ELECTRODES INCLUDING MATERIALS WITH POSITIVE TEMPERATURE COEFFICIENT (PTC)

Abstract

An electrode for a battery cell includes a current collector and an active material layer disposed on the current collector. In some examples, the active material layer includes an active material, a conductive additive, a positive temperature coefficient (PTC) material, and a binder. In other examples, the active material layer comprises active material with an outer coating of PTC material. In other examples, a PTC layer is disposed on the active material layer.

Description

INITIATIONThe information included in this section serves to generally illustrate the context of the disclosure. Work of the present inventors, insofar as they are described in this section, as well as aspects of the description that otherwise do not apply as the prior art at the time of application, are neither expressly nor silently admitted as prior art against the present disclosure.The present disclosure relates to battery cells, and more particularly to electrodes and methods for making electrodes for battery cells.Electric vehicles (EVs), such as battery-powered electric vehicles (BEVs), hybrid vehicles, and / or fuel cell vehicles, include one or more electric machines and a battery system having one or more battery cells, modules, and / or packs. A power control system is used to control the charging and / or discharging operation of the battery system during the charging operation and / or the trip.Battery cells include cathode electrodes, anode electrodes, and separators. The cathode electrodes comprise a layer of cathodic active material disposed on a cathode current collector. The anode electrodes include a layer of anodic active material disposed on an anode current collector.SUMMARYAn electrode for a battery cell includes a current collector and an active material layer disposed on the current collector. The active material layer includes an active material, a conductive additive, a positive temperature coefficient (PTC) material, and a binder.In other cases, the active material is in a range of 80 wt% to 99 wt%, the PTC material is in a range of 0.5 wt% to 20 wt%, the conductive additive is in a range of 0.5 wt% to 20 wt%, and the binder is in a range of 0.5 wt% to 10 wt%. The active material is in a range of 80 wt.% to 99 wt.%, the PTC material is in a range of 1 wt.% to 5 wt.%, the conductive additive is in a range of 0.5 wt.% to 20 wt.%, and the binder is in a range of 0.5 wt.% to 10 wt.%.In other cases, the PTC material has a Curie temperature in the range of 80° C. to 200° C. The PTC material has a Curie temperature in a range from 80° C. to 140° C.In other cases, the PTC material includes an inorganic material selected from a group consisting of metal oxide, BaTiO 3, V 2 O 5 and combinations thereof. The PTC material includes an organic material selected from a group consisting of polymethyl methacrylate (PMMA) or polydimethylsiloxane (PDMS).In other cases, the PTC material is doped with one or more elements selected from the group consisting of lanthanum (La), cerium (Ce), antimony (Sb), yttrium (Y), tungsten (W), titanium (Ti), tantalum (Ta), niobium (Nb), cobalt (Co), chlorine (Cl), iodine (I), bromine (Br), and combinations thereof.An electrode for a battery cell includes a current collector and an active material layer disposed on the current collector. The active material layer includes an active material having an outer coating layer comprising a positive temperature coefficient (PTC) material, a conductive additive, and a binder.In other cases, the PTC material has a Curie temperature in the range of 80° C. to 200° C. The PTC material has a Curie temperature in a range from 80° C. to 140° C. The PTC material includes an inorganic material selected from a group consisting of metal oxide, BaTiO 3, V 2 O 5 and combinations thereof. The PTC material includes an organic material selected from a group consisting of polymethyl methacrylate (PMMA) or polydimethylsiloxane (PDMS). The outer coating layer has a thickness in a range of 50 nm to 2 μm. The outer coating layer has a thickness in the range of 200 nm to 500 nm.An electrode for a battery cell includes a current collector and an active material layer disposed on the current collector. The active material layer includes an active material, a conductive additive, and a binder. A positive temperature coefficient (PTC) layer is disposed on the active material layer and includes a PTC material.In other cases, the PTC material has a Curie temperature in the range of 80° C. to 200° C. The PTC material has a Curie temperature in a range from 80° C. to 140° C.The PTC material includes an inorganic material selected from a group consisting of metal oxide, BaTiO 3, V 2 O 5 and combinations thereof. The PTC material includes an organic material selected from a group consisting of polymethyl methacrylate (PMMA) or polydimethylsiloxane (PDMS).Further areas of applicability of the present disclosure will become apparent from the detailed description, claims and drawings. The detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure.BRIEF DESCRIPTION OF THE DRAWINGSThe present disclosure will be better understood from the detailed description and the accompanying drawings, in which: FIG. 1 is a side cross-sectional view of a battery cell having anode and cathode electrodes and separators in accordance with the present disclosure; FIG. 2 is a side cross-sectional view of a cathode electrode with a PTC-coated cathodic active material in accordance with the present disclosure; FIG. 3 is a side cross-sectional view of an anode electrode with a PTC-coated anodic active material according to the present disclosure; FIG. 4 is a side cross-sectional view of an active material particle with a PTC coating in accordance with the present disclosure; FIG. 5 is a side cross-sectional view of a cathode electrode having a layer of cathodic active material including PTC material in accordance with the present disclosure; FIG. 6 is a side cross-sectional view of an anode electrode having an anodic active material layer containing PTC material in accordance with the present disclosure; FIG. 7 is a side cross-sectional view of a cathode electrode with a PTC layer according to the present disclosure; FIG. 8 is a side cross-sectional view of an anode electrode with a PTC layer according to the present disclosure; FIGS. 9A through 9D are flowcharts of the method of manufacturing an electrode having an active material layer containing PTC material according to the present disclosure; FIG. 10A is a plot of heat flux versus temperature for battery cells with and without PTC material according to the present disclosure; FIGS. 10B and 10C are diagrams showing the results of a formation cycle and C-rate test for battery cells with and without PTC material according to the present disclosure.In the drawings, reference numerals may be used repeatedly to identify similar and / or identical elements.DETAILED DESCRIPTIONAlthough the battery cells according to the present disclosure are described in the context of vehicles, the battery cells may also be used in other applications, e.g., in stationary applications.In battery cells, a rapid temperature rise may occur when triggered by objects penetrating a housing of the battery cell (e.g., a nail or other sharp object), spread of heat, and / or short circuits. The rapid temperature rise can lead to shrinkage of the separator, melting and also to short circuits. As can be seen, the reduction in heat generation due to short circuits can serve to prevent thermal runaway.The present disclosure relates to electrodes including a positive temperature coefficient (PTC) material, the resistance of which increases significantly at a Curie temperature in response to an increased temperature of the battery cell. The PTC material may be used, for example, as a coating on active material particles, such as PTC particles mixed with the active material layer, and / or in a PTC layer between the active material layer and an adjacent separation layer.As can be seen, the resistance of the PTC material increases significantly as the temperature of the battery cell increases above the Curie temperature. The PTC material may include, for example, BaTiO 3 which has up to about 100° C. a resistance of -10 1 ohms, which then rapidly increases to -10 5 ohms at 175° C. In some examples, the Curie temperature of the PTC material is adjusted or lowered to a temperature that is below the melting temperature of the separator (e.g., less than 150° C.) by doping or using an additive.In some examples, the resistance of the PTC material increases so much in response to the increased temperature that an effective open circuit is formed. As the cell temperature rises above the Curie temperature of the PTC material, the resistance of the battery cell rises rapidly. The increased resistance reduces the current flow to prevent a further temperature rise and / or suppresses or prevents short circuits.Referring to FIG. 1, a battery cell 10 includes C cathode electrodes 20, A anode electrodes 40, and S separators 32 arranged in a predetermined order in a battery cell stack 12, where C, S, and A are integers greater than zero. The battery cell stack 12 is disposed in a case 50. The C cathode electrodes 20-1, 20-2,..., and 20-C include layers 24 of cathodic active material disposed on one or both sides of a cathode current collector 26.In some examples, the A anode electrodes 40 and the C cathode electrodes 20 exchange lithium ions during charging / discharging. The A anode electrodes 40-1, 40-2,..., and 40-A include layers 42 of anodic active material disposed on one or both sides of the anode current collectors 46. In some examples, the layers 24 of cathodic active material and / or the layers of anodic active material comprise a coating or self-supporting film with one or more active materials, one or more conductive additives, and / or one or more binder materials cast or laminated to the current collectors. The cathode electrodes and / or the anode electrodes include a positive temperature coefficient (PTC) material as described further below.In some examples, the cathode current collector 26 and / or the anode current collector 46 include metal foil, metal mesh, perforated metal, three-dimensional (3D) metal foam, and / or expanded metal. In some examples, the current collectors are made of one or more materials selected from the group consisting of copper, stainless steel, brass, bronze, zinc, aluminum, and / or alloys thereof. The outer tabs 28 and 48 are connected to the current collectors of the cathode and anode electrodes, respectively, and may be disposed on the same side or on different sides of the battery cell stack 12. The outer tabs 28 and 48 are connected to the poles of the battery cells.Referring now to FIGS. 2 and 3, examples of cathode and anode electrodes are shown. In Fig. 2, the cathode electrode 20 is shown in more detail. The cathodic active material layer 24 of the cathode electrode 20 includes a cathodic active material 62 coated with a PTC material as shown in Figure 4, an optional conductive additive 64, and an optional binder 66.In FIG. 3, the anode electrode 40 is shown in more detail. The anodic active material layer 42 of the anode electrode 40 includes an anodic active material 72 coated with a PTC material as shown in FIG. 4, an optional conductive additive 64, and an optional binder 66.Referring now to FIG. 4, a particle 80 of the active material for a cathode or anode electrode is shown coated with a PTC coating 84. In some examples, the PTC coating 84 interrupts the electronic paths to the active material 80 at high temperatures in the range of 80° C. to 200° C. In some examples, the PTC coating 84 interrupts the electronic paths to the active material 80 at high temperatures in the range of 80° C. to 140° C. In some examples, the thickness of the PTC coating is in a range of 50 nm to 2 μm. In some examples, the thickness of the PTC coating is in the range of 200 nm to 500 nm.Referring now to FIGS. 5 and 6, the cathode electrodes and / or anode electrodes may include PTC material mixed with other materials in the active material layer. In Figure 5, the cathode electrode 20 includes the layer 24 of cathodic active material mixed with PTC particles 90.In FIG. 6, the anode electrode 40 includes the layer 42 of anodic active material mixed with PTC particles 94. The PTC particles 90 and 94 act as a conductive filler at lower temperatures when the temperature of the battery cell is below the Curie temperature (e.g., 120° C.). As the temperature of the battery cell rises above the Curie temperature, the PTC material 90 and 94 acts as an electron blocker (due to the increased resistance) to shut down the battery cell and prevent further thermal problems. In some examples, the PTC particles 90 and 94 comprise 0.5 to 20 wt % of the active material layer. In some examples, the PTC particles comprise 1 to 5 wt % of the active material layer.Referring now to FIGS. 7 and 8, a PTC layer may be used. In FIG. 7, the cathode electrode 20 includes a PTC layer 110 disposed between the layer 24 of cathodic active material and an adjacent separator. In FIG. 8, the anode electrode includes a PTC layer 114. The PTC layers 110 and / or 114 have a significantly increased resistance at elevated temperatures in order to reduce or prevent short circuits. As can be appreciated, the cathode and / or anode electrodes may include various combinations of the PTC material (e.g., the PTC coating of the active material, PTC particles in the active material, and / or the PTC layer between the active material and the adjacent separator).Referring now to Figure 9A, a method of making an electrode having an active material layer containing PTC particles is shown. At 320, a slurry of active material, binder, and conductive filler is mixed with PTC particles. At 324, the mixture is printed or cast onto a current collector. The mixture is printed with, for example, a gravure printing machine or cast with a casting machine.In FIG. 9B, a method for forming a PTC coating is shown. The method includes dissolving a PTC precursor in a solution (e.g., solvent-based or aqueous) containing active material particles at 330. The solution is heated at 334 for a predetermined time and then cooled. The solid particles are filtered at 338 and optionally rinsed. The particles are calcined at a predetermined temperature (e.g., 500° C. to 1000° C.) for a predetermined period of time at 342.In FIG. 9C, a method of coating a PTC layer on an electrode active material layer is shown. The method includes mixing a slurry with a PTC material and a binder at 350. The mixture is printed or cast onto an active material layer of the electrode at 354. For example, a gravure printing machine or a casting machine may be used.In Fig. 9D, another method of coating a PTC layer on active material particles is shown. The active material and the PTC material are mixed at 360 and placed in a mechanical melting machine. The mechanical melting machine mechanically presses the PTC material into the active material, creating a coated active material at 364.In some examples, the electrode active material layer includes the active material in a range of 80 wt % to 99 wt %, the PTC material in a range of 0.5 wt % to 20 wt % (e.g., 1 wt % to 5 wt %), the conductive filler in a range of 0.5 wt % to 20 wt %, and the binder in a range of 0.5 wt % to 10 wt %. In some examples, the stress on the electrode is in a range of 2 mAh / cm 2 to 10 mAh / cm 2. In some examples, the stress on the electrode is in a range of 3 mAh / cm 2 to 6 mAh / cm 2.In some examples, the PTC material includes an inorganic material selected from a group consisting of metal oxide, BaTiO 3, V 2 O 5 and combinations thereof. In some examples, the PTC material further includes a dopant and / or additive for adjusting the Curie temperature. The PTC material may include, for example, BaTiO 3 with a dopant (e.g., lanthanum (La), cerium (Ce), antimony (Sb), yttrium (Y), tungsten (W), titanium (Ti), tantalum (Ta), niobium (Nb), cobalt (Co), chlorine (Cl), iodine (I), bromine (Br)), and / or an additive (e.g., SiO 2, Al 2 O 3). In some examples, the PTC material includes an organic material selected from a group consisting of polymethylmethacrylate (PMMA) or polydimethylsiloxane (PDMS). In some examples, the doping and / or additive is used to lower the Curie temperature of the PTC material below 150° C.In some examples, the Curie temperature of the PTC material is in a range from 80° C. to 200° C. In some examples, the Curie temperature of the PTC material is less than 150° C. In some examples, the Curie temperature of the PTC material is in a range from 80° C. to 140° C.In some examples, the cathodic active material is selected from a group consisting of lithium nickel cobalt manganese (NCM), lithium nickel cobalt manganese aluminum (NCMA), lithium nickel cobalt aluminum oxide (NCA), lithium nickel manganese aluminum (NMA), nickel metal (NM), lithium nickel oxide (LNO), lithium iron phosphate (LFP), lithium manganese iron phosphate (MFMP), lithium cobalt oxide (LCO), and combinations thereof. In some examples, the morphology includes primary and secondary Ni-rich cathodes of the mono-sized particle type or of the bimodal type. In some examples, D50is in a range from 1 μm to 20 μm. In some examples, the primary type is in a range of 3 μm to 6 μm and the secondary type is in a range of 3 μm to 15 μm.In some examples, the anodic active material is selected from a group consisting of graphite, hard carbon, lithium silicon oxide (LSO), silicon (Si), and silicon oxide (SiO x). In some examples, the morphology of the Si-based material includes nanoparticles, nanofibers, nanotubes, and microparticles. In some examples, the conductive filler is selected from a group consisting of graphite, graphene, carbon black, graphene oxide, Super P, acetylene black, carbon nanofibers, carbon nanotubes, and combinations thereof.In some examples, the binder is selected from a group consisting of polyvinylidene difluoride (PVDF), polytetrafluoroethylene (PTFE), CMS, styrene-butadiene rubber (SBR), polyacrylic acid (PAA), PAA-PHEA, and combinations thereof. In some examples, the PAA is neutralized by sodium hydroxide (NaOH) or lithium hydroxide (LiOH), sodium polyacrylate (PAANa), PAAH 0.2 N 0.8 or lithium polyacrylic acid (LiPAA).Referring to FIG. 10A, a plot shows heat flux versus temperature for a battery cell having a cathode electrode containing the PTC material compared to the same battery cell without the PTC material. In this example, the cathodic active material includes NCMA and the anodic active material includes graphite. The layer of cathodic active material includes the cathodic active material (e.g., NCMA), PTC material, conductive additive (e.g., Super P), and binder (e.g., PVDF) at a ratio of 86 / 10 / 2 / 2 wt % (or 96 / 2 / 2 when no PTC material is used). The peak strength occurs at -220 °C and decreases from ∼15 W / g to ∼5 W / g.Referring to FIGS. 10B and 10C, a test of the formation cycle and the capacity rate of battery cells with and without PTC material is shown. The tests illustrate a comparable performance of the battery cells with and without PTC material. In FIG. 10C, a portion of the active material has been replaced with the PTC material that has a higher conductivity and provides better performance at some charging speeds (e.g., 2C) and comparable performance at other charging speeds.The foregoing description is for illustrative purposes only and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure may be practiced in a variety of forms. Therefore, while this disclosure includes specific examples, the true scope of the disclosure should not be so limited as other modifications will become apparent upon examination of the drawings, the specification, and the following claims. It should be understood that one or more steps within a method may be performed in different orders (or concurrently) without altering the principles of the present disclosure. Although each of the above-described embodiments has particular features, one or more of these features described with respect to any embodiment of the disclosure may be implemented in and / or combined with features of any other embodiments, even if this combination is not expressly described. In other words, the described embodiments are not mutually exclusive, and permutations of one or more embodiments with one another remain within the scope of this disclosure.Spatial and functional relationships between elements (e.g., between modules, circuit elements, semiconductor layers, etc.) are described with various terms including "connected," "engaged," "coupled," "adjacent," "next to," "top on," "over," "under," and "arranged.". Where a relationship between first and second elements is not expressly described as "direct" in the above disclosure, this relationship may be a direct relationship in which no other intervening elements are present between the first and second elements, but also an indirect relationship in which one or more intervening elements are present (either spatially or functionally) between the first and second elements. As used herein, the term "A, B, and / or C" should be construed as being logical (A ORed with B ORed with C) using a non-exclusive logical OR operation and should not be understood as "at least one of A, at least one of B, and at least one of C.".In the figures, the direction of an arrow as indicated by the arrow head generally illustrates the flow of information (e.g., data or instructions) of interest for the illustration. For example, if element A and element B exchange a variety of information, but the information transmitted from element A to element B is relevant for illustration, the arrow may point from element A to element B. This unidirectional arrow does not mean that no other information is transmitted from element B to element A. Further, for information sent from element A to element B, element B may send requests for or acknowledgments for the information to element A.

Claims

An electrode for a battery cell, comprising: a current collector; and an active material layer disposed on the current collector, comprising: an active material; a conductive additive; a positive temperature coefficient (PTC) material; and a binder.The electrode of claim 1, wherein the active material is in a range of 80 wt% to 99 wt%, the PTC material is in a range of 0.5 wt% to 20 wt%, the conductive additive is in a range of 0.5 wt% to 20 wt%, and the binder is in a range of 0.5 wt% to 10 wt%.The electrode of claim 1, wherein the active material is in a range of 80 wt% to 99 wt%, the PTC material is in a range of 1 wt% to 5 wt%, the conductive additive is in a range of 0.5 wt% to 20 wt%, and the binder is in a range of 0.5 wt% to 10 wt%.The electrode of claim 1, wherein the PTC material has a Curie temperature in the range of 80°C to 200°C.The electrode of claim 1, wherein the PTC material has a Curie temperature in the range of 80°C to 140°C.The electrode of claim 1, wherein the PTC material includes an inorganic material selected from a group consisting of metal oxide, BaTiO 3, V 2 O 5 and combinations thereof.The electrode of claim 1, wherein the PTC material includes an organic material selected from a group consisting of polymethyl methacrylate (PMMA) or polydimethylsiloxane (PDMS).The electrode of claim 1, wherein the PTC material is doped with one or more elements selected from a group consisting of lanthanum (La), cerium (Ce), antimony (Sb), yttrium (Y), tungsten (W), titanium (Ti), tantalum (Ta), niobium (Nb), cobalt (Co), chlorine (Cl), iodine (I), bromine (Br), and combinations thereof.An electrode for a battery cell, comprising: a current collector; and an active material layer disposed on the current collector, comprising: an active material having an outer coating layer comprising a positive temperature coefficient (PTC) material; a conductive additive; and a binder.The electrode of claim 9, wherein the PTC material has a Curie temperature in the range of 80°C to 200°C.

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