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CN-122003741-A - Free standing electrode film for electrochemical cells and method of making same

CN122003741ACN 122003741 ACN122003741 ACN 122003741ACN-122003741-A

Abstract

A freestanding electrode film (16) for an electrochemical cell (12) comprising a binder system having a first binder (20) and a second binder (22) and an active material (18) contained in the binder system, wherein the first binder (20) is a fluorine-free binder, and wherein the second binder (22) is a non-fibril forming binder having an average particle size d 50 in the range of 40 to 200 nm. The binder system is free of Polytetrafluoroethylene (PTFE) and/or cellulose based binders. An electrode (10), an electrochemical cell (12) and a method of producing a freestanding electrode film (16) are also presented.

Inventors

  • T. WELLER
  • J. Moss
  • S. Z. Damnali
  • M. HORN
  • B-i.h. Hogg
  • K. HUBER
  • S. Stozhevich

Assignees

  • 宝马股份公司

Dates

Publication Date
20260508
Application Date
20240912
Priority Date
20231009

Claims (10)

  1. 1. A free-standing electrode film (16) for an electrochemical cell (12) includes a binder system having a first binder (20) and a second binder (22) and an active material (18) contained in the binder system, Wherein the first binder (20) is a fluorine-free, fibril-forming binder, Wherein the second binder (22) is a non-fibril forming binder having an average particle size d 50 in the range of 40 to 200 nm, and Wherein the binder system is free of polytetrafluoroethylene and/or cellulose based binders.
  2. 2. The free standing electrode film (16) of claim 1 wherein the fluorine-free, fibril forming binder is a high molecular weight polyolefin, preferably a high molecular weight polyethylene.
  3. 3. The free standing electrode film (16) of claim 1 or 2, wherein the non-fibril forming binder is selected from the group consisting of polyvinylidene fluoride, polar modified polyvinylidene fluoride, polyvinylidene fluoride copolymers, and combinations thereof.
  4. 4. The free standing electrode film (16) according to any of the preceding claims, wherein the non-fibril forming binder has an average particle size d 50 in the range of 40 to 200 nm.
  5. 5. The free standing electrode film (16) according to any of the preceding claims, wherein the binder system has up to 50 weight percent, in particular 5 to 30 weight percent, preferably 10 to 25 weight percent of the second binder, in each case relative to the total weight of the binder system.
  6. 6. The free standing electrode film (16) according to any one of the preceding claims, wherein the binder system is present in the free standing electrode film (16) in a proportion of 0.25 to 5 weight percent, preferably in a proportion of 0.5 to 3 weight percent, relative to the total weight of the free standing electrode film (16).
  7. 7. The free standing electrode film (16) according to any one of the preceding claims, wherein the free standing electrode film (16) is prepared in a dry process.
  8. 8. An electrode (10) for an electrochemical cell (12) comprising a freestanding electrode film (16) according to any of the preceding claims.
  9. 9. An electrochemical cell (12) having an electrode (10) according to claim 8.
  10. 10. A method of preparing a freestanding electrode film (16) for an electrochemical cell (12), comprising the steps of: Providing a first binder (20), a second binder (22) and an active material (18), wherein the first binder (20) is a fluorine-free, fibril-forming binder and the second binder (22) is a non-fibril-forming binder, and wherein the first binder (20) and the second binder (22) are free of polytetrafluoroethylene and/or cellulose-based binders, -Mixing the first binder (20), the second binder (22) and the active material (18) to form an intermediate electrode film, and -Pressing the intermediate electrode film into the free standing electrode film (16).

Description

Free standing electrode film for electrochemical cells and method of making same Technical Field The present invention relates to a freestanding (freistehend) electrode film for an electrochemical cell, an electrode for an electrochemical cell having such an electrode film, an electrochemical cell having such an electrode, and a method of preparing a freestanding electrode film. Background In order to prepare electrodes for electrochemical cells, methods are known in the art in which solvent-based coating substances (so-called "pastes") are applied to a current collector (e.g. a metal current collector foil), wherein such coating substances comprise an electrochemically active material, an electrode binder and additives (e.g. conductive additives and a carrier solvent). Such a method requires a drying step in which the solvent used is removed. Thereby creating additional costs and significant technical and energy costs. From US 10 741 843 B2, free-standing electrode films are known which are obtainable in a production process in which the use of a carrier solvent is dispensed with. The electrode film comprises a composite binder comprising Polytetrafluoroethylene (PTFE) and poly (ethylene oxide) (PEO) that may be fibrillated or formed into fibrils. However, the use of PTFE is associated with high costs due to the higher fluorine fraction. In addition, PTFE-based binders are not sufficiently stable chemically, in particular electrochemically, in all applications. For example, the use of PTFE-based binders in their anodes and lithiated graphite or silicon or metallic lithium based electrochemical cells may cause the PTFE to decompose into lithium fluoride (LiF) and amorphous carbon. For example, polytetrafluoroethylene in Guobao Li et al ："The influence of polytetrafluorethylene reduction on the capacity loss of the carbon anode for lithium ion batteries"（ reduces the effect on capacity loss of a lithium ion battery carbon anode) (Solid State Ionics, volume 90 (1-4), pages 221-225, 2019, doi: 10.1016/S0167-2738 (96) 00367-0), PTFE used as a binder in the electrodes of a lithium ion battery contributes irreversibly to the formation loss of the lithium ion battery because lithium present in the lithium ion battery is partially converted to lithium fluoride (LiF) by reaction with PTFE and is thereby consumed. This is associated with irreversible capacity losses in the electrochemical cell that reduce the energy density or specific energy of the electrochemical cell. In addition, PTFE is increasingly undesirable from an ecological point of view, as the process of preparing PTFE relies on toxic chemicals and PTFE can only degrade very slowly in the environment. US 11,545,666 B2 also discloses dry processed and free standing composite electrode films having a fibrillatable binder and a particulate non-fibrillatable binder. The fibrillatable binder can be traced back to PTFE, while the non-fibrillatable binder is a cellulose-based binder. However, the use of cellulose-based binders results in unsatisfactory adhesion between the particles (especially active materials and conductive additives) present in the electrode film and between the composite electrode film and the conventional current collector. Disclosure of Invention It is therefore an object of the present invention to provide free-standing electrode films and electrodes and electrochemical cells comprising said free-standing electrode films, which have mechanically and chemically, in particular electrochemically stable electrode films and good adhesion properties and which can be produced in particular in a dry process. In particular, the use of PTFE should be dispensed with. The object of the invention is achieved by a free standing electrode film for an electrochemical cell comprising a binder system with a first binder and a second binder and an active material accommodated in the binder system, wherein the first binder is a fluorine-free binder and wherein the second binder is a non-fibril forming binder having an average particle size d 50 in the range of 40 to 200 nm (nicht-fibrillenbildend). The binder system is free of Polytetrafluoroethylene (PTFE) and/or cellulose based binders. The invention is based on the basic idea that on the one hand a stable and in particular dryable electrode film is provided by using a combination of a fibril forming binder (fibrillenbildend) and a non-fibril forming binder. For this purpose, the non-fibril-forming binder is present in the electrode film in a particle size in which it can act in the sense of a punctiform binder which, in addition to the fibril-forming binder, fixes the other constituent components present in the electrode film to one another. Correspondingly, according to the invention, the non-fibril forming binder is not present in the active material as a kind of coil surrounding the active material and other constituent components (e.g. conductive additives) in the electrode film. At the same time, th