Negative electrode material for secondary battery comprising polymer protective layer and method for preparing same

Abstract

The present invention relates to: a negative electrode material for a secondary battery, comprising a polymer protective layer; and a method for preparing same. According to the present invention, by coating a silicon-based negative electrode material with a single layer or multiple layers of a monomer or copolymer, direct contact between a high-capacity negative electrode material and an electrolyte can be prevented, thus preventing the mechanical degradation (pulverization) of the negative electrode material which is caused by intercalation of lithium ions. In addition, it is possible to suppress side reactions such as the formation of a solid electrolyte interface (SEI) layer, which is formed on the surface of a negative electrode material due to the decomposition of an electrolyte in an initial reaction. Thus, according to the present invention, by uniformly coating the polymer protective layer onto the surface of the negative electrode material, the lifespan characteristics of a secondary battery are enhanced while maintaining the characteristics of existing negative electrode materials at equivalent or higher levels. Therefore, it is expected that the negative electrode material can be effectively applied as a negative electrode material for a secondary battery.

Description

Negative electrode material for secondary battery including polymer protective layer and method for manufacturing same

[0001] The present invention relates to a secondary battery negative electrode material including a polymer protective layer and a method for manufacturing the same, and more specifically, to a secondary battery negative electrode material coated with a polymer protective layer capable of suppressing volume expansion due to insertion of lithium ions and preventing mechanical destruction by coating a single layer or multiple layers of a polymer monomer or copolymer on the surface of the negative electrode material, thereby increasing the lifespan characteristics of the secondary battery, and a method for manufacturing the same.

[0002] Lithium-ion batteries, consisting of a cathode / anode / separator / electrolyte, are high-energy-density energy storage devices capable of reversibly converting chemical and electrical energy and rechargeable and dischargeable. They are widely used in small electronic devices such as mobile phones and laptops. Recently, their application in hybrid electric vehicles (HEVs), plug-in electric vehicles (plug-in EVs), e-bikes, and energy storage systems (ESS) has been rapidly expanding due to environmental concerns, high oil prices, and concerns about energy efficiency and storage.

[0003] Currently, carbon-based materials are primarily used as anode materials for secondary batteries, but their reversible capacity is extremely low, at around 350 mAh / g. With the recent rapid development of large-scale energy storage applications, research is actively underway to develop high-capacity materials to replace carbon-based anode materials.

[0004] Si (theoretical capacity 4,200 mAh / g) is attracting attention as a substitute for carbon-based anode materials in secondary batteries, but it has problems such as a volume expansion of up to 400% during charging, decomposition, pulverization, or cracking of the active material during repeated charging and discharging, or side reactions at the interface between the anode and electrolyte, which adversely affect the lifespan and thermal stability of the electrode.

[0005] The problem to be solved by the present invention is to provide a silicon-based negative electrode material for a secondary battery that can suppress volume expansion due to insertion of lithium ions and prevent mechanical destruction.

[0006] Another technical problem to be solved in the present invention is to provide a method for manufacturing the silicon-based negative electrode material for the secondary battery.

[0007] In addition, another technical problem to be solved in the present invention is to provide a lithium ion secondary battery including the silicon-based negative electrode material for the secondary battery.

[0008] In order to solve the above-mentioned technical problem, the present invention provides a silicon-based negative electrode material for a secondary battery, characterized in that a polymer protective layer is coated on the surface of the negative electrode material.

[0009] Preferably, the polymer protective layer is selected from the group consisting of 2-hydroxyethyl methacrylate (HEMA), 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (V4D4), 2,4,6-trivinyl-2,4,6-trimethyl cyclotrisiloxane, polyacrylonitrile (PAN), polyacrylic acid (PAA), divinylbenzene, hexavinyldisiloxane, 1H,1H,2H,2H-perfluorodecyl acrylate, glycidyl methacrylate, ethylene glycol dimethacrylate 4-vinyl-pyridine, 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecablueorodecyl methacrylate, It is characterized by being composed of one or more monomers selected from the group consisting of 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl methacrylate and 2-dimethylaminoethyl methacrylate or a copolymer thereof.

[0010] The copolymer is characterized by being at least one selected from the group consisting of glycidyl methacrylate-co-2-(dimethylamino)ethyl methacrylate (GMA-co-DMAEMA), 2-hydroxyethyl methacrylate-co-2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (HEMA-co-V4D4), and ethylene glycol dimethacrylate-co-divinylbenzene (EGDMA-co-PFDA).

[0011] Preferably, the polymer protective layer is Al2O x , SiO x and TiO x It may additionally include one or more inorganic substances selected from the group consisting of (X is a number from 1 to 10).

[0012] Preferably, the polymer protective layer may be formed of a single layer or multiple layers.

[0013] Preferably, the thickness of the polymer protective layer is characterized by being 1 to 1,000 nm.

[0014] Preferably, the polymer protective layer is characterized in that the thickness deviation is less than 30%.

[0015] Preferably, the polymer protective layer is characterized in that it is formed by a dry polymer vapor deposition method.

[0016] Preferably, the polymer protective layer is characterized by having a surface coverage ratio (Rsc, polymer-coated area / negative electrode material surface area) of 95% or more on the surface of the porous substrate.

[0017] Preferably, the cathode material coated with the polymer protective layer is characterized in that the surface roughness (Sa) roughness value change rate and the specific surface area (BET) change rate are each less than 10%.

[0018] Preferably, the negative electrode material is characterized by being at least one selected from the group consisting of silicon nanoparticles, silicon nanowires, porous silicon nanoparticles, silicon nanotubes, carbon nanotubes, and graphite.

[0019] In order to solve the other technical problems mentioned above, the present invention provides a method for manufacturing a silicon-based negative electrode material for a secondary battery coated with a polymer protective layer, characterized in that a polymer protective layer is coated on the surface of the silicon-based negative electrode material for a secondary battery using a chemical vapor deposition method.

[0020] Preferably, the process of coating the polymer protective layer is characterized by being performed for 1 to 600 minutes under conditions of a temperature of 10 to 80°C and a pressure of 1 mTorr to 500 Torr.

[0021] In addition, in order to solve the other technical problems mentioned above, the present invention provides a lithium ion secondary battery including a negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and an electrolyte, wherein the negative electrode includes a negative electrode material including a polymer protective layer.

[0022] In this way, according to the present invention, by coating a silicon-based negative electrode material with a single or multiple layer of a polymer monomer or copolymer, direct contact between the high-capacity negative electrode material and the electrolyte is prevented, thereby preventing mechanical destruction (pulverization) of the negative electrode material due to lithium ion insertion. In addition, side reactions such as the formation of a solid electrolyte interface (SEI) layer on the surface of the negative electrode material due to the decomposition of the electrolyte in the initial reaction can be suppressed. Therefore, according to the present invention, since the polymer protective layer is uniformly coated on the surface of the negative electrode material, the characteristics of existing negative electrode materials are maintained at an equivalent level or higher, while the lifespan characteristics of secondary batteries are increased, and thus it is expected that the present invention can be usefully applied as an negative electrode material for secondary batteries.

[0023] The following drawings attached to this specification illustrate preferred embodiments of the present invention and, together with the contents of the invention described above, serve to further understand the technical idea of ​​the present invention, and therefore, the present invention should not be interpreted as being limited to matters described in such drawings.

[0024] Figure 1 illustrates a form in which a polymer protective layer is coated on the surface of a silicon-based negative electrode material according to the present invention.

[0025] Figure 2 illustrates an example in which a polymer protective layer is coated in a multilayer of three layers on the surface of a silicon-based negative electrode material according to the present invention.

[0026] Figure 3 illustrates the morphology of silicon nanoparticles (A), porous silicon nanoparticles (B), and silicon nanowires (C) coated with a polymer protective layer.

[0027] Figure 4 illustrates an example of a form in which a polymer protective layer is coated on a cathode material composed of silicon and graphite.

[0028] Figure 5 illustrates an example of a form in which a polymer protective layer is coated on a cathode material composed of a binder together with silicon and graphite.

[0029] Figure 6 is a transmission electron microscope (TEM) image of a cathode material coated with a polymer protective layer.

[0030] Figure 7 shows the results of analyzing the components of a cathode material coated with a polymer protective layer according to the present invention.

[0031] Figure 8 is a photograph of a cathode material slurry manufactured using a cathode material coated with a polymer protective layer according to the present invention.

[0032] Figure 9 is a photograph of a cathode manufactured using a cathode material coated with a polymer protective layer according to the present invention.

[0033] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily implement the present invention. However, the present invention may be implemented in various different embodiments and is not limited to the embodiments described herein. Like reference numerals designate similar parts throughout the specification.

[0034] The present invention provides a silicon-based negative electrode material for a secondary battery, characterized in that a polymer protective layer is coated on the surface of the negative electrode material.

[0035] Figure 1 illustrates a form in which a polymer protective layer is coated on the surface of a silicon-based negative electrode material according to the present invention.

[0036] According to the present invention, the polymer protective layer coated on the surface of the negative electrode material is an acrylate-based polymer, which prevents direct contact between the high-capacity negative electrode material and the electrolyte, thereby preventing mechanical destruction (pulverization) of the negative electrode material due to insertion of lithium ions, and suppresses side reactions such as decomposition of the electrolyte in the initial reaction and formation of an SEI layer on the surface of the negative electrode material.

[0037] According to one embodiment of the present invention, the polymer protective layer is selected from the group consisting of 2-hydroxyethyl methacrylate (HEMA), 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (V4D4), 2,4,6-trivinyl-2,4,6-trimethyl cyclotrisiloxane, polyacrylonitrile (PAN), polyacrylic acid (PAA), divinylbenzene, hexavinyldisiloxane, 1H,1H,2H,2H-perfluorodecyl acrylate, glycidyl methacrylate, ethylene glycol dimethacrylate 4-vinyl-pyridine, 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecablueorodecyl methacrylate, It is characterized by being at least one monomer selected from the group consisting of 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl methacrylate and 2-dimethylaminoethyl methacrylate or a copolymer thereof.

[0038] The above copolymer can be manufactured by selecting and combining two or more of the above monomers, and there are no special restrictions on the selection and combination thereof. Specifically, for example, it may be at least one selected from the group consisting of glycidyl methacrylate-co-2-(dimethylamino)ethyl methacrylate (GMA-co-DMAEMA), 2-hydroxyethyl methacrylate-co-2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (HEMA-co-V4D4) and ethylene glycol dimethacrylate-co-divinylbenzene (EGDMA-co-PFDA), and in particular, glycidyl methacrylate-co-2-(dimethylamino)ethyl methacrylate (GMA-co-DMAEMA) and 2-hydroxyethyl methacrylate-co-2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (HEMA-co-V4D4) are preferred, but are not particularly limited thereto.

[0039] The above polymer protective layer may be composed of a copolymer using two or more monomers, and the proportion of each polymer constituting the copolymer is 1 to 99%, preferably 10 to 90%, but is not limited thereto.

[0040] These copolymers can be composed of monomer combinations of polymers with different roles, such as hydrophilicity, water repellency, and enhanced bonding, allowing for the design of desired properties. For example, a copolymer with a precise surface energy can be designed by combining hydrophilic and water repellent monomers, and used as a polymer protective layer, but this is not limited to this.

[0041] According to one embodiment of the present invention, the polymer protective layer may be formed of a single layer or multiple layers, and preferably may be formed of 1 to 3 layers.

[0042] Figure 2 illustrates an example in which a polymer protective layer is coated in a multilayer of three layers on the surface of a silicon-based negative electrode material according to the present invention.

[0043] According to a specific embodiment of the present invention, each of the layers may be formed of polymer layers having different functions. Specifically, for example, the first polymer protective layer close to the silicon surface may be formed of a polymer for improving adhesion to silicon, the second polymer protective layer coated thereon may be formed of a polymer for improving silicon rigidity, and the third polymer protective layer coated thereon may be formed of a polymer for considering wettability with an electrolyte.

[0044] According to one embodiment of the present invention, the first polymer protective layer is selected from the group consisting of 2-hydroxyethyl methacrylate (HEMA), 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (V4D4), 2,4,6-trivinyl-2,4,6-trimenylcyclosiloxane, divinylbenzene, hexavinyldisiloxane, 1H,1H,2H,2H-perfluorodecyl acrylate, glycidyl methacrylate, ethylene glycol dimethacrylate 4-vinyl-pyridine, 2-hydroxyethyl methacrylate, 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecablueorodecyl methacrylate and It may be at least one selected from the group consisting of 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl methacrylate, acrylic acid and acrylonitrile, glycidyl methacrylate-co-2-(dimethylamino)ethyl methacrylate (GMA-co-DMAEMA) and 2-hydroxyethylmethacrylate-co-2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (HEMA-co-V4D4), and 2-hydroxyethylmethacrylate-co-2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (HEMA-co-V4D4) is particularly preferred.

[0045] The polymer constituting the first polymer protective layer as described above can improve bonding strength with the silicon negative electrode material.

[0046] According to one embodiment of the present invention, the second polymer protective layer is selected from the group consisting of polyacrylonitrile (PAN), polyacrylic acid (PAA), 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane, 2,4,6-trivinyl-2,4,6-trimethylcyclotrisiloxane, divinylbenzene, hexavinyldisiloxane, 1H,1H,2H,2H-perfluorodecyl acrylate, glycidyl methacrylate, ethylene glycol dimethacrylate 4-vinyl-pyridine, 2-hydroxyethyl methacrylate, 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecablue orodecyl methacrylate, It may be at least one selected from the group consisting of 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl methacrylate and 2-dimethylaminoethyl methacrylate, and polyacrylonitrile (PAN) or polyacrylic acid (PAA) is particularly preferred.

[0047] The polymer constituting the second polymer protective layer as described above is a high-strength, high-elongation polymer, and by coating the negative electrode material, the life characteristics of the negative electrode material can be maintained or improved.

[0048] According to one embodiment of the present invention, the third polymer protective layer may be at least one selected from the group consisting of polyacrylonitrile (PAN), polyacrylic acid (PAA), 2-hydroxyethyl methacrylate (HEMA), 4-vinyl-pyridine, 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (V4D4) and glycidyl methacrylate-co-2-(dimethylamino)ethyl methacrylate (GMA-co-DMAEMA), and polyacrylonitrile (PAN) or polyacrylic acid (PAA) is particularly preferred.

[0049] The polymer constituting the third polymer protective layer, as described above, can maintain or improve the lifespan of the negative electrode material. Furthermore, it can alter surface energy to enhance bonding with the binder, improve wettability with the electrolyte, and enhance adhesion between the negative electrode and the separator during the battery manufacturing process.

[0050] According to one embodiment of the present invention, the polymer protective layer may further include an inorganic material, and the inorganic material may be made of a metal oxide, for example, Al2O x , SiO x and TiO x It may include one or more selected from the group consisting of (X is an integer from 1 to 10).

[0051] According to one embodiment of the present invention, a single-layer or multi-layer polymer protective layer can be formed by a dry polymer vapor deposition method, and this dry polymer vapor deposition method can be an initiator-based chemical vapor deposition (iCVD), but is not particularly limited thereto.

[0052] The above "iCVD" refers to a process that causes polymerization of monomers by decomposing a gaseous initiator into radicals. In this iCVD process, the deposition of a polymer protective layer occurs by supplying energy such as a heated filament heat source or UV.

[0053] As the above initiator, a peroxide such as tert-butyl peroxide (TBPO) or benzophenone can be used. TBPO is a volatile substance with a boiling point of about 110°C, and is thermally decomposed at around 150°C to form radicals, and benzophenone is decomposed by light such as UV to form radicals.

[0054] According to one embodiment of the present invention, the process of coating the polymer protective layer can be performed for 1 to 600 minutes under conditions of a temperature of 10 to 80°C and a pressure of 1 mTorr to 500 Torr, for example, it can be performed for 30 minutes under conditions of a temperature of 20°C and a pressure of 200 mTorr.

[0055] If the above coating temperature is less than 10°C, the composition of the coating equipment becomes complicated and the manufacturing cost increases, which is a disadvantage, and if the above coating temperature exceeds 80°C, the adsorption of the monomer is not easy.

[0056] If the coating pressure is less than 1 mTorr, the reaction speed may be too slow, and if the coating pressure exceeds 500 Torr, it may be difficult to activate the initiator.

[0057] If the coating time is less than 1 minute, the desired coating thickness of the polymer protective layer cannot be reached, and if the coating time exceeds 600 minutes, the coating thickness may become too thick, which may reduce the breathability of the separator.

[0058] According to one embodiment of the present invention, the polymer protective layer may have a surface coverage ratio (Rsc, polymer-coated area / negative electrode material surface area) of 95% or more on the surface of the negative electrode material, and may uniformly and evenly coat the inner surface of the pores formed in the porous substrate.

[0059] According to one embodiment of the present invention, the thickness of the polymer protective layer may be 1 to 1,000 nm, preferably 3 to 100 nm. In this case, if the thickness of the polymer protective layer is less than 1 nm, there is a problem that the protective layer is destroyed during the shrinkage and expansion process, and if the thickness of the polymer protective layer exceeds 1,000 nm, there is a problem that the performance of the negative electrode material is reduced due to an increase in the electrical resistance of the protective layer.

[0060] According to one embodiment of the present invention, the polymer protective layer can be uniformly and smoothly coated, and specifically, the polymer protective layer coated on the surface of the negative electrode material may have a thickness variation of less than 30%, preferably less than 20%, and more preferably less than 10%. In this case, if the thickness variation of the polymer protective layer exceeds 30%, a weak point may occur, which may prevent the polymer protective layer from performing its protective role, thereby causing a deterioration in the performance of the negative electrode material. In addition, there is a concern that the durability may be reduced compared to the negative electrode material on which the polymer protective layer is uniformly formed, or the silicon may be exposed to the electrolyte, generating an unstable solid electrolyte interface (SEI) layer, which may deteriorate due to repeated charging and discharging, thereby causing the silicon powder to be damaged.

[0061] According to one embodiment of the present invention, the negative electrode material is characterized by being at least one selected from the group consisting of silicon nanoparticles, silicon nanowires, porous silicon nanoparticles, silicon nanotubes, carbon nanotubes, and graphite.

[0062] The size of the above silicon particles may be 5 nm to 500 μm, preferably 5 nm to 1000 nm.

[0063] Figure 3 illustrates the morphology of silicon nanoparticles (A), porous silicon nanoparticles (B), and silicon nanowires (C) coated with a polymer protective layer.

[0064] Figure 4 illustrates an example of a form in which a polymer protective layer is coated on a cathode material composed of silicon and graphite.

[0065] The above negative electrode material may include a binder, and the type of binder is one commonly used in the art and there is no particular limitation thereon.

[0066] Figure 5 illustrates an example of a form in which a polymer protective layer is coated on a cathode material composed of a binder together with silicon and graphite.

[0067] According to one embodiment of the present invention, the cathode material coated with the polymer protective layer is characterized in that the surface roughness (Sa) roughness value change rate and the specific surface area (BET) change rate are each less than 10%.

[0068] Meanwhile, the present invention provides a method for manufacturing a silicon-based negative electrode material for a secondary battery coated with a polymer protective layer, characterized in that a polymer protective layer is coated on the surface of the silicon-based negative electrode material using a dry polymer vapor deposition method.

[0069] According to one embodiment of the present invention, the process of coating the polymer protective layer is characterized in that it is performed for 1 to 600 minutes under conditions of a temperature of 10 to 80°C and a pressure of 1 mTorr to 500 Torr.

[0070] When the above polymer protective layer is formed in multiple layers, the method may include a step of coating a first polymer protective layer on the surface of a porous substrate, a step of coating a second polymer protective layer on the porous substrate coated with the first polymer protective layer, and a step of coating a third polymer protective layer on the porous substrate coated with the second polymer protective layer.

[0071] In addition, the present invention provides a lithium ion secondary battery including a negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and an electrolyte, wherein the negative electrode includes a negative electrode material including a polymer protective layer.

[0072] The lithium-ion secondary battery of the present invention can be manufactured using conventional methods known in the art, without any particular limitations. For example, it can be manufactured by assembling a separator coated with a polymer protective layer according to the present invention between the positive and negative electrodes, and then injecting an electrolyte.

[0073] The method for manufacturing the electrode is not particularly limited, and the negative electrode material or positive electrode material can be manufactured in a form in which it is bonded to the electrode current collector according to a conventional method known in the art.

[0074] The cathode material may be a conventional one, and for example, lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or a composite oxide formed by a combination thereof may be used.

[0075] The electrolyte is A + B - As a salt with the same structure as A + is Li + , Na + , K + B containing an ion composed of an alkali metal cation or a combination thereof; - is PF6 - , BF4 - , Cl - , Br - , I - , ClO4 - , AsF6 - , CH3CO2 - , CF3SO - , NCF3(SO2)2 - , CCF2(SO2)3 - Salts containing anions such as or combinations thereof are dissolved or dissociated in organic solvents such as propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), gamma butyrolactone (γ-butyrolactone) or mixtures thereof, but are not limited thereto.

[0076] Electrolyte injection can be performed at an appropriate stage during the battery manufacturing process, depending on the final product's manufacturing process and required properties. This can be done before battery assembly or during the final assembly stage.

[0077] In this way, according to the present invention, by coating a silicon-based negative electrode material with a single or multiple layer of a polymer monomer or copolymer, direct contact between the high-capacity negative electrode material and the electrolyte is prevented, thereby preventing mechanical destruction (pulverization) of the negative electrode material due to lithium ion insertion. In addition, side reactions such as the formation of a solid electrolyte interface (SEI) layer on the surface of the negative electrode material due to the decomposition of the electrolyte in the initial reaction can be suppressed. Therefore, according to the present invention, since the polymer protective layer is uniformly coated on the surface of the negative electrode material, the characteristics of existing negative electrode materials are maintained at an equivalent level or higher, while the lifespan characteristics of secondary batteries are increased, and thus it is expected that the present invention can be usefully applied as an negative electrode material for secondary batteries.

[0078] Hereinafter, the present invention will be described in more detail using examples. These examples are intended solely to illustrate the present invention more specifically, and it will be apparent to those skilled in the art that the scope of the present invention is not limited by these examples.

[0079]

[0080] <Example 1>

[0081] Silicon non-spherical particles with a size of 350 nm based on D50 were prepared by crushing.

[0082] Next, approximately 100 mL each of the monomer 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (V4D4) (Merck, 96%) and the initiator tert-Butyl peroxide (Merck, 95%) were charged into the iCVD coating equipment equipped with a monomer canister and an initiator canister.

[0083] Next, the monomer canister was heated to about 50°C, and the initiator canister was heated to about 40°C, and silicone non-spherical particles were placed in the coating effective area within the iCVD coating equipment, and a vacuum state was maintained while maintaining the temperature at 25°C.

[0084] Finally, the filament temperature was heated to approximately 150°C to activate the initiator, and then the coating area and the canister were evacuated, and the monomer and initiator were supplied to maintain the pressure of the coating area at approximately 200 mTorr.

[0085] At this time, the formation time of the polymer protective layer was approximately 10 minutes, and the thickness of the polymer protective layer was 5 nm.

[0086] Figure 6 is a transmission electron microscope (TEM) image of a cathode material coated with a polymer protective layer. As can be seen here, according to the present invention, it can be confirmed that the polymer protective layer is uniformly and smoothly coated on the surface of the cathode material.

[0087]

[0088] <Example 2>

[0089] The process was the same as in Example 1, except that the reactor temperature was maintained at 20°C, the monomer canister at 50°C, and the initiator canister at 40°C. The filament temperature was set to 150°C and the pressure to 200 mTorr, thereby producing a cathode material with a polymer protective layer thickness of 20 nm. At this time, the formation time of the polymer protective layer was approximately 40 minutes.

[0090] Figure 7 shows the results of analyzing the components of a cathode material coated with a polymer protective layer according to the present invention.

[0091]

[0092] <Example 3>

[0093] The process was the same as Example 1, except that the reactor temperature was maintained at 20°C, the monomer canister at 50°C, and the initiator canister at 40°C. The filament temperature was set to 150°C and the pressure to 200 mTorr, respectively, to produce a cathode material with a polymer protective layer thickness of 500 nm. At this time, the formation time of the polymer protective layer was approximately 600 minutes.

[0094]

[0095] <Example 4>

[0096] The negative electrode material was manufactured in the same manner as in Example 1, but the iCVD process was performed twice to form a 10 nm thick first polymer protective layer (pV4D4) and a 10 nm thick second polymer protective layer (PAN) on the surface of the silicon nanoparticles. The formation times of the first polymer protective layer and the second polymer protective layer were 30 minutes and 50 minutes, respectively.

[0097]

[0098] <Example 5>

[0099] The negative electrode material was manufactured in the same manner as in Example 1, but the iCVD process was performed three times to form a 5 nm thick first polymer protective layer (pV4D4), a 10 nm thick second polymer protective layer (polyacrylonitrile, PAN), and a 5 nm thick third polymer protective layer (polyacrylic acid, PAA) on the surface of the silicon nanoparticles. The formation times of the first polymer protective layer, the second polymer protective layer, and the third polymer protective layer were 15 minutes, 50 minutes, and 20 minutes, respectively.

[0100]

[0101] <Comparative Example 1>

[0102] Silicon non-spherical particles with a size of 350 nm based on D50 produced by the crushing method were used as a cathode material without coating a polymer protective layer.

[0103]

[0104] <Test Example 1> Performance Analysis of Cathode Materials

[0105] In order to evaluate the performance of a negative electrode material having a polymer protective layer coated on the surface of the negative electrode material according to the present invention, a secondary battery was manufactured using the negative electrode material manufactured according to Example 2 and Comparative Example 1, and then the performance of the negative electrode material was analyzed.

[0106]

[0107] Coin cell manufacturing process

[0108] The cells were fabricated with 1M LiPF6 in EC / DEC (3:7 v / v) + 5% FEC electrolyte, Super P (1 wt%) conductive agent, CMC (1.5 wt%), SBR (2.5 wt%) binder, 5.399 mg / cm2 loading level of cross-section, Li metal (700 μm) cathode material, polyethylene (9 μm thick) separator, 1.46 g / cc composite density, 0.5T Space, 2032 Coin Cell electrode size, and a total of 3 charge / discharge tests were performed. The formation and capacity retention measurement conditions are as follows.

[0109] - Charge method: CC / CV, 0.1 C / 0.005 V, Cut-off 0.05 C

[0110] - Discharge method: CC, 0.1 C, End-voltage 1.5 V (2cycles)

[0111]

[0112] [Formation Conditions]

[0113] - Charge method: CC / CV, 0.5 C / 0.005 V, Cut-off 0.05 C

[0114] - Discharge method: CC, 0.5 C, End-voltage 1.5 V (100cycles)

[0115]

[0116] [Capacity retention measurement conditions]

[0117] The silicon-based negative electrode material manufactured in Example 2 and Comparative Example 1 was mixed with natural graphite in a ratio of 1:9 and 2:8, and a conductive material and a binder were added to manufacture a negative electrode material slurry.

[0118] Figure 8 is a photograph of a cathode material slurry manufactured using a cathode material coated with a polymer protective layer according to the present invention.

[0119] Afterwards, the slurry was coated on copper foil and pressed, and finally, the cathode required for the coin test was manufactured. The performance of the cathode material was analyzed and shown in Table 1 below.

[0120] Figure 9 is a photograph of a cathode manufactured using a cathode material coated with a polymer protective layer according to the present invention.

[0121]

[0122]

[0123] As shown in Table 1 above, it was confirmed that the battery performance, such as the initial discharge capacity, initial efficiency, and life characteristics, of the negative electrode material of Example 2 coated with a polymer protective layer according to the present invention were significantly improved compared to the negative electrode material of Comparative Example 1.

[0124] <Test Example 2> Performance Analysis of Cathode Materials

[0125] Following the experiment of the above Test Example 1, the performance of the negative electrode material was additionally evaluated by fixing the ratio of silicon and natural graphite to 2:8.

[0126] The test method was performed in the same manner as in Test Example 1 above. Table 2 below shows the results.

[0127]

[0128] As shown in Table 2 above, it was confirmed that the negative electrode materials of Examples 1 to 5 coated with a polymer protective layer according to the present invention showed improved battery performance, such as initial discharge capacity, initial efficiency, and life characteristics, compared to the negative electrode material of Comparative Example 1. However, in the case of Example 3, it was confirmed that the initial discharge capacity was significantly reduced due to an increase in the electrical resistance of the negative electrode active material by excessively covering the silicon in the case of a coating that was too thick. In addition, it was confirmed that the protective characteristics were significantly improved in the case of Examples 4 and 5 protected by multi-layered polymer layers.

[0129] While specific aspects of the present invention have been described in detail above, it should be apparent to those skilled in the art that these specific descriptions are merely preferred embodiments and do not limit the scope of the present invention. Therefore, the substantial scope of the present invention is defined by the appended claims and their equivalents.

[0130]

[0131] In this way, according to the present invention, by coating a silicon-based negative electrode material with a single or multiple layers of a polymer monomer or copolymer, direct contact between the high-capacity negative electrode material and the electrolyte is prevented, thereby preventing mechanical destruction (pulverization) of the negative electrode material due to lithium ion insertion. In addition, side reactions such as the formation of a solid electrolyte interface (SEI) layer on the surface of the negative electrode material due to the decomposition of the electrolyte in the initial reaction can be suppressed. Therefore, according to the present invention, since the polymer protective layer is uniformly coated on the surface of the negative electrode material, the characteristics of existing negative electrode materials are maintained at an equivalent level or higher, while the lifespan characteristics of secondary batteries are increased, and thus it is expected that the present invention can be usefully applied as an negative electrode material for secondary batteries.

Claims

1. A silicon-based negative electrode material for a secondary battery, characterized in that a polymer protective layer is coated on the surface of the negative electrode material.

2. In paragraph 1, The above polymer protective layer is selected from the group consisting of 2-hydroxyethyl methacrylate (HEMA), 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (V4D4), 2,4,6-trivinyl-2,4,6-trimethyl cyclotrisiloxane, polyacrylonitrile (PAN), polyacrylic acid (PAA), divinylbenzene, hexavinyldisiloxane, 1H,1H,2H,2H-perfluorodecyl acrylate, glycidyl methacrylate, ethylene glycol dimethacrylate 4-vinyl-pyridine, 3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecablueorodecyl methacrylate, A silicon-based negative electrode material for a secondary battery, characterized in that it comprises at least one monomer selected from the group consisting of 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl methacrylate and 2-dimethylaminoethyl methacrylate or a copolymer thereof.

3. In paragraph 2, A silicon-based negative electrode material for a secondary battery, characterized in that the copolymer is at least one selected from the group consisting of glycidyl methacrylate-co-2-(dimethylamino)ethyl methacrylate (GMA-co-DMAEMA), 2-hydroxyethyl methacrylate-co-2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (HEMA-co-V4D4), and ethylene glycol dimethacrylate-co-divinylbenzene (EGDMA-co-PFDA).

4. In paragraph 1, The above polymer protective layer is Al2O x , SiO x and TiO x A silicon-based negative electrode material for a secondary battery, characterized in that it additionally contains one or more inorganic substances selected from the group consisting of (X is a number from 1 to 10).

5. In paragraph 1, A silicon-based negative electrode material for a secondary battery, characterized in that the polymer protective layer is composed of a single layer or multiple layers.

6. In paragraph 1, A silicon-based negative electrode material for a secondary battery, characterized in that the thickness of the polymer protective layer is 1 to 1,000 nm.

7. In paragraph 6, A silicon-based negative electrode material for a secondary battery, characterized in that the above polymer protective layer has a thickness deviation of less than 30%.

8. In paragraph 1, A silicon-based negative electrode material for a secondary battery, characterized in that the polymer protective layer is formed by a dry polymer vapor deposition method.

9. In paragraph 1, A silicon-based negative electrode material for a secondary battery, characterized in that the polymer protective layer has a surface coverage ratio (Rsc, polymer-coated area / negative electrode material surface area) of 95% or more on the surface of a porous substrate.

10. In paragraph 1, A silicon-based negative electrode material for a secondary battery, characterized in that the negative electrode material coated with the polymer protective layer has a surface roughness (Sa) roughness value change rate and a specific surface area (BET) change rate each of less than 10%.

11. In paragraph 1, A silicon-based negative electrode material for a secondary battery, characterized in that the negative electrode material is at least one selected from the group consisting of silicon nanoparticles, silicon nanowires, porous silicon nanoparticles, silicon nanotubes, carbon nanotubes, and graphite.

12. A method for manufacturing a silicon-based negative electrode material for a secondary battery coated with a polymer protective layer, characterized in that a polymer protective layer is coated on the surface of the silicon-based negative electrode material for a secondary battery using a dry polymer vapor deposition method.

13. In paragraph 12, A method for manufacturing a silicon-based negative electrode material for a secondary battery coated with a polymer protective layer, characterized in that the process of coating the polymer protective layer is performed for 1 to 600 minutes under conditions of a temperature of 10 to 80°C and a pressure of 1 mTorr to 500 Torr.

14. In a lithium ion secondary battery including a cathode, an anode, a separator interposed between the cathode and the anode, and an electrolyte, A lithium ion secondary battery characterized in that the negative electrode is a negative electrode including a negative electrode material coated with a polymer protective layer according to any one of claims 1 to 11.

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