A lithium ion battery separator, a method for preparing the same, and a lithium ion battery using the same

Abstract

The present disclosure relates to a lithium ion battery separator, a preparation method thereof and a lithium ion battery using the same, the lithium ion battery separator comprising a base layer and a coating layer, the coating layer comprising LiOH, the coating amount of the LiOH being 1-6 wt% relative to the weight of the base layer. The above-mentioned separator can inhibit the elution of transition metals and the deposition of the negative electrode while not increasing the internal resistance of the battery, avoiding the use of too much high impedance vinylene carbonate additive.

Description

Technical Field

[0001] This disclosure relates to the field of lithium-ion battery manufacturing, specifically to a lithium-ion battery separator, a method for preparing the same, and a lithium-ion battery using the same. Background Technology

[0002] Lithium iron phosphate (LFP) batteries are gradually becoming the mainstream power battery technology due to their excellent safety performance, low cost, and long lifespan. It is generally believed that the olivine crystal structure of LFP materials is very stable and can withstand tens of thousands of cycles. A significant drawback of LFP is that iron ions detach from the positive electrode and deposit on the negative electrode during cycling. This iron deposition not only damages the solid electrolyte interphase (SEI) film on the negative electrode, causing capacity loss, but can also create short circuits, posing safety hazards. There are two common methods in the industry to suppress iron deposition: one is to bake away as much moisture as possible inside the battery; the other is to add a large amount of vinylene carbonate (VC) electrolyte additive. VC is recognized as the most effective additive for suppressing iron deposition, but it is also a consumable additive. During cycling, the graphite on the negative electrode repeatedly expands and contracts, and VC is continuously consumed to form a new SEI film. To ensure long cycle life of LFP batteries, a large amount of VC must be added initially. However, VC easily forms a very dense SEI film on the negative electrode, leading to a significant increase in battery impedance, which greatly affects battery power and room temperature cycle performance. Summary of the Invention

[0003] The purpose of this disclosure is to provide a lithium-ion battery separator, a method for preparing the same, and a lithium-ion battery using the same. The separator can suppress the dissolution of transition metals and the deposition of negative electrode without increasing the internal resistance of the battery, and avoids the use of excessive high-resistivity vinylene carbonate additives.

[0004] To achieve the above objectives, the first aspect of this disclosure provides a lithium-ion battery separator, the lithium-ion battery separator comprising a substrate layer and a coating layer, the coating layer comprising LiOH;

[0005] The amount of LiOH coated is 1 to 6% by weight relative to the weight of the substrate layer.

[0006] Optionally, the amount of LiOH coated is 2 to 3% by weight relative to the weight of the substrate layer.

[0007] Optionally, the thickness of the substrate layer is 4~15μm;

[0008] The thickness of the coating layer is 0.5~5μm;

[0009] The thickness of the lithium-ion battery separator is 4.5~20μm.

[0010] Optionally, the matrix layer contains one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene and polyvinylidene fluoride, preferably one or more of polyethylene, polypropylene and polyvinylidene fluoride.

[0011] The second aspect of this disclosure provides a method for preparing a lithium-ion battery separator, the method comprising: coating a slurry containing LiOH onto a substrate layer, and then drying the substrate layer to form a coating layer containing LiOH.

[0012] The amount of LiOH coated is 1 to 6% by weight relative to the weight of the substrate layer.

[0013] Optionally, the drying conditions include: a time of 1 to 50 minutes and a temperature of 50 to 150°C.

[0014] Optionally, the matrix layer contains one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene and polyvinylidene fluoride, preferably one or more of polyethylene, polypropylene and polyvinylidene fluoride.

[0015] The thickness of the substrate layer is 4~15μm;

[0016] The solvent in the slurry includes one or more of water, acetone, and N-methylpyrrolidone;

[0017] The slurry contains an adhesive, which includes one or more of polyacrylic acid, styrene-butadiene rubber, and polyvinylidene fluoride, and the content of the adhesive is 1-10% by weight.

[0018] The slurry contains additives, including sodium carboxymethyl cellulose and / or polyvinylpyrrolidone, and the content of the additives is 1-5% by weight.

[0019] The slurry has a solid content of 30-80% by weight.

[0020] The third aspect of this disclosure provides a lithium-ion battery separator prepared using the method described in the second aspect of this disclosure.

[0021] This disclosure provides a lithium-ion battery in a fourth aspect, the lithium-ion battery comprising a positive electrode, a negative electrode, an electrolyte, and a lithium-ion battery separator as described in the first or third aspect of this disclosure;

[0022] The coating layer of the lithium-ion battery separator faces the positive electrode.

[0023] Optionally, the electrolyte contains vinylene carbonate;

[0024] The content of vinylene carbonate Y is 3% by weight or less, preferably 2% by weight or less, relative to the total weight of the electrolyte.

[0025] Optionally, in the lithium-ion battery, the coating amount X of LiOH and the content Y of vinylene carbonate have the relationship shown in formula (1);

[0026] A = X / 2 + Y (1)

[0027] A is 2 or higher, preferably 3 or higher.

[0028] Optionally, the active material of the positive electrode includes phosphate positive electrode materials, preferably one or more of lithium iron phosphate, manganese phosphate and lithium manganese iron phosphate;

[0029] The active material of the negative electrode includes one or more of the following: soft carbon, hard carbon, artificial graphite, natural graphite, elemental silicon, silicon oxide, silicon-carbon composite, lithium titanate, and elemental metals that can form alloys with lithium.

[0030] Optionally, the electrolyte contains lithium salt and solvent;

[0031] The lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0032] The solvent includes ester solvents, preferably one or more of ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, polycarbonate, ethyl propionate and ethyl acetate.

[0033] Through the above technical solution, the separator of this disclosure has a coating layer containing a specific amount of LiOH. On the one hand, it absorbs free acid in the electrolyte, reducing the dissolution of transition metal ions; on the other hand, the transition metal ions dissolved from the positive electrode, during their diffusion to the negative electrode through the separator, react with the LiOH on the separator, which can prevent the deposition of transition metal ions on the negative electrode and damage the SEI film, while releasing active lithium ions to provide more active lithium for the battery. Using the separator of this disclosure to prepare lithium-ion batteries can avoid the excessive use of vinylene carbonate, which increases the internal resistance of the battery, and can also reduce the deposition of transition metals on the negative electrode, improving the lifespan of the lithium-ion battery and the capacity retention rate under high-temperature cycling conditions.

[0034] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0035] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings:

[0036] Figure 1 This is a scanning electron microscope image of the coating layer of the diaphragm prepared in Example 1 of this disclosure.

[0037] Figure 2 This is a scanning electron microscope image of the coating layer of the diaphragm prepared in Comparative Example 1 of this disclosure. Detailed Implementation

[0038] The following provides a detailed description of specific embodiments of this disclosure. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit this disclosure.

[0039] The first aspect of this disclosure provides a lithium-ion battery separator, the lithium-ion battery separator comprising a substrate layer and a coating layer, the coating layer comprising LiOH;

[0040] The amount of LiOH coated is 1 to 6% by weight relative to the weight of the substrate layer.

[0041] To further reduce the dissolution of transition metals and the deposition of negative electrodes, according to one embodiment of this disclosure, the coating amount of LiOH is 2 to 3 times the weight of the substrate layer.

[0042] To avoid battery performance degradation due to excessive film thickness, according to one embodiment of this disclosure, the thickness of the substrate layer is 4~15μm; the thickness of the coating layer is 0.5~5μm; and the thickness of the lithium-ion battery separator is 4.5~20μm.

[0043] According to one embodiment of this disclosure, the composition of the matrix layer used is conventional in the art, such as including one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene and polyvinylidene fluoride, preferably including one or more of polyethylene, polypropylene and polyvinylidene fluoride.

[0044] The second aspect of this disclosure provides a method for preparing a lithium-ion battery separator, wherein a slurry containing LiOH is coated onto a substrate layer and then dried to form a coating layer containing LiOH on the substrate layer;

[0045] The amount of LiOH coated is 1 to 6% by weight relative to the weight of the substrate layer.

[0046] The method disclosed herein forms a coating layer by coating a substrate layer with a slurry containing LiOH. The method disclosed herein is simple in steps and is conducive to industrial production. The prepared lithium-ion battery separator can suppress the dissolution of transition metals and the deposition of negative electrode without increasing the internal resistance of the battery, significantly improve the capacity retention rate of the battery during high-temperature cycling, and avoid the use of too much high-resistivity vinylene carbonate additive.

[0047] According to one embodiment of this disclosure, the amount of LiOH coated is 2 to 3 by weight relative to the weight of the substrate layer.

[0048] In this disclosure, the coating method is conventional in the art, such as scraping, rolling, spraying, etc.

[0049] In order to ensure that LiOH is evenly distributed on the substrate layer and to avoid affecting the substrate layer, according to one embodiment of the present disclosure, the drying conditions include: a time of 1 to 50 minutes and a temperature of 50 to 150°C.

[0050] According to one embodiment of this disclosure, the matrix layer comprises one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene and polyvinylidene fluoride, preferably containing one or more of polyethylene, polypropylene and polyvinylidene fluoride.

[0051] According to one embodiment of this disclosure, the thickness of the substrate layer is 4~15μm.

[0052] According to one embodiment of this disclosure, the solvent in the slurry includes one or more of water, acetone, and N-methylpyrrolidone.

[0053] According to one embodiment of this disclosure, the slurry contains an adhesive, the adhesive comprising one or more of polyacrylic acid, styrene-butadiene rubber and polyvinylidene fluoride, and the content of the adhesive is 1 to 10 by weight.

[0054] According to one embodiment of this disclosure, the slurry contains an additive, which includes one or more of sodium carboxymethyl cellulose and polyvinylpyrrolidone, and the content of the additive is 1 to 5% by weight.

[0055] According to one embodiment of this disclosure, the slurry has a solid content of 30-80% by weight.

[0056] The third aspect of this disclosure provides a lithium-ion battery separator prepared using the method described in the second aspect of this disclosure.

[0057] This disclosure provides a lithium-ion battery in a fourth aspect, the lithium-ion battery comprising a positive electrode, a negative electrode, an electrolyte, and a lithium-ion battery separator as described in the first or third aspect of this disclosure;

[0058] The coating layer of the lithium-ion battery separator faces the positive electrode.

[0059] According to one embodiment of this disclosure, the electrolyte contains vinylene carbonate; the content of vinylene carbonate Y relative to the total weight of the electrolyte is 3% by weight or less, preferably 2% by weight or less; wherein, "content of vinylene carbonate" refers to the content of vinylene carbonate in the electrolyte after battery formation; the above content can avoid the increase of internal resistance of lithium-ion battery caused by excessive content, and can further reduce the deposition of transition metals on the negative electrode.

[0060] According to one embodiment of the present disclosure, in the lithium-ion battery, the coating amount X of LiOH and the content Y of vinylene carbonate have the relationship shown in formula (1).

[0061] A = X / 2 + Y (1)

[0062] A is 2 or more, preferably 3 or more, for example 3 to 6; lithium-ion batteries with the above content relationship can reduce the amount of negative electrode transition metal deposition without increasing the battery internal resistance, and avoid increasing the manufacturing cost.

[0063] According to one embodiment of this disclosure, the active material of the positive electrode includes a phosphate positive electrode material, preferably one or more of lithium iron phosphate, manganese phosphate, and lithium manganese iron phosphate.

[0064] According to one embodiment of this disclosure, the active material of the negative electrode includes one or more of soft carbon, hard carbon, artificial graphite, natural graphite, elemental silicon, silicon oxide, silicon-carbon composite, lithium titanate, and elemental metals that can form alloys with lithium.

[0065] In this disclosure, the methods and conditions for preparing the positive and negative electrode sheets are conventional in the art.

[0066] According to one embodiment of this disclosure, the electrolyte contains a lithium salt and a solvent; the lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate; the solvent includes ester solvents, preferably one or more of ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, polycarbonate, ethyl propionate, and ethyl acetate.

[0067] According to one embodiment of this disclosure, the electrolyte contains a phosphorus-based additive, which includes one or more of tripropynyl phosphate, tris(trimethylsilane)phosphite, and dimethyl methylphosphonate.

[0068] According to one embodiment of this disclosure, the electrolyte contains a sulfur-based additive, which includes one or more of methylene disulfonate, vinylene sulfate, propane sulfonate lactone, and vinyl sulfate.

[0069] In this disclosure, the contents of lithium salts, phosphorus-based additives, and sulfur-based additives in the electrolyte are conventional in the art.

[0070] The present invention will be described in detail below through embodiments, but is not limited to the following embodiments.

[0071] Unless otherwise specified, all reagents used in the following examples and comparative examples were commercially available.

[0072] The thickness of the substrate layer, coating layer, and diaphragm was measured using a micrometer.

[0073] Examples 1-11

[0074] (1) Preparation of positive electrode sheet

[0075] The active material lithium iron phosphate, the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) are mixed with the solvent N-methylpyrrolidone in a weight ratio of 96:2:2 to obtain a slurry with a solid content of 50% by weight. The slurry is coated on the current collector Al foil, dried, rolled, and die-cut to obtain the positive electrode sheet of the lithium-ion secondary battery.

[0076] (2) Preparation of negative electrode sheet

[0077] Surface-treated graphite, conductive agent acetylene black, adhesive styrene-butadiene rubber (SBR), thickener sodium carboxymethyl cellulose (CMC) are thoroughly mixed with solvent deionized water in a weight ratio of 95:2:2:1 to obtain a slurry with a solid content of 50% by weight. This slurry is coated onto current collector Cu foil, dried, rolled, and die-cut to obtain the negative electrode sheet of a lithium-ion secondary battery.

[0078] (3) Preparation of electrolyte

[0079] LiPF6 (1M concentration), a certain amount of vinylene carbonate (VC) additive, and solvents ethylene carbonate (EV) and ethyl methyl carbonate (EMC) were mixed (EC:EMC weight ratio = 30:70) to obtain the electrolyte.

[0080] (4) Preparation of the diaphragm

[0081] A PE film (polyethylene film, surface density 7 g / m³) with a thickness of 12 μm. 2As the substrate layer, a slurry containing LiOH, PVDF binder (concentration of 5% by weight) and polyvinylpyrrolidone additive (concentration of 3% by weight) (solvent is N-methylpyrrolidone, solid content is 40% by weight) was sprayed onto the substrate layer and dried at 100°C for 15 min to obtain a lithium-ion battery separator. The composition and parameters are listed in Table 1.

[0082] The coating layer of the diaphragm prepared in Example 1 was tested by scanning electron microscopy, and the results are as follows: Figure 1 As shown.

[0083] (5) Preparation of lithium-ion secondary batteries

[0084] The prepared positive electrode, negative electrode, and separator are stacked, baked, injected with liquid, soaked, formed, aged, degassed, and capacity tested to obtain the finished battery.

[0085] Comparative Examples 1-4

[0086] Lithium-ion batteries were prepared using the method described in Example 1, except that LiOH was replaced with Al2O3. The relevant parameters are listed in Table 1.

[0087] The coating layer of the diaphragm prepared in Comparative Example 1 was tested by scanning electron microscopy, and the results are as follows: Figure 2 As shown.

[0088] Table 1

[0089]

[0090] The content Y of vinylene carbonate in Table 1 above represents the content of vinylene carbonate in the electrolyte after battery formation. The test method is gas chromatography-mass spectrometry (GC-MS).

[0091] In Table 1 above, the coating amount X represents the coating amount of LiOH in the examples and the coating amount of Al2O3 in the comparative examples.

[0092] Test Example 1: Initial Battery Discharge Capacity

[0093] The battery formation process involves charging at 0.05C for 2 hours at 45℃, switching to 0.2C constant current and constant voltage until 3.8V (0.05C) is cut off, and then discharging to 2V by 1 / 3. The first battery discharge capacity is then measured.

[0094] Test Example 2 DCIR

[0095] First, adjust the battery to 50% SOC and let it stand for 30 minutes to obtain a stable voltage V1; then discharge it at a rate of 1.5C for 30 seconds to obtain a discharge voltage V2. The DCIR of the battery is defined as (V1-V2) / 1.5C.

[0096] Test Example 3 Capacity Retention

[0097] The lithium-ion batteries prepared in the examples and comparative examples were subjected to 200 cycles at 1C (2.0V→3.8V range) at a high temperature of 60°C, and the capacity retention rate was calculated.

[0098] Test Example 4: Iron Deposition Amount at the Negative Electrode

[0099] The negative electrode is obtained by disassembling a lithium-ion battery, and the iron content of the negative electrode is tested by inductively coupled plasma atomic emission spectrometry (ICP).

[0100] The test results for test examples 1-4 are listed in Table 2.

[0101] Table 2

[0102]

[0103] Based on the above data, it can be seen that the separator can alleviate the increase in internal resistance while inhibiting the dissolution of transition metals and the deposition of negative electrode. The prepared lithium-ion battery has a high capacity retention rate, low internal resistance and iron deposition.

[0104] The preferred embodiments of this disclosure have been described in detail above. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0105] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0106] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode, a negative electrode, an electrolyte, and a lithium-ion battery separator. The lithium-ion battery separator includes a substrate layer and a coating layer, wherein the coating layer includes LiOH; The amount of LiOH coated is 1-6% by weight relative to the weight of the substrate layer. The coating layer of the lithium-ion battery separator faces the positive electrode; The electrolyte contains vinylene carbonate; The content of vinylene carbonate Y is less than 3% by weight relative to the total weight of the electrolyte; In the lithium-ion battery, the coating amount X of LiOH and the content Y of vinylene carbonate have the relationship shown in formula (1); A = X / 2 + Y (1) A is 2 or higher.

2. The lithium-ion battery according to claim 1, wherein, The amount of LiOH coated is 2 to 3% by weight relative to the weight of the substrate layer.

3. The lithium-ion battery according to claim 1, wherein, The thickness of the substrate layer is 4~15μm; The thickness of the coating layer is 0.5~5μm; The thickness of the lithium-ion battery separator is 4.5~20μm.

4. The lithium-ion battery according to claim 1, wherein, The matrix layer contains one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene and polyvinylidene fluoride.

5. The lithium-ion battery according to claim 1, wherein, The substrate layer contains one or more of polyethylene, polypropylene, and polyvinylidene fluoride.

6. The lithium-ion battery according to claim 1, wherein, The content of vinylene carbonate Y is less than 2% by weight relative to the total weight of the electrolyte.

7. The lithium-ion battery according to claim 1, wherein, A is 3 or higher.

8. The lithium-ion battery according to claim 1, wherein, The active material of the positive electrode includes phosphate positive electrode material; The active material of the negative electrode includes one or more of the following: soft carbon, hard carbon, artificial graphite, natural graphite, elemental silicon, silicon oxide, silicon-carbon composite, lithium titanate, and elemental metals that can form alloys with lithium.

9. The lithium-ion battery according to claim 8, wherein, The active material of the positive electrode includes one or more of lithium iron phosphate, manganese phosphate, and lithium manganese iron phosphate.

10. The lithium-ion battery according to claim 1, wherein, The electrolyte contains lithium salt and solvent; The lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate. The solvent includes ester solvents.

11. The lithium-ion battery according to claim 10, wherein, The solvent includes one or more of ethylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, polycarbonate, ethyl propionate, and ethyl acetate.

12. A method for preparing the lithium-ion battery separator according to any one of claims 1 to 11, characterized in that, The method includes: coating a slurry containing LiOH onto a substrate layer, and then drying it to form a coating layer containing LiOH on the substrate layer; The amount of LiOH coated is 1 to 6 by weight relative to the weight of the substrate layer.

13. The method according to claim 12, wherein, The drying conditions include: a time of 1 to 50 minutes and a temperature of 50 to 150°C.

14. The method according to claim 12, wherein, The substrate layer contains one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride; The thickness of the substrate layer is 4~15μm; The solvent in the slurry includes one or more of water, acetone, and N-methylpyrrolidone; The slurry contains an adhesive, which includes one or more of polyacrylic acid, styrene-butadiene rubber, and polyvinylidene fluoride, and the content of the adhesive is 1-10% by weight. The slurry contains additives, including sodium carboxymethyl cellulose and / or polyvinylpyrrolidone, and the content of the additives is 1-5% by weight. The solid content of the slurry is 30-80% by weight.

15. The method according to claim 12, wherein, The substrate layer contains one or more of polyethylene, polypropylene, and polyvinylidene fluoride.

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