Nonaqueous electrolyte power storage element, power storage device, and method for manufacturing negative electrode

Abstract

A nonaqueous electrolyte power storage element according to one aspect of the present invention includes: a positive electrode; a negative electrode; and a nonaqueous electrolyte. The negative electrode includes: a negative electrode active material layer containing metallic lithium; and a protective layer laminated on the negative electrode active material layer. The protective layer includes: a polymer having a structural unit derived from an unsaturated cyclic carbonate; and a porous sheet that supports at least a portion of the polymer.

Description

Nonaqueous electrolyte storage element, storage device, and method for manufacturing negative electrode

[0001] The present invention relates to a nonaqueous electrolyte storage element, a storage device, and a method for manufacturing a negative electrode.

[0002] Due to their high energy density, non-aqueous electrolyte secondary batteries, such as lithium ion secondary batteries, are widely used in electronic devices such as personal computers and communication terminals, as well as in automobiles. Non-aqueous electrolyte secondary batteries generally have a pair of electrodes electrically isolated by a separator and a non-aqueous electrolyte interposed between the electrodes, and are configured to charge and discharge by transferring charge-transporting ions between the electrodes. In addition to non-aqueous electrolyte secondary batteries, capacitors such as lithium ion capacitors and electric double layer capacitors are also widely used as non-aqueous electrolyte storage elements.

[0003] In recent years, in order to increase the capacity of nonaqueous electrolyte storage elements, there has been a demand for higher-capacity negative electrodes. Metallic lithium has a significantly higher discharge capacity per mass of active material than graphite, which is currently widely used as a negative electrode active material in nonaqueous electrolyte storage elements. For this reason, nonaqueous electrolyte storage elements using metallic lithium as a negative electrode active material have been proposed (see Prior Art Document 1).

[0004] Special Publication No. 2020-517054

[0005] When metallic lithium is used as the negative electrode active material, there is a concern that branch-like metallic lithium (dendrites) may be deposited on the surface of the negative electrode.

[0006] An object of the present invention is to provide a nonaqueous electrolyte energy storage element and an energy storage device that include a negative electrode containing metallic lithium and that can suppress dendrite precipitation in the negative electrode, as well as to provide a method for producing a negative electrode that contains metallic lithium and that can suppress dendrite precipitation.

[0007] A non-aqueous electrolyte storage element according to one aspect of the present invention includes a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the negative electrode has a negative electrode active material layer containing metallic lithium and a protective layer laminated on the negative electrode active material layer, and the protective layer includes a polymer having a structural unit derived from an unsaturated cyclic carbonate and a porous sheet supporting at least a portion of the polymer.

[0008] An electricity storage device according to another aspect of the present invention includes two or more electricity storage elements and one or more nonaqueous electrolyte electricity storage elements according to the one aspect of the present invention.

[0009] A method for producing a negative electrode according to another aspect of the present invention includes preparing a negative electrode material having a negative electrode active material layer containing metallic lithium, preparing a polymer solution containing a polymer having a structural unit derived from an unsaturated cyclic carbonate, preparing a porous sheet, and laminating a protective layer on the negative electrode active material layer using the polymer solution and the porous sheet, wherein the protective layer includes the polymer and a porous sheet supporting at least a portion of the polymer.

[0010] According to one aspect of the present invention, it is possible to provide a nonaqueous electrolyte storage element and a storage device that include a negative electrode containing metallic lithium and that can suppress dendrite precipitation in the negative electrode, as well as a method for manufacturing a negative electrode that contains metallic lithium and that can suppress dendrite precipitation.

[0011] FIG. 1 is a schematic cross-sectional view of an electrode body of a nonaqueous electrolyte storage element according to one embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of an electrode body of a nonaqueous electrolyte storage element different from that of FIG. 1. FIG. 3 is a schematic cross-sectional view of an electrode body of a nonaqueous electrolyte storage element different from that of FIGS. 1 and 2. FIG. 4 is a see-through perspective view showing one embodiment of a nonaqueous electrolyte storage element. FIG. 5 is a schematic view showing one embodiment of an electricity storage device formed by assembling a plurality of nonaqueous electrolyte storage elements. FIG. 6 is an SEM cross-sectional image of an electrode body in a nonaqueous electrolyte storage element of Reference Example 1. FIG. 7 is an SEM cross-sectional image of an electrode body in a nonaqueous electrolyte storage element of Example 2.

[0012] First, an outline of the method for manufacturing the nonaqueous electrolyte storage element and the negative electrode disclosed in this specification will be described.

[0013] [1] A nonaqueous electrolyte storage element according to one aspect of the present invention includes a positive electrode, a negative electrode, and a nonaqueous electrolyte. The negative electrode has a negative electrode active material layer containing metallic lithium and a protective layer laminated on the negative electrode active material layer. The protective layer includes a polymer having a structural unit derived from an unsaturated cyclic carbonate and a porous sheet supporting at least a portion of the polymer.

[0014] The nonaqueous electrolyte storage element described in [1] above can suppress dendrite precipitation on the negative electrode. While the reason for this is unclear, the following reason is presumed. Dendrites gradually grow due to the uneven deposition of metallic lithium on the negative electrode during charge / discharge cycles. Therefore, it is believed that maintaining a uniform deposition pattern of metallic lithium along the negative electrode surface can suppress dendrite precipitation. The nonaqueous electrolyte storage element described in [1] above has a protective layer laminated on the negative electrode active material layer containing metallic lithium. Therefore, when metallic lithium precipitates on the negative electrode during charging, the metallic lithium precipitates sandwiched between the negative electrode active material layer and the protective layer. Furthermore, because the protective layer contains a polymer having structural units derived from an unsaturated cyclic carbonate, the surface of the protective layer is likely to be maintained smooth and dense. Furthermore, because the protective layer contains a porous sheet supporting at least a portion of the polymer having structural units derived from an unsaturated cyclic carbonate, the mechanical strength of the protective layer is high, and the shape of the protective layer is likely to be stably maintained. Therefore, in the nonaqueous electrolyte storage element described in [1] above, metallic lithium is likely to be deposited uniformly along the surface of the negative electrode active material layer, and deposition of dendrites in the negative electrode can be suppressed.

[0015] [2] The nonaqueous electrolyte storage element according to [1] above may further include a porous separator interposed between the positive electrode and the negative electrode and holding the nonaqueous electrolyte.

[0016] The nonaqueous electrolyte storage element described in [2] above further includes the porous separator that holds the nonaqueous electrolyte, which facilitates the supply of sufficient charge-transporting ions from the separator to the negative electrode, thereby suppressing an increase in the resistance of the nonaqueous electrolyte storage element.

[0017] [3] In the nonaqueous electrolyte storage element according to [1] or [2] above, the protective layer may have a polymer layer containing the polymer and laminated on the negative electrode active material layer, at least a portion of the polymer in the polymer layer may be supported on the porous sheet, and the average thickness of the polymer layer may be 1 μm or more.

[0018] In the nonaqueous electrolyte storage element described in [3] above, since the protective layer has the polymer layer laminated on the negative electrode active material layer, the surface of the protective layer facing the negative electrode active material layer is more likely to be maintained smooth and dense. Furthermore, since the average thickness of the polymer layer is equal to or greater than the lower limit, the polymer layer is more likely to be maintained stably. Therefore, precipitation of dendrites in the negative electrode can be more reliably suppressed.

[0019] [4] In the nonaqueous electrolyte storage element according to any one of [1] to [3] above, the positive electrode may contain a sulfur-based active material, and the nonaqueous electrolyte may contain a carbonate.

[0020] The nonaqueous electrolyte storage element described in [4] above has a positive electrode containing a sulfur-based active material, and therefore, when combined with the negative electrode containing metallic lithium, the discharge capacity can be increased. In addition, when the positive electrode contains a sulfur-based active material, a nonaqueous electrolyte containing carbonate is preferably used.

[0021] [5] In the nonaqueous electrolyte storage element according to any one of [1] to [4] above, the protective layer may further contain a lithium salt, and the content of the lithium salt based on the polymer may be 1 mol / kg or more.

[0022] In the nonaqueous electrolyte storage element described in [5] above, the protective layer further contains a lithium salt, and the content of the lithium salt relative to the polymer is equal to or greater than the lower limit. This makes it possible to suppress warping of the negative electrode when the protective layer is laminated. Furthermore, the ion permeability of the protective layer is improved, thereby suppressing an increase in the resistance of the negative electrode due to the protective layer. Furthermore, the flexibility of the protective layer is improved, thereby suppressing the occurrence of cracks in the protective layer.

[0023] The contents of the polymer and the lithium salt in the protective layer are measured based on a sample prepared by the following procedure. A nonaqueous electrolyte storage element is discharged at a constant current of 0.1 C to a discharge end voltage during normal use to obtain a discharged state. The discharged nonaqueous electrolyte storage element is disassembled, the negative electrode is removed, and the negative electrode is thoroughly washed with dimethyl carbonate and then dried under reduced pressure at room temperature. The protective layer laminated on the negative electrode active material layer is then separated from the negative electrode and collected as a sample. The operations from disassembly of the nonaqueous electrolyte storage element to collection of the sample are performed in a dry air atmosphere with a dew point of −40° C. or lower. “During normal use” refers to the case where the nonaqueous electrolyte storage element is used under charge / discharge conditions recommended or specified for the nonaqueous electrolyte storage element, and, if equipment for using the nonaqueous electrolyte storage element is available, the nonaqueous electrolyte storage element is used with that equipment.

[0024] [6] In the nonaqueous electrolyte storage element according to any one of [1] to [5] above, the porous sheet has an air permeability of 100 sec / 100 cm ３ It may be the following:

[0025] "Air permeability" is also called the Gurley value, and is the value measured at a constant pressure difference of 100 cm ３ This indicates the time it takes for air to pass through a sample with a certain area, and is a value measured in accordance with JIS-P-8117 (2009).

[0026] In the nonaqueous electrolyte storage element described in [6] above, the air permeability of the porous sheet is equal to or less than the upper limit, and therefore the nonaqueous electrolyte can move more easily through the protective layer, thereby increasing the ion permeability of the protective layer, and therefore an increase in the resistance of the negative electrode due to the protective layer can be suppressed.

[0027] [7] In the nonaqueous electrolyte storage element according to any one of [1] to [6] above, the porous sheet may not include an inorganic compound layer on the outermost surface on the negative electrode active material layer side.

[0028] When the porous sheet includes an inorganic compound layer on the outermost surface facing the negative electrode active material layer, metallic lithium is likely to deposit non-uniformly between the inorganic compound and the negative electrode active material layer. In contrast, in the nonaqueous electrolyte storage element described above in [7], the porous sheet does not include an inorganic compound layer on the outermost surface facing the negative electrode active material layer, so metallic lithium is likely to deposit uniformly along the surface of the negative electrode active material layer, and dendrite deposition in the negative electrode can be further suppressed.

[0029] [8] An electricity storage device according to another aspect of the present invention includes two or more electricity storage elements, and includes one or more of the nonaqueous electrolyte electricity storage elements according to any one of [1] to [7].

[0030] The electricity storage device according to the above [8] includes one or more of the nonaqueous electrolyte electricity storage elements according to any one of the above [1] to [7], and therefore can suppress the deposition of dendrites in the negative electrode.

[0031] [9] A method for producing a negative electrode according to another aspect of the present invention includes preparing a negative electrode material having a negative electrode active material layer containing metallic lithium, preparing a polymer solution containing a polymer having a structural unit derived from an unsaturated cyclic carbonate, preparing a porous sheet, and laminating a protective layer on the negative electrode active material layer using the polymer solution and the porous sheet, wherein the protective layer includes the polymer and a porous sheet supporting at least a portion of the polymer.

[0032] The method for producing a negative electrode described in [9] above can produce a negative electrode having a protective layer laminated on a negative electrode active material layer containing metallic lithium. In this negative electrode, when metallic lithium precipitates on the negative electrode during charging, the metallic lithium precipitates sandwiched between the negative electrode active material layer and the protective layer. Furthermore, because the protective layer contains a polymer having structural units derived from an unsaturated cyclic carbonate, the surface of the protective layer is easily maintained smooth and dense. Furthermore, because the protective layer contains a porous sheet supporting at least a portion of the polymer having structural units derived from an unsaturated cyclic carbonate, the mechanical strength of the protective layer is high, and the shape of the protective layer is easily maintained stably. Therefore, the method for producing a negative electrode described in [9] above can produce a negative electrode in which metallic lithium is easily precipitated uniformly along the surface of the negative electrode active material layer and dendrite precipitation in the negative electrode is suppressed.

[0033] Hereinafter, a nonaqueous electrolyte storage element, a storage device, a method for manufacturing a nonaqueous electrolyte storage element, and other embodiments according to one embodiment of the present invention will be described in detail. A method for manufacturing a negative electrode according to one embodiment of the present invention will be described in the description of the method for manufacturing a nonaqueous electrolyte storage element. Note that the names of the components (elementary components) used in each embodiment may differ from the names of the components (elementary components) used in the background art.

[0034] <Non-aqueous electrolyte storage element> A non-aqueous electrolyte storage element according to one embodiment of the present invention includes an electrode assembly having a positive electrode and a negative electrode, a non-aqueous electrolyte, and a container for accommodating the electrode assembly and the non-aqueous electrolyte. The negative electrode includes a negative electrode active material layer containing metallic lithium and a protective layer laminated on the negative electrode active material layer. The protective layer includes a polymer having a structural unit derived from an unsaturated cyclic carbonate and a porous sheet supporting at least a portion of the polymer.

[0035] The electrode assembly is a laminated type in which a plurality of positive electrodes and a plurality of negative electrodes are laminated, or a wound type in which positive electrodes and negative electrodes are laminated with a separator interposed therebetween and wound. The electrode assembly may further include a separator interposed between the positive electrodes and the negative electrodes. In this case, the electrode assembly is formed in a state in which the positive electrodes and negative electrodes are laminated with the separator interposed therebetween.

[0036] The non-aqueous electrolyte is present in a state of being contained in the positive electrode, the negative electrode, and, in some cases, the separator. As an example of the non-aqueous electrolyte storage element, a non-aqueous electrolyte secondary battery will be described.

[0037] This nonaqueous electrolyte storage element has a protective layer laminated on a negative electrode active material layer containing metallic lithium. Therefore, when metallic lithium precipitates on the negative electrode during charging, the metallic lithium precipitates sandwiched between the negative electrode active material layer and the protective layer. Furthermore, because the protective layer contains a polymer having structural units derived from an unsaturated cyclic carbonate, the surface of the protective layer is likely to be maintained smooth and dense. Furthermore, because the protective layer contains a porous sheet supporting at least a portion of the polymer having structural units derived from an unsaturated cyclic carbonate, the mechanical strength of the protective layer is high, and the shape of the protective layer is likely to be stably maintained. Therefore, in this nonaqueous electrolyte storage element, metallic lithium is likely to precipitate uniformly along the surface of the negative electrode active material layer, and dendrite precipitation in the negative electrode can be suppressed.

[0038] FIG. 1 is a schematic cross-sectional view of an electrode assembly of a nonaqueous electrolyte storage element according to one embodiment of the present invention. The electrode assembly is formed by stacking a positive electrode 1 and a negative electrode 2 with a separator 3 interposed therebetween. The positive electrode 1 includes a positive electrode substrate 11 and a positive electrode active material layer 12 stacked on the positive electrode substrate 11. The negative electrode 2 includes a negative electrode substrate 21, a negative electrode active material layer 22 containing metallic lithium stacked on the negative electrode substrate 21, and a protective layer 23 stacked on the negative electrode active material layer 22. In the electrode assembly, the positive electrode substrate 11, the positive electrode active material layer 12, the separator 3, the protective layer 23, the negative electrode active material layer 22, and the negative electrode substrate 21 are stacked in this order. Note that intermediate layers 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 these are omitted from FIG. 1 .

[0039] The protective layer 23 includes a non-supported layer 23b, which is a layer of a polymer having structural units derived from an unsaturated cyclic carbonate and is not supported on the porous sheet, and a supported layer 23a, which contains the polymer and is supported on the porous sheet. The supported layer 23a is formed in a state in which the pores of the porous sheet are filled with the polymer. In this embodiment, the supported layer 23a is disposed opposite the separator 3, and the non-supported layer 23b is disposed opposite the negative electrode substrate 21. In other words, the supported layer 23a and the non-supported layer 23b collectively form a polymer layer that contains the polymer and is laminated on the negative electrode active material layer 22.

[0040] In this embodiment, metallic lithium contained in the anode active material layer 22 can be precipitated between the anode active material layer 22 and the protective layer 23, more specifically, between the anode active material layer 22 and the non-supported layer 23b (between the anode active material layer 22 and the polymer layer) during charging. As described above, the surface of the protective layer 23 is likely to be maintained smooth and dense, and the shape of the protective layer 23 is also likely to be stably maintained, so that metallic lithium is likely to be precipitated uniformly along the surface of the anode active material layer 22. In other words, a smooth metallic lithium layer is likely to be formed between the anode active material layer 22 and the protective layer 23 (between the anode active material layer 22 and the non-supported layer 23b).

[0041] The average thickness of the porous sheet (support layer 23a) may be 1 μm or more and 20 μm or less, 2 μm or more and 18 μm or less, or 4 μm or more and 16 μm or less. When the average thickness of the porous sheet (support layer 23a) is within the above range, the shape of the protective layer 23 is more likely to be maintained stably.

[0042] The average thickness of the non-supporting layer 23b may be 0.5 μm or more and 5 μm or less, 0.8 μm or more and 4 μm or less, or 1 μm or more and 3 μm or less. When the average thickness of the non-supporting layer 23b is within the above range, the surface of the porous sheet is sufficiently covered with the polymer. Therefore, the surface of the protective layer 23 is more likely to be maintained smooth and dense.

[0043] The average thickness of the polymer layer (the total of the supported layer 23 a and the non-supported layer 23 b) 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 or more and 20 μm or less. When the average thickness of the polymer layer is within the above range, the shape of the protective layer 23 is more likely to be maintained stably.

[0044] In this embodiment, the separator 3 is porous and can retain a non-aqueous electrolyte. Because the separator 3 is porous and can retain a non-aqueous electrolyte, a sufficient amount of charge-transporting ions such as lithium ions can be easily supplied from the separator 3 to the positive electrode 1 and the negative electrode 2. This makes it possible to suppress an increase in the resistance of the non-aqueous electrolyte storage element.

[0045] FIG. 2 is a schematic cross-sectional view of an electrode assembly of a nonaqueous electrolyte storage element according to another embodiment of the present invention. The electrode assembly is formed by stacking a positive electrode 1 and a negative electrode 8 with a separator 3 interposed therebetween. The negative electrode 8 includes a negative electrode substrate 81, a negative electrode active material layer 82 containing metallic lithium stacked on the negative electrode substrate 81, and a protective layer 83 stacked on the negative electrode active material layer 82. In the electrode assembly, the positive electrode substrate 11, the positive electrode active material layer 12, the separator 3, the protective layer 83, the negative electrode active material layer 82, and the negative electrode substrate 81 are stacked in this order. Note that intermediate layers 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 these are omitted from FIG. 2 .

[0046] The protective layer 83 includes a polymer having a structural unit derived from an unsaturated cyclic carbonate and a porous sheet supporting the polymer. More specifically, the protective layer 83 consists only of a support layer containing the polymer supported on the porous sheet. The protective layer 83 is formed in a state in which the pores of the porous sheet are filled with the polymer. In other words, the support layer (protective layer 83) includes the polymer and forms a polymer layer laminated on the negative electrode active material layer 82.

[0047] In this embodiment, metallic lithium contained in the negative electrode active material layer 82 can be precipitated 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 likely to be maintained smooth and dense, and the shape of the protective layer 83 is also likely to be stably maintained. Therefore, metallic lithium is likely to be precipitated uniformly along the surface of the negative electrode active material layer 82. In other words, a smooth layer of metallic lithium is likely to be formed between the negative electrode active material layer 82 and the protective layer 83.

[0048] The average thickness of the protective layer 83 may be the same as the average thickness of the polymer layer (the total of the supported layer 23a and the unsupported layer 23b) described above.

[0049] FIG. 3 is a schematic cross-sectional view of an electrode body of a nonaqueous electrolyte storage element according to yet another embodiment of the present invention. The electrode body is formed by stacking a positive electrode 1 and a negative electrode 9. The negative electrode 9 includes 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 in this order. Note that intermediate layers 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 these are omitted from FIG. 3 .

[0050] The protective layer 93 includes a polymer having structural units derived from an unsaturated cyclic carbonate and a porous sheet supporting the polymer. More specifically, the protective layer 93 includes a porous layer 93c, which is a layer of a porous sheet that does not support the polymer, and a support layer 93a, which includes the polymer and is supported on the porous sheet. The support layer 93a is formed in a state in which the pores of the porous sheet are filled with the polymer. In this embodiment, the support layer 93a is disposed opposite the negative electrode active material layer 92, and the porous layer 93c is disposed opposite the positive electrode active material layer 92. In other words, the support layer 93a includes the polymer and forms a polymer layer laminated on the negative electrode active material layer 92.

[0051] In this embodiment, metallic lithium contained in the negative electrode active material layer 92 can precipitate between the negative electrode active material layer 92 and the protective layer 93, more specifically, between the negative electrode active material layer 92 and the support 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 likely to be maintained smooth and dense, and the shape of the protective layer 93 is also likely to be stably maintained, so that metallic lithium is likely to be uniformly precipitated along the surface of the negative electrode active material layer 92. In other words, a smooth layer of metallic lithium is likely to be formed between the negative electrode active material layer 92 and the protective layer 93 (between the negative electrode active material layer 92 and the support layer 93a).

[0052] In this embodiment, the porous layer 93c of the protective layer 93 can retain a non-aqueous electrolyte. Because the porous layer 93c can retain a non-aqueous electrolyte in this manner, sufficient charge-transporting ions such as lithium ions are likely to be supplied from the porous layer 93c to the positive electrode 1 and the negative electrode 9. When the protective layer 93 is configured to partially retain a non-aqueous electrolyte in this manner, it is not necessary to provide an additional separator or the like between the positive electrode 1 and the negative electrode 9 for retaining the non-aqueous electrolyte. Therefore, a good balance can be achieved between the mechanical strength of the protective layer 93 and the ion permeability between the positive electrode 1 and the negative electrode 9.

[0053] The average thickness of the support layer 93 a may be the same as the average thickness of the polymer layer (the sum of the support layer 23 a and the non-support layer 23 b) described above. The average thickness of the porous layer 93 c is not particularly limited, but may be, for example, 1 μm or more and 20 μm or less.

[0054] The positive electrode, negative electrode, separator, and nonaqueous electrolyte of the nonaqueous electrolyte storage element according to one embodiment of the present invention will be described in detail below.

[0055] (Positive Electrode) The positive electrode has a positive electrode substrate and a positive electrode active material layer disposed on the positive electrode substrate directly or via an intermediate layer.

[0056] The positive electrode substrate has electrical conductivity. Whether or not it has electrical conductivity is determined by whether or not the volume resistivity measured in accordance with JIS-H-0505 (1975) is 10 ７The resistance is determined using Ω cm as a threshold value. Metals such as aluminum, titanium, tantalum, and stainless steel, or alloys thereof, are used as the material for the positive electrode substrate. Among these, aluminum or aluminum alloys are preferred from the viewpoints of potential resistance, high conductivity, and cost. Examples of the positive electrode substrate include foil, vapor-deposited film, mesh, and porous material, with foil being preferred from the viewpoint of cost. Therefore, aluminum foil or aluminum alloy foil is preferred as the positive electrode substrate. Examples of aluminum or aluminum alloys include A1085, A3003, and A1N30, as specified in JIS-H-4000 (2014) or JIS-H-4160 (2006).

[0057] The intermediate layer is a layer disposed between the positive electrode substrate and the positive electrode active material layer. The intermediate layer contains a conductive agent such as carbon particles to reduce the contact resistance between the positive electrode substrate and the positive electrode active material layer. The configuration of the intermediate layer is not particularly limited, and may contain, for example, a binder and a conductive agent.

[0058] The positive electrode active material layer preferably contains a sulfur-based active material, more preferably a composite of porous carbon and a sulfur-based active material. The positive electrode active material layer contains optional components such as a conductive agent, a binder, a thickener, and a filler as needed. The positive electrode active material layer is usually formed from a positive electrode mixture containing the composite and other optional components.

[0059] The composite of porous carbon and sulfur-based active material may have a form in which the porous carbon and sulfur-based active material are contained in a single particle. The composite may have a form in which at least a portion of the sulfur-based active material is disposed in the pores of the porous carbon. In other words, the composite may have a form in which at least a portion of the sulfur-based active material is impregnated into the porous carbon. In addition, the composite usually has a coating derived from the nonaqueous electrolyte formed on its surface. It is preferable that this coating is also formed in the pores of the composite.

[0060] Porous carbon is a porous body containing carbon as the main constituent element. The main constituent element refers to the element that is most abundant on a mass basis. The carbon content in the porous carbon is preferably 80 mass% or more, more preferably 90 mass% or more, and even more preferably 95 mass% or more. The porous carbon may be composed essentially of carbon element only. The porous carbon may further contain other elements such as oxygen element in addition to carbon element.

[0061] The content of porous carbon in the composite (the mass ratio of porous carbon to the mass of the entire composite) is preferably 10% by mass or more and 50% by mass or less, more preferably 20% by mass or more and 45% by mass or less, and even more preferably 30% by mass or more and 40% by mass or less. By setting the content of porous carbon in the composite within the above range, it is possible to increase the discharge capacity of the nonaqueous electrolyte storage element, etc.

[0062] The sulfur-based active material functions as a positive electrode active material. The sulfur-based active material may be elemental sulfur or a sulfur compound. Examples of sulfur compounds include metal sulfides such as lithium sulfide, organic disulfide compounds, and organic sulfur compounds such as carbon sulfide compounds. The sulfur-based active material has advantages such as a high theoretical capacity and low cost.

[0063] When the sulfur-based active material forms a composite, the content of the sulfur-based active material in the composite (the mass ratio of the sulfur-based active material to the mass of the entire composite) is preferably 50% by mass or more and 90% by mass or less, more preferably 55% by mass or more and 80% by mass or less, and even more preferably 60% by mass or more and 70% by mass or less. By setting the content of the sulfur-based active material in the composite within the above range, it is possible to increase the discharge capacity of the nonaqueous electrolyte storage element, etc.

[0064] The main elements constituting the composite are carbon and sulfur. The composite may further contain oxygen, and may further contain fluorine and the like. The oxygen and fluorine may be elements constituting a coating derived from the nonaqueous electrolyte. This coating may also contain carbon, hydrogen, lithium, and the like.

[0065] The content of the sulfur-based active material in the positive electrode active material layer is preferably 50% by mass to 90% by mass, more preferably 60% by mass to 80% by mass, which can increase the discharge capacity and the energy density.

[0066] When the sulfur-based active material forms a composite, the content of the composite in the positive electrode active material layer is preferably 60% by mass to 95% by mass, more preferably 70% by mass to 90% by mass. By setting the content of the composite within the above range, it is possible to increase the discharge capacity and the energy density.

[0067] The positive electrode active material layer may contain a positive electrode active material other than the sulfur-based active material, provided that the content of the sulfur-based active material in the total positive electrode active material 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.

[0068] The conductive agent is not particularly limited as long as it is a material having electrical conductivity. Note that this conductive agent does not include the porous carbon that constitutes the composite. Examples of such conductive agents include carbonaceous materials, metals, conductive ceramics, etc. Examples of carbonaceous materials include graphite, non-graphitic carbon, graphene-based carbon, etc. Examples of non-graphitic carbon include carbon nanofiber, pitch-based carbon fiber, carbon black, etc. Examples of carbon black include furnace black, acetylene black, ketjen black, etc. Examples of graphene-based carbon include graphene, carbon nanotubes (CNT), fullerene, etc. The conductive agent may be in the form of powder, fiber, etc. As the conductive agent, one of these materials may be used alone, or two or more may be mixed. These materials may also be used in combination. For example, a composite of carbon black and CNT may be used. Among these, carbon black is preferred from the viewpoints of electronic conductivity and coatability, and acetylene black is particularly preferred. It is also preferable to use carbon black (preferably acetylene black) and CNT (preferably single-walled carbon nanotubes) in combination.

[0069] The content of the conductive agent in the positive electrode active material layer is preferably 1% by mass or more and 20% by mass or less, and more preferably 3% by mass or more and 15% by mass or less. By setting the content of the conductive agent in this range, the energy density of the nonaqueous electrolyte storage element can be increased.

[0070] Examples of binders include thermoplastic resins such as fluororesins (polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), etc.), polyethylene, polypropylene, polyacrylic, polyimide, and polyacrylic acid (PAA); elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), and fluororubber; and polysaccharide polymers.

[0071] The content of the binder in the positive electrode active material layer is preferably 1% by mass to 10% by mass, more preferably 3% by mass to 9% by mass. By setting the binder content within this range, the composite and the like can be stably maintained.

[0072] Examples of thickeners include polysaccharide polymers such as carboxymethyl cellulose (CMC) and methyl cellulose. When the thickener has a functional group that reacts with lithium or the like, the functional group may be deactivated in advance by methylation or the like. The content of the thickener in the positive electrode active material layer is preferably 0.5% by mass or more and 10% by mass or less, and more preferably 2% by mass or more and 5% by mass or less. In one embodiment of the present invention, the positive electrode active material layer may not contain a thickener.

[0073] The filler is not particularly limited. 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, 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, mineral-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, and artificial products thereof. The content of the filler in the positive electrode active material layer is preferably, for example, 0.1% by mass or more and 10% by mass or less. In one embodiment of the present invention, the positive electrode active material layer may not contain a filler.

[0074] The positive electrode active material layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, and I; typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba; and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Nb, and W as components other than the sulfur-based active material, other positive electrode active material other than the sulfur-based active material, porous carbon, conductive agent, binder, thickener, and filler.

[0075] The negative electrode has a negative electrode substrate, a negative electrode active material layer disposed on the negative electrode substrate directly or via an intermediate layer, and a protective layer. The configuration of the intermediate layer is not particularly limited and can be selected from the configurations exemplified for the positive electrode above, for example.

[0076] The negative electrode substrate is conductive. Metals such as copper, nickel, stainless steel, and nickel-plated steel, alloys thereof, and carbonaceous materials are used as the material of the negative electrode substrate. Among these, copper or copper alloys are preferred. Examples of the negative electrode substrate include foil, vapor-deposited film, mesh, and porous material, with foil being preferred from the viewpoint of cost. 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.

[0077] 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 setting the average thickness of the negative electrode substrate within the above range, the strength of the negative electrode substrate can be increased while increasing the energy density per volume of the nonaqueous electrolyte storage element.

[0078] The negative electrode active material layer contains metallic lithium. The metallic lithium is a component that functions as a negative electrode active material. The metallic lithium may exist as pure metallic lithium consisting essentially of lithium element alone, or may exist as a lithium alloy containing other metal elements. Examples of the lithium alloy include a lithium-silver alloy, a lithium-zinc alloy, a lithium-calcium alloy, a lithium-aluminum alloy, a lithium-magnesium alloy, and a lithium-indium alloy. The lithium alloy may contain multiple metal elements other than lithium element.

[0079] The negative electrode active material layer may be a layer made only 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.

[0080] The negative electrode active material layer may be a pure metal lithium foil or a lithium alloy foil. The negative electrode active material layer may be a non-porous layer (solid layer). The negative electrode active material layer may be a porous layer containing metallic lithium. The average thickness of the negative electrode active material layer in the charged state is preferably 5 μm to 1,000 μm, more preferably 10 μm to 500 μm, and even more preferably 30 μm to 300 μm. The "average thickness of the negative electrode active material layer in the charged state" refers to the average thickness of one negative electrode active material layer in the charged state. For example, when negative electrode active material layers are provided on both sides of the negative electrode substrate, the "average thickness of the negative electrode active material layer in the charged state" refers to the value per side. The "charged state" refers to a state in which the non-aqueous electrolyte storage element is charged at a constant current and constant voltage at a current of 0.1 C to the end-of-charge voltage during normal use.

[0081] The negative electrode active material layer may further contain a negative electrode active material other than metallic lithium, provided that the content of metallic lithium relative to all the negative electrode active materials contained in the negative electrode active material layer is preferably 90 mass% or more, more preferably 99 mass% or more, and even more preferably 100 mass%.

[0082] The negative electrode active material layer may further contain optional components such as a conductive agent, a binder, a thickener, a filler, etc. The optional components such as the conductive agent, the binder, the thickener, and the filler can be selected from the materials exemplified for the positive electrode above.

[0083] The negative electrode active material layer may contain typical non-metallic elements such as B, N, P, F, Cl, Br, and I; typical metallic elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga, Ge, Sn, Sr, and Ba; and transition metal elements such as Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, and W as components other than the negative electrode active material, conductive agent, binder, thickener, and filler.

[0084] The protective layer includes a polymer having a structural unit derived from an unsaturated cyclic carbonate 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-supported layer, which is a layer of the polymer, outside the porous sheet. Furthermore, the porous sheet may have a portion that does not support the polymer.

[0085] The unsaturated cyclic carbonate, which is the monomer that forms the basis of the polymer, is a cyclic carbonate having an unsaturated bond between carbon atoms. Examples of unsaturated cyclic carbonates include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), 1-phenylvinylene carbonate, and 1,2-diphenylvinylene carbonate. Of these, VC is preferred. That is, examples of the polymer having a structural unit derived from an unsaturated cyclic carbonate include polyvinylene carbonate, polyvinyl ethylene carbonate, a polymer of 1-phenylvinylene carbonate, and a polymer of 1,2-diphenylvinylene carbonate, with polyvinylene carbonate being preferred. The polymer having a structural unit derived from an unsaturated cyclic carbonate may be composed of structural units derived from one or more types of unsaturated cyclic carbonates. Furthermore, a mixture of multiple types of the polymers may be used.

[0086] The polymer contained in the protective layer may be a copolymer having a structural unit derived from an unsaturated cyclic carbonate and another structural unit. The monomer that forms the basis of the other structural unit preferably contains a vinyl group, more preferably contains an acryloyl group, and even more preferably contains an acryloyloxy group. The monomer that forms the basis of the other structural unit also preferably contains a cyclic structure. Examples of the cyclic structure contained in the monomer that forms the basis of the other structural unit include an aliphatic carbon ring, an aliphatic heterocycle, and an aromatic heterocycle, and a five-membered aliphatic heterocycle is preferred. An example of the monomer that forms the basis of the other structural unit is tetrahydrofurfuryl acrylate. The copolymer contained in the protective layer may be a copolymer having a structural unit derived from vinylene carbonate and a structural unit derived from tetrahydrofurfuryl acrylate.

[0087] The content of the polymer having a structural unit derived from an unsaturated cyclic carbonate in the polymer contained in the protective layer is preferably 50% by mass or more, and more preferably 70% by mass or more, 80% by mass or more, 90% by mass or more, or 95% by mass or more in some cases. The content of the polymer having a structural unit derived from an unsaturated cyclic carbonate in the protective layer may be 100% by mass.

[0088] The content of the polymer having a structural unit derived from vinylene carbonate in the polymer contained in the protective layer is preferably 50% by mass or more, and in some cases 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 may be 100% by mass.

[0089] The porous sheet can be appropriately selected from known separators used in energy storage elements. Examples of the shape of the porous sheet include woven fabric, nonwoven fabric, and porous resin film. Among these shapes, porous resin film is preferred from the viewpoint of strength. Examples of materials for the porous sheet include polyolefins such as polyethylene and polypropylene, polyimide, and aramid. A composite material of these resins may also be used as the porous sheet.

[0090] The porous sheet preferably does not include an inorganic compound layer on its outermost surface adjacent to the negative electrode active material layer. By not including an inorganic compound layer on its outermost surface adjacent to the negative electrode active material layer, metallic lithium is more likely to be uniformly deposited along the surface of the negative electrode active material layer, thereby further suppressing dendrite deposition in the negative electrode. Furthermore, from the viewpoint of suppressing an increase in the resistance of the negative electrode, it may be preferable that the porous sheet does not include 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 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; covalently bonded crystals such as silicon and diamond; mineral-derived substances such as talc, montmorillonite, boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, and mica, as well as artificial products thereof.

[0091] The upper limit of the air permeability of the porous sheet is 100 seconds / 100 cm from the viewpoint of increasing the ion permeability in the protective layer. ３ is preferred, and 70 seconds / 100 cm ３ More preferably, 50 seconds / 100 cm ３ More preferably, 30 seconds / 100 cm ３ On the other hand, the lower limit of the air permeability of the porous sheet is not particularly limited, but is preferably 1 sec / 100 cm ３ 5 seconds / 100 cm ３ 10 seconds / 100 cm ３ may be.

[0092] It is preferable that the protective layer further contains a lithium salt. The lithium salt is contained in the protective layer in a state where it is mixed with, for example, a polymer having a structural unit derived from an unsaturated cyclic carbonate. When the protective layer contains a mixture of the polymer and the lithium salt, the flexibility of the protective layer can be increased and the occurrence of cracks in the protective layer can be suppressed. The lithium salt can be appropriately selected from known lithium salts. The lithium salt can be LiPF６ , LiPO ２ F ２ , LiClO ４ , lithium imide salts, etc. Among these, lithium imide salts are preferred. One or more kinds of lithium salts can be used.

[0093] The lithium imide salt preferably has a fluorine atom, specifically, for example, a fluorosulfonyl group, a difluorophosphonyl group, a fluoroalkyl group, or the like. Among the lithium imide salts, lithium sulfonylimide salts are preferred, and LiN(SO ２ CF ３ ) ２ (lithium bis(trifluoromethanesulfonyl)imide: LiTFSI) and LiN(SO ２ F) ２ (Lithium bis(fluorosulfonyl)imide: LiFSI) is more preferred, and LiTFSI is even more preferred.

[0094] The lower limit of the lithium salt content in the protective layer based on the polymer having a structural unit derived from an unsaturated cyclic carbonate is preferably 1 mol / kg, more preferably 3 mol / kg, and even more preferably 5 mol / kg. When the lithium salt content is equal to or greater than the above lower limit, warping of the negative electrode and cracking in the protective layer can be more reliably suppressed. Furthermore, an increase in the resistance of the negative electrode due to the protective layer can be more reliably suppressed. On the other hand, the upper limit of the lithium salt content is preferably 15 mol / kg, more preferably 12 mol / kg, and even more preferably 10 mol / kg, from the viewpoint of ensuring the density and strength of the protective layer.

[0095] (Separator) The nonaqueous electrolyte storage element may include a separator as described above. The separator can be appropriately selected from known separators. A porous separator capable of retaining a nonaqueous electrolyte is preferred. Examples of separators that can be used include a separator consisting of only a substrate layer, and a separator in which a heat-resistant layer containing heat-resistant particles and a binder is formed on one or both surfaces of the substrate layer. Examples of the shape of the substrate layer of the separator include woven fabric, nonwoven fabric, and porous resin film. Among these shapes, porous resin film is preferred from the viewpoint of strength, and nonwoven fabric is preferred from the viewpoint of nonaqueous electrolyte retention. As the material for the substrate layer of the separator, polyolefins such as polyethylene and polypropylene are preferred from the viewpoint of shutdown function, and polyimide and aramid are preferred from the viewpoint of oxidative decomposition resistance. A composite material of these resins may also be used for the substrate layer of the separator.

[0096] The heat-resistant particles contained in the heat-resistant layer preferably exhibit a mass loss of 5% or less when heated from room temperature to 500°C in an air atmosphere at 1 atmosphere, and more preferably exhibit a mass loss of 5% or less when heated from room temperature to 800°C. Examples of materials exhibiting a mass loss of a predetermined amount or less include inorganic compounds. That is, the heat-resistant layer may be an inorganic particle layer containing inorganic particles and a binder. Examples of inorganic compounds include those described above in the description of the porous sheet of the negative electrode. As the inorganic compound, these substances may be used alone or in the form of a composite, or two or more of them may be mixed and used. Among inorganic compounds, silicon oxide, aluminum oxide, or aluminosilicate is preferred from the viewpoint of safety of the nonaqueous electrolyte storage element.

[0097] The porosity of the separator is preferably 80% by volume or less from the viewpoint of strength, and is preferably 20% by volume or more from the viewpoint of discharge performance. Here, "porosity" refers to a volume-based value measured with a mercury porosimeter.

[0098] The separator may be a polymer gel composed of a polymer and a nonaqueous electrolyte. Examples of polymers include polyacrylonitrile, polyethylene oxide, polypropylene oxide, polymethyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, and polyvinylidene fluoride. The use of a polymer gel has the effect of suppressing leakage. The separator may be a combination of a porous resin film or nonwoven fabric, as described above. However, from the viewpoint of increasing the strength of the separator and suppressing short circuits due to dendrite precipitation in the negative electrode, it is preferable that the separator is not a polymer gel (a porous resin film, etc.).

[0099] Except for the case where the polymer gel is used as the separator, the separator may be the same as the porous sheet described above.

[0100] (Non-aqueous Electrolyte) The non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. The non-aqueous solvent preferably contains a carbonate.

[0101] Examples of carbonates include fluorinated chain carbonates, fluorinated cyclic carbonates, chain carbonates that do not contain fluorine atoms, and cyclic carbonates that do not contain fluorine atoms.Examples of fluorinated chain carbonates include trifluoroethyl methyl carbonate (TFEMC), bis(trifluoroethyl) carbonate (FDEC), etc.Examples of fluorinated cyclic carbonates include fluorinated ethylene carbonates such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate, fluorinated propylene carbonates such as fluoromethylethylene carbonate, and fluorinated butylene carbonates such as trifluoroethylethylene carbonate.Examples of chain carbonates that do not contain fluorine atoms include diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diphenyl carbonate, etc. Examples of fluorine atom-free cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), vinylethylene carbonate (VEC), chloroethylene carbonate, styrene carbonate, catechol carbonate, 1-phenylvinylene carbonate, and 1,2-diphenylvinylene carbonate. Among these, fluorinated cyclic carbonates and fluorine atom-free cyclic carbonates are preferred. Furthermore, FEC is preferred as the fluorinated cyclic carbonate, and VC is more preferred as the fluorine atom-free cyclic carbonate. One or more carbonates can be used.

[0102] The non-aqueous solvent may contain an organic solvent other than carbonate. Examples of such organic solvents include esters, ethers, amides, lactones, nitriles, sulfones, and sulfites. However, the content of carbonate in the non-aqueous solvent is preferably 50% by volume or more and 100% by volume or less, more preferably 70% by volume or more and 100% by volume or less, and even more preferably 90% by volume or more and 100% by volume or less. The content of carbonate in the non-aqueous solvent may be 100% by volume.

[0103] The electrolyte salt is preferably a lithium salt. The lithium salt can be appropriately selected from known lithium salts. Examples of the lithium salt include LiPF ６ , LiPO ２ F ２ , LiClO ４ , lithium imide salts, etc. One or more kinds of lithium salts can be used.

[0104] The lithium salt is preferably a lithium imide salt, which means not only a lithium imide salt having a structure in which two carbonyl groups are bonded to a nitrogen atom, but also a lithium imide salt having a structure in which two sulfonyl groups are bonded to a nitrogen atom, a lithium imide salt having a structure in which two phosphonyl groups are bonded to a nitrogen atom, etc.

[0105] The lithium imide salt is LiN(SO ２ F) ２ (lithium bis(fluorosulfonyl)imide: LiFSI), LiN(SO ２ CF ３ ) ２ (lithium bis(trifluoromethanesulfonyl)imide: LiTFSI), LiN(SO ２ C ２ F ５ ) ２ (lithium bis(pentafluoroethanesulfonyl)imide: LiBETI), LiN(SO ２ C ４ F ９ ) ２ (lithium bis(nonafluorobutanesulfonyl)imide), CF ３ -SO ２ -N-SO ２ -N-SO ２ CF ３ Li ２ , FSO ２ -N-SO ２ -C ４ F ９ Li, CF ３ -SO ２ -N-SO ２ -CF ２ -SO ２ -N-SO ２ -CF ３ Li２ , C.F. ３ -SO ２ -N-SO ２ -CF ２ -SO ３ Li ２ , C.F. ３ -SO ２ -N-SO ２ -CF ２ -SO ２ -C(-SO ２ CF ３ ) ２ Li ２ Lithium sulfonylimide salts such as LiN(POF ２ ) ２ Examples include lithium phosphonylimide salts such as lithium bis(difluorophosphonyl)imide (LiDFPI).

[0106] The lithium imide salt preferably has a fluorine atom, specifically, for example, a fluorosulfonyl group, a difluorophosphonyl 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.

[0107] The content of lithium salt in the non-aqueous electrolyte is 0.1 mol / dm at 20°C and 1 atmosphere. ３ 2.5mol / dm or more ３ It is preferably 0.3 mol / dm or less. ３ 2.0mol / dm or more ３ It is more preferable that it is 0.5 mol / dm or less. ３ More than 1.7mol / dm ３ It is more preferable that it is 0.7 mol / dm or less. ３ 1.5mol / dm or more ３ By setting the content of the lithium salt within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

[0108] The non-aqueous electrolyte may contain additives in addition to the non-aqueous solvent and the electrolyte salt. Examples of the additives include aromatic compounds such as biphenyl, alkylbiphenyl, 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; succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, and cyclohexanedicarboxylic anhydride; ethylene sulfite, propylene sulfite, and dimethyl sulfite. Examples of such additives include 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-propene sultone, 1,3-propane sultone, 1,4-butane sultone, 1,4-butene sultone, perfluorooctane, tristrimethylsilyl borate, tristrimethylsilyl phosphate, and tetrakistrimethylsilyl titanate. These additives may be used alone or in combination of two or more.

[0109] The content of the additive contained in the non-aqueous electrolyte is preferably 0.01% by mass to 10% by mass, more preferably 0.1% by mass to 7% by mass, even more preferably 0.2% by mass to 5% by mass, and particularly preferably 0.3% by mass to 3% by mass, based on the total mass of the 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, and further improve safety.

[0110] The shape of the nonaqueous electrolyte storage element of this embodiment is not particularly limited, and examples thereof include cylindrical batteries, prismatic batteries, flat batteries, coin batteries, and button batteries.

[0111] Figure 4 shows a nonaqueous electrolyte storage element 10 as an example of a prismatic battery. This figure is a see-through view of the interior of the container. An electrode assembly 4 having a positive electrode and a negative electrode is housed in a prismatic container 5. The positive electrode is electrically connected to a positive electrode terminal 6 via a positive electrode lead 61. The negative electrode is electrically connected to a negative electrode terminal 7 via a negative electrode lead 71.

[0112] <Electricity Storage Device> The nonaqueous electrolyte storage element of the present embodiment can be mounted as an electricity storage unit (battery module) comprising a plurality of nonaqueous electrolyte storage elements in a power source for an automobile such as an EV, HEV, or PHEV, a power source for electronic devices such as a personal computer or a communication terminal, or a power source for power storage, etc. In this case, the technology of the present invention may be applied to at least one of the nonaqueous electrolyte storage elements included in the electricity storage unit.

[0113] An electricity storage device according to one embodiment of the present invention includes two or more electricity storage elements, and includes one or more nonaqueous electrolyte storage elements according to one embodiment of the present invention (hereinafter referred to as the "second embodiment"). It is sufficient that the technology according to one embodiment of the present invention is applied to at least one nonaqueous electrolyte storage element included in the electricity storage device according to the second embodiment, and the electricity storage device may include one nonaqueous electrolyte storage element according to one embodiment of the present invention and one or more storage elements not according to one embodiment of the present invention, or may include two or more nonaqueous electrolyte storage elements according to one embodiment of the present invention.

[0114] 5 shows an example of an energy storage device 300 according to a second embodiment in which energy storage units 200, each of which is an assembly of two or more electrically connected nonaqueous electrolyte energy storage elements 10, are further assembled. The energy storage device 300 may include a bus bar (not shown) that electrically connects two or more nonaqueous electrolyte energy storage elements 10, a bus bar (not shown) that electrically connects 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) that monitors the status of one or more nonaqueous electrolyte energy storage elements 10.

[0115] <Method for Manufacturing Nonaqueous Electrolyte Storage Element> The method for manufacturing the nonaqueous electrolyte storage element of this embodiment can be appropriately selected from known methods. The manufacturing method includes, for example, preparing an electrode assembly, preparing a nonaqueous electrolyte, and housing the electrode assembly and the nonaqueous electrolyte in a container. Preparing the electrode assembly includes preparing a positive electrode, preparing a negative electrode, and forming the electrode assembly by stacking or winding the positive electrode and the negative electrode with a separator interposed therebetween. Hereinafter, preparing the negative electrode will be described in detail as a method for manufacturing a negative electrode according to one embodiment of the present invention.

[0116] (Method for Manufacturing Negative Electrode) A method for manufacturing a negative electrode according to one embodiment of the present invention includes: preparing a negative electrode material having a negative electrode active material layer containing metallic lithium; preparing a polymer solution containing a polymer having structural units derived from an unsaturated cyclic carbonate; preparing a porous sheet; and laminating a protective layer on the negative electrode active material layer using the polymer solution and the porous sheet. The protective layer includes the polymer and a porous sheet supporting at least a portion of the polymer.

[0117] Preparing the negative electrode material may be preparing the negative electrode substrate and negative electrode active material layer described in the description of the negative electrode of the nonaqueous electrolyte storage element.

[0118] The preparation of a polymer solution containing a polymer having structural units derived from the unsaturated cyclic carbonate may be performed by dissolving the polymer (or copolymer) described in the description of the negative electrode of the nonaqueous electrolyte storage element in an organic solvent. This polymer solution may optionally be mixed with the lithium salt described in the description of the negative electrode of the nonaqueous electrolyte storage element. The polymer can be obtained, for example, by polymerizing a monomer such as an unsaturated cyclic carbonate in a solution in which the monomer is soluble, dropping the polymer into a poor solvent such as ethanol to precipitate it, and then washing and drying it.

[0119] The preparation of the porous sheet may be the preparation of the porous sheet described in the description of the negative electrode of the nonaqueous electrolyte storage element.

[0120] The protective layer may be formed by, for example, applying a polymer solution to the negative electrode active material layer, placing a porous sheet on the polymer solution, and drying the polymer solution and the porous sheet. That is, by placing a porous sheet on the polymer solution, allowing the polymer solution to penetrate into the porous sheet, and then drying, a protective layer including a porous sheet supporting the polymer contained in the polymer solution can be obtained.

[0121] <Other Embodiments> The nonaqueous electrolyte storage element of the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the spirit of the present invention. For example, the configuration of one embodiment may be added to the configuration of another embodiment, or part of the configuration of one embodiment may be replaced with the configuration of another embodiment or well-known technology. Furthermore, part of the configuration of one embodiment may be deleted. Furthermore, well-known technology may be added to the configuration of one embodiment.

[0122] In the above embodiment, the nonaqueous electrolyte storage element is used as a chargeable and dischargeable nonaqueous electrolyte secondary battery (lithium ion secondary battery), but the type, shape, size, capacity, etc. of the nonaqueous electrolyte storage element are arbitrary. The present invention can also be applied to various secondary batteries, electric double layer capacitors, lithium ion capacitors, and other capacitors.

[0123] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0124] [Example 1] (Preparation of Positive Electrode) Porous carbon and elemental sulfur were mixed in a mass ratio of 30:70. This mixture was placed in a sealed reaction vessel, which was then placed in a sealed electric furnace. After 1 hour of argon flow, the mixture was heated to 150°C at a rate of 5°C / min and held for 5 hours. Then, the mixture was allowed to cool to 80°C, the temperature at which elemental sulfur solidifies. The mixture was then heated again to 300°C at a rate of 5°C / min and held for 2 hours to prepare a composite. A positive electrode mixture paste was prepared using water as a dispersion medium, the composite obtained above, acetylene black and single-walled carbon nanotubes as conductive agents, CMC as a thickener, and PAA and SBR as binders. This positive electrode mixture paste was applied to an aluminum positive electrode substrate and dried to prepare a positive electrode.

[0125] (Preparation of Negative Electrode) Sheet-shaped metallic lithium was prepared as the negative electrode substrate and the negative electrode active material layer. Meanwhile, polyvinylene carbonate (PVCA) was dissolved in a mixed solvent of dimethyl sulfoxide (DMSO) and tetrahydrofuran (THF), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was further mixed to prepare a polymer solution. The LiTFSI was mixed so that the content was 1 mol / kg based on the PVCA. The polymer solution was then applied onto the metallic lithium, and the applied portion was coated with an air permeability of 30 seconds / 100 cm. ３ A porous sheet having an average thickness of 10 μm was placed on the negative electrode active material layer to obtain a negative electrode material. This porous sheet did not have an inorganic compound layer (inorganic particle layer). The negative electrode material was pre-dried at 80° C. for 30 minutes and then dried under reduced pressure at 80° C. for 24 hours to obtain a negative electrode having a protective layer formed on the negative electrode active material layer.

[0126] (Preparation of non-aqueous electrolyte) LiTFSI was added to a non-aqueous solvent, which was a mixture of fluoroethylene carbonate (FEC) and vinylene carbonate (VC) in a volume ratio of 50:50, at a concentration of 1.0 mol / dm ３ A non-aqueous electrolyte solution was prepared by dissolving the ammonium hydroxide in the solution at a concentration of 1.0.

[0127] (Assembly of Energy Storage Element and Initial Discharge) A nonaqueous electrolyte energy storage element was assembled using the above-mentioned positive electrode, negative electrode, porous resin film separator having inorganic particle layers on both sides, and nonaqueous electrolyte. This nonaqueous electrolyte energy storage element was initially discharged at 25° C. with a discharge current of 0.1 C and a discharge cut-off voltage of 1.0 V, to obtain a nonaqueous electrolyte energy storage element of Example 1.

[0128] [Comparative Examples 1 to 3] Non-aqueous electrolyte storage elements of Comparative Examples 1 to 3 were obtained in the same manner as in Example 1, except that in preparing the negative electrode, the content of LiTFSI was set as shown in Table 1 and a protective layer was formed without using a porous sheet.

[0129] [Examples 2 to 6] Non-aqueous electrolyte storage elements of Examples 2 to 6 were obtained in the same manner as in Example 1, except that in preparing the negative electrode, the content of LiTFSI was set as shown in Table 1 and a porous sheet having an air permeability shown in Table 1 was used. Unlike Examples 1 to 5, the porous sheet used in the non-aqueous electrolyte storage element of Example 6 had a layer of a heat-resistant inorganic compound (inorganic particle layer) as the outermost layer on the positive electrode side.

[0130] Reference Example 1 A nonaqueous electrolyte storage element of Reference Example 1 was obtained in the same manner as in Example 1, except that a sheet of metallic lithium without a protective layer was used as the negative electrode.

[0131] [Evaluation] The obtained nonaqueous electrolyte storage elements were evaluated for the presence or absence of cracks in the protective layer (film formability), the resistance of the nonaqueous electrolyte storage element, and the deposition state of metallic lithium as follows.

[0132] (Presence or absence of cracks in the protective layer) The presence or absence of cracks in the protective layer was confirmed by cutting a 5 mm × 5 mm test piece from the negative electrode removed from each nonaqueous electrolyte storage element, washed, and dried under reduced pressure using the same procedure as in measuring the lithium salt content in the protective layer described above. The presence or absence of cracks in the protective layer was confirmed by checking the surface SEM image of the test piece obtained using a scanning electron microscope (SEM). The confirmation results are shown in Table 1.

[0133] (Resistance of Nonaqueous Electrolyte Storage Element) For each of the obtained nonaqueous electrolyte storage elements, AC impedance measurements were performed under conditions of a voltage amplitude of 10 mV and a frequency range of 7 MHz to 100 mHz, and the real component of the impedance at 0.1 MHz was taken as the resistance of each nonaqueous electrolyte storage element. The resistances of the obtained nonaqueous electrolyte storage elements are shown in Table 1.

[0134] (Deposition form of metallic lithium) Each of the obtained nonaqueous electrolyte storage elements was subjected to constant-current / constant-voltage charging at 25° C. with a charging current of 0.1 C and a charge cut-off voltage of 3.0 V, followed by constant-current discharging at 25° C. with a discharging current of 0.1 C and a discharge cut-off voltage of 1.0 V, followed by a 10-minute rest period. These charge and discharge steps constitute one cycle, and were repeated 11 times.

[0135] After the second charge cycle, a 5 mm x 5 mm negative electrode specimen obtained using the same procedure as in the case of checking for cracks in the protective layer described above was used to obtain a cross-sectional SEM image of the negative electrode using a scanning electron microscope (SEM). In the cross-sectional SEM image of the negative electrode, a non-smooth deposition morphology was defined as a specimen in which the boundaries between the deposited metallic lithium and the negative electrode active material layer and protective layer were observed, while a smooth deposition morphology was defined as a specimen in which the boundaries between the deposited metallic lithium and the negative electrode active material layer and protective layer were not observed. The evaluation results are shown in Table 1. Furthermore, after the 11th charge cycle, a cross-sectional SEM image of the negative electrode was obtained using a scanning electron microscope (SEM) using a 5 mm x 5 mm negative electrode specimen obtained using the same procedure as described above. The cross-sectional SEM image of the negative electrode of Reference Example 1 at this time is shown in FIG. 6, and the cross-sectional SEM image of the negative electrode of Example 2 is shown in FIG. 7.

[0136]

[0137] As shown in Table 1, metallic lithium was deposited unevenly in Comparative Examples 1 to 3 in which the protective layer did not include a porous sheet, whereas metallic lithium was deposited smoothly in Examples 1 to 6 in which the protective layer included a porous sheet. In other words, it was demonstrated that when the protective layer of the negative electrode includes a porous sheet supporting a polymer, the deposition of dendrites can be suppressed.

[0138] In FIG. 6, A indicates the separator and voids, B indicates the layer where metallic lithium is deposited, and C indicates metallic lithium in the negative electrode active material layer. In the cross section of the negative electrode of Reference Example 1, the boundary between the deposited metallic lithium and the negative electrode active material layer and the protective layer is observed, and the metallic lithium deposition surface is not uniform. In FIG. 7, D indicates the separator and voids, E indicates the protective layer, and F indicates the layer where metallic lithium is deposited and metallic lithium in the negative electrode active material layer. In the cross section of the negative electrode of Example 2, the protective layer has a light-colored layer of polymer only (non-supported layer) on the side facing the negative electrode active material layer (lower part of FIG. 7), and a layer of polymer supported on a dark-colored porous sheet (supported layer) on the opposite side from the negative electrode active material layer (upper part of FIG. 7). The protective layer as a whole forms a polymer layer in which at least a portion of the polymer is supported on the porous sheet. From FIG. 7, the average thickness of the protective layer is about 10 μm. No boundaries between the deposited metallic lithium and the negative electrode active material layer or protective layer were observed in the cross section of the negative electrode of Example 2. That is, it is believed that metallic lithium was deposited uniformly and smoothly in Example 2.

[0139] Comparing Comparative Examples 1 to 3, when the protective layer did not contain LiTFSI, cracks occurred in the protective layer, but when the protective layer contained LiTFSI, cracks did not occur in the protective layer. The reason for this is thought to be that the flexibility of the protective layer was improved by the inclusion of LiTFSI in the protective layer.

[0140] Comparing Comparative Examples 1 to 3, increasing the LiTFSI content in the protective layer reduced the resistance of the nonaqueous electrolyte storage element, possibly because the inclusion of LiTFSI in the protective layer increased the ion permeability of the protective layer.

[0141] Comparing Examples 2 to 5, in which the porous sheet of the protective layer did not have an inorganic particle layer and the protective layer had the same LiTFSI content, the resistance of the nonaqueous electrolyte storage element tended to decrease as the air permeability of the porous sheet decreased, possibly because the ion permeability of the protective layer increased as the air permeability of the porous sheet decreased.

[0142] The present invention 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.

[0143] REFERENCE SIGNS LIST 10 Non-aqueous electrolyte storage element 1 Positive electrode 11 Positive electrode substrate 12 Positive electrode active material layer 2, 8, 9 Negative electrode 21, 81, 91 Negative electrode substrate 22, 82, 92 Negative electrode active material layer 23, 83, 93 Protective layer 23a, 93a Support layer 23b Non-support layer 93c Porous layer 3 Separator 4 Electrode body 5 Container 6 Positive electrode terminal 61 Positive electrode lead 7 Negative electrode terminal 71 Negative electrode lead 200 Energy storage unit 300 Energy storage device

Claims

1. A non-aqueous electrolyte storage element comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the negative electrode has a negative electrode active material layer containing metallic lithium and a protective layer laminated on the negative electrode active material layer, and the protective layer includes a polymer having a structural unit derived from an unsaturated cyclic carbonate and a porous sheet supporting at least a portion of the polymer.

2. The nonaqueous electrolyte storage element according to claim 1, further comprising a porous separator interposed between said positive electrode and said negative electrode and for holding said nonaqueous electrolyte.

3. A nonaqueous electrolyte storage element as described in claim 1 or 2, wherein the protective layer has a polymer layer containing the polymer and laminated on the negative electrode active material layer, at least a portion of the polymer in the polymer layer is supported on the porous sheet, and the average thickness of the polymer layer is 1 μm or more.

4. The non-aqueous 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 a carbonate.

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

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

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

8. An electricity storage device comprising two or more electricity storage elements, and comprising at least one nonaqueous electrolyte electricity storage element according to claim 1 or 2.

9. A method for manufacturing a negative electrode, comprising: preparing a negative electrode material having a negative electrode active material layer containing metallic lithium; preparing a polymer solution containing a polymer having a structural unit derived from an unsaturated cyclic carbonate; preparing a porous sheet; and laminating a protective layer on the negative electrode active material layer using the polymer solution and the porous sheet, wherein the protective layer includes the polymer and a porous sheet supporting at least a portion of the polymer.

Images