Composite anode for lithium secondary battery and its manufacturing method

Abstract

The present invention relates to a composite negative electrode for a lithium secondary battery and a method for manufacturing the same. The method for manufacturing a composite negative electrode for a lithium secondary battery according to the present invention allows for the production of a composite negative electrode for a lithium secondary battery in which lithium metal or a lithium metal composite is evenly distributed and positioned using a simple pulse electrodeposition method while minimizing the amount of lithium used. Therefore, it has excellent stability and economic efficiency. The composite negative electrode for a lithium secondary battery produced in this manner has the advantage of suppressing the growth of lithium dendrites during charging, as the lithium metal or a lithium metal composite is uniformly positioned on a porous conductor.

Description

Technology Field

[0001] The present invention relates to a composite negative electrode for a lithium secondary battery and a method for manufacturing the same. Background Technology

[0002] With the development of the information and communication industry, there is a growing demand for the miniaturization, lightweighting, thinning, and portability of electronic devices, leading to an increasing need for higher energy density in lithium-ion batteries used as power sources for these devices.

[0003] Lithium secondary batteries, specifically lithium-ion batteries (LIBs), are the batteries that best meet these requirements. They have high energy density and are easy to design, so they have been adopted as power sources for many portable devices.

[0004] Recently, as the scope of application for lithium-ion batteries has expanded from conventional small electronic devices to large electronic devices, automobiles, and smart grids, there is a demand for lithium-ion batteries that can maintain excellent performance not only at room temperature but also in harsher external environments, such as high or low temperatures.

[0005] At this time, lithium, used in lithium secondary batteries, is a material with the lowest electromotive force among elements, and by using it as the negative electrode of the battery, a battery with high energy density can be expected.

[0006] However, in the case of a negative electrode using lithium metal, if lithium foil is used as the negative electrode, it may precipitate in the form of dendrites on the surface of the negative electrode during charging. The formed dendrites are very dangerous as they cause internal short circuits when they come into contact with the positive electrode, and furthermore, if charging and discharging are repeated, they detach from the surface of the negative electrode and generate lithium in the form of fine particles that cannot be used for charging and discharging, thereby reducing the charge / discharge capacity. Therefore, there was a difficulty in manufacturing a secondary battery with a long charge / discharge cycle life.

[0007] In addition, conventional methods of manufacturing a cathode using a slurry made of lithium powder had problems such as explosion due to the high reactivity of the lithium powder, large variations in the particle size distribution of the lithium powder, and high maintenance costs because the reactor had to be maintained at a high temperature for a long time. Prior art literature

[0008] Republic of Korea Registered Patent Publication No. 10-1762773 The problem to be solved

[0009] The present invention is intended to solve the above-mentioned problems, and its specific objectives are as follows.

[0010] The present invention aims to provide a method for manufacturing a composite negative electrode for a lithium secondary battery by applying voltage or current under specific conditions to pulse electrodeposit lithium metal onto a porous conductor.

[0011] In addition, the present invention aims to provide a composite negative electrode for a lithium secondary battery comprising a porous conductor and a lithium metal or lithium metal composite evenly positioned on the porous conductor in a specific content and a specific size.

[0012] The objectives of the present invention are not limited to those mentioned above. The objectives of the present invention will become clearer from the following description and will be realized by the means and combinations thereof described in the claims. means of solving the problem

[0013] A method for manufacturing a composite negative electrode for a lithium secondary battery according to one aspect comprises the steps of: preparing an electrolyte containing a lithium salt and a solvent; arranging a working electrode containing a porous conductor and a counter electrode containing lithium metal within the electrolyte; and applying a voltage or current through a power supply device connected to the working electrode and the counter electrode to pulse electrodeposit lithium metal onto the porous conductor.

[0014] The above lithium salt may include one or more selected from the group consisting of LiPF6, LiBF4, LiTFSI, LiClO4, LiTf, LiAsF6, LiFSA, LiBOB, LiDFOB, LiBETI, LiDCTA, LiTDI, LiPDI, LiI, LiF, and LiCl.

[0015] The above solvent may include one or more selected from organic solvents and ionic liquids.

[0016] The above lithium salt may be included in the electrolyte at a concentration of 0.05 M to 2 M.

[0017] The porous conductor may include one or more selected from the group consisting of carbon nanotubes, carbon felt, carbon paper, and carbon fiber.

[0018] When the above pulse electrodeposition occurs, the voltage may be applied at a value 1.0V to 2V higher than the absolute value of the lithium reduction potential.

[0019] When performing the above pulse electrodeposition, the number of pulses may be 50 to 2000 times.

[0020] When performing the above pulse electrodeposition, the pulse time may be 10 ms to 1000 ms.

[0021] When the above pulse electrodeposition is performed, the operating temperature may be 200℃ or lower.

[0022] The method may further include the step of plating a lithium alloy onto the porous conductor.

[0023] The above lithium alloy may include i) lithium (Li) and ii) one or more selected from the group consisting of gold (Au), silver (Ag), tin (Sn), copper (Cu), aluminum (Al), magnesium (Mg), nickel (Ni), titanium (Ti), silicon (Si), and antimony (Sb).

[0024] During the above pulse electrodeposition, lithium metal can be pulse electrodeposited on the lithium alloy.

[0025] The above pulse electrodeposited product may further include a step of surface modification.

[0026] A composite negative electrode for a lithium secondary battery according to another aspect may include a porous conductor; and a lithium metal uniformly positioned on the porous conductor.

[0027] The content of the lithium metal may be 0.05 weight% to 30 weight% based on 100 weight% of the total composite cathode.

[0028] The size of the lithium metal may be 5 nm to 100 nm.

[0029] A composite negative electrode for a lithium secondary battery according to another aspect comprises a porous conductor; and a lithium metal composite uniformly positioned on the porous conductor, wherein the lithium metal composite comprises lithium metal on a lithium alloy.

[0030] The above lithium alloy may include i) lithium (Li) and ii) one or more selected from the group consisting of gold (Au), silver (Ag), tin (Sn), copper (Cu), aluminum (Al), magnesium (Mg), nickel (Ni), titanium (Ti), silicon (Si), and antimony (Sb).

[0031] The size of the lithium metal composite may be 10 μm to 200 μm. Effects of the invention

[0032] The method for manufacturing a composite negative electrode for a lithium secondary battery according to the present invention has the advantage of excellent economic efficiency, such as significantly reducing the number of manufacturing process steps, because it enables the production of a composite negative electrode for a lithium secondary battery in which lithium metal or a lithium metal composite is evenly distributed using a simple pulse electrodeposition method while minimizing the amount of lithium used.

[0033] In addition, the composite negative electrode for a lithium secondary battery manufactured by the manufacturing method according to the present invention has the advantage of being able to suppress the growth of lithium dendrites during charging, as lithium metal or a lithium metal composite is uniformly located on a porous conductor.

[0034] The effects of the present invention are not limited to those mentioned above. It should be understood that the effects of the present invention include all effects that can be inferred from the following description. Brief explanation of the drawing

[0035] FIG. 1 is a cross-sectional view and an enlarged view of a composite negative electrode for a lithium secondary battery containing lithium metal according to the present invention. FIG. 2 is a cross-sectional view and an enlarged view of a composite negative electrode for a lithium secondary battery containing a lithium metal composite according to the present invention. Figure 3 is an FE-SEM image of the surface of a composite negative electrode (including a lithium metal composite) for a lithium secondary battery prepared according to Preparation Example 1. Figure 4 is a graph showing the results of lithium particle removal according to the pulse level of a composite negative electrode (including a lithium metal composite) for a lithium secondary battery prepared according to Example 1. FIG. 5 is a charge-discharge graph of an all-solid-state battery according to Example 1, Comparative Example 1, and Comparative Example 2 above. Figure 6 is a graph of the cycle characteristic evaluation results of all-solid-state batteries according to Example 1, Comparative Example 1, and Comparative Example 2. FIGS. 7a to 7c are graphs of the cycle characteristic evaluation results of all-solid-state batteries according to Example 1 (Fig. 7a), Comparative Example 1 (Fig. 7b), and Comparative Example 2 (Fig. 7c). Specific details for implementing the invention

[0036] The above objects, other objects, features, and advantages of the present invention will be easily understood through the following preferred embodiments associated with the accompanying drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided to ensure that the disclosed content is thorough and complete and to ensure that the spirit of the invention is sufficiently conveyed to a person skilled in the art.

[0037] In describing each drawing, similar reference numerals have been used for similar components. In the attached drawings, the dimensions of the structures are depicted enlarged from their actual size for clarity of the invention. Terms such as "first," "second," etc., may be used to describe various components, but said components should not be limited by said terms. These terms are used solely for the purpose of distinguishing one component from another. For example, without departing from the scope of the invention, the first component may be named the second component, and similarly, the second component may be named the first component. A singular expression includes a plural expression unless the context clearly indicates otherwise.

[0038] In this specification, terms such as "comprising" or "having" are intended to specify the existence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof. Furthermore, when a part such as a layer, film, region, or plate is described as being "on" another part, this includes not only the case where it is "immediately above" the other part, but also the case where there is another part in between. Conversely, when a part such as a layer, film, region, or plate is described as being "below" another part, this includes not only the case where it is "immediately below" the other part, but also the case where there is another part in between.

[0039] Unless otherwise specified, all numbers, values, and / or expressions used herein to represent amounts of ingredients, reaction conditions, polymer compositions, and formulations should be understood to be modified by the term “approximately” in all cases, as these numbers are essentially approximations reflecting the various uncertainties of measurement that occur in obtaining these values ​​among other things. Furthermore, where numerical ranges are disclosed herein, such ranges are continuous and, unless otherwise indicated, include all values ​​from the minimum value of such range to the maximum value including said maximum value. Moreover, where such ranges refer to integers, they include all integers from the minimum value to said maximum value including said maximum value, unless otherwise indicated.

[0040] In this specification, where a range is described for a variable, it will be understood that the variable includes all values ​​within the described range, including the described endpoints of the range. For example, the range “5 to 10” will be understood to include not only the values ​​5, 6, 7, 8, 9, and 10, but also any sub-ranges such as 6 to 10, 7 to 10, 6 to 9, 7 to 9, etc., and any values ​​between integers valid for the category of the described range, such as 5.5, 6.5, 7.5, 5.5 to 8.5, and 6.5 to 9. Also, for example, the range “10% to 30%” will be understood to include all integers including values ​​such as 10%, 11%, 12%, 13%, etc. and up to 30%, as well as any sub-range such as 10% to 15%, 12% to 18%, 20% to 30%, etc., and any value between valid integers within the stated range category such as 10.5%, 15.5%, 25.5%, etc.

[0042] Conventionally, when lithium used in lithium secondary batteries is used in the form of lithium foil for the negative electrode, there is a problem of high manufacturing costs due to the large amount of lithium used. Furthermore, during charging, not only do dendrites grow and precipitate on the surface of the negative electrode, but as lithium undergoes repeated plating and stripping during charging and discharging, the contact surface with the current collector decreases, reducing the electron transport path and causing an uneven current distribution, thereby accelerating the growth of lithium dendrites. Consequently, if the aforementioned growing and accelerated dendrites come into contact with the positive electrode, they cause an internal short circuit, which is very dangerous. Additionally, if charging and discharging are repeated, they detach from the surface of the negative electrode, generating lithium in the form of fine particles that cannot be used for charging and discharging, which reduces the charge / discharge capacity.

[0043] In addition, conventional methods of manufacturing a cathode using a slurry made of lithium powder had problems such as explosion due to the high reactivity of the lithium powder, large variations in the particle size distribution of the lithium powder, and high maintenance costs because the reactor had to be maintained at a high temperature for a long time.

[0044] Accordingly, the inventors of the present invention, having conducted diligent research to solve the above problem, discovered that when manufacturing a composite negative electrode for a lithium secondary battery by applying voltage or current under specific conditions to pulse electrodeposit lithium metal onto a porous conductor, the growth of lithium dendrites can be significantly suppressed by including a porous conductor and a lithium metal or lithium metal composite evenly distributed on the porous conductor in a specific amount and size, and thus completed the present invention.

[0046] A method for manufacturing a composite negative electrode for a lithium secondary battery according to the present invention comprises the steps of: preparing an electrolyte containing a lithium salt and a solvent (S10); arranging a working electrode containing a porous conductor and a counter electrode containing lithium metal within the electrolyte (S20); and applying a voltage or current through a power supply device connected to the working electrode and the counter electrode to pulse electrodeposit lithium metal onto the porous conductor (S30).

[0047] The term "pulse electrodeposition" used in the present invention means electrodepositing lithium metal onto a working electrode containing a porous conductor through electrolysis by applying pulse voltage or current periodically for a certain period of time through a power supply device connected to a working electrode and a counter electrode.

[0048] The step of preparing the above electrolyte (S10) is a step of preparing an electrolyte used for electrolysis for pulse electrodeposition.

[0049] The above electrolyte may include a lithium salt and a solvent.

[0050] The above lithium salt is not particularly limited as long as it is a salt that enables lithium ions to move through electrolysis for pulse electrodeposition, and may include, for example, one or more selected from the group consisting of LiPF6, LiBF4, LiTFSI, LiClO4, LiTf, LiAsF6, LiFSA, LiBOB, LiDFOB, LiBETI, LiDCTA, LiTDI, LiPDI, and LiI, LiF, and LiCl, and is not limited to including only specific components.

[0051] The above solvent is not particularly limited as long as it is a substance capable of dissolving the lithium salt, and specifically, it may include one or more selected from organic solvents and ionic liquids. For example, the organic solvent may include one or more selected from the group consisting of PC, EC, DME, DEC, DMC, FEC, DOL, DMI, DMSO, TEGDME, EEE, PEGDME, and DEGDME, and is not limited to including only specific components. In addition, the above ionic liquid may include one or more selected as a combination of one or more cations selected from the group consisting of EMIM, BMIM, PP13, Py14, DEME, and DMPI, etc., and one or more anions selected from the group consisting of FSA, TFSI, BF4, PF6, Cl, Br, I, AcO, AlCl4, and EtSO4, etc., and is not limited to including only specific components.

[0052] The concentration of the lithium salt can be appropriately adjusted as long as sufficient lithium ions are supplied during pulse electrodeposition. Preferably, as the operating temperature increases and the viscosity of the electrolyte decreases, a higher concentration of lithium salt can be used. More preferably, it can be included in the electrolyte at a concentration of 0.05 M to 2 M. If the concentration of the lithium salt is too low outside of the above range, sufficient ions are not supplied for nucleation and particle growth, which may cause non-uniformity in distribution and particle size. If the concentration of the lithium salt is too high, dissolution and precipitation of the lithium salt may occur, or the ionic conductivity of the electrolyte may be low, resulting in a disadvantage of low current efficiency.

[0053] The step of placing electrodes in the electrolyte (S20) is a step of preparing and placing a working electrode and a counter electrode, which are a two-electrode system, in the electrolyte prepared in the step S10 in order to perform pulse electrodeposition.

[0054] Specifically, the working electrode is an electrode that undergoes pulse electrodeposition in the electrolysis reaction and may be an electrode in which a reduction reaction has occurred. The working electrode may be a platinum electrode, a gold electrode, a carbon electrode, a mercury electrode, a nickel electrode, etc., and preferably, it may be a carbon electrode containing carbon as a porous conductor with a large specific surface area and electrochemical stability.

[0055] The porous conductor is a conductive material containing carbon, and is not particularly limited as long as it is used as a negative electrode for a lithium secondary battery and is capable of charging and discharging lithium ions, and may include, for example, one or more selected from the group consisting of carbon nanotubes, carbon felt, and carbon fiber.

[0056] The above counter electrode may be an auxiliary electrode that receives or sends current to enable the reaction of the working electrode to be performed smoothly, thereby allowing charge to move and complete the electrical circuit. The above counter electrode may be a carbon electrode, a nickel electrode, a steel electrode, a platinum electrode, a lithium electrode, etc., and preferably, a lithium electrode may be used to reduce lithium metal by pulse electrodeposition.

[0057] The step of pulse electrodepositing the lithium metal (S30) is a step of manufacturing a composite negative electrode for a lithium secondary battery by pulse electrodepositing the lithium metal on a porous conductor through a power supply device connected to a working electrode and a counter electrode by applying voltage or current.

[0058] Specifically, during the pulse electrodeposition, favorable electrolytic conditions advantageous for lithium metal electrodeposition can be achieved by repeatedly applying a voltage under specific conditions and resting. At this time, the distribution and particle size of the reduced lithium metal can be controlled by adjusting the time for applying the pulse potential, the resting time, and the number of repetitions.

[0059] Specifically, the voltage identified according to the constituting pulse electrodeposition system is a value 1.0V to 2V higher than the absolute value of the lithium reduction potential (e.g., Li + +e - →Li metal In the case of -3.04V, it is desirable to apply a voltage of -4.04 to -5.04V. If the voltage is applied too low outside the above range, the nucleation energy is not exceeded, so a sufficient amount of nuclei are not generated, and if it is applied too high, there is a disadvantage that particles are electrodeposited with high particle density and irregular shapes.

[0060] In addition, when applying voltage under the above conditions during the pulse electrodeposition, the pulse time may be 10 ms to 1000 ms. If the pulse time is too short outside this range, the amount of lithium ions reduced on the electrode surface is sparse, and if the pulse time is too long, conditions for particle growth become dominant, making it difficult to form a uniform particle size.

[0061] The above pulse electrodeposition is defined as one cycle in which the voltage is applied for the pulse time within the above voltage range, followed by a rest period of 0.2 to 2 times the pulse time. The number of pulses defining one cycle may be 50 to 2000, preferably 100 to 1000. If the number of pulses is too small outside of the above range, there is a disadvantage that the size of the reduced lithium particles is too small, and if the number of pulses is too large, there is a disadvantage that irregular and coarse lithium in the form of clusters is deposited rather than in the form of independent particles.

[0062] When performing the above pulse electrodeposition, the pulse temperature may vary depending on the solvent of the electrolyte included. For example, in the case of a pulse system for an electrolyte prepared with an organic solvent, the pulse temperature may be 60°C or lower, and preferably 40°C to 50°C. In addition, in the case of a pulse system for an electrolyte prepared with an ionic liquid, the pulse temperature may be 200°C or lower, and preferably 80°C to 150°C. If the pulse temperature is too low outside the above range, there is a disadvantage that the solubility of the lithium salt is low and, in the case of an ionic liquid electrolyte, the viscosity increases; and if it is too high, in the case of an organic solvent, there is a disadvantage that the solvent evaporates and the lithium salt precipitates.

[0063] That is, during the above-mentioned pulse electrodeposition, the dispersion of lithium metal on the porous conductor can be controlled by adjusting the voltage and the number of pulses, so that the lithium metal can be uniformly distributed on the porous conductor, and the size of the lithium metal can be appropriately controlled by adjusting the pulse time, so that the growth of dendrites on the finally produced composite negative electrode for a lithium secondary battery can be efficiently suppressed.

[0064] In addition, the present invention allows for the pulse electrodeposition step to be performed by preparing a composite porous conductor in which a metal capable of alloying with lithium is plated on a porous conductor prior to pulse electrodeposition, and then utilizing this as a working electrode. By plating the metal on the porous conductor, the energy generated to form lithium metal during pulse electrodeposition is reduced, thereby enabling efficient pulse electrodeposition. Furthermore, the plated lithium alloy facilitates the diffusion of lithium during subsequent charging and discharging on the surface, which has the advantage of suppressing irregular dendrite growth.

[0065] Specifically, the step (S15) of preparing the composite porous conductor can be performed by plating using a conventional method that can be used to plate a lithium alloy on the porous conductor in the present invention, for example, by electroplating, electroless plating, physical coating, etc.

[0066] At this time, the lithium alloy used is a metal capable of deionizing lithium metal ions and alloying into lithium metal during subsequent charging and discharging, and may be, for example, an alloy metal comprising i) lithium (Li) and ii) one or more selected from the group consisting of gold (Au), silver (Ag), tin (Sn), copper (Cu), aluminum (Al), magnesium (Mg), nickel (Ni), titanium (Ti), silicon (Si), and antimony (Sb), and is not limited to comprising only specific metals.

[0067] Next, a pulse electrodeposition step is performed in the same manner as the above step so that, as a result, lithium metal is pulse electrodeposited on the lithium alloy, and finally, a composite negative electrode for a lithium secondary battery can be manufactured including a lithium metal composite uniformly located on a porous conductor, which includes lithium metal on the lithium alloy.

[0068] In addition, the method for manufacturing a composite negative electrode for a lithium secondary battery according to the present invention may further include a step (S40) of additionally surface modifying the pulsed electrodeposited product.

[0069] The above surface modification method is not particularly limited as long as it is a method capable of improving wettability on the surface of the pulsed electrodeposited product, and, for example, surface modification can be performed by a method such as nitrogen doping.

[0070] When wettability is improved on the surface of the resulting product through the above surface modification, the movement of lithium ions becomes more smooth, which not only allows for more uniform reduction of lithium metal during charging and discharging but also has the advantage of more efficiently suppressing irregular dendrite growth even at high current densities.

[0071] In other words, the method for manufacturing a composite negative electrode for a lithium secondary battery according to the present invention enables the production of a composite negative electrode for a lithium secondary battery in which lithium metal or a lithium metal composite is evenly distributed using a simple pulse electrodeposition method while minimizing the amount of lithium used, thereby having the advantage of excellent stability as well as excellent economic efficiency.

[0072] FIG. 1 is a cross-sectional view and an enlarged view of a composite negative electrode for a lithium secondary battery containing lithium metal according to the present invention. Referring thereto, the composite negative electrode (1) for a lithium secondary battery according to the present invention is manufactured by the above manufacturing method and includes a porous conductor (10) and a lithium metal (20) uniformly positioned on the porous conductor. The composite negative electrode for a lithium secondary battery containing lithium metal may include content that substantially overlaps with the manufacturing method of the composite negative electrode for a lithium secondary battery described above, and the description of the overlapping parts may be omitted.

[0073] The content of lithium metal uniformly located on the porous conductor may be 0.05 weight% to 30 weight% based on 100 weight% of the total composite cathode.

[0074] The size of the lithium metal distributed in the porous conductor may be 5 nm to 100 nm, and preferably 10 nm to 30 nm. If the size of the lithium metal is too small outside of the above range, it does not provide a sufficient reaction area, which has the disadvantage that the lithium ions of the positive electrode may be consumed by an irreversible reaction during the initial battery reaction. If the size is too large, it cannot maintain a single particle shape and forms a cluster of coarse particles or an irregular surface, which causes a current concentration phenomenon.

[0075] Meanwhile, FIG. 2 is a cross-sectional view and an enlarged view of a composite negative electrode for a lithium secondary battery containing a lithium metal composite according to the present invention. Referring to the above, the composite negative electrode (1') for a lithium secondary battery according to the present invention is manufactured by the above manufacturing method and includes a porous conductor (10) and a lithium metal composite (40) uniformly positioned on the porous conductor. At this time, the lithium metal composite (40) is characterized by including a lithium metal (20) on a lithium alloy (30). The composite negative electrode for a lithium secondary battery containing the above lithium metal composite may include content that substantially overlaps with the manufacturing method of the composite negative electrode for a lithium secondary battery described above, and the description of the overlapping parts may be omitted.

[0076] The size of the lithium metal composite distributed in the porous conductor may be 10 μm to 200 μm. If the size of the lithium metal composite is too small outside of this range, it may not accommodate sufficient lithium, which is a disadvantage as some lithium may be reduced to the copper current collector, and if the size is too large, the thickness of the negative electrode layer becomes excessively thick, which is a disadvantage as the gravimetric energy density decreases.

[0077] That is, the composite negative electrode for a lithium secondary battery according to the present invention has the advantage of efficiently suppressing the growth of lithium dendrites during charging, as lithium metal or a lithium metal composite is uniformly positioned in a specific size on a porous conductor.

[0079] In addition, the lithium secondary battery according to the present invention may include a positive electrode, an electrolyte membrane, and a composite negative electrode for a lithium secondary battery according to the present invention. Specifically, the positive current collectors, the positive electrode, the electrolyte membrane, the composite negative electrode, and the negative current collector may be sequentially stacked. It may include content that substantially overlaps with the aforementioned composite negative electrode for a lithium secondary battery, and the description of the overlapping parts may be omitted.

[0080] The above-mentioned positive current collector may be an aluminum foil, etc.

[0081] The above-mentioned positive electrode is a positive electrode layer that can be used in a conventional lithium secondary battery and may include a solid electrolyte and an active material.

[0082] It may be an oxide active material or a sulfide active material. For example, the oxide active material is LiCoO2, LiMnO2, LiNiO2, LiVO2, Li 1+x Ni 1 / 3 Co 1 / 3 Mn 1 / 3 Rock salt layer type active materials such as O2, LiMn2O4, Li(Ni 0.5 Mn 1.5 Spinel-type active materials such as )O4, inverse spinel-type active materials such as LiNiVO4 and LiCoVO4, olivine-type active materials such as LiFePO4, LiMnPO4, LiCoPO4, and LiNiPO4, silicon-containing active materials such as Li2FeSiO4 and Li2MnSiO4, LiNi 0.8 Co (0.2-x) Al x A salt-layered active material in which a portion of the transition metal is replaced with a heterogeneous metal, such as O2 (0<x<0.2), Li 1+x Mn 2-x-y M y Spinel-type active material in which a portion of the transition metal is replaced with a heterogeneous metal, such as O4 (M is at least one of Al, Mg, Co, Fe, Ni, Zn and 0 < x+y < 2), Li4Ti5O 12 It may be lithium titanate, etc. In addition, the sulfide active material may be copper chevrell, iron sulfide, cobalt sulfide, nickel sulfide, etc.

[0083] The above-mentioned solid electrolyte is a component responsible for lithium ion conduction and may be an oxide-based solid electrolyte or a sulfide-based solid electrolyte. However, it is preferable to use a sulfide-based solid electrolyte with high lithium ion conductivity.

[0084] Specifically, the solid electrolyte may be a solid electrolyte according to the following chemical formula 1.

[0085] [Chemical Formula 1]

[0086] L a Mb P c S d X e

[0087] (In the above chemical formula 1, L is one or more elements selected from the group consisting of alkali metals, M is one or more elements selected from the group consisting of B, Al, Ga, In, Si, Ge, Sn, Pb, As, Sb, Bi, Ti, V, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Hf, Ta, and W, X is one element selected from the group consisting of F, Cl, Br, I, and O, and 0≤a≤12, 0≤b≤6, 0≤c≤6, 0≤d≤12, and 0≤e≤9)

[0088] More preferably, Li6PS5Cl, Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-LiCl, Li2S-P2S5-LiBr, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (where m and n are positive numbers, and Z is one of Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (where x and y are positive numbers, and M is one of P, Si, Ge, B, Al, Ga, or In), Li 10 GeP2S 12 It may include one or more types selected from a group consisting of the following.

[0089] In addition, the anode layer may further include a conductive material to improve electrical conductivity. Preferably, it may include carbon black, conducting graphite, ethylene black, graphene, etc.

[0090] The above-mentioned negative current collector may be a metal thin film comprising a metal selected from the group consisting of copper (Cu), nickel (Ni), and combinations thereof.

[0091] In addition, the lithium secondary battery according to the present invention can be joined to a flow path using a gasket or the like.

[0093] The present invention will be explained in more detail through the following examples. The following examples are merely illustrative to aid in understanding the present invention and do not limit the scope of the present invention.

[0095] Preparation Example 1: Preparation of a composite negative electrode for a lithium secondary battery comprising a lithium metal composite

[0096] An electrolyte for electrodepositing lithium metal particles onto a porous conductor was prepared by mixing a lithium salt of 1 M lithium bis(trifluoromethanesulfony)imide (LiTFSI) with an ionic liquid N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide (Py14TFSI) as the electrolyte and stirring at a temperature of 80°C for 1 hour (S10). Since the ionic liquid, which consists solely of ions, exhibits a relatively higher viscosity than other organic solvents, propylene carbonate was mixed into the electrolyte at a weight ratio of 20%. A two-electrode electrolytic system was constructed using carbon fiber as the working electrode and a lithium ribbon as the counter electrode in the above electrolyte. At this time, the working electrode and the counter electrode were placed at a distance of 5 mm, and the surface area of ​​the counter electrode was made sufficiently larger than the reaction surface area of ​​the working electrode (S20). .

[0097] As shown in Equation 1, the shape of lithium metal particles formed in a lithium metal composite can be controlled by varying the pulse level; when a high pulse level is applied by controlling the applied voltage to be high and the pulse time to be short, the particle size becomes smaller and the number of particles per unit area increases. Conversely, when a low pulse level is applied by lowering the applied voltage or controlling the pulse time to be long, the nucleation rate decreases and conditions for particle growth become dominant; consequently, a composite is obtained in which the number of particles decreases and coarse particles are distributed. Utilizing the above characteristics, 1.5 V vs.Li reduction Pulse voltage is applied to pulse electrodeposition such that the number of pulses is 1,000 during a pulse time of 1,000 ms, thereby depositing 100 nm on the surface of the conductive structure 2 A lithium metal composite was manufactured having 24 to 29 lithium metal particles formed per unit area (S30).

[0099] Example 1: Preparation of an all-solid-state battery comprising a composite negative electrode (including a lithium metal composite) for a lithium secondary battery

[0100] A positive electrode slurry was prepared by mixing a positive electrode active material (NCM711), a solid electrolyte (Li6PS5Cl), a conductive agent (Super-C), and a rubber-based binder. The positive electrode obtained therefrom was prepared by coating the slurry onto an aluminum foil and drying it. The positive electrode obtained therefrom was punched to a size of Φ13 and used as a positive electrode layer. A solid electrolyte layer of 0.15 to 1.5 g and a lithium metal composite prepared in Example 1 were introduced as a negative electrode layer, and an all-solid-state battery was prepared by pressure molding at a pressure of 200 to 500 MPa.

[0102] Comparative Example 1: Lithium foil negative electrode and all-solid-state battery manufacturing method

[0103] A lithium foil negative electrode was manufactured by punching a 200 μm thick lithium foil and a copper current collector to a size of Φ13 and sequentially stacking them. An all-solid-state battery was fabricated using the same method as in Example 1, except that the lithium foil negative electrode was used as the negative electrode layer.

[0105] Comparative Example 2: Lithium powder anode and all-solid-state battery manufacturing method

[0106] A binder solution was prepared by mixing 2 to 15 weight percent of polyvinylidene fluoride (PVDF) with N-methylpyrrolidone (NMP) as a solvent. Lithium powder with a size of 10 to 30 μm was added to this solution in a weight percent of 85 to 98 percent, mixed, and then coated onto a copper current collector to dry the solvent. The dried electrode was punched to a size of Φ13 to produce a lithium powder negative electrode. An all-solid-state battery was fabricated using the same method as in Example 1, except that the lithium powder negative electrode was used as the negative electrode layer.

[0108] Experimental Example 1: Preparation of Lithium Metal Composite and Particle Size Control

[0109] Figure 3 is an FE-SEM image of the surface of a composite negative electrode (including a lithium metal composite) for a lithium secondary battery prepared according to Example 1. Referring to Figure 3, it can be confirmed that lithium metal particles with a size of 10 to 30 nm are evenly distributed on the surface of the carbon fiber, and the number and particle size of the lithium metal particles can be determined by controlling the pulse level. Since the pulse level is proportional to the pulse voltage (V) and inversely proportional to the pulse time (s), it can be determined as shown in Equation 1 below. For example, when the applied voltage is -4.5 V and the pulse time is 1000 ms, the pulse voltage is 1.5 V, so the pulse level is 15.

[0110]

[0111] Figure 4 is a graph showing the results of lithium particle removal according to the pulse level of a composite negative electrode (including a lithium metal composite) for a lithium secondary battery prepared according to Preparation Example 1. Referring to this, when the pulse level is low, ranging from 1 to 9, the number of lithium particles generated is 100 nm 2 It can be seen that when the pulse level is high at 15 to 20, a relatively low number of 7 to 12 particles are formed, and particle growth is dominant, resulting in the formation of coarse particles, and when the pulse level is high at 15 to 20, a large number of lithium particles are generated at 35 to 42 particles per unit area.

[0113] Experimental Example 2: Comparison of Charge & Discharge Characteristics of All-Solid State Batteries

[0114] All-solid-state batteries were manufactured according to Example 1, Comparative Example 1, and Comparative Example 2, and then the cell temperature was maintained at 60°C and charging and discharging were performed at a rate of 0.1C in a voltage range of 3.0 to 4.3V to evaluate the charge-discharge characteristics. The results are shown in Tables 1 and 2 and Figure 5.

[0115] Specifically, FIG. 5 is a charge-discharge graph of an all-solid-state battery according to Example 1, Comparative Example 1, and Comparative Example 2.

[0116] division Lithium metal weight (mg) Lithium weight ratio in cathode (%) Example 1 0.056 0.06 Comparative Example 1 12.6 100 Comparative Example 2 2.5 95

[0117] division Discharge capacity (mAh / g) Coulomb efficiency (%) Example 1 184.4 84.6 Comparative Example 1 183.7 83.4 Comparative Example 2 176.4 80.2

[0118] Referring to Tables 1 and 2 and Figure 5 above, it can be seen that when a lithium anode composite and a lithium foil are used as the anode layer, the initial capacity is approximately 183 mAh / g, showing the same performance, whereas in the case of an all-solid-state battery using a lithium powder anode as the anode layer, the initial capacity is relatively lower at 176 mAh / g. At this time, the Coulomb efficiency is 84.6%, 83.5%, and 80.3%, respectively, with the lithium powder anode formed with many grain boundaries and binder having the lowest efficiency. It can be seen that the efficiency is improved by about 1% compared to lithium foil because the conductive structure secures a stable electron transport path.

[0120] Experimental Example 2: Evaluation of All-Solid State Battery Cycle Life

[0121] All-solid-state batteries were manufactured according to Example 1, Comparative Example 1, and Comparative Example 2, and then the results of evaluating cycle characteristics by maintaining the cell temperature at 60°C and performing charging and discharging at a C-rate of 0.5C in a voltage range of 3.0 to 4.3V are shown in Table 3 and Figure 6.

[0122] Specifically, FIG. 6 is a graph of the cycle characteristic evaluation results of all-solid-state batteries according to Example 1, Comparative Example 1, and Comparative Example 2.

[0123] division Discharge capacity (mAh / g) Dose retention rate (%) Example 1 159.8 96.3 Comparative Example 1 157.3 94.5 Comparative Example 2 150 95.4

[0124] Referring to Figure 6 and Table 3, it can be seen that after 30 charge-discharge cycles, the residual capacities are 159.8 mAh / g, 157.3 mAh / g, and 150.0 mAh / g, respectively, and the capacity retention rates based on the first cycle are 96.3%, 94.5%, and 95.4%, respectively. In the case of Example 1, it can be confirmed that the discharge capacity and capacity retention rate are the best, while Comparative Example 1 shows the lowest capacity retention rate and predicts that the residual capacity decreases significantly as the cycle progresses, and it can be confirmed that Comparative Example 2 has a higher capacity retention rate than Comparative Example 1 but a relatively lower discharge capacity.

[0126] Experimental Example 3: Impedance Evaluation

[0127] All-solid-state batteries were prepared according to Example 1, Comparative Example 1, and Comparative Example 2, and the results of impedance evaluation measured by applying an amplitude of 10 mV in a frequency range of 1 MHz to 0.1 Hz are shown in FIGS. 7a to 7c.

[0128] Specifically, FIGS. 7a to 7c are graphs of the cycle characteristic evaluation results of all-solid-state batteries according to Example 1 (Fig. 7a), Comparative Example 1 (Fig. 7b), and Comparative Example 2 (Fig. 7c).

[0129] Referring to FIGS. 7a to 7c, the initial cell resistance of Example 1 and Comparative Example 1 is similar, while that of Comparative Example 2 is about 30% higher, confirming that this trend is similar due to the same cause as in Experimental Example 1. In the case of Example 1, there is almost no change in cell resistance after the cycle, whereas in Comparative Examples 1 and 2, it can be seen that the resistance of the entire cell increases or the resistance element changes. That is, unlike Comparative Examples 1 and 2, it can be seen that in Example 1, a stable oxidation / reduction reaction of lithium is maintained during the charging and discharging process. Explanation of the symbols

[0130] 1, 1' : Composite negative electrode for lithium-ion battery 10 : Porous conductor 20 : Lithium metal 30 : Lithium alloy 40 : Lithium metal composite

Claims

Claim 1 A method for manufacturing a composite negative electrode for a lithium secondary battery, comprising: a step of preparing an electrolyte containing a lithium salt and a solvent; a step of arranging a working electrode containing a porous conductor and a counter electrode containing lithium metal within the electrolyte; and a step of pulse electrodepositing lithium metal on the porous conductor by applying voltage or current through a power supply device connected to the working electrode and the counter electrode, wherein prior to the pulse electrodeposition, a step of plating a metal capable of alloying with lithium on the porous conductor. Claim 2 A method for manufacturing a composite negative electrode for a lithium secondary battery according to claim 1, wherein the lithium salt comprises one or more selected from the group consisting of LiPF6, LiBF4, LiTFSI, LiClO4, LiTf, LiAsF6, LiFSA, LiBOB, LiDFOB, LiBETI, LiDCTA, LiTDI, LiPDI, LiI, LiF, and LiCl. Claim 3 A method for manufacturing a composite negative electrode for a lithium secondary battery according to claim 1, wherein the solvent comprises one or more selected from organic solvents and ionic liquids. Claim 4 A method for manufacturing a composite negative electrode for a lithium secondary battery according to claim 1, wherein the lithium salt is included in the electrolyte at a concentration of 0.05 M to 2 M. Claim 5 A method for manufacturing a composite negative electrode for a lithium secondary battery according to claim 1, wherein the porous conductor comprises one or more selected from the group consisting of carbon nanotubes, carbon felt, carbon paper, and carbon fiber. Claim 6 A method for manufacturing a composite negative electrode for a lithium secondary battery according to claim 1, wherein, during the pulse electrodeposition, the voltage is applied at a value 1.0V to 2V higher than the absolute value of the lithium reduction potential. Claim 7 A method for manufacturing a composite negative electrode for a lithium secondary battery according to claim 1, wherein, during the pulse electrodeposition, the number of pulses is 50 to 2000. Claim 8 A method for manufacturing a composite negative electrode for a lithium secondary battery according to claim 1, wherein, during the pulse electrodeposition, the pulse time is 10 ms to 1000 ms. Claim 9 A method for manufacturing a composite negative electrode for a lithium secondary battery according to claim 1, wherein the operating temperature during the pulse electrodeposition is 200℃ or lower. Claim 10 A method for manufacturing a composite negative electrode for a lithium secondary battery, wherein, in claim 1, the step of plating a lithium alloy on the porous conductor is further included. Claim 11 A method for manufacturing a composite negative electrode for a lithium secondary battery according to claim 10, wherein the lithium alloy comprises i) lithium (Li) and ii) one or more selected from the group consisting of gold (Au), silver (Ag), tin (Sn), copper (Cu), aluminum (Al), magnesium (Mg), nickel (Ni), titanium (Ti), silicon (Si), and antimony (Sb). Claim 12 A method for manufacturing a composite negative electrode for a lithium secondary battery, wherein, in the 10th paragraph, lithium metal is pulse-electrodeposited on a lithium alloy during the pulse electrodeposition. Claim 13 A method for manufacturing a composite negative electrode for a lithium secondary battery, wherein, in claim 1, the method further comprises a step of surface modification of the pulsed electrodeposited product. Claim 14 delete Claim 15 delete Claim 16 delete Claim 17 A method for manufacturing a composite negative electrode for a lithium secondary battery according to claim 1, wherein the composite negative electrode for a lithium secondary battery comprises a porous conductor; and a lithium metal composite uniformly positioned on the porous conductor, and wherein the lithium metal composite comprises lithium metal on a lithium alloy. Claim 18 delete Claim 19 A method for manufacturing a composite negative electrode for a lithium secondary battery according to claim 17, wherein the size of the lithium metal composite is 10 μm to 200 μm.

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