JP2020115443A - Lithium ion secondary battery negative electrode material, lithium ion secondary battery, and manufacturing method for lithium ion secondary battery negative electrode materials - Google Patents

Abstract

To provide a lithium ion secondary battery negative electrode material, a lithium ion secondary battery, and a manufacturing method for lithium ion secondary battery negative electrode materials that provide excellent first time Coulomb efficiency.SOLUTION: A lithium ion secondary battery negative electrode material according to the present invention is a compound containing at least Si and O as constituent elements and provides peaks at 2θ=26.5° and 28.5°in X-ray diffraction measurement, where a ratio of strength of the peak at 26.5°to that of the peak at 28.5°is made to be 0.2 or more. A lithium ion secondary battery 1 according to the present invention includes a positive electrode 2, a negative electrode 3, and an electrolyte, the negative electrode 3 containing the lithium ion secondary battery negative electrode material. A manufacturing method for lithium ion secondary battery negative electrode materials according to the present invention includes: a mixing step S1 of mixing SiO with Li and halogen; and a firing step S2 of performing firing under an inert atmosphere at a temperature higher than 700°C and lower than 1000°C.SELECTED DRAWING: Figure 1

Description

The present invention relates to a negative electrode material for a lithium ion secondary battery, a lithium ion secondary battery, and a method for producing a negative electrode material for a lithium ion secondary battery.

Lithium ion secondary batteries are used in various portable electronic devices. 2. Description of the Related Art In recent years, due to higher performance of electronic devices and expansion of battery applications for automobiles and the like, lithium ion secondary batteries are required to have higher capacities. Since the capacity of the battery largely depends on the capacity of the electrode material used, a high capacity electrode material is required. At present, graphite is mainly used as a negative electrode material for lithium-ion secondary batteries, but since it is already used in a region close to the theoretical capacity, further increase in capacity cannot be expected. Therefore, silicon monoxide (SiO) has attracted attention as a new high capacity negative electrode material. A negative electrode using SiO (hereinafter sometimes referred to as “SiO negative electrode”) has an advantage that a high capacity can be obtained, but has a problem of low initial Coulombic efficiency (first charge/discharge efficiency). There is. The initial Coulombic efficiency is the ratio of the discharge capacity to the capacity charged at the time of charging when the secondary battery is first charged under predetermined conditions and then discharged, and is expressed as a percentage. Say. That is, the initial coulombic efficiency is calculated by “initial coulombic efficiency (%)={discharge capacity (Ah)/charge capacity (Ah)}×100”. The higher the initial coulombic efficiency is, the more the charged charging capacity can be discharged, which is preferable.

At present, intensive research is being conducted to solve the above-mentioned problems, and many results (techniques) have been proposed. Among them, for example, in Patent Document 1, in a negative electrode material for a non-aqueous electrolyte secondary battery having negative electrode active material particles, the negative electrode active material particles are SiO _x (0.5≦x≦1.6). And a carbon coating layer made of a carbon component coating the surface of the silicon compound, wherein the negative electrode active material particles contain a SiO ₂ component having a calcified silica structure, and in X-ray diffraction, A negative electrode material for a non-aqueous electrolyte secondary battery has been proposed in which the half-value width (2θ) of the diffraction peak obtained at around 21.825° is 0.15° or less. Note that Patent Document 1 describes that the lower the crystallinity of the Si component of the silicon compound, the better. Then, according to Patent Document 1, it is described that the configuration described above makes it possible to increase the battery capacity and improve the cycle characteristics and the initial charge/discharge characteristics.

JP, 2018-78114, A

In the SiO negative electrode, in the process of inserting Li (defined as charging), a Si-Li compound and a Li-Si-O compound are formed. The formation of these compounds is caused by the consumption of a large amount of Li during the initial charging. On the other hand, in the process of desorbing Li (defined as discharge), Li is desorbed from the Li—Si compound, but Li is hardly desorbed from the Li—Si—O compound. This means that there is an irreversible reaction in the charge/discharge reaction of the SiO negative electrode. And, this is a cause of lowering the initial Coulombic efficiency of the SiO negative electrode.

In the invention described in Patent Document 1, a silicon compound represented by SiO _x (0.5≦x≦1.6) is used for the negative electrode active material particles. Then, in the invention described in Patent Document 1, the negative electrode active material particles contain a SiO ₂ component having a calcified silica structure, and in X-ray diffraction, the full width at half maximum of the diffraction peak obtained near 21.825° ( 2θ) is set to 0.15° or less. In Patent Document 1, by configuring the negative electrode active material particles with such a structure, the modification of the SiO ₂ component by the insertion and desorption of Li can be efficiently progressed, and the irreversible capacity of the battery is further reduced. It can be done. In Patent Document _1, to include _{Li 4 SiO 4, Li 6 Si} 2 O 7, Li 2 at least one kind of Li compounds of the SiO ₃ (corresponding to Li-SiO compound mentioned above), It is described as preferable because the effect can be exhibited more effectively.

The method described in Patent Document 1 can also improve the initial Coulombic efficiency. However, as described above, Li is hardly desorbed from the Li-Si-O compound during discharge. Therefore, although the method described in Patent Document 1 is expected to improve the initial Coulombic efficiency, the improvement effect is not sufficient from the amount of Li consumed for the formation of the Li-Si-O compound. There is a possibility that I cannot say it.

The present invention has been made in view of the above circumstances, and provides a negative electrode material for a lithium ion secondary battery having excellent initial Coulombic efficiency, a lithium ion secondary battery, and a method for manufacturing a negative electrode material for a lithium ion secondary battery. Is an issue.

As a result of earnest research to solve the above-mentioned problems, the present inventor has found that oxygen in SiO contributes to the formation of a Li-Si-O compound that does not desorb Li in discharge. Then, the present inventor found that the oxygen-containing domain in SiO was made inactive to Li by making the crystalline SiO ₂ highly crystalline, and the formation of the Li—Si—O compound could be suppressed, and by this, The inventors have found that the initial Coulombic efficiency can be improved and have completed the present invention.

The negative electrode material for a lithium ion secondary battery according to the present invention, which has solved the above-mentioned problems, is a compound containing at least Si and O as constituent elements, and has 2θ=26.5° and 28.5° in X-ray diffraction measurement. There is a peak, and the peak intensity at 26.5° is 0.2 times or more the peak intensity at 28.5°.

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the negative electrode material for lithium ion secondary batteries excellent in initial Coulombic efficiency, a lithium ion secondary battery, and the negative electrode material for lithium ion secondary batteries can be provided.
Problems, configurations and effects other than those described above will be clarified by the following description of the embodiments.

It is the schematic explanatory drawing which illustrated the main components (portion which contributes to an electrochemical reaction) of the lithium ion secondary battery which concerns on this embodiment. It is a flowchart explaining the content of the manufacturing method of the negative electrode material for lithium ion secondary batteries which concerns on this embodiment. FIG. 3 is an X-ray diffraction chart showing a diffraction chart of the negative electrode active material according to Example 1 and a diffraction chart of the negative electrode active materials according to Comparative Example 1 and Comparative Example 2 obtained by X-ray diffraction measurement.

Hereinafter, one embodiment of a negative electrode material for a lithium ion secondary battery, a lithium ion secondary battery, and a method for producing a negative electrode material for a lithium ion secondary battery according to the present invention will be described in detail with reference to the drawings as appropriate.
In addition, "-" described in this specification is used to mean that the numerical values described before and after the "-" have a lower limit value and an upper limit value. In the numerical ranges described stepwise in the present specification, the upper limit or the lower limit described in one numerical range may be replaced with the upper limit or the lower limit described in other steps. The upper limit value or the lower limit value of the numerical range described in this specification may be replaced with the value shown in the examples.

Each member described in this specification may be used alone or in combination of a plurality of materials selected from the material group constituting each member. Further, each member described in the present specification may be composed only of the materials described in the present specification, and other materials not described in the present specification within a range not impairing the effects of the present invention. May have.

<Configuration of lithium-ion secondary battery 1>
FIG. 1 is a schematic explanatory diagram illustrating main components (portions that contribute to an electrochemical reaction) of a lithium ion secondary battery 1 according to this embodiment. Here, the lithium ion secondary battery refers to an electrochemical device capable of storing or utilizing electric energy by occluding/desorbing (releasing) Li in the electrode. The lithium-ion secondary battery is called by another name such as a lithium-ion battery and a non-aqueous electrolyte secondary battery, and any battery is the subject of the present invention.

As shown in FIG. 1, in a lithium ion secondary battery 1 according to this embodiment, a positive electrode 2 and a negative electrode 3 that directly contribute to an electrochemical reaction are arranged opposite to each other. The separator 4 is provided between the positive electrode 2 and the negative electrode 3. Further, an electrolyte is provided for enabling the movement of Li between the positive electrode 2 and the negative electrode 3. As the electrolyte, for example, an organic solvent in which a lithium salt is dissolved can be used. In this embodiment, the positive electrode 2, the negative electrode 3, and the separator 4 are impregnated with an electrolyte. The negative electrode active material according to the present embodiment (corresponding to the “negative electrode material for lithium ion secondary battery” in the claims) is included in the negative electrode layer 7 of the negative electrode 3 (note that the negative electrode active material is not illustrated. No). The negative electrode active material will be described later.

<Positive electrode 2, positive electrode layer 5>
The positive electrode 2 is composed of a positive electrode layer 5 and a positive electrode current collector 6. The positive electrode layer 5 is composed of a positive electrode active material, a conductive agent, and a binder.

<Cathode active material>
The positive electrode active material is a material into which lithium ions are desorbed during the charging process and lithium ions desorbed from the negative electrode active material in the negative electrode layer 7 are inserted during the discharging process. As the positive electrode active material, a lithium composite oxide having a transition metal is desirable. As the positive electrode active material, for example, the composition _{formula: LiMO 2, Li 1 + x} M 1-x O 2, LiM 2 O 4, LiMPO 4, LiMVO z, LiMBO 3, Li 2 MSiO 4, LiMn 2-y M y O 4 A compound represented by the following formula can be used. In addition, in these compounds, M is a metal. Examples of M include at least one or more selected from Co, Ni, Mn, Fe, Cr, Zn, Ta, Al, Mg, Cu, Cd, Mo, Nb, W, Ru and the like. x can take any number less than or equal to 0.33. y can take any number less than or equal to 0.5. z is the oxygen concentration contained in the compound, and can be an arbitrary integer of 0 or more. Further, as the positive electrode active material, for example, chalcogenide such as sulfur, TiS ₂ , MoS ₂ , Mo ₆ S ₈ and TiSe ₂ , vanadium oxide such as V ₂ O ₅ , halide such as FeF ₃ and polyanion are constituted. An oxide such as Fe(MoO ₄ ) ₃ , Fe ₂ (SO ₄ ) ₃ or Li ₃ Fe ₂ (PO ₄ ) ₃ or a quinone-based organic crystal can also be used. The element ratio may deviate from the stoichiometric composition. In this embodiment, there is no limitation on the positive electrode active material, and materials other than the above-mentioned materials can be used.

<Conductive agent>
The conductive agent improves the conductivity of the positive electrode layer 5. As the conductive agent, for example, Ketjen black, acetylene black, graphite and the like can be used, but the conductive agent is not limited thereto.

<Binder>
The binder binds the positive electrode active material in the positive electrode and the conductive agent. As the binder, for example, polyvinylidene fluoride, styrene/butadiene rubber, carboxyl/methyl cellulose, cellulose acetate, ethyl cellulose, fluororubber, ethylene/propylene rubber, polyacrylic acid, polyimide, polyamide and the like can be used. Not limited.

<Cathode current collector 6>
The positive electrode current collector 6 collects current from the positive electrode layer 5. As the positive electrode current collector 6, for example, aluminum foil, stainless steel foil, titanium foil, or the like can be used, but the positive electrode current collector 6 is not limited thereto.

<Preparation of positive electrode layer 5>
In order to produce the positive electrode layer 5, it is preferable to mix a positive electrode active material, a conductive agent, and a binder, and then add a solvent to prepare a positive electrode slurry. The solvent used to prepare the positive electrode slurry may be any solvent that can dissolve the binder, and examples thereof include 1-methyl-2-pyrrolidone and water, but are not limited thereto. A known kneader or disperser can be used for the dispersion treatment of the positive electrode active material, the conductive agent and the binder in the solvent.
The mixing ratio of the positive electrode active material, the conductive agent, and the binder is, for example, 80 to 99:0.5 to 10:0.5 when the total of the positive electrode active material:conductive agent:binder is 100. It may be ten or the like. Further, the solvent can be used in a mass ratio of 0.1 to 2 times the mass of the powder mixture.

The positive electrode layer 5 is prepared by applying the prepared positive electrode slurry to the positive electrode current collector 6 by, for example, a doctor blade method, a dipping method, or a spray method, drying the solvent, and press-molding it with a roll press. Can be made.

<Negative electrode 3, negative electrode layer 7>
The negative electrode 3 includes a negative electrode layer 7 and a negative electrode current collector 8. The negative electrode layer 7 is composed of a negative electrode active material, a conductive agent, and a binder.

<Negative electrode active material>
The negative electrode active material is a material into which lithium ions are desorbed in the discharging process and lithium ions desorbed from the positive electrode active material in the positive electrode layer 5 are inserted in the charging process.
The negative electrode active material in the present embodiment is a compound containing at least Si and O as constituent elements. The negative electrode active material in the present embodiment preferably further contains SiO ₂ in at least a part of the compound. The compound (negative electrode active material) in the present embodiment has peaks at 2θ (diffraction angle)=26.5° and 28.5° in X-ray diffraction measurement, and the peak at 26.5° The intensity is 0.2 times or more of the peak intensity of 28.5°.

Here, in the present specification, the peak intensity means the height of the peak. The peak intensity (peak height) is related to the crystallinity of the corresponding substance, and the higher the crystallinity, the stronger (higher) the peak intensity is obtained. Conversely, the lower the crystallinity, the weaker (lower) peak intensity is obtained. In other words, if the crystallinity is high, the molecular structures corresponding to the peaks are aligned (that is, the distances between atoms, distances between molecules, distances between atoms, etc. are uniform). , The X-ray diffraction intensities obtained at the same diffraction angle are integrated, and the peak intensity increases. On the contrary, when the crystallinity is low, the molecular structures corresponding to the peaks are not aligned, so that X-ray diffraction intensities can be obtained at various diffraction angles, making it difficult to integrate the peaks. Become. Therefore, it can be said that a peak having a sharp shape in X-ray diffraction measurement has a high crystallinity, and a peak having a broad shape (a shape spread laterally) has a low crystallinity.

In the X-ray diffraction measurement of the negative electrode active material, the above-mentioned peak at 2θ=26.5° is based on hexagonal SiO ₂ . Moreover, in the X-ray diffraction measurement of the negative electrode active material, the above-mentioned peak at 2θ=28.5° is based on Si. Then, in the negative electrode active material according to the present embodiment, as described above, the peak intensity of 2θ=26.5° (peak intensity of SiO ₂ ) is the same as the peak intensity of 2θ=28.5° (Si). 0.2 times the peak intensity). This means that the negative electrode active material according to this embodiment surely contains SiO ₂ having high crystallinity together with Si. In the present embodiment, the negative electrode active material has a peak of 2θ=26.5° (has SiO ₂ having high crystallinity), so that the initial Coulombic efficiency can be improved.
In addition, this structure can be suitably manufactured by the method for manufacturing a negative electrode material for a lithium ion secondary battery according to this embodiment described later.
In addition, the X-ray diffraction measurement can be performed using a known X-ray diffractometer under general conditions that are usually set.

In addition, in the present embodiment, the compound containing Si and O preferably further contains Li and halogen. Examples of halogen include fluorine, chlorine, bromine and iodine. Examples of Li and halogen include LiF. When the compound containing Si and O contains Li and halogen, it is considered that the compound can be crystallized by causing a reaction of SiO+SiO→Si+SiO ₂ when fired under predetermined conditions, as described later. In order to cause this reaction and crystallization more appropriately, the molar ratio of Li to Si (molar ratio of Li/molar ratio of Si) is preferably 1/100 or more and 1/1 or less, and 1/50 or more. It is more preferably 1/1 or less.

<Reasons for improving initial coulombic efficiency>
Here, the reason why the presence of SiO ₂ having high crystallinity in the negative electrode active material improves the initial Coulombic efficiency will be described.
As mentioned above, Li-SiO compound not eliminated the Li in the discharge (for _example, Li 4 SiO ₄₎ oxygen in SiO is to generate contribute. That is, when the negative electrode active material is the SiO negative electrode of the conventional configuration that does not adopt the configuration of this embodiment, the reaction mechanism regarding SiO during charging and discharging is as follows.
^{(Charging) 4SiO + 17.2Li + + 17.2e -} → 3SiLi 4.4 + Li 4 SiO 4
(Discharge) 3SiLi _4.4 →3Si+13.2Li ⁺ +13.2e ⁻

Thus, if the SiO negative electrode of conventional construction, 17.2 pieces of Li ⁺ 4 pieces of Li of ⁺ to produce a Li-SiO compound bonded with oxygen in the SiO. Since the compound does not desorb Li during discharge, the amount of Li that can move between the positive electrode 2 and the negative electrode 3 is reduced, which causes a decrease in initial Coulombic efficiency. Therefore, if the Li-Si-O compound is not formed during the initial charge, the Li that can move between the positive electrode 2 and the negative electrode 3 will not decrease, and the initial Coulombic efficiency will be improved.

As can be seen from the reaction mechanism of SiO during the first charge and discharge, SiO is involved in the formation of the Li-Si-O compound. Therefore, when the amount of SiO in the negative electrode active material before charging is small (preferably, when there is no SiO), the amount of Li-Si-O compound produced is considered to be reduced. On the other hand, when considering SiO _2, it is considered that due to the structure of SiO ₂ (for example, due to a bond or reactivity), Li has a form in which it is difficult for Li to bond later. That is, it is considered that SiO ₂ has a form inactive with respect to Li. Therefore, by reducing the amount of SiO in the negative electrode active material (preferably eliminating SiO), the presence of SiO ₂ having high crystallinity makes it possible to suppress the formation of Li—Si—O compounds during charging, and to suppress the initial coulomb. It is believed that efficiency will improve.

In this embodiment, based on such consideration, SiO which is a forming material of the negative electrode active material is treated under a predetermined condition to change to SiO+SiO→Si+SiO _2, and as described above, Li—Si—O at the time of initial charging. It suppresses the formation of compounds. That is, in the negative electrode active material according to the present embodiment, SiO capable of forming a Li—Si—O compound is changed to SiO ₂ to prevent Li from binding without being desorbed. It should be noted that Si produced simultaneously with SiO ₂ can easily absorb and desorb Li, as can be seen from the reaction mechanism at the time of the initial charge and discharge. Therefore, the negative electrode active material according to the present embodiment has the above-described configuration, that is, X-ray diffraction measurement has peaks at 2θ=26.5° and 28.5°, and the peak intensity at 26.5° is The initial Coulombic efficiency is improved by adopting a configuration in which the peak intensity at 28.5° is 0.2 times or more. The effect of this configuration can be obtained by the presence of highly crystalline SiO ₂ in the negative electrode active material, so the peak intensity at 26.5° is 0.2 times the peak intensity at 28.5°. Even if it is less than (for example, 0.1 times), the corresponding effect can be obtained, but from the viewpoint of surely obtaining the desired effect of the present invention, it is specified to be 0.2 times or more. From the viewpoint of more reliably achieving the desired effect of the present invention, the peak intensity at 26.5° is preferably greater than 0.6 times the peak intensity at 28.5°, and is 0.9 times or more. Is more preferable. The upper limit of the strength ratio is not specified, but if the upper limit is specified, it can be set to, for example, 10 times.

The negative electrode active material according to this embodiment preferably has a carbon coating. Since the conductivity is improved in this way, the initial Coulombic efficiency can be improved by, for example, 5 to 6%. The carbon coating can be formed, for example, by performing thermal decomposition CVD (Chemical Vapor Deposition) on the manufactured negative electrode active material.

<Conductive agent, binder, negative electrode current collector 8>
The conductive agent and the binder used for the negative electrode 3 may be the same as those for the positive electrode 2.
The negative electrode current collector 8 can be, for example, a copper foil, a stainless steel foil, or the like, but is not limited to these.

<Production of Negative Electrode Layer 7>
In order to produce the negative electrode layer 7, it is preferable to mix a negative electrode active material, a conductive agent, and a binder, and then add a solvent to prepare a negative electrode slurry. The solvent used for preparing the negative electrode slurry may be any solvent as long as it can dissolve the binder, and examples thereof include 1-methyl-2-pyrrolidone and water, but are not limited thereto. A known kneader, disperser or the like can be used for the dispersion treatment of the negative electrode active material, the conductive agent and the binder in the solvent.
The mixing ratio of the negative electrode active material, the conductive agent, and the binder is, for example, 60 to 98:0.5 to 20:0.5, when the total ratio of the negative electrode active material:conductive agent:binder is 100. It can be 20 or the like. Further, the solvent can be used in a mass ratio of 0.1 to 2 times the mass of the powder mixture.

The negative electrode layer 7 is prepared by applying the prepared negative electrode slurry to the negative electrode current collector 8 by, for example, a doctor blade method, a dipping method, or a spray method, drying the solvent, and press-molding with a roll press. Can be made.

<Separator 4>
The separator 4 insulates the positive electrode 2 and the negative electrode 3 (prevents a short circuit), and transmits lithium ions between the positive electrode 2 and the negative electrode 3. As the separator 4, for example, a microporous film or non-woven fabric such as polyethylene, polypropylene, polyethylene terephthalate, polyethylene naphthalate, polybutylene terephthalate, polyacrylonitrile, polyaramid, polyamide imide, polyimide, cellulose, or a modified product of cellulose is used. However, the present invention is not limited to these. The thickness of the separator 4 is preferably 40 μm or less from the viewpoint of increasing the output of the battery. By using the separator 4 having such a thickness, the capacity per volume of the battery can be increased.

The thicknesses and shapes of the positive electrode 2 (the positive electrode layer 5 and the positive electrode current collector 6), the negative electrode 3 (the negative electrode layer 7 and the negative electrode current collector 8), and the separator 4 described above can be arbitrarily set.
Moreover, the positive electrode 2, the negative electrode 3, and the separator 4 can be used as one group, and a plurality of groups can be used together. In this case, it is preferable to provide a separator (not shown) for preventing a short circuit between the two groups. As the separator, the separator 4 described above can be used.

<Electrolyte>
As the electrolyte, an organic solvent in which a lithium salt is dissolved can be used.
As the organic solvent of the electrolyte, for example, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, formamide, dimethylformamide, trimethyl phosphate, triethyl phosphate, trisulfite, Dimethyl methylphosphonate and the like can be used, but are not limited thereto. As the organic solvent for the electrolyte, any one selected from the above can be used, and two or more kinds can be used in combination. Additives such as vinylene carbonate, fluoroethylene carbonate, and ethylene sulfite may be added to the electrolyte.
As the lithium salt of the electrolyte, for example, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiN(SO ₂ CF ₃ ) ₂ and LiN(SO ₂ CF ₂ CF ₃ ) ₂ can be used, but the lithium salt is not limited thereto. ..
It is also possible to use a solid electrolyte instead of the above-mentioned electrolyte. Examples of solid _{electrolytes,} may be used, such as _{Li 3 BO 3 -Li 2 SO 4} , Li 7 La 3 Zr 2 O 12, Li 10 GeP 2 S 12, but are not limited to.

<Other configurations of lithium-ion secondary battery 1>
As described above, FIG. 1 illustrates the main constituent elements (portion that contributes to the electrochemical reaction) of the lithium ion secondary battery 1, and regarding other configurations other than the portion that contributes to the electrochemical reaction, Not shown. Examples of the other configurations of the lithium ion secondary battery 1 include an exterior body (not shown) that houses the lithium ion secondary battery 1 described above. The outer package can be formed in an arbitrary shape with a material having corrosion resistance to the electrolyte. The exterior body can be formed of, for example, a bottomed cylindrical or bottomed rectangular tube-shaped main body and a lid body that closes the opening of the main body. In this case, the outer package can be preferably formed of a metal material such as aluminum, stainless steel, or nickel-plated steel. Further, in this case, a resin sealing material may be interposed between the main body and the lid in order to prevent the electrolyte or the like from leaking out from the gap, if necessary. Furthermore, as the outer package, for example, one that is sealed with an arbitrary laminate material can be used.

Further, examples of the other configurations include a positive electrode tab and a negative electrode tab (neither is shown). The positive electrode tab is connected to the positive electrode current collector 6, extends to the outside of the outer package, and is connected to an external power source or the like. The negative electrode tab is connected to the negative electrode current collector 8, extends to the outside of the outer package, and is connected to an external power source or the like.
When the lithium-ion secondary battery 1 is used as a dry battery or a button battery, the positive electrode current collector 6 can be connected to the lid with a positive electrode lead piece (not shown), and the negative electrode current collector 8 can be connected to the negative electrode lead. A piece (not shown) can connect to the bottom of the body.
The positive electrode tab, the negative electrode tab, the positive electrode lead piece, and the negative electrode lead piece can be arbitrarily selected from aluminum foil, copper foil, stainless steel foil, titanium foil, and the like, but are not limited thereto.

<Method for producing negative electrode material for lithium-ion secondary battery>
Next, with reference to FIG. 2, a method for manufacturing the negative electrode material for a lithium ion secondary battery according to the present embodiment (hereinafter, simply referred to as “the present manufacturing method”) will be described. In the description of this manufacturing method, the same components as those already described are designated by the same reference numerals, and the description thereof may be omitted.

FIG. 2 is a flowchart illustrating the content of the method for producing the negative electrode material for lithium-ion secondary battery according to the present embodiment.
As shown in FIG. 2, the present manufacturing method is a method for manufacturing the above-described negative electrode material for a lithium ion secondary battery (negative electrode active material), and includes a mixing step S1 and a firing step S2. In the present manufacturing method, these steps are performed in this order.

<Mixing step S1>
The mixing step S1 is a step of adding, to SiO, a compound having an effect of improving the crystallinity of SiO ₂ in the subsequent firing step 2 and mixing. Examples of the compound having the effect of improving the crystallinity of SiO ₂ include Li and halogen. LiF is a preferred and specific example of the compound having the effect of improving the crystallinity of SiO ₂ . In the following description, LiF will be described as a compound having an effect of improving the crystallinity of SiO ₂ , that is, Li and halogen. The mixing step S1 can be performed using a known kneader. The mixing ratio of SiO and LiF can be set arbitrarily. For example, the molar ratio of Li to Si is preferably 1/100 or more and 1/1 or less, and 1/50 or more and 1/1 or less. Is more preferable.

<Firing step S2>
The firing step S2 is a step of firing the materials obtained by mixing in the mixing step S1 in an inert atmosphere. The inert atmosphere can be formed by replacing the air in the chamber for firing with an inert gas. As the inert gas, for example, helium gas, neon gas, argon gas and the like can be mentioned, but any gas having a low oxygen concentration can be used without being limited thereto. When firing is performed in an inert atmosphere at a temperature higher than 700° C. and lower than 1000° C., preferably near 900° C., a reaction of SiO+SiO→Si+SiO ₂ proceeds and crystallization of SiO ₂ proceeds. Here, as described in the item of [Example], it is confirmed that LiF is not decomposed in the manufactured negative electrode active material by X-ray diffraction measurement, and that it is inactive without using LiF. Since the peak of SiO ₂ is not detected even if baked at 900° C. in the atmosphere, it is considered that LiF plays a role of a catalyst that promotes the reaction of SiO+SiO→Si+SiO ₂ and promotes crystallization of SiO _2. .. Therefore, by performing the firing step S2 under the above conditions, as described above, there are peaks at 2θ=26.5° and 28.5° in the X-ray diffraction measurement, and the peak intensity at 26.5° is A negative electrode active material having a peak intensity of 28.5° or more 0.2 times or more can be manufactured. On the other hand, if the firing temperature is 700° C. or lower, the temperature is too low and the reaction does not proceed sufficiently. Therefore, the negative electrode active material having the above-mentioned peak and peak intensity cannot be manufactured. When the firing temperature is 1000° C. or higher, the temperature is too high, so that SiO and LiF react with each other to form a compound such as Li ₂ SiF ₆ . Therefore, the firing temperature in the firing step S2 is higher than 700°C and lower than 1000°C as described above. The firing temperature is preferably 800 to 950°C, and more preferably 900°C, for example. The firing time in the firing step S2 can be set to, for example, 1 to 20 hours, but is not limited thereto as long as the negative electrode active material having the above-mentioned peak and peak intensity can be produced. The firing time can be, for example, 10 hours.

As described above, the negative electrode material for the lithium ion secondary battery (negative electrode active material) according to the present embodiment is a compound containing at least Si and O as constituent elements, and 2θ=26. There are peaks at 5° and 28.5°, and the peak intensity at 26.5° is 0.2 times or more the peak intensity at 28.5°. Since the negative electrode active material according to the present embodiment has such a configuration, the above-described effects can be exhibited, and the initial Coulombic efficiency is high.
Moreover, since the lithium ion secondary battery 1 according to the present embodiment contains the negative electrode active material according to the present embodiment, the initial Coulombic efficiency is high.
Then, the method for manufacturing the negative electrode material (negative electrode active material) for a lithium ion secondary battery according to this embodiment can manufacture the negative electrode active material according to this embodiment having high initial Coulombic efficiency.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.

The negative electrode active material according to Example 1 was manufactured as follows, and an electrochemical cell was prepared by using the negative electrode active material.

<Example 1>
<Manufacture of negative electrode active material>
SiO and LiF were mixed so that the molar ratio of Li to Si was 1/1, and the obtained mixture was fired at 900° C. for 10 hours in an argon atmosphere to give the negative electrode active material of Example 1. Manufactured.

<Preparation of electrochemical cell>
The manufactured negative electrode active material, a conductive agent, and a binder were mixed in a mass ratio of 70:15:15, and then a solvent was added to the mixture of powders in a mass ratio of 1:1. A negative electrode slurry was prepared. Ketjen black was used as the conductive agent, polyacrylic acid was used as the binder, and 1-methyl-2-pyrrolidone was used as the solvent.
The prepared negative electrode slurry was attached onto a copper foil as the negative electrode current collector 8 by the doctor blade method, dried, and pressure-molded by a roll press to prepare a negative electrode layer 7.

A 30 μm thick separator 4 composed of three layers of polypropylene/polyethylene/polypropylene was prepared. Then, the positive electrode is arranged so that the positive electrode is in contact with one surface of the separator 4, and the negative electrode layer 7 is in contact with the other surface of the separator 4, so that the negative electrode layer 7 and the negative electrode current collector 8 are provided. Was placed. In addition, lithium metal with stable performance was used for the positive electrode.

Then, ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate were mixed at a volume ratio of 1:1:1, and then vinylene carbonate was added at 1% by mass ratio to prepare an organic solvent for the electrolyte. 1.0 mol/L of LiPF ₆ was dissolved as a lithium salt in the prepared organic solvent to prepare an electrolyte. Further, the electrochemical cell was sealed in a glass container to suppress the volatilization of the electrolyte.

<Charge/discharge evaluation>
Charge/discharge evaluation was performed on the electrochemical cell manufactured as described above.
The charge/discharge test in charge/discharge evaluation was performed under the following conditions. That is, the electrochemical cell is charged with a constant current at 0.25 CA in the initial charge, and is charged until the current value of the constant voltage charge becomes 0.125 CA after the voltage reaches 0 V, and is fixed at 1.5 V at 0.25 CA. The current was discharged.
Then, using the obtained discharge capacity (Ah) and charge capacity (Ah), the initial Coulombic efficiency (%) was calculated from the formula of {discharge capacity (Ah)/charge capacity (Ah)}×100. The results are shown in Table 1. Note that the current that can discharge the manufactured electrode in one hour is defined as 1 CA.

<Evaluation of crystal structure>
Moreover, the crystal structure of the manufactured negative electrode active material was evaluated using X-ray diffraction measurement. A value obtained by dividing the peak intensity of SiO ₂ observed at 2θ=26.5° by the peak intensity of Si observed at 2θ=28.5° is shown in Table 1 as an XRD intensity ratio. Further, FIG. 3 shows a diffraction chart obtained by X-ray diffraction measurement. In addition, in FIG. 3, the diffraction charts of the negative electrode active materials according to Comparative Example 1 and Comparative Example 2 are also shown together with the diffraction chart of the negative electrode active material according to Example 1.

<Example 2>
In Example 2, a negative electrode active material was produced under the same conditions as in Example 1 except that SiO and LiF were mixed at a molar ratio of Li to Si of 1/8. Then, in the same manner as in Example 1, the charge/discharge evaluation and the crystal structure evaluation were performed. Table 1 shows the XRD intensity ratio and the initial Coulombic efficiency of the negative electrode active material according to Example 2.

<Example 3>
In Example 3, a negative electrode active material was produced under the same conditions as in Example 1 except that SiO and LiF were mixed at a molar ratio of Li to Si of 1/50. Then, in the same manner as in Example 1, the charge/discharge evaluation and the crystal structure evaluation were performed. Table 1 shows the XRD intensity ratio and the initial Coulombic efficiency of the negative electrode active material according to Example 3.

<Example 4>
In Example 4, a negative electrode active material was manufactured under the same conditions as in Example 1 except that SiO and LiF were mixed so that the molar ratio of Li to Si was 1/100. Then, in the same manner as in Example 1, the charge/discharge evaluation and the crystal structure evaluation were performed. Table 1 shows the XRD intensity ratio and the initial Coulombic efficiency of the negative electrode active material according to Example 4.

<Comparative Example 1>
In Comparative Example 1, a negative electrode active material was manufactured under the same conditions as in Example 1, except that LiF was not used and firing was not performed. Then, in the same manner as in Example 1, the charge/discharge evaluation and the crystal structure evaluation were performed. Table 1 shows the XRD intensity ratio and the initial Coulombic efficiency of the negative electrode active material according to Comparative Example 1. Further, FIG. 3 shows a diffraction chart of the negative electrode active material according to Comparative Example 1.

<Comparative example 2>
In Comparative Example 2, a negative electrode active material was manufactured under the same conditions as in Example 1 except that LiF was not added. Then, in the same manner as in Example 1, the charge/discharge evaluation and the crystal structure evaluation were performed. Table 1 shows the XRD intensity ratio and the initial Coulombic efficiency of the negative electrode active material according to Comparative Example 2. Further, FIG. 3 shows a diffraction chart of the negative electrode active material according to Comparative Example 2.

<Comparative example 3>
In Comparative Example 3, a negative electrode active material was manufactured under the same conditions as in Example 1 except that LiOH.H ₂ O was used instead of LiF. Then, in the same manner as in Example 1, the charge/discharge evaluation and the crystal structure evaluation were performed. Table 1 shows the XRD intensity ratio and the initial Coulombic efficiency of the negative electrode active material according to Comparative Example 3.

<Comparative example 4>
In Comparative Example 4, a negative electrode active material was manufactured under the same conditions as in Example 1 except that Li ₂ CO ₃ was used instead of LiF. Then, in the same manner as in Example 1, the charge/discharge evaluation and the crystal structure evaluation were performed. Table 1 shows the XRD intensity ratio and the initial Coulombic efficiency of the negative electrode active material according to Comparative Example 4.

<Comparative Example 5>
In Comparative Example 5, a negative electrode active material was manufactured under the same conditions as in Example 1 except that the firing temperature was changed to 700°C. Then, in the same manner as in Example 1, the charge/discharge evaluation and the crystal structure evaluation were performed. Table 1 shows the XRD intensity ratio and the initial Coulombic efficiency of the negative electrode active material according to Comparative Example 5.

<Comparative example 6>
In Comparative Example 6, a negative electrode active material was manufactured under the same conditions as in Example 1 except that the firing temperature was changed to 1000°C. Then, in the same manner as in Example 1, the charge/discharge evaluation and the crystal structure evaluation were performed. Table 1 shows the XRD intensity ratio and the initial Coulombic efficiency of the negative electrode active material according to Comparative Example 6.

<Results>
As shown in Table 1, the negative electrode active materials according to Examples 1 to 4 had an initial Coulombic efficiency of more than 70%, which was an excellent result. Further, in the negative electrode active materials according to Examples 1 to 4, peaks were confirmed at 2θ=26.5° and 28.5° in X-ray diffraction measurement (see the diffraction chart of Example 1 shown in FIG. 3). Although the diffraction charts of Examples 2 to 4 are not shown in FIG. 3, peaks are confirmed at the same 2θ (diffraction angle).) Then, as shown in Table 1, the peak intensity of 26.5° (hexagonal SiO ₂ peak intensity) in the negative electrode active materials according to Examples 1 to 4 is 0 of the peak intensity of 28.5°. 0.2 times or more (XRD intensity ratio is 0.2 times or more). This indicates that the crystallization of SiO ₂ was sufficiently advanced. From these results, the reason why the initial coulombic efficiencies of the negative electrode active materials according to Examples 1 to 4 were excellent was that a highly crystalline SiO ₂ domain that was inactive against lithium was formed, and the lithium consumption was irreversible during the initial charging. It was considered that this was because the formation of the Li-Si-O compound accompanied by was suppressed. In this respect, the invention proposed in Patent Document 1 described in the item of [Summary of the Invention], that is, containing an SiO ₂ component having a calcified silica structure, and obtained in the vicinity of 21.825° in X-ray diffraction When the half-width (2θ) of the diffraction peak is 0.15° or less, the negative electrode material for a non-aqueous electrolyte secondary battery or the crystallinity of the Si component of the silicon compound is lower, and the Li—Si—O compound is contained. It can be said that the technical idea is different from that of the negative electrode material for non-aqueous electrolyte secondary batteries, which can exert the effect more effectively.

On the other hand, the negative electrode active materials according to Comparative Examples 1 to 6 had an initial Coulombic efficiency of less than 70%, which was not a satisfactory result. In the negative electrode active materials according to Comparative Examples 1 to 6, in the X-ray diffraction measurement, the hexagonal SiO ₂ peak (peak at 2θ=26.5°) was not observed, and the XRD intensity ratio was zero. These results indicate that the method used in Comparative Examples 1 to 6 was unable to form a highly crystalline SiO ₂ domain, and a high initial Coulombic efficiency was not obtained. In particular, from the results of Comparative Example 3 and Comparative Example 4, it was found that the compound to be mixed when manufacturing the negative electrode active material does not necessarily have to contain only Li, but needs to contain LiF. From the results of Comparative Example 5 and Comparative Example 6, it was found that the firing temperature is also important when manufacturing the negative electrode active material.

Further, as shown in FIG. 3, a LiF peak was confirmed in the negative electrode active material according to Example 1. From this, it was confirmed that LiF was not decomposed by firing during the production of the negative electrode active material. Further, as can be seen by comparing Examples 1 to 4 and Comparative Example 2, it was possible to crystallize SiO ₂ by using LiF. That is, it was found that the use of LiF can promote the crystallization of SiO ₂ . From these, it was considered that LiF plays a role of a catalyst in the firing step S2 for producing the negative electrode active material. In addition, from the results of this time using LiF, it was speculated that the same effect could be obtained as long as it contained Li and halogen (chlorine, bromine, iodine) having the same reactivity as LiF.

From the above results, it was found that the initial Coulombic efficiency of the SiO negative electrode can be improved by converting the oxygen-containing domain of SiO into highly crystalline SiO ₂ .

As described above, the lithium ion secondary battery negative electrode material, the lithium ion secondary battery and the method for producing the lithium ion secondary battery negative electrode material according to the present invention have been described in detail with reference to the embodiments and examples. The present invention is not limited to this, and various modifications are included. For example, the above-described embodiments have been described in detail in order to explain the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. Further, it is possible to add/delete/replace other configurations with respect to a part of the configurations of the respective embodiments.

DESCRIPTION OF SYMBOLS 1 Lithium ion secondary battery 2 Positive electrode 3 Negative electrode 4 Separator 5 Positive electrode layer 6 Positive electrode current collector 7 Negative electrode layer 8 Negative electrode current collector S1 Mixing step S2 Firing step

Claims (9)

A compound containing at least Si and O as constituent elements,
In X-ray diffraction measurement, there are peaks at 2θ=26.5° and 28.5°,
The negative electrode material for a lithium ion secondary battery, wherein the peak intensity at 26.5° is 0.2 times or more the peak intensity at 28.5°. The lithium-ion secondary battery negative electrode material according to claim 1,
A negative electrode material for a lithium ion secondary battery, characterized in that at least a part of the compound contains SiO ₂ . The lithium-ion secondary battery negative electrode material according to claim 1,
The said compound further contains Li and halogen, The negative electrode material for lithium ion secondary batteries characterized by the above-mentioned. The negative electrode material for a lithium ion secondary battery according to claim 3,
The negative electrode material for a lithium ion secondary battery, wherein the molar ratio of Li to Si is 1/100 or more and 1/1 or less. The negative electrode material for a lithium ion secondary battery according to claim 3,
The negative electrode material for a lithium ion secondary battery, wherein the molar ratio of Li to Si is 1/50 or more and 1/1 or less. The negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 5,
A negative electrode material for a lithium ion secondary battery, which has a carbon coating on its surface. A lithium-ion secondary battery including a positive electrode, a negative electrode, and an electrolyte,
A lithium ion secondary battery, wherein the negative electrode includes the negative electrode material for a lithium ion secondary battery according to any one of claims 1 to 5. A method for producing a negative electrode material for a lithium ion secondary battery, which is a compound containing at least Si and O as constituent elements,
A mixing step of mixing SiO, Li and halogen;
A firing step of firing the mixed SiO, Li and the halogen under an inert atmosphere at a temperature higher than 700° C. and lower than 1000° C.;
A method for producing a negative electrode material for a lithium-ion secondary battery, comprising: The method for producing a negative electrode material for a lithium ion secondary battery according to claim 8,
The negative electrode for a lithium ion secondary battery, wherein the SiO, the Li and the halogen are mixed so that a molar ratio of Li to Si is 1/100 or more and 1/1 or less in the mixing step. Material manufacturing method.

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