the groove.

[0031] Preferably, the cover element covers at least 50 % of the section of the groove, in which the current collector system is arranged, more preferred at least 70 %, even more preferred at least 80 %, and most preferred at least 90 %. In a particularly preferred embodiment the cover element completely covers the section of the groove, in which the current collector system is arranged.

[0032] Preferably, at least 50 % of the space in between cover element and current collector system is filled with a layer of carbonaceous or carbide material, preferably at least 70 %, even more preferred at least 80 %, and most preferred at least 90 %. In a particularly preferred embodi- ment the carbonaceous and / or carbide-based material, completely fills the space in between cover element and current collector system. Most preferably, the layer height of the carbona- ceous or carbide-based material layer filling the space between cover element and current collector system is at least 8 mm, more preferred at least 10 mm, or even at least 15 mm, throughout the whole layer to ensure a ramming, however, the height of this layer is preferably also less than 35 mm, and more preferably less than 25 mm. Particularly preferred is a range of 8-35 mm, more preferred 10-30 mm and most preferred 15-25 mm. In this context "height” relates to the vertical extension of the protective layer of carbonaceous and / or carbide-based filling material in the operating position of the cathode current collector assembly.

[0033] By the above described preferred features, the inventive protection effect can be further en- hanced.

[0034] Preferably, the cover element comprises or consists of a material selected from the group consisting of metals or alloys, such as steel, carbon fiber-reinforced carbon, graphite, concrete, ceramics or mixtures of the foregoing.

[0035] Particularly preferred is a steel selected from the group consisting of carbon steel, low-carbon steel, chromium-based steel, nickel-based steel or chromium nickel-based steel or alloy steel.

[0036] Without being bound by this theory the inventors assume that the protecting effect with a metal cover element is particularly pronounced as the combination of metal (cover element) and carbon-based filling material impedes the diffusion of a large variety of different metals and impurities, which may be present and accumulated during the electrolysis process.

[0037] In a preferred embodiment the groove comprises a dove-tail shaped cross section, which can help further increasing the inventive beneficial effects.

[0038] Particularly preferred is the use of a carbonaceous material as filling material in between the cover element and the copper or copper alloy current collector system.

[0039] Particularly preferred are ramming paste and / or an electrically conductive glue comprising a carbonaceous material and / or a carbide material as filler. The ramming paste and / or the electrically conductive glue further comprise a binder, such as an unmodified or modified tar or a PAH (polycyclic aromatic hydrocarbon)-free binder for ramming paste.

[0040] Fillers are solid particles in a mixture with a liquid (binder), to form a paste or glue or cement.

[0041] In another preferred embodiment the filling material is a carbide material. A carbide material is a hard chemical compound of ceramic or refractory nature consisting of a metal or half metal and carbon. Particularly preferred is SIC, due to its high hardness and oxidation stability.

[0042] Of course, also the use of a combination of carbonaceous and carbide-based materials is en- compassed by the invention.

[0043] The form of the filling material is preferably selected from cloth, mesh, foam, paste, foil, fabric, layer of glue or a combination of the foregoing. Most preferred are layers of glue or pastes, as they allow for thermal expansion during the heat up process of the cell.

[0044] In a preferred embodiment of the invention the cathode is a rectangular cathode block, with a preferably rectangular shaped groove extending along a longitudinal surface of the cathode block.

[0045] Preferably, the current collector system comprises a current collector bar, which is preferably rectangular-shaped.

[0046] In a preferred embodiment of the invention the current collector system is at least partially cladded with a protective steel layer.

[0047] Preferably, at least 50 % of the surface of the current collector system is cladded with a pro- tective steel layer cladding, more preferably at least 60 %, even more preferably at least 70 % and most preferably at least 80 %. In a particularly preferred embodiment the surface of the current collector system is completely cladded with a protective steel layer cladding. In case the cathode current collector system comprises a conductor element, the above values relate to the surface without taking into account the second portion arranged in the recess of the conductor element.

[0048] Preferably, at least 50 % of the surface of the first portion of the current collector system is cladded with a protective steel layer cladding, more preferably at least 60%, even more pref- erably at least 70 % and most preferably at least 80 %. In a particularly preferred embodiment the surface of the first portion of the current collector system is completely cladded. Thereby, deleterious effects of the diffusion of aluminum or other products produced in operation of the electrolysis cell can be reduced.

[0049] Preferably, the volume ratio of the copper or copper alloy of the current collector system to the protective steel layer is at least 200% and preferably at least 300% or more preferably at least 400%.

[0050] Preferably, the protective steel layer has a thickness from 0.05 mm to 6 mm, more preferred from 0.15 mm to 4 mm, even more preferred from 1.5 mm to 3 mm.

[0051] The thin protective steel layer preferably comprises or consists of a steel selected from carbon steel, low-carbon steel, chromium-based steel, nickel-based steel or chromium nickel based steel or alloy steel.

[0052] In a preferred embodiment of the invention the copper or copper alloy is in the form of a bar of rectangular cross-section that is protected at least on one side facing the cathode with the protective steel layer, preferably on all sides facing the cathode, and most preferably on all sides.

[0053] In case the current collector system comprises a protective steel layer, i.e. is at least partially cladded with a protective steel layer, the protective steel layer is in direct contact with the walls of the groove of the carbonaceous cathode.

[0054] Preferably, the protective steel layer is coated with an additional top layer and / or under layer of copper, nickel and / or chromium and / or a graphite paint or foil layer, wherein more preferably the additional top layer and / or underlayer has a thickness from 1 pm to 1 mm.

[0055] The surface of the current collector system can be roughened or provided with recesses such as grooves or projections such as fins or ribs to increase the surface area between the cathode and the current collector system thereby enhancing contact between the elements.

[0056] In a preferred embodiment of the invention the current collector system is at least partially cladded with an insulator in particular with layers of insulating material such as alumina, insu- lating glue or cement or any insulating material capable to withstand up to 1 ,200°C. In a preferred embodiment of the invention the current collector system, and / or the steel pro- tective layer in case the current collector system is at least partially cladded with one, are in direct contact with the carbonaceous cathode.

[0057] In a preferred embodiment of the invention the cover element, which at least partially covers the groove with the current collector system arranged therein, is fastened to the cathode via fastening means.

[0058] Fastening means are for example screws, bolts, keys, studs, rivets, anchors, nails, pins or inserts. Most preferred are screws, in particular with a bean shape to prevent thermal expan- sion.

[0059] In a preferred embodiment of the invention the cathode current collector assembly is config- ured in such a way that the groove is arranged at the bottom side of the cathode current col- lector assembly in the operating position of the cathode current collector assembly in the elec- trolysis cell.

[0060] The invention also relates to a kit-of-parts, i.e. a system of separate elements, for manufactur- ing the inventive cathode current collector assembly. The kit-of-parts comprises: a) a copper or copper alloy current collector system, b) a carbonaceous cathode with a groove for receiving a first portion of the current collector system, and c) a cover element, and d) a filling material selected from carbonaceous and / or carbide-based materials.

[0061] The invention also relates to a cathode current collector and connector assembly for an alumi- num electrolysis cell comprising the inventive cathode current collector assembly and an ad- ditional conductor element (e.g. bar-shaped), preferably comprising or consisting of steel, to which preferably the terminal end part(s) of the collector bar is / are connected. Said steel con- ductor bar(s) can be connected at a connecting point to an external current supply busbar to extract the current outside the cell. Preferably, the conductor bar comprises a greater cross- sectional area than the collector bar and thereby restricting the heat flux out of the cell and avoiding cryolite freezing.

[0062] The invention also relates to an aluminum electrolysis cell comprising the inventive cathode current collector assembly. The invention also relates to the use of the inventive cathode current collector assembly in the electrolytic production of aluminum, wherein the cover element protects the cathode current collector system in the groove against infiltration of aluminum produced in the electrolytic pro- cess.

[0063] The invention also relates to the use of a cover element which at least partially covers the groove of a carbonaceous cathode of an aluminum electrolysis cell with a current collector system arranged therein for protecting the cathode current collector system against aluminum infiltration in the electrolysis process.

[0064] EXAMPLES

[0065] The invention will now be explained in more detail with the aid of specific embodiments in accordance with the invention as well as with the aid of the accompanying figures.

[0066] Inventive example

[0067] A cathode block with copper current collector system of outer dimensions 550 x 450 x 3200 mm (width x height x length) is equipped with a rectangular groove of dimensions 40 x 95 mm (width x depth). A rectangular collector system of copper with cross-section of 40 x 80 mm is placed into the groove, leaving a void of 15 mm height above the collector bar system. This void is filled with carbonaceous ramming paste, which is compacted by a conventional pneu- matic ramming tool. After filling the void, a stainless-steel plate of 2 mm thickness, width 80 mm and length 3200 mm is laid over the filled groove, stretching over the cathode block by 20 mm on each side while covering the entire length of the cathode block. The steel plate is at- tached to the cathode block by means of steel screws each 500 mm, starting at 100 mm from either end.

[0068] Comparative example

[0069] A cathode block with copper current collector system of outer dimensions 550 x 450 x 3200 mm (width x height x length) is equipped with a rectangular groove of dimensions 40 x 125 mm (width x depth). A rectangular collector system of copper with cross-section of 40 x 80 mm is placed into the groove, leaving a void of 45 mm height above the collector bar system. This void is filled with carbonaceous ramming paste, which is compacted by a conventional pneu- matic ramming tool.

[0070] The inventive example gives a projected cell life increase of 9 % vs. the comparative example.

[0071] Figures

[0072] Further advantages, features and possible applications will become apparent from the follow- ing description of preferred embodiments and the associated figures. The figures show:

[0073] Fig. 1 shows a cross-sectional view of a cathode current collector assembly according to the state of the art.

[0074] Fig. 2 shows a cross-sectional view of an inventive cathode current collector assembly with a cover element, which flushes with the cathode surface.

[0075] Fig. 3 shows a cross-sectional view of an inventive cathode current collector assembly with a cover element, arranged on top of the cathode surface.

[0076] Fig. 4 shows a cross-sectional view of an inventive cathode current collector assembly with two cover elements, which flush with the cathode surface.

[0077] Fig. 5 shows a cross-sectional view of an inventive cathode current collector assembly with a dove-tail shaped groove and a cover element, which flushes with the cathode surface.

[0078] Detailed description

[0079] Fig. 1 depicts a cross-sectional view of a cathode current collector assembly according to the state of the art. Shown is the manufacturing position of the assembly, which is 180° rotated in comparison to the final operation position within the electrolysis cell. In this assembly a rectan- gular cathode block 1 comprises a groove recessed in a horizontal surface, in which a current collector bar 2 is arranged. In general, the current collector bar can be in direct contact with the cathode block ora conductive carbonaceous layer, e.g. of ramming paste, can be arranged between the surfaces. The groove is filled up with aid of ramming paste 3 as filling material, which flushes with the top cathode surface.

[0080] Fig. 2 depicts a cross-sectional view of an inventive cathode current collector assembly with a cover element 7. In this assembly a cathode block 1 comprises a groove recessed in a hori- zontal surface, in which a current collector bar 2 is arranged. In general, the current collector bar can be in direct contact with the cathode block or a conductive carbonaceous layer, e.g. of ramming paste, can be arranged between the surfaces. The groove is filled up with aid of ramming paste 3 as filling material, however, the layer does not completely fill the groove. Instead a cover element 7 in form of a plate closes the groove so that it flushes with the cathode surface. In comparison to the prior art shown in Fig. 1 the height of ramming paste layer h14 is significantly decreased. Consequently, the height of the groove, h25 as well as the height of the wearable cathode material h36 is significantly increased.

[0081] Fig. 3 depicts a cross-sectional view of an inventive cathode current collector assembly with a cover element 7. In this assembly a cathode block 1 comprises a groove recessed in a hori- zontal surface, in which a current collector bar 2 is arranged. In general, the current collector bar can be in direct contact with the cathode block or a conductive carbonaceous layer, e.g. of ramming paste, can be arranged between the surfaces. The groove is filled up with aid of ramming paste 3 as filling material, and the layer completely fills the groove. On top of the layer and the surface of the cathode block a cover element 7 is arranged and fixed by fastening means (not shown). In comparison to the prior art shown in Fig. 1 the height of ramming paste layer h14 is significantly decreased. Consequently, the height of the groove, h25, as well as the height of the wearable cathode material h36 is significantly increased.

[0082] Fig. 4 depicts a cross-sectional view of an inventive cathode current collector assembly with two cover elements 7, which flush with the cathode surface. In this assembly a cathode block 1 comprises four parallel grooves recessed in a horizontal surface, each with a current collector bar 2 arranged therein. In general, the current collector bar can be in direct contact with the cathode block or a conductive carbonaceous layer, e.g. of ramming paste, can be arranged between the surfaces. The groove is filled up with aid of ramming paste 3 as filling material (not shown), and the layer completely fills the groove. On top of the layer and the surface of the cathode block two cover elements 7 are arranged, each covering two complete grooves and fixed by fasting means 8. At the terminal ends part (into and out of the plane of projection) the current collector bars can be connected to an external busbar, preferably via an optional interposed conductor element (e.g. conductor bar of steel).

[0083] Fig. 5 depicts a cross-sectional view of an inventive cathode current collector assembly with a dove-tail shaped groove and a cover element 7, which flushes with the cathode surface. In this assembly a cathode block 1 comprises a groove, in which a current collector bar 2 is arranged. In general, the current collector bar can be in direct contact with the cathode block or a con- ductive carbonaceous layer, e.g. of ramming paste, can be arranged between the surfaces. The groove is filled up with aid of ramming paste 3 as filling material, however, the layer does not completely fill the groove. Instead a cover element 7 closes the groove so that it flushes with the cathode surface. REFERENCE SIGNS

[0084] 1 Cathode block

[0085] 2 Current collector bar 3 Ramming paste layer

[0086] 4 Height of ramming paste layer h1

[0087] 5 Height of groove h2

[0088] 6 Height of wearable cathode material h3

[0089] 7 Cover element 8 Fastening means

Claims

C l a i m s 1. Cathode current collector assembly for an aluminum electrolysis cell comprising a) a copper or copper alloy current collector system, b) a carbonaceous cathode with a groove for receiving at least a first portion of the current collector system, wherein at least the first portion of the current collector system is arranged in the groove of the carbonaceous cathode, characterized in that the cathode current collector assembly further comprises c) a cover element, which at least partially covers the groove with the first portion of the current collector system arranged therein, and d) a filling material selected from carbonaceous and / or carbide-based materials, arranged in between cover element and the first portion of the copper or copper alloy current collector system.

2. Cathode current collector assembly according to claim 1 , wherein the cover el- ement is a plate at least partially arranged Inside the groove, so that the current collector system and the filling material are arranged between carbonaceous cath- ode and plate.

3. Cathode current collector assembly according to claim 1 , wherein the cover el- ement is a plate at least partially arranged on the surface of the cathode, so that the current collector system and the filling material are arranged between carbona- ceous cathode and plate.

4. Cathode current collector assembly according to any of the preceding claims, wherein the cover element comprises or consists of any of the materials selected from the group consisting of metals, such as steel, carbon-fiber-reinforced carbon, graphite, ceramics or mixtures thereof.

5. Cathode current collector assembly according to any of the preceding claims, wherein the groove comprises a dove-tail shaped cross section.

6. Cathode current collector assembly according to any of the preceding claims, wherein the carbonaceous and / or carbide-based materials are selected from the group consisting of ramming paste and conductive glue.

7. Cathode current collector assembly according to any of the preceding claims, wherein the cathode is a rectangular cathode block and / or the current collector sys- tem is a current collector bar, which is preferably rectangular.

8. Cathode current collector assembly according to any of the preceding claims, wherein the current collector system is at least partially cladded with a protective steel layer.

9. Cathode current collector assembly according to any of the preceding claims, wherein the current collector system, and / or the steel protective layer in case the current collector system is at least partially cladded with one, are in direct contact with the cathode.

10. Cathode current collector assembly according to any of the preceding claims, wherein the cover element, which at least partially covers the groove with the cur- rent collector system arranged therein, is fastened to the cathode via fastening means.

11. Cathode current collector assembly according to any of the preceding claims, wherein the cathode current collector assembly is configured in such a way that the groove is arranged at the bottom side of the cathode current collector assembly in the operating position of the cathode current collector assembly.

12. Kit-of-parts for manufacturing a cathode current collector assembly according to any of the preceding claims comprising a) a copper or copper alloy current collector system, b) a carbonaceous cathode with a groove for receiving at least a first portion of the current collector system, and c) a cover element, which at least partially covers the groove with the current col- lector system arranged therein, and d) a filling material selected from carbonaceous and / or carbide-based materials.

13. Aluminum electrolysis cell comprising a cathode current collector assembly ac- cording to any of the claims 1-11.

14. Use of a cover element at least partially covering the groove of a carbonaceous cathode of an aluminum electrolysis cell with a current collector system arranged therein for protecting the cathode current collector system against aluminum infil- tration in the electrolysis process.

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