KR100800968B1 - Method for Improvement of Performance of Si Thin Film Anode for Lithium Rechargeable Battery - Google Patents

Abstract

In the lithium secondary battery using the Si-based negative electrode active material, the present invention provides a surface treatment such that the surface of the negative electrode current collector has a specific morphology, and preferably a state in which a bias voltage is applied to the surface-treated negative electrode current collector. Depositing a silicon film as a negative electrode active material by sputtering, and / or interposing an adhesive layer between the surface-treated negative electrode current collector and the silicon film, thereby enhancing the bonding force between the negative electrode current collector and the active material and ultimately improving the charge / discharge cycle characteristics. Provide a method.

Description

Method for Improvement of Performance of Si Thin Film Anode for Lithium Rechargeable Battery}             

1A and 1B are SEM pictures of the surface and vertical cross section of a silicon thin film deposited on Si-wafer by sputtering in Example 2;

2A and 2B are SEM images of the surface and vertical section of the silicon thin film deposited on Si-wafer by applying a bias voltage during sputtering in Example 2. FIG.

3A and 3B are surface SEM photographs of a silicon thin film deposited on Ni foil in Example 2;

4A and 4B are graphs showing charge and discharge profiles of lithium secondary batteries in Example 2;

5A-5D are SEM pictures of the surface of Cu foil in Example 3 and Comparative Examples 1-3;

6 is a graph showing charge and discharge cycle characteristics of the lithium secondary batteries prepared in Example 3 and Comparative Examples 1 to 3;

7 is a graph showing charge and discharge cycle characteristics of a lithium secondary battery in Example 4;

8A and 8B are SEM images of the surface of the silicon thin film after one and eighteen charge and discharge cycles in Example 4;

9A and 9B are SEM images of the surface of the silicon thin film after one and eighteen charge and discharge cycles in Example 3. FIG.

The present invention relates to a method for improving the charge and discharge cycle characteristics of a lithium secondary battery using a Si-based negative electrode active material, and more particularly, the surface of the negative electrode current collector is surface-treated to have a specific morphology, preferably Between the negative electrode current collector and the active material by depositing a silicon film as a negative electrode active material by sputtering in a state where a bias voltage is applied to the surface-treated negative electrode current collector, and / or interposing an adhesive layer between the surface treated negative electrode current collector and the silicon film. It provides a way to enhance the binding force of the ultimately improve the charge and discharge cycle characteristics.

As the development and demand for mobile devices increases, the demand for secondary batteries as energy sources is increasing rapidly. Among them, many researches have been conducted and commercialized and widely used for lithium secondary batteries with high energy density and discharge voltage. It is used.                         

Recently, a lithium secondary battery using a Li-Si-based active material as a negative electrode has attracted much attention. The theoretical specific capacity of pure silicon (Si) is 4200 mAh / g, much higher than 372 mAh / g of graphite carbon. However, Si suffers a large volume change during continuous charge and discharge cycles, which leads to mechanical and electrical degradation, and therefore poor cycle characteristics have been pointed out as a problem.

As part of an effort to solve these charge and discharge cycle characteristics, some prior art proposes a new structure electrode in which a surface of a copper current collector is roughened and an amorphous silicon film is deposited thereon. While these electrodes show high reversible capacities of 3000 mAh / g or more, there is still a need for improvements in cycle characteristics.

The reason for the decrease in capacity during the cycle is generally known to result from the loss of electrical contact between the silicon film and the current collector. Therefore, if a method of improving electrical contact between the silicon film and the current collector in a lithium secondary battery composed of a Li-Si-based negative electrode can be developed, a lithium secondary battery having excellent charge / discharge cycle characteristics may be manufactured.

The present invention aims to solve the problems of the prior art as described above and the technical problems that have been requested from the past. That is, an object of the present invention is to provide a method for improving charge and discharge cycle characteristics in a lithium secondary battery using a Si-based negative electrode active material.

The inventors have conducted extensive research and various experiments to solve the loss of electrical contact between the silicon film and the negative electrode current collector during charging and discharging, which are the most problematic problems in a lithium secondary battery including a Si-based negative electrode active material. The electrical contact loss can be greatly improved when is treated to have a specific surface morphology, and furthermore, a bias voltage is applied to the current collector in the process of depositing a silicon film on the surface-treated negative current collector by sputtering. The present invention has been found to significantly improve the charge / discharge cycle characteristics of a battery by applying and / or interposing an adhesive layer between a silicon film and a negative electrode current collector, thereby completing the present invention.

Therefore, in the lithium secondary battery using the Si-based negative electrode active material, the method for improving the charge-discharge cycle characteristics according to the present invention has a grain boundary of 5 ~ 100 ㎛ size over the entire surface of the negative electrode current collector And surface treatment of the negative electrode current collector so as to have a surface morphology in which valleys of at least 1 μm or more are formed at the contact points of the grain boundaries.

According to the experiments of the present inventors, the negative electrode current collector having the surface morphology as described above significantly increases the adhesion between the silicon film and the negative electrode current collector when the silicon film is deposited on its surface, so that the silicon film as the negative electrode active material during charge and discharge has a large volume. Even with the change, it was confirmed that the electrical contact loss with the negative electrode current collector is small.                     

The negative electrode current collector is manufactured to a thickness of approximately 3 to 500 μm. Such a negative electrode current collector is not particularly limited as long as it has conductivity without causing chemical change in the battery. For example, the surface of copper, nickel, stainless steel, aluminum, titanium, calcined carbon, copper or stainless steel The surface treated with carbon, nickel, titanium, silver, and the like, aluminum-cadmium alloy, and the like can be used, and preferably copper, nickel or stainless steel is used. The negative electrode current collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a nonwoven fabric, and the like.

It is known in the art to process the surface of the negative electrode current collector to form fine concavities and convexities, but examples of improving the charge / discharge cycle characteristics of the Si-based negative active material by forming a specific surface morphology as in the present invention are still confirmed. It wasn't. Furthermore, even when the surface is treated to form fine concavities and convexities as in the prior art, when the surface morphology of the present invention does not have a charge and discharge cycle characteristic, it can be confirmed in Examples and Comparative Examples to be described later.

As the Si-based anode active material, amorphous silicon or nanocrystalline silicon may be preferable. In addition, other elements can be added to form alloy-like structures to mitigate the volume expansion of Si itself and to improve the electrical conductivity of silicon. At this time, as an element that can be added, for example, zirconium (Zr), titanium (Ti), iron (Fe), vanadium (V), cobalt (Co), nickel (Ni), copper (Cu), chromium ( Cr), manganese (Mn), molybdenum (Mo), tantalum (Ta), tungsten (W), tin (Sn), silver (Ag), aluminum (Al), and the like. Two or more of may be used together.                     

In the present invention, the size of the grain boundary is 5 to 100 μm as defined above, and if the grain size is too small, it is difficult to induce the formation of a self-organized micro columnar structure through the grain boundary. , A problem arises in that stress dispersion becomes difficult during volume expansion of the negative electrode active material generated in the reaction of Li and Si. On the contrary, if the size of the grain boundary is too large, a problem may occur in that the stress dispersing and relaxation effect in the grain boundary formed when the deposited anode active material reacts with Li is large.

In addition, if the depth of the bone formed at the site where the grain boundaries are in contact with is 1 ㎛ or more as defined above, if the depth is too small, in the process of forming cracks caused by the volume expansion of Si during the reaction of Li and Si However, it is not preferable because cracks may be difficult to induce along the valleys in which the grain boundaries meet, or induction of self-organized microstructure formation through the grain boundaries may be difficult.

The method of forming the surface morphology on the surface of the negative electrode current collector may be various, and examples thereof include chemical or electrical etching by a wet method, reactive gas or ion etching by a dry method, and the like.

As an example, in the case of chemical etching, when using Cu or Ni as the negative electrode current collector, a mixture of FeCl ₃ / HCl / H ₂ O (ratio = 1: 8.5: 33.7 (vol.%)) Is preferably used as the etchant. Can be used. Since the etching time may vary depending on various factors such as the type of the negative electrode current collector and the type of the etchant, it may be determined under such a condition that the surface morphology may be formed in consideration of these factors.

A silicon film is deposited as an active material on an anode current collector having such a surface morphology to manufacture a cathode for a lithium secondary battery. However, the method of depositing a silicon film is not limited to the following, for example, sputtering or LPCVD (Low Pressure) Chemical Vapor Deposition), PECVD (Plasma Enhanced Chemical Vapor Deposition PECVD), vacuum evaporation, and the like. Preferably, sputtering method can be used. The thickness of the silicon film is preferably about 0.5 to 10 mu m in order to ensure proper function as the negative electrode active material.

As a preferred example, when depositing a silicon film by the sputtering, a bias voltage may be applied to the negative electrode current collector to further improve the bonding force between the silicon film and the negative electrode current collector. The bias voltage is preferably in the range of approximately -25 to -200V.

The increase in adhesion of the silicon film to the negative electrode current collector by the application of a bias voltage during sputtering is an enhanced mutual interaction between the silicon film and the negative electrode current collector due to bombardment by energetic ions during sputtering under bias voltage application. It may be related to an intermixing reaction.

As another preferred example, it may be configured to further include an adhesive layer at the interface between the silicon film and the negative electrode current collector. The thickness of the adhesive layer is not particularly limited as long as it does not impair the function of the negative electrode, but is preferably in the range of approximately 50 to 500 kPa.                     

According to the experiments of the present inventors, a lithium secondary battery constructed using a negative electrode having an adhesive layer between a surface-treated negative electrode current collector and a silicon film as described above forms a unique surface morphology in the silicon film after several charge and discharge cycles. It was confirmed that. Details of this are described in Example 4 below, and it is assumed that the charge and discharge cycle characteristics are remarkably improved due to this phenomenon.

The adhesive layer is made of a material having excellent chemical affinity for both the component of the silicon film and the component of the negative electrode current collector without affecting the action of the negative electrode. For example, when Cu or Ni is used as the negative electrode current collector, the adhesive layer may be particularly preferably a zirconium thin film.

As described above, the present invention is directed to (a) treating the surface of the negative electrode current collector so that a specific surface morphology is formed, and preferably (b) depositing a silicon film on the surface treated negative electrode current collector by sputtering. By applying a bias voltage to the current collector or (c) forming an adhesive layer between the negative electrode current collector and the silicon film, the bonding force between the silicon film and the negative electrode current collector is strengthened, and ultimately, the charge and discharge cycle characteristics are improved. However, of course, in the case of including all three elements described above, the superior effect desired by the present invention can be obtained.

In some cases, after the adhesive layer is formed on the negative electrode current collector, heat treatment may be performed to further enhance the bonding force between the negative electrode current collector and the adhesive layer. The heat treatment causes an interfacial reaction between the negative electrode current collector and the adhesive layer, which means that some components of the negative electrode current collector are diffused into the adhesive layer, and conversely, some components of the adhesive layer are diffused into the negative electrode current collector, thereby increasing the bonding force as the affinity increases. Done. The heat treatment can be performed, for example, for 10 seconds to 30 minutes at 100 to 400 ° C.

The present invention also relates to a lithium secondary battery composed of a negative electrode treated or prepared by the above method, a positive electrode, a separator, and a lithium salt-containing nonaqueous electrolyte.

The positive electrode is prepared by, for example, applying a mixture of a positive electrode active material, a conductive agent, and a binder onto a positive electrode current collector, followed by drying, and optionally, a filler may be further added to the mixture.

The positive electrode current collector is generally made to a thickness of 3 to 500 ㎛. Such a positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. For example, the surface of stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel Surface treated with carbon, nickel, titanium, silver or the like can be used. The current collector may form fine irregularities on its surface to increase the adhesion of the positive electrode active material, and may be in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a nonwoven fabric.

The lithium transition metal oxide as the positive electrode active material may be a layered compound such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), or a compound substituted with one or more transition metals; Lithium manganese oxides such as Li _{1 + x} Mn _2-x O ₄ (where x is 0 to 0.33), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO _2, and the like; Lithium copper oxide (Li ₂ CuO ₂ ); Vanadium oxides such as LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , Cu ₂ V ₂ O ₇ and the like; Ni-site type lithium nickel oxide represented by the formula LiNi _1-x M _x O ₂ , wherein 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 (wherein M = Co, Ni, Fe, Cr, Zn or Ta and x = 0.01 to 0.1) or Li ₂ Mn ₃ MO ₈ (wherein M = Fe, Co, Lithium manganese composite oxide represented by Ni, Cu or Zn); LiMn ₂ O _{4 in} which a part of Li in the formula is substituted with alkaline earth metal ions; Disulfide compounds; Or Fe ₂ (MoO ₄ ) ₃ , and the like, but are not limited thereto.

The conductive agent is typically added in an amount of 1 to 50 wt% based on the total weight of the mixture including the positive electrode active material. Such a conductive agent is not particularly limited as long as it has conductivity without causing chemical change in the battery. Examples of the conductive agent include graphite such as natural graphite and artificial graphite; Carbon blacks such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and summer black; Conductive fibers such as carbon fibers and metal fibers; Metal powders such as carbon fluoride powder, aluminum powder and nickel powder; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive metal oxides such as titanium oxide; Conductive materials such as polyphenylene derivatives and the like can be used.

The binder is a component that assists in bonding the active material and the conductive agent to the current collector, and is generally added in an amount of 1 to 50 wt% based on the total weight of the mixture including the positive electrode active material. Examples of such binders include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, Polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butylene rubber, fluororubber, various copolymers, and the like.

The filler is optionally used as a component for inhibiting expansion of the positive electrode, and is not particularly limited as long as it is a fibrous material without causing chemical change in the battery. Examples of the filler include olefin polymers such as polyethylene and polypropylene; Fibrous materials, such as glass fiber and carbon fiber, are used.

The separator is interposed between the cathode and the anode, and an insulating thin film having high ion permeability and mechanical strength is used. The pore diameter of the membrane is generally 0.01 ~ 10 ㎛ ㎛, thickness is generally 5 ~ 300 ㎛. As such a separator, for example, olefin polymers such as chemical resistance and hydrophobic polypropylene; Sheets or non-woven fabrics made of glass fibers or polyethylene are used. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also serve as a separator.

The lithium salt-containing non-aqueous electrolyte consists of a nonaqueous electrolyte and lithium. As the nonaqueous electrolyte, a nonaqueous electrolyte, a solid electrolyte, an inorganic solid electrolyte, and the like are used.

As said non-aqueous electrolyte, N-methyl- 2-pyrrolidinone, a propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, gamma-butyl Low lactone, 1,2-dimethoxy ethane, tetrahydroxy franc, 2-methyl tetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolon, formamide, dimethylformamide, dioxolon, aceto Nitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxy methane, dioxorone derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative Aprotic organic solvents such as tetrahydrofuran derivatives, ethers, methyl pyroionate and ethyl propionate can be used.

Examples of the organic solid electrolytes include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphate ester polymers, polyedgetion lysine, polyester sulfides, polyvinyl alcohols, polyvinylidene fluorides, Polymers containing ionic dissociating groups and the like can be used.

Examples of the inorganic solid electrolyte include Li ₃ N, LiI, Li ₅ NI ₂ , Li ₃ N-LiI-LiOH, LiSiO ₄ , LiSiO ₄ -LiI-LiOH, Li ₂ SiS ₃ , Li ₄ SiO ₄ , Nitrides, halides, sulfates and the like of Li, such as Li ₄ SiO ₄ -LiI-LiOH, Li ₃ PO ₄ -Li ₂ S-SiS ₂ , and the like, may be used.

The lithium salt is a good material to be dissolved in the non-aqueous 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) 2 NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate and imide have.

In addition, for the purpose of improving charge / discharge characteristics, flame retardancy, etc., for example, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, hexaphosphate triamide, etc. Nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N, N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxy ethanol, aluminum trichloride, etc. It may be. In some cases, in order to impart nonflammability, halogen-containing solvents such as carbon tetrachloride and ethylene trifluoride may be further included, and carbon dioxide gas may be further included to improve high temperature storage characteristics.

The above is an exemplary description of the components of the battery that can be configured using the aluminum-based positive electrode current collector according to the present invention, in which case some of the components are excluded or substituted or other components are to be added. It may be.

Hereinafter, the present invention will be described in detail by way of examples, but the scope of the present invention is not limited thereto.

Example 1

Using the etching liquid mixture of FeCl ₃ in 2.4 M HCl aqueous solution in a final concentration of about 0.4 M by etching for one minute surface of the Ni foil was subjected to a surface treatment. A 5000 mm3 Si thin film was formed from a 2 "diameter Si target (99.99%) by rf magnetron sputtering on the so-treated Ni foil current collector. The sputtering was performed by argon gas after vacuum pumping to 2 x 10 ^-6 Torr. Was performed in a chamber set to 5 mTorr.

In order to confirm the electrochemical properties of the Si thin film electrode, pure Li foil was used as an anode, and a mixed solvent of ethylene carbonate (EC) / diethylene carbonate (DEC) as an electrolyte (volume ratio = 1: 1) to use the mixture was added a 1 M LiPF _6, was prepared in two 2016 coin cell. These batteries were assembled in an argon glove box and subjected to more than 30 charge and discharge experiments at 0-1.2 V using 100 mA / cm ² current at 30 ° C. As a result, excellent charge and discharge cycle characteristics were confirmed.

Example 2

In order to confirm the effect of applying the bias voltage in the sputtering process, (a) the deposition of the Si thin film on the Si-wafer by sputtering, and (b) as described above while applying a DC bias voltage of-100 V The sputtering was carried out to deposit an Si thin film on Si-wafer.

1A and 1B show scanning electron microscopy (SEM) images of the surface (FIG. 1A) and the vertical cross section (FIG. 1B) of the Si thin film obtained in the above experiment (a), and FIGS. 2A and 2B show the experiment (b). SEM images of the surface (FIG. 2A) and the vertical cross section (FIG. 2B) of the Si thin film obtained in FIG.

The Si thin film of Experiment (a) showed a columnar structure with a rough surface morphology and cross section, whereas the Si thin film of Experiment (b) had a smoother deposition surface due to the application of bias voltage. It can be seen.

Charge and discharge experiments were performed on these Si thin films as in Example 1. A surface SEM photograph of the Si thin film (experiment (a)) after one charge and discharge cycle is shown in FIG. 3A, and a graph showing the charge and discharge profile is shown in FIG. 4A. In addition, a SEM image of the surface of the Si thin film (experiment (b)) after one charge and discharge cycle is shown in FIG. 3B, and a graph showing the charge and discharge profile is shown in FIG. 4B. In comparison, the lithium secondary battery using the Si thin film of Experiment (b) showed relatively low initial irreversible capacity and relatively high charge / discharge cycle characteristics as shown in FIG. 4B. Inferred from the results of the SEM photographs of FIGS. 3A and 3B, it appears to be mainly due to the increase in adhesion of the Si thin film by application of a bias voltage.

Example 3

The Cu foil was surface-treated in the same manner as in Example 1 using Cu foil instead of Ni foil, and the experiment was repeated by applying a DC bias voltage of −100 V in the same manner as in Example 2.

A SEM photograph of the surface of the etched Cu foil is shown in FIG. 5A, and the charge and discharge cycle characteristics for a cell fabricated using such Cu foil is shown in FIG. 6.

Comparative Example 1-3

Except for the fact that no etching was performed (Comparative Example 1), or an etching solution as shown in Table 1 was used instead of the FeCl ₃ / HCl / H ₂ O etching solution, and the etching time was changed (Comparative Examples 2 and 3). Was repeated the experiment in the same manner as in Example 3.

Etching solution Etching time Surface SEM photo Example 3 FeCl ₃ + HCl + H ₂ O 1 min 5a Comparative Example 1 - 0 5b Comparative Example 2 HNO ₃ + H ₂ O 3 min Fig 5c Comparative Example 3 FeCl ₃ + H ₂ O 5 min 5d

SEM photographs of each surface of the etched Cu foil are disclosed in FIGS. 5B-5D. It is noted that the surface morphology of the Cu foil of Example 3 (FIG. 5A) differs greatly from that of Comparative Examples 1-3 (FIGS. 5B-5D). That is, it can be confirmed that the grain boundary portion is developed somewhat broadly and deeply on the surface of the Cu foil of Example 3.

In addition, the charge and discharge cycle characteristics of the batteries of Comparative Examples 1 to 3 is shown in the graph of Figure 6 with the results of Example 3. These results show that the charge / discharge cycle characteristics of the battery have a deep correlation with the surface morphology of the Cu substrate, and show particularly excellent results in the battery of Example 3.

The influence on the improvement of the cycle characteristics of the surface roughness of the Cu substrate results from the formation of the micro columnar structure during charge and discharge. Proper surface treatment of the Cu substrate by etching provides a thin film of excellent self-organized microcircular structure, thereby reducing stress and tensile forces caused by changes in volume during charge and discharge cycles. Thus, as shown in Figure 6, the battery of Example 3 shows an excellent capacity storage capacity compared to the batteries of Comparative Examples 1 to 3.

Example 4                     

Except that the Zr layer was deposited to 100 kHz by applying a direct current bias voltage of-100 V to the substrate by the rf magnetron sputtering method on the surface of the Cu foil etched in Example 3, and then a Si thin film was deposited thereon. The experiment was repeated in the same manner as in Example 3.

7 shows the cycle characteristics of the battery prepared in this example together with the results for the battery of Example 3, the charge and discharge cycle characteristics were further increased by interposing the Zr layer between the Cu foil and the Si thin film. It can be seen.

8A and 8B show SEM images of the Si thin film after one charge and discharge cycle and 18 charge and discharge cycles, respectively, for the battery of this example. In contrast, FIGS. 9A and 9B disclose SEM images of the Si thin film after one charge and discharge cycle and 18 charge and discharge cycles for the battery of Example 3, respectively. Comparing FIGS. 8B and 9B, cracks are formed in all of these electrodes after 18 charge / discharge cycles, but there is a big difference in terms of structure. That is, FIG. 8B shows wide gaps formed along the grain boundary profile of the Cu substrate as shown in FIG. 1A and narrows again in a number of islands surrounded by such wide gaps. gaps are formed, showing a structure in which fine islands of small and uniform size are formed by narrow gaps as a whole. The fine columnar structure thus formed was shown to be stable during the charge and discharge cycle as shown in FIG. 7. This is possible because Si can be strongly adhered to the Cu substrate by interposing a Zr layer as an adhesive layer between the Cu current collector and the Si thin film. In comparison, FIG. 9B illustrates a structure in which islands and cracks are randomly distributed and islands have a relatively large size. Moreover, it can be seen that some islands have detached from the Cu substrate. Therefore, it can be seen that the introduction of the Zr adhesive layer at the interface between the Si thin film and the Cu substrate can fundamentally solve the problem of the capacity gradually decreasing during the charge and discharge cycle.

As described above, according to the method of the present invention, since the bonding force between the silicon film and the current collector as the negative electrode active material can be enhanced to minimize the electrical contact loss during the charge and discharge process, a lithium secondary battery having excellent charge and discharge cycle characteristics It can manufacture.

Those skilled in the art to which the present invention pertains will be able to make various applications and modifications within the scope of the present invention based on the above contents.

Claims (10)

In a lithium secondary battery using a Si-based negative electrode active material, a grain boundary having a size of 5 to 100 μm over the entire surface of a negative electrode current collector of Cu or Ni, and a valley having a depth of at least 1 μm or more in contact with the grain boundaries And surface treating the negative electrode current collector to have the surface morphology formed thereon, forming a zirconium thin film as an adhesive layer on the surface-treated negative electrode current collector, and then depositing a silicon film as a negative electrode active material thereon. To improve the charge and discharge cycle characteristics of a lithium secondary battery. The method according to claim 1, wherein the surface treatment is performed by chemical or electrical etching by wet method or reactive gas or ion etching by dry method. The method of claim 2, wherein in the case of chemical etching a mixture of FeCl ₃ / HCl / H ₂ O is used as the etchant. delete delete delete The method of claim 1, wherein after forming an adhesive layer on the surface-treated negative electrode current collector, a silicon film as a negative electrode active material is deposited on the adhesive layer by sputtering while a bias voltage is applied to the negative electrode current collector. . 8. The method of claim 7, wherein the adhesive layer is formed on the negative electrode current collector and then heat treated to further strengthen the bonding force between the negative electrode current collector and the adhesive layer. The method of claim 8, wherein the heat treatment is performed at 100 to 400 ° C. for 10 seconds to 30 minutes. A lithium secondary battery comprising a negative electrode treated or prepared by the method according to claim 1, a positive electrode, a separator, and a lithium salt-containing nonaqueous electrolyte.

Images