Separators with improved wettability for secondary batteries

Abstract

Disclosed is a new or improved polyolefin separator for use in secondary batteries, especially sodium-ion batteries and high-density lithium ion batteries. The battery separator comprises a porous polyolefin membrane. The membrane may have a surfactant, e.g., a cross-linkable surfactant, provided on or impregnated into at least one surface thereof to improve wettability with respect to polar solvents like propylene carbonate (PC). Also, at least one surface of the membrane may be treated to improve wettability with respect to polar solvents like propylene carbonate (PC). In another embodiment, an organic solvent based PVDF or PVDF:HFP copolymer coating is coated on and into a high porosity separator or base film. This PVDF or PVDF:HFP layer can function as a 3D sub film intercalated to the base film to increase wettability and mechanical strength.

Description

SEPARATORS WITH IMPROVED WETTABILITY FOR SECONDARY BATTERIES FIELD

[0001] This application relates to new or improved separators, durable wettability separators, and coated battery separators for use in high energy density applications, improved wettability with respect to propylene carbonate (PC) solvent electrolyte separators, batteries incorporating same, and related methods. The coated battery separators disclosed herein may be surfactant coated, surfactant coated and ceramic coated, or PVDF coated. BACKGROUND

[0002] There is increasing demand for batteries for high energy density applications. High density applications generate more dendrites during cycling than lower energy density applications. In some cases, dendrites grow across the separator, connecting the two electrodes and causing a short circuit. Celgard, LLC of Charlotte, North Carolina designed the first ceramic coated separators, which among other things, help block dendrite growth and prevent shorts (see US patent 6,432,586).

[0003] In batteries for these high energy density applications, electrolyte ion concentration (e.g., Na+, Li+, etc.) is high, and consequently, the viscosity of the electrolyte is higher. High viscosity electrolytes may not wet out polyolefin (PO) separators like lower viscosity electrolytes do. Thus improvement in separator wettability for use in batteries for these high density or viscosity applications is needed.

[0004] In Na+ ion batteries, the electrolyte, which typically uses propylene carbonate (PC) as the solvent, may not wet out polyolefin (PO) separators well. This is true regardless of the viscosity of the electrolyte. Thus, improvement in polyolefin separator wettability for use in secondary or rechargeable batteries such as Na+ ion batteries is needed. BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Fig.1 is a separator according to some embodiments described herein.

[0006] Fig.2 is a separator according to some embodiments described herein.

[0007] Fig.3 is a separator according to some embodiments described herein. 1

[0008] Fig.4 is an image of a completely wettable Example as described herein.

[0009] Fig.5 is a separator according to some embodiments described herein. DESCRIPTION

[0010] Described herein are new or improved separators, durable wettability separators, and coated battery separators for use in high energy density or high viscosity or increased polarity electrolyte applications, improved wettability with respect to propylene carbonate (PC) solvent electrolytes, batteries incorporating same, and related methods. Described herein is a possibly preferred new or improved polyolefin (PO) battery separator that exhibits improved wettability with respect to propylene carbonate (PC) solvent or propylene carbonate (PC) solvent electrolytes. These polyolefin separators may be used in Na+ ion batteries, where it was previously difficult to use polyolefin battery separators due to their hydrophobic nature. These new or improved separators may also be used in higher density lithium-ion batteries. In higher density lithium-ion batteries, increased Li+ ion concentration leads to increased polarity of the electrolyte. Typically, at least certain hydrophobic polyolefin separators may not wet as well in this increased polarity electrolyte.

[0011] In one aspect, object or embodiment of the present disclosure or invention, a separator for a secondary battery comprises a porous polyolefin (PO) membrane (such as a polyethylene (PE) or polypropylene (PP) membrane), wherein the separator exhibits a contact angle from 0° to 15°, from 0° to 10°, or from 0° to 5° with respect to propylene carbonate (PC) solvent within 20 seconds of the PC solvent being placed on the separator. The membrane may be a polyolefin monolayer, bilayer, trilayer, or multilayer membrane (such as but not limited to PO, PE, PP, PO / PO, PE / PE, PP / PP, PO / PO / PO, PE / PE / PE, PP / PP / PP, PE / PP, PE / PP / PE, PP / PE / PP, PE / PE / PP, PP / PP / PE, PO / PO / PO / PO, and the like). The porous polyolefin membrane may comprise at least one of polyethylene (PE), polypropylene (PP), blends of polyethylene, blends of polypropylene, copolymers of polyethylene, copolymers of polypropylene, copolymers of polyethylene and polypropylene, and combinations thereof. Also, at least one surface of the polyolefin membrane may be treated using at least one of a primer, corona, plasma, vapor deposition, IR, MW, and UV treatment or material. 2

[0012] In some embodiments, a surfactant is provided on at least one surface of the porous polyolefin membrane to improve wettability, including wettability with respect to PC solvent or propylene carbonate (PC) solvent electrolytes. The surfactant, in some embodiments, may be a cross-linkable surfactant. The cross-linkable surfactant may have two or more, three or more, or four or more functional groups selected from vinyl groups, allyl groups, and epoxy groups. In some embodiments, examples of cross- linkable surfactants are poly(ethylene glycol) diacrylate (PEGDA) and poly(ethylene glycol) diglycidyl ether (PEGDE). By using a cross-linkable surfactant, and later performing a cross-linking reaction to form a cross-linked surfactant layer, an issue of the surfactant being washed off by an electrolyte in a secondary battery may be resolved and durable wettability may be accomplished.

[0013] In some preferred embodiments, the surfactant is provided on at least one surface of the porous polyolefin membrane and allowed to impregnate the porous polyolefin membrane. A part of or the whole membrane may be impregnated. Then cross-linking may be performed. This may improve the mechanical strength of the membrane in addition to improving wettability of the whole film and not just a surface thereof.

[0014] In some embodiments, the surfactant is provided on at least one surface of the porous polyolefin membrane along with a ceramic.

[0015] In some embodiments, a ceramic layer is provided to the same side of the porous polyolefin membrane as the surfactant has been provided on. The ceramic layer is provided on top of the provided surfactant.

[0016] Addition of a ceramic or provision of a ceramic layer may protect the surfactant from oxidation or reduction by electrodes in the secondary battery.

[0017] In other embodiments, to improve wettability of the porous polyolefin membrane, one or more surfaces of the membrane are treated. Treatments may include primers, corona, plasma, vapor deposition, UV, e-beam, x-ray, impregnation, and / or the like (with or without surfactant and / or ceramic coating).

[0018] The porous polyolefin membrane may be made using a wet-process, a dry- process using fillers, waxes, low solvent add, low oil add, or nucleating agents as pore- formers, or a dry-process that does not use solvents, oils, or pore-formers, e.g., the 3  Celgard® dry-stretch process. The membrane may be a monolayer, bi-layer, trilayer, or multilayer membrane or film. The membrane may be formed by lamination and / or co- extrusion.

[0019] In another aspect, object, or embodiment, a new or improved battery or secondary battery, including for example, lithium-ion and sodium-ion batteries or secondary batteries may include the new or improved battery separators.

[0020] In some embodiments, the electrolyte may be a high-viscosity electrolyte having a viscosity in the range from 2 to 20 centipoise (cP), 5 to 20 cP, or 10 to 20 cP.

[0021] In some embodiments, the secondary battery may be a lithium battery. The electrolyte in the lithium ion battery may comprise ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and ethylene carbonate (EC). In a high density lithium-ion battery, the electrolyte may have a high-viscosity and not wet or wet well at least certain polyolefin porous membrane separators. In this application, the new or improved separator described herein may be particularly helpful.

[0022] In some embodiments, the secondary battery may be a sodium-ion battery. In a sodium-ion battery, the electrolyte may comprise propylene carbonate (PC) as the solvent. In such applications, the improved battery separator described herein has excellent wettability with respect to PC solvent, e.g., a contact angle of 0° to 15° within 20 seconds after the PC solvent is placed on the battery separator.

[0023] In some embodiments, an acid layer is provided on at least one surface of the porous polyolefin membrane. The acid layer comprises a phosphoric acid (PO4-) or phosphorous acid (PO3-). The acid layer may be bonded to the porous polyolefin membrane by cross-linking. For example, e-beam, x-ray, or UV light cross-linking techniques may be used.

[0024] Disclosed are new or improved polyolefin separators for use in secondary batteries, especially sodium-ion batteries and high-density lithium ion batteries. The battery separator comprises a porous polyolefin membrane. The membrane may have a surfactant, e.g., a cross-linkable surfactant, provided on or impregnated into at least one surface thereof to improve wettability with respect to polar solvents like propylene carbonate (PC). Also, at least one surface of the membrane may be treated with plasma 4  treatment or UV treatment to improve wettability with respect to polar solvents like propylene carbonate (PC).

[0025] Disclosed are new or improved separators, durable wettability separators, coated battery separators for use in high energy density applications, improved wettability with respect to propylene carbonate (PC) solvent electrolyte separators, batteries incorporating same, and related methods. The coated battery separators disclosed herein may be surfactant coated or surfactant coated and ceramic coated.

[0026] Described herein are new or improved separators, durable wettability separators, coated battery separators for use in high energy density applications, improved wettability with respect to propylene carbonate (PC) solvent electrolyte separators, batteries incorporating same, and related methods. Described herein is a possibly preferred new or improved polyolefin battery separator that exhibits improved wettability with respect to propylene carbonate (PC) solvent or propylene carbonate (PC) solvent electrolytes. These polyolefin separators may be used in Na+ ion batteries, where it was previously difficult to use polyolefin battery separators due to their hydrophobic nature. These new or improved separators may also be used in higher density lithium-ion batteries. In higher density lithium-ion batteries, increased Li+ ion concentration leads to increased polarity of the electrolyte. Typically, at least certain hydrophobic polyolefin separators may not wet as well in this increased polarity electrolyte.

[0027] Further, in accordance with another embodiment, an organic solvent based PVDF or PVDF:HFP copolymer coating is coated on and into a high porosity separator or base film (preferably greater than 60% porosity or more). This PVDF or PVDF:HFP layer can function as a 3D sub film intercalated to the base film to increase wettability and mechanical strength.

[0028] In accordance with certain possibly preferred non-limiting examples of at least selected aspects, objects or embodiments of the disclosure or invention, the following examples are provided: 5  EXAMPLES

[0029] The same Celgard® polyolefin separator, separator membrane, or base film was used in each example.

[0030] Example 1: A slurry was prepared comprising poly(ethylene glycol) diacrylate (PEGDA) as the cross-linkable surfactant, an acrylic binder, and water as a solvent. The slurry was coated onto at least one surface of a polyolefin battery separator (a Celgard® battery separator), and cross-linked to provide the cross-linked surfactant layer.

[0031] Example 2: is like Example 1, except that a ceramic layer may be provided on top of the cross-linked surfactant layer.

[0032] Example 3: A slurry was prepared comprising poly(ethylene glycol) diglycidyl ether (PEGDE) as the cross-linkable surfactant, an acrylic binder, and water, IPA, Aceton or NMP as a solvent. The slurry may be impregnated into a polyolefin battery separator (the same Celgard® battery separator as used in Example 1), and then cross- linked to provide the cross-linked surfactant layer.

[0033] Example 4 is like Example 3, except that a ceramic layer may be provided on top of the cross-linked surfactant layer.

[0034] Example 5 is like Example 1, except that the slurry may further comprise alumina, boehmite, TiO2, MgO, SiO2, all types of ceramics, etc.

[0035] Example 6 is like Example 3, except that the slurry may further comprise alumina, boehmite, TiO2, MgO, SiO2, all types of ceramics, etc.

[0036] Example 7 a polyolefin separator (the same Celgard® separator used in Examples 1 and 3) was provided, and at least one surface of the separator was plasma treated to provide hydrophilicity by adding –OH, -COOH, -COO, -CO, -NH, -NH2, or NH3 functional groups. –CO and –OH groups were particularly added.

[0037] Example 8 a polyolefin separator (the same Celgard® separator used in Examples 1 and 3) was provided, and at least one surface of the separator may be UV treated to provide hydrophilicity by adding –OH, -COOH, -COO, -CO, -NH, -NH2, or NH3 functional groups. For UV treatment, the separator may be soaked in an acid or base, and then treated with UV light. 6

[0038] Example 9 a polyolefin separator (the same Celgard® separator used in Examples 1 and 3) was provided, and –PO4 groups may be grafted on at least one surface of the separator. This is done using gamma radiation.

[0039] Example 10 A slurry may be prepared comprising Aliphatic amine or Aromatic amine such as Tetraethylenepentamine (TEPA) to react with any epoxy or ether and all those components are dissolved into IPA, Acetone or NMP. The slurry is impregnated into a polyolefin battery separator (the same Celgard® battery separator as used in Example 1), and then cross-linked to provide the cross-linked sublayer in the separators. The crosslinked sub-structure can not only improve wettability of separator but also mechanical strength of the original separator.

[0040] Example 11 is like Example 10, except that a ceramic layer may be provided on top of the cross-linked surfactant layer.

[0041] Example 12 is like Example 10, except that the slurry may further comprise alumina, boehmite, TiO2, MgO, SiO2, all types of ceramics, etc.

[0042] Wettability of Examples 1-12 is measured with respect to propylene carbonate (PC) solvent. PC solvent was provided on a side of the membrane provided with a cross-linked surfactant layer, treated with UV, treated with plasma, etc.

[0043] Wettability measurements (contact angle) with PC solvent are provided in the Table below for the Celgard® separator used in the Examples, and for each of the Examples 1-12 wherein the separator has been surface treated, provided with a cross- linked surfactant layer, or provided with a cross-linked surfactant layer and a ceramic layer. PC is commonly used as the electrolyte in sodium-ion batteries. It is uncommon for lithium-ion battery usage. PC is a problem in lithium-ion battery because it may exfoliate graphite, damaging the anode. Common solvents for lithium-ion batteries include, but are not limited to ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and ethylene carbonate (EC). In high density applications, Li+ ion concentration increases, the polarity of the solvent increases, and the solvent does not wet the polyolefin separator as well. 7  Table 1 Sample Celgard Ex. Ex. Ex.3 Ex.4 Ex.5 Ex.6 Ex.7 Ex.8 ® sep. 1 2 °8  Table 2 Sample Ex.9 Ex.10 Ex.11 Ex.12 Contact 0°-15° 0°-15° 0°-15° 0°-15°n e xampes, a conac ange ess an , an more o en 0°, was produced after 5 seconds or less. These examples were considered completely wettable.

[0045] In the Examples above, by forming a cross-linked surfactant layer, it is more difficult or impossible for the electrolyte to wash off the surfactant when the separator is used in a secondary battery (e.g., a sodium-ion battery or a lithium-ion battery). By impregnating the polyolefin porous membrane with a slurry in some examples, mechanical strength of the separator is improved. It is believed that this is because of the addition of another layer or sublayer on the membrane.

[0046] Use of plasma or UV treatment to provide a hydrophilic surface also avoids a prior issue of surfactant being washed off by the electrolyte in the battery.

[0047] Providing the cross-linked surfactant layer also increases the mechanical strength of the battery separator compared to the membrane without the cross-linked surfactant layer.

[0048] In the Examples where a ceramic coating layer is provided, the ceramic layer may protect the cross-linked surfactant layer from oxidation and / or reduction.

[0049] In accordance with at least one object, aspect or embodiment of the disclosure or invention, the prior issues or needs may be addressed by or there is provided or 9  disclosed a new or improved polyolefin separator for use in secondary batteries, especially sodium-ion batteries and high-density lithium ion batteries, a battery separator that comprises a porous polyolefin membrane, a membrane that may have a surfactant, a membrane that may have a cross-linkable surfactant provided on or impregnated into at least one surface thereof to improve wettability with respect to polar solvents like propylene carbonate (PC), at least one surface of the membrane may be treated to improve wettability with respect to polar solvents like propylene carbonate (PC), an organic solvent based PVDF or PVDF:HFP copolymer coating may be coated on and into a high porosity separator or base film, a PVDF or PVDF:HFP layer can function as a 3D sub film intercalated to the base film to increase wettability and mechanical strength, and the like.

[0050] In accordance with at least one object, aspect or embodiment of the disclosure or invention, the prior issues or needs may be addressed by or there is provided or disclosed:

[0051] A separator for a secondary battery, comprising: a porous polyolefin membrane, wherein the separator exhibits a contact angle from 0° to 15° with respect to propylene carbonate (PC) solvent within 20 seconds after the solvent is placed on the membrane.

[0052] The above separator, wherein the contact angle is from 0° to 10°.

[0053] The above separator, wherein the contact angle is from 0° to 5° within 5 seconds after the PC solvent is placed on the membrane.

[0054] The above separator, wherein the contact angle is 0° within 5 seconds after the PC solvent is placed on the membrane.

[0055] The above separator, wherein a surfactant is provided on at least into the porous polyolefin membrane, and optionally impregnated into the porous polyolefin membrane.

[0056] The above separator, wherein the surfactant is a cross-linkable surfactant.

[0057] The above separator, wherein the cross-linkable surfactant has two or more functional groups selected from vinyl groups, allyl groups, and epoxy groups. 10

[0058] The above separator, wherein the surfactant is one or more selected from poly(ethylene glycol) diacrylate (PEGDA) and poly(ethylene glycol) diglycidyl ether (PEGDE).

[0059] The above separator, wherein the cross-linkable surfactant has three or more functional groups.

[0060] The above separator, wherein the cross-linkable surfactant has four or more functional groups.

[0061] The above separator, wherein the surfactant and a ceramic are provided together on at least one surface of the porous polyolefin membrane.

[0062] The above separator, wherein the surfactant and a ceramic are provided together on at least one surface of the porous polyolefin membrane.

[0063] The above separator, wherein a ceramic layer is provided to the same surface as the surfactant so that the ceramic layer is on top of the surfactant.

[0064] The above separator, wherein a ceramic layer is provided to the same surface as the surfactant so that the ceramic layer is on top of the surfactant.

[0065] The above separator, wherein at least one surface of the porous polyolefin membrane has been treated to improve wettability.

[0066] The above separator, wherein at least one surface of the porous polyolefin membrane was treated using at least one of plasma treatment and UV treatment.

[0067] The above separator, wherein an acid layer is provided on at least one surface of the porous polyolefin membrane.

[0068] The above separator, wherein the acid layer comprises a phosphoric acid (PO4-) or phosphorous acid (PO3-).

[0069] The above separator, wherein the acid layer is bonded to the porous polyolefin membrane by cross-linking.

[0070] The above separator, wherein a slurry comprising an aliphatic amine or aromatic amine is provided on at least one surface of the porous polyolefin membrane and cross-linked.

[0071] The above separator, wherein the slurry is impregnated into the membrane.

[0072] The above separator, wherein the slurry comprises tetraethylenepentamine (TEPA). 11

[0073] The above separator, wherein the slurry further comprises a ceramic selected from alumina, boehmite, TiO2, MgO, SiO2, or combinations thereof.

[0074] The above separator, wherein the porous polyolefin membrane comprises at least one of polyethylene (PE), polypropylene (PP), blends of polyethylene, blends of polypropylene, copolymers of polyethylene, copolymers of polypropylene, copolymers of polyethylene and polypropylene, and combinations thereof.

[0075] The above separator, wherein at least one surface of the porous polyolefin membrane was treated using at least one of a primer, corona, plasma, vapor deposition, IR, MW, and UV treatment or material.

[0076] A secondary battery comprising any of the above separators.

[0077] The above secondary battery, wherein an electrolyte of the battery has a viscosity in the range from 2 to 20 centipoise (cP), 5 to 20 cP, or 10 to 20 cP.

[0078] The above secondary battery, wherein the secondary battery is a lithium-ion battery.

[0079] The above secondary battery, wherein an electrolyte of the lithium ion battery comprises one or more selected from ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and ethylene carbonate (EC).

[0080] The above secondary battery, wherein the secondary battery is a sodium-ion battery.

[0081] The above secondary battery of claim 28, wherein an electrolyte of the sodium- ion battery comprises propylene carbonate (PC).

[0082] A coated separator comprises: a high porosity microporous separator membrane or base film (preferably greater than 60% porosity or more) with a coating thereon and into the pores with an organic solvent based PVDF or PVDF:HFP copolymer coating to form a PVDF or PVDF:HFP layer that can function as a 3D sub film intercalated to the base film to increase wettability and mechanical strength.

[0083] The above coated separator, wherein the high porosity microporous separator membrane or base film comprises at least one of polyolefin (PO), polyethylene (PE), polypropylene (PP), blends of polyethylene, blends of polypropylene, copolymers of polyethylene, copolymers of polypropylene, copolymers of polyethylene and polypropylene, and combinations thereof. 12

[0084] The above coated separator, wherein at least one surface of the high porosity microporous separator membrane or base film was treated using at least one of a primer, corona, plasma, vapor deposition, IR, MW, and UV treatment or material.

[0085] A secondary battery comprising the above coated separator.

[0086] A new or improved polyolefin separator for use in secondary batteries, especially sodium-ion batteries and high-density lithium ion batteries, the battery separator comprises a porous polyolefin membrane, the membrane may have a surfactant, e.g., a cross-linkable surfactant, provided on or impregnated into at least one surface thereof to improve wettability with respect to polar solvents like propylene carbonate (PC), at least one surface of the membrane may be treated to improve wettability with respect to polar solvents like propylene carbonate (PC), an organic solvent based PVDF or PVDF:HFP copolymer coating is coated on and into a high porosity separator or base film, the PVDF or PVDF:HFP layer can function as a 3D sub film intercalated to the base film to increase wettability and mechanical strength, and / or the like as shown, described or claimed herein.

[0087] The present application or invention is not limited to the above-described aspects, objects, embodiments, or examples. 13

Claims

CLAIMS 1. A separator for a secondary battery, comprising: a porous polyolefin membrane, wherein the separator exhibits a contact angle from 0° to 15° with respect to propylene carbonate (PC) solvent within 20 seconds after the solvent is placed on the membrane.

2. The separator of claim 1, wherein the contact angle is from 0° to 10°.

3. The separator of claim 1, wherein the contact angle is from 0° to 5° within 5 seconds after the PC solvent is placed on the membrane.

4. The separator of claim 1, wherein the contact angle is 0° within 5 seconds after the PC solvent is placed on the membrane.

5. The separator of any one of claims 1 to 5, wherein a surfactant is provided on at least into the porous polyolefin membrane, and optionally impregnated into the porous polyolefin membrane.

6. The separator of claim 5, wherein the surfactant is a cross-linkable surfactant.

7. The separator of claim 6, wherein the cross-linkable surfactant has two or more functional groups selected from vinyl groups, allyl groups, and epoxy groups.

8. The separator of claim 7, wherein the surfactant is one or more selected from poly(ethylene glycol) diacrylate (PEGDA) and poly(ethylene glycol) diglycidyl ether (PEGDE).

9. The separator of claim 7, wherein the cross-linkable surfactant has three or more functional groups.

10. The separator of claim 7, wherein the cross-linkable surfactant has four or more functional groups.

11. The separator of claim 5, wherein the surfactant and a ceramic are provided together on at least one surface of the porous polyolefin membrane.

12. The separator of claim 6, wherein the surfactant and a ceramic are provided together on at least one surface of the porous polyolefin membrane.

13. The separator of claim 5, wherein a ceramic layer is provided to the same surface as the surfactant so that the ceramic layer is on top of the surfactant.

14. The separator of claim 6, wherein a ceramic layer is provided to the same surface as the surfactant so that the ceramic layer is on top of the surfactant. 14  15. The separator of claim 1, wherein at least one surface of the porous polyolefin membrane has been treated to improve wettability.

16. The separator of claim 15, wherein at least one surface of the porous polyolefin membrane was treated using at least one of plasma treatment and UV treatment.

17. A secondary battery comprising the separator of claim 1.

18. A secondary battery comprising the separator of claim 5.

19. A secondary battery comprising the separator of claim 6.

20. A secondary battery comprising the separator of claim 11.

21. A secondary battery comprising the separator of claim 12.

22. A secondary battery comprising the separator of claim 13.

23. A secondary battery comprising the separator of claim 14.

24. A secondary battery comprising the separator of claim 15.

25. The secondary battery any one of claims 17 to 24, wherein an electrolyte of the battery has a viscosity in the range from 2 to 20 centipoise (cP), 5 to 20 cP, or 10 to 20 cP.

26. The secondary battery any one of claims 17 to 24, wherein the secondary battery is a lithium-ion battery.

27. The secondary battery of claim 26, wherein an electrolyte of the lithium ion battery comprises one or more selected from ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and ethylene carbonate (EC).

28. The secondary battery of any one of claims 17 to 24, wherein the secondary battery is a sodium-ion battery.

29. The secondary battery of claim 28, wherein an electrolyte of the sodium-ion battery comprises propylene carbonate (PC).

30. The separator of claim 1, wherein an acid layer is provided on at least one surface of the porous polyolefin membrane.

31. The separator of claim 30, wherein the acid layer comprises a phosphoric acid (PO4-) or phosphorous acid (PO3-).

32. The separator of claim 30 or 31, wherein the acid layer is bonded to the porous polyolefin membrane by cross-linking.

33. A secondary battery comprising the separator of claim 30 or 31. 15  34. The separator of claim 1, wherein a slurry comprising an aliphatic amine or aromatic amine is provided on at least one surface of the porous polyolefin membrane and cross- linked.

35. The separator of claim 34, wherein the slurry is impregnated into the membrane.

36. The separator of claim 34, wherein the slurry comprises tetraethylenepentamine (TEPA).

37. The separator of claim 34, wherein the slurry further comprises a ceramic selected from alumina, boehmite, TiO2, MgO, SiO2, or combinations thereof.

38. A coated separator comprises: a high porosity microporous separator membrane or base film (preferably greater than 60% porosity or more) with a coating thereon and into the pores with an organic solvent based PVDF or PVDF:HFP copolymer coating to form a PVDF or PVDF:HFP layer that can function as a 3D sub film intercalated to the base film to increase wettability and mechanical strength.

39. The separator of any one of claims 1 to 16, 30 to 32, and 34 to 37, wherein the porous polyolefin membrane comprises at least one of polyethylene, polypropylene, blends of polyethylene, blends of polypropylene, copolymers of polyethylene, copolymers of polypropylene, copolymers of polyethylene and polypropylene, and combinations thereof.

40. The coated separator of claim 38, wherein the high porosity microporous separator membrane or base film comprises at least one of polyolefin, polyethylene, polypropylene, blends of polyethylene, blends of polypropylene, copolymers of polyethylene, copolymers of polypropylene, copolymers of polyethylene and polypropylene, and combinations thereof.

41. The separator of claim 1 or claim 15, wherein at least one surface of the porous polyolefin membrane was treated using at least one of a primer, corona, plasma, vapor deposition, IR, MW, and UV treatment or material.

42. The coated separator of claim 38, wherein at least one surface of the high porosity microporous separator membrane or base film was treated using at least one of a primer, corona, plasma, vapor deposition, IR, MW, and UV treatment or material.

43. A new or improved polyolefin separator for use in secondary batteries, especially sodium-ion batteries and high-density lithium ion batteries, the battery separator 16  comprises a porous polyolefin membrane, the membrane may have a surfactant, e.g., a cross-linkable surfactant, provided on or impregnated into at least one surface thereof to improve wettability with respect to polar solvents like propylene carbonate (PC), at least one surface of the membrane may be treated to improve wettability with respect to polar solvents like propylene carbonate (PC), an organic solvent based PVDF or PVDF:HFP copolymer coating is coated on and into a high porosity separator or base film, the PVDF or PVDF:HFP layer can function as a 3D sub film intercalated to the base film to increase wettability and mechanical strength, and / or the like as shown, described or claimed herein. 17

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