Lithium secondary battery

Abstract

The present invention provides a lithium secondary battery which has excellent energy efficiency per unit volume or unit weight. A lithium secondary battery according to one embodiment of the present invention is provided with a positive electrode, a negative electrode that does not comprise a negative electrode active material, and a separator that is arranged between the positive electrode and the negative electrode. At least a part of the edge of the negative electrode and the edge of the separator corresponding to the part of the edge of the negative electrode are arranged in the same position when viewed in plan.

Description

[Technical field]

[0001] The present invention relates to a lithium secondary battery. [Background technology]

[0002] In recent years, technology for converting natural energy such as solar or wind power into electrical energy has been attracting attention. Accordingly, various secondary batteries have been developed as electricity storage devices that are highly safe and capable of storing a large amount of electrical energy.

[0003] Among them, lithium secondary batteries, which charge and discharge by transferring lithium ions between a positive electrode and a negative electrode, are known to exhibit high voltage and high energy density. A typical lithium secondary battery is the lithium ion secondary battery (LIB), which has active materials capable of retaining lithium elements in the positive electrode and the negative electrode, and charges and discharges by transferring lithium ions between the positive electrode active material and the negative electrode active material.

[0004] Furthermore, in order to achieve high energy density, lithium secondary batteries (lithium metal batteries; LMBs) have been developed that use lithium metal as the negative electrode active material instead of materials that can insert lithium ions, such as carbon materials. For example, Patent Document 1 discloses a rechargeable battery that uses a lithium metal-based electrode as the negative electrode.

[0005] In addition, for the purpose of further increasing the energy density and improving productivity, lithium secondary batteries using negative electrodes that do not have negative electrode active materials such as carbon materials and lithium metal have been developed. For example, Patent Document 2 discloses a lithium secondary battery including a positive electrode, a negative electrode, a separator and an electrolyte interposed between them, in which metal particles are formed on a negative electrode current collector, and are transferred from the positive electrode by charging to form lithium metal on the negative electrode current collector in the negative electrode. Patent Document 2 discloses that such a lithium secondary battery can provide a lithium secondary battery with improved performance and life by solving problems caused by the reactivity of lithium metal and problems that occur during the assembly process. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 2006-500755 [Patent Document 2] Special Publication No. 2019-505971 Summary of the Invention [Problem to be solved by the invention]

[0007] In the above-mentioned lithium secondary battery, a pouch-type (or sometimes called laminate-type) lithium secondary battery may be constructed by stacking a positive electrode and a negative electrode with a separator interposed therebetween and encasing them in a laminate sheet. In such a pouch-type lithium secondary battery, in order to prevent the negative electrode active material deposited on the negative electrode from being separated from the negative electrode and coming into contact with the positive electrode to cause a short circuit, the edges of the positive electrode and the negative electrode are arranged with a margin provided so that they are spaced apart from the edge of the sheet-like separator by a certain amount or more. In this specification, the margin refers to the distance in plan view between the edge of the separator and the edge of the positive electrode or the negative electrode.

[0008] However, when such a margin is provided, the positive and negative electrodes must be made slightly smaller than the separator, which limits the size of the electrodes and therefore limits the energy density per unit volume and weight.

[0009] The present invention aims to increase the energy per unit volume and weight of a lithium secondary battery. [Means for solving the problem]

[0010] A lithium secondary battery according to one embodiment of the present invention includes a positive electrode, a negative electrode that does not have a negative electrode active material, and a separator disposed between the positive electrode and the negative electrode. In the lithium secondary battery, at least a portion of the edge of the negative electrode and an edge of the separator that corresponds to an edge of the portion of the negative electrode are disposed at the same position in a plan view.

[0011] The inventors have found that in a configuration in which the negative electrode does not have a negative electrode active material, it is possible to prevent short circuits between the electrodes without providing a margin between the edge of the separator and the edge of the negative electrode. The reason for this is presumed to be that since the negative electrode does not have an active material, the wrapping around of the material at the end face of the negative electrode material can be eliminated. In the lithium secondary battery of the present invention, the negative electrode does not have a negative electrode active material, and the edge of the separator and the edge of the negative electrode are at the same position in a plan view, that is, the margin, which is the distance between the edge of the separator and the edge of the negative electrode in a plan view, is substantially zero. This makes it possible to make the negative electrode larger than before while preventing short circuits between the electrodes. According to such a lithium secondary battery of the present invention, it is possible to make a configuration that increases the energy efficiency per unit volume and unit weight.

[0012] In the lithium secondary battery, the negative electrode and the separator are preferably rectangular, and at least one side of the rectangular negative electrode is preferably located at the same position as a side of the rectangular separator corresponding to the side of the negative electrode in a plan view.

[0013] In such a lithium secondary battery, a lithium secondary battery having a rectangular negative electrode and separator can be configured to have a larger negative electrode than conventional batteries, thereby increasing the energy efficiency per unit volume and unit weight of the lithium secondary battery.

[0014] In the lithium secondary battery, it is preferable that the other side of the negative electrode other than at least one side is located inward in a plan view from the other side of the separator corresponding to the other side of the negative electrode, and the distance between the other side of the negative electrode and the corresponding other side of the separator in a plan view is preferably 0.3 mm to 5.0 mm.

[0015] In such a lithium secondary battery, the margin, which is the distance between the edge of the separator and the edge of the negative electrode in a plan view, is set to substantially 0 for some of the four sides of the negative electrode in a plan view, and a margin of 0.3 mm to 5.0 mm is provided for the other sides. This configuration allows a configuration having a larger negative electrode than conventional ones while providing a minimum margin where necessary.

[0016] In the above-mentioned lithium secondary battery, it is preferable that the four sides of the negative electrode and the four sides of the separator are arranged at the same positions in a plan view.

[0017] In such a lithium secondary battery, the size of the negative electrode in a plan view can be made the same as the size of the separator, which allows for a larger negative electrode and results in a lithium secondary battery with improved energy efficiency per unit volume and unit weight.

[0018] In the above-mentioned lithium secondary battery, the edge of the positive electrode is preferably located inside the corresponding edge of the negative electrode in a plan view, and the distance between the edge of the positive electrode and the corresponding edge of the negative electrode in a plan view is preferably 0.3 mm or more.

[0019] Moreover, a lithium secondary battery according to one embodiment of the present invention includes a positive electrode, a negative electrode having no negative electrode active material, a separator disposed between the positive electrode and the negative electrode, and an exterior body that encloses the positive electrode, the negative electrode, and the separator. In this lithium secondary battery, at least a portion of the edge of the separator and an edge of the negative electrode on the same side as the portion of the edge are configured to be at the same distance from the inner wall of the exterior body that faces the separator.

[0020] In the above-mentioned lithium secondary battery, the negative electrode enclosed in the exterior body can be configured to be at least partially larger than in the past, thereby increasing the energy efficiency per unit volume and unit weight of the lithium secondary battery. Effect of the Invention

[0021] According to the present invention, it is possible to provide a lithium secondary battery having improved energy efficiency per unit volume and unit weight. [Brief description of the drawings]

[0022] [Figure 1] FIG. 1 is a plan view of a lithium secondary battery according to an embodiment of the present invention. [Diagram 2] 1 is a plan view showing a portion of a lithium secondary battery including a positive electrode, a negative electrode, and a separator according to an embodiment of the present invention. [Diagram 3] 1 is a diagram showing a part of a cross section of a lithium secondary battery according to an embodiment of the present invention. [Figure 4] FIG. 2 is a plan view showing a part of a lithium secondary battery including a positive electrode, a negative electrode, and a separator according to Modification 1 of the present invention. [Diagram 5] FIG. 11 is a plan view showing a part of a lithium secondary battery including a positive electrode, a negative electrode, and a separator according to Modification 2 of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Hereinafter, an embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described in detail with reference to the drawings as necessary. In the drawings, the same elements are given the same reference numerals, and duplicated explanations will be omitted. Furthermore, unless otherwise specified, positional relationships such as up, down, left, and right are based on the positional relationships shown in the drawings. Furthermore, the dimensional ratios of the drawings are not limited to those shown in the drawings.

[0024] [Lithium secondary battery configuration] Fig. 1 is a plan view showing the configuration of a lithium secondary battery 1 according to an embodiment of the present invention. Fig. 2 is a plan view showing a part of the lithium secondary battery 1 including a positive electrode, a negative electrode, and a separator according to an embodiment of the present invention. Fig. 3 is a diagram showing a part of a cross section of the lithium secondary battery 1.

[0025] As shown in Figs. 1 to 3, the lithium secondary battery 1 includes a positive electrode 11, a negative electrode 12, and a separator 13 disposed between the positive electrode 11 and the negative electrode 12. As shown in the cross-sectional view of Fig. 3, the positive electrode 11, the negative electrode 12, and the separator 13 are laminated in layers. As shown in Fig. 1, the lithium secondary battery 1 is configured by laminating a plurality of sets (cells) of the positive electrode 11, the negative electrode 12, and the separator 13. These positive electrodes 11, the negative electrodes 12, and the separator 13 are sealed in an exterior body 14 to form a pouch cell. A plurality of sets of the positive electrode 11, the negative electrode 12, and the separator 13 are enclosed in one pouch cell, but one set of the positive electrode 11, the negative electrode 12, and the separator 13 may be enclosed in one pouch cell. As shown in FIG. 1 and FIG. 2, a positive electrode terminal 15 and a negative electrode terminal 16 are connected to the positive electrode 11 and the negative electrode 12, respectively. These positive electrode terminals 15 and negative electrode terminals 16 are configured to extend outside the exterior body 14 constituting the pouch cell and be connected to an external circuit. As shown in FIG. 1 and FIG. 2, the surface of the lithium secondary battery 1 viewed from the direction in which the positive electrode 11, the negative electrode 12, and the separator 13 are stacked is a flat surface, and the shape is rectangular (square), but is not limited thereto. The shapes of the positive electrode 11, the negative electrode 12, and the separator 13 in plan view can be any shape, such as a circle, an ellipse, or a polygon, depending on the application. The shapes of the positive electrode 11, the negative electrode 12, and the separator 13 in plan view may be similar to each other.

[0026] The separator 13 prevents the positive electrode 11 and the negative electrode 12 from coming into contact with each other and causing a short circuit in the battery. In the lithium secondary battery 1 of this embodiment, since there is no active material in the negative electrode, the material of the end face of the negative electrode material can be prevented from wrapping around, so that the positive electrode 11 and the negative electrode 12 can be prevented from being short-circuited. Therefore, in the past, it was necessary to provide a negative electrode / separator margin (or simply "margin"), which is the distance between the edge 12a of the negative electrode 12 and the edge 13a of the separator 13 in a plan view, and to configure the edge 12a of the negative electrode 12 to be retreated inward from the edge 13a of the separator 13, but in the lithium secondary battery 1, it is not necessary to provide the margin. In the lithium secondary battery 1 of this embodiment, as shown in the cross-sectional view of FIG. 3, the margin between the edge 13a of the separator 13 and the edge 12a of the negative electrode 12 can be eliminated and substantially reduced to zero. At this time, for example, as shown in FIG. 2, the edge 12a of the negative electrode 12 and the edge 13a of the separator 13 are at the same position in a plan view at positions corresponding to sides A, B, and C. At the position corresponding to side D, the edge 12a of the negative electrode 12 and the edge 13a of the separator 13 are not at the same position in a plan view, and a margin is provided. In other words, at the position corresponding to side D, the edge 12a of the negative electrode 12 is arranged so as to be located inside the edge 13a of the separator 13 in a plan view. Also, at this position, the edge 11a of the positive electrode 11 is arranged so as to be located inside the edge 12a of the negative electrode 12 in a plan view. At the positions corresponding to sides A, B, and C, the edge 12a of the negative electrode 12 and the edge 13a of the separator 13 abut against the inner wall 14a of the exterior body 14 as shown in FIG.

[0027] On the other hand, in the lithium secondary battery 1, the positive electrode / separator margin, which is the distance between the edge 11a of the positive electrode 11 and the edge 13a of the separator 13, is set in the range of 0.3 mm to 0.5 mm, for example.

[0028] Even if the negative electrode / separator margin is substantially 0, an error of about ±0.3 mm may occur due to dimensional variations during manufacturing of the positive electrode 11, the negative electrode 12, and the separator 13, or misalignment during lamination. In this specification, even if the configuration has some margin due to dimensional variations and misalignment during manufacturing, the margin is considered to be substantially 0. The margin is considered to be substantially 0, in other words, the edge 12a of the negative electrode 12 and the edge 13a of the separator 13 are considered to be in the same position, for example, when the margin is 0.3 mm or less, preferably when the margin is 0.2 mm or less, and more preferably when the margin is 0.1 mm or less.

[0029] In addition, the edge 12a of the negative electrode 12 and the edge 13a of the separator 13 may not necessarily be in contact with the inner wall 14a of the exterior body 14. However, it is preferable that the edge 12a of the negative electrode 12 and the edge 13a of the separator 13 are at least partially at substantially the same distance from the opposing inner wall 14a of the exterior body 14. For the same reason, the distances between the inner wall 14a of the exterior body 14 and the edge 12a of the negative electrode 12 and the edge 13a of the separator 13 are considered to be substantially the same when the difference in the distances is within 0.3 mm, preferably within 0.2 mm, and more preferably within 0.1 mm.

[0030] 4, edge 12c of negative electrode 12B may have a configuration in which the margin is substantially zero at positions corresponding to all of its four sides A, B, C, and D. Also, as in the modification shown in FIG. 5, edge 12e of negative electrode 12D may have a margin of substantially zero only at a position corresponding to side B, and a margin may be provided at positions corresponding to the other sides. Note that, at the locations corresponding to the sides with the margins, edge 12a of negative electrode 12 is positioned inside edge 13a of separator 13, and edge 11a of positive electrode 11 is positioned inside edge 12a of negative electrode 12 in plan view.

[0031] That is, in the lithium secondary battery 1 of this embodiment, the rectangular negative electrode 12 and separator 13 are configured so that the margin is substantially zero on at least one side of the negative electrode 12 in a plan view, thereby making the negative electrode 12 larger than in the conventional configuration while preventing short circuits of the electrodes. Since the size of the negative electrode 12 can be increased as the number of sides of the negative electrode 12 that have a margin that is substantially zero increases, it is preferable to make the margin substantially zero on all four sides of the negative electrode 12. This makes it possible to achieve a configuration that increases the energy efficiency per unit volume and unit weight of the lithium secondary battery 1.

[0032] In addition, the margin is preferably set in the range of 0.3 mm to 5.0 mm on the side where the margin is provided. The minimum distance of the margin is preferably smaller than the manufacturing variation in the size of the negative electrode 12 and the separator 13, and may be 0.2 mm or more or 0.1 mm or more. Although it is preferable that the maximum distance of the margin is small, it is preferably 5.0 mm or less as described above, more preferably 3.0 mm or less, and even more preferably 1.0 mm or less.

[0033] Also, by making the margin, which is the distance between the edge of the negative electrode and the edge of the separator of the lithium secondary battery, at least partially substantially zero, a certain effect can be obtained in terms of making the negative electrode larger. For example, in a cylindrical cell in which the positive electrode 11, the negative electrode 12, and the separator 13 of the lithium secondary battery 1 are stacked and arranged in a cylindrical shape, the negative electrode can be made larger by providing a portion where the margin, which is the distance between the edge of the negative electrode 12 and the edge of the separator 13, is substantially zero, in the same manner as described above.

[0034] The lithium secondary battery of the present embodiment disclosed in this specification is typically a liquid electrolyte-based lithium secondary battery (particularly a nonaqueous electrolyte-based lithium secondary battery) having an electrolyte solution, a solid or semi-solid electrolyte-based lithium secondary battery having a polymer electrolyte, or a gel electrolyte-based lithium secondary battery having a gel electrolyte. However, as long as the problem of the present invention is solved, the lithium secondary battery of the present embodiment may be other than the above, for example, an all-solid-state battery having an inorganic solid electrolyte.

[0035] (Negative electrode) The negative electrode 12 does not have a negative electrode active material. In this specification, the term "negative electrode active material" refers to a material that causes an electrode reaction, i.e., an oxidation reaction and a reduction reaction, at the negative electrode. Specifically, the negative electrode active material of this embodiment includes a host material of lithium metal and lithium element (lithium ion or lithium metal). The host material of lithium element means a material provided to hold lithium ion or lithium metal in the negative electrode 12. The mechanism of such holding is not particularly limited, but includes, for example, intercalation, alloying, and occlusion of metal clusters, and is typically intercalation.

[0036] In the lithium secondary battery 1 of this embodiment, since the negative electrode 12 does not have a negative electrode active material before the initial charge of the battery, lithium metal is deposited on the negative electrode 12, and the deposited lithium metal is charged and discharged by electrolytic elution. Therefore, in the lithium secondary battery 1 of this embodiment, the volume occupied by the negative electrode active material and the mass of the negative electrode active material are reduced compared to a lithium secondary battery having a negative electrode active material, and the volume and mass of the entire battery are reduced, so that the energy density is in principle high.

[0037] In the lithium secondary battery 1 of this embodiment, the negative electrode 12 does not have a negative electrode active material before the initial charge of the battery, lithium metal is deposited on the negative electrode when the battery is charged, and the deposited lithium metal is electrolytically dissolved when the battery is discharged. Therefore, in the lithium secondary battery 1 of this embodiment, the negative electrode 12 functions as a negative electrode current collector.

[0038] The lithium secondary battery 1 of this embodiment differs from a lithium ion battery (LIB) and a lithium metal battery (LMB) in the following respects.

[0039] In a lithium ion battery (LIB), the negative electrode has a host material of lithium element (lithium ion or lithium metal), and when the battery is charged, the material is filled with lithium element, and when the host material releases the lithium element, the battery is discharged. The LIB differs from the lithium secondary battery 1 of this embodiment in that the negative electrode has a host material of lithium element.

[0040] A lithium metal battery (LMB) is manufactured using an electrode having lithium metal on its surface or elemental lithium metal as the negative electrode. That is, the LMB differs from the lithium secondary battery 1 of this embodiment in that the negative electrode has lithium metal as the negative electrode active material immediately after the battery is assembled, i.e., before the initial charge of the battery. The LMB is manufactured using an electrode containing highly flammable and reactive lithium metal, but the lithium secondary battery of this embodiment is manufactured using a negative electrode that does not contain lithium metal, and is therefore safer and more productive. Furthermore, the lithium secondary battery 1 of this embodiment is superior in energy density and cycle characteristics to the LMB.

[0042] In this specification, the term "lithium secondary battery having a negative electrode that does not have a negative electrode active material" means that the negative electrode does not have a negative electrode active material before the initial charge of the battery. Therefore, the phrase "negative electrode that does not have a negative electrode active material" may be rephrased as "negative electrode that does not have a negative electrode active material before the initial charge of the battery", "negative electrode that does not have a negative electrode active material other than lithium metal regardless of the charge state of the battery and does not have lithium metal before the initial charge", or "negative electrode current collector that does not have lithium metal before the initial charge", etc. In addition, the term "lithium battery having a negative electrode that does not have a negative electrode active material" may be rephrased as an anode-free lithium battery, a zero anode lithium battery, or an anode-less lithium battery.

[0043] In this specification, the term "before initial charge" refers to the state of the battery from assembly to the first charge, and the term "at the end of discharge" refers to the state in which a discharge reaction involving the positive electrode active material does not substantially occur even if the battery voltage is further reduced, and the battery voltage at this time is, for example, 1.0 to 3.5 V, 2.0 to 3.2 V, or 2.5 to 3.0 V.

[0046] In the lithium secondary battery 1 of this embodiment, when the battery voltage is 2.5 V or more and 3.5 V or less, the lithium metal content may be 10 mass % or less (preferably 5.0 mass % or less, and may be 1.0 mass % or less) relative to the entire negative electrode; or when the battery voltage is 2.5 V or more and 3.0 V or less, the lithium metal content may be 10 mass % or less (preferably 5.0 mass % or less, and may be 1.0 mass % or less) relative to the entire negative electrode.

[0047] In the lithium secondary battery 1 of this embodiment, the mass M of lithium metal deposited on the negative electrode when the battery voltage is 4.2 V is 4.2 The mass M of lithium metal deposited on the negative electrode when the battery voltage is 3.0 V 3.0 Ratio of M 3.0 / M 4.2 is preferably 30% or less, more preferably 25% or less, and further preferably 20% or less. 3.0 / M 4.2 may be 1.0% or more, 2.0% or more, 3.0% or more, or 4.0% or more.

[0048] Examples of the negative electrode active material in this specification include lithium metal and alloys containing lithium metal, carbon-based materials, metal oxides, and metals that are alloyed with lithium and alloys containing the metals.The carbon-based materials include, but are not limited to, graphene, graphite, hard carbon, mesoporous carbon, carbon nanotubes, and carbon nanohorns.The metal oxides include, but are not limited to, titanium oxide compounds, tin oxide compounds, and cobalt oxide compounds.The metals that are alloyed with lithium include, but are not limited to, silicon, germanium, tin, lead, aluminum, and gallium.

[0049] The negative electrode 12 is not particularly limited as long as it does not have a negative electrode active material and can be used as a current collector, but examples thereof include an electrode made of at least one selected from the group consisting of Cu, Ni, Ti, Fe, other metals that do not alloy with Li, their alloys, and stainless steel (SUS), and preferably an electrode made of at least one selected from the group consisting of Cu, Ni, their alloys, and stainless steel (SUS). When such a negative electrode is used, the energy density and productivity of the battery tend to be further improved.

[0050] When SUS is used for the negative electrode, various types of SUS known in the art can be used. The above-mentioned negative electrode materials are used alone or in combination of two or more. In this specification, the term "metal that does not form an alloy with Li" refers to a metal that does not react with lithium ions or lithium metal to form an alloy under the operating conditions of a lithium secondary battery.

[0051] The negative electrode 12 is preferably made of at least one selected from the group consisting of Cu, Ni, Ti, Fe, and alloys thereof, and stainless steel (SUS), and more preferably made of at least one selected from the group consisting of Cu, Ni, and alloys thereof, and stainless steel (SUS). The negative electrode 12 is further preferably made of Cu, Ni, alloys thereof, or stainless steel (SUS). When such a negative electrode 12 is used, the energy density and productivity of the battery tend to be further improved.

[0052] The average thickness of the negative electrode 12 in this embodiment is preferably 4 μm or more and 20 μm or less, more preferably 5 μm or more and 18 μm or less, and further preferably 6 μm or more and 15 μm or less. According to such an embodiment, the volume occupied by the negative electrode in the lithium secondary battery is reduced, and the energy density of the lithium secondary battery 1 is further improved.

[0053] In this specification, the term "average thickness" refers to the arithmetic mean of thicknesses measured at three or more locations on a target component when the target component is magnified and observed using a scanning electron microscope or optical microscope.

[0054] (positive electrode) The positive electrode 11 is not particularly limited as long as it has a positive electrode active material and is generally used in lithium secondary batteries, and a known material can be appropriately selected depending on the application of the lithium secondary battery. Since the positive electrode 11 has a positive electrode active material, it has high stability and output voltage. The positive electrode active material is formed on the surface of the positive electrode 11 as a positive electrode active material layer 11b.

[0055] In this specification, the "positive electrode active material" refers to a material that causes an electrode reaction, i.e., an oxidation reaction and a reduction reaction, at the positive electrode. Specifically, a host material of a lithium element (typically, a lithium ion) can be mentioned. The positive electrode active material in this specification is typically a material that causes an oxidation-reduction reaction under the condition that the voltage of the lithium secondary battery of this embodiment is in the range of 3.0 to 4.2 V, or a material that causes an oxidation-reduction reaction under the condition that the voltage of the lithium secondary battery of this embodiment is in the range of 3.0 to 4.2 V (vs. Li / Li +It is a substance that undergoes an oxidation-reduction reaction in the potential range of the reference electrode.

[0056] Such positive electrode active materials include, but are not limited to, metal oxides and metal phosphates. Metal oxides include, but are not limited to, cobalt oxide compounds, manganese oxide compounds, and nickel oxide compounds. Metal phosphates include, but are not limited to, iron phosphate compounds, and cobalt phosphate compounds.

[0057] A typical positive electrode active material is LiCoO 2 , LiNi x Co y Mn z O(x+y+z=1), LiNi x Co y Al z O(x+y+z=1), LiNi x Mn y O(x+y=1), LiNiO 2 , LiMn 2 O 4 , LiFePO, LiCoPO, LiFeOF, LiNiOF, and LiTiS 2 The above-mentioned positive electrode active materials are used alone or in combination of two or more. The positive electrode active material of the present embodiment is preferably LiCoO 2 , LiNi x Co y Mn z O(x+y+z=1), LiNi x Co y Al z O(x+y+z=1), LiNi x Mn y O(x+y=1), LiNiO 2 , and LiMn 2 O 4 At least one selected from the group consisting of:

[0058] The positive electrode 11 may contain components other than the above-mentioned positive electrode active material. Such components are not particularly limited, but may include, for example, known conductive assistants, binders, solid polymer electrolytes, and inorganic solid electrolytes.

[0059] The conductive assistant in the positive electrode 11 is not particularly limited, but examples thereof include carbon black, single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT), carbon nanofibers (CF), and acetylene black.

[0060] The binder is not particularly limited, but examples thereof include polyvinylidene fluoride, polytetrafluoroethylene, styrene butadiene rubber, acrylic resin, polyimide resin, etc. The above-mentioned conductive assistant and binder may be used alone or in combination of two or more kinds.

[0061] The content of the positive electrode active material in the positive electrode 11 may be, for example, 50 mass % or more and 100 mass % or less with respect to the entire positive electrode 11.

[0062] Regarding the conductive auxiliary agent, the blending amount during the production of the positive electrode of this embodiment and the content at the end of discharge of the battery may be, for example, 0.5 mass % to 30 mass % or less, 1.0 mass % to 20 mass % or less, or 1.5 mass % to 10 mass % or less, relative to the total mass of the positive electrode.

[0063] Regarding the binder, the blending amount during the production of the positive electrode of this embodiment and the content at the end of discharge of the battery may be, for example, 0.5 mass % to 30 mass % or less, 1.0 mass % to 20 mass % or less, or 1.5 mass % to 10 mass % or less, relative to the total mass of the positive electrode.

[0064] Regarding the electrolyte, the blending amount during the production of the positive electrode of this embodiment and the content at the end of discharge of the battery may be, for example, 0.5 mass % to 30 mass % or less, 1.0 mass % to 20 mass % or less, or 1.5 mass % to 10 mass % or less, relative to the total mass of the positive electrode.

[0065] The average thickness of the positive electrode of this embodiment is, for example, 10 μm to 300 μm, preferably 30 μm to 200 μm, or 50 μm to 150 μm, although the average thickness of the positive electrode can be appropriately adjusted according to the desired battery capacity.

[0066] (Separator) The separator 13 of this embodiment is a member for preventing the battery from being short-circuited by isolating the positive electrode 11 and the negative electrode 12, while ensuring the ionic conductivity of lithium ions that serve as charge carriers between the positive electrode 11 and the negative electrode 12. That is, the separator 13 has a function of isolating the positive electrode 11 and the negative electrode 12, and a function of ensuring the ionic conductivity of lithium ions. As such a separator, a member having the above two functions may be used alone, or two or more members having the above one function may be used in combination. The separator is not particularly limited as long as it has the above-mentioned function, and examples of the separator include insulating porous members, polymer electrolytes, gel electrolytes, and inorganic solid electrolytes, and is typically at least one selected from the group consisting of insulating porous members, polymer electrolytes, and gel electrolytes.

[0067] When the separator 13 includes an insulating porous member, the pores of the member are filled with an ion-conductive substance, so that the member exhibits ion conductivity. Examples of the substance to be filled include an electrolytic solution, a polymer electrolyte, and a gel electrolyte.

[0068] In the present embodiment, the separator 13 may be made of one or more of an insulating porous material, a polymer electrolyte, or a gel electrolyte. However, when an insulating porous material is used alone as the separator, the lithium secondary battery must further include an electrolyte to ensure ion conductivity.

[0069] The material constituting the insulating porous member is not particularly limited, but may be, for example, an insulating polymer material, specifically, polyethylene (PE) and polypropylene (PP). That is, the separator of the present embodiment may be a porous polyethylene (PE) film, a porous polypropylene (PP) film, or a laminated structure thereof.

[0070] The polymer electrolyte is not particularly limited, but examples thereof include solid polymer electrolytes mainly containing a polymer and an electrolyte, and semi-solid polymer electrolytes mainly containing a polymer, an electrolyte, and a plasticizer.

[0071] The gel electrolyte is not particularly limited, but may be, for example, one that mainly contains a polymer and a liquid electrolyte (that is, a solvent and an electrolyte).

[0072] Polymers that may be included in the polymer electrolyte and gel electrolyte include, but are not limited to, polymers containing functional groups containing oxygen atoms such as ether and ester, halogen groups, and polar groups such as cyano groups.Specific examples include resins having ethylene oxide units in the main chain and / or side chain such as polyethylene oxide (PEO), resins having propylene oxide units in the main chain and / or side chain such as polypropylene oxide (PPO), acrylic resins, vinyl resins, ester resins, nylon resins, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polysiloxane, polyphosphazene, polymethyl methacrylate, polyamide, polyimide, aramid, polylactic acid, polyurethane, polyacetal, polysulfone, polyethylene carbonate, polypropylene carbonate, and polytetrafluoroethylene.The above-mentioned resins may be used alone or in combination of two or more.

[0073] Examples of electrolytes contained in the polymer electrolyte and the gel electrolyte include salts of Li, Na, K, Ca, and Mg. Typically, in this embodiment, the polymer electrolyte and the gel electrolyte contain a lithium salt.

[0074] The lithium salt is not particularly limited, but examples thereof include LiI, LiCl, LiBr, LiF, and LiBF. 4 , LiPF 6 , LiAsF 6 , LiSO 3 CF 3 , LiN(SO 2 F) 2 , LiN(SO 2 CF 3 ) 2 , LiN(SO 2 CF 3 CF 3 ) 2 , LiB(O 2 C 2 H 4 ) 2 , LiB(C 2 O 4 ) 2 , LiB(O 2 C 2 H 4 )F 2 , LiB(OCOCF 3 ) 4 , LiNO 3 , and Li 2 SO 4 LiN(SO 2 F) 2 , LiN(SO 2 CF 3 ) 2 , and LiN(SO 2 CF 3 CF 3 ) 2 The salt or lithium salt may be at least one selected from the group consisting of: The salt or lithium salt may be used alone or in combination of two or more.

[0075] The blending ratio of the polymer and the lithium salt in the polymer electrolyte and the gel electrolyte may be determined by the ratio of the polar group of the polymer to the lithium atom of the lithium salt. For example, when the polymer has oxygen atoms, the blending ratio may be determined by the ratio ([Li] / [O]) of the number of oxygen atoms of the polymer to the number of lithium atoms of the lithium salt. In the polymer electrolyte and the gel electrolyte, the blending ratio of the polymer and the lithium salt may be adjusted so that the ratio ([Li] / [O]) is, for example, 0.02 to 0.20, 0.03 to 0.15, or 0.04 to 0.12.

[0076] The solvent contained in the gel electrolyte is not particularly limited, but for example, the solvents that can be contained in the electrolyte solution described later can be used alone or in combination of two or more. Preferred examples of the solvent are the same as those in the electrolyte solution described later. The plasticizer contained in the semi-solid polymer electrolyte is not particularly limited, but may include, for example, components similar to the solvent that may be contained in the gel electrolyte, and various oligomers.

[0077] The separator 13 of this embodiment may be coated with a separator coating layer. The separator coating layer may cover both sides of the separator 13, or may cover only one side. The separator coating layer is not particularly limited as long as it is a member that does not react with lithium ions, but it is preferable that it is a layer that can firmly bond the separator and a layer adjacent to the separator. Examples of such separator coating layers include, but are not particularly limited to, polyvinylidene fluoride (PVDF), a mixture of styrene butadiene rubber and carboxymethyl cellulose (SBR-CMC), polyacrylic acid (PAA), lithium polyacrylate (Li-PAA), polyimide (PI), polyamideimide (PAI), and a binder such as aramid. The separator coating layer may be formed by adding inorganic particles such as silica, alumina, titania, zirconia, magnesium oxide, magnesium hydroxide, and lithium nitrate to the binder.

[0078] The average thickness of the separator 13 in this embodiment is preferably 20 μm or less, more preferably 18 μm or less, and even more preferably 15 μm or less. According to such an embodiment, the volume occupied by the separator in the lithium secondary battery 1 is reduced, and the energy density of the lithium secondary battery is further improved. In addition, the average thickness of the separator 13 is preferably 5 μm or more, more preferably 7 μm or more, and even more preferably 10 μm or more. According to such an embodiment, the positive electrode 11 and the negative electrode 12 can be more reliably isolated from each other, and the battery can be further prevented from being short-circuited.

[0079] (electrolyte) It is preferable that the lithium secondary battery 1 further comprises an electrolytic solution. The electrolytic solution is a liquid containing a solvent and an electrolyte, and has ion conductivity. The electrolytic solution may be called a liquid electrolyte, and acts as a conductive path for lithium ions. For this reason, when a lithium secondary battery has an electrolytic solution, the internal resistance tends to be further reduced, and the energy density, capacity, and cycle characteristics tend to be further improved. The electrolytic solution may be impregnated into the separator 13, or the finished lithium secondary battery 1 may be a product in which the electrolytic solution is enclosed together with a laminate of the negative electrode, the separator, the positive electrode, and the positive electrode current collector.

[0080] The electrolyte contained in the electrolytic solution may be any electrolyte that can be contained in the polymer electrolyte or gel electrolyte, particularly the above-mentioned lithium salts, which may be used alone or in combination of two or more. The preferred lithium salts are the same as those in the polymer electrolyte and gel electrolyte.

[0081] Examples of the solvent contained in the electrolytic solution include non-aqueous solvents having fluorine atoms (hereinafter referred to as "fluorinated solvents") and non-aqueous solvents not having fluorine atoms (hereinafter referred to as "non-fluorinated solvents").

[0082] The fluorinated solvent is not particularly limited, but examples thereof include 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, and 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether.

[0083] The non-fluorine solvent is not particularly limited, but examples thereof include triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,2-dimethoxyethane, dimethoxyethane, dimethoxypropane, dimethoxybutane, diethylene glycol dimethyl ether, acetonitrile, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, chloroethylene carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, trimethyl phosphate, triethyl phosphate, and 12-crown-4.

[0084] The above fluorinated solvents and / or non-fluorinated solvents may be used alone or in any combination of two or more in any ratio. The contents of the fluorinated solvent and non-fluorinated solvent are not particularly limited, and the ratio of the fluorinated solvent to the entire solvent may be 0 to 100% by volume, or the ratio of the non-fluorinated solvent to the entire solvent may be 0 to 100% by volume.

[0085] (Exterior body) The exterior body 14 accommodates and hermetically seals the positive electrode 11, the negative electrode 12, the separator 13, the electrolyte, etc. of the lithium secondary battery 1. The material of the exterior body 14 is, for example, a laminate film.

[0086] (Positive and negative terminals) The positive electrode terminal 15 has one end connected to the positive electrode 11, extends outside the exterior body 14, and the other end connected to an external circuit (not shown). The negative electrode terminal 16 has one end connected to the negative electrode 12, extends outside the exterior body 14, and the other end connected to an external circuit (not shown). The material of the positive electrode terminal 15 and the negative electrode terminal 16 is not particularly limited as long as it is conductive, and examples of the material include Al, Ni, and the like. EXAMPLES

[0087] [Experiment on cell failure rate] Here, an experiment was carried out using either the lithium secondary battery 1 of this embodiment or a conventional lithium secondary battery to determine the cell defect rate while changing the margin, which is the distance between the edge 13a of the separator 13 and the edge 12a of the negative electrode 12 in a plan view. Note that the examples are experiments using the lithium secondary battery 1 of this embodiment, and the comparative examples are experiments carried out for comparison with the lithium secondary battery 1 of this embodiment.

[0088] The following lithium secondary batteries were used in the experiments. In Comparative Examples 1 to 3, conventional lithium secondary batteries in which the negative electrode contained a negative electrode active material were used. In these lithium secondary batteries, the negative electrode capacity was set to 350 mAh / g, and the NP ratio, which is the capacity ratio of the negative electrode / positive electrode, was set to 1.05. In Comparative Examples 4 to 7 and the Example, lithium secondary batteries in which the negative electrode did not contain a negative electrode active material were used. Copper foil (Cu foil) was used for the negative electrode. The number of stacked sets of positive electrodes, separators, and negative electrodes was 25. The positive electrode area capacity was 25 mg / cm. 2 , or 10 mg / cm 2The positive electrode active material capacity was 200mAh / g, and the active material ratio was 97%. The positive electrode / negative electrode margin, which is the distance between the edge of the positive electrode and the edge of the negative electrode, was 2mm. The negative electrode / separator margin (margin), which is the distance between the negative electrode and the separator, was changed between 0 and 2.5mm. In addition, the number of sides with this margin other than 0 was changed from 0 to 4 as the number of sides with margin. That is, if the number of sides with margin is 4, it indicates that the margin is provided on all sides of the rectangle, and if the number of sides with margin is 1, it indicates that the margin is provided on only one side of the four sides of the rectangle. While changing these conditions, the volumetric energy density (Wh / L) and the cell defect rate (%) were obtained as follows.

[0089] [Comparative Examples 1 to 3] A conventional lithium secondary battery containing a negative electrode active material in the negative electrode was used in Comparative Examples 1 to 3. The conditions and experimental results of Comparative Examples 1 to 3 are as shown in Table 1 below.

[0090] [Table 1]

[0091] In the lithium secondary batteries of Comparative Examples 1 to 3, the volume energy density was 700 to 710, which was smaller than that of the lithium secondary battery 1 of this embodiment in which the negative electrode described below does not contain a negative electrode active material. In Comparative Example 1, a margin of 2.5 mm was provided, and the cell failure rate was less than 0.001%. In Comparative Example 2, a margin of 0.5 mm was provided, and the cell failure rate was 0.02%. In Comparative Example 3, the margin was set to 0, and the cell failure rate was 5%.

[0092] In this way, in conventional lithium secondary batteries that contain anode active material, the cell defect rate increases when the margin is reduced. In particular, when the margin is set to 0, the cell defect rate is high.

[0093] [Comparative Examples 4 to 5, and Example 1] In the following comparative examples and examples, a lithium secondary battery in which the negative electrode does not contain a negative electrode active material is used. 2 The conditions and experimental results of Comparative Examples 4 to 5 and Example 1 in which the above conditions were set are shown in Table 2 below.

[0094] [Table 2]

[0095] In the lithium secondary battery of Comparative Example 4, a margin of 2.5 mm was provided, and the volumetric energy density was 1484 Wh / L and the cell defect rate was less than 0.001%. In the lithium secondary battery of Comparative Example 5, a margin of 0.5 mm was provided, and the volumetric energy density was 1658 Wh / L and the cell defect rate was 0.003%. In the lithium secondary battery of Example 1, the margin was set to 0, and the volumetric energy density was 1707 Wh / L and the cell defect rate was 0.009%.

[0096] [Comparative Examples 6 to 7, and Example 2] In Comparative Examples 6 to 7 and Example 2, the positive electrode coating capacity was 10 mg / cm 2 The following conditions and experimental results are as shown in Table 3 below.

[0097] [Table 3]

[0098] In the lithium secondary battery of Comparative Example 6, a margin of 2.5 mm was provided, and the volumetric energy density was 1129 Wh / L and the cell defect rate was less than 0.001%. In the lithium secondary battery of Comparative Example 7, a margin of 0.5 mm was provided, and the volumetric energy density was 1261 Wh / L and the cell defect rate was 0.002%. In the lithium secondary battery of Example 2, the margin was set to 0, and the volumetric energy density was 1298 Wh / L and the cell defect rate was 0.005%.

[0099] [Examples 3 to 5] In Examples 3 to 5, the positive electrode coating capacity was set to 10 mg / cm as in Example 2. 2 The experiment was carried out by changing the number of sides with margins from 1 to 3. The margin on the sides with margins was 0.5 mm, and the margin on the sides other than the sides with margins was 0. The conditions and experimental results of Examples 3 to 5 are shown in Table 4 below.

[0100] [Table 4]

[0101] A margin was provided on only one of the four sides in the lithium secondary battery of Example 3. The volumetric energy density of the lithium secondary battery of Example 3 was 1292 Wh / L, and the cell defect rate was 0.004%.

[0102] In the lithium secondary battery of Example 4, margins were provided on two of the four sides. The volumetric energy density of the lithium secondary battery of Example 4 was 1285 Wh / L, and the cell defect rate was 0.0035%.

[0103] In the lithium secondary battery of Example 5, margins were provided on three of the four sides. The volumetric energy density of the lithium secondary battery of Example 5 was 1273 Wh / L, and the cell defect rate was 0.003%.

[0104] As can be seen from the comparison between the above Comparative Examples 4 to 7 and Examples 1 and 2, in the lithium secondary battery of this embodiment in which the negative electrode does not contain a negative electrode active material, when the margin is set to 0, a high volumetric energy density can be obtained while suppressing the cell failure rate to a low level. Also, as can be seen from Examples 2 to 5, the volumetric energy density increases and the cell failure rate decreases as the number of sides in which the margin is set to 0 increases. However, even when the margin is set to 0 on all sides, the cell failure rate is relatively good and practical.

[0105] [Variations] The above-described embodiment is an example for explaining the present invention, and is not intended to limit the present invention to only the embodiment. The present invention can be modified in various ways without departing from the gist of the invention.

[0106] For example, the lithium secondary battery may have a current collector arranged to contact the positive electrode or the negative electrode. In this case, the positive electrode terminal and the negative electrode terminal are connected to the current collector. The current collector is not particularly limited, but may be, for example, a current collector that can be used for the negative electrode material. In addition, when the lithium secondary battery does not have a current collector, the negative electrode and the positive electrode themselves act as current collectors.

[0107] The above-described embodiments are intended to facilitate understanding of the present invention, and are not intended to limit the present invention. The elements of the embodiments, as well as their arrangements, materials, conditions, shapes, sizes, etc., are not limited to those shown as examples and can be changed as appropriate. In addition, configurations shown in different embodiments can be partially substituted or combined with each other. [Industrial Applicability]

[0108] INDUSTRIAL APPLICABILITY The lithium secondary battery of the present invention has excellent energy efficiency per unit volume and unit weight, and is therefore industrially applicable as an electricity storage device for various applications. [Explanation of symbols]

[0109] REFERENCE SIGNS LIST 1...Lithium secondary battery, 11...Positive electrode, 12...Negative electrode, 13...Separator, 14...Exterior body, 15...Positive electrode terminal, 16...Negative electrode terminal

Claims

1. A positive electrode and a negative electrode that does not have a negative electrode active material other than lithium metal regardless of the charging state of the battery and does not have lithium metal before initial charging; A separator disposed between the positive electrode and the negative electrode, at least a part of an edge of the negative electrode and an edge of the separator corresponding to the part of an edge of the negative electrode are disposed at the same position in a plan view, The negative electrode and the separator are each rectangular. Lithium secondary battery.

2. 2 . The lithium secondary battery according to claim 1 , wherein at least one side of the negative electrode is disposed at the same position in a plan view as a side of the separator corresponding to the side of the negative electrode.

3. The lithium secondary battery according to claim 2 , wherein the other side of the negative electrode other than the at least one side is located more inward than the other side of the separator corresponding to the other side of the negative electrode in a plan view.

4. 4. The lithium secondary battery according to claim 3, wherein a distance between the other side of the negative electrode and the corresponding other side of the separator in a plan view is 0.3 mm or more and 5.0 mm or less.

5. 2. The lithium secondary battery according to claim 1, wherein four sides of the negative electrode and four sides of the separator are disposed at the same positions in a plan view.

6. 6. The lithium secondary battery according to claim 1, wherein an edge of the positive electrode is located more inward than a corresponding edge of the negative electrode in a plan view.

7. 7. The lithium secondary battery according to claim 6, wherein a distance between an edge of the positive electrode and a corresponding edge of the negative electrode in a plan view is 0.3 mm or more.

8. A positive electrode and a negative electrode that does not have a negative electrode active material other than lithium metal regardless of the charging state of the battery and does not have lithium metal before initial charging; a separator disposed between the positive electrode and the negative electrode; an exterior body that encapsulates the positive electrode, the negative electrode, and the separator; at least a part of an edge of the separator and an edge of the negative electrode on the same side as the part of the edge are disposed at the same position in a plan view, The negative electrode and the separator are each rectangular. Lithium secondary battery.

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