WO2017085908A1 - 負極活物質、混合負極活物質材料、非水電解質二次電池用負極、リチウムイオン二次電池、負極活物質の製造方法、及びリチウムイオン二次電池の製造方法 - Google Patents
負極活物質、混合負極活物質材料、非水電解質二次電池用負極、リチウムイオン二次電池、負極活物質の製造方法、及びリチウムイオン二次電池の製造方法 Download PDFInfo
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Definitions
- the present invention relates to a negative electrode active material, a mixed negative electrode active material, a negative electrode for a non-aqueous electrolyte secondary battery, a lithium ion secondary battery, a method for producing a negative electrode active material, and a method for producing a lithium ion secondary battery.
- This secondary battery is not limited to a small electronic device, but is also considered to be applied to a large-sized electronic device represented by an automobile or the like, or an electric power storage system represented by a house.
- lithium ion secondary batteries are highly expected because they are small in size and easy to increase in capacity, and can obtain higher energy density than lead batteries and nickel cadmium batteries.
- the above lithium ion secondary battery includes a positive electrode, a negative electrode, and a separator together with an electrolyte, and the negative electrode includes a negative electrode active material involved in a charge / discharge reaction.
- the negative electrode active material As the negative electrode active material, a carbon material is widely used, but further improvement in battery capacity is required due to recent market demand.
- silicon As a negative electrode active material, use of silicon as a negative electrode active material has been studied. This is because the theoretical capacity of silicon (4199 mAh / g) is 10 times or more larger than the theoretical capacity of graphite (372 mAh / g), so that significant improvement in battery capacity can be expected.
- the development of a siliceous material as a negative electrode active material has been examined not only for silicon itself but also for compounds represented by alloys and oxides.
- the shape of the active material has been studied from a standard coating type for carbon materials to an integrated type directly deposited on a current collector.
- the negative electrode active material when silicon is used as the negative electrode active material as the main raw material, the negative electrode active material expands and contracts during charge / discharge, and therefore, it tends to break mainly near the surface of the negative electrode active material. Further, an ionic material is generated inside the active material, and the negative electrode active material is easily broken. When the negative electrode active material surface layer is cracked, a new surface is generated thereby increasing the reaction area of the active material. At this time, a decomposition reaction of the electrolytic solution occurs on the new surface, and a coating that is a decomposition product of the electrolytic solution is formed on the new surface, so that the electrolytic solution is consumed. For this reason, the cycle characteristics are likely to deteriorate.
- silicon and amorphous silicon dioxide are simultaneously deposited using a vapor phase method (see, for example, Patent Document 1). Further, in order to obtain a high battery capacity and safety, a carbon material (electron conductive material) is provided on the surface layer of the silicon oxide particles (see, for example, Patent Document 2). Furthermore, in order to improve cycle characteristics and obtain high input / output characteristics, an active material containing silicon and oxygen is produced, and an active material layer having a high oxygen ratio in the vicinity of the current collector is formed ( For example, see Patent Document 3). Further, in order to improve cycle characteristics, oxygen is contained in the silicon active material, the average oxygen content is 40 at% or less, and the oxygen content is increased at a location close to the current collector. (For example, refer to Patent Document 4).
- Si phase (for example, see Patent Document 5) by using a nanocomposite containing SiO 2, M y O metal oxide in order to improve the initial charge and discharge efficiency.
- the molar ratio of oxygen to silicon in the negative electrode active material is set to 0.1 to 1.2, and the difference between the maximum and minimum molar ratios in the vicinity of the active material and current collector interface The active material is controlled within a range of 0.4 or less (see, for example, Patent Document 7).
- Patent Document 8 a metal oxide containing lithium is used (see, for example, Patent Document 8).
- a hydrophobic layer such as a silane compound is formed on the surface layer of the siliceous material (see, for example, Patent Document 9).
- conductivity is imparted by using silicon oxide and forming a graphite film on the surface layer (see, for example, Patent Document 10).
- Patent Document 10 with respect to the shift value obtained from the Raman spectra for graphite coating, with broad peaks appearing at 1330 cm -1 and 1580 cm -1, their intensity ratio I 1330 / I 1580 is 1.5 ⁇ I 1330 / I 1580 ⁇ 3.
- particles having a silicon microcrystalline phase dispersed in silicon dioxide are used in order to improve high battery capacity and cycle characteristics (see, for example, Patent Document 11). Further, in order to improve overcharge and overdischarge characteristics, silicon oxide in which the atomic ratio of silicon and oxygen is controlled to 1: y (0 ⁇ y ⁇ 2) is used (see, for example, Patent Document 12).
- lithium ion secondary batteries which are the main power sources, are required to have an increased battery capacity.
- development of a lithium ion secondary battery including a negative electrode using a silicon-based active material as a main material is desired.
- a lithium ion secondary battery using a silicon-based active material is desired to have initial efficiency and cycle characteristics that are similar to those of a lithium ion secondary battery using a carbon-based active material.
- a negative electrode active material that exhibits the same initial efficiency and cycle stability as a lithium ion secondary battery using a carbon-based active material has not been proposed.
- the present invention has been made in view of the above problems, and when used as a negative electrode active material of a lithium ion secondary battery, it can increase battery capacity and improve cycle characteristics and initial charge / discharge characteristics.
- An object of the present invention is to provide a possible negative electrode active material, a mixed negative electrode active material containing this negative electrode active material, a negative electrode for a non-aqueous electrolyte secondary battery containing this mixed negative electrode active material, and a lithium ion secondary battery.
- Another object of the present invention is to provide a method for producing a negative electrode active material excellent in battery characteristics as described above and a method for producing a lithium ion secondary battery.
- the present invention provides a negative electrode active material including negative electrode active material particles, wherein the negative electrode active material particles include a silicon compound (SiO x : 0.5 ⁇ x ⁇ 1.6).
- a silicon compound particle is contained, and the silicon compound particle has a peak derived from amorphous silicon (also referred to as a-Si) obtained at ⁇ 40 to ⁇ 60 ppm as a chemical shift value obtained from a 29 Si-MAS-NMR spectrum. That the intensity A of the peak derived from silicon dioxide obtained in the vicinity of ⁇ 110 ppm and the intensity C of the peak derived from Si obtained in the vicinity of ⁇ 83 ppm satisfy the following formulas 1 and 2.
- a negative electrode active material is provided.
- the irreversible component generated by the reaction of a part of the silicon dioxide with lithium is charged when the battery is charged. Since it can fully reduce, it becomes a negative electrode active material which has high battery initial stage efficiency.
- Equation 2 that is, when the silicon dioxide component is sufficiently small with respect to the Si component, the irreversible component generated during battery charging can be further reduced as described above, so that a higher battery. A negative electrode active material having initial efficiency is obtained. Therefore, the negative electrode active material of the present invention has a large battery capacity and can improve initial efficiency and cycle characteristics.
- the negative electrode active material particles preferably include at least one of Li 2 SiO 3 and Li 4 SiO 4 .
- Such a negative electrode active material is obtained by modifying a SiO 2 component part, which is destabilized during insertion / extraction of lithium during charging / discharging of a battery, into a relatively stable lithium silicate in advance. Therefore, the irreversible capacity generated during charging can be reduced.
- the chemical shift value obtained from the 29 Si-MAS-NMR spectrum has a peak in the vicinity of -130 ppm.
- the peak where the chemical shift value appears in the vicinity of ⁇ 130 ppm is considered to be derived from amorphous silicon. Therefore, since the ratio of the amorphous silicon component is larger, the initial efficiency and cycle characteristics can be further improved.
- the silicon compound particles have a half-value width (2 ⁇ ) of a diffraction peak caused by an Si (111) crystal plane obtained by X-ray diffraction of 1.2 ° or more and a crystallite size corresponding to the crystal plane. Is preferably 7.5 nm or less.
- the negative electrode active material in which the silicon compound particles have the above-described silicon crystallinity is used as the negative electrode active material of the lithium ion secondary battery, better cycle characteristics and initial charge / discharge characteristics can be obtained.
- a test cell comprising a negative electrode containing a mixture of the negative electrode active material and the carbon-based active material and counter lithium is prepared, and in the test cell, charging is performed such that current is inserted so that lithium is inserted into the negative electrode active material.
- 30 times of charge / discharge consisting of discharge through which current flows so as to desorb lithium from the negative electrode active material, and the discharge capacity Q in each charge / discharge is differentiated by the potential V of the negative electrode with respect to the counter lithium.
- the above-mentioned peak in the V-dQ / dV curve is similar to the peak of the siliceous material, and the discharge curve on the higher potential side rises sharply, so that the capacity is easily developed when designing the battery. Moreover, if the said peak expresses by charge / discharge within 30 times, it will become a negative electrode active material in which a stable bulk is formed.
- the negative electrode active material particles preferably have a median diameter of 1.0 ⁇ m to 15 ⁇ m.
- the median diameter is 1.0 ⁇ m or more, an increase in battery irreversible capacity due to an increase in surface area per mass can be suppressed.
- the median diameter is set to 15 ⁇ m or less, the particles are difficult to break and a new surface is difficult to appear.
- the negative electrode active material particles preferably include a carbon material in the surface layer portion.
- the conductivity can be improved.
- the average thickness of the carbon material is preferably 10 nm or more and 5000 nm or less.
- the average thickness of the carbon material is 10 nm or more, conductivity can be improved. Moreover, if the average thickness of the carbon material to be coated is 5000 nm or less, a sufficient amount of silicon compound particles can be secured by using a negative electrode active material including such negative electrode active material particles in a lithium ion secondary battery. , Battery capacity reduction can be suppressed.
- a mixed negative electrode active material comprising the above negative electrode active material and a carbon-based active material.
- the conductivity of the negative electrode active material layer can be improved by including the carbon-based active material together with the negative electrode active material (silicon-based negative electrode active material) of the present invention.
- the expansion stress associated with charging can be relaxed.
- the battery capacity can be increased by mixing the silicon negative electrode active material with the carbon active material.
- the present invention includes the above mixed negative electrode active material, and the ratio of the mass of the negative electrode active material to the total mass of the negative electrode active material and the carbon-based active material is 6
- a negative electrode for a non-aqueous electrolyte secondary battery characterized by being at least mass%.
- the ratio of the mass of the negative electrode active material (silicon-based negative electrode active material) to the total mass of the negative electrode active material (silicon-based negative electrode active material) and the carbon-based active material is 6% by mass or more, the battery capacity is further increased. It becomes possible to improve.
- the present invention includes a negative electrode active material layer formed of the above mixed negative electrode active material and a negative electrode current collector, and the negative electrode active material layer includes the negative electrode current collector.
- a negative electrode for a nonaqueous electrolyte secondary battery wherein the negative electrode current collector contains carbon and sulfur, and the content thereof is 70 ppm by mass or less.
- the negative electrode current collector constituting the negative electrode includes carbon and sulfur in the above amounts, deformation of the negative electrode during charging can be suppressed.
- the present invention provides a lithium ion secondary battery using a negative electrode containing the above negative electrode active material.
- a lithium ion secondary battery using a negative electrode containing such a negative electrode active material has high capacity and good cycle characteristics and initial charge / discharge characteristics.
- the present invention provides a method for producing a negative electrode active material including negative electrode active material particles containing silicon compound particles, wherein the silicon compound (SiO x : 0.5 ⁇ x ⁇ 1). .6), and a chemical shift value obtained from the 29 Si-MAS-NMR spectrum is obtained at ⁇ 40 to ⁇ 60 ppm from the negative electrode active material particles.
- the peak intensity A derived from amorphous silicon, the peak intensity B derived from the silicon dioxide region obtained in the vicinity of ⁇ 110 ppm, and the peak intensity C derived from Si obtained in the vicinity of ⁇ 83 ppm are expressed by the following formulas 1 and A negative active material, wherein a negative electrode active material is produced using the selected negative electrode active material particles.
- the negative electrode active material By selecting the silicon-based active material particles in this way to produce the negative electrode active material, the high capacity and good cycle characteristics and initial charge / discharge characteristics when used as the negative electrode active material of a lithium ion secondary battery
- the negative electrode active material which has can be manufactured.
- the present invention produces a negative electrode using the negative electrode active material produced by the method for producing a negative electrode active material, and produces a lithium ion secondary battery using the produced negative electrode.
- a method for manufacturing a lithium ion secondary battery is provided.
- the negative electrode active material of the present invention When the negative electrode active material of the present invention is used as a negative electrode active material for a secondary battery, a high capacity and good cycle characteristics and initial charge / discharge characteristics can be obtained. Moreover, the same effect is acquired also in the mixed negative electrode active material material containing this negative electrode active material, a negative electrode, and a lithium ion secondary battery. Moreover, if it is a manufacturing method of the negative electrode active material of this invention, when it uses as a negative electrode active material of a secondary battery, the negative electrode active material which has a favorable cycling characteristic and an initial stage charge / discharge characteristic can be manufactured.
- FIG. 1 It is sectional drawing which shows the structure of the negative electrode for lithium ion secondary batteries of this invention. It is a figure showing the structural example (laminate film type) of the lithium secondary battery of this invention. It is an example of a spectrum obtained when SiOx containing amorphous silicon is measured using 29 Si-MAS-NMR. It is a 29 Si-MAS-NMR spectrum measured in Example 1-1, Comparative example 1-1, and Comparative example 1-2. 7 is a graph showing an increase rate of battery capacity in Example 7-1 and Comparative Example 7-2.
- Lithium ion secondary batteries using silicon-based active materials are expected to have initial charge / discharge characteristics and cycle characteristics similar to those of lithium-ion secondary batteries using carbon-based active materials.
- a silicon-based active material that exhibits the same initial efficiency and cycle stability as the lithium ion secondary battery used has not been proposed.
- the inventors of the present invention have made extensive studies in order to obtain a negative electrode active material that has a high battery capacity and good cycle characteristics and initial efficiency when used in a secondary battery, and has reached the present invention.
- the negative electrode active material of the present invention includes negative electrode active material particles.
- the negative electrode active material particles contain silicon compound particles containing a silicon compound (SiO x : 0.5 ⁇ x ⁇ 1.6).
- the silicon compound particles have a chemical shift value obtained from the 29 Si-MAS-NMR spectrum, peak intensity A derived from amorphous silicon obtained at ⁇ 40 to ⁇ 60 ppm, and silicon dioxide obtained at around ⁇ 110 ppm.
- the peak intensity B and the peak intensity C derived from Si obtained in the vicinity of ⁇ 83 ppm satisfy the following formulas 1 and 2.
- the negative electrode active material of the present invention since the silicon dioxide component is small with respect to the amorphous silicon component, generation of Si—Li can be suppressed, and the stability of the negative electrode active material with respect to an aqueous slurry or the like during electrode production is improved. . As a result, a negative electrode active material having good cycle characteristics when a secondary battery is obtained.
- the formula 2 that is, in the silicon compound particles, if the silicon dioxide component is sufficiently small with respect to the Si component, the negative electrode active material having higher battery initial efficiency is obtained as described above.
- the peak derived from amorphous silicon is a gentle peak in the region where the chemical shift value of the 29 Si-MAS-NMR spectrum is ⁇ 40 to ⁇ 60 ppm. appear.
- the peak obtained in the vicinity of ⁇ 130 ppm is presumed to be derived from amorphous silicon. It also has a peak around ⁇ 83 ppm.
- the negative electrode active material particles in the present invention preferably have a peak around ⁇ 130 ppm as a chemical shift value obtained from a 29 Si-MAS-NMR spectrum. In such a case, since the ratio of the amorphous silicon component is larger, initial efficiency and cycle characteristics can be further improved.
- the region of ⁇ 40 to ⁇ 60 ppm derived from amorphous silicon clearly has a gradual peak, but may not have a maximum value.
- the peak intensity A is the maximum value of the spectrum intensity in the range of ⁇ 40 to ⁇ 60 ppm.
- the peak around ⁇ 110 ppm derived from silicon dioxide may not have the maximum value, but in this case, the peak intensity B is the intensity at ⁇ 110 ppm.
- FIG. 1 shows a cross-sectional configuration of a negative electrode for a nonaqueous electrolyte secondary battery (hereinafter also referred to as “negative electrode”) according to an embodiment of the present invention.
- the negative electrode 10 is configured to have a negative electrode active material layer 12 on a negative electrode current collector 11.
- the negative electrode active material layer 12 may be provided on both surfaces or only one surface of the negative electrode current collector 11. Furthermore, the negative electrode current collector 11 may be omitted as long as the negative electrode active material of the present invention is used.
- the negative electrode current collector 11 is an excellent conductive material and is made of a material that is excellent in mechanical strength.
- Examples of the conductive material that can be used for the negative electrode current collector 11 include copper (Cu) and nickel (Ni). This conductive material is preferably a material that does not form an intermetallic compound with lithium (Li).
- the negative electrode current collector 11 preferably contains carbon (C) or sulfur (S) in addition to the main element. This is because the physical strength of the negative electrode current collector is improved.
- the current collector contains the above-described element, there is an effect of suppressing electrode deformation including the current collector.
- content of said content element is not specifically limited, Especially, it is preferable that it is 70 mass ppm or less, respectively. This is because a higher deformation suppressing effect can be obtained. Such a deformation suppressing effect can further improve the cycle characteristics.
- the surface of the negative electrode current collector 11 may be roughened or may not be roughened.
- the roughened negative electrode current collector is, for example, a metal foil subjected to electrolytic treatment, embossing treatment, or chemical etching treatment.
- the non-roughened negative electrode current collector is, for example, a rolled metal foil.
- the negative electrode active material layer 12 contains the negative electrode active material of the present invention capable of occluding and releasing lithium ions, and from the viewpoint of battery design, further, other materials such as a negative electrode binder (binder) and a conductive aid. May be included.
- the negative electrode active material includes negative electrode active material particles, and the negative electrode active material particles include silicon compound particles containing a silicon compound (SiO x : 0.5 ⁇ x ⁇ 1.6).
- the negative electrode active material layer 12 may include a mixed negative electrode active material containing the negative electrode active material (silicon-based negative electrode active material) of the present invention and a carbon-based active material.
- the carbon-based active material include pyrolytic carbons, cokes, glassy carbon fibers, organic polymer compound fired bodies, carbon blacks, and the like.
- the mass ratio of the silicon-based negative electrode active material to the total mass of the silicon-based negative electrode active material and the carbon-based active material is preferably 6% by mass or more. If the ratio of the mass of the negative electrode active material of the present invention to the total mass of the silicon-based negative electrode active material and the carbon-based active material is 6% by mass or more, the battery capacity can be reliably improved.
- the negative electrode active material of the present invention contains silicon compound particles, and the silicon compound particles are a silicon oxide material containing a silicon compound (SiO x : 0.5 ⁇ x ⁇ 1.6).
- the composition is preferably such that x is close to 1. This is because high cycle characteristics can be obtained.
- the composition of the silicon compound in the present invention does not necessarily mean a purity of 100%, and may contain a trace amount of impurity elements.
- the silicon compound particles contain at least one of Li 2 SiO 3 and Li 4 SiO 4 .
- the SiO 2 component part which is destabilized at the time of charging / discharging of the battery and destabilized at the time of charging / discharging, is modified in advance to another lithium silicate. The generated irreversible capacity can be reduced.
- the battery characteristics are improved when at least one of Li 4 SiO 4 and Li 2 SiO 3 is present in the bulk of the silicon compound particles, but the battery characteristics are further improved when the two types of Li compounds are present together.
- These lithium silicates can be quantified by NMR (Nuclear Magnetic Resonance) or XPS (X-ray photoelectron spectroscopy: X-ray photoelectron spectroscopy). The XPS and NMR measurements can be performed, for example, under the following conditions.
- XPS ⁇ Device X-ray photoelectron spectrometer, ⁇ X-ray source: Monochromatic Al K ⁇ ray, ⁇ X-ray spot diameter: 100 ⁇ m, Ar ion gun sputtering conditions: 0.5 kV / 2 mm ⁇ 2 mm.
- 29 Si MAS NMR (magic angle rotating nuclear magnetic resonance) Apparatus 700 NMR spectrometer manufactured by Bruker, ⁇ Probe: 4mmHR-MAS rotor 50 ⁇ L, Sample rotation speed: 10 kHz, -Measurement environment temperature: 25 ° C.
- the silicon compound particles have a half-value width (2 ⁇ ) of a diffraction peak due to the Si (111) crystal plane obtained by X-ray diffraction of 1.2 ° or more, and the crystallite size corresponding to the crystal plane is It is preferable that it is 7.5 nm or less.
- the silicon crystallinity of the silicon compound in the silicon compound particles is preferably as low as possible. In particular, if the amount of Si crystal is small, battery characteristics can be improved, and a stable Li compound can be generated.
- the negative electrode active material particles preferably include a carbon material in the surface layer portion.
- the conductivity can be improved. Therefore, when the negative electrode active material containing such negative electrode active material particles is used as the negative electrode active material of a secondary battery. Battery characteristics can be improved.
- the average thickness of the carbon material in the surface layer portion of the negative electrode active material particles is preferably 10 nm or more and 5000 nm or less. If the average thickness of the carbon material is 10 nm or more, conductivity can be improved, and if the average thickness of the carbon material to be coated is 5000 nm or less, the negative electrode active material containing such negative electrode active material particles is converted into lithium ion When used as a negative electrode active material for a secondary battery, a decrease in battery capacity can be suppressed.
- the average thickness of the carbon material can be calculated by the following procedure, for example. First, negative electrode active material particles are observed at an arbitrary magnification using a TEM (transmission electron microscope). This magnification is preferably a magnification capable of visually confirming the thickness of the carbon material so that the thickness can be measured. Subsequently, the thickness of the carbon material is measured at any 15 points. In this case, it is preferable to set the measurement position widely and randomly without concentrating on a specific place as much as possible. Finally, the average value of the thicknesses of the 15 carbon materials is calculated.
- TEM transmission electron microscope
- the coverage of the carbon material is not particularly limited, but is preferably as high as possible. A coverage of 30% or more is preferable because electric conductivity is further improved.
- the method for coating the carbon material is not particularly limited, but a sugar carbonization method and a pyrolysis method of hydrocarbon gas are preferable. This is because the coverage can be improved.
- the median diameter (D 50 : particle diameter when the cumulative volume becomes 50%) of the negative electrode active material particles is 1.0 ⁇ m or more and 15 ⁇ m or less. This is because, if the median diameter is in the above range, lithium ions are easily occluded and released during charging and discharging, and the particles are difficult to break.
- the median diameter is 1.0 ⁇ m or more, the surface area per mass can be reduced, and an increase in battery irreversible capacity can be suppressed.
- the median diameter is set to 15 ⁇ m or less, the particles are difficult to break and a new surface is difficult to appear.
- the negative electrode active material (silicon-based active material) of the present invention is a test cell comprising a negative electrode containing a mixture of the silicon-based active material and a carbon-based active material and counter electrode lithium, and in the test cell, Charging / discharging consisting of charging in which current is inserted to insert lithium into the silicon-based active material and discharging in which current is discharged to detach lithium from the silicon-based active material is performed 30 times, and the discharge capacity Q in each charging / discharging is determined.
- the negative electrode during the Xth and subsequent discharges (1 ⁇ X ⁇ 30) It is preferable that the potential V of the electrode has a peak in the range of 0.40V to 0.55V.
- the above-mentioned peak in the V-dQ / dV curve is similar to the peak of the siliceous material, and the discharge curve on the higher potential side rises sharply, so that the capacity is easily developed when designing the battery.
- it is a negative electrode active material which the said peak expresses by charge / discharge within 30 times, it can be judged that the stable bulk is formed.
- the negative electrode binder contained in the negative electrode active material layer for example, one or more of polymer materials, synthetic rubbers and the like can be used.
- the polymer material include polyvinylidene fluoride, polyimide, polyamideimide, aramid, polyacrylic acid, lithium polyacrylate, and carboxymethylcellulose.
- the synthetic rubber include styrene butadiene rubber, fluorine rubber, and ethylene propylene diene.
- the negative electrode conductive additive for example, one or more carbon materials such as carbon black, acetylene black, graphite, ketjen black, carbon nanotube, and carbon nanofiber can be used.
- the negative electrode active material layer is formed by, for example, a coating method.
- the coating method is a method in which negative electrode active material particles and the above-mentioned binder, and the like, and a conductive additive and a carbon material are mixed as necessary, and then dispersed and applied in an organic solvent or water.
- the negative electrode can be produced, for example, by the following procedure. First, the manufacturing method of the negative electrode active material used for a negative electrode is demonstrated. First, negative electrode active material particles containing silicon compound particles containing a silicon compound (SiO x : 0.5 ⁇ x ⁇ 1.6) are prepared. Then, from the negative electrode active material particles, as the chemical shift value obtained from the 29 Si-MAS-NMR spectrum, the peak intensity A derived from amorphous silicon obtained at ⁇ 40 to ⁇ 60 ppm and the silicon dioxide obtained at around ⁇ 110 ppm Those having the peak intensity B derived from the region and the peak intensity C derived from Si obtained in the vicinity of ⁇ 83 ppm satisfy the following formulas 1 and 2. And the negative electrode active material is manufactured using the selected negative electrode active material particles. B ⁇ 1.5 ⁇ A (1) B ⁇ C (2)
- a step of coating the silicon compound particles with a carbon material may be further included.
- the negative electrode active material particles in which the surface of the silicon compound particles is coated with a carbon material are excellent in conductivity.
- this process for example, by generating lithium silicate such as Li 2 SiO 3 or Li 4 SiO 4 in the bulk, irreversible capacity generated during charging can be reduced.
- the negative electrode active material can be produced as follows. First, a raw material for generating silicon oxide gas is heated in a temperature range of 900 ° C. to 1600 ° C. under reduced pressure in the presence of an inert gas to generate silicon oxide gas. Considering the surface oxygen of the metal silicon powder and the presence of a trace amount of oxygen in the reaction furnace, the mixing molar ratio is preferably in the range of 0.8 ⁇ metal silicon powder / silicon dioxide powder ⁇ 1.3.
- the generated silicon oxide gas is solidified and deposited on the adsorption plate.
- a silicon oxide deposit is taken out in a state where the temperature in the reactor is lowered to 100 ° C. or lower, and pulverized and powdered using a ball mill, a jet mill or the like.
- silicon compound particles can be produced. Note that the Si crystallites in the silicon compound particles can be controlled by changing the vaporization temperature or by heat treatment after generation.
- a carbon material layer may be formed on the surface layer of the silicon compound particles.
- a thermal decomposition CVD method is desirable. A method for generating a carbon material layer by pyrolytic CVD will be described.
- silicon compound particles are set in a furnace.
- hydrocarbon gas is introduced into the furnace to raise the temperature in the furnace.
- the decomposition temperature is not particularly limited, but is preferably 1200 ° C. or lower, and more preferably 950 ° C. or lower. By setting the decomposition temperature to 1200 ° C. or lower, unintended disproportionation of the silicon compound particles can be suppressed.
- a carbon layer is generated on the surface of the silicon compound particles. Thereby, negative electrode active material particles can be manufactured.
- the hydrocarbon gas used as the raw material for the carbon material is not particularly limited, but it is desirable that n ⁇ 3 in the C n H m composition. If n ⁇ 3, the production cost can be reduced, and the physical properties of the decomposition product can be improved.
- the negative electrode active material particles produced as described above may be modified by inserting Li.
- the negative electrode active material particles may contain at least one of Li 2 SiO 3 and Li 4 SiO 4 .
- Li insertion is preferably performed by a redox method.
- lithium can be inserted by first immersing the negative electrode active material particles in a solution A in which lithium is dissolved in an ether solvent.
- the solution A may further contain a polycyclic aromatic compound or a linear polyphenylene compound.
- active lithium can be desorbed from the negative electrode active material particles by immersing the negative electrode active material particles in a solution B containing a polycyclic aromatic compound or a derivative thereof.
- the solvent of the solution B for example, an ether solvent, a ketone solvent, an ester solvent, an alcohol solvent, an amine solvent, or a mixed solvent thereof can be used.
- the active material lithium is further removed from the negative electrode active material particles by immersing the negative electrode active material particles in a solution C containing an alcohol solvent, a carboxylic acid solvent, water, or a mixed solvent thereof. Many can be detached.
- a solution C ′ containing a compound having a quinoid structure in the molecule as a solute and containing an ether solvent, a ketone solvent, an ester solvent, or a mixed solvent thereof as a solvent may be used.
- the immersion of the negative electrode active material particles in the solutions B, C, and C ′ may be repeated.
- the peak intensity A derived from amorphous silicon obtained at ⁇ 40 to ⁇ 60 ppm and around ⁇ 110 ppm satisfy the following formulas 1 and 2.
- 29 Si-MAS-NMR can be carried out under the following conditions.
- 29 Si MAS NMR Apparatus 700 NMR spectrometer manufactured by Bruker, ⁇ Probe: 4mmHR-MAS rotor 50 ⁇ L, Sample rotation speed: 10 kHz, -Measurement environment temperature: 25 ° C.
- the intensity of the peak is represented by the height of the peak from the baseline calculated from the 29 Si-MAS-NMR spectrum.
- the baseline can be determined by a normal method.
- the selection of the negative electrode active material particles does not necessarily have to be performed every time the negative electrode active material is produced. If the production conditions satisfying the above formulas 1 and 2 are found and selected, then the selected conditions and The negative electrode active material can be manufactured under the same conditions.
- the negative electrode active material produced as described above is mixed with other materials such as a negative electrode binder and a conductive aid to form a negative electrode mixture, and then an organic solvent or water is added to obtain a slurry. Next, the above slurry is applied to the surface of the negative electrode current collector and dried to form a negative electrode active material layer. At this time, you may perform a heat press etc. as needed. Further, if the negative electrode current collector contains 70 ppm or less of carbon and sulfur, an effect of suppressing deformation of the negative electrode can be obtained.
- a negative electrode can be produced as described above.
- the lithium ion secondary battery of the present invention uses a negative electrode containing the negative electrode active material of the present invention.
- a laminated film type lithium ion secondary battery is taken as an example.
- a laminated film type lithium ion secondary battery 20 shown in FIG. 2 is one in which a wound electrode body 21 is accommodated mainly in a sheet-like exterior member 25. This wound body has a separator between a positive electrode and a negative electrode and is wound. There is also a case where a separator is provided between the positive electrode and the negative electrode and a laminate is accommodated.
- the positive electrode lead 22 is attached to the positive electrode
- the negative electrode lead 23 is attached to the negative electrode.
- the outermost peripheral part of the electrode body is protected by a protective tape.
- the positive and negative electrode leads are led out in one direction from the inside of the exterior member 25 to the outside.
- the positive electrode lead 22 is formed of a conductive material such as aluminum
- the negative electrode lead 23 is formed of a conductive material such as nickel or copper.
- the exterior member 25 is, for example, a laminate film in which a fusion layer, a metal layer, and a surface protective layer are laminated in this order.
- This laminate film is composed of two films so that the fusion layer faces the electrode body 21.
- the outer peripheral edges of the fusion layer are bonded together with an adhesive or an adhesive.
- the fused part is, for example, a film such as polyethylene or polypropylene, and the metal part is aluminum foil or the like.
- the protective layer is, for example, nylon.
- An adhesion film 24 is inserted between the exterior member 25 and the positive and negative electrode leads to prevent intrusion of outside air.
- This material is, for example, polyethylene, polypropylene, or polyolefin resin.
- the positive electrode has, for example, a positive electrode active material layer on both sides or one side of the positive electrode current collector, similarly to the negative electrode 10 of FIG.
- the positive electrode current collector is made of, for example, a conductive material such as aluminum.
- the positive electrode active material layer includes one or more positive electrode materials capable of occluding and releasing lithium ions, and includes other materials such as a binder, a conductive additive, and a dispersant depending on the design. You can leave. In this case, details regarding the binder and the conductive additive are the same as, for example, the negative electrode binder and the negative electrode conductive additive already described.
- a lithium-containing compound is desirable.
- the lithium-containing compound include a composite oxide composed of lithium and a transition metal element, or a phosphate compound having lithium and a transition metal element.
- compounds having at least one of nickel, iron, manganese, and cobalt are preferable.
- These chemical formulas are represented by, for example, Li x M1O 2 or Li y M2PO 4 .
- M1 and M2 represent at least one or more transition metal elements.
- the values of x and y vary depending on the battery charge / discharge state, but are generally expressed as 0.05 ⁇ x ⁇ 1.10 and 0.05 ⁇ y ⁇ 1.10.
- Examples of the composite oxide having lithium and a transition metal element include lithium cobalt composite oxide (Li x CoO 2 ) and lithium nickel composite oxide (Li x NiO 2 ).
- Examples of the phosphate compound having lithium and a transition metal element include a lithium iron phosphate compound (LiFePO 4 ) or a lithium iron manganese phosphate compound (LiFe 1-u Mn u PO 4 (0 ⁇ u ⁇ 1)). Is mentioned. This is because, when these positive electrode materials are used, a high battery capacity can be obtained and excellent cycle characteristics can be obtained.
- the negative electrode has the same configuration as the above-described negative electrode 10 for a lithium ion secondary battery in FIG. 1.
- the negative electrode has negative electrode active material layers 12 on both surfaces of the current collector 11.
- the negative electrode preferably has a negative electrode charge capacity larger than the electric capacity (charge capacity as a battery) obtained from the positive electrode active material agent. This is because the deposition of lithium metal on the negative electrode can be suppressed.
- the positive electrode active material layer is provided on a part of both surfaces of the positive electrode current collector, and the negative electrode active material layer is also provided on a part of both surfaces of the negative electrode current collector.
- the negative electrode active material layer provided on the negative electrode current collector is provided with a region where there is no opposing positive electrode active material layer. This is to perform a stable battery design.
- the non-opposing region that is, the region where the negative electrode active material layer and the positive electrode active material layer are not opposed to each other, there is almost no influence of charge / discharge. Therefore, the state of the negative electrode active material layer is maintained as it is immediately after formation. This makes it possible to accurately examine the composition with good reproducibility without depending on the presence or absence of charge / discharge, such as the composition of the negative electrode active material.
- the separator separates the positive electrode and the negative electrode, and allows lithium ions to pass through while preventing current short-circuiting due to bipolar contact.
- This separator is formed of, for example, a porous film made of synthetic resin or ceramic, and may have a laminated structure in which two or more kinds of porous films are laminated.
- the synthetic resin include polytetrafluoroethylene, polypropylene, and polyethylene.
- Electrode At least a part of the active material layer or the separator is impregnated with a liquid electrolyte (electrolytic solution).
- This electrolytic solution has an electrolyte salt dissolved in a solvent, and may contain other materials such as additives.
- a non-aqueous solvent for example, a non-aqueous solvent can be used.
- the non-aqueous solvent include ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, 1,2-dimethoxyethane, and tetrahydrofuran.
- a high viscosity solvent such as ethylene carbonate or propylene carbonate
- a low viscosity solvent such as dimethyl carbonate, ethyl methyl carbonate or diethyl carbonate. This is because the dissociation property and ion mobility of the electrolyte salt are improved.
- the halogenated chain carbonate ester is a chain carbonate ester having halogen as a constituent element (at least one hydrogen is replaced by halogen).
- the halogenated cyclic carbonate is a cyclic carbonate having halogen as a constituent element (that is, at least one hydrogen is replaced by a halogen).
- halogen is not particularly limited, but fluorine is preferred. This is because a film having a better quality than other halogens is formed. Further, the larger the number of halogens, the better. This is because the resulting coating is more stable and the decomposition reaction of the electrolyte is reduced.
- halogenated chain carbonate examples include fluoromethyl methyl carbonate and difluoromethyl methyl carbonate.
- halogenated cyclic carbonate examples include 4-fluoro-1,3-dioxolane-2-one, 4,5-difluoro-1,3-dioxolane-2-one, and the like.
- the solvent additive contains an unsaturated carbon bond cyclic carbonate. This is because a stable film is formed on the surface of the negative electrode during charging and discharging, and the decomposition reaction of the electrolytic solution can be suppressed.
- unsaturated carbon bond cyclic ester carbonate include vinylene carbonate and vinyl ethylene carbonate.
- sultone cyclic sulfonic acid ester
- solvent additive examples include propane sultone and propene sultone.
- the solvent preferably contains an acid anhydride. This is because the chemical stability of the electrolytic solution is improved.
- the acid anhydride include propanedisulfonic acid anhydride.
- the electrolyte salt can contain, for example, any one or more of light metal salts such as lithium salts.
- the lithium salt include lithium hexafluorophosphate (LiPF 6 ) and lithium tetrafluoroborate (LiBF 4 ).
- the content of the electrolyte salt is preferably 0.5 mol / kg or more and 2.5 mol / kg or less with respect to the solvent. This is because high ionic conductivity is obtained.
- a negative electrode is produced using the negative electrode active material manufactured with the manufacturing method of said negative electrode active material of this invention, and a lithium ion secondary battery is manufactured using this produced negative electrode.
- a positive electrode is produced using the positive electrode material described above.
- a positive electrode active material and, if necessary, a binder, a conductive additive and the like are mixed to form a positive electrode mixture, and then dispersed in an organic solvent to form a positive electrode mixture slurry.
- the mixture slurry is applied to the positive electrode current collector with a coating apparatus such as a die coater having a knife roll or a die head, and dried with hot air to obtain a positive electrode active material layer.
- the positive electrode active material layer is compression molded with a roll press or the like. At this time, heating may be performed, or heating or compression may be repeated a plurality of times.
- a negative electrode is produced by forming a negative electrode active material layer on the negative electrode current collector using the same operating procedure as the production of the negative electrode 10 for lithium ion secondary batteries described above.
- the positive electrode lead 22 is attached to the positive electrode current collector as shown in FIG. 2 and the negative electrode lead 23 is attached to the negative electrode current collector by ultrasonic welding or the like.
- the positive electrode and the negative electrode are laminated or wound via a separator to produce a wound electrode body 21, and a protective tape is adhered to the outermost periphery thereof.
- the wound body is molded so as to have a flat shape.
- the insulating portions of the exterior member are bonded to each other by a heat fusion method, and the wound electrode body is released in only one direction. Enclose.
- An adhesion film is inserted between the positive electrode lead and the negative electrode lead and the exterior member.
- a predetermined amount of the adjusted electrolytic solution is introduced from the release portion, and vacuum impregnation is performed. After impregnation, the release part is bonded by a vacuum heat fusion method. As described above, the laminated film type lithium ion secondary battery 20 can be manufactured.
- Example 1-1 The laminate film type lithium secondary battery 20 shown in FIG. 2 was produced by the following procedure.
- the positive electrode active material is 95% by mass of LiNi 0.7 Co 0.25 Al 0.05 O, which is a lithium nickel cobalt composite oxide (NCA), 2.5% by mass of a positive electrode conductive additive, and a positive electrode binder ( Polyvinylidene fluoride: PVDF) 2.5% by mass was mixed to prepare a positive electrode mixture.
- the positive electrode mixture was dispersed in an organic solvent (N-methyl-2-pyrrolidone: NMP) to obtain a paste slurry.
- the slurry was applied to both surfaces of the positive electrode current collector with a coating apparatus having a die head, and dried with a hot air drying apparatus. At this time, a positive electrode current collector having a thickness of 15 ⁇ m was used.
- compression molding was performed with a roll press.
- a negative electrode active material was produced as follows. A raw material mixed with metallic silicon and silicon dioxide was introduced into a reaction furnace, and vaporized in a 10 Pa vacuum atmosphere was deposited on an adsorption plate, cooled sufficiently, and then the deposit was taken out and pulverized with a ball mill. . The x value of SiO x of the silicon compound particles thus obtained was 1.0. Subsequently, the particle size of the silicon compound particles was adjusted by classification. Then, the carbon material was coat
- lithium was inserted into the negative electrode active material particles by a redox method to be modified.
- the negative electrode active material particles were immersed in a solution (solution A 1 ) in which lithium pieces and biphenyl were dissolved in tetrahydrofuran (hereinafter also referred to as THF).
- the solution A 1 of Example 1-1 was obtained by dissolving biphenyl in a THF solvent at a concentration of 1 mol / L, and then adding a lithium piece having a mass of 10% by mass with respect to the mixed solution of THF and biphenyl. Produced.
- the temperature of the solution when the negative electrode active material particles were immersed was 20 ° C., and the immersion time was 48 hours. Thereafter, the negative electrode active material particles were collected by filtration. Through the above treatment, lithium was inserted into the negative electrode active material particles.
- solution B a solution in which naphthalene was dissolved in THF.
- Solution B of Example 1-1 was prepared by dissolving naphthalene in a THF solvent at a concentration of 2 mol / L. Further, the temperature of the solution when the negative electrode active material particles were immersed was 20 ° C., and the immersion time was 30 hours. Thereafter, the negative electrode active material particles were collected by filtration.
- the negative electrode active material particles after being brought into contact with the solution B were immersed in a solution (solution C) in which p-benzoquinone was dissolved in THF at a concentration of 1 mol / L.
- the immersion time was 10 hours.
- the negative electrode active material particles were collected by filtration.
- the negative electrode active material particles were washed, and the negative electrode active material particles after the washing treatment were dried under reduced pressure.
- a peak was also obtained at a position where the chemical shift value was near -130 ppm. This peak is also assumed to be a peak derived from amorphous silicon.
- the negative electrode active material particles prepared as described above and the carbon-based active material were blended at a mass ratio of 1: 9 to prepare a negative electrode active material.
- a mixture of natural graphite and artificial graphite coated with a pitch layer at a mass ratio of 5: 5 was used as the carbon-based active material.
- the median diameter of the carbon-based active material was 20 ⁇ m.
- the prepared negative electrode active material conductive additive 1 (carbon nanotube, CNT), conductive additive 2 (carbon fine particles having a median diameter of about 50 nm), styrene butadiene rubber (styrene butadiene copolymer, hereinafter referred to as SBR), Carboxymethylcellulose (hereinafter referred to as CMC) was mixed at a dry mass ratio of 92.5: 1: 1: 2.5: 3, and then diluted with pure water to obtain a negative electrode mixture slurry.
- SBR and CMC are negative electrode binders (negative electrode binder).
- an electrolytic copper foil having a thickness of 15 ⁇ m was used as the negative electrode current collector.
- This electrolytic copper foil contained carbon and sulfur at a concentration of 70 mass ppm.
- the negative electrode mixture slurry was applied to the negative electrode current collector and dried in a vacuum atmosphere at 100 ° C. for 1 hour.
- the amount of deposition (also referred to as area density) of the negative electrode active material layer per unit area on one side of the negative electrode after drying was 5 mg / cm 2 .
- an electrolyte salt lithium hexafluorophosphate: LiPF 6
- FEC fluoro-1,3-dioxolan-2-one
- EC ethylene carbonate
- DMC dimethyl carbonate
- an electrolyte salt lithium hexafluorophosphate: LiPF 6
- the content of the electrolyte salt was 1.2 mol / kg with respect to the solvent.
- a secondary battery was assembled as follows. First, an aluminum lead was ultrasonically welded to one end of the positive electrode current collector, and a nickel lead was welded to one end of the negative electrode current collector. Subsequently, a positive electrode, a separator, a negative electrode, and a separator were laminated in this order, and wound in the longitudinal direction to obtain a wound electrode body. The end portion was fixed with a PET protective tape. As the separator, a laminated film (thickness: 12 ⁇ m) sandwiched between a film mainly composed of porous polyethylene and a film mainly composed of porous polypropylene was used.
- the outer peripheral edges excluding one side were heat-sealed, and the electrode body was housed inside.
- the exterior member a nylon film, an aluminum foil, and an aluminum laminate film in which a polypropylene film was laminated were used.
- an electrolytic solution prepared from the opening was injected, impregnated in a vacuum atmosphere, heat-sealed, and sealed.
- the cycle characteristics were examined as follows. First, in order to stabilize the battery, charge and discharge was performed for 2 cycles at 0.2 C in an atmosphere at 25 ° C., and the discharge capacity at the second cycle was measured. Subsequently, charge and discharge were performed until the total number of cycles reached 499 cycles, and the discharge capacity was measured each time. Finally, the discharge capacity at the 500th cycle obtained by 0.2 C charge / discharge was divided by the discharge capacity at the second cycle to calculate a capacity retention rate (hereinafter also simply referred to as a retention rate). In the normal cycle, that is, from the 3rd cycle to the 499th cycle, charging and discharging were performed with a charge of 0.7 C and a discharge of 0.5 C.
- initial efficiency (initial discharge capacity / initial charge capacity) ⁇ 100.
- initial efficiency (%) (initial discharge capacity / initial charge capacity) ⁇ 100.
- the atmosphere and temperature were the same as when the cycle characteristics were examined.
- a 2032 size coin cell type test cell was prepared from the negative electrode and the counter electrode lithium prepared as described above, and the discharge behavior was evaluated. More specifically, first, constant current and constant voltage charging was performed up to 0 V with the counter electrode Li, and the charging was terminated when the current density reached 0.05 mA / cm 2 . Then, constant current discharge was performed to 1.2V. The current density at this time was 0.2 mA / cm 2 . This charge / discharge was repeated 30 times, and from the data obtained in each charge / discharge, a graph was drawn with the vertical axis representing the rate of change in capacity (dQ / dV) and the horizontal axis representing the voltage (V). It was confirmed whether a peak was obtained in the range of .55 (V).
- the initial efficiency of the silicon-based active material alone was calculated as follows. First, the prepared negative electrode active material particles and polyacrylic acid were mixed at a mass ratio of 85:15, and this mixture was applied to a copper foil. The area density of the mixture applied at this time was about 2 mg / cm 2 . Thereafter, after vacuum drying at 90 ° C. for 1 hour, constant current and constant voltage charging was started at a voltage of 0 V and a current density of 0.2 mA / cm 2 using a counter electrode Li in the form of a 2032 size coin battery. And constant current constant voltage charge was stopped when the electric current value became 0.1 mA. Subsequently, constant current discharge was performed and the discharge was stopped when the voltage reached 1.2V.
- the current density during discharging was the same as that for charging.
- the initial efficiency of the silicon-based active material alone is (discharge capacity) / (charge capacity) ⁇ 100 ( %).
- the initial efficiency of SiOx alone was calculated using this formula. As a result, the initial efficiency of SiOx alone was 85.4%.
- Comparative Example 1-1 As shown in FIG. 4, in the same manner as in Example 1-1, except that negative electrode active material particles in which peak intensities A, B, and C in the 29 Si-MAS-NMR spectrum do not satisfy Formula 1 and Formula 2 were used. A secondary battery was manufactured. As can be seen from FIG. 4, the spectrum has the highest intensity B of the peak derived from the silicon dioxide region obtained in the vicinity of ⁇ 110 ppm in the chemical shift value. Note that it was not possible to determine whether or not the chemical shift value of the 29 Si-MAS-NMR spectrum had a peak in the vicinity of -130 ppm. In Comparative Example 1-1, negative electrode active material particles produced by the same procedure as Example 1-1 were used except that the modification of Example 1-1 was not performed.
- a coin cell type test cell of 2032 size was produced from the same negative electrode and counter lithium as the secondary battery produced in Comparative Example 1-1, and the discharge behavior was evaluated in the same manner as in Example 1-1. .
- a peak was obtained in the range of V to 0.4 to 0.55 (V) in charge and discharge within 30 times.
- the initial efficiency of SiOx alone was calculated in the same manner as in Example 1-1. The initial efficiency of SiOx alone was 71%.
- Example 1-2 As shown in FIG. 4, a secondary battery was obtained in the same manner as in Example 1-1 except that negative electrode active material particles whose peak intensities A, B, and C in the 29 Si-MAS-NMR spectrum did not satisfy Formula 1 were used. Was manufactured. A peak appeared in the chemical shift value of the 29 Si-MAS-NMR spectrum near -130 ppm.
- Comparative Example 1-2 the negative electrode active material particles were modified in the same procedure as in Example 1-1 except that the immersion time in each solution of the negative electrode active material particles was half that of Example 1-1. Negative electrode active material particles were used. In the oxidation-reduction method, the depth at which Li is inserted into the negative electrode active material particles can be adjusted by adjusting the immersion time in the solution and the stirring conditions. Thereby, peak intensity A, B, C can be adjusted. In Example 1-1, Li was inserted to a depth deeper than that of Comparative Example 1-2.
- a coin cell type test cell of 2032 size was produced from the same negative electrode and counter lithium as the secondary battery produced in Comparative Example 1-2, and the discharge behavior was evaluated in the same manner as in Example 1-1. .
- a peak was obtained in the range of V to 0.4 to 0.55 (V) in charge and discharge within 30 times.
- the initial efficiency of SiOx alone was calculated in the same manner as in Example 1-1.
- the initial efficiency of SiOx alone was 80.1%.
- the negative electrode active material particles of Example 1-1 and Comparative Examples 1-1 and 1-2 had the following properties.
- the median diameter D 50 of the negative electrode active material particles was 4.0 ⁇ m.
- the silicon compound has a half-value width (2 ⁇ ) of a diffraction peak due to the Si (111) crystal plane obtained by X-ray diffraction of 2.593 °, and the crystallite size due to the Si (111) crystal plane is It was 3.29 nm.
- the average thickness of the carbon material on the surface of the negative electrode active material particles was 100 nm.
- Table 1 shows the results of Example 1-1 and Comparative Examples 1-1 and 1-2.
- Example 1-1 satisfying both Expression 1 and Expression 2, the initial efficiency was improved as compared with Comparative Examples 1-1 and 1-2.
- the negative electrode end potential was lowered by improving the negative electrode efficiency, and the Li silicate decomposition region was shifted in a direction in which it was difficult to use, so the cycle maintenance ratio was also improved.
- the positive electrode using NCA has an initial efficiency of about 89% in the actual battery usage range, which is similar to the efficiency of the negative electrode manufactured in Example 1-1. Therefore, the positive electrode side can be used safely.
- Example 2-1 and 2-2 Comparative Examples 2-1 and 2-2
- a secondary battery was manufactured in the same manner as Example 1-1 except that the amount of oxygen in the bulk of the silicon compound was adjusted. In this case, the amount of oxygen was adjusted by changing the ratio of metal silicon and silicon dioxide in the raw material of the silicon compound and the heating temperature.
- Table 2 shows the values of x of the silicon compounds represented by SiO x in Examples 2-1 and 2-2 and Comparative Examples 2-1 and 2-2.
- Examples 3-1 to 3-4, Comparative Examples 3-1 and 3-2 A secondary battery was fabricated under the same conditions as in Example 1-1 except that the crystallinity of the silicon compound particles was changed as shown in Table 3, and the cycle characteristics and initial efficiency were evaluated. Note that the crystallinity in the silicon compound particles can be controlled by changing the vaporization temperature of the raw material or by heat treatment after the formation of the silicon compound particles. Further, when the crystallinity of the silicon compound particles is high as in Comparative Examples 3-1 and 3-2, the value of the peak intensity A derived from amorphous silicon is smaller than the peak intensity B of silicon dioxide. 1 was not satisfied.
- the capacity retention ratio and the initial efficiency changed according to the crystallinity of the silicon compound particles.
- a high capacity retention ratio was obtained with a low crystalline material having a half width of 1.2 ° or more and a crystallite size attributable to the Si (111) plane of 7.5 nm or less.
- Example 4-1 to 4-5 A secondary battery was fabricated under the same conditions as in Example 1-1 except that the median diameter of the negative electrode active material particles was changed as shown in Table 4, and the cycle characteristics and initial efficiency were evaluated.
- the maintenance ratio was improved. This is presumably because the surface area per mass of the silicon compound was not too large, the area where the side reaction occurred could be reduced, and consumption of the electrolyte could be suppressed.
- the median diameter is 15 ⁇ m or less, particles are difficult to break during charging, and SEI (solid electrolyte interface) due to a new surface is difficult to be generated during charging / discharging, so that loss of reversible Li can be suppressed.
- the median diameter of the silicon-based active material particles is 15 ⁇ m or less, the amount of expansion of the silicon compound particles during charging does not increase, so that physical and electrical destruction of the negative electrode active material layer due to expansion can be prevented.
- Example 5-1 A secondary battery was fabricated under the same conditions as in Example 1-1 except that the surface of the silicon compound particles was not coated with a carbon material, and the cycle characteristics and initial efficiency were evaluated.
- Examples 5-2 to 5-6 A secondary battery was fabricated under the same conditions as in Example 1-1 except that the average thickness of the carbon material coated on the surface of the silicon compound particles was changed, and the cycle characteristics and initial efficiency were evaluated.
- the average thickness of the carbon material can be adjusted by changing the CVD conditions.
- the conductivity is particularly improved when the average thickness of the carbon material is 10 nm or more, the capacity retention ratio and the initial efficiency can be improved.
- the average thickness of the carbon material is 5000 nm or less, the amount of silicon compound particles can be sufficiently secured in battery design, and the battery capacity does not decrease.
- Example 6-1 A secondary battery was fabricated under the same conditions as in Example 1-1, except that a copper foil containing no carbon and sulfur was used as the negative electrode current collector, and the cycle characteristics and initial efficiency were evaluated.
- the negative electrode current collector contains carbon and sulfur of 70 mass ppm or less, the strength of the current collector is improved. Therefore, when using a silicon-based negative electrode active material having a large expansion and contraction during charging / discharging of the secondary battery, it is possible to suppress the deformation and distortion of the current collector, and the battery characteristics as in Example 1-1, particularly Cycle characteristics are improved.
- Example 7-1 A secondary battery was produced under the same conditions as in Example 1-1 except that the mass ratio of the negative electrode active material particles (silicon-based active material particles) in the negative electrode active material was changed, and the rate of increase in battery capacity was evaluated. .
- Comparative Example 7-1 A secondary battery was fabricated under the same conditions as Comparative Example 1-1 except that the mass ratio of the negative electrode active material particles (silicon-based active material particles) in the negative electrode active material was changed, and the rate of increase in battery capacity was evaluated. .
- FIG. 5 is a graph showing the relationship between the ratio of the silicon-based active material particles to the total amount of the negative electrode active material in Example 7-1 and Comparative Example 7-1 and the increase rate of the battery capacity of the secondary battery. As can be seen from FIG. 5, when the ratio of the silicon-based compound in Example 7-1 was 6% by mass or more, the increase rate of the battery capacity was larger than that in Comparative Example 7-1, and the volume energy density was Increase significantly.
- the present invention is not limited to the above embodiment.
- the above-described embodiment is an exemplification, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same effects. Are included in the technical scope.
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Abstract
Description
B≦1.5×A ・・・ (1)
B<C ・・・ (2)
B≦1.5×A ・・・ (1)
B<C ・・・ (2)
B≦1.5×A ・・・ (1)
B<C ・・・ (2)
まず、非水電解質二次電池用負極について説明する。図1は本発明の一実施形態における非水電解質二次電池用負極(以下、「負極」とも呼称する)の断面構成を表している。
図1に示したように、負極10は、負極集電体11の上に負極活物質層12を有する構成になっている。この負極活物質層12は負極集電体11の両面、又は、片面だけに設けられていても良い。さらに、本発明の負極活物質が用いられたものであれば、負極集電体11はなくてもよい。
負極集電体11は、優れた導電性材料であり、かつ、機械的な強度に長けた物で構成される。負極集電体11に用いることができる導電性材料として、例えば銅(Cu)やニッケル(Ni)があげられる。この導電性材料は、リチウム(Li)と金属間化合物を形成しない材料であることが好ましい。
負極活物質層12は、リチウムイオンを吸蔵、放出可能な本発明の負極活物質を含んでおり、電池設計上の観点から、さらに、負極結着剤(バインダ)や導電助剤など他の材料を含んでいてもよい。負極活物質は負極活物質粒子を含み、負極活物質粒子はケイ素化合物(SiOx:0.5≦x≦1.6)を含有するケイ素化合物粒子を含む。
XPS
・装置: X線光電子分光装置、
・X線源: 単色化Al Kα線、
・X線スポット径: 100μm、
・Arイオン銃スパッタ条件: 0.5kV/2mm×2mm。
29Si MAS NMR(マジック角回転核磁気共鳴)
・装置: Bruker社製700NMR分光器、
・プローブ: 4mmHR-MASローター 50μL、
・試料回転速度: 10kHz、
・測定環境温度: 25℃。
負極は、例えば、以下の手順により製造できる。まず、負極に使用する負極活物質の製造方法を説明する。最初に、ケイ素化合物(SiOx:0.5≦x≦1.6)を含むケイ素化合物粒子を含有する負極活物質粒子を作製する。その後、負極活物質粒子から、29Si-MAS-NMR スペクトルから得られるケミカルシフト値として、-40~-60ppmに得られるアモルファスケイ素に由来するピークの強度Aと、-110ppm付近に得られる二酸化ケイ素領域に由来するピークの強度B、及び-83ppm付近に得られるSiに由来するピークの強度Cが、下記式1及び式2を満たすものを選別する。そして、選別した負極活物質粒子を用いて、負極活物質を製造する。
B≦1.5×A ・・・ (1)
B<C ・・・ (2)
B≦1.5×A ・・・ (1)
B<C ・・・ (2)
29Si MAS NMR
・装置: Bruker社製700NMR分光器、
・プローブ: 4mmHR-MASローター 50μL、
・試料回転速度: 10kHz、
・測定環境温度: 25℃。
次に、本発明のリチウムイオン二次電池について説明する。本発明のリチウムイオン二次電池は、本発明の負極活物質を含む負極を用いたものである。ここでは具体例として、ラミネートフィルム型のリチウムイオン二次電池を例に挙げる。
図2に示すラミネートフィルム型のリチウムイオン二次電池20は、主にシート状の外装部材25の内部に巻回電極体21が収納されたものである。この巻回体は正極、負極間にセパレータを有し、巻回されたものである。また正極、負極間にセパレータを有し積層体を収納した場合も存在する。どちらの電極体においても、正極に正極リード22が取り付けられ、負極に負極リード23が取り付けられている。電極体の最外周部は保護テープにより保護されている。
正極は、例えば、図1の負極10と同様に、正極集電体の両面又は片面に正極活物質層を有している。
負極は、上記した図1のリチウムイオン二次電池用負極10と同様の構成を有し、例えば、集電体11の両面に負極活物質層12を有している。この負極は、正極活物質剤から得られる電気容量(電池として充電容量)に対して、負極充電容量が大きくなることが好ましい。負極上でのリチウム金属の析出を抑制することができるためである。
セパレータは正極、負極を隔離し、両極接触に伴う電流短絡を防止しつつ、リチウムイオンを通過させるものである。このセパレータは、例えば合成樹脂、あるいはセラミックからなる多孔質膜により形成されており、2種以上の多孔質膜が積層された積層構造を有しても良い。合成樹脂として例えば、ポリテトラフルオロエチレン、ポリプロピレン、ポリエチレンなどが挙げられる。
活物質層の少なくとも一部、又は、セパレータには、液状の電解質(電解液)が含浸されている。この電解液は、溶媒中に電解質塩が溶解されており、添加剤など他の材料を含んでいても良い。
本発明では、上記の本発明の負極活物質の製造方法によって製造した負極活物質を用いて負極を作製し、該作製した負極を用いてリチウムイオン二次電池を製造する。
以下の手順により、図2に示したラミネートフィルム型リチウム二次電池20を作製した。
B≦1.5×A ・・・ (1)
B<C ・・・ (2)
図4に示すように、29Si-MAS-NMRスペクトルにおけるピーク強度A、B、Cが式1及び式2を満たさない負極活物質粒子を用いたこと以外、実施例1-1と同様に、二次電池の製造を行った。図4からわかるように、ケミカルシフト値が-110ppm付近に得られる二酸化ケイ素領域に由来するピークの強度Bが最も大きいスペクトルとなっている。なお、29Si-MAS-NMRスペクトルのケミカルシフト値が-130ppm付近にピークが有るか否かは判別することができなかった。比較例1-1では、実施例1-1の改質を行っていないこと以外、実施例1-1と同様の手順で作製した負極活物質粒子を用いた。
図4に示すように、29Si-MAS-NMRスペクトルにおけるピーク強度A、B、Cが式1を満たさない負極活物質粒子を用いたこと以外、実施例1-1と同様に、二次電池の製造を行った。なお、29Si-MAS-NMRスペクトルのケミカルシフト値が-130ppm付近にピークが発現していた。
ケイ素化合物のバルク内酸素量を調整したことを除き、実施例1-1と同様に、二次電池の製造を行った。この場合、ケイ素化合物の原料中の金属ケイ素と二酸化ケイ素との比率や加熱温度を変化させることで、酸素量を調整した。実施例2-1、2-2、比較例2-1、2-2における、SiOxで表されるケイ素化合物のxの値を表2中に示した。
ケイ素化合物粒子の結晶性を表3のように変化させたこと以外、実施例1-1と同じ条件で二次電池を作製し、サイクル特性及び初回効率を評価した。なお、ケイ素化合物粒子中の結晶性は、原料の気化温度の変更、又は、ケイ素化合物粒子の生成後の熱処理で制御できる。また、比較例3-1、3-2のようにケイ素化合物粒子の結晶性が高い場合、二酸化ケイ素のピーク強度Bに対して、アモルファスケイ素に由来するピーク強度Aの値が小さくなるため、式1を満たさなかった。
負極活物質粒子のメジアン径を表4のように変化させたこと以外、実施例1-1と同じ条件で二次電池を作製し、サイクル特性及び初回効率を評価した。
ケイ素化合物粒子の表面に炭素材を被覆しなかったこと以外、実施例1-1と同じ条件で二次電池を作製し、サイクル特性及び初回効率を評価した。
ケイ素化合物粒子の表面に被覆された炭素材の平均厚さを変更したこと以外、実施例1-1と同じ条件で二次電池を作製し、サイクル特性及び初回効率を評価した。炭素材の平均厚さは、CVD条件を変更することで調整できる。
負極の集電体として、炭素及び硫黄を含まない銅箔を用いたこと以外、実施例1-1と同じ条件で二次電池を作製し、サイクル特性及び初回効率を評価した。
負極活物質中の負極活物質粒子(ケイ素系活物質粒子)の質量の割合を変更したこと以外、実施例1-1と同じ条件で二次電池を作製し、電池容量の増加率を評価した。
負極活物質中の負極活物質粒子(ケイ素系活物質粒子)の質量の割合を変更したこと以外、比較例1-1と同じ条件で二次電池を作製し、電池容量の増加率を評価した。
Claims (14)
- 負極活物質粒子を含む負極活物質であって、
前記負極活物質粒子は、ケイ素化合物(SiOx:0.5≦x≦1.6)を含むケイ素化合物粒子を含有し、
前記ケイ素化合物粒子は、29Si-MAS-NMR スペクトルから得られるケミカルシフト値として、-40~-60ppmに得られるアモルファスケイ素に由来するピークの強度A、-110ppm付近に得られる二酸化ケイ素に由来するピークの強度B、及び-83ppm付近に得られるSiに由来するピークの強度Cが、下記式1及び式2を満たすものであることを特徴とする負極活物質。
B≦1.5×A ・・・ (1)
B<C ・・・ (2) - 前記負極活物質粒子は、Li2SiO3及びLi4SiO4のうち少なくとも1種以上を含むものであることを特徴とする請求項1に記載の負極活物質。
- 前記29Si-MAS-NMR スペクトルから得られるケミカルシフト値として-130ppm付近にピークを有するものであることを特徴とする請求項1又は請求項2に記載の負極活物質。
- 前記ケイ素化合物粒子は、X線回折により得られるSi(111)結晶面に起因する回折ピークの半値幅(2θ)が1.2°以上であるとともに、その結晶面に対応する結晶子サイズは7.5nm以下であることを特徴とする請求項1から請求項3のいずれか1項に記載の負極活物質。
- 前記負極活物質と炭素系活物質との混合物を含む負極電極と対極リチウムとから成る試験セルを作製し、該試験セルにおいて、前記負極活物質にリチウムを挿入するよう電流を流す充電と、前記負極活物質からリチウムを脱離するよう電流を流す放電とから成る充放電を30回実施し、各充放電における放電容量Qを前記対極リチウムを基準とする前記負極電極の電位Vで微分した微分値dQ/dVと前記電位Vとの関係を示すグラフを描いた場合に、X回目以降(1≦X≦30)の放電時における、前記負極電極の電位Vが0.40V~0.55Vの範囲にピークを有するものであることを特徴とする請求項1から請求項4のいずれか1項に記載の負極活物質。
- 前記負極活物質粒子はメジアン径が1.0μm以上15μm以下であることを特徴とする請求項1から請求項5のいずれか1項に記載の負極活物質。
- 前記負極活物質粒子は、表層部に炭素材を含むことを特徴とする請求項1から請求項6のいずれか1項に記載の負極活物質。
- 前記炭素材の平均厚さは10nm以上5000nm以下であることを特徴とする請求項7に記載の負極活物質。
- 請求項1から請求項8のいずれか1項に記載の負極活物質と炭素系活物質とを含むことを特徴とする混合負極活物質材料。
- 請求項9に記載の混合負極活物質材料を含み、前記負極活物質と前記炭素系活物質の質量の合計に対する、前記負極活物質の質量の割合が6質量%以上であることを特徴とする非水電解質二次電池用負極。
- 請求項9に記載の混合負極活物質材料で形成された負極活物質層と、
負極集電体とを有し、
前記負極活物質層は前記負極集電体上に形成されており、
前記負極集電体は炭素及び硫黄を含むとともに、それらの含有量がいずれも70質量ppm以下であることを特徴とする非水電解質二次電池用負極。 - 負極として、請求項1から請求項8のいずれか1項に記載の負極活物質を含む負極を用いたものであることを特徴とするリチウムイオン二次電池。
- ケイ素化合物粒子を含有する負極活物質粒子を含む負極活物質を製造する方法であって、
ケイ素化合物(SiOx:0.5≦x≦1.6)を含むケイ素化合物粒子を含有する負極活物質粒子を作製する工程と、
前記負極活物質粒子から、29Si-MAS-NMR スペクトルから得られるケミカルシフト値として、-40~-60ppmに得られるアモルファスケイ素に由来するピークの強度A、-110ppm付近に得られる二酸化ケイ素領域に由来するピークの強度B、及び-83ppm付近に得られるSiに由来するピークの強度Cが、下記式1及び式2を満たすものを選別する工程とを含み、
該選別した前記負極活物質粒子を用いて、負極活物質を製造することを特徴とする負極活物質の製造方法。
B≦1.5×A ・・・ (1)
B<C ・・・ (2) - 請求項13に記載の負極活物質の製造方法によって製造した負極活物質を用いて負極を作製し、該作製した負極を用いてリチウムイオン二次電池を製造することを特徴とするリチウムイオン二次電池の製造方法。
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CN201680067715.6A CN108292747A (zh) | 2015-11-18 | 2016-10-31 | 负极活性物质、混合负极活性物质材料、非水电解质二次电池用负极、锂离子二次电池、负极活性物质的制造方法、以及锂离子二次电池的制造方法 |
KR1020187013700A KR20180080240A (ko) | 2015-11-18 | 2016-10-31 | 부극 활물질, 혼합 부극 활물질 재료, 비수 전해질 이차 전지용 부극, 리튬 이온 이차 전지, 부극 활물질의 제조 방법 및 리튬 이온 이차 전지의 제조 방법 |
CN202210480218.6A CN114744183B (zh) | 2015-11-18 | 2016-10-31 | 负极活性物质及制造方法、混合负极活性物质材料、负极、锂离子二次电池及制造方法 |
US15/772,623 US11430980B2 (en) | 2015-11-18 | 2016-10-31 | Negative electrode active material, mixed negative electrode active material, negative electrode for nonaqueous electrolyte secondary battery, lithium ion secondary battery, production method of negative electrode active material, and production method of lithium ion secondary battery |
EP16865912.6A EP3364482A4 (en) | 2015-11-18 | 2016-10-31 | NEGATIVE ELECTRODE ACTIVE MATERIAL AND METHOD FOR MANUFACTURING SAME, MIXED NEGATIVE ELECTRODE ACTIVE MATERIAL, NEGATIVE ELECTRODE FOR NONAQUEOUS ELECTROLYTE SECONDARY BATTERY, AND LITHIUM-ION SECONDARY BATTERY, AND METHOD FOR MANUFACTURING THE SAME |
US17/865,556 US20220352503A1 (en) | 2015-11-18 | 2022-07-15 | Negative electrode active material, mixed negative electrode active material, negative electrode for nonaqueous electrolyte secondary battery, lithium ion secondary battery, production method of negative electrode active material, and production method of lithium ion secondary battery |
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JP2015225477A JP6460960B2 (ja) | 2015-11-18 | 2015-11-18 | 負極活物質、混合負極活物質材料、非水電解質二次電池用負極、リチウムイオン二次電池、負極活物質の製造方法、及びリチウムイオン二次電池の製造方法 |
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US17/865,556 Division US20220352503A1 (en) | 2015-11-18 | 2022-07-15 | Negative electrode active material, mixed negative electrode active material, negative electrode for nonaqueous electrolyte secondary battery, lithium ion secondary battery, production method of negative electrode active material, and production method of lithium ion secondary battery |
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JP2019119638A (ja) * | 2017-12-28 | 2019-07-22 | Jnc株式会社 | シリコン系ナノ粒子含有水素ポリシルセスキオキサン、ケイ素酸化物構造体及びそれらの製造方法 |
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JP6683221B2 (ja) * | 2018-07-26 | 2020-04-15 | トヨタ自動車株式会社 | 負極、非水電解液二次電池、および負極の製造方法 |
JP7156921B2 (ja) * | 2018-11-28 | 2022-10-19 | 信越化学工業株式会社 | 負極活物質及びその製造方法 |
US20220069296A1 (en) * | 2018-12-19 | 2022-03-03 | Dic Corporation | Silicon nanoparticles, non-aqueous secondary battery negative electrode active material using said silicon nanoparticles, and secondary battery |
US20230035333A1 (en) * | 2019-12-26 | 2023-02-02 | Panasonic Intellectual Property Management Co., Ltd. | Negative electrode active material for secondary batteries, and secondary battery |
WO2021217327A1 (zh) * | 2020-04-27 | 2021-11-04 | 宁德新能源科技有限公司 | 一种负极复合材料及其应用 |
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JP2019119638A (ja) * | 2017-12-28 | 2019-07-22 | Jnc株式会社 | シリコン系ナノ粒子含有水素ポリシルセスキオキサン、ケイ素酸化物構造体及びそれらの製造方法 |
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TW201731146A (zh) | 2017-09-01 |
CN108292747A (zh) | 2018-07-17 |
JP6460960B2 (ja) | 2019-01-30 |
KR20180080240A (ko) | 2018-07-11 |
JP2017097955A (ja) | 2017-06-01 |
EP3364482A1 (en) | 2018-08-22 |
US20180323424A1 (en) | 2018-11-08 |
US20220352503A1 (en) | 2022-11-03 |
US11430980B2 (en) | 2022-08-30 |
CN114744183A (zh) | 2022-07-12 |
EP3364482A4 (en) | 2019-06-12 |
TWI705605B (zh) | 2020-09-21 |
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