Nonaqueous electrolyte power storage element and power storage device

Abstract

A nonaqueous electrolyte power storage element according to one embodiment of the present invention comprises a positive electrode having a positive electrode active material layer containing a positive electrode active material and a conductive agent, the positive electrode active material containing a lithium transition metal composite oxide containing a nickel element and a manganese element and having an α-NaFeO2 structure, the lithium transition metal composite oxide having a diffraction angle 2θ with a diffraction peak present in the range of 20° to 22° inclusive in the X-ray diffraction diagram using CuKα rays, the lithium transition metal composite oxide having a differential pore volume distribution curve having a peak in the pore diameter range of 30 nm to 70 nm inclusive, the differential pore volume at a maximum of the peak being 4.0×10-5 cm3 nm-1 g -1 or more, the conductive agent including a carbon nanotube.

Description

Nonaqueous electrolyte energy storage element and energy storage device

[0001] The present invention relates to a non-aqueous electrolyte electricity storage element and an electricity storage device.

[0002] The applications of non-aqueous electrolyte storage elements, such as lithium secondary batteries, have been expanding in recent years, and there is a demand for the development of various positive electrode active materials. ２ Lithium transition metal composite oxides having a crystalline structure have been investigated, and one example is LiCoO ２ Non-aqueous electrolyte secondary batteries using α-NaFeO have been widely used. ２ Among lithium transition metal composite oxides having a crystalline structure, so-called lithium-excess active materials have been developed in which the molar ratio of lithium to all metal elements other than lithium (Li / Me) exceeds 1 (Patent Documents 1 and 2).

[0003] In conventional non-aqueous electrolyte storage elements using a lithium-excess active material in the positive electrode, the positive electrode potential is generally set to 4.5 V vs. Li / Li in order to activate the lithium-excess active material and achieve a large discharge capacity. ＋ The positive electrode potential is 4.5 V vs. Li / Li. ＋ In Patent Document 1, a non-aqueous electrolyte secondary battery using a lithium-excess active material in the positive electrode and silicon and carbon in the negative electrode is charged and discharged initially, and the positive electrode potential reaches 4.60 V vs. Li / Li. ＋ In Patent Document 2, during the initial charge and discharge of a non-aqueous electrolyte secondary battery using a lithium-excess active material in the positive electrode and graphite in the negative electrode, the charge is continued until the voltage reaches 4.7 V, i.e., the positive electrode potential reaches 4.5 V vs. Li / Li. ＋ Charging continues until the battery reaches this level.

[0004] JP 2012-104335 A JP 2013-191390 A

[0005] The inventors have found that when a nonaqueous electrolyte storage element using a lithium-excess active material in the positive electrode is subjected to high-potential chemical formation, the capacity retention rate after charge-discharge cycling tends to decrease. In other words, the inventors have found that a nonaqueous electrolyte storage element including a lithium-excess active material that has not been subjected to high-potential chemical formation has the advantage of having a high capacity retention rate after charge-discharge cycling. This is presumably because, when high-potential chemical formation is not performed, the lithium-excess active material is gradually activated by repeated charge-discharge cycles during use, and the number of lithium ions released from the lithium-excess active material during charge-discharge gradually increases.

[0006] On the other hand, nonaqueous electrolyte energy storage elements including such lithium-excess active materials that have not been subjected to high-potential chemical formation have insufficient performance in low-temperature environments, and their discharge capacity is small in low-temperature environments both initially and after storage in high-temperature environments, and improvements are desired.

[0007] An object of the present invention is to provide a nonaqueous electrolyte energy storage element and an energy storage device, which are provided with a positive electrode made of a lithium-excess active material that has not been subjected to high-potential chemical formation, and which have a large discharge capacity in a low-temperature environment initially and after storage in a high-temperature environment.

[0008] A nonaqueous electrolyte storage element according to one aspect of the present invention includes a positive electrode having a positive electrode active material layer containing a positive electrode active material and a conductive agent, the positive electrode active material containing nickel and manganese and having a structure of α-NaFeO ２ In an X-ray diffraction pattern of the lithium transition metal composite oxide using CuKα radiation, a diffraction peak is present in a range of a diffraction angle 2θ of 20° or more and 22° or less, and a differential pore volume distribution curve of the lithium transition metal composite oxide has a peak in a pore diameter range of 30 nm or more and 70 nm or less, and the differential pore volume at the maximum of the peak is 4.0 × 10 －５ cm ３ nm －１ g －１ The conductive agent contains carbon nanotubes.

[0009] A power storage device according to another embodiment of the present invention includes one or more nonaqueous electrolyte power storage elements according to one embodiment of the present invention, and includes two or more power storage elements.

[0010] According to one aspect of the present invention, it is possible to provide a nonaqueous electrolyte energy storage element and an energy storage device, which include a lithium-excess active material in a positive electrode that has not been subjected to high-potential chemical formation, and which have a large initial discharge capacity and a large discharge capacity in a low-temperature environment after storage in a high-temperature environment.

[0011] Fig. 1 is a perspective view showing a nonaqueous electrolyte energy storage element according to one embodiment of the present invention. Fig. 2 is a schematic diagram showing an energy storage device including a plurality of nonaqueous electrolyte energy storage elements according to one embodiment of the present invention. Fig. 3 is a differential pore volume distribution curve of the lithium transition metal composite oxide used in Example 3.

[0012] First, an outline of the nonaqueous electrolyte electricity storage element and electricity storage device disclosed in this specification will be described.

[0013] [1] A nonaqueous electrolyte storage element according to one aspect of the present invention includes a positive electrode having a positive electrode active material layer containing a positive electrode active material and a conductive agent, the positive electrode active material containing nickel and manganese and having a structure of α-NaFeO ２ In an X-ray diffraction pattern of the lithium transition metal composite oxide using CuKα radiation, a diffraction peak is present in a range of a diffraction angle 2θ of 20° or more and 22° or less, and a differential pore volume distribution curve of the lithium transition metal composite oxide has a peak in a pore diameter range of 30 nm or more and 70 nm or less, and the differential pore volume at the maximum of the peak is 4.0 × 10 －５ cm ３ nm －１ g －１ The conductive agent contains carbon nanotubes.

[0014] The nonaqueous electrolyte storage element described in [1] above is a nonaqueous electrolyte storage element having a positive electrode made of a lithium-excess active material that has not been subjected to high-potential chemical formation, and has a large discharge capacity in a low-temperature environment, both initially and after storage in a high-temperature environment. The reason for this effect is not clear, but the following reason is presumed. First, the nonaqueous electrolyte storage element described in [1] above has a positive electrode active material containing nickel and manganese, and is composed of α-NaFeO ２ The positive electrode is provided with a lithium transition metal composite oxide having a structure in which a diffraction peak exists in the range of a diffraction angle 2θ of 20° or more and 22° or less in an X-ray diffraction diagram using CuKα radiation. Here, in an X-ray diffraction diagram using CuKα radiation for the synthesized lithium-excess active material before charge / discharge, a diffraction peak exists in the range of a diffraction angle 2θ of 20° or more and 22° or less. This diffraction peak existing in the range of a diffraction angle 2θ of 20° or more and 22° or less is Li[Li １／３ Mn ２／３ ]O ２ The diffraction peaks are based on monoclinic crystals of the Li-type, and the positive electrode potential is 4.5 V vs. Li / Li. ＋ When charging is performed to or above this range, the symmetry of the crystal changes as the lithium element in the crystal is removed, and the peak disappears. In other words, the presence of a diffraction peak in the range of the diffraction angle 2θ of 20° to 22° indicates that high-potential chemical formation (positive electrode potential is 4.5 V vs. Li / Li) ＋This means that the lithium-excess active material has not been subjected to high-potential chemical formation (charging to or above this level). Conventional nonaqueous electrolyte storage elements having a positive electrode made of a lithium-excess active material that has not been subjected to high-potential chemical formation exhibit insufficient performance in low-temperature environments, likely due to the low electronic and ionic conductivity of the lithium-excess active material itself. In contrast, the nonaqueous electrolyte storage element described in [1] uses a lithium-excess active material with a relatively large pore volume, with a pore diameter ranging from 30 nm to 70 nm. This increases the contact area between the lithium-excess active material and the nonaqueous electrolyte, reducing the interfacial resistance between the lithium-excess active material and the nonaqueous electrolyte. This is thought to result in a large discharge capacity both initially and at low temperatures after storage at high temperatures. On the other hand, if a lithium-excess active material with an excessively large pore volume is used, the discharge capacity may not be increased at low temperatures after storage at high temperatures. This is thought to be because, if the pore volume of the positive electrode active material is too large, a coating resulting from a side reaction with the nonaqueous electrolyte is excessively formed on the surface of the positive electrode active material during storage at high temperatures. Furthermore, conductive agents are a component that significantly affects the specific surface area of ​​the positive electrode active material layer. In contrast, in the nonaqueous electrolyte storage element described in [1] above, carbon nanotubes are used as at least a portion of the conductive agent contained in the positive electrode active material layer. The specific surface area of ​​carbon nanotubes is significantly smaller than that of commonly used conductive agents such as carbon black. Therefore, in the nonaqueous electrolyte storage element described in [1] above, even when a lithium-excess active material with a relatively large pore volume is used, the specific surface area of ​​the positive electrode active material layer is kept relatively small, thereby suppressing film formation during storage in a high-temperature environment. Therefore, in the nonaqueous electrolyte storage element described in [1] above, even when a lithium-excess active material with a large pore volume is used, the discharge capacity can be increased in a low-temperature environment after storage in a high-temperature environment. Furthermore, carbon nanotubes can sufficiently enhance the electronic conductivity of the positive electrode active material layer even in relatively small amounts compared to other conductive agents.Therefore, in the nonaqueous electrolyte storage element described in [1] above, the content of the conductive agent in the positive electrode active material layer can be reduced, and as a result, the content of the positive electrode active material in the positive electrode active material layer can be increased, thereby increasing the discharge capacity initially and in a low-temperature environment after storage in a high-temperature environment. From the above, it is presumed that the nonaqueous electrolyte storage element described in [1] above has a large discharge capacity initially and in a low-temperature environment after storage in a high-temperature environment, even though it is a nonaqueous electrolyte storage element having a lithium-excess active material in the positive electrode that has not been subjected to high-potential chemical formation.

[0015] The composition of the lithium transition metal composite oxide in this specification refers to the composition before charge / discharge, or, if contained in the positive electrode of a nonaqueous electrolyte storage element, the composition after treatment according to the following procedure. First, the nonaqueous electrolyte storage element is charged at a constant current of 0.05 C until the end-of-charge voltage in normal use is reached, and then fully charged. After a 30-minute rest, the element is discharged at a constant current of 0.05 C until the end-of-charge voltage in normal use is reached. The element is disassembled, the positive electrode is removed, and a test battery is assembled using the removed positive electrode as the working electrode and a metallic lithium electrode as the counter electrode. Pure metallic lithium is used for the metallic lithium electrode. For the test battery, a current of 10 mA per 1 g of positive electrode active material is applied, and the positive electrode potential is 2.0 V vs. Li / Li. ＋ The positive electrode is then disassembled again and the positive electrode is removed. The removed positive electrode is then washed with dimethyl carbonate. The positive electrode active material layer containing the lithium transition metal composite oxide is then peeled from the positive electrode substrate, and the positive electrode active material layer is washed with a solvent capable of dissolving the binder to remove the binder. The positive electrode active material layer is then washed with water and dried under reduced pressure at room temperature for 24 hours to obtain a lithium transition metal composite oxide. The obtained lithium transition metal composite oxide is then subjected to measurement. The operations from disassembling the nonaqueous electrolyte storage element to obtaining the lithium transition metal composite oxide are carried out in an argon atmosphere with a dew point of −60°C or lower. Here, “normal use” refers to the case where the nonaqueous electrolyte storage element is used under charge and discharge conditions recommended or specified for the nonaqueous electrolyte storage element, and, if equipment for using the nonaqueous electrolyte storage element is available, the nonaqueous electrolyte storage element is used with that equipment.

[0016] The crystal structure of the lithium transition metal composite oxide is determined by X-ray diffraction measurement. X-ray diffraction measurement of the lithium transition metal composite oxide is performed on the sample before charge / discharge or on the sample obtained by the above-described procedure for measuring the composition. Specifically, X-ray diffraction measurement is performed by powder X-ray diffraction measurement using an X-ray diffractometer (Rigaku's "MiniFlex II"), with a CuKα radiation source, a tube voltage of 30 kV, and a tube current of 15 mA. The diffracted X-rays pass through a 30 μm-thick Kβ filter and are detected by a high-speed one-dimensional detector (D / teX Ultra 2). The sampling width is 0.02°, the scan speed is 5° / min, the divergence slit width is 0.625°, the receiving slit width is 13 mm (OPEN), and the scattering slit width is 8 mm.

[0017] The pore volume distribution of the lithium transition metal composite oxide is measured before charge / discharge or after treatment using the procedure for measuring the composition described above. Specifically, the measurement is performed according to the following procedure. The pore volume distribution is measured using Quantachrome's "autosorb iQ" and control / analysis software "ASiQwin." 1.00 g of the lithium transition metal composite oxide sample to be measured is placed in a measurement sample tube and vacuum-dried at 120°C for 12 hours to thoroughly remove moisture from the sample. Next, adsorption and desorption isotherms are measured using a nitrogen gas adsorption method using liquid nitrogen within a relative pressure P / P0 (P0 = approximately 770 mmHg) range of 0 to 1. The pore volume distribution is then calculated using the BJH method using the desorption isotherm.

[0018] [2] In the nonaqueous electrolyte storage element according to [1] above, the content of the manganese element relative to all metal elements other than lithium element in the lithium transition metal composite oxide may be 0.4 or more and 0.8 or less in molar ratio.

[0019] In conventional nonaqueous electrolyte energy storage elements, when the molar ratio of manganese to all metal elements other than lithium in the lithium transition metal composite oxide is 0.4 or more and 0.8 or less, the content of manganese, which has low electronic conductivity, is relatively high, and therefore performance in low-temperature environments tends to be further reduced. Therefore, in the nonaqueous electrolyte energy storage element described in [2] above, the effect of increasing discharge capacity in low-temperature environments, both initially and after storage in high-temperature environments, is particularly pronounced.

[0020] [3] In the nonaqueous electrolyte storage element according to the above [1] or [2], the content of the positive electrode active material in the positive electrode active material layer may be 97% by mass or more and 99% by mass or less.

[0021] The nonaqueous electrolyte storage element described in [3] above has a sufficiently large content of the positive electrode active material in the positive electrode active material layer, and therefore can further increase the discharge capacity in an initial state and in a low-temperature environment after storage in a high-temperature environment.

[0022] [4] In the nonaqueous electrolyte storage element according to any one of [1] to [3] above, the content of the conductive agent in the positive electrode active material layer may be 0.4% by mass or more and 3% by mass or less.

[0023] The nonaqueous electrolyte storage element described in [4] above has a suitably small content of conductive agent in the positive electrode active material layer, thereby enabling a large content of positive electrode active material. Furthermore, in the nonaqueous electrolyte storage element described in [4] above, the conductive agent contained in the positive electrode active material layer contains carbon nanotubes, enabling sufficient electronic conductivity to be exhibited even with such a small content of conductive agent. Therefore, the nonaqueous electrolyte storage element described in [4] above can further increase discharge capacity in a low-temperature environment, both initially and after storage in a high-temperature environment.

[0024] [5] A power storage device according to another embodiment of the present invention includes one or more nonaqueous electrolyte power storage elements according to any one of [1] to [4] above, and two or more power storage elements.

[0025] The electricity storage device described in [5] above includes one or more nonaqueous electrolyte electricity storage elements described in any one of [1] to [4] above, and therefore has a large discharge capacity in an initial state and in a low-temperature environment after storage in a high-temperature environment.

[0026] A nonaqueous electrolyte electricity storage element according to one embodiment of the present invention, a method for manufacturing a nonaqueous electrolyte electricity storage element, an electricity storage device, and other embodiments will be described in detail below.

[0027] <Non-aqueous electrolyte storage element> A non-aqueous electrolyte storage element according to one embodiment of the present invention includes a positive electrode, a negative electrode, a non-aqueous electrolyte, and a container that accommodates these. The non-aqueous electrolyte storage element may further include a separator that is interposed between the positive electrode and the negative electrode to electrically insulate the positive electrode from the negative electrode. The positive electrode, the negative electrode, and any separator typically constitute an electrode assembly. At least a portion of the non-aqueous electrolyte typically exists in a state of being impregnated into the electrode assembly. The non-aqueous electrolyte storage element according to one embodiment of the present invention may further include other components.

[0028] For example, a nonaqueous electrolyte storage element 1 according to one embodiment of the present invention shown in Fig. 1 includes an electrode assembly 2, a nonaqueous electrolyte (not shown), and a rectangular parallelepiped container 3 that accommodates these. The nonaqueous electrolyte storage element 1 of Fig. 1 further includes a positive electrode lead 4, a positive electrode external terminal 5, a negative electrode lead 6, and a negative electrode external terminal 7. The positive electrode lead 4 and the negative electrode lead 6 are accommodated in the container 3 together with the electrode assembly 2 and the like. The positive electrode external terminal 5 and the negative electrode external terminal 7 are provided outside the container 3. The positive electrode constituting the electrode assembly 2 is electrically connected to the positive electrode external terminal 5 via the positive electrode lead 4. The negative electrode constituting the electrode assembly 2 is electrically connected to the negative electrode external terminal 7 via the negative electrode lead 6.

[0029] The nonaqueous electrolyte storage element of the present invention may be a nonaqueous electrolyte secondary battery. Below, the main components constituting the nonaqueous electrolyte storage element according to one embodiment of the present invention will be described in detail, focusing on the case where the nonaqueous electrolyte storage element is a nonaqueous electrolyte secondary battery (particularly a lithium ion secondary battery), but this is not intended to limit the scope of application of the present invention.

[0030] The lower and upper limits of each numerical range described in the embodiments of the present invention can be combined in any manner.

[0031] (Positive electrode) The positive electrode has a positive electrode substrate and a positive electrode active material layer laminated on the positive electrode substrate directly or via an intermediate layer. Usually, the positive electrode has a portion where the positive electrode substrate is exposed. This exposed portion of the positive electrode substrate is usually connected to the above-mentioned positive electrode lead. The positive electrode may have a shape such as a sheet, plate, or strip.

[0032] The thickness of the positive electrode is appropriately set depending on the application of the nonaqueous electrolyte storage element. The average thickness of the positive electrode may be, for example, 30 μm or more and 1,000 μm or less. The lower limit of the average thickness of the positive electrode may be 50 μm, 100 μm, or 200 μm. The upper limit of the average thickness of the positive electrode may be 500 μm, 400 μm, 300 μm, 200 μm, or 100 μm. The average thickness of the positive electrode is the average thickness of the portion where the positive electrode active material layer is laminated directly on the positive electrode substrate or via an intermediate layer. In the case where both the portion where the positive electrode active material layer is laminated on both sides of the positive electrode substrate and the portion where the positive electrode active material layer is laminated on only one side of the positive electrode substrate are present, the average thickness of the portion where the positive electrode active material layer is laminated on both sides of the positive electrode substrate is taken as the average thickness. In addition, in this specification, "average thickness" means the average value of thicknesses measured at any five positions.

[0033] The positive electrode substrate has electrical conductivity. In this specification, "having electrical conductivity" means that the volume resistivity is 10 －２ The volume resistivity is a value measured in accordance with JIS-H-0505 (1975). On the other hand, in this specification, "not having electrical conductivity" or "having (electrical) insulation" means that the volume resistivity is 10 ７ It means that the resistance is Ω·cm or more.

[0034] Examples of materials for the positive electrode substrate include metals such as aluminum, titanium, iron, and alloys thereof (stainless steel, etc.). Among these, aluminum or an aluminum alloy is preferred from the viewpoints of potential resistance, high electronic conductivity, and cost.

[0035] The positive electrode substrate has a shape such as a sheet, plate, or strip. Examples of the positive electrode substrate include foil, vapor-deposited film, mesh, and porous material, and foil is preferred. The positive electrode substrate may be, for example, aluminum foil or aluminum alloy foil.

[0036] The average thickness of the positive electrode substrate may be, for example, 3 μm or more and 50 μm or less. The lower limit of the average thickness of the positive electrode substrate may be 5 μm, 8 μm, 10 μm, or 15 μm. The upper limit of the average thickness of the positive electrode substrate may be 40 μm, 30 μm, 20 μm, or 15 μm.

[0037] The intermediate layer is a layer disposed between the positive electrode substrate and the positive electrode active material layer. The intermediate layer contains, for example, a conductive agent and a binder. When the intermediate layer contains a conductive agent, the contact resistance between the positive electrode substrate and the positive electrode active material layer can be reduced. Examples of the conductive agent and binder used in the intermediate layer include the same conductive agent and binder used in the positive electrode active material layer described below.

[0038] The positive electrode active material layer contains a positive electrode active material and a conductive agent. The positive electrode active material layer contains optional components such as a binder, a thickener, and a filler as needed. The positive electrode active material layer may be formed from a positive electrode mixture containing a positive electrode active material, a conductive agent, and other optional components. The positive electrode active material layer may be provided on only one side or on both sides of a positive electrode substrate having a shape such as a sheet.

[0039] (Positive electrode active material) The positive electrode active material contains nickel and manganese and is α-NaFeO ２ The lithium transition metal composite oxide has the structure.

[0040] In the X-ray diffraction diagram using CuKα radiation of the lithium transition metal composite oxide, a diffraction peak exists in the range of a diffraction angle 2θ of 20° to 22°. The existence of such a diffraction peak, i.e., the absence of high-potential chemical conversion, can improve the capacity retention rate after charge-discharge cycling when a lithium-excess active material is used.

[0041] The differential pore volume distribution curve of the lithium transition metal composite oxide has a peak in the pore diameter range of 30 nm to 70 nm. The lower limit of the differential pore volume at the maximum of the peak is 4.0 × 10 －５ cm ３ nm －１ g －１ is 4.2 × 10 －５ cm ３ nm －１ g －１ , 4.5 × 10 －５ cm ３ nm －１ g －１ , 4.8 × 10 －５ cm ３ nm －１ g －１ , 5.0 × 10 －５ cm ３ nm －１ g －１ , 5.3 × 10 －５ cm ３ nm －１ g －１ , 5.5 × 10 －５ cm ３ nm －１ g －１ , 5.7 × 10 －５ cm ３ nm －１ g －１ , 6.0 × 10 －５ cm ３ nm －１ g －１ or 6.3 x 10 －５ cm ３ nm －１ g －１ In this way, when the lithium transition metal composite oxide has a sufficient volume of pores having a pore diameter of 30 nm or more and 70 nm or less, the contact area with the non-aqueous electrolyte increases, and thus the discharge capacity can be increased in a low-temperature environment after storage in a high-temperature environment and at the initial stage. The upper limit of the differential pore volume at the maximum of the peak is, for example, 10.0 × 10 －５ cm ３ nm －１ g －１ 9.0 × 10 －５ cm ３ nm －１ g－１ , 8.0 × 10 －５ cm ３ nm －１ g －１ , 7.0 × 10 －５ cm ３ nm －１ g －１ , 6.3 × 10 －５ cm ３ nm －１ g －１ , 6.0 × 10 －５ cm ３ nm －１ g －１ , 5.7 × 10 －５ cm ３ nm －１ g －１ , 5.3 × 10 －５ cm ３ nm －１ g －１ , 5.0 × 10 －５ cm ３ nm －１ g －１ or 4.5 x 10 －５ cm ３ nm －１ g －１ may be.

[0042] The differential pore volume distribution curve of the lithium transition metal composite oxide may have a peak in a pore diameter range other than 30 nm or more and 70 nm or less. However, in the differential pore volume distribution curve of the lithium transition metal composite oxide in the pore diameter range of 0 nm or more and 700 nm or less, it is preferable that the peak in the pore diameter range of 30 nm or more and 70 nm or less is the largest peak. Furthermore, in the differential pore volume distribution curve of the lithium transition metal composite oxide in the pore diameter range of 0 nm or more and 700 nm or less, it is also preferable that the peak only exists in the pore diameter range of 30 nm or more and 70 nm or less. Furthermore, the differential pore volume distribution curve of the lithium transition metal composite oxide may have one peak in the pore diameter range of 30 nm or more and 70 nm or less. Note that when there are two or more peaks in the pore diameter range of 30 nm or more and 70 nm or less, the largest differential pore volume among the differential pore volumes at the maximum of each peak is 4.0 × 10 －５ cm３ nm －１ g －１ Anything above that is fine.

[0043] The pore volume distribution of the lithium transition metal composite oxide can be controlled, for example, by adjusting the conditions for producing the precursor, as described below. Specifically, the pore volume distribution can be controlled by adjusting the pH of the aqueous solution used in producing the precursor.

[0044] The manganese content (Mn / Me) relative to all metal elements other than lithium (Me) in the lithium transition metal composite oxide may be, for example, in a molar ratio of 0.3 to 0.9, preferably 0.4 to 0.8, more preferably 0.45 to 0.75, or may be 0.50 to 0.70. When the manganese content (Mn / Me) is within the above range, the effect of increasing the discharge capacity in an initial state and in a low-temperature environment after storage in a high-temperature environment is particularly pronounced.

[0045] The content of nickel element (Ni / Me) relative to all metal elements other than lithium element (Me) in the lithium transition metal composite oxide is preferably 0.1 to 0.6 in molar ratio, more preferably 0.2 to 0.5, and even more preferably 0.3 to 0.4 in molar ratio. By setting the content of nickel element (Ni / Me) within the above range, it is possible to increase the discharge capacity in an initial state and in a low-temperature environment after storage in a high-temperature environment.

[0046] The total content ((Ni+Mn) / Me) of nickel and manganese relative to all metal elements (Me) other than lithium in the lithium transition metal composite oxide is preferably 0.7 or more and 1.0 or less, more preferably 0.8 or more and 1.0 or less, even more preferably 0.9 or more and 1.0 or less, in terms of molar ratio, and may be 0.95 or more and 1.0 or less.

[0047] The lithium transition metal composite oxide may further contain metal elements other than lithium, nickel, and manganese, such as cobalt and aluminum.

[0048] The content (Co / Me) of cobalt element relative to all metal elements (Me) other than lithium element in the lithium transition metal composite oxide may be, for example, 0.0 or more and 0.3 or less, or 0.05 or more and 0.2 or less, in terms of molar ratio. The upper limit of the content (Co / Me) of cobalt element relative to all metal elements (Me) other than lithium element in the lithium transition metal composite oxide may be 0.1 or 0.05, in terms of molar ratio.

[0049] The lithium transition metal composite oxide may contain, as metal elements other than lithium, substantially only nickel and manganese, or substantially only nickel, manganese, and cobalt. 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). α may be 0.05 or more and 0.4 or less, or 0.08 or more and 0.3 or less. The preferred ranges of β, γ, and δ are the same as the preferred ranges of the molar content of each element relative to all metal elements (Me) other than lithium in the lithium transition metal composite oxide described above.

[0050] The lithium content (Li / Me) relative to all metal elements other than lithium (Me) in the lithium transition metal composite oxide is preferably more than 1.00 and not more than 1.50, or may be 1.05 or more and not more than 1.40, or may be 1.10 or more and not more than 1.30, in terms of molar ratio. Such a lithium transition metal composite oxide can exhibit particularly good properties as a lithium-excess active material.

[0051] The lithium transition metal composite oxide can be produced by a conventional method, for example, by firing a mixture containing a precursor and a lithium source. Hereinafter, a method for producing the lithium transition metal composite oxide according to the above method will be described in detail.

[0052] Lithium transition metal composite oxides can usually be obtained by preparing raw materials containing metal elements (Li, Ni, Mn, etc.) according to the composition of the desired lithium transition metal composite oxide and then calcining the raw materials. To produce a lithium transition metal composite oxide of the desired composition, known methods include the so-called "solid-phase method," in which salts of each element, such as Li, Ni, and Mn, are mixed and calcined, and the "coprecipitation method," in which a coprecipitated precursor in which Ni, Mn, etc. are present in a single particle is prepared in advance, and then a Li salt is mixed with this and calcined. Of these methods, the coprecipitation method is preferred because it is easy to obtain a target product in which each element is distributed uniformly and has an optimized density. The coprecipitation method will be described below.

[0053] Precursors obtained by coprecipitation generally include hydroxide precursors and carbonate precursors, among which the method of producing hydroxide precursors is preferred because it can produce lithium transition metal composite oxides that have high density and can increase discharge capacity, etc.

[0054] When producing a hydroxide precursor, it is preferable to drop an alkaline aqueous solution containing an alkali metal hydroxide (neutralizing agent), a complexing agent, and a reducing agent into water (aqueous solution) in an alkaline reaction vessel together with a solution (raw material solution) containing each metal element (Me) other than lithium, to co-precipitate a transition metal hydroxide, which is a hydroxide precursor. Examples of alkali metal hydroxides that can be used include sodium hydroxide, lithium hydroxide, and potassium hydroxide. Examples of complexing agents that can be used include ammonia, ammonium sulfate, and ammonium nitrate. Examples of reducing agents that can be used include hydrazine and sodium borohydride.

[0055] When producing a carbonate precursor, an alkaline aqueous solution containing a neutralizing agent such as sodium carbonate or lithium carbonate and a complexing agent is dropped into water (aqueous solution) in a reaction tank maintained at an alkaline temperature, together with a solution (raw material solution) containing each metal element (Me) other than lithium, to co-precipitate a transition metal carbonate, which is a carbonate precursor.

[0056] Regarding raw materials for the precursor, nickel compounds include nickel hydroxide, nickel carbonate, nickel sulfate, nickel nitrate, nickel acetate, etc., and manganese compounds include manganese oxide, manganese carbonate, manganese sulfate, manganese nitrate, manganese acetate, etc.

[0057] When preparing the precursor, it is preferable to remove dissolved oxygen from the water before adding the raw material solution dropwise in order to prevent oxidation of manganese and other elements present in the precursor. A method for removing dissolved oxygen includes bubbling with a gas that is substantially free of oxygen. Examples of the oxygen-free gas include, but are not limited to, nitrogen gas, argon gas, and carbon dioxide gas.

[0058] The pH of the aqueous solution used to prepare the precursor by coprecipitating compounds containing metal elements other than lithium in the aqueous solution is preferably in the range of 10.5 to 12.0, more preferably in the range of 10.6 to 11.8. By preparing the precursor within this pH range, the differential pore volume distribution curve has a peak in the pore diameter range of 30 nm to 70 nm, and the differential pore volume at the maximum of the peak is 4.0 × 10 －５ cm ３ nm －１ g －１ The lithium transition metal composite oxide having the above properties can be easily obtained. ３ / min or more 10cm ３ / min or less.

[0059] NH in the reaction vessel ３ When a complexing agent such as methyl methacrylate is present and certain convection conditions are applied, continuing stirring after the end of dropwise addition of the raw material solution promotes the rotation of the particles and the revolution of the particles within the stirring tank, and in this process, the particles collide with each other and grow stepwise into concentric spherical shapes. That is, the coprecipitated precursor is formed through a two-step reaction: a metal complex formation reaction when the raw material solution is dropped into the reaction tank, and a precipitation formation reaction that occurs while the metal complex remains in the reaction tank.

[0060] The preferable duration of stirring after completion of dropwise addition of the raw material solution, i.e., the reaction time, is affected by the size of the reaction vessel, stirring conditions, pH, reaction temperature, etc., but is preferably, for example, from 0.5 hours to 20 hours, and more preferably from 1 hour to 15 hours.

[0061] The precursor obtained by the above method is mixed with a lithium salt as a lithium source, and the mixture is fired to obtain a lithium transition metal composite oxide. As the lithium salt, lithium hydroxide, lithium carbonate, etc. can be used. In addition to these lithium salts, LiF, Li ２ SO ４ or Li ３ P.O. ４ The total amount of lithium salt is preferably about 1 to 5 mol % in excess, in anticipation of the loss of part of the lithium salt during firing.

[0062] The firing temperature can be, for example, 750° C. to 1,000° C. The lithium transition metal composite oxide obtained through firing may be subjected to pulverization, classification, etc., as necessary.

[0063] The positive electrode active material layer may further contain a positive electrode active material other than the lithium transition metal composite oxide. Various conventionally known positive electrode active materials can be used as the other positive electrode active material. However, it is preferable that the positive electrode active material contained in the positive electrode active material layer is substantially the lithium transition metal composite oxide. The lower limit of the content of the lithium transition metal composite oxide in the positive electrode active material contained in the positive electrode active material layer is preferably 60% by mass, more preferably 80% by mass, even more preferably 90% by mass, and even more preferably 95% by mass, 99% by mass, or 99.5% by mass. The upper limit of the content of the lithium transition metal composite oxide in the positive electrode active material contained in the positive electrode active material layer may be 100% by mass. The positive electrode active material contained in the positive electrode active material layer may be the lithium transition metal composite oxide alone. When the positive electrode active material is substantially composed of the lithium transition metal composite oxide alone, the effect of increasing the discharge capacity in a low-temperature environment, both initially and after storage in a high-temperature environment, is particularly pronounced.

[0064] The positive electrode active material and the lithium transition metal composite oxide are usually particulate. The average particle size of the positive electrode active material or the lithium transition metal composite oxide may be, for example, 1 μm or more and 30 μm or less, preferably 5 μm or more and 20 μm or less, and more preferably 8 μm or more and 15 μm or less. By setting the average particle size of the positive electrode active material to the above lower limit or more, the production or handling of the positive electrode active material becomes easier. By setting the average particle size of the positive electrode active material to the above upper limit or less, the electronic conductivity of the positive electrode active material layer is improved. Note that when a composite of the positive electrode active material and another material is used, the average particle size of the composite is taken as the average particle size of the positive electrode active material. "Average particle size" refers to the value (D50) at which the volume-based cumulative distribution is 50% as calculated in accordance with JIS-Z-8819-2 (2001) based on the particle size distribution measured by laser diffraction / scattering in a diluted solution obtained by diluting particles with a solvent in accordance with JIS-Z-8825 (2013). As a method for obtaining particles of the positive electrode active material and the negative electrode active material described below with a predetermined particle size, a known method using, for example, a pulverizer, a classifier, or the like can be employed.

[0065] The lower limit of the content of the positive electrode active material or the lithium transition metal composite oxide in the positive electrode active material layer may be, for example, 80 mass%, 90 mass%, or 95 mass%, but is preferably 97 mass%, more preferably 98 mass%. The upper limit of the content of the positive electrode active material or the lithium transition metal composite oxide in the positive electrode active material layer is preferably 99 mass%. By increasing the content of the positive electrode active material or the lithium transition metal composite oxide in the positive electrode active material layer in this way, the discharge capacity can be further increased in a low-temperature environment, both initially and after storage in a high-temperature environment.

[0066] (Conductive Agent) The conductive agent is usually a component made of a material having electrical conductivity. Even when the volume resistivity of the conductive agent cannot be measured directly, it is possible to measure the volume resistivity by measuring the volume resistivity of the conductive agent when the volume resistivity is 10 －２ A material known to have a resistivity of Ω·cm or less is considered a conductive agent.

[0067] The conductive agent contained in the positive electrode active material layer includes carbon nanotubes (CNT). Examples of CNT include single-walled carbon nanotubes (SWCNT) formed from a single layer of graphene and multi-walled carbon nanotubes (MWCNT) formed from two or more layers (e.g., 2 to 20 layers) of graphene, with multi-walled carbon nanotubes being preferred. The structure of the CNT is not particularly limited and may be any type, such as a chiral (spiral) type, a zigzag type, or an armchair type. The CNT may also contain a catalyst metal (e.g., Fe, Co, and a platinum group element (Ru, Rh, Pd, Os, Ir, Pt)) used in the synthesis of the CNT.

[0068] The average diameter of the CNTs may be, for example, 0.3 nm to 100 nm, 0.5 nm to 50 nm, or 1 nm to 20 nm. The upper limit of this average diameter may be 10 nm, 5 nm, or 3 nm. By using CNTs with a relatively small average diameter, good electron conduction paths tend to be formed.

[0069] The average aspect ratio of the CNTs (average length to average diameter) is not particularly limited, but is, for example, 10 or more. The lower limit of the aspect ratio of the CNTs may be 20, 50, 100, 500, or 1,000. The upper limit of the aspect ratio of the CNTs may be, for example, 100,000, 50,000, 20,000, or 10,000. The use of CNTs with a relatively high aspect ratio tends to facilitate the formation of good electron conduction paths.

[0070] The average diameter and average aspect ratio of CNTs are the average values ​​measured from any 10 CNTs observed under an electron microscope.

[0071] CNTs can be obtained by, for example, forming a polymer into a fiber form by a spinning method or the like and then heat-treating the fiber in an inert atmosphere, or by a vapor phase growth method in which an organic compound is reacted at high temperature in the presence of a catalyst, etc. Commercially available CNTs can be used.

[0072] The lower limit of the CNT content in the conductive agent contained in the positive electrode active material layer is preferably 20% by mass, more preferably 30% by mass, even more preferably 40% by mass, and even more preferably 50% by mass, 60% by mass, 70% by mass, 80% by mass, 90% by mass, 95% by mass, or 99% by mass. The upper limit of the CNT content in the conductive agent contained in the positive electrode active material layer may be 100% by mass. By increasing the proportion of CNT in the conductive agent contained in the positive electrode active material layer, it is possible to increase the discharge capacity in an initial state and in a low-temperature environment after storage in a high-temperature environment. The conductive agent contained in the positive electrode active material layer may be mainly composed of CNT. The term "main component" refers to the component with the highest content by mass.

[0073] The positive electrode active material layer may contain a conductive agent other than CNT. Examples of the conductive agent include carbon materials other than CNT, metals, conductive ceramics, etc. The carbon material refers to a material containing carbon as the primary constituent element. The primary constituent element refers to the element with the highest content by mass. For example, the carbon content in the carbon material may be 80% by mass or more, 90% by mass or more, 95% by mass, 99% by mass, or 99.9% by mass or more. The carbon material is preferably a carbon material other than an uncarbonized polymer compound. Examples of carbon materials other than CNT include graphite, non-graphitic carbon, graphene-based carbon, etc. Examples of non-graphitic carbon include pitch-based carbon fiber and carbon black. Examples of carbon black include furnace black, acetylene black, and ketjen black. Examples of graphene-based carbon include graphene and fullerene.

[0074] The lower limit of the CNT content among the carbon materials (CNT and carbon materials other than CNT) constituting the conductive agent contained in the positive electrode active material layer is preferably 20% by mass, more preferably 30% by mass, even more preferably 40% by mass, and even more preferably 50% by mass, 60% by mass, 70% by mass, 80% by mass, 90% by mass, 95% by mass, or 99% by mass. The upper limit of the CNT content among the carbon materials constituting the conductive agent contained in the positive electrode active material layer may be 100% by mass. By increasing the proportion of CNT among the carbon materials serving as the conductive agent contained in the positive electrode active material layer, the discharge capacity can be increased initially and in a low-temperature environment after storage in a high-temperature environment.

[0075] The lower limit of the content of the conductive agent or CNT in the positive electrode active material layer may be 0.1% by mass, preferably 0.4% by mass, and more preferably 0.7% by mass. The upper limit of the content of the conductive agent or CNT in the positive electrode active material layer may be 5% by mass, preferably 3% by mass, more preferably 2% by mass, and even more preferably 1.5% by mass. By relatively reducing the content of the conductive agent or CNT in the positive electrode active material layer, the content of the positive electrode active material can be increased, thereby increasing the discharge capacity in a low-temperature environment, both initially and after storage in a high-temperature environment. Furthermore, since the conductive agent in the positive electrode active material layer contains CNT, sufficient electronic conductivity can be exhibited even when the content of the conductive agent or CNT is relatively small.

[0076] (Other Components in the Positive Electrode Active Material Layer) Examples of the binder include water-based binders and organic solvent-based binders.

[0077] The aqueous binder is a binder that dissolves or disperses in water. The aqueous binder may be a binder that dissolves or disperses 1 part by mass or more in 100 parts by mass of water at 20°C. When a positive electrode active material layer is formed using a positive electrode mixture paste whose dispersion medium is water or a mixed solvent mainly composed of water, an aqueous binder (a water-soluble or water-dispersible polymer material) can be used. Examples of aqueous binders include polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyacrylic acid, polymethacrylic acid, polytetrafluoroethylene, styrene-butadiene rubber, polyethylene, polypropylene, nitrile-butadiene rubber, and cellulose.

[0078] The organic solvent-based binder is a binder that dissolves or disperses in an organic solvent (e.g., N-methylpyrrolidone). The organic solvent-based binder may be a binder that dissolves or disperses at 1 part by mass or more per 100 parts by mass of an organic solvent (e.g., N-methylpyrrolidone) at 20°C. When a positive electrode active material layer is formed using a positive electrode mixture paste whose dispersion medium is an organic solvent or a mixed solvent mainly composed of an organic solvent, an organic solvent-based binder (a polymer material that is soluble or dispersible in an organic solvent) can be used. Examples of organic solvent-based binders include polyvinylidene fluoride, copolymers of vinylidene fluoride and hexafluoropropylene, copolymers of ethylene and vinyl alcohol, polyacrylonitrile, polyphosphazene, polysiloxane, polyvinyl acetate, polymethyl methacrylate, polystyrene, polycarbonate, polyamide, polyimide, polyamideimide, crosslinked polymers of cellulose and chitosan pyrrolidone carboxylate, chitosan derivatives, and the like.

[0079] The binder may be a fluororesin (polytetrafluoroethylene, polyvinylidene fluoride, etc.), a polyolefin (polyethylene, polypropylene, etc.), an elastomer (ethylene propylene diene rubber, styrene butadiene rubber, fluororubber, etc.), a polysaccharide polymer (cellulose, chitosan derivatives, etc.), etc. One or more types of binders can be used.

[0080] The content of the binder in the positive electrode active material layer is preferably 0.1% by mass or more and 10% by mass or less, more preferably 0.5% by mass or more and 8% by mass or less, and even more preferably 0.7% by mass or more and 6% by mass or less. The upper limit of the binder content may be 5%, 4%, 3%, 2%, or 1.5% by mass. By setting the binder content within the above range, it is possible to stably hold the positive electrode active material, etc. The technology disclosed herein can also be implemented in an embodiment in which the positive electrode active material layer does not contain a binder.

[0081] Examples of thickeners include polysaccharide polymers such as carboxymethyl cellulose and methyl cellulose. When the thickener has a functional group that reacts with lithium or the like, the functional group may be deactivated in advance by methylation or the like. The thickener may function as a binder. One or more types of thickeners may be used. When the positive electrode active material layer contains a thickener, the content of the thickener in the positive electrode active material layer is preferably 0.1% by mass or more and 8% by mass or less, more preferably 5% by mass or less, even more preferably 2% by mass or less, and even more preferably 1% by mass or less or 0.1% by mass or less. The technology disclosed herein may also be implemented in an embodiment in which the positive electrode active material layer does not contain a thickener.

[0082] The filler is not particularly limited. The filler may be a component other than the positive electrode active material, conductive agent, binder, and thickener, and may be intentionally added. The filler may be added to fill gaps in the positive electrode active material layer, or may be added for other purposes. The filler may be an organic substance such as polyolefin, or an inorganic substance such as an inorganic oxide, hydroxide, or carbonate. One or more fillers may be used. When the positive electrode active material layer contains a filler, the content of the filler in the positive electrode active material layer may be 0.01% by mass or more and 8% by mass or less, typically preferably 5% by mass or less, more preferably 2% by mass or less, and even more preferably 1% by mass or less or 0.1% by mass or less. The technology disclosed herein may also be implemented in an embodiment in which the positive electrode active material layer does not contain a filler.

[0083] The positive electrode active material layer may further contain other components in addition to the positive electrode active material, conductive agent, binder, thickener, and filler. These other components include those unintentionally generated in the positive electrode active material layer. The positive electrode active material layer may also contain unintentionally contained impurities as the other components, as long as the effects of the present invention are achieved. The upper limit of the content of the other components in the positive electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass. The upper limit of the content of the unintentionally generated components in the positive electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass. The upper limit of the content of the unintentionally contained impurities in the positive electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass.

[0084] The thickness of the positive electrode active material layer is appropriately set depending on the type of positive electrode active material, the application of the nonaqueous electrolyte storage element, and the like. The average thickness of one positive electrode active material layer may be, for example, 5 μm or more and 1,000 μm or less. The lower limit of the average thickness of one positive electrode active material layer may be 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, or 100 μm. The upper limit of the average thickness of one positive electrode active material layer may be 800 μm, 500 μm, 200 μm, 100 μm, 80 μm, 60 μm, or 40 μm. The mass per unit area of ​​one positive electrode active material layer is, for example, 4 mg / cm. ２ 100mg / cm or more ２ The lower limit of the mass per unit area of ​​one positive electrode active material layer may be 6 mg / cm or less. ２ , 8 mg / cm ２ or 10 mg / cm ２ The upper limit of the mass per unit area of ​​one positive electrode active material layer is 50 mg / cm ２ , 20 mg / cm ２ , 15 mg / cm ２ , 12 mg / cm ２ or 10 mg / cm ２ may be.

[0085] The porosity of the positive electrode active material layer may be, for example, 20% or more and 50% or less. The lower limit of the porosity of the positive electrode active material layer may be 25%, 30%, or 35%. The upper limit of the porosity of the positive electrode active material layer may be 45%, 40%, or 35%. The "porosity (%)" of the positive electrode active material layer and the negative electrode active material layer described later is calculated by dividing the apparent volume (volume including voids) of the positive (negative) electrode active material layer by V. １ The sum of the actual volumes of the materials constituting the positive (negative) electrode active material layer is V ２ In this case, (1-V ２ / V １ The sum of the actual volumes of the materials constituting the positive (negative) electrode active material layer, V ２ can be calculated from the content of each material in the positive (negative) electrode active material layer and the true density of each material.

[0086] (Method for manufacturing positive electrode) The positive electrode can be manufactured by a known method. The positive electrode can be manufactured, for example, by applying a paste-like positive electrode mixture (positive electrode mixture paste) to a positive electrode substrate directly or via an intermediate layer, and drying the paste to form a positive electrode active material layer. The positive electrode mixture paste usually contains a positive electrode active material, a conductive agent, other optional components, and a dispersion medium. After drying, the positive electrode active material layer may be pressed, etc.

[0087] (Negative electrode) The negative electrode has a negative electrode substrate and a negative electrode active material layer laminated on the negative electrode substrate directly or via an intermediate layer. Usually, the negative electrode has a portion where the negative electrode substrate is exposed. This portion where the negative electrode substrate is exposed is usually connected to the above-mentioned negative electrode lead. The negative electrode may have a shape such as a sheet, plate, or strip.

[0088] The thickness of the negative electrode is appropriately set depending on the application of the nonaqueous electrolyte storage element, etc. The average thickness of the negative electrode may be, for example, 30 μm or more and 1,000 μm or less. The lower limit of the average thickness of the negative electrode may be 50 μm, 100 μm, or 200 μm. The upper limit of the average thickness of the negative electrode may be 500 μm, 400 μm, 300 μm, 200 μm, or 100 μm. The average thickness of the negative electrode is the average thickness of a portion where the negative electrode active material layer is laminated on the negative electrode substrate directly or via an intermediate layer. When there are both a portion where the negative electrode active material layer is laminated on both sides of the negative electrode substrate and a portion where the negative electrode active material layer is laminated on only one side of the negative electrode substrate, the average thickness of the portion where the negative electrode active material layer is laminated on both sides of the negative electrode substrate is taken as the average thickness.

[0089] The negative electrode substrate is conductive. Examples of materials for the negative electrode substrate include metals such as copper, nickel, iron, and alloys thereof (e.g., stainless steel), and carbon materials. Among these, copper or copper alloys are preferred.

[0090] The negative electrode substrate has a shape such as a sheet, plate, or strip. Examples of the form of the negative electrode substrate include foil, vapor-deposited film, mesh, and porous material, and foil is preferred. The negative electrode substrate may be, for example, copper foil or copper alloy foil.

[0091] The average thickness of the negative electrode substrate may be, for example, 2 μm or more and 35 μm or less. The lower limit of the average thickness of the negative electrode substrate may be 3 μm, 4 μm, 5 μm, or 10 μm. The upper limit of the average thickness of the negative electrode substrate may be 30 μm, 20 μm, 15 μm, or 10 μm.

[0092] The structure of the intermediate layer of the negative electrode is not particularly limited, and can be selected from the structures exemplified for the intermediate layer of the positive electrode, for example.

[0093] The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer contains optional components such as a conductive agent, a binder, a thickener, and a filler, as necessary. The optional components such as the conductive agent, the binder, the thickener, and the filler can be selected from the materials exemplified for the positive electrode above. However, the conductive agent contained in the negative electrode active material layer is not limited to one containing CNTs. The negative electrode active material layer may be formed from a negative electrode mixture containing a negative electrode active material and other optional components. The negative electrode active material layer may be provided on only one side or on both sides of a negative electrode substrate having a shape such as a sheet.

[0094] As the negative electrode active material, a known negative electrode active material can be used. A material capable of absorbing and releasing lithium ions is usually used as the negative electrode active material for a lithium ion secondary battery. Examples of the negative electrode active material include metallic lithium; metals or semimetals such as silicon and tin; metal oxides or semimetal oxides such as silicon oxide, titanium oxide, and tin oxide; Li ４ Ti ５ O １２ , LiTiO ２ , TiNb ２ O ７ Examples of the negative electrode active material include titanium-containing oxides such as those mentioned above; polyphosphate compounds; silicon carbide; and carbon materials such as graphite and non-graphitic carbon. Among these materials, carbon materials are preferred, and graphite or non-graphitic carbon is more preferred. The surface of graphite may be coated with another material such as non-graphitic carbon. One or more negative electrode active materials may be used.

[0095] "Graphite" refers to a graphite material that has an average lattice spacing (d ００２ ) is 0.33 nm or more and less than 0.34 nm. Examples of graphite include natural graphite and artificial graphite.

[0096] "Non-graphitic carbon" refers to a carbon material that has an average lattice spacing (d ００２ ) refers to a carbon material having a particle size of 0.34 nm or more and 0.42 nm or less. Non-graphitizable carbon includes non-graphitizable carbon and graphitizable carbon. "Non-graphitizable carbon" refers to a carbon material having a particle size of 0.34 nm or more and 0.42 nm or less.００２ The term "easily graphitizable carbon" refers to a carbon material having a particle size of 0.36 nm or more and 0.42 nm or less. ００２ The term "carbon material" refers to a carbon material having a particle size of 0.34 nm or more and less than 0.36 nm.

[0097] Here, the "discharged state" of the carbon material refers to a state in which the carbon material, which is the negative electrode active material, is discharged so that lithium ions that can be absorbed and released during charging and discharging are sufficiently released from the carbon material. For example, this refers to a state in which the open circuit voltage of a half cell using a negative electrode containing a carbon material as the negative electrode active material as the working electrode and metallic lithium as the counter electrode is 0.7 V or higher.

[0098] The negative electrode active material may be particulate. The average particle size of the negative electrode active material may be, for example, 1 nm or more and 100 μm or less. When the negative electrode active material is a carbon material, a titanium-containing oxide, a polyphosphate compound, or the like, the average particle size may be 1 μm or more and 100 μm or less. When the negative electrode active material is Si, Sn, Si oxide, Sn oxide, or the like, the average particle size may be 1 nm or more and 1 μm or less. By setting the average particle size of the negative electrode active material to be equal to or greater than the above lower limit, the production or handling of the negative electrode active material becomes easier. By setting the average particle size of the negative electrode active material to be equal to or less than the above upper limit, the electronic conductivity of the negative electrode active material layer is improved.

[0099] The content of the negative electrode active material in the negative electrode active material layer is, for example, preferably 60% by mass to 99% by mass, more preferably 90% by mass to 98% by mass. By setting the content of the negative electrode active material within this range, both high energy density and manufacturability of the negative electrode active material layer can be achieved.

[0100] When the negative electrode active material is a metal such as metallic lithium, the negative electrode active material layer may be in the form of a foil. The metallic lithium may exist as pure metallic lithium consisting essentially of elemental lithium, or may exist as a lithium alloy containing other metal elements. When the negative electrode active material is a metal such as metallic lithium, the content of elemental lithium in the negative electrode active material layer may be 90% by mass or more, 99% by mass or more, or even 100% by mass.

[0101] When the negative electrode active material layer contains a conductive agent, the content of the conductive agent in the negative electrode active material layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less. The content of the conductive agent in the negative electrode active material layer may be 5% by mass or less, or may be 2% by mass or less. The technology disclosed herein may also be implemented in an embodiment in which the negative electrode active material layer does not contain a conductive agent.

[0102] When the negative electrode active material layer contains a binder, the content of the binder in the negative electrode active material layer is preferably 0.1 mass% to 10 mass%, more preferably 0.5 mass% to 8 mass%. The content of the binder in the negative electrode active material layer may be 5 mass% or less, or may be 2 mass% or less. The technology disclosed herein may also be implemented in an embodiment in which the negative electrode active material layer does not contain a binder.

[0103] When the negative electrode active material layer contains a thickener, the content of the thickener in the negative electrode active material layer is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 0.5% by mass or more and 8% by mass or less. The content of the thickener in the negative electrode active material layer may be 5% by mass or less, or may be 2% by mass or less. The technology disclosed herein may also be implemented in an embodiment in which the negative electrode active material layer does not contain a thickener.

[0104] The filler in the negative electrode active material layer may be a component other than the negative electrode active material, conductive agent, binder, and thickener, and may be an intentionally contained component. The filler may be contained as a component to fill gaps in the negative electrode active material layer, or may be contained for another purpose. When the negative electrode active material layer contains a filler, the content of the filler in the negative electrode active material layer may be 0.1% by mass or more and 8% by mass or less, and typically 5% by mass or less is preferred, and 2% by mass or less is more preferred. The technology disclosed herein may also be implemented in an embodiment in which the negative electrode active material layer does not contain a filler.

[0105] The negative electrode active material layer may further contain other components in addition to the negative electrode active material, conductive agent, binder, thickener, and filler. These other components include those unintentionally present in the negative electrode active material layer. The negative electrode active material layer may also contain unintentionally present impurities as other components, as long as the effects of the present invention are achieved. The upper limit of the content of the other components in the negative electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass. The upper limit of the content of the unintentionally present components in the negative electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass. The upper limit of the content of the unintentionally present impurities in the negative electrode active material layer may be 10% by mass, 5%, 2%, 1%, 0.1%, or 0.01% by mass.

[0106] The thickness of the negative electrode active material layer is appropriately set depending on the type of negative electrode active material, the application of the non-aqueous electrolyte storage element, and the like. The average thickness of one negative electrode active material layer may be, for example, 5 μm or more and 1,000 μm or less. The lower limit of the average thickness of one negative electrode active material layer may be 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, or 100 μm. The upper limit of the average thickness of one negative electrode active material layer may be 800 μm, 500 μm, 200 μm, 100 μm, 80 μm, 60 μm, or 40 μm. The mass per unit area of ​​one negative electrode active material layer is, for example, 2 mg / cm. ２ 50mg / cm or more ２ The lower limit of the mass per unit area of ​​one negative electrode active material layer may be 3 mg / cm or less. ２ , 4 mg / cm ２ , 5 mg / cm ２ or 6 mg / cm ２ The upper limit of the mass per unit area of ​​one negative electrode active material layer is 30 mg / cm ２ , 20 mg / cm ２ , 15 mg / cm ２ , 12 mg / cm ２ or 10 mg / cm ２ may be.

[0107] The porosity of the negative electrode active material layer may be, for example, 30% or more and 70% or less. The lower limit of the porosity of the negative electrode active material layer may be 35%, 40%, or 45%. The upper limit of the porosity of the negative electrode active material layer may be 60%, 50%, or 40%. When the negative electrode active material layer is in a foil shape, for example, the porosity of the negative electrode active material layer may be 0%.

[0108] (Method for manufacturing a negative electrode) The negative electrode can be manufactured by a known method. The negative electrode can be manufactured, for example, in the same manner as in the above-described method for manufacturing a positive electrode, by applying a paste-like negative electrode mixture (negative electrode mixture paste) to a negative electrode substrate directly or via an intermediate layer, and drying it to form a negative electrode active material layer. The negative electrode mixture paste usually contains a negative electrode active material, other optional components, and a dispersion medium. After drying, the negative electrode active material layer may be pressed, etc. When the negative electrode active material is a metal such as metallic lithium, it can also be manufactured by laminating a metal foil on the negative electrode substrate directly or via an intermediate layer, and pressing, etc.

[0109] (Separator) A known separator can be used as the separator, for example, a separator consisting of only a base layer, or a separator in which an inorganic layer containing inorganic particles and a binder is formed on one or both surfaces of a base layer.

[0110] Examples of the form of the separator substrate layer include woven fabric, nonwoven fabric, and porous resin film. Among these forms, porous resin film is preferred from the viewpoint of strength, and nonwoven fabric is preferred from the viewpoint of nonaqueous electrolyte retention. The material of the separator substrate layer is not particularly limited as long as it has insulating properties, but resins such as polyolefin (polyethylene, polypropylene, etc.), polyimide, and aramid are preferred.

[0111] Examples of inorganic compounds constituting the inorganic particles include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, and magnesium oxide; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium titanate; covalently bonded crystals such as silicon; mineral resource-derived substances such as talc, zeolite, kaolin, bentonite, and mica, or artificial products thereof. One or more types of inorganic particles can be used. The average particle size of the inorganic particles is preferably, for example, 0.5 μm to 10 μm. The content of the inorganic particles in the inorganic layer is preferably 50% by mass to 99% by mass, more preferably 80% by mass to 98% by mass.

[0112] Examples of binders used in the inorganic layer include the same binders as those exemplified for the positive electrode active material layer.

[0113] The porosity of the separator may be, for example, 20% or more and 80% or less. The lower limit of the porosity of the separator may be 30%, 40%, or 50% from the viewpoint of discharge performance, etc. The upper limit of the porosity of the separator may be 70%, 60%, or 50% from the viewpoint of strength, etc. In this specification, "porosity" refers to a volume-based value measured with a mercury porosimeter.

[0114] The average thickness of the separator may be, for example, 10 μm or more and 40 μm or less, or 15 μm or more and 30 μm or less.

[0115] The separator may be a polymer gel composed of a polymer and a non-aqueous electrolyte, or may be a combination of the porous resin film, nonwoven fabric, or the like described above and a polymer gel.

[0116] (Electrode Body) As the electrode body, for example, a wound type electrode body, a laminated type electrode body, or the like having a known structure can be used.

[0117] A wound electrode body has a structure in which a positive electrode and a negative electrode are wound in an insulated state. The wound electrode body may be cylindrical (columnar) or flat. The electrode body 2 provided in the nonaqueous electrolyte storage element 1 of FIG. 1 is a flat wound electrode body. The wound electrode body can be produced, for example, by the following procedure. First, a positive electrode, a separator, and a negative electrode, each formed in a strip shape, are stacked in this order to obtain a laminate. The wound electrode body is obtained by rolling this laminate.

[0118] A laminated electrode assembly has a structure in which one or more positive electrodes and one or more negative electrodes are stacked in an insulated state. For example, a laminated electrode assembly can be obtained by stacking a positive electrode, a separator, and a negative electrode, each of which is formed into a rectangular shape, in this order.

[0119] As the electrode body, for example, one having a structure in which at least one of the positive electrode and the negative electrode is folded in an accordion-like manner and stacked can also be used.

[0120] (Non-aqueous electrolyte) A known non-aqueous electrolyte can be used as the non-aqueous electrolyte. The non-aqueous electrolyte is a medium responsible for transporting charge-transporting ions (usually lithium ions) between the positive electrode and the negative electrode, and is substantially free of water. The water content in the non-aqueous electrolyte may be, for example, 10,000 ppm or less, 5,000 ppm or less, 1,000 ppm or less, 500 ppm or less, or 100 ppm or less, preferably 50 ppm or less, and more preferably 20 ppm or less. Examples of non-aqueous electrolytes include non-aqueous electrolyte solutions and solid electrolytes. A non-aqueous electrolyte solution and a solid electrolyte may be used in combination. The non-aqueous electrolyte preferably contains a non-aqueous electrolyte solution, and more preferably is a non-aqueous electrolyte solution.

[0121] (Non-aqueous Electrolyte) The non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent.

[0122] As the non-aqueous solvent, known non-aqueous solvents can be used. Examples of non-aqueous solvents include carbonates, esters, ethers, amides, and nitriles. Examples of carbonates include cyclic carbonates and chain carbonates. Examples of esters include carboxylic acid esters, phosphate esters, and sulfonic acid esters. Non-aqueous solvents in which some of the hydrogen atoms contained in these compounds have been substituted with halogen atoms may also be used. One or more non-aqueous solvents can be used.

[0123] The term "cyclic carbonate" refers to a carbonate having a ring structure containing a carbonate group (-O-C(=O)-O-). Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, vinylethylene carbonate, chloroethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, styrene carbonate, 1-phenylvinylene carbonate, and 1,2-diphenylvinylene carbonate. The cyclic carbonate may be a saturated cyclic carbonate such as ethylene carbonate, or an unsaturated cyclic carbonate such as vinylene carbonate. "Saturated" refers to the absence of a carbon-carbon unsaturated bond (a carbon-carbon double bond or a carbon-carbon triple bond). "Unsaturated" refers to the presence of a carbon-carbon unsaturated bond. As the cyclic carbonate, saturated cyclic carbonates are preferred, and ethylene carbonate is more preferred.

[0124] The chain carbonate means a carbonate that does not have a ring structure containing a carbonate group. Examples of the chain carbonate include diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, diphenyl carbonate, trifluoroethyl methyl carbonate, and bis(trifluoroethyl) carbonate. The chain carbonate may be a saturated chain carbonate such as dimethyl carbonate, or an unsaturated chain carbonate such as diphenyl carbonate. The chain carbonate is preferably a saturated chain carbonate, and more preferably ethyl methyl carbonate.

[0125] The non-aqueous solvent preferably contains a carbonate, and more preferably contains a cyclic carbonate and a chain carbonate. The content of the carbonate in the non-aqueous solvent is preferably 80% by volume or more and 100% by volume or less, and may be 99% by volume or more and 100% by volume or less, or even 100% by volume. The use of a cyclic carbonate can promote dissociation of the electrolyte salt and increase the ionic conductivity of the non-aqueous electrolyte. The use of a chain carbonate can reduce the viscosity of the non-aqueous electrolyte. When a cyclic carbonate and a chain carbonate are used in combination, the volume ratio of the cyclic carbonate to the chain carbonate (cyclic carbonate:chain carbonate) is preferably in the range of, for example, 5:95 to 50:50.

[0126] The electrolyte salt may be a known electrolyte salt. Lithium salt is usually used as the electrolyte salt. One or more kinds of electrolyte salts may be used.

[0127] The lithium salt is LiPF ６ , LiPO ２ F ２ , LiBF ４ , LiClO ４ Inorganic lithium salts such as LiN(SO ２ F) ２ , LiN(SO ２ CF ３ ) ２ , LiN(SO ２ C ２ F ５ ) ２ , LiN(SO ２ CF ３ ) (SO ２ C ４ F ９ ), imide salts such as LiB(C ２ O ４ ) ２ , LiBF ２ (C ２ O ４ ), LiPF ２ (C ２ O ４ ) ２ Lithium oxalate salts such as LiN(SO ２ F) ２Among these, inorganic lithium salts are preferred, and LiPF ６ In some cases, an imide salt is also preferred.

[0128] The content of the electrolyte salt in the non-aqueous electrolyte solution is 0.1 mol / dm at 20°C and 1 atmosphere. ３ 2.5mol / dm or more ３ Preferably, 0.3 mol / dm or less ３ 2.0mol / dm or more ３ More preferably, 0.5 mol / dm or less ３ More than 1.7mol / dm ３ More preferably, 0.7 mol / dm or less ３ 1.5mol / dm or more ３ The following is particularly preferred: By setting the content of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

[0129] The non-aqueous electrolyte may contain an additive in addition to the non-aqueous solvent and the electrolyte salt. One or more additives may be used. When an additive is used in the non-aqueous electrolyte, the content of the additive in the non-aqueous electrolyte is preferably 0.01% by mass to 10% by mass, more preferably 0.1% by mass to 7% by mass, even more preferably 0.2% by mass to 5% by mass, and particularly preferably 0.3% by mass to 3% by mass.

[0130] (Solid Electrolyte) The solid electrolyte can be selected from any material that has charge-transporting ion (usually lithium ion) conductivity and is solid at room temperature (e.g., 20°C). Examples of the solid electrolyte include sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, halide solid electrolytes, and polymer solid electrolytes. One or more types of solid electrolytes can be used.

[0131] (Container) The container accommodates the electrode assembly and the non-aqueous electrolyte in its internal space. Materials for the container include metal materials such as aluminum and stainless steel, and resin materials, with metal materials being preferred from the standpoint of strength, etc. Composite materials of metal and resin materials can also be used.

[0132] The shape of the container is not particularly limited, and may be cylindrical, rectangular (square), disk-like, etc. The container may also be in the shape of a sheet formed from a metal-resin composite film.

[0133] (Positive Electrode Potential at End-of-Charge Voltage in Normal Use) In the nonaqueous electrolyte storage element according to one embodiment of the present invention, the positive electrode potential at the end-of-charge voltage in normal use (positive electrode potential) is not particularly limited. ＋ Above 4.5V vs. Li / Li ＋ Preferably, it is less than 4.0 V vs. Li / Li ＋ Above 4.45V vs. Li / Li ＋ More preferably, it is less than 4.2 V vs. Li / Li ＋ Above 4.4V vs. Li / Li ＋ It is more preferable that the positive electrode potential at the end-of-charge voltage during normal use (positive electrode potential) is equal to or greater than the above lower limit, thereby making it possible to increase the discharge capacity in a low-temperature environment initially and after storage in a high-temperature environment. Furthermore, by making the positive electrode potential at the end-of-charge voltage during normal use less than the above upper limit, the nonaqueous electrolyte storage element is stored, used, etc. in a state without being subjected to high-potential formation, thereby increasing the discharge capacity in a low-temperature environment after storage in a high-temperature environment.

[0134] (Shape, Use, etc. of Nonaqueous Electrolyte Storage Element) The shape of the nonaqueous electrolyte storage element according to one embodiment of the present invention is not particularly limited. The nonaqueous electrolyte storage element may be, for example, a cylindrical battery, a prismatic battery, a flat battery, a coin battery, a button battery, etc.

[0135] The use of the nonaqueous electrolyte electricity storage element according to one embodiment of the present invention is not particularly limited, and the nonaqueous electrolyte electricity storage element can be used, for example, as a power source for automobiles such as electric vehicles, hybrid vehicles, and plug-in hybrid vehicles, a power source for electronic devices such as personal computers and communication terminals, a power source for power storage, etc.

[0136] The nonaqueous electrolyte electricity storage element of the present invention may be used singly or in plural. When the required output and required voltage are small, the nonaqueous electrolyte electricity storage element may be used singly. On the other hand, when at least one of the required output and required voltage is large, the nonaqueous electrolyte electricity storage element may be used as an electricity storage device in combination with other nonaqueous electrolyte electricity storage elements. In an electricity storage device in which a plurality of nonaqueous electrolyte electricity storage elements are combined, at least one nonaqueous electrolyte electricity storage element included in the electricity storage device may be the nonaqueous electrolyte electricity storage element according to one embodiment of the present invention. The electricity storage device will be described in detail later.

[0137] In a nonaqueous electrolyte energy storage element according to one embodiment of the present invention, for example, the container may be constrained so as to maintain a constant thickness, or may not be constrained in this manner. Alternatively, the container may be constrained so as to apply a constant load to it. When the container is constrained, expansion of the container due to charge / discharge cycles, etc., may be suppressed, and deterioration of charge / discharge performance may be suppressed. When the container is constrained, a load may or may not be applied to the electrode assembly within the container. For example, a constraining member that performs such constraining may be provided in the nonaqueous electrolyte energy storage element or the energy storage device.

[0138] <Method for manufacturing nonaqueous electrolyte storage element> A nonaqueous electrolyte storage element according to one embodiment of the present invention can be manufactured by a known method. The method for manufacturing the nonaqueous electrolyte storage element includes, for example, preparing a positive electrode, preparing a negative electrode, preparing a nonaqueous electrolyte, and housing the positive electrode, negative electrode, and nonaqueous electrolyte in a container. The manufacturing method may also include preparing a separator, and manufacturing an electrode assembly using the positive electrode, negative electrode, and separator. Housing the positive electrode, negative electrode, and nonaqueous electrolyte in a container may include housing the electrode assembly and nonaqueous electrolyte in the container.

[0139] Preparing a positive electrode may mean manufacturing a positive electrode. Manufacturing a positive electrode can be performed by the method described above. Preparing a negative electrode may mean manufacturing a negative electrode. Manufacturing a negative electrode can be performed by the method described above. Preparing a non-aqueous electrolyte may mean preparing a non-aqueous electrolyte. The non-aqueous electrolyte can be prepared, for example, by dissolving an electrolyte salt in a non-aqueous solvent. The positive electrode, negative electrode, separator, non-aqueous electrolyte, etc. may be prepared by purchasing, etc.

[0140] The electrode assembly (or the positive electrode and negative electrode) and the nonaqueous electrolyte can be housed in a container by a known method. When the nonaqueous electrolyte is a nonaqueous electrolyte solution, for example, the electrode assembly (or the positive electrode and negative electrode) is first housed in a container, and then the nonaqueous electrolyte solution is poured into the container through an inlet provided in the container. The inlet is sealed after the nonaqueous electrolyte solution is poured into the container. The method for producing the nonaqueous electrolyte storage element may further include initially charging and discharging the assembled nonaqueous electrolyte storage element that has not yet been charged or discharged.

[0141] When the non-charged / discharged non-aqueous electrolyte storage element was initially charged and discharged, the positive electrode potential (positive electrode potential) was 4.5 V vs. Li / Li ＋ By using such a production method, it is possible to obtain a non-aqueous electrolyte storage element using a lithium transition metal composite oxide that has not been subjected to high-potential chemical formation.

[0142] In this manufacturing method, the initial charge / discharge may be performed, for example, to confirm the capacity. In other words, the initial charge / discharge is simply the first charge / discharge performed after assembling an uncharged / discharged nonaqueous electrolyte storage element. The number of charge / discharge cycles in the initial charge / discharge may be one or two, or may be three or more.

[0143] The positive electrode potential (positive electrode potential) at the end of charge during the initial charge / discharge was 4.45 V vs. Li / Li ＋ It may be less than 4.4V vs. Li / Li ＋ The positive electrode potential may be, for example, 3.8 V vs. Li / Li ＋or more, 4.0 V vs. Li / Li ＋ or more than 4.2V vs. Li / Li ＋ It may be more than that.

[0144] The nonaqueous electrolyte storage element according to one embodiment of the present invention may be manufactured by other methods. For example, when the nonaqueous electrolyte storage element according to one embodiment of the present invention is an all-solid-state battery, it may be manufactured by pressing the materials for forming the positive electrode, separator, and negative electrode individually or collectively.

[0145] <Electricity Storage Device> The nonaqueous electrolyte energy storage element of the present embodiment can be mounted as an energy storage unit (battery module) comprising a plurality of energy storage elements in an automobile power source such as an electric vehicle (EV), a hybrid electric vehicle (HEV), or a plug-in hybrid electric vehicle (PHEV), a power source for electronic devices such as a personal computer or a communication terminal, or a power storage power source, etc. In this case, the technology of the present invention may be applied to at least one nonaqueous electrolyte energy storage element included in the energy storage unit.

[0146] An electricity storage device according to one embodiment of the present invention includes one or more nonaqueous electrolyte electricity storage elements according to one embodiment of the present invention, and includes two or more electricity storage elements (hereinafter referred to as the "second embodiment"). It is sufficient that the technology according to one embodiment of the present invention is applied to at least one electricity storage element included in the electricity storage device according to the second embodiment, and the electricity storage device may include one nonaqueous electrolyte electricity storage element according to one embodiment of the present invention, and one or more electricity storage elements not according to one embodiment of the present invention, or may include two or more nonaqueous electrolyte electricity storage elements according to one embodiment of the present invention.

[0147] 2 includes a plurality of energy storage units 20. Each energy storage unit 20 includes a plurality of electrically connected nonaqueous electrolyte energy storage elements 1. The energy storage device 30 according to the second embodiment may include a bus bar (not shown) that electrically connects the plurality of nonaqueous electrolyte energy storage elements 1, a bus bar (not shown) that electrically connects the plurality of energy storage units 20, and the like. The energy storage unit 20 or the energy storage device 30 may include a state monitoring device (not shown) that monitors the state of one or more nonaqueous electrolyte energy storage elements 1.

[0148] <Other Embodiments> The nonaqueous electrolyte storage element of the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the spirit of the present invention. For example, the configuration of one embodiment can be added to the configuration of another embodiment, or part of the configuration of one embodiment can be replaced with the configuration of another embodiment or well-known technology. Furthermore, part of the configuration of one embodiment can be deleted. Also, well-known technology can be added to the configuration of one embodiment.

[0149] In the above embodiment, the nonaqueous electrolyte storage element is used as a chargeable and dischargeable nonaqueous electrolyte secondary battery, but the nonaqueous electrolyte storage element may be of any type, shape, size, capacity, etc. The present invention can also be applied to various secondary batteries, electric double layer capacitors, lithium ion capacitors, and other capacitors.

[0150] In the above embodiment, the electrode assembly is described in which a separator is interposed between the positive electrode and the negative electrode. However, the electrode assembly may not include a separator. For example, the positive electrode and the negative electrode may be in direct contact with each other, with a non-conductive layer formed on the active material layer of the positive electrode or the negative electrode. In this way, the positive electrode and the negative electrode may further include layers other than the substrate, the intermediate layer, and the active material layer. Furthermore, the positive electrode and the negative electrode may not have a layer structure.

[0151] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0152] [Example 1] (Preparation of lithium transition metal composite oxide) First, 1 mol / dm ３ NiSO ４ and MnSO ４ (Ni:Mn molar ratio 1:2, SO ４ The ion concentration is 1 mol / dm ３ NiSO ４ and MnSO ４ (aqueous solution of a mixture consisting of ３and 0.5 mol / dm ３ NH ３ aqueous solution and 0.5 mol / dm ３ NH ２ NH ２ The mixed solution of the aqueous solution was dropped to prepare a hydroxide precursor in which Ni and Mn were dispersed in a single particle. Next, this precursor was taken out of the reaction vessel and dissolved in LiOH. ２ The mixture was solid-phase mixed with O so that the molar ratio of Li / Me was 1.3. The mixture was then fired at a firing temperature of 900°C in an air atmosphere to obtain Li. １．１３ Ni ０．２９ Mn ０．５８ O ２ (Li １．１３ (Ni １／３ Mn ２／３ ) ０．８７ O ２ The lithium transition metal composite oxide was subjected to powder X-ray diffraction measurement by the method described above. The lithium transition metal composite oxide was found to be α-NaFeO ２ It was confirmed that the lithium transition metal composite oxide had a structure, and that an X-ray diffraction pattern using CuKα radiation showed a diffraction peak in the diffraction angle 2θ range of 20° to 22°. The pore volume distribution of the obtained lithium transition metal composite oxide was measured using the method described above. The differential pore volume distribution curve of this lithium transition metal composite oxide had a peak in the pore diameter range of 30 nm to 70 nm, and the differential pore volume at the maximum of the peak was 4.0 × 10 －５ cm ３ nm －１ g －１ It was.

[0153] (Preparation of Positive Electrode) A positive electrode mixture paste containing the above-mentioned lithium transition metal composite oxide as a positive electrode active material, multi-walled carbon nanotubes (CNT) as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder in a mass ratio of 98.0:1.0:1.0 in terms of solid content, and N-methylpyrrolidone (NMP) as a dispersion medium was prepared. This positive electrode mixture paste was applied to aluminum foil as a positive electrode substrate. Then, the mixture was dried and the layer of the dried positive electrode mixture paste was pressed to obtain a positive electrode.

[0154] (Preparation of negative electrode) A negative electrode mixture paste containing graphite as a negative electrode active material, styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener in a mass ratio of 96.4:2.1:1.5 in terms of solid content, and water as a dispersion medium was prepared. This negative electrode mixture paste was applied to copper foil as a negative electrode substrate. Then, the paste was dried and the layer of the dried negative electrode mixture paste was pressed to obtain a negative electrode.

[0155] (Assembly of Uncharged and Discharged Non-Aqueous Electrolyte Storage Element) An electrode assembly was fabricated using the positive electrode, the negative electrode, and a polyolefin microporous membrane as a separator. The non-aqueous electrolyte was prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 30:35:35 in a non-aqueous solvent, and lithium hexafluorophosphate (LiPF ) was added as an electrolyte salt. ６ ) to 1.0 mol / dm ３ The electrode assembly and the nonaqueous electrolyte were placed in a container to obtain a non-charged / discharged nonaqueous electrolyte storage element.

[0156] (Initial Charge / Discharge) The obtained non-charged / discharged non-aqueous electrolyte storage element was initially charged / discharged at 25° C. in the following manner: charging current: 0.1 C, end-of-charge voltage: 4.25 V (positive electrode final potential: 4.35 V vs. Li / Li ＋ The battery was charged at a constant current and constant voltage. The charge termination condition was the time when the current decayed to 0.02 C. After a 10-minute rest period, the battery was charged at a discharge current of 0.1 C and a discharge termination voltage of 2.4 V (positive electrode final potential 2.5 V vs. Li / Li). ＋) was discharged at a constant current. By the above-described procedure, the nonaqueous electrolyte electricity storage element of Example 1 was obtained.

[0157] Examples 2 to 7, Comparative Examples 10 and 11 Non-aqueous electrolyte storage elements of Examples 2 to 7 and Comparative Examples 10 and 11 were obtained in the same manner as in Example 1, except that the pH of the aqueous solution used to produce a precursor in the preparation of a lithium transition metal composite oxide was changed as shown in Table 1, and a lithium transition metal composite oxide was used in which the differential pore volume at the maximum of the peak in the pore diameter range of 30 nm to 70 nm in the differential pore volume distribution curve had the value shown in Table 1. As an example, the differential pore volume distribution curve obtained in Example 3 is shown in Figure 3.

[0158] Comparative Examples 1 to 9 The pH of the aqueous solution used to produce the precursor in the preparation of the lithium transition metal composite oxide was changed as shown in Table 1, and a lithium transition metal composite oxide was used in which the differential pore volume at the maximum of the peak in the pore diameter range of 30 nm to 70 nm in the differential pore volume distribution curve had the value shown in Table 1. A positive electrode mixture paste was also prepared containing the lithium transition metal composite oxide as the positive electrode active material, acetylene black (AB) as the conductive agent, and PVDF as the binder in a mass ratio of 94.5:4.0:1.5 calculated on solid content, with NMP as the dispersion medium. The nonaqueous electrolyte storage elements of Comparative Examples 1 to 9 were obtained in the same manner as in Example 1, except for the above points.

[0159] Reference Example 1: LiNi as a lithium transition metal composite oxide ０．６ Co ０．２ Mn ０．２ O ２ A nonaqueous electrolyte storage element of Reference Example 1 was obtained in the same manner as in Comparative Example 1, except that (NCM622) was used.

[0160] (1) Measurement of discharge capacity in an initial low-temperature environment Each nonaqueous electrolyte storage element was placed in a thermostatic chamber at 25°C, with a charging current of 0.1 C and a charge cut-off voltage of 4.25 V (positive electrode final potential 4.35 V vs. Li / Li ＋The battery was charged at a constant current and constant voltage at -30°C for 3 hours or more. The battery was then stored in a thermostatic chamber at -30°C for 3 hours or more, and then charged at a constant current and constant voltage of 0.1C and a discharge end voltage of 2.4V (positive electrode final potential 2.5V vs. Li / Li). ＋ ) was discharged at a constant current of 0.05V. The discharge capacity at this time was defined as the initial discharge capacity in a low-temperature environment. The discharge capacity was a value based on the mass of the positive electrode active material layer. The results are shown in Table 1.

[0161] (2) Measurement of discharge capacity in a low-temperature environment after storage in a high-temperature environment Next, each nonaqueous electrolyte storage element was stored in a thermostatic chamber at 25°C with a charging current of 0.1 C and a charge cut-off voltage of 4.25 V (positive electrode final potential 4.35 V vs. Li / Li ＋ The nonaqueous electrolyte storage element was charged at a constant current and constant voltage at 85°C for 7 days. The charge termination condition was the time when the current attenuated to 0.02 C. Subsequently, each nonaqueous electrolyte storage element was stored in a thermostatic chamber at 85°C for 7 days. Subsequently, after storing the nonaqueous electrolyte storage element in a thermostatic chamber at 25°C for 3 hours or more, the nonaqueous electrolyte storage element was charged at a discharge current of 1.0 C and a discharge termination voltage of 2.4 V (positive electrode final potential 2.5 V vs. Li / Li). ＋ The discharge capacity was then measured in the same manner as in the "Measurement of initial discharge capacity in a low-temperature environment" above, and this was taken as the discharge capacity in a low-temperature environment after storage in a high-temperature environment. The results are shown in Table 1.

[0162] In each nonaqueous electrolyte storage element, the positive electrode potential (positive electrode potential) was 4.5 V vs. Li / Li at the initial charge / discharge and evaluation stages. ＋ Therefore, it can be estimated that the lithium transition metal composite oxide in the positive electrode of each of the nonaqueous electrolyte storage elements of the Examples and Comparative Examples has a diffraction peak in the range of diffraction angle 2θ of 20° or more and 22° or less in an X-ray diffraction pattern using CuKα radiation.

[0163]

[0164] As shown in Table 1, the use of a lithium transition metal composite oxide having a large differential pore volume at the maximum of the peak in the pore diameter range of 30 nm to 70 nm in the differential pore volume distribution curve tended to increase the initial discharge capacity in a low-temperature environment. However, as shown in Comparative Examples 8 and 9, when the conductive agent in the positive electrode active material layer was only AB, if the differential pore volume at the maximum of the peak in the pore diameter range of 30 nm to 70 nm in the differential pore volume distribution curve was too large, the discharge capacity in a low-temperature environment after storage in a high-temperature environment decreased. In contrast, as shown in Examples 6 and 7, when the conductive agent in the positive electrode active material layer contained CNT, even if the differential pore volume at the maximum of the peak in the pore diameter range of 30 nm to 70 nm in the differential pore volume distribution curve was large, the discharge capacity in a low-temperature environment after storage in a high-temperature environment did not decrease. Thus, in each of the nonaqueous electrolyte storage elements of Examples 1 to 7, the initial discharge capacity in a low-temperature environment was 78 mAhg －１ The discharge capacity in a low temperature environment after storage in a high temperature environment is 75mAhg. －１ As described above, the discharge capacity was large initially and in a low temperature environment after storage in a high temperature environment.

[0165] The present invention can be applied to nonaqueous electrolyte storage elements used as power sources for electronic devices such as personal computers and communication terminals, automobiles, industrial equipment, and the like.

[0166] REFERENCE SIGNS LIST 1 nonaqueous electrolyte energy storage element 2 electrode body 3 container 4 positive electrode lead 5 positive electrode external terminal 6 negative electrode lead 7 negative electrode external terminal 20 energy storage unit 30 energy storage device

Claims

1. A positive electrode having a positive electrode active material layer containing a positive electrode active material and a conductive agent, wherein the positive electrode active material contains nickel and manganese and is α-NaFeO ２ The lithium transition metal composite oxide has a structure in which, in an X-ray diffraction pattern using CuKα radiation of the lithium transition metal composite oxide, a diffraction peak exists in a diffraction angle 2θ range of 20° or more and 22° or less, and a differential pore volume distribution curve of the lithium transition metal composite oxide has a peak in a pore diameter range of 30 nm or more and 70 nm or less, and the differential pore volume at the maximum of the peak is 4.0 × 10 －５ cm ３ nm －１ g －１ The nonaqueous electrolyte electricity storage element is as described above, wherein the conductive agent contains carbon nanotubes.

2. The nonaqueous electrolyte storage element according to claim 1, wherein the content of said manganese element relative to all metal elements other than lithium element in said lithium transition metal composite oxide is in the range of 0.4 to 0.8 in terms of molar ratio.

3. The nonaqueous electrolyte storage element according to claim 1 or 2, wherein the content of the positive electrode active material in the positive electrode active material layer is 97% by mass or more and 99% by mass or less.

4. The nonaqueous electrolyte storage element according to claim 1 or 2, wherein the content of the conductive agent in the positive electrode active material layer is 0.4% by mass or more and 3% by mass or less.

5. An electricity storage device comprising one or more nonaqueous electrolyte electricity storage elements according to claim 1 and two or more electricity storage elements.

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