JP2020017513A - Active material and battery - Google Patents

Abstract

To provide a novel active material having a small volume change due to charge and discharge.SOLUTION: There is provided an active material having a composition represented by NaMSi(M is a metal element other than Na, and x and y satisfy 0<x, 0≤y, y≤x, and 0<x+y<8), and having a silicon clathrate type I crystal phase.SELECTED DRAWING: Figure 7

Description

  The present disclosure relates to active materials and batteries.

  BACKGROUND ART In recent years, batteries have been actively developed. For example, in the automobile industry, the development of batteries used for electric vehicles or hybrid vehicles is underway. Further, Si particles are known as an active material used for a battery.

  For example, Patent Document 1 includes an all-solid-state battery including a positive electrode active material layer, a solid electrolyte layer, and a negative-electrode active material layer, and a control device that controls a charge / discharge voltage when the all-solid-state battery is used. An all-solid-state battery system is disclosed, and further, silicon particles are disclosed as alloy-based negative electrode active material particles. Patent Literature 1 discloses that a constraint pressure is applied to a cell by a constraint jig.

  Patent Literature 2 discloses a battery electrode containing a silicon clathrate. Non-Patent Document 1 discloses that a compound having a silicon clathrate II type crystal phase is used as a negative electrode active material of a lithium ion battery.

JP 2017-059534 A US Patent Application Publication No. 2012/0021283

Thorsten Langer et al., “Electrochemical Lithiation of Silicon Clathrate-II”, Journal of The Electrochemical Society, 159 (8) A1318-A1322 (2012)

  Si particles have a large theoretical capacity and are effective in increasing the energy density of a battery. On the other hand, the volume change of the Si particles during charging and discharging is large.

  The present disclosure has been made in view of the above circumstances, and has as its main object to provide a novel active material having a small volume change due to charge and discharge. Note that the active material in the present disclosure may be referred to as a silicon clathrate compound.

In order to solve the above problems, the present _disclosure, the _{Na x M y Si 46 (M} , a metal element other than Na, x and y, 0 <x, 0 ≦ y , y ≦ x, 0 < x + y <8), and an active material having a silicon clathrate type I crystal phase.

  According to the present disclosure, since the active material has a specific composition and a crystalline phase, an active material that has a small volume change due to charge and discharge can be obtained.

  In the above disclosure, the active material may have the silicon clathrate I-type crystal phase as a main phase.

  In the above disclosure, the crystal phase of the silicon clathrate type I is 2θ = 30.33 ° ± 1.00 °, 31.60 ° ± 1.00 °, and 32.30 ° in X-ray diffraction measurement using CuKα ray. It may have a peak at a position of 82 ° ± 1.00 °, 52.39 ° ± 1.00 °, 55.49 ° ± 1.00 °.

  In the above disclosure, the active material may not have a diamond-type Si crystal phase.

In the above disclosure, the active material has a diamond-type Si crystal phase, and the diamond-type Si crystal phase is 2θ = 28.44 ° ± 1.00 ° in X-ray diffraction measurement using CuKα radiation. has a peak at the position, the 2 [Theta] = 32.82 diffraction intensity of the peak of ° ± 1.00 ° and _{I a,} the diffraction intensity of the peak of the _{2θ = 28.44 ° ± 1.00 ° I} B when _a, I B / _{I a} is larger than 0, it may be 0.1 or less.

  In the above disclosure, the x and the y may satisfy 2.9 ≦ x, 2.9 ≦ x + y ≦ 7.1.

  Further, the present disclosure provides a battery having a positive electrode layer, an electrolyte layer, and a negative electrode layer in this order, wherein the negative electrode layer contains the above-described active material.

  According to the present disclosure, since the negative electrode layer contains the above-described active material (silicon clathrate compound), a battery with a small volume change due to charge and discharge can be provided. Therefore, a battery having good battery characteristics such as capacity can be obtained.

  In the above disclosure, the electrolyte layer may contain an inorganic solid electrolyte.

  In the above disclosure, the electrolyte layer may contain an electrolytic solution.

  In the above disclosure, the battery may be a lithium ion battery.

  In the above disclosure, the battery may be a sodium ion battery.

  The active material according to the present disclosure has an effect that a volume change due to charge and discharge is small.

FIG. 2 is an explanatory diagram illustrating an active material according to the present disclosure. 1 is a schematic sectional view illustrating an example of a battery according to the present disclosure. 5 is a flowchart illustrating an example of a method for manufacturing an active material according to the present disclosure. 4 is a result of XRD measurement for the negative electrode active materials obtained in Example 1 and Comparative Example 1. 4 is a result of TEM observation of the negative electrode active material obtained in Example 1. 4 is a result of a charge / discharge test for the evaluation batteries obtained in Example 1 and Comparative Example 1. 4 shows the results of the increase in restraint pressure in the evaluation batteries obtained in Example 1 and Comparative Example 1. 4 is a result of XRD measurement for the evaluation batteries obtained in Example 1 and Comparative Example 1. 9 is a result of XRD measurement on the negative electrode active material obtained in Example 2. 9 is a result of XRD measurement on the negative electrode active material obtained in Comparative Example 2. 9 is a result of XRD measurement of the negative electrode active material obtained in Example 3. 9 is a result of XRD measurement on the negative electrode active material obtained in Comparative Example 3. 9 is a result of XRD measurement on the negative electrode active material obtained in Example 4. 13 is a result of XRD measurement on the negative electrode active material obtained in Example 5. 9 is a result of XRD measurement of the negative electrode active material obtained in Comparative Example 4. It is a graph which shows the relationship between Na amount x and restraint pressure increase amount.

  Hereinafter, the active material and the battery according to the present disclosure will be described in detail.

A. Active material in the active material present _disclosure, the _{Na x M y Si 46 (M} , a metal element other than Na, x and y, 0 <x, 0 ≦ y, the y ≦ x, 0 <x + y <8 And a silicon clathrate type I crystal phase.

  According to the present disclosure, since the active material has a specific composition and a crystalline phase, an active material that has a small volume change due to charge and discharge can be obtained. Since the active material according to the present disclosure has a small volume change due to charge and discharge, a battery having good battery characteristics such as capacity and cycle characteristics can be obtained. In particular, in the case of an all-solid battery, it is generally necessary to apply a high confining pressure in order to suppress a change in volume due to charging and discharging. However, by using the active material in the present disclosure, it is possible to reduce the confining pressure. As a result, the size of the restraining jig can be suppressed.

  Further, the active material in the present disclosure has a silicon clathrate I-type crystal phase. In the silicon clathrate type I crystal phase, as shown in FIG. 1A, a polyhedron including a pentagon or a hexagon is formed by a plurality of Si elements. The polyhedron has a space capable of containing metal ions such as Li ions inside. By inserting metal ions into this space, a volume change due to charging and discharging can be suppressed. In addition, since the silicon clathrate I-type crystal phase has a space in which metal ions can be contained, there is an advantage that the crystal structure is easily maintained even when charge and discharge are repeated. Note that ordinary Si particles have a diamond-type crystal phase. In the diamond type crystal phase, a tetrahedron is formed by a plurality of Si elements as shown in FIG. Since the tetrahedron does not have a space capable of containing metal ions such as Li ions inside, the volume change due to charge and discharge is large.

  Patent Literature 2 discloses a battery electrode containing a silicon clathrate. On the other hand, in Patent Document 2, the silicon clathrate is not actually synthesized, but the stress strain and the like of various LiSi compounds are evaluated by simulation. Patent Document 2 does not describe or suggest a silicon clathrate containing an Na element.

Non-Patent Document 1 discloses that a compound having a silicon clathrate II type crystal phase is used as a negative electrode active material of a lithium ion battery. More specifically, a lithium ion battery using a compound having a composition represented by Na _x Si ₁₃₆ and having a silicon clathrate II type crystal phase as a negative electrode active material is disclosed. On the other hand, in lines 8 to 12 of the left column of A1318 of Non-Patent Document 1, when Na is desorbed from Na ₈ Si ₄₆ (silicon clathrate I type), Na _x Si ₁₃₆ (silicon clathrate II type) ) Is obtained. In other words, there is no description or suggestion that a silicon clathrate type I crystal phase can be maintained while desorbing Na.

The active material according to the present disclosure can be said to be a novel active material in that it has a composition in which Na is smaller than that of Na ₈ Si ₄₆ and has a silicon clathrate I-type crystal phase. The reason that such an active material was obtained is that it was synthesized under the conditions described below. In particular, since the active material in the present disclosure has a composition in which Na is smaller than that of Na ₈ Si ₄₆ , the active material can include more metal ions such as Li ions, and in that respect, a change in volume due to charge and discharge can be suppressed. Further, the active material in the present disclosure has a silicon clathrate I-type crystal phase. Since the silicon clathrate I-type crystal phase contains a large proportion of Si polyhedron with a large space compared to the silicon clathrate II-type crystal phase, it suppresses volume expansion and maintains the crystal structure when metal ions are inserted. This is advantageous in that respect.

Active material in this _disclosure, Na _x M y _{Si 46} (the M, a metal element other than Na, x and y, 0 <x, 0 ≦ y , satisfy y ≦ x, 0 <x + y <8) It has a composition represented by M is a metal element other than Na, for example, an alkali metal element. Examples of the alkali metal element include a Li element, a K element, an Rb element, and a Cs element. Another example of M is an alkaline earth metal element. Examples of the alkaline earth metal element include a Mg element, a Ca element, a Sr element, and a Ba element. Further, other examples of M include Group 11 elements such as Cu element, Ag element and Au element; Group 12 elements such as Zn element; B element, Al element, Ga element, In element and Tl element. Group 13 elements; Group 14 elements such as Ge elements; Group 15 elements such as Sb elements; Group 16 elements such as Te elements; and lanthanoids such as La elements and Eu elements. Further, as M, a transition metal element such as a Ni element may be used.

  The above x usually satisfies 0 <x, may satisfy 0.1 ≦ x, may satisfy 0.5 ≦ x, may satisfy 1.5 ≦ x, and may satisfy 2.5 ≦ x May be satisfied, or 2.9 ≦ x may be satisfied. On the other hand, x satisfies, for example, x <8, may satisfy x ≦ 7.5, may satisfy x ≦ 7.1, or may satisfy x ≦ 6. Further, the above y may be 0 or may satisfy 0 <y. Further, x and y satisfy y ≦ x. The molar ratio of the above x to the sum of the above x and y ((x / (x + y)) is usually 0.5 or more, 0.7 or more, or 0.9 or more. Good.

  The sum of the above x and y (x + y) usually satisfies 0 <x + y, may satisfy 0.1 ≦ x + y, may satisfy 0.5 ≦ x + y, or satisfies 1.5 ≦ x + y And may satisfy 2.5 ≦ x + y or 2.9 ≦ x + y. On the other hand, x + y usually satisfies x + y <8, may satisfy x + y ≦ 7.5, may satisfy x + y ≦ 7.1, or may satisfy x + y ≦ 6.

  The active material in the present disclosure has a silicon clathrate type I crystal phase. In particular, the active material in the present disclosure preferably has a silicon clathrate I-type crystal phase as a main phase. “Having a silicon clathrate I-type crystal phase as a main phase” means that any peak belonging to the silicon clathrate I-type crystal phase has the highest diffraction intensity among peaks observed by X-ray diffraction measurement. Is a large peak. The crystalline phase of silicon clathrate I type usually belongs to the space group (Pm-3n). The silicon clathrate I-type crystal phase contains at least Na element and Si element, may contain M element, and may not contain M element.

  In the X-ray diffraction measurement using CuKα ray, 2θ = 19.44 °, 21.32 °, 30.33 °, 31.60 °, 32.82 °, 36. It has typical peaks at 29 °, 52.39 °, and 55.49 °. These peak positions may fluctuate in a range of ± 1.00 °, may fluctuate in a range of ± 0.50 °, or fluctuate in a range of ± 0.30 °. Is also good. Note that when metal ions such as lithium ions are inserted into the silicon clathrate I-type crystal phase, a peak shift may occur. Therefore, it is preferable to perform XRD measurement in a state where no metal ion is inserted.

  Further, the active material in the present disclosure preferably does not have a diamond-type Si crystal phase, but may have a small amount. The diamond-type Si crystal phase is typically located at 2θ = 28.44 °, 47.31 °, 56.10 °, 69.17 °, 76.37 ° in X-ray diffraction measurement using CuKα radiation. Has a strong peak. These peak positions may fluctuate in a range of ± 1.00 °, may fluctuate in a range of ± 0.50 °, or fluctuate in a range of ± 0.30 °. Is also good.

Here, the diffraction intensity of the peak of 2θ = 32.82 ° ± 1.00 ° in the silicon clathrate I type crystal phase and _{I A,} 2θ = 28.44 ° ± in diamond-type Si crystal phase 1.00 diffraction intensity of the peak of ° a and I _B. Ratio of _{I B} for _{I A (I B / I A} ) is preferably smaller. The value of I _B / _{I A} is, for example, 1.2 or less, may be 1.0 or less, may be 0.5 or less, may be 0.3 or less, 0.2 Or less, may be 0.1 or less, may be 0.08 or less, and may be 0.06 or less. On the other _hand, the value of I B / _{I A} may be 0, may be greater than 0.

  Further, the active material in the present disclosure preferably does not have a silicon clathrate II type crystal phase, but may have a small amount. The silicon clathrate type II crystal phase usually belongs to the space group (Fd-3m). The crystal phase of the silicon clathrate type II crystal was found to be 2θ = 20.09 °, 21.00 °, 26.51 °, 31.72 °, 36.26 °, 53.X in X-ray diffraction measurement using CuKα radiation. It has a typical peak at 01 °. These peak positions may fluctuate in a range of ± 1.00 °, may fluctuate in a range of ± 0.50 °, or fluctuate in a range of ± 0.30 °. Is also good.

Here, the diffraction intensity of the peak of 2θ = 26.51 ° ± 1.00 ° in the silicon clathrate II type crystal phase and _{I C.} Ratio of _{I C} for _{I A (I C / I A} ) is preferably smaller. The value of I _C / I _A is, for example, 1 or less, may be 0.8 or less, may be 0.6 or less, may be 0.4 or less, and may be 0.2 or less. And may be 0.1 or less. On the other hand, the value of I _C / I _A may be 0 or may be larger than 0.

  Further, the active material in the present disclosure preferably does not have a Zintl phase, but may have a small amount. In the X-ray diffraction measurement using CuKα ray, 2θ = 16.10 °, 16.56 °, 17.64 °, 20.16 °, 27.96 °, 33.60 °, 35.68 for the gintle phase. °, 40.22 ° and 41.14 ° have typical peaks. These peak positions may fluctuate in a range of ± 1.00 °, may fluctuate in a range of ± 0.50 °, or fluctuate in a range of ± 0.30 °. Is also good.

Here, the diffraction intensity of the peak of 2θ = 33.60 ° ± 1.00 ° in Jintoru phase and _{I D.} Ratio of _{I D} for _{I A (I D / I A} ) is preferably smaller. The value of I _D / I _A is, for example, 0.5 or less, may be 0.25 or less, may be 0.1 or less, or may be 0.05 or less. On the other hand, the value of I _D / I _A may be 0 or may be larger than 0.

  Examples of the shape of the active material in the present disclosure include a particle shape. The average primary particle diameter of the active material is, for example, 50 nm or more, may be 100 nm or more, or may be 150 nm or more. On the other hand, the average primary particle diameter of the active material is, for example, 3000 nm or less, may be 1500 nm or less, or may be 1000 nm or less. The average secondary particle diameter of the active material is, for example, 1 μm or more, 2 μm or more, 5 μm or more, or 7 μm or more. On the other hand, the average secondary particle diameter of the active material is, for example, 60 μm or less, and may be 40 μm or less. The average primary particle diameter and the average secondary particle diameter can be determined by, for example, observation with a scanning electron microscope (SEM). The number of samples is preferably large, for example, 20 or more, 50 or more, or 100 or more. The average primary particle diameter and the average secondary particle diameter can be appropriately adjusted, for example, by appropriately changing the production conditions of the active material or performing classification.

  Further, the active material in the present disclosure is generally used for a battery. The battery will be described in detail in “B. Battery” described later. Further, the active material in the present disclosure may be a negative electrode active material or a positive electrode active material, but the former is preferable.

  The method for producing an active material according to the present disclosure is not particularly limited. For example, a first heat treatment step of performing heat treatment on a mixture containing Si particles and Na alone (metallic Na) to synthesize a NaSi compound having a gintle phase. And a second heat treatment step of subjecting the NaSi compound to heat treatment under reduced pressure to desorb Na.

  In the first heat treatment step, the ratio of the Si particles and the simple substance of Na is not particularly limited. And may be 1.1 mole parts or more. On the other hand, with respect to 1 mol part of the Si particles, the amount of Na alone is, for example, 1.5 mol parts or less, 1.3 mol parts or less, or 1.2 mol parts or less.

  The heat treatment temperature in the first heat treatment step is, for example, 500 ° C. or more and 1000 ° C. or less. The heat treatment time in the first heat treatment step is, for example, 1 hour or more and 50 hours or less. In particular, by performing heat treatment under at least one condition of about 700 ° C. (for example, 650 ° C. or more and 750 ° C. or less) and about 20 hours (for example, 15 hours or more and 25 hours or less), a desired active material is easily obtained. .

  In the second heat treatment step, the pressure during the heat treatment is, for example, 10 Pa or less, may be 1 Pa or less, or may be 0.1 Pa or less. The heat treatment temperature in the second heat treatment step is, for example, 100 ° C. or more and 650 ° C. or less. The heat treatment time in the second heat treatment step is, for example, 30 minutes or more and 20 hours or less. In particular, by performing the heat treatment under at least one condition of about 450 ° C. (eg, 400 ° C. or more and 500 ° C. or less) and about 5 hours (eg, 2 hours or more and 8 hours or less), a desired active material is easily obtained. . By the second heat treatment step, the active material according to the present disclosure can be obtained.

B. Battery FIG. 2 is a schematic cross-sectional view illustrating an example of a battery according to the present disclosure. The battery 10 shown in FIG. 2 has a positive electrode layer 1, an electrolyte layer 2, and a negative electrode layer 3 in this order in the thickness direction. Further, the battery 10 includes a positive electrode current collector 4 for collecting the current of the positive electrode layer 1 and a negative electrode current collector 5 for collecting the current of the negative electrode layer 3. Although not particularly shown, the battery 10 may have a known exterior body. One feature of the present disclosure is that the negative electrode layer 3 contains the active material described in the above “A. Active Material”.

  According to the present disclosure, since the negative electrode layer contains the above-described active material (silicon clathrate compound), a battery with a small volume change due to charge and discharge can be provided. Therefore, a battery having good battery characteristics such as capacity can be obtained.

1. Negative electrode layer The negative electrode layer is a layer containing at least a negative electrode active material. In the present disclosure, the active material (silicon clathrate compound) described in the above “A. Active Material” is used as the negative electrode active material.

  The negative electrode layer may contain only a silicon clathrate compound as the negative electrode active material, or may contain another active material. In the latter case, the proportion of the silicon clathrate compound in all the negative electrode active materials may be, for example, 50% by weight or more, 70% by weight or more, or 90% by weight or more.

  The ratio of the negative electrode active material in the negative electrode layer is, for example, 20% by weight or more, 30% by weight or more, or 40% by weight or more. On the other hand, the ratio of the negative electrode active material is, for example, 80% by weight or less, 70% by weight or less, or 60% by weight or less.

  Further, the negative electrode layer may contain at least one of an electrolyte, a conductive material, and a binder, if necessary. The electrolyte will be described in detail in “3. Electrolyte layer” described later.

  Examples of the conductive material include a carbon material, metal particles, and a conductive polymer. Examples of the carbon material include a particulate carbon material such as acetylene black (AB) and Ketjen black (KB), and a fibrous carbon material such as carbon fiber, carbon nanotube (CNT), and carbon nanofiber (CNF). . Examples of the metal particles include particles of Ni, Cu, Fe, SUS, and the like. Examples of the conductive polymer include polyacetylene-based polymers such as polyacetylene; polyaniline-based polymers such as polyaniline; and polypyrroles such as a copolymer of ethyl 3-methyl-4-pyrrolecarboxylate and butyl 3-methyl-4-pyrrolecarboxylate. Polypolymers such as PEDOT obtained by polymerizing 3,4-ethylenedioxythiophene; Polyphenylene polymers such as polyparaphenylene; Polyphenylene vinylene polymers such as polyparaphenylene vinylene; Polyacene polymers such as polyacene; Polyazulene Of polyazulene-based polymers.

  Examples of the binder include rubber binders such as butadiene rubber, hydrogenated butadiene rubber, styrene butadiene rubber (SBR), hydrogenated styrene butadiene rubber, nitrile butadiene rubber, hydrogenated nitrile butadiene rubber, and ethylene propylene rubber; PVDF), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVDF-HFP), fluoride binders such as polytetrafluoroethylene and fluororubber. Other examples of the binder include polyolefin-based thermoplastic resins such as polyethylene, polypropylene and polystyrene; imide-based resins such as polyimide and polyamide-imide; amide-based resins such as polyamide; polymethyl acrylate, polyethyl acrylate, and polypropyl. Acrylic resin such as acrylate, polybutyl acrylate, polyhexyl acrylate, poly 2-ethylhexyl acrylate, polydecyl acrylate, polyacrylic acid; polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, poly 2-ethylhexyl methacrylate, polymethacryl Methacrylic acid resins such as acids; polycarboxylic acids such as polyitaconic acid, polycrotonic acid, polyfumaric acid, polyangelic acid, and carboxymethyl cellulose; It is below.

  Other examples of the binder include polyethylene oxide, polypropylene oxide, polyacrylonitrile, polyethylene glycol dimethacrylate, polyethylene glycol acrylate, polyethylene vinyl acetate, polyglycidol, polysiloxane, polydimethylsiloxane, polyvinyl acetate, polyvinyl alcohol, and polycarbonate. , A polyamine, a polyalkyl carbonate, a polynitrile, a polydiene, a polyphosphazene, an unsaturated polyester obtained by copolymerizing maleic anhydride and glycols, and a polyethylene oxide derivative having a substituent. Further, as the binder, a copolymer obtained by copolymerizing two or more types of monomers constituting the specific polymer described above may be selected. As the binder, polysaccharides such as glycogen, cellulose, chitin, agarose, carrageenan, heparin, hyaluronic acid, pectin, amylopectin, xyloglucan, and amylose can also be used. These binders can also be used as a dispersion such as an emulsion.

  The thickness of the negative electrode layer is, for example, 0.1 μm or more and 1000 μm or less.

2. Positive electrode layer The positive electrode layer is a layer containing at least a positive electrode active material. Further, the positive electrode layer may contain at least one of an electrolyte, a conductive material, and a binder, if necessary.

Examples of the positive electrode active material include an oxide active material. Examples of the oxide active material used for the lithium ion battery include LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , LiVO ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , and LiNi _0.8 Co _0.15 Al _0.05 O ₂ , LiNi _0.5 Mn _0.5 O ₂ , LiNi _0.33 Mn _0.67 O ₂ , LiNi _0.8 Co _0.1 Mn _0.1 O ₂ , LiNi _0.6 Co _{0 .2 Mn 0.2 O 2, LiNi 0.5} Co 0.2 Mn 0.3 O 2 rock salt layered type, such as active _{material; Li 2 MnO 3, Li 1.2} Mn 0.54 Co 0.13 Ni 0 _.13 O ₂ , Li _1.3 Nb _0.3 Mn _0.4 O ₂ , Li _1.2 Ti _0.4 Mn _0.4 O ₂ , Li _1.3 Nb _0.3 Fe _0.4 O _2, etc. Having a Li excess composition, Active material utilizing some oxygen redox _{discharge; LiMn 2 O 4, Li 4} Ti 5 O 12, Li (Ni 0.5 Mn 1.5) spinel active material _{O 4} or the _like; LiFePO _4, LiMnPO 4, LiNiPO _4, olivine type active material of LiCoPO _{4 such; Li 3 V 2 (PO 4} ) 3 or the like of Nasicon Katakatsu _material; Li 2 FeSiO ₄ silicate-type active materials such as; LiFeP ₂ O _7, etc. of pyrochlore type active material No. Alternatively, LiVPO ₄ F or LiFeSO ₄ F can be used as the oxide active material.

Further, a coat layer containing a Li ion conductive oxide may be formed on the surface of the oxide active material. This is because a reaction between the oxide active material and the solid electrolyte (particularly, a sulfide solid electrolyte) can be suppressed. The Li ion conductive oxide, for example, lithium niobate, such as _{LiNbO 3, Li 4 Ti 5 O} 12 , etc. of the lithium titanate, lithium tungstate such LiWO _3, lithium tantalate or the like LiTaO _3, LiMoO ₃ etc. And lithium phosphates such as Li ₃ PO ₄ . Further, an oxide solid electrolyte described later may be used as the Li ion conductive oxide. The thickness of the coat layer is, for example, 1 nm or more. On the other hand, the thickness of the coat layer is, for example, 30 nm or less, and may be 15 nm or less.

On the other hand, the oxide active material used for the sodium ion battery, for example, O ₃ type layered active material, P ₂ type layered active material, P ₃ type layered active materials include Alluaudite Katakatsu material. Specific examples of such oxide active _{material, NaFeO 2, NaNiO 2, NaCoO} 2, NaMnO 2, NaVO 2, Na (Ni X Mn 1-X) O 2 (0 <X <1), Na (Fe _{X Mn 1-X) O 2} , (0 <X <1), Na (Ni X Co Y Mn 1-X-Y) O 2 (0 <X <1,0 <Y <1), Na z FeO 2 _{(0.6 <z <1),} Na z NiO 2 (0.6 <z <1), Na z CoO 2 (0.6 <z <1), Na z MnO 2 (0.6 <z <1 _{), Na z VO 2 (0.6} <z <1), Na z (Ni X Mn 1-X) O 2 (0 <X <1,0.6 <z <1), Na z (Fe X Mn _{1-X) O 2, (} 0 <X <1,0.6 <z <1), Na z (Ni X Co Y Mn 1-X-Y) O 2 (0 <X <1,0 <Y < 1 _{0.6 <z <1), NaFeO} 2, NaNiO 2, NaCoO 2, NaMnO 2, NaVO 2, Na (Ni X Mn 1-X) O 2 (0 <X <1), Na (Fe X Mn 1- _{X) O 2, (0 <} X <1), Na (Ni X Co Y Mn 1-X-Y) O 2 (0 <X <1,0 <Y <1), Na 2 Fe 2 (SO 4) ₃ , NaVPO ₄ F, Na ₂ FePO ₄ F, Na ₃ V ₂ (PO ₄ ) ₃ , Na ₄ M ₃ (PO ₄ ) ₂ P ₂ O ₇ (M is at least one of Co, Ni, Fe and Mn ).

Examples of the shape of the positive electrode active material include a particle shape. The average particle size (D ₅₀ ) of the positive electrode active material is not particularly limited, but is, for example, 10 nm or more, and may be 100 nm or more. On the other hand, the average particle diameter (D ₅₀ ) of the positive electrode active material is, for example, 50 μm or less, and may be 20 μm or less. The average particle size (D ₅₀ ) can be calculated, for example, from measurement using a laser diffraction particle size distribution meter or a scanning electron microscope (SEM).

  The ratio of the positive electrode active material in the positive electrode layer is, for example, 20% by weight or more, 30% by weight or more, or 40% by weight or more. On the other hand, the ratio of the positive electrode active material is, for example, 80% by weight or less, 70% by weight or less, or 60% by weight or less.

  The conductive material and the binder used for the positive electrode layer are the same as those described in the above “1. Negative electrode layer”, and thus description thereof is omitted here. On the other hand, the electrolyte used for the positive electrode layer will be described in detail in “3.

  The thickness of the positive electrode layer is, for example, 0.1 μm or more and 1000 μm or less.

3. Electrolyte layer The electrolyte layer is a layer formed between the positive electrode layer and the negative electrode layer, and contains at least an electrolyte. The electrolyte may be a solid electrolyte, a liquid electrolyte (electrolyte solution), or a mixture thereof. The type of the electrolyte is not particularly limited, and can be appropriately selected according to the type of the battery.

  The solid electrolyte typically includes an inorganic solid electrolyte such as a sulfide solid electrolyte, an oxide solid electrolyte, a nitride solid electrolyte, and a halide solid electrolyte; and an organic polymer electrolyte such as a polymer electrolyte.

  Examples of the sulfide solid electrolyte having lithium ion conductivity include a Li element and an X element (X is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In). And a solid electrolyte containing the S element. Further, the sulfide solid electrolyte may further contain at least one of an O element and a halogen element. Examples of the halogen element include an F element, a Cl element, a Br element, and an I element.

  The sulfide solid electrolyte may be a glass-based sulfide solid electrolyte, a glass-ceramic-based sulfide solid electrolyte, or a crystalline sulfide solid electrolyte.

The glass-based sulfide solid electrolyte may include an ion conductor containing a Li element, an A element (A is at least one of P, As, Sb, Si, Ge, Al and B), and an S element. preferable. Further, the ionic conductor preferably has a high Li content. Also, the ion conductor, the anion structure of the ortho-composition _(PS ^{4 3-} structure, _SiS ^{4 4-structure,} _GeS ^{4 4-structure,} _AlS ^{3 3-} structure, _BS ^{3 3-} structure) as the main component of the anionic It is preferred to have. This is because chemical stability is high. The proportion of the anion structure in the ortho composition is preferably at least 70 mol%, more preferably at least 90 mol%, based on the total anion structure in the ion conductor. The ratio of the ortho-structure anion structure can be determined, for example, by Raman spectroscopy, NMR, or XPS.

  The glass-based sulfide solid electrolyte may contain lithium halide in addition to the ionic conductor. Examples of the lithium halide include LiF, LiCl, LiBr and LiI, and among them, LiCl, LiBr and LiI are preferable. The ratio of LiX (X = F, I, Cl, Br) in the glass-based sulfide solid electrolyte is, for example, 5 mol% or more, and may be 15 mol% or more. On the other hand, the ratio of LiX is, for example, 30 mol% or less, and may be 25 mol% or less.

The glass-ceramic sulfide solid electrolyte can be obtained, for example, by subjecting the above-described glass sulfide solid electrolyte to heat treatment. Specific examples of the glass-ceramic-based sulfide solid electrolyte include xLi ₂ S · (100-x) P ₂ S ₅ (70 ≦ x ≦ 80), yLiI · zLiBr · (100-yz) (xLi ₂ S · (100-x) P ₂ S ₅ ) (70 ≦ x ≦ 80, 0 ≦ y ≦ 30, 0 ≦ z ≦ 30).

Examples of the crystalline sulfide solid electrolyte include a Thio-LISICON type solid electrolyte, an LGPS type solid electrolyte, and an aldirodite type solid electrolyte. Examples of the Thio-LISICON solid electrolyte include Li _(4-x) Ge _(1-x) P _x S ₄ (x satisfies 0 <x <1). Examples of the LGPS solid electrolyte include Li _(4-x) Ge _(1-x) P _x S ₄ (x satisfies 0 <x <1). Note that Sb, Si, Sn, B, Al, Ga, In, Ti, Zr, V, and Nb may be used instead of at least one of Ge and P. Further, a part of Li may be replaced with Na, K, Mg, Ca, Zn. Further, a part of S may be substituted with halogen (F, Cl, Br, I). Examples of the aldirodite type solid electrolyte include Li _7-x-2y PS _6-xy X _y , Li _8-x-2y SiS _6-xy X _y , and Li _8-x-2y GeS _{6-x- y} X _y, and the like. Note that X is at least one of F, Cl, Br, and I, and x and y satisfy 0 ≦ x and 0 ≦ y.

Examples of the oxide solid electrolyte having lithium ion conductivity include, for example, Li element and Y element (Y is at least one of Nb, B, Al, Si, P, Ti, Zr, Mo, W, and S). ) And solid electrolytes containing the O element. Specific _{examples, Li 7 La 3 Zr 2 O} 12, Li 7-x La 3 (Zr 2-x Nb x) O 12 (0 ≦ x ≦ 2), Li 5 La 3 Nb 2 garnet type _{O 12,} etc. Solid electrolytes; perovskite-type solid electrolytes such as (Li, La) TiO ₃ , (Li, La) NbO ₃ and (Li, Sr) (Ta, Zr) O ₃ ; Li (Al, Ti) (PO ₄ ) ₃ , Nasicon-type solid electrolyte of Li (Al, Ga) (PO ₄ ) ₃ ; Li-PO-based solid electrolyte such as Li ₃ PO ₄ , LIPON (a compound in which part of O of Li ₃ PO ₄ is substituted by N) _{; Li 3 BO 3, Li 3} BO 3 in Li-BO-based solid electrolyte such as compounds obtained by substituting C for a portion of O may be mentioned.

On the other hand, examples of the oxide solid electrolyte having sodium ion conductivity include a NASICON-type solid electrolyte, a perovskite-type solid electrolyte, and β-alumina. In addition, as the nitride solid electrolyte having lithium ion conductivity, for example, Li ₃ N is given. Examples of the halide solid electrolyte having lithium ion conductivity include LiCl, LiI, LiBr, and Li ₃ YCl ₆ .

  Further, the polymer electrolyte preferably has an ion conductive unit. Examples of the ion conductive unit include, for example, polyethylene oxide, polypropylene oxide, polymethacrylate, polyacrylate, polydimethylsiloxane, polyacrylic acid, polymethacrylic acid, polyethylene vinyl acetate, polyimide, polyamine, polyamide, and polyalkyl carbonate. , Polynitrile, polyphosphazene, polyolefin, and polydiene. The polymer electrolyte may have one or more ion conductive units. Further, the polymer electrolyte preferably has a supporting salt described later. Further, a plastic crystal may be used as the polymer electrolyte.

On the other hand, the electrolytic solution preferably contains a supporting salt and a solvent. Note that an ionic liquid may be used as the electrolytic solution. Examples of the supporting salt (lithium salt) of the electrolyte having lithium ion conductivity include inorganic lithium salts such as LiPF ₆ , LiBF ₄ , LiClO ₄ , and LiAsF ₆ , LiCF ₃ SO ₃ , and LiN (CF ₃ SO ₂ ) _{2. , LiN (C 2 F 5 SO} 2) 2, LiN (FSO 2) 2, LiC (CF 3 SO 2) and other organic lithium salt of _3, and the like. On the other hand, as a supporting salt (sodium salt) of an electrolyte having sodium ion conductivity, for example, inorganic sodium salts such as NaPF ₆ , NaBF ₄ , NaClO ₄ , and NaAsF ₆ , NaCF ₃ SO ₃ , and NaN (CF ₃ SO ₂₎ ) ₂ , NaN (C ₂ F ₅ SO ₂ ) ₂ , NaN (FSO ₂ ) ₂ , and NaC (CF ₃ SO ₂ ) ₃ .

  The solvent used for the electrolytic solution is not particularly limited, but is preferably a mixed solvent containing a high dielectric constant solvent and a low viscosity solvent. Examples of the high dielectric constant solvent include cyclic esters (cyclic carbonates) such as ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate (BC), γ-butyrolactone, sulfolane, N-methylpyrrolidone (NMP), , 3-dimethyl-2-imidazolidinone (DMI). On the other hand, examples of the low-viscosity solvent include, for example, chain esters (chain carbonates) such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC), acetates such as methyl acetate, ethyl acetate, and the like. Ethers such as -methyltetrahydrofuran. Note that the solvent used for the electrolytic solution may be a non-aqueous solvent or an aqueous solvent.

In addition, an ionic liquid can be used as the electrolyte or the solvent. The ionic liquid has a cation part and an anion part. Examples of the cation moiety include organic nitrogen-based (imidazolium salts, ammonium salts, pyridinium salts, piperidinium salts and the like), organic phosphorus-based (phosphonium salts and the like), and organic sulfur-based (sulfonium salts and the like). On the other hand, as the anion portion, for example, AlCl ₄ ⁻ , NO ₂ ⁻ , NO ₃ ⁻ , I ⁻ , BF ₄ ⁻ , PF ₆ ⁻ , SbF ₆ ⁻ , NbF ₆ ⁻ , F (HF) _2.3 ⁻ , CH ^{_{3 CO 2 -, CH 3 SO}} 3 -, CF 3 SO 3 -, (CF 3 SO 2) 2 N -, (FSO 2) 2 N - include.

  Further, a solvated ionic liquid can also be used as the electrolytic solution. The solvated ionic liquid is obtained, for example, by mixing the above-mentioned supporting salt with glymes such as tetraglyme and triglyme. The ratio between the glymes and the supporting salt is preferably, for example, a molar ratio of about 1: 1.

  The concentration of the supporting salt in the electrolytic solution is, for example, 0.3 mol / L or more, may be 0.5 mol / L or more, or may be 0.8 mol / L or more. On the other hand, the concentration of the supporting salt in the electrolytic solution is, for example, 6 mol / L or less, and may be 3 mol / L or less. Further, in the present disclosure, a gel may be added by adding a polymer to the electrolytic solution. Examples of the polymer include polyethylene oxide (PEO), polyacrylonitrile (PAN) or polymethyl methacrylate (PMMA), and polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP).

  Further, the electrolyte layer may have a separator. The material of the separator may be an organic material or an inorganic material. Specific examples include a porous membrane such as polyethylene (PE), polypropylene (PP), cellulose, polyvinylidene fluoride, polyamide, and polyimide; a nonwoven fabric such as a resin nonwoven fabric and a glass fiber nonwoven fabric; and a ceramic porous membrane. Further, the separator may have a single-layer structure or a laminated structure.

  The thickness of the electrolyte layer is, for example, 0.1 μm or more and 1000 μm or less. The electrolyte layer may contain a filler such as inorganic particles and organic particles.

4. Other Configurations The battery according to the present disclosure has at least the negative electrode layer, the positive electrode layer, and the electrolyte layer described above. Further, it usually has a positive electrode current collector for collecting current of the positive electrode layer and a negative electrode current collector for collecting current of the negative electrode layer. Examples of the material of the positive electrode current collector include SUS, aluminum, nickel, iron, titanium, and carbon. On the other hand, examples of the material of the negative electrode current collector include SUS, copper, nickel, and carbon. Note that the thickness and shape of the positive electrode current collector and the negative electrode current collector are preferably selected as appropriate depending on the use of the battery. Further, each of the positive electrode current collector and the negative electrode current collector may have a protective layer on the surface on the electrolyte layer side. Examples of the protective layer include a carbon coat layer, a resin coat layer, and a metal plating layer.

  Further, the battery according to the present disclosure may further include a restraining jig that applies a restraining pressure to the positive electrode layer, the electrolyte layer, and the negative electrode layer along the thickness direction. As the restraining jig, a known jig can be used. The confining pressure is, for example, 0.1 MPa or more, may be 1 MPa or more, or may be 5 MPa or more. On the other hand, the constraint pressure is, for example, 100 MPa or less, may be 50 MPa or less, or may be 20 MPa or less.

5. Battery A battery in the present disclosure is a battery in which metal ions are conducted between a positive electrode layer and a negative electrode layer. Examples of such a battery include a lithium ion battery, a sodium ion battery, a potassium ion battery, a magnesium ion battery, and a calcium ion battery. Further, the battery in the present disclosure may be a liquid battery in which the electrolyte layer contains an electrolytic solution, or may be an all-solid battery in which the electrolyte layer contains a solid electrolyte.

  In addition, the battery according to the present disclosure may be a primary battery or a secondary battery, but is preferably a secondary battery. This is because it can be repeatedly charged and discharged and is useful, for example, as a vehicle-mounted battery. The secondary battery includes the use of the secondary battery as a primary battery (use for the first charge only).

  Further, the battery in the present disclosure may be a unit cell or a stacked battery. The stacked battery may be a monopolar stacked battery (a stacked battery of a parallel connection type) or a bipolar stacked battery (a stacked battery of a series connection type). Examples of the shape of the battery include a coin type, a laminate type, a cylindrical type, and a square type.

  Note that the present disclosure is not limited to the above embodiment. The above embodiment is an exemplification, and has substantially the same configuration as the technical idea described in the claims of the present disclosure, and any device having the same function and effect will not be described. It is within the technical scope of the disclosure.

[Example 1]
(Synthesis of negative electrode active material)
A negative electrode active material was synthesized according to the flow shown in FIG. Si particles (purity: 99.999%) and metallic Na (purity: 99.5%) were weighed at a molar ratio of Si particles: metallic Na = 1: 1.1, and charged into a crucible made of boron nitride. And sealed under an Ar atmosphere. Thereafter, heat treatment was performed at 700 ° C. for 20 hours. Thus, a NaSi compound (a compound having a gintle phase) was obtained. The obtained NaSi compound was pulverized, and heat-treated at 450 ° C. for 5 hours under vacuum (about 0.1 Pa) to remove Na. The obtained compound was ground in a mortar. Thereafter, the particle size was adjusted by classification to obtain negative electrode active material particles (average secondary particle diameter = 5 μm).

(Preparation of battery for evaluation)
0.4 g of solid electrolyte particles (Li ₃ PS ₄ ), 0.8 g of the obtained negative electrode active material particles, 0.06 g of a conductive material (VGCF), and a binder solution (a butyl butyrate solution containing a PVDF-based resin at 5% by weight) 0.32 g was added to a polypropylene container. The container was subjected to ultrasonic treatment for 30 seconds using an ultrasonic dispersing device, and then subjected to shaking using a shaker for 30 minutes to obtain a slurry. The obtained slurry was applied on a negative electrode current collector (copper foil) by a blade method using an applicator, air-dried for 60 minutes, and then dried on a hot plate adjusted to 100 ° C. for 30 minutes. Thereby, a negative electrode structure having a negative electrode layer and a negative electrode current collector was obtained.

Next, 0.3 g of solid electrolyte particles (Li ₃ PS ₄ ), 2 g of positive electrode active material particles (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ), 0.03 g of a conductive material (VGCF), and a binder solution ( 0.3 g of a butyl butyrate solution containing a PVDF resin at 5% by weight) was added to a polypropylene container. The container was subjected to ultrasonic treatment for 30 seconds using an ultrasonic dispersing device, and then subjected to shaking using a shaker for 30 minutes to obtain a slurry. The obtained slurry was applied on a positive electrode current collector (aluminum foil) by a blade method using an applicator, air-dried for 60 minutes, and then dried on a hot plate adjusted to 100 ° C. for 30 minutes. Thus, a positive electrode structure having a positive electrode layer and a positive electrode current collector was obtained.

Next, 0.4 g of solid electrolyte particles (Li ₃ PS ₄ , average particle size D ₅₀ = 2 μm) and 0.05 g of a binder solution (heptane solution containing 5% by weight of an ABR resin) were added to a polypropylene container. did. The container was subjected to ultrasonic treatment for 30 seconds using an ultrasonic dispersing device, and then subjected to shaking using a shaker for 30 minutes to obtain a slurry. The obtained slurry was applied on a support (aluminum foil) by a blade method using an applicator, air-dried for 60 minutes, and then dried on a hot plate adjusted to 100 ° C. for 30 minutes. Thus, a solid electrolyte layer was formed.

  Next, the negative electrode structure, the solid electrolyte layer, and the positive electrode structure were laminated in this order, and the obtained laminate was pressed at 130 ° C. and 200 MPa for 3 minutes to obtain a battery for evaluation.

[Comparative Example 1]
Si particles having a diamond-type crystal phase (average secondary particle diameter = 3 μm) were used as a negative electrode active material for comparison. A battery for evaluation was obtained in the same manner as in Example 1 except that this negative electrode active material was used.

[Evaluation]
(XRD measurement)
The negative electrode active materials obtained in Example 1 and Comparative Example 1 were subjected to X-ray diffraction (XRD) measurement using CuKα radiation. The result is shown in FIG. As shown in FIG. 4A, in Example 1, 2θ = 19.44 °, 21.32 °, 30.33 °, 31.60 °, 32.82 °, 36.29 °, 52.39. ° and 55.49 °, a typical peak of a silicon clathrate type I crystal phase was confirmed. On the other hand, as shown in FIG. 4B, in Comparative Example 1, a typical peak of a diamond-type Si crystal phase was confirmed.

In addition, as shown in FIG. 4A, in Example 1, a slight peak of a diamond-type Si crystal phase was observed at a position of 2θ = 28.44 °. The diffraction intensity of the peak of 2 [Theta] = 32.82 ° in the silicon clathrate I type crystal phase and _{I A,} the diffraction intensity of the peak of 2 [Theta] = 28.44 ° in diamond-type Si crystal phase when the _{I B} , _I B / _{I a} was 0.08.

(SEM-EDX measurement)
The negative electrode active material obtained in Example 1 was subjected to SEM-EDX (scanning electron microscope-energy dispersive X-ray spectroscopy) measurement to measure Na / Si. As a result, Na / Si was 0.1. That is, it was confirmed that the negative electrode active material obtained in Example 1 had a composition represented by Na _4.6 Si ₄₆ .

(TEM observation)
The negative electrode active material obtained in Example 1 was observed with a transmission electron microscope (TEM). The identification of the silicon clathrate type I crystal phase is also possible by TEM observation. FIG. 5A shows an image obtained by Fourier-transforming the diffraction spot. The white spot in FIG. 5A indicates the position of Si, and FIG. 5B corresponds to the crystal structure diagram of FIG. As shown in FIGS. 5A and 5B, the space is expanded in the crystal structure, and when Li is schematically arranged, it is suggested that Li easily enters the space in the crystal structure. Was. From the TEM image, the primary particle size of the active material was approximately in the range of 100 nm to several μm. The lattice constant of the silicon clathrate type I crystal phase was about 1.015 nm.

(Charge / discharge test)
A charge / discharge test was performed on the evaluation batteries obtained in Example 1 and Comparative Example 1. The conditions of the charge / discharge test were a constraint pressure (fixed size) of 5 MPa, a charge of 0.1 C, a discharge of 1 C, a cut voltage of 3.0 V to 4.55 V, and an initial charge capacity and an initial discharge capacity were obtained. The results are shown in FIG. At the time of the first charge, the restraint pressure of the evaluation battery was monitored, the restraint pressure at 4.55 V was measured, and the increase in the restraint pressure from the state before charge / discharge was determined. The results are shown in FIG. In addition, the result of the restraint pressure increase amount in Table 1 is a relative value when the result of Comparative Example 1 is set to 100.

  As shown in FIG. 6 and Table 1, Example 1 and Comparative Example 1 exhibited almost the same charge / discharge behavior. That is, it was confirmed that the active material according to the present disclosure has the same performance as the conventional Si particles. On the other hand, as shown in FIG. 7 and Table 1, it was confirmed that in Example 1, the increase in the constraining pressure was significantly smaller than that in Comparative Example 1, that is, the volume change was significantly smaller.

  The evaluation batteries obtained in Example 1 and Comparative Example 1 were subjected to a constraint pressure (fixed size) of 5 MPa, a charge of 1/3 C, a discharge of 1/3 C, and a cut voltage of 3.0 V to 4.55 V. 5 cycles of charge / discharge were performed. The charge capacity and discharge capacity at the fifth cycle were determined. Table 2 shows the results. Further, at the time of charging in the fifth cycle, the restraining pressure of the evaluation battery was monitored, the restraining pressure at 4.55 V was measured, and the increase in the restraining pressure from the state before charge and discharge was obtained. Table 2 shows the results. In addition, the result of the restraint pressure increase amount in Table 2 is a relative value when the result of Comparative Example 1 is set to 100.

  As shown in Table 2, it was confirmed that even after 5 cycles, the increase in the confining pressure in Example 1 was significantly smaller than that in Comparative Example 1, that is, the change in volume was significantly smaller. The battery for evaluation after 5 cycles was disassembled, and XRD measurement was performed in a glove box in an Ar atmosphere. FIG. 8 shows the result. 8A and 8B, the upper row shows the results of XRD measurement on the negative electrode active material before charging and discharging, and the lower row shows the results of XRD measurement on the evaluation battery after 5 cycles. 8, CA indicates a positive electrode active material, SE indicates a solid electrolyte, and Cu indicates a copper foil.

  As shown in FIG. 8A, in Comparative Example 1, the peak derived from the negative electrode active material (Si particles having a diamond-type crystal phase) completely disappeared by five cycles of charge and discharge. It was confirmed that the substance was amorphous. Since amorphous is generally lower in density than crystal, it is considered to be a cause of a large volume change due to charge and discharge.

  On the other hand, as shown in FIG. 8 (b), in Example 1, even after 5 cycles of charge / discharge, the negative electrode active material (active material having a silicon clathrate I-type crystal phase) is derived. A peak was observed. The reason is that the silicon clathrate I-type crystal phase, by performing Li insertion and desorption using its internal space, was able to alleviate the stress applied to the Si—Si bond and suppress the amorphousization. Conceivable. Therefore, as shown in Table 2, in Example 1, it is assumed that the increase in the constraining pressure was suppressed.

[Example 2]
Si particles (purity: 99.999%) and metallic Na (purity: 99.5%) were weighed at a molar ratio of Si particles: metallic Na = 1: 1.1, and charged into a crucible made of boron nitride. And sealed under an Ar atmosphere. Thereafter, heat treatment was performed at 700 ° C. for 20 hours. Thus, a NaSi compound (gintle) was obtained. The obtained NaSi compound was pulverized and heat-treated at 400 ° C. for 5 hours under vacuum (about 0.05 Pa) to desorb Na. The obtained compound was ground in a mortar to obtain an active material. A battery for evaluation was obtained in the same manner as in Example 1, except that the obtained active material was used.

[Evaluation]
(XRD measurement)
The negative electrode active material obtained in Example 2 was subjected to X-ray diffraction (XRD) measurement using CuKα radiation. FIG. 9 shows the result. As shown in FIG. 9, it was confirmed that the negative electrode active material obtained in Example 2 had a silicon clathrate I type crystal phase as a main crystal phase, similarly to the negative electrode active material obtained in Example 1. Was done. On the other hand, in the negative electrode active material obtained in Example 2, peaks of a silicon clathrate II type crystal phase, a diamond type Si crystal phase, and a gintle phase were also confirmed. Thus, it was suggested that the active material in the present disclosure is easily affected by the manufacturing conditions.

[Comparative Example 2]
Si particles (purity: 99.999%) and metallic Na (purity: 99.5%) were weighed at a molar ratio of Si particles: metallic Na = 1: 1.1, and charged into a crucible made of boron nitride. And sealed under an Ar atmosphere. Thereafter, heat treatment was performed at 700 ° C. for 20 hours. Thus, a NaSi compound (a compound having a gintle phase) was obtained. The obtained NaSi compound was pulverized and heated under vacuum (about 0.1 Pa) at a rate of temperature increase of 15 ° C./min. After reaching 400 ° C., heat treatment was performed for 5 hours to desorb Na. The obtained compound was ground in a mortar. Thereafter, the particle size was adjusted by classification to obtain negative electrode active material particles A (average secondary particle size = 5 μm) and negative electrode active material particles B (average secondary particle size = 3 μm).

Next, 0.4 g of solid electrolyte particles (Li ₃ PS ₄ ), 0.8 g of the obtained negative electrode active material particles A, 0.06 g of a conductive material (VGCF), and a binder solution (butyric acid containing 5% by weight of a PVDF resin) (Butyl solution) 0.32 g was added to a polypropylene container. The container was subjected to ultrasonic treatment using an ultrasonic dispersing device for 30 seconds, and then subjected to shaking using a shaker for 30 minutes, thereby obtaining a slurry A having a relatively large content of the negative electrode active material.

Further, 0.7 g of solid electrolyte particles (Li ₃ PS ₄ ), 0.6 g of the obtained negative electrode active material particles B, 0.06 g of a conductive material (VGCF), and a binder solution (butyl butyrate containing 5% by weight of a PVDF-based resin) Solution) 0.24 g was added to a polypropylene container. The container was subjected to ultrasonic treatment using an ultrasonic dispersing device for 30 seconds, and then subjected to shaking using a shaker for 30 minutes, thereby obtaining a slurry B having a relatively small content of the negative electrode active material.

  The slurry A was applied on a negative electrode current collector (copper foil) by a blade method using an applicator, and air-dried for 60 minutes. Thereafter, the slurry B was applied on the dried coating film by a blade method using an applicator, and air-dried for 60 minutes. Then, it dried on the hot plate adjusted to 100 degreeC for 30 minutes. Thereby, a negative electrode structure having a negative electrode layer and a negative electrode current collector was obtained. A battery for evaluation was obtained in the same manner as in Example 1 except that the obtained negative electrode structure was used.

[Examples 3 to 5, Comparative Examples 3 and 4]
An evaluation battery was obtained in the same manner as in Comparative Example 2, except that the vacuum heat treatment conditions were changed to the conditions described in Table 3.

[Evaluation]
(XRD measurement)
The negative electrode active materials obtained in Examples 3 to 5 and Comparative Examples 2 to 4 were subjected to X-ray diffraction (XRD) measurement using CuKα radiation. The results are shown in FIGS. As shown in FIG. 10, in Comparative Example 2, the peak of the silicon clathrate I-type crystal phase was confirmed, and at the same time, the peak of the gintle phase was slightly confirmed. On the other hand, in Comparative Example 2, the peak of the diamond-type Si crystal phase was not confirmed. Further, as shown in FIGS. 11 to 13, in Examples 3 and 4 and Comparative Example 3, the peak of the silicon clathrate I-type crystal phase was confirmed, and at the same time, the peak of the diamond-type Si crystal phase was observed. Was slightly confirmed. Further, in Example 5, a peak of a silicon clathrate I-type crystal phase and a peak of a diamond-type Si crystal phase were confirmed. On the other hand, in Comparative Example 4, the peak of the diamond-type Si crystal phase was confirmed, but the peak of the silicon clathrate I-type crystal phase was not confirmed. Further, based on the respective chart _to determine the value of _I B / I _A. Table 3 shows the results.

(SEM-EDX measurement)
The negative electrode active materials obtained in Examples 3 to 5 and Comparative Examples 2 to 4 were subjected to SEM-EDX (scanning electron microscope-energy dispersive X-ray spectroscopy) measurement to measure Na / Si. Na / Si was calculated from the atomic number ratio based on the signal intensity ratio of Na and Si by EDX analysis. _X in Na _x Si ₄₆ was determined from Na / Si. Table 3 shows the results.

(Charge / discharge test)
A charge / discharge test was performed on the evaluation batteries obtained in Examples 3 to 5 and Comparative Examples 2 to 4. The conditions of the charge / discharge test were a constraint pressure (fixed size) of 5 MPa, a charge of 0.1 C, a discharge of 1 C, a cut voltage of 3.0 V to 4.55 V, and an initial charge capacity and an initial discharge capacity were obtained. Table 3 shows the results. At the time of the first charge, the restraint pressure of the evaluation battery was monitored, the restraint pressure at 4.55 V was measured, and the increase in the restraint pressure from the state before charge / discharge was determined. Table 3 shows the results. In addition, the result of the restraint pressure increase amount in Table 3 is a relative value when the result of Comparative Example 3 is set to 100. FIG. 16 shows the relationship between the amount x of Na and the amount of increase in the confining pressure.

  As shown in Table 3, Examples 3 to 5 and Comparative Examples 2 to 4 had substantially the same charge capacity and discharge capacity as Comparative Example 1. That is, it was confirmed that the active materials obtained in Examples 3 to 5 and Comparative Examples 2 to 4 had the same performance as conventional Si particles. As shown in Table 3 and FIG. 16, it was confirmed that Examples 3 to 5 had a smaller increase in restraint pressure, that is, a smaller volume change, than Comparative Examples 2 and 4. The reason why the increase in the constraining pressure in Example 3 is smaller than that in Comparative Examples 2 and 3 is that Li is inserted into the site where Na should be located in the silicon clathrate I-type crystal structure. This is presumed to be because the volume change as the negative electrode active material was suppressed. On the other hand, the reason why the increase in the constraining pressure in Comparative Example 4 was larger than that in Example 5 is that, as shown in FIG. 15, not a silicon clathrate I-type crystal phase but a diamond-type Si crystal. It is presumed that the phase was precipitated.

DESCRIPTION OF SYMBOLS 1 ... Positive electrode layer 2 ... Electrolyte layer 3 ... Negative electrode layer 4 ... Positive electrode current collector 5 ... Negative electrode current collector 10 ... Battery

Claims (11)

Na _x M _y Si ₄₆ (M is a metal element other than Na, x and y, 0 <x, 0 ≦ y , y ≦ x, 0 < satisfy x + y <8) have a composition represented by And an active material having a silicon clathrate type I crystal phase.   The active material according to claim 1, wherein the active material has the silicon clathrate I-type crystal phase as a main phase.   In the X-ray diffraction measurement using CuKα radiation, the crystal phase of the silicon clathrate I type was 2θ = 30.33 ° ± 1.00 °, 31.60 ° ± 1.00 °, 32.82 ° ± 1. 3. The active material according to claim 1, wherein the active material has peaks at 0.00 °, 52.39 ° ± 1.00 °, and 55.49 ° ± 1.00 °. 4.   The active material according to any one of claims 1 to 3, wherein the active material does not have a diamond-type Si crystal phase. The active material has a diamond-type Si crystal phase,
The diamond-type Si crystal phase has a peak at a position of 2θ = 28.44 ° ± 1.00 ° in X-ray diffraction measurement using CuKα radiation,
Wherein the diffraction intensity of the peak of 2θ = 32.82 ° ± 1.00 ° and _{I A,} the diffraction intensity of the peak of the 2θ = 28.44 ° ± 1.00 ° when the _{I B, I B} / I _a is greater than 0, 0.1 or less, the active material of claim 3.   The active material according to claim 1, wherein the x and the y satisfy 2.9 ≦ x, 2.9 ≦ x + y ≦ 7.1. A battery having a positive electrode layer, an electrolyte layer, and a negative electrode layer in this order,
A battery, wherein the negative electrode layer contains the active material according to any one of claims 1 to 6.   The battery according to claim 7, wherein the electrolyte layer contains an inorganic solid electrolyte.   The battery according to claim 7, wherein the electrolyte layer contains an electrolytic solution.   The battery according to any one of claims 7 to 9, wherein the battery is a lithium ion battery.   The battery according to any one of claims 7 to 9, wherein the battery is a sodium ion battery.