Negative electrode for non-aqueous electrolyte storage element and non-aqueous electrolyte storage element

Abstract

To provide a negative electrode for a non-aqueous electrolyte storage element that can achieve both a low internal resistance (DC resistance) and a high capacity retention rate after charge / discharge cycles for the non-aqueous electrolyte storage element, and a non-aqueous electrolyte storage element that achieves both a low internal resistance (DC resistance) and a high capacity retention rate after charge / discharge cycles.SOLUTION: A negative electrode for a non-aqueous electrolyte storage element according to an embodiment of the present invention includes a negative electrode active material layer containing a carbon-based active material, a cellulose derivative, and a layered silicate, and the content of the cellulose derivative in the negative electrode active material layer is less than 0.8 mass%.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a negative electrode for a non-aqueous electrolyte storage element and a non-aqueous electrolyte storage element.

Background Art

[0002] Non-aqueous electrolyte secondary batteries typified by lithium-ion secondary batteries are widely used in electronic devices such as personal computers and communication terminals, and automobiles because of their high energy density. As non-aqueous electrolyte storage elements other than non-aqueous electrolyte secondary batteries, capacitors such as lithium-ion capacitors and electric double layer capacitors are also widely popular.

[0003] As a non-aqueous electrolyte storage element, those having an electrode body in which a positive electrode containing a positive electrode active material and a negative electrode containing a negative electrode active material are laminated via a separator are common. Such an electrode body is housed in a container together with a non-aqueous electrolyte to constitute a non-aqueous electrolyte storage element. As the negative electrode active material, carbon-based active materials such as graphite are widely used. Further, a cellulose derivative such as carboxymethyl cellulose may be used as a thickener together with the carbon-based active material in the negative electrode (see Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] As the performance of a non-aqueous electrolyte storage element, it is required that the internal resistance (DC resistance) is low, the capacity retention rate after charge and discharge cycles is high, and the like.

[0006] An object of the present invention is to provide a negative electrode for a non-aqueous electrolyte storage element that can achieve both a low internal resistance (DC resistance) of the non-aqueous electrolyte storage element and a high capacity retention rate after charge and discharge cycles, and a non-aqueous electrolyte storage element in which a low internal resistance (DC resistance) and a high capacity retention rate after charge and discharge cycles are compatible.

Means for Solving the Problems

[0007] The negative electrode for a non-aqueous electrolyte storage element according to one aspect of the present invention includes a negative electrode active material layer containing a carbon-based active material, a cellulose derivative, and a layered silicate, and the content of the cellulose derivative in the negative electrode active material layer is less than 0.8% by mass.

[0008] The non-aqueous electrolyte storage element according to one aspect of the present invention includes the negative electrode for a non-aqueous electrolyte storage element according to one aspect of the present invention.

Effects of the Invention

[0009] The negative electrode for a non-aqueous electrolyte storage element according to one aspect of the present invention can achieve both a low internal resistance (DC resistance) of the non-aqueous electrolyte storage element and a high capacity retention rate after charge and discharge cycles. The non-aqueous electrolyte storage element according to one aspect of the present invention has both a low internal resistance (DC resistance) and a high capacity retention rate after charge and discharge cycles.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0011] First, an overview of the negative electrode for a non-aqueous electrolyte storage element and the non-aqueous electrolyte storage element disclosed by this specification will be described.

[0012] [1] The negative electrode for a non-aqueous electrolyte storage element according to one aspect of the present invention includes a negative electrode active material layer containing a carbon-based active material, a cellulose derivative, and a layered silicate, and the content of the cellulose derivative in the negative electrode active material layer is less than 0.8% by mass.

[0013] The negative electrode for a non-aqueous electrolyte storage element described in the above [1] can achieve both a low internal resistance (DC resistance) of the non-aqueous electrolyte storage element and a high capacity retention rate after charge and discharge cycles. Although the reason for this is not clear, the following reasons are speculated. By reducing the content of the cellulose derivative contained in the negative electrode active material layer, the uncoated portion on the surface of the carbon-based active material by the cellulose derivative increases. As a result, the insertion and desorption of charge transport ions such as lithium ions on the surface of the carbon-based active material become easy, so that the internal resistance (DC resistance) can be lowered. Here, it is considered that the cellulose derivative exhibits a function as a binder in addition to its function as a thickener. Therefore, when the content of the cellulose derivative is reduced, the binding force between carbon-based active materials and the like decreases. In this case, due to the expansion and contraction of the carbon-based active material accompanying repeated charge and discharge, the electron conduction path is likely to be cut off, and the capacity retention rate after charge and discharge cycles tends to be low. On the other hand, the layered silicate has the property of cross-linking the cellulose derivative. Therefore, even when the content of the cellulose derivative is small, the presence of the layered silicate can increase the binding force between carbon-based active materials and the like, and can suppress the decrease in the capacity retention rate after charge and discharge cycles. Furthermore, due to the cross-linking of the cellulose derivative by the layered silicate, the covering of the surface of the carbon-based active material by the excess cellulose derivative is suppressed, so that the internal resistance (DC resistance) also becomes low. For these reasons, it is speculated that according to the negative electrode for a non-aqueous electrolyte storage element described in the above [1], both a low internal resistance (DC resistance) of the non-aqueous electrolyte storage element and a high capacity retention rate after charge and discharge cycles can be achieved.

[0014] The "carbon-based active material" refers to a carbon material that is a negative electrode active material. The carbon material refers to a material mainly composed of a carbon element. The main constituent element refers to the element with the highest content on a mass basis.

[0015] [2] In the negative electrode for a non-aqueous electrolyte storage element according to [1] above, the carbonaceous active material may contain natural graphite.

[0016] Natural graphite generally tends to have a lower resistance compared to artificial graphite and other carbonaceous active materials. Therefore, according to the negative electrode for a non-aqueous electrolyte storage element described in [2] above, the internal resistance (DC resistance) of the non-aqueous electrolyte storage element can be made lower.

[0017] "Graphite" refers to a carbon material (carbonaceous active material) having an average lattice plane spacing (d 002 ) of 0.33 nm or more and less than 0.34 nm as determined by X-ray diffraction method before charge-discharge or in the discharged state. Here, the "discharged state" of the carbon material means a state in which charge transport ions that can be occluded and released with charge-discharge are sufficiently released from the carbon material that is the negative electrode active material. For example, in a half-cell using a negative electrode containing a carbon material as the working electrode and metallic lithium as the counter electrode, it is a state where the open circuit voltage is 0.7 V or more.

[0018] "Natural graphite" refers to graphite mined from natural resources. Natural graphite shows four peaks in the X-ray diffraction pattern using CuKα rays measured before charge-discharge or in the discharged state in the range of diffraction angle 2θ from 40° to 50°. These four peaks are said to be two peaks derived from a hexagonal crystal structure and two peaks derived from a rhombohedral crystal structure. In the case of artificial graphite, generally, only two peaks derived from a hexagonal crystal structure appear. In the X-ray diffraction pattern, the ratio of the peak intensity derived from the (012) plane to the peak intensity derived from the (100) plane ((012) / (100)) is preferably 0.3 or more, more preferably 0.4 or more. The ratio of the peak intensities ((012) / (100)) is preferably 0.6 or less. Here, the (100) plane is derived from a hexagonal crystal structure, and the (012) plane is derived from a rhombohedral crystal structure.

[0019] The X-ray diffraction measurement using CuKα rays is performed according to the following procedure. A carbon material to be used for the measurement is filled into a sample holder for X-ray diffraction measurement. Powder X-ray diffraction measurement is carried out using an X-ray diffractometer (Rigaku's "MiniFlex II"). The radiation source is CuKα rays, the tube voltage is 30 kV, the tube current is 15 mA, and the diffracted X-rays are detected by a high-speed one-dimensional detector (model number: D / teX Ultra 2) through a Kβ filter with a thickness of 30 μm. The sampling width is 0.01°, the scan speed is 5° / min, the divergence slit width is 0.625°, the receiving slit width is 13 mm (OPEN), and the scattering slit width is 8 mm. When preparing the carbon material (carbon-based active material) to be used for the measurement from the assembled non-aqueous electrolyte storage element, specifically, the carbon material is brought into the above discharge state by the following method. First, the non-aqueous electrolyte storage element is discharged at a constant current of 0.1C to the discharge cut-off voltage during normal use. Then, the non-aqueous electrolyte storage element is disassembled and the negative electrode is taken out. A half-cell is assembled with the taken-out negative electrode as the working electrode and metallic lithium as the counter electrode. When the open-circuit voltage in this half-cell is less than 0.7V, the half-cell is discharged at a current of 0.1C so that the open-circuit voltage becomes 0.7V or more. Note that the discharge in the above half-cell refers to an oxidation reaction in which charge-transporting ions are released from the carbon material, which is the negative electrode active material. The half-cell is disassembled, the negative electrode is taken out, thoroughly washed with dimethyl carbonate or the like, and then dried under reduced pressure at room temperature to collect the carbon material. The operations from the disassembly of the non-aqueous electrolyte storage element to the preparation of the carbon material to be measured are carried out in a dry air atmosphere with a dew point of -40°C or lower. Here, normal use means the case where the non-aqueous electrolyte storage element is used under the charge-discharge conditions recommended or specified for the non-aqueous electrolyte storage element.

[0020] [3] In the negative electrode for a non-aqueous electrolyte storage element described in the above [1] or [2], the content of the above layered silicate may be more than 25 parts by mass and less than 100 parts by mass with respect to 100 parts by mass of the above cellulose derivative.

[0021] According to the negative electrode for a non-aqueous electrolyte storage element described in [3] above, since the content of the layered silicate with respect to the cellulose derivative is optimized, the internal resistance (DC resistance) of the non-aqueous electrolyte storage element can be made lower, and the capacity retention rate after charge-discharge cycles can be made higher.

[0022] [4] The non-aqueous electrolyte storage element according to one aspect of the present invention includes the negative electrode for a non-aqueous electrolyte storage element described in any one of [1] to [3] above.

[0023] Since the non-aqueous electrolyte storage element described in [4] above includes the negative electrode for a non-aqueous electrolyte storage element described in any one of [1] to [3] above, both a low internal resistance (DC resistance) and a high capacity retention rate after charge-discharge cycles are achieved.

[0024] [5] In the non-aqueous electrolyte storage element described in [4] above, it further includes a non-aqueous electrolyte containing a non-fluorinated solvent, and the content of the non-fluorinated solvent in the non-aqueous solvent may exceed 80% by volume.

[0025] When a fluorinated solvent is used in the non-aqueous electrolyte storage element, generally, due to gas generation accompanying the decomposition of the fluorinated solvent during charge-discharge and the formation of a film derived from the fluorinated solvent, the capacity retention rate after charge-discharge cycles tends to decrease and the internal resistance (DC resistance) also tends to increase. Therefore, according to the non-aqueous electrolyte storage element described in [5] above, in which the content of the non-fluorinated solvent in the non-aqueous solvent is large and the content of the fluorinated solvent is small, the internal resistance (DC resistance) becomes lower and the capacity retention rate after charge-discharge cycles becomes higher.

[0026] The "non-fluorinated solvent" refers to a solvent that does not have a fluorine element. The "fluorinated solvent" refers to a solvent that has a fluorine element.

[0027] The type and content of the components (non-aqueous solvents) contained in the non-aqueous electrolyte are identified by Liquid Chromatography-Mass Spectrometry (LC-MS) and Gas Chromatography-Mass spectrometry (GC-MS). Specifically, it is carried out as follows. Note that the measurements of LC-MS and GC-MS are to be continuously performed under the same conditions respectively. (1) Sampling of the non-aqueous electrolyte First, disassemble the non-aqueous electrolyte storage element to take out the non-aqueous electrolyte. If it cannot be taken out, perform centrifugation on the non-aqueous electrolyte storage element to take out the non-aqueous electrolyte. If it still cannot be taken out even after centrifugation, inject an appropriate extraction solvent (e.g., acetonitrile) into the non-aqueous electrolyte storage element and take out the non-aqueous electrolyte diluted with the extraction solvent. (2) LC-MS Analyze the components of the sampled non-aqueous electrolyte by LC-MS. The LC-MS analysis is carried out in the order of the following qualitative analysis and quantitative analysis. For the LC-MS analysis apparatus, use "Acquity H" and "Xevo G2-5QTof" manufactured by Waters. Use water as the solvent for the eluent. (Qualitative analysis) Subject the measurement sample (non-aqueous electrolyte) to LC-MS analysis. If the peaks in the obtained liquid chromatogram are not separated, perform GC-MS analysis described later instead of LC-MS analysis. If the peaks are separated, predict the components contained in the measurement sample from the MS spectra of each peak. Subject known samples of the predicted components (hereinafter referred to as "predicted components") to LC-MS analysis. Compare the retention time and MS spectrum of the peak corresponding to each predicted component in the measurement sample with the retention time and MS spectrum of the peak of the known sample of each predicted component. If they match, presume that the above prediction is correct. (Quantitative analysis) The quantitative analysis is carried out by the calibration curve method. First, perform LC-MS measurement on known samples of predicted components with known concentrations, obtain the peak areas, and create a calibration curve. The calibration curve has a determination coefficient (r 2) is created so that it is 0.999 or more and 1 or less. From the calibration curve and the area of the peak of the predicted component of the measurement sample, the content of the predicted component in the measurement sample is determined. The above operations are performed for all the peaks detected by LC-MS analysis of the measurement sample to determine the content of each predicted component. (3) GC-MS The analysis by GC-MS is performed in the following order of qualitative analysis and quantitative analysis. As the apparatus for GC-MS analysis, "5975C" manufactured by Agilent is used. Argon is used as the carrier gas. (Qualitative analysis) The measurement sample (non-aqueous electrolyte) is subjected to GC-MS analysis. The components contained in the sample are predicted from the MS spectra of the respective peaks of the obtained gas chromatogram. A known sample of the predicted component is subjected to GC-MS analysis. The retention time and MS spectrum of the peak corresponding to each predicted component of the measurement sample are compared with the retention time and MS spectrum of the peak of the known sample of each predicted component. If they match, it is presumed that the above prediction is correct. (Quantitative analysis) The quantitative analysis is performed by the calibration curve method. The quantitative analysis by GC-MS is performed in the same procedure as the above-described quantitative analysis by LC-MS to determine the content of each predicted component. (4) Calculation of the content of each component The total content of each non-aqueous solvent among each predicted component (i.e., each component) measured by LC-MS or GC-MS is taken as the total amount of the non-aqueous solvent, and the content of each non-aqueous solvent is calculated. In calculating the content (volume %) of each non-aqueous solvent with respect to the total amount of the non-aqueous solvent, the value obtained by converting the content of each non-aqueous solvent based on mass measured by LC-MS or GC-MS into volume at 20°C is used, and the total of the volume-converted contents of each non-aqueous solvent is taken as the total amount of the non-aqueous solvent. Also, when an extraction solvent is used, the extraction solvent is excluded from consideration.

[0028] [6] In the non-aqueous electrolyte storage element described in the above [4] or [5], it may be for an automobile.

[0029] The non-aqueous electrolyte storage element described in [6] above has both a low internal resistance (DC resistance) and a high capacity retention rate after charge and discharge cycles. Therefore, the non-aqueous electrolyte storage element described in [6] above is particularly useful as a power source for automobiles.

[0030] Hereinafter, the negative electrode for a non-aqueous electrolyte storage element, the non-aqueous electrolyte storage element, the power storage device, the method for manufacturing the non-aqueous electrolyte storage element, and other embodiments according to an embodiment of the present invention will be described in detail. Note that the names of the constituent members (each constituent element) used in each embodiment may be different from the names of the constituent members (each constituent element) used in the background art.

[0031] <Negative electrode for non-aqueous electrolyte storage element> The negative electrode for a non-aqueous electrolyte storage element according to an embodiment of the present invention (hereinafter also referred to as "negative electrode") includes a negative electrode substrate and a negative electrode active material layer disposed directly or via an intermediate layer on the negative electrode substrate. The negative electrode is a negative electrode used in a non-aqueous electrolyte storage element such as a non-aqueous electrolyte secondary battery.

[0032] (Negative electrode substrate) The negative electrode substrate has conductivity. Whether it has "conductivity" or not is determined with a volume resistivity measured in accordance with JIS-H-0505 (1975) of 10 -2 Ω·cm as a threshold value. As the material of the negative electrode substrate, metals such as copper, nickel, stainless steel, nickel-plated steel, or alloys thereof, carbon materials, etc. are used. Among these, copper or a copper alloy is preferable. Examples of the negative electrode substrate include a foil, a vapor deposition film, a mesh, a porous material, etc., and a foil is preferable from the viewpoint of cost. Therefore, a copper foil or a copper alloy foil is preferable as the negative electrode substrate. Examples of the copper foil include a rolled copper foil, an electrolytic copper foil, etc.

[0033] The average thickness of the negative electrode substrate is preferably 2 μm or more and 35 μm or less, more preferably 3 μm or more and 30 μm or less, still more preferably 4 μm or more and 25 μm or less, and particularly preferably 5 μm or more and 20 μm or less. By setting the average thickness of the negative electrode substrate within the above range, it is possible to increase the strength of the negative electrode substrate while increasing the energy density per unit volume of the non-aqueous electrolyte storage element. Note that the "average thickness" refers to the average value of the thicknesses measured at any five locations.

[0034] (Intermediate layer) The intermediate layer is a layer disposed between the negative electrode substrate and the negative electrode active material layer. The intermediate layer contains a conductive agent such as carbon particles to reduce the contact resistance between the negative electrode substrate and the negative electrode active material layer. The configuration of the intermediate layer is not particularly limited, and for example, it contains a binder and a conductive agent.

[0035] (Negative electrode active material layer) The negative electrode active material layer contains a carbon-based active material, a cellulose derivative, and a layered silicate. The negative electrode active material layer may contain, as necessary, other negative electrode active materials other than the carbon-based active material, other thickeners other than the cellulose derivative, a conductive agent, a binder, filler, and other optional components.

[0036] The carbon-based active material is a component that functions as a negative electrode active material. The carbon-based active material may further contain other elements such as a hydrogen element, a nitrogen element, and an oxygen element in addition to the carbon element. The lower limit of the carbon element content in the carbon-based active material is preferably 70% by mass, more preferably 80% by mass, and may be 90% by mass, 95% by mass, or 97% by mass. The upper limit of the carbon element content in the carbon-based active material may be 100% by mass or 99% by mass. The carbon element content in the carbon-based active material may be in the range of any combination of the above-mentioned lower limit and the above-mentioned upper limit.

[0037] Examples of the carbon-based active material include graphite (graphite) and non-graphitic carbon (easily graphitizable carbon or hardly graphitizable carbon). The carbon-based active material may be used alone or in combination of two or more.

[0038] "Non-graphitic carbon" refers to a carbon material (carbon-based active material) with an average lattice plane spacing (d 002 ) of 0.34 nm or more and 0.42 nm or less for the (002) plane determined by X-ray diffraction before charge-discharge or in a discharged state.

[0039] "Graphitization-resistant carbon" refers to a carbon material where the above d 002 is 0.36 nm or more and 0.42 nm or less.

[0040] "Graphitization-easy carbon" refers to a carbon material where the above d 002 is 0.34 nm or more and less than 0.36 nm.

[0041] As the carbon-based active material, graphite is preferred. Graphite may be either artificial graphite or natural graphite, but natural graphite is preferably used. In other words, the carbon-based active material preferably contains graphite, and more preferably contains natural graphite. By using such a carbon-based active material, the internal resistance (DC resistance) of the non-aqueous electrolyte storage element can be made lower.

[0042] Examples of natural graphite include flake graphite, massive graphite (flake graphite), and earthy graphite. Natural graphite may be spheroidized natural graphite obtained by spheroidizing flaky natural graphite or the like. Note that the surface of the graphite particles may be coated with other materials (for example, other carbon materials such as non-graphitic carbon).

[0043] The carbon-based active material is usually in a particulate form. The average particle size of the carbon-based active material is preferably, for example, 3 μm or more and 30 μm or less, and more preferably 5 μm or more and 20 μm or less. By setting the average particle size of the carbon-based active material to be equal to or greater than the above lower limit, the production or handling of the carbon-based active material becomes easier. By setting the average particle size of the carbon-based active material to be equal to or less than the above upper limit, the surface area of the carbon-based active material increases, and the internal resistance (DC resistance) of the non-aqueous electrolyte storage element can be made lower.

[0044] "Average particle size" means a value at which the volume-based cumulative distribution calculated in accordance with JIS-Z-8819-2 (2001) is 50% based on the particle size distribution measured by the laser diffraction / scattering method for a dilution obtained by diluting particles with a solvent, in accordance with JIS-Z-8825 (2013).

[0045] In order to obtain a carbon-based active material with a predetermined particle size, a crusher, a classifier, etc. are used. As the pulverization method, for example, methods using a mortar, a ball mill, a sand mill, a vibration ball mill, a planetary ball mill, a jet mill, a counter jet mill, a swirling air flow type jet mill, a sieve, etc. can be mentioned. During pulverization, wet pulverization in which water or an organic solvent such as hexane coexists can also be used. As the classification method, a sieve, an air classifier, etc. are used as needed for both dry and wet processes.

[0046] The lower limit of the content of the carbon-based active material in the negative electrode active material layer is preferably, for example, 90% by mass, more preferably 95.0% by mass, still more preferably 96.0% by mass, further preferably 97.0% by mass, and even more preferably 97.5% by mass. By the content of the carbon-based active material in the negative electrode active material layer being equal to or higher than the above lower limit, the energy density can be increased, etc. On the other hand, the upper limit of the content of the carbon-based active material in the negative electrode active material layer is preferably 99.5% by mass, and more preferably 99.0% by mass. By the content of the carbon-based active material in the negative electrode active material layer being equal to or lower than the above upper limit, other components can be sufficiently contained, etc., and as a result, the internal resistance (DC resistance) of the non-aqueous electrolyte storage element can be made lower, and the capacity retention rate after charge-discharge cycles can be made higher. The content of the carbon-based active material in the negative electrode active material layer may be in a range combined with any of the above-mentioned lower limits and any of the above-mentioned upper limits.

[0047] The negative electrode active material layer may contain other negative electrode active materials other than the carbon-based active material. Examples of other negative electrode active materials include metallic lithium; metals or semi-metals such as Si and Sn; metal oxides or semi-metal oxides such as Si oxide, Ti oxide, and Sn oxide; Li4Ti5O 12 、LiTiO 2、Titanium-containing oxides such as TiNb2O7; polyphosphoric acid compounds and the like can be mentioned. However, the content ratio of the carbon-based active material to all the negative electrode active materials is preferably 80% by mass or more, more preferably 90% by mass or more, further preferably 99% by mass or more, even more preferably 99.9% by mass or more, and particularly preferably 100% by mass. Thus, when the negative electrode active material consists substantially only of the carbon-based active material, the effect that both the internal resistance (DC resistance) of the non-aqueous electrolyte storage element is low and the capacity retention rate after charge and discharge cycles is high can be particularly sufficiently achieved.

[0048] Cellulose derivatives are usually thickeners when forming the negative electrode active material layer by coating the negative electrode binder paste or the like, and can also function as binders for binding between carbon-based active materials and the like.

[0049] Cellulose derivatives are compounds having a structure in which at least a part of the hydrogen atoms of the hydroxy groups possessed by cellulose are substituted with other groups. Examples of cellulose derivatives include carboxyalkyl celluloses (carboxymethyl cellulose (CMC), carboxyethyl cellulose, carboxypropyl cellulose, etc.), alkyl celluloses (methyl cellulose, ethyl cellulose, etc.), hydroxyalkyl celluloses (hydroxyethyl cellulose, hydroxypropyl cellulose, hydroxyethylmethyl cellulose, hydroxypropylmethyl cellulose, etc.), cellulose acetate phthalate, hydroxypropylmethyl cellulose phthalate, acetyl cellulose, etc. Among these, carboxyalkyl celluloses are preferred, and CMC is more preferred. Cellulose derivatives may be used alone or in combination of two or more.

[0050] Part or all of the cellulose derivatives may exist in the form of salts. Examples of the salt form include alkali metal salts (for example, sodium salts), ammonium salts, and the like.

[0051] The content of the cellulose derivative in the negative electrode active material layer is less than 0.8% by mass, preferably 0.7% by mass or less, more preferably 0.6% by mass or less, still more preferably 0.5% by mass or less, and may even be 0.4% by mass or less. By making the content of the cellulose derivative less than the above upper limit, the internal resistance (DC resistance) of the non-aqueous electrolyte storage element can be lowered. The content of the cellulose derivative in the negative electrode active material layer is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, and still more preferably 0.3% by mass or more. By making the content of the cellulose derivative not less than the above lower limit, the thickening function, binding function, etc. of the cellulose derivative can be sufficiently exhibited. The content of the cellulose derivative in the negative electrode active material layer may be in the range of any combination of the above-mentioned lower limit and the above-mentioned upper limit.

[0052] The negative electrode active material layer may contain a thickener other than the cellulose derivative. Examples of other thickeners include polysaccharide polymers other than cellulose derivatives. However, the content ratio of the cellulose derivative to all thickeners is preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 99% by mass or more, even more preferably 99.9% by mass or more, and particularly preferably 100% by mass.

[0053] Layered silicate is generally a silicate having a tetrahedral layer in which the tetrahedral structure of silicon oxide is connected in a planar manner. The layered silicate may be composed of the above tetrahedral layer and an octahedral layer in which an octahedral structure centered on a central metal atom such as a magnesium atom, a lithium atom, or a sodium atom is connected in a planar manner. The layered silicate may have a structure in which the above tetrahedral layer and the above octahedral layer are alternately laminated.

[0054] The layered silicate may contain one or more cations of metals such as alkali metals (e.g., lithium, sodium, potassium, etc.), alkaline earth metals (magnesium, calcium, etc.), aluminum, transition metals, etc. Among these, it is preferably contains at least one cation of lithium, sodium, and magnesium, more preferably contains cations of sodium and magnesium, and even more preferably contains cations of lithium, sodium, and magnesium.

[0055] Examples of the layered silicate include clay minerals such as kaolinite group, smectite group, mica group, etc. Examples of the clay minerals of the kaolinite group include kaolinite, etc. Examples of the clay minerals of the smectite group include montmorillonite, bentonite, saponite, hectorite, paydellite, stevensite, nontronite, etc. Examples of the clay minerals of the mica group include vermiculite, halloysite, tetrasilicic mica, etc. The layered silicate may be of natural origin or a synthetic product.

[0056] The layered silicate is usually in particulate form. The layered silicate may be plate-like particles. The average primary particle size of the layered silicate is preferably, for example, 1 nm or more and 1 μm or less, more preferably 5 nm or more and 200 nm or less, and even more preferably 10 nm or more and 60 nm or less. By using the layered silicate having such a relatively small particle size, the layered silicate can exhibit particularly excellent cross-linking performance and the like. The "average primary particle size" of the layered silicate is the average value of the primary particle sizes of any 10 primary particles constituting the layered silicate observed in a scanning electron microscope (SEM). A primary particle is a particle in which no grain boundary is observed in appearance in the above SEM observation. The primary particle size in the primary particle is the major axis. In addition, the shortest diameter passing through the center of the minimum circumscribed circle of the primary 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.

[0057] The layered silicate can be produced by a conventionally known method. The layered silicate can be obtained, for example, by heating a solution in which a metal salt such as sodium, magnesium, or lithium and sodium silicate are mixed to obtain a precipitate, and then filtering, washing, drying, pulverizing, etc. the obtained precipitate. Commercially available products can also be used as the layered silicate.

[0058] As the lower limit of the content of the layered silicate in the negative electrode active material layer, 0.05% by mass is preferable, 0.10% by mass is more preferable, 0.15% by mass is further preferable, and 0.20% by mass may also be acceptable. By setting the content of the layered silicate to be equal to or higher than the above lower limit, the effects of including the layered silicate can be particularly sufficiently exhibited. As the upper limit of the content of the layered silicate in the negative electrode active material layer, 2% by mass is preferable, 1% by mass is more preferable, 0.5% by mass is further preferable, 0.3% by mass is even more preferable, and 0.2% by mass or 0.20% by mass may also be acceptable. By setting the content of the layered silicate to be equal to or lower than the above upper limit, the content of the carbon-based active material in the negative electrode active material layer can be relatively increased, and the energy density of the non-aqueous electrolyte storage element can be increased, etc. The content of the layered silicate in the negative electrode active material layer may be in the range obtained by combining any of the above-mentioned lower limits and any of the above-mentioned upper limits.

[0059] Also, the content of the layered silicate is preferably more than 25 parts by mass and less than 100 parts by mass, more preferably 40 parts by mass or more and 90 parts by mass or less, further preferably 50 parts by mass or more and 85 parts by mass or less, and even more preferably 60 parts by mass or more and 80 parts by mass or less with respect to 100 parts by mass of the cellulose derivative. By setting the content of the layered silicate with respect to the cellulose derivative within the above range, the content of the layered silicate with respect to the cellulose derivative is optimized, the internal resistance (DC resistance) of the non-aqueous electrolyte storage element can be made lower, and the capacity retention rate after charge and discharge cycles can be made higher.

[0060] The conductive agent is not particularly limited as long as it is a material having conductivity. Examples of such conductive agents include, for example, carbon materials other than the above-described carbon-based active materials, metals, conductive ceramics, and the like. Examples of other carbon materials include non-graphitic carbon, graphene-based carbon, and the like. Examples of non-graphitic carbon include carbon nanofibers, pitch-based carbon fibers, carbon black, and the like. Examples of carbon black include furnace black, acetylene black, ketjen black, and the like. Examples of graphene-based carbon include graphene, carbon nanotubes (CNTs), fullerenes, and the like. Examples of the shape of the conductive agent include powder form, fibrous form, and the like. As the conductive agent, one of these materials may be used alone, or two or more of them may be mixed and used. Further, these materials may be used in a composite form. For example, a material obtained by compositing carbon black and CNTs may be used.

[0061] When the conductive agent is contained in the negative electrode active material layer, the content of the conductive agent in the negative electrode active material layer can be, for example, 1% by mass or more and 10% 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, 1% by mass or less, 0.1% by mass or less, or 0% by mass. Since the negative electrode active material layer of the negative electrode contains a carbon-based active material, it usually has sufficient electron conductivity. Therefore, in one embodiment of the present invention, the conductive agent may not be contained in the negative electrode active material layer. Further, fibrous conductive agents such as CNTs and conductive agents having a large specific surface area such as carbon black can adsorb charge transport ions such as lithium ions and cause a decrease in capacity and the like. Therefore, from the viewpoint of durability, there may be cases where it is preferable that the conductive agent is not contained in the negative electrode active material layer.

[0062] Examples of the binder include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyacrylic, and polyimide; elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; and polysaccharide polymers. Among these, elastomers are preferred as the binder, and SBR is more preferred. One or more kinds of binders can be used. As described above, in one embodiment of the present invention, in the negative electrode, the cellulose derivative also has a function as a binder. However, the cellulose derivative shall not be included in the binder as a component constituting the negative electrode active material layer.

[0063] The content of the binder in the negative electrode active material layer is preferably 0.1% by mass or more and 5% by mass or less, more preferably 0.3% by mass or more and 3% by mass or less, and even more preferably 0.5% by mass or more and 1.5% by mass or less. By setting the content of the binder within the above range, carbon-based active materials and the like can be stably held.

[0064] The filler is not particularly limited. In the components of the negative electrode active material layer, the layered silicate shall not be included in the filler. Examples of the filler include polyolefins such as polypropylene and polyethylene, inorganic oxides such as silicon dioxide, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, and magnesium oxide, hydroxides such as magnesium hydroxide, calcium hydroxide, and aluminum hydroxide, carbonates such as calcium carbonate, sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium sulfate, nitrides such as aluminum nitride and silicon nitride, boehmite, zeolite, apatite, spinel, etc., substances derived from mineral resources other than layered silicates, or artificial products thereof. The content of the filler in the negative electrode active material layer can be, for example, 0.1% by mass or more and 5% by mass or less. The content of the filler in the negative electrode active material layer may also be 1% by mass or less, 0.1% by mass or less, or even 0% by mass.

[0065] The negative electrode active material layer may contain, as components other than carbon-based active materials, other negative electrode active materials, cellulose derivatives, other thickeners, layered silicates, conductive agents, binders, and fillers, typical non-metal elements such as B, N, P, F, Cl, Br, I, etc., typical metal elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, Ba, etc., and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, W, etc.

[0066] The lower limit of the porosity of the negative electrode active material layer may be, for example, 20%, preferably 25%, and more preferably 30%. By setting the porosity of the negative electrode active material layer to be not less than the above lower limit, it is possible to achieve both a low internal resistance (DC resistance) of the non-aqueous electrolyte storage element and a high capacity retention rate after charge-discharge cycles. The upper limit of the porosity of the negative electrode active material layer may be 60% or 50%. The porosity of the negative electrode active material layer may be in the range obtained by combining any of the above-mentioned lower limits and any of the above-mentioned upper limits.

[0067] The "porosity (%)" of the negative electrode active material layer is obtained by the calculation formula of (1 - V2 / V1)×100, where V1 is the apparent volume (volume including voids) of the negative electrode active material layer, and V2 is the sum of the solid volumes of the respective materials constituting the negative electrode active material layer. The sum V2 of the solid volumes of the respective materials constituting the negative electrode active material layer can be calculated from the content of each material in the negative electrode active material layer and the true density of each material.

[0068] The production of the negative electrode can be carried out, for example, by applying a negative electrode mixture paste directly to the negative electrode substrate or via an intermediate layer and then drying it. After drying, pressing or the like may be carried out as necessary. The negative electrode mixture paste contains each component constituting the negative electrode active material layer, such as carbon-based active materials, cellulose derivatives, layered silicates, and binders, which are optional components. The negative electrode mixture paste usually further contains a dispersion medium. Water is preferred as the dispersion medium used in the negative electrode mixture paste.

[0069] <Non-aqueous electrolyte storage element> The non-aqueous electrolyte energy storage device according to one embodiment of the present invention includes an electrode body having a positive electrode, a negative electrode, and a separator, a non-aqueous electrolyte, and a container that houses the electrode body and the non-aqueous electrolyte. The electrode body is usually a laminated type in which a plurality of positive electrodes and a plurality of negative electrodes are laminated via a separator, or a wound type in which the positive electrode and the negative electrode are wound in a state of being laminated via a separator. The non-aqueous electrolyte exists in a state of being immersed in the positive electrode, the negative electrode, and the separator. As an example of the non-aqueous electrolyte energy storage device, a non-aqueous electrolyte secondary battery (hereinafter, also simply referred to as "secondary battery") will be described.

[0070] (Positive Electrode) The positive electrode has a positive electrode substrate and a positive electrode active material layer disposed directly or via an intermediate layer on the positive electrode substrate. The configuration of the intermediate layer is not particularly limited, and can be selected, for example, from the configurations exemplified for the negative electrode above.

[0071] The positive electrode substrate has conductivity. As the material of the positive electrode substrate, metals such as aluminum, titanium, tantalum, and stainless steel, or alloys thereof are used. Among these, aluminum or an aluminum alloy is preferable from the viewpoints of potential resistance, high conductivity, and cost. Examples of the positive electrode substrate include a foil, a vapor deposition film, a mesh, and a porous material, and a foil is preferable from the viewpoint of cost. Therefore, an aluminum foil or an aluminum alloy foil is preferable as the positive electrode substrate. Examples of aluminum or an aluminum alloy include A1085, A3003, A1N30, etc. defined in JIS-H-4000 (2014) or JIS-H4160 (2006).

[0072] The average thickness of the positive electrode substrate is preferably 3 μm or more and 50 μm or less, more preferably 5 μm or more and 40 μm or less, still more preferably 8 μm or more and 30 μm or less, and particularly preferably 10 μm or more and 25 μm or less. By setting the average thickness of the positive electrode substrate within the above range, it is possible to increase the strength of the positive electrode substrate while increasing the energy density per unit volume of the non-aqueous electrolyte energy storage device.

[0073] The positive electrode active material layer contains a positive electrode active material. The positive electrode active material layer optionally contains optional components such as a conductive agent, a binder, a thickener, and a filler. The optional components such as a conductive agent, a binder, a thickener, and a filler can be selected from the materials exemplified for the negative electrode above. The thickener for the positive electrode active material layer may be a cellulose derivative, may be another thickener, or these may be used in combination. The filler for the positive electrode active material layer may be a layered silicate, may be another filler, or these may be used in combination.

[0074] The positive electrode active material can be appropriately selected from known positive electrode active materials. As the positive electrode active material for a lithium ion secondary battery, a material that can occlude and release lithium ions is usually used. Examples of the positive electrode active material include lithium transition metal composite oxides having an α-NaFeO2-type crystal structure, lithium transition metal composite oxides having a spinel-type crystal structure, polyanion compounds, chalcogen compounds, sulfur, and the like. Examples of the lithium transition metal composite oxide having an α-NaFeO2-type crystal structure include Li[Li x Ni (1-x) O2 (0 ≦ x < 0.5), Li[Li x Ni γ Co (1-x-γ) O2 (0 ≦ x < 0.5, 0 < γ < 1, 0 < 1 - x - γ), Li[Li x Co (1-x) O2 (0 ≦ x < 0.5), Li[Li x Ni γ Mn (1-x-γ) O2 (0 ≦ x < 0.5, 0 < γ < 1, 0 < 1 - x - γ), Li[Li x Ni γ Mn β Co (1-x-γ-β) O2 (0 ≦ x < 0.5, 0 < γ, 0 < β, 0.5 < γ + β < 1, 0 < 1 - x - γ - β), Li[Li x Ni γ Co β Al (1-x-γ-β) O2 (0 ≦ x < 0.5, 0 < γ, 0 < β, 0.5 < γ + β < 1, 0 < 1 - x - γ - β), etc. Examples of the lithium transition metal composite oxide having a spinel-type crystal structure include Li x Mn2O4, Li xNi γ Mn (2-γ) Examples include O4. Examples of polyanion compounds include LiFePO4, LiMnPO4, LiNiPO4, LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, Li2CoPO4F, etc. Examples of chalcogen compounds include titanium disulfide, molybdenum disulfide, molybdenum dioxide, etc. Atoms or polyanions in these materials may be partially substituted with atoms or anion species composed of other elements. The surfaces of these materials may be coated with other materials. In the positive electrode active material layer, one of these materials may be used alone, or two or more of them may be used in combination.

[0075] The positive electrode active material is usually in the form of particles (powder). The average particle size of the positive electrode active material is preferably, for example, 0.1 μm or more and 20 μm or less. By setting the average particle size of the positive electrode active material to be equal to or greater than the above lower limit, the production or handling of the positive electrode active material becomes easier. By setting the average particle size of the positive electrode active material to be equal to or less than the above upper limit, the electron conductivity of the positive electrode active material layer is improved. When using a composite of the positive electrode active material and other materials, the average particle size of the composite is taken as the average particle size of the positive electrode active material. To obtain powder with a predetermined particle size, a pulverizer, a classifier, etc. are used. The pulverization method and the classification method can be selected, for example, from the methods exemplified for the negative electrode above.

[0076] The content of the positive electrode active material in the positive electrode active material layer is preferably 50% by mass or more and 99% by mass or less, more preferably 70% by mass or more and 98% by mass or less, and even more preferably 80% by mass or more and 95% by mass or less. By setting the content of the positive electrode active material within the above range, both high energy density and manufacturability of the positive electrode active material layer can be achieved.

[0077] The content of the conductive agent in the positive electrode active material layer is preferably 1% by mass or more and 10% by mass or less, more preferably 2% by mass or more and 6% by mass or less. By setting the content of the conductive agent within the above range, the energy density of the non-aqueous electrolyte storage element can be increased.

[0078] The content of the binder in the positive electrode active material layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 2% by mass or more and 6% by mass or less. By setting the content of the binder within the above range, the positive electrode active material can be stably held.

[0079] As the content of the thickener in the positive electrode active material layer, for example, it can be 0.1% by mass or more and 5% by mass or less. The content of the thickener in the positive electrode active material layer may be 1% by mass or less, 0.1% by mass or less, or even 0% by mass.

[0080] As the content of the filler in the positive electrode active material layer, for example, it can be 0.1% by mass or more and 5% by mass or less. The content of the filler in the positive electrode active material layer may be 1% by mass or less, 0.1% by mass or less, or even 0% by mass.

[0081] The positive electrode active material layer may contain typical non-metal elements such as B, N, P, F, Cl, Br, I, etc., typical metal elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, Ba, etc., and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, W, etc. as components other than the positive electrode active material, conductive agent, binder, thickener, and filler.

[0082] The positive electrode can be manufactured, for example, by applying a positive electrode mixture paste directly to the positive electrode substrate or through an intermediate layer and then drying it. After drying, pressing or the like may be performed as necessary. The positive electrode mixture paste contains the positive electrode active material and each component constituting the positive electrode active material layer, such as a conductive agent and a binder, which are optional components. The positive electrode mixture paste usually further contains a dispersion medium.

[0083] (Negative electrode) The negative electrode provided in the energy storage element is the negative electrode described above as the negative electrode according to an embodiment of the present invention.

[0084] (Separator) The separator can be appropriately selected from known separators. As the separator, for example, a separator composed only of a base material layer, a separator having a heat-resistant layer containing heat-resistant particles and a binder formed on one or both surfaces of the base material layer, etc. can be used. Examples of the shape of the base material layer of the separator include woven fabric, non-woven fabric, porous resin film, etc. Among these shapes, a porous resin film is preferable from the viewpoint of strength, and a non-woven fabric is preferable from the viewpoint of the retention of non-aqueous electrolyte. As the material of the base material layer of the separator, polyolefins such as polyethylene and polypropylene are preferable from the viewpoint of the shutdown function, and polyimides, aramids, etc. are preferable from the viewpoint of oxidation decomposition resistance. As the base material layer of the separator, a material obtained by compounding these resins may be used.

[0085] The heat-resistant particles contained in the heat-resistant layer preferably have a mass reduction of 5% or less when the temperature is raised from room temperature to 500 °C in an air atmosphere at 1 atm, and more preferably have a mass reduction of 5% or less when the temperature is raised from room temperature to 800 °C. Examples of materials having a mass reduction of a predetermined value or less include inorganic compounds. Examples of inorganic compounds include oxides such as iron oxide, silicon dioxide, aluminum oxide, titanium dioxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicate; 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 and diamond; mineral resource-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or artificial products thereof, etc. As the inorganic compound, these substances may be used alone or in combination, or two or more of them may be mixed and used. Among these inorganic compounds, silicon dioxide, aluminum oxide, or aluminosilicate is preferable from the viewpoint of the safety of non-aqueous electrolyte storage elements.

[0086] The porosity of the separator is preferably 80% by volume or less from the viewpoint of strength, and preferably 20% by volume or more from the viewpoint of discharge performance. Here, the "porosity" is a volume-based value and means the measured value by a mercury porosimeter.

[0087] As the separator, a polymer gel composed of a polymer and a non-aqueous electrolyte may be used. Examples of the polymer include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polyvinyl acetate, polyvinyl pyrrolidone, polyvinylidene fluoride, and the like. Using a polymer gel has the effect of suppressing liquid leakage. As the separator, a porous resin film or non-woven fabric as described above may be used in combination with a polymer gel.

[0088] (Non-aqueous electrolyte) The non-aqueous electrolyte can be appropriately selected from known non-aqueous electrolytes. A non-aqueous electrolyte solution may be used as the non-aqueous electrolyte. The non-aqueous electrolyte solution contains a non-aqueous solvent and an electrolyte salt dissolved in this non-aqueous solvent.

[0089] The non-aqueous solvent can be appropriately selected from known non-aqueous solvents. Examples of the non-aqueous solvent include cyclic carbonates, chain carbonates, carboxylic acid esters, phosphate esters, sulfonic acid esters, ethers, amides, nitriles, and the like. As the non-aqueous solvent, a solvent in which a part of the hydrogen atoms contained in these compounds is substituted with a halogen may be used. However, the non-aqueous solvent is preferably a non-fluorinated solvent and more preferably a non-halogenated solvent. The "non-halogenated solvent" means a solvent having no halogen element. The non-aqueous solvent may be a solvent composed only of carbon element, hydrogen element and oxygen element as a more suitable non-fluorinated solvent or non-halogenated solvent.

[0090] Examples of the cyclic carbonate include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), chloroethylene carbonate, fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), styrene carbonate, 1-phenylvinylene carbonate, 1,2-diphenylvinylene carbonate, and the like. Among these, non-fluorinated cyclic carbonates are preferred, and EC is more preferred.

[0091] Examples of the chain carbonate include diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diphenyl carbonate, trifluoroethyl methyl carbonate, bis(trifluoroethyl) carbonate, and the like. Among these, non-fluorinated chain carbonates are preferred, and EMC and DMC are more preferred.

[0092] As the non-aqueous solvent, it is preferable to use a cyclic carbonate or a chain carbonate, and it is more preferable to use them in combination. By using a cyclic carbonate, the dissociation of the electrolyte salt can be promoted to improve the ionic conductivity of the non-aqueous electrolyte. By using a chain carbonate, the viscosity of the non-aqueous electrolyte can be kept low. When using a cyclic carbonate and a chain carbonate in combination, the volume ratio of the cyclic carbonate to the chain carbonate (cyclic carbonate: chain carbonate) is preferably in the range of, for example, 5:95 to 50:50.

[0093] The non-aqueous solvent preferably contains a non-fluorinated solvent, more preferably contains a non-fluorinated cyclic carbonate or a non-fluorinated chain carbonate, and even more preferably contains both a non-fluorinated cyclic carbonate and a non-fluorinated chain carbonate. The content of the non-fluorinated solvent in the non-aqueous solvent is preferably more than 80% by volume, more preferably 90% by volume or more, even more preferably 95% by volume or more, and still even more preferably 99% by volume or more. When the non-aqueous solvent is mainly composed of the non-fluorinated solvent, the internal resistance (DC resistance) of the non-aqueous electrolyte storage element becomes lower, and the capacity retention rate after charge and discharge cycles becomes higher. The upper limit of the content of the non-fluorinated solvent in the non-aqueous solvent may be 100% by volume. The content of the non-fluorinated solvent in the non-aqueous solvent may be in the range combined with any of the above-mentioned lower limits and the above-mentioned upper limits.

[0094] As the electrolyte salt, it can be appropriately selected from known electrolyte salts. Examples of the electrolyte salt include lithium salts, sodium salts, potassium salts, magnesium salts, onium salts, etc. Among these, lithium salts are preferred.

[0095] Examples of the lithium salt include inorganic lithium salts such as LiPF6, LiPO2F2, LiBF4, LiClO4, LiN(SO2F)2, lithium oxalate salts such as lithium bis(oxalate) borate (LiBOB), lithium difluorooxalate borate (LiFOB), lithium bis(oxalate) difluorophosphate (LiFOP), and lithium salts having a halogenated hydrocarbon group such as LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), LiC(SO2CF3)3, LiC(SO2C2F5)3. Among these, inorganic lithium salts are preferred, and LiPF6 is more preferred.

[0096] The content of the electrolyte salt in the non-aqueous electrolyte is preferably 0.1 mol / dm 3 or more and 2.5 mol / dm 3 or less at 20 °C and 1 atm, more preferably 0.3 mol / dm 3 or more and 2.0 mol / dm 3More preferably, it is as follows: 0.5 mol / dm 3 or more and 1.7 mol / dm 3 or less. Even more preferably, it is as follows: 0.7 mol / dm 3 or more and 1.5 mol / dm 3 or less. By setting the content of the electrolyte salt within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

[0097] In addition to the non-aqueous solvent and the electrolyte salt, the non-aqueous electrolyte may contain an additive. Examples of the additive include aromatic compounds such as biphenyl, alkyl biphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; partial halides of the aromatic compounds such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene; halogenated anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole; vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, cyclohexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, dimethyl sulfite, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, ethylene sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethylene sulfoxide, diphenyl sulfide, 4,4'-bis(2,2-dioxo-1,3,2-dioxathiolane), 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, thioanisole, diphenyl disulfide, dipyridinium disulfide, 1,3-propenesultone, 1,3-propanesultone, 1,4-butanesultone, 1,4-butenesultone, perfluorooctane, tris(trimethylsilyl) borate, tris(trimethylsilyl) phosphate, tetrakis(trimethylsilyl) titanate, lithium monofluorophosphate, and lithium difluorophosphate. These additives may be used alone or in combination of two or more.

[0098] The content of the additive contained in the non-aqueous electrolyte is preferably 0.01% by mass or more and 10% by mass or less, more preferably 0.1% by mass or more and 7% by mass or less, still more preferably 0.2% by mass or more and 5% by mass or less, and particularly preferably 0.3% by mass or more and 3% by mass or less, based on the mass of the entire non-aqueous electrolyte. By setting the content of the additive within the above range, it is possible to improve the capacity retention performance or cycle performance after high-temperature storage, or to further improve the safety.

[0099] For the non-aqueous electrolyte, a solid electrolyte may be used, or a non-aqueous electrolyte and a solid electrolyte may be used in combination.

[0100] As the solid electrolyte, any material having ion conductivity such as lithium, sodium, calcium, etc. and being solid at room temperature (for example, from 15°C to 25°C) can be selected. Examples of the solid electrolyte include sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, polymer solid electrolytes, etc.

[0101] Examples of the sulfide solid electrolyte include Li2S-P2S5, LiI-Li2S-P2S5, Li 10 Ge-P2S 12 and the like.

[0102] The non-aqueous electrolyte storage element according to an embodiment of the present invention can be used for various applications similar to conventional non-aqueous electrolyte storage elements, and is particularly suitable as a power source for automobiles. In a power source for an automobile, high output and excellent life performance are required. Therefore, the non-aqueous electrolyte storage element of this embodiment, in which both a low internal resistance (DC resistance) and a high capacity retention rate after charge and discharge cycles are achieved, is suitable for use in automobiles. Examples of automobiles include electric vehicles (EVs), hybrid vehicles (HEVs), plug-in hybrid vehicles (PHEVs), etc. In addition, the power source for an automobile also includes a power source for starting the engine of an automobile such as a gasoline vehicle.

[0103] The shape of the non-aqueous electrolyte storage element of the present embodiment is not particularly limited, and examples thereof include a cylindrical battery, a prismatic battery, a flat battery, a coin-shaped battery, a button-shaped battery, and the like.

[0104] FIG. 1 shows a non-aqueous electrolyte storage element 1 as an example of a prismatic battery. Note that this figure is a perspective view of the inside of the container. An electrode body 2 having a positive electrode and a negative electrode wound with a separator interposed therebetween is housed in a prismatic container 3. The positive electrode is electrically connected to the positive electrode terminal 4 via the positive electrode lead 41. The negative electrode is electrically connected to the negative electrode terminal 5 via the negative electrode lead 51.

[0105] <Power storage device> The non-aqueous electrolyte storage element of the present embodiment can be mounted as a power storage unit (battery module) configured by aggregating a plurality of non-aqueous electrolyte storage elements for a power source for automobiles, a power source for electronic devices such as personal computers and communication terminals, or a power source for power storage. In this case, the technology of the present invention may be applied to at least one non-aqueous electrolyte storage element included in the power storage unit.

[0106] FIG. 2 shows an example of a power storage device 30 in which power storage units 20 in which two or more non-aqueous electrolyte storage elements 1 electrically connected are aggregated are further aggregated. The power storage device 30 may include a bus bar (not shown) for electrically connecting two or more non-aqueous electrolyte storage elements 1, a bus bar (not shown) for electrically connecting two or more power storage units 20, and the like. The power storage unit 20 or the power storage device 30 may include a state monitoring device (not shown) for monitoring the state of one or more non-aqueous electrolyte storage elements.

[0107] <Method for manufacturing non-aqueous electrolyte storage element> The method for manufacturing the non-aqueous electrolyte storage element of the present embodiment can be appropriately selected from known methods. The manufacturing method includes, for example, preparing an electrode body, preparing a non-aqueous electrolyte, and housing the electrode body and the non-aqueous electrolyte in a container. Preparing the electrode body includes preparing a positive electrode and a negative electrode, and forming the electrode body by laminating or winding the positive electrode and the negative electrode with a separator interposed therebetween.

[0108] The method of accommodating the non-aqueous electrolyte in a container can be appropriately selected from known methods. For example, when using a non-aqueous electrolyte solution as the non-aqueous electrolyte, after injecting the non-aqueous electrolyte solution from the injection port formed in the container, the injection port may be sealed.

[0109] <Other Embodiments> In addition, the negative electrode for the non-aqueous electrolyte storage element and the non-aqueous electrolyte storage element of the present invention are not limited to the above embodiments, and various modifications may be made without departing from the gist of the present invention. For example, the configuration of one embodiment can be added with the configuration of another embodiment, and a part of the configuration of one embodiment can be replaced with the configuration of another embodiment or well-known technology. Furthermore, a part of the configuration of one embodiment can be deleted. Also, well-known technology can be added to the configuration of one embodiment.

[0110] In the above embodiment, the case where the non-aqueous electrolyte storage element is used as a rechargeable non-aqueous electrolyte secondary battery (for example, a lithium-ion secondary battery) has been described. However, the type, shape, dimensions, capacity, etc. of the non-aqueous electrolyte storage element are arbitrary. The present invention can also be applied to various secondary batteries, electric double layer capacitors, or capacitors such as lithium-ion capacitors.

[0111] In the above embodiment, the electrode body in which the positive electrode and the negative electrode are laminated via a separator has been described. However, the electrode body may not include a separator. For example, the positive electrode and the negative electrode may be in direct contact with each other in a state where a layer having no conductivity is formed on the active material layer of the positive electrode or the negative electrode.

Examples

[0112] Hereinafter, the present invention will be described more specifically by way of examples. However, the present invention is not limited to the following examples.

[0113] [Example 1] (Fabrication of Negative Electrode) Natural graphite, which is a carbon-based active material, styrene-butadiene rubber (SBR) as a binder, carboxymethyl cellulose (CMC) as a cellulose derivative, lithium magnesium sodium silicate (Laponite RD manufactured by BYK), which is a layered silicate, and water as a dispersion medium were mixed to prepare a negative electrode mixture paste. The mass ratio of the carbon-based active material, binder, cellulose derivative, and layered silicate was 98.20:1.00:0.50:0.30 (in terms of solid content). The negative electrode mixture paste was applied to both sides of a copper foil serving as a negative electrode substrate and dried. Thereafter, roll pressing was performed to obtain a negative electrode in which negative electrode active material layers were laminated on both sides of the negative electrode substrate. The porosity of the negative electrode active material layer was 45%.

[0114] (Fabrication of the positive electrode) LiNi as the positive electrode active material 1 / 3 Co 1 / 3 Mn 1 / 3 O2, acetylene black (AB) as a conductive agent, polyvinylidene fluoride (PVDF) as a binder, and N-methylpyrrolidone (NMP) as a dispersion medium were used to prepare a positive electrode mixture paste. The mass ratio of the positive electrode active material, conductive agent, and binder was 93:4:3 (in terms of solid content). The positive electrode mixture paste was applied to both sides of an aluminum foil serving as a positive electrode substrate and dried. Thereafter, roll pressing was performed to obtain a positive electrode in which positive electrode active material layers were laminated on both sides of the positive electrode substrate.

[0115] (Fabrication of the non-aqueous electrolyte) LiPF6 was dissolved in a mixed solvent obtained by mixing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) at a volume ratio of 30:35:35 to obtain a non-aqueous electrolyte at a concentration of 1.2 mol / dm 3 .

[0116] (Fabrication of the non-aqueous electrolyte storage element) An electrode body was fabricated by laminating the above positive electrode and the above negative electrode via a separator. A microporous membrane made of polyolefin was used as the separator. The electrode body was housed in a container, the above non-aqueous electrolyte was injected therein, and then sealed to obtain the non-aqueous electrolyte storage element of Example 1.

[0117] [Examples 2 to 3, Comparative Examples 1 to 4] In the production of the negative electrode, except that the contents of the cellulose derivative and the layered silicate in the negative electrode active material layer were made as described in Table 1, each non-aqueous electrolyte storage element of Examples 2 to 3 and Comparative Examples 1 to 4 was obtained in the same manner as in Example 1. Regarding the components other than the cellulose derivative and the layered silicate, the content of the binder was set to 1.00% by mass in all examples and comparative examples, and the content of the carbonaceous active material was adjusted so that the total content of the carbonaceous active material, the binder, the cellulose derivative, and the layered silicate was 100.00% by mass.

[0118] (Initial charge and discharge) For each of the obtained non-aqueous electrolyte storage elements, initial charge and discharge were performed under the following conditions. In a constant temperature bath at 25°C, constant current charging was performed with a charging current of 1.0C and a charging end voltage of 4.20V, and then constant voltage charging was performed at 4.20V. The end condition of charging was set until the total charging time reached 3 hours. After providing a 10-minute rest period, constant current discharging was performed with a discharging current of 1.0C and a discharging end voltage of 2.50V, and a 10-minute rest was provided. These charging and discharging processes were regarded as one cycle, and two cycles were performed. The discharge electric quantity in the second cycle was taken as the initial discharge capacity.

[0119] (Internal resistance (DC resistance)) Next, for each non-aqueous electrolyte storage element, constant current charging was performed at a charging current of 1.0C in a temperature environment of 25°C to adjust the state of charge (SOC) to 50%. After storing each non-aqueous electrolyte storage element in a constant temperature bath at -10°C for 4 hours, it was charged at a constant current of 0.2C, 0.5C, or 1.0C for 10 seconds respectively. After each charging was completed, constant current discharging was performed at a current of 0.2C to adjust the SOC to 50%. The relationship between the current in each charging and the voltage 1 second after the start of charging was plotted, and the internal resistance (DC resistance) was obtained from the slope of the straight line obtained from the three points of plotting. The obtained internal resistance (DC resistance) is shown in Table 1 as a relative value with the value of the non-aqueous electrolyte storage element of Comparative Example 1 as a reference (100%).

[0120] (Capacity retention rate) Next, the following charge-discharge cycle test was conducted. For each non-aqueous electrolyte storage element, constant current charging was performed at a charging current of 8.0C in a temperature environment of 55°C, and the state of charge (SOC) was adjusted to 85%. Subsequently, without providing a rest time, constant current discharging was performed at a discharging current of 8.0C, and the state of charge (SOC) was adjusted to 15%. Using the voltage at the time of adjusting the state of charge (SOC) to 85% in the first cycle as the charge termination voltage and the voltage at the time of adjusting the state of charge (SOC) to 15% as the discharge termination voltage, a charge-discharge cycle of 1,000 hours was carried out at a constant current of 8.0C for both charging and discharging, without providing a rest time after charging and discharging. Thereafter, one cycle of charge-discharge was performed under the same conditions as the above-described initial charge-discharge, and the discharge electric quantity at this time was defined as the discharge capacity after the charge-discharge cycle. The percentage of the discharge capacity after the charge-discharge cycle with respect to the initial discharge capacity was determined as the capacity retention rate. Table 1 shows the relative values of the capacity retention rate obtained, with the value of the non-aqueous electrolyte storage element of Comparative Example 1 as the reference (100%).

[0121]

Table 1

[0122] As can be seen from the comparison of Comparative Examples 1 to 3, although the internal resistance (DC resistance) tended to decrease by reducing the content of the cellulose derivative in the negative electrode active material layer, when the content of the cellulose derivative was reduced too much, the capacity retention rate after the charge-discharge cycle decreased. Also, as in Comparative Example 4, when a layered silicate was contained while the content of the cellulose derivative was high, the internal resistance (DC resistance) increased. The non-aqueous electrolyte storage elements of Examples 1 to 3 had an internal resistance (DC resistance) (relative value) of 90% or less and a capacity retention rate (relative value) after the charge-discharge cycle of 100% or more. By setting the content of the cellulose derivative in the negative electrode active material layer to less than 0.8% by mass and containing a layered silicate, it was possible to achieve both a low internal resistance (DC resistance) and a high capacity retention rate after the charge-discharge cycle.

Industrial Applicability

[0123] Since the present invention has excellent charge acceptance performance and can withstand repeated rapid charge and discharge many times, it can be applied to non-aqueous electrolyte storage elements used as power sources for electronic devices such as personal computers and communication terminals, and automobiles, etc.

Explanation of Signs

[0124] 1 Non-aqueous electrolyte storage element 2 Electrode body 3 Container 4 Positive electrode terminal 41 Positive electrode lead 5 Negative electrode terminal 51 Negative electrode lead 20 Power storage unit 30 Power storage device

Claims

1. A negative electrode for a non-aqueous electrolyte storage element, comprising a negative electrode active material layer containing a carbonaceous active material, a cellulose derivative, and a layered silicate, wherein the content of the cellulose derivative in the negative electrode active material layer is less than 0.8% by mass.

2. The negative electrode for a non-aqueous electrolyte storage element according to Claim 1, wherein the carbonaceous active material contains natural graphite.

3. The negative electrode for a non-aqueous electrolyte storage element according to Claim 1 or Claim 2, wherein the content of the layered silicate is more than 25 parts by mass and less than 100 parts by mass with respect to 100 parts by mass of the cellulose derivative.

4. A non-aqueous electrolyte storage element comprising the negative electrode for a non-aqueous electrolyte storage element according to Claim 1 or Claim 2.

5. Further comprising a non-aqueous electrolyte containing a non-fluorinated solvent-containing non-aqueous solvent, wherein the content of the non-fluorinated solvent in the non-aqueous solvent is more than 80% by volume. The non-aqueous electrolyte storage element according to Claim 4.

6. The non-aqueous electrolyte storage element according to Claim 4, which is for an automobile.

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