WO2024100141A2

WO2024100141A2 - Cathode current collector and connector assembly for an aluminum electrolysis cell

Info

Publication number: WO2024100141A2
Application number: PCT/EP2023/081194
Authority: WO
Inventors: René VON KAENEL; Seweryn MIELNIK; Markus Pfeffer; Gualtiero SPINETTI; Oscar VERA GARCIA
Original assignee: Tokai Cobex Gmbh; Novalum Sa
Priority date: 2022-11-09
Filing date: 2023-11-08
Publication date: 2024-05-16
Also published as: DE102022129668A1; WO2024100141A3

Abstract

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

Description

Cathode current collector and connector assembly for an aluminum electrolysis cell

FIELD OF THE INVENTION

BACKGROUND OF THE INVENTION

Aluminium is produced by the Hall-Heroult process, by electrolysis of alumina dissolved in cryolite based electrolytes at temperature up to 1000°C. A typical Hall-Heroult cell 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 cell.

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 very 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 magnetic field and current density produce the Lorentz force field which itself generates the metal surface contour, the metal velocity field defines the basic environment for the magnetohydrodynamic 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 needed magneto-hydrodynamic status to satisfy good cell stability (low ACD) but the solutions using copper inserts often need sophisticated machining processes.

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 comprise a central part located under a central part of the carbon cathode, usually directly located into a cathode slot or through-hole as support, 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 conductive glue and/or an electrically conductive flexible foil or sheet applied over the surface of the highly electrically conductive collector bar. The copper collector bar comprises one or two outer parts located adjacent 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-sectional area than the highly electrically conductive connector bar, said steel conductor bar(s) extending outwardly for connection to an external current supply busbar.

In this known arrangement, the terminal end parts of the highly electrically conductive metal bar are preferably electrically connected in series to the steel conductor bar forming a transition joint wherein the highly electrically conductive metal bar and the steel conductor bar are secured together by welding, by electrically-conductive glue and/or by means for applying a mechanical pressure such as a clamp to achieve a press fit. Alternatively, the secured end parts are threaded together. The steel bars forming the transition joint extend outwardly for connection to a busbar network external of the cell, the outwardly-extending end portions of the steel bars having an increased cross-section to reduce voltage drop and assure thermal balance of the cell. The known arrangement with steel bars forming a transition joint is partly satisfactory because it produces an adequate heat loss for a small overvoltage penalty. However, the copper/steel contact is complicated and leads to increased manufacturing cost, whereas these copper/steel contacts are susceptible to degradation over time leading to poor contact. Further, it has turned out that there is a high risk, that such a connection fails and results in lost connections and/or high voltage drops and energy losses. This drastically impacts the cell performance.

Therefore, WO 2018/019888 A1 suggests to simplify the collector bar assembly by using a copper bar as one piece going from inside the carbon cathode directly outside the cell, where it can be connected at the position the steel conductor element was formerly located. Whereas dispensing with the steel conductor element ensures a simplification to a certain extent, however, in order to realize a reduction in heat flux to avoid freezing of the cryolite the copper bar design has to be adjusted at the terminal end parts and/or additional connecting elements such as copper or aluminum flexes have to be implemented. Performing the respective design adjustments can be laborious and costly, which is the reason, why there is still a need for improvement as regards a simple and efficient design for the current transition elements.

OBJECT OF THE INVENTION

Consequently, it is an object of the present invention to provide a cathode current collector and connector assembly for an aluminum electrolysis cell, which has a higher and more reliable performance, which is cost-effective, and which enables performing electrolysis with a permanent low contact resistance as well as low voltage drops and without the risk of cryolite freezing during operation of the electrolysis cell.

DESCRIPTION OF THE INVENTION

The above problems are solved by a cathode current collector and connector assembly for an aluminum electrolysis cell comprising a) a copper or copper alloy current collector system with an optional protective steel layer cladding at least partially cladding the current collector system, b) a carbonaceous cathode with a groove for receiving a first portion of the current collector system, c) a steel conductor element with a recess for receiving a second portion of the current collector system, wherein the first portion of the current collector system is arranged in the groove of the carbonaceous cathode, and wherein the second portion of the current collector system is arranged in the recess of the steel conductor element and wherein the second portion of the current collector system is at least partially in direct contact with the steel conductor element.

A cathode current collector and connector current collector assembly comprises a carbonaceous cathode with a groove recessed in one of its surfaces, in which a current collector system is at least partially arranged. The assembly further comprises a conductor element, preferably comprising or consisting of steel, to which the terminal end part(s) of the current collector system (e.g. in form of a collector bar) is/are electrically connected. Said steel conductor element is connected to an external current supply busbar to extract the current outside the cell. The conductor element preferably comprises a recess, wherein a second portion of the current collector system is at least partially arranged in this recess. The electrical current flows from the carbon cathode into the copper bar then through the steel conductor element to the external current supply busbar to lead the current to the next cell. In case both the collector- as well as the conductor element have the geometric shape of a bar, the conductor bar preferably comprises a greater cross-sectional area than the collector bar, thereby further restricting the heat flux out of the cell and avoiding cryolite freezing.

The groove as well as the corresponding (“negative”) current collector system ran have different 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.

The current collector system and/or the steel conductor element can consist of one or more elements, in particular bar shaped elements. Particularly preferred are rectangular bar shaped elements. Preferably, the current collector system comprises at least two longitudinal, rectangular bar elements, which are spaced apart by a thermal expansion gap or insulating material.

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.

With the second portion of the current collector system arranged in the recess of the steel conductor element and an at least partially direct contact with the steel conductor element, the inventors could observe the formation of a reliable connection between current collector system and steel conductor element after heating up of the electrolysis cell with the implemented current collector system.

With the high temperatures during heat up and electrolysis the second portion of the collector element (e.g. in form of a bar) arranged in the recess expands and is pressed against the steel conductor element. Without being bound by this theory, the inventors assume that with the heating and the pressure caused by the expansion a diffusion process at the direct copper- steel-interface is initiated, in which copper and steel create a stable and permanent material connection with a very low contact resistance. This thermal-fit connection is reliable and com- paringly simple to realize. Further, by use of the steel conductor element heat flux out of the cell can be reduced in order to attain cell stability and avoid cryolite freezing.

Preferably, the recess of the steel bar is formed to block the movement of the copper current collector system in two or more, more preferably three or more, even more preferably four or more or even five of the six spatial directions (illustrated in figure 1 : Yi, Y2, Xi, X2, Z1, Z2) under normal conditions according to DIN 1341 , when the second portion of the copper current collector system is arranged in the recess of the steel conductor element.

Preferably, the recess of the steel conductor element (e.g. in form of a bar) is formed to block the movement of the second portion of the current collector system in one or more additional spatial directions under operating conditions of a Hall-Heroult process in comparison to normal conditions.

Preferably, the recess of the steel bar is formed to block the movement of the second portion of the current collector system by friction and/or material fit. In a particularly preferred embodiment, the recess has the form of a pocket, which blocks the movement in four (one side open pocket) or five (fully surrounding pocket) of the six spatial directions. As with increasing movement constraints the pressure increases, the above effects are enhanced in such embodiments and a tight friction and material fit can be obtained. In case the recess is a pocket, which fully surrounds the steel bar, the beneficial effects are maximized.

For the purposes of fixing the copper current collector system in its position, the steel conductor element may comprise several subelements, e.g. the pocket can be formed by two half sections, which can be assembled to surround the second portion of the current collector system. Another option is to create a pocket, which solely blocks the movement in four spatial directions, place the second portion of the current collector system in the pocket and close, i.e. cover the pocket with a steel plate, which may be welded or otherwise connected to the rest of the steel conductor element.

After arranging the copper current collector system in the recess (e.g. in form of a pocket), a cover element can be used to completely “close” the recess, i.e. cover the accessible interspace between copper current collector system and steel conductor element inside the recess.

In a preferred embodiment of the invention, the steel conductor element is a steel conductor bar, which is preferably rectangular shaped.

In a preferred embodiment of the invention, the current collector system is at least partially cladded with a protective steel layer cladding, wherein the first portion of the current collector system is at least partially, preferably completely, cladded with the optional protective steel layer cladding.

Preferably, at least 50 % of the surface of the current collector system is cladded with a protective 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 is completely cladded with a protective steel cladding. The above values relate to the surface without taking into account the second portion arranged in the recess of the conductor element

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 preferably 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.

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%.

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.

The 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.

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 thin steel layer, preferably on all sides facing the cathode.

In case the current collector system comprises a steel protective 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 a groove of the carbonaceous cathode.

Preferably, the protective steel layer is coated with an additional top layer and/or underlayer 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.

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.

In a preferred embodiment of the invention the current collector system optionally with a steel cladding is at least partially (further) cladded with an insulator in particular with layers of insulating material such as alumina, insulating 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 protective layer in case the current collector system is at least partially cladded with one, are in direct contact with the carbonaceous cathode.

The steel cladding can also be welded to the steel conductor element to completely “close” the recess (e.g. in form of a pocket), i.e. cover the accessible interspace between copper current collector system and steel conductor element in the recess.

The inventors have found out that the beneficial effects are increasing by increasing direct contact surface. Therefore at least 50 %, preferably at least 70 %, more preferably at least 80 % and most preferably at least 90 % of the surface of the second portion of the current collector system are in direct contact with the steel conductor element. In a particular preferred embodiment, the complete surface of the second portion of the current collector system is in direct contact with the steel conductor element.

Preferably, at least 50 % of the contact surface between second portion of the current collector system and steel conductor element is formed with a direct contact, more preferably at least 70 % and most preferably at least 80 %. In a particularly preferred embodiment the whole contact surface is formed with a direct contact.

As a steel cladding of the current collector system may increase the contact resistance, in a preferred embodiment of the invention, the second portion of the current collector system is at least partially, preferably completely free, of an optional protective steel layer cladding.

The surface of the current collector system can be roughened or provided with recesses such as grooves or projections such as fins to enhance contact with the carbon cathode.

In a preferred embodiment of the invention, the surface of the second portion of the current collector system, which is not in direct contact with the steel conductor element, is at least partly covered with a carbonaceous material, i.e. the carbonaceous material is arranged in between current collector system and steel conductor bar.

By filling some of the volume between copper current collector system and steel conductor bar an extreme pressure increase during heating up of the electrolysis can be avoided. Expanded graphite materials are preferred, as they are inert materials with high temperature resistance, which do not influence or contaminate the connection. In a preferred embodiment of the invention, the current collector system comprises a third portion different from the first and the second, which is arranged outside the recess of the steel conductor element and the groove of the carbonaceous cathode, wherein this third portion is surrounded by a protective shell, which preferably comprises a material selected from SiC, ramming paste, steel cover plate, refractory material or a mixture of the foregoing. Most preferred is a shell with an inner layer of SiC, ramming paste, refractory material or mixtures of the foregoing and an outer steel cover layer, whereby the inner layer is arranged in between current collector system and outer steel cover layer.

In a preferred embodiment of the invention, the second portion of the current collector system arranged in the recess of the steel conductor element has a pin-shape, i.e. the form of a preferably circular, cylinder. Such a form has the advantage, that the corresponding negative form in the steel conductor element, in which the second portion is to be fitted, can easily be obtained by drilling. The pin can be pressed into the drilled hole to ensure a tight friction fit.

Preferably, the current collector system comprises several elements, whereas one element, which comprises the second portion of the current collector system, which is arranged in the recess of the steel conductor element, is connectable to the rest of the current collector system, in particular to its first portion. Such a connection is preferably realized by an appropriate measure such as a pin-fit-technique, as described above or any other fitting technique, which ensures a friction and/or material fit at the electrolysis temperature (-950 °C).

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

In a preferred embodiment of the invention the cathode is a rectangular cathode block.

In a preferred embodiment of the invention, the recess of the steel conductor element has a volume VR and the second portion of the current collector system arranged in the recess of the steel conductor element has a volume Vzs, wherein is in the range of 0.9 to 1 .0, preferably

0.92 to 0.98, under normal conditions according to DIN 1341 .

These values enable a thermal fit design, which provides a reliable and stable connection. The minimum air gap in between the materials at room temperature with an already good contact is further improved at higher temperature and thermal expansion of the materials. Copper will expand thermally more than steel during heating up of the cell, thereby creating a permanent high pressure between materials, which results in a pronounced diffusion process, which is strengthening the connection between the materials. Particularly preferred is in this context that the recess has the form of a pocket, in which the second portion of the current collector system is arranged.

The invention also relates a kit-of-parts, i.e. a system of separate elements, for manufacturing a cathode current collector and connector assembly according to any of the preceding claims comprising a) a copper or copper alloy current collector system with an optional protective steel layer cladding, b) a carbonaceous cathode with a groove for receiving a first portion of the current collector system, and c) a steel conductor element with a recess for receiving a second portion of the current collector system.

The invention also relates an aluminum electrolysis cell comprising the inventive cathode current collector and connector assembly and a current supply bus bar, wherein the conductor element of the cathode current collector and connector assembly is electrically connected to the supply bus bar, preferably by means of a copper or aluminum flexible.

The invention also relates to the use of a direct contact between a copper or copper alloy current collector system with an optional protective steel layer cladding and a steel conductor element in a cathode assembly for an aluminum electrolysis cell for decreasing the voltage drop in an aluminum electrolysis process.

EXAMPLES

The invention will now be explained in more detail with the aid of specific embodiments in accordance with the invention and with the aid of the accompanying figures.

Inventive example

A cathode block with rectangular copper current collector system of outer dimensions 550 x 450 x 3200 mm (width x height x length) is equipped with a groove of dimensions 44 x 130 mm (width x depth). A rectangular collector system of copper with cross-section of 44 x 84 mm is placed into the groove, comprising a copper bar of cross-section 40 x 80 mm clad with steel of a thickness of 2 mm, and covered by ramming paste. The cross-section of the rectangular steel conductor element is 120 x 120 mm, with a length of 300 mm, with a pocket with an rectangular opening of 80 x 80 x 160 mm (width x depth x length) to receive the complete steel- clad-free copper end section of the collector bar, as schematically shown in Fig. 2. The pocket receives a portion of 150 mm length of the copper end section of the collector bar. The cavity is closed with a flush steel plate and connected with the steel conductor element by welding. The steel-cladding of the remaining section of the collector bar touching the steel conductor element surface is welded to the steel conductor element, to further protect the copper from aggressive compounds within the cell.

Comparative example

A cathode block with copper current collector system of outer dimensions 550 x 450 x 3,200 mm (width x height x length) is equipped with a slot of dimensions 44 x 130 mm (width x depth). A rectangular collector system of copper with cross-section of 44 x 84 mm is placed into the slot, comprising a copper bar of cross-section 40 x 80 mm clad with steel of a thickness of 2 mm, and covered by ramming paste. The cross-section of the steel conductor element is 120 x 120 mm, with a length of 300 mm, with a pocket with an opening of 81 x 80.5 x 160 mm (width x depth x length) to receive the complete steel-clad-free copper end section of the collector bar, as schematically shown in Fig. 2, but with an electrically conductive glue layer of 0.5 mm thickness between copper and steel surfaces. The pocket receives a portion of 150 mm length of the copper end section of the collector bar. The cavity is closed with a flush steel plate and connected with the steel conductor element by welding. The steel-cladding of the remaining section of the collector bar touching the steel conductor element surface is welded to the steel conductor element, to further protect the copper from aggressive compounds within the cell. With the glue-free assembly of the inventive example a cathode voltage drop reduction of 30 mV vs. the comparative example was achieved.

Figures

Further advantages, features and possible applications will become apparent from the following description of preferred embodiments and the associated figures. The figures show:

Fig. 1 shows a longitudinal-sectional view of an inventive cathode current collector and connector assembly.

Fig. 2 shows a partially exploded view of a part of the inventive cathode current collector and connector assembly.

Fig. 3 shows the terminal end part of an inventive cathode current collector and connector assembly.

Fig. 4 shows a longitudinal-sectional view of an inventive cathode current collector and connector assembly with a pin-shaped current collector element.

Detailed description

Fig. 1 depicts a longitudinal section of an inventive cathode current collector and connector assembly. Shown is the final operation position within the electrolysis cell. In this assembly a cathode block 1 comprises a groove recessed in a horizontal surface along the longitudinal direction (along x-axis), in which a first portion of 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 cathode current collector and connector assembly further comprises a conductor element 3, preferably made of steel, with a recess, in which a second portion of the current collector system is arranged.

Fig. 2 depicts a partially exploded view of a part of the inventive cathode current collector and connector assembly, namely the connection of conductor element and current collector system. This part comprises two longitudinal current collector bars 2, which are cladded at a first portion with a protective steel layer. This first portion is to be arranged in the groove of the carbonaceous cathode (not shown). The current collector bars further comprise a second uncladded portion 5, which is to be arranged in a recess (here: in form of a pocket) of the

SUBSTITUTE SHEET (RULE 26) conductor element 3. In the figure one of the current collector bars 2 is already arranged in the recess of the conductor element 3. The other current collector bar 2 is to be inserted in the pocket, which restricts movement of the uncladded portion 5 in fourof the six spatial directions. After positioning of the uncladded portion within the pocket, the pocket is closed with a steel plate 6. Thereby, movement of the uncladded portion is restricted in an additional spatial direction.

Fig. 3 depicts a photograph of the terminal end part of an inventive cathode current collector and connector assembly. In this assembly a cathode block 1 comprises two grooves recessed in a horizontal surface, in which a first portion of the two current collector bars are arranged. The current collector bars protrude out of the groove and are connected to the conductor element 2 by arranging a second portion within a recess of the conductor element. The third portion of the current collector bars protruding out of the groove, which is not arranged in the recess of the conductor element, is embedded in a protective shell 7 formed by refractory material and an outer surrounding steel plate. For transportation purposes the current collector bars are secured to the carbonaceous cathode 1 by fastening means 8.

Fig. 4 depicts a longitudinal section of an inventive cathode current collector and connector assembly with a pin-shaped current collector element 9. In this assembly a cathode block 1 comprises a groove recessed in a horizontal surface along the longitudinal direction (along x- axis), in which a first portion of 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 cathode current collector and connector assembly further comprises a conductor element 3, preferably made of steel, with a recess. The current collector system comprises an additional pin-shaped connecting element 9, which is arranged in a recess of the current collector bar and the recess of the steel conductor element, thereby providing an electrical connection between the elements.

REFERENCE SIGNS

1 Cathode block

2 (cladded) Current collector bar 3 Conductor element

4 Pocket

5 Second portion of the current collector bar

6 Steel plate

7 Protective shell 8 Fastening means

9 Pin-shaped current collector element

Claims

CLAIMS Cathode current collector and connector assembly for an aluminum electrolysis cell comprising a) a copper or copper alloy current collector system with an optional protective steel layer cladding at least partially cladding the current collector system, b) a carbonaceous cathode with a groove for receiving a first portion of the current collector system, c) a steel conductor element with a recess for receiving a second portion of the current collector system, wherein the first portion of the current collector system is arranged in the groove of the carbonaceous cathode, and characterized in that the second portion of the current collector system is at least partially in direct contact with the steel conductor element. Cathode current collector and connector assembly according to claim 1 , wherein the steel conductor element is a steel conductor bar, which is preferably rectangular shaped. Cathode current collector and connector assembly according to any of the preceding claims, wherein the current collector system is at least partially cladded with the optional protective steel layer cladding, wherein the first portion of the current collector system is at least partially, preferably completely, cladded with the optional protective steel layer cladding. Cathode current collector and connector assembly according to any of the preceding claims, wherein the second portion of the current collector system is at least partially, preferably completely free, of an optional protective steel layer cladding. Cathode current collector and connector assembly according to any of the preceding claims, wherein the current collector system is cladded with the optional protective steel layer cladding, wherein the steel layer cladding and the steel conductor bar are partially connected via welding. Cathode current collector and connector assembly according to any of the preceding claims, wherein the surface of the second portion of the current collector system, which is not in direct contact with the steel conductor element, is at least partly covered with a carbonaceous material. Cathode current collector and connector assembly according to any of the preceding claims, wherein the current collector system comprises a third portion different from the first and the second, which is arranged outside the recess of the steel conductor element and the groove of the carbonaceous cathode, wherein this third portion is surrounded by a protective shell, which preferably comprises a material selected from SiC, ramming paste, a steel cover plate, refractory materials or combinations of the foregoing. Cathode current collector and connector assembly according to any of the preceding claims, wherein the second portion of the current collector system arranged in the recess of the steel conductor element has a pin-shape and/or is preferably separable from the rest of the current collector system. Cathode current collector and connector assembly according to any of the preceding claims, wherein the current collector system is a current collector bar, which is preferably rectangular shaped. Cathode current collector and connector assembly according to any of the preceding claims, wherein the recess of the steel conductor element has a volume VR and the second portion of the current collector system arranged in the recess of the steel conductor element has a volume V2S, wherein is in the range of 0.9 to 1 .0,

preferably 0.92 to 0.98, under normal conditions according to DIN 1341. Kit-of-parts for manufacturing a cathode current collector and connector assembly according to any of the preceding claims comprising a) a copper or copper alloy current collector system with an optional protective steel layer cladding, b) a carbonaceous cathode with a groove for receiving a first portion of the current collector system, and c) a steel conductor element with a recess for receiving a second portion of the current collector system. Aluminum electrolysis plant or Aluminum electrolysis cell comprising a cathode current collector and connector assembly according to any of the claims 1-10 and a supply bus bar, wherein the conductor element of the cathode current collector and connector assembly is electrically connected to the current supply bus bar, preferably by means of a copper or aluminum flexible. Use of a direct contact between a copper or copper alloy current collector system with an optional protective steel layer cladding and a steel conductor element in a cathode assembly for an aluminum electrolysis cell for decreasing the voltage drop in an aluminum electrolysis process.