WO2023008093A1 - 負極活物質及びその製造方法 - Google Patents
負極活物質及びその製造方法 Download PDFInfo
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- WO2023008093A1 WO2023008093A1 PCT/JP2022/026370 JP2022026370W WO2023008093A1 WO 2023008093 A1 WO2023008093 A1 WO 2023008093A1 JP 2022026370 W JP2022026370 W JP 2022026370W WO 2023008093 A1 WO2023008093 A1 WO 2023008093A1
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- Prior art keywords
- negative electrode
- active material
- electrode active
- peak
- silicon oxide
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- 238000004519 manufacturing process Methods 0.000 title claims description 16
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Images
Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/362—Composites
- H01M4/366—Composites as layered products
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B32/00—Carbon; Compounds thereof
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B33/00—Silicon; Compounds thereof
- C01B33/02—Silicon
- C01B33/021—Preparation
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B33/00—Silicon; Compounds thereof
- C01B33/113—Silicon oxides; Hydrates thereof
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/483—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides for non-aqueous cells
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/021—Physical characteristics, e.g. porosity, surface area
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/027—Negative electrodes
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M2220/00—Batteries for particular applications
- H01M2220/30—Batteries in portable systems, e.g. mobile phone, laptop
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Definitions
- the present invention relates to a negative electrode active material and a method for producing the same.
- lithium-ion secondary batteries are highly expected because they are small and easy to increase in capacity, and they can obtain higher energy density than lead-acid batteries and nickel-cadmium batteries.
- the lithium-ion secondary battery described above includes a positive electrode, a negative electrode, a separator, and an electrolytic solution, and the negative electrode contains a negative electrode active material involved in charge-discharge reactions.
- the negative electrode active material expands and contracts during charging and discharging, so cracking occurs mainly near the surface layer of the negative electrode active material.
- an ionic substance is generated inside the active material, making the negative electrode active material fragile.
- a new surface is generated thereby increasing the reaction area of the active material.
- a decomposition reaction of the electrolytic solution occurs on the new surface, and a film, which is a decomposition product of the electrolytic solution, is formed on the new surface, so that the electrolytic solution is consumed.
- cycle characteristics tend to deteriorate.
- silicon and amorphous silicon dioxide are simultaneously deposited using a vapor phase method (see Patent Document 1, for example).
- a carbon material electroconductive material
- an active material containing silicon and oxygen is produced, and an active material layer with a high oxygen ratio is formed in the vicinity of the current collector (for example, see Patent Document 3).
- oxygen is contained in the silicon active material, and the average oxygen content is 40 at % or less, and the oxygen content is increased near the current collector. (see, for example, Patent Document 4).
- a nanocomposite containing Si phase, SiO 2 , and M y O metal oxide is used to improve the initial charge/discharge efficiency (see, for example, Patent Document 5).
- the molar ratio of oxygen to silicon in the negative electrode active material is set to 0.1 to 1.2, and the difference between the maximum and minimum molar ratios near the interface between the active material and the current collector is 0.4 or less (see Patent Document 7, for example).
- a metal oxide containing lithium is used (see, for example, Patent Document 8).
- a hydrophobic layer such as a silane compound is formed on the surface layer of the silicon material (see, for example, Patent Document 9).
- silicon oxide is used, and conductivity is imparted by forming a graphite film on the surface layer (see, for example, Patent Document 10).
- broad peaks appear at 1330 cm ⁇ 1 and 1580 cm ⁇ 1 with respect to the shift values obtained from the RAMAN spectrum of the graphite film, and their intensity ratio I 1330 /I 1580 is 1.5 ⁇ I 1330 /I 1580 ⁇ 3.
- particles having a silicon microcrystalline phase dispersed in silicon dioxide are used in order to increase battery capacity and improve cycle characteristics (see, for example, Patent Document 11).
- a silicon oxide in which the atomic ratio of silicon and oxygen is controlled to 1:y (0 ⁇ y ⁇ 2) is used (see Patent Document 12, for example).
- Non-Patent Document 1 Japanese Patent Document 1
- the silicon oxide proposed by Hohl is a composite of Si 0+ to Si 4+ and has various oxidation states (Non-Patent Document 2).
- Kapaklis also proposed a disproportionated structure in which silicon oxide is divided into Si and SiO 2 by applying a thermal load (Non-Patent Document 3).
- Non-Patent Document 4 Among silicon oxides having a disproportionated structure, Miyachi et al. focused on Si and SiO2 that contribute to charging and discharging (Non-Patent Document 4), and Yamada et al. (Non-Patent Document 5).
- Si and SiO 2 that constitute silicon oxide react with Li, and are divided into Li silicide, Li silicate, and partially unreacted SiO 2 .
- the Li silicate produced here is irreversible, and once formed, it is a stable substance that does not release Li.
- the capacity per mass calculated from this reaction formula has a value close to the experimental value, and is recognized as a reaction mechanism of silicon oxide.
- Kim et al. identified Li silicate, an irreversible component associated with charging and discharging of silicon oxide, as Li 4 SiO 4 using 7 Li-MAS-NMR and 29 Si-MAS-NMR (Non-Patent Document 6).
- This irreversible capacity is the weakest point of silicon oxide, and improvement is desired. Therefore, Kim et al. used a Li pre-doping method in which Li silicate is formed in advance to greatly improve the initial efficiency as a battery and create a negative electrode that can withstand practical use (Non-Patent Document 7).
- Patent Document 13 a method of treating the powder has been proposed, and the irreversible capacity has been improved.
- lithium-ion secondary batteries which are the main power source for these devices, have been required to have increased battery capacity.
- the development of a lithium ion secondary battery comprising a negative electrode using a silicon material as a main material is desired.
- lithium ion secondary batteries using a silicon material are desired to have initial charge/discharge characteristics and cycle characteristics that are close to those of lithium ion secondary batteries using a carbon-based active material. Therefore, the cycle characteristics and the initial charge/discharge characteristics have been improved by using silicon oxides modified by the insertion and partial elimination of Li as the negative electrode active material.
- the present invention has been made in view of the above problems, and it is possible to increase the battery capacity accompanying the improvement of the initial efficiency (also referred to as initial efficiency), and a negative electrode active material capable of realizing sufficient battery cycle characteristics. and a manufacturing method thereof.
- the present invention provides a negative electrode active material containing negative electrode active material particles, wherein the negative electrode active material particles contain silicon oxide particles coated with a carbon layer, and the silicon oxide particles are , Li 2 SiO 3 and has the strongest peak A near 102 eV in the Si2p spectrum obtained by XPS analysis.
- a negative electrode active material characterized in that it has the second strongest peak B, and the intensity of the Si:0 valence peak C obtained near 99 eV is half or less of the intensity of the peak A.
- the negative electrode active material of the present invention (hereinafter also referred to as a silicon-based negative electrode active material) contains negative electrode active material particles containing silicon oxide particles (hereinafter also referred to as silicon-based negative electrode active material particles), thereby improving battery capacity. can.
- the silicon oxide particles contain Li 2 SiO 3 , the initial efficiency is improved, the slurry can be stabilized before coating, a good electrode is obtained, and the battery characteristics are improved.
- this Li 2 SiO 3 has a peak near 102 eV in the Si2p spectrum obtained by XPS analysis. The fact that this peak is the strongest contributes to stability during charge/discharge and slurrying.
- the Si2p spectrum obtained by XPS analysis must have a low-valence Si compound state peak near 100 eV. This is because the composite compound of Si, Li, and O, rather than the Si—Li reaction, contributes to charging and discharging. However, if this peak becomes too strong, the peak of Li 2 SiO 3 becomes small and the structural stability deteriorates, so it must be the second strongest peak. In addition, in the Si2p spectrum, the zero-valence peak intensity of Si near 99 eV must be less than half the peak intensity of Li 2 SiO 3 . This is because the more 0 valence of Si, the faster the deterioration.
- the negative electrode active material preferably has a phase structure of three or more.
- the contained Li silicate (Li 2 SiO 3 ) has a peak near 102 eV to near 102.5 eV in the Si2p spectrum obtained by XPS analysis. is difficult to shift. This means that it is possible to prevent the crystallinity of Li silicate (Li 2 SiO 3 ) from increasing, and as a result, the diffusibility of Li can be ensured.
- the negative electrode active material particles have the strongest peak near 531 eV in the outermost layer, a peak near 528 eV below it, and a peak near 532.5 eV below it. It is preferably composed of three or more phase structures from the surface to the inside, which have peaks.
- the peak near 531 eV indicates the peak of the C,O compound present in the surface layer
- the peak near 528 eV indicates the low-valence Si peak. ing. Therefore, as described above, in the XPS analysis of the negative electrode active material particles, the O1s spectrum obtained in the surface layer has a C,O compound peak, and the O1s spectrum obtained in the lower phase has a low-valence Si peak. This facilitates the insertion of Li into the negative electrode active material particles.
- the inside of the negative electrode active material particle bulk has a peak on the higher energy side, so that the structure can be stabilized.
- the peak obtained near 532.5 eV is preferably divided into two peaks near 532 eV and near 533 eV.
- the O1s peak generated on the highest energy side inside the negative electrode active material particle bulk is divided into the vicinity of 532 eV and the vicinity of 533 eV, so that the silicate component that diffuses Li with lower resistance and stabilizes the structure. It can be composed of a silicate component that dissolves.
- the negative electrode active material particles have a peak attributed to the Si (111) crystal plane obtained by X-ray diffraction using Cu—K ⁇ rays before charging and discharging the negative electrode active material particles, and the crystal
- the crystallite size corresponding to the plane is 5.0 nm or less
- the ratio of the peak intensity G due to the Si (111) crystal face to the peak intensity H due to the Li 2 SiO 3 (111) crystal face G/H is the following formula (1) 0.4 ⁇ G/H ⁇ 1.0 (1) is preferably satisfied.
- the crystallite size is preferably 5.0 nm or less and is preferably substantially amorphous.
- Li 2 SiO 3 also exhibits crystallinity, but the higher the crystallinity of Li 2 SiO 3 , the more stable the structure, but the higher the resistance.
- the crystallinity is low, it tends to be eluted into the slurry, so there is an optimum range. Therefore, it is preferable to satisfy the above formula (1).
- the negative electrode active material particles have a median diameter of 5.5 ⁇ m or more and 15 ⁇ m or less.
- the median diameter of the negative electrode active material particles is 5.5 ⁇ m or more, the reaction with the electrolytic solution is suppressed, and deterioration of battery characteristics can be suppressed.
- the median diameter of the negative electrode active material particles is 15 ⁇ m or less, the expansion of the active material due to charging and discharging can be suppressed, and electronic contact can be ensured.
- the carbon layer preferably has a portion existing in a compound state with oxygen on the outermost layer.
- the carbon layer has a portion that exists in a compound state with oxygen on the outermost layer, so it is possible to generate a substance similar to the film structure generated during charging and discharging, so it is possible to further improve battery characteristics. becomes.
- the present invention includes the steps of producing silicon oxide particles, coating the silicon oxide particles with a carbon layer, inserting lithium into the silicon oxide particles coated with the carbon layer by an oxidation-reduction method,
- a negative electrode active material particle is produced by a step of heat-treating lithium-inserted silicon oxide particles to obtain silicon oxide particles containing Li 2 SiO 3 , and the produced negative electrode active material particles are used as a negative electrode active material. wherein the temperature during the lithium insertion and the temperature of the heat treatment are adjusted so that the silicon oxide particles exhibit the strongest peak A near 102 eV in the Si2p spectrum obtained by XPS analysis.
- a method for producing a negative electrode active material characterized in that the intensity is half or less of the peak A.
- the negative electrode active material of the present invention can achieve high initial efficiency, high capacity, and high cycle characteristics when used as a negative electrode active material for secondary batteries. Further, according to the method for producing a negative electrode active material of the present invention, it is possible to obtain a negative electrode active material having high capacity and good initial charge/discharge characteristics when used as a negative electrode active material for a secondary battery while obtaining good cycle characteristics. can be manufactured.
- FIG. 1 is a Si2p spectrum obtained by XPS analysis in Example 1.
- FIG. 2 is a Si2p spectrum obtained by XPS analysis in Example 2.
- FIG. 10 is a Si2p spectrum obtained by XPS analysis in Example 3.
- FIG. 4 is a Si2p spectrum obtained by XPS analysis in Comparative Example 1.
- FIG. 4 is a Si2p spectrum obtained by XPS analysis in Comparative Example 2.
- FIG. 10 is a Si2p spectrum obtained by XPS analysis in Comparative Example 3.
- FIG. 10 is a Si2p spectrum obtained by XPS analysis in Comparative Example 4.
- FIG. 10 is a Si2p spectrum obtained by XPS analysis in Comparative Example 5.
- FIG. 1 is an O1s spectrum obtained by XPS analysis in Example 1.
- FIG. 1 is an O1s spectrum obtained by XPS analysis in Example 1.
- FIG. 1 is an O1s spectrum obtained by XPS analysis in Example 1.
- FIG. 1 is an O1s spectrum obtained by XPS analysis in
- FIG. 4 is an O1s spectrum obtained by XPS analysis in Comparative Example 1.
- FIG. 4 is an O1s spectrum obtained by XPS analysis in Comparative Example 2.
- FIG. BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which shows an example of a structure of the negative electrode for lithium ion secondary batteries containing the negative electrode active material of this invention.
- Lithium ion secondary batteries using this silicon oxide are desired to have initial charge/discharge characteristics that are close to those of lithium ion secondary batteries using a carbonaceous active material.
- Li-doped SiO capable of improving initial charge/discharge characteristics
- cycle characteristics close to those of carbon-based active materials are desired.
- no silicon-based negative electrode active material has been proposed that exhibits battery characteristics equivalent to those of carbon-based active materials when used as a negative electrode active material for lithium ion secondary batteries.
- the present inventors have developed a negative electrode active material that can improve initial charge-discharge characteristics while obtaining high cycle characteristics when used as a negative electrode active material of a secondary battery, and as a result, increase the battery capacity.
- the present invention has been achieved through extensive studies.
- a negative electrode active material of the present invention is a negative electrode active material comprising negative electrode active material particles, the negative electrode active material particles containing silicon oxide particles coated with a carbon layer, and the silicon oxide particles being Li 2 SiO 3 , and in the Si2p spectrum obtained by XPS analysis, it has the strongest peak A near 102 eV and has a valence of 1 to 3 near 100 eV.
- the negative electrode active material is characterized in that it has a strong peak B, and the intensity of the Si:0 valence peak C obtained near 99 eV is less than half the intensity of the peak A.
- XPS analysis can be performed, for example, by using a scanning X-ray photoelectron spectrometer PHI Quantera II manufactured by ULVAC-PHI.
- the diameter of the X-ray beam can be set to 100 ⁇ m, and a neutralization gun can be used.
- the negative electrode active material of the present invention contains negative electrode active material particles containing silicon oxide particles, the battery capacity can be improved. Also, by forming Li 2 SiO 3 on the silicon oxide particles, the slurry can be stabilized before coating, a good electrode can be obtained, and battery characteristics are improved. In addition, this Li 2 SiO 3 has a peak near 102 eV in the Si2p spectrum obtained by XPS analysis. The fact that this peak is the strongest contributes to stability during charge/discharge and slurrying. In addition, the negative electrode active material of the present invention must have a low valence Si compound state near 100 eV in the Si2p spectrum obtained by XPS analysis.
- the composite compound of Si, Li, and O rather than the Si—Li reaction, contributes to charging and discharging.
- this peak becomes too strong, the peak of Li 2 SiO 3 near 102 eV becomes small, and the structural stability deteriorates.
- the zero-valent peak of Si near 99 eV must be half or less than the peak intensity of Li 2 SiO 3 near 102 eV. This is because the more 0 valence of Si, the faster the deterioration.
- the carbon coating provides electrical conductivity and has a certain effect on water resistance.
- the negative electrode active material of the present invention preferably has a three or more phase structure.
- the contained Li silicate (Li 2 SiO 3 ) is less likely to shift the peak from around 102 eV to around 102.5 eV in the Si2p spectrum obtained by XPS analysis. This means that it is possible to prevent the crystallinity of Li silicate (Li 2 SiO 3 ) from increasing, and as a result, the diffusibility of Li can be ensured.
- the negative electrode active material particles have the strongest peak near 531 eV in the O1s spectrum obtained by XPS analysis in the outermost layer, and a peak near 528 eV below it. It is preferable to have three or more phase structures from the surface layer to the inside, which has a peak near 532.5 eV in the lower part.
- the peak near 531 eV indicates the peak of the C,O compound present in the surface layer
- the peak near 528 eV indicates the peak of low-valence Si. Therefore, as described above, the negative electrode active material particles have a C,O compound peak in the surface layer and a low valence Si peak in the lower phase, so that Li is inserted into the negative electrode active material particles. easier.
- the inside of the negative electrode active material particle bulk has a peak on the higher energy side, so that the structure can be stabilized.
- the negative electrode active material particles in the O1s spectrum obtained by XPS analysis, the peak obtained near 532.5 eV is divided into two peaks near 532 eV and near 533 eV. preferable.
- the peak of O1s generated on the highest energy side inside the negative electrode active material particle bulk be divided into two near 532 eV and near 533 eV.
- it can be composed of a silicate component that has a lower resistance and diffuses Li and a silicate component that stabilizes the structure.
- the negative electrode active material particles of the present invention preferably have the following configuration before charging and discharging the negative electrode active material particles. That is, it preferably has a peak attributed to the Si (111) crystal plane obtained by X-ray diffraction using Cu—K ⁇ rays, and the crystallite size corresponding to the crystal plane is 5.0 nm or less. Furthermore, together with this, the ratio G/H of the peak intensity G due to the Si (111) crystal face to the peak intensity H due to the Li 2 SiO 3 (111) crystal face is expressed by the following formula (1) 0.4 ⁇ G/H ⁇ 1.0 (1) is preferably satisfied.
- the silicon oxide particles contain as little crystalline Si as possible.
- the crystallite size is preferably 5.0 nm or less and is preferably substantially amorphous.
- Li 2 SiO 3 also exhibits crystallinity, but the higher the crystallinity of Li 2 SiO 3 , the more stable the structure, but the higher the resistance.
- the crystallinity is low, it tends to be eluted into the slurry, so there is an optimum range. Therefore, it is preferable to satisfy the above formula (1).
- the negative electrode active material particles preferably have a median diameter of 5.5 ⁇ m or more and 15 ⁇ m or less.
- the median diameter of the negative electrode active material particles is 5.5 ⁇ m or more, the reaction with the electrolytic solution is suppressed, and deterioration of battery characteristics can be suppressed.
- the median diameter of the negative electrode active material particles is 15 ⁇ m or less, the expansion of the active material due to charging and discharging can be suppressed, and electronic contact can be ensured.
- the carbon layer preferably has a portion existing in a compound state with oxygen in the outermost layer.
- the carbon layer has a portion that exists in a compound state with oxygen on the outermost layer, so it is possible to generate a substance similar to the film structure generated during charging and discharging, so it is possible to further improve battery characteristics. becomes.
- FIG. 12 shows a cross-sectional view of a negative electrode containing the negative electrode active material of the present invention.
- the negative electrode 10 has a structure in which a negative electrode active material layer 12 is provided on a negative electrode current collector 11 .
- the negative electrode active material layer 12 may be provided on both sides of the negative electrode current collector 11 or only on one side. Furthermore, the negative electrode current collector 11 may be omitted as long as the negative electrode active material of the present invention is used.
- the negative electrode current collector 11 is made of an excellent conductive material and has high mechanical strength.
- Examples of conductive materials that can be used for the negative electrode current collector 11 include copper (Cu) and nickel (Ni). This conductive material is preferably a material that does not form an intermetallic compound with lithium (Li).
- the negative electrode current collector 11 preferably contains carbon (C) and sulfur (S) in addition to the main elements. This is because the physical strength of the negative electrode current collector is improved. This is because, in particular, in the case of having an active material layer that expands during charging, if the current collector contains the above element, it has the effect of suppressing deformation of the electrode including the current collector.
- the contents of the above-mentioned contained elements are not particularly limited, they are preferably 100 ppm by mass or less. This is because a higher deformation suppressing effect can be obtained. Cycle characteristics can be further improved by such a deformation suppression effect.
- the surface of the negative electrode current collector 11 may or may not be roughened.
- the roughened negative electrode current collector is, for example, an electrolytically treated, embossed, or chemically etched metal foil.
- the non-roughened negative electrode current collector is, for example, a rolled metal foil.
- the negative electrode active material layer 12 contains the negative electrode active material of the present invention capable of intercalating and deintercalating lithium ions. may contain The negative electrode active material contains negative electrode active material particles, and the negative electrode active material particles contain silicon oxide particles.
- the negative electrode active material layer 12 may contain a mixed negative electrode active material containing the negative electrode active material (silicon-based negative electrode active material) of the present invention and a carbon-based active material.
- a mixed negative electrode active material containing the negative electrode active material (silicon-based negative electrode active material) of the present invention and a carbon-based active material As a result, the electrical resistance of the negative electrode active material layer is reduced, and the expansion stress associated with charging can be alleviated.
- Examples of carbon-based active materials that can be used include pyrolytic carbons, cokes, vitreous carbon fibers, baked organic polymer compounds, and carbon blacks.
- the negative electrode active material of the present invention contains silicon oxide particles.
- the ratio of silicon to oxygen in the silicon oxide constituting the silicon oxide particles is preferably SiO x : 0.8 ⁇ x ⁇ 1.2. If x is 0.8 or more, the oxygen ratio is higher than that of simple silicon, so the cycle characteristics are good. If x is 1.2 or less, it is preferable because the resistance of the silicon oxide particles does not become too high. Above all, it is preferable that x is close to 1 in the composition of SiO x . This is because high cycle characteristics can be obtained.
- the composition of the silicon oxide particles in the present invention does not necessarily mean 100% purity, and may contain trace amounts of impurity elements.
- the negative electrode active material particles contain silicon oxide particles coated with a carbon layer, and the silicon oxide particles contain Li 2 SiO 3 as a Li compound. contains. Furthermore, this silicon oxide particle has the strongest peak A near 102 eV in the Si2p spectrum obtained by XPS analysis, and corresponds to a low valence Si compound having a valence of 1 to 3 near 100 eV. It has the second strongest peak B, and the intensity of Si:0 valence peak C obtained near 99 eV is less than half the intensity of peak A.
- the degree of enlargement of Li silicate and the degree of crystallization of Si can be confirmed by XRD (X-ray Diffraction).
- XRD measurement can be performed, for example, under the following conditions.
- X-ray diffraction apparatus for example, D8 ADVANCE manufactured by Bruker can be used.
- the X-ray source was Cu K ⁇ rays, using a Ni filter, an output of 40 kV/40 mA, a slit width of 0.3°, a step width of 0.008°, and a counting time of 0.15 seconds per step from 10-40°. Measure up to
- the negative electrode binder contained in the negative electrode active material layer for example, one or more of polymer materials, synthetic rubbers, and the like can be used.
- polymeric materials include polyvinylidene fluoride, polyimide, polyamideimide, aramid, polyacrylic acid, lithium polyacrylate, sodium polyacrylate, and carboxymethylcellulose.
- Synthetic rubbers include, for example, styrene-butadiene-based rubber, fluorine-based rubber, and ethylene propylene diene.
- the negative electrode conductive aid for example, one or more of carbon materials such as carbon black, acetylene black, graphite, ketjen black, carbon nanotubes, and carbon nanofibers can be used.
- the negative electrode active material layer is formed, for example, by a coating method.
- the coating method is a method in which the silicon-based negative electrode active material and the above-mentioned binder are mixed, and if necessary, a conductive aid and a carbon-based active material are mixed, and then the mixture is dispersed in an organic solvent or water and applied. .
- the method for producing a negative electrode active material of the present invention there are steps of producing silicon oxide particles, coating the silicon oxide particles with a carbon layer, and inserting lithium into the silicon oxide particles coated with the carbon layer by an oxidation-reduction method. and a step of heat-treating the lithium-inserted silicon oxide particles to obtain silicon oxide particles containing Li 2 SiO 3 to prepare negative electrode active material particles, and using the prepared negative electrode active material particles for the negative electrode.
- Manufacture an active material At this time, by adjusting the temperature at the time of lithium insertion and the temperature of the heat treatment, the silicon oxide particles have the strongest peak A near 102 eV and a value near 100 eV in the Si2p spectrum obtained by XPS analysis.
- the negative electrode active material is produced, for example, by the following procedure.
- silicon oxide particles are produced.
- silicon oxide represented by SiO x (0.5 ⁇ x ⁇ 1.6) as the silicon oxide particles will be described.
- a raw material that generates silicon oxide gas is heated in the presence of an inert gas under reduced pressure in a temperature range of 900° C. to 1600° C. to generate silicon oxide gas.
- the raw material can be a mixture of metallic silicon powder and silicon dioxide powder.
- the mixing molar ratio is preferably in the range of 0.9 ⁇ metallic silicon powder/silicon dioxide powder ⁇ 1.2.
- the generated silicon oxide gas is solidified and deposited on the adsorption plate.
- the silicon oxide deposit is taken out while the temperature in the reactor is lowered to 100° C. or less, and pulverized by using a ball mill, a jet mill, or the like to be powdered.
- silicon oxide particles can be produced.
- the Si crystallites in the silicon oxide particles can be controlled by changing the vaporization temperature of the raw material that generates the silicon oxide gas, or by heat treatment after the silicon oxide particles are produced.
- a layer of carbon material is generated on the surface of the silicon oxide particles.
- Pyrolytic CVD is desirable as the method for producing the carbon material layer.
- An example of a method of producing a layer of carbon material by pyrolytic CVD is described below.
- silicon oxide particles are set in a furnace.
- a hydrocarbon gas is introduced into the furnace to raise the temperature inside the furnace.
- the decomposition temperature is desirably 900° C. or lower, more desirably 850° C. or lower. By setting the decomposition temperature to 900° C. or lower, unintended disproportionation of the active material particles can be suppressed.
- a carbon layer is formed on the surface of the silicon oxide particles.
- the hydrocarbon gas used as the raw material of the carbon material is not particularly limited, but it is desirable that n ⁇ 2 in the C n H m composition. If n ⁇ 2, the production cost can be reduced, and the physical properties of the decomposition products can be improved.
- Li is inserted into the silicon oxide particles produced as described above.
- negative electrode active material particles containing silicon oxide particles into which lithium is inserted are produced. That is, as a result, the silicon oxide particles are modified, and a Li compound (Li silicate) is generated inside the silicon oxide particles.
- the insertion of Li is performed by the oxidation-reduction method as described above.
- lithium can be inserted by first immersing the silicon active material particles in a solution A in which lithium is dissolved in an ether solvent.
- This solution A may further contain a polycyclic aromatic compound or a linear polyphenylene compound.
- active lithium can be desorbed from the silicon active material particles by immersing the silicon active material particles in a solution B containing a polycyclic aromatic compound or a derivative thereof.
- Solvents for this solution B can be, for example, ether solvents, ketone solvents, ester solvents, alcohol solvents, amine solvents, or mixed solvents thereof.
- the obtained silicon active material particles may be heat-treated under an inert gas.
- the Li compound can be stabilized by heat treatment. After that, it may be washed with alcohol, alkaline water in which lithium carbonate is dissolved, weak acid, pure water, or the like.
- Ether solvents used for solution A include diethyl ether, tert-butyl methyl ether, tetrahydrofuran, dioxane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, or mixed solvents thereof. can be used. Among these, it is particularly preferable to use tetrahydrofuran, dioxane, and 1,2-dimethoxyethane. These solvents are preferably dehydrated and preferably deoxygenated.
- polycyclic aromatic compound contained in the solution A one or more of naphthalene, anthracene, phenanthrene, naphthacene, pentacene, pyrene, picene, triphenylene, coronene, chrysene and derivatives thereof can be used.
- chain polyphenylene compound one or more of biphenyl, terphenyl, and derivatives thereof can be used.
- polycyclic aromatic compound contained in solution B one or more of naphthalene, anthracene, phenanthrene, naphthacene, pentacene, pyrene, picene, triphenylene, coronene, chrysene, and derivatives thereof can be used.
- ether-based solvent for solution B diethyl ether, tert-butyl methyl ether, tetrahydrofuran, dioxane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and the like can be used. .
- Acetone, acetophenone, etc. can be used as the ketone-based solvent.
- ester solvent methyl formate, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, and the like can be used.
- Methanol, ethanol, propanol, isopropyl alcohol, etc. can be used as alcohol-based solvents.
- amine-based solvent methylamine, ethylamine, ethylenediamine, etc. can be used.
- the Li silicate thus produced is mainly Li 4 SiO 4 , and it is difficult to produce a battery as it is. Therefore, heat treatment is performed to convert to Li 2 SiO 3 , but the degree of crystallization of Li silicate and Si changes depending on the temperature at this time.
- the reaction temperature during Li insertion is also relevant.
- the crystallinity of Si is expressed in the heat treatment of the next step, although the crystallinity of Li silicate does not increase that much. becomes important.
- the reactivity at the time of Li insertion is too low, the reactivity is low. At least 50°C or higher is preferred. At such a temperature, reactivity during Li insertion can be ensured. By increasing the reactivity at the time of Li insertion to a predetermined level or more, it is possible to prevent the Li concentration in the particle surface layer from becoming too high, and as a result, suppress the progress of disproportionation of the surface layer during the heat treatment in the next step. can do.
- the C, O compound in the outermost layer does not contain oxygen, such as biphenyl, a polycyclic aromatic compound, and O cannot be introduced from a substance that forms a complex with Li. Therefore, O contained in solvent A must be used.
- O contained in solvent A When Li is released from the complex, it is desirable to decompose and generate Li by entraining the solvent. However, since it is unstable as it is, it is preferable to apply a heat treatment to form a stabilization layer while partially decomposing. It is called a pseudo SEI film, and when used as a battery, it is possible to smartly transfer Li.
- Li silicate states can be created by using the vacuum state, inert gas flow rate (internal pressure), retort thickness, and rotational speed as factors.
- inert gas flow rate internal pressure
- retort thickness thickness
- rotational speed rotational speed
- the silicon oxide particles are most intense near 102 eV in the Si2p spectrum obtained by XPS analysis. It has a peak A, has a second strongest peak B corresponding to a low valence Si compound having a valence of any of 1 to 3 near 100 eV, and a Si: 0 valence peak obtained near 99 eV. Adjust so that the intensity of C is less than half that of peak A to be produced.
- the temperature during lithium insertion and the heat treatment temperature are adjusted, and it is preferable to additionally adjust the temperature during SiO deposition and the CVD temperature.
- the negative electrode active material produced as described above is mixed with other materials such as a negative electrode binder and a conductive aid to form a negative electrode mixture, and then an organic solvent or water is added to form a slurry. Next, the above slurry is applied to the surface of the negative electrode current collector and dried to form a negative electrode active material layer. At this time, heat pressing or the like may be performed as necessary.
- a negative electrode can be produced in the manner described above.
- the separator separates the positive electrode from the negative electrode and allows lithium ions to pass therethrough while preventing current short circuit due to contact between the two electrodes.
- This separator is formed of a porous film made of synthetic resin or ceramic, for example, and may have a laminated structure in which two or more kinds of porous films are laminated.
- synthetic resins include polytetrafluoroethylene, polypropylene, and polyethylene.
- Electrode At least part of the active material layer or the separator is impregnated with a liquid electrolyte (electrolytic solution).
- electrolytic solution has an electrolytic salt dissolved in a solvent, and may contain other materials such as additives.
- Non-aqueous solvents include, for example, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, methylpropyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran and the like.
- ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethylmethyl carbonate it is desirable to use at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethylmethyl carbonate. This is because better characteristics can be obtained.
- the solvent contains at least one of a halogenated chain carbonate or a halogenated cyclic carbonate.
- a halogenated chain carbonate is a chain carbonate having halogen as a constituent element (at least one hydrogen is substituted with halogen).
- a halogenated cyclic carbonate is a cyclic carbonate having halogen as a constituent element (that is, at least one hydrogen is substituted with halogen).
- halogen is not particularly limited, but fluorine is preferred. This is because it forms a better film than other halogens. Moreover, the larger the number of halogens, the better. This is because the coating obtained is more stable and the decomposition reaction of the electrolyte is reduced.
- halogenated chain carbonates include fluoromethylmethyl carbonate and difluoromethylmethyl carbonate.
- Halogenated cyclic carbonates include 4-fluoro-1,3-dioxolan-2-one and 4,5-difluoro-1,3-dioxolan-2-one.
- an unsaturated carbon-bonded cyclic carbonate As a solvent additive, it is preferable to contain an unsaturated carbon-bonded cyclic carbonate. This is because a stable film is formed on the surface of the negative electrode during charging and discharging, and the decomposition reaction of the electrolytic solution can be suppressed.
- unsaturated carbon-bonded cyclic ester carbonates include vinylene carbonate and vinylethylene carbonate.
- sultone cyclic sulfonate
- solvent additive examples include propane sultone and propene sultone.
- the solvent preferably contains an acid anhydride. This is because the chemical stability of the electrolytic solution is improved.
- Acid anhydrides include, for example, propanedisulfonic anhydride.
- the electrolyte salt can include, for example, any one or more of light metal salts such as lithium salts.
- lithium salts include lithium hexafluorophosphate (LiPF 6 ) and lithium tetrafluoroborate (LiBF 4 ).
- the content of the electrolyte salt is preferably 0.5 mol/kg or more and 2.5 mol/kg or less with respect to the solvent. This is because high ionic conductivity can be obtained.
- a negative electrode active material was produced as follows. A raw material obtained by mixing metal silicon and silicon dioxide was introduced into a reactor, vaporized in a vacuum atmosphere of 10 Pa, deposited on an adsorption plate, cooled sufficiently, and then the deposit was taken out and pulverized with a ball mill. . The value of x in SiO x of the silicon oxide particles thus obtained was 1.0. Subsequently, the particle size of the silicon oxide particles was adjusted by classification. Thereafter, thermal decomposition CVD was performed at a temperature in the range of 700° C. to 900° C. to coat the surface of the silicon oxide particles with a carbon material.
- the silicon oxide particles were reformed by inserting lithium into them by an oxidation-reduction method. After that, it was reformed by heating in the range of 450°C to 650°C.
- the prepared negative electrode active material (silicon oxide particles), graphite, conductive aid 1 (carbon nanotube, CNT), conductive aid 2 (carbon fine particles having a median diameter of about 50 nm), sodium polyacrylate, carboxymethylcellulose ( CMC) was mixed at a dry mass ratio of 9.3:83.7:1:1:4:1, and then diluted with pure water to obtain a negative electrode mixture slurry.
- An electrolytic copper foil having a thickness of 15 ⁇ m was used as the negative electrode current collector.
- This electrolytic copper foil contained carbon and sulfur at a concentration of 70 mass ppm each.
- the negative electrode mixture slurry was applied to the negative electrode current collector and dried at 100° C. for 1 hour in a vacuum atmosphere. After drying, the deposition amount of the negative electrode active material layer per unit area (also referred to as area density) on one side of the negative electrode was 7.0 mg/cm 2 .
- an electrolyte salt lithium hexafluorophosphate: LiPF 6
- vinylene carbonate (VC) and fluoroethylene carbonate (FEC) were added at 1.0 wt % and 2.0 wt %, respectively.
- the initial efficiency was measured under the following conditions. ⁇ First, the charging rate was set to 0.03C. At this time, charging was performed in CCCV mode. CV was 0 V and final current was 0.04 mA. - CC discharge was performed at a discharge rate of 0.03C and a discharge voltage of 1.2V.
- initial efficiency (sometimes called "initial efficiency") was calculated.
- the cycle characteristics were investigated as follows. First, two cycles of charge and discharge were performed at 0.2C in an atmosphere of 25°C for battery stabilization, and the discharge capacity of the second cycle was measured. The battery cycle characteristics were calculated from the discharge capacity at the 3rd cycle, and the battery test was stopped at 100 cycles. Charging and discharging were performed at 0.7C for charging and 0.5C for discharging. The charge voltage was 4.3V, the discharge final voltage was 2.5V, and the charge final rate was 0.07C.
- a scanning X-ray photoelectron spectrometer PHI Quantera II manufactured by ULVAC-Phi was used.
- the diameter of the X-ray beam was 100 ⁇ m, and a neutralization gun was used.
- Example 1 The Li doping treatment was performed at a temperature 15°C lower than the boiling point of the solvent (diglyme), and the stabilization treatment temperature after doping was 580°C.
- Example 2 In the same manner as in Example 1, however, the temperature during Li doping was set to 60° C. lower than the boiling point, and the doping treatment was performed gently. After that, the stabilization treatment temperature was also set as low as 570°C.
- Example 1 As a result, compared to Example 1, it was possible to further reduce the amount of 0-valent silicon. As a result, cycle characteristics and initial efficiency were also improved from those of Example 1.
- Example 3 As in Example 1, except that the reaction temperature during Li doping was set to be 10°C lower than the boiling point, and the heat treatment temperature was 600°C.
- Example 3 the Si2p spectrum obtained by XPS analysis of the negative electrode active material of the present invention satisfied the requirements, and the cycle characteristics and initial efficiency were good.
- Example 4 The same as in Example 1, except that the temperature during Li doping was set higher than in Example 1 by 10°C. Moreover, the same heat treatment temperature as in Example 1 was used.
- Example 4 the Si2p spectrum obtained by XPS analysis of the negative electrode active material of the present invention satisfied the requirements, and the cycle characteristics and initial efficiency were good. However, the Si crystallite size increased and crystallization progressed. As a result, the cycle characteristics were lower than those of Examples 1 to 3, but the results were better than those of Comparative Examples described later.
- Example 5 to 8 The reaction temperature was set as in Example 1, but the heat treatment temperature was changed to change the crystallinity.
- the crystallite size corresponding to the Si (111) crystal plane was 5 nm or less, and there was a tendency that the lower the crystallinity, the better the cycle characteristics.
- the Li doping treatment was not performed, the initial efficiency was low and the battery characteristics were poor. Also, the maximum value of Si2p is also on the high energy side, and has a shape different from that of Example 1. It can be seen that the state of O1s is also uniform.
- Comparative Example 2 The material of Comparative Example 1 and LiH were mixed and heat-treated at 620° C. to form a Li dope.
- Si2p is a numerical value close to that of Comparative Example 1, and the waveform of O1s is also similar. It is also found that thermal doping promotes disproportionation and crystallization, and Si(111) becomes crystalline.
- Comparative Example 3 The raw material of Comparative Example 1 was Li-doped in the same manner as in Example 1. After that, heat treatment was performed at a temperature of 620° C. to immobilize the Li silicate structure in the bulk.
- a low-valence silicon compound was formed, and it became an electrochemically unstable structure that easily disproportionated due to repeated charging and discharging.
- Comparative Example 4 The raw material of Comparative Example 1 was Li-doped in the same manner as in Example 1. The temperature during Li doping was set 10° C. higher than in Example 1. Also, the reaction rate with Li was increased.
- the present invention is not limited to the above embodiments.
- the above-described embodiment is an example, and any device having substantially the same configuration as the technical idea described in the claims of the present invention and exhibiting the same effect is the present invention. included in the technical scope of
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Abstract
Description
2SiO(Si+SiO2) + 6.85Li+ + 6.85e-
→ 1.4Li3.75Si + 0.4Li4SiO4 + 0.2SiO2
反応式ではケイ素酸化物を構成するSiとSiO2がLiと反応し、LiシリサイドとLiシリケート、一部未反応であるSiO2にわかれる。
0.4≦G/H≦1.0 ・・・(1)
を満たすことが好ましい。
本発明の負極活物質は、負極活物質粒子を含む負極活物質であって、前記負極活物質粒子は、炭素層で被覆された酸化ケイ素粒子を含有し、前記酸化ケイ素粒子は、Li2SiO3を有するとともに、XPS解析で得られるSi2pスペクトルにおいて、102eV近傍に最も強いピークAを有し、100eV近傍に価数が1~3のいずれかである低価数Si化合物に該当する2番目に強いピークBを有し、99eV近傍に得られるSi:0価数のピークCの強度が、前記ピークAの強度の半分以下であることを特徴とする負極活物質である。
0.4≦G/H≦1.0 ・・・(1)
を満たすことが好ましい。
<非水電解質二次電池用負極>
続いて、このような本発明の負極活物質を含む二次電池の負極の構成について説明する。
負極集電体11は、優れた導電性材料であり、かつ、機械的な強度に長けた物で構成される。負極集電体11に用いることができる導電性材料として、例えば銅(Cu)やニッケル(Ni)が挙げられる。この導電性材料は、リチウム(Li)と金属間化合物を形成しない材料であることが好ましい。
負極活物質層12は、リチウムイオンを吸蔵、放出可能な本発明の負極活物質を含んでおり、電池設計上の観点から、さらに、負極結着剤(バインダ)や導電助剤など他の材料を含んでいてもよい。負極活物質は負極活物質粒子を含み、負極活物質粒子は酸化ケイ素粒子を含む。
・X線回折装置としては、例えばBruker社製のD8 ADVANCEを使用できる。X線源はCu Kα線、Niフィルターを使用して、出力40kV/40mA、スリット幅0.3°、ステップ幅0.008°、1ステップあたり0.15秒の計数時間にて10-40°まで測定する。
続いて、本発明の負極活物質を製造する方法の一例を説明する。
セパレータは正極と負極を隔離し、両極接触に伴う電流短絡を防止しつつ、リチウムイオンを通過させるものである。このセパレータは、例えば合成樹脂、あるいはセラミックからなる多孔質膜により形成されており、2種以上の多孔質膜が積層された積層構造を有しても良い。合成樹脂として例えば、ポリテトラフルオロエチレン、ポリプロピレン、ポリエチレンなどが挙げられる。
活物質層の少なくとも一部、又は、セパレータには、液状の電解質(電解液)が含浸されている。この電解液は、溶媒中に電解質塩が溶解されており、添加剤など他の材料を含んでいても良い。
まず、負極活物質を以下のようにして作製した。金属ケイ素と二酸化ケイ素を混合した原料を反応炉に導入し、10Paの真空度の雰囲気中で気化させたものを吸着板上に堆積させ、十分に冷却した後、堆積物を取出しボールミルで粉砕した。このようにして得た酸化ケイ素粒子のSiOxのxの値は1.0であった。続いて、酸化ケイ素粒子の粒径を分級により調整した。その後、熱分解CVDを700℃から900℃の範囲で行うことで、酸化ケイ素粒子の表面に炭素材を被覆した。
・まず充電レートを0.03C相当で行った。このとき、CCCVモードで充電を行った。CVは0Vで終止電流は0.04mAとした。
・放電レートは同様に0.03C、放電電圧は1.2V、CC放電を行った。
溶媒(ジグリム)の沸点より15℃低い温度でLiドープ処理を行い、ドープ後の安定化処理温度を580℃でおこなった。
実施例1と同様に、ただし、Liドープ時の温度を沸点より60℃低く設定し、緩やかにドープ処理を行った。その後、安定化処理温度も、570℃と低く設定した。
実施例1と同様に、ただし、Liドープ時の反応温度を沸点より10℃低い条件に設定し、熱処理温度を600℃とした。
実施例1と同様に、ただし、Liドープ時の温度を実施例1よりも10℃高く設定した。また、実施例1と同じ熱処理温度とした。
反応温度を実施例1と同様に設定し、ただし、熱処理温度を変化させ、結晶性を変化させた。
負極活物質粒子における最適な粒径を見出すため、原料の粒径を変化させた。
実施例1と比較して、Liドープ処理を行わないSiO/C材を製造した。
比較例1の材料とLiHを混ぜ、620℃で熱処理を行うことでLiドープを形成した。
比較例1の原料に、実施例1と同じ手法でLiドープを行った。その後、熱処理温度を620℃で実施し、バルク内のLiシリケート構造を固定化した。
比較例1の原料に、実施例1と同じ手法でLiドープを行った。Liドープ時の温度を実施例1よりも10℃高く設定した。また、Liとの反応速度を速めた。
比較例4と同様な材料を比較例3と同じ温度で安定化処理を行った
Claims (8)
- 負極活物質粒子を含む負極活物質であって、
前記負極活物質粒子は、炭素層で被覆された酸化ケイ素粒子を含有し、
前記酸化ケイ素粒子は、Li2SiO3を有するとともに、XPS解析で得られるSi2pスペクトルにおいて、102eV近傍に最も強いピークAを有し、100eV近傍に価数が1~3のいずれかである低価数Si化合物に該当する2番目に強いピークBを有し、99eV近傍に得られるSi:0価数のピークCの強度が、前記ピークAの強度の半分以下であることを特徴とする負極活物質。 - 前記負極活物質は、3つ以上の相構造を有することを特徴とする請求項1に記載の負極活物質。
- 前記負極活物質粒子は、XPS解析で得られるO1sスペクトルにおいて、最表層は531eV近傍に最も強いピークを有し、その下部に528eV近傍のピークを有し、その下部に532.5eV近傍にピークを有する、表層から内部にかけて、3つ以上の相構造で構成されることを特徴とする請求項1又は請求項2に記載の負極活物質。
- 前記負極活物質粒子は、前記XPS解析で得られるO1sスペクトルにおいて、532.5eV近傍に得られるピークは、532eV近傍と533eV近傍の2つのピークに分かれていることを特徴とする請求項3に記載の負極活物質。
- 前記負極活物質粒子は、前記負極活物質粒子を充放電する前において、Cu-Kα線を用いたX線回折により得られるSi(111)結晶面に起因するピークを有し、該結晶面に対応する結晶子サイズは5.0nm以下であり、かつ、Li2SiO3(111)結晶面に起因するピークの強度Hに対する前記Si(111)結晶面に起因するピークの強度Gの比率G/Hは、下記の式(1)
0.4≦G/H≦1.0 ・・・(1)
を満たすことを特徴とする請求項1から請求項4のいずれか1項に記載の負極活物質。 - 前記負極活物質粒子はメジアン径が5.5μm以上15μm以下であることを特徴とする請求項1から請求項5のいずれか1項に記載の負極活物質。
- 前記炭素層は、最表層に、酸素と化合物状態で存在する部分を有することを特徴とする請求項1から請求項6のいずれか1項に記載の負極活物質。
- 酸化ケイ素粒子を作製する工程と、
前記酸化ケイ素粒子を炭素層で被覆する工程と、
前記炭素層で被覆した酸化ケイ素粒子に酸化還元法によりリチウムを挿入する工程と、
前記リチウムを挿入した酸化ケイ素粒子を熱処理することにより、Li2SiO3を含有する酸化ケイ素粒子とする工程と
により、負極活物質粒子を作製し、該作製した負極活物質粒子を用いて負極活物質を製造する方法であって、
前記リチウムの挿入の際の温度と、前記熱処理の温度を調整することにより、前記酸化ケイ素粒子を、XPS解析で得られるSi2pスペクトルにおいて、102eV近傍に最も強いピークAを有し、100eV近傍に価数が1~3のいずれかである低価数Si化合物に該当する2番目に強いピークBを有し、99eV近傍に得られるSi:0価数のピークCの強度が、前記ピークAの半分以下であるものとすることを特徴とする負極活物質の製造方法。
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