WO2024147953A1

WO2024147953A1 - Coating for a separator in an electrochemical cell and a method of manufacturing thereof

Info

Publication number: WO2024147953A1
Application number: PCT/US2023/085890
Authority: WO
Inventors: Shane JACKOWSKI; David Shepard; Bing Tan; Yuhao Liao
Original assignee: Pacific Industrial Development Corporation
Priority date: 2023-01-05
Filing date: 2023-12-26
Publication date: 2024-07-11

Abstract

A separator for use in an electrochemical cell, such as a cell used in a secondary Li-ion battery and a method of manufacturing such a separator. The separator includes a polymeric or aramidic membrane with graphene oxide coated crystalline Boehmite particles. The graphene oxide coated Boehmite particles are either dispersed within at least a portion of the polymeric or aramidic membrane or applied in the form of a coating onto at least a portion of a surface of the polymeric or aramidic membrane. The graphene oxide coated Boehmite particles have an average particle size (D5o) that is less than 5,000 nanometers (nm).

Description

Coating for a Separator in an Electrochemical Cell and a Method of Manufacturing Thereof

FIELD

[0001] This invention generally relates to a separator in an electrochemical cell, particularly, in a lithium-ion secondary battery. More specifically, this disclosure relates to a separator that includes crystalline graphene oxide coated Boehmite particles as a portion thereof.

BACKGROUND

[0002] The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

[0003] In operation, an electrochemical cell, such as a secondary cell for a lithium- ion battery, generally includes a negative electrode, a non-aqueous electrolyte, a separator, a positive electrode, and a current collector for each of the electrodes. All of these components are sealed in a case, an enclosure, a pouch, a bag, a cylindrical shell, or the like (generally called the battery’s “housing”). Separators usually are polyolefin membranes with micro-meter-size pores, which prevent physical contact the between positive and negative electrodes, while allowing for the transport of ions (e.g., lithium ions) back and forth between the electrodes. A non-aqueous electrolyte, which is an organic solution of a metal salt, such as a lithium salt, is placed between each electrode and the separator.

[0004] Since a polyolefin membrane, such as, for example, polyethylene (PE) and polypropylene (PP), is poorly wet by the non-aqueous electrolyte, the impedance for ion transport increases and results in a poor high-rate capability. More importantly, the polyolefin membrane may be subject to shrinkage at an elevated temperature during the operation of the electrochemical cell (e.g., secondary cell of a lithium-ion battery), thereby, increasing the risk of a short circuit and leading eventually to a possible occurrence of a fire or explosion. Furthermore, the softness of the polyolefin membrane allows for the growth and penetration of dendrites, e.g., lithium dendrites, which adds to the concern for safety. The ability to enhance the wettability of the membrane, reduce the shrinkage of the membrane during operation, and limit or eliminate the potential for a fire or explosion is desirable. [0005] In addition, conventional high-energy, high-rate, and low-cost goals for the construction and use of an electrochemical process, such as that found in secondary lithium-ion batteries, requires that the separator be relatively thin and able to be manufactured at a low cost. One way to make the separator naturally thinner is to incorporate inorganic particles. Several examples of inorganic particles include silica, alumina, magnesium oxide, titanium oxide, zirconium oxide, alumina silicate, calcium silicate, magnesium silicate, calcium carbonate, boehmite, kaolin, zeolite, aluminum hydroxide, magnesium hydroxide, and perovskites. Some of these inorganic particles, like fillers, may assist in strengthening the polymer membrane, preventing heat shrinkage, and improving electrolyte wetting. However, such particles usually are difficult to disperse in order to form uniform membranes. The use of dispersants and cross-link agents may be added to avoid this aggregation issue. However, the use of such dispersants and cross-linking agents will increase the overall manufacturing cost and provide additional safety concerns associated with using the electrochemical cell.

SUMMARY

[0006] This disclosure provides a separator for use in an electrochemical cell that includes a cathode; an anode; and a non-aqueous electrolyte. This separator generally comprises a polymeric or aramidic membrane placed between the cathode and anode, such that the separator separates the anode and a portion of the electrolyte from the cathode and the remaining portion of the electrolyte; wherein the polymeric or aramidic membrane is permeable to the reversible flow of ions there through; and graphene oxide coated Boehmite particles having an average particle size (D50) that is less than 5,000 nanometers (nm) applied to the polymeric or aramidic membrane. The graphene oxide coated Boehmite particles are either dispersed within at least a portion of the polymeric or aramidic membrane or applied in the form of a coating onto at least a portion of a surface of the polymeric or aramidic membrane.

[0007] According to one aspect of the present disclosure, the average particle size (D50) of the graphene oxide coated Boehmite particles is in the range of about 10 nm to about 3,000 nm. When desirable, the graphene oxide coated Boehmite particles may exhibit one or more of the following: i) a morphology that is plate-like, cubic, spherical, or a combination thereof; ii) a surface area that is in the range of about 1 .0 m²/g to about 100 m²/g; and iii) a pore volume in the range of 0.1 -2.0 cc/g. These graphene oxide coated Boehmite particles are dispersible in an aqueous-based or nonaqueous-based solution having a pH that ranges from about 3.0 to about 11.0. Alternatively, the graphene oxide coated crystalline Boehmite particles have an average particle size (dso) that is greater than 100 nanometers and less than 2,000 nanometers. The graphene oxide coated crystalline Boehmite particles may also comprise a crystallite size that is between about 30 nanometers to 150 nanometers. The graphene oxide coated crystalline Boehmite particles may comprise graphene oxide in an amount ranging from 0.25 wt.% to 5 wt.% relative to the overall weight of the graphene oxide coated crystalline Boehmite particles.

[0008] According to another aspect of the present disclosure, the coating comprises the graphene oxide coated Boehmite particles and an organic binder, such that the graphene oxide coated Boehmite particles account for about 10 wt.% to 99 wt.% of the overall weight of the coating. The organic binder may comprise, without limitation, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polyvinylpyrrolidone (PVP), polypropylene oxide (PPO), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), sodium ammonium alginate (SAA), styrene-butadiene rubber (SBR), or a mixture thereof.

[0009] The polymeric or aramidic membrane general may comprise, but not be limited to, a polyolefin, polypropylene; poly(methyl methacrylate)-g rafted, siloxane grafted polyethylene; polyvinylidene fluoride (PVDF) nanofiber webs; or blends thereof.

[0010] According to another aspect of the present disclosure, an electrochemical cell is provided that generally comprises a cathode as part of a positive electrode; an anode as part of a negative electrode; a non-aqueous electrolyte that supports the reversible flow of ions between the positive electrode and the negative electrode; and a separator as previously described above and as further defined herein. The positive electrode may comprise a lithium transition metal oxide or a lithium transition metal phosphate; while the negative electrode comprises graphite, a lithium titanium oxide, silicon metal, or lithium metal; and the non-aqueous electrolyte is a solution of a lithium salt dispersed in an organic solution.

[0011] The electrochemical cell may be a pouch cell having a charge and a discharge resistance that is less than an identical pouch cell containing a Boehmite containing separator without the inclusion of graphene oxide. This pouch cell may undergo less degassing than the identical cell comprising the Boehmite containing separator without the inclusion of graphene oxide.

[0012] When desirable, the electrochemical cell may a secondary cell in a lithium- ion battery. The lithium-ion secondary battery may comprise one or more electrochemical cells and a housing having an internal wall that encapsulates the one or more electrochemical cells.

[0013] According to yet another aspect of the present disclosure, a method of forming a separator that includes graphene oxide coated crystalline Boehmite particles is provided. This method generally comprises the steps of: preparing an aqueous slurry comprising a mixture of large aluminum oxide precursors, a highly dispersible grade of Boehmite, graphene oxide, water, and optionally a dispersing agent; adjusting pH of the slurry to be between 8 and 12; heating the slurry to a temperature between 120°C and 250°C for a duration of time that is from about 1 hour to 72 hours; collecting a wet cake that forms from the slurry; drying the wet cake to obtain the graphene oxide coated crystalline Boehmite particles; wherein the graphene oxide coated crystalline Boehmite particles exhibit an average particle size (d₅o) that is less than 5,000 nanometers; forming a polymeric or aramidic membrane; and forming the separator containing the graphene oxide coated crystalline Boehmite particles as previously described above or as further defined herein, wherein the graphene oxide coated Boehmite particles are either dispersed within at least a portion of the polymeric or aramidic membrane during the forming of the polymeric or aramidic membrane or applied in the form of a coating onto at least a portion of a surface of the formed polymeric or aramidic membrane. The dispersing agent may comprise, without limitation, a polyacrylic acid dispersant.

[0014] When desirable, the method may further include one or more of the following: i) the pH of the slurry is adjusted to greater than 11 ; ii) the slurry is heated to a temperature between 180°C to 220°C; and iii) the slurry is heated for a time duration between 4 hours to 48 hours. The graphene oxide coated crystalline boehmite particles used in this method may have an average particle size (dso) that is greater than 10 nanometers and less than 3,000 nanometers; while the large aluminum oxide precursors have an average particle size (D50) of at least 50 micrometers; and the highly dispersible Boehmite has a particle size that is less than 100 nanometers. Alternatively, the graphene oxide coated crystalline Boehmite particles have an average particle size (dso) that is greater than 100 nanometers and less than 2,000 nanometers; and the graphene oxide coated crystalline Boehmite particles comprise a crystallite size that is between about 30 nanometers to 150 nanometers. The graphene oxide coated crystalline Boehmite particles may comprise graphene oxide in an amount ranging from 0.25 wt.% to 5 wt.% relative to the overall weight of the graphene oxide coated crystalline Boehmite particles.

[0015] Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

DESCRIPTION OF THE DRAWINGS

[0016] In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings. The components in each of the drawings may not necessarily be drawn to scale, but rather emphasis is placed upon illustrating the principles of the invention.

[0017] Figs. 1A to 1 D are schematic representations in cross-sectional view of a separator containing graphene oxide coated crystalline Boehmite particles formed according to the teachings of the present disclosure.

[0018] Figs. 2A to 2C are schematic representations in cross-sectional view of graphene oxide coated crystalline Boehmite particles according to the teachings of the present disclosure.

[0019] Fig. 3 a schematic representation of an electrochemical cell comprising a separator that contains a polymeric or aramidic membrane and graphene oxide coated crystalline particles according to the teachings of the present disclosure.

[0020] Fig. 4 is a flow chart depicting a process for forming a separator comprising graphene oxide coated crystalline particles according to the teachings of the present disclosure.

[0021] Fig. 5A is a schematic representation of a lithium-ion secondary battery formed according to the teachings of the present disclosure showing the layering of four secondary cells including two of the secondary cells of Fig. 3 to form a larger mixed cell. [0022] Fig. 5B is a schematic representation of a lithium-ion secondary battery formed according to the teachings of the present disclosure showing the incorporaiton of four secondary cells including two of the secondary cells of Fig. 3 in series.

[0023] Fig. 6 is an x-ray diffraction (XRD) pattern measured for graphene oxide crystalline Boehmite formed according to the teachings of the present disclosure.

[0024] Fig. 7 is a scanning electron micrograph (SEM) obtained along with an energy dispersive x-ray spectrograph (EDS) of Al, O, C, Na, and Si for a graphene oxide coated crystalline Boehmite formed according to the teachings of the present disclosure.

[0025] Fig. 8 is a graphical plot of voltage versus specific capacity that compares the 1 ^st charge of a half-cell constructed according to the teachings of the present disclosure having a graphene oxide coated crystalline Boehmite separator against the 1^st charge of another half-cell that contains an uncoated crystalline Boehmite separator.

[0026] Fig. 9 is a graphical plot of voltage versus specific capacity that compares the 1^st discharge of a half-cell constructed according to the teachings of the present disclosure having a graphene oxide coated crystalline Boehmite separator against the 1^st discharge of another half-cell that contains an uncoated crystalline Boehmite separator.

[0027] Fig. 10 is a table that summarizes the charge and discharge capacity measured in Fig.’s 8 and 9.

[0028] The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

[0029] The following description is merely exemplary in nature and is in no way intended to limit the present disclosure or its application or uses. For example, the graphene oxide coated crystalline Boehmite particles made and used in conjunction with a separator according to the teachings contained herein is described throughout the present disclosure in relation to a secondary cell for use in a lithium-ion secondary battery in order to more fully illustrate the structural elements and the use thereof. The incorporation and use of such particles in other applications, including without limitation, with a separator used in any electrochemical cell or in a primary cell for a lithium-ion battery, is contemplated to be within the scope of the present disclosure. It should be understood that throughout the description and drawings, corresponding reference numerals indicate like or corresponding parts and features.

[0030] The main difference between a lithium-ion battery and a lithium ion secondary battery is that the lithium battery represents a battery that includes a primary cell and a lithium-ion secondary battery represents a battery that includes a secondary cell. The term "primary cell" refers to a battery cell that is not easily or safely rechargeable, while the term “secondary cell” refers to a battery cell that may be recharged. As used herein a “cell” refers to the basic electrochemical unit of a battery that contains the electrodes, separator, and electrolyte. In comparison, a “battery” refers to a collection of cell(s), e.g., one or more cells, and includes a housing, electrical connections, and possibly electronics for control and protection.

[0031] Since lithium-ion (e.g., primary cell) batteries are not rechargeable, their current shelf life is about three years, after that, they are worthless. Even with such a limited lifetime, lithium batteries can offer more in the way of capacity than lithium-ion secondary batteries. Lithium-ion batteries use lithium metal as the anode of the battery unlike lithium ion secondary batteries that can use a number of other materials to form the anode. One key advantage of lithium-ion secondary cell batteries is that they are rechargeable several times before becoming ineffective. The ability of a lithium-ion secondary battery to undergo the charge-discharge cycle multiple times arises from the reversibility of the redox reactions that take place. Lithium-ion secondary batteries, because of the high energy density, are widely applied as the energy sources in many portable electronic devices (e.g., cell phones, laptop computers, etc.), power tools, electric vehicles, and grid energy storage.

[0032] For the purpose of this disclosure, the terms "about" and "substantially" are used herein with respect to measurable values and ranges due to expected variations known to those skilled in the art (e.g., limitations and variability in measurements).

[0033] For the purpose of this disclosure, the terms "at least one" and "one or more of” an element are used interchangeably and may have the same meaning. These terms, which refer to the inclusion of a single element or a plurality of the elements, may also be represented by the suffix "(s)"at the end of the element. For example, "at least one particle", "one or more particles", and "particle(s)" may be used interchangeably and are intended to have the same meaning. [0034] According to one aspect of the present disclosure a separator for use in an electrochemical cell that also includes a cathode, an anode, and a non-aqueous electrolyte is provided. This separator generally comprises a polymeric or aramidic membrane placed between the cathode and anode, such that the separator separates the anode and a portion of the electrolyte from the cathode and the remaining portion of the electrolyte. This polymeric or aramidic membrane is permeable to the reversible flow of ions there through. Graphene oxide coated Boehmite particles having an average particle size (D50) that is less than 5,000 nanometers (nm) are applied to the polymeric or aramidic membrane.

[0035] Referring to Fig. 1A to Fig. 1 D, the graphene oxide coated crystalline Boehmite particles 10 may be either dispersed within the polymeric or aramidic membrane 5 (shown in Fig. 1A) or applied in the form of a coating 7 onto at least a portion of a surface of the polymeric or aramidic membrane 5 (shown in Fig. 1 B); alternatively, to one or more entire side of the polymeric or aramidic membrane 5 (shown in Fig.’s 1 C & 1 D). In each case, the separator 1 is shown to comprise both the polymeric or aramidic membrane 5 and the graphene oxide coated crystalline Boehmite particles 10. The coating 7 generally comprises an organic binder 13 in addition to the graphene oxide coated crystalline Boehmite particles 10.

[0036] The incorporation of the graphene oxide coated Boehmite particles with the separator provides multiple benefits to an electrochemical cell. For example, a separator comprising the graphene oxide coated Boehmite particles may provide for a decrease in charging and discharging resistance encountered during the operation of the cell. In addition, the presence of these particles can assist in decreasing the amount of degassing that occurs. Since the graphene oxide coated Boehmite particles may be incorporated with the separator (e.g., polymeric or aramidic membrane) either as an additive within the separator or as a coating applied to the surface of the separator, the particles may act as fillers for the polymeric or aramidic membrane or in the applied protective coating layer. Thus, the graphene oxide coated crystalline Boehmite particles may also strengthen the polymer membrane, prevent heating shrinkage, and improve electrolyte wetting. The graphene oxide coated crystalline Boehmite particles may also be capable of mitigating dendrite formation and retarding the potential occurrence of a fire or explosion. Further benefits of using a separator comprising graphene oxide coated crystalline Boehmite particles are discussed and become evident throughout the remainder of this specification.

[0037] Referring now to Fig.’s 2A to 2C, the graphene oxide coated crystalline Boehmite particles 10 generally comprise a crystalline Boehmite core 15 with graphene oxide 17 being present on or in at least a portion of the external surface of the core 15 (shown in Fig. 2A). Alternatively, the graphene oxide 17 is present on a substantial portion of the surface of the core 15 (shown in Fig. 2B); alternatively, the graphene oxide 17 encapsulates the core 15 (shown in Fig. 2C). The graphene oxide coated crystalline Boehmite particles may comprise graphene oxide in an amount ranging from about 0.1 wt.% to about 10 wt.% relative to the overall weight of the graphene oxide coated crystalline Boehmite particles. Alternatively, the graphene oxide coated crystalline Boehmite particles may comprise graphene oxide in an amount ranging from about 0.25 wt.% to 5 wt.%; alternatively, from about 0.35 wt.% to about 3.5 wt.%; alternatively, less than 2.5 wt.% and greater than 0.5 wt.%, relative to the overall weight of the graphene oxide coated crystalline Boehmite particles.

[0038] As previously discussed above and further defined herein, the graphene oxide coated crystalline Boehmite particles may have an average particle size (D₅o) that is less than 5,000 nanometers (nm). Alternatively, the average particle size (D50) of the graphene oxide coated Boehmite particles is in the range of about 10 nm to about 3,000 nm; alternatively, greater than 10 nm and less than 3,000 nm. When desirable, the graphene oxide coated crystalline Boehmite particles may have an average particle size (dso) that is greater than 100 nanometers and less than 2,000 nanometers. Alternatively, the graphene oxide coated crystalline Boehmite particles have an average particle size (dso) that is less than 1 ,500 nm; alternatively, in the range of about 10 nm to about 500 nm.

[0039] The graphene oxide coated crystalline Boehmite particles may also comprise a crystallite size that is between 10 nanometers to 200 nanometers; alternatively, in the range of about 15 nanometers to about 175 nanometers; alternatively, about 30 nanometers to 150 nanometers; alternatively, about 20 nm to about 100 nm. A crystallite represents the smallest size, e.g., a single crystal in powder form. In comparison, the particle size of the graphene oxide coated crystalline Boehmite particles may be the same or larger than the crystallite size; alternatively, the particle size is larger than the crystallite size. In other words, the particles may represent a single crystal or an agglomeration of multiple crystals.

[0040] The graphene oxide coated crystalline Boehmite particles exhibit a morphology that is either platelet, cubic, or spherical or a combination thereof. These graphene oxide coated crystalline Boehmite particles may also exhibit a surface area of 0.5 m²/g to about 500 m²/g; alternatively, 1.0 m²/g to 100 m²/g; alternatively, about 5.0 m²/g to about 80 m²/g. The pore volume exhibited by the graphene oxide coated crystalline Boehmite particles is on the order of about 0.05 cc/g to about 3.0 cc/g; alternatively, 0.1 cc/g to about 2.0 cc/g; alternatively, about 0.3 cc/g to about 1 .5 cc/g. [0041] Scanning electron microscopy (SEM) or other optical or digital imaging methodology known in the art may be used to determine the shape and/or morphology of the inorganic material. The average particle size and particle size distributions may be measured using any conventional technique, such as sieving, microscopy, Coulter counting, dynamic light scattering, or particle imaging analysis, to name a few. Alternatively, a laser particle analyzer is used for the determination of average particle size and its corresponding particle size distribution. The measurement of surface area and pore volume for the inorganic material may be accomplished using any known technique, including without limitation, microscopy, small angle x-ray scattering, mercury porosimetry, and Brunauer, Emmett, and Teller (BET) analysis. Alternatively, the surface area and pore volume is determined using Brunauer, Emmett, and Teller (BET) analysis.

[0042] The graphene oxide coated Boehmite particles are dispersible in an aqueous-based solution or a nonaqueous-based solution that has a pH in the range of about 3.0 to about 11 .0. This type of dispersion may be utilized during any known process that is configured to form a polymeric or aramidic membrane, such that the particles become dispersed within the separator. In addition, the graphene oxide coated Boehmite particles may be combined with an organic binder to for a coating formulation that may be applied to at least a portion of a surface of the polymeric or aramidic membrane; alternatively, the coating may be applied to either one side or both sides of the polymeric or aramidic membrane; alternatively, at least one entire side of the polymeric or aramidic membrane is coated. The mass amount of the graphene oxide coated Boehmite particles present in the coating formulation is such that the final applied (i.e. , dried or cured) coating comprises about 10 wt.% to 99 wt.% of the particles based on the overall weight of the final applied or dried coating. Alternatively, the amount of the graphene oxide coated Boehmite particles present in the final applied coating is in the range of at least 20 wt.%; alternatively, less than 90 wt.%; alternatively, between 25 wt.% and 85 wt.%.

[0043] The organic binder utilized in the coating formulation may comprise polyvinyl alcohol (PVA), polyethylene oxide (PEO), polyvinylpyrrolidone (PVP), polypropylene oxide (PPO), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), sodium alginate or ammonium alginate or a combination thereof (SAA), styrene-butadiene rubber (SBR), or a mixture thereof. Alternatively, the organic binder is polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide (PPO), or a mixture thereof.

[0044] The polymeric or aramidic membrane used to form the separator may comprise, without limitation, polyolefin-based materials with semi-crystalline structure, such as polyethylene, polypropylene, and blends thereof, as well as micro-porous poly(methyl methacrylate)-grafted, siloxane grafted polyethylene, and polyvinylidene fluoride (PVDF) nanofiber webs. Alternatively, the polymeric or aramidic membrane is a polyolefin, such as polyethylene, polypropylene, or a blend thereof.

[0045] According to another aspect of the present disclosure, an electrochemical cell is provided that incorporates a separator as described above and/or as further defined herein that contains graphene oxide coated crystalline Boehmite particles. Referring now to Fig. 3 the electrochemical cell 25 generally comprises a cathode 30 as part of a positive electrode 35; an anode 40 as part of a negative electrode 45; a non-aqueous electrolyte 50 that supports the reversible flow of ions 51 between the positive electrode 35 and the negative electrode 45; and a separator 1 that includes both a polymeric or aramidic membrane and graphene oxide coated crystalline Boehmite particles as previously discussed above and as further defined herein.

[0046] The positive electrode 35 comprises an active material that acts as the cathode 30 for the cell 25 and a current collector 31 that is in contact with the cathode 30, such that the ions 51 flow from the cathode 30 to the anode 40 when the cell 25 is charging. Similarly, the negative electrode 45 comprises an active material that acts as an anode 40 for the cell 25 and a current collector 41 that is in contact with the anode 40, such that ions 51 flow from the anode 40 to the cathode 30 when the cell 25 is discharging. The contact between the cathode 30 and the current collector 31 , as well as the contact between the anode 40 and the current collector 41 , may be independently selected to be direct or indirect contact; alternatively, the contact between the anode 40 or cathode 30 and the corresponding current collector 41 , 31 is directly made.

[0047] Still referring to Fig. 3, the active materials in the positive electrode 35 and the negative electrode 45 may be any material known to perform this function in an electrochemical cell, e.g., in a secondary cell of a lithium-ion battery. The active material used in the positive electrode 35 may include, but not be limited to lithium transition metal oxides or transition metal phosphates. Several examples of active materials that may be used in the positive electrode 35 include, without limitation, LiCoC>2, LiMn2O4, LiNii-x-yCOxMn_yO2 (x+y<2/3), zLi2MnO3 (1-z)LiNii-_x-yCo_xMn_yO2 (x+y<2/3), LiNio.5Mn1.5O4, and LiFePO4. Alternatively, the active material in the positive electrode 35 comprises a lithium transition metal oxide or a lithium transition metal phosphate.

[0048] The active materials used in the negative electrode 45 may include, but not be limited to graphite and Li4TisOi2, as well as silicon and lithium metal. The current collectors 31 , 41 in both the positive 35 and negative 45 electrodes may be made of any metal known in the art for use in an electrode of an electrochemical cell or lithium battery, such as for example, aluminum for the cathode and copper for the anode. The cathode 30 and anode 40 in the positive 35 and negative 45 electrodes are generally made up of two dissimilar active materials.

[0049] The non-aqueous electrolyte 50 is selected, such that it supports the oxidation/reduction process and provides a medium for ions 51 (e.g., lithium-ions) to flow between the anode 40 and cathode 30. The non-aqueous electrolyte 50 may be a solution of an inorganic salt in an organic solvent. Several specific examples of lithium salts used in the secondary cell of a lithium battery, include, without limitation, lithium hexafluorophosphate (LiPFe), lithium bis(oxalato)-borate (LiBOB), and lithium bis(trif luoro methane sulfonyl)imide (LiTFSi). The inorganic salts may form a solution with an organic solvent, such as, for example, ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), propylene carbonate (PC), vinylene carbonate (VC), and fluoroethylene carbonate (PEC), to name a few. A specific example of an electrolyte for use in a secondary cell of a lithium battery is a 1 molar solution of LiPFe in a mixture of ethylene carbonate and diethyl carbonate (EC/DEC = 50/50 vol.). [0050] The crystalline graphene oxide coated Boehmite particles and at least one polymeric or aramidic membrane may be made into a separator that can then be used inside a lithium-ion secondary battery, which allows for a decrease in charging and discharging resistance, as well as a decrease in any degassing associated with the battery. In other words, the electrochemical cell 25 of Fig. 3 may represent a secondary cell 25 for use in a lithium-ion secondary battery. In this specific application, the ions 51 that reversibly flow between the anode 40 and the cathode 30 are lithium ions (Li⁺).

[0051] According to another aspect of the present disclosure, a method of forming a separator comprising graphene oxide coated crystalline Boehmite particles is provided. Referring now to Fig. 4, this method 100 generally comprises preparing 105 an aqueous slurry; adjusting 110 the pH of the slurry to be between 8 and 12; heating 115 the slurry; collecting 120 a wet cake that forms from the slurry; drying 125 the wet cake to obtain graphene oxide coated crystalline Boehmite particles; forming 130 a polymeric or aramidic membrane; and forming 135 a separator that contains the graphene oxide coated crystalline Boehmite particles. The aqueous slurry generally comprises a mixture of large aluminum oxide precursors, a highly dispersible grade of Boehmite, graphene oxide, water, and optionally a dispersing agent. The slurry is heated to a temperature between 120°C and 250°C for a duration of time that is from about 1 hour to 72 hours. The graphene oxide coated crystalline Boehmite particles formed by this method 100 exhibit an average particle size (dso) that is less than 5,000 nanometers. The separator may be formed with the graphene oxide coated Boehmite particles either dispersed within at least a portion of the polymeric or aramidic membrane during the formation of the polymeric or aramidic membrane or applied in the form of a coating onto at least a portion of a surface of the formed polymeric or aramidic membrane.

[0052] The large aluminum oxide precursors may have an average particle size (Dso) that is at least 50 micrometers (pm). Alternatively, the large aluminum precursors may have an average particle size (D50) that is between 55 pm to about 500 pm; alternatively, about 60 micrometers to about 300 micrometers; alternatively, between about 50 micrometers and 100 micrometers. The large aluminum oxide precursors may be a coarse grade of Gibbsite. [0053] The highly dispersible grade of Boehmite may have an average particle size (D50) that is less than 100 nanometers (nm). Alternatively, this highly dispersible grade of Boehmite has a particle size less than 90 nanometers; alternatively, in the range of

1 nm and 95 nm; alternatively, between 5 nm and 90 nm. The highly dispersible Boehmite may act as a “seed” material.

[0054] When desirable, the method may include one or more of the following: i) adjusting the pH of the slurry to be greater than 11 ; ii) heating the slurry to a temperature that is between 180°C to 220°C; and iii) heating the slurry for a time duration that is between 4 hours to 48 hours. Alternatively, the pH of the slurry is adjusted to be in the range of 11 to 13; alternatively, 11 .5 to 12.5. The temperature to which the slurry is heated may alternatively range from 140°C to 240°C; alternatively, 165°C to 230°C; alternatively, about 180°C for a period of time that ranges from about

2 hours to 70 hours; alternatively, between 2 hours and 50 hours; alternatively, from about 3 hours to 60 hours; alternatively, from about 6 hours to 36 hours; alternatively, between 4 hours and 48 hours.

[0055] Referring once again to Figs. 1A to 1 D, the graphene oxide coated crystalline Boehmite particles 10 are included as part of the separator 1 . The graphene oxide coated crystalline Boehmite particles 10 may be incorporated into the polymeric or aramidic membrane 5 either as an additive or filler within the separator 1 or as a coating 7 applied to the surface of the separator 1 . Alternatively, the graphene oxide coated crystalline Boehmite particles 10 may be applied to one-side of the separator 1 or to both-sides of the separator 1 . The amount of the graphene oxide coated crystalline Boehmite particles 10 present in the electrochemical cell may be up to 100 wt.%; alternatively, up to 75 wt.%; alternatively, up to 50 wt.%; alternatively, between 1 wt.% and 50 wt.%; alternatively, between 10 wt.% and 60 wt.%, relative to the overall weight of the separator 1 .

[0056] A separator 1 plays a significant role in the safety, durability, and high-rate performance of an electrochemical cell, such as a secondary cell for a lithium-ion battery. A polymeric or aramidic membrane is electrically insulating and separates the positive and negative electrodes completely to avoid an internal short circuit. The polymeric or aramidic membrane usually is not ionically conductive, but rather has large pores filled with the non-aqueous electrolyte, allowing for the transport of ions. [0057] According to another aspect of the present disclosure, one or more secondary cells may be combined to form a larger electrochemical cell, such as a lithium-ion secondary battery. In Fig. 5A, an example of such a battery 55A is shown in which four (4) secondary cells 25 are layered to form a larger single secondary cell that is encapsulated to produce the lithium-ion secondary battery 55A. In Fig. 5B, another example of a battery is shown, in which four (4) secondary cells are stacked or placed in series to form a larger capacity battery 55B with each cell being individually contained. In each of Figs. 5A and 5B, the batteries 55A, 55B are shown with two separators 1 configured according to the present disclosure and two separators 1 C configured as conventional polymeric or aramidic membranes without the inclusion of any graphene oxide coated crystalline Boehmite particles incorporated therewith. The incorporation of only one separator 1 formed herein into the batteries 55A, 55B is necessary, although each battery cell 25 may include such a separator 1 (e.g., no conventional separators 1 C) without departing from the scope of the present disclosure.

[0058] The lithium-ion secondary batteries 55A, 55B also includes a housing 60 having an internal wall in which the one or more secondary cells 25 (e.g., electrochemical cells) are enclosed or encapsulated in order to provide for both physical and environmental protection. One skilled in the art will understand that although the battery 55A, 55B shown in Fig.’s 5A or 5B incorporates four secondary cells that such a battery 55A, 55B may include any other number of secondary cells. [0059] One skilled in the art will also appreciate that although Fig. 5A and Fig. 5B demonstrate the incorporation of secondary cells 25 into a lithium-ion secondary battery 55A, 55B, the same principles may be used to encompass, encapsulate, or encase one or more electrochemical cells 25 into a housing 60 for use in another application.

[0060] The housing 60 may be constructed of any material known for such use in the art and be of any desired geometry required or desired for a specific application. For example, lithium-ion batteries generally are housed in three different main form factors or geometries, namely, cylindrical, prismatic, or soft pouch. The housing 60 for a cylindrical battery may be made of aluminum, steel, or the like. Prismatic batteries generally comprise a housing 60 that is rectangular shaped rather than cylindrical. Soft pouch housings 60 may be made in a variety of shapes and sizes. These soft housings may be comprised of an aluminum foil pouch coated with a plastic on the inside, outside, or both. The soft housing 60 may also be a polymeric or aramidic-type encasing. The polymer composition used for the housing 60 may be any known polymeric or aramidic materials that are conventionally used in lithium-ion secondary batteries. One specific example, among many, include the use of a laminate pouch that comprises a polyolefin layer on the inside and a polyamide layer on the outside. A soft housing 60 needs to be designed such that the housing 60 provides mechanical protection for the secondary cells 25 present in the battery 55A, 55B.

[0061] The specific examples provided in this disclosure are given to illustrate various embodiments of the invention and should not be construed to limit the scope of the disclosure. The embodiments have been described in a way which enables a clear and concise specification to be written, but it is intended and will be appreciated that embodiments may be variously combined or separated without parting from the invention. For example, it will be appreciated that all preferred features described herein are applicable to all aspects of the invention described herein.

[0062] Example 1 - Method of forming Graphene Oxide Coated Crystalline Boehmite Particles

[0063] A total of 5,000 grams of deionized (DI) water is combined with 248 grams of a 2.5% graphene oxide solution (6.2 grams of graphene oxide) under mixing conditions. A total of 1 ,000 grams of Gibbsite (coarse grade alumina) and 240 grams of a highly dispersible Boehmite (WDB-12x, Pacific Industrial Development Corporation, Ann Arbor, Michigan) is added to the water and graphene oxide to form a slurry. The slurry is mixed for 30 minutes to ensure homogeneity. The acidity /basicity of the slurry is then adjusted to a pH of 1 1.2-11.6 using sodium hydroxide crystals. The slurry is placed into a Parr 2-Gallon autoclave and heated to a temperature of 180°C for the duration of 4 hours with continued stirring of the slurry at a speed of 300 rpm. The slurry is then removed and filtered and washed with DI water to obtain a wet cake. The wet cake is dried in a drying oven overnight at 120°C (about 12-14 hours) to obtain the graphene oxide coated crystalline Boehmite particles. When desirable, the graphene oxide solution may comprise anywhere between 0.1 wt.% to 10 wt.% based on the overall weight of the solution.

[0064] The Applicant has found that when an optional dispersant is utilized, the wet cake may be placed back into a water-based solution and mixed with the dispersant. In this case, the resulting solution may be spray dried to obtain the desired graphene oxide coated crystalline Boehmite particles. When utilized, the dispersing agent may be, without limitation, an organic or polymeric or aramidic dispersant. This organic dispersant may comprise, but not be limited to, a polyacrylic acid dispersant. A specific example of a commercially available dispersant is Solsperse™ AC5170 (Lubrizol Corp., Ohio).

[0065] It is desirable that the graphene oxide coated crystalline Boehmite particles incorporated with the polymeric or aramidic membrane to form a separator be substantially dry and free of moisture. Residual moisture present in a Li-ion battery may be detrimental to the life-time of the battery. More specifically, lithium-ion secondary batteries may experience degradation in capacity due to prolonged exposure to moisture (e.g., water), hydrogen fluoride (HF), and/or dissolved transitionmetal ions (TMⁿ⁺). In fact, the lifetime of a lithium-ion secondary battery can become severely limited once 20% or more of the original reversible capacity is lost or becomes irreversible. Below are the detrimental reactions that may occur in a Li-ion battery with moisture residue.

LiPFe + H₂O HF + LiFj, + H3PO4

UMO2 + HF > LiFj + M²⁺ + H2O, wherein M stands for transition metal.

[0066] The collected particles are verified by x-ray diffraction (XRD) to be a crystalline Boehmite coated with graphene oxide as shown in Fig. 6. The presence of crystalline Boehmite is verified in the XRD spectrum as the peaks at the reflections corresponding to the 020 and 021 planes.

[0067] The resulting particle distribution of the collected particles is also measured using a Horiba LA930WET with the average particle size (dso) being determined to be 330 nanometers. Referring now to Fig. 7, scanning electron micrograph (SEM) obtained along with an energy dispersive x-ray spectrograph (EDS) was used to observe carbon (C) and oxygen (O) coated on the surface of the Boehmite indicating that graphene oxide is present on the surface thereof. The graphene oxide coated crystalline Boehmite particles formed in this example are suitable for use in applications without having to introduce a milling or grinding step to further reduce the average particle size. This example demonstrates the formation of a graphene oxide coated crystalline Boehmite particles according to the present disclosure without having to grind or mill the raw material or product to have the graphene oxide coated crystalline Boehmite exhibit an average particle size (cho) that is suitable for use as a separator coating in battery systems.

[0068] Example 2 - Method of forming Crystalline Boehmite Particles for Comparison Evaluation

[0069] A total of 5,000 grams of deionized (DI) water is combined with a total of 1 ,000 grams of Gibbsite (coarse grade alumina) and 240 grams of a highly dispersible Boehmite (WDB-12x, Pacific Industrial Development Corporation, Ann Arbor, Michigan) to form a slurry. The slurry is mixed for 30 minutes to ensure homogeneity. The acidity /basicity of the slurry is then adjusted to a pH of 11.2-11.6 using sodium hydroxide crystals. The slurry is placed into a Parr 2-Gallon autoclave and heated to a temperature of 180°C for the duration of 4 hours with continued stirring of the slurry at a speed of 300 rpm. The slurry is then removed and filtered and washed with DI water to obtain a wet cake. The wet cake is dried in an oven overnight at 120°C (about 12-14 hours).

[0070] The collected particles are verified by x-ray diffraction (XRD) to be a crystalline Boehmite. The crystalline Boehmite is verified in the XRD spectrum as the peaks at the reflections 020 and 021 as previously described above in Example 1 .

[0071 ] The particle distribution of the collected Boehmite particles is also measured using a Horiba LA930WET with the average particle size (dso) being determined to be 300 nanometers. The crystalline Boehmite particles formed in this example are suitable for use in applications without having to introduce a milling or grinding step to further reduce the average particle size. This example demonstrates the formation of a crystalline Boehmite particles that do not contain any graphene oxide at or near the surface of the particles.

[0072] Evaluation Method 1 - Pouch Cell Formation

[0073] Electrochemical charge and discharge tests were made in pouch cells. The negative electrode was LiMn2O4 as the active cathode material. The LiMn2O4 electrode was prepared by a doctor blade method. The positive electrode utilized a lithium (Li) tablet as the active anode material. The cathode electrode slurry was prepared by mixing Li n2O4, carbon nanotubes, CNTs (50 wt.% solution) and polyvinylidene fluoride, PVDF (6 wt% solution) in a mass ratio of 97 : 1.5 : 1.5 using N-methyl pyrrolidone (NMP) as the solvent. The resulting slurry was then pasted onto the aluminum foil substrate. Prior to use, the LiMn2O4 electrode was dried in a vacuum oven at 110°C for2 hours. The capacity loading of LiMn2O4 was 0.8 mAh/cm². A lithium (Li) tablet was utilized as the counter electrode and LiPFe (1 M) in ethylene carbonate/dimethyl carbonate (EC/DMC, 3:7 vol.%, 1 vol.% VC, 2 vol.% FEC) was used as the electrolyte. The pouch cells were assembled in an argon-fi lied glovebox. [0074] Graphene oxide coated crystalline Boehmite particles from Example 1 were cast on a polymeric or aramidic Celgard® 2400 membrane to form the separator. In this respect, the graphene oxide coated crystalline Boehmite particles were mixed with 2 wt.% styrene-butadiene rubber (SBR) and 20 wt.% polyvinyl alcohol (PVA) dissolved in deionized water to form a slurry having a mass ratio of 70 : 28 : 2. The slurry was coated onto the Celgard® 2400. Prior to use, the coated separators were dried in air for 1 hour and then vacuum dried at 110°C overnight. The coating thickness is about 4 micrometers (pm). These pouch cells comprising these separators formed according to the teachings of the present disclosure were labeled as FR500-graphene or FR500-GO.

[0075] Similarly, crystalline Boehmite particles from Example 2 were cast on a polymeric or aramidic Celgard® 2400 membrane to form the separator following the same procedure as described above for the graphene oxide coated crystalline Boehmite particles from Example 1 . However, in this case, the pouch cells comprising the comparable separators containing the crystalline Boehmite particles (no graphene oxide) were labeled as FR500.

[0076] Evaluation Method 2 - Battery Testing Conditions

[0077] The discharging/charging tests for the pouch cells labelled as FR500 and FR500-graphene were performed on a LAND CT3001A battery test system at a cutoff voltage from 3.0 V to 4.25 V at room temperature, respectively, and the current densities were 0.09 mA/g (corresponding to a C/10 rate), 0.045 mA/g (C/20 rate) and 4.5 mA/g (5C rate). For the formation cycle as shown in Fig. 8, the cells were charged to a cut-off voltage of 4.25 V with a current density 0.09 mA/g (C/10 rate). At the midcharge stage, the charge was completed with a lower current density of 0.045 mA/g (C/20 rate) to the end of the charge for the cells. Both of the pouch cells (i.e. , FR500 and FR500-GG) were found to perform similarly as shown in Fig. 8.

[0078] The cells were then discharged as shown in Fig. 9 to a cut-off voltage of 3.0 V with a current density 0.09 mA/g (C/10 rate). After the formation cycle, the cells were charged to a cut-off voltage of 4.25 V with a current density 0.09 mA/g (C/10 rate) and completed with a lower current density of 0.045 mA/g (C/20 rate) to the end of the charge for the cells again. The cells were then discharged to the 50% state of charge (SOC) for 5 hours, rested for 30 minutes, and then utilized at a higher current density 4.5 mA/g (5C rate) to charge the cells for 10 seconds, followed by resting the cells for another 30 minutes and discharging the cells with a current density 4.5 mA/g (5C rate) for 10 seconds. Both of the pouch cells (i.e., FR500 and FR500-GO) again were found to perform similarly as shown in Fig. 9. The measured values for both the charge and discharge capacities for each of the half-cells comprising either FR500 or FR500- graphene is provided in Fig. 10 below for further comparison demonstrating substantially similar performance.

[0079] The charging and discharging resistances were calculated by voltage change versus charging/discharging current during the 5C pulse at 50% SOC. A summary of the charging and discharging resistances for different separator coatings in cells is provided in Table 1 below. In addition, a pouch cell comprising a separator of only polypropylene, PP (Celgard® 2400) was also tested for an additional comparison. As demonstrated in Table 1 , the charging and discharging resistance of the cells containing the comparable separator (FR500) were found to be on the order of 91-94 Ohms, while the charging and discharging resistance of the cells containing the separators (FR500-GO) formed according to the teachings of the present disclosure were found be substantially less at 45-51 Ohms. The resistance exhibited by the cells containing the graphene oxide coated crystalline Boehmite particles (FR500-GO) were only slightly greater than the 36-38 Ohm resistance exhibited by the cells containing conventional polypropylene (PP) separators.

[0080] Table 1

[0081] In addition, the pouch cells that contain a separator formed according to the teachings of the present disclosure, which includes the graphene oxide coated crystalline Boehmite particles, were observed to undergo less degassing than identical cells containing a Boehmite separator without the inclusion of graphene oxide.

[0082] Those ski I led-i n-the-art, in light of the present disclosure, will appreciate that many changes can be made in the specific embodiments which are disclosed herein and still obtain alike or similar result without departing from or exceeding the spirit or scope of the disclosure. One skilled in the art will further understand that any properties reported herein represent properties that are routinely measured and can be obtained by multiple different methods. The methods described herein represent one such method and other methods may be utilized without exceeding the scope of the present disclosure.

[0083] The foregoing description of various forms of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Numerous modifications or variations are possible in light of the above teachings. The forms discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to utilize the invention in various forms and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled.

Claims

CLAIMS What is claimed is:

1. A separator for use in an electrochemical cell that includes a cathode; an anode; and a non-aqueous electrolyte, the separator comprising: a polymeric or aramidic membrane placed between the cathode and anode, such that the separator separates the anode and a portion of the electrolyte from the cathode and the remaining portion of the electrolyte; wherein the polymeric or aramidic membrane is permeable to the reversible flow of ions there through; and graphene oxide coated Boehmite particles having an average particle size (D50) that is less than 5,000 nanometers (nm) applied to the polymeric or aramidic membrane; wherein the graphene oxide coated Boehmite particles are either dispersed within at least a portion of the polymeric or aramidic membrane or applied in the form of a coating onto at least a portion of a surface of the polymeric or aramidic membrane.

2. The separator according to claim 1 , wherein the average particle size (D50) of the graphene oxide coated Boehmite particles is in the range of about 10 nm to about 3,000 nm.

3. The separator according to any of claims 1 and 2, wherein the graphene oxide coated Boehmite particles exhibit one or more of the following: i) a morphology that is plate-like, cubic, spherical, or a combination thereof; ii) a surface area that is in the range of about 1 .0 m²/g to about 100 m²/g; and iii) a pore volume in the range of 0.1 -2.0 cc/g.

4. The separator according to any of claims 1 to 3, wherein the graphene oxide coated Boehmite particles are dispersible in an aqueous-based or nonaqueousbased solution having a pH that ranges from about 3.0 to about 11.0.

5. The separator according to any of claims 1 to 4, wherein the coating comprises the graphene oxide coated Boehmite particles and an organic binder, such that the graphene oxide coated Boehmite particles account for about 10 wt.% to 99 wt.% of the overall weight of the coating; wherein the organic binder comprises polyvinyl alcohol (PVA), polyethylene oxide (PEO), polyvinylpyrrolidone (PVP), polypropylene oxide (PPO), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), sodium ammonium alginate (SAA), styrenebutadiene rubber (SBR), or a mixture thereof.

6. The separator according to any of claims 1 to 5, wherein the polymeric or aramidic membrane comprises a polyolefin, polypropylene; poly(methyl methacrylate)-grafted, siloxane grafted polyethylene; polyvinylidene fluoride (PVDF) nanofiber webs; or blends thereof.

7. The separator according to any of claims 1 to 6, wherein the graphene oxide coated crystalline Boehmite particles have an average particle size (d₅o) that is greater than 100 nanometers and less than 2,000 nanometers; wherein the graphene oxide coated crystalline Boehmite particles comprise a crystallite size that is between about 30 nanometers to 150 nanometers.

8. The separator according to any of claims 1 or 7, wherein the graphene oxide coated crystalline Boehmite particles comprise graphene oxide in an amount ranging from 0.25 wt.% to 5 wt.% relative to the overall weight of the graphene oxide coated crystalline Boehmite particles.

9. An electrochemical cell comprising: a cathode as part of a positive electrode; an anode as part of a negative electrode; a non-aqueous electrolyte that supports the reversible flow of ions between the positive electrode and the negative electrode; and a separator according to any of claims 1 to 8.

10. The electrochemical cell according to claim 9, wherein the positive electrode comprises a lithium transition metal oxide or a lithium transition metal phosphate; the negative electrode comprises graphite, a lithium titanium oxide, silicon metal, or lithium metal; and the non-aqueous electrolyte is a solution of a lithium salt dispersed in an organic solution.

11 . The electrochemical cell according to any of claims 9 to 10, wherein the electrochemical cell is a pouch cell having a charge and a discharge resistance that is less than an identical pouch cell containing a Boehmite containing separator without the inclusion of graphene oxide.

12. The electrochemical cell according to claim 11 , wherein the pouch cell undergoes less degassing than the identical cell comprising the Boehmite containing separator without the inclusion of graphene oxide.

13. The electrochemical cell according to any of claims 9 to 12, wherein the electrochemical cell is a secondary cell in a lithium-ion battery.

14. A lithium-ion secondary battery comprising one or more electrochemical cells according to any of claims 9 to 12 and a housing having an internal wall that encapsulates the one or more electrochemical cells.

15. A method of forming a separator that includes graphene oxide coated crystalline Boehmite particles, the method comprising: preparing an aqueous slurry comprising a mixture of large aluminum oxide precursors, a highly dispersible grade of Boehmite, graphene oxide, water, and optionally a dispersing agent; adjusting pH of the slurry to be between 8 and 12; heating the slurry to a temperature between 120°C and 250°C for a duration of time that is from about 1 hour to 72 hours; collecting a wet cake that forms from the slurry; drying the wet cake to obtain the graphene oxide coated crystalline Boehmite particles; wherein the graphene oxide coated crystalline Boehmite particles exhibit an average particle size (dso) that is less than 5,000 nanometers; forming a polymeric or aramidic membrane; and forming the separator containing the graphene oxide coated crystalline Boehmite particles, wherein the graphene oxide coated Boehmite particles are either dispersed within at least a portion of the polymeric or aramidic membrane during the forming of the polymeric or aramidic membrane or applied in the form of a coating onto at least a portion of a surface of the formed polymeric or aramidic membrane.

16. The method according to claim 15, wherein the dispersing agent is a polyacrylic acid dispersant.

17. The method according to any of claims 15 to 16, wherein the method includes one or more of the following: i) the pH of the slurry is adjusted to greater than 11 ; ii) the slurry is heated to a temperature between 180°C to 220°C; and iii) the slurry is heated for a time duration between 4 hours to 48 hours.

18. The method according to any of claims 15 to 17, wherein the graphene oxide coated crystalline boehmite particles have an average particle size (dso) that is greater than 10 nanometers and less than 3,000 nanometers; wherein the large aluminum oxide precursors have an average particle size (D50) of at least 50 micrometers; wherein the highly dispersible Boehmite has a particle size that is less than 100 nanometers.

19. The method according to any of claims 15 to 18, wherein the graphene oxide coated crystalline Boehmite particles have an average particle size (dso) that is greater than 100 nanometers and less than 2,000 nanometers; wherein the graphene oxide coated crystalline Boehmite particles comprise a crystallite size that is between about 30 nanometers to 150 nanometers.

20. The method according to any of claims 15 to 19, wherein the graphene oxide coated crystalline Boehmite particles comprise graphene oxide in an amount ranging from 0.25 wt.% to 5 wt.% relative to the overall weight of the graphene oxide coated crystalline Boehmite particles.