Silicon-carbon composite negative electrode material composition comprising hybrid additive of polysaccharide substance and nano-carbon material, method for producing silicon-carbon composite negative electrode material composition, and silicon-carbon composite negative electrode material manufactured thereby

Abstract

The present invention relates to a silicon-carbon composite negative electrode material composition comprising nano-silicon particles, a carbon-based substance, and an additive, wherein the additive is a hybrid of a polysaccharide substance and a nano-carbon material.

Description

A silicon-carbon composite anode material composition comprising an additive hybridized with a polysaccharide material and a nano carbon material, a method for producing a silicon-carbon composite anode material, and a silicon-carbon composite anode material produced thereby

[0001] The present invention relates to a silicon-carbon composite anode material composition comprising an additive hybridized with a polysaccharide material and a nano carbon material, a method for producing a silicon-carbon composite anode material, and a silicon-carbon composite anode material produced thereby.

[0002] Lithium secondary batteries are widely used in a wide range of applications, from portable electronic devices to electric vehicles, due to their high energy density, long lifespan, and high voltage. Previously, research to increase the capacity of lithium secondary batteries primarily focused on cathode active materials. However, as capacity enhancement through cathode active materials has reached its limits, research on anode active materials has recently become increasingly active. In particular, interest is growing in silicon anode materials, which have a theoretical capacity approximately 10 times higher than that of graphite, the traditional anode material.

[0003] Silicon anode materials possess a theoretical capacity approximately 10 times higher than that of graphite (approximately 4,200 mAh / g), making them highly promising as anode materials for lithium secondary batteries. However, silicon anode materials suffer from a serious problem: their volume expands by more than 300% during charging and discharging, hindering their commercialization. This volume expansion during charging and discharging induces the atomization of silicon particles, which leads to the continuous destruction and reconstruction of the surface Solid Electrolyte Interphase (SEI), increasing lithium consumption and shortening the battery's lifespan. Suppressing the atomization phenomenon, or even preventing further SEI formation if it does occur, is key to the commercialization of silicon anode materials.

[0004] Volume expansion and subsequent differentiation are caused by stress due to differences in the crystal structure of the silicon alloy phase reacting with lithium and the silicon matrix. To minimize this stress, the transition from silicon to the lithium alloy phase must occur uniformly and temporarily. Nano-sizing silicon particles is the most effective way to solve this problem. As the silicon particle size decreases, the fracture toughness due to volume expansion decreases. Theoretically, fracture due to volume expansion can be suppressed at silicon particle sizes below 150 nm. However, the particles must be sufficiently small to minimize the concentration difference due to lithium diffusion and prevent differentiation due to crystallographic mismatch.

[0005] Even if silicon particles are nanosized, not all problems are solved. Even if silicon particles are sufficiently nanosized, the increased specific surface area leads to the formation of a larger SEI layer, which increases lithium loss due to the initial irreversible reaction. Moreover, if physical contact occurs between nanoparticles during volume expansion, electrochemical recombination occurs, leading to particle regrowth. Therefore, the function of suppressing micronization is lost during the initial several charge / discharge cycles. In other words, even if silicon particles are nanosized, if they remain in an aggregated state, it is difficult to expect an improved battery life.

[0006] Currently commercially available silicon anode materials are divided into oxide silicon anode materials and silicon-carbon composites. These employ a strategy of incorporating nano-sized silicon into an electrochemically stable substrate, thereby blocking direct reaction between the nano-silicon particles and the electrolyte and suppressing additional SEI formation due to micronization.

[0007] While oxide-silicon anode materials offer superior cycle life compared to silicon-carbon composite anode materials, they suffer from low initial efficiency, difficulty in achieving high capacity, and high processing costs due to their synthesis via a chemical vapor deposition process. In particular, the low initial efficiency requires more cathode material for complete cell design, further increasing the cost of batteries using oxide-silicon anode materials.

[0008] On the other hand, silicon-carbon composite anode materials have low process costs and are advantageous in securing initial efficiency and capacity, but have the disadvantage of poor cycle life characteristics. The main reason for the limited cycle life characteristics of silicon-carbon anode materials is that the size of the nano-silicon particles contained in the material is larger than that of oxide silicon anode materials. Nano-silicon used in silicon-carbon anode materials is usually nano-sized particles obtained through pulverization of silicon and mixed and assembled with carbon materials. Since the size of the nanoparticles obtained through the pulverization process is limited to the level of tens to hundreds of nanometers, there is a very large difference in the size of the nano-domains electrochemically formed within the oxide silicon.

[0009] To improve the low cycle life of silicon-carbon composite anode materials, research is underway on a bottom-up process that grows nano-sized silicon on a porous carbon substrate, rather than the top-down process that mechanically and chemically reduces the size of existing large particles. However, the bottom-up process is complex and uses expensive silicon precursors, which increases costs. Furthermore, both the top-down and bottom-up processes have a fundamental problem: they struggle to achieve uniform particle dispersion due to the agglomeration tendency of the nanoparticles, which reduces their surface energy.

[0010] Therefore, new research and technological development to overcome these problems are necessary to improve the performance of silicon anode materials.

[0011] One object of the present invention is to provide a silicon-carbon composite anode material having excellent initial efficiency while having life characteristics equal to or greater than those of oxide silicon anode materials.

[0012] Meanwhile, other unspecified purposes of the present invention will be additionally considered within a range that can be easily inferred from the detailed description and effects thereof below.

[0013] To achieve the purpose proposed above, the following solutions are proposed.

[0014] A silicon-carbon composite negative electrode material composition according to one embodiment of the present invention comprises nano silicon particles, a carbonaceous material, and an additive, wherein the additive is a hybrid of a polysaccharide material and a nano carbon material.

[0015] In one embodiment, the additive may be a hybrid of the polysaccharide material and the nano carbon material in a sheet form.

[0016] In one embodiment, the polysaccharide material may be at least one selected from the group consisting of cellulose, glucose, sucrose, cellulose nanofabric, starch, and structural isomers thereof.

[0017] In one embodiment, the nano carbon material may be at least one selected from the group consisting of carbon nanotubes, carbon nanofibers, and graphene.

[0018] In one embodiment, the polysaccharide material can coat the nanocarbon material.

[0019] A method for manufacturing a silicon-carbon composite anode material composition according to another embodiment of the present invention includes a step of forming secondary particles by mixing nano silicon particles, a carbonaceous material, and an additive, a step of heat-treating the formed secondary particles in an inert gas atmosphere to form a composite in which the carbonaceous material is graphitized, and a step of pulverizing the composite to manufacture a silicon-carbon composite anode material.

[0020] In another embodiment, a method for preparing an additive includes a step of mixing a polysaccharide material powder in distilled water to form a first mixture, a step of adding a nano carbon material and distilled water to the first mixture and mixing again to form a second mixture, a step of drying the second mixture until moisture disappears to form a dried product, and a step of pulverizing the dried product to form an additive.

[0021] In another embodiment, a step of forming a carbon coating layer on the surface of the silicon-carbon composite negative electrode material may be further performed.

[0022] In another embodiment, the additive becomes a porous material by forming pores during the heat treatment process, and the nano silicon particles can have a stable energy level due to the pores, thereby having uniform dispersibility.

[0023] A silicon-carbon composite negative electrode material according to another embodiment of the present invention may be manufactured by the manufacturing method of the other embodiment described above.

[0024] The silicon-carbon composite negative electrode material composition of the present invention comprises nano silicon particles, a carbon-based material, and an additive, wherein the additive is characterized in that it is a hybrid of a polysaccharide material and a nano carbon material.

[0025] In the process of manufacturing a silicon-carbon composite cathode material, simply adding the above-described additive induces uniform dispersion of nano silicon particles, improves the mechanical strength of the carbon substrate, and forms a uniform electrically conductive structure by the nano carbon material.

[0026] Therefore, a lithium secondary battery using a silicon-carbon composite anode material manufactured by the manufacturing method proposed in the present invention has the effect of having a high lifespan characteristic at the level of an oxide silicon-based anode material containing nano-domains of 5 to 20 nm, despite being a silicon-carbon composite anode material using nano-silicon particles of 100 to 200 nm, by suppressing the regrowth and differentiation of nano-silicon particles during the charge and discharge process.

[0027] In addition, the silicon-carbon composite anode material manufactured by the manufacturing method proposed in the present invention has the advantage of excellent initial efficiency, which is an advantage of conventional silicon-carbon composite anode materials, and has the advantage of very low process costs because almost no solvent is used in the manufacturing process.

[0028] Meanwhile, even if the effect is not explicitly mentioned herein, it is added that the effect and its provisional effect described in the following specification expected by the technical features of the present invention are treated as described in the specification of the present invention.

[0029] Figure 1 is a schematic flow chart of a method for manufacturing a silicon-carbon composite negative electrode material of the present invention.

[0030] Figure 2 is an electron microscope photograph of the additive of Example 1.

[0031] Figure 3 is an electron microscope photograph of the additive of Figure 2 after heat treatment at a temperature of 900 degrees or higher in an inert gas atmosphere.

[0032] Figure 4 is an electron microscope photograph of secondary particles formed by mixing nano silicon particles, pitch particles, and additives of Example 1.

[0033] Figure 5 is an electron microscope photograph of a silicon-carbon composite negative electrode material manufactured by performing a graphitization process on the secondary particles of Figure 4.

[0034] Figure 6 is an electron microscope photograph of the silicon-carbon composite negative electrode material of Comparative Example 1 and Example 2.

[0035] Figure 7 shows a transmission electron microscope image (left) and an EDS mapping image (right) of the silicon-carbon composite negative electrode material of Comparative Example 1 and Example 1.

[0036] Figure 8 shows the results of evaluating the cycle-life characteristics of a single half-cell of the negative electrode materials of Comparative Example 1, Comparative Example 2, Example 1, and Example 2, including the results of evaluating the cycle-efficiency (left) and cycle-discharge capacity (right).

[0037] Figure 9 shows the results of evaluating the cycle-life characteristics of graphite-mixed half-cells of the negative electrode materials of Comparative Example 1, Comparative Example 2, Comparative Example 3, Example 1, and Example 2, and the cycle-efficiency (left) and cycle-capacity (right) are evaluated.

[0038] Figure 10 is a graph showing the results of powder resistance measurement of the negative electrode material of Comparative Example 1 and Example 1.

[0039] Figure 11 is an electron microscope photograph of a particle cross-section after 50 single half-cell charge / discharge cycles of the negative electrode materials of Comparative Example 1, Example 1, and Example 2.

[0040] Figure 12 is an electron microscope photograph of the particle surface of the negative electrode material of Comparative Example 1 and Example 2 before and after repeated charge / discharge of a single half-cell.

[0041] Figure 13 shows the results of a single half performance evaluation of the negative electrode material of the comparative example and the example.

[0042] Figure 14 shows the cycle-efficiency (top) and cycle-capacity retention rate graphs (bottom) as the full-cell evaluation results of Comparative Example 2, Comparative Example 3, and Example 2.

[0043] Figure 15 shows performance figures according to the full-cell evaluation results of Comparative Example 2, Comparative Example 3, and Example 2.

[0044] It is to be understood that the attached drawings are provided for reference only to help understand the technical concept of the present invention, and the scope of the present invention is not limited thereby.

[0045] Hereinafter, with reference to the drawings, the configuration of the present invention, guided by various embodiments thereof, and the effects resulting from such configurations will be examined. In describing the present invention, detailed descriptions of related, well-known functions that are obvious to those skilled in the art and that may unnecessarily obscure the gist of the present invention will be omitted.

[0046] The present invention aims to provide a silicon-carbon composite anode material having excellent initial efficiency while possessing lifespan characteristics equivalent to or superior to those of oxide silicon anode materials. Furthermore, the present invention seeks to provide a silicon-carbon composite anode material that is advantageous for commercialization due to its low process cost.

[0047] A silicon-carbon composite negative electrode material composition according to one embodiment of the present invention includes nano silicon particles, a carbon-based material, and an additive.

[0048] Nano silicon particles may be obtained by crushing micron-sized silicon. At this time, the average particle size of the nano silicon particles may be 200 nm or less, preferably 150 nm or less, and more preferably 100 nm or less.

[0049] The precursors of carbonaceous materials include hard carbon, soft carbon, petroleum pitch, coal pitch, mesophase pitch, and calcined coke, but may also be composed of one or a combination of two or more of these.

[0050] The weight ratio of the nano silicon particles and the carbon material may be 1:0.5 to 1:2, preferably 1:0.8 to 1:1.2, and more preferably 1:0.9 to 1:1.1.

[0051] Meanwhile, the additive in the present invention is characterized by being a hybrid of a polysaccharide material and a nano carbon material.

[0052] The content of the additive in the composition may be 1 to 5 wt%. When the content of the additive is less than 1 wt%, it has little effect on the properties of the silicon-carbon composite negative electrode material composition, and when the content of the additive exceeds 5 wt%, it is difficult to composite the silicon-carbon.

[0053] As the polysaccharide material, at least one selected from the group consisting of cellulose, glucose, sucrose, cellulose nanofabric, starch, and structural isomers thereof can be used.

[0054] Nano carbon materials can be used as carbon isotropes with linear (1-D) or planar (2-D) nanostructures, such as carbon nanotubes, carbon nanofibers, and graphene.

[0055] The weight ratio of the polysaccharide material to the nano carbon material may be 3:1 to 0.5:1, preferably 2:1 to 1:1, and more preferably 1.7:1 to 1.3:1.

[0056] As described above, the polysaccharide material and the nanocarbon material exist in a hybrid form. Here, hybridization means that the polysaccharide material coats the nanocarbon material, but overall, it forms a plane, and at least one plane overlaps. In other words, when the polysaccharide material and the nanocarbon material hybridize, they take on a woven fabric-like form. Generally, when only the nanocarbon material (e.g., carbon nanotubes) is dried, they form a bundle. However, when the polysaccharide material and the nanocarbon material are mixed together and dried as in the present invention, the nanocarbon material spreads out evenly and hybridizes into a sheet form. When such an additive is mixed with nanosilicon particles, the sheet-shaped additive mixes as if it were wrapping the silicon particles, and in this process, the nanocarbon material is coated in a uniformly dispersed state.

[0057] When the additive of the present invention is further added to nano silicon particles and carbon-based materials and mixed in a mixer, secondary particles in which nano silicon particles and nano carbon materials are mixed are assembled inside the carbon-based material by mechanical energy (impact, friction, stress, etc.) transmitted during the mixing process, and the nano carbon materials that had a woven cloth-like shape are all dispersed during this process and individually dispersed in the secondary particles.

[0058] Meanwhile, the additive used in the present invention forms pores and a porous structure when heat-treated in an inert gas atmosphere at a temperature of 900°C or higher. Therefore, during the heat treatment of secondary particles, the additive provides pores, thereby inducing the nano-silicon particles to have a stable energy level and uniform dispersion.

[0059] Below, a manufacturing method for manufacturing a silicon-carbon composite anode material using a silicon-carbon composite anode material composition according to one embodiment of the present invention will be described.

[0060] Figure 1 is a schematic flow chart of a method for manufacturing a silicon-carbon composite negative electrode material according to another embodiment of the present invention.

[0061] At this time, the method for preparing the additive includes a step of mixing a polysaccharide material powder in distilled water to form a first mixture, a step of adding a nano carbon material and distilled water to the first mixture and mixing again to form a second mixture, a step of drying the second mixture until moisture disappears to form a dried product, and a step of pulverizing the dried product to form an additive.

[0062] Here's a more detailed look at it: First, 95 to 105 parts by weight of polysaccharide material powder is added to 100 parts by weight of distilled water, and mixed at room temperature to form a first mixture. Nanocarbon material and distilled water are further added to the first mixture. The nanocarbon material is added so that the weight ratio of the polysaccharide material to the nanocarbon material is 3:1 to 0.5:1. The distilled water can be added so that the weight ratio of the total solid content to the total distilled water is 0.8 to 2 wt%. After further adding the nanocarbon material and distilled water to the first mixture, they are well mixed to form a second mixture. Then, the second mixture is dried using a convection dryer until moisture disappears to form a dried product. The dried product is ground using a grinder to produce an additive.

[0063] Secondary particles are then formed by mixing nano silicon particles, carbon-based materials, and additives.

[0064] Nano silicon particles can be used whose average particle size is controlled to be 200 nm or less, preferably 150 nm or less, and more preferably 100 nm or less through a mechanical grinding process. In addition, carbon-based materials can also be used whose average particle size is controlled to be 5 ㎛ or less. The weight ratio of the nano silicon particles to the carbon-based material can be 1:0.5 to 1:1.2, preferably 1:0.8 to 1:1.2, and more preferably 1:0.9 to 1:1.1. The content of the additive can be 1 to 5 wt%.

[0065] Nano-silicon particles, carbon-based materials, and additives are mixed using a mixer for 45 to 75 minutes. The nano-silicon particles, carbon-based materials, and additives are assembled into secondary particles by the mechanical energy (impact, friction, stress, etc.) transmitted during the mixing process.

[0066] The formed secondary particles are heat-treated in an inert gas atmosphere to form a composite in which the carbonaceous material is graphitized. As the inert gas, at least one selected from the group consisting of helium (He), neon (Ne), argon (Ar), nitrogen (N2), krypton (Kr), and xenon (Xe) can be used. The heat-treatment temperature is a temperature at which the carbonaceous material can be graphitized, and in the case where the carbonaceous material is pitch, it can be 900°C or higher.

[0067] Next, the composite is pulverized. The composite is pulverized through a pulverizer so that the average particle size is 30 ㎛ or less, preferably 20 ㎛ or less, to manufacture a silicon-carbon composite negative electrode material.

[0068] A carbon coating layer is formed on the surface of the additionally manufactured silicon-carbon composite anode material. The manufactured silicon-carbon composite anode material is loaded into a furnace, and a vacuum pump is used to sufficiently maintain the inside of the furnace in a low vacuum state. Next, an inert gas is introduced into the furnace until the pressure reaches atmospheric pressure to create an inert gas atmosphere. Thereafter, the temperature is increased to 1000°C or higher, and CH4 gas and H2 gas are reacted to form a carbon coating layer on the surface of the silicon-carbon anode material.

[0069] In the process of manufacturing a silicon-carbon composite anode material, simply adding the above-described additive induces uniform dispersion of nano-silicon particles, improves the mechanical rigidity of the carbon substrate, and forms a uniform electrically conductive structure by the nano-carbon material. Therefore, a lithium secondary battery using a silicon-carbon composite anode material manufactured by the manufacturing method of the present invention described above suppresses the regrowth and micronization of nano-silicon particles during the charge and discharge process, and thus has the effect of having high life characteristics on the level of an oxide silicon-based anode material containing nano-domains on the level of 5 to 20 nm, despite being a silicon-carbon composite anode material using nano-silicon particles on the level of 100 to 200 nm.

[0070] In addition, the silicon-carbon composite anode material manufactured by the manufacturing method proposed in the present invention has the advantage of excellent initial efficiency, which is an advantage of conventional silicon-carbon composite anode materials, and has the advantage of very low process costs because almost no solvent is used in the manufacturing process.

[0071]

[0072] Example 1

[0073] First, the additive was prepared. Carboxylmethylcellulose (CMC) powder was added to distilled water at a weight ratio of 1:1 and mixed at room temperature to prepare a first mixture. Single-walled carbon nanotube (SWCNT) powder and distilled water were added to the first mixture and mixed so that the weight ratio of total solids to the total distilled water was 1 wt% to prepare a second mixture. The second mixture was dried in a convection dryer until all moisture disappeared and then pulverized using a pulverizer to prepare an additive.

[0074] A silicon-carbon composite anode material was manufactured using nano silicon particles, pitch, and additives.

[0075] Silicon particles with an average particle size of 150 nm or less and pitch particles with an average particle size of 5 μm or less were prepared as additives through a mechanical grinding process using micron-sized silicon particles. The nano-silicon particles and pitch particles were mixed in a weight ratio of 1:1 and then placed in a mixer with 5 wt% of the additive to form secondary particles. The secondary particles were heated to a temperature of 900 degrees or more in an inert gas atmosphere to graphitize the pitch and form a composite. The composite was ground in a grinder to an average particle size of 30 μm or less to produce a silicon-carbon composite anode material.

[0076]

[0077] Example 2

[0078] A carbon coating layer was formed on the silicon-carbon composite anode material of Example 1. The silicon-carbon composite anode material of Example 1 was placed in a tube furnace, and a low vacuum was sufficiently maintained using a vacuum pump. Then, an inert gas was introduced until the pressure reached atmospheric pressure to create an Ar atmosphere. The temperature inside the tube furnace was raised to 1000°C or higher, and then the carbon coating layer was formed by reacting with CH4 gas and H2 gas, and then cooled to room temperature again in an inert gas atmosphere.

[0079]

[0080] Example 3

[0081] In the additive manufacturing process of Example 1, sucrose (SCR) was used instead of carboxymethylcellulose (CMC), and the rest is the same as Example 1.

[0082]

[0083] Example 4

[0084] In the additive manufacturing process of Example 1, glucose (GCR) was used instead of carboxymethylcellulose (CMC), and the rest is the same as Example 1.

[0085]

[0086] Example 5

[0087] In the additive manufacturing process of Example 1, cellulose nanofabric (CF) was used instead of carboxymethyl cellulose (CMC), and the rest is the same as Example 1.

[0088]

[0089] Example 6

[0090] In the additive manufacturing process of Example 1, thin-walled carbon nanotubes (TWCNTs) were used instead of single-walled carbon nanotubes (SWCNTs), and the rest is the same as Example 1.

[0091]

[0092] Example 7

[0093] In the additive manufacturing process of Example 1, multilayer graphene (MLG) was used instead of single-walled carbon nanotubes (SWCNT), and the rest is the same as Example 1.

[0094]

[0095] Example 8

[0096] In the additive manufacturing process of Example 1, carbon nanofibers (CNF) were used instead of single-wall carbon nanotubes (SWCNTs), and the rest is the same as Example 1.

[0097]

[0098] Comparative Example 1

[0099] A silicon-carbon composite negative electrode material was manufactured in Example 1, excluding the additives, and otherwise the same as Example 1.

[0100]

[0101] Comparative Example 2

[0102] A commercial oxide silicon anode material was prepared.

[0103]

[0104] Comparative Example 3

[0105] A commercial silicon-carbon composite cathode material was prepared.

[0106]

[0107] Experimental example

[0108] Figure 2 is an electron microscope photograph of the additive of Example 1. Referring to Figure 2, it can be confirmed that the additive is a hybrid of a polysaccharide material and a nanocarbon material. Hybridization means that the polysaccharide material coats the nanocarbon material, but overall, it forms a plane, and at least one of the planes overlaps. As the polysaccharide material and the nanocarbon material hybridize, it takes on a woven fabric-like form.

[0109] Figure 3 is an electron microscope photograph of the additive of Figure 2 after heat treatment at a temperature of 900 degrees or higher in an inert gas atmosphere. Comparing Figures 2 and 3, fine pores are formed on the surface of the additive, unlike before the heat treatment. The pores formed in the additive during the heat treatment process provide a location where the additive can have a stable energy level in the nano silicon particles during the heat treatment process of manufacturing a silicon-carbon composite anode material, thereby inducing a uniform dispersion phase.

[0110] Figure 4 is an electron microscope photograph of secondary particles formed by mixing nano-silicon particles, pitch particles, and additives of Example 1. Examining Figure 4, it can be seen that the single-walled carbon nanotubes of the additives, which were initially aggregated in a woven form, are now dispersed and present in the form of individual fibers, and that the nano-silicon particles are also uniformly dispersed within the pitch substrate.

[0111] Fig. 5 is an electron microscope photograph of a silicon-carbon composite anode material manufactured by performing a graphitization process on the secondary particles of Fig. 4. As shown in Fig. 5, the manufactured silicon-carbon composite anode material has an average diameter of 10 to 25 μm, and its surface has a form in which nano-silicon particles with an average particle size of 100 nm are uniformly dispersed by coating them with graphitized pitch. Compared to the image before heat treatment of Fig. 4, it can be seen that the pitch shrinks in volume as it is graphitized, resulting in more surface pores; however, it can be confirmed that single-walled carbon nanotubes cross between each pore to maintain an electron transport path between the nano-silicon particles.

[0112] Fig. 6 is an electron microscope photograph of the silicon-carbon composite anode material of Comparative Example 1 and Example 2. Compared with the microscope photograph of the anode material of Example 1 in Fig. 5, in the case of Comparative Example 1, which does not include an additive, it can be confirmed that a colony shape in which nano-silicon particles are partially aggregated is observed and no electrical conduction path is provided between the pores. Furthermore, in the case of Example 2, it can be confirmed that a structure that can provide a more efficient electron conduction path is formed by more densely filling the pores by the carbon coating layer (coated graphite film).

[0113] Figure 7 shows a transmission electron microscope image (left) and an EDS mapping image (right) of the silicon-carbon composite anode material of Comparative Example 1 and Example 1. Compared to the anode material of Comparative Example 1, it can be confirmed that the anode material of Example 1 including the additive shows a more dispersed particle shape, and the mapping results further confirm that the silicon particles (bright areas) are individually dispersed and not aggregated with each other.

[0114] Figure 8 shows the results of evaluating the cycle-life characteristics of a single half-cell of the negative electrode materials of Comparative Example 1, Comparative Example 2, Example 1, and Example 2, including the results of evaluating the cycle-efficiency (left) and cycle-discharge capacity (right).

[0115] The cycle-life characteristics evaluation of a half-cell using only the negative electrode material was performed as follows. The solid content, which was mixed with the negative electrode material, binder (CMC), and conductive material (SWCNT) in a weight ratio of 80:14:6, was mixed with distilled water in a mass ratio of 1:1 to prepare a slurry, which was then coated on a copper collector using a microfilm applicator and compressed using a roll press to manufacture a negative electrode plate with a thickness of approximately 5 μm and an areal capacity of 0.5–0.7 mAh / cm2. The manufactured negative electrode plate was assembled into a 2032 coin cell standard with a Li-metal positive electrode, cell-guard 2400 separator, and FEC 10 wt% + ED / DEC 1:1 1M LiPF6 electrolyte. The assembled coin cells were charged and discharged in the following order to evaluate the cycle-life characteristics.

[0116] Discharge: CC cutoff (0.01V-1.5V) at target c-rate

[0117] Charge: Target c-rate CC cutoff (1.5V - 0.01V), CV cutoff (1 / 10 of target rate)

[0118] Mars process: 0.1C-rate 1 charge / discharge, 0.2C-rate 2 charge / discharge, 0.5C-rate 2 charge / discharge

[0119] Life cycle: 0.5C-rate

[0120]

[0121] Referring to Fig. 8, in the case of cycle-discharge capacity (right), all examples and comparative examples showed high life efficiency. However, in the case of cycle efficiency (left), it was confirmed that the efficiency of Example 1 using an additive increased significantly compared to Comparative Example 1. In particular, in the case of Example 2 in which a carbon coating layer was formed, it was confirmed that the efficiency result according to the progress of charge and discharge was improved to a level equivalent to that of Comparative Example 2, which is a commercial silicon oxide-based negative electrode material, and the charge and discharge cycle from the initial stage to efficiency stabilization was short and showed relatively high efficiency, which means that the additional loading of unnecessary positive electrode material can be reduced.

[0122] Figure 9 shows the results of evaluating the cycle-life characteristics of graphite-mixed half-cells of the negative electrode materials of Comparative Example 1, Comparative Example 2, Comparative Example 3, Example 1, and Example 2, and the cycle-efficiency (left) and cycle-capacity (right) are evaluated.

[0123] The cycle-life characteristics of graphite-blended half-cells were evaluated as follows. A mixed anode material with graphite to obtain a specific capacity of 450-550 mAh / g was used, and the mixed anode material: CMC: SBR: SWCNT was mixed in a weight ratio of 96.9:1.5:1.5:0.1 to prepare a solid, and the solid was mixed with distilled water in a mass ratio of 1:1 to prepare a slurry, which was then coated on a copper current collector using a microfilm applicator and compressed with a roll press to obtain a thickness of approximately 15 μm and a density of 2.5-3.0 mAh / cm. 2 A negative electrode plate having an areal capacity of was manufactured. The manufactured negative electrode plate was assembled into a 2032 coin cell standard with a Li-metal positive electrode, cell-guard 2400 separator, and FEC 10 wt% + ED / DEC 1:1 1M LiPF6 electrolyte. The assembled coin cell was charged and discharged in the following order to evaluate the cycle-life characteristics.

[0124] Discharge: CC cutoff (0.01V-1.5V) at target c-rate

[0125] Charge: Target c-rate CC cutoff (1.5V - 0.01V), CV cutoff (1 / 10 of target rate)

[0126] Mars process: 0.1C-rate 1 charge / discharge, 0.2C-rate 2 charge / discharge, 0.5C-rate 2 charge / discharge

[0127] Life cycle: 0.5C-rate

[0128]

[0129] In order to more accurately compare and evaluate the commercial oxide silicon-based anode material and the silicon-carbon hybrid anode material, the commercial silicon-carbon composite anode material (Comparative Example 3) with a specific capacity of 500 mAh / g was used as a reference. By mixing the anode materials of Comparative Examples 1 and 2 and Examples 1 and 2 with graphite, the capacity was adjusted to 450 to 550 mAh / g, and half-cells with the same areal capacity of the anode plates were manufactured, and their performances were evaluated. The silicon-carbon composite anode material of Comparative Example 1 without any additives showed almost the same cycle-efficiency characteristics as the commercial silicon-carbon composite anode material, and in contrast, the anode material of Example 1 with the additive added showed a high efficiency improvement, as in the results of FIG. 8. In particular, the anode material of Example 2 with a carbon coating layer formed thereon was confirmed to have an efficiency improvement equivalent to or greater than that of the commercial silicon oxide-based anode material of Comparative Example 2.

[0130] Fig. 10 is a graph showing the results of powder resistance measurements of the negative electrode materials of Comparative Example 1 and Example 1. As can be seen from the graph of Fig. 10, it can be confirmed that the electrical conductivity and mechanical stiffness of the particles in the negative electrode material of Example 1 with an additive are improved compared to Comparative Example 1.

[0131] Fig. 11 is an electron microscope photograph of the cross-section of particles of the negative electrode materials of Comparative Example 1, Examples 1, and 2 after 50 single half-cell charge-discharge cycles. In the case of the negative electrode material of Comparative Example 1 without an additive, isolated nano-silicon particles were observed that did not participate in the charge-discharge reaction during the 50 charge-discharge cycles. In contrast, in the case of the negative electrode materials of Examples 1 and 2 with an additive, the nano-silicon particles were still densely packed in the carbon matrix even though their shape changed due to volume expansion as they participated in the charge-discharge. This is because, as in the results of Fig. 10 above, the carbon nanotubes uniformly dispersed through the additive provided a stable electron transfer path even during repeated volume expansion-contraction processes, and at the same time, they were able to strengthen the carbon matrix to resist mechanical deformation.

[0132] Fig. 12 is an electron microscope photograph of the particle surface before and after repeated charge / discharge of a single half-cell of the negative electrode materials of Comparative Example 1 and Example 2. In the case of Comparative Example 1, cracks occurred in the carbon substrate due to repeated volume expansion and contraction during charge / discharge, and as a result, the nano-silicon particles were continuously exposed to the electrolyte, and as shown in Fig. 12, most of the nano-silicon particles on the surface were finely divided and showed a deteriorated shape like a lace shape. In contrast, the surface of the negative electrode material of Example 2 showed almost the same surface shape as before charge / discharge, and it could be confirmed that most of the silicon particles were not deteriorated.

[0133] Figure 13 shows the results of the single half performance evaluation of the negative electrode materials of comparative examples and examples. As can be seen in Examples 3 to 5, even when various other sugars or structural isomers thereof are used instead of carboxymethylcellulose (CMC) as the polysaccharide material in the additive, the initial efficiency is higher than that of the silicon oxide-based negative electrode material, and the lifespan is improved to a level equivalent to that of the silicon oxide-based negative electrode material. In addition, as can be seen in Examples 6 to 8, even when a carbon allotrope with a linear (1-D) or planar (2-D) nanostructure is used instead of single-walled carbon nanotubes (SWCNTs) as the nano carbon material in the additive, the initial efficiency is higher than that of the silicon oxide-based negative electrode material, and the lifespan is improved to a level equivalent to that of the silicon oxide-based negative electrode material.

[0134] Figure 14 shows the cycle-efficiency (top) and cycle-capacity maintenance rate graphs (bottom) as the full-cell evaluation results of Comparative Example 2, Comparative Example 3, and Example 2, and Figure 15 shows the performance figures according to the full-cell evaluation results of Comparative Example 2, Comparative Example 3, and Example 2.

[0135] In Fig. 9, a full-cell performance evaluation was conducted with an NCM (6:2:2) cathode using each negative electrode plate with the same capacity and area capacity and the same electrolyte and separator.

[0136] As a result, it was confirmed that the efficiency of the negative electrode material of Example 2 was significantly superior to that of the conventional commercial silicon-carbon composite negative electrode material (Comparative Example 3), and that it had the same level of stability (average efficiency of 20-150) as the conventional commercial silicon oxide-based negative electrode material (Comparative Example 2) while reaching high efficiency more quickly. As a result, it was confirmed that the capacity retention rate (lifespan) of the lithium ion secondary battery using the silicon-carbon composite negative electrode material suggested in Example 2 of the present invention was higher.

[0137] The scope of protection of the present invention is not limited to the description and expression of the embodiments explicitly described above. Furthermore, it should be noted that the scope of protection of the present invention may not be limited by obvious modifications or substitutions within the technical field to which the present invention pertains.

Claims

1. Containing nano silicon particles, carbon-based materials and additives, The above additive is a silicon-carbon composite negative electrode material composition in which a polysaccharide material and a nano carbon material are hybridized.

2. In paragraph 1, The above additive is a silicon-carbon composite negative electrode material composition in which the polysaccharide material and the nano carbon material are hybridized in a sheet form.

3. In paragraph 1, A silicon-carbon composite negative electrode material composition wherein the polysaccharide material is at least one selected from the group consisting of cellulose, glucose, sucrose, cellulose nanofabric, and structural isomers thereof.

4. In paragraph 1, The above nano carbon material is a silicon-carbon composite negative electrode material composition comprising at least one selected from the group consisting of carbon nanotubes, carbon nanofibers, and graphene.

5. In paragraph 1, The above polysaccharide material is a silicon-carbon composite negative electrode material composition coating the above nano carbon material. 6.(a) A step of forming secondary particles by mixing nano silicon particles, carbon-based materials and additives; (b) a step of heat-treating the formed secondary particles in an inert gas atmosphere to form a composite in which the carbonaceous material is graphitized; and (c) a step of crushing the complex to produce a silicon-carbon composite negative electrode material; The above additive is a method for manufacturing a silicon-carbon composite negative electrode material which is a hybrid of a polysaccharide material and a nano carbon material.

7. In paragraph 6, The above additives are, A step of mixing a polysaccharide substance powder into distilled water to form a first mixture; A step of adding nano carbon material and distilled water to the first mixture and mixing again to form a second mixture; A step of drying the second mixture until moisture disappears to form a dried product; and A method for producing a silicon-carbon composite negative electrode material, the method comprising the steps of: crushing a dry material to form an additive; 8. In paragraph 6, A method for manufacturing a silicon-carbon composite negative electrode material, wherein a step of forming a carbon coating layer on the surface of the silicon-carbon composite negative electrode material is further performed after the above step (c).

9. In paragraph 6, A method for manufacturing a silicon-carbon composite negative electrode material in which the additive forms pores during a heat treatment process in the above step (b) to become a porous material, and the nano silicon particles have a stable energy level due to the pores and have uniform dispersibility.

10. A silicon-carbon composite negative electrode material manufactured by the manufacturing method of any one of claims 6 to 9.

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