WO2022259920A1 - 負極活物質、負極及びリチウムイオン二次電池 - Google Patents
負極活物質、負極及びリチウムイオン二次電池 Download PDFInfo
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- WO2022259920A1 WO2022259920A1 PCT/JP2022/022173 JP2022022173W WO2022259920A1 WO 2022259920 A1 WO2022259920 A1 WO 2022259920A1 JP 2022022173 W JP2022022173 W JP 2022022173W WO 2022259920 A1 WO2022259920 A1 WO 2022259920A1
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- Prior art keywords
- negative electrode
- active material
- electrode active
- particles
- silicon monoxide
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Classifications
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- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
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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
- 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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- H—ELECTRICITY
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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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- H—ELECTRICITY
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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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- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
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- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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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
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/483—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides for non-aqueous cells
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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
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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
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
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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
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
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- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/027—Negative electrodes
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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
Definitions
- the present invention relates to a negative electrode active material, a negative electrode, and a lithium ion secondary battery.
- lithium-ion secondary batteries are becoming more and more popular because they are easy to make smaller and have higher capacity, and they have a higher energy density than lead-acid batteries and nickel-cadmium batteries.
- the lithium-ion secondary battery described above includes a positive electrode, a negative electrode, a separator, and an electrolytic solution, and the negative electrode contains a negative electrode active material involved in charge-discharge reactions.
- the negative electrode active material expands and contracts during charging and discharging, and cracks are likely to occur mainly near the surface layer of the negative electrode active material.
- an ionic substance is generated inside the active material, making the negative electrode active material fragile.
- a new surface is generated thereby increasing the reaction area of the active material.
- a decomposition reaction of the electrolytic solution occurs on the new surface, and a film, which is a decomposition product of the electrolytic solution, is formed on the new surface, so that the electrolytic solution is consumed.
- cycle characteristics tend to deteriorate.
- silicon and amorphous silicon dioxide are simultaneously deposited using a vapor phase method (see Patent Document 1, for example).
- a carbon material electroconductive material
- an active material containing silicon and oxygen is produced, and an active material layer with a high oxygen ratio is formed in the vicinity of the current collector (for example, see Patent Document 3).
- the silicon active material contains oxygen so that the average oxygen content is 40 atomic % or less, and the oxygen content is increased near the current collector. (see, for example, Patent Document 4).
- a nanocomposite containing Si phase, SiO 2 , and M y O metal oxide is used to improve the initial charge/discharge efficiency (see, for example, Patent Document 5).
- the molar ratio of oxygen to silicon in the negative electrode active material is set to 0.1 to 1.2, and the difference between the maximum and minimum molar ratios near the interface between the active material and the current collector is is 0.4 or less (see Patent Document 7, for example).
- a metal oxide containing lithium is used (see, for example, Patent Document 8).
- a hydrophobic layer such as a silane compound is formed on the surface layer of the silicon material (see Patent Document 9, for example).
- Patent Document 10 silicon oxide is used, and conductivity is imparted by forming a graphite film on the surface layer.
- Patent Document 10 broad peaks appear at 1330 cm ⁇ 1 and 1580 cm ⁇ 1 with respect to the shift values obtained from the RAMAN spectrum of the graphite film, and their intensity ratio I 1330 /I 1580 is 1.5 ⁇ I 1330 /I 1580 ⁇ 3.
- particles having a silicon microcrystalline phase dispersed in silicon dioxide are used (see, for example, Patent Document 11).
- silicon oxide in which the atomic ratio of silicon and oxygen is controlled to 1:y (0 ⁇ y ⁇ 2) is used (see Patent Document 12, for example).
- Non-Patent Document 1 The silicon oxide proposed by Hohl is a composite of Si 0+ to Si 4+ and has various oxidation states (Non-Patent Document 2).
- Kapaklis also proposed a disproportionated structure in which Si and SiO 2 are separated by applying a thermal load to silicon oxide (Non-Patent Document 3).
- Miyachi et al. pay attention to Si and SiO 2 that contribute to charging and discharging among silicon oxides having a disproportionated structure (Non-Patent Document 4).
- silicon oxide powder with a defined particle size distribution of mode diameter, D50 and D90 is used (for example, Patent Document 13).
- D50 indicates cumulative 50% diameter
- D90 indicates cumulative 90% diameter
- other numerical values are the same.
- D90, D90/D10, and fine powder amount of 1 ⁇ m or less of silicon oxide powder subjected to wet classification with water after ball mill pulverization are specified (for example, Patent Document 14).
- silicon oxide powder having a defined D50/D10 of the silicon oxide powder before forming the carbon film and a BET specific surface area of the negative electrode active material after forming the carbon film is used (for example, Patent document 15).
- Non-Patent Document 5 2SiO(Si+SiO 2 ) + 6.85Li + + 6.85e ⁇ ⁇ 1.4Li 3.75Si + 0.4Li 4 SiO 4 + 0.2SiO 2
- Si and SiO 2 that constitute silicon oxide react with Li, and are divided into Li silicide, Li silicate, and partially unreacted SiO 2 .
- the Li silicate produced here is irreversible, and once formed, it is a stable substance that does not release Li.
- the capacity per mass calculated from this reaction formula has a value close to the experimental value, and is recognized as a reaction mechanism of silicon oxide.
- Kim et al. identified Li silicate, an irreversible component associated with charging and discharging of silicon oxide, as Li 4 SiO 4 using 7 Li-MAS-NMR and 29 Si-MAS-NMR (Non-Patent Document 6. ).
- This irreversible capacity is the weakest point of silicon oxide, and improvement is desired. Therefore, Kim et al. used a Li pre-doping method in which Li silicate is formed in advance to greatly improve the initial efficiency as a battery and create a negative electrode that can withstand practical use (Non-Patent Document 7).
- Patent Document 16 a method of treating the powder has been proposed, and the irreversible capacity has been improved.
- Lithium-ion secondary batteries using silicon-based materials with high charge-discharge capacity are desired to have high capacity, high initial efficiency, and cycle characteristics that can withstand practical levels.
- silicon-based materials silicon oxide has the potential to obtain higher cycle characteristics, and the initial efficiency has also been greatly improved by lithium doping.
- the suppression of decomposition of the electrolyte solution on the surface of the negative electrode active material is insufficient during repeated charging and discharging, and cycle characteristics that can withstand a practical level are not obtained. was not
- Patent Document 14 specifies D90/D10 and the amount of fine powder of 1 ⁇ m or less by performing wet classification with water, using SiO x powder with a different surface Si oxidation state and a significantly different value of x. , the relative evaluation of initial efficiency and cycle characteristics and particle size distribution was not possible.
- Patent Document 15 specifies D50 and D50/D10 of SiO x powder (obtained by wet classification with water as in Patent Document 14).
- the examples only describe the difference in the initial discharge capacity among the relatively small particle diameters of 4.41 to 5.35 ⁇ m in D50.
- cycle characteristics (10 cycles) there is no difference in cycle characteristics (10 cycles) in the comparative example of 36 ⁇ m.
- cycle characteristics 10 cycles
- the evaluation of coin batteries repeated charge/discharge cycles deteriorate the Li positive electrode, making it unsuitable for long-term cycle tests exceeding 50 cycles. Therefore, in order to evaluate the deterioration of the negative electrode due to the reaction between the electrolyte and the negative electrode active material, more than 100 charge-discharge cycles are required. must be done in
- fine powder with a particle size of 1 ⁇ m or less has a large specific surface area, it is a major factor in deteriorating cycle characteristics. , requires definition with a particle size greater than 1 ⁇ m.
- the present invention has been made in view of the problems described above, and a negative electrode capable of improving cycle characteristics while maintaining high initial efficiency when used as a negative electrode active material for a negative electrode of a secondary battery.
- the object is to provide an active material.
- the present invention provides a negative electrode active material comprising silicon monoxide particles coated with a carbon film and doped with lithium, wherein the silicon monoxide particles are obtained by laser diffraction particle size distribution measurement.
- the integrated value of the relative particle amount with a particle diameter of 1 ⁇ m or less is 1% or less
- the integrated value of the relative particle amount with a particle diameter of 5 ⁇ m or less is 20% or less
- the cumulative 50% diameter D50 is 6.
- a negative electrode active material that satisfies 0 ⁇ m ⁇ D50 ⁇ 15.0 ⁇ m.
- the negative electrode active material of the present invention is a negative electrode active material comprising silicon monoxide particles doped with lithium, it is possible to maintain a high initial efficiency and to have the particle size distribution as described above. In a long-term cycle test in which the above is repeated, the reaction with the electrolytic solution on the particle surface of the negative electrode active material is suppressed, and the cycle characteristics of the battery can be greatly improved.
- the silicon monoxide particles preferably have an integrated value of 10% or less of the relative amount of particles having a particle diameter of 5 ⁇ m or less.
- the silicon monoxide particles preferably satisfy 18.0 ⁇ m ⁇ D99.9 ⁇ 50.0 ⁇ m, where D99.9 is the cumulative 99.9% particle diameter.
- the reaction with the electrolytic solution on the particle surface is more effectively suppressed, and the cycle characteristics of the battery can be greatly improved.
- the negative electrode active material of the present invention it is preferable that at least part of lithium in the silicon monoxide particles coated with the carbon film and doped with lithium is present as Li 2 SiO 3 .
- doped lithium exists as Li 2 SiO 3 in such a negative electrode active material, excellent charge/discharge characteristics and cycle characteristics can be obtained when used as a battery.
- the silicon monoxide particles coated with the carbon film and doped with lithium are subjected to X-ray diffraction using Cu—K ⁇ rays before charging and discharging the negative electrode active material.
- the ratio A/B of the intensity A of the peak attributed to the Si (111) crystal plane to the intensity B preferably satisfies 0.5 ⁇ A/B ⁇ 1.0.
- a negative electrode active material with A/B in such a range has an appropriate amount of lithium doping, and excellent charge/discharge characteristics and cycle characteristics can be obtained when used in a battery.
- the true density of the silicon monoxide particles coated with the carbon film and doped with lithium is preferably greater than 2.3 g/cc and less than 2.4 g/cc.
- the reaction rate between silicon monoxide and doped lithium is within the desired range, and the negative electrode active material is such that Li is appropriately inserted into the silicon monoxide particles. Therefore, cycle characteristics are further improved.
- the present invention also provides a negative electrode that includes the negative electrode active material described above.
- the present invention also provides a lithium ion secondary battery comprising the above negative electrode, positive electrode, separator, and electrolyte.
- Such a lithium-ion secondary battery suppresses the reaction with the electrolytic solution on the surface of the negative electrode active material particles, and greatly improves the cycle characteristics of the battery while maintaining excellent initial battery characteristics. can be improved to
- the negative electrode active material of the present invention has the range of powder characteristics as described above, in a long-term cycle test in which charging and discharging are repeated, the reaction with the electrolyte solution on the surface of the silicon monoxide particles is suppressed, and an excellent initial battery is obtained. Long-term cycle characteristics can be greatly improved while maintaining the characteristics.
- FIG. 4 is a frequency accumulation graph of relative particle amounts of silicon monoxide particles in Examples 1, 2, 4 and Comparative Example 2.
- FIG. 4 is a frequency accumulation graph of relative particle amounts of silicon monoxide particles in Examples 1, 2, 4 and Comparative Example 2.
- the present inventors have found that the particle size of the monosilicon oxide particles serving as the base material of the negative electrode active material. As a result of intensive studies on control, it was found that it is possible to greatly improve the cycle characteristics while maintaining the initial charge-discharge characteristics in a specific particle size distribution and powder physical properties, leading to the present invention. .
- the negative electrode active material of the present invention is a negative electrode active material composed of silicon monoxide particles coated with a carbon film and doped with lithium. Furthermore, the silicon monoxide particles satisfy the following conditions in the volume standard distribution measured by a laser diffraction particle size distribution analyzer. ⁇ The integrated value of the relative amount of particles with a particle diameter of 1 ⁇ m or less is 1% or less, ⁇ The integrated value of the relative particle amount with a particle diameter of 5 ⁇ m or less is 20% or less, - Cumulative 50% diameter D50 is 6.0 ⁇ m ⁇ D50 ⁇ 15.0 ⁇ m.
- the integrated value of the relative amount of particles having a particle diameter of 5 ⁇ m or less is 10% or less.
- the silicon monoxide particles contained in the negative electrode active material of the present invention preferably satisfy 18.0 ⁇ m ⁇ D99.9 ⁇ 50.0 ⁇ m, where D99.9 is the cumulative 99.9% particle diameter.
- Silicon oxide is a generic term for amorphous silicon oxide, and silicon oxide before disproportionation is represented by the general formula SiOx (0.5 ⁇ x ⁇ 1.6).
- This silicon oxide can be obtained, for example, by heating a mixture of silicon dioxide and metal silicon and then cooling and precipitating silicon monoxide gas produced, thereby obtaining silicon monoxide (SiO) in which x is 1 or close to 1. For example, 0.9 ⁇ x ⁇ 1.1.
- the silicon monoxide particles within the specific particle size range of the present invention described above, they can be appropriately adjusted by treatments such as pulverization and classification.
- Well-known equipment can be used for grinding.
- ball mills, media agitation mills, and rollers are used to pulverize crushed materials by moving pulverizing media such as balls and beads, and using the impact force, friction force, and compression force resulting from the kinetic energy.
- a jet mill that pulverizes the crushed material by colliding it with the lining material at high speed or colliding with each other, and crushing it by the impact force caused by the impact, and the impact caused by the rotation of the rotor with fixed hammers, blades, pins, etc.
- Dry classification mainly uses air flow, and the processes of dispersion, separation (separation of fine and coarse particles), collection (separation of solid and gas), and discharge are performed sequentially or simultaneously, and interference between particles, particle
- pretreatment adjustment of moisture, dispersibility, humidity, etc.
- pulverization and classification are performed at once, and a desired particle size distribution can be obtained.
- jet mill pulverization is performed so that the BET specific surface area of the silicon monoxide particles does not increase, and the small particle size side is cut by air flow classification with a classifier. is preferred.
- the cumulative 50% diameter D50 of the silicon monoxide particles is, as described above, 6.0 to 15.0 ⁇ m, preferably 7.5 to 15.0 ⁇ m.
- the cumulative 99.9% diameter D99.9 of the silicon monoxide particles is preferably 18.0 to 50.0 ⁇ m, more preferably 25.0 to 50.0 ⁇ m.
- D99.9 is 50.0 ⁇ m or less, expansion and contraction of coarse particles due to charging and discharging can be suppressed, and the risk of loss of conductive paths in the negative electrode active material layer can be reduced.
- the particle size distribution of the silicon monoxide particles can be confirmed with a laser diffraction particle size distribution analyzer, for example, under the following conditions.
- the BET specific surface area of the silicon monoxide particles serving as the substrate is preferably 1.0 to 10 m 2 /g. 0 to 3.5 m 2 /g is more preferred.
- the BET specific surface area is preferably 1.0 m 2 /g or more. The reason for this is that it is industrially difficult to produce silicon monoxide particles with a BET specific surface area of less than 1.0 m 2 /g for silicon monoxide particles of 6.0 ⁇ m ⁇ D50 ⁇ 15.0 ⁇ m. is.
- a method of imparting conductivity to the silicon monoxide particles and improving battery characteristics a method of mixing with conductive particles such as graphite, a method of coating the surface of the composite particles with a carbon film, and both.
- Chemical vapor deposition (CVD) is a suitable method for coating with a carbon coating.
- CVD chemical vapor deposition
- Chemical vapor deposition can be applied under both normal pressure and reduced pressure.
- generally known apparatuses such as a batch type furnace, a continuous furnace such as a rotary kiln and a roller hearth kiln, and a fluidized bed can be used as the apparatus used in the step of forming the carbon coating.
- the vapor deposition apparatus is a batch type furnace in which the particles are left stationary, the carbon can be more uniformly coated by carrying out the vapor deposition under reduced pressure, and the battery characteristics can be improved.
- the thermal decomposition temperature, deposition rate, and characteristics of the carbon film formed after vapor deposition largely depend on the substance used. may differ.
- the uniformity of the carbon film on the surface of a substance with a high deposition rate is not sufficient, and on the other hand, if a high temperature is required for decomposition, the silicon crystals in the silicon monoxide particles to be coated grow too large during deposition at a high temperature. As a result, the discharge efficiency and cycle characteristics may deteriorate. Therefore, the CVD temperature range is more preferably 950° C. or lower, and most preferably 850° C. or lower.
- Raw materials for organic gases that can be thermally decomposed to produce carbon include hydrocarbons such as methane, ethane, ethylene, acetylene, propane, butane, butene, pentane, isobutane, and hexane, benzene, toluene, xylene, styrene, ethylbenzene, Diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, cumarone, pyridine, anthracene, phenanthrene and other monocyclic to tricyclic aromatic hydrocarbons, gas light oil obtained in the tar distillation process, creosote oil, anthracene oil and naphtha cracked tar oil. These can be used singly or in combination of two or more. From an economical point of view, it is preferable to use a hydrocarbon gas with a composition of CxHy.
- the coating amount of the carbon coating is preferably 1.0% by mass or more and 5.0% by mass or less with respect to the entire carbon-coated coated particles. Although it depends on the particles to be coated, by setting the carbon coating amount to 1.0% by mass or more, generally sufficient conductivity can be maintained. In addition, by setting the carbon coating amount to 5.0% by mass or less, the proportion of carbon in the negative electrode active material can be moderated without excessively increasing, and it can be used as a negative electrode active material for lithium ion secondary batteries. The charge/discharge capacity can be ensured when the battery is used.
- the silicon monoxide particles coated with the carbon film are doped with Li to prepare negative electrode active material particles containing the Li-doped silicon monoxide particles.
- Silicon monoxide particles are modified by Li doping to generate Li compounds inside the silicon monoxide particles.
- Li doping is preferably performed by an oxidation-reduction method. This Li doping can reduce the irreversible capacity of the silicon monoxide particles, contributing to the improvement of the initial efficiency.
- lithium can be inserted by first immersing the silicon monoxide particles in a solution A in which lithium is dissolved in an ether solvent.
- This solution A may further contain a polycyclic aromatic compound or a linear polyphenylene compound.
- active lithium can be desorbed from the silicon monoxide particles by immersing the silicon monoxide particles in a solution B containing a polycyclic aromatic compound or a derivative thereof.
- Solvents for this solution B can be, for example, ether solvents, ketone solvents, ester solvents, alcohol solvents, amine solvents, or mixed solvents thereof.
- the obtained silicon monoxide particles may be heat-treated under an inert gas.
- the heat treatment can stabilize the Li compound.
- the heat treatment temperature is preferably 450 to 700°C, more preferably 500 to 650°C. After that, it may be washed with alcohol, alkaline water in which lithium carbonate is dissolved, weak acid, pure water, or the like.
- Ether solvents used for solution A include diethyl ether, tert-butyl methyl ether, tetrahydrofuran, dioxane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, or mixed solvents thereof. can be used. Among these, it is particularly preferable to use tetrahydrofuran, dioxane, and 1,2-dimethoxyethane. These solvents are preferably dehydrated and preferably deoxygenated.
- polycyclic aromatic compound contained in the solution A one or more of naphthalene, anthracene, phenanthrene, naphthacene, pentacene, pyrene, picene, triphenylene, coronene, chrysene and derivatives thereof can be used.
- chain polyphenylene compound one or more of biphenyl, terphenyl, and derivatives thereof can be used.
- polycyclic aromatic compound contained in solution B one or more of naphthalene, anthracene, phenanthrene, naphthacene, pentacene, pyrene, picene, triphenylene, coronene, chrysene, and derivatives thereof can be used.
- ether-based solvent for solution B diethyl ether, tert-butyl methyl ether, tetrahydrofuran, dioxane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and the like can be used. .
- Acetone, acetophenone, etc. can be used as the ketone-based solvent.
- ester solvent methyl formate, methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, and the like can be used.
- Methanol, ethanol, propanol, isopropyl alcohol, etc. can be used as alcohol-based solvents.
- amine-based solvent methylamine, ethylamine, ethylenediamine, etc. can be used.
- a lithium ion secondary battery can be produced by producing a negative electrode using the negative electrode active material in which silicon monoxide particles are coated with a carbon film and doped with lithium.
- the Si crystallite size and the crystallinity of lithium silicate can be confirmed using, for example, the following XRD apparatus.
- ⁇ XRD Bruker D8 ADVANCE
- the X-ray source was Cu K ⁇ rays, using a Ni filter, an output of 40 kV/40 mA, a slit width of 0.3°, a step width of 0.008°, and a counting time of 0.15 seconds per step from 10-40°. Measure up to
- the peak intensity A of Si (111) in the negative electrode active material and the peak of Li 2 SiO 3 (111) appearing near 2 ⁇ 26.5 ⁇ 0.3 °
- their ratio A/B is preferably 0.5 ⁇ A/B ⁇ 1.0.
- the negative electrode active material within this range has an appropriate amount of lithium doping and an appropriate heat treatment temperature, and excellent charge/discharge characteristics and cycle characteristics can be obtained when used as a battery.
- the true density of the carbon-coated and lithium-doped silicon monoxide particles in the present invention is preferably greater than 2.3 g/cc and less than 2.4 g/cc. This true density varies depending on the degree of lithium doping to the silicon monoxide particles. When the true density is within the above range, the reaction rate between silicon monoxide and doped lithium is within the desired range, and the negative electrode active material is such that Li is appropriately inserted into the silicon monoxide particles. Therefore, cycle characteristics are further improved.
- a conductive agent such as carbon or graphite
- the type of the conductive agent is not particularly limited, and any electronically conductive material that does not cause decomposition or deterioration in the constructed battery may be used.
- metal particles and metal fibers such as Al, Ti, Fe, Ni, Cu, Zn, Ag, Sn, Si, natural graphite, artificial graphite, various coke particles, mesophase carbon, vapor growth carbon fiber, pitch Graphite such as carbon-based carbon fiber, PAN-based carbon fiber, and various resin sintered bodies can be used.
- An example of the method for preparing the negative electrode is as follows.
- the above negative electrode active material, optionally a conductive agent, other additives such as a binder such as carboxymethyl cellulose (hereinafter referred to as CMC), and a solvent such as an organic solvent or water are kneaded to form a paste. and apply this mixture to the current collector sheet.
- CMC carboxymethyl cellulose
- a solvent such as an organic solvent or water
- the current collector sheet materials such as copper foil and nickel foil, which are usually used as current collectors for negative electrodes, can be used without particular limitations on thickness and surface treatment.
- the molding method for molding the mixture into a sheet is not particularly limited, and a known method can be used.
- the lithium ion secondary battery of the present invention is a lithium ion secondary battery having at least a positive electrode, a negative electrode, and a lithium ion conductive non-aqueous electrolyte, wherein the negative electrode contains the negative electrode active material according to the present invention. It was used. Other materials such as the positive electrode, electrolyte, separator, and the like, and the shape of the battery, etc., may be those known in the art, and are not particularly limited. As described above, the negative electrode active material of the present invention has good battery characteristics (charge/discharge capacity and cycle characteristics) when used as a negative electrode active material for lithium ion secondary batteries, and is particularly excellent in cycle durability. is.
- transition metal oxides such as LiCoO 2 , LiNiO 2 , LiMn 2 O 4 , V 2 O 5 , MnO 2 , TiS 2 and MoS 2 , lithium, and chalcogen compounds are used.
- a non-aqueous solution containing a lithium salt such as lithium hexafluorophosphate or lithium perchlorate is used.
- a lithium salt such as lithium hexafluorophosphate or lithium perchlorate
- the non-aqueous solvent propylene carbonate, ethylene carbonate, diethyl carbonate, dimethoxyethane, ⁇ -butyrolactone, 2-methyltetrahydrofuran, etc. may be used singly or in combination of two or more.
- Various other non-aqueous electrolytes and solid electrolytes can also be used.
- a jaw crusher manufactured by Maekawa Kogyosho
- a ball mill manufactured by Makino
- the particles were pulverized with a jet mill (KJ800, manufactured by Kurimoto, Ltd.) under the conditions of a compressed air pressure of 0.58 MPa and a classifier rotation speed of 3,500 rpm, and collected with a cyclone.
- a jet mill KJ800, manufactured by Kurimoto, Ltd.
- a classifier rotation speed 3500 rpm
- the particles were measured with a laser diffraction particle size distribution analyzer (Shimadzu Corporation SALD-3100) under conditions of a refractive index of 2.05-0.00i
- the integrated value of the relative particle amount with a particle diameter of 1 ⁇ m or less was 0.0.
- the integrated value of the relative particle amount having a particle diameter of 5 ⁇ m or less is 20.0%
- the D50 is 7.9 ⁇ m
- the D99.9 is 28.1 ⁇ m
- the BET specific surface area is 2.9 m 2 /g. there were.
- the particles were spread on a tray so that the powder layer had a thickness of 10 mm, and charged into a batch heating furnace. Then, the temperature inside the furnace was raised to 850° C. at a heating rate of 200° C./hr while reducing the pressure inside the furnace with an oil rotary vacuum pump. After reaching 850° C., the furnace was aerated with propane at 0.3 L/min, and carbon coating treatment was performed for 12 hours. After the propane was stopped, the temperature in the furnace was lowered and cooled, and the collected agglomerates were pulverized to obtain black particles. The black particles were conductive particles having a carbon coating amount (the mass of the carbon coating relative to the mass of the entire black particles) of 2.8% by mass.
- the silicon monoxide particles were doped with lithium by an oxidation-reduction method, and the particles were heat-treated at 600° C. in an inert gas atmosphere for modification.
- the resulting negative electrode active material had a D50 of 7.9 ⁇ m and a true density of 2.34 g/cc. Further, when the negative electrode active material was measured by X-ray diffraction using Cu—K ⁇ rays, it had a peak attributed to the Si (111) crystal plane, and the crystallite size corresponding to the Si (111) crystal plane was It was 5.0 nm. Further, in the X-ray diffraction measurement, the ratio A/B of the peak intensity A caused by the Si (111) crystal face to the peak intensity B caused by the Li 2 SiO 3 (111) crystal face was 0.55. there were.
- negative electrode active material graphite, conductive aid 1 (carbon nanotube, CNT), conductive aid 2 (carbon fine particles having a median diameter of about 50 nm), sodium polyacrylate, and CMC were mixed at 9.3:83.7:1. After mixing at a dry mass ratio of :1:4:1, the mixture was diluted with pure water to obtain a negative electrode mixture slurry.
- This slurry was applied to a copper foil having a thickness of 15 ⁇ m and dried in a vacuum atmosphere at 100° C. for 1 hour. After drying, the deposition amount of the negative electrode active material layer per unit area (also referred to as area density) on one side of the negative electrode was 7.0 mg/cm 2 .
- an electrolyte salt lithium hexafluorophosphate: LiPF 6
- vinylene carbonate (VC) and fluoroethylene carbonate (FEC) were added in amounts of 1.0% by mass and 2.0% by mass, respectively.
- a Li foil with a thickness of 1 mm was punched into a diameter of 16 mm and attached to the aluminum clad.
- the obtained electrode was punched out to have a diameter of 15 mm, and was faced to the Li counter electrode with a separator interposed therebetween.
- the initial efficiency was measured under the following conditions. First, the charge rate was set to 0.03C. Charging was performed in CCCV mode. CV was 0 V and final current was 0.04 mA. CC discharge was performed at a discharge rate of 0.03 C and a discharge voltage of 1.2 V in the same manner.
- initial efficiency (initial discharge capacity/initial charge capacity) ⁇ 100.
- LCO lithium cobalt oxide
- the cycle characteristics were investigated as follows. First, two cycles of charge and discharge were performed at 0.2C in an atmosphere of 25°C for battery stabilization, and the discharge capacity of the second cycle was measured. The battery cycle characteristics were calculated from the discharge capacity at the third cycle, and the battery test was stopped when the discharge capacity maintenance rate reached 70%. Charging and discharging were performed at 0.7C for charging and 0.5C for discharging. The charge voltage was 4.3V, the discharge final voltage was 2.5V, and the charge final rate was 0.07C.
- Example 7 A negative electrode active material was prepared in the same manner as in Example 1, except that the same silicon monoxide particles with D50 adjusted to 7.9 ⁇ m as in Example 1 were used, and the heat treatment temperature after lithium doping was set to 630 ° C., A negative electrode was produced and battery evaluation was performed.
- Example 8 A negative electrode active material was prepared in the same manner as in Example 1, except that silicon monoxide particles with D50 adjusted to 7.9 ⁇ m as in Example 1 were used, and the heat treatment temperature after lithium doping was set to 700° C., A negative electrode was produced and battery evaluation was performed.
- Comparative Examples 5-7 In Comparative Examples 5 to 7, the carbon-coated silicon monoxide particles obtained in Examples 1, 2, and 4 were not subjected to lithium doping treatment, and negative electrodes were produced as they were, and battery evaluations were performed. .
- Example 9 A negative electrode active material was prepared in the same manner as in Example 1, except that the same silicon monoxide particles with D50 adjusted to 7.9 ⁇ m as in Example 1 were used, and the heat treatment temperature after lithium doping was set to 730 ° C., A negative electrode was produced and battery evaluation was performed.
- Example 10 A negative electrode active material was produced in the same manner as in Example 1, except that silicon monoxide particles with D50 adjusted to 7.9 ⁇ m as in Example 1 were used, and the heat treatment temperature after lithium doping was set to 800 ° C., A negative electrode was produced and battery evaluation was performed.
- Table 1 shows the powder physical properties and battery properties of Examples and Comparative Examples. Further, FIG. 1 shows a frequency integration graph of relative particle amounts of silicon monoxide particles in Examples 1, 2, 4 and Comparative Example 2. In FIG. As shown in FIG. 1, Examples 1, 2 and 4 satisfy the particle size distribution of the present invention, but Comparative Example 2 does not satisfy the range of the particle size distribution of the present invention.
- Examples 1 to 10 are lithium ion secondary batteries with significantly improved cycle characteristics while maintaining initial charge/discharge characteristics as compared to Comparative Examples 1 to 7.
- the relative amount of particles having a particle size of 5 ⁇ m or less in Examples 2 to 4 and 6 was 10% or less, extremely excellent cycle characteristics were obtained.
- Comparative Examples 1 and 2 since the relative amount of particles having a particle diameter of 5 ⁇ m or less was large, the cycle characteristics as good as those of Examples could not be obtained.
- Comparative Examples 3 and 4 it was confirmed that the negative electrode active material comprising silicon monoxide particles having a particle size distribution with a D99.9 exceeding 50 ⁇ m deteriorates the cycle characteristics.
- the present invention is not limited to the above embodiments.
- the above embodiment is an example, and any device that has substantially the same configuration as the technical idea described in the claims of the present invention and produces similar effects is the present invention. It is included in the technical scope of the invention.
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Abstract
Description
2SiO(Si+SiO2) + 6.85Li+ + 6.85e-
→ 1.4Li3.75Si + 0.4Li4SiO4 + 0.2SiO2
反応式ではケイ素酸化物を構成するSiとSiO2がLiと反応し、LiシリサイドとLiシリケート、一部未反応であるSiO2にわかれる。
本発明の負極活物質は、炭素被膜で被覆され、かつリチウムがドープされた一酸化珪素粒子からなる負極活物質である。さらに、当該一酸化珪素粒子は、レーザー回折法粒度分布測定装置で測定した体積基準分布において、以下の条件を満たす。
・粒子径が1μm以下の相対粒子量の積算値が1%以下、
・粒子径が5μm以下の相対粒子量の積算値が20%以下、
・累積50%径D50が6.0μm≦D50≦15.0μm。
・装置: 島津製作所SALD-3100
・屈折率: 2.05-0.00i
・XRD:Bruker社 D8 ADVANCE
X線源はCu Kα線、Niフィルターを使用して、出力40kV/40mA、スリット幅0.3°、ステップ幅0.008°、1ステップあたり0.15秒の計数時間にて10-40°まで測定する。
上記負極活物質を用いて負極を作製する場合、さらにカーボンや黒鉛等の導電剤を添加することができる。この場合においても導電剤の種類は特に限定されず、構成された電池において、分解や変質を起こさない電子伝導性の材料であればよい。具体的にはAl,Ti,Fe,Ni,Cu,Zn,Ag,Sn,Si等の金属粒子や金属繊維又は天然黒鉛、人造黒鉛、各種のコークス粒子、メソフェーズ炭素、気相成長炭素繊維、ピッチ系炭素繊維、PAN系炭素繊維、各種の樹脂焼成体等の黒鉛を用いることができる。
本発明のリチウムイオン二次電池は、少なくとも、正極と、負極と、リチウムイオン導電性の非水電解質とを有するリチウムイオン二次電池であって、上記負極に、本発明に係る負極活物質が用いられたものである。その他の正極、電解質、セパレータ等の材料及び電池形状等は公知のものを使用することができ、特に限定されない。上述のように、本発明の負極活物質は、リチウムイオン二次電池用の負極活物質として用いた場合の電池特性(充放電容量及びサイクル特性)が良好で、特にサイクル耐久性に優れたものである。
まず、二酸化珪素と金属珪素との混合物を加熱して生成した一酸化珪素ガスを冷却・析出することで、xがほぼ1.0の一酸化珪素(SiOx)を得た。次に、このSiOx(x=1.0)をジョークラッシャー(前川工業所製)で粗砕し、さらに、ボールミル(マキノ製)で15分間粉砕し、D50が100μmの一酸化珪素粒子を得た。この粒子をジェットミル(栗本鐵工所製KJ800)で、圧縮空気の圧力0.58MPa、分級機の回転数3,500rpmの条件で微粉砕し、サイクロンで回収した。この粒子をレーザー回折法粒度分布測定装置(島津製作所SALD-3100)で屈折率2.05-0.00iの条件で測定したところ、粒子径が1μm以下の相対粒子量の積算値が0.0%、粒子径が5μm以下の相対粒子量の積算値が20.0%、D50が7.9μm、D99.9が28.1μm、BET比表面積が2.9m2/gの一酸化珪素粒子であった。
次に、以下の方法で、得られた炭素被膜粒子を負極活物質として用いた電池評価を行った。
実施例1と同じSiOx(x=1.0)を同様にボールミルでD50を100μmにした。次のジェットミル工程で分級機の回転数、粉砕圧および雰囲気制御を行い、表1に示される粉体物性を有する一酸化珪素粒子を作製した。実施例1と同様の方法で、一酸化珪素粒子に炭素膜を被覆させ、リチウムドープを行い、導電性粒子を作製した。このようにして得られた導電性粒子を用いて負極を作製し、電池評価を行った。
実施例1と同じD50を7.9μmに調整した一酸化珪素粒子を用い、リチウムドープ後の熱処理温度を630℃としたこと以外は、実施例1と同様の方法で負極活物質を作製し、負極を作製して電池評価を行った。
実施例1と同じD50を7.9μmに調整した一酸化珪素粒子を用い、リチウムドープ後の熱処理温度を700℃としたこと以外は、実施例1と同様の方法で負極活物質を作製し、負極を作製して電池評価を行った。
比較例5~7では、それぞれ、実施例1、2、4で得られた炭素被膜で被覆した一酸化珪素粒子に、リチウムドープ処理を行わずに、そのまま負極を作製し、電池評価を行った。
実施例1と同じD50を7.9μmに調整した一酸化珪素粒子を用い、リチウムドープ後の熱処理温度を730℃としたこと以外は、実施例1と同様の方法で負極活物質を作製し、負極を作製して電池評価を行った。
実施例1と同じD50を7.9μmに調整した一酸化珪素粒子を用い、リチウムドープ後の熱処理温度を800℃としたこと以外は、実施例1と同様の方法で負極活物質を作製し、負極を作製して電池評価を行った。
Claims (8)
- 炭素被膜で被覆され、かつリチウムがドープされた一酸化珪素粒子からなる負極活物質であって、
前記一酸化珪素粒子は、レーザー回折法粒度分布測定装置で測定した体積基準分布において、
粒子径が1μm以下の相対粒子量の積算値が1%以下、
粒子径が5μm以下の相対粒子量の積算値が20%以下、
累積50%径D50が6.0μm≦D50≦15.0μm
を満たすことを特徴とする負極活物質。 - 前記一酸化珪素粒子は、前記粒子径が5μm以下の相対粒子量の積算値が10%以下であることを特徴とする請求項1に記載の負極活物質。
- 前記一酸化珪素粒子は、累積99.9%粒子径をD99.9としたときに18.0μm≦D99.9≦50.0μmであることを特徴とする請求項1又は請求項2に記載の負極活物質。
- 前記炭素被膜で被覆され、かつリチウムがドープされた一酸化珪素粒子は、リチウムの少なくともその一部がLi2SiO3として存在することを特徴とする請求項1から請求項3のいずれか1項に記載の負極活物質。
- 前記炭素被膜で被覆され、かつリチウムがドープされた一酸化珪素粒子は、負極活物質を充放電する前において、Cu-Kα線を用いたX線回折により得られるSi(111)結晶面に起因するピークを有し、該結晶面に対応する結晶子サイズは5.0nm以下であり、かつ、Li2SiO3(111)結晶面に起因するピークの強度Bに対する前記Si(111)結晶面に起因するピークの強度Aの比率A/Bは、0.5≦A/B≦1.0を満たすことを特徴とする請求項1から請求項4のいずれか1項に記載の負極活物質。
- 前記炭素被膜で被覆され、かつリチウムがドープされた一酸化珪素粒子の真密度は、2.3g/ccより大きく、2.4g/ccより小さいことを特徴とする請求項1から請求項5のいずれか1項に記載の負極活物質。
- 請求項1から請求項6のいずれか1項に記載の負極活物質を含むことを特徴とする負極。
- 請求項7に記載の負極と、正極と、セパレータと、電解質とを具備することを特徴とするリチウムイオン二次電池。
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CN117501474A (zh) | 2024-02-02 |
TW202315195A (zh) | 2023-04-01 |
EP4354547A1 (en) | 2024-04-17 |
KR20240019114A (ko) | 2024-02-14 |
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