Patent Application
20150263352
This application claims priority under 35 U.S.C. §119 to patent application no. EP 14 159 484.6-1359, filed on Mar. 13, 2014 in the European Patent Office, the disclosure of which is incorporated herein by reference in its entirety.
The present disclosure is related to an electrochemical component, particularly a coating for an electrode of an electrode assembly for a Lithium/Air battery cell.
U.S. Pat. No. 5,510,209 is related to a solid polymer electrolyte-based oxygen battery. A polymer-based battery comprises metal anodes in an oxygen gas cathode. The oxygen is not stored in the battery but rather it accessed from the environment. The solid-state battery is constructed by sandwiching a metal ion-conductive polymer electrolyte film between a metal anode (negative electrode) and a composite carbon electrode which serves as the cathode current collector, on which the electro-active oxygen is reduced during discharge of the battery to generate electric current. The metal anodes include lithium, magnesium, sodium, calcium, aluminum and zinc.
EP 1 262 048 B1 is related to an electrode/separator laminate for galvanic cells and a process for its manufacture. According to the method disclosed in EP 1261 048 B1 a method is provided for producing an electrode/separator laminate for electrochemical elements which contains at least one lithium-intercalating electrode, which is composed of a PVdF-HFP copolymer, where in the polymer matrix electrochemically active material, which are insoluble in the polymer, are finely dispersed. The PVdF-HFP copolymer is dissolved in a solvent and is mixed with electrochemically active materials. The pasty substance obtained in this way is extruded to form a sheet and is then laminated with the polyolefine separator which is coated with the PVdF-HFP copolymer. In each case a PVdF-HFP copolymer is used, having a proportion of HFP >8% by weight. It appears to be very likely that in future battery systems, such as consumer or stationary applications, systems will be developed which are not based on intercalation like the established Lithium/Ion technology. A promising battery technology, which is in development, is the Lithium/Air or Lithium/Oxygen system which makes use of a conversion process instead of an intercalation process. Lithium/Air battery cells contain a metallic lithium anode and an oxygen electrode and can therefore realize a high specific energy cell level. A system 10 with a metallic lithium anode and an oxygen electrode is described in the aforementioned U.S. Pat. No. 5,510,209.
In 2012 a review on common challenges for Lithium/Air technology was published by Jake Christensen et al. in Journal of the Electrochemical Society, 15 159 (2) R1-R30 (2012).
The state of the art in electrode processing is electrode binders such as polyvinylidene difluoride (PVdF) or polyvinylidene difluoride-co-hexafluoropropylene (PVdF-HFP). Such polymer binders provide good adhesion between microscopic particles; however, they establish electrical insulators. This in turn means that the composite electrode with PVdF shows a decreased loading capacity. Polymer electrode binder such as PVdF-HFP are well described in literature as briefly discussed in EP 1 261 048 81.
Electrode binders such as PVdF establish electrical insulators and even a few mass-% in the electrode composite decreases the loading capacity considerably. If in battery cell designing using electrode insulator is disclaimed, one can only achieve very low loading such as 100 nm-1000 nm. With such low loadings of active material, battery cells cannot be commercialized because of the disadvantageous ratio between active and passive materials, not to name but a few, such as collector foil electrolyte and separator. For Lithium/Air technology, the level of carbon loading on the cathode (oxygen electrode) is limited to ca. 1000 nm. Above this thickness, the carbon films become unstable and show poor adhesion between the carbon particles and between carbon electrode and metallic collector foil.
An object of this present disclosure is to increase the loading capacity of an electrode of an electrode assembly for a Lithium/Air battery cell.
A still further object of the present disclosure is to increase the ratio between active and passive materials of a battery cell, particularly a Lithium/Air battery cell.
According to the present disclosure, an electrochemical component, particularly a coating for an electrode of an electrode assembly of a Lithium/Air battery cell, is provided, wherein said electrode is provided with a layer of disperse graphite and carbon black.
Surprisingly, an electrode composite of disperse graphite and carbon black allows to apply a higher loading capacity of this mixture as compared to pure carbon black material. The loading capacity of the disperse graphite/carbon black blend allows to form films or layers up to a thickness of about 10,000 nm (≅10 μm) without using an electrode binder. The fact that the disperse graphite does not constitute an electrical insulator results in a higher loading capacity in [mAh/g] for the battery cell and thus results in an increased battery cell power behavior. Still further, the ratio between active and passive materials has been shifted according to the present disclosure to realize a high energy Lithium/Air battery cell. According to the present disclosure, said electrode is a cathode of said electrode assembly (oxygen electrode).
Said electrochemical component according to the present disclosure has a thickness between 1000 nm (μm) up to 10,000 nm (10 μm), which exceeds current thicknesses of film layers applied, which are in the range between 100 nm and 1000 nm, which results in a very low loading capacity. With such low loadings on active materials, battery cells cannot be commercialized since the ratio between active material and passive material such as collector foil, electrolyte or separator is too disadvantageous.
In an alternative embodiment according to the present disclosure, the electrical component, i.e. said layer can be made in a thickness which exceeds 10,000 nm (10 μm) and in this case contains an electrode binder such as polyvinylidene difluoride (PVdF) or polyvinylidene difluoride-co-hexafluoropropylene (PVdF-HFP).
In one embodiment of the present disclosure, said electrochemical component is made as a layer comprising 90 wt.-% carbon black, e.g. Super P or Super C, Timcal, Belgium, and 10 wt.-% disperse graphite, e.g. MeMB (6-28), GFG5, 10 reduced graphene oxide or Timcal KS6L. In a further very advantageous embodiment of the present disclosure, said layer contains 80 wt.-% carbon black, e.g. Super P or Super C, Timcal, Belgium, and 20 wt.-% disperse graphite, e.g. MeMB (6-28), GFG5, reduced graphene oxide or Timcal KS6L.
The present disclosure is related to a method for producing an electrochemical component. In a first method step, a suspension is produced containing carbon black and disperse graphite. In a second method step, said suspension is sprayed by means of an airbrush on a coating grid. In a resulting method step, a stable layer is obtained having a thickness up to 10,000 nm (≅10 μm).
By means of said method, a suspension can be produced which contains 90 wt.-% carbon black and 10 wt.-% disperse graphite. In an alternative, a suspension can be produced containing 80 wt.-% carbon black and 20 wt.-% disperse graphite.
According to the method provided by the present disclosure, said suspension is sprayed on a coating grid, for instance a nickel mesh.
Said electrochemical component according to the present disclosure is used in an electrode assembly of a Lithium/Air battery cell of a battery module in a Hybrid Electrical Vehicle (HEV), a Plug-in Hybrid Electric Vehicle (PHEV) or an Electric Vehicle (EV).
By means of the present disclosure in Lithium/Air battery technology, the level of carbon-loading on the electrode assembly, particularly on the cathode (oxygen electrode) is increased since the thickness of the electrochemical component, the layer of disperse graphite and carbon black, exceeds the thickness of the layer according to prior art solutions by the factor 10. By means of the present disclosure, the disadvantage, according to which a carbon film of pure carbon becoming unstable, further showing poor adhesion between the carbon electrode and a metallic collector foil is eliminated. The thickness of the electrochemical component according to the present disclosure is between 1000 nm (1 μm) and 10,000 nm (10 μm). Due to this thickness range of the electrochemical component according to the present disclosure, no binding agent, particularly no electrode binder such as polyvinylidene difluoride (PVdF) or polyvinylidene difluoride-co-hexafluoropropylene (PVdF-HFP), is necessary in this range of thickness. Thus, in a thickness range of the electrochemical component according to the present disclosure between 1000 nm (1 μm) and 10,000 nm (10 μm) no binder is present, which otherwise may have electrical insulation properties, i.e. due to the absence of the polymer binders the composite electrodes according to the present disclosure show an increased loading capacity. The fact that the blend, according to the present disclosure, of disperse graphite and carbon black and the fact that the graphite in this blend is not an electrical insulator leads to a higher loading capacity in mAh for the battery cell and an increased cell power. According to the present disclosure, the ratio between active and passive materials is shifted to realize a high energy Lithium/Air battery cell.
According to the present disclosure, higher thicknesses of the electrochemical component can be reached as well. In case the thickness of the electrochemical component exceeds 10,000 nm (10 μm), an electrode binding agent such as polyvinylidene difluoride (PVdF) or polyvinylidene difluoride-co-hexafluoropropylene (PVdF-HFP) is used. Due to the binding material, higher thicknesses of the electrochemical component can be obtained. Even though an electrode binder such as polyvinylidene difluoride (PVdF) is present, the blend of disperse graphite and carbon black according to the present disclosure shows advantages. Due to the low specific surface of the disperse graphite compared to carbon black, less electrode binding agent is required for obtaining a similar electrode adhesion behavior. Therefore, a disperse graphite/carbon black electrode can be prepared using a lower amount of electrode binding agent, having insulating properties. When compared with electrode assemblies according to the prior art, using the present disclosure a higher specific energy Lithium/Air battery cell can be obtained.
According to the present disclosure and given the higher thickness of the electrochemical component, i.e. the thickness of the layer between 1000 nm (1 μm) and 10,000 nm (10 μm), the ratio between active material and passive materials, such as collector foil, electrolyte and separator, used in a battery cell is shifted advantageously to the active material, allowing a commercialization of the Lithium/Air battery cell system.
The electrochemical component according to the present disclosure is produced by airbrush coating. Airbrush coating allows for an easy manufacturing and is a reliable process for industrial application.
The present disclosure will be described further using the drawings, in which
In
Said Lithium/Air battery cells are used for battery modules, which in turn are assembled in battery packs for secondary batteries, i.e. said high voltage batteries as a power source for the electrical drives of a Hybrid Electrical Vehicle (HEV), a Plug-in Hybrid Electric Vehicle (PHEV) or an Electric Vehicle (EV).
In
A second constant current discharge voltage profile 16 was obtained for a second material for the electrode composite, i.e. the electrochemical component according to the present disclosure being a suspension 54 of 90 wt.-% Super P (Timcal Belgium) and 10 wt.-% MCMB (6-28), GFG5, KS6L or reduced graphene oxide. The second constant current discharge voltage profile 16 is characterized by an enhanced loading capacity 10 of about 2000 mAh/g. A turning point 22 of said second constant current discharge voltage profile 16 being characterized by a voltage of about 2.6 V and a loading capacity of 2100 mAh/g. As can be derived from
Comparing said constant current discharge voltage profiles 14, 16, 18 according to
From
For higher film thicknesses 64 of the electrochemical component according to the present disclosure, an electrode binder such as polyvinylidene difluoride (PVdF), e.g. Kynar 2801, Arkema, France, is added to the respective suspensions 54. In this case, a suspension 54 of disperse graphite, carbon black and the electrode binder is used. For higher film thicknesses 64, i.e. exceeding 10,000 nm (10 μm) and even more, the addition of electrode binder still has advantages. Due to the low specific surface of disperse graphite as compared to carbon black, a mixture of these materials requires less electrode binding agent for obtaining a similar electrode adhesion. Therefore, a disperse graphite/carbon black mixture for use as an electrochemical component on an electrode of an electrode assembly can be prepared with less insulating electrode binder, i.e. less polyvinylidene difluoride (PVdF) or polyvinylidene difluoride-co-hexafluoropropylene (PVdF-HFP), thus further decreasing electrical insulating properties. That means that a higher specific energy of the Lithium/Air-battery cell according to the present disclosure is obtained.
When using the present disclosure, a state of the art electrode processing is optimized. Due to the fact that a higher film thickness 64 of the electrochemical component, i.e. said layer 62 to be applied to one of the electrodes of said electrode assembly, is obtained by an industrial process as airbrush coating 50, as shown in
Even higher film thicknesses 64 of the electrochemical component, i.e. said layer 62, obtained of the suspensions 54 are feasible. The blend of dispersed graphite with carbon black has excellent adhesion properties to the electrode material, not requiring a polymer binding agent in the thickness range between 1000 nm (1 μm) and 10,000 nm (10 μm). For higher film thicknesses 64, however, a binder such as polyvinylidene difluoride (PVdF), e.g. Kynar 2801, Arkema, France, may be added to the suspension 54, which requires an even higher loading capacity of the electrochemical component, i.e. said film or layer 62 obtained from the dried suspension 54. In the thickness range exceeding 10,000 nm (10 μm), the binding agent does not even affect the loading capacity due to its insulating property due to the low specific surface of graphite as compared to carbon black in the blend according to the present disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 14159484.6 | Mar 2014 | EP | regional |
