JP2012248454A - Positive electrode, and all-solid nonaqueous electrolyte battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an all-solid nonaqueous electrolyte battery having a high discharge capacity and excellent cycle characteristics, and a positive electrode for the all-solid nonaqueous electrolyte battery.SOLUTION: An all-solid nonaqueous electrolyte battery 100 comprises a positive electrode 1, a negative electrode 2, and a solid electrolyte layer 3 intervening between the electrodes 1 and 2. The positive electrode 1 comprises a positive electrode active material layer 12 composed of an unsintered body containing a first active material powder, a second active material powder, and a conduction assistant powder. The first active material powder expands during discharges and shrinks during charges. On the other hand, the second active material powder shrinks during discharges and expands during charges. The percentage content of the conduction assistant powder in the positive electrode active material layer 12 is in the range of 1 to 5 mass%.

Description

  The present invention relates to an all-solid-type nonaqueous electrolyte battery including a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the electrodes, and a positive electrode used for the all-solid-type nonaqueous electrolyte battery.

  A nonaqueous electrolyte battery using lithium ions for battery reaction includes a positive electrode, a negative electrode, and an electrolyte layer interposed between these electrodes. Each electrode includes an active material layer containing an active material and a current collector having a current collecting function. Since this non-aqueous electrolyte battery exchanges Li ions between the positive electrode active material layer and the negative electrode active material layer during charge and discharge, these active material layers repeatedly expand and contract. When the electrode repeatedly expands and contracts, problems such as the active material layer peeling from the current collector occur. In particular, such a problem is remarkable in a positive electrode that is generally thicker than the negative electrode, and it has been desired to take measures.

  As measures against the above-described problems, for example, in Patent Documents 1 and 2, two types of active materials are contained in the positive electrode active material layer of a non-aqueous electrolyte battery using a non-aqueous electrolyte. Specifically, the positive electrode active material layer is composed of a positive electrode active material whose crystal structure expands during charging and a positive electrode active material whose crystal structure contracts during charging.

JP-A-5-82131 JP-A-8-50895

  However, in the technique described in the above-mentioned patent document, although the cycle characteristics are improved by suppressing the volume change of the active material layer itself, only a nonaqueous electrolyte battery with a low utilization rate of the positive electrode active material and a small discharge capacity can be produced. It was. If the active material that expands and the active material that contracts are mixed in the active material layer, the contact or bonding between the active materials becomes insufficient with charge / discharge of the battery, and the active material utilization rate It is guessed that this is because In Patent Document 2, sintering is performed so that the contact or bonding between the active materials is easily maintained even when the battery is charged / discharged. However, by sintering, at the interface between the two types of active materials. Interdiffusion occurs and the utilization factor of the active material decreases.

  In recent years, an all-solid-state nonaqueous electrolyte battery having an electrolyte layer as a solid has also been proposed in order to solve problems such as boiling of the electrolyte and liquid leakage in a nonaqueous electrolyte battery using a nonaqueous electrolyte. ing. As a result of the study by the present inventors, in the all solid-state non-aqueous electrolyte battery, when a positive electrode active material layer containing two kinds of active materials is applied, the problem that the utilization rate of the positive electrode active material is reduced is more remarkable. It became clear to become.

  The present invention has been made in view of the above circumstances, and one of its purposes is an all-solid-state non-aqueous electrolyte battery having a high discharge capacity and excellent cycle characteristics, and the all-solid-type non-aqueous electrolyte battery. It is in providing the positive electrode made.

(1) The present invention is a positive electrode used in an all-solid-state nonaqueous electrolyte battery including a positive electrode, a negative electrode, and a solid electrolyte layer interposed between these electrodes, the first active material powder and the second active material The positive electrode active material layer which consists of a non-sintered body containing a substance powder and a conductive support agent powder is provided. The first active material powder expands during discharge and contracts during charging. Conversely, the second active material powder shrinks during discharge and expands during charging. Moreover, content of the conductive support agent powder in a positive electrode active material layer is 1-5 mass%.

  By limiting the content (% by mass) of the conductive additive powder in the positive electrode active material layer, the discharge capacity is high, and the discharge capacity is excellent in cycle characteristics that do not easily decrease with charge / discharge of the battery. A water electrolyte battery can be obtained. The discharge capacity of the battery is increased by limiting the content of the conductive auxiliary powder, so that the conductive auxiliary powder has a particle size distribution that allows good conduction between the positive electrode active materials in the positive electrode active material layer. It is guessed that it is because there is. In addition, it is presumed that the cycle characteristics of the battery are excellent because the conductive auxiliary powder having a good particle size distribution maintains good conduction between the positive electrode active materials whose volume changes with charge and discharge. The

(2) As one embodiment of the positive electrode of the present invention, the first active material powder is a positive electrode active material having a spinel crystal structure, and the second active material powder is a positive electrode active material having a layered rock salt crystal structure.

  A positive electrode active material having a spinel crystal structure tends to expand during discharge and contract during charge, and is suitable as a first active material powder. Moreover, the positive electrode active material having a layered rock salt crystal structure tends to contract during discharge and expand during charge, and is suitable as a second active material powder.

(3) As one embodiment of the positive electrode of the present invention, the first active material powder having a spinel crystal structure contains Li, Ni, and Mn, and the second active material powder having a layered rock salt crystal structure is Li, And Co is preferably contained.

By using an active material containing the above element, the discharge capacity of the battery can be improved. As a typical first active material powder, LiNi _0.5 Mn _1.5 O _{4 and the} like can be mentioned. Further, as a typical second active material powder, and the like LiCoO _2.

(4) As one form of this invention positive electrode, it is preferable that the ratio of said 1st active material powder and 2nd active material powder is 1: 2 to 2: 1 by volume%.

  When the amount of the first active material powder in the positive electrode active material layer is significantly larger than that of the second active material powder or vice versa, it is difficult to obtain the effect of suppressing the volume change of the positive electrode active material layer due to charge / discharge. . On the other hand, when the mixing ratio of both active materials is in the above range, the above effect can be sufficiently obtained.

(5) The all solid-state nonaqueous electrolyte battery of the present invention is interposed between the electrodes of the present invention according to any one of the above (1) to (4), a negative electrode having a negative electrode active material layer, and these electrodes. And a solid electrolyte layer.

  The all-solid-state nonaqueous electrolyte battery of the present invention including the positive electrode of the present invention has an excellent discharge capacity and excellent cycle characteristics, and therefore can be used for various applications.

  When an all-solid-state nonaqueous electrolyte battery is produced using the positive electrode of the present invention, expansion / shrinkage of the entire positive electrode active material layer accompanying charge / discharge is suppressed, and conduction between the active materials in the positive electrode active material layer is good. Therefore, an all-solid-state nonaqueous electrolyte battery having a high discharge capacity and excellent cycle characteristics can be obtained.

It is a schematic block diagram of the nonaqueous electrolyte battery which concerns on embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<Overall configuration>
FIG. 1 is a schematic view showing an example of the all solid-state nonaqueous electrolyte battery of the present invention. The all-solid-state nonaqueous electrolyte battery 100 includes a positive electrode 1, a solid electrolyte layer (SE layer) 3, and a negative electrode 2. The positive electrode 1 further includes a positive electrode current collector 11 and a positive electrode active material layer 12, and the negative electrode 2 further includes a negative electrode current collector 21 and a negative electrode active material layer 22. The most characteristic feature of the battery 100 is that the positive electrode active material layer 12 of the positive electrode 1 includes two kinds of positive electrode active material powders and conductive additive powders, and the conductive auxiliary agent powders in the positive electrode active material layers 12. The content of is limited. Hereinafter, each component provided in the battery 100 will be described in detail.

≪Positive electrode≫
(Positive electrode current collector)
The positive electrode current collector 11 may be composed of only a conductive material, or may be composed of a conductive material film formed on an insulating substrate. In the latter case, the conductive material film functions as a current collector. As the conductive material, one selected from Al, Ni, alloys thereof, and stainless steel can be suitably used.

(Positive electrode active material layer)
The positive electrode active material layer 12 includes different types of first active material powder and second active material powder. The first active material powder is a positive electrode active material powder that expands during discharge and contracts during charging. As the first active material powder, a positive electrode active material having a spinel crystal structure, for example, a material containing Li and Mn (such as LiMn ₂ O ₄ ), a material containing Li, Ni, and Mn (LiNi _{0. 5} Mn _1.5 O ₄ etc.). In particular, the latter positive electrode active material is preferable in terms of improving the discharge capacity of the battery 100. Note that some of the elements in the above composition formula may be substituted with other elements, or there may be Li deficiency or O deficiency.

The second active material powder is a positive electrode active material powder that shrinks during discharge and expands during charging. As the second active material powder, a positive electrode active material having a layered rock salt type crystal structure, for example, a material containing Li and Ni (such as LiNiO ₂ ), a material containing Li and Mn (such as LiMnO ₂ ), Li and Examples thereof include those containing Co (LiCoO _{2 and the} like). In particular, a material containing Li and Co is preferable in terms of improving the discharge capacity of the battery 100. Note that some of the elements in the above composition formula may be substituted with other elements, or there may be Li deficiency or O deficiency.

  The ratio of the first active material powder to the second active material powder is preferably 1: 2 to 2: 1 by volume%. By setting it as such a ratio, the volume change of the positive electrode active material layer 12 can be suppressed effectively.

  Moreover, the positive electrode active material layer 12 contains a conductive additive powder. Content of the conductive support agent powder in the positive electrode active material layer 12 shall be 1-5 mass%. As the material of the conductive assistant powder, a carbon-based material such as carbon black or acetylene black can be used.

  In addition, the positive electrode active material layer 12 may contain a solid electrolyte powder or a binder. The solid electrolyte powder can improve Li ion conductivity in the positive electrode active material layer 12. As the solid electrolyte, the same solid electrolyte that can be used for the SE layer 3 described later can be used. The solid electrolyte used for the positive electrode active material layer 12 may be different from that used for the SE layer 3, but is preferably the same. The binder is used to bond powders constituting the positive electrode active material layer 12 when the positive electrode active material layer 12 is formed by compressing the powder. For example, polyvinylidene fluoride is used. be able to.

≪SE layer≫
The SE layer 3 is, for example, an oxide solid electrolyte such as LiPON, or an amorphous film of a sulfide-based solid electrolyte containing Li ₂ S and P ₂ S ₅ (may contain P ₂ O ₅ as necessary). Alternatively, it can be composed of a polycrystalline film or the like. The SE layer 3 can be formed by using a solid phase method or a vapor phase method.

≪Negative electrode≫
(Negative electrode current collector)
Similarly to the positive electrode current collector 11, the negative electrode current collector 21 may be composed of only a conductive material, or may be composed of a conductive material formed on an insulating substrate. As the conductive material, one selected from Cu, Ni, Fe, Cr, alloys thereof, and stainless steel can be suitably used.

(Negative electrode active material layer)
The negative electrode active material layer 22 can be made of, for example, metal Li or a compound capable of forming an alloy with metal Li. Examples of the latter include lithium titanate (such as Li ₄ Ti ₅ O ₁₂ or Li ₂ TiO ₃ ). Note that the negative electrode active material layer 22 made of metal Li can also serve as the negative electrode current collector 21, and in this case, the negative electrode current collector 21 can be omitted.

  Similarly to the positive electrode active material layer 12, the negative electrode active material layer 22 may contain a solid electrolyte powder, a conductive additive powder, a binder, and the like.

≪Others≫
When the positive electrode active material layer 12 includes an oxide active material and the SE layer 3 includes a sulfide solid electrolyte, a depletion layer is formed in the vicinity of the interface between the layers 12 and 3, thereby degrading the characteristics of the battery 100. There is. As a countermeasure, it is preferable to form an intermediate layer (not shown) between these layers 12 and 3 for suppressing the formation of a depletion layer. Examples of the material for the intermediate layer include LiTaO ₃ and LiNbO ₃ .

The all-solid-state nonaqueous electrolyte batteries of Samples 1 to 12 described below were prepared, and the cycle characteristics of each battery were evaluated by measuring the capacity retention rate (%) of each battery. The capacity retention rate was determined by dividing the discharge capacity at the 100th cycle by the discharge capacity at the first cycle. The charge / discharge conditions were a cut-off voltage of 3.0-4.2 V and a current density of 0.05 mA / cm ² .

<Samples 1 to 4>
The batteries of Samples 1 to 4 have the following configuration. The difference between the samples is only the content of the conductive additive powder contained in the positive electrode active material layer. Table 1 shows the content of the conductive additive powder in each sample. In Table 1, the content of the conductive additive powder is shown in both mass% and volume%.

[Positive electrode current collector] Stainless steel [Positive electrode active material layer] Positive electrode active material powder of LiCoO ₂ and LiNi _0.5 Mn _1.5 O ₄ mixed in a volume ratio of 50:50, solid electrolyte powder, The proportion of the positive electrode active material powder in the entire pressure-formed body containing the conductive auxiliary powder and the binder is 44% by volume, and the proportion of the solid electrolyte powder is 47% by volume.
Including [SE layer] ... vapor deposition film of sulfide solid electrolyte [negative electrode active material layer] ... negative electrode active material powder of the lithium titanate _{(Li 4 Ti 5 O 12)} , a solid electrolyte powder, conductive additive powder, and a binder The proportion of the negative electrode active material powder in the whole of the pressure-formed body is 45% by volume, and the proportion of the solid electrolyte powder is 45% by volume.
[Negative electrode current collector] ... Stainless steel

<Samples 5 to 12>
The difference between the batteries of Samples 5 to 12 and the batteries of Samples 1 to 4 described above is that the positive electrode active material contained in the positive electrode active material layer is one kind. Specifically, LiCoO ₂ was used as the positive electrode active material in the batteries of Samples 5 to 8, and LiNi _0.5 Mn _1.5 O ₄ was used as the positive electrode active material in the batteries of Samples 9 to 12. Table 1 shows the content of the conductive additive powder in the batteries of Samples 5 to 12.

From the results of Table 1, in the positive electrode active material layer, LiNi _0.5 Mn _1.5 O ₄ (first active material powder) that expands during discharging and contracts during charging, and contracts during discharging and expands during charging. It has been found that inclusion of LiCoO ₂ (second active material powder) can effectively suppress a decrease in the discharge capacity of the battery after 100 cycles. Furthermore, it has been found that by adjusting the content of the conductive additive powder in the positive electrode active material layer to 1 to 5% by mass, it is possible to almost eliminate the decrease in the discharge capacity of the battery after 100 cycles. In particular, good results were obtained by adjusting the content of the conductive additive powder to 3 to 5% by mass.

  The embodiment of the present invention is not limited to the above-described embodiment, and can be appropriately changed without departing from the gist of the present invention.

  The positive electrode of the present invention can be suitably used as a constituent member of an all-solid-state nonaqueous electrolyte battery having a high discharge capacity and excellent cycle characteristics. Moreover, the all solid-state nonaqueous electrolyte battery of the present invention can be suitably used as a power source for portable devices.

100 all solid-state nonaqueous electrolyte battery 1 positive electrode 11 positive electrode current collector 12 positive electrode active material layer 2 negative electrode 21 negative electrode current collector 22 negative electrode active material layer 3 solid electrolyte layer (SE layer)

Claims (5)

A positive electrode used in an all-solid-type nonaqueous electrolyte battery including a positive electrode, a negative electrode, and a solid electrolyte layer interposed between the electrodes,
A first active material powder that expands upon discharge and contracts upon charge;
A second active material powder that shrinks during discharge and expands during charge;
A positive electrode active material layer comprising a non-sintered body containing a conductive additive powder,
Content of the said conductive support agent powder in the said positive electrode active material layer is 1-5 mass%, The positive electrode characterized by the above-mentioned. The first active material powder is a positive electrode active material having a spinel crystal structure,
The positive electrode according to claim 1, wherein the second active material powder is a positive electrode active material having a layered rock salt crystal structure. The first active material powder having a spinel crystal structure contains Li, Ni, and Mn,
3. The positive electrode according to claim 2, wherein the second active material powder having a layered rock salt type crystal structure contains Li and Co. 4.   The ratio of said 1st active material powder and 2nd active material powder is 1: 2 to 2: 1 by volume%, The positive electrode of any one of Claims 1-3 characterized by the above-mentioned. The positive electrode according to any one of claims 1 to 4,
A negative electrode having a negative electrode active material layer;
A solid electrolyte layer interposed between these electrodes;
An all-solid-state non-aqueous electrolyte battery comprising:

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