JP7318344B2 - NON-AQUEOUS ELECTROLYTE STORAGE ELEMENT, METHOD FOR USING THE SAME, AND METHOD FOR MANUFACTURING THE SAME - Google Patents

Description

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

Non-aqueous electrolyte power storage devices represented by lithium secondary batteries have been increasingly used in recent years, and there is a demand for the development of higher capacity positive electrode materials. Conventionally, a lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure has been studied as a positive electrode active material for a nonaqueous electrolyte storage element, and a nonaqueous electrolyte secondary battery using LiCoO ₂ has been widely put into practical use. there is Manganese, which is abundant as an earth resource, is used as the transition metal (Me) that constitutes the lithium-transition metal composite oxide, and the molar ratio (Li/Me) of lithium to the transition metal that constitutes the lithium-transition metal composite oxide is approximately 1. A non-aqueous electrolyte secondary battery using a so-called LiMeO ₂ type active material, in which the molar ratio (Mn/Me) of manganese in the transition metal is 0.5 or less, has also been put into practical use.

On the other hand, in recent years, among lithium-transition metal composite oxides having an α-NaFeO ₂ type crystal structure, so-called lithium-excess type active materials in which the molar ratio of lithium to the transition metal (Li/Me) exceeds 1 are known. (Patent Documents 1 and 2). This active material is 4.5V vs. Li/Li ⁺ or more 5.0V vs. A feature is that a region in which the potential change is relatively gentle with respect to the amount of charged electricity is observed within the potential range of Li/Li ⁺ or lower. In the non-aqueous electrolyte storage element using such a lithium-excess type active material, charging is performed at an early stage until the end of the charging process in which a region where the potential change is relatively gradual is observed, so that the charging potential after that is not much. It is attracting attention because it has a higher discharge capacity than the LiMeO ₂ -type active material, even if it is not expensive.

In a conventional non-aqueous electrolyte storage element using a lithium-excess active material for the positive electrode, the positive electrode potential is generally 4.6 V vs. It is manufactured through initial charge/discharge up to Li/Li ⁺ or more. In Patent Document 1, during the initial charge/discharge of a non-aqueous electrolyte secondary battery in which a lithium-excess active material is used for the positive electrode and silicon and carbon are used for the negative electrode, the positive electrode potential is 4.60 V vs. Charging is carried out up to Li/Li ⁺ . In Patent Document 2, during the initial charge/discharge of a non-aqueous electrolyte secondary battery using a lithium-excess type active material for the positive electrode and graphite for the negative electrode, the voltage reaches 4.7 V, that is, the positive electrode potential is 4.7V. 8V vs. Charging is carried out up to Li/Li ⁺ .

JP 2012-104335 A JP 2013-191390 A

A non-aqueous electrolyte storage element using the lithium-excess type active material as described above for the positive electrode has the disadvantage that the capacity retention rate is low in charging/discharging cycles.

An object of the present invention is to provide a non-aqueous electrolyte storage element using a lithium-excess type active material for the positive electrode, the non-aqueous electrolyte storage element having a high capacity retention rate in charge/discharge cycles, and such a non-aqueous electrolyte storage element. It is to provide a method of use and a method of manufacture.

A non-aqueous electrolyte power storage element according to an aspect of the present invention includes a positive electrode having a positive electrode mixture containing a positive electrode active material, the positive electrode active material having an α-NaFeO ₂ structure and Li _1+α Me _1-α O ₂ (0<α<1; Me is a transition metal including Ni and Mn), and the positive electrode is supplied with 9 mA/mass of the positive electrode mixture. A current density of 2.00 V vs. After discharging up to Li/Li ⁺ , the potential is 4.80 V vs. When the charge and potential up to Li/Li ⁺ is 2.00 V vs. The non-aqueous electrolyte storage element satisfies the following formula (1) when the charge/discharge is performed for two cycles including discharge to Li/Li ⁺ .
(C _2A /C _2B )×100−(C _1A /C _1B )×100≧1.0 (1)
(In formula (1), C _1A is the amount of electricity charged from the start of charging until the potential reaches 4.45 V vs. Li/Li ⁺ during the first cycle of charging and discharging. C _1B is the amount of charge from the start of charging until the potential reaches 4.80 V vs. Li/Li ⁺ during the charging of the first cycle of the charging and discharging.C _2A is the second cycle of the charging and discharging is the amount of electricity charged from the start of charging until the potential reaches 4.45 V vs. Li/Li ⁺ .C _2B is the amount of charge from the start of charging during the second cycle of charging and discharging. It is the amount of electricity charged until the potential reaches 4.80 V vs. Li/Li ⁺ .)

A method of using a non-aqueous electrolyte storage element according to another aspect of the present invention is such that the positive electrode potential is 4.30 V vs. Li/Li ⁺ greater than 4.60V vs. This is a method of using the non-aqueous electrolyte power storage element of one embodiment of the present invention, comprising charging to less than Li/Li ⁺ .

In another aspect of the present invention, there is provided a method for manufacturing a non-aqueous electrolyte storage element, wherein the maximum attainable potential of the positive electrode is 4.60 V vs. A method for manufacturing a non-aqueous electrolyte power storage element according to one embodiment of the present invention, comprising performing initial charge/discharge at less than Li/Li ⁺ .

A non-aqueous electrolyte power storage element according to one embodiment of the present invention is a non-aqueous electrolyte power storage element using a lithium-excess active material for a positive electrode, and has a high capacity retention rate in charge-discharge cycles.
According to the method of using the non-aqueous electrolyte storage element according to another aspect of the present invention, the non-aqueous electrolyte storage element using the lithium-excess active material for the positive electrode can be used with a high capacity retention rate.
According to a method for manufacturing a non-aqueous electrolyte energy storage device according to another aspect of the present invention, a non-aqueous electrolyte energy storage device using a lithium-excess type active material for a positive electrode and having a high capacity retention rate in charge-discharge cycles is a non-aqueous electrolyte energy storage device. A water electrolyte storage device can be manufactured.

FIG. 1 is a charge/discharge curve (a diagram showing changes in voltage with respect to charge/discharge quantity of electricity) of the non-aqueous electrolyte storage element (test battery) of Example 1. FIG. FIG. 2 is a charge/discharge curve (a diagram showing changes in voltage with respect to charge/discharge quantity of electricity) of the non-aqueous electrolyte storage element (test battery) of Comparative Example 1. FIG. FIG. 3 is a triangular phase diagram of the composition of the lithium-transition metal composite oxide of the non-aqueous electrolyte storage element according to one embodiment of the present invention. 4 is a graph showing the energy densities of the non-aqueous electrolyte storage elements of Examples 1 to 5 and 14 to 18 and Comparative Examples 1 and 4. FIG. FIG. 5 is an external perspective view showing a non-aqueous electrolyte storage element according to one embodiment of the present invention. FIG. 6 is a schematic diagram showing a power storage device configured by assembling a plurality of non-aqueous electrolyte power storage elements according to one embodiment of the present invention.

First, an outline of the non-aqueous electrolyte storage element disclosed by the present specification, its usage method, and its manufacturing method will be described.

A non-aqueous electrolyte power storage element according to an aspect of the present invention includes a positive electrode having a positive electrode mixture containing a positive electrode active material, the positive electrode active material having an α-NaFeO ₂ structure and Li _1+α Me _1-α O ₂ (0<α<1; Me is a transition metal including Ni and Mn), and the positive electrode is supplied with 9 mA/mass of the positive electrode mixture. A current density of 2.00 V vs. After discharging up to Li/Li ⁺ , the potential is 4.80 V vs. When the charge and potential up to Li/Li ⁺ is 2.00 V vs. The non-aqueous electrolyte storage element satisfies the following formula (1) when the charge/discharge is performed for two cycles including discharge to Li/Li ⁺ .
(C _2A /C _2B )×100−(C _1A /C _1B )×100≧1.0 (1)
(In formula (1), C _1A is the amount of electricity charged from the start of charging until the potential reaches 4.45 V vs. Li/Li ⁺ during the first cycle of charging and discharging. C _1B is the amount of charge from the start of charging until the potential reaches 4.80 V vs. Li/Li ⁺ during the charging of the first cycle of the charging and discharging.C _2A is the second cycle of the charging and discharging is the amount of electricity charged from the start of charging until the potential reaches 4.45 V vs. Li/Li ⁺ .C _2B is the amount of charge from the start of charging during the second cycle of charging and discharging. It is the amount of electricity charged until the potential reaches 4.80 V vs. Li/Li ⁺ .)

The non-aqueous electrolyte power storage element is a non-aqueous electrolyte using a lithium-excess type active material (a lithium transition metal composite oxide having an α-NaFeO ₂ structure and represented by Li _1+α Me _1-α O ₂ ) for a positive electrode. It is an electrolyte storage device and has a high capacity retention rate in charge/discharge cycles. Although the reason why such an effect occurs is not clear, the following is presumed.

(Technical significance of formula (1))
First, the technical significance of the above formula (1) will be described with reference to FIGS. FIG. 1 is a charge/discharge curve when the non-aqueous electrolyte storage element (test battery) according to Example 1 of the present invention is subjected to the above two cycles of charge/discharge. FIG. 2 is a charge/discharge curve when the non-aqueous electrolyte storage element (test battery) according to Comparative Example 1 of the present invention is subjected to the above two cycles of charge/discharge. In FIGS. 1 and 2, the horizontal axis represents the amount of charge (C _1B or C _2B ) in charging from the start of charging until the voltage reaches 4.80 V (positive electrode potential is 4.80 V vs. Li/Li ⁺ ). , or the relative amount of electricity (%) with the discharge amount of electricity in the discharge from the start of discharge until the voltage reaches 2.00 V (the positive electrode potential is 2.00 V vs. Li/Li ⁺ ) as the reference (100%). In addition, when the negative electrode material is metallic lithium, the dissolution/precipitation reaction resistance of metallic lithium in the negative electrode is extremely low. can be regarded as

In the nonaqueous electrolyte storage element of Comparative Example 1, the positive electrode potential was 4.6 V vs. Charging up to Li/Li ⁺ is taking place. As described above, when the lithium-excess active material is initially charged until the positive electrode potential reaches a high potential, 4.5 V vs. Li/Li ⁺ or more 5.0V vs. A feature is that a region in which the potential change is relatively gentle with respect to the amount of charged electricity is observed within the potential range of Li/Li ⁺ or lower. Then, when charging is performed in which a region in which this potential change is relatively gradual is observed, even if charging is performed until the positive electrode potential reaches a similarly high potential, this region in which the potential change is relatively gradual will again appear. Observations are generally considered non-existent. Moreover, the lithium-excess type active material can be considered as a solid solution of LiMeO ₂ and Li ₂ MnO ₃ , and it is believed that lithium ions are also present at transition metal sites in Li ₂ MnO ₃ . In the lithium-excess type active material, lithium ions present at such transition metal sites have a positive electrode potential of 4.6 V vs. It is considered that since the detachment becomes easier by charging up to Li/Li ⁺ , a large charge-discharge capacity can be obtained (activated) in the subsequent charge-discharge. Hereinafter, "charging until the positive electrode potential reaches 4.6 V vs. Li/Li ⁺ or more to activate the lithium-excess type active material" is also referred to as high potential formation.

In the non-aqueous electrolyte storage element of Comparative Example 1 in which high potential formation is performed in the initial charge and discharge, the voltage in the two cycles of charge and discharge is 4.80 V (positive electrode potential is 4.80 V vs. Li/Li ⁺ ). 4.5V vs. Li/Li ⁺ or more 4.8V vs. Within the potential range of Li/Li ⁺ or less, no region in which the potential change is relatively gentle with respect to the charge quantity of electricity is observed. Therefore, there is almost no difference between the charging curve of the first cycle and the charging curve of the second cycle.

On the other hand, in the non-aqueous electrolyte storage element of Example 1, the positive electrode potential was 4.6 V vs. Charging to Li/Li ⁺ has not occurred. Therefore, high potential formation is performed only in the first cycle of the above two charging/discharging cycles, and 4.5 V vs. Li/Li ⁺ or more 4.8V vs. Within the potential range of Li/Li ⁺ or less, a region in which the potential change is relatively gentle with respect to the amount of charged electricity is observed. Also, the region where the potential change is relatively gentle is not observed in the second cycle.

For this reason, in Example 1, the potential was 4.80 V vs. from the start of charging in the first cycle. From the start of charging, the potential is 4.45 V vs. the amount of charged electricity up to Li/Li ⁺ . The amount of charged electricity (C _1A /C _1B ) until reaching Li/Li ⁺ is relatively small, while the potential from the start of charging in the second cycle is 4.80 V vs. From the start of charging, the potential is 4.45 V vs. the amount of charged electricity up to Li/Li ⁺ . The amount of charged electricity (C _2A /C _2B ) up to Li/Li ⁺ increases. That is, in the case of Example 1, the difference between C _1A /C _1B and C _2A /C _2B is large. On the other hand, in the case of Comparative Example 1, almost the same behavior is exhibited in the first cycle and the second cycle, so there is almost no difference between C _1A /C _1B and C _2A /C _2B . Thus, satisfying formula (1) means that the lithium-excess type active material is not sufficiently high-potentially formed.

(Guess why the effect occurs)
On the other hand, in the non-aqueous electrolyte storage element, it is speculated that one of the causes of the decrease in the capacity retention rate is that the negative electrode consumes lithium ions that contribute to charging and discharging due to side reactions during charging and discharging. Here, in a non-aqueous electrolyte storage element having a lithium-excess type active material that has not been sufficiently high-potentially formed, the lithium-excess type active material is gradually activated and charged with repeated charging and discharging during use. It is presumed that the lithium ions desorbed from the lithium-rich active material during discharge can gradually increase. Hereinafter, "the gradual activation of the lithium-excess active material due to repeated charging and discharging during use" is also referred to as time-dependent formation. Therefore, according to the non-aqueous electrolyte power storage device according to one aspect of the present invention, the consumption of lithium ions by the negative electrode in the charge-discharge cycle can be supplemented by replenishment from the lithium-excess type active material of the positive electrode, so that the capacity can be maintained. presumed to be high. Also, in the non-aqueous electrolyte storage element, even if it is left in a charged state for example, the anodization may progress over time. Therefore, according to the non-aqueous electrolyte power storage device, it is possible to suppress a decrease in the capacity retention rate after standing.

The following procedure is used to obtain the value of the above formula (1) for the positive electrode. First, the non-aqueous electrolyte storage element is brought into a discharged state, the non-aqueous electrolyte storage element is disassembled, and the positive electrode is taken out. A test battery (single-electrode battery) is assembled using the removed positive electrode as the working electrode and the metallic lithium electrode as the counter electrode. The operations from dismantling the non-aqueous electrolyte storage element to assembling the test battery are performed in an argon atmosphere with a dew point of -60°C or less. For the assembled test cell, the potential was 2.00 V vs. Two cycles of charging and discharging are performed to obtain the value of the above formula (1) and to discharge until Li/Li 2 ⁺ . Two cycles of charging and discharging for obtaining the value of the above formula (1) are performed in an environment of 25° C., with a rest period of 30 minutes between charging and discharging.

In addition, the composition of the lithium-transition metal composite oxide has a potential of 2.00 V vs. The composition is analyzed by dismantling in a state in which discharge to Li/Li ⁺ is performed.

The difference (Mn/Me- Ni/Me) is preferably 0.02 or more and 0.2 or less.

In the lithium-transition metal composite oxide, the molar ratio difference (Mn/Me-Ni/Me) is 0.2 or less, so that when used at a relatively low charge upper limit potential (charging during normal use When the positive electrode potential at the final voltage is relatively low), the non-aqueous electrolyte storage element has a large discharge capacity and a high energy density. On the other hand, when the molar ratio difference (Mn/Me—Ni/Me) is 0.02 or more, the action of chemical formation over time is enhanced, and the capacity retention rate is further enhanced. Although the reason why such an effect occurs is not clear, the following is presumed. As described above, _the lithium-rich active material can be considered as a solid solution of _Li2MnO3 and _LiMeO2 . Further, if LiMeO ₂ is regarded as a solid solution of LiNi _0.5 Mn _0.5 O ₂ and LiCoO ₂ , the lithium-excess type active material is Li ₂ MnO ₃ and LiNi _0.5 Mn _0.5 O _{2 .} It can be regarded as a solid solution with LiCoO ₂ and its composition can be represented by the triangular phase diagram shown in FIG. In the triangular phase diagram of FIG. 3, the lithium-transition metal composite oxide (lithium-excess active material) satisfying 0.02≦(Mn/Me—Ni/Me)≦0.2 has the composition in the shaded area. Become. Here, in the lithium-transition metal composite oxide having a composition with a high proportion of Li ₂ MnO ₃ , relatively many lithium ions exist at the transition metal sites of Li ₂ MnO ₃ among the lithium ions. In the non-aqueous electrolyte energy storage device according to one aspect of the present invention, formation of a sufficiently high potential is not performed, and when used at a relatively low charge upper limit potential, lithium ions present at transition metal sites are difficult to desorb. Therefore, a lithium-transition metal composite oxide having a composition with a high proportion of Li ₂ MnO ₃ does not have a large discharge capacity. On the other hand, lithium transition metal composite oxides satisfying (Mn/Me—Ni/Me)≦0.2 have a low ratio of Li ₂ MnO ₃ and can be regarded as a solid solution mainly composed of LiMeO ₂ . Most of the ions are lithium ions existing at lithium sites. Lithium ions present at lithium sites are likely to be desorbed even when used at a relatively low charge upper limit potential, even if they are not converted to a high potential. Therefore, when the lithium-transition metal composite oxide satisfies (Mn/Me—Ni/Me)≦0.2, it is presumed that the discharge capacity is large and the energy density is also high. On the other hand, in a lithium-transition metal composite oxide having a composition with a high proportion of Li ₂ MnO ₃ , there are sufficient lithium ions present at the transition metal sites that can be gradually eliminated by chemical formation over time. Therefore, when the lithium-transition metal composite oxide satisfies 0.02≦(Mn/Me—Ni/Me), it is presumed that the action of chemical formation over time occurs sufficiently, and the capacity retention rate increases further. Note that the "relatively low charge upper limit potential" is, for example, a charge upper limit potential of 4.50 V vs. Li/Li ⁺ or less, 4.45V vs. It may be Li/Li ⁺ or less.

The molar ratio (Mn/Me) of Mn to the transition metal (Me) in the lithium-transition metal composite oxide is preferably 0.5 or less. By setting the Mn/Me ratio in the lithium-transition metal composite oxide to 0.5 or less, particularly when used at a relatively low charge upper limit potential (when the positive electrode potential at the end of charge voltage during normal use is relatively low) , the non-aqueous electrolyte storage element has a large discharge capacity and a high energy density. Although the reason why such an effect occurs is not clear, as shown in the triangular phase diagram of FIG. .2 can be regarded as a solid solution with a high proportion of LiMeO ₂ . As a result, it is presumed that the discharge capacity can be increased and the energy density can be increased in the same manner as when (Mn/Me--Ni/Me).ltoreq.0.2 is satisfied.

The molar ratio (Mn/Me) of Mn to the transition metal (Me) in the lithium-transition metal composite oxide is preferably greater than 0.36. By setting the Mn/Me ratio in the lithium-transition metal composite oxide to more than 0.36, the capacity retention rate is further increased. It is presumed that the reason why such an effect occurs is that a relatively high proportion of Mn allows a sufficient amount of lithium ions to exist at the transition metal site, thereby enhancing the action of chemical formation over time.

The molar ratio (Mn/Me) of Mn to the transition metal (Me) in the lithium-transition metal composite oxide is preferably more than 0.36 and 0.5 or less. By setting Mn/Me in the lithium-transition metal composite oxide to more than 0.36 and not more than 0.5, it is possible to achieve a suitable balance between a high capacity retention rate and energy density of the non-aqueous electrolyte storage element.

The molar ratio (Co/Me) of Co to the transition metal (Me) in the lithium-transition metal composite oxide is preferably less than 0.45. By setting the molar ratio of Co to less than 0.45, it is possible to suppress the use of expensive Co and reduce costs while exhibiting a sufficient capacity retention rate.

The content of the lithium-transition metal composite oxide in the positive electrode active material is preferably more than 70% by mass. In this way, by increasing the content ratio of the lithium transition metal composite oxide, that is, the lithium-excess type active material that has not been subjected to high-potential chemical conversion, in the positive electrode active material, a sufficient effect of chemical conversion over time is exhibited, and the capacity retention rate is improved. can be higher.

In the non-aqueous electrolyte power storage device according to one aspect of the present invention, the positive electrode potential at the end-of-charge voltage during normal use is 4.60 V vs. It is preferably less than Li/Li ⁺ . The positive electrode potential at the charging end voltage during normal use is 4.60 V vs. When the ratio is less than Li/Li ⁺ , chemical formation over time progresses gradually as charging and discharging are repeated many times, so the capacity retention rate can be increased.

Note that "during normal use" refers to a case where the non-aqueous electrolyte storage element is used under charging conditions recommended or specified for the non-aqueous electrolyte storage element. For example, when a charger for the non-aqueous electrolyte storage element is prepared, it means that the non-aqueous electrolyte storage element is used by applying the charger.

In the non-aqueous electrolyte power storage device according to one aspect of the present invention, the positive electrode potential at the end-of-charge voltage during normal use is 4.30 V vs. It is preferably greater than Li/Li ⁺ . The positive electrode potential at the charging end voltage during normal use is 4.30 V vs. When the Li/Li ^{2 +} ratio is greater than that, chemical formation over time sufficiently progresses during charging during normal use, so that the capacity retention rate can be increased.

In the non-aqueous electrolyte power storage device according to one aspect of the present invention, the positive electrode potential at the end-of-charge voltage during normal use is 4.30 V vs. Li/Li ⁺ greater than 4.60V vs. It is preferably less than Li/Li ⁺ . By setting the positive electrode potential at the charge cutoff voltage during normal use within the above range, the degree of progress of chemical formation (activation of the lithium-excess active material) accompanying charging during use is optimized, and the consumption rate of lithium by the negative electrode. and the replenishment rate of lithium from the lithium-transition metal composite oxide are balanced, so the capacity retention rate is further increased.

A method of using a non-aqueous electrolyte storage element according to another aspect of the present invention is such that the positive electrode potential is 4.30 V vs. Li/Li ⁺ greater than 4.60V vs. This is a method of using the non-aqueous electrolyte power storage element of one embodiment of the present invention, comprising charging to less than Li/Li ⁺ .

According to this method of use, since chemical formation is gradually performed over time as the battery is charged during use, the lithium-excess type active material (having an α-NaFeO ₂ structure and represented by Li _1+α Me _1-α O ₂ A non-aqueous electrolyte storage element using a lithium transition metal composite oxide (lithium transition metal composite oxide) for the positive electrode can be used with a high capacity retention rate.

In another aspect of the present invention, there is provided a method for manufacturing a non-aqueous electrolyte storage element, wherein the maximum attainable potential of the positive electrode is 4.60 V vs. A method for manufacturing a non-aqueous electrolyte power storage element according to one embodiment of the present invention, comprising performing initial charge/discharge at less than Li/Li ⁺ .

According to the production method, since high potential formation is not performed in the initial charge and discharge, the lithium-excess type active material (a lithium transition metal having an α-NaFeO ₂ structure and represented by Li _1+α Me _1-α O ₂ It is possible to manufacture a non-aqueous electrolyte storage element using a composite oxide) as a positive electrode and having a high capacity retention rate in charge-discharge cycles.

Hereinafter, a non-aqueous electrolyte storage element, a method for using the same, and a method for manufacturing the same according to one embodiment of the present invention will be described in detail.

<Non-aqueous electrolyte storage element>
A non-aqueous electrolyte storage element according to one embodiment of the present invention has a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode and the negative electrode normally form an electrode assembly alternately stacked or wound with a separator interposed therebetween. This electrode assembly is housed in a container, and the container is filled with a non-aqueous electrolyte. A non-aqueous electrolyte is interposed between the positive electrode and the negative electrode. Moreover, as a container, a known metal container, a resin container, or the like that is commonly used can be used. Hereinafter, a non-aqueous electrolyte secondary battery (hereinafter also simply referred to as a "secondary battery") will be described as an example of a non-aqueous electrolyte storage element.

(positive electrode)
The positive electrode has a positive electrode base material and a positive electrode active material layer disposed directly on the positive electrode base material or via an intermediate layer.

A positive electrode base material has electroconductivity. Having “conductivity” means having a volume resistivity of 10 ⁷ Ω·cm or less as measured in accordance with JIS-H-0505 (1975), and “non-conductivity” It means that the volume resistivity is more than 10 ⁷ Ω·cm. As the material for the positive electrode substrate, metals such as aluminum, titanium, tantalum and stainless steel, or alloys thereof are used. Among these, aluminum or an aluminum alloy is preferable from the viewpoint of potential resistance, high conductivity, and cost. Examples of positive electrode substrates include foils and deposited films, and foils are preferred from the viewpoint of cost. Therefore, aluminum foil or aluminum alloy foil is preferable as the positive electrode substrate. Examples of aluminum or aluminum alloy include A1085 and A3003 defined in JIS-H-4000 (2014).

The lower limit of the average thickness of the positive electrode substrate is preferably 5 μm, more preferably 10 μm. The upper limit of the average thickness of the positive electrode substrate is preferably 50 μm, more preferably 40 μm. By setting the average thickness of the positive electrode substrate to the above lower limit or more, the strength of the positive electrode substrate can be increased. By making the average thickness of the positive electrode substrate equal to or less than the above upper limit, the energy density per volume of the secondary battery can be increased. For these reasons, it is preferable that the average thickness of the positive electrode substrate be at least one of the above lower limits and not more than any of the above upper limits. "Average thickness" refers to a value obtained by dividing the punched mass when a substrate having a predetermined area is punched out by the true density and the punched area of the substrate. The same definition applies when using the "average thickness" for other members or the like.

The intermediate layer is a layer arranged between the positive electrode substrate and the positive electrode active material layer. The structure of the intermediate layer is not particularly limited, and includes, for example, a resin binder and conductive particles. The intermediate layer reduces the contact resistance between the positive electrode substrate and the positive electrode active material layer, for example, by containing conductive particles such as carbon particles.

The positive electrode active material layer is a layer of a positive electrode mixture containing a positive electrode active material. The positive electrode active material layer (positive electrode mixture) may contain optional components such as a conductive agent, a binder, a thickener, a filler, and the like, if necessary, in addition to the positive electrode active material.

The positive electrode active material has an α-NaFeO ₂ structure and is a lithium transition metal represented by Li _1+α Me _1-α O ₂ (0<α<1; Me is a transition metal including Ni and Mn). Contains complex oxides. This lithium-transition metal composite oxide is a so-called lithium-excess active material.

The transition metal (Me) contained in the lithium-transition metal composite oxide includes Ni and Mn. This transition metal preferably further contains Co. Preferably, the transition metal consists essentially of Ni and Mn, or consists essentially of Ni, Mn and Co. The lithium transition metal composite oxide is Li _1+α (Ni _β Co _γ Mn _δ ) _1-α O ₂ (0<α<1, 0<β<1, 0≤γ<1, 0<δ<1, β+γ+δ= 1) may be represented.

The molar ratio of lithium (Li) to the transition metal (Me) in the lithium-transition metal composite oxide, that is, (1+α)/(1−α) is preferably 1.1 or more and 1.4 or less, and 1.15 or more and 1 0.25 or less is more preferred. By making (1+α)/(1−α) equal to or higher than the above lower limit, sufficient chemical formation over time can easily occur, and the capacity retention rate can be further increased. In addition, by setting (1+α)/(1−α) to the above upper limit or less, the secondary battery has sufficient discharge capacity and high energy density even when used at a relatively low charge upper limit potential. becomes. The molar ratio (mass ratio) of each element in the lithium-transition metal composite oxide is equal to the atomic number ratio.

The molar ratio of Ni to the transition metal (Me) in the lithium-transition metal composite oxide (Ni/Me), that is, β may be, for example, 0.1 or more and 0.7 or less, but may be 0.2 or more and 0.2 or more. 0.6 or less is preferable, and 0.3 or more and 0.5 or less is more preferable. By making the ratio of Ni/Me equal to or higher than the above lower limit, the discharge capacity can be increased and the energy density can be increased particularly when the battery is used at a relatively low charge upper limit potential. By making the ratio of Ni/Me equal to or less than the above upper limit, the capacity retention rate and the like can be further increased.

The molar ratio (Co/Me) of Co to the transition metal (Me) in the lithium-transition metal composite oxide, that is, γ may be, for example, 0 or more and 0.6 or less, but may be 0.05 or more and 0.45. Less than is preferable, and 0.1 or more and 0.3 or less is more preferable. By setting the ratio of Co/Me to the above lower limit or more, the discharge capacity of the secondary battery may be increased and the energy density may be increased. On the other hand, by making Co/Me equal to or less than the above upper limit, raw material costs can be suppressed while exhibiting a sufficient capacity retention rate.

The molar ratio (Mn/Me) of Mn to the transition metal (Me) in the lithium-transition metal composite oxide, that is, δ may be, for example, 0.3 or more and 0.7 or less, but more than 0.36 and 0 0.5 or less is preferable, and 0.4 or more and less than 0.5 is more preferable. When the Mn/Me ratio is equal to or higher than the above lower limit, the effect of chemical conversion over time is enhanced, and the capacity retention rate can be enhanced. By making Mn/Me equal to or less than the above upper limit, it is possible to increase the discharge capacity and increase the energy density particularly when used at a relatively low charge upper limit potential.

The difference (Mn/Me- Ni/Me) may be, for example, more than 0 and 0.5 or less, preferably 0.02 or more and 0.2 or less, and more preferably 0.03 or more and 0.10 or less. By setting the Mn/Me—Ni/Me to the above upper limit or less, it is possible to increase the discharge capacity and increase the energy density, particularly when used at a relatively low upper limit charge potential. By setting the Mn/Me—Ni/Me to the above lower limit or more, the effect of chemical conversion over time is increased, and the capacity retention rate is further increased.

The lithium-transition metal composite oxide may contain other transition metals or the like within the range in which the effects of the present invention are exhibited, or may be mixed with other transition metals or the like as impurities. In addition, the lithium-transition metal composite oxide may be coated with other metal oxide (for example, alumina or the like) or the like.

The above lithium-transition metal composite oxide can be produced by a conventionally known method. For example, the lithium-transition metal composite oxide is prepared by preparing a raw material containing metal elements (Li, Ni, Mn, etc.) constituting the intended composite oxide according to the composition of the intended composite oxide, and can be obtained by firing the

The positive electrode active material may contain a positive electrode active material other than the lithium-transition metal composite oxide. The content of the lithium transition metal composite oxide in the positive electrode active material may be, for example, 50% by mass or more, preferably more than 70% by mass, more preferably 80% by mass or more, and even more preferably 90% by mass or more. , more preferably 99% by mass or more, and may be substantially 100% by mass. By increasing the content of the lithium-transition metal composite oxide in the positive electrode active material, the capacity retention rate can be further increased.

The positive electrode active material other than the lithium-transition metal composite oxide can be appropriately selected from known positive electrode active materials commonly used in lithium ion secondary batteries and the like. A material capable of intercalating and deintercalating lithium ions is usually used as the positive electrode active material. Examples thereof include the above-described LiMeO ₂ type active material, lithium transition metal oxide having a spinel crystal structure, polyanion compound, chalcogen compound, sulfur, and the like.

The average particle size of the positive electrode active material is preferably, for example, 0.1 μm or more and 20 μm or less. By making the average particle size of the positive electrode active material equal to or more than the above lower limit, manufacturing or handling of the positive electrode active material becomes easy. By setting the average particle size of the positive electrode active material to the above upper limit or less, the electron conductivity of the positive electrode active material layer is improved. Here, the "average particle size" is based on the particle size distribution measured by a laser diffraction/scattering method for a diluted solution in which the particles are diluted with a solvent in accordance with JIS-Z-8825 (2013). Z-8819-2 (2001) means the value at which the volume-based integrated distribution calculated according to 50%.

A pulverizer, a classifier, or the like is used to obtain particles of a positive electrode active material or the like in a predetermined shape. Pulverization methods include, for example, methods using a mortar, ball mill, sand mill, vibrating ball mill, planetary ball mill, jet mill, counter jet mill, whirling jet mill, or sieve. At the time of pulverization, wet pulverization in which water or an organic solvent such as hexane is allowed to coexist can also be used. As a classification method, a sieve, an air classifier, or the like is used as necessary, both dry and wet.

The lower limit of the content of the positive electrode active material in the positive electrode active material layer (positive electrode mixture) is preferably 70% by mass, more preferably 80% by mass, and even more preferably 90% by mass. The upper limit of the content of the positive electrode active material is preferably 98% by mass, more preferably 96% by mass. By setting the content of the positive electrode active material within the above range, the electric capacity of the secondary battery can be increased. The content of the positive electrode active material in the positive electrode active material layer can be at least one of the above lower limits and not more than any of the above upper limits.

Further, when the content of the positive electrode active material in the positive electrode active material layer (positive electrode mixture) is within the above range (for example, 70% by mass or more), the content of the positive electrode active material in the positive electrode mixture is It does not substantially affect the measured value ((C _2A /C _2B ) × 100-(C _1A /C _1B ) × 100) based on two cycles of charging and discharging performed at a current density of 9 mA / g per mass of the mixture. do not have.

The conductive agent is not particularly limited as long as it is a conductive material. Examples of such conductive agents include graphite; carbon blacks such as furnace black and acetylene black; metals; and conductive ceramics. The shape of the conductive agent may be powdery, fibrous, or the like. Among these, acetylene black is preferable from the viewpoint of electronic conductivity and coatability.

The lower limit of the content of the conductive agent in the positive electrode active material layer (positive electrode mixture) is preferably 1% by mass, more preferably 2% by mass. The upper limit of the content of the conductive agent is preferably 10% by mass, more preferably 5% by mass. By setting the content of the conductive agent within the above range, the electric capacity of the secondary battery can be increased. For these reasons, the content of the conductive agent is preferably at least one of the above lower limits and not more than any of the above upper limits.

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

The lower limit of the binder content in the positive electrode active material layer (positive electrode mixture) is preferably 1% by mass, more preferably 2% by mass. The upper limit of the binder content is preferably 10% by mass, more preferably 5% by mass. By setting the content of the binder within the above range, the active material can be stably retained. For these reasons, the content of the binder is preferably at least one of the above lower limits and not more than any of the above upper limits.

Examples of thickeners include polysaccharide polymers such as carboxymethylcellulose (CMC) and methylcellulose. When the thickener has a functional group that reacts with lithium or the like, the functional group may be previously deactivated by methylation or the like.

A filler is not specifically limited. Examples of fillers include polyolefins such as polypropylene and polyethylene, silica, alumina, zeolite, glass, and alumina silicate.

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

(charged electricity amount of positive electrode)
With respect to the positive electrode, a current density of 9 mA/g per mass of the positive electrode mixture causes a potential of 2.00 V vs. After discharging up to Li/Li ⁺ , the potential is 4.80 V vs. When the charge and potential up to Li/Li ⁺ is 2.00 V vs. The amount of charged electricity when performing two cycles of charging and discharging until reaching Li/Li ⁺ satisfies the following formula (1).
(C _2A /C _2B )×100−(C _1A /C _1B )×100≧1.0 (1)
In the formula (1), C _1A has a potential of 4.45 V vs. 4.45 V vs. It is the charge amount of electricity up to Li/Li ⁺ . C _1B has a potential of 4.80 V vs. It is the charge amount of electricity up to Li/Li ⁺ . C _2A has a potential of 4.45 V vs. It is the charge amount of electricity up to Li/Li ⁺ . C _2B has a potential of 4.80 V vs. It is the charge amount of electricity up to Li/Li ⁺ .

The lower limit of the left side of the above formula (1), that is, "(C _2A /C _2B )×100−(C _1A /C _1B )×100" is preferably 1.5, 2.0, 3.0, 4.0. 0 or 5.0 may be more preferred. “(C _2A /C _2B )×100−(C _1A /C _1B )×100” indicates the degree of insufficient high potential formation as described above. Therefore, when "(C _2A /C _2B )×100−(C _1A /C _1B )×100" is equal to or greater than the above lower limit, formation over time tends to occur more easily, and the capacity retention rate tends to increase. On the other hand, the upper limit of "(C _2A /C _2B )×100−(C _1A /C _1B )×100" is, for example, 20, preferably 10, and may be 5.0.

(negative electrode)
The negative electrode has a negative electrode substrate and a negative electrode active material layer disposed directly on the negative electrode substrate or via an intermediate layer. The structure of the intermediate layer of the negative electrode is not particularly limited, and may have the same structure as that of the intermediate layer of the positive electrode.

A negative electrode base material has electroconductivity. As the material of the negative electrode base material, metals such as copper, nickel, stainless steel, nickel-plated steel, and aluminum, or alloys thereof are used. Among these, copper or a copper alloy is preferred. Examples of negative electrode substrates include foils and vapor deposition films, and foils are preferred from the viewpoint of cost. Therefore, copper foil or copper alloy foil is preferable as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil.

The lower limit of the average thickness of the negative electrode substrate is preferably 3 μm, more preferably 5 μm. The upper limit of the average thickness of the negative electrode substrate is preferably 30 μm, more preferably 20 μm. By making the average thickness of the negative electrode base material equal to or greater than the above lower limit, the strength of the negative electrode base material can be increased. The energy density per volume of the secondary battery can be increased by setting the average thickness of the negative electrode substrate to the above upper limit or less. For these reasons, the average thickness of the negative electrode substrate is preferably at least any one of the above lower limits and not more than any of the above upper limits.

The negative electrode active material layer is a layer of a negative electrode mixture containing a negative electrode active material. The negative electrode active material layer (negative electrode mixture) may contain arbitrary components such as a conductive agent, a binder, a thickener, a filler, and the like, in addition to the negative electrode active material, if necessary. Optional components such as a conductive agent, a binder, a thickener, and a filler may be the same as those used for the positive electrode active material layer. The content of each of these optional components in the negative electrode active material layer can be within the range described as the content of these in the positive electrode active material layer.

The negative electrode active material can be appropriately selected from known negative electrode active materials. Materials capable of intercalating and deintercalating lithium ions are usually used as negative electrode active materials for lithium ion secondary batteries. Examples of the negative electrode active material include metal Li; metals or metalloids such as Si and Sn; metal oxides and metalloid oxides such as Si oxide, Ti oxide and Sn oxide; Li ₄ Ti ₅ O ₁₂ ; Titanium-containing oxides such as LiTiO _{2 and} TiNb ₂ O ₇ ; polyphosphate compounds; silicon carbide; carbon materials such as graphite and non-graphitizable carbon (easily graphitizable carbon or non-graphitizable carbon) be done. In the negative electrode active material layer, one type of these materials may be used alone, or two or more types may be mixed and used.

“Graphite” refers to a carbon material having an average lattice spacing (d ₀₀₂ ) of the (002) plane determined by X-ray diffraction before charging/discharging or in a discharged state of 0.33 nm or more and less than 0.34 nm. Graphite includes natural graphite and artificial graphite. Artificial graphite is preferable from the viewpoint that a material with stable physical properties can be obtained.

“Non-graphitic carbon” means a carbon material having an average lattice spacing (d ₀₀₂ ) of the (002) plane determined by X-ray diffraction before charging/discharging or in a discharged state of 0.34 nm or more and 0.42 nm or less. say. Non-graphitizable carbon includes non-graphitizable carbon and graphitizable carbon. Examples of non-graphitic carbon include resin-derived materials, petroleum pitch or petroleum pitch-derived materials, petroleum coke or petroleum coke-derived materials, plant-derived materials, and alcohol-derived materials.

Here, the “discharged state” that defines graphite and non-graphitic carbon refers to a single electrode battery using a negative electrode containing a carbon material as a negative electrode active material as a working electrode and metal Li as a counter electrode. .7V or higher. Since the potential of the metal Li counter electrode in the open circuit state is approximately equal to the oxidation-reduction potential of Li, the open-circuit voltage in the above monopolar battery is approximately the same as the potential of the negative electrode containing the carbon material with respect to the oxidation-reduction potential of Li. . In other words, the open circuit voltage of 0.7 V or higher in the above monopolar battery means that lithium ions that can be inserted and extracted are sufficiently released from the carbon material that is the negative electrode active material during charging and discharging. .

The term “non-graphitizable carbon” refers to a carbon material having a d ₀₀₂ of 0.36 nm or more and 0.42 nm or less.

“Graphitizable carbon” refers to a carbon material having a d ₀₀₂ of 0.34 nm or more and less than 0.36 nm.

In order to obtain a secondary battery with a higher capacity retention rate, the negative electrode active material is preferably a carbon material, and more preferably graphite. When a carbon material is used as the negative electrode active material, the content of the carbon material in the total negative electrode active material may be 50% by mass or more, 70% by mass or more, or 90% by mass or more. may be substantially 100% by mass.

On the other hand, when a negative electrode active material such as Si, Sn, or oxides thereof that consumes a particularly large amount of lithium is used, the advantage of the present invention that lithium can be replenished from the positive electrode by chemical formation over time can be fully enjoyed. However, since a secondary battery using any negative electrode active material generally consumes lithium to some extent, the present invention can be applied regardless of the type of negative electrode active material. Moreover, by using Si, Sn, oxides thereof, or the like as the negative electrode active material, the discharge capacity can be increased. Si, Sn and oxides thereof may be used together with the carbon material. The content of Si, Sn, and their oxides in the total negative electrode active material may be, for example, 1% by mass or more and 90% by mass or less, or 5% by mass or more and 70% by mass or less.

The negative electrode active material is usually particles (powder). The average particle size of the negative electrode active material can be, for example, 1 nm or more and 100 μm or less. By making the average particle size of the negative electrode active material equal to or greater than the above lower limit, the production or handling of the negative electrode active material is facilitated. By setting the average particle size of the negative electrode active material to the above upper limit or less, the electron conductivity of the active material layer is improved. A pulverizer, a classifier, or the like is used to obtain powder having a predetermined particle size. The pulverization method and the powder class method can be selected from, for example, the methods exemplified for the positive electrode.

The content of the negative electrode active material in the negative electrode active material layer (negative electrode mixture) is preferably 60% by mass or more and 99% by mass or less, more preferably 90% by mass or more and 98% by mass or less. By setting the content of the negative electrode active material within the above range, it is possible to achieve both high energy density and manufacturability of the negative electrode active material layer.

The negative electrode active material layer contains typical nonmetallic elements such as B, N, P, F, Cl, Br, and I, Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, Ba, and the like. and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, and W are used as negative electrode active materials, conductive agents, binders, and thickeners. You may contain as a component other than a sticky agent and a filler.

(separator)
The separator can be appropriately selected from known separators. As the separator, for example, a separator consisting of only a substrate layer, a separator having a heat-resistant layer containing heat-resistant particles and a binder formed on one or both surfaces of a substrate layer, or the like can be used. Examples of the material of the base material layer of the separator include woven fabric, nonwoven fabric, and porous resin film. Among these materials, a porous resin film is preferred from the viewpoint of strength, and a non-woven fabric is preferred from the viewpoint of retention of the non-aqueous electrolyte. As the material for the base layer of the separator, polyolefins such as polyethylene and polypropylene are preferable from the viewpoint of shutdown function, and polyimide, aramid, and the like are preferable from the viewpoint of oxidative decomposition resistance. A material obtained by combining these resins may be used as the base material layer of the separator.

The heat-resistant particles contained in the heat-resistant layer preferably have a mass reduction of 5% or less at 500° C. in air, more preferably 5% or less at 800° C. in air. An inorganic compound can be mentioned as a material whose mass reduction is less than or equal to a predetermined value. Inorganic compounds such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, barium titanate, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, oxides such as aluminosilicate; magnesium hydroxide, water Hydroxides such as calcium oxide and aluminum hydroxide; Nitrides such as aluminum nitride and silicon nitride; Carbonates such as calcium carbonate; Sulfates such as barium sulfate; Poorly soluble ion crystals such as calcium fluoride and barium fluoride covalent crystals such as silicon and diamond; mineral resource-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica; . As the inorganic compound, a single substance or a composite of these substances may be used alone, or two or more of them may be mixed and used. Among these inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicate is preferable from the viewpoint of safety of secondary batteries.

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, the "porosity" is a volume-based value and means a value measured with a mercury porosimeter.

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

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

The non-aqueous solvent can be appropriately selected from known non-aqueous solvents. Non-aqueous solvents include cyclic carbonates, chain carbonates, carboxylic acid esters, phosphoric acid esters, sulfonic acid esters, ethers, amides, nitriles and the like. As the non-aqueous solvent, those in which some of the hydrogen atoms contained in these compounds are substituted with halogens may be used. For example, by using a fluorinated compound (fluorinated cyclic carbonate, fluorinated chain carbonate, etc.), it can be sufficiently used even under conditions where the positive electrode potential reaches a high potential.

Cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinylethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), and difluoroethylene carbonate. (DFEC), styrene carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate and the like. Among these, EC, PC and FEC are preferred.

Chain carbonates include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, methyltrifluoroethyl carbonate (MFEC), bis(trifluoroethyl) carbonate and the like. Among these, EMC and MFEC are preferred.

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

The electrolyte salt can be appropriately selected from known electrolyte salts. Examples of electrolyte salts include lithium salts, sodium salts, potassium salts, magnesium salts, onium salts and the like. Among these, lithium salts are preferred.

Lithium salts include inorganic lithium salts such as LiPF ₆ , LiPO ₂ F ₂ , LiBF ₄ , LiClO ₄ and LiN(SO ₂ F) ₂ , LiSO ₃ CF ₃ , LiN(SO ₂ CF ₃ ) ₂ , LiN(SO _{2 C2F5 ) 2} , LiN( _{SO2CF3 )} ( _{SO2C4F9 )} , LiC( _SO2CF3 ) ₃ , _{LiC ( SO2C2F5 ) 3} and other halogenated _hydrocarbon groups and lithium salts having Among these, inorganic lithium salts are preferred, and _LiPF6 is more preferred.

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

The non-aqueous electrolyte may contain additives. Examples of additives include aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran; -Partial halides of the above aromatic compounds such as cyclohexylfluorobenzene and p-cyclohexylfluorobenzene; Halogenated anisole compounds; succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, dimethyl sulfate, ethylene sulfate, sulfolane, dimethylsulfone, diethylsulfone, dimethylsulfoxide, diethylsulfoxide, tetramethylenesulfoxide, diphenylsulfide, 4,4′-bis(2,2-dioxo-1,3,2-dioxathiolane), 4-methylsulfonyloxymethyl- 2,2-dioxo-1,3,2-dioxathiolane, thioanisole, diphenyl disulfide, dipyridinium disulfide, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakistrimethylsilyl titanate and the like. These additives may be used singly or in combination of two or more.

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

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

The solid electrolyte can be selected from any materials such as lithium, sodium, calcium, etc., which have ion conductivity and are solid at room temperature (for example, 15° C. or higher and 25° C. or lower). Examples of solid electrolytes include sulfide solid electrolytes, oxide solid electrolytes, oxynitride solid electrolytes, and polymer solid electrolytes.

Examples of sulfide solid electrolytes for lithium ion secondary batteries include Li ₂ SP ₂ S ₅ system and the like. Examples of sulfide solid electrolytes include Li ₂ SP ₂ S ₅ , LiI—Li ₂ SP ₂ S ₅ , Li ₁₀ Ge—P ₂ S ₁₂ and the like.

(Positive potential at the end of charge voltage during normal use)
In the secondary battery (non-aqueous electrolyte storage element), the positive electrode potential at the charging end voltage during normal use is 4.60 V vs. Li/Li ⁺ is preferably less than 4.55V vs. Li/Li ⁺ or less is more preferable, and 4.50 V vs. Li/Li ⁺ or 4.45V vs. Li/Li ⁺ or less may be even more preferred. By setting the positive electrode potential at the end-of-charge voltage during normal use to the above upper limit or less, formation over time gradually progresses with repeated charging and discharging many times, so that the capacity retention rate can be increased.

In the secondary battery, the positive electrode potential at the charging end voltage during normal use is 4.30 V vs. Li/Li ⁺ is preferred, 4.35 V vs. Li/Li ⁺ or more is more preferable, and 4.40 V vs. Li/Li ⁺ or higher may be even more preferable in some cases. By setting the positive electrode potential at the end-of-charge voltage during normal use to the above lower limit or higher, formation over time proceeds sufficiently during normal charging, so that the capacity retention rate can be increased. Further, by increasing the charge upper limit potential, the discharge capacity can be increased and the energy density can be increased.

The positive electrode potential at the end-of-charge voltage during normal use of the secondary battery may be within the range between any of the above upper limits and any of the above lower limits.

(Application)
The application of the secondary battery is not particularly limited, and it can be used for the same applications as conventionally known secondary batteries. Since it is presumed that the secondary battery is able to increase the capacity retention rate due to the occurrence of chemical formation over time, when charging, it is usually charged to a predetermined end-of-charge voltage (predetermined end-of-charge potential). The secondary battery can be particularly preferably applied to applications where the battery is charged until the SOC (state of charge) reaches 100%. Examples of such applications include power supply applications such as portable electronic devices (mobile phones, laptop computers, tablet terminals, etc.), electric toys, electric shavers, electric vehicles (EV), and plug-in hybrid vehicles (PHEV). be able to.

<How to use the non-aqueous electrolyte storage element>
A method of using the non-aqueous electrolyte storage element according to one embodiment of the present invention is to set the non-aqueous electrolyte storage element to a positive electrode potential of 4.30 V vs. Li/Li ⁺ greater than 4.60V vs. Charging to less than Li/Li ⁺ is provided. By using it in this way, that is, by repeatedly charging it to such a potential, chemical formation occurs gradually with the passage of time. Can be used at maintenance rate.

The upper limit of the positive electrode potential (charge upper limit potential) in this charging is 4.55 V vs. Li/Li ⁺ or less, 4.50V vs. Li/Li ⁺ or 4.45V vs. It may be Li/Li ⁺ . Further, the lower limit of the positive electrode potential (upper limit charging potential) in this charging is 4.35 V vs. Li/Li ⁺ , 4.40V vs. It may be Li/Li ⁺ .

This method of use may be the same as the method of use of conventionally known non-aqueous electrolyte storage elements, except that the positive electrode potential (upper limit charge potential) in charging is set within the above range.

<Method for producing non-aqueous electrolyte storage element>
A non-aqueous electrolyte storage element according to an embodiment of the present invention is produced by assembling an uncharged/discharged non-aqueous electrolyte storage element including a positive electrode, a negative electrode, and a non-aqueous electrolyte, and initially charging the un-charged/discharged non-aqueous electrolyte storage element. Prepare to discharge. In this initial charge/discharge, the maximum potential of the positive electrode was 4.60 V vs. Initial charging is performed to be less than Li/Li ⁺ . According to such a production method, since high potential formation is not performed in the initial charge and discharge, the non-aqueous electrolyte storage element using the lithium-excess type active material for the positive electrode has a high capacity retention rate in charge and discharge cycles. A water electrolyte storage device can be manufactured.

In the production method, the initial charge/discharge may not actively activate the lithium-excess type active material, but may be performed, for example, to confirm the capacity. That is, the initial charge/discharge is charge/discharge performed only after the non-aqueous electrolyte storage element (uncharged/discharged non-aqueous electrolyte storage element) is assembled. The number of times of charge/discharge in the initial charge/discharge may be one or two, or may be three or more.

The maximum potential of the positive electrode in the initial charge/discharge was 4.55 V vs. Li/Li ⁺ or less, 4.50V vs. Li/Li ⁺ or 4.45V vs. It may be Li/Li ⁺ or less. On the other hand, the lower limit of the maximum potential of the positive electrode in the initial charge/discharge is not particularly limited, and is, for example, 4.30 V vs. Li/Li ⁺ may be greater than 4.35V vs. Li/Li ⁺ or more or 4.40 V vs. It may be Li/Li ⁺ or more.

Assembling an uncharged/discharged non-aqueous electrolyte storage element including a positive electrode, a negative electrode, and a non-aqueous electrolyte includes, for example, preparing an electrode body, preparing a non-aqueous electrolyte, and storing the electrode body and the non-aqueous electrolyte in a container. a. Preparing the electrode body includes preparing a positive electrode, preparing a negative electrode, and forming an electrode body by laminating or winding the positive electrode and the negative electrode with a separator interposed therebetween.

Preparing the positive electrode can be performed by applying the positive electrode material mixture paste directly or via an intermediate layer to the positive electrode base material and drying the paste. The positive electrode mixture paste contains components such as a positive electrode active material, components constituting a positive electrode active material layer (positive electrode mixture), and a dispersion medium. The positive electrode active material includes the lithium-transition metal composite oxide (lithium-excess active material). Similarly, a negative electrode can be prepared by, for example, applying a negative electrode material mixture paste directly or via an intermediate layer to a negative electrode substrate, and drying the paste. The negative electrode mixture paste contains each component constituting the negative electrode active material layer (negative electrode mixture) such as the negative electrode active material, and a dispersion medium.

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

Further, in the above embodiments, the non-aqueous electrolyte storage element is mainly a non-aqueous electrolyte secondary battery, but other non-aqueous electrolyte storage elements may be used. Other non-aqueous electrolyte storage elements include capacitors (electric double layer capacitors, lithium ion capacitors) and the like.

FIG. 5 shows a schematic diagram of a rectangular non-aqueous electrolyte storage element 1 (non-aqueous electrolyte secondary battery), which is one embodiment of the non-aqueous electrolyte storage element according to the present invention. In addition, the same figure is taken as the figure which saw through the inside of a container. In the non-aqueous electrolyte storage element 1 shown in FIG. 5, the electrode body 2 is accommodated in the container 3 . The electrode body 2 is formed by winding a positive electrode including a positive electrode active material and a negative electrode including a negative electrode active material with a separator interposed therebetween. The positive electrode is electrically connected to the positive terminal 4 via the positive lead 41 , and the negative electrode is electrically connected to the negative terminal 5 via the negative lead 51 .

The configuration of the non-aqueous electrolyte storage element according to the present invention is not particularly limited, and examples thereof include cylindrical batteries, prismatic batteries (rectangular batteries), flat batteries, and the like. The present invention can also be implemented as a power storage device including a plurality of non-aqueous electrolyte power storage elements described above. One embodiment of a power storage device is shown in FIG. In FIG. 6 , the power storage device 30 includes a plurality of power storage units 20 . Each power storage unit 20 includes a plurality of nonaqueous electrolyte power storage elements 1 . The power storage device 30 can be mounted as a power supply for automobiles such as electric vehicles (EV) and plug-in hybrid vehicles (PHEV).

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

[Example 1] Preparation of test battery (non-aqueous electrolyte storage element) having positive electrode A (excessive lithium active material) (preparation of positive electrode A)
As _a positive _{electrode active} material _{, a} lithium transition metal composite oxide ( _{positive electrode} An active material A) was prepared.
Positive electrode active material A: acetylene black (AB): polyvinylidene fluoride (PVDF) = 90:5:5 in terms of mass ratio (in terms of solid matter), and using N-methylpyrrolidone (NMP) as a dispersion medium. A mixture paste was prepared. This positive electrode mixture paste was applied to an aluminum foil (thickness: 15 μm) as a positive electrode base material and dried to obtain a positive electrode A.

(Assembly of test battery)
A test battery (non-aqueous electrolyte storage element) was assembled using the positive electrode A as a working electrode and metal lithium as a counter electrode. As a non-aqueous electrolyte, 1.0 mol of lithium hexafluorophosphate (LiPF ₆ ) as an electrolyte salt was added to a non-aqueous solvent obtained by mixing EC (ethylene carbonate) and EMC (ethyl methyl carbonate) at a volume ratio of 30:70. A ^polyolefin microporous membrane was used as a separator.

(initial charge/discharge)
The resulting test battery (uncharged/discharged nonaqueous electrolyte storage element) before initial charge/discharge was subjected to 5 cycles of initial charge/discharge at 25° C. in the following manner to obtain a nonaqueous electrolyte storage element. rice field. Here, a rest period of 10 minutes was provided after all charging and after discharging. The amount of discharged electricity in the second cycle of the following initial charge/discharge was taken as the discharge capacity. In the following tests, voltage control was performed between the working electrode and the counter electrode, but since the dissolution/precipitation reaction resistance of metallic lithium in the counter electrode is extremely low, the voltage between the terminals during charging and discharging was determined using metallic lithium. It can be considered equal to the potential of the working electrode with respect to the reference electrode.
(first cycle)
Constant-current constant-voltage charging was performed at a charging current of 0.1 C (18 mA/g per mass of the positive electrode active material), a charge cut-off voltage of 4.35 V (positive electrode potential of 4.35 V vs. Li/Li ⁺ ), and a total charging time of 15 hours. rice field. After that, constant current discharge was performed at a discharge current of 0.2C and a discharge final voltage of 2.5V.
(2nd to 5th cycle)
Constant-current constant-voltage charging was performed at a charging current of 0.2 C (36 mA/g per mass of the positive electrode active material), a charge cut-off voltage of 4.35 V (positive electrode potential of 4.35 V vs. Li/Li ⁺ ), and a total charging time of 8 hours. rice field. After that, constant current discharge was performed at a discharge current of 0.2C and a discharge final voltage of 2.5V.

(Two cycles of charging and discharging for obtaining the value of the above formula (1))
Two cycles of charging and discharging were performed at 25° C. in the following manner to determine the value of the above formula (1) for the test battery that had completed the initial charging and discharging. Here, since it is known that the test battery has a metallic lithium electrode as the counter electrode, the operation of removing the positive electrode and reassembling the test battery was not performed.
First, constant current discharge was performed at a current density of 9 mA/g per mass of the positive electrode mixture until the terminal voltage reached 2.00 V (positive electrode potential 2.00 V vs. Li/Li ⁺ ).
Next, constant-current charging was performed at a current density of 9 mA/g per mass of the positive electrode mixture and a charge termination voltage of 4.80 V (positive electrode potential 4.80 V vs. Li/Li ⁺ ). Thereafter, constant current discharge was performed at a current density of 9 mA/g per mass of the positive electrode mixture and a discharge final voltage of 2.00 V (positive electrode potential 2.00 V vs. Li/Li ⁺ ). Two cycles of this charging and discharging were performed. In addition, a rest period of 30 minutes was provided after charging and after discharging.

(Evaluation of charging curve)
From the above two-cycle charge-discharge cycle test,
In the first cycle charging, the voltage from the start of charging to 4.80 V (the positive electrode potential is 4.80 V vs. Li/Li ⁺ ) for the amount of charge (C _1B ) from the start of charging to the voltage of 4.45 V ( The percentage of the charged quantity of electricity (C _1A ) until the positive electrode potential reaches 4.45 V vs. Li/Li ⁺ ((C _1A /C _1B )×100),
In the second cycle charging, the voltage from the start of charging to 4.80 V (the positive electrode potential is 4.80 V vs. Li/Li ⁺ ) for the amount of charge electricity (C _2B ) from the start of charging to 4.45 V ( The percentage of the charged quantity of electricity (C _2A ) until the positive electrode potential reaches 4.45 V vs. Li/Li ⁺ ) ((C _2A /C _2B ) × 100), and the difference between them ((C _2A /C _2B )×100−(C _1A /C _1B )×100) was obtained. These values are shown in Table 1.

[Examples 2 to 5, Comparative Example 1]
The same operation as in Example 1 was performed except that the charge end voltage (positive electrode potential at the end of charge) in the 1st to 3rd cycles in the “initial charge and discharge” of Example 1 was as shown in Table 1. A discharge test and charge curve were evaluated. Table 1 shows the obtained values.

As for the charge/discharge curves in the two-cycle charge/discharge test, the charge/discharge curve of Example 1 is shown in FIG. 1, and the charge/discharge curve of Comparative Example 1 is shown in FIG.

As shown in Table 1, the end-of-charge voltage during the initial charge and discharge was less than 4.6 V, and the maximum potential of the positive electrode (positive electrode potential at the end-of-charge voltage) was 4.6 V vs. In Examples 1 to 5, which are less than Li/Li ⁺ , the value of (C _2A /C _2B )×100−(C _1A /C _1B )×100 is 1.0 or more. That is, it can be evaluated that they are insufficient in high-potential formation and have sufficient ability to undergo aging formation. This tendency increases as the positive electrode potential decreases. On the other hand, the end-of-charge voltage in the initial charge/discharge was 4.6 V, and the maximum potential of the positive electrode was 4.6 V vs. In Comparative Example 1 with Li/Li ⁺ , the value of (C _2A /C _2B )×100−(C _1A /C _1B )×100 is 0.7. In other words, it can be evaluated that Comparative Example 1 is sufficiently high-potential formation and does not have sufficient ability to undergo aging formation.

Further, as shown in FIG. 1, in Example 1, in the first cycle, the voltage range of 4.5 V or more and 4.8 V or less (4.5 V vs. Li/Li ⁺ or more and 5.0 V vs. Li/ A region where the voltage change is relatively gentle with respect to the amount of charged electricity is observed within the range of positive electrode potential below Li ⁺ . In the second cycle, no region where the voltage change is relatively gentle is observed. On the other hand, as shown in FIG. 2, in Comparative Example 1, no region in which the voltage change is relatively moderate is observed in any cycle. These charge-discharge curves also show that in Comparative Example 1, a sufficient high-potential formation has already occurred during the initial charge-discharge, whereas in Example 1, high-potential formation has not been sufficiently performed. It can be said that it has sufficient ability to be chemically formed over time.

[Example 6] Fabrication of non-aqueous electrolyte storage element having positive electrode A (excessive lithium active material) and negative electrode A (SiO—Gr) (preparation of positive electrode A)
A positive electrode A was obtained in the same manner as in Example 1.

(Preparation of negative electrode A)
As a negative electrode active material, a negative electrode active material A was used in which silicon oxide (SiO) coated with non-graphitic carbon and graphite (Gr) were mixed at a ratio of 2:8 (mass ratio).
Negative electrode containing negative electrode active material A: styrene-butadiene rubber (SBR): carboxymethyl cellulose (CMC) at a mass ratio of 94.8: 4.0: 1.2 (in terms of solid content) and using water as a dispersion medium A mixture paste was prepared. This negative electrode mixture paste was applied to a strip-shaped copper foil (thickness: 20 μm) as a negative electrode substrate and dried to obtain a negative electrode A.

(Preparation of non-aqueous electrolyte A)
1. Lithium hexafluorophosphate (LiPF ₆ ) as an electrolyte salt was added to a non-aqueous solvent in which EC (ethylene carbonate), PC (propylene carbonate), and EMC (ethyl methyl carbonate) were mixed at a volume ratio of 25:5:70. A non-aqueous electrolyte A was prepared by dissolving so as to have a content of 0 mol/dm ³ .

(Assembly of non-aqueous electrolyte storage element)
A polyolefin microporous film coated with a heat-resistant layer was prepared as a separator. An electrode body was produced by laminating the positive electrode A and the negative electrode A with the separator interposed therebetween. This electrode body was placed in a container made of a metal-resin composite film, and after the non-aqueous electrolyte A was injected therein, the container was sealed by heat welding.

(initial charge/discharge)
The obtained non-aqueous electrolyte storage element before initial charge/discharge (uncharged/discharged non-aqueous electrolyte storage element) was subjected to initial charge/discharge at 25° C. in the following manner. Based on the design rated capacity of the non-aqueous electrolyte storage element, constant current charging was performed with a charging current of 0.1 C and a total charging time of 3 hours, followed by a rest period of 12 hours. After that, constant-current and constant-voltage charging was performed with a charging current of 0.1 C, a charging cut-off voltage of 4.15 V (positive electrode potential of 4.25 V vs. Li/Li ⁺ ), and a total charging time of 13 hours, followed by a rest period of 10 minutes. rice field. After that, constant current discharge was performed at a discharge current of 0.2C and a discharge final voltage of 2.5V. A non-aqueous electrolyte storage device was completed through the above procedure.

(Measurement of initial discharge capacity)
Next, the initial discharge capacity of the completed non-aqueous electrolyte storage element was confirmed at 25° C. in the following manner.
(first cycle)
Constant-current and constant-voltage charging was performed at a charging current of 0.2 C, a charging cut-off voltage of 4.15 V (positive electrode potential of 4.25 V vs. Li/Li ⁺ ), and a total charging time of 8 hours. After that, constant current discharge was performed at a discharge current of 0.2C and a discharge final voltage of 2.5V.
(second cycle)
After that, constant-current and constant-voltage charging was performed with a charging current of 0.2 C, a charge termination voltage of 4.15 V (positive electrode potential of 4.25 V vs. Li/Li ⁺ ), and a total charging time of 8 hours. After that, constant current discharge was performed at a discharge current of 1.0C and a discharge final voltage of 2.5V. Thereafter, constant current discharge was performed at a discharge current of 0.2 C and a discharge final voltage of 2.5 V as residual discharge.
A rest period of 10 minutes was provided after charging and after discharging. The amount of electricity discharged in the first cycle of discharge (discharge at a discharge current of 0.2 C) was taken as the initial discharge capacity.

(Charge-discharge cycle test)
A charge/discharge cycle test was performed at 45° C. in the following manner for the non-aqueous electrolyte storage element for which the initial discharge capacity was confirmed. Constant-current and constant-voltage charging was performed at a charging current of 1.0 C and a charge termination voltage of 4.15 V (positive electrode potential of 4.25 V vs. Li/Li ⁺ ). The charging termination condition was the time when the current value attenuated to 0.05C. After that, constant current discharge was performed with a discharge current of 1.0 C and a discharge final voltage corresponding to an SOC of 10%. A rest period of 10 minutes was provided after charging and after discharging. This charging/discharging was performed 100 cycles.

(Measurement of discharge capacity after charge-discharge cycle test)
After the charge-discharge cycle test, constant current discharge was performed at 25° C. with a discharge current of 0.2 C and a discharge final voltage of 2.5 V as residual discharge. After that, the discharge capacity after the charge-discharge cycle test was measured in the same procedure as "measurement of initial discharge capacity". The discharge capacity after the charge/discharge cycle test relative to the initial discharge capacity was obtained as the capacity retention rate. Table 2 shows the obtained capacity retention ratios.

[Examples 7 to 10]
All charge end voltages in "Initial charge/discharge", "Measurement of initial discharge capacity", "Charge/discharge cycle test" and "Measurement of discharge capacity after charge/discharge cycle test" in Example 6 are shown in Table 2. Each non-aqueous electrolyte storage element was obtained by performing the same operation as in Example 6 except for the above, and the capacity retention rate was measured. Table 2 shows the obtained capacity retention ratios.

[Examples 11 to 13, Comparative Example 3]
Instead of non-aqueous electrolyte A in Example 6, non-aqueous electrolyte B prepared in the following manner was used, and "initial charge and discharge", "measurement of initial discharge capacity", "charge-discharge cycle test" and The same operation as in Example 6 was performed except that all the charge end voltages in "Measurement of discharge capacity after charge-discharge cycle test" were set to the values shown in Table 2, and each non-aqueous electrolyte storage element was obtained. Retention rate was measured. Table 2 shows the obtained capacity retention ratios.

(Preparation of non-aqueous electrolyte B)
1.0 mol/dm ³ of lithium hexafluorophosphate (LiPF ₆ ) as an electrolyte salt was added to a non-aqueous solvent obtained by mixing FEC (fluoroethylene carbonate) and MFEC (methyltrifluoroethyl carbonate) at a volume ratio of 30:70. A non-aqueous electrolyte B was prepared by dissolving so as to obtain the content.

[Comparative Example 2] Fabrication of non-aqueous electrolyte storage element having positive electrode X (LiMeO ₂ type active material) and negative electrode A (SiO—Gr) Table 2 shows all the end-of-charge voltages in "initial charge/discharge", "initial charge/discharge capacity measurement", "charge/discharge cycle test", and "discharge capacity measurement after charge/discharge cycle test". Each non-aqueous electrolyte storage element was obtained by performing the same operation as in Example 6 except that the value was changed, and the capacity retention rate was measured. Table 2 shows the obtained capacity retention ratios.

(Preparation of positive electrode X)
As a positive electrode active material, a lithium transition metal composite oxide (positive electrode active material X) having an α-NaFeO ₂ structure and represented by Li _1.0 Ni _0.5 Co _0.2 Mn _0.3 O ₂ is used. Got ready.
Positive electrode active material X: acetylene black (AB): polyvinylidene fluoride (PVDF) at a mass ratio of 93:4:3 (in terms of solid matter), and using N-methylpyrrolidone (NMP) as a dispersion medium. A mixture paste was prepared. This positive electrode mixture paste was applied to an aluminum foil (thickness: 15 μm) as a positive electrode base material and dried to obtain a positive electrode X.

As shown in Table 2, the lithium-excess type active material (positive electrode active material A) was used, and the end-of-charge voltage was less than 4.50 V from the initial charge/discharge to use (during the charge-discharge cycle test). The positive electrode potential in the voltage is 4.60 V vs. The non-aqueous electrolyte storage elements of Examples 6 to 13, in which the Li/Li ⁺ ratio is less than 97.0%, have excellent capacity retention rates of 97.0% or more. Among them, the end-of-charge voltage is more than 4.20 V and less than 4.50 V, and the positive electrode potential at the end-of-charge voltage is 4.30 V vs. Li/Li ⁺ greater than 4.60V vs. Examples 8 to 13, which were used in the range of less than Li/Li ⁺ , had a capacity retention rate of 98.0% or more, and were particularly excellent in capacity retention rate. It is presumed that by using the positive electrode after charging it to a potential within a predetermined range, chemical formation over time progresses and the capacity retention rate increases.

[Example 14] Production of a single electrode battery (test battery) having a positive electrode B (excessive lithium type active material) Instead of the positive electrode active material A in Example 1, a battery having an α-NaFeO ₂ structure and _{Li1. 14} (Ni _0.33 Mn _0.67 ) _0.86 O ₂ Lithium transition metal composite oxide (positive electrode active material B) was used, and the mass ratio of positive electrode active material B: acetylene black (AB ): Polyvinylidene fluoride (PVDF) = 94: 4.5: 1.5 (converted to solid matter) A positive electrode B was obtained in the same manner as in Example 1, except that a positive electrode mixture paste was used. . Further, in the same manner as in Example 1 except that the positive electrode B was used in place of the positive electrode A in Example 1, the "assembly of the test battery" and the "initial charge/discharge" were performed.

[Examples 15 to 18, Comparative Example 4]
The same operation as in Example 14 was performed except that the end-of-charge voltage (positive electrode potential at the end of charge) of the first to third cycles in the "initial charge-discharge" of Example 1 was set as shown in Table 3.

The discharge capacity, average discharge potential and energy density were obtained based on the second cycle discharge in the "initial charge/discharge" of Examples 1 to 5 and 14 to 18 and Comparative Examples 1 and 4. Table 3 shows the results. Graphs representing the energy densities of Examples 1 to 5 and 14 to 18 and Comparative Examples 1 and 4 are shown in FIG.

As shown in Table 3 and FIG. 4, in the non-aqueous electrolyte storage elements of Examples 1 to 5 using the positive electrode active material A satisfying 0.02≦(Mn/Me—Ni/Me)≦0.2, In particular, even when the charge upper limit potential (the positive electrode potential at the end of charge voltage) is relatively low, it can be seen that the battery has a sufficient discharge capacity and a high energy density.

(Standing test)
[Example 19] Fabrication of non-aqueous electrolyte storage element having positive electrode A (excessive lithium active material) and negative electrode A (SiO-Gr) In the same procedure as in Example 6, the positive electrode active material A ( _Li An uncharged/discharged non-aqueous electrolyte storage element using Ni _0.39 Co _γ0.15 Mn _0.46 ) _0.92 O ₂ ) and negative electrode active material A (SiO—Gr) was assembled. After that, "initial charge/discharge" and "measurement of initial discharge capacity" were performed in the same manner as in Example 6 except that the charge end voltage was 4.25 V (positive electrode potential 4.35 V vs. Li/Li ⁺ ). rice field.

[Comparative Example 5] Fabrication of non-aqueous electrolyte storage element having positive electrode X (LiMeO ₂ type active material) and negative electrode A ( _SiO —Gr) _0.5 Co _0.2 Mn _0.3 O ₂ ) and negative electrode active material A (SiO—Gr), except for assembling an uncharged/discharged non-aqueous electrolyte storage element. gone.

For each of the non-aqueous electrolyte storage elements obtained in Example 19 and Comparative Example 5, the charging current was 0.2 C, the charging end voltage was 4.25 V (positive electrode potential 4.35 V vs. Li/Li ⁺ ), and the total charging time was 8 hours. constant-current and constant-voltage charging was performed. The non-aqueous electrolyte storage element thus charged was left in a constant temperature bath at 45° C. for 15 days and 33 days. Thereafter, constant current discharge was performed at 25° C. with a discharge current of 0.2 C and a discharge final voltage of 2.5 V as residual discharge. Subsequently, the discharge capacity after standing was measured in the same procedure as "measurement of initial discharge capacity" in Example 6 above. The discharge capacity after standing relative to the initial discharge capacity was obtained as the capacity retention rate. Table 4 shows the obtained results (capacity retention rate).

As shown in Table 4, the non-aqueous electrolyte storage element of Example 19, in which the lithium-excess type active material (positive electrode active material A) was used and the high potential formation was not sufficiently performed in the initial charge/discharge, the LiMeO ₂ type active material Compared to the non-aqueous electrolyte storage element of Comparative Example 5 using the material (positive electrode active material X), the capacity retention rate after being left at high temperature is high. This is presumably because the non-aqueous electrolyte storage element of Example 19 was left at a high temperature in a charged state, thereby gradually undergoing chemical formation over time.

[Example 20] Production of non-aqueous electrolyte storage element having positive electrode A (excessive lithium active material) and negative electrode B (Gr) (production of positive electrode A)
A positive electrode A was obtained in the same manner as in Example 1.

(Preparation of negative electrode B)
Graphite (Gr: negative electrode active material B) was used as the negative electrode active material. A negative electrode containing a negative electrode active material B: styrene-butadiene rubber (SBR): carboxymethyl cellulose (CMC) at a mass ratio of 97.3: 1.5: 1.2 (in terms of solid content) and using water as a dispersion medium. A mixture paste was prepared. This negative electrode mixture paste was applied to a strip-shaped copper foil (thickness: 10 μm) as a negative electrode base material and dried to obtain a negative electrode B.

(Preparation of non-aqueous electrolyte C)
A solution was prepared by dissolving lithium hexafluorophosphate (LiPF ₆ ) as an electrolyte salt in a non-aqueous solvent in which FEC and EMC were mixed at a volume ratio of 5:95 so that the content was 1.0 mol/dm ³ . and non-aqueous electrolyte C was obtained.

(Assembly of non-aqueous electrolyte storage element)
A polyolefin microporous film coated with a heat-resistant layer was prepared as a separator. An electrode assembly was produced by winding the positive electrode A and the negative electrode B with the separator interposed therebetween. This electrode body was placed in a container made of a metal-resin composite film, and after the non-aqueous electrolyte C was injected therein, the container was sealed by heat welding.

(initial charge/discharge)
The obtained non-aqueous electrolyte storage element before initial charge/discharge (uncharged/discharged non-aqueous electrolyte storage element) was subjected to initial charge/discharge at 25° C. in the following manner. Constant-current and constant-voltage charging was performed at a charging current of 0.1 C and a charge termination voltage of 4.25 V (positive electrode potential of 4.35 V vs. Li/Li ⁺ ). The charging termination condition was the time when the current value attenuated to 0.05C. Thereafter, constant current discharge was performed with a discharge current of 0.1C and a discharge final voltage of 2.5V.

(Measurement of discharge capacity)
Then, the following three cycles of charging and discharging were performed at 25° C., and the initial discharge capacity was confirmed. The amount of discharged electricity in the second cycle was taken as the initial discharge capacity.
(first cycle)
Constant-current and constant-voltage charging was performed at a charging current of 0.1 C and a charge termination voltage of 4.25 V (positive electrode potential of 4.35 V vs. Li/Li ⁺ ). The charging termination condition was the time when the current value attenuated to 0.05C. Thereafter, constant current discharge was performed with a discharge current of 0.1C and a discharge final voltage of 2.5V.
(second cycle)
Constant-current and constant-voltage charging was performed at a charging current of 0.2 C and a charge termination voltage of 4.25 V (positive electrode potential of 4.35 V vs. Li/Li ⁺ ). The charging termination condition was the time when the current value attenuated to 0.05C. After that, constant current discharge was performed with a discharge current of 0.2C and a discharge final voltage of 2.5V.
(3rd cycle)
Constant current and constant voltage charging was performed at a charging current of 1.0 C and a charge termination voltage of 4.25 V (positive electrode potential of 4.35 V vs. Li/Li ⁺ ). The charging termination condition was the time when the current value attenuated to 0.05C. After that, constant current discharge was performed with a discharge current of 1.0 C and a discharge final voltage of 2.5 V.

(Charge-discharge cycle test)
A charge/discharge cycle test was performed at 45° C. in the following manner for the non-aqueous electrolyte storage element for which the initial discharge capacity was confirmed. Constant current and constant voltage charging was performed at a charging current of 1.0 C and a charge termination voltage of 4.25 V (positive electrode potential of 4.35 V vs. Li/Li ⁺ ). The charging termination condition was the time when the current value attenuated to 0.05C. After that, constant current discharge was performed with a discharge current of 1.0 C and a discharge final voltage of 2.5 V. A rest period of 10 minutes was provided after charging and after discharging. This charging/discharging was carried out for 700 cycles.

(Measurement of discharge capacity after charge-discharge cycle test)
After 400 cycles, 600 cycles, and 700 cycles in the charge/discharge cycle test, the non-aqueous electrolyte storage elements were subjected to 3 cycles of charge/discharge in the same manner as in the above "measurement of discharge capacity" to confirm the discharge capacity. The amount of discharged electricity in the second cycle was defined as the discharge capacity after each cycle. The discharge capacity after each cycle relative to the initial discharge capacity was obtained as the capacity retention rate. Table 5 shows the obtained capacity retention ratios.

[Example 21]
Except that the end-of-charge voltage in the “initial charge/discharge”, “measurement of discharge capacity”, and “charge/discharge cycle test” in Example 20 was set to 4.30 V (positive electrode potential 4.40 V vs. Li/Li ⁺ ) A non-aqueous electrolyte storage element was obtained by performing the same operation as in Example 20, and the capacity retention rate was measured. Table 5 shows the obtained capacity retention ratios.

[Comparative Example 6] Fabrication of non-aqueous electrolyte storage element having positive electrode X (L iMeO ₂ type active material) and negative electrode B (Gr) Example 20 except that positive electrode X was used instead of positive electrode A A non-aqueous electrolyte storage element was obtained by performing the same operation as in Example 20, and the capacity retention rate was measured. Table 5 shows the obtained capacity retention ratios.

[Comparative Example 7] Fabrication of non-aqueous electrolyte storage element having positive electrode A (excessive lithium active material) and negative electrode B (Gr) .60 V vs. Li/Li ⁺ ), and the end-of-charge voltage in the “measurement of discharge capacity” and the “charge-discharge cycle test” was set to 4.35 V (positive electrode potential 4.45 V vs. Li / Li ⁺ ) A non-aqueous electrolyte storage element was obtained by performing the same operation as in Example 20, and the capacity retention rate was measured. Table 5 shows the obtained capacity retention ratios.

As shown in Table 5, the lithium-excess type active material (positive electrode active material A) was used as the positive electrode active material, and graphite (negative electrode active material B) was used as the negative electrode active material. ), the end-of-charge voltage is less than 4.50 V, and the positive electrode potential at the end-of-charge voltage is 4.60 V vs. It can be seen that the non-aqueous electrolyte storage elements of Examples 20 and 21, in which the ratio is less than Li/Li ⁺ , have high capacity retention rates even after long-term charge-discharge cycles.

[Example 22] Production of non-aqueous electrolyte storage element having positive electrode B (excessive lithium active material) and negative electrode B (Gr) (production of positive electrode B)
A positive electrode B was obtained in the same manner as in Example 14.

(Preparation of negative electrode B)
A negative electrode B was obtained in the same manner as in Example 20.

(Preparation of non-aqueous electrolyte D)
A solution was prepared by dissolving lithium hexafluorophosphate (LiPF ₆ ) as an electrolyte salt in a non-aqueous solvent in which EC and EMC were mixed at a volume ratio of 30:70 so as to have a content of 1.0 mol/dm ³ . and a non-aqueous electrolyte D was obtained.

(Assembly of non-aqueous electrolyte storage element)
A polyolefin microporous film coated with a heat-resistant layer was prepared as a separator. An electrode assembly was produced by winding the positive electrode B and the negative electrode B with the separator interposed therebetween. This electrode assembly was placed in a metal container, and the non-aqueous electrolyte D was injected thereinto, followed by sealing.

(initial charge/discharge)
The obtained non-aqueous electrolyte storage element before initial charge/discharge (uncharged/discharged non-aqueous electrolyte storage element) was subjected to initial charge/discharge at 25° C. in the following manner. Constant-current and constant-voltage charging was performed at a charging current of 0.1 C and a charge termination voltage of 4.45 V (positive electrode potential of 4.55 V vs. Li/Li ⁺ ). The charging termination condition was the time when the current value attenuated to 0.05C. After that, constant current discharge was performed with a discharge current of 0.1 C and a discharge final voltage of 2.0 V.

(Measurement of discharge capacity)
Then, the following three cycles of charging and discharging were performed at 25° C., and the initial discharge capacity was confirmed. The amount of discharged electricity in the second cycle was taken as the initial discharge capacity.
(first cycle)
Constant current and constant voltage charging was performed at a charging current of 0.1 C and a charge termination voltage of 4.45 V (positive electrode potential of 4.55 V vs. Li/Li ⁺ ). The charging termination condition was the time when the current value attenuated to 0.05C. After that, constant current discharge was performed with a discharge current of 0.1 C and a discharge final voltage of 2.0 V.
(second cycle)
Constant-current and constant-voltage charging was performed at a charging current of 0.2 C and a charge termination voltage of 4.45 V (positive electrode potential of 4.55 V vs. Li/Li ⁺ ). The charging termination condition was the time when the current value attenuated to 0.05C. After that, constant current discharge was performed with a discharge current of 0.2C and a discharge final voltage of 2.0V.
(3rd cycle)
Constant current and constant voltage charging was performed at a charging current of 1.0 C and a charge termination voltage of 4.45 V (positive electrode potential of 4.55 V vs. Li/Li ⁺ ). The charging termination condition was the time when the current value attenuated to 0.05C. After that, constant current discharge was performed with a discharge current of 1.0 C and a discharge final voltage of 2.0 V.

(Charge-discharge cycle test)
A charge/discharge cycle test was performed at 45° C. in the following manner for the non-aqueous electrolyte storage element for which the initial discharge capacity was confirmed. Constant-current charging was performed at a charging current of 1.0 C and a charging end voltage of 4.45 V (positive electrode potential of 4.55 V vs. Li/Li ⁺ ). After that, constant current discharge was performed with a discharge current of 1.0 C and a discharge final voltage of 2.0 V. A rest period of 10 minutes was provided after charging and after discharging. This charging/discharging was performed for 400 cycles.

(Measurement of discharge capacity after charge-discharge cycle test)
After 400 cycles in the charge-discharge cycle test, the non-aqueous electrolyte storage element was subjected to 3 cycles of charge-discharge in the same manner as in the above "measurement of discharge capacity", and the discharge capacity was confirmed. The amount of discharged electricity in the second cycle was defined as the discharge capacity after each cycle. The discharge capacity after each cycle relative to the initial discharge capacity was obtained as the capacity retention rate. Table 6 shows the obtained capacity retention ratios.

[Comparative Example 8]
Except that the end-of-charge voltage in the “initial charge/discharge”, “measurement of discharge capacity”, and “charge/discharge cycle test” in Example 22 was set to 4.50 V (positive electrode potential 4.60 V vs. Li/Li ⁺ ) A non-aqueous electrolyte storage element was obtained by performing the same operation as in Example 22, and the capacity retention rate was measured. Table 6 shows the obtained capacity retention ratios.

As shown in Table 6, the lithium-excess type active material (positive electrode active material B) was used as the positive electrode active material, and graphite (negative electrode active material B) was used as the negative electrode active material. ), the end-of-charge voltage is less than 4.50 V, and the positive electrode potential at the end-of-charge voltage is 4.60 V vs. It can be seen that the non-aqueous electrolyte storage element of Example 22, which has a ratio of less than Li/Li ⁺ , also has a high capacity retention rate in charge-discharge cycles.

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

1 Nonaqueous electrolyte storage element 2 Electrode body 3 Container 4 Positive electrode terminal 41 Positive electrode lead 5 Negative electrode terminal 51 Negative electrode lead 20 Storage unit 30 Storage device

Claims (5)

A positive electrode having a positive electrode mixture containing a positive electrode active material,
The positive electrode active material has an α-NaFeO ₂ structure and a lithium transition represented by Li _1+α Me _1-α O ₂ (0<α<1; Me is a transition metal including Ni and Mn.) including metal composite oxides,
The difference (Mn/Me- Ni/Me) is more than 0 and 0.10 or less,
With respect to the positive electrode, a current density of 9 mA/g per mass of the positive electrode mixture causes a potential of 2.00 V vs. After discharging up to Li/Li ⁺ , the potential is 4.80 V vs. When the charge and potential up to Li/Li ⁺ is 2.00 V vs. A non-aqueous electrolyte storage element in which the amount of charged electricity when performing two cycles of charging and discharging until reaching Li/Li ⁺ satisfies the following formula (1).
(C _2A /C _2B )×100−(C _1A /C _1B )×100≧1.0 (1)
(In formula (1), C _1A is the amount of electricity charged from the start of charging until the potential reaches 4.45 V vs. Li/Li ⁺ during the first cycle of charging and discharging. C _1B is the amount of charge from the start of charging until the potential reaches 4.80 V vs. Li/Li ⁺ during the charging of the first cycle of the charging and discharging.C _2A is the second cycle of the charging and discharging is the amount of electricity charged from the start of charging until the potential reaches 4.45 V vs. Li/Li ⁺ .C _2B is the amount of charge from the start of charging during the second cycle of charging and discharging. It is the amount of electricity charged until the potential reaches 4.80 V vs. Li/Li ⁺ .) A positive electrode having a positive electrode mixture containing a positive electrode active material,
The positive electrode active material is α-NaFeO ₂ structure and Li _1+α Me _1-α O. ₂ (0 < α < 1; Me is a transition metal containing Ni and Mn.) Contains a lithium transition metal composite oxide represented by
The molar ratio ((1+α)/(1-α)) of lithium (Li) to the transition metal (Me) in the lithium-transition metal composite oxide is 1.15 or more, and the amount of Mn in the transition metal (Me) The molar ratio (Mn/Me) is 0.5 or less,
With respect to the positive electrode, a current density of 9 mA/g per mass of the positive electrode mixture causes a potential of 2.00 V vs. Li/Li ⁺ After discharging up to , the potential is 4.80 V vs. Li/Li ⁺ until the charge and potential is 2.00 V vs. Li/Li ⁺ The non-aqueous electrolyte storage element satisfies the following formula (1) when charging and discharging are performed for two cycles.
(C _2A /C _2B )×100-(C _1A /C _1B )×100≧1.0 (1)
(In formula (1), C _1A , the potential is 4.45 V vs. Li/Li ⁺ is the amount of electricity charged up to C. _1B , the potential is 4.80 V vs. Li/Li ⁺ is the amount of electricity charged up to C. _2A , the potential is 4.45 V vs. Li/Li ⁺ is the amount of electricity charged up to C. _2B , the potential is 4.80 V vs. Li/Li ⁺ is the amount of electricity charged up to ) A positive electrode having a positive electrode mixture containing a positive electrode active material and a negative electrode containing a negative electrode active material,
The positive electrode active material is α-NaFeO ₂ structure and Li _1+α Me _1-α O. ₂ (0 < α < 1; Me is a transition metal containing Ni and Mn.) Contains a lithium transition metal composite oxide represented by
The content of Si, Sn and their oxides in the total negative electrode active material in the negative electrode is 1% by mass or more,
With respect to the positive electrode, a current density of 9 mA/g per mass of the positive electrode mixture causes a potential of 2.00 V vs. Li/Li ⁺ After discharging up to , the potential is 4.80 V vs. Li/Li ⁺ until the charge and potential is 2.00 V vs. Li/Li ⁺ The non-aqueous electrolyte storage element satisfies the following formula (1) when charging and discharging are performed for two cycles.
(C _2A /C _2B )×100-(C _1A /C _1B )×100≧1.0 (1)
(In formula (1), C _1A , the potential is 4.45 V vs. Li/Li ⁺ is the amount of electricity charged up to C. _1B , the potential is 4.80 V vs. Li/Li ⁺ is the amount of electricity charged up to C. _2A , the potential is 4.45 V vs. Li/Li ⁺ is the amount of electricity charged up to C. _2B , the potential is 4.80 V vs. Li/Li ⁺ is the amount of electricity charged up to ) The positive electrode potential is 4.30 V vs. Li/Li ⁺ greater than 4.60V vs. A method of using the non-aqueous electrolyte storage element according to any one of claims 1 to 3 , comprising charging to less than Li/Li ⁺ . The maximum reaching potential of the positive electrode is 4.60 V vs. 4. The method for manufacturing a non-aqueous electrolyte storage element according to claim 1 , comprising performing initial charge/discharge at less than Li/Li ⁺ .

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