JP2006120437A - Solid electrolyte battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve problems that in a lithium battery using a solid electrolyte, in order to make smooth the transfer of lithium ions between active material particles and solid electrolyte particles, since amorphous silica is bonded to the interface of these particles, the solid electrolyte is reduced by charge discharge, or reacts with moisture penetrated from the outside, and thereby, the ionic conductivity is deteriorated and cycle characteristics are decreased. <P>SOLUTION: A solid electrolyte layer is formed with a lithium ion conductive compound represented by general formula Li<SB>x</SB>PT<SB>y</SB>O<SB>z</SB>or Li<SB>x</SB>MO<SB>y</SB>N<SB>z</SB>, stable in charge discharge, and having high humidity-resistance. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a lithium battery having amorphous silica at the interface between an active material and a solid electrolyte.

  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-mentioned demand, an organic electrolyte, or a gel polymer electrolyte obtained by making it non-fluid using a polymer or a gelling agent, and various non-aqueous electrolytes such as solid electrolytes are used as electrolytes, and lithium ions are charged. Nonaqueous electrolyte lithium batteries have been developed as transfer media. Furthermore, materials that exhibit reversible potential by reversibly occluding and releasing lithium ions with various electrolytes such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , and low reversible potentials such as graphite and various carbon bodies. A simple substance, an alloy, or a compound showing the above has been discovered, and a battery that uses these as active materials for a positive electrode and a negative electrode has been developed. For example, lithium and transition metal composite oxides such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ are excellent active material materials for positive electrodes, and graphite, silicon, and tin are excellent active material materials for negative electrodes. Any of them is a typical active material.

  However, since the non-aqueous electrolyte lithium battery uses an electrolytic solution, there is a concern about liquid leakage, which is the biggest cause of trouble related to the battery. In particular, a non-aqueous electrolyte lithium battery uses a flammable organic electrolyte, and thus is uneasy in terms of safety.

Thus, many attempts have been made to use solid electrolytes instead of organic electrolytes. Research is also actively conducted on the application of chemically stable inorganic compounds as one of the solid electrolytes. Some solid electrolytes having ion conductivity at room temperature of 10 ⁻⁴ to 10 ⁻³ S / cm and a level comparable to an organic electrolyte have been studied. As such a solid electrolyte, for example, there is a lithium ion conductive oxide represented by Li _{1 + x} M _x Ti _2-x (PO ₄ ) ₃ [M is Al or Ga]. Such an oxide is commonly called LISICON, and its composition and synthesis conditions have been studied by many researchers.

  However, since such an oxide is in point contact with the active material, resistance to ion conduction between particles is high, and lithium ions are difficult to move smoothly between particles. Therefore, a method has been proposed in which amorphous silica is interposed between the active material particles and the solid electrolyte particles made of LISICON (for example, Patent Document 1).

  Specifically, a slurry containing positive electrode active material particles and amorphous silica raw material is applied to a current collector, dried and heat-treated to obtain a positive electrode. A slurry containing LISICON particles and amorphous silica raw material is applied onto the positive electrode, and this is dried and heat-treated to form a coating layer. In this configuration, it is considered that amorphous silica is formed around the active material particles and the LISICON particles, and these provide hopping sites necessary for migration of lithium ions.

On the other hand, in an electrolyte membrane obtained by sputtering lithium phosphate (Li ₃ PO ₄ ) in nitrogen, it is known that a part of oxygen is replaced by nitrogen and, as a result, exhibits lithium ion conductivity. (For example, patent document 2). This electrolyte is called LIPON and is expected to be applied to batteries.
JP 2001-210374 A US Pat. No. 5,597,660

  However, even if a technique such as Patent Document 1 is used, the lithium ion conductivity between the solid electrolyte particles is not sufficient, so that the internal impedance of the battery becomes large and the output current density is reduced. As a countermeasure, the use of LIPON of Patent Document 2 instead of the solid electrolyte particles of Patent Document 1 eliminates the problem of lithium ion conductivity between the solid electrolyte particles, reduces the internal impedance of the battery, and is practical. A simple battery.

  However, even in a very small amount of LIPON, when it comes into contact with moisture, phosphorus (P) that originally existed in a +5 valence is reduced to phosphorus having 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, due to the decrease in lithium ion conductivity of the electrolyte layer, 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 solid electrolyte with respect to moisture and ion conductivity. That is, an object of the present invention is to suppress deterioration of the solid electrolyte layer as described above, suppress an increase in impedance of the entire battery, enhance a battery characteristic deterioration suppressing function, and ensure excellent cycle characteristics.

  In order to solve the above-described problems, the solid electrolyte battery of the present invention includes a positive electrode containing a positive electrode active material that releases lithium ions during charging and capable of reversible oxidation and reduction of lithium ions, and reduces lithium ions during charging. And a negative electrode including a negative electrode active material capable of reversible oxidation-reduction of lithium ions, a solid electrolyte having a lithium ion conductivity interposed between the positive electrode and the negative electrode, and an interface between the active material and the solid electrolyte. With bonded amorphous silica. The solid electrolyte is an ion conductive inorganic compound represented by general formula 1 or general formula 2.

General formula 1: Li _x PT _y O _z (where T is the element symbol Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Ag, Ta, W, Pt and At least one element selected from the element group consisting of Au, and 2.0 ≦ x ≦ 7.0, 0.01 ≦ y ≦ 1.0, 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)
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 materials constituting these solid electrolyte layers have high lithium ion conductivity and good resistance to reduction during charging and discharging. Therefore, excellent battery characteristics are maintained over a long charge / discharge cycle. And since it is excellent in moisture resistance, the fall of lithium ion conductivity is suppressed also with respect to the penetration | invasion of the water | moisture content from the outside. As a result, excellent battery characteristics are maintained over a long period of use.

  According to the present invention, by ensuring the stability of the solid electrolyte against moisture and ionic conductivity, the movement of lithium ions between the active material and the solid electrolyte is facilitated, so that the resistance is reduced and the charge is reduced. A fixed electrolyte battery having excellent discharge cycle characteristics can be provided.

  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 schematic cross-sectional view of the battery according to the first embodiment. The battery includes a negative electrode 1, a positive electrode 2 opposed to the negative electrode 1, and a solid electrolyte layer 3 interposed therebetween to conduct lithium ions. The negative electrode 1 and the positive electrode 2 are housed in the protective layer 4 together with the solid electrolyte layer 3. The positive electrode 2 includes a positive electrode active material that releases lithium ions during charging and is capable of reversible oxidation-reduction of lithium ions. The negative electrode 1 includes a negative electrode active material capable of reducing lithium ions during charging and capable of reversibly oxidizing and reducing lithium ions.

The positive electrode 2 includes a positive electrode current collector (hereinafter referred to as current collector) 7 and an active material layer 8 containing a positive electrode active material. A positive electrode lead 7 </ b> A is connected to the current collector 7. In the active material layer 8, amorphous silica particles are chemically bonded to the interface of the active material particles. In the solid electrolyte layer 3, amorphous silica particles are chemically bonded to the interface between the solid electrolyte layer 3 represented by the general formula Li _x PT _y O _z and the active material layer 8. Here, T is at least one element selected from the group consisting of element symbols Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Ag, Ta, W, Pt and Au. It is a seed element, and 2.0 ≦ x ≦ 7.0, 0.01 ≦ y ≦ 1.0, and 3.5 ≦ z ≦ 8.0. It is noted that the above composition Li _x PT _y O _z is a material that has been discovered by the present inventors and has excellent lithium ion conductivity and moisture resistance.

  A good conductor such as aluminum, iron, gold, or carbon is applied to the current collector 7. The current collector 7 may be used by forming the above-mentioned good conductor material into a thin film by a vapor deposition method or a sputtering method on a substrate having self-shape-retaining properties such as a thin plate such as silicon, silica, alumina, and a carbon sintered body. Good. When the good conductor material itself has a self-shape-retaining property such as a metal plate, a metal film, or a metal foil, the substrate can be omitted.

As the positive electrode active material, known oxides and compounds such as LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ can be applied as in the case of a general lithium battery. These active material powders are mixed with tetraalkoxysilane, stirred for a predetermined time, and dried to obtain a powder composed of active material particles chemically bonded with amorphous silica. Or you may make it react by ultraviolet irradiation, after mixing the powder of an active material material with tetraalkoxysilane. The obtained powder is mixed with a conductive powder such as carbon black, a binder such as polyvinylidene fluoride or polytetrafluoroethylene, and a mixing solvent such as N-methylpyrrolidone to prepare a slurry. This slurry is applied on the current collector 7 and dried to form the active material layer 8.

The solid electrolyte layer 3 is formed directly by vapor deposition or sputtering on the positive electrode 2 in which amorphous silica is previously formed on the joint surface with the solid electrolyte layer 3. In this case, there is an advantage that the thickness of the solid electrolyte layer 3 can be extremely reduced. Hereinafter, a method for forming a thin film of a solid electrolyte represented by the general formula Li _x PT _y O _z will be described.

When the solid electrolyte layer 3 is formed into a thin film, a dry thin film process is performed using lithium phosphate and transition metals such as tungsten, molybdenum, and tantalum specified as T components or their metal oxides as targets or vapor deposition sources. Form with. That is, various thin film deposition methods such as a vapor deposition method, a resistance heating vapor deposition method, a high frequency heating vapor deposition method, a laser ablation vapor deposition method, an ion beam vapor deposition method, or a sputtering method, an rf magnetron sputtering method, etc. in an argon or vacuum environment Is preferably formed on the active material layer 8. It may also be applied to a mixture of Li ₂ O and _P 2 _{O 5} in place of the lithium phosphate.

Here, it is preferable to use a compound such as a transition metal oxide in addition to the T component alone as the T component target or vapor deposition source. In such a solid electrolyte, the valences of lithium atom, phosphorus atom and oxygen atom are +1 valence, +5 valence and -2 valence, respectively. The T component is the same as the 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 T component is considered to be incorporated in the lithium phosphate in a metallic state, and thus becomes zero-valent. 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. With an infrared detector, nitrogen can be detected as N ₂ gas with a highly sensitive thermal conductivity detector. x is obtained by using the above valence and assuming that the overall valence is zero.

The composition Li _x PT _y O _z of the solid electrolyte layer 3 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 conduction of the solid electrolyte layer 3 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 sufficiently obtain excellent ion conductivity and a function of suppressing decomposition in a wet environment, 2.0 ≦ x ≦ 7.0, 0.01 ≦ y ≦ 1.0 3.5 ≦ z ≦ 8.0 is desirable. 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, 3.5 ≦ 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.

Li _x PT _y O _z formed as described above exhibits superior stability compared to LIPON, which is conventionally known as a lithium ion conductor.

That is, the solid electrolyte layer 3 composed of Li _x PT _y O _z and the active material layer chemically bonded with amorphous silica is stable against charge and discharge and also stable against moisture. A decrease in ion conductivity of the layer 3 is suppressed. Therefore, good battery characteristics due to the smooth conduction of lithium ions between the solid electrolyte layer 3 and the active material layer 8 are sustained over a long period of time.

  For the protective layer 4, all materials and shapes such as a laminate film generally used for a battery configured by applying a lithium compound, a lithium alloy, or the like are applicable. In addition, a button type battery may be configured using a case, a gasket or the like instead of the protective layer 4. Further, a metal case such as a cylindrical case, an elliptic flat case, or a square case may be used as the case.

  The negative electrode 1 can use, as an active material, a simple substance, an alloy, or a compound that absorbs lithium ions such as graphite, various carbons, tin, silicon, and other nitrides and exhibits a potential close to lithium, in addition to lithium metal. When powder is used as the negative electrode active material and mixed with a binder or a solvent to form a negative electrode current collector, it is preferable to chemically bond amorphous silica to the negative electrode active material particles as in the positive electrode 2. . In this case, amorphous silica is bonded to the interface between the negative electrode active material and the solid electrolyte.

  Further, when a thin film of lithium metal is formed as the negative electrode 1, since lithium ions easily move between the lithium metal and the solid electrolyte, it is not necessary to form amorphous silica at the interface. Note that a negative electrode lead 9A is attached to the current collector 9, and is drawn out of the battery. When lithium metal foil is used as the negative electrode 1, the current collector 9 may not be provided, and the negative electrode lead 9A may be directly attached to the lithium metal foil.

  By producing a solid electrolyte battery as described above, ion conduction from the active material particles to the solid electrolyte layer is performed smoothly, and the solid electrolyte layer 3 is stable against moisture, so that low resistance is good. Charge / discharge characteristics can be maintained over a long period of time.

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

  Here, the case where the negative electrode 1, the positive electrode 2, and the solid electrolyte layer 3 are formed by thin film formation will be described. FIG. 2 is a schematic cross-sectional view of a battery manufactured as follows.

First, preparation of the positive electrode 2 will be described. Silicon (Si) was used as a substrate, and gold (Au) was deposited to a thickness of 100 μm to produce a current collector 7. Next, the current collector 7 was attached to the holder of the vacuum evaporation apparatus. Using a 2 cm × 2 cm metal mask, appropriate amounts of cobalt metal (Co) and lithium metal (Li) as source materials were filled in the respective electron beam evaporation crucibles. After exhausting the inside of the apparatus, a 1: 1 mixed gas (volume ratio) of argon and oxygen was introduced and maintained at 1 × 10 ⁻³ to 1 × 10 ⁻¹ Pa. Thereafter, the source material was irradiated with an electron beam of 10 kV and 100 to 180 mA from an electron gun to evaporate the source, and after 20 minutes had elapsed from the start of evaporation, all electron irradiation was stopped. After a thin film having a thickness of 2 μm was produced by the above operation, a heat treatment was performed at 800 ° C. for 2 hours in an oxygen atmosphere to obtain a LiCoO ₂ film 8A that is a thin film of a positive electrode active material. Next, the current collector 7 on which the LiCoO ₂ film 8A was formed was immersed in tetramethoxysilane and left at room temperature while stirring. Thereafter, the current collector 7 was taken out and dried at 120 ° C. for 2 hours.

The surface of the positive electrode active material layer 8 thus obtained was verified by X-ray, but no SiO ₂ peak was detected. On the other hand, when measured by XPS, a peak derived from Si—O was confirmed. From the above results, it was confirmed that the silica film 8B formed on the LiCoO ₂ film 8A was amorphous.

Next, the solid electrolyte layer 3 made of Li _x PT _y O _z having a thickness of 2.5 μm was formed on the silica film 8B by rf sputtering. In this case, in samples 1 to 17, Li ₃ PO ₄ having a diameter of 4 inches and a transition metal as shown in Table 1 as the transition metal element T were used as targets, respectively, and Li ₃ PO ₄ in an argon atmosphere of 5 mTorr. Was applied with 100 W rf power, and for transition metal T, 25 W rf power was applied and sputtering was performed for 50 minutes. The thickness of the obtained solid electrolyte layer 3 was about 0.15 μm. The composition of the formed solid electrolyte layer 3 was obtained by inductively coupled high-frequency plasma spectroscopy (ICP spectroscopy) as described above using a sample prepared by placing a platinum plate beside the current collector 7 when the solid electrolyte layer 3 was formed. Method). According to this technique, the composition of the composition was Li _2.8 PT _0.2 O _3.9 .

For comparison, Comparative Sample 1 in which a layer made of a nitride of lithium phosphate (LIPON) was formed instead of the solid electrolyte layer 3 of Sample 1 was produced. In forming the LIPON layer, 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 LIPON layer was about 0.2 μm. Table 1 shows the configuration of the above samples.

  Next, on the solid electrolyte layer 3 formed on the positive electrode 2 as described above, lithium metal was evaporated to a size of 1.8 cm × 1.8 cm and a thickness of 2 μm to form the negative electrode 1. Furthermore, copper was vapor-deposited thereon to form a negative electrode current collector 9 having a thickness of 100 nm. Then, the leads 7A and 9A were attached to the current collectors 7 and 9, respectively, and the other ends of the leads 7A and 9A were covered with the protective layer 4 so that the battery was completed. The protective layer 4 was formed by applying and curing an epoxy resin.

  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 manner, the ratio of the discharge capacity during the cycle to the initial discharge capacity, that is, the change in the capacity retention rate was examined. In addition, the capacity retention rates after 100 cycles were compared. The results are shown in Table 1.

First, the relationship (cycle characteristics) between the capacity retention ratio and the number of cycles of the battery of sample 1 and the battery of comparative sample is shown in FIG. As is clear from FIG. 3, in Comparative Sample 1 in which LIPON was formed as a conventional ionic conductor on the solid electrolyte layer, the capacity retention rate was lowered early. On the other hand, in the battery of sample 1 in which tungsten (W) is selected as the T component and the solid electrolyte layer 3 made of the general formula Li _x PT _y O _z is formed, the cycle characteristics are remarkably improved compared to the comparative sample. It was.

Further, as is apparent from Table 1, the capacity retention rate of Comparative Sample 1 using the solid electrolyte layer made of LIPON was 42.6%. On the other hand, the batteries of Samples 1 to 17 in which the solid electrolyte layer 3 made of Li _x PT _y O _z was formed maintained a capacity retention rate of 60% or more even at 100 cycles, and exhibited excellent cycle characteristics.

Next, the results of investigation of the range of y values in the composition formula _Li x _PT y _{O z.} Here, a case where W is applied as the T component will be described as an example.

As shown in Table 2, Samples 1A to 1H were prepared. In these productions, a solid consisting of a composition of Li _x PW _y O _z in which the sputtering rf power is changed in the configuration of sample 1 and W / P (that is, y value), which is the molar ratio of W and P, is different. Electrolyte layer 3 was formed. W / P corresponds to y in the composition formula. Other conditions were in accordance with Sample 1. W / P was 0.005, 0.01, 0.05, 0.1, 0.2, 0.5, 0.6, and 0.8 with respect to samples 1A to 1H, respectively. The same thing as the comparative sample 1 of Example 1 was produced for the comparison.

Using these samples, batteries were prepared in the same manner as in Sample 1, and evaluated in the same manner as in Example 1. FIG. 4 shows the relationship between the capacity maintenance ratio at the 100th cycle and W / P when a battery in which Li _x PW _y O _z having different W / P is formed on the solid electrolyte layer 3 is charged and discharged. . As is clear from FIG. 4, the capacity retention rate was 0.01 or more and 0.5 or less, and the capacity retention rate was 60% or more, indicating good characteristics.

  Next, the case where the raw material of the solid electrolyte layer 3 is changed will be described. First, the case where the transition metal oxide shown in Table 3 is used instead of the simple substance of the transition metal element T when the solid electrolyte layer 3 is formed will be described.

  A battery was fabricated in the same manner as Sample 1, except that the transition metal oxide shown in Table 3 was used instead of the transition metal T as the sputtering target. The same thing as the comparative sample 1 of Example 1 was produced for the comparison. Table 3 shows the composition of the solid electrolyte layer 3 in Samples 1J to 13J and 15J and Comparative Sample 1. Table 3 shows the capacity retention rate after 100 cycles, which is the result of evaluating the obtained battery under the same conditions as in Example 1.

As is clear from Table 3, the capacity retention rate of Comparative Sample 1 was 42.6%, whereas Samples 1J to 13J and 15J in which the solid electrolyte layer 3 made of Li _x PT _y O _z was formed were used. The battery exhibited a capacity retention rate of 60% or more even after 100 cycles, and exhibited excellent cycle characteristics. Thus, cycle characteristics are improved even when a transition metal oxide is used as a raw material in addition to a single transition metal.

  Next, the case where lithium oxyacid salts as shown in Table 4 are used instead of the transition metal element T alone as a target when forming the solid electrolyte layer 3 will be described.

  A battery was fabricated in the same manner as Sample 1, except that the lithium oxyacid salt shown in Table 4 was used as the sputtering target. The same thing as the comparative sample 1 of Example 1 was produced for the comparison. Table 4 shows the composition of the solid electrolyte layer 3 in Samples 1K to 7K, 12K, and 13K, and Comparative Sample 1 and the capacity retention rate after 100 cycles, which is the result of evaluating the obtained battery under the same conditions.

As apparent from Table 4, the capacity retention rate of Comparative Sample 1 was 42.6%, whereas Samples 1K to 7K, 12K, and 13K in which a solid electrolyte layer composed of Li _x PT _y O _z was formed. The battery exhibited a capacity retention rate of 60% or more even after 100 cycles, and exhibited excellent cycle characteristics. As described above, even when lithium oxyacid salt is used as a raw material in addition to the transition metal alone, the cycle characteristics are improved.

Next, when the solid electrolyte layer 3 is formed, the result of examination on the y value when lithium oxyacid salt is used instead of the transition metal element T alone as a target is shown. Here, a case where lithium tungstate (Li ₂ WO ₄ ) is used will be described as an example.

As shown in Table 5, samples 1KA to 1KF were prepared. In these productions, the sputtering rf power was changed in the configuration of the sample 1K to form the solid electrolyte layer 3 made of a composition of Li _x PW _y O _z having a different W / P molar ratio of W and P. . W / P corresponds to y in the composition formula. Other conditions were the same as for sample 1K. W / P was 0.01, 0.1, 0.25, 0.33, 1.0, and 2.0 for samples 1KA to 1KF, respectively. The same thing as the comparative sample 1 of Example 1 was produced for the comparison. Table 5 also shows the compositions of the solid electrolyte layers 3 in Samples 1KA to 1KF and Comparative Sample 1.

These sample batteries were made and evaluated. FIG. 5 shows the relationship between the capacity retention rate and W / P after 100 cycles after charging / discharging of a battery in which Li _x PW _y O _z having different W / P is formed on the solid electrolyte layer 3. . As is clear from FIG. 5, the capacity retention rate was 0.01 or more and 1.0 or less, and the capacity retention rate was 60% or more, indicating good characteristics.

Comparing FIG. 4 and FIG. 5, when Li ₂ WO ₄ is used instead of W as a target, the capacity retention rate is lower than when the target is W even with the same W / P (ie, y value). However, even when W / P is greater than 0.5 and 1.0 or less, the capacity retention rate is 60% or more.

The reason for this is not clear, but as described above, when a single transition metal is used as a sputtering target, it has a zero valence and tends to increase electronic conductivity. For this reason, it is preferable that the y value be smaller than when lithium oxyacid salt is used as the target. In another study, it has been found that the reactivity of the solid electrolyte layer 3 and metallic lithium changes depending on the magnitude of W / P (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 the solid electrolyte layer 3 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 during discharge and lithium is deposited, 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 view showing the concept of the basic structure in the second embodiment of the present invention is the same as FIG. 1 and FIG. The solid electrolyte layer 3 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 lithium ion 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 solid electrolyte is kept stable, and a decrease in ionic conductivity in a wet environment is suppressed. _Li x _MO y _{N z,} which is formed as described above, has high lithium ion conductivity, compared with LISICON, difficult to be reduced during charging and discharging. Further, it exhibits much better stability against moisture than lithium phosphate and LIPON, which are conventionally known as lithium ion conductors.

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 solid electrolyte layer 3. 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> 0.5, the skeletal structure is easily destroyed. Impairs ionic conductivity.

In order to form the Li _x MO _y N _z solid electrolyte layer 3, 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 a solid electrolyte, the valences of lithium atoms and oxygen atoms 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 produced 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 (analysis using an inert gas-impulse heating 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 manufacturing method of the negative electrode 1 and the positive electrode 2, the forming method and the thickness of the solid electrolyte layer 3, and the like are the same as those of the first embodiment.

  By producing a solid electrolyte battery as described above, the ion conduction from the active material particles to the solid electrolyte layer is smoothly performed, and the solid electrolyte layer 3 is stable against oxidation / reduction and moisture accompanying charge / discharge. The low charge and good charge / discharge characteristics are maintained over a long period of time.

The features and effects of the embodiments of the present invention will be described below with specific examples. As an example, a LiCoO ₂ film 8A was formed on a current collector 7 formed by vapor-depositing Au on a substrate made of Si in the same manner as in sample 1 in the first embodiment, and a silica film 8B was formed thereon. The case where the solid electrolyte layer 3 made of a composition of Li _x MO _y N _z is formed will be described later.

  For the formation of the solid electrolyte layer 3, lithium oxyacid salts shown in Table 6 were used as targets, respectively, 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 3 hours. The thickness of the obtained solid electrolyte layer 3 was approximately 2.0 μm.

  Table 6 shows the composition of the solid electrolyte layer 3 of each sample. The composition of the formed solid electrolyte layer 3 was obtained by inductively coupled high-frequency plasma spectroscopy (ICP) using a sample prepared by placing a platinum plate on the side of the current collector 7 when the solid electrolyte layer 3 was formed. Spectroscopic analysis method) and the like.

  Thereafter, a sample battery was produced in the same manner as in Example 1. For comparison, a battery of Comparative Sample 1 in Example 1 was produced. These batteries were evaluated under the same conditions as in the Examples, and the capacity retention ratio after 100 cycles of charge / discharge as a result is shown in Table 6.

The comparative sample 1 using the solid electrolyte layer made of LIPON had a capacity retention rate of 42.6%, whereas the batteries of the samples 21 to 28 formed with the solid electrolyte layer 3 made of Li _x MO _y N _z Exhibited a capacity retention rate of 60% or more even after 100 cycles, and exhibited excellent cycle characteristics.

  Next, an example in which the solid electrolyte layer 3 is formed using a mixture of two types of lithium oxyacid salts as a sputtering target will be described.

  Nitriding of the lithium oxyacid salt shown in Table 7 under the same conditions as Samples 21 to 28 except that the mixture of lithium oxyacid salt shown in Table 7 (molar ratio 1: 1) was used for forming the solid electrolyte layer 3. The batteries of Samples 31 to 43 in which the solid electrolyte layer 3 made of a material was formed were 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 and evaluation results of the solid electrolyte layer 3.

As is clear from Table 7, the batteries of Samples 31 to 43 also showed a capacity retention rate of 60% or more even after 100 cycles, and exhibited excellent cycle characteristics. Thus, in the composition Li _x MO _y N _z forming the solid electrolyte layer 3, the component M may be composed of a plurality of elements. Although data is not shown, the T component in the first embodiment may also be composed of a plurality of elements.

Next, the results of investigation of the range of z values in the composition formula _Li x _MO y _{N z.} Here, a case where Si is applied as an M component will be described as an example.

In the production of Samples 21A to 21H shown in Table 8, Li _x SiO _y N in which the N / Si which is the molar ratio of N to Si in the composition of the solid electrolyte layer 3 is changed by changing the nitrogen pressure in the configuration of Sample 21. _A solid electrolyte layer 3 made of the composition of _z was formed. N / Si corresponds to z in the composition formula. Other conditions were in accordance with Sample 21. Table 8 shows the composition of the solid electrolyte layer 3. N / Si was 0.005, 0.01, 0.1, 0.3, 0.5, 0.6, 0.8, and 1.0 for samples 21A to 21H, respectively.

Using these samples, 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. FIG. 6 shows the relationship between the capacity retention rate and N / Si after 100 cycles after charging and discharging a battery in which Li _x SiO _y N _z having different N / Si was formed on the solid electrolyte layer 3. Yes.

  As is apparent from FIG. 6, the capacity retention rate greatly depends on N / Si, and an improvement effect was observed at 0.01 or more. Further, as the value of N / Si increased, the capacity retention rate also increased, and the highest value was stably obtained when the value of N / Si was 0.3 to 0.5. However, when it exceeded 0.5, the capacity retention rate suddenly decreased, and when 0.8, practicality was completely lost. From the above results, it is considered that N / Si is most preferably in the range of 0.3 to 0.5.

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.

Although not shown in the data, the M component of Li _x MO _y N _z is at least one element selected from the element group consisting of B, Ge, Al, C, Ga and S other than Si, 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. Similar results were obtained when ≦ x ≦ 5.0, 3.05 ≦ y ≦ 3.99, and 0.01 ≦ z ≦ 0.5.

The solid electrolyte battery according to the present invention has a configuration in which amorphous silica is formed at the interface between an active material and a solid electrolyte made of either the general formula Li _x PT _y O _z or the general formula Li _x MO _y N _z. Have. In this solid electrolyte battery, the junction necessary for the movement of lithium between the active material particles and the solid electrolyte particles is ensured, and at the same time, the solid electrolyte is stable against reduction during charge and discharge, and moisture from the outside The deterioration of the lithium ion conductivity of the solid electrolyte due to the penetration of is suppressed. As a result, excellent battery characteristics are maintained over a long period of use, and the cycle characteristics are greatly improved.

Schematic sectional view showing the basic configuration of the battery according to Embodiments 1 and 2 of the present invention. Schematic sectional view showing another basic configuration of the battery according to the first and second embodiments of the present invention. Cycle characteristic diagram according to Embodiment 1 of the present invention The figure which shows the relationship between W / P of an inorganic compound layer composition and capacity | capacitance maintenance factor in Embodiment 1 of this invention. The other figure which shows the relationship between W / P of an inorganic compound layer composition in Embodiment 1 of this invention, and a capacity | capacitance maintenance factor. The figure which shows the relationship between N / Si of an inorganic compound layer composition in Embodiment 2 of this invention, and a capacity | capacitance maintenance factor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Negative electrode 2 Positive electrode 3 Solid electrolyte 4 Protective layer 7 Positive electrode collector 8 Active material layer 8A LiCoO ₂ film 8B Amorphous silica film 9 Current collector

Claims (4)

A positive electrode containing a positive electrode active material capable of releasing lithium ions during charging and capable of reversible oxidation-reduction of lithium ions; and a negative electrode active material capable of reducing lithium ions during charging and capable of reversible oxidation-reduction of lithium ions. A negative electrode containing, a solid electrolyte interposed between the positive electrode and the negative electrode, having lithium ion conductivity, and chemically bonded to an interface between at least one of the positive electrode active material and the negative electrode active material and the solid electrolyte An amorphous silica, and the solid electrolyte is Li _x PT _y O _z (where T is an element symbol Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, 2. at least one element selected from the group consisting of Ru, Ag, Ta, W, Pt and Au, and 2.0 ≦ x ≦ 7.0, 0.01 ≦ y ≦ 1.0, 5 ≦ z ≦ 8.0) The solid electrolyte battery is a compound. 2. The solid electrolyte battery according to claim 1, wherein 2.0 ≦ x ≦ 3.0, 0.01 ≦ y ≦ 0.50, and 3.5 ≦ z ≦ 4.0. 2. The solid electrolyte battery according to claim 1, wherein 2.0 ≦ x ≦ 3.0, 0.01 ≦ y ≦ 1.0, and 3.5 ≦ z ≦ 7.0. A positive electrode containing a positive electrode active material capable of releasing lithium ions during charging and capable of reversible oxidation-reduction of lithium ions; and a negative electrode active material capable of reducing lithium ions during charging and capable of reversible oxidation-reduction of lithium ions. A negative electrode containing, a solid electrolyte interposed between the positive electrode and the negative electrode, having lithium ion conductivity, and chemically bonded to an interface between at least one of the positive electrode active material and the negative electrode active material and the solid electrolyte An amorphous silica, wherein the solid electrolyte is Li _x MO _y N _z (where M is at least selected from the element group consisting of element symbols Si, B, Ge, Al, C, Ga and S) One element 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 0.0, 3.05 ≦ y ≦ 3.99, and 0.01 ≦ z ≦ 0.5).

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