WO2018056615A1 - Negative electrode comprising multiple protection layers and lithium secondary battery comprising same - Google Patents

Abstract

The present invention relates to a negative electrode comprising multiple protection layers and a lithium secondary battery comprising same, wherein the multiple protection layers physically inhibit lithium dendrite growth on an electrode surface, and at the same time, are capable of effectively transferring lithium ions to a lithium metal electrode and exhibit excellent ionic conductivity, and thus the protection layers themselves do not apply as resistance layers, thereby preventing the occurrence of an overvoltage when charging/discharging, and thus preventing the degradation of battery performance and enabling stability to be secured when driving the battery.

Description

Anode including multiple protective layers and Lithium secondary battery comprising same

This application claims the benefit of priority based on Korean Patent Application No. 10-2016-0120602 of September 21, 2016 and Korean Patent Application No. 10-2017-0092180 of July 20, 2017. All content disclosed in the literature is included as part of this specification.

The present invention relates to a negative electrode including a multiple protective layer and a lithium secondary battery including the same, and more particularly, to effectively inhibit the growth of dendrite (Dendrite) and has a high ion conductivity, negative electrode comprising a multi protective layer And it relates to a lithium secondary battery comprising the same.

Recently, interest in energy storage technology is increasing. As the field of application extends to the energy of mobile phones, camcorders, notebook PCs, and even electric vehicles, efforts for research and development of electrochemical devices are becoming more concrete.

The electrochemical device is the field that is receiving the most attention in this respect, and the development of secondary batteries that can be charged and discharged among them is the focus of attention, and in recent years to improve the capacity density and energy efficiency in the development of such R & D on the design of new electrodes and batteries is ongoing.

 Among the secondary batteries currently applied, lithium secondary batteries developed in the early 1990s have a higher operating voltage and a higher energy density than conventional batteries such as Ni-MH, Ni-Cd, and sulfuric acid-lead batteries that use an aqueous electrolyte solution. I am in the spotlight.

The lithium secondary battery has a structure in which an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode is stacked or wound, and the electrode assembly is embedded in a battery case and a nonaqueous electrolyte is injected into the lithium secondary battery. do. The lithium secondary battery produces electrical energy by oxidation and reduction reactions when lithium ions are inserted / desorbed from the positive electrode and the negative electrode.

In general, lithium metal, carbon, and the like are used as active materials for the negative electrode of a lithium secondary battery, and lithium oxide, transition metal oxide, metal chalcogen compound, and conductive polymer are used as the active materials for the positive electrode.

Most lithium secondary batteries using lithium metal as a negative electrode attach lithium foil on a copper current collector or use lithium metal sheet itself as an electrode. Lithium metal has attracted great attention as a high capacity cathode material due to its low potential and large capacity.

When lithium metal is used as a negative electrode, electron density nonuniformity may occur on the surface of lithium metal due to various factors when the battery is driven. The lithium dendrite in the form of twigs is formed on the surface of the electrode, so that protrusions are formed or grown on the surface of the electrode, thereby making the electrode surface very rough. These lithium dendrites, along with deterioration of the cell, cause severe damage to the separator and short circuit of the cell. As a result, there is a risk of explosion and fire of the battery due to an increase in the battery temperature.

In order to solve this problem, a research has been conducted to introduce a polymer protective layer or an inorganic solid protective layer to the lithium metal layer, increase the salt concentration of an electrolyte solution, or apply an appropriate additive. However, the effects of these studies on lithium dendrites are insignificant. Therefore, solving the problem through the shape modification of the lithium metal anode itself may be an effective alternative.

[Preceding technical literature]

[Patent Documents]

(Patent Document 1) Republic of Korea Patent Publication No. 10-1621410 "Lithium electrode and lithium secondary battery comprising the same"

(Patent Document 2) Korean Unexamined Patent Publication No. 10-2016-0052351 "A lithium metal electrode having a stable protective layer and a lithium secondary battery comprising the same"

As described above, lithium dendrites of the lithium secondary battery are precipitated on the surface of the negative electrode, thereby causing volume expansion of the cell. Accordingly, the present inventors have conducted various studies, and have found a way to solve the problem caused by the dendrite through the structural modification of the electrode and completed the present invention.

Therefore, an object of the present invention is to solve the problem of the volume expansion of the cell due to lithium dendrites through the deformation of the electrode structure, and to provide a lithium secondary battery with improved battery performance.

In order to achieve the above object,

The present invention is a lithium metal layer;

A first protective layer formed on the lithium metal layer and maintaining an interface with the lithium metal layer;

A second protective layer formed on the first protective layer and physically inhibiting growth of dendrites; And

It provides a negative electrode for a lithium secondary battery comprising a; a third protective layer formed on the second protective layer and supporting the structure of the second protective layer.

In this case, the first protective layer may have an ion conductivity of 10 ⁻⁷ S / Cm or more, and an electrolyte absorbance of 150 wt% or more.

In this case, the first protective layer may include one or more selected from the group consisting of polyvinyllidene fluoride-co-hexafluoropropylene (PVdF-HFP) polymer, polyurethane-based polymer, and polyacrylic-based polymer.

In this case, the second protective layer may have a Young's modulus of 5 GPa or more, a Li ion conductivity of 10 ⁻⁷ S / Cm or more, and an electrolyte absorption of 150 wt% or less.

At this time, the second protective layer is LiPON (Lithium Phosphorus Oxynitride), LiBON (Lithium Boron Oxynitride), zirconium oxide, β-alumina, LISICON (Lithium Super Ionic Conductor) compound, Li ₂ SP ₂ S _{5 type} compound, Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Li ₄ SiO ₄ -LiI-LiOH, Li ₂ S, Li ₂ S-SiS ₂ , Li ₂ S-GeS ₂ , Li ₂ SB ₂ S ₅ , Li ₂ S-Al ₂ S ₂ , Li ₂ O-Al ₂ O ₃ -TiO ₂ -P ₂ O ₅ (LATP), It may include at least one selected from the group consisting of CaF ₂ , AgI, RbAg ₄ I ₅ , PVdF-HFP polymer, polyurethane-based polymer, polypropylene-based polymer and polycarbonate-based polymer.

In this case, the third protective layer may have an ionic conductivity of 10 ⁻⁵ S / Cm or more and an electrolyte absorbency of 150 wt% or less.

In this case, the third protective layer may include one or more selected from the group consisting of PVdF-HFP polymer, polyurethane-based polymer and polyacrylic-based polymer.

In addition, the present invention is a lithium metal layer; And

It provides a negative electrode for a lithium secondary battery comprising a; three or more layers independently selected from the group consisting of a dendrite growth inhibitory layer, a single ion conductive layer and a polymer layer.

In this case, the dendrite growth inhibiting layer may include at least one selected from the group consisting of PVdF-HFP polymer, LiPON, LiBON, polyurethane-based polymer, polypropylene-based polymer and polycarbonate-based polymer.

In addition, the present invention provides a lithium secondary battery including the negative electrode.

The multiple protective layer according to the present invention can physically inhibit the growth of lithium dendrites on the electrode surface and at the same time can effectively transfer lithium ions to the lithium metal electrode and has excellent ion conductivity so that the protective layer itself does not act as a resistive layer. Since the overvoltage is not applied at the time of discharging, it is possible to prevent performance degradation of the battery and to ensure stability when driving the battery.

Therefore, the lithium electrode including the multiple protective layer of the present invention is preferably applicable as a negative electrode of a lithium secondary battery, which is a large-capacity energy storage device from most small electronic devices using various devices, for example, lithium metal as a negative electrode. Applicable to the back.

1 is a schematic view of an electrode for a lithium secondary battery according to an embodiment of the present invention.

Hereinafter, with reference to the accompanying drawings to be easily carried out by those skilled in the art will be described in detail. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the scope of the present invention.

The present invention is a lithium metal layer 110;

A first protective layer 120 formed on the lithium metal layer 110 to maintain an interface with the lithium metal layer 110;

A second protective layer 130 formed on the first protective layer 120 and physically inhibiting growth of dendrites; And

It is formed on the second protective layer 130 and the third protective layer 140 for supporting the structure of the second protective layer 130; provides a negative electrode 100 for a lithium secondary battery comprising a. .

1 is a view showing a negative electrode 100 for a lithium secondary battery according to an embodiment of the present invention.

Referring to FIG. 1, in the lithium secondary battery anode 100 of the present invention, the first protective layer 120, the second protective layer 130, and the third protective layer 140 are sequentially disposed on the lithium metal layer 110. Formed. Although the first protective layer 120, the second protective layer 130, and the third protective layer 140 are formed only on one surface of the lithium metal layer 110 in FIG. 2, both surfaces of the lithium metal layer 110 may be formed.

In general, when lithium metal is used as a battery negative electrode, the following problems exist. First, lithium is an alkali metal and explosively reacts with water, making it difficult to manufacture and use in a general environment. Second, when lithium is used as a negative electrode, a passivation layer is formed by reacting with electrolyte, water, impurities in a battery, lithium salt, and the like, and this layer causes a local current density difference to form dendritic lithium dendrite. In addition, the dendrite thus formed may grow and cause an internal short circuit directly between the anode and the pores of the separator, thereby causing the battery to explode. Third, lithium is a soft metal and its mechanical strength is low, so its handling is very poor for use without additional surface treatment.

Thus, in the present invention, the growth of the dendrite may be prevented by forming the first protective layer 120, the second protective layer 130, and the third protective layer 140 on the lithium metal layer 110.

According to an embodiment of the present invention, the lithium metal layer 110 may use a plate-shaped metal. The lithium metal layer 110 may be adjusted in width depending on the shape of the electrode to facilitate electrode manufacturing. The thickness of the lithium metal layer may be 1 to 50 μm.

Since the first protective layer 120, the second protective layer 130, and the third protective layer 140 are stacked on the lithium metal layer 110, smooth movement of lithium ions between the lithium metal layer 110 and the electrolyte is performed. For this purpose, ionic conductivity for lithium ions may be basically required. Therefore, it is preferable that all three protective layers have a Li ion conductivity of at least 10 ⁻⁷ S / Cm or more.

In addition, the first protective layer 120, the second protective layer 130, and the third protective layer 140 have respective roles to be described later in the triple stacked structure, and when the triple stacked structure is as described above, dendrites The effect of inhibiting the growth of and the effect of maintaining the ionic conductivity may be best.

In addition, the protective layer may require an electrolyte absorbance (uptake) of a predetermined range or more or less, the first protective layer may have an electrolyte absorbance of 150% or more, and the second protective layer and the third protective layer may be 150 It may have an electrolyte absorbency of less than or equal to%.

Here, electrolyte absorbency means how much the said protective layer can absorb electrolyte solution, and shows how much the mass after absorption increases compared with the mass before electrolyte absorption of a protective layer. The first protective layer may have an electrolyte absorbency of 150% or more to increase ion conductivity, and may physically be flexible to wrap growing lithium, thereby maintaining an interface between the lithium metal layer and the second protective layer. The second protective layer and the third protective layer has an electrolyte absorbency of 150% or less, have relatively hard physical properties, and can effectively suppress dendrite formation.

According to an embodiment of the present invention, the first protective layer 120 is formed on the lithium metal layer 110, and maintains an interface between the lithium metal layer 110 and the protective layer while the lithium ion battery is charged and discharged. It plays a role.

The first protective layer 120 has a Li ion conductivity of 10 ^-7 S / Cm or more, the electrolyte absorbance may be 150% by weight or more, preferably 150 ~ 250% by weight, PVdF-HFP polymer, poly It may include one or more selected from the group consisting of a urethane-based polymer and a polyacrylic polymer. The first protective layer 120 may be physically relatively flexible due to high electrolyte absorption and may be suitable for maintaining an interface.

The content of HFP in the PVdF-HFP may be 15% by weight or more, the shore hardness of the polyurethane-based polymer may be 80 A or less, and the crosslinking density of the polyacrylic polymer may be 10 ⁻⁴ mol / g or less. If the Shore hardness is too low, the volume of the battery may increase because the amount of the electrolyte impregnation is too high. If the crosslinking density is too high, the ion conductivity may decrease and the resistance may increase.

When the first protective layer 120 is not formed, the interface between the lithium metal layer 110 and the protective layer is not maintained in the lithium ion battery, which may cause a decrease in battery capacity due to an increase in resistance.

Therefore, the thickness of the first protective layer 120 is sufficient to apply only enough to maintain the interface, and if too thick, the thickness of the first protective layer 120 is 1 to 10 because it causes an increase in unnecessary thickness of the electrode. May be μm.

According to one embodiment of the invention, the second protective layer 130 is formed on the first protective layer 120, and serves to physically inhibit the growth of the dendrite.

Therefore, the second protective layer 130 preferably has strong physical strength and ion conductivity. The second protective layer 130 has a Young's modulus of 5 GPa or more, a Li ion conductivity of 10 ⁻⁷ S / Cm or more, and an electrolyte absorbency of 150 wt% or less, preferably 30 to 150 wt% Can be.

In addition, the second protective layer 130 is LiPON, LiBON, zirconium oxide, β-alumina, LISICON (Lithium Super Ionic Conductor) compound, Li ₂ SP ₂ S ₅ compound, Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Li ₄ SiO ₄ -LiI-LiOH, Li ₂ S, Li ₂ S-SiS ₂ , Li ₂ S-GeS ₂ , Li ₂ SB ₂ S ₅ , Li ₂ S-Al ₂ S ₂ , Li ₂ O-Al ₂ O ₃ -TiO ₂ -P ₂ O ₅ (LATP), CaF ₂ , AgI, RbAg ₄ I ₅ , PVdF-HFP may comprise one or more selected from the group consisting of polymers, polyurethane-based polymers, polypropylene-based polymers and polycarbonate-based polymers.

The content of HFP in the PVdF-HFP may be 5% by weight or less, the shore hardness of the polyurethane-based polymer may be 75D or more, and the porosity of the polypropylene-based polymer may be 5-50%. If the Shore hardness is less than or equal to the above range, it may be difficult to physically inhibit the growth of dendrites. In addition, if the porosity is too low, there may be a capacity decrease due to the increase in resistance, and if too high, it may be difficult to suppress the dendrite growth.

The Young's modulus is an elastic modulus that indicates the degree of stretching and deformation of the object when the object is stretched from both sides. The Young's modulus is also referred to as the length elastic modulus. The second protective layer 130 physically suppresses the growth of dendrites, so It is preferable to have a Young's modulus as a physical property. Methods of measuring Young's modulus are known to those skilled in the art, and one exemplary instrument used to measure Young's modulus is the Universal Testing Machine.

Since the second protective layer 130 not only suppresses the growth of the dendrite but also has conductivity, it can smoothly transfer lithium ions to the electrode, thereby increasing battery life and improving battery performance.

In addition, if the thickness of the second protective layer 130 is too thin, it may be difficult to effectively suppress the growth of the dendrite, on the contrary, if the thickness is too thick, relative capacity loss may occur due to unnecessary thickness increase, the second protective layer The thickness of the 130 may be 1 ~ 10㎛.

According to an embodiment of the present invention, the third protective layer 140 is formed on the second protective layer 130 and serves as a support for supporting the structure of the second protective layer 130. That is, the third protective layer 140 serves to physically support the second protective layer 130.

The third protective layer 140 has an ionic conductivity of 10 ^-5 S / Cm or more, the electrolyte absorption may be 150% by weight or less, preferably 10 to 150% by weight, PVdF-HFP polymer, polyurethane-based It may include one or more selected from the group consisting of a polymer and a polyacrylic polymer.

The HFP content of the PVdF-HFP may be 5 to 15% by weight, the shore hardness of the polyurethane-based polymer may be 80A to 75D, and the crosslinking density of the polyacrylic polymer may be 0.01 M / cm ^{3 or} more.

In addition, if the thickness of the third protective layer 140 is too thin, it may be difficult to support the structure of the second protective layer 130. On the contrary, if the thickness is too thick, a relative capacity loss may occur due to unnecessary thickness increase. The thickness of the third protective layer 140 may be 1 ~ 10㎛.

An electrolyte salt such as a lithium salt may be added to the polymer included in the first protective layer, the second protective layer, and the third protective layer to improve Li ion conductivity, and the lithium salt is typically used in an electrolyte for a lithium secondary battery. Those used may be used without limitation. For example is the above lithium salt anion ^{F -, Cl -, Br -} , I -, NO 3 -, N (CN) 2 -, BF 4 -, ClO 4 -, PF 6 -, (CF 3) 2 PF _{^{4 -, (CF 3) 3}} PF 3 -, (CF 3) 4 PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 - _{, (CF 3 SO 2) 2} N -, (FSO 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, ( CF ₃ SO _{2) 3} C ^- from the group consisting of ^{_{-, CF 3 (CF 2)}} 7 SO 3 -, CF 3 CO 2 -, CH 3 CO 2 -, SCN - , and _{(CF 3 CF 2 SO 2)} 2 N It may include one or more selected.

The formation method of the first protective layer 120, the second protective layer 130 and the third protective layer 140 is not particularly limited, and the PVdF-HFP polymer, polyurethane, polyacrylic and polypropylene polymer, etc. In the case, the polymer or monomer may be mixed with a solvent coating solution and then formed by employing reaction sputtering, microgravure coating, comma coating, slot die coating, spray coating, dip coating, flow coating, and the like. In addition, the solid electrolyte such as LiPON and LiBON may be used by mixing with a binder and the like in a powder state.

According to a preferred embodiment of the present invention, the negative electrode for a lithium secondary battery has a first protective layer containing PVdF-HFP of 20% by weight HFP, a second protective layer containing LiPON and 5% by weight of HFP on a lithium metal layer The third protective layer including PVdF-HFP may be manufactured by laminating, and the lithium electrode having such a structure may effectively inhibit the growth of dendrites.

The lithium secondary battery electrode according to the present invention may have various widths and lengths depending on the shape of the battery. If necessary, a lithium secondary battery electrode manufactured in various widths may be wound and cut as necessary.

In addition, the present invention is a lithium metal layer; And

It provides a negative electrode 100 for a lithium secondary battery comprising a; three or more layers independently selected from the group consisting of a dendrite growth inhibitory layer, a single ion conductive layer and a polymer layer.

The dendrites growth inhibiting layer means the second protective layer 130 and may include one or more selected from the group consisting of LiPON, LiBON, polyurethane-based polymers, polypropylene-based polymers, and polycarbonate-based polymers.

The single ion conductive layer may comprise inorganic, organic, and mixed organic-inorganic polymeric materials. As used herein, the term "single ion conducting layer" means a layer that selectively or exclusively allows passage of cations of a single load. The single ion conductive layer has the ability to selectively or exclusively transfer cations, such as lithium ions, and may include, for example, the polymers disclosed in US Pat. No. 5,731,104 to Ventura et al. In one embodiment, the single ion conductive layer may contain a single ion conductive glass that is conductive to lithium ions. Among the suitable glasses are those that may be characterized as comprising a "modifier" portion and a "network" portion known in the art. The modifier can typically be a metal oxide of a metal ion that is conductive in glass. The network former may typically be a metal chalcogenide, such as a metal oxide or sulfide.

In addition, the single ion conductive layer is lithium silicate, lithium borate, lithium aluminate, lithium phosphate, lithium phosphorus oxynitride, lithium silicosulfide, lithium germanosulphide, lithium lanthanum oxide, lithium titanium oxide, lithium boro And a glassy layer containing a glassy material comprising at least one selected from the group consisting of sulfides, lithium aluminosulfides, and lithium phosphosulfides. In one embodiment, the single ion conducting layer may contain lithium phosphorus oxynitride. Electrolyte films of lithium phosphorus oxynitride are disclosed, for example, in US Pat. No. 5,569,520 (Bates).

The polymer layer may include one or more selected from the group consisting of, but not limited to, electrically conductive polymers, ion conductive polymers, sulfonated polymers, and hydrocarbon polymers. Suitable electrically conductive polymers include, but are not limited to, poly (p-phenylene), polyacetylene, poly (phenylenevinylene), polyazulene, poly (perinaphthalene), polyacene and poly (naphthalene-2,6- Diyl), including those described in US Pat. No. 5,648,187 (Skotheim). Suitable ion conductive polymers may also include ion conductive polymers known to be useful in solid polymer electrolytes and gel polymer electrolytes for lithium electrochemical cells such as polyethylene oxide. Suitable sulfonated polymers may include sulfonated siloxane polymers, sulfonated polystyrene-ethylene-butylene polymers, and sulfonated polystyrene polymers. Suitable hydrocarbon polymers may also include ethylene-propylene polymers, polystyrene polymers, and the like.

The polymer layer is also described in US Patent Application Serial No. 09 / 399,967 (co-applicant Ying) for protective coatings on alkyl acrylate, glycol acrylate, polyglycol acrylate, polyglycol vinyl ether, polyglycol divinyl ether and separator layers. Crosslinked polymer materials formed from the polymerization of monomers, including those described in " For example, the crosslinked polymer material may be polydivinyl poly (ethylene glycol). The crosslinked polymeric material may further contain salts such as lithium salts to enhance ionic conductivity. In one embodiment, the multilayer polymer layer may include a crosslinked polymer.

However, effective dendrite growth inhibition may be difficult with each of the above layers, the dendrite growth inhibition layer physically inhibits growth, and the single ion conductive layer and the polymer layer support and inhibit the growth layer. It can have a beneficial effect on suppression. Therefore, when the respective layers are stacked in combination, the effect of inhibiting dendrite growth may be improved.

In another aspect, the present invention provides a lithium secondary battery comprising the negative electrode (100).

Lithium secondary battery according to the present invention can be manufactured through a known technique carried out by those skilled in the art for the remaining configuration except for the structure and characteristics of the above-described negative electrode 100, will be described in detail below.

Common lithium secondary battery is a negative electrode; anode; Separation membrane interposed between them; And an electrolyte; and the negative electrode of the lithium secondary battery of the present invention may include a negative electrode including the multiple protective layer of the present invention.

The positive electrode may be manufactured in the form of a positive electrode by forming a composition including a positive electrode active material, a conductive material, and a binder on a positive electrode current collector.

The positive electrode active material is LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li (Ni _a Co _b Mn _c ) O ₂ (0 <a <1, 0 <b <1, 0 <c <1, a + b + c = 1), LiNi _{1 - y} CoyO ₂ , LiCo _{1 - y} MnyO ₂ , LiNi _{1 - y} MnyO ₂ (O ≦ y <1), Li (Ni _a Co _b Mn _c ) O ₄ (0 <a <2, 0 <b <2 , 0 <c <2, a + b + c = 2), LiMn 2 - z NizO 4, LiMn 2 - z CozO 4 (0 <z <2), LiCoPO 4 and LiFePO ₄ Any one selected from the group consisting of or a mixture of two or more thereof can be used. In addition to these oxides, sulfides, selenides, and halides may also be used. In a more preferred example, the positive electrode active material may be LiCoO ₂ suitable for a high power battery.

The conductive material is a component for further improving the conductivity of the positive electrode active material. Examples of the conductive material include graphite such as natural graphite and artificial graphite; Carbon blacks such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder and nickel powder; Conductive whiskers such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The binder maintains a positive electrode active material in a positive electrode current collector and has a function of organically connecting the positive electrode active materials. For example, polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), and carboxymethyl cellulose ( CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber, fluorine Rubber, these various copolymers, etc. are mentioned.

The positive electrode current collector is the same as described above in the negative electrode current collector, and generally, a thin aluminum plate may be used for the positive electrode current collector.

The positive electrode composition may be coated on a positive electrode current collector using a conventional method known in the art, and for example, a dipping method, a spray method, a roll court method, and a gravure printing method. Various methods may be used, such as a bar court method, a die coating method, a comma coating method, or a mixture thereof.

The positive electrode and the positive electrode composition which have undergone such a coating process are then dried through evaporation of a solvent or a dispersion medium, compactness of the coating film and adhesion between the coating film and the current collector. At this time, the drying is carried out according to a conventional method, which is not particularly limited.

The separator is not particularly limited in material, and physically separates the positive electrode and the negative electrode, and has electrolyte and ion permeability, and can be used without particular limitation as long as they are commonly used as separators in electrochemical devices, but are porous and visionary. As the conductive or insulating material, it is particularly desirable to have low resistance to ion migration of the electrolyte solution and excellent electrolyte electrolyte moisture content. For example, a polyolefin-based porous membrane or a nonwoven fabric may be used, but is not particularly limited thereto.

Examples of the polyolefin-based porous membrane, polyolefin-based polymers such as polyethylene, polypropylene, polybutylene, polypentene, such as high density polyethylene, linear low density polyethylene, low density polyethylene, ultra high molecular weight polyethylene, respectively, or a mixture thereof There is a curtain.

The nonwoven fabric is, for example, polyphenyleneoxide, polyimide, polyamide, polycarbonate, polyethyleneterephthalate, polyethylenenaphthalate in addition to the aforementioned polyolefin-based nonwoven fabric. , Polybutyleneterephthalate, polyphenylenesulfide, polyacetal, polyethersulfone, polyetheretherketone, polyester, etc., alone or in combination A nonwoven fabric formed of a polymer mixed therewith is possible, and the nonwoven fabric is a fiber form forming a porous web, and includes a spunbond or meltblown form composed of long fibers.

The thickness of the separator is not particularly limited, but is preferably in the range of 1 to 100 μm, more preferably in the range of 5 to 50 μm. When the thickness of the separator is less than 1 μm, mechanical properties may not be maintained. When the separator is more than 100 μm, the separator may act as a resistance layer, thereby degrading battery performance.

Pore size and porosity of the separator is not particularly limited, but the pore size is 0.1 to 50 ㎛, porosity is preferably 10 to 95%. If the pore size of the separator is less than 0.1 ㎛ or porosity is less than 10%, the separator acts as a resistive layer, mechanical properties cannot be maintained when the pore size exceeds 50 ㎛ or porosity exceeds 95% .

The electrolyte may be a nonaqueous electrolyte or a solid electrolyte which does not react with lithium metal, but is preferably a nonaqueous electrolyte and includes an electrolyte salt and an organic solvent.

The electrolyte salt contained in the nonaqueous electrolyte is a lithium salt. The lithium salt may be used without limitation those conventionally used in the lithium secondary battery electrolyte. For example is the above lithium salt anion ^{F -, Cl -, Br -} , I -, NO 3 -, N (CN) 2 -, BF 4 -, ClO 4 -, PF 6 -, (CF 3) 2 PF _{^{4 -, (CF 3) 3}} PF 3 -, (CF 3) 4 PF 2 -, (CF 3) 5 PF -, (CF 3) 6 P -, CF 3 SO 3 -, CF 3 CF 2 SO 3 - _{, (CF 3 SO 2) 2} N -, (FSO 2) 2 N -, CF 3 CF 2 (CF 3) 2 CO -, (CF 3 SO 2) 2 CH -, (SF 5) 3 C -, ( CF ₃ SO _{2) 3} C ^- from the group consisting of ^{_{-, CF 3 (CF 2)}} 7 SO 3 -, CF 3 CO 2 -, CH 3 CO 2 -, SCN - , and _{(CF 3 CF 2 SO 2)} 2 N Any one selected or two or more thereof may be included.

As the organic solvent included in the non-aqueous electrolyte, those conventionally used in a lithium secondary battery electrolyte may be used without limitation, and for example, ethers, esters, amides, linear carbonates, cyclic carbonates, etc. may be used alone or in combination of two or more. Can be used. Among them, carbonate compounds which are typically cyclic carbonates, linear carbonates, or mixtures thereof may be included.

Specific examples of the cyclic carbonate compound include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate and any one selected from the group consisting of halides thereof or mixtures of two or more thereof. These halides include, for example, fluoroethylene carbonate (FEC), but are not limited thereto.

In addition, specific examples of the linear carbonate compound may be any one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethylmethyl carbonate (EMC), methylpropyl carbonate and ethylpropyl carbonate. Mixtures of two or more of them may be representatively used, but are not limited thereto.

In particular, ethylene carbonate and propylene carbonate, which are cyclic carbonates among the carbonate-based organic solvents, have high dielectric constants and may dissociate lithium salts in the electrolyte more efficiently. By using a low viscosity, low dielectric constant linear carbonate mixed in an appropriate ratio it can be made an electrolyte having a higher electrical conductivity.

In addition, as the ether in the organic solvent, any one selected from the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methylethyl ether, methylpropyl ether, and ethylpropyl ether, or a mixture of two or more thereof may be used. It is not limited to this.

And esters in the organic solvent include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ Any one or a mixture of two or more selected from the group consisting of -valerolactone and ε-caprolactone may be used, but is not limited thereto.

The injection of the nonaqueous electrolyte may be performed at an appropriate step in the manufacturing process of the electrochemical device, depending on the manufacturing process and the required physical properties of the final product. That is, it may be applied before the electrochemical device assembly or the final step of the electrochemical device assembly.

The lithium secondary battery according to the present invention may be a lamination (stacking) and folding (folding) process of the separator and the electrode in addition to the winding (winding) which is a general process. In addition, the case of the battery may be cylindrical, square, pouch type or coin type.

As described above, since the lithium secondary battery including the negative electrode according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, portable devices such as mobile phones, notebook computers, digital cameras, and hybrid electric vehicles (hybrid) It is useful for electric vehicle fields such as electric vehicle (HEV).

[Description of the code]

100: negative electrode for lithium secondary battery

110: lithium metal layer

120: first protective layer

130: second protective layer

140: third protective layer

Hereinafter, preferred examples and experimental examples are presented to help understand the present invention. However, the following Examples and Experimental Examples are only for better understanding of the present invention, and the present invention is not limited to the following Examples and Experimental Examples.

<Example 1> Preparation of a lithium secondary battery comprising a negative electrode coated with a multilayer protective layer

Formation of a first protective layer containing 20 wt% PVdF-HFP, a second protective layer comprising LiPON, and a third protective layer comprising 5 wt% PVdF-HFP of HFP on a lithium metal plate anode having a thickness of 20 μm. It was.

The first protective layer was prepared by adding 20% by weight of PVdF-HFP to HFP in a solvent NMP to prepare a 20% by weight solution, followed by slot die coating on the lithium metal plate, and drying at 120 ° C. for 30 minutes to form a thickness of 2 μm.

The second protective layer was formed on the first protective layer by sputtering a solution containing LiPON to a thickness of 1 μm.

The third protective layer was prepared by adding 5 wt% PVdF-HFP of HFP to the solvent NMP to prepare a 10 wt% solution, and then drying at 120 ° C. for 30 minutes after slot die coating on the second protective layer to form a thickness of 2 μm. It was.

In addition, a cathode was prepared using LCO (LiCoO ₂ ) as the cathode active material. N-methylpyrrolidone (NMP) as a solvent, LCO: Super-P: PVDF = 95: 2.5: 2.5 by mixing in a weight ratio to prepare a slurry and coated on a 12μm thick aluminum foil 70μm thick A positive electrode was prepared.

A polyethylene having a thickness of 20 μm was interposed between the positive electrode and the negative electrode as a separator, followed by ethylene carbonate (EC): diethyl carbonate (DEC): dimethyl carbonate (DMC) = 1: 2: 1 (v / v) in a lithium salt. LiPF ₆ 1.0M, an electrolyte solution containing 2% by weight of vinylene carbonate (VC) as an additive was injected to prepare a lithium secondary battery.

<Example 2> Preparation of a lithium secondary battery comprising a negative electrode coated with a multilayer protective layer

On the lithium metal plate negative electrode having a thickness of 20 μm, a first protective layer containing polyurethane, a second protective layer containing LiPON, and a third protective layer containing 5 wt% of PVdF-HFP were formed.

The first protective layer was prepared by adding polyurethane (Shore hardness 80A) to the solvent NMP to prepare a 20% by weight solution, and then coating the die-die on the lithium metal plate and drying at 120 ° C. for 30 minutes to form a thickness of 2 μm.

The second protective layer was formed on the first protective layer by sputtering a solution containing LiPON to a thickness of 1 μm.

The third protective layer was prepared by adding 5 wt% PVdF-HFP of HFP to the solvent NMP to prepare a 10 wt% solution, and then drying at 120 ° C. for 30 minutes after slot die coating on the second protective layer to form a thickness of 2 μm. It was.

In addition, a cathode was prepared using LCO (LiCoO ₂ ) as the cathode active material. N-methylpyrrolidone (NMP) as a solvent, LCO: Super-P: PVDF = 95: 2.5: 2.5 by mixing in a weight ratio to prepare a slurry and coated on a 12μm thick aluminum foil 70μm thick A positive electrode was prepared.

A polyethylene having a thickness of 20 μm was interposed between the positive electrode and the negative electrode as a separator, followed by ethylene carbonate (EC): diethyl carbonate (DEC): dimethyl carbonate (DMC) = 1: 2: 1 (v / v) in a lithium salt. LiPF ₆ 1.0M, an electrolyte solution containing 2% by weight of vinylene carbonate (VC) as an additive was injected to prepare a lithium secondary battery.

<Example 3> Preparation of a lithium secondary battery comprising a negative electrode coated with a multilayer protective layer

On the lithium metal plate anode having a thickness of 20 μm, a first protective layer containing 20 wt% of PVdF-HFP, a second protective layer containing LiBON, and a third protective layer including 5 wt% of PVdF-HFP were formed. It was.

The first protective layer was prepared by adding 20% by weight of PVdF-HFP to HFP in a solvent NMP to prepare a 20% by weight solution, followed by slot die coating on the lithium metal plate, and drying at 120 ° C. for 30 minutes to form a thickness of 2 μm.

The second protective layer was formed on the first protective layer by sputtering a solution containing LiBON to a thickness of 1 μm.

The third protective layer was prepared by adding 5 wt% PVdF-HFP of HFP to the solvent NMP to prepare a 10 wt% solution, and then drying at 120 ° C. for 30 minutes after slot die coating on the second protective layer to form a thickness of 2 μm. It was.

In addition, a cathode was prepared using LCO (LiCoO ₂ ) as the cathode active material. N-methylpyrrolidone (NMP) as a solvent, LCO: Super-P: PVDF = 95: 2.5: 2.5 by mixing in a weight ratio to prepare a slurry and coated on a 12μm thick aluminum foil 70μm thick A positive electrode was prepared.

A polyethylene having a thickness of 20 μm was interposed between the positive electrode and the negative electrode as a separator, followed by ethylene carbonate (EC): diethyl carbonate (DEC): dimethyl carbonate (DMC) = 1: 2: 1 (v / v) in a lithium salt. LiPF ₆ 1.0M, an electrolyte solution containing 2% by weight of vinylene carbonate (VC) as an additive was injected to prepare a lithium secondary battery.

<Example 4> Preparation of a lithium secondary battery comprising a negative electrode coated with a multilayer protective layer

On the lithium metal plate negative electrode having a thickness of 20 μm, a first protective layer containing 20 wt% PVdF-HFP, a second protective layer including LiPON, and a third protective layer including polyurethane were formed.

The first protective layer was prepared by adding 20% by weight of PVdF-HFP to HFP in a solvent NMP to prepare a 20% by weight solution, followed by slot die coating on the lithium metal plate, and drying at 120 ° C. for 30 minutes to form a thickness of 2 μm.

The second protective layer was formed on the first protective layer by sputtering a solution containing LiPON to a thickness of 1 μm.

The third protective layer was prepared by adding polyurethane (Shore hardness 75D) to the solvent NMP to prepare a solution of 20% by weight, and after drying the slot die coating on the second protective layer for 30 minutes at 120 ℃ to form a thickness of 2㎛ .

In addition, a cathode was prepared using LCO (LiCoO ₂ ) as the cathode active material. N-methylpyrrolidone (NMP) as a solvent, LCO: Super-P: PVDF = 95: 2.5: 2.5 by mixing in a weight ratio to prepare a slurry and coated on a 12μm thick aluminum foil 70μm thick A positive electrode was prepared.

A polyethylene having a thickness of 20 μm was interposed between the positive electrode and the negative electrode as a separator, followed by ethylene carbonate (EC): diethyl carbonate (DEC): dimethyl carbonate (DMC) = 1: 2: 1 (v / v) in a lithium salt. LiPF ₆ 1.0M, an electrolyte solution containing 2% by weight of vinylene carbonate (VC) as an additive was injected to prepare a lithium secondary battery.

Comparative Example 1 Fabrication of Li-Ion Battery Except Multilayer Protective Layer

The same procedure as in Example 1 was performed except that the first protective layer, the second protective layer, and the third protective layer were not manufactured and coated in Example 1.

Comparative Example 2 Manufacture of Li-Ion Battery Excluding the First Protective Layer

Except that the first protective layer was not prepared and coated in Example 1 was prepared in the same manner as in Example 1.

Comparative Example 3 Fabrication of Li-Ion Battery Except for Second Protective Layer

Except that the second protective layer was not prepared and coated in Example 1 was prepared in the same manner as in Example 1.

Comparative Example 4 Fabrication of Li-Ion Battery Excluding Third Protective Layer

Except that the third protective layer was not prepared and coated in Example 1 was prepared in the same manner as in Example 1.

Experimental Example Battery Performance Evaluation

Performance evaluation was performed for each battery prepared in Examples 1 to 4 and Comparative Examples. At this time, the charging and discharging conditions are as follows.

Charge rate 0.2C, voltage 4.25V, CC / CV (5% current cut at 1C)

Discharge: Rate 0.5C, Voltage 3V, CC

The number of cycles when the discharge capacity reached 80% compared to the initial capacity of the battery while repeating the cycle under the above conditions was measured, the results are shown in Table 1 below.

Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 80% discharge capacity cycles 198 181 195 196 75 76 105 153

As shown in Table 1, in Examples 1 to 4 to which all of the first to third protective layers were applied, lithium dendrite growth was suppressed and the number of cycles reaching 80% of the discharge capacity was significantly increased compared to Comparative Examples 1 to 4. It can be seen that.

In Comparative Example 2 without forming the first protective layer, the cell performance was not improved due to poor interface formation, and in Comparative Example 3 without forming the second protective layer, the dendrite growth was suppressed due to insufficient strength. Power fell. In Comparative Example 4, in which the third protective layer was not formed, the second protective layer was destroyed during the cycle and the performance of the battery was degraded because the pressure caused by the volume change due to the suppression of the dendrite growth of the second protective layer was not relieved. In Comparative Example 1, since the protective layer of the present invention was not formed, the cycle number reaching the discharge capacity of 80% was the smallest. That is, the battery of Example 1 of the present invention showed the best battery performance.

Claims (10)

Lithium metal layer; A first protective layer formed on the lithium metal layer and maintaining an interface with the lithium metal layer; A second protective layer formed on the first protective layer and physically inhibiting growth of dendrites; And And a third protective layer formed on the second protective layer and supporting the structure of the second protective layer. The method of claim 1, The first protective layer has a ionic conductivity of 10 ^-7 S / Cm or more, the electrolyte absorbance is 150% by weight or more, the negative electrode for a lithium secondary battery. The method of claim 1, The first protective layer is a lithium secondary battery negative electrode, characterized in that it comprises at least one selected from the group consisting of PVdF-HFP polymer, polyurethane-based polymer and polyacrylic-based polymer. The method of claim 1, The second protective layer has a Young's modulus of 5 GPa or more, a Li ion conductivity of 10 ⁻⁷ S / Cm or more, and an electrolyte absorbency of 150 wt% or less, characterized in that the lithium secondary battery negative electrode. The method of claim 1, The second protective layer is LiPON, LiBON, zirconium oxide, β-alumina, LISICON compound, Li ₂ SP ₂ S ₅ compound, Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Li ₄ SiO ₄ -LiI-LiOH, Li ₂ S, Li ₂ S-SiS ₂ , Li ₂ S-GeS ₂ , Li ₂ SB ₂ S ₅ , Li ₂ S-Al ₂ S ₂ , Li ₂ O-Al ₂ O ₃ -TiO ₂ -P ₂ O ₅ , CaF ₂ , AgI, RbAg ₄ I ₅ , PVdF-HFP polymer, polyurethane polymer, polypropylene A negative electrode for a lithium secondary battery, characterized in that it comprises at least one selected from the group consisting of a polymer and a polycarbonate-based polymer. The method of claim 1, The third protective layer has a ionic conductivity of 10 ^-5 S / Cm or more, the electrolyte absorbance is 150% by weight or less, characterized in that the lithium secondary battery negative electrode. The method of claim 1, The third protective layer is a lithium secondary battery negative electrode, characterized in that it comprises at least one selected from the group consisting of PVdF-HFP polymer, polyurethane-based polymer and polyacrylic-based polymer. Lithium metal layer; And At least three layers independently selected from the group consisting of a dendrite growth inhibitory layer, a single ion conductive layer and a polymer layer; a negative electrode for a lithium secondary battery comprising a. The method of claim 8, The dendrite growth inhibiting layer is a lithium secondary battery negative electrode comprising at least one selected from the group consisting of PVdF-HFP polymer, LiPON, LiBON, polyurethane-based polymer, polypropylene-based polymer and polycarbonate-based polymer. A lithium secondary battery comprising the negative electrode of any one of claims 1 to 9.

Images