JP2006120337A - Negative electrode for battery and battery using this - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve problems that the ionic conductivity of an inorganic compound is deteriorated by minute moisture left without being removed in an electrolyte to decrease the cycle characteristics of a battery in the battery constituted of a negative electrode formed by depositing an ion conductivity inorganic compound layer on a conductor substrate for deposition, a positive electrode, and the electrolyte interposed between the inorganic compound layer and the positive electrode, and depositing lithium on the conductor substrate for deposition by charging. <P>SOLUTION: The inorganic compound layer is formed with a material represented by general formula L<SB>x</SB>PT<SB>y</SB>O<SB>z</SB>or L<SB>x</SB>MO<SB>y</SB>N<SB>z</SB>which is an inorganic compound having ionic conductivity and stable in a wet environment. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a negative electrode including a deposition substrate on which lithium is deposited, and a battery using the same.

  In recent years, with the development of portable devices such as personal computers and mobile phones, the demand for batteries as power sources has increased. A battery used for the above applications is required to be used at room temperature, and at the same time, a high energy density and excellent cycle characteristics are required.

  In response to the above demand, lithium has a lower potential than other metals and is active, and by combining this with a positive electrode, formation of a battery with high electromotive force and high energy density can be expected. Therefore, research and development of a room temperature type lithium battery using the above lithium as an active material has been actively conducted. Among them, the configuration using lithium metal (including lithium alloy) for the negative electrode has a high possibility of downsizing. Therefore, many batteries combined with various positive electrode active materials and lithium ion conductive electrolytes have been developed, and each has practicality. Some studies are underway, and some of them have been put to practical use.

Further, regarding positive electrode materials when these lithium metals are used as negative electrodes, compounds such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , or a large number of compounds such as sulfur (S) and simple substances are known. ing. As for the electrolyte, an organic electrolyte, a gel polymer, a solid form, and a combination of a large number of materials are known.

  In general, a lithium metal negative electrode is a basic battery component that can be combined with any battery system regardless of the variety of forms and types of positive electrodes and electrolytes.

  By the way, lithium metal is so active that it reacts with a very small amount of water contained in a so-called non-aqueous electrolyte material, and not only has a safety problem in producing a negative electrode, but also reacts with water. A component that interferes with the battery reaction is also produced, affecting the characteristics.

  Therefore, as one method for ensuring safety and quality, a method in which the negative electrode is not directly composed of metallic lithium has been studied. That is, the structure of a secondary battery in which a safe conductor metal such as copper (Cu) or nickel (Ni) is used for a lithium deposition substrate to form a negative electrode and lithium is deposited on this deposition substrate has been studied. Yes.

Further, in the above configuration, when lithium is deposited on the deposition substrate, it is necessary to suppress dendritic precipitates and non-uniform deposition. As the means, a lithium ion conductive inorganic compound layer (hereinafter referred to as an inorganic compound layer) such as lithium phosphate (Li ₃ PO ₄ ) or lithium nitride phosphate (LIPON) is formed on the surface of the deposition substrate, For example, Patent Document 1 discloses a negative electrode having a structure in which lithium is deposited on a deposition substrate with an inorganic compound layer interposed therebetween and a battery using the negative electrode.
JP 2004-87402 A

However, in general, a minute amount of moisture of 10 ppm level that cannot be easily removed remains in the electrolyte. In the above configuration, Li ₃ PO ₄ and LIPON originally have a +5 valence when in contact with moisture even in a very small amount. Phosphorus (P) present in is reduced to phosphorus with a low degree of oxidation. As a result, a phenomenon occurs in which the compound is decomposed and the ionic conductivity is significantly reduced. In such a case, the inorganic compound layer becomes a resistance, the impedance of the entire negative electrode increases, and the battery characteristics deteriorate.

  An object of the present invention is to suppress deterioration of battery characteristics by ensuring stability of the inorganic compound layer with respect to moisture and ensuring ionic conductivity. That is, the deterioration of the inorganic compound layer as described above is suppressed, the increase in impedance of the entire negative electrode is suppressed, the battery characteristic deterioration suppressing function is enhanced, and a battery negative electrode having excellent cycle characteristics and a battery using the same are provided. For the purpose.

  In order to solve the above problems, a negative electrode for a battery of the present invention is provided on a deposition conductor substrate for depositing lithium metal and the surface of the deposition conductor substrate, and is represented by the following general formula 1 or general formula 2. It has the inorganic compound layer represented by either.

Formula _{1: Li x PT y O z} ( where T is an element symbols Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Ag, Ta, W, Pt and Au And at least one element selected from the element group consisting of 2.0 ≦ x ≦ 7.0, 0.01 ≦ y ≦ 1.0, and 3.5 ≦ z ≦ 8.0. Is 2.0 ≦ x ≦ 3.0, 0.01 ≦ y ≦ 0.5, 3.5 ≦ z ≦ 4.0, or 2.0 ≦ x ≦ 3.0, 0.01 ≦ y ≦ 1. 0, 3.5 ≦ z ≦ 7.0)
General formula 2: Li _x MO _y N _z (where M is at least one element selected from the element group consisting of element symbols Si, B, Ge, Al, C, Ga, and S; 6 ≦ x ≦ 1.0, 1.05 ≦ y ≦ 1.99, and 0.01 ≦ z ≦ 0.5, or 1.6 ≦ x ≦ 2.0, 2.05 ≦ y ≦ 2.99, And 0.01 ≦ z ≦ 0.5, or 1.6 ≦ x ≦ 2.0, 3.05 ≦ y ≦ 3.99, and 0.01 ≦ z ≦ 0.5, or 4.6 ≦ x ≦ 5.0, 3.05 ≦ y ≦ 3.99, and 0.01 ≦ z ≦ 0.5)
The negative electrode does not contain lithium metal before charging, but has lithium metal between the deposition conductor substrate and the inorganic compound layer after charging. Since the materials constituting these inorganic compound layers have high lithium ion conductivity and excellent moisture resistance, a decrease in lithium ion conductivity is suppressed even when in contact with an electrolyte in which moisture remains. As a result, excellent battery characteristics are maintained over a long charge / discharge cycle.

  Furthermore, it is preferable to provide a base that supports the deposition conductor substrate from the opposite side of the inorganic compound layer. As a result, the deposition conductor substrate can be made thin by a dry thin film process such as vapor deposition or a wet thin film process such as plating, and the negative electrode can be reduced in weight.

  Furthermore, the battery according to the present invention is a battery using the battery negative electrode.

  ADVANTAGE OF THE INVENTION According to this invention, the stability with respect to the water | moisture content of the negative electrode itself which deposits and melt | dissolves lithium metal, and the cycling characteristics in the battery using such a negative electrode can be improved significantly.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the following contents as long as it is based on the basic features described in this specification.

(Embodiment 1)
FIG. 1 is a cross-sectional view of a battery using a negative electrode according to the first embodiment. The battery includes a negative electrode 1, a positive electrode 2 that faces the negative electrode 1 and reduces lithium ions during discharge, and an electrolyte 3 that is interposed therebetween and conducts lithium ions. The negative electrode 1 and the positive electrode 2 are accommodated in the case 6 using the gasket 4 and the lid 5 together with the electrolyte 3. The positive electrode 2 includes a positive electrode current collector 7 and an active material layer 8 containing a positive electrode active material.

  The negative electrode 1 has a film-forming substrate (hereinafter referred to as “substrate”) 9, a deposition conductor substrate (hereinafter referred to as “substrate”) 10, and an inorganic compound layer 11 formed on the surface of the substrate 10.

  The base body 9 is a shape holding body of the negative electrode 1, and a thin plate such as a metal plate, glass, silica, or alumina, or a sintered body can be used as the base body. In addition, since it is a nonelectroconductive material other than a metal plate, it is necessary to ensure electroconductivity with the case 6. FIG. The substrate 9 is preferably made of a material having a lower density than the metal constituting the substrate 10 from the viewpoint of reducing the weight of the negative electrode.

  The substrate 10 includes at least one element selected from copper, nickel, titanium, molybdenum, tantalum, iron, and carbon, or a metal having low reactivity with lithium, such as an alloy, steel, or stainless steel including at least one of these elements. Alloys are preferred. The deposition substrate may react with lithium. For example, Si, Sn, and their alloys are mentioned. In addition, it is preferable to deposit the metal on the substrate 9 in the form of a foil layer in order to reduce the thickness. That is, if the substrate 10 is made thin by a dry thin film process such as vapor deposition or a wet thin film process such as plating, the negative electrode 1 can be reduced in weight.

  FIG. 2 is a schematic cross-sectional view showing another configuration of the negative electrode in the present embodiment. In FIG. 2, the substrate 10 also serves as the base 9. That is, when a conductive material such as a metal plate or metal foil is used as the substrate 9, the substrate 9 can be omitted as shown in FIG.

Inorganic compound layer 11 _is composed of Li x _PT y _{O z.} T is at least one element selected from the element group consisting of element symbols Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Ag, Ta, W, Pt and Au And 2.0 ≦ x ≦ 7.0, 0.01 ≦ y ≦ 1.0, and 3.5 ≦ z ≦ 8.0. Desirably 2.0 ≦ x ≦ 3.0, 0.01 ≦ y ≦ 0.5, 3.5 ≦ z ≦ 4.0, or 2.0 ≦ x ≦ 3.0, 0.01 ≦ y ≦ 1 0.0, 3.5 ≦ z ≦ 7.0. Prior to describing the configuration and operation of the present embodiment, it is noted that the above composition Li _x PT _y O _z is a material having excellent conductivity and moisture resistance discovered by the present inventors. .

The composition Li _x PT _y O _z of the inorganic compound layer 11 is composed of a constituent element component of lithium phosphate and a transition metal group T. In this composition, when the composition is in contact with water molecules, decomposition of the lithium phosphate component is suppressed by reducing the T component, which is a transition metal, in preference to phosphorus atoms, and the ionic conductivity of the inorganic compound layer 11 itself. The decline in sex is suppressed.

In the composition Li _x PT _y O _z , the transition metal T component gives priority to the reaction with water molecules over the reduction of phosphorus, and even if incorporated in lithium phosphate at the atomic level, It may be mixed at the particle level.

In order for the composition of Li _x PT _y O _z to have an excellent ion conductivity and a sufficient function of suppressing the decomposition of the ion conductive solid in a wet environment, 2.0 ≦ x ≦ 7.0, 0.01 ≦ It is desirable that y ≦ 1.0 and 3.5 ≦ z ≦ 8.0. This composition is 2.0 ≦ x ≦ 3.0, 0.01 ≦ y ≦ 0.50 when a transition metal is used as a target for the transition metal T component when forming Li _x PT _y O _z . 3.5 ≦ z ≦ 4.0, 2.0 ≦ x ≦ 3.0, 0.01 ≦ y ≦ 1.0, 3.51 ≦ z ≦ 7 when a transition metal oxide is used, lithium transition metal When an oxide is used, 2.0 ≦ x ≦ 7.0, 0.01 ≦ y ≦ 1.0, and 3.5 ≦ z ≦ 8.0.

  Next, the form of each layer forming the negative electrode 1 will be described. Each of the above layers is preferably formed by sequentially laminating a substrate 9, a substrate 10, and an inorganic compound layer 11 as shown in FIG. In that case, although the formation area and shape of a layer are arbitrary, it is preferable to completely cover the board | substrate 10 with the inorganic compound layer 11. FIG. In the case of a battery configuration in which both surfaces of the negative electrode 1 face the positive electrode 2, a configuration in which the substrate 10 and the inorganic compound layer 11 are provided on both surfaces of the positive electrode 2 facing each other is preferable. Although the thickness of the inorganic compound layer 11 is arbitrary, it is preferable to make it a thin film of 0.05 to 10 μm in consideration of a protective ability against a moist environment, impedance, physical strength and the like.

Next, a method for forming the inorganic compound layer 11 will be described. When an ion conductive inorganic compound represented by Li _x PT _y O _z is applied to the negative electrode 1, a transition metal such as tungsten, molybdenum, tantalum or the like, or a metal oxide thereof, defined as lithium phosphate and T component is used. An evaporation source or target is formed by a dry thin film process. That is, various thin film deposition methods such as vapor deposition, resistance heating vapor deposition, high frequency heating vapor deposition, laser ablation vapor deposition, ion beam vapor deposition, etc., or sputtering, RF magnetron sputtering, etc. in argon or vacuum environment Is preferably applied to form a thin film on the substrate 10. Further, as the evaporation source or the target, it may be applied to a mixture of Li 2 _O and P ₂ O ₅ in place of the lithium phosphate.

In such an inorganic compound, the valences of a lithium atom, a phosphorus atom, and an oxygen atom are +1, +5, and −2, respectively. The transition metal element T has the same valence in the state of the compound when the compound is used as a target. On the other hand, when a single transition metal is used as a target, the transition metal element T is considered to be incorporated in the lithium phosphate in a metallic state, and thus has zero valence. As a method for obtaining x, y, and z in the prepared Li _x PT _y O _z , the ratio of phosphorus atoms is first set to 1. Next, y is calculated by obtaining the ratio between the T component and the phosphorus atom by inductively coupled high-frequency plasma spectroscopy (ICP spectroscopy) or the like. Furthermore, z is calculated by obtaining the ratio of oxygen to phosphorus atoms or transition metal atoms by a technique such as nitrogen oxygen analysis. In the nitrogen-oxygen analysis, for example, oxygen and nitrogen contained in the material are extracted by an inert gas-impulse heating and melting method, which is thermal decomposition at a high temperature, and oxygen is used as a CO gas for high sensitivity non-dispersion. It can detect with an infrared detector, and can detect with a highly sensitive thermal conductivity detector by using nitrogen as N ₂ gas. x is obtained by using the above valence and assuming that the overall valence is zero.

  For the electrolyte 3, the case 6, and other components, all materials and shapes generally used for batteries configured by applying lithium metal or lithium alloy to the negative electrode are applicable.

  For the material of the active material layer 8 of the positive electrode 2, a material capable of electrochemically occluding and releasing lithium ions, such as lithium cobaltate, lithium nickelate, lithium manganate, or a mixture or composite compound thereof, is used. .

  As the electrolyte 3, an electrolyte solution in which a solute is dissolved in an organic solvent, or a so-called polymer electrolyte layer containing these and non-fluidized with a polymer can be applied. In the case of using at least an electrolyte solution, it is preferable to use a separator such as polyethylene between the positive electrode 2 and the negative electrode 1 and impregnate the solution.

  The material of the electrolyte 3 is selected based on the redox potential of the active material contained in the active material layer 8. Solutes preferably used for the electrolyte 3 include lithium fluoride, lithium chloride, lithium bromide, lithium iodide, lithium nitride, lithium phosphate, lithium silicate, lithium sulfide, lithium phosphide, etc., which are generally used in lithium batteries. The applicable salt can be applied.

  Further, organic solvents for dissolving the above salts include propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyllactone, tetrahydrofuran, 2- Lithium, generally one or more mixtures such as methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, acetonitrile, propylnitrile, anisole, acetate, propionate, etc. Solvents such as those used in batteries can be applied.

  By producing the negative electrode 1 as described above, the moisture resistance of the negative electrode 1 can be increased, and deterioration of charge / discharge cycle characteristics of a battery using the negative electrode 1 can be suppressed. Such a negative electrode 1 can be applied to all lithium batteries using lithium metal or a lithium alloy as a negative electrode, and the storage stability and charge / discharge cycle characteristics are improved.

  FIG. 3 is a schematic cross-sectional view of the negative electrode in FIG. 1 in a charged state. When the battery is charged and discharged, as shown in FIG. 3, lithium 31 precipitates and dissolves on the interface between the inorganic compound layer 11 and the substrate 10 not directly in contact with the electrolyte 3 through the inorganic compound layer 11, It functions as a negative electrode for the first time. That is, the inorganic compound layer 11 faces the electrolyte 3 and plays a role of a movement path to the substrate 10 on which lithium ions are isolated from the electrolyte 3. Even if the electrolyte 3 contains moisture in this configuration, the inorganic compound layer 11 can continue the role of the ion transfer path without being affected by the moisture of the electrolyte 3.

  The features and effects of the embodiments of the present invention will be described below with specific examples.

A substrate 10 made of copper (Cu) was formed on a base 9 made of stainless steel (SUS304) as described below, and an inorganic compound layer 11 made of a composition of Li _x PT _y O _z was formed thereon.

  First, preparation of the substrate 10 will be described. On the base body 9 made of SUS304, a Cu layer having a thickness of 500 nm was formed as a substrate 10 using a sputtering apparatus.

Next, preparation of the inorganic compound layer 11 will be described. In samples 1 to 17, Li ₃ PO ₄ having a diameter of 4 inches and the transition metal shown in Table 1 as the transition metal element T were used as targets, respectively, and 100 W RF was applied to Li ₃ PO ₄ in an argon atmosphere of 5 mTorr. Power was applied, and the transition metal T was sputtered for 10 minutes under the condition of RF power of 25 W. The thickness of the obtained inorganic compound layer 11 was about 0.15 μm. The composition of the inorganic compound layer 11 was measured by inductively coupled high-frequency plasma spectroscopy (ICP spectroscopy) on a sample prepared by placing a platinum plate beside the substrate when forming the inorganic compound layer. When the ratio of the transition metal element in the inorganic compound layer 11 was examined, the composition was Li _2.8 PT _0.2 O _3.9 .

In order to compare the characteristics of Samples 1 to 17 with the related art, Comparative Sample 1 in which LIPON was formed as a conventional inorganic compound layer instead of the inorganic compound layer 11 of Sample 1 was produced. In forming LIPON, Li ₃ PO ₄ was used as a target, and sputtering was performed for 10 minutes under a nitrogen atmosphere, 5 mTorr, and 100 W of RF power. The thickness of the obtained inorganic compound layer was about 0.2 μm.

Next, in order to evaluate the cycle characteristics of the various negative electrodes 1 produced as described above and batteries using the same, a positive electrode 2 using a LiCoO ₂ composite oxide as an active material was produced by the following procedure, and a secondary battery was produced. Was made.

The positive electrode 2 was produced as follows. First, LiCoO ₂ composite oxide as a positive electrode active material, acetylene black as a conductive agent, and polyvinylidene fluoride as a binder were mixed at a weight ratio of 90: 5: 5. This was dispersed in N-methylpyrrolidone as a dispersion medium to produce a positive electrode mixture. Next, this positive electrode mixture was applied onto a positive electrode current collector 7 made of an aluminum foil by a doctor blade method, dried by heating, and then pressed to form a positive electrode active material layer 8. Subsequently, a lid 5 serving as a positive electrode terminal was attached to the positive electrode current collector 7.

The electrolyte 3 was prepared by mixing ethylene carbonate and ethyl methyl carbonate at a volume ratio of 1: 1, and dissolving 1 mol / L of LiPF ₆ therein. This solution was used by impregnating a microporous polyethylene film having a porosity of about 40% and a thickness of 30 μm, which is usually commercially available as a separator. When the water content of the electrolyte 3 was measured by the Karl Fischer method, it was 12 ppm.

  Next, each of the above batteries was housed in a constant temperature bath at a temperature of 20 ° C. and a relative humidity of 50%, and a charge / discharge cycle test was conducted. At that time, the current value that discharges the design capacity in 5 hours, that is, the constant current charge until the battery voltage reaches 4.2 V at a 5-hour rate, then switches to the constant voltage charge of 4.2 V, the current value is the constant current charge The battery was charged until it dropped to 5% of the value. During discharging, constant current discharging was performed until the battery voltage reached 3 V at the same current value as during constant current charging, and the capacity was measured. In this way, the ratio of the discharge capacity during the cycle to the initial discharge capacity, that is, the change in the capacity maintenance ratio was examined, and the capacity maintenance ratio after 100 cycles was compared as necessary. The results are shown in Table 1. In addition, when the negative electrode 1 after charging was disassembled and examined, it was confirmed that lithium was deposited on the interface between the inorganic compound layer 11 and the substrate 10.

In comparative sample 1 using an inorganic compound layer made of LIPON, the capacity retention rate after 100 cycles was 39.1%. On the other hand, sample 1 in which an inorganic compound layer made of Li _x PT _y O _z was formed. The batteries of ˜17 maintained a capacity retention rate of 55% or more even after 100 cycles, and exhibited excellent cycle characteristics.

  FIG. 4 shows the relationship (cycle characteristics) between the discharge capacity retention rate and the cycle number of the battery of sample 1 and the battery of comparative sample 1. As is clear from the figure, in the comparative sample 1 in which LIPON was formed as a conventional ionic conductor in the inorganic compound layer, the capacity retention rate was lowered early. On the other hand, in the battery of sample 1 in which tungsten (W) was selected as the T component, the cycle characteristics were remarkably improved as compared with comparative sample 1.

In the preparation of Samples 1A to 1H shown in Table 2, the sputtering RF power was changed in the configuration of Sample 1, and the composition of Li _x PW _y O _z having different W / P molar ratios of W and P was used. An inorganic compound layer 11 was formed. W / P corresponds to y in the composition formula. Other conditions were in accordance with Sample 1. In addition, in order to compare the characteristics of Samples 1A to 1H with the prior art, instead of the inorganic compound layer 11 of Sample 1, a comparative sample prepared without adding W to the target, that is, a layer made of a conventional material LIPON was formed. 2 was produced. In forming the LIPON layer, Li ₃ PO ₄ was used as a target, and sputtering was performed for 10 minutes under conditions of 5 mTorr and 100 W of RF power. The thickness of the LIPON layer was 0.2 μm. Table 2 shows the configuration of the above samples.

FIG. 5 is produced by the same method as in Example 1 using a negative electrode formed by forming Li _x PW _y O _z having different W / P molar ratios (ie, y values) on the inorganic compound layer 11. The relationship between the capacity retention ratio at the 100th cycle and y obtained as a result of charging and discharging the battery under the same conditions as in Example 1 is shown. As is apparent from FIG. 5, when y is not less than 0.01 and not more than 0.5, the capacity retention rate at the 100th cycle is not less than 55%, indicating good characteristics.

Further, in order to see the reactivity with metal lithium, a dew point temperature that was formed directly Li _x PT _y O _z on the surface of the metallic lithium was allowed to stand for 2 weeks under a dry air environment -40 ° C.. As a result, discoloration was observed on the surface of metallic lithium when y was 0.6 or more.

  From the above results, the preferable range of y is 0.01 or more and 0.5 or less.

  A battery was fabricated in the same manner as in Example 1 except that the transition metal oxide shown in Table 3 was used in place of the transition metal element T alone when forming the inorganic compound layer 11. The obtained batteries were designated as Samples 18 to 31, respectively. Table 3 shows the composition of the inorganic compound layer 11 in Samples 18 to 31. For comparison, a battery in which the inorganic compound layer 11 is LIPON was produced by the same method as in Example 1, and this was designated as Comparative Sample 3. This comparative sample 3 is the same as the comparative sample 1 of Example 1. Table 3 shows the results of evaluating the obtained battery under the same conditions as in Example 1.

In Comparative Sample 3 using an inorganic compound layer made of LIPON, the discharge capacity retention rate after 100 cycles was 39.1%. On the other hand, an inorganic compound layer made of Li _x PT _y O _z was formed. The batteries of Samples 18 to 31 showed a discharge capacity retention rate of 55% or more even after 100 cycles, and showed excellent cycle characteristics.

  When the inorganic compound layer 11 is formed, a battery is manufactured in the same manner as in Example 1 except that a lithium transition metal oxide as shown in Table 4 is used instead of the transition metal element T as a target. did. The batteries thus obtained were designated as Samples 32 to 40, respectively. Table 4 shows the composition of the inorganic compound layer 11 in Samples 32 to 40. For comparison, a sample in which the inorganic compound layer 11 was made of LIPON was produced by the same method as in Example 1, and this was designated as Comparative Sample 4. This comparative sample 4 is the same as the comparative sample 1 of Example 1. Table 4 shows the results of evaluating the obtained battery under the same conditions as in Example 1.

In Comparative Sample 4 using the inorganic compound layer made of LIPON, the capacity retention rate after 100 cycles was 39.1%. On the other hand, the batteries of Samples 32 to 40 in which the inorganic compound layer made of Li _x PT _y O _z was formed exhibited a capacity retention rate of approximately 55% or more even after 100 cycles, and showed excellent cycle characteristics.

When forming the inorganic compound layer 11, lithium tungstate (Li ₂ WO ₄ ), which is a lithium oxyacid salt, was used instead of the transition metal element T alone as a target. A battery was fabricated in the same manner as in Example 1 except that the molar ratio W / P of tungsten (W) to phosphorus atom (P) (that is, the value of y) was changed as shown in Table 5. The batteries thus obtained were designated as cells 41 to 46, respectively. The cell 43 is the same as the cell 32 of the fourth embodiment. For comparison, a sample in which the inorganic compound layer 11 is made of LIPON was produced by the same method as in Example 1, and this was designated as Comparative Sample 5. This comparative sample 5 is the same as the comparative sample 1 of Example 1. Table 5 shows the results of evaluating the obtained battery under the same conditions as in Example 1.

  FIG. 6 shows a plot of the values in Table 5. From this figure, when y is in the range of 0.01 to 1.0, the capacity retention after 100 cycles is 55% or more, and excellent cycle characteristics are shown.

Comparing FIG. 5 and FIG. 6, when Li ₂ WO ₄ is used instead of W as a target, the capacity retention rate is lower than that when the target is W even if the value of y is the same. However, even when y is larger than 0.5 and 1.0 or less, the capacity retention rate is 55% or more.

The reason for this is not clear, but in another study, it has been found that the reactivity between the inorganic compound layer 11 and metallic lithium changes depending on the magnitude of the y value. That is, when Li _x PW _y O _z is formed directly on the surface of metallic lithium and left in a dry air environment having a dew point temperature of −40 ° C. for 2 weeks, the surface of metallic lithium is observed, and the y value is large. In some cases discoloration is seen. When W is used as the target, discoloration is observed when the y value is greater than 0.5, but when Li ₂ WO ₄ is used as the target, the discoloration occurs when the y value is greater than 1.0. It can be seen. That is, it can be seen that the reactivity between Li _x PT _y O _z and metallic lithium is low even when the y value is greater than 0.5 and less than or equal to 1.0. Since lithium ions are reduced in the negative electrode 1 at the time of discharge, the same reaction occurs, and it is assumed that such a result is obtained.

  As described above, the y value that is the molar ratio of the T component to P has an appropriate range. Depending on the target from which the T component is obtained, the appropriate ranges of the x value and the z value are automatically determined according to the y value. This is because the valence of each atom is determined as described above. That is, when the target is a transition metal, 2.0 ≦ x ≦ 3.0, 0.01 ≦ y ≦ 0.5, and 3.5 ≦ z ≦ 4.0, and the target is a transition metal oxide. 2.0 ≦ x ≦ 3.0, 0.01 ≦ y ≦ 1.0, 3.5 ≦ z ≦ 7.0, and 2.0 ≦ x ≦ when the target is a lithium oxyacid salt. 7.0, 0.01 ≦ y ≦ 1.0, and 3.5 ≦ z ≦ 8.0.

(Embodiment 2)
The conceptual diagram showing the basic structure in the second embodiment of the present invention is the same as FIG. The inorganic compound layer 11 in the negative electrode 1 according to the present embodiment is made of Li _x MO _y N _z . M is at least one element selected from the element group consisting of element symbols Si, B, Ge, Al, C, Ga and S, and 0.6 ≦ x ≦ 1.0, 1.05 ≦ y ≦ 1.99, and 0.01 ≦ z ≦ 0.5, or 1.6 ≦ x ≦ 2.0, 2.05 ≦ y ≦ 2.99, and 0.01 ≦ z ≦ 0.5, or 1. 6 ≦ x ≦ 2.0, 3.05 ≦ y ≦ 3.99, and 0.01 ≦ z ≦ 0.5, or 4.6 ≦ x ≦ 5.0, 3.05 ≦ y ≦ 3.99, And 0.01 ≦ z ≦ 0.5. The composition Li _x MO _y N _z is also a material with excellent conductivity and moisture resistance discovered by the present inventors.

The bond between the component element M and oxygen in Li _x MO _y N _z is a composition in which a thermodynamically stable bond is formed in comparison with the bond between phosphorus and oxygen in lithium nitride phosphate. Therefore, even when this composition is in contact with water molecules, the structure of the inorganic compound is kept stable, and the decrease in ionic conductivity in a wet environment is suppressed. Further, by stabilizing the inorganic compound layer 11, strong protection of the lithium 31 deposited between the inorganic compound layer 11 and the substrate 10 is achieved.

In the composition Li _x MO _y N _z , the bond between the M component and oxygen serves to form a more stable bond than the bond between phosphorus and oxygen in lithium nitride phosphate even in a wet environment. On the other hand, Li _x MO _y N _z is required to exhibit favorable ionic conductivity.

From the above viewpoint, the range of the element ratio constituting the composition part is when the lithium oxyacid salt is LiBiO ₂ , LiAlO ₂ or LiGaO _2, that is, in the above general formula, when M is Bi, Al or Ga, It is preferred that 0.6 ≦ x ≦ 1.0, 1.05 ≦ y ≦ 1.99, and 0.01 ≦ z ≦ 0.5.

When the lithium oxyacid salt is Li ₂ SiO ₃ , Li ₂ GeO ₃ or Li ₂ CO _3, that is, in the above general formula, when M is Si, Ge or C, 1.6 ≦ x ≦ 2.0 2.05 ≦ y ≦ 2.99 and 0.01 ≦ z ≦ 0.5.

When the lithium oxyacid salt is Li ₂ SO _4, that is, in the above general formula, when M is S, 1.6 ≦ x ≦ 2.0, 3.05 ≦ y ≦ 3.99, and It is preferable that 01 ≦ z ≦ 0.5.

When the lithium oxyacid salt is Li ₅ AlO _4, that is, in the above general formula, when M is Al, 4.6 ≦ x ≦ 5.0, 3.05 ≦ y ≦ 3.99, and It is preferable that 01 ≦ z ≦ 0.5.

  x and y can be changed according to the amount and type of lithium oxyacid salt used as a raw material, and z can be changed according to the amount and pressure of nitrogen in forming the inorganic compound layer 11. From the viewpoint of ionic conductivity, the range of z is particularly important, and if it is less than 0.01, there is a problem in ionic conductivity. Conversely, if z exceeds 0.5, the skeletal structure tends to be destroyed, In either case, the ionic conductivity is hindered.

In order to form the inorganic compound layer 11 of Li _x MO _y N _z, a lithium phosphate compound and Li ₂ SiO ₃ , LiBO ₂ , LiAlO ₂ , Li ₅ AlO ₄ , Li ₂ GeO ₃ , LiGaO ₂ , It is preferable to use a lithium oxyacid salt containing an M element group such as Li ₂ SO ₄ or Li ₂ CO ₃ . For the incorporation of N, it is preferable to apply a sputtering method using nitrogen gas or a vapor deposition method in a nitrogen atmosphere to replace some of the oxygen atoms with nitrogen atoms. In place of the above lithium oxyacid salt, an oxide of M element such as Li ₂ O and SiO ₂ , B ₂ O ₃ , GeO _2, Al ₂ O ₃ , Ga ₂ O ₃ or a mixture thereof should be used as a target. Is possible. In such an inorganic compound, the valences of the lithium atom and the oxygen atom are +1 and -2, respectively. The nitrogen atom is trivalent. The M element is the same as the valence in the compound used as the target.

As a method for obtaining x, y, and z in the prepared Li _x MO _y N _z , first, the ratio of M element is set to 1. Next, y and z are calculated by a method such as nitrogen oxygen analysis (inert gas-impulse heating and melting method) for the ratio of oxygen atoms and nitrogen atoms to M element. x is obtained by using the above valence and assuming that the overall valence is zero.

  Other than this, the formation method of the substrate 10, the form of the substrate 9, the formation method and thickness of the inorganic compound layer 11 are the same as those in the first embodiment.

  By producing the negative electrode 1 as described above, the durability of the negative electrode 1 in a wet environment can be improved, and the cycle characteristic deterioration suppressing function of a battery using the negative electrode 1 can be enhanced. As described above, the negative electrode 1 can be applied to almost all lithium battery systems regardless of the form and the combination of the positive electrode active material and the electrolyte 6. That is, it can be applied to all lithium batteries using lithium metal or a lithium alloy as a negative electrode, and the storage stability and charge / discharge cycle characteristics are improved.

  When the battery is charged and discharged, lithium precipitates and dissolves on the interface between the inorganic compound layer 11 not directly in contact with the electrolyte 3 and the substrate 10 via the inorganic compound layer 11 and functions as a negative electrode for the first time. That is, the inorganic compound layer 11 faces the electrolyte 3 and plays a role of a movement path to the substrate 10 on which lithium ions are isolated from the electrolyte 3. Even if the electrolyte 3 contains moisture in this configuration, the inorganic compound layer 11 can continue the role of the ion transfer path without being affected by the moisture of the electrolyte 3.

  The features and effects of the embodiments of the present invention will be described below with specific examples.

As an example, the substrate 10 made of Cu is formed on the substrate 9 made of SUS304 in the same manner as the sample 1 in the first embodiment, and the inorganic compound layer 11 made of the composition of Li _x MO _y N _z is formed thereon. did.

  For the formation of the inorganic compound layer 11, lithium oxyacid salts shown in Table 6 were used as targets, respectively, and RF magnetron sputtering was used, and sputtering was performed using nitrogen gas. The sputtering conditions were an internal pressure of 2.7 Pa, a gas flow rate of 10 sccm, a high frequency irradiation power of 200 W, and a sputtering time of 20 minutes. The thickness of the obtained inorganic compound layer 11 was about 0.15 μm.

  A battery was produced in the same manner as in Example 1 using the negative electrode 1 thus obtained. The obtained batteries were designated as Samples 50 to 57, respectively. Table 6 shows the composition of the inorganic compound layer 11 of each sample. For comparison, a battery in which the inorganic compound layer 11 was made of LIPON was produced by the same method as in Example 1, and this was designated as Comparative Sample 6. The comparative sample 6 is the same as the comparative sample 1 of Example 1. Table 6 shows the results of evaluating the obtained samples under the same conditions as in Example 1.

In the comparative sample 6 using the inorganic compound layer 11 made of LIPON, the capacity retention rate after 100 cycles was 39.1%. On the other hand, the sample in which the inorganic compound layer made of Li _x MO _y N _z was formed The batteries of 50 to 57 showed a capacity retention rate of 55% or more even after 100 cycles, and showed excellent cycle characteristics.

  The lithium oxyacid salt nitride shown in Table 7 was used under the same conditions as in Example 6 except that the mixture of the lithium oxyacid salt shown in Table 7 (molar ratio 1: 1) was used to form the inorganic compound layer 11. The negative electrode in which the inorganic compound layer 11 which consists of was formed was obtained. Except for this, a battery was produced under the same conditions as in Example 6, and the cycle characteristics were evaluated under the same conditions as in Example 1. Table 7 shows the composition of the inorganic compound layer 11 and the evaluation results.

  As shown in Example 6, the comparative sample 6 using the inorganic compound layer made of LIPON had a capacity retention rate of 39.1% after 100 cycles, whereas it has the composition shown in Table 7. The batteries of Samples 58 to 70 on which the inorganic compound layer was formed showed a discharge capacity retention rate of 55% or more even after 100 cycles, and showed excellent cycle characteristics.

Here, for a battery configured by forming Li _x MO _y N _z with different molar ratios of nitrogen and silicon (N / Si) as the inorganic compound layer 11, charging and discharging are performed under the same conditions as in Example 1. The relationship between the capacity retention after the cycle and the N / Si molar ratio (that is, the value of z) was evaluated.

In the production of samples 50A to 50H shown in Table 8, an inorganic compound composed of a Li _x MO _y N _z composition in which the value of z in the composition of the inorganic compound layer 11 is different by changing the nitrogen pressure in the configuration of the sample 50 Layer 11 was formed. Other conditions were the same as in Example 6. Table 8 shows the composition of the inorganic compound layer 11. Moreover, the result evaluated by the method similar to Example 1 is shown in FIG.

  As is apparent from FIG. 7, the capacity retention rate greatly depends on z, and an improvement effect was observed at 0.01 or more. Further, as the z value increased, the capacity retention rate also increased, and the highest value was stably obtained when z was 0.3 or more and 0.5 or less. However, when z exceeded 0.5, the capacity retention rate suddenly decreased, and when z was 0.8, practicality was completely lost. From the above results, it is considered that z is 0.3 to 0.5 in the most preferable range.

As described above, the z value that is the molar ratio of N to Si has an appropriate range. When lithium oxyacid salt is used as the sputtering target, the appropriate ranges of the x value and the y value are automatically determined according to the z value. This is because the valence of each atom is determined as described above. That is, when the lithium oxyacid salt is LiBiO ₂ , LiAlO ₂ or LiGaO _2, that is, in the above general formula, when M is Bi, Al or Ga, 0.6 ≦ x ≦ 1.0, 1.05 ≦ y ≦ 1.99 and 0.01 ≦ z ≦ 0.5. When the lithium oxyacid salt is Li ₂ SiO ₃ , Li ₂ GeO ₃ or Li ₂ CO _3, that is, in the above general formula, when M is Si, Ge or C, 1.6 ≦ x ≦ 2.0 2.05 ≦ y ≦ 2.99 and 0.01 ≦ z ≦ 0.5. When the lithium oxyacid salt is Li ₂ SO _4, that is, in the above general formula, when M is S, 1.6 ≦ x ≦ 2.0, 3.05 ≦ y ≦ 3.99, and 01 ≦ z ≦ 0.5. When the lithium oxyacid salt is Li ₅ AlO _4, that is, in the above general formula, when M is Al, 4.6 ≦ x ≦ 5.0, 3.05 ≦ y ≦ 3.99, and 01 ≦ z ≦ 0.5.

  In the above description, a coin-type battery has been described as an example. However, a plate-shaped electrode and an electrolyte are stacked and laminated, or a cylinder formed by winding a strip-shaped electrode through a separator containing an electrolyte. The present invention may be applied to a battery having an oval shape or cross section.

  According to the present invention, a negative electrode including a conductive substrate for deposition and an inorganic compound layer is configured, and a battery configured using the positive electrode and the electrolyte layer is configured to provide a lithium battery having excellent cycle characteristics. .

Schematic sectional view showing the basic configuration of the battery and the negative electrode used therefor in Embodiments 1 and 2 of the present invention Schematic sectional view showing another configuration of the negative electrode in the first and second embodiments of the present invention FIG. 2 is a schematic sectional view of the negative electrode in a charged state. Cycle characteristic diagram in Example 1 of the present invention The figure which shows the relationship between y of an inorganic compound layer composition in Example 2 of this invention, and a capacity | capacitance maintenance factor. The figure which shows the relationship between y of an inorganic compound layer composition in Example 5 of this invention, and a capacity | capacitance maintenance factor. The figure which shows the relationship between z of an inorganic compound layer composition in Example 8 of this invention, and a capacity | capacitance maintenance factor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Negative electrode 2 Positive electrode 3 Electrolyte 4 Gasket 5 Lid 6 Case 7 Positive electrode collector 8 Active material layer 9 Film-forming base 10 Deposition conductor substrate 11 Inorganic compound layer 31 Lithium

Claims (7)

A deposition conductor substrate for depositing lithium metal, and Li _x PT _y O _z provided on the surface of the deposition conductor substrate, wherein T is an element symbol Ti, V, Cr, Mn, Fe, Co, Ni , Cu, Zr, Nb, Mo, Ru, Ag, Ta, W, Pt and Au, and at least one element selected from the group consisting of 2.0 ≦ x ≦ 7.0, 0.01 <= Y <= 1.0, 3.5 <= z <= 8.0) The negative electrode for batteries provided with the lithium ion conductive inorganic compound layer represented. 2. The negative electrode for a battery according to claim 1, wherein 2.0 ≦ x ≦ 3.0, 0.01 ≦ y ≦ 0.5, and 3.5 ≦ z ≦ 4.0. 2. The negative electrode for a battery according to claim 1, wherein 2.0 ≦ x ≦ 3.0, 0.01 ≦ y ≦ 1.0, and 3.5 ≦ z ≦ 7.0. A deposition conductor substrate for depositing lithium metal, and Li _x MO _y N _z (where M is an element symbol Si, B, Ge, Al, C, Ga, and S) provided on the surface of the deposition conductor substrate; At least one element selected from the element group consisting of 0.6 ≦ x ≦ 1.0, 1.05 ≦ y ≦ 1.99, and 0.01 ≦ z ≦ 0.5, or 1. 6 ≦ x ≦ 2.0, 2.05 ≦ y ≦ 2.99, and 0.01 ≦ z ≦ 0.5, or 1.6 ≦ x ≦ 2.0, 3.05 ≦ y ≦ 3.99, And lithium ion conductivity represented by 0.01 ≦ z ≦ 0.5, or 4.6 ≦ x ≦ 5.0, 3.05 ≦ y ≦ 3.99, and 0.01 ≦ z ≦ 0.5 A negative electrode for a battery comprising an inorganic compound layer. The negative electrode for a battery according to any one of claims 1 to 4, further comprising lithium metal deposited between the conductive substrate for deposition and the lithium ion conductive inorganic compound layer. The battery negative electrode according to any one of claims 1 to 5, further comprising a base for supporting the deposition conductor substrate from the opposite side of the lithium ion conductive inorganic compound layer. A battery comprising the negative electrode for a battery according to any one of claims 1 to 6, an electrolyte that conducts lithium ions, and a positive electrode that reversibly absorbs and releases lithium ions.

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