JP7852211B2 - Negative electrode for non-aqueous electrolyte energy storage element, non-aqueous electrolyte energy storage element, and method for manufacturing the same. - Google Patents

Description

This invention relates to a negative electrode for a non-aqueous electrolyte energy storage element, a non-aqueous electrolyte energy storage element, and methods for manufacturing the same.

Non-aqueous electrolyte secondary batteries, such as lithium-ion batteries, are widely used in electronic devices like personal computers and communication terminals, as well as automobiles, due to their high energy density. Generally, these non-aqueous electrolyte secondary batteries consist of a pair of electrodes electrically isolated by a separator, and a non-aqueous electrolyte interposed between these electrodes. Charging and discharging occur through the transfer of ions between the two electrodes. In addition to non-aqueous electrolyte secondary batteries, capacitors such as lithium-ion capacitors and electric double-layer capacitors are also widely used as non-aqueous electrolyte energy storage elements. Lithium metal is known as a high-energy-density negative electrode active material used in non-aqueous electrolyte energy storage elements (see Patent Documents 1 and 2).

Japanese Patent Publication No. 2016-100065 Japanese Patent Application Publication No. 07-245099

For non-aqueous electrolyte energy storage elements to exhibit good charge and discharge performance, it is preferable to use electrodes that are less prone to polarization. The object of the present invention is to provide a negative electrode containing metallic lithium in which polarization is suppressed, a non-aqueous electrolyte energy storage element equipped with such a negative electrode, and methods for manufacturing these.

One aspect of the present invention relates to a negative electrode for a non-aqueous electrolyte energy storage element, comprising a negative electrode active material layer containing metallic lithium and a coating layer laminated on the surface of the negative electrode active material layer, the coating layer containing zinc element particles.

Another aspect of the present invention relates to a method for manufacturing a negative electrode for a non-aqueous electrolyte energy storage element, comprising forming a coating layer on the surface of a negative electrode active material layer containing metallic lithium using a coating layer forming material containing zinc element particles.

Another aspect of the present invention relates to a non-aqueous electrolyte energy storage element, which is a non-aqueous electrolyte energy storage element comprising a negative electrode according to one aspect of the present invention.

Another aspect of the present invention relates to a method for manufacturing a non-aqueous electrolyte energy storage element, which comprises manufacturing a non-aqueous electrolyte energy storage element using a negative electrode according to one aspect of the present invention, or a negative electrode obtained by a method for manufacturing a negative electrode according to one aspect of the present invention.

According to one aspect of the present invention, it is possible to provide a negative electrode containing metallic lithium in which polarization is suppressed, a non-aqueous electrolyte energy storage element equipped with such a negative electrode, and a method for manufacturing these.

Figure 1 is a perspective view showing one embodiment of a non-aqueous electrolyte energy storage element. Figure 2 is a schematic diagram showing one embodiment of an energy storage device constructed by assembling multiple non-aqueous electrolyte energy storage elements. Figure 3A shows the charge and discharge curves of the non-aqueous electrolyte energy storage elements in Example 1 and Comparative Example 4. Figure 3B is an enlarged view of the charging curve immediately after the start of charging in Figure 3A. Figure 4A shows the charge and discharge curves of the non-aqueous electrolyte energy storage elements for Comparative Example 1 and Comparative Example 4. Figure 4B is an enlarged view of the charging curve immediately after the start of charging in Figure 4A. Figure 5A shows the charge and discharge curves of each non-aqueous electrolyte energy storage element from Comparative Examples 2 to 4. Figure 5B is an enlarged view of the charging curve immediately after the start of charging in Figure 5A.

First, an overview of the negative electrode for a non-aqueous electrolyte energy storage element, the method for manufacturing the negative electrode for a non-aqueous electrolyte energy storage element, the non-aqueous electrolyte energy storage element, and the method for manufacturing the non-aqueous electrolyte energy storage element disclosed herein will be described.

A negative electrode for a non-aqueous electrolyte energy storage element according to one aspect of the present invention comprises a negative electrode active material layer containing metallic lithium and a coating layer containing zinc element particles laminated on the surface of the negative electrode active material layer.

The negative electrode in question is a negative electrode containing metallic lithium, and its polarization is suppressed. While the reason for this is not entirely clear, the following reason is speculated: When particles containing zinc come into contact with the surface of the negative electrode active material layer containing metallic lithium, at least a portion of the particles react with the metallic lithium on the surface of the negative electrode active material layer. In this case, it is thought that at least a portion of the zinc element contained in the particles within the coating layer exists in the form of metallic zinc or a zinc-lithium alloy. When such a coating layer is formed on the surface of the negative electrode active material layer containing metallic lithium, the electrical resistance becomes lower compared to when no coating layer is formed, and this is presumed to suppress polarization. Similarly, when particles containing metallic zinc are used as the zinc-containing particles, it is presumed that the same effect occurs as a result of the formation of a coating layer with low electrical resistance.

It is preferable that the zinc-containing particles are at least one of zinc oxide particles and their reaction products. A negative electrode having such particles in the coating layer further suppresses polarization. Furthermore, in this case, the coating layer can be formed using zinc oxide particles, resulting in excellent productivity.

It is preferable that the coating layer consists substantially only of particles containing the zinc element. A negative electrode with such a coating layer exhibits more suppressed polarization. While the reason for this is unclear, it is speculated that if the coating layer substantially contains no other components besides the zinc element particles, the electrical resistance of the coating layer tends to be lower.

Furthermore, the statement that the coating layer consists substantially only of particles containing zinc element means that trace amounts of other components may be present in addition to the zinc element particles. For example, the statement that the coating layer consists substantially only of particles containing zinc element means that the content of zinc element particles in the coating layer is 99% by mass or more, and preferably 99.9% by mass or more.

Another aspect of the present invention relates to a method for manufacturing a negative electrode, which involves forming a coating layer on the surface of a negative electrode active material layer containing metallic lithium using a coating layer forming material containing zinc element particles.

According to this negative electrode manufacturing method, a negative electrode containing metallic lithium can be manufactured in which polarization is suppressed.

Another aspect of the present invention relates to a non-aqueous electrolyte energy storage element, which is a non-aqueous electrolyte energy storage element comprising a negative electrode according to one aspect of the present invention.

This non-aqueous electrolyte energy storage element has a negative electrode containing metallic lithium, and because it is equipped with a negative electrode with suppressed polarization, it exhibits good charge and discharge performance.

Another aspect of the present invention relates to a method for manufacturing a non-aqueous electrolyte energy storage element, which comprises manufacturing a non-aqueous electrolyte energy storage element using a negative electrode according to one aspect of the present invention, or a negative electrode obtained by a method for manufacturing a negative electrode according to one aspect of the present invention.

According to the method for manufacturing the non-aqueous electrolyte energy storage element, it is possible to manufacture a non-aqueous electrolyte energy storage element comprising a negative electrode containing metallic lithium, wherein polarization is suppressed.

The following describes in detail an embodiment of the negative electrode for a non-aqueous electrolyte energy storage element, a method for manufacturing the negative electrode for a non-aqueous electrolyte energy storage element, a non-aqueous electrolyte energy storage element, a non-aqueous electrolyte energy storage device, a method for manufacturing the non-aqueous electrolyte energy storage element, and other embodiments. Note that the names of the components (parts) used in each embodiment may differ from the names of the components (parts) used in the background art.

<Negative electrode>
A negative electrode for a non-aqueous electrolyte energy storage element according to one embodiment of the present invention comprises a negative electrode substrate, a negative electrode active material layer, and a coating layer. In this negative electrode, the negative electrode substrate, the negative electrode active material layer, and the coating layer are laminated in this order. The negative electrode active material layer may be laminated directly on both sides of the negative electrode substrate or via an intermediate layer. When the negative electrode active material layer is provided on both sides of the negative electrode substrate, it is preferable that the coating layer is provided on the surface of each negative electrode active material layer that does not face the negative electrode substrate. This negative electrode is used in a non-aqueous electrolyte energy storage element. This negative electrode is particularly suitable for use as a negative electrode for a non-aqueous electrolyte energy storage element.

The negative electrode substrate is conductive. Whether or not it is conductive is determined by a volume resistivity of ^10⁷ Ω·cm, measured in accordance with JIS-H-0505 (1975), with a threshold value of 10⁷ Ω·cm. The negative electrode substrate can be made of metals such as copper, nickel, stainless steel, nickel-plated steel, or alloys thereof, or carbonaceous materials. Among these, copper or copper alloys are preferred. Examples of negative electrode substrates include foil, vapor-deposited film, mesh, and porous material, with foil being preferred from a cost standpoint. Therefore, copper foil or copper alloy foil is preferred as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil.

The average thickness of the negative electrode substrate is preferably 2 μm to 35 μm, more preferably 3 μm to 30 μm, even more preferably 4 μm to 25 μm, and particularly preferably 5 μm to 20 μm. By setting the average thickness of the negative electrode substrate within the above range, the strength of the negative electrode substrate can be increased while simultaneously increasing the energy density per unit volume of the non-aqueous electrolyte energy storage element. The "average thickness" of the negative electrode substrate refers to the value obtained by dividing the punched mass when a predetermined area of the negative electrode substrate is punched by the true density of the negative electrode substrate and the punched area. The same applies to the average thickness of the positive electrode substrate, which will be described later.

The intermediate layer is a layer placed between the negative electrode substrate and the negative electrode active material layer. The intermediate layer contains a conductive agent, such as carbon particles, to reduce the contact resistance between the negative electrode substrate and the negative electrode active material layer. The composition of the intermediate layer is not particularly limited and may include, for example, a binder and a conductive agent.

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

The negative electrode active material layer may be a layer consisting substantially of metallic lithium. The metallic lithium content 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 metallic lithium foil or lithium alloy foil. The negative electrode active material layer may be a non-porous layer (solid layer). Alternatively, the negative electrode active material layer may be a porous layer containing particles of metallic lithium. The average thickness of the negative electrode active material layer is preferably 1 μm to 1,000 μm, more preferably 10 μm to 500 μm, and even more preferably 30 μm to 300 μm.

The coating layer is a layer laminated on the surface of the negative electrode active material layer that does not face the negative electrode substrate. The coating layer contains particles containing zinc. The zinc element may exist as elemental zinc (metallic zinc), as a zinc alloy, or as a compound containing zinc. The compound containing zinc may be either an inorganic compound or an organic compound, and an inorganic compound may be preferred. Specific examples of compounds containing zinc include zinc oxide (ZnO), zinc hydroxide (Zn(OH) _₂ ), zinc carbonate ( _ZnCO₃ ), zinc sulfate ( _ZnSO₄ ), zinc sulfide ( _ZnS ), and zinc aluminate ( _ZnAl₂O₄ ). A single particle containing zinc may contain multiple compounds containing zinc, or it may contain elemental zinc and a compound containing zinc. The particles containing zinc may further contain compounds that do not contain zinc, or metals other than metallic zinc. Furthermore, the particles containing zinc may be a mixture or composite of two or more particles containing zinc. The surface of the zinc-containing particles may be coated with other materials.

The zinc-containing particles are preferably particles containing only zinc as a metallic and metalloid element (e.g., zinc oxide particles, zinc hydroxide particles, zinc carbonate particles, zinc sulfide particles, mixed particles thereof, reaction products thereof, etc.), and more preferably at least one of zinc oxide particles and their reaction products (reaction products of zinc oxide particles). Zinc oxide particles refer to particles whose main component is zinc oxide. Similarly, for zinc hydroxide particles, etc., the main component refers to particles whose main component is its compound (zinc hydroxide, etc.). The main component refers to the component with the highest mass content. The zinc oxide content in zinc oxide particles is preferably 90% by mass or more, and more preferably 99% by mass or more. Zinc oxide particles may consist substantially of only zinc oxide. The same applies to zinc hydroxide particles, etc.

The reaction products of zinc oxide particles are typically particles produced when zinc oxide particles react with metallic lithium in the negative electrode active material layer. Specifically, metallic lithium is thought to reduce zinc oxide, producing metallic zinc or a zinc-lithium alloy. That is, it is preferable that the reaction products of zinc oxide particles contain metallic zinc. Furthermore, the reaction products of zinc oxide particles may also contain particles that result from the reaction between zinc oxide and metallic lithium, such as compounds containing zinc and lithium, or compounds containing zinc, oxygen, and hydrogen. Additionally, the reaction products of zinc oxide particles may be particles produced by reactions with substances other than metallic lithium, such as other components in the coating layer other than zinc-containing particles, or particles produced by reactions with the dispersion medium used to form the coating layer.

The average particle size of the zinc-containing particles is preferably 1 nm to 1 mm, more preferably 3 nm to 200 nm, even more preferably 5 nm to 100 nm, and even more preferably 10 nm to 50 nm. By setting the average particle size of the zinc-containing particles within the above range, polarization is further suppressed, for example, by lowering the resistance.

The "average particle size" of zinc-containing particles is the average value of the Ferret diameter of primary particles observed using a TEM (transmission electron microscope) or SEM (scanning electron microscope). This average Ferret diameter is based on 100 primary particles extracted while avoiding extremely large and extremely small particles.

The coating layer may contain components other than zinc-containing particles. Examples of such other components include zinc-free compound particles, metal particles other than metallic zinc, binders, and components derived from the dispersion medium used to form the coating layer. However, to enhance the effect of suppressing polarization, it is preferable that the coating layer consists substantially only of zinc-containing particles. Specifically, the zinc-containing particle content in the coating layer may be, for example, 90% by mass or more, but 99% by mass or more is preferable, and 99.9% by mass or more is more preferable. In the negative electrode, even if the coating layer consists substantially only of zinc-containing particles, it is considered that the coating layer is laminated onto the surface of the negative electrode active material layer due to welding or other attractive forces or bonds between the metallic lithium in the negative electrode active material layer and the zinc-containing particles in the coating layer, and among the zinc-containing particles themselves.

Furthermore, the coating layer is preferably composed of substantially inorganic materials. These inorganic materials include inorganic materials that form particles containing the zinc element. The inorganic content in the coating layer is preferably 90% by mass or more, more preferably 99% by mass or more, and even more preferably 99.9% by mass or more. When the coating layer is composed of substantially inorganic materials, polarization is more suppressed, for example, because the electrical resistance tends to be lower.

The average thickness of the coating layer is preferably 0.1 μm to 100 μm, more preferably 0.5 μm to 50 μm, even more preferably 1 μm to 30 μm, and even more preferably 2 μm to 15 μm. By setting the average thickness of the coating layer within the above range, the effect of reducing electrical resistance is sufficiently achieved, and polarization is further reduced. The "average thickness" of the coating layer is the average value of the thickness measured at five arbitrary locations based on the cross-sectional SEM image.

The coating layer is typically a porous layer. This porous nature allows, for example, lithium ions in a non-aqueous electrolyte (a non-aqueous electrolyte) to permeate the coating layer easily. Generally, if a cross-sectional SEM image of the coating layer reveals the presence of zinc-containing particles and inter-particle voids, then the coating layer can be considered porous.

<Method for manufacturing the negative electrode>
A method for manufacturing a negative electrode according to one embodiment of the present invention comprises forming a coating layer on the surface of a negative electrode active material layer containing metallic lithium using a coating layer forming material containing zinc element particles. This manufacturing method can be the same as that for conventionally known negative electrodes for non-aqueous electrolyte energy storage elements, except for the formation of the coating layer in this manner. For example, before forming the coating layer, the negative electrode active material layer containing metallic lithium can be laminated directly onto a negative electrode substrate or via an intermediate layer, and the negative electrode can be obtained in the state before the coating layer is formed by pressing or the like. 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 present embodiment of the present invention described above, and may be metallic lithium foil or lithium alloy foil.

The coating layer forming material may be, for example, a dispersion containing zinc-containing particles and a dispersion medium. The coating layer can be formed by applying such a coating layer forming material to the surface of the negative electrode active material layer and drying the dispersion medium. The coating layer may also be formed by methods other than application, such as immersion. Furthermore, the coating layer may be formed by a coating layer forming material consisting solely of zinc-containing particles, using a dry coating method or the like.

The specific and preferred forms of the negative electrode and coating layer formed by this manufacturing method are the same as those of the negative electrode and coating layer provided on the negative electrode according to the embodiment of the present invention described above.

<Non-aqueous electrolyte energy storage element>
A non-aqueous electrolyte energy storage element (hereinafter also simply referred to as "energy storage element") according to one embodiment of the present invention comprises an electrode body having a positive electrode, a negative electrode, and a separator, a non-aqueous electrolyte, and a container for housing the electrode body and the non-aqueous electrolyte. The electrode body is usually a stacked type in which a plurality of positive electrodes and a plurality of negative electrodes are stacked with a separator in between, or a wound type in which the positive electrode and negative electrode are wound in a stacked state with a separator in between. The non-aqueous electrolyte exists contained within the positive electrode, negative electrode, and separator. As an example of a non-aqueous electrolyte energy storage element, a non-aqueous electrolyte secondary battery (hereinafter also simply referred to as "secondary battery") will be described.

(positive electrode)
The positive electrode comprises a positive electrode substrate and a positive electrode active material layer disposed directly on the positive electrode substrate 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 is electrically conductive. While the positive electrode substrate can have the same configuration as the negative electrode substrate, the material used is typically a metal such as aluminum, titanium, tantalum, or stainless steel, or an alloy thereof. Among these, aluminum or an aluminum alloy is preferred from the viewpoint of high potential resistance, high conductivity, and cost. Examples of positive electrode substrates include foil, vapor-deposited film, mesh, and porous material, with foil being preferred from a cost perspective. Therefore, aluminum foil or aluminum alloy foil is preferred as the positive electrode substrate. Examples of aluminum or aluminum alloys include A1085, A3003, and A1N30 as specified in JIS-H-4000 (2014) or JIS-H4160 (2006).

The average thickness of the positive electrode substrate is preferably 3 μm to 50 μm, more preferably 5 μm to 40 μm, even more preferably 8 μm to 30 μm, and particularly preferably 10 μm to 25 μm. By setting the average thickness of the positive electrode substrate within the above range, the strength of the positive electrode substrate can be increased while simultaneously increasing the energy density per unit volume of the secondary battery.

The positive electrode active material layer contains the positive electrode active material. The positive electrode active material layer may optionally contain components such as conductive agents, binders, thickeners, and fillers.

The positive electrode active material can be appropriately selected from known positive electrode active materials. For lithium secondary batteries, materials that can intercept and release lithium ions are usually used as positive electrode active materials. Examples of positive electrode active materials include lithium transition metal composite oxides having an α- _NaFeO2 crystal structure, lithium transition metal composite oxides having a spinel crystal structure, polyanion compounds, chalcogen compounds, sulfur, and the like. Examples of lithium transition metal composite oxides having α-NaFeO ₂ type crystal structure include Li[Li _x Ni _(1-x) ]O ₂ (0≦x<0.5), 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 Examples include _γ Co _β Al _(1-x-γ-β) ]O ₂ (0 ≤ x < 0.5, 0 < γ, 0 < β, 0.5 < γ + β < 1). Examples of lithium transition metal composite oxides 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 polyanion compounds include LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , LiCoPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , Li ₂ MnSiO ₄ , and Li ₂ CoPO ₄ F. Examples of chalcogen compounds include titanium disulfide, molybdenum disulfide, and molybdenum dioxide. The atoms or polyanions in these materials may be partially substituted with atoms or anions of other elements. The surfaces 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 may be used in mixture form.

As the positive electrode active material, a lithium transition metal composite oxide is preferred, and a lithium transition metal composite oxide having an α- _NaFeO2 type crystal structure is more preferred. 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- _NaFeO2 type crystal structure, the molar ratio of lithium (Li) to the transition metal (Me) (Li/Me) is preferably greater than 1.0, more preferably 1.1 or greater, more preferably 1.2 or greater, and even more preferably 1.3 or greater. By using such a lithium transition metal composite oxide, the electrical capacity can be increased. The upper limit of the molar ratio of lithium to the transition metal (Li/Me) is preferably 1.6, and more preferably 1.5.

As a lithium transition metal composite oxide having an α-NaFeO2 _type crystal structure, the compound represented by the following formula (1) is preferred.
Li _1+α Me _1-α O ₂ ...(1)
In equation (1), Me is a transition metal containing Ni or Mn. 0 < α < 1.

In formula (1), Me preferably contains Ni and Mn. Me is preferably composed substantially of two elements, Ni and Mn, or three elements, Ni, Mn, and Co. Me may also contain other transition metals.

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

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

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

In equation (1), the molar ratio of Li to Me (Li/Me), i.e., (1+α)/(1-α), is preferably greater than 1.0 (α>0), more preferably 1.1 or greater, even more preferably 1.2 or greater, and even more preferably 1.3 or greater. On the other hand, the upper limit of this molar ratio (Li/Me) is preferably 1.6, and more preferably 1.5. Setting the molar ratio (Li/Me) within the above range increases the electrical capacitance.

Lithium transition metal composite oxides having a molar ratio (Li/Me) of lithium (Li) to the transition metal (Me) greater than 1.0 are preferably those in which no diffraction peaks exist in the range of 20° to 22° in the X-ray diffraction pattern using CuKα rays. Lithium transition metal composite oxides having a molar ratio (Li/Me) of lithium (Li) to the transition metal (Me) greater than 1.0 generally exhibit increased capacitance after undergoing initial charge and discharge until the positive electrode potential reaches, for example, 4.5 V vs. Li/Li ⁺ or higher. Furthermore, due to changes in the crystal structure during such initial charge and discharge, diffraction peaks that existed in the range of 20° to 22° before the initial charge and discharge disappear. In other words, a lithium transition metal composite oxide having a molar ratio (Li/Me) of lithium (Li) to the transition metal (Me) greater than 1.0, and in which no diffraction peaks exist in the range of 20° to 22° in the X-ray diffraction pattern, exhibits high capacitance.

In this specification, the composition ratio of lithium transition metal composite oxide refers to the composition ratio when the device is fully discharged by the following method. First, the non-aqueous electrolyte energy storage element is charged with a constant current of 0.05 C until it reaches the charging termination voltage for normal use, bringing it to a fully charged state. After a 30-minute rest, it is discharged with a constant current of 0.05 C until it reaches the lower limit voltage for normal use. The device is disassembled, the positive electrode is removed, and a test battery is assembled with a metallic lithium electrode as the counter electrode. A constant current discharge is performed at a current of 10 mA per gram of positive electrode mixture until the positive electrode potential reaches 2.0 V vs. Li/Li ⁺ , adjusting the positive electrode to a fully discharged state. Here, pure metallic lithium, not a lithium alloy, is used for the metallic lithium electrode. The device is disassembled again, and the positive electrode is removed. The non-aqueous electrolyte adhering to the removed positive electrode is thoroughly washed using dimethyl carbonate, and after drying at room temperature overnight, the lithium transition metal composite oxide, the positive electrode active material, is collected. The collected lithium transition metal composite oxide will be subjected to measurement. The entire process, from dismantling the non-aqueous electrolyte energy storage device to collecting the lithium transition metal composite oxide, will be carried out in an argon atmosphere with a dew point of -60°C or lower.

X-ray diffraction measurements of lithium transition metal composite oxides are performed on lithium transition metal composite oxides that have been brought to a fully discharged state using the method described above. Specifically, the X-ray diffraction measurement is performed by powder X-ray diffraction using an X-ray diffractometer (Rigaku's "MiniFlex II"), with the radiation source being CuKα rays, the tube voltage being 30 kV, and the tube current being 15 mA. At this time, the diffracted X-rays pass through a 30 μm thick Kβ filter 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 divergence slit width is 0.625°, the 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 relative to all positive electrode active materials is preferably 50% by mass, more preferably 80% by mass, and even more preferably 95% by mass. The content of the lithium transition metal composite oxide relative to all positive electrode active materials may be 100% by mass.

The positive electrode active material is usually in the form of particles (powder). The average particle size of the positive electrode active material is preferably, for example, between 0.1 μm and 20 μm. Setting the average particle size of the positive electrode active material above the lower limit facilitates its manufacture and handling. Setting the average particle size of the positive electrode active material below the upper limit improves the electronic conductivity of the positive electrode active material layer. When using a composite material of the positive electrode active material and other materials, the average particle size of the composite material is considered the average particle size of the positive electrode active material.

To obtain powder with a specified particle size, grinders and classifiers are used. Grinding methods include, for example, using mortars, ball mills, sand mills, vibrating ball mills, planetary ball mills, jet mills, counter-jet mills, swirling airflow jet mills, or sieves. Wet grinding, using water or organic solvents such as hexane, can also be employed during grinding. For classification, sieves and air-powered classifiers are used as needed, both dry and wet.

The content of the positive electrode active material in the positive electrode active material layer is preferably 50% to 99% by mass, more preferably 70% to 98% by mass, and even more preferably 80% to 95% by mass. By setting the positive electrode active material content within the above range, both high energy density and manufacturability of the positive electrode active material layer can be achieved.

The conductive agent is not particularly limited as long as it is a material that possesses conductivity. Examples of such conductive agents include carbonaceous materials, metals, and conductive ceramics. Examples of carbonaceous materials include graphitized carbon, non-graphitized carbon, and graphene-based carbon. Examples of non-graphitized carbon include carbon nanofibers, pitch-based carbon fibers, and carbon black. Examples of carbon black include furnace black, acetylene black, and Ketjen black. Examples of graphene-based carbon include graphene, carbon nanotubes (CNTs), and fullerenes. The conductive agent can take the form of powder or fiber. As a conductive agent, one of these materials may be used alone, or two or more may be used in mixture form. Furthermore, these materials may be used in composite form. For example, a composite material of carbon black and CNTs may be used. Among these, carbon black is preferred from the viewpoint of electronic conductivity and coating properties, and acetylene black is particularly preferred.

The content of the conductive agent in the positive electrode active material layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less. By setting the conductive agent content within the above range, the energy density of the secondary battery can be increased.

Examples of binders include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyacrylic, and polyimide; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; and polysaccharide polymers.

The binder content in the positive electrode active material layer is preferably 1% to 10% by mass, and more preferably 3% to 9% by mass. By keeping the binder content within this range, the active material can be stably retained.

Examples of thickening agents include polysaccharide polymers such as carboxymethylcellulose (CMC) and methylcellulose. If the thickening agent has a functional group that reacts with lithium, etc., this functional group may be deactivated beforehand by methylation or other means.

The filler is not particularly limited. Examples of fillers include polyolefins such as polypropylene and polyethylene; inorganic oxides such as silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates; hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide; carbonates such as calcium carbonate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium sulfate; nitrides such as aluminum nitride and silicon nitride; mineral resource-derived materials or artificial products thereof, such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica.

The positive electrode active material layer may contain typical nonmetallic elements such as B, N, P, F, Cl, Br, and I, typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba, and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, and W as components other than the positive electrode active material, conductive agent, binder, thickener, and filler.

(Negative electrode)
The negative electrode provided in the non-aqueous electrolyte energy storage element according to one embodiment of the present invention is the negative electrode according to the above-described embodiment of the present invention.

(Separator)
The separator can be appropriately selected from known separators. Examples of separators include a separator consisting only of a base layer, or a separator in which a heat-resistant layer containing heat-resistant particles and a binder is formed on one or both sides of the base layer. Examples of the base layer shape of the separator include woven fabric, nonwoven fabric, and porous resin film. Among these shapes, porous resin film is preferred from the viewpoint of strength, and nonwoven fabric is preferred from the viewpoint of liquid retention of non-aqueous electrolytes. As for the material of the base layer of the separator, polyolefins such as polyethylene and polypropylene are preferred from the viewpoint of shutdown function, and polyimide and aramid are preferred from the viewpoint of oxidative degradation resistance. A composite material of these resins may also be used as the base layer of the separator.

The heat-resistant particles contained in the heat-resistant layer preferably have a mass reduction of 5% or less when heated from room temperature to 500°C in an air atmosphere of 1 atmosphere, and more preferably have a mass reduction of 5% or less when heated from room temperature to 800°C. Inorganic compounds are examples of materials with a mass reduction of less than the predetermined amount. Examples of inorganic compounds include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium titanate; covalent crystals such as silicon and diamond; mineral resource-derived materials such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof. These inorganic compounds may be used individually or in combination, or two or more may be used as a mixture. Among these inorganic compounds, silicon dioxide, aluminum oxide, or aluminosilicates are preferred from the viewpoint of safety for energy storage elements.

The porosity of the separator is preferably 80% by volume or less from the viewpoint of strength, and preferably 20% by volume or more from the viewpoint of discharge performance. Here, "porosity" refers to a volume-based value and means the measurement value obtained using a mercury porosimeter.

A polymer gel composed of a polymer and a non-aqueous electrolyte may be used as a separator. Examples of polymers include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, and polyvinylidene fluoride. Using a polymer gel has the effect of suppressing leakage. A polymer gel may also be used in combination with a porous resin film or nonwoven fabric as described above as a separator.

(Non-aqueous electrolytes)
As the non-aqueous electrolyte, it can be appropriately selected from known non-aqueous electrolytes. A non-aqueous electrolyte solution may be used as the non-aqueous electrolyte. The non-aqueous electrolyte solution contains a non-aqueous solvent and an electrolyte salt dissolved in this non-aqueous solvent.

As the non-aqueous solvent, it can be appropriately selected from known non-aqueous solvents. Examples of non-aqueous solvents include cyclic carbonates, linear carbonates, carboxylic acid esters, phosphate esters, sulfonic acid esters, ethers, amides, and nitriles. As the non-aqueous solvent, compounds in which some of the hydrogen atoms are substituted with halogens may also be used.

It is preferable to use a cyclic carbonate or a linear carbonate as the non-aqueous solvent, and more preferable to use both a cyclic carbonate and a linear carbonate in combination. Using a cyclic carbonate can promote the dissociation of the electrolyte salt, thereby improving the ionic conductivity of the non-aqueous electrolyte. Using a linear carbonate can keep the viscosity of the non-aqueous electrolyte low. When using both a cyclic carbonate and a linear carbonate in combination, the volume ratio of the cyclic carbonate to the linear carbonate (cyclic carbonate:linear carbonate) is preferably in the range of 5:95 to 50:50.

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

As for cyclic carbonates, fluorinated cyclic carbonates such as fluoroethylene carbonate, difluoroethylene carbonate, fluoromethylethylene carbonate, and trifluoroethylethylene carbonate are preferred from the viewpoint of oxidation resistance and other factors.

Examples of linear carbonates include diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, diphenyl carbonate, 2,2,2-trifluoroethyl methyl carbonate, bis(2,2,2-trifluoroethyl) carbonate, and ethyl-2,2,2-trifluoroethyl carbonate.

As for the linear carbonate, fluorinated linear carbonates such as 2,2,2-trifluoroethylmethyl carbonate, bis(2,2,2-trifluoroethyl) carbonate, and ethyl-2,2,2-trifluoroethyl carbonate are preferred from the viewpoint of oxidation resistance and other factors.

The content of carbonates (cyclic carbonates and linear carbonates) relative to the total non-aqueous solvent is preferably 50% to 100% by volume, more preferably 80% or more by volume, and even more preferably 90% or more by volume, 95% or more by volume, or 99% or more by volume.

The non-aqueous solvent preferably contains a fluorinated solvent. The content of the fluorinated solvent relative to the total non-aqueous solvent is preferably 60% by volume or more, more preferably 90% by volume or more, even more preferably 99% by volume or more, and particularly preferably 100% by volume. A fluorinated solvent refers to a solvent (non-aqueous solvent) having a fluorine atom in its molecule, such as fluorinated carbonates (fluorinated linear carbonates and fluorinated cyclic carbonates) and fluorinated ethers. By including a fluorinated solvent in this way, preferably at or above the lower limit mentioned above, oxidation resistance and other properties can be improved.

Electrolyte salts are typically lithium salts. Examples of lithium salts include inorganic _lithium salts such as _LiPF₂₆ , _{LiPO₂₆F₂} , _LiBF₄ , _LiClO₄ , and _LiN ( _SO₂F ) _₂ ; lithium oxalate salts such as lithium bis(oxalate)borate (LiBOB), lithium difluorooxalate borate (LiFOB), and lithium bis( _oxalate )difluorophosphate ( _LiFOP ); and lithium salts having halogenated hydrocarbon groups such as _LiSO₃CF₃ , _LiN ( _SO₂CF₃ ) _₂ , _LiN ( _{SO₂C₂F₅} ) _₂ , LiN( _SO₂CF₃ ) _{( SO₂C₄F₹ ) ,} LiC( _SO₂CF₃ ) _{₃ ,} and LiC( _{SO₂C₂F₅ ) ₃} . Among these, inorganic lithium salts are preferred, and _LiPF6 is more preferred. Furthermore, from the viewpoint of oxidation resistance and other factors, electrolyte salts containing fluorine atoms are preferred.

The electrolyte salt content in the non-aqueous electrolyte is preferably 0.1 mol/dm³ to ^2.5 mol/dm³ at 20°C and ¹ atm, more preferably 0.3 mol/dm³ to ^2.0 mol/dm³, even ^more preferably 0.5 mol/dm³ to ^1.7 mol/ ^dm³ , and particularly preferably 0.7 mol/dm³ to 1.5 mol/dm³ at 20°C and ^{1 atm} . By setting the electrolyte salt content within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

Non-aqueous electrolytes may contain additives in addition to the non-aqueous solvent and electrolyte salt. Examples of additives include: aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; partially halides of the aforementioned aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene; halogenated anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole; vinylene carbonate, methylvinylene carbonate, ethylvinylene carbonate, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic acid anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, and propane sult. Examples include propensultone, butanesultone, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethylsulfone, dimethyl sulfoxide, diethylsulfoxide, tetramethylene sulfoxide, diphenyl sulfide, 4,4'-bis(2,2-dioxo-1,3,2-dioxathiolane), 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisole, diphenyl disulfide, dipyridinium disulfide, 1,3-propensultone, 1,3-propanesultone, 1,4-butanesultone, 1,4-butensultone, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakithrimethylsilyl titanate, lithium monofluorophosphate, lithium difluorophosphate, etc. These additives may be used individually or in combination of two or more.

The additive content in the non-aqueous electrolyte is preferably 0.01% to 10% by mass relative to the total mass of the non-aqueous electrolyte, more preferably 0.1% to 7% by mass, even more preferably 0.2% to 5% by mass, and particularly preferably 0.3% to 3% by mass. By setting the additive content within the above range, it is possible to improve the capacity retention performance or cycle performance after high-temperature storage, and to further enhance safety.

For non-aqueous electrolytes, solid electrolytes may be used, or non-aqueous electrolytes and solid electrolytes may be used in combination.

The solid electrolyte can be selected from any material that has lithium-ion conductivity and is solid at room temperature (e.g., 15°C to 25°C). Examples of solid electrolytes include sulfide solid electrolytes, oxide solid electrolytes, oxynitride solid electrolytes, and polymer solid electrolytes.

Examples of sulfide solid electrolytes include _Li₂S - _P₂S₅ , _LiI - _Li₂S - _{P₂S₅ , and Li₁₀Ge} - _P₂S₁₂ .

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

The upper limit of the positive electrode potential at the charging termination voltage during normal use of the non-aqueous electrolyte energy storage element is, for example, 5.0V (vs. Li/Li ⁺ ), but may also be 4.8V (vs. Li/Li ⁺ ), or 4.7V (vs. Li/Li ⁺ ).

Furthermore, "normal use" refers to using a non-aqueous electrolyte energy storage element under the recommended or specified charging conditions. For example, if a charger for the non-aqueous electrolyte energy storage element is available, this refers to using that charger when using the element.

The shape of the non-aqueous electrolyte energy storage element in this embodiment is not particularly limited; examples include cylindrical batteries, prismatic batteries, flat batteries, coin-type batteries, button-type batteries, and the like.

Figure 1 shows a non-aqueous electrolyte energy storage element 1 as an example of a rectangular battery. Note that this figure is a transparent view of the inside of the container. An electrode body 2, having a positive electrode and a negative electrode wound around a separator, is housed in a rectangular container 3. The positive electrode is electrically connected to the positive electrode terminal 4 via a positive electrode lead 41. The negative electrode is electrically connected to the negative electrode terminal 5 via a negative electrode lead 51.

<Energy Storage Device>
The non-aqueous electrolyte energy storage element of this embodiment can be mounted as an energy storage unit (battery module) composed of multiple non-aqueous electrolyte energy storage elements 1 in power supplies for automobiles such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), power supplies for electronic devices such as personal computers and communication terminals, or power storage power supplies. In this case, it is sufficient that the technology of the present invention is applied to at least one of the non-aqueous electrolyte energy storage elements included in the energy storage unit.

Figure 2 shows an example of a power storage device 30, which is formed by further assembling power storage units 20, each containing two or more electrically connected non-aqueous electrolyte energy storage elements 1. The power storage device 30 may include busbars (not shown) for electrically connecting two or more non-aqueous electrolyte energy storage elements 1, busbars (not shown) for electrically connecting two or more power storage units 20, etc. The power storage unit 20 or the power storage device 30 may also include a condition monitoring device (not shown) for monitoring the state of one or more non-aqueous electrolyte energy storage elements.

<Manufacturing method for non-aqueous electrolyte energy storage elements>
A method for manufacturing a non-aqueous electrolyte energy storage element according to one embodiment of the present invention comprises manufacturing a non-aqueous electrolyte energy storage element using the negative electrode according to the above-described embodiment of the present invention, or a negative electrode obtained by the method for manufacturing the negative electrode according to the above-described embodiment of the present invention.

The specific and preferred embodiments of the negative electrode used in these manufacturing methods are the same as those described above as the negative electrode according to one embodiment of the present invention.

Specifically, the method for manufacturing a non-aqueous electrolyte energy storage element comprises, for example, preparing an electrode body, preparing a non-aqueous electrolyte, and housing the electrode body and non-aqueous electrolyte in a container. Preparing the electrode body involves preparing a positive electrode and a negative electrode, and forming the electrode body by stacking or winding the positive electrode and negative electrode via a separator. The negative electrode prepared here is the negative electrode according to the embodiment of the present invention described above, or a negative electrode obtained by the method for manufacturing the negative electrode according to the embodiment of the present invention described above.

The method for housing the non-aqueous electrolyte in a container can be appropriately selected from known methods. For example, when using a non-aqueous electrolyte solution, the non-aqueous electrolyte solution can be injected through an inlet formed in the container, and then the inlet can be sealed.

The method for manufacturing the non-aqueous electrolyte energy storage element may further include performing initial charging and discharging on the assembled uncharged non-aqueous electrolyte energy storage element. For example, if the positive electrode active material of the non-aqueous electrolyte energy storage element is a lithium transition metal composite oxide in which the molar ratio of lithium (Li) to the transition metal (Me) (Li/Me) is greater than 1.0, the capacity will increase after undergoing initial charging and discharging. The number of charge and discharge cycles in the initial charging and discharging may be one, two, or three or more. If the positive electrode active material of the non-aqueous electrolyte energy storage element is a lithium transition metal composite oxide in which the molar ratio of lithium (Li) to the transition metal (Me) (Li/Me) is greater than 1.0, the positive electrode potential (positive electrode target potential) at the charging termination voltage during initial charging and discharging is preferably 4.5V vs. Li/Li ⁺ or 4.7V vs. Li/Li ⁺ or less.

<Other Embodiments>
Furthermore, the non-aqueous electrolyte energy storage element of the present invention is not limited to the above embodiments, and various modifications may be made without departing from the spirit of the present invention. For example, the configuration of one embodiment may be added to the configuration of another embodiment, and a part of the configuration of one embodiment may be replaced with the configuration of another embodiment or known technology. In addition, a part of the configuration of one embodiment may be deleted. Also, known technology may be added to the configuration of one embodiment.

In the above embodiment, the case in which the non-aqueous electrolyte energy storage element is used as a rechargeable non-aqueous electrolyte secondary battery (lithium secondary battery) was described, but the type, shape, dimensions, capacity, etc. of the non-aqueous electrolyte energy storage element are arbitrary. The present invention can also be applied to various secondary batteries, electric double-layer capacitors, or capacitors such as lithium-ion capacitors. Furthermore, the non-aqueous electrolyte energy storage element of the present invention can also be applied to lithium-air batteries.

In the above embodiment, an electrode body in which the positive and negative electrodes are stacked with a separator in between was described. However, the electrode body does not necessarily have a separator. For example, the positive and negative electrodes may be in direct contact with each other, with a non-conductive layer formed as the outermost layer of either the positive or negative electrode.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

The particles used as the coating layer forming material in the examples and comparative examples are shown below.
ZnO particles: Manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., average particle size 20 nm
_{Al₂O₃ particles} : Manufactured by Nippon Aerosil Co., Ltd., average particle size 13 nm
_SiO₂ particles: Manufactured by Nippon Aerosil Co., Ltd., average particle size 12 nm
_TiO2 particles: Manufactured by Nippon Aerosil Co., Ltd., average particle size 20 nm
The average particle sizes of the above particles were all measured using TEM in accordance with the method described above.

[Example 1]
(Fabrication of the positive electrode)
As the positive electrode active material, a lithium transition metal composite oxide having an α-NaFeO2 _type crystal structure and represented as Li₁ _{+ αMe₁ - αO₂} (where Me is a transition metal) was used. Here, the molar ratio of Li to Me, Li/Me, was 1.33, and Me consisted of Ni and Mn, with Ni:Mn present in a molar ratio of 1:2.

A positive electrode mixture paste was prepared using N-methylpyrrolidone (NMP) as the dispersion medium, containing the above-mentioned positive electrode active material, acetylene black (AB) as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder in a solid content mass ratio of 92.5:4.5:3. The positive electrode mixture paste was applied to one side of an aluminum foil substrate, dried, and then pressed to produce a positive electrode with a positive electrode active material layer laminated on one side of the substrate.

(Fabrication of the negative electrode)
A copper foil (average thickness 10 μm), which serves as the negative electrode substrate, was laminated with a metallic lithium foil (average thickness 60 μm: 100% pure metallic lithium by mass) as the negative electrode active material layer on one side, and then pressed.
A coating layer forming material containing ZnO particles was prepared by dispersing the above-mentioned ZnO particles in dimethyl sulfoxide. The coating layer forming material was applied to the surface of the negative electrode active material layer using a spray gun. After application, it was dried on a hot plate set to 100°C, and then vacuum dried at 60°C. This resulted in a negative electrode in which the negative electrode substrate, negative electrode active material layer, and coating layer were stacked in that order. The average thickness of the formed coating layer was 5 μm.

(Preparation of non-aqueous electrolytes)
_LiPF6 was dissolved at a concentration of 1 mol/ ^dm³ in a mixed solvent prepared by mixing fluoroethylene carbonate (FEC) and 2,2,2-trifluoroethylmethyl carbonate (TFEMC) in a volume ratio of 30:70 to obtain a non-aqueous electrolyte.

(Fabrication of non-aqueous electrolyte energy storage elements)
An electrode body was fabricated by laminating the positive electrode and the negative electrode with a polyolefin microporous membrane acting as a separator. This electrode body was placed in a container made of a metal-resin composite film, and the non-aqueous electrolyte was injected into it. The container was then sealed and compressed from the outside at 0.3 MPa to obtain the non-aqueous electrolyte energy storage element of Example 1.

[Comparative Example 1]
A negative electrode and non-aqueous electrolyte energy storage element of Comparative Example 1 were obtained in the same manner as in Example 1, except that the ZnO particles were replaced with _{Al₂O₃ particles} .

[Comparative Example 2]
A negative electrode and a non-aqueous electrolyte energy storage element of Comparative Example 2 were obtained in the same manner as in Example 1, except that the ZnO particles were replaced with _SiO2 particles.

[Comparative Example 3]
A negative electrode and a non-aqueous electrolyte energy storage element of Comparative Example 3 were obtained in the same manner as in Example 1, except that the ZnO particles were replaced with _TiO2 particles.

[Comparative Example 4]
A negative electrode and a non-aqueous electrolyte energy storage element of Comparative Example 4 were obtained in the same manner as in Example 1, except that a coating layer was not formed on the negative electrode.

(Charge/discharge)
Each obtained non-aqueous electrolyte energy storage element underwent its first charge and discharge under the following conditions: Constant current and constant voltage charging was performed at 25°C with a charging current of 0.1C and a charging termination voltage of 4.6V. Charging was terminated when the charging current reached 0.02C. A 10-minute rest period was then observed. Subsequently, constant current discharge was performed with a discharge current of 0.1C and a discharge termination voltage of 2.0V.

Figure 3A shows the charge-discharge curves for each non-aqueous electrolyte energy storage element in Example 1 and Comparative Example 4 during the initial charge-discharge cycle described above. Figure 3B shows an enlarged view of the charge curve immediately after the start of charging in Figure 3A.

Figure 4A shows the charge-discharge curves for each non-aqueous electrolyte energy storage element in Comparative Example 1 and Comparative Example 4 during the initial charge-discharge cycle described above. Figure 4B shows an enlarged view of the charge curve immediately after the start of charging in Figure 4A.

Figure 5A shows the charge-discharge curves for each non-aqueous electrolyte energy storage element in Comparative Examples 2, 3, and 4 during the initial charge-discharge cycle described above. Figure 5B shows an enlarged view of the charge curve immediately after the start of charging in Figure 5A.

As shown in Figures 3A and 3B, the non-aqueous electrolyte energy storage element of Example 1, which has a negative electrode with a coating layer formed using a coating layer forming material containing ZnO particles, exhibits a lower charging voltage and suppressed polarization compared to the non-aqueous electrolyte energy storage element of Comparative Example 4, which has a negative electrode without a coating layer. On the other hand, as shown in Figures 4A, 4B, 5A, and 5B, in the non-aqueous electrolyte energy storage elements of Comparative Examples 1 to ₃ , which have negative electrodes with a coating layer formed using a coating layer forming material containing _Al₂O₃ particles, _SiO₂ particles, or _TiO₂ particles, no polarization suppression effect was observed compared to the non-aqueous electrolyte energy storage element of Comparative Example 4, which has a negative electrode without a coating layer. Rather, as clearly shown in Figure 4B, in the case of the non-aqueous _electrolyte energy storage element of Comparative Example 1, which has a negative electrode with a coating layer formed using a coating layer forming material containing _Al₂O₃ particles, the charging voltage was higher and polarization was greater compared to the non-aqueous electrolyte energy storage element of Comparative Example 4, which has a negative electrode without a coating layer. Furthermore, as shown in Figure 5B, in the non-aqueous electrolyte energy storage elements of Comparative Examples 2 and 3, which are equipped with a negative electrode having a coating layer formed with a coating layer forming material containing _SiO2 particles or _TiO2 particles, the charging voltage was higher immediately after the start of charging, resulting in greater polarization, compared to the non-aqueous electrolyte energy storage element of Comparative Example 4, which is equipped with a negative electrode without a coating layer.

(Measurement of AC resistance)
The AC resistance of each non-aqueous electrolyte energy storage element in Example 1 and Comparative Example 4, before charging and discharging, was measured at 25°C and 1 kHz. The AC resistance of the non-aqueous electrolyte energy storage element in Example 1 was 6.93 Ω, and the AC resistance of the non-aqueous electrolyte energy storage element in Comparative Example 4 was 14.96 Ω. It is presumed that when a coating layer is formed using a coating layer forming material containing ZnO particles, the electrical resistance of the negative electrode surface is reduced, thereby suppressing polarization.

This invention can be applied to non-aqueous electrolyte energy storage elements used as power sources for electronic devices such as personal computers and communication terminals, as well as automobiles.

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

Claims (7)

Anode substrate and
A negative electrode active material layer containing metallic lithium is laminated on the above negative electrode substrate ,
The negative electrode active material layer comprises a coating layer containing zinc-containing particles laminated on its surface,
The average particle size of the zinc element-containing particles is 3 nm or more and 200 nm or less.
The particles containing the zinc element described above are at least one of zinc oxide particles and their reaction products.
The average thickness of the above coating layer is 1 μm or more and 30 μm or less.
A negative electrode for a non-aqueous electrolyte energy storage element , wherein the above-mentioned coating layer is laminated on the surface of the negative electrode active material layer that does not face the negative electrode substrate . A negative electrode active material layer containing metallic lithium,
The negative electrode active material layer comprises a coating layer containing zinc-containing particles laminated on its surface,
The average particle size of the zinc element-containing particles is 3 nm or more and 200 nm or less.
The above-mentioned particles containing the element zinc are at least one of zinc oxide particles and their reaction products.
The average thickness of the above coating layer is 1 μm or more and 30 μm or less.
A negative electrode for a non-aqueous electrolyte energy storage element , wherein the metallic lithium content in the negative electrode active material layer is 90% by mass or more . Anode substrate and
A negative electrode active material layer containing metallic lithium is laminated on the above negative electrode substrate ,
The negative electrode active material layer comprises a coating layer containing zinc-containing particles laminated on its surface,
The average particle size of the zinc element-containing particles is 3 nm or more and 200 nm or less.
The content of particles containing the above zinc element in the above coating layer is 99% by mass or more.
A negative electrode for a non-aqueous electrolyte energy storage element , wherein the above-mentioned coating layer is laminated on the surface of the negative electrode active material layer that does not face the negative electrode substrate . A negative electrode active material layer containing metallic lithium,
The negative electrode active material layer comprises a coating layer containing zinc-containing particles laminated on its surface,
The average particle size of the zinc element-containing particles is 3 nm or more and 200 nm or less.
The content of particles containing the above zinc element in the above coating layer is 99% by mass or more.
A negative electrode for a non-aqueous electrolyte energy storage element , wherein the metallic lithium content in the negative electrode active material layer is 90% by mass or more . The method comprises laminating a negative electrode active material layer onto a negative electrode substrate, and forming a coating layer on the surface of the negative electrode active material layer containing metallic lithium using a coating layer forming material containing zinc element particles.
The average particle size of the zinc element-containing particles is 3 nm or more and 200 nm or less.
The above-mentioned particles containing the element zinc are at least one of zinc oxide particles and their reaction products.
The average thickness of the above coating layer is 1 μm or more and 30 μm or less.
A method for manufacturing a negative electrode for a non-aqueous electrolyte energy storage element , wherein the above-mentioned coating layer is laminated on the surface of the negative electrode active material layer that does not face the negative electrode substrate . A non-aqueous electrolyte energy storage element comprising the negative electrode according to any one of claims 1 to 4 . A method for manufacturing a non-aqueous electrolyte energy storage element, comprising manufacturing a non-aqueous electrolyte energy storage element using a negative electrode described in any one of claims 1 to 4 , or a negative electrode obtained by the method for manufacturing a negative electrode described in claim 5.