JP6911545B2 - Negative electrode and non-aqueous electrolyte power storage element - Google Patents

Description

The present invention relates to a negative electrode and a non-aqueous electrolyte power storage device.

Non-aqueous electrolyte secondary batteries represented by lithium ion secondary batteries are widely used in electronic devices such as personal computers and communication terminals, automobiles, etc. due to their high energy density. The non-aqueous electrolyte secondary battery generally has a pair of electrodes electrically separated by a separator and a non-aqueous electrolyte interposed between the electrodes, and transfers ions between the two electrodes. It is configured to charge and discharge. In addition, capacitors such as lithium ion capacitors and electric double layer capacitors are also widely used as non-aqueous electrolyte storage elements other than non-aqueous electrolyte secondary batteries.

A carbon material such as graphite, a metal oxide, or the like is used as the active material contained in the negative electrode of the non-aqueous electrolyte power storage element. Development of various active materials is being promoted in order to increase the capacity of the power storage element, and Non-Patent Document 1 describes that GeO ₂ is used as the negative electrode.

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

The non-aqueous electrolyte power storage element is required to have a large discharge capacity and a high maintenance rate. However, although _{the non-aqueous electrolyte power storage element using the above GeO 2} as the negative electrode has a certain discharge capacity, the capacity retention rate is not high.

The present invention has been made based on the above circumstances, and an object of the present invention is that when used in a non-aqueous electrolyte storage element, the non-aqueous electrolyte storage element has a sufficient discharge capacity and a high discharge capacity retention rate. It is an object of the present invention to provide a negative electrode capable of combining the above, and a non-aqueous electrolyte power storage element having the negative electrode.

One aspect of the present invention made to solve the above problems includes a negative electrode mixture containing germanium and a composite oxide containing an alkali metal, an alkaline earth metal or a combination thereof as a main component, and the above-mentioned composite oxidation. It is a negative electrode for a non-aqueous electrolyte power storage element in which the atomic number ratio (O / Ge) of oxygen to germanium in an object is 2.1 or more and 3.2 or less.

Another aspect of the present invention is a non-aqueous electrolyte power 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 has a negative electrode capable of having a sufficient discharge capacity and a high discharge capacity retention rate, and a non-aqueous electrolyte storage element having the negative electrode. The element can be provided.

FIG. 1 is an external perspective view showing a non-aqueous electrolyte power storage element according to an embodiment of the present invention. FIG. 2 is a schematic view showing a power storage device configured by assembling a plurality of non-aqueous 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 non-aqueous electrolyte power storage element of Example 1. FIG. 5 is a discharge curve of the non-aqueous electrolyte power storage element of Example 2.

The negative electrode according to the embodiment of the present invention includes a negative electrode mixture containing germanium and a composite oxide containing an alkali metal, an alkaline earth metal or a combination thereof as a main component, and oxygen for germanium in the composite oxide. It is a negative electrode for a non-aqueous electrolyte power storage element having an atomic number ratio (O / Ge) of 2.1 or more and 3.2 or less.

When the negative electrode is used for a non-aqueous electrolyte storage element, the non-aqueous electrolyte storage element can have a sufficient discharge capacity and a high discharge capacity retention rate. The reason for this is not clear, but the following reasons can be inferred. In the negative electrode, the atomic number ratio (O / Ge) of oxygen to germanium in the composite oxide which is the main component of the negative electrode mixture is 2.1 or more. That is, the content ratio of oxygen atoms that are not redox during charging / discharging is higher than _{that of GeO 2 (O / Ge = 2) and the like.} Therefore, it is presumed that the stress associated with the redox of germanium during charging and discharging, which causes deterioration, is alleviated and the capacity retention rate is increased. On the other hand, the atomic number ratio (O / Ge) of oxygen to germanium in the composite oxide is 3.2 or less, a sufficient amount of germanium that causes redox is present, and a diffusible pathway such as lithium is sufficient. It is presumed that the presence can have a sufficient discharge capacity.

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

In the present specification, the composite oxide acts as a negative electrode active material, and "charges" the reduction reaction in which lithium ions or the like are occluded with respect to the negative electrode active material (composite oxide), lithium ions or the like. The oxidation reaction in which is released 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 (0.0-1.2V)} to be discharged in the range of 0.0~1.2V (vs.Li/Li ⁺⁾ for _{0.0-2.0V) (Q (0.0 -1.2V)} / Q _(0.0-2.0V) ) is preferably 80% or more.

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

The ratio of the number of atoms of the transition metal to germanium in the composite oxide of the negative electrode is preferably less than 1. When the content ratio of the transition metal is low and the content ratio of germanium is relatively high as described above, the discharge capacity and the like become better. Further, 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 lowering the content ratio of the transition metal, the composition is less likely to cause a conversion reaction that causes a decrease in the capacity retention rate, and the capacity retention rate can be further increased. The "transition metal" refers to a group 3 to 12 element.

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

Hereinafter, the negative electrode and the non-aqueous electrolyte power storage device according to the embodiment of the present invention will be described in detail in order.

<Negative electrode>
The negative electrode according to the embodiment of the present invention is a negative electrode for a non-aqueous electrolyte power storage element. The negative electrode includes a negative electrode base material and a negative electrode mixture layer arranged directly on the negative electrode base material or via an intermediate layer.

The negative electrode base material has conductivity. As the material of the negative electrode base material, metals such as copper, nickel, stainless steel and nickel-plated steel or alloys thereof are used, and copper or a copper alloy is preferable. Further, as a form of forming the negative electrode base material, a foil, a vapor-deposited film and the like can be mentioned, and the foil is preferable from the viewpoint of cost. That is, copper foil is preferable as the negative electrode base material. Examples of the copper foil include rolled copper foil and electrolytic copper foil.

The intermediate layer is a coating layer on the surface of the negative electrode base material, and contains conductive particles such as carbon particles to reduce the contact resistance between the negative electrode base material and the negative electrode mixture layer. The composition of the intermediate layer is not particularly limited, and can be formed by, for example, a composition containing a resin binder and conductive particles. Incidentally, to have a "conductive" means that the volume resistivity is measured according to JIS-H-0505 (1975 years) is not more than 10 ⁷ Ω · cm, and "non-conductive" means that the volume resistivity is 10 ⁷ Ω · cm greater.

The negative electrode mixture 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 a "specific metal element"). It is a layer formed from a so-called negative electrode mixture containing an oxide as a main component. The composite oxide functions as a negative electrode active material. The negative electrode mixture may contain other optional components such as a negative electrode active material, a conductive agent, a binder, a thickener, and a filler, if necessary. The negative electrode mixture layer is formed by applying a slurry of the negative electrode mixture.

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

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. These may be contained in only one kind, or may be contained in two or more kinds. 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 fluctuates greatly due to charging and discharging, the composition ratio of specific metal elements may be larger than that at the time of synthesis at the end of discharge, and the theory of the raw material of specific metal elements at the time of synthesis Since it is generally added in excess of the composition ratio, the content of the specific metal element in the composite oxide does not have a great influence on the performance as a negative electrode active material. For example, the lower limit of the atomic number ratio (A / Ge) of the specific metal element (A) to germanium in the composite oxide may be 0.1 or 0.5. Further, the upper limit of the atomic number ratio (A / Ge) may be 5 or 2.

The composite oxide may contain germanium, a specific metal element, and an element other than oxygen as long as it does not affect the action and effect of the present invention. Such other optional elements include metal elements (including metalloid elements) such as aluminum, silicon, titanium, vanadium, manganese, iron, cobalt, nickel and copper, and non-metal elements such as nitrogen, fluorine and bromine. Can be mentioned. The upper limit of the atomic number ratio of these arbitrary elements to the total number of atoms of the composite oxide is preferably 0.5, more preferably 0.2, further preferably 0.1, and even more preferably 0.01. , 0.001 is particularly preferable. This optional element may not be substantially contained.

The ratio of the number of atoms of the transition metal to germanium in the composite oxide is preferably less than 1. The upper limit of the atomic number ratio of the transition metal to germanium in the composite oxide is more preferably 0.5, more preferably 0.1, and even more preferably 0.01. It is more preferable that the composite oxide contains substantially no transition metal. When the content ratio of the transition metal is low as described above, the discharge capacity and the capacity retention rate become better.

The composite oxide can be preferably represented by the following formula (1).
A _x G _{y Oz} ... (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 the above formula (1), an alkali metal is preferable, and lithium (Li) is more preferable. A may be one kind or two or more kinds.

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 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 composite oxides represented by the above formula (1).

Examples of the composite oxide other than the composite 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 O ₉ , CaCu ₃ Ge ₄ O _{12 and the} like can be mentioned.

The composite oxide may be crystalline or amorphous. 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, PBCA or the like. Among these, the composite oxide preferably has a crystal structure of CMC21 or Pcca. However, the crystal structure may not be maintained due to repeated charging and discharging. Therefore, it is preferable that the crystal structure before charging / discharging belongs to the space group.

The 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 Co., Ltd.) with a CuKα ray as the radiation source, a tube voltage of 30 kV, and a tube current of 15 mA. .. At this time, the diffracted X-rays pass through a Kβ filter having a thickness of 30 μm and are detected by a high-speed one-dimensional detector (D / teX Ultra 2). The sampling width is 0.01 °, the scan speed is 5 ° / min, the divergent 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 "RIETAN2000" program (F. Izumi and T. Ikeda, Matter. Sci. Forum, 198 (2000).). can. For the space group, the same result can be obtained by using the 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, etc.) and a compound containing a specific metal element (Li ₂ CO _3, etc.) are mixed at a predetermined ratio and treated by a firing method, a mechanochemical method, or the like. Obtainable. The composite oxide obtained through such treatment is usually in the form of 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, still more preferably 60% by mass. 65% by mass is even more preferable. By setting the content of the composite oxide to the above lower limit or more, the discharge capacity can be further increased. On the other hand, the upper limit of this content may be, for example, 95% by mass or 80% by mass. By setting the content of the composite oxide to the above upper limit or less, it is possible to contain a sufficient amount of the conductive agent, and it is possible to secure sufficient conductivity and the like.

The other negative electrode active material that may be contained in the negative electrode mixture layer (negative electrode mixture) is not particularly limited, and conventionally known negative electrode active materials can be mentioned.

The conductive agent is a substance having conductivity. Examples of the shape of the conductive agent include powder and fibrous. The conductive agent is not particularly limited as long as it is a conductive material that does not adversely affect the performance of the power storage element. Examples of such a conductive agent include natural or artificial graphite, carbon black such as furnace black, acetylene black, and Ketjen black, metals, conductive ceramics, and the like, and acetylene black is preferable. The reason for this is as follows. Graphite and carbon black also function as negative electrode active materials, but their discharge capacities are smaller than the discharge capacities of the composite oxide. Therefore, in order to increase the discharge capacity, it is preferable to reduce the amount of these conductive agents as much as possible. On the other hand, acetylene black has the property of being able to form a network structure in which particles are connected. Graphite, on the other hand, usually does not have the property of forming such a network structure. Therefore, 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.

The lower limit of the content of the conductive agent in the negative electrode mixture layer (negative electrode mixture) is, for example, 5% by mass, preferably 10% by mass. Sufficient conductivity can be exhibited by setting the content of the conductive agent to be equal to or higher than the above lower limit. On the other hand, the upper limit of this content is, for example, 30% by mass, preferably 25% by mass. By setting the content of the conductive agent to the above upper limit or less, a sufficient amount of the composite oxide can be contained, and the discharge capacity can be further increased.

Examples of the binder (binding agent) include fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), thermoplastic resins such as polyethylene, polypropylene, and polyimide; and ethylene-propylene-diene rubber (EPDM). Elastomers such as sulfonated EPDM, styrene butadiene rubber (SBR), and fluororubber; and thermoplastic polymers can be mentioned.

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

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

It is preferable that the negative electrode satisfies the following relationship in the discharge process after charging to 0.0 V (vs. Li ^{/ Li +).} _{Let Q (0.0-2.0V)} be the amount of electricity discharged in the range of 0.0 to 2.0V (vs. Li / Li ⁺ ). Of these, the amount 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 energy Q _{(0.0-1.2V) with} respect to the electric energy Q _(0.0-2.0V) , that is, the ratio (Q _(0.0-1.2V) / Q _{(0.0-2.). The lower limit of 0V)} ) is preferably 80%, more preferably 90%, and even more preferably 95%. When the ratio (Q _(0.0-1.2V) / Q _(0.0-2.0V) ) is equal to or higher than the above lower limit, charging / discharging with less conversion reaction can be performed, and the capacity retention rate can be improved. Can be enhanced. The upper limit of this ratio (Q _(0.0-1.2V) / Q _(0.0-2.0V) ) may be 100% or 99%. The above potential is the negative electrode potential in the charging / discharging process of the power storage element using the negative electrode as the negative electrode.

<Non-aqueous electrolyte power storage element>
The non-aqueous electrolyte power storage device according to the embodiment of the present invention has a positive electrode, a negative electrode, and a non-aqueous electrolyte. Hereinafter, a non-aqueous electrolyte secondary battery will be described as an example of the non-aqueous electrolyte power storage element. The positive electrode and the negative electrode usually form electrode bodies that are alternately superposed by stacking or winding through a separator. The electrode body is housed in a case, and the case is filled with a non-aqueous electrolyte. The non-aqueous electrolyte is interposed between the positive electrode and the negative electrode. Further, as the above case, a known metal case, resin case or the like which is usually used as a case of a non-aqueous electrolyte secondary battery can be used.

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

The positive electrode base material has conductivity. As the material of the base material, metals such as aluminum, copper, titanium, tantalum, and stainless steel or alloys thereof are used. Among these, aluminum and aluminum alloys are preferable from the viewpoint of balance of potential resistance, high conductivity and cost. Further, as a form of forming the positive electrode base material, a foil, a vapor-deposited film and the like can be mentioned, and the foil is preferable from the viewpoint of cost. That is, 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. Further, the positive electrode mixture forming the positive electrode mixture layer contains optional components such as a conductive agent, a binder (binding agent), a thickener, and a filler, if necessary. As the optional component such as the conductive agent, the binder, the thickener, and the filler, the same one as the above-mentioned negative electrode mixture layer can be used.

As the positive electrode active material, conventionally known positive electrode active materials for non-aqueous electrolyte power storage elements are used. As a specific positive electrode active material, for example _{, a composite oxide represented by Li x} MO _y (M represents at least one transition metal other than Mo) ( _{Li x having a layered α-NaFeO type 2} crystal structure). It has a spinel-type crystal structure such as _{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, etc. 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, X is For example, it represents a polyanion compound (representing 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 CoPO ₄ F, etc.).

(Negative electrode)
As the negative electrode, the negative electrode according to the 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 non-woven 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 non-woven fabric is preferable from the viewpoint of liquid retention of a non-aqueous electrolyte. As the main component of the separator, polyolefins such as polyethylene and polypropylene are preferable from the viewpoint of strength, and polyimide and aramid are preferable from the viewpoint of oxidative decomposition resistance. Moreover, you may combine these resins.

An inorganic layer may be arranged between the separator and the electrode (usually the positive electrode). This inorganic layer is a porous layer also called a heat-resistant layer or the like. Further, a separator having an inorganic layer formed on 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.

(Non-aqueous electrolyte)
As the non-aqueous electrolyte, a known electrolyte usually used for a non-aqueous electrolyte power storage element (secondary battery) can be used. The non-aqueous electrolyte contains 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. Chain carbonate and the like 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} , and LiN (SO). 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 and} other fluorinated hydrocarbon groups Lithium salt having the above can be mentioned.

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

The non-aqueous electrolyte power storage element can be manufactured by using the negative electrode according to the embodiment of the present invention as the negative electrode. In the manufacturing method, for example, a step of manufacturing a positive electrode, a step of manufacturing a negative electrode, a step of preparing a non-aqueous electrolyte, and an electrode body in which a positive electrode and a negative electrode are laminated or wound alternately via a separator are superimposed. A step of forming the positive electrode and a negative electrode (electrode body) in a case, and a step of injecting the non-aqueous electrolyte into the case are provided. After injection, a non-aqueous electrolyte power storage element can be obtained by sealing the injection port.

<Other Embodiments>
The present invention is not limited to the above embodiment, and can be implemented in various modifications and improvements in addition to the above embodiment. For example, the negative electrode does not have to be provided with an intermediate layer, and the negative electrode mixture does not have to form a clear layer. For example, the negative electrode may have a structure in which a negative electrode mixture is supported on a mesh-shaped negative electrode base material. Further, in the above-described embodiment, the non-aqueous electrolyte storage element is mainly a secondary battery, but other non-aqueous electrolyte storage elements may be used. Examples of other non-aqueous electrolyte storage elements include capacitors (electric double layer capacitors, lithium ion capacitors) and the like.

FIG. 1 shows a schematic view of a rectangular non-aqueous electrolyte storage element (secondary battery) 1 which is an embodiment of the non-aqueous electrolyte storage element. The figure is a perspective view of the inside of the container. In the non-aqueous electrolyte power storage element 1 shown in FIG. 1, the electrode body 2 is housed in a container (case) 3. The electrode body 2 is formed by winding a positive electrode having a positive electrode active material and a negative electrode having a negative electrode active material through 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 non-aqueous electrolyte power storage element (secondary battery) is not particularly limited, and examples thereof include a cylindrical battery, a square battery (rectangular battery), and a flat battery. The present invention can also be realized as a power storage device including a plurality of the above-mentioned non-aqueous electrolyte power storage elements. An embodiment of the 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 non-aqueous electrolyte power storage elements 1. The power storage device 30 can be mounted as a power source for automobiles such as electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid vehicles (PHEV).

Hereinafter, the present invention will be described in more detail with reference to Examples, but 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 High Purity Chemicals) 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 and containing 90 g (about 250) of zirconia balls having a diameter of 5 mm. Further 10 mL of ethanol was added to this pot and the pot was covered. This was set in a planetary ball mill (“pulverisette 5” manufactured by FRITSCH), mixed at a revolution speed of 300 rpm for 9 minutes, and then paused for 1 minute, which was repeated a total of 6 times. The mixture was dried in a dryer at 80 ° C. for 3 hours or more 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 the crucible was placed in a tabletop vacuum / gas replacement furnace (“KDF75” of Denken Hydental Co., Ltd.). Then, the temperature was raised from room temperature to 800 ° C. for 10 hours under normal pressure in an air stream, maintained at this temperature for 4 hours, and then naturally allowed to cool to room temperature. In this way, a lithium germanium composite oxide represented by the _{composition formula Li 2} Ge ₄ O _{9 was prepared.}

[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. The lithium germanium composite oxide represented by _{the composition formula Li 2} GeO ₃ was prepared 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 for 4 hours at this temperature. A magnesium germanium composite oxide represented by the _{composition formula MgGeO 3} was prepared 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 High Purity 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. The lithium germanium composite oxide represented by the _{composition formula Li 6} Ge ₂ O ₇ was prepared 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 held at this temperature for 4 hours. Therefore, a lithium germanium composite oxide represented by _{the composition formula Li 4 GeO 4} was prepared in the same manner as in Example 1.

[Analysis of composite oxides]
The oxides obtained in Examples 1 to 3 and Comparative Examples 1 to 3 were analyzed by the following methods. Powder X-ray diffraction measurement was performed using an X-ray diffractometer (“MiniFlex II” manufactured by 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 scan speed was 5 ° / min, the divergent 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 pattern of the oxides of Examples 1 to 3 and Comparative Examples 1 to 3 is shown in FIG. The obtained X-ray diffraction data was analyzed using the above-mentioned "PDXL" program.

As a result of the above analysis, as a result of the analysis of each oxide of Examples and Comparative Examples, the space groups to which they can be assigned are as follows. It was confirmed that it belongs to the crystal structure as described in 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)

[Manufacturing of non-aqueous electrolyte power 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, a negative electrode was prepared in the following manner. 2.275 g of the synthesized oxide powder and 0.700 g of acetylene black (AB) were weighed. These were put into a zirconia pot having an internal volume of 80 mL and containing 90 g (about 250) of zirconia balls having a diameter of 5 mm. Further 10 mL of ethanol was added to this pot and the pot was covered. This was set in a planetary ball mill (“pulverisette 5” manufactured by FRITSCH), mixed at a revolution speed of 300 rpm for 9 minutes, and then paused for 1 minute, which was repeated 7 times in total. The mixture was dried in a dryer at 75 ° C. for 3 hours or longer to prepare a mixed powder. 2.275 g of this mixed powder, a 12 mass% N-methylpyrrolidone (NMP) solution of PVDF and NMP were placed in a predetermined plastic container and covered in a glove box maintaining an argon atmosphere. This was set in a stirring defoaming device (Shinky's "Awatori Rentaro" (trade name)) and kneaded sufficiently 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 base material 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 a roll press was performed to obtain a negative electrode.

A test battery was assembled using each of the above 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 metal lithium was used as the counter electrode in close contact with the nickel foil current collector. Here, a sufficient amount of metallic lithium was arranged so that the capacity of the test battery was not limited by the counter electrode. As an electrolyte, a solution in _{which LiPF 6} is dissolved in a mixed solvent having an ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / dimethyl carbonate (DMC) volume ratio of 6: 7: 7 so as to have a concentration of 1 mol / L. Was used. As a separator, a polypropylene microporous membrane surface-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 electrodes are used so that the open ends of the positive electrode terminal and the negative electrode terminal are exposed to the outside. Was stored. Next, the fusion allowance in which the inner surfaces of the metal resin composite film faced each other was hermetically sealed except for the portion to be the injection hole, the electrolytic solution was injected, and then the injection hole was sealed.

[Charge / discharge test]
In the following test, the voltage was controlled between the working electrode and the counter electrode, but since the dissolution / precipitation reaction resistance of metallic lithium at the counter electrode is extremely low, the voltage between terminals during charging and discharging is referred to using metallic lithium. It can be regarded as equal to the potential of the working pole with respect to the pole. Further, in the following test, the above composite oxide was used as a negative electrode active material used for the negative electrode of a non-aqueous electrolyte power storage element, which was assumed to start from charging in combination with a positive electrode containing lithium that can be electrochemically occluded and released. For the purpose of evaluation, the operation was started by energizing the composite oxide in the reducing direction, which is a reaction in which lithium ions are occluded electrochemically.

A charge / discharge cycle test was conducted in a constant temperature bath set at 25 ° C. using the non-aqueous electrolyte power storage device obtained by using the oxides of Examples 1 to 3 and Comparative Examples 1 to 3. Charging is constant current constant voltage (CCCV) charging, the lower limit potential of charging is 0.0V (vs. Li ^/ Li +), and the charging termination condition is when the charging current is attenuated to 2 mA / g or the lower limit potential of charging is reached. It was set as the time when 3 hours or 15 hours had passed since then. This time is shown in Table 1 as "maximum charging CV 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 for charging was 100 mA / g with respect to the mass of the negative electrode active material contained in the negative electrode. The constant current value of the discharge was 20 mA / g with respect to the mass of the negative electrode active material contained in the negative electrode. The above charging and discharging were regarded as one cycle, and this cycle was carried out for 10 cycles. In each cycle, a rest period of 10 minutes was set after charging and discharging. Table 1 shows the discharge capacity of 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 the "capacity retention rate (%)". This capacity retention rate is also shown in Table 1. In addition, the discharge electricity ratio (Q _(0.0-1.2V) / Q _(0.0-2.0V) ) 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.

The discharge curves of the third, seventh, and tenth cycles of Example 1 are shown in FIG. The discharge curves of 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 prepared in the same procedure as in Example 1 except that the _{electrochemically inert Al 2} O ₃ was used instead of the oxide. Then, the charging end condition is set to the time when 15 hours have passed after reaching the charging lower limit potential, and the same conditions are applied except that the constant current value for charging is 10 mA / g and the constant current value for discharge is 10 mA / g. A charge / discharge test was conducted. The discharge capacity per mass _{of Al 2} O ₃ in the third cycle of the AB battery _{is 69 mAh / Al 2} O _3- g, and the ratio (Q _(0.0-1.2V) / Q _(0.0-2.0V) ). Was 82.6%.

As shown in Table 1, the non-aqueous electrolyte power storage devices of Examples 1 to 3 using the composite oxide having an O / Ge ratio of 2.1 or more and 3.2 or more are used even when the contribution of AB is excluded. It can be seen that it has a large discharge capacity of 200 mAh / g or more and a high capacity retention rate of 90% or more. In particular, the discharge capacity of the non-aqueous electrolyte power storage element of Examples 1 and 2 using the 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 significantly increased as compared with the case where graphite is used as the main component. Further, the non-aqueous electrolyte power storage elements of Examples 1 to 3 have a ratio (Q _(0.0-1.2V) / Q _(0.0-2.0V) ) of 94.5% or more, and 1 It is presumed that the conversion reaction, which tends to occur at a high potential of .2 V (vs. Li / Li ^{+) or higher, hardly occurs, thereby exhibiting a high capacity retention rate.}

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

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 negative electrodes and negative electrode active materials provided therein.

1 Non-aqueous electrolyte power storage element 2 Electrode body 3 Container 4 Positive electrode terminal 4'Positive lead 5 Negative terminal 5'Negative electrode lead 20 Power storage unit 30 Power storage device

Claims (4)

A negative electrode mixture containing germanium and a composite oxide containing an alkali metal, an alkaline earth metal, or a combination thereof as a main component is provided.
The negative electrode for a non-aqueous electrolyte power storage element in which the atomic number ratio (O / Ge) of oxygen to germanium in the composite oxide is 2.1 or more and 3.2 or less (however, the composite oxide is Li ₂ GeO ₃₎ . Except in some cases.) . 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 ⁺⁾ 0.0~1.2V for _.0V) (the ratio of the quantity of electricity _{Q (0.0-1.2V)} to be discharged in a range of vs.Li/Li _{⁺⁾ (Q (0.0-1.2V)} / Q _(0.0-2.0V) ) is 80% or more of the negative electrode according to claim 1. The negative electrode according to claim 1 or 2, wherein the ratio of the number of atoms of the transition metal to germanium in the composite oxide is less than 1. A non-aqueous electrolyte power storage element having a negative electrode according to any one of claims 1 to 3.

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