WO2018131606A1 - シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体及びその製造方法、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
シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体及びその製造方法、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 silicon nanoparticle-containing hydrogen polysilsesquioxane fired product-metal oxide composite and a method for producing the same. Furthermore, a negative electrode active material for a lithium ion battery including the silicon nanoparticle-containing hydrogen polysilsesquioxane fired product-metal oxide complex, a negative electrode for a lithium ion battery including the negative electrode active material, and a negative electrode for the lithium ion battery The present invention relates to a lithium ion battery including
- 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 discloses that a material in which a silicon oxide having a silicon concentration gradient is coated with titanium oxide is used as a negative electrode active material of a lithium ion secondary battery, thereby obtaining a battery having a high capacity and improved cycle characteristics.
- Patent Document 3 proposes that a material in which silicon oxide particles on which silicon nanoparticles are dispersed is coated with titanium oxide is used as a negative electrode material for a secondary battery.
- Non-Patent Document 1 discloses that a material in which silicon oxide is coated with anatase-type titanium oxide is used as a negative electrode material for a lithium ion battery.
- any known technique using a material obtained by coating titanium oxide on a silicon oxide compound has a certain degree of improvement in initial capacity and cycle characteristics, repeated charging and discharging are performed.
- the capacity that can be used reversibly decreases gradually, and cycle characteristics that can withstand practical use have not been obtained.
- the production method of the negative electrode material is inferior in productivity, and as a result, is a technique that requires high costs.
- Lithium ion secondary battery negative electrode active materials are still required to solve such problems of conventional negative electrode materials, extremely suppress charge / discharge cycle deterioration, and exhibit excellent charge / discharge characteristics at a high capacity. It has been. Further, the manufacturing method is required to be excellent in productivity.
- the subject of this invention is providing the negative electrode active material for secondary batteries which can respond to such a request
- the present inventors have obtained excellent charge / discharge cycle characteristics when a specific silicon nanoparticle-containing hydrogen polysilsesquioxane fired product-metal oxide composite is used. It has been found that the present invention provides a lithium ion battery having a high capacity, an excellent initial charge / discharge efficiency, and a capacity retention rate.
- a silicon nanoparticle-containing hydrogen polysilsesquioxane calcined product-metal oxide composite comprising a silicon nanoparticle-containing hydrogen polysilsesquioxane calcined product and a metal oxide
- the silicon nanoparticle-containing hydrogen polysilsesquioxane baked product is: 5% to 95% by weight of silicon nanoparticles having a volume-based average particle size of more than 10 nm and less than 500 nm, and a hydrogen polysilsesquion that covers the silicon nanoparticles and chemically bonds to the surface of the silicon nanoparticles.
- Oxan-derived silicon oxide structure It is represented by the general formula SiO x H y (0.01 ⁇ x ⁇ 1.35, 0 ⁇ y ⁇ 0.35), A silicon nanoparticle-containing hydrogen polysilsesquioxane fired product having a Si—H bond,
- the metal oxide is a metal oxide composed of one or more kinds of metals selected from titanium, zinc, zirconium, aluminum, and iron, silicon nanoparticle-containing hydrogen polysilsesquioxane fired product-metal oxide Complex.
- the silicon nanoparticles according to any one of [1] to [3], wherein at least part of the surface of the silicon nanoparticle-containing hydrogen polysilsesquioxane baked product is coated with the metal oxide. Containing hydrogen polysilsesquioxane fired product-metal oxide composite.
- the silicon nanoparticle-containing hydrogen polysilsesquioxane fired product-metal oxide composite contains more than 0 wt% and 10 wt% or less of the metal oxide, either [1] or [4] 2.
- a negative electrode active material for a lithium ion battery comprising the silicon nanoparticle-containing hydrogen polysilsesquioxane fired product-metal oxide complex according to any one of [1] to [6].
- a negative electrode for a lithium ion battery comprising the negative electrode active material for a lithium ion battery according to [7].
- a method for producing a silicon nanoparticle-containing hydrogen polysilsesquioxane fired product-metal oxide composite comprising a silicon nanoparticle-containing hydrogen polysilsesquioxane fired product and a metal oxide
- the silicon nanoparticle-containing hydrogen polysilsesquioxane baked product is: 5% to 95% by weight of silicon nanoparticles having a volume-based average particle size of more than 10 nm and less than 500 nm, and a hydrogen polysilsesquion that covers the silicon nanoparticles and chemically bonds to the surface of the silicon nanoparticles.
- Oxan-derived silicon oxide structure It is represented by the general formula SiO x H y (0.01 ⁇ x ⁇ 1.35, 0 ⁇ y ⁇ 0.35), A silicon nanoparticle-containing hydrogen polysilsesquioxane fired product having a Si—H bond,
- the metal oxide is a metal oxide composed of one or more metals selected from titanium, zinc, zirconium, aluminum, and iron,
- the manufacturing method includes: By hydrolyzing the solution containing the metal alkoxide of the metal oxide in the presence of the silicon nanoparticle-containing hydrogen polysilsesquioxane fired product, the silicon nanoparticle-containing hydrogen polysilsesquioxane fired product is obtained.
- the lithium ion battery using the sintered silicon nanoparticle-containing hydrogen polysilsesquioxane-metal oxide composite of the present invention as a negative electrode active material can only be charged and discharged at high speed by the composite of metal oxide.
- a specific silicon nanoparticle-containing hydrogen polysilsesquioxane fired product is used, it has excellent charge / discharge cycle characteristics, high capacity, and excellent initial charge / discharge efficiency and capacity retention rate.
- FIG. 1 shows the silicon nanoparticle-containing hydrogen polysilsesquioxane calcined product (3) obtained in Example 3 by infrared spectroscopy (IR), and the silicon nanoparticle-containing hydrogen polysilsesquiz obtained in Comparative Example 1.
- the figure which shows IR absorption spectrum of the silicon monoxide powder obtained in the oxan fired product (5), the silicon nanoparticle-containing hydrogen polysilsesquiosan fired product (6) obtained in Comparative Example 2, and Comparative Example 3. is there.
- FIG. 2 is a diagram showing a spectrum of X-ray photoelectron spectroscopy analysis of the silicon nanoparticle-containing hydrogen polysilsesquioxane fired product-titanium oxide composite (1) obtained in Example 1.
- FIG. 3 is a scanning electron microscope (SEM) photograph of the silicon nanoparticle-containing hydrogen polysilsesquioxane fired product-titanium oxide composite (4) obtained in Example 4.
- FIG. 4 is a diagram illustrating a configuration example of a coin-type lithium ion battery.
- the silicon nanoparticle-containing hydrogen polysilsesquioxane calcined product-metal oxide composite of the present invention is obtained by combining a silicon nanoparticle-containing hydrogen polysilsesquioxane calcined product with a metal oxide and heat-treating it. be able to.
- the silicon nanoparticle-containing hydrogen polysilsesquioxane fired product is obtained by firing silicon nanoparticle-containing hydrogen polysilsesquioxane (a precursor of silicon nanoparticle-containing hydrogen polysilsesquioxane fired product). be able to.
- the silicon nanoparticle-containing hydrogen polysilsesquioxane will be described, then the silicon nanoparticle-containing hydrogen polysilsesquioxane fired product, and then the silicon nanoparticle-containing hydrogen polysilsesquioxane fired product-metal The oxide composite will be described.
- Silicon nanoparticle-containing hydrogen polysilsesquioxane synthesizes a hydrogen silsesquioxane polymer (HPSQ) by hydrolyzing and condensing a silicon compound represented by formula (1) (also referred to as polycondensation reaction).
- HPSQ hydrogen silsesquioxane polymer
- 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, silicon nanoparticle-containing hydrogen polysilsesquioxane can be easily obtained. Moreover, when the silicon compound represented by Formula (1) is used, the silicon nanoparticle-containing hydrogen polysilsesquioxane obtained when the obtained silicon nanoparticle-containing hydrogen polysilsesquioxane is heat-treated in a non-oxidizing atmosphere. There is also an advantage that it is easy to control the amount of Si—H bonds in the fired product of oxan.
- the hydrolysis and polycondensation reaction of a mixture obtained by adding silicon nanoparticles to the silicon compound represented by the formula (1) will be described.
- Hydrolysis can be carried out in a known manner, 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 normal temperature or in a heated state. 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 and the like, for example, as described later, the target silicon nanoparticle-containing hydrogen It can set suitably according to polysilsesquioxane.
- 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.
- Silicon nanoparticle-containing hydrogen polysilsesquioxane (precursor of silicon nanoparticle-containing hydrogen polysilsesquioxane calcined product) is obtained by hydrolyzing and polymerizing the compound of formula (1) in the presence of silicon nanoparticles. Can be obtained by doing
- 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. Usually less than 5% by weight with respect to the particles. And silicon nanoparticles essentially free of carbon or metal can also be used.
- 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 usually blended in an amount of 5 to 95% by weight with respect to the silicon nanoparticle-containing hydrogen polysilsesquioxane fired product. When it is 5% by weight or more, when the fired product is used as a negative electrode active material of a lithium ion battery, the initial charge / discharge efficiency is high, and the effect of being combined with silicon nanoparticles is obtained, and it is 95% by weight or less. When used as a negative electrode active material of a lithium ion battery, the expansion / contraction rate of the negative electrode active material due to charge / discharge does not increase due to stress relaxation of the composite hydrogen silsesquioxane, and the capacity retention rate is maintained.
- the lower limit of the amount of silicon nanoparticles is preferably 10% by weight or more, more preferably 20% by weight or more.
- the upper limit of the amount of silicon nanoparticles is preferably 90% by weight or less, more preferably 80% by weight or less.
- the liquid fraction is separated and removed by a known method such as filtration, centrifugation, or tilting, and in some cases, further washed with water or organic solvent, and then dried, and the present invention.
- the silicon nanoparticle-containing hydrogen polysilsesquioxane can be obtained.
- the intensity of the maximum absorption peak (peak 2-1) in the absorption band is I 2-1
- the intensity of the maximum absorption peak (peak 2-2) in the absorption band on the lower wavenumber side than 1100 cm ⁇ 1 is I 2-2
- the intensity ratio (I 2-1 / I 2-2 ) may exceed 1.
- 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 nanoparticles 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 absorption band on the higher wave number side than 1100 cm ⁇ 1 is derived from the linear bond of siloxane
- the absorption band on the lower wave number side than 1100 cm ⁇ 1 is It is attributed to being derived from both linear and cyclic bonds of siloxane.
- the silicon nanoparticles and the hydrogen polysilsesquioxane form a network through a strong chemical bond (Si—O—Si bond).
- This network is maintained even after firing, and the hydrogen polysilsesquioxane skeleton acts as a buffer layer for the expansion and contraction of silicon nanoparticles, and as a result, suppresses the refinement of silicon nanoparticles generated during repeated charge and discharge It is inferred that
- the silicon nanoparticle-containing hydrogen polysilsesquioxane thus obtained has primary particles which are spherical particles having a submicron particle size further aggregated to form secondary aggregates having a particle size of several microns.
- the small primary particles relieve the stress during expansion and contraction that occurs during repeated charge and discharge when the fired product of silicon nanoparticle-containing hydrogen polysilsesquioxane is used as a negative electrode material for a lithium ion battery. As a result, 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 silicon nanoparticle-containing hydrogen polysilsesquioxane baked product is obtained by heat-treating the silicon nanoparticle-containing hydrogen polysilsesquioxane obtained by the above method in a non-oxidizing atmosphere.
- non-oxidizing means that the silicon nanoparticle-containing hydrogen polysilsesquioxane is not oxidized, but the silicon nanoparticle-containing hydrogen polysilsesquioxane is substantially not oxidized.
- I 1 refers to the intensity of the peak having the maximum absorption intensity (peak 1) in the absorption band of 820 to 920 cm ⁇ 1 derived from the Si—H bond in the spectrum measured by infrared spectroscopy. .
- the silicon nanoparticle-containing hydrogen polysilsesquioxane fired product contains silicon (Si), oxygen (O) and hydrogen (H), and has a general formula of SiO x H y (0.01 ⁇ x ⁇ 1). .35, 0 ⁇ y ⁇ 0.35).
- the initial charge / discharge efficiency and the cycle capacity retention ratio are balanced with sufficient battery capacity.
- a negative electrode active material having excellent charge / discharge characteristics can be obtained.
- the obtained secondary battery has improved charge / discharge capacity and capacity retention rate. It has good cycle characteristics.
- the fired product of silicon nanoparticle-containing hydrogen polysilsesquioxane has a maximum absorption peak (peak 1) out of an absorption band of 820 to 920 cm ⁇ 1 derived from Si—H bonds in the spectrum measured by infrared spectroscopy.
- intensity ratio (I 1 / I 2 ) is preferably in the range of 0.01 to 0.35.
- 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. 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 high wavenumber side is I 2-1
- the intensity of the maximum absorption peak (peak 2-2) in the absorption band on the low wavenumber side from 1100 cm ⁇ 1 is I 2 ⁇
- the intensity ratio (I 2-1 / I 2-2 ) is preferably more than 1.
- the heat treatment of the silicon nanoparticle-containing hydrogen polysilsesquioxane is preferably performed in a non-oxidizing atmosphere.
- a non-oxidizing atmosphere includes an inert gas atmosphere, an atmosphere from which oxygen is removed by high vacuum (an atmosphere from which oxygen is removed to the extent that it does not hinder the formation of the desired silicon nanoparticle-containing hydrogen polysilsesquioxane baked product) A reducing atmosphere and an atmosphere in which these atmospheres are used in combination.
- the inert gas include nitrogen, argon, helium and the like.
- 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 heat treatment time is not particularly limited, but is usually 15 minutes to 10 hours, preferably 30 minutes to 5 hours.
- the silicon nanoparticle-containing hydrogen polysilsesquioxane fired product is obtained by the above heat treatment, and the above-described elemental analysis results show that SiO x H y (0.01 ⁇ x ⁇ 1.35, 0 ⁇ y ⁇ 0. 35) and the ratio (I 1 / I 2 ) of the intensity (I 1 ) of peak 1 and the intensity (I 2 ) of peak 2 by infrared spectroscopy is in the range of 0.01 to 0.35. What is necessary is just to select the heat processing conditions suitably.
- the silicon nanoparticle-containing hydrogen polysilsesquioxane calcined product that can be used in the present invention thus obtained is obtained by heat-treating the silicon nanoparticle-containing hydrogen polysilsesquioxane obtained by the synthesis method of the present invention.
- the shape is such that primary particles, which are spherical particles having a particle size of submicron, further aggregate to form secondary aggregates having a particle size of several microns.
- the silicon nanoparticle-containing hydrogen polysilsesquioxane fired product-metal oxide composite has a small primary particle, so that when it is used as a negative electrode material for a lithium ion battery, By relaxing the stress, 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 silicon nanoparticle-containing hydrogen polysilsesquioxane baked product-metal oxide composite is a composite of a metal oxide and a heat treatment of the silicon nanoparticle-containing hydrogen polysilsesquioxane baked product obtained by the above method. Can be obtained. Therefore, first, a method for producing a silicon nanoparticle-containing hydrogen polysilsesquioxane fired product-metal oxide composite precursor (compositing a silicon nanoparticle-containing hydrogen polysilsesquioxane fired product with a metal oxide) explain.
- composite means that the metal oxide is fused and integrated with the silicon nanoparticle-containing hydrogen polysilsesquioxane fired product, and the silicon nanoparticle-containing hydrogen polysilsesquioxane is integrated.
- covers covers is also included.
- the silicon nanoparticle-containing hydrogen polysilsesquioxane baked product-metal oxide composite is preferably such that the metal oxide covers the silicon nanoparticle-containing hydrogen polysilsesquioxane baked product particles.
- the coating does not need to cover the entire particle, and it is sufficient that a part of the silicon nanoparticle-containing hydrogen polysilsesquioxane baked product is covered.
- Various methods can be used as a method of coating the metal nanoparticles on the silicon nanoparticle-containing hydrogen polysilsesquioxane baked product.
- a method of adding a silicon nanoparticle-containing hydrogen polysilsesquioxane fired product to a suspension in which metal oxide particles are suspended in a solvent followed by filtration, drying, and the like. Suspends the fired product of silicon nanoparticle-containing hydrogen polysilsesquioxane in a liquid metal alkoxide, and then causes a condensation reaction to form a metal oxide coating on the surface of the fired product of silicon nanoparticle-containing hydrogen polysilsesquioxane. It is a method of coating and drying.
- a metal oxide containing at least one selected from titanium, zinc, zirconium, aluminum, and iron is preferable, and an oxide containing titanium is more preferable.
- an oxide containing titanium a metal oxide containing 80% by weight or more of titanium with respect to all metal elements is preferable, and a metal oxide containing 90% by weight or more of titanium is preferable.
- examples of such a metal oxide include a metal oxide (that is, titanium oxide) that is titanium except for impurities as a metal element.
- the metal oxide further includes hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, ruthenium, cobalt, rhodium, iridium, nickel, palladium, cerium, indium, germanium, bismuth, antimony, cadmium, copper
- at least one member of the group consisting of silver may be included as a constituent element.
- Examples of the raw material used for coating the metal oxide include metal alkoxide.
- the coating is made of titanium oxide, it is alkoxy titanium.
- As the alkoxy titanium tetraalkoxy titanium (titanium tetraalkoxide), aryloxy is used. Trialkoxytitanium, diaryl dialkoxytitanium and the like can be mentioned.
- Tetraalkoxy titanium is preferred, and specific examples include tetraoctoxy titanium, tetra n-butoxy titanium, tetra i-propoxy titanium, tetrakis (2-ethylhexyloxy) titanium and the like.
- the condensation reaction of the silicon nanoparticle-containing hydrogen polysilsesquioxane baked product in suspension and a metal alkoxide such as alkoxytitanium is a known method, for example, in a solvent such as alcohol or DMF, and if necessary, such as hydrochloric acid. It can be carried out at room temperature or under heating in the presence of an inorganic acid and / or an organic acid such as acetic acid and water.
- the reaction conditions are ⁇ 20 ° C. to 50 ° C., preferably 0 ° C. to 40 ° C., particularly preferably 10 ° C. to 30 ° C., for 0.5 hours to 20 hours, preferably 1 hour to 10 hours with stirring.
- the reaction is particularly preferably carried out for 1 to 5 hours.
- the usage ratio of the silicon nanoparticle-containing hydrogen polysilsesquioxane fired product and the metal alkoxide is such that the metal oxide is based on the silicon nanoparticle-containing hydrogen polysilsesquioxane fired product-metal oxide complex as a whole.
- it is used in a range of more than 0% by weight and 10% by weight or less, preferably 0.1% by weight or more and 10% by weight or less, more preferably 0.2% by weight or more and 8% by weight or less.
- the condensation reaction After completion of the condensation reaction, it is dried under reduced pressure, or the liquid part is separated and removed by filtration or centrifugation, etc., and in some cases, after washing with a solvent and dried, the silicon nanoparticle-containing hydrogen polysilsesquioxane baked product-metal An oxide composite precursor can be obtained.
- the silicon nanoparticle-containing hydrogen polysilsesquioxane calcined product-metal oxide composite is inert to the silicon nanoparticle-containing hydrogen polysilsesquioxane calcined product-metal oxide composite precursor obtained by the above method. Obtained by heat treatment in a gas atmosphere.
- the heat treatment temperature at which high-capacity and excellent charge / discharge characteristics are exhibited, in which charge / discharge cycle deterioration is extremely suppressed is 200 ° C. to 900 ° C., preferably 250 ° C. to 850 ° C., more preferably 250 ° C. to 800 ° C.
- the heat treatment time is not particularly limited, but is usually 30 minutes to 10 hours, preferably 1 hour to 8 hours.
- the silicon nanoparticle-containing hydrogen polysilsesquioxane fired product-metal oxide composite obtained in this way has a metal oxide on or inside the silicon nanoparticle-containing hydrogen polysilsesquioxane fired product. It is a composite.
- the silicon nanoparticle-containing hydrogen polysilsesquioxane fired product-metal oxide composite obtained in the example is attributed to titanium 2p electrons of titanium oxide by X-ray photoelectron spectroscopy analysis (see FIG. 2). A peak and a peak attributed to oxygen 1s electrons of titanium oxide are confirmed.
- the silicon nanoparticle-containing hydrogen polysilsesquioxane baked product-metal oxide composite of the example the silicon nanoparticle-containing hydrogen polysilsesquioxane baked product was coated in a titanium oxide state. It is thought that.
- the following three actions are conceivable as functions of the composite metal oxide, particularly titanium oxide.
- the first is to impart conductivity to the active material.
- titanium oxide itself is an insulator, it becomes a conductor when electrons are injected into the conduction band by inserting lithium, and the electron conductivity on the surface of the active material can be greatly improved during charging.
- the second is to promote the delivery of lithium at the active material-electrolyte interface.
- Charging reaction of silicon nanoparticle-containing hydrogen polysilsesquioxane calcined product requires a large amount of energy for the reaction to proceed with the cleavage of the silicon-oxygen bond. As a result, the active barrier at the electrolyte-active material interface is reduced, and a smooth charge / discharge reaction can proceed.
- the third is the shape stabilization effect. Since titanium oxide can be desorbed and inserted without causing structural changes, when titanium oxide is placed on the surface, it stabilizes the shape and suppresses the decomposition reaction of the electrolyte due to the loss of the active material or the emergence of a new surface. Can do.
- the silicon oxide used in the present invention itself has a high charge / discharge cycle stability, but it is considered that coating with titanium oxide adds the above-described action to obtain a higher charge / discharge cycle stability. .
- the above effects are not only found in titanium oxide but also in metal oxides containing zinc, zirconium, aluminum, iron and the like.
- the present invention to combine or coat a carbon-based material on the silicon nanoparticle-containing hydrogen polysilsesquioxane fired product-metal oxide composite.
- the carbon-based material in the silicon nanoparticle-containing hydrogen polysilsesquioxane fired product-metal oxide composite is formed by a mechanical mixing method using mechanofusion, a ball mill, or a vibration mill. A method of dispersing a substance is 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 silicon nanoparticle-containing hydrogen polysilsesquioxane fired product-metal oxide composite and the carbon-based material can be combined or coated at an arbitrary ratio.
- the negative electrode in the lithium ion secondary battery is a fired product of silicon nanoparticle-containing hydrogen polysilsesquioxane-metal oxide composite or a fired product of silicon nanoparticle-containing hydrogen polysilsesquioxane coated or coated with the carbon-based material.
- a negative electrode active material containing a metal oxide composite examples include silicon nanoparticle-containing hydrogen polysilsesquioxane baked product-metal oxide composite, or silicon nanoparticle-containing hydrogen polysilsesquioxane baked product composited or coated with the carbon-based material-metal oxide.
- a negative electrode active material containing a composite material and a negative electrode mixed material containing a binder may be formed into a fixed shape, or may be manufactured by a method of applying the negative electrode mixed material to a current collector such as a copper foil. Good.
- the method for forming the negative electrode is not particularly limited, and a known method can be used.
- a silicon nanoparticle-containing hydrogen polysilsesquioxane baked product-metal oxide composite or a silicon nanoparticle-containing hydrogen polysilsesquioxane baked product-metal oxide obtained by combining the carbon-based material.
- a negative electrode active material containing a composite, a binder, and, if necessary, a negative electrode material composition containing a conductive material, etc. are prepared, and this is a rod-shaped body mainly composed of copper, nickel, stainless steel, a plate-shaped body, A current collector such as a foil-like body or a net-like body is directly coated, or a negative electrode material composition is separately cast on a support, and a negative electrode active material film peeled off from the support is laminated on the current collector.
- a negative electrode plate can be obtained.
- 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.
- a lithium ion battery using a negative electrode active material containing a silicon nanoparticle-containing hydrogen polysilsesquioxane fired product-metal oxide composite can be manufactured 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.
- 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 mixed solvent thereof.
- a solvent such as methyldioxolane, N, N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide, dioxan
- 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 aspect of the silicon nanoparticle-containing hydrogen polysilsesquioxane baked product-metal oxide composite is a silicon nanoparticle used in the silicon nanoparticle-containing hydrogen polysilsesquioxane baked product-metal oxide composite.
- the particle-containing hydrogen polysilsesquioxane fired product has a maximum absorption peak in an absorption band of 820 to 920 cm ⁇ 1 derived from the Si—H bond in the spectrum measured by infrared spectroscopy.
- the intensity ratio (I 1 / I 2 ) is in the range of 0.01 to 0.35, and the general formula SiO x H y (0.01 ⁇ x ⁇ 1.35, 0 ⁇ y as shown in the elemental analysis values in Table 1) ⁇ 0.35) is a silicon nanoparticle-containing hydrogen polysilsesquioxane fired product represented by ⁇ 0.35).
- a lithium ion battery manufactured using a negative electrode active material comprising a silicon nanoparticle-containing hydrogen polysilsesquioxane fired material-metal oxide composite having these characteristics has a high capacity and good initial charge / discharge efficiency. Excellent cycle characteristics.
- silicon nanoparticle-containing hydrogen polysilsesquioxane baked product-metal oxide composite is a silicon nanoparticle-containing hydrogen polysiloxane used in the silicon nanoparticle-containing hydrogen polysilsesquioxane baked product-metal oxide composite.
- Rusesukiokisan baked product the maximum in the spectrum measured by infrared spectroscopy, of the absorption band of 1000 ⁇ 1250 cm -1 derived from Si-O-Si bond, the absorption band from 1100 cm -1 high frequency side
- the intensity of the absorption peak (peak 2-1) is I 2-1
- the intensity of the maximum absorption peak (peak 2-2) in the absorption band on the lower wavenumber side than 1100 cm ⁇ 1 is I 2-2
- the intensity ratio (I 2-1 / I 2-2 ) is a fired product of silicon nanoparticle-containing hydrogen polysilsesquioxane characterized by exceeding 1.
- Such a silicon nanoparticle-containing hydrogen polysilsesquioxane fired product has a strong chemical bond (Si-O-Si bond) between the surface of the silicon nanoparticle and the silicon oxide structure (derived from hydrogen polysilsesquioxane). It is suggested that a network is formed. This network is maintained even after firing, and the skeleton of the silicon oxide structure serves as a buffer layer for the expansion and contraction of the silicon nanoparticles. As a result, miniaturization of the silicon nanoparticles generated during repeated charge and discharge is suppressed. It is inferred that
- Infrared spectroscopy measurement Infrared spectroscopy measurement is performed by using a Nicolet iS5 FT-IR manufactured by Thermo Fisher Scientific as an infrared spectroscopic apparatus, and transmission measurement by the KBr method (resolution: 4 cm ⁇ 1 , number of scans: 16 times, data interval: 1.928 cm ⁇ 1 , In the detector DTGS KBr), the intensity of the peak 1 derived from the Si—H bond at 820 to 920 cm ⁇ 1 (I 1 ) and the peak 2 derived from the Si—O—Si bond at 1000 to 1250 cm ⁇ 1 Intensity (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 silicon, oxygen, and titanium contents were measured by RBS spectrum analysis, and the hydrogen content was measured by analysis using RBS and HFS spectra.
- RBS Rutherford backscattering analysis
- HFS hydrogen forward scattering analysis
- the measurement apparatus was 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 ⁇ .
- the titanium oxide coating layer was analyzed using an X-ray photoelectron spectrometer PHI Quanara SXM [ULVAC-PHI] with an AlK ⁇ monochromatic X-ray source, output 15 kV / 25 W, beam diameter 100 ⁇ m ⁇ , and Ti2p, O1s The state of the complex was identified from the peak position and peak shape.
- a lithium ion battery was prepared using a negative electrode active material containing a sample of a predetermined example or comparative example, and the charge / discharge characteristics of the battery were measured as follows. Using BTS2005W manufactured by Nagano Co., Ltd., charged with constant current at a current of 100 mA per 1 g of silicon nanoparticle-containing hydrogen polysilsesquioxane calcined product-metal oxide complex until reaching 0.001 V against the Li electrode, Next, constant voltage charging was carried out while maintaining a voltage of 0.001 V until the current reached a current value of 20 mA or less per gram of active material.
- the cell that had been fully charged was subjected to a constant current discharge at a current of 100 mA per gram of active material until the voltage reached 1.5 V after a rest period of about 30 minutes.
- the charge capacity is calculated from the integrated current value until the constant voltage charge is completed, and the discharge capacity is calculated from the integrated current value until the battery voltage reaches 1.5 V, and the initial discharge capacity is calculated as the initial charge capacity.
- the value obtained by dividing the value by the capacity in terms of 100 minutes was defined as the initial charge / discharge efficiency.
- the circuit was paused for 30 minutes.
- the charge / discharge cycle characteristics were also performed under the same conditions.
- the charge / discharge efficiency was the ratio of the discharge capacity to the initial (first charge / discharge cycle) charge capacity
- the capacity retention ratio was the ratio of the discharge capacity at the 100th charge / discharge cycle to the initial discharge capacity.
- Example 1 Preparation of silicon nanoparticle-containing hydrogen polysilsesquioxane powder (1)
- a 500 ml three-necked flask is charged with this silicon nanoparticle dispersion, 2.43 g (24 mmol) of hydrochloric acid having a concentration of 36% by weight and 218.6 g of pure water, and stirred at room temperature for 10 minutes to make silicon nanoparticles as a whole.
- 45 g (274 mmol) of triethoxysilane manufactured by Tokyo Chemical Industry Co., Ltd. was added dropwise at 25 ° C. while stirring. After completion of the dropwise addition, 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 16.4 g of hydrogen nanopolysilsesquioxane powder (1) containing silicon nanoparticles.
- the silicon nanoparticle-containing hydrogen polysilsesquioxane 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 silicon having a maximum particle size of 32 ⁇ m. 9.58 g of nanoparticle-containing hydrogen polysilsesquioxane baked product (1) was obtained.
- the whole flask was transferred to a vacuum dryer and heated under reduced pressure at 60 ° C. for 1 hour to recover silicon nanoparticle-containing hydrogen polysilsesquioxane calcined product-titanium oxide composite precursor powder (1). .
- This slurry composition was transferred to a thin film swirl type high speed mixer (Filmix 40-40 type) manufactured by Plymix Co., Ltd., and stirred and dispersed at a rotational speed of 20 m / s for 30 seconds.
- the slurry after the dispersion treatment was applied to a copper foil roll with a thickness of 200 ⁇ m by a doctor blade method.
- the negative electrode sheet was pressed with a 2t small precision roll press (manufactured by Sank Metal). After pressing, an 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 (SIBATA) to prepare a negative electrode body.
- a 2t small precision roll press manufactured by Sank Metal.
- an 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 (SIBATA) to prepare a negative electrode body.
- Example 2 (Preparation of silicon nanoparticle-containing hydrogen polysilsesquioxane powder (2)) Put 200 g of pure water and 19.2 g of silicon nanopowder (Sigma Aldrich, ⁇ 100 nm (volume-based average particle diameter, but exceeds 10 nm)) in a 500 ml poly beaker, and use an ultrasonic cleaner to prepare a silicon nanoparticle dispersed aqueous solution. Prepared. A 3 l separable flask was charged with this silicon nanoparticle dispersion, 12.2 g (120 mmol) of 36 wt% hydrochloric acid and 0.94 kg of pure water, and stirred at room temperature for 10 minutes to disperse the entire silicon nanoparticles.
- silicon nanopowder Sigma Aldrich, ⁇ 100 nm (volume-based average particle diameter, but exceeds 10 nm)
- trimethoxysilane manufactured by Tokyo Chemical Industry Co., Ltd.
- 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 95.2 g of silicon nanoparticle-containing hydrogen polysilsesquioxane powder (2).
- Example 3 Preparation of silicon nanoparticle-containing hydrogen polysilsesquioxane powder (3)
- the amount of silicon nanopowder Sigma Aldrich, less than 100 nm (volume-based average particle size, but more than 10 nm)
- Preparation was carried out in the same procedure as in Example 2 to obtain silicon nanoparticle-containing hydrogen polysilsesquioxane powder (3).
- Example 4 (Production of silicon nanoparticle-containing hydrogen polysilsesquioxane baked product-titanium oxide composite (4)) The same as Example 1 except that the amount of tetraisopropoxytitanium (Alfa Aesar 95% reagent) was changed to 0.87 g using the silicon nanoparticle-containing hydrogen polysilsesquioxane powder (3). The coating treatment was performed according to the procedure and the heat treatment was performed to obtain a silicon nanoparticle-containing hydrogen polysilsesquioxane fired product-titanium oxide composite (4).
- FIG. 3 shows a photograph of the obtained silicon nanoparticle-containing hydrogen polysilsesquioxane fired product-titanium oxide composite (4) taken with an electron microscope (SEM).
- Example 5 (Production of silicon nanoparticle-containing hydrogen polysilsesquioxane fired product-titanium oxide composite (5)) The same procedure as in Example 1 except that the amount of tetraisopropoxytitanium (Alfa Aesar 95% reagent) was changed to 2.54 g using the silicon nanoparticle-containing hydrogen polysilsesquioxane powder (3). The coating treatment was performed according to the procedure and the heat treatment was performed to obtain a silicon nanoparticle-containing hydrogen polysilsesquioxane fired product-titanium oxide composite (5).
- Example 6 Preparation of silicon nanoparticle-containing hydrogen polysilsesquioxane powder (4)
- preparation was carried out in the same procedure as in Example 2, except that the amount of trimethoxysilane (manufactured by Tokyo Chemical Industry Co., Ltd.) was changed to 23.9 g.
- trimethoxysilane manufactured by Tokyo Chemical Industry Co., Ltd.
- a silicon nanoparticle-containing hydrogen polysilsesquioxane powder (4) was obtained.
- Table 1 shows the results of infrared spectroscopic measurement and elemental analysis of the silicon monoxide used. Except for using the silicon monoxide in place of the silicon nanoparticle-containing hydrogen polysilsesquioxane fired product (1), a negative electrode body was prepared and obtained after titanium oxide coating was performed in the same manner as in Example 1. A lithium ion secondary battery was produced in the same manner as in Example 1 except that the negative electrode body was used, and the battery characteristics were evaluated. The battery characteristic evaluation results are shown in Table 1.
- the fired product obtained by heat treating sesquioxane is coated with titanium oxide. Both the initial capacity and the discharge capacity at the 100th time have a higher capacity than the conventional carbon-based negative electrode active material, and the capacity is reduced. Therefore, it can be evaluated that the negative electrode active material of the present invention can withstand practical use as a negative electrode material.
- the silicon nanoparticle-containing hydrogen polysilsesquioxane baked product fired at a temperature exceeding 1000 ° C. shown in Comparative Example 1 does not have an appropriate amount of Si—H bond, and contains the silicon nanoparticles of Comparative Example 2 Since the hydrogen polysilsesquioxane baked product has too many Si-H bonds, the characteristics of the battery employing the negative electrode made from these baked products are excellent in cycle characteristics, but the initial discharge capacity is extremely high. It was low and impractical. Moreover, in Comparative Example 3, since the silicon oxide containing no hydrogen was used, the battery characteristics employing the negative electrode using the negative electrode active material produced from the titanium oxide-coated one adopted the negative electrode active material of the present invention.
- the initial discharge capacity shows a certain value, but the capacity suddenly decreases and the capacity is lower than that using the carbon-based negative electrode active material.
- the battery characteristics are negative electrode active materials that cannot exhibit the characteristics of conventional batteries.
- a negative electrode active material for a lithium ion secondary battery obtained by the method of the present invention and a negative electrode formed by using the negative electrode active material have excellent capacity and excellent charge / discharge characteristics.
- a lithium ion secondary battery having cycle characteristics can be obtained.
- the present invention is a useful technique in the field of batteries, particularly 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にはケイ素濃度傾斜のあるケイ素酸化物に酸化チタンを被覆した材料は、リチウムイオン二次電池の負極活物質として用いると、高容量で改良されたサイクル特性を有する電池が得られることが開示されている。
また、特許文献3にはケイ素ナノ粒子分が分散したケイ素酸化物粒子表面に酸化チタンを被覆した材料を二次電池用負極材として使用することが提案されている。
さらにまた、非特許文献1にはケイ素酸化物にアナターゼ型の酸化チタンを被覆した材料がリチウムイオン電池の負極材料に用いることが開示されている。
さらに、負極材料の製造方法としては生産性に劣り、結果として高いコストを必要とする技術であった。
本発明の課題は、このような要求に応じることができる二次電池用負極活物質を提供することであり、また、高い生産性で前記二次電池用負極活物質の製造を実施することができる製造方法を提供することである。
[1] シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物及び金属酸化物から構成されるシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体であって、
前記シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物は、
10nmを超え500nm未満の体積基準平均粒径を有するシリコンナノ粒子を5重量%から95重量%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する水素ポリシルセスキオキサン由来のケイ素酸化物構造とを含み、
一般式 SiOxHy(0.01<x<1.35、0<y<0.35)で表わされ、
Si-H結合を有する、シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物であり、
前記金属酸化物は、チタン、亜鉛、ジルコニウム、アルミニウム、及び鉄から選ばれる一種類以上の金属から構成される金属酸化物である、シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体。
[2] 前記シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物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]に記載のシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体。
[3] 前記シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物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]又は[2]に記載のシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体。
[4] 前記シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物の表面の少なくとも一部は、前記金属酸化物により被覆されている、[1]乃至[3]のいずれかに記載のシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体。
[5] 前記シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体は、0重量%を超え10重量%以下の前記金属酸化物を含む、[1]又は[4]のいずれかに記載のシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体。
[6] 前記金属酸化物が、酸化チタンである、[1]又は[5]]のいずれかに記載のシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体。
[7] [1]から[6]のいずれか1項に記載のシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体を含むリチウムイオン電池用負極活物質。
[8] [7]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。
[9] [8]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。
前記シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物は、
10nmを超え500nm未満の体積基準平均粒径を有するシリコンナノ粒子を5重量%から95重量%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する水素ポリシルセスキオキサン由来のケイ素酸化物構造とを含み、
一般式 SiOxHy(0.01<x<1.35、0<y<0.35)で表わされ、
Si-H結合を有する、シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物であり、
前記金属酸化物は、チタン、亜鉛、ジルコニウム、アルミニウム、及び鉄から選ばれる一種類以上の金属から構成される金属酸化物であり、
前記製造方法は、
前記シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物の存在下で、前記金属酸化物の金属のアルコキシドを含む溶液を加水分解することにより、前記シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物の表面の少なくとも一部を前記金属酸化物で被覆する工程と、
金属酸化物で被覆したシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物を、不活性ガス雰囲気下で200℃から900℃の温度範囲で熱処理する工程とを含む、製造方法。
[11] 前記金属のアルコキシドが、チタニウムテトラアルコキシドである、[10]に記載の製造方法。
本発明のシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体は、シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物と、金属酸化物を複合化し、加熱処理することによって得ることができる。また、シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物は、シリコンナノ粒子含有水素ポリシルセスキオキサン(シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物の前駆体)を焼成することにより、得ることができる。したがって、まず、シリコンナノ粒子含有水素ポリシルセスキオキサンについて説明し、次に、シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物、その後、シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体について説明することにする。
シリコンナノ粒子含有水素ポリシルセスキオキサンは、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(重縮合反応ともいう)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、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、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、酸及び水並びにこれらに由来する物質を含有していてもよい。
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、例えば、後述するように目的とするシリコンナノ粒子含有水素ポリシルセスキオキサン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。
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。そして、本質的に炭素又は金属を含まないシリコンナノ粒子を用いることもできる。
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/重合が進められるため、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。
シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物は、上記の方法で得られたシリコンナノ粒子含有水素ポリシルセスキオキサン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、文言的にはシリコンナノ粒子含有水素ポリシルセスキオキサンを酸化させないことを意味するものであるが、実質的にはシリコンナノ粒子含有水素ポリシルセスキオキサン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、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、吸収強度が最大のピーク(ピーク1)の強度をいう。このようにして得られたシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物の組成を元素分析により測定すると、本発明のシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体を構成するシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物は、ケイ素(Si)、酸素(O)及び水素(H)を含有しており、一般式SiOxHy(0.01<x<1.35、0<y<0.35)で表示される。
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の範囲であれば、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。
非酸化性雰囲気としては、不活性ガス雰囲気、高真空により酸素を除去した雰囲気(目的とするシリコンナノ粒子含有水素ポリシルセスキオキサン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。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Si-H結合が多すぎ、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り、さらに表面に強固なSiO2層が発達し、リチウムの挿入脱離を阻害するため容量が発現しにくくなる。
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。
シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体は、上記の方法で得られたシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物に金属酸化物を複合化し、それを熱処理することによって得ることができる。したがって、まず、シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体前駆体の製造方法(シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物を金属酸化物と複合させること)について説明する。
シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体は、上記の方法で得られたシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体前駆体を不活性ガス雰囲気下で、熱処理して得られる。充放電サイクル劣化が極めて抑制された、高容量で優れた充放電特性を発現させる熱処理温度は200℃から900℃、好ましくは250℃から850℃、より好ましくは250℃から800℃である。
熱処理時間は、特に限定されないが、通常30分から10時間、好ましくは1時間から8時間である。
本発明に用いるケイ素酸化物はそれ自身が高い充放電サイクル安定性を有するが、酸化チタンを被覆することで、以上のような作用が加わり更に高い充放電サイクル安定性が得られるものと考えられる。上記効果は、酸化チタンだけでなく、亜鉛、ジルコニウム、アルミニウム、及び鉄等を含む金属酸化物にも見られる効果である。
次に、シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体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、シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体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、シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体内に炭素系物質を分散させる方法が挙げられる。
リウムイオン二次電池における負極は、シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体あるいは前記炭素系物質を複合又は被覆させたシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体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、シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体あるいは前記炭素系物質を複合又は被覆させたシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体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。
シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体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」、「酸化チタン被覆層の分析」の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)、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付近のピークの強度をI2-1、1070cm-1付近のピークの強度を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。ケイ素、酸素、チタンの含有量はRBSスペクトル解析にて計測し、水素含有量はRBSとHFSのスペクトルを用いた解析により計測した。また、酸化チタン含有量は、チタンが全て二酸化チタン化していると仮定し、チタン含有量を(TiO2/Ti=79.87/47.87=1.67)1.67倍することにより換算した。
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。
酸化チタン被覆層の分析は、X線光電子分光分析装置 PHI Quanera SXM[ULVAC-PHI]を用い、X線源に単色化されたAlKα、出力15kV/25W、ビーム径100μmφで行い、Ti2p、O1sのピーク位置とピーク形状から複合体の状態を特定した。
所定の実施例又は比較例の試料を含有する負極活物質を用いてリチウムイオン電池を作製し、電池の充放電特性を、次のようにして測定した。
株式会社ナガノ製BTS2005Wを用い、シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体1g当たり、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、初回の放電容量を初回の充電容量で除した値を100分率で表したものを初期充放電効率とした。各充放電の切り替え時には、30分間、開回路で休止した。
なお、充放電効率は、初回(充放電の第1サイクル目)の充電容量に対する放電容量の比率とし、容量維持率は初回の放電容量に対する、充放電100サイクル目の放電容量の比率とした。
(シリコンナノ粒子含有水素ポリシルセスキオキサン粉体(1)の調製)
50mlポリビーカーに純水20gとシリコンナノパウダー(シグマアルドリッチ、100nm未満(体積基準平均粒径、ただし、10nmは超える))1.92gを入れ、超音波洗浄機にてシリコンナノ粒子分散水溶液を調製した。500mlの三つ口フラスコに、このシリコンナノ粒子分散液と36重量%濃度の塩酸2.43g(24mmol)及び純水218.6g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(東京化成工業社製)45g(274mmol)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、シリコンナノ粒子含有水素ポリシルセスキオキサン粉体(1)16.4gを得た。
得られたシリコンナノ粒子含有水素ポリシルセスキオキサン粉体(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、シリコンナノ粒子含有水素ポリシルセスキオキサンの焼成物を得た。
次いで、得られたシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物を乳鉢にて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であるシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物(1)9.58gを得た。
エタノール(和光純薬:特級試薬)45mlを仕込んだ200mlナス型フラスコに、得られたシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物(1)9.5gを投入し、超音波洗浄器で3分間、マグネチックスターラーで5分間分散処理を行う。分散処理後、撹拌しながらテトライソプロポキシチタニウム(Alfa Aesar 95%試薬)1.78gを滴下し、室温下で撹拌を1.5時間継続した。1.5時間後、撹拌を停止しエバポレータを使って溶媒を濃縮した。溶媒が揮発したところでフラスコごと減圧乾燥器に移し、1時間60℃で加熱減圧乾燥してシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-チタン酸化物複合体前駆体粉末(1)を回収した。
回収したシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-チタン酸化物複合体前駆体粉末(1)を前記ケイ素酸化物の調製と同様に真空パージ式チューブ炉 KTF43N1-VPSにセットし、熱処理条件として、ア「調製」への修正を提案されております。これでよろしいかと存じます。ルゴンガス雰囲気下にて、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、400℃で1時間焼成した。次いで乳鉢による解砕とステンレス製篩よる分級を行い、最大粒子径が32μmである粉粒状のシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-チタン酸化物複合体(1)9.8gを得た。得られたシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-チタン酸化物複合体(1)のチタンの化学状態を調べるため、X線光電子分光装置を用いて、表面分析を行った結果、チタンは酸化チタンとして表面に結合していることを確認した。X線光電子分光分析 Ti2p及びO1sのスペクトルを図2に示す。
カルボキシメチルセルロースの2重量%水溶液20g中に、前記シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-チタン酸化物複合体(1)3.2gと0.4gのデンカ株式会社製アセチレンブラックを加え、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。
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(FEC)を5重量%添加したものを使用した。
次いで、リチウムイオン二次電池の電池特性の評価を既述の方法で実施した。
結果を表1に示す。
(シリコンナノ粒子含有水素ポリシルセスキオキサン粉体(2)の調製)
500mlポリビーカーに純水200gとシリコンナノパウダー(シグマアルドリッチ、<100nm未満(体積基準平均粒径、ただし、10nmは超える))19.2gを入れ、超音波洗浄機にてシリコンナノ粒子分散水溶液を調製した。3lのセパラブルフラスコに、このシリコンナノ粒子分散液と36重量%濃度の塩酸12.2g(120mmol)及び純水0.94kg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分散させ、撹拌下にトリメトキシシラン(東京化成工業社製)167g(1.37mol)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、シリコンナノ粒子含有水素ポリシルセスキオキサン粉体(2)95.2gを得た。
得られたシリコンナノ粒子含有水素ポリシルセスキオキサン粉体(2)を用いて、実施例1と同様の方法で、シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物(2)を調製した。
得られたシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物(2)を用いて、実施例1のシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物(1)を用いたときと同様にして、酸化チタン被覆処理を行い、熱処理を行って、シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-チタン酸化物複合体(2)を得た。
得られたシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-チタン酸化物複合体(2)を用いて、実施例1のシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-チタン酸化物複合体(1)を用いたときと同様にして、負極体を作製し、それを備えたリチウムイオン電池の電池特性を評価した。
(シリコンナノ粒子含有水素ポリシルセスキオキサン粉体(3)の調製)
シリコンナノ粒子含有水素ポリシルセスキオキサンの調製において、シリコンナノパウダー(シグマアルドリッチ、100nm未満(体積基準平均粒径、ただし、10nmは超える))仕込み量を、77.0gに変えた以外は、実施例2と同様の手順で、調製を行い、シリコンナノ粒子含有水素ポリシルセスキオキサン粉体(3)を得た。
得られたシリコンナノ粒子含有水素ポリシルセスキオキサン粉体(3)を用いて、実施例1と同様の方法で、シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物(3)を調製した。得られたシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物(3)の赤外分光スペクトルを図1に示す(図1では、実施例3と表記する)。
得られたシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物(3)を用いて、実施例2のシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物(2)を用いたときと同様にして、酸化チタン被覆処理を行い、熱処理を行って、シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-チタン酸化物複合体(3)を得た。
得られたシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-チタン酸化物複合体(3)を用いて、実施例1のシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-チタン酸化物複合体(1)を用いたときと同様にして、負極体を作製し、それを備えたリチウムイオン電池の電池特性を評価した。
(シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-チタン酸化物複合体(4)の製造)
シリコンナノ粒子含有水素ポリシルセスキオキサン粉体(3)を用いて、テトライソプロポキシチタニウム(Alfa Aesar 95%試薬)の仕込み量を、0.87gに変えた以外は、実施例1と同様の手順で被覆処理を行い、熱処理を行って、シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-チタン酸化物複合体(4)を得た。得られたシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-チタン酸化物複合体(4)の電子顕微鏡(SEM)による写真を図3に示す。
得られたシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-チタン酸化物複合体(4)を用いて、実施例1のシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-チタン酸化物複合体(1)を用いたときと同様にして、負極体を作製し、それを備えたリチウムイオン電池の電池特性を評価した。
(シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-チタン酸化物複合体(5)の製造)
シリコンナノ粒子含有水素ポリシルセスキオキサン粉体(3)を用いて、テトライソプロポキシチタニウム(Alfa Aesar 95%試薬)の仕込み量を、2.54gに変えた以外は、実施例1と同様の手順で被覆処理を行い、熱処理を行って、シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-チタン酸化物複合体(5)を得た。
得られたシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-チタン酸化物複合体(5)を用いて、実施例1のシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-チタン酸化物複合体(1)を用いたときと同様にして、負極体を作製し、それを備えたリチウムイオン電池の電池特性を評価した。
(シリコンナノ粒子含有水素ポリシルセスキオキサン粉体(4)の調製)
シリコンナノ粒子含有水素ポリシルセスキオキサンの調製において、トリメトキシシラン(東京化成工業社製)の滴下量を、23.9gに変えた以外は、実施例2と同様の手順で、調製を行い、シリコンナノ粒子含有水素ポリシルセスキオキサン粉体(4)を得た。
得られたシリコンナノ粒子含有水素ポリシルセスキオキサン粉体(4)を用いて、実施例1と同様の方法で、シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物(4)を調製した。
得られたシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物(4)を用いて、実施例1のシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物(1)を用いたときと同様にして、酸化チタン被覆処理を行い、熱処理を行って、シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-チタン酸化物複合体(6)を得た。
得られたシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-チタン酸化物複合体(6)を用いて、実施例1のシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-チタン酸化物複合体(1)を用いたときと同様にして、負極体を作製し、それを備えたリチウムイオン電池の電池特性を評価した。
(シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物(5)の調製)
シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物の調製において、熱処理における焼成温度を1100℃にしたこと以外は、実施例3と同様に行い、シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物(5)を得た。
得られたシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物(5)の赤外分光測定の結果を図1に、元素分析結果を表1に示す(図1では、比較例1と表記する)。
得られたシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物(5)を用いて、実施例1のシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物(1)を用いたときと同様にして、酸化チタン被覆処理を行い、熱処理を行って、シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-チタン酸化物複合体(7)を得た。
得られたシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-チタン酸化物複合体(7)を用いて、実施例1のシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-チタン酸化物複合体(1)を用いたときと同様にして、負極体を作製し、それを備えたリチウムイオン電池の電池特性を評価した。電池特性評価結果を表1に示す。
(シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物(6)の調製)
シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物の調製において、熱処理における焼成温度を500℃にしたこと以外は、実施例3と同様に行い、シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物(6)を得た。
得られたシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物(6)の赤外分光測定の結果を図1に、元素分析結果を表1に示す(図1では、比較例2と表記する)。
得られたシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物(6)を用いて、実施例1のシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物(1)を用いたときと同様にして、酸化チタン被覆処理を行い、熱処理を行って、シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-チタン酸化物複合体(8)を得た。
得られたシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-チタン酸化物複合体(8)を用いて、実施例1のシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-チタン酸化物複合体(1)を用いたときと同様にして、負極体を作製し、それを備えたリチウムイオン電池の電池特性を評価した。電池特性評価結果を表1に示す
[比較例3]
ケイ素酸化物として、市販の一酸化ケイ素(アルドリッチ社製 under325mesh)を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である一酸化ケイ素粉末を用いた。
用いた一酸化ケイ素の赤外分光測定の結果、及び元素分析結果を表1に示す。上記一酸化ケイ素をシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物(1)の代わりに用いた以外は、実施例1と同様に酸化チタン被覆を行った後に負極体を作製し、得られた負極体を用いた以外は実施例1と同様にしてリチウムイオン二次電池を作製し、電池特性を評価した。電池特性評価結果を表1に示す。
また、比較例3においては、水素を含まないケイ素酸化物を使用したため、酸化チタン被覆したものから作製された負極活物質を用いた負極を採用した電池特性は、本発明の負極活物質を採用した負極と同じ条件下で作製した電池特性と比較したとき、初回放電容量は一定程度の値を示すものの、急激に容量が低下し、さらに、炭素系負極活物質を用いたものより容量が低くなるなど、電池特性としては従来の電池のような特性を示し得ない負極活物質である。
2:セパレータ
3:リチウム対極
Claims (11)
- シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物及び金属酸化物から構成されるシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体であって、
前記シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物は、
10nmを超え500nm未満の体積基準平均粒径を有するシリコンナノ粒子を5重量%から95重量%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する水素ポリシルセスキオキサン由来のケイ素酸化物構造とを含み、
一般式 SiOxHy(0.01<x<1.35、0<y<0.35)で表わされ、
Si-H結合を有する、シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物であり、
前記金属酸化物は、チタン、亜鉛、ジルコニウム、アルミニウム、及び鉄から選ばれる一種類以上の金属から構成される金属酸化物である、シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体。 - 前記シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物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に記載のシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体。
- 前記シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物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又は2に記載のシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体。
- 前記シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物の表面の少なくとも一部は、前記金属酸化物により被覆されている、請求項1乃至3のいずれか一項に記載のシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体。
- 前記シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体は、0重量%を超え10重量%以下の前記金属酸化物を含む、請求項1から4のいずれか一項に記載のシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体。
- 前記金属酸化物が、酸化チタンである、請求項1~5のいずれか一項に記載のシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体。
- 請求項1から6のいずれか1項に記載のシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体を含むリチウムイオン電池用負極活物質。
- 請求項7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8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。
- シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物及び金属酸化物から構成されるシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物-金属酸化物複合体の製造方法であって、
前記シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物は、
10nmを超え500nm未満の体積基準平均粒径を有するシリコンナノ粒子を5重量%から95重量%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する水素ポリシルセスキオキサン由来のケイ素酸化物構造とを含み、
一般式 SiOxHy(0.01<x<1.35、0<y<0.35)で表わされ、
Si-H結合を有する、シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物であり、
前記金属酸化物は、チタン、亜鉛、ジルコニウム、アルミニウム、及び鉄から選ばれる一種類以上の金属から構成される金属酸化物であり、
前記製造方法は、
前記シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物の存在下で、前記金属酸化物の金属のアルコキシドを含む溶液を加水分解することにより、前記シリコンナノ粒子含有水素ポリシルセスキオキサン焼成物の表面の少なくとも一部を前記金属酸化物で被覆する工程と、
金属酸化物で被覆したシリコンナノ粒子含有水素ポリシルセスキオキサン焼成物を、不活性ガス雰囲気下で200℃から900℃の温度範囲で熱処理する工程とを含む、製造方法。 - 前記金属のアルコキシドが、チタニウムテトラアルコキシドである、請求項10に記載の製造方法。
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WO2020179409A1 (ja) * | 2019-03-01 | 2020-09-10 | Jnc株式会社 | SiOC構造体並びにこれを用いた負極用組成物、負極及び二次電池 |
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