Negative electrode active material for secondary battery and negative electrode material and secondary battery comprising same

Abstract

The present invention relates to: a negative electrode active material for a secondary battery; and a negative electrode material and a secondary battery each comprising same, the negative electrode active material comprising silicon particles and a compound on the silicon particles, the compound comprising carbon atoms and at least one of oxygen atoms and nitrogen atoms, wherein the compound has a ratio of the number of carbon atoms: the number of nitrogen atoms or oxygen atoms of 1: 0.35 to 0.85.

Description

Negative electrode active material for secondary batteries, negative electrode materials containing the same, and secondary batteries

[0001] The present invention relates to a negative electrode active material for a secondary battery, a negative electrode material including the same, and a secondary battery.

[0002]

[0003] The rapid growth of the secondary battery market has led to a surge in demand for high-capacity batteries, which in turn has fueled a surge in demand for silicon-based anode active materials, which theoretically offer high capacities. However, volume expansion during charge / discharge cycles can lead to physical cracking and side reactions, making it difficult to achieve the theoretical capacity. Furthermore, the anode is damaged by the desorption of the anode active material, limiting its ability to achieve high cycle performance.

[0004] To overcome the volume expansion of these silicon-based negative electrode active materials, research is being conducted on the composition and structure of the active material itself, including silicon / carbon composites, hollow structures, and core-shell structures, as well as on suppressing volume expansion by improving the bonding strength with the binder.

[0005]

[0006] The purpose of the present invention is to provide a negative electrode active material for a secondary battery, which contains at least one of carbon atoms and oxygen atoms or nitrogen atoms in a certain ratio on a silicon particle to maintain the shape of the electrode when the volume of the silicon particle changes.

[0007] In addition, an object of the present invention is to provide a negative electrode material including the negative electrode active material for a secondary battery.

[0008] In addition, an object of the present invention is to provide a secondary battery including the negative electrode material.

[0009]

[0010] The problems to be solved by the present invention are not limited to the problem(s) mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the description below.

[0011]

[0012] In order to achieve the above object, the present invention provides a negative electrode active material for a secondary battery, comprising: silicon particles; and a compound including at least one of carbon atoms and oxygen atoms or nitrogen atoms on the silicon particles, wherein the compound has a ratio of the number of carbon atoms: the number of nitrogen atoms or the number of oxygen atoms of 1:0.35 to 0.85.

[0013] The above compound may have a ratio of carbon atoms to nitrogen atoms or oxygen atoms of 1:0.7 to 0.8.

[0014] The number of carbon atoms in the above compound may be 1 to 1500.

[0015] The compound may contain at least one nitrogen atom and at least one oxygen atom.

[0016] The ratio of the number of nitrogen atoms to the number of oxygen atoms contained in the above compound may be 1:0.25 to 1.

[0017] The compound may include at least one hydrogen-bonding functional group selected from the group consisting of a urethane group, a urea group, a carbonyl group, an amine group, a hydroxyl group, a carboxyl group, an imide group, an amide group, an ether group, and combinations thereof.

[0018] The weight average molecular weight of the above compound may be 30 to 40,000 g / mol.

[0019]

[0020] In addition, the present invention provides a negative electrode material for a secondary battery, including the negative electrode active material; a conductive material; and a binder.

[0021] The above binder may include at least one functional group selected from the group consisting of -OH, -COOH, -O-, -CONH2, -CN, and combinations thereof.

[0022] The above binder may be at least one aqueous binder selected from the group consisting of carboxymethylcellulose (CMC), polyacylic acid (PAA), polyvinyl alcohol (PVA), polyethylene glycol (PEG), polyacrylonitrile (PAN), polyacryl amide (PAM), and combinations thereof.

[0023] Based on 100 parts by weight of the total negative electrode material for the secondary battery, the negative electrode active material may be comprised of 50 to 99 parts by weight; the binder of 0.5 to 30 parts by weight; and the conductive material of 0.05 to 20 parts by weight.

[0024]

[0025] In addition, the present invention provides a secondary battery including a negative electrode including the negative electrode material for the secondary battery; a positive electrode; a separator; and an electrolyte.

[0026] The above secondary battery may be a sodium or lithium secondary battery.

[0027]

[0028] The present invention can provide a silicon-based negative electrode active material for a secondary battery, which comprises a compound containing carbon atoms and oxygen atoms or nitrogen atoms in a certain ratio on silicon particles to improve hydrogen bonding strength with a binder, thereby maintaining the shape of an electrode when the volume of the silicon particles expands.

[0029] In addition, the present invention can provide a secondary battery having improved capacity retention rate by improving hydrogen bonding strength with a binder when including a negative electrode material using the negative electrode active material.

[0030]

[0031] The effects of the present invention are not limited to the effects described above, and should be understood to include all effects that can be inferred from the detailed description of the present invention or the composition of the invention described in the claims.

[0032]

[0033] Hereinafter, embodiments of the present invention will be described in detail. However, these are presented as examples and are not intended to limit the present invention. The present invention is defined solely by the scope of the claims set forth below.

[0034]

[0035] In one embodiment of the present invention, a negative electrode active material for a secondary battery is provided, comprising: silicon particles; and a compound including at least one of a carbon atom and an oxygen atom or a nitrogen atom on the silicon particles.

[0036] In the present invention, when it is said that a certain substance exists "on" another substance, this includes not only the case where substance C is in direct contact with substance A, but also the case where another substance B exists between substance C and substance A. Here, the case where substance C is in direct contact with substance A may mean that substance C is "directly bonded" to substance A, and the case where another substance B exists between substance C and substance A may mean that substance C is "indirectly bonded" to substance A. In addition, the "direct bond" or "indirect bond" may mean that substance C is chemically bonded to substance A.

[0037] In one embodiment, the compound on the silicon particle may be present on the surface of the silicon particle, or may be present on another material disposed on the silicon particle, and the silicon particle on which the compound is present on the surface may be one in which the compound is directly or indirectly bound to surround part or the entire surface of the silicon particle.

[0038] In one embodiment, the "direct bond" may be a bond between the silicon particle and the compound, for example, a covalent bond, an ionic bond, a hydrogen bond, or a van der Waals bond, and the type of bond is not limited thereto. In one embodiment, the "indirect bond" may be a bond between the silicon particle and the compound via another substance, and the other substance may be an adhesive, a binder, or a coupling agent, for example, the coupling agent may be a silane coupling agent, and the bond may be a covalent bond, an ionic bond, a hydrogen bond, or a van der Waals bond, and the type of bond is not limited thereto.

[0039] In one embodiment, the silicon particles may improve the capacity performance of a secondary battery while minimizing destruction of the particles even when the volume of the particles expands as lithium ions are inserted.

[0040] In one embodiment, the silicon particles comprise silicon (Si), silicon oxide (SiO x , 0<x≤2), silicon-carbon composites and Si-Y alloys (Y is any one element selected from the group consisting of alkali metals, alkaline earth metals, transition metals, group 13 elements, group 14 elements and rare earth elements).

[0041] In one embodiment, the silicon-carbon composite may mean a carbon layer on a silicon particle. Specifically, the carbon layer may include any one selected from the group consisting of crystalline carbon, amorphous carbon, and combinations thereof, and more specifically, may include a combination of crystalline carbon and amorphous carbon. Specifically, the carbon layer may include crystalline carbon derived from pitch and amorphous carbon derived from a carbon precursor. Since the carbon layer includes crystalline carbon and amorphous carbon, the conductivity and durability of the negative electrode active material are improved, and thus the capacity and maintenance rate of the battery can be significantly improved.

[0042] Examples of the carbon source for generating the above crystalline carbon include pitch such as coal tar pitch, petroleum pitch, aromatic carbon materials such as sugars, lignin, and cellulose, polyacrylonitrile, etc. Specifically, when pitch is used as the carbon source for generating the above crystalline carbon, it can have the advantage of being able to control the content of carbon remaining after heat treatment by up to 80% through the softening point.

[0043] The carbon precursor that generates the above amorphous carbon may be, for example, a hydrocarbon in the form of a gas, and specifically, may be acetylene, toluene, methane, etc. The carbon precursor may be deposited as an amorphous carbon layer on silicon particles through chemical vapor deposition (CVD). Since the carbon precursor is continuously supplied in the form of a gas during the process of depositing the carbon layer including the amorphous carbon, a carbon layer without voids can be formed. Accordingly, it is possible to suppress the formation of an excessive solid electrolyte interphase (SEI) layer during the charge / discharge process and simultaneously perform the role of a protective film that protects the silicon from volume expansion.

[0044] In one embodiment, the silicon particles may be composed of needle-shaped, spherical, plate-shaped, spherical, or a combination thereof, and have an average particle diameter (D 50 ) may be 500 nm or less, specifically 10 to 500 nm, 20 to 300 nm, or 30 to 200 nm.

[0045] In one embodiment, the ratio of the number of carbon atoms: the number of nitrogen atoms or the number of oxygen atoms contained in the compound on the silicon particle may be 1:0.35 to 0.85, 0.5 to 0.85, or 1:0.7 to 0.8. When the ratio of the number of carbon atoms: the number of nitrogen atoms or the number of oxygen atoms satisfies the above-described range, the shape of the electrode comprising the silicon particle as a component can be maintained when the volume of the electrode changes, and durability can be improved.

[0046] In one embodiment, the number of carbon atoms of the compound may be 1 to 1500, 1 to 1000, 1 to 800, 1 to 600, 1 to 300, 1 to 100, 1 to 50, 1 to 30, or 1 to 20. When the number of carbon atoms of the compound satisfies the above-described range, the shape of the electrode comprising the silicon particles as a component can be maintained when the volume of the electrode changes, and durability can be improved.

[0047] In one embodiment, the compound may include at least one of a nitrogen atom and an oxygen atom, and specifically, may include at least one nitrogen atom and one oxygen atom each capable of hydrogen bonding, at least two nitrogen atoms and two oxygen atoms each, or 1 to 10 nitrogen atoms and two oxygen atoms each, thereby improving hydrogen bonding strength with the binder described below. In particular, since the electronegativity of oxygen atoms is greater than that of nitrogen atoms, the more oxygen atoms the compound includes, the better the hydrogen bonding strength between the binder and the silicon particles.

[0048] In one embodiment, the compound may have a ratio of the number of carbon atoms: the sum of the number of nitrogen atoms and the number of oxygen atoms of 1:0.35 to 0.85, 0.5 to 0.85, or 1:0.7 to 0.8. When the ratio of the number of carbon atoms: the sum of the number of nitrogen atoms and the number of oxygen atoms satisfies the above-described range, the shape of the electrode comprising the silicon particles as a component can be maintained when the volume of the electrode changes, and durability can be improved.

[0049] In one embodiment, the ratio of the number of nitrogen atoms to the number of oxygen atoms capable of forming hydrogen bonds contained in the compound may be 0.25 to 1, 0.3 to 1, 0.3 to 0.5, or 0.33 to 0.43. When the number of nitrogen atoms and the number of oxygen atoms contained in the compound, or the ratio of the number of nitrogen atoms to the number of oxygen atoms, satisfies the above-described range, when the silicon particles are used as a negative electrode active material, the bonding strength with a binder can be improved, so that the shape of the electrode comprising the silicon particles as a component can be maintained when the volume of the electrode changes, and durability can be improved.

[0050] In one embodiment, when the compound has 1 to 50, 1 to 30, 1 to 20, 2 to 15, 2 to 13, 3 to 13, 6 to 13, or 12 to 13 carbon atoms, and includes at least one nitrogen atom and one oxygen atom capable of hydrogen bonding, at least two nitrogen atoms and two oxygen atoms, or 1 to 10 nitrogen atoms and two oxygen atoms, and satisfies all of the ratios of the number of carbon atoms: the sum of the number of nitrogen atoms and the number of oxygen atoms, the shape of the electrode comprising silicon particles as a component can be more effectively maintained when the volume of the electrode changes.

[0051] In one embodiment, the compound may be a single-molecular organic compound or a low-molecular organic compound, and has the advantage of relatively less reduction in electrical conductivity and capacity compared to when using a high-molecular organic compound.

[0052] In one embodiment, the compound may include at least one hydrogen-bonding functional group selected from the group consisting of a urethane group, a urea group, a carbonyl group, an amine group, a hydroxyl group, a carboxyl group, an imide group, an amide group, an ether group, and combinations thereof.

[0053] In one embodiment, the compound may include at least one of a hydrogen bond donor and a hydrogen bond acceptor by including the hydrogen bonding functional group described above, thereby enhancing hydrogen bonding with the binder or enhancing hydrogen bonding between silicon particles.

[0054] In the present invention, a hydrogen bonding functional group may mean a functional group capable of forming a hydrogen bond.

[0055] In one embodiment, the compound may be at least one selected from a compound containing a urethane group and a urea group, chitosan, polyrhodanine, polyimide, polyethyleneimine, polyethylene glycol, 3-amino-1-propanol, and poly(methyl methacrylamide).

[0056] In one embodiment, the compound including a urethane group and a urea group may be a urethane-urea prepolymer, and the urethane-urea prepolymer may be a reaction product of a polyol and a diisocyanate compound, and may include a urethane group (-OCONH-) and a urea group (-NHCONH-). In one embodiment, the polyol may be at least one selected from the group consisting of ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, propylene glycol, trimethylene glycol, polyethylene glycol, phenyldiglycol, and combinations thereof.

[0057] In one embodiment, the diisocyanate may be at least one selected from the group consisting of hexamethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, octamethylene diisocyanate, trimethylhexamethylene diisocyanate, lysine diisocyanate, and combinations thereof.

[0058] In one embodiment, the equivalent ratio of the polyol and the diisocyanate compound may be 1:1 to 5, 1:1 to 4, 1:1 to 3, 1:1 to 2, 1:1 to 1.5, or 1:1.1.

[0059] In one embodiment, the weight average molecular weight of the compound may be 30 to 40,000 g / mol, 50 to 30,000 g / mol, 200 to 25,000 g / mol, or 300 to 25,000 g / mol. When the weight average molecular weight of the compound satisfies the above range, the electrode adhesion is excellent, and the shape of the electrode can be maintained when the volume of the electrode changes.

[0060] In one embodiment, the silicon particle may have a compound including at least one of an oxygen atom and a nitrogen atom directly bonded to the surface of the silicon particle, or a silane coupling agent may be bonded to the silicon particle to strengthen the bond between the silicon particle and the compound, and the silane coupling agent and the compound may be secondarily bonded to form an indirect bond between the silicon particle and the compound.

[0061] In one embodiment, when the silicon particle and the compound are indirectly bonded, the number of carbon atoms, the number of nitrogen atoms, and the number of oxygen atoms of the compound may include the number of carbon atoms, the number of nitrogen atoms, and the number of oxygen atoms of the silane coupling agent.

[0062] In one embodiment, the silane coupling agent may include an alkoxy group and an amine group.

[0063] In one embodiment, the silane coupling agent may be at least one selected from the group consisting of 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, (3-glycidyloxypropyl)triethoxysilane, (3-glycidyloxypropyl)trimethoxysilane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, diethoxy(3-glycidyloxypropyl)methoxysilane, (3-mercaptopropyl)trimethoxysilane, (3-mercaptopropyl)triethoxysilane, and combinations thereof.

[0064]

[0065] In one embodiment of the present invention, a negative electrode material for a secondary battery is provided, comprising: a negative electrode active material; a conductive material; and a binder.

[0066] The above negative electrode active material is the same as the negative electrode active material described above, and any content that overlaps with the content described in the above negative electrode active material will not be described again.

[0067] In one embodiment, based on 100 parts by weight of the total negative electrode material, 50 to 99 parts by weight, 60 to 90 parts by weight, or 70 to 90 parts by weight of the negative electrode active material may be included. If the weight ratio of the negative electrode active material is less than the above numerical range, the electrode capacity is low and the resistance increases, and if it exceeds the above numerical range, the binding force between the electrode components is reduced, resulting in electrode detachment after the cycle, making it difficult to achieve desirable performance as a battery.

[0068] In one embodiment, the binder may include, as a polymerization unit, a monomer including at least one hydrogen-bonding functional group selected from the group consisting of at least one carboxyl group (-COOH), a hydroxyl group (-OH), an ether group (-O-), an amide group (-CONH2), a nitrile group (-CN), and combinations thereof. Since the binder includes a hydrogen-bonding functional group, it may form a hydrogen bond with the negative electrode active material. The binder may include a polymer including, as a polymerization unit, a monomer including a hydrogen-bonding functional group among conventional binders used in negative electrode materials for secondary batteries.

[0069] In one embodiment, the binder may be at least one aqueous binder selected from the group consisting of carboxymethylcellulose (CMC), polyacylic acid (PAA), polyvinyl alcohol (PVA), polyethylene glycol (PEG), polyacrylonitrile (PAN), polyacryl amide (PAM), and combinations thereof.

[0070] In one embodiment, the binder may be an aqueous binder such as commonly used styrene-butadiene rubber (SBR), hydroxyethyl cellulose (HEC), sodium alginate, guar gum, gellan gum, dextran, gelatin, acrylate copolymers, hydroxypropyl methylcellulose (HPMC), etc.

[0071] In one embodiment, based on 100 parts by weight of the total negative electrode material, 0.5 to 30 parts by weight, 1 to 25 parts by weight, or 5 to 20 parts by weight of the binder may be included. If the weight ratio of the binder is less than the above numerical range, the binding force between the electrode components decreases, causing electrode detachment after the cycle, resulting in a reduction in the lifespan. If the weight ratio exceeds the above numerical range, the resistance of the electrode increases and the battery output decreases, making it difficult to achieve desirable performance as a battery.

[0072] In one embodiment, the silicon particle-shaped compound used as the negative electrode active material included in the negative electrode material for the secondary battery, the compound containing at least one carbon atom, one oxygen atom, and one nitrogen atom, can form a hydrogen bond with the binder. In particular, the compound contains a large number of hydrogen bonding sites, and thus can further enhance the hydrogen bonding strength with the binder, thereby effectively maintaining the electrode shape when the volume of the negative electrode active material expands during charge and discharge of the secondary battery, thereby having the effect of improving the life characteristics of the electrode for the secondary battery.

[0073] The above hydrogen bond is generally known to have a weaker bonding strength than ionic bonds and covalent bonds, but stronger than van der Waals forces.

[0074] In one embodiment, the binder and the silicon particles are connected to each other by hydrogen bonds, so that the electrode shape can be maintained while the shape of the particles is appropriately maintained even when the silicon particles expand and contract due to charging and discharging of the secondary battery. On the other hand, when the bond between the binder and the silicon particles is formed by ionic bonds or covalent bonds, the bonding strength between the binder and the silicon particles is too strong, making it difficult to buffer the force caused by the expansion and contraction of the silicon particles during charging and discharging, which may damage the binder or cause cracks to occur in some of the active material. In addition, when the bond between the binder and the silicon particles is formed by van der Waals forces, the bonding strength may be weak, making it difficult to maintain effective bonding strength and a desirable electrode shape between the binder and the silicon particles.

[0075] In one embodiment, the conductive material may be a conventional conductive material used in conductive materials for secondary batteries. The conductive material may be included in an anode material for secondary batteries to increase conductivity within the electrode for secondary batteries, thereby improving battery performance.

[0076] In one embodiment, the conductive material may be particulate carbon (Super P).

[0077] In one embodiment, the conductive material may be included in an amount of 0.05 to 20 parts by weight, 1 to 15 parts by weight, or 5 to 15 parts by weight, based on 100 parts by weight of the total negative electrode material. When the conductive material is included in the above-described range, excellent conductivity is achieved, resulting in desirable output characteristics and capacity retention.

[0078] In one embodiment, the negative electrode material may further include pure silicon particles in addition to silicon particles including a compound on the silicon particles as a negative electrode active material.

[0079]

[0080] In one embodiment of the present invention, a secondary battery is provided, comprising: a negative electrode including a negative electrode material for a secondary battery; a positive electrode; a separator; and an electrolyte.

[0081] The above secondary battery may be a sodium secondary battery or a lithium secondary battery.

[0082] The negative electrode material for a secondary battery included in the above negative electrode is the same as the negative electrode material for a secondary battery described above, and any content that overlaps with the content described in the negative electrode material for a secondary battery described above is briefly explained or omitted.

[0083] In one embodiment, the negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode active material layer may be formed using the negative electrode material for a secondary battery described above, and may include a negative electrode active material, a conductive material, and a binder.

[0084] In one embodiment, the negative electrode current collector may serve as a passage to transfer electrons from the outside to cause an electrochemical reaction in the negative electrode active material or to receive electrons from the negative electrode active material and send them to the outside. For example, the negative electrode current collector may be made of copper, stainless steel, nickel, titanium, calcined carbon, or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. Specifically, a transition metal that adsorbs carbon well, such as copper or nickel, may be used as the current collector. For example, the thickness of the negative electrode current collector may be 6 μm to 55 μm, but the thickness of the negative electrode current collector is not limited thereto.

[0085]

[0086] In one embodiment, the positive electrode may include a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. The positive electrode active material layer may include a positive electrode active material, a conductive material, and a positive electrode binder.

[0087] In one embodiment, the positive electrode current collector is not particularly limited as long as it has high conductivity without causing chemical changes in the battery. Specifically, the positive electrode current collector may be made of copper, stainless steel, aluminum, titanium, calcined carbon, stainless steel surface-treated with carbon, nickel, titanium, silver, etc., an aluminum-cadmium alloy, etc. The positive electrode current collector may typically have a thickness of 6 to 20 μm.

[0088] In one embodiment, the cathode active material may include a lithium transition metal oxide. The lithium transition metal oxide may be, for example, Li x1 CoO2(0.5 <x1<1.3), Li x2 NiO2(0.5 <x2<1.3), Li x3 MnO2(0.5 <x3<1.3), Li x4 Mn2O4(0.5 <x4<1.3), Li x5 (Ni a1 Co b1 Mn c1 )O2(0.5 <x5<1.3, 0<a1<1, 0<b1<1, 0<c1<1, a1+b1+c1=1), Li x6 Ni 1-y1 Co y1 O2(0.5 <x6<1.3, 0<y1<1), Li x7 Co 1-y2 Mn y2 O2(0.5 <x7<1.3, 0≤y2<1), Li x8 Ni 1-y3 Mn y3 O2(0.5 <x8<1.3, 0≤y3<1), Li x9 (Ni a2 Co b2 Mn c2 )O4(0.5 <x9<1.3, 0<a2<2, 0<b2<2, 0<c2<2, a2+b2+c2=2), Li x10 Mn 2-z1 Ni z1 O4(0.5 <x10<1.3, 0<z1<2), Li x11 Mn 2-z2 Co z2O4(0.5 <x11<1.3, 0<z2<2), Li x12 CoPO4(0.5 <x12<1.3) 및 Li x13 FePO4(0.5 <x13<1.3)로 이루어진 군에서 선택되는 하나 이상일 수 있다.

[0089] In one embodiment, the conductive material used in the positive electrode may be the same as or different from the conductive material used in the negative electrode.

[0090] In one embodiment, the positive electrode binder may be the same as or different from the binder used in the negative electrode.

[0091]

[0092] In one embodiment, the separator may be composed of a porous substrate or may include a porous substrate and a coating layer.

[0093] The porous substrate according to the present invention can be a porous structure having high resistance to electrolyte and fine pore diameters, capable of providing a path for lithium ions to move while electrically insulating the negative electrode and the positive electrode to prevent short circuits.

[0094] In some examples, any organic or inorganic material having electrical insulation properties may be used as a constituent material of the porous substrate without particular limitation. The porous substrate may include, for example, at least one selected from the group consisting of polyolefin, polyethylene terephthalate, polybutylene terephthalate, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulphone, polyphenyleneoxide, polyphenylenesulfide, and polyethylenenaphthalate, and may specifically include polyolefin. Polyolefin not only has excellent coating properties, but also allows for thinning the separator, increasing the ratio of the electrode active material layer in the battery, and thus increasing the capacity per volume.

[0095] In one embodiment, the weight average molecular weight (Mw) of the polyolefin may be 100,000 to 500,000 g / mol. If the weight average molecular weight of the polyolefin is less than the above numerical range, it may be difficult to secure sufficient mechanical properties, and if it exceeds the above numerical range, the shutdown function may not be implemented or molding may become difficult. The shutdown function refers to the function of blocking the movement of ions and preventing thermal runaway of the battery by melting the thermoplastic resin and closing the pores of the porous substrate when the temperature of the secondary battery increases.

[0096] In one embodiment, the thickness of the porous substrate may be, for example, 3 to 50 μm or 4 to 30 μm. If the thickness of the porous substrate is less than the numerical range, the function of the conductive barrier may not be sufficient, and if it exceeds the numerical range, the resistance of the separator may excessively increase.

[0097] In one embodiment, the average diameter of the pores included in the porous substrate may be, for example, 10 to 100 nm. The pores included in the porous substrate have a structure that is interconnected with each other, so that gas or liquid can pass from one side of the porous substrate to the other side.

[0098] In one embodiment, the separator may include a coating layer disposed on at least one surface of the porous substrate, which can improve the mechanical strength and heat resistance of the separator for a secondary battery and increase ionic conductivity within the secondary battery.

[0099] In one embodiment, the coating layer may include a binder polymer and inorganic particles.

[0100] The above binder polymer can connect and stably fix inorganic particles. The binder polymer may be, for example, polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethylmethacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinylacetate, poly(ethylene-co-vinyl acetate), polyethylene oxide, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, One or more selected from the group consisting of cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, carboxyl methyl cellulose, acrylonitrile-styrene butadiene copolymer, polyimide, and styrene-butadiene rubber may be used in combination.

[0101] In one embodiment, the weight ratio of the inorganic particles and the binder polymer (inorganic particles: binder polymer) may be 50:50 to 99:1, specifically 70:30 to 95:5. If the content ratio of the inorganic particles to the binder polymer is less than the above numerical range, the content of the binder polymer may increase, thereby deteriorating the thermal stability improvement performance of the separator, and the pore size and porosity may decrease due to a decrease in the empty space formed between the inorganic particles, thereby causing a deterioration in the performance of the final battery, and if the content of the binder polymer is exceeded, the content of the binder polymer may be too small, thereby weakening the peeling resistance of the coating layer.

[0102] In one embodiment, the inorganic particles can contribute to improving the mechanical strength and heat resistance of the separator for secondary batteries. Specifically, the inorganic particles are not particularly limited as long as they are electrochemically stable. That is, the inorganic particles that can be used in the present invention can be used within the operating voltage range of the secondary battery to which they are applied (e.g., Li / Li). + There are no particular limitations as long as no oxidation and / or reduction reaction occurs at a voltage of 0 to 5 V as a reference. For example, when using inorganic particles with a high dielectric constant as inorganic particles, it can contribute to increasing the degree of dissociation of electrolyte salts, such as lithium salts, in the liquid electrolyte, thereby improving the ionic conductivity of the electrolyte.

[0103] For the reasons described above, the inorganic particles may be inorganic particles having a dielectric constant of 5 or more, inorganic particles having lithium ion transport capability, or a mixture thereof.

[0104] In one embodiment, the inorganic particles having a dielectric constant of 5 or more are Al2O3, SiO2, ZrO2, AlO(OH), Al(OH)3, Mg(OH)2, BaSO4, TiO2, BaTiO3, Pb(Zr x Ti 1-x )O3(PZT, where 0 <x<1), Pb 1-x La x Zr 1-y Tiy O3 (PLZT, where 0 < x < 1, 0 < y < 1), (1-x)Pb(Mg 1 / 3 Nb 2 / 3 )O 3-x The inorganic particles having lithium ion transport capability may be one or a mixture of two or more selected from the group consisting of PbTiO3 (PMN-PT, where 0 < x < 1), HfO2, SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO and SiC. In some examples, the inorganic particles having lithium ion transport capability are lithium phosphate (Li3PO4), lithium titanium phosphate (Li x Ti y (PO4)3, 0< x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z (PO4)3, 0 < x < 2, 0 < y < 1, 0 < z < 3), (LiAlTiP) x O y Series glass (0 < x < 4, 0 < y < 13), lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3), lithium germanium thiophosphate (Li x Ge y P z S w , 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride (Li x N y , 0 < x <4, 0 < y < 2), SiS2 series glass(Li x Si y S z , 0 < x < 3, 0 < y < 2, 0 < z < 4) and P2S5 series glass(Li x P y S z, 0 < x < 3, 0 < y < 3, 0 < z < 7) may be one or a mixture of two or more selected from the group consisting of. In some examples, the average particle diameter (D) of the inorganic particles 50 ) may be 1 nm to 10 μm, specifically 10 nm to 2 μm, and more specifically 50 nm to 1 μm, for forming a coating layer of uniform thickness and an appropriate porosity. The "average particle diameter (D50)" refers to the particle diameter at the 50% point of the cumulative distribution of the number of particles according to particle diameter. The average particle diameter can be measured using a laser diffraction method. Specifically, after dispersing the target powder in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac S3500) and measuring the difference in diffraction pattern according to particle size when the particles pass through a laser beam, thereby calculating the particle size distribution.

[0105] In one embodiment, the thickness of the coating layer may be 0.1 to 10 μm, specifically 1 to 3 μm, and more specifically 1.4 to 1.6 μm. When the thickness of the coating layer satisfies the above numerical range, the insulation and thermal stability of the separator can be increased, while the energy density of the battery can be improved.

[0106]

[0107] In one embodiment, the electrolyte is A + B - It may contain a lithium salt having the same structure as A. Here, A + is Li + , Na + , K + Contains ions composed of alkali metal cations or combinations thereof, such as B - is PF6 - , BF4 - , Cl - , Br - , I - , ClO4- , AsF6 - , CH3CO2 - , CF3SO3 - , N(CF3SO2)2 - , C(CF2SO2)3 - It may be any one selected from the group consisting of anions such as or a combination thereof.

[0108] In one embodiment, the electrolyte may further include a solvent that dissolves the lithium salt. For example, the solvent may be dissolved or dissociated in an organic solvent selected from the group consisting of 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 is not limited thereto.

[0109] In one embodiment, the electrolyte may further include an additive for forming a stable solid electrolyte interphase (SEI). For example, the additive may include at least one selected from the group consisting of lithium tribis(fluorosulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(oxalate)borate (LiBOB), lithium hexafluorophosphate (LiPF6), and lithium fluoride (LiF). In this case, the interaction between the negative electrode active material of some embodiments and the electrolyte including the additive may form an SEI having a stable and uniform thickness at the interface where the electrolyte and the negative electrode come into contact. Accordingly, the life performance and rapid charging performance of the electrochemical device may be further improved.

[0110] In one embodiment, the secondary battery (e.g., electrochemical device) may further include a solid electrolyte interphase (SEI) formed on the surface of the negative electrode. Specifically, by including a stable and uniformly thick solid electrolyte interphase (SEI) on the surface of the negative electrode, the life performance and rapid charging performance of the electrochemical device may be further improved.

[0111] In one embodiment, the solid electrolyte interphase (SEI) may comprise lithium fluoride (LiF), wherein the lithium fluoride (LiF) may be derived from the negative active material of some embodiments and / or the additive.

[0112] In one embodiment, the thickness of the SEI may be 1 to 150 nm.

[0113] In one embodiment, the thickness deviation of the SEI may be 10% or less compared to the thickness average.

[0114] In one embodiment, the secondary battery can be used as a unit cell, and can be used as a battery module including the unit cell, a battery pack including the battery module, and a device including the battery pack as a power source. The devices include, but are not limited to, small devices such as computers, mobile phones, and power tools, and medium to large devices such as electric vehicles including electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid electric vehicles (PHEV) that are powered by an electric motor and move; electric two-wheeled vehicles including electric bicycles (E-bikes) and electric scooters; electric golf carts; and power storage systems.

[0115]

[0116] The above description has explained the technical idea of ​​the present invention using one embodiment. Those skilled in the art will appreciate that various modifications and variations can be made without departing from the essential characteristics of the present invention. Therefore, the embodiments described in the present invention are not intended to limit the technical idea of ​​the present invention, but rather to explain it, and the scope of the technical idea of ​​the present invention is not limited by these embodiments. The scope of protection of the present invention should be interpreted by the claims, and all technical ideas within a scope equivalent thereto should be interpreted as being included within the scope of the rights of the present invention.

[0117]

[0118] [Synthesis example]

[0119] Synthesis Example 1: Manufacturing of Silicon Particles

[0120] Milled silicon particles (D50: 120 nm) and pitch powder were dispersed in ethanol, and then the dispersion was sprayed using a spray dryer to produce silicon particles. The content of the milled silicon particles was adjusted to 3 wt% based on the total weight of the dispersion. Using the nozzle-type spray dryer, a pressure (100 torr) was applied through an inert gas (Ar) to an extent that droplets could be sprayed evenly, and the outlet temperature of the spray dryer was set to 85°C to produce silicon particles with an average size (D50) of 9 μm. Thereafter, the silicon particles with an average size (D50) of 9 μm were fed into a kiln, and acetylene gas was additionally fed according to a chemical vapor deposition process to perform heat treatment at 600°C to produce silicon particles with a laminated carbon layer.

[0121]

[0122] Synthesis Example 2: Polyimide Preparation

[0123] In a flask equipped with a nitrogen injector, a condenser, and a stirrer, 100 g of n-methyl-2-pyrrolidone (NMP) and 0.05 mol of ethylenediamine (EDA) were stirred and cooled to 0°C. Then, 0.05 mol of pyromellitic dianhydride (PMDA) was slowly added dropwise over 1 hour, and the mixture was stirred at room temperature. Afterwards, the temperature was gradually increased and maintained at 80°C for 2 hours, 120°C for 2 hours, and 150°C for 2 hours to proceed with the cyclization reaction. After cooling to room temperature, the synthesized polyimide was purified and dried to synthesize a polyimide with a weight-average molecular weight of 12,000. The final composite was analyzed by FT-IR to confirm the formation of a polyimide structure by confirming the C=O bond peak and C-N bond peak, which are characteristic peaks of imide.

[0124]

[0125] [Example]

[0126] Example 1

[0127] 20 g of silicon particles (D50, 9 μm) manufactured according to the above Synthetic Example 1 were dispersed in 4 L of ethanol, 2 g of 3-aminopropyltriethoxysilane (APTES) was added, and the mixture was reacted at 80°C for 24 hours, centrifuged to remove the solvent and unreacted materials, and vacuum-dried. 10 g of the above reactant was dispersed in 1 L of dimethylformamide (DMF), and 1 g of ethylene glycol (EG) and hexamethylene diisocyanate (HDI) at an equivalent ratio of 1:1.1 was added, and the mixture was reacted at 80°C for 24 hours, and DMF and unreacted materials were removed and vacuum-dried to manufacture silicon particles (hereinafter "negative active material-1") having a (N+O) / C of 0.77, in which a urethane-urea prepolymer (Mw=348 g / mol) exists on the particles.

[0128] The above negative electrode active material-1, Super-P, and polyacrylic acid (PAA) were mixed in a weight ratio of 80:10:10, and distilled water was added as a solvent to adjust the viscosity, thereby producing a negative electrode material having a total solid content of 50 wt%. The produced negative electrode material was coated on a current collector (copper foil) having a thickness of 18 μm, dried at 90°C for 2 hours, and then adjusted to a combined density of 1.3 g / cc using a roll press, and then dried in a vacuum oven at 90°C for 24 hours to produce a negative electrode.

[0129]

[0130] Example 2

[0131] 10 g of silicon particles manufactured according to the above Synthesis Example 1 were dispersed in 1 L of dimethylformamide (DMF), 1 g of polyrhodanine (Mw=20,000 g / mol) was added, and the mixture was stirred at 80°C for 24 hours. After filtering to remove DMF, the mixture was vacuum-dried to manufacture silicon particles (hereinafter “negative active material-2”) having (N+O) / C of 0.67 and polyrhodanine present on the particles.

[0132] Using the above negative electrode active material-2, a negative electrode material and a negative electrode were manufactured in the same manner as in Example 1.

[0133]

[0134] Example 3

[0135] In the above Example 2, except that chitosan (Mw=25,000 g / mol) was used instead of polyrhodanine, silicon particles (hereinafter referred to as "negative electrode active material-3") having a (N+O) / C of 0.83 in which chitosan exists on the particle surface, a negative electrode material, and a negative electrode were manufactured using the same method and conditions as in the above Example 2.

[0136]

[0137] Example 4

[0138] In the above Example 3, except that chitosan (chitosan, Mw=40,000) was used instead of chitosan (chitosan, Mw=25,000 g / mol), silicon particles (hereinafter “negative electrode active material-4”) having (N+O) / C of 0.83 in which chitosan exists on the particle were manufactured using the same method and conditions as in the above Example 3, a negative electrode material, and a negative electrode.

[0139]

[0140] Example 5

[0141] In the above Example 2, except that polyimide (Mw=12,000 g / mol) manufactured according to the above Synthesis Example 2 was used instead of polyrhodanine, silicon particles (hereinafter “negative electrode active material-5”), a negative electrode material, and a negative electrode having (N+O) / C of 0.67 in which polyimide exists on the particle were manufactured using the same method and conditions as in the above Example 2.

[0142]

[0143] Example 6

[0144] In the above Example 2, except that polyethyleneimine (Mw=2,500 g / mol) was used instead of polyrhodanine, silicon particles (hereinafter referred to as "negative electrode active material-6"), a negative electrode material, and a negative electrode having (N+O) / C of 0.50 in which polyethyleneimine exists on the particle were manufactured using the same method and conditions as in the above Example 2.

[0145]

[0146] Example 7

[0147] In the above Example 2, except that polyethylene glycol (Mw=1,000 g / mol) was used instead of polyrhodanine, silicon particles (hereinafter referred to as "negative electrode active material-7"), a negative electrode material, and a negative electrode having (N+O) / C of 0.50 and polyethylene glycol present on the particles were manufactured using the same method and conditions as in the above Example 2.

[0148]

[0149] Example 8

[0150] In the above Example 2, except that 3-amino-1-propanol (Mw = 75 g / mol) was used instead of polyrhodanine, silicon particles (hereinafter referred to as "negative electrode active material-8") having (N+O) / C of 0.67 in which 3-amino-1-propanol exists on the particles were manufactured using the same method and conditions as in the above Example 2, a negative electrode material, and a negative electrode.

[0151]

[0152] Example 9

[0153] In the above Example 2, except that poly(methyl methacrylamide) (Mw=10,000 g / mol) was used instead of polyrhodanine, silicon particles (hereinafter “negative electrode active material-9”), a negative electrode material, and a negative electrode having (N+O) / C of 0.40 in which poly(methyl methacrylamide) exists on the particles were manufactured using the same method and conditions as in the above Example 2.

[0154]

[0155] [Comparative example]

[0156] Comparative Example 1

[0157] In the above Example 2, except that polyvinylpyrrolidine (Mw = 9,700 g / mol) was used instead of polyrhodanine, silicon particles (hereinafter referred to as "negative electrode active material-10"), a negative electrode material, and a negative electrode having (N+O) / C of 0.33 in which polyvinylpyrrolidine exists on the particle were manufactured using the same method and conditions as in the above Example 2.

[0158]

[0159]

[0160] Comparative Example 2

[0161] In the above Example 2, except that theobromine (Mw = 180 g / mol) was used instead of polyrhodanine, silicon particles (hereinafter referred to as "negative electrode active material-11") having a (N+O) / C of 0.86 and in which theobromine exists on the particle were manufactured using the same method and conditions as in the above Example 2, a negative electrode material, and a negative electrode.

[0162]

[0163] [Experimental Example]

[0164] Atomic number measurement

[0165] In order to measure the number of atoms of the surface-modified compounds of the above negative active materials-1 to-11, X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance (NMR), and mass spectrometry (MALDI-TOF-MS) were used to comprehensively analyze and measure the number of atoms.

[0166] Each of the above negative active materials-1 to-11 was prepared in pellet form and analyzed for atomic ratio using a Thermo Scientific ESCALAB 250Xi. In addition, each of the negative active materials-1 to-11 was dispersed in a solvent to selectively extract organic components, and the solution was centrifuged to remove silicon precipitates, and the supernatant was concentrated and used for analysis. 1 H-NMR and 13 The number of constituent atoms was quantitatively estimated based on the spectral results by performing C-NMR analysis, and the number of carbon, oxygen, and nitrogen atoms was finally analyzed based on the XPS and NMR results through MALDI-TOF MS analysis, and the results are shown in Table 1. Here, the number of carbon, oxygen, and nitrogen atoms was quantitatively calculated as the number of atoms included per repeating unit, and the number of each atom of the carbon layer laminated on the silicon particle is not included.

[0167] CNO(N+O) / CExample 113370.77Example 23110.67Example 36140.83Example 46140.83Example 512260.67Example 62100.50Example 72010.50Example 83110.67Example 95110.40Comparative Example 16110.33Comparative Example 27420.86

[0168]

[0169] Half-cell manufacturing

[0170] After arranging the negative electrode, polyethylene separator (80 μm thick), and counter electrode (lithium metal with a thickness of 300 μm) manufactured in the above examples and comparative examples in that order, a membrane-electrode assembly was manufactured under an inert gas atmosphere. After placing the membrane-electrode assembly in a battery case, an electrolyte solution in which 1.15 M LiPF6 was dissolved in a mixed solvent of fluoroethylene carbonate (FEC) and dimethylcarbonate (DMC) in a volume ratio of 3:7 was injected to manufacture half-cells of the experimental examples and comparative examples.

[0171]

[0172] Performance Evaluation

[0173] 1. Electrochemical performance evaluation

[0174] For the fabricated half-cells, the initial coulombic efficiency was measured at a current of 0.1 C, and the capacity retention was evaluated at a current of 0.5 C. Specifically, the formation process was performed by charging at a charge rate of 0.5 C in a constant current (CC) / constant voltage (CV) manner until the voltage reached 0.05 V (vs. Li), and then performing a cycle of discharging at a discharge rate of 0.5 C with a cut-off of 1.5 V. Subsequently, charging at 0.5 C in a CC / CV manner until the voltage reached 0.05 V, and discharging at 0.5 C to 1.5 V were repeated, and the specific capacity, initial coulombic efficiency, and capacity retention were measured for up to 100 cycles, and the results are shown in Table 2.

[0175]

[0176] 2. Electrode expansion rate (%)

[0177] The thickness of the electrode used in the above-mentioned manufactured half-cell was measured before each cycle, and the cell, which had undergone a capacity retention evaluation for 100 cycles, was disassembled under an inert gas atmosphere to measure the thickness and calculate the expansion rate of the electrode, and the results are shown in Table 2 below.

[0178]

[0179] 3. Electrode adhesion (N)

[0180] The electrodes manufactured in the above experimental examples and comparative experimental examples were evaluated for adhesive strength through a 180° peel test. 12 x 20 mm 2 The force when a 3M tape was attached to an electrode of the size and removed at a speed of 10 mm / min using a universal testing machine (UTM) was measured, and the results are shown in Table 2 below.

[0181] Single electrode capacity (mAh / g) Initial coulombic efficiency (%) Retention @100 cycle (%) Electrode expansion rate (%) Electrode adhesion (N) Experimental example 11, 75087.5841052.5 Experimental example 21, 68086.3781122.0 Experimental example 31, 70586.7811102.2 Experimental example 41, 67586.2771141.9 Experimental example 51, 71586.9811092.3 Experimental example 61, 69086.5811132.0 Experimental example 71, 70086.9821102.2 Experimental example 81, 68086.2791152.0 Experimental example 91,65086.0751201.8Comparative Experimental Example 11,54082.2481551.1Comparative Experimental Example 21,63085.3631491.4

[0182] While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the exemplary embodiments disclosed herein, and that various modifications may be made by those skilled in the art within the scope of the technical spirit of the invention. Furthermore, even if the operational effects of the configurations of the invention have not been explicitly described and explained while describing the exemplary embodiments of the invention, it is also to be understood that the effects predictable by the configurations should be acknowledged.

Claims

1. Silicon particles; and Comprising a compound containing at least one of a carbon atom and an oxygen atom or a nitrogen atom on the silicon particle, The above compound is a negative electrode active material for a secondary battery, wherein the ratio of the number of carbon atoms: the number of nitrogen atoms or the number of oxygen atoms is 1: 0.35 to 0.

85.

2. In paragraph 1, The above compound is a negative electrode active material for a secondary battery, wherein the ratio of the number of carbon atoms: the number of nitrogen atoms or the number of oxygen atoms is 1: 0.7 to 0.

8.

3. In paragraph 1, A negative electrode active material for a secondary battery, wherein the number of carbon atoms in the above compound is 1 to 1,500.

4. In paragraph 1, A negative electrode active material for a secondary battery, wherein the compound contains at least one nitrogen atom and at least one oxygen atom.

5. In paragraph 4, A negative electrode active material for a secondary battery, wherein the ratio of the number of nitrogen atoms to the number of oxygen atoms contained in the compound is 1:0.25 to 1.

6. In paragraph 1, The above compound is a negative electrode active material for a secondary battery, comprising at least one hydrogen-bonding functional group selected from the group consisting of a urethane group, a urea group, a carbonyl group, an amine group, a hydroxyl group, a carboxyl group, an imide group, an amide group, an ether group, and combinations thereof.

7. In paragraph 1, A negative electrode active material for a secondary battery, wherein the weight average molecular weight of the compound is 30 to 40,000 g / mol.

8. Negative active material according to Article 1; Challenge; and A negative electrode material for a secondary battery comprising a binder.

9. In paragraph 8, A negative electrode material for a secondary battery, wherein the binder comprises at least one hydrogen-bonding functional group selected from the group consisting of -OH, -COOH, -O-, -CONH2, -CN, and combinations thereof.

10. In paragraph 9, A negative electrode material for a secondary battery, wherein the binder is at least one aqueous binder selected from the group consisting of carboxymethylcellulose (CMC), polyacylic acid (PAA), polyvinyl alcohol (PVA), polyethylene glycol (PEG), polyacrylonitrile (PAN), polyacryl amide (PAM), and combinations thereof.

11. In paragraph 8, Based on 100 parts by weight of the above secondary battery negative electrode material, 50 to 99 parts by weight of the above negative electrode active material; 0.5 to 30 parts by weight of the above binder; and A negative electrode material for a secondary battery, comprising 0.05 to 20 parts by weight of the above-mentioned conductive material.

12. A negative electrode comprising a negative electrode material for a secondary battery according to Article 8; anode; membrane; and A secondary battery containing an electrolyte.

13. In paragraph 12, A secondary battery, wherein the secondary battery is a sodium or lithium secondary battery.