Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/58—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
• • 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

• This disclosure relates to negative electrode active materials and batteries.
• the negative electrode active material which is the main component of the negative electrode, is one of the important factors in increasing the capacity of batteries, and various studies on negative electrode active materials are being conducted. Among these, the use of materials containing silicon (Si-containing materials) has attracted attention as negative electrode active materials with high theoretical capacity density.
• Patent Document 1 discloses an anode active material comprising composite particles including a lithium aluminate phase and a silicon phase dispersed within the lithium aluminate phase.
• the anode active material disclosed in Patent Document 1 comprises composite particles (hereinafter sometimes referred to as "LAX particles") in which a silicon phase is dispersed within a lithium aluminate phase that has excellent alkali resistance, thereby reducing side reactions that occur in the early stages of charging and discharging in a lithium ion secondary battery, and suppressing a decrease in the initial charging and discharging efficiency.
• LAX particles composite particles
• negative electrode active materials containing LAX particles can suppress the decrease in initial charge/discharge efficiency in batteries.
• negative electrode active materials containing LAX particles have issues with durability during charging and discharging, and there is a need to improve the cycle characteristics of the battery.
• This disclosure provides a negative electrode active material that can improve the cycle characteristics of a battery.
• the negative electrode active material of the present disclosure is an alkali aluminate phase containing at least one alkali metal element and Al; a silicon phase dispersed within the alkali aluminate phase; a carbon phase dispersed within the alkali aluminate phase; A mother particle comprising: In the cross section of the primary particle of the base particle, the area ratio occupied by the carbon phase is 4% or more and 25% or less.
• the technology disclosed herein can provide a negative electrode active material that can improve the cycle characteristics of a battery.
• FIG. 1 is a cross-sectional view showing a schematic configuration of an example of a base particle included in the negative electrode active material according to this embodiment.
• FIG. 2 is a cross-sectional view showing a schematic configuration of a composite particle including the base particle shown in FIG. 1 and a conductive layer covering at least a part of the surface of the base particle.
• FIG. 3 is a cross-sectional view showing a schematic configuration of an example of a battery according to this embodiment.
• FIG. 4 is a cross-sectional view showing a schematic configuration of another example of the battery according to the present embodiment.
• a negative electrode active material including a composite particle such as LAX particles which includes an alkali aluminate phase such as a lithium aluminate phase containing at least one alkali metal element and Al, and a silicon phase dispersed in the alkali aluminate phase, can reduce side reactions in the early stages of charging and discharging a battery, and suppress a decrease in the initial charging and discharging efficiency.
• the alkali aluminate phase has excellent alkali resistance.
• a negative electrode active material including composite particles in which a silicon phase is dispersed in such an alkali aluminate phase can reduce side reactions in the early stages of charging a battery, and achieve high initial efficiency.
• the negative electrode active material containing the above composite particles containing an alkaline aluminate phase does not have sufficient durability against charging and discharging, and there is room for improvement in the cycle characteristics.
• the present inventors investigated the cause of this they found that because the alkaline aluminate phase has a high melting point and softening point, many voids are likely to occur inside when the alkaline aluminate phase is produced by a sintering process, and that the presence of these voids makes the particle structure prone to collapse due to expansion and contraction caused by charging and discharging.
• the present inventors conducted extensive research focusing on the internal structure of the particles that can suppress the collapse of the particle structure due to expansion and contraction caused by charging and discharging, and discovered that by dispersing a carbon phase inside the particles at a specific area ratio, it is possible to improve the durability of the particles and effectively improve the cycle characteristics of the battery, which led to the idea of the negative electrode active material of the present disclosure described below.
• the negative electrode active material according to the present embodiment includes base particles.
• Fig. 1 is a cross-sectional view showing a schematic configuration of an example of the base particles included in the negative electrode active material according to the present embodiment.
• the mother particle 10 of the negative electrode active material includes an alkaline aluminate phase 11, a silicon phase 12 dispersed within the alkaline aluminate phase 11, and a carbon phase 13 dispersed within the alkaline aluminate phase 11.
• the area ratio occupied by the carbon phase 13 is 4% or more and 25% or less.
• the carbon phase 13 is dispersed within the alkali aluminate phase 11 so that the area ratio in the cross section of the primary particle of the base particle 10 is 4% or more and 25% or less.
• This configuration suppresses the collapse of the particle structure of the base particle 10 (e.g., the occurrence of cracks and fractures) caused by the expansion and contraction of the negative electrode active material accompanying the charging and discharging of the battery.
• the negative electrode active material according to this embodiment can improve the durability against charging and discharging, and as a result, the cycle characteristics of the battery can be improved.
• the alkaline aluminate phase 11 has excellent alkali resistance. Therefore, the negative electrode active material containing the base particles 10 is prevented from undergoing side reactions with alkali metal ions such as Li ions during initial charging, and the deterioration of the negative electrode active material due to side reactions and the decrease in initial capacity due to deterioration are suppressed. In other words, the negative electrode active material according to this embodiment not only improves the cycle characteristics of the battery described above, but also prevents the decrease in initial charge/discharge efficiency.
• the term "mother particle” refers to a particulate structure made of a material in which a silicon phase 12 and a carbon phase 13 are dispersed in a matrix of an alkaline aluminate phase 11. Therefore, for example, a coating layer such as a conductive layer provided on the surface of the mother particle, as described below, is not included in the mother particle.
• the above-mentioned area ratio of the carbon phase 13 specified in this specification is the ratio of the total area occupied by the carbon phase 13 dispersed inside the mother particle 10, when the cross-sectional area of the primary particles of the mother particle 10 is taken as the total area. Therefore, for example, when a coating layer such as a conductive layer is provided on the surface of the mother particle 10 and the coating layer contains carbon, in secondary particles formed by agglomeration of the mother particles 10, the carbon contained in the coating layer located inside the secondary particles is naturally not included in the above-mentioned area ratio of the carbon phase 13.
• the area ratio of the carbon phase 13 in the cross section of the primary particle of the base particle 10 can be determined by elemental mapping analysis using energy dispersive X-ray (EDX). Details of the method of analyzing the carbon phase 13 (i.e., carbon element) in the cross section of the base particle using EDX will be described later together with the analysis of other elements.
• EDX energy dispersive X-ray
• the area ratio of the carbon phase 13 by elemental mapping using EDX for example, if a coating layer such as a conductive layer is provided on the surface of the base particle 10 and the coating layer contains carbon, it is necessary to prevent the carbon element contained in the coating layer from being calculated as the area of the carbon phase 13 inside the base particle 10, and to reliably calculate the area of the carbon phase 13 dispersed inside the base particle 10. Therefore, when determining the area ratio of the carbon phase 13 in the cross section of the base particle 10, a region 200 nm or more inward from the particle surface is used.
• the area ratio of the carbon phase 13 in the cross section of the primary particle of the mother particle 10 may be 5% or more and 20% or less.
• the negative electrode active material according to this embodiment can further improve the cycle characteristics of the battery.
• the base particle 10 may further contain other elements in addition to the alkali aluminate phase 11, the silicon phase 12, and the carbon phase 13.
• the negative electrode active material according to this embodiment may further include a conductive layer that covers at least a portion of the surface of the base particle 10.
• the negative electrode active material according to this embodiment may include a composite particle 20 that includes the base particle 10 and a conductive layer 21 that covers at least a portion of the surface of the base particle.
• FIG. 2 is a cross-sectional view showing a schematic configuration of a composite particle 20 including the mother particle 10 shown in FIG. 1 and a conductive layer 21 that covers at least a portion of the surface of the mother particle 10.
• a negative electrode active material including a composite particle 20 in which at least a portion of the surface of the mother particle 10 is covered with a conductive layer 21 as shown in FIG. 2 can improve conductivity.
• the base particle 10 has a sea-island structure in which a plurality of fine silicon phases 12 and carbon phases 13 (i.e., islands) are dispersed in a matrix (i.e., sea portion) of an alkali aluminate phase 11.
• the alkali aluminate phase 11 has good ion conductivity.
• This structure allows the silicon phase 12 to smoothly absorb and release alkali metal ions via the alkali aluminate phase 11.
• This structure allows the alkali aluminate phase 11 to mitigate stress associated with the expansion and contraction of the silicon phase 12 during charging and discharging, thereby suppressing cracks and fractures in the base particle 10.
• the inclusion of silicon can achieve both high capacity and improved cycle characteristics.
• the mother particles 10 may be contained in the negative electrode active material in the form of primary particles, or in the form of secondary particles formed by combining a plurality of primary particles.
• the average particle size of the secondary particles of the mother particles 10 is, for example, 1 ⁇ m or more and 25 ⁇ m or less, and may be 4 ⁇ m or more and 15 ⁇ m or less.
• the negative electrode active material according to this embodiment makes it easier to obtain good cycle characteristics of the battery.
• the surface area of the mother particles 10 is also of an appropriate size, and capacity reduction due to side reactions with the non-aqueous electrolyte is also suppressed.
• the average particle size of the base particles 10 refers to the particle size (volume average particle size) at which the volume cumulative value is 50% in the particle size distribution measured by the laser diffraction scattering method.
• the "LA-750" manufactured by Horiba Ltd. can be used as the measuring device. Note that when the surface of the base particle 10 is covered with the conductive layer 21, i.e., in the composite particle 20, the thickness of the conductive layer 21 is thin enough that it does not substantially affect the average particle size of the base particle 10. Therefore, the average particle size of the composite particle 20 can be regarded as the average particle size of the base particle 10.
• the base particles 10 can be removed from the battery, for example, by the following method. Note that the following method is just one example.
• a fully discharged battery is disassembled to remove the negative electrode, which is then washed with, for example, anhydrous ethyl methyl carbonate or dimethyl carbonate to remove non-aqueous electrolyte components.
• the negative electrode mixture layer is peeled off from the current collector (e.g., copper foil) that is the negative electrode core, and the mixture layer is crushed in a mortar to obtain a sample powder.
• the sample powder is dried in a dry atmosphere for about 1 hour, and then immersed in, for example, gently boiled 6M hydrochloric acid for about 10 minutes to remove elements derived from other than the base particles 10.
• the sample powder is washed with ion-exchanged water, filtered, and dried at, for example, 200°C for 1 hour.
• the fully discharged state is a state in which the depth of discharge (DOD) is 90% or more (the state of charge (SOC) is 10% or less).
• the alkali aluminate phase 11 contains at least one alkali metal element, aluminum (Al), and oxygen (O).
• the alkali aluminate phase 11 is a phase containing alkali aluminate, which is a composite oxide containing at least one alkali metal element and Al.
• the alkaline aluminate phase 11 has good ionic conductivity, and ions such as Li ions can be smoothly absorbed and released by the silicon phase 12 via the alkaline aluminate phase 11.
• the alkali aluminate phase 11 contains lithium aluminate.
• the composition of lithium aluminate can be expressed by the formula Li u AlO (3+u)/2 .
• u in the formula may be, for example, more than 0 and not more than 5, or more than 0 and not more than 1.
• the alkali aluminate phase 11 may contain, for example, at least one selected from the group consisting of LiAl5O8, Li2Al4O7 , LiAlO2 , and Li5AlO4 , or may contain LiAlO2 as a main component .
• the "main component” means a component that occupies 50 mass% or more of the total mass of the alkali aluminate phase 11.
• the content of LiAlO2 may be 70 mass% or more.
• the atomic ratio of O to Al in the alkaline aluminate (O/Al) is, for example, 1.6 or more and 4 or less.
• the atomic ratio of alkali metal (MA) to Al in the alkaline aluminate (MA/Al) is, for example, 1/5 or more and 5 or less.
• the stability and ionic conductivity of the alkaline aluminate phase 11 are improved.
• the stability of the alkaline aluminate phase 11 includes both the chemical stability (alkali resistance) and the thermal stability of the alkaline aluminate phase 11.
• An alkali metal element is an element belonging to Group 1 in the periodic table. That is, the alkali aluminate phase 11 contains at least one element selected from the group consisting of Li, Na, K, Rb, Cs, and Fr.
• the alkali metal element may include at least one selected from the group consisting of Li, Na, and K.
• the alkali metal element may include at least one selected from the group consisting of Li and Na, or may include Li.
• the alkali aluminate phase 11 may contain two types of alkali metal elements.
• the alkali aluminate phase 11 may contain at least two selected from the group consisting of Li, Na, and K, or may contain Li and Na.
• the alkali aluminate phase 11 may contain the element M in addition to the alkali metal elements, Al, and O.
• element M is at least one selected from the group consisting of calcium (Ca), magnesium (Mg), zirconium (Zr), iron (Fe), boron (B), phosphorus (P), and lanthanum (La).
• element M contains an element exemplified above as element M, for example, the stability and ionic conductivity of the alkali aluminate phase 11 are further improved. In addition, side reactions caused by contact between the alkali aluminate phase 31 and the electrolyte are suppressed.
• element M it is desirable for element M to contain at least one selected from the group consisting of Zr, Fe, P, and B. La can further improve the initial charge/discharge efficiency.
• the element M may be B. That is, the alkali aluminate phase 11 may further contain B.
• the addition of B can reduce the number of voids contained in the base particles 20. This suppresses the deterioration of the particle structure caused by the voids in the base particles 10, thereby further improving the cycle characteristics of the battery.
• the element M may form a compound.
• the compound may be, for example, an oxide of the element M or an aluminate of the element M depending on the type of the element M.
• the content of the element M is, for example, 0.3 mol % or more and 3 mol % or less with respect to the total amount of elements other than oxygen.
• the alkaline aluminate phase 11 may further contain trace amounts of elements such as chromium (Cr), nickel (Ni), manganese (Mn), copper (Cu), and molybdenum (Mo).
• the alkali aluminate phase 11 may be amorphous. In this case, the effects of expansion and contraction of the silicon phase 12 can be more effectively mitigated.
• a fine Al2O3 phase having high crystallinity may be dispersed in the alkali aluminate phase 11.
• the Al2O3 phase is distributed in an island shape in the matrix of the alkali aluminate phase 11, for example.
• the expansion and cracking of the alkali aluminate phase 11 due to the expansion and contraction of the silicon phase 12 is easily suppressed, and the effect of improving the cycle characteristics is enhanced.
• the content of Al2O3 in the base particle 10 is, for example, 10 mass% or less.
• the silicon phase 12 is a phase of simple Si, and repeatedly absorbs and releases Li ions as the battery is charged and discharged. The capacity is generated by a Faraday reaction involving the silicon phase 12.
• the silicon phase 12 has a large capacity. Furthermore, the silicon phase 12 also expands and contracts to a large extent as it is charged and discharged.
• the silicon phase 12 is dispersed within the alkaline aluminate phase 11, and therefore the stress caused by the expansion and contraction of the silicon phase 12 is alleviated by the alkaline aluminate phase 11.
• the silicon phase 12 may contain crystalline silicon.
• the silicon phase 12 is composed of, for example, a plurality of crystallites.
• the crystallite size of the silicon phase 12 may be 30 nm or less, 20 nm or less, or 15 nm or less.
• the crystallite size of the silicon phase 12 is calculated by the Scherrer formula from the half-width of the diffraction peak derived from the Si(111) plane in the X-ray diffraction pattern obtained by X-ray diffraction measurement using Cu-K ⁇ radiation.
• the lower limit of the crystallite size of silicon phase 12 is not particularly limited, but an example is 1 nm.
• An example of a suitable crystallite size of silicon phase 12 is 1 nm or more and 15 nm or less, and may be 5 nm or more and 11 nm or less.
• the crystallite size of silicon phase 12 is 1 nm or more, for example, the surface area of silicon phase 12 can be kept small, making it difficult for deterioration of silicon phase 12 accompanied by the generation of irreversible capacity to occur.
• the crystallite size is 15 nm or less, the expansion and contraction of silicon phase 12 is easily made uniform, and the stress generated in mother particle 10 is effectively alleviated.
• the silicon phase 12 may be particulate.
• the silicon phase 12 is particulate, for example, at least before the first charge.
• the average particle size of the silicon phase 12 may be 1 nm or more and 1000 nm or less.
• the average particle size of the silicon phase 12 may be 500 nm or less, 200 nm or less, or 50 nm or less.
• the average particle size of the silicon phase 12 may be 400 nm or less, or 100 nm or less.
• the average particle size of the silicon phase 12 can be measured using a scanning electron microscope (SEM) image obtained by observing the mother particle 10 in which the cross section of the silicon phase 12 is exposed. Specifically, the average particle size of the silicon phase 12 can be calculated by averaging the maximum diameters of 100 silicon phases 12 randomly selected from the cross-sectional SEM image of the mother particle 10.
• SEM scanning electron microscope
• the content of silicon phase 12 in the mother particle 10 may be 30 mass% or more, 35 mass% or more, or 55 mass% or more. From the viewpoint of improving cycle characteristics, the content of silicon phase 12 in the mother particle 10 may be 95 mass% or less, 75 mass% or less, or 70 mass% or less. In this case, the amount of silicon phase 12 exposed on the surface of the mother particle 10 without being covered by the alkali aluminate phase 11 is reduced, and side reactions between the electrolyte and the silicon phase 12 are also suppressed.
• the content of silicon phase 12 in the mother particle 10 may be 30 mass% or more and 90 mass% or less, or 35 mass% or more and 75 mass% or less.
• the content of silicon phase 12 in the base particle 10 can be determined by quantifying the amount of Si that constitutes the silicon phase 12 in the base particle 10 using Si-NMR, as described below.
• the carbon phase 13 is a phase of a carbon material.
• the carbon material include graphite such as natural graphite, artificial graphite, and graphitized mesophase carbon, amorphous carbon, soft carbon, and hard carbon.
• the carbon material may be amorphous carbon.
• Examples of amorphous carbon include carbon black, burned pitch, coke, activated carbon, and the like.
• the shape of the carbon phase 13 may be particulate.
• the shape of the particles is not particularly limited, and examples include spherical, angular, plate-like, linear, etc.
• the size of the carbon phase 13 is not particularly limited.
• the average particle size of the carbon phase 13 may be 1 nm or more and 1000 nm or less, 10 nm or more and 500 nm or less, or 10 nm or more and 200 nm or less.
• the average particle size of the carbon phase 13 can be measured using an SEM image obtained by SEM observation of the mother particle 10 in which the cross section of the carbon phase 13 is exposed. Specifically, the average particle size of the carbon phase 13 can be calculated by averaging the maximum diameters of 100 carbon phases 13 randomly selected from the cross-sectional SEM image of the mother particle 10.
• the base particle 10 may be substantially free of lithium silicate and SiO 2.
• the total content of lithium silicate and SiO 2 in the base particle 10 may be, for example, 3 mass % or less.
• the ratio of the mass of Al element (mAl) to the total mass of elements excluding oxygen element and carbon element may be 10 mass% or more and 47 mass% or less, or 11.5 mass% or more and 45.5 mass% or less.
• the ratio of the mass of alkali metal element (mMA) to the total mass of elements excluding oxygen element and carbon element may be 0.7 mass% or more and 13.5 mass% or less, 1.0 mass% or more and 9.5 mass% or less, or 1.5 mass% or more and 3.5 mass% or less.
• the above configuration can improve the stability and ionic conductivity of the alkali aluminate phase 11.
• the above stability includes both chemical stability (alkali resistance) and thermal stability.
• the ratio (mMA/mAl) of the ratio of the mass of the alkali metal element (mMA) to the total mass of elements excluding oxygen and carbon to the ratio (mAl) of the mass of the Al element to the total mass of elements excluding oxygen and carbon may be 0.04 or more and 0.50 or less, or 0.05 or more and 0.25 or less, from the viewpoints of the stability of the alkali aluminate phase 11, ionic conductivity, and reduced porosity, etc.
• the ratio (mSi) of the mass of silicon (Si) to the total mass of elements excluding oxygen and carbon may be 40% by mass or more and 90% by mass or less, or 50.8% by mass or more and 85.5% by mass or less.
• the ratio (mSi) of the mass of Si is the amount of Si that constitutes the silicon phase 12 in the mother particle 10.
• the ratio of the mass of B (mB) to the total mass of elements excluding oxygen and carbon in the mother particle 10 may be 1 mass% or more and 20 mass% or less, or 2 mass% or more and 15 mass% or less.
• the ratio (mAl/mB) of the mass ratio of Al (mAl) to the mass ratio of B (mB) may be 1.0 or more and 30.0 or less, 1.0 or more and 20.0 or less, or 1.0 or more and 10.0 or less.
• mAl/mB is 30.0 or less, the effect of reducing voids in the base particle 10 may be more pronounced. This suppresses deterioration of the particle structure caused by voids in the base particle 10, and effectively improves the cycle characteristics of the battery.
• mAl/mB is 1.0 or more, the decrease in initial charge/discharge efficiency can be reduced. Therefore, when mAl/mB is within the above range, both improved cycle characteristics and good initial charge/discharge efficiency can be achieved.
• pores 14 may be present in the base particle 10.
• the total pore volume of pores having a diameter of 10 nm or more and 200 nm or less in the base particle 10 calculated by the BJH (Barrett-Joyner-Halenda) method is preferably 0.05 cm 3 /g or less, more preferably 0.04 cm 3 /g or less.
• This configuration more effectively suppresses the collapse of the particle structure of the base particle 10 caused by the expansion and contraction of the negative electrode active material accompanying the charging and discharging of the battery.
• the negative electrode active material according to this embodiment can improve the durability against charging and discharging, and as a result, the cycle characteristics of the battery can be further improved.
• the lower limit of the total pore volume is not particularly limited, but is preferably 0.001 cm 3 /g, and is, for example, 0.003 cm 3 /g.
• the total pore volume of the pores having a diameter of 10 nm or more and 200 nm or less calculated by the BJH method in the composite particle 20 including the base particle 10 and the conductive layer 21 is preferably 0.05 cm 3 /g or less, more preferably 0.04 cm 3 /g or less.
• the lower limit of the total pore volume is not particularly limited, but is preferably 0.001 cm 3 /g, and is, for example, 0.003 cm 3 /g.
• the total pore volume of the base particle 10 or the composite particle 20 can be controlled by adjusting the addition of element M (e.g., B) to the alkali aluminate phase 11 described above, the sintering temperature in the manufacturing process of the base particle 10, the compressive force applied to the particle during sintering, and mMA/mAl.
• the total pore volume can be controlled to 0.05 cm 3 /g or less by filling the pores formed inside the base particle 10 with another material (hereinafter referred to as a filling material) when producing the base particle 10.
• a filling material examples include carbon materials and resin materials.
• the base particle 10 containing the pores and the amount of the carbon material selected in consideration of the pore size and pore volume contained in the base particle 10 may be mixed, and the mixture may be heat-treated to fill the pores of the base particle 10 with the carbon material.
• the total pore volume can be controlled to 0.05 cm 3 /g or less.
• the porosity of the base particle 10 before the first charge/discharge may be 25% or less. By keeping the porosity of the base particle 10 at 25% or less, the deterioration of the negative electrode active material is further suppressed, and the cycle characteristics of the battery are further improved.
• the porosity of the base particle 10 may be 20% or less, or may be 15% or less.
• the lower limit of the porosity is not particularly limited, but an example is 1%.
• the porosity of the base particle 10 means the proportion of voids in the cross section of the base particle 10.
• the porosity of the base particle 10 can be measured using an SEM image of the cross section of the negative electrode active material in which the cross section of the base particle 10 is exposed.
• the porosity of the base particle 10 is calculated by extracting the void area by binarizing the SEM image using image analysis software (e.g., imageJ) and dividing the total area of the voids by the total area of the particle cross section.
• the porosity of the base particle 10 can be controlled by adding element M (e.g., B) to the above-mentioned alkali aluminate phase 11, adjusting the sintering temperature in the manufacturing process of the base particle 10, the compressive force applied to the particle during sintering, and mMA/mAl, etc.
• element M e.g., B
• the mother particle 10 may have a Vickers hardness of 300 HV or more.
• the Vickers hardness of the mother particle 10 is more preferably 350 HV or more, and may be 400 HV or more, or 500 HV or more.
• the Vickers hardness of the base particle 10 can be measured using a Vickers hardness tester. Specifically, the base particle 10 is embedded in a thermosetting resin and polished with #400 abrasive paper to expose the cross section of the base particle 10. The cross section is then mirror-finished with #2000 abrasive paper and buff polishing. The Vickers hardness is measured under conditions of a load of 1 kg and a holding time of 15 seconds.
• the upper limit of the Vickers hardness of the base particle 10 is not particularly limited, but is, for example, 1500 HV.
• the content of each element in the base particle 10 is measured by the following method.
• the oxygen content can be measured using an oxygen, nitrogen, and hydrogen analyzer.
• the Si content can be measured using NMR.
• the carbon content can be measured using a carbon and sulfur analyzer.
• the content of other elements can be measured by inductively coupled plasma emission spectrometry (ICP). If it is not possible to measure by ICP, it can also be measured using energy dispersive X-ray (EDX). If it is not possible to measure by either ICP or EDX, it can also be measured by Auger electron spectroscopy (AES).
• the composition of the alkali aluminate phase 11 can be determined from the content of each element.
• the negative electrode When measuring from the state of the battery, for example, a fully discharged battery is disassembled, the negative electrode is removed, and the negative electrode is washed with, for example, anhydrous ethyl methyl carbonate or dimethyl carbonate to remove non-aqueous electrolyte components, dried, and then the cross section of the resulting negative electrode mixture layer is analyzed using a cross-section polisher.
• the base particle can be removed from the battery by removing the negative electrode mixture layer from the negative electrode removed from the battery, pulverizing it, and removing elements derived from other than the base particle 10.
• the base particle may be removed from the battery in the form of a composite particle having a conductive layer on its surface, and each element of the base particle may be determined based on the analysis results of each element in the composite particle, or the conductive layer may be removed using an appropriate means depending on the constituent material of the conductive layer, and the internal portion of the base particle may be analyzed.
• ICP Inductively Coupled Plasma Atomic Emission Spectroscopy
• EDX ⁇ Energy Dispersive X-ray (EDX)> From the reflected electron image of the cross section of the negative electrode active material in which the cross section of the mother particle 10 is exposed, element mapping analysis is performed by EDX.
• the content area of the target element is calculated using image analysis software. The observation magnification is, for example, 2000 to 20000 times.
• 10 mother particles 10 with a maximum particle diameter of 5 ⁇ m or more are randomly selected from the cross-sectional image of the reflected electron image of the negative electrode mixture layer containing the negative electrode active material, and element mapping analysis is performed for each of them by EDX.
• the measured values of the content area of a predetermined element contained in the 10 particles are averaged to calculate the content of the target element.
• Desirable measurement conditions for cross-sectional SEM-EDX analysis are shown below.
• Processing equipment JEOL, SM-09010 (Cross Section Polisher) Processing conditions: Acceleration voltage 6 kV Current value: 140 ⁇ A Degree of vacuum: 1 ⁇ 10 ⁇ 3 Pa to 2 ⁇ 10 ⁇ 3 Pa
• Measuring device Hitachi SU-70 electron microscope Acceleration voltage during analysis: 10 kV Field: Free mode Probe current mode: Medium Probe current range: High Anode Ap.: 3 OBJ Ap.: 2 Analysis area: 1 ⁇ m square Analysis software: EDAX Genesis CPS: 20500 Lsec: 50 Time constant: 3.2
• elemental mapping analysis using EDX is used as a method for determining the area ratio occupied by the carbon phase 13 in the cross section of the primary particle of the mother particle 10.
• a region 200 nm or more inward from the particle surface is used when determining the area occupied by the carbon phase 13.
• AES ⁇ Auger Electron Spectroscopy
• 10 base particles 10 having a maximum particle diameter of 5 ⁇ m or more are randomly selected from the cross-sectional image of the backscattered electron image of the negative electrode mixture layer containing the negative electrode active material, and a qualitative and quantitative analysis of the elements is performed for each of them using an AES analyzer.
• the content of a predetermined element contained in the 10 particles is averaged to calculate the content.
• a coating may be formed on the surface of the base particle 10 due to decomposition of the non-aqueous electrolyte, etc.
• a conductive layer may be provided on the surface of the base particle 10. Therefore, not only when determining the area ratio of the carbon phase 13 in the cross section of the primary particle of the base particle 10, but also when EDX analysis and AES analysis are performed on a range, for example, 200 nm or more inward from the peripheral edge of the cross section of the particle so that the thin coating and conductive layer are not included in the measurement range.
• the oxygen content in the base particle 10 can be measured using an oxygen/nitrogen/hydrogen analyzer (for example, EGMA-830 manufactured by Horiba, Ltd.).
• the sample is placed in a Ni capsule, which is then placed in a carbon crucible heated at 5.75 kW together with Sn pellets and Ni pellets as flux, and the released carbon monoxide gas is detected.
• a calibration curve is created using a standard sample Y2O3 , and the oxygen content of the sample is calculated.
• ⁇ Nuclear magnetic resonance spectroscopy (NMR)> The amount of Si constituting the silicon phase 12 in the base particle 10 can be quantified using Si-NMR. Desirable measurement conditions for Si-NMR are shown below. Measurement equipment: Solid-state nuclear magnetic resonance spectrometer (INOVA-400), manufactured by Varian Probe: Varian 7mm CPMAS-2 MAS: 4.2kHz MAS speed: 4kHz Pulse: DD (45° pulse + signal acquisition time 1H decoupled) Repeat time: 1200 sec to 3000 sec Observation width: 100kHz Observation center: Around -100 ppm Signal acquisition time: 0.05 sec Accumulation count: 560 Sample amount: 207.6 mg
• the carbon content in the base particle 10 i.e., the content of the carbon phase 13 in the base particle, can be measured using a carbon/sulfur analyzer (for example, EMIA-520 model manufactured by Horiba, Ltd.).
• EMIA-520 model manufactured by Horiba, Ltd.
• a sample is weighed out on a magnetic board, a combustion improver is added, and the board is inserted into a combustion furnace (carrier gas: oxygen) heated to 1350°C, and the amount of carbon dioxide gas generated during combustion is detected by infrared absorption.
• a calibration curve is prepared using, for example, carbon steel (carbon content: 0.49%) manufactured by Bureau of Analysed Samples Ltd., and the carbon content of the sample is calculated.
• XRD X-ray diffraction
• the conductive layer 21 covers at least a part of the surface of the base particle.
• the conductive layer 21 may cover the entire surface of the base particle.
• the conductive layer 21 is, for example, a thin film layer containing a conductive material.
• the negative electrode active material according to this embodiment further includes the conductive layer 21 that covers at least a part of the surface of the base particle 10, thereby improving the conductivity of the negative electrode active material.
• the conductive material may be a conductive carbon material. That is, the conductive layer 21 may contain carbon.
• the carbon material graphite such as natural graphite, artificial graphite, and graphitized mesophase carbon, amorphous carbon, soft carbon, and hard carbon can be used.
• the carbon material may be amorphous carbon. As described above, it is easy to form a thin conductive layer 21 that covers the surface of the base particle. Examples of amorphous carbon include carbon black, burned pitch, coke, and activated carbon.
• the thickness of the conductive layer 21 is desirably thin enough not to affect the average particle size of the composite particles 20, i.e., so that the average particle size of the composite particles 20 does not increase significantly with respect to the average particle size of the parent particles.
• the thickness of the conductive layer 21 may be 1 nm or more and 200 nm or less, or 5 nm or more and 100 nm or less, taking into consideration ensuring electrical conductivity and the diffusibility of ions such as Li ions.
• the thickness of the conductive layer 21 can be measured by SEM observation or transmission electron microscope (TEM) observation of a cross section of the negative electrode active material in which the cross section of the composite particle 20 is exposed.
• the negative electrode active material of the present disclosure includes, for example, the production of base particles 10.
• the base particles 10 are produced, for example, by a production method including the following first to fifth steps.
• First step a step of obtaining a raw material alkali aluminate (hereinafter referred to as "raw material aluminate").
• Second step A step of compounding the raw aluminate and raw silicon to obtain a composite intermediate in which the raw silicon is dispersed in the raw aluminate.
• the third step is to heat treat the composite intermediate to obtain a sintered body containing an alkali aluminate phase 11 and a silicon phase 12 dispersed within the alkali aluminate phase 11.
• Fourth step A step of pulverizing the sintered body to obtain a precursor of the base particles 10.
• Fifth step a step of filling pores present inside the precursor of the base particle 10 with a carbon material to form a carbon phase 13 and obtain the base particle 10.
• the first step includes, for example, a step of mixing an aluminum compound, a compound containing an alkali metal element, and, if necessary, a compound containing element M to obtain a mixture, and a step of calcining the mixture to obtain a raw aluminate.
• the calcination is performed, for example, in an oxidizing atmosphere.
• the calcination temperature may be 400° C. or more and 1200° C. or less, or 700° C. or more and 1100° C. or less.
• aluminum compounds examples include aluminum oxide, aluminum hydroxide, aluminum carbonate, etc.
• One type of aluminum compound may be used alone, or two or more types may be used in combination.
• Examples of compounds containing an alkali metal element include lithium carbonate, lithium oxide, lithium hydroxide, lithium hydride, sodium carbonate, sodium oxide, sodium hydroxide, sodium hydride, potassium carbonate, potassium oxide, potassium hydroxide, potassium hydride, etc.
• Compounds containing an alkali metal element may be used alone or in combination of two or more.
• the compound containing element M is, for example, a boron compound.
• boron compounds include boron oxide, boric acid, borax, sodium tetraborate, etc.
• One type of boron compound may be used alone, or two or more types may be used in combination.
• the ratio (mMA/mAl) may be, for example, 0.04 or more and 0.50 or less, or 0.05 or more and 0.25 or less, as described above.
• the ratio of the masses of the alkali metal elements (mMA) may be, for example, 1.0 mass% or more and 9.5 mass% or less, as described above.
• the first step aluminum compounds that have not reacted with the compound containing an alkali metal element during the preparation of the raw aluminate may remain in the raw aluminate.
• the amount of aluminum compound used is large relative to the compound containing an alkali metal element, the aluminum compounds are likely to remain.
• the aluminum compound remaining in the raw aluminate is Al2O3
• an Al2O3 phase dispersed in the alkali aluminate phase 11 may be formed in the finally obtained mother particles.
• the mixture of the raw aluminate and the raw silicon is pulverized while applying a shear force to obtain a finely divided composite intermediate.
• the raw silicon is, for example, coarse silicon particles having an average particle size of several ⁇ m to several tens of ⁇ m.
• the silicon particles may be prepared so that the crystallite size of the silicon phase 12 calculated from the half-width of the diffraction peak derived from the Si(111) plane in the X-ray diffraction pattern of the negative electrode active material or the mother particle by Scherrer's formula is 15 nm or less. It is also possible to synthesize silicon nanoparticles and raw aluminate nanoparticles and mix them together without using a pulverizer.
• the composite intermediate is sintered while applying pressure to the finely divided composite intermediate by hot pressing or the like to obtain a sintered body.
• the pressure applied to the composite intermediate is, for example, 100 MPa or more, and may be 100 MPa or more and 300 MPa or less.
• the higher the pressure in the third step the more likely the voids in the composite particles are to be reduced.
• It is desirable to sinter the composite intermediate in an inert atmosphere for example, an atmosphere of argon, nitrogen, etc.).
• the sintering conditions in the third step also affect the crystallites of the silicon phase 12, and generally, the higher the sintering temperature, the larger the crystallite size.
• the firing temperature is 450°C or more and 1000°C or less. If the firing temperature is within this range, it is easy to form a structure in which minute silicon phases 12 are dispersed within the alkaline aluminate phase 11 with low crystallinity. The raw material aluminate is stable at this temperature and hardly reacts with silicon.
• the firing temperature may be 550°C or more and 950°C or less, or 650°C or more and 900°C or less. In order to reduce voids in the base particle 10, it is desirable to fire at a temperature of 650°C or more.
• the firing time is, for example, 1 hour or more and 10 hours or less.
• the fourth step is a step of pulverizing the base particles 10 so that they have a desired particle size distribution.
• the base particles 10 are pulverized so that the median diameter of the base particles 10 is 1 ⁇ m or more and 25 ⁇ m or less. In this way, precursors of the base particles 10 are obtained.
• the fifth step is a step of filling the pores present inside the precursor of the base particle 10 obtained in the fourth step with a carbon material to form a carbon phase 13, thereby obtaining the base particle 10.
• the sintered body formed in the third step has pores inside. Therefore, the precursor of the base particle 10 obtained by pulverizing the sintered body in the fourth step has pores inside.
• the carbon phase 13 is formed by filling the pores with a carbon material to obtain the base particle 10.
• the precursor of the base particle 10 containing pores is mixed with an amount of carbon material selected in consideration of the pore size and pore volume contained in the precursor of the base particle 10, and the mixture is fired to fill the pores of the base particle 10 with the carbon material.
• the base particle 10 can be produced in which the area ratio of the carbon phase 13 in the cross section of the primary particle is 4% or more and 25% or less.
• the carbon material used to form the carbon phase 13 is, for example, coal pitch, petroleum pitch, phenol resin, or the like.
• the mother particles 10 can be manufactured by the above steps 1 to 5.
• the following sixth step is further carried out.
• Sixth step a step of forming a conductive layer 21 on the surface of the base particle 10 including the alkali aluminate phase 11 , the silicon phase 12 , and the carbon phase 13 .
• the conductive material constituting the conductive layer 21 is preferably a conductive carbon material.
• methods for coating the surface of the base particles with a carbon material include a CVD method using hydrocarbon gases such as acetylene and methane as raw materials, and a method in which coal pitch, petroleum pitch, phenolic resin, etc. is mixed with the base particles and heated to carbonize them. Carbon black may also be attached to the surface of the base particles.
• the mixture of the base particles 10 and the carbon material is heated in an inert atmosphere (e.g., an atmosphere of argon, nitrogen, etc.) at 700°C or higher and 950°C or lower to form a conductive layer 21 on the surface of the base particles.
• an inert atmosphere e.g., an atmosphere of argon, nitrogen, etc.
• the fifth and sixth steps may be performed simultaneously.
• the amount of carbon material used and the heat treatment conditions may be adjusted so that the carbon phase 13, whose area ratio is 4% or more and 25% or less in the cross section of the primary particle of the base particle 10, and the conductive layer 21 can be formed simultaneously.
• the battery according to the present embodiment includes a negative electrode, a positive electrode, and an electrolyte.
• the negative electrode contains the negative electrode active material according to the present embodiment.
• the negative electrode contains the negative electrode active material according to the present embodiment, and therefore the cycle characteristics are improved, and the initial charge/discharge efficiency is improved.
• FIG. 3 is a longitudinal cross-sectional view showing a schematic example of a battery according to this embodiment.
• Battery 100 is a cylindrical battery that includes a cylindrical battery case, a wound electrode group 34, and an electrolyte (not shown).
• the electrode group 34 is housed within the battery case and is in contact with the electrolyte.
• the battery case is composed of a case body 35, which is a cylindrical metal container with a bottom, and a sealing body 36 that seals the opening of the case body 35.
• a gasket 47 is disposed between the case body 35 and the sealing body 36. The gasket 47 ensures that the battery case is airtight.
• insulating plates 37 and 38 are disposed on both ends of the electrode group 34 in the direction of the winding axis of the electrode group 34.
• the case body 35 has, for example, a step portion 41.
• the step portion 41 can be formed by partially pressing the side wall of the case body 35 from the outside.
• the step portion 41 may be formed in an annular shape on the side wall of the case body 35 along the circumferential direction of an imaginary circle defined by the case body 35.
• the sealing body 36 is supported, for example, by the surface of the step portion 41 on the opening side.
• the sealing body 36 includes a filter 42, a lower valve body 43, an insulating member 44, an upper valve body 45, and a cap 46. In the sealing body 36, these components are layered in this order.
• the sealing body 36 is attached to the opening of the case body 35 so that the cap 46 is located on the outside of the case body 35 and the filter 42 is located on the inside of the case body 35.
• Each of the above-mentioned components constituting the sealing body 36 is, for example, disk-shaped or ring-shaped.
• the above-mentioned components are electrically connected to each other, except for the insulating member 44.
• the electrode group 34 has a positive electrode 31, a separator 32, and a negative electrode 33.
• the positive electrode 31, the separator 32, and the negative electrode 33 are all strip-shaped.
• the width direction of the strip-shaped positive electrode 31 and negative electrode 33 is, for example, parallel to the winding axis of the electrode group 34.
• the separator 32 is disposed between the positive electrode 31 and the negative electrode 33.
• the positive electrode 31 and the negative electrode 33 are wound in a spiral shape with the separator 32 interposed between these electrodes.
• the positive electrodes 31 and negative electrodes 33 are alternately stacked in the radial direction of an imaginary circle defined by the case body 35, with a separator 32 interposed between these electrodes.
• the positive electrode 31 is electrically connected to a cap 46, which also serves as a positive electrode terminal, via a positive electrode lead 39.
• One end of the positive electrode lead 39 is connected, for example, near the center of the positive electrode 31 in the longitudinal direction of the positive electrode 31.
• the positive electrode lead 39 extends from the positive electrode 31 to the filter 42 through a through hole formed in the insulating plate 37.
• the other end of the positive electrode lead 39 is welded, for example, to the surface of the filter 42 facing the electrode group 34.
• the negative electrode 33 is electrically connected to the case body 35, which also serves as a negative electrode terminal, via a negative electrode lead 40.
• One end of the negative electrode lead 40 is connected, for example, to an end of the negative electrode 33 in the longitudinal direction of the negative electrode 33.
• the other end of the negative electrode lead 40 is welded, for example, to the inner bottom surface of the case body 35.
• the components of the battery 100 are described in detail below.
• the positive electrode 31 includes a material that has the property of absorbing and releasing metal ions (e.g., lithium ions).
• the positive electrode 31 includes, for example, a positive electrode active material.
• the positive electrode 31 may include a positive electrode current collector and a positive electrode mixture layer supported on the surface of the positive electrode current collector.
• the positive electrode mixture layer includes a positive electrode active material.
• the positive electrode active material include lithium-containing transition metal oxides, lithium-containing transition metal phosphates, transition metal fluorides, polyanion materials, fluorinated polyanion materials, transition metal sulfides, transition metal oxysulfides, and transition metal oxynitrides.
• the manufacturing cost of the battery can be reduced and the average discharge voltage can be increased.
• the lithium-containing transition metal oxides include lithium cobalt oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, and lithium nickel manganese oxide.
• the lithium-containing transition metal phosphates include lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, and lithium nickel phosphate. At least one selected from these positive electrode active materials can be used.
• the positive electrode mixture layer may contain a conductive additive, an ion conductor, and a binder as necessary.
• the conductive assistant and ion conductor are used to reduce the resistance of the electrode.
• the conductive assistant include carbon materials and conductive polymer compounds.
• the carbon materials include carbon black, graphite, acetylene black, carbon nanotubes, carbon nanofibers, graphene, fullerene, and graphite oxide.
• the conductive polymer compounds include polyaniline, polypyrrole, and polythiophene. At least one selected from these conductive assistants can be used.
• Binders are used to improve the binding of the materials that make up the electrodes.
• binders include polymeric materials such as polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polytetrafluoroethylene, carboxymethyl cellulose, polyacrylic acid, styrene-butadiene copolymer rubber, polypropylene, polyethylene, and polyimide. At least one selected from these binders can be used.
• the positive electrode current collector is, for example, a sheet or film made of a metal material such as aluminum, an aluminum alloy, stainless steel, titanium, or a titanium alloy.
• the sheet or film may be porous or non-porous.
• Metal foil, metal mesh, or the like may be used as the sheet or film.
• a carbon material may be applied to the surface of the positive electrode current collector as a conductive auxiliary material.
• the negative electrode 33 includes the negative electrode active material according to this embodiment.
• the negative electrode 33 includes, for example, a negative electrode current collector and a negative electrode mixture layer supported on the surface of the negative electrode current collector.
• the negative electrode current collector is a foil made of a metallic material such as stainless steel, nickel, nickel alloy, copper, or copper alloy.
• the negative electrode mixture layer contains the negative electrode active material according to this embodiment.
• the negative electrode mixture layer may contain other materials such as a conductive assistant, an ion conductor, and a binder, as necessary.
• the materials described above for the positive electrode mixture layer can also be used as the conductive assistant, the ion conductor, and the binder for the negative electrode mixture layer.
• the electrolyte may contain a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent.
• concentration of the lithium salt in the electrolyte may be, for example, 0.5 mol/L or more and 2 mol/L or less. By controlling the lithium salt concentration within the above range, an electrolyte having excellent ionic conductivity and appropriate viscosity can be obtained. However, the lithium salt concentration is not limited to the above.
• Cyclic carbonates, chain carbonates, cyclic ethers, chain ethers, nitriles, amides, etc. may be used as non-aqueous solvents. One selected from these solvents may be used, or two or more may be used in combination.
• lithium salt examples include lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bisperfluoroethylsulfonylimide (LiN(SO 2 C 2 F 5 ) 2 ), LiAsF 6 , LiCF 3 SO 3 , and lithium difluoro(oxalato)borate.
• LiPF 6 lithium hexafluorophosphate
• LiBF 4 lithium tetrafluoroborate
• LiClO 4 lithium perchlorate
• LiFSI lithium bis(fluorosulfonyl)imide
• LiTFSI lithium bis(trifluoromethanesulfonyl)imide
• the separator 32 has high ion permeability and has appropriate mechanical strength and insulating properties.
• the separator 32 may be made of a microporous thin film, a woven fabric, a nonwoven fabric, or the like.
• the separator 32 may be made of a polymer, for example.
• the polymer may be a polyolefin, such as polypropylene or polyethylene.
• the electrolyte may be impregnated into a polymer provided as a separator, for example.
• the battery of the present disclosure may have a structure in which the electrolyte and the polymer are used in combination.
• the battery of the present disclosure may further include a solid electrolyte as an electrolyte. That is, the battery of the present disclosure may have a hybrid structure in which an electrolytic solution and a solid electrolyte are used in combination.
• solid electrolyte materials are halide solid electrolytes, sulfide solid electrolytes, oxide solid electrolytes, and organic polymer solid electrolytes.
• halide solid electrolyte refers to a solid electrolyte containing a halogen element as the main component of the anions.
• Sulfide solid electrolyte refers to a solid electrolyte containing sulfur as the main component of the anions.
• Oxide solid electrolyte refers to a solid electrolyte containing oxygen as the main component of the anions.
• the main component of the anions refers to the anion with the largest substance amount among all the anions that make up the solid electrolyte.
• the configuration example shown in FIG. 3 is described, that is, a cylindrical nonaqueous electrolyte secondary battery in which a wound electrode group in which a positive electrode and a negative electrode are wound with a separator interposed therebetween and an electrolyte solution are housed in an exterior body.
• the battery according to this disclosure is not limited to this configuration example.
• the battery according to this disclosure may be in any form, such as a square type, a coin type, a button type, a laminate type, etc.
• an electrode group of another form such as an electrode group in which a positive electrode and a negative electrode are stacked with a separator interposed therebetween, may be used.
• FIG. 4 is a cross-sectional view showing a schematic configuration of another example of a battery according to this embodiment.
• the battery 200 includes a positive electrode 210, an electrolyte layer 220, and a negative electrode 230.
• the negative electrode 230 contains the negative electrode active material according to this embodiment.
• the electrolyte layer 220 is disposed between the positive electrode 210 and the negative electrode 230.
• the battery 200 is, for example, an all-solid-state battery.
• the positive electrode 210 includes a positive electrode current collector 211 and a positive electrode mixture layer 212 supported on the surface of the positive electrode current collector 211.
• the positive electrode mixture layer 212 is located between the positive electrode current collector 211 and the electrolyte layer 220.
• the positive electrode current collector 211 and the positive electrode mixture layer 212 can be made of the materials described above for the positive electrode 31 in the battery 100.
• the positive electrode mixture layer 212 may contain a solid electrolyte.
• solid electrolytes include the solid electrolytes described above as the electrolyte in the battery 100.
• the electrolyte layer 220 is a layer that contains an electrolyte.
• the electrolyte is, for example, a solid electrolyte.
• the electrolyte layer 220 may be a solid electrolyte layer. Examples of solid electrolytes include the solid electrolytes described above as the electrolyte in the battery 100.
• the electrolyte layer 220 may further include a binder.
• a binder the materials described above for the positive electrode mixture layer of the battery 100 can also be used for the electrolyte layer 220.
• the negative electrode 230 includes a negative electrode current collector 231 and a negative electrode mixture layer 232 supported by the negative electrode current collector 231.
• the negative electrode mixture layer 232 contains the negative electrode active material according to this embodiment.
• the negative electrode mixture layer 232 is located between the negative electrode current collector 231 and the electrolyte layer 220.
• the materials described above for the negative electrode 33 in the battery 100 can be used for the negative electrode current collector 231 and the negative electrode mixture layer 232.
• the negative electrode mixture layer 232 may contain a solid electrolyte.
• solid electrolytes include the solid electrolytes described above as the electrolyte in the battery 100.
• the battery 200 can be configured as a battery of various shapes, such as a coin type, a cylindrical type, a rectangular type, a sheet type, a button type, a flat type, a laminated type, etc.
• the negative electrode active material according to Technology 1 can improve durability against charging and discharging, and as a result, the cycle characteristics of the battery can be improved.
• This configuration allows the negative electrode active material according to Technology 2 to have improved durability against charging and discharging, and as a result, the cycle characteristics of the battery can be improved.
• the alkali aluminate phase further comprises B; The negative electrode active material according to Technology 1 or 2.
• This configuration reduces the number of voids in the base particles, which can further improve the cycle characteristics of the battery.
• the ratio of the mass of Al element to the total mass of elements excluding oxygen element and carbon element is mAl
• the ratio of the mass of the B element to the total mass of elements excluding oxygen and carbon is mB
• the ratio (mAl/mB) is 1.0 or more and 30.0 or less;
• This configuration can make the effect of B in reducing voids in the base particles more pronounced. This suppresses the deterioration of the particle structure caused by voids in the base particles, effectively improving the cycle characteristics of the battery.
• the alkali metal element includes at least one selected from the group consisting of Li, Na, and K;
• the negative electrode active material according to any one of claims 1 to 4.
• the negative electrode active material according to Technology 5 can further improve the cycle characteristics of the battery.
• the base particle further includes a conductive layer that covers at least a part of the surface of the base particle.
• the negative electrode active material according to any one of claims 1 to 5.
• This configuration improves the conductivity of the negative electrode active material, improving battery characteristics.
• This configuration results in a battery with improved cycle characteristics.
• Example 1 [Preparation of mother particles]
• a raw aluminate was obtained by mixing Al2O3 , Li2CO3 , and B2O3 and firing the mixture in air at 750°C for 10 hours.
• the mixing ratio of Al2O3 , Li2CO3 , and B2O3 was adjusted so that the constituent elements of the lithium aluminate phase, which is an alkali aluminate phase, had the element ratio shown in Table 1.
• the raw aluminate was pulverized to an average particle size of 10 ⁇ m.
• Raw silicon (3N, average particle size 10 ⁇ m) was mixed with the raw aluminate (average particle size 10 ⁇ m) obtained in the first step.
• the mixing ratio of the raw silicon and the raw aluminate was adjusted so that the elements constituting the base particles had the element ratio shown in Table 1.
• the mixture was filled into a pot (SUS, volume: 500 mL) of a planetary ball mill (Fritsch, P-5), 24 SUS balls (diameter 20 mm) were placed in the pot, the lid was closed, and the mixture was pulverized at 200 rpm for 50 hours in an inert atmosphere.
• the powdered mixture obtained in the second step was taken out into an inert atmosphere, and sintered at 700° C. for 4 hours in the inert atmosphere while applying a pressure of 200 MPa using a hot press machine, thereby obtaining a sintered body of the mixture.
• the sintered body obtained in the third step was pulverized and passed through a 40 ⁇ m mesh to obtain a precursor of mother particles in which a silicon phase was dispersed in a lithium aluminate phase, which was an alkali aluminate phase.
• Coal pitch (MCP250, manufactured by JFE Chemical Corporation) was mixed with the precursor of the base particles obtained in the fourth step. The mixture was fired at 800° C. for 5 hours in an inert atmosphere to fill the internal pores of the precursor of the base particles with the carbon material by coal pitch, and to form a conductive layer containing a conductive carbon material on the surface of the base particles. That is, in the fifth step, the amount of coal pitch to be added was adjusted in consideration of the formation of a conductive layer and a carbon phase in the base particles. The amount of coal pitch added was 20 mass% with respect to the total mass of the base particles and the coal pitch, as shown in Table 1. Then, composite particles having a conductive layer and an average particle size of 5 ⁇ m were obtained using a sieve.
• the contents of Li, Al, B, and Si relative to the total mass of elements excluding oxygen and carbon in the mother particles, and the area ratio of the carbon phase in the cross section of the primary particle of the mother particles were determined, and the measurement results are shown in Table 1.
• the contents of Li, Al, B, and Si were determined from the feed ratio of the raw materials. When the contents of each element in the obtained mother particles were measured using ICP and Si-NMR, the results were almost the same as the contents of each element determined from the feed ratio.
• Table 1 shows the contents of each element determined from the feed ratio.
• the area ratio of the carbon phase in the cross section of the primary particle of the mother particle was measured by element mapping analysis using EDX under the measurement conditions exemplified above.
• the negative electrode slurry was applied to both sides of the copper foil, which was the negative electrode current collector, and the coating was dried and then rolled to prepare a negative electrode in which a negative electrode mixture layer with a density of 1.5 g / cm 3 was formed on both sides of the copper foil.
• NMP N-methyl-2-pyrrolidone
• LiPF 6 lithium hexafluorophosphate
• EC ethylene carbonate
• DEC diethyl carbonate
• non-aqueous electrolyte secondary battery The positive electrode and the negative electrode with the leads attached were wound with a separator interposed therebetween to prepare a wound electrode body, which was then inserted into an exterior body made of an aluminum laminate film and vacuum dried at 105° C. for 2 hours. After that, a nonaqueous electrolyte was injected, and the opening of the exterior body was sealed to obtain a nonaqueous electrolyte secondary battery.
• Example 2 In the preparation of the base particles, the firing temperature was changed to 800° C. in the third step, and the amount of coal pitch added in the fifth step was changed to 10 mass % with respect to the total mass of the base particles and the coal pitch, as shown in Table 1. Other than these, base particles were prepared in the same manner as in Example 1, and a nonaqueous electrolyte secondary battery was fabricated.
• Example 3 In the preparation of the base particles, the firing temperature in the third step was changed to 800° C. Except for this, base particles were prepared in the same manner as in Example 1, and a nonaqueous electrolyte secondary battery was fabricated.
• Capacity retention rate (%) (200th cycle discharge capacity ⁇ 1st cycle discharge capacity) ⁇ 100
• the technology disclosed herein is useful for batteries such as lithium-ion secondary batteries.

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