Non-aqueous electrolyte electric power storage element

Abstract

A non-aqueous electrolyte electric power storage element according to one aspect of the present invention comprises: a negative electrode that has a negative electrode active material including a silicon-based active material; and a positive electrode, wherein, in a dQ / dV curve that is based on changes in a voltage V and a discharge electricity amount Q between the negative electrode and the positive electrode in a discharge process, in which V is the horizontal axis and dQ / dV is the vertical axis, the maximum of a peak derived from the discharge of the silicon-based active material is positioned in a range of 3.39 V or less.

Description

Non-aqueous electrolyte energy storage element

[0001] This invention relates to a non-aqueous electrolyte energy storage element.

[0002] Non-aqueous electrolyte secondary batteries, such as lithium-ion secondary batteries, are widely used in electronic devices like personal computers and communication terminals, as well as automobiles, due to their high energy density. Generally, non-aqueous electrolyte secondary batteries consist of an electrode body with a pair of electrodes electrically isolated by a separator, and a non-aqueous electrolyte interposed between the electrodes. They are configured to charge and discharge by transferring charge-transporting ions between the two electrodes. Besides secondary batteries, capacitors such as lithium-ion capacitors and electric double-layer capacitors are also widely used as non-aqueous electrolyte energy storage elements.

[0003] One such non-aqueous electrolyte energy storage element has been developed in which a silicon-based active material is used as the active material for the negative electrode (see Patent Documents 1 and 2). Silicon-based active materials have the advantage of having a larger charge / discharge capacity per unit mass compared to carbon materials, which are widely used as negative electrode active materials.

[0004] Japanese Patent Publication No. 2011-113863 Japanese Patent Publication No. 2015-053152

[0005] However, silicon-based active materials exhibit greater volume changes due to expansion and contraction during charging and discharging compared to carbon materials. Repeated expansion and contraction can easily lead to particle cracking and electrical isolation. Therefore, non-aqueous electrolyte energy storage devices using silicon-based active materials have low capacity retention rates during charge-discharge cycles.

[0006] The object of the present invention is to provide a non-aqueous electrolyte energy storage element that uses a silicon-based active material as the negative electrode and has a high capacity retention rate during charge-discharge cycles.

[0007] A non-aqueous electrolyte energy storage element according to one aspect of the present invention comprises a negative electrode having a negative electrode active material containing a silicon-based active material and a positive electrode, and in a dQ / dV curve with the horizontal axis being V and the vertical axis being dQ / dV, based on the changes in voltage V and discharge amount Q between the negative electrode and the positive electrode during the discharge process, the maximum of the peak originating from the discharge of the silicon-based active material is located in the range of 3.39 [V] or less.

[0008] According to one aspect of the present invention, it is possible to provide a non-aqueous electrolyte energy storage element that uses a silicon-based active material as the negative electrode and has a high capacity retention rate during charge-discharge cycles.

[0009] Figure 1 is a perspective view showing a non-aqueous electrolyte energy storage element according to one embodiment of the present invention. Figure 2 is a schematic diagram showing an energy storage device comprising multiple non-aqueous electrolyte energy storage elements according to one embodiment of the present invention. Figure 3 is a graph showing the dQ / dV curve of the non-aqueous electrolyte energy storage element of Example 1. Figure 4 is a graph showing the dQ / dV curve of the non-aqueous electrolyte energy storage element of Comparative Example 1.

[0010] First, an overview of the non-aqueous electrolyte energy storage elements disclosed herein will be provided.

[0011] [1] A non-aqueous electrolyte energy storage element according to one aspect of the present invention comprises a negative electrode having a negative electrode active material containing a silicon-based active material and a positive electrode, wherein in a dQ / dV curve with V on the horizontal axis and dQ / dV on the vertical axis, based on the changes in voltage V and discharge amount Q between the negative electrode and the positive electrode during the discharge process, the maximum of the peak originating from the discharge of the silicon-based active material is located in the range of 3.39 [V] or less.

[0012] The non-aqueous electrolyte energy storage element described in [1] above is a non-aqueous electrolyte energy storage element that uses a silicon-based active material as the negative electrode and has a high capacity retention rate in charge-discharge cycles. The reason for this effect is not clear, but the following is speculated. In conventional non-aqueous electrolyte energy storage elements that use a silicon-based active material as the negative electrode, the increase in negative electrode potential during discharge can cause cracking of silicon-based active material particles and electrical isolation. More specifically, during charging, silicide (e.g., lithium silicide) is formed on the particle surface of the silicon-based active material by the reaction of the silicon-based active material with charge transport ions. Subsequently, during discharge, the desorption reaction of charge transport ions from the silicide proceeds, causing the negative electrode potential to increase near the discharge state. Along with the formation of the silicide and the desorption reaction of charge transport ions from the silicide, a large expansion and contraction of the silicon-based active material occurs, resulting in volume changes and particle cracking. In this way, a new reaction field is formed between the silicon-based active material and charge transport ions during the next charge, causing the silicide formation reaction to proceed further during the next charge. This repetition can lead to further particle cracking and electrical isolation of the silicon-based active material. When a new reaction field is formed between the silicon-based active material and charge transport ions due to such particle cracking, the capacitance balance between the positive and negative electrodes changes, and a phenomenon is observed in the dQ / dV curve during the discharge process in which the peak originating from the discharge of the silicon-based active material shifts to the higher voltage side. When the non-aqueous electrolyte energy storage element is of the positive electrode capacity limiting type, the rise in the negative electrode potential is suppressed near the discharge state during discharge, making it easier to suppress the occurrence of this phenomenon in which the peak originating from the discharge of the silicon-based active material shifts to the higher voltage side. The "positive electrode capacity limiting type" will be described in detail later. In contrast, in the non-aqueous electrolyte energy storage element described in [1] above, the maximum peak originating from the discharge of the silicon-based active material is located in the range of 3.39 [V] or less in the dQ / dV curve during the discharge process. Therefore, the rise in the negative electrode potential near the discharge state is suppressed during discharge, so as to suppress the formation of a new reaction field between the silicon-based active material and charge transport ions.Therefore, repeated expansion and contraction of silicon-based active materials makes it less likely for particles to crack or for electrical isolation to occur, thus improving the capacity retention rate during charge-discharge cycles.

[0013] The relationship between the peak maximum originating from the discharge of the silicon-based active material being located in the range of 3.39 [V] or less and the suppression of the rise in negative electrode potential near the point of discharge during discharge is explained as follows. The non-aqueous electrolyte energy storage element described in [1] above is usually configured such that the difference between the initial charge capacity and the initial discharge capacity at the positive electrode (initial irreversible capacity of the positive electrode) is greater than the difference between the initial charge capacity and the initial discharge capacity at the negative electrode (initial irreversible capacity of the negative electrode) (hereinafter, such a configuration is also referred to as the "positive electrode capacity limiting type"). In other words, such a non-aqueous electrolyte energy storage element is configured such that, near the point of discharge during discharge, the positive electrode potential drops sufficiently before the negative electrode potential rises sufficiently, thus reaching the discharge state. In other words, near the point of discharge during discharge, the rise in the negative electrode potential is considered to be smaller than the drop in the positive electrode potential accompanying the decrease in voltage of the non-aqueous electrolyte energy storage element. In this configuration, the negative electrode potential only reaches the range where cracking of silicon-based active material particles can occur by sufficiently increasing the discharge depth of the non-aqueous electrolyte energy storage element (sufficiently decreasing the voltage between the negative and positive electrodes). Therefore, in the dQ / dV curve during the discharge process, the fact that the peak originating from the discharge of the silicon-based active material is located in a relatively low voltage range means that, near the point of discharge, the increase in the negative electrode potential is smaller than the decrease in the positive electrode potential due to the decrease in the voltage of the non-aqueous electrolyte energy storage element, and thus the increase in the negative electrode potential is suppressed, preventing it from reaching the range where cracking of silicon-based active material particles can occur.

[0014] A "silicon-based active material" refers to a material that contains the element silicon and can be used as a negative electrode active material.

[0015] The location of the peak maximum originating from the discharge of silicon-based active material is identified in non-aqueous electrolyte energy storage elements (hereinafter also referred to as "evaluation energy storage elements") that are shipped from the manufacturing plant and distributed to the market by the following procedure (1) to (5). Furthermore, for evaluation energy storage elements in which the components of the negative electrode active material have been identified, the location is identified by the following procedure (2) to (5). Multiple evaluation energy storage elements are prepared. In addition, charging and discharging of the evaluation energy storage elements and test batteries is performed at 25°C.

[0016] (1) Confirmation and evaluation of components in the negative electrode active material: The negative electrode is removed from the energy storage element and processed by ion milling to expose the cross-section of the negative electrode active material layer. During processing by ion milling, copper foil, adhesive carbon tape, aluminum foil, negative electrode (negative electrode substrate and negative electrode active material layer), aluminum foil, adhesive carbon tape, and copper foil are laminated in this order, and the negative electrode is fixed during processing. Elemental mapping is performed on the cross-section of the negative electrode active material layer processed in this way using scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX) to identify the main components of the negative electrode active material contained in the negative electrode active material layer. If silicon is detected from the cross-section of the negative electrode active material as a result of elemental mapping, the negative electrode active material is considered to contain silicon-based active material. Also, if carbon is detected from the cross-section of the negative electrode active material, for example, the negative electrode active material is considered to contain carbon-based active material. "Carbon-based active material" refers to the carbon material that is the negative electrode active material. "Carbon material" refers to a material whose main constituent element is carbon. The main constituent element is the element that is present in the largest quantity by mass.

[0017] The negative electrode from the evaluation energy storage element is extracted using the following procedure. First, the evaluation energy storage element is discharged at a constant current of 0.05C until it reaches the discharge termination voltage during normal use. It is then disassembled, the negative electrode is extracted, and test battery A is assembled using the extracted negative electrode as the working electrode and metallic lithium as the counter electrode. Pure metallic lithium is used for the metallic lithium electrode here. For test battery A, with a current of 50mA per gram of negative electrode active material, the closed-circuit potential of the negative electrode is 2.0V (vs. Li / Li ＋Constant current discharge is performed until the negative electrode active material is fully discharged. Next, the test battery A is disassembled and the negative electrode is removed. The removed negative electrode is washed with dimethyl carbonate. After that, it is washed with water, dried under reduced pressure at room temperature for 24 hours, and then subjected to cross-sectional observation. The disassembly of the evaluation energy storage element and test battery A is carried out in an argon atmosphere with a dew point of -60°C or lower. "Normal use" refers to the case where the evaluation energy storage element is used under the charge and discharge conditions recommended or specified for the evaluation energy storage element, and if equipment for using the evaluation energy storage element is available, it refers to the case where that equipment is used.

[0018] (2) Obtaining dQ / dV curves during the discharge process of the positive and negative electrodes. The evaluation energy storage element is discharged at a constant current of 0.05C until it reaches the discharge termination voltage during normal use. After that, the evaluation energy storage element is disassembled and the positive and negative electrodes are removed. The removed positive electrode is used as the working electrode and metallic lithium is used as the counter electrode to assemble the first test battery. Pure metallic lithium is used for the metallic lithium electrode here. For the first test battery, the potential of the positive electrode (working electrode) is compared to the positive electrode potential (V vs. Li / Li) of the disassembled evaluation energy storage element in the state of 100% SOC. ＋ After performing constant current constant voltage charging with a current equivalent to 0.2C in the evaluation energy storage element until the value of ) is reached, the potential of the positive electrode (working electrode) is 3.0V (vs. Li / Li) with a current equivalent to 0.2C in the evaluation energy storage element. ＋ Constant current discharge is performed until the voltage reaches 0.02V, and the discharge capacity of the positive electrode is measured. At the same time, a first dQ / dV curve is determined based on the changes in the voltage V and discharge amount Q between the negative and positive electrodes during the discharge process of the first test battery. In this specification, the dQ / dV curve is drawn based on data obtained for each 0.02V change in voltage V. Furthermore, the extracted negative electrode is used as the working electrode, and metallic lithium is used as the counter electrode to assemble the second test battery. Pure metallic lithium is used for the metallic lithium electrode here. For the second test battery, the potential of the negative electrode (working electrode) is set to the negative electrode potential (V vs. Li / Li) in the disassembled evaluation energy storage element at 100% SOC. ＋After constant current charging is performed with a current equivalent to 0.2C in the evaluation energy storage element until the value of ) is reached, the potential of the negative electrode (working electrode) is 2.0V (vs. Li / Li) with a current equivalent to 0.2C in the evaluation energy storage element. ＋ Constant current discharge is performed until the value reaches 0, and the discharge capacity of the negative electrode is measured. At the same time, a second dQ / dV curve is determined based on the changes in the voltage V between the negative and positive electrodes and the amount of discharged electricity Q during the discharge process of the second test battery. In the second test battery, the operation of applying current in the direction that electrochemically reduces the negative electrode is called charging, and the operation of applying current in the direction that electrochemically oxidizes the negative electrode is called discharging.

[0019] (3) Confirmation of positive electrode capacity limiting type If the discharge capacity of the positive electrode is smaller than the discharge capacity of the negative electrode, the evaluation energy storage element is considered to be a positive electrode capacity limiting type.

[0020] (4) Confirmation of the position of the peak maximum of the second dQ / dV curve Confirm the position of the peak maximum of the second dQ / dV curve obtained in (2) above. As a method for confirming the position of the peak maximum, component-specific dQ / dV curves for each major component of the negative electrode active material confirmed in (1) above may be prepared as comparative data, and the position of the peak maximum may be confirmed. Examples of such component-specific dQ / dV curves include the dQ / dV curve of silicon-based active material obtained from a silicon-based active material test battery assembled in the same procedure as the second test battery using a negative electrode containing only silicon-based active material as the negative electrode active material, and the dQ / dV curve of carbon-based active material obtained from a carbon-based active material test battery assembled in the same procedure as the second test battery using a negative electrode containing only carbon-based active material as the negative electrode active material. Then, by comparing the second dQ / dV curve with the component-specific dQ / dV curves, we can determine which component each peak in the second dQ / dV curve originates from, and confirm the relative positions of their maxima.

[0021] (5) Obtaining the dQ / dV curve during the discharge process of the evaluation energy storage element and confirming the position of the peak maximum originating from the discharge of silicon-based active material The evaluation energy storage element is charged with a constant current of 0.05C until it reaches a state of 100% SOC. After a 30-minute pause, it is discharged with a constant current of 0.2C until it reaches the discharge termination voltage during normal use. The dQ / dV curve of the evaluation energy storage element is determined based on the changes in the voltage V between the negative and positive electrodes and the amount of discharged electricity Q during the discharge process at this time. By comparing the dQ / dV curve of the evaluation energy storage element with the position of the peak maximum of each peak in the second dQ / dV curve confirmed in (4) above and the first dQ / dV curve, the position of the peak maximum originating from the discharge of silicon-based active material in the dQ / dV curve of the evaluation energy storage element is identified.

[0022] [2] In the non-aqueous electrolyte energy storage element described in [1] above, the silicon-based active material may be silicon oxide, silicon carbide, or silicon as a single element.

[0023] The non-aqueous electrolyte energy storage element described in [2] above is a preferred embodiment of the present invention, which has a high capacity retention rate in charge-discharge cycles and makes it easy to secure a large discharge capacity.

[0024] [3] In the non-aqueous electrolyte energy storage element described in [1] or [2] above, the negative electrode active material may further contain a carbon-based active material.

[0025] The non-aqueous electrolyte energy storage element described in [3] above can further improve the capacity retention rate during charge-discharge cycles by lowering the negative electrode potential near the point where the discharge state is reached during discharge.

[0026] [4] In the non-aqueous electrolyte energy storage element described in [3] above, the positive electrode has a positive electrode active material containing a lithium transition metal composite oxide in which the nickel element content relative to all metal elements other than lithium is 70 mol% or more, and the carbon-based active material may also contain artificial graphite.

[0027] The non-aqueous electrolyte energy storage element described in [4] above can be easily made into a positive electrode capacity-limited type. When the non-aqueous electrolyte energy storage element is a positive electrode capacity-limited type, the negative electrode potential near the discharge termination voltage during normal use becomes lower, which can further increase the capacity retention rate during the charge-discharge cycle.

[0028] The elemental composition ratio of lithium transition metal composite oxides is measured either on the lithium transition metal composite oxide before charging and discharging, or, in the case of lithium transition metal composite oxide contained in the positive electrode of an evaluation energy storage element, on a sample treated with the following procedure. First, the evaluation energy storage element is charged with a constant current of 0.05C until it reaches the charging termination voltage for normal use, bringing it to a fully charged state. After a 30-minute rest, it is discharged with a constant current of 0.05C until it reaches the discharge termination voltage for normal use. It is then disassembled, the positive electrode is removed, and test battery B is assembled with the removed positive electrode as the working electrode and the metallic lithium electrode as the counter electrode. Pure metallic lithium is used for the metallic lithium electrode here. For test battery B, the positive electrode potential is 2.0V (vs. Li / Li) with a current of 10mA per gram of positive electrode active material. ＋ Constant current discharge is performed until the positive electrode is fully discharged. The device is disassembled again and the positive electrode is removed. The removed positive electrode is washed with dimethyl carbonate. Then, the positive electrode active material layer containing the lithium transition metal composite oxide is peeled off 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. After that, it is washed with water and dried under reduced pressure at room temperature for 24 hours to obtain the lithium transition metal composite oxide. The obtained lithium transition metal composite oxide is subjected to measurement. The work from disassembling the evaluation energy storage element to obtaining the lithium transition metal composite oxide is performed in an argon atmosphere with a dew point of -60°C or lower.

[0029] "Artificial graphite" refers to graphite that is produced artificially. "Graphite" is defined as the average lattice plane spacing (d) of the (002) plane, which is determined by X-ray diffraction before charging or discharging or during the discharge state. ００２) refers to carbon materials with a wavelength of 0.33 nm or more and less than 0.34 nm. Here, the "discharge state" of the carbon material as a carbon-based active material means a state in which sufficient lithium ions that can be absorbed and released during charging and discharging are released from the carbon-based active material. For example, in a half-cell using a negative electrode containing a carbon-based active material as the working electrode and metallic lithium as the counter electrode, this is a state in which the open-circuit voltage is 0.7 V or higher. Artificial graphite may be such that in the X-ray diffraction pattern using CuKα rays, only two peaks appear in the diffraction angle 2θ range of 40° to 50°. In the case of natural graphite, it is said that a total of four peaks appear in the diffraction angle 2θ range of 40° to 50°: two peaks originating from the hexagonal crystal system structure and two peaks originating from the rhombohedral crystal system structure. In contrast, in the case of artificial graphite, it is generally said that only two peaks originating from the hexagonal crystal system structure appear. X-ray diffraction measurements of carbon-based active materials are performed on the carbon-based active material before charging and discharging, or, in the case of carbon-based active materials contained in the negative electrode of a non-aqueous electrolyte energy storage element, on a material treated using the same procedure as for measuring the silicon oxide content in the negative electrode active material. X-ray diffraction measurements of carbon-based active materials are performed by powder X-ray diffraction measurement using an X-ray diffractometer (Rigaku "MiniFlex II"), with the radiation source being CuKα rays, the tube voltage being 30kV, and the tube current being 15mA. At this time, the diffracted X-rays pass through a 30μm 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 diverging slit width is 0.625°, the receiving slit width is 13mm (OPEN), and the scattering slit width is 8mm. Furthermore, the Kα2 line is removed from the CuKα line, and an X-ray diffraction pattern based on the Kα1 line is obtained.

[0030] [5] In the non-aqueous electrolyte energy storage element according to any one of [1] to [4] above, the negative electrode comprises a negative electrode active material layer having the negative electrode active material, and the mass per unit area of ​​one layer of the negative electrode active material layer is 2 [mg / cm²]. ２ This is also acceptable.

[0031] The non-aqueous electrolyte energy storage element described in [5] above can increase the discharge capacity, etc. Furthermore, if the mass per unit area of ​​one negative electrode active material layer is large, cracks in the negative electrode active material layer are likely to occur due to the large expansion and contraction of the silicon-based active material. However, as described above, in the present invention, cracks in the silicon-based active material particles are less likely to occur, so by having a large mass per unit area of ​​one negative electrode active material layer, it is possible to achieve both a large discharge capacity and an improved capacity retention rate in charge-discharge cycles.

[0032] A non-aqueous electrolyte energy storage element, a method for manufacturing a non-aqueous electrolyte energy storage element, an energy storage device, and other embodiments according to one embodiment of the present invention will be described in detail below.

[0033] <Non-aqueous electrolyte energy storage element> A non-aqueous electrolyte energy storage element according to one embodiment of the present invention comprises a positive electrode, a negative electrode, a non-aqueous electrolyte, and a container for housing them. The non-aqueous electrolyte energy storage element may further include a separator interposed between the positive electrode and the negative electrode to electrically insulate them. The positive electrode, the negative electrode, and any separator typically constitute an electrode body. At least a portion of the non-aqueous electrolyte is usually present in a state of being impregnated into the electrode body. The non-aqueous electrolyte energy storage element according to one embodiment of the present invention may further include other components.

[0034] For example, the non-aqueous electrolyte energy storage element 1 shown in Figure 1, according to one embodiment of the present invention, comprises an electrode body 2, a non-aqueous electrolyte (not shown), and a rectangular parallelepiped container 3 that houses them. The non-aqueous electrolyte energy storage element 1 in Figure 1 further comprises 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 housed together with the electrode body 2, etc., inside the container 3. 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 body 2 is electrically connected to the positive electrode external terminal 5 via the positive electrode lead 4. The negative electrode constituting the electrode body 2 is electrically connected to the negative electrode external terminal 7 via the negative electrode lead 6.

[0035] The non-aqueous electrolyte storage element of the present invention may be a non-aqueous electrolyte secondary battery. Hereinafter, the main members and the like constituting the non-aqueous electrolyte storage element according to an embodiment of the present invention will be described in detail centering on the case where the non-aqueous electrolyte storage element is a non-aqueous electrolyte secondary battery (particularly a lithium ion secondary battery), but it is not intended to limit the application target of the present invention.

[0036] In addition, the lower limit value and the upper limit value of each numerical range described in the embodiments of the present invention can be arbitrarily combined (however, the upper limit is larger than the lower limit). Further, regarding the lower limit value and the upper limit value in the numerical range, it means that the numerical range includes the lower limit value and the upper limit value. That is, when the lower limit value is A, it means that it is A or more. Similarly, when the upper limit value is B, it means that it is B or less.

[0037] The positive electrode has a positive electrode substrate and a positive electrode active material layer laminated directly or via an intermediate layer on the positive electrode substrate. Usually, the positive electrode has a portion where the positive electrode substrate is exposed. The portion where the positive electrode substrate is exposed is usually connected to the above-described positive electrode lead. The positive electrode may have a shape such as a sheet shape, a plate shape, or a strip shape, for example.

[0038] The thickness of the positive electrode is appropriately set according to the use of the non-aqueous electrolyte storage element and the like. The average thickness of the positive electrode may be, for example, 3 μm or more and 1,000 μm or less. The lower limit of the average thickness of the positive electrode may be 5 μm, 10 μm, 20 μm, 30 μm, 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, 150 μm, 100 μm, or 50 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 or via an intermediate layer on the positive electrode substrate, and when 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 exist, it is the average thickness of the portion where the positive electrode active material layer is laminated on both sides of the positive electrode substrate. Further, in this specification, "average thickness" means the average value of the thicknesses measured at any five locations.

[0039] The positive electrode substrate has conductivity. In this specification, "having conductivity" means that the volume resistivity is 10 －２This means that the volume resistivity is Ω·cm or less. The volume resistivity shall be the value measured in accordance with JIS-H-0505 (1975). However, if it is difficult to adopt the measurement method in accordance with JIS-H-0505 (1975), such as when it is difficult to prepare a test specimen that conforms to the standard, then another measurement method that can obtain equivalent results shall be used as a substitute. In this specification, "not conductive" or "having (electrical) insulating properties" means that the above volume resistivity is 10 ７ This means it is greater than or equal to Ω·cm.

[0040] Examples of materials for the positive electrode substrate include metals such as aluminum, titanium, iron, and their alloys (stainless steel, etc.). Among these, aluminum or aluminum alloys are preferred from the viewpoint of high potential resistance, high electronic conductivity, and cost.

[0041] The positive electrode substrate has a shape such as a sheet, plate, or strip. Examples of positive electrode substrate forms include foil, vapor-deposited film, mesh, and porous material, with foil being preferred. The positive electrode substrate may also be, for example, aluminum foil or aluminum alloy foil.

[0042] The average thickness of the positive electrode substrate may be, for example, 1 μm or more and 50 μm or less. The lower limit of the average thickness of the positive electrode substrate may be 3 μm, 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, 15 μm, or 10 μm.

[0043] The intermediate layer is a layer placed between the positive electrode substrate and the positive electrode active material layer. The intermediate layer includes, 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 conductive agents and binders used in the intermediate layer are the same as those used in the positive electrode active material layer, which will be described later.

[0044] The positive electrode active material layer contains a positive electrode active material. The positive electrode active material layer may optionally contain conductive agents, binders, thickeners, fillers, and other optional components. The positive electrode active material layer may be formed from a positive electrode mixture containing the positive electrode active material and other optional components. The positive electrode active material layer may be provided on only one side of a positive electrode substrate having a shape such as a sheet, or on both sides.

[0045] For the positive electrode active material, known positive electrode active materials can be used. For lithium-ion secondary batteries, materials capable of intercalating and releasing lithium ions are typically used. Examples of positive electrode active materials include lithium transition metal composite oxides, polyanion compounds, chalcogen compounds, sulfur-based materials, and lithium oxide. One or more positive electrode active materials can be used.

[0046] Examples of transition metal elements included in lithium transition metal composite oxides include nickel, cobalt, and manganese. Lithium transition metal composite oxides may also contain typical metal elements such as aluminum. An example of a lithium transition metal composite oxide is α-NaFeO ２ Examples include lithium transition metal composite oxides having a type crystal structure and lithium transition metal composite oxides having a spinel-type crystal structure.

[0047] α-NaFeO ２ Examples of lithium transition metal composite oxides having a type crystal structure include those represented by formula (i), which will be described later.

[0048] Li is a lithium transition metal composite oxide having a spinel-type crystal structure. α Mb β O ４ X γExamples include those expressed as follows: (Mb is a metallic element or metalloid element other than lithium, and is at least one transition metal element. X is at least one element other than lithium, Mb, and oxygen. 0.90 ≤ α ≤ 1.33, 0 ≤ γ ≤ 1. β is a value determined according to the valencies of α, γ, Mb and X, and 1.5 ≤ β ≤ 2.5.) Mb preferably contains Mn. The Mn content relative to Mb (Mn / Mb) is preferably 50 mol% or more, and more preferably 80 mol% or more.

[0049] A polyanionic compound is a compound composed of a polyanion (i.e., a polyvalent oxo acid anion) and a cation. Preferably, the polyanionic compound contains lithium cations and transition metal cations as cations. Examples of polyanionic compounds include Li α Mc β (AO γ ) δ X ε (A is at least one element selected from the group consisting of boron, aluminum, silicon, phosphorus, sulfur, chlorine, titanium, vanadium, chromium, molybdenum, and tungsten. Mc is a metallic or metalloid element that is neither lithium nor an element selected as A, and is at least one transition metal element. X is at least one element other than lithium, Mc, A, and oxygen. 0.5 ≤ α ≤ 3, 0 < β ≤ 2, 2 ≤ γ ≤ 4, 1 ≤ δ ≤ 3, 0 ≤ ε ≤ 1.) Examples include those expressed as follows. Specifically, for example, LiFePO ４ LiMnPO ４ LiMn ｘ Fe １－ｘ PO ４ (0<x<1), LiNiPO ４ LiCoPO ４ Li ３ V ２ (PO ４ ) ３ Li ２ MnSiO ４ Li ２ CoPO ４ F, Li ２ FeP ２ O７ Li ２ MnP ２ O ７ Li ２ CoP ２ O ７ LiVP ２ O ７ These are some examples. The surface of the polyanionic compound particles may be coated with other materials (for example, carbon materials as described later).

[0050] Examples of chalcogen compounds include titanium disulfide, molybdenum disulfide, and molybdenum dioxide.

[0051] Examples of sulfur-based materials include elemental sulfur, metal sulfides such as lithium sulfide, organic disulfide compounds, and organic sulfur compounds such as carbon sulfide compounds.

[0052] The atoms or polyanions in these materials, which are the positive electrode active materials, may be partially substituted with atoms or anions of other elements. These materials may also be coated on the surface with other materials.

[0053] A lithium transition metal composite oxide is preferred as the positive electrode active material, and α-NaFeO ２ A lithium transition metal composite oxide having a crystalline structure is more preferable. Furthermore, in the lithium transition metal composite oxide, the nickel content relative to all metal elements other than lithium is preferably 70 mol% or more, more preferably 75 mol% or more, and even more preferably 80 mol% or more. In the lithium transition metal composite oxide, the nickel content relative to all metal elements other than lithium may be 100 mol% or less, 90 mol% or less, or 85 mol% or less.

[0054] Lithium transition metal composite oxides are preferably compounds represented by the following formula (i): Li α Ma β O ２ X γ... (i) In equation (i), Ma is a metallic element or metalloid other than lithium, and is at least one transition metal element. X is at least one element other than lithium, Ma, and oxygen. 0.9 ≤ α ≤ 1.5 and 0 ≤ γ ≤ 1. β is a value determined by the valencies of α, γ, Ma, and X, and 0.5 ≤ β ≤ 1.5.

[0055] In formula (i), Ma preferably contains at least one of Ni, Co, and Mn, more preferably contains Ni, even more preferably contains Ni, Co, and Mn, and even more preferably is substantially composed of three elements: Ni, Co, and Mn. Ma may also contain other metallic elements. These other metallic elements may be transition metals or typical metallic elements.

[0056] In formula (i), the molar ratio of Ni to Ma (Ni / Ma) may be, for example, 0.5 or more and 1.0 or less, but is preferably 0.7 or more and 0.9 or less, and more preferably 0.75 or more and 0.85 or less.

[0057] In equation (i), the molar ratio of Co to Ma (Co / Ma) may be, for example, 0 or more and 0.3 or less, or 0.05 or more and 0.2 or less.

[0058] In equation (i), the molar ratio of Mn to Ma (Mn / Ma) may be, for example, 0 or more and 0.3 or less, or 0.05 or more and 0.2 or less.

[0059] In formula (i), the molar ratio of the total of Ni, Co, and Mn to Ma ((Ni + Co + Mn) / Ma) is preferably 0.9 or more and 1.0 or less, and more preferably 0.99 or more and 1.00 or less.

[0060] In formula (i), the upper limit of the molar ratio of Li to Ma (Li / Ma), i.e., α / β, is preferably 1.6, and may be more preferably 1.5, 1.4, 1.2, 1.1, or 1.05. The lower limit of the molar ratio (Li / Ma) is preferably 0.95, more preferably 1.0, and may be greater than 1.0.

[0061] By using a lithium transition metal composite oxide with the above composition, the initial irreversible capacity of the positive electrode is increased, making it easy to configure the non-aqueous electrolyte energy storage element with the positive electrode capacity limiting type described above. By adopting the positive electrode capacity limiting type configuration, the advantages of the present invention can be easily and significantly obtained.

[0062] The positive electrode active material is usually in particulate form. The average particle size of the positive electrode active material is preferably, for example, 0.1 μm or more and 20 μm or less. Setting the average particle size of the positive electrode active material above the lower limit facilitates the manufacture and handling of the positive electrode active material. Setting the average particle size of the positive electrode active material below the upper limit improves the electronic conductivity of the positive electrode active material layer. When a composite material of the positive electrode active material and other materials is used, the average particle size of the composite material is considered the average particle size of the positive electrode active material. "Average particle size" refers to the value (D50) at which the volume-based integrated distribution, calculated according to JIS-Z-8819-2 (2001), is 50%, based on the particle size distribution measured by laser diffraction / scattering on a dilution of particles diluted with a solvent, in accordance with JIS-Z-8825 (2013). For obtaining particles of the positive electrode active material and the negative electrode active material described later with predetermined particle sizes, known methods using, for example, pulverizers and classifiers can be employed.

[0063] The positive electrode active material preferably contains single-particle particles. Single-particle particles refer to particles in which the ratio of the average particle size to the average primary particle size is 3 or less. By using single-particle particles as the positive electrode active material, the initial irreversible capacity of the positive electrode is increased, making it easier to achieve the positive electrode capacity limiting configuration described above. The content of single-particle particles in the positive electrode active material is preferably 20% by mass or more and 100% by mass or less, and may be 40% by mass or more and 100% by mass or less.

[0064] The "average primary particle diameter" of the positive electrode active material is the average value of the primary particle diameters of any 50 primary particles constituting the positive electrode active material, as observed by a scanning electron microscope (SEM). Primary particles are particles in which no grain boundaries are observed externally in the SEM observation. The primary particle diameter of a primary particle is determined as follows: The shortest diameter passing through the center of the smallest circumscribed circle of the primary particle is defined as the minor diameter, and the diameter passing through the center and perpendicular to the minor diameter is defined as the major diameter. The average value of the major and minor diameters is defined as the particle diameter. If there are two or more shortest diameters, the longest perpendicular diameter is defined as the minor diameter. The "average particle size" of the positive electrode active material is a value obtained by measurement using the laser diffraction / scattering method described above. Furthermore, it has been confirmed that the average particle size based on the above measurements is in close agreement with the average secondary particle diameter, which is the average of the particle diameters of each particle (secondary particle) measured by extracting 50 particles from the SEM image of the particles, avoiding extremely large and extremely small particles. The particle diameter of each particle based on the measurement from this SEM image is determined as follows: The shortest diameter passing through the center of the smallest circumscribed circle of each particle is defined as the minor axis, and the diameter passing through the center and perpendicular to the minor axis is defined as the major axis. The average of the major axis and the minor axis is defined as the particle diameter of each particle. If there are two or more shortest diameters, the longest perpendicular diameter is defined as the minor axis.

[0065] The content of the positive electrode active material in the positive electrode active material layer is preferably 70% by mass or more and 99% by mass or less, and more preferably 70% by mass or more and 98% by mass or less. The lower limit of the content of the positive electrode active material in the positive electrode active material layer may be 80% by mass, or 90%, 95%, or 97% by mass. By setting the content of the positive electrode active material within the above range, it is possible to achieve both high energy density and manufacturability in the positive electrode active material layer.

[0066] Conductive agents are typically components made of conductive materials. Even if the volume resistivity of a conductive agent cannot be directly measured, the volume resistivity is 10 －２Materials whose conductivity is known to be Ω·cm or less are classified as conductive agents. Examples of conductive agents include carbon materials, metals, and conductive ceramics. A carbon material is a material whose main constituent element is carbon. The main constituent element is the element with the highest mass content. For example, the carbon content in a 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. It is preferable that the carbon material is a carbon material other than a non-carbonized polymer compound. Examples of carbon materials include graphite, non-graphitic carbon, and graphene-based carbon. Examples of non-graphitic carbon include carbon nanofibers, pitch-based carbon fibers, and carbon black. Examples of carbon black include furnace black, acetylene black, and Ketjen black. Examples of graphene-based carbon include graphene, carbon nanotubes (CNT), and fullerene. Conductive agents can take the form of powder or fibers. One or more types of conductive agents can be used. These materials may also be used as a composite of conductive agents. For example, a composite material of carbon black and CNTs may be used.

[0067] As the conductive agent, carbon materials are preferred, more preferably at least one of carbon black and CNTs is used, and even more preferably both carbon black and CNTs are used.

[0068] The content of the conductive agent in the positive electrode active material layer is preferably 0.1% by mass or more and 10% by mass or less, more preferably 1.0% by mass or more and 9% by mass or less, and even more preferably 1.2% by mass or more and 8% by mass or less. The upper limit of the conductive agent content may be 5% by mass, 4% by mass, 3% by mass, or 2% by mass. By setting the conductive agent content within the above range, it is possible to increase the energy density of the non-aqueous electrolyte energy storage element. The technology disclosed herein can also be implemented in a form in which the positive electrode active material layer does not contain a conductive agent.

[0069] Examples of binders include water-based binders and organic solvent-based binders.

[0070] A water-based binder is a binder that dissolves or disperses in water. A water-based binder may be one in mass or more that dissolves or disperses in 100 parts by mass of water at 20°C. When forming a positive electrode active material layer using a positive electrode mixture paste in which the dispersion medium is water or a mixed solvent mainly composed of water, a water-based binder (a water-soluble or water-dispersible polymer material) can be used. Examples of water-based binders include polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyacrylic acid, polymethacrylic acid, polytetrafluoroethylene, styrene-butadiene rubber, polyethylene, polypropylene, nitrile-butadiene rubber, and cellulose.

[0071] An organic solvent-based binder is a binder that dissolves or disperses in an organic solvent (e.g., N-methylpyrrolidone). An 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 forming a positive electrode active material layer using a positive electrode mixture paste in which the dispersion medium is an organic solvent or a mixed solvent mainly composed of an organic solvent, an organic solvent-based binder (a polymer material having solubility or dispersibility 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, and derivatives of chitosan.

[0072] 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 may be used.

[0073] The binder content 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 9% by mass or less, and even more preferably 0.8% by mass or more and 8% by mass or less. The upper limit of the binder content may be 5% by mass, 4% by mass, 3% by mass, or 2% by mass. By setting the binder content within the above range, the positive electrode active material can be stably maintained. The technology disclosed herein can also be implemented in a form in which the positive electrode active material layer does not contain a binder.

[0074] Examples of thickening agents include polysaccharide polymers such as carboxymethylcellulose and methylcellulose. If the thickening agent has a functional group that reacts with lithium, etc., this functional group may be deactivated beforehand by methylation or the like. The thickening agent may also function as a binder. One or more types of thickening agents can be used. When the positive electrode active material layer contains a thickening agent, the content of the thickening agent 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. The technology disclosed herein can also be carried out in a form in which the positive electrode active material layer does not contain a thickening agent.

[0075] 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 a component that is intentionally included. The filler may be included as a component that fills gaps in the positive electrode active material layer, or it may be included for other purposes. The filler may be an organic substance such as a polyolefin, or an inorganic substance such as an inorganic oxide, hydroxide, or carbonate. One or more types of fillers may be used. When the positive electrode active material layer contains a filler, the filler content in the positive electrode active material layer can be 0.1% by mass or more and 8% by mass or less, usually preferably 5% by mass or less, more preferably 2% by mass or less, and even more preferably 1% by mass or less. The technology disclosed herein can also be carried out in a form in which the positive electrode active material layer does not contain a filler.

[0076] The positive electrode active material layer may further contain other components besides the positive electrode active material, conductive agent, binder, thickener, and filler. These other components may include those unintentionally present in the positive electrode active material layer. Furthermore, the positive electrode active material layer may contain impurities unintentionally present as these other components, insofar as they achieve the effects of the present invention. The upper limit of the content of these other components in the positive electrode active material layer may be 10% by mass, or 5%, 2%, 1%, 0.1%, or 0.01% by mass. The upper limit of the content of unintentionally present components in the positive electrode active material layer may be 10% by mass, or 5%, 2%, 1%, 0.1%, or 0.01% by mass. The upper limit of the content of unintentionally present impurities in the positive electrode active material layer may be 10% by mass, or 5%, 2%, 1%, 0.1%, or 0.01% by mass.

[0077] For example, a lower limit for the mass per unit area in one positive electrode active material layer is 3 mg / cm². ２ Preferably, 6 mg / cm ２ More preferably, 10 mg / cm² ２ This is even more preferable. The upper limit for the mass per unit area in one positive electrode active material layer is 50 mg / cm². ２ Preferably, 30 mg / cm³ ２ More preferably, 20 mg / cm² ２ That is even more preferable.

[0078] 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 taking the apparent volume (volume including voids) of the positive (negative) electrode active material layer as V １ Let V be the sum of the actual volumes of each material constituting the positive (negative) electrode active material layer. ２ In that case, (1-V ２ / V １ It is calculated using the formula ) × 100. V is the sum of the actual volumes of each material constituting the positive (negative) electrode active material layer. ２This can be calculated from the content of each material in the positive (negative) electrode active material layer and the true density of each material.

[0079] (Method for Manufacturing the Positive Electrode) The positive electrode can be manufactured by known methods. The positive electrode can be manufactured, for example, by applying a paste-like positive electrode mixture (positive electrode mixture paste) directly to a positive electrode substrate or via an intermediate layer, and drying it to form a positive electrode active material layer. The positive electrode mixture paste usually contains positive electrode active material, other optional components, and a dispersion medium. After drying, the positive electrode active material layer may be pressed. From the viewpoint of making the non-aqueous electrolyte energy storage element according to one embodiment of the present invention a positive electrode capacity-limited type configuration, it may be preferable to press the positive electrode active material layer. That is, by applying a load to the positive electrode active material layer, the BET specific surface area of ​​the positive electrode active material layer tends to increase, and as a result, the contact area between the positive electrode active material and the non-aqueous electrolyte tends to increase during the first charge and discharge, so it is thought that the initial irreversible capacity per unit area of ​​the positive electrode will increase.

[0080] (Negative electrode) The negative electrode comprises a negative electrode substrate and a negative electrode active material layer laminated directly to the negative electrode substrate or via an intermediate layer. Typically, the negative electrode has a portion where the negative electrode substrate is exposed. This exposed portion of the negative electrode substrate is usually connected to the negative electrode lead described above. The negative electrode may have a shape such as a sheet, plate, or strip.

[0081] The thickness of the negative electrode is set appropriately according to the application of the non-aqueous electrolyte energy storage element. The average thickness of the negative electrode may be, for example, 3 μm or more and 1,000 μm or less. The lower limit of the average thickness of the negative electrode may be 4 μm, 5 μm, 10 μm, 20 μm, 30 μm, 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, 250 μm, 200 μm, 150 μm, 100 μm, or 50 μm. The average thickness of the negative electrode is the average thickness of the portion in which the negative electrode active material layer is laminated directly to the negative electrode substrate or via an intermediate layer. If there are portions in which the negative electrode active material layer is laminated on both sides of the negative electrode substrate and portions in which the negative electrode active material layer is laminated on only one side of the negative electrode substrate, then the average thickness of the portion in which the negative electrode active material layer is laminated on both sides of the negative electrode substrate shall be used.

[0082] The negative electrode substrate is electrically conductive. Examples of materials for the negative electrode substrate include metals such as copper, nickel, titanium, iron, and their alloys (such as stainless steel), as well as carbon materials. Among these, copper or copper alloys are preferred.

[0083] The negative electrode substrate has a shape such as a sheet, plate, or strip. Examples of negative electrode substrate forms include foil, vapor-deposited film, mesh, and porous material, with foil being preferred. The negative electrode substrate may also be, for example, copper foil or copper alloy foil.

[0084] The average thickness of the negative electrode substrate may be, for example, 1 μm or more and 35 μm or less. The lower limit of the average thickness of the negative electrode substrate may be 2 μm, 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, 10 μm, or 5 μm.

[0085] The configuration of the negative electrode intermediate layer is not particularly limited; for example, it can be selected from the configurations exemplified for the positive electrode intermediate layer.

[0086] The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer optionally contains optional components such as a conductive agent, binder, thickener, and filler. The optional components such as the conductive agent, binder, thickener, and filler can be selected from the materials exemplified above for the positive electrode. The negative electrode active material layer may be formed from a negative electrode mixture containing the negative electrode active material and other optional components. The negative electrode active material layer may be provided on only one side of a negative electrode substrate having a shape such as a sheet, or on both sides.

[0087] The negative electrode active material includes a silicon-based active material. Examples of silicon-based active materials include elemental silicon or compounds containing silicon. Examples of compounds containing silicon include silicon oxide (SiO₂). ｘ Examples of silicon-based active materials include silicon nitride, silicon carbide, and metallic silicon compounds (where x is 0 < x < 2, preferably 0.8 ≤ x ≤ 1.2). Examples of metallic silicon compounds include compounds containing silicon along with elements such as aluminum, tin, zinc, nickel, copper, titanium, vanadium, and magnesium. Other silicon-based active materials include SiO / Si / SiO２ It may be a composite material such as a composite material. The silicon-based active material may also be pre-doped. That is, for example, the silicon-based active material may further contain lithium. One or more silicon-based active materials can be used. Among the silicon-based active materials, silicon oxide, silicon carbide, or elemental silicon are preferred, and silicon oxide is more preferred.

[0088] The silicon-based active material is typically particulate. The average particle size of the silicon-based active material is preferably, for example, 0.1 μm to 20 μm.

[0089] The silicon-based active material may have its surface coated with a conductive material such as a carbonaceous material. By using a silicon-based active material in this form, the electronic conductivity of the negative electrode active material layer can be increased. When the silicon-based active material is in the form of particles or the like coated with a conductive material, the mass ratio of the conductive material to the total amount of the silicon-based active material and the conductive material coating it is preferably, for example, 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.

[0090] The lower limit of the silicon-based active material content in the negative electrode active material (the proportion of silicon-based active material in the total negative electrode active material) is preferably 1% by mass, more preferably 2% by mass, even more preferably 3% by mass, and even more preferably 4% by mass. By setting the silicon-based active material content to above the above lower limit, the discharge capacity of the non-aqueous electrolyte energy storage element can be increased. On the other hand, the upper limit of this content may be, for example, 100% by mass, but is preferably 30% by mass, more preferably 15% by mass, and even more preferably 10% by mass, 8% by mass, or 6% by mass. By setting the silicon-based active material content to below the above upper limit, the capacity retention rate in the charge-discharge cycle of the non-aqueous electrolyte energy storage element can be further increased.

[0091] The negative electrode active material preferably further contains a carbon-based active material. Examples of carbon-based active materials include graphite and non-graphitic carbon. The mass content of the carbon element in the carbon-based active 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.

[0092] "Non-graphite carbon" refers to the average lattice plane spacing (d) of the (002) plane, which is determined by X-ray diffraction before charging / discharging or during the discharge state. ００２ ) refers to carbon materials with a nautical index of 0.34 nm or more and 0.42 nm or less. Non-graphitic carbons include poorly graphitizable carbons and easily graphitizable carbons. "Potentially graphitizable carbon" refers to the above d ００２ This refers to carbon materials with a wavelength of 0.36 nm or more and 0.42 nm or less. "Easily graphitizable carbon" refers to the above d ００２ This refers to carbon materials with a nautical radius of 0.34 nm or more and less than 0.36 nm.

[0093] As the carbon-based active material, graphite is preferred, and artificial graphite is more preferred. By using such a carbon-based active material together with the silicon-based active material, the initial irreversible capacity of the negative electrode is reduced, making it easier to achieve the positive electrode capacity limiting configuration described above. The graphite may have its surface coated with other materials such as non-graphitic carbon. The average particle size of the graphite can be, for example, 1 μm to 100 μm.

[0094] The lower limit of the carbon-based active material content in the negative electrode active material may be, for example, 1% by mass, but 70% by mass is preferred, 85% by mass is more preferred, and 92% by mass is even more preferred. By setting the carbon-based active material content to be above the above lower limit, the capacity retention rate in the charge-discharge cycle of the non-aqueous electrolyte energy storage element can be further increased. On the other hand, the upper limit of this content is preferably 99% by mass, more preferably 98% by mass, and even more preferably 96% by mass. By setting the carbon-based active material content to be below the above upper limit, the discharge capacity of the non-aqueous electrolyte energy storage element can be increased.

[0095] When the negative electrode active material contains both a silicon-based active material and a carbon-based active material, the lower limit of the silicon-based active material content relative to the total content of the silicon-based active material and the carbon-based active material is preferably 1% by mass, more preferably 2% by mass, even more preferably 3% by mass, and even more preferably 4% by mass. By setting the silicon-based active material content to be above the above lower limit, the discharge capacity of the non-aqueous electrolyte energy storage element can be increased. On the other hand, the upper limit of this content may be, for example, 99% by mass, but is preferably 30% by mass, more preferably 15% by mass, and even more preferably 8% by mass. By setting the silicon-based active material content to be below the above upper limit, the capacity retention rate in the charge-discharge cycle of the non-aqueous electrolyte energy storage element can be further increased.

[0096] The negative electrode active material may further contain known negative electrode active materials commonly used in lithium-ion secondary batteries, etc., other than silicon-based and carbon-based active materials. However, the lower limit of the total content of silicon-based and carbon-based active materials relative to the negative electrode active material is preferably 90% by mass, and more preferably 99% by mass. On the other hand, the upper limit of this total content may be 100% by mass. Thus, by using only silicon-based active materials, or only silicon-based and carbon-based active materials, as the negative electrode active material, the effects of the present invention are more fully realized.

[0097] The content of the negative electrode active material in the negative electrode active material layer is preferably, for example, 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. The lower limit of the content of the negative electrode active material in the negative electrode active material layer may be 95% by mass, 96% by mass or 97% by mass. By setting the content of the negative electrode active material within the above range, it is possible to achieve both high energy density and manufacturability in the negative electrode active material layer.

[0098] 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, 2% by mass or less, or 1% by mass or less. The technology disclosed herein can also be carried out in a form in which the negative electrode active material layer does not contain a conductive agent.

[0099] When the negative electrode active material layer contains a binder, the binder content 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 binder content in the negative electrode active material layer may be 5% by mass or less, or 2% by mass or less. The technology disclosed herein can also be carried out in a form in which the negative electrode active material layer does not contain a binder.

[0100] When the negative electrode active material layer contains a thickening agent, the content of the thickening agent 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 thickening agent in the negative electrode active material layer may be 5% by mass or less, 2% by mass or less, or 1% by mass or less. The technology disclosed herein can also be carried out in a form in which the negative electrode active material layer does not contain a thickening agent.

[0101] The filler in the negative electrode active material layer is a component other than the negative electrode active material, conductive agent, binder, and thickener, and may be a component that is intentionally included. The filler may be included as a component that fills gaps in the negative electrode active material layer, or it may be included for other purposes. When the negative electrode active material layer contains a filler, the filler content in the negative electrode active material layer can be 0.1% by mass or more and 8% by mass or less, usually 5% by mass or less is preferred, 2% by mass or less is more preferred, and 1% by mass or less is even more preferred. The technology disclosed herein can also be carried out in a form in which the negative electrode active material layer does not contain a filler.

[0102] The negative electrode active material layer may further contain other components besides the negative electrode active material, conductive agent, binder, thickener, and filler. These other components may include those unintentionally present in the negative electrode active material layer. Furthermore, the negative electrode active material layer may contain impurities unintentionally present as these other components, insofar as they achieve the effects of the present invention. The upper limit of the content of these other components in the negative electrode active material layer may be 10% by mass, or 5%, 2%, 1%, 0.1%, or 0.01% by mass. The upper limit of the content of unintentionally present components in the negative electrode active material layer may be 10% by mass, or 5%, 2%, 1%, 0.1%, or 0.01% by mass. The upper limit of the content of unintentionally present impurities in the negative electrode active material layer may be 10% by mass, or 5%, 2%, 1%, 0.1%, or 0.01% by mass.

[0103] The lower limit of the mass per unit area in one negative electrode active material layer is 2 mg / cm². ２ Preferably, 5 mg / cm ２ More preferably, 7 mg / cm ２ This is even more preferable. By having the mass per unit area of ​​one negative electrode active material layer be greater than or equal to the above lower limit, the discharge capacity of the non-aqueous electrolyte energy storage element can be increased. The upper limit for the mass per unit area of ​​one negative electrode active material layer is 30 mg / cm². ２ Preferably, 20 mg / cm³ ２ More preferably, 10 mg / cm² ２ That is even more preferable.

[0104] The porosity of the negative electrode active material layer may be, for example, 30% to 70%. 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%.

[0105] (Method for Manufacturing the Negative Electrode) The negative electrode can be manufactured by known methods. The negative electrode can be manufactured, for example, in the same way as the method for manufacturing the positive electrode described above, by applying a paste-like negative electrode mixture (negative electrode mixture paste) directly to the negative electrode substrate or via an intermediate layer, and drying it to form a negative electrode active material layer. After drying, the negative electrode active material layer may be pressed or otherwise subjected to the process. If the negative electrode active material is a metal such as metallic lithium, it can also be manufactured by laminating metal foil directly to the negative electrode substrate or via an intermediate layer, and then pressing it (e.g., roll rolling).

[0106] (Position of the peak maximum of the dQ / dV curve) In a non-aqueous electrolyte energy storage element according to one embodiment of the present invention, the dQ / dV curve, with V on the horizontal axis and dQ / dV on the vertical axis, which is based on the change in the voltage V (terminal voltage V) between the negative electrode and the positive electrode and the amount of discharged electricity Q during the discharge process, has a peak originating from the discharge of the silicon-based active material. The upper limit of the voltage V at the position of the peak maximum is 3.39 [V], preferably 3.38 [V], more preferably 3.37 [V], and may also be 3.36 [V]. When the voltage V at the position of the peak maximum is below the upper limit, the negative electrode potential becomes low in the vicinity of reaching the discharge state during discharge, suppressing cracking and electrical isolation of silicon-based active material particles during the charge-discharge cycle, and as a result, the capacity retention rate during the charge-discharge cycle is increased. The lower limit of the voltage V at the position of the peak maxima described above is not particularly limited, but may be, for example, 2.80 [V], 2.90 [V], 3.00 [V], 3.10 [V], 3.20 [V], or 3.30 [V].

[0107] A method for adjusting the voltage V at the peak of the above-mentioned peak to 3.39 [V] or less is to adjust the initial irreversible capacitance Q per unit area of ​​the positive electrode. ＣＸ To increase the initial irreversible capacity Q per unit area of ​​the negative electrode ＡＸ One method is to appropriately combine methods to reduce the value. Per unit area of ​​the positive electrode refers to the value per unit area of ​​the positive electrode active material layer that contributes to charging and discharging while facing the negative electrode active material layer. Similarly, per unit area of ​​the negative electrode refers to the value per unit area of ​​the negative electrode active material layer that contributes to charging and discharging while facing the positive electrode active material layer.

[0108] The above Q ＣＸ and the above Q ＡＸ are calculated as follows. First, the difference (Q ＣＸ ) between the initial irreversible capacity per unit area of the positive electrode (Q ＡＸ ) and the initial irreversible capacity per unit area of the negative electrode (Q ＣＸ - Q ＡＸ ) is obtained. For the test battery A described in the above " (1) Confirmation of components in the negative electrode active material", when constant current discharge is performed until the negative electrode active material reaches a fully discharged state, the amount of electricity per unit area of the negative electrode discharged is the initial irreversible capacity per unit area of the positive electrode (Q ＣＸ ) and the initial irreversible capacity per unit area of the negative electrode (Q ＡＸ ) difference (Q ＣＸ - Q ＡＸ ). Next, for the above test battery A, after performing constant current discharge until the negative electrode active material reaches a fully discharged state, it is disassembled, the negative electrode (working electrode) is taken out, the negative electrode active material layer with the negative electrode substrate removed is dissolved in aqua regia, and the lithium ion content in the dissolved components is measured by ion chromatography. From this lithium ion content and the area of the negative electrode (working electrode), the initial irreversible capacity per unit area of the negative electrode (Q ＡＸ ) is calculated. Also, from this Q ＡＸ and the above (Q ＣＸ - Q ＡＸ ), the initial irreversible capacity per unit area of the positive electrode (Q ＣＸ ) is calculated.

[0109] As a method for increasing the initial irreversible capacity Q ＣＸ per unit area of the positive electrode, as described above, using a lithium transition metal composite oxide as the positive electrode active material, increasing the nickel content in the lithium transition metal composite oxide, using single particle system particles as the positive electrode active material, pressing the positive electrode active material layer, using a positive electrode active material with a large particle size, using a lithium excess active material, etc., can be mentioned. The lithium excess active material refers to those in which 1.0 < α / β among the lithium transition metal composite compounds represented by the above formula (i). Also, when the mass of the positive electrode active material per unit area in one layer of the positive electrode active material layer is increased, the initial irreversible capacity Q ＣＸ per unit area of the positive electrode is also increased.increases.

[0110] As a method for reducing the initial irreversible capacity Q per unit area of the negative electrode, in addition to using a carbon-based active material together with a silicon-based active material as the negative electrode active material as described above, doping the negative electrode active material with lithium or the like in advance, reducing the specific surface area of the negative electrode active material layer, etc. can be mentioned. Also, when the mass of the negative electrode active material per unit area in one layer of the negative electrode active material layer is reduced, the initial irreversible capacity Q per unit area of the negative electrode ＡＸ also decreases. ＡＸ

[0111] In addition, by adjusting the composition of the non-aqueous electrolyte (for example, adjusting additives, etc.), the above Q ＣＸ and the above Q ＡＸ can also be adjusted.

[0112] (Specific Q ＣＸ / Q ＣＸ ＡＸ ) In the non-aqueous electrolyte storage element according to an embodiment of the present invention, the ratio Q ＡＸ of the initial irreversible capacity Q per unit area of the positive electrode to the initial irreversible capacity Q per unit area of the negative electrode ＡＸ is preferably at least 1.5, and may be 1.51 or 1.52. When the ratio Q ＣＸ is at least the above lower limit, the negative electrode potential becomes low in the vicinity of reaching the discharge state during discharge, and the capacity retention rate in the charge-discharge cycle increases. The upper limit of the ratio Q <0000n03> / Q ＡＸ may be, for example, 2.0, or may be 1.8, 1.6 or 1.55. ＣＸ ＡＸ ＣＸ ＡＸ ＣＸ ＡＸ ＡＸ (Separator) A known separator can be used as the separator. As the separator, for example, a separator composed only of a base material layer, a separator in which an inorganic layer containing inorganic particles and a binder is formed on one or both surfaces of the base material layer, etc. can be used. <00004c8>

[0113]

[0114] Examples of the substrate layer form of the separator 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 liquid retention of non-aqueous electrolytes. The material of the substrate layer of the separator is not particularly limited as long as it has insulating properties, but resins such as polyolefins (polyethylene, polypropylene, etc.), polyimide, and aramid are preferred.

[0115] 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; covalent crystals such as silicon; mineral resource-derived materials such as talc, zeolite, kaolin, bentonite, and mica, or their artificial counterparts. 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 inorganic particle content in the inorganic layer is preferably 50% to 99% by mass, and more preferably 80% to 98% by mass.

[0116] Examples of binders used in the inorganic layer include those similar to those exemplified in the positive electrode active material layer.

[0117] The porosity of the separator may be, for example, 20% or more and 80% or less. The lower limit of the separator's porosity may be 30%, 40%, or 50% from the viewpoint of discharge performance, etc. The upper limit of the separator's porosity may be 70%, 60%, or 50% from the viewpoint of strength, etc. In this specification, "porosity" refers to a volume-based value and means a measurement value obtained using a mercury porosimeter.

[0118] 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.

[0119] A polymer gel composed of a polymer and a non-aqueous electrolyte may be used as a separator. A polymer gel may also be used in combination with a porous resin film, nonwoven fabric, etc., as described above, as a separator.

[0120] (Electrode Body) As the electrode body, known structures such as wound electrode bodies and laminated electrode bodies can be used.

[0121] A wound electrode has a structure in which the positive electrode and negative electrode are wound together while being insulated. The wound electrode may be cylindrical or flattened. The electrode 2 of the non-aqueous electrolyte energy storage element 1 in Figure 1 is a flattened wound electrode. A wound electrode can be manufactured, for example, by the following procedure. First, a laminate is obtained by stacking a positive electrode, a separator, and a negative electrode, each formed in a strip shape. A wound electrode is obtained by winding this laminate.

[0122] A laminated electrode body 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 body can be obtained by stacking a positive electrode, a separator, and a negative electrode, each formed in a rectangular shape.

[0123] Other electrode structures can also be used, such as those in which at least one of the positive and negative electrodes is folded in a bellows-like manner and stacked.

[0124] (Non-aqueous electrolyte) Known non-aqueous electrolytes can be used as the non-aqueous electrolyte. A non-aqueous electrolyte is a medium that is responsible for transporting charge transport ions (e.g., lithium ions) between the positive electrode and the negative electrode, and which 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, 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. Non-aqueous electrolyte solutions and solid electrolytes may be used in combination. In one embodiment of the present invention, the non-aqueous electrolyte may be a non-aqueous electrolyte solution. That is, only a non-aqueous electrolyte solution may be used as the non-aqueous electrolyte. Furthermore, the non-aqueous electrolyte energy storage element may be a non-aqueous electrolyte energy storage element or a non-aqueous electrolyte secondary battery.

[0125] (Non-aqueous electrolyte) A non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in this non-aqueous solvent.

[0126] Any known non-aqueous solvent can be used. Examples of non-aqueous solvents include carbonates, esters, ethers, amides, and nitriles. Examples of carbonates include cyclic carbonates and linear carbonates. Examples of esters include carboxylic acid esters, phosphate esters, and sulfonic acid esters. As non-aqueous solvents, compounds in which some of the hydrogen atoms contained in these compounds are substituted with halogen atoms may also be used. One or more non-aqueous solvents can be used.

[0127] A cyclic carbonate is 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. A cyclic carbonate may be a saturated cyclic carbonate such as ethylene carbonate, or an unsaturated cyclic carbonate such as vinylene carbonate. "Saturated" means not having carbon-carbon unsaturated bonds (carbon-carbon double bonds and carbon-carbon triple bonds). "Unsaturated" means having carbon-carbon unsaturated bonds. As the cyclic carbonate, saturated cyclic carbonates are preferred, and ethylene carbonates are more preferred.

[0128] A chain-like carbonate refers to a carbonate that does not have a ring structure containing a carbonate group. Examples of chain-like carbonates include diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, diphenyl carbonate, trifluoroethyl methyl carbonate, and bis(trifluoroethyl) carbonate. The chain-like carbonate may be a saturated chain-like carbonate such as dimethyl carbonate, or an unsaturated chain-like carbonate such as diphenyl carbonate. A saturated chain-like carbonate is preferred as the chain-like carbonate, and ethyl methyl carbonate is more preferred.

[0129] The non-aqueous solvent preferably contains carbonate, and more preferably contains both cyclic carbonate and linear carbonate. The carbonate content in the non-aqueous solvent is preferably 80% to 100% by volume, may be 99% to 100% by volume, or 100% by volume. Using cyclic carbonate can promote the dissociation of the electrolyte salt and increase the ionic conductivity of the non-aqueous electrolyte. Using linear carbonate can keep the viscosity of the non-aqueous electrolyte low. When using both cyclic carbonate and linear carbonate, the volume ratio of cyclic carbonate to linear carbonate (cyclic carbonate: linear carbonate) is preferably in the range of 5:95 to 50:50.

[0130] An electrolyte salt is an ionic compound in which the cation is a charge transport ion and which is solid at room temperature (20°C) at 1 atmosphere. Known electrolyte salts can be used. Examples of electrolyte salts include lithium salts, sodium salts, potassium salts, magnesium salts, and onium salts. Among these, lithium salts are preferred. One or more electrolyte salts can be used.

[0131] LiPF is an example of a lithium salt. ６ LiPO ２ F ２ LiBF ４ LiClO ４ Inorganic lithium salts such as LiN(SO4) 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 ) and other imide salts, LiB(C ２ O ４ ) ２ LiBF ２ (C ２ O ４ ), LiPF２ (C ２ O ４ ) ２ Examples include lithium oxalate salts such as LiN(SO4). ２ F) ２ This also applies to inorganic lithium salts. Among these, inorganic lithium salts are preferred, and LiPF ６ This is more preferable. In some cases, an imide salt may also be preferable.

[0132] The electrolyte salt content in the non-aqueous electrolyte is 0.1 mol / dm³ at 20°C and 1 atm. ３ 2.5mol / dm or more ３ The following is preferred: 0.3 mol / dm ３ 2.0mol / dm or more ３ The following is more preferable: 0.5 mol / dm ３ More than 1.7mol / dm ３ The following is even more preferable: 0.7 mol / dm ３ 1.5mol / dm or more ３ The following is particularly preferable. By setting the electrolyte salt content within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

[0133] The non-aqueous electrolyte may contain additives in addition to the non-aqueous solvent and electrolyte salt. One or more types of additives may be used. When additives are used in the non-aqueous electrolyte, the additive content in the non-aqueous electrolyte is preferably 0.01% to 10% by mass, more preferably 0.1% to 7% by mass, even more preferably 0.2% to 5% by mass, and particularly preferably 0.3% to 3% by mass. By adjusting the type and content of the additives, the initial irreversible capacity Q per unit area of ​​the negative electrode of the non-aqueous electrolyte energy storage element can be adjusted. ＡＸ and the initial irreversible capacitance Q per unit area of ​​the positive electrode ＣＸ It can be adjusted.

[0134] (Solid Electrolyte) The solid electrolyte can be selected from any material that has ionic conductivity, such as lithium, sodium, and calcium, and is solid at room temperature (20°C). Examples of solid electrolytes 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.

[0135] (Container) The container houses the electrode body and non-aqueous electrolyte in its internal space. The container material can be a metal material such as aluminum or stainless steel, or a resin material, with metal materials being preferred from the viewpoint of strength, etc. A composite material of metal and resin materials can also be used.

[0136] The shape of the container is not particularly limited, but it can be cylindrical, rectangular (square), disc-shaped, etc. The container may also be in the form of a sheet or other shape formed from a metal-resin composite film.

[0137] (Shape and application of non-aqueous electrolyte energy storage element) The shape of the non-aqueous electrolyte energy storage element according to one embodiment of the present invention is not particularly limited. The non-aqueous electrolyte energy storage element may be, for example, a cylindrical battery, a prismatic battery, a flat battery, a coin cell battery, a button cell battery, etc.

[0138] The applications of the non-aqueous electrolyte energy storage element according to one embodiment of the present invention are not particularly limited. The non-aqueous electrolyte energy storage element can be used, for example, as a power source for automobiles such as electric vehicles, hybrid vehicles, and plug-in hybrid vehicles, as a power source for electronic devices such as personal computers and communication terminals, and as a power storage power source.

[0139] The non-aqueous electrolyte energy storage element of the present invention can be used individually or in combination. The non-aqueous electrolyte energy storage element may be used individually when the required output and voltage are small. On the other hand, when at least one of the required output and voltage is large, the non-aqueous electrolyte energy storage element may be used as part of an energy storage device combined with other non-aqueous electrolyte energy storage elements. In an energy storage device composed of multiple non-aqueous electrolyte energy storage elements, at least one of the non-aqueous electrolyte energy storage elements included in the energy storage device may be a non-aqueous electrolyte energy storage element according to one embodiment of the present invention. The energy storage device will be described in detail later.

[0140] In the non-aqueous electrolyte energy storage element according to one embodiment of the present invention, the container may be restrained to maintain a certain thickness, or it may not be restrained in such a way. Alternatively, the container may be restrained to have a certain load applied to it. When the container is restrained, expansion of the container due to charge-discharge cycles, etc., may be suppressed, and a decrease in charge-discharge performance may be suppressed. When the container is restrained, the electrode body inside the container may or may not have a load applied to it. For example, the non-aqueous electrolyte energy storage element or energy storage device may be provided with a restraining member that performs such restraint.

[0141] <Method for Manufacturing a Non-Aqueous Electrolyte Energy Storage Element> A non-aqueous electrolyte energy storage element according to one embodiment of the present invention can be manufactured by a known method. The method for manufacturing the non-aqueous electrolyte energy storage element includes, for example, preparing a positive electrode, preparing a negative electrode, preparing a non-aqueous electrolyte, and housing the positive electrode, negative electrode, and non-aqueous electrolyte in a container. The manufacturing method may also include preparing a separator, and manufacturing an electrode body using the positive electrode, negative electrode, and separator. Housing the positive electrode, negative electrode, and non-aqueous electrolyte in a container may be equivalent to housing the electrode body and non-aqueous electrolyte in a container.

[0142] Preparing the positive electrode may also mean manufacturing the positive electrode. The positive electrode can be manufactured by the method described above. Preparing the negative electrode may also mean manufacturing the negative electrode. The negative electrode can be manufactured by the method described above. Preparing the non-aqueous electrolyte may also mean preparing the 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 purchase or other means.

[0143] The electrode bodies (or positive and negative electrodes) and the non-aqueous electrolyte can be housed in a container by known methods. If the non-aqueous electrolyte is a non-aqueous electrolyte solution, for example, the electrode bodies (or positive and negative electrodes) can be housed in the container first, and then the non-aqueous electrolyte solution can be injected through an inlet provided in the container. The inlet can be sealed after the non-aqueous electrolyte solution has been injected.

[0144] The method for manufacturing the non-aqueous electrolyte energy storage element may further include initial charging and discharging of the assembled uncharged / discharged energy storage element.

[0145] <Energy Storage Device> The energy storage device 30 in Figure 2 comprises a plurality of energy storage units 20. Each energy storage unit 20 comprises a plurality of electrically connected non-aqueous electrolyte energy storage elements 1. The energy storage device 30 may also include busbars (not shown) for electrically connecting the plurality of non-aqueous electrolyte energy storage elements 1, busbars (not shown) for electrically connecting the plurality of energy storage units 20, etc. The energy storage unit 20 or the energy storage device 30 may also include a condition monitoring device (not shown) for monitoring the state of one or more non-aqueous electrolyte energy storage elements 1.

[0146] <Other Embodiments> The non-aqueous electrolyte energy storage element of the present invention is not limited to the embodiments described above, and various modifications may be made without departing from the spirit of the present invention. For example, the configuration of one embodiment may be added to the configuration of another embodiment, and a part of the configuration of one embodiment may be replaced with the configuration of another embodiment or with well-known technology. Furthermore, a part of the configuration of one embodiment may be deleted. Also, well-known technology may be added to the configuration of one embodiment.

[0147] In the above embodiment, a case in which a non-aqueous electrolyte energy storage element is used as a rechargeable non-aqueous electrolyte secondary battery was described, but the type, shape, dimensions, capacity, etc. of the non-aqueous electrolyte energy storage element are arbitrary. The present invention can also be applied to various secondary batteries, electric double-layer capacitors, lithium-ion capacitors, and other capacitors.

[0148] In the above embodiment, an electrode body in which a separator is interposed between the positive electrode and the negative electrode was described, but the electrode body does not need to have 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 either the positive electrode or the negative electrode. Thus, the positive electrode and the negative electrode may further have layers other than the base material, intermediate layer, and active material layer. Furthermore, the positive electrode and the negative electrode do not need to have a layered structure.

[0149] 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.

[0150] [Example 1] (Preparation of positive electrode) As the positive electrode active material, a mixture of single-particle system particles and particles other than single-particle system particles (secondary particles) was prepared using α-NaFeO ２ LiNi is a lithium transition metal composite oxide having a type crystal structure. ０．８ Co ０．１ Mn ０．１ O ２ (NCM811) was prepared. In Table 1, single-particle systems are referred to as "single particles," and particles other than single-particle systems (secondary particles) are referred to as "secondary particles." A positive electrode mixture paste was prepared containing the above positive electrode active material, carbon black (CB), and polyvinylidene fluoride (PVDF) in a mass ratio of 97.0:2.0:1.0 (on a solid basis), with N-methylpyrrolidone (NMP) as the dispersion medium. This positive electrode mixture paste was applied to a strip of aluminum foil as the positive electrode substrate and dried to remove the NMP. 1 cm ２ The amount of positive electrode mixture paste applied per unit area (mass per unit area in one positive electrode active material layer) is 15.4 mg / cm² in terms of solid content. ２ This was then compressed using a roller press to form the positive electrode active material layer, and then dried under reduced pressure to obtain the positive electrode. The initial irreversible capacity Q per unit area of ​​the obtained positive electrode was...ＣＸ It is 427 μAh / cm² ２ , initial discharge capacity (initial reversible capacity) Q ＣＹ It is 2990 μAh / cm² ２ It is known that...

[0151] (Fabrication of the negative electrode) A mixture of silicon-based and carbon-based active materials was prepared as the negative electrode active material. Silicon oxide was used as the silicon-based active material. Artificial graphite was used as the carbon-based active material. The silicon-based active material content in the negative electrode active material was set to 5% by mass. A negative electrode mixture paste was prepared containing the above negative electrode active material, styrene-butadiene rubber (SBR), and carboxymethylcellulose (CMC) in a mass ratio of 98.0:1.0:1.0 (on a solid content basis), with water as the dispersion medium. This negative electrode mixture paste was applied to a strip of copper foil as the negative electrode substrate and dried to remove the water. 1 cm ２ The amount of negative electrode mixture paste applied per unit area (mass per unit area in one negative electrode active material layer) is 8.93 mg / cm² in terms of solid content. ２ This was then compressed using a roller press to form the negative electrode active material layer, and then dried under reduced pressure to obtain the negative electrode. The initial irreversible capacity Q per unit area of ​​the obtained negative electrode was... ＡＸ It is 271 μAh / cm² ２ , initial discharge capacity (initial reversible capacity) Q ＡＹ It is 3579 μAh / cm² ２ It is known that...

[0152] (Preparation of non-aqueous electrolyte) A non-aqueous solvent is prepared by mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 30:35:35, to which lithium hexafluorophosphate (LiPF) is added as the electrolyte salt. ６ ) 1.0 mol / dm ３ A non-aqueous electrolyte was prepared by mixing the components to achieve the specified content.

[0153] (Fabrication of Non-Aqueous Electrolyte Energy Storage Element) A microporous polyolefin membrane with an inorganic layer formed on one side was prepared as a separator. An electrode body was fabricated by stacking the positive electrode and the negative electrode via this separator. The separator was positioned so that the side with the inorganic layer faced the positive electrode. This electrode body was placed in a rectangular container, the non-aqueous electrolyte was injected into it, and then the container was sealed.

[0154] (Initial Charge / Discharge) The obtained non-aqueous electrolyte energy storage element underwent three initial charge / discharge cycles at 25°C according to the following procedure. In the first cycle, constant current and constant voltage charging was performed with a charging current of 0.2C, a charging termination voltage of 4.18V, and a total charging time of 7 hours, followed by a 10-minute rest period. Subsequently, constant current discharge was performed with a discharge current of 0.2C and a discharge termination voltage of 2.75V, followed by a 10-minute rest period. Table 1 shows the position of the peak maximum originating from the discharge of the silicon-based active material in the dQ / dV curve of the non-aqueous electrolyte energy storage element during this discharge. Figure 3 shows the dQ / dV curve of the non-aqueous electrolyte energy storage element of Example 1. The arrows in Figure 3 indicate the position of the peak maximum originating from the discharge of the silicon-based active material. In the second and third cycles, constant current and constant voltage charging was performed with a charging current of 1C, a charging termination voltage of 4.18V, and a total charging time of 3 hours, followed by a 10-minute rest period. Subsequently, constant current discharge was performed with a discharge current of 1C and a discharge termination voltage of 2.75V, followed by a 10-minute rest period. The initial charge and discharge was performed using the above procedure. This resulted in obtaining the non-aqueous electrolyte energy storage element of Example 1. Table 1 shows the various measurements for the non-aqueous electrolyte energy storage element of Example 1.

[0155] [Example 2] As the positive electrode active material, α-NaFeO was prepared by mixing single-particle system particles and particles other than single-particle system particles (secondary particles) in a different ratio than in Example 1. ２ LiNi is a lithium transition metal composite oxide having a type crystal structure. ０．８ Co ０．１ Mn ０．１ O ２ A non-aqueous electrolyte energy storage element of Example 2 was obtained in the same manner as in Example 1, except that the necessary materials were prepared. The measured values ​​for each of the non-aqueous electrolyte energy storage elements of Example 2 are shown in Table 1.

[0156] [Comparative Example 1] (Preparation of the positive electrode) The positive electrode active material is a single-particle system, α-NaFeO ２ LiNi is a lithium transition metal composite oxide having a type crystal structure. ０．６ Co ０．２ Mn ０．２ O ２ (NCM622) was prepared. A positive electrode mixture paste was prepared containing the above positive electrode active material, CB, and PVDF in a mass ratio of 97.0:2.0:1.0 (on a solid basis), with NMP as the dispersion medium. This positive electrode mixture paste was applied to a strip of aluminum foil as the positive electrode substrate and dried to remove the NMP. 1 cm ２ The amount of positive electrode mixture paste applied per unit area (mass per unit area in one positive electrode active material layer) is 17.0 mg / cm² in terms of solid content. ２ This was then compressed using a roller press to form the positive electrode active material layer, and then dried under reduced pressure to obtain the positive electrode. The initial irreversible capacity Q per unit area of ​​the obtained positive electrode was... ＣＸ It is 383 μAh / cm² ２ , initial discharge capacity (initial reversible capacity) Q ＣＹ It is 3036 μAh / cm² ２ It is known that...

[0157] (Fabrication of the negative electrode) A mixture of silicon-based and carbon-based active materials was prepared as the negative electrode active material. Silicon oxide was used as the silicon-based active material. A mixture of natural graphite and artificial graphite in a mass ratio of 1:1 was used as the carbon-based active material. The silicon-based active material content in the negative electrode active material was set to 5% by mass. A negative electrode mixture paste was prepared containing the above negative electrode active material, SBR, and CMC in a mass ratio of 98.0:1.0:1.0 (on a solid content basis), with water as the dispersion medium. This negative electrode mixture paste was applied to a strip of copper foil as the negative electrode substrate and dried to remove the water. 1 cm ２ The amount of negative electrode mixture paste applied per unit area (mass per unit area in one negative electrode active material layer) is 8.80 mg / cm² in terms of solid content. ２ This was then compressed using a roller press to form the negative electrode active material layer, and then dried under reduced pressure to obtain the negative electrode. The initial irreversible capacity Q per unit area of ​​the obtained negative electrode was... ＡＸ It is 318 μAh / cm² ２, initial discharge capacity (initial reversible capacity) Q ＡＹ It is 3540 μAh / cm² ２ It is known that...

[0158] (Preparation of non-aqueous electrolyte) A non-aqueous electrolyte was prepared in the same manner as in Example 1.

[0159] (Fabrication of Non-Aqueous Electrolyte Energy Storage Element) A microporous polyolefin membrane with an inorganic layer formed on one side was prepared as a separator. An electrode body was fabricated by stacking the positive electrode and the negative electrode via this separator. The separator was positioned so that the side with the inorganic layer faced the positive electrode. This electrode body was placed in a rectangular container, the non-aqueous electrolyte was injected into it, and then the container was sealed.

[0160] (Initial Charge / Discharge) The obtained non-aqueous electrolyte energy storage element underwent three initial charge / discharge cycles at 25°C according to the following procedure. In the first cycle, constant current and constant voltage charging was performed with a charging current of 0.2C, a charging termination voltage of 4.25V, and a total charging time of 7 hours, followed by a 10-minute rest period. Subsequently, constant current discharge was performed with a discharge current of 0.2C and a discharge termination voltage of 2.75V, followed by a 10-minute rest period. Table 1 shows the position of the peak maximum originating from the discharge of the silicon-based active material in the dQ / dV curve of the non-aqueous electrolyte energy storage element during this discharge. Figure 4 shows the dQ / dV curve of the non-aqueous electrolyte energy storage element of Comparative Example 1. The arrows in Figure 4 indicate the position of the peak maximum originating from the discharge of the silicon-based active material. In the second and third cycles, constant current and constant voltage charging was performed with a charging current of 1C, a charging termination voltage of 4.25V, and a total charging time of 3 hours, followed by a 10-minute rest period. Subsequently, constant current discharge was performed with a discharge current of 1C and a discharge termination voltage of 2.75V, followed by a 10-minute rest period. The initial charge and discharge were performed using the above procedure. This yielded the non-aqueous electrolyte energy storage element of Comparative Example 1. Table 1 shows the various measurements for the non-aqueous electrolyte energy storage element of Comparative Example 1.

[0161] [Comparative Example 2] A mixture of silicon-based active material and carbon-based active material was prepared as the negative electrode active material. Silicon oxide was used as the silicon-based active material. Artificial graphite was used as the carbon-based active material. The content of the silicon-based active material in the negative electrode active material was 5% by mass. The above negative electrode active material was used, and 1 cm ２ The amount of negative electrode mixture paste applied per unit area (mass per unit area in one negative electrode active material layer) is 8.93 mg / cm² in terms of solid content. ２ A non-aqueous electrolyte energy storage element of Comparative Example 2 was obtained in the same manner as in Comparative Example 1, except for the aforementioned difference. The measured values ​​for each of the non-aqueous electrolyte energy storage elements of Comparative Example 2 are shown in Table 1.

[0162] [Evaluation] (Capacity retention rate in charge-discharge cycles) Charge-discharge cycle tests were performed on each of the non-aqueous electrolyte energy storage elements obtained in the examples and comparative examples in the following manner. Constant current and constant voltage charging was performed in a constant temperature bath at 45°C with a charging current of 1.0C, a charging termination voltage of 4.18V (4.33V for each of the non-aqueous electrolyte energy storage elements in the comparative examples), and a total charging time of 3 hours, followed by a 10-minute rest period. Then, constant current discharge was performed with a discharge current of 1.0C and a discharge termination voltage of 2.75V, followed by a 10-minute rest period. This charge-discharge cycle was performed 1000 times. The capacity retention rate in charge-discharge cycles was calculated as the percentage of the discharge capacity at the 1000th cycle to the discharge capacity at the 1st cycle in this charge-discharge cycle test. The results are shown in Table 1.

[0163]

[0164] As shown in Table 1, in each of the non-aqueous electrolyte energy storage elements in Examples 1 and 2, where the maximum peak originating from the discharge of the silicon-based active material in the dQ / dV curve is in the range of 3.39 [V] or less, the capacity retention rate exceeded 90%, indicating a high capacity retention rate during charge-discharge cycles.

[0165] This invention can be applied to non-aqueous electrolyte energy storage elements used as power sources for electronic devices such as personal computers and communication terminals, as well as automobiles and the like.

[0166] 1. Non-aqueous 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 non-aqueous electrolyte energy storage element comprising a negative electrode having a negative electrode active material containing a silicon-based active material, and a positive electrode, wherein in a dQ / dV curve with V on the horizontal axis and dQ / dV on the vertical axis, based on the changes in voltage V and discharge amount Q between the negative electrode and the positive electrode during the discharge process, the maximum peak originating from the discharge of the silicon-based active material is located in the range of 3.39 [V] or less.

2. The non-aqueous electrolyte energy storage element according to claim 1, wherein the silicon-based active material is silicon oxide, silicon carbide, or elemental silicon.

3. The non-aqueous electrolyte energy storage element according to claim 1 or claim 2, wherein the negative electrode active material further comprises a carbon-based active material.

4. The non-aqueous electrolyte energy storage element according to claim 3, wherein the positive electrode has a positive electrode active material comprising a lithium transition metal composite oxide in which the nickel element content relative to all metal elements other than lithium is 70 mol% or more, and the carbon-based active material comprises artificial graphite.

5. The negative electrode comprises a negative electrode active material layer having the negative electrode active material, and the mass per unit area of ​​one layer of the negative electrode active material layer is 2 [mg / cm²]. ２ The non-aqueous electrolyte energy storage element according to claim 1 or claim 2, which is as described above.

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