Battery cell with PTFE and manufacturing process, motor vehicle with an energy storage device

Abstract

A battery cell for an energy storage device is described, comprising a positive electrode, a negative electrode and a liquid electrolyte, wherein the negative electrode comprises PTFE and the liquid electrolyte comprises at least one additive, wherein the decomposition voltage of the at least one additive is greater than 0.8 V relative to Li / Li+ as a reference system.

Description

The present disclosure relates to a battery cell for a motor vehicle with an energy storage device. The disclosure relates equally to a battery cell and / or a motor vehicle with an energy storage device and a manufacturing process for a battery cell. Lithium-ion batteries are used in a wide variety of mobile electronic applications. The demand for affordable and long-lasting energy storage devices is high. Electromobility, in particular, is significantly driven by battery technology, which depends on the ongoing development of battery cell chemistry. Solvent-free electrode manufacturing, also known as "dry coating," promises cost and energy reductions compared to the conventional "wet coating" process. A polytetrafluoroethylene (PTFE) binder is primarily used for solvent-free dry coating. A possible corresponding process is described, for example, in patent application WO2023179969A1. In the potential range of the negative electrode, PTFE decomposes, irreversibly consuming lithium. This lithium is then no longer available for energy storage. US11545667B2 describes the formation of a protective layer around the PTFE to prevent Li / Li+ from reaching the PTFE. The PTFE binder particles are first manufactured with the ionically insulating protective layer and then mixed with the active electrode material. The mixture is then milled and calendered to form an electrode layer. This process can damage the ionically insulating protective layer. Against the background of this prior art, one object of the present disclosure is to provide a device and a method, each of which is suitable for enriching the prior art and improving at least the aforementioned aspects of the prior art. In particular, it is the object of the disclosure to produce a battery cell in which PTFE can be used as a binder and formation losses are reduced. Likewise, it is the object of the disclosure to provide a method for producing a battery cell with PTFE. The problem is solved by the features of the independent claims. The dependent claims contain further developments of the disclosure. The problem is then solved according to one aspect of the disclosure by a battery cell for an energy storage device, comprising a positive electrode, a negative electrode and a liquid electrolyte, wherein the negative electrode comprises PTFE, characterized in that the liquid electrolyte comprises at least one additive, wherein the decomposition voltage of the at least one additive is greater than 0.8 V relative to Li / Li+ as a reference system. According to one aspect of the disclosure, the battery cell comprises further additives. Two additives with a decomposition voltage of the additive greater than 0.8V relative to Li / Li+ as a reference system are also suitable to solve the problem of the present disclosure. Optionally, the liquid electrolyte and / or one of the electrodes may contain further additives and / or conductive substances to influence the properties of the electrolyte and thus of the battery cell. Other additives and / or conductive substances may also be added to the liquid electrolyte within the battery cell. These may serve other purposes. In particular, at least one additive is selected from a lithium salt, a carbonate, a sultone, a borate, a nitrile, tris(trimethylsilyl) phosphates or phosphides, 1,3,2-dioxathiolanes 2,2-dioxide, 1,5,2,4-dioxadithianes 2,2,4,4-tetraoxide, tetravinylsilanes, fluoroethylene carbonate, vinylene carbonate, lithium difluoro(oxalato)borate(1-), lithium difluorobis(oxalato)phosphate, tris(trimethylsilyl) phosphide, 1,3-propane sultones, 1,3,2-dioxathiolanes 2,2-dioxide, 1,5,2,4-dioxadithianes 2,2,4,4-tetraoxide and / or ethylene sulfites. According to another aspect of the disclosure, the problem is also solved by a battery cell for an energy storage device, comprising a positive electrode, a negative electrode and a liquid electrolyte, wherein the negative electrode comprises PTFE, characterized in that the PTFE is coated with an electrically insulating coating. In particular, the electrically insulating coating around the PTFE in the battery cell is formed in a formation step. The formation of a battery cell occurs during the first charging cycle, that is, during the first charging and discharging. Due to the potential during formation, at least one additive decomposes, and the decomposition products combine with lithium ions to form an electrically insulating layer around the PTFE. Selecting the right additive enables the use of PTFE in battery cells. Compared to other binders such as rubber or cellulose, PTFE has the advantage of being suitable for dry-coating processes. Dry-coating offers several advantages over wet-coating in battery cell manufacturing. Firstly, it eliminates the need for organic and sometimes toxic solvents. Secondly, it reduces energy-intensive process steps that also require additional production capacity, such as drying the electrode layer and regenerating the solvent. Furthermore, it minimizes potential defects that can compromise the quality of the final product, such as residual solvents, binder migration, or cracks that can occur during the drying process. The use of PTFE in battery cells, particularly in lithium-ion battery cells, has so far been limited by the fact that PTFE reacts with lithium ions in an undesirable side reaction. This leads to a reduction in the lithium ions available for energy storage and degrades the battery cell. By adding additives with a decomposition voltage greater than 0.8 V relative to Li / Li+ as a reference system, not only is a material added that decomposes instead of PTFE and prevents the undesired side reaction, but it also forms an electrically insulating coating around the PTFE. This coating prevents the PTFE from undergoing the undesired side reaction over the lifetime of the electrode and in subsequent charge and discharge cycles, thus halting the progressive consumption of lithium ions. Furthermore, preventing PTFE decomposition helps to better preserve the binding properties of PTFE, thereby maintaining the mechanical stability of the electrode over its lifetime. According to another aspect of the disclosure, the problem is also solved by a method for manufacturing a battery cell with a negative electrode, a positive electrode and a liquid electrolyte, comprising the steps of: - joining a negative electrode film, wherein the negative electrode film comprises PTFE, and a positive electrode film to form an electrochemical cell; - filling the electrochemical cell with a liquid electrolyte, wherein the liquid electrolyte comprises at least one additive, wherein the decomposition voltage of the at least one additive is greater than 0.8 V relative to Li / Li+ as a reference system; and - forming the battery cell. The production of the negative electrode with PTFE is described in WO2023 / 179969A1. In particular, the components of the negative electrode are processed in an extruder, during which the PTFE is at least partially fibrillated. The negative electrode is then rolled into a free-standing electrode film, which can also be directly laminated onto a metallic current collector. The positive electrode film is produced in the same way, and the negative and positive electrode films are combined to form an electrochemical cell. In a final step, the liquid electrolyte is added to the electrochemical cell. All common materials for lithium-ion batteries are suitable as active materials for the positive electrode, such as lithium cobalt oxide (LCO), lithium manganese oxide spinel (LMO), lithium nickel cobalt manganese (NMC), lithium iron phosphate (LFP), lithium nickel cobalt aluminum oxide (NCA), or nickel cobalt manganese aluminum (NCMA).All common materials for lithium-ion batteries are suitable as active materials for the negative electrode, such as graphite, silicon, or silicon / carbon composites. All common liquid electrolytes for lithium-ion batteries are suitable as liquid electrolytes, such as LiPF6, LiBF4, and LiBOB in solvents like organic carbonates. In particular, the manufacturing process involves forming the battery cell to create an electrically insulating coating around the PTFE. This formation takes place during the first charging and discharging cycles. Preferably, this initial charging and discharging occurs under standardized conditions. According to another aspect of the disclosure, the problem is also solved by a motor vehicle comprising an energy storage device comprising a plurality of battery cells with PTFE, wherein the PTFE is coated with an electrically insulating coating. The above description can be summarized in other words, and with reference to a specific embodiment that is described as not limiting to the present disclosure, as follows: By using one or more electrolyte components, for example as additives or solvents, which decompose in the first cycle at higher potentials than the PTFE, which decomposes at approximately 0.8 V vs. Li / Li+, an electrically non-conductive interface is formed around the PTFE, which can also be referred to as the polymer-electrolyte interphase (PEI). This manufacturing step is also called formation. This electrically non-conductive interface (PEI) suppresses the decomposition reaction of the PTFE. One embodiment of each is described below with reference to the figures. Fig. 1 schematically shows a battery cell (3) before formation; Fig. 2 schematically shows a battery cell (103) after formation; Fig. 2a shows in detail PTFE fibrils with an electrically insulating coating (6); Fig. 3 shows a schematic representation of a vehicle (7) with an energy storage device (8) comprising a plurality of battery cells (1, 103); and Fig. 4 shows a manufacturing process for a battery cell (103). Fig. 1 schematically shows a battery cell 3 before formation according to one aspect of the disclosure. The battery cell 3 comprises a negative electrode 5 made of PTFE and a positive electrode 4 and is filled with the liquid electrolyte 1, which includes the at least one additive 2. The decomposition voltage of the at least one additive 2 is greater than 0.8 V relative to Li / Li+ as a reference system. In addition to the one additive 2, further optional components are added to the electrolyte and / or the electrodes 4 or 5. The PTFE is schematically represented in Fig. 1 as oval fibrils. The two electrodes 4 and 5 are in full-surface contact with each other. Further optional layers, such as a membrane between the electrodes 4 and 5 and / or current-discharge foils on the positive electrode 4 and / or the negative electrode 5, are optionally possible. Fig. 2 shows a battery cell 103 after formation. The positive electrode 4 and the negative electrode 5 are in full-surface contact with each other. The PTFE fibrils of the negative electrode 5 are enclosed by an electrically insulating coating 6 formed from the additive 2. Figure 2a shows a detailed view of a PTFE fibril enclosed by an electrically insulating coating 6. The coating 6 prevents electrons from reaching the PTFE and initiating unwanted side reactions. Figure 3 schematically depicts a motor vehicle 7 with an energy storage device 8. A plurality of battery cells 103a to 103x are interconnected in the battery storage device 8. The battery cells 103a to 103x have TPFE fibrils in their negative electrodes 5, which are coated with an electrically insulating coating 6, as described for Figure 2. In a first embodiment, the energy storage device 8 is equipped with battery cells 3a to 3x according to Figure 1, and the formation takes place through the first charging and discharging of the energy storage device 7. In a further embodiment, the energy storage device 7 is equipped with pre-formed battery cells 103a to 103x according to Figure 2. Typical manufacturing steps for producing battery cells, such as heating and shearing PTFE, are carried out before coating, so that the coating 6 cannot be damaged by further manufacturing steps. Fig. 4 shows an exemplary manufacturing method for a battery cell 3 and a battery cell 103. All components of the negative electrode 5 and PTFE are fed into an extruder 11 via the hopper 10, where they are mixed and heated. A negative electrode 5 is formed from this mixture, in which the PTFE has already been processed, for example, sheared and fibrillated. The negative electrode 5 is joined with a positive electrode 4 to form an electrochemical cell 50. The electrochemical cell 50 is then filled with liquid electrolyte 1. The liquid electrolyte comprises at least one additive 2 whose decomposition voltage is greater than 0.8 V relative to Li / Li+ as a reference system. The resulting battery cell 3 is formed into the formed battery cell 103 by charging and discharging. Simultaneously, the electrically insulating coating 6 forms around the PTFE, consuming at least one additive 2. Reference symbol (part of the description) 1, 101 liquid electrolyte 2 additive 3, 103 battery cell 4 positive electrode 5 negative electrode 6 electrically insulating coating 7 motor vehicle 8 energy storage device 9 manufacturing process 10 funnel 11 extruder 50 electrochemical cell QUOTES INCLUDED IN THE DESCRIPTION This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature WO 2023179969A1 [0002, 0016]US 11545667B2

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Claims

Battery cell (3) for an energy storage device, comprising a positive electrode (4), a negative electrode (5) and a liquid electrolyte (1), wherein the negative electrode (5) comprises PTFE, characterized in that the liquid electrolyte (1) comprises at least one additive (2), wherein the decomposition voltage of the at least one additive (2) is greater than 0.8 V relative to Li / Li+ as a reference system. Battery cell (3) according to claim 1, wherein the at least one additive (2) is selected from a lithium salt, a carbonate, a sultone, a borate, a nitrile, tris(trimethylsilyl) phosphates or phosphides, 1,3,2-dioxathiolanes 2,2-dioxide, 1,5,2,4-dioxadithianaes 2,2,4,4-tetraoxide, tetravinylsilanes, fluoroethylene carbonate, vinylene carbonate, lithium difluoro(oxalato)borate(1-), lithium difluorobis(oxalato)phosphate, tris(trimethylsilyl) phosphide, 1,3-propanesultone, 1,3,2-dioxathiolanes 2,2-dioxide, 1,5,2,4-dioxadithianaes 2,2,4,4-tetraoxide and / or ethylene sulfites. Battery cell (3) according to claim 1 or 2, wherein the liquid electrolyte comprises further additives and / or conductive additives. Battery cell (103) for an energy storage device, comprising a positive electrode (4), a negative electrode (5) and a liquid electrolyte (1), wherein the negative electrode (5) comprises PTFE, characterized in that the PTFE is coated with an electrically insulating coating (6). Battery cell (103) according to claim 4, wherein the electrically insulating coating (6) of the PTFE is formed in a formation step. A method for producing a battery cell (103) with a positive electrode (4), a negative electrode (5) and a liquid electrolyte according to claim 4, comprising the steps of: - joining a negative electrode film (5), wherein the negative electrode film comprises PTFE, and a positive electrode film (4) to form an electrochemical cell (50); - filling the electrochemical cell (50) with a liquid electrolyte (1), wherein the liquid electrolyte (1) comprises at least one additive (2), wherein the decomposition voltage of the at least one additive (2) is greater than 0.8 V relative to Li / Li+ as a reference system; and - forming the battery cell (103). Method according to claim 6, wherein the PTFE is at least partially fibrillated before formation. Method according to claim 6 or 7, wherein the formation of the battery cell (3) creates an electrically insulating coating (6) around the PTFE. Motor vehicle (7) comprising an energy storage device (8) comprising a plurality of battery cells (3) according to claim 4 .

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