JP7469434B2 - Nonaqueous electrolyte battery and method of manufacturing same - Google Patents

Description

The present invention relates to a non-aqueous electrolyte battery with good high-temperature storage characteristics and a method for manufacturing the same.

Non-aqueous electrolyte batteries are used for a variety of purposes, taking advantage of their characteristics such as high capacity and high voltage. In particular, in recent years, the demand for non-aqueous electrolyte batteries for in-vehicle equipment has been growing.

Conventionally, non-aqueous electrolyte primary batteries have been used as power sources for in-vehicle electronic devices. These batteries have better storage characteristics than commonly used non-aqueous electrolyte secondary batteries, and experience almost no capacity loss even when stored for long periods of time (several years or more).

Metallic lithium and lithium alloys such as Li-Al (lithium-aluminum) alloy are used as the negative electrode active material in the non-aqueous electrolyte primary battery. However, since lithium alloys can also be used as the negative electrode active material in non-aqueous electrolyte secondary batteries, it has been proposed to stabilize the battery characteristics by constructing the negative electrode using a clad material made of a metal capable of absorbing and releasing lithium and a different metal that does not have the ability to absorb and release lithium (Patent Documents 1 and 2).

In addition, a non-aqueous electrolyte battery has been proposed that can be repeatedly charged and has improved storage characteristics in high-temperature environments. The battery has a laminate containing a metal substrate layer that does not alloy with Li and an Al active layer on both sides of the metal substrate layer, and uses a clad material as the negative electrode in which a Li-Al alloy is formed on the surface side of the Al active layer (Patent Document 3).

Japanese Patent Application Laid-Open No. 8-293302 Japanese Patent Application Laid-Open No. 10-106628 International Publication No. 2016/039323

On the other hand, the non-aqueous electrolyte battery disclosed in Patent Document 3, which uses a clad material as the negative electrode, can be repeatedly charged and has improved storage characteristics in high-temperature environments, but the clad material is expensive and there are problems with the metal that makes up the metal substrate layer of the clad material dissolving into the non-aqueous electrolyte when the battery is overdischarged, adversely affecting the battery characteristics.

To address this issue, it is possible to use an inexpensive aluminum plate for the negative electrode instead of an expensive clad material, as partially disclosed in Patent Document 2. However, if only an aluminum plate is used for the negative electrode, when the battery is overcharged, Al and Li react excessively, and the thickness of the Li-Al alloy layer formed on both sides of the aluminum plate gradually increases and the thickness of the aluminum plate (Al layer) gradually decreases. As a result, the negative electrode itself expands due to the formation of the Li-Al alloy layer, and ultimately the Al layer breaks because it cannot withstand the stress caused by the expansion of the negative electrode, and the reliability of the battery in a high-temperature environment is reduced. In particular, in the case of a prismatic battery in which a wound electrode body is enclosed in a prismatic exterior body, a large stress is applied to the R part of the negative electrode, and there is a greater concern about a decrease in the reliability of the battery.

The present invention solves the above problems by providing a non-aqueous electrolyte battery that can maintain the strength of the negative electrode even when aluminum is used alone as the negative electrode material, and has high long-term reliability in high-temperature environments.

The nonaqueous electrolyte battery of the present invention is a nonaqueous electrolyte battery including a positive electrode, a negative electrode, a nonaqueous electrolyte, and a separator, the positive electrode includes a positive electrode current collector and a positive electrode mixture layer formed on the positive electrode current collector, the positive electrode mixture layer is capable of absorbing and releasing Li ions, the area of the negative electrode is larger than the area of the positive electrode mixture layer of the positive electrode, and the negative electrode is disposed so as to cover the entire surface of the positive electrode mixture layer via the separator, the negative electrode includes an Al layer and a Li-Al alloy layer formed on the surface of the Al layer, and the tensile strength of the negative electrode is 4 N/mm or more.

Further, a method for producing the nonaqueous electrolyte battery of the present invention is a method for producing the nonaqueous electrolyte battery of the present invention, and includes the steps of: preparing a positive electrode having a positive electrode mixture layer formed on at least one surface of a positive electrode current collector and having a capacity of 0.68 mAh/ ^cm2 or more and 4.87 mAh/ ^cm2 or less; preparing a negative electrode precursor made of an aluminum base material having an area larger than an area of the positive electrode mixture layer of the positive electrode and a thickness of 30 μm or more and 150 μm or less; arranging the negative electrode precursor via a separator so as to cover the entire surface of the positive electrode mixture layer of the positive electrode to produce an electrode body; and sealing the electrode body and a nonaqueous electrolyte in an exterior body and then charging.

The present invention provides a non-aqueous electrolyte battery that has high long-term reliability even in high-temperature environments.

FIG. 1 is a schematic cross-sectional view of an aluminum substrate used in a negative electrode precursor. FIG. 2 is a schematic cross-sectional view of the negative electrode after the initial charge. FIG. 3 is a perspective view that typically illustrates a nonaqueous electrolyte battery according to the embodiment. FIG. 4 is a cross-sectional view taken along line II of FIG.

An embodiment of the nonaqueous electrolyte battery disclosed in this application will be described. The nonaqueous electrolyte battery of this embodiment includes a positive electrode, a negative electrode, a nonaqueous electrolyte, and a separator. The positive electrode includes a positive electrode current collector and a positive electrode mixture layer formed on the positive electrode current collector. The positive electrode mixture layer is capable of absorbing and releasing Li ions. The area of the negative electrode is larger than the area of the positive electrode mixture layer of the positive electrode. The negative electrode is disposed so as to cover the entire surface of the positive electrode mixture layer via the separator. The negative electrode includes an Al layer and a Li-Al alloy layer formed on the surface of the Al layer. The tensile strength of the negative electrode is 4 N/mm or more.

The nonaqueous electrolyte battery of this embodiment has the above-mentioned configuration, which improves long-term reliability in high-temperature environments.

Li (metallic Li) and Li-Al alloys (alloys of Li and Al) have a lower ability to accept Li (Li ions) than carbon materials, and non-aqueous electrolyte secondary batteries that use these as the negative electrode active materials tend to experience a rapid loss of capacity when repeatedly charged and discharged. For this reason, carbon materials such as graphite are commonly used as the negative electrode active material in conventional non-aqueous electrolyte secondary batteries that are intended to be used by repeatedly charging and discharging.

However, non-aqueous electrolyte secondary batteries that use carbon materials as the negative electrode active material are prone to self-discharge, and are prone to capacity loss when stored in a charged state.

For these reasons, non-aqueous electrolyte primary batteries, which have better storage characteristics than conventional non-aqueous electrolyte secondary batteries and experience almost no capacity loss even when stored for long periods of time (several years or more), are used for batteries to be used in in-vehicle devices and outdoor equipment.

On the other hand, even for these applications, there is a demand for batteries that can be recharged a few to several dozen times, even if they do not require repeated charging and discharging like normal secondary batteries, due to reasons such as ease of maintenance.

Therefore, in the nonaqueous electrolyte battery of this embodiment, a Li-Al alloy formed on the surface of the Al layer is used as the negative electrode active material so that high storage characteristics and high capacity can be achieved, particularly when the battery is used in high-temperature environments such as in vehicles or outdoor equipment, and a certain number of charging cycles can be achieved.

In addition, when aluminum is used as the negative electrode material, a negative electrode precursor is formed from aluminum foil or the like, and the negative electrode precursor, a positive electrode, a separator, a non-aqueous electrolyte, and the like are stored in a battery, and then initial charging (chemical formation) is performed to electrochemically react the aluminum foil with Li ions in the non-aqueous electrolyte to form a Li-Al alloy on the surface of the aluminum foil, and a negative electrode having an Al layer and a Li-Al alloy layer formed on the surface of the Al layer is formed and used. If Li-Al alloy is formed on the surface of the aluminum foil indefinitely during this initial charging, the Al layer that serves as the core material of the negative electrode becomes too thin and the strength decreases, and in the worst case, the aluminum foil becomes entirely Li-Al alloy, the core material of the negative electrode disappears, and the strength of the negative electrode is extremely reduced. Therefore, in this embodiment, in order to maintain the strength of the negative electrode and ensure the reliability of the battery, the tensile strength of the negative electrode is set to 4 N/mm or more. Setting the tensile strength of the negative electrode to 4 N/mm or more essentially means that the thickness of the Al layer that serves as the core material of the negative electrode is maintained at a certain level or more to maintain the strength.

The components of the nonaqueous electrolyte battery of this embodiment are described below.

<Negative Electrode>
In forming the negative electrode of the non-aqueous electrolyte battery of this embodiment, no current collector is used, and only an Al base material (such as an Al foil) is used as a negative electrode precursor. Specifically, the negative electrode precursor made of the Al base material is used as it is for assembling a battery, and the Al of the Al base material is electrochemically reacted with Li ions in the non-aqueous electrolyte by charging after assembly, to form a negative electrode having an Al layer and a Li-Al alloy layer formed on the surface of the Al layer.

The negative electrode always has an Al layer of a certain thickness, which serves as the core material of the negative electrode, allowing the tensile strength of the negative electrode to be 4 N/mm or more. The tensile strength of the negative electrode is more preferably 7 N/mm or more. On the other hand, if the tensile strength of the negative electrode is too high, the thickness of the Al layer becomes too large, the volume of the core material that does not contribute to charging and discharging increases, and the volumetric energy density of the battery decreases. Therefore, the upper limit of the tensile strength is preferably about 11 N/mm.

Examples of the Al base material include foil made of Al (and unavoidable impurities), and foil made of an Al alloy (the content of the alloy components is, for example, 50 mass% or less in total) containing Cu, Fe, Ni, Co, Mn, Cr, V, Ti, Zr, Nb, Mo, etc. as alloy components, with the balance being Al and unavoidable impurities. For example, when the alloy component of the Al base material is Cu, the Cu content is preferably 7 mass% or less, more preferably 2 mass% or less, and even more preferably 0.4 mass% or less. Within this range, the elution of Cu during overdischarge can be more reliably suppressed.

The thickness of the Al base material as the negative electrode precursor is preferably 30 μm or more, more preferably 40 μm or more, and preferably 150 μm or less, and more preferably 100 μm or less. If the thickness of the Al base material is within the above range, the tensile strength of the negative electrode after charging can be 4 N/mm or more, while the capacity of the negative electrode can be a certain level or more. However, since the nonaqueous electrolyte battery of this embodiment is configured with a positive electrode capacity regulation, when the thickness of the Al base material as the negative electrode precursor is 30 μm or more and 150 μm or less, in order to make the tensile strength of the negative electrode after charging 4 N/mm or more, the capacity of the positive electrode is preferably 0.68 mAh/cm ² or more and 4.87 mAh/cm ² or less, and more preferably 3.65 mAh/cm ² or less.

A negative electrode lead body can be provided on the Al substrate used as the negative electrode precursor in accordance with standard methods.

Figure 1 shows a cross-sectional view that shows a schematic example of an Al base material used in the negative electrode precursor of the nonaqueous electrolyte battery of this embodiment. In Figure 1, the thickness a of the Al base material (negative electrode precursor) 100 is set to 30 μm or more and 150 μm or less.

Figure 2 shows a cross-sectional view that shows a schematic example of a state in which the Al base material 100 in Figure 1 is initially charged (formed) to form a negative electrode. In Figure 2, the negative electrode 200 comprises an Al layer 201 and a Li-Al alloy layer 202 formed on the surface of the Al layer 201. The thickness b of the Al layer 201 is smaller than the thickness a of the Al base material in Figure 1 due to the formation of the Li-Al alloy layer 202. On the other hand, the thickness c of the Li-Al alloy layer 202 expands in the direction of the arrow in Figure 2 due to the reaction between Al and Li ions, so that the thickness (c + b + c) of the negative electrode 200 is larger than the initial thickness a of the Al base material layer. However, in reality, the reaction between the Al base layer and Li ions does not necessarily occur uniformly, and undulations occur at the interface between the Al layer 201 and the Li-Al alloy layer 202. Therefore, the thickness b of the Al layer 201 and the thickness c of the Li-Al alloy layer 202 vary depending on the location, but the thickness a of the Al base before chemical conversion is usually uniform.

In addition, in the nonaqueous electrolyte battery of this embodiment, the area of the negative electrode is set to be larger than the area of the positive electrode mixture layer capable of absorbing and releasing Li ions of the positive electrode described later, and further, since the negative electrode is arranged to cover the entire surface of the positive electrode mixture layer via a separator, the end of the negative electrode is a portion that does not face the positive electrode mixture layer, and it is considered that a Li-Al alloy layer is not substantially formed in that portion. Therefore, when the overall thickness of the Al layer of the negative electrode is observed, the thickness b of the Al layer in the portion where the Li-Al alloy layer is formed is smaller than the thickness a of the Al base material before the first charge, but the thickness of the Al layer in the portion where the Li-Al alloy layer is not formed maintains the thickness a of the Al base material before the first charge, so that when the entire negative electrode is observed, the maximum thickness of the Al layer coincides with the thickness a of the Al base material (negative electrode precursor) before the first charge.

The positive electrode mixture layer here refers to the portion of the positive electrode that can absorb and release Li ions. For example, if a layer containing a positive electrode active material is formed on a positive electrode current collector, and then a layer that inhibits the permeation of Li ions (such as tape) is attached to the layer, the layer in the attached portion does not correspond to the positive electrode mixture layer as defined in this embodiment.

The Al layer 201 and the Li-Al alloy layer 202 in FIG. 2 can be distinguished by observing the cross section of the negative electrode with a scanning electron microscope (SEM). In addition, whether or not the negative electrode is broken can also be confirmed by observing the cross section of the negative electrode with a SEM.

<Positive electrode>
For the positive electrode of the nonaqueous electrolyte battery of this embodiment, for example, a structure having a positive electrode mixture layer containing a positive electrode active material, a conductive assistant, a binder, etc. on one side or both sides of a positive electrode current collector can be used. As described above, when the maximum thickness of the Al layer of the negative electrode is 30 μm or more and 150 μm or less, that is, when the thickness of the Al base material which is the negative electrode precursor before the initial charge (chemical formation) is 30 μm or more and 150 μm or less, it is preferable that the capacity of the positive electrode is set to 0.68 mAh / cm ² or more and 4.87 mAh / cm ² or less. This prevents the Al base material of the negative electrode precursor from reacting too much with Li ions, causing the thickness of the Al layer of the negative electrode to become too thin, and the tensile strength of the negative electrode to fall below 4 N / mm.

The capacity of the positive electrode is measured as follows. That is, the nonaqueous electrolyte battery of this embodiment is disassembled after the initial charge (chemical formation) to take out the positive electrode. Thereafter, when the taken out positive electrode has a positive electrode mixture layer only on one side of the positive electrode current collector, the positive electrode mixture layer of the positive electrode is cut out to a size of 1 cm ² to obtain a positive electrode capacity measurement sample. When the taken out positive electrode has a positive electrode mixture layer on both sides of the positive electrode current collector, the positive electrode mixture layer on one side is removed from the taken out positive electrode, and the positive electrode mixture layer of the positive electrode from which the positive electrode mixture layer has been removed is cut out to a size of 1 cm ² to obtain a positive electrode capacity measurement sample. Next, the positive electrode capacity measurement sample is combined with Li foil to prepare a model cell. As the nonaqueous electrolyte of this model cell, the same nonaqueous electrolyte as that used in the nonaqueous electrolyte battery of this embodiment is used. Next, this model cell is charged at a constant current of 0.25 mA to a predetermined voltage, which is the initial charging voltage of the nonaqueous electrolyte battery plus 0.35 V, and then is charged at a constant voltage until the charging current drops to 0.025 mA at the predetermined voltage. Thereafter, the cell is discharged at a constant current of 0.25 mA to 3 V, and the capacity at that time is the capacity of the positive electrode.

The mass of the positive electrode mixture layer per one side of the positive electrode current collector is preferably 7 mg/cm ² or more and 30 mg/cm ² or less, and more preferably 8.5 mg/cm ² or more and 25 mg/cm ² or less. If the mass of the positive electrode mixture layer is less than 7 mg/cm ² , the discharge load per unit mass of the positive electrode active material during high-rate discharge increases, resulting in a decrease in output characteristics. If the mass of the positive electrode mixture layer exceeds 30 mg/cm ² , it may be difficult to set the upper limit of the positive electrode capacity to 4.87 mAh/cm ² .

The mass of the positive electrode mixture layer can be controlled by adjusting the amount of positive electrode mixture applied per unit area on the positive electrode current collector.

The positive electrode active material is not particularly limited, but it is preferable to use a lithium-containing nickel layered oxide.

In general, the positive electrode active material reacts with the non-aqueous electrolyte in a high-temperature environment, and reaction products are deposited on the positive electrode, and gas is generated at the same time. When lithium cobalt oxide, which is commonly used in non-aqueous electrolyte batteries such as lithium-ion secondary batteries, is used as the positive electrode active material, the surface of the lithium cobalt oxide reacts with the non-aqueous electrolyte at high temperatures, and reaction products containing Co are deposited on the surface of the positive electrode, and gas is generated at the same time. The reaction products containing Co are further decomposed, and Co is dissolved into the non-aqueous electrolyte. Then, the surface of the lithium cobalt oxide reacts with the non-aqueous electrolyte again, and reaction products containing Co are generated and gas is generated. In other words, if the positive electrode active material contains a large amount of lithium cobalt oxide, Co continues to dissolve and gas continues to be generated every time the battery is exposed to high temperatures.

However, the lithium-containing nickel layered oxide reacts with the non-aqueous electrolyte at high temperatures to produce Ni-containing reaction products and generate gas, but the Ni-containing reaction products do not decompose and remain on the positive electrode to form a coating. Furthermore, even if the battery is subsequently exposed to high temperatures, Ni elution and gas generation are suppressed. Therefore, metal elution is unlikely to occur even at high temperatures when the battery is charged. Therefore, gas generation can be suppressed even when the battery is stored at high temperatures for a long period of time, and a decrease in discharge capacity can be suppressed.

As the lithium-containing nickel layered oxide, it is preferable to use a composite oxide represented by the following general formula (1). By using a composite oxide represented by the following general formula (1), not only can gas generation during long-term storage be suppressed, but also an increase in resistance can be suppressed.

_{Li1 +xNi1 - yzM1yM2zO2} ^{( 1} ₎

In the general formula (1), M ¹ is at least one element selected from the group consisting of Co, Mn, Al, Mg, Zr, Mo, Ti, Ba, W, and Er, M ² is an element other than Li, Ni, and M ¹ , and -0.1≦x≦0.1, 0≦y<0.85, and 0≦z≦0.05.

When Co is present in the crystal lattice of the composite oxide represented by the general formula (1), the irreversible reaction caused by the phase transition of the lithium-containing composite oxide due to the insertion and removal of Li during charging and discharging of the nonaqueous electrolyte battery can be mitigated, and the reversibility of the crystal structure of the composite oxide can be increased, making it possible to construct a nonaqueous electrolyte battery with a longer charge-discharge cycle life.

When the composite oxide represented by the general formula (1) contains Mg, when a phase transition of the composite oxide occurs due to desorption and insertion of Li, Mg ²⁺ is transferred to the Li site, thereby mitigating an irreversible reaction, and the reversibility of the layered crystal structure of the composite oxide represented by the space group R3-m is improved.

When the composite oxide represented by the general formula (1) contains Mn, the tetravalent Mn stabilizes the unstable tetravalent Ni, making it possible to construct a nonaqueous electrolyte battery with a longer charge/discharge cycle life.

When the composite oxide represented by the general formula (1) contains W or Mo, the rate of crystal expansion and contraction during charging and discharging can be reduced, leading to improved charge and discharge cycle characteristics of the battery.

When Al is present in the crystal lattice of the complex oxide represented by the general formula (1), the crystal structure can be stabilized and its thermal stability can be improved, making it possible to construct a nonaqueous electrolyte battery with higher safety. Furthermore, the presence of Al in the grain boundaries and surfaces of the particles of the complex oxide can improve the stability over time and suppress side reactions with the nonaqueous electrolyte, making it possible to construct a nonaqueous electrolyte battery with a longer life.

When Er is present at the grain boundaries or on the surface of the particles of the composite oxide represented by the general formula (1), it reduces the catalytic activity on the surface of the positive electrode active material, and can suppress the decomposition of the nonaqueous electrolyte.

In the composite oxide represented by the general formula (1), when an alkaline earth metal element such as Ba is contained in the particles, the growth of the primary particles is promoted and the crystallinity of the composite oxide is improved, thereby suppressing side reactions with the nonaqueous electrolyte and enabling the construction of a battery that is less likely to swell during high-temperature storage.

In the composite oxide represented by the general formula (1), when Ti is contained in the particles, Ti is arranged in crystal defects such as oxygen vacancies in the _LiNiO2 type crystal structure, thereby stabilizing the crystal structure. This enhances the reversibility of the reaction of the composite oxide, making it possible to configure a nonaqueous electrolyte battery having better charge-discharge cycle characteristics.

When the composite oxide represented by the general formula (1) contains Zr, the presence of Zr at the grain boundaries and surfaces of the composite oxide particles suppresses the surface activity of the composite oxide without impairing its electrochemical properties. In addition, the effect of Zr in suppressing the activity of the particle surfaces makes it possible to construct a nonaqueous electrolyte battery with better storage properties and a longer life.

In the composite oxide represented by the general formula (1), the element ^M1 may or may not contain each of the above elements depending on the desired properties.

The composite oxide represented by the general formula (1) may or may not contain ^M2 , which is an element other than Li, Ni, and ^M1. If z, which represents the content of the element ^M2 , is 0.05 or less, the effect of this embodiment is not hindered, but it is more preferably 0.01 or less.

The composition of the positive electrode active material can be analyzed using the ICP (Inductive Coupled Plasma) method as follows. First, 0.2 g of the positive electrode active material to be measured is taken and placed in a 100 mL container. Then, 5 mL of pure water, 2 mL of aqua regia, and 10 mL of pure water are added in that order, and the mixture is heated and dissolved. After cooling, the mixture is further diluted 25 times with pure water, and the composition is analyzed by the calibration curve method using an ICP analyzer "ICP-757" (product name) manufactured by JARRELASH. The composition amount can be derived from the results obtained.

The positive electrode active material may contain one type of the lithium-containing nickel layered oxide, or may contain two or more types.

In addition, the positive electrode active material can contain other lithium-containing composite oxides different from the lithium-containing nickel layered oxide, depending on the desired battery characteristics.

Examples of the lithium-containing composite oxide different from _{the lithium-containing nickel layered oxide include lithium cobalt oxides such as LiCoO2, lithium manganese oxides such as LiMnO2 and Li2MnO3 , lithium -} containing composite oxides having a spinel structure such as _LiMn2O4 and Li4 _{/ 3Ti5 / 3O4} , lithium-containing composite oxides having an olivine structure such as _LiFePO4 , and oxides having these oxides as basic compositions and some of the constituent elements replaced with other elements. These lithium-containing composite oxides may also be used alone or in combination of two or more.

Even if the positive electrode active material contains a lithium-containing composite oxide different from the lithium-containing nickel layered oxide, the positive electrode active material preferably contains 50% by mass or more of the lithium-containing nickel layered oxide, and more preferably contains 80% by mass or more of the lithium-containing nickel layered oxide. This is because the effect of the lithium-containing nickel layered oxide can be obtained well.

Examples of conductive assistants for the positive electrode mixture layer include carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; carbon fibers; and other carbon materials; conductive fibers such as metal fibers; carbon fluoride; metal powders such as copper and nickel; and organic conductive materials such as polyphenylene derivatives.

Examples of binders for the positive electrode mixture layer include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyvinylpyrrolidone (PVP), etc.

The positive electrode can be manufactured, for example, by dispersing a positive electrode mixture containing a positive electrode active material, a conductive assistant, a binder, etc., in an organic solvent such as N-methyl-2-pyrrolidone (NMP) or water to prepare a paint containing the positive electrode mixture (paste, slurry, etc.), applying this paint containing the positive electrode mixture to one or both sides of a current collector, drying it, and, if necessary, carrying out a pressing process.

The positive electrode mixture may be used to form a molded body, and a part or all of one side of the molded body may be attached to a positive electrode current collector to form a positive electrode. The positive electrode mixture molded body and the positive electrode current collector may be attached to each other by pressing or the like.

The positive electrode current collector may be made of a metal such as Al or an Al alloy, a punched metal, a mesh, or an expanded metal, but typically, Al foil is used. The thickness of the positive electrode current collector is preferably 10 to 30 μm.

The composition of the positive electrode mixture layer is preferably, for example, 80.0 to 99.8% by mass of positive electrode active material, 0.1 to 10% by mass of conductive additive, and 0.1 to 10% by mass of binder. The thickness of the positive electrode mixture layer is preferably 15 to 100 μm per side of the current collector.

A positive electrode lead body can be attached to the positive electrode current collector in the usual manner.

<Separator>
The separator preferably has a property of blocking its pores (i.e., a shutdown function) at 80° C. or higher (more preferably 100° C. or higher) and 170° C. or lower (more preferably 150° C. or lower), and a separator used in nonaqueous electrolyte batteries such as ordinary lithium ion secondary batteries, for example, a microporous membrane made of polyolefin such as polyethylene (PE) or polypropylene (PP), can be used. The microporous membrane constituting the separator may be, for example, one using only PE or one using only PP, or may be a laminate of a microporous membrane made of PE and a microporous membrane made of PP. The thickness of the separator is preferably, for example, 10 to 30 μm.

<Electrode body>
In the nonaqueous electrolyte battery of this embodiment, the positive electrode and the negative electrode are used in the form of, for example, an electrode body constructed by stacking them with a separator interposed therebetween, a wound electrode body formed by further winding the electrode body into a spiral shape, or a laminated electrode body in which a plurality of positive electrodes and a plurality of negative electrodes are alternately stacked. Compared to a cylindrical battery, in the case of a prismatic battery in which a wound electrode body is enclosed in a prismatic exterior body, a large stress is particularly applied to the R portion of the negative electrode. Therefore, even if aluminum is used alone as the negative electrode material, the strength of the negative electrode can be maintained, and the nonaqueous electrolyte battery configuration of this embodiment, which can ensure long-term reliability in a high-temperature environment, is preferably used.

<Non-aqueous electrolyte>
The non-aqueous electrolyte used is a solution in which a lithium salt is dissolved in an organic solvent.

Examples of organic solvents for non-aqueous electrolytes include cyclic carbonates such as ethylene carbonate, propylene carbonate (PC), butylene carbonate, and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; chain esters such as methyl propionate; cyclic esters such as compounds having lactone rings; chain ethers such as dimethoxyethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme, and tetraglyme; cyclic ethers such as dioxane, tetrahydrofuran, and 2-methyltetrahydrofuran; nitriles such as acetonitrile, propionitrile, and methoxypropionitrile; sulfites such as ethylene glycol sulfite; and the like. Two or more of these can also be mixed and used. In order to obtain a battery with better characteristics, it is desirable to use a combination that can obtain high conductivity, such as a mixed solvent of a cyclic carbonate and the chain carbonate exemplified above.

It is also preferable to use PC as the organic solvent for the non-aqueous electrolyte. PC contributes to ensuring the discharge characteristics of non-aqueous electrolyte batteries, especially at low temperatures. For example, ethylene carbonate is often used as the organic solvent for the non-aqueous electrolyte in non-aqueous electrolyte batteries, but PC has a lower freezing point than ethylene carbonate, making it possible to improve the output characteristics of the battery even in low-temperature environments.

Furthermore, from the viewpoint of further improving the discharge characteristics of a nonaqueous electrolyte battery at low temperatures, it is preferable to use a compound having a lactone ring together with PC as the organic solvent of the nonaqueous electrolyte.

Examples of compounds having a lactone ring include γ-butyrolactone and lactones having a substituent at the α-position.

The lactones having a substituent at the α-position are preferably, for example, five-membered rings (having four carbon atoms in the ring). The lactones may have one or two substituents at the α-position.

The substituents include hydrocarbon groups and halogen groups (fluoro, chloro, bromo, and iodine groups). The hydrocarbon groups are preferably alkyl and aryl groups, and preferably have 1 to 15 carbon atoms (more preferably 6 or less). When the substituent is a hydrocarbon group, more preferably a methyl, ethyl, propyl, butyl, or phenyl group.

Specific examples of lactones having a substituent at the α-position include α-methyl-γ-butyrolactone, α-ethyl-γ-butyrolactone, α-propyl-γ-butyrolactone, α-butyl-γ-butyrolactone, α-phenyl-γ-butyrolactone, α-fluoro-γ-butyrolactone, α-chloro-γ-butyrolactone, α-bromo-γ-butyrolactone, α-iodo-γ-butyrolactone, α,α-dimethyl-γ-butyrolactone, and α,α-di Examples of the ethyl-γ-butyrolactone include ethyl-γ-butyrolactone, α,α-diphenyl-γ-butyrolactone, α-ethyl-α-methyl-γ-butyrolactone, α-methyl-α-phenyl-γ-butyrolactone, α,α-difluoro-γ-butyrolactone, α,α-dichloro-γ-butyrolactone, α,α-dibromo-γ-butyrolactone, and α,α-diiodo-γ-butyrolactone. Only one of these may be used, or two or more may be used in combination. Among these, α-methyl-γ-butyrolactone is more preferable.

The content of PC in all organic solvents used in the nonaqueous electrolyte is preferably 10% by volume or more, and more preferably 30% by volume or more, from the viewpoint of ensuring the above-mentioned effects of its use. As described above, the organic solvent in the nonaqueous electrolyte may be only PC, so the upper limit of the suitable content of PC in all organic solvents used in the nonaqueous electrolyte is 100% by volume.

When using a compound having a lactone ring, in order to ensure the desired effect of its use, the content of the compound having a lactone ring in all organic solvents used in the nonaqueous electrolyte is preferably 0.1% by mass or more, and it is desirable to use the compound within a range that satisfies this preferred value and in which the content of PC in all organic solvents satisfies the above-mentioned preferred value.

It is preferable to use LiBF4 as the lithium salt for the nonaqueous electrolyte, since LiBF4 has high heat resistance and can improve the storage characteristics of the nonaqueous electrolyte battery in a high-temperature environment, and also has the function of suppressing corrosion _of aluminum used in the battery.

Other lithium salts for non-aqueous electrolytes include, for example, _LiClO4 , _LiPF6 , _LiAsF6 , _LiSbF6 , _{LiCF3SO3 , LiCF3CO2, Li2C2F4(SO3)2, LiN(CF3SO2)2 , LiC ( CF3SO2)3 , LiCnF2n + 1SO3 ( 2 ≦ n ≦ 7 )} , LiN( _RfOSO2 ) ₂ [where Rf is a fluoroalkyl group] _, and the like.

The concentration of the lithium salt in the non-aqueous electrolyte is preferably 0.6 mol/L or more, and more preferably 0.9 mol/L or more.

The concentration of all lithium salts in the non-aqueous electrolyte is preferably 1.8 mol/L or less, more preferably 1.6 mol/L or less. Therefore, when only _LiBF4 is used as the lithium salt, it is preferable to use it in a range where its concentration satisfies the above-mentioned preferred upper limit. On the other hand, when other lithium salts are used together with _LiBF4 , it is preferable to use it in a range where the concentration of _LiBF4 satisfies the above-mentioned preferred lower limit and the concentration of all lithium salts satisfies the above-mentioned preferred upper limit.

It is also preferable to add a nitrile compound as an additive to the non-aqueous electrolyte. By using a non-aqueous electrolyte with an added nitrile compound, the nitrile compound is adsorbed onto the surface of the positive electrode active material to form a coating, and this coating suppresses gas generation due to oxidative decomposition of the non-aqueous electrolyte, making it possible to suppress swelling of the battery, especially when stored in a high-temperature environment.

Examples of nitrile compounds to be added to the non-aqueous electrolyte include mononitriles such as acetonitrile, propionitrile, butyronitrile, valeronitrile, benzonitrile, and acrylonitrile; dinitriles such as malononitrile, succinonitrile, glutaronitrile, adiponitrile, 1,4-dicyanoheptane, 1,5-dicyanopentane (pimelonitrile), 1,6-dicyanohexane (suberonitrile), 1,7-dicyanoheptane (azelaonitrile), 2,6-dicyanoheptane, 1,8-dicyanooctane, 2,7-dicyanooctane, 1,9-dicyanononane, 2,8-dicyanononane, 1,10-dicyanodecane, 1,6-dicyanodecane, and 2,4-dimethylglutaronitrile; cyclic nitriles such as benzonitrile; and alkoxy-substituted nitriles such as methoxyacetonitrile. Only one of these may be used, or two or more may be used. Among these nitrile compounds, dinitriles are more preferred, and adiponitrile, pimelonitrile and suberonitrile are even more preferred.

From the viewpoint of ensuring the above-mentioned effects of the use of the nonaqueous electrolyte, the content of the nitrile compound in the nonaqueous electrolyte used in the battery is preferably 0.1% by mass or more, and more preferably 1% by mass or more. However, if the amount of the nitrile compound in the nonaqueous electrolyte is too large, the discharge characteristics of the battery at low temperatures tend to deteriorate. Therefore, from the viewpoint of limiting the amount of the nitrile compound in the nonaqueous electrolyte to some extent and improving the discharge characteristics of the battery at low temperatures, the content of the nitrile compound in the nonaqueous electrolyte used in the battery is preferably 10% by mass or less, and more preferably 5% by mass or less.

In addition, the non-aqueous electrolyte preferably contains a phosphoric acid compound or a boric acid compound having a group represented by the following general formula (2) in the molecule.

In the general formula (2), X is Si, Ge or Sn, and R ¹ , R ² and R ³ each independently represent an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms or an aryl group having 6 to 10 carbon atoms, in which some or all of the hydrogen atoms may be substituted with fluorine.

For example, batteries used in in-vehicle devices and outdoor equipment can be used not only in high-temperature environments but also in cold regions. In low-temperature environments, the operability of the battery decreases compared to room temperature, and batteries that have deteriorated over time tend to have poorer discharge characteristics. Therefore, it is preferable to have batteries that can be placed in a high-temperature environment for a certain period of time (in a state roughly equivalent to that of deterioration over time) and then be able to discharge at a high rate even in a low-temperature environment, assuming use in a variety of temperatures.

In the nonaqueous electrolyte battery of this embodiment, if a nonaqueous electrolyte containing a phosphoric acid compound or a boric acid compound having a group represented by the general formula (2) in the molecule is used, the high-rate discharge characteristics in a low-temperature environment after long-term storage at high temperatures can be improved. The reason for this is unclear, but the inventors speculate as follows.

When a non-aqueous electrolyte containing a phosphoric acid compound or a boric acid compound having a group represented by the general formula (2) in its molecule is used, the phosphoric acid compound or the boric acid compound forms a low-resistance, strong coating on the surface of the above-mentioned positive electrode active material, so that the coating is not destroyed even when the battery is stored at high temperatures for a long period of time, and therefore elution of metal from the positive electrode active material can be suppressed. In addition, since this coating does not easily inhibit the insertion of Li ions even at low temperatures, the high-rate discharge characteristics at low temperatures of a battery after long-term storage at high temperatures can be improved.

Furthermore, the phosphoric acid compound or boric acid compound acts on the negative electrode of a non-aqueous electrolyte battery to form a coating. It is believed that the phosphoric acid compound or boric acid compound reduces the amount of Li used when forming a coating on the negative electrode surface, forming a thin and high-quality coating on the negative electrode surface. As a result, the coating on the negative electrode surface is not destroyed even during long-term storage at high temperatures, so deterioration of the negative electrode can be suppressed. In addition, this coating does not easily inhibit the desorption of Li ions even at low temperatures. For these reasons, the high-rate discharge characteristics at low temperatures of a battery after long-term storage at high temperatures can be improved.

As described above, by combining the specific positive electrode and specific negative electrode according to this embodiment with the nonaqueous electrolyte solution containing the phosphoric acid compound or boric acid compound, the above-mentioned actions function synergistically, resulting in a battery with better storage characteristics in high-temperature environments and capable of adapting to temperature changes.

In the general formula (2), X is Si, Ge or Sn, with Si being more preferred. That is, the phosphoric acid compound is more preferably a phosphoric acid silyl ester, and the boric acid compound is more preferably a boric acid silyl ester. In addition, in the general formula (2), R ¹ , R ² and R ³ are each independently an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, or an aryl group having 6 to 10 carbon atoms, with a methyl group or an ethyl group being more preferred. As the group represented by the general formula (2), a trimethylsilyl group is particularly preferred.

In addition, in the phosphoric acid compound, only one of the hydrogen atoms of the phosphoric acid may be substituted with a group represented by the general formula (2), two of the hydrogen atoms of the phosphoric acid may be substituted with a group represented by the general formula (2), or all three of the hydrogen atoms of the phosphoric acid may be substituted with a group represented by the general formula (2). However, it is more preferable that all three of the hydrogen atoms of the phosphoric acid are substituted with a group represented by the general formula (2).

As such a phosphate compound, tris(trimethylsilyl) phosphate is particularly preferred.

In addition, in the boric acid compound, only one of the hydrogen atoms of the boric acid may be substituted with a group represented by the general formula (2), two of the hydrogen atoms of the boric acid may be substituted with a group represented by the general formula (2), or all three of the hydrogen atoms of the boric acid may be substituted with a group represented by the general formula (2). However, it is more preferable that all three of the hydrogen atoms of the boric acid are substituted with a group represented by the general formula (2).

As such a boric acid compound, tris(trimethylsilyl) borate is particularly preferred.

In order to better ensure the above-mentioned effects of the use of the non-aqueous electrolyte, the content of the phosphoric acid compound or boric acid compound having a group represented by the general formula (2) in the molecule in the non-aqueous electrolyte used in the battery is preferably 0.2% by mass or more, and more preferably 0.5% by mass or more. In addition, if the content is too high, a large amount of gas will be generated during the formation of the coating, so the content of the phosphoric acid compound or boric acid compound having a group represented by the general formula (2) in the molecule in the non-aqueous electrolyte used in the battery is preferably 7% by mass or less, more preferably 5% by mass or less, and particularly preferably 3% by mass or less.

In the non-aqueous electrolyte battery, it is particularly preferable to use a non-aqueous electrolyte containing _LiBF4 as a lithium salt, PC as an organic solvent, and further containing a nitrile compound in addition to the phosphoric acid compound or boric acid compound. When such a non-aqueous electrolyte is used, the actions of the components function synergistically, and the swelling of the battery during high-temperature storage can be more highly suppressed, and the discharge characteristics in a low-temperature environment (for example, −20° C. or lower) after high-temperature storage can be further improved.

Additives such as vinylene carbonates, 1,3-propane sultone, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, and t-butylbenzene can also be added to these non-aqueous electrolytes as appropriate to further improve various battery characteristics. Furthermore, the non-aqueous electrolytes may be made into a gel (gel electrolyte) using a gelling agent such as a known polymer.

<Non-aqueous electrolyte battery>
The nonaqueous electrolyte battery of this embodiment is manufactured, for example, by loading the electrode body into an exterior body, injecting a nonaqueous electrolyte into the exterior body to immerse the electrode body in the nonaqueous electrolyte, and then sealing the opening of the exterior body. The exterior body may be an exterior can made of steel, aluminum, or aluminum alloy, or an exterior body made of a laminate film on which a metal is vapor-deposited.

The nonaqueous electrolyte battery of this embodiment is configured with positive electrode capacity regulation, so the end of charging can be detected by controlling the amount of charge electricity or the charging voltage, and it is therefore possible to set the charging end conditions in advance on the charging circuit side.

After assembly, it is preferable to perform an aging treatment at a relatively high temperature (e.g., 60°C) while the battery is fully charged. This aging treatment promotes the formation of a Li-Al alloy in the negative electrode, thereby further improving the discharge capacity and output characteristics of the battery.

Next, an embodiment of a method for manufacturing a nonaqueous electrolyte battery disclosed in the present application will be described. The method for manufacturing a nonaqueous electrolyte battery of this embodiment is a method for manufacturing a nonaqueous electrolyte battery of the above embodiment, and includes the steps of preparing a positive electrode having a positive electrode mixture layer formed on at least one side of a positive electrode current collector and a capacity of 0.68 mAh/ ^cm2 to 4.87 mAh/ ^cm2 , preparing a negative electrode precursor made of an aluminum base material having an area larger than the area of the positive electrode mixture layer of the positive electrode and a thickness of 30 μm to 150 μm, disposing the negative electrode precursor via a separator so as to cover the entire surface of the positive electrode mixture layer of the positive electrode to prepare an electrode body, and sealing the electrode body and a nonaqueous electrolyte in an exterior body and then charging.

In the step of preparing the positive electrode, the positive electrode described in the nonaqueous electrolyte battery of the above embodiment is prepared. In the step of preparing the negative electrode precursor, the negative electrode precursor described in the nonaqueous electrolyte battery of the above embodiment is prepared. In addition, the separator and the nonaqueous electrolyte are the same as those described in the nonaqueous electrolyte battery of the above embodiment.

By using an Al base material having a thickness of 30 μm or more and 150 μm or less as the negative electrode precursor and a positive electrode having a capacity of 0.68 mAh/cm ² or more and 4.87 mAh/cm ² or less, after the initial charging (chemical formation) step, a negative electrode having an Al layer and a Li-Al alloy layer formed on the surface of the Al layer is formed, and the tensile strength of the negative electrode can be made 4 N/mm or more. Once the negative electrode is formed, even if charging and discharging are performed again, there is no significant change in the thickness of the Al layer constituting the negative electrode, and the negative electrode can maintain a constant tensile strength.

In this way, the manufacturing method of this embodiment makes it possible to maintain the strength of the negative electrode even when aluminum is used alone as the negative electrode material, and to provide a nonaqueous electrolyte battery that has high long-term reliability in high-temperature environments.

The present invention will be described in detail below based on examples. However, the following examples do not limit the present invention.

Example 1
<Preparation of Positive Electrode>
First, a positive electrode mixture-containing slurry was prepared by dispersing 97 parts by mass of lithium-containing nickel layered oxide represented by LiNi _0.33 Co _0.33 Mn _0.33 O ₂ , which is a positive electrode active material, 1.5 parts by mass of acetylene black, which is a conductive assistant, and 1.5 parts by mass of PVDF, which is a binder, in NMP. Next, the positive electrode mixture-containing slurry was applied to both sides of an Al foil having a thickness of 12 μm, dried, and pressed to form a positive electrode mixture layer of a mass of 10 mg/cm ² per side on both sides of the Al foil current collector. Furthermore, a belt-shaped positive electrode having a length of 974 mm and a width of 40 mm was produced by pressing the positive electrode mixture layer. However, a part of the applied surface of the slurry was provided with a portion where the Al foil was exposed without forming a positive electrode mixture layer, and an Al lead body for conductive connection with the outside of the battery was ultrasonically welded to the portion where the Al foil was exposed.

<Preparation of negative electrode precursor>
A strip of Al foil having a thickness of 70 μm, a length of 988 mm, and a width of 44 mm was used as the negative electrode precursor, with a Ni lead body ultrasonically welded to the end of the Al foil for conductive connection to the outside of the battery.

<Preparation of electrode body>
The positive electrode and the negative electrode precursor were laminated with a separator made of a 16 μm-thick microporous film made of PE interposed therebetween, wound in a spiral shape, and then crushed to prepare a flat wound electrode body.

<Preparation of non-aqueous electrolyte>
LiBF ₄ was dissolved at a concentration of 1.2 mol/L in a mixed solvent of propylene carbonate (PC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 17:63:20, and adiponitrile was further added in an amount of 5 mass% and tris(trimethylsilyl: TMSP) phosphate in an amount of 2 mass% to prepare a nonaqueous electrolyte solution.

<Battery assembly>
The wound electrode body and the nonaqueous electrolyte were enclosed in an aluminum alloy outer can having a thickness of 0.8 mm and a size of 103450, thereby producing a rectangular nonaqueous electrolyte battery having a rated capacity of 800 mAh as shown in FIGS. 3 and 4.

Now, referring to Fig. 3 and Fig. 4, Fig. 3 is a perspective view showing a non-aqueous electrolyte battery of this embodiment, and Fig. 4 is a cross-sectional view taken along line I-I in Fig. 3. In Fig. 4, the inner peripheral portion of the electrode body and the separator are not shown in cross section. In Fig. 3 and Fig. 4, the positive electrode 1 and the negative electrode 2 are spirally wound with the separator 3 interposed therebetween, and then pressed to be flattened to form a flat wound electrode body 6, which is housed in a rectangular (rectangular cylindrical) exterior can 4 together with the non-aqueous electrolyte. However, in Fig. 4, to avoid complication, the Al foil used as the current collector in the production of the positive electrode 1 and the non-aqueous electrolyte are not shown.

The exterior can 4 is made of an aluminum alloy and constitutes the exterior body of the battery, and this exterior can 4 also serves as the positive electrode terminal. An insulator 5 made of a polyethylene sheet is placed at the bottom of the exterior can 4, and a positive electrode lead body 7 and a negative electrode lead body 8 connected to one end of the positive electrode 1 and the negative electrode 2 are drawn out from a flat wound electrode body 6 consisting of a positive electrode 1, a negative electrode 2, and a separator 3. A stainless steel terminal 11 is attached to an aluminum alloy sealing cover plate 9 that seals the opening of the exterior can 4 via a polypropylene insulating packing 10, and a stainless steel lead plate 13 is attached to this terminal 11 via an insulator 12.

The cover plate 9 is inserted into the opening of the exterior can 4, and the joint between the two is welded to seal the opening of the exterior can 4 and hermetically seal the inside of the battery. The cover plate 9 is also provided with a non-aqueous electrolyte injection port 14, which is welded and sealed with a sealing member inserted therein, ensuring the hermeticity of the battery. Furthermore, the cover plate 9 is provided with a split vent 15 as a mechanism for releasing internal gas to the outside when the temperature of the battery rises.

Example 2
A nonaqueous electrolyte battery was fabricated in the same manner as in Example 1, except that an Al foil having a thickness of 38 μm, a length of 988 mm and a width of 44 mm was used as the negative electrode precursor.

Example 3
An Al foil having a thickness of 56 μm, a length of 988 mm, and a width of 44 mm was used as the negative electrode precursor. A positive electrode was produced in the same manner as in Example 1, except that a positive electrode mixture layer was formed on both sides of the Al foil current collector at a mass of 25 mg/ ^cm2 per side. A nonaqueous electrolyte battery was produced in the same manner as in Example 1, except that the negative electrode precursor and the positive electrode were used.

Example 4
A positive _electrode was _prepared in the same manner as in Example 1, except that 97 parts by mass of a lithium-containing _nickel layered oxide represented by _{LiNi0.80Co0.15Al0.05O2} was used as the positive electrode active material instead of the positive electrode active material of Example 1. A nonaqueous electrolyte battery was prepared in the same manner as in Example 1, except that this positive electrode was used.

Example 5
A positive electrode was _prepared in the same manner as in Example 1, except that 97 parts by mass of _a lithium-containing nickel layered oxide represented by _{LiNi0.5Co0.2Mn0.3O2} was used as the positive electrode active material instead of _the positive electrode active material of Example 1. A nonaqueous electrolyte battery was prepared in the same manner as in Example 1, except that this positive electrode was used.

Example 6
A positive electrode was prepared in the same manner as in Example 1, except that 97 parts by mass of a lithium-containing composite oxide represented by _LiCoO2 was used as the positive electrode active material instead of the positive electrode active material of Example 1. A nonaqueous electrolyte battery was prepared in the same manner as in Example 1, except that this positive electrode was used.

(Example 7)
A positive electrode was prepared in the same manner as in Example 1, except that 97 parts by mass of a _lithium -containing composite oxide represented by _LiMn2O4 was used as the positive electrode active material instead of the positive electrode active material of Example 1. A nonaqueous electrolyte battery was prepared in the same manner as in Example 1, except that this positive electrode was used.

(Example 8)
As the negative electrode precursor, an Al foil having a thickness of 31 μm, a length of 988 mm, and a width of 44 mm was used. Moreover, instead of the positive electrode active material of Example 1, 97 parts by mass of a lithium-containing composite oxide represented by LiMn ₂ O ₄ was used as the positive electrode active material, and a positive electrode mixture layer having a mass of 7 mg/cm ² per side was formed on both sides of the Al foil current collector. A positive electrode was produced in the same manner as in Example 1. A nonaqueous electrolyte battery was produced in the same manner as in Example 1, except that the negative electrode precursor and the positive electrode were used.

Example 9
A positive electrode was produced in the same manner as in Example 1, except _that 97 parts by mass of _{a lithium} -containing composite oxide represented by _{LiNi0.80Co0.15Al0.05O2} was used as the positive electrode active material instead of the positive electrode active material of Example 1, and a positive electrode mixture layer was formed on both sides of an Al foil current collector with a mass of 30 mg/cm2 ^per side. A nonaqueous electrolyte battery was produced in the same manner as in Example 1, except that this positive electrode was used.

(Comparative Example 1)
A nonaqueous electrolyte battery was fabricated in the same manner as in Example 1, except that an Al foil having a thickness of 25 μm, a length of 988 mm and a width of 44 mm was used as the negative electrode precursor.

(Comparative Example 2)
An Al foil having a thickness of 60 μm, a length of 988 mm, and a width of 44 mm was used as the negative electrode precursor. A positive electrode was produced in the same manner as in Example 1, except that a positive electrode mixture layer was formed on both sides of the Al foil current collector at a mass of 40 mg/ ^cm2 per side. A nonaqueous electrolyte battery was produced in the same manner as in Example 1, except that the negative electrode precursor and the positive electrode were used.

(Comparative Example 3)
An Al foil having a thickness of 40 μm, a length of 988 mm, and a width of 44 mm was used as the negative electrode precursor. A positive electrode was produced in the same manner as in Example 1, except that a positive electrode mixture layer was formed on both sides of the Al foil current collector with a mass of 20 mg/cm ² per side. A nonaqueous electrolyte battery was produced in the same manner as in Example 1, except that the negative electrode precursor and the positive electrode were used.

Table 1 shows the configuration of the positive electrodes of the nonaqueous electrolyte batteries of Examples 1 to 9 and Comparative Examples 1 to 3.

The positive electrode capacity, negative electrode tensile strength, and high-temperature storage characteristics were evaluated for the nonaqueous electrolyte batteries of Examples 1 to 9 and Comparative Examples 1 to 3.

<Positive electrode capacity>
For each battery of the examples and comparative examples, the initial charge (formation) was performed at a constant current (100 mA)/constant voltage (3.8 V), and the charging was stopped when the charging current dropped to 10 mA to make it fully charged. Next, each battery was disassembled, the positive electrode was taken out, the positive electrode mixture layer on one side of the taken out positive electrode was removed, and the portion of the positive electrode mixture layer of the positive electrode from which the positive electrode mixture layer was removed was cut out to a size of 1 cm ² to obtain a positive electrode capacity measurement sample. Then, the positive electrode capacity measurement sample was combined with Li foil to prepare a model cell. As the nonaqueous electrolyte of this model cell, the same nonaqueous electrolyte as that used in each battery was used. Next, this model cell was charged at a constant current of 0.25 mA to 4.15 V, which is the initial charging voltage of each battery plus 0.35 V of 3.8 V, and then constant voltage charging was performed at a voltage of 4.15 V until the charging current dropped to 0.025 mA. Thereafter, the battery was discharged at a constant current of 0.25 mA until the voltage reached 3 V, and the capacity at that time was recorded as the capacity of the positive electrode.

<Tensile strength of negative electrode>
For each battery of the examples and comparative examples, an initial charge (formation) was performed at a constant current (100 mA)/constant voltage (3.8 V), and when the charging current dropped to 10 mA, charging was stopped to fully charge the battery. Each battery in this fully charged state was disassembled to remove the negative electrode, and the negative electrode was cut into a rectangular shape of 10 mm x 50 mm to prepare a test piece. This test piece was attached to a tensile tester "SDT-52 type" (product name) manufactured by Imada Seisakusho Co., Ltd. with a chuck distance of 30 mm, and a tensile test was performed at a crosshead speed of 10 mm/min to measure the tensile strength.

<High temperature storage characteristics>
Each battery in the Examples and Comparative Examples was initially charged (formed) at a constant current (100 mA)/constant voltage (3.8 V), and when the charging current dropped to 10 mA, charging was stopped to fully charge the battery. Each fully charged battery was discharged at a constant current of 2000 mA to 2.0 V, and the initial discharge capacity was determined.

Next, each battery was fully charged under the same conditions as the initial charging described above and stored at 100°C for 150 days. After that, it was fully charged under the same conditions as above and discharged at a constant current of 2000 mA in an environment of 20°C until the voltage reached 2.0 V, and the discharge capacity after storage was calculated.

Next, the capacity retention rate after storage was calculated by the following formula, and the high-temperature storage characteristics were evaluated according to the following evaluation criteria.
Capacity retention rate (%)=(discharge capacity after storage/initial discharge capacity)×100
If the capacity retention rate is 70% or more, the high-temperature storage characteristics are excellent (○).
If the capacity retention rate is 50-69%, the high temperature storage characteristics are good (△).
If the capacity retention rate is 49% or less, the high-temperature storage characteristics are poor (×).

The above evaluation results are shown in Table 2.

From Table 2, it can be seen that the batteries of Examples 1 to 9, in which the tensile strength of the negative electrode was 4 N/mm or more, were able to be rated as excellent or good in high-temperature storage characteristics, and batteries with high long-term reliability in high-temperature environments were realized. On the other hand, the batteries of Comparative Examples 1 to 3, in which the tensile strength of the negative electrode was below 4 N/mm, were rated as poor in high-temperature storage characteristics, and it can be seen that the high-temperature storage characteristics were inferior.

The nonaqueous electrolyte battery disclosed in this application has high long-term reliability in high-temperature environments, and by taking advantage of these characteristics, it can be favorably applied to applications that require good capacity to be maintained for a long period of time in high-temperature environments, such as power sources for in-vehicle equipment and outdoor equipment.

REFERENCE SIGNS LIST 1 Positive electrode 2 Negative electrode 3 Separator 4 Outer can 5 Insulator 6 Wound electrode body 7 Positive electrode lead body 8 Negative electrode lead body 9 Cover plate 10 Insulating packing 11 Terminal 12 Insulator 13 Lead plate 14 Non-aqueous electrolyte injection port 15 Cracked vent 100 Al substrate (negative electrode precursor)
200 negative electrode 201 Al layer 202 Li-Al alloy layer

Claims (10)

A non-aqueous electrolyte battery including a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator,
the positive electrode includes a positive electrode current collector and a positive electrode mixture layer formed on the positive electrode current collector,
The positive electrode mixture layer is capable of absorbing and releasing Li ions,
an area of the negative electrode is larger than an area of the positive electrode mixture layer of the positive electrode, and the negative electrode is disposed so as to cover an entire surface of the positive electrode mixture layer via the separator;
the negative electrode comprises an Al layer and a Li-Al alloy layer formed on a surface of the Al layer,
The negative electrode has a tensile strength of 4 N/mm or more;
The maximum thickness of the Al layer is 30 μm or more and 150 μm or less,
The capacity of the positive electrode is 0.68 mAh/cm ² or more and 4.87 mAh/cm ² or less,
The positive electrode mixture layer contains, as a positive electrode active material, at least one selected from the group consisting of lithium cobalt oxide, lithium manganese oxide, and lithium-containing composite oxide having an olivine structure. The positive electrode mixture layer is formed on at least one surface of the positive electrode current collector,
2. The nonaqueous electrolyte battery in accordance with claim 1, wherein the mass of the positive electrode mixture layer per one surface of the positive electrode current collector is 7 mg/cm ^<2> or more and 30 mg/cm ^<2> or less. the positive electrode, the negative electrode, and the separator form a wound electrode body;
3. The nonaqueous electrolyte battery according to claim 1, wherein the wound electrode body is enclosed in a prismatic exterior body. 4. The nonaqueous electrolyte battery according to claim 1, wherein the nonaqueous electrolyte further contains a phosphoric acid compound or a boric acid compound having a group represented by the following general formula (2) in the molecule:

In the general formula (2), X is Si, Ge or Sn, and R ¹ , R ² and R ³ each independently represent an alkyl group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms or an aryl group having 6 to 10 carbon atoms, in which some or all of the hydrogen atoms may be substituted with fluorine. The nonaqueous electrolyte battery according to claim 4, wherein the nonaqueous electrolyte contains tris(trimethylsilyl) phosphate as a phosphate compound having a group represented by the general formula (2) in its molecule. The nonaqueous electrolyte battery according to claim 4, wherein the nonaqueous electrolyte contains tris(trimethylsilyl) borate as a boric acid compound having a group represented by the general formula (2) in its molecule. The nonaqueous electrolyte battery according to any one of claims 1 to 6, wherein the nonaqueous electrolyte contains _LiBF4 as a lithium salt, contains propylene carbonate as an organic solvent, and further contains a nitrile compound. The nonaqueous electrolyte battery according to claim 7, wherein the nonaqueous electrolyte contains at least one nitrile compound selected from the group consisting of suberonitrile, pimelonitrile, and adiponitrile. The nonaqueous electrolyte battery according to claim 7 or 8, wherein the content of the nitrile compound in the nonaqueous electrolyte is 0.1% by mass or more and 10% by mass or less. A method for producing the nonaqueous electrolyte battery according to any one of claims 1 to 9, comprising the steps of:
A step of preparing a positive electrode having a positive electrode mixture layer formed on at least one surface of a positive electrode current collector and a capacity of 0.68 mAh/ ^cm2 or more and 4.87 mAh/ ^cm2 or less;
preparing a negative electrode precursor having an area larger than an area of the positive electrode mixture layer of the positive electrode and made of an aluminum base material having a thickness of 30 μm or more and 150 μm or less;
a step of disposing the negative electrode precursor via a separator so as to cover an entire surface of the positive electrode mixture layer of the positive electrode to prepare an electrode body;
and sealing the electrode assembly and the nonaqueous electrolyte in an exterior body and then charging the battery.

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