JP2019023969A - Anode active material and battery - Google Patents

Abstract

To provide an anode active material having appropriate reaction potential and high discharge capacity.SOLUTION: Disclosed anode active material comprises: a layered structure constituted of carbon and boron; and strontium or barium. In the spectrum obtained by analyzing the anode active material by X-ray photoelectron spectroscopy, defining the total peak areas of all peaks which appears in the range of bound energy of 184.0-196.5 eV as S1, and defining the peak area of peaks appearing in the bound energy range of 187.0-188.5 eV as S2, the ratio S2/S1 is, for example, 0.4 or more.SELECTED DRAWING: Figure 3

Description

  The present disclosure relates to a negative electrode active material and a battery.

  As a negative electrode active material of a non-aqueous electrolyte secondary battery represented by a lithium ion secondary battery, a graphite-based carbon material is widely used. In a graphite-based carbon material, the reaction potential at which lithium ions are occluded and released is about 0.1 V with respect to the standard potential of lithium metal. This potential is close to the lithium metal deposition potential (0 V). Therefore, when a slight voltage drop occurs due to an external factor or the like, there is a risk that lithium metal is deposited and the positive electrode and the negative electrode are short-circuited.

  By increasing the reaction potential of the negative electrode active material and increasing the difference between the reaction potential and the deposition potential of lithium metal, it is possible to prevent lithium metal from being easily deposited even if a voltage drop occurs. However, when the reaction potential of the negative electrode active material becomes too high, the capacity density of the battery decreases. In order to realize a battery having both safety and capacity density, it is important to examine the reaction potential of the negative electrode active material.

  Patent Document 1 discloses an electrode using a lithium titanium oxide-based material. The reaction potential at which lithium ions are occluded and released from this electrode is as high as about 1.55 V with respect to the standard potential of lithium metal.

Japanese Patent No. 4435926

  However, the discharge capacity of the lithium titanium oxide-based material as the negative electrode active material is essentially small. Therefore, a negative electrode active material having an appropriate reaction potential and a large discharge capacity is desired.

That is, this disclosure
A layered structure composed of carbon and boron;
With strontium or barium,
A negative electrode active material is provided.

  According to the present disclosure, a negative electrode active material having a low risk of lithium metal deposition and a large discharge capacity can be realized.

FIG. 1 is a schematic cross-sectional view of a battery according to an embodiment of the present disclosure. FIG. 2 shows an XDR spectrum by simulation and an XRD spectrum of the negative electrode active materials of Samples 2, 7, 9, and 10. FIG. 3 is a B1sXPS spectrum of the negative electrode active material of Sample 2.

(Knowledge that became the basis of this disclosure)
An example of a method for increasing the lithium ion reaction potential of graphite is to dissolve boron in the graphite. However, it is boron dissolved in the carbon skeleton by substitution with a carbon atom that contributes to an increase in the reaction potential. This boron state is observed as a peak appearing in a bound energy range of 187 eV or more and 188.5 eV or less in a spectrum obtained by X-ray photoelectron spectroscopy.

  When only boron is dissolved in graphite, the upper limit concentration of boron is 5% or less in terms of molar ratio. Therefore, the effect of raising the reaction potential is slight. The present inventors can increase the solid solution concentration of boron in the graphite-based carbon material by adding an element other than boron to graphite together with boron, and that the effect of increasing the reaction potential can be sufficiently obtained. Predicted. As a result, the inventors have arrived at the configuration of the present disclosure.

The negative electrode active material according to the first aspect of the present disclosure is:
A layered structure composed of carbon and boron;
With strontium or barium,
It is equipped with.

  According to the first aspect, a negative electrode active material having a low risk of lithium metal deposition and a large discharge capacity can be realized.

  In the second aspect of the present disclosure, for example, the layered structure of the negative electrode active material according to the first aspect includes layers, and the strontium or the barium exists between the layers. According to such a configuration, a negative electrode active material having a larger discharge capacity can be realized.

  In the third aspect of the present disclosure, for example, in the negative electrode active material according to the first or second aspect, the spectrum obtained when the negative electrode active material is analyzed by X-ray photoelectron spectroscopy is 187.0 eV or more and 188.5 eV. There are peaks in the following binding energy range. The observation of this peak means that boron is sufficiently dissolved in the carbon layer. The reaction potential of the negative electrode active material can be sufficiently increased by the solid solution of boron in the carbon layer.

  In the fourth aspect of the present disclosure, for example, in the negative electrode active material according to the first to third aspects, the spectrum obtained when the negative electrode active material is analyzed by X-ray photoelectron spectroscopy is 184.0 eV or more and 196.5 eV. There are a plurality of peaks in the following binding energy range, and the peak area of the peak appearing in the binding energy range of 187.0 eV or more and 188.5 eV or less is the largest among the plurality of peaks. According to such a configuration, a negative electrode active material having a higher discharge potential and a larger discharge capacity can be realized.

  In the fifth aspect of the present disclosure, for example, in the negative electrode active material according to the first to fourth aspects, the spectrum obtained when the negative electrode active material is analyzed by X-ray photoelectron spectroscopy is 184.0 eV or more and 196.5 eV. When the sum of the peak areas of all the peaks appearing in the following binding energy range is defined as S1, and the peak area of the peak appearing in the binding energy range of 187.0 eV or more and 188.5 eV or less is defined as S2, the ratio S2 / S1 is 0.4 or more. According to such a configuration, a negative electrode active material having a higher discharge potential and a larger discharge capacity can be realized.

In the sixth aspect of the present disclosure, for example, the negative electrode active material according to the first to fifth aspects is represented by the following composition formula (1). According to such a configuration, a negative electrode active material having a high discharge potential and a large discharge capacity can be realized.
_{M x B y C z ··· (} 1)
[In formula (1), M is strontium or barium;
x, y and z are each greater than 0;
The relationship y / (y + z) ≦ 0.2 is satisfied. ]

The battery according to the seventh aspect of the present disclosure is:
A negative electrode comprising a negative electrode active material according to any one of the first to seventh aspects;
A positive electrode;
Electrolyte,
It is equipped with.

  According to the seventh aspect, a battery having a low risk of lithium metal deposition and a large discharge capacity can be realized.

  In the eighth aspect of the present disclosure, for example, the negative electrode of the battery according to the seventh aspect includes the negative electrode active material as a main component. According to such a configuration, a battery having a larger discharge capacity density can be realized.

  Hereinafter, embodiments of the present disclosure will be described. The present disclosure is not limited to the following embodiments.

(Embodiment 1)
The negative electrode active material of this embodiment includes strontium or barium and a layered structure. Strontium or barium is supported in a layered structure. The layered structure is composed of carbon and boron.

  The present inventors examined the influence of the state and amount of boron added to the carbon material on the reaction potential. As a result, it has been found that the reaction potential increases with an increase in the proportion of boron dissolved in the carbon layer. Furthermore, it has been found that it is effective to contain strontium or barium in the carbon material in order to allow boron in a solid solution state to exist stably. The reason is considered as follows, for example.

Examples of the presence state of boron in the carbon material include boron bonded to carbon, boron bonded to boron, boron bonded to oxygen or nitrogen contained in a minute amount, and the like. Boron atoms bonded to carbon include boron atoms that are solid-solved in the carbon layer, boron atoms that are solid-solved between layers between the carbon layers, boron atoms that constitute carbides such as B ₄ C, and the like. . Since the number of electrons in boron is one less than the number of electrons in carbon, when boron atoms are dissolved in the carbon layer, the electron density of conjugated electrons in the carbon layer decreases. The Fermi energy of the material (graphite-like compound) in the case where boron dissolved in the carbon layer is present is lower than the Fermi energy in the case of no boron (graphite). As a result, the reaction potential at which lithium ions are occluded and released increases.

  The reason why the addition of strontium or barium is effective for stabilizing the solid solution state of boron in the carbon layer is considered as follows.

  The number of electrons in boron is one less than the number of electrons in carbon. If the atomic concentration of boron in a solid solution state is increased, the electrical neutrality cannot be maintained. However, if strontium atoms or barium atoms exist in the vicinity of the network of the carbon layer in which boron is dissolved, or between the layers of the carbon layer, a part of the deficient electrons are supplied from strontium or barium, resulting in electrical neutrality. Is guaranteed. Thus, it is considered that by adding strontium or barium together with boron to a carbon material such as graphite, the solid solution state of boron is stabilized as compared with the case where these elements are not added.

  In the negative electrode active material of this embodiment, the layered structure may have an interlayer. At this time, strontium or barium may exist between the layers. According to such a configuration, a negative electrode active material having a larger discharge capacity can be realized.

  The bonding state of boron can be examined by X-ray photoelectron spectroscopy. Specifically, the difference in the bonding state of boron is observed as a chemical shift of a peak derived from the 1s orbital of boron. A peak derived from the B1s orbital appears in a range of binding energy of approximately 184.0 eV or more and 196.5 eV or less. In this specification, an XPS spectrum in the range of a binding energy of 184.0 eV or more and 196.5 eV or less is also referred to as “B1sXPS spectrum”.

  In the spectrum obtained by analyzing the negative electrode active material of this embodiment by X-ray photoelectron spectroscopy, a peak exists in the range of the binding energy of 187.0 eV or more and 188.5 eV or less. The observation of this peak means that boron is sufficiently dissolved in the carbon layer. The reaction potential of the negative electrode active material can be sufficiently increased by the solid solution of boron in the carbon layer.

  When boron in various bonded states is present in the negative electrode active material, a plurality of peaks appear in the B1sXPS spectrum. In other words, there are a plurality of peaks in the bound energy range of 184.0 eV or more and 196.5 eV or less. Among these peaks, it is desirable that the peak area of the peak appearing in the bound energy range of 187.0 eV or more and 188.5 eV or less is the largest. The observation of this peak means that boron is sufficiently dissolved in the carbon layer. According to such a configuration, a negative electrode active material having a higher discharge potential and a larger discharge capacity can be realized.

  The sum of the peak areas of all peaks that appear in the bound energy range of 184.0 eV or more and 196.5 eV or less can be defined as S1. A peak area of a peak appearing in a bound energy range of 187.0 eV or more and 188.5 eV or less is defined as S2. At this time, the ratio S2 / S1 may be 0.4 or more. According to such a configuration, a negative electrode active material having a higher discharge potential and a larger discharge capacity can be realized. The upper limit of ratio S2 / S1 is not specifically limited, For example, it is 1.0.

  The negative electrode active material of the present embodiment may be a material represented by the following composition formula (1). In formula (1), M is strontium or barium. x, y, and z are values greater than 0, respectively. In the formula (1), the relationship y / (y + z) ≦ 0.2 may be satisfied. That is, in the negative electrode active material of this embodiment, even if the ratio of the number of boron atoms to the total (B + C) of the number of boron atoms and the number of carbon atoms (B / (B + C)) is 0.2 or less. Good. According to such a configuration, a negative electrode active material having a high discharge potential and a large discharge capacity can be realized. The lower limit of the ratio (B / (B + C)) is not particularly limited, and is 0.03, for example.

_{M x B y C z ··· (} 1)

  It can be confirmed by X-ray diffraction (XRD) measurement that the negative electrode active material of this embodiment has a layered structure. The composition ratio of carbon, boron, and strontium (or barium) can be specified by, for example, inductively coupled plasma (ICP) emission spectroscopy.

  The amount of boron in various bonded states can be quantified by X-ray photoelectron spectroscopy. Specifically, each peak appearing in the B1sXPS spectrum is defined by a Gaussian function or a Lorentz function, and fitting is performed. The integrated intensity (= peak area) of each peak is obtained from the fitting curve. When the peak is asymmetric, calculation may be performed in consideration of asymmetry.

  The negative electrode active material of this embodiment can be manufactured by the method described below.

  A carbon source, a boron source, and a strontium source or a barium source are thoroughly mixed. The resulting mixture is fired under an inert atmosphere. Thereby, the negative electrode active material of this embodiment is obtained.

  As the carbon source, at least one selected from a graphite material, an organic material, and an amorphous carbon material can be used. When a graphite material is used as the carbon source, solid solution of boron and strontium or barium in the graphite material proceeds simultaneously. When an organic material or an amorphous carbon material is used as the carbon source, graphitization of the carbon source and solid solution of each element in the graphite proceed simultaneously.

  A synthetic resin such as polyvinyl alcohol can be used as the organic material. The shape of the synthetic resin is not particularly limited and is, for example, a sheet shape, a fiber shape, or a particle shape. In view of processing after firing, a particulate or short fiber synthetic resin having a size of 1 to 100 μm is desirable.

  As the amorphous carbon material, soft carbon such as petroleum coke and coal coke can be used. The shape of the soft carbon is not particularly limited and is, for example, a sheet shape, a fiber shape or a particle shape. Considering processing after firing, particulate or short fiber soft carbon having a size of 1 to 100 μm is desirable.

  As the boron source, boron, boric acid, calcium boride and the like can be used. Diboride such as aluminum diboride and magnesium diboride can also be used as a source of boron.

  As the strontium source, strontium metal, strontium hydride, strontium hydroxide, strontium carbide, strontium carbonate, strontium boride and the like can be used.

  As the barium source, barium metal, barium hydride, barium hydroxide, barium carbide, barium carbonate, barium boride and the like can be used.

  The firing temperature is, for example, 1000 ° C. to 2200 ° C. The firing atmosphere is desirably an inert atmosphere. An inert gas such as nitrogen gas, argon gas, helium gas, or neon gas can be suitably used for the inert atmosphere. From the viewpoint of cost, nitrogen gas is desirable. By firing at a temperature lower than 1000 ° C., elements other than carbon evaporate from the raw material used as the carbon source, and carbonization of the raw material proceeds. The graphitization of carbon proceeds by firing at 1000 ° C. to 2200 ° C. Along with carbon graphitization, the carbon source, boron source and strontium source or barium source react to advance solid solution of boron in the graphite crystal and solid solution of strontium or barium between the graphite layers. .

  The ratio of the constituent elements in the negative electrode active material can be adjusted by appropriately selecting the type of raw material, the mixing ratio of the raw materials, the firing conditions of the raw material mixture, the reprocessing conditions after firing, and the like. The kind of raw material means the kind of carbon source, the kind of boron source, the kind of strontium source, and the kind of barium source. The mixing ratio of the raw materials means a mixing ratio of a carbon source, a boron source, and a strontium source or a barium source. The reprocessing after firing includes acid cleaning, additional heat treatment, and the like.

  As described above, the negative electrode active material of the present embodiment can be manufactured through a process of mixing raw materials and a process of firing the obtained raw material mixture in an inert atmosphere. In the step of mixing the raw materials, a carbon source, a boron source, and a strontium source or a barium source are mixed.

(Embodiment 2)
The second embodiment will be described below. The description overlapping with the first embodiment will be omitted as appropriate.

  As shown in FIG. 1, the battery 10 of this embodiment includes a negative electrode 13, a positive electrode 16, a separator 17, and an exterior 18. The negative electrode 13 includes a negative electrode current collector 11 and a negative electrode active material layer 12 (negative electrode mixture layer). The negative electrode active material layer 12 is provided on the negative electrode current collector 11. The positive electrode 16 includes a positive electrode current collector 14 and a positive electrode active material layer 15 (positive electrode mixture layer). The positive electrode active material layer 15 is provided on the positive electrode current collector 14. A separator 17 is disposed between the negative electrode 13 and the positive electrode 16. The negative electrode 13 and the positive electrode 16 face each other through the separator 17. The negative electrode 13, the positive electrode 16, and the separator 17 are housed in an exterior 18.

  The battery 10 is, for example, a nonaqueous electrolyte secondary battery or an all-solid secondary battery. The battery 10 is typically a lithium ion secondary battery.

  The negative electrode active material layer 12 includes the negative electrode active material described in the first embodiment. The negative electrode active material layer 12 may contain a second negative electrode active material, a conductive additive, an ionic conductor, a binder, and the like as necessary. The second negative electrode active material is a negative electrode active material having a composition different from that of the negative electrode active material described in Embodiment 1, and is a material capable of inserting and extracting lithium ions.

  The negative electrode active material layer 12 may contain the negative electrode active material described in Embodiment 1 as a main component. The “main component” means a component that is contained most by mass ratio. The negative electrode active material layer 12 may include 50% or more of the negative electrode active material described in Embodiment 1 in a mass ratio with respect to the entire negative electrode active material layer 12, or may include 70% or more. According to such a configuration, the battery 10 having a larger discharge capacity density can be realized.

  The negative electrode active material layer 12 includes a negative electrode active material as a main component, and may further include inevitable impurities. The inevitable impurities include starting materials used when synthesizing the negative electrode active material, by-products generated when synthesizing the negative electrode active material, decomposition products thereof, and the like. The negative electrode active material layer 12 may contain 100% of the negative electrode active material described in Embodiment 1 in a mass ratio with respect to the entire negative electrode active material layer 12 except for inevitable impurities.

The conductive assistant and the ionic conductor are used for reducing the resistance of the negative electrode 13. Examples of conductive assistants include carbon materials such as carbon black, graphite, acetylene black, carbon nanotubes, carbon nanofibers, graphene, fullerene, graphite oxide, and conductive polymer compounds such as polyaniline, polypyrrole, and polythiophene. Can be used. As the ionic conductor, a gel electrolyte such as polymethyl methacrylate and polymethyl methacrylate, an organic solid electrolyte such as polyethylene oxide, and an inorganic solid electrolyte such as Li ₇ La ₃ Zr ₂ O ₁₂ can be used.

  The binder is used for improving the binding property of the material constituting the negative electrode 13. As a binder, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polytetrafluoroethylene, carboxymethylcellulose, polyacrylic acid, styrene-butadiene copolymer rubber, polypropylene, Polymer materials such as polyethylene and polyimide can be used.

  As the negative electrode current collector 11, a sheet or a film made of a metal material such as stainless steel, nickel, copper, or an alloy thereof can be used. The sheet or film may be porous or non-porous. As the sheet or film, a metal foil, a metal mesh or the like is used. A carbon material such as carbon may be applied to the surface of the negative electrode current collector 11 as a conductive auxiliary material. In this case, the resistance value is reduced, the catalytic effect is imparted, or the negative electrode active material layer 12 and the negative electrode current collector 11 are chemically or physically bonded to each other to thereby form the negative electrode active material layer 12 and the negative electrode current collector. 11 is strengthened.

  The positive electrode active material layer 15 includes a positive electrode active material capable of inserting and extracting lithium ions. The positive electrode active material layer 15 may contain a conductive additive, an ionic conductor, a binder, and the like as necessary. The same materials as those usable for the negative electrode active material layer 12 can be used for the positive electrode active material layer 15 as the conductive assistant, the ionic conductor, and the binder.

  As the positive electrode active material, lithium-containing transition metal oxides, transition metal fluorides, polyanion materials, fluorinated polyanion materials, transition metal sulfides, and the like can be used. Lithium-containing transition metal oxides are desirable because of low manufacturing costs and high average discharge voltage.

  As the positive electrode current collector 14, a sheet or film made of a metal material such as aluminum, stainless steel, titanium, or an alloy thereof can be used. Aluminum and its alloys are suitable for the material of the positive electrode current collector 14 because they are inexpensive and easily thin. The sheet or film may be porous or non-porous. As the sheet or film, a metal foil, a metal mesh or the like is used. A carbon material such as carbon may be applied to the surface of the positive electrode current collector 14 as a conductive auxiliary material. In this case, the resistance value is reduced, the catalytic effect is imparted, or the positive electrode active material layer 15 and the positive electrode current collector 14 are chemically or physically combined to form the positive electrode active material layer 15 and the positive electrode current collector. 14 is strengthened.

  Battery 10 further includes an electrolyte. The electrolyte may be a non-aqueous electrolyte. As the electrolyte, an electrolytic solution containing a lithium salt and a nonaqueous solvent, a gel electrolyte, a solid electrolyte, or the like can be used. When the electrolyte is a liquid, the electrolyte is impregnated in each of the negative electrode 13, the positive electrode 16, and the separator 17. When the electrolyte is solid, the separator 17 can be composed of the electrolyte. The solid electrolyte may be included in the negative electrode 13 or may be included in the positive electrode 16.

As lithium salts, lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium perchlorate (LiClO ₄ ), lithium bistrifluoromethylsulfonylimide (LiN (SO ₂ CF ₃ ) ₂ ), Bisperfluoroethylsulfonylimide lithium (LiN (SO ₂ C ₂ F ₅ ) ₂ ), bisfluoromethylsulfonylimide lithium (LiN (SO ₂ F) ₂ ), LiAsF ₆ , LiCF ₃ SO ₃ , difluoro (oxalato) Lithium borate or the like can be used. One kind selected from these electrolyte salts may be used, or two or more kinds may be used in combination. From the viewpoint of safety, thermal stability and ion conductivity of the battery 10, LiPF ₆ is desirable.

  As the non-aqueous solvent, cyclic carbonate, chain carbonate, ester, cyclic ether, chain ether, nitrile, amide and the like can be used. One kind selected from these solvents may be used, or two or more kinds may be used in combination.

  As the cyclic carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, or the like can be used. In these compounds, some or all of the hydrogen atoms may be substituted with fluorine. As the fluorine-substituted cyclic carbonate, trifluoropropylene carbonate, fluoroethyl carbonate, or the like can be used.

  As the chain carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate and the like can be used. In these compounds, some or all of the hydrogen atoms may be substituted with fluorine.

  As the ester, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone and the like can be used.

  1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,4-dioxane, 1,3,5-trioxane as cyclic ether , Furan, 2-methylfuran, 1,8-cineol, crown ether, and the like can be used.

  As chain ether, 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl ether, Methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxy Methane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, tetraethylene It recalls dimethyl may be used.

  As the nitrile, acetonitrile or the like can be used.

  As the amide, dimethylformamide or the like can be used.

  As the solid electrolyte, an organic polymer solid electrolyte, an oxide solid electrolyte, a sulfide solid electrolyte, or the like can be used.

  A compound of a polymer and a lithium salt can be used as the organic polymer solid electrolyte. The polymer may have an ethylene oxide structure. When the polymer has an ethylene oxide structure, the organic polymer solid electrolyte can contain a large amount of lithium salt, and the ionic conductivity of the organic polymer solid electrolyte is increased.

As an oxide solid electrolyte, a NASICON solid electrolyte typified by LiTi ₂ (PO ₄ ) ₃ and its element substitution, a (LaLi) TiO ₃ perovskite solid electrolyte, Li ₁₄ ZnGe ₄ O ₁₆ , Li ₄ SiO ₄ LISICON type solid electrolytes typified by LiGeO ₄ and their element substitutions, garnet type solid electrolytes typified by Li ₇ La ₃ Zr ₂ O ₁₂ and its element substitutions, Li ₃ N and its H substitutions, Li ₃ PO ₄ and its N-substituted product can be used.

As a sulfide solid electrolyte, Li ₂ S—P ₂ S ₅ , Li ₂ S—SiS ₂ , Li ₂ S—B ₂ S ₃ , Li ₂ S—GeS ₂ , Li _3.25 Ge _0.25 P _0.75 S ₄ , Li ₁₀ GeP such as ₂ S ₁₂ can be used. These sulfide materials include LiX (X: F, Cl, Br, I), MO _p , Li _q MO _p (M: P, Si, Ge, B, Al, Ga, or In) (p, q: natural number) Etc. may be added.

The sulfide solid electrolyte is rich in moldability and has high ionic conductivity. Therefore, the battery 10 which has a higher energy density is realizable by using a sulfide solid electrolyte as a solid electrolyte. Among sulfide solid electrolytes, Li ₂ S—P ₂ S ₅ has high electrochemical stability and high ionic conductivity. If Li ₂ S—P ₂ S ₅ is used as the solid electrolyte, the battery 10 having a higher energy density can be realized.

  The shape of the battery 10 is not particularly limited. Various shapes such as a coin shape, a cylindrical shape, a square shape, a sheet shape, a button shape, a flat shape, and a laminated shape can be adopted as the shape of the battery 10.

  The following example is an example, and the present disclosure is not limited to the following example.

(Sample 1)
[Production of negative electrode active material]
Graphite powder having an average particle diameter of 1 μm, strontium hydride powder, and boron powder were pulverized and mixed using an agate mortar to obtain a raw material mixture. The amount of strontium hydride powder was 93.4% in terms of mass relative to the graphite powder. The amount of boron powder was 22.5% in terms of mass with respect to graphite powder.

  The raw material mixture is put in a firing furnace (Ar gas flow rate 1 L / min) in an Ar atmosphere, and the temperature inside the firing furnace is increased from room temperature to 1800 ° C. at a rate of 5 ° C. per minute, and then at 1800 ° C. for 5 hours. Retained. Then, heating was stopped and the fired product was taken out from the firing furnace after natural cooling. The fired product was pulverized in an agate mortar to obtain a negative electrode active material powder of Sample 1.

[Analysis of negative electrode active material]
Using a desktop X-ray diffractometer (MiniFlex300 / 600 manufactured by Rigaku Corporation), powder X-ray diffraction measurement of the negative electrode active material of Sample 1 was performed. The negative electrode active material of Sample 1 had a layered structure as the main phase. The layered structure was composed of carbon and boron, and strontium was present between the layers of the layered structure.

The composition of the negative electrode active material of Sample 1 was examined using an inductively coupled plasma emission spectrometer (CIROS-120 manufactured by Spectro). The composition of the negative electrode active material of Sample 1 was Sr _0.07 B _0.19 C _0.74 , and the ratio B / (B + C) was 19.56%.

  An XPS spectrum of the negative electrode active material of Sample 1 was obtained using an X-ray photoelectron spectrometer (PHI5600 manufactured by ULVAC-PHI). The X-ray source was Al (AlKα). XPS spectra were obtained in the range of binding energy from 184.0 to 196.5 eV. The peak areas of all peaks present in the obtained XPS spectrum were calculated by the method described above. The total S1 of these peak areas was calculated. Among the peaks present in the obtained XPS spectrum, the peak area S2 of the peak that appeared in the bound energy range of 187.0 to 188.5 eV was calculated. From the ratio (S2 / S1), among all the boron contained in the negative electrode active material of Sample 1, the ratio of boron dissolved in the carbon layer was calculated. The proportion of boron dissolved in the carbon layer was 48.81% in atomic ratio.

[Production of test electrode]
The negative electrode active material of Sample 1, acetylene black as a conductive additive, and polyvinylidene fluoride as a binder were sufficiently mixed using an agate mortar. Thereby, a negative electrode mixture was obtained. The mass ratio of the negative electrode active material, acetylene black, and polyvinylidene fluoride was 7: 2: 1. The negative electrode mixture was dispersed in an NMP solvent to prepare a slurry. The slurry was apply | coated on Cu current collector using the coating machine. The coating film on the Cu current collector was dried to obtain an electrode plate. After rolling the electrode plate with a rolling mill, it was punched into a square shape with a diameter of 20 mm. A lead terminal was attached to a square electrode plate to obtain a test electrode of Sample 1.

[Production of evaluation cell]
A lithium secondary battery (evaluation cell) was prepared by the method described below using the test electrode of Sample 1, a counter electrode made of lithium metal, and a reference electrode made of lithium metal. The electrolytic solution was prepared and the evaluation cell was produced in a glove box having an Ar atmosphere with a dew point of −60 degrees or less and an oxygen value of 1 ppm or less.

Ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate were mixed at a volume ratio of 5:70:25 to obtain a mixed solvent. Lithium hexafluorophosphate (LiPF ₆ ) was dissolved in this mixed solvent at a concentration of 1.4 mol / liter to obtain an electrolytic solution. A lithium metal foil was pressure-bonded to a square nickel mesh having a side of 20 mm to obtain a counter electrode. A separator of a polyethylene microporous membrane was impregnated with an electrolytic solution. A separator was disposed between the test electrode and the counter electrode, and the test electrode and the counter electrode were opposed to each other. The test electrode, the counter electrode, and the separator were accommodated in the exterior, and the exterior was sealed. Thereby, an evaluation cell of Sample 1 was obtained.

[Charge / discharge test]
The charge / discharge test of the evaluation cell of Sample 1 was performed to evaluate the charge / discharge characteristics. The charge / discharge test was performed in a constant temperature bath at 25 ° C. In the charge / discharge test, the evaluation cell was charged and rested for 20 minutes, and then the evaluation cell was discharged. The battery was charged at a constant current of 5 mA per 1 cm ² test electrode until the potential difference between the test electrode and the reference electrode reached 0V. Thereafter, discharging was performed at a constant current of 5 mA per 1 cm ² of the test electrode until the potential difference between the test electrode and the reference electrode reached 2V. The reaction potential of the negative electrode active material of Sample 1 was 1.40 V, and the initial discharge capacity was 299 mAh / g.

(Sample 2)
A negative electrode active material of Sample 2 was produced in the same manner as Sample 1, except that the ratio of raw materials was changed. In Sample 2, the amount of strontium hydride powder was 74.7% in terms of mass relative to the graphite powder. The amount of boron powder was 18.0% in terms of mass relative to graphite powder.

  The result of the XRD measurement of the negative electrode active material of Sample 2 is shown in FIG. In FIG. 2, the peak indicated by a square mark is a peak derived from the layered structure of the graphite-like compound. In the diffraction pattern of sample 9, the peak indicated by a triangle is a peak derived from hexaboride. The negative electrode active material of Sample 2 had a layered structure composed of carbon and boron. Strontium was contained between the layers of the layered structure. In sample 2, the generation of impurities was not confirmed.

  Whether each sample has a layered structure was determined by the following method. First, using a crystal structure drawing tool “VESTA”, a model of a structure in which Sr or Ba atoms were inserted between layers of carbon hexagonal network composed of carbon and boron was created. Next, the XRD spectrum of the model was simulated using a Rietveld analysis tool “Rietan-FP”. The results are shown in FIG. When the actual measurement results were in good agreement with the simulation results, it was determined that the negative electrode active material of each sample had a layered structure.

The composition of the negative electrode active material of Sample 2 was Sr _0.06 B _0.15 C _0.84 , and the ratio B / (B + C) was 15.15%. From the result of XPS measurement, the ratio of boron dissolved in the carbon layer was calculated. The proportion of boron dissolved in the carbon layer was 56.80% in atomic ratio. Using the negative electrode active material of Sample 2, a test electrode and an evaluation cell were prepared in the same manner as Sample 1, and charge / discharge characteristics were evaluated. The reaction potential of the negative electrode active material of Sample 2 was 1.02 V, and the initial discharge capacity was 308 mAh / g.

  FIG. 3 is a B1sXPS spectrum after peak separation of the negative electrode active material of Sample 2. In sample 2, five peaks appeared in the binding energy range of 184.0 to 196.5 eV (peak Nos. 1 to 5). First, the peak areas of all the peaks (peak Nos. 1 to 5) were calculated, and the sum thereof was calculated. Next, the peak area of the peak (peak No. 1) that appeared in the bound energy range of 187.0 to 188.5 eV was calculated. No. for the total peak area S1. The ratio of the peak area S2 of the peak 1 (S2 / S1) was 56.80%. The ratio of the peak area of each peak to the total peak area was as shown in FIG.

(Sample 3)
A negative electrode active material of Sample 3 was produced in the same manner as Sample 1, except that the ratio of the raw materials was changed. In Sample 3, the amount of strontium hydride powder was 62.2% in terms of mass relative to the graphite powder. The amount of boron powder was 15.0% in terms of mass relative to graphite powder.

  The negative electrode active material of Sample 3 had a layered structure composed of carbon and boron. Strontium was contained between the layers of the layered structure. In Sample 3, a small amount of graphite was confirmed as an impurity.

The composition of the negative electrode active material of Sample 3 was Sr _0.06 B _0.13 C _0.83 , and the ratio B / (B + C) was 13.13%. From the result of XPS measurement, the ratio of boron dissolved in the carbon layer was calculated. The proportion of boron dissolved in the carbon layer was 52.20% in atomic ratio. Using the negative electrode active material of Sample 3, test electrodes and evaluation cells were prepared in the same manner as Sample 1, and charge / discharge characteristics were evaluated. The reaction potential of the negative electrode active material of Sample 3 was 0.93 V, and the initial discharge capacity was 321 mAh / g.

(Sample 4)
A negative electrode active material of Sample 4 was produced in the same manner as Sample 1, except that the ratio of the raw materials was changed. In Sample 4, the amount of strontium hydride powder was 53.3% in terms of mass relative to the graphite powder. The amount of boron powder was 12.9% in terms of mass relative to graphite powder.

  The negative electrode active material of Sample 4 had a layered structure composed of carbon and boron. Strontium was contained between the layers of the layered structure. In sample 4, the production of a small amount of graphite as an impurity was confirmed.

The composition of the negative electrode active material of Sample 4 was Sr _0.04 B _0.10 C _0.85 , and the ratio B / (B + C) was 10.40%. From the result of XPS measurement, the ratio of boron dissolved in the carbon layer was calculated. The proportion of boron dissolved in the carbon layer was 50.10% in atomic ratio. Using the negative electrode active material of Sample 4, test electrodes and evaluation cells were prepared in the same manner as Sample 1, and charge / discharge characteristics were evaluated. The reaction potential of the negative electrode active material of Sample 4 was 0.82 V, and the initial discharge capacity was 329 mAh / g.

(Sample 5)
A negative electrode active material of Sample 5 was prepared in the same manner as Sample 1, except that barium hydride powder was used instead of strontium hydride powder. In Sample 5, the amount of barium hydride powder was 145.1% in terms of mass with respect to the graphite powder. The amount of boron powder was 22.5% in terms of mass with respect to graphite powder.

  The negative electrode active material of Sample 5 had a layered structure composed of carbon and boron. Barium was contained between the layers of the layered structure. In Sample 5, the production of a small amount of barium boride as an impurity was confirmed.

The composition of the negative electrode active material of Sample 5 was Ba _0.09 B _0.13 C _0.76 , and the ratio B / (B + C) was 16.82%. From the result of XPS measurement, the ratio of boron dissolved in the carbon layer was calculated. The proportion of boron dissolved in the carbon layer was 40.05% in atomic ratio. Using the negative electrode active material of Sample 5, test electrodes and evaluation cells were prepared in the same manner as Sample 1, and charge / discharge characteristics were evaluated. The reaction potential of the negative electrode active material of Sample 5 was 1.78 V, and the initial discharge capacity was 174 mAh / g.

(Sample 6)
A negative electrode active material of Sample 6 was produced in the same manner as Sample 5, except that the ratio of the raw materials was changed. In Sample 6, the amount of barium hydride powder was 116.1% in terms of mass relative to the graphite powder. The amount of boron powder was 18.4% in terms of mass with respect to graphite powder.

  The negative electrode active material of Sample 6 had a layered structure composed of carbon and boron. Barium was contained between the layers of the layered structure. In Sample 6, the generation of impurities was not confirmed.

The composition of the negative electrode active material of Sample 6 was Ba _0.07 B _0.12 C _0.81 , and the ratio B / (B + C) was 12.95%. From the result of XPS measurement, the ratio of boron dissolved in the carbon layer was calculated. The proportion of boron dissolved in the carbon layer was 43.81% in atomic ratio. Using the negative electrode active material of Sample 6, a test electrode and an evaluation cell were prepared in the same manner as Sample 1, and charge / discharge characteristics were evaluated. The reaction potential of the negative electrode active material of Sample 6 was 1.30 V, and the initial discharge capacity was 176 mAh / g.

(Sample 7)
A negative electrode active material of Sample 7 was produced in the same manner as Sample 5, except that the ratio of the raw materials was changed. In Sample 7, the amount of barium hydride powder was 96.8% in terms of mass relative to the graphite powder. The amount of boron powder was 15.0% in terms of mass relative to graphite powder.

  The result of the XRD measurement of the negative electrode active material of Sample 7 is shown in FIG. The negative electrode active material of Sample 7 had a layered structure composed of carbon and boron. Barium was contained between the layers of the layered structure. In sample 7, the generation of impurities was not confirmed.

The composition of the negative electrode active material of Sample 7 was Ba _0.06 B _0.10 C _0.83 , and the ratio B / (B + C) was 10.79%. From the result of XPS measurement, the ratio of boron dissolved in the carbon layer was calculated. The proportion of boron dissolved in the carbon layer was 40.20% in atomic ratio. Using the negative electrode active material of Sample 7, test electrodes and evaluation cells were prepared in the same manner as Sample 1, and charge / discharge characteristics were evaluated. The reaction potential of the negative electrode active material of Sample 7 was 0.83 V, and the initial discharge capacity was 181 mAh / g.

(Sample 8)
A negative electrode active material of Sample 8 was produced in the same manner as Sample 5, except that the ratio of the raw materials was changed. In Sample 8, the amount of barium hydride powder was 82.9% in terms of mass relative to the graphite powder. The amount of boron powder was 12.9% in terms of mass relative to graphite powder.

  The negative electrode active material of Sample 8 had a layered structure composed of carbon and boron. Barium was contained between the layers of the layered structure. In Sample 8, the production of a small amount of graphite as an impurity was confirmed.

The composition of the negative electrode active material of Sample 8 was Ba _0.05 B _0.09 C _0.86 , and the ratio B / (B + C) was 9.04%. From the result of XPS measurement, the ratio of boron dissolved in the carbon layer was calculated. The proportion of boron dissolved in the carbon layer was 41.32% in atomic ratio. Using the negative electrode active material of Sample 8, a test electrode and an evaluation cell were prepared in the same manner as Sample 1, and charge / discharge characteristics were evaluated. The reaction potential of the negative electrode active material of Sample 8 was 0.79 V, and the initial discharge capacity was 201 mAh / g.

(Sample 9)
A negative electrode active material of Sample 9 was produced in the same manner as Sample 1, except that the ratio of the raw materials was changed. In Sample 9, the amount of strontium hydride powder was 124.5% in terms of mass relative to the graphite powder. The amount of boron powder was 30.0% in terms of mass relative to graphite powder.

  The negative electrode active material of Sample 9 had a layered structure composed of carbon and boron as the main phase. Strontium was contained between the layers of the layered structure.

The composition of the negative electrode active material of Sample 9 was Sr _0.09 B _0.21 C _0.70 , and the ratio B / (B + C) was 23.86%. From the result of XPS measurement, the ratio of boron dissolved in the carbon layer was calculated. The proportion of boron dissolved in the carbon layer was 39.91% in atomic ratio. Using the negative electrode active material of Sample 9, test electrodes and evaluation cells were prepared in the same manner as Sample 1, and charge / discharge characteristics were evaluated. The reaction potential of the negative electrode active material of Sample 9 was 1.54 V, and the initial discharge capacity was 227 mAh / g.

(Sample 10)
A negative electrode active material of Sample 10 was produced in the same manner as Sample 5, except that the ratio of the raw materials was changed. In Sample 10, the amount of barium hydride powder was 193.5% in terms of mass relative to the graphite powder. The amount of boron powder was 30.0% in terms of mass relative to graphite powder.

  The negative electrode active material of Sample 10 had a layered structure composed of carbon and boron. Barium was contained between the layers of the layered structure. In Sample 10, the production of a small amount of barium boride as an impurity was confirmed.

The composition of the negative electrode active material of Sample 10 was Ba _0.11 B _0.22 C _0.67 , and the ratio B / (B + C) was 24.58%. From the result of XPS measurement, the ratio of boron dissolved in the carbon layer was calculated. The proportion of boron dissolved in the carbon layer was 32.40% in atomic ratio. Using the negative electrode active material of Sample 10, a test electrode and an evaluation cell were prepared in the same manner as Sample 1, and the charge / discharge characteristics were evaluated. The reaction potential of the negative electrode active material of Sample 10 was 1.65 V, and the initial discharge capacity was 114 mAh / g.

(Sample 11)
L ₄ T ₅ O ₁₂ produced by a known method was used as the negative electrode active material of Sample 11. Using the negative electrode active material of Sample 11, test electrodes and evaluation cells were prepared in the same manner as Sample 1, and charge / discharge characteristics were evaluated. The reaction potential of the negative electrode active material of Sample 11 was 1.57 V, and the initial discharge capacity was 172 mAh / g.

  As shown in Table 1, the reaction potential increased as the solid solution amount of boron increased. However, when the ratio of boron dissolved in the carbon layer was low, the rate at which the reaction potential increased was small. This suggests that the reaction potential of occlusion and release of lithium ions is increased by boron dissolved in the carbon layer, while other existing boron does not have the same effect.

  As the boron content increases, the amount of strontium or barium required to maintain a stable layered structure also increases. Since strontium or barium is present at a position competing with the lithium ion storage site, if these ratios are too high, the amount of lithium ions that can be stored decreases. That is, the discharge capacity decreases. By appropriately adjusting the ratio B / (B + C), both a high reaction potential and a discharge capacity can be achieved.

  The negative electrode active material of the present disclosure is useful as a negative electrode active material of a battery such as a lithium secondary battery.

DESCRIPTION OF SYMBOLS 10 Battery 11 Negative electrode collector 12 Negative electrode active material layer 13 Negative electrode 14 Positive electrode collector 15 Positive electrode active material layer 16 Positive electrode 17 Separator 18 Exterior

Claims (8)

A layered structure composed of carbon and boron;
With strontium or barium,
A negative electrode active material comprising: The layered structure has an interlayer,
The negative electrode active material according to claim 1, wherein the strontium or the barium is present between the layers.   3. The negative electrode active material according to claim 1, wherein a peak is present in a binding energy range of 187.0 eV or more and 188.5 eV or less in a spectrum obtained when the negative electrode active material is analyzed by X-ray photoelectron spectroscopy. . In the spectrum obtained when the negative electrode active material is analyzed by X-ray photoelectron spectroscopy, there are a plurality of peaks in the bound energy range of 184.0 eV or more and 196.5 eV or less,
4. The negative electrode active material according to claim 1, wherein a peak area of a peak appearing in a bound energy range of 187.0 eV or more and 188.5 eV or less is the largest among the plurality of peaks. In the spectrum obtained when the negative electrode active material is analyzed by X-ray photoelectron spectroscopy, the sum of the peak areas of all peaks appearing in the bound energy range of 184.0 eV or more and 196.5 eV or less is S1, 187.0 eV or more. When the peak area of the peak appearing in the bound energy range of 188.5 eV or less is defined as S2,
The negative electrode active material according to claim 1, wherein the ratio S2 / S1 is 0.4 or more. The negative electrode active material according to claim 1, which is represented by the following composition formula (1).
_{M x B y C z ··· (} 1)
[In formula (1), M is strontium or barium;
x, y and z are each greater than 0;
The relationship y / (y + z) ≦ 0.2 is satisfied. ] A negative electrode comprising the negative electrode active material according to claim 1;
A positive electrode;
Electrolyte,
With a battery.   The battery according to claim 7, wherein the negative electrode includes the negative electrode active material as a main component.

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