KR20220142830A - Separator for lithium battery which uses lithium metal as anode thereof - Google Patents

Abstract

The present invention relates to a CaCO_3-based functional separator technology for suppressing the generation of lithium metal dendrites generated in a lithium-based secondary battery using lithium metal as a negative electrode. The separator technology introducing CaCO_3, according to the present invention, can effectively suppress the generation and growth of lithium metal dendrites formed on a surface by repeated charging and discharging when lithium metal is used as a negative electrode. In addition, due to the effective suppression of lithium metal dendrite generation, the life characteristics of lithium-based secondary batteries may be improved.

Description

Separator for lithium battery which uses lithium metal as anode thereof}

The present invention relates to a CaCO ₃ based functional separator technology for suppressing the generation of lithium metal dendrites generated in a lithium-based secondary battery using lithium metal as an anode.

With the rapid development of electrical, electronic, telecommunications and computer industries, the demand for high-capacity batteries is increasing. In response to such a demand, a lithium metal secondary battery using a lithium metal or a lithium alloy as an anode as an anode having a high energy density is attracting attention. A lithium metal secondary battery is a secondary battery using lithium metal or a lithium alloy as an anode. Lithium metal has a relatively low density and has a very low standard reduction potential of -3.045 V (SHE: based on a standard hydrogen electrode), attracting the most attention as an electrode material for high-energy-density batteries.

In LMB (Lithium Metal Battery), Li-S (Lithium Sulfur) battery, Lithium-air battery, etc. that use lithium metal as a negative electrode, when repeated charging and discharging proceed, lithium metal dendrites are formed on the surface of lithium metal used as a negative electrode. is created and grows. In the case of the lithium metal dendrite produced in this way, it penetrates the separator and causes a short circuit with the positive electrode, and in the related art, it even causes ignition and explosion. Due to these fatal drawbacks, the commercialization of secondary batteries using lithium metal as an anode has not been made.

Recently, various studies have been conducted to inhibit the generation and growth of lithium metal dendrites, and representative studies are as follows.

1) Research on inhibiting lithium metal dendrite formation by forming an artificial SEI layer on the surface of lithium metal through electrolyte additives

2) Research on suppressing lithium metal dendrite formation by forming artificial patterns or three-dimensional structures on the surface of lithium metal

3) Research on the formation and growth of lithium metal dendrites by forming a protective film on the surface of lithium metal using a polymer

Conventional separators used in lithium-based secondary batteries are mostly polyolefin-based separators directly used or coated with Al ₂ O ₃ . A polyolefin microporous film is widely used as a battery separator for various batteries due to its chemical stability and excellent physical properties. On the other hand, as a characteristic required for a separator, there is stability against heat shrinkage. That is, when the secondary battery generates heat, the temperature may rise to 150 ~ 160 °C, and when the separator is contracted, the electrolyte moves freely to both ends, resulting in a rapid temperature rise due to a large amount of chemical reaction. Since this causes a fire or explosion, which causes a problem in product reliability, it is important to improve the heat resistance of the separator. Therefore, in order to prevent the above problems and improve heat resistance, a method of dip-coating an inorganic material such as PVDF-HFP binder or Al ₂ O ₃ , SiO ₂ , TiO ₂ etc. on the surface of the separator is generally used.

In the case of the above-mentioned separator, since it is not a separator specialized for the generation and suppression of lithium metal dendrites, its use as a lithium-based secondary battery using lithium metal as an anode is inevitably limited. Therefore, there is a need for a new concept separator for suppressing the generation of lithium metal dendrites generated in lithium-based secondary batteries using lithium metal as an anode.

Domestic Patent Publication No. 10-2018-0030533

An object of the present invention is to provide a new concept separator for suppressing the generation and growth of dendrites on the surface of the above-mentioned lithium metal. Specifically, in the separator of the present invention, CaCO ₃ is coated or directly introduced into the separator for secondary batteries, and Ca is electrodeposited on the lithium metal surface through a substitution reaction between Ca of CaCO ₃ on the surface of the lithium metal and lithium on the surface of the lithium metal. This is to provide a functional separator that inhibits the generation and growth of lithium metal dendrites that occur on the surface of lithium metal by inducing a change in energy of

According to an aspect of the present invention, there is provided a separator for a lithium-based secondary battery using a lithium metal as an anode, comprising a porous separator coated with CaCO ₃ on one or both surfaces of a porous membrane or nonwoven fabric.

According to an embodiment of the present invention, the thickness of the coating may be 0.01 μm to 50 μm.

According to an embodiment of the present invention, the porosity of the porous membrane or nonwoven fabric may be 30 to 50%.

According to an embodiment of the present invention, the porous membrane or nonwoven fabric is polyolefin, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone. , polyphenylene oxide, polyphenylene sulfide, and may include one or more polymers selected from the group consisting of polyethylene naphthalate.

According to an embodiment of the present invention, the polyolefin may include at least one selected from the group consisting of polyethylene and polypropylene.

According to another aspect of the present invention, a positive electrode;

a negative electrode comprising lithium metal;

Interposed between the positive electrode and the negative electrode, a porous membrane or a porous separator coated with CaCO ₃ on one side or both sides of a nonwoven fabric; and

A lithium-based secondary battery including an electrolyte is provided.

The separator technology introducing CaCO ₃ according to the present invention can effectively suppress the generation and growth of lithium metal dendrites formed on the surface by repeated charging and discharging when lithium metal is used as an anode. In addition, due to the effective suppression of lithium metal dendrite generation, it is possible to obtain the result of improving the lifespan characteristics of the lithium-based secondary battery.

1 shows a comparison of the microstructure of the PE membrane and the CaCO ₃ -PE membrane used in this study. (a) Normal PE membrane, (b) CaCO ₃ -PE membrane
2 is a photograph of the surface and cross-section of each separator or lithium metal before and after 10 cycles of use.
(a), (b) Lithium metal surface CaCO ₃ -PE separator photo before use
(e), (f) Photo of lithium metal surface PE separator before use
(c), (d) Lithium metal cross-section CaCO ₃ -PE separator photo after 10 cycles
(g), (h) Photo of lithium metal cross-section PE separator after 10 cycles
3 is a CaCO ₃ -PE separator, a PE separator, an Al ₂ O ₃ -PE separator is an experimental result regarding the life characteristics of the lithium secondary battery including the separator.

The present invention relates to a separator of a lithium-based secondary battery using a lithium metal as a negative electrode, including a porous separator coated with CaCO ₃ on one or both surfaces of a porous membrane or a nonwoven fabric, or a lithium-based lithium-based separator in which the porous separator is interposed between the positive and negative electrodes It relates to secondary batteries.

The CaCO ₃ coated porous separator can effectively inhibit the growth of lithium dendrites, and thus can prevent short circuit and ignition problems caused by lithium dendrites, thereby greatly contributing to the stability of lithium secondary batteries. have.

In the present invention, the thickness of the porous coating layer is not particularly limited, but may be preferably in the range of 0.01 μm to 50 μm, or 0.5 μm to 20 μm in order to prevent an increase in internal resistance of the battery and ensure safety.

The porosity of the porous coating layer is preferably 20 to 50%. In this case, the porosity means a volume ratio of the pores to the total volume of the porous coating layer. If the porosity of the porous coating layer is less than 20%, there may be a problem of difficulty in impregnating the electrolyte, and conversely, if it exceeds 50%, there may be a problem of poor safety. The method for measuring the porosity of the porous coating layer is not particularly limited, and the size (micro) and mesopore volume, etc., are measured using a BET (Brunauer-Emmett- Teller) measurement method using a generally used adsorption gas such as nitrogen. It may be measured, or it may be measured using a commonly used mercury permeation method (Hg porosimeter).

The porous membrane or nonwoven fabric may include polyolefin such as polyethylene, polypropylene, polybutylene, and polypentene, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone. , polyether sulfone, polyphenylene oxide, polyphenylene sulfide and polyethylene naphthalate may include a porous membrane or non-woven fabric formed of one or more polymers selected from the group consisting of. Among them, it is preferable from a commercial standpoint to use a porous membrane or a nonwoven fabric formed of one or more polymers selected from the group consisting of polyethylene and polypropylene.

Meanwhile, the present invention provides a lithium secondary battery including the separator. The configuration of the positive electrode, the negative electrode, and the electrolyte of the lithium secondary battery may be used without limitation in a configuration used in a conventional lithium secondary battery. In the present invention, the positive electrode includes a positive electrode current collector and a positive electrode mixture. The positive electrode current collector, like the negative electrode current collector, is not particularly limited as long as it has high conductivity without causing a chemical change in the battery, for example, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel. Carbon, nickel, titanium, silver or the like surface-treated on the surface of the may be used. The positive electrode current collector may use various forms such as a film, sheet, foil, net, porous body, foam, nonwoven body, etc. having fine irregularities formed on the surface so as to increase adhesion with the positive electrode active material. For example, an aluminum thin plate may be used as the positive electrode current collector, but is not limited thereto.

As the electrolyte in the lithium secondary battery of the present invention, an electrolyte typically used in a lithium secondary battery, that is, an electrolyte containing a lithium salt and a non-aqueous organic solvent, an organic solid electrolyte, an inorganic solid electrolyte, and the like may be used. The non-aqueous organic solvent is, for example, N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, gamma-butyrolactone, 1, 2-dimethoxyethane, 1,2-diethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, 4-methyl-1,3-dioxene , diethyl ether, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3 -Dimethyl-2-imidazolidinone, a propylene carbonate derivative, a tetrahydrofuran derivative, ether, an aprotic organic solvent, such as methyl propionate, ethyl propionate, can be used.

The lithium salt is a material readily soluble in the non-aqueous electrolyte, for example, LiCl, LiBr, LiI, LiClO4, LiBF ₄ , LiB10Cl ₁₀ , LiPF ₆ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , LiSCN, LiC ₄ BO ₈ , LiCF ₃ CO ₂ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiN(SO ₂ CF ₃ ) ₂ , LiN(SO ₂ C ₂ F ₅ ) ₂ , LiC ₄ F9SO ₃ , LiC(CF ₃ SO ₂ ) ₃ , chloroborane lithium, lower aliphatic lithium carboxylate, 4-phenyl borate lithium imide, and the like can be used.

Examples of the organic solid electrolyte include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphoric acid ester polymers, poly agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene fluoride, A polymer containing a secondary dissociating group or the like may be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS3, Li4SiO4, Li4SiO ₄ -LiI -LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ Nitride, halide, sulfate, etc. of Li may be used.

In addition, the electrolyte may further include other additives for the purpose of improving charge/discharge characteristics, flame retardancy, and the like. Examples of the additive include pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazoli Dinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol, aluminum trichloride, fluoroethylene carbonate (FEC), propene sultone (PRS), vinylene carbonate ( VC) and the like.

The form of the lithium secondary battery as described above is not particularly limited, and may be, for example, a jelly-roll type, a stack type, a stack-folding type (including a stack-Z-folding type), or a lamination-stack type, preferably It may be stack-folding. The manufacturing method of the lithium secondary battery of the present invention is not particularly limited, but specifically, after manufacturing an electrode assembly in which the positive electrode, the separator, and the negative electrode are sequentially stacked, put it in a battery case, and then inject the electrolyte into the upper part of the case It can be manufactured by sealing and assembling with a cap plate and a gasket.

Hereinafter, the present invention will be described in more detail through examples. However, the following examples are intended to illustrate the present invention, and the scope of the present invention is not limited thereto. Rather, the content introduced herein is thorough and complete, and is provided to sufficiently convey the spirit of the present invention to those of ordinary skill in the art.

[Example]

The separator, which is the core technology of the present invention, is coated with a CaCO ₃ ceramic material on a polyethylene (PE) or polypropylene (PP) separator or various types of electrospun separator, or directly introduced into a fiber to inhibit lithium metal dendrite formation and growth. will do In the present invention, a CaCO ₃ PE membrane coated with PVDF-HFP polymer (hereinafter referred to as CaCO ₃ -PE membrane) was used, and a PE membrane and Al ₂ O ₃ were used as comparative examples in the life test. In FIG. 1, the microstructure of the PE membrane and the CaCO ₃ -PE membrane used in the present invention was compared and shown.

As can be seen from FIG. 1 , it was confirmed that a large amount of CaCO ₃ was coated on the surface of the PE separator. In order to check whether the proposed separator inhibits the generation and growth of lithium dendrites generated in the lithium metal negative electrode, a lithium metal/separator/lithium metal type symmetric coin cell was prepared and charged and discharged after 10 cycles of lithium metal surface structure was looked at and the results are shown in FIG. 2 . As can be seen from FIG. 2, when the CaCO ₃ -PE separator is applied, it is difficult to find lithium metal dendrite formation on the lithium metal surface. could confirm that there was In addition, as a result of the cross-sectional photo observation, when the CaCO ₃ -PE separator was applied, lithium metal was electrodeposited in a flat form, whereas when a general PE separator was applied, it was clearly confirmed that dendrites were formed thickly on the lithium metal surface. there was.

In order to check the effect of lithium dendrite formation on the lifespan characteristics of LMB (Lithium Metal Battery), a coin-half cell in the form of LCO/separator/lithium metal was manufactured (electrolyte: EC: DEC with 10 wt% FEC) and life test was conducted. The conditions of charging and discharging of the life test were as follows.

Charge: 0.5C, cut off: 4.2V, CC-CV

Discharge: 0.5C CC, cut off: 3V CC

The results of a general PE membrane (control group), Al ₂ O ₃ -PE membrane, and CaCO ₃ -PE membrane are shown in FIG. 3 . As a result of the life test, it was confirmed that when CaCO ₃ -PE membrane was applied, it exhibited superior lifespan characteristics compared to general PE membrane or Al ₂ O ₃ -PE membrane. When CaCO ₃ -PE membrane was applied, it was confirmed that the performance was still close to 100% even after using 80 cycles. On the other hand, after 80 cycles, when a normal PE separator was applied, only about 60% of the performance remained, and when an Al ₂ O ₃ -PE separator was applied, about 80% of the performance remained. The reason for these life characteristics results is that in the case of a PE separator, serious lithium metal dendrites are generated during the charging and discharging process, which causes electrolyte depletion quickly, whereas when a CaCO ₃ -PE separator is applied, lithium metal dendrite formation is suppressed and electrolyte is depleted. because it causes the

Claims (6)

Including a porous separator coated with CaCO ₃ on one or both sides of a porous membrane or nonwoven fabric,
A separator for lithium-based secondary batteries using lithium metal as an anode.
According to claim 1,
The thickness of the coating is characterized in that 0.01 μm to 50 μm,
A separator for a lithium-based secondary battery using lithium metal as an anode.
According to claim 1,
The porosity of the porous membrane or nonwoven fabric is characterized in that 30 to 50%,
A separator for a lithium-based secondary battery using lithium metal as an anode.
According to claim 1,
The porous membrane or nonwoven fabric is polyolefin, polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyether ether ketone, polyether sulfone, polyphenylene oxide, polyphenylene Characterized in that it contains at least one polymer selected from the group consisting of sulfide and polyethylene naphthalate,
A separator for a lithium-based secondary battery using lithium metal as an anode.
5. The method of claim 4,
The polyolefin is characterized in that it comprises at least one selected from the group consisting of polyethylene and polypropylene,
A separator for a lithium-based secondary battery using lithium metal as an anode.
anode; a negative electrode comprising lithium metal; A lithium-based secondary battery comprising a porous separator interposed between the positive electrode and the negative electrode and an electrolyte, wherein the porous separator is the separator of any one of claims 1 to 5.

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