WO2013183524A1

WO2013183524A1 - Nonaqueous electrolyte secondary battery

Info

Publication number: WO2013183524A1
Application number: PCT/JP2013/064951
Authority: WO
Inventors: 徹也梶田; 慎芹澤; 入山　次郎
Original assignee: 日本電気株式会社
Priority date: 2012-06-04
Filing date: 2013-05-29
Publication date: 2013-12-12
Also published as: JPWO2013183524A1

Abstract

The present invention relates to a negative electrode which has a negative electrode active material layer that contains at least one substance selected from the group consisting of silicon, silicon oxide and carbon, and which is characterized in that the negative electrode is doped with lithium by bringing the negative electrode active material layer into contact with a lithium source and carrying out a heat treatment in the presence of an ionic liquid.

Description

Nonaqueous electrolyte secondary battery

The present invention relates to a high capacity non-aqueous electrolyte secondary battery using a high capacity active material for a negative electrode.

Nowadays, with the spread of mobile devices such as mobile phones and laptop computers, the role of secondary batteries as a power source is regarded as important. These secondary batteries are small, light and have a high capacity, and are required to have performance and high safety which are not easily deteriorated even after repeated charge and discharge. Lithium ion secondary batteries are currently most frequently used.

Carbon (C) such as graphite and hard carbon is mainly used for the negative electrode of the lithium ion secondary battery. Although carbon can repeat charge / discharge cycles satisfactorily, the capacity has already been used up to near the theoretical capacity, so a significant increase in capacity cannot be expected in the future. On the other hand, there is a strong demand for improving the capacity of lithium ion secondary batteries, and negative electrode materials having a higher capacity than carbon are being studied.

An example of a negative electrode material capable of realizing a high capacity is silicon (Si). Although the negative electrode using Si has a large amount of occlusion and release of lithium ions per unit volume and a high capacity, when the lithium ions are occluded and released, the electrode active material itself has a large expansion and contraction, so that the pulverization proceeds. The irreversible capacity in the first charge / discharge is large, and a portion not used for charge / discharge is formed on the positive electrode side. There is also a problem that the charge / discharge cycle life is short.

Patent Document 1 proposes a method using Si oxide as a negative electrode active material as a measure for reducing the initial irreversible capacity using Si and improving the charge / discharge cycle life. In Patent Document 1, since the volume expansion / contraction per unit mass of the active material can be reduced by using Si oxide as the negative electrode active material, improvement in cycle characteristics has been confirmed. On the other hand, since the conductivity of the oxide is low, the current collecting property is lowered, and the irreversible capacity in charge / discharge is large.

Further, as a method for further improving the capacity and charge / discharge cycle life, Patent Document 2 proposes a method using particles obtained by combining a carbon material with Si and Si oxide as a negative electrode active material. Although the improvement of the cycle characteristics is confirmed by this, it is still insufficient, and the improvement of the initial charge / discharge efficiency is insufficient.

As a countermeasure for the first irreversible capacity, an attempt is made to electrochemically charge the irreversible capacity in advance. The method of charging electrochemically is excellent in that it can be charged according to the purpose by controlling the amount of energized electricity, but it is complicated and productivity because it is reassembled as a battery after charging the electrode once. Very low.

In addition, as a countermeasure for the first irreversible capacity, lithium-containing composite nitridation represented by Si oxide and Li _3-x M _x N (M represents a transition metal and 0 ≦ x ≦ 0.8) is used for the negative electrode. Patent Document 3 proposes a non-aqueous electrolyte lithium ion secondary battery using a mixed active material with a product. The lithium-containing composite nitride is excellent in terms of compensating the irreversible capacity of the Si oxide, but the capacity per mass of the lithium-containing composite nitride is about 800 mAh / g, which is small compared to the Si oxide, and only the Si oxide is used. There is a problem that the energy density of the battery is smaller than the energy density of the battery when used as the negative electrode active material.

Patent Document 4 proposes a method of doping Li to the negative electrode in advance by attaching Li metal to the negative electrode and heating, but the doping time tends to be long, the doping tends to be non-uniform. There is a problem that is high.

Japanese Patent Laid-Open No. 06-325765 JP 2004-139886 A JP 2000-164207 A JP 2007-214109 A

In view of the problems as described above, an object of the present invention is to provide a negative electrode for a non-aqueous electrolyte secondary battery having a high capacity, a manufacturing method thereof, and a non-aqueous electrolyte secondary battery having the negative electrode.

The present invention is a negative electrode having a negative electrode active material layer containing at least one selected from the group consisting of silicon, silicon oxide and carbon, and in the presence of an ionic liquid, the negative electrode active material layer and the lithium source The present invention relates to a negative electrode that is doped with lithium by performing a heat treatment by contacting the same, and a method for producing the same.

According to the present invention, a negative electrode for a non-aqueous electrolyte secondary battery having a high capacity can be provided, and the manufacturing time of the negative electrode can be shortened.

FIG. 3 is a schematic cross-sectional view showing a structure of an electrode element included in a laminated laminate type secondary battery. It is sectional drawing of the negative electrode for nonaqueous electrolyte secondary batteries which concerns on this invention.

(Secondary battery)
In the secondary battery according to this embodiment, an electrode element in which a positive electrode and a negative electrode are arranged to face each other, and an electrolytic solution are included in an outer package. The shape of the secondary battery may be any of a cylindrical type, a flat wound square type, a laminated square type, a coin type, a flat wound laminated type, and a laminated laminate type, and a laminated laminate type is preferable. Hereinafter, a laminated laminate type secondary battery will be described.

FIG. 1 is a schematic cross-sectional view showing the structure of an electrode element included in a laminated laminate type secondary battery. This electrode element is formed by alternately stacking a plurality of positive electrodes c and a plurality of negative electrodes a with a separator b interposed therebetween. The positive electrode current collector e of each positive electrode c is welded to and electrically connected to each other at an end portion not covered with the positive electrode active material, and a positive electrode terminal f is welded to the welded portion. A negative electrode current collector d of each negative electrode a is welded and electrically connected to each other at an end portion not covered with the negative electrode active material, and a negative electrode terminal g is welded to the welded portion.

(Negative electrode)
In the present embodiment, the negative electrode has a negative electrode active material layer containing a negative electrode active material containing at least one selected from the group consisting of silicon, silicon oxide, and carbon, and in the presence of an ionic liquid, Lithium is doped by performing a heat treatment by bringing the negative electrode active material layer and the lithium source into contact with each other. Hereinafter, in the present specification, the negative electrode before being doped with lithium may be referred to as a “negative electrode structure”.

The inventors of the present invention, as a result of earnestly studying the problem that when doping Li by a method of heating Li metal in contact with the negative electrode in advance, the doping time is long and tends to be non-uniform, It was found that the low ionic conductivity was the cause. Then, the knowledge which can perform this Li dope process rapidly and uniformly by introduce | transducing the liquid with Li ion conductivity in a negative electrode was acquired. Based on these findings, the present invention has been completed.

Also, it has been found that an ionic liquid that does not decompose even when the heating temperature is high is optimal as the Li ion conductive liquid to be introduced.

In the present embodiment, the negative electrode active material includes at least one selected from the group consisting of silicon, silicon oxide, and carbon, preferably includes silicon, and more preferably includes all of silicon, silicon oxide, and carbon. . Examples of the silicon oxide include silicon dioxide (SiO ₂ ) and SiOx (x> 0, preferably 0 <x ≦ 2). Examples of the carbon include carbon that performs charging and discharging, such as graphite and hard carbon. These may use only 1 type and may use 2 or more types together.

As described above, the negative electrode active material may include at least one of silicon, silicon oxide, and carbon. These contents are not particularly limited. For example, the contents of silicon, silicon oxide, and carbon with respect to the total of silicon, silicon oxide, and carbon are 5% by mass to 90% by mass, and 5% by mass, respectively. % To 90% by mass and 2% to 80% by mass are preferable. Further, the content of each silicon, silicon oxide, and carbon with respect to the total of silicon, silicon oxide, and carbon is 20% by mass to 50% by mass, 40% by mass to 70% by mass, and 2% by mass, respectively. More preferably, it is 30 mass% or less.

The negative electrode structure is produced by forming a negative electrode active material layer on a negative electrode current collector using a mixture in which a negative electrode active material and a negative electrode binder are mixed. Examples of the negative electrode binder include thermosetting compounds represented by polyimide, polyamide, polyamideimide, polyacrylic acid resin, polymethacrylic acid resin, and the like. The content of the negative electrode binder is preferably in the range of 1 to 30% by mass and more preferably 2 to 25% by mass with respect to the total amount of the negative electrode active material and the negative electrode binder. By setting the content to 1% by mass or more, the adhesion between the active materials or between the active material and the current collector is improved, and the cycle characteristics are improved. Moreover, by setting it as 30 mass% or less, an active material ratio can improve and a negative electrode capacity | capacitance can be improved.

The mixture containing the negative electrode active material and the negative electrode binder can further contain a solvent such as N-methyl-2-pyrrolidone (NMP). A paste prepared by kneading the mixture and solvent is applied onto a negative electrode current collector such as a copper foil and rolled to form a coated electrode plate, or directly pressed to form a pressure molded electrode plate. The negative electrode structure can be fabricated by processing into the form. Specifically, for example, silicon powder, silicon oxide powder, carbon powder, and a negative electrode binder are dispersed in a solvent and kneaded. Subsequently, the kneaded product is applied onto a negative electrode current collector made of a metal foil, and dried in a high-temperature atmosphere to produce a negative electrode structure in which a negative electrode active material layer is formed on the negative electrode current collector. it can.

In the negative electrode active material layer, a material that does not charge and discharge, such as carbon black and acetylene black, may be mixed in order to impart conductivity as necessary. The electrode density of the negative electrode active material layer is preferably 0.5 g / cm ³ or more and 2.0 g / cm ³ or less. When the electrode density is less than 0.5 g / cm ³ , the absolute value of the discharge capacity is small, and there are cases where the merit for the carbon material cannot be obtained. On the other hand, when the electrode density exceeds 2.0 g / cm ³ , it is difficult to impregnate the electrode with the electrolytic solution, and the discharge capacity may be reduced.

As the negative electrode current collector, aluminum, nickel, copper, silver, and alloys thereof are preferable in view of electrochemical stability. Examples of the shape include foil, flat plate, and mesh. The thickness of the negative electrode current collector is preferably 4 to 100 μm because it is preferable to maintain the strength, and more preferably 5 to 30 μm in order to increase the energy density.

In the present embodiment, in the presence of an ionic liquid, lithium is doped by bringing the negative electrode active material layer in the negative electrode structure into contact with the lithium source and performing a heat treatment (hereinafter referred to as “lithium pre-doping treatment”). May be described). By the presence of the ionic liquid during the lithium pre-doping treatment, lithium can be uniformly and rapidly doped into the negative electrode structure.

The ionic liquid is a salt composed of a cation and an anion that shows a liquid state at −10 ° C. to 100 ° C. In the present embodiment, the ionic liquid preferably has lithium ion conductivity. Since the ionic liquid generally has a high decomposition temperature, it is stable even when heated when doping the negative electrode structure with lithium.

Examples of the anion constituting the ionic liquid include (CF ₃ SO ₂ ) ₂ N ⁻ (also referred to as TFSI), (C ₂ F ₅ SO ₂ ) ₂ N ⁻ (also referred to as BETI), and (FSO ₂ ) ₂ N ^−. (Also referred to as FSI), (C ₄ F ₉ SO ₂ ) ₂ N ⁻ , (CF ₃ SO ₂ ) ₃ C ⁻ , (C ₂ F ₅ SO ₂ ) ₃ C ⁻ , BF ₄ ⁻ , AlF ₄ ⁻ , PF ₆ ^{_{^{_{^{-, AsF 6 -, SbF 6}}}}} -, ClO 4 -, AlCl 4 -, CF 3 SO 3 -, C 2 F 5 SO 3 -, C 3 F 7 SO 3 -, C 4 F 9 SO 3 -, CH 3 SO ₃ ⁻ , C ₂ H ₅ SO ₃ ⁻ , CH ₃ OSO ₃ ⁻ , C ₂ H ₅ OSO ₃ ⁻ , (CF ₃ ) ₃ PF ₃ ⁻ , (C ₂ F ₅ ) ₃ PF ₃ ⁻ , (C ₃ F ₇ ) ₃ PF ₃ ^- or (C ₄ F ₉ ) ₃ PF _3- ^{and the} like. Further, it may be a cyclic anion such as (CF ₂ SO ₂ ) ₂ N ⁻ (referred to as C-TFSI) or (CF ₂ ) ₃ (SO ₂ ) ₂ N ⁻ . Among these, as the anion constituting the ionic liquid, TFSI, BETI, FSI or _{_{_{_{(C 4 F 9 SO 2)}}}} 2 N - imide anion are preferable, TFSI or FSI is more preferable.

Examples of the cation constituting the ionic liquid include lithium, imidazolium, ammonium, pyridinium, pyrrolidinium, piperidinium, phosphonium, and sulfonium. Examples of the imidazolium include 1-ethyl-3-methylimidazolium (EMI), 1-methyl-3-octylimidazolium (MOI), 1,3-dimethylimidazolium, 1,3-diethylimidazolium, 1 Examples include -propyl-3-methylimidazolium, 1-butyl-3-methylimidazolium, 1-hexyl-3-methylimidazolium, or 1-ethyl-2,3-dimethylimidazolium. Examples of ammonium include tetrabutylammonium, tetraethylammonium, triethylmethylammonium, N, N-dimethyl-N-methyl-N- (2-methoxyethyl) ammonium (DEME), trimethylhexylammonium (TMHA), or N, N, N-trimethyl-N-propylammonium and the like can be mentioned. Examples of pyridinium include 1-butyl-3-methylpyridinium and 1-butylpyridinium. Examples of pyrrolidinium include 1-methyl-1-propyl-pyrrolidinium (MPPy), 1-butyl-1-methylpyrrolidinium (BMP), and N-methyl-N-propylpyrrolidinium (P13). It is done. Examples of piperidinium include 1-methyl-1-propyl-piperidinium (MPPi), 1-ethyl-1-methylpiperidinium, N-methyl-N-propylpiperidinium (PP13), and the like. . Examples of phosphonium include triethylmethoxyethylphosphonium (TEMEP), triethylmethylphosphonium, triethylhexylphosphonium, and the like. Examples of the sulfonium include triethylsulfonium (TES), triethylmethylsulfonium, triethylhexylsulfonium, and the like. Of these, lithium, MPPy, EMI, PP13, and P13 are preferable.

In addition, each of these anions and cations may be used alone or in combination of two or more.

Among the above ionic liquids, MPPy-TFSI, BMP-TFSI, EMI-TFSI, TEMEP-TFSI or TES-TFSI are preferable, and MPPy-TFSI, BMP-TFSI or EMI-TFSI are more preferable. Moreover, an ionic liquid may be used individually by 1 type, and 2 or more types may be mixed and used for it.

In this embodiment, the negative electrode is subjected to a lithium pre-doping process in the presence of an ionic liquid. As a method for causing the ionic liquid to be present on the negative electrode, it is preferable to apply the ionic liquid on the negative electrode active material layer of the negative electrode structure. As another method, the ionic liquid may be sprayed and sprayed on the negative electrode active material layer of the negative electrode structure, or the negative electrode structure may be immersed in the ionic liquid.

The ionic liquid is preferably applied to part or all of the surface of the negative electrode active material layer of the negative electrode structure. Examples of a method for applying the ionic liquid include a doctor blade method and a large coater method.

FIG. 2 is a schematic cross-sectional view showing a negative electrode structure. In this negative electrode, a negative electrode active material layer 1 is formed on a negative electrode current collector 2, and an ionic liquid 3 is immersed in the negative electrode active material.

As a method of the lithium pre-doping treatment, a method of heating the surface of the negative electrode active material layer on which the ionic liquid is applied and the lithium source in contact is preferable. The lithium source is preferably in the form of a sheet in order to uniformly contact the negative electrode structure, and examples thereof include metal foils mainly composed of lithium such as rolled lithium foil and vapor-deposited lithium foil. Examples of the base material of the sheet include metals such as copper and plastic films such as PET. If the heating temperature exceeds the melting point of metallic lithium (180.5 ° C), the molten lithium will flow out to places other than the electrodes, and efficient diffusion will not be performed. It is more preferable to carry out at 60 ° C. or higher and 120 ° C. or lower, and 60 ° C. or higher and 80 ° C. or lower is particularly preferable. The heating time is not particularly limited, but is preferably 10 minutes to 48 hours, more preferably 10 minutes to 30 minutes, and even more preferably 10 minutes to 15 minutes. In this embodiment, the presence of the ionic liquid makes it possible to perform the lithium doping process uniformly in a short time. Since metallic lithium reacts violently with moisture, all operations are preferably performed in a low humidity environment.

(Positive electrode)
The positive electrode is formed, for example, by binding a positive electrode active material so as to cover the positive electrode current collector with a positive electrode binder.

As the positive electrode active material is not particularly _{_{_{limited, LiMnO 2, LixMn 2 O 4}}} (0 <x <2), Li 2 MnO 3, LixMn 1.5 Ni 0.5 O 4 (0 <x <2) or the like Lithium manganate having a layered structure or lithium manganate having a spinel structure; LiCoO ₂ , LiNiO ₂ or a part of these transition metals replaced with another metal; LiNi _1/3 Co _1/3 Mn _{1 /} Lithium transition metal oxides in which more than half of specific transition metals such as ₃ O ₂ are present; Li in excess of the stoichiometric composition in these lithium transition metal oxides; Lithium oxide such as LiFePO ₄ Etc. Further, these metal oxides were partially substituted with Al, Fe, P, Ti, Si, Pb, Sn, In, Bi, Ag, Ba, Ca, Hg, Pd, Pt, Te, Zn, La, etc. Materials can also be used. In _{_{_{particular, Li α Ni β Co γ Al}}} δ O 2 (1 ≦ α ≦ 2, β + γ + δ = 1, β ≧ 0.7, γ ≦ 0.2) or _{_{_{_{Li α Ni β Co γ Mn δ}}}} O 2 (1 ≦ α ≦ 1.2, β + γ + δ = 1, β ≧ 0.6, γ ≦ 0.2). A positive electrode active material can be used individually by 1 type or in combination of 2 or more types.

Also, radical materials or the like can be used as the positive electrode active material.

As the positive electrode binder, the same negative electrode binder can be used. Among these, polyvinylidene fluoride is preferable from the viewpoint of versatility and low cost. The amount of the positive electrode binder to be used is preferably 2 to 15 parts by mass with respect to 100 parts by mass of the positive electrode active material from the viewpoints of “sufficient binding force” and “high energy” which are in a trade-off relationship. .

As the positive electrode current collector, the same as the negative electrode current collector can be used.

A conductive auxiliary material may be added to the positive electrode active material layer containing the positive electrode active material for the purpose of reducing impedance. Examples of the conductive auxiliary material include carbonaceous fine particles such as graphite, carbon black, and acetylene black.

(Electrolyte)
As the electrolytic solution, a solution in which a lithium salt is dissolved as an electrolyte in a solvent can be used. Solvents include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC). ), Chain carbonates such as dipropyl carbonate (DPC), aliphatic carboxylic acid esters such as methyl formate, methyl acetate and ethyl propionate, γ-lactones such as γ-butyrolactone, 1,2-diethoxyethane (DEE), chain ethers such as ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, acetamide, dimethylform Amide, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, And aprotic organic solvents such as propylene carbonate derivatives, tetrahydrofuran derivatives, ethyl ether, 1,3-propane sultone, anisole, N-methylpyrrolidone, and fluorinated carboxylic acid esters. These can be used alone or in combination of two or more. Among these, propylene carbonate, ethylene carbonate, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are preferably used alone or in combination.

Examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiAlCl ₄ , LiClO ₄ , LiBF ₄ , LiSbF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ CO ₃ , LiC (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ _{_{_{_{SO 2) 2, LiN (C}}}} 2 F 5 SO 2) 2, LiB 10 Cl 10, lower aliphatic lithium carboxylate, chloroborane lithium, lithium tetraphenylborate, LiBr, include LiI, LiSCN, LiCl, imides and the like It is done. These can be used alone or in combination of two or more.

The electrolyte concentration of the electrolytic solution can be, for example, 0.5 mol / l to 1.5 mol / l. If electrolyte concentration is 1.5 mol / l or less, the increase in the density and viscosity of electrolyte solution can be suppressed. Moreover, if electrolyte concentration is 0.5 mol / l or more, the electrical conductivity of electrolyte solution can be made enough. A polymer electrolyte may be used instead of the electrolyte.

(Separator)
As the separator, a porous film such as polypropylene or polyethylene or a nonwoven fabric can be used. Moreover, what laminated | stacked them can also be used as a separator. Alternatively, polyimide, polyamideimide, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), cellulose, or glass fiber having high heat resistance can be used. Moreover, the textile separator which bundled those fibers and made it into a thread form and made it into a textile fabric can also be used.

(Exterior body)
The exterior body can be appropriately selected as long as it is stable to the electrolytic solution and has a sufficient water vapor barrier property. For example, in the case of a laminated laminate type secondary battery, a laminate film made of aluminum, silica-coated polypropylene, polyethylene, or the like can be used as the outer package. In particular, it is preferable to use an aluminum laminate film from the viewpoint of suppressing volume expansion.

Hereinafter, the present embodiment will be specifically described by way of examples, but the present invention is not limited to the following examples.

[Examples 1 and 2]
(Preparation of negative electrode)
In this example, a mixture in which the molar ratio of Si, SiO ₂ and carbon (C) was 1: 1: 0.8 was used as the negative electrode active material. Si powder as the Si raw material using carbon powder as the SiO ₂ raw material SiO ₂ powder as the carbon source, and a negative electrode active material as a mixture thereof.

This negative electrode active material was mixed with polyimide as a negative electrode binder at a weight ratio of 85:15 (negative electrode active material: negative electrode binder), and an electrode material mixed with NMP as a solvent had a thickness of 10 μm. This was coated on a copper foil and dried at 125 ° C. for 5 minutes. Thereafter, compression molding was performed with a roll press, and drying was performed again in a drying furnace at 350 ° C. for 30 minutes in an N ₂ atmosphere. The copper foil on which the negative electrode active material layer was formed was punched out to 30 × 28 mm to produce a negative electrode.

(Li dope)
An ionic liquid of 1.0 mol / L LiTFSI / MPPy-TFSI was applied to the negative electrode surface, and a 3.2 × 3.4 mm Li foil was attached to the negative electrode. The laminate was sealed and left in a high-temperature bath at 60 ° C. for 10 minutes.

(Production of battery)
The negative electrode was taken out, washed with DEC, and then punched into two 12φ circles from the negative electrode, and the charge / discharge characteristics were confirmed at 20 ° C. with a model cell using metallic lithium as a counter electrode. The electric potential during charging is 0.02 mV vs.. Li / Li +, and the potential during discharge is 1000 mV vs. Li / Li +. The results are shown in Table 1.

As shown in Table 1, in the model cells of Examples 1 and 2, the difference between the initial charge capacity and the initial discharge capacity is small, and the capacity is reduced due to the irreversible capacity of the negative electrode active material containing Si, SiO ₂ , and carbon. It was suppressed.

Moreover, it carried out like Example 1 except the temperature of the thermostat having been 80 degreeC. The results are shown in Table 2.

Moreover, it carried out like Example 1 except the temperature of the thermostat having been 50 degreeC. The results are shown in Table 3.

Moreover, it carried out like Example 1 except the temperature of the thermostat having been 100 degreeC. The results are shown in Table 4.

[Comparative example]
A model cell was similarly produced in the case where Li was doped under the same conditions as in Example 1 except that the ionic liquid was not introduced and Li was attached to the negative electrode. The results are shown in Table 5.

A model cell was similarly produced in the case where Li was doped under the same conditions as in Example 1 except that a carbonate-based electrolyte was introduced instead of the ionic liquid and Li was attached to the negative electrode. The results are shown in Table 6.

As described above, in the manufacturing process of the negative electrode including the negative electrode active material including at least one selected from the group consisting of Si, Si oxide, and carbon, the Li metal is pasted in the presence of the ionic liquid and the temperature is increased. Thus, Li could be doped more rapidly and more uniformly. It was also confirmed that the heating temperature was preferably 60 ° C. to 80 ° C. from the viewpoint of the amount of lithium to be doped.

a negative electrode b separator c positive electrode d negative electrode current collector e positive electrode current collector f positive electrode terminal g negative electrode terminal 1 negative electrode active material layer 2 negative electrode current collector 3 ionic liquid

Claims

A negative electrode having a negative electrode active material layer containing at least one selected from the group consisting of silicon, silicon oxide and carbon,
A negative electrode which is doped with lithium by performing heat treatment by bringing the negative electrode active material layer into contact with a lithium source in the presence of an ionic liquid.
The negative electrode according to claim 1, wherein the temperature of the heat treatment is 60 to 80 ° C.
The negative electrode according to claim 1 or 2, wherein the lithium source is a metal foil mainly composed of lithium.
The lithium is doped by applying an ionic liquid on the surface of the negative electrode active material layer and then applying a heat treatment by applying a metal foil mainly composed of lithium on the negative electrode active material layer. Item 4. The negative electrode according to any one of Items 1 to 3.
The negative electrode according to any one of claims 1 to 4, wherein the ionic liquid is MPPy-TFSI.
A secondary battery comprising the negative electrode according to any one of claims 1 to 5.
Forming a negative electrode active material layer containing a negative electrode active material containing at least one selected from the group consisting of silicon, silicon oxide and carbon on a negative electrode current collector;
Doping lithium into the negative electrode active material by bringing the negative electrode active material layer into contact with a lithium source and performing a heat treatment in the presence of an ionic liquid;
A method for producing a negative electrode comprising:
Forming a negative electrode active material layer containing at least one selected from the group consisting of silicon, silicon oxide and carbon on the negative electrode current collector;
Applying an ionic liquid to the surface of the negative electrode active material layer;
Attaching a metal foil mainly composed of lithium on the negative electrode active material layer coated with the ionic liquid, and performing a heat treatment;
The manufacturing method of the negative electrode characterized by including.
Forming a negative electrode active material layer containing a negative electrode active material containing at least one selected from the group consisting of silicon, silicon oxide and carbon on a negative electrode current collector;
Producing a negative electrode in which lithium is doped into the negative electrode active material by bringing the negative electrode active material layer into contact with a lithium source and performing a heat treatment in the presence of an ionic liquid;
The manufacturing method of the secondary battery containing this.