WO2019122423A1

WO2019122423A1 - Article comprising a substrate and a porous layer comprising polyolefin particles

Info

Publication number: WO2019122423A1
Application number: PCT/EP2018/086780
Authority: WO
Inventors: Leonardus Gerardus Bernardus Bremer; Francois Antoine Marie Op Den Buijsch; Petrus Henricus Maria Elemans; Jun Qiu; MengMeng ZONG
Original assignee: Dsm Ip Assets B.V.
Priority date: 2017-12-21
Filing date: 2018-12-21
Publication date: 2019-06-27

Abstract

This invention relates to an article comprising a substrate and a porous layer, which porous layer comprises polyolefin particles having a mass-median- diameter, d50, of between 0.1 micrometer and 5.0 micrometer as measured with a Malvern Mastersizer 2000 and wherein the polyolefin has a MFI of at most 1000 (dg/min) at 2.16 kg/190 °C, ISO 1133 and the polyolefin particles have an acid number of at most 4.0 mg KOH/g. The invention also relates to a method to prepare the article as well as a dispersion useful to be employed to the method.

Description

ARTICLE COMPRISING A SUBSTRATE AND A POROUS LAYER COMPRISING

POLYOLEFIN PARTICLES

This invention relates to an article comprising a substrate and a porous layer comprising polyolefin particles, a method to prepare such article and a dispersion which may be employed in the method to prepare the article.

Articles comprising a substrate and a porous layer of polyethylene particles are known and are for example disclosed in US2013/0022858. This document discloses a separator for batteries with a non-woven as substrate and a porous layer of thermoplastic particles which are smaller than the mean pore size of the non-woven.

To achieve such layer, the particles of a dispersion have been flocculated into larger floes. Disadvantage of this method is that the thickness of the porous layer is larger than the average size of the particles. Strongly flocculated particles yield a high porosity and permeability, but a thick layer, which is undesirable, as thick layers entail substantial dead-weight in the battery separator. Moreover, the layers in the examples are 25 pm thick and have only 15% porosity and employ particles with an acid number of 35 mg/gm.

Articles comprising a substrate and a porous layer of larger particles are also known and are for example disclosed in US2013/0017431. This document describes a separator for batteries with a non-woven substrate coated with particles with a number average particle size that is at least equal to the mean flow pore size. The particles disclosed in this document are oxidized polyethylene, which usually results in a high acid number.

Polyolefin dispersions with higher molecular weight and lower particle sizes are known from for example US2005/271888, but these usually have a high acid number, which may result in unwanted swelling when applied as a layer in battery separators or on other substrates. Such dispersions often form a non-porous film upon drying.

EP2485297A discloses a separator with a base film and a powder, which powder is different from the base film. All powders have a low molecular weight, which may result in insufficient mechanical properties.

A general way to prepare polyolefin dispersions with low particle size is by using acid-functional polyolefins and thus having a high acid number, neutralizing the acid groups with amines, metal hydroxides, or other bases and subsequently mixing the molten resin in hot water; an emulsification process. By adding surfactants, the particle size can be further reduced as known by a person skilled in the art. The acid functional polyolefins are known as emulsifiable polyolefins, or emulsifiable waxes if they have a low molecular weight.

Polyolefins and waxes with an acid number below 10 mg KOH/g are generally known as“non-emulsifiable”. Other processes such as micronization, grinding, milling, prilling, usually lead to bigger particles, above 5 pm, especially if the polymer is not a low molecular wax but has a molecular weight above 50 kDa. Particles with lower size than 5 pm and higher acid number than 15 mg KOH/g lead to insufficient porosity unless they are applied in a significant smaller amount than needed to form a layer.

Polyolefin dispersions with lower particle size and acid number below 10 mg KOH/g are for example described in Polymer, 45 (2004) 5961-5968. Coating a porous substrate with such particles enables thin homogeneous coatings, but the presence of the surfactant may block the pores in an analogous way as in the case of particles with higher acid numbers. There are also other academic studies where emulsion polymerization of ethylene is used to prepare very small particles. An example is described in Macromolecules 2014, 47, 6591 -6600, but again the amount of surfactant relative to the amount of polyethylene is large and such particles are usually far below 0.5 pm, which may cause blockage of pores.

It is thus an object of the present invention to provide an article comprising a substrate and a porous layer, which exhibit these drawbacks to a lesser extent.

This has been accomplished by an article comprising a substrate and a porous layer, which porous layer comprises polyolefin particles having a mass- median-diameter, d50, of between 0.1 micrometer and 5.0 micrometer as measured with a Malvern Mastersizer 2000 and wherein the polyolefin has a MFI of at most 1000 (dg/min) at 2.16 kg/190 °C, ISO 1133 and the polyolefin particles have an acid number of at most 4.0 mg KOH/g. Surprisingly, the article exhibits a porous layer comprising polyolefin particles, which layer may be very thin. Surprisingly, the porous layer may have a thickness that is at most 5 pm, preferably at most 3 pm, more preferably at most 2 pm, while maintaining porosity. The article may be used in several applications, e.g. battery separator, electrode, membranes. Surprisingly, the porous layer in combination with a substrate may function as shutdown membrane when applied in a battery, thereby combining porosity and the ability to melt upon reaching higher temperatures. Dispersion is herein defined as a phase in which particles are dispersed in a

continuous phase of a different composition. The continuous phase may be a gas or a liquid and may for example be air or water but also ethanol, propanol, n-methyl pyrrolidone, or typical battery liquids like ethyl-carbonate or methyl-carbonate and their mixtures. A dispersion thus includes particles in air, which for example may be obtainable after freeze drying.

Figure 1 is a schematic representation of an embodiment of the article according to the invention. Polyolefin particles are numbered 1-20. Between the polyolefin particles pores or voids are present, which make the layer porous, and for example allow for transport of other materials, e.g. lithium salts when used in a battery application. The black material of the particles, and thus part of the particles, may consist of for example acid-groups or surfactants and may contain absorbed liquid if the porous layer is wet. This material is needed in a particle dispersion with particle size below 5 pm to stabilizes the particles, but it may block the pores of the porous layer.

Figure 2 is a schematic representation of another embodiment of the article according to the invention. Polyolefin particles are numbered 1-15, and this embodiment also shows other particles being present in the porous layer, which are numbered A, B, C. These particles do not comprise polyolefin, and may for example be ceramic particles like S1O2, AI2O3, ZrC>2 and other metal oxides and hydroxides, carbon materials like graphene, carbon black or carbon nanotubes, conductive polymer particles like PEDOT and other polythiophenes, polypyrroles, polyacethylene or polyaniline or metal particles or metal fibers or Li binding materials like graphite, silicon, tin or aluminium as well as combinations thereof.

“Polyolefin particles” are herein understood to be particles comprising polyolefin, which are exemplified in Figures 1 and 2 by the numbered particles 1-20, 1- 15 respectively. Polyolefin particles may thus comprise further ingredients, such as polyethylene oxide polyalkylene oxide block copolymer, as described below and indicated as a black layer in figures 1 and 2.

Substrate

The article according to the invention comprises a substrate. The substrate can have a wide range of applications, such as a non-woven, a woven, a membrane, a part of a separator for batteries, an electrode, current collector, packaging material, and includes a wide variety of materials, such as plastics including polyolefins, wool, cotton, metal films or plates, wood, paper, ceramics. The substrate may be porous itself, as may for example be the case when the substrate is a membrane, a non-woven and/or a part of a separator for batteries.

Substrates have already functionalities by itself like porosity and/or strength. Such functionalities are in general known by a person skilled in the art.

Specific substrates have a quantified range of functionalities and the porous layer can either modify this range or add a new functionality.

Substrates being part of a separator may for example be made of polyethylene (PE), polypropylene (PP) or a laminate of both PE and PP. Typical thickness of a substrate for a separator is between 5 to 25 micrometer. Typical porosity values for substrates for separators are between 20 and 60%. The substrate being part of a separator may also be a non-woven. Typical thickness of a non-woven for separators include 10 to 40 micrometer.

The substrate may also be a solid. Substrate can be a copper foil or for example a porous structure itself which may subsequently coated to create the porous layer.

The substrate may also be part of an electrode for use in batteries, including cathode and/or anode. Porous layer

The article according to the invention comprises a porous layer comprising polyolefin particles having a mass-median-diameter, d50, between 0.1 micrometer and 5.0 micrometer and preferably a span (d90-d10)/d50 below 2, as measured with a Malvern Mastersizer 2000 and wherein the polyolefin has an MFI of at most 1000 (dg/min) at 2.16 kg/190 °C, ISO 1133 and the polyolefin particles have an acid number of at most 4.0 mg KOH/g. Preferably, the MFI is at most 700 and most preferred at most 500. Preferably, the polyolefin particles have a mass-median- diameter, d50, between 0.5 and 3.0 micrometer, and even more preferred between 0.1 and 2.5 micrometer.

“Porous layer” is herein understood as including being porous for both liquid and ions in a liquid, especially Li ions in a wet state, as well as air. This can be measured by electrical resistance or impedance measurements. Such measurements are a preferred method in the case of a porous layer on a non-porous substrate. Also, the layer on a dry article may be permeable for air. This can be measured on a porous substrate by a Guriy measurement. The effect of the porous layer is preferably less than 30 Guriy seconds on top of the value of the substrate without the porous layer.

Preferably, the acid number of the polyolefin particles is at most 1.0 mg KOH/g and even more preferred the acid number is at most 0.5 mg KOH/g. The acid number may even be as low as at most 0.2 mg KOH/g, or at most 0.1 mg KOH/g and may even be at most 0.01 mg KOH/g and even be 0 mg KOH/g. A lower acid number has the advantage that smaller polyolefin particles can be used in the dispersion and as a result that thinner coatings and thus a thinner porous layer can be achieved. The porosity and permeability of a low acid number porous coating on a separator is higher compared to a coating made with particles having a higher acid number with the same size. Polyolefin particles with a low acid number also penetrate less inside pores of a substrate, in case the substrate is porous itself, because they feel attractive hydrophobic interaction with hydrophobic substrates and stick to the surface before entering a pore. Furthermore, a low acid number may prevent adhesion to most other materials except polyolefins and it makes the surface of a coating more hydrophobic.

Preferably the polyolefin is polyethylene, as this has the advantage that the melting temperature may be adjusted between 40 to 135 °C, by the degree of branching of the polyethylene. A controlled way to do this is by employing various comonomers such as alpha olefins, such as propene, 1 -butene, 1-pentene, 1 -hexene, 1-heptene, 1-octene. There are many variations in molecular weight and branching of the polymeric chain known to people skilled in the art. Preferred in this disclosure are linear polyethylenes with a narrow molecular weight distribution and short branching. In one embodiment, the polyolefin is a linear low density polyethylene with 1-octene.

The porous layer may optionally comprise a polyethylene oxide polyalkylene oxide block copolymer in an amount of at most 7 wt% with respect to the total weight of the polyolefin particles in the porous layer, more preferably the amount is at most 4 wt%, and most preferred at most 2 wt%. A low amount, or even absence of polyethylene oxide polyalkylene oxide block copolymer, has the advantage that interference with pores is reduced.

The polyethylene oxide polyalkylene oxide block copolymer includes di- and triblock copolymers, such as for example polyethylene oxide polypropylene (PEO-PPO), PEO-PPO-PEO, PEO-polytetrahydrofurane (pTHF), PEO-pTHF-PEO. Preferred is PEO-PPO-PEO, as for example available under the name Synperonic PE/F108 of Croda, INCI“Poloxamer 338” and BASF Pluronic F108. The porous layer comprises polyolefin particles, preferably the amount of polyolefin particles is at least 50 wt%, with respect to the total weight of the porous layer. More preferably, the amount of polyolefin particles is at least 60 wt%, and even more preferred at least 70 wt%. The porous layer may optionally contain other particles such as carbon black or other inert polymeric spheres or ceramics, preferably in quantities less than 50 wt% of the total weight of the porous layer so that the functions of the polyolefin are significant. Other optional particles in the porous layer may for example be S1O2, AI2O3, Zr0₂ and other metal oxides and hydroxides, carbon materials like graphene, carbon black or carbon nanotubes, conductive polymer particles like PEDOT and other polythiophenes, polypyrroles, polyacethylene or polyaniline or metal particles or metal fibers or Li binding materials like graphite, silicon, tin or aluminium as well as combinations thereof.

The article according to the invention may exhibit a narrow pore size distribution that is depending on the size of the particles in the porous layer and their polydispersity. When applied as separator for batteries, the porous layer may provide a safety function as shut down of the battery separator, if heated above a certain temperature that can be chosen as a function of the melting temperature of the polyolefin particles.

Methods for preparing the article

The invention also relates to methods for preparing the article according to the invention. Methods always comprise the following steps;

a) Providing a substrate;

b) Providing a dispersion;

c) Coating of the dispersion unto the substrate thereby obtaining a coated

substrate;

d) Drying the coated substrate thereby obtaining the article.

The substrate as disclosed in step a) encompasses all embodiments as elaborated above. The dispersion provided in step b) comprises polyolefin particles having mass-median-diameter, d50, of between 0.1 micrometer and 5.0 micrometer and wherein the polyolefin has a MFI of at most 1000 at 2.16 kg/190 °C, ISO 1 133, and a polyethylene oxide polyalkylene oxide block copolymer and the polyolefin particles in the dispersion have an acid number of at most 4.0 mg KOH/g. Step c) includes coating methods which are known to the people skilled in the art like dip coating, roll coating, spray coating, immersion coating, Metering rod or Meyer Bar Coating, Spin Coating, Langmuir - Blodgett coating technology or simple deposition. Further steps as optionally employed in the method for preparing the article include introducing a wetting agent, leveling agent and/or binder to the dispersion to facilitate coating.

Depending on the amount of polyethylene oxide polyalkylene oxide block copolymer in the dispersion, the coated substrate may be subjected to a washing step, in order to reduce the amount of polyethylene oxide polyalkylene oxide block copolymer. Alternatively, the dispersion as provided in step b) already contains a relatively low amount of polyethylene oxide polyalkylene oxide block copolymer, in which a washing step of the coated substrate may be omitted.

An advantage of employing a dispersion comprising a relative high amount of polyethylene oxide polyalkylene oxide block copolymer, similar to the dispersion disclosed in Polymer 45 (2004) 5961-5968, is that the dispersion is very stable. However, a disadvantage is that additional step is required to lower the amount of polyethylene oxide polyalkylene oxide block copolymer. After step c) the amount of polyethylene oxide polyalkylene oxide block copolymer as compared to the polyolefin particles in the porous layer has to be lowered, by for example rinsing, permeation in for example water, ethanol or other liquids.

The method may also be performed with a dispersion comprising a relative low amount of polyethylene oxide polyalkylene oxide block copolymer. The amount of polyethylene oxide polyalkylene oxide block copolymer may be lowered by concentrating the polyolefin particles in the dispersion. Concentration of the polyolefin particles can for example be done by centrifugation of a diluted dispersion and a cream of concentrated polyolefin particles can then be recovered. The degree of dilution determines the remaining amount of polyethylene oxide polyalkylene oxide block copolymer in the obtained cream. The cream can be stored wet, or it can be freeze dried into a powder that can be stored for long time. Such cream or powder can be re- dispersed and diluted in water using for example a rotor - stator mixer or other mixers that avoid air-intake. Dispersions that are prepared this way are stable for some time but may slowly start flocculating resulting in solidification within a few days. Before flocculation, the dispersion can be used for coating and due to the slowly increasing hydrophobicity of the particles they show self-assembly at hydrophobic substrates. This results in dense monolayers of particles on top of the substrate. Such particles also form monolayers at the water - air interface. Therefore Langmuir - Blodgett coating technology can advantageously be applied. The particles can be spread on the water - air interface from solutions in various solvents like chloroform, alkanes, ethanol, isopropanol. The advantage of this technology is more control of the morphology of the film and the number of particles that are deposited. Monolayers can be compressed to dense structures with small pores and relative low permeability, but they can also be less compressed and have less particles per area. The latter will result in more permeability.

Still another embodiment of a dispersion comprising a relative low amount of polyethylene oxide polyalkylene oxide block copolymer, is by employing additives that anchor to the polyolefin particle surface and that stabilize the particles in the dispersion. Anchoring of stabilizing groups may be by chemical grafting or by the addition of amphiphilic molecules with a high affinity for the polyolefin. There are many different stabilizers known by a person skilled in the art. Some examples are PE-PEO block copolymers, trisiloxane- ethoxylates, alkane-carboxylic acid salts, saponified copolymers of maleic anhydride and alpha olefins and dioctyl sulfosuccinate salts. Some commercial examples are Byk 348, Byk LP X 20990, Byk LP C 22134, Dow Corning 67 or Dow corning 500W, Cytec Aerosol OT. Many of such stabilizers are also known as wetting agents. Wetting agents as such are known to a person skilled in the art and they have the advantage of wetting of the substrates, especially if they are apolar like most battery separators. The advantage of anchoring the stabilizers after making the particles instead of using the stabilizers while preparing the dispersion is that much less stabilizer is needed to stabilize than to make the dispersion.

Subsequently, in step d), the coated substrate is dried using methods as known by people skilled in the art. In order to keep the porosity, it is advantageous that the maximum temperature during drying is lower than the melting or softening point of the particles. For good adhesion to polyolefins the particles preferably need to melt to some extent.

Dispersions

The invention also relates to a dispersion, being an intermediate product, which may advantageously be applied in the method according to the invention. The dispersion according to the invention comprises polyolefin particles having mass-median-diameter, d50, of between 0.1 micrometer and 5.0 micrometer and wherein the polyolefin has a MFI of at most 1000 at 2.16 kg/190 °C, ISO 1 133, and optionally a polyethylene oxide polyalkylene oxide block copolymer in an amount of at most 10 wt% with respect to the total weight of the polyolefin particles, and the polyolefin particles have an acid number of at most 4.0 mg KOH/g. Preferably, the MFI is at most 700 and most preferred at most 500. Preferably, the polyolefin particles have a mass-median-diameter, d50, between 0.5 and 3.0 micrometer, and even more preferred between 0.1 and 2.5 micrometer.

The polyethylene oxide polyalkylene oxide block copolymer includes di- and triblock copolymers, such as for example polyethylene oxide polypropylene (PEO-PPO), PEO-PPO-PEO, PEO-polytetrahydrofurane (pTHF), PEO-pTHF-PEO. Preferred is PEO-PPO-PEO.

Acid number of polyolefin particles in a dispersion is measured by titration with a 0.001 n poly-DADMAC solution in water. The equivalence point of the titration is detected by a BTG Mijtek Streaming current detector for colloidal charge measurement. Dispersions are first diluted in water to a concentration of 3 to 6% solids. Then 300 pi of the dispersion is added to roughly 15 ml demineralized water and the pH is adjusted by adding 1 ml 0.1 M NH₃/NH₄ ⁺ buffer pH=10 and its value remains between 9.5 and 10 during the titration. The amount of 0.001 n poly-DADMAC solution in water that is needed to neutralize the acid groups is used to calculate the acid number, AN, expressed in mg KOH per g dried solids via the formula AN = ml 1 meq polyDADMAC / mg solids x 56.2 mg/mmol.

Preferably, the dispersion comprises polyolefin particles in an amount of at least 30 wt%, based on the total weight of the dispersion. Preferably the polyolefin is polyethylene, as this has the advantage that there are many different types available with melting temperatures between 40 to more than 120 °C. The melting temperature and the density of the polyethylene are dependent on the crystallinity. The highest level of crystallinity and density is obtained in linear, un-branched high density polyethylene and its melting point is about 135 °C. Branching of the molecule results in lower density and melting points and this can be achieved during the polymerization reaction with metallocene catalysts by employing various comonomers in small quantities, such as linear or branched alpha olefins, such as propene, 1 -butene, 1-pentene, 1 -hexene, 1- heptene, 1-octene and 4-methyl-1-pentene. Increasing the branching leads to a depression of melting point and density for metallocene grade LLDPE. For Ziegler grades the increased branching leads to lower density but Tm will plateau at about 120 °C and will have a broad melting behavior due to inhomogeneous incorporation of the branches. Therefore, linear low density polyethylenes are the preferred materials.

Commercial examples are available in a wide range of MFI values, with various co- monomers and melting points. Examples include materials of Borealis, Queo 8210 or 8230 with melting point of 75 °C, Queo 0210, Queo 1007, Ineos Eltex PF6180AA, PF1315AA or PF1320AA with melting points close to 100 °C and to the higher density and melting point domain SABIC HDPE CC2056 with a melting point of 132 °C. Further commercial materials include Exceed, Enable and Exact grades of Exxon, Marlex of Chevron Phillips Chemical, Elite and Affinity of Dow or TUX and Evolue of MITSUI.

In one embodiment the polyolefin is a linear low density polyethylene with 1-octene. The advantage of these materials is that they combine a high flow after melting with good mechanical properties after crystallization.

Preferably, the dispersion has an optional amount of polyethylene oxide polyalkylene oxide block copolymer of at most 9 wt%, more preferred at most 8 wt% and even most preferred at most 7 wt%, with respect to the total weight of the polyolefin particles. The advantage of having a low content of polyethylene oxide polyalkylene oxide block copolymer is that a washing step may be omitted to reduce the content of polyethylene oxide polyalkylene oxide block copolymer. For certain applications, a washing step is not feasible, and thus a dispersion according to the invention may advantageously be used to provide a porous layer onto substrates which cannot be washed. A higher amount of polyethylene oxide polyalkylene oxide block copolymer increases the stability of the dispersion.

The polyolefin particles in the dispersion have an acid number of at most 4.0 mg KOH/g, preferably an acid number of at most 1.0 mg KOH/g and even more preferred an acid number of at most 0.5 mg KOH/g.

In one embodiment, the dispersion has a low liquid content of for example less than 10 wt%, with respect to the total weight of the dispersion, more preferably less than 5 wt%. This has the advantage that stability of the dispersion is enhanced, which for example facilitates transportation of the dispersion. Obtaining a low liquid content may for example be achieved by freeze drying the dispersion.

In another embodiment, the dispersion may comprise a liquid in an amount of for example at least 50 wt%, with respect to the total weight of the dispersion. The presence of a liquid facilitates application of the dispersion onto the substrate. The term“liquid” is known to a person skilled in the art. A suitable liquid may for example be water, ethanol, propanol, or typical battery liquids like ethyl-carbonate or methyl-carbonate and mixtures thereof. Preferably, the liquid is water, as this has the advantage that it is non-hazardous.

In one embodiment, the dispersion contains a wetting agent.

Surprisingly, presence of a wetting agent enhances the stability of the dispersion. Examples

Materials used to prepare polyolefin particle dispersions

Linear ethylene-octene copolymers and other PE copolymers:

Queo 8210 of Borealis; MFI 10 (2.16 kg/190 °C, ISO 1 133);

Queo 0210 of Borealis; MFI 10 (2.16 kg/190 °C, ISO 1 133);

Queo 1007 of Borealis; MFI 7 (2.16 kg/190 °C, ISO 1 133);

Queo 0230 of Borealis; MFI 30 (2.16 kg/190 °C, ISO 1 133);

Sabic HDPE CC3054; MFI 30 (2.16 kg/190 °C, ISO 1 133);

Dow Affinity GA 1950; MFI 500 (2.16 kg/190 °C, ISO 1 133);

Blend Queo 8201 of Borealis; MFI 1 .1 (2.16 kg/190 °C, ISO 1 133) and Affinity GA 1950 50% m/m

Polyethylene oxide polyalkylene oxide block copolymer;

Synperonic PE/F108 of Croda

Synperonic PE/F68 of Croda.

Demineralized water.

Table 1. Amounts of the materials that are used to prepare polyolefin particle dispersions.

Polyolefin dispersions were prepared with a Berstorff ZE25R twin- screw extruder (#2 - #6) or with a Haake batch mixer (#1 , #7 - #10). Ingredients are listed in Table 1. For #2 - #6, the polyolefin was dosed together with polyethylene oxide polyalkylene oxide block copolymer to the extruder. The first three houses of the extruder were designed to melt and compact the ingredients such to create a melt lock. Heated water was injected to the melt at house 4 and house 7 and mixing and transport elements took care for intense mixing of the composition. A throttle barrel in house 10 kept the extruder well filled and a third water injection at house 1 1 diluted the composition into a low viscous dispersion that was further mixed and cooled down in houses 12, 13 and 14 after which it was collected.

The Haake batch mixer was filled with the polyolefin material that is first molten and mixed intensively. Subsequently, the Synperonic PE/F108 is added to the blend and again mixed intensively before slowly adding the water.

The size of the polyolefin particles can be decreased by using a higher molecular weight PEO-PPO-PEO block copolymer or by using a polyolefin with a higher MFI value.

Washing and purification of the dispersions

Dispersion #2 was mixed in a ratio 1 :1 mass/mass with water and then the polyolefin particles were separated by centrifugation for 30 minutes in a centriflex lab centrifuge (Siebtechnik GmbH) running at 4000 RPM. The creamed cake was diluted in demi water and referred to as dispersion #2a.

Dispersion #4 was mixed in a ratio 1 :1 mass/mass with water and 200g of this dilute dispersion was subject to diafiltration in an Amicon Stirred Cell of 400ML with a 0.2 pm Nuclepore Polycarbonate membrane. At first a small sample of permeate was collected and then diafiltration was started via a container with water placed about 50 cm above the stirred cell. The hydrostatic pressure was forcing the water into the dispersion through the filter. One liter of water was passed through the dispersion and after some time during the process the stirrer stopped because the Synperonic PE/F108 is washed out to such extent that the PE particles are no longer stable in water and coagulate to a solid cake on the filter. Some rest of the water permeates through this cake that contained about 70% dry matter after it was collected. The dry matter content is determined on a Mettler Toledo HR73 Halogen Moisture Analyzer set at 200°C temperature. The initial permeate is a clear liquid and contains 5.4% solids. In the end the solids content of the permeate is less than 0.5%.

The filtered cake is dispersed in a small amount of water and this polyolefin particle dispersion had a solids content of 48.9% and is referred to as dispersion #4a.

Dispersion #6 was also diluted with water 1 :1 mass/mass and 5 centrifuge tubes were filled with 40 g dispersion each and placed in an Eppendorf 5430R centrifuge. They were centrifuged at 7800 RPM for 45 minutes and 46 g solid creamed material was collected. The solids are dispersed with a Sonics Vibracell probe after adding 46 g water and this dispersion is called dispersion #6a.

Dispersion #7 was diluted; 100 g product and 300 g water, and concentrated with the Amicon stirred cell with 0.2 pm Nuclepore membrane to 100 g. This dispersion is dispersion #7a.

Table 2. Data about dispersions

and a PE separator. As the particles in table 2 of examples #1 to #3 all consisted of polyolefin, the acid number of the polyolefin and of the polyolefin particles is the same and stated in Table 2. The air permeability was measured with the Gurley test method according to ISO 5636-5. using a measuring area of 6.45 cm² (1 square inch) and a weight of 567 grams. The Gurley value of the separator was obtained using a Gurley- type densometer (41 10N and 4320EN, Gurley precision instrument) by measuring the time of 100 cc air to pass through the separator.

Base weight (BW) was determined according to ASTM D3776 and reported in g/m².

The base weight was calculated using the following equation

mass

BW -

A

Wherein,

BW= base weight or total mass per surface area in g/m²

Mass= mass of the sample in gram

A= surface area of the sample in m²

Thickness was measured according to ISO04593. Thickness was determined using Millitron 1234-1 C thickness scanner the thickness scanner has a lower plane surface an an upper plane measuring surface with a diameter of 1 1.3 mm (100 mm²) parallel to the lower surface. The thickness scanner has a probe of Millimar (P2004 MA/4 mm, Mahr) with a pressure of 0.75 ± 0.15 N. Table 3. Results of non-woven separator and porous layer

Table 4. Results of PE separator and porous layer

Aquaseal and DOW Hypod dispersions resulted in film formation instead of obtaining a porous layer. #1 , #2, #3 and M200 resulted in a porous layer for air permeation. However, M200 exhibited a very high swelling ratio (107%) when subjected to an electrolyte (1 Mol LiPF6 EC/DMC 1 :1 vol/vol) for 4 days at 60 °C, which is undesirable when employed in batteries, as the swelling also results in a non-porous layer in electrolyte. Dispersion #2a exhibited a swelling ratio of only 9.1%. The swelling ratio is the mass increase of the dried material in the electrolyte divided by the mass of the dried material.

Membrane permeability tests

A Pall 25 mm Acrodisc filter with 1.2 pm Versapor membrane was permeated with 2.5 ml of a mixture of 1.0 g dispersion #1 and 44 g demineralized water. The mixture (1 % solids content) easily permeated the filter and the permeate was clear. Subsequently, the coated filter was flushed with 7.5 ml demineralized water. To test the pore size of the filter 0.49 pm red fluorescing Polymer Microspheres of Duke Scientific were used. The coated filter stopped all microspheres that are deposit as a red layer on top of the porous layer on the filter substrate. The non-coated filter stopped only a very small fraction < 10% of the microspheres. The experiment was repeated with more dilute dispersion #1 in water; respectively at 0.1% Wt solids content and 0.01% Wt solids. Again 2.5 ml of these dispersions were permeated through clean filters with 1.2 pm membranes, the filters were subsequently permeated with 7.5 ml demineralized water, and the pore size was tested. The filter with 2.5 ml 0.1 % dispersion deposited on its surface retained more than 90% of the 0.49 pm spheres but the filter with 2.5 ml 0.01 % dispersion stopped only a small fraction < 10% of the microspheres.

The dispersions of table 2 were diluted with water to obtain dilute dispersions with 1% mass/mass solids content. Of each of the dispersions a coating layer was applied on 200 nm PVDF membranes in Pall 25 mm Acrodisc filters by permeating 2.6 ml dispersion through the membrane. This is particularly easy for the dispersions according to the invention, and comparative dispersions A, D, E and F could also be applied on the substrate. In comparative dispersions B and C, the filter blocks before permeating the 2.6 ml dispersion.

Subsequently, more dispersion was pressed through the filter at a constant pressure of 1.4 bar and the amount of permeate after 2 minutes was measured. Results are given in table 5.

Table 5. Permeability of membranes with particles from table 2.

Guriy shutdown tests of dry separators

Porous layers were applied on substrates by using a a 12 pm spiral wire applicator (K- bar). More specifically, a battery separator was used as substrate and formulations were coated, resulting in a porous layer and thus in an article according to the invention. The separator was placed on a paper sheet on top of a glass plate and the bar with a layer of coating formulation was drawn by hand over the separator. In other coating experiments a mechanical device was used and here the separator was placed on paper on top of a rubber sheet. The layer thickness was adjusted by the

concentration of the polyethylene dispersion. The substrate, the hardness of the material beneath the substrate, and the speed and pressure on the K-bar have also some effect on the amount of material that was coated on the substrate. The amount of porous layer was determined by measuring the base-weight.

Coating formulations comprising polyolefin particle dispersions #4 (formulation A), #4a (formulation B), and #6a (formulation C) were prepared as described in table 6. The substrates were 15 pm polyethylene separators and polyethylene separators (PE) with a ceramic coating on both sides (PE-Alox). After applying the coating formulation, the separators were stored for 1 h at the indicated temperature to dry the coating and to obtain adhesion to the separator substrate (table 7). Adhesion can also be achieved by using a binder and in formulation D, polyolefin particle dispersion #7a was used as binder. Another material that was needed for coating a porous layer on a polyethylene porous substrate is a wetting agent. Dow Corning 500W additive was used for this purpose. The additive also had a very positive effect on the stability of the coating formulations and dispersion #6 needed slightly more additive than dispersion #4 to obtain homogeneous coated layers.

Table 6. Formulations used to coat substrates with a 12 pm K-bar

Table 7. Articles (coated separators) prepared with the coating formulations of table 6 comprising polyolefin particle dispersions of table 2 and relevant processing parameters.

Substrates without porous layer and thus comparative experiments, in this case separators #0-1 and #0-2, and articles comprising a substrate and a porous layer, in this case coated separators, were stored at several temperatures for 1 h. After storing the Guriy was measured. A shut-down, indicated by a strong increase of the Guriy, was observed for articles according to the invention, thus the coated separators (see table 8).

Table 8. Shut-down of the articles. Indicated are the Guriy seconds measured after storing the article for 1 h in an oven with the indicated temperature. Guriy values were measured at room temperature after cooling the articles.

Article #4a-1 shows a shutdown of the permeability at 100 °C. Article #6a-1 shows no clear shut-down because the substrate started to shrink at lower temperatures than the temperature where the polyolefin particles started to melt. In this test the separator could freely shrink, and this is the reason for apparent shut-down of #0-1 and #6a-1 , as indicated by a ^*. The ceramic coating stopped this shrinking and article #6a-2 shuts down from about 120 °C. Without the polyolefin particles porous layer, #0-2

comparative experiment, the permeability increased with temperature before shut-down occurs at the melting point of the separator.

Guriy shutdown test after immersion in hot aprotic solvent

The kinetics of the shut-down was tested by immersion of the articles, #6a-2 and #6a-3 in a hot aprotic solvent; tetraglyme. The article was immersed for 1 s in the hot liquid and subsequently quenched, while removing the absorbed liquid, in a bath filled with ethanol. The Guriy test was performed after drying the article at ambient conditions. At temperatures below 120 °C this immersion and fast heating had no influence on the Guriy value. At 125 °C the porous polyolefin particles layer forms a film within 1 s and the Guriy value was increased to 428 s. Article #6a-3 with a somewhat thinner porous layer did not shut down at this condition. Above 130 °C the articles shrunk in the hot liquid, also if they are slowly heated from 120 °C to 140 °C. The ceramic layer turned out to be less effective at wet conditions but the shut-down of the porous PE layer can avoid reaching such elevated temperature in a battery.

Article #4a-1 was heated in the same set-up. At 88°C 1 s the Gurley value was almost not changed and 199 s. At 104 °C 1 s the Guriy value increased to 309 s and at 1 18 °C to 319 s. During longer immersion the Guriy increased further to 615 s (5 minutes at 1 15 °C). The comparative example #0-1 had a Guriy of 199 s after 5 minutes immersion in 115 °C tetraglyme.

Electric shutdown tests in electrolyte

Articles #4-1 , #4a-1 , and comparative experiment #0-1 were tested in impedance measurements in a battery environment. Five specimens of each article were stacked and soaked with a battery fluid, LP30. The temperature was increased in steps of 10 °C starting at 20 °C until 130 °C and then back to 20 °C. Each temperature was maintained for 4 hours and every 5 minutes an impedance spectrum was measured. The impedance measurement lasts 1 min 25 s and was followed by a 3 min 35 s OCV step. Comparative experiment #0-1 showed no shutdown at any of the tested temperatures and the resistance is < 10 Ohm. Article #4-1 showed an increased resistivity while heating to 90 °C (120 Ohm at 1 kHz) and a second increase while heating to 120 °C (500 Ohm at 1 kHz). Article #4a-1 showed an increased resistivity while heating to 100 °C (1000 Ohm at 1 kHz) further increasing while heating to 120 °C (4500 Ohm at 1 kHz).

Claims

1. An article comprising a substrate and a porous layer, which porous layer comprises polyolefin particles having a mass-median-diameter, d50, of between 0.1 micrometer and 5.0 micrometer as measured with a Malvern

Mastersizer 2000 and wherein the polyolefin has a MFI of at most 1000 (dg/min) at 2.16 kg/190 °C, ISO 1 133 and the polyolefin particles have an acid number of at most 4.0 mg KOH/g.

2. The article according to claim 1 , wherein the polyolefin particles have an acid number of at most 1.0 mg KOH/g.

3. The article according to claim 1 or 2, wherein the porous layer has a thickness of at most 5 micrometer.

4. The article according to any one of claims 1 to 3, wherein the d50 is between 0.5 micrometer and 3.0 micrometer.

5. The article according to any one of the preceding claims, wherein the porous layer comprises a polyethylene oxide polyalkylene oxide block copolymer in an amount of at most 7 wt% with respect to the total weight of the polyolefin particles in the porous layer, preferably at most 4 wt% and even more preferred at most 2 wt%.

6. The article according to claim 5, wherein the polyethylene oxide polyalkylene oxide block copolymer is PEO-PPO-PEO block copolymer.

7. The article according to any one of the preceding claims, wherein the

polyolefin is polyethylene.

8. The article according to any one of the preceding claims, wherein the amount of polyolefin particles is at least 50 wt%, with respect to the total weight of the porous layer.

9. The article according to any one of the preceding claims, wherein the

substrate is porous.

10. The article according to any one of the preceding claims, wherein the article is a battery separator.

1 1. Method for preparing an article according to any one of the preceding claims comprising a substrate and a porous layer, comprising at least the following steps:

a) Providing a substrate; b) Providing a dispersion comprising polyolefin particles having mass-median- diameter, d50, of between 0.1 micrometer and 5.0 micrometer and wherein the polyolefin has a MFI of at most 1000 (dg/min) at 2.16 kg/190 °C, ISO 1 133, and a polyethylene oxide polyalkylene oxide block copolymer, wherein the polyolefin particles have an acid number of at most 4.0 mg KOH/g, and a liquid and optionally other components;

c) Coating of the dispersion unto the substrate thereby obtaining a coated substrate;

d) Drying the coated substrate thereby obtaining the article.

12. Method according to claim 1 1 , wherein the dispersion provided in b)

comprises a polyethylene oxide polyalkylene oxide block copolymer in an amount of at most 7 wt% with respect to the total weight of polyolefin particles, preferably at most 4 wt% and even more preferred at most 2 wt%.

13. Dispersion comprising polyolefin particles having mass-median-diameter, d50, of between 0.1 micrometer and 5.0 micrometer and wherein the polyolefin has a MFI of at most 1000 at 2.16 kg/190 °C, ISO 1133, and optionally

polyethylene oxide polyalkylene oxide block copolymer in an amount of at most 10 wt% with respect to the total weight of the polyolefin, and the polyolefin particles have an acid number of at most 4.0 mg KOH/g.

14. Dispersion according to claim 13, wherein the dispersion has a liquid content of less than 10 wt% with respect to the total weight of the dispersion.

15. Dispersion according to claim 13, further comprising a liquid in an amount of at least 50 wt% with respect to the total weight of the dispersion.

16. Dispersion according to claim any one of claims 13 to 15, wherein the liquid is water.