TW202346205A - Nano silicon, nano silicon slurry, method for producing nano silicon, active material for secondary batteries, and secondary battery - Google Patents

Abstract

The present invention relates to: an active material for secondary batteries, the active material being used for lithium ion secondary batteries; and a secondary battery which comprises the active material for secondary batteries as a negative electrode active material. The present invention provides a negative electrode active material for secondary batteries, the negative electrode active material enabling the achievement of a secondary battery which has excellent cycle characteristics, initial coulombic efficiency and capacity retention rate. The present invention provides a nano silicon which has a specific surface area of 100 to 400 m2/g, while containing 5 to 45 atom% of oxygen atoms if the sum of oxygen atoms and silicon atoms is taken as 100 atom%. It is preferable that the nano silicon has a crystallite diameter of 5 to 14 nm. It is also preferable that the nano silicon has a volume average particle diameter of 10 to 200 nm. The present invention provides: an active material for secondary batteries, the active material comprising this nano silicon; and a secondary battery which contains the active material for secondary batteries in the negative electrode.

Description

Nanosilicon, nanosilicon slurry, nanosilicon manufacturing method, secondary battery active material and secondary battery

The present invention relates to a kind of nano-silicon, nano-silicon slurry and a manufacturing method of the above-mentioned nano-silicon. Furthermore, the present invention relates to a secondary battery active material containing the above-mentioned nanosilica, a negative electrode containing the above-mentioned secondary battery active material, and a secondary battery including the above-mentioned negative electrode.

Non-aqueous electrolyte secondary batteries are used in mobile devices, hybrid and electric vehicles, household batteries, etc., and they need to have a balance of various characteristics such as capacitance, safety, and operational stability. Furthermore, in recent years, with the miniaturization of various electronic equipment and communication equipment and the rapid spread of gasoline-electric hybrid vehicles, there is a strong need to develop a power supply with higher capacity and better cycle characteristics or discharge rate characteristics as a driving power supply for these equipment. Lithium-ion secondary battery with further improved various battery characteristics.

Since silicon has a large theoretical capacitance, research is underway to use silicon as a negative electrode active material to increase the capacity of lithium-ion secondary batteries. However, the difference between the volume expansion and contraction of silicon is large when repeated charging and discharging are performed, and the silicon particles will break during repeated charging and discharging. As a result, secondary batteries using silicon as the negative electrode active material have poor cycle characteristics.

Non-Patent Document 1 describes that cracking of silicon particles having a particle diameter of 150 nm or less can be suppressed. Furthermore, Patent Document 1 describes a negative electrode active material for secondary batteries using silicon particles with nanometer-sized particles. Prior art documents Patent documents

Patent document 1: Japanese Patent Application Publication No. 2021-180124 Non-patent document

Non-patent literature: Xiao et al., ACS Nano, 6, 1522-1531(2012)

[Problem to be solved by the invention]

However, even if the secondary battery active material uses silicon particles with the particle size described in Non-Patent Document 1 or Patent Document 1, when charge and discharge are repeatedly performed, the particles may break, resulting in insufficient cycle characteristics. Furthermore, when an active material for secondary batteries using silicon particles with a small particle size is used, the capacitance and initial Coulomb efficiency are insufficient. Therefore, there is a need to develop an active material for lithium secondary batteries using silicon particles with improved cycle characteristics, capacitance, and initial Coulombic efficiency.

The inventors of the present invention paid attention to the particle size of the silicon particles and the degree of surface oxidation of the silicon particles, and developed an active material for secondary batteries that is excellent in cycle characteristics, capacitance, and initial Coulombic efficiency. As a result, an active material for secondary batteries that is excellent in cyclability, capacitance, and initial coulombic efficiency of lithium secondary batteries was discovered. That is, the present invention relates to a secondary battery active material used in a lithium ion secondary battery and a secondary battery including the above-mentioned secondary battery active material as a negative electrode active material, and its object is to provide silicon particles. Active material for secondary batteries used to provide secondary batteries with excellent cycleability, initial Coulombic efficiency, and capacity retention. Furthermore, an object of the present invention is to provide a method for manufacturing silicon particles used in the above-mentioned active material for secondary batteries. [Technical means to solve the problem]

The present invention has the following aspects. [1] Nano-silicon with a specific surface area of 100 to 400 m ² /g and an oxygen atom ratio of 5 to 45 atom% relative to the silicon atom. [2] Nano-silicon as described in [1] above has a crystallite diameter of 5 to 14 nm. [3] The silicon nanoparticles described in [1] or [2] above have a volume average particle size of 10 to 200 nm.

Furthermore, the present invention has the following aspects. [4] A nanosilicon slurry, which contains the nanosilicon described in any one of the above [1] to [3], a dispersant and a solvent.

Furthermore, the present invention has the following aspects. [5] A method for manufacturing nano-silicon, which involves wet-processing silicon powder in a non-aqueous solvent with a temperature of 60°C or less and a moisture concentration of 10,000 ppm or less in a gas environment with a dew point temperature of -60°C or less. Crush. [6] The method for producing silicon nanoparticles as described in the above [5], which contains at least one kind of interface active agent selected from the group consisting of cationic surfactants, anionic surfactants, and amphoteric surfactants. The above-mentioned wet grinding is carried out in a non-aqueous solvent. [7] The method for producing silicon nanoparticles as described in the above [5] or [6], wherein in the wet grinding, the volume average particle diameter is 1 to 20 μm in a non-aqueous solvent and the oxygen atoms are Silicon powder with a silicon atom content of less than 10 atom% is wet-pulverized. [8] The manufacturing method of silicon nanoparticles as described in any one of [5] to [7] above, wherein the purity of the silicon powder in the above-mentioned wet grinding is 99 mass% or more.

Furthermore, the present invention has the following aspects. [9] A method for manufacturing an active material for secondary batteries, which involves mixing nanosilicon obtained by the method for manufacturing nanosilicon according to any one of the above [5] to [8] and resin, and drying Calcined in an inert gas environment. [10] An active material for secondary batteries containing the silicon nanoparticles described in any one of the above [1] to [3]. [11] A negative electrode for secondary batteries, which contains the active material for secondary batteries described in [10] above. [12] A secondary battery including the negative electrode for secondary batteries described in [11] above. [The effect of the invention]

According to the present invention, a secondary battery active material for a lithium ion secondary battery and a secondary battery including the above-mentioned secondary battery active material as a negative electrode active material are provided. Active material for secondary batteries with excellent capacity retention rate. Furthermore, the present invention provides a method for manufacturing silicon particles used in the above-mentioned active material for secondary batteries.

The specific surface area of the nanosilicon of the present invention (hereinafter also referred to as "this nanosilicon") is 100 to 400 m ² /g, and the oxygen atoms are 5 to 45 atom% relative to the silicon atoms. Here, "oxygen atoms are 5 to 45 atom% relative to silicon atoms" means that the number of oxygen atoms in this nanosilicon divided by the number of silicon atoms is 5 to 45 when expressed in atom%, and the following is also Same thing. As mentioned above, it is considered that silicon particles with a smaller particle size can suppress breakage of the silicon particles even if the volume changes due to repeated charging and discharging. On the other hand, it is considered that the surface area of silicon particles with a smaller particle size becomes larger and the surface oxidation rate of the silicon particles becomes larger. The result is considered to be that the secondary battery active material containing silicon particles with a small particle size suppresses deterioration in cycle characteristics due to repeated charge and discharge, but has poor capacitance and initial Coulomb efficiency.

The nano-silicon particles have a volume average particle size of nanometer level. Due to the smaller particle size, the cycle characteristics are improved. In addition, it is believed that the surface area is equivalent to or larger than that of conventional silicon particles, but the oxygen atom content rate is suppressed to a low level, thereby achieving improvements in capacitance and initial Coulomb efficiency.

The volume average particle size is nanometer level means that the volume average particle size is in nanometers, and the volume average particle size is usually 1 to 999 nm. When the silicon particles exceed 1000 nm, the dispersibility may become poor when the silicon slurry is made, the pressure may increase during stirring, and the productivity may decrease. From these viewpoints, the volume average particle size of the silicon nanoparticles is preferably 10 to 200 nm, more preferably 10 to 100 nm, and further preferably 20 to 70 nm. Furthermore, the volume average particle size is the D50 value that can be measured using a laser diffraction particle size analyzer. D50 can be measured by dynamic light scattering using a laser particle size analyzer or the like. Regarding the volume average particle size of the present silicon nanoparticles, when a volume cumulative distribution curve is drawn from the small diameter side in the particle size distribution, the particle size at 50% accumulation is the above average particle size.

The specific surface area of this nanosilicon is 100 to 400 m ² /g. The above-mentioned specific surface area is a value determined by the BET method, and can be determined by nitrogen adsorption measurement. For example, the specific surface area can be measured using a specific surface area measuring device. From the viewpoint of capacitance and initial Coulomb efficiency, the specific surface area of the silicon nanoparticles is preferably 100 to 300 m ² /g, and further preferably 100 to 230 m ² /g.

As mentioned above, the oxygen atomic weight in the present nano-silicon is 5 to 45 atm% relative to the silicon atoms. It is believed that by using the present nanosilicon with an average particle size as small as the above range and an oxygen atomic weight within the above range as the negative active material of a secondary battery, cyclability, initial Coulombic efficiency and capacity retention can be achieved Secondary battery with excellent efficiency. From the perspective of initial Coulombic efficiency and capacity retention, the oxygen atomic weight in the present nanosilicon is preferably 5 to 30 atm%, more preferably 5 to 25 atm%, and further preferably 5 to 15%. Regarding the oxygen atomic weight, after baking the silicon nanoparticles at a temperature of 300 to 800°C to volatilize the additives, the oxygen atomic weight was obtained by composition analysis using SEM-EDS (JSM-7900F manufactured by JEOL). In addition to silicon atoms and oxygen atoms, this nanosilicon can also contain carbon atoms and nitrogen atoms. When nitrogen atoms are included, from the viewpoint of generating silicon nitride and causing a decrease in capacity, the content is preferably 5 mass % or less.

The shape of the silicon nanoparticles can be any of granular, needle-shaped, and flake-like, as long as the silicon nanoparticles satisfy the above specific surface area and oxygen atomic weight, preferably crystalline. In the case where the silicon nanoparticles are crystalline, from the viewpoint of initial Coulomb efficiency and capacity retention rate, it is preferable to be the crystallite diameter obtained from the diffraction peak attributed to Si (111) in X-ray diffraction ( Hereinafter, also referred to as "crystalline diameter") is in the range of 5 to 14 nm. The crystallite diameter is more preferably 12 nm or less, further preferably 10 nm or less.

From the perspective of charge and discharge performance when used as a negative electrode active material, the length of the long axis direction of the silicon nanoparticles is preferably 30 to 300 nm, and the thickness is preferably 1 to 60 nm. From the viewpoint of charge and discharge performance when used as a negative electrode active material, a needle-like or sheet-like shape in which the ratio of thickness to length, that is, the so-called aspect ratio, is 0.5 or less is preferred. Regarding the morphology of this nanosilicon, the average particle size can be measured by dynamic light scattering, but it can be further determined by analysis using a transmission electron microscope (TEM) or a field emission scanning electron microscope (FE-SEM). Samples with the above aspect ratios can be identified easily and precisely. When the negative electrode active material of the secondary battery material of the present invention is included, the sample can be cut using a focused ion beam (FIB) and the cross section can be observed by FE-SEM, or the sample can be sliced and observed by TEM. Identify the status of this nanosilicon. Furthermore, the aspect ratio of the above-mentioned nano-silicon is calculated based on 50 particles in the main part of the sample within the field of view shown in the TEM image.

When the present nanosilica is used as an active material for a secondary battery, the present nanosilica can be directly used as the active material, or can be used as an active material for a secondary battery containing the present nanosilica in the matrix phase. From the viewpoint of the stability of the active material for secondary batteries, it is preferable to use an active material whose matrix phase contains the present nanosilica as the active material for secondary batteries.

When an active material containing the present nanosilica is used as an active material for a secondary battery, the above-mentioned matrix phase can absorb and release substances that release lithium ions. Substances that can absorb and release are substances that can store lithium ions in the matrix phase when the battery is charged and release lithium ions from the matrix phase when the battery is discharged. In lithium secondary batteries, the above cycle of storage and release is repeated. Examples of substances that can absorb and release lithium ions include graphite, silicon dioxide, titanium oxide, and compounds containing silicon, oxygen, and carbon. The above-mentioned matrix phase is preferably composed of these substances to improve the primary efficiency and From the viewpoint of capacity retention, it is more preferably composed of a compound containing silicon, oxygen, and carbon. As a compound containing silicon, oxygen, and carbon, silicon oxycarbonate can be exemplified.

Silicon oxycarbide is composed of a compound containing silicon, oxygen, and carbon. Among them, a structure containing a three-dimensional network structure of silicon-oxygen-carbon skeleton and free carbon is preferred. Here, free carbon is carbon not included in the three-dimensional skeleton of silicon-oxygen-carbon. Free carbon includes carbon existing in the form of a carbon phase, carbon bonded between carbons in the carbon phase, and carbon bonded to the silicon-oxygen-carbon skeleton and the carbon phase.

Silicon oxycarbide is preferably represented by the following formula (1). SiOxCy (1) In formula (1), x represents the molar ratio of oxygen relative to silicon, and y represents the molar ratio of carbon relative to silicon. When an active material containing the present nanosilica and a matrix phase is used in a secondary battery, from the viewpoint of excellent balance between charge and discharge performance and capacity retention rate, 1≦x<2 is preferred, and 1≦x<2 is more preferred. 1≦x≦1.9, and more preferably 1≦x≦1.8. In addition, when the active material containing the present nanosilica and the matrix phase is used in a secondary battery, from the viewpoint of the balance between charge and discharge performance and primary Coulomb efficiency, 1≦y≦20 is preferred, and more preferred is 1.2≦y≦15.

The above x and y can be found by measuring the mass content of each element and converting it into molar ratio (atomic number ratio). At this time, the content of oxygen and carbon can be quantified by using an inorganic element analysis device, and the content of silicon can be quantified by using an ICP luminescence analysis device (ICP-OES). Furthermore, the measurement of the above-mentioned x and y is preferably carried out by the above-mentioned method, but it is also possible to perform partial analysis of the active material, obtain a large number of measurements of the content ratio data obtained thereby, and similarly deduce the overall active material. Contains ratio. Examples of local analysis include energy dispersive X-ray spectroscopy (SEM-EDX) or electron probe microanalysis (EPMA).

The matrix phase is a silicon oxycarbon phase composed of silicon oxycarbon. In the case of a three-dimensional network structure containing a silicon-oxygen-carbon skeleton and a structure of free carbon, the chemistry of the silicon-oxygen-carbon skeleton in the silicon oxycarbon phase It has high stability, obtains a composite structure with free carbon, and has small volume changes in the storage and release of lithium. By tightly wrapping the present nanosilicon in the composite structure of silicon-oxygen-carbon skeleton and free carbon, the volume change of the present nanosilicon in absorbing and releasing lithium can be further suppressed. As a result, when the active material containing the present nanosilica and the matrix phase is used as the negative electrode active material, the present nanosilica in the negative electrode plays a role as a main component that exhibits charge and discharge performance, and at the same time, the silicon oxycarbide phase The particle breakage caused by the volume change of the silicon nanoparticles during charging and discharging is further suppressed, and the cycleability of the lithium secondary battery is further improved.

Furthermore, if the compound constituting the silicon carbon oxide phase has a three-dimensional network structure including a silicon-oxygen-carbon skeleton and free carbon, then in the silicon-oxygen-carbon skeleton, due to the proximity of lithium ions, the silicon-oxygen-carbon skeleton The internal electron distribution changes, forming electrostatic bonds or coordination bonds between the silicon-oxygen-carbon skeleton and lithium ions. Lithium ions are stored in the silicon-oxygen-carbon skeleton through this electrostatic bond or coordination bond. On the other hand, since the coordination bond energy is relatively low, the deintercalation reaction of lithium ions easily occurs. That is, it is believed that the silicon-oxygen-carbon skeleton can reversibly cause the intercalation and deintercalation reactions of lithium ions during charge and discharge.

The silicon oxycarbide may also contain nitrogen in addition to silicon, oxygen, and carbon. In the following method for manufacturing an active material including the present nanosilica and a matrix phase, nitrogen atoms can be introduced into the silicon oxycarbide phase in the form of atomic groups, and the above atomic groups include in the molecule the nitrogen atoms contained in the raw materials used as The raw materials used for functional groups include, for example, phenolic resins or polysiloxane compounds, nitrogen compounds such as other dispersants, and nitrogen used in the baking process. Since the silicon oxycarbide phase contains nitrogen, the charge-discharge performance or capacity retention rate tends to be excellent when the active material containing the nano-silicon and the matrix phase is used as the negative electrode active material. When the compound constituting the silicon oxycarb phase is a compound containing silicon, oxygen, carbon, and nitrogen, the silicon oxycarb phase preferably contains a compound represented by the following formula (2). SiOaCbNc (2) In formula (2), a and b have the same meaning as above, and c represents the molar ratio of nitrogen to silicon. In the case where the silicon oxycarbide phase contains the compound represented by the above formula (2), from the viewpoint of the charge-discharge performance or capacity retention rate when the active material containing nano-silicon is used in a secondary battery, it is better than Preferably, 1≦a≦2, 1≦b≦20, 0<c≦0.5, more preferably 1≦a≦1.9, 1.2≦b≦15, 0<c≦0.4.

The above a, b and c can be obtained by measuring the mass content of the element and converting it into a molar ratio (atomic number ratio) in the same manner as the above x and y. The measurement of a, b and c is the same as the above-mentioned x and y. It is preferably carried out by the method described above. However, it is also possible to perform local analysis of the active substance and obtain a large number of measurements of the content ratio data obtained thereby. , the overall content ratio of the active material can be derived by analogy. Examples of local analysis include energy dispersive X-ray spectroscopy (SEM-EDX) or electron probe microanalysis (EPMA).

If the average particle size of the active material containing the present nanosilica and the matrix phase is too small, as the specific surface area increases significantly, when a secondary battery using the active material as the negative active material is made, the solid-phase interface electrolyte will be charged and discharged during charging and discharging. The amount of decomposition products (hereinafter also referred to as "SEI") may increase, resulting in a decrease in the reversible charge and discharge capacity per unit volume. If the average particle diameter is too large, there is a risk of peeling off from the current collector when the electrode film is produced. Therefore, when the matrix phase contains the active material of nanosilica, its volume average particle size is preferably between 2 μm and 15 μm. The volume average particle size of the active material containing nanosilica in the matrix phase is preferably 2.5 μm or more, especially 3.0 μm or more. Furthermore, the volume average particle diameter of the active material is more preferably 12 μm or less, particularly preferably 10 μm or less. The volume average particle diameter is the value of D50 mentioned above.

The specific surface area of the active material containing nanosilica in the matrix phase is preferably 0.3 m ² /g or more and 10 m ² /g or less. The specific surface area of the active material containing nanosilica in the matrix phase is preferably more than 0.5 m ² /g, particularly preferably more than 1.0 m ² /g. Furthermore, the specific surface area of the active material is more preferably 9.0 m ² /g or less, even more preferably 8.0 m ² /g or less. If the specific surface area is within the above range, the amount of solvent absorbed during electrode production can be appropriately maintained, and the amount of binder used to maintain adhesiveness can also be appropriately maintained. In addition, the above-mentioned specific surface area is a value obtained by the BET method in the same manner as above, and can be obtained by nitrogen adsorption measurement. For example, it can be measured using a specific surface area measuring device.

When the matrix phase contains the active material of silicon oxycarb, the silicon oxycarb is preferably free carbon with a silicon-oxygen-carbon skeleton structure and composed only of carbon elements. When silicon oxycarbide contains free carbon, in the Raman spectrum of the active material, a G band of 1590 cm ^-1 belonging to the long period carbon lattice structure of graphite and disordered or defective graphite are observed The scattering peak near 1330 cm ^-1 of the D band of the short-period carbon lattice structure. The intensity ratio I (G band)/I (D band) of the scattering peak intensity I (D band) of the D band relative to the scattering peak intensity I (G band) of the G band is preferably 0.7 or more and 2 or less. The above-mentioned scattering peak intensity ratio I (G band)/I (D band) is more preferably 0.7 or more and 1.8 or less. The fact that the above scattering peak intensity ratio I (G band)/I (D band) is within the above range means the following for free carbon in the matrix.

Some of the carbon atoms in the free carbon are bonded to some of the silicon atoms in the silicon-oxygen-carbon skeleton. This free carbon is an important component that affects charge and discharge characteristics. Free carbon is mainly formed in the silicon-oxygen-carbon skeleton composed of SiO ₂ C ₂ , SiO ₃ C and SiO ₄ , and is bonded with part of the silicon atoms in the silicon-oxygen-carbon skeleton, so inside the silicon-oxygen-carbon skeleton , and electron transfer is more likely to occur between silicon atoms and free carbon on the surface. Therefore, it is believed that when an active material containing nanosilica in the matrix phase is used as a negative electrode active material in a secondary battery, the intercalation and deintercalation reaction of lithium ions during charge and discharge proceeds rapidly, and the charge and discharge characteristics are improved. In addition, it is believed that the intercalation and deintercalation reactions of lithium ions may cause expansion and contraction of the active material, but the presence of free carbon in its vicinity alleviates the expansion and contraction of the entire active material, which has the effect of greatly improving the capacity retention rate.

Free carbon is formed along with the thermal decomposition of silicon-containing compounds and carbon source resin in an inert gas environment during the production of silicon carbonate phase. Specifically, the carbonizable part in the molecular structure of the silicon-containing compound and the carbon source resin is thermally decomposed at high temperature in an inactive environment and becomes a carbon component. This part of the carbon is bonded to part of the silicon-oxygen-carbon skeleton. . The carbonizable component is preferably a hydrocarbon, more preferably an alkyl group, an alkylene group, an olefin group, an alkyne group, or an aromatic group, and among these, an aromatic group is even more preferable.

In addition, it is believed that the presence of free carbon can lead to the resistance-reducing effect of the active material. When the active material is used to form the negative electrode of a secondary battery, the reaction inside the active material occurs uniformly and smoothly, thereby achieving charge and discharge performance. Active material for secondary batteries with excellent balance between capacity retention and capacity retention. The introduction of free carbon can only come from silicon-containing compounds, but by using a carbon source resin together, it is expected to increase the amount and effect of free carbon. The type of carbon source resin is not particularly limited, but a carbon compound containing a six-membered ring of carbon is preferred.

In addition to using Raman spectroscopy, the existence state of the above-mentioned free carbon can also be identified using a thermogravimetric differential thermal analysis device (TG-DTA). Unlike the carbon atoms in the silicon-oxygen-carbon skeleton, free carbon is prone to thermal decomposition in the atmosphere. The amount of carbon present can be determined based on the thermal weight reduction measured in the presence of air. That is, the carbon amount can be quantified by using TG-DTA. In addition, based on the thermal weight reduction behavior, it is easy to grasp changes in thermal decomposition temperature behavior such as the decomposition reaction starting temperature, the decomposition reaction end temperature, the number of thermal decomposition reaction species, and the temperature of the maximum weight loss among each thermal decomposition reaction species. The temperature values of these behaviors can be used to determine the state of the carbon. On the other hand, it is believed that the carbon atoms in the silicon-oxygen-carbon skeleton, that is, the carbon atoms bonded to the silicon atoms constituting the above-mentioned SiO ₂ C ₂ , SiO ₃ C and SiO ₄ , have extremely strong chemical bonds, so they are thermally stable. It is relatively high and will not thermally decompose in the atmosphere within the temperature range measured by the thermal analysis device. In addition, since the carbon in the carbon oxide silicon phase of the active material has characteristics similar to amorphous carbon, it will thermally decompose in the atmosphere in the temperature range of about 550°C to 900°C. As a result, weight is drastically reduced. The maximum temperature of the TG-DTA measurement conditions is not particularly limited. However, in order to completely complete the thermal decomposition reaction of carbon, it is better to conduct the TG-DTA measurement in the atmosphere at a temperature of about 25°C to about 1000°C or above.

In addition, the surface of the above-mentioned active material may be coated with a coating material. As the coating material, a material that is expected to achieve electronic conductivity, lithium ion conductivity, and the effect of suppressing the decomposition of the electrolyte solution is preferred. Examples of the above-mentioned coating materials include electronically conductive materials such as carbon, titanium, and nickel. Among them, from the viewpoint of improving the chemical stability or thermal stability of the negative electrode active material, carbon is preferred, and low crystallinity carbon is more preferred.

When the coating material is low crystalline carbon, the average thickness of the coating layer is preferably from 10 nm to 300 nm. Moreover, when the total amount of active materials is 100 mass %, the content of low crystalline carbon is preferably 1 to 30 mass %. When the coating material is carbon, the carbon coating is preferably formed on the surface of the active material by a vapor deposition method. From the viewpoint of improving the chemical stability or thermal stability of the active material, when the total amount of the mass of the active material and the mass of the carbon coating is 100 mass %, the amount of the carbon coating is preferably 1 mass % or more. 10% by mass or less. Furthermore, the so-called mass of the active material refers to the mass of the present nanosilicon when the active material is composed only of the present nanosilicon, and when the active material consists of the present nanosilicon and the matrix phase, it is the total of the two. quantity. For example, when the matrix phase is composed of silicon oxycarbide, it is the total amount of silicon nanoparticles and silicon oxycarbide. When the silicon oxycarbide contains nitrogen, the total amount also includes nitrogen. When the active material contains other third components described below, the total amount also includes the third component.

In addition to the above-mentioned components, the active material may also contain other required third components. Examples of the third component include silicate compounds of at least one metal selected from the group consisting of Li, K, Na, Ca, Mg, and Al (hereinafter also referred to as "metal silicate compounds") . Silicate compounds are usually compounds containing the following anions, which have a structure centered on one or more silicon atoms and surrounded by electronegative ligands, and the metal silicate compounds are selected from Li A salt of at least one metal from the group consisting of , K, Na, Ca, Mg and Al and a compound containing the above anion. As compounds containing the above-mentioned anions, orthosilicate ions (SiO ₄ ^4- ), metasilicate ions (SiO ₃ ^2- ), pyrosilicate ions (Si ₂ O ₇ ^6- ), and cyclic silicate ions are known. (Si ₃ O ₉ ^6- or Si ₆ O ₁₈ ^12- ) and other silicate ions. This silicate compound is preferably a silicate compound that is a salt of a metasilicate ion and at least one metal selected from the group consisting of Li, K, Na, Ca, Mg and Al. Among the above metals, Li or Mg is preferred.

The metal silicate compound contains at least one type of metal selected from the group consisting of Li, K, Na, Ca, Mg, and Al, and may contain two or more types of these metals. When there are two or more metals, one silicate ion may contain multiple metals, or it may be a mixture of silicate compounds containing different metals. Moreover, the metal silicate compound may contain other metals, as long as it contains at least one metal selected from the group consisting of Li, K, Na, Ca, Mg, and Al. The metal silicate compound is preferably a lithium silicate compound or a magnesium silicate compound, more preferably lithium metasilicate (Li ₂ SiO ₃ ) or magnesium metasilicate (MgSiO ₃ ), particularly preferably magnesium metasilicate (MgSiO ₃ ).

Examples of the manufacturing method of this nanosilicon include the following manufacturing method (hereinafter also referred to as "this manufacturing method"), that is, in a gas environment with a dew point temperature of -60°C or lower, at a temperature of 60°C or lower and a moisture concentration The silicon powder is wet-pulverized in a non-aqueous solvent with a concentration of less than 10,000 ppm. The dew point temperature is the temperature at which condensation occurs when cooling a gas, and becomes an indicator of the humidity in the gas. "In a gas environment with a dew point temperature of -60°C or lower" is a gas environment in which condensation begins to occur when cooled to -60°C, indicating a state in which the moisture content in the gas is low. If the dew point temperature exceeds -60°C, a large amount of water will be mixed into the solvent during the wet grinding process, resulting in poor dispersion and gelation of the silicon particles, which will reduce productivity.

The dew point temperature can be calculated approximately using the saturated water vapor pressure table of JIS Z 8806 "Humidity - Measurement Method". The gas environment is usually an inert gas environment, and from an operational point of view, a nitrogen environment is preferred. In the case of nitrogen, a dew point temperature below -60°C means that the moisture content in the nitrogen is 10.67 ppm. This manufacturing method involves wet grinding of silicon powder in a non-aqueous solvent with a temperature below 60°C and a moisture concentration below 10,000 ppm in the above gas environment. From the viewpoint of suppressing solvent evaporation and gelation of silicon particles, the temperature is preferably 40° C. or lower.

From the viewpoint of suppressing solvent volatilization and silicon oxidation, the temperature of the non-aqueous solvent is preferably 40°C or lower. Examples of non-aqueous solvents include: acetone, methyl ethyl ketone, methyl isobutyl ketone, and diisobutyl ketone among ketones; ethanol, methanol, n-propanol, and isopropanol among alcohols; Aromatic benzene, toluene, xylene, etc. From the viewpoint of a decrease in initial efficiency caused by silicon oxidation, the moisture concentration of the non-aqueous solvent is preferably 10,000 ppm or less, more preferably 5,000 ppm or less, further preferably 1,000 ppm or less, and most preferably 600 ppm or less. The moisture concentration of the non-aqueous solvent can be controlled within the above range by, for example, the following methods: adding a dehydrating agent to the non-aqueous solvent before use, and filtering and separating the dehydrating agent after a certain period of time; or performing a dehydration treatment on the non-aqueous solvent before use. Distillation; managing the dew point of the environment. In non-aqueous solvents, the concentration of silicon particles is preferably 5 to 50 mass%.

The silicon particles are wet-pulverized in a non-aqueous solvent at the above-mentioned temperature and moisture concentration. The silicon particles used are composed of zero-valent silicon. If the volume average particle diameter of the silicon particles is too small, the dispersibility may become poor, resulting in decreased productivity. Therefore, the volume average particle diameter of the silicon particles is preferably 1 μm or more, and more preferably 3 μm or more. When the volume average particle diameter of the silicon particles is too large, productivity may also decrease. Therefore, the volume average particle diameter is preferably 20 μm or less, more preferably 10 μm or less, and further preferably 5 μm or less. The volume average particle diameter is the same as the above-mentioned D50, and the measurement method is also the same as the above-mentioned. From the viewpoint of reducing the oxygen atomic weight of the obtained nano-silicon, the oxygen atoms of the silicon particles used relative to the silicon atoms are preferably 10 atm% or less, more preferably 5 atm% or less, and still more preferably is less than 2 atm%.

When the purity of the silicon particles used does not reach 99% by mass, the metal is easily eluted when the present nanosilica is used as the negative electrode active material, and it may be difficult to handle as a battery. Therefore, the purity of the silicon particles used is preferably 99 mass% or more, more preferably 99.9 mass%, and still more preferably 99.99 mass%.

Examples of grinders used for wet grinding include grinders such as ball mills, bead mills, and jet mills. The above-mentioned nanosilica with a nanoscale average particle size is obtained by controlling the following crushing conditions for classification, that is, the bead size of the above-mentioned crusher is 0.5 mm or less, and the bead filling rate is 50 to 95 vоl %, the peripheral speed of the rotor is 2 to 14 m/s or the crushing time is 0.5 to 24 h. The preferred particle size of beads is 0.2 mm or less. The peripheral speed of the rotor of the bead mill is preferably 4 to 12 m/s, more preferably 6 to 12 m/s.

In the above-mentioned wet grinding, a dispersant can also be added to promote the grinding of silicon particles. Types of dispersants include aqueous or non-aqueous dispersants, and non-aqueous dispersants are preferred. Examples of types of non-aqueous dispersants include polymer types such as polyether type, alcohol type, polyalkylene polyamine type, polycarboxylic acid partial alkyl ester type, etc., and low molecular weight types such as polyol ester type, alkyl polyamine type, etc. type, polyphosphate series and other inorganic types. When the above-mentioned dispersant is added, the mass of the silicon particles is preferably in the range of 5 mass % to 60 mass %, and more preferably 5 mass % to 30 mass %.

Furthermore, in the above-mentioned wet grinding, at least one surfactant selected from the group consisting of cationic surfactants, anionic surfactants and amphoteric surfactants can also be added to improve the silicon particles used. The dispersibility promotes the crushing of silicon particles. Examples of cationic surfactants include aliphatic amine salts, aliphatic quaternary ammonium salts, aromatic quaternary ammonium salts and heterocyclic quaternary ammonium salts. The amine value of the cationic surfactant is, for example, 1 to 100 mgKOH/g, preferably 5 to 80 mgKOH/g, more preferably 10 to 48 mgKOH/g, especially 35 to 48 mgKOH/g. If the amine value is within the above range, the re-aggregation of the pulverized and nanonized silicon particles is suppressed, and the thickening of the slurry can be suppressed. As a result, the cycle characteristics, charge and discharge capacity, and initial Coulomb efficiency of the battery can be improved. Excellent. As the cationic surfactant, specifically, DISPERBYK9077 (manufactured by BYK Additives & Instruments, DISPERBYK is a registered trademark) can be used.

Examples of the anionic surfactant include carboxylates, sulfonates, sulfate ester salts, and phosphate ester salts. The acid value of the anionic surfactant is, for example, 1 to 200 mgKOH/g, preferably 10 to 180 mgKOH/g, and more preferably 50 to 150 mgKOH/g. If the acid value is within the above range, the wettability of the silicon particles in the dispersion medium is improved, so the viscosity increase of the slurry can be suppressed. As a result, the battery has excellent cycle characteristics, charge and discharge capacity, and initial Coulombic efficiency. As the anionic surfactant, specifically, DISPERBYK111 (manufactured by BYK Additives & Instruments) can be used.

The surfactant may be an amphoteric surfactant having the above-described amine value and acid value, or a cationic and anionic surfactant having the above-described amine value and acid value may be used in combination. Amphoteric surfactants are surfactants that exhibit the properties of anionic surfactants in the alkaline range and exhibit the properties of cationic surfactants in the acidic range. Examples include carboxylates, amino acids, and beets. Alkaline compounds. As the amphoteric surfactant, specifically, ANTI-TERRA (registered trademark)-U100 (manufactured by BYK Additives & Instruments) can be used. When the above-mentioned surfactant is added, the addition amount is preferably 5 to 60 mass%, more preferably 5 to 40 mass%, and further preferably 5 to 20 mass% relative to the mass of the silicon particles.

When producing an active material for secondary batteries containing the present nanosilica in the matrix phase (hereinafter, also referred to as "the present active material"), the present active material can be, for example, mixed with the present nanosilica and resin, and dried. It is then produced by roasting in an inert gas environment. As mentioned above, the matrix phase is composed of a substance that can absorb and release lithium ions. Therefore, the resin mixed with the nano-silicon only needs to be a resin that can absorb and release lithium ions by roasting. As mentioned above, as a material that can absorb and release lithium ions, graphite, silicon dioxide, titanium oxide, and compounds containing silicon, oxygen, and carbon can be exemplified. Therefore, as a resin mixed with the present nanosilica, it can be Examples include polysiloxane-based resin and carbon source resin.

When mixing the present nanosilicon and resin, from the viewpoint of mixing the two uniformly, it is preferable to prepare a nanosilicon slurry in which the present nanosilicon is dispersed in a solvent. From the perspective of dispersibility, the silicon nanoslurry is preferably a silicon nanoslurry containing the above-mentioned nanosilicon, a dispersant and a solvent (hereinafter, also referred to as "the present nanosilicon slurry"). The dispersant contained in this nano silicon slurry is the same as above, and the solvent is water or the same non-aqueous solvent as the above-mentioned non-aqueous solvent. Preferred dispersants and non-aqueous solvents are also the same as above. In addition, the present nanosilica slurry may also contain a surfactant. Examples of the surfactant include at least one selected from the group consisting of the same cationic surfactants, anionic surfactants and amphoteric surfactants as described above. The present nanosilica slurry preferably contains the present nanosilica, a dispersant and a non-aqueous solvent. The present nanosilicon slurry is more preferably a slurry obtained by using the above-mentioned dispersant in the above-mentioned production method, and dispersing the present nanosilicon in the above-mentioned non-aqueous solvent without separating the obtained nanosilicon. At this time, when the above-mentioned non-aqueous solvent and a dispersant added as necessary are included, when the total amount of the dispersant and the present nanosilica is 100 mass %, the amount of the present nanosilica is preferably 5 mass % % to 40 mass%, more preferably 10 mass% to 30 mass%.

When the matrix phase of the present active material contains the above-mentioned silicon oxycarbide, it is appropriate to use a mixture of a polysiloxane compound and a carbon source resin as the resin. When the mixture of polysiloxane compound and carbon source resin is mixed with the present nanosilicon, it is appropriate to use the present nanosilicon slurry. Mix the present nanosilica slurry with a mixture of polysiloxane compound and carbon source resin, remove the solvent to obtain a precursor, roast the obtained precursor to obtain a roasted product, and pulverize it if necessary, thereby obtaining The desired average particle size or specific surface area of the active material.

Examples of the polysiloxane compound include a resin containing at least one of a polycarbosilane structure, a polysilazane structure, a polysilane structure, and a polysiloxane structure. It may be a resin containing only these structures, or it may be a composite resin having at least one of these structures as a segment and chemically bonded with other polymer segments. Composite forms include graft copolymerization, block copolymerization, random copolymerization, alternating copolymerization, etc. Examples include: a composite resin having a graft structure in which a polysiloxane segment is chemically bonded to the side chain of a polymer segment; a block structure having a polysiloxane segment chemically bonded to the end of a polymer segment; Composite resin, etc.

A polysiloxane compound in which the polysiloxane segment has a structural unit represented by the following general formula (S-1) and/or the following general formula (S-2) is preferred. Among them, the polysiloxane compound preferably has a carboxyl group, an epoxy group, an amine group or a polyether group on the side chain or terminal of the main skeleton of the siloxane bond (Si-O-Si).

In addition, in the above-mentioned general formulas (S-1) and (S-2), R ¹ represents an aromatic hydrocarbon group or an alkyl group, an epoxy group, a carboxyl group, etc. which may have a substituent. R ² and R ³ respectively represent an alkyl group, a cycloalkyl group, an aryl group or an aralkyl group, an epoxy group, a carboxyl group, etc.

Examples of the alkyl group include: methyl, ethyl, propyl, isopropyl, butyl, isobutyl, second butyl, third butyl, pentyl, isopentyl, neopentyl, Third pentyl, 1-methylbutyl, 2-methylbutyl, 1,2-dimethylpropyl, 1-ethylpropyl, hexyl, isohexyl, 1-methylpentyl, 2- Methylpentyl, 3-methylpentyl, 1,1-dimethylbutyl, 1,2-dimethylbutyl, 2,2-dimethylbutyl, 1-ethylbutyl, 1 ,1,2-trimethylpropyl, 1,2,2-trimethylpropyl, 1-ethyl-2-methylpropyl, 1-ethyl-1-methylpropyl, etc. Examples of the cycloalkyl group include cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, and the like.

Examples of the aryl group include phenyl, naphthyl, 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, 4-vinylphenyl, and 3-isopropylphenyl. wait.

Examples of the aralkyl group include benzyl group, diphenylmethyl, naphthylmethyl, and the like.

Examples of the polymer segment other than the polysiloxane segment that the polysiloxane compound has include acrylic polymers, fluoroolefin polymers, vinyl ester polymers, aromatic vinyl polymers, and polysiloxane polymers. Ethylene polymer segments such as olefin polymers, or polymer segments such as polyurethane polymer segments, polyester polymer segments, polyether polymer segments, etc. Among them, an ethylene polymer segment is preferred.

The polysiloxane compound can be a composite resin in which polysiloxane segments and polymer segments are bonded through a structure represented by the following structural formula (S-3), or it can be a three-dimensional network of polysiloxane. Oxane structure.

Furthermore, in the formula, the carbon atom is the carbon atom constituting the polymer chain segment, and the two silicon atoms are the silicon atoms constituting the polysiloxane chain segment.

The polysiloxane segment of the polysiloxane compound may have functional groups that can react by heating, such as polymerizable double bonds, in the polysiloxane segment. By heat-treating the polysiloxane compound before thermal decomposition, a cross-linking reaction proceeds and the polysiloxane compound becomes a solid state, whereby the thermal decomposition treatment can be easily performed.

Examples of polymerizable double bonds include vinyl groups, (meth)acrylyl groups, and the like. It is preferable that there are 2 or more polymerizable double bonds in the polysiloxane segment, more preferably 3 to 200 are present, and still more preferably 3 to 50 are present. Furthermore, by using a composite resin having two or more polymerizable double bonds as the polysiloxane compound, the crosslinking reaction can be easily performed.

The polysiloxane segment may also have a silanol group and/or a hydrolyzable silicon group. Examples of the hydrolyzable group in the hydrolyzable silicon group include: halogen atom, alkoxy group, substituted alkoxy group, acyloxy group, phenoxy group, mercapto group, amino group, amide group, amineoxy group, amide group, An amineoxy group, an alkenyloxy group, etc. can be converted into a silanol group by hydrolyzing these groups. A solid polysiloxane compound can be obtained by performing a hydrolysis condensation reaction between the hydroxyl group in the silanol group or the hydrolyzable group in the hydrolyzable silicon group in parallel with the thermal hardening reaction.

The silanol group described in the present invention is a silicon-containing group having a hydroxyl group directly bonded to silicon atoms. The hydrolyzable silicon group according to the present invention is a silicon-containing group having a hydrolyzable group directly bonded to a silicon atom. Specific examples thereof include a group represented by the following general formula (S-4).

Furthermore, in the formula, R ⁴ is a monovalent organic group such as an alkyl group, an aryl group or an aralkyl group, and R ⁵ is a halogen atom, an alkoxy group, an acyloxy group, an allyloxy group, a mercapto group, an amine group, or an amide group. group, amineoxy group, iminoxy group or alkenyloxy group. In addition, b is an integer from 0 to 2.

Examples of the alkyl group include: methyl, ethyl, propyl, isopropyl, butyl, isobutyl, second butyl, third butyl, pentyl, isopentyl, neopentyl, Third pentyl, 1-methylbutyl, 2-methylbutyl, 1,2-dimethylpropyl, 1-ethylpropyl, hexyl, isohexyl, 1-methylpentyl, 2- Methylpentyl, 3-methylpentyl, 1,1-dimethylbutyl, 1,2-dimethylbutyl, 2,2-dimethylbutyl, 1-ethylbutyl, 1 ,1,2-trimethylpropyl, 1,2,2-trimethylpropyl, 1-ethyl-2-methylpropyl, 1-ethyl-1-methylpropyl, etc.

Examples of the aryl group include phenyl, naphthyl, 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, 4-vinylphenyl, and 3-isopropylphenyl. wait.

Examples of the aralkyl group include benzyl group, diphenylmethyl, naphthylmethyl, and the like.

Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, and the like.

Examples of the alkoxy group include a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, a second butoxy group, a third butoxy group, and the like.

Examples of the acyloxy group include a formyloxy group, an acetyloxy group, a propionyloxy group, a butyloxy group, a pivalyloxy group, a pentyloxy group, a phenylethyloxy group, and an acetyloxy group. Acetyloxy, benzyloxy, naphthyloxy, etc.

Examples of the allyloxy group include phenoxy group, naphthyloxy group, and the like.

Examples of the alkenyloxy group include vinyloxy group, allyloxy group, 1-propenyloxy group, isopropenyloxy group, 2-butenyloxy group, 3-butenyloxy group, and 2-pentenyloxy group. , 3-methyl-3-butenyloxy, 2-hexenyloxy, etc.

Examples of the polysiloxane segment having a structural unit represented by the general formula (S-1) and/or the general formula (S-2) include those having the following structures.

The polymer segment may also have various functional groups as necessary within the scope that does not impair the effects of the present invention. As the functional group, for example, carboxyl group, blocked carboxyl group, carboxylic anhydride group, tertiary amine group, hydroxyl group, blocked hydroxyl group, cyclic carbonate group, epoxy group, carbonyl group, primary amide group, diamine group, amide group, urethane group, functional group represented by the following structural formula (S-5), etc.

Moreover, the said polymer segment may have polymerizable double bonds, such as a vinyl group and a (meth)acrylyl group.

The polysiloxane compound is preferably produced by, for example, the methods shown in the following (1) to (3).

Method (1) Prepare in advance a polymer segment containing a silanol group and/or a hydrolyzable silicon group as the raw material for the above-mentioned polymer segment, and combine the polymer segment with a silanol group and/or a hydrolyzable silicon group. Mix with the polymerizable double bond silane compound to carry out hydrolysis and condensation reaction.

Method (2) Prepare in advance a polymer segment containing a silanol group and/or a hydrolyzable silicon group as the raw material of the above polymer segment. Furthermore, polysiloxane is also prepared in advance by subjecting a silane compound having both a silanol group and/or a hydrolyzable silicon group and a polymerizable double bond to a hydrolysis condensation reaction. Then, the polymer segments are mixed with polysiloxane for hydrolysis and condensation reaction.

Method (3) Mix the above-mentioned polymer segment, a silane compound having both a silanol group and/or a hydrolyzable silicon group and a polymerizable double bond, and polysiloxane to perform a hydrolysis condensation reaction. Polysiloxane compounds are obtained by the above method. Examples of the polysiloxane compound include Ceranate (registered trademark) series (organic-inorganic hybrid coating resin; manufactured by DIC Co., Ltd.) or Compoceran SQ series (sesquioxane type mixture; Arakawa Chemical Industry Co., Ltd. Ltd.).

The above-mentioned carbon source resin is preferably a synthetic resin or a natural chemical raw material that has good miscibility with the polysiloxane compound, is carbonized by high-temperature baking in an inactive environment, and has an aromatic functional group.

Examples of synthetic resins include thermoplastic resins such as polyvinyl alcohol and polyacrylic acid, and thermosetting resins such as phenolic resins and furan resins. Examples of natural chemical raw materials include heavy oils, and particularly examples of tar pitch include coal tar, tar light oil, tar medium oil, tar heavy oil, naphthalene oil, anthracene oil, coal tar pitch, asphalt oil, and mesophase pitch. , oxygen cross-linked petroleum asphalt, heavy oil, etc., from the perspective of obtaining or removing impurities at a low price, it is better to use phenolic resin.

In particular, the carbon source resin is preferably a resin containing an aromatic hydrocarbon moiety. The resin containing an aromatic hydrocarbon moiety is preferably a phenolic resin, an epoxy resin, or a thermosetting resin. The phenolic resin is preferably a soluble phenolic resin. Examples of the phenolic resin include the SUMILITERESIN series (soluble phenolic resin; manufactured by Sumitomo Bakelite Co., Ltd.).

The present nanosilicon slurry, preferably the above-mentioned present nanosilicon slurry, is mixed with the mixture of the above-mentioned polysiloxane compound and carbon source resin, and the solvent is removed to obtain a precursor. The mixture containing the polysiloxane compound and the carbon source resin is preferably in a state where the polysiloxane compound and the carbon source resin are evenly mixed. The above mixing is carried out using devices with dispersing and mixing functions. Examples of devices with dispersing and mixing functions include mixers, ultrasonic mixers, premix dispersers, etc. In the solvent removal and drying operations for distilling and removing organic solvents, dryers, vacuum dryers, spray dryers, etc. can be used.

The precursor is preferably a solid component containing 3% to 50% by mass of the present nanosilica, 15% to 85% by mass of the polysiloxane compound, and 3% to 70% by mass of the carbon source resin. It is more preferable that the solid content of the silicon oxide particles is 8 to 40 mass%, the solid content of the polysiloxane compound is 20 to 70 mass%, and the carbon content is 3 to 60 mass%. The solid content of the source resin.

The precursor obtained above is roasted in an inert gas environment to completely decompose the thermally decomposable organic components to obtain a roasted product. Regarding the calcination temperature, for example, the thermally decomposable organic component can be completely decomposed by calcination at a temperature in which the maximum limit temperature is in the range of 900°C to 1200°C. In addition, the polysiloxane compound and the carbon source resin are converted into a silicon carbonate phase having a silicon-oxygen-carbon skeleton and free carbon by the energy of high-temperature treatment.

The roasting is carried out according to the roasting program specified by the heating rate, the holding time at a certain temperature, etc. Furthermore, the maximum limit temperature is the maximum temperature set, which will strongly affect the structure or performance of the roasted product. Through the maximum extreme temperature, the fine structure of the active material, which maintains the chemical bonding state of silicon and carbon in the silicon carbonate phase, can be precisely controlled, thereby obtaining better charge and discharge characteristics.

The roasting method is not particularly limited, as long as a reaction device with a heating function is used in an inert gas environment, and the process can be carried out by a continuous method or a batch method. For roasting equipment, fluidized bed reactors, rotary furnaces, vertical moving bed reactors, tunnel kilns, batch heating furnaces, rotary kilns, etc. can be appropriately selected depending on the purpose.

The present active material is obtained by pulverizing the obtained roasted product and classifying it if necessary. Grinding can be carried out in one step to the desired particle size, or in divided steps. For example, when producing an active material of about 10 μm from the roasted product of lumps or aggregated particles of 10 mm or more, coarse crushing is performed using a jaw crusher, a roller crusher, etc. into particles of about 1 mm, and then used Grow mills, ball mills, etc. can be used to reduce the particle size to about 100 μm, and then bead mills, jet mills, etc. can be used to grind the particles to about 10 μm. Particles produced by grinding may contain coarse particles, and classification is performed in order to remove them and to remove fine powder to adjust the particle size distribution. The classifiers used are divided into wind classifiers, wet classifiers, etc. depending on the purpose. When removing coarse particles, the sieving classification method can achieve the purpose reliably, so it is better. Furthermore, when the precursor mixture is controlled to a shape close to the target particle size by spray drying or the like before calcination, and the calcination is performed in this shape, the grinding step can also be omitted.

When the active material contains a silicate compound of at least one metal selected from the group consisting of Li, K, Na, Ca, Mg and Al, the slurry of the present oxidized silicon particles and polysiloxane are A salt of at least one metal selected from the group consisting of Li, K, Na, Ca, Mg and Al is added to a suspension obtained by mixing a mixture of an alkane compound and a carbon source resin, and then, by mixing with the above The same operation is carried out to obtain the active material having the above silicate compound. Examples of the salt of at least one metal selected from the group consisting of Li, K, Na, Ca, Mg, and Al include halides, hydroxides, such as fluorides, chlorides, and bromides of these metals. Carbonate etc.

The above-mentioned metal salt may be a salt of two or more metals, one salt may contain multiple metals, or it may be a mixture of salts containing different metals. When the above-mentioned metal salt is added to the suspension, the amount of the metal salt added relative to the molar number of the silicon oxide particles is preferably 0.01 to 0.4 in terms of molar ratio. When the salt of the above metal is soluble in an organic solvent, the salt of the above metal can be dissolved in the organic solvent and added to the suspension for mixing. When the above-mentioned metal salt is insoluble in the organic solvent, the particles of the metal salt can be dispersed in the organic solvent and then added to the above-mentioned suspension for mixing. From the viewpoint of improving the dispersion effect, the salt of the above metal is preferably nanoparticles with an average particle diameter of 100 nm or less. As the above-mentioned organic solvent, alcohols, ketones, etc. can be appropriately used, and aromatic hydrocarbon solvents such as toluene, xylene, naphthalene, and methylnaphthalene can also be used.

By uniformly dispersing the metal salt in the suspension, the molecules of the metal salt can be fully contacted with the present nanosilica. When silicon oxide exists on the surface or periphery of the present nanosilicon, the molecules of the metal salt and the present nanosilicon are fully reacted with each other by allowing the molecules of the metal salt to react in a solid phase with the present nanosilicon. Contact allows the above-mentioned silicate compound to exist near the surface of the nano-silicon. In order to make the concentration of the above-mentioned silicate compound near the surface of the present nano-silicon higher than the concentration of the silicon oxycarbide, it is important to increase the contact state between the above-mentioned metal salt and the present silicon oxide particles. Furthermore, by using organic additives to surface-modify the molecules of the above-mentioned metal salts, they can be attached near the surface of the silicon nanoparticles. The molecular structure of the organic additive is not particularly limited, and is preferably a molecular structure that can physically or chemically bond with the dispersant present on the surface of the nano-silicon. Examples of the above physical or chemical bonding include: electrostatic interaction, hydrogen bonding, intermolecular van der Waals force, ionic bonding, covalent bonding, etc. During high-temperature baking, the surface of the nano-silicon can be coated with the above-mentioned silicate compound through a solid-phase reaction between the molecules of the metal salt and the silicon oxide on the surface of the nano-silicon.

This active material has excellent cyclability, initial Coulombic efficiency and capacity retention rate, and exhibits good characteristics in secondary batteries used as negative electrodes containing this active material. Specifically, a slurry composed of the active material, an organic binder, and other conductive additives added as needed can be coated in a thin film on the current collector copper foil to form a negative electrode. Alternatively, carbon materials such as graphite may be added to the above slurry to produce a negative electrode. Examples of carbon materials include natural graphite, artificial graphite, amorphous carbon such as hard carbon and soft carbon, and the like.

For example, it can be obtained by kneading the active material, a binder as an organic binder, and a solvent using a mixer, a ball mill, a high-speed sand mill, a pressure kneader, and other dispersing devices to prepare the negative electrode material. slurry and apply it to the current collector to form a negative electrode layer. In addition, it can also be obtained by molding the pasty negative electrode material slurry into a shape such as sheet or granular form and integrating it with a current collector.

Examples of the organic binder include styrene-butadiene rubber copolymer (hereinafter also referred to as "SBR"); methyl (meth)acrylate, ethyl (meth)acrylate, (methyl) Ethylenically unsaturated carboxylic acid esters such as butyl acrylate, (meth)acrylonitrile, and hydroxyethyl (meth)acrylate, and ethylene such as acrylic acid, methacrylic acid, itaconic acid, fumaric acid, and maleic acid Unsaturated carboxylic acid copolymers such as (meth)acrylic acid copolymers composed of unsaturated carboxylic acids; polyvinylidene fluoride, polyethylene oxide, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polyvinyl chloride Polymer compounds such as imine, polyamide imine, and carboxymethylcellulose (hereinafter also referred to as "CMC").

Depending on their physical properties, some of these organic binders are dispersed or dissolved in water, and some are dissolved in organic solvents such as N-methyl-2-pyrrolidone (NMP). The content ratio of the organic binder in the negative electrode layer of the negative electrode of the lithium ion secondary battery is preferably 1 mass% to 30 mass%, more preferably 2 mass% to 20 mass%, and further preferably 3 mass% to 15 mass% .

When the content ratio of the organic binder is 1% by mass or more, the adhesion becomes better, thereby further suppressing the cracking of the negative electrode structure due to expansion and contraction during charging and discharging. On the other hand, when the content is 30% by mass or less, the increase in electrode resistance is further suppressed. Within this range, the chemical stability of this active material is relatively high, and water-based adhesives can also be used, so it is easy to operate in practical terms.

In addition, conductive auxiliary materials may also be mixed into the above-mentioned negative electrode material slurry if necessary. Examples of conductive auxiliary materials include carbon black, graphite, acetylene black, or oxides or nitrides exhibiting conductivity. The usage amount of the conductive additive can be set to about 1 mass % to 15 mass % relative to the negative electrode active material of the present invention.

In addition, as the material and shape of the above-mentioned current collector, for example, those made of copper, nickel, titanium, stainless steel, etc. into a foil shape, a perforated foil shape, a mesh shape, or the like can be used. In addition, porous materials such as porous metal (foamed metal) or carbon paper can also be used.

Examples of methods for applying the negative electrode material slurry to the current collector include metal mask printing, electrostatic coating, dip coating, spray coating, roll coating, doctor blade, and gravure coating. method, screen printing method, etc. After coating, it is advisable to use a flat press, a calender roller, etc. for calendering if necessary.

In addition, the above-mentioned negative electrode material slurry is made into a sheet shape or a granular shape, and the integration with the current collector can be performed using, for example, a roller, a press, or a combination thereof.

The negative electrode layer formed on the above-mentioned current collector or the negative electrode layer integrated with the current collector is preferably heat-treated according to the organic binder used. For example, when using water-based styrene-butadiene rubber copolymer (SBR), etc., heat treatment can be performed at 100 to 130°C. In the case of adhesives, it is preferable to perform heat treatment at 150 to 450°C.

Through this heat treatment, the solvent is removed, the binder is hardened to increase the strength, and the adhesion between particles and between the particles and the current collector can be improved. Furthermore, the heat treatment is preferably performed in an inactive environment such as helium, argon, nitrogen, or a vacuum environment to prevent oxidation of the current collector during the treatment process.

In addition, after heat treatment, it is preferable to perform pressure treatment on the negative electrode. In the negative electrode using this active material, the electrode density is preferably 1 g/cm ³ to 1.8 g/cm ³ , more preferably 1.1 g/cm ³ to 1.7 g/cm ³ , and further preferably 1.2 g/cm ³ to 1.6 g/cm ³ . The higher the electrode density, the more the adhesion and the volumetric capacity density of the electrode tend to increase. On the other hand, if the electrode density is too high, the voids in the electrode will be reduced, which may lead to a weakening of the effect of suppressing the volume expansion of silicon and a decrease in the capacity retention rate. Therefore, the optimal range of electrode density is selected.

The secondary battery of the present invention contains the above-mentioned active material in the negative electrode. As a secondary battery having a negative electrode containing the present active material, a non-aqueous electrolyte secondary battery and a solid electrolyte secondary battery are preferred. In particular, it exhibits excellent performance when used as a negative electrode of a non-aqueous electrolyte secondary battery.

For example, when the secondary battery of the present invention is used in a wet electrolyte secondary battery, the positive electrode and the negative electrode separator containing the negative electrode active material of the present invention are arranged to face each other, and the electrolyte is injected into the secondary battery. .

Like the negative electrode, the positive electrode can be obtained by forming a positive electrode layer on the surface of a current collector. In this case, a strip made of a metal or alloy such as aluminum, titanium, stainless steel, etc. can be used as the current collector, such as a foil, a perforated foil, a mesh, or the like.

The positive electrode material used for the positive electrode layer is not particularly limited. In non-aqueous electrolyte secondary batteries, when producing lithium ion secondary batteries, for example, metal compounds, metal oxides, metal sulfides, or conductive polymer materials that can be doped or embedded with lithium ions can be used. For example, the following materials can be used alone or in combination: lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), lithium manganate (LiMnO ₂ ), and their composite oxides (LiCoxNiyMnzO ₂ , x+y+z =1), lithium manganese spinel (LiMn ₂ O ₄ ), lithium vanadium compound, V ₂ O ₅ , V ₆ O ₁₃ , VO ₂ , MnO ₂ , TiO ₂ , MoV ₂ O ₈ , TiS ₂ , V ₂ S _5. VS ₂ , MoS ₂ , MoS ₃ , Cr ₃ O ₈ , Cr ₂ O ₅ , olivine LiMPO ₄ (where M is Co, Ni, Mn or Fe), polyacetylene, polyaniline, polypyrrole, poly Conductive polymers such as thiophene and polyacene, porous carbon, etc.

As the separator, for example, nonwoven fabrics, cloths, microporous films, or combinations thereof containing polyolefins such as polyethylene and polypropylene as the main component can be used. Furthermore, when the positive electrode and the negative electrode of the non-aqueous electrolyte secondary battery to be produced are not in direct contact with each other, there is no need to use a separator.

As the electrolyte, for example, so-called organic electrolysis can be used, in which lithium salts such as LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiBF ₄ , and LiSO ₃ CF ₃ are dissolved in the following non-aqueous solvent as a single component or a mixture of two or more components. liquid, namely, ethyl carbonate, propylene carbonate, butyl carbonate, vinyl carbonate, ethyl fluoride carbonate, cyclopentanone, cyclobutane, 3-methylcyclobutane, 2,4-di Methylcycloterine, 3-methyl-1,3- Azolidin-2-one, γ-butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, butyl methyl carbonate, ethyl propyl carbonate, butyl ethyl carbonate , dipropyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, ethyl acetate, etc.

The structure of the secondary battery of the present invention is not particularly limited, but is usually a structure obtained by winding the positive electrode, the negative electrode, and an optional separator into a flat spiral shape to form a wound electrode plate group. , or these are laminated into flat plates to form a laminated plate group, and the electrode group is sealed in an outer casing. Furthermore, the half-cell used in the examples of the present invention was configured to have the active material as the main component of the negative electrode, and a simple evaluation using metallic lithium as the counter electrode was conducted in order to more clearly compare the cycle characteristics of the active material itself.

Secondary batteries using this active material are not particularly limited and can be used as paper batteries, button batteries, coin batteries, laminated batteries, cylindrical batteries, square batteries, etc. The above-mentioned negative active material of the present invention can also be applied to all electrochemical devices that use intercalation and deintercalation of lithium ions as a charging and discharging mechanism, such as hybrid capacitors, solid lithium secondary batteries, etc.

As described above, when the present active material is used as a negative electrode active material of a secondary battery, a secondary battery excellent in cycleability, initial Coulombic efficiency, and capacity retention rate can be provided. The active material can be used as a negative electrode by the above method, and a secondary battery with the above negative electrode can be made.

The above has been directed to the present nanosilicon, the present nanosilicon slurry containing the present nanosilicon, the present nanosilicon manufacturing method, the present active material containing the present nanosilicon, and the secondary battery containing the present active material in the negative electrode. Although the description has been made, the present invention is not limited to the configuration of the above-mentioned embodiment. The present nanosilicon, the present nanosilicon slurry, the present active material, and the secondary battery containing the present active material in the negative electrode can add other arbitrary structures to the structures of the above embodiments, and can also be replaced with any structures that perform the same function. Furthermore, in the present method of manufacturing silicon nanoparticles and the present method of manufacturing active material, other arbitrary steps can be added to the structure of the above-mentioned embodiments, or any steps that perform the same function can be replaced. Example

Hereinafter, the present invention will be described in detail using examples, but the present invention is not limited to these examples. Furthermore, the half-cell used in the examples of the present invention was configured to have this active material as the main component of the negative electrode, and a simple evaluation using metallic lithium as the counter electrode was conducted in order to more clearly compare the cycle characteristics of the active material itself.

Synthesis Example 1: Preparation of polysiloxane compound (Synthesis of the condensate of methyltrimethoxysilane (a1)) Add 1,421 mass to a reaction vessel equipped with a stirrer, thermometer, dropping funnel, condenser tube and nitrogen inlet of methyltrimethoxysilane (hereinafter, referred to as "MTMS"), and heat it to 60°C. Then, a mixture of 0.17 parts by mass of isopropyl acid phosphate ("Phoslex A-3" manufactured by SC Organic Chemicals Co., Ltd.) and 207 parts by mass of deionized water was added dropwise to the reaction vessel over 5 minutes. Stir at a temperature of 80°C for 4 hours to proceed with the hydrolysis and condensation reaction of MTMS. The condensate obtained by the above hydrolysis condensation reaction is distilled at a temperature of 40 to 60°C and a reduced pressure of 40 to 1.3 kPa. Furthermore, "under reduced pressure of 40 to 1.3 kPa" means that the reduced pressure condition is 40 kPa when the distillation of methanol is started, and the pressure is finally reduced to 1.3 kPa. The same is true in the following records. By removing the methanol and water generated during the above reaction, 1,000 parts by mass of a liquid containing a condensate of MTMS with a number average molecular weight of 1,000 to 5,000 (hereinafter also referred to as "a1") is obtained. The active ingredient of the obtained liquid was 70% by mass. In addition, the above-mentioned active ingredient is a value obtained by dividing the theoretical yield (parts by mass) by the actual yield (parts by mass) after the condensation reaction when all the methoxy groups of the silane monomer such as MTMS undergo a condensation reaction [silane monomer] Calculate the theoretical yield (mass parts)/actual yield after the condensation reaction (mass parts) when all the methoxy groups undergo the condensation reaction.

(Manufacture of curable resin composition) Into a reaction vessel equipped with a stirrer, thermometer, dropping funnel, condenser tube and nitrogen inlet, 150 parts by mass of butanol (hereinafter also referred to as "BuOH") and 105 parts by mass of phenyltrimethoxysilane (hereinafter, also referred to as "PTMS") and 277 parts by mass of dimethyldimethoxysilane (hereinafter, also referred to as "DMDMS"), and heated to 80°C. Then, a mixture containing the following components: 21 parts by mass of methyl methacrylate (hereinafter, also referred to as "MMA") and 4 parts by mass of methacrylic acid was added dropwise to the reaction vessel at this temperature over 6 hours. Butyl ester (hereinafter, also referred to as "BMA"), 3 parts by mass of butyric acid (hereinafter, also referred to as "BA"), 2 parts by mass of methacryloxypropyltrimethoxysilane (hereinafter, also referred to as "BA") (denoted as "MPTS"), 3 parts by mass of BuOH and 0.6 parts by mass of butyl peroxy-2-ethylhexanoate (hereinafter, also denoted as "TBPEH"). After completion of the dropwise addition, the reaction was continued at the same temperature for 20 hours to obtain an organic solvent solution of the ethylene polymer (a2) having a hydrolyzable silicon group and a number average molecular weight of 10,000.

Then, a mixture of 0.04 parts by mass of isopropyl acid phosphate ("Phoslex A-3" manufactured by SC Organic Chemical Co., Ltd.) and 112 parts by mass of deionized water was added dropwise over 5 minutes, and further stirred at this temperature. The hydrolysis condensation reaction is carried out for 10 hours, thereby obtaining a liquid containing a composite resin, which is a hydrolyzable silicon group of the ethylene polymer (a2) and a polysiloxane derived from the above-mentioned PTMS and DMDMS. It is formed by bonding silicon group and silanol group. Then, 472 parts by mass of the condensate (a1) of MTMS obtained in Synthesis Example 1 and 80 parts by mass of deionized water were added to the liquid, and the liquid was stirred for 10 hours to perform a hydrolysis condensation reaction. Distillation was performed under the same conditions as in Synthesis Example 1 to remove the generated methanol and water. Then, 250 parts by mass of BuOH was added to obtain 1,000 parts by mass of a curable resin composition having a non-volatile content of 60.1% by mass.

Example 1 70 g of commercially available silicon powder (manufactured by High Purity Chemicals) with a silicon purity of 99.9 mass %, a volume average particle diameter of 3.2 μm, and an oxygen content of 3.5 atom% relative to silicon, DISPERBYK9077 (manufactured by BYK Additives & Instruments) , DISPERBYK is a registered trademark) is set to 28 g, and methyl ethyl ketone (hereinafter, also referred to as "MEK") is set to 280 g. Mix in a stirring tank and stir thoroughly. Cover the stirring tank and supply nitrogen with a dew point of -70°C to make the tank an inert gas environment. The initial concentration of water was 0.058% by mass. The mixed solution was wet-pulverized using a bead mill (Ultra Apex Mill UAM-015 manufactured by Hiroshima Metal & Machinery Co., Ltd.) for 1.5 hours to obtain silicon nanoparticles uniformly dispersed in the dispersion medium. The diameter of the beads in the bead mill is set to 0.2 mm, and the temperature of the mixed liquid during the wet grinding process is set to below 40°C. Nano-silicon with a specific surface area of 105 m ² /g, a crystallite diameter of 13.5 nm, an oxygen ratio of 12.5 atom% to silicon, and a volume average particle size of 180 nm was obtained.

The slurry containing the above-mentioned nanosilicon, the curable resin composition of Synthesis Example 1, and the phenolic resin (SUMILITERESIN PR-53570 manufactured by Sumitomo Bakelite) were calculated as SiOC/C/Si=10 based on the composition after baking. Mix in a /40/50 ratio and add to a three-neck detachable flask. Cap one port, and connect the nitrogen inlet pipe and solvent capture device to the other two ports. Nitrogen gas was introduced into the flask, and the mixture was stirred using a magnetic stirrer. At the same time, the flask was heated to 120°C using an oil bath, and the solvent was distilled off until the stirring bar could no longer move. Thereafter, the mixture was cooled to room temperature to obtain a dried resin which is a calcined precursor. Thereafter, the calcined precursor, that is, the dried resin, was calcined in a nitrogen atmosphere at a temperature of 1050° C. for 6 hours to obtain a black solid. The obtained black solid matter is pulverized using a planetary ball mill to obtain negative active material powder.

According to the measurement results of powder X-ray diffraction (XRD) using Cu-Kα rays for the obtained negative electrode active material powder, no diffraction peak at 2θ=28.4° attributed to the Si (111) crystal plane was detected. According to the results of energy dispersive X-ray spectroscopy (EDS), the nitrogen content is 0.2 mass%. Furthermore, the Raman scattering analysis measurement results showed a peak near 1590 cm ^-1 belonging to the G band of carbon and a peak near 1330 cm ^-1 belonging to the D band, with an intensity ratio of I(G band)/I( D band) is 1.4.

A mixed slurry containing 80% by mass of the above-mentioned negative active material powder, 10% by mass of acetylene black as a conductive additive, and 10% by mass of a mixture of CMC and SBR as a binder was prepared, and a film was formed on the copper foil. Thereafter, it was dried under reduced pressure at 110° C., and a half cell was produced using Li metal foil as a counter electrode. For this half cell, a secondary battery charge and discharge measuring device (manufactured by Beidou Corporation) was used to evaluate the charge and discharge characteristics by setting the cutoff voltage range to 0.005 to 1.5 V. The measurement results of the charge and discharge characteristics showed that the initial discharge capacity was 1630 mAh/g, the initial efficiency was 86%, and the retention rate after 5 cycles was 91%.

For the evaluation of the full battery, a single-layer sheet using LiCoO ₂ as the cathode active material and aluminum foil as the current collector was used as the cathode material to produce a cathode film, and graphite powder was used to produce a cathode film with a discharge capacity design value of 450 mAh/g. Mix it with active material powder to make a negative electrode film. As a nonaqueous electrolyte, lithium hexafluorophosphate dissolved in ethyl carbonate (hereinafter, also referred to as "EC") and diethyl carbonate (hereinafter, also referred to as "DEC") at a concentration of 1 mol/L was used. A non-aqueous electrolyte solution obtained from a mixed liquid with a volume ratio of 1/1 was used as a separator, and a polyethylene microporous film with a thickness of 30 μm was used to produce a laminated lithium ion secondary battery. At 25°C, charge the laminated lithium-ion secondary battery at a constant current of 1.2 mA (0.25 c based on the positive electrode) until the voltage of the test battery reaches 4.2 V. After reaching 4.2 V, the battery voltage is maintained Charge by reducing the current to 4.2 V and find the discharge capacity. Taking charge and discharge in the voltage range of 2.5 V to 4.2 V as one cycle, the capacity retention rate after 300 cycles is 90%. After charging and discharging, disassemble the laminated battery in an argon atmosphere in the glove box, take out the negative electrode, wash it with EC/DEC mixture, then let it stand to dry, and then measure the thickness of the electrode film. The rate of change in the thickness of the negative electrode film before and after charging and discharging was taken as the negative electrode expansion rate. The negative electrode expansion rate is 19%. The results are shown in Table 1.

Examples 2 to 12 Except that the weight % of the additives of the mixed liquid and the grinding time of wet grinding when wet grinding using a bead mill were set to the conditions described in Table 1, the beads were used in the same manner as in Example 1. The machine is used for wet grinding, and the produced nano-silicon is used to produce negative active materials. The negative active material was used to prepare a half-cell in the same manner as in Example 1, and the charge and discharge characteristics were evaluated. The results are shown in Table 1.

Example 13 Except that the initial moisture concentration of the mixed liquid was set to 0.49% by mass when the bead mill was used for wet pulverization, the bead mill was used for wet pulverization in the same manner as in Example 1, and the prepared nanosilica was used. to make negative active materials. The negative active material was used to prepare a half-cell in the same manner as in Example 1, and the charge and discharge characteristics were evaluated. The results are shown in Table 1.

Examples 14 to 18 Except for the volume average particle size of the raw silicon powder and the amount of oxygen relative to silicon in the raw silicon powder during wet grinding using a bead mill, a bead mill was used in the same manner as in Example 1. The machine is used for wet grinding, and the produced nano-silicon is used to produce negative active materials. The negative active material was used to prepare a half-cell in the same manner as in Example 1, and the charge and discharge characteristics were evaluated. The results are shown in Table 1.

Example 19 Except that the silicon purity of the raw silicon powder when wet-pulverized using a bead mill is 99% by weight, the volume average particle diameter is 4.6 μm, and the amount of oxygen relative to silicon is 1.5 atom%, it is the same as in Examples. 1 In the same way, use a bead mill for wet grinding, and use the prepared silicon nanoparticles to make negative electrode active materials. The negative active material was used to prepare a half-cell in the same manner as in Example 1, and the charge and discharge characteristics were evaluated. The results are shown in Table 1.

Comparative Example 1 Except that no additives were added, wet grinding was carried out using a bead mill in the same manner as Example 1. The viscosity increase is severe, gelation occurs during crushing, and the bead mill stops running. Because the slurry containing nanosilica has gelled, it is not suitable for the next step and cannot be continued.

Comparative Example 2 Wet pulverization was carried out using a bead mill in the same manner as in Example 1, except that the initial moisture concentration was 2.51% by mass and the liquid temperature was 60°C or above for wet pulverization. The viscosity increase is severe, gelation occurs during crushing, and the bead mill stops running. Because the slurry containing nanosilica has gelled, it is not suitable for the next step and cannot be continued.

Comparative Example 3 Wet grinding was carried out using a bead mill in the same manner as in Example 1, except that the dew point of the nitrogen supplied to the stirring tank was -40°C or above. The viscosity increase is severe, gelation occurs during crushing, and the bead mill stops running. Because the slurry containing nanosilica has gelled, it is not suitable for the next step and cannot be continued.

Comparative Example 4 Except for calcining the precursor of the negative active material in air, the negative active material was prepared in the same manner as in Example 1, and then a half-cell was produced. The measurement results of the charge and discharge characteristics showed that the initial discharge capacity was 1090 mAh/g and the initial efficiency was 61.2%. The results are shown in Table 1.

Comparative Example 5 Except for using silicon powder with a volume average particle diameter of 0.5 μm and an oxygen content of 16 atom% relative to silicon as a raw material, wet grinding and preparation of negative electrode active materials were carried out in the same manner as in Example 1. and the production of half cells. The agglomerates are not loose, the separator (screen) is clogged, and the pressure in the bead mill rises, causing the bead mill to stop running. No further crushing can be carried out.

Comparative Example 6 Wet pulverization was carried out in the same manner as in Example 1, except that silicon powder with a volume average particle diameter of 30 μm and an oxygen content of 0.3 atom% relative to silicon was used as a raw material. Unable to crush coarse particles, the separator of the bead mill is blocked and the screen is clogged. The pressure inside the bead mill increases, causing the bead mill to stop running. Unable to proceed further.

[Evaluation Method] Each evaluation method is as follows. Volume average particle size: Measured using a laser diffraction particle size distribution measuring device (Mastersizer 3000 manufactured by Malvern Panalytical). Specific surface area: Measured by nitrogen adsorption measurement using the BET method using a specific surface area measuring device (BELSORP-mini manufactured by BELJAPAN Corporation). ²⁹ Si-NMR: JNM-ECA600 manufactured by JEOL RESONANCE Co., Ltd. was used.

Evaluation of battery characteristics: Use a secondary battery charge and discharge test device (manufactured by Beidou Electric Co., Ltd.) to measure the battery characteristics. At room temperature 25°C, the cut-off voltage range is 0.005 to 1.5 V, and the charge and discharge rate is 0.1 C (1 to 3 cycles) and 0.2 C (after 4 cycles), conduct an evaluation test of charge and discharge characteristics under the set conditions of constant current-constant voltage charging/constant current discharge. Each time you switch between charging and discharging, leave it in an open circuit state for 30 minutes. The discharge capacity, charging capacity, initial Coulombic efficiency and cyclability (in this case, refers to the capacity retention rate of the full battery after 5 cycles of charge and discharge at 25°C), and the negative electrode expansion rate are calculated as follows. The charge capacity and discharge capacity of the active material: determined by charge and discharge measurements of the half cell. Initial Coulombic efficiency of active material (%) = Initial discharge capacity (mAh/g)/Initial charge capacity (mAh/g) Capacity retention rate (%@5th time) = 5th negative electrode discharge capacity (mAh/g)/ The initial discharge capacity of the negative electrode (mAh/g) is determined by measuring the full battery (laminated battery).

[Table 1] manufacturing conditions result Physical properties of raw material silicon powder Process conditions Process characteristics Nano-Si physical properties Battery properties Volume average particle size [μm] Amount of oxygen relative to silicon [atom%] Silicon purity [mass %] Initial concentration of moisture [mass %] Liquid temperature [℃] Ambient gas dew point [℃] Additive dosage [mass %] Crushing time[h] roasting environment Can wet crushing be performed? Screen clogged Amount of oxygen relative to silicon [atom%] Specific surface area [m ² /g] Crystallite diameter [nm] Volume average particle size [nm] Discharge capacity [mAh/g] Initial efficiency[%] Maintenance rate after 5 cycles [%] Example 1 3.2 3.5 99.9 0.058 <40 -70 40 1.5 Nitrogen 〇 without 12.5 105 13.5 180 1630 86 91 Example 2 3.2 3.5 99.9 0.058 <40 -70 40 2.0 Nitrogen 〇 without 17.0 122 12.2 62 1600 84 93 Example 3 3.2 3.5 99.9 0.058 <40 -70 40 3.0 Nitrogen 〇 without 22.0 198 10.4 42 1490 82 95 Example 4 3.2 3.5 99.9 0.058 <40 -70 40 9.0 Nitrogen 〇 without 40.9 395 5.6 29 1265 75 96 Example 5 3.2 3.5 99.9 0.055 <40 -70 5 1.5 Nitrogen 〇 without 6.4 102 13.3 190 1780 89 91 Example 6 3.2 3.5 99.9 0.055 <40 -70 5 2.0 Nitrogen 〇 without 10.9 130 12.0 60 1700 87 93 Example 7 3.2 3.5 99.9 0.055 <40 -70 5 3.0 Nitrogen 〇 without 15.9 204 10.2 41 1630 84 94 Example 8 3.2 3.5 99.9 0.055 <40 -70 5 9.0 Nitrogen 〇 without 31.5 380 6.0 30 1280 78 96 Example 9 3.2 3.5 99.9 0.086 <40 -65 40 2.5 Nitrogen 〇 without 21.2 143 12 58 1490 83 93 Example 10 3.2 3.5 99.9 0.059 <40 -70 40 1 Nitrogen 〇 without 15.8 117 12.6 98.6 1580 83 92 Example 11 3.2 3.5 99.9 0.059 <40 -70 40 1.5 Nitrogen 〇 without 19.1 - - 60.1 1510 82.5 93.2 Example 12 3.2 3.5 99.9 0.059 <40 -70 40 5 Nitrogen 〇 without - - - 31.2 1320 77 96 Example 13 3.2 3.5 99.9 0.49 <40 -70 - - Nitrogen 〇 without 21.1 - - - 1490 82 93 Example 14 1.2 8 99.9 0.089 <40 -70 - - Nitrogen 〇 without twenty four - - - 1400 81.1 - Example 15 4.6 1.5 99.9 0.059 <40 -70 - - Nitrogen 〇 without 17 122 - 62 1600 84 92.5 Implement column 16 9.5 0.7 99.9 0.091 <40 -70 - - Nitrogen 〇 without 16.7 - - - 1620 84.4 - Example 17 18.9 0.4 99.9 0.073 <40 -70 - - Nitrogen 〇 without 16 - - - 1660 85 - Example 18 1.1 1.5 99.9 0.69 <40 -70 - - Nitrogen 〇 without 17.1 - - - 1590 83.8 92.8 Example 19 4.6 1.5 99 0.073 <40 -70 - - Nitrogen 〇 without 17.5 - - - 1580 84.1 - Comparative example 1 3.2 3.5 99.9 0.066 <40 -70 0 5 Nitrogen × have 4.5 50 - >1000 - - - Comparative example 2 3.2 3.5 93.9 2.51 >60 -70 - - Nitrogen × have - - - - - - - Comparative example 3 3.2 3.5 99.9 0.075 <60 >-40 - - Nitrogen × have - - - - - - - Comparative example 4 3.2 3.5 99.9 0.059 <40 -70 40 - air 〇 without 20.7 138 12.1 60 1090 61.2 - Comparative example 5 0.5 16 99.9 0.057 <40 -70 - - Nitrogen × have - - - - - - - Comparative example 6 30 0.3 99.9 0.33 <40 -70 - - Nitrogen × have - - - - - - -

According to the above results, it can be seen that when the present nanosilica is used as the negative electrode active material, the cyclability, initial Coulombic efficiency and capacity retention rate are all high, and the balance of the characteristics of these secondary batteries is excellent. Furthermore, a secondary battery containing the present active material as a negative electrode active material has excellent battery characteristics.

without

without

Claims (12)

A kind of nano silicon has a specific surface area of 100 to 400 m ² /g, and oxygen atoms are 5 to 45 atom% relative to silicon atoms. For example, the nano-silicon of claim 1 has a crystallite diameter of 5 to 14 nm. For example, the volume average particle size of silicon nanoparticles in claim 1 or 2 is 10 to 200 nm. A nanosilicon slurry comprising the nanosilicon of claim 1 or 2, a dispersant and a solvent. A method for manufacturing nano-silicon, which involves wet-pulverizing silicon powder in a non-aqueous solvent with a temperature below 60°C and a moisture concentration below 10,000 ppm in a gas environment with a dew point temperature of -60°C or below. As claimed in claim 5, the method for producing nanosilica is in a non-aqueous solvent containing at least one surfactant selected from the group consisting of cationic surfactants, anionic surfactants and amphoteric surfactants. The above-mentioned wet grinding is carried out. For example, the manufacturing method of nano-silica according to claim 5 or 6, wherein in the above-mentioned wet grinding, the volume average particle diameter is 1 to 20 μm in a non-aqueous solvent and the oxygen atom is 10 atom% or less relative to the silicon atom. Silicon powder is wet-pulverized. The method for producing nano-silicon according to claim 5 or 6, wherein in the above-mentioned wet grinding, the purity of the silicon powder is 99 mass% or more. A method for manufacturing an active material for secondary batteries, which includes mixing nano-silicon obtained by the method for manufacturing nano-silicon according to claim 5 or 6 with resin, drying and then baking in an inactive gas environment. An active material for secondary batteries, which contains silicon nanoparticles according to claim 1 or 2. A negative electrode for secondary batteries, which contains the active material for secondary batteries of claim 10. A secondary battery including the negative electrode for the secondary battery of claim 11.