Title of invention: negative electrode for lithium secondary battery, lithium secondary battery including the same, and method for manufacturing the same
Technical field
[One]
This application claims the benefit of priority based on Korean Patent Application No. 10-2018-0132011 filed on October 31, 2018, and all contents disclosed in the documents of the Korean patent application are included as part of this specification.
Background
[2]
As the price of energy sources rises due to the depletion of fossil fuels and interest in environmental pollution increases, the demand for eco-friendly alternative energy sources is becoming an indispensable factor for future life. In particular, technology development for mobile devices As the demand and demand increase, the demand for secondary batteries as an energy source is rapidly increasing.
[3]
Typically, in terms of the shape of the battery, there is a high demand for prismatic secondary batteries and pouch-type secondary batteries that can be applied to products such as mobile phones with a thin thickness. There is high demand for lithium secondary batteries such as lithium ion polymer batteries.
[4]
In general, secondary batteries form a positive electrode and a negative electrode by coating an electrode mixture containing an electrode active material on the surface of a current collector, and form an electrode assembly with a separator interposed therebetween, and then a cylindrical or rectangular metal can or an aluminum laminate sheet. It is mounted inside the pouch-shaped case of the electrode assembly, and is manufactured by mainly injecting or impregnating a liquid electrolyte into the electrode assembly or using a solid electrolyte.
[5]
In general, a carbon material such as graphite is used as a negative electrode of a lithium secondary battery, but the theoretical capacity density of carbon is 372 mAh/g (833 mAh/cm 3 ). Therefore, in order to improve the energy density of the negative electrode, silicon (Si) and tin (Sn) alloyed with lithium, oxides and alloys thereof, and the like are considered as negative electrode materials. Among them, silicon-based materials have attracted attention due to their low price and high capacity (4200mAh/g).
[6]
Meanwhile, in the carbon-based negative active material, a solid electrolyte interface (SEI) layer is formed on the surface of the negative active material during the initial charging/discharging process (activation process). During the charging and discharging process, the electrolyte is depleted and the battery capacity decreases.
[7]
Further, although the silicon-based material exhibits a high capacity, a problem of a large initial irreversible capacity occurs. In the charge/discharge reaction of a lithium secondary battery, lithium released from the positive electrode is inserted into the negative electrode during charging, and is desorbed from the negative electrode during discharge and returned to the positive electrode. A large amount of lithium inserted in the negative electrode cannot be returned to the positive electrode again, and thus the initial irreversible capacity increases. When the initial irreversible capacity increases, the battery capacity and cycle rapidly decrease.
[8]
As one of the methods for solving the problems related to the initial irreversibility, a (pre-lithiation) technique in which lithium is pre-inserted into the negative electrode has been attempted. Among them, the direct lithium contact method is a method of directly laminating a thin film of lithium on the negative electrode layer.After assembling the cell, an electrolyte is injected to move the lithium in the lithium layer to the negative electrode to increase the lithium content in the negative electrode, thereby reducing the irreversible capacity. I tried to solve the problem.
[9]
However, when manufacturing a lithium secondary battery, there is often a time delay when the electrolyte is injected after assembling the cell or until the initial charging and discharging.The lithium in the lithium layer attached to the negative electrode before the injection of the electrolyte is uneven in the electrode. There is a problem that the resistance increases due to solid-diffusion, or the loss of the amount of lithium occurs due to diffusion of lithium into the atmosphere.
[10]
On the other hand, Korean Patent Laid-Open No. 10-2018-0057513 discloses that during (pre) lithiation by the direct lithium contact method, when the material of the electrode layer and the lithium layer are directly contacted, lithiation occurs, which raises the problem of fire or explosion. A technique of interposing an anti-lithiation layer between lithium layers is disclosed. However, the proposed technology is for the purpose of preventing accidents such as fire during the prelithiation process, and the solution of the present invention, such as lithium loss, which occurs as the time to inject the electrolyte after laminating a lithium metal thin film on the negative electrode is delayed. The problem is not recognized, and the thickness of the anti-lithiation layer is 0.5 to 5 μm, and the anti-lithiation layer increases the resistance, resulting in a problem of deteriorating battery performance.
Detailed description of the invention
Technical challenge
[11]
An object of the present invention is to provide a novel (pre) prelithiation method for a negative electrode for a lithium ion battery, a negative electrode prepared by the method, and a lithium ion secondary battery including the negative electrode.
[12]
In addition, an object of the present invention is to minimize the loss of the amount of lithium and to reduce the amount of side reactions of lithium by mitigating the solid-diffusion rate of lithium that occurs as the time from assembling the cell to the electrolyte solution is delayed.
[13]
Another object of the present invention is to provide a method for (pre)lithiation of a negative electrode for a secondary battery with improved battery performance by improving the problem of increasing the resistance of the lithium diffusion rate control layer.
Means of solving the task
[14]
In order to solve the above problems, the negative electrode for a lithium secondary battery of the present invention includes a current collector; A negative electrode mixture layer formed on the current collector; A lithium diffusion rate control layer formed on the negative electrode mixture layer by atomic layer deposition; And a lithium layer formed on the lithium diffusion rate control layer. Includes.
[15]
In one embodiment of the present invention, the lithium diffusion rate control layer is characterized in that it controls the diffusion of lithium in the lithium layer into the negative electrode mixture layer until the electrolyte is injected.
[16]
In one embodiment of the present invention, the lithium diffusion rate control layer is characterized in that it controls diffusion of lithium in the lithium layer into the negative electrode mixture layer until the initial charge and discharge.
[17]
In one embodiment of the present invention, the thickness of the lithium diffusion rate control layer may be 0.1 to 100 nm, more preferably 0.5 to 50 nm.
[18]
In one embodiment of the present invention, the negative electrode mixture layer may include one compound or a mixture of two or more selected from the group consisting of SiOx (0< x ≤ 2), SnO, and SnO 2 .
[19]
In an embodiment of the present invention, the material of the lithium diffusion rate control layer is Al 2 O 3 , TiO 2 , ZrO 2 , HfO 2 , Ta 2 O 5 , Nb 2 O 5 , Y 2 O 3 , MbO, CeO 2 , SiO 2 , La 2 O 3 , Ln 2 O 3 , Lu 2 O 3 , PrAlO 3 , Er 2 O 3 , HfAlO, HfSiO, ZrSiO, ZrAlO, HfON, HfSiON, SrTiO 3 , BaTiO 3 , BST and Laminates may include one or more selected from the group consisting of, and more preferably Al 2 O 3 .
[20]
In one embodiment of the present invention, the thickness ratio of the lithium diffusion rate control layer and the lithium layer may be 1:100 to 1:20000.
[21]
The method of manufacturing a lithium ion battery of the present invention includes the steps of (S11) forming a negative electrode mixture layer on a current collector; (S12) forming a lithium thin film layer on the surface of the peeling plate; (S13) forming a lithium diffusion rate control layer by repeating the atomic layer deposition process of introducing a metal oxide on the lithium thin film layer; (S14) preparing a negative electrode by stacking the results of (S11) and (S13) so that the negative electrode mixture layer and the lithium diffusion rate control layer face each other; (S15) preparing an electrode assembly including the negative electrode prepared in step (S14); And (S16) injecting an electrolyte solution into the electrode assembly. Includes.
[22]
In addition, a method of manufacturing a rechargeable lithium battery according to an exemplary embodiment of the present invention includes the steps of (S21) forming a negative electrode mixture layer on a current collector; (S22) forming a lithium diffusion rate control layer by repeating the atomic layer deposition process of introducing a metal oxide on the negative electrode mixture layer; (S23) preparing a negative electrode by laminating a lithium thin film on the lithium diffusion rate control layer; (S24) preparing an electrode assembly including the negative electrode prepared in step (S23); And (S25) injecting an electrolyte solution into the electrode assembly. Includes.
[23]
At this time, the lithium diffusion rate control layer controls diffusion of lithium in the lithium layer into the negative electrode mixture layer before the electrolyte is injected.
[24]
According to an embodiment of the present invention, the atomic layer deposition process may be performed until the thickness of the lithium diffusion rate control layer is 0.1 to 100 nm, more preferably 0.5 to 50 nm.
[25]
According to an embodiment of the present invention, the atomic layer deposition process of step (S13) or step (S22) includes: placing the result of (S12) or the result of (S21) in a chamber; Supplying a metal atom into the chamber; Supplying a purge gas into the chamber; Supplying an oxidizing agent into the chamber to form a metal oxide layer; And supplying a purge gas into the chamber to remove unreacted oxidizing agent.
Effects of the Invention
[26]
The negative electrode according to the present invention has a lithium diffusion rate control layer between the lithium thin film and the negative electrode mixture layer, so that the rate at which lithium is diffused in the prelithiation process can be controlled, and the cycle characteristics by suppressing loss of lithium or side reactions of lithium. Can be improved.
[27]
In addition, the manufacturing method of a lithium ion secondary battery according to the manufacturing method of the present invention has the advantage of minimizing an increase in resistance due to the material properties of the lithium diffusion rate controlling layer by forming a very thin lithium diffusion rate control layer by atomic layer deposition. have.
Brief description of the drawing
[28]
1 is a schematic view showing the structure of a negative electrode according to an embodiment of the present invention.
[29]
2 and 3 schematically show a method of manufacturing a negative electrode according to an embodiment of the present invention.
[30]
4 to 8 are schematic diagrams showing an atomic layer deposition process for forming the lithium diffusion rate control layer of the present invention.
Best mode for carrying out the invention
[31]
Terms used in the present specification and claims should not be construed as being limited to a conventional or dictionary meaning, and that the inventor can appropriately define the concept of terms in order to describe his or her invention in the best way. Based on the principle, it should be interpreted as a meaning and concept consistent with the technical idea of ​​the invention. Therefore, the configuration shown in the embodiments described in the present specification is only one of the most preferred embodiments of the present invention and does not represent all of the technical spirit of the present invention, and various equivalents that can replace them at the time of the present application And it should be understood that there may be variations.
[32]
In the entire specification of the present application, when a certain part is said to be ``connected'' with another part, this includes not only ``directly connected'' but also ``electrically connected'' with another element interposed therebetween. .
[33]
In the entire specification of the present application, when a certain part "includes" a certain constituent element, it means that other constituent elements may be further included rather than excluding other constituent elements unless otherwise stated.
[34]
The terms "about", "substantially" and the like used throughout the specification of the present application are used as a meaning at or close to the numerical value when manufacturing and material tolerances specific to the stated meaning are presented, and are accurate to aid the understanding of the present application. Or absolute figures are used to prevent unreasonable use of the stated disclosure by unconscionable infringers.
[35]
In the entire specification of the present application, the term "combination(s) thereof" included in the expression of the Makushi format refers to one or more mixtures or combinations selected from the group consisting of the constituent elements described in the expression of the Makushi format, It means to include at least one selected from the group consisting of the above constituent elements.
[36]
The present invention relates to a cathode for an electrochemical device and an electrochemical device including the same. In the present invention, the electrochemical device includes all devices that undergo an electrochemical reaction, and specific examples include all types of primary and secondary batteries, fuel cells, solar cells, or capacitors. Particularly, among the secondary batteries, a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery is preferred.
[37]
In the entire specification of the present application, the description of "A and/or B" means "A or B or both".
[38]
[39]
Hereinafter, the present invention will be described in more detail.
[40]
As a negative electrode active material, a material made of silicon or carbon material inevitably causes a decrease in the capacity of the battery due to its initial high irreversible property. As one of the methods to solve this problem, a prelithiation technique in which lithium is pre-inserted into the negative electrode is being attempted. Among them, the direct lithium contact method is a method of directly laminating a thin film of lithium on the negative electrode layer.After assembling the cell, an electrolyte is injected to move the lithium in the lithium layer to the negative electrode to increase the lithium content in the negative electrode, thereby reducing the irreversible capacity. It's a way to solve the problem.
[41]
However, when manufacturing a lithium secondary ion battery, there is often a time delay until the electrolyte is injected after cell assembly.Before injection of the electrolyte, the lithium in the lithium layer attached to the negative electrode is unevenly transferred into the electrode ( Solid-diffusion) resistance increases or lithium diffuses into the atmosphere, resulting in loss of the amount of lithium.
[42]
Accordingly, the present invention discloses a new electrode structure and a lithium secondary battery having the same by interposing a lithium diffusion rate control layer between the negative electrode mixture layer and the lithium layer to solve the above-described problem.
[43]
[44]
1 is a cross-sectional view of a cathode 100 according to an embodiment of the present invention, specifically showing a structure of a cathode before prelithiation. Referring to FIG. 1, the negative electrode 100 includes a current collector 110; A negative electrode mixture layer 120 formed on the current collector 110; A lithium diffusion rate control layer 130 formed on the negative electrode mixture layer 120 by atomic layer deposition; And a lithium layer 140 formed on the lithium diffusion rate control layer 130; it has a sequentially stacked structure.
[45]
The negative electrode 100 of the present invention is provided with a lithium diffusion rate control layer 130 between the negative electrode mixture layer 120 and the lithium layer 140 to control (relax) the diffusion rate of lithium from the lithium layer and into the negative electrode mixture layer. Helps lithium to diffuse in a uniform distribution.
[46]
As described later, in the present invention, prelithiation proceeds during the injection of the electrolyte solution and/or the first charging and discharging. Accordingly, the lithium diffusion control layer functions as a diffusion prevention layer that prevents lithium diffusion until the electrolyte injection and/or the initial charge/discharge time point. Meanwhile, after the prelithiation process is performed, the lithium diffusion rate control layer may function as an insulating layer between the negative electrode and the positive electrode when the lithium diffusion rate control layer is eluted in the electrolyte and removed or remains.
[47]
Furthermore, the lithium diffusion rate control layer 130 of the present invention is formed by an atomic layer deposition method to implement a thin thickness in the order of nanometers, thereby improving the problem that the lithium diffusion rate control layer increases the resistance. In forming the lithium diffusion rate control layer, conventionally, a polymer solution was simply applied or coated. In this case, it is difficult to implement a thin film of several or tens of nanometers, so that it has a thickness of several to several hundreds of micrometers. However, when the thickness of the speed control layer has a thickness of several to several hundreds of micrometers, the resistance of the battery may increase. However, in the present invention, since the rate control layer is formed by the atomic layer deposition method, a thin film of several to tens of nanometers can be implemented.
[48]
[49]
Hereinafter, the lithium diffusion rate control layer will be described in more detail.
[50]
According to a specific embodiment of the present invention, the rate control layer may include a metal oxide or metalloid oxide material having insulating properties. Specifically, Al 2 O 3 , TiO 2 , ZrO 2 , HfO 2 , Ta 2 O 5 , Nb 2 O 5 , Y 2 O 3 , MbO, CeO 2 , SiO 2 , La 2 O 3 , Ln 2 O 3 , Lu 2 O 3 , PrAlO 3 , Er 2 O 3 , HfAlO, HfSiO, ZrSiO, ZrAlO, HfON, HfSiON, SrTiO 3 , BaTiO 3 , BST (barium strontium titanate oxide) and Laminates may include one or two or more selected from the group consisting of.
[51]
By interposing the (quasi) metal oxide having insulating properties between the sound-grade mixture layer and the lithium layer, the lithium in the lithium layer is prevented from diffusing into the negative electrode mixture layer until the injection of the electrolyte solution or the first charge and discharge, while pre-lithiation. There is also an advantage in that the remaining metal oxide layer protects the surface of the negative electrode, helping to improve the safety of the battery at high temperatures. In this respect, Al 2 O 3 , TiO 2 , ZrO 2, CeO 2 , Y 2 O 3 , SiO 2 can be said to be preferable as a material constituting the rate control layer of the present invention, and the most preferable material is Al 2 O 3 to be. Al 2 O 3 is the most suitable material to be applied as a lithium diffusion rate control layer in the present invention because it is easy to obtain precursors for atomic layer deposition treatment and because the price is inexpensive, research related to atomic layer deposition is most actively conducted.
[52]
In the present invention, since the lithium diffusion rate control layer must be compressed enough to allow the lithium layer and the negative electrode mixture layer to be energized under the activation pressure range applied during the initial charging and discharging, the thickness of the lithium diffusion rate control layer is reduced. For this purpose, a lithium diffusion rate control layer is formed by atomic layer deposition.
[53]
The thickness of the lithium diffusion rate control layer may be 0.1 to 100 nm, more preferably 0.5 to 50 nm. When the thickness of the lithium diffusion rate control layer is too thin to be less than 0.1 nm, it is energized after attaching the lithium thin film and before performing the prelithiation process, making it difficult to function as a lithium diffusion rate preventing layer, and lithiumization may become non-uniform. Conversely, when the thickness of the lithium diffusion rate control layer exceeds 100 nm and is too thick, conduction between the lithium layer and the negative electrode is hindered, so that it may be difficult for lithium to smoothly diffuse into the negative electrode, and resistance increases.
[54]
[55]
By providing the rate control layer having the above characteristics, there is an effect of reducing the loss of lithium amount and the amount of lithium side reactions by mitigating the diffusion of lithium before injecting the electrolyte, and the thickness of the rate control layer is several to tens of nanometers. It is possible to minimize the increase in resistance by having a.
[56]
The lithium diffusion rate control layer may be a single layer, but if necessary, it may have a two-layer structure of the first lithium diffusion rate control layer and the second lithium diffusion rate control layer, and may have a multilayer structure of three or more layers. . In this case, the material of each layer constituting the lithium diffusion rate control layer may be of a different type or may be a metal oxide of the same material.
[57]
[58]
Hereinafter, the lithium layer will be described in detail.
[59]
The lithium layer is used as a source for lithiation of the negative electrode active material included in the negative electrode mixture layer. It moves inside, and a residual amount may exist on the surface of the speed control layer even after pre-lithiation is completed to some extent.
[60]
The lithium layer contains lithium metal. In a specific embodiment of the present invention, the lithium layer may be formed by electroplating, electroplating, or chemical vapor deposition, or may be laminated by bonding a lithium metal thin film to the speed control layer by pressing.
[61]
The thickness of the lithium layer may be appropriately selected in consideration of the loading amount of the negative electrode, and specifically has a thickness of 0.1 μm to 40 μm, preferably 1 μm to 20 μm.
[62]
The thickness ratio of the lithium diffusion rate control layer and the lithium layer may be 1:100 to 1:20000. If the lithium diffusion rate control layer is too thick outside the above ratio, the lithium diffusion rate control layer is insufficient and the irreversible capacity may increase. It is difficult to exhibit the function as a lithium diffusion rate prevention layer.
[63]
[64]
Hereinafter, the current collector and the negative electrode mixture layer constituting the negative electrode of the present invention will be described in detail.
[65]
The current collector is generally made to have a thickness of 3 μm to 500 μm. Such a current collector is not particularly limited as long as it has high conductivity without causing chemical changes to the battery, for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or the surface of aluminum or stainless steel. For example, those treated with carbon, nickel, titanium, or the like may be used.
[66]
The negative electrode mixture layer includes a negative electrode active material, a binder, and a conductive material. The negative electrode according to the present invention may be prepared by applying a mixture of a negative active material, a conductive material, and a binder on the current collector and then drying it, and if necessary, a filler may be further included in the mixture.
[67]
In a specific embodiment of the present invention, the negative active material includes a (semi) metal oxide, and the (semi) metal oxide may be in the form of particles or a powder containing the particles.
[68]
The (semi)metal compound is one or more selected from the group consisting of Si, Sn, Al, Sb, Bi, As, Ge, Pb, Zn, Cd, In, TI, Ga, and alloys thereof. Preferably, the negative active material may include one type of compound or a mixture of two or more types selected from the group consisting of SiO x (0< x ≤ 2), SnO, and SnO 2 .
[69]
Meanwhile, in a specific embodiment of the present invention, the metal oxide may include a shell portion including a carbon material on at least a part of the surface of the particle. The carbon material may be bonded, attached, or coated on the surface of the (semi)metal oxide particle. The carbon material may include at least one selected from the group consisting of crystalline carbon, natural graphite, artificial graphite, kish graphite, graphitized carbon fiber, graphitized mesocarbon microbead, and amorphous carbon. In addition, the graphite is soft carbon, hard carbon, pyrolytic carbon, liquid crystal pitch based carbon fiber, meso-carbon microbeads, liquid crystal pitch (mesophase piches), petroleum coal-based coke (petroleum or coal tar pitch derived cokes), and may include those obtained by graphitizing at least one selected from the group consisting of activated carbon.
[70]
[71]
According to a preferred embodiment of the present invention, a 50% particle diameter (D 50 ) of the metal oxide volume cumulative particle size distribution is 2 μm or more and 5 μm or less. Further, the 90% particle diameter (D 90 ) of the cumulative volume particle size distribution of the particles is 25 µm or less, preferably 15 µm or less, and more preferably 10 µm or less. Further, the maximum particle diameter of the cumulative volume particle size distribution is 35 µm or less, preferably 25 µm or less. The measurement of the 50% particle diameter, 90% particle diameter, and the maximum particle diameter of the volume cumulative particle size distribution can be obtained by, for example, the cumulative frequency when measured using a laser diffraction particle size distribution measuring apparatus manufactured by Nikiso Corporation.
[72]
[73]
The binder is a component that aids in bonding of an active material and a conductive material and bonding to a current collector, and is typically added in an amount of 1 to 30% by weight based on the total weight of the electrode mixture. As such a binder, the high molecular weight polyacrylonitrile-acrylic acid copolymer may be used, but is not limited thereto. Other examples include polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose, starch, hydroxypropylcellulose, recycled cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene, alcohol And various copolymers such as fonned EDPM, styrene rubber, butyrene rubber, and fluorine rubber.
[74]
[75]
The conductive material may be typically added in an amount of 1 to 30% by weight based on the total weight of the mixture including the negative active material. Such a conductive material is not particularly limited as long as it has conductivity without causing chemical changes in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; Carbon blacks such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride, aluminum, and nickel powder; Conductive whiskey such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; A conductive material such as a polyphenylene derivative may be used, but is not limited thereto.
[76]
[77]
In the present invention, the negative electrode may be prepared in the following order. First, a negative electrode mixture layer is formed on the surface of the current collector (S11). Next, a release plate is prepared, and a lithium thin film layer is formed by laminating a lithium thin film on the surface thereof (S12). Subsequently, an atomic layer deposition process of introducing a metal oxide on the lithium thin film layer is repeated to form a lithium diffusion rate control layer (S13). In the present invention, the release plate may be used without limitation as long as the release plate can be easily removed from the laminate manufactured by sequentially stacking a lithium layer and a lithium diffusion rate control layer. It may be a resin film layer. Next, a negative electrode is manufactured by stacking the results of (S11) and (S13) so that the negative electrode mixture layer and the lithium diffusion rate control layer face each other (S14). 2 is a schematic diagram of the method for manufacturing the negative electrode described above. Thereafter, the electrode assembly is assembled by interposing a separator between the negative electrode and the positive electrode (S15), and an electrolyte is injected into the electrode assembly (S16), thereby manufacturing a secondary battery.
[78]
Alternatively, the negative electrode according to the present invention may be prepared by forming a lithium diffusion rate control layer on the negative electrode mixture layer without using a peeling plate, and then forming a lithium layer on the surface of the control layer. Specifically, forming a negative electrode mixture layer on the current collector (S21); Forming a lithium diffusion rate control layer by repeating an atomic layer deposition process of introducing a metal oxide on the negative electrode mixture layer (S22); Manufacturing a negative electrode by laminating a lithium thin film on the lithium diffusion rate control layer (S23); Manufacturing an electrode assembly including the negative electrode prepared in step (S23) (S24); And injecting an electrolyte solution into the electrode assembly (S25). Here, the formation of the lithium layer and the formation of the lithium diffusion rate control layer may refer to the above-described method. 3 is a schematic diagram of the method for manufacturing the negative electrode described above.
[79]
[80]
Hereinafter, the atomic layer deposition process of the present invention will be described in detail.
[81]
Atomic Layer Deposition (ALD) is a self-controlled deposition process, and since deposition is possible by precisely controlling the thickness of a thin film, it was selected as a method of forming the rate control layer of the present invention.
[82]
In the present invention, a lithium diffusion rate control layer was formed on the lithium thin film layer of the result of step (S12) or the negative electrode mixture layer of the result of step (S21) by using the polymer precursor as a raw material for the deposition process.
[83]
The atomic layer deposition process may include placing a result of the step (S12) or the result of the step (S21) in a chamber (S31), and supplying a metal atom into the chamber; Supplying a purge gas into the chamber; Supplying an oxidizing agent into the chamber to form a metal oxide layer; And supplying a purge gas into the chamber to remove unreacted oxidizing agent.
[84]
When placing the result of step (S12) or the result of step (S21) in the chamber, it is preferable to maintain the temperature inside the chamber at 100 to 500°C. If the temperature of the chamber is less than 100° C., the reactivity of the reaction material is not easy in the subsequent process, and if it exceeds 500° C., the metal oxide thin film is not crystallized, which is not preferable.
[85]
In addition, it is preferable to adjust the pressure inside the chamber to be 0.1 to 3.0 torr. If the pressure is less than 0.1 torr, the reactivity of the metal atoms supplied in the subsequent process is not easy, and if the pressure exceeds 3.0 torr, the process control is not easy, which is not preferable.
[86]
Referring to FIG. 4, after placing the result of the (S12) step or the result of the (S21) step in the chamber 200 that satisfies the above temperature and pressure conditions, (semi)metal or The (semi) metal precursor is added as a reactant. The (semi) metal or (semi) metal precursor is a group consisting of Al, Ti, Zr, Hf, Ta, Nb, Y, Mb, Ce, Si, La, Ln, Lu, Pr, Er, Sr, Ba and Laminates It may contain one or two or more atoms selected from.
[87]
Next, referring to FIG. 5, a (semi) metal is placed on top of each lithium thin film layer 20 or negative electrode mixture layer 20' of the result of step (S12) or the result of step (S21) positioned in the chamber as described above. Alternatively, by providing a (semi)metal precursor material, the first portion 30' of the (semi)metal atom is chemically adsorbed on the lithium thin film layer 20 or the negative electrode mixture layer 20'. In addition, the second part 30" of the metal atom excluding the first part is physically adsorbed to the first part or drifted on the chamber.
[88]
The next step is to provide a purge gas into the chamber. Examples of the purge gas may include an inert gas such as argon gas or nitrogen gas. At this time, the purge gas may be provided for about 1 to 50 seconds, more preferably 3 to 25 seconds, and most preferably 5 to 10 seconds. By providing the purge gas into the chamber as described above, the second portion that is drifting in the chamber or physically adsorbed to the first portion as shown in FIG. 6 is removed. As a result, precursor molecules 30a of the chemically adsorbed first portion remain on the lithium thin film layer or the anode mixture layer.
[89]
Instead of providing the purge gas, even if the inside of the chamber is kept in a vacuum state for about 1 to 20 seconds, it is possible to remove the second part that is drifting in the chamber or physically adsorbed to the first part.
[90]
In addition, even if the purge gas is introduced and vacuum purge is performed together, it is possible to remove the second part drifting in the chamber or physically adsorbed to the first part.
[91]
Next, as shown in FIG. 7, after the above steps are performed, an oxidizing agent 40 is supplied into the chamber. As an example of the oxidizing agent, one selected from the group consisting of O 3 , O 2 , H 2 O, plasma O 2 and remote plasma O 2 may be used alone, and in some cases, two or more may be mixed and used.
[92]
In the present invention, it is preferable to supply the oxidizing agent into the chamber for about 0.5 to 10 seconds. The oxidizing agent oxidizes the precursor molecules by chemically reacting with the precursor molecules 30a, which are the first portions of the reactant chemically adsorbed on the negative electrode mixture layer or the lithium thin film layer.
[93]
Next, in order to remove the oxidizing agent that has not reacted with the first portion of the metal atom, a purge gas of the same type as above is supplied. The type and introduction time of the purge gas are the same as described above. In this way, by providing a purge gas into the chamber, an oxidizing agent that has not chemically reacted with the metal atom is removed from the chamber as shown in FIG. 8. Accordingly, the metal oxide layer 50 is formed on the lithium thin film layer or the negative electrode mixture layer.
[94]
If necessary, the above steps may be repeated at least one or more times. In this case, the thickness of the metal oxide layer on the lithium thin film layer or the negative electrode mixture layer is adjusted according to the number of repetitions of the above processes.
[95]
According to an embodiment of the present invention, after placing the result of the (S12) step or the result of the (S21) step in a chamber, the (semi)metal or (semi)metal precursor material, the purge gas and the An oxidizing agent may be supplied together to form a metal oxide layer.
[96]
[97]
Hereinafter, the (pre) lithiation process of the present invention will be described in detail.
[98]
In one embodiment of the present invention, the (pre) lithiation of the negative electrode is performed in the electrolyte injection and/or initial charge/discharge step after the battery is manufactured, and at this time, at least a part of the negative active material included in the negative electrode mixture layer is lithiated. In one embodiment of the present invention, the battery includes a negative electrode, a positive electrode, and an electrode assembly in which a separator is interposed between the negative electrode and the positive electrode. After inserting the electrode assembly into an appropriate exterior material, an electrolyte is injected and sealed It can be prepared in a way.
[99]
In the present invention, lithiation may be performed by injection of an electrolyte solution. That is, when the electrolyte is injected, an electrode assembly including constituent elements such as electrodes is impregnated with the electrolyte. At this time, while the lithium diffusion rate control layer of the present invention is eluted and removed, lithium in the lithium layer may be diffused into the negative electrode mixture layer.
[100]
After injecting the electrolyte, a current is first applied to the battery to perform initial charging and discharging (formation) to activate the battery. The activation process may be performed while a predetermined pressure is applied to the battery. As described above, when a material that is compressed under a predetermined pressure and capable of energizing is used as a control layer, lithium may be diffused into the negative electrode mixture layer through an activation process under a predetermined pressure.
[101]
The negative electrode active material included in the negative electrode mixture layer, especially the above-described (semi)metal oxide and lithium, may be combined to form an alloy by this prelithiation, and a part of lithium may be inserted into the crystal structure of the negative electrode active material . In addition, there is an advantage that lithium ions can be well transferred to the inside of the negative electrode through the electrolyte in the progress of prelithiation, and thus uniform prelithiation can be performed throughout the entire negative electrode body.
[102]
In the present invention, since the rate control layer is interposed between the negative electrode mixture layer and the lithium layer, the diffusion of lithium is prevented by the control layer in the state before the injection of the electrolyte solution, so that prelithiation hardly proceeds. Almost all of the prelithiation can be performed after the electrode assembly and the electrolyte is injected into the electrode assembly and/or in the initial charge/discharge step.
[103]
Meanwhile, in some cases, the initial charging and discharging is preferably performed in a state in which a predetermined pressure is applied to the battery to energize the control layer and the negative electrode. Thereafter, as long as the lithium metal remains in the lithium layer, the prelithiation may be continuously performed, and may be affected, such as being accelerated by charging and discharging the battery.
[104]
[105]
Hereinafter, the secondary battery of the present invention will be described in detail.
[106]
The present invention provides a lithium secondary battery comprising a negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and an electrolyte, wherein the negative electrode has the above-described structural characteristics.
[107]
The positive electrode may be prepared by applying a mixture of a positive electrode active material, a conductive material, and a binder on a positive electrode current collector and then drying it, and if necessary, a filler may be further included in the mixture. The positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO 2 ) or lithium nickel oxide (LiNiO 2 ), or a compound substituted with one or more transition metals; Lithium manganese oxides such as the formula Li 1+x Mn 2-x O 4 (wherein x is 0 to 0.33), LiMnO 3 , LiMn 2 O 3 , and LiMnO 2 ; Lithium copper oxide (Li 2 CuO 2 ); LiV 3 O 8 , LiFe 3 O 4 , V 2 O Vanadium oxides such as 5 and Cu 2 V 2 O 7 ; Ni site-type lithium nickel oxide represented by the formula LiNi 1-x M x O 2 (where M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, and x = 0.01 to 0.3); Formula LiMn 2-x M x O 2 (where M = Co, Ni, Fe, Cr, Zn or Ta, and x = 0.01 to 0.1) or Li 2 Mn 3 MO 8 (where M = Fe, Co, A lithium manganese composite oxide represented by Ni, Cu, or Zn); LiMn 2 O 4 in which part of Li in the formula is substituted with alkaline earth metal ions ; Disulfide compounds; Fe 2 (MoO 4 ) Although 3 etc. are mentioned, it is not limited only to these.
[108]
For the positive electrode, the conductive material, the current collector, and the binder may refer to the contents of the negative electrode.
[109]
As the separator, an insulating thin film having high ion permeability and mechanical strength may be used. The processing diameter of the separator is generally 0.01 to 10 μm, and the thickness may be 5 to 300 μm. Non-limiting examples of such a separator include olefin-based polymers such as polypropylene having chemical resistance and hydrophobicity; And a sheet made of glass fiber or polyethylene, or a nonwoven fabric. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.
[110]
In the present invention, the electrolyte solution contains an organic solvent and a predetermined amount of lithium salt, and the components of the organic solvent include N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene Carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyllolactone, 1,2-dimethoxy ethane, tetrahydroxy franc (franc), 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1, 3-dioxolone, formamide, dimethylformamide, dioxolone, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate tryster, trimethoxymethane, dioxolone derivative, sulfolane, methyl sulfolane, Aprotic organic solvents such as 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethers, methyl pyropionate, and ethyl propionate may be used.
[111]
The lithium salt is a material that is soluble in the electrolyte, for example, LiCl, LiBr, LiI, LiClO 4 , LiBF 4 , LiB 10 Cl 10 , LiPF 6 , LiCF 3 SO 3 , LiCF 3 CO 2 , LiAsF 6 , LiSbF 6 , LiAlCl 4 , CH 3 SO 3 Li, CF 3 SO 3 Li, (CF 3 SO 2 ) 2NLi, lithium chloroborane, lithium lower aliphatic carboxylic acid, lithium tetraphenylborate, imide, and the like can be used.
[112]
[113]
The secondary battery of the present invention may be manufactured by storing/sealing an electrode assembly in which the positive electrode and the negative electrode are alternately stacked with a separator in an exterior material such as a battery case together with an electrolyte. The manufacturing method of the secondary battery can be used without limitation in a conventional method.
[114]
[115]
According to another embodiment of the present invention, a battery module including the secondary battery as a unit cell and a battery pack including the same are provided. Since the battery module and the battery pack include a secondary battery that exhibits excellent fast charging characteristics in high loading, it can be used as a power source for an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage system.
[116]
[117]
Meanwhile, for battery elements not described above in the present specification, for example, a conductive material, reference may be made to elements commonly used in the battery field, particularly in the lithium secondary battery field.
[118]
[119]
Hereinafter, examples will be described in detail to aid understanding of the present invention. However, the embodiments according to the present invention may be modified in various other forms, and the scope of the present invention should not be construed as being limited by the following examples. Embodiments of the present invention are provided to more completely describe the present invention to those of ordinary skill in the art.
[120]
[121]
Example of preparation of negative electrode
[122]
SiO (D50: 3.2㎛) and artificial graphite were mixed in a weight ratio of 3:7 to be used as a negative electrode active material. The negative active material, SBR binder, CMC, and acetylene black were added to water in a weight ratio of 93:3:1.5:2.5 to prepare a negative electrode mixture. The mixture was uniformly coated on a 10 μm copper foil, a drying temperature of 90° C., and a coating speed of 0.2 m/min. The coated negative electrode had a target thickness by rolling the electrode according to the porosity of 30%. Then, it was dried in a vacuum oven at 180° C. for 12 hours.
[123]
[124]
Example 1
[125]
Preparation of a negative electrode having a lithium diffusion rate control layer and a lithium layer
[126]
The cathode of the preparation example was placed in a chamber (150° C., 0.1 torr), and trimethyl aluminum and H 2 O gas were injected together with nitrogen gas at a pressure of 1 torr at a ratio of 17:1. The atomic layer deposition process was repeatedly performed until the thickness of the Al 2 O 3 layer on the negative electrode mixture layer became about 3 nm by the following reactions (A) and (B) .
[127]
(A) Al-OH* + Al(CH 3 ) 3 + Al-O- Al(CH 3 ) 2 * + CH 4
[128]
(B) Al-CH 3 * +H2O + Al-OH* + CH 4
[129]
Thereafter, a 10 μm-thick lithium thin film was laminated to prepare a negative electrode.
[130]
[131]
Manufacturing of half coin cell
[132]
Coin cells were prepared in the order of negative electrode/separator (polypropylene porous film (20 μm, Celgard)/lithium foil) using lithium foil and stainless steel upper and lower plates as the obtained negative electrode and the counter electrode of the prepared negative electrode. Immediately after the electrolyte was injected, the electrolyte was a mixture of ethylene carbonate and ethyl methyl carbonate in a mass ratio of 3:7.
[133]
[134]
Example 2
[135]
A battery was manufactured in the same manner as in Example 1, except that the injection time of the electrolyte solution in Example 1 was changed to 2 hours after assembly of the coin cell.
[136]
[137]
Comparative Example 1
[138]
A battery was manufactured in the same manner as in Example 1, except that the atomic layer deposition process of forming an Al 2 O 3 layer on the negative electrode mixture layer was omitted in Example 1.
[139]
[140]
Comparative Example 2
[141]
A battery was manufactured in the same manner as in Comparative Example 1, except that the injection point of the electrolyte was changed to 2 hours after coin cell assembly.
[142]
[143]
Example 3
[144]
Manufacture of anode
[145]
As a positive electrode active material, LiCoO 2 , SBR binder, CMC, and acetylene black were added to water in a weight ratio of 93:3:1.5:2.5 to prepare a positive electrode mixture. The mixture was uniformly coated on 10 μm aluminum foil, and dried in a vacuum oven at 50° C. for 12 hours to prepare a positive electrode.
[146]
Preparation of mono cell
[147]
Using the obtained positive electrode and the negative electrode having a lithium diffusion rate control layer and a lithium layer prepared in Example 1, a negative electrode/separator (polypropylene porous film (20 μm, Celgard)/anode in the order of 1- A stacked mono cell was fabricated, and an electrolyte was injected 2 hours after the assembly of the mono cell, wherein the electrolyte was a mixture of ethylene carbonate and ethyl methyl carbonate in a mass ratio of 3:7.
[148]
[149]
Comparative Example 3
[150]
After preparing the negative electrode prepared as in Comparative Example 1 and the positive electrode prepared as in Example 3, a negative electrode/separator (a porous film made of polypropylene (20 μm, Celgard)/anode, in that order, a 1-stack mono cell After assembling the mono cell, the electrolyte was injected 2 hours later, wherein the electrolyte was a mixture of ethylene carbonate and ethyl methyl carbonate in a mass ratio of 3:7.
[151]
[152]
Comparative Example 4
[153]
Preparation of a negative electrode having a lithium diffusion rate control layer manufactured by a coating method
[154]
In preparing the negative electrode provided with the lithium diffusion rate control layer and the lithium layer in Example 1, a solution casting of a polymethyl methacrylate solution (0.5wt% PMMA (Mw: 890k) in anisole solution) on the negative electrode mixture layer After coating by the method, it was dried at 80° C. for 24 hours to form a lithium diffusion rate control layer. Thereafter, a negative electrode was manufactured in the same manner as in Example 1. At this time, the thickness of the polymethyl methacrylate layer is 200 nm.
[155]
Preparation of mono cell
[156]
After preparing the prepared negative electrode and the positive electrode prepared as in Example 3, a 1-stack mono cell was prepared in the order of a negative electrode/separator (polypropylene porous film (20 μm, Celgard)/anode). After assembling, the electrolyte was injected 2 hours later, wherein the electrolyte was a mixture of ethylene carbonate and ethyl methyl carbonate in a mass ratio of 3:7.
[157]
[158]
Experimental Example 1
[159]
The batteries prepared in each Example and Comparative Example were first discharged to 0.1C to 1.5V in CC mode, and then charged to CC/CV mode under 0.1C, 5mV, 0.005C cut conditions, and discharge to 0.1C. By proceeding in the CC mode up to 1.5V, irreversible capacity was performed during the initial charge/discharge. The total dosage is the sum of the Li intercalation capacity and the SEI generation capacity. Here, as for the Li intercalation capacity, the capacity of lithium inserted in the negative electrode can be obtained by measuring the initial capacity up to 1.5V discharge. In addition, the SEI generation capacity will limit the 1 st irreversible capacity of the lithiation negative electrode from the 1 st irreversible capacity of the negative electrode before lithiation .
[160]
[Table 1]
When to inject the electrolyte division Total dosage(mAh/cm 2 )
Inject immediately after cell production Comparative Example 1 1.40
Example 1 1.41
Infusion after 2 hours after cell production Comparative Example 2 1.17
Comparative Example 3 1.17
Comparative Example 4 1.40
Example 2 1.38
Example 3 1.41
[161]
It was confirmed that the amount of lithiation was similar in Example 1 and Comparative Example 1 in which an electrolyte was injected immediately after coin cell fabrication. However, when the electrolyte was injected after 2 hours after cell fabrication, Comparative Examples 2 and 3 without the lithium diffusion rate control layer had the amount of lithiation, and Examples 2 and 3 provided with the lithium diffusion rate control layer Compared with Comparative Example 4, it was found to be significantly lower. Accordingly, it was confirmed that loss of lithium was small before performing lithiation in the negative electrode provided with the lithium diffusion rate control layer of the present invention.
[162]
[163]
Experimental Example 2
[164]
For the cells of Example 3 and Comparative Examples 3 and 4, in order to measure the resistance, a 2.5C discharge current was applied for 30 seconds in the SOC 50 state, and the resistance was substituted by the following equation through the voltage change before/after the current application. Measurements were made and the results are shown in Table 2.
[165]
Resistance = (Vi-Vf)/I
[166]
(In the above equation, Vi is the current applied voltage, Vf is the voltage after the current is applied, and I is the amount of current)
[167]
[Table 2]
When to inject the electrolyte division Resistance (@SOC 50, ohm)
Infusion after 2 hours after cell production Comparative Example 3 0.83
Comparative Example 4 1.05
Example 3 0.75
[168]
Since Comparative Example 3 does not have a lithium diffusion rate control layer, the resistance value is lower than that of Comparative Example 4 with a lithium diffusion rate control layer. Example 3 is provided with a lithium diffusion rate control layer as in Comparative Example 4, but the thickness of the lithium diffusion rate control layer is much thinner compared to Comparative Example 4, it can be confirmed that the resistance is low, which is the lithium diffusion rate control layer. It is equal to or lower than Comparative Example 3, which is not equipped. Accordingly, it was confirmed that the resistance of the negative electrode provided with the lithium diffusion rate control layer of the present invention did not increase.
[169]
[Explanation of code]
[170]
1: chamber
[171]
30: metal atom
[172]
30': first part of chemically adsorbed metal atom
[173]
30": the second part of a metal atom that is physically adsorbed or drifting
[174]
30a: first partial precursor of chemisorbed metal atom
[175]
40: oxidizing agent
[176]
50: metal oxide layer
[177]
100: cathode
[178]
10', 110: current collector
[179]
20', 120: negative electrode mixture layer
[180]
130: lithium diffusion rate control layer
[181]
20,140: lithium layer
[182]
10,150: peeling plate
Claims
[Claim 1]
Current collector; A negative electrode mixture layer formed on the current collector, a lithium diffusion rate controlling layer formed on the negative electrode mixture layer by atomic layer deposition, and a lithium layer formed on the lithium diffusion rate controlling layer; A negative electrode for a lithium secondary battery comprising a.
[Claim 2]
The negative electrode for a lithium secondary battery according to claim 1, wherein the lithium diffusion rate control layer controls diffusion of lithium in the lithium layer into the negative electrode mixture layer until the electrolyte is injected.
[Claim 3]
The negative electrode for a lithium secondary battery according to claim 1, wherein the lithium diffusion rate control layer controls diffusion of lithium in the lithium layer into the negative electrode mixture layer until the first charge and discharge.
[Claim 4]
The negative electrode for a lithium secondary battery according to claim 1, wherein the thickness of the lithium diffusion rate control layer is 0.1 to 100 nm.
[Claim 5]
The negative electrode for a lithium secondary battery according to claim 1, wherein the thickness of the lithium diffusion rate control layer is 0.5 to 50 nm.
[Claim 6]
The negative electrode for a lithium secondary battery according to claim 1, wherein the negative electrode mixture layer comprises one compound or a mixture of two or more selected from the group consisting of SiO x (0