Title of Invention: Anode for secondary battery, manufacturing method thereof, and lithium metal secondary battery comprising same
technical field
[One]
Cross-Citation with Related Application(s)
[2]
This application claims the benefit of priority based on Korean Patent Application No. 10-2019-0172498 dated December 20, 2019, and all contents disclosed in the literature of the Korean patent application are incorporated as a part of this specification.
[3]
The present invention can be formed by a more simplified method, and includes a negative electrode for a secondary battery including a negative electrode protective layer capable of effectively inhibiting the growth of needle-shaped dendrites generated in the negative electrode of a lithium metal secondary battery, a manufacturing method thereof, and lithium metal including the same It relates to secondary batteries.
background
[4]
A lithium metal secondary battery is a battery to which an anode active material of a lithium metal (Li-metal) material is applied, and has the advantage of having a theoretically very high energy density and capacity compared to a conventional battery to which a graphite-based or lithium alloy-based anode is applied. There is this. Accordingly, in order to apply such a lithium metal secondary battery to a battery requiring high energy density, research and development on it is continued.
[5]
However, in a lithium metal secondary battery, due to the characteristics of lithium metal, which is an anode active material, the volume change of the anode is very large during the charging/discharging process, and lithium generated during charging grows in a needle shape to form lithium dendrites. There is a problem. If the growth of such lithium dendrites continues, a short circuit of the cell may occur through the separator, and as a result, a major problem in battery performance or safety problems such as ignition may occur.
[6]
On the other hand, in the case of lithium metal used as an anode material in the lithium metal secondary battery, since the reactivity with the electrolyte is high, an irreversible reaction may occur continuously in the charging/discharging process. The surface film produced by such an irreversible reaction not only collapses due to a large volume change during charging and discharging, causing an additional irreversible reaction, but also lowers the coulombic efficiency of the cell and the cell performance due to the continuous irreversible reaction. A problem of lowering this overall may also occur.
[7]
Due to the major disadvantages of these lithium metal anodes, various materials and methods have been applied to the lithium metal anode surface from the past in order to suppress the problems caused by the continuous irreversible reaction of the lithium metal surface and the disadvantages caused by lithium dendrite growth. Research and attempts to form a cathodic protection layer have been continuously made.
[8]
In the past, a method of forming a cathode protective layer on the surface of a lithium metal anode by applying atomic layer deposition (ALD) or molecular layer deposition (MLD) has been mainly studied and applied. In the case of such an atomic layer deposition method and molecular layer deposition method, although there is an advantage of uniformly forming a nano-scale thin cathode protective layer, it is necessary to form a high vacuum for this process to proceed, and separately expensive equipment is required. This has the disadvantage of greatly reducing the economic feasibility of the overall process. Moreover, in the case of the atomic layer deposition method, the overall process step is complicated and the deposition rate is very slow, so there are also disadvantages that it is difficult to apply in the mass production process.
[9]
Due to the problems of the atomic layer deposition method, attempts have been made to form a cathodic protection layer by applying other chemical methods and materials, but it is still possible to effectively suppress the growth of needle-shaped dendrites, while still using the atomic layer deposition method. A technology capable of forming a uniform and thin cathode protective layer has not yet been developed.
[10]
Due to all the problems of the prior art, it can be formed by a more simplified method, so it is possible to form a negative electrode protective layer that has high mass productivity, and can effectively inhibit the growth of needle-shaped dendrites generated in the negative electrode of a lithium metal secondary battery. There is a continuous demand for the development of existing technologies.
DETAILED DESCRIPTION OF THE INVENTION
technical challenge
[11]
Accordingly, the present invention is to provide a negative electrode for a secondary battery including a negative electrode protective layer that can be formed by a more simplified method and can effectively suppress the growth of needle-like dendrites generated in the negative electrode of a lithium metal secondary battery, and a method for manufacturing the same .
[12]
In addition, the present invention is to provide a lithium metal secondary battery including the negative electrode for the secondary battery.
means of solving the problem
[13]
The present invention is a negative electrode current collector;
[14]
a lithium metal (Li-metal) thin film formed on the anode current collector; and
[15]
It provides a negative electrode for a secondary battery, comprising a negative electrode protective layer containing diazonium ions chemically bonded to the lithium metal thin film.
[16]
The present invention also provides a method of forming the negative electrode for a secondary battery, comprising the step of forming a diazonium ion or a salt thereof by reacting a nitrite compound and an amine compound on a lithium metal thin film.
[17]
In addition, the present invention provides a lithium metal secondary battery including the negative electrode for the secondary battery, an electrolyte, and a positive electrode.
Effects of the Invention
[18]
According to the present invention, on a lithium metal thin film, an amine compound and a nitrite compound are reacted in a solvent to form a diazonium ion, etc., in a very simplified method of forming a nanoscale negative electrode protective layer having a very thin and uniform thickness on a lithium metal. can be effectively formed.
[19]
Such a cathode protective layer can be formed by a very simplified process compared to the atomic layer deposition method, and can have a very uniform and thin thickness comparable to the protective layer formed by the atomic layer deposition method. In addition, the diazonium ion-containing negative electrode protective layer formed in this way can solve various problems occurring on the negative electrode of a lithium metal secondary battery, for example, problems caused by continuous irreversible reactions and/or problems caused by needle-shaped lithium dendrite growth. Since it can be effectively suppressed, it can greatly contribute to improving the performance and lifespan characteristics of a mass-produced lithium metal secondary battery.
Brief description of the drawing
[20]
1 is a view showing the results of analyzing the surface of the cathode on which the cathode protective layer is formed in Example 1 by TEM (left) and EELS (right) mapping, respectively.
Modes for carrying out the invention
[21]
In the present specification, when a part "includes" a certain component, this means that other components may be further included rather than excluding other components unless otherwise stated. As used throughout this specification, the terms "about," "substantially," and the like are used in a sense at or close to the numerical value when the manufacturing and material tolerances inherent in the stated meaning are presented, and are intended to enhance the understanding of this application. To help, precise or absolute figures are used to prevent unfair use by unscrupulous infringers of the stated disclosure. The term "step of" or "step of" to the extent used throughout this specification does not mean "step for".
[22]
In the present specification, the term "combination of these" included in the expression of the Markush format means one or more mixtures or combinations selected from the group consisting of the components described in the expression of the Markush format, and the components It means to include one or more selected from the group consisting of.
[23]
[24]
Based on the above definition, embodiments of the present invention will be described in detail. However, these are presented as examples, and the present invention is not limited thereto, and the present invention is only defined by the scope of the claims to be described later.
[25]
According to one embodiment of the invention, a negative electrode current collector; a lithium metal (Li-metal) thin film formed on the anode current collector; and a negative electrode protective layer including diazonium ions chemically bonded to the lithium metal thin film.
[26]
The present inventors continued their research to form a negative electrode protective layer that can effectively suppress various problems on a lithium metal negative electrode with a more simplified process, having a thin and uniform thickness. As a result of these continuous studies, by applying a diazonium ion formation reaction to form a diazonium ion-containing negative electrode protective layer on a lithium metal negative electrode, it was confirmed that the above-mentioned requirements could be satisfied and the invention was completed. .
[27]
As confirmed in the following examples, the negative electrode protective layer containing diazonium ions included in the negative electrode of one embodiment is very simplified to form diazonium ions by reacting an amine compound and a nitrite compound in a solvent on a lithium metal thin film In this method, it can be formed to have a very thin and uniform thickness of nanoscale on lithium metal. The negative electrode protective layer may be formed to have a very thin and uniform thickness while the diazonium ion-containing compound is chemically bonded to the surface of the lithium metal negative electrode in the form of a graft bond, along with the formation of the diazonium ion.
[28]
Accordingly, the cathode protective layer can be formed by a single reaction step process that is very simplified compared to the atomic layer deposition method, and can have a very uniform and thin thickness comparable to the protective layer formed by the atomic layer deposition method. In addition, the diazonium ion-containing negative electrode protective layer formed in this way can solve various problems occurring on the negative electrode of a lithium metal secondary battery, for example, problems caused by continuous irreversible reactions and/or problems caused by needle-shaped lithium dendrite growth. It was confirmed that it can be effectively suppressed.
[29]
Therefore, the negative electrode for a secondary battery of one embodiment has very high mass productivity compared to the atomic layer deposition method, etc., and effectively suppresses the growth of needle-shaped lithium dendrites, etc., and can greatly contribute to the improvement of the performance and lifespan characteristics of the lithium metal secondary battery.
[30]
[31]
Hereinafter, a negative electrode for a secondary battery according to an embodiment of the present invention, a method for manufacturing the same, and a lithium metal secondary battery including the same will be described in more detail.
[32]
[33]
Anode for lithium metal secondary battery
[34]
As described above, the negative electrode for a secondary battery of one embodiment includes a lithium metal thin film formed on a negative electrode current collector, and includes a negative electrode protective layer including diazonium ions chemically bonded to the lithium metal thin film.
[35]
In the negative electrode of this embodiment, the negative electrode protective layer may include a diazonium ion formed by reacting an amine compound to which a predetermined organic group is bonded and a nitrite compound:
[36]
[Scheme 1]
[37]
A-NH 2 + NO 2 - + 2H + → AN + ≡N + 2H 2 O
[38]
Accordingly, the negative electrode protective layer may include a diazonium ion represented by the following Chemical Formula 1 or a salt of the diazonium ion, for example, a halogen salt of the diazonium ion.
[39]
[Formula 1]
[40]
AN + ≡N
[41]
In Schemes 1 and 1, A is a substituted or unsubstituted C1-C20 alkyl group, or a substituted or unsubstituted C6-C40 aryl group. In this case, the alkyl group or the aryl group is substituted with an alkyl group having 1 to 20 carbon atoms, a nitro group (-NO 2 ), an alkoxy group, an amine group, a halogen, a carboxy group (-COOH), -SO 3 H, -SH or -CS, It may be unsubstituted.
[42]
In such a negative electrode protective layer, the organic group A included in the diazonium ion may be chemically bonded to the surface of the lithium metal thin film in the form of a graft bond or the like by the action of the diazonium ion and a radical reaction based thereon. As a result, the negative electrode protective layer can effectively suppress problems such as an irreversible reaction and/or needle-shaped lithium dendrite growth and a short circuit on the lithium metal thin film serving as the negative electrode of the secondary battery.
[43]
In addition, the cathode protective layer including such diazonium ions may have a thickness of 1 nm to 1 μm, or 2 to 500 nm, or 5 to 300 nm. By applying the diazonium ion formation reaction of Reaction Formula 1, etc., the cathode protective layer having the above thickness can be appropriately formed by controlling the thickness. In addition, by forming the negative electrode protective layer having such a thickness, the growth of needle-shaped dentrites on the surface of the negative electrode may be effectively suppressed, and the capacity characteristics of the negative electrode and the lithium metal secondary battery including the same may not be impaired.
[44]
Meanwhile, in the negative electrode of the above-described embodiment, the copper current collector may be generally formed to have a thickness of 3 to 500 μm. In addition, the lithium metal thin film formed on the copper current collector may have a thickness of 1 to 100 μm, or 2 to 50 μm, or 3 to 30 μm, depending on a typical configuration of a lithium metal secondary battery. In addition, the lithium metal method may be formed on the copper current collector through methods widely known in the art, such as deposition, electrolytic plating, and rolling.
[45]
According to another embodiment of the present invention, there is provided a method for manufacturing a negative electrode for a secondary battery of the above-described embodiment. The method of manufacturing the negative electrode may include reacting a nitrite compound and an amine compound on the lithium metal thin film to form a diazonium ion or a salt thereof.
[46]
In a more specific example, the method for manufacturing the negative electrode may further include reacting the diazonium ion formed through the above reaction step, a compound including the same, or a salt thereof with the lithium metal thin film. By this reaction with the lithium metal thin film, the diazonium ions, for example, the organic group A contained therein, are chemically bonded to the lithium metal thin film in the form of a graft bond to form a negative electrode protective layer and an anode in one embodiment can be
[47]
However, the reaction step of the diazonium ion and the lithium metal thin film does not substantially proceed separately from the step of forming the diazonium ion or a salt thereof, and the reaction step for the formation of the diazonium ion and the like and in a single solvent system may proceed voluntarily.
[48]
As such, since the above-described diazonium ion-containing cathode protective layer can be formed through a single process in a substantially single solvent system, the process of forming the cathode protective layer can be very simplified compared to the conventional atomic layer deposition method, etc. , as a result, it can be very easily applied to the mass production process of lithium metal secondary batteries.
[49]
On the other hand, in the process of forming the above-described cathode protective layer, the types of amine compounds, nitrite compounds and solvents for the formation of the diazonium ions are not particularly limited, and are applicable to form diazonium ions or salts thereof from the past. Any known ingredient may be used.
[50]
For example, as the amine compound, a compound of Formula 2 may be used, and depending on the type of organic group A bonded to Formula 1, a compound in which the corresponding organic group is bonded to an amine group may be appropriately selected and used:
[51]
[Formula 2]
[52]
A-NH 2
[53]
In Formula 2, A is as defined in Formula 1.
[54]
In addition, as the nitrite compound that reacts with the amine compound to form a diazonium ion, tert-butyl nitrite or sodium nitrite may be used. In addition, the amine compound and the nitrite compound can react effectively to form a diazonium ion, and their reaction step, if necessary, may be performed in the presence of an acid such as hydrochloric acid.
[55]
In addition, the step of forming the diazonium ion and the reaction step with the lithium metal thin film carried out in the same solvent system may be carried out in an organic solvent such as acetonitrile or tetrahydrofuran. More specifically, these reaction steps may proceed by, for example, a method of reacting the amine compound and the nitrite compound in the organic solvent in a state in which the lithium metal thin film formed on the negative electrode current collector is immersed in the organic solvent. have.
[56]
On the other hand, the negative electrode for a secondary battery of one embodiment can be manufactured by a conventional method of forming the negative electrode of a lithium metal secondary battery, except for forming the negative electrode protective layer containing diazonium ions by the above-described method. A description will be omitted.
[57]
lithium metal secondary battery
[58]
Meanwhile, according to another embodiment of the present invention, there is provided a lithium metal secondary battery including the negative electrode for a secondary battery of the embodiment described above. Such a secondary battery includes the negative electrode of the above-described embodiment; It may include an electrolyte, and an anode.
[59]
Meanwhile, the electrolyte of the lithium metal secondary battery may be a liquid electrolyte (ie, an electrolyte) or a solid electrolyte.
[60]
When the electrolyte of the lithium metal secondary battery is a liquid electrolyte, it includes a non-aqueous organic solvent and a lithium salt.
[61]
The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can move.
[62]
The type of the non-aqueous organic solvent is not particularly limited, and an ether-based, carbonate-based, ester-based, ketone-based, alcohol-based or aprotic solvent may be used. Examples of the carbonate-based solvent include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethylmethyl carbonate (EMC), methylethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), etc. may be used, and as the ester solvent, methyl acetate, ethyl acetate, n-propyl acetate, 1,1-dimethyl Ethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, decanolide (decanolide), valerolactone, mevalonolactone (mevalonolactone), caprolactone (caprolactone) and the like may be used. As the ether-based solvent, dimethyl ether, 1,2-dimethoxyethane (1,2-DIMETHOXYETHANE), dibutyl ether, tetraglyme, diglyme, 2-methyltetrahydrofuran, tetrahydrofuran, etc. may be used, and the ketone-based solvent may include cyclohexanone. In addition, as the alcohol-based solvent, ethyl alcohol, isopropyl alcohol, etc. may be used, and the aprotic solvent is R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group, nitriles such as nitriles such as dimethylformamide, dioxolanes such as 1,3-dioxolane, sulfolanes, etc. may be used. Among them, an ether-based solvent or a carbonate-based solvent can be appropriately used from the viewpoint of improving the lifespan characteristics of the lithium metal secondary battery.
[63]
In addition, the non-aqueous organic solvent may be used alone or in a mixture of one or more, and when one or more are mixed and used, the mixing ratio can be appropriately adjusted according to the desired battery performance, which is for those engaged in the art. can be widely understood.
[64]
In addition, in the case of the carbonate-based solvent, it is preferable to use a mixture of a cyclic carbonate and a chain carbonate. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte may be excellent.
[65]
The non-aqueous organic solvent may further include the aromatic hydrocarbon-based organic solvent in the carbonate-based solvent. In this case, the carbonate-based solvent and the aromatic hydrocarbon-based organic solvent may be mixed in a volume ratio of about 1:1 to about 30:1.
[66]
As the aromatic hydrocarbon-based organic solvent, an aromatic hydrocarbon-based compound represented by the following Chemical Formula 1 may be used.
[67]
[Formula 3]
[68]

[69]
In Formula 3, R 1 to R 6 are each independently hydrogen, halogen, a C1 to C10 alkyl group, a C1 to C10 haloalkyl group, or a combination thereof.
[70]
The aromatic hydrocarbon-based organic solvent is benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene , 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2, 4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1,2,4 -triiodobenzene, toluene, fluorotoluene, 1,2-difluorotoluene, 1,3-difluorotoluene, 1,4-difluorotoluene, 1,2,3-trifluorotoluene, 1,2,4-trifluorotoluene, chlorotoluene, 1,2-dichlorotoluene, 1,3-dichlorotoluene, 1,4-dichlorotoluene, 1,2,3-trichlorotoluene, 1,2,4 -Trichlorotoluene, iodotoluene, 1,2-diiodotoluene, 1,3-diiodotoluene, 1,4-diiodotoluene, 1,2,3-triiodotoluene, 1,2,4- Triiodotoluene, xylene, or a combination thereof may be used.
[71]
The non-aqueous organic solvent may further include vinylene carbonate or an ethylene carbonate-based compound represented by the following Chemical Formula 4 to improve battery life.
[72]
[Formula 2]
[73]

[74]
In Formula 4, R 7 and R 8 are each independently hydrogen, a halogen group, a cyano group (CN), a nitro group (NO 2 ), or a C1 to C5 fluoroalkyl group, and at least one of R 7 and R 8 is a halogen group, a cyano group (CN), a nitro group (NO 2 ), or a C1 to C5 fluoroalkyl group.
[75]
Representative examples of the ethylene carbonate-based compound include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, fluoroethylene carbonate, and the like. can When the vinylene carbonate or the ethylene carbonate-based compound is further used, the lifespan can be improved by appropriately adjusting the amount used.
[76]
In the electrolyte of the lithium metal secondary battery, the lithium salt is dissolved in the organic solvent and serves as a source of lithium ions to enable the basic operation of the lithium metal secondary battery of another embodiment, and between the positive electrode and the negative electrode It can play a role in promoting the movement of lithium ions.
[77]
As the lithium salt, a lithium salt widely applied to an electrolyte may be used. For example, lithium bis(fluorosulfonyl) imide (LiFSI) may be used. In addition, LiPF 6 , LiBF 4 , LiSbF 6 , LiAsF 6 , LiC 4 F 9 SO 3 , LiClO 4 , LiAlO 2 , LiAlCl 4 , LiN(C x F 2x+1 SO 2 )(C y F 2y+1 SO 2 ), where x and y are natural numbers, LiCl, LiI, LiB(C 2 O 4 ) 2 (lithium bis(oxalato) borate; LiBOB), or a combination thereof may be used.
[78]
In addition, in the electrolyte, the concentration of the lithium salt may be controlled within the range of 0.1 to 5.0M. Within this range, the electrolyte may have appropriate conductivity and viscosity, and lithium ions may effectively move within the lithium metal secondary battery. However, this is only an example, and the invention is not limited thereto.
[79]
The electrolyte may be impregnated in a porous separator positioned between the negative electrode and the positive electrode. Here, the porous separator separates the negative electrode from the positive electrode and provides a passage for lithium ions to move, and any one commonly used in lithium batteries may be used. That is, a material having low resistance to ion movement of the electrolyte and excellent moisture content of the electrolyte may be used.　
[80]
For example, as selected from glass fiber, polyester, Teflon, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), or a combination thereof, nonwoven fabric or woven fabric may be used. For example, a polyolefin-based polymer separator such as polyethylene or polypropylene is mainly used, and a coated separator containing a ceramic component or a polymer material may be used to secure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure. have.
[81]
Meanwhile, when the electrolyte of the lithium metal secondary battery is a solid electrolyte, a solid electrolyte that can be used is not particularly limited.
[82]
In addition, regardless of the electrolyte of the lithium metal secondary battery, the positive electrode may include a positive electrode current collector and a positive electrode mixture layer positioned on the positive electrode current collector.
[83]
In this case, the positive electrode mixture layer may be prepared by mixing a positive electrode active material and a binder, in some cases, a conductive material or a filler, in a solvent to prepare a positive electrode mixture in a slurry state, and applying the positive electrode mixture to the positive electrode current collector. Since such a method for manufacturing a positive electrode is widely known in the art, a detailed description thereof will be omitted herein.
[84]
The positive active material is not particularly limited as long as it is a material capable of reversible intercalation and deintercalation of lithium ions. metals of, for example, cobalt, manganese, nickel, iron, or combinations thereof; and lithium;
[85]
As a more specific example, as the positive electrode active material, a compound represented by any one of the following formulas may be used. Li a A 1-b R b D 2 (wherein 0.90 ≤ a ≤ 1.8 and 0 ≤ b ≤ 0.5); Li a E 1-b R b O 2-c D c (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, and 0 ≤ c ≤ 0.05); LiE 2-b R b O 4-c D c (wherein 0 ≤ b ≤ 0.5 and 0 ≤ c ≤ 0.05); Li a Ni 1-bc Co b R c D α(wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, and 0 < α ≤ 2); Li a Ni 1-bc Co b R c O 2-α Z α (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α < 2); Li a Ni 1-bc Co b R c O 2-α Z 2 (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α < 2); Li a Ni 1-bc Mn b R c D α(wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05, and 0 < α ≤ 2); Li a Ni 1-bc Mn b R c O 2-α Z α (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α < 2); Li a Ni 1-bc Mn b R c O 2-α Z 2 (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05 and 0 < α < 2); Li a Ni b E c G d O 2(Wherein, 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, and 0.001 ≤ d ≤ 0.1); Li a Ni b Co c Mn d G e O 2 (wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5 and 0 ≤ e ≤ 0.1); Li a NiG b O 2 (wherein 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li a CoG b O 2 (wherein 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li a MnG b O 2 (wherein 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); Li a Mn 2 G b O 4 (wherein 0.90 ≤ a ≤ 1.8 and 0.001 ≤ b ≤ 0.1); QO 2 ; QS 2 ; LiQS 2 ; V 2 O 5 ; LiV 2 O 5 ; LiTO 2 ; LiNiVO 4 ; Li (3-f) J 2 (PO 4 ) 3 (0 ≤ f ≤ 2); Li (3-f) Fe 2 (PO 4 ) 3 (0 ≤ f ≤ 2); and LiFePO 4 .
[86]
In the above formula, A is Ni, Co, Mn, or a combination thereof; R is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P or a combination thereof; E is Co, Mn, or a combination thereof; Z is F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or a combination thereof; Q is Ti, Mo, Mn, or a combination thereof; T is Cr, V, Fe, Sc, Y or a combination thereof; J is V, Cr, Mn, Co, Ni, Cu, or a combination thereof.
[87]
Of course, a compound having a coating layer on the surface of the compound may be used, or a mixture of the compound and a compound having a coating layer may be used. The coating layer is a coating element compound, and may include oxide, hydroxide, oxyhydroxide of a coating element, oxycarbonate of a coating element, or hydroxycarbonate of a coating element. The compound constituting these coating layers may be amorphous or crystalline. As the coating element included in the coating layer, Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof may be used. In the coating layer forming process, any coating method may be used as long as it can be coated by a method that does not adversely affect the physical properties of the positive electrode active material by using these elements in the compound (eg, spray coating, dipping, etc., for this Since it is a content that can be well understood by those engaged in the field, a detailed description will be omitted.
[88]
The positive electrode current collector is generally made to have a thickness of 3 to 500 μm. The positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel. Carbon, nickel, titanium, silver, etc. surface-treated on the surface of the can be used. The current collector may increase the adhesive force of the positive electrode active material by forming fine irregularities on its surface, and various forms such as a film, sheet, foil, net, porous body, foam body, and non-woven body are possible.
[89]
The conductive material is not particularly limited as long as it has conductivity without causing a chemical change in the battery. For example, graphite such as natural graphite or artificial graphite; carbon black, 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, aluminum, and nickel powder; conductive whiskeys such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives may be used.
[90]
The lithium metal secondary battery of the embodiment may be used not only in a unit cell used as a power source for a small device, but also as a unit cell in a medium/large battery module including a plurality of battery cells. Furthermore, a battery pack including the battery module may be configured.
[91]
[92]
Hereinafter, preferred examples of the invention, comparative examples, and experimental examples for evaluating them are described. However, the following examples are only preferred examples of the present invention, and the present invention is not limited thereto.
[93]
[94]
Example 1: Preparation of a negative electrode with a diazonium ion-containing negative electrode protective layer
[95]
After dissolving 10 mmol of 4-nitroaniline and 10 mmol of tert-butyl nitrite in 50 mL of acetonitrile, lithium metal was immersed at 25° C. for 2 hours. Thereafter, the negative electrode was washed using acetonitrile and vacuum dried for 12 hours to prepare a negative electrode having a negative electrode protective layer.
[96]
[97]
Experimental Example 1: Surface analysis for each negative electrode (confirmation of the formation of a protective layer)
[98]
The surface of the negative electrode formed in the above example was analyzed by TEM and electron energy loss spectroscopy (EELS) mapping. The results of this surface analysis are shown in FIG. 1 . Referring to the right drawing of FIG. 1 (EELS analysis result), it is confirmed that the nitrogen component derived from diazonium ions is well distributed on the surface of the anode, and from this, it is confirmed that the cathode protective layer is uniformly and well formed on the surface of the anode did. In addition, it was confirmed that the nitrogen component in the negative electrode protective layer was included in an amount of 6.16% by weight.
[99]
[100]
Example 2: Preparation of a lithium metal secondary battery including the negative electrode of Example
[101]
LiNi 0.5 Mn 1.5 O 4 as a positive electrode active material, Super-P as a conductive material, and polyvinylidene fluoride (PVDF) as a binder, respectively, and a weight ratio of positive electrode active material: conductive material: binder to 94:3:3 to form a mixed mixture. A positive electrode active material slurry was prepared by adding NMP as a solvent to this mixture. The cathode active material slurry was coated on one side of an aluminum foil (thickness: 10 μm), and dried at 120° C. for 30 minutes. After the prepared positive electrode was punched out to a diameter of 11 mm, it was dried under vacuum at 120° C. for 12 hours to prepare a positive electrode.
[102]
[103]
A 2032-type coin cell was prepared in a glove box in an argon atmosphere using each negative electrode sample of Example 1 and the positive electrode. In this case, a PP/PE/PP multilayer separator was used as the separator, and 1.3 M LiPF 6 dissolved in a mixed solvent of DMC, EMC, and DEC (30: 20: 50 in Vol%) was used as an electrolyte solution. , 100 μL was injected into the coin cell. Thus, a lithium metal secondary battery of Example 2 was prepared.
[104]
[105]
Comparative Example 1: Preparation of a lithium metal secondary battery
[106]
A lithium metal secondary battery of Comparative Example 1 was prepared in the same manner as in Example 2, except that, instead of the negative electrode of Example 1, a lithium metal without a negative electrode protective layer was used as the negative electrode.
[107]
[108]
Experimental Example 2: Evaluation of capacity retention rate and short circuit evaluation of secondary batteries (confirmation of dendrite growth inhibition characteristics)
[109]
Using the cells prepared in Example 2 and Comparative Example 1, first, charging and discharging were performed three times at a current density of 12 mA·g -1 . Thereafter, a constant current charge/discharge test was performed in the range of 3.5V to 4.9V. At this time, a charge/discharge test was performed at a current density of 120 mA˙g -1 at 60° C. to evaluate a cycle in which the capacity retention rate compared to the capacity during the initial charge/discharge was 80%, and is shown in Table 1 below.
[110]
On the other hand, using the cells prepared in Example 2 and Comparative Example 1, the time of occurrence of a short circuit in the cell was evaluated by the following method. That is, charging was performed up to 4.9V with a current density of 12 mA˙g -1 , and a time point at which a cell short circuit occurred by continuously applying a constant voltage of 4.9V was confirmed. Table 1 shows the elapsed time until the cell short circuit occurs.
[111]
For reference, during the charging process of a lithium metal secondary battery, a lithium electrodeposition reaction occurs on the negative electrode surface, and as a result, needle-shaped dendrites grow. If these needle-like dendrites continue to grow by continuation of the charge, they may break through the separator and cause a short circuit of the cell. Accordingly, the elapsed time until the occurrence of the short circuit of the cell may reflect the growth of acicular dendrites on the cathode surface and the degree of inhibition thereof.
[112]
[113]
[Table 1]
Capacity retention rate (80%) When a cell short occurs (time)
Comparative Example 1 52 cycles 21 hours
Example 2 76 cycles 34 hours
[114]
Referring to Table 1, it was confirmed that in Example 2, acicular dendrite growth was effectively suppressed by the formation of the cathodic protection layer, and the elapsed time until the occurrence of a cell short circuit was very long compared to Comparative Example 1. In addition, it was confirmed that the battery of Example 2 exhibited an 80% capacity retention rate in a very long cycle compared to Comparative Example 1 and could have excellent lifespan characteristics by suppressing the growth of acicular dendrites and the like.
Claims
[Claim 1]
negative electrode current collector; a lithium metal (Li-metal) thin film formed on the anode current collector; and a negative electrode protective layer containing diazonium ions chemically bonded to the lithium metal thin film.
[Claim 2]
The negative electrode for a secondary battery according to claim 1, wherein the negative electrode protective layer contains a diazonium ion of the following Chemical Formula 1 or a salt of the diazonium ion: [Formula 1] AN + ≡N In Chemical Formula 1, A is A is a substituted or unsubstituted C1-C20 alkyl group, or a substituted or unsubstituted C6-C40 aryl group.
[Claim 3]
The negative electrode for a secondary battery according to claim 2, wherein the organic group A included in the diazonium ion is graft-coupled to the surface of the lithium metal thin film.
[Claim 4]
The negative electrode for a secondary battery according to claim 1, wherein the negative electrode protective layer has a thickness of 1 nm to 1 μm.
[Claim 5]
The negative electrode for a secondary battery according to claim 1, wherein the negative electrode current collector comprises copper.
[Claim 6]
The method of claim 1, comprising the step of forming a diazonium ion or a salt thereof by reacting a nitrite compound and an amine compound on a lithium metal thin film.
[Claim 7]
The method of claim 6 , further comprising reacting the diazonium ions with the lithium metal thin film.
[Claim 8]
The method of claim 7, wherein the step of forming the diazonium ion or a salt thereof and the reaction step with the lithium metal thin film are spontaneously sequentially performed in a single solvent system.
[Claim 9]
The method of claim 6, wherein the amine compound is a compound of Formula 2 below: [Formula 2] A-NH 2 In Formula 2, A is a substituted or unsubstituted C1-C20 alkyl group, or substituted or an unsubstituted C6-C40 aryl group.
[Claim 10]
The method of claim 6 , wherein the nitrite compound comprises tert-butyl nitrite or sodium nitrite.
[Claim 11]
The method of claim 8 , wherein the step of forming the diazonium ion or a salt thereof and the reaction step with the lithium metal thin film are performed in an organic solvent of acetonitrile or tetrahydrofuran.
[Claim 12]
A lithium metal secondary battery comprising the negative electrode of claim 1, an electrolyte, and a positive electrode.
[Claim 13]
13. The method of claim 12, wherein the positive electrode comprises a positive electrode active material, the positive electrode active material, cobalt, manganese, nickel, iron, or a metal of a combination thereof; and lithium; and a lithium metal secondary battery comprising at least one of a composite oxide of lithium.
[Claim 14]
The method of claim 12, wherein the electrolyte, lithium bis (fluorosulfonyl) imide (Lithium bis (fluorosulfonyl) imide, LiFSI), LiPF 6 , LiBF 4 , LiSbF 6 , LiAsF 6 , LiC 4 F 9 SO 3 , LiClO 4 , LiAlO 2 , LiAlCl 4 , LiN(C x F 2x+1 SO 2 )(C y F 2y+1 SO 2 ), where x and y are natural numbers, LiCl, LiI, LiB(C 2 O 4 ) 2(Lithium bis (oxalato) borate; LiBOB) or a lithium salt selected from a combination thereof; and a non-aqueous organic solvent; A lithium metal secondary battery comprising a.