WO2018131608A1 - ポリシルセスキオキサン被覆シリコンナノ粒子又はその焼成物及びその製造方法、リチウムイオン電池用負極活物質、リチウムイオン電池用負極、及びリチウムイオン電池 - Google Patents
ポリシルセスキオキサン被覆シリコンナノ粒子又はその焼成物及びその製造方法、リチウムイオン電池用負極活物質、リチウムイオン電池用負極、及びリチウムイオン電池 Download PDFInfo
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Definitions
- the present invention relates to a fired product of polysilsesquioxane-coated silicon nanoparticles having a chemical bond between the surface of silicon nanoparticles and hydrogen polysilsesquioxane, and the fired product of polysilsesquioxane-coated silicon nanoparticles.
- the present invention relates to a negative electrode active material for lithium ion battery, a negative electrode for lithium ion battery including the negative electrode active material, and a lithium ion battery including the negative electrode for lithium ion battery.
- a lithium intercalation compound that releases lithium ions from the interlayer is used as a cathode material, and lithium ions are occluded and released during charging / discharging between layers between crystal planes (The development of rocking chair type lithium ion batteries using a carbonaceous material typified by graphite or the like, which can be intercalated, as a negative electrode material has been developed and put into practical use.
- Non-aqueous electrolyte secondary batteries that use lithium compounds as negative electrodes have high voltage and high energy density, and among them, lithium metal has been the subject of many studies as a negative electrode active material because of its abundant battery capacity. became.
- lithium metal when lithium metal is used as the negative electrode, a lot of dendritic lithium is deposited on the surface of the negative electrode lithium during charging, so that the charge / discharge efficiency is reduced, or the dendritic lithium grows, causing a short circuit with the positive electrode. There is a case.
- lithium metal itself is unstable and highly reactive, and is sensitive to heat and impact, there remains a problem in commercializing a negative electrode using lithium metal. Therefore, a carbon-based negative electrode that occludes and releases lithium has been used as a negative electrode active material instead of lithium metal (Patent Document 1).
- the carbon-based negative electrode has solved various problems of lithium metal and has greatly contributed to the spread of lithium ion batteries.
- Lithium ion batteries using carbon-based negative electrodes have inherently low battery capacity due to the porous structure of carbon.
- the theoretical capacity is about 372 mAh / g when the composition is LiC 6 . This is only about 10% compared with the theoretical capacity of lithium metal being 3860 mAh / g. Under such circumstances, in spite of the above-mentioned problems, studies are actively being made to improve the battery capacity by introducing a metal such as lithium into the negative electrode again.
- the use of a material mainly composed of a metal that can be alloyed with lithium, such as Si, Sn, or Al, as the negative electrode active material has been studied.
- substances that can be alloyed with lithium, such as Si and Sn are accompanied by volume expansion during the alloying reaction with lithium, so that the metal material particles are pulverized, so that the contact between the metal material particles decreases.
- an electrically isolated active material is generated in the electrode.
- the metal material particles are detached from the electrode, resulting in an increase in internal resistance and a decrease in capacity. As a result, the cycle characteristics are deteriorated, and the electrolyte decomposition reaction due to the expansion of the specific surface area becomes serious. ing.
- Patent Document 2 includes silicon and oxygen, and a silicon oxide having a ratio of oxygen to silicon of 0 to 2 can obtain good charge / discharge cycle performance when used as a negative electrode active material of a lithium ion battery.
- Patent Document 3 proposes a method using a fired product of hydrogen polysilsesquioxane as a silicon oxide-based negative electrode active material containing an amorphous silicon oxide having a nanoporous structure.
- Patent Document 4 by making a structure in which a silicon-containing core and silicon nanoparticles formed on the surface of the core are arranged, the disadvantage of the volume expansion coefficient is complemented during charging and discharging, and silicon and oxygen are easily added.
- a silicon oxide capable of adjusting the ratio of the above.
- the silicon oxide compound of the above document is a compound that is essentially different from the polysilsesquioxane-coated silicon nanoparticles of the present invention or a fired product thereof. Furthermore, the above document does not suggest any chemical bond between the silicon nanoparticles and the silicon oxide, and the polysilsesquioxane-coated silicon nanoparticles fired product of the present invention is also used as a structure. It is judged to be heterogeneous.
- the battery performance when used as a battery negative electrode active material is recognized to have a certain degree of improvement, but the discharge capacity, the initial charge / discharge efficiency, the capacity maintenance rate in the charge / discharge cycle, or more than two performances
- the level has reached a level at which there is no problem, and it has not been a technology that can provide a negative electrode active material that exhibits balanced battery performance and is highly practical.
- An object of the present invention is to provide a new silicon oxide as a negative electrode active material for a secondary battery, in which the obtained battery has excellent cycle characteristics, and has good initial discharge efficiency and high charge capacity. It is to provide a physical structure.
- the present inventors have excellent cycle characteristics when used as a negative electrode active material for a lithium ion battery, and are excellent.
- the present inventors have found a fired product of polysilsesquioxane-coated silicon nanoparticles that also exhibits excellent initial discharge efficiency and high charge capacity, and has led to the present invention.
- TEM transmission electron microscope
- the polysilsesquioxane coated silicon nanoparticles was determined by infrared spectroscopy, of the absorption band of 1000 ⁇ 1250 cm -1 derived from Si-O-Si bond, high wave number from 1100 cm -1
- the intensity of the maximum absorption peak in the absorption band on the side is I 2-1
- the intensity of the maximum absorption peak in the absorption band on the lower wavenumber side than 1100 cm ⁇ 1 is I 2-2
- the intensity of the maximum absorption peak of the absorption band of 820 to 920 cm ⁇ 1 derived from the Si—H bond is I 1
- the intensity ratio (I 1 / I 2 ) is 0.01 to 0.1 when the maximum absorption peak intensity is I 2 .
- a negative electrode active material for a lithium ion battery comprising a fired product of the polysilsesquioxane-coated silicon nanoparticles according to any one of [1] to [3].
- a negative electrode for a lithium ion battery comprising the negative electrode active material for a lithium ion battery according to [4].
- a lithium ion battery comprising the lithium ion battery negative electrode according to [5].
- the thickness of the polysilsesquioxane observed with a transmission electron microscope (TEM) is 1 nm or more and 30 nm or less.
- the manufacturing method includes a step of hydrolyzing and condensing a silicon compound represented by the formula (1) (also referred to as polycondensation reaction) in the presence of silicon nanoparticles.
- HSi (R) 3 (1) (Wherein R is the same or different, halogen, hydrogen, substituted or unsubstituted alkoxy having 1 to 10 carbon atoms, substituted or unsubstituted aryloxy having 6 to 20 carbon atoms, and 7 to 30 carbon atoms) A group selected from substituted or unsubstituted arylalkoxy, provided that it is a substituted or unsubstituted alkoxy group having 1 to 10 carbon atoms, a substituted or unsubstituted aryloxy group having 6 to 20 carbon atoms, and 7 carbon atoms.
- any hydrogen may be substituted with a halogen.
- a lithium ion battery obtained by using a negative electrode active material for a lithium ion battery including a fired product of polysilsesquioxane-coated silicon nanoparticles having a specific structure according to the present invention has excellent cycle characteristics and is excellent. Also shows initial discharge efficiency and high charge capacity.
- FIG. 1 shows a polysilsesquioxane-coated silicon nanoparticle fired product (1) obtained in Example 1 by infrared spectroscopy (IR), and a polysilsesquioxane-coated silicon nanoparticle obtained in Example 2. It is a figure which shows IR absorption spectrum of a baked product (2) and the silicon nanoparticle mixed silicon oxide (1) obtained in Comparative Example 1.
- FIG. 2 is a transmission electron microscope (TEM) photograph of the polysilsesquioxane-coated silicon nanoparticle fired product (1) obtained in Example 1.
- 3 is a scanning electron microscope (SEM) photograph of the polysilsesquioxane-coated silicon nanoparticle fired product (1) obtained in Example 1.
- FIG. FIG. 4 is a diagram illustrating a configuration example of a coin-type lithium ion battery.
- the fired polysilsesquioxane-coated silicon nanoparticles of the present invention can be obtained by firing polysilsesquioxane-coated silicon nanoparticles (precursor of fired polysilsesquioxane-coated silicon nanoparticles). It can. First, the polysilsesquioxane-coated silicon nanoparticles will be described, and then the polysilsesquioxane-coated silicon nanoparticles fired product will be described.
- Polysilsesquioxane-coated silicon nanoparticles are mixed in the process of synthesizing hydrogen silsesquioxane polymer (HPSQ) by hydrolyzing and condensing the silicon compound represented by formula (1).
- HPSQ hydrogen silsesquioxane polymer
- a manufacturing method is not specifically limited. For example, a method of hydrolyzing and condensing a mixture obtained by adding silicon nanopowder to a silicon compound represented by formula (1), or dropping a silicon compound represented by formula (1) in a solvent in which silicon nanopowder is dispersed And a method of hydrolysis and condensation reaction.
- R is the same or different and is a group selected from halogen, hydrogen, substituted or unsubstituted alkoxy having 1 to 10 carbons, and substituted or unsubstituted aryloxy having 6 to 20 carbons It is. However, in the substituted or unsubstituted alkoxy group having 1 to 10 carbon atoms and the substituted or unsubstituted aryloxy group having 6 to 20 carbon atoms, any hydrogen may be substituted with a halogen.
- silicon compound represented by the formula (1) include the following compounds.
- trihalogenated silane such as trichlorosilane, trifluorosilane, tribromosilane, dichlorosilane, dihalogenated silane, tri-n-butoxysilane, tri-t-butoxysilane, tri-n-propoxysilane, tri-i -Trialkoxysilanes such as propoxysilane, di-n-butoxyethoxysilane, triethoxysilane, trimethoxysilane, diethoxysilane, dialkoxysilanes, triaryloxysilane, diaryloxysilane, diaryloxyethoxysilane, etc.
- Aryloxysilane or aryloxyalkoxysilane can be mentioned.
- trihalogenated silanes or trialkoxysilanes are preferable from the viewpoints of reactivity, availability, and production costs, and trihalogenated silanes are particularly preferable.
- These silicon compounds represented by the formula (1) may be used singly or in combination of two or more.
- the silicon compound represented by the formula (1) has high hydrolyzability and condensation reactivity, and when it is used, polysilsesquioxane-coated silicon nanoparticles can be easily obtained. Moreover, when the silicon compound represented by Formula (1) is used, the polysilsesquioxane-coated silicon nanoparticles obtained when the obtained polysilsesquioxane-coated silicon nanoparticles are heat-treated in a non-oxidizing atmosphere. The fired product also has the advantage that it appropriately provides Si—H bonds.
- hydrolysis can be performed by a known method, for example, in a solvent such as alcohol or DMF, in the presence of an inorganic acid such as hydrochloric acid or an organic acid such as acetic acid, and water, at room temperature or in a heated state. can do. Therefore, in addition to the hydrolyzate of the silicon compound represented by the formula (1), the reaction solution after hydrolysis may contain a solvent, an acid, water, and a substance derived therefrom.
- the silicon compound represented by the formula (1) may not be completely hydrolyzed, and a part thereof may remain.
- the polycondensation reaction of the hydrolyzate partially proceeds.
- the degree to which the polycondensation reaction proceeds can be controlled by the hydrolysis temperature, hydrolysis time, acidity, and / or solvent, etc., depending on the target polysilsesquioxane-coated silicon nanoparticles. Can be set appropriately.
- reaction conditions a silicon compound represented by the formula (1) is added to an acidic aqueous solution with stirring, and the temperature is -20 ° C to 50 ° C, preferably 0 ° C to 40 ° C, particularly preferably 10 ° C to 30 ° C.
- the reaction is carried out at a temperature of 0.5 to 20 hours, preferably 1 to 10 hours, particularly preferably 1 to 5 hours.
- an organic acid or an inorganic acid can be used as the acid used for the pH adjustment.
- examples of the organic acid include formic acid, acetic acid, propionic acid, oxalic acid, and citric acid
- examples of the inorganic acid include hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid.
- hydrochloric acid and acetic acid are preferred because the hydrolysis reaction and subsequent polycondensation reaction can be easily controlled, and acquisition, pH adjustment, and treatment after the reaction are also easy.
- a halogenated silane such as trichlorosilane is used as the silicon compound represented by the formula (1)
- an acidic aqueous solution is formed in the presence of water. This is one of the preferred embodiments of the invention.
- Polysilsesquioxane-coated silicon nanoparticles undergo a hydrolysis and polymerization reaction of the compound of formula (1) in the presence of silicon nanoparticles. Can be obtained.
- the silicon nanoparticles used are not particularly limited as long as the volume-based average particle diameter is more than 10 nm and less than 500 nm.
- the lower limit of the volume-based average particle diameter is preferably more than 20 nm, and more preferably more than 30 nm.
- the upper limit of the volume-based average particle diameter is preferably less than 400 nm, and more preferably less than 300 nm.
- silicon nanoparticles silicon nanopowder is preferably used as the silicon nanoparticles.
- the silicon nanoparticles used are preferably silicon nanoparticles that do not contain particles having a particle size of 1000 nm or more.
- the silicon nanoparticles may contain other components other than silicon as long as the effects of the present invention are not impaired.
- the silicon nanoparticles can contain carbon, metals, and the like. It is usually less than 5% by weight with respect to silicon nanoparticles.
- volume-based average particle size means a particle size calculated based on the volume, and may be simply referred to as an average particle size in the present specification.
- Silicon nanoparticles are blended so that the coating thickness is 1 nm or more and 30 nm or less with respect to the total amount of the polysilsesquioxane-coated silicon nanoparticles obtained.
- the proportion of silicon nanoparticles in the total weight of the polysilsesquioxane-coated silicon nanoparticles is approximately 25% to 95% by weight, but the coating thickness varies greatly depending on the particle size, so it is limited to the above weight proportion. Is not to be done.
- the liquid fraction After completion of the hydrolysis reaction and polycondensation reaction, the liquid fraction is separated and removed by a known method such as filtration, centrifugation, or tilting. In some cases, it is further washed with water or organic solvent and then dried. Sesquioxane-coated silicon nanoparticles can be obtained.
- the peak intensity ratio exceeding 1 suggests that there is a chemical bond between the silicon nanoparticles present inside and the hydrogen polysilsesquioxane, and this chemical bond It is assumed that the particle collapse caused by the expansion and contraction of the silicon particles during the charge / discharge cycle is suppressed by the presence of.
- the absorption band of 1000 to 1250 cm ⁇ 1 in the IR spectrum of hydrogen polysilsesquioxane is derived from the asymmetric stretching vibration of Si—O—Si, and in the case of a linear bond, a plurality of absorption bands at 1000 to 1250 cm ⁇ 1. In the case of a cyclic bond, one absorption is generally observed at 1000 to 1100 cm ⁇ 1 .
- the polymerization ends are compared with each other rather than the reaction in which the polymerization ends and monomers react to form a linear siloxane. It is assumed that the reaction in which cyclic siloxane is reacted and the energy of the system is reduced, it can be easily predicted that the peak 2-2 becomes larger than the peak 2-1.
- the hydrolysis / polymerization of the silicon compound of the formula (1) proceeds in the presence of silicon nanoparticles, the terminal portion of the chain Si—O—Si skeleton contained in the HPSQ polymer to be produced is the surface of the silicon nanoparticles.
- the silicon nanoparticles and the polysilsesquioxane form a network via a strong chemical bond (Si—O—Si bond).
- This network is maintained even after firing, and the polysilsesquioxane skeleton serves as a buffer layer for the expansion and contraction of the silicon nanoparticles, and as a result, suppresses the refinement of the silicon nanoparticles that occur during repeated charge and discharge. It is presumed that
- the small primary particles relieve the stress during expansion and contraction that occurs when charging and discharging are repeated when the fired product of polysilsesquioxane-coated silicon nanoparticles is used as a negative electrode material for a lithium ion battery. Therefore, cycle deterioration is suppressed and cycle characteristics are improved. Further, having a complicated secondary aggregation structure makes the binding property with the binder good, and further exhibits excellent cycle characteristics.
- the fired product of the polysilsesquioxane-coated silicon nanoparticles is obtained by the heat treatment of the polysilsesquioxane-coated silicon nanoparticles obtained in the above manner in a non-oxidizing atmosphere.
- non-oxidizing means that the polysilsesquioxane-coated silicon nanoparticles are not oxidized in terms of words, but are substantially polysilsesquioxane-coated silicon nanoparticles.
- I 1 refers to the intensity (I 1 ) of the maximum peak (peak 1) derived from the Si—H bond at 820 to 920 cm ⁇ 1 .
- the polysilsesquioxane-coated silicon nanoparticle fired product thus obtained contains silicon (Si), oxygen (O), and hydrogen (H), and is represented by the general formula SiO x H y.
- the polysilsesquioxane-coated silicon nanoparticle fired product has a maximum absorption peak (peak 1) in an absorption band of 820 to 920 cm ⁇ 1 derived from the Si—H bond in the spectrum measured by infrared spectroscopy.
- the ratio (I 1 / I 2 ) of the intensity of peak 1 (I 1 ) and the intensity of peak 2 (I 2 ) (I 1 / I 2 ) of the fired product is preferably from 0.01 to 0.35, more preferably from 0.01. If it is in the range of 0.30, more preferably in the range of 0.03 to 0.20, due to the presence of an appropriate amount of Si—H bond, a high discharge capacity and good initial charge / discharge when used as a negative electrode active material of a lithium ion battery Efficiency and cycle characteristics can be developed.
- the intensity of the maximum absorption peak (peak 2-1) in the absorption band on the several side is I 2-1
- the intensity of the maximum absorption peak (peak 2-2) in the absorption band on the lower wave number side than 1100 cm ⁇ 1 is I 2-2.
- the intensity ratio (I 2-1 / I 2-2 ) is preferably greater than 1.
- the peak intensity ratio exceeds 1, it has a chemical bond between the silicon nanoparticles present in the fired product of the polysilsesquioxane-coated silicon nanoparticles and the hydrogen polysilsesquioxane. It is speculated that the presence of this chemical bond suppresses particle collapse caused by silicon particle expansion and contraction during the charge / discharge cycle.
- the heat treatment of the polysilsesquioxane-coated silicon nanoparticles is preferably performed in a non-oxidizing atmosphere.
- the non-oxidizing atmosphere may be an inert gas atmosphere or an atmosphere in which oxygen is removed by high vacuum (oxygen is removed to the extent that it does not hinder the formation of the desired polysilsesquioxane-coated silicon nanoparticle fired product.
- examples of the inert gas include nitrogen, argon, and helium.
- the reducing atmosphere includes an atmosphere containing a reducing gas such as hydrogen.
- a mixed gas atmosphere of 2% by volume or more of hydrogen gas and inert gas can be used.
- a hydrogen gas atmosphere can also be used as the reducing atmosphere.
- the polysilsesquioxane-coated silicon nanoparticles begin to dehydrogenate Si—H bonds from around 600 ° C., and Si—Si bonds are generated.
- Si—Si bond is appropriately grown, it becomes an excellent Li storage site and becomes a source of high charge capacity.
- the heat treatment time is not particularly limited, but is usually 15 minutes to 10 hours, preferably 30 minutes to 5 hours.
- a fired product of polysilsesquioxane-coated silicon nanoparticles having a coating thickness of 1 nm or more and 30 nm or less is obtained. If it is 1 nm or more, the deterioration of the battery can be suppressed. If the thickness of the coating is 30 nm or less, a battery having high capacity and initial charge / discharge efficiency can be obtained.
- the polysilsesquioxane-coated silicon nanoparticle fired product of the present invention thus obtained has an entire surface of silicon nanoparticles of 1 nm to 30 nm, as is apparent from the transmission electron microscope (TEM) photograph shown in FIG. Is covered with a polysilsesquioxane layer of thickness. Further, as is apparent from the scanning electron microscope (SEM) photograph shown in FIG. 3, primary particles, which are spherical particles having a submicron particle size, further aggregate to form secondary aggregates having a particle size of several microns. ing.
- TEM transmission electron microscope
- SEM scanning electron microscope
- the polysilsesquioxane-coated silicon nanoparticle fired product is combined or coated with a carbon-based material.
- a method of dispersing the calcined product of the polysilsesquioxane-coated silicon nanoparticles and the carbon-based material by a mechanical mixing method using a mechanofusion, a ball mill, a vibration mill, or the like. Can be mentioned.
- the carbon-based material include carbon-based materials such as graphite, carbon black, fullerene, carbon nanotube, carbon nanofoam, pitch-based carbon fiber, polyacrylonitrile-based carbon fiber, and amorphous carbon.
- the polysilsesquioxane-coated silicon nanoparticle fired product and the carbon-based material can be combined or coated at an arbitrary ratio.
- the negative electrode in the lithium ion secondary battery according to the present invention contains the polysilsesquioxane-coated silicon nanoparticle fired product or the polysilsesquioxane-coated silicon nanoparticle fired product obtained by combining or coating the carbon-based material.
- a negative electrode active material examples include a negative electrode active material and a binder including a fired polysilsesquioxane-coated silicon nanoparticle or a fired polysilsesquioxane-coated silicon nanoparticle obtained by combining or coating the carbon-based material.
- the negative electrode mixed material may be formed into a certain shape, or may be manufactured by a method in which the negative electrode mixed material is applied to a current collector such as a copper foil.
- the method for forming the negative electrode is not particularly limited, and a known method can be used.
- a polysilsesquioxane-coated silicon nanoparticle fired product or a negative active material containing a polysilsesquioxane-coated silicon nanoparticle fired product obtained by combining the carbon-based material, a binder, and If necessary, prepare a negative electrode material composition containing a conductive material, etc., and coat it directly on a current collector such as a rod-like body, plate-like body, foil-like body, or net-like body mainly composed of copper, nickel, stainless steel, etc.
- a negative electrode plate can be obtained by casting the negative electrode material composition separately on a support and laminating the negative electrode active material film peeled off from the support on a current collector.
- the negative electrode of the present invention is not limited to the above-listed forms, and forms other than the listed forms are possible.
- binder those commonly used in the secondary battery, a Si-H bonds and interactions on the anode active material, COO - as long as having a functional group such as a group, either Can also be used, and examples include carboxymethylcellulose, polyacrylic acid, alginic acid, glucomannan, amylose, saccharose and derivatives and polymers thereof, and respective alkali metal salts, as well as polyimide resins and polyimideamide resins. These binders may be used singly or as a mixture. Further, the binder is further improved in binding property with the current collector, improved in dispersibility, and improved in conductivity of the binder itself. A component imparting a function, for example, a styrene-butadiene rubber polymer or a styrene-isoprene rubber polymer may be added and mixed.
- the lithium ion battery using the negative electrode active material comprising the polysilsesquioxane-coated silicon nanoparticle fired product of the present invention can be produced as follows. First, a positive electrode active material composition capable of reversibly occluding and releasing lithium ions, a conductive additive, a binder, and a solvent are mixed to prepare a positive electrode active material composition. Similarly to the negative electrode, the positive electrode active material composition is directly coated on a metal current collector and dried by a known method to prepare a positive electrode plate. It is also possible to produce a positive electrode by separately casting the positive electrode active material composition on a support and then laminating the film obtained by peeling from the support on a metal current collector. The method for forming the positive electrode is not particularly limited, and a known method can be used.
- the positive electrode active material is not particularly limited as long as it is a lithium metal composite oxide and is generally used in the field of the secondary battery.
- lithium cobaltate, lithium nickelate, spinel structure examples thereof include lithium manganate having lithium, cobalt lithium manganate, iron phosphate having an olivine structure, so-called ternary lithium metal composite oxide, nickel lithium metal composite oxide, and the like.
- V 2 O 5 , TiS, MoS, and the like which are compounds capable of de-insertion of lithium ions, can also be used.
- the conductive auxiliary agent is not particularly limited as long as it is generally used in lithium ion batteries, and may be any electron conductive material that does not cause decomposition or alteration in the constituted battery. Specific examples include carbon black (acetylene black and the like), graphite fine particles, vapor grown carbon fiber, and combinations of two or more thereof.
- the binder include vinylidene fluoride / propylene hexafluoride copolymer, polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene and a mixture thereof, styrene butadiene rubber. Examples thereof include, but are not limited to, polymers.
- the solvent examples include, but are not limited to, N-methylpyrrolidone, acetone, water and the like.
- the content of the positive electrode active material, the conductive additive, the binder and the solvent is set to an amount that can be generally used in a lithium ion battery.
- the separator interposed between the positive electrode and the negative electrode is not particularly limited as long as it is generally used in lithium ion batteries. Those having low resistance to ion migration of the electrolyte or excellent electrolyte solution impregnation ability are preferred. Specifically, it is a material selected from glass fiber, polyester, polyethylene, polypropylene, polytetrafluoroethylene, polyimide, or a compound thereof, and may be in the form of a nonwoven fabric or a woven fabric.
- a rollable separator made of a material such as polyethylene or polypropylene is used, and in the case of a lithium ion polymer battery, a separator excellent in organic electrolyte solution impregnation ability. It is preferable to use
- electrolyte examples include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, butylene carbonate, dibutyl carbonate, benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, ⁇ -butyrolactone, dioxolane, 4 -Hexafluoride in a solvent such as methyldioxolane, N, N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene or diethyl ether or a mixture thereof Lithium phosphate, lithium boron tetrafluoride, lithium antimony lithium, lithium arsenic hexafluoride, Lithium chlorate, lithium triflu
- non-aqueous electrolytes and solid electrolytes can also be used.
- various ionic liquids to which lithium ions are added can be used, pseudo solid electrolytes in which ionic liquids and fine powders are mixed, lithium ion conductive solid electrolytes, and the like can be used.
- the above-mentioned electrolytic solution may appropriately contain a compound that promotes stable film formation on the surface of the negative electrode active material.
- a compound that promotes stable film formation on the surface of the negative electrode active material for example, vinylene carbonate (VC), fluorobenzene, cyclic fluorinated carbonate [fluoroethylene carbonate (FEC), trifluoropropylene carbonate (TFPC), etc.], or chain fluorinated carbonate [trifluorodimethyl carbonate (TFDMC), Fluorinated carbonates such as fluorodiethyl carbonate (TFDEC) and trifluoroethyl methyl carbonate (TFEMC) are effective.
- the cyclic fluorinated carbonate and the chain fluorinated carbonate can also be used as a solvent, such as ethylene carbonate.
- a separator is disposed between the positive electrode plate and the negative electrode plate as described above to form a battery structure.
- the battery structure is wound or folded and placed in a cylindrical battery case or a square battery case, and then an electrolyte is injected to complete a lithium ion battery.
- the battery structure is laminated in a bicell structure, it is impregnated with an organic electrolyte, and the obtained product is put in a pouch and sealed to complete a lithium ion polymer battery.
- One embodiment of a fired product of polysilsesquioxane-coated silicon nanoparticles formed by heat-treating polysilsesquioxane-coated silicon nanoparticles is derived from Si—H bonds in the spectrum measured by infrared spectroscopy.
- the intensity of the maximum absorption peak (peak 1) out of the absorption band of 820 to 920 cm ⁇ 1 is I 1
- the maximum absorption peak (peak 2) out of the 1000 to 1250 cm ⁇ 1 absorption band derived from the Si—O—Si bond strength of the case of a I 2 is in the range from 0.01 to 0.35, the thickness of the coating, 1 nm or more and 30nm or less, the policy Rusesquioxane-coated silicon nanoparticle fired product.
- a lithium ion battery manufactured using a negative electrode active material containing a fired polysilsesquioxane-coated silicon nanoparticle having these characteristics has excellent cycle characteristics and good initial charge / discharge efficiency. , And high capacity.
- One aspect of the fired product of the polysilsesquioxane-coated silicon nanoparticles of the present invention is 1100 cm out of an absorption band of 1000 to 1250 cm ⁇ 1 derived from Si—O—Si bonds in a spectrum measured by infrared spectroscopy.
- the intensity of the maximum absorption peak (peak 2-1) in the absorption band on the higher wave number side than ⁇ 1 is the intensity of the maximum absorption peak (peak 2-2) in the absorption band on the lower wave number side than I 2-1 , 1100 cm ⁇ 1.
- the intensity ratio (I 2-1 / I 2-2) is a polysilsesquioxane coated silicon nanoparticles baked product, characterized in that more than one.
- the polysilsesquioxane-coated silicon nanoparticles prepared in Examples 1 to 5 and Comparative Example 1 and the fired products thereof were subjected to various analyzes and evaluations.
- “Infrared spectroscopy measurement”, “elemental analysis measurement”, “observation / photographing by scanning microscope (SEM)”, “observation / photographing by transmission microscope (TEM)”, and coating layer in each example and comparative example The measuring device and measuring method of “thickness measurement” and “evaluation of battery characteristics” are as follows.
- Infrared spectroscopy measurement uses Nicolet iS5 FT-IR manufactured by Thermo Fisher Scientific as an infrared spectrometer, and transmission measurement by KBr method (resolution: 4 cm ⁇ 1 , number of scans: 16 times, data interval: 1.928 cm ⁇ 1 , At the detector DTGS KBr), the intensity (I 1 ) of the peak 1 derived from the Si—H bond at 820 to 920 cm ⁇ 1 and the peak 2 derived from the Si—O—Si bond at 1000 to 1250 cm ⁇ 1. Strength (I 2 ) was measured.
- Each peak intensity was obtained by connecting the start point and end point of the target peak with a straight line, partially correcting the baseline, and then measuring the height from the baseline to the peak top.
- elemental analysis measurement For elemental analysis measurement, after the sample powder is hardened into a pellet, the sample is irradiated with He ions accelerated to 2.3 MeV, and the energy spectrum of backscattered particles and the energy spectrum of forward-scattered hydrogen atoms are analyzed. Thus, the RBS (Rutherford backscattering analysis) / HFS (hydrogen forward scattering analysis) method was used to obtain a highly accurate composition value including hydrogen.
- the measurement apparatus is Pelletron 3SDH manufactured by National Electrostatics Corporation. Incident ions: 2.3 MeV He, RBS / HFS simultaneous measurement, Incident angle: 75 deg. , Scattering angle: 160 deg. Sample current: 4 nA, beam diameter: 2 mm ⁇ .
- TEM transmission microscope
- FEI transmission microscope
- the sample powder was embedded in a resin and thinned with an ultramicrotome.
- the thickness of the coating layer was determined by measuring the thickness of the coating layer for each particle photographed in a photograph taken by TEM and calculating the average value of ten particles.
- the charge / discharge characteristics of a lithium ion secondary battery or the like using the negative electrode active material containing the fired product of the polysilsesquioxane-coated silicon nanoparticles of the present invention were measured as follows. Using BTS2005W manufactured by Nagano Co., Ltd., charged with a constant current at a current of 100 mA per 1 g weight of the polysilsesquioxane-coated silicon nanoparticle fired product until reaching 0.001 V against the Li electrode, then 0.001 V While maintaining the voltage, constant voltage charging was performed until the current reached a current value of 20 mA or less per gram of active material.
- the charged cell was subjected to a constant current discharge until the voltage reached 1.5 V at a current of 100 mA per gram of active material after a rest period of about 30 minutes.
- the charge capacity was calculated from the integrated current value until the constant voltage charge was completed, and the discharge capacity was calculated from the integrated current value until the battery voltage reached 1.5V.
- the circuit was paused for 30 minutes.
- the discharge capacity at the 500th cycle is the discharge capacity at the 500th cycle when the charge / discharge is one cycle.
- the charge / discharge efficiency was the ratio of the discharge capacity to the initial (first charge / discharge cycle) charge capacity
- the capacity maintenance ratio was the ratio of the discharge capacity at the 50th charge / discharge cycle to the initial discharge capacity.
- Example 1 Preparation of polysilsesquioxane-coated silicon nanoparticle powder (1)
- a 100 ml poly beaker put 70 g of pure water and 20.5 g of silicon nanopowder (Si-10, Si-10 average particle size, not including particles with a particle size of 1000 nm or more) and treat with an ultrasonic homogenizer for 2 minutes.
- silicon nanopowder Si-10, Si-10 average particle size, not including particles with a particle size of 1000 nm or more
- the obtained polysilsesquioxane-coated silicon nanoparticle fired product is pulverized and pulverized in a mortar for 5 minutes, and classified using a stainless steel sieve having an opening of 32 ⁇ m, whereby a polysil having a maximum particle size of 32 ⁇ m. 9.75 g of a sesquioxane-coated silicon nanoparticle fired product (1) was obtained.
- the infrared spectrum of the obtained polysilsesquioxane-coated silicon nanoparticle fired product (1) is shown in FIG. 1, a photograph taken with a transmission electron microscope (TEM), and a photograph taken with a scanning electron microscope (SEM). As shown in FIG. The thickness of the coating layer was 26 nm.
- This slurry composition was transferred to a thin film swirl type high speed mixer (Filmix 40-40 type) manufactured by Plymix, and stirred and dispersed for 30 seconds at a rotation speed of 20 m / s.
- the slurry after the dispersion treatment was applied to a copper foil roll with a thickness of 200 ⁇ m by a doctor blade method. After coating, it was dried for 90 minutes on a hot plate at 80 ° C. After drying, the negative electrode sheet was pressed with a 2t small precision roll press (manufactured by Sank Metal). After pressing, the electrode was punched with an electrode punching punch HSNG-EP with a diameter of 14.50 mm, and dried under reduced pressure at 80 ° C. for 16 hours in a glass tube oven GTO-200 (manufactured by SIBATA) to prepare a negative electrode.
- a 2032 type coin battery having the structure shown in FIG. 4 was produced.
- metallic lithium as the counter electrode 3
- a microporous polypropylene film as the separator 2
- ethylene carbonate and diethyl carbonate in which LiPF 6 was dissolved at a ratio of 1 mol / L as the electrolyte solution 1: 1 (volume ratio) was used by adding 5% by weight of fluoroethylene carbonate to a mixed solvent.
- evaluation of the battery characteristics of the lithium ion battery was performed by the method described above.
- Example 2 Preparation of polysilsesquioxane-coated silicon nanoparticle powder (2)
- a 100 ml poly beaker put 50 g of pure water and 13.58 g of silicon nanopowder (Si-10 average particle size 100 nm, excluding particles with a particle size of 1000 nm or more) and treat with an ultrasonic homogenizer for 2 minutes.
- silicon nanopowder Si-10 average particle size 100 nm, excluding particles with a particle size of 1000 nm or more
- a 500 ml three-necked flask was charged with this silicon fine particle dispersion, 2.22 g (21 mmol) of 35 wt% hydrochloric acid and 161 g of pure water, and stirred at room temperature for 10 minutes to disperse the silicon nanoparticles throughout. While stirring, 19.9 g (121 mmol) of triethoxysilane (Tokyo Kasei) was added dropwise at 25 ° C. After completion of the dropwise addition, a hydrolysis reaction and a condensation reaction were performed for 2 hours at 25 ° C. with stirring. After the reaction time had elapsed, the reaction product was filtered through a membrane filter (pore size 0.45 ⁇ m, hydrophilic) to recover a solid. The obtained solid was dried under reduced pressure at 80 ° C. for 10 hours to obtain 20.0 g of a polysilsesquioxane-coated silicon nanoparticle powder (2).
- Example 3 Preparation of polysilsesquioxane-coated silicon nanoparticle powder (3)
- a 100 ml beaker put 50 g of pure water and 17.6 g of silicon nanopowder (S-10 manufactured by Si-10 with an average particle size of 100 nm and no particles with a particle size of 1000 nm or more) and treat it with an ultrasonic homogenizer for 2 minutes. Then, a silicon nanoparticle dispersed aqueous solution was prepared.
- a 500 ml three-necked flask is charged with this silicon fine particle dispersion, 1.67 g (28 mmol) of acetic acid (Wako special grade reagent) and 223 g of pure water, and stirred for 10 minutes at room temperature to disperse the silicon nanoparticles as a whole. 7.36 g (44.9 mmol) of triethoxysilane (Tokyo Kasei) was added dropwise at 25 ° C. After completion of the dropwise addition, a hydrolysis reaction and a condensation reaction were performed for 2 hours at 25 ° C. with stirring. After the reaction time had elapsed, the reaction product was filtered through a membrane filter (pore size 0.45 ⁇ m, hydrophilic) to recover a solid. The obtained solid was dried under reduced pressure at 80 ° C. for 10 hours to obtain 20.0 g of a polysilsesquioxane-coated silicon nanoparticle powder (3).
- Example 4 Preparation of polysilsesquioxane-coated silicon nanoparticle powder (4)
- a 100 ml beaker put 50 g of pure water and 15.5 g of silicon nanopowder (Nanomakers Pure Si NM Si99 average particle size of 75 nm, excluding particles with a particle size of 1000 nm or more) and treat with an ultrasonic homogenizer for 2 minutes.
- a silicon nanoparticle-dispersed aqueous solution was prepared.
- a 500 ml three-necked flask is charged with this silicon fine particle dispersion, 2.54 g (24 mmol) of 35 wt% hydrochloric acid and 190 g of pure water, and stirred at room temperature for 10 minutes to disperse the silicon nanoparticles throughout.
- 13.9 g (85 mmol) of triethoxysilane (Tokyo Kasei) was added dropwise at 25 ° C.
- a hydrolysis reaction and a condensation reaction were performed for 2 hours at 25 ° C. with stirring.
- the reaction product was filtered through a membrane filter (pore size 0.45 ⁇ m, hydrophilic) to recover a solid.
- the obtained solid was dried under reduced pressure at 80 ° C. for 10 hours to obtain 20.0 g of polysilsesquioxane-coated silicon nanoparticle powder (4).
- Example 5 The same treatment as in Example 4 was performed except that the silicon nanonano powder was NM Si ⁇ C99 (average particle size 75 nm, not including particles with a particle size of 1000 nm or more) manufactured by Nanomakers, and polysilsesquioxane-coated silicon nanoparticle fired 9.84 g of product (5) was obtained.
- Batteries that employ the results of infrared spectroscopic measurement of the fired polysilsesquioxane-coated silicon nanoparticles obtained in Examples 1 to 5 of the present invention, the results of elemental analysis, and the negative electrode produced using each negative electrode active material The evaluation results of the characteristics are as shown in Table 1.
- Silicon monoxide powder having a maximum particle size of 20 ⁇ m was obtained by classifying commercially available silicon monoxide (under 325 mesh manufactured by Aldrich) using a 20 ⁇ m stainless steel sieve. 4.41 g of silicon monoxide of 20 ⁇ m or less was placed in a planetary ball mill for 10 minutes using 11.2 g of silicon nanopowder (Nanomakers Pure Si NM Si99 average particle size 75 nm), a zirconia container and a zirconia ball. Milling treatment was mixed to obtain silicon nanoparticle mixed silicon oxide (1).
- a negative electrode body was produced in the same manner as in Example 2 except that the silicon nanoparticle composite silicon oxide (1) of Comparative Example 1 was used.
- TEM transmission electron microscope
- the negative electrode active material for a lithium ion battery produced from a fired product obtained by heat-treating polysilsesquioxane-coated silicon nanoparticles that is 1 nm or more and 30 nm or less has an initial discharge capacity and a discharge capacity at the 50th cycle.
- the battery characteristics using a negative electrode using a negative electrode active material prepared from a silicon oxide in which the surface of the silicon nanoparticles does not have a chemical bond and does not have a Si—H bond As shown in Comparative Example 1, the battery characteristics using a negative electrode using a negative electrode active material prepared from a silicon oxide in which the surface of the silicon nanoparticles does not have a chemical bond and does not have a Si—H bond.
- the initial charge and discharge efficiency shows a certain value, but the capacity is drastically decreased, and the lithium ion It has not reached a practical level as a battery.
- a negative electrode active material for a lithium ion battery using a fired product of polysilsesquioxane-coated silicon nanoparticles obtained by the production method of the present invention, and a negative electrode formed using the negative electrode active material, are used in a lithium ion battery.
- a lithium ion battery having a remarkably high capacity and practical initial charge / discharge efficiency and cycle characteristics can be obtained.
- the present invention is particularly useful in the field of batteries. This technique is useful in the field of secondary batteries.
- Negative electrode material 2 Separator 3: Lithium counter electrode
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Abstract
Description
このような小型、軽量な高容量の二次電池としては、今日、リチウムイオンを層間から放出するリチウムインターカレーション化合物を正極物質に、リチウムイオンを結晶面間の層間に充放電時に吸蔵放出(インターカレート)できる黒鉛などに代表される炭素質材料を負極物質に用いた、ロッキングチェア型のリチウムイオン電池の開発が進み、実用化されて一般的に使用されている。
そこで、リチウム金属に代わる負極活物質として、リチウムを吸蔵、放出する炭素系負極が用いられるようになった(特許文献1)。
炭素系負極を使用するリチウムイオン電池は、炭素の多孔性構造のため、本質的に低い電池容量を有する。例えば、使用されている炭素として最も結晶性の高い黒鉛の場合でも、理論容量は、LiC6の組成であるとき、372mAh/gほどである。これは、リチウム金属の理論容量が3860mAh/gであることに比べれば、僅か10%ほどに過ぎない。このような状況から、前記したような問題点があるにもかかわらず、再びリチウムのような金属を負極に導入し、電池の容量を向上させようという研究が活発に試みられている。
例えば、特許文献2にはケイ素と酸素を含み、ケイ素に対する酸素の比が0~2であるケイ素酸化物は、リチウムイオン電池の負極活物質として使用した場合、良好な充放電サイクル性能を得ることが開示されている。
また、特許文献3にはナノ気孔構造を含む非晶質ケイ素酸化物を含むケイ素酸化物系負極活物質として、水素ポリシルセスキオキサンの焼成物を用いる方法が提案されている。
さらに、特許文献4にはケイ素を含むコアとコア表面に形成されたシリコンナノ粒子を配置した構造体を作ることにより、充放電の際に体積膨張率の短所を補完し、容易にケイ素と酸素の比率を調節することが可能なケイ素酸化物が提案されている。
本発明の課題は、得られた電池が得られた電池が優れたサイクル特性を有し、かつ、良好な初期放電効率、高充電容量をも示す二次電池用負極活物質として、新しいケイ素酸化物系構造体を提供することである。
[1] 体積基準平均粒径が10nmを超え500nm未満であり、且つ粒径が1000nm以上の粒子を含まないシリコンナノ粒子と、前記シリコンナノ粒子を被覆し、前記シリコンナノ粒子の表面に化学的に結合しているポリシルセスキオキサンとを含み、Si-H結合を有し、透過型電子顕微鏡(TEM)で観察される前記ポリシルセスキオキサンの厚さが、1nm以上30nm以下である、ポリシルセスキオキサン被覆シリコンナノ粒子又はその焼成物。
[2] 前記ポリシルセスキオキサン被覆シリコンナノ粒子を赤外分光法により測定したスペクトルにおいて、Si-O-Si結合に由来する1000~1250cm-1の吸収帯のうち、1100cm-1より高波数側の吸収帯における最大吸収ピークの強度をI2-1、1100cm-1より低波数側の吸収帯における最大吸収ピークの強度をI2-2とした場合に、強度比(I2-1/I2-2)が、1を超える[1]に記載のポリシルセスキオキサン被覆シリコンナノ粒子又はその焼成物。
[3] 前記ポリシルセスキオキサン被覆シリコンナノ粒子を赤外分光法により測定したスペクトルにおいて、Si-H結合に由来する820~920cm-1の吸収帯のうち、最大吸収ピークの強度をI1、Si-O-Si結合に由来する1000~1250cm-1吸収帯のうち、最大吸収ピークの強度をI2とした場合に、強度比(I1/I2)が、0.01から0.35の範囲にある[1]又は[2]に記載のポリシルセスキオキサン被覆シリコンナノ粒子の焼成物。
[4] [1]から[3]のいずれか一項に記載のポリシルセスキオキサン被覆シリコンナノ粒子の焼成物を含むリチウムイオン電池用負極活物質。
[5] [4]に記載のリチウムイオン電池用負極活物質を含むリチウムイオン電池用負極。
[6] [5]に記載のリチウムイオン電池用負極を備えたリチウムイオン電池。
前記製造方法は、シリコンナノ粒子の存在下で、式(1)で示されるケイ素化合物を加水分解および縮合反応(重縮合反応ともいう)させる工程を含む、製造方法。
HSi(R)3 (1)
(式中、Rは、それぞれ同一あるいは異なる、ハロゲン、水素、炭素数1~10の置換または非置換のアルコキシ、炭素数6~20の置換または非置換のアリールオキシ、および炭素数7~30の置換または非置換のアリールアルコキシから選択される基である。但し、炭素数1~10の置換または非置換のアルコキシ基、炭素数6~20の置換または非置換のアリールオキシ基、および炭素数7~30の置換または非置換のアリールアルコキシ基において、任意の水素はハロゲンで置換されていてもよい。)
[8] 加水分解及び縮合反応させる工程の後に、非酸化性雰囲気下で焼成する工程をさらに含む、[7]に記載のポリシルセスキオキサン被覆シリコンナノ粒子の焼成物の製造方法。
本発明のポリシルセスキオキサン被覆シリコンナノ粒子焼成物は、ポリシルセスキオキサン被覆シリコンナノ粒子(ポリシルセスキオキサン被覆シリコンナノ粒子焼成物の前駆体)を焼成することにより、得ることができる。まず、ポリシルセスキオキサン被覆シリコンナノ粒子を説明し、次に、ポリシルセスキオキサン被覆シリコンナノ粒子焼成物について説明する。
ポリシルセスキオキサン被覆シリコンナノ粒子は、式(1)で示されるケイ素化合物を加水分解および縮合反応をさせて、水素シルセスキオキサン重合物(HPSQ)を合成する過程でシリコンナノ粒子を混合することにより得ることができるが、製造方法は特に限定されるものではない。例えば、式(1)で示されるケイ素化合物にシリコンナノパウダーを加えた混合物を加水分解および縮合反応させる方法、もしくはシリコンナノパウダーを分散させた溶媒中に式(1)で示されるケイ素化合物を滴下して加水分解および縮合反応させる方法を挙げることができる。
式(1)において、Rは、それぞれ同一あるいは異なる、ハロゲン、水素、炭素数1~10の置換または非置換のアルコキシ、および炭素数6~20の置換または非置換のアリールオキシから選択される基である。但し、炭素数1~10の置換または非置換のアルコキシ基、および炭素数6~20の置換または非置換のアリールオキシ基において、任意の水素はハロゲンで置換されていてもよい。
例えば、トリクロロシラン、トリフルオロシラン、トリブロモシラン、ジクロロシラン等のトリハロゲン化シランやジハロゲン化シラン、トリ-n-ブトキシシラン、トリ-t-ブトキシシラン、トリ-n-プロポキシシラン、トリ-i-プロポキシシラン、ジ-n-ブトキシエトキシシラン、トリエトキシシラン、トリメトキシシラン、ジエトキシシラン等のトリアルコキシシランやジアルコキシシラン、更にはトリアリールオキシシラン、ジアリールオキシシラン、ジアリールオキシエトキシシラン等のアリールオキシシランまたはアリールオキシアルコキシシランが挙げられる。
加水分解は、公知の方法で行うことができ、例えば、アルコール又はDMF等の溶媒中、塩酸等の無機酸又は酢酸等の有機酸、および水の存在下で、常温又は加熱した状態で、実施することができる。したがって、加水分解後の反応液中には式(1)で表されるケイ素化合物の加水分解物に加えて、溶媒、酸、水及びこれらに由来する物質を含有してもよい。
なお、加水分解反応に加えて、加水分解物の重縮合反応も部分的に進行する。
ここで、重縮合反応が進行する程度は、加水分解温度、加水分解時間、酸性度、及び/又は、溶媒等によって制御することができ、目的とするポリシルセスキオキサン被覆シリコンナノ粒子に応じて適宜に設定することができる。
反応条件としては、撹拌下、酸性水溶液中に式(1)で表されるケイ素化合物を添加し、-20℃~50℃、好ましくは0℃~40℃、特に好ましくは10℃~30℃の温度で0.5時間~20時間、好ましくは1時間~10時間、特に好ましくは1時間~5時間反応させる。
具体的には、有機酸としてはギ酸、酢酸、プロピオン酸、シュウ酸、クエン酸などが例示され、無機酸としては塩酸、硫酸、硝酸、リン酸などが例示される。これらの中でも加水分解反応およびその後の重縮合反応の制御が容易にでき、入手やpH調整、および反応後の処理も容易であることから塩酸及び酢酸が好ましい。
また、式(1)で表されるケイ素化合物としてトリクロロシラン等のハロゲン化シランを用いた場合には、水の存在下で酸性水溶液が形成されるので、特に酸を別途加える必要は無く、本発明の好ましい態様の一つである。
なお、シリコンナノ粒子は、本発明の効果を損なわない範囲で、ケイ素以外の他の成分を含有していてもよく、例えば、炭素、金属類などを含むことができるが、その含有量は、シリコンナノ粒子に対して、通常5重量%未満である。
一方、シリコンナノ粒子共存下で式(1)のケイ素化合物の加水分解/重合が進める場合は、生成するHPSQ重合体に含まれる鎖状Si-O-Si骨格の末端部がシリコンナノ粒子表面のシラノール骨格と反応すると、そこで重合が停止し、鎖状Si-O-Si構造が保持されることになる。その結果として、式(1)のケイ素化合物単独で反応させた場合と比較して環状Si-O-Si骨格の生成が抑制されるものと考えられる。更に、この割合は、環状化結合の割合は熱処理後も概ね維持されるため、焼成後であっても、I2-1/I2-2>1の状態も維持される。
ポリシルセスキオキサン被覆シリコンナノ粒子焼成物は、上記の方法で得られポリシルセスキオキサン被覆シリコンナノ粒子を非酸化性雰囲気下で、熱処理して得られる。本明細書でいう「非酸化性」は、文言的にはポリシルセスキオキサン被覆シリコンナノ粒子を酸化させないことを意味するものであるが、実質的にはポリシルセスキオキサン被覆シリコンナノ粒子を熱処理する際に二酸化ケイ素の生成を本発明の効果に悪影響を与えない程度に抑えられていればよく(すなわちI1/I2の値が本発明で規定する数値範囲内となればよく)、したがって「非酸化性」もその目的を達成できるように酸素が除去されていればよい。ここで、I1とは、820~920cm-1にあるSi-H結合に由来する最大ピーク(ピーク1)の強度(I1)を言う。このようにして得られたポリシルセスキオキサン被覆シリコンナノ粒子焼成物は、ケイ素(Si)、酸素(O)及び水素(H)を含有しており、一般式SiOxHyで表示される、ポリシルセスキオキサン被覆シリコンナノ粒子焼成物である。
焼成物の上記のピーク1の強度(I1)とピーク2の強度(I2)の比(I1/I2)は、好ましくは0.01から0.35、より好ましくは0.01から0.30、さらに好ましくは0.03から0.20の範囲にあれば、適量のSi-H結合の存在により、リチウムイオン電池の負極活物質とした場合に高い放電容量、良好な初期充放電効率およびサイクル特性を発現させることができる。
非酸化性雰囲気は、不活性ガス雰囲気、高真空により酸素を除去した雰囲気(目的とするポリシルセスキオキサン被覆シリコンナノ粒子焼成物の生成を阻害しない程度に酸素が除去されている雰囲気であればよい)、還元性雰囲気およびこれらの雰囲気を併用した雰囲気が包含される。ここで、不活性ガスとしては、窒素、アルゴン、ヘリウムなどが挙げられる。これらの不活性ガスは、一般に使用されている高純度規格のものであれば問題なく使用できる。また、不活性気体を用いることなく、高真空により酸素を除去した雰囲気でもよい。還元性雰囲気としては、水素などの還元性ガスを含む雰囲気が包含される。例えば、2容積%以上の水素ガスと不活性ガスとの混合ガス雰囲気が挙げられる。また、還元性雰囲気として、水素ガス雰囲気も使用することができる。
したがって、高容量と良好なサイクル特性を共に発現させるには適量のSi-H結合を残存させることが必要となり、そのような条件を満足させる熱処理温度は通常600℃から1000℃、好ましくは750℃から900℃である。600℃未満では放電容量が十分でなく、1000℃を超えるとSi-H結合が消失してしまうため良好なサイクル特性が得られなくなる。
熱処理時間は、特に限定されないが通常15分から10時間、好ましくは30分から5時間である。
次に、前記ポリシルセスキオキサン被覆シリコンナノ粒子焼成物を含むリチウムイオン電池用負極活物質について説明する。
したがって、前記ポリシルセスキオキサン被覆シリコンナノ粒子焼成物に炭素系物質を複合又は被覆させることも本発明の一態様である。
炭素系物質を複合又は被覆させるには、メカノフュージョンやボールミルあるいは振動ミル等を用いた機械的混合法等により、前記ポリシルセスキオキサン被覆シリコンナノ粒子焼成物と炭素系物質を分散させる方法が挙げられる。
本発明に係るリウムイオン二次電池における負極は、前記ポリシルセスキオキサン被覆シリコンナノ粒子焼成物あるいは前記炭素系物質を複合又は被覆させたポリシルセスキオキサン被覆シリコンナノ粒子焼成物を含有する負極活物質を用いて製造される。
負極としては、例えば、ポリシルセスキオキサン被覆シリコンナノ粒子焼成物あるいは前記炭素系物質を複合又は被覆させたポリシルセスキオキサン被覆シリコンナノ粒子焼成物を含む負極活物質および結着剤を含む負極混合材料を一定の形状に成形したものでもよく、該負極混合材料を銅箔などの集電体に塗布させる方法で製造されたものでもよい。負極の成形方法は、特に限定されず、公知の方法を用いることができる。
本発明のポリシルセスキオキサン被覆シリコンナノ粒子焼成物を含んでなる負極活物質を用いたリチウムイオン電池は、次のように製造できる。
まず、リチウムイオンを可逆的に吸蔵及び放出可能な正極活物質、導電助剤、結着剤及び溶媒を混合して正極活物質組成物を準備する。前記正極活物質組成物を負極と同様、公知の方法にて金属集電体上に直接コーティング及び乾燥し、正極極板を準備する。
前記正極活物質組成物を別途、支持体上にキャスティングした後、この支持体から剥離して得たフィルムを金属集電体上にラミネートして正極を製造することも可能である。正極の成形方法は、特に限定されず、公知の方法を用いることができる。
この時、正極活物質、導電助剤、結着剤及び溶媒の含有量は、リチウムイオン電池で一般的に使用することができる量とする。
より具体的には、リチウムイオン電池の場合には、ポリエチレン、ポリプロピレンのような材料からなる巻き取り可能なセパレータを使用し、リチウムイオンポリマー電池の場合には、有機電解液含浸能に優れたセパレータを使用する事が好ましい。
各実施例及び比較例における「赤外分光法測定」、「元素分析測定」、「走査型顕微鏡(SEM)による観察・撮影」、「透過型顕微鏡(TEM)による観察・撮影、及び被覆層の厚さ計測」の測定装置及び測定方法並びに「電池特性の評価」は、以下のとおりである。
赤外分光法測定は、赤外分光装置として、Thermo Fisher Scientific製 Nicolet iS5 FT-IRを用いて、KBr法による透過測定(分解能4cm-1、スキャン回数16回、データ間隔 1.928cm-1、検出器 DTGS KBr)にて、820~920cm-1にあるSi-H結合に由来するピーク1の強度(I1)および、1000~1250cm-1にあるSi-O-Si結合に由来するピーク2の強度(I2)を測定した。なお、各々のピーク強度は、対象のピークの始点と終点を直線で結び、部分的にベースライン補正を行った後、ベースラインからピークトップまでの高さを計測して求めた。Si-O-Si結合に由来するピークは、2箇所に存在するため、ピーク分離を行いピーク位置が1170cm-1~1230cm-1付近の大きなピークの強度をI2-1、1070cm-1付近の大きなピークの強度をI2-2とし、2つのピークのうち高強度なピークの強度をI2と規定した。
元素分析測定については、試料粉末をペレット状に固めたのち、2.3MeVに加速したHeイオンを試料に照射し、後方散乱粒子のエネルギースペクトル、及び前方散乱された水素原子のエネルギースペクトルを解析することにより水素を含めた確度の高い組成値が得られるRBS(ラザフォード後方散乱分析)/HFS(水素前方散乱分析)法により行った。測定装置はNational Electrostatics Corporation製 Pelletron 3SDHにて、入射イオン:2.3MeV He、RBS/HFS同時測定時入射角:75deg.、散乱角:160deg.、試料電流:4nA、ビーム径:2mmφの条件で測定した。
試料粉末を、超高分解能分析走査電子顕微鏡(Hitachi製 商品名SU-70)により観察、撮影した。
試料について、装置名:電界放射型透過分析電子顕微鏡(FEI製 TecnaiG2F20)で観察・撮影した。観察条件は、加速電圧200kVであり、透過電子顕微鏡像は、明視野像であった。また、前処理として、試料粉末を樹脂に包埋し、ウルトラミクロトームにより薄片化した。
被覆層の厚さは、TEMによる撮影した写真に撮影された粒子ごとの被覆層の厚さを計測し、10個の粒子の平均値を算出した。
本発明のポリシルセスキオキサン被覆シリコンナノ粒子焼成物を含有する負極活物質を用いたリチウムイオン二次電池等の充放電特性は、次のようにして測定した。
株式会社ナガノ製BTS2005Wを用い、ポリシルセスキオキサン被覆シリコンナノ粒子焼成物1g重量あたり、100mAの電流で、Li電極に対して0.001Vに達するまで定電流充電し、次に0.001Vの電圧を維持しつつ、電流が活物質1g当たり20mA以下の電流値になるまで定電圧充電を実施した。
充電が完了したセルは、約30分間の休止期間を経た後、活物質1g当たり100mAの電流で電圧が1.5Vに達するまで定電流放電を行った。
また、充電容量は、定電圧充電が終了するまで積算電流値から計算し、放電容量は、電池電圧が1.5Vに到達するまでの積算電流値から計算した。各充放電の切り替え時には、30分間、開回路で休止した。
(ポリシルセスキオキサン被覆シリコンナノ粒子紛体(1)の調製)
100mlポリビーカーに純水70gとシリコンナノパウダー(S’tile社製 Si-10 平均粒径100nm、粒径1000nm以上の粒子は含まない)20.5gを入れ、超音波ホモジナイザーにて2分間処理して、シリコンナノ粒子分散水溶液を作製した。1000mlの三つ口フラスコに、このシリコン微粒子分散液と35重量%濃度の塩酸3.24g(31mmol)及び純水247gを仕込み、室温にて10分攪拌してシリコンナノ粒子を全体に分散させ、撹拌下にトリエトキシシラン(東京化成)60.0g(366mmol)を25℃にて滴下した。滴下終了後、撹拌しながら25℃にて加水分解反応および縮合反応を2時間行った。
反応時間経過後、反応物をメンブランフィルター(孔径0.45μm、親水性)にてろ過し、固体を回収した。得られた固体を80℃にて10時間、減圧乾燥し、ポリシルセスキオキサン被覆シリコンナノ粒子紛体(1)39.2gを得た。
前記ポリシルセスキオキサン被覆シリコンナノ粒子紛体(1)10.0gをSSA-Sグレードのアルミナ製ボートにのせた後、該ボートを真空パージ式チューブ炉 KTF43N1-VPS(光洋サーモシステム社製)にセットし、熱処理条件として、アルゴンガス雰囲気下(高純度アルゴンガス99.999%)にて、アルゴンガスを250ml/分の流量で供給しつつ、4℃/分の割合で昇温し、900℃で1時間焼成することで、ポリシルセスキオキサン被覆シリコンナノ粒子焼成物を得た。
次いで、得られたポリシルセスキオキサン被覆シリコンナノ粒子焼成物を乳鉢にて5分間解砕粉砕し、目開き32μmのステンレス製篩を用いて分級することにより最大粒子径が32μmであるポリシルセスキオキサン被覆シリコンナノ粒子焼成物(1)、9.75gを得た。
得られたポリシルセスキオキサン被覆シリコンナノ粒子焼成物(1)の赤外分光スペクトルを図1に、透過型電子顕微鏡(TEM)による写真を図2、走査型電子顕微鏡(SEM)による写真を図3に示す。被覆層の厚さは、26nmであった。
カルボキシメチルセルロースの2重量%水溶液20g中に、前記ポリシルセスキオキサン被覆シリコンナノ粒子焼成物(1)3.0gと0.4gのデンカ株式会社製アセチレンブラック、及び0.2gの昭和電工株式会社製の気相法炭素繊維(気相成長炭素繊維)VGCF-Hを加え、フラスコ内で攪拌子を用いて15分間混合した後、固形分濃度が15重量%となるよう蒸留水を加え、さらに15分間撹拌してスラリー状組成物を調製した。このスラリー状組成物をプライミックス社製の薄膜旋回型高速ミキサー(フィルミックス40-40型)に移し、回転数20m/sで30秒間、撹拌分散を行った。分散処理後のスラリーを、ドクターブレード法により、銅箔ロール上にスラリーを200μmの厚さにて塗工した。
塗工後、80℃のホットプレートにて90分間乾燥した。乾燥後、負極シートを2t小型精密ロールプレス(サンクメタル社製)にてプレスした。プレス後、φ14.50mmの電極打ち抜きパンチHSNG-EPにて電極を打ち抜き、ガラスチューブオーブンGTO―200(SIBATA社製)にて、80℃で、16時間減圧乾燥を行い、負極を作製した。
図4に示す構造の2032型コイン電池を作製した。負極1として上記負極体、対極3として金属リチウム、セパレータ2として微多孔性のポリプロピレン製フィルムを使用し、電解液としてLiPF6を1モル/Lの割合で溶解させたエチレンカーボネートとジエチルカーボネート1:1(体積比)混合溶媒にフルオロエチレンカーボネートを5重量%添加したものを使用した。
次いで、リチウムイオン電池の電池特性の評価を既述の方法で実施した。
(ポリシルセスキオキサン被覆シリコンナノ粒子紛体(2)の調製)
100mlポリビーカーに純水50gとシリコンナノパウダー(S’tile社製 Si-10 平均粒径100nm、粒径1000nm以上の粒子は含まない)13.58gを入れ、超音波ホモジナイザーにて2分間処理して、シリコンナノ粒子分散水溶液を作製した。500mlの三つ口フラスコに、このシリコン微粒子分散液と35重量%濃度の塩酸2.22g(21mmol)及び純水161gを仕込み、室温にて10分攪拌してシリコンナノ粒子を全体に分散させ、撹拌下にトリエトキシシラン(東京化成)19.9g(121mmol)を25℃にて滴下した。滴下終了後、撹拌しながら25℃にて加水分解反応および縮合反応を2時間行った。
反応時間経過後、反応物をメンブランフィルター(孔径0.45μm、親水性)にてろ過し、固体を回収した。得られた固体を80℃にて10時間、減圧乾燥し、ポリシルセスキオキサン被覆シリコンナノ粒子紛体(2)20.0gを得た。
ポリシルセスキオキサン被覆シリコンナノ粒子粉体(2)10.0gを用い、実施例1と同様の方法で焼成物の調製を行い、ポリシルセスキオキサン被覆シリコンナノ粒子焼成物(2)9.82gを得た。得られたポリシルセスキオキサン被覆シリコンナノ粒子焼成物(2)の赤外分光スペクトルを図1に示す。透過型電子顕微鏡によって撮影したポリシルセスキオキサン被覆シリコンナノ粒子焼成物(2)の被覆層の厚さは、10nmであった。
ポリシルセスキオキサン被覆シリコンナノ粒子焼成物(2)について、実施例1と同様に負極体を作製し、リチウムイオン電池の電池特性を評価した。
(ポリシルセスキオキサン被覆シリコンナノ粒子紛体(3)の調製)
100mlビーカーに純水50gとシリコンナノパウダー(S’tile社製 Si-10 平均粒径100nm、粒径1000nm以上の粒子は含まない)17.6gを入れ、超音波ホモジナイザーにて2分間処理して、シリコンナノ粒子分散水溶液を作製した。500ml三つ口フラスコに、このシリコン微粒子分散液と酢酸(和光特級試薬)1.67g(28mmol)及び純水223gを仕込み、室温にて10分攪拌してシリコンナノ粒子を全体に分散させ、撹拌下にトリエトキシシラン(東京化成)7.36g(44.9mmol)を25℃にて滴下した。滴下終了後、撹拌しながら25℃にて加水分解反応および縮合反応を2時間行った。
反応時間経過後、反応物をメンブランフィルター(孔径0.45μm、親水性)にてろ過し、固体を回収した。得られた固体を80℃にて10時間、減圧乾燥し、ポリシルセスキオキサン被覆シリコンナノ粒子紛体(3)20.0gを得た。
ポリシルセスキオキサン被覆シリコンナノ粒子紛体(3)10.0gを用い、実施例1と同様の方法で焼成物の調製を行い、ポリシルセスキオキサン被覆シリコンナノ粒子焼成物(3)9.88gを得た。透過型電子顕微鏡によって撮影したポリシルセスキオキサン被覆シリコンナノ粒子焼成物(3)の被覆層の厚さは、3nmであった。
ポリシルセスキオキサン被覆シリコンナノ粒子焼成物(3)について、実施例1と同様に負極体を作製し、リチウムイオン電池の電池特性を評価した。
(ポリシルセスキオキサン被覆シリコンナノ粒子紛体(4)の調製)
100mlビーカーに純水50gとシリコンナノパウダー(Nanomakers社製 Pure Si NM Si99 平均粒径75nm、粒径1000nm以上の粒子は含まない)15.5gを入れ、超音波ホモジナイザーにて2分間処理して、シリコンナノ粒子分散水溶液を作製した。500mlの三つ口フラスコに、このシリコン微粒子分散液と35重量%濃度の塩酸2.54g(24 mmol)及び純水190gを仕込み、室温にて10分攪拌してシリコンナノ粒子を全体に分散させ、撹拌下にトリエトキシシラン(東京化成)13.9g(85mmol)を25℃にて滴下した。滴下終了後、撹拌しながら25℃にて加水分解反応および縮合反応を2時間行った。
反応時間経過後、反応物をメンブランフィルター(孔径0.45μm、親水性)にてろ過し、固体を回収した。得られた固体を80℃にて10時間、減圧乾燥し、ポリシルセスキオキサン被覆シリコンナノ粒子粉体(4)20.0gを得た。
ポリシルセスキオキサン被覆シリコンナノ粒子粉体(4)10.0gを用い、実施例1と同様の方法で焼成物の調製を行い、ポリシルセスキオキサン被覆シリコンナノ粒子焼成物(4)9.81gを得た。透過型電子顕微鏡によって撮影したポリシルセスキオキサン被覆シリコンナノ粒子焼成物(4)の被覆層の厚さは、5nmであった。
ポリシルセスキオキサン被覆シリコンナノ粒子焼成物(4)について、実施例1と同様に負極体を作製し、リチウムイオン電池の電池特性を評価した。
前記シリコンナノナノパウダーをNanomakers社製NM SiΩC99(平均粒径75nm、粒径1000nm以上の粒子は含まない)にした以外は実施例4と同様に処理を行い、ポリシルセスキオキサン被覆シリコンナノ粒子焼成物(5)9.84gを得た。透過型電子顕微鏡によって撮影したポリシルセスキオキサン被覆シリコンナノ粒子焼成物(5)の被覆層の厚さは、5nmであった。
得られたポリシルセスキオキサン被覆シリコンナノ粒子焼成物(5)を用い、実施例1と同様の方法で負極体の作製を行い、リチウムイオン二次電池の電池特性を評価した。
市販の一酸化珪素(アルドリッチ社製 under325mesh)を20μmのステンレス製篩を用いて分級することにより最大粒子径が20μmである一酸化ケイ素粉末を得た。該20μm以下の一酸化珪素4.41gを、シリコンナノパウダー(Nanomakers社製 Pure Si NM Si99 平均粒径75nm)11.2gとジルコニア製の容器とジルコニア製ボールを用いて遊星ボールミルにて10分間ボールミリング処理混合し、シリコンナノ粒子混合ケイ素酸化物(1)を得た。該シリコンナノ粒子混合ケイ素酸化物(1)にカルボキシメチルセルロースの2重量%水溶液5gを加え、ジルコニア製の容器とジルコニア製ボールを用いて遊星ボールミルにて2時間ボールミリング処理を行い、真空乾燥機にて100℃で8時間乾燥して水分を除去してシリコンナノ粒子複合ケイ素酸化物(1)15.6gを得た。得られたシリコンナノ粒子混合ケイ素酸化物(1)の赤外分光スペクトルを図1に示す。
比較例1のシリコンナノ粒子複合ケイ素酸化物(1)を用いた以外は、実施例2と同様に行い負極体を作製した。
負極体として、前記シリコンナノ粒子複合ケイ素酸化物(1)から作製された負極を用いた以外は、実施例1のポリシルセスキオキサン被覆シリコンナノ粒子焼成物(1)を用いたときと同様にしてリチウムイオン電池を作製し、それを備えた電池特性を評価した。
2:セパレータ
3:リチウム対極
Claims (8)
- 体積基準平均粒径が10nmを超え500nm未満であり、且つ粒径が1000nm以上の粒子を含まないシリコンナノ粒子と、前記シリコンナノ粒子を被覆し、前記シリコンナノ粒子の表面に化学的に結合しているポリシルセスキオキサンとを含み、
Si-H結合を有し、
透過型電子顕微鏡(TEM)で観察される前記ポリシルセスキオキサンの厚さが、1nm以上30nm以下である、ポリシルセスキオキサン被覆シリコンナノ粒子又はその焼成物。 - 前記ポリシルセスキオキサン被覆シリコンナノ粒子を赤外分光法により測定したスペクトルにおいて、Si-O-Si結合に由来する1000~1250cm-1の吸収帯のうち、1100cm-1より高波数側の吸収帯における最大吸収ピークの強度をI2-1、1100cm-1より低波数側の吸収帯における最大吸収ピークの強度をI2-2とした場合に、強度比(I2-1/I2-2)が、1を超える請求項1に記載のポリシルセスキオキサン被覆シリコンナノ粒子又はその焼成物。
- 前記ポリシルセスキオキサン被覆シリコンナノ粒子を赤外分光法により測定したスペクトルにおいて、Si-H結合に由来する820~920cm-1の吸収帯のうち、最大吸収ピークの強度をI1、Si-O-Si結合に由来する1000~1250cm-1吸収帯のうち、最大吸収ピークの強度をI2とした場合に、強度比(I1/I2)が、0.01から0.35の範囲にある請求項1又は2に記載のポリシルセスキオキサン被覆シリコンナノ粒子の焼成物。
- 請求項1から3のいずれか一項に記載のポリシルセスキオキサン被覆シリコンナノ粒子の焼成物を含むリチウムイオン電池用負極活物質。
- 請求項4に記載のリチウムイオン電池用負極活物質を含むリチウムイオン電池用負極。
- 請求項5に記載のリチウムイオン電池用負極を備えたリチウムイオン電池。
- ポリシルセスキオキサン被覆シリコンナノ粒子又はその焼成物の製造方法であって、
前記ポリシルセスキオキサン被覆シリコンナノ粒子は、体積基準平均粒径が10nmを超え500nm未満であり、且つ粒径が1000nm以上の粒子を含まないシリコンナノ粒子と、前記シリコンナノ粒子を被覆し、前記シリコンナノ粒子の表面に化学的に結合しているポリシルセスキオキサンとを含み、
Si-H結合を有し、
透過型電子顕微鏡(TEM)で観察される前記ポリシルセスキオキサンの厚さが、1nm以上30nm以下であり、
前記製造方法は、シリコンナノ粒子の存在下で、式(1)で示されるケイ素化合物を加水分解および縮合反応させる工程を含む、製造方法。
HSi(R)3 (1)
(式中、Rは、それぞれ同一あるいは異なる、ハロゲン、水素、炭素数1~10の置換または非置換のアルコキシ、炭素数6~20の置換または非置換のアリールオキシ、および炭素数7~30の置換または非置換のアリールアルコキシから選択される基である。但し、炭素数1~10の置換または非置換のアルコキシ基、炭素数6~20の置換または非置換のアリールオキシ基、および炭素数7~30の置換または非置換のアリールアルコキシ基において、任意の水素はハロゲンで置換されていてもよい。) - 加水分解及び縮合反応させる工程の後に、非酸化性雰囲気下で焼成する工程をさらに含む、請求項7に記載のポリシルセスキオキサン被覆シリコンナノ粒子の焼成物の製造方法。
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JP2020059631A (ja) * | 2018-10-11 | 2020-04-16 | 学校法人東京電機大学 | 微細突起を有するシリコン微粒子の製造方法、及びシリコン微粒子 |
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JP2020138895A (ja) * | 2019-03-01 | 2020-09-03 | Jnc株式会社 | シリコン系微粒子/シリコン含有ポリマー複合体、SiOC構造体、並びにSiOC構造体を用いた負極用組成物、負極及び二次電池 |
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US20190363354A1 (en) | 2019-11-28 |
US11031591B2 (en) | 2021-06-08 |
KR20190069573A (ko) | 2019-06-19 |
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