SEPARATORS COATED WITH ENDOTHERMAL PHASE-CHANGE MATERIAL FOR BATTERIES

Abstract

A battery component is provided. The battery component may include a separator comprising a porous substrate, a ceramic coating on a surface of the porous substrate, and solid, non-encapsulated endothermic phase-change material particles on or in the ceramic coating, configured to melt upon reaching a phase transition temperature and fill pores in the surface.

Description

FIELD OF TECHNOLOGYThe present disclosure relates to phase change material coatings for separators in lithium ion batteries.GENERAL STATE OF THE ARTLithium ion batteries have been used for energy storage in portable electronics, large scale smart grids, and electric vehicles. A lithium ion battery consists of three major functional components, namely the anode or negative electrode, the cathode or positive electrode and the electrolyte. Typically, a separator is placed between the negative electrode and the positive electrode to prevent physical contact and thus electrical short circuit of the two electrodes while receiving electrolyte and allowing ion transport between the electrodes. Generally, the separator is not directly involved in a chemical reaction in the battery, but plays a role in determining battery performance, including lifetime, energy density, and power density, by affecting the kinetics of the battery cell. A separator should be chemically, mechanically, and electrochemically stable in the highly reactive environment within the battery during operation.SUMMARYAccording to one embodiment, a battery component is provided that includes a separator. The separator includes a porous substrate, a ceramic coating on a surface of the porous substrate, and solid unencapsulated endothermic phase change material particles on or within the ceramic coating. The solid unencapsulated endothermic phase change materials are configured to melt when a phase transition temperature is reached and fill pores in the surface of the porous substrate.In an alternative embodiment, a battery cell is provided that includes positive and negative electrodes, a separator disposed between the electrodes, and an electrolyte that saturates the separator and contacts the electrodes. The separator includes a porous substrate, a ceramic coating on opposite sides of the porous substrate, and solid unencapsulated endothermic phase change material particles on or within the ceramic coating. The solid unencapsulated endothermic phase change material particles are configured to melt when a phase transition temperature is reached, fill pores on the sides of the porous substrate, and prevent ion transport between the electrodes.In yet another embodiment, a battery cell is provided that includes positive and negative electrodes, a separator disposed between the electrodes, and electrolytes that saturate the separator and are in contact with the electrodes. The separator includes a porous substrate and solid unencapsulated endothermic phase change material particles. The solid unencapsulated endothermic phase change material particles are configured to melt when a phase transition temperature is reached, fill pores on the porous substrate, and prevent ion transport between the electrodes.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1A is a schematic illustration of a separator according to an embodiment. FIG. 1B is a schematic illustration of a separator according to another embodiment. FIG. 2A is a schematic illustration of a separator according to an alternative embodiment. FIG. 2B is a schematic illustration of a separator according to yet another embodiment. FIG. 3 is a schematic illustration of the separator of FIG. 1B after the phase change material has undergone a phase change. FIG. 4 is a cross-sectional view of a battery device including an example separator.DETAILED DESCRIPTIONEmbodiments are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments may take various and alternative forms. The figures are not necessarily to scale. Some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art.Various features illustrated and described with respect to any of the figures may be combined with features illustrated in one or more other figures to produce embodiments that are not expressly illustrated or described. The illustrated combinations of features provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of this disclosure may be desirable for specific applications or implementations.Lithium ion batteries include electrodes, an electrolyte, and separators. Separators physically separate positive and negative electrodes to prevent internal shorts. Separators may include polyolefin-based porous films. The typical thickness of a polyolefin-based porous film is between 5 and 30 μm.Separators may also provide a function called shutdown to prevent thermal runaway. Thermal runaway is a self-sustaining increase in temperature within a battery cell that results in chemical reactions that generate heat. This may occur when the battery is exposed to conditions that cause it to overheat, including overcharge, short circuit, or exposure to high temperatures. The thermal runaway may cause the electrolyte to collapse and release gases and / or degrade internal components.As the battery cell temperature approaches the melting point of a separator, commonly referred to as a shutdown temperature, the separator pores close and block the migration of lithium ions between electrodes, thereby preventing further electrochemical operation, which in turn prevents battery cell temperature from increasing and thermal runaway.Conventional separators can be made by mixing high density polyethylene ("HDPE") and ultra high molecular weight polyethylene ("UHMWPE") for mechanical strength and thermal stability. The use of UHMWPE raises the shutdown temperature, which is typically above 140°C due to the increased molecular weight and high crystallinity. A lower shutdown temperature, such as 130° C. or less, could speed the shutdown. A separator made using a resin having a lower crystallinity and a lower melting point can lower the shutdown temperature by lowering the melting point of the separator. However, this may affect the mechanical strength of the porous film.A phase change material ("PCM") is a material that releases or absorbs energy during and during the phase transition that can be used to provide useful heating or cooling properties. Generally, the transition from one of the first two basic states of the matter, solid and liquid, occurs. A PCM may be applied to a battery separator to further control the shutdown temperature of the battery cell.According to an embodiment of the present disclosure, the heat absorbing or endothermic PCM is coated on a porous separator film. The PCM may have a melting point of about 130° C. or less. Upon heating caused by a short-circuit, overcharge, or other over-heat generating event, the PCM approaches its phase transition temperature. During the phase change, the PCM endothermically absorbs heat and melts, changing from the solid state to the liquid state or to a highly viscous state. The liquid or highly viscous state of the PCM allows the material to fill and close the separator pores. The liquid or high viscosity material filling the pores increases the resistance of the separator and can ultimately result in thermal shutdown by interrupting lithium ion transport.Thus, the PCM coating may perform two functions: an additional and more efficient shutdown layer than melting the porous film by allowing the cell to shut down at a lower temperature without compromising the mechanical properties of the porous film, and endothermic heat absorption, thereby cooling hot spots and affecting heat control in the battery cell.In one example, PCM may be coated on a single side of a separator. In another example, PCM may be coated on both sides of a separator. PCM may include a hydrocarbon, such as polyolefins, paraffins, or a combination thereof. PCM may include a polymer such as polyolefins, fluoropolymers, polyethylene oxides, acrylics, or a combination thereof. PCM may also include ionic liquids. PCM may be selected from a single or a combination of these materials. Depending on the material selected, the melting point of the PCM is in the range of about 90 to 150° C., and preferably between about 110 and 130° C. PCM particles may have a D50of about 0.1 to 2 μm. The PCM coating may have a thickness of about 0.5 to 10 μm.The separator may include a ceramic coating layer. The ceramic coating layer may affect the thermal stability, mechanical stability, and electrolyte wettability of the separator. The ceramic particles may include alumina, boehmite, silica, or a combination thereof. The average ceramic particle size may be between about 0.1 and 2 μm, and preferably between 0.2 and 1 μm.In one example, the PCM is coated on the surface of the ceramic coating layer. The PCM may be coated on one or opposite sides of the separator. In another example, PCM may be embedded in the ceramic coating layer. The PCM may be embedded in one or opposite sides of the separator.A binder material may be used to hold ceramic particles, PCM particles, or both together and to the porous film. The binders include acrylic, carboxymethylcellulose, methylcellulose, styrene-butadiene rubber, polyvinyl alcohol, polyvinyl pyrrolidone, fluoropolymers, polyurethane, polyacrylamide, curable monomers, or a combination thereof.FIG. 1A schematically illustrates an example separator 10 according to an embodiment. The separator 10 includes a porous substrate 12, a ceramic coating 14 on a surface of the porous substrate 12, and solid unencapsulated endothermic PCM particles 16 on the ceramic coating 14. the ceramic coating 14 may include ceramic particles including alumina, boehmite, silica, or a combination thereof having a D50of about 0.1 to 2 μm. PCM particles 16 may be a hydrocarbon including polyolefins, paraffins, or a combination thereof. PCM particles 16 may also be a polymer including polyolefins, fluoropolymers, polyethylene oxides, acrylics, or a combination thereof. PCM particles 16 may also be ionic liquids.In a variation illustrated in FIG. 1B, the separator 10 may include solid, non-encapsulated endothermic PCM particles 16 on the ceramic coating 14 on opposite sides of the porous substrate 12. In any variation, the PCM particles 16 may have a D50of about 0.1 to 2 μm and a phase transition temperature or melting point of about 90 to 150° C., but preferably in the range of 110 to 130° C. The PCM particles 16 may form a layer on the ceramic coating 14 having a thickness of about 0.5 to 10 μm.FIG. 2A schematically illustrates an example separator 20 according to another embodiment. The separator 20 includes a porous substrate 22, a ceramic coating 24 on a surface of the porous substrate 22, and solid unencapsulated endothermic PCM particles 26 embedded in the ceramic coating 24. the ceramic coating 24 may include ceramic particles including alumina, boehmite, silica, or a combination thereof having a D50of about 0.1 to 2 μm. PCM particles 26 may be a hydrocarbon including polyolefins, paraffins, or a combination thereof. PCM particles 26 may also be a polymer including polyolefins, fluoropolymers, polyethylene oxides, acrylics, or a combination thereof. PCM particles 26 may also be ionic liquids.In a variation illustrated in FIG. 2B, the separator 20 may include solid, non-encapsulated endothermic PCM particles 26 embedded in the ceramic coating 24 on opposite sides of the porous substrate 22. In any variation, the PCM particles 26 may have a D50of about 0.1 to 2 μm and a phase transition temperature or melting point of about 90 to 150° C., but preferably in the range of 110 to 130° C.FIG. 3 schematically illustrates an example separator 30 after reaching the phase transition temperature of the PCM, according to an embodiment. The separator 30 includes a porous substrate 32, a ceramic coating 34 on a surface of the porous substrate 32, and solid unencapsulated endothermic PCM particles 36 on the ceramic coating 34. the PCM particles 36 absorbed heat and turned from solid to liquid or to a highly viscous state after reaching a phase transition temperature, thereby subsequently filling pores in the surface of the porous substrate 32, thereby increasing the resistance across the separator 30 and hindering or preventing ion transport across the separator 30.FIG. 4 is a cross-sectional view of an example battery device 400. The battery device 400 includes a negative electrode 402, a positive electrode 404, and a separator 406 according to an embodiment. Although not shown, the battery device 400 includes an electrolyte between and in contact with the negative electrode 402 and the positive electrode 404. The negative electrode 402 is an electrode that contains a material that undergoes oxidation reactions in which atoms release electrons during operation, and may include carbon materials such as graphite or lithium metal. The positive electrode 404 is an electrode containing a material undergoing reduction reactions in which atoms receive electrons during operation, and may include lithium metal oxides. The separator 406 includes a porous substrate 408, a ceramic coating 410 on a surface of the porous substrate 408, and solid unencapsulated endothermic PCM particles 412 on the ceramic coating 410. In an alternative embodiment, the separator 406 may include solid unencapsulated PCM particles on the ceramic coating 410 on opposite sides of the porous substrate 408. In a yet alternative embodiment, the separator 406 may include solid unencapsulated PCM particles embedded in the ceramic coating 410 on one or opposite sides of the porous substrate 408.PCM particles 412 may have a phase transition temperature or melting point of about 90 to 150° C., but preferably in the range of 110 to 130° C. When the battery device 400 reaches the phase transition temperature, the PCM particles 412 absorb heat and transition from a solid to a liquid or a high viscosity state, filling the pores of the porous substrate 408 and increasing the resistance across the separator 406, thereby hindering or preventing ion transport from the negative electrode 402 to the positive electrode 404.While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The terms used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of these disclosed subject matters.As previously described, the features of various embodiments may be combined to form further embodiments of the invention that may not be expressly described or illustrated. While various embodiments could have been described as providing or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art will understand that one / more features or characteristics may be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes may include, but are not limited to, strength, durability, marketability, appearance, packaging, size, serviceability, weight, mikroability, ease of assembly, etc. Thus, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for particular applications.According to the present invention, there is provided a battery component comprising: a separator including a porous substrate, a ceramic coating on a surface of the porous substrate, and solid unencapsulated phase change endothermic material particles on or within the ceramic coating and configured to melt and fill pores in the surface upon reaching a phase transition temperature.According to an embodiment, the phase change material particles include a hydrocarbon.In one embodiment, the hydrocarbon is a polyolefin, a paraffin, or a combination thereof.According to an embodiment, the phase change material includes a polymer.In one embodiment, the polymer is polyolefins, fluoropolymers, polyethylene oxides, acrylics, or a combination thereof.According to an embodiment, the phase change material includes an ionic liquid.According to an embodiment, the solid unencapsulated endothermic phase change material particles form a layer on the ceramic coating having a thickness of about 0.5 to 10 μm.According to one embodiment, the phase transition temperature is in the range of about 90 to 150° C.According to the present invention, there is provided a battery cell comprising: positive and negative electrodes; a separator disposed between the electrodes, comprising a porous substrate, a ceramic coating on opposite sides of the porous substrate, and solid unencapsulated endothermic phase change material particles on or within the ceramic coating and configured to melt, fill pores on the sides, and prevent ion transport between the electrodes upon reaching a phase transition temperature; and electrolyte saturating the separator and in contact with the electrodes.According to an embodiment, the phase change material includes a hydrocarbon.In one embodiment, the hydrocarbon is polyolefins, paraffins, or a combination thereof.According to an embodiment, the phase change material includes a polymer.In one embodiment, the polymer is polyolefins, fluoropolymers, polyethylene oxides, acrylics, or a combination thereof.According to an embodiment, the phase change material includes an ionic liquid.According to the present invention, there is provided a battery cell comprising: positive and negative electrodes; a separator disposed between the electrodes, comprising a porous substrate and solid unencapsulated phase change endothermic material particles configured to melt, fill pores on the porous substrate, and prevent ion transport between the electrodes upon reaching a phase transition temperature; and electrolyte saturating the separator and in contact with the electrodes.According to an embodiment, the separator further includes a ceramic coating configured to increase permeability and electrolyte wettability.According to an embodiment, the ceramic particles include alumina, boehmite, silica, or a combination thereof.According to one embodiment, the ceramic particles have a D50between 0.1 and 2 μm.

Claims

A battery component comprising: a separator including a porous substrate, a ceramic coating on a surface of the porous substrate, and solid unencapsulated endothermic phase change material particles on or within the ceramic coating and configured to melt and fill pores in the surface upon reaching a phase transition temperature.The separator of claim 1, wherein the phase change material particles comprise a hydrocarbon.The separator of claim 2, wherein the hydrocarbon is a polyolefin, a paraffin, or a combination thereof.The separator of claim 1, wherein the phase change material particles comprise a polymer.The separator of claim 4, wherein the polymer is polyolefins, fluoropolymers, polyethylene oxides, acrylics, or a combination thereof.The separator of claim 1, wherein the phase change material includes an ionic liquid.The separator of claim 1, wherein the solid unencapsulated endothermic phase change material particles form a layer on the ceramic coating having a thickness of about 0.5 to 10 μm.The separator of claim 1, wherein the phase transition temperature is in the range of about 90 to 150°C.A battery cell comprising: positive and negative electrodes; a separator disposed between the electrodes that includes a porous substrate, a ceramic coating on opposing sides of the porous substrate, and solid unencapsulated phase change endothermic material particles on or within the ceramic coating and configured to melt, fill pores on the sides, and prevent ion transport between the electrodes upon reaching a phase transition temperature; and an electrolyte that saturates the separator and contacts the electrodes.The battery cell of claim 9, wherein the phase change material includes a hydrocarbon.The battery cell of claim 10, wherein the hydrocarbon is polyolefins, paraffins, or a combination thereof.The battery cell of claim 9, wherein the phase change material comprises a polymer.The battery cell of claim 12, wherein the polymer is polyolefins, fluoropolymers, polyethylene oxides, acrylics, or a combination thereof.The battery cell of claim 9, wherein the phase change material includes an ionic liquid.A battery cell comprising: positive and negative electrodes; a separator disposed between the electrodes that includes a porous substrate and solid unencapsulated phase change endothermic material particles and is configured to melt, fill pores on the porous substrate, and prevent ion transport between the electrodes upon reaching a phase transition temperature; and an electrolyte that saturates the separator and contacts the electrodes.

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