METHOD OF MANUFACTURING ANODE FOR LITHIUM SECONDARY BATTERY INCLUDING PRE-LITIGATION

Abstract

Proposed is a method of manufacturing an anode for a lithium secondary battery, including a pre-lithiation step.

Claims

1. A method of manufacturing an anode for a lithium secondary battery, the method comprising: preparing an anode comprising an anode current collector, and a coating layer disposed on the anode current collector and comprising a carbon material; immersing the anode in a pre-lithiation solution; and immersing the anode in a stabilizing solution, wherein the pre-lithiation solution comprises a pre-lithiated compound comprising lithium and a biphenyl-based compound, wherein the stabilizing solution comprises at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), methyl vinylene carbonate (meVC), ethylene carbonate (EC), or any combination thereof, and wherein a lithium doping amount of the anode is about 1 mAh/cm.sup.2 or less.

2. The method of claim 1, wherein the coating layer comprises the carbon material and a metal capable of alloying with the lithium.

3. The method of claim 2, wherein the metal capable of alloying with the lithium comprises at least one of silver (Ag), magnesium (Mg), aluminum (Al), gallium (Ga), zinc (Zn), bismuth (Bi), tin (Sn), indium (In), antimony (Sb), lead (Pb), silicon (Si), germanium (Ge), or any combination thereof.

4. The method of claim 1, wherein a concentration of the pre-lithiation compound is about 0.1 M to 1 M.

5. The method of claim 1, wherein a molar ratio of the lithium and the biphenyl-based compound is about 0.5:1 to 6:1.

6. The method of claim 1, wherein the biphenyl-based compound is represented by the following Formula 1. ##STR00004## wherein, in Formula 1, R1 to R10 each comprises an alkyl group having 1 to 3 of carbon atoms.

7. The method of claim 1, wherein the pre-lithiation solution further comprises a solvent, and wherein the solvent comprises at least one of dimethyl ether (DME), 2-methyl tetrahydrofuran, tetrahydropyranyl, or any combination thereof

8. The method of claim 1, wherein the anode is immersed in the pre-lithiation solution at a temperature of about 25° C. to 60° C. for about 10 seconds to 30 minutes.

9. The method of claim 1, wherein the anode is immersed in the stabilizing solution to form a film on the anode, and the film comprises a C—O bond, a C═O bond, and an R—CO—R′ bond.

10. The method of claim 9, wherein a thickness of the film is about 200 nm or less.

11. The method of claim 1, wherein the anode is immersed in the stabilizing solution for about 10 to 60 minutes.

12. An anode for a lithium secondary battery, the anode comprising: an anode current collector; and a coating layer disposed on the anode current collector.

13. The anode of claim 12, wherein the coating layer comprises a carbon material and a metal capable of alloying with lithium.

14. The anode of claim 13, wherein the metal capable of alloying with the lithium comprises at least one of silver (Ag), magnesium (Mg), aluminum (Al), gallium (Ga), zinc (Zn), bismuth (Bi), tin (Sn), indium (In), antimony (Sb), lead (Pb), silicon (Si), germanium (Ge), or any combination thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG. 1 shows an all-solid-state battery according to an exemplary embodiment of the present disclosure;

[0031] FIG. 2 shows an anode according to an exemplary embodiment of the present disclosure;

[0032] FIG. 3 shows a reference diagram for explaining the state of charge of the all-solid-state battery according to an exemplary embodiment of the present disclosure;

[0033] FIG. 4 shows initial efficiency of the anode of Examples 1 to 3 and Comparative Example 1;

[0034] FIG. 5A shows the anode according to Example 3 before doping with lithium analyzed by a scanning electron microscope;

[0035] FIG. 5B shows the anode according to Example 3 after doping with lithium analyzed by a scanning electron microscope;

[0036] FIG. 6 shows OCV change width of the anode according to Examples 3 to 6;

[0037] FIG. 7 shows the surface of the anode according to Examples 3 and 4 analyzed by Fourier transform infrared spectrometer (FTIR);

[0038] FIG. 8 shows the degree of decrease in initial efficiency when the anode according to Examples 3 and 4 is exposed to a dry atmosphere; and

[0039] FIG. 9 shows charge and discharge characteristics of the all-solid-state battery according to Example 7 and Comparative Example 2.

[0040] It may be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the present disclosure. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particularly intended application and use environment.

[0041] In the figures, reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing.

DETAILED DESCRIPTION

[0042] Reference will now be made in detail to various embodiments of the present invention(s), examples of which are illustrated in the accompanying drawings and described below. While the present disclosure(s) will be described in conjunction with exemplary embodiments, it will be understood that the present description is not intended to limit the present disclosure(s) to those exemplary embodiments. On the contrary, the present disclosure(s) is/are intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the present disclosure as defined by the appended claims.

[0043] The above objectives, other objectives, features, and advantages of the present disclosure will be easily understood through the following exemplary embodiments in conjunction with the accompanying drawings. However, the present disclosure is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided so that the disclosed content may be thorough and complete, and the spirit of the present disclosure may be sufficiently conveyed to those skilled in the art.

[0044] Like reference numerals have been used for like elements in describing each figure. In the accompanying drawings, the dimensions of the structures are enlarged than the actual size for clarity of the present disclosure. Terms such as first, second, etc., may be used to describe various elements, but the elements should not be limited by the terms. The above terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present disclosure, a first component may be referred to as a second component, and similarly, a second component may also be referred to as a first component. The singular expression includes the plural expression unless the context clearly dictates otherwise.

[0045] In the present specification, the term “include” or “have” should be understood to designate that one or more of the described features, numbers, steps, operations, components, or a combination thereof exist, and the possibility of addition of one or more other features or numbers, operations, components, or combinations thereof should not be excluded in advance. Also, when a part of a layer, film, region, plate, etc., is said to be “on” another part, this includes not only the case where it is “on” another part but also the case where there is another part in between. Conversely, when a part of a layer, film, region, plate, etc. is said to be “under” another part, this includes not only cases where it is “directly under” another part but also a case where another part is in the middle.

[0046] Unless otherwise specified, all numbers, values, and/or expressions expressing quantities of ingredients, reaction conditions, polymer compositions, and formulations used herein contain all numbers, values and/or expressions in which such numbers essentially occur in obtaining such values, among others. Since they are approximations reflecting various uncertainties in the measurement, it should be understood as being modified by the term “about” in all cases. In addition, when a numerical range is disclosed in this disclosure, this range is continuous and includes all values from the minimum to the maximum value containing the maximum value of this range unless otherwise indicated. Furthermore, when such a range refers to an integer, all integers, including the minimum value to the maximum value containing the maximum value, are included unless otherwise indicated.

[0047] FIG. 1 shows an all-solid-state battery according to an exemplary embodiment of the present disclosure. The all-solid-state battery may include an anode 10, a solid electrolyte layer 20 disposed on the anode 10, a cathode active material layer 30 disposed on the solid electrolyte layer 20, and the cathode current collector 40 disposed on the cathode active material layer 30.

[0048] FIG. 2 shows the anode according to an exemplary embodiment of the present disclosure. The anode 10 may include an anode current collector 11, and a coating layer 12 disposed on the anode current collector.

[0049] The cathode current collector 40 may be a plate-shaped, sheet-shaped, or thin substrate composed of a conductive material. The cathode current collector 40 may include aluminum (Al), stainless steel (SUS), or the like.

[0050] The cathode active material layer 30 may include a cathode active material, a solid electrolyte, a conductive material, a binder, and the like.

[0051] The cathode active material may include an oxide active material or a sulfide active material.

[0052] The oxide active material may include a rock salt layer type active material such as LiCoO.sub.2, LiMnO.sub.2, LiNiO.sub.2, LiVO.sub.2, Li.sub.1+xNi.sub.1/3Co.sub.1/3Mn.sub.1/3O.sub.2, etc., a spinel type active material such as LiMn.sub.2O.sub.4, Li(Ni.sub.0.5Mn.sub.1/3O.sub.4, a reverse spinel type active material such as LiNiVO.sub.4 and LiCoVO.sub.4, an olivine type active material such as LiFePO.sub.4, LiMnPO.sub.4, LiCoPO.sub.4, LiNiPO.sub.4, silicon-containing active material such as Li.sub.2FeSiO.sub.4, Li.sub.2MnSiO.sub.4, a rock salt layer type active material in which a part of the transition metal is substituted with a dissimilar metal such as LiNi.sub.0.8Co.sub.(0.2-x)Al.sub.x(0<x<0.2), a spinel type active material in which a part of the transition metal is substituted with a dissimilar metal such as Li.sub.1+xMn.sub.2-x-yMyO.sub.4 (M is at least one of Al, Mg, Co, Fe, Ni, Zn, and 0<x+y<2), and a lithium titanate such as Li.sub.4Ti.sub.5O.sub.12, or the like.

[0053] The sulfide active material may include copper Chevrel, iron sulfide, cobalt sulfide, nickel sulfide, or the like.

[0054] The solid electrolyte may include an oxide solid electrolyte or a sulfide solid electrolyte. However, the solid electrolyte may be preferable to use a sulfide-based solid electrolyte having high lithium ion conductivity. The sulfide-based solid electrolyte is not particularly limited but may include Li.sub.2S—P.sub.2S.sub.5, Li.sub.2S—P.sub.2S.sub.5—LiI, Li.sub.2S—P.sub.2S.sub.5—LiCl, Li.sub.2S—P.sub.2S.sub.5—LiBr, Li.sub.2S—P.sub.2S.sub.5—Li.sub.2O, Li.sub.2S—P.sub.2S.sub.5—Li.sub.2S—O—LiI, Li.sub.2S—SiS.sub.2, Li.sub.2S—SiS.sub.2—LiI, Li.sub.2S—SiS.sub.2—LiBr, Li.sub.2S—SiS.sub.2—LiCl, Li.sub.2S—SiS.sub.2—B.sub.2S.sub.3—LiI, Li.sub.2S—SiS.sub.2—P.sub.2S.sub.5—LiI, Li.sub.2S—B.sub.2S.sub.2, Li.sub.2S—P.sub.2S.sub.5—Z.sub.mS.sub.n (where m and n are positive numbers, and Z is one of Ge, Zn, and Ga), Li.sub.2S—GeS.sub.2, Li.sub.2S—SiS.sub.2-—Li.sub.3PO.sub.4, Li.sub.2S—SiS.sub.2—Li.sub.xMO.sub.y (where x and y are positive numbers, M is one of P, Si, Ge, B, Al, Ga, In), Li.sub.10GeP.sub.2S.sub.12, and the like.

[0055] The conductive material may include carbon black, conducting graphite, ethylene black, graphene, or the like.

[0056] The binder may include butadiene rubber (BR), nitrile butadiene rubber (NBR), hydrogenated nitrile butadiene rubber (HNBR), polyvinylidene difluoride (PVDF), polytetrafluoroethylene (PTFE), carboxymethylcellulose (CMC), or the like.

[0057] The solid electrolyte layer 20 is interposed between the cathode active material layer 30 and the anode 10 to conduct lithium ions between both components.

[0058] The solid electrolyte layer 20 may include an oxide-based or a sulfide-based solid electrolyte. However, the solid electrolyte may be preferable to use a sulfide-based solid electrolyte having high lithium ion conductivity. The sulfide-based solid electrolyte is not particularly limited but may include Li.sub.2S—P.sub.2S.sub.5, Li.sub.2S—P.sub.2S.sub.5—LiI, Li.sub.2S—P.sub.2S.sub.5—LiCl, Li.sub.2S—P.sub.2S.sub.5—LiBr, Li.sub.2S—P.sub.2S.sub.5—Li.sub.2O, Li.sub.2S—P.sub.2S.sub.5—Li.sub.2O—LiI, Li.sub.2S—SiS.sub.5, Li.sub.2S—SiS.sub.2—LiI, Li.sub.2S—SiS.sub.2—LiBr, Li.sub.2S—SiS.sub.2—LiCl, Li.sub.2S—SiS.sub.2—B.sub.2S.sub.3—LiI, Li.sub.2S—SiS.sub.2—P.sub.2S.sub.5—LiI, Li.sub.2S—B.sub.2S.sub.3, Li.sub.2S—P.sub.2S.sub.5—Z.sub.mS.sub.n (where m and n are positive numbers, and Z is one of Ge, Zn, and Ga), Li.sub.2S—GeS.sub.2, Li.sub.2S—SiS.sub.2—Li.sub.3PO.sub.4, Li.sub.2S—SiS.sub.2—Li.sub.xMO.sub.y (where x and y are positive numbers, M is one of P, Si, Ge, B, Al, Ga, In), Li.sub.10GeP.sub.2Si.sub.2, and the like.

[0059] According to an exemplary embodiment of the present disclosure, the all-solid-state battery may include the anode 10 that does not include any anode active material layer. That is, the all-solid-state battery may be a kind of anode-free system. FIG. 3 shows a reference diagram for explaining the state of charge of the all-solid-state battery according to an exemplary embodiment of the present disclosure. The all-solid-state battery may store lithium ions coming from the cathode active material layer in the form of lithium metal (Li) at the interface between the anode current collector 11 and the coating layer 12 during charging.

[0060] The anode current collector 11 may be a plate-shaped, sheet-shaped, or thin substrate composed of a conductive material. The material constituting the anode current collector 11 is not particularly limited but may include, for example, copper (Cu), nickel (Ni), stainless steel (SUS), or the like.

[0061] The anode current collector 11 may have a thickness of about 0.1 μm to 10 μm.

[0062] The coating layer 12 may include a carbon material and a metal capable of alloying with lithium.

[0063] The carbon material may include amorphous carbon. The amorphous carbon is not particularly limited but may include at least one selected from the group consisting of furnace black, acetylene black, Ketj en black, graphene, and a combination thereof.

[0064] The metal capable of alloying th lithium may include at least one selecd from the group consisting of silver (Ag), magnesium (Mg), aluminum (Al), gallium (Ga), zinc (Zn), bismuth (Bi), tin (Sn), indium (In), antimony (Sb), lead (Pb), silicon (Si), germanium (Ge), and a combination thereof.

[0065] The method for manufacturing the anode 10 according to an exemplary embodiment of the present disclosure may include: preparing the anode 10 including the anode current collector 11 and the coating layer 12 disposed on the anode current collector 11 and including the carbon material; and immersing the anode in a pre-lithiation solution.

[0066] As described above, the anode current collector and the coating layer will be omitted below.

[0067] The present disclosure is characterized in that the anode 10 is easily prelithiated by preparing a pre-lithiation solution including a pre-lithiation compound with high reducibility and immersing the anode 10 therein.

[0068] The pre-lithiated solution may be prepared by adding a pre-lithiated compound to a solvent.

[0069] The solvent may include at least one solvent selected from the group consisting of dimethyl ether (DME), 2-methyl tetrahydrofuran, tetrahydropyranyl, and a combination thereof

[0070] The pre-lithiated compound may include lithium and a biphenyl-based compound.

[0071] The biphenyl-based compound may include one represented by the following Formula 1.

##STR00002##

[0072] In Formula 1, R1 to R10 may each include an alkyl group having 1 to 3 of carbon atoms.

[0073] In the solvent, the lithium and the biphenyl-based compound may be converted as follows to form a high reducibility solution.

##STR00003##

[0074] The anode may be prelithiated by immersing the anode in the pre-lithiation solution at a temperature of about 25° C. to 60° C. for about 1 second to 60 minutes.

[0075] The degree of the pre-lithiation is not particularly limited, but the lithium doping amount may be set to be about 30% or less compared to the full charge of the anode. For example, the pre-lithiation may be performed so that the lithium doping amount is 1 mAh/cm.sup.2 or less.

[0076] The method of manufacturing the anode may further include immersing the prelithiated anode in a stabilizing solution. This is to prevent side reactions between the anode and other components by stabilizing the surface of the prelithiated anode.

[0077] The stabilizing solution may include at least one selected from the group consisting of fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), methyl vinylene carbonate (meVC), ethylene carbonate (EC), and a combination thereof

[0078] A film may be formed on the anode by immersing the anode in a stabilizing solution.

[0079] The film may be a kind of solid electrolyte interface layer.

[0080] The composition of the coating film may vary depending on the type of the stabilizing solution but may include a compound having a C—O bond, a C═O bond, and an R—CO—R′ bond.

[0081] The film may have a thickness of about 200 nm or less.

[0082] The anode may be immersed in the stabilizing solution for about 10 to 60 minutes.

[0083] Hereinafter, another form of the present disclosure will be described in more detail through the following examples. The following examples are merely illustrative to help the understanding of the present disclosure, and the scope of the present disclosure is not limited thereto.

Examples 1 to 3 and Comparative Example 1

[0084] A nickel thin film having a thickness of about 10 μm was prepared as an anode current collector. An anode was prepared by forming a coating layer on the anode current collector to have a thickness of about 8 μm, including Super C65 as a carbon material, silver (Ag) as a metal capable of alloying with lithium, and polyvinylidene fluoride (PVDF) as a binder.

[0085] The anode was prelithiated by immersing the anode in a pre-lithiation solution. The immersion conditions of each Example are as follows.

[0086] Example 1: 50° C. and 15 minutes

[0087] Example 2: 60° C. and 15 minutes

[0088] Example 3: 60° C. and 30 minutes

[0089] The pre-lithiation solution was prepared by adding a pre-lithiation compound including lithium and biphenyl in a molar ratio of 4:1 to a concentration of about 0.5 M in a mixed solvent of 2-methyl tetrahydrofuran and tetrahydropyranyl.

[0090] Comparative Example 1 was set as an anode without pre-lithiation.

[0091] The following experiment was performed by manufacturing a coin cell with each anode. In this case, 1.0 M LiPF.sub.6 in EC/DEC (1:1 v/v)+10 vol % FEC was used as the electrolyte.

[0092] FIG. 4 shows initial efficiency of the anode of Examples 1 to 3 and Comparative Example 1. In FIG. 4, pristine means Comparative Example 1, 50° C. 15 minutes means Example 1, 60° C. 15 minutes means Example 2, and 60° C. 30 minutes means Example 3.

[0093] Table 1 below summarizes the initial efficiencies of each anode based on the results of FIG. 4.

TABLE-US-00001 TABLE 1 <Comparative Division Example 1> <Example 1> <Example 2> <Example 3> Initial OCV 1.96 V 0.36 V 0.36 V 0.33 V (V vs. Li/Li.sup.+) Initial 65.6 88.2 89.0 89.0 efficiency (%)

[0094] Referring to this Table 1, it can be seen that the initial efficiency of the anode can be greatly increased through pre-lithiation.

[0095] FIG. 5A shows the anode according to Example 3 before pre-lithiation analyzed by a scanning electron microscope. FIG. 5B shows the anode according to Example 3 after pre-lithiation analyzed by a scanning electron microscope.

[0096] Table 2 below shows the lithium desorption capacity of the anode and the coulombic efficiency of the second charging cycle.

TABLE-US-00002 TABLE 2 Division <Example 3> Lithium desorption capacity 0.036 (mAh/cm.sup.2) Coulombic efficiency of 2nd 81.8 charging Cycle (%)

[0097] It can be seen that the anode is doped with lithium through the increase in the particle size of FIG. 5B compared to FIG. 5A and the expression of the charging capacity as shown in Table 2.

Examples 4 to 6

[0098] The anode, according to Example 3, was immersed in fluoroethylene carbonate (FEC) as a stabilizing solution for 10 minutes (Example 4), 30 minutes (Example 5), and 60 minutes (Example 6), respectively.

[0099] FIG. 6 shows OCV change width of the anode according to Examples 3 to 6. In FIG. 6, prelithiated is a result of Example 3, prelithiated+FEC 10 minutes is a result of Example 4, prelithiated+FEC 30 minutes is a result of Example 5, and prelithiated+FEC 60 minutes is a result of Example 6.

[0100] Referring to FIG. 6, it can be seen that as the immersion time for the stabilizing solution is increased, the change width of the open circuit voltage (OCV) is significantly reduced. Since the change in OCV means a side reaction with the electrolyte, it can be seen that the anode treated with the stabilizing solution is stable because the reactivity to the electrolyte is greatly reduced.

[0101] For the anode, according to Example 3 and Example 4, the OCV change was observed for 60 minutes, and the initial efficiency was measured. The results are shown in Table 3 below.

TABLE-US-00003 TABLE 3 Division <Example 3> <Example 4> OCV increase 175 32 in 60 min. (mV) 1.sup.st CE (%) 90.3 90.6

[0102] In Example 4, a stabilizing film was formed on the anode, and the OCV change was reduced by about 20% compared to Example 3, and the initial efficiency was maintained similarly so that the lithium doping effect was preserved.

[0103] On the other hand, a small change in OCV means that a stable film was formed, and the same 1.sup.st CE means that it is electrochemically equivalent. That is, it can be understood that Example 4 obtained both the effects of pre-lithiation and stable film formation.

[0104] FIG. 7 shows the surface of the anode according to Examples 3 and 4 analyzed by Fourier transform infrared spectrometer (FTIR). In FIG. 7, prelithiated is a result of Example 3, and prelithiated+FEC 10 minutes is a result of Example 4. Referring to FIG. 7, it can be seen that a film including a compound having a C—O bond, a C═O bond, and an R—CO—R′ bond was formed on the electrode surface of Example 4 treated with the stabilizing solution.

[0105] FIG. 8 shows the degree of decrease in initial efficiency when the anode, according to Examples 3 and 4, is exposed to a dry atmosphere. The exposure time was set to about 10 minutes. The results are summarized in Table 4 below.

TABLE-US-00004 TABLE 4 Atmospheric exposure None 10 minutes to dry air Division <Example 3> <Example 4> <Example 3> <Example 4> 1.sup.st CE (%) 91.1 88.0 82.7 82.3

[0106] Referring to this Table 4, in Example 3, when exposed to drying air for 10 minutes, the initial efficiency decreases by about 8.4%, whereas in Example 4, the degree of decrease is small to about 5.7%. Through this, it can be seen that the decrease in initial efficiency can be reduced through surface stabilization of the anode.

Example 7 and Comparative Example 2

[0107] All-solid-state batteries, according to Example 7 and Comparative Example 2, were prepared using the anode according to Example 4 and Comparative Example 1, respectively. A sulfide-based solid electrolyte was used as the electrolyte.

[0108] FIG. 9 shows the charge and discharge characteristics of the all-solid-state battery according to Example 7 and Comparative Example 2. The results are summarized in Table 5 below.

TABLE-US-00005 TABLE 5 Unit charge Unit discharge First coulombic capacity capacity Division efficiency (%) (mAh g.sup.−1) (mAh g.sup.−1) <Comparative 85.1 200.0 170.3 Example 2> <Example 7> 86.3 205.1 177.1

[0109] Referring to this Table 5, it can be seen that Example 7 is superior to Comparative Example 2 in all of the first coulombic efficiency, unit charge capacity, and unit discharge capacity.

[0110] The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present disclosure to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described in order to explain certain principles of the present disclosure and their practical application, to enable others skilled in the art to make and utilize various exemplary embodiments of the present invention, as well as various alternatives and modifications thereof. It is intended that the scope of the present disclosure be defined by the Claims appended hereto and their equivalents.