JP2022091637A - Negative electrode for nonaqueous electrolyte electricity-storage device, nonaqueous electrolyte electricity-storage device, and manufacturing method of them - Google Patents

Abstract

To provide a negative electrode capable of suppressing the deterioration of a discharge capacity and a coulomb efficiency of a nonaqueous electrolyte electricity-storage device due to a discharge cycle.SOLUTION: According to an embodiment of the present invention, a negative electrode for a nonaqueous electrolyte electricity-storage device includes: a negative electrode active material layer containing a metal lithium; and a porous layer laminated on a front surface of the negative electrode active material layer and containing inorganic particles, in which a void ratio of the porous layer is 50% or more.SELECTED DRAWING: Figure 1

Description

The present invention relates to a negative electrode for a non-aqueous electrolyte storage element, a non-aqueous electrolyte storage element, and a method for manufacturing the same.

Non-aqueous electrolyte secondary batteries typified by lithium ion secondary batteries are widely used in personal computers, electronic devices such as communication terminals, automobiles, etc. due to their high energy density. The non-aqueous electrolyte secondary battery generally has a pair of electrodes electrically separated by a separator and a non-aqueous electrolyte interposed between the electrodes, and transfers ions between the two electrodes. It is configured to charge and discharge. In addition, capacitors such as lithium ion capacitors and electric double layer capacitors are also widely used as non-aqueous electrolyte storage elements other than non-aqueous electrolyte secondary batteries. Metallic lithium is known as a negative electrode active material having a high energy density used in a non-aqueous electrolyte power storage element (see Patent Documents 1 and 2).

Japanese Unexamined Patent Publication No. 2016-100065 Japanese Unexamined Patent Publication No. 07-24599

In the non-aqueous electrolyte power storage element, it is desirable that the charge / discharge performance such as the discharge capacity and the Coulomb efficiency is maintained in good condition from the initial state even if the charge / discharge cycle is repeated. However, especially when the negative electrode is a non-aqueous electrolyte power storage element containing metallic lithium, the performance tends to be significantly deteriorated due to the charge / discharge cycle.

The present invention has been made based on the above circumstances, and an object thereof is a negative electrode containing metallic lithium, and a decrease in discharge capacity and Coulomb efficiency of a non-aqueous electrolyte storage element due to a charge / discharge cycle. It is an object of the present invention to provide a negative electrode capable of suppressing the above-mentioned factors, a non-aqueous electrolyte power storage element provided with such a negative electrode, and a method for manufacturing the same.

One aspect of the present invention has a negative electrode active material layer containing metallic lithium and a porous layer containing inorganic particles laminated on the surface of the negative electrode active material layer, and the void ratio of the porous layer. Is a negative electrode for a non-aqueous electrolyte power storage element having a value of 50% or more.

Another aspect of the present invention is to form a porous layer having a porosity of 50% or more on the surface of the negative electrode active material layer containing metallic lithium by using a porous layer forming material containing inorganic particles. It is a method of manufacturing a negative electrode for a non-aqueous electrolyte power storage element provided.

Another aspect of the present invention is a non-aqueous electrolyte power storage element including a negative electrode according to the present invention.

Another aspect of the present invention comprises a negative electrode and a separator, wherein the negative electrode is a negative electrode active material layer containing metallic lithium and a porous layer containing inorganic particles laminated on the surface of the negative electrode active material layer. The non-aqueous electrolyte storage element has a void ratio of the porous layer of the negative electrode higher than that of the separator.

Another aspect of the present invention comprises producing a non-aqueous electrolyte power storage element using the negative electrode according to one aspect of the present invention or the negative electrode obtained by the method for manufacturing a negative electrode according to one aspect of the present invention. This is a method for manufacturing a water electrolyte storage element.

Another aspect of the present invention comprises manufacturing a non-aqueous electrolyte power storage element using a negative electrode and a separator, wherein the negative electrode is a negative electrode active material layer containing metallic lithium and the surface of the negative electrode active material layer. This is a method for manufacturing a non-aqueous electrolyte power storage element, which has a porous layer containing inorganic particles laminated in the above, and the void ratio of the porous layer of the negative electrode is higher than the void ratio of the separator.

According to one aspect of the present invention, a negative electrode containing metallic lithium, which can suppress a decrease in discharge capacity and Coulomb efficiency of a non-aqueous electrolyte storage element due to a charge / discharge cycle, such a negative electrode. It is possible to provide a non-aqueous electrolyte power storage element provided, and a method for producing these.

FIG. 1 is an external perspective view showing a non-aqueous electrolyte power storage element according to an embodiment of the present invention. FIG. 2 is a schematic view showing a power storage device configured by assembling a plurality of non-aqueous electrolyte power storage elements according to an embodiment of the present invention. FIG. 3A is a graph showing changes in the capacity retention rate of the non-aqueous electrolyte power storage element of Example 1 for each cycle. FIG. 3B is a graph showing changes in the Coulomb efficiency (Coulombic efficiency) of the non-aqueous electrolyte power storage element of Example 1 for each cycle. FIG. 4A is a graph showing changes in the capacity retention rate of the non-aqueous electrolyte power storage element of Example 2 for each cycle. FIG. 4B is a graph showing changes in the Coulomb efficiency of the non-aqueous electrolyte power storage element of Example 2 for each cycle. FIG. 5A is a graph showing changes in the capacity retention rate of the non-aqueous electrolyte power storage element of Example 3 for each cycle. FIG. 5B is a graph showing changes in the Coulomb efficiency of the non-aqueous electrolyte power storage element of Example 3 for each cycle. FIG. 6A is a graph showing changes in the capacity retention rate of the non-aqueous electrolyte power storage element of Example 4 for each cycle. FIG. 6B is a graph showing changes in the Coulomb efficiency of the non-aqueous electrolyte power storage element of Example 4 for each cycle. FIG. 7A is a graph showing changes in the capacity retention rate of the non-aqueous electrolyte power storage element of Example 5 for each cycle. FIG. 7B is a graph showing changes in the Coulomb efficiency of the non-aqueous electrolyte power storage element of Example 5 for each cycle. FIG. 8A is a graph showing changes in the capacity retention rate of the non-aqueous electrolyte power storage element of Example 6 for each cycle. FIG. 8B is a graph showing changes in the Coulomb efficiency of the non-aqueous electrolyte power storage element of Example 6 for each cycle. FIG. 9A is a graph showing changes in the capacity retention rate of the non-aqueous electrolyte power storage element of Example 7 for each cycle. FIG. 9B is a graph showing changes in the Coulomb efficiency of the non-aqueous electrolyte power storage element of Example 7 for each cycle. FIG. 10A is a graph showing changes in the capacity retention rate of the non-aqueous electrolyte power storage element of Example 8 for each cycle. FIG. 10B is a graph showing changes in the Coulomb efficiency of the non-aqueous electrolyte power storage element of Example 8 for each cycle. FIG. 11A is a graph showing changes in the capacity retention rate of the non-aqueous electrolyte power storage element of Example 9 for each cycle. FIG. 11B is a graph showing changes in the Coulomb efficiency of the non-aqueous electrolyte power storage element of Example 9 for each cycle. FIG. 12A is a graph showing changes in the capacity retention rate of the non-aqueous electrolyte power storage element of Comparative Example 1 for each cycle. FIG. 12B is a graph showing changes in the Coulomb efficiency of the non-aqueous electrolyte power storage device of Comparative Example 1 for each cycle. FIG. 13A is a graph showing changes in the capacity retention rate of the non-aqueous electrolyte power storage element of Comparative Example 2 for each cycle. FIG. 13B is a graph showing changes in the Coulomb efficiency of the non-aqueous electrolyte power storage element of Comparative Example 2 for each cycle.

First, an outline of a negative electrode, a method for manufacturing a negative electrode, a non-aqueous electrolyte power storage element, and a method for manufacturing a non-water electrolyte power storage element disclosed in the present specification will be described.

The negative electrode according to one aspect of the present invention has a negative electrode active material layer containing metallic lithium and a porous layer containing inorganic particles laminated on the surface of the negative electrode active material layer, and the porous layer. It is a negative electrode for a non-aqueous electrolyte power storage element having a void ratio of 50% or more.

The negative electrode is a negative electrode containing metallic lithium, and can suppress a decrease in discharge capacity and Coulomb efficiency of the non-aqueous electrolyte storage element due to a charge / discharge cycle. The reason for this is not clear, but the following reasons are presumed. Generally, in a non-aqueous electrolyte power storage element provided with a negative electrode containing metallic lithium, metallic lithium precipitates in a dendritic shape on the surface of the negative electrode during charging (hereinafter, metallic lithium in a dendritic form is referred to as "dendrite". .), This dendrite grows with repeated charging and discharging. Then, it is considered that the grown dendrite penetrates the separator and comes into contact with the positive electrode to cause a slight short circuit, which causes a decrease in discharge capacity and Coulomb efficiency. Specifically, in a non-aqueous electrolyte storage element provided with a negative electrode containing metallic lithium, lithium ions are released from the positive electrode during charging and diffuse or migrate in the non-aqueous electrolyte in the pores of the porous separator. When the lithium ion is deposited as metallic lithium after reaching the surface of the negative electrode, the concentration of lithium ions supplied to the portion of the surface of the negative electrode active material facing the pores of the separator is higher than that of the portion facing other than the pores of the separator. Since it is relatively high, it is considered that the precipitation of metallic lithium is likely to occur non-uniformly in the plane direction in this portion, and the dendrite is also likely to grow. On the other hand, in the case of the non-aqueous electrolyte power storage element provided with the negative electrode according to one aspect of the present invention, the non-water in the pores of the separator is provided by providing the porous layer having a high void ratio on the surface of the negative electrode active material layer. The lithium ions that have diffused or migrated in the electrolyte further diffuse or migrate in the non-aqueous electrolyte in the pores of the porous layer, so that the concentration of the supplied lithium ions is made uniform in the plane direction and the negative electrode active material. Reach the layer surface. Therefore, it is considered that the precipitation of metallic lithium is less uneven and the growth of dendrites is suppressed. In particular, in general, the separator is often formed into a porous shape by stretching, and the pores of the separator tend to be formed relatively linearly with respect to the thickness direction, that is, two-dimensionally. On the other hand, the porous layer containing the inorganic particles is formed in a shape in which the pores are three-dimensionally expanded by the gaps between the inorganic particles. Therefore, the lithium ions that have diffused or migrated in the non-aqueous electrolyte in the pores of the separator with a relatively linear and non-uniform distribution in the plane direction are the non-water in the pores of the porous layer of the negative electrode. By diffusing or migrating in the electrolyte, the concentration is made uniform in the plane direction. From the above, in the non-aqueous electrolyte power storage element provided with the negative electrode according to one aspect of the present invention, the growth of dendrites accompanying the charge / discharge cycle is suppressed, and as a result, the decrease in discharge capacity and Coulomb efficiency is suppressed. It is presumed that.

The "porosity" of the porous layer is a value calculated by the following formula (I) from the average thickness of the porous layer, the mass per unit area, and the true density. The "average thickness" of the porous layer is an average value of the thickness measured at any five locations. The "true density" of the porous layer is a value calculated from the true density and composition ratio of each material constituting the porous layer.
Porosity (%) = 100-W / (ρ ₁ x t) x 100 ... (I)
W: Mass per unit area of the porous layer [g · cm ^-2 ]
ρ ₁ : True density of the porous layer [g · cm ^-3 ]
t: Average thickness of the porous layer [cm]

The porosity of the porous layer is preferably 80% or more. When the porosity of the porous layer is further increased in this way, the concentration of lithium ions supplied to the surface of the negative electrode active material layer by the porous layer is made more uniform in the planar direction, and the non-aqueous electrolyte storage associated with the charge / discharge cycle is stored. It is possible to further suppress the decrease in the discharge capacity and the Coulomb efficiency of the element.

The average particle size of the inorganic particles is preferably 50 nm or less. It is more preferable that the average particle size of the inorganic particles is 20 nm or less. When the average particle size of the inorganic particles in the porous layer is small, the concentration of lithium ions supplied to the surface of the negative electrode active material layer by the porous layer is made more uniform in the planar direction, and the non-aqueous electrolyte storage associated with the charge / discharge cycle is stored. It is possible to further suppress the decrease in the discharge capacity and the Coulomb efficiency of the element.

The "average particle size" of the inorganic particles means a value obtained by the following method from the specific surface area and the true density of the inorganic particles. The "specific surface area" of the inorganic particles is determined by the following method. First, the pore size distribution of the inorganic particles is measured by using the nitrogen adsorption method. This measurement can be performed by "autosorb iQ" manufactured by Quantachrome. Five points are extracted from the region of P / P0 = 0.06 to 0.3 of the obtained adsorption isotherm, a BET plot is performed, and the specific surface area (BET specific surface area) is calculated from the y-intercept and slope of the straight line. From the calculated specific surface area of the inorganic particles and the true density of the inorganic particles, the average particle size is obtained by the following formula (II).
D = 6 / (ρ ₂ × s) ・ ・ ・ (II)
D: Average particle size of the inorganic particles ρ ₂ : True density of the inorganic particles s: Specific surface area of the inorganic particles The average particle size of the inorganic particles based on the above measurement is obtained from the scanning electron microscope (SEM) image of the porous layer. It should be almost the same as the D50 particle size (value at which the volume-based integrated distribution is 50%) obtained from the particle size measured by extracting 100 inorganic particles while avoiding extremely large and extremely small inorganic particles. Has been confirmed. The particle size of each inorganic particle in the measurement from this SEM image is calculated as a ferret diameter, and the volume of each inorganic particle is calculated as a sphere having a ferret diameter as a diameter.

It is preferable that the porous layer is substantially composed of only the inorganic particles. In such a case, it is possible to further suppress the decrease in the discharge capacity and the Coulomb efficiency of the non-aqueous electrolyte power storage element due to the charge / discharge cycle. The reason for this is not clear, but if other components such as a binder are present in the porous layer, the other components such as the binder are reduced and decomposed, so that a part of the porous layer is disintegrated and the metal is locally present. As a result of the formation of a portion where lithium is likely to precipitate, it is considered that the growth of dendrite is promoted in this portion. On the other hand, when the porous layer is substantially composed of only inorganic particles, the porous layer is maintained without being reduced and decomposed, and the growth of dendrites can be suppressed. It is presumed that the decrease in discharge capacity and Coulomb efficiency is further suppressed.

The fact that the porous layer is substantially composed of only inorganic particles means that other components may be contained in a trace amount in addition to the inorganic particles. The fact that the porous layer is substantially composed of only inorganic particles means that, for example, the content of the inorganic particles in the porous layer is 99% by mass or more, and the content is preferably 99.9% by mass or more. ..

In the method for producing a negative electrode according to one aspect of the present invention, a porous layer having a porosity of 50% or more is formed on the surface of a negative electrode active material layer containing metallic lithium by using a porous layer forming material containing inorganic particles. It is a method of manufacturing a negative electrode for a non-aqueous electrolyte power storage element that comprises forming.

According to the method for manufacturing the negative electrode, it is possible to manufacture a negative electrode containing metallic lithium and capable of suppressing a decrease in discharge capacity and Coulomb efficiency of a non-aqueous electrolyte storage element due to a charge / discharge cycle. ..

The non-aqueous electrolyte storage element according to one aspect of the present invention is the non-aqueous electrolyte storage element (A) provided with the negative electrode according to one aspect of the present invention.

Since the non-aqueous electrolyte power storage element (A) includes the negative electrode according to one aspect of the present invention, the decrease in discharge capacity and coulombic efficiency due to the charge / discharge cycle is suppressed.

The non-aqueous electrolyte power storage element according to another aspect of the present invention includes a negative electrode and a separator, and the negative electrode is an inorganic layer in which the negative electrode active material layer containing metallic lithium and the surface of the negative electrode active material layer are laminated. The non-aqueous electrolyte power storage element (B) has a porous layer containing particles, and the void ratio of the porous layer of the negative electrode is higher than the void ratio of the separator.

Although the non-aqueous electrolyte power storage element (B) also has a negative electrode containing metallic lithium, the decrease in discharge capacity and Coulomb efficiency due to the charge / discharge cycle is suppressed. The reason why such an effect is exhibited is that, as in the case of using the negative electrode according to the embodiment of the present invention described above, the non-aqueous electrolyte in the pores of the separator is diffused in a non-uniform distribution in the plane direction. Alternatively, it is presumed that the migrating lithium ions diffuse or migrate in the non-aqueous electrolyte in the pores of the porous layer having a relatively high void ratio, so that the concentration is made uniform in the plane direction. To.

The "porosity" of the separator is a value calculated by the same method as the above-mentioned porosity of the porous layer.

In the non-aqueous electrolyte storage element (A) and the non-aqueous electrolyte storage element (B), it is preferable that the positive electrode potential at the end-of-charge voltage during normal use is 4.5 V (vs. Li / Li ⁺ ) or more. By setting the positive electrode potential at the end-of-charge voltage during normal use to 4.5 V (vs. Li / Li ⁺ ) or more, the discharge capacity of the non-aqueous electrolyte power storage element can be increased and the energy density can be increased.

The term "normal use" refers to the case where the non-aqueous electrolyte power storage element is used by adopting the charging conditions recommended or specified for the non-water electrolyte power storage element. For example, when a charger for a non-aqueous electrolyte power storage element is prepared, it means a case where the charger is applied to use the non-water electrolyte power storage element.

The method for manufacturing a non-aqueous electrolyte power storage element according to one aspect of the present invention uses a negative electrode according to one aspect of the present invention or a negative electrode obtained by the method for manufacturing a negative electrode according to one aspect of the present invention. It is a method (A) for manufacturing a non-aqueous electrolyte power storage element comprising manufacturing the device.

The method for manufacturing a non-aqueous electrolyte power storage element according to another aspect of the present invention comprises manufacturing a non-aqueous electrolyte power storage element using a negative electrode and a separator, and the negative electrode is a negative electrode active material containing metallic lithium. A non-aqueous electrolyte having a layer and a porous layer containing inorganic particles laminated on the surface of the negative electrode active material layer, and the void ratio of the porous layer of the negative electrode is higher than the void ratio of the separator. This is a method (B) for manufacturing a power storage element.

According to the method for manufacturing the non-aqueous electrolyte power storage element (A) and the method for manufacturing the non-water electrolyte power storage element (B), the non-aqueous electrolyte power storage element is provided with a negative electrode containing metallic lithium and is associated with a charge / discharge cycle. It is possible to manufacture a non-aqueous electrolyte power storage element in which a decrease in discharge capacity and Coulomb efficiency is suppressed.

Hereinafter, the negative electrode, the method for manufacturing the negative electrode, the non-aqueous electrolyte power storage element, and the method for manufacturing the non-water electrolyte power storage element according to the embodiment of the present invention will be described in order.

<Negative electrode>
The negative electrode according to the embodiment of the present invention has a negative electrode base material, a negative electrode active material layer, and a porous layer. The negative electrode has a structure in which a negative electrode base material, a negative electrode active material layer, and a porous layer are laminated in this order. The negative electrode active material layer may be laminated directly on both sides of the negative electrode base material or via an intermediate layer. When the negative electrode active material layer is provided on both sides of the negative electrode base material, it is preferable that the porous layer is provided on the surface of each negative electrode active material layer on the side not facing the negative electrode base material. The negative electrode is used for a non-aqueous electrolyte power storage element.

The negative electrode substrate has conductivity. "Having conductivity" means that the volume resistivity measured according to JIS-H-0505 (1975) is ¹⁰⁷ Ω · cm or less, and "non-conductive" means. It means that the volume resistivity is more than ¹⁰⁷ Ω · cm. As the material of the negative electrode base material, metals such as copper, nickel, stainless steel and nickel-plated steel, alloys thereof, carbonaceous materials and the like are used, and copper or copper alloy is preferable. In addition, examples of the form of forming the negative electrode base material include foils and thin-film deposition films, and foils are preferable from the viewpoint of cost. That is, a copper foil is preferable as the negative electrode base material. Examples of the copper foil include rolled copper foil and electrolytic copper foil.

The average thickness of the negative electrode substrate is preferably 2 μm or more and 35 μm or less, more preferably 3 μm or more and 30 μm or less, further preferably 4 μm or more and 25 μm or less, and particularly preferably 5 μm or more and 20 μm or less. By setting the average thickness of the negative electrode base material within the above range, it is possible to increase the energy density per volume of the non-aqueous electrolyte power storage element while increasing the strength of the negative electrode base material. The "average thickness" of the negative electrode base material means a value obtained by dividing the punched mass when punching a negative electrode base material having a predetermined area by the true density and the punched area of the negative electrode base material. The same applies to the average thickness of the negative electrode active material layer and the positive electrode base material, which will be described later.

The intermediate layer is a coating layer on the surface of the negative electrode base material, and contains a conductive agent such as carbon particles to reduce the contact resistance between the negative electrode base material and the negative electrode active material layer. The composition of the intermediate layer is not particularly limited, and can be formed by, for example, a composition containing a binder and a conductive agent.

The negative electrode active material layer contains metallic lithium. Metallic lithium is a component that functions as a negative electrode active material. The metallic lithium may exist as pure metallic lithium consisting substantially only of lithium elements, or may exist as a lithium alloy containing other metallic elements. Examples of the lithium alloy include lithium silver alloy, lithium zinc alloy, lithium calcium alloy, lithium aluminum alloy, lithium magnesium alloy, lithium indium alloy and the like. The lithium alloy may contain a plurality of metal elements other than lithium.

The negative electrode active material layer may be a layer substantially composed only of metallic lithium. The content of metallic lithium in the negative electrode active material layer may be 90% by mass or more, 99% by mass or more, or 100% by mass.

The negative electrode active material layer may be a metallic lithium foil or a lithium alloy foil. The negative electrode active material layer may be a non-porous layer (solid layer). Further, the negative electrode active material layer may be a porous layer having particles containing metallic lithium. The average thickness of the negative electrode active material layer is preferably 5 μm or more and 1,000 μm or less, more preferably 10 μm or more and 500 μm or less, and further preferably 30 μm or more and 300 μm or less.

The porous layer is a porous layer laminated on the surface of the negative electrode active material layer. The lower limit of the porosity of the porous layer is 50%, preferably 60%, more preferably 70%, even more preferably 75%, even more preferably 80%, and even more preferably 85%. Further, the porosity of the porous layer is preferably more than 70% or more than 80%. By setting the void ratio of the porous layer to the above lower limit or higher, the concentration of lithium ions diffusing or migrating in the non-aqueous electrolyte in the pores of the porous layer is sufficiently made uniform in the planar direction, and the negative electrode is provided. It is possible to suppress a decrease in discharge capacity and Coulomb efficiency due to the charge / discharge cycle of the non-aqueous electrolyte power storage element. On the other hand, the upper limit of the porosity of the porous layer is preferably 98%, more preferably 95%, and even more preferably 92%. By setting the porosity of the porous layer to the above upper limit or less, the porous layer can have sufficient strength and the like. The porosity of the porous layer may be in the range of one of the above-mentioned lower limit or more and one of the above-mentioned lower limit or less.

The porous layer contains inorganic particles. Inorganic particles refer to particles composed of an inorganic material. The inorganic material may be either an inorganic compound or a simple substance of an inorganic element, but an inorganic compound is preferable. Examples of the inorganic compound include oxides such as silicon oxide, aluminum oxide, titanium oxide, zinc oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide and aluminosilicate; magnesium hydroxide, calcium hydroxide and water. Hydroxides such as aluminum oxide; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ion crystals such as calcium fluoride, barium fluoride and barium titanate Examples include mineral resource-derived substances such as montmorillonite, boehmite, apatite, mulite, spinel, and quartz, or man-made products thereof. These inorganic materials may be present in the porous layer as reaction products that have reacted with, for example, metallic lithium. Among these inorganic materials, oxides are preferable, silicon oxide, aluminum oxide and titanium oxide are more preferable, and silicon oxide and aluminum oxide are further preferable. As the inorganic particles, a single substance or a complex of these inorganic materials may be used alone, or two or more kinds thereof may be mixed and used. The surface of the inorganic particles may be coated with another material.

The average particle size of the inorganic particles is preferably 1 nm or more and 1 mm or less, more preferably 2 nm or more and 200 nm or less, further preferably 3 nm or more and 50 nm or less, further preferably 4 nm or more and 30 nm or less, further preferably 5 nm or more and 25 nm or less, further preferably 6 nm. More than 20 nm or less is more preferable. By setting the average particle size of the inorganic particles to the above upper limit or less, the concentration of lithium ions diffusing or migrating in the non-aqueous electrolyte in the pores of the porous layer is particularly sufficiently uniformed in the planar direction, and the negative electrode is set. It is possible to further suppress the decrease in discharge capacity and Coulomb efficiency associated with the charge / discharge cycle of the non-aqueous electrolyte power storage element provided. On the other hand, by setting the average particle size of the inorganic particles to the above lower limit or higher, the diffusivity or migrating property of lithium ions in the non-aqueous electrolyte in the pores of the porous layer is enhanced, and the charge / discharge performance of the non-aqueous electrolyte power storage element is enhanced. Can be enhanced.

The specific surface area of the inorganic particles is preferably 1 m ² / g or more and 500 m ² / g or less, more preferably 10 m ² / g or more and 400 m ² / g or less, further preferably 30 m ² / g or more and 300 m ² / g or less, and 70 m. More preferably, it is ² / g or more and 250 m ² / g or less. By using the inorganic particles having such a specific surface area, it is possible to further suppress the decrease in discharge capacity and Coulomb efficiency associated with the charge / discharge cycle of the non-aqueous electrolyte power storage element provided with the negative electrode. In particular, when the specific surface area of the inorganic particles is equal to or higher than the above lower limit, the concentration of lithium ions diffusing or migrating the non-aqueous electrolyte in the pores of the porous layer is made more uniform in the planar direction, and as a result, the negative electrode is concerned. It is possible to further suppress the decrease in discharge capacity and Coulomb efficiency associated with the charge / discharge cycle of the non-aqueous electrolyte power storage element.

The porous layer may contain components other than the inorganic particles. Examples of such other components include a binder, a component derived from the dispersion medium used when forming the porous layer, and the like. However, in order to enhance the effect of suppressing the decrease in discharge capacity and Coulomb efficiency associated with the charge / discharge cycle of the non-aqueous electrolyte power storage element provided with the negative electrode, it is preferable that the porous layer is substantially composed of only inorganic particles. .. Specifically, the content of the inorganic particles in the porous layer may be, for example, 80% by mass or more or 90% by mass or more, preferably 99% by mass or more, and more preferably 99.9% by mass or more. In the negative electrode, van der Waals force, anchor effect, welding, or some other attractive force or bond occurs between the metallic lithium in the negative electrode active material layer and the inorganic particles in the porous layer and between the inorganic particles. Therefore, it is considered that the porous layer is laminated on the surface of the negative electrode active material layer even when the porous layer is substantially composed of only inorganic particles.

Further, it is preferable that the porous layer is substantially composed of only inorganic substances. The inorganic substances also include the inorganic particles. The content of the inorganic substance in the porous layer is preferably 90% by mass or more, more preferably 99% by mass or more, still more preferably 99.9% by mass or more. When the porous layer is substantially composed of only inorganic substances, the porous layer is maintained without being reduced and decomposed, and the growth of dendrites can be suppressed. It is presumed that the decrease in the amount of water is suppressed.

The average thickness of the porous layer is preferably 1 μm or more and 100 μm or less, more preferably 2 μm or more and 50 μm or less, further preferably 2 μm or more and 40 μm or less, still more preferably 5 μm or more and 30 μm or less, and further preferably 10 μm or more and 20 μm or less. Sometimes. By setting the average thickness of the porous layer to be equal to or greater than the above lower limit or exceeding the above lower limit, the diffusivity of lithium ions transmitted through the porous layer is enhanced, and as a result, the charge / discharge cycle of the non-aqueous electrolyte power storage element provided with the negative electrode is enhanced. It is possible to further suppress the decrease in discharge capacity and Coulomb efficiency due to the above. On the other hand, by setting the average thickness of the porous layer to the above upper limit or less, it is possible to increase the energy density of the negative electrode and the non-aqueous electrolyte power storage element provided with the negative electrode.

<Manufacturing method of negative electrode>
In the method for manufacturing a negative electrode according to an embodiment of the present invention, a porous layer having a porosity of 50% or more is provided on the surface of a negative electrode active material layer containing metallic lithium by using a porous layer forming material containing inorganic particles. Prepare to form. The manufacturing method can be manufactured by the same method as the conventionally known negative electrode for a non-aqueous electrolyte power storage element, except that the porous layer is formed in this way. For example, prior to the formation of the porous layer, the negative electrode active material layer containing metallic lithium is laminated on the negative electrode base material directly or via an intermediate layer and pressed to form the porous layer. A negative electrode in the previous state can be obtained. The negative electrode active material layer containing metallic lithium is the same as the negative electrode active material layer provided in the negative electrode according to the above-described embodiment of the present invention, and may be a metallic lithium foil or a lithium alloy foil.

The porous layer forming material may be, for example, a dispersion liquid containing inorganic particles and a dispersion medium. The porous layer can be formed by applying such a porous layer forming material to the surface of the negative electrode active material layer and drying the dispersion medium. The porous layer may be formed by a method other than coating, such as dipping. Further, a porous layer forming material composed of only inorganic particles may be used, and the porous layer may be formed by dry coating or the like.

The porosity of the porous layer can be adjusted by adjusting the average particle size, specific surface area, etc. of the inorganic particles used. However, for example, even when inorganic particles having the same specific surface area are used, the porosity of the formed porous layer may be different depending on the shape of the inorganic particles, other manufacturing conditions, and the like. Further, when the porous layer forming material does not contain solids other than inorganic particles, the porosity of the obtained porous layer tends to increase.

The specific form and the preferred form of the porous layer formed by the production method are the same as those provided in the negative electrode according to the above-described embodiment of the present invention.

<Non-water electrolyte power storage element>
The non-aqueous electrolyte power storage element according to one embodiment of the present invention includes a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte. Hereinafter, as an example of the non-aqueous electrolyte power storage element, a non-aqueous electrolyte secondary battery (hereinafter, also simply referred to as “secondary battery”) will be described. The positive electrode and the negative electrode are alternately superimposed by laminating or winding via a separator. That is, a laminated or wound type electrode body is formed by the positive electrode, the negative electrode and the separator. The electrode body is housed in a container, and the container is filled with a non-aqueous electrolyte. The non-aqueous electrolyte is interposed between the positive electrode and the negative electrode, and is also impregnated with the separator. Further, as the container, a known metal container, resin container, or the like usually used as a container for a secondary battery can be used.

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

The positive electrode substrate has conductivity. The positive electrode base material may have the same structure as the negative electrode base material, but as the material, a metal such as aluminum, titanium, tantalum, or stainless steel or an alloy thereof is used. Among these, aluminum and aluminum alloys are preferable from the viewpoint of the balance between potential resistance, high conductivity and cost. Further, examples of the formation form of the positive electrode base material include foil, a vapor-deposited film, and the like, and foil is preferable from the viewpoint of cost. That is, aluminum foil is preferable as the positive electrode base material. Examples of aluminum or aluminum alloy include A1085 and A3003 specified in JIS-H-4000 (2014).

The average thickness of the positive electrode substrate is preferably 3 μm or more and 50 μm or less, more preferably 5 μm or more and 40 μm or less, further preferably 8 μm or more and 30 μm or less, and particularly preferably 10 μm or more and 25 μm or less. By setting the average thickness of the positive electrode base material in the above range, it is possible to increase the energy density per volume of the secondary battery while increasing the strength of the positive electrode base material.

The positive electrode active material layer is a layer formed from a so-called positive electrode mixture containing a positive electrode active material. The positive electrode mixture forming the positive electrode active material layer may contain an optional component such as a conductive agent, a binder, a thickener, and a filler, if necessary.

The positive electrode active material can be appropriately selected from known positive electrode active materials. As the positive electrode active material for a lithium secondary battery, a material capable of occluding and releasing lithium ions is usually used. Examples of the positive electrode active material include a lithium transition metal composite oxide having an α-NaFeO type ₂ crystal structure, a lithium transition metal composite oxide having a spinel type crystal structure, a polyanionic compound, a chalcogen compound, sulfur and the like. Examples of the lithium transition metal composite oxide having an α-NaFeO type ₂ crystal structure include Li [Li _x Ni _1-x ] O ₂ (0 ≦ x <0.5) and Li [Li _x Ni _γ Co _1-x . _-Γ ] O ₂ (0 ≦ x <0.5, 0 <γ <1), Li [Li _x Co _1-x ] O ₂ (0 ≦ x <0.5), Li [Li _x Ni _γ Mn ₁ ) -X _-γ ] O ₂ (0≤x <0.5, 0 <γ <1), Li [Li _x Ni _γ Mn _β Co _1-x-γ-β ] O ₂ (0≤x <0.5) , 0 <γ, 0 <β, 0.5 <γ + β <1), Li [Li _x Ni _γ Co _β Al _1-x-γ-β ] O ₂ (0 ≦ x <0.5, 0 <γ, Examples thereof include 0 <β, 0.5 <γ + β <1). Examples of the lithium transition metal composite oxide having a spinel-type crystal structure include Li _x Mn ₂ O ₄ and Li _x Ni _γ Mn _2-γ O ₄ . Examples of the polyanionic compound include LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , LiCoPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , Li ₂ MnSiO ₄ , Li ₂ CoPO ₄ F and the like. Examples of the chalcogen compound include titanium disulfide, molybdenum disulfide, molybdenum dioxide and the like. The atoms or polyanions in these materials may be partially substituted with atoms or anion species consisting of other elements. The surface of these materials may be coated with other materials. In the positive electrode active material layer, one of these materials may be used alone, or two or more of them may be mixed and used.

As the positive electrode active material, a lithium transition metal composite oxide is preferable, and a lithium transition metal composite oxide having an α-NaFeO type ₂ crystal structure is more preferable. The lithium transition metal composite oxide preferably contains nickel or manganese as the transition metal, and more preferably contains both nickel and manganese. The lithium transition metal composite oxide may further contain other transition metals such as cobalt. In the lithium transition metal composite oxide having an α-NaFeO type ₂ crystal structure, the molar ratio (Li / Me) of lithium (Li) to the transition metal (Me) is preferably more than 1, preferably 1.1 or more. Is more preferably 1.2 or more, and even more preferably 1.3 or more. By using such a lithium transition metal composite oxide, the electric capacity can be increased. Further, in the case of a non-aqueous electrolyte power storage element using such a positive electrode active material, it tends to be used at a high current density, and usually, dendrite easily grows on the surface of the negative electrode containing metallic lithium, and it is used in the charge / discharge cycle. The associated discharge capacity and Coulomb efficiency are likely to decrease. Therefore, in the case of the non-aqueous electrolyte power storage element provided with the positive electrode containing the lithium transition metal composite oxide, the effect of suppressing the decrease in discharge capacity and Coulomb efficiency associated with the charge / discharge cycle can be more remarkably enjoyed. The upper limit of the molar ratio (Li / Me) of lithium to the transition metal is preferably 1.6, more preferably 1.5.

As the lithium transition metal composite oxide having an α-NaFeO type ₂ crystal structure, a compound represented by the following formula (1) is preferable.
Li _{1 + α} Me _1-α O ₂ ... (1)
In formula (1), Me is a transition metal containing Ni or Mn. 0 <α <1.

Me in the formula (1) preferably contains Ni and Mn. It is preferable that Me is substantially composed of two elements of Ni and Mn or three elements of Ni, Mn and Co. Me may contain other transition metals.

In the formula (1), the lower limit of the molar ratio of Ni to Me (Ni / Me) is preferably 0.1, more preferably 0.2. On the other hand, as the upper limit of this molar ratio (Ni / Me), 0.5 is preferable, and 0.45 is more preferable. By setting the molar ratio (Ni / Me) in the above range, the energy density is improved.

In the formula (1), the lower limit of the molar ratio (Mn / Me) of Mn to Me is preferably 0.5, more preferably 0.55, and even more preferably 0.6. On the other hand, as the upper limit of this molar ratio (Mn / Me), 0.75 is preferable, and 0.7 is more preferable. By setting the molar ratio (Mn / Me) in the above range, the energy density is improved.

In the formula (1), the upper limit of the molar ratio (Co / Me) of Co to Me is preferably 0.3, more preferably 0.2, and even more preferably 0.1. The lower limit of this molar ratio (Co / Me) or this molar ratio (Co / Me) may be 0.

In the formula (1), the molar ratio (Li / Me) of Li to Me, that is, (1 + α) / (1-α) is preferably more than 1.0 (α> 0), more preferably 1.1 or more. , 1.2 or more is more preferable, and 1.3 or more is even more preferable. On the other hand, as the upper limit of this molar ratio (Li / Me), 1.6 is preferable, and 1.5 is more preferable. By setting the molar ratio (Li / Me) in the above range, the electric capacity becomes large.

The lithium transition metal composite oxide having a molar ratio (Li / Me) of lithium (Li) of more than 1 to the transition metal (Me) is in the range of 20 ° or more and 22 ° or less in the X-ray diffraction diagram using CuKα rays. It is preferable that there is no diffraction peak. A lithium transition metal composite oxide having a molar ratio (Li / Me) of lithium (Li) to the transition metal (Me) of more than 1 generally has a positive electrode potential of, for example, 4.5 V vs. The electric capacity is increased by undergoing initial charging / discharging up to Li / Li ⁺ or higher. Further, due to such a change in the crystal structure during the initial charge / discharge, the diffraction peak existing in the range of 20 ° or more and 22 ° or less before the initial charge / discharge disappears. That is, it is a lithium transition metal composite oxide in which the molar ratio (Li / Me) of lithium (Li) to the transition metal (Me) is more than 1, and it is diffracted in the range of 20 ° or more and 22 ° or less in the above X-ray diffraction diagram. The positive electrode active material having no peak has a large electric capacity.

The composition ratio of the lithium transition metal composite oxide in the present specification refers to the composition ratio when the lithium transition metal composite oxide is brought into a completely discharged state by the following method. First, the non-aqueous electrolyte power storage element is constantly charged with a current of 0.05 C until the charge end voltage at the time of normal use is reached, and the state is fully charged. After a 30-minute pause, a constant current discharge is performed with a current of 0.05 C to the lower limit voltage during normal use. Disassembled, the positive electrode was taken out, a test battery with a metallic lithium electrode as the counter electrode was assembled, and the positive electrode potential was 2.0 V vs. at a current value of 10 mA per 1 g of the positive electrode mixture. A constant current discharge is performed until Li / Li ⁺ , and the positive electrode is adjusted to a completely discharged state. For the metallic lithium electrode here, pure metallic lithium is used instead of a lithium alloy. Re-disassemble and take out the positive electrode. The non-aqueous electrolyte adhering to the removed positive electrode is thoroughly washed with dimethyl carbonate, dried at room temperature for 24 hours, and then the lithium transition metal composite oxide of the positive electrode active material is collected. The collected lithium transition metal composite oxide is used for measurement. The work from dismantling the non-aqueous electrolyte power storage element to collecting the lithium transition metal composite oxide is performed in an argon atmosphere with a dew point of −60 ° C. or lower.

The X-ray diffraction measurement for the lithium transition metal composite oxide is performed on the lithium transition metal composite oxide that has been completely discharged by the above method. Specifically, the X-ray diffraction measurement is performed by powder X-ray diffraction measurement using an X-diffraction device (“MiniFlex II” manufactured by Rigaku), where the radiation source is CuKα ray, the tube voltage is 30 kV, and the tube current is 15 mA. At this time, the diffracted X-rays pass through a Kβ filter having a thickness of 30 μm and are detected by a high-speed one-dimensional detector (D / teX Ultra 2). The sampling width is 0.02 °, the scan speed is 5 ° / min, the divergent slit width is 0.625 °, the light receiving slit width is 13 mm (OPEN), and the scattering slit width is 8 mm.

The lower limit of the content of the lithium transition metal composite oxide with respect to all the positive electrode active materials is preferably 50% by mass, more preferably 80% by mass, still more preferably 95% by mass. The content of the lithium transition metal composite oxide with respect to all the positive electrode active materials may be 100% by mass.

The average particle size of the positive electrode active material is preferably 0.1 μm or more and 20 μm or less, for example. By setting the average particle size of the positive electrode active material to the above lower limit or more, the production or handling of the positive electrode active material becomes easy. By setting the average particle size of the positive electrode active material to the above upper limit or less, the electron conductivity of the positive electrode active material layer is improved.

A crusher, a classifier, or the like is used to obtain particles of the positive electrode active material in a predetermined shape. Examples of the crushing method include a method using a mortar, a ball mill, a sand mill, a vibrating ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling air flow type jet mill, a sieve, or the like. At the time of pulverization, wet pulverization in which water or an organic solvent such as hexane coexists can also be used. As a classification method, a sieve, a wind power classifier, or the like is used as needed for both dry type and wet type.

The content of the positive electrode active material in the positive electrode active material layer is preferably 70% by mass or more and 98% by mass or less, more preferably 80% by mass or more and 97% by mass or less, and further preferably 90% by mass or more and 96% by mass or less. By setting the content of the positive electrode active material in the above range, the electric capacity of the secondary battery can be increased.

The conductive agent is not particularly limited as long as it is a conductive material. Examples of such a conductive agent include carbonaceous materials; metals; conductive ceramics and the like. Examples of carbonaceous materials include graphite and carbon black. Examples of the type of carbon black include furnace black, acetylene black, and ketjen black. Among these, carbonaceous materials are preferable from the viewpoint of conductivity and coatability. Of these, acetylene black and ketjen black are preferable. Examples of the shape of the conductive agent include powder, sheet, and fibrous.

The content of the conductive agent in the positive electrode active material layer is preferably 1% by mass or more and 40% by mass or less, and more preferably 2% by mass or more and 10% by mass or less. By setting the content of the conductive agent in the above range, the energy density of the secondary battery can be increased.

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

The content of the binder in the positive electrode active material layer is preferably 0.5% by mass or more and 10% by mass or less, and more preferably 1% by mass or more and 6% by mass or less. By setting the content of the binder in the above range, the active substance can be stably retained.

Examples of the thickener include polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose. When the thickener has a functional group that reacts with lithium, it is preferable to inactivate this functional group by methylation or the like in advance. In one aspect of the invention, it may be preferable that the thickener is not contained in the positive electrode active material layer.

The filler is not particularly limited. Fillers include polyolefins such as polypropylene and polyethylene, silicon dioxide, aluminum oxide, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, inorganic oxides such as aluminosilicate, magnesium hydroxide, calcium hydroxide, and water. Hydroxides such as aluminum oxide, carbonates such as calcium carbonate, sparingly soluble ion crystals such as calcium fluoride, barium fluoride, barium sulfate, nitrides such as aluminum nitride and silicon nitride, talc, montmorillonite, boehmite and zeolite. , Apatite, Kaolin, Murite, Spinel, Olivin, Serisite, Bentnite, Mica and other mineral resource-derived substances or man-made products thereof. In one aspect of the present invention, it may be preferable that the filler is not contained in the positive electrode active material layer.

The positive electrode active material layer includes typical non-metal elements such as B, N, P, F, Cl, Br, I, Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, Ba and the like. Typical metal elements of Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, W and other transition metal elements are used as positive electrode active materials, conductive agents, binders, thickeners and fillers. It may be contained as a component other than.

(Negative electrode)
The negative electrode provided in the secondary battery according to the embodiment of the present invention is the negative electrode according to the above-described embodiment of the present invention. That is, the secondary battery is a so-called lithium secondary battery.

The negative electrode provided in the secondary battery according to another embodiment of the present invention is a negative electrode having a porous layer having a porosity higher than that of the separator. The specific embodiment of the negative electrode of this embodiment is the same as the negative electrode according to the above-described embodiment of the present invention, except that the porosity of the porous layer is not essential to be 50% or more. The difference between the porosity of the porous layer of the negative electrode and the porosity of the separator is preferably 5% or more, more preferably 15% or more, 25% or more, 35% or more, or 40% or more. The difference between the porosity of the porous layer of the negative electrode and the porosity of the separator may be, for example, 70% or less, 60% or less, or 50% or less.

(Separator)
The separator is arranged between the positive electrode and the negative electrode. Therefore, the porous layer of the negative electrode is usually in a state of directly overlapping the separator.

The separator can be appropriately selected from known separators. As the separator, for example, a separator composed of only a base material layer, a separator having a heat-resistant layer containing heat-resistant particles and a binder formed on one surface or both surfaces of the base material layer can be used. The substrate layer of the separator may contain heat resistant particles. Examples of the form of the base material layer of the separator include woven fabrics, non-woven fabrics, and porous resin films. Among these forms, a porous resin film is preferable from the viewpoint of strength, and a non-woven fabric is preferable from the viewpoint of liquid retention of a non-aqueous electrolyte. Further, from the viewpoint of more effectively obtaining the advantages of the negative electrode and the non-aqueous electrolyte according to the embodiment of the present invention, a porous resin film having a porous structure formed by stretching is usually preferable.

As the material of the base material layer of the separator, polyolefins such as polyethylene and polypropylene are preferable from the viewpoint of shutdown function, and polyimide and aramid are preferable from the viewpoint of oxidative decomposition resistance. As the base material layer of the separator, a material in which these resins are combined may be used.

The heat-resistant particles contained in the heat-resistant layer and the base material layer preferably have a mass reduction of 5% or less when heated from room temperature to 500 ° C. in the atmosphere, and mass when heated from room temperature to 800 ° C. in the atmosphere. It is more preferable that the decrease is 5% or less. Inorganic compounds can be mentioned as a material whose mass loss when heated is less than or equal to a predetermined value. Examples of the inorganic compound include those exemplified as the inorganic compound constituting the inorganic particles in the porous layer of the negative electrode. Among the inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicate is preferable from the viewpoint of safety of the secondary battery.

The porosity (porosity) of the separator is preferably 80% or less, more preferably 60% or less, and even more preferably less than 50% from the viewpoint of strength. On the other hand, the porosity of the separator is preferably 20% or more from the viewpoint of discharge performance. Further, as described above, in one of the embodiments of the present invention, the porosity of the separator is lower than the porosity of the porous layer of the negative electrode.

As the separator, a polymer gel composed of a polymer and a non-aqueous electrolyte may be used. Examples of the polymer include polyalkyl methacrylates such as polyacrylonitrile, polyethylene oxide, polypropylene oxide, polyethylene carbonate, polypropylene carbonate, polyvinyl carbonate and polymethyl methacrylate, polyalkyl acrylates such as polymethyl acrylate, polyvinyl ethylene carbonate and polyvinyl. Acrylate, polyvinylpyrrolidone, polymaleic acid and its derivatives, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, etc., and copolymers of the monomers constituting these polymers, and polymers thereof. Examples include mixtures. Further, these polymers may be combined with an inorganic salt or an ionic liquid. The use of polymer gel has the effect of suppressing liquid leakage. As the separator, a polymer gel may be used in combination with a porous resin film or a non-woven fabric as described above.

(Non-water electrolyte)
As the non-aqueous electrolyte, a non-aqueous electrolyte solution containing a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent is usually preferably used.

As the non-aqueous solvent, a known non-aqueous solvent can be appropriately selected. Examples of the non-aqueous solvent include cyclic carbonates, chain carbonates, carboxylic acid esters, phosphoric acid esters, sulfonic acid esters, ethers, amides, nitriles and the like. As the non-aqueous solvent, a solvent in which some of the hydrogen atoms contained in these compounds are replaced with halogen may be used.

As the non-aqueous solvent, it is preferable to use at least one of the cyclic carbonate and the chain carbonate, and it is more preferable to use the cyclic carbonate and the chain carbonate in combination. By using the cyclic carbonate, the dissociation of the electrolyte salt can be promoted and the ionic conductivity of the non-aqueous electrolyte can be improved. By using the chain carbonate, the viscosity of the non-aqueous electrolyte can be kept low. When the cyclic carbonate and the chain carbonate are used in combination, the volume ratio of the cyclic carbonate to the chain carbonate (cyclic carbonate: chain carbonate) is preferably in the range of, for example, 5:95 to 50:50.

Examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, vinylethylene carbonate, chloroethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, fluoromethylethylene carbonate, trifluoroethylethylene carbonate, styrene carbonate, and catechol carbonate. Examples thereof include 1-phenylvinylene carbonate and 1,2-diphenylvinylene carbonate.

As the cyclic carbonate, a fluorinated cyclic carbonate such as fluoroethylene carbonate, difluoroethylene carbonate, fluoromethylethylene carbonate, or trifluoroethylethylene carbonate is preferable from the viewpoint of oxidation resistance and the like.

Chain carbonates include diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate, diphenyl carbonate, 2,2,2-trifluoroethylmethyl carbonate, bis (2,2,2-trifluoroethyl) carbonate, ethyl-2,2. , 2-Trifluoroethyl carbonate and the like.

The chain carbonate includes 2,2,2-trifluoroethylmethyl carbonate, bis (2,2,2-trifluoroethyl) carbonate, and ethyl-2,2,2-trifluoro from the viewpoint of oxidation resistance and the like. Fluorinated chain carbonates such as ethyl carbonate are preferable.

The content of carbonate (cyclic carbonate and chain carbonate) with respect to the total non-aqueous solvent is preferably 50% by volume or more and 100% by volume or less, more preferably 80% by volume or more, and 90% by volume or more, 95% by volume or more or 99% by volume. % Or more may be more preferable.

The non-aqueous solvent preferably contains a fluorinated solvent. The content of the fluorinated solvent with respect to the total non-aqueous solvent is preferably 60% by volume or more, more preferably 90% by volume or more, further preferably 99% by volume or more, and particularly preferably 100% by volume. The fluorinated solvent refers to a solvent (non-aqueous solvent) having a fluorine atom in the molecule, such as a fluorinated carbonate (fluorinated chain carbonate and a fluorinated cyclic carbonate) and a fluorinated ether. By containing the fluorinated solvent in this way, preferably at the above lower limit or higher, the oxidation resistance and the like can be further improved.

The electrolyte salt is usually a lithium salt. Lithium salts include inorganic lithium salts such as LiPF ₆ , LiPO ₂ F ₂ , LiBF ₄ , LiClO ₄ , LiN (SO ₂ F) ₂ , LiSO ₃ CF ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ ). C ₂ F ₅ ) ₂ , LiN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ), LiC (SO ₂ CF ₃ ) ₃ , LiC (SO ₂ C ₂ F ₅ ) ₃ and other halogenated hydrocarbon groups Examples thereof include lithium salts having. Among these, an inorganic lithium salt is preferable, and LiPF ₆ is more preferable. Further, from the viewpoint of oxidation resistance and the like, the electrolyte salt preferably contains a fluorine atom.

The content of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 mol / dm ³ or more and 2.5 mol / dm ³ or less, more preferably 0.3 mol / dm ³ or more and 2.0 mol / dm ³ or less, and more preferably 0.5 mol / dm. More preferably, it is dm ³ or more and 1.7 mol / dm ³ or less, and particularly preferably 0.7 mol / dm ³ or more and 1.5 mol / dm ³ or less. By setting the content of the electrolyte salt in the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

The non-aqueous electrolyte may contain additives. Examples of the additive include aromatic compounds such as biphenyl, alkyl biphenyl, terphenyl, a partially hydride of turphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, and dibenzofuran; 2-fluorobiphenyl, o-cyclohexyl. Partial halides of the above aromatic compounds such as fluorobenzene and p-cyclohexylfluorobenzene; succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic acid anhydride; sulfite. Ethylene, propylene sulfite, dimethyl sulfite, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, 4,4'-bis (2,2-dioxo-1, 3,2-Dioxathiolane), 4-Methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisol, diphenyldisulfide, dipyridinium disulfide, perfluorooctane, tristrimethylsilyl borate, tris phosphate Examples thereof include trimethylsilyl and tetrakistrimethylsilyl titanate. These additives may be used alone or in combination of two or more.

The content of the additive contained in the non-aqueous electrolyte is preferably 0.01% by mass or more and 10% by mass or less, more preferably 0.1% by mass or more and 7% by mass or less, and 0.2. More preferably, it is more preferably mass% or more and 5% by mass or less, and particularly preferably 0.3% by mass or more and 3% by mass or less. By setting the content of the additive in the above range, it is possible to improve the capacity maintenance performance or charge / discharge cycle performance of the secondary battery after high-temperature storage, and further improve the safety.

As the non-aqueous electrolyte, a solid electrolyte may be used, or a non-aqueous electrolyte solution and a solid electrolyte may be used in combination.

The solid electrolyte can be selected from any material having lithium ion conductivity and being solid at room temperature (for example, 15 ° C to 25 ° C). Examples of the solid electrolyte include a sulfide solid electrolyte, an oxide solid electrolyte, an oxynitride solid electrolyte, a polymer solid electrolyte and the like.

(Usage pattern, etc.)
In the secondary battery (non-aqueous electrolyte power storage element), the positive potential at the end-of-charge voltage during normal use is, for example, 4.3 V (vs. Li / Li ⁺ ) or more or 4.4 V (vs. Li / Li ⁺ ). ) Or higher, but more preferably 4.5 V (vs. Li / Li ⁺ ) or higher, and even more preferably 4.55 V (vs. Li / Li ⁺ ) or higher. By setting the positive electrode potential at the end-of-charge voltage during normal use to the above lower limit or higher, the discharge capacity of the secondary battery can be increased and the energy density can be increased.

The upper limit of the positive potential at the end-of-charge voltage of the secondary battery during normal use is, for example, 5.0 V (vs. Li / Li ⁺ ), even if it is 4.8 V (vs. Li / Li ⁺ ). Well, it may be 4.7V (vs. Li / Li ⁺ ).

On the surface of the negative electrode containing metallic lithium, dendrites tend to grow easily when the current density during charging is high. Therefore, the non-aqueous electrolyte power storage element according to the embodiment of the present invention can be suitably applied to applications in which charging with a high current density is performed. Examples of such applications include power supplies for automobiles such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid vehicles (PHEVs), power supplies for regenerative power charging, and the like.

The shape of the non-aqueous electrolyte power storage element of the present embodiment is not particularly limited, and examples thereof include a cylindrical battery, a square battery, a flat battery, a coin battery, and a button battery.

FIG. 1 shows a non-aqueous electrolyte power storage element 1 as an example of a square battery. The figure is a perspective view of the inside of the container. The electrode body 2 having the positive electrode and the negative electrode wound around the separator is housed in the square container 3. The positive electrode is electrically connected to the positive electrode terminal 4 via the positive electrode lead 41. The negative electrode is electrically connected to the negative electrode terminal 5 via the negative electrode lead 51.

<Structure of non-aqueous electrolyte power storage device>
The non-aqueous electrolyte storage element of the present embodiment includes a plurality of non-aqueous electrolyte storage elements in a power source for automobiles such as EV, HEV, PHEV, a power source for electronic devices such as a personal computer and a communication terminal, a power source for power storage, and the like. It can be mounted as a power storage unit (battery module) assembled together. In this case, the technique according to the embodiment of the present invention may be applied to at least one non-aqueous electrolyte power storage element included in the power storage unit.

FIG. 2 shows an example of a power storage device 30 in which a power storage unit 20 in which two or more electrically connected non-aqueous electrolyte power storage elements 1 are assembled is further assembled. The power storage device 30 includes a bus bar (not shown) for electrically connecting two or more non-aqueous electrolyte power storage elements 1, a bus bar (not shown) for electrically connecting two or more power storage units 20 and the like. May be good. The power storage unit 20 or the power storage device 30 may include a condition monitoring device (not shown) for monitoring the state of one or more non-aqueous electrolyte power storage elements.

<Manufacturing method of non-aqueous electrolyte power storage element>
The method for manufacturing a non-aqueous electrolyte power storage element according to an embodiment of the present invention is a negative electrode obtained by the above-mentioned negative electrode according to the embodiment of the present invention or the above-mentioned negative electrode according to the embodiment of the present invention. It is provided to manufacture a non-aqueous electrolyte power storage element using the above.

Further, the method for manufacturing a non-aqueous electrolyte power storage element according to another embodiment of the present invention comprises manufacturing a non-aqueous electrolyte power storage element using a negative electrode and a separator, and the negative electrode is a negative electrode containing metallic lithium. It has an active material layer and a porous layer containing inorganic particles laminated on the surface of the negative electrode active material layer, and the void ratio of the porous layer of the negative electrode is higher than the void ratio of the separator.

Specific and preferred embodiments of the negative electrode and the separator used in these manufacturing methods are described above as the negative electrode and the separator provided in the negative electrode according to the embodiment of the present invention or the non-aqueous electrolyte power storage element according to the embodiment of the present invention. Similar to the one.

Specifically, the method for manufacturing the non-aqueous electrolyte power storage element is to prepare or manufacture a positive electrode, prepare or manufacture a negative electrode, prepare or prepare a non-aqueous electrolyte, prepare or manufacture a separator, and prepare or manufacture a positive electrode and a negative electrode. To form an electrode body alternately superimposed by laminating or winding through a separator, to house the positive electrode and the negative electrode (electrode body) in a container, and to inject the non-aqueous electrolyte into the container. Be prepared for that. After the injection, the non-aqueous electrolyte power storage element can be obtained by sealing the injection port.

The method for manufacturing the non-aqueous electrolyte storage element may further include initial charging / discharging of the assembled uncharged / discharged non-aqueous electrolyte storage element. For example, when a lithium transition metal composite oxide having a molar ratio (Li / Me) of lithium (Li) to the transition metal (Me) of more than 1 is used as the positive electrode active material of the non-aqueous electrolyte power storage element, the initial charge is applied. The capacity increases as it goes through the discharge. The number of charge / discharge in the initial charge / discharge may be once or twice, or may be three or more. When a lithium transition metal composite oxide having a molar ratio (Li / Me) of lithium (Li) to the transition metal (Me) of more than 1 is used as the positive electrode active material of the non-aqueous electrolyte power storage element, initial charge / discharge is performed. The positive electrode potential (positive electrode reaching potential) at the end-of-charge voltage in the above is 4.5 V vs. Li / Li ⁺ or more 4.7V vs. It is preferably Li / Li ⁺ or less.

<Other embodiments>
The present invention is not limited to the above embodiment, and various modifications may be made without departing from the gist of the present invention. For example, the configuration of one embodiment can be added to the configuration of another embodiment, and a part of the configuration of one embodiment can be replaced with the configuration of another embodiment or a well-known technique. In addition, some of the configurations of certain embodiments can be deleted. Further, a well-known technique can be added to the configuration of a certain embodiment.

In the above embodiment, the case where the non-aqueous electrolyte storage element is used as a chargeable / dischargeable non-aqueous electrolyte secondary battery (lithium battery) has been described, but the type, shape, size, capacity, etc. of the non-aqueous electrolyte storage element are arbitrary. Is. The non-aqueous electrolyte power storage element of the present invention can also be applied to capacitors such as various non-aqueous electrolyte secondary batteries, electric double layer capacitors and lithium ion capacitors. Further, the non-aqueous electrolyte power storage element of the present invention can also be applied to a lithium-air battery.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples.
The porosity and average thickness of the porous layer, the specific surface area and average particle size of the inorganic particles, and the porosity of the separator in the following examples are values measured by the above method.

[Example 1]
(Preparation of positive electrode)
As the positive electrode active material, a lithium transition metal composite oxide having an α-NaFeO type ₂ crystal structure and represented by Li _{1 + α} Me _1-α O ₂ (Me is a transition metal) was used. Here, the molar ratio Li / Me of Li and Me was 1.33, and Me was composed of Ni and Mn and contained Ni: Mn = 1: 2.

Using N-methylpyrrolidone (NMP) as a dispersion medium, the positive electrode active material, acetylene black (AB) as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder have a mass ratio of 92.5: 4.5: 3. A positive electrode paste contained in (solid content equivalent) was prepared. The positive electrode paste was applied to one side of an aluminum foil as a positive electrode base material, dried, and then pressed to prepare a positive electrode having a positive electrode active material layer arranged on one side of the positive electrode base material.

(Manufacturing of negative electrode)
A commercially available product was prepared in which a metallic lithium foil (average thickness 60 μm: pure metallic lithium of 100% by mass of metallic lithium) was laminated as a negative electrode active material layer on one side of a copper foil (average thickness 10 μm) which is a negative electrode base material. .. Inorganic particles A (Al ₂ O ₃ particles, specific surface area 88 m ² / g, average particle size 18 nm) were dispersed in dimethyl sulfoxide to prepare a porous layer forming material. Using a spray gun, the porous layer forming material was applied to the surface of the negative electrode active material layer. After coating, it was dried on a hot plate set at 100 ° C., and then vacuum dried at 60 ° C. As a result, a negative electrode in which the negative electrode base material, the negative electrode active material layer, and the porous layer were laminated in this order was obtained. The formed porous layer had a porosity of 84% and an average thickness of 2 μm.

(Preparation of non-aqueous electrolyte)
LiPF ₆ was dissolved in a mixed solvent in which fluoroethylene carbonate (FEC) and 2,2,2-trifluoroethylmethyl carbonate (TFEMC) were mixed at a volume ratio of 30:70 at a concentration of 1 mol / dm ³ , and a non-aqueous electrolyte was added. And said.

(Manufacturing of non-aqueous electrolyte power storage element)
An electrode body was produced by laminating the positive electrode and the negative electrode via a microporous polyolefin membrane (porosity 44%) which is a separator. This electrode body was housed in a container made of a metal resin composite film, and the above-mentioned non-aqueous electrolyte was injected therein. After that, the container was closed and the container was pressed from the outside at 0.3 MPa to obtain the non-aqueous electrolyte power storage element of Example 1.

[Examples 2 to 8 and Comparative Examples 1 and 2]
Examples 2 to 8 and Comparative Examples 1 and 2 are the same as in Example 1 except that the inorganic particles shown in Table 1 are used to form the porous layer having the porosity and the average thickness shown in Table 1. Each negative electrode and non-aqueous electrolyte power storage element of the above were obtained. In Comparative Example 1, the porous layer was not formed on the negative electrode.

[Example 9]
Inorganic particles A and PVDF as a binder were dispersed in dimethyl sulfoxide at a mass ratio of 80:20 to prepare a porous layer forming material, and the same as in Example 2 except that this porous layer forming material was used. The negative electrode and the non-aqueous electrolyte storage element of Example 9 were obtained.

(Initial charge / discharge)
Each of the obtained non-aqueous electrolyte power storage elements was initially charged and discharged under the following conditions. At 25 ° C., constant current and constant voltage charging was performed with a charging current of 0.1 C and a charge termination voltage of 4.6 V. The charging end condition was set until the charging current reached 0.02C. After that, a rest period of 10 minutes was provided. Then, a constant current discharge was performed with a discharge current of 0.1 C and a discharge end voltage of 2.0 V, and then a rest period of 10 minutes was provided. This charge / discharge cycle was performed for two cycles.

(Charge / discharge cycle test)
Then, the following charge / discharge cycle test was performed. At 25 ° C., constant current and constant voltage charging was performed with a charging current of 0.2 C and a charge termination voltage of 4.6 V. The charging end condition was until the charging current reached 0.02C. After that, a rest period of 10 minutes was provided. Then, a constant current discharge was performed with a discharge current of 0.1 C and a discharge end voltage of 2.0 V, and then a rest period of 10 minutes was provided. This charge / discharge cycle was repeated, and the number of cycles when the capacity retention rate (discharge capacity with respect to the discharge capacity of the first cycle) was less than 90% and the number of cycles when the Coulomb efficiency was less than 96% were recorded. The results are shown in Table 1.
Further, FIG. 3A shows a graph showing the change in the capacity retention rate of the non-aqueous electrolyte power storage element of Example 1 for each cycle, and FIG. 3B shows a graph showing the change in the Coulomb efficiency for each cycle. FIG. 4A shows a graph showing the change in the capacity retention rate of the non-aqueous electrolyte power storage element of Example 2 for each cycle, and FIG. 4B shows a graph showing the change in the Coulomb efficiency for each cycle. A graph showing the change in the capacity retention rate for each cycle of the non-aqueous electrolyte power storage element of Example 3 is shown in FIG. 5A, and a graph showing the change in the Coulomb efficiency for each cycle is shown in FIG. 5B. A graph showing the change in the capacity retention rate for each cycle of the non-aqueous electrolyte power storage element of Example 4 is shown in FIG. 6A, and a graph showing the change in the Coulomb efficiency for each cycle is shown in FIG. 6B. A graph showing the change in the capacity retention rate for each cycle of the non-aqueous electrolyte power storage element of Example 5 is shown in FIG. 7A, and a graph showing the change in the Coulomb efficiency for each cycle is shown in FIG. 7B. A graph showing the change in the capacity retention rate for each cycle of the non-aqueous electrolyte power storage element of Example 6 is shown in FIG. 8A, and a graph showing the change in the Coulomb efficiency for each cycle is shown in FIG. 8B. A graph showing the change in the capacity retention rate for each cycle of the non-aqueous electrolyte power storage element of Example 7 is shown in FIG. 9A, and a graph showing the change in the Coulomb efficiency for each cycle is shown in FIG. 9B. A graph showing the change in the capacity retention rate for each cycle of the non-aqueous electrolyte power storage element of Example 8 is shown in FIG. 10A, and a graph showing the change in the Coulomb efficiency for each cycle is shown in FIG. 10B. A graph showing the change in the capacity retention rate for each cycle of the non-aqueous electrolyte power storage element of Example 9 is shown in FIG. 11A, and a graph showing the change in the Coulomb efficiency for each cycle is shown in FIG. 11B. A graph showing the change in the capacity retention rate for each cycle of the non-aqueous electrolyte power storage element of Comparative Example 1 is shown in FIG. 12A, and a graph showing the change in the Coulomb efficiency for each cycle is shown in FIG. 12B. A graph showing the change in the capacity retention rate for each cycle of the non-aqueous electrolyte power storage element of Comparative Example 2 is shown in FIG. 13A, and a graph showing the change in the Coulomb efficiency for each cycle is shown in FIG. 13B.

As shown in Table 1, each of the non-aqueous electrolyte power storage elements of Examples 1 to 9 including the negative electrode having a negative electrode having a porosity of 50% or more has the number of cycles when the capacity retention rate is less than 90%. The number of cycles when the Coulomb efficiency was less than 96% was larger than that of the non-aqueous electrolyte power storage element of Comparative Example 1 provided with the negative electrode having no porous layer. It can be seen that in each of the non-aqueous electrolyte power storage elements of Examples 1 to 9, the decrease in discharge capacity and Coulomb efficiency associated with the charge / discharge cycle was suppressed. On the other hand, the non-aqueous electrolyte storage element of Comparative Example 2 having a negative electrode having a porous layer having a void ratio of less than 50% has a smaller number of cycles than the non-aqueous electrolyte storage element of Comparative Example 1 and is filled. As a result, the decrease in discharge capacity and Coulomb efficiency with the discharge cycle is promoted. From these, it can be seen that by forming a porous layer having a high porosity on the negative electrode, it is possible to suppress a decrease in discharge capacity and Coulomb efficiency due to a charge / discharge cycle. Further, it can be seen that by making the porosity of the porous layer formed on the negative electrode higher than the porosity of the separator, it is possible to suppress the decrease in discharge capacity and Coulomb efficiency due to the charge / discharge cycle.

Among the examples, when compared with Examples 1 to 8 in which the porous layer is substantially composed of only inorganic particles, each of Examples 1 to 3, 7 and 8 in which the porosity of the porous layer is 80% or more. As for the non-aqueous electrolyte power storage element, the number of each cycle described above exceeded 40 times. In addition, in these examples, the inorganic particles having an average particle diameter of 50 nm or less were used, and it is considered that the average particle diameter of the inorganic particles also has an influence. Further, in each of the non-aqueous electrolyte power storage elements of Examples 1 to 3 and 7 using inorganic particles having an average particle size of 20 nm or less, the number of each cycle exceeds 50 times, and among these, the porous layer Each of the non-aqueous electrolyte power storage elements of Examples 2, 3 and 7 having an average thickness of more than 5 μm had 55 or more cycles in each of the above cycles. In this way, by adjusting the average particle size of the inorganic particles and the average thickness of the porous layer in addition to the porosity of the porous layer formed on the negative electrode, the discharge capacity and the Coulomb efficiency associated with the charge / discharge cycle can be adjusted. It can be seen that the decrease can be further suppressed. Further, from the comparison between Example 2 and Example 9 in which only the mass ratio of the inorganic particles and the binder in the porous layer is different, when the porous layer is substantially composed of only inorganic particles, the discharge accompanying the charge / discharge cycle is performed. It can be seen that the decrease in capacity and Coulomb efficiency can be further suppressed.

The present invention can be applied to personal computers, electronic devices such as communication terminals, non-aqueous electrolyte power storage elements used as power sources for automobiles, and the like.

1 Non-aqueous electrolyte power storage element 2 Electrode body 3 Container 4 Positive terminal 41 Positive lead 5 Negative terminal 51 Negative lead 20 Power storage unit 30 Power storage device

Claims (11)

Negative electrode active material layer containing metallic lithium and
It has a porous layer containing inorganic particles laminated on the surface of the negative electrode active material layer.
A negative electrode for a non-aqueous electrolyte power storage element having a porosity of 50% or more in the porous layer. The negative electrode according to claim 1, wherein the porosity of the porous layer is 80% or more. The negative electrode according to claim 1 or 2, wherein the average particle size of the inorganic particles is 50 nm or less. The negative electrode according to claim 3, wherein the average particle size of the inorganic particles is 20 nm or less. The negative electrode according to any one of claims 1 to 4, wherein the porous layer is substantially composed of only the inorganic particles. Negative electrode for non-aqueous electrolyte power storage element, which comprises forming a porous layer having a porosity of 50% or more on the surface of a negative electrode active material layer containing metallic lithium by a porous layer forming material containing inorganic particles. Manufacturing method. A non-aqueous electrolyte power storage device comprising the negative electrode according to any one of claims 1 to 5. Equipped with a negative electrode and a separator,
The negative electrode has a negative electrode active material layer containing metallic lithium and a porous layer containing inorganic particles laminated on the surface of the negative electrode active material layer.
A non-aqueous electrolyte power storage element in which the porosity of the porous layer of the negative electrode is higher than the porosity of the separator. The non-aqueous electrolyte power storage element according to claim 7 or 8, wherein the positive electrode potential at the end-of-charge voltage during normal use is 4.5 V (vs. Li / Li ⁺ ) or more. A non-aqueous electrolyte storage device comprising producing a non-aqueous electrolyte power storage element using the negative electrode according to any one of claims 1 to 5 or the negative electrode obtained by the negative electrode manufacturing method according to claim 6. Manufacturing method of power storage element. A non-aqueous electrolyte power storage element is provided by using a negative electrode and a separator.
The negative electrode has a negative electrode active material layer containing metallic lithium and a porous layer containing inorganic particles laminated on the surface of the negative electrode active material layer.
A method for manufacturing a non-aqueous electrolyte power storage element in which the porosity of the porous layer of the negative electrode is higher than the porosity of the separator.

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