Battery separator substrate including dense layer formed on support layer, and method for preparing the same

Abstract

A lithium ion battery separator substrate, a preparation method and application thereof are provided. The substrate comprises a support layer and a dense layer, wherein the support layer comprises superfine main fibers, thermoplastic bonded fibers and the nanofibers, and the dense layer comprises nanofibers. The substrate has excellent high-temperature resistance performance, the substrate still has certain strength after being processed at 300° C. for 1 h, and the heat shrinkage rate is less than 5.0%; the substrate has a uniform and compact double-layer structure without a pinhole. Therefore, the requirements concerning heat resistance, porosity and strength of the substrate are met.

Claims

1. A method of preparing a lithium ion battery separator substrate, comprising: mixing fiber materials of a support layer and a nano layer respectively with water, and then each independently defiberizing, beating and mixing to obtain pulps, and then diluting the pulps with water by a flushing pump to add water to an on-wire concentration; feeding the diluted pulps of the support layer and the nano layer to a double-layer hydraulic inclined wire former, wherein the pulp of the nano layer enters an upper flow channel and the pulp of the support layer enters a lower flow channel, laminating the pulp of each flow channel in the same area and then making papers at the same time, and draining to obtain a wet paper sheet, forming the wet paper sheet for the substrate; drying the wet paper sheet for the substrate obtained to obtain a dry paper sheet for the substrate by a Yankee dryer; and calendering the dry paper sheet for the substrate obtained by a metal roller and a soft roller to obtain the substrate; wherein, in weight percent, the support layer consists of 30-65 wt % of superfine main fibers, 30-65 wt % of thermoplastic bonded fibers and 5-30 wt % of first nanofibers; the nano layer consists of second nanofibers; wherein, the superfine main fibers are the superfine main fibers are stretched polyethylene terephthalate fibers (stretched PET), polyacrylonitrile fibers (PAN) and/or polyamide fibers (PA); the thermoplastic bonded fibers are unstretched polyethylene terephthalate fibers (unstretched PET), PP/PE bi-component fibers or PET/co-PET bi-component fibers; the first nanofibers and the second nanofibers are independently fibrillated poly-p-phenylene terephthalamide (PPTA) nanofibers, fibrillated lyocell nanofibers, fibrillated poly-p-phenylene benzodioxazole (PBO) nanofibers or fibrillated polyacrylonitrile (PAN) nanofibers; wherein, the superfine main fibers have a fiber diameter of 1-3 μm; the superfine main fibers have a fiber length of 2-4 mm; the thermoplastic bonded fibers have a fiber diameter of 3-5 μm; the thermoplastic bonded fibers have a fiber length of 2-4 mm; the first nanofibers and the second nanofibers have a beating degree of 60-95° SR; wherein, in weight percent, an amount of the support layer is in a range of 60-95 wt % based on the total basis weight of the separator substrate and an amount of the nano layer is in a range of 5-40 wt % based on the total basis weight of the separator substrate.

2. The method according to claim 1, wherein, when the thermoplastic bonded fibers in the support layer are the unstretched PET fibers, a drying temperature is 120° C., and a calendering temperature is 170-220° C.

3. The method according to claim 1, wherein, a thickness of the substrate is 10-25 μm; a basis weight of the substrate is 8-17 g/m.sup.2; an average pore size of the substrate is less than 3 μm; and a maximum pore size of the substrate is less than 5 μm.

4. The method according to claim 1, wherein, when the thermoplastic bonded fibers in the support layer are the PET/co-PET bi-component fibers or the PP/PE bi-component fibers, a drying temperature is 90° C.; and a calendering temperature is 110-140° C.

5. The method according to claim 1, wherein, the fibrillated poly-p-phenylene terephthalamide (PPTA) nanofibers have a beating degree of 60-85° SR; the fibrillated lyocell nanofibers have a beating degree of 70-95° SR; and the fibrillated poly-p-phenylene benzoxadiazole (PBO) nanofibers and the fibrillated polyacrylonitrile (PAN) nanofibers have a beating degree of 85° SR.

6. The method according to claim 1, wherein, the solid weight percent concentrations of the pulps of the support layer and the nano layer are both 0.2 wt % before diluting with water; the on-wire concentration of the pulp of the support layer is 0.01-0.05 wt %; the on-wire concentration of the pulp of the nano layer is 0.002-0.05 wt %; the flow rate of the pulp of the support layer is 160-3000 m.sup.3/h; the flow rate of the pulp of the nano layer is 40-750 m.sup.3/h; a drying temperature is 80-130° C.; and a calendering temperature is 110-220° C.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) Embodiments of the disclosure are described in detail below with reference to the attached drawing figures, wherein:

(2) FIG. 1 is a schematic diagram of the apparent morphology of a lithium ion battery separator substrate prepared in Examples 1-63 of the disclosure.

(3) FIG. 2 is a schematic structural view of a HYDROFORMER™, a type of double-layer hydraulic inclined wire former, used in the disclosure, wherein A represents a pulp distributor, B represents a rectifying zone, C represents a substrate forming zone, and D represents a formed wet paper sheet of the substrate.

DETAILED DESCRIPTION OF THE DISCLOSURE

(4) The disclosure will be further described below in conjunction with specific embodiments. It should be understood that the embodiments of the disclosure are only used to illustrate the disclosure, and are not intended to limit the scope of the disclosure.

(5) The experimental methods without specific conditions in the following examples are generally performed under conventional conditions or according to the conditions recommended by the manufacturer. Unless otherwise defined, all professional and scientific terms used in the text have the same meaning as familiar to those skilled in the art.

(6) In addition, any methods and materials similar or equivalent to the described content can be applied to the method of the disclosure. The preferred implementation methods and materials described herein are for demonstration purposes only.

(7) The following Examples 1-63 and Comparative Examples 1-11 only disclose examples of using some fiber materials to prepare substrates, and other fiber materials and combinations thereof given in the disclosure may also be used to prepare the substrate of the disclosure. The HYDROFORMER™, a type of double-layer hydraulic inclined wire former, used in Examples 1-63 of the disclosure is shown in FIG. 2, and the appearance of the prepared lithium ion battery separator substrate is shown in FIG. 1.

Example 1

(8) A lithium ion battery separator substrate is consisting of a two-layer structure of a support layer and a dense layer, and is prepared by the following method:

(9) Step a: Mixing the fiber materials of the support layer and the dense layer respectively with water in the defibizer according to the formulas shown in Table 1, defiberizing and beating to a solid weight percent concentration of 0.2 wt %, and then diluting by the flushing pump, wherein the fiber material of the support layer is diluted to a solid weight percent concentration of 0.02375 wt % to obtain Pulp 1; the fiber material of the dense layer is diluted to a solid weight percent concentration of 0.005 wt % to obtain Pulp 2.

(10) Step b: Respectively feeding the pulp 1 and the pulp 2 obtained in step a into the HYDROFORMER™, a type of double-layer hydraulic inclined wire former, wherein the pulp 1 enters the lower flow channel at a flow rate of 740 m.sup.3/h, the pulp 2 enters the upper flow channel at a flow rate of 185 m.sup.3/h; after rectification, making papers of the two layers at the same time, and draining to obtain a wet paper sheet for the substrate.

(11) Step c: Drying the wet paper sheet for the substrate obtained in step b to obtain a dry paper sheet for the substrate at a temperature of 120° C. by a Yankee dryer.

(12) Step d: Calendering the dry paper sheet for the substrate obtained in Step c at a temperature of 190° C. by a metal roller and a soft roller to obtain the lithium ion battery separator substrate of the disclosure.

Examples 2-4, 35-40, 47, 48

(13) A lithium ion battery separator substrate is consisting of a two-layer structure of a support layer and a dense layer. The formulas of the support layer and the dense layer are shown in Table 1. The preparation method is the same as that in Example 1.

Example 5

(14) A lithium ion battery separator substrate is consisting of a two-layer structure of a support layer and a dense layer. The formulas of the support layer and the dense layer are shown in Table 1. The separator substrate is prepared by the following method:

(15) Step a: Mixing the fiber materials of the support layer and the dense layer respectively with water in the defibizer according to the formulas shown in Table 1, defiberizing and beating to a solid weight percent concentration of 0.2 wt %, and then diluting by the flushing pump, wherein the fiber material of the support layer is diluted to a solid weight percent concentration of 0.02 wt % to obtain Pulp 1; the fiber material of the dense layer is diluted to a solid weight percent concentration of 0.02 wt % to obtain Pulp 2.

(16) Step b: Respectively feeding the pulp 1 and the pulp 2 obtained in step a into the HYDROFORMER™, a type of double-layer hydraulic inclined wire former, wherein the pulp 1 enters the lower flow channel at a flow rate of 740 m.sup.3/h, the pulp 2 enters the upper flow channel at a flow rate of 185 m.sup.3/h; after rectification, making papers of the two layers at the same time, and draining to obtain a wet paper sheet for the substrate.

(17) Step c: Drying the wet paper sheet for the substrate obtained in step b to obtain a dry paper sheet for the substrate at a temperature of 120° C. by a Yankee dryer.

(18) Step d: Calendering the dry paper sheet for the substrate obtained in Step c at a temperature of 190° C. by a metal roller and a soft roller to obtain the lithium ion battery separator substrate of the present disclosure.

Examples 6-8, 13-15, 22-28, 41-44, 61-63

(19) A lithium ion battery separator substrate is consisting of a two-layer structure of a support layer and a dense layer. The formulas of the support layer and the dense layer are shown in Table 1. The preparation method is the same as that in Example 5.

Example 9

(20) A lithium ion battery separator substrate is consisting of a two-layer structure of a support layer and a dense layer. The formulas of the support layer and the dense layer are shown in Table 1. The separator substrate is prepared by the following method:

(21) Step a: Mixing the fiber materials of the support layer and the dense layer respectively with water in the defibizer according to the formulas shown in Table 1, defiberizing and beating to a solid weight percent concentration of 0.2 wt %, and then diluting by the flushing pump, wherein the fiber material of the support layer is diluted to a solid weight percent concentration of 0.015 wt % to obtain Pulp 1; the fiber material of the dense layer is diluted to a solid weight percent concentration of 0.04 wt % to obtain Pulp 2.

(22) Step b: Respectively feeding the pulp 1 and the pulp 2 obtained in step a to the HYDROFORMER™, a type of double-layer hydraulic inclined wire former, wherein the pulp 1 enters the lower flow channel at a flow rate of 740 m.sup.3/h, the pulp 2 enters the upper flow channel at a flow rate of 185 m.sup.3/h; after rectification, making papers of the two layers at the same time, and draining to obtain a wet paper sheet for the substrate.

(23) Step c: Drying the wet paper sheet for the substrate obtained in step b to obtain a dry paper sheet for the substrate at a temperature of 120° C. by a Yankee dryer.

(24) Step d: Calendering the dry paper sheet for the substrate obtained in Step c at a temperature of 190° C. by a metal roller and a soft roller to obtain the lithium ion battery separator substrate of the disclosure.

Examples 10-12, 29-34, 45-46

(25) A lithium ion battery separator substrate is consisting of a two-layer structure of a support layer and a dense layer. The formulas of the support layer and the dense layer are shown in Table 1. The preparation method is the same as that in Example 9.

Examples 16, 19, 51-52, 55-56

(26) A lithium ion battery separator substrate is consisting of a two-layer structure of a support layer and a dense layer. The formulas of the support layer and the dense layer are shown in Table 1. The separator substrate is prepared by the following method:

(27) Step a and Step b are the same as in Example 5.

(28) Step c: Drying the wet paper sheet for the substrate obtained in step b to obtain a dry paper sheet for the substrate at a temperature of 90° C. by a Yankee dryer.

(29) Step d: Calendering the dry paper sheet for the substrate obtained in Step c at a temperature of 120° C. by a metal roller and a soft roller to obtain the lithium ion battery separator substrate of the disclosure.

Examples 17-18, 20-21, 59-60

(30) A lithium ion battery separator substrate is consisting of a two-layer structure of a support layer and a dense layer. The formulas of the support layer and the dense layer are shown in Table 1. The separator substrate is prepared by the following method:

(31) Step a and Step b are the same as in Example 9.

(32) Step c: Drying the wet paper sheet for the substrate obtained in step b to obtain a dry paper sheet for the substrate at a temperature of 90° C. by a Yankee dryer.

(33) Step d: Calendering the dry paper sheet for the substrate obtained in Step c at a temperature of 120° C. by a metal roller and a soft roller to obtain the lithium ion battery separator substrate of the disclosure.

Examples 49-50, 53-54, 57-58

(34) A lithium ion battery separator substrate is consisting of a two-layer structure of a support layer and a dense layer. The formulas of the support layer and the dense layer are shown in Table 1. The separator substrate is prepared by the following method:

(35) Step a and Step b are the same as in Example 1.

(36) Step c: Drying the wet paper sheet for the substrate obtained in step b to obtain a dry paper sheet for the substrate at a temperature of 90° C. by a Yankee dryer.

(37) Step d: Calendering the dry paper sheet for the substrate obtained in Step c at a temperature of 120° C. by a metal roller and a soft roller to obtain the lithium ion battery separator substrate of the disclosure.

Comparative Example 1

(38) A lithium ion battery separator substrate is consisting of a single layer structure. The formula of the single layer is shown in Table 2. The separator substrate is prepared by the following method:

(39) Step a: Mixing the fiber material with water in the defibizer according to the formula shown in Table 2, defiberizing and beating to a solid weight percent concentration of 0.2 wt %, and then diluting the fiber material by the flushing pump to a solid weight percent concentration of 0.02 wt % to obtain a pulp.

(40) Step b: Feeding the pulp obtained in step a to an inclined wire paper machine, wherein the flow rate of the pulp is 925 m.sup.3/h; after rectification, and draining to obtain a wet paper sheet for the substrate.

(41) Step c: Drying the wet paper sheet for the substrate obtained in step b to obtain a dry paper sheet for the substrate at a temperature of 120° C. by a Yankee dryer.

(42) Step d: Calendering the dry paper sheet for the substrate obtained in Step c at a temperature of 190° C. by a metal roller and a soft roller to obtain the single-layer lithium ion battery separator substrate.

Comparative Example 2

(43) A lithium ion battery separator substrate is consisting of a single layer structure. The formula of the single layer is shown in Table 2. The preparation method is the same as that in Comparative Example 1.

Comparative Examples 3-5

(44) A lithium ion battery separator substrate is consisting of a two-layer structure of a support layer and a dense layer. The formulas of the support layer and the dense layer are shown in Table 2. The preparation method is the same as that in Example 5.

Comparative Examples 6-7

(45) A lithium ion battery separator substrate is consisting of a two-layer structure of a support layer and a dense layer. The formulas of the support layer and the dense layer are shown in Table 2. The preparation method is the same as that in Example 1.

Comparative Example 8

(46) A lithium ion battery separator substrate is consisting of a two-layer structure of a support layer and a dense layer, and is prepared by the following method:

(47) Step a: Mixing the fiber materials of the support layer and the dense layer respectively with water in the defibizer according to the formulas shown in Table 2, defiberizing and beating to a solid weight percent concentration of 0.2 wt %, and then diluting by the flushing pump, wherein the fiber material of the support layer is diluted to a solid weight percent concentration of 0.0125 wt % to obtain Pulp 1; the fiber material of the dense layer is diluted to a solid weight percent concentration of 0.05 wt % to obtain Pulp 2.

(48) Step b, step c and step d are the same as in Example 1.

Comparative Examples 9-10

(49) A lithium ion battery separator substrate is consisting of a two-layer structure of a support layer and a dense layer. The formulas of the support layer and the dense layer are shown in Table 2. The separator substrate is prepared by the following method:

(50) Step a and step b are the same as in Example 5.

(51) Step c: Drying the wet paper sheet for the substrate obtained in step b to obtain a dry paper sheet for the substrate at a temperature of 90° C. by a Yankee dryer.

(52) Step d: Calendering the dry paper sheet for the substrate obtained in Step c at a temperature of 120° C. by a metal roller and a soft roller to obtain the lithium ion battery separator substrate of the disclosure.

Comparative Example 11

(53) Chinese Patent CN201410496299.4 discloses a substrate for separators for lithium secondary batteries. The substrate for a separator is prepared by the following method: Using a disc mill, mix solvent-spun cellulose fibers 10% by mass, oriented crystalline polyethylene terephthalate (PET) short fibers 50% by mass and unstretched binder polyester fibers 40% by mass together, wherein the solvent-spun cellulose fibers have an average fiber diameter of 10 m, a fiber length of 4 mm, and a freeness of 97 ml; the oriented crystalline polyethylene terephthalate (PET) short fibers have an average fiber diameter of 2.4 m and fiber length of 3 mm; unstretched binder polyester fibers have an average fiber diameter of 4.4 m and fiber length of 3 mm; and then dissociate in the pulp machine water to obtain a uniform papermaking pulp (0.3 mass % concentration) on the basis of agitation using an agitator. The inclined short wire is used as the first layer and the rotary wire is used as the second layer, and the weight ratio of unit area of the inclined short wire to the rotary wire is set to 50:50 to laminate the papermaking pulp to obtain a wet sheet. After drying at a Yankee dryer temperature of 130° C., calender by a metal roller and an elastic roller with a surface temperature of 195° C. to obtain a weight per unit area of 8.2 g/m.sup.2 and a thickness of 14.2 m of the substrate for separators for lithium secondary batteries.

(54) TABLE-US-00001 TABLE 1 Fiber formulation of Examples 1-63 (wt %) Nanofibers (the Superfine first nanofibers Proportion based main Thermoplastic or the second on the total Examples fibers bonded fibers nanofibers) basis weight Example 1 Support layer 45%.sup.a) 40% .sup.d)  15% .sup.i) 95% Dense layer — — 100% .sup.j)  5% Example 2 Support layer 30%.sup.a) 65% .sup.d)  5% .sup.i) 95% Dense layer — — 100% .sup.j)  5% Example 3 Support layer 65%.sup.a) 30% .sup.d)  5% .sup.i) 95% Dense layer — — 100% .sup.j)  5% Example 4 Support layer 40% .sup.a) 30% .sup.d)  30% .sup.i) 95% Dense layer — — 100% .sup.j)  5% Example 5 Support layer 45% .sup.a) 40% .sup.d)  15% .sup.i) 80% Dense layer — — 100% .sup.j) 20% Example 6 Support layer 30% .sup.a) 65% .sup.d)  5% .sup.i) 80% Dense layer — — 100% .sup.j) 20% Example 7 Support layer 65% .sup.a) 30% .sup.d)  5% .sup.i) 80% Dense layer — — 100% .sup.j) 20% Example 8 Support layer 40% .sup.a) 30% .sup.d)  30% .sup.i) 80% Dense layer — — 100% .sup.j) 20% Example 9 Support layer 45% .sup.a) 40% .sup.d)  15% .sup.i) 60% Dense layer — — 100% .sup.j) 40% Example 10 Support layer 30% .sup.a) 65% .sup.d)  5% .sup.i) 60% Dense layer — — 100% .sup.j) 40% Example 11 Support layer 65% .sup.a) 30% .sup.d)  5% .sup.i) 60% Dense layer — — 100% .sup.j) 40% Example 12 Support layer 40% .sup.a) 30% .sup.d)  30% .sup.i) 60% Dense layer — — 100% .sup.j) 40% Example 13 Support layer 30% .sup.b) 65% .sup.d)  5% .sup.i) 80% Dense layer — — 100% .sup.j) 20% Example 14 Support layer 30% .sup.c) 65% .sup.d)  5% .sup.i) 80% Dense layer — — 100% .sup.j) 20% Example 15 Support layer 10% .sup.a) 65% .sup.d)  5% .sup.i) 80% 10% .sup.b) 10% .sup.c) Dense layer — — 100% .sup.j) 20% Example 16 Support layer 40% .sup.a) 30% .sup.e)  30% .sup.i) 80% Dense layer — — 100% .sup.j) 20% Example 17 Support layer 30% .sup.a) 65% .sup.e)  5% .sup.i) 60% Dense layer — — 100% .sup.j) 40% Example 18 Support layer 40% .sup.a) 30% .sup.e)  30% .sup.i) 60% Dense layer — — 100% .sup.j) 40% Example 19 Support layer 40% .sup.a) 30% .sup.f)  30% .sup.i) 80% Dense layer — — 100% .sup.j) 20% Example 20 Support layer 30% .sup.a) 65% .sup.f)  5% .sup.i) 60% Dense layer — — 100% .sup.j) 40% Example 21 Support layer 40% .sup.a) 30% .sup.f)  30% .sup.i) 60% Dense layer — — 100% .sup.j) 40% Example 22 Support layer 30% .sup.a) 65% .sup.d)  5% .sup.j) 80% Dense layer — — 100% .sup.i) 20% Example 23 Support layer 30% .sup.a) 65% .sup.d)  5% .sup.i) 80% Dense layer — — 100% .sup.i) 20% Example 24 Support layer 30% .sup.a) 65% .sup.d)  5% .sup.i) 80% Dense layer — —  50% .sup.i) 20%  50% .sup.j) Example 25 Support layer 30% .sup.a) 65% .sup.d)  .sup. 5% .sup.g) 80% Dense layer — —  100% .sup.h) 20% Example 26 Support layer 45% .sup.b) 40% .sup.d)  15% .sup.i) 80% Dense layer — — 100% .sup.j) 20% Example 27 Support layer 45% .sup.c) 40% .sup.d)  15% .sup.i) 80% Dense layer — — 100% .sup.j) 20% Example 28 Support layer 12% .sup.a) 40% .sup.d)  15% .sup.i) 80% 12% .sup.b) 11% .sup.c) Dense layer — — 100% .sup.j) 20% Example 29 Support layer 30% .sup.b) 65% .sup.d)  5% .sup.i) 60% Dense layer — — 100% .sup.j) 40% Example 30 Support layer 30% .sup.c) 65% .sup.d)  5% .sup.i) 60% Dense layer — — 100% .sup.j) 40% Example 31 Support layer 10% .sup.a) 65% .sup.d)  5% .sup.i) 60% 10% .sup.b) 10% .sup.c) Dense layer — — 100% .sup.j) 40% Example 32 Support layer 45% .sup.b) 40% .sup.d)  15% .sup.i) 60% Dense layer — — 100% .sup.j) 40% Example 33 Support layer 45% .sup.c) 40% .sup.d)  15% .sup.i) 60% Dense layer — — 100% .sup.j) 40% Example 34 Support layer 12% .sup.a) 40% .sup.d)  15% .sup.i) 60% 12% .sup.b) 11% .sup.c) Dense layer — — 100% .sup.j) 40% Example 35 Support layer 30% .sup.b) 65% .sup.d)  5% .sup.i) 95% Dense layer — — 100% .sup.j)  5% Example 36 Support layer 30% .sup.c) 65% .sup.d)  5% .sup.i) 95% Dense layer — — 100% .sup.j)  5% Example 37 Support layer 10% .sup.a) 65% .sup.d)  5% .sup.i) 95% 10% .sup.b) 10% .sup.c) Dense layer — — 100% .sup.j)  5% Example 38 Support layer 45% .sup.b) 40% .sup.d)  15% .sup.i) 95% Dense layer — — 100% .sup.j)  5% Example 39 Support layer 45% .sup.c) 40% .sup.d)  15% .sup.i) 95% Dense layer — — 100% .sup.j)  5% Example 40 Support layer 12% .sup.a) 40% .sup.d)  15% .sup.i) 95% 12% .sup.b) 11% .sup.c) Dense layer — — 100% .sup.j)  5% Example 41 Support layer 45% .sup.a) 40% .sup.d)  15% .sup.j) 80% Dense layer — — 100% .sup.i) 20% Example 42 Support layer 45% .sup.a) 40% .sup.d) .sup. 15% .sup.g) 80% Dense layer — —  100% .sup.h) 20% Example 43 Support layer 45% .sup.a) 40% .sup.d)  15% .sup.i) 80% Dense layer — — 100% .sup.i) 20% Example 44 Support layer 45% .sup.a) 40% .sup.d)  15% .sup.i) 80% Dense layer — —  50% .sup.i) 20%  50% .sup.j) Example 45 Support layer 30% .sup.a) 65% .sup.d)  5% .sup.i) 60% Dense layer — — 100% .sup.i) 40% Example 46 Support layer 30% .sup.a) 65% .sup.d)  5% .sup.i) 60% Dense layer — —  50% .sup.i) 40%  50% .sup.j) Example 47 Support layer 30% .sup.a) 65% .sup.d)  5% .sup.i) 95% Dense layer — — 100% .sup.i)  5% Example 48 Support layer 30% .sup.a) 65% .sup.d)  5% .sup.i) 95% Dense layer — —  50% .sup.i)  5%  50% .sup.j) Example 49 Support layer 40% .sup.a) 30% .sup.e)  30% .sup.i) 95% Dense layer — — 100% .sup.j)  5% Example 50 Support layer 40% .sup.a) 30% .sup.f)  30% .sup.i) 95% Dense layer — — 100% .sup.j)  5% Example 51 Support layer 30% .sup.a) 65% .sup.e)  5% .sup.i) 80% Dense layer — — 100% .sup.j) 20% Example 52 Support layer 30% .sup.a) 65% .sup.f)  5% .sup.i) 80% Dense layer — — 100% .sup.j) 20% Example 53 Support layer 30% .sup.a) 65% .sup.e)  5% .sup.i) 95% Dense layer — — 100% .sup.j)  5% Example 54 Support layer 30% .sup.a) 65% .sup.f)  5% .sup.i) 95% Dense layer — — 100% .sup.j)  5% Example 55 Support layer 45% .sup.a) 40% .sup.e)  15% .sup.i) 80% Dense layer — — 100% .sup.j) 20% Example 56 Support layer 45% .sup.a) 40% .sup.f)  15% .sup.i) 80% Dense layer — — 100% .sup.j) 20% Example 57 Support layer 45% .sup.a) 40% .sup.e)  15% .sup.i) 95% Dense layer — — 100% .sup.j)  5% Example 58 Support layer 45% .sup.a) 40% .sup.f)  15% .sup.i) 95% Dense layer — — 100% .sup.j)  5% Example 59 Support layer 45% .sup.a) 40% .sup.e)  15% .sup.i) 60% Dense layer — — 100% .sup.j) 40% Example 60 Support layer 45% .sup.a) 40% .sup.f)  15% .sup.i) 60% Dense layer — — 100% .sup.j) 40% Example 61 Support layer 45% .sup.a) 40% .sup.d)  15% .sup.i) 80% Dense layer — —  20% .sup.i) 20%  80% .sup.j) Example 62 Support layer 45% .sup.a) 40% .sup.d)  15% .sup.i) 80% Dense layer — —  100% .sup.k) 20% Example 63 Support layer 45% .sup.a) 40% .sup.d) .sup. 15% .sup.k) 80% Dense layer — — 100% .sup.l) 20% Note: .sup.a) Stretched PET fiber with a fiber diameter of 2 μm and a fiber length of 3 mm; .sup.b) PAN fiber with a fiber diameter of 2 μm and a fiber length of 3 mm; .sup.c) PA fiber with a fiber diameter of 2 μm and a fiber length of 3 mm; .sup.d) Unstretched PET fiber with a fiber diameter of 4 μm and a fiber length of 3 mm; .sup.e) PET/co-PET bi-component fiber with a fiber diameter of 4 μm and a fiber length of 3 mm; .sup.f) PP/PE bi-component fiber with a fiber diameter of 4 μm and a fiber length of 3 mm; .sup.g) Fibrillated Tencel nanofiber with a beating degree of 70°SR, Lenzing, Austria; .sup.h) Fibrillated PPTA nanofiber with a beating degree of 60°SR, DuPont Kevlar of the United States; .sup.i) Fibrillated Tencel nanofiber with a beating degree of 95°SR, Lenzing, Austria; .sup.j) Fibrillated PPTA nanofiber with a beating degree of 85°SR, DuPont Kevlar of the United States; .sup.k) Fibrillated PBO nanofiber with a beating degree of 85°SR, Japan Toyobo Company; .sup.l) Fibrillated PAN nanofiber with a beating degree of 85°SR.

(55) TABLE-US-00002 TABLE 2 Fiber formulas (wt %) of Comparative Examples 1-10 Superfine Thermoplastic Proportion based main bonded on the total Examples fibers fibers Nanofibers basis weight Comparative Single-layer 50% .sup.a) 50% .sup.b) — 100%  Example 1 Comparative Single-layer 45% .sup.a) 40% .sup.b)  .sup. 15% .sup.e) 100%  Example 2 Comparative Support layer 45% .sup.a) 40% .sup.b)  .sup. 15% .sup.e) 80% Example 3 Dense layer 20% .sup.a) —  80% .sup.f) 20% Comparative Support layer 50% .sup.a) 50% .sup.b) — 80% Example 4 Dense layer — — 100% .sup.f) 20% Comparative Support layer 75% .sup.a) 20% .sup.b)  .sup. 5% .sup.e) 80% Example 5 Dense layer — — 100% .sup.f) 20% Comparative Support layer 30% .sup.a) 30% .sup.b)  .sup. 40% .sup.e) 95% Example 6 Dense layer — — 100% .sup.f)  5% Comparative Support layer 30% .sup.a) 30% .sup.b)  40% .sup.f) 95% Example 7 Dense layer — — 100% .sup.f)  5% Comparative Support layer 45% .sup.a) 40% .sup.b)  .sup. 15% .sup.e) 50% Example 8 Dense layer — — 100% .sup.f) 50% Comparative Support layer 75% .sup.a) 20% .sup.c)  .sup. 5% .sup.e) 80% Example 9 Dense layer — — 100% .sup.f) 20% Comparative Support layer 75% .sup.a) 20% .sup.d)  .sup. 5% .sup.e) 80% Example 10 Dense layer — — 100% .sup.f) 20% Note: .sup.a) Stretched PET fiber with a fiber diameter of 2 μm and a fiber length of 3 mm; .sup.b) Unstretched PET fiber with a fiber diameter of 4 μm and a fiber length of 3 mm; .sup.c) PET/co-PET bi-component fiber with a fiber diameter of 4 μm and a fiber length of 3 mm; .sup.d) PP/PE bi-component fiber with a fiber diameter of 4 μm and a fiber length of 3 mm; .sup.e) Fibrillated Tencel nanofiber with a beating degree of 95°SR, Lenzing, Austria; .sup.f) Fibrillated PPTA nanofiber with a beating degree of 85°SR, DuPont Kevlar of the United States.

(56) Performance Test of the Lithium Ion Battery Separator Substrate

(57) The lithium ion battery separator substrates prepared in Examples 1-63 and Comparative Examples 1-11 were tested for performance. The test items and methods are as follows:

(58) 1. Basis weight, thickness and tensile strength: measured by TAPPI standard.

(59) 2. Average pore size and maximum pore size: measured using a PMI pore size analyzer.

(60) 3. Heat shrinkage rate

(61) The dimensional stability of the substrate at a certain temperature can be characterized by the thermal stability of the substrate, usually expressed in heat shrinkage rate. Test of the heat shrinkage rate of the substrate as follows:

(62) Cutting the substrate into squares with side length L.sub.b, and then respectively placing the substrate in an environment of 110° C. and 300° C. for 1 hour, testing the side length L.sub.a of the substrate, and calculating the shrinkage rate according to the following formula:
Shrinkage rate(%)=(L.sub.b−L.sub.a)/L.sub.b×100

(63) 4. Substrate strength retention

(64) The substrate was placed in a 300° C. environment for 1 hour and taken out. The strength retention of the substrate was evaluated according to the following criteria:

(65) ∘: Fold the substrate 10 times without breaking;

(66) Δ: Fold the substrate 2-10 times and break;

(67) x: Fold the substrate once and break.

(68) TABLE-US-00003 TABLE 3 Performance test parameter of the lithium ion battery separator substrate of the disclosure Average Maximum Heat Basis Tensile Pore Pore Shrinkage weight Thickness Strength Size Size Rate % at Strength Examples g/m.sup.2 μm N/m μm μm 300° C. Retention 1 11.8 19.3 832 1.93 3.35 4.7 Δ 2 12.3 19.8 1025 2.63 4.85 4.8 Δ 3 11.9 19.8 608 2.58 4.73 4.8 Δ 4 12.2 18.4 583 1.42 2.43 4.5 Δ 5 12.0 18.6 723 1.52 2.58 2.8 ∘ 6 12.2 19.1 925 1.81 3.12 3.0 ∘ 7 11.9 19.1 545 1.76 2.87 3.0 ∘ 8 11.7 17.9 519 1.02 1.96 2.6 ∘ 9 12.2 17.8 489 0.89 1.65 2.0 ∘ 10 11.8 18.2 673 1.05 1.95 2.2 ∘ 11 12.2 18.2 453 1.01 1.91 2.2 ∘ 12 12.1 17.3 432 0.52 1.34 1.8 ∘ 13 12.2 19.8 854 1.96 3.53 3.2 ∘ 14 12.1 20.2 847 2.04 3.61 3.2 ∘ 15 12.0 19.7 876 1.92 3.43 3.2 ∘ 16 11.8 18.9 474 1.23 2.18 2.8 ∘ 17 11.8 19.2 596 1.21 2.15 2.2 ∘ 18 12.1 18.3 403 0.64 1.52 1.8 ∘ 19 11.7 18.9 476 1.25 2.23 2.6 ∘ 20 11.9 20.2 623 1.35 2.34 2.2 ∘ 21 12.1 19.3 408 0.62 1.50 1.8 Δ 22 12.1 19.2 915 1.93 3.37 3.2 Δ 23 11.9 19.1 953 1.79 3.09 3.4 Δ 24 11.8 19.3 934 1.81 3.11 3.1 ∘ 25 11.9 19.4 912 1.96 3.43 3.2 ∘ 26 12.2 19.5 652 1.58 2.67 2.8 ∘ 27 12.1 19.4 642 1.59 2.70 2.8 ∘ 28 12.0 19.0 681 1.55 2.62 2.8 ∘ 29 12.2 18.8 625 1.17 2.11 2.2 ∘ 30 11.9 18.9 620 1.15 2.07 2.2 ∘ 31 12.0 18.4 643 1.12 2.04 2.2 ∘ 32 11.6 17.8 443 0.93 1.75 2.0 ∘ 33 11.9 17.8 434 0.92 1.73 2.0 ∘ 34 11.9 17.8 458 0.91 1.70 2.0 ∘ 35 12.2 19.8 925 2.72 4.98 4.8 ∘ 36 12.0 19.8 914 2.71 4.96 4.8 ∘ 37 11.7 19.8 978 2.68 4.91 4.8 ∘ 38 12.2 20.3 758 1.99 3.48 4.7 ∘ 39 12.0 20.4 749 1.98 3.46 4.7 ∘ 40 12.2 19.7 783 1.95 3.38 4.7 ∘ 41 12.2 18.6 701 1.59 2.78 2.9 Δ 42 11.9 18.6 708 1.61 2.84 3.0 ∘ 43 11.9 18.6 746 1.50 2.51 3.2 Δ 44 11.8 18.6 734 1.51 2.53 2.9 Δ 45 11.8 18.2 698 1.02 1.92 2.2 Δ 46 11.9 18.2 686 1.03 1.93 2.2 Δ 47 11.8 19.8 1054 2.58 4.73 4.9 Δ 48 11.9 19.8 1035 2.60 4.82 4.8 Δ 49 12.1 19.4 529 1.52 2.42 4.5 ∘ 50 12.0 19.4 526 1.53 2.47 4.5 ∘ 51 11.9 20.3 839 1.95 3.50 3.2 ∘ 52 11.8 20.5 821 1.97 3.55 3.2 ∘ 53 12.1 20.8 954 2.69 4.92 2.8 ∘ 54 12.1 20.8 945 2.71 4.97 2.8 ∘ 55 12.1 19.6 634 1.62 2.73 2.8 ∘ 56 11.9 19.6 623 1.64 2.78 2.8 ∘ 57 11.9 20.3 753 1.99 3.50 4.7 ∘ 58 12.0 20.3 743 2.01 3.52 4.7 ∘ 59 12.1 18.8 434 0.93 1.78 2.2 ∘ 60 11.9 18.8 428 0.97 1.83 2.2 ∘ 61 11.8 18.6 682 1.49 2.56 2.9 ∘ 62 12.1 18.6 673 1.58 2.67 2.8 ∘ 63 12.0 18.6 668 1.62 2.73 2.8 ∘ Note: The lithium ion battery separator substrate of the disclosure has a heat shrinkage rate of zero at 110° C., and shrinkage only begins when it is close to 300° C.

(69) TABLE-US-00004 TABLE 4 Performance test parameter of the lithium ion battery separator substrate Average Maximum Heat Basis Tensile Pore Pore Shrinkage weight Thickness Strength Size Size Rate % at Strength Parameter g/m.sup.2 μm N/m μm μm 300° C. Retention Comparative 11.8 20.3 1069 5.30 100.4 Melting x Example 1 Comparative 12.3 19.5 903 3.53 15.5 15.0 Δ Example 2 Comparative 12.2 18.8 854 2.68 7.49 7.8 ∘ Example 3 Comparative 12.0 19.3 789 2.53 6.55 3.2 ∘ Example 4 Comparative 11.9 19.1 314 1.82 2.96 3.0 ∘ Example 5 Comparative 11.7 17.9 365 1.55 2.59 4.5 Δ Example 6 Comparative 12.2 17.9 345 1.65 2.77 4.5 Δ Example 7 Comparative 11.8 17.4 332 0.73 1.58 1.8 ∘ Example 8 Comparative 11.8 19.1 283 1.79 2.94 3.0 ∘ Example 9 Comparative 11.9 19.1 276 1.81 2.95 3.0 ∘ Example 10 Comparative 8.2 14.2 636 5.58 8.02 25.0 Δ Example 11

(70) It can be seen from Table 3 that the lithium ion battery separator substrates obtained in Examples 1-63 of the disclosure have a basis weight of about 11 to 13 g/m.sup.2 and a thickness of 17 to 21 μm. The separator substrates comprise a support layer and a dense layer. In weight percent, the proportion of the support layer is in a range of 60-95% based on the total basis weight of the separator substrate and an proportion of the dense layer is in a range of 5-40% based on the total basis weight of the separator substrate. In the support layer, the amount of stretched PET fibers is 30-65%, the amount of unstretched PET fibers is 30-65% and the amount of nanofibers is 5-30%. The dense layer is made of 100% nanofibers. According to the above requirements, the lithium ion battery separator substrates are made of HYDROFORMER™, a type of double-layer hydraulic inclined wire former. The maximum pore size of the lithium ion battery separator substrates is less than 5 μm, the strength is greater than 400 N/m, and the maximum can reach 1054 N/m. The heat shrinkage rate at 110° C. is zero, and the separator substrate still has a certain strength at 300° C. for 1 hour and the heat shrinkage rate is less than 5.0%, preferably less than 2%, which is enough to ensure that the separator prepared directly from the substrate or the separator coated with other materials such as ceramic particles have excellent thermal stability and the thickness of the separator is thinner.

(71) It can be seen from Table 4 that in Comparative Example 1, the single-layer substrate is only made of PET fibers with pinholes, wherein the pore size is too large, and melting occurs at 300° C.; in Comparative Example 2, the single-layer substrate is made of PET fibers and fibrillated lyocell nanofibers, wherein the pore size is too large, the heat shrinkage rate of the substrate is 15.0% after treatment at 300° C. for 1 h, and the substrate is damaged after folding; in Comparative Example 3, the two layers substrate is made by a HYDROFORMER™, a type of double-layer hydraulic inclined wire former, and the dense layer of the substrate is added with 20% stretched PET fiber and 80% fibrillated PPTA fiber, so that the substrate has a heat shrinkage rate of 7.8% after treatment at 300° C. for 1 hour; in Comparative Example 4, the support layer does not use nanofibers, which causes the maximum pore diameter of the substrate to be too large; in Comparative Examples 5-10, the substrate strength cannot meet the requirements; in Comparative Example 11, the maximum pore diameter of the separator described is too large, and there is no double-layer structure, the heat shrinkage rate is 25.0% after treatment at 300° C. for 1 hour.

(72) It should be understood that the disclosure described herein is not limited to specific methodologies, experimental protocols, or reagents, as these may vary. The discussion and examples provided herein are presented to describe specific embodiments and are not intended to limit the scope of the disclosure, which is limited only by the claims.