JP6194719B2 - All solid battery - Google Patents

Description

  The present invention relates to an all solid state battery, and more particularly to an all solid state battery using lithium-containing vanadium phosphate having a NASICON structure as a positive electrode active material in an all solid state battery.

  In recent years, the demand for batteries as a power source for portable electronic devices such as mobile phones and portable personal computers has greatly increased. As a battery used for such an application, there is a lithium ion secondary battery. In a lithium ion secondary battery, an organic electrolyte (electrolytic solution) in which a lithium salt is dissolved in an organic solvent or the like is conventionally used as a medium for moving ions, such as a carbonate ester or an ether organic solvent. ing.

  However, in the battery having the above configuration, there is a risk that the electrolyte solution leaks. Further, there is a problem that an organic solvent or the like used for the electrolytic solution is a combustible substance. Therefore, it is required to increase the safety of the battery.

  Therefore, in order to increase the safety of the lithium ion secondary battery, it has been proposed to use a solid electrolyte as the electrolyte instead of the organic solvent electrolyte. Furthermore, development of an all-solid battery in which not only a solid electrolyte is used as an electrolyte but also other constituent elements are made of solid is underway.

For example, International Publication No. 2012/063874 pamphlet (Patent Document 1) describes a sintered all solid state battery. The all solid state battery disclosed here uses, for example, a lithium-containing vanadium phosphate compound: Li ₃ V ₂ (PO ₄ ) ₃ having a NASICON structure as a positive electrode active material.

International Publication No. 2012/063874 Pamphlet

  As a result of investigations by the inventors, in an all-solid battery composed entirely of solid including the active material, the deterioration factor of the battery is not the volume change of the active material accompanying charge / discharge, but rather the center of the active material. It was found that the deterioration of the active material due to the valence change of the metal seems to be the main factor.

  It has also been found that such a tendency is remarkable in an all-solid battery configured with a solid body, particularly an all-solid battery configured with a sintered body.

  Accordingly, an object of the present invention is to suppress deterioration of the positive electrode active material due to a change in the valence of V in an all solid state battery using a lithium-containing vanadium phosphate compound having a NASICON structure as the positive electrode active material. .

The present invention is directed to an all solid state battery comprising a solid electrolyte layer, and a positive electrode layer and a negative electrode layer disposed with the solid electrolyte layer interposed therebetween, and including lithium-containing vanadium phosphate having a NASICON structure as a positive electrode active material. be one that is, to solve the technical problems described above, the lithium-containing vanadium phosphate has the general _{formula: Li 3 + x V 2-} y M y (PO 4) 3 ( however, x: -0. 4 ≦ x ≦ 0.2, y: 0.00 <y ≦ 0.20, and M: an element having 6 coordination with an ionic radius larger than V) .

Said M which is an element having the same 6-coordination as V is preferably Mg, Ca, Sr, Sc, Y, Ti, Zr, Hf, Nb, Ta, Mo, Zn, Cd, In, Tl, Sn, At least one element selected from the group consisting of Pb, Sb and Bi, more preferably from the group consisting of Mg, Ca, Sr, Sc, Y, Zr, Hf, Zn, Cd, In, Sn and Pb At least one element selected.

Preferably, the general formula: in _{Li 3 + x V 2-y} M y (PO 4) 3, y is 0.01 ≦ y ≦ 0.05.

  The present invention is advantageously applied to an all solid state battery in which at least a positive electrode layer and a solid electrolyte layer are joined by sintering.

  According to the present invention, it is possible to suppress the deterioration of the positive electrode active material accompanying the change in the valence of V. Although the cause is not exactly known, it is presumed that oxygen desorption from the lithium-containing vanadium phosphate accompanying charge / discharge is suppressed.

It is sectional drawing which shows typically the battery laminated body 1 with which the all-solid-state battery by one Embodiment of this invention is equipped.

  First, an all solid state battery according to an embodiment of the present invention will be described. The all-solid battery is configured with a battery stack 1 as shown in FIG. The battery stack 1 includes a solid electrolyte layer 2 including a solid electrolyte, and a positive electrode layer 3 and a negative electrode layer 4 disposed so as to face each other with the solid electrolyte layer 2 interposed therebetween.

  The positive electrode active material contained in the positive electrode layer 3 includes lithium-containing vanadium phosphate having a NASICON structure, and the lithium-containing vanadium phosphate is obtained by substituting a part of the V site with an element having 6-coordination. . As described above, if a part of the V site in the lithium-containing vanadium phosphate is replaced with an element having 6-coordination, the deterioration of the positive electrode active material due to the change in the valence of V can be suppressed. It was found from experiments described later that the deterioration can be suppressed. Although the cause is not exactly known, it is presumed that oxygen desorption from the lithium-containing vanadium phosphate accompanying charge / discharge is suppressed.

The element to be replaced is selected from the group consisting of Mg, Ca, Sr, Sc, Y, Ti, Zr, Hf, Nb, Ta, Mo, Zn, Cd, In, Tl, Sn, Pb, Sb, and Bi. When at least one element is used, the output of the all solid state battery can be further increased. This is because the Li ion path in the crystal structure of Li ₃ V ₂ (PO ₄ ) ₃ is expanded by substituting with an element having an ionic radius larger than V (trivalent, tetravalent, pentavalent element). It is guessed.

More preferably, at least one element selected from the group consisting of Mg, Ca, Sr, Sc, Y, Zr, Hf, Zn, Cd, In, Sn, and Pb is used as the element to be replaced. Not only can the output of the all-solid-state battery be further increased, but the substitution can be made at the six-coordinate site of Li ₃ V ₂ (PO ₄ ) _{3 because} the valence is limited to one. The element itself does not change in valence, and deterioration of the positive electrode active material can be further suppressed.

The lithium-containing vanadium phosphate having a NASICON structure contained in the positive electrode active material according to the present invention is represented by the general formula: Li _{3 + x} V _{2- y My} (PO ₄ ) ₃ . Here, by selecting the element substitution amount y at the site of V in the range of 0.00 <y ≦ 0.20, the reduction of the charge / discharge capacity due to the generation of the heterogeneous phase is suppressed. Furthermore, a higher effect can be obtained by selecting the element substitution amount y in the range of 0.01 ≦ y ≦ 0.05. The amount of Li varies within the range for valence compensation depending on the amount of substitution element and its valence. “3 + x”, which is the amount of Li in the above general formula, varies in the range of 2.6 to 3.2. If expressed by “x”, it varies in the range of −0.4 ≦ x ≦ 0.2.

  At least the positive electrode layer 3 is joined to the solid electrolyte layer 2 by sintering. The effects as described above are more prominent when at least the positive electrode layer 3 and the solid electrolyte layer 2 are formed of such a sintered body.

For the above-mentioned solid electrolyte, for example, a material having ion conductivity and small enough to have negligible electronic conductivity can be used. Examples of such materials include lithium halide, lithium nitride, lithium oxyacid salt, and derivatives thereof. In addition, Li—PO system compounds such as lithium phosphate (Li ₃ PO ₄ ), LiPON (LiPO _4−x N _x ) in which nitrogen is mixed with lithium phosphate, Li—Si—O such as Li ₄ SiO ₄ Compounds such as La-based compounds, Li-P-Si-O based compounds, Li-V-Si-O based compounds, La _0.51 Li _0.35 TiO _2.94 , La _0.55 Li _0.35 TiO ₃ , Li _3x La _{2 / 3-x} TiO ₃ A compound having a lobskite structure, a compound having a garnet structure having Li, La, and Zr such as Li ₇ La ₃ Zr ₂ O ₁₂ can be given. You may use sulfide materials, such as a Li-PS-system and a Li-Ge-PS system.

The solid electrolyte particularly preferably contains a compound having a NASICON structure. The composition of the compound having a NASICON structure is represented by Li _x A _y (PO ₄ ) ₃ (1 ≦ x ≦ 2, 1 ≦ y ≦ 2, A is at least one of Ti, Ge, Al, Ga and Zr). In addition, a part of P may be substituted with B, Si or the like. Examples of the compound having a NASICON structure include Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ and Li _1.5 Al _0.5 Ti _1.5 (PO ₄ ) ₃ .

The negative electrode active material contained in the negative electrode layer 4 may include the above-described positive electrode active material according to the present invention. In addition, a graphite-lithium compound, a lithium alloy such as Li—Al, Li ₃ V ₂ (PO ₄ ) at least one selected from the group consisting of NASICON type lithium-containing phosphate compounds such as ₃ and Li ₃ Fe ₂ (PO ₄ ) ₃ , Li ₄ Ti ₅ O ₁₂ , Ti, Si, Sn, Cr, Fe and Mo An oxide of a seed element or the like is used. Specifically, it preferably contains at least one oxide selected from the group consisting of titanium oxide, silicon oxide, niobium oxide, tin oxide, chromium oxide, iron oxide and molybdenum oxide. Such an oxide has a large capacity per weight and a low potential with respect to Li. Therefore, in the all fixed batteries, the capacity density is large, the battery voltage is increased, and the energy density can be increased.

  Although not shown in FIG. 1, a current collector layer may be disposed on the surface of the positive electrode layer 3 and the negative electrode layer 4 opposite to the solid electrolyte layer 2 side. As a material for the current collector layer, for example, an electron conductive material such as carbon, metal, oxide, or the like is used. The current collector layer may include a material that sinters the electron conductive material by firing, such as fused glass, or the electron conductive material is fixed by annealing at about 100 to 200 ° C., such as a thermosetting resin. Materials that can be included may be included. A material such as an adhesive that can fix the electron conductive material without heat treatment may be included. In addition, it is not preferable that the current collector layer contains an ion-conducting material such as a solid electrolyte material because the battery stack 1 may be internally short-circuited through the current collector layer.

  Hereinafter, experimental examples carried out to confirm the effects of the present invention will be described.

<Preparation of positive electrode active material>
As raw materials, lithium carbonate (Li ₂ CO ₃ ), vanadium pentoxide (V ₂ O ₅ ), ammonium dihydrogen phosphate (NH ₄ H ₂ PO ₄ ), niobium oxide (Nb ₂ O ₅ ), yttrium oxide (Y ₂ O ₃ ) and aluminum oxide (Al ₂ O ₃ ) were prepared. As can be seen from these raw materials, Nb, Y and Al were used as substitution elements in this experimental example.

Next, the raw material, the _{Li 3 + x V 2-y} M y (PO 4) 3, as M to replace a portion of the V-site, an element shown in the column of "substitution elements M" in Table 1 This was replaced with the amount shown in the column “Substitution amount y”, and weighed so as to obtain the composition shown in the column “Positive electrode active material composition”.

  Next, the weighed raw materials are mixed, baked for 2 hours at a temperature of 600 ° C. in an air atmosphere, and after removing volatile components, put into a polyethylene container, add water, and cobblestone with a diameter of 5 mm on a pot rack. The fired powder was pulverized by rotating for 48 hours at a rotation speed of 150 rpm.

Next, after removing moisture from the pulverized baked powder on a hot plate heated to a temperature of 120 ° C., the baked powder is mixed with acetylene black as a conductive auxiliary agent, and 930 in a nitrogen atmosphere. Positive electrode active material according to Samples 1 to 7 having a composition shown in the column of “Composition of positive electrode active material” in Table 1 at a temperature of 20 ° C .: Li _{3 + x} V _{2− y My} (PO ₄ ) Got ₃ . The amount of acetylene black supported was 10 parts by weight with respect to 100 parts by weight of lithium-containing vanadium phosphate as the positive electrode active material.

  Table 1 shows the “ion radius of the substitution element”. For reference, the ionic radius of V is 0.54 to 0.64cm.

<Crystal structure analysis of positive electrode active material>
In order to analyze the crystal structure of the positive electrode active material according to each of Samples 1 to 7, measurement was performed by an XRD (X-ray diffractometer) at a scan speed of 4.0 ° / min and an angle measurement range of 10 ° to 60 °. .

As a result, a JCPDS (Joint Committee on Powder Diffraction Standards) card (card number 78-1106) of Li ₃ Fe ₂ (PO ₄ ) ₃ which is a NASICON type lithium-containing phosphate compound, excluding the positive electrode active material according to sample 4 It was confirmed that it was a lithium-containing compound having a NASICON structure, and formation of a heterogeneous phase was not confirmed.

On the other hand, the positive electrode active material according to Sample 4 was confirmed to contain Nb ₂ O ₅ as a heterogeneous phase in addition to the NASICON crystal phase.

<Preparation of solid electrolyte>
A lithium-containing germanium phosphate glass having a composition of Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ was prepared as a solid electrolyte. This lithium-containing germanium phosphate glass precipitates a NASICON type crystal phase represented by Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ by heat treatment.

<Preparation of positive electrode slurry and solid electrolyte slurry>
After dissolving the polyvinyl alcohol resin in an organic solvent containing ethanol, the positive electrode active material according to each of samples 1 to 7 is added thereto, and the mixture is rotated on a pot rack at a rotation speed of 150 rpm for 24 hours. A positive electrode active material slurry was prepared. Here, the weight ratio of the positive electrode active material to the polyvinyl alcohol resin was 80:20.

  Using the solid electrolyte glass powder described above, a solid electrolyte slurry was prepared through the same operation as that of the positive electrode active material slurry. A part of the solid electrolyte slurry thus obtained was used to obtain a positive electrode slurry as follows.

  The positive electrode active material slurry and the solid electrolyte slurry described above were mixed at a weight ratio of 50:50 to obtain a positive electrode slurry according to each of samples 1 to 7.

<Production of green sheet>
The positive electrode slurry according to each of Samples 1 to 7 was formed into a positive electrode green sheet having a thickness of 50 μm using a comma coater.

  On the other hand, the remaining part of the solid electrolyte slurry produced as described above was also formed into a solid electrolyte green sheet having a thickness of 100 μm using a comma coater.

<Production of sample battery>
A sample battery was fabricated as follows by combining the positive electrode green sheet and the solid electrolyte green sheet according to each of the above samples 1 to 7. Note that the sample battery is merely a battery for evaluating the positive electrode active material, and to be exact, it is not an all-solid battery in that an electrolyte is used in part.

  After the positive electrode green sheet and the solid electrolyte green sheet are punched into a circle having a diameter of 12 mm, the solid electrolyte green sheet is laminated on the positive electrode green sheet, and thermocompression-bonded at a temperature of 80 ° C. under a load of 1 ton Got. The weight of the positive electrode active material was about 2.5 mg.

  Next, the laminate was sandwiched between two alumina ceramic plates, fired at a temperature of 500 ° C. in a nitrogen atmosphere containing a slight amount of oxygen to remove organic substances, and then at 600 ° C. in a nitrogen atmosphere. And fired again to obtain a sintered body.

  The obtained sintered body was dried at a temperature of 100 ° C. to remove moisture, and then a metal Li plate serving as a negative electrode was laminated on the sintered body through a PMMA gel electrolyte impregnated with an electrolytic solution. And a 2032 type coin cell to obtain a sample battery according to each of samples 1 to 7.

<Evaluation of sample battery>
About the sample battery which concerns on each of the samples 1-7, the constant current constant voltage charge / discharge measurement was performed 100 cycles with the electric current of 50 microamperes in the range of voltage 3.0-4.7V.

  In each column of “1st cycle” and “100th cycle” in Table 2, the respective discharge capacities of the first cycle and the 10th cycle obtained by the constant current / constant voltage charge / discharge measurement are shown. . The discharge capacity is converted per weight of the positive electrode active material. In the column of “100th cycle / 1st cycle” in Table 2, the ratio [%] of the discharge capacity at the 100th cycle to the discharge capacity at the 1st cycle is shown.

  In the lithium-containing vanadium phosphate, the value of “100th cycle / 1st cycle” is high and excellent in all of Samples 1 to 6 except Sample 7 in which part of the V site was not substituted with another element. It was confirmed that it had cycle stability.

  In particular, Samples 1 to 3, 5, and 6 in which the “substitution amount y” is in the range of 0.01 to 0.2 have higher cycle stability, and the “substitution amount y” is 0.01 to 0.2. Samples 1, 2, 5 and 6 in a more limited range, such as 05, had even higher cycle stability.

  On the other hand, the “substitution amount y” is the highest at 0.25, and as described above, in the sample 4 configured using the positive electrode active material in which a heterogeneous phase was observed by XRD, the cycle stability was 7 Although better, results were lower than Samples 1-3, 5 and 6.

  As the “substitution amount y” increases, the discharge capacity at the first cycle tends to decrease. This is because the ratio of substitution elements not directly involved in the charge / discharge reaction (valence change) increases. Presumed to be.

  Next, with respect to the sample batteries according to each of the samples 2, 5, 6 and 7, the constant current and constant voltage charge / discharge measurement was performed at a current of 500 μA in the voltage range of 3.0 to 4.7 V, and the same as in the above case. The discharge capacity was determined by the method. The result is shown in the column of “500 μA” in Table 3. In the column of “50 μA” in Table 3, the value of “First cycle” in Table 2 obtained as described above is directly transferred.

  As can be seen from Table 3, Samples 2 and 5 constituted by using lithium-containing vanadium phosphate each substituted with Nb and Y having a larger ionic radius than V had a high discharge capacity even at a high current of 500 μA, and the output The characteristics were higher compared to sample 7 which was not substituted.

  On the other hand, the sample 6 constituted by using lithium-containing vanadium phosphate substituted with Al having a smaller ion radius than V had the same output characteristics as the sample 7 not substituted.

From the above, in addition to the effect of improving cycle stability by replacing a part of the V site of Li ₃ V ₂ (PO ₄ ) ₃ with a hexacoordinate element having an ionic radius larger than V in particular. It has become clear that the output of the solid state battery can be increased. This effect is not limited to the case where the substituting elements are Nb and Y. The same effect can be obtained by using other elements as long as the element has the same 6-coordinate as V and has an ionic radius larger than V. Can be easily estimated.

  Further, it has been clarified that when the element having a smaller ion radius than V is substituted, the output characteristics cannot be greatly improved.

In the above experimental example, the raw material powder of Li _1.5 Al _0.5 Ge _1.5 (PO ₄ ) ₃ as the solid electrolyte was an amorphous body, but the raw material powder is not limited to an amorphous body, The same effect can be obtained even with the body.

  Further, in this experimental example, the one having the crystal structure of lithium-containing vanadium phosphate was used at the time of slurry preparation, but a precursor that changes to the crystal structure of lithium-containing vanadium phosphate at the time of sintering the laminate was also used. Good.

  In the experimental examples, acetylene black was used as the carbon powder to be added at the time of firing lithium-containing vanadium phosphate. However, as the carbon powder, all of the carbon powder remained without being burned off during firing, and the electron conductivity after firing was reduced. Whatever you have can be used. Therefore, for example, an organic compound that exhibits electronic conductivity by firing may be used in place of the carbon powder.

DESCRIPTION OF SYMBOLS 1 Battery laminated body 2 Solid electrolyte layer 3 Positive electrode layer 4 Negative electrode layer

Claims (5)

A solid electrolyte layer, and a positive electrode layer and a negative electrode layer disposed across the solid electrolyte layer,
As a cathode active material includes a lithium-containing vanadium phosphate having the NASICON structure, the lithium-containing vanadium phosphate has the general _{formula: Li 3 + x V 2-} y M y (PO 4) 3 ( however, x: -0 .4 ≦ x ≦ 0.2, y: 0.00 <y ≦ 0.20, M: an element having 6-coordination having an ionic radius larger than V).
All solid battery. M is at least one selected from the group consisting of Mg, Ca, Sr, Sc, Y, Ti, Zr, Hf, Nb, Ta, Mo, Zn, Cd, In, Tl, Sn, Pb, Sb and Bi. The all-solid-state battery of Claim 1 which is these elements. The all-solid-state battery according to claim 1, wherein M is at least one element selected from the group consisting of Mg, Ca, Sr, Sc, Y, Zr, Hf, Zn, Cd, In, Sn, and Pb. . The all-solid-state battery according to claim 1, wherein y is 0.01 ≦ y ≦ 0.05. The all solid state battery according to any one of claims 1 to 4 , wherein at least the positive electrode layer and the solid electrolyte layer are joined by sintering.

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