KR20170071236A - Solid electrolyte with ionic conducting coating layer, and lithium secondary battery comprising thereof - Google Patents

Abstract

The present invention relates to a solid electrolyte having an ion conductive coating layer and a lithium secondary battery comprising the same. More particularly, the present invention relates to a solid electrolyte having an ion conductive coating layer formed on at least one surface of a lithium ion conductor, The present invention relates to a secondary battery.
The lithium secondary battery suppresses the side reaction between the solid electrolyte and the electrode interface, and accordingly, the rate of increase of the initial resistance in the battery is reduced, so that the lithium secondary battery can maintain a stable internal resistance and thus can be used as an energy storage material in various fields.

Description

TECHNICAL FIELD The present invention relates to a solid electrolyte having an ion conductive coating layer and a lithium secondary battery comprising the ion conductive coating layer,

The present invention relates to a solid electrolyte having an ion conductive coating layer and a lithium secondary battery comprising the solid electrolyte. More particularly, the present invention relates to a solid electrolyte and a lithium secondary battery including the ion conductive coating layer, And more particularly, to a lithium secondary battery which can exhibit a lithium secondary battery.

Recently, interest in energy storage technology is increasing. As the application fields of cell phones, camcorders, notebook PCs and even electric vehicles are expanding, efforts for research and development of electrochemical devices are becoming more and more specified. Among various electrochemical devices, a lithium secondary battery capable of charging and discharging, having a high operating voltage, and having a much higher energy density is in the spotlight.

The lithium secondary battery is manufactured by using a material capable of intercalating and deintercalating lithium ions as active materials for the positive and negative electrodes and a porous separator between the positive and negative electrodes and injecting a liquid electrolyte. Electricity is generated or consumed by the redox reaction resulting from insertion and desorption of lithium ions. Such a lithium secondary battery should basically be stable in the operating voltage range of the battery, and have a capability of transferring ions at a sufficiently high speed.

The performance of such a lithium secondary battery may vary depending on the configuration of the battery. Particularly, the characteristics of the electrolyte which causes the electrode reaction in contact with the anode or the cathode has a direct influence on the performance of the battery.

For example, a lithium secondary battery using a liquid electrolyte such as a non-aqueous electrolytic solution is advantageous in large discharge capacity and energy density. However, decomposition starts at a voltage of 2.5 V or more, and there is a high risk of electrolyte leakage, fire and explosion, and may cause self-discharge and overheating of the lithium secondary battery. Accordingly, a method of using a solid electrolyte which is safe and reliable by replacing the liquid electrolyte has been proposed.

Since the lithium ion conductor constituting the solid electrolyte is a single ion conductor in which only Li ions migrate, there is no danger of ignition as compared with the case of using a liquid electrolyte. Therefore, the solid electrolyte is suitable for a lithium battery for an electric vehicle, a large-sized battery, and the like. However, the solid electrolyte has a lower ionic conductivity than the liquid electrolyte, has a high interface contact resistance, and generates hydrogen sulfide by reaction with water.

Generally, the solid electrolyte is divided into a ceramic-based solid electrolyte and a polymer-based solid electrolyte, and the ceramic-based solid electrolyte is again divided into a sulfide-based solid electrolyte and an oxide-based solid electrolyte. Examples of the oxide-based solid electrolyte include solid electrolytes such as lithium-aluminum-titanium-phosphate (LATP) and lithium-aluminum-germanium-phosphate (LAGP) oxides having a Natrium Super Ionic Conductor Are mainly used. These solid electrolytes have high ion conductivity and are stable to moisture in the air, but have a problem in that the resistance increases due to the interface side reaction when they are in contact with the lithium metal electrode.

In order to suppress such side reactions, a method of introducing an ion conductive polymer film between a cathode and a solid electrolyte has been proposed. However, it is difficult to control the thickness of the ion conductive polymer film. As a result, the ion conductive polymer film is applied as a thick polymer film having a thickness of about 10 탆 or more.

Therefore, it was necessary to develop a new technology to overcome these limitations.

A laminate including an active material layer and a solid electrolyte layer, and a pre-solid lithium secondary battery using the same (Korea Patent No. 1150069) An electrolyte for a lithium ion secondary battery and a lithium ion secondary battery comprising the electrolyte (Korean Patent No. 1422908)

In order to solve the problems of the prior art, the inventors of the present invention conducted various studies and found that when an ion conductive coating layer containing polypodamine and a lithium salt is formed on the surface of the lithium ion conductor layer constituting the solid electrolyte, It has been confirmed that the interface between the electrolyte and the electrode is stabilized and the initial resistance inside the cell including the solid electrolyte can be kept constant, thereby completing the present invention.

Accordingly, an object of the present invention is to stabilize the interface between the solid electrolyte and the electrode, and to keep the initial resistance in the battery constant.

In order to achieve the above object,

There is provided a solid electrolyte in which an ion conductive coating layer is formed on at least one surface of a lithium ion conductor layer, the ion conductive coating layer comprising polypodamine and a lithium salt.

At this time, the ion conductive coating layer may further include an ion conductive polymer.

In addition,

1. A lithium secondary battery comprising a positive electrode, a negative electrode and a solid electrolyte interposed therebetween,

And the solid electrolyte is the solid electrolyte described above.

In the lithium secondary battery including the solid electrolyte of the present invention, since the side reaction between the solid electrolyte and the electrode interface is suppressed and the increase rate of the initial resistance in the battery is reduced, the stable internal resistance is maintained.

1 is a cross-sectional image of a solid electrolyte according to Example 1 of the present invention observed by a scanning electron microscope (SEM).
2 is a cross-sectional image of a solid electrolyte according to Example 2 of the present invention observed by a scanning electron microscope (SEM).
3 is a cross-sectional image of a solid electrolyte according to Comparative Example 1 of the present invention observed by a scanning electron microscope (SEM).
FIG. 4 is a graph showing an initial resistance increase pattern over time of a lithium secondary battery including a solid electrolyte according to an embodiment of the present invention and Comparative Example 1. FIG.
5 is a graph showing an initial resistance increase rate of a lithium secondary battery including a solid electrolyte according to an embodiment of the present invention and Comparative Example 1 over time.

The present invention provides a solid electrolyte in which an ion conductive coating layer is formed on at least one surface of a lithium ion conductor layer, comprising a polydodamine and a lithium salt.

The ion conductive coating layer may further include an ion conductive polymer.

The present invention also provides a lithium secondary battery comprising a positive electrode, a negative electrode, and a solid electrolyte interposed therebetween,

And the solid electrolyte is the solid electrolyte described above.

The lithium secondary battery including the solid electrolyte according to the present invention can suppress the interfacial side reaction between the solid electrolyte and the electrode and significantly reduce the initial resistance increase rate and maintain the stable internal resistance.

Hereinafter, the present invention will be described in more detail. It is to be understood, however, that the scope of the present invention is not limited thereto and that the present invention covers all of the equivalent scope of the following description.

The lithium ion conductor layer constituting the solid electrolyte suggested in the present invention has a problem that the interface resistance increases due to the interface reaction when the lithium ion conductor contacts the lithium metal of the anode and / or the cathode, that is, the reduction reaction of Ti and Ge by lithium ion Surface treatment or coating. Specifically, the lithium ion conductor layer of the present invention may include an ion conductive coating layer including at least one surface of which includes polydodamine and lithium salt, and the ion conductive coating layer may further include an ion conductive polymer.

When the lithium salt and the ion conductive polymer are dissolved and dissolved in a common solvent, the lithium salt is not coated well, and the ion conductive polymer forms an excessively thick coating film, and the initial resistance due to the coating film is increased. It is possible to form an ion conductive coating layer with an appropriate thickness and effectively maintain the stability of the interface on the contact surface with the lithium metal.

Specifically, the lithium ion conductor layer proposed in the present invention is not particularly limited as long as it has lithium ion conductivity. That is, all known lithium ion conductors used in the field of lithium batteries can be used and commercially available ones can be purchased and used. For example, the lithium ion conductor layer may be composed of any one or a mixture of two or more of oxide, phosphate, nitride, and sulfide-based lithium ion conductors.

Preferably _{Li 1/8 La 5/8} TiO 3 Li 3x La 2 / 3x TiO 3 ((x = 0.1 Li +) perop Sky de structure of lithium, such as in-lanthanum-titanium-oxide (lithium lanthanum titanate, LLTO) system (for _{example, Li 1/8 La 5/8 TiO} 3 , _{etc.); Li 7 La 3 Zr 2} O 12 Li-like-lanthanum-zirconium-oxide (lithium lanthanum zirconium oxide, LLZO) system; Li ₄ LISICON-based, such as _{Zn (GeO 4) 4; Li} 1.3 Al 0.3 Ti 1.7 (PO 4) 3 Li 1 + x Al x Ti 2 -x , such as (PO ₄₎ of lithium _{3 (0 <x <1)} - aluminum Lithium-aluminum-germanium-phosphates (LAGP) such as Li _{1 + x} Al _x Ge _{2 -x} (PO ₄ ) ₃ (0 <x <1); lithium phosphorous oxynitride ); And sulfide compounds such as Li ₂ SP ₂ S _5, and the like.

Of these materials, NASICON type Li _{1 + x} Al _x M _{2 - x} (PO ₄ ) ₃ (where M is Ti or Ge and 0 <x <1) may be used.

Because NASICON type lithium ion conductor layer is stable to oxygen and moisture in the atmosphere, it reacts with moisture in the atmosphere to generate H ₂ S toxic gas and decomposes. Therefore, it must be manufactured in dry room condition There is a process advantage over the sulfide-based ion conductor layer that has limitations.

The lithium ion conductor layer constituting the solid electrolyte may have a pellet-shaped or sintered body, or a film form. It may preferably be of the pellet type, in which case it may have a high porosity. Specifically, it may have a porosity of 0.01 vol% or more, more specifically 0.01 to 20 vol%.

The powder particles constituting the lithium ion conductor layer may have an average particle diameter (D ₅₀ ) of 0.1 to 5 μm.

If the average particle diameter (D ₅₀ ) of the powder particles constituting the lithium ion conductor layer is less than 0.1 탆, there is a fear of aggregation among the particles. If the average particle diameter exceeds 5 탆, the lithium ion conductivity may be lowered due to the reduction of the specific surface area . At this time, the average particle size of the particles constituting the lithium ion conductor layer can be measured by laser diffraction scattering method. However, the present invention is not limited thereto. The lithium ion conductor layer may be made of a powder of glass ceramics as described above, but it may be manufactured in a bulk form.

Meanwhile, the solid electrolyte may further include a binder polymer between the lithium ion conductor layer having an ion conductive coating layer or a binder polymer for improving adhesion between the solid electrolyte and the electrode. The binder polymer can be used without any particular limitation as long as it is electrochemically stable. More specifically, the binder polymer may be at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-cotylchlorethylene, polymethyl methacrylate, methacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, polyethylene-co-vinyl acetate, polyethylene oxide, cellulose acetate cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose (also referred to as &quot; cyanoethylcellulose, cyanoethylcellulose, Acrylonitrile-styrene-butadiene copolymer or polyimide, and the like, and any of them may be used. One or a mixture of two or more may be used.

When the lithium secondary battery is a pre-solid battery that does not contain an electrolyte, the ion conductive polymer may replace the electrolyte solution and the binder. As the ion conductive polymer, polyethylene oxide (PEO), polypropylene oxide (PPO), polysiloxane or the like can be used.

The binder polymer may be contained in an amount of 1 to 30 parts by weight, more specifically 2 to 20 parts by weight based on 100 parts by weight of the lithium ion conductor layer having the ion conductive coating layer of the present invention. When the content of the binder polymer satisfies the above range, desorption of the lithium ion conductor layer can be suitably prevented, and an increase in internal resistance of the electrochemical device can be prevented.

Particularly, the solid electrolyte according to the present invention includes polydodamine in the ion conductive coating layer formed on the ion conductor layer. The above-mentioned polydopamine has an advantage of being able to control the thickness of a thin film formed depending on the concentration of the initial dopamine and the coating time, and to attract other substances present in the solution when they are coated on the surface of a substance, There is a feature to be coated (co-coating property). Therefore, in the present invention, polydopamine is used together with a lithium salt and an ion conductive polymer to control the coating property and the thickness of the ion conductive coating layer. Of course, the physical properties of polydopamine itself also serve to reduce the rate of resistance change.

Polydodamine is a polymer produced by the polymerization of DOPA (3,4-dihydroxy-phenylalanine) or its derivatives.

[Chemical Formula 1]

Specifically, DOPA (ii) or a derivative thereof forms a coating layer containing polypodamine (i) on one side of the lithium ion conductor layer through self-polymerization as shown in Reaction Scheme 1 below.

[Reaction Scheme 1]

 However, in the present invention, the polydopamine may include not only polymers of DOPA and derivatives thereof but also polydopamine which conforms to the required properties by modifying functional groups of the polydodamine to the extent that the object of the present invention is not impaired. The derivative of DOPA is a derivative in which at least one of the hydrogen atoms in DOPA is substituted with a thiol group, a primary amino group, a secondary amino group, a nitrile group, an aldehyde group, An imidazole group, an azide group, a halide group, a polyhexamethylene dithiocarbonate group, a hydroxyl group, a carboxyl group, a carboxylic ester group, Carboxamide, carboxamide, and the like.

The ion conductive coating layer formed on the lithium ion conductor layer of the present invention includes a lithium salt.

To the lithium salt is preferably LiTFSI, LiCl, LiBr, LiI, LiClO 4, LiBF 4, LiB 10 Cl 10, LiPF 6, LiAsF 6, LiSbF 6, LiAlCl 4, LiSCN, 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 F ₉ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ , (CF ₃ SO ₂ ) Chloroborane lithium, lower aliphatic carboxylic acid lithium, 4-phenylborate lithium imide, and combinations thereof. And more preferably lithium bis-trifluoromethanesulfonimide (LiTFSI).

The lithium salt is contained in an amount of 0.01 to 25% by weight, preferably 0.01 to 5% by weight, based on the total weight of the ion conductive coating layer. When the lithium salt in the ion conductive coating layer is contained in an amount less than the above range, the effects of securing the interfacial stability and reducing the internal resistance of the present invention are insignificant. When the lithium salt is contained in an amount exceeding the above range, The coating ability on the lithium ion conductor layer is weakened and it is difficult for the ion conductive coating layer to be formed properly.

In addition, the ion conductive polymer layer formed on at least one surface of the lithium ion conductor layer of the present invention may further include an ion conductive polymer.

The ion conductive polymer is preferably selected from the group consisting of a polyethylene derivative, a polyethylene oxide derivative, a polypropylene oxide derivative, a phosphate ester polymer, an agitation lysine, a polyester sulfide, a polyvinyl alcohol, a polyvinylidene fluoride, A polymer containing a group, and a combination thereof. More preferably, it may be polyethylene glycol (PEG).

The ion conductive polymer is contained in an amount of 1 to 50% by weight, and preferably 1 to 10% by weight based on the total weight of the ion conductive coating layer. When the ion conductive polymer in the ion conductive coating layer is contained in an amount less than the above range, the effect of securing the interfacial stability and reducing the internal resistance of the present invention is insignificant. When the ion conductive polymer is contained in an amount exceeding the above range, the amount of the ion conductive polymer The ion conductive coating layer is excessively thick, and in this case, there arises a problem that the ion conductive coating layer itself acts as a single resistor.

As described above, since the ion conductive coating layer formed on the lithium ion conductor layer of the present invention can be formed on at least one surface of the lithium ion conductor layer, the ion conductive coating layer can be formed on only one side of the lithium ion conductor layer, Or may be formed on both sides to contact both the positive electrode and the negative electrode.

The ion conductive coating layer formed on either side may independently cover all of one surface of the lithium ion conductor layer or cover a part of one surface of the lithium ion conductor layer. When the ion conductive coating layer covers the entire surface of one side of the lithium ion conductor layer, the side reaction due to the contact between the solid electrolyte and the cathode or anode of the lithium metal can be more effectively blocked as compared with the case where the ion conductive coating layer covers only a part. When the ion conductive coating layer partially covers one side of the lithium ion conductor layer, lithium ions can more easily move through the non-coated portion, thereby reducing the interfacial resistance. Accordingly, it is desirable to form the ion conductive coating layer in an appropriate form in consideration of the kind and specific characteristics of the lithium ion conductor layer.

The thickness of the formed ion conductive coating layer is preferably 1 to 200 nm, more preferably 10 to 100 nm. The thickness of the ionically conductive coating layer is appropriately controlled by adjusting the initial reactant concentration and the coating time. Within the above-mentioned preferable thickness range, an excessive increase in internal resistance of the lithium secondary battery can be suppressed and the adhesion force between the solid electrolyte and the electrode can be appropriately maintained. If the thickness of the ion conductive coating layer is less than the preferable thickness range, the effect of suppressing the side reaction with the electrolyte and reducing the interface resistance is insufficient. If the thickness is too large, the ion conductive coating layer itself acts as a resistance, There is a concern.

The solid electrolyte of the present invention including the lithium ion conductor and the ion conductive coating layer described above can be produced according to a conventional solid electrolyte production method except that a lithium ion conductive coating layer is formed. Specifically, the solid electrolyte may be formed by coating a solution of dopamine or a derivative thereof, a lithium salt or an ion conductive polymer on at least one surface of a lithium ion conductor layer using various surface treatment methods such as coating, spraying, and dipping, Followed by drying to produce a lithium ion conductor layer having an ion conductive coating layer.

The solution in which the dopamine or its derivative is dissolved can be prepared by dissolving dopamine or a derivative thereof in an aqueous solvent, specifically water or a buffer solution based on distilled water (10 mM tris buffer solution, pH 8.5). Further, in order for dopamine to form a poly dopamine coating layer through spontaneous polymerization, it is preferable that the solution is maintained in a weak base (pH 8.5) state constantly. Accordingly, the pH of the solution in which the dopamine or derivative thereof is dissolved may be 7 to 10, more specifically 7 to 9. Within the above-mentioned pH range, dopamine or derivatives thereof can be self-polymerized.

In addition, the lithium ion conductor for forming the ion conductive coating layer may preferably be in the form of a pellet. The lithium ion conductor layer in pellet form can be produced in the form of a pellet by putting a powdery lithium ion conductor into a press and applying appropriate pressure. At this time, it is preferable to selectively reduce the interface resistance by sintering the lithium ion conductor of the pellet type produced at a high temperature, and then form the ion conductive coating layer.

Meanwhile, the present invention provides a lithium secondary battery including the solid electrolyte formed between the positive electrode and the negative electrode.

The lithium secondary battery of the present invention may be in the form of a lithium metal battery, a lithium ion battery, or a lithium polymer battery, but is preferably a lithium metal battery.

In the lithium secondary battery, the solid electrolyte can act as an electrolyte and a separation membrane while preventing side reactions and an initial resistance increase between the solid electrolyte and the lithium metal interface as described above.

The positive electrode of the lithium secondary battery is formed on the positive electrode collector and includes a lithium transition metal oxide as a positive electrode active material.

As the cathode current collector, a porous body such as a mesh or mesh shape may be used, and a porous metal plate such as stainless steel, nickel, aluminum, or the like may be used, but not limited thereto, and any material that can be used as a collector in the related art It is possible. The cathode current collector may be coated with an oxidation-resistant metal or alloy coating to prevent oxidation.

In the positive electrode, a compound capable of reversibly intercalating and deintercalating lithium (a lithium intercalation compound) may be used as the positive electrode active material. Specifically, lithium-containing transition metal oxides can be used. More specifically, LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li (Ni _a Co _b Mn _c ) O ₂ (0 <a < 0 <b <1, 0 < c <1, a + b + c = 1), LiNi 1 - y Co y O 2, LiCo 1 - y Mn y O 2, LiNi 1 - y Mn y O 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 Ni _z O ₄ , LiMn _{2 - z} Co _z O ₄ (0 <z <2), LiCoPO ₄ and LiFePO _4, and combinations thereof. In addition to these oxides, sulfide, selenide and halide may be used. In addition, lithium-free cathode active materials which are initially lithium-free are also possible, for example, TiS ₂ , FeS ₂ or V ₂ O ₅ .

In addition, the positive electrode may also include a conductive material. The conductive material may be porous. Therefore, any conductive material having porosity and conductivity may be used without limitation, and for example, a carbon-based material having porosity may be used. Examples of the carbon-based material include carbon black, graphite, graphene, activated carbon, carbon fiber, and carbon nanotube (CNT). Examples of the conductive material include metallic conductive materials such as metal fibers and metal mesh; Metallic powder such as copper, silver, nickel, and aluminum; Or an organic conductive material such as a polyphenylene derivative can also be used. The conductive materials may be used alone or in combination.

In addition, the anode may further include a binder. As the binder,

A thermoplastic resin or a thermosetting resin can be used. More specifically, examples of the binder include polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene-butadiene rubber, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, Vinylidene-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, vinylidene fluoride-pentafluoropropylene copolymer, Propylene-tetrafluoroethylene copolymer, ethylene-chlorotrifluoroethylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer A copolymer, an ethylene-acrylic acid copolymer or the like may be used alone or in combination, It not limited to all possible as long as they can be used as binders in the art.

On the other hand, when the lithium secondary battery is a pre-solid battery that does not contain an electrolyte, the ion conductive polymer can replace the electrolyte solution and the binder. As the ion conductive polymer, polyethylene oxide (PEO), polypropylene oxide (PPO), polysiloxane or the like can be used. The positive electrode may be prepared by mixing a positive electrode active material, a conductive material, and optionally a binder to prepare a composition for forming a positive electrode active material layer, coating the positive electrode active material on at least one surface of the positive electrode current collector, and drying and rolling. Alternatively, the composition for forming the cathode active material layer may be cast on a separate support, and then a film obtained by peeling the support from the support may be laminated on the cathode current collector.

Meanwhile, in the lithium secondary battery, the negative electrode includes lithium metal as a negative electrode active material capable of absorbing and desorbing lithium. Lithium metal is useful as a negative electrode of a lithium secondary battery having a high energy density and excellent discharge capacity holding characteristics because of low density and low standard reduction potential.

A lithium secondary battery having a solid electrolyte including a lithium ion conductor layer formed with an ion conductive coating layer according to the present invention can shorten the time required for charging and discharging and improve the charge and discharge life.

Specifically, the solid electrolyte having the ion conductive coating layer according to the present invention is excellent in adhesion with the electrode, effectively transferring lithium ions, reducing the inter-interface side reaction between the solid electrolyte and the electrode, and significantly reducing the rate of increase in initial resistance inside the battery do. As a result, the output density characteristics of the battery are improved, and the rate characteristics are improved as the irreversible capacity is reduced, so that the time required for charging or discharging the battery is shortened and the charge and discharge life is improved. Accordingly, it is desirable to provide an electric vehicle such as a portable device such as a mobile phone, a notebook computer, a digital camera, a camcorder, or the like that requires a fast charging speed, a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (plug-in HEV, PHEV) Fields, and medium to large energy storage systems.

Hereinafter, examples, comparative examples and experimental examples are presented to help understand the contents of the present invention. However, the following test example corresponds to one test example of the constitution and effect of the present invention, and the scope and effect of the present invention are not limited thereto.

 [ Example  One] Solid electrolyte (Ion conductor LAGP ) - Polydopamine + TFSI ) Produce

^{LiTFSI 75.7mg (2.64 x 10 - 4} mol) was dissolved it in 25ml Tris-HCl buffer (pH 8.5mM ) dopamine (Dopamine) 50mg (2.64 x 10 - 4 mol) was added and dissolved (dopamine is added And self polymerization occurs immediately after dissolution in a few seconds). Immediately after the addition of dopamine, the LAGP pellet, which is an oxide electrolyte, was put into the solution, and then left to stand at room temperature for 17 hours to perform surface coating.

After coating, the Li _{1 + x} Al _x Ge _{2 x} (PO ₄ ) ₃ (LAGP) pellets were taken out and washed thoroughly with distilled water to remove any entangled debris on the surface, and a bath type sonicator Sonication was performed for 3 minutes to remove residual debris.

Thereafter, the pellet was air-dried at room temperature, sufficiently dried, and then a symmetric cell with Li metal was prepared.

[ Example  2] Solid electrolyte (Ion conductor LAGP ) - Polydopamine + TFSI + PEG) manufacture

Except that polyethylene glycol (PEG, MW 8000) was added to the buffer to dissolve it first, and then LiTFSI salt was added to dissolve it.

[ Comparative Example  One] The solid electrolyte (ion conductor (LAGP))  Produce

Li ₁ , a lithium ion conductor in powder form _{. 5} Al _{0 . 5} Ge _{1 . 5} P ₃ O ₁₂ were put into a press and pressed into a pellet form, and sintered to prepare a sintered pellet-shaped Li _1.5 Al _0.5 Ge _1.5 P ₃ O ₁₂ (average particle diameter (D ₅₀ ) = 2 μm).

[ Experimental Example  1] Observation photograph

The solid electrolytes prepared in Examples 1 and 2 and Comparative Example 1 were observed through a scanning electron microscope (SEM).

Observation results are shown in Figs.

1 is an image of a cross section of a solid electrolyte of Example 1. Fig. Referring to FIG. 1, it can be seen that an ion conductive coating layer is formed on the upper surface of the lithium ion conductor layer. The ion conductive coating layer has a thickness ranging from 20 nm to 80 nm depending on the coating position.

2 is a cross-sectional observation image of the solid electrolyte of Example 2. Fig. Referring to FIG. 2, it can be seen that an ion conductive coating layer is formed on the upper surface of the lithium ion conductor, similarly to FIG.

3 is an image of a cross section of a solid electrolyte of Comparative Example 1. Fig. As shown in FIG. 3, the ion conductive coating layer is not formed on the lithium ion conductor.

[ Experimental Example  2] Initial resistance change with time

The initial resistance values of lithium secondary battery cells including the solid electrolytes of Examples 1 to 2 and Comparative Example 1 were observed with time.

The experimental results are shown in the graph of FIG.

Referring to FIG. 4, in the case of Example 1, the ionic conductive coating layer of lithium salt and polydodamine is formed, which means that the resistance increase over time is not large. In addition, in the case of Example 2, the initial resistance (day 0) value was lowered and the rate of increase was not greater than that of Example 1 by further including polyethylene glycol in the ion conductive coating layer. The graph form of Example 2 tended to increase slightly on the first day, but then became almost horizontal, and after 4 days, the resistance value remained almost the same level with little change. On the other hand, in the case of Comparative Example 1, the initial resistance was small due to no surface treatment for forming the coating layer, but the continuous interfacial reaction progressed with time, and the resistance rapidly increased.

With respect to the above experimental results, the rate of change of the initial resistance at the 7th day from day 0 is shown in the graph of FIG.

Referring to FIG. 5, it can be seen that the resistance increase rate of Example 1 was 22%, and that of Example 2 was 123%, which was significantly lower than 777% of Comparative Example 1.

In particular, in the case of Examples 1 and 2, the initial resistance value (day 0) was somewhat larger than that of Comparative Example 1 due to the influence of the ion conductive coating layer, but the resistance value after 7 days was the same as that of Comparative Example 1 1) smaller than Comparative Example 1 (Example 2) can be confirmed.

From the experimental results, it can be seen that the lithium secondary battery including the solid electrolyte in which the ion conductive coating layer according to the present invention is formed maintains the interfacial stability between the solid electrolyte and the electrode, and as a result, the initial resistance increase rate is reduced.

The lithium secondary battery according to the present invention can be applied to a portable device such as a cellular phone, a notebook computer, a digital camera, a camcorder, and the like, a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle , PHEV), and middle and large-sized energy storage systems.

Claims (11)

A solid electrolyte in which an ion conductive coating layer is formed on at least one side of a lithium ion conductor layer, the ion conductive coating layer comprising polypodamine and a lithium salt.
The method according to claim 1,
The lithium ion conductor may be a lithium-lanthanum-titanium oxide system, a lithium-lanthanum-zirconium oxide system, a LISICON system, a lithium- aluminum- titanium- phosphate system, a lithium- aluminum- germanium- phosphate system, a lithium phosphorus oxy- A nitrile-based lithium ion conductor, and a combination thereof.
The method according to claim 1,
Wherein the lithium ion conductor is Li _{1 + X} Al _x M _{2 -X} (PO ₄ ) ₃ (wherein M is Ti or Ge, and 0 <x <1).
The method according to claim 1,
The lithium salt LiTFSI, LiCl, LiBr, LiI, LiClO4, LiBF 4, LiB 10 Cl 10, LiPF 6, LiAsF 6, LiSbF 6, LiAlCl 4, LiSCN, 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 F 9 SO 3, LiC (CF 3 SO 2) 3, (CF 3 SO 2) · 2NLi, chloroborane lithium, A lower aliphatic carboxylic acid lithium, a 4-phenylborate lithium imide, and a combination thereof.
The method according to claim 1,
Wherein the lithium salt comprises 0.1 to 25% by weight based on the total weight of the ion conductive coating layer.
The method according to claim 1,
Wherein the ion conductive coating layer further comprises an ion conductive polymer.
The method according to claim 6,
Wherein the ion conductive polymer includes at least one selected from the group consisting of polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, agitation lysine, polyester sulfide, polyvinyl alcohol, polyvinylidene, A polymer, and a combination thereof.
The method according to claim 6,
Wherein the ion conductive polymer is contained in an amount of 1 to 50 wt% based on the total weight of the ion conductive coating layer.
The method according to claim 1,
Wherein the thickness of the ion conductive coating layer is 1 to 200 nm.
1. A lithium secondary battery comprising a positive electrode, a negative electrode and a solid electrolyte interposed therebetween,
Wherein the solid electrolyte is the solid electrolyte according to any one of claims 1 to 9.
11. The method of claim 10,
Wherein the lithium secondary battery is a lithium metal battery.

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