Method for producing electrode for secondary batteries, and secondary battery using same

Abstract

[Problem] To provide: a method for producing a negative electrode for secondary batteries, the negative electrode having a large capacity density and being less susceptible to a decrease in capacity even if charging and discharging are repeated; and a secondary battery which is produced by said method and which has a large energy density and a long charge / discharge cycle life. [Solution] The above-described problem is solved by a method for producing an electrode for secondary batteries, the method including: a step for forming an electrode active material layer, which contains at least an electrode active material, a conductive material, and a binder, so as to produce an electrode layer to be pre-doped; and a pre-doping step for bringing a liquid, gel-like, or solid electrolyte that contains lithium into contact with the electrode layer to be pre-doped, and introducing lithium ions thereinto by means of an electrochemical method while applying pressure. The pre-doping step performed by means of an electrochemical method is carried out within the temperature range of 30°C to 120°C inclusive.

Description

Method for manufacturing secondary battery electrode and secondary battery using the same

[0001] The present invention relates to a method for producing an electrode for a secondary battery, and a secondary battery using the same. More specifically, the present invention relates to a method for producing an electrode for a secondary battery, which includes a step of forming an electrode active material layer containing at least an electrode active material, a conductive material, and a binder to prepare a pre-doped electrode layer, and a pre-doping step of contacting the pre-doped electrode layer with a liquid, gel, or solid electrolyte containing lithium and introducing lithium ions by an electrochemical method while applying pressure, wherein the pre-doping step by the electrochemical method is performed at a temperature range of 30° C. to 120° C., and a secondary battery using the same.

[0002] As the markets for portable electronic devices and electric vehicles expand, batteries used in these devices are required to have high energy densities. Secondary batteries have been developed that utilize the electrochemical reactions associated with the transfer of electric charge using alkali metal ions such as lithium as charge carriers. Lithium-ion secondary batteries, in particular, are widely used due to their high energy density.

[0003] Lithium-ion secondary batteries use lithium-containing transition metal oxides as the positive electrode active material and graphite as the negative electrode active material. Charging and discharging are performed by utilizing the intercalation and deintercalation reactions of lithium ions into these positive and negative electrode active materials. However, there is a need for the development of new technologies to achieve even higher energy density in lithium-ion secondary batteries.

[0004] In response to these demands, for example, Patent Document 1 proposes a nonaqueous secondary battery that is excellent in overcharge safety, has a high capacity, and is low cost. This secondary battery is characterized in that, in a configuration comprising a positive electrode sheet containing a positive electrode active material, a negative electrode sheet containing a negative electrode material capable of absorbing and desorbing lithium, and a nonaqueous electrolyte containing a lithium salt, a) the main positive electrode active material contains Mn, b) the negative electrode sheet has a multilayer configuration comprising a layer mainly made of a negative electrode material capable of absorbing and desorbing lithium and at least one auxiliary layer containing insoluble particles, and c) a metal foil mainly made of lithium is attached to the negative electrode sheet. It is disclosed that this provides a secondary battery with a high energy density.

[0005] The energy density of a secondary battery depends on the product of the electron charge (i.e., capacity density) that can be accumulated per molecular weight of the active material and the difference in redox potential between the positive and negative electrode active materials. The capacity density increases as the molecular weight of the active material decreases and the number of electrons that can react increases. Regarding the negative electrode active material, silicon and silicon compounds, which can react with a large number of electrons, have been considered as high-capacity materials. For example, silicon can react with multiple lithium atoms. Assuming a four-electron reaction, the theoretical capacity is 3817 Ah / kg, more than 10 times that of conventional graphite negative electrodes (372 Ah / kg). However, silicon and silicon compounds have problems such as low initial charge / discharge efficiency due to their large irreversible capacity, and short charge / discharge cycle life due to deformation during charge / discharge. These problems have hindered their practical application.

[0006] To address these issues, for example, Patent Document 2 discloses a method in which a buffer layer and a lithium-containing layer formed by a vapor phase method are sequentially disposed on a negative electrode composite layer containing a negative electrode material composed of a core containing a silicon compound and a carbon coating layer covering the core's surface, and lithium from the lithium-containing layer is absorbed into the negative electrode material by electrochemical reaction. In this method, the buffer layer, which suppresses a rapid reaction when absorbing lithium into the negative electrode material, faces the negative electrode material. This prevents uneven reaction between the silicon compound and lithium and prevents electrode curvature due to deformation of the negative electrode composite layer. In this method, the necessary amount of lithium is absorbed into the negative electrode material while electrochemically controlling the amount of lithium absorbed. This prevents the formation of dendrites due to excess lithium and the resulting degradation of battery performance. As a result, a nonaqueous secondary battery with high capacity and excellent battery performance can be provided.

[0007] As in Patent Documents 1 and 2, a method of reacting lithium in advance using a metal foil or a lithium-containing layer mainly containing lithium is called pre-doping, and various methods have been proposed because it can reduce the irreversible capacity of the negative electrode. For example, Patent Document 3 proposes a method that suppresses adsorption of moisture and nitrogen when using a vacuum device in the pre-doping process of the negative electrode active material, thereby enabling uniformity and quantitation of the concentration and shortening of the pre-doping time.

[0008] On the other hand, electrodes containing silicon or silicon compounds have the problem of the electrode layer expanding during the pre-doping process, and a technology has been proposed in which pre-doping is performed by contacting a lithium metal foil with a negative electrode under pressure. For example, Patent Document 4 discloses a method for manufacturing a lithium ion secondary battery that can reduce cell expansion associated with the occlusion of lithium ions in the negative electrode active material layer. According to this method, in a lithium ion secondary battery having a negative electrode and a positive electrode, a perforated conductive plate serving as a pressure jig is provided inside the secondary battery to apply pressure, thereby suppressing expansion of the electrode stack.

[0009] Patent Document 5 describes a method for producing a secondary battery including an electrolyte layer containing a solid electrolyte and an electrode containing an electrode active material, in which the electrode and the electrolyte layer or the electrode and the current collector are brought into contact with each other, and then the contact surface between the lithium source and the negative electrode is pressurized for pre-doping, thereby obtaining a compacted laminate of current collector / positive electrode / electrolyte layer / negative electrode.

[0010] Patent Document 6 discloses a doping system comprising an electrode unit for transporting a doping layer containing alkali metal ions and an electrode precursor, an electrical connection unit, and a porous insulating member.

[0011] Patent Document 7 discloses a method for producing a negative electrode for a secondary battery, which comprises a step of forming a negative electrode containing a silicon-based compound, and a pre-doping step of bringing a negative electrode active material layer into contact with an electrolyte solution containing lithium and applying pressure to introduce lithium ions by an electrochemical method.

[0012] Patent Document 8 discloses a pre-doping method in which lithium ions are doped into a negative electrode active material at a specific potential, thereby suppressing gas generation during initial charging and lithium dendrite generation during charging and discharging.

[0013] JP 2000-182602 A JP 2007-242590 A JP 2014-120555 A JP 2016-110777 A JP 2014-86222 A WO 2017 / 146223 A1 A WO 2019 / 088139 A1 A JP 2019 / 021634 A

[0014] In the above Patent Documents 1 to 5, pre-doping is performed by placing lithium on the negative electrode or depositing it by vapor deposition, but these methods make it difficult to perform pre-doping uniformly, and the manufacturing process, the performance of the produced electrodes, and secondary batteries are prone to variation, resulting in stability issues. Furthermore, Patent Document 6 performs pre-doping using an electrochemical method, which enables accurate and uniform pre-doping by controlling the voltage and charge amount, but there is a problem that pre-doping takes a long time because voltage is applied via an electrolyte, which limits the charge movement (current). Furthermore, Patent Document 7 discloses a method of pre-doping using an electrochemical method in which an electrode and a lithium source are closely attached via an insulating porous film while applying pressure. According to this method, the lithium source and the electrode to be pre-doped are closely attached, making pre-doping with a large current possible, but there are limitations, and further speedup is required.

[0015] As described above, a secondary battery with a high energy density and a stable and simple pre-doping method for producing the same have not yet been found.

[0016] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a method for producing a negative electrode for a secondary battery that has a high capacity density and is resistant to capacity reduction even with repeated charge and discharge, and a secondary battery produced thereby that has a high energy density and a long charge and discharge cycle life.

[0017] The method for manufacturing an electrode for a secondary battery according to the present invention comprises a step of forming an electrode active material layer containing at least an electrode active material, a conductive material and a binder to prepare a pre-doped electrode layer, and a pre-doping step of contacting the pre-doped electrode layer with a liquid, gel or solid electrolyte containing lithium and introducing lithium ions by an electrochemical method while applying pressure, characterized in that the pre-doping step by the electrochemical method is carried out at a temperature range of 30°C or higher and 120°C or lower.

[0018] In the method for manufacturing an electrode for a secondary battery according to the present invention, the process of pre-doping lithium by the electrochemical method is characterized in that lithium or a lithium-containing metal is used as a counter electrode and a voltage of 0 V or less is applied to the pre-doped electrode layer relative to the counter electrode.

[0019] In the method for producing an electrode for a secondary battery according to the present invention, the electrode active material is a negative electrode active material containing silicon or a silicon compound.

[0020] A secondary battery according to the present invention is characterized by comprising a secondary battery electrode manufactured by the above-described method for manufacturing a secondary battery electrode, and a liquid, gel, or solid electrolyte.

[0021] According to the present invention, uniform pre-doping can be efficiently performed by contacting a negative electrode active material layer as an electrode active material layer with an electrolyte solution containing lithium ions and applying pressure while maintaining a temperature of 30°C or higher and 120°C or lower. Since electrochemical pre-doping makes it easy to control the amount of current, it is possible to control the amount of lithium ions introduced into the negative electrode active material layer and form a passive layer at the interface between the electrolyte solution and the negative electrode active material. As a result, a high-capacity secondary battery negative electrode that is resistant to deterioration even after repeated charge-discharge cycles can be produced.

[0022] Furthermore, in the present invention, by performing pre-doping under pressure, it is possible to easily pass a large current and shorten the time required for pre-doping. Furthermore, by maintaining the pre-doping temperature at 30°C or higher and 120°C or lower, it is possible to uniformly and efficiently produce a high-quality passivation layer that is resistant to deterioration even with repeated charge-discharge cycles. As a result, it is possible to efficiently obtain a secondary battery with a high energy density and a long charge-discharge cycle life.

[0023] The above summary of the invention does not list all of the necessary features of the present invention, and subcombinations of these features may also constitute inventions.

[0024] Fig. 1 is a schematic diagram showing an example of a pre-doping step constituting a manufacturing method according to the present invention. Fig. 2 is a schematic diagram showing another example of a pre-doping step constituting a manufacturing method according to the present invention. Fig. 3 is a schematic diagram showing yet another example of a pre-doping step constituting a manufacturing method according to the present invention. Fig. 4 is a cross-sectional view showing an example of a secondary battery according to the present invention. Fig. 5 is a graph showing a change in voltage in the pre-doping process of electrodes produced in Example 1 and Comparative Example 1. Fig. 6 is a photograph showing the surface of the electrodes produced in Example 1 and Comparative Example 1 after pre-doping. The photograph on the left is Example 1, and the photograph on the right is Comparative Example 1.

[0025] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the technical scope of the present invention should be determined based on the description of the scope of the claims, and is not limited to the following embodiments.

[0026] The method for manufacturing a secondary battery electrode according to the present invention includes a step of forming an electrode active material layer containing at least an electrode active material, a conductive material, and a binder to prepare a pre-doped electrode layer, and a pre-doping step of contacting the pre-doped electrode layer with a liquid, gel, or solid electrolyte containing lithium and introducing lithium ions by an electrochemical method while applying pressure, characterized in that the pre-doping step by the electrochemical method is carried out at a temperature range of 30° C. to 120° C. This manufacturing method makes it possible to obtain a secondary battery with a high energy density and a long charge / discharge cycle life.

[0027] The steps will be described in detail below.

[0028] [Electrode Formation Step] In this embodiment, the electrode formation step is performed in the same manner as in the electrode formation step for conventional non-aqueous secondary batteries. Specifically, the electrode active material, conductive material, and binder are mixed with a solvent to form a slurry, which is then applied to an electrode current collector and dried.

[0029] In this embodiment, there is no particular limitation on the negative electrode active material, which is the electrode active material to be subjected to the pre-doping process. Any material conventionally used as an electrode for a secondary battery can be used as appropriate. Examples of the negative electrode active material include silicon-based materials such as silicon, SiO, and SiC; carbon materials such as artificial graphite, coated natural graphite, natural graphite, soft carbon, and hard carbon; and lithium transition metal composite oxides (e.g., Li ４ Ti ５ O １２ ), metal materials, lithium alloy-based negative electrode materials, etc. In the present invention, two or more negative electrode active materials may be used in combination as needed.

[0030] Examples of conductive materials for forming electrodes include carbon materials and conductive polymers. Examples of carbon materials include graphite, carbon black (e.g., acetylene black, ketjen black, etc.), coke, amorphous carbon, carbon fiber, carbon nanotubes, graphene, etc. Examples of conductive polymers include polyaniline, polypyrrole, polythiophene, polyacetylene, polyacene, etc. These conductive materials may be used alone or in combination of two or more.

[0031] In this embodiment, the binder is a material that binds together the particulate electrode active material, conductive material, and electrode current collector, and examples thereof include polyvinylidene fluoride, polytetrafluoroethylene, polyhexafluoropropylene, polyethylene oxide, carboxymethyl cellulose, polyacrylic acid, polyimide, polyamide, styrene-butadiene rubber, and derivatives thereof. These binders may be used alone or in combination of two or more.

[0032] In an embodiment, the electrode current collector holds the electrode active material layer. Examples of materials for the electrode current collector include copper, aluminum, stainless steel, nickel, titanium, and alloys thereof. The metal layer may be a foil, mesh, punched metal, expanded metal, or the like. The thickness of the electrode current collector is not particularly limited, but may be 3 to 200 μm, and preferably 5 to 20 μm.

[0033] The type of solvent in which the electrode active material, conductive material, and binder are mixed to form a slurry, and / or the blending ratio of the negative electrode active material and the organic solvent can be set as desired, taking into consideration the required characteristics of the secondary battery, productivity, etc. Examples of organic solvents that form the slurry include basic solvents such as dimethyl sulfoxide, dimethylformamide, 1-methyl-2-pyrrolidone, propylene carbonate, diethyl carbonate, dimethyl carbonate, and γ-butyrolactone; non-aqueous solvents such as acetonitrile, tetrahydrofuran, nitrobenzene, and acetone; and protic solvents such as methanol, ethanol, and water.

[0034] Another method for forming an electrode is to mix an electrode active material with a conductive material, a binder, and / or an ion-conductive material without using a solvent, and then mold the mixture under pressure.

[0035] [Pre-doping Step] This step involves doping the electrode active material with lithium. In the present invention, a lithium-containing electrolyte solution or a solid or gel electrolyte is contacted and impregnated into the negative electrode active material layer, and a voltage is applied between the negative electrode and a lithium-containing counter electrode while maintaining a temperature of 30°C to 120°C and applying pressure, thereby electrochemically introducing lithium ions. This manufacturing method makes it easy to control the charge amount, i.e., the pre-doping amount, and because a passive layer is formed on the surface of the negative electrode active material by pre-doping, a secondary battery negative electrode 14 with a long charge-discharge cycle life can be produced. Furthermore, by performing pre-doping while maintaining a temperature of 30°C to 120°C and applying pressure, a large current can be easily passed, thereby shortening the time required for pre-doping. Furthermore, solvents that are below their freezing point at 25°C or that have high viscosity due to being close to their freezing point can also be used as solvents for the pre-doping electrolyte. As a result, a secondary battery electrode with high energy and low capacity loss even with repeated charge-discharge cycles can be produced in a short time.

[0036] In this embodiment, for example, in the configuration shown in FIG. 2, when pre-doping is performed by an electrochemical method through a liquid-permeable elastic body containing a lithium-containing electrolyte or a solid or gel electrolyte in the electrode layer, the pre-doping is performed while maintaining the temperature at 30° C. or higher and 120° C. or lower and applying pressure.

[0037] 1 to 3 show examples of a pre-doping device for performing the pre-doping process. The pre-doping device shown in FIG. 1 includes a pre-doped electrode layer 2 to be pre-doped and a counter electrode 3 made of lithium metal in contact with a liquid-permeable elastic body 4 containing a lithium-containing electrolyte or a solid or gel electrolyte. In this device, lithium is introduced from the counter electrode 3 into the active material contained in the pre-doped electrode layer by an electrochemical method. A power source for applying a constant current or low voltage is connected between the pre-doped electrode layer 2 and the counter electrode 3, and a voltage system and an ammeter are also connected as necessary. In this device, the temperature is controlled by placing the entire device in a thermostatic chamber or by incorporating a heater into the pressure plate.

[0038] In the pre-doping device illustrated in FIG. 2 , the counter electrode 3 is a lithium metal provided on the surface of a cylindrical roll, and is in contact with the pre-doped double-sided electrode 5 via a liquid-permeable elastic body 4 containing a lithium-containing electrolyte or a solid or gel electrolyte. In this device, the rotation of the roll-shaped counter electrode 3 acts to transport a long working electrode, enabling continuous production and increasing productivity. In this device, the material and thickness of the counter electrode 3 are not particularly limited, and the material and size (roll width, roll diameter) of the roll are also not particularly limited and can be selected arbitrarily depending on productivity, device scale, electrical conductivity, etc. In this device, pressure can be applied between the counter electrode 3 and the pre-doped double-sided electrode 5 by applying tension to the pre-doped double-sided electrode 5, and the temperature can be controlled by placing the entire device in a thermostatic bath or by incorporating a heater into the roll.

[0039] The pre-doping device illustrated in Figure 3 is the pre-doping device of Figure 1, but with an electrode unwinding and winding mechanism. Lithium foil is laminated on the upper and lower pressure plates 6, 6, and a liquid-permeable elastic body 4 (also referred to as a liquid-permeable film) made of a porous film impregnated with a pre-doping electrolyte is laminated on its surface. A pre-doped double-sided electrode 5, consisting of a current collector (pre-doped electrode current collector 1) foil coated with electrodes (pre-doped electrode layer 2) on both sides, is inserted between the upper and lower liquid-permeable elastic bodies 4. Pressure and temperature are applied to a certain length of the pre-doped double-sided electrode 5, applying voltage between the lithium foil and the pre-doped double-sided electrode 5. After a predetermined amount of electricity flows, the upper and lower pressure plates 6, 6 are opened to move the pre-doped double-sided electrode 5, while simultaneously replenishing the electrolyte. The pressure and temperature are again controlled to perform pre-doping. In Figure 3, reference numeral 3 denotes a counter electrode, reference numeral 7 denotes an unwinding roll, and reference numeral 8 denotes a winding roll.

[0040] In the present invention, pre-doping is performed electrochemically while maintaining a temperature between 30°C and 120°C and applying pressure. Figure 5 shows the change in charge when an electrode using silicon as the active material is pre-doped using the device configured as shown in Figure 1. It can be seen that when a constant current of 200 mA / g per active material is applied at room temperature, pre-doping up to a charge of 1000 mAh / g is possible, but it takes a long time (5 hours). Increasing the current can shorten the pre-doping time, but at, for example, 10 A / g, the voltage drops to -1 V and then increases. In this case, lithium metal is partially deposited on the electrode surface, and uniform pre-doping is not achieved (photo on the right side of Figure 6). In contrast, when pre-doping is performed under pressure at 60°C, pre-doping is possible without lithium metal precipitation even at 10 A / g (photo on the left side of Figure 6). In this case, the pre-doping time up to 1000 mA / g is 6 minutes. Pre-doping up to about 150 mAh / g, which compensates for irreversible capacity, can be carried out within one minute, which is excellent for mass production.

[0041] Each component in the pre-doping process will be outlined below.

[0042] (Pre-doped electrode) The pre-doped electrode layer 2 is an electrode to be pre-doped, and is usually a pre-doped electrode layer 2 containing an electrode active material formed on a pre-doped electrode collector 1 such as copper foil, aluminum foil, or stainless steel foil. The composition and thickness of the pre-doped electrode layer 2 are not particularly limited, and conventionally known secondary battery electrodes are used. In the present invention, the pre-doped electrode layer 2 may be formed on one side or both sides of the pre-doped electrode collector 1, but it is preferable to form the pre-doped electrode layer 2 on both sides of the pre-doped electrode collector 1 because there is little deformation due to volume change of the pre-doped electrode layer 2 after pre-doping.

[0043] (Counter Electrode) The counter electrode 3 is an electrode that comes into contact with the working electrode via the liquid-permeable elastic body 4 and generates lithium to be introduced into the pre-doped electrode layer 2. The counter electrode 3 may be formed into a roll made of a column or a cylinder, or may be formed into a plate. The material and thickness of the counter electrode 3 are not particularly limited, but lithium metal or an alloy containing lithium is used. Examples of lithium alloys include Li ３ Al and the like.

[0044] (Liquid-permeable elastic body) The liquid-permeable elastic body 4 is provided on the counter electrode 3 (or on the entire circumference in the case of a roll). The counter electrode 3 and the pre-doped electrode layer 2 come into contact through this liquid-permeable elastic body 4, applying pressure and causing an electrochemical reaction to proceed via the electrolyte. The liquid-permeable elastic body 4 is not particularly limited as long as it has the function of permeating and impregnating the electrolyte. However, it is preferably a porous material that can achieve both liquid permeation and impregnation, is resistant to the electrolyte, and can transmit pressure. A microporous membrane, nonwoven fabric, or woven fabric having through holes from the front surface to the back surface of the liquid-permeable elastic body 4, and a polymer membrane such as polyethylene, polypropylene, cellulose, or polyurethane that is stable against the electrolyte can be used. The thickness of the liquid-permeable elastic body 4 is also not particularly limited. However, if it is too thin, the possibility of micro-short circuits increases. Conversely, if it is too thick, the resistance between the pre-doped electrode layer 2 and the counter electrode 3 increases, reducing efficiency. Therefore, it is arbitrarily selected within the range of, for example, 10 μm to 5 mm.

[0045] In the present invention, the gap between the pre-doped electrode layer 2 and the counter electrode 3 can be adjusted by selecting the thickness of the liquid-permeable elastic body 4. Note that Figures 1 and 3 have a mechanism (referred to as a gap adjustment mechanism) that can arbitrarily control the gap between the pressure plates 6, and this gap adjustment mechanism can apply pressure to the pre-doped electrode layer 2 via the liquid-permeable elastic body 4. As described above, the present invention is characterized in that a non-conductive liquid-permeable elastic body is used to prevent short circuits, and pressure electrolytic pre-doping is performed via such a liquid-permeable elastic body while applying a voltage from the outside and controlling the temperature.

[0046] (Pre-doping electrolyte) The pre-doping electrolyte contains metal ions for pre-doping. As the metal ions for pre-doping, lithium ions are preferred in terms of energy density and output density as a secondary battery. In the present invention, the electrolyte solution is interposed between the pre-doped electrode layer 2 and the counter electrode 3 to transport charge carriers between the two electrodes. The presence of the electrolyte 18 can be achieved by impregnation of the electrolyte with the liquid-permeable elastic body 4 described above. In the present invention, the temperature of the electrolyte 18 is also controlled to be between 30°C and 120°C.

[0047] In the present invention, the electrolyte is not particularly limited as long as it has ion conductivity. －６ Liquid, gel, and solid electrolytes having an ionic conductivity of 100 S / cm or more can be used. In the present invention, liquid and gel electrolytes are preferably used as the electrolyte due to their ease of reaction. In the case of a liquid, the electrolyte is an organic solvent containing an electrolyte salt, and the electrolyte salt is, for example, LiPF ６ , LiClO ４ , LiBF ４ , LiCF ３ SO ３ , LiN(CF ３ SO ２ ) ２ , LiN(C ２ F ５ SO ２ ) ２ , LiC(CF ３ SO ３ ) ３ , LiC(C ２ F ５ SO２ ) ３ Examples of suitable organic solvents include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, tetrahydrofuran, dioxolane, dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, propyl methyl sulfone, isopropyl methyl sulfone, propyl ethyl sulfone, isopropyl ethyl sulfone, dipropyl sulfone, diisopropyl sulfone, sulfolane, pentamethylene sulfone, hexamethylene sulfone, 3-methyl sulfolane, 2,4-dimethyl sulfolane, N,N-dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, and mixtures thereof. In the present invention, the concentration of the electrolyte salt is not particularly limited, but can be selected from a range of 0.1 mol / L to 2.5 mol / L, and a common concentration such as 1 mol / L may also be used. The ionic conductivity of the electrolyte can be measured by placing platinum electrodes of a predetermined area opposite each other and measuring the AC impedance.

[0048] The pre-doping electrolyte may contain an electrolyte additive such as fluoroethylene carbonate, vinylene carbonate, hydrofluoroether, or biphenyl.

[0049] (Pressure) Pressure is applied when the pre-doping is performed by an electrochemical method by contacting the liquid-permeable elastic body 4 containing lithium ions with the pre-doped electrode layer 2. In the present invention, by performing pre-doping under pressure, the time required for the treatment can be shortened and pre-doping can be performed uniformly, and as a result, a secondary battery negative electrode 14 having a high energy density and a capacity that is less likely to decrease even after repeated charge and discharge can be obtained.

[0050] In the present invention, the pressure is not particularly limited, but is applied at a level that does not deform the pre-doped electrode layer 2, or at a level that does not affect the characteristics even if the pre-doped electrode layer 2 is slightly deformed. Specifically, for example, it may be in the range of 0.1 MPa or more and 20 MPa or less. In particular, when a pressure of 0.5 MPa or more is applied, the expansion of the negative electrode 14 due to pre-doping is suppressed, and its effect (high energy density and less capacity reduction even with repeated charge and discharge) becomes significant. When the pressure is less than 0.1 MPa, the pressure may be too small and sufficient pre-doping may not be performed. When a pressure exceeding 20 MPa is applied, the pre-doped electrode layer 2 may be deformed due to the high pressure, or the voids impregnated with the electrolyte may decrease, slowing down the progress of pre-doping. The pressure is measured as the pressure applied to a rectangle, for example, 1 cm long and 1 cm wide, and can be measured using, for example, a load cell or pressure-sensitive paper.

[0051] The pressure is adjusted and controlled by controlling the spacing between the pressure plates 6, or in the case of roll-shaped opposing electrodes, by applying tension to the pre-doped double-sided electrode 5. Generally, electrochemical reactions are carried out by immersing two electrodes in an electrolyte solution so that no external mechanical force is applied, but the present inventors have found that by introducing lithium ions into the pre-doped electrode layer 2 under pressure and within a specific temperature range, deformation of the pre-doped double-sided electrode 5 after pre-doping can be suppressed, and uniform pre-doping can be carried out in a short time.

[0052] (Electrolytic pre-doping) Electrolytic pre-doping is performed by applying a constant current or a constant voltage between the pre-doped electrode layer 2 and the counter electrode 3. By this electrolytic pre-doping, lithium ions impregnated in the liquid-permeable elastic body 4 can be pre-doped into the pre-doped electrode layer 2.

[0053] In the present invention, the voltage, current, voltage profile, etc. used for electrolytic pre-doping are not particularly limited, and may be a constant voltage or a constant current. In the case of constant voltage electrolysis, it is preferable to apply a constant voltage of 0.05 V or less. The amount of pre-doping is controlled by the amount of charge (current and time), and is preferably performed at or above the irreversible capacity of the pre-doped electrode layer 2.

[0054] When the pre-doped electrode layer 2 is silicon, the pre-doping amount of lithium is preferably 0.01 mole or more per mole of silicon atom, more preferably 0.1 mole or more. The upper limit of the pre-doping amount is not particularly limited, but if it is 3 moles or more, there is a possibility that the amount exceeds the range that lithium can be absorbed when it moves during the charge / discharge process.

[0055] In the present invention, a stabilizing layer called a passive layer is formed on the surface of the active material constituting the pre-doped electrode layer 2 obtained by electrolytic pre-doping, which is generated by reaction of the electrolyte and additives. This passive layer is preferable because it acts to extend the charge-discharge cycle life.

[0056] The method for producing a secondary battery electrode according to the present invention is carried out electrochemically under pressure, thereby forming a stable passive layer. This allows for the production of a high-energy, stable electrode. Additionally, controlling the temperature to 30°C to 120°C shortens the reaction time and enables uniform pre-doping. Another advantage is that it allows for a wider variety of electrolyte solvents to be used, such as those with high freezing points. Research by the present inventors has shown that a pre-doping temperature of 120°C or higher reduces the charge-discharge cycle life, presumably due to a decline in the quality of the passive film produced.

[0057] [Secondary Battery] The secondary battery according to the present invention has at least a positive electrode, a negative electrode, and an electrolyte, and is characterized in that the negative electrode is the pre-doped negative electrode for a secondary battery according to the present invention. The form of the secondary battery is not particularly limited, but the example shown in Fig. 4 is a coin-type secondary battery. In this example, the secondary battery has a positive electrode 12, a negative electrode 14, and an electrolyte 18, and is also composed of a positive electrode case 10, a negative electrode case 11, a gasket 17, a separator 13, and a metal spring (elastic body) 16.

[0058] (Structural Elements) The positive electrode case 10 is provided as an exterior member for the positive electrode 12 and serves as a positive electrode current collector. An electrode layer composed of an electrochemically oxidizable and reducible positive electrode active material and a conductive material is disposed in the center of the bottom of the positive electrode case 10. A separator 13 made of a porous sheet or film such as a microporous membrane, nonwoven fabric, or woven fabric is laminated on the positive electrode 12. A pre-doped negative electrode 14 is disposed on the separator. A metal negative electrode current collector 15 is laminated on the negative electrode 14. A metal spring 16 is placed on the negative electrode current collector 15. While a coin-type secondary battery is described here, the battery shape is not particularly limited, and cylindrical, prismatic, sheet, and other types can also be used. The packaging method is also not particularly limited, and a metal case, molded resin, aluminum laminate film, and the like may be used.

[0059] In Fig. 4, the negative electrode case 11 is fixed to the positive electrode case 10 against the biasing force of a metal spring 16. A positive electrode 12, a separator 13, a negative electrode 14, and a negative electrode current collector 15 are stacked and placed in the internal space formed by fixing the positive electrode case 10 and the negative electrode case 11, and the internal space is filled with an electrolyte 18. The gap between the positive electrode case 10 and the negative electrode case 11 that forms the internal space is sealed via a gasket 17.

[0060] (Positive electrode and negative electrode) In the present invention, the electrode active material constituting the positive electrode is not particularly limited, and a compound that undergoes an electrochemically reversible oxidation-reduction reaction is used. Examples of such compounds include lithium manganese composite oxide, lithium cobalt oxide, lithium nickel oxide, lithium manganese spinel, and compounds of the general formula: LiNi ｘ Co ｙ Mn ｚ O ２ Olivine-type LiMPO, a composite metal oxide represented by (x + y + z = 1, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1) ４ Examples of the conductive material include lithium metal oxides such as lithium carbide (wherein M is one or more elements selected from Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, and Zr), conductive polymers such as polypyrrole and polyaniline, and organic compounds such as compounds having a thioketone group.

[0061] In the present invention, the positive electrode 12 can be produced by a conventionally known method, that is, by mixing a positive electrode active material such as a lithium metal oxide or an organic compound with a conductive material and a binder, adding a solvent to prepare a slurry, and applying the slurry to an electrode foil serving as a current collector by a conventionally known method, followed by drying.

[0062] In the present invention, the negative electrode 14 is prepared by a conventional method and pre-doped. The electrode active material constituting the negative electrode is not particularly limited, and a compound that undergoes an electrochemically reversible oxidation-reduction reaction is used. Examples of such compounds include graphite such as artificial graphite, natural graphite, and coated natural graphite, carbon materials such as soft carbon and hard carbon, and Li ４ Ti ５ O １２ Examples of the material include lithium transition metal composite oxides such as silicon and SiO 2 , silicon compounds such as silicon and SiO 2 , and mixtures of silicon compounds such as silicon and SiO 2 with graphite, sulfur or compounds containing sulfur, and compounds containing a quinone structure. In the present invention, the pre-doped electrode layer can be formed in the same manner as in the conventional method, for example, by mixing an electrode active material with a conductive material (such as graphite) and a binder, adding a solvent to prepare a slurry, and applying the slurry to an electrode foil that serves as a current collector by a conventionally known method, and then drying the slurry.

[0063] In the present invention, the conductive material used to prepare the positive electrode and negative electrode is not particularly limited, and examples thereof include carbonaceous particles such as carbon black, ketjen black, and acetylene black; carbonaceous fibers such as vapor-grown carbon fibers, carbon nanotubes, and carbon nanohorns; and carbonaceous sheets such as graphene. Two or more of these conductive materials can be used in combination as needed. The solvent is also not particularly limited, and examples thereof include aprotic solvents such as N-methylpyrrolidone, dimethyl sulfoxide, dimethylformamide, propylene carbonate, diethyl carbonate, dimethyl carbonate, γ-butyrolactone, acetonitrile, tetrahydrofuran, nitrobenzene, and acetone; methanol, ethanol, and water. The binder is not particularly limited as long as it binds the electrode active material and the conductive material; examples thereof include various resins such as polyethylene, polyvinylidene fluoride, polyhexafluoropropylene, polytetrafluoroethylene, polyethylene oxide, carboxymethyl cellulose, styrene butadiene rubber, polyacrylic acid, and polyimide resin. Preferably, polyacrylic acid and its derivatives, polyimide, polyamide and their derivatives are preferred from the viewpoint that the adhesion between the active materials can be maintained even after the pressure applied in the pre-doping step described below is released.

[0064] (Electrolyte) In the present invention, the electrolyte 18 is interposed between the positive electrode 12 and the negative electrode 14 to transport charge carriers between the two electrodes. There are no particular limitations on the electrolyte 18 as long as it has ion conductivity. －６ Liquid, gel, and solid electrolytes having an ionic conductivity of 1000 S / cm or more can be used. In the present invention, liquid and gel electrolytes are preferably used as the electrolyte due to their ease of reaction. In the case of a liquid, the electrolyte is an organic solvent containing an electrolyte salt, and the electrolyte salt is, for example, LiPF ６ , LiClO ４ , LiBF ４ , LiCF ３ SO ３ , LiN(CF ３ SO ２ ) ２ , LiN(C ２F ５ SO ２ ) ２ , LiC(CF ３ SO ３ ) ３ , LiC(C ２ F ５ SO ２ ) ３ Examples of the organic solvent include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, tetrahydrofuran, dioxolane, dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, propyl methyl sulfone, isopropyl methyl sulfone, propyl ethyl sulfone, isopropyl ethyl sulfone, dipropyl sulfone, diisopropyl sulfone, sulfolane, pentamethylene sulfone, hexamethylene sulfone, 3-methyl sulfolane, 2,4-dimethyl sulfolane, N,N-dimethylformamide, dimethylacetamide, N-methyl-2-pyrrolidone, and mixed solvents thereof.

[0065] In the present invention, the concentration of the electrolyte salt is not particularly limited, but can be selected arbitrarily within the range of 0.1 mol / L to 2.5 mol / L, and a common concentration such as 1 mol / L may be used. Furthermore, an electrolyte additive such as fluoroethylene carbonate, vinylene carbonate, hydrofluoroether, or biphenyl may be added to the electrolyte.

[0066] The electrolyte 18 may be a gel electrolyte obtained by impregnating a polymer compound with a solvent to form a gel, an ionic liquid, a symmetric glycol diether such as glyme, or a chain sulfone. Examples of the polymer compound include vinylidene fluoride polymers such as polyvinylidene fluoride, vinylidene fluoride-tetrafluoroethylene copolymer, and vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, acrylonitrile polymers such as acrylonitrile-methyl methacrylate copolymer, polyethylene oxide, ethylene oxide-propylene oxide copolymer, and polymers of these acrylates or methacrylates containing an electrolytic solution.

[0067] [Method for Manufacturing Secondary Battery] The method for manufacturing a secondary battery according to the present invention is a method for manufacturing the aforementioned secondary battery 9, and is a method for manufacturing a secondary battery having at least a positive electrode 12, a negative electrode 14, and an electrolyte 18. The secondary battery 9 manufactured by this method has the characteristics of a low irreversible capacity because the negative electrode 14 is pre-doped, and a high energy density and a low capacity decrease even with repeated charge-discharge cycles because a passive layer is present on the surface of the negative electrode active material. Furthermore, because pre-doping by an electrochemical method is performed under pressure within a specific temperature range, the battery is also characterized by smoothness and excellent adhesion to the electrode.

[0068] A general method for manufacturing a lithium ion secondary battery includes an electrode forming step, an electrode and separator lamination step, an electrolyte injection / impregnation step, an electrode extraction step, an exterior packaging step, etc. In the present invention, a general method for manufacturing a lithium ion secondary battery can be used except for the above-mentioned pre-doping step for the pre-doped electrode layer.

[0069] The technical scope of the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

[0070] The present invention will be further described in more detail below with reference to examples and comparative examples.

[0071] [Example 1] (Preparation of Secondary Battery) 7.0 g of silicon powder, 1.5 g of acetylene black, and 15 g of a 10% aqueous solution of 60% neutralized sodium polyacrylate with an average molecular weight of 490,000 were weighed out, and purified water was added and mixed uniformly to form a mixture. Purified water was further added to this mixture to adjust the viscosity, and a negative electrode slurry for coating the negative electrode active material layer was prepared. This slurry was applied to a Cu foil with a coating thickness of 100 μm, a width of 130 mm, and a thickness of 20 μm using a knife roll coater, and dried at 80 ° C. Then, a 25 μm electrode layer was formed on the Cu foil current collector by roll pressing. This negative electrode active material layer formation process resulted in a pre-doped electrode having a gray electrode layer with silicon as the active material on the current collector.

[0072] The obtained electrode was cut into a length of 20 mm and a width of 50 mm, and a tab for electrode extraction was welded to the uncoated part. Next, in a dry room with a dew point of −45° C. or less, a nonwoven fabric having a thickness of 100 μm was laminated, and 1M of LiPF ６ An electrolyte solution consisting of a mixed solution of 10% by volume of fluoroethylene carbonate, 27% by volume of ethylene carbonate, and 63% by volume of diethyl carbonate containing 10% by volume of fluoroethylene carbonate was dropped onto the electrode, and a lithium foil-laminated copper foil (lithium foil thickness: 100 μm) cut into a length of 25 mm and a width of 55 mm was laminated on the electrode. An insulating stainless steel plate was placed on the outside of the lithium foil-laminated copper foil thus prepared, and the temperature was kept at 60° C. and pressurized at a pressure of 1.0 MPa, and a constant current electrolysis reaction was performed on the negative electrode active material at 10 A / g up to 1000 mAh / g.

[0073] Curve a in Figure 4 is a graph showing the change in voltage versus capacity. These results demonstrate that pre-doping under pressure at 60°C ensures a smooth reaction even at a current as high as 10 A / g. It took 6 minutes to reach 1000 mAh / g. After the reaction was complete, the negative electrode, which had turned black, was removed, washed with dimethyl carbonate, and air-dried in a dry room to obtain a negative electrode made of silicon pre-doped with lithium.

[0074] Next, 9.4 g of nickel-cobalt-manganese lithium oxide (Ni:Co:Mn = 1:1:1, LiNMC), 0.4 g of acetylene black, and 0.3 g of polyvinylidene fluoride (PVDF) were weighed out and kneaded with NMP to form a mixture. NMP was further added to this mixture to adjust the viscosity, and a positive electrode slurry for coating was prepared. This positive electrode slurry was coated on an Al foil with a coating thickness of 150 μm, a width of 130 mm, and a thickness of 20 μm using a knife roll coater, and dried at 120 ° C. Thereafter, by roll pressing, a 60 μm thick positive electrode active material layer was formed on the aluminum foil as a current collector, and a positive electrode using LiNMC as the positive electrode active material was obtained.

[0075] The positive electrode prepared as described above was punched out to a diameter of 13 mm and placed on the positive electrode case of a coin-type battery, and a 20 μm thick separator made of a polypropylene porous film was laminated on top of it. Furthermore, a pre-doped negative electrode punched out to a diameter of 14 mm was laminated and impregnated with an electrolyte solution consisting of a 10% by volume fluoroethylene carbonate, 27% by volume ethylene carbonate, and 63% by volume diethyl carbonate mixed solution containing 1M LiPF6. Next, as shown in FIG. 4, the pre-doped negative electrode and a metal spring were placed on top of each other, and the negative electrode side member, the periphery of which was covered with a gasket, was placed on top of each other, and the exterior was sealed using a crimping machine. In this way, a sealed coin-type secondary battery was prepared, consisting of LiNMC as the positive electrode active material and silicon pre-doped with lithium as the negative electrode active material.

[0076] (Confirmation of Secondary Battery Operation) The produced coin-type secondary battery was charged at a constant current of 0.54 mA until the voltage reached 4.2 V, and then discharged at a constant current of 0.54 mA until the voltage reached 2.5 V. As a result, it was confirmed that this cell was a secondary battery with a discharge capacity of 3.1 mAh. After that, it was repeatedly charged and discharged in the range of 2.5 to 4.2 V, and the capacity density was 80% or more of the initial value even after 100 cycles, confirming that this was a secondary battery with a long cycle life and little capacity loss even after repeated charge and discharge.

[0077] Comparative Example 1 (Preparation of Secondary Battery) The coated negative electrode prepared by the method of Example 1 was cut out in the same manner as in Example 1, a nonwoven fabric was laminated thereon, an electrolyte solution was dropped thereon, and a lithium-laminated copper foil was further laminated thereon. A stainless steel plate that had been insulated in the same manner as in Example 1 was laminated on the outside of the electrode and lithium-laminated copper foil prepared in this manner. A constant current electrolysis reaction was carried out on the negative electrode active material at 10 A / g up to 1000 mAh / g in the same manner as in Example 1, except that the temperature was changed to 25°C instead of 60°C.

[0078] The change in voltage versus capacity at this time is shown in curve b of Figure 5. From this result, it was found that pre-doping at a large current of 10 A / g at 25°C did not proceed uniformly even under pressure. After the reaction was completed, a gray precipitate thought to be metallic lithium was formed on the electrode surface (photograph on the left side of Figure 6), so a battery was not fabricated.

[0079] Comparative Example 2 (Preparation of Secondary Battery) The coated negative electrode prepared by the method of Example 1 was cut out in the same manner as in Example 1, a nonwoven fabric was laminated thereon, an electrolyte solution was dropped thereon, and a lithium-laminated copper foil was further laminated thereon. A stainless steel plate that had been insulated in the same manner as in Example 1 was laminated on the outside of the electrode and lithium-laminated copper foil prepared in this manner. A constant current electrolysis reaction was carried out on the negative electrode active material up to 1000 mAh / g in the same manner as in Example 1, except that the temperature was 25°C instead of 60°C and the current was 200 mA / g.

[0080] The change in voltage versus capacity at this time is shown in curve c of Figure 5. From these results, it was found that a smooth reaction occurred even at 25°C with 200 mA / g pre-doping. It took 5 hours to reach 1000 mAh / g. After the reaction was completed, the negative electrode, which had turned black, was removed, washed with dimethyl carbonate, and air-dried in a dry room to obtain a negative electrode made of silicon pre-doped with lithium.

[0081] Using the negative electrode made of silicon pre-doped with lithium obtained in this way, a sealed coin-type secondary battery made of LiNMC as the positive electrode active material and silicon pre-doped with lithium as the negative electrode active material was produced in the same manner as in Example 1.

[0082] (Confirmation of Secondary Battery Operation) The coin-shaped secondary battery fabricated was charged at a constant current of 0.54 mA until the voltage reached 4.2 V, and then discharged at a constant current of 0.54 mA until the voltage reached 2.5 V. As a result, it was confirmed that this cell was a secondary battery with a discharge capacity of 2.1 mAh. After repeated charge and discharge in the range of 2.5 to 4.2 V, the capacity density remained at 80% or more of the initial capacity even after 100 cycles, confirming that this secondary battery had a long cycle life with little capacity loss even after repeated charge and discharge. However, in this case, the time required to reach 1000 mAh / g with pre-doping was 5 hours, making it unsuitable for mass production.

[0083] Comparative Example 3 (Preparation of Secondary Battery) The coated negative electrode prepared by the method of Example 1 was cut out in the same manner as in Example 1, a nonwoven fabric was laminated thereon, an electrolyte solution was dropped thereon, and a lithium-laminated copper foil was further laminated thereon. A stainless steel plate that had been insulated in the same manner as in Example 1 was laminated on the outside of the electrode and lithium-laminated copper foil prepared in this manner. A constant current electrolysis reaction was carried out on the negative electrode active material up to 1000 mAh / g in the same manner as in Example 1, except that the temperature was 125°C instead of 60°C.

[0084] After the reaction was completed, the negative electrode, which had turned black, was taken out, washed with dimethyl carbonate, and air-dried in a dry room to obtain a negative electrode made of silicon pre-doped with lithium.

[0085] Using the negative electrode made of silicon pre-doped with lithium obtained in this manner, a sealed coin-type secondary battery made of LiNMC as the positive electrode active material and silicon pre-doped with lithium as the negative electrode active material was produced in the same manner as in Example 1.

[0086] (Confirmation of Secondary Battery Operation) The produced coin-type secondary battery was charged at a constant current of 0.54 mA until the voltage reached 4.2 V, and then discharged at a constant current of 0.54 mA until the voltage reached 2.5 V. As a result, it was confirmed that this cell was a secondary battery with a discharge capacity of 2.1 mAh. After that, when it was repeatedly charged and discharged in the range of 2.5 to 4.2 V, the capacity density fell to 80% or less of the initial value after 100 cycles, and it was confirmed that this secondary battery had a short charge-discharge cycle life.

[0087] [Example 2] (Preparation of Secondary Battery) 1.0 g of silicon powder, 7.0 g of artificial graphite, 1.2 g of acetylene black, and 8 g of a 10% solution of polyvinylidene fluoride with an average molecular weight of 50,000 in N-methylpyrrolidone were weighed out, and N-methylpyrrolidone was added to adjust the viscosity, to prepare a negative electrode slurry for coating. This slurry was coated onto a 20 μm thick Cu foil with a coating thickness of 100 μm, a width of 130 mm, and a thickness of 100 μm using a knife roll coater, and dried at 80 ° C. Then, by roll pressing, a 40 μm thick negative electrode active material layer was formed on the Cu foil current collector, and a coated electrode was obtained using silicon-containing artificial graphite as the active material and polyvinylidene fluoride as the binder.

[0088] Using the obtained electrode, a nonwoven fabric containing an electrolyte solution and a lithium foil-laminated copper foil were laminated in the same manner as in Example 1. The temperature was maintained at 60 ° C., and a constant current electrolysis reaction was carried out on the negative electrode active material at 10 A / g up to 1000 mAh / g while applying pressure of 1.0 MPa. The time required to reach 1000 mAh / g was 6 minutes. After the reaction was completed, the negative electrode, which had turned black, was removed, washed with dimethyl carbonate, and air-dried in a dry room to obtain a negative electrode made of silicon pre-doped with lithium.

[0089] Using the negative electrode made of silicon pre-doped with lithium obtained in this manner, a sealed coin-type secondary battery made of LiNMC as the positive electrode active material and silicon pre-doped with lithium as the negative electrode active material was produced in the same manner as in Example 1.

[0090] (Confirmation of Secondary Battery Operation) The produced coin-type secondary battery was charged at a constant current of 0.54 mA until the voltage reached 4.2 V, and then discharged at a constant current of 0.54 mA until the voltage reached 2.5 V. As a result, it was confirmed that this cell was a secondary battery with a discharge capacity of 3.1 mAh. After that, it was repeatedly charged and discharged in the range of 2.5 to 4.2 V, and the capacity density was 80% or more of the initial value even after 100 cycles, confirming that this was a secondary battery with a long cycle life and little capacity loss even after repeated charge and discharge.

[0091] [Example 3] (Preparation of Secondary Battery) 1.0 g of SiO powder, 7.0 g of artificial graphite, 1.5 g of acetylene black, and 15 g of a 10% aqueous solution of sodium polyacrylate with an average molecular weight of 450,000 were weighed out, and purified water was added and kneaded to homogeneity. Purified water was further added to this mixture to adjust the viscosity, and a negative electrode ink for coating was prepared. This ink was coated and dried in the same manner as in Example 1, and pre-doped under a pressure of 1.0 MPa in the same manner as in Example 1 to prepare a negative electrode containing SiO and acetylene black.

[0092] A sealed coin-type secondary battery was fabricated in the same manner as in Example 1, except that a negative electrode containing SiO and artificial graphite was used instead of the negative electrode containing silicon and acetylene black in Example 1. The positive electrode was LiNMC, and the negative electrode was composed of SiO and graphite pre-doped with lithium under pressure.

[0093] (Confirmation of Secondary Battery Operation) The produced coin-type secondary battery was charged at a constant current of 0.24 mA until the voltage reached 4.0 V, and then discharged at a constant current of 0.24 mA until the voltage reached 1.5 V. As a result, it was confirmed that this cell was a secondary battery with a discharge capacity of 4.1 mAh. After that, it was repeatedly charged and discharged in the range of 1.5 to 4.0 V, and the capacity density was 80% or more of the initial value even after 100 cycles, confirming that this was a secondary battery with a long cycle life and little capacity loss even after repeated charge and discharge.

[0094] [Example 4] 9.0 g of artificial graphite, 0.5 g of acetylene black, and 4 g of an N-methylpyrrolidone solution containing 12% polyvinylidene fluoride with an average molecular weight of 500,000 were weighed out and kneaded to prepare a negative electrode ink for coating. This ink was coated and dried in the same manner as in Example 1, and pre-doped under a pressure of 1.0 MPa in the same manner as in Example 1 to prepare a negative electrode containing artificial graphite.

[0095] A sealed coin-type secondary battery was fabricated in the same manner as in Example 1, except that a negative electrode containing artificial graphite was used instead of the negative electrode containing silicon and acetylene black in Example 1. The positive electrode was LiNMC, and the negative electrode was artificial graphite pre-doped with lithium under pressure.

[0096] (Confirmation of Secondary Battery Operation) The produced coin-type secondary battery was charged at a constant current of 0.24 mA until the voltage reached 4.0 V, and then discharged at a constant current of 0.24 mA until the voltage reached 2.5 V. As a result, it was confirmed that this cell was a secondary battery with a discharge capacity of 2.1 mAh. After that, it was repeatedly charged and discharged in the range of 2.5 to 4.0 V, and the capacity density was 80% or more of the initial value even after 100 cycles, confirming that this was a secondary battery with a long cycle life and little capacity loss even after repeated charge and discharge.

[0097] [Example 5] (Preparation of Secondary Battery) 7.5 g of rubeanic acid, 1.5 g of vapor-grown carbon fiber (VGCF), and 1.0 g of polytetrafluoroethylene resin binder were weighed out, and purified water was added and kneaded while uniformly mixing. Ion-exchanged water was further added to this mixture to adjust the viscosity, producing a positive electrode coating slurry. This slurry was applied to a 20 μm thick Al foil with a coating thickness of 100 μm, a width of 130 mm, and a thickness of 20 μm using a knife roll coater, dried at 80° C., and then punched out into a circle with a diameter of 12 mm to prepare a positive electrode containing rubeanic acid.

[0098] The positive electrode prepared as described above was placed on the positive electrode case of a coin-type battery, and a separator made of a polypropylene porous film with a thickness of 20 μm was laminated thereon. Further, the pre-doped silicon negative electrode prepared by the method of Example 1 was laminated thereon, and 1M LiN(C ２ F ５ SO ２ ) ２ The battery was impregnated with an electrolyte solution consisting of sulfolane containing . Next, a negative electrode current collector plate and a metal spring were placed on top of the negative electrode member whose periphery was covered with a gasket, and the exterior was sealed using a crimping machine. In this way, a sealed coin-type secondary battery was fabricated, which consisted of rubeanic acid as the positive electrode active material and silicon pre-doped with lithium as the negative electrode active material.

[0099] (Confirmation of Secondary Battery Operation) The produced coin-type secondary battery was charged at a constant current of 0.24 mA until the voltage reached 4.0 V, and then discharged at a constant current of 0.24 mA until the voltage reached 1.5 V. As a result, it was confirmed that this cell was a secondary battery with a discharge capacity of 4.1 mAh. After that, it was repeatedly charged and discharged in the range of 1.5 to 4.0 V, and the capacity density was 50% or more of the initial value even after 100 cycles, confirming that this was a secondary battery with a long cycle life and little capacity loss even after repeated charge and discharge.

[0100] REFERENCE SIGNS LIST 1 Pre-doped electrode current collector 2 Pre-doped electrode layer 3 Counter electrode 4 Liquid-permeable elastic body 5 Pre-doped double-sided electrode 6 Pressure plate 7 Unwinding roll 8 Winding roll 9 Secondary battery 10 Positive electrode case 11 Negative electrode case 12 Positive electrode 13 Separator 14 Negative electrode 15 Negative electrode current collector 16 Metal spring 17 Gasket 18 Electrolyte

Claims

1. A method for manufacturing an electrode for a secondary battery, comprising the steps of forming an electrode active material layer containing at least an electrode active material, a conductive material and a binder to prepare a pre-doped electrode layer, and a pre-doping step of contacting the pre-doped electrode layer with a liquid, gel or solid electrolyte containing lithium and introducing lithium ions by an electrochemical method while applying pressure, characterized in that the pre-doping step by the electrochemical method is carried out at a temperature range of 30°C or higher and 120°C or lower.

2. The method for producing an electrode for a secondary battery according to claim 1, wherein the electrode active material is a negative electrode active material made of sulfur or a compound containing sulfur.

3. The method for producing an electrode for a secondary battery according to claim 1, wherein the electrode active material is a negative electrode active material made of a compound containing a quinone structure.

4. The method for producing an electrode for a secondary battery according to claim 1, wherein the electrode active material is a negative electrode active material made of silicon or a silicon compound.

5. The method for producing an electrode for a secondary battery according to claim 1, wherein the electrode active material is a negative electrode active material made of graphite.

6. A method for manufacturing an electrode for a secondary battery described in any one of claims 1 to 5, wherein the process of pre-doping lithium by the electrochemical method uses lithium or a lithium-containing metal as a counter electrode and applies a voltage of 0 V or less to the pre-doped electrode layer relative to the counter electrode.

7. A secondary battery having at least a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode or the positive electrode is an electrode for a secondary battery manufactured by the method for manufacturing an electrode for a secondary battery according to any one of claims 1 to 6.

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