Nonaqueous electrolyte storage element, method of using same, and method of manufacturing same

Abstract

To provide a non-aqueous electrolyte power storage element excellent in output performance and high in capacity maintenance rate in a charge and discharge cycle, an application and a manufacturing method of such a non-aqueous electrolyte power storage element.SOLUTION: The present invention relates to a non-aqueous electrolyte power storage element comprising a positive electrode containing a lithium transition metal composite oxide having an α-NaFeO2 structure. The lithium transition metal composite oxide contains nickel and manganese. A content of lithium with respect to a transition metal in the lithium transition metal composite oxide exceeds 1.0 in a molar ratio. In an X-ray diffraction diagram using CuKα rays of the lithium transition metal composite oxide, a diffraction peak exists within a range from 20° or more to 22° or less, and a total pore volume of the lithium transition metal composite oxide is 4 mm3 / g or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a non-aqueous electrolyte electricity storage element, a method for using the same, and a method for producing the same. [Background technology]

[0002] The applications of non-aqueous electrolyte energy storage devices, such as lithium secondary batteries, have expanded in recent years, necessitating the development of various positive electrode active materials. Lithium transition metal composite oxides with an α-NaFeO2 crystal structure have been investigated as positive electrode active materials for non-aqueous electrolyte energy storage devices, and non-aqueous electrolyte secondary batteries using LiCoO2 have been widely commercialized. Manganese, a globally abundant resource, is used as the transition metal (Me) constituting the lithium transition metal composite oxide. Non-aqueous electrolyte secondary batteries using so-called LiMeO2-type active materials, in which the molar ratio of lithium to the transition metal (Li / Me) constituting the lithium transition metal composite oxide is approximately 1, have also been commercialized.

[0003] Meanwhile, in recent years, so-called lithium-excess active materials have been developed among lithium transition metal composite oxides having an α-NaFeO2-type crystal structure, in which the molar ratio of lithium to transition metal (Li / Me) exceeds 1 (Patent Documents 1 and 2). Non-aqueous electrolyte energy storage elements using such lithium-excess active materials have attracted attention because they have a larger discharge capacity than LiMeO2-type active materials.

[0004] In conventional non-aqueous electrolyte storage elements that use 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 achieve the above-mentioned effects. + 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 manufactured by undergoing initial charge and discharge until 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 4.8 V vs. Li / Li.+ Charging continues until [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-104335 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-191390 Summary of the Invention [Problem to be solved by the invention]

[0006] Conventional non-aqueous electrolyte energy storage elements using a lithium-excess active material in the positive electrode have the disadvantage of insufficient output performance. Furthermore, non-aqueous electrolyte energy storage elements are desired to have a high capacity retention rate during charge-discharge cycles.

[0007] An object of the present invention is to provide a nonaqueous electrolyte electricity storage element that has excellent output performance and a high capacity retention rate during charge / discharge cycles, as well as a method for using and a method for producing such a nonaqueous electrolyte electricity storage element. [Means for solving the problem]

[0008] A nonaqueous electrolyte energy storage element according to one embodiment of the present invention includes a positive electrode containing a lithium transition metal composite oxide having an α-NaFeO2 structure, the lithium transition metal composite oxide containing nickel and manganese, a lithium content relative to the transition metal in the lithium transition metal composite oxide exceeding 1.0 in terms of molar ratio, a diffraction peak in an X-ray diffraction pattern using CuKα radiation for the lithium transition metal composite oxide in a range of 20° to 22°, and a total pore volume of the lithium transition metal composite oxide being 4 mm2. 3 / g or more.

[0009] A method of using a nonaqueous electrolyte storage element according to another embodiment of the present invention is to +and charging the nonaqueous electrolyte energy storage element of one embodiment of the present invention within a range of less than 1000 W.

[0010] In another embodiment of the present invention, a method for producing a nonaqueous electrolyte storage element is provided. + The method for manufacturing a nonaqueous electrolyte energy storage element according to one embodiment of the present invention includes performing initial charging and discharging within a range of less than 1000 kJ / s. [Effects of the Invention]

[0011] A nonaqueous electrolyte energy storage element according to one embodiment of the present invention has excellent output performance and a high capacity retention rate during charge-discharge cycles. According to the method for using a nonaqueous electrolyte storage element according to another aspect of the present invention, the nonaqueous electrolyte storage element can be used with excellent output performance and while maintaining a high capacity retention rate even after repeated charge and discharge. According to the method for producing a nonaqueous electrolyte storage element according to another aspect of the present invention, it is possible to produce a nonaqueous electrolyte storage element that has excellent output performance and a high capacity retention rate during charge-discharge cycles. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is an external perspective view showing a nonaqueous electrolyte electricity storage element according to one embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram showing an electricity storage device constructed by assembling a plurality of nonaqueous electrolyte electricity storage elements according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] First, an outline of the nonaqueous electrolyte electricity storage element disclosed in this specification, its method of use, and its manufacturing method will be described.

[0014] A nonaqueous electrolyte energy storage element according to one embodiment of the present invention includes a positive electrode containing a lithium transition metal composite oxide having an α-NaFeO2 structure, the lithium transition metal composite oxide containing nickel and manganese, a lithium content relative to the transition metal in the lithium transition metal composite oxide exceeding 1.0 in terms of molar ratio, a diffraction peak in an X-ray diffraction pattern using CuKα radiation for the lithium transition metal composite oxide in a range of 20° to 22°, and a total pore volume of the lithium transition metal composite oxide being 4 mm2. 3 / g or more.

[0015] A nonaqueous electrolyte energy storage element according to one embodiment of the present invention has excellent output performance. The reason for this effect is unclear, but the following is presumed. The lithium transition metal composite oxide provided in the positive electrode of the nonaqueous electrolyte energy storage element is a lithium transition metal composite oxide having a diffraction peak in the range of a diffraction angle 2θ of 20° or more and 22° or less in an X-ray diffraction pattern. In an X-ray diffraction pattern of a synthesized lithium-excess active material (a lithium transition metal composite oxide having an α-NaFeO2 structure and having a lithium content relative to the transition metal in a molar ratio of more than 1.0) before charge / discharge, Li[Li 1 / 3 Mn 2 / 3 In conventional non-aqueous electrolyte energy storage devices using a lithium-excess active material, the positive electrode potential is set to 4.5 V vs. Li / Li as described above in order to activate the lithium-excess active material. + The initial charge and discharge is performed until the positive electrode potential reaches 4.5V vs. Li / Li + The diffraction peaks in the range of 20° to 22° are observed when the positive electrode potential is 4.5V vs. Li / Li. + When charging is performed to above this range, the symmetry of the crystal changes as lithium is removed from the crystal, and the peak disappears. In other words, the presence of a diffraction peak in the range of 20° to 22° indicates that the positive electrode potential is 4.5 V vs. Li / Li +This means that the positive electrode potential is not 4.5V vs. Li / Li. + If the battery is charged to this level, the output performance will decrease due to the so-called cation mixing, in which transition metal ions present in the transition metal sites in the crystal move to the lithium sites. + If the charge is not performed to a value exceeding 4 mm or more and a diffraction peak is present in the range of 20° to 22°, it is presumed that the occurrence of the cation mixing is suppressed, resulting in excellent output performance. Furthermore, the total pore volume of the lithium transition metal composite oxide provided in the positive electrode of the nonaqueous electrolyte energy storage element is 4 mm or less. 3 / g or more and has a large surface area, it is expected that the output performance will be excellent.

[0016] Furthermore, the nonaqueous electrolyte energy storage element according to one embodiment of the present invention also has a high capacity retention rate during charge-discharge cycles. The reason for this is also unclear, but the following reason is presumed to be one of the causes of the decrease in capacity retention rate in conventional nonaqueous electrolyte energy storage elements. In conventional nonaqueous electrolyte energy storage elements using a lithium-excess active material, as described above, the positive electrode potential is 4.5 V vs. Li / Li. + High-potential formation is performed by the initial charge / discharge up to this point. In contrast, in a nonaqueous electrolyte storage element having a lithium-excess active material that has not been subjected to the above-described high-potential formation, it is presumed that the lithium-excess active material is gradually activated with repeated charge / discharge during use, and the number of lithium ions released from the lithium-excess active material during charge / discharge gradually increases (hereinafter, the "gradual activation of the lithium-excess active material with repeated charge / discharge during use" is also referred to as aging formation). For this reason, with this nonaqueous electrolyte storage element, the consumption of lithium ions by the negative electrode during charge / discharge cycles can be compensated for by replenishment from the lithium-excess active material in the positive electrode, and therefore it is presumed that the capacity retention rate is high.

[0017] The composition ratio of the lithium transition metal composite oxide in this specification refers to the composition ratio when the device is fully discharged using the following method. First, the nonaqueous electrolyte storage element is charged at a constant current of 0.05 C until the end-of-charge voltage for normal use is reached, and then fully charged. After a 30-minute rest, the device is discharged at a constant current of 0.05 C until the lower limit voltage for normal use is reached. The device is then disassembled, the positive electrode is removed, and a test battery is assembled using a metallic lithium electrode as the counter electrode. At a current of 10 mA per 1 g of positive electrode mixture, the positive electrode potential is measured at 2.0 V vs. Li / Li. + The positive electrode is adjusted to a fully discharged state by constant current discharge until the positive electrode reaches a fully discharged state. The device is disassembled again and the positive electrode is removed. The nonaqueous electrolyte adhering to the removed positive electrode is thoroughly washed with dimethyl carbonate, and after drying at room temperature for one day, the lithium transition metal composite oxide, the positive electrode active material, is extracted. The extracted lithium transition metal composite oxide is subjected to measurement. The operations from disassembly to measurement of the nonaqueous electrolyte storage element are carried out in an argon atmosphere with a dew point of -60°C or less. Here, "normal use" refers to the case where the nonaqueous electrolyte storage element is used under the charge / discharge conditions recommended or specified for the nonaqueous electrolyte storage element, and if a charger for the nonaqueous electrolyte storage element is provided, the nonaqueous electrolyte storage element is used with the charger.

[0018] X-ray diffraction measurements of the lithium transition metal composite oxide were performed on the lithium transition metal composite oxide in a fully discharged state using the method described above. Specifically, the X-ray diffraction measurements were performed by powder X-ray diffraction 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 passed through a 30 μm-thick Kβ filter and were detected by a high-speed one-dimensional detector (D / teX Ultra 2). The sampling width was 0.02°, the scan speed was 5° / min, the divergence slit width was 0.625°, the receiving slit width was 13 mm (open), and the scattering slit width was 8 mm.

[0019] The total pore volume and peak differential pore volume of the lithium transition metal composite oxide, described below, are values ​​determined by the BJH method from an adsorption isotherm obtained using a nitrogen gas adsorption method. Specifically, the total pore volume and peak differential pore volume are measured using the following method. 1.00 g of powder of the sample to be measured (lithium transition metal composite oxide) 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 liquid nitrogen in a relative pressure P / P0 (P0 = approximately 770 mmHg) range of 0 to 1 by nitrogen gas adsorption. The pore distribution is then evaluated by calculation using the desorption isotherm using the BJH method, and the total pore volume and peak differential pore volume are determined.

[0020] In the nonaqueous electrolyte storage element according to one embodiment of the present invention, the positive electrode potential at the end-of-charge voltage during normal use is 4.5 V vs. Li / Li + It is preferable that the positive electrode potential at the end of charge during normal use is less than 4.5 V vs. Li / Li + When the temperature is less than 100° C., chemical formation with time gradually progresses as charging and discharging are repeated many times, and therefore the capacity retention rate can be further increased.

[0021] A method of using a nonaqueous electrolyte storage element according to another embodiment of the present invention is to + and charging the nonaqueous electrolyte energy storage element of one embodiment of the present invention within a range of less than 1000 W.

[0022] According to this usage method, cation mixing is suppressed, and a lithium-excess active material having a large total pore volume is used as the positive electrode active material, so that the nonaqueous electrolyte storage element can be used with excellent output performance and a high capacity retention rate.

[0023] In another embodiment of the present invention, a method for producing a nonaqueous electrolyte storage element is provided. +The method for manufacturing a nonaqueous electrolyte energy storage element according to one embodiment of the present invention includes performing initial charging and discharging within a range of less than 1000 kJ / s.

[0024] This production method suppresses cation mixing and uses a lithium-excess active material with a large total pore volume as the positive electrode active material, making it possible to produce a nonaqueous electrolyte energy storage element with excellent output performance.Furthermore, this production method makes it possible to produce a nonaqueous electrolyte energy storage element with a high capacity retention rate during charge-discharge cycles.

[0025] A nonaqueous electrolyte electricity storage element according to one embodiment of the present invention, a method for using the same, and a method for producing the same will be described in detail below.

[0026] <Non-aqueous electrolyte energy storage element> A nonaqueous electrolyte storage element according to one embodiment of the present invention has a positive electrode, a negative electrode, and a nonaqueous electrolyte. The positive electrode and the negative electrode are usually stacked or wound alternately with a separator interposed therebetween to form an electrode assembly. This electrode assembly is housed in a container, which is filled with a nonaqueous electrolyte. The nonaqueous electrolyte is interposed between the positive electrode and the negative electrode. The container may be a commonly used known metal container, a resin container, or the like. Hereinafter, a nonaqueous electrolyte secondary battery (hereinafter simply referred to as a "secondary battery") will be described as an example of a nonaqueous electrolyte storage element.

[0027] (positive electrode) The positive electrode has a positive electrode substrate and a positive electrode active material layer disposed on the positive electrode substrate directly or via an intermediate layer.

[0028] The positive electrode substrate has electrical conductivity. "Conductivity" means that the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 7 "Non-conductive" means that the volume resistivity is 10 Ω·cm or less. 7This means that the resistance exceeds Ω·cm. Metals such as aluminum, titanium, tantalum, and stainless steel, or alloys of these, are used as materials for the positive electrode substrate. Among these, aluminum or aluminum alloys are preferred from the viewpoints of potential resistance, high conductivity, and cost. Examples of positive electrode substrates include foils and vapor-deposited films, with foil being preferred from the viewpoint of cost. Therefore, aluminum foil or aluminum alloy foil is preferred as the positive electrode substrate. Examples of aluminum or aluminum alloys include A1085 and A3003 specified in JIS-H-4000 (2014).

[0029] The average thickness of the positive electrode substrate is preferably 5 μm or more and 50 μm or less, and more preferably 10 μm or more and 40 μm or less. By making the average thickness of the positive electrode substrate equal to or greater than the lower limit, the strength of the positive electrode substrate can be increased. By making the average thickness of the positive electrode substrate equal to or less than the upper limit, the energy density per volume of the secondary battery can be increased. "Average thickness" refers to the average value of thickness measured at any 10 points. The same definition is used when "average thickness" is used for other materials, etc.

[0030] The intermediate layer is a layer disposed between the positive electrode substrate and the positive electrode active material layer. The configuration of the intermediate layer is not particularly limited, and may include, for example, a resin binder and conductive particles. The intermediate layer may include, for example, conductive particles such as carbon particles, thereby reducing the contact resistance between the positive electrode substrate and the positive electrode active material layer.

[0031] The positive electrode active material layer is a layer of a positive electrode mixture containing a positive electrode active material. The positive electrode active material layer (positive electrode mixture) may contain optional components such as a conductive agent, a binder, a thickener, and a filler as needed in addition to the positive electrode active material.

[0032] The positive electrode active material includes a lithium transition metal composite oxide having an α-NaFeO2 structure. The lithium transition metal composite oxide has a molar ratio (Li / Me) of lithium (Li) to transition metal (Me) exceeding 1.0. This lithium transition metal composite oxide is a so-called lithium-excess active material. In addition, in the X-ray diffraction pattern of the lithium transition metal composite oxide using CuKα radiation, a diffraction peak exists in the diffraction angle 2θ range of 20° to 22°.

[0033] The transition metal (Me) contained in the lithium transition metal composite oxide includes nickel (Ni) and manganese (Mn). It may be preferable that the transition metal further includes cobalt (Co). It is preferable that the transition metal essentially consists of Ni and Mn, or essentially consists of Ni, Mn, and Co. The lithium transition metal composite oxide is Li 1+α (Ni β Co γ Mn δ ) 1-α It may be expressed as O2(0<α<1, 0<β<1, 0≦γ<1, 0<δ<1, β+γ+δ=1).

[0034] The molar ratio of lithium (Li) to transition metal (Me) in the lithium transition metal composite oxide, i.e., (1 + α) / (1 - α), is preferably 1.05 or more and 1.5 or less, more preferably 1.1 or more and 1.4 or less, and in some cases, even more preferably 1.2 or more and 1.35 or less. By setting (1 + α) / (1 - α) to the above lower limit or more, the capacity retention rate during charge / discharge cycles can be further improved. Furthermore, by setting (1 + α) / (1 - α) to the above upper limit or less, the output performance can be further improved. Note that the molar ratio (ratio of amounts of substance) of each element in the lithium transition metal composite oxide is equal to the ratio of the number of atoms.

[0035] The molar ratio (Ni / Me) of Ni to the transition metal (Me) in the lithium transition metal composite oxide, i.e., β, may be, for example, 0.1 or more and 0.8 or less, preferably 0.2 or more and 0.7 or less, and more preferably 0.3 or more and 0.6 or less. By setting Ni / Me to the above lower limit or more, output performance, energy density, etc. can be improved. By setting Ni / Me to the above upper limit or less, capacity retention, etc. can be further improved.

[0036] The molar ratio (Co / Me) of Co to the transition metal (Me) in the lithium transition metal composite oxide, i.e., γ, may be, for example, 0 or more and 0.6 or less, or 0.1 or more and 0.3 or less. By setting Co / Me to the above lower limit or more, it is possible to improve output performance, energy density, etc. On the other hand, by setting Co / Me to the above upper limit or less, it is possible to suppress raw material costs while exhibiting a sufficient capacity retention rate.

[0037] The molar ratio (Mn / Me) of Mn to the transition metal (Me) in the lithium transition metal composite oxide, i.e., δ, may be, for example, 0.8 or less, preferably 0.7 or less, and more preferably 0.35 to 0.6. By setting Mn / Me at or above the lower limit, the effect of chemical conversion over time is enhanced, and the capacity retention rate can be increased. By setting Mn / Me at or below the upper limit, output performance, energy density, etc. can be improved.

[0038] The lithium transition metal composite oxide may contain other transition metals or may be mixed as impurities within the range in which the effects of the present invention are achieved. Furthermore, the lithium transition metal composite oxide may be coated with other metal oxides (e.g., alumina).

[0039] The lower limit of the total pore volume of the lithium transition metal composite oxide is 4 mm 3 / g, 10 mm 3 / g, 15mm 3 / g, 20mm 3 / g, 25mm 3 / g or 30mm 3 / g may be preferable. When the total pore volume of the lithium transition metal composite oxide is equal to or greater than the above lower limit, the output performance tends to be further improved. On the other hand, the upper limit of the total pore volume is, for example, 100 mm 3 / g, 50mm 3 / g is preferred, 40mm 3 / g, 35mm 3 / g, 30mm 3 / g or 25mm 3 / g may be more preferable. When the total pore volume of the lithium transition metal composite oxide is equal to or less than the above upper limit, the capacity retention rate during charge / discharge cycles tends to be improved. The total pore volume may be equal to or greater than any of the above lower limits and equal to or less than any of the above upper limits.

[0040] The peak differential pore volume of the lithium transition metal composite oxide is not particularly limited, and may be 0.01 mm 3 / (g·nm) or more 2mm 3 / (g·nm) or less, and 0.02 mm 3 / (g·nm) or more 0.5mm 3 / (g·nm) or less is preferable, and 0.3 mm 3 When the peak differential pore volume is relatively small, the lithium transition metal composite oxide has a relatively high density, and the energy density of the nonaqueous electrolyte energy storage element can be increased. 3 Lithium transition metal composite oxides with a surface area of ​​0.1g / (g·nm) or less can be obtained, for example, by using a hydroxide precursor, which will be described later, as a precursor.

[0041] The lithium transition metal composite oxide 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. Known methods for producing a lithium transition metal composite oxide of the desired composition include the so-called "solid-phase method," in which salts of Li, Ni, Mn, etc. are mixed and calcined, and the "coprecipitation method," in which a coprecipitated precursor is prepared in advance, in which Ni, Mn, etc. are present in a single particle, and then a Li salt is mixed with this and calcined. Of these methods, the coprecipitation method is preferred, as it is easy to obtain a target product in which each element is distributed uniformly. The coprecipitation method will be described in detail below.

[0042] Precursors obtained by coprecipitation generally include hydroxide precursors and carbonate precursors. Among them, the method for producing hydroxide precursors is to finally produce a total pore volume of 4 mm3 by controlling the pH of the solution, reaction time, etc. 3 / g or more, it is easy to obtain a lithium transition metal composite oxide.

[0043] When producing a hydroxide precursor, it is preferable to add an alkaline solution containing an alkali metal hydroxide (neutralizing agent), a complexing agent, and a reducing agent to a reaction vessel maintained at an alkaline temperature, together with a solution containing a transition metal (Me), to co-precipitate the transition metal hydroxide. Examples of the complexing agent that can be used include ammonia, ammonium sulfate, and ammonium nitrate. Examples of the reducing agent that can be used include hydrazine and sodium borohydride. Examples of the alkali metal hydroxide that can be used include sodium hydroxide, lithium hydroxide, and potassium hydroxide.

[0044] When preparing a precursor, Mn is easily oxidized, so it is not easy to prepare a precursor in which, for example, Ni, Co, and Mn are uniformly distributed in a divalent state, and uniform mixing of Ni, Co, and Mn at the atomic level is likely to be insufficient. Therefore, in order to suppress oxidation of Mn present in the precursor, it is preferable to remove dissolved oxygen from the solution. One method for removing dissolved oxygen is to bubbling with an oxygen-free gas. Examples of oxygen-free gases include, but are not limited to, nitrogen gas, argon gas, carbon dioxide gas, etc.

[0045] The pH of the solution used to prepare a precursor by coprecipitating a compound containing Ni, Mn, etc. in the solution is not limited, but when preparing the precursor as a hydroxide precursor, it is preferably set to 9 to 11, more preferably 9.5 to 10.5. By controlling the pH within this range when preparing the hydroxide precursor, it is possible to obtain a solution with a total pore volume of 4 mm 3 / g or more of lithium transition metal composite oxides tend to be obtained.

[0046] Regarding the precursor raw materials, Ni compounds include nickel hydroxide, nickel carbonate, nickel sulfate, nickel nitrate, and nickel acetate. Co compounds include cobalt sulfate, cobalt nitrate, and cobalt acetate. Mn compounds include manganese oxide, manganese carbonate, manganese sulfate, manganese nitrate, and manganese acetate.

[0047] The dripping speed of the raw material aqueous solution affects the uniformity of element distribution within a particle of the precursor to be produced. The preferred dripping speed is 30 cm, although it is affected by factors such as the size of the reaction vessel, stirring conditions, pH, and reaction temperature. 3 / min or less is preferable. In order to improve output performance and discharge capacity, the dripping speed should be 10cm 3 / min or less is preferable, and 5cm 3 The lower limit of the dripping speed is, for example, 0.1 cm / min or less. 3 / min.

[0048] When a complexing agent such as NH3 is present in the reaction vessel and certain convection conditions are applied, continued stirring after the dropwise addition of the raw aqueous solution promotes particle rotation and revolution within the stirring vessel. During this process, particles collide with each other and gradually grow into concentric spheres. In other words, the coprecipitated precursor is formed through a two-stage reaction: a metal complex formation reaction when the raw aqueous solution is dropped into the reaction vessel, and a precipitation reaction that occurs while the metal complex remains in the reaction vessel. Here, the total pore volume of the final lithium transition metal composite oxide can be adjusted by appropriately adjusting the time for which further stirring is continued after the dropwise addition of the raw aqueous solution, i.e., the reaction time.

[0049] The preferred duration of stirring after the dropwise addition of the raw material aqueous solution, i.e., the reaction time, is affected by the size of the reaction vessel, stirring conditions, pH, reaction temperature, etc., but is preferably set to a value where the total pore volume is 4 mm 3 To obtain a lithium transition metal composite oxide having a specific surface area of ​​1 / g or more, the reaction time is preferably 20 hours or less, more preferably 15 hours or less. On the other hand, to sufficiently grow the particles into uniform spherical particles, the reaction time is preferably 0.5 hours or more, more preferably 1 hour or more.

[0050] The precursor obtained by the above method is mixed with a Li compound and calcined to obtain a lithium transition metal composite oxide. Examples of Li compounds that can be used include lithium hydroxide and lithium carbonate. These Li compounds can also be used together with LiF, Li2SO4, or Li3PO4 as sintering aids. The addition ratio of these sintering aids is preferably 1 to 10 mol% relative to the total amount of Li compounds. The total amount of Li compounds is preferably about 1 to 5 mol% in excess, anticipating that some of the Li compounds will disappear during calcination.

[0051] The calcination temperature is preferably 750°C or higher and 1,000°C or lower. By setting the calcination temperature at or above the lower limit, lithium transition metal composite oxide particles with a high degree of sintering can be obtained, thereby improving charge-discharge cycle performance. On the other hand, by setting the calcination temperature at or below the upper limit, it is possible to suppress a decrease in discharge performance due to, for example, a structural change from the layered α-NaFeO2 structure to a rock salt cubic structure.

[0052] The positive electrode active material may contain a positive electrode active material other than the lithium transition metal composite oxide. The content of the lithium transition metal composite oxide in the positive electrode active material may be, for example, 50% by mass or more, preferably more than 70% by mass, more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 99% by mass or more, and may even be substantially 100% by mass. By increasing the content ratio of the lithium transition metal composite oxide in the positive electrode active material, it is possible to further improve output performance and capacity retention rate.

[0053] The positive electrode active material other than the lithium transition metal composite oxide can be appropriately selected from known positive electrode active materials commonly used in lithium ion secondary batteries, etc. The positive electrode active material is typically a material capable of absorbing and releasing lithium ions. Examples include the LiMeO2-type active material, lithium transition metal oxides having a spinel crystal structure, polyanion compounds, chalcogen compounds, sulfur, etc.

[0054] The average particle size of the positive electrode active material is preferably, for example, 0.1 μm or more and 20 μm or less. By setting the average particle size of the positive electrode active material to the above lower limit or more, the positive electrode active material becomes easier to manufacture and handle. 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 improves. Here, the "average particle size" refers to the value at which the volume-based cumulative distribution calculated in accordance with JIS-Z-8819-2 (2001) is 50% based on the particle size distribution measured by laser diffraction / scattering method for a diluted solution obtained by diluting particles with a solvent in accordance with JIS-Z-8825 (2013).

[0055] To obtain particles of a positive electrode active material or the like in a predetermined shape, a pulverizer, a classifier, or the like is used. Examples of pulverization methods include methods using a mortar, a ball mill, a sand mill, a vibration ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling airflow jet mill, or a sieve. Wet pulverization in the presence of water or an organic solvent such as hexane can also be used during pulverization. As a classification method, a sieve, an air classifier, or the like is used as needed for both dry and wet methods.

[0056] The content of the positive electrode active material in the positive electrode active material layer (positive electrode mixture) is preferably 70% by mass or more and 98% by mass or less, more preferably 80% by mass or more and 97% by mass or less, and even more preferably 90% by mass or more and 96% by mass or less. By setting the content of the positive electrode active material within the above range, the electrical capacity of the secondary battery can be increased.

[0057] The conductive agent is not particularly limited as long as it is a material having electrical conductivity. Examples of such conductive agents include graphite; carbon black such as furnace black and acetylene black; metals; and conductive ceramics. The conductive agent may be in the form of powder or fiber. Among these, acetylene black is preferred from the viewpoints of electronic conductivity and coatability.

[0058] The content of the conductive agent in the positive electrode active material layer (positive electrode mixture) is preferably 1% by mass or more and 10% by mass or less, and more preferably 2% by mass or more and 5% by mass or less. By setting the content of the conductive agent within this range, the electric capacity of the secondary battery can be increased.

[0059] Examples of binders include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, and polyimide; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; and polysaccharide polymers.

[0060] The content of the binder in the positive electrode active material layer (positive electrode mixture) is preferably 1% by mass to 10% by mass, more preferably 2% by mass to 5% by mass. By setting the binder content within this range, the active material can be stably maintained.

[0061] Examples of thickeners include polysaccharide polymers such as carboxymethyl cellulose (CMC), methyl cellulose, etc. When the thickener has a functional group that reacts with lithium or the like, this functional group may be deactivated in advance by methylation or the like.

[0062] The filler is not particularly limited, and examples of the filler include polyolefins such as polypropylene and polyethylene, silica, alumina, zeolite, glass, and alumina silicate.

[0063] The positive electrode active material layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, and I; typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba; and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, and W as components other than the positive electrode active material, conductive agent, binder, thickener, and filler.

[0064] (Negative electrode) The negative electrode has a negative electrode substrate and a negative electrode active material layer disposed on the negative electrode substrate directly or via an intermediate layer. The configuration of the intermediate layer of the negative electrode is not particularly limited and can be the same as that of the intermediate layer of the positive electrode.

[0065] The negative electrode substrate is conductive. Metals such as copper, nickel, stainless steel, nickel-plated steel, and aluminum, or alloys thereof, are used as the material for the negative electrode substrate. Among these, copper or a copper alloy is preferred. Examples of the negative electrode substrate include foils and vapor-deposited films, with foils being preferred from the viewpoint of cost. Therefore, copper foil or a copper alloy foil is preferred as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil.

[0066] The average thickness of the negative electrode substrate is preferably 3 μm or more and 30 μm or less, and more preferably 5 μm or more and 20 μm or less. By making the average thickness of the negative electrode substrate equal to or greater than the lower limit, the strength of the negative electrode substrate can be increased. By making the average thickness of the negative electrode substrate equal to or less than the upper limit, the energy density per volume of the secondary battery can be increased.

[0067] The negative electrode active material layer is a layer of a negative electrode mixture containing a negative electrode active material. The negative electrode active material layer (negative electrode mixture) may contain optional components such as a conductive agent, a binder, a thickener, and a filler, as needed, in addition to the negative electrode active material. The optional components such as the conductive agent, the binder, the thickener, and the filler may be the same as those in the positive electrode active material layer. The content of each of these optional components in the negative electrode active material layer may be within the range described as the content of each of these optional components in the positive electrode active material layer.

[0068] The negative electrode active material can be appropriately selected from known negative electrode active materials. A material capable of absorbing and releasing lithium ions is usually used as the negative electrode active material for lithium ion secondary batteries. Examples of the negative electrode active material include metallic Li; metals or semimetals such as Si and Sn; metal oxides or semimetal oxides such as Si oxide, Ti oxide, and Sn oxide; and Li4Ti5O 12 , LiTiO 2、 Examples of the material include titanium-containing oxides such as TiNbO, polyphosphate compounds, silicon carbide, and carbon materials such as graphite and non-graphitizable carbon (easily graphitizable carbon or non-graphitizable carbon). In the negative electrode active material layer, one of these materials may be used alone, or two or more may be used in combination.

[0069] "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. Artificial graphite is preferred from the viewpoint of being able to obtain a material with stable physical properties.

[0070] "Non-graphitic carbon" refers to carbon that has an average lattice spacing (d 002 ) is 0.34 nm or more and 0.42 nm or less. Non-graphitic carbon includes non-graphitizable carbon and graphitizable carbon. Examples of non-graphitic carbon include resin-derived materials, petroleum pitch or petroleum pitch-derived materials, petroleum coke or petroleum coke-derived materials, plant-derived materials, and alcohol-derived materials.

[0071] Here, the "discharged state" that defines graphite and non-graphitic carbon refers to a state in which an open circuit voltage is 0.7 V or higher in a single-electrode battery using a negative electrode containing a carbon material as the negative electrode active material as a working electrode and metallic Li as a counter electrode. Since the potential of the metallic Li counter electrode in the open circuit state is approximately equal to the redox potential of Li, the open circuit voltage in the single-electrode battery is approximately equal to the potential of the negative electrode containing the carbon material relative to the redox potential of Li. In other words, an open circuit voltage of 0.7 V or higher in the single-electrode battery means that lithium ions that can be absorbed and released during charging and discharging have been sufficiently released from the carbon material, which is the negative electrode active material.

[0072] "Non-graphitizable carbon" means the above d 002 This refers to carbon materials with a particle size of 0.36 nm or more and 0.42 nm or less.

[0073] "Graphitizable carbon" means the above d 002 This refers to carbon materials with a particle size of 0.34 nm or more and less than 0.36 nm.

[0074] In order to obtain a secondary battery with a higher capacity retention rate, a carbon material is preferred, and graphite is more preferred, as the negative electrode active material. When a carbon material is used as the negative electrode active material, the content of the carbon material in the total negative electrode active material may be 50% by mass or more, 70% by mass or more, 90% by mass or more, or substantially 100% by mass.

[0075] The negative electrode active material is usually in the form of particles (powder). The average particle size of the negative electrode active material can be, for example, 1 nm or more and 100 μm or less. By setting the average particle size of the negative electrode active material to the above lower limit or more, the negative electrode active material becomes easy to manufacture or handle. By setting the average particle size of the negative electrode active material to the above upper limit or less, the electronic conductivity of the active material layer improves. To obtain powder with a predetermined particle size, a pulverizer, a classifier, or the like is used. The pulverization method and the powder classification method can be selected, for example, from the methods exemplified above for the positive electrode.

[0076] The content of the negative electrode active material in the negative electrode active material layer (negative electrode mixture) is preferably 60% by mass or more and 99% by mass or less, and more preferably 90% by mass or more and 98% by mass or less. 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.

[0077] The negative electrode active material layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, and I; typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba; and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, and W as components other than the negative electrode active material, conductive agent, binder, thickener, and filler.

[0078] (separator) The separator can be appropriately selected from known separators. Examples of separators that can be used include separators consisting of only a substrate layer and separators in which a heat-resistant layer containing heat-resistant particles and a binder is formed on one or both surfaces of the substrate layer. Examples of materials for the substrate layer of the separator include woven fabric, nonwoven fabric, and porous resin film. Among these materials, porous resin film is preferred from the viewpoint of strength, and nonwoven fabric is preferred from the viewpoint of non-aqueous electrolyte retention. Materials for the substrate layer of the separator are preferably polyolefins such as polyethylene and polypropylene from the viewpoint of shutdown function, and polyimide and aramid from the viewpoint of oxidative decomposition resistance. A composite material of these resins may also be used for the substrate layer of the separator.

[0079] The heat-resistant particles contained in the heat-resistant layer preferably exhibit a mass loss of 5% or less at 500°C in air, and more preferably a mass loss of 5% or less at 800°C in air. Examples of materials exhibiting a mass loss of a predetermined amount or less include inorganic compounds. Examples of inorganic compounds include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, barium titanate, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates; hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide; 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 and barium fluoride; covalent crystals such as silicon and diamond; mineral-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, as well as artificial products thereof. As the inorganic compound, these substances may be used alone or in the form of a complex, or two or more of them may be used in combination. Among these inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicate is preferred from the viewpoint of the safety of the secondary battery.

[0080] The porosity of the separator is preferably 80% by volume or less from the viewpoint of strength, and is preferably 20% by volume or more from the viewpoint of discharge performance. Here, "porosity" refers to a volume-based value measured with a mercury porosimeter.

[0081] The separator may be a polymer gel composed of a polymer and a non-aqueous electrolyte. Examples of polymers include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, and polyvinylidene fluoride. The use of a polymer gel has the effect of suppressing leakage. The separator may be a combination of the porous resin film or nonwoven fabric described above and a polymer gel.

[0082] (non-aqueous electrolyte) The nonaqueous electrolyte can be appropriately selected from known nonaqueous electrolytes. The nonaqueous electrolyte may be a nonaqueous electrolytic solution. The nonaqueous electrolytic solution includes a nonaqueous solvent and an electrolyte salt dissolved in the nonaqueous solvent.

[0083] The nonaqueous solvent can be appropriately selected from known nonaqueous solvents. Examples of nonaqueous solvents include cyclic carbonates, chain carbonates, carboxylic acid esters, phosphate esters, sulfonic acid esters, ethers, amides, and nitriles. Compounds in which some of the hydrogen atoms contained in these compounds have been substituted with halogens may also be used as nonaqueous solvents. For example, by using fluorinated compounds (fluorinated cyclic carbonates, fluorinated chain carbonates, etc.), the nonaqueous solvent can be used sufficiently even under conditions in which the positive electrode potential reaches a high potential.

[0084] Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinylethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), styrene carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate, etc. Among these, EC, PC, and FEC are preferred.

[0085] Examples of chain carbonates include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, methyl trifluoroethyl carbonate (MFEC), bis(trifluoroethyl) carbonate, etc. Among these, EMC and MFEC are preferred.

[0086] It is preferable to use a cyclic carbonate or a chain carbonate as the non-aqueous solvent, and it is more preferable to use a combination of a cyclic carbonate and a chain carbonate. The use of a cyclic carbonate can promote dissociation of the electrolyte salt and improve 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.

[0087] The electrolyte salt can be appropriately selected from known electrolyte salts, such as lithium salts, sodium salts, potassium salts, magnesium salts, and onium salts. Of these, lithium salts are preferred.

[0088] Examples of lithium salts include inorganic lithium salts such as LiPF6, LiPO2F2, LiBF4, LiClO4, and LiN(SO2F)2, and lithium salts having a halogenated hydrocarbon group such as LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), LiC(SO2CF3)3, and LiC(SO2C2F5)3. Among these, inorganic lithium salts are preferred, and LiPF6 is more preferred.

[0089] The content of the electrolyte salt in the non-aqueous electrolyte is 0.1 mol / dm 3 More than 2.5mol / dm 3 It is preferable that the value is 0.3 mol / dm or less. 3 More than 2.0mol / dm 3 It is more preferable that it is 0.5 mol / dm or less. 3 More than 1.7mol / dm 3 It is more preferable that it is 0.7 mol / dm or less. 3 More than 1.5mol / dm 3 By setting the content of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

[0090] The non-aqueous electrolyte may contain an additive. Examples of the additive include aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; partial halides of the above aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene; halogenated anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole; succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, and cyclohexyl benzene. hexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, 4,4'-bis(2,2-dioxo-1,3,2-dioxathiolane), 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisole, diphenyl disulfide, dipyridinium disulfide, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, tetrakistrimethylsilyl titanate, etc. These additives may be used alone or in combination of two or more.

[0091] The content of the additive contained 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. By setting the content of the additive within the above range, it is possible to improve the capacity retention performance or cycle performance after high-temperature storage, and further improve safety.

[0092] The non-aqueous electrolyte may be a solid electrolyte, or a non-aqueous electrolytic solution and a solid electrolyte may be used in combination.

[0093] The solid electrolyte can be selected from any material that has ionic conductivity of lithium, sodium, calcium, etc., and is solid at room temperature (for example, 15° C. to 25° C.) Examples of the solid electrolyte include sulfide solid electrolytes, oxide solid electrolytes, oxynitride solid electrolytes, and polymer solid electrolytes.

[0094] In the case of a lithium ion secondary battery, examples of sulfide solid electrolytes include Li2S-P2S5 systems. Examples of sulfide solid electrolytes include Li2S-P2S5, LiI-Li2S-P2S5, and Li 10 Ge-P2S 12 etc.

[0095] (Positive electrode potential at the end of charge voltage during normal use) In the secondary battery (non-aqueous electrolyte storage element), the positive electrode potential (positive electrode potential) at the end-of-charge voltage during normal use is not particularly limited, but is preferably 4.5 V vs. Li / Li + Less than 4.45V vs. Li / Li is preferable. + Less than 4.4V vs. Li / Li is preferable. + The following may be even more preferable in some cases: By setting the positive electrode potential at the end-of-charge voltage during normal use to the above upper limit or less, chemical formation over time gradually progresses as charge and discharge are repeated many times, and the capacity retention rate can be increased.

[0096] In this secondary battery, the positive electrode potential at the end of charge voltage during normal use is 4.3 V vs. Li / Li + Above 4.35V vs. Li / Li is preferred + More than 4.4V vs. Li / Li is preferable. + In some cases, the above is even more preferable. By setting the positive electrode potential at the end-of-charge voltage during normal use to the above lower limit or higher, the time-dependent chemical formation progresses sufficiently during normal charging, thereby improving the capacity retention rate. Furthermore, by increasing the upper charge potential limit, the discharge capacity can be increased, and the energy density, output performance, etc. can be improved.

[0097] The positive electrode potential at the end-of-charge voltage during normal use of the secondary battery may be set within the range between any of the above upper limits and any of the above lower limits.

[0098] (Application) The use of the secondary battery is not particularly limited, and it can be used for the same purposes as conventionally known secondary batteries. It is believed that the capacity retention rate of the secondary battery can be increased by the generation of chemical formation over time. Therefore, the secondary battery is particularly suitable for applications in which the battery is typically charged to a predetermined end-of-charge voltage (predetermined end-of-charge potential), i.e., charged until the SOC (state of charge) reaches 100%. Examples of such applications include power sources for portable electronic devices (such as mobile phones, laptop computers, and tablet devices), electric toys, electric shavers, electric vehicles (EVs), and plug-in hybrid vehicles (PHEVs).

[0099] <How to use the nonaqueous electrolyte energy storage element> The method of using the nonaqueous electrolyte electricity storage element according to one embodiment of the present invention is not particularly limited, but the following method is preferable: That is, the method of using the nonaqueous electrolyte electricity storage element according to one embodiment of the present invention is to use the nonaqueous electrolyte electricity storage element in a battery with a positive electrode potential (positive electrode ultimate potential) of 4.5 V vs. Li / Li. + By using the battery in this manner, aging is gradually carried out as the battery is charged, and therefore a nonaqueous electrolyte energy storage element using a lithium-excess active material in the positive electrode can be used with a high capacity retention rate.

[0100] The upper limit of the positive electrode potential (positive electrode potential) in this charging is 4.45 V vs. Li / Li + The lower limit of the positive electrode potential in this charging is 4.3 V vs. Li / Li. + Above 4.35V vs. Li / Li is preferred + More than 4.4V vs. Li / Li is preferable. + In some cases, the above is even more preferable.

[0101] This method of use may be the same as the method of use of a conventionally known non-aqueous electrolyte storage element, except that the positive electrode potential (potential reached by the positive electrode) during charging is set as described above.

[0102] <Method of manufacturing nonaqueous electrolyte energy storage element> A method for manufacturing a nonaqueous electrolyte storage element according to one embodiment of the present invention includes assembling an uncharged / discharged nonaqueous electrolyte storage element including a positive electrode, a negative electrode, and a nonaqueous electrolyte, and initially charging / discharging the uncharged / discharged nonaqueous electrolyte storage element. During this initial charging / discharging, the positive electrode potential (potential reached by the positive electrode) is 4.5 V vs. Li / Li. + According to this manufacturing method, high-potential formation is not performed during the initial charge and discharge, and therefore a nonaqueous electrolyte energy storage element having a high capacity retention rate during charge and discharge cycles can be manufactured.

[0103] In this manufacturing method, the initial charge / discharge is not intended to actively activate the lithium-excess active material, but may be performed, for example, to confirm the capacity. That is, the initial charge / discharge is simply the first charge / discharge performed after assembling the nonaqueous electrolyte storage element (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.

[0104] The upper limit of the positive electrode potential (positive electrode potential) during initial charge / discharge is 4.45 V vs. Li / Li + may be less than 4.4V vs. Li / Li + On the other hand, the lower limit of the positive electrode potential during initial charge and discharge is not particularly limited, and may be, for example, 4.3 V vs. Li / Li + May be over 4.35V vs. Li / Li + or above 4.4V vs. Li / Li + It may be more than that.

[0105] Assembling a non-charged / discharged non-aqueous electrolyte storage element including a positive electrode, a negative electrode, and a non-aqueous electrolyte includes, for example, preparing an electrode assembly, preparing a non-aqueous electrolyte, and housing the electrode assembly and the non-aqueous electrolyte in a container. Preparing the electrode assembly includes preparing a positive electrode, preparing a negative electrode, and stacking or winding the positive electrode and the negative electrode with a separator interposed therebetween to form the electrode assembly.

[0106] The positive electrode can be prepared by applying a positive electrode mixture paste to a positive electrode substrate directly or via an intermediate layer, and then drying the paste. The positive electrode mixture paste contains components constituting the positive electrode active material layer (positive electrode mixture), such as a positive electrode active material, and a dispersion medium. The positive electrode active material contains the lithium transition metal composite oxide (lithium-excess active material). The method for producing the lithium transition metal composite oxide is as described above.

[0107] The negative electrode can be prepared, for example, by applying a negative electrode mixture paste to a negative electrode substrate directly or via an intermediate layer, and then drying the paste. The negative electrode mixture paste contains components constituting the negative electrode active material layer (negative electrode mixture), such as a negative electrode active material, and a dispersion medium.

[0108] <Other embodiments> The energy storage device 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.

[0109] Although the above-described embodiments have been described mainly with reference to the nonaqueous electrolyte secondary battery as the nonaqueous electrolyte storage element, other nonaqueous electrolyte storage elements may also be used, such as capacitors (electric double layer capacitors, lithium ion capacitors).

[0110] FIG. 1 is a schematic diagram of a rectangular nonaqueous electrolyte storage element 1 (nonaqueous electrolyte secondary battery) that is one embodiment of the nonaqueous electrolyte storage element according to the present invention. The figure is a see-through view of the inside of a container. The nonaqueous electrolyte storage element 1 shown in FIG. 1 has an electrode assembly 2 housed in a container 3. The electrode assembly 2 is formed by winding a positive electrode including a positive electrode active material and a negative electrode including a negative electrode active material with a separator interposed therebetween. The positive electrode is electrically connected to a positive electrode terminal 4 via a positive electrode lead 41, and the negative electrode is electrically connected to a negative electrode terminal 5 via a negative electrode lead 51.

[0111] The configuration of the nonaqueous electrolyte energy storage element according to the present invention is not particularly limited, and examples include cylindrical batteries, prismatic batteries (rectangular batteries), and flat batteries. The present invention can also be realized as an energy storage device including a plurality of the above-described nonaqueous electrolyte energy storage elements. One embodiment of the energy storage device is shown in FIG. 2. In FIG. 2, an energy storage device 30 includes a plurality of energy storage units 20. Each energy storage unit 20 includes a plurality of nonaqueous electrolyte energy storage elements 1. The energy storage device 30 can be installed as a power source for automobiles such as electric vehicles (EVs) and plug-in hybrid vehicles (PHEVs). [Example]

[0112] 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.

[0113] [Example 1] (Preparation of lithium transition metal composite oxides) 315.4 g of nickel sulfate hexahydrate, 170.4 g of cobalt sulfate heptahydrate, and 535.7 g of manganese sulfate pentahydrate were weighed out. The total amount of these was added to 4 dmℓ of ion-exchanged water. 3 The molar ratio of Ni:Co:Mn was 30:15:55. 3 Next, a 5 dm 3 2 dm 3The oxygen contained in the ion-exchanged water was removed by bubbling nitrogen gas for 30 minutes. The temperature of the reaction vessel was set to 50°C (±2°C), and the inside of the reaction vessel was stirred at a rotation speed of 1,500 rpm using a paddle blade equipped with a stirring motor, so that sufficient convection occurred inside the reaction vessel. The sulfate aqueous solution was poured into the reaction vessel to a depth of 1.5 cm. 3 The solution was added dropwise to the reaction vessel at a rate of 4.0 mol / dm 3 of sodium hydroxide, 1.25 mol / dm 3 of ammonia, and 0.1 mol / dm 3 The pH in the reaction vessel was controlled to be always kept at 10.0 (±0.1) by appropriately adding dropwise the mixed alkaline solution containing hydrazine, and by discharging a part of the reaction solution by overflow, the total volume of the reaction solution was always kept at 2 dm 3 The reaction solution was controlled so as not to exceed the specified value. The reaction solution was collected within 2 hours of the start of the dropwise addition of the sulfuric acid aqueous solution, starting from 10 hours after the start of the dropwise addition, and allowed to stand at room temperature for 12 hours or more. In other words, the reaction solution was collected between 10 and 12 hours of reaction time. This was filtered, washed, and dried to obtain a hydroxide precursor. 2.315 g of the obtained hydroxide precursor was mixed with 1.214 g of lithium hydroxide monohydrate and thoroughly mixed using an agate automatic mortar to prepare a mixed powder with a Li / (Ni, Co, Mn) molar ratio (Li / Me) of 1.10. The mixture was molded into pellets with a diameter of 25 mm at a pressure of 6 MPa using a pelletizer. The amount of mixed powder used for pelletization was determined based on the estimated mass of the final product, which was 2.5 g. One pellet was placed in an alumina boat approximately 100 mm in length and placed in a box-type electric furnace (model number: AMF20). The temperature was raised from room temperature to 900 °C over 10 hours under atmospheric pressure in an air atmosphere, and then fired at 900 °C for 5 hours. The interior dimensions of the box-type electric furnace were 10 cm long, 20 cm wide, and 30 cm deep, with heating wires spaced 20 cm apart across the width. After firing, the heater was turned off and the alumina boat was left in the furnace to cool naturally. As a result, the furnace temperature dropped to about 200°C after 5 hours, but the temperature drop rate thereafter was somewhat slow. After a day and a night, it was confirmed that the furnace temperature had dropped below 100°C, and the pellets were then removed and lightly crushed in an agate mortar to ensure a uniform particle size. In this way, a lithium transition metal composite oxide (Ni:Co:Mn = 30:15:55, Li / Me = 1.10) was prepared. Powder X-ray diffraction measurements were performed on the obtained lithium transition metal composite oxide using an X-ray diffractometer (Rigaku, Model: MiniFlex II). It was confirmed that the obtained lithium transition metal composite oxide had an α-NaFeO2 structure and that the X-ray diffraction pattern showed a diffraction peak in the range of 20° to 22°. Furthermore, in the X-ray diffraction pattern, the ratio (I21 / I18) of the difference between the maximum and minimum intensity values ​​in the diffraction angle 2θ range of 17° to 19° (I18) to the difference between the maximum and minimum intensity values ​​in the diffraction angle 2θ range of 20° to 22° (I21) was 0.020. The total pore volume of the obtained lithium transition metal composite oxide was measured by the above-mentioned method. 3 The peak differential pore volume was measured by the above-mentioned method and was found to be 0.08 mm 3 / (g·nm).

[0114] (Preparation of positive electrode) A positive electrode mixture paste containing the above-mentioned lithium transition metal composite oxide (positive electrode active material), acetylene black (AB), and polyvinylidene fluoride (PVDF) in a mass ratio of 90:5:5 (solids equivalent) and N-methylpyrrolidone (NMP) as a dispersion medium was prepared. This positive electrode mixture paste was applied to an aluminum foil (thickness 15 μm) as a positive electrode substrate and dried to obtain a positive electrode.

[0115] (Preparation of negative electrode) A negative electrode mixture paste containing graphite (as the negative electrode active material), styrene butadiene rubber (SBR), and carboxymethyl cellulose (CMC) in a mass ratio (solid content equivalent) of 96:3.2:0.8 was prepared using water as the dispersion medium. This negative electrode mixture paste was applied to copper foil (thickness 10 μm) as the negative electrode substrate and dried to obtain a negative electrode.

[0116] (Test battery assembly) A test battery (non-aqueous electrolyte energy storage element) was assembled using the positive electrode and the negative electrode. The non-aqueous electrolyte was a non-aqueous solvent mixture of EC (ethylene carbonate), EMC (ethyl methyl carbonate), and dimethyl carbonate (DMC) in a volume ratio of 30:35:35, with 1.0 mol / dm lithium hexafluorophosphate (LiPF) as the electrolyte salt. 3 A solution in which the content of the polymer was dissolved was used, and a microporous polyolefin film was used as the separator.

[0117] (Initial charge / discharge) The obtained nonaqueous electrolyte storage element before initial charge / discharge (non-charged / discharged nonaqueous electrolyte storage element) was subjected to initial charge / discharge at 25°C in the following manner: charging current 0.1 C, charge cut-off voltage 4.3 V (positive electrode final potential 4.4 V vs. Li / Li +) constant current constant voltage charging was performed. The charge termination condition was the time when the current value decayed to 0.02 C. Thereafter, constant current discharge was performed with a discharge current of 0.1 C and a discharge termination voltage of 2.5 V. A rest period of 10 minutes was provided after charging. By the above procedure, a nonaqueous electrolyte storage element of Example 1 was obtained.

[0118] [Examples 2 to 17, Comparative Examples 1 to 9] The nonaqueous electrolyte storage elements of Examples 2 to 17 and Comparative Examples 1 to 9 were obtained in the same manner as in Example 1, except that the amounts of nickel sulfate hexahydrate, cobalt sulfate heptahydrate, and manganese sulfate pentahydrate used, as well as the amounts of the hydroxide precursor and lithium hydroxide monohydrate used, were adjusted so that the molar ratio of Ni, Co, and Mn (Ni:Co:Mn) and the molar ratio of lithium to transition metal (Li / Me) in the target lithium transition metal composite oxide would be the values ​​shown in Table 1, the elapsed time from the start of dropwise addition of the aqueous sulfuric acid solution to the start of collection of the reaction solution was set to the time shown in Table 1, and the potential reached by the positive electrode during initial charge and discharge was set to the potential shown in Table 1.

[0119] The total pore volume of the lithium transition metal composite oxides obtained in each of the examples and comparative examples was measured using the method described above. The measurement results are shown in Table 1. In addition, for each nonaqueous electrolyte storage element, after the initial charge / discharge, a positive electrode active material (lithium transition metal composite oxide) in a fully discharged state was taken out using the method described above and subjected to X-ray diffraction measurement to confirm the presence or absence of a diffraction peak in the range of 20° to 22°. The results are shown in Table 1.

[0120] (Charge-discharge cycle test) For each non-aqueous electrolyte storage element whose initial discharge capacity had been confirmed, a charge-discharge cycle test was carried out at 45°C as follows: charging current 1.0 C, charge cut-off voltage 4.3 V (positive electrode final potential 4.4 V vs. Li / Li + The battery was charged at a constant current and constant voltage at 1.0 C. The charge termination condition was when the current value decayed to 0.05 C. Subsequently, the battery was discharged at a constant current of 1.0 C and a discharge termination voltage of 2.5 V. A 10-minute rest period was provided after each charge and discharge. This charge / discharge cycle was repeated 100 times. The capacity retention rate was calculated as the ratio of the discharge capacity at the 100th cycle to the discharge capacity at the 1st cycle. The obtained capacity retention rates are shown in Table 1.

[0121] (output performance) The resulting nonaqueous electrolyte storage elements were initially charged and discharged in the same manner as described above. Subsequently, they were charged at a constant current of 1.0 C at 25°C until the SOC reached 50%, and then discharged at 0.2 C, 0.5 C, and 1.0 C at 25°C for 30 seconds each. The relationship between the current and the voltage 10 seconds after the start of discharge was plotted. The three plots were fitted using the least squares method to obtain a straight line. The current value was calculated by extrapolating the straight line to the discharge cutoff voltage of 2.5 V, and the output was calculated by multiplying it by the voltage value. The resulting output is shown in Table 1.

[0122] [Table 1]

[0123] As shown in Table 1, the nonaqueous electrolyte energy storage elements of Comparative Examples 1 and 9, which used a lithium transition metal composite oxide that did not have a diffraction peak in the range of 20° to 22° in the X-ray diffraction pattern, rather than a lithium-excess active material, had low capacity retention rates after charge-discharge cycles. 3 The nonaqueous electrolyte energy storage elements of Comparative Examples 2 to 7, which used a lithium-excess active material (lithium transition metal composite oxide) with a Li / Li ratio of less than 1 / g, had a high capacity retention rate after charge / discharge cycling, but had low output. + The nonaqueous electrolyte energy storage element of Comparative Example 8, in which the diffraction peaks in the range of 20° to 22° in the X-ray diffraction diagram disappeared, had a low capacity retention rate after charge-discharge cycles and a low output. 3The nonaqueous electrolyte energy storage elements of Examples 1 to 17, which used a lithium-excess active material (lithium transition metal composite oxide) having an X-ray diffraction pattern in a range of 20° to 22°, exhibited high output and also high capacity retention rates after charge-discharge cycling.

[0124] Furthermore, a comparison of Examples 8 to 15 and Comparative Examples 3 to 7 shows that a lithium-excess active material (lithium transition metal composite oxide) with a large total pore volume can be obtained by shortening the elapsed time (reaction time) from the start of dropwise addition of the sulfuric acid aqueous solution to the start of collection of the reaction solution.

[0125] As can be seen from the comparison between Comparative Examples 1 and 9, when a non-lithium-excess LiMeO2-type active material was used, the output did not increase even when the total pore volume was increased. It is presumed that the effect of increasing the total pore volume to improve output performance is a unique effect that occurs in the case of a lithium-excess active material. [Industrial Applicability]

[0126] 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. [Explanation of symbols]

[0127] 1. Non-aqueous electrolyte energy storage element 2 Electrode body 3 containers 4 Positive terminal 41 Positive lead 5 Negative terminal 51 Negative lead 20 Energy storage unit 30 Energy storage device

Claims

1. α-NaFeO ２ a nonaqueous electrolyte storage element that is in an uncharged / discharged state, the nonaqueous electrolyte storage element having a positive electrode containing a lithium transition metal composite oxide having a structure; and an initial charge / discharge of the nonaqueous electrolyte storage element in the uncharged / discharged state, the maximum potential of the positive electrode being less than 4.5 V (vs. Li / Li + ), the lithium transition metal composite oxide contains nickel and manganese, the lithium content relative to the transition metal in the lithium transition metal composite oxide is 1.05 or more and 1.5 or less in molar ratio; the content of manganese relative to the transition metal in the lithium transition metal composite oxide is 0.4 or more and 0.7 or less in terms of molar ratio; The total pore volume of the lithium transition metal composite oxide is 4 mm ３ / g or more 50mm ３ / g or less, The nonaqueous electrolyte storage element has a lithium transition metal composite oxide contained in a positive electrode of the completed nonaqueous electrolyte storage element, and in an X-ray diffraction pattern using CuKα rays, a diffraction peak is present in the range of 20° or more and 22° or less.

2. The positive electrode potential at the end of charge voltage during normal use is 4.5 V vs. Li / Li ＋ The nonaqueous electrolyte storage element according to claim 1 , wherein the nonaqueous electrolyte storage element has a molecular weight of less than 1000 kJ / cm 2 .

3. Positive electrode potential: 4.5 V vs. Li / Li ＋ 3. A method for using the nonaqueous electrolyte storage element according to claim 1, further comprising charging the element within a range of less than 1000 kJ / s.

4. Positive electrode potential: 4.5 V vs. Li / Li ＋ The method for producing a nonaqueous electrolyte storage element according to claim 1 or 2, further comprising carrying out initial charging and discharging within a range of less than 1000 kJ / s.

Images