阅读说明：本技术 填充有纳米颗粒的多孔膜及相关方法 (Porous membranes filled with nanoparticles and related methods ) 是由 C·格伦·温斯利 石烈 于 2014-09-18 设计创作，主要内容包括：一种膜包括由聚合物材料制成的多孔膜或层,所述聚合物材料在其中分散有平均粒度小于约1微米的许多表面经处理(或涂布)的颗粒(或陶瓷颗粒)。聚合物材料可选自聚烯烃、聚酰胺、聚酯、它们的共聚物以及它们的组合。颗粒可选自勃姆石(AlOOH)、SiO-(2)、TiO-(2)、Al-(2)O-(3)、BaSO-(4)、CaCO-(3)、BN以及它们的组合,或者颗粒可以是勃姆石。表面处理(或涂布)可以是具有反应性端部和非极性端部的分子。在将颗粒与聚合物材料混合之前可以将其在低分子量蜡中预混合。膜可用作电池隔板。(A membrane includes a porous membrane or layer made of a polymeric material having dispersed therein a plurality of surface treated (or coated) particles (or ceramic particles) having an average particle size of less than about 1 micron. The polymeric material may be selected from the group consisting of polyolefins, polyamides, polyesters, copolymers thereof, and combinations thereof. The particles can be selected from boehmite (AlOOH), SiO 2 、TiO 2 、Al 2 O 3 、BaSO 4 、CaCO 3 BN, and combinations thereof, or the particles may be boehmite. The surface treatment (or coating) may be a molecule having a reactive end and a non-polar end. The particles may be pre-mixed in a low molecular weight wax prior to mixing with the polymeric material. The membrane may be used as a battery separator.)

1. A battery, comprising: a negative electrode, a positive electrode, a separator sandwiched between the negative electrode and the positive electrode, an electrolyte circulating between the negative electrode and the positive electrode,

the separator comprises a porous membrane or layer made of a polymeric material having dispersed therein a plurality of wax-coated surface-treated boehmite particles having an average particle size of 20-200 nm; the film comprises up to 10 wt% boehmite particles.

2. The battery of claim 1, wherein the polymeric material is selected from the group consisting of polyolefins, polyamides, polyesters, copolymers thereof, and combinations thereof; preferably, the polyolefin is selected from the group consisting of polyethylene, polypropylene, polybutylene, polymethylpentene, copolymers thereof, and combinations thereof.

3. The battery of claim 1, wherein the plurality of wax-coated surface-treated boehmite particles comprise 9.5-10% by weight of the polymeric material.

4. The battery of claim 1, wherein the surface treatment is a molecule of a reactive end and a non-polar end.

5. The battery of claim 1, wherein the membrane is a layer of a multilayer separator; the battery is a lithium battery; the battery is a secondary lithium battery; alternatively, the battery is a lead acid battery.

6. The battery of claim 1, wherein,

said porous membrane or layer made of a polymeric material having dispersed therein a plurality of surface treated particles having an average particle size of less than about 1 micron;

the film further comprises a wax on the surface-treated particles;

the plurality of surface treated particles comprise 0.1-30% by weight of the polymeric material;

the particles comprise a surface treatment or coating selected from boehmite (AlOOH), SiO₂、TiO₂、Al₂O₃、BaSO₄、CaCO₃BN, and combinations thereof; and/or

The average particle size is less than about 500 nanometers.

7. A method of making a membrane comprising the steps of:

mixing the dried surface-treated particles with a wax, thereby forming a first mixture;

mixing the first mixture with a polymeric material, thereby forming a second mixture; and

forming the second mixture into a porous membrane.

8. The method of claim 7, wherein,

the first mixing step comprises heating, and the first mixture is a fluid;

the wax has a molecular weight in the range of 800-;

forming the second mixture into a microporous membrane comprises: extruding the second mixture into a sheet or tube, annealing the sheet or tube, and stretching the annealed sheet or tube;

the polymeric material is selected from the group consisting of polyolefins, polyamides, polyesters, copolymers thereof, and combinations thereof;

the polyolefin is selected from the group consisting of polyethylene, polypropylene, polybutylene, polymethylpentene, copolymers thereof, and combinations thereof;

said plurality of surface treated particles comprises 0.1-30% by weight of said polymeric material;

the particles comprise a surface treatment or coating selected from boehmite (AlOOH), SiO₂、TiO₂、Al₂O₃、BaSO₄、CaCO₃BN, and combinations thereof;

the average particle size is less than about 500 nanometers; and/or

The surface treatment is a molecule having a reactive end and a non-polar end.

9. A film, comprising: a microporous membrane made of a polymeric material having a plurality of boehmite particles dispersed therein, preferably, the membrane comprises a wax; preferably, the polymeric material is selected from the group consisting of polyolefins, polyamides, polyesters, copolymers thereof, and combinations thereof; and/or, the plurality of boehmite particles comprises 0.1-30% by weight of the polymeric material.

10. A battery separator comprising the membrane of claim 1 or 9, preferably the membrane is a layer of a multilayer separator.

Technical Field

The present invention relates to particle-filled/impregnated membranes, microporous membranes filled/impregnated with surface-treated (or coated) nanoparticles, battery separators, related methods of manufacture and/or use, and the like.

Background

Battery separators filled with ceramic particles and coated with ceramic particles for secondary lithium batteries are known, such as those described in respective U.S. patent No. US7,790,320 and U.S. patent No. US6,432,586, each hereby incorporated by reference. It is believed that these separators enhance the thermal resistance and stiffness (strength and rigidity) of the polymer (e.g., polyolefin) layer by, for example, blocking dendrites, preventing short circuits, andstructure) to improve the safety of the secondary lithium battery. Typically, the particles of the prior art comprise considerable (some particle sizes)>1 micron) SiO₂、TiO₂、Al₂O₃、BaSO₄、CaCO₃And the like. However, these ceramic particles can be difficult to load and disperse into the polymeric material due to surface energy differences between the particles and the polymeric resin material. These problems become even more severe as the particle size moves from the micrometer range to the nanometer range as the surface energy of the particles increases even more.

Thus, the problem is to load and disperse at least some ceramic particles into the polymer resin used to form the membrane (e.g., battery separator).

Disclosure of Invention

In accordance with at least selected embodiments, the membranes of the present invention comprise a porous membrane or layer made of a polymeric material having dispersed therein surface treated (or coated) particles (or ceramic particles) having an average particle size of less than about 1 micron. The polymeric material may be selected from the group consisting of polyolefins, polyamides, polyesters, copolymers thereof, and combinations thereof. The particles can be selected from boehmite (AlOOH), SiO₂、TiO₂、Al₂O₃、BaSO₄、CaCO₃BN, and combinations thereof. The surface treatment (or coating) on the particle or nanoparticle may be a molecule having a reactive end that can be bound to the surface of the particle or nanoparticle and a non-polar end that can be bound to the polymeric material. The surface coating preferably modifies the surface energy of the particles to be similar to the surface energy of the polymeric material. With similar surface energies, the nanoparticles can be better mixed or blended with the polymeric material. In the case of porous polymer materials used as battery separator membranes, the separators of the present invention have been made with additional optional inventive steps in the preparation of ceramic nanoparticles and polymer resin blends. Since the surface-treated ceramic nanoparticles tend to aggregate and form agglomerates, additional treatments are suggested to eliminate this problem. It is also preferable to use the surface-treated ceramic particles in combination with a polymer materialPrior to mixing, the coating was uniformly coated with a low molecular weight wax. Blending of the waxed surface treated ceramic nanoparticles with a polymeric material successfully addresses the problems associated with non-uniform mixing and dispersion of the ceramic particles and polymeric material.

Drawings

For the purpose of illustrating the invention, there is shown in the drawings a form that is presently preferred; it is to be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown.

Fig. 1 is a schematic illustration of a surface-coated ceramic particle having reactive ends and non-polar ends.

Fig. 2 depicts a schematic of a surface-coated ceramic particle having a branched hydrocarbon tail around the periphery of the particle.

Fig. 3 is a Scanning Electron Microscope (SEM) image (surface) of a typical (prior art) microporous membrane made by a dry stretch manufacturing process, such as the Celgard dry process.

Fig. 4 is an SEM image (surface) of a typical (prior art) microporous membrane made by a wet-stretch process.

Fig. 5 is an SEM image (surface) of a porous membrane made by a particle stretching method (prior art).

Fig. 6 is a SEM image (cross-section) of the edge of a multilayer film, with the upper and lower layers being similar or identical polymers and the middle layer being a different polymer (prior art).

FIG. 7 is an SEM image of one embodiment of a surface of a membrane of the present invention.

Fig. 8 is an SEM image of another embodiment of the surface of the inventive membrane.

Fig. 9 is a graph comparing battery cycle results for a filled membrane of the present invention with a conventional microporous membrane.

Detailed Description

In accordance with at least certain embodiments, the present invention is directed to a membrane comprising a porous membrane or layer made of a polymeric material having dispersed therein a plurality of surface treated particles (or surface treated ceramic particles) having an average particle size of less than about 1 micron; or to a membrane comprising a porous membrane or layer made of a polymeric material having dispersed therein a plurality of particles such as boehmite particles; a battery separator; related methods of manufacture or use; and so on.

In accordance with at least selected embodiments, the present invention relates to a membrane comprising a microporous membrane or layer made of a polymeric material having dispersed therein a plurality of surface treated particles (or surface treated ceramic particles) or wax coated surface treated particles (or surface treated ceramic particles) having an average particle size of less than about 1 micron, or a membrane comprising a microporous membrane or layer made of a polymeric material having dispersed therein a plurality of boehmite particles.

The membrane or layer of the microporous membrane made of the polymeric material having dispersed therein the plurality of surface treated particles (or surface treated ceramic particles) or waxed surface treated particles (or surface treated ceramic particles) having an average particle size of less than about 1 micron or the microporous membrane made of the polymeric material having dispersed therein the plurality of boehmite particles may be one layer of a multilayer membrane or separator. Preferably, the membrane or layer comprises a microporous membrane made of a polymeric material having dispersed therein a plurality of boehmite particles having an average particle size of less than about 1 micron.

Membrane as used herein preferably refers to a solid or continuous polymeric sheet or film having a plurality of pores or micropores therethrough. The membrane may also be a non-woven structure (i.e., made from a plurality of fibers (filaments or staple fibers); and in some embodiments, the membrane is a layer of a multilayer composite or product that may include one or more porous films, one or more non-woven structures [ i.e., made from a plurality of fibers (filaments or staple fibers) ], one or more coatings, one or more ceramic coatings, and/or other layers.

The polymeric material may be any polymeric material. The polymeric material may be a thermoplastic polymer. In one embodiment, the polymeric material may be selected from the group consisting of polyolefins, polyamides, polyesters, copolymers thereof, and combinations thereof. In another possibly preferred embodiment, the polyolefin may be selected from the group consisting of polyethylene, polypropylene, polybutylene, polymethylpentene, copolymers thereof, and combinations thereof.

In one embodiment, the polymeric material may comprise up to about 99.9 weight percent of the total weight of the film or layer. In another embodiment, the polymeric material may comprise 75 to 97.5 weight percent of the total weight of the film or layer. In yet another embodiment, the polymeric material may comprise 80 to 95 weight percent of the total weight of the film or layer. In yet another embodiment, the polymeric material may comprise 87.5 to 92.5 weight percent of the total weight of the film or layer. In another embodiment, the polymeric material may comprise 90 weight percent of the total weight of the film or layer.

The particles may be loaded into the polymeric material at any level. In one embodiment, the particles may comprise from about 0.1 to 30% or from about 0.1 to 10% or less than about 10% or from 2 to 10% by weight (or any subset thereof) based on the weight of the film (polymeric material and particles). In yet another embodiment, the particles may comprise 1 to 10 weight percent of the total weight of the film or 2 to 8 weight percent of the total weight of the film or 3 to 5 weight percent of the total weight of the film or 4 weight percent of the total weight of the film (or any subset thereof).

Prior to loading the particles or nanoparticles into the polymeric material or mixing and blending the particles or nanoparticles with the polymeric material, the surface of the particles or nanoparticles is first preferably treated with specially designed molecules to have reactive functional end groups and non-polar functional end groups. The reactive end of the molecule may be bound to the surface of the particle or nanoparticle and the non-polar end of the molecule may be bound to the polymeric material.

Fig. 1 depicts exemplary surface-treated particles or nanoparticles, wherein the "star" symbol represents a reactive functional end group, which in the case of boehmite is an "-OH" group. The non-polar functional end group on the other end of the molecule is a hydrocarbon that may have up to 20 carbon atoms. In addition, the hydrocarbon moiety may contain single or double bonds capable of undergoing a reaction to add one or more additional hydrocarbon functional groups as side chains. The length of these hydrocarbon portions of the molecule can be long enough that the hydrocarbon non-polar functional end groups can surround the exterior of the ceramic particle, effectively increasing the volume occupied by the particle, as depicted in fig. 2. The hydrocarbon tail surrounding the ceramic particle has a surface energy similar to that of the polymeric material. In one embodiment, the non-polar end may be an aliphatic hydrocarbon in which the number of carbons is <20 and which contains double bonds, but any end group capable of intermixing (or interacting) with the polymeric material or surrounding the particle may be used. For example, in one embodiment, the aliphatic hydrocarbons may have 20 or fewer carbons (≦ 20 carbons), in another embodiment in the range of from 5 to 20 hydrocarbons, and in another embodiment in the range of from 10 to 20 hydrocarbons, and in another embodiment in the range of from 12 to 18 hydrocarbons (and any subset thereof). The non-polar end may be single-stranded or branched. While not wishing to be bound by any particular theory, it is believed that the surface treatment molecules bind to the particles using the reactive ends, while the non-polar ends themselves surround the particles. The surface energy of the particles is now similar to the polymeric material, which facilitates dispersion of the particles into the polymeric material having a similar surface energy. The coated or treated particles may be further coated (over-coated) with a wax or polymer.

Preferably, the surface coating on the particle alters the surface energy of the particle to be similar to the surface energy of the polymeric material. With similar surface energies, the nanoparticles can be better mixed, dispersed, or blended with one or more polymeric materials.

In the case of polymeric materials used as battery separator membranes, the separator of the present invention has been made using additional inventive steps in the preparation of ceramic nanoparticles and polymer resin blends. Since the surface-treated ceramic nanoparticles are liable to aggregate and form agglomerates, a second surface treatment is suggested to solve this problem. For example, the surface treated ceramic particles are uniformly coated with a polyolefin (polypropylene or polyethylene) having a low molecular weight in the approximate range of 800-. The low molecular weight wax has a melting temperature of about 130 to 160 degrees celsius. When the polymeric material is, for example, isotactic polypropylene, the wax may also be isotactic polypropylene. Waxing or treating the surface treated particles reduces the surface energy of the particles. For example, the surface energy of the boehmite particles without surface treatment is in the range of 60 to 80 ergs/cm²Of the order of (A), and the surface energy of the PP is 32+/-2 ergs/cm². The particles being waxedThe surface energy is reduced to approximately correspond to the surface energy of the polymeric material, which facilitates uniform mixing of the particles into the polymeric material.

The wax may be applied in a liquid state and dried to produce wax-coated surface treated ceramic particles or nanoparticles. The application of the wax coating is an effective dispersion method to homogeneously blend the nanoparticles with the polymeric material. Its presence facilitates the uniform dispersion of the nanoparticles into the polymer. Blending of the waxed surface treated ceramic nanoparticles with a polymeric material successfully addresses the problems associated with non-uniform mixing of the ceramic particles and the polymeric material. Fig. 7 shows an SEM micrograph of the surface of an exemplary inventive separator membrane containing wax-coated surface-treated nanoparticles. The particles were mixed so homogeneously that they were difficult to see in the lamellae and pores of the microporous membrane, but a homogeneous dispersion was seen by close-up viewing of the micrograph. Figure 8 also shows an SEM micrograph of a separator membrane of the present invention with wax-coated surface treated particles very well mixed into the polymer separator membrane. Figure 3 shows a microporous membrane made by a comparative dry process without any nanoparticles for comparison.

The particles may be loaded into the polymeric material at any level. In one embodiment, the particles may comprise from about 0.1 to 30% or from about 0.1 to 10% or less than about 10% or from 2 to 10% by weight (or any subset thereof) based on the weight of the polymeric material and the particles. In yet another embodiment, the particles may comprise 1 to 10 weight percent of the total weight of the film or 2 to 8 weight percent of the total weight of the film or 3 to 5 weight percent of the total weight of the film or 4 weight percent of the total weight of the film (or any subset thereof).

The particles may be any particles or ceramic particles. In one embodiment, the ceramic particles may be selected from boehmite (AlOOH), SiO₂、TiO₂、Al₂O₃、BaSO₄、CaCO₃BN, and combinations thereof. In another embodiment, the particles may be boehmite. Boehmite particles are commercially available from sasol of john nestle in south africa.

In one embodiment, the particles have a size range of less than 1 micron. In other embodiments, the particle size range may be less than about 500 nanometers or less than about 300 nanometers or less than about 200 nanometers or in the range of about 20 to about 200 nanometers (and any range included therein).

While not wishing to be bound by any particular theory, it is believed that the inclusion of nanoparticles affects the growth of crystalline lamellae of the polymeric material. It has been observed that inclusion of up to 10% by weight of nanoparticles alters crystal growth such that during pore formation, pores are generally about 15% smaller than commonly observed.

The surface treatment (or coating) molecule may be selected from the group consisting of fatty acids, fatty acid enol esters, fatty alcohols, fatty amines, fatty acid esters, fatty nitriles, and combinations thereof. One such material is available from lubon corporation of wilcliff, ohio.

The wax may be any low molecular weight polymer or oligomer. The wax should be selected to be compatible with the polymeric material (e.g., the wax should be miscible or at least partially miscible with the polymeric material). For example, if the polymeric material is a polyolefin, the wax may be a similar (but not necessarily identical) polyolefin. By low molecular weight is meant a molecular weight less than that of the polymeric material. The molecular weight of a wax can be expressed in terms of molecular weight or viscosity. The molecular weight may be in the 800-5000 range or in the 1000-5000 range or in the 2000-5000 range. The viscosity may be less than or equal to 10 centipoise over the temperature range of 150 ℃ and 180 ℃.

The pre-mixture of wax and particles may have any mixing ratio. In one embodiment, there are more waxes than particles. In another embodiment, the particles may comprise 30 to 50 weight percent of the premix and the wax may comprise 50 to 70 weight percent of the premix. In another embodiment, the particle to wax ratio may be 2: 3. In one embodiment, the wax may comprise 1.5 to 15 weight percent of the total weight of the film or layer; or 3 to 12 wt% of the total weight of the film or layer; or 4.5 to 7.5 wt% of the total weight of the film or layer; or 6 wt% (or any subset thereof) of the total weight of the film or layer.

The aforementioned films may be used in any application. In one embodiment, the membrane is a porous or microporous membrane used as a battery separator. The membrane in this application may be one or more layers of a multilayer separator or the only layer of a separator.

The foregoing membrane may be assembled into any battery when used as a battery separator (or at least one layer or sheet of a separator). The battery may include a negative electrode, a positive electrode with a separator sandwiched therebetween, and an electrolyte in communication between the negative electrode and the positive electrode. The battery may be a primary or secondary battery. The secondary battery may be a lithium battery or a lead-acid battery.

The particles may be incorporated into the polymeric material in any manner and subsequently formed into a film. In one embodiment, the dried surface-treated ceramic particles are mixed with a wax to form a pre-mix; mixing the pre-mixture with a polymeric material, thereby forming a second mixture; and forming the second mixture into a microporous membrane. The first (pre) mixing step may include heating such that the first mixture is a fluid (e.g., a liquid).

The membrane may be formed in any manner (e.g., made microporous). In one embodiment, the film may be formed by: extruding the second mixture into a sheet or tube, annealing the sheet or tube, and stretching the annealed sheet or tube. In another embodiment, the film may be formed by: extruding the second mixture into a sheet, calendering the sheet, and extracting the pore-forming material from the calendered sheet.

Multiple beneficial effects can be observed when the aforementioned films are assembled into a battery (e.g., a secondary lithium battery). Some examples are: 1) the surface energy of the entire membrane is greatly increased, which results in much faster absorption of typical lithium ion electrolytes; 2) the effective surface friction coefficient tends to decrease because the presence of particles slightly increases the surface roughness; and/or 3) the presence of chemically active ceramic particles (e.g., surface treated boehmite) will scavenge undesirable hydrofluoric acid (HF) within the lithium ion battery, which in turn will contribute to a longer cycle life of the battery. These three examples of property changes or improvements are observed when the loading of nanoparticles is less than 10 wt% and perhaps as low as 2 wt%. If the loading is much greater than 10 wt%, the creation of pore structures may become difficult and in some cases the fabrication of films with porosities > 30% may not be accomplished. The actual upper limit depends on acceptable separator performance. Furthermore, it is believed that the presence of the nanoparticles alters the normal crystal growth behavior in the sheet of precursor film. The particles alter the integrity of the crystal growth. The overall conclusion is that the addition of up to 10 wt% nanoparticles results in a crystal size and hence pore size that is about 15% smaller than the standard.

Examples

A masterbatch was prepared consisting of 40% by weight of the masterbatch of surface treated nanoparticles (surface treated boehmite having an average diameter of 20-200 nm) and 60% by weight of the masterbatch of a low molecular weight (800-.

The masterbatch was melt extruded at 9.5% by weight with isotactic polypropylene using a standard ring die (i.e., a standard blown film process as is well known in the art) to form a 20 micron (thick) precursor.

The precursor is made microporous by conventional dry-stretch methods (see, e.g., Kesting, R.E., Synthetic Polymer Membranes, A Structural Peractive, 2 nd edition, Wiley-Interscience, NY, NY, 1985, page 290-297, incorporated herein by reference). The stretching conditions include: 20% cold stretching (room temperature) and 120% hot stretching (125 ℃). The resulting film had: a thickness of 22.1 microns; gurley values of 26.1 seconds (ASTM method) and 650 seconds (JIS method); and a porosity of 31.1%. Significant amounts of boehmite nanoparticles were well incorporated into the PP resin without any sign of interfacial failure during stretching. This is due to the proper surface coating and/or treatment of the particles. Fig. 5 shows interfacial failure during stretching of prior art particles under large scale particle stretching.

The aforementioned film (filled with surface-treated nanoparticles) was formed into a conventional coin cell and subjected to 100 cycles. Fig. 7 shows a comparison to a similar coin cell using an unfilled CELGARD 2500 membrane (Gurley of 200 seconds-JIS method). The comparison shows that there is no significant difference between the performance of these particular cells.

The surface treated boehmite nanoparticle/polymer blends of the invention can produce battery separator films that can act as hydrofluoric acid scavengers in batteries, effectively extending the cycle life of the battery at a much lower cost than coating the battery separator film with an alumina-containing coating. It was determined that 10-15% by weight of the surface-treated boehmite nanoparticles incorporated into the film also produced excellent HF removal.

In accordance with at least selected embodiments, objects, and aspects of the present invention, a membrane includes a porous membrane or layer made of a polymeric material having dispersed therein a plurality of surface treated (or coated) particles (or ceramic particles) having an average particle size of less than about 1 micron (other additives, agents, or materials may be added to the mix or mixture). The polymeric material may be selected from the group consisting of polyolefins, polyamides, polyesters, copolymers thereof, and combinations thereof. The particles can be selected from boehmite (AlOOH), SiO₂、TiO₂、Al₂O₃、BaSO₄、CaCO₃BN, and combinations thereof, or the particles may be boehmite. The surface treatment (or coating) may be a molecule having a reactive end and a non-polar end. The particles may be pre-mixed in a low molecular weight wax prior to mixing with the polymeric material. The membrane may serve as at least one layer of a battery separator.

The present invention may be embodied in other forms without departing from the spirit or essential attributes thereof, and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention.