Self-contacting electrode

Abstract

The present invention relates to a method for manufacturing an electrochemical cell (1), comprising: providing a current collector grid (2), the current collector grid defining a receptacle (20) for receiving at least one electrode segment (3), arranging the at least one electrode segment (3) in said receptacle (20) so that the current collector grid (2) is arranged on an outside (3a) of the at least one electrode segment (3), and allowing the at least one electrode segment (3) to swell so that the at least one electrode segment (3) presses with its outside (3a) against the current collector grid (2).

Description

[0001] Applicant: LITRONIK Batterietechnologie GmbH

[0002] Date: 05.09.2025

[0003] Our Reference: 23.073P-WO

[0004] Self-contacting electrode

[0005] The present invention relates to a method for manufacturing an electrochemical cell, particularly a primary battery. Furthermore, the present invention relates to electrochemical cells, particularly primary batteries. Furthermore, the present invention relates to implantable medical devices comprising an electrochemical cell according to the present invention.

[0006] According to the state of the art, electrodes, particularly cathodes, of such electrochemical cells are often formed using common dry pressing or wet coating processes utilizing an internal current collector.

[0007] However, such manufacturing processes have proven to be rather complex in case of miniaturized batteries with internal current collectors. Further, the small dissipation surface of the typical internal current collector of a miniaturized electrode comprises only a relatively small current rating.

[0008] Based on the above, the problem to be solved by the present invention is to provide an improved method for manufacturing an electrochemical cell as well as an improved electrochemical cell.

[0009] This problem is solved by a method having the features of claim 1 and an electrochemical cell having the features of claim 15. Further aspects of the present invention are disclosed below. Preferred embodiments of the aspects according to the present invention are stated in the corresponding dependent claims and are described below. According to claim 1, a method for manufacturing an electrochemical cell is disclosed, the method comprising:

[0010] - providing a current collector grid, the current collector grid defining a receptacle for receiving at least one electrode segment of an electrode, particularly cathode,

[0011] - arranging the at least one electrode segment in said receptacle so that the current collector grid encompasses the at least one electrode segment at least partially on an outside of the at least one electrode segment, and

[0012] - allowing the at least one electrode segment to swell so that the at least one electrode segment presses with its outside against an inside of the current collector grid to contact the current collector grid.

[0013] Particularly, the current collector grid is electrically connected, particularly joined with a current collector tab, wherein particularly, the current collector grid and the current collector tab form a current collector. Particularly, the current collector tab is designed or configured to be electrically connected to an internal contact within an electrochemical, e.g., a ground contact to an electrically conductive housing of the electrochemical cell or a feedthrough conductor of an electrical feedthrough of the electrochemical cell. In one embodiment, the current collector grid and the current collector tab are integrally formed in one piece.

[0014] Particularly, the present invention allows to manufacture electrodes without an internal current collector, more specifically without a current collector embedded in the electrode, and to efficiently provide electrical contacting of the electrode material to the current collector grid in the electrochemical cell. Furthermore, as will be described in more detail below, in case the electrode is formed out of several electrode segments, the method allows to coalesce the electrode segments into a single, particularly homogeneous electrode (electrical and ionic bonding). Particularly, due to the segmentation of the electrode body, initially more wetting surfaces are available for electrolyte supply.

[0015] According to an embodiment of the method, the electrochemical cell is or forms part of a primary battery. In an embodiment, the electrode segment comprises carbon monofluoride (CFx) or manganese dioxide (MnCh). In one embodiment, the electrochemical cell comprises an alkali metal as electrode active material. In one embodiment, the alkali metal is selected from lithium, sodium and potassium, wherein lithium is preferred.

[0016] 23.037P-WO | 05.09.2025 According to an embodiment of the method, the current collector grid is provided by shaping a precursor grid design as a substantially flat sheet of material such that the receptacle is formed. In one embodiment, the current collector grid is shaped by bending the flat sheet of material into a shape such that the receptacle in the desired form is formed. In one embodiment, the flat sheet of material is shaped, particularly bent, around a die or template, wherein particularly the die or template has a cross-section, particularly in terms of shape and dimension, that is substantially equal to the cross-section of the electrode segment to be arranged in the receptacle of the current collector grid. For example, the die or template may have a circular cross-section with a diameter substantially equal to the diameter of an electrode segment having a circular cross-section to be arranged in the receptacle. In another example, the die or template has a rectangular or prismatic cross-section with a width substantially equal to an electrode segment having a rectangular or prismatic cross-section to be arranged in the receptacle.

[0017] According to an embodiment, electrode segment is provided by pouring electrode material, particularly comprising an electrode active and optionally a binder and / or one or more conductive additive into a mold, particularly a press mold, and optionally compacting the electrode material, e.g. with a stamp or punch.

[0018] Furthermore, according to an embodiment of the method according to the invention, the current collector grid comprises interconnected struts defining a plurality of openings. In an embodiment, the openings are hexagonal, wherein particularly the respective opening comprises a hexagonal contour.

[0019] According to yet another embodiment of the method of the invention, upon said swelling, the at least one electrode segment protrudes into said openings so that the at least one electrode segment becomes mechanically anchored in the current collector grid and comprises a good electrical contact to the current collector gird.

[0020] Furthermore, in an embodiment of the method, the current collector grid extends in an axial direction and comprises a continuous gap extending in the axial direction, particularly over the whole length of the current collector grid in the axial direction.

[0021] 23.037P-WO | 05.09.2025 According to yet another embodiment of the method according to the present invention, allowing the at least one electrode segment to swell comprises contacting the at least one electrode segment with an electrolyte which causes electrolyte intake of the respective electrode segment through the outside of the respective electrode segment and subsequently an increase in volume of the respective electrode segment.

[0022] Particularly, in an embodiment of the method according to the present invention said electrolyte comprises one of: a non-aqueous, preferably aprotic, solvent; an ester; an ether; a dialkyl carbonate; a tetrahydrofuran; a methyl acetate; diglyme (bis(2- m ethoxy ethyl)ether); triglyme (tri s(2-m ethoxy ethyl)ether); tetraglyme (tetra(2- m ethoxy ethyl)ether); 1,2-dimethoxy ethane; 1,2-di ethoxy ethane; 1 -ethoxy -2- methoxyethane; dimethyl carbonate; diethyl carbonate; dipropyl carbonate; ethyl methyl carbonate; methyl propyl carbonate; ethyl propyl carbonate; a cyclic carbonate; a cyclic ester; a cyclic amide; propylene carbonate; ethylene carbonate; butylene carbonate; y- butyrolactone; N-methyl pyrrolidinone; a polar non-aqueous solvent; acetonitrile; dimethyl sulfoxide; dimethyl formamide; dimethyl acetamide.

[0023] In a further embodiment of the method, the electrolyte comprises at least one conductive salt. The conductive salt is preferably an inorganic alkali metal salt, wherein particularly the alkali metal cation can be the same as the active anode material. Suitable anions are PFe , BF4, AsF6, SbF6, C1O4, O2, AlCh , GaCU", SCN , SO3(C6F5) , C(SO2CF3)3, N(SO2CF3)2 and SO3CF3among others.

[0024] According to yet a further embodiment of the method according to the present invention, allowing the at least one electrode segment to swell further comprises operating (i.e. discharging) the electrochemical cell / battery thereby causing the at least one electrode segment (or the multiple electrode segments) to swell. This further volume expansion of the respective electrode segment can be caused by a chemical reaction during operation, e.g., the generation of LiF according to Li+CFx LiF+C.

[0025] According to a further embodiment of the method, the current collector grid defines a receptacle for receiving a plurality of electrode segments of the electrode (particularly

[0026] 23.037P-WO | 05.09.2025 cathode), wherein the method particularly comprises arranging said plurality of electrode segments in said receptacle so that the current collector grid is arranged on an outside of the electrode segments and particularly encompasses the latter at least partially (e.g. when the current collector grid comprises said gap). Particularly, utilizing a plurality of electrode segments to build up the electrode allows to freely scale and design the electrode geometry via the number and shape of the electrode segments.

[0027] Furthermore, in an embodiment, upon said operating, the electrode segments coalesce to form a single electrode (that is ideally homogeneous), so as to provide electronic and ionic contact between each two neighboring electrode segments.

[0028] According to yet another embodiment, the current collector grid and the at least one electrode segment or said plurality of electrode segments accommodated therein are surrounded by an electrically insulating separator. In a further embodiment of the method the separator comprises one of: a non-metallic material, a polymer, polyethylene, polypropylene, polyamide, Nylon, a fluoropolymer, an ethylene tetrafluoroethylene copolymer (ETFE), polytetrafluoroethylene (PTFE). Preferably, the separator is designed in form of a weldable bag.

[0029] According to a further embodiment of the method, the respective electrode segment is cylindrical. According to another embodiment, the respective electrode segment can comprise a prism shape (i.e., may be a polyhedron having opposing n-sided polygon bases).

[0030] Furthermore, according to an embodiment of the method, the respective electrode segment is made from a dry-pressed powder, particularly having a mean grain size in the range of 1 pm to 50 pm. Furthermore, according to an embodiment of the method, the powder comprises 85 wt% CFx (carbon monofluoride), 10 wt% graphite, particularly expanded graphite BNB90, 5 wt% binder, particularly PVDF (Polyvinylidene fluoride).

[0031] In yet another embodiment of the method, the respective electrode segment is made out of a granulated active material comprising a plurality of granules. Particularly, the granulated active material or granulate is characterized by mean grain size in the range of 200 pm to

[0032] 23.037P-WO | 05.09.2025 800 pm. Particularly, in an embodiment, the respective granule comprises between 90 wt% and 97 wt% CFx (carbon monofluoride).

[0033] The term “mean grain size” is used in the meaning known to the skilled person. It particularly refers to the median of a grain size distribution of particles, e.g., of particles of the active material in form of a powder or a granulate. This value is also known as D50. Suitable methods for determining the particle size or the grain size distribution include laser diffraction analysis, or small angle scattering (e.g., using X-rays or neutron radiation).

[0034] According to a further aspect of the present invention, an electrochemical cell manufactured by means of the method according to the present invention is disclosed. Particularly, the electrochemical cell can be or form part of a primary or secondary battery.

[0035] According to yet another aspect of the present invention, an electrochemical cell is disclosed, the electrochemical cell comprising:

[0036] - a current collector grid, the current collector grid defining a receptacle,

[0037] - an electrode (particularly cathode) accommodated in said receptacle so that the current collector grid is arranged on an outside of the electrode and particularly encompasses the electrode at least partially.

[0038] In an embodiment, the current collector grid is electrically connected, particularly joined with a current collector tab, wherein particularly, the current collector grid and the current collector tab form a current collector. Particularly, the current collector tab is designed or configured to be electrically connected to an internal contact within an electrochemical, e.g., a ground contact to an electrically conductive housing of the electrochemical cell or a feedthrough conductor of an electrical feedthrough of the electrochemical cell. In one embodiment, the current collector grid and the current collector tab are integrally formed in one piece.

[0039] In an embodiment of the electrochemical cell, the current collector grid comprises interconnected struts defining a plurality of openings, wherein in an embodiment the openings are hexagonal, e.g., comprise a hexagonal contour or cross section.

[0040] 23.037P-WO | 05.09.2025 Furthermore, in an embodiment of the electrochemical cell, the current collector grid extends in an axial direction and comprises a continuous gap extending in the axial direction, particularly over the whole length of the current collector grid in the axial direction. This may lend the grid a certain amount of flexibility in a direction perpendicular to the axial direction.

[0041] According to an embodiment of the electrochemical cell, the electrode is swollen into said openings of the current collector grid, particularly such that the electrode presses with its outside against the current collector grid to contact the current collector grid.

[0042] Furthermore, according to an embodiment the electrode can comprise a plurality of electrode segments connected to one another to form the electrode (see also above). Particularly, according to an embodiment, the electrochemical cell is designed to generate said swelling by intake of an electrolyte into the electrode segment(s) and / or by operating (i.e. discharging) the electrochemical cell. Furthermore, in an embodiment, the electrochemical cell is designed to let the electrode segments coalesce upon said operating of the electrochemical cell.

[0043] Furthermore, according to an embodiment of the present invention, the electrochemical cell is or forms part of a primary battery or a secondary battery.

[0044] In one embodiment, the electrochemical cell comprises a housing, particularly formed two at least two housing parts. In one embodiment, the first housing part is formed by a can or beaker and the second housing part is formed by a lid. In one embodiment, the housing is formed by an electrically conductive material, particularly a biocompatible material, more particular a biocompatible metal or alloy, e.g. stainless- steel, titanium or a titanium alloy. In one embodiment, the housing of the electrochemical cell is hermetically sealed, for example the housing part are hermetically joined with one another, e.g., welded. In one embodiment, the electrochemical cell comprises an electrical feedthrough comprising an electrically insulating body, e.g., glass or a glass solder, and a feedthrough conductor, e.g., made of a metal, e.g., molybdenum, and optionally a ferrule or flange, particularly made from the same material as the housing, wherein the electrically feedthrough is arranged in an opening of a housing part, e.g,, lid. In one embodiment, the current collector grid is

[0045] 23.037P-WO | 05.09.2025 electrically connected, particularly via a current collector tab, to the feedthrough conductor. In another embodiment, the current collector grid is electrically connected to a housing portion, e.g., the lid or the can.

[0046] According to yet another aspect of the present invention, an implantable medical device is disclosed, particularly in form of an intracardiac pacemaker or an implantable cardiac monitor, the implantable medical device comprising an electrochemical cell according to the present invention and / or manufactured by a method according to the present invention.

[0047] In the following, embodiments as well as further features and advantages are described with reference to the Figures, wherein

[0048] Fig. 1 shows an embodiment of a method and electrochemical cell according to the invention comprising two cylindrical electrode segments,

[0049] Fig. 2 shows a modification of the embodiment shown in Fig. 1, wherein the electrode is formed out of four electrode segments,

[0050] Fig. 3 shows ingrowth of the electrode segments into the openings of the current collector grid,

[0051] Fig. 4 self-contacted electrode segments at EOL of the battery, and

[0052] The present invention relates to the production of electrodes 30 without internal current collectors that are comprising at least one electrode segment 3, particularly multiple electrode segments 3 (with e.g. cylindrical or prismatic geometry), wherein such an electrode 30 allows subsequent self-contacting at the current collector 2 during operation / discharge of the electrochemical cell / battery 1 by swelling the electrode active material into the grid openings 23 of the current collector grid 2. The electrode geometry and thus the electrochemical cell / battery 1 may be freely scaled via the number of electrode segments 3 without an internal current collector.

[0053] 23.037P-WO | 05.09.2025 During battery operation, the electrode segments 3 combine to form a single (ideally a homogeneous) electrode body 30, thus providing electronic and ionic contact between the segments 3.

[0054] Particularly, the present invention achieves self-contacting of the cathode material to the current collector grid 2 and mutual contact of the electrode segments 3. Thus, it is possible to initially form the electrode 30 out of multiple segments 3 which simplifies the manufacturing of the electrodes and further simplifies the geometry for both internal and external current collectors.

[0055] Fig. 1 indicates an embodiment of the method and electrochemical cell 1 according to the present invention, wherein the electrode 30, particularly cathode, comprises two cylindrical electrode segments 3 that are arranged on top of one another in an axial direction of the electrochemical cell 1. Particularly, the current collector grid 2 is a tubular structure defining an interior space 20, herein denoted as receptacle 20, extending in the axial direction, wherein the grid 2 may comprise a continuous gap 21 in the axial direction. The receptacle 20 serves for accommodating the electrode segments 3 therein (cf. e.g., Fig. 3). Furthermore, the current collector grid 2 comprises interconnected struts 22 defining a plurality of openings 23 that can be hexagonal as shown e.g., in Fig. 1. Due to the swelling of the electrode segments 3, which is caused by electrolyte intake and operation of the electrochemical cell 1, the electrode segments 3 protrude into said openings 23 of the grid 2 as indicated in Fig. 3. Thus, the outsides 3a of the segments 3 are tightly pressed against the current collector grid’s 2 inside. Furthermore, operation of the electrochemical cell 1 causes the segments 3 to connect to one another to form a single electrode 30 as indicated in Fig. 4 showing the region 31 where the segments 3 have coalesced. Furthermore, the current collector grid 2 and the electrode segments 3 contained therein are enclosed by a separator as indicated in Fig. 1.

[0056] The current collector grid 2 may be electrically connected to a current collector tab configured to electrically connect the current collector grid 2 to an internal contact of the electrochemical cell. Particularly, the current collector grid and the current collector tab may be integrally formed in one-piece.

[0057] 23.037P-WO | 05.09.2025 Particularly, the current collector grid 2 may be formed by shaping a substantially flat sheet of material into the desired form. Particularly, the flat sheet of material may be bend around a die or punch defining the shape of the receptacle 21 of the current collector grid 2. For example, a flat sheet of material may be bent or rolled around the die or punch design in form of a cylindrical rod, thereby yielding a current collector 2 with a tubular receptacle 21 as shown in Figs 1 and 2.

[0058] As shown in Fig. 1, the electrode 30 may be formed out of two cylindrical electrode segments 3. Fig. 2 shows a modification of this embodiment, wherein here the electrode 30 is formed from four cylindrical electrode segments 3 that are stacked on top of one another in the axial direction of the electrochemical cell 1.

[0059] According to an example of the present invention, the electrode segments 3 shown e.g., in Figs. 1 to 4 may be made from dry-pressed powders articularly, from a dry blend containing 85% CFx, 10% expanded graphite BNB90, 5% PVDF using particularly a punch / die process (D = 4.3 mm, H = 4.5 mm). The electrode segments 3 may be vacuum dried, particularly for use in lithium batteries. After vacuum drying, the electrode segments 3 are stacked and placed in a sleeve-shaped current collector grid 2 (see e.g., above) and welded in a separator, e.g., in form of a pocket. Particularly, contacting of the grid 2 can take place in two phases, wherein in a first phase the electrode segment stack is contacted with an electrolyte which leads to a corresponding swelling of the segments 3 into the openings 23 of the grid 2. Particularly, the electrolyte uptake takes place through the outsides 3a of the segments, particularly through the shell or front surfaces of the electrode segments 3 (a higher number of segments allows the surfaces for the initial electrolyte uptake to be increased). In a second phase, further swelling by volume expansion is caused by the formation of LiF during discharge which leads to mechanical anchoring of the segments 3 in the grid’s openings 23, where the reaction formation of carbon (Li + CFx LiF + C) on the surface favors contacting to the metallic current collector grid 2. Furthermore, LiF and C bridge formation supports a connection of the adjacent surfaces of the segments and thus a macroscopic coalescence of the cathode segments 3 into a single electrode 30.

[0060] 23.037P-WO | 05.09.2025 Furthermore, in an alternative example, the e.g., cylindrical electrode segments 3 may be made of granulated active material, wherein particularly the granules can contain 90 to 97 wt% CFx.

[0061] The electrochemical cell 1 according to the present invention may be used as power source of an implantable medical device. As described before, the electrochemical cell 1 comprises a cathode 30 comprising cylindrical electrode segments 3 accommodated in an outer current collector grid 2 that is designed as described in conjunction with Figs. 1 and 2 above. This assembly is in turn enclosed by the separator 4. Particularly, the current collector grid 2 may be formed from one of: titanium, a titanium alloy stainless steel or aluminum.

[0062] Furthermore, the electrochemical cell 1 comprises an anode which may comprise two anode segments formed as cylinder half shells which are arranged on the separator 4, wherein each of the anode segments may be in turn surrounded by a further (anode) current collector grid. Similar to the cathode’s current collector grid 2, the further current collector grid 2 may comprises interconnected struts delimiting e.g., hexagonal openings. Both the cathode current collector grid 2 and the anode current collector grids may be thus arranged coaxially. The further current collector grid may e.g., be formed from one of: titanium, a titanium alloy, nickel, stainless steel. Furthermore, the anode 5 can comprise an alkali metal, particularly selected from lithium, sodium or potassium.

[0063] Furthermore, each anode segment may be enclosed or enveloped by an anode separator. The electrochemical cell 1 may comprise an electrically conductive cylindrical housing closed by a lid on a face side of the housing, wherein the lid may comprise a glass feedthrough with a feedthrough pin for electrically contacting the cathode 30. The anode may be electrically connected to the electrically conductive housing, e.g., via the anode current collector grid. The electrically conductive housing may be preferably formed form titanium or a titanium alloy.

[0064] Particularly, the present invention allows in an advantageous fashion to assemble noncontacting electrode segments without an internal current collector using a simple powder compaction process, wherein contacting of at least one electrode segment to the current collector grid or mutual contact between multiple electrode segment is performed in the

[0065] 23.037P-WO | 05.09.2025 battery via electrolyte intake and operation of the electrochemical cell / battery. Furthermore, the electrode geometry is scalable via the number of electrode segments. Optionally, the electrode segments can consist of a CFx dry blend or a CFx granulate. Furthermore, the circumferential current collector grid provides a relatively large area leading to a high current rating.

[0066] 23.037P-WO | 05.09.2025

Claims

Claims1. A method for manufacturing an electrochemical cell (1), comprising:- providing a current collector grid (2), the current collector grid defining a receptacle (20) for receiving at least one electrode segment (3),- arranging the at least one electrode segment (3) in said receptacle (20) so that the current collector grid (2) is arranged on an outside (3a) of the at least one electrode segment (3), and- allowing the at least one electrode segment (3) to swell so that the at least one electrode segment (3) presses with its outside (3a) against the current collector grid (2).

2. The method according to claim 1, wherein the current collector grid (2) comprises interconnected struts (22) defining a plurality of openings (23).

3. The method according to claim 2, wherein the openings (23) are hexagonal.

4. The method according to claim 2 or 3, wherein upon said swelling the at least one electrode segment (3) protrudes into said openings (23).

5. The method according to one of the preceding claims, wherein allowing the at least one electrode segment (3) to swell comprises contacting the at least one electrode segment (3) with an electrolyte.

6. The method according to one of the preceding claims, wherein allowing the at least one electrode segment (3) to swell comprises operating the electrochemical cell (1) thereby causing the at least one electrode segment (3) to swell.

7. The method according to one of the preceding claims, wherein the current collector grid (2) defines a receptacle (21) for receiving a plurality of electrode segments, wherein the method comprises arranging a plurality of electrode segments (3) in said receptacle (20) so that the current collector grid (2) is arranged on an outside (3a) of the respective electrode segment (3).23.037P-WO | 05.09.20258. The method according to claims 6 and 7, wherein upon said operating, neighboring electrode segments (3) of said plurality of electrode segments (3) connect to one another to form a single electrode (30).

9. The method according to one of the preceding claims, wherein the current collector grid (2) and the at least one electrode segment (3) accommodated therein are surrounded by a separator (4).

10. The method according to one of the preceding claims, wherein the respective electrode segment (3) is cylindrical or comprises a prism shape.

11. The method according to one of the preceding claims, wherein the respective electrode segment (3) is made from a dry -pressed powder.

12. The method according to claim 11, wherein the powder comprises 85 wt% CFx,10 wt% graphite, particularly expanded graphite BNB90, and 5 wt% binder, particularly PVDF.

13. The method according to one of the claims 1 to 10, wherein the respective electrode segment (3) is made out of a granulated active material comprising a plurality of granules, particularly characterized by mean grain size in the range of 200 pm to 800 pm.

14. The method according to claim 13, wherein the respective granule comprises between 90 wt% and 97 wt% CFx.

15. An implantable medical device comprising an electrochemical cell (1), the electrochemical cell (1) comprising:- a current collector grid (2), the current collector grid (2) defining a receptacle (20), and- an electrode (3, 30) accommodated in said receptacle (20) so that the current collector grid (2) is arranged on an outside of the electrode (30).23.037P-WO | 05.09.2025

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