WO2024242105A1 - 二次電池用負極活物質および二次電池 - Google Patents

二次電池用負極活物質および二次電池 Download PDF

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WO2024242105A1
WO2024242105A1 PCT/JP2024/018678 JP2024018678W WO2024242105A1 WO 2024242105 A1 WO2024242105 A1 WO 2024242105A1 JP 2024018678 W JP2024018678 W JP 2024018678W WO 2024242105 A1 WO2024242105 A1 WO 2024242105A1
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negative electrode
silicon
phase
active material
secondary battery
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French (fr)
Japanese (ja)
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公 小泉
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Panasonic Intellectual Property Management Co Ltd
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Panasonic Intellectual Property Management Co Ltd
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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

  • This disclosure relates to negative electrode active materials for secondary batteries and secondary batteries.
  • a negative electrode active material capable of absorbing and releasing lithium ions is used in the negative electrode of secondary batteries, such as lithium-ion secondary batteries, and graphite is generally used as such a negative electrode active material.
  • materials containing silicon, which have a higher capacity density than graphite, have been considered for the negative electrode active material.
  • Patent Document 1 proposes a negative electrode active material for secondary batteries, which comprises "silicate composite particles including a silicate phase and silicon particles dispersed within the silicate phase, the silicate phase being an oxide phase including Si, O, and an alkali metal, the alkali metal including at least K and Li.”
  • one aspect of the present disclosure relates to a negative electrode active material for a secondary battery, comprising silicon-containing particles including an ion-conducting phase and a silicon phase dispersed within the ion-conducting phase, the silicon-containing particles including lithium and element A1, the concentration of element A1 being greater at the surface portion than in the interior of the silicon-containing particles, and the element A1 being at least one element selected from the group consisting of alkali metal elements other than lithium and Group 2 elements of the long form periodic table.
  • Another aspect of the present disclosure relates to a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, the negative electrode including the above-mentioned negative electrode active material for secondary batteries.
  • FIG. 1 is a cross-sectional view illustrating a schematic example of a negative electrode active material (silicon-containing particles) according to an embodiment of the present disclosure.
  • 1 is a schematic perspective view of a secondary battery according to an embodiment of the present disclosure, with a portion cut away;
  • the negative electrode active material for a secondary battery includes silicon-containing particles.
  • the silicon-containing particles include an ion-conducting phase and a silicon phase dispersed within the ion-conducting phase.
  • the silicon-containing particles include lithium (Li) and element A1.
  • the concentration of element A1 is greater at the surface of the silicon-containing particles than in the interior.
  • Element A1 is at least one element selected from the group consisting of alkali metal elements other than lithium and Group 2 elements of the long form periodic table.
  • the silicon-containing particles are also referred to as "composite particles.” Silicon is also referred to as "silicon" or "Si.”
  • the composite particle may contain one type of element A1 or may contain multiple types.
  • the composite particle contains multiple types of element A1
  • the total concentration of the multiple types is greater at the surface of the composite particle than in the interior.
  • the concentration of each of the multiple types may be greater at the surface of the composite particle than in the interior.
  • the ion conductive phase may include, for example, at least one selected from the group consisting of a silicate phase and a silicon oxide phase.
  • at least one of the silicate phase and the silicon oxide phase is also referred to as a "silicon compound phase”.
  • the silicon compound phase may form an amorphous phase.
  • Composite particles in which a silicon phase is dispersed within a silicate phase are also referred to as "silicate phase-containing composite particles”.
  • Silicate phase-containing composite particles in which the silicate phase is a lithium silicate phase are also referred to as "lithium silicate phase-containing composite particles”.
  • Composite particles in which a silicon phase is dispersed within a silicon oxide phase are also referred to as "silicon oxide phase-containing composite particles”.
  • a composite particle contains Li and element A1
  • the concentration of element A1 is greater on the surface of the composite particle than inside
  • the reactivity of the composite particle is significantly improved, and the rate characteristics (rapid charge/discharge characteristics) are significantly improved by improving the overvoltage.
  • the detailed mechanism by which the reactivity of the composite particles is improved is unknown, but it is speculated as follows.
  • the presence of a large amount of element A1, which has a large ionization tendency, on the surface side of the composite particles promotes desolvation of Li ions on the surface of the composite particles.
  • the presence of a large amount of element A1, which has a larger ionic radius than Li, on the surface side of the composite particles causes distortion in the amorphous structure of the ion conductive phase on the surface of the composite particles, improving the diffusion rate of Li ions inside the composite particles. It is speculated that these factors improve the reactivity of the composite particles (the reactivity of Li with the ion conductive phase).
  • the composite particles of the present disclosure have a lower concentration of element A1 in the interior than in the surface.
  • the reactivity of a silicon-containing material improves, it becomes more likely that particle cracks will occur during charging and discharging, and side reactions will progress due to contact between the active surface created by the particle cracks and the electrolyte, which tends to deteriorate the cycle characteristics.
  • the reactivity is improved by increasing the concentration of element A1 in the particle surface, but the concentration of element A1 is low inside the particles, which makes it possible to suppress particle cracking and the resulting deterioration of cycle characteristics.
  • the present disclosure can achieve both excellent rate characteristics and cycle characteristics.
  • the element A1 and lithium are contained in the ion conductive phase.
  • the element A1 and lithium are contained in the ion conductive phase, including the case where the element A1 and lithium are present at the interface between the ion conductive phase and the silicon phase and the case where they are present on the surface of the composite particle.
  • the element A1 may be contained as a compound containing the element A1 (such as an oxide) or may be contained in a solid solution state.
  • the lithium may be contained as a compound containing lithium (such as lithium silicate) or may be contained in a solid solution state.
  • Alkali metal elements other than lithium include potassium (K), sodium (Na), etc.
  • Group 2 elements of the long periodic table include magnesium (Mg), calcium (Ca), etc.
  • Element A1 is preferably at least one selected from the group consisting of potassium, sodium, magnesium, and calcium.
  • the composite particle has a higher concentration of element A1 at the surface than in the interior. If the concentration of element A1 at a depth of 100 nm from the surface of the composite particle is X mass %, and the concentration of element A1 in the entire composite particle is Y mass %, the ratio of X/Y may be 2 or more, 3 or more, 5 or more, 10 or more, or 15 or more. Concentration X is, for example, 0.1 to 20 mass %. Concentration Y is, for example, 0.05 to 5 mass %.
  • the concentration X is the proportion (mass ratio) of element A1 among all elements present at a depth of 100 nm from the surface of the composite particle.
  • the concentration X (mass%) of element A1 at a depth of 100 nm from the surface of the composite particle can be determined by X-ray photoelectron spectroscopy (XPS), energy dispersive X-ray spectroscopy using a scanning electron microscope (SEM-EDX), etc.
  • the concentration Y is the proportion (mass ratio) of element A1 in the entire composite particle.
  • the concentration Y (mass%) of element A1 in the entire composite particle can be determined by inductively coupled plasma optical emission spectroscopy (ICP), SEM-EDX analysis, etc. Details of ICP analysis and SEM-EDX analysis of composite particles will be described later.
  • Lithium may be distributed uniformly throughout the composite particle (depth direction), or the concentration of lithium may be higher at the surface than inside the composite particle. At least one selected from the group consisting of Li 2 CO 3 , Li 2 O, and LiOH may be attached to the surface of the composite particle. These compounds can be used as raw materials containing Li in the process of preparing the composite particle (the second step described below), and may remain on the surface of the particle as an unreacted substance. The lithium contained in the composite particle may also include lithium remaining as an unreacted substance.
  • the composite particle may contain element A2 (an element other than lithium, element A1, silicon, and oxygen).
  • element A2 is contained in the ion conductive phase.
  • the element A2 being contained in the ion conductive phase includes the case where element A2 is present at the interface between the ion conductive phase and the silicon phase and the case where element A2 is present on the surface of the composite particle.
  • the element A2 may be contained as a compound (such as an oxide) containing element A2, or may be contained in a solid solution state.
  • element A2 is at least one selected from the group consisting of aluminum (Al), boron (B), bismuth (Bi), antimony (Sb), germanium (Ge), zirconium (Zr), titanium (Ti), phosphorus (P), vanadium (V), tungsten (W) and lanthanum (La).
  • the content of element A2 in the composite particle may be 0.01 mass% or more with respect to the entire composite particle.
  • the composite particle may contain one type of element A2 or multiple types of element A2. There is no particular limitation on the concentration distribution of element A2 in the depth direction of the composite particle.
  • the composite particles have a structure in which the silicon phase is dispersed in the ion-conducting phase (matrix).
  • the stress caused by the expansion and contraction of the silicon phase during charging and discharging is alleviated by the ion-conducting phase, and cracks and fractures of the composite particles are suppressed. Therefore, it is possible to achieve both high capacity due to the inclusion of silicon and improved cycle characteristics.
  • the ion-conducting phase may be composed of one phase or multiple phases.
  • the silicon oxide phase is composed of a compound of Si and O.
  • the main component (e.g., 95 to 100 mass%) of the silicon oxide phase may be silicon dioxide.
  • the composite particles may be silicon oxide phase-containing composite particles.
  • the silicon oxide phase-containing composite particles are represented by, for example, the formula SiO x (0.5 ⁇ x ⁇ 1.6).
  • the silicate phase is composed of a compound containing a metal element, silicon (Si), and oxygen (O).
  • the metal element include an alkali metal element such as lithium and an element of Group 2 of the long periodic table.
  • the silicate phase preferably contains at least lithium silicate. In this case, the lithium ions can easily enter and leave the silicate phase.
  • the lithium silicate phase has a smaller irreversible capacity than the silicon oxide phase.
  • the composite particles may be silicate phase-containing composite particles.
  • the ion conductive phase may contain, for example, a silicate phase as a main component and a small amount of a silicon oxide phase.
  • the "main component” refers to a component that occupies 50% by mass or more of the total mass of the silicon compound phase, and may occupy 70% by mass or more of the component.
  • the silicate phase (lithium silicate phase) may contain at least one selected from the group consisting of Li 2 Si 2 O 5 , Li 2 SiO 3 , and Li 4 SiO 4 .
  • the atomic ratio of O to Si in lithium silicate: O/Si is, for example, greater than 2 and less than 4.
  • O/Si ratio is greater than 2 and less than 4.
  • z in the formula described below is 0 ⁇ z ⁇ 2
  • the O/Si ratio is greater than 2 and less than 3.
  • the atomic ratio of Li to Si in lithium silicate: Li/Si is, for example, greater than 0 and less than 4.
  • the average particle size of the fine silicon phase (before the first charge) dispersed within the ion conductive phase may be 500 nm or less, 200 nm or more, or 50 nm or less.
  • the average particle size of the silicon phase is measured by observing the cross section of the composite particle using a SEM or TEM. Specifically, it is determined by averaging the maximum diameters of any 100 silicon phases.
  • the silicon phase dispersed within the ion-conducting phase is a particulate phase of simple silicon (Si) and is composed of one or more crystallites.
  • the crystallite size of the silicon phase may be 50 nm or less, preferably 20 nm or less, and more preferably 10 nm or less.
  • the lower limit of the crystallite size of the silicon phase is, for example, 5 nm or more.
  • the crystallite size of the silicon phase is calculated by the Scherrer formula from the half-width of the diffraction peak assigned to the Si (111) plane in the X-ray diffraction (XRD) pattern.
  • the content of the silicon phase in the composite particles may be 30 mass% or more (or 57 mass% or more) and 90 mass% or less, or may be 35 mass% or more and 75 mass% or less, based on the entire composite particle.
  • the average particle size of the composite particles is, for example, 1 ⁇ m or more and 25 ⁇ m or less, or may be 4 ⁇ m or more and 15 ⁇ m or less. In the above range, good battery performance is likely to be obtained.
  • the average particle size of the composite particles is the particle size (volume average particle size) at which the volume accumulated 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.
  • a conductive layer may be formed on the surface of the composite particle.
  • the conductive layer contains, for example, a conductive carbon material.
  • the thickness of the conductive layer is preferably thin enough not to substantially affect the average particle size of the composite particle. From the viewpoint of ensuring electrical conductivity, the thickness of the conductive layer is preferably 1 nm or more.
  • the conductive layer is formed by mixing the raw material of the conductive carbon material with the composite particles, and then calcining the mixture to carbonize the raw material of the conductive carbon material.
  • the raw material of the conductive material include coal pitch or coal tar pitch, petroleum pitch, and phenolic resin.
  • the mixture of the raw material of the conductive carbon material and the composite particles is calcined, for example, in an inert atmosphere (for example, an atmosphere of argon, nitrogen, etc.).
  • the calcination temperature is preferably 450°C or higher and 1000°C or lower. In the above temperature range, it is easy to form a highly conductive layer in the silicate phase with low crystallinity.
  • the calcination temperature is preferably 550°C or higher and 900°C or lower, and more preferably 650°C or higher and 850°C or lower.
  • the calcination time is, for example, 1 hour or higher and 10 hours or lower.
  • the formation of the conductive layer on the surface of the composite particles may be performed after the second step (addition of element A1, etc.) described later.
  • the process for preparing the silicon-containing particles includes, for example, a first step and a second step.
  • a composite particle is prepared.
  • the composite particle (ion conductive phase) prepared in the first step contains lithium
  • the second step a large amount of element A1 (or element A1 and lithium) is added to the surface side of the composite particle.
  • the composite particle (ion conductive phase) prepared in the first step does not contain lithium
  • a large amount of lithium and element A1 are added to the surface side of the composite particle.
  • a composite particle is prepared that includes an ion-conducting phase and a silicon phase dispersed within the ion-conducting phase,
  • the ion-conducting phase includes at least one silicon compound phase selected from the group consisting of a silicate phase and a silicon oxide phase.
  • the composite particles (ion conductive phase) prepared in the first step may not contain element A1, or may contain element A1.
  • the composite particles (ion conductive phase) prepared in the first step may contain element A2.
  • silicon oxide phase-containing composite particles for example, composite particles represented by the formula SiO x (0.5 ⁇ x ⁇ 1.6) may be prepared.
  • the SiO x particles can be prepared, for example, by mixing SiO 2 and Si particles, heating under vacuum conditions, obtaining vapor, and then solidifying.
  • the element A2 may be contained in the SiO x particles (silicon oxide phase) by adding the element A2 or a compound containing the element A2 to the SiO 2 and Si particles that are the sublimation source.
  • composite particles containing a silicon phase having a small crystallite size of, for example, 20 nm or less can be obtained.
  • silicate phase-containing composite particles for example, composite particles containing a lithium silicate phase represented by Li 2z SiO 2+z (0 ⁇ z ⁇ 2) may be prepared.
  • the silicate phase-containing composite particles can be obtained, for example, by pulverizing a mixture of silicate (lithium silicate) and raw silicon with stirring in a ball mill or the like to form fine particles, heat-treating the mixture in an inert atmosphere, and pulverizing the sintered product obtained by the heat treatment.
  • the silicate used as the raw material for the composite particles may contain element A2. The method for producing the lithium silicate phase-containing composite particles will be described in detail later.
  • raw materials containing element A1 include carbonates, hydroxides, oxides, etc. If the composite particles prepared in the first step do not contain element A2, the melt may contain a raw material containing element A2.
  • the above X/Y ratio (concentration gradient of element A1 in the depth direction of the composite particle) can be adjusted, for example, by the size (particle size) of the composite particle in the first step, the time of introducing the composite particle into the melt in the second step, the temperature of the melt in the second step (heating temperature of the raw material containing element A1), etc.
  • the amount of element A1 added may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of the composite particle.
  • the amount of lithium added may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of the composite particle.
  • the amount of element A1 (or Li and element A1) added to the composite particle can be adjusted, for example, by the amount of composite particle added to the melt.
  • the composite particles may be heat-treated after the second step.
  • the heat treatment may cause crystal growth of the silicon phase of the composite particles to increase the crystallite size.
  • the crystallite size of the silicon phase may be increased appropriately to improve the initial charge/discharge efficiency.
  • Step (i) step of obtaining lithium silicate
  • the raw material for lithium silicate is a raw material mixture containing a Si-containing raw material and a Li raw material in a predetermined ratio.
  • the raw material mixture may contain other elements M as necessary. Examples of element M include element A2.
  • a mixture of a predetermined amount of the above raw materials is melted, and the molten liquid is passed through a metal roll to form flakes to produce lithium silicate.
  • the flaked silicate is then crystallized by heat treatment in an air atmosphere at a temperature above the glass transition point and below the melting point.
  • the flaked silicate can also be used without being crystallized. It is also possible to produce silicate by a solid-phase reaction by firing a mixture of a predetermined amount of the above raw materials at a temperature below the melting point without melting it.
  • Silicon or silicon monoxide can be used as the Si raw material.
  • lithium carbonate, lithium oxide, lithium hydroxide, lithium hydride, etc. can be used as the Li raw material.
  • oxides, hydroxides, carbonates, hydrides, nitrates, sulfates, etc. of each element can be used as the raw material containing element M.
  • the lithium silicate there may be residual Si raw material that has not reacted with the Li raw material. The remaining Si raw material is dispersed in the lithium silicate as fine crystals of silicon oxide.
  • Step (ii) (Step of Obtaining Silicate Composite Particles)
  • the lithium silicate is mixed with raw silicon to form a composite.
  • the composite particles are produced through the following steps (a) to (c).
  • Step (a) First, raw silicon powder and lithium silicate powder are mixed in a mass ratio of, for example, 20:80 to 95:5.
  • the raw silicon may be coarse silicon particles having an average particle size of several ⁇ m to several tens of ⁇ m.
  • Step (b) the mixture of raw silicon and lithium silicate is pulverized and compounded while being finely divided using a pulverizing device such as a ball mill.
  • a pulverizing device such as a ball mill.
  • an organic solvent may be added to the mixture and wet-pulverized.
  • a predetermined amount of the organic solvent may be charged into the pulverizing vessel at once at the beginning of the pulverization, or a predetermined amount of the organic solvent may be charged into the pulverizing vessel intermittently in multiple batches during the pulverization process.
  • the organic solvent serves to prevent the material to be pulverized from adhering to the inner wall of the pulverizing vessel.
  • the organic solvent that can be used includes alcohols, ethers, fatty acids, alkanes, cycloalkanes, silicate esters, metal alkoxides, etc.
  • the raw silicon used may be coarse silicon particles with an average particle size of several ⁇ m to several tens of ⁇ m. It is preferable to control the crystallite size of the silicon particles (silicon phase) finally obtained, calculated from the half-width of the diffraction peak assigned to the Si (111) plane in the X-ray diffraction pattern using the Scherrer formula, to be 5 nm or more and 50 nm or less.
  • the raw silicon and lithium silicate may be separately microparticulated and then mixed.
  • silicon nanoparticles and amorphous lithium silicate nanoparticles may be produced and then mixed without using a grinding device.
  • the nanoparticles may be produced using known methods such as a gas phase method (e.g., a plasma method) or a liquid phase method (e.g., a liquid phase reduction method).
  • Step (c) the pulverized material is sintered while applying pressure with a hot press or the like to obtain a sintered body.
  • the sintering is performed, for example, in an inert atmosphere (for example, an atmosphere of argon, nitrogen, etc.).
  • the sintering temperature is preferably 450°C or higher and 1000°C or lower. In the above temperature range, it is easy to disperse fine silicon particles in the silicate phase with low crystallinity.
  • the lithium silicate softens and flows to fill the gaps between the silicon particles.
  • a dense block-shaped sintered body can be obtained with the silicate phase as the sea part and the silicon particles (silicon phase) as the island part.
  • the sintering temperature is preferably 550°C or higher and 900°C or lower, more preferably 650°C or higher and 850°C or lower.
  • the sintering time is, for example, 1 hour or higher and 10 hours or lower.
  • the sintered body thus obtained is pulverized to obtain composite particles.
  • composite particles having a desired average particle size can be obtained.
  • composite particles having a silicate phase as a matrix and a silicon phase dispersed in the matrix can be obtained.
  • composition of the composite particles can be determined, for example, by the following analytical methods:
  • ⁇ EDX> From the cross-sectional image of the backscattered electron image of the negative electrode mixture layer by SEM, 10 composite particles with a maximum particle diameter of 5 ⁇ m or more are randomly selected, and elemental mapping analysis is performed on each of them by energy dispersive X-ray (EDX).
  • the area ratio of the target element is calculated using image analysis software.
  • the observation magnification is preferably 2000 to 20000 times.
  • the measured values of the area ratio of a predetermined element contained in the 10 particles are averaged.
  • the content of the target element is calculated from the obtained average value.
  • ⁇ SEM-EDX measurement conditions > Processing equipment: JEOL, SM-09010 (Cross Section Polisher) Processing conditions: Acceleration voltage 6 kV Current value: 140 ⁇ A Vacuum degree: 1 ⁇ 10 -3 ⁇ 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 Apr.: 2 Analysis area: 1 ⁇ m square Analysis software: EDAX Genesis CPS: 20500 Lsec: 50 Time constant: 3.2
  • ⁇ ICP> A sample of the composite particles is completely dissolved in a heated acid solution (a mixed acid of hydrofluoric acid, nitric acid, and sulfuric acid), and the carbon remaining in the solution is filtered off. The filtrate is then analyzed by inductively coupled plasma emission spectrometry (ICP) to measure the spectral intensity of each element. A calibration curve is then created using commercially available standard solutions of the elements, and the content of each element contained in the composite particles is calculated.
  • ICP inductively coupled plasma emission spectrometry
  • the contents of elements A1 and A2 contained in the composite particles can be quantitatively analyzed in accordance with JIS R3105 (1995) (method of analysis of borosilicate glass).
  • Silicate phase-containing composite particles contain a silicate phase and a silicon phase, which can be distinguished and quantified using Si-NMR.
  • the Si content obtained by the above method is the sum of the amount of Si constituting the silicon phase and the amount of Si in the silicate phase.
  • the amount of Si element contained in the composite particles is distributed between the silicate phase and the silicon phase using the results of quantitative analysis by Si-NMR.
  • the standard substance required for quantification can be a mixture containing a silicate phase and a silicon phase in a specified ratio with a known Si content.
  • Si-NMR measurement conditions Desirable conditions for Si-NMR measurement 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
  • FIG. 1 is a cross-sectional view that illustrates an example of a negative electrode active material (composite particles).
  • the negative electrode active material 20 includes a composite particle 23 (mother particle).
  • the composite particle 23 includes an ion conductive phase 21 and a silicon phase (silicon particles) 22 dispersed in the ion conductive phase 21.
  • the composite particle 23 has a sea-island structure in which fine silicon phases 22 are dispersed in a matrix of the ion conductive phase 21.
  • the surface of the composite particle 23 is covered with a conductive layer 26.
  • the composite particle 23 (ion conductive phase 21) contains element A1 and lithium. The concentration of element A1 is higher on the surface side (the side closer to the conductive layer 26) of the composite particle 23 than on the inner side.
  • the secondary battery according to the embodiment of the present disclosure includes a positive electrode, a negative electrode, and an electrolyte.
  • the negative electrode contains the above-mentioned negative electrode active material for a secondary battery.
  • the negative electrode of the secondary battery and other components will be described below.
  • the negative electrode includes, for example, a negative electrode mixture layer containing the above-mentioned negative electrode active material for secondary batteries, and a negative electrode current collector supporting the negative electrode mixture layer.
  • the negative electrode mixture layer can be formed by applying a negative electrode slurry in which the negative electrode mixture is dispersed in a dispersion medium to the surface of the negative electrode current collector and drying it. The coating film after drying may be rolled as necessary.
  • the negative electrode mixture layer may be formed on one surface of the negative electrode current collector, or on both surfaces.
  • the negative electrode mixture contains the above-mentioned negative electrode active material for secondary batteries as an essential component, and may contain binders, conductive agents, thickeners, etc. as optional components.
  • the silicon phase in the composite particles can absorb many lithium ions, which contributes to increasing the capacity of the negative electrode.
  • the content of the composite particles in the negative electrode mixture layer may be 1 mass% or more and 50 mass% or less with respect to the entire negative electrode mixture layer.
  • the negative electrode active material may further contain other active material materials that electrochemically absorb and release lithium ions.
  • a carbon-based active material is preferable as the other active material material. Since the composite particles expand and contract in volume with charging and discharging, if the ratio of the composite particles in the negative electrode active material increases, poor contact between the negative electrode active material and the negative electrode current collector is likely to occur with charging and discharging. On the other hand, by using the composite particles in combination with a carbon-based active material, it is possible to achieve excellent cycle characteristics while imparting the high capacity of the silicon phase to the negative electrode.
  • the ratio of the composite particles to the total of the composite particles and the carbon-based active material is preferably, for example, 0.5 to 15 mass%, more preferably 1 to 5 mass%. This makes it easier to achieve both high capacity and improved cycle characteristics.
  • carbon-based active materials examples include graphite, easily graphitized carbon (soft carbon), and non-graphitizable carbon (hard carbon). Of these, graphite is preferred because of its excellent charge/discharge stability and low irreversible capacity.
  • Graphite refers to a material having a graphite-type crystal structure, and includes, for example, natural graphite, artificial graphite, and graphitized mesophase carbon particles. Carbon-based active materials may be used alone or in combination of two or more types.
  • a non-porous conductive substrate such as metal foil
  • a porous conductive substrate such as a mesh, net, or punched sheet
  • the material for the negative electrode current collector include stainless steel, nickel, nickel alloy, copper, and copper alloy.
  • a thickness of 1 to 50 ⁇ m is preferable, and 5 to 20 ⁇ m is more preferable.
  • binders include fluororesin, polyolefin resin, polyamide resin, polyimide resin, vinyl resin, styrene-butadiene copolymer rubber (SBR), polyacrylic acid and its derivatives. These may be used alone or in combination of two or more.
  • conductive agents include carbon black, conductive fibers, carbon fluoride, and organic conductive materials. These may be used alone or in combination of two or more.
  • thickeners include carboxymethyl cellulose (CMC), polyvinyl alcohol, and the like. These may be used alone or in combination of two or more.
  • dispersion media examples include water, alcohol, ether, N-methyl-2-pyrrolidone (NMP), and mixtures of these.
  • the positive electrode includes, for example, 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 can be formed by applying a positive electrode slurry in which the positive electrode mixture is dispersed in a dispersion medium to the surface of the positive electrode current collector and drying it. The coating film after drying may be rolled as necessary.
  • the positive electrode mixture layer may be formed on one surface or both surfaces of the positive electrode current collector.
  • the positive electrode mixture contains a positive electrode active material as an essential component, and can contain optional components such as a binder and a conductive agent.
  • a lithium transition metal composite oxide can be used as the positive electrode active material.
  • the lithium transition metal composite oxide include LiaCoO2, LiaNiO2 , LiaMnO2 , LiaCobNi1 - bO2 , LiaCobM1 -bOc, LiaNi1-bMbOc, LiaMn2O4, LiaMn2-bMbO4 , LiMePO4 , and Li2MePO4F .
  • M is at least one selected from the group consisting of Na, Mg, Sc , Y , Mn , Fe, Co , Ni, Cu , Zn, Al , Cr, Pb, Sb , and B.
  • Me contains at least a transition element (e.g., contains at least one selected from the group consisting of Mn, Fe, Co, and Ni), where 0 ⁇ a ⁇ 1.2, 0 ⁇ b ⁇ 0.9, and 2.0 ⁇ c ⁇ 2.3.
  • the value a which indicates the molar ratio of lithium, increases or decreases with charge and discharge.
  • binder and conductive agent the same ones as those exemplified for the negative electrode can be used.
  • conductive agent graphite such as natural graphite or artificial graphite can be used.
  • the shape and thickness of the positive electrode current collector can be selected from the same shape and range as the negative electrode current collector.
  • Examples of materials for the positive electrode current collector include stainless steel, aluminum, aluminum alloy, and titanium.
  • the electrolyte may be a liquid electrolyte (electrolytic solution), a gel electrolyte, or a solid electrolyte.
  • the liquid electrolyte is, for example, an electrolytic solution containing a non-aqueous solvent and a salt dissolved in the non-aqueous solvent.
  • the concentration of the salt in the electrolytic solution is, for example, 0.5 mol/L or more and 2 mol/L or less.
  • the electrolytic solution may contain a known additive.
  • the gel electrolyte contains a salt and a matrix polymer, or a salt, a non-aqueous solvent, and a matrix polymer.
  • a matrix polymer for example, a polymer material that absorbs the non-aqueous solvent and gels is used. Examples of the polymer material include fluororesin, acrylic resin, polyether resin, and polyethylene oxide.
  • solid electrolyte for example, a material known in all-solid-state lithium-ion secondary batteries (e.g., oxide-based solid electrolyte, sulfide-based solid electrolyte, halide-based solid electrolyte, etc.) is used.
  • oxide-based solid electrolyte e.g., oxide-based solid electrolyte, sulfide-based solid electrolyte, halide-based solid electrolyte, etc.
  • a liquid non-aqueous electrolyte is prepared by dissolving a salt in a non-aqueous solvent.
  • the salt is an electrolyte salt that ionizes in the electrolyte, and may include, for example, a lithium salt.
  • the electrolyte may include various additives.
  • the electrolyte is usually used in liquid form, but may also have its fluidity restricted by a gelling agent or the like.
  • non-aqueous solvents examples include cyclic carbonates, chain carbonates, cyclic carboxylates, and chain carboxylates.
  • cyclic carbonates examples include propylene carbonate (PC), ethylene carbonate (EC), and vinylene carbonate (VC).
  • chain carbonates include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC).
  • cyclic carboxylates include ⁇ -butyrolactone (GBL), and ⁇ -valerolactone (GVL).
  • chain carboxylates examples include methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate (EP).
  • the non-aqueous solvents may be used alone or in combination of two or more.
  • non-aqueous solvents include cyclic ethers, chain ethers, nitriles such as acetonitrile, and amides such as dimethylformamide.
  • lithium salts of chlorine-containing acids LiClO4 , LiAlCl4 , LiB10Cl10 , etc.
  • lithium salts of fluorine-containing acids LiPF6 , LiBF4 , LiSbF6 , LiAsF6, LiCF3SO3 , LiCF3CO2 , etc.
  • lithium salts of fluorine- containing acid imides LiN( CF3SO2 ) 2 , LiN( CF3SO2 ) (C4F9SO2 ), LiN( C2F5SO2 ) 2 , etc. )
  • lithium halides LiCl, LiBr , LiI, etc.
  • the lithium salts may be used alone or in combination of two or more.
  • the concentration of the lithium salt in the electrolyte may be 1 mol/liter or more and 2 mol/liter or less, or may be 1 mol/liter or more and 1.5 mol/liter or less.
  • the lithium salt concentration is not limited to the above.
  • the separator has high ion permeability and has appropriate mechanical strength and insulation properties.
  • a microporous thin film, a woven fabric, a nonwoven fabric, etc. can be used.
  • a polyolefin such as polypropylene or polyethylene can be used.
  • a secondary battery is a structure in which an electrode group formed by winding a positive electrode and a negative electrode with a separator interposed therebetween, and a non-aqueous electrolyte are housed in an exterior body.
  • an electrode group formed by winding a positive electrode and a negative electrode with a separator interposed therebetween, and a non-aqueous electrolyte are housed in an exterior body.
  • other types of electrode groups may be used, such as a stacked type electrode group formed by stacking a positive electrode and a negative electrode with a separator interposed therebetween.
  • the secondary battery may be in any type, such as a cylindrical type, a square type, a coin type, a button type, a laminate type, etc.
  • FIG. 2 is a schematic perspective view of a secondary battery according to an embodiment of the present disclosure with a portion cut away.
  • the battery comprises a bottomed rectangular battery case 4, and an electrode group 1 and a non-aqueous electrolyte (not shown) housed within the battery case 4.
  • the electrode group 1 has a long strip-shaped negative electrode, a long strip-shaped positive electrode, and a separator interposed between them to prevent direct contact.
  • the electrode group 1 is formed by winding the negative electrode, positive electrode, and separator around a flat winding core and then removing the winding core.
  • One end of the negative electrode lead 3 is attached to the negative electrode collector by welding or the like.
  • the other end of the negative electrode lead 3 is electrically connected to the negative electrode terminal 6 provided on the sealing plate 5 via a resin insulating plate (not shown).
  • the negative electrode terminal 6 is insulated from the sealing plate 5 by a resin gasket 7.
  • One end of the positive electrode lead 2 is attached to the positive electrode collector by welding or the like.
  • the other end of the positive electrode lead 2 is connected to the back surface of the sealing plate 5 via an insulating plate.
  • the positive electrode lead 2 is electrically connected to the battery case 4, which also serves as the positive electrode terminal.
  • the insulating plate separates the electrode group 1 from the sealing plate 5 and separates the negative electrode lead 3 from the battery case 4.
  • the periphery of the sealing plate 5 fits into the open end of the battery case 4, and the fitting portion is laser welded. In this way, the opening of the battery case 4 is sealed with the sealing plate 5.
  • the non-aqueous electrolyte injection hole provided in the sealing plate 5 is blocked by a plug 8.
  • the concentration of the element A1 at a depth of 100 nm from the surface of the silicon-containing particle is X% by mass, When the concentration of the element A1 in the entire silicon-containing particle is Y mass%, 3.
  • the silicon-containing particles contain element A2, The element A2 is at least one selected from the group consisting of aluminum, boron, bismuth, antimony, germanium, zirconium, titanium, phosphorus, vanadium, tungsten, and lanthanum.
  • the content of the element A2 in the silicon-containing particle is 0.01 mass% or more with respect to the entirety of the silicon-containing particle.
  • the content of the silicon phase in the silicon-containing particles is 30 mass% or more and 90 mass% or less with respect to the whole of the silicon-containing particles.
  • the negative electrode active material for a secondary battery according to any one of claims 1 to 10, wherein at least one selected from the group consisting of Li 2 CO 3 , Li 2 O, and LiOH is attached to the surface of the silicon-containing particle.
  • the negative electrode of the secondary battery includes the negative electrode active material for the secondary battery according to any one of Techniques 1 to 11.
  • the negative electrode comprises a negative electrode mixture layer containing the negative electrode active material for secondary batteries, and a negative electrode current collector supporting the negative electrode mixture layer,
  • the secondary battery according to claim 12, wherein the content of the silicon-containing particles in the negative electrode mixture layer is 1 mass % or more and 50 mass % or less with respect to the entire negative electrode mixture layer.
  • Example 1 Preparation of silicon oxide phase-containing composite particles SiO2 and Si particles were mixed and heated under vacuum conditions to obtain vapor, which was then solidified. In this manner, SiOx particles (composite particles containing silicon oxide phase) were produced. At this time, aluminum metal and boron compounds were added to the mixture of SiO2 and Si particles, which was the sublimation source, to allow the SiOx particles (silicon oxide phase) to contain aluminum and boron.
  • the crystallite size of the silicon phase was 6 nm.
  • the main component of the silicon oxide phase was SiO 2.
  • the content of the silicon phase in the silicon oxide phase-containing composite particles was 51 mass%.
  • the contents of Li, Na, K, Al, and B in the composite particles were the values shown in Table 1.
  • the particle size of the SiO x particles and the time of introducing the SiO x particles into the melt were appropriately adjusted to set the X/Y ratio of the K concentration to 6.
  • the concentration X was obtained by the above-mentioned XPS method, and the concentration Y was obtained by the above-mentioned ICP emission spectroscopy.
  • the concentration X was obtained from the atomic ratio data obtained by the XPS method.
  • Graphite and composite particles having a conductive layer were mixed in a mass ratio of 90:10 and used as a negative electrode active material.
  • 1 part by mass of carboxymethyl cellulose (CMC) and 1.5 parts by mass of styrene butadiene rubber (SBR) were added to 97.5 parts by mass of the negative electrode active material, and a predetermined amount of water was further added to prepare a negative electrode slurry.
  • CMC carboxymethyl cellulose
  • SBR styrene butadiene rubber
  • the negative electrode slurry was applied to both sides of the copper foil negative electrode current collector, the coating was dried, rolled, and then cut to a specified size to obtain a negative electrode with a negative electrode mixture layer formed on both sides of the negative electrode current collector. At this time, a negative electrode current collector exposed portion was provided on part of the negative electrode.
  • a positive electrode slurry was prepared by adding 2.5 parts by mass of acetylene black and 2.5 parts by mass of polyvinylidene fluoride to 95 parts by mass of the positive electrode active material, and further adding an appropriate amount of N-methyl-2- pyrrolidone ( NMP ) .
  • the positive electrode active material used was a lithium transition metal composite oxide represented by LiNi0.88Co0.09Al0.03O2 .
  • the positive electrode slurry was applied to both sides of the aluminum foil positive electrode current collector, the coating was dried, rolled, and then cut to a specified size to obtain a positive electrode with a positive electrode mixture layer formed on both sides of the positive electrode current collector. At this time, a positive electrode current collector exposed portion was provided on part of the positive electrode.
  • Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 20:5:75 to obtain a mixed solvent.
  • Lithium hexafluorophosphate was dissolved in the mixed solvent at a concentration of 1 mol/L to prepare a nonaqueous electrolyte.
  • the negative electrode and lithium metal foil (counter electrode) prepared above were prepared. Leads were attached to the negative electrode (negative electrode current collector exposed portion) and the lithium metal foil.
  • the negative electrode and the lithium metal foil were spirally wound with a polyolefin separator interposed therebetween, and then pressed in the radial direction to prepare a flat electrode body. A polyolefin microporous film was used as the separator.
  • the electrode body was housed in an exterior body made of an aluminum laminate sheet, and after the nonaqueous electrolyte was injected, the opening of the exterior body was sealed. At this time, a part of the leads attached to the negative electrode and the counter electrode were exposed from the exterior body. In this way, a test cell e1 was obtained.
  • the test cell was prepared under an argon atmosphere.
  • the positive and negative electrodes prepared as described above were prepared. Leads were attached to the exposed current collectors of the positive and negative electrodes, respectively.
  • the positive and negative electrodes were spirally wound with a polyolefin separator interposed therebetween, and then pressed in the radial direction to prepare a flat electrode body. A polyolefin microporous film was used as the separator.
  • the electrode body was housed in an exterior body made of an aluminum laminate sheet, and after a non-aqueous electrolyte was injected, the opening of the exterior body was sealed. At this time, a part of the leads attached to the positive and negative electrodes were exposed from the exterior body. In this way, a secondary battery E1 for evaluation was obtained.
  • Example 2 A test cell e2 and a secondary battery E2 were produced and evaluated in the same manner as in Example 1, except that the silicon oxide phase-containing composite particles to which Li and element A1 (K and Na) were added were further heat-treated at 800° C. for 5 hours in an inert atmosphere.
  • the crystallite size of the silicon phase was 6 nm.
  • the X/Y ratio of the K concentration was set to 18 by appropriately adjusting the time for which the silicon oxide phase-containing composite particles were added to the melt.
  • Example 3 The same silicon oxide phase-containing composite particles as in Example 1 were prepared. In an inert atmosphere, a mixture of Li2CO3 and MgCO3 was heated to 500°C to melt, and the silicon oxide phase-containing composite particles were added to the melt. In this way, a large amount of Li and element A1 (Mg) was added to the surface side of the silicon oxide phase-containing composite particles.
  • the contents of Li, Mg, Al, and B in the composite particles were the values shown in Table 1.
  • the particle size of the SiO x particles and the time of introducing the SiO x particles into the melt were appropriately adjusted to set the X/Y ratio of the Mg concentration to 20.
  • the silicon oxide phase-containing composite particles to which Li and element A1 (Mg) were added were subjected to heat treatment in an inert atmosphere at a specified temperature and time.
  • the crystallite size of the silicon phase was 13 nm.
  • test cell e3 and a secondary battery E3 were produced and evaluated in the same manner as in Example 1, except that the composite particles produced above were used.
  • Examples 4 and 5 Preparation of Lithium Silicate Phase-Containing Composite Particles
  • Li 2 CO 3 lithium carbonate
  • SiO 2 silicon dioxide
  • a raw material containing element A2 silicon dioxide
  • the mixture was obtained so that the atomic ratio of Li to Si: Si/Li was 1.05.
  • Aluminum oxide (Al 2 O 3 ) and boron oxide (B 2 O 3 ) were used as raw materials containing element A2.
  • the mixture was fired at 800° C. for 10 hours in an inert gas atmosphere to obtain lithium silicate containing Al and B.
  • the obtained lithium silicate was pulverized to an average particle size of 10 ⁇ m.
  • the ground lithium silicate containing Al and B was mixed with raw silicon (3N, average particle size 10 ⁇ m) in a mass ratio of 40:60.
  • the mixture was loaded into a pot (SUS, volume: 500 mL) of a planetary ball mill (Fritsch, P-5).
  • SUS planetary ball mill
  • 24 SUS balls were placed in the pot, the lid was closed, and the mixture was ground at 200 rpm for 50 hours in an inert atmosphere.
  • the powder mixture was then removed from the inert atmosphere and sintered at 600°C for 4 hours in an inert atmosphere while applying pressure from a hot press machine, to obtain a sintered body of the mixture.
  • the obtained sintered body of the mixture was pulverized and passed through a 40 ⁇ m mesh to obtain composite particles (composite particles containing a lithium silicate phase). After that, a sieve was used to obtain composite particles with an average particle size of 10 ⁇ m.
  • the crystallite size of the silicon phase was 50 nm.
  • the main component of the silicate phase was Li 2 Si 2 O 5 , and the content of the silicon phase in the lithium silicate phase-containing composite particles was about 60 mass %.
  • the contents of Li, Na, K, Al, and B in the composite particles were the values shown in Table 1.
  • the particle size of the composite particles and the time of adding the composite particles to the melt were appropriately adjusted to set the X/Y ratio of the K concentration to 3.
  • test cells e4 to e5 and secondary batteries E4 to E5 were prepared and evaluated in the same manner as in Example 1.
  • Comparative Example 1 The silicon oxide phase of the composite particles did not contain Al and B. Lithium and element A1 were not added to the composite particles. Except for the above, a test cell r1 and a secondary battery R1 were produced in the same manner as in Example 1 and evaluated.
  • Comparative Example 2 A test cell r2 and a secondary battery R2 were produced and evaluated in the same manner as in Example 1, except that lithium and element A1 were not added to the composite particles.
  • Comparative Example 3 A test cell r3 and a secondary battery R3 were produced and evaluated in the same manner as in Example 1, except that element A1 was not added to the composite particles.
  • Comparative Examples 4 and 5 A mixture was obtained by mixing lithium carbonate (Li 2 CO 3 ) as a Li raw material, silicon dioxide (SiO 2 ) as a Si raw material, a raw material containing element A1, and a raw material containing element A2. The mixture was obtained so that the atomic ratio of Li to Si: Si/Li was 1.05. Sodium carbonate (Na 2 CO 3 ) and potassium carbonate (K 2 CO 3 ) were used as raw materials containing element A1. Aluminum oxide (Al 2 O 3 ) and boron oxide (B 2 O 3 ) were used as raw materials containing element A2. The mixture was fired at 800° C. for 10 hours in an inert gas atmosphere to obtain lithium silicate containing Na, K, Al, and B.
  • Composite particles containing a lithium silicate phase were prepared in the same manner as in Example 3, except that lithium silicate containing Na, K, Al, and B was used instead of lithium silicate containing Al and B.
  • the contents of Li, Na, K, Al, and B in the composite particles were as shown in Table 1.
  • element A1 Na and K
  • the X/Y ratio of the K concentration in the obtained composite particle was 1.
  • the X/Y ratio of the Na concentration was also 1.
  • test cells r4 to r5 and secondary batteries R4 to R5 were prepared and evaluated in the same manner as in Example 1.
  • Table 1 also shows the X/Y ratio of the K or Mg concentration.
  • E1 (e1) to E2 (e2), E4 (e4) to E5 (e5), and R4 (r4) to R5 (r5) the composite particles contained K and Na as element A1, but the X/Y ratio of the Na concentration was the same as the X/Y ratio of the K concentration.
  • the contents of Li, Na, K, Al, and B in the composite particles in Table 1 represent the mass ratio to the entire composite particles produced.
  • the reactivity of the composite particles was high, and the rate characteristics were improved (e1 to e5).
  • cracking of the composite particles was suppressed, and the deterioration of cycle characteristics due to particle cracking was suppressed (E1 to E5).
  • the reactivity of the composite particles was low, and the rate characteristics were deteriorated (r1 to r5).
  • the secondary battery disclosed herein is useful as a main power source for mobile communication devices, portable electronic devices, etc.

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2009016245A (ja) * 2007-07-06 2009-01-22 Sony Corp 負極材料、負極および電池、ならびにそれらの製造方法
WO2022044454A1 (ja) * 2020-08-27 2022-03-03 パナソニックＩｐマネジメント株式会社 非水電解質二次電池用負極材料および非水電解質二次電池
WO2022059340A1 (ja) * 2020-09-18 2022-03-24 株式会社村田製作所 二次電池用負極活物質、二次電池用負極および二次電池

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2009016245A (ja) * 2007-07-06 2009-01-22 Sony Corp 負極材料、負極および電池、ならびにそれらの製造方法
WO2022044454A1 (ja) * 2020-08-27 2022-03-03 パナソニックＩｐマネジメント株式会社 非水電解質二次電池用負極材料および非水電解質二次電池
WO2022059340A1 (ja) * 2020-09-18 2022-03-24 株式会社村田製作所 二次電池用負極活物質、二次電池用負極および二次電池

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