JP2018206615A - Negative electrode and nonaqueous electrolyte power storage element - Google Patents

Abstract

To provide: a negative electrode enabling a nonaqueous electrolyte power storage element to have both sufficient discharge capacity and high discharge capacity retention rate when the negative electrode is used in the nonaqueous electrolyte power storage element; and a nonaqueous electrolyte power storage element having the negative electrode.SOLUTION: According to an embodiment of the present invention, there is provided a negative electrode for a nonaqueous electrolyte power storage element, which includes a negative electrode mixture mainly consisting of a composite oxide that contains germanium and alkali metal, alkali earth metal or a combination thereof, the composite oxide having an atomic ratio (O/Ge) of oxygen to germanium of 2.1 or more and 3.2 or less.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a negative electrode and a nonaqueous electrolyte storage element.

  Nonaqueous electrolyte secondary batteries typified by lithium ion secondary batteries are widely used in electronic devices such as personal computers and communication terminals, automobiles and the like because of their high energy density. The nonaqueous electrolyte secondary battery generally has a pair of electrodes electrically isolated by a separator and a nonaqueous electrolyte interposed between the electrodes, and transfers ions between the electrodes. It is comprised so that it may charge / discharge. In addition, capacitors such as lithium ion capacitors and electric double layer capacitors are widely used as nonaqueous electrolyte storage elements other than nonaqueous electrolyte secondary batteries.

As the active material contained in the negative electrode of the nonaqueous electrolyte storage element, a carbon material such as graphite, a metal oxide, or the like is used. Various active materials have been developed for increasing the capacity of power storage elements, and Non-Patent Document 1 describes that GeO ₂ was used for the negative electrode.

Youngsik Kim, Haesuk Hwang, Katerine Lawler, Steve W. Martin, Jaefil Cho, “Electrochimica Acta”, 2008, Volume 53, p5058-5064.

The nonaqueous electrolyte storage element is required to have a high retention rate in addition to a large discharge capacity. However, the nonaqueous electrolyte storage element using GeO ₂ as a negative electrode has a certain amount of discharge capacity, but does not have a high capacity retention rate.

  The present invention has been made based on the circumstances as described above, and its purpose is to provide a sufficient discharge capacity and a high discharge capacity maintenance rate when used in a non-aqueous electrolyte storage element. It is providing the negative electrode which can combine these, and the nonaqueous electrolyte electrical storage element which has this negative electrode.

  One embodiment of the present invention made to solve the above problems includes a negative electrode mixture mainly containing a composite oxide containing germanium and an alkali metal, an alkaline earth metal, or a combination thereof, and the composite oxide This is a negative electrode for a non-aqueous electrolyte storage element in which the atomic ratio (O / Ge) of oxygen to germanium in the product is 2.1 or more and 3.2 or less.

  Another embodiment of the present invention is a nonaqueous electrolyte electricity storage device having the negative electrode.

  According to the present invention, when used in a non-aqueous electrolyte storage element, the non-aqueous electrolyte storage element can have both a sufficient discharge capacity and a high discharge capacity retention rate, and a non-aqueous electrolyte storage having the negative electrode An element can be provided.

FIG. 1 is an external perspective view showing a nonaqueous electrolyte storage element according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing a power storage device configured by assembling a plurality of nonaqueous electrolyte power storage elements according to an embodiment of the present invention. FIG. 3 is an X-ray diffraction pattern of the oxides of Examples 1 to 3 and Comparative Examples 1 to 3. FIG. 4 is a discharge curve of the nonaqueous electrolyte electricity storage device of Example 1. FIG. 5 is a discharge curve of the nonaqueous electrolyte electricity storage device of Example 2.

  A negative electrode according to an embodiment of the present invention includes a negative electrode mixture mainly composed of a complex oxide containing germanium and an alkali metal, an alkaline earth metal, or a combination thereof, and oxygen relative to germanium in the complex oxide. Is a negative electrode for a non-aqueous electrolyte electricity storage device having an atomic ratio (O / Ge) of 2.1 or more and 3.2 or less.

When the negative electrode is used for a nonaqueous electrolyte storage element, the nonaqueous electrolyte storage element can have both a sufficient discharge capacity and a high discharge capacity retention rate. Although this reason is not certain, the following reason is guessed. In the negative electrode, the atomic ratio (O / Ge) of oxygen to germanium in the composite oxide that is the main component of the negative electrode mixture is 2.1 or more. That is, as compared with GeO ₂ (O / Ge = 2) or the like, the content ratio of oxygen atoms that are not oxidized / reduced during charge / discharge is high. For this reason, it is presumed that the stress accompanying the oxidation / reduction of germanium during charge / discharge, which causes deterioration, is alleviated and the capacity maintenance rate is increased. On the other hand, the atomic ratio (O / Ge) of oxygen to germanium in the composite oxide is 3.2 or less, there is a sufficient amount of germanium that causes redox, and there is a sufficient diffusible route for lithium and the like. It is estimated that it can have a sufficient discharge capacity.

  Here, the “main component” of the negative electrode mixture refers to a main component having a high content ratio in the negative electrode mixture. For example, the “main component” of the negative electrode composite material may be a component having a content ratio of 10% by mass or more, 30% by mass or more, or 50% by mass or more. Alternatively, the “main component” of the negative electrode mixture may be a component having the highest mass-based content ratio among the components of the negative electrode mixture.

  In the present specification, the composite oxide functions as a negative electrode active material, and a reduction reaction in which lithium ions and the like are occluded with respect to the negative electrode active material (composite oxide) is “charged”, lithium ions, and the like. The oxidation reaction that releases is called “discharge”.

The In the negative electrode, 0.0 V in the discharge process after charging until (vs.Li/Li ^+), 0.0~2.0V electric quantity is discharged at a range of _(vs.Li/Li ⁺⁾ _Q ( The ratio of the quantity of electricity Q _{(0.0-1.2 V)} discharged in the range of 0.0 to 1.2 V (vs. Li / Li ⁺ ₎ to 0.0-2.0 _V) (Q _{(0.0 -1.2V)} / Q _(0.0-2.0V) ) is preferably 80% or more.

According to the knowledge of the inventors, discharge at a potential higher than about 1.2 V (vs. Li ^/ Li ⁺ ) is mainly caused by a conversion reaction, and this reaction is a factor that lowers the capacity maintenance rate. Guessed. On the other hand, the high ratio (Q _{(0.0-1.2 V)} / Q _{(0.0-2.0 V)} ) indicates that the potential is 1.2 V (vs. Li ^/ Li ⁺ ) or less. Indicates that the reaction is the main component. Therefore, when the ratio (Q _{(0.0-1.2 V)} / Q _{(0.0-2.0 V)} ) is 80% or more, the capacity retention rate can be further increased.

  The atomic ratio of transition metal to germanium in the composite oxide of the negative electrode is preferably less than 1. Thus, when the content rate of a transition metal is low and the content rate of germanium is relatively high, discharge capacity etc. become more favorable. For example, when transition metals, such as copper, cobalt, iron, and zinc, are contained, the conversion reaction derived from these transition metals tends to proceed at a high potential. Therefore, by reducing the content ratio of the transition metal, a composition that hardly causes a conversion reaction that causes a decrease in the capacity retention rate is obtained, and the capacity retention rate can be further increased. “Transition metal” refers to a Group 3-12 element.

  The nonaqueous electrolyte storage element according to an embodiment of the present invention is a nonaqueous electrolyte storage element having the negative electrode. The non-aqueous electrolyte storage element has both a sufficient discharge capacity and a high discharge capacity maintenance rate.

  Hereinafter, a negative electrode and a nonaqueous electrolyte storage element according to an embodiment of the present invention will be described in detail.

<Negative electrode>
The negative electrode which concerns on one Embodiment of this invention is a negative electrode for nonaqueous electrolyte electrical storage elements. The negative electrode includes a negative electrode substrate and a negative electrode mixture layer disposed on the negative electrode substrate directly or via an intermediate layer.

  The negative electrode substrate has conductivity. As a material of the negative electrode substrate, metals such as copper, nickel, stainless steel, nickel-plated steel or alloys thereof are used, and copper or copper alloys are preferable. Moreover, foil, a vapor deposition film, etc. are mentioned as a formation form of a negative electrode base material, and foil is preferable from the surface of cost. That is, copper foil is preferable as the negative electrode substrate. Examples of the copper foil include rolled copper foil and electrolytic copper foil.

The said intermediate | middle layer is a coating layer of the surface of a negative electrode base material, and reduces the contact resistance of a negative electrode base material and a negative electrode compound material layer by containing electroconductive particles, such as a carbon particle. The configuration of the intermediate layer is not particularly limited, and can be formed of a composition containing a resin binder and conductive particles, for example. “Conductive” means that the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 ⁷ Ω · cm or less, and “nonconductive” Means that the volume resistivity is more than 10 ⁷ Ω · cm.

  The negative electrode composite layer is a composite containing germanium and an alkali metal, an alkaline earth metal, or a combination thereof (hereinafter, “alkali metal, alkaline earth metal, or a combination thereof” is also referred to as “specific metal element”). It is a layer formed from a so-called negative electrode mixture mainly composed of an oxide. The composite oxide functions as a negative electrode active material. The negative electrode mixture can contain optional components such as other negative electrode active materials, conductive agents, binders, thickeners, and fillers as necessary. The negative electrode mixture layer is formed by applying a slurry of the negative electrode mixture.

  The composite oxide includes germanium, a specific metal element, and oxygen as constituent elements. The lower limit of the atomic ratio (O / Ge) of oxygen to germanium in this composite oxide is 2.1, preferably 2.2, more preferably 2.25, and even more preferably 2.5. By making this atomic ratio more than the above lower limit, the capacity retention rate can be increased. On the other hand, the upper limit of the atomic ratio (O / Ge) is 3.2, preferably 3, and more preferably 2.5. The discharge capacity can be increased by setting the atomic ratio to the upper limit or less.

  Specific metal elements contained in the composite oxide include alkali metals such as lithium, sodium, potassium, and rubidium, and alkaline earth metals such as magnesium, calcium, and strontium. One of these may be contained, or two or more thereof may be contained. As the specific metal element, an alkali metal is preferable, and lithium is more preferable. When the specific metal element is an alkaline earth metal, magnesium is preferable as the alkaline earth metal.

  The content of the specific metal element in the composite oxide is not particularly limited. The composition ratio of specific metal elements such as lithium varies greatly due to charge and discharge, the composition ratio of specific metal elements may be larger than at the time of synthesis at the end of discharge, and the specific metal element raw material is theorized during synthesis Since addition in excess of the composition ratio is generally performed, the content of the specific metal element in the composite oxide does not significantly affect the performance as a negative electrode active material. For example, the lower limit of the atomic ratio (A / Ge) of the specific metal element (A) to germanium in the composite oxide may be 0.1 or 0.5. In addition, the upper limit of this atomic ratio (A / Ge) may be 5 or 2.

  The complex oxide may contain germanium, a specific metal element, and an element other than oxygen as long as the effects of the present invention are not affected. Such other optional elements include metal elements (including semi-metal elements) such as aluminum, silicon, titanium, vanadium, manganese, iron, cobalt, nickel and copper, and non-metallic elements such as nitrogen, fluorine and bromine. Is mentioned. The upper limit of the atomic ratio of these optional elements in the total number of atoms of the composite oxide is preferably 0.5, more preferably 0.2, still more preferably 0.1, and still more preferably 0.01. 0.001 is particularly preferable. This optional element may not be substantially contained.

  The atomic ratio of transition metal to germanium in the composite oxide is preferably less than 1. The upper limit of the atomic ratio of transition metal to germanium in the composite oxide is more preferably 0.5, more preferably 0.1, and still more preferably 0.01. In the composite oxide, it is more preferable that the transition metal is not substantially contained. Thus, when the content rate of a transition metal is low, a discharge capacity and a capacity maintenance rate become more favorable.

The composite oxide can be preferably represented by the following formula (1).
A _x Ge _y O _z (1)
In formula (1), A is an alkali metal, an alkaline earth metal, or a combination thereof. 0 <x, 0 <y, 0 <z, 2.1 ≦ z / y ≦ 3.2. )

  As A in said Formula (1), an alkali metal is preferable and lithium (Li) is more preferable. A may be one type or two or more types.

  Regarding x and y in the above formula (1), the lower limit of x / y may be 0.1 or 0.5. On the other hand, the upper limit of x / y may be 5 or 2.

  Regarding y and z in the above formula (1), the lower limit of z / y is preferably 2.2, more preferably 2.25, and even more preferably 2.5. On the other hand, the upper limit of z / y is preferably 3, and may be more preferably 2.5.

Examples of the composite oxide include Li ₂ Ge ₄ O ₉ , Li ₄ Ge ₅ O ₁₂ , Li ₂ GeO ₃ , Na ₂ Ge ₄ O ₉ , Na ₂ GeO ₃ , K ₂ Ge ₈ O ₁₇ , and K ₂ Ge ₄ O. ₉ , K ₂ GeO ₃ , MgGeO ₃ , MgGe ₄ O ₉ , Mg ₂ GeO ₃ , CaGe ₂ O ₅ , CaGe ₄ O ₉ , CaGeO ₃ , SrGe ₄ O ₉ , SrGe ₄ O ₉ , SrGeO ₃ , CaMgGe ₂ O ₆ BaMgGe ₂ O ₆ , SrMgGe ₂ O _{6 and the} like. These are complex oxides represented by the above formula (1).

Examples of the complex oxide other than the complex oxide represented by the above formula (1) include Li ₂ CoGe ₃ O ₈ , KGaGe ₃ O ₈ , K ₂ TiGe ₃ O ₉ , Cs ₂ TiGe ₃ O ₉ , and Rb ₂ TiGe. _{3 O 9, BaTiGe 3 O 9} , RbNbGe 3 O 9, KTaGe 3 O 9, RbTaGe 3 O 9, CaZnGe 2 O 6, SrZnGe 2 O 6, K 2 SnGe 3 O 9, Cs 2 SnGe 3 O 9, BaSnGe 3 Examples include O ₉ and CaCu ₃ Ge ₄ O ₁₂ .

  The composite oxide may be crystalline or non-crystalline. The crystal structure when the composite oxide is crystalline is not particularly limited. The composite oxide may have a crystal structure such as CMC21, Pcca, or PBCA. Among these, the composite oxide preferably has a CMC21 or Pcca crystal structure. However, the crystal structure may not be maintained by repeated charge and discharge. Therefore, it is preferable that the crystal structure before charging / discharging belongs to the space group.

  X-ray diffraction measurement of the composite oxide is performed by powder X-ray diffraction measurement using an X-ray diffractometer (“MiniFlex II” manufactured by Rigaku), with the source being CuKα ray, the tube voltage being 30 kV and the tube current being 15 mA. . At this time, the diffracted X-rays are detected by a high-speed one-dimensional detector (D / teX Ultra 2) through a Kβ filter having a thickness of 30 μm. The sampling width is 0.01 °, the scanning speed is 5 ° / min, the divergence slit width is 0.625 °, the light receiving slit width is 13 mm (OPEN), and the scattering slit width is 8 mm. Based on the obtained X-ray diffraction data, the crystal structure can be analyzed by Rietveld analysis using the “Rietan 2000” program (F. Izumi and T. Ikeda, Mater. Sci. Forum, 198 (2000)). it can. For the space group, the same result can be obtained by using comprehensive powder X-ray analysis software “PDXL” (manufactured by Rigaku).

The method for obtaining the composite oxide is not limited. Specifically, for example, an oxide containing germanium (GeO ₂ or the like) and a compound containing a specific metal element (Li ₂ CO ₃ or the like) are mixed at a predetermined ratio and processed by a firing method, a mechanochemical method, or the like. Can be obtained. The composite oxide obtained through such treatment is usually in the form of a powder.

  The lower limit of the content of the composite oxide in the negative electrode mixture layer (negative electrode mixture) is, for example, 10% by mass, preferably 30% by mass, more preferably 50% by mass, further preferably 60% by mass, 65 mass% is still more preferable. By setting the content of the composite oxide to the lower limit or more, the discharge capacity can be further increased. On the other hand, the upper limit of the content may be, for example, 95% by mass or 80% by mass. By making content of the said complex oxide below the said upper limit, a sufficient quantity of electrically conductive agents can be contained etc., sufficient electroconductivity etc. can be ensured.

  It does not specifically limit as another negative electrode active material which may be contained in the said negative electrode compound material layer (negative electrode compound material), A conventionally well-known negative electrode active material can be mentioned.

  The conductive agent is a substance having conductivity. Examples of the shape of the conductive agent include powder and fiber. The conductive agent is not particularly limited as long as it is a conductive material that does not adversely affect the performance of the storage element. Examples of such a conductive agent include natural or artificial graphite, furnace black, acetylene black, carbon black such as ketjen black, metal, conductive ceramics, and the like, and acetylene black is preferable. The reason for this is as follows. Graphite and carbon black also function as a negative electrode active material, but their discharge capacity is smaller than that of the composite oxide. Therefore, in order to increase the discharge capacity, it is preferable to reduce these conductive agents as much as possible. On the other hand, acetylene black has a property that it can form a network structure in which particles are connected. In contrast, graphite usually does not have the property of forming such a network structure. For this reason, by using acetylene black, a good conductive path can be formed even in a small amount. Therefore, when acetylene black is used, the content of the composite oxide can be sufficiently increased, and the discharge capacity can be further increased while ensuring good conductivity.

  As a minimum of content of the above-mentioned conductive agent in the above-mentioned negative electrode compound layer (negative electrode compound material), it is 5 mass%, for example, and 10 mass% is preferred. By setting the content of the conductive agent to the lower limit or higher, sufficient conductivity can be exhibited. On the other hand, as an upper limit of this content, it is 30 mass%, for example, and 25 mass% is preferable. By making content of the said electrically conductive agent below the said upper limit, sufficient quantity of complex oxide can be contained etc., discharge capacity can be enlarged more, etc.

  As the binder (binder), thermoplastic resins such as fluororesin (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyimide; ethylene-propylene-diene rubber (EPDM), Examples thereof include elastomers such as sulfonated EPDM, styrene butadiene rubber (SBR) and fluororubber; polysaccharide polymers and the like.

  Examples of the thickener include polysaccharide polymers such as carboxymethylcellulose (CMC) and methylcellulose. When the thickener has a functional group that reacts with lithium, it is preferable to deactivate this functional group in advance by methylation or the like.

  The filler is not particularly limited as long as it does not adversely affect the performance of the storage element. Examples of the main component of the filler include polyolefins such as polypropylene and polyethylene, silica, alumina, zeolite, and glass.

In the said negative electrode, it is preferable to satisfy | fill the following relationships in the discharge process after charging to 0.0V (vs.Li/Li ^<+> ). The amount of electricity discharged in the range of 0.0 to 2.0 V (vs. Li / Li ⁺ ) is defined as Q _{(0.0-2.0 V)} . Among these, the quantity of electricity discharged in the range of 0.0 to 1.2 V (vs. Li / Li ⁺ ) is defined as Q _{(0.0-1.2 V)} . The electric quantity Q _{(0.0-1.2 V)} to the electric quantity Q _{(0.0-2.0 V)} , that is, the ratio (Q _{(0.0-1.2 V)} / Q _{(0.0-2. 0V)} ) is preferably 80%, more preferably 90%, and even more preferably 95%. When the ratio (Q _{(0.0-1.2 V)} / Q _{(0.0-2.0 V)} ) is _{equal to} or higher than the lower limit, charging / discharging with less conversion reaction can be performed, and the capacity retention rate can be further increased. Can be increased. The upper limit of this ratio (Q _(0.0-1.2V) / Q _(0.0-2.0V) ) may be 100% or 99%. Note that the above-described potential is a negative electrode potential in a charge / discharge process of a power storage element using the negative electrode as a negative electrode.

<Nonaqueous electrolyte storage element>
A nonaqueous electrolyte storage element according to an embodiment of the present invention includes a positive electrode, a negative electrode, and a nonaqueous electrolyte. Hereinafter, a nonaqueous electrolyte secondary battery will be described as an example of a nonaqueous electrolyte storage element. The positive electrode and the negative electrode usually form an electrode body that is alternately superposed by stacking or winding via a separator. This electrode body is housed in a case, and the case is filled with a nonaqueous electrolyte. The non-aqueous electrolyte is interposed between the positive electrode and the negative electrode. In addition, as the case, a known metal case, a resin case, or the like that is usually used as a case of a nonaqueous electrolyte secondary battery can be used.

(Positive electrode)
The positive electrode has a positive electrode base material and a positive electrode mixture layer disposed on the positive electrode base material directly or via an intermediate layer. The intermediate layer can have the same structure as the intermediate layer of the negative electrode.

  The positive electrode base material has conductivity. As the material of the substrate, metals such as aluminum, copper, titanium, tantalum, stainless steel, or alloys thereof are used. Among these, aluminum and aluminum alloys are preferable from the balance of potential resistance, high conductivity and cost. Moreover, foil, a vapor deposition film, etc. are mentioned as a formation form of a positive electrode base material, and foil is preferable from the surface of cost. That is, an aluminum foil is preferable as the positive electrode base material.

  The positive electrode mixture layer is formed of a so-called positive electrode mixture containing a positive electrode active material. In addition, the positive electrode mixture forming the positive electrode mixture layer includes optional components such as a conductive agent, a binder (binder), a thickener, and a filler as necessary. As the optional components such as the conductive agent, the binder, the thickener, and the filler, the same materials as those of the negative electrode mixture layer described above can be used.

As the positive electrode active material, a conventionally known material is used as the positive electrode active material of the nonaqueous electrolyte storage element. As a specific positive electrode active material, for example, a composite oxide (Li _x having a layered α-NaFeO ₂ type crystal structure) represented by Li _x MO _y (M represents at least one transition metal other than Mo) is used. _{CoO 2, Li x NiO 2,} Li x MnO 3, Li x Ni α Co (1-α) O 2, Li x Ni α Mn β Co (1-α-β) O 2 or the like, having a spinel type crystal structure Li _x Mn ₂ O ₄ , Li _x Ni _α Mn _(2-α) O _4, etc.), Li _w M ′ _x (XO _y ) _z (M ′ represents at least one transition metal other than Mo, and X represents For example, polyanion compounds represented by P, Si, B, V, etc. (LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , LiCoPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , Li ₂ MnSiO ₄ , Li ₂ CoP O ₄ F etc.).

(Negative electrode)
As the negative electrode, the negative electrode according to one embodiment of the present invention is used. The details of the negative electrode are as described above.

(Separator)
As the material of the separator, for example, a woven fabric, a nonwoven fabric, a porous resin film, or the like is used. Among these, a porous resin film is preferable from the viewpoint of strength, and a nonwoven fabric is preferable from the viewpoint of liquid retention of the nonaqueous electrolyte. The main component of the separator is preferably a polyolefin such as polyethylene or polypropylene from the viewpoint of strength, and is preferably polyimide or aramid from the viewpoint of resistance to oxidative degradation. These resins may be combined.

  An inorganic layer may be provided between the separator and the electrode (usually a positive electrode). This inorganic layer is a porous layer also called a heat-resistant layer. Moreover, the separator by which the inorganic layer was formed in one surface of the porous resin film can also be used. The inorganic layer is usually composed of inorganic particles and a binder, and may contain other components.

(Nonaqueous electrolyte)
As said nonaqueous electrolyte, the well-known electrolyte normally used for a nonaqueous electrolyte electrical storage element (secondary battery) can be used. The non-aqueous electrolyte includes a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.

  Examples of the non-aqueous solvent include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and the like. A chain carbonate etc. can be mentioned.

Examples of the electrolyte salt include lithium salt, sodium salt, potassium salt, magnesium salt, onium salt, and the like, but lithium salt is preferable. Examples of the lithium salt include inorganic lithium salts such as LiPF ₆ , LiPO ₂ F ₂ , LiBF ₄ , LiClO ₄ , LiN (SO ₂ F) ₂ , LiSO ₃ CF ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO Fluorohydrocarbon groups such as ₂ C ₂ F ₅ ) ₂ , LiN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ), LiC (SO ₂ CF ₃ ) ₃ , LiC (SO ₂ C ₂ F ₅ ) ₃ A lithium salt having

  As the non-aqueous electrolyte, a room temperature molten salt, an ionic liquid, a polymer solid electrolyte, or the like can be used.

  The non-aqueous electrolyte electricity storage element can be manufactured by using the negative electrode according to one embodiment of the present invention as the negative electrode. The manufacturing method includes, for example, a step of producing a positive electrode, a step of producing a negative electrode, a step of preparing a nonaqueous electrolyte, and an electrode body in which the positive electrode and the negative electrode are alternately superposed by being stacked or wound via a separator. Forming a positive electrode and a negative electrode (electrode body) in a case, and injecting the nonaqueous electrolyte into the case. After the injection, the nonaqueous electrolyte storage element can be obtained by sealing the injection port.

<Other embodiments>
The present invention is not limited to the above-described embodiment, and can be implemented in a mode in which various changes and improvements are made in addition to the above-described mode. For example, in the negative electrode, the intermediate layer may not be provided, and the negative electrode mixture may not form a clear layer. For example, the negative electrode may have a structure in which a negative electrode mixture is supported on a mesh-like negative electrode substrate. Further, in the above embodiment, the description has been made centering on the form in which the nonaqueous electrolyte storage element is a secondary battery, but other nonaqueous electrolyte storage elements may be used. Examples of other nonaqueous electrolyte storage elements include capacitors (electric double layer capacitors, lithium ion capacitors) and the like.

  FIG. 1 shows a schematic diagram of a rectangular nonaqueous electrolyte storage element (secondary battery) 1 which is an embodiment of the nonaqueous electrolyte storage element. In the figure, the inside of the container is seen through. In the nonaqueous electrolyte storage element 1 shown in FIG. 1, an electrode body 2 is housed in a container (case) 3. The electrode body 2 is formed by winding a positive electrode including a positive electrode active material and a negative electrode including a negative electrode active material via a separator. The positive electrode is electrically connected to the positive electrode terminal 4 via the positive electrode lead 4 ′, and the negative electrode is electrically connected to the negative electrode terminal 5 via the negative electrode lead 5 ′.

  The configuration of the nonaqueous electrolyte storage element (secondary battery) is not particularly limited, and examples thereof include a cylindrical battery, a square battery (rectangular battery), a flat battery, and the like. The present invention can also be realized as a power storage device including a plurality of the above nonaqueous electrolyte power storage elements. One embodiment of a power storage device is shown in FIG. In FIG. 2, the power storage device 30 includes a plurality of power storage units 20. Each power storage unit 20 includes a plurality of nonaqueous electrolyte power storage elements 1. The power storage device 30 can be mounted as a power source for vehicles such as an electric vehicle (EV), a hybrid vehicle (HEV), a plug-in hybrid vehicle (PHEV), and the like.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples.

[Example 1] (Synthesis of Li ₂ Ge ₄ O ₉ )
Lithium carbonate (Li ₂ CO ₃ ) (manufactured by Nacalai Tesque) and germanium oxide (GeO ₂ ) (manufactured by Koyo Chemical Co., Ltd.) were weighed so that the molar ratio of Li: Ge was 1: 2. These were put into a zirconia pot having an internal volume of 80 mL containing 90 g (about 250 pieces) of zirconia balls having a diameter of 5 mm. An additional 10 mL of ethanol was added to the pot and the lid was covered. This was set on a planetary ball mill ("Pulverisete 5" manufactured by FRITSCH), mixed for 9 minutes at a revolution speed of 300 rpm, and then put into a pause for 1 minute, a total of 6 times. This mixture was dried with an oven at 80 ° C. for 3 hours or longer to obtain a mixed powder. This mixed powder was placed in an alumina crucible (model number: 1-7745-07) having a capacity of 30 mL, and this crucible was placed in a tabletop vacuum / gas displacement furnace (“KDF75” manufactured by Denken Haydental). Next, the temperature was raised from room temperature to 800 ° C. in an air stream under normal pressure for 10 hours, and kept at this temperature for 4 hours, and then allowed to cool naturally to room temperature. In this way, a lithium germanium composite oxide represented by the composition formula Li ₂ Ge ₄ O ₉ was produced.

[Example 2] (Synthesis of Li ₂ GeO ₃ )
Except that Li ₂ CO ₃ and GeO ₂ were weighed so that the molar ratio of Li: Ge was 2: 1 and that the temperature was raised from room temperature to 950 ° C. in 10 hours and kept at this temperature for 4 hours. Then, a lithium germanium composite oxide represented by the composition formula Li ₂ GeO ₃ was produced in the same manner as in Example 1.

Example 3 (Synthesis of MgGeO ₃ )
Magnesium oxide MgO (manufactured by Nacalai Tesque) and GeO ₂ were weighed so that the molar ratio of Mg: Ge was 1: 1, and the temperature was raised from room temperature to 950 ° C. in 10 hours, and at this temperature for 4 hours A magnesium germanium composite oxide represented by the composition formula MgGeO ₃ was produced in the same manner as in Example 1 except that the oxide was retained.

[Comparative Example 1] Germanium oxide (GeO ₂ )
Germanium oxide (GeO ₂ ) (manufactured by Koyo Chemical Co., Ltd.) was prepared.

[Comparative Example 2] (Synthesis of Li ₆ Ge ₂ O ₇ )
Except that Li ₂ CO ₃ and GeO ₂ were weighed so that the molar ratio of Li: Ge was 3: 1 and that the temperature was raised from room temperature to 1050 ° C. in 10 hours and kept at this temperature for 4 hours. Then, a lithium germanium composite oxide represented by the composition formula Li ₆ Ge ₂ O ₇ was produced in the same manner as in Example 1.

[Comparative Example 3] (Synthesis of Li ₄ GeO ₄ )
Except that Li ₂ CO ₃ and GeO ₂ were weighed so that the molar ratio of Li: Ge was 4: 1 and that the temperature was raised from room temperature to 850 ° C. in 10 hours and kept at this temperature for 4 hours. Then, a lithium germanium composite oxide represented by the composition formula Li ₄ GeO ₄ was produced in the same manner as in Example 1.

[Analysis of complex oxides]
The oxides obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were analyzed by the following method. Powder X-ray diffraction measurement was carried out using an X-ray diffractometer (“MiniFlex II” from Rigaku). The radiation source was CuKα ray, the tube voltage was 30 kV, the tube current was 15 mA, and the diffracted X-ray was detected by a high-speed one-dimensional detector (model number: D / teX Ultra 2) through a Kβ filter having a thickness of 30 μm. The sampling width was 0.01 °, the scanning speed was 5 ° / min, the divergence slit width was 0.625 °, the light receiving slit width was 13 mm (OPEN), and the scattering slit width was 8 mm. The X-ray diffraction patterns of the oxides of Examples 1 to 3 and Comparative Examples 1 to 3 are shown in FIG. The obtained X-ray diffraction data was analyzed using the “PDXL” program.

As a result of the above analysis, as a result of the analysis of each oxide of the example and the comparative example, the assignable space groups are as follows. It was confirmed that the crystal structure belonged to the PDF database.
Example 1 (Li ₂ Ge ₄ O ₉ )
Space group Pcca (54) (PDF card number: 00-037-1363)
Example 2 (Li ₂ GeO ₃ )
Space group CMC21 (36) (PDF card number: 00-001-1146)
Example 3 (MgGeO ₃ )
Space group PBCA (61) (PDF card number: 00-000-5132)
Comparative Example 1 (GeO ₂ )
Space group P3121 (152) (PDF card number: 00-001-0362)
Comparative Example 2 (Li ₆ Ge ₂ O ₇ )
Space group P21 / n (14) (PDF card number: 01-075-1524)
Comparative Example 3 (Li ₄ GeO ₄ )
Space group Bmmb (63) (PDF card number: 01-072-1587)

[Production of nonaqueous electrolyte storage element (test battery)]
Using each oxide obtained in Examples 1 to 3 and Comparative Examples 1 to 3 as a negative electrode active material, negative electrodes were produced in the following manner. 2.275 g of each oxide powder synthesized and 0.700 g of acetylene black (AB) were weighed. These were put into a zirconia pot having an internal volume of 80 mL containing 90 g (about 250 pieces) of zirconia balls having a diameter of 5 mm. An additional 10 mL of ethanol was added to the pot and the lid was covered. This operation was set on a planetary ball mill ("Pulverisete 5" manufactured by FRITSCH), mixed for 9 minutes at a revolution speed of 300 rpm, and then put into a rest for 1 minute for a total of 7 times. This mixture was dried with a dryer at 75 ° C. for 3 hours or more to prepare a mixed powder. 2.275 g of this mixed powder, 12% by mass N-methylpyrrolidone (NMP) solution of PVDF and NMP were placed in a predetermined plastic container, and the lid was covered in a glove box maintained in an argon atmosphere. This was set in a stirring defoaming apparatus (“Shinky's“ Awatori Netaro ”(trade name)) and sufficiently kneaded at 2000 rpm to prepare a slurry using N-methylpyrrolidone (NMP) as a dispersion medium. . The mass ratio of the negative electrode active material, AB, and PVDF in the slurry is 65:20:15. This slurry was applied to one side of a copper foil substrate having a thickness of 20 μm. This was placed on a hot plate at 80 ° C. for 60 minutes to evaporate the dispersion medium, and then subjected to roll press to obtain a negative electrode.

A test battery was assembled using each of the negative electrodes as a working electrode, and the behavior as a negative electrode was evaluated. For the purpose of accurately observing the single behavior, a counter electrode in which metallic lithium was adhered to a nickel foil current collector was used. Here, a sufficient amount of metallic lithium was arranged so that the capacity of the test battery was not limited by the counter electrode. A solution obtained by dissolving LiPF ₆ as an electrolyte in a mixed solvent of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / dimethyl carbonate (DMC) in a volume ratio of 6: 7: 7 so that the concentration becomes 1 mol / L. Was used. As the separator, a polypropylene microporous film whose surface was modified with polyacrylate was used. A metal resin composite film made of polyethylene terephthalate (15 μm) / aluminum foil (50 μm) / metal-adhesive polypropylene film (50 μm) is used for the exterior body, and the electrodes are exposed so that the open ends of the positive electrode terminal and the negative electrode terminal are exposed to the outside. Stowed. Subsequently, the fusion allowance in which the inner surfaces of the metal resin composite film face each other was hermetically sealed except for a portion serving as a liquid injection hole, and the liquid injection hole was sealed after pouring the electrolytic solution.

[Charge / discharge test]
In the following tests, voltage control was performed between the working electrode and the counter electrode, but the resistance between metal lithium dissolution and precipitation at the counter electrode was extremely low, so the voltage between terminals during charging and discharging was a reference using metal lithium. It can be regarded as being equal to the potential of the working electrode with respect to the pole. In the following tests, the composite oxide was used as a negative electrode active material for a negative electrode of a nonaqueous electrolyte storage element that was assumed to start from charging in combination with a positive electrode containing lithium that can be occluded and released electrochemically. Since it aims at evaluating, it started from operation which supplies with electricity to the reduction | restoration direction which is a reaction in which lithium ion is occluded electrochemically with respect to the said complex oxide.

A charge / discharge cycle test was performed in a thermostatic chamber set at 25 ° C. using the nonaqueous electrolyte electricity storage devices obtained using the oxides of Examples 1 to 3 and Comparative Examples 1 to 3. Charging is constant current constant voltage (CCCV) charging, the charging lower limit potential is 0.0 V (vs. Li ^/ Li ⁺ ), and the charge termination condition is reached when the charging current decays to 2 mA / g or reaches the charging lower limit potential. 3 hours or 15 hours have passed since then. This time is shown in Table 1 as “Charging CV Maximum Time”. The discharge was a constant current (CC) discharge, and the discharge end potential was 2.0 V (vs. Li ^/ Li ⁺ ). The constant current value of charge was 100 mA / g with respect to the mass of the negative electrode active material which a negative electrode contains. The constant current value of discharge was 20 mA / g with respect to the mass of the negative electrode active material which a negative electrode contains. The above charge and discharge were made into 1 cycle, and this cycle was implemented 10 cycles. In each cycle, a pause time of 10 minutes was set after charging and discharging. Table 1 shows the discharge capacity at the third cycle in this charge / discharge cycle test. The ratio of the discharge capacity at the 10th cycle to the discharge capacity at the 3rd cycle was determined as “capacity maintenance ratio (%)”. This capacity retention rate is also shown in Table 1. Further, the discharge electricity quantity ratio (Q _{(0.0-1.2 V)} / Q _{(0.0-2.0 V)} ) in the discharge process of the third cycle was determined. This ratio (Q _(0.0-1.2V) / Q _(0.0-2.0V) ) is also shown in Table 1.

  FIG. 4 shows the discharge curves of the third, seventh and tenth cycles of Example 1. The discharge curves for the third, seventh and tenth cycles of Example 2 are shown in FIG.

The working electrode (negative electrode) according to the above Examples and Comparative Examples contains acetylene black (AB). Therefore, since the observed charge / discharge behavior includes the contribution of AB, it is necessary to consider the contribution. Therefore, a test battery (hereinafter referred to as “AB battery”) was produced in the same procedure as in Example 1 except that electrochemically inactive Al ₂ O ₃ was used instead of the oxide. The charge termination condition is the time when 15 hours have passed since reaching the charge lower limit potential, and the same conditions except that the constant current value for charging is 10 mA / g and the constant current value for discharging is 10 mA / g. The charge / discharge test was conducted. The discharge capacity per ₃ mass of Al ₂ O ₃ in the third cycle in the AB battery is 69 mAh / Al ₂ O ₃ -g, ratio (Q _{(0.0-1.2 V)} / Q _{(0.0-2.0 V)} ) Was 82.6%.

As shown in Table 1, the non-aqueous electrolyte electricity storage devices of Examples 1 to 3 using a composite oxide having an O / Ge ratio of 2.1 or more and 3.2 or more are also in the case where the contribution of AB is removed. It can be seen that the battery has a large discharge capacity of 200 mAh / g or more and a high capacity maintenance rate exceeding 90%. In particular, the discharge capacity of the nonaqueous electrolyte electricity storage devices of Examples 1 and 2 using a composite oxide containing lithium as the specific metal element is significantly larger than the theoretical capacity of graphite (372 mAh / g). . Therefore, when the composite oxides of Examples 1 and 2 are used as the main component of the negative electrode mixture, the discharge capacity can be remarkably increased as compared with the case where graphite is used as the main component. In addition, the non-aqueous electrolyte storage elements of Examples 1 to 3 have a ratio (Q _{(0.0-1.2 V)} / Q _{(0.0-2.0 V)} ) of 94.5% or more, It is presumed that almost no conversion reaction tends to occur at a high potential of .2 V (vs. Li / Li ⁺ ) or higher, thereby exhibiting a high capacity retention rate.

  On the other hand, Comparative Example 1 using an oxide having an O / Ge ratio of less than 2.1 had a large capacity, but a low capacity retention rate. In Comparative Examples 2 and 3 using an oxide having an O / Ge ratio exceeding 3.2, the discharge capacity itself was small although the capacity retention rate was high.

  The present invention can be applied to electronic devices such as personal computers and communication terminals, non-aqueous electrolyte secondary batteries used as power sources for automobiles, and the negative and negative electrode active materials provided therein.

DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte electrical storage element 2 Electrode body 3 Container 4 Positive electrode terminal 4 'Positive electrode lead 5 Negative electrode terminal 5' Negative electrode lead 20 The electrical storage unit 30 The electrical storage apparatus

Claims (4)

A negative electrode mixture mainly composed of a complex oxide containing germanium and an alkali metal, an alkaline earth metal, or a combination thereof,
The negative electrode for nonaqueous electrolyte electrical storage elements whose atomic ratio (O / Ge) of oxygen with respect to germanium in the said complex oxide is 2.1-3.2. 0.0V in the discharge process after being charged up to (vs.Li/Li ^+), the electric quantity _{Q (0.0-2} to be discharged in the range of 0.0~2.0V (vs.Li/Li ⁺⁾ _{Ratio of} electric quantity Q _{(0.0-1.2 V)} discharged in the range of 0.0 to 1.2 V (vs. Li / Li ⁺ ₎ to 0.0 _V) (Q _{(0.0-1.2 V)} The negative electrode according to claim 1, wherein _/Q(0.0-2.0V) ) is 80% or more.   The negative electrode according to claim 1 or 2, wherein the composite oxide has an atomic ratio of transition metal to germanium of less than 1. The nonaqueous electrolyte electrical storage element which has a negative electrode of any one of Claims 1-3.

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