Secondary batteries

Abstract

Provided is a secondary battery including an electrode comprising an electrode active material and another electrode constituent material different from the electrode active material. In such a secondary battery, at least a part of the electrode active material is covered with a coating material, and at least a part of the other electrode constituent material is also covered with a coating material.

Description

[Technical Field]

[0001] The present invention relates to a secondary battery, and more particularly to a lithium-ion secondary battery. [Background technology]

[0002] Secondary batteries are so-called storage batteries that can be repeatedly charged and discharged, and are used in a variety of applications, including mobile devices such as mobile phones, smartphones, and laptops, as well as in battery packs for hybrid and electric vehicles. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication (WO) 2017 / 199891 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-137947 [Patent Document 3] Japanese Patent Application Laid-Open No. 2008-16232 [Patent Document 4] Japanese Patent Application Laid-Open No. 2008-16236 [Patent Document 5] Japanese Patent Application Laid-Open No. 2016-33854 [Patent Document 6] Japanese Patent Application Laid-Open No. 2009-152214 [Non-patent literature]

[0004] [Non-Patent Document 1] Journal of The Electrochemical Society,162(8)A1516-A1522(2015) Summary of the Invention [Problem to be solved by the invention]

[0005] The inventors of the present invention have realized that there are problems to be overcome with conventional secondary batteries and have found the need to take measures to address these problems. Specifically, the inventors have found the following problems:

[0006] A secondary battery generally has a structure in which a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte solution are sealed in an exterior body.

[0007] The positive and negative electrodes contain electrode active materials, and the positive electrode in particular contains positive electrode active material particles as the electrode active material. For example, Patent Documents 1 to 6 and Non-Patent Document 1 disclose that lithium ion secondary batteries contain particles of lithium transition metal composite oxides or the like as the positive electrode active material.

[0008] When the positive electrode active material contains particles of a lithium transition metal composite oxide or the like, there is a risk that unreacted lithium compounds derived from the raw materials may react with organic solvents or the like (see Patent Document 1), or that such unreacted lithium compounds derived from the raw materials may react with the electrolyte solution to generate gas (see Patent Document 2). When such an electrode active material is mixed with a conductive additive or the like, the electrode active material particles may break, exposing the fractured surfaces of the particles and easily causing a deterioration reaction between the electrode active material and the electrolyte solution (see Patent Documents 3 and 4).

[0009] As described above, the stability of a secondary battery may be insufficient due to undesired side reactions of the electrode active material and the electrolyte, and it can be said that conventional secondary batteries may have insufficient battery characteristics, such as cycle characteristics, due to the electrode active material (see Patent Documents 5 and 6).

[0010] In the inventions described in Patent Documents 1 to 6, the surfaces of electrode active material particles, particularly the primary particles, are covered or coated with a compound such as an oxide, but it has been found that this is still not sufficient in terms of improving the cycle characteristics of secondary batteries, and there is room for further improvement.

[0011] More specifically, in a secondary battery, the electrode usually contains other electrode constituent materials other than the electrode active material, such as a conductive additive, in addition to the electrode active material. Therefore, it is thought that such other electrode constituent materials may also react with the electrolyte solution, etc., and the cycle characteristics may be reduced.

[0012] The present invention has been made in view of the above problems, and a main object of the present invention is to provide a secondary battery having improved cycle characteristics. [Means for solving the problem]

[0013] The inventors of the present application attempted to solve the above problems by taking a new approach rather than simply extending the conventional technology, and as a result, they have invented a secondary battery that achieves the above-mentioned main object.

[0014] Research by the present inventors has revealed that not only the electrode active material contained in the electrode of a secondary battery, but also other electrode constituent materials such as conductive additives may react with the electrolyte, etc., which may result in a deterioration of battery characteristics such as cycle characteristics.

[0015] As a result of extensive research, the inventors of the present application have found that in the electrodes of secondary batteries, by attaching a coating material similar to that of the electrode active material to the surfaces of not only the electrode active material but also other electrode constituent materials other than the electrode active material, or by covering the surfaces of the other electrode constituent materials with a coating material, further improved cycle characteristics can be obtained.

[0016] The present invention provides a secondary battery including an electrode comprising an electrode active material and other electrode constituent materials other than the electrode active material, wherein at least a portion of the electrode active material is covered with a coating material, and at least a portion of the other electrode constituent materials is also covered with the coating material. [Effects of the Invention]

[0017] According to the present invention, a secondary battery having improved cycle characteristics can be obtained. The effects described in this specification are merely examples and are not limiting, and additional effects may also be provided. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 shows a cross section of an electrode assembly that can be used in a secondary battery according to one embodiment of the present invention (A: planar stacked electrode assembly, B: wound electrode assembly). [Figure 2] FIG. 2 is an image showing the results of mapping analysis (atomic mapping) by scanning transmission electron microscope-energy dispersive X-ray spectroscopy (STEM-EDX) on the positive electrode material layer of the positive electrode included in the coin cell produced in Example 9. [Figure 3] FIG. 3 is an image showing the results of mapping analysis (atomic mapping) by scanning transmission electron microscope-energy dispersive X-ray spectroscopy (STEM-EDX) on the positive electrode material layer of the positive electrode included in the coin cell produced in Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, the present invention will be described in more detail using a secondary battery according to an embodiment of the present invention as an example. Although the description will be made with reference to the drawings as needed, various elements in the drawings are merely shown schematically and exemplarily to facilitate understanding of the present invention, and the appearance and / or dimensional ratios may differ from those of the actual objects.

[0020] The "cross-sectional view" directly or indirectly described in this specification is based on a virtual cross section of the secondary battery cut along the stacking direction or overlapping direction of the electrode assemblies and / or electrode constituent units or electrode constituent layers that constitute the secondary battery (see Figure 1). Similarly, the "thickness" direction directly or indirectly described in this specification is based on the stacking direction of the electrode materials that constitute the secondary battery. For example, in the case of a "secondary battery having a thickness like a plate" such as a button-type (or coin-type), the "thickness" direction corresponds to the plate thickness direction of such a secondary battery. The "plane" used indirectly in this specification is based on a sketch of an object viewed from above or below along the thickness direction.

[0021] Furthermore, the terms "upper-lower direction" and "left-right direction" used directly or indirectly in this specification correspond to the upper-lower direction and left-right direction in the drawings, respectively. Unless otherwise specified, the same reference numerals or symbols indicate the same members and / or parts or the same meanings. In a preferred embodiment, the vertical downward direction (i.e., the direction in which gravity acts) can be considered to correspond to the "downward direction," and the opposite direction to that can be considered to correspond to the "upward direction."

[0022] [Basic structure of secondary batteries] The term "secondary battery" as used herein refers to a battery that can be repeatedly charged and discharged. Therefore, the secondary battery according to one embodiment of the present invention is not limited to the name, and may also include, for example, an electricity storage device.

[0023] A secondary battery according to one embodiment of the present invention comprises an electrode assembly formed by stacking electrode constituent units or electrode constituent layers, each including, for example, a positive electrode, a negative electrode, and a separator. For example, FIGS. 1(A) and 1(B) illustrate an electrode assembly 10. As shown in the figure, a positive electrode 1 and a negative electrode 2 may be stacked with a separator 3 interposed therebetween to form an electrode constituent unit 5 (or electrode unit). At least one such electrode constituent unit 5 may be stacked to form the electrode assembly 10.

[0024] For example, in FIG. 1(A), the electrode constituent units 5 have a planar laminated structure in which they are not wound but are laminated in a planar manner.

[0025] For example, in Fig. 1(B), the electrode constituent unit 5 has a wound laminate structure wound in a spiral shape. In other words, Fig. 1(B) may have a wound structure in which an electrode constituent unit 5 (or electrode unit) including a positive electrode 1, a negative electrode 2, and a separator 3 disposed between the positive electrode and the negative electrode is wound in a roll shape. Note that Fig. 1(B) merely illustrates an example of a wound laminate structure of an electrode assembly, and the electrode assembly may be placed inside an exterior body with the cross section shown in Fig. 1(B) facing "upward" or "downward."

[0026] The planar stacking structure or the wound structure of the electrode assembly is merely an example, and the structure of the electrode assembly is not necessarily limited to the planar stacking structure or the wound structure, and the electrode assembly may have other structures, such as a so-called stack-and-folding structure in which the positive electrode, separator, and negative electrode are stacked on a long film and then folded.

[0027] In the secondary battery of the present disclosure, such an electrode assembly may be enclosed in an exterior body together with an electrolyte (e.g., a non-aqueous electrolyte). For example, the electrode assembly may be enclosed in an exterior body together with a liquid electrolyte (e.g., an electrolytic solution, which in some embodiments contains an organic solvent or the like).

[0028] The positive electrode is composed of at least a positive electrode material layer as an electrode material layer and, if necessary, a positive electrode current collector. The positive electrode material layer contains a positive electrode active material as an electrode active material. The positive electrode may or may not have a positive electrode current collector. If the positive electrode has a positive electrode current collector, the positive electrode may have a positive electrode material layer on at least one side of the positive electrode current collector. For example, each of the multiple positive electrodes in the electrode assembly may have a positive electrode material layer on both sides of the positive electrode current collector, or may have a positive electrode material layer on only one side of the positive electrode current collector. The positive electrode current collector may have, for example, a foil form. More specifically, the positive electrode current collector may be composed of a metal foil.

[0029] The negative electrode is composed of at least a negative electrode material layer as an electrode material layer and, if necessary, a negative electrode current collector. The negative electrode material layer contains a negative electrode active material as an electrode active material. The negative electrode may or may not have a negative electrode current collector. If the negative electrode has a negative electrode current collector, the negative electrode may have a negative electrode material layer on at least one side of the negative electrode current collector. For example, each of the multiple negative electrodes in the electrode assembly may have a negative electrode material layer on both sides of the negative electrode current collector, or may have a negative electrode material layer on only one side of the negative electrode current collector. The negative electrode current collector may have, for example, a foil form. More specifically, the negative electrode current collector may be composed of a metal foil.

[0030] The electrode active materials that can be contained in the positive electrode material layer and the negative electrode material layer, i.e., the positive electrode active material and the negative electrode active material, are substances that can directly participate in the transfer of electrons in a secondary battery, and are the main substances of the positive electrode and the negative electrode that are responsible for battery reactions such as charging and discharging, i.e., charging and discharging.

[0031] More specifically, ions can be introduced into the electrolyte due to the "positive electrode active material that can be contained in the positive electrode material layer" and the "negative electrode active material that can be contained in the negative electrode material layer." These ions move between the positive electrode and the negative electrode, transferring electrons and enabling charging and discharging.

[0032] The positive electrode material layer and the negative electrode material layer may be layers capable of absorbing and releasing lithium ions. In other words, the secondary battery according to one embodiment of the present invention may be, for example, a non-aqueous electrolyte secondary battery in which lithium ions can move between the positive electrode and the negative electrode via the non-aqueous electrolyte to charge and discharge the battery.

[0033] When lithium ions are involved in charging and discharging, the secondary battery according to one embodiment of the present invention may correspond to a so-called “lithium ion battery.” In a lithium ion battery, the positive electrode and the negative electrode have layers capable of absorbing and releasing lithium ions.

[0034] Specifically, the positive electrode active material of the positive electrode material layer may be configured to contain larger particles (hereinafter also referred to as "secondary particles") formed by aggregation and / or aggregation of smaller particles (hereinafter referred to as "primary particles") of the positive electrode active material. The average particle size of the secondary particles is not particularly limited and may be, for example, 1 μm to 100 μm, 1 μm to 50 μm, or 3 μm to 30 μm.

[0035] In the present disclosure, the value of the average particle size can be determined, for example, by a particle size distribution analyzer. The particle size can also be determined, for example, by image analysis. In such cases, the average value of particle size measurements taken at any 10 locations may be used as the value of the average particle size.

[0036] The positive electrode may contain a binder in its positive electrode material layer. This is merely an example, but when contact between particles of the positive electrode active material is involved, the positive electrode material layer may contain a binder to ensure sufficient contact and / or shape retention. The positive electrode may also contain a conductive material such as a conductive additive (e.g., conductive particles, preferably conductive particles having a particle shape in cross-section) in its positive electrode material layer. For example, the conductive additive may be contained in the positive electrode material layer to facilitate smooth electron transfer that can promote the battery reaction.

[0037] Specifically, the negative electrode active material of the negative electrode material layer may be configured to contain larger particles (secondary particles) formed by aggregation and / or aggregation of smaller particles (primary particles) of the negative electrode active material. The average particle size of such secondary particles is not particularly limited and may be, for example, 1 μm to 100 μm, 1 μm to 50 μm, or 3 μm to 30 μm.

[0038] The negative electrode may contain a binder in its negative electrode material layer. This is merely an example, but when contact between particles of the negative electrode active material is involved, the negative electrode material layer may contain a binder to ensure sufficient contact and / or shape retention. The negative electrode may also contain a conductive material such as a conductive additive (e.g., conductive particles, preferably conductive particles having a particle shape in cross-section) in its negative electrode material layer. For example, the conductive additive may be contained in the negative electrode material layer to facilitate smooth electron transfer that can promote the battery reaction.

[0039] Because the electrode material layers contain a plurality of components, such as the positive electrode material layer and the negative electrode material layer, they can be referred to as the "positive electrode composite layer" and the "negative electrode composite layer," respectively.

[0040] The positive electrode active material may be, for example, a material that contributes to the absorption and desorption of lithium ions. From this perspective, the positive electrode active material may be, for example, a lithium-containing metal compound or a lithium-containing oxide (such as a lithium-containing composite oxide). More specifically, the positive electrode active material may be a lithium metal compound or a lithium transition metal composite oxide containing lithium and at least one transition metal selected from the group consisting of cobalt, nickel, manganese, and iron.

[0041] In other words, the positive electrode layer of the secondary battery according to one embodiment of the present invention may contain such a lithium metal compound or lithium transition metal composite oxide as the positive electrode active material, for example, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium iron phosphate, or a material in which part of the transition metal in these materials is replaced with another metal.

[0042] Such positive electrode active materials may be contained as a single species, or may be contained in combination of two or more species.

[0043] The content of the positive electrode active material in the positive electrode layer is not particularly limited, and may be 60% by weight or more and less than 100% by weight, 60% by weight or more and 98% by weight or less, 70% by weight or more and 98% by weight or less, for example, 85% by weight or more and 98% by weight or less, relative to the total weight of the positive electrode layer (in other words, the positive electrode layer being 100% by weight).

[0044] The binder that can be contained in the positive electrode layer is not particularly limited, and examples of the binder for the positive electrode layer include at least one selected from the group consisting of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, and polytetrafluoroethylene.

[0045] The content of the binder in the positive electrode material layer may be, for example, 1 wt % to 20 wt % inclusive, 1 wt % to 10 wt % inclusive, 1 wt % to 8 wt % inclusive, 1 wt % to 5 wt % inclusive, or 1 wt % to 3 wt % inclusive, relative to the total weight of the positive electrode material layer (in other words, the positive electrode material layer being 100 wt %).

[0046] The conductive additive that can be contained in the positive electrode layer is not particularly limited. For example, the conductive additive can be carbon black such as thermal black, furnace black, channel black, ketjen black, and / or acetylene black, graphite such as natural graphite and / or artificial graphite, tubular or fibrous carbon such as carbon nanotubes and / or vapor-grown carbon fibers, metal powder such as copper, nickel, aluminum, and / or silver, and / or conductive polymer such as polyphenylene and / or polyphenylene derivatives.

[0047] The content of the conductive additive in the positive electrode layer may be, for example, 1 wt % or more relative to the total weight of the positive electrode layer (in other words, assuming the positive electrode layer is 100 wt %). The content of the conductive additive in the positive electrode layer may be, for example, 1 wt % to 20 wt %, 1 wt % to 10 wt %, 1 wt % to 8 wt %, or 1 wt % to 5 wt %, assuming the positive electrode layer is 100 wt %.

[0048] The thickness of the positive electrode layer is not particularly limited. For example, the thickness of the positive electrode layer may be 1 μm or more and 300 μm or less, or 5 μm or more and 200 μm or less. The thickness of the positive electrode layer is the thickness inside the secondary battery, and may be the average value of measurements taken at any 10 points.

[0049] The negative electrode active material may be a material that contributes to the absorption and desorption of lithium ions, such as various carbon materials, oxides, and / or lithium alloys, metallic lithium, etc.

[0050] Examples of various carbon materials for the negative electrode active material include graphite (more specifically, natural graphite and / or artificial graphite), hard carbon, soft carbon, and / or diamond-like carbon. For example, graphite in particular has high electronic conductivity and excellent adhesion to the negative electrode current collector.

[0051] The oxide of the negative electrode active material may be at least one selected from the group consisting of silicon oxide, tin oxide, indium oxide, zinc oxide, and lithium oxide. Such oxides may have an amorphous structure, as this makes them less susceptible to deterioration due to inhomogeneities such as grain boundaries or defects.

[0052] The lithium alloy of the negative electrode active material may be an alloy of a metal capable of forming an alloy with lithium. For example, it may be a binary, ternary, or higher alloy of lithium with a metal such as Al, Si, Pb, Sn, In, Bi, Ag, Ba, Ca, Hg, Pd, Pt, Te, Zn, and / or La. Such an alloy may have an amorphous structure, for example. This is because it is less susceptible to deterioration due to inhomogeneities such as grain boundaries or defects.

[0053] The content of the negative electrode active material in the negative electrode layer is not particularly limited, and may be 60% by weight or more but less than 100% by weight, 60% by weight or more but 98% by weight or less, 70% by weight or more but 98% by weight or less, for example, 85% by weight or more but 98% by weight or less, relative to the total weight of the negative electrode layer (in other words, the negative electrode layer being 100% by weight).

[0054] The binder that can be contained in the negative electrode layer is not particularly limited, and examples of the binder for the negative electrode layer include at least one selected from the group consisting of styrene-butadiene rubber, polyacrylic acid, polyvinylidene fluoride, polyimide resins, and polyamide-imide resins.

[0055] The content of the binder in the negative electrode material layer may be, for example, 1 wt % or more and 20 wt % or less, preferably 1 wt % or more and 10 wt % or less, more preferably 1 wt % or more and 8 wt % or less, 1 wt % or more and 5 wt % or less, or 1 wt % or more and 3 wt % or less, relative to the total weight of the negative electrode material layer (in other words, the negative electrode material layer being 100 wt %).

[0056] The conductive additive that can be contained in the negative electrode material layer is not particularly limited. For example, the conductive additive can be carbon black such as thermal black, furnace black, channel black, ketjen black, and / or acetylene black, graphite such as natural graphite and / or artificial graphite, tubular or fibrous carbon such as carbon nanotubes and / or vapor-grown carbon fibers, metal powder such as copper, nickel, aluminum, and / or silver, and / or conductive polymer such as polyphenylene and / or polyphenylene derivatives.

[0057] The content of the conductive additive in the negative electrode layer may be, for example, 1 wt % or more relative to the total weight of the negative electrode layer (in other words, assuming the negative electrode layer to be 100 wt %). The content of the conductive additive in the negative electrode layer may be, for example, 1 wt % to 20 wt %, 1 wt % to 10 wt %, 1 wt % to 8 wt %, or 1 wt % to 5 wt %, assuming the negative electrode layer to be 100 wt %.

[0058] The dimensions of the negative electrode layer are not particularly limited. For example, the dimensions of the negative electrode layer may be 1 μm or more and 300 μm or less, or 5 μm or more and 200 μm or less. The thickness of the negative electrode layer is the thickness inside the secondary battery, and the average value of measurements taken at any 10 points may be used.

[0059] The positive and negative electrode current collectors that can be used for the positive and negative electrodes are components that can collect and supply electrons generated in the electrode active material due to the battery reaction. Such current collectors may be sheet-like metal components and may be porous or perforated. For example, the current collectors may be metal foils, punched metals, meshes, expanded metals, and / or plates.

[0060] The positive electrode current collector that can be used for the positive electrode may be made of a metal foil containing at least one selected from the group consisting of aluminum, stainless steel, nickel, etc. As just one example, the positive electrode current collector may be an aluminum foil.

[0061] The negative electrode current collector that can be used for the negative electrode may be made of a metal foil containing at least one selected from the group consisting of copper, stainless steel, nickel, etc. As just one example, the negative electrode current collector may be a copper foil.

[0062] In the present disclosure, stainless steel refers to an alloy steel containing chromium or chromium and nickel, as defined in, for example, "JIS G 0203 Iron and Steel Terminology."

[0063] The thickness of the positive electrode current collector and the negative electrode current collector is not particularly limited. For example, the thickness of the positive electrode current collector and the negative electrode current collector may each be 1 μm or more and 100 μm or less, for example, 10 μm or more and 70 μm or less. The thickness of the positive electrode current collector and the negative electrode current collector is the thickness inside the secondary battery, and may be the average value of measurements taken at any 10 points.

[0064] The separator that can be used for the positive electrode and the negative electrode is a member that can be provided from the viewpoint of preventing a short circuit due to contact between the positive electrode and the negative electrode and / or retaining an electrolyte, etc. In other words, the separator can be said to be a member that prevents electronic contact between the positive electrode and the negative electrode while allowing ions to pass through.

[0065] For example, the separator may be a porous or microporous insulating member having a thin film shape due to its small thickness. For example, a microporous polyolefin film may be used as the separator.

[0066] The microporous membrane that can be used as the separator may contain, for example, only polyethylene (PE) or only polypropylene (PP) as the polyolefin. Furthermore, the separator may be a laminate that can be composed of a "microporous membrane made of PE" and a "microporous membrane made of PP." The surface of the separator may be covered with an inorganic particle coating layer and / or an adhesive layer. The surface of the separator may have adhesive properties.

[0067] The thickness of the separator is not particularly limited. For example, the thickness of the separator may be 1 μm or more and 100 μm or less, for example, 5 μm or more and 20 μm or less. The thickness of the separator is the thickness inside the secondary battery (particularly the thickness between the positive electrode and the negative electrode), and the average value of measurements taken at any 10 points may be used.

[0068] In the present invention, the separator should not be particularly limited by its name, and may be a solid electrolyte, a gel electrolyte, and / or insulating inorganic particles that can have the same function.

[0069] The positive electrode can be obtained, for example, by applying a positive electrode layer slurry prepared by mixing a positive electrode active material, and optionally a binder, and optionally a conductive additive, in a dispersion medium (e.g., a medium such as an organic solvent) to a positive electrode current collector, drying the slurry, and then rolling the dried coating film with a roll press or the like. The negative electrode can be obtained, for example, by applying a negative electrode layer slurry prepared by mixing a negative electrode active material, and optionally a binder, and optionally a conductive additive, in a dispersion medium (e.g., a medium such as an organic solvent) to a negative electrode current collector, drying the slurry, and then rolling the dried coating film with a roll press or the like.

[0070] In a secondary battery according to one embodiment of the present invention, for example, an electrode assembly including an electrode component unit or electrode component layer including a positive electrode, a negative electrode, and a separator may be enclosed in an exterior body together with an electrolyte. The electrolyte can assist the migration of metal ions that may be released from the electrodes (positive electrode and / or negative electrode). The electrolyte may be a "non-aqueous" electrolyte containing an organic electrolyte and / or an organic solvent. Alternatively, the electrolyte may be an "aqueous" electrolyte containing water.

[0071] When the positive electrode and negative electrode have layers capable of absorbing and releasing lithium ions, the electrolyte may be a "non-aqueous" electrolyte (hereinafter referred to as "nonaqueous electrolyte") containing an organic electrolyte and / or an organic solvent. That is, the electrolyte may be a non-aqueous electrolyte. The electrolyte contains metal ions that can be released from the electrodes (positive electrode and / or negative electrode), and therefore, the electrolyte can assist the migration of metal ions in the battery reaction.

[0072] A secondary battery according to one embodiment of the present invention may be a non-aqueous electrolyte secondary battery that uses a non-aqueous electrolyte containing a non-aqueous solvent and a solute as the electrolyte. The electrolyte may be in a liquid or gel form (in the present disclosure, a liquid non-aqueous electrolyte may also be referred to as a "nonaqueous electrolyte solution").

[0073] The nonaqueous electrolyte may be an electrolyte containing a nonaqueous solvent and a solute. A specific solvent for the nonaqueous electrolyte may contain at least a carbonate. The carbonate may be a cyclic carbonate and / or a chain carbonate.

[0074] Although not particularly limited, examples of cyclic carbonates include at least one selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC) and vinylene carbonate (VC).

[0075] The chain carbonates may include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and dipropyl carbonate (DPC).

[0076] By way of example only, in one preferred embodiment of the present invention, a combination of a cyclic carbonate and a chain carbonate may be used as the solvent for the non-aqueous electrolyte, such as a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC), or a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC). The solute of the non-aqueous electrolyte is not particularly limited, but may be, for example, a Li salt such as LiPF6 and / or LiBF4.

[0077] In the secondary battery of the present disclosure, an electrode assembly can be configured from a positive electrode, a negative electrode, and a separator that can be disposed between the positive electrode and the negative electrode. In the present disclosure, the electrode assembly can have any structure. For example, the electrode assembly can have a stacked structure (e.g., a planar stacked structure), a wound structure (e.g., a jelly roll structure), or a stack-and-folded structure.

[0078] The exterior body of a secondary battery is a member that can house or encase, for example, an electrode assembly formed by stacking electrode constituent units including a positive electrode, a negative electrode, and a separator, or electrode constituent layers.

[0079] The exterior body is not particularly limited, and may be, for example, a flexible pouch (soft bag) or a hard case (hard housing).

[0080] When the outer packaging body is a flexible pouch, the flexible pouch is typically formed from a laminate film. For example, sealing can be achieved by heat-sealing the periphery. The laminate film may have a multilayer film structure in which a metal foil and a polymer film are laminated. Specifically, a three-layer structure consisting of an outer polymer film, a metal foil, and an inner polymer film is exemplified. The outer polymer film contributes to preventing damage to the metal foil due to moisture permeation and / or contact, and polymers such as polyamide and / or polyester are preferably used. The metal foil contributes to preventing moisture and / or gas permeation. Foils made of copper, aluminum, and / or stainless steel are preferably used. The inner polymer film protects the metal foil from the electrolyte contained therein and contributes to melt sealing during heat sealing. Polyolefins (e.g., polypropylene) or acid-modified polyolefins are preferably used. The thickness of the laminate film in a flexible pouch is not particularly limited and may be, for example, 1 μm to 1 mm.

[0081] When the exterior body is a hard case, the hard case may typically be formed from a metal plate. For example, sealing may be achieved by irradiating the peripheral portion with a laser. The metal plate may be made of a metal material such as aluminum, nickel, iron, copper, and / or stainless steel. The thickness of the metal plate is not particularly limited and may be, for example, 1 μm or more and 1 mm or less. When the exterior body is a hard case, the exterior body may have a two-part configuration, for example, a first exterior body and a second exterior body.

[0082] In a preferred embodiment, the exterior body may be a metal exterior body made of a non-laminated metal plate.

[0083] In the present invention, the basic configuration of the secondary battery described above may be appropriately changed or modified as necessary.

[0084] [Features of the Secondary Battery Disclosed Herein] The secondary battery of the present disclosure relates to a secondary battery having an electrode (hereinafter sometimes referred to as the "electrode of the present disclosure") comprising an electrode active material and other electrode constituent materials other than the electrode active material. In the electrode according to the present disclosure, at least a portion of the electrode active material is covered with a coating material, and at least a portion of the other electrode constituent materials are also covered with a coating material.

[0085] In the present disclosure, the "electrode active material" is contained in the electrode material layer and corresponds to an electrode constituent material. Such an electrode active material may be a positive electrode active material or a negative electrode active material. The positive electrode of the electrode assembly of the secondary battery contains the positive electrode active material as its electrode constituent material (e.g., the positive electrode material layer contains positive electrode active material particles). The negative electrode of the electrode assembly of the secondary battery contains the negative electrode active material as its electrode constituent material (e.g., the negative electrode material layer contains negative electrode active material particles). As for the specific positive electrode active material and negative electrode active material, the positive electrode active material and negative electrode active material described above, respectively, may be used without particular limitation.

[0086] As described above, the electrode active material is a material that can be contained in the electrodes of an electrode assembly of a secondary battery such as a lithium ion battery. The electrode assembly has a structure in which at least one electrode constituent unit or electrode constituent layer, each including at least a positive electrode, a negative electrode, and a separator, is stacked. The electrode assembly may be, for example, either a planar stacked type electrode assembly (see FIG. 1(A)) or a wound type electrode assembly (see FIG. 1(B)). mosquito may be.

[0087] The average primary particle diameters of the positive electrode active material particles and the negative electrode active material particles are not particularly limited and may be the same as or similar to the average primary particle diameter of the electrode active material particles contained in the lithium ion secondary battery. For example, the average primary particle diameters of the positive electrode active material particles and the negative electrode active material particles may be, for example, 0.1 μm or more and 1 μm or less.

[0088] In the present disclosure, "electrode constituent materials other than the electrode active material" refers to substances or materials that can be contained in an electrode (more specifically, an electrode material layer), excluding the electrode active material (hereinafter, sometimes simply referred to as "other electrode constituent materials"). As the other electrode constituent materials in the present disclosure, one or more types of substances or materials may be contained in an electrode (particularly an electrode material layer).

[0089] The other electrode constituent material is, for example, a conductive additive. As described above, the conductive additive corresponds to an electrode constituent material that can be included in an electrode to facilitate the transfer of electrons that can promote the battery reaction. Here, the inventors of the present application have found that the conductive additive included together with the electrode active material in the electrode material layer may react with, for example, the electrolyte and / or organic solvent to generate gas, which may degrade the cycle characteristics. Without being bound by a particular theory, in the present disclosure, by covering such a conductive additive together with the electrode active material with a coating material, undesirable side reactions (particularly gas generation) in the secondary battery can be suppressed, and battery characteristics such as cycle characteristics can be further improved.

[0090] The form of the conductive additive is not particularly limited. For example, the conductive additive may be contained in the electrode material layer in a plurality of forms in a cross-sectional view of the electrode material layer. The conductive additive may also be contained in the electrode material layer so as to form particles and / or fibers in a cross-sectional view of the electrode material layer. In this case, the conductive additive may be used in powder form as its raw material. The conductive additive contained together with the electrode active material in the electrode material layer may be at least one selected from the group consisting of carbon black, graphite, tubular or fibrous carbon, metal particles, and conductive polymers. More specifically, the carbon black may be at least one selected from the group consisting of thermal black, furnace black, channel black, ketjen black, and acetylene black. The graphite may be at least one selected from the group consisting of natural graphite and artificial graphite. The metal particles may be particles containing at least one metal selected from the group consisting of copper, nickel, aluminum, and silver. The conductive polymer may be at least one polymer selected from polyphenylene and polyphenylene derivatives.

[0091] In a preferred embodiment, the conductive additive of the electrode (i.e., the conductive material contained in the electrode material layer) is carbon black. That is, the electrode may contain carbon black as another electrode constituent material, and at least a portion of the electrode active material may be covered with a coating material, and at least a portion of the carbon black may also be covered with a coating material. In a more specific example, for example, a positive electrode may contain carbon black particles as another electrode constituent material, and at least a portion of the positive electrode active material particles may be covered with a coating material, and at least a portion of the carbon black particles may also be covered with a coating material. It can be said that in the electrode material layer, two different types of particles may be covered with the same coating material.

[0092] In a preferred embodiment, the conductive material may have a granular form (particularly a granular form in cross section). In such a case, the average primary particle size of the conductive material is not particularly limited and may be, for example, about 0.01 μm or more and 0.1 μm or less.

[0093] The average particle size of the "electrode active material" and "other electrode constituent materials" (i.e., the average primary particle size described above and the average particle size of the secondary particles described below) may be determined, for example, based on an image. For example, a cross-section of the electrode assembly may be observed with an optical microscope or an electron microscope, and the average value calculated by measuring the lengths of 10 randomly selected particles may be used. In such a microscopic image, a line may be drawn from one end of each particle to the other, and the distance between the two points with the longest length may be taken as the particle size.

[0094] The term "coating material" refers to at least a material or layer that covers at least a portion of the surface of an electrode active material, particularly at least a portion of the surface of an electrode active material particle (primary particle), or that chemically and / or physically adheres to at least a portion of such an electrode active material (hereinafter, these may be collectively referred to as "coating layer"). The coating material as a whole is made of a substance or material that is different from the electrode active material.

[0095] In the present disclosure, the term "coating" refers to a material or layer that covers not only the electrode active material but also at least a portion of other electrode components (particularly, covers at least a portion of the surface of particles of other electrode components) or that chemically and / or physically adheres to at least a portion of such other electrode components. The coating is entirely composed of a substance or material that is different from the other electrode components. That is, in the present disclosure, the coating preferably comprises a substance or material that is different from not only the electrode active material but also the other electrode components.

[0096] "Covering" at least a portion of the electrode active material and at least a portion of the other electrode components with a coating material includes embodiments in which both the electrode active material and the other electrode components are partially or entirely coated with the coating material and / or the coating material is partially or entirely attached to the electrode active material and / or the other electrode components. Furthermore, in certain embodiments, the coating material is not necessarily present only on the exterior of the electrode active material and / or the other electrode components. For example, due to factors such as the manufacturing method, the coating material or its components may additionally or alternatively be present inside the electrode active material and / or the other electrode components (for example, when the electrode active material is in the form of secondary particles, such an "interior" may be considered to be the region inside the secondary particles).

[0097] In the present disclosure, by covering both the electrode active material and other electrode constituent materials with a coating material, a synergistic effect can be achieved, which can improve battery characteristics such as cycle characteristics in the secondary battery and / or improve the chemical stability of the secondary battery. For example, by covering both the electrode active material and other electrode constituent materials with a coating material, undesired side reactions can be suppressed (preferably, generation of gas that is inconvenient when the battery is used can be suppressed), and battery characteristics such as cycle characteristics can be improved efficiently and / or as desired.

[0098] Thus, the electrode of the present disclosure is characterized in that at least a portion of the electrode active material is covered with a coating material, and at least a portion of the other electrode constituent materials are also covered with a coating material, so that the above-mentioned advantageous effects are achieved. In one embodiment, for example, in a cross-sectional view of the electrode material layer, the coating material may be provided so as to straddle both the electrode active material and the other electrode constituent materials.

[0099] In the electrode of the present disclosure, the coating material covering the electrode active material and the coating material covering the other electrode constituent materials may be substantially the same. In other words, the coating material covering the electrode active material and the coating material covering the other electrode constituent materials may have substantially the same material. When they are the same or substantially the same, this is likely to produce the effect of improving battery characteristics such as cycle characteristics. In the present disclosure, the coating material being "substantially the same" means that the coating material covering the electrode active material and the coating material covering the other electrode constituent materials contain at least one of the same elements derived from the same coating raw material. For example, STEM-EDX (Scanning Transmission Electron Microscope-Energy Dispersive X-ray Spectroscopy) can be used to confirm that the coating material covering the electrode active material and the coating material covering the other electrode constituent materials are made of the same or substantially the same material.

[0100] In the present disclosure, the coating material may have a layer form. That is, the coating material may form a film on the electrode active material and / or other electrode components. Here, the elements constituting the coating material of the present disclosure may be conducive to the layer or film form. For example, the coating material may contain elements that can participate in the formation of a layer or film made of a compound or oxide containing bonds between metal atoms and oxygen atoms. That is, the coating material contained in the electrode material layer may comprise, for example, a compound containing a bond between a metal atom and an oxygen atom (hereinafter also referred to as a "compound containing a metal-oxygen bond") or an element capable of forming a metal oxide. In short, in a preferred embodiment, the coating material comprises a compound containing a metal-oxygen bond or a metal oxide.

[0101] A coating material containing a compound or metal oxide containing a metal-oxygen bond can easily partially or completely cover both the electrode active material and other electrode components. Furthermore, a compound or metal oxide containing a metal-oxygen bond can easily suppress undesired side reactions in the electrode. For example, a compound or metal oxide containing a metal-oxygen bond can easily suppress the generation of undesired gas in the electrode, which can easily contribute to improving battery characteristics such as cycle performance. Furthermore, a compound or metal oxide containing a metal-oxygen bond as a coating material can more successfully achieve both the effect of suppressing an increase in the cycle resistance degradation rate and the effect of improving the cycle retention rate, as described in detail below, among other cycle performance characteristics.

[0102] In the present disclosure, the terms "compound containing a metal-oxygen bond" and "metal oxide" can be used interchangeably. Thus, in some embodiments, a "compound containing a metal-oxygen bond" can correspond to a metal oxide, or a metal oxide can correspond to a "compound containing a metal-oxygen bond."

[0103] In the present disclosure, the coating material may contain at least one element selected from the group consisting of boron (B), silicon (Si), and tungsten (W). These elements tend to function as elements that do not adversely inhibit the movement of ions involved in the battery reaction in the electrode. Furthermore, the inclusion of these elements in the coating material makes it easier to achieve both the effect of suppressing an increase in the cycle resistance degradation rate and the effect of improving the cycle retention rate.

[0104] In a preferred embodiment, the coating material contains at least boron. That is, the coating material may be a material containing at least boron element. In this case, the effect of improving the battery characteristics can be more favorable. In particular, the effect of suppressing an increase in the cycle resistance deterioration rate and improving the cycle retention rate can be more easily realized.

[0105] In a preferred embodiment, the coating material contains at least silicon. That is, the coating material may be a material containing at least silicon element. In this case, the effect of improving the battery characteristics can be more favorable. In particular, the effect of suppressing an increase in the cycle resistance deterioration rate and improving the cycle retention rate can be more easily realized.

[0106] An element selected from the group consisting of boron (B), silicon (Si), and tungsten (W) may participate in a compound or metal oxide containing a metal-oxygen bond in the coating material together with oxygen (O). For example, in the coating material, an element selected from the group consisting of boron (B), silicon (Si), and tungsten (W) may form a metal-oxygen bond or an oxide together with oxygen (O). Note that in this disclosure, a substance or compound containing oxygen (O) (particularly, a "compound containing a metal-oxygen bond") may be referred to as an oxide, and these terms may be interpreted as synonymous. In this disclosure, boron (B) and silicon (Si) may be considered as metals. Therefore, an element selected from the group consisting of boron (B), silicon (Si), and tungsten (W) may form a compound or metal oxide containing a metal-oxygen bond together with oxygen (O).

[0107] In the present disclosure, the covering material may contain lithium (Li). Lithium tends to act as an element that does not adversely hinder the movement of ions, particularly lithium ions, involved in the battery reaction at the electrode. Furthermore, the inclusion of lithium in the covering material makes it easier to achieve both the effect of suppressing an increase in the cycle resistance deterioration rate and the effect of improving the cycle retention rate.

[0108] The lithium (Li) element may participate in a compound or oxide containing a metal-oxygen bond in the coating material together with the oxygen (O) element. For example, in the coating material, the lithium (Li) element may form a compound or metal oxide containing a metal-oxygen bond together with the oxygen (O) element. In the present disclosure, the lithium (Li) element may form a compound or oxide containing a metal-oxygen bond together with at least one element selected from the group consisting of boron (B), silicon (Si), and tungsten (W) and oxygen (O).

[0109] The lithium (Li) that can be contained in the coating material may be derived from the coating raw material described in detail below, and / or may be derived from the electrode active material, its impurities, unreacted materials, etc.

[0110] In the invention according to the present disclosure, the coating material may contain elements other than those mentioned above, such as carbon (C) and / or hydrogen (H).

[0111] In this disclosure, a source material or raw material from which a "coating material" can be formed is referred to as a "coating raw material." The "coating raw material" may contain at least one element selected from the group consisting of the elements listed above, boron (B), silicon (Si), tungsten (W), lithium (Li), oxygen (O), carbon (C), and hydrogen (H).

[0112] In the electrode of the present disclosure, the electrode active material may be composed of secondary particles formed by aggregation and / or aggregation of multiple primary particles. When the electrode active material is in the form of secondary particles, it becomes easier to dispose a coating material inside or on the inside of the electrode active material (secondary particles). That is, in the positive electrode and / or negative electrode (particularly the positive electrode material layer and / or negative electrode material layer) according to the present disclosure, a coating material may be present inside or on the inside of the electrode active material having the form of secondary particles. When a coating material is present inside or on the inside of the electrode active material in this manner, battery characteristics are more likely to be improved. In particular, the effect of simultaneously suppressing an increase in the cycle resistance degradation rate and improving the cycle retention rate is more likely to be realized.

[0113] More specifically, a coating material may be present in the voids of the electrode active material (secondary particles) and / or at least a portion of the surfaces of the primary particles and / or at least a portion of the grain boundaries between the primary particles. In the present disclosure, "voids" may also be understood as gaps or gaps that may exist inside the outer contours of secondary particles (for example, in one embodiment, the regions existing between primary particles may be considered "voids").

[0114] In particular, the coating material may be present on at least a portion of the surfaces of the primary particles exposed in the voids of the electrode active material having the form of secondary particles and on at least a portion of the grain boundaries between the primary particles. For example, in a cross-sectional view, adjacent particles of the electrode active material may be continuously arranged with the coating material interposed therebetween.

[0115] The presence of a coating material in the voids of the electrode active material (secondary particles) and / or at least a portion of the surfaces of the primary particles and / or at least a portion of the grain boundaries between the primary particles facilitates improvement in the cycle characteristics of the secondary battery, i.e., facilitates suppression of undesirable side reactions such as gas generation, thereby facilitating both suppression of an increase in the cycle resistance degradation rate and improvement of the cycle retention rate.

[0116] The electrode active material may have pores. In this regard, the primary particles and / or secondary particles of the electrode active material may have pores. For example, the voids in an electrode active material in the form of secondary particles may be in the form of pores. The pores in the electrode active material may have a pore form that falls into at least one category of so-called micropores (or micropores), mesopores, and macropores. For example, the electrode active material may have mesopores (e.g., pore sizes of 2 nm to 50 nm), and a coating material may be provided on the electrode active material having such mesopores. In a preferred embodiment, the electrode active material in the form of secondary particles may have pores such as mesopores (e.g., 2 nm to 50 nm). In this case, the coating material is more likely to be disposed inside or within the electrode active material in the form of secondary particles. For example, the coating material is more likely to be disposed in the voids inside or within the electrode active material (secondary particles) and / or at least a portion of the surface of the primary particles and / or at least a portion of the grain boundaries between the primary particles. Such pores such as mesopores can be confirmed, for example, by adsorption-desorption isotherms.

[0117] In the electrode of the present disclosure, the other electrode constituent material may be composed of secondary particles formed by aggregation and / or aggregation of a plurality of primary particles. When the other electrode constituent material is in the form of secondary particles, the coating material is also likely to be disposed inside or on the inside of the other electrode constituent material (secondary particles).

[0118] More specifically, the coating material can be present in the voids of other electrode constituent materials (secondary particles) and / or at least part of the surfaces of the primary particles and / or at least part of the grain boundaries between the primary particles.

[0119] The presence of a coating material inside or within other electrode components tends to improve the battery characteristics of the secondary battery. For example, when a coating material is present inside or within other electrode components in the form of secondary particles, undesirable side reactions such as gas generation tend to be suppressed, which in turn tends to both suppress an increase in the cycle resistance degradation rate and improve the cycle retention rate.

[0120] The other electrode constituent material may have a porous morphology. In this regard, the primary particles and / or secondary particles of the other electrode constituent material may have pores. For example, the voids of the other electrode constituent material having the form of secondary particles may be pores. The pores of the other electrode constituent material may have a pore morphology that falls into at least one category of so-called micropores (or micropores), mesopores, and macropores. For example, the other electrode constituent material may have mesopores, and a coating material may be provided on the other electrode constituent material having such mesopores. In a preferred embodiment, the other electrode constituent material having the form of secondary particles may have pores such as mesopores (e.g., 2 nm to 50 nm). In such a case, the coating material is more likely to be disposed inside or within the other electrode constituent material having the form of secondary particles. For example, the coating material is more likely to be disposed inside or within the voids and / or at least a portion of the surface of the primary particles and / or at least a portion of the grain boundaries between the primary particles within or within the other electrode constituent material (secondary particles). Pores such as mesopores in such other electrode constituent materials can be confirmed by adsorption / desorption isotherms in the same manner as above.

[0121] The coating material may be, for example, 0.01 wt % or more relative to 100 wt % of the electrode material layer of the electrode (in other words, relative to the total weight of the electrode material layer). The content of the coating material in the electrode material layer may be, for example, 0.01 wt % to 5.0 wt %, 0.05 wt % to 5.0 wt %, 0.05 wt % to 2.0 wt %, 0.05 wt % to 1.5 wt %, 0.05 wt % to 1.2 wt %, 0.05 wt % to 1.0 wt %, 0.05 wt % to 0.5 wt %, 0.1 wt % to 1.2 wt %, 0.1 wt % to 1.0 wt %, or 0.1 wt % to 0.5 wt % (based on the total weight of the electrode material layer). In one embodiment, the content of the coating material in the electrode material layer may be, for example, 0.3 wt % to 1.2 wt %, 0.3 wt % to 1.1 wt %, 0.3 wt % to 1.0 wt %, 0.4 wt % to 1.2 wt %, 0.4 wt % to 1.1 wt %, 0.4 wt % to 1.0 wt %, 0.5 wt % to 1.2 wt %, 0.5 wt % to 1.1 wt %, or 0.5 wt % to 1.0 wt % (based on the total weight of the electrode material layer). In other words, the coating material may be contained in the electrode material layer so as to achieve such an adhesion amount or coating amount.

[0122] In the present disclosure, the term "electrode material layer" refers to an electrode layer comprising an electrode active material and other electrode components. ExtremeThe term "coating" refers to at least a layer, and more specifically refers to a positive electrode material layer and a negative electrode material layer, respectively. When the electrode assembly includes multiple positive electrode material layers, in at least one of the layers, both the positive electrode active material and other electrode components (e.g., a positive electrode conductive additive such as positive electrode conductive particles) may be covered with a coating material. In a preferred embodiment, at least one positive electrode material layer may have a portion or region where the positive electrode active material is entirely or entirely covered with a coating material, and other electrode components are also entirely or entirely covered with a coating material. Similarly, when the electrode assembly includes multiple negative electrode material layers, in at least one of the layers, both the negative electrode active material and other electrode components (e.g., a negative electrode conductive additive such as negative electrode conductive particles) may be covered with a coating material. In a preferred embodiment, at least one negative electrode material layer may have a portion or region where the negative electrode active material is entirely or entirely covered with a coating material, and other electrode components are also entirely or entirely covered with a coating material.

[0123] The proportion or adhesion amount or coating amount of the coating material in the electrode material layer (in other words, the adhesion amount or coating amount of the coating material on the electrode active material and other electrode components) can be quantified using a measurement method such as inductively coupled plasma (ICP) atomic emission spectroscopy.

[0124] Furthermore, adhesion of the coating material to the electrode active material and other electrode constituent materials can be confirmed by, for example, STEM-EDX (Scanning Transmission Electron Microscope-Energy Dispersive X-ray Spectrometer).

[0125] These will be explained in more detail. First, in STEM-EDX, as a pretreatment, a thin piece of the electrode material layer is cut out by a focused ion beam (FIB) method. Any method known to those skilled in the art may be used for this cutting. Next, by performing a mapping analysis on the cut out thin piece using STEM-EDX measurement, it can be confirmed that "at least a portion of the electrode active material and at least a portion of the other electrode constituent materials are covered with a coating material." Furthermore, in the case of quantifying the coating material using inductively coupled plasma (ICP) atomic emission spectroscopy, the electrode material layer is first subjected to a dissolution treatment as a pretreatment. Any method known to those skilled in the art can be used for this dissolution treatment. The electrode material sample obtained by the dissolution treatment is then subjected to ICP atomic emission spectroscopy to quantify the coating material.

[0126] When the coating material is contained in an amount within the above range, battery characteristics such as cycle characteristics are likely to be improved. For example, undesirable side reactions such as gas generation are likely to be suppressed, which in turn is likely to result in both suppression of an increase in the cycle resistance deterioration rate and an improvement in the cycle retention rate.

[0127] The content of other electrode constituent materials in the electrode material layer is not particularly limited, and may be, for example, 2 wt % to 40 wt % or 2 wt % to 30 wt % or 2 wt % to 15 wt % relative to the total weight of the electrode material layer (in other words, the electrode material layer being 100 wt %).

[0128] When the electrode material layer contains other electrode constituent materials such as a conductive additive, the proportion of the other electrode constituent materials including the conductive additive relative to the total weight of the electrode material layer (in other words, the electrode material layer being 100% by weight) is not particularly limited and may be, for example, 1% by weight to 32% by weight, 1% by weight to 30% by weight, 1% by weight to 20% by weight, 1% by weight to 10% by weight, 1% by weight to 7% by weight, or 1% by weight to 5% by weight, etc. For example, the content of the conductive additive itself in the electrode material layer may be in the above weight % range.

[0129] The secondary battery of the present disclosure may be a lithium ion battery, that is, in a preferred embodiment, the secondary battery has a positive electrode and a negative electrode capable of absorbing and releasing lithium ions as electrodes.

[0130] In lithium-ion batteries, metallic lithium and / or graphite may be used as the negative electrode, while an electrode containing an electrode active material and other electrode components covered with the above-mentioned coating material may serve as the positive electrode. In other words, in a preferred embodiment, the electrode provided with the coating material corresponds to the positive electrode, and at least a portion of the positive electrode active material is covered with the coating material, and at least a portion of the other electrode components in the positive electrode are also covered with the coating material. Because undesirable side reactions tend to occur at the positive electrode (undesirable gas generation tends to occur at the positive electrode during battery use), the effect of facilitating improvement of battery characteristics such as cycle characteristics is likely to be realized. It is preferable that the positive electrode contains a lithium-containing metal compound or a lithium transition metal composite oxide as the electrode active material (cathode active material). This is because the effect of facilitating improvement of battery characteristics such as cycle characteristics is likely to be realized.

[0131] (Formation of coating material) This section provides a detailed explanation of the "coating raw materials" that contribute to the formation of coating materials. The coating raw materials are materials that can form coating materials / coating layers on both the electrode active material and other electrode constituent materials by coming into contact with both the electrode active material and other electrode constituent materials.

[0132] The coating raw material may contain, for example, at least one element selected from the group consisting of boron (B), silicon (Si), tungsten (W), lithium (Li), oxygen (O), carbon (C), and hydrogen (H). In a preferred embodiment, the coating raw material contains at least one element selected from the group consisting of boron (B), silicon (Si), tungsten (W), and lithium (Li), and preferably contains at least one element selected from the group consisting of boron (B), silicon (Si), and tungsten (W), and / or lithium (Li). A coating raw material containing such elements is more likely to make contact with both the electrode active material and other electrode components. For example, the inclusion of such elements makes it easier to form a coating material having a material containing a compound or metal oxide containing a metal-oxygen bond so as to span both the electrode active material and other electrode components.

[0133] The coating raw material may be a coating raw material containing at least boron (B) (hereinafter also referred to as a "boron-based coating raw material"). The boron-based coating raw material may be a compound or oxide containing a metal-oxygen bond (i.e., a compound containing oxygen (O) and hydrogen (H) together with elemental boron (B), or a compound containing oxygen (O) together with elemental boron (B)). Specific boron-based coating raw materials include compounds containing a metal-oxygen bond, such as boric acid, for example, metaboric acid (HBO), orthoboric acid (HBO), or tetraboric acid (salt), or compounds containing oxygen (O) and hydrogen (H) together with elemental boron (B), and / or compounds containing a metal-oxygen bond, such as boron oxide (BO), or compounds containing oxygen (O) together with elemental boron (B). Commercially available boron-based coating raw materials can be used. However, the boron-based coating raw material is not necessarily limited to the above. If high solubility in a solvent and ease of processing are important, it is preferable to use boric acid, such as orthoboric acid (H3BO3), as the coating raw material. The boron-based coating raw material can form a coating material or coating layer containing mainly boron (B). For example, the boron-based coating raw material can react with lithium derived from the electrode active material, unreacted lithium metal, or lithium compounds (LiOH, etc.) on the surfaces of the electrode active material and other electrode components to form a coating material or coating layer containing boron (B). More specifically, lithium boron compounds containing lithium (Li) and boron (B), such as lithium boron oxides (LiBO2, Li3BO3, etc.), can be formed.

[0134] The coating raw material may be a coating raw material containing at least silicon (Si) (hereinafter also referred to as a "silicon-based coating raw material"). The silicon-based coating raw material may be a compound or oxide containing a metal-oxygen bond (i.e., a compound containing silicon (Si) as an element together with oxygen (O) and hydrogen (H), or a compound containing silicon (Si) as an element together with oxygen (O)). Specific silicon-based coating raw materials include, for example, compounds containing a metal-oxygen bond such as silicon dioxide (SiO2) or compounds containing silicon (Si) as an element together with oxygen (O), and / or compounds containing a metal-oxygen bond such as silicic acid, e.g., orthosilicic acid (H2SiO4), metasilicic acid (H2SiO3), metadisilicic acid (H2SiO5), or compounds containing silicon (Si) as an element together with oxygen (O) and hydrogen (H). Such silicon dioxide, orthosilicic acid, metasilicic acid, and metadisilicic acid may be commercially available. However, the silicon-based coating raw material is not necessarily limited to these. The silicon-based coating raw material can suitably form a coating material or coating layer containing silicon (Si), such as a silicon coating or a silica film.

[0135] As the silicon-based coating raw material according to the present disclosure, for example, a silicon compound containing no silicon (Si)-carbon (C) bonds in one molecule (hereinafter referred to as a "first silicon compound") and / or a silicon compound containing one or more silicon (Si)-carbon (C) bonds in one molecule (hereinafter referred to as a "second silicon compound") may be used independently or in combination.

[0136] The "first silicon compound" that does not contain a Si-C bond may be, for example, a compound represented by the following general formula (1) or a mixture thereof.

[0137] [ka]

[0138] In equation (1), the four R 1 may each independently be an alkyl group having 1 to 15 carbon atoms. 1 are each independently preferably an alkyl group having 1 to 10 carbon atoms, and may be, for example, an alkyl group having 1 to 8, 1 to 7, 1 to 6, 1 to 5, 1 to 4, 1 to 3, or 1 to 2 carbon atoms. More specific examples of such alkyl groups include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, and an n-decyl group.

[0139] When such a "first silicon compound" that does not contain a Si-C bond is used, the electrode according to the present disclosure produces a coating material that contains "first silicon that does not contain a Si-C bond." Examples of the "first silicon compound" that does not contain a Si-C bond include tetramethoxysilane (TMOS) and / or tetraethoxysilane (TEOS). The compound represented by general formula (1) can be obtained commercially or can be produced by known methods. For example, TMOS and TEOS are commercially available products manufactured by Tokyo Chemical Industry Co., Ltd. In the present disclosure, such a silicon-based coating raw material (first silicon compound) may also be referred to as a "first silicon alkoxide." Furthermore, because it does not contain a Si-C bond, it may also be referred to as an "inorganic silicon alkoxide." The coating material containing the above-mentioned "first silicon not containing Si-C bonds" preferably has at least the molecular structure or molecular moiety represented by the above general formula (1).

[0140] On the other hand, the "second silicon compound" containing a Si-C bond may be, for example, a compound represented by the following general formula (2A), or a mixture thereof.

[0141] [ka]

[0142] In formula (2A), three R 21 and the three R's 22 may each independently be an alkyl group having 1 to 15 carbon atoms. From the viewpoint of further improving the cycle characteristics, 21 and the three R's 22 are each independently preferably an alkyl group having 1 to 10 carbon atoms, and may be, for example, an alkyl group having 1 to 8, 1 to 7, 1 to 6, 1 to 5, 1 to 4, 1 to 3, or 1 to 2 carbon atoms. More specific examples of such alkyl groups include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, and an n-decyl group. 21 and the three R's 22 may each independently represent a different group or may represent the same group. 2 R may be a divalent hydrocarbon group having 1 to 20 carbon atoms, and from the viewpoint of further improving cycle characteristics, is preferably a divalent hydrocarbon group having 1 to 10 carbon atoms, and more preferably a divalent hydrocarbon group having 2 to 8 carbon atoms. 2 The divalent hydrocarbon group as R may be a divalent saturated aliphatic hydrocarbon group (e.g., an alkylene group) or a divalent unsaturated aliphatic hydrocarbon group (e.g., an alkenylene group). 2From the viewpoint of further improving cycle characteristics, the divalent hydrocarbon group as R is preferably a divalent saturated aliphatic hydrocarbon group (particularly an alkylene group). 2 Examples of the divalent saturated aliphatic hydrocarbon group (particularly an alkylene group) as the group include -(CH2) p Examples of suitable hydrocarbon groups include hydrocarbon groups represented by the formula - (wherein p is preferably an integer of 1 to 10, for example, an integer of 2 to 8, 2 to 7, or 2 to 6).

[0143] Examples of the "second silicon compound" containing such a Si-C bond include 1,2-bis(trimethoxysilyl)ethane (BTMSE), 1,2-bis(triethoxysilyl)ethane (BTESE), and / or 1,6-bis(trimethoxysilyl)hexane (BTMSH). The compound represented by general formula (2A) can be obtained commercially or can be produced by known methods. For example, BTMSE, BTESE, and BTMSH are commercially available products manufactured by Tokyo Chemical Industry Co., Ltd.

[0144] Furthermore, the "second silicon compound" containing a Si-C bond may be, for example, a compound represented by the following general formula (2B), or a mixture thereof.

[0145] [ka]

[0146] In formula (2B), two R 23 and two R 24 may each independently be an alkyl group having 1 to 15 carbon atoms. 23 and two R 24are each independently preferably an alkyl group having 1 to 10 carbon atoms, and may be, for example, an alkyl group having 1 to 8, 1 to 7, 1 to 6, 1 to 5, 1 to 4, 1 to 3, or 1 to 2 carbon atoms. More specific examples of such alkyl groups include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, and an n-decyl group. 23 and two R 24 may each independently represent a different group or may represent the same group.

[0147] An example of such a "second silicon compound" containing a Si-C bond is dimethyldimethoxysilane (DMDMS). The compound represented by general formula (2B) can be obtained commercially or can be produced by a known method. For example, DMDMS is available commercially from Tokyo Chemical Industry Co., Ltd.

[0148] Furthermore, the "second silicon compound" containing a Si-C bond may be, for example, a compound represented by the following general formula (2C), or a mixture thereof.

[0149] [ka]

[0150] In formula (2C), R 26 may be an alkyl group having 1 to 15 carbon atoms. From the viewpoint of further improving the cycle characteristics, R 26is preferably an alkyl group having 1 to 10 carbon atoms, and may be, for example, an alkyl group having 1 to 8, 1 to 7, 1 to 6, 1 to 5, 1 to 4, 1 to 3, or 1 to 2 carbon atoms. More specific examples of such alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, n-hexyl, n-heptyl, n-octyl, n-nonyl, and n-decyl groups. 26 are each independently selected from the alkyl groups described above, and may all be different from each other or any two of them may be different. 26 may be the same groups selected from the alkyl groups described above. 25 may be a monovalent hydrocarbon group having 5 to 30 carbon atoms. From the viewpoint of further improving the cycle characteristics, R 25 is preferably a monovalent hydrocarbon group having 5 to 24 carbon atoms, for example, a monovalent hydrocarbon group having 5 to 20 carbon atoms, 5 to 15 carbon atoms, 5 to 10 carbon atoms, 5 to 9 carbon atoms, 5 to 8 carbon atoms, 5 to 7 carbon atoms, or 5 to 6 carbon atoms. 25 The monovalent hydrocarbon group as R may be a saturated aliphatic hydrocarbon group (e.g., an alkyl group) or an unsaturated aliphatic hydrocarbon group (e.g., an alkenyl group). 25 In order to further improve the cycle characteristics, the monovalent hydrocarbon group as R is preferably a saturated aliphatic hydrocarbon group (particularly an alkyl group). 25 More specific examples of monovalent saturated aliphatic hydrocarbon groups (particularly alkyl groups) as the aryl group include a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, a nonadecyl group, and an eicosyl group.

[0151] An example of such a "second silicon compound" containing a Si-C bond is hexyltrimethoxysilane (HTMS). The compound represented by general formula (2C) can be obtained commercially or can be produced by a known method. For example, HTMS is commercially available from Tokyo Chemical Industry Co., Ltd.

[0152] In the case of the "second silicon compound" containing the Si-C bond as described above, the electrode according to the present disclosure produces a coating material containing "second silicon containing an Si-C bond." The "second silicon compound" containing an Si-C bond can also be referred to as a "second silicon alkoxide." Furthermore, since it contains an Si-C bond, it can also be referred to as an "organic silicon alkoxide." The coating material containing the above-mentioned "second silicon containing an Si-C bond" preferably has at least one of the molecular structures or molecular moieties represented by the above general formulas (2A) to (2C).

[0153] A first silicon compound and a second silicon compound may be used in combination as the silicon-based coating raw material. In other words, in a preferred embodiment, the coating material comprises a "first silicon that does not contain an Si-C bond" and a "second silicon that contains an Si-C bond." In the present disclosure, the coating material may be an inorganic-organic hybrid silicon-based coating material that is a suitable combination of an inorganic silicon alkoxide and an organic silicon alkoxide. Such inorganic-organic hybrid silicon-based coating materials are more likely to improve battery characteristics, such as cycle characteristics, of secondary batteries. For example, in secondary batteries in which the coating material comprises first silicon and second silicon, undesirable side reactions such as gas generation are more likely to be suppressed, which in turn is more likely to suppress an increase in the cycle resistance degradation rate and improve the cycle retention rate. Additionally or alternatively, when the coating material includes the first silicon and the second silicon, the coating material or coating layer may be more easily and successfully disposed inside the secondary particles of the electrode active material and / or other electrode components, making the above-mentioned advantageous effects more likely to be manifested. The coating material comprising the "first silicon not containing Si-C bonds" and the "second silicon containing Si-C bonds" preferably comprises a molecular structure or molecular moiety represented by the general formula (1) above and at least one of the molecular structures or molecular moieties represented by the general formulas (2A) to (2C) above. In other words, in a preferred embodiment, the coating material comprising the "first silicon not containing Si-C bonds" and the "second silicon containing Si-C bonds" may be a coating material containing Si-C bond moieties and Si-O bond moieties (preferably randomly arranged). The nature of such a coating material (e.g., a coating material comprising the "first silicon not containing Si-C bonds" and the "second silicon containing Si-C bonds") can be determined or confirmed from the raw materials described above. Furthermore, the nature of such a coating material can also be confirmed by identifying the composition of the constituent materials using nuclear magnetic resonance (NMR) spectroscopy and / or Time of Flight-SIMS, although this is not intended to limit the scope of the present disclosure.

[0154] As a combination of the first silicon compound and the second silicon compound, a combination in which at least the first silicon compound is tetraethoxysilane (TEOS) is preferred. In other words, a coating material containing the first silicon and the second silicon is preferably based on at least TEOS. This is because the effect of improving the cycle characteristics of a secondary battery is more likely to be apparent. For example, combinations of the first silicon compound and the second silicon compound can include a combination of tetraethoxysilane (TEOS) and 1,2-bis(triethoxysilyl)ethane (BTESE), a combination of tetraethoxysilane (TEOS) and dimethyldimethoxysilane (DMDMS), a combination of tetraethoxysilane (TEOS) and hexyltrimethoxysilane (HTMS), a combination of tetraethoxysilane (TEOS) and 1,6-bis(trimethoxysilyl)hexane (BTMSH), and / or a combination of tetraethoxysilane (TEOS) and 1,2-bis(trimethoxysilyl)ethane (BTMSE).

[0155] When the first silicon compound and the second silicon compound are used in combination, there are no particular limitations on the blending ratio, and the weight ratio of the first silicon compound / the second silicon compound may be, for example, within the range of 1 / 99 to 99 / 1.

[0156] The coating raw material may be a coating raw material containing at least tungsten (W) (hereinafter also referred to as a "tungsten-based coating raw material"). The tungsten-based coating raw material may be a compound or oxide containing a metal-oxygen bond (i.e., a compound containing tungsten (W) as an element as well as oxygen (O) and hydrogen (H), or a compound containing tungsten (W) as an element as well as oxygen (O)). Specific examples of the tungsten-based coating raw material include tungsten trioxide (WO) and / or tungstic acid (HWO). (However, the tungsten-based coating raw material is not necessarily limited to these.) The use of such a tungsten-based coating raw material is likely to result in improved battery characteristics, such as cycle characteristics, for the electrode active material and other electrode components. For example, when the coating material contains tungsten, undesirable side reactions, such as gas generation, are likely to be suppressed in secondary batteries, which in turn is likely to result in suppression of an increase in the cycle resistance degradation rate and improvement of the cycle retention rate.

[0157] The coating raw material may be a coating raw material containing lithium (Li) (hereinafter also referred to as "lithium-based coating raw material"). The lithium-based coating raw material may be a compound or oxide containing a metal-oxygen bond (i.e., a compound containing oxygen (O) and hydrogen (H) together with elemental lithium (Li), or a compound containing oxygen (O) together with elemental lithium (Li). Specific lithium-based coating raw materials include lithium-containing boron compounds, such as compounds containing a metal-oxygen bond, such as lithium metaborate (BLiO), lithium tetraborate (LiB), and lithium triborate (LiB), or compounds containing boron (B) and oxygen (O) together with elemental lithium (Li), and lithium-containing silicon compounds, such as lithium polysilicate (LiSiO). 11), lithium metasilicate (Li2SiO3), lithium orthosilicate (Li4SiO4), or other compounds containing a metal-oxygen bond or compounds containing silicon (Si) and oxygen (O) together with lithium (Li) as the element; and / or lithium-containing tungsten compounds, for example, lithium tungstate (Li2WO4), or other compounds containing a metal-oxygen bond or compounds containing tungsten (W) and oxygen (O) together with lithium (Li) as the element (however, lithium-based coating raw materials are not necessarily limited to these).

[0158] Among the lithium-based coating raw materials, the lithium-containing boron compound can form a coating material containing a lithium boron compound containing lithium (Li) and boron (B), such as lithium boron oxide (LiBO2 and / or Li3BO3).

[0159] Among the lithium-based coating raw materials, lithium-containing silicon compounds can form coating materials as silicon films containing lithium (Li).

[0160] Lithium-containing tungsten compounds can form coatings including lithium tungsten oxide.

[0161] The use of such a lithium-based coated raw material can more suitably coat the electrode active material and other electrode constituent materials, and is likely to result in improved battery characteristics such as cycle characteristics. For example, when the coating material contains lithium, undesirable side reactions such as gas generation are likely to be suppressed in secondary batteries, which in turn is likely to result in suppression of an increase in the cycle resistance deterioration rate and improvement of the cycle retention rate.

[0162] It should be noted that the above-mentioned "boron-based coated raw materials," "silicon-based coated raw materials," and "tungsten-based coated raw materials" may contain lithium (Li) as an element, and all such compounds may be defined as being classified as "lithium-based coated raw materials." In this regard, in this disclosure, "boron-based," "silicon-based," "tungsten-based," and "lithium-based," etc., related to coating materials or coated raw materials may be interpreted as overlapping, such that one of them also applies to the other.

[0163] In the present disclosure, the coating raw material can be used in an amount of, for example, 0.05 wt % to 5.0 wt % (i.e., based on 100 wt % of the electrode material layer of the electrode (i.e., based on the total weight of the electrode material layer), 0.05 wt % to 2.0 wt %, 0.05 wt % to 1.5 wt %, 0.05 wt % to 1.2 wt %, 0.05 wt % to 1.0 wt %, 0.05 wt % to 0.5 wt %, 0.1 wt % to 1.2 wt %, 0.1 wt % to 1.0 wt %, or 0.1 wt % to 0.5 wt %. Within the above ranges, a coating material that coats both the electrode active material and other electrode components can be successfully formed. This also facilitates the formation of a coating material or coating layer inside or on the inside of secondary particles of the electrode active material and / or other electrode components. In the present disclosure, a portion of the coating material or coating layer may be composed of the coating raw material. That is, in the present disclosure, at least a portion of the coating material or coating layer may be made from the coating raw material.

[0164] In the present disclosure, the coating raw materials are merely examples, and the present invention is not necessarily limited to the above-mentioned examples.

[0165] (Coating of electrode active material and other electrode components) There are no particular limitations on the method for covering the electrode active material and other electrode constituent materials with the coating material. In a preferred embodiment, the coating material or coating layer can be formed on both the electrode active material and other electrode constituent materials by contacting the above-mentioned coating raw material with the electrode active material and other electrode constituent materials.

[0166] When the coating raw material is brought into contact with the electrode active material and other electrode constituent materials, the following steps (1) to (3) may be carried out. For example, (1) if necessary, the coating raw material is dissolved in a solvent to prepare a coating solution, (2) the electrode active material and other electrode constituent materials are added to this coating solution, mixed and stirred, and (3) if necessary, the solvent is removed by heating and drying. This allows at least a portion of the electrode active material and at least a portion of the other electrode constituent materials to be covered with the coating material. That is, through such contact treatment, an electrode material layer can be obtained in which the electrode active material and other electrode constituent materials are both covered with the coating material.

[0167] (1) A step of dissolving the coating raw material in a solvent to prepare a coating solution The solvent for preparing the coating solution is not particularly limited as long as it can dissolve the above-mentioned coating raw materials. There are also no particular limitations on the order of addition, temperature, and / or stirring time. There are also no particular limitations on the concentration of the coating raw materials in the coating solution. The step (1) of preparing the coating solution is an optional step and may be omitted. For example, if the coating raw material can be brought into direct contact with the electrode active material and other electrode constituent materials, there is no need to use a solvent, and therefore step (1) may be omitted.

[0168] (2) A step of adding and mixing the electrode active material and other electrode constituent materials into the coating solution and stirring the mixture. The electrode active material and other electrode constituent materials are added to the coating solution prepared in the above step (1), and then mixed and stirred. There are no particular limitations on the order of addition, temperature and / or stirring time. The electrode active material and other electrode constituent materials may each be in the form of granules, that is, primary particle powders. There are no particular restrictions on the particle size (average primary particle size) of the primary particles of the electrode active material, but it is, for example, 0.1 μm or more and 1 μm or less. There are no particular restrictions on the particle size (average primary particle size) of the primary particles of the other electrode constituent materials, but it is, for example, 0.01 μm or more and 0.1 μm or less. The particle size of such primary particles (average primary particle size) can be confirmed from a photograph taken with an electron microscope (SEM, TEM, STEM, etc.).

[0169] (3) A process of removing the solvent by heating and drying The mixed solution prepared in step (2) above is heated to remove the solvent and dry, thereby obtaining a powder of secondary particles of the electrode active material and other electrode constituent materials coated with the coating material formed from the coating raw material. There are no particular restrictions on the heating temperature and / or heating time. The drying step in step (3) is an optional step and may be omitted.

[0170] In the above coating treatment, the electrode active material and other electrode constituent materials are simultaneously coated, but the electrode active material and other electrode constituent materials may be coated independently and separately.

[0171] (Secondary battery manufacturing method) The secondary battery of the present disclosure can be manufactured based on a conventionally known manufacturing method, except that an electrode active material and other electrode constituent materials coated with a coating material are used. More specifically, an electrode can be produced in the same manner as in the conventional method by using an electrode active material coated with a coating material and other electrode constituent materials in a slurry for forming an electrode material layer of the electrode. The electrode active material and other electrode constituent materials coated with a coating material can be used for either the positive electrode or the negative electrode. In terms of more clearly demonstrating the effects of the present disclosure, it is preferable that the electrode active material and other electrode constituent materials coated with a coating material be applied to the positive electrode. In other words, in a secondary battery having a positive electrode (more specifically, a positive electrode material layer thereof) in which the electrode active material and other electrode constituent materials are coated with a coating material, the effect of facilitating improvement of battery characteristics such as cycle characteristics is readily apparent. For example, in the case of a lithium-ion battery, undesirable side reactions are likely to occur in the positive electrode (especially gas is relatively likely to be generated during battery use), which tends to deteriorate battery characteristics such as cycle characteristics.

[0172] (Battery characteristics) The secondary battery of the present disclosure includes, in particular, an electrode active material and other electrode components at least partially coated with a coating material, and can provide desired characteristics. For example, battery characteristics such as cycle characteristics can be improved. More specifically, undesirable side reactions at the electrode can be easily suppressed, which in turn can easily suppress an increase in the cycle resistance degradation rate and improve the cycle retention rate.

[0173] The cycle characteristics of a secondary battery that can be repeatedly charged and discharged are not particularly limited, and examples thereof include the "cycle retention rate" and the "cycle resistance degradation rate." That is, in a preferred embodiment, the cycle characteristics referred to in the present disclosure refer to battery characteristics that correspond to at least the "cycle retention rate" and / or the "cycle resistance degradation rate."

[0174] (Cycle maintenance rate) In the present disclosure, the term "cycle retention rate" refers to the retention rate of the discharge capacity of a secondary battery. In a charge / discharge cycle test of a secondary battery, the cycle retention rate is defined as the ratio, expressed as a percentage (%), of the "discharge capacity after n cycles" to the "discharge capacity after 1 cycle" in a charge / discharge test of, for example, n cycles (e.g., n=100, i.e., 100 cycles). The closer the value of the "cycle retention rate (%)" is to 100%, the higher the performance of the secondary battery. The secondary battery of the present disclosure preferably has a cycle retention rate of 80% or more, and more preferably has a cycle retention rate of 90% or more.

[0175] (Cycle resistance degradation rate) In the present disclosure, the "cycle resistance deterioration rate" refers to the rate of increase in electrode resistance, i.e., the deterioration rate of the electrode. For example, the cycle resistance deterioration rate is defined as the ratio, expressed as a percentage (%), of the electrode resistance increased after the charge-discharge cycle test to the electrode resistance before the charge-discharge cycle test ("electrode resistance after the charge-discharge cycle test" - "electrode resistance before the charge-discharge cycle test"). The smaller the value of "cycle resistance deterioration rate (%)", the higher the performance as a secondary battery. The secondary battery of the present disclosure preferably has a cycle resistance deterioration rate of less than 550%, and more preferably has a cycle resistance deterioration rate of less than 500%.

[0176] The present invention will be described in more detail below with reference to examples, but the present invention should not be construed as being limited to the following examples. [Example]

[0177] Example 1: Manufacturing of secondary battery Step A: Coating of electrode active material and conductive additive The positive electrode active material and the conductive additive were both coated according to the following steps (1) to (3). (1) A step of dissolving the coating raw material in a solvent to prepare a coating solution 0.250 g of boric acid (coating raw material) and 62.50 g of N-methyl-2-pyrrolidone (NMP) (solvent) were weighed and mixed. The coating solution was prepared by stirring for 10 minutes until the boric acid was completely dissolved in the solvent (NMP). (2) A step of adding a positive electrode active material and a conductive additive to the coating solution, mixing them, and stirring them. A predetermined amount of powder (particles) of lithium nickel oxide (NCA) (positive electrode active material) and powder (particles) of carbon black (conductive additive) were added to the coating solution prepared in the above step (1), mixed, and stirred at room temperature for 30 minutes. The mixing ratio of the positive electrode active material (NCA) and the conductive additive (carbon black) was 100% by weight of the positive electrode active material and 3.2% by weight of the conductive additive. (3) A process of removing the solvent by heating and drying The mixed solution prepared in the above step (2) was heated at 100°C for 10 hours to remove the solvent and dry it, thereby obtaining powders of the positive electrode active material and the conductive additive coated with a coating material formed from the coating raw material (boric acid).

[0178] Step B: Preparation of positive electrode sheet The coated positive electrode active material (NCA) and conductive additive (carbon black) from step A were mixed with polyvinylidene fluoride as a binder. The resulting mixture was dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode layer slurry (coated positive electrode active material: 95 wt %, coated conductive additive: 3 wt %, polyvinylidene fluoride: 2 wt %). Next, this positive electrode layer slurry was uniformly applied to a strip of aluminum foil (positive electrode current collector) having a thickness of 15 μm, to form a coating of the positive electrode layer slurry on the aluminum foil. Subsequently, the coating film was dried with hot air and then compression molded with a roll press to produce a sheet having a positive electrode material layer formed from the positive electrode layer slurry (positive electrode sheet). The positive electrode sheet prepared above was punched into a circle (φ16.5 mm) and vacuum dried at 120°C for 10 hours using a vacuum dryer to prepare a positive electrode sheet with dimensions suitable for a 2016-type coin cell (coin-shaped secondary battery).

[0179] Step C: Coin cell fabrication A metallic lithium (Li) disk (0.24 mm thick, 17 mm diameter) was prepared by punching. The punched metallic lithium (Li) disk was laminated on a stainless steel (SUS) plate (200 μm thick) as the negative electrode material layer. This plate was placed in a stainless steel anode cup with the metallic lithium negative electrode material layer facing up. Thereafter, a polyolefin separator was punched into a disk shape (thickness 15 μm, diameter 17.5 mm) by punching, and the separator was laminated on the lithium negative electrode material layer. The separator was impregnated with 150 μL of electrolyte, and the electrolyte was allowed to penetrate into the voids in the negative electrode. The electrolyte used was a liquid electrolyte (non-aqueous electrolyte) prepared by dissolving lithium hexafluorophosphate (LiPF) as a solute (electrolyte salt) at a concentration of 1 mol / L in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a mass ratio of EC:EMC = 3:7. The positive electrode sheet prepared in the above step B was laminated on the separator with the positive electrode material layer facing downwards. Next, an aluminum plate was laminated on the aluminum foil (positive electrode current collector) of the positive electrode sheet. Finally, a stainless steel cathode cup was laminated onto the aluminum plate. A coin cell (2016 type) was produced by placing a gasket (insulating material) between the periphery of the anode cup and the periphery of the cathode cup, and then sealing the anode cup and cathode cup with a crimping machine to form an outer casing.

[0180] The fact that the positive electrode active material and the conductive additive were covered with the coating material was confirmed by STEM-EDX (Scanning Transmission Electron Microscope-Energy Dispersive X-ray Spectrometer). More specifically, as a pretreatment, a thin piece of the positive electrode material layer was cut out by a focused ion beam (FIB) method, and then the cut-out piece was subjected to mapping analysis using STEM-EDX measurement, which confirmed that "at least a portion of the positive electrode active material and at least a portion of the conductive additive were covered with the coating material." The coating weight or coating amount of the coating material is shown in Table 1 below as a percentage (%) of the weight relative to the total weight of the positive electrode material layer (i.e., the total weight of the positive electrode material layer is 100 wt %). The amount of the coating material was quantified using ICP atomic emission spectroscopy. Specifically, as a pretreatment, the positive electrode material layer was subjected to a dissolution treatment, and the coating material content (i.e., coating amount) was determined by measuring using ICP atomic emission spectroscopy. Note that ICP atomic emission spectroscopy confirmed that the coating material contained boron (B) element derived from boric acid (the coating raw material).

[0181] Examples 2 to 4 A coin cell was produced in the same manner as in Example 1, except that the coating amount shown in Table 1 was used.

[0182] Examples 5 to 9 Coin cells were prepared in the same manner as in Example 1, except that a combination of tetraethoxysilane (TEOS) (first silicon alkoxide) and 1,2-bis(triethoxysilyl)ethane (BTESE) (second silicon alkoxide) was used as the coating raw materials, and the coating amount shown in Table 1 was used. Furthermore, ICP atomic emission spectroscopy confirmed that the coating material contained silicon (Si) derived from the coating raw material.

[0183] As a representative example, an image is shown in Figure 2. Figure 2 relates to Example 9, and the presence of a coating material in the positive electrode layer of the coin cell produced in Example 9 was confirmed by STEM-EDX (Scanning Transmission Electron Microscope-Energy Dispersive X-ray Spectrometer) (see Figure 2). The atomic mapping shown in Figure 2 demonstrated that the surface of the positive electrode active material and the surface of the conductive additive were simultaneously coated with a coating material (coating material having the same material).

[0184] FIG. 2(A) shows that the surface of the positive electrode active material (NCA) and the surface of the conductive additive (carbon black) are both coated with a coating material (TEOS / BTESE). Figure 2(B) shows the distribution of silicon (Si) atoms derived from the coating material (TEOS / BTESE). It was confirmed that silicon (Si) atoms were present in both the positive electrode active material (NCA) and the conductive additive (carbon black). FIG. 2(C) shows the distribution of nickel (Ni) atoms derived from the positive electrode active material (NCA). FIG. 2(D) shows the distribution of carbon (C) atoms derived from the conductive additive (carbon black).

[0185] Example 10 Coin cells were fabricated in the same manner as in Example 8, except that the positive electrode active material used had a coating material detected inside it. The presence of the coating material inside the positive electrode active material was confirmed by STEM-EDX (Scanning Transmission Electron Microscope-Energy Dispersive X-ray Spectroscopy) of the cross section of the positive electrode active material particles. Furthermore, the positive electrode active material used in Example 10 was confirmed to have mesopores (2 nm to 50 nm) by adsorption / desorption isotherms. More specifically, the presence of mesopores in the positive electrode active material was confirmed by measurement using a pore size distribution analyzer and analysis using the BJH (Barrett, Joyner, and Halenda) method.

[0186] Example 11 Coin cells were produced in the same manner as in Example 1, except that a combination of tetraethoxysilane (TEOS) (first silicon alkoxide) and hexyltrimethoxysilane (HTMS) (second silicon alkoxide) was used as the coating raw materials, and the coating amount shown in Table 1 was used. Furthermore, ICP atomic emission spectroscopy confirmed that the coating material contained silicon (Si) derived from the coating raw material.

[0187] Example 12 Coin cells were fabricated in the same manner as in Example 1, except that a combination of tetraethoxysilane (TEOS) (first silicon alkoxide) and 1,6-bis(trimethoxysilyl)hexane (BTMSH) (second silicon alkoxide) was used as the coating raw materials, and the coating amount shown in Table 1 was used. Furthermore, ICP atomic emission spectroscopy confirmed that the coating material contained silicon (Si) derived from the coating raw material.

[0188] Examples 13 to 15 Coin cells were produced in the same manner as in Example 1, except that a combination of tetraethoxysilane (TEOS) (first silicon alkoxide) and dimethyldimethoxysilane (DMDMS) (second silicon alkoxide) was used as the coating raw materials and coated at the coating amounts shown in Table 1. Furthermore, ICP atomic emission spectroscopy confirmed that the coating material contained silicon (Si) derived from the coating raw material.

[0189] Example 16 Coin cells were prepared in the same manner as in Example 1, except that a combination of tetraethoxysilane (TEOS) (first silicon alkoxide) and 1,2-bis(trimethoxysilyl)ethane (BTMSE) (second silicon alkoxide) was used as the coating raw materials, and the coating amount shown in Table 1 was used. Furthermore, ICP atomic emission spectroscopy confirmed that the coating material contained silicon (Si) derived from the coating raw material.

[0190] Example 17 A coin cell was produced in the same manner as in Example 1, except that lithium metaborate was used as the coating raw material and the coating amount shown in Table 1 was used. In addition, ICP atomic emission spectroscopy confirmed that boron (B) and lithium (Li) derived from the coating raw materials were contained as elements in the coating material.

[0191] Example 18 A coin cell was produced in the same manner as in Example 1, except that lithium polysilicate was used as the coating raw material and the coating amount shown in Table 1 was used. Furthermore, ICP atomic emission spectroscopy confirmed that silicon (Si) and lithium (Li) derived from the coating raw materials were contained as elements in the coating material.

[0192] Comparative Example 1 A coin cell was fabricated in the same manner as in Example 1, except that a positive electrode active material and a conductive additive that had not been subjected to a coating treatment were used.

[0193] The positive electrode layer of the coin cell produced in Comparative Example 1 was observed by STEM-EDX in the same manner as in Example 9 (see FIG. 3).

[0194] FIG. 3(A) shows that neither the positive electrode active material (NCA) nor the conductive additive (carbon black) is coated with a coating material. Figure 3(B) shows the distribution of silicon (Si) atoms. The image in Figure 3(B) reveals that no coating material is present in the positive electrode layer of Comparative Example 1. The dots in Figure 3(B) indicate noise or contamination levels, and no coating material is substantially present in the positive electrode layer of Comparative Example 1. Here, "no coating material is substantially present" means that the presence of coating material at a noise or contamination level is acceptable. FIG. 3(C) shows the distribution of nickel (Ni) atoms derived from the positive electrode active material (NCA). FIG. 3(D) shows the distribution of carbon (C) atoms derived from the conductive additive (carbon black).

[0195] Comparative Example 2 A coin cell was produced in the same manner as in Example 1, except that the conductive additive was not coated, and only the positive electrode active material was coated in the amount shown in Table 1.

[0196] [Initial charge / discharge check] An initial charge / discharge test was carried out on each of the coin cells produced in the examples and comparative examples using a commercially available charge / discharge characteristic evaluation device. In the initial charge / discharge test, each coin cell prepared in the examples and comparative examples was first charged at a constant current and constant voltage of 0.1 C in a thermostatic chamber at 25° C. up to an upper limit voltage of 4.25 V and a lower limit current of 0.005 C. After charging, the battery was rested for 10 minutes and then discharged at a current of 0.1C to a lower limit voltage of 2.0V. The coin cells produced in the examples and comparative examples were all confirmed to be capable of initial charging and discharging, and were found to function as secondary batteries.

[0197] For each of the coin cells fabricated in the examples and comparative examples, the battery characteristics of "cycle retention rate" and "cycle resistance degradation rate" were determined according to the procedures described below. The results are shown in Table 1 below.

[0198] [Table 1]

[0199] In the "active material coating" column in the table, ○ indicates "coated" and × indicates "not coated." That is, with regard to "active material coating," "○" indicates that at least a portion of the active material is coated with a coating material, and "×" indicates that the active material is not coated with a coating material. In the column for "Conductive additive coating" in the table, ○ indicates "Coated" and × indicates "Not coated." That is, with regard to "Conductive additive coating," "○" indicates that at least a portion of the conductive additive is covered with a coating material, and "×" indicates that the conductive additive is not covered with a coating material. In the column of "Coating inside active material" in the table, ○ indicates "coated" and × indicates "not coated." That is, with regard to "coating inside active material," "○" indicates that the active material was covered with a coating material such that the coating material was present in the inner region of the electrode active material having the form of secondary particles, and "×" indicates that such a coating form of the active material in which the coating material was present in the inner region of the electrode active material was not observed.

[0200] [Charge / discharge cycle test] A charge-discharge cycle test was carried out in a constant temperature bath at 60°C according to the following steps (1) to (4). (1) The coin cells manufactured in the examples and comparative examples were each subjected to constant current / constant voltage charging at a current of 1.0 C up to an upper voltage of 4.25 V and a lower current of 0.01 C. Note that each coin cell manufactured in the examples and comparative examples was used after a 3-hour rest. (2) After charging, a one-minute rest period was performed. (3) Discharge was performed at a current of 5.0 C down to a lower limit voltage of 2.5 V. (4) After discharge, a 5-minute rest period was allowed. This charge-discharge test was carried out for 100 cycles. After each charge-discharge cycle test, the discharge capacity of the coin cells manufactured in the examples and comparative examples was determined.

[0201] [Cycle maintenance rate] The "cycle retention rate" was calculated as a ratio of the discharge capacity according to the following formula. Cycle retention rate (%) = (discharge capacity after 100 cycles) / (discharge capacity after 1 cycle) × 100

[0202] The evaluation criteria for "cycle retention rate" were as follows: The results are shown in Table 1 above. ◎ (Very good): 90% or more ○ (Good): 80% or more but less than 90% × (very bad): Less than 80%

[0203] [Cycle resistance degradation rate] The "cycle resistance deterioration rate" was calculated as a ratio of the positive electrode resistance according to the following formula. Cycle resistance deterioration rate (%) = (positive electrode resistance after charge-discharge cycle test - positive electrode resistance before charge-discharge cycle test) / (positive electrode resistance before charge-discharge cycle test) × 100

[0204] In the formula, the "positive electrode resistance before the charge-discharge cycle test" and the "positive electrode resistance after the charge-discharge cycle test" were determined by EIS measurement as follows.

[0205] (Positive electrode resistance before charge / discharge cycle test) Prior to the charge-discharge cycle test, each coin cell prepared in the examples and comparative examples was charged at a constant current and constant voltage of 0.1 C in a thermostatic chamber at 25°C to an upper voltage of 4.25 V and a lower current of 0.005 C, and prepared to a 100% state of charge. EIS measurements were performed at a voltage amplitude of 10 mV, varying the frequency from 1 MHz to 0.1 Hz. From the EIS measurement results, the semicircular component from 500 Hz to 1 Hz was used as the positive electrode resistance, and the positive electrode resistance value was measured.

[0206] (Positive electrode resistance after charge / discharge cycle test) After the charge-discharge cycle test (after 100 cycles), EIS measurement was performed in the same manner as above to measure the positive electrode resistance after the charge-discharge cycle test.

[0207] The evaluation criteria for the "cycle resistance deterioration rate" were as follows: The results are shown in Table 1 above. ◎ (Very good): Less than 500% ○ (Good): 500% or more but less than 550% △ (bad): 550% or more but less than 600% × (very bad): 600% or more

[0208] In the coin cell produced in Comparative Example 1, neither the positive electrode active material nor the conductive additive was covered with a coating material. Therefore, it was found that the battery characteristics, such as the cycle resistance degradation rate, were significantly reduced due to factors such as the side reactions of both the positive electrode active material and the conductive additive with the electrolyte solution and organic solvent. More specifically, the cycle resistance degradation rate of the coin cell in Comparative Example 1 was 600% or more, and the rating was "very poor (×)."

[0209] In the coin cell produced in Comparative Example 2, only the positive electrode active material was covered with a coating material. The conductive additive was not covered with a coating material. Therefore, compared to the coin cell of Comparative Example 1, the cycle resistance degradation rate improved to between 550% and 600%, but the rating was "poor (△)."

[0210] In contrast, in the coin cells fabricated in Examples 1 to 18 of the present invention, the positive electrode active material and conductive additive are all covered with a coating material. More specifically, they are covered with a coating material containing elements derived from the coating raw materials (such as boron (B), silicon (Si), and / or lithium (Li)). This significantly suppresses side reactions between the positive electrode active material and conductive additive and the electrolyte or organic solvent, thereby further improving battery characteristics in terms of both cycle retention rate and cycle resistance degradation rate. More specifically, the evaluations of both the cycle retention rate and the cycle resistance deterioration rate were "very good (◎)" or "good (◯)."

[0211] Furthermore, in the coin cell produced in Example 10 of the present invention, a coating material is present inside or within the electrode active material in the form of secondary particles, and the coating material is present on at least a portion of the surface of the primary particles contained in the positive electrode active material (secondary particles), in the voids of the primary particles inside the positive electrode active material (secondary particles), and in the grain boundaries between the primary particles. This means that it is possible to further improve battery characteristics such as cycle retention rate and cycle resistance degradation rate. More specifically, the coin cell produced in Example 10 was evaluated as "very good (A)" in both the cycle retention rate and cycle resistance deterioration rate.

[0212] As described above, the secondary batteries of Examples 1 to 18 of the present invention have electrode active materials and other electrode constituent materials covered with coating materials, and therefore have superior chemical stability (for example, superior chemical stability due to factors such as the ability to further suppress undesirable side reactions) and improved cycle characteristics.

[0213] Although the embodiments of the present invention have been described in detail above using examples, they are merely typical examples. Therefore, it will be readily understood by those skilled in the art that the present invention is not limited to these embodiments and that various other aspects are possible.

[0214] For example, although the above description refers to a compound containing a metal-oxygen bond or a metal oxide as the coating material, the coating material is not necessarily limited to a material containing a compound containing a metal-oxygen bond or a metal oxide. As long as the function of the secondary battery is not adversely affected, the coating material may be made of an appropriate material that can coat both the electrode active material and other electrode constituent materials in the electrode material layer.

[0215] In addition, although the above description refers to the first silicon compound and the second silicon compound, each of the first silicon compound and the second silicon compound may be a compound known as a silane coupling agent capable of forming a silicon film. In such a case, another silane coupling agent may be used as the silicon-based coating raw material in the electrode of the present disclosure. [Industrial Applicability]

[0216] The secondary battery according to one embodiment of the present invention can be used in various fields where battery use or power storage is conceivable. For example, the secondary battery according to one embodiment of the present invention can be used in the electrical, information, and communications fields where electrical and electronic devices can be used (e.g., electrical and electronic devices or mobile devices including small electronic devices such as mobile phones, smartphones, laptops, digital cameras, activity monitors, arm computers, electronic paper, wearable devices, RFID tags, card-type electronic money, and smart watches), household and small industrial applications (e.g., power tools, golf carts, and household, nursing care, and industrial robots), large industrial applications (e.g., forklifts, elevators, and harbor cranes), transportation systems (e.g., hybrid automobiles, electric automobiles, buses, trains, electrically assisted bicycles, and electric motorcycles), power system applications (e.g., various power generation systems, road conditioners, smart grids, and general household power storage systems), medical applications (medical devices such as earphones and hearing aids), pharmaceutical applications (medical management systems), IoT, and space and deep-sea applications (e.g., space probes and submersible research vessels). [Explanation of symbols]

[0217] 1 positive electrode 2 negative electrode 3 Separator 5 Electrode Unit 10 Electrode assembly

Claims

1. The electrode comprises an electrode comprising an electrode active material and other electrode constituent materials other than the electrode active material, At least a portion of the electrode active material is covered with a coating material, and at least a portion of the other electrode constituent materials is also covered with the coating material, the electrode active material is composed of secondary particles formed by aggregation of a plurality of primary particles, the coating material comprises at least silicon, the electrode is a positive electrode, at least a portion of the positive electrode active material is covered with the coating material, and at least a portion of the other electrode constituent materials is also covered with the coating material; A secondary battery comprising a lithium transition metal composite oxide as the positive electrode active material.

2. The electrode comprises an electrode comprising an electrode active material and other electrode constituent materials other than the electrode active material, At least a portion of the electrode active material is covered with a coating material, and at least a portion of the other electrode constituent materials is also covered with the coating material, the coating material comprises at least boron, the electrode is a positive electrode, at least a portion of the positive electrode active material is covered with the coating material, and at least a portion of the other electrode constituent materials is also covered with the coating material; A secondary battery comprising a lithium transition metal composite oxide as the positive electrode active material.

3. The electrode comprises an electrode comprising an electrode active material and other electrode constituent materials other than the electrode active material, At least a portion of the electrode active material is covered with a coating material, and at least a portion of the other electrode constituent materials is also covered with the coating material, the electrode active material is composed of secondary particles formed by aggregation of a plurality of primary particles, the coating material comprises at least silicon, The secondary battery, wherein the coating material comprises first silicon not containing Si—C bonds and second silicon containing Si—C bonds.

4. The electrode comprises an electrode comprising an electrode active material and other electrode constituent materials other than the electrode active material, At least a portion of the electrode active material is covered with a coating material, and at least a portion of the other electrode constituent materials is also covered with the coating material, the coating material comprises at least boron and silicon; The secondary battery, wherein the coating material comprises first silicon not containing Si—C bonds and second silicon containing Si—C bonds.

5. 5. The secondary battery according to claim 1, wherein the other electrode constituent material is a conductive additive.

6. 6. The secondary battery according to claim 1, wherein the coating material comprises a metal oxide.

7. 7. The secondary battery according to claim 1, wherein the coating material contains at least one selected from the group consisting of boron, silicon, and tungsten.

8. 3. The secondary battery according to claim 1, wherein the coating material comprises a first silicon not containing a Si—C bond and a second silicon containing a Si—C bond.

9. 9. The secondary battery according to claim 1, wherein the coating material contains lithium.

10. The secondary battery according to claim 2 or 4, wherein the electrode active material is composed of secondary particles formed by aggregation of a plurality of primary particles.

11. The secondary battery according to claim 1 or 3, wherein the coating material is present inside or within the electrode active material having the form of secondary particles.

12. The secondary battery according to claim 1 or 3, wherein the coating material is present in voids of the secondary particles and / or at least a portion of the surfaces of the primary particles and / or at least a portion of the grain boundaries between the primary particles.

13. 13. The secondary battery according to claim 1, wherein the coating material is contained in an amount of 0.05% by weight to 5.0% by weight with respect to 100% by weight of the electrode material layer of the electrode.

14. The secondary battery according to any one of claims 1 to 13, wherein the other electrode constituent material is carbon black, and at least a portion of the electrode active material is covered with the coating material, and at least a portion of the carbon black is also covered with the coating material.

15. 5. The secondary battery according to claim 3, wherein the electrode is a positive electrode, and at least a portion of the positive electrode active material is covered with the coating material, and at least a portion of the other electrode constituent materials is also covered with the coating material.

16. The secondary battery according to claim 15 , comprising a lithium transition metal composite oxide as the positive electrode active material.

17. The secondary battery according to any one of claims 1 to 16, wherein the coating material covering the electrode active material and the coating material covering the other electrode constituent materials are made of a material containing at least one of the same elements derived from the same coating raw material.

18. 5. The secondary battery according to claim 3, wherein the electrodes are a positive electrode and a negative electrode capable of absorbing and releasing lithium ions.

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