Non-aqueous electrolyte secondary battery, power storage device, and method for manufacturing negative electrode

Abstract

One aspect of the present invention provides a non-aqueous electrolyte energy storage element comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte. The negative electrode has a negative electrode active material layer comprising lithium metal and a protective layer stacked on the negative electrode active material layer. The protective layer comprises a polymer having structural units derived from unsaturated cyclic carbonates and a porous sheet carrying at least a portion of the polymer.

Description

Technical Field

[0001] This invention relates to a method for manufacturing non-aqueous electrolyte energy storage elements, energy storage devices, and negative electrodes. Background Technology

[0002] Non-aqueous electrolyte secondary batteries, represented by lithium-ion batteries, are widely used in electronic devices such as personal computers and communication terminals, as well as automobiles, due to their high energy density. A non-aqueous electrolyte secondary battery typically consists of a pair of electrodes electrically isolated by a separator and a non-aqueous electrolyte between the electrodes. Charging and discharging occur through the transfer of charge and ion exchange between the two electrodes. In addition, capacitors such as lithium-ion capacitors and electric double-layer capacitors are also widely used as non-aqueous electrolyte energy storage components besides non-aqueous electrolyte secondary batteries.

[0003] In recent years, the increasing capacity of non-aqueous electrolyte energy storage devices has necessitated higher capacity negative electrodes. Compared to graphite, which is currently widely used as the negative electrode active material in non-aqueous electrolyte energy storage devices, lithium metal has a significantly higher discharge capacity per unit mass of active material. Therefore, a non-aqueous electrolyte energy storage device using lithium metal as the negative electrode active material has been proposed (refer to existing literature 1).

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Publication No. 2020-517054 Summary of the Invention

[0007] When using lithium metal as the negative electrode active material, it is possible for dendritic lithium metal (dendritic crystals) to precipitate on the negative electrode surface.

[0008] The purpose of this invention is to provide a non-aqueous electrolyte energy storage element and energy storage device having a negative electrode containing lithium metal and capable of suppressing dendrite precipitation in the negative electrode, and to provide a method for manufacturing a negative electrode containing lithium metal and capable of suppressing dendrite precipitation.

[0009] One aspect of the present invention provides a non-aqueous electrolyte energy storage element comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte. The negative electrode has a negative electrode active material layer comprising lithium metal and a protective layer stacked on the negative electrode active material layer. The protective layer comprises a polymer having structural units derived from unsaturated cyclic carbonates and a porous sheet carrying at least a portion of the polymer.

[0010] Another aspect of the present invention provides an energy storage device comprising two or more energy storage elements, and one or more non-aqueous electrolyte energy storage elements according to another aspect of the present invention.

[0011] Another aspect of the present invention provides a method for manufacturing a negative electrode comprising the following steps: preparing a negative electrode material having a negative electrode active material layer containing lithium metal; preparing a polymer solution comprising a polymer having structural units derived from unsaturated cyclic carbonates; preparing a porous sheet; and, using the polymer solution and the porous sheet, laminating a protective layer onto the negative electrode active material layer; wherein the protective layer comprises the polymer and a porous sheet carrying at least a portion of the polymer.

[0012] According to one aspect of the present invention, a non-aqueous electrolyte energy storage element and energy storage device having a negative electrode containing lithium metal and capable of suppressing dendrite precipitation in the negative electrode can be provided, as well as a method for manufacturing a negative electrode containing lithium metal and capable of suppressing dendrite precipitation can be provided. Attached Figure Description

[0013] Figure 1 This is a schematic cross-sectional view of the electrode body of a non-aqueous electrolyte energy storage element according to one embodiment of the present invention.

[0014] Figure 2 Is with Figure 1 Schematic cross-sectional views of the electrode bodies of different non-aqueous electrolyte energy storage elements.

[0015] Figure 3 Is with Figure 1 and Figure 2 Schematic cross-sectional views of the electrode bodies of different non-aqueous electrolyte energy storage elements.

[0016] Figure 4 This is a perspective view showing one embodiment of a non-aqueous electrolyte energy storage device.

[0017] Figure 5 This is a schematic diagram illustrating one embodiment of an energy storage device composed of multiple non-aqueous electrolyte energy storage elements.

[0018] Figure 6 The image shown is a SEM cross-sectional image of the electrode in the non-aqueous electrolyte energy storage element of Example 1.

[0019] Figure 7 This is a SEM cross-sectional image of the electrode body in the non-aqueous electrolyte energy storage element of Example 2. Detailed Implementation

[0020] First, a summary of the manufacturing method of the non-aqueous electrolyte energy storage element and the negative electrode disclosed in this specification will be given.

[0021] [1] A non-aqueous electrolyte storage element of one aspect of the present invention includes a positive electrode, a negative electrode, and a non-aqueous electrolyte; the negative electrode has a negative electrode active material layer comprising lithium metal and a protective layer stacked on the negative electrode active material layer, the protective layer comprising a polymer having structural units derived from unsaturated cyclic carbonates and a porous sheet carrying at least a portion of the polymer.

[0022] The non-aqueous electrolyte energy storage device described in [1] above can suppress dendrite deposition in the negative electrode. The reason for this is uncertain, but it is speculated that the following reasons apply. During charge-discharge cycles, metallic lithium is unevenly deposited at the negative electrode, thereby causing dendrites to gradually grow. Therefore, it is believed that by uniformly maintaining the deposition morphology of metallic lithium along the surface of the negative electrode, dendrite deposition can be suppressed. In the non-aqueous electrolyte energy storage device described in [1] above, since a protective layer is stacked on the negative electrode active material layer containing metallic lithium, when metallic lithium is deposited at the negative electrode during charging, the metallic lithium is deposited in a state sandwiched between the negative electrode active material layer and the protective layer. In addition, since the protective layer contains a polymer having structural units from unsaturated cyclic carbonates, the surface of the protective layer can be easily maintained smoothly and densely. Furthermore, since the protective layer contains a porous sheet carrying at least a portion of the polymer having structural units from unsaturated cyclic carbonates, the protective layer has high mechanical strength and can easily and stably maintain its shape. Therefore, in the non-aqueous electrolyte energy storage device described in [1] above, metallic lithium is easily deposited uniformly along the surface of the negative electrode active material layer, which can suppress the precipitation of dendrites in the negative electrode.

[0023] [2] The non-aqueous electrolyte storage element described in [1] above may further have a porous insulating element between the positive and negative electrodes and retain the non-aqueous electrolyte.

[0024] The non-aqueous electrolyte storage element described in [2] further comprises a porous insulating member that retains the non-aqueous electrolyte, thus facilitating the supply of sufficient charge transport ions from the insulating member to the negative electrode. Therefore, the increase in resistance of the non-aqueous electrolyte storage element can be suppressed.

[0025] [3] In the non-aqueous electrolyte storage element described in [1] or [2] above, the protective layer may have a polymer layer containing the polymer and stacked on the negative electrode active material layer, at least a portion of the polymer in the polymer layer may be carried on the porous sheet, and the average thickness of the polymer layer may be 1 μm or more.

[0026] In the non-aqueous electrolyte energy storage device described in [3] above, since the protective layer has the polymer layer stacked on top of the negative electrode active material layer, it is easier to maintain the surface of the protective layer opposite to the negative electrode active material layer smoothly and densely. Furthermore, since the average thickness of the polymer layer is above the lower limit, the polymer layer is easily and stably maintained. Therefore, the precipitation of dendrites in the negative electrode can be suppressed more reliably.

[0027] [4] In any of the above-described [1] to [3] non-aqueous electrolyte storage devices, the positive electrode may contain a sulfur-based active material and the non-aqueous electrolyte may contain carbonate.

[0028] In the non-aqueous electrolyte energy storage device described in [4] above, since the positive electrode contains a sulfur-based active material, the discharge capacity can be increased by combining it with a negative electrode containing metallic lithium. Furthermore, when the positive electrode contains a sulfur-based active material, a non-aqueous electrolyte containing carbonate is preferred.

[0029] [5] In any of the above-described non-aqueous electrolyte storage elements [1] to [4], the protective layer may further contain lithium salt, and the content of the lithium salt based on the polymer may be 1 mol / kg or more.

[0030] In the non-aqueous electrolyte energy storage element described in [5] above, the protective layer further includes lithium salt, and the content of the lithium salt based on the polymer is at or above the lower limit. This allows for the suppression of warping of the negative electrode during the lamination of the protective layer. Furthermore, it improves the ion permeability of the protective layer, suppressing the increase in resistance of the negative electrode caused by the protective layer. Moreover, it improves the flexibility of the protective layer, suppressing the formation of cracks in the protective layer.

[0031] The contents of the aforementioned polymer and lithium salt in the protective layer are determined based on a sample prepared according to the following steps. The non-aqueous electrolyte storage element is discharged at a constant current of 0.1C to the discharge termination voltage under normal use, thereby forming a discharge state. The non-aqueous electrolyte storage element in this discharge state is disassembled, the negative electrode is removed, thoroughly cleaned with dimethyl carbonate, and then dried under reduced pressure at room temperature. Then, the protective layer laminated on the negative electrode active material layer is separated from the negative electrode and collected as a sample. The operation from disassembling the non-aqueous electrolyte storage element to collecting the sample is performed in a dry air atmosphere with a dew point below -40°C. "Under normal use" refers to using the non-aqueous electrolyte storage element under the recommended or specified charge and discharge conditions; if equipment for using the non-aqueous electrolyte storage element is available, it refers to using the non-aqueous electrolyte storage element with that equipment.

[0032] [6] In any of the non-aqueous electrolyte energy storage elements described in [1] to [5] above, the air permeability of the porous sheet can be 100 seconds / 100 cm. 3 the following.

[0033] "Breathability," also known as the Gurley value, represents the air permeability at a pressure difference of 100 cm². 3 The time it takes for air to pass through a sample of a certain area is a value determined according to JIS-P-8117 (2009).

[0034] In the non-aqueous electrolyte storage element described in [6] above, since the air permeability of the porous sheet is below the upper limit, the non-aqueous electrolyte can easily move in the protective layer, thereby increasing the ion permeability in the protective layer and thus suppressing the increase in the resistance of the negative electrode caused by the protective layer.

[0035] [7] In any of the above-described [1] to [6] non-aqueous electrolyte storage elements, the porous sheet may not contain an inorganic compound layer on the outermost surface of the negative electrode active material layer side.

[0036] When the outermost surface of the porous sheet on the negative electrode active material layer side contains a layer of inorganic compounds, metallic lithium deposited between the inorganic compounds and the negative electrode active material layer tends to deposit unevenly. In contrast, in the non-aqueous electrolyte energy storage device described in [7] above, since the outermost surface of the porous sheet on the negative electrode active material layer side does not contain a layer of inorganic compounds, metallic lithium tends to deposit evenly along the surface of the negative electrode active material layer, further suppressing the deposition of dendrites in the negative electrode.

[0037] [8] The energy storage device of another aspect of the present invention comprises two or more energy storage elements, and comprises one or more non-aqueous electrolyte energy storage elements described in any one of [1] to [7].

[0038] The energy storage device described in [8] above has one or more non-aqueous electrolyte energy storage elements described in any of [1] to [7] above, thus it can suppress the precipitation of dendrites in the negative electrode.

[0039] [9] Another aspect of the present invention provides a method for manufacturing a negative electrode comprising: preparing a negative electrode material having a negative electrode active material layer containing lithium metal; preparing a polymer solution containing a polymer having structural units derived from unsaturated cyclic carbonates; preparing a porous sheet; and using the polymer solution and the porous sheet, laminating a protective layer onto the negative electrode active material layer; wherein the protective layer comprises the polymer and a porous sheet carrying at least a portion of the polymer.

[0040] The method for manufacturing a negative electrode described in [9] above enables the production of a negative electrode having a protective layer laminated on a negative electrode active material layer containing lithium metal. In this negative electrode, when lithium metal is deposited at the negative electrode during charging, the lithium metal is deposited in a state sandwiched between the negative electrode active material layer and the protective layer. Furthermore, since the protective layer contains a polymer having structural units derived from unsaturated cyclic carbonates, the surface of the protective layer can be easily maintained smoothly and densely. Moreover, since the protective layer contains a porous sheet supporting at least a portion of the polymer having structural units derived from unsaturated cyclic carbonates, the protective layer has high mechanical strength and can easily and stably maintain its shape. Therefore, in the method for manufacturing a negative electrode described in [9] above, lithium metal can be easily and uniformly deposited along the surface of the negative electrode active material layer, enabling the production of a negative electrode that suppresses the precipitation of dendrites in the negative electrode.

[0041] Hereinafter, a non-aqueous electrolyte energy storage element, an energy storage device, a method for manufacturing a non-aqueous electrolyte energy storage element, and other embodiments of the present invention will be described in detail. The method for manufacturing the negative electrode according to one embodiment of the present invention will be described in the description of the method for manufacturing a non-aqueous electrolyte energy storage element. It should be noted that the names of the constituent components (elements) used in each embodiment are sometimes different from the names of the constituent components (elements) used in the prior art.

[0042] Non-aqueous electrolyte energy storage components

[0043] One embodiment of the present invention provides a non-aqueous electrolyte energy storage device comprising: an electrode body having a positive electrode and a negative electrode, a non-aqueous electrolyte, and a container for containing the electrode body and the non-aqueous electrolyte. The negative electrode has a negative electrode active material layer comprising lithium metal and a protective layer laminated thereon. Furthermore, the protective layer comprises a polymer having structural units derived from unsaturated cyclic carbonates and a porous sheet supporting at least a portion of the polymer.

[0044] The electrode body is either a stacked type consisting of multiple positive electrodes and multiple negative electrodes, or a wound type consisting of positive and negative electrodes stacked together with an insulating member separating them. The electrode body may further include an insulating member between the positive and negative electrodes. In this case, the electrode body is formed with positive and negative electrodes stacked together with an insulating member separating them.

[0045] The non-aqueous electrolyte exists in a state where it is contained in the positive and negative electrodes, and further, depending on the situation, in the separator. As an example of a non-aqueous electrolyte energy storage element, a non-aqueous electrolyte secondary battery will be described.

[0046] In this non-aqueous electrolyte energy storage device, because a protective layer is stacked on top of the negative electrode active material layer containing metallic lithium, when metallic lithium is deposited at the negative electrode during charging, the lithium is deposited in a state sandwiched between the negative electrode active material layer and the protective layer. Furthermore, since the protective layer contains a polymer having structural units derived from unsaturated cyclic carbonates, its surface is easily maintained smoothly and densely. Moreover, because the protective layer contains porous sheets supporting at least a portion of the polymer having structural units derived from unsaturated cyclic carbonates, the protective layer has high mechanical strength and easily maintains its shape stably. Therefore, in this non-aqueous electrolyte energy storage device, metallic lithium readily and uniformly deposits along the surface of the negative electrode active material layer, suppressing dendrite formation in the negative electrode.

[0047] Figure 1 This is a schematic cross-sectional view of the electrode body of a non-aqueous electrolyte energy storage device according to an embodiment of the present invention. The electrode body is formed with a positive electrode 1 and a negative electrode 2 stacked together, separated by an insulating member 3. The positive electrode 1 has a positive electrode substrate 11 and a positive electrode active material layer 12 stacked on the positive electrode substrate 11. The negative electrode 2 has a negative electrode substrate 21, a negative electrode active material layer 22 stacked on the negative electrode substrate 21 and containing lithium metal, and a protective layer 23 stacked on the negative electrode active material layer 22. In the electrode body, the positive electrode substrate 11, the positive electrode active material layer 12, the insulating member 3, the protective layer 23, the negative electrode active material layer 22, and the negative electrode substrate 21 are stacked sequentially. It should be noted that an intermediate layer may be provided between the positive electrode substrate 11 and the positive electrode active material layer 12, and between the negative electrode substrate 21 and the negative electrode active material layer 22, but from Figure 1 omitted.

[0048] The protective layer 23 comprises: a non-supported layer 23b, which is a layer of polymer having structural units derived from unsaturated cyclic carbonates not supported on the porous sheet; and a supported layer 23a, which contains the aforementioned polymer supported on the porous sheet. The supported layer 23a is formed such that the pores of the porous sheet are filled with the aforementioned polymer. In this embodiment, the supported layer 23a is disposed opposite to the separator 3, and the non-supported layer 23b is disposed opposite to the negative electrode substrate 21. In other words, the supported layer 23a and the non-supported layer 23b are integrally formed as a polymer layer containing the aforementioned polymer and stacked on the negative electrode active material layer 22.

[0049] In this embodiment, the lithium metal contained in the negative electrode active material layer 22 can be deposited between the negative electrode active material layer 22 and the protective layer 23, and more specifically between the negative electrode active material layer 22 and the unsupported layer 23b (between the negative electrode active material layer 22 and the polymer layer) during charging. As described above, the surface of the protective layer 23 is easily and densely maintained, and the shape of the protective layer 23 is easily and stably maintained, so the lithium metal is easily and uniformly deposited along the surface of the negative electrode active material layer 22. That is, a smooth lithium metal layer is easily formed between the negative electrode active material layer 22 and the protective layer 23 (between the negative electrode active material layer 22 and the unsupported layer 23b).

[0050] The average thickness of the porous sheet (supporting layer 23a) can be 1 μm to 20 μm, 2 μm to 18 μm, or 4 μm to 16 μm. By having the average thickness of the porous sheet (supporting layer 23a) within the above range, it is easier to maintain the shape of the protective layer 23 more stably.

[0051] The average thickness of the non-supporting layer 23b can be 0.5 μm to 5 μm, 0.8 μm to 4 μm, or 1 μm to 3 μm. With the average thickness of the non-supporting layer 23b within the above range, the surface of the porous sheet is sufficiently covered by the polymer. Therefore, it is easier to maintain a smoother and denser surface of the protective layer 23.

[0052] The average thickness of the polymer layer (the sum of the supporting layer 23a and the non-supporting layer 23b) is preferably 1 μm or more and 25 μm or less, more preferably 3 μm or more and 22 μm or less, and even more preferably 5 μm to 20 μm. By making the average thickness of the polymer layer within the above range, it is easier to maintain the shape of the protective layer 23 more stably.

[0053] In this embodiment, the separator 3 is porous and capable of retaining the non-aqueous electrolyte. Because the separator 3 is porous and can retain the non-aqueous electrolyte, sufficient lithium ions and other charge transport ions can be easily supplied from the separator 3 to the positive electrode 1 and the negative electrode 2. Therefore, the increase in resistance of the non-aqueous electrolyte energy storage element can be suppressed.

[0054] Figure 2This is a schematic cross-sectional view of the electrode body of a non-aqueous electrolyte energy storage element according to another embodiment of the present invention. The electrode body is formed with a positive electrode 1 and a negative electrode 8 stacked together, separated by an insulating member 3. The negative electrode 8 has a negative electrode substrate 81, a negative electrode active material layer 82 containing lithium metal stacked on the negative electrode substrate 81, and a protective layer 83 stacked on the negative electrode active material layer 82. In the electrode body, the positive electrode substrate 11, the positive electrode active material layer 12, the insulating member 3, the protective layer 83, the negative electrode active material layer 82, and the negative electrode substrate 81 are stacked sequentially. It should be noted that an intermediate layer may be provided between the positive electrode substrate 11 and the positive electrode active material layer 12, and between the negative electrode substrate 81 and the negative electrode active material layer 82, but from Figure 2 omitted.

[0055] The protective layer 83 comprises a polymer having structural units derived from unsaturated cyclic carbonates and a porous sheet supporting the polymer. More specifically, the protective layer 83 consists solely of a supporting layer comprising the polymer supported on the porous sheet. The protective layer 83 is formed such that the pores of the porous sheet are filled with the polymer. In other words, the supporting layer (protective layer 83) forms a polymer layer comprising the polymer and stacked on the negative electrode active material layer 82.

[0056] In this embodiment, the metallic lithium contained in the negative electrode active material layer 82 can be deposited between the negative electrode active material layer 82 and the protective layer 83 (between the negative electrode active material layer 82 and the polymer layer) during charging. As described above, the surface of the protective layer 83 is easily and densely maintained, and the shape of the protective layer 83 is also easily and stably maintained. Therefore, metallic lithium is easily and uniformly deposited along the surface of the negative electrode active material layer 82. That is, a smooth layer of metallic lithium is easily formed between the negative electrode active material layer 82 and the protective layer 83.

[0057] The average thickness of the protective layer 83 can be the same as the average thickness of the polymer layer (the sum of the supporting layer 23a and the non-supporting layer 23b).

[0058] Figure 3 This is a schematic cross-sectional view of the electrode body of a non-aqueous electrolyte energy storage device according to another embodiment of the present invention. The electrode body is formed in a stacked state of a positive electrode 1 and a negative electrode 9. The negative electrode 9 has a negative electrode substrate 91, a negative electrode active material layer 92 containing metallic lithium stacked on the negative electrode substrate 91, and a protective layer 93 stacked on the negative electrode active material layer 92. In the electrode body, the positive electrode substrate 11, the positive electrode active material layer 12, the protective layer 93, the negative electrode active material layer 92, and the negative electrode substrate 91 are stacked sequentially. It should be noted that an intermediate layer may be provided between the positive electrode substrate 11 and the positive electrode active material layer 12, and between the negative electrode substrate 91 and the negative electrode active material layer 92, but from Figure 3 omitted.

[0059] The protective layer 93 comprises a polymer having structural units derived from unsaturated cyclic carbonates and a porous sheet supporting the polymer. More specifically, the protective layer 93 comprises: a porous layer 93c, which is a layer of porous sheet without supporting the polymer; and a supporting layer 93a, which comprises the polymer supported on the porous sheet. The supporting layer 93a is formed such that the pores of the porous sheet are filled with the polymer. In this embodiment, the supporting layer 93a is disposed opposite to the negative electrode active material layer 92, and the porous layer 93c is disposed opposite to the positive electrode active material layer 12. In other words, the supporting layer 93a forms a polymer layer comprising the polymer and stacked on the negative electrode active material layer 92.

[0060] In this embodiment, the lithium metal contained in the negative electrode active material layer 92 can be deposited between the negative electrode active material layer 92 and the protective layer 93, and more specifically between the negative electrode active material layer 92 and the supporting layer 93a (between the negative electrode active material layer 92 and the polymer layer) during charging. As described above, the surface of the protective layer 93 is easily and densely maintained, and the shape of the protective layer 93 is easily and stably maintained, so the lithium metal is easily and uniformly deposited along the surface of the negative electrode active material layer 92. That is, a smooth lithium metal layer is easily formed between the negative electrode active material layer 92 and the protective layer 93 (between the negative electrode active material layer 92 and the supporting layer 93a).

[0061] In this embodiment, the porous layer 93c of the protective layer 93 can retain the non-aqueous electrolyte. Because the porous layer 93c retains the non-aqueous electrolyte, it is easy to supply sufficient lithium ions and other charge-transfer ions to the positive electrode 1 and the negative electrode 9. If the protective layer 93 is configured to partially retain the non-aqueous electrolyte, it is not necessary to add a separator or similar component between the positive electrode 1 and the negative electrode 9 to retain the non-aqueous electrolyte. Therefore, the mechanical strength of the protective layer 93 and the ion permeability between the positive electrode 1 and the negative electrode 9 can be balanced.

[0062] The average thickness of the supporting layer 93a can be the same as the average thickness of the polymer layers (the sum of the supporting layer 23a and the non-supporting layer 23b). The average thickness of the porous layer 93c is not particularly limited, and can be, for example, 1 μm to 20 μm.

[0063] The following is a detailed description of the positive electrode, negative electrode, separator, and non-aqueous electrolyte of a non-aqueous electrolyte energy storage element according to one embodiment of the present invention.

[0064] (positive electrode)

[0065] The positive electrode has a positive electrode substrate and a layer of positive electrode active material disposed directly or through an intermediate layer on the positive electrode substrate.

[0066] The positive electrode substrate is conductive. Whether it is "conductive" is determined by a volume resistivity of 10⁻⁶ Ω·cm, as measured according to JIS-H-0505 (1975). 7 Ω cm is used as a threshold for determination. The material used for the positive electrode substrate includes metals such as aluminum, titanium, tantalum, and stainless steel, or their alloys. Among these, aluminum or aluminum alloys are preferred from the viewpoints of potential resistance, high conductivity, and cost. Examples of positive electrode substrates include foil, vapor-deposited film, mesh, and porous materials; from a cost perspective, foil is preferred. Therefore, aluminum foil or aluminum alloy foil is preferred as the positive electrode substrate. Examples of aluminum or aluminum alloys include A1085, A3003, and AlN30 as specified in JIS-H-4000 (2014) or JIS-H-4160 (2006).

[0067] The interlayer is a layer disposed between the positive electrode substrate and the positive electrode active material layer. The interlayer reduces the contact resistance between the positive electrode substrate and the positive electrode active material layer by including conductive agents such as carbon particles. The composition of the interlayer is not particularly limited; for example, it may include a binder and a conductive agent.

[0068] The positive electrode active material layer preferably contains sulfur-based active materials, and more preferably contains a composite of porous carbon and sulfur-based active materials. The positive electrode active material layer may, as needed, contain any components such as conductive agents, binders, thickeners, and fillers. The positive electrode active material layer is typically formed from a positive electrode compound containing the composite and other arbitrary components.

[0069] As a composite of porous carbon and sulfur-based active substances, examples include a form in which porous carbon and sulfur-based active substances are contained in a single particle. The composite can be a form in which at least a portion of the sulfur-based active substance is disposed within the pores of the porous carbon. In other words, it can be a form in which at least a portion of the sulfur-based active substance is impregnated in porous carbon. Furthermore, in the composite, a film derived from a non-aqueous electrolyte is typically formed on the surface. This film is preferably also formed within the pores of the composite.

[0070] Porous carbon is a porous body with carbon as its main constituent element. The main constituent element refers to the element with the highest content by mass. The carbon content in porous carbon is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more. Porous carbon may be substantially composed of only carbon. In addition to carbon, porous carbon may also contain other elements such as oxygen.

[0071] The content of porous carbon in the composite (the mass ratio of porous carbon to the total mass of the composite) is preferably 10% to 50% by mass, more preferably 20% to 45% by mass, and even more preferably 30% to 40% by mass. By setting the content of porous carbon in the composite to the above range, the discharge capacity of non-aqueous electrolyte energy storage elements can be increased.

[0072] Sulfur-based active materials function as positive electrode active materials. These materials can be elemental sulfur or sulfur compounds. Examples of sulfur compounds include metal sulfides such as lithium sulfide, organic disulfide compounds, and organic sulfur compounds such as carbon sulfides. Sulfur-based active materials have advantages such as high theoretical capacity and low cost.

[0073] When a complex of sulfur-based active materials is formed, the content of the sulfur-based active materials in the complex (the mass ratio of the sulfur-based active materials to the total mass of the complex) is preferably 50% to 90% by mass, more preferably 55% to 80% by mass, and even more preferably 60% to 70% by mass. By setting the content of the sulfur-based active materials in the complex to the above range, the discharge capacity of non-aqueous electrolyte energy storage elements can be increased.

[0074] The main elements constituting the complex are carbon and sulfur. The complex may further include oxygen, and also fluorine, etc. Oxygen and fluorine, etc., can be elements constituting the coating from the non-aqueous electrolyte. This coating may also include carbon, hydrogen, lithium, etc.

[0075] The content of sulfur-based active material in the positive electrode active material layer is preferably 50% to 90% by mass, more preferably 60% to 80% by mass. By having the content of sulfur-based active material in the above range, the discharge capacity and energy density can be increased.

[0076] When a complex of sulfur-based active materials is formed, the content of the complex in the positive electrode active material layer is preferably 60% to 95% by mass, more preferably 70% to 90% by mass. By setting the content of the complex within the above range, the discharge capacity and energy density can be increased.

[0077] The positive electrode active material layer may contain other positive electrode active materials besides sulfur-based active materials. However, the content of sulfur-based active materials in all positive electrode active materials is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, even more preferably 99% by mass or more, and particularly preferably 100% by mass.

[0078] There are no particular limitations on the conductive agent as long as it is a conductive material. It should be noted that the conductive agent does not contain porous carbon constituting the composite. Examples of such conductive agents include carbonaceous materials, metals, and conductive ceramics. Examples of carbonaceous materials include graphite, non-graphite carbon, and graphene-based carbon. Examples of non-graphite 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 (CNTs), and fullerenes. Examples of the conductive agent's form include powder and fibrous forms. One of these materials can be used alone, or two or more can be used in combination. Furthermore, these materials can be used in combination. For example, a material obtained by combining carbon black and CNTs can be used. From the viewpoint of electronic conductivity and coatability, carbon black is preferred, and acetylene black is preferred. In addition, carbon black (preferably acetylene black) and CNT (preferably monolayer carbon nanotubes) are also preferred to be used together.

[0079] The content of the conductive agent in the positive electrode active material layer is preferably 1% to 20% by mass, more preferably 3% to 15% by mass. By setting the content of the conductive agent within the above range, the energy density of the non-aqueous electrolyte energy storage element can be improved.

[0080] Examples of adhesives include thermoplastic resins such as fluoropolymers (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF)), polyethylene, polypropylene, polyacrylic acid, polyimide, and polyacrylic acid (PAA); elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; and polysaccharide polymers.

[0081] The binder content in the positive electrode active material layer is preferably 1% to 10% by mass, more preferably 3% to 9% by mass. By keeping the binder content within the above range, the composite and the like can be stably maintained.

[0082] Examples of thickeners include polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose. When the thickener has functional groups that react with lithium, these functional groups can be deactivated beforehand by methylation or the like. The content of the thickener in the positive electrode active material layer is preferably 0.5% to 10% by mass, more preferably 2% to 5% by mass. In one embodiment of the present invention, the positive electrode active material layer may not contain a thickener.

[0083] The filler is not particularly limited. Examples of fillers include polyolefins such as polypropylene and polyethylene, inorganic oxides such as silica, alumina, titanium dioxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates, 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, talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, or substances derived from mineral resources or their synthetic forms. The content of the filler in the positive electrode active material layer is preferably, for example, 0.1% to 10% by mass. In one embodiment of the present invention, the positive electrode active material layer may not contain any filler.

[0084] The positive electrode active material layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, I, typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, Ba, transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, W as sulfide active materials, other positive electrode active materials besides sulfide active materials, porous carbon, conductive agents, binders, thickeners, and components other than fillers.

[0085] (negative electrode)

[0086] The negative electrode has a negative electrode substrate, a negative electrode active material layer disposed directly on the negative electrode substrate or separated from it by an intermediate layer, and a protective layer. The composition of the intermediate layer is not particularly limited, and can be selected from the composition exemplified in the positive electrode described above.

[0087] The negative electrode substrate is conductive. Materials used for the negative electrode substrate include metals such as copper, nickel, stainless steel, nickel-plated steel, or their alloys, as well as carbonaceous materials. Copper or copper alloys are preferred. Examples of negative electrode substrates include foil, vapor-deposited film, mesh, and porous materials; from a cost perspective, foil is preferred. Therefore, copper foil or copper alloy foil is preferred as the negative electrode substrate. Examples of copper foil include rolled copper foil and electrolytic copper foil.

[0088] The average thickness of the negative electrode substrate is preferably 2 μm to 35 μm, more preferably 3 μm to 30 μm, even more preferably 4 μm to 25 μm, and particularly preferably 5 μm to 20 μm. By making the average thickness of the negative electrode substrate within the above range, the energy density per unit volume of the non-aqueous electrolyte energy storage device can be increased, while the strength of the negative electrode substrate can also be improved.

[0089] The negative electrode active material layer contains metallic lithium. Metallic lithium is the component that functions as the negative electrode active material. Metallic lithium can exist as pure metallic lithium, which is essentially composed of only lithium, or as a lithium alloy containing other metal elements. Examples of lithium alloys include lithium-silver alloys, lithium-zinc alloys, lithium-calcium alloys, lithium-aluminum alloys, lithium-magnesium alloys, and lithium-indium alloys. Lithium alloys can also contain multiple metal elements other than lithium.

[0090] The negative electrode active material layer may be a layer composed solely of metallic lithium. The content of metallic lithium in the negative electrode active material layer is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 99% by mass or more.

[0091] The negative electrode active material layer can be a pure lithium metal foil or a lithium alloy foil. The negative electrode active material layer can be a non-porous layer (solid layer). Alternatively, it can be a porous layer containing lithium metal. The average thickness of the negative electrode active material layer in the charged state is preferably 5 μm to 1000 μm, more preferably 10 μm to 500 μm, and even more preferably 30 μm to 300 μm. It should be noted that "average thickness of the negative electrode active material layer in the charged state" refers to the average thickness of a single negative electrode active material layer in the charged state. For example, if negative electrode active material layers are provided on both sides of the negative electrode substrate, "average thickness of the negative electrode active material layer in the charged state" is the value for each side. Furthermore, "charged state" refers to the state in which a non-aqueous electrolyte energy storage element is charged at a constant current and constant voltage of 0.1C to the charging termination voltage used in normal operation.

[0092] The negative electrode active material layer may further include other negative electrode active materials besides lithium metal. Preferably, the content of lithium metal relative to all negative electrode active materials contained in the negative electrode active material layer is 90% by mass or more, more preferably 99% by mass or more, and even more preferably 100% by mass.

[0093] The negative electrode active material layer may further include any components such as conductive agents, binders, thickeners, and fillers, as needed. These components can be selected from the materials exemplified in the above-mentioned positive electrode.

[0094] The negative electrode active material layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, I, typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, Ba, and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, W as components other than negative electrode active materials, conductive agents, binders, thickeners, and fillers.

[0095] The protective layer comprises a polymer having structural units derived from unsaturated cyclic carbonates and a porous sheet supporting at least a portion of the polymer. As described above, a portion of the polymer may not be supported on the porous sheet and may form a non-supporting layer as a layer of the polymer on the outside of the porous sheet. Additionally, the porous sheet may have a portion that does not support the polymer.

[0096] The unsaturated cyclic carbonate, which is a monomer that forms a group in the polymer described above, is a cyclic carbonate having unsaturated bonds between carbon atoms. Examples of unsaturated cyclic carbonates include vinylene carbonate (VC), ethylene carbonate (VEC), 1-phenylvinylene carbonate, and 1,2-diphenylvinylene carbonate. Among these, VC is preferred. That is, examples of polymers having structural units derived from unsaturated cyclic carbonates include polymers of polyvinylene carbonate, polyethylene ethylene carbonate, 1-phenylvinylene carbonate, and 1,2-diphenylvinylene carbonate, among which polyvinylene carbonate is preferred. The polymers having structural units derived from unsaturated cyclic carbonates can be composed of one or more structural units derived from unsaturated cyclic carbonates. Furthermore, multiple polymers described above can be mixed and used.

[0097] The polymer contained in the protective layer may be a copolymer having structural units derived from unsaturated cyclic carbonates and other structural units. The monomers that form the other structural units preferably contain vinyl groups, more preferably acryloyl groups, and even more preferably acryloyloxy groups. Furthermore, the monomers that form the other structural units preferably contain cyclic structures. Examples of cyclic structures contained in the monomers that form the other structural units include aliphatic carbocyclic rings, aliphatic heterocyclic rings, aromatic heterocyclic rings, etc., with a five-membered ring aliphatic heterocyclic rings being preferred. Examples of monomers that form the other structural units include tetrahydrofurfuryl acrylate. Examples of copolymers contained in the protective layer include copolymers having structural units derived from vinylene carbonate and structural units derived from tetrahydrofurfuryl acrylate.

[0098] The content of polymers containing structural units derived from unsaturated cyclic carbonates in the protective layer is preferably 50% by mass or more, and sometimes more preferably 70% by mass or more, 80% by mass or more, 90% by mass or more, or 95% by mass or more. The content of polymers containing structural units derived from unsaturated cyclic carbonates in the protective layer can be 100% by mass.

[0099] The content of polymers containing structural units derived from vinylene carbonate in the protective layer is preferably 50% by mass or more, and sometimes more preferably 70% by mass or more, 80% by mass or more, 90% by mass or more, or 95% by mass or more. The above content can be 100% by mass.

[0100] The porous sheet can be appropriately selected from known insulating materials used in energy storage elements. Examples of shapes for the porous sheet include woven fabric, nonwoven fabric, and porous resin membranes. Among these shapes, porous resin membranes are preferred from a strength point of view. Examples of materials for the porous sheet include polyolefins such as polyethylene and polypropylene, polyimide, and aromatic polyamides. Materials composed of these resins can also be used as porous sheets.

[0101] The porous sheet preferably has an outermost surface on the negative electrode active material layer side that does not contain inorganic compounds. By having an outermost surface on the negative electrode active material layer side that does not contain inorganic compounds, metallic lithium can easily and uniformly deposit along the surface of the negative electrode active material layer, further suppressing dendrite formation in the negative electrode. Furthermore, from the viewpoint of suppressing increased resistance in the negative electrode, it is sometimes preferable that the porous sheet does not contain an inorganic compound layer. Examples of inorganic compounds include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, strontium oxide, barium oxide, magnesium oxide, and aluminosilicates; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; insoluble ionic crystals such as calcium fluoride, barium fluoride, and barium titanate; covalently bonded crystals such as silicon and diamond; and substances derived from mineral resources or their man-made products, such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica.

[0102] As the upper limit of the air permeability of the porous sheet, from the viewpoint of improving the ion permeability in the protective layer, it is preferably 100 seconds / 100cm. 3 More preferably 70 seconds per 100cm 3 Further optimized is 50 seconds / 100cm 3 A further optimized value is 30 seconds per 100cm. 3 On the other hand, there is no specific limit to the lower limit of the air permeability of porous sheets; it can be 1 second / 100cm. 3 It can be 5 seconds / 100cm 3 It can also be 10 seconds per 100cm. 3 .

[0103] The protective layer preferably further comprises a lithium salt. The lithium salt is included in the protective layer, for example, in a state of being mixed with a polymer having structural units derived from unsaturated cyclic carbonates. By including the above-mentioned mixture of polymer and lithium salt in the protective layer, the flexibility of the protective layer can be improved, and crack formation in the protective layer can be suppressed. As the lithium salt, a suitable selection can be made from known lithium salts. Examples of lithium salts include LiPF6, LiPO2F2, LiClO4, and lithium imide salts. Among these, lithium imide salts are preferred. One or more lithium salts can be used.

[0104] The lithium imide salt preferably has a fluorine atom, specifically, for example, it preferably has a fluorosulfonyl group, a difluorophosphonoyl group, a fluoroalkyl group, etc. Among the lithium imide salts, lithium sulfonylimide salts are preferred, more preferably LiN(SO2CF3)2 (lithium bis(trifluoromethanesulfonyl)imide: LiTFSI) and LiN(SO2F)2 (lithium bis(fluorosulfonyl)imide: LiFSI), and even more preferably LiTFSI.

[0105] The lower limit for the content of lithium salt in the protective layer, based on a polymer having structural units derived from unsaturated cyclic carbonates, is preferably 1 mol / kg, more preferably 3 mol / kg, and even more preferably 5 mol / kg. When the lithium salt content is above the aforementioned lower limit, the warping of the negative electrode and cracking of the protective layer can be suppressed more reliably. Furthermore, the increase in the resistance of the negative electrode caused by the protective layer can be suppressed more reliably. On the other hand, the upper limit for the lithium salt content, from the viewpoint of ensuring the density and strength of the protective layer, is preferably 15 mol / kg, more preferably 12 mol / kg, and even more preferably 10 mol / kg.

[0106] (Isolation component)

[0107] As described above, non-aqueous electrolyte storage devices can include an isolator. The isolator can be appropriately selected from known isolators. As an isolator, a porous isolator that retains the aforementioned non-aqueous electrolyte is preferred. Examples of isolators include those consisting only of a substrate layer, or those with a heat-resistant layer containing heat-resistant particles and an adhesive formed on one or both sides of the substrate layer. Examples of the shape of the substrate layer for the isolator include woven fabric, non-woven fabric, and porous resin membrane. Among these shapes, porous resin membrane is preferred from the viewpoint of strength, and non-woven fabric is preferred from the viewpoint of retaining the non-aqueous electrolyte. As for the material of the substrate layer for the isolator, from the viewpoint of insulating function, polyolefins such as polyethylene and polypropylene are preferred, and from the viewpoint of resistance to oxidative decomposition, polyimide and aromatic polyamide are preferred. Materials composed of these resins can be used as the substrate layer for the isolator.

[0108] The heat-resistant particles contained in the heat-resistant layer preferably have a mass reduction of 5% or less when heated from room temperature to 500°C in an air atmosphere at 1 atmosphere, and more preferably have a mass reduction of 5% or less when heated from room temperature to 800°C. Inorganic compounds can be cited as materials for achieving this specified mass reduction. That is, the heat-resistant layer can be an inorganic particle layer containing inorganic particles and a binder. Examples of inorganic compounds include, for instance, the inorganic compounds described in the description of the porous sheet of the negative electrode. These substances can be used alone as monomers or in combination, or two or more can be used in combination. From the viewpoint of the safety of non-aqueous electrolyte energy storage elements, silicon oxide, aluminum oxide, or aluminosilicates are preferred among the inorganic compounds.

[0109] From a strength point of view, the porosity of the separator is preferably 80% by volume or less, and from a discharge performance point of view, preferably 20% by volume or more. Here, "porosity" is a volume-based value, referring to the value measured with a mercury porosimeter.

[0110] As a separator, a polymer gel composed of a polymer and a non-aqueous electrolyte can be used. Examples of polymers include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, and polyvinylidene fluoride. Using a polymer gel has the effect of suppressing leakage. As a separator, a porous resin membrane or nonwoven fabric, as described above, can be used in conjunction with the polymer gel. However, from the viewpoint of suppressing short circuits caused by dendrite precipitation in the negative electrode by increasing the strength of the separator, a separator other than a polymer gel (but rather a porous resin membrane, etc.) is preferred.

[0111] Except when the aforementioned polymer gel is used as the spacer, the spacer can be the same as the aforementioned porous sheet.

[0112] (Non-aqueous electrolyte)

[0113] The non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. The non-aqueous solvent preferably comprises a carbonate.

[0114] Examples of carbonates include fluorinated chain carbonates, fluorinated cyclic carbonates, chain carbonates without fluorine atoms, and cyclic carbonates without fluorine atoms. Examples of fluorinated chain carbonates include trifluoroethylmethyl carbonate (TFEMC) and bis(trifluoroethyl) carbonate (FDEC). Examples of fluorinated cyclic carbonates include fluoroethylene carbonate (FEC), difluoroethylene carbonate, fluoropropylene carbonate, trifluoroethyl ethylene carbonate, and fluorobutyl carbonate. Examples of chain carbonates without fluorine atoms include diethyl carbonate (DEC), methyl ethyl carbonate (EMC), dimethyl carbonate (DMC), and diphenyl carbonate. Examples of cyclic carbonates without fluorine atoms include ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinylene carbonate (VC), ethylene ethylene carbonate (VEC), ethylene chlorocarbonate, styrene carbonate, catechol carbonate, 1-phenylvinylene carbonate, and 1,2-diphenylvinylene carbonate. Fluorinated cyclic carbonates and cyclic carbonates without fluorine atoms are preferred. Furthermore, FEC is preferred as a fluorinated cyclic carbonate, and VC is more preferred as a cyclic carbonate without fluorine atoms. One or more types of carbonates may be used.

[0115] The non-aqueous solvent may contain other organic solvents besides carbonates. Examples of such other organic solvents include esters, ethers, amides, lactones, nitriles, sulfones, and sulfites. However, the carbonate content in the non-aqueous solvent is preferably 50% to 100% by volume, more preferably 70% to 100% by volume, and even more preferably 90% to 100% by volume. The carbonate content in the non-aqueous solvent may be 100% by volume.

[0116] Lithium salts are preferred as electrolyte salts. A suitable selection from known lithium salts can be made. Examples of lithium salts include LiPF6, LiPO2F2, LiClO4, and lithium imide salts. One or more lithium salts can be used.

[0117] Lithium imide salts are preferred as lithium salts. Lithium imide salts include not only those with a structure having two carbonyl groups bonded to a nitrogen atom, but also those with a structure having two sulfonyl groups bonded to a nitrogen atom, and those with a structure having two phosphonyl groups bonded to a nitrogen atom.

[0118] Examples of lithium imine salts include LiN(SO2F)2 (lithium bis(fluorosulfonyl)imine: LiFSI), LiN(SO2CF3)2 (lithium bis(trifluoromethanesulfonyl)imine: LiTFSI), LiN(SO2C2F5)2 (lithium bis(pentafluoroethanesulfonyl)imine: LiBETI), LiN(SO2C4F9)2 (lithium bis(nonafluorobutyryl)imine), CF3-SO2-N-SO2-N-SO2CF3Li2, F Sulfonylimide lithium salts such as SO2-N-SO2-C4F9Li, CF3-SO2-N-SO2-CF2-SO2-N-SO2-CF3Li2, CF3-SO2-N-SO2-CF2-SO3Li2, and CF3-SO2-N-SO2-CF2-SO2-C(-SO2CF3)2Li2; and phosphonylimide lithium salts such as LiN(POF2)2 (lithium bis(difluorophosphoryl)imide: LiDFPI).

[0119] The lithium imide salt preferably has a fluorine atom, specifically, for example, it preferably has a fluorosulfonyl group, a difluorophosphonoyl group, a fluoroalkyl group, etc. Among the lithium imide salts, lithium sulfonylimide salts are preferred, LiTFSI and LiFSI are more preferred, and LiTFSI is even more preferred.

[0120] The lithium salt content in the non-aqueous electrolyte is preferably 0.1 mol / dm³ at 20°C and 1 atmosphere. 3 ~2.5mol / dm 3 More preferably 0.3 mol / dm 3 ~2.0 mol / dm 3 Further preferably 0.5 mol / dm 3 ~1.7mol / dm 3 The preferred value is 0.7 mol / dm³. 3 ~1.5mol / dm 3 By maintaining the lithium salt content within the aforementioned range, the ionic conductivity of the non-aqueous electrolyte can be improved.

[0121] In addition to non-aqueous solvents and electrolyte salts, non-aqueous electrolytes may also contain additives. Examples of additives include aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, tert-butylbenzene, tert-amylbenzene, diphenyl ether, and dibenzofuran; partially halogenated 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; and succinic anhydride, glutaric anhydride, maleic anhydride, citrate anhydride, pentene anhydride, and tannins. Coumaric anhydride, cyclohexanedicarboxylic anhydride; vinyl sulfite, propylene sulfite, dimethyl sulfite, methyl methanesulfonate, busulfan, methyl toluenesulfonate, dimethyl sulfate, vinyl sulfate, sulfolane, dimethyl sulfone, diethyl sulfone, dimethyl sulfoxide, diethyl sulfoxide, tetramethyl sulfoxide, diphenyl sulfide, 4,4'-bis(2,2-dioxo-1,3,2-dioxothiapentane), 4-methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxothiapentane, thioanisole, diphenyl disulfide, dipyridine Disulfide, 1,3-propenesulfonyl lactone, 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, 1,4-butenesulfonyl lactone, perfluorooctane, tris(trimethylsilyl) borate, tris(trimethylsilyl) phosphate, tetra(trimethylsilyl) titanate, etc. These additives can be used alone or in combination of two or more.

[0122] The content of additives in the non-aqueous electrolyte is preferably 0.01% to 10% by mass relative to the total mass of the non-aqueous electrolyte, 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 setting the content of additives within the above range, it is possible to improve the capacity maintenance performance or cycling performance after high-temperature storage, or further improve safety.

[0123] The shape of the non-aqueous electrolyte energy storage element in this embodiment is not particularly limited. Examples include cylindrical batteries, square batteries, flat batteries, coin-shaped batteries, and button batteries.

[0124] Figure 4 A non-aqueous electrolyte storage element 10 is shown as an example of a square battery. It should be noted that this figure is a perspective view of the interior of the container. Electrode bodies 4, having positive and negative electrodes, are housed in a square container 5. The positive electrode is electrically connected to the positive terminal 6 via a positive electrode wire 61. The negative electrode is electrically connected to the negative terminal 7 via a negative electrode wire 71.

[0125] <Electronic Storage Devices>

[0126] The non-aqueous electrolyte energy storage element of this embodiment can be used as an energy storage unit (battery module) composed of multiple non-aqueous electrolyte energy storage elements and mounted in power supplies for automobiles such as EVs, HEVs, and PHEVs, power supplies for electronic devices such as personal computers and communication terminals, or energy storage power supplies. In this case, the technology of this invention can be applied to at least one non-aqueous electrolyte energy storage element included in the energy storage unit.

[0127] One embodiment of the energy storage device of the present invention includes two or more energy storage elements, and includes one or more non-aqueous electrolyte energy storage elements of the present invention described in one embodiment of the present invention (hereinafter referred to as "second embodiment"). The technology of one embodiment of the present invention can be applied to at least one non-aqueous electrolyte energy storage element included in the energy storage device of the second embodiment. It is possible to include one non-aqueous electrolyte energy storage element of the present invention and one or more energy storage elements unrelated to one embodiment of the present invention, or it is possible to include two or more non-aqueous electrolyte energy storage elements of the present invention described in one embodiment of the present invention.

[0128] Figure 5 An example of a second embodiment of an energy storage device 300 is shown, which further comprises energy storage units 200 consisting of two or more electrically connected non-aqueous electrolyte energy storage elements 10. The energy storage device 300 may include a busbar (not shown) electrically connecting two or more non-aqueous electrolyte energy storage elements 10, a busbar (not shown) electrically connecting two or more energy storage units 200, etc. The energy storage unit 200 or the energy storage device 300 may include a status monitoring device (not shown) for monitoring the status of one or more non-aqueous electrolyte energy storage elements 10.

[0129] <Methods for Manufacturing Non-Aqueous Electrolyte Energy Storage Components>

[0130] The manufacturing method of the non-aqueous electrolyte energy storage element of this embodiment can be appropriately selected from known methods. This manufacturing method includes, for example, the following steps: preparing an electrode body; preparing a non-aqueous electrolyte; and storing the electrode body and the non-aqueous electrolyte in a container. Preparing the electrode body includes the following steps: preparing a positive electrode; preparing a negative electrode; and forming the electrode body by stacking or winding the positive and negative electrodes with a spacer in between. Hereinafter, a method for manufacturing the negative electrode, as an embodiment of the present invention, will be described in detail.

[0131] (Method for manufacturing the negative electrode)

[0132] A method for manufacturing a negative electrode according to one embodiment of the present invention includes the following steps: preparing a negative electrode material having a negative electrode active material layer comprising lithium metal; preparing a polymer solution comprising a polymer having structural units derived from unsaturated cyclic carbonates; preparing a porous sheet; and using the polymer solution and the porous sheet, laminating a protective layer onto the negative electrode active material layer. The protective layer comprises the polymer and a porous sheet carrying at least a portion of the polymer.

[0133] The negative electrode material can be the negative electrode substrate and negative electrode active material layer described in the instructions for preparing the negative electrode of the non-aqueous electrolyte energy storage element.

[0134] The preparation of a polymer solution comprising a polymer having structural units derived from the aforementioned unsaturated cyclic carbonates can be achieved by dissolving the aforementioned polymer (or copolymer) described in the description of the negative electrode of the non-aqueous electrolyte storage element in an organic solvent. A lithium salt described in the description of the negative electrode of the non-aqueous electrolyte storage element may be appropriately mixed into the polymer solution. The aforementioned polymer is obtained, for example, by polymerizing monomers such as unsaturated cyclic carbonates in a monomer-soluble solution, then adding the polymer dropwise to a poor solvent such as ethanol to precipitate it, followed by washing and drying.

[0135] The porous sheet described above can be the porous sheet used in the instructions for preparing the negative electrode of the non-aqueous electrolyte energy storage element.

[0136] The aforementioned protective layer can be laminated, for example, by coating a polymer solution onto a negative electrode active material layer, placing a porous sheet in the polymer solution, and then drying the polymer solution and the porous sheet. That is, the porous sheet is placed in the polymer solution, allowing the polymer solution to immerse the porous sheet, and then dried, thereby obtaining a protective layer containing a porous sheet carrying the polymer contained in the polymer solution.

[0137] <Other Implementation Methods>

[0138] It should be noted that the non-aqueous electrolyte energy storage element of the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the invention. For example, the configuration of other embodiments can be added to the configuration of a certain embodiment; in addition, a part of the configuration of a certain embodiment can be replaced with the configuration of other embodiments or known technology. Furthermore, a part of the configuration of a certain embodiment can be deleted. In addition, known technology can be added to the configuration of a certain embodiment.

[0139] The above embodiments describe the use of non-aqueous electrolyte energy storage elements as rechargeable non-aqueous electrolyte secondary batteries (lithium-ion secondary batteries), but the type, shape, size, and capacity of the non-aqueous electrolyte energy storage elements are arbitrary. This invention can also be applied to various secondary batteries, double-layer capacitors, or lithium-ion capacitors.

[0140] Example

[0141] The present invention will now be described in more detail with reference to embodiments, but the present invention is not limited to the following embodiments.

[0142] [Example 1]

[0143] (The production of the positive electrode)

[0144] Porous carbon and elemental sulfur were mixed at a mass ratio of 30:70. This mixture was placed in a sealed reaction vessel, which was then placed inside a sealed electric furnace. After 1 hour of argon flow, the temperature was increased to 150°C at a rate of 5°C / min and held for 5 hours. The mixture was then cooled to the solidification temperature of elemental sulfur, 80°C, and then again increased to 300°C at a rate of 5°C / min and held for 2 hours to perform heat treatment and produce the composite.

[0145] Using water as a dispersion medium, a positive electrode paste containing the aforementioned composite, acetylene black and monolayer carbon nanotubes as conductive agents, CMC as a thickener, and PAA and SBR as binders was prepared. This positive electrode paste was coated onto an aluminum positive electrode substrate and dried to fabricate the positive electrode.

[0146] (Preparation of the negative electrode)

[0147] A sheet-like lithium metal was prepared as both the negative electrode substrate and the negative electrode active material layer. Meanwhile, a polymer solution was prepared by dissolving polyvinyl carbonate (PVCA) in a mixed solvent of dimethyl sulfoxide (DMSO) and tetrahydrofuran (THF), and further mixing in lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). It should be noted that LiTFSI was mixed at a concentration of 1 mol / kg based on PVCA. Then, the polymer solution was coated onto the lithium metal, and the coated portion was subjected to an air permeability of 30 seconds / 100 cm⁻¹. 3 A porous sheet with an average thickness of 10 μm was used to obtain the negative electrode material. This porous sheet did not have an inorganic compound layer (inorganic particle layer). Then, the negative electrode material was temporarily dried at 80°C for 30 minutes, followed by vacuum drying at 80°C for 24 hours, thereby obtaining a negative electrode with a protective layer formed on the negative electrode active material layer.

[0148] (Preparation of non-aqueous electrolytes)

[0149] In a solvent prepared by mixing fluoroethylene carbonate (FEC) and vinylene carbonate (VC) in a 50:50 volume ratio as a non-aqueous solvent, at a concentration of 1.0 mol / dm³ 3 LiTFSI was dissolved at a concentration of 1000 to prepare a non-aqueous electrolyte.

[0150] (Assembly of energy storage components and initial discharge)

[0151] Using the aforementioned positive electrode, negative electrode, porous resin membrane separator with inorganic particle layers on both sides, and non-aqueous electrolyte, a non-aqueous electrolyte energy storage element was assembled. The non-aqueous electrolyte energy storage element was initially discharged at 25°C with a discharge current of 0.1C and a discharge termination voltage of 1.0V to obtain the non-aqueous electrolyte energy storage element of Example 1.

[0152] [Comparative Examples 1 to 3]

[0153] In the preparation of the negative electrode, the content of LiTFSI is as described in Table 1, and a protective layer is formed without using a porous sheet. Otherwise, the non-aqueous electrolyte storage devices of Comparative Examples 1 to 3 are obtained by following the same steps as in Example 1.

[0154] [Examples 2 to 6]

[0155] In the preparation of the negative electrode, the LiTFSI content was as described in Table 1, and a porous sheet with the permeability shown in Table 1 was used. Otherwise, the non-aqueous electrolyte energy storage elements of Examples 2 to 6 were obtained following the same steps as in Example 1. It should be noted that the porous sheet used in the non-aqueous electrolyte energy storage element of Example 6 is different from that in Examples 1 to 5, and the outermost layer on the positive electrode side has a heat-resistant inorganic compound layer (inorganic particle layer).

[0156] [Reference Example 1]

[0157] As the negative electrode, sheet-like metallic lithium without a protective layer is used. Otherwise, the non-aqueous electrolyte energy storage element of Reference Example 1 is obtained by following the same steps as in Example 1.

[0158] [evaluate]

[0159] For the obtained non-aqueous electrolyte energy storage device, the presence or absence of cracks in the protective layer (film formation), the resistance of the non-aqueous electrolyte energy storage device, and the deposition morphology of metallic lithium are evaluated as follows.

[0160] (Presence or absence of cracks in the protective layer)

[0161] The presence or absence of cracks in the protective layer was confirmed by cutting 5mm × 5mm test pieces from the negative electrode of each non-aqueous electrolyte storage element, following the same procedure as for determining the lithium salt content in the protective layer. The presence or absence of cracks in the protective layer was confirmed by examining the surface SEM images of the test pieces obtained using a scanning electron microscope (SEM). The confirmation results are shown in Table 1.

[0162] (Resistance of non-aqueous electrolyte energy storage components)

[0163] Under conditions of a voltage amplitude of 10mV and a frequency range of 7MHz to 100mHz, the AC impedance of the obtained non-aqueous electrolyte energy storage element was measured, and the real component of the impedance at 0.1MHz was taken as the resistance of the non-aqueous electrolyte energy storage element. The resistances of the obtained non-aqueous electrolyte energy storage elements are shown in Table 1.

[0164] (Forms of lithium metal precipitation)

[0165] For each non-aqueous electrolyte energy storage element obtained, constant current and constant voltage charging was performed at 25°C with a charging current of 0.1C and a charging termination voltage of 3.0V. After constant current discharging at 25°C with a discharging current of 0.1C and a discharging termination voltage of 1.0V, a 10-minute rest period was set. These charging and discharging processes were considered as one cycle, and 11 cycles were repeated.

[0166] After the second charging cycle, a 5mm × 5mm negative electrode test piece, obtained using the same steps as those used to confirm the presence or absence of cracks in the protective layer, was subjected to a cross-sectional SEM image using a scanning electron microscope (SEM). In the cross-sectional SEM image of the negative electrode, the morphology of the boundary between the observed deposited lithium metal and the negative electrode active material layer and the protective layer was defined as a non-smooth deposited morphology, while the morphology of the boundary between the observed lithium metal and the negative electrode active material layer and the protective layer was defined as a smooth deposited morphology. The evaluation results are shown in Table 1. Furthermore, after the 11th charging cycle, a 5mm × 5mm negative electrode test piece, obtained using the same steps as described above, was subjected to a cross-sectional SEM image using a scanning electron microscope (SEM). The cross-sectional SEM image of the negative electrode of Reference Example 1 at this time is shown in Table 1. Figure 6 The cross-sectional SEM image of the negative electrode in Example 2 is shown below. Figure 7 .

[0167]

[0168] As shown in Table 1, in Comparative Examples 1 to 3 where the protective layer did not contain porous sheets, lithium metal precipitated unevenly, while in Examples 1 to 6 where the protective layer contained porous sheets, lithium metal precipitated smoothly. That is, it shows that when the protective layer of the negative electrode contains porous sheets carrying polymers, dendrite precipitation can be suppressed.

[0169] exist Figure 6 In the diagram, A represents the separator / void portion, B represents the lithium metal deposition layer, and C represents the lithium metal in the negative electrode active material layer. In the cross-section of the negative electrode in Reference Example 1, the boundary between the deposited lithium metal and the negative electrode active material layer and protective layer is observed, and the lithium metal deposition surface is also uneven. Figure 7In the diagram, D represents the separator / void portion, E represents the protective layer, and F represents the lithium metal deposited layer and the lithium metal of the negative electrode active material layer. In the cross-section of the negative electrode in Example 2, the protective layer is on the side opposite to the negative electrode active material layer ( Figure 7 The lower part has a layer of polymer (non-supported layer) that is only light in color, on the side opposite to the negative electrode active material layer. Figure 7 The upper part has a layer (supporting layer) of polymer supported on a dark-colored porous sheet. A protective layer is formed integrally, with at least a portion of the polymer supported on the porous sheet polymer layer. According to... Figure 7 The average thickness of the protective layer is approximately 10 μm. In the cross-section of the negative electrode in Example 2, no boundary was observed between the deposited lithium metal and the negative electrode active material layer and the protective layer. That is, it is considered that the lithium metal was deposited uniformly and smoothly in Example 2.

[0170] Comparing Comparative Examples 1 to 3, cracks appeared in the protective layer when it did not contain LiTFSI, but no cracks appeared in the protective layer when it contained LiTFSI. The reason given is that the inclusion of LiTFSI in the protective layer improves its flexibility.

[0171] Comparing Comparative Examples 1 to 3, it was found that increasing the LiTFSI content in the protective layer reduced the resistance of the non-aqueous electrolyte energy storage element. The rationale is that the presence of LiTFSI in the protective layer increases ion permeability.

[0172] Comparing Examples 2 to 5, where the porous sheet of the protective layer does not have an inorganic particle layer and the LiTFSI content of the protective layer is the same, it was found that the lower the air permeability of the porous sheet, the more likely the resistance of the non-aqueous electrolyte energy storage element would decrease. The rationale is that the lower the air permeability of the porous sheet, the higher the ion permeability in the protective layer.

[0173] Industrial availability

[0174] This invention can be applied to electronic devices such as personal computers and communication terminals, as well as non-aqueous electrolyte energy storage components used as power sources for automobiles, etc.

[0175] Symbol Explanation

[0176] 10 Non-aqueous electrolyte energy storage components

[0177] 1 Positive electrode

[0178] 11 Positive electrode substrate

[0179] 12 Positive Electrode Active Material Layer

[0180] 2, 8, 9 negative electrodes

[0181] 21, 81, 91 negative electrode substrates

[0182] 22, 82, 92 negative electrode active material layers

[0183] 23, 83, 93 protective layers

[0184] 23a and 93a load-bearing layers

[0185] 23b Non-load-bearing layer

[0186] 93c porous layer

[0187] 3 isolation components

[0188] 4-electrode body

[0189] 5 containers

[0190] 6 positive extremes

[0191] 61 Positive wire

[0192] 7 negative extremes

[0193] 71 Negative conductor

[0194] 200 energy storage units

[0195] 300 energy storage device

Claims

1. A non-aqueous electrolyte energy storage element, comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte. The negative electrode has a negative electrode active material layer containing metallic lithium and a protective layer stacked on the negative electrode active material layer. The protective layer comprises a polymer having structural units derived from unsaturated cyclic carbonates and a porous sheet carrying at least a portion of the polymer.

2. The nonaqueous electrolyte storage element according to claim 1, wherein It further has a porous separator located between the positive electrode and the negative electrode and retaining the non-aqueous electrolyte.

3. The nonaqueous electrolyte storage element according to claim 1 or 2, wherein The protective layer has a polymer layer comprising the polymer and stacked on top of the negative electrode active material layer. At least a portion of the polymer in the polymer layer is supported on the porous sheet. The average thickness of the polymer layer is greater than 1 μm.

4. The nonaqueous electrolyte storage element according to claim 1 or 2, wherein The positive electrode contains a sulfur-based active material, and the non-aqueous electrolyte contains carbonate.

5. The nonaqueous electrolyte storage element according to claim 1 or 2, wherein The protective layer further comprises a lithium salt, wherein the lithium salt content based on the polymer is 1 mol / kg or more.

6. The nonaqueous electrolyte storage element according to claim 1 or 2, wherein The air permeability of the porous sheet is 100 seconds / 100 cm 3 The following.

7. The nonaqueous electrolyte storage element according to claim 1 or 2, wherein The outermost surface of the porous sheet on the side of the negative electrode active material layer does not contain an inorganic compound layer.

8. An energy storage device comprising two or more energy storage elements, and comprising one or more non-aqueous electrolyte energy storage elements as described in claim 1 or 2.

9. A method for manufacturing a negative electrode, comprising the following steps: Prepare an anode material having a negative electrode active material layer containing metallic lithium. Prepare polymer solutions comprising polymers having structural units derived from unsaturated cyclic carbonates. Prepare the multi-well plate, and Using the polymer solution and the porous sheet, a protective layer is stacked on the negative electrode active material layer; The protective layer comprises the polymer and a porous sheet carrying at least a portion of the polymer.

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