WO2015025443A1 - 負極活物質、負極活物質材料、負極電極、リチウムイオン二次電池、負極活物質の製造方法、並びに、リチウムイオン二次電池の製造方法 - Google Patents
負極活物質、負極活物質材料、負極電極、リチウムイオン二次電池、負極活物質の製造方法、並びに、リチウムイオン二次電池の製造方法 Download PDFInfo
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- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
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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
- C01B33/113—Silicon oxides; Hydrates thereof
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- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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- H01M10/058—Construction or manufacture
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- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/134—Electrodes based on metals, Si or alloys
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- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/139—Processes of manufacture
- H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
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- 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
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- 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
- H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
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- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
- H01M4/625—Carbon or graphite
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- H—ELECTRICITY
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- 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
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- H—ELECTRICITY
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- 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
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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
- H01M4/04—Processes of manufacture in general
- H01M4/0402—Methods of deposition of the material
- H01M4/0404—Methods of deposition of the material by coating on electrode collectors
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- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/362—Composites
- H01M4/364—Composites as mixtures
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- H—ELECTRICITY
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- 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
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- 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
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- 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
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
Definitions
- the present invention relates to a negative electrode active material capable of occluding and releasing lithium ions, a negative electrode active material containing the negative electrode active material, a negative electrode having a negative electrode active material layer formed of the negative electrode active material, and the negative electrode.
- the present invention relates to a lithium ion secondary battery.
- This secondary battery is not limited to a small electronic device, but is also considered to be applied to a large-sized electronic device represented by an automobile or the like, or an electric power storage system represented by a house.
- lithium ion secondary batteries are highly expected because they are small in size and easy to increase in capacity, and can obtain higher energy density than lead batteries and nickel cadmium batteries.
- the above lithium ion secondary battery includes a positive electrode, a negative electrode, and a separator together with an electrolyte, and the negative electrode includes a negative electrode active material involved in a charge / discharge reaction.
- this negative electrode active material a carbon material is widely used, but further improvement in battery capacity is required due to recent market demand.
- silicon As a negative electrode active material, use of silicon as a negative electrode active material has been studied. This is because the theoretical capacity of silicon (4199 mAh / g) is 10 times or more larger than the theoretical capacity of graphite (372 mAh / g), so that significant improvement in battery capacity can be expected.
- the development of a siliceous material as a negative electrode active material has been examined not only for silicon itself but also for compounds represented by alloys and oxides.
- the shape of the active material has been studied from a standard coating type for carbon materials to an integrated type directly deposited on a current collector.
- the negative electrode active material when silicon is used as the negative electrode active material as the main raw material, the negative electrode active material expands and contracts during charge / discharge, and therefore, it tends to break mainly near the surface of the negative electrode active material. Further, an ionic material is generated inside the active material, and the negative electrode active material is easily broken. When the negative electrode active material surface layer is cracked, a new surface is generated thereby increasing the reaction area of the active material. At this time, a decomposition reaction of the electrolytic solution occurs on the new surface, and a coating that is a decomposition product of the electrolytic solution is formed on the new surface, so that the electrolytic solution is consumed. For this reason, the cycle characteristics are likely to deteriorate.
- silicon and amorphous silicon dioxide are deposited simultaneously using a vapor phase method (see, for example, Patent Document 1). Further, in order to obtain a high battery capacity and safety, a carbon material (electron conductive material) is provided on the surface layer of the silicon oxide particles (see, for example, Patent Document 2). Furthermore, in order to improve cycle characteristics and obtain high input / output characteristics, an active material containing silicon and oxygen is produced, and an active material layer having a high oxygen ratio in the vicinity of the current collector is formed ( For example, see Patent Document 3). Further, in order to improve cycle characteristics, oxygen is contained in the silicon active material, the average oxygen content is 40 at% or less, and the oxygen content is increased at a location close to the current collector. (For example, refer to Patent Document 4).
- Si phase (for example, see Patent Document 5) by using a nanocomposite containing SiO 2, M y O metal oxide in order to improve the initial charge and discharge efficiency.
- 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 in the vicinity of the active material and current collector interface The active material is controlled within a range of 0.4 or less (see, for example, Patent Document 7).
- Patent Document 8 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 siliceous material (see, for example, Patent Document 9).
- conductivity is imparted by using silicon oxide and forming a graphite film on the surface layer (see, for example, Patent Document 10).
- Patent Document 10 with respect to the shift value obtained from the RAMAN spectrum for graphite coating, with broad peaks appearing at 1330 cm -1 and 1580 cm -1, 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 improve high battery capacity and cycle characteristics (see, for example, Patent Document 11). Further, in order to improve overcharge and overdischarge characteristics, silicon oxide in which the atomic ratio of silicon and oxygen is controlled to 1: y (0 ⁇ y ⁇ 2) is used (see, for example, Patent Document 12).
- lithium ion secondary batteries which are the main power sources, are required to have an increased battery capacity.
- development of a lithium ion secondary battery composed of a negative electrode using a siliceous material as a main material is desired.
- the lithium ion secondary battery using a siliceous material is desired to have a cycle characteristic close to that of a lithium ion secondary battery using a carbon material.
- a negative electrode active material that exhibits cycle stability equivalent to that of a lithium ion secondary battery using a carbon material has not been proposed.
- the present invention has been made in view of the above problems, and when used as a negative electrode active material of a lithium ion secondary battery, it is possible to improve battery capacity, cycle characteristics, and initial charge / discharge characteristics.
- a negative electrode active material, a negative electrode active material containing the negative electrode active material, a negative electrode having a negative electrode active material layer formed of the negative electrode active material, and a lithium ion secondary battery using the negative electrode With the goal.
- the present invention provides a negative electrode active material including negative electrode active material particles, wherein the negative electrode active material particles are made of SiO x (0.5 ⁇ x ⁇ 1.6).
- the silicon-based material obtained from 29Si-MAS-NMR spectrum, the Si region peak value intensity value A given at ⁇ 50 to ⁇ 95 ppm as the chemical shift value, and the chemical shift value ⁇ 96 to ⁇
- the peak value intensity value B of SiO 2 region given at 150 ppm satisfies the relationship of A / B ⁇ 0.8.
- the negative electrode active material including the negative electrode active material particles containing the silicon-based material is converted into lithium ion.
- the negative electrode active material for a secondary battery it has a high battery capacity and good cycle characteristics and initial charge / discharge characteristics.
- the negative electrode active material particles preferably have a peak value in a range given by -70 to -85 ppm as a chemical shift value obtained from 29Si-MAS-NMR spectrum. By setting the peak value of the Si region of the negative electrode active material particles in the above range, better cycle characteristics can be obtained.
- the negative electrode active material particles preferably include at least two or more peaks in a peak range obtained from 29Si-MAS-NMR spectrum and given as a chemical shift value of ⁇ 50 to ⁇ 95 ppm. Better initial charge / discharge characteristics can be obtained when there are two or more Si region peaks in the negative electrode active material particles.
- the negative electrode active material particles correspond to at least one of Li 2 SiO 3 and Li 4 SiO 4 in a peak range obtained from 29Si-MAS-NMR spectrum and given as a chemical shift value of ⁇ 50 to ⁇ 95 ppm. It is preferable to include a peak.
- the negative electrode active material particles can preferably contain the above lithium silicate.
- the negative electrode active material particles preferably include a peak corresponding to metal Si within a peak range obtained from 29Si-MAS-NMR spectrum and given as a chemical shift value of ⁇ 50 to ⁇ 95 ppm.
- the negative electrode active material particles can suitably contain the above-described metal Si state.
- the negative electrode active material particles preferably include at least one of Li 2 SiO 3 , Li 4 SiO 4 , Li 2 O, and Li 2 CO 3 .
- the negative electrode active material particles having such a configuration can be suitably used.
- the negative electrode active material particles include at least two of Li 2 SiO 3 , Li 4 SiO 4 , Li 2 O, and Li 2 CO 3 .
- the negative electrode active material particles having such a configuration can be suitably used.
- the Li 2 SiO 3 preferably has a half-value width (2 ⁇ ) of a diffraction peak obtained near 38.2680 ° obtained by X-ray diffraction of 0.75 ° or more.
- the negative electrode active material particles contain Li 2 SiO 3 having such crystallinity, better cycle characteristics and initial charge / discharge characteristics can be obtained.
- the Li 4 SiO 4 preferably has a half width (2 ⁇ ) of a diffraction peak obtained near 23.9661 ° obtained by X-ray diffraction of 0.2 ° or more.
- the negative electrode active material particles contain Li 2 SiO 3 having such crystallinity, better cycle characteristics and initial charge / discharge characteristics can be obtained.
- the Li 2 SiO 3 and the Li 4 SiO 4 are preferably amorphous. As described above, when the negative electrode active material particles contain the amorphous Li compound, better cycle characteristics and initial charge / discharge characteristics can be obtained.
- the negative electrode active material particles preferably include a fluorine compound having an island shape or unevenness on at least a part of its surface.
- a fluorine compound having an island shape or unevenness on at least a part of its surface.
- the fluorine compound is preferably lithium fluoride or a decomposition product of LiPF 6 .
- the above can be suitably used as the fluorine compound on the surface of the negative electrode active material particles.
- the negative electrode active material has a half-width (2 ⁇ ) of a diffraction peak due to the (111) crystal plane obtained by X-ray diffraction of 1.2 ° or more, and a crystallite size corresponding to the crystal plane is 7. It is preferable that it is 5 nm or less.
- the negative electrode active material has the above crystallinity, better cycle characteristics and initial charge / discharge characteristics can be obtained when such a negative electrode active material is used as the negative electrode active material of a lithium ion secondary battery.
- the median diameter of the negative electrode active material particles is preferably 0.5 ⁇ m or more and 20 ⁇ m or less. When the median diameter of the negative electrode active material particles is within the above range, better cycle characteristics can be obtained when a negative electrode active material containing such negative electrode active material particles is used as the negative electrode active material of a lithium ion secondary battery. In addition, initial charge / discharge characteristics can be obtained.
- the negative electrode active material particles preferably include a carbon material in a surface layer portion. As described above, since the negative electrode active material particles include a carbon material in the surface layer portion, conductivity can be improved. Therefore, the negative electrode active material including such negative electrode active material particles is used as a negative electrode active material for a lithium ion secondary battery. When used as a material, battery characteristics can be improved when a negative electrode active material including such negative electrode active material particles is used as a negative electrode active material of a lithium ion secondary battery.
- the average thickness of the carbon material to be coated is preferably 1 nm or more and 5000 nm or less. If the average thickness of the carbon material to be coated is 1 nm or more, improved conductivity is obtained. If the average thickness of the carbon material to be coated is 5000 nm or less, the negative electrode active material containing such negative electrode active material particles is lithium. When used as a negative electrode active material for an ion secondary battery, a decrease in battery capacity can be suppressed.
- the negative electrode active material particles have SiO x , carbon, and a fluorine compound at least partially, or have SiO x and a fluorine compound.
- the negative electrode active material particles having such a configuration can be suitably used.
- the average coverage of the coating layer made of the fluorine compound is preferably 30% or more. By using the above average coverage, better cycle characteristics and initial charge / discharge characteristics can be obtained when a negative electrode active material containing such negative electrode active material particles is used as a negative electrode active material of a lithium ion secondary battery. It is done.
- the average coverage of the coating layer made of the carbon material is preferably 30% or more. By setting the average coverage as described above, better load characteristics can be obtained when a negative electrode active material including such negative electrode active material particles is used as a negative electrode active material of a lithium ion secondary battery.
- the negative electrode active material layer material preferably contains the negative electrode active material and a carbon material.
- the conductivity of the negative electrode active material layer can be improved by including the carbon material together with the negative electrode active material of the present invention as a material for forming the negative electrode active material layer.
- the present invention also includes a negative electrode active material layer formed of the negative electrode active material of the present invention and a negative electrode current collector, and the negative electrode active material layer is formed on the negative electrode current collector.
- the negative electrode current collector includes carbon and sulfur, and the content thereof is 100 ppm or less.
- the negative electrode current collector constituting the negative electrode includes carbon and sulfur as described above, so that deformation of the negative electrode during charging can be suppressed.
- the present invention provides a lithium ion secondary battery using a negative electrode containing any of the negative electrode active materials described above as a negative electrode.
- a lithium ion secondary battery using a negative electrode containing such a negative electrode active material has a high capacity and good cycle characteristics and initial charge / discharge characteristics.
- the present invention is a method for producing a negative electrode active material comprising negative electrode active material particles containing a silicon-based material composed of SiO x , wherein the x is 0.5 or more and 1.6 as the silicon-based material.
- the peak value intensity value A of the Si region given by -50 to -95 ppm as the chemical shift value and the chemical shift value given by -96 to -150 ppm obtained from 29Si-MAS-NMR spectrum.
- a method for producing a negative electrode active material wherein a material having a peak value intensity value B in the SiO 2 region satisfying a relationship of A / B ⁇ 0.8 is selected and used.
- a silicon-based material in this way and producing a negative electrode active material, when used as a negative electrode active material of a lithium ion secondary battery, it has high capacity and good cycle characteristics and initial charge / discharge characteristics.
- the negative electrode active material which has can be manufactured.
- a negative electrode is produced using the negative electrode active material produced by the method for producing a negative electrode active material, and a lithium ion secondary battery is produced using the produced negative electrode.
- a method for manufacturing a secondary battery is provided.
- This manufacturing method uses a negative electrode active material including negative electrode active material particles containing a silicon-based material selected as described above, so that lithium ions have high capacity and good cycle characteristics and initial charge / discharge characteristics.
- a secondary battery can be manufactured.
- the negative electrode active material of the present invention when used as the negative electrode active material of a lithium ion secondary battery, high capacity and good cycle characteristics and initial charge / discharge characteristics can be obtained. Moreover, if it is the manufacturing method of the negative electrode active material of this invention, the negative electrode active material for lithium ion secondary batteries which has favorable cycling characteristics and initial stage charge / discharge characteristics can be manufactured.
- FIG. 1 It is sectional drawing which shows the structure of the negative electrode for lithium ion secondary batteries of this invention. It is a TEM photograph showing the cross-sectional structure of negative electrode active material particles. It is a figure showing the structural example (laminate film type) of the lithium secondary battery of this invention. It is the SEM photograph which shows the cross-section of a negative electrode active material particle, the EDX mapping photograph which shows the cross-section of a negative electrode active material particle, and the composition produced
- the present invention will be described in detail as an example of an embodiment with reference to the drawings, but the present invention is not limited thereto.
- a negative electrode using a silicon material as a main material as a negative electrode of a lithium ion secondary battery has been studied.
- the lithium ion secondary battery using this silicon material is expected to have cycle characteristics similar to those of a lithium ion secondary battery using a carbon material, but the cycle is equivalent to that of a lithium ion secondary battery using a carbon material.
- No proposal has been made for a negative electrode active material exhibiting stability.
- the inventors have made extensive studies on a negative electrode active material that can provide good cycle characteristics when used as a negative electrode of a lithium ion secondary battery.
- the silicon-based material has a composition ratio of SiO x (0.5 ⁇ x ⁇ 1.6) and is obtained from 29Si-MAS-NMR spectrum with a chemical shift value of ⁇ 50 to ⁇ 95 ppm.
- the peak value intensity value A of the given Si region and the peak value strength value B of the SiO 2 region given as a chemical shift value of ⁇ 96 to ⁇ 150 ppm satisfy the relationship of A / B ⁇ 0.8.
- FIG. 1 illustrates a cross-sectional configuration of a negative electrode for a lithium ion secondary battery (hereinafter referred to as “negative electrode”) according to an embodiment of the present invention
- FIG. It is a photograph (Microscope: Transmission electron microscope).
- the negative electrode 10 is configured to have a negative electrode active material layer 12 on a negative electrode current collector 11. Further, the negative electrode active material layer 12 may be provided on both surfaces or only one surface of the negative electrode current collector 11. 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 12 is an excellent conductive material and is composed of a material having high mechanical strength.
- the conductive material include copper (Cu) and nickel (Ni).
- the 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) or sulfur (S) in addition to the main element. This is because the physical strength of the negative electrode current collector 11 is improved.
- the current collector contains the above-described element, there is an effect of suppressing electrode deformation including the current collector.
- content of said content element is not specifically limited, Especially it is preferable that it is 100 ppm or less. This is because a higher deformation suppressing effect can be obtained.
- the surface of the negative electrode current collector 11 may be roughened or may not be roughened.
- the roughened negative electrode current collector is, for example, a metal foil subjected to electrolytic treatment, embossing treatment, or chemical etching treatment.
- the non-roughened negative electrode current collector is, for example, a rolled metal foil.
- the negative electrode active material layer 11 includes a plurality of particulate negative electrode active materials (hereinafter referred to as negative electrode active material particles) capable of occluding and releasing lithium ions. From the viewpoint of battery design, the negative electrode binder is further included. (Binder) and other materials such as a conductive aid may be included.
- the negative electrode active material particles are composed of a core part capable of inserting and extracting lithium ions, a carbon coating part capable of obtaining electrical conductivity, and a fluorine compound part having an effect of suppressing the decomposition reaction of the electrolytic solution. Confirmed by EDX photograph. In this case, occlusion and release of lithium ions may be performed in at least a part of the carbon coating portion.
- the fluorine compound part covers at least a part of the surface of the negative electrode active material particles. In this case, the covering portion is effective in any of an island shape, a film shape, and an uneven shape.
- the negative electrode active material particles are a silicon oxide material containing a silicon-based material (SiO x : 0.5 ⁇ x ⁇ 1.6), and it is preferable that x is close to 1 as the composition of the silicon-based material. This is because high cycle characteristics can be obtained.
- the siliceous material composition in the present invention does not necessarily mean 100% purity, and may contain a trace amount of impurity elements.
- the silicon-based material has a Si region peak intensity value A given by ⁇ 50 to ⁇ 95 ppm as a chemical shift value obtained from 29Si-MAS-NMR spectrum and a SiO 2 region given by ⁇ 96 to ⁇ 150 ppm as a chemical shift value.
- the peak intensity value B satisfies the relationship of A / B ⁇ 0.8, stable battery characteristics can be obtained.
- the peak intensity value means the peak height at the peak value. Further, when there are a plurality of peaks, the peak intensity value can be obtained as the sum of the plurality of peak heights.
- Li 4 SiO 4 , Li 2 SiO 3 , Li 2 O, and Li 2 CO 3 show particularly good characteristics.
- an electrochemical method is preferably used as a method for producing the selective compound (Li compound).
- a selective compound can be produced by changing conditions such as potential regulation with respect to the lithium counter electrode or current regulation. Further, the selective compound is partially produced by an electrochemical method, and then dried in a carbonic acid atmosphere or an oxygen atmosphere to obtain a denser substance.
- Li compounds can be quantified by NMR (Nuclear Magnetic Resonance) or XPS (X-ray photoelectron spectroscopy X-ray photoelectron spectroscopy).
- NMR Nuclear Magnetic Resonance
- XPS X-ray photoelectron spectroscopy X-ray photoelectron spectroscopy
- an X-ray photoelectron spectrometer is used as an apparatus, a monochromatic AlK ⁇ ray is used as an X-ray source, an X-ray spot diameter is 100 ⁇ m ⁇ , and an Ar ion gun sputtering condition is 0.5 kV / It was 2 mm ⁇ 2 mm.
- Li compound formation in the Si region can be reduced or avoided, and the substance becomes stable in the air, in the aqueous slurry, or in the solvent slurry. Moreover, according to said method, it is possible to make a more stable substance compared with the thermal reforming which makes a compound at random.
- Li 4 SiO 4 , Li 2 SiO 3 , Li 2 O, and Li 2 CO 3 generated in the bulk improves the characteristics. It is a case where two or more of these coexist.
- save characteristic of powder improves dramatically by producing
- the material of the fluorine compound include LiF and LiPF 6 decomposition products, and LiF is most desirable.
- generation method of a fluorine compound is not specifically limited, The electrochemical method is the most preferable.
- the lower the crystallinity of the negative electrode active material, the better, and the half-value width (2 ⁇ ) of the diffraction peak attributed to the Si (111) crystal plane obtained by X-ray diffraction is 1.2 ° or more, and it also originates from the crystal plane
- the crystallite size is desirably 7.5 nm or less.
- the presence of Si crystals not only deteriorates battery characteristics, but also makes it difficult to generate a stable Li compound.
- the median diameter (D 50 : particle diameter when the cumulative volume is 50%) of the negative electrode active material particles is not particularly limited, but is preferably 0.5 ⁇ m to 20 ⁇ m. This is because, if the median diameter is in the above range, lithium ions are easily occluded and released during charging and discharging, and the particles are difficult to break. By setting the median diameter to 0.5 ⁇ m or more, an increase in battery irreversible capacity due to an increase in surface area can be suppressed. On the other hand, by setting the median diameter to 20 ⁇ m or less, it is possible to prevent the particles from being easily broken and a new surface from being easily produced.
- the average thickness of the carbon coating is not particularly limited, but is preferably 1 nm to 5000 nm. By setting the average thickness to 1 nm or more, electrical conductivity can be improved. It can suppress that battery capacity falls by making average thickness 5000 nm or less.
- the average thickness of the coated carbon part is calculated by the following procedure, for example.
- the negative electrode active material is observed with a TEM at an arbitrary magnification.
- This magnification is preferably a magnification by which the thickness of the covering portion can be visually confirmed so that the thickness can be measured.
- the thickness of the covering portion is measured at any 15 points. In this case, it is preferable to set the measurement position widely and randomly without concentrating on a specific place as much as possible.
- the average value of the thicknesses of the 15 covering portions is calculated.
- the coverage of the carbon material is not particularly limited, but is preferably as high as possible. If the coverage is 30% or more, sufficient electrical conductivity can be obtained.
- the method for coating the carbon material is not particularly limited, but a sugar carbonization method and a pyrolysis method of hydrocarbon gas are preferable. This is because the coverage can be improved.
- the negative electrode binder for example, one or more of polymer materials, synthetic rubbers, and the like can be used.
- the polymer material include polyvinylidene fluoride, polyimide, polyamideimide, aramid, polyacrylic acid, lithium polyacrylate, and carboxymethylcellulose.
- the synthetic rubber include styrene butadiene rubber, fluorine rubber, and ethylene propylene diene.
- the negative electrode conductive additive for example, one or more carbon materials such as carbon black, acetylene black, graphite, ketjen black, carbon nanotube, and carbon nanofiber can be used.
- the negative electrode active material layer 12 may be produced in a mixed state with a carbon material. As a result, the electrical resistance of the negative electrode active material layer 12 can be reduced and the expansion stress associated with charging can be reduced.
- the carbon material include pyrolytic carbons, cokes, glassy carbon fibers, organic polymer compound fired bodies, and carbon blacks.
- the negative electrode active material layer 12 is formed by, for example, a coating method.
- the coating method is a method in which negative electrode active material particles and the above-mentioned binder, and the like, and a conductive additive and a carbon material are mixed as necessary, and then dispersed and applied in an organic solvent or water.
- the negative electrode 10 is manufactured by the following procedure, for example. First, a raw material that generates silicon oxide gas is heated in a temperature range of 900 ° C. to 1600 ° C. under reduced pressure in the presence of an inert gas to generate silicon oxide gas. At this time, the raw material is a mixture of metal silicon powder and silicon dioxide powder, and considering the surface oxygen of the metal silicon powder and the presence of trace amounts of oxygen in the reactor, the mixing molar ratio is 0.8 ⁇ metal silicon powder / It is desirable that the silicon dioxide powder is in the range of ⁇ 1.3. Next, the generated gas is solidified and deposited on the adsorption plate. Next, the deposit is taken out with the temperature in the reactor lowered to 100 ° C.
- Si crystallites in the particles are controlled by changing the vaporization temperature or by heat treatment after generation.
- the deposited SiO film may be formed by directly depositing the generated silicon oxide gas on the copper foil.
- a carbon layer is preferably formed on the surface layer of the obtained silicon oxide powder material.
- a thermal decomposition CVD method is desirable.
- a method for generating a carbon material layer by pyrolytic CVD will be described.
- silicon oxide powder is set in a furnace.
- hydrocarbon gas is introduced into the furnace to raise the temperature in the furnace.
- the decomposition temperature is not particularly limited, but is preferably 1200 ° C. or lower, and more preferably 950 ° C. or lower. By making the decomposition temperature 1200 ° C. or less, disproportionation of the active material particles can be suppressed.
- a carbon layer is formed on the silicon oxide powder.
- hydrocarbon gas is not particularly limited, it is desirable in C n H m composition is n ⁇ 3. If n ⁇ 3, the production cost can be reduced, and the physical properties of the decomposition product can be improved.
- in-bulk reforming can be performed using the in-bulk reforming apparatus 20 shown in FIG.
- the reformer 20 in the bulk is disposed in the bathtub 27 filled with the organic solvent 23, the positive electrode (lithium source) 21 disposed in the bathtub 27 and connected to one of the power sources 26, and the bathtub 27. It has a powder storage container 25 connected to the other side of the power source 26 and a separator 24 provided between the positive electrode 21 and the powder storage container 25.
- reference numeral 22 is silicon oxide powder.
- the modified active material is then dried in an oxygen atmosphere, a carbon dioxide atmosphere, a fluorine atmosphere, or a hydrogen atmosphere.
- an oxygen atmosphere a carbon dioxide atmosphere, a fluorine atmosphere, or a hydrogen atmosphere.
- the temperature is not particularly limited, but it is desirable to set the temperature to 800 ° C. or lower. This is because particle disproportionation can be suppressed.
- the fluorine compound is desirably generated by changing the potential and temperature conditions. Thereby, a denser film can be obtained.
- lithium fluoride is desirably held at 45 ° C. or higher when Li is inserted or removed.
- the obtained modified particles may not contain a carbon layer. However, when more uniform control is required in the reforming process in the bulk, it is necessary to reduce the potential distribution, and it is desirable that a carbon layer exists.
- organic solvent 23 in the bathtub 27 ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, fluoromethyl methyl carbonate, difluoromethyl methyl carbonate, or the like can be used.
- electrolyte salt contained in the organic solvent 23 lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), or the like can be used.
- the positive electrode 21 may use a Li foil or a Li-containing compound. Furthermore, as the Li-containing compound, lithium carbonate, lithium oxide, lithium chloride, lithium cobaltate, lithium olivine, or the like can be used.
- the negative electrode active material particles and other materials such as a negative electrode binder and a conductive additive are mixed to form a negative electrode mixture, and then an organic solvent or water is added to obtain a slurry.
- the negative electrode mixture slurry is applied to the surface of the negative electrode current collector 11 and dried to form the negative electrode active material layer 12. At this time, you may perform a heat press etc. as needed.
- in-bulk modification is applied to the silicon oxide powder, but in-bulk modification can be performed with the silica material applied to the electrode, and the silica material and carbon material are mixed and applied to the electrode. In-bulk reforming can be performed in the state.
- the negative electrode described above by changing the SiO 2 component present in the bulk of the negative electrode active material particles into a stable Li compound, the initial efficiency of the battery and the stability of the active material accompanying cycle characteristics are improved.
- the peak intensity value A in the Si region obtained from 29Si-MAS-NMR spectrum and the peak intensity value B in the SiO 2 region must satisfy the relationship of A / B ⁇ 0.8.
- Li silicate and lithium carbonate are generated on the surface layer, higher effects can be obtained.
- coating the anode active material particles with a carbon material can make the compound state in the bulk more uniform, and the presence of fluoride in the surface layer of the anode active material particles can stabilize the active material. Property can be improved and higher effects can be obtained.
- the negative electrode current collector 11 contains 100 ppm or less of carbon and sulfur, an effect of suppressing deformation of the electrode including the current collector can be obtained.
- a laminated film type secondary battery 30 shown in FIG. 3 is one in which a wound electrode body 31 is accommodated mainly in a sheet-like exterior member 35. This wound body has a separator between a positive electrode and a negative electrode and is wound. There is also a case where a separator is provided between the positive electrode and the negative electrode and a laminate is accommodated.
- the positive electrode lead 32 is attached to the positive electrode
- the negative electrode lead 33 is attached to the negative electrode.
- the outermost peripheral part of the electrode body is protected by a protective tape.
- the positive and negative electrode leads are led out in one direction from the inside of the exterior member 35 to the outside, for example.
- the positive electrode lead 32 is formed of a conductive material such as aluminum
- the negative electrode lead 33 is formed of a conductive material such as nickel or copper.
- the exterior member 35 is, for example, a laminate film in which a fusion layer, a metal layer, and a surface protective layer are laminated in this order.
- This laminate film is formed of two films so that the fusion layer faces the electrode body 31.
- the outer peripheral edges of the fusion layer are bonded together with an adhesive or an adhesive.
- the fusion layer is, for example, a film of polyethylene or polypropylene, and the metal layer is aluminum foil or the like.
- the protective layer is, for example, nylon.
- An adhesion film 34 is inserted between the exterior member 35 and the positive and negative electrode leads to prevent intrusion of outside air.
- This material is, for example, polyethylene, polypropylene, or polyolefin resin.
- the positive electrode has, for example, a positive electrode active material layer on both surfaces or one surface of the positive electrode current collector, similarly to the negative electrode 10 of FIG.
- the positive electrode current collector is formed of, for example, a conductive material such as aluminum.
- the positive electrode active material layer includes one or more of positive electrode materials capable of occluding and releasing lithium ions, and includes other materials such as a binder, a conductive additive, and a dispersant depending on the design. You may go out.
- the details regarding the binder and the conductive additive can be the same as, for example, the negative electrode binder and the negative electrode conductive additive already described.
- a lithium-containing compound is desirable.
- the lithium-containing compound include a composite oxide composed of lithium and a transition metal element, or a phosphate compound having lithium and a transition metal element.
- these positive electrode materials compounds having at least one of nickel, iron, manganese, and cobalt are preferable.
- the chemical formulas of these positive electrode materials are represented by, for example, Li x M1O 2 or Li y M2PO 4 .
- M1 and M2 represent at least one or more transition metal elements, and the values of x and y vary depending on the battery charge / discharge state, but generally 0.05 ⁇ x ⁇ 1 .10, 0.05 ⁇ y ⁇ 1.10.
- Examples of the composite oxide having lithium and a transition metal element include lithium cobalt composite oxide (Li x CoO 2 ) and lithium nickel composite oxide (Li x NiO 2 ).
- the negative electrode has the same configuration as the negative electrode 10 for lithium ion secondary battery in FIG. 1 described above, and has, for example, a negative electrode active material layer on both sides of the current collector.
- This negative electrode preferably has a negative electrode charge capacity larger than the electric capacity (charge capacity as a battery) obtained from the positive electrode active material agent. Thereby, precipitation of lithium metal on the negative electrode can be suppressed.
- the positive electrode active material layer is provided on a part of both surfaces of the positive electrode current collector, and the negative electrode active material layer is also provided on a part of both surfaces of the negative electrode current collector.
- the negative electrode active material layer provided on the negative electrode current collector is provided with a region where there is no opposing positive electrode active material layer. This is to perform a stable battery design.
- the separator separates the positive electrode and the negative electrode, and allows lithium ions to pass through while preventing current short-circuiting due to bipolar contact.
- This separator is formed of, for example, a porous film made of synthetic resin or ceramic, and may have a laminated structure in which two or more kinds of porous films are laminated.
- the synthetic resin include polytetrafluoroethylene, polypropylene, and polyethylene.
- Electrode At least a part of the active material layer or the separator is impregnated with a liquid electrolyte (electrolytic solution).
- This electrolytic solution has an electrolyte salt dissolved in a solvent, and may contain other materials such as additives.
- a non-aqueous solvent can be used as the solvent.
- the non-aqueous solvent include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran and the like.
- the dissociation property and ion mobility of the electrolyte salt are improved by using a combination of a high viscosity solvent such as ethylene carbonate and propylene carbonate and a low viscosity solvent such as dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. be able to.
- a high viscosity solvent such as ethylene carbonate and propylene carbonate
- a low viscosity solvent such as dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.
- a halogenated chain carbonate ester or a halogenated cyclic carbonate ester is contained as a solvent.
- the halogenated chain carbonate ester is a chain carbonate ester having halogen as a constituent element (at least one hydrogen is replaced by halogen).
- the halogenated cyclic carbonate is a cyclic carbonate having halogen as a constituent element (that is, at least one hydrogen is replaced by a halogen).
- halogen is not particularly limited, but fluorine is preferred. This is because a film having a better quality than other halogens is formed. Further, the larger the number of halogens, the better. This is because the resulting coating is more stable and the decomposition reaction of the electrolyte is reduced.
- halogenated chain carbonate examples include fluoromethyl methyl carbonate and difluoromethyl methyl carbonate.
- halogenated cyclic carbonate examples include 4-fluoro-1,3-dioxolane-2-one, 4,5-difluoro-1,3-dioxolane-2-one, and the like.
- the solvent additive contains an unsaturated carbon bond cyclic carbonate. This is because a stable film is formed on the negative electrode surface during charging and discharging, and the decomposition reaction of the electrolytic solution can be suppressed.
- unsaturated carbon-bonded cyclic ester carbonate include vinylene carbonate and vinyl ethylene carbonate.
- sultone cyclic sulfonic acid ester
- 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.
- the acid anhydride include propanedisulfonic acid anhydride.
- the electrolyte salt can contain, for example, any one or more of light metal salts such as lithium salts.
- the lithium salt 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 ion conductivity is obtained.
- a positive electrode is manufactured using the positive electrode material described above.
- a positive electrode active material and, if necessary, a binder, a conductive additive and the like are mixed to form a positive electrode mixture, and then dispersed in an organic solvent to obtain a positive electrode mixture slurry.
- the mixture slurry is applied to the positive electrode current collector with a coating apparatus such as a die coater having a knife roll or a die head, and dried with hot air to obtain a positive electrode active material layer.
- the positive electrode active material layer is compression molded with a roll press or the like. At this time, it may be heated or repeated a plurality of times.
- a positive electrode active material layer is formed on both surfaces of the positive electrode current collector. At this time, the active material application lengths on both sides may be shifted.
- a negative electrode is produced by forming a negative electrode active material layer on the negative electrode current collector using the same operation procedure as that of the negative electrode 10 for lithium ion secondary batteries described above.
- the electrolytic solution is adjusted.
- the positive electrode lead 32 is attached to the positive electrode current collector and the negative electrode lead 33 is attached to the negative electrode current collector by ultrasonic welding or the like.
- the positive electrode and the negative electrode are laminated or wound through a separator to produce a wound electrode body 31, and a protective tape is adhered to the outermost periphery thereof.
- the wound body is molded so as to have a flat shape.
- the insulating portions of the exterior member 35 are adhered to each other by a thermal fusion method, and the wound electrode body is released in only one direction. Enclose.
- the laminated film type secondary battery 30 can be manufactured as described above.
- Example 1-1 to Example 1-5) The laminate film type lithium secondary battery 30 shown in FIG. 3 was produced by the following procedure.
- the positive electrode active material is a mixture of 95% by mass of LiCoO 2 which is a lithium cobalt composite oxide, 2.5% by mass of a positive electrode conductive additive, and 2.5% by mass of a positive electrode binder (polyvinylidene fluoride: PVDF).
- a positive electrode mixture was obtained.
- the positive electrode mixture was dispersed in an organic solvent (N-methyl-2-pyrrolidone: NMP) to obtain a paste slurry.
- the slurry was applied to both surfaces of the positive electrode current collector with a coating apparatus having a die head, and dried with a hot air drying apparatus. At this time, a positive electrode current collector having a thickness of 15 ⁇ m was used.
- compression molding was performed with a roll press.
- a negative electrode was produced.
- the negative electrode active material a raw material mixed with metallic silicon and silicon dioxide is introduced into a reaction furnace, vaporized in a vacuum atmosphere of 10 Pa is deposited on an adsorption plate, sufficiently cooled, and then the deposit is taken out. It grind
- the produced powder was reformed in bulk using an electrochemical method in a 1: 1 mixed solvent of propylene carbonate and ethylene carbonate (containing 1.3 mol / Kg of electrolyte salt) using the bulk reformer 20. Went. The obtained material was dried in a carbon dioxide atmosphere as necessary.
- the negative electrode active material particles and the negative electrode binder precursor, the conductive auxiliary agent 1 and the conductive auxiliary agent 2 were mixed at a dry weight ratio of 80: 8: 10: 2, and then diluted with NMP to obtain a paste form.
- Negative electrode mixture slurry In this case, NMP was used as a solvent for the polyamic acid.
- an electrolyte salt lithium hexafluorophosphate: LiPF 6
- FEC fluoro-1,3-dioxolan-2-one
- EC ethylene carbonate
- DMC dimethyl carbonate
- an electrolyte salt lithium hexafluorophosphate: LiPF 6
- the content of the electrolyte salt was 1.2 mol / kg with respect to the solvent.
- a secondary battery was assembled as follows. First, an aluminum lead was ultrasonically welded to one end of the positive electrode current collector, and a nickel lead was welded to one end of the negative electrode current collector. Subsequently, a positive electrode, a separator, a negative electrode, and a separator were laminated in this order, and wound in the longitudinal direction to obtain a wound electrode body. The end portion was fixed with a PET protective tape. As the separator, a laminated film (thickness: 12 ⁇ m) sandwiched between a film mainly composed of porous polyethylene and a film mainly composed of porous polypropylene was used.
- the outer peripheral edges excluding one side were heat-sealed, and the electrode body was housed inside.
- the exterior member a nylon film, an aluminum foil, and an aluminum laminate film in which a polypropylene film was laminated were used.
- an electrolytic solution prepared from the opening was injected, impregnated in a vacuum atmosphere, heat-sealed, and sealed.
- Example 1-1 to Example 1-5 x of SiO x is fixed at 0.9, Si / SiO 2 component generated in the bulk is changed, and the peak value intensity value A of the Si region is changed. And the ratio of the peak value intensity value B in the SiO 2 region: A (Si) / B (SiO 2 ) was changed.
- a (Si) / B (SiO 2 ) is 0.8, 1.5, 2, and 3.
- the median diameter of the negative electrode active material particles is 4 ⁇ m
- the half width (2 ⁇ ) of the diffraction peak due to the (111) crystal plane obtained by X-ray diffraction of the negative electrode active material is 1.22 °
- the negative electrode active material The material Si (111) crystallite was 7.21 nm, and the lithium compound contained in the negative electrode active material particles was amorphous Li 4 SiO 4 .
- Example 1-1 to Example 1-5 the cycle characteristics and initial charge / discharge characteristics of the secondary batteries were examined.
- the cycle characteristics were examined as follows. First, in order to stabilize the battery, charge and discharge was performed for 2 cycles in an atmosphere at 25 ° C., and the discharge capacity at the second cycle was measured. Subsequently, charge and discharge were performed until the total number of cycles reached 100, and the discharge capacity was measured each time. Finally, the discharge capacity at the 100th cycle was divided by the discharge capacity at the second cycle, and the capacity retention rate was calculated.
- the battery was charged at a constant current density of 2.5 mA / cm 2 until 4.2 V was reached, and the current density was 0.25 mA / cm at a constant voltage of 4.2 V when the voltage reached 4.2 V. Charged until 2 was reached. During discharging, discharging was performed at a constant current density of 2.5 mA / cm 2 until the voltage reached 2.5V.
- the initial efficiency (%) (initial discharge capacity / initial charge capacity) ⁇ 100 was calculated.
- the atmosphere and temperature were the same as when the cycle characteristics were examined, and the charge / discharge conditions were 0.2 times the cycle characteristics.
- Table 1 shows the measurement results of Comparative Examples 1-1 to 1-4 and Examples 1-1 to 1-5.
- the peak value B in the SiO 2 region obtained from 29Si-MAS-NMR spectrum was small and high battery characteristics were obtained.
- a (Si) / B (SiO 2 ) is set to 0.8 or more, the SiO 2 part, which is the Li reaction site, can be reduced in advance, thereby improving the initial efficiency of the battery and stabilizing the Li compound in bulk.
- the battery deterioration accompanying charging / discharging can be suppressed by existing in or on the surface.
- Example 2-1 to Example 2-4 Secondary batteries were fabricated in the same manner as in Examples 1-1 to 1-5. However, A (Si) / B (SiO 2 ) was fixed to 2 and the oxygen content in the bulk was changed. In this case, the amount of oxygen in the deposit was changed by changing the ratio of the evaporation starting material and the evaporation temperature.
- the x values of SiO x in Example 2-1, Example 2-2, Example 2-3, and Example 2-4 were 0.5, 0.7, 1.2, and 1.6, respectively. .
- Example 2-1 to Example 2-4 the cycle characteristics and the initial charge / discharge characteristics of the secondary batteries were examined in the same manner as Example 1-1 to Example 1-5.
- Table 2 shows the measurement results of Comparative Examples 2-1 to 2-2 and Examples 2-1 to 2-4.
- Table 1-4 also shows Examples 1-4 in which x of SiO x is 0.9.
- Example 3-1 to Example 3-12 Secondary batteries were fabricated in the same manner as in Examples 1-1 to 1-5. However, A (Si) / B (SiO 2 ) is fixed to 2 and x of SiO x is fixed to 0.9, and the potential, current amount, and insertion / extraction method of Li are controlled and generated during lithium compound production. The state of inclusion (lithium compound) to be changed was changed. In addition, the gas atmosphere was adjusted after generation, and the state of the inclusion was changed by heat drying to obtain a more stable material. For example, Li 4 SiO 4 is divided into Li 2 SiO 3 and Li 2 CO 3 by applying heat in a carbon dioxide atmosphere. By adopting these reactions and realizing the optimal bulk state, the capacity retention rate and the initial efficiency were improved.
- the obtained Li compound can be confirmed by XPS.
- Li 4 SiO 4 is given by a binding energy around 532 eV
- Li 2 SiO 3 is given by a binding energy around 530 eV.
- the obtained Li compound can also be confirmed by 29Si-MAS-NMR spectrum.
- the crystallinity of the produced inclusions was changed. The degree of crystallinity can be controlled by heat treatment in a non-atmospheric atmosphere after Li insertion and desorption.
- Example 3-1 to Example 3-12 the cycle characteristics and the initial charge / discharge characteristics of the secondary batteries were examined in the same manner as in Examples 1-1 to 1-5.
- Table 3 shows the measurement results of Example 3-1 to Example 3-12.
- Table 1-4 also shows Examples 1-4 in which the produced content is amorphous Li 4 SiO 4 .
- the produced lithium compound is substantially amorphous. This is because when the degree of crystallinity is high, the resistance of the active material is increased.
- the half width (2 ⁇ ) representing the crystallinity is preferably 0.2 ° or more, and the inclusion is Li 2 SiO 3. In this case, the half width (2 ⁇ ) is preferably 0.75 ° or more.
- the lithium compound was made into an amorphous state to produce a secondary battery. Furthermore, as can be seen from Table 3, when a plurality of lithium compounds are produced, better initial charge / discharge characteristics can be obtained.
- Example 4-1 to Example 4-3 Secondary batteries were fabricated in the same manner as in Examples 1-1 to 1-5. However, A (Si) / B (SiO 2 ) is fixed to 2, x of SiO x is fixed to 0.9, and the lithium compound contained is amorphous Li 4 SiO 4 , Li 2 SiO 3 , and Li 2 CO 3 is used, and in the bulk reforming process, the Li compound is generated, the potential and current are controlled, and the use of warming in a solvent is used to generate a fluorine compound on the active material surface layer. went. In Example 4-1, Example 4-2, and Example 4-3, the produced fluorine compounds were LiF, LiPF 6 decomposition product, and LiF + LiPF 6 decomposition product, respectively.
- Example 4-1 to Example 4-3 the cycle characteristics and initial charge / discharge characteristics of the secondary batteries were examined in the same manner as Example 1-1 to Example 1-5.
- Table 4 shows the measurement results of Example 4-1 to Example 4-3.
- Table 3 also shows Examples 3-6 in which no fluorine compound was produced.
- Examples 5-1 to 5-9 Secondary batteries were fabricated in the same manner as in Examples 1-1 to 1-5. However, A (Si) / B (SiO 2 ) is fixed to 2, x of SiO x is fixed to 0.9, and the lithium compound contained is amorphous Li 4 SiO 4 , Li 2 SiO 3 , and Li 2 CO 3 was used, and the active material surface layer was coated with LiF at a coverage of 50%. In addition, the crystallinity of the active material was changed.
- the half-value width is calculated to be 20 ° or more, but it is a result of fitting using analysis software, and a peak is not substantially obtained. Therefore, it can be said that Example 5-9 is substantially amorphous.
- Example 5-1 to Example 5-9 the cycle characteristics and the initial charge / discharge characteristics of the secondary batteries were examined in the same manner as Example 1-1 to Example 1-5.
- the measurement results of Example 5-1 to Example 5-9 are shown in Table 5.
- the capacity retention ratio and the initial efficiency changed according to the crystallinity of the active material.
- higher capacity retention and initial efficiency are obtained with a low crystalline material having a half width of 1.2 ° or more or a crystallite size of 7.5 nm or less due to the Si (111) plane.
- the best characteristics were obtained when the active material was amorphous.
- Example 6-1 Secondary batteries were fabricated in the same manner as in Examples 1-1 to 1-5. However, A (Si) / B (SiO 2 ) is fixed to 2, x of SiO x is fixed to 0.9, and the lithium compound contained is amorphous Li 4 SiO 4 , Li 2 SiO 3 , and Li 2 CO 3 was used, and the surface layer of the active material was coated with LiF at a coverage of 50%. Further, the crystallinity of the negative electrode active material had a full width at half maximum (2 ⁇ ) of 20.221. Further, the peak value of the Si region of 29Si-MAS-NMR spectrum was changed. In Example 6-1, the peak value of the negative electrode active material particles was ⁇ 78 ppm, which was in the range of ⁇ 70 to ⁇ 85 ppm (see FIG. 6).
- Example 6-1 the cycle characteristics and the initial charge / discharge characteristics of the secondary battery were examined in the same manner as in Examples 1-1 to 1-5.
- the measurement results of Example 6-1 are shown in Table 6.
- Table 6 also shows Example 5-9 in which the peak value of the Si region of the 29Si-MAS-NMR spectrum of the negative electrode active material particles is ⁇ 87 as shown in FIG.
- the capacity retention ratio is improved by shifting the peak value of the Si region of the 29Si-MAS-NMR spectrum of the negative electrode active material particles into the range of -70 to -85 ppm. Therefore, it is more desirable that the peak value of the Si region of the 29Si-MAS-NMR spectrum of the negative electrode active material particles be in the range of -70 to -85 ppm.
- the peak of the Si region of 29Si-MAS-NMR spectrum is obtained in the region of ⁇ 85 ppm or less, but it is shifted to the low magnetic field side as described above by changing the bond angle of Si—O—Si or the like. be able to. That is, a more stable bulk situation is realized by shifting the Si bond angle.
- Example 7-1 to Example 7-6) Secondary batteries were fabricated in the same manner as in Examples 1-1 to 1-5. However, A (Si) / B (SiO 2 ) is fixed to 2, x of SiO x is fixed to 0.9, and the lithium compound contained is amorphous Li 4 SiO 4 , Li 2 SiO 3 , and Li 2 CO 3 was used, and the surface layer of the active material was coated with LiF at a coverage of 50%. Further, the crystallinity of the negative electrode active material had a half width (2 ⁇ ) of 1.271. Furthermore, the median diameter of the negative electrode active material particles was changed.
- Example 7-1 In Example 7-1, Example 7-2, Example 7-3, Example 7-4, Example 7-5, and Example 7-6, the median diameter of the negative electrode active material particles was 0. They were 1 ⁇ m, 0.5 ⁇ m, 1 ⁇ m, 10 ⁇ m, 20 ⁇ m, and 30 ⁇ m.
- Example 7-1 to Example 7-6 the cycle characteristics and initial charge / discharge characteristics of the secondary batteries were examined in the same manner as in Examples 1-1 to 1-5.
- Table 7 shows the measurement results of Example 7-1 to Example 7-6.
- Table 5 also shows Example 5-4 in which the median diameter of the negative electrode active material particles was 4 ⁇ m.
- Example 8-1 to Example 8-7 Secondary batteries were fabricated in the same manner as in Examples 1-1 to 1-5. However, A (Si) / B (SiO 2 ) is fixed to 2, x of SiO x is fixed to 0.9, and the lithium compound contained is amorphous Li 4 SiO 4 , Li 2 SiO 3 , and Li 2 CO 3 was used, and the surface layer of the negative electrode active material was coated with LiF at a coverage of 50%. Further, the crystallinity of the negative electrode active material had a half width (2 ⁇ ) of 1.271. Further, a carbon layer was formed on the surface layer portion of the negative electrode active material particles using a thermal decomposition CVD method.
- Example 8-7 the film thickness of the carbon layer is Respectively, 1 nm, 100 nm, 200 nm, 500 nm, 1000 nm, 5000 nm, and 7500 nm, the coverage of Example 8-1 was 60%, and the coverage of Examples 8-2 to 8-7 was 80%. It was.
- Example 8-1 to Example 8-7 the cycle characteristics and initial charge / discharge characteristics of the secondary batteries were examined in the same manner as in Examples 1-1 to 1-5.
- Table 7 shows the measurement results of Example 8-1 to Example 8-7.
- Table 5 also shows Example 5-4 in which the carbon layer is not formed on the surface layer portion of the negative electrode active material particles.
- the conductivity is improved when the thickness of the carbon layer is 1 nm or more, the battery characteristics (capacity maintenance ratio and initial efficiency) can be improved.
- the thickness of the carbon layer is greater than 7000 nm, the battery capacity is reduced in terms of battery design. Therefore, when considering the battery capacity and battery characteristics, 1 nm to 5000 nm is more desirable.
- Example 9-1 to Example 9-4 Secondary batteries were fabricated in the same manner as in Examples 1-1 to 1-5. However, A (Si) / B (SiO 2 ) is fixed to 2, x of SiO x is fixed to 0.9, and the lithium compound contained is amorphous Li 4 SiO 4 , Li 2 SiO 3 , and Li 2 CO 3 was used, and the surface layer of the negative electrode active material was coated with LiF at a coverage of 50%. Further, the crystallinity of the negative electrode active material had a half width (2 ⁇ ) of 1.271. Furthermore, the film thickness of the carbon layer of the surface layer portion of the negative electrode active material particles was set to 100 nm, and the coverage was changed. In Example 9-1, Example 9-2, Example 9-3, and Example 9-4, the coverage of the carbon layer was 20%, 30%, 50%, and 90%, respectively.
- Example 9-1 to Example 9-4 the cycle characteristics and the initial charge / discharge characteristics of the secondary batteries were examined in the same manner as in Examples 1-1 to 1-5. Furthermore, the load characteristics of Example 8-2 and Example 9-1 to Example 9-4 in which the coverage of the carbon layer was 80% were examined. Here, load characteristics, in which the capacity when discharged at a discharge current of 2 mA / cm 2 per negative electrode unit area, divided by the capacity when discharged at a discharge current of 0.25 mA / cm 2 per negative electrode unit area is there. Table 9 shows the measurement results of Example 8-2 and Examples 9-1 to 9-4.
- Example 10-1 to Example 10-3 Secondary batteries were fabricated in the same manner as in Examples 1-1 to 1-5.
- a (Si) / B (SiO 2 ) is 2, x of SiO x is 0.9, and the lithium compound contained is amorphous Li 4 SiO 4 , Li 2 SiO 3 , and Li 2 CO 3.
- the surface layer of the negative electrode active material was covered with LiF. Further, the crystallinity of the negative electrode active material had a half width (2 ⁇ ) of 1.271.
- the film thickness of the carbon layer of the surface layer portion of the negative electrode active material particles was 100 nm, the coverage was 80%, and the coverage of the LiF layer covering the surface layer of the negative electrode active material was changed.
- the coverage of the LiF layer was 20%, 30%, and 70%, respectively.
- the coverage of the fluorine compound on the surface layer is calculated from the TEM-EDX mapping photograph shown in FIG. A method for calculating the coverage will be described below.
- a powder sample negative electrode active material particles
- platinum is deposited on the surface of the powder sample by vacuum evaporation.
- tungsten is deposited on the surface of platinum by a focused ion beam (FIB) method
- the thin film was further processed at an acceleration voltage of 30 kV.
- the state of the fluorine compound covering the particle surface layer was grasped by performing EDX analysis while confirming the particles by image observation.
- the coverage of the fluorine compound can be calculated by the ratio between the outer circumference of the particle and the length of the fluorine compound covering the particle, similarly to the coverage of the carbon layer.
- Example 10-1 to Example 10-3 the cycle characteristics and initial charge / discharge characteristics of the secondary batteries were examined in the same manner as in Examples 1-1 to 1-5.
- Table 10 shows the measurement results of Example 10-1 to Example 10-3.
- Table 10 also shows Example 8-2 in which the coverage of the LiF layer was 50%.
- Example 11-1 to Example 11-3 Secondary batteries were fabricated in the same manner as in Examples 1-1 to 1-5.
- a (Si) / B (SiO 2 ) is 2, x of SiO x is 0.9, and the lithium compound contained is amorphous Li 4 SiO 4 , Li 2 SiO 3 , and Li 2 CO 3.
- the surface layer of the negative electrode active material was coated with LiF at a coverage of 50%. Further, the crystallinity of the negative electrode active material had a half width (2 ⁇ ) of 1.271.
- the film thickness of the carbon layer of the surface layer part of the negative electrode active material particles was 100 nm, and the coverage was 80%.
- Example 11-1 C (carbon) and S (sulfur) were contained in the negative electrode current collector, and the content thereof was changed.
- the C and S contents of the negative electrode current collector were 200 ppm, 100 ppm, and 50 ppm, respectively.
- Example 11-1 to Example 11-3 and Example 8-2 in which C and S were not contained in the negative electrode current collector, the presence or absence of deformation of the negative electrode during charging was examined.
- Table 11 shows the evaluation results of Examples 11-1 to 11-3 and Example 8-2.
- Example 12-1 to Example 12-7 Secondary batteries were fabricated in the same manner as in Examples 1-1 to 1-5.
- a (Si) / B (SiO 2 ) is 2, x of SiO x is 0.9, and the lithium compound contained is amorphous Li 4 SiO 4 , Li 2 SiO 3 , and Li 2 CO 3.
- the surface layer of the negative electrode active material was coated with LiF at a coverage of 50%. Further, the crystallinity of the negative electrode active material had a half width (2 ⁇ ) of 1.271.
- the film thickness of the carbon layer of the surface layer part of the negative electrode active material particles was 100 nm, and the coverage was 80%. Further, various negative electrode binders were used.
- Example 12-1 Example 12-2, Example 12-3, Example 12-4, Example 12-5, Example 12-6, and Example 12-7
- the negative electrode binder was Polyvinylidene fluoride, aramid, polyacrylic acid, lithium polyacrylate, polyimide carbide, polyethylene, and polymaleic acid.
- Example 12-1 to Example 12-7 the cycle characteristics and the initial charge / discharge characteristics of the secondary batteries were examined in the same manner as Example 1-1 to Example 1-5.
- Table 12 shows the measurement results of Example 12-1 to Example 12-7.
- Table 12 also shows Example 8-2 in which the negative electrode binder is polyimide.
- Example 13-1 to Example 13-5 Secondary batteries were fabricated in the same manner as in Examples 1-1 to 1-5.
- a (Si) / B (SiO 2 ) is 2, x of SiO x is 0.9, and the lithium compound contained is amorphous Li 4 SiO 4 , Li 2 SiO 3 , and Li 2 CO 3.
- the surface layer of the negative electrode active material was coated with LiF at a coverage of 50%. Further, the crystallinity of the negative electrode active material had a half width (2 ⁇ ) of 1.271.
- the film thickness of the carbon layer of the surface layer part of the negative electrode active material particles was 100 nm, and the coverage was 80%. Further, various methods for modifying the bulk of silicon-based materials were used.
- Example 13-1 Example 13-2, Example 13-3, Example 13-4, and Example 13-5
- the reforming methods are the short method, the potential / current control + Li insertion method, the heat, respectively.
- This is a method of repeating the dope method, vacuum deposition method, potential / current control + Li partial insertion method after inserting Li three times.
- the potential / current control + Li insertion method is a method of inserting Li into the bulk while controlling the potential / current supplied to the Li source 21 using the in-bulk reformer 20 shown in FIG. is there.
- the potential / current control + Li partial insertion after Li insertion method uses the in-bulk reformer 20 shown in FIG. 5 to insert Li into the bulk while controlling the potential / current supplied to the Li source 21. Later, the inserted lithium is partially removed while controlling the potential and current.
- the short method uses a potential difference generated between the Li source 21 and the powder storage container 25 without performing potential control or current control by electrically short-circuiting the Li source 21 and the powder storage container 25. This is a method of inserting Li.
- the thermal doping method is a method in which a silicon material and Li metal or a Li compound are mixed and heat treatment is performed.
- the vacuum deposition method is a method in which Li metal, lithium carbonate, or the like is vaporized by heating using a resistance heating method in a vacuum chamber depressurized to 10 ⁇ 2 Pa or less, and this vapor is sprayed onto the powder of the silicon-based material. It is a method to do.
- Example 13-1 to Example 13-5 the cycle characteristics and the initial charge / discharge characteristics of the secondary batteries were examined in the same manner as in Examples 1-1 to 1-5.
- Table 13 shows the measurement results of Example 13-1 to Example 13-5.
- Table 13 also shows Example 8-2 in which the reforming method is potential / current control + Li partial insertion after Li insertion.
- the potential / current control + partial separation method after Li insertion is desirable. Further, it is more desirable to perform the insertion / desorption a plurality of times. On the other hand, it has been found that the thermal doping method does not become a method for reforming into a higher quality active material. Further, it was found that the vacuum deposition method does not achieve a more uniform modification, and therefore does not reach the partial release method after potential / current control + Li insertion.
- Example 14-1 to Example 14-7) Secondary batteries were fabricated in the same manner as in Examples 1-1 to 1-5. However, A (Si) / B (SiO 2 ) is 2, x of SiO x is 0.9, and the lithium compound contained is amorphous Li 4 SiO 4 , Li 2 SiO 3 , and Li 2 CO 3.
- the surface layer of the negative electrode active material was coated with LiF at a coverage of 50%. Further, the crystallinity of the negative electrode active material had a half width (2 ⁇ ) of 1.271. Furthermore, various types of silicon-based materials were modified in the bulk.
- Example 14-1 and Example 14-3 to Example 14-7 as the reforming method, the potential / current control + Li partial insertion after Li insertion method is used, while in Example 14-2, the reforming is performed.
- a vacuum deposition method was used.
- the modification in the bulk was performed in a state where the SiO film was directly formed on the copper foil by vapor deposition, and in Example 14-3
- thermal decomposition CVD that is, a method in which siloxane and argon gas are introduced into a vacuum chamber and heat is applied at 650 ° C. or more to thermally decompose and deposit on a substrate
- In-bulk modification was carried out with the SiO film formed directly on the copper foil.
- Example 14-4 the unmodified silica material was applied to the electrode and then reformed in the bulk.
- Examples 14-5 to 14-7 the carbon material and the unmodified material were modified. In-bulk modification was performed after the silica material was mixed and applied to the electrode.
- Example 14-5 mixed application was performed with 50 mass% of the silica material and 50 mass% of the carbon material
- Example 14-6 mixed application was performed with 30 mass% of the silica material and 70 mass% of the carbon material.
- No. 14-5 mixed coating was performed with 50 mass% of the silica material and 50 mass% of the carbon material.
- Example 14-1 to Example 14-7 the cycle characteristics and the initial charge / discharge characteristics of the secondary batteries were examined in the same manner as Example 1-1 to Example 1-5.
- Table 14 shows the measurement results of Example 14-1 to Example 14-7.
- Table 14 also shows Example 8-2 in which the reforming method is potential / current control + Li partial insertion after Li insertion, and reforming in bulk in a powder state as a reforming form.
- the capacity retention rate and initial efficiency are improved by creating an SiO film directly on the copper foil by vapor deposition and modifying it using an electrochemical method, and the SiO film directly on the copper foil by pyrolytic CVD.
- the initial efficiency is improved by making the material and modifying it using an electrochemical method.
- the capacity retention rate and the initial efficiency are improved by applying an unmodified siliceous material to the electrode and then performing modification using an electrochemical method.
- the carbon material and the unmodified siliceous material can be mixed and applied to the electrode, and then modified using an electrochemical method to selectively modify the siliceous material. Utilizing the characteristics, the silicon material can improve the battery energy density, increasing the proportion of carbon material, and improving the capacity retention rate and initial efficiency.
- the siliceous material reacts with Li at a higher Li potential than the carbon material, Li can be selectively inserted into the siliceous material by controlling the potential at a potential at which Li can easily enter the siliceous material, so the potential control was used. Modification is effective.
- Example 15-1 to Example 15-7) Secondary batteries were fabricated in the same manner as in Examples 1-1 to 1-5.
- a (Si) / B (SiO 2 ) is 2, x of SiO x is 0.9, and the lithium compound contained is amorphous Li 4 SiO 4 , Li 2 SiO 3 , and Li 2 CO 3.
- the surface layer of the negative electrode active material was coated with LiF at a coverage of 50%. Further, the crystallinity of the negative electrode active material had a half width (2 ⁇ ) of 1.271.
- the film thickness of the carbon layer of the surface layer part of the negative electrode active material particles was 100 nm, and the coverage was 80%.
- Example 15-1 Li partial insertion after Li insertion method was used, and powder coating was used as the modification mode.
- Various types of reforming sources Li sources
- Li sources Li sources
- Lithium metal, lithium chloride, lithium carbonate, lithium oxide, lithium olivine, Ni-containing lithium composite oxide, and Mn-containing lithium composite oxide were used.
- Example 15-1 to Example 15-7 the cycle characteristics and the initial charge / discharge characteristics of the secondary batteries were examined in the same manner as in Examples 1-1 to 1-5.
- Table 15 shows the measurement results of Example 15-1 to Example 15-7.
- Table 15 also shows Example 8-2 in which lithium cobaltate was used as the reforming source.
- the reforming source is not particularly limited, but a more stable material is desirable in consideration of the manufacturing process.
- Lithium composite oxide is preferable to lithium metal, for example, lithium cobaltate and lithium olivine iron are preferable.
- olivine iron lithium is particularly desirable because it has a low charging potential and can be industrially reduced in cost and has excellent output characteristics.
- the lithium composite oxide has an advantage that it can be reused by repeating insertion and removal of lithium for a certain amount and then mixing with a lithium-containing composite material and performing heat treatment. Note that the lithium composite oxide is substantially similar to the positive electrode material that has deteriorated to a greater degree than the battery grade, but when used as a reforming source, it is acceptable even if the battery characteristics are particularly low.
- the present invention is not limited to the above embodiment.
- the above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.
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Abstract
Description
この二次電池は、小型の電子機器に限らず、自動車などに代表される大型の電子機器、家屋などに代表される電力貯蔵システムへの適用も検討されている。
電池容量向上のために、負極活物質材としてケイ素を用いることが検討されている。なぜならば、ケイ素の理論容量(4199mAh/g)は黒鉛の理論容量(372mAh/g)よりも10倍以上大きいため、電池容量の大幅な向上を期待できるからである。
負極活物質材としてのケイ素材の開発はケイ素単体だけではなく、合金、酸化物に代表される化合物などについても検討されている。
また、活物質形状は、炭素材では標準的な塗布型から、集電体に直接堆積する一体型まで検討されている。
負極活物質表層が割れると、それによって新表面が生じ、活物質の反応面積が増加する。この時、新表面において電解液の分解反応が生じるとともに、新表面に電解液の分解物である被膜が形成されるため電解液が消費される。このためサイクル特性が低下しやすくなる。
また、高い電池容量や安全性を得るために、ケイ素酸化物粒子の表層に炭素材(電子伝導材)を設けている(例えば特許文献2参照)。
さらに、サイクル特性を改善するとともに高入出力特性を得るために、ケイ素及び酸素を含有する活物質を作製し、かつ、集電体近傍での酸素比率が高い活物質層を形成している(例えば特許文献3参照)。
また、サイクル特性向上させるために、ケイ素活物質中に酸素を含有させ、平均酸素含有量が40at%以下であり、かつ集電体に近い場所で酸素含有量が多くなるように形成している(例えば特許文献4参照)。
また、サイクル特性改善のため、SiO2(0.8≦x≦1.5、粒径範囲=1μm~50μm)と炭素材を混合して高温焼成している(例えば特許文献6参照)。
また、サイクル特性改善のために、負極活物質中におけるケイ素に対する酸素のモル比を0.1~1.2とし、活物質、集電体界面近傍におけるモル比の最大値、最小値との差が0.4以下となる範囲で活物質の制御を行っている(例えば特許文献7参照)。
また、電池負荷特性を向上させるため、リチウムを含有した金属酸化物を用いている(例えば特許文献8参照)。
また、サイクル特性を改善させるために、ケイ素材表層にシラン化合物などの疎水層を形成している(例えば特許文献9参照)。
また、サイクル特性改善のため、酸化ケイ素を用い、その表層に黒鉛被膜を形成することで導電性を付与している(例えば特許文献10参照)。特許文献10において、黒鉛被膜に関するRAMANスペクトルから得られるシフト値に関して、1330cm-1及び1580cm-1にブロードなピークが現れるとともに、それらの強度比I1330/I1580が1.5<I1330/I1580<3となっている。
また、高い電池容量、サイクル特性の改善のため、二酸化ケイ素中に分散されたケイ素微結晶相を有する粒子を用いている(例えば、特許文献11参照)。
また、過充電、過放電特性を向上させるために、ケイ素と酸素の原子数比を1:y(0<y<2)に制御したケイ素酸化物を用いている(例えば特許文献12参照)。
この問題を解決する1つの手法として、ケイ素材を主材として用いた負極からなるリチウムイオン二次電池の開発が望まれている。
また、ケイ素材を用いたリチウムイオン二次電池は、炭素材を用いたリチウムイオン二次電池と同等に近いサイクル特性が望まれている。
しかしながら、炭素材を用いたリチウムイオン二次電池と同等のサイクル安定性を示す負極活物質を提案するには至っていなかった。
負極活物質粒子のSi領域のピーク値を上記の範囲とすることで、より良好なサイクル特性が得られる。
負極活物質粒子のSi領域のピークが2つ以上あることで、より良好な初期充放電特性が得られる。
負極活物質粒子に上記のようなリチウムシリケートを好適に含有させることができる。
負極活物質粒子に上記のようなメタルSiの状態のものを好適に含有させることができる。
このような構成の負極活物質粒子を好適に用いることができる。
このような構成の負極活物質粒子を好適に用いることができる。
このような結晶性を有するLi2SiO3を負極活物質粒子が含むことで、より良好なサイクル特性及び初期充放電特性が得られる。
このような結晶性を有するLi2SiO3を負極活物質粒子が含むことで、より良好なサイクル特性及び初期充放電特性が得られる。
このように、非晶質のLi化合物を負極活物質粒子が含むことで、より良好なサイクル特性及び初期充放電特性が得られる。
このように、負極活物質粒子がその表面にフッ素化合物を有することで、より良好な初期充放電特性が得られるとともに、活物質材料の長期保存安定性が向上する。
このように、負極活物質粒子の表面のフッ素化合物として、上記のようなものを好適に用いることができる。
負極活物質が上記の結晶性を有することで、このような負極活物質をリチウムイオン二次電池の負極活物質として用いた際に、より良好なサイクル特性及び初期充放電特性が得られる。
負極活物質粒子のメジアン径が上記の範囲内にあることで、このような負極活物質粒子を含む負極活物質をリチウムイオン二次電池の負極活物質として用いた際に、より良好なサイクル特性及び初期充放電特性が得られる。
このように、負極活物質粒子がその表層部に炭素材を含むことで、導電性の向上が得られるため、このような負極活物質粒子を含む負極活物質をリチウムイオン二次電池の負極活物質として用いた際に、このような負極活物質粒子を含む負極活物質をリチウムイオン二次電池の負極活物質として用いた際に、電池特性を向上させることができる。
被覆する炭素材の平均厚さが1nm以上であれば導電性向上が得られ、被覆する炭素材の平均厚さが5000nm以下であれば、このような負極活物質粒子を含む負極活物質をリチウムイオン二次電池の負極活物質として用いた際に、電池容量の低下を抑制することができる。
このような構成の負極活物質粒子を好適に用いることができる。
上記の平均被覆率とすることで、このような負極活物質粒子を含む負極活物質をリチウムイオン二次電池の負極活物質として用いた際に、より良好なサイクル特性及び初期充放電特性が得られる。
上記の平均被覆率とすることで、このような負極活物質粒子を含む負極活物質をリチウムイオン二次電池の負極活物質として用いた際に、より良好な負荷特性が得られる。
このように、負極活物質層を形成する材料として、本発明の負極活物質とともに炭素材料を含むことで、負極活物質層の導電性を向上させることができる。
前述のように、リチウムイオン二次電池の電池容量を増加させる1つの手法として、ケイ素材を主材として用いた負極をリチウムイオン二次電池の負極として用いることが検討されている。
このケイ素材を用いたリチウムイオン二次電池は、炭素材を用いたリチウムイオン二次電池と同等に近いサイクル特性が望まれているが、炭素材を用いたリチウムイオン二次電池と同等のサイクル安定性を示す負極活物質を提案するには至っていなかった。
その結果、ケイ素系材料として、SiOx(0.5≦x≦1.6)の組成比を有し、及び、29Si-MAS-NMR spectrumから得られる、ケミカルシフト値として-50~-95ppmで与えられるSi領域のピーク値強度値Aと、ケミカルシフト値として-96~-150ppmで与えられるSiO2領域のピーク値強度値Bが、A/B≧0.8という関係を満たすものを用いることで、このケイ素系材料を含有する負極活物質粒子を含む負極活物質をリチウムイオン二次電池の負極活物質として用いた際に、良好なサイクル特性及び初期充放電特性が得られることを見出し、本発明をなすに至った。
まず、リチウムイオン二次電池用負極について、説明する。
図1は本発明の一実施形態におけるリチウムイオン二次電池用負極(以下、「負極」と記述)の断面構成を表しており、図2は負極活物質粒子の断面構造を示すTEM(Transmission Electron Microscope:透過型電子顕微鏡)写真である。
図1に示すように、負極10は、負極集電体11の上に負極活物質層12を有する構成になっている。また、負極活物質層12は負極集電体11の両面、又は、片面だけに設けられていても良い。さらに、本発明の負極活物質が用いられたものであれば、負極集電体11はなくてもよい。
負極集電体12は、優れた導電性材料であり、かつ、機械的な強度が大きい物で構成される。導電性材料として、例えば銅(Cu)やニッケル(Ni)があげられる。
また、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。
特に、充電時に膨張する活物質層を負極が有する場合、集電体が上記の元素を含んでいれば、集電体を含む電極変形を抑制する効果がある。
上記の含有元素の含有量は特に限定されないが、中でも100ppm以下であることが好ましい。なぜならば、より高い変形抑制効果が得られるからである。
負極活物質層11は、リチウムイオンを吸蔵、放出可能な複数の粒子状負極活物質(以下、負極活物質粒子と称する)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。
なお、本発明におけるケイ素材組成は必ずしも純度100%を意味しているわけではなく、微量の不純物元素を含んでいてもよい。
ここで、ピーク強度値とは、ピーク値におけるピーク高さを意味する。また、ピークが複数ある場合は、ピーク強度値は複数のピーク高さの和で求めることができる。
なお、29Si-MAS-NMR spectumの測定において、装置としてBruker社製700NMR分光器を用い、プローブとして4mmHR-MASローター 50μLを用い、試料回転速度は10kHzとし、測定環境温度は25℃とした。
その中でも、Li4SiO4、Li2SiO3、Li2O、Li2CO3は特に良い特性を示す。
選択的化合物(Li化合物)の作製方法としては、電気化学法を用いることが好ましい。
リチウム対極に対する電位規制、又は、電流規制などの条件を変更することで、選択的化合物の作製が可能となる。
また、選択的化合物は一部電気化学法により生成した後に、炭酸雰囲気下、又は、または酸素雰囲気下などで乾燥させることでより緻密な物質を得られる。
Li化合物はNMR(Nuclear Magnetic Resonance:核磁気共鳴)又はXPS(X-ray photoelectron spectroscopyX線光電子分光)で定量可能である。
なお、XPSでのLi化合物の定量において、装置としてX線光電子分光装置を用い、X線源として単色化AlKα線を用い、X線スポット径を100μmφとし、Arイオン銃スパッタ条件を0.5kV/2mm×2mmとした。
また、上記の手法によれば、ランダムに化合物化する熱改質と比較して、より安定した物質を作ることが可能である。
フッ素化合物の材質としては、LiF、LiPF6の分解物が挙げられるが、LiFが最も望ましい。また、フッ素化合物の生成手法は特に限定しないが、電気化学法が最も好ましい。
特にSi結晶が存在することで電池特性を悪化させるだけではなく、安定的なLi化合物の生成が難しくなる。
メジアン径が上記の範囲であれば、充放電時においてリチウムイオンの吸蔵放出がされやすくなるとともに、粒子が割れにくくなるからである。メジアン径を0.5μm以上とすることで、表面積の増加により電池不可逆容量が増加することを抑制することができる。一方で、メジアン径を20μm以下とすることで、粒子が割れやすくなり新表面が出やすくなることを抑制することができる。
平均厚さを1nm以上とすることで、電気伝導性を向上させることができる。
平均厚さを5000nm以下とすることで、電池容量が低下することを抑制することができる。
先ず、図2に示すようにTEMにより任意の倍率で負極活物質を観察する。この倍率は、厚さを測定できるように、目視で被覆部の厚さを確認できる倍率が好ましい。
続いて、任意の15点において、被覆部の厚さを測定する。この場合、できるだけ特定の場所に集中せず、広くランダムに測定位置を設定することが好ましい。
最後に、上記の15点の被覆部の厚さの平均値を算出する。
炭素材の被覆手法は特に限定されないが、糖炭化法、炭化水素ガスの熱分解法が好ましい。なぜならば、被覆率を向上させることができるからである。
高分子材料は、例えば、ポリフッ化ビニリデン、ポリイミド、ポリアミドイミド、アラミド、ポリアクリル酸、ポリアクリル酸リチウム、カルボキシメチルセルロースなどである。
合成ゴムは、例えば、スチレンブタジエン系ゴム、フッ素系ゴム、エチレンプロピレンジエンなどである。
負極10は、例えば、以下の手順により製造される。
先ず、酸化珪素ガスを発生する原料を不活性ガスの存在下、減圧下で900℃~1600℃の温度範囲で加熱し、酸化ケイ素ガスを発生させる。このとき、原料は金属珪素粉末と二酸化珪素粉末との混合であり、金属珪素粉末の表面酸素及び反応炉中の微量酸素の存在を考慮すると、混合モル比が、0.8<金属珪素粉末/二酸化珪素粉末<1.3の範囲であることが望ましい。
次に、発生したガスは吸着板上で固体化され、堆積される。
次に、反応炉内温度を100℃以下に下げた状態で堆積物を取出し、ボールミル、ジェットミルなどを用いて粉砕、粉末化を行う。
なお、粒子中のSi結晶子は、気化温度の変更、又は、生成後の熱処理で制御される。
また、発生した酸化ケイ素ガスを直接銅箔に堆積させることで、蒸着SiO膜を形成してもよい。
熱分解CVD法で炭素材の層を生成する方法について説明する。
先ず、酸化ケイ素粉末を炉内にセットする。
次に、炉内に炭化水素ガスを導入し、炉内温度を昇温させる。
分解温度は特に限定しないが、1200℃以下が望ましく、より望ましいのは950℃以下である。分解温度を1200℃以下にすることで、活物質粒子の不均化を抑制することができる。
所定の温度まで炉内温度を昇温させた後に、酸化ケイ素粉末に炭素層を生成する。
また、炭化水素ガスは特に限定しないが、CnHm組成においてn≦3であることが望ましい。n≦3であれは、製造コストを低くでき、また、分解生成物の物性を良好にすることができる。
バルク内改質は電気化学的にLiを挿入し得ることが望ましい。この時、挿入電位、脱離電位の調整や電流密度、浴槽温度、挿入脱離回数を変化させることでバルク内生成物質を制御することができる。
特に装置構造を限定しないが、例えば、図5に示すバルク内改質装置20を用いて、バルク内改質を行うことができる。
バルク内改質装置20は、有機溶媒23で満たされた浴槽27と、浴槽27内に配置され、電源26の一方に接続された陽電極(リチウム源)21と、浴槽27内に配置され、電源26の他方に接続された粉末格納容器25と、陽電極21と粉末格納容器25との間に設けられたセパレータ24とを有している。なお、図5において参照番号22は酸化ケイ素粉末である。
特に、フッ化リチウムは、Li挿入、Li離脱のときに45℃以上で保持することが望ましい。
また、有機溶媒23に含まれる電解質塩として、六フッ化リン酸リチウム(LiPF6)、四フッ化ホウ酸リチウム(LiBF4)などを用いることができる。
次に負極集電体11の表面に、上記の負極合剤スラリーを塗布し、乾燥させて、負極活物質層12を形成する。この時、必要に応じて加熱プレスなどを行ってもよい。
次に、上記したリチウムイオン二次電池用負極を用いたリチウムイオン二次電池について、図3を参照しながら説明する。
図3に示すラミネートフィルム型二次電池30は、主にシート状の外装部材35の内部に倦回電極体31が収納されたものである。この倦回体は正極、負極間にセパレータを有し、倦回されたものである。また正極、負極間にセパレータを有し積層体を収納した場合も存在する。
どちらの電極体においても、正極に正極リード32が取り付けられ、負極に負極リード33が取り付けられている。電極体の最外周部は保護テープにより保護されている。
融着層は、例えばポリエチレンやポリプロピレンなどのフィルムであり、金属層はアルミ箔などである。保護層は例えば、ナイロンなどである。
正極は、例えば、図1の負極10と同様に、正極集電体の両面または片面に正極活物質層を有している。
正極集電体は、例えば、アルミニウムなどの導電性材により形成されている。
正極活物質層は、リチウムイオンの吸蔵放出可能な正極材のいずれか1種または2種以上を含んでおり、設計に応じて結着剤、導電助剤、分散剤などの他の材料を含んでいてもよい。この場合、結着剤、導電助剤に関する詳細は、例えば、既に記述した負極結着剤、負極導電助剤と同様とすることができる。
これらの正極材の化学式は、例えば、LixM1O2、又は、LiyM2PO4で表される。上記の化学式中、M1、M2は少なくとも1種以上の遷移金属元素を示しており、x、yの値は電池充放電状態によって異なる値を示すが、一般的に、0.05≦x≦1.10、0.05≦y≦1.10で示される。
負極は、上記した図1のリチウムイオン二次電池用負極10と同様の構成を有し、例えば、集電体の両面に負極活物質層を有している。この負極は、正極活物質剤から得られる電気容量(電池としての充電容量)に対して、負極充電容量が大きくなることが好ましい。これにより、負極上でのリチウム金属の析出を抑制することができる。
セパレータは正極、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。
またこの場合、炭酸エチレン、炭酸プロピレンなどの高粘度溶媒と、炭酸ジメチル、炭酸エチルメチル、炭酸ジエチルなどの低粘度溶媒とを組み合わせて用いることで、電解質塩の解離性やイオン移動度を向上させることができる。
これにより、充放電時、特に充電時において、負極活物質表面に安定な被膜が形成される。
ここで、ハロゲン化鎖状炭酸エステルとは、ハロゲンを構成元素として有する(少なくとも1つの水素がハロゲンにより置換された)鎖状炭酸エステルである。また、ハロゲン化環状炭酸エステルとは、ハロゲンを構成元素として有する(すなわち、少なくとも1つの水素がハロゲンにより置換された)環状炭酸エステルである。
最初に上記した正極材を用い正極電極を作製する。
先ず、正極活物質と、必要に応じて結着剤、導電助剤などを混合し正極合剤とした後に、有機溶剤に分散させ正極合剤スラリーとする。
続いて、ナイフロールまたはダイヘッドを有するダイコーターなどのコーティング装置で正極集電体に合剤スラリーを塗布し、熱風乾燥させて正極活物質層を得る。
最後に、ロールプレス機などで正極活物質層を圧縮成型する。この時、加熱または複数回繰り返しても良い。
ここで、正極集電体の両面に正極活物質層を形成する。この時、両面部の活物質塗布長がずれていても良い。
続いて、正極と負極とをセパレータを介して積層、または倦回させて倦回電極体31を作製し、その最外周部に保護テープを接着させる。次に、扁平な形状となるように巻回体を成型する。
続いて、折りたたんだフィルム状の外装部材の間に倦回電極体を挟み込んだ後、熱融着法により外装部材35の絶縁部同士を接着させ、一方向のみ解放状態にて、倦回電極体を封入する。正極リード、および負極リードと外装部材の間に密着フィルムを挿入する。
解放部から上記調整した電解液を所定量投入し、真空含浸を行う。含浸後、解放部を真空熱融着法により接着させる。
以上のようにして、ラミネートフィルム型二次電池30を製造することができる。
以下の手順により、図3に示したラミネートフィルム型リチウム二次電池30を作製した。
粒径を調整した後、必要に応じて熱分解CVDを行うことで炭素層で被覆した。
作製した粉末は、バルク内改質装置20を用いて、プロピレンカーボネート及びエチレンカーボネートの1:1混合溶媒(電解質塩を1.3mol/Kg含んでいる)中で電気化学法を用いバルク内改質を行った。
得られた材料は必要に応じて炭酸雰囲気下で乾燥処理を行った。
続いて、負極活物質粒子と負極結着剤の前駆体、導電助剤1と導電助剤2とを80:8:10:2の乾燥重量比で混合した後、NMPで希釈してペースト状の負極合剤スラリーとした。この場合には、ポリアミック酸の溶媒としてNMPを用いた。
続いて、コーティング装置で負極集電体の両面に負極合剤スラリーを塗布してから乾燥させた。この負極集電体としては、電解銅箔(厚さ=15μm)を用いた。
最後に、真空雰囲気中で400℃1時間焼成した。これにより、負極結着剤(ポリイミド)が形成された。
最初に、正極集電体の一端にアルミリードを超音波溶接し、負極集電体の一端にはニッケルリードを溶接した。
続いて、正極、セパレータ、負極、セパレータをこの順に積層し、長手方向に倦回させ倦回電極体を得た。その捲き終わり部分をPET保護テープで固定した。セパレータは多孔性ポリプロピレンを主成分とするフィルムにより多孔性ポリエチレンを主成分とするフィルムに挟まれた積層フィルム(厚さ12μm)を用いた。
続いて、外装部材間に電極体を挟んだ後、一辺を除く外周縁部同士を熱融着し、内部に電極体を収納した。外装部材はナイロンフィルム、アルミ箔及び、ポリプロピレンフィルムが積層されたアルミラミネートフィルムを用いた。
続いて、開口部から調整した電解液を注入し、真空雰囲気下で含浸した後、熱融着し、封止した。
また、負極活物質粒子のメジアン径は4μmであり、負極活物質のX線回折により得られる(111)結晶面に起因する回折ピークの半値幅(2θ)は1.22°であり、負極活物質のSi(111)結晶子は7.21nmであり、負極活物質粒子に含まれるリチウム化合物は、非晶質のLi4SiO4であった。
最初に、電池安定化のため25℃の雰囲気下、2サイクル充放電を行い、2サイクル目の放電容量を測定した。
続いて、総サイクル数が100サイクルとなるまで充放電を行い、その都度放電容量を測定した。
最後に、100サイクル目の放電容量を2サイクル目の放電容量で割り、容量維持率を算出した。
なお、サイクル条件として、4.2Vに達するまで定電流密度、2.5mA/cm2で充電し、4.2Vの電圧に達した段階で4.2V定電圧で電流密度が0.25mA/cm2に達するまで充電した。また、放電時は2.5mA/cm2の定電流密度で電圧が2.5Vに達するまで放電した。
なお、雰囲気及び温度はサイクル特性を調べた場合と同様にし、充放電条件はサイクル特性の0.2倍で行った。
実施例1-1~実施例1-5と同様にして二次電池を作製した。ただし、比較例1-1~比較例1-4においても、A(Si)/B(SiO2)を変化させた。比較例1-1、比較例1-2、比較例1-3、比較例1-4のA(Si)/B(SiO2)は、それぞれ、0.1、0.3、0.5、0.65であった。
また、比較例1-1~比較例1-4についても、実施例1-1~実施例1-5と同様にして、二次電池のサイクル特性および初回充放電特性を調べた。
A(Si)/B(SiO2)を0.8以上とすることで、Li反応サイトであるSiO2部を予め低減でき、それにより、電池初期効率が向上するとともに、安定したLi化合物がバルク内、または表面に存在することで充放電に伴う電池劣化を抑制することができる。
実施例1-1~実施例1-5と同様にして二次電池を作製した。ただし、A(Si)/B(SiO2)は2に固定し、バルク内酸素量を変化させた。この場合、気化出発材の比率や気化温度を変化させることで、堆積物の酸素量を変化させた。
実施例2-1、実施例2-2、実施例2-3、実施例2-4のSiOxのxは、それぞれ、0.5、0.7、1.2、1.6であった。
実施例2-1~実施例2-4について、実施例1-1~実施例1-5と同様にして、二次電池のサイクル特性および初回充放電特性を調べた。
実施例1-1~実施例1-5と同様にして二次電池を作製した。ただし、A(Si)/B(SiO2)は2に固定し、バルク内酸素量を変化させた。この場合、気化出発材の比率や気化温度を変化させることで、堆積物の酸素量を変化させた。
比較例2-1、比較例2-2のSiOxのxは、それぞれ、0.3、1.8であった。
また、比較例2-1~比較例2-2についても、実施例1-1~実施例1-5と同様にして、二次電池のサイクル特性および初回充放電特性を調べた。
また、SiOxのxが0.9である実施例1-4も表2に示されている。
実施例1-1~実施例1-5と同様にして二次電池を作製した。ただし、A(Si)/B(SiO2)は2に固定し、SiOxのxは0.9に固定し、リチウム化合物作製時の電位,電流量,Liの挿入離脱手法を制御し,生成される含有物(リチウム化合物)の状態を変化させた。
また、生成後にガス雰囲気を調整し、熱乾燥させることで含有物の状態を変化させ、より安定な材質とした。
例えば、Li4SiO4は二酸化炭素雰囲気下で熱を加えることで、Li2SiO3とLi2CO3に分かれる。
これらの反応などを取り入れ、最適なバルク状態を実現することで、容量維持率、初期効率の向上を実現した。
得られたLi化合物はXPSで確認可能であり、例えば、Li4SiO4は532eV付近の結合エネルギーで与えられ、Li2SiO3は530eV付近の結合エネルギーで与えられる。
また、得られたLi化合物は、29Si-MAS-NMR spectrumでも確認可能である。
さらに、生成される含有物の結晶度を変化させた。結晶化度はLiの挿入、脱離後の非大気雰囲気下の熱処理で制御可能である。
実施例3-1~実施例3-12の測定結果を表3に示す。
また、生成される含有物が非晶質のLi4SiO4である実施例1-4も表3に示されている。
また、表3からわかるように、含有物がLi4SiO4である場合には、結晶度を表す半値幅(2θ)は0.2°以上であることが好ましく、含有物がLi2SiO3である場合には、半値幅(2θ)は0.75°以上であることが好ましい。
なお、上記の結果を考慮して、以降の実施例においてはリチウム化合物を非晶質状態にして二次電池を作製した。
さらに、表3からわかるように、生成されるリチウム化合物が複数である場合に、より良好な初期充放電特性が得られる。
実施例1-1~実施例1-5と同様にして二次電池を作製した。ただし、A(Si)/B(SiO2)は2に固定し、SiOxのxは0.9に固定し、含有するリチウム化合物は非晶質のLi4SiO4、Li2SiO3、及びLi2CO3とし、バルク改質処理において、Li化合物を生成するとともに、電位、電流を制御し,また、溶媒中での加温保持などを用いることで、活物質表層にフッ素化合物の生成を行った。
実施例4-1、実施例4-2、実施例4-3において、生成されたフッ素化合物は、それぞれ、LiF、LiPF6分解物、LiF+LiPF6分解物であった。
実施例4-1~実施例4-3の測定結果を表4に示す。
また、フッ素化合物が生成されていない実施例3-6も表4に示されている。
実施例1-1~実施例1-5と同様にして二次電池を作製した。ただし、A(Si)/B(SiO2)は2に固定し、SiOxのxは0.9に固定し、含有するリチウム化合物は非晶質のLi4SiO4、Li2SiO3、及びLi2CO3とし、活物質表層をLiFを用いて被覆率50%で被覆した。また、活物質の結晶性を変化させた。
実施例5-1、実施例5-2、実施例5-3、実施例5-4、実施例5-5、実施例5-6、実施例5-7、実施例5-8、実施例5-9において、結晶性を表す半値幅(2θ)は、それぞれ、0.756°、0.796°、1.025°、1.271°、1.845°、2.257°、2.593°、10.123°、20.221°であり、Si(111)結晶子は、それぞれ、11.42nm、10.84nm、8.55nm、6.63nm、4.62nm、3.77nm、3.29nm、1.524nm、0nmであった。
なお、実施例5-9では半値幅を20°以上と算出しているが、解析ソフトを用いフィッティングした結果であり、実質的にピークは得られていない。従って、実施例5-9では実質的に非晶質であると言える。
実施例5-1~実施例5-9の測定結果を表5に示す。
特に、半値幅が1.2°以上、又は、Si(111)面に起因する結晶子サイズ7.5nm以下の低結晶性材料で、より高い容量維持率、初期効率が得られている。
その中でも、活物質が非結晶である場合には、最も良い特性が得られた。
実施例1-1~実施例1-5と同様にして二次電池を作製した。ただし、A(Si)/B(SiO2)は2に固定し、SiOxのxは0.9に固定し、含有するリチウム化合物は非晶質のLi4SiO4、Li2SiO3、及びLi2CO3とし、活物質の表層をLiFを用いて被覆率50%で被覆した。また、負極活物質の結晶性は半値幅(2θ)が20.221であった。
さらに、29Si-MAS-NMR spectrumのSi領域のピーク値を変化させた。
実施例6-1において、負極活物質粒子のピーク値は、-70~-85ppmの範囲内である-78ppmであった(図6を参照)。
実施例6-1の測定結果を表6に示す。
また、図6に示されるように負極活物質粒子の29Si-MAS-NMR spectrumのSi領域のピーク値が-87である実施例5-9についても表6に示されている。
従って、負極活物質粒子の29Si-MAS-NMR spectrumのSi領域のピーク値が-70~-85ppmの範囲内にあることがより望ましい。
通常、29Si-MAS-NMR spectrumのSi領域のピークは-85ppm以下の領域で得られるが、Si-O-Siなどの結合角を変化させることで上記範囲のような低磁場側へとシフトさせることができる。すなわち、Siの結合角をシフトさせることで、より安定的なバルク状況を実現している。
実施例1-1~実施例1-5と同様にして二次電池を作製した。ただし、A(Si)/B(SiO2)は2に固定し、SiOxのxは0.9に固定し、含有するリチウム化合物は非晶質のLi4SiO4、Li2SiO3、及びLi2CO3とし、活物質の表層をLiFを用いて被覆率50%で被覆した。また、負極活物質の結晶性は半値幅(2θ)が1.271であった。
さらに、負極活物質粒子のメジアン径を変化させた。
実施例7-1、実施例7-2、実施例7-3、実施例7-4、実施例7-5、実施例7-6において、負極活物質粒子のメジアン径は、それぞれ、0.1μm、0.5μm、1μm、10μm、20μm、30μmであった。
実施例7-1~実施例7-6の測定結果を表7に示す。
また、負極活物質粒子のメジアン径が4μmである実施例5-4も表7に示されている。
実施例1-1~実施例1-5と同様にして二次電池を作製した。ただし、A(Si)/B(SiO2)は2に固定し、SiOxのxは0.9に固定し、含有するリチウム化合物は非晶質のLi4SiO4、Li2SiO3、及びLi2CO3とし、負極活物質の表層をLiFを用いて被覆率50%で被覆した。また、負極活物質の結晶性は半値幅(2θ)が1.271であった。
さらに、負極活物質粒子の表層部に、熱分解CVD法を用いて炭素層を成膜した。
実施例8-1、実施例8-2、実施例8-3、実施例8-4、実施例8-5、実施例8-6、実施例8-7において、炭素層の膜厚は、それぞれ、1nm、100nm、200nm、500nm、1000nm、5000nm、7500nmであり、実施例8-1の被覆率は60%であり、実施例8-2~実施例8-7被覆率は80%であった。
実施例8-1~実施例8-7の測定結果を表7に示す。
また、負極活物質粒子の表層部に炭素層を形成しない実施例5-4も表8に示されている。
しかしながら、炭素層の膜厚が7000nmより厚くなると、電池設計上、電池容量の低下となるため、電池容量及び電池特性を考慮すると1nm~5000nmがより望ましい。
実施例1-1~実施例1-5と同様にして二次電池を作製した。ただし、A(Si)/B(SiO2)は2に固定し、SiOxのxは0.9に固定し、含有するリチウム化合物は非晶質のLi4SiO4、Li2SiO3、及びLi2CO3とし、負極活物質の表層をLiFを用いて被覆率50%で被覆した。また、負極活物質の結晶性は半値幅(2θ)が1.271であった。
さらに、負極活物質粒子の表層部の炭素層の膜厚を100nmとし、被覆率を変化させた。
実施例9-1、実施例9-2、実施例9-3、実施例9-4において、炭素層の被覆率は、それぞれ、20%、30%、50%、90%であった。
さらに、炭素層の被覆率が80%である実施例8-2と、実施例9-1~実施例9-4について、負荷特性を調べた。
ここで、負荷特性は、負極単位面積当たりの放電電流2mA/cm2で放電したときの容量を、負極単位面積当たりの放電電流0.25mA/cm2で放電したときの容量で割ったものである。
実施例8-2、実施例9-1~実施例9-4の測定結果を表9に示す。
実施例1-1~実施例1-5と同様にして二次電池を作製した。ただし、A(Si)/B(SiO2)は2とし、SiOxのxは0.9とし、含有するリチウム化合物は非晶質のLi4SiO4、Li2SiO3、及びLi2CO3とし、負極活物質の表層をLiFで被覆した。また、負極活物質の結晶性は半値幅(2θ)が1.271であった。
さらに、負極活物質粒子の表層部の炭素層の膜厚を100nmとし、その被覆率を80%とし、負極活物質の表層を被覆するLiF層の被覆率を変化させた。
実施例10-1、実施例10-2、実施例10-3において、LiF層の被覆率は、それぞれ、20%、30%、70%であった。
先ず、銅箔表面に接着剤を塗布した後、その接着剤の上に粉体サンプル(負極活物質粒子)をふりかける。
続いて、真空蒸着法により粉体サンプルの表面に白金を堆積させる。
続いて、集束イオンビーム(FIB:Focused Ion Beam)法により、白金の表面にタングステンを堆積させた後、さらに加速電圧=30kVで薄膜加工した。
最後に、高角散乱暗視野走査(High Angle Annular Dark Fields Scanning)TEM(加速電圧=200kV)により負極活物質粒子の断面を観察した。
画像観察で粒子を確認しながらEDXの分析を行うことで、粒子表層を覆うフッ素化合物の状態を把握した。
フッ素化合物の被覆率は、炭素層の被覆率と同様に、粒子の外周と、その粒子を覆うフッ素化合物の長さとの比で算出することができる。
実施例10-1~実施例10-3の測定結果を表10に示す。
また、LiF層の被覆率が50%である実施例8-2も表10に示されている。
実施例1-1~実施例1-5と同様にして二次電池を作製した。ただし、A(Si)/B(SiO2)は2とし、SiOxのxは0.9とし、含有するリチウム化合物は非晶質のLi4SiO4、Li2SiO3、及びLi2CO3とし、負極活物質の表層をLiFを用いて被覆率50%で被覆した。また、負極活物質の結晶性は半値幅(2θ)が1.271であった。
また、負極活物質粒子の表層部の炭素層の膜厚を100nmとし、その被覆率を80%とした。
さらに、負極集電体にC(炭素)及びS(硫黄)を含有させ、その含有量を変化させた。
実施例11-1、実施例11-2、実施例11-3において、負極集電体のC及びSの含有量は、それぞれ、200ppm、100ppm、50ppmであった。
実施例11-1~実施例11-3、実施例8-2の評価結果を表11に示す。
実施例1-1~実施例1-5と同様にして二次電池を作製した。ただし、A(Si)/B(SiO2)は2とし、SiOxのxは0.9とし、含有するリチウム化合物は非晶質のLi4SiO4、Li2SiO3、及びLi2CO3とし、負極活物質の表層をLiFを用いて被覆率50%で被覆した。また、負極活物質の結晶性は半値幅(2θ)が1.271であった。
また、負極活物質粒子の表層部の炭素層の膜厚を100nmとし、その被覆率を80%とした。
さらに、負極結着剤として、さまざまなものを用いた。
実施例12-1、実施例12-2、実施例12-3、実施例12-4、実施例12-5、実施例12-6、実施例12-7において、負極結着剤は、それぞれ、ポリフッ化ビニリデン、アラミド、ポリアクリル酸、ポリアクリル酸リチウム、炭化ポリイミド、ポリエチレン、ポリマレイン酸であった。
実施例12-1~実施例12-7の測定結果を表12に示す。
また、負極結着剤がポリイミドである実施例8-2も表12に示されている。
実施例1-1~実施例1-5と同様にして二次電池を作製した。ただし、A(Si)/B(SiO2)は2とし、SiOxのxは0.9とし、含有するリチウム化合物は非晶質のLi4SiO4、Li2SiO3、及びLi2CO3とし、負極活物質の表層をLiFを用いて被覆率50%で被覆した。また、負極活物質の結晶性は半値幅(2θ)が1.271であった。
また、負極活物質粒子の表層部の炭素層の膜厚を100nmとし、その被覆率を80%とした。
さらに、ケイ素系材料のバルク内改質方法として、さまざまなものを用いた。
実施例13-1、実施例13-2、実施例13-3、実施例13-4、実施例13-5において、改質方法は、それぞれ、ショート法、電位・電流制御+Li挿入法、熱ドープ法、真空蒸着法、電位・電流制御+Li挿入後一部離脱法を3回繰り返す方法である。
また、電位・電流制御+Li挿入後一部離脱法とは、図5に示すバルク内改質装置20を用いて、Li源21に供給する電位・電流を制御しながらLiをバルク内に挿入した後に、電位・電流を制御しながら挿入したリチウムを一部離脱させる方法である。
また、ショート法とは、Li源21と粉末格納容器25と電気的にショートして、電位制御や電流制御を行わずに、Li源21と粉末格納容器25との間に発生する電位差を用いてLiを挿入する方法である。
また、熱ドープ法とは、ケイ素材料とLi金属、又は、Li化合物を混合し、熱処理を行う方法である。
また、真空蒸着法とは、10-2Pa以下に減圧した真空チャンバー内で、抵抗加熱法を用いてLiメタル、又は炭酸リチウムなどを加熱気化させて、ケイ素系材料の粉末にこの蒸気を噴霧する方法である。
実施例13-1~実施例13-5の測定結果を表13に示す。
また、改質方法が電位・電流制御+Li挿入後一部離脱法である実施例8-2も表13に示されている。
一方、熱ドープ法は、より良質な活物質に改質される方法にはならないことがわかった。
また、真空蒸着法は、より均一な改質にならないため、電位・電流制御+Li挿入後一部離脱法には及ばないことがわかった。
実施例1-1~実施例1-5と同様にして二次電池を作製した。ただし、A(Si)/B(SiO2)は2とし、SiOxのxは0.9とし、含有するリチウム化合物は非晶質のLi4SiO4、Li2SiO3、及びLi2CO3とし、負極活物質の表層をLiFを用いて被覆率50%で被覆した。また、負極活物質の結晶性は半値幅(2θ)が1.271であった。
さらに、ケイ素系材料のバルク内改質形態として、さまざまなものを用いた。
実施例14-1、実施例14-3~実施例14-7において、改質方法として、電位・電流制御+Li挿入後一部離脱法を用いる一方で、実施例14-2においては、改質方法として、真空蒸着法を用いた。
また、実施例14-1、実施例14-2においては、改質形態として、蒸着により銅箔に直接SiO膜を形成した状態でバルク内改質を行っており、実施例14-3においては、改質形態として、熱分解CVD(すなわち、シロキサンとアルゴンガスを真空チャンバーに導入させた状態で650℃以上の熱を加えることで、熱分解させて基板上に析出させて成膜する方法)により銅箔に直接SiO膜を形成した状態でバルク内改質を行った。
さらに、実施例14-4においては、未改質のケイ素材を電極に塗布した後にバルク内改質を行い、実施例14-5~実施例14-7においては、炭素材と未改質のケイ素材を電極に混合塗布した後にバルク内改質を行った。
実施例14-5では、ケイ素材50質量%、炭素材50質量%で混合塗布を行い、実施例14-6では、ケイ素材30質量%、炭素材70質量%で混合塗布を行い、実施例14-5では、ケイ素材50質量%、炭素材50質量%で混合塗布を行った。
実施例14-1~実施例14-7の測定結果を表14に示す。
また、改質方法が電位・電流制御+Li挿入後一部離脱法であり、改質形態として粉末状態でバルク内改質を行う実施例8-2も表14に示されている。
また、未改質のケイ素材を電極に塗布した後に電気化学法を用いて改質を行うことで、容量維持率、初期効率が向上している。
特に、炭素材と未改質ケイ素材を電極に混合塗布した後に電気化学法を用いて改質を行うことで、選択的にケイ素材へ改質を行うことが可能であり、炭素材本来の特性を生かしつつ、ケイ素材によって電池エネルギー密度の向上が可能となり、炭素材の割合が増えるとともに、容量維持率、初期効率が向上している。
ケイ素材は炭素材よりも高い対Li電位でLiと反応するため、Liがケイ素材に入りやすい電位で電位制御を行うことでケイ素材に選択的にLiを挿入できるので、電位制御を用いた改質が効果的である。
実施例1-1~実施例1-5と同様にして二次電池を作製した。ただし、A(Si)/B(SiO2)は2とし、SiOxのxは0.9とし、含有するリチウム化合物は非晶質のLi4SiO4、Li2SiO3、及びLi2CO3とし、負極活物質の表層をLiFを用いて被覆率50%で被覆した。また、負極活物質の結晶性は半値幅(2θ)が1.271であった。
また、負極活物質粒子の表層部の炭素層の膜厚を100nmとし、その被覆率を80%とした。
さらに、ケイ素系材料のバルク内改質方法として、電位・電流制御+Li挿入後一部離脱法を用い、改質形態として粉末塗布を用いた。
そして、改質源(Li源)として、さまざまなものを用いた。
実施例15-1、実施例15-2、実施例15-3、実施例15-4、実施例15-5、実施例15-6、実施例15-7において、改質源として、それぞれ、リチウムメタル、塩化リチウム、炭酸リチウム、酸化リチウム、オリビン鉄リチウム、Ni含有リチウム複合酸化物、Mn含有リチウム複合酸化物を用いた。
実施例15-1~実施例15-7の測定結果を表15に示す。
また、改質源として、コバルト酸リチウムを用いた実施例8-2も表15に示されている。
従って、改質源は特に限定することはないが、製造プロセスを考慮した場合に、より安定的な物質が望ましい。
リチウムメタルよりはリチウム複合酸化物が望ましく、例えばコバルト酸リチウム、オリビン鉄リチウムが望ましい。
中でもオリビン鉄リチウムは充電電位が低いことから工業的に低コスト化が可能であり、また出力特性も良好であるので、特に望ましい。
また、リチウム複合酸化物はある一定以上リチウムの挿入・脱離を繰り返した後に、リチウム含有複合物質と混合し、熱処理を行うことで再利用が可能となるという利点を有している。
なお、リチウム複合酸化物は、実質的に電池グレードより大きく劣化した正極材と類似しているが、改質源として使用する場合には、特に電池特性は低くても許容される。
Claims (24)
- 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、SiOx(0.5≦x≦1.6)からなるケイ素系材料を含有し、
前記ケイ素系材料において、29Si-MAS-NMR spectrumから得られる、ケミカルシフト値として-50~-95ppmで与えられるSi領域のピーク値強度値Aと、ケミカルシフト値として-96~-150ppmで与えられるSiO2領域のピーク値強度値Bが、A/B≧0.8という関係を満たすものであることを特徴とする負極活物質。 - 前記負極活物質粒子は、29Si-MAS-NMR spectrumから得られる、ケミカルシフト値として-70~-85ppmで与えられる範囲にピーク値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、29Si-MAS-NMR spectrumから得られる、ケミカルシフト値として-50~-95ppmで与えられるピーク範囲内に少なくとも2つ以上のピークを含む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、29Si-MAS-NMR spectrumから得られる、ケミカルシフト値として-50~-95ppmで与えられるピーク範囲内に少なくともLi2SiO3、Li4SiO4のうち1つ以上に対応するピークを含む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、29Si-MAS-NMR spectrumから得られる、ケミカルシフト値として-50~-95ppmで与えられるピーク範囲内にメタルSiに対応するピークを含む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、Li2SiO3、Li4SiO4、Li2O、及び、Li2CO3のうち少なくとも1種以上を含む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、Li2SiO3、Li4SiO4、Li2O、及び、Li2CO3のうち少なくとも2種以上を含むことを特徴とする請求項6に記載の負極活物質。
- 前記Li2SiO3は、X線回折により得られる38.2680°付近で得られる回折ピークの半値幅(2θ)が0.75°以上であることを特徴とする請求項6又は請求項7に記載の負極活物質。
- 前記Li4SiO4は、X線回折により得られる23.9661°付近で得られる回折ピークの半値幅(2θ)は0.2°以上であることを特徴とする請求項6又は請求項7に記載の負極活物質。
- 前記Li2SiO3及び前記Li4SiO4は、非晶質であることを特徴とする請求項6又は請求項7に記載の負極活物質。
- 前記負極活物質粒子は、その表面の少なくとも一部にアイランド状、膜状、または、凹凸を有する形状のフッ素化合物を有することを特徴とする請求項1乃至請求項10のいずれか一項に記載の負極活物質。
- 前記フッ素化合物は、フッ化リチウム、又は、LiPF6の分解物であることを特徴とする請求項11に記載の負極活物質。
- 前記負極活物質は、X線回折により得られる(111)結晶面に起因する回折ピークの半値幅(2θ)が1.2°以上であるとともに、その結晶面に対応する結晶子サイズは7.5nm以下であることを特徴とする請求項1乃至請求項12のいずれか一項に記載の負極活物質。
- 前記負極活物質粒子のメジアン径は0.5μm以上、20μm以下であることを特徴とする請求項1乃至請求項13のいずれか一項に記載の負極活物質。
- 前記負極活物質粒子は、表層部に炭素材を含むことを特徴とする請求項1乃至請求項14のいずれか一項に記載の負極活物質。
- 前記被覆する炭素材の平均厚さは1nm以上、5000nm以下であることを特徴とする請求項15に記載の負極活物質。
- 前記負極活物質粒子は、少なくともその一部にSiOxと、炭素と、フッ素化合物を有するか、又は、SiOxと、フッ素化合物を有することを特徴とする請求項1乃至請求項16のいずれか一項に記載の負極活物質。
- 前記フッ素化合物からなる被覆層の平均被覆率は30%以上であることを特徴とする請求項11又は請求項12に記載の負極活物質。
- 前記炭素材からなる被覆層の平均被覆率は30%以上であることを特徴とする請求項15又は請求項16に記載の負極活物質。
- 請求項1乃至請求項19のいずれか一項に記載の負極活物質と、炭素材料とを含むことを特徴とする負極活物質材料。
- 請求項20に記載の負極活物質材料で形成された負極活物質層と、
負極集電体とを有し、
前記負極活物質層は前記負極集電体上に形成されており、
前記負極集電体は炭素および硫黄を含むとともに、それらの含有量がいずれも100ppm以下であることを特徴とする負極電極。 - 負極電極として、請求項1乃至請求項19のいずれか一項に記載の負極活物質を含む負極電極を用いたものであることを特徴とするリチウムイオン二次電池。
- SiOxからなるケイ素系材料を含有する負極活物質粒子を含む負極活物質を製造する方法であって、
前記ケイ素系材料として、前記xが0.5以上、1.6以下であり、かつ、29Si-MAS-NMR spectrumから得られる、ケミカルシフト値として-50~-95ppmで与えられるSi領域のピーク値強度値Aと、ケミカルシフト値として-96~-150ppmで与えられるSiO2領域のピーク値強度値Bが、A/B≧0.8という関係を満たすものを選別して使用することを特徴とする負極活物質の製造方法。 - 請求項23に記載の負極活物質の製造方法によって製造した負極活物質を用いて負極を作製し、該作製した負極を用いてリチウムイオン二次電池を製造することを特徴とするリチウムイオン二次電池の製造方法。
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CN107611347A (zh) | 2018-01-19 |
CN105474438A (zh) | 2016-04-06 |
US10566607B2 (en) | 2020-02-18 |
JP6457590B2 (ja) | 2019-01-23 |
US20160233484A1 (en) | 2016-08-11 |
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