Rechargeable battery with improved battery separator

Abstract

A secondary battery that generates or contains metal ion contaminants selected from copper ions, manganese ions, nickel ions, cobalt ions, iron ions, aluminum ions, chromium ions, molybdenum ions, tin ions, or combinations thereof, the battery comprising: a negative electrode; a positive electrode; a coated or uncoated battery separator between the negative electrode and the positive electrode, the coated or uncoated battery separator comprising a scavenging layer; a coated or uncoated battery separator between the negative electrode and the positive electrode; and an electrolyte. The battery exhibits improved yields in initial charging and aging processes and a long service life due to the separator reducing or eliminating metal ion contamination of the battery.

Description

[Technical Field]

[0001] This application relates to an improved battery separator, and more particularly to a secondary battery comprising a battery separator capable of reducing or removing metal ion contamination in secondary batteries, especially those prone to metal ion contamination. [Background technology]

[0002] Electrode materials commonly used in secondary batteries may contain transition metals, including iron (Fe), manganese (Mn), nickel (Ni), cobalt (Co), aluminum (Al), chromium (Cr), molybdenum (Mo), tin (Sn), and others. For example, some exemplary electrode materials may include lithium nickel cobalt manganese oxide (NMC or NCM), lithium iron phosphate (LFP), lithium nickel manganese spinel (LMNO), lithium nickel cobalt aluminum oxide (NCA), lithium manganese oxide (LMO), lithium cobalt oxide (LCO), or combinations thereof. Some of these electrode materials interact with the electrolyte, resulting in the presence of transition metal ions in the electrolyte. Under suitable conditions, these metal ions can be reduced to a metallic form. This metallic plating, in particular, leads to dendrite growth. When dendrites grow through the separator and connect the two electrodes, a short circuit occurs. Also, if the graphite electrode becomes toxic, for example, a plating of transition metal ions may occur on the electrode. This may result in a reduced battery lifespan.

[0003] Another source of metallic contamination may be metal equipment used to manufacture battery components and / or batteries, such as brushes and rollers. Metal equipment may be a source of cobalt, copper, zinc, chromium, or iron ions in the battery.

[0004] Figure 12 illustrates two problems arising from metal contamination in batteries: internal short-circuit self-discharge and deactivation of the negative electrode material, which contributes to capacity reduction. [Overview of the Initiative] Problem to be Solved by the Invention

[0005] From the foregoing viewpoint, a method for reducing, alleviating, or removing metallic contamination in a battery may be desirable. Means for Solving the Problem

[0006] In one aspect, a secondary battery that generates or contains metal ion contaminants selected from, but not limited to, copper ions, manganese ions, nickel ions, cobalt ions, iron ions, chromium ions, molybdenum ions, tin ions, or combinations thereof is described. The metal ion contaminants may originate from the electrode materials of the battery. For example, the positive electrode material of the battery may comprise lithium nickel cobalt manganese oxide (NMC or NCM), lithium iron phosphate (LFP), lithium nickel manganese spinel (LMNO), lithium nickel cobalt aluminum oxide (NCA), lithium manganese oxide (LMO), lithium cobalt oxide (LCO), or combinations thereof. Alternatively or additionally, the presence of the metal ion contaminants may be due to metallic equipment such as brushes and rollers used in the battery manufacturing process. The secondary battery described herein may advantageously reduce or eliminate the metallic contamination problem by using the separator described herein, as compared with a battery that does not use such a separator.

[0007] The secondary battery described herein may comprise the following components: a negative electrode, a positive electrode, a coated or uncoated battery separator provided with a trapping layer between the negative electrode and the positive electrode, and an electrolyte. The battery separator may be provided with the trapping layer that is a part of the separator. For example, the trapping layer may be located in the center of the battery separator or on the side of the battery separator closest to the negative electrode. Alternatively or in addition to the trapping layer being a part of the battery separator, the trapping layer may be provided as a coating or as one layer of a coating on the side of the battery separator facing the negative electrode.

[0008] For embodiments where the capture layer is part of the separator, the potential difference of the capture layer relative to Li+ / Li is in the range of +0.0 V to +5.0 V, +0.0 V to +4.0 V, +0.0 V to +3.5 V, +0.0 V to +3.0 V, +0.0 V to +2.5 V, +0.0 V to +2.0 V, +0.0 V to +1.5 V, or +0.0 V to 1.0 V.

[0009] In embodiments where the capture layer is part of the separator, the capture layer may have a bulk or volume resistivity of 10 4 ~10 9 Ω·cm, 10 5 ~10 9 Ω·cm, 10 6 ~10 9 Ω·cm, 10 7 ~10 9 Ω·cm, or 10 8 ~10 9 Ω·cm. In some preferred embodiments, the bulk or volume resistivity may be 10 4 ~10 9 Ω·cm, 10 4 ~10 8 Ω·cm or 10 4 ~10 7 Ω·cm. A particularly preferred resistivity may be 10 4 ~10 8 Ω·cm or 10 4 ~10 7 Ω·cm.

[0010] In some embodiments, the capture layer may be incorporated as part of the separator by a lamination process, a co-extrusion process, or a combination of lamination and co-extrusion processes.

[0011] In embodiments where the capture layer is part of the separator, the capture layer may contain carbon and a polymer. In some embodiments, the carbon may be conductive carbon. The carbon may be selected from carbon black, acetylene black, carbon nanotubes, graphene, or a combination thereof. In some other embodiments where the capture layer is part of the separator, the capture layer may contain a conductive polymer. For example, the conductive polymer may be polyacetylene, polythiophene, polyaniline, polypyrrole, or a combination thereof.

[0012] In embodiments comprising a trapping layer as a coating or as one layer of a coating, the potential difference of the trapping layer with respect to Li+ / Li is +0.0V to +5.0V, +0.0V to +4.0V, +0.0V to +3.5V, +0.0V to +3.0V, +0.0V to +2.5V, +0.0V to +2.0V, +0.0V to +1.5V, or +0.0V to 1.0V.

[0013] In embodiments in which the trapping layer is provided as a coating or as one layer of a coating, the trapping layer is 10 4 ~10 9 Ω·cm, 10 4 ~10 8 Ω·cm, or 10 4 ~10 7 It may have a bulk or volume resistivity of Ω·cm.

[0014] In embodiments comprising a capture layer as a coating or as one layer of a coating, the capture layer may contain carbon and a polymer. In some embodiments, the carbon may be conductive carbon. The carbon may be selected from carbon black, acetylene black, carbon nanotubes, graphene, or a combination thereof. In embodiments comprising a capture layer as a coating or as one layer of a coating, the capture layer may contain a conductive polymer. For example, the conductive polymer may be polyacetylene, polythiophene, polyaniline, polypyrrole, or a combination thereof. [Brief explanation of the drawing]

[0015] [Figure 1] Figure 1 shows a secondary battery according to several embodiments described herein. [Figure 2] Figure 2 shows a secondary battery according to several embodiments described herein. [Figure 3] Figure 3 shows a secondary battery according to several embodiments described herein. [Figure 4] Figure 4 shows a secondary battery according to several embodiments described herein. [Figure 5] Figure 5 shows a secondary battery according to several embodiments described herein. [Figure 6] Figure 6 shows a secondary battery according to several embodiments described herein. [Figure 7] Figure 7 shows a secondary battery according to several embodiments described herein. [Figure 8] Figure 8 shows a secondary battery according to several embodiments described herein. [Figure 9] Figure 9 shows a secondary battery according to several embodiments described herein. [Figure 10] Figure 10 shows a secondary battery according to several embodiments described herein. [Figure 11] Figure 11 shows a secondary battery according to several embodiments described herein. [Figure 12] Figure 12 is a schematic diagram illustrating two problems arising from metal contamination in secondary batteries. [Figure 13] Figure 13 is a schematic diagram illustrating one solution to prevent, reduce, or mitigate problems arising from metal contamination in secondary batteries. [Figure 14] Figure 14 is a schematic diagram of a comparative embodiment and an embodiment of the present invention described herein, the embodiment of the present invention includes calculation results showing that the self-discharge is more than 1,000 times lower than that of the comparative embodiment. [Figure 15] Figure 15 shows SEM images of battery separators according to several embodiments described herein. [Figure 16] Figure 16 is a schematic diagram of a battery cell according to some embodiments described herein. [Figure 17] Figure 17 is a graph showing the voltage over time for the present and comparative embodiments of the present invention described herein. [Figure 18] Figure 18 is an SEM image showing metal deposition in the embodiments of the present invention and comparative embodiments described herein. [Figure 19] Figure 19 includes SEM images of a metal trapping layer before and after metal trapping according to several embodiments described herein. [Modes for carrying out the invention]

[0016] This specification discloses secondary batteries that have or are prone to metallic contamination, and whose service life is improved, at least to some extent, by the separator used herein. The battery comprises, or may essentially comprise, a negative electrode, a positive electrode, a separator between the negative electrode and the positive electrode, and an electrolyte. The separator may be a coated separator or an uncoated separator, and the trapping layer may be part of the separator, part of the coating, or both part of the separator and part of the coating. If the trapping layer is part of the separator, it is preferable that the trapping layer is in the center of the separator or on the side of the separator closest to the negative electrode. If the trapping layer is part of the coating (trapping layer coating), the trapping layer is part of the coating on the side of the separator facing the negative electrode. Examples of secondary batteries according to some embodiments described herein are shown in Figures 1-11 and elsewhere.

[0017] positive electrode The positive electrode of the secondary battery described herein is not particularly limited, but may preferably be a positive electrode material that generates metal ion contamination in the battery. For example, the positive electrode material may be a transition metal-containing compound that can be used as a positive electrode. In some embodiments, the positive electrode material may be selected from lithium nickel cobalt manganese oxide (NMC or NCM), lithium iron phosphate (LFP), lithium nickel manganese spinel (LMNO), lithium nickel cobalt aluminum oxide (NCA), lithium manganese oxide (LMO), lithium cobalt oxide (LCO), or a combination thereof.

[0018] negative electrode The negative electrode material for the secondary battery described herein is not limited and may be any negative electrode material for use in a secondary battery. In some preferred embodiments, the negative electrode material may be one that is prone to metal ion contamination, such as graphite.

[0019] electrolyte The electrolyte material for the secondary battery described herein is not particularly limited, and any electrolyte material for use in a secondary battery may be used. In some preferred embodiments, the electrolyte is a liquid electrolyte.

[0020] Separator In this specification, the separator may be one of the following: an uncoated separator having a trapping layer, a coated separator having a coating that provides a trapping layer, a coated separator having a trapping layer, or a coated separator having both a coating and a trapping layer.

[0021] Uncoated separator with a trapping layer An uncoated separator with a trapping layer may be a porous membrane having one or more trapping layers. The one or more trapping layers may be multiple outer layers (see Figures 2, 3, and 13), multiple inner layers (see Figures 1 and 11), or, if two or more trapping layers are present, both inner layers and multiple outer layers. The trapping layers may be incorporated into the separator by any means, including but not limited to co-extrusion, lamination, or both. For example, to form the two-layer uncoated separator shown in Figure 1, the trapping layer material and the polyolefin-containing material may be co-extruded and then stretched to form pores. Alternatively, the trapping layer material and the polyolefin-containing material may be extruded separately to form two separate non-porous precursors. These precursors may be laminated together before or after stretching to form the two-layer uncoated separator shown in Figure 1. The polyolefin-containing material may consist of, or essentially consist of, polypropylene, polyethylene, or copolymers, terpolymers, or blends thereof.

[0022] In a preferred embodiment, the uncoated separator with a capture layer may be a microporous film.

[0023] An uncoated separator with a trapping layer may be formed by any method, but in a preferred embodiment, the uncoated separator with a trapping layer may be formed by a dry stretching method such as the Celgard dry stretching method. The dry stretching method consists of, or essentially consists of, an extrusion (or co-extrusion) step, an annealing step, and a stretching (uniscrew or biscrew) step. The dry stretching method uses no solvent or oil, or only a minimal amount. The uncoated separator with a trapping layer may also be formed by a wet process using a solvent and / or oil. For example, a solvent and / or oil may be used in the wet process to form pores.

[0024] Covered separator with a trapping layer The coated separator may consist of, or essentially consist of, a separator having the aforementioned trapping layer (see Figures 4-6 and 10) or a separator without the trapping layer (see Figures 7-9), and a coating on at least one side of the separator. The coating may consist of, or essentially consist of, a trapping layer (see Figures 7-10). In some embodiments, the coating comprises two or more layers, and the trapping layer is one of these layers (see Figures 8-10). The other layers of the two or more layered coating may be a ceramic coating layer, a polymer coating layer, a shutdown coating layer, or a combination thereof. In a preferred embodiment, the coating with the trapping layer is on the side of the separator facing the negative electrode.

[0025] The trapping layer-less separator is not particularly limited and may be any porous or microporous membrane suitable for use as a battery separator. In some preferred embodiments, the trapping layer-less separator may consist of or essentially consist of one or more polyolefins, including polypropylene, polyethylene, copolymers thereof, or mixtures thereof. The trapping layer-less separator may be a single-layer, double-layer, triple-layer, or multilayer membrane. The trapping layer-less separator may be formed by any method, but in preferred embodiments, it may be formed by a dry stretching method such as the Celgard dry stretching method. The dry stretching method may consist of or essentially consist of an extrusion (or co-extrusion) step, an annealing step, and a stretching (uniaxial or biaxial) step. The dry stretching method uses no solvent or oil, or only a minimal amount thereof. The trapping layer-less separator may also be formed by a wet process using solvents and / or oils. For example, in a wet process, a solvent and / or oil may be used to form pores.

[0026] capture layer The trapping layer, whether part of the separator, part of the coating, or both, may have a potential difference relative to Li+ / Li in the range of +0.0V to +5.0V, +0.0V to +4.5V, +0.0V to +4.0V, +0.0V to +3.5V, +0.0V to +3.0V, +0.0V to +2.5V, +0.0V to +2.0V, +0.0V to +1.5V, or +0.0V to +1.0V. For example, to enable the trapping layer to trap copper ions, the potential difference would need to be +3.38. Li+ / Li is -3.04V relative to H2 / 2H+, and Cu 2+ The voltage of / Cu is +0.34V, so for the trapping layer to trap copper ions, there would need to be a potential difference of at least +3.38V relative to Li+ / Li.

[0027] The capture layer may be part of the separator, part of the coding, or both, 10-10 9 Ω·cm, 10~10 8 Ω·cm, 10~10 7 Ω·cm, 10~10 6 Ω·cm, 10~10 5 Ω·cm, 10~10 4 Ω·cm, 10~10 3 Ω·cm, or 10-10 2 It has a bulk or volume resistivity of Ω·cm. In some preferred embodiments, 10 4 ~10 9 Ω·cm, 10 4 ~10 8 Ω·cm, or 10 4 ~10 7 A resistivity of Ω·cm is preferable. As shown in Figure 14, using a trapping layer having a bulk or volume resistivity within this preferred range results in a self-discharge current 1,000 times lower than in embodiments without a trapping layer. 4 When the resistance drops below Ω·cm, a high self-discharge current is observed, and the bulk or volume resistivity is 10 7When the resistivity exceeds Ω·cm, the metal trapping function decreases, and the amount of metal deposited increases. This can be seen in Figure 16, which shows that the amount of metal deposited is high in Example 6, while in Example 5 the resistivity is 10 5 In comparison to Ω·cm, in Example 6, the bulk or volume resistivity is 10 10 It has a metal trapping layer with a density of Ω·cm.

[0028] In some preferred embodiments, the trapping layer may consist of, or essentially consist of, carbon and a polymer. In some particularly preferred embodiments, the carbon may be conductive carbon such as carbon nanotubes. In some embodiments, the carbon is selected from carbon black, acetylene black, carbon nanotubes, graphene, or a combination thereof.

[0029] In other preferred embodiments, the capture layer may consist of, or essentially consist of, a conductive polymer. The conductive polymer may be selected from polyacetylene, polythiophene, polyaniline, polypyrrole, or a combination thereof. [Examples]

[0030] Table 1 below shows the reduction potentials of certain transition metal ions and the minimum potential difference from Li+ / Li that the capture layer must have to capture each of the metal ions listed in the table. Capturing transition metal ions may refer to plating these ions onto the surface of the capture layer.

[0031] [Table 1]

[0032] Example 1 A battery separator as shown in Figures 1, 2, 3, or 11 is formed by co-extruding polypropylene and a trapping layer material containing polypropylene and carbon nanotubes. The potential difference of the trapping layer with respect to Li+ / Li is -3.04V with respect to H2 / 2H+, but becomes less than +3.39V after being electrically connected to the negative electrode. Conductive trapping layer (bulk or volume resistivity 10 4 ~10 9 Ω·cm, 10 4 ~10 8 Ω·cm, or 10 4 ~10 7 The conductive trapping layer (bulk or volume resistivity 10) is electrically connected by bringing it into contact with the negative electrode. 4 ~10 9 Ω·cm, 10 4 ~10 8 Ω·cm, or 10 4 ~10 7 The Ω·cm resistor is electrically connected to the negative electrode as follows: The negative electrode is brought into contact with the trapping layer facing the negative electrode. Metal dendrites grow from the negative electrode to the inner trapping layer. Therefore, this trapping layer can reduce and trap each of the transition metals listed in Table 1.

[0033] Example 2 To form the structures shown in Figures 7-9, a trapping layer coating is formed on a polypropylene single-layer battery separator. This coating contains carbon nanotubes and a polymer binder. The potential difference of the trapping layer coating with respect to Li+ / Li is -3.04V with respect to H2 / 2H+, but becomes less than +3.39V after being electrically connected to the negative electrode. Conductive trapping (bulk or volume resistivity 10 4 ~10 9 Ω·cm, 10 4 ~10 8 Ω·cm, or 10 4 ~10 7 The Ω·cm resistor is electrically connected to the negative electrode as follows: The negative electrode is brought into contact with the trapping layer facing the negative electrode. Metal dendrites grow from the negative electrode to the inner trapping layer. Therefore, this trapping layer can reduce and trap each of the transition metals listed in Table 1.

[0034] Example 3 Example 3 is similar to Example 1 except that the capture layer material contains a conductive polymer and does not contain polypropylene and carbon nanotubes.

[0035] Example 4 Example 4 is similar to Example 2 except that the capture layer contains a conductive polymer and does not contain carbon nanotubes and polymer binders.

[0036] Examples 5 and 6 and Comparative Example 1 Examples 5 and 6, and Comparative Example 1, were prepared by coating the surface of a 16 μm polyolefin three-layer battery separator with a slurry containing the compositions shown in Table 2. The coating in each example was 4 μm thick. Figure 15 shows an SEM image of a three-layer battery separator coated with a slurry containing carbon nanotubes (CNTs).

[0037] [Table 2]

[0038] Cells were formed using the separators of Examples 5, 6, and 7. The cell configuration was as follows: The cell structure was a stacked cell (36 mAh). The electrode size was 50 mm × 30 mm. The positive electrode material was NCM111, and the negative electrode material was graphite. The electrolyte was EC / EMC = 1 / 2, 1M LiPF6, VC 1 wt%. 50 μm copper particles were placed on the positive electrode to mimic contaminating metals. A schematic diagram of this cell is shown in Figure 16.

[0039] The charging and discharging conditions were as follows: The charging conditions were 4.2V CCCV 1mA 0.2mA cutoff. The aging period was 3 days (voltage drop was confirmed by internal short circuit). The temperature was 25℃.

[0040] The results are shown in Figures 17, 18, and 19. Figure 17 shows that the comparative example separator exhibits a large voltage drop over time. Therefore, due to the effect of the metal-capturing separator, the self-discharge level during aging is small. It was confirmed that the short-circuit resistance during internal short circuits is increased and the discharge current is small due to the effect of the high-resistance metal-capturing layer. Figure 18 shows an image of the negative electrode surface obtained after disassembling the cell following the cell aging process. The metal-capturing separators (Examples 5 and 6) showed reduced copper (metal contamination) deposition on the negative electrode compared to Comparative Example 1, which did not use a metal-capturing separator. This is because the separators in Examples 5 and 6 capture copper. Example 5, with its high CNT content (low resistance), is more efficient than Example 6, with its low CNT content (high resistance). Figure 19 shows that the CNTs in the metal-capturing separator capture copper. Comparing the images "before capture" and "after metal capture," it can be seen that the CNTs become thicker because copper is deposited on them.

Claims

1. A secondary battery that generates or contains metal ion contaminants selected from copper ions, manganese ions, nickel ions, cobalt ions, iron ions, chromium ions, molybdenum ions, tin ions, or combinations thereof, wherein the secondary battery is The negative electrode and, Positive electrode and, A covered or uncovered battery separator between the negative electrode and the positive electrode, comprising a battery separator with a trapping layer, Electrolytes and Equipped with, The trapping layer comprises at least carbon and a polymer, wherein the carbon is selected from carbon black, acetylene black, carbon nanotubes, graphene, or a combination thereof, and has a bulk or volume resistivity of 10⁴ to 10⁹ Ω·cm. The secondary battery wherein the trapping layer has a potential difference with respect to Li+ / Li in the range of +0.0V to +3.39V, or +0.0V to +3.0V.

2. The battery according to claim 1, wherein the battery separator is a coated battery separator having a coating on the side facing the negative electrode, and the coating comprises the trapping layer.

3. The aforementioned trapping layer is This is a coating on the side facing the negative electrode; Located in the center of the aforementioned battery separator; or It is located on the side of the battery separator closest to the negative electrode; The battery according to claim 1, wherein at least one of the following:

4. The battery according to claim 1, wherein the battery separator is provided with the capture layer in the center of the battery separator or on the side of the battery separator closest to the negative electrode.

5. The battery according to claim 4, wherein the battery separator has the capture layer in the center of the battery separator.

6. The battery according to claim 4, wherein the battery separator is provided with the trapping layer on the side of the battery separator closest to the negative electrode.

7. The battery according to any one of claims 4 to 6, wherein the capture layer of the battery separator is a co-extruded layer, a laminate, or a co-extruded laminate.

8. The battery according to claim 7, wherein the capture layer of the battery separator is a co-extruded layer or a co-extruded laminate.

9. The battery according to any one of claims 4 to 6, wherein the capture layer further comprises a conductive polymer.

10. The battery according to claim 9, wherein the conductive polymer is selected from polyacetylene, polythiophene, polyaniline, polypyrrole, or a combination thereof.

11. The battery according to claim 1, wherein the positive electrode comprises lithium nickel cobalt manganese oxide (NMC or NCM), lithium iron phosphate (LFP), lithium nickel manganese spinel (LMNO), lithium nickel cobalt aluminum oxide (NCA), lithium manganese oxide (LMO), lithium cobalt oxide (LCO), or a combination thereof.

12. Copper ions, manganese ions, nickel ions, cobalt ions, iron ions, chromium ions, molybdenum ions, tin ions, or combinations thereof generate or contain metal ion contaminants, and are placed between the negative and positive electrodes of a battery, and are coated or uncoated, The battery separator is provided with a capture layer on at least one side or in the center, The trapping layer comprises at least carbon and a polymer, wherein the carbon is selected from carbon black, acetylene black, carbon nanotubes, graphene, or a combination thereof, and has a bulk or volume resistivity of 10⁴ to 10⁹ Ω·cm. The trapping layer has a potential difference with respect to Li+ / Li in the range of +0.0V to +3.39V, or +0.0V to +3.0V, and The aforementioned trapping layer is The coating on the side facing the negative electrode; 10 ４ ~10 ９ Having a bulk or volume resistivity of Ω·cm; 10 ４ ~10 ８ Having a bulk or volume resistivity of Ω·cm; 10 ４ ~10 ７ Having a bulk or volume resistivity of Ω·cm; Furthermore, it includes a conductive polymer; The conductive polymer comprises polyacetylene, polythiophene, polyaniline, polypyrrole, or a combination thereof; The battery separator is located in the center, or It is located on the side of the battery separator closest to the negative electrode; A battery separator, which is at least one of the following.

13. The battery separator according to claim 12, wherein the capture layer of the battery separator is a co-extruded layer, a laminate, or a co-extruded laminate.

14. The battery separator according to claim 12, wherein the capture layer of the battery separator is a co-extruded layer or a co-extruded laminate.

15. The battery separator is provided as described in claim 12, A secondary battery that generates or contains metal ion contaminants selected from copper ions, manganese ions, nickel ions, cobalt ions, iron ions, chromium ions, molybdenum ions, tin ions, or combinations thereof.

16. The trapping layer is The battery according to claim 1, having a bulk or volume resistivity of 10⁴ to 10⁸ Ω·cm, or having a bulk or volume resistivity of 10⁴ to 10⁷ Ω·cm.

17. The trapping layer is The battery according to claim 1, comprising a conductive polymer and / or a conductive polymer selected from polyacetylene, polythiophene, polyaniline, polypyrrole, or a combination thereof.

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