Secondary battery and battery pack

Abstract

Embodiments of the present invention relate to secondary batteries and battery packs. The present invention provides long-life secondary batteries and battery packs. According to an embodiment, a secondary battery comprising an electrode assembly and an electrolyte is provided. The electrode assembly has a structure in which at least one electrode, including a current collector and at least one electrode containing an active material layer respectively disposed on its two main surfaces, is stacked or wound. The active material layer includes at least one positive electrode active material layer and at least one negative electrode active material layer. The concentration of a compound containing at least one selected from sulfur, boron, phosphorus, and fluorine in the outermost positive electrode portion of the electrode assembly, which is located on the outermost side of the electrode assembly, is higher than the concentration of the same compound in the inner positive electrode portion located further inside the electrode assembly than the outermost positive electrode portion.

Description

Technical Field

[0001] Embodiments of the present invention relate to secondary batteries and battery packs. Background Technology

[0002] In recent years, research and development of secondary batteries, such as lithium-ion batteries and other non-aqueous electrolyte batteries, which are high-energy-density batteries, has been booming. These non-aqueous electrolyte batteries are expected to serve as power sources for hybrid electric vehicles, electric vehicles, and uninterrupted power supplies for mobile phone base stations. Therefore, in addition to high energy density, secondary batteries are also required to have excellent performance characteristics such as rapid charge / discharge capabilities and long-term reliability. Summary of the Invention

[0003] This invention provides a long-life secondary battery and battery pack.

[0004] According to an embodiment, a secondary battery comprising an electrode assembly and an electrolyte is provided. The electrode assembly has a structure in which at least one electrode, including a current collector and at least one electrode containing an active material layer respectively disposed on its two main surfaces, is stacked or wound. The active material layer includes at least one positive electrode active material layer and at least one negative electrode active material layer. In a portion of the electrode containing the positive electrode active material layer, the concentration of a compound containing at least one selected from sulfur, boron, phosphorus, and fluorine in the outermost positive electrode portion of the electrode assembly is higher than the concentration of the same compound in the inner positive electrode portion located further inside the electrode assembly than the outermost positive electrode portion.

[0005] According to other embodiments, a battery pack having the above-described secondary battery is provided.

[0006] The aforementioned secondary batteries and battery packs can exhibit a long lifespan. Attached Figure Description

[0007] Figure 1 This is a cross-sectional view that schematically illustrates an example of a secondary battery embodiment.

[0008] Figure 2 It is Figure 1 An enlarged cross-sectional view of part A of the secondary battery shown.

[0009] Figure 3 This is a partial cutaway perspective view schematically illustrating another example of a secondary battery according to an embodiment.

[0010] Figure 4 yes Figure 3 An enlarged cross-sectional view of part B of the secondary battery shown.

[0011] Figure 5 This is a perspective view that schematically illustrates an example of a battery pack embodiment.

[0012] Figure 6 This is an exploded perspective view that schematically illustrates an example of a battery pack embodiment.

[0013] Figure 7 It means Figure 6 A block diagram of an example of the circuitry for the battery pack shown.

[0014] [Symbol Explanation] 1…Electrode assembly, 2…Outer packaging component, 3…Negative electrode, 3a…Negative electrode current collector, 3b…Layer containing negative electrode active material, 3c…Negative electrode current collector tab, 4…Separator, 5…Positive electrode, 5a…Positive electrode current collector, 5b…Layer containing positive electrode active material, 6…Negative terminal, 7…Positive terminal, 13…Outermost negative electrode, 13a…Outermost layer containing negative electrode active material, 15…Outermost positive electrode, 15a…Outermost layer containing positive electrode active material, 21…Busbar, 22…Positive electrode side lead, 22a…Other end, 23…Negative electrode side lead, 23a…Other end, 24…Adhesive tape, 30…Outermost part of negative electrode, 30a… The outermost layer containing negative electrode active material, 31… storage container, 32… cover, 33… protective sheet, 34… printed circuit board, 35… wiring, 50… outermost positive electrode layer, 50a… outermost layer containing positive electrode active material, 100… secondary battery, 200… battery pack, 300… battery pack, 342… positive electrode side connector, 343… negative electrode side connector, 345… thermistor, 346… protection circuit, 342a… wiring, 343a… wiring, 350… external terminal for power supply, 352… positive side terminal, 353… negative side terminal, 348a… positive side wiring, 348b… negative side wiring. Detailed Implementation

[0015] A typical electrode for a secondary battery has a structure in which layers containing active materials are formed on both sides of a current collector such as a metal foil. These active material layers contain electrode materials, including electrode active materials, which participate in the charge-discharge reactions of the battery. In a lithium-ion secondary battery, lithium ions, functioning as charge carriers, move back and forth between the positive and negative electrodes during charge-discharge cycles. Specifically, lithium ions are inserted into the electrode active materials contained in the positive and negative electrodes, or detach from the electrode active materials to participate in the charge-discharge reactions. Most of the lithium-ion conduction between the positive and negative electrodes occurs between their respective opposite surfaces. That is, lithium-ion conduction occurs between the positive electrode active material layer on the negative electrode side of the positive current collector and the negative electrode active material layer on the positive electrode side of the negative current collector.

[0016] In a lithium-ion secondary battery with an outermost negative electrode in an alternating negative and positive electrode array, one of the negative electrode active material layers on both sides of the negative current collector is not opposite the positive electrode. Although this non-opposite negative electrode portion is not opposite the positive electrode, lithium ions (Li...) are observed to... + The phenomenon of embedding the negative electrode into the non-opposite part. This is caused by Li. + As the electrode is embedded into the non-opposite portion of the negative electrode, the potential of the positive electrode active material layer opposite to another layer containing negative electrode active material located on the back side, sandwiching the negative electrode current collector, increases. This increase in potential accelerates the degradation of the positive electrode, i.e., the outermost positive electrode.

[0017] Hereinafter, embodiments will be described with appropriate reference to the accompanying drawings. Furthermore, common structures will be labeled with the same reference numerals in the embodiments, and repeated descriptions will be omitted. Additionally, the drawings are schematic diagrams intended to facilitate the explanation and understanding of the embodiments; their shapes, dimensions, proportions, etc., may differ from those of the actual device, but these can be appropriately modified with reference to the following description and known techniques.

[0018] (First Implementation) According to a first embodiment, a secondary battery comprising an electrode assembly and an electrolyte is provided. The electrode assembly comprises at least one electrode, which includes a current collector and active material layers respectively disposed on two main surfaces of the current collector. The electrode assembly has a structure formed by stacking or winding at least one electrode. The active material layers include at least one positive electrode active material layer and at least one negative electrode active material layer. The concentration of a compound containing at least one selected from sulfur, boron, phosphorus, and fluorine in the outermost positive electrode portion of the electrode assembly, which is located on the outermost side of the positive electrode active material layer, is higher than the concentration of the same compound in the inner positive electrode portion located further inside the electrode assembly than the outermost positive electrode portion.

[0019] At least one electrode may be, for example, a plurality of electrodes comprising at least one positive electrode having a layer of positive active material on each side of the current collector and at least one negative electrode having a layer of negative active material on each side of the current collector. Alternatively, an electrode may be one or more bipolar electrodes having a layer of positive active material on one main surface of the same current collector and a layer of negative active material on another main surface on its back side.

[0020] Hereinafter, the outermost positive electrode, located closest to the outer edge of the electrode group among multiple positive electrodes that may be included in an electrode group, and the portion of a single positive electrode or a single layer containing positive electrode active material that is located closest to the outer edge of the electrode group, are collectively referred to as the outermost positive electrode portion. Similarly, the outermost negative electrode, located on the outermost side of the electrode group among multiple negative electrodes that may be included in an electrode group, and the portion of a single negative electrode or a single layer containing negative electrode active material that is located on the outermost side of the electrode group, are collectively referred to as the outermost negative electrode portion.

[0021] In this secondary battery, the outermost positive electrode contains a high concentration of compounds containing any one or more of sulfur (S), boron (B), phosphorus (P), and fluorine (F). It should be noted that "high concentration" here means, for example, that the concentration of the aforementioned compounds in the outermost positive electrode is 1.1 times or more than the concentration of the aforementioned compounds in the inner positive electrode. This high concentration of the aforementioned compounds in the outermost positive electrode indicates that a film of these compounds has formed there. This film helps suppress the degradation of the outermost positive electrode, which may lead to potential rise. The same film can also be formed in the portions of other positive electrodes located inside the electrode assembly, other than the outermost positive electrode, but due to the presence of Li... + The embedding of the negative electrode non-opposite portion of the outermost negative electrode portion towards the outside of the electrode assembly may cause a larger coating on the outermost positive electrode portion, which may result in a potential increase. A specific example of a compound constituting the coating is sulfur oxides (so-called SOx).

[0022] More specifically, among the positive electrode layers containing positive active material, the outermost layer, located on the outermost side of the electrode assembly, has the most film formed and contains the highest amounts of S, B, P, and F compounds. This outermost layer, located closest to the non-opposite portion of the negative electrode, is most strongly affected by Li. + The effect of embedding into the negative electrode non-opposite portion. Specifically, in the energy spectrum obtained by hard X-ray photoelectron spectroscopy (HAXPES), the peak area attributable to S, B, P, and F compounds, for the outermost positive electrode active material layer, can be greater than 1.1 times the peak area at the inner positive electrode portion, for example, it can be increased to less than 10 times. It should be noted that the outermost positive electrode active material layer can be an independent positive electrode active material layer that is entirely located on the outermost layer of the electrode assembly, or it can refer to a portion of the positive electrode active material layer that is located on the outermost layer of other positive electrode active material layers that extend into the interior of the electrode assembly. In addition, the outermost positive electrode active material layer can, for example, be opposite to a negative electrode active material layer located on the back side of the negative electrode current collector relative to the negative electrode non-opposite portion. Alternatively, the outermost positive electrode active material layer itself can be disposed on the back side of the current collector relative to the negative electrode non-opposite portion, thus forming a bipolar electrode.

[0023] The aforementioned coating is specifically designed to make Li... + The negative electrode non-opposite portion is embedded, thus preferentially forming in the outermost positive electrode portion. That is, utilizing the fact that Li + The phenomenon of potential rise in the outermost positive electrode due to the embedding of the negative electrode into the non-opposite portion is used to form a coating, which protects the outermost positive electrode from the adverse effects of subsequent potential rises. Details of the adjustment of coating formation will be described later.

[0024] As described above, Li is embedded in the outermost layer containing the negative electrode active material, i.e., the non-opposite portion of the negative electrode, located in the electrode assembly. + The negative electrode active material layer may contain, for example, lithium in an amount equivalent to more than 10 mAh / g, which translates to a battery capacity of 10 mAh / g. This level of lithium content can be achieved through ultra-low rate charging. In typical rate charging, Li... + It is difficult to embed into the non-opposite portion of the negative electrode. When a film is formed on the positive electrode, the film forms evenly across the outermost layer and other portions. Therefore, with repeated use of the battery, Li... + It can gradually embed into the negative electrode non-opposite part, but when the outermost positive electrode part, which is more affected by it, is initially regulated, it cannot form a large amount of film. Therefore, in the regulation at normal rate, it cannot suppress the adverse effects caused by the potential rise of the outermost positive electrode part.

[0025] The secondary battery may further include a separator disposed between the positive electrode active material layer and the negative electrode active material layer in the electrode assembly. The electrolyte can be retained in the electrode assembly.

[0026] In addition, the secondary battery can be further equipped with an outer packaging component that houses the electrode assembly and electrolyte.

[0027] Furthermore, the secondary battery can further have a positive terminal electrically connected to the layer containing the positive electrode active material and a negative terminal electrically connected to the layer containing the negative electrode active material.

[0028] The secondary battery can be, for example, a lithium secondary battery. Alternatively, secondary batteries include non-aqueous electrolyte secondary batteries containing a non-aqueous electrolyte.

[0029] The following provides a detailed description of the positive electrode, negative electrode, electrolyte, separator, outer packaging components, positive terminal, and negative terminal.

[0030] 1) Positive electrode The positive electrode may comprise a positive current collector and a layer containing a positive active material. The layer containing the positive active material may be formed on one or both sides of the current collector. The layer containing the positive active material may comprise the positive active material and any conductive agent and binder.

[0031] As positive electrode active materials, oxides or sulfides can be used, for example. The positive electrode, as a positive electrode active material, can contain only one compound, or it can contain two or more compounds in combination. Examples of oxides and sulfides include compounds capable of intercalating and deintercalating Li or Li ions.

[0032] Such compounds include, for example, manganese dioxide (MnO2), iron oxide, copper oxide, nickel oxide, and lithium manganese complex oxides (e.g., Li). x Mn2O4 or Li x MnO2: 0 < x ≤ 1), lithium-nickel composite oxides (e.g., Li) x NiO2, 0 < x ≤ 1), lithium-cobalt composite oxides (e.g., Li) x CoO2, 0 < x ≤ 1), lithium nickel cobalt composite oxides (e.g., Li) x Ni 1-y Co y O2, 0 < x ≤ 1, 0 < y < 1), lithium manganese cobalt composite oxides (e.g., Li) x Mn y Co 1-y O2, 0 < x ≤ 1, 0 < y < 1), lithium manganese nickel composite oxides with spinel structure (e.g., Li) x Mn 2-y Ni y O4, 0 < x ≤ 1, 0 < y < 2), lithium phosphates with olivine structures (e.g., Li) x FePO4, 0 < x ≤ 1, Li x Fe 1-y Mn y PO4, 0<x≤1, 0<y≤1, Li x CoPO4, 0 < x ≤ 1), ferric sulfate (Fe2(SO4)3), vanadium oxides (e.g., V2O5), and lithium nickel cobalt manganese composite oxides (Li x Ni 1-y-z Co y Mn z O2, 0<x≤1, 0<y<1, 0<z<1, y+z<1).

[0033] Examples of compounds preferred as positive electrode active materials, as described above, include lithium manganese composite oxides having a spinel structure (e.g., Li). x Mn₂O₄; 0 < x ≤ 1), lithium-nickel composite oxides (e.g., Li₂O₄); x NiO2; 0 < x ≤ 1), lithium cobalt composite oxides (e.g., Li) x CoO2; 0 < x ≤ 1), lithium nickel cobalt composite oxides (e.g., Li) x Ni 1-y Coy O2; 0 < x ≤ 1, 0 < y < 1), lithium manganese nickel composite oxides with spinel structure (e.g., Li x Mn 2-y Ni y O4; 0 < x ≤ 1, 0 < y < 2), lithium manganese cobalt composite oxides (e.g., Li) x Mn y Co 1-y O2; 0 < x ≤ 1, 0 < y < 1), lithium iron phosphate (e.g., Li) x FePO4; 0<x≤1) and lithium nickel cobalt manganese composite oxide (Li x Ni 1-y-z Co y Mn z O2; 0 < x ≤ 1, 0 < y < 1, 0 < z < 1, y + z < 1). If these compounds are used as positive electrode active materials, the positive electrode potential can be increased.

[0034] Among these, lithium manganese-nickel composite oxides and lithium nickel-cobalt-manganese composite oxides are preferred. The charge-discharge reactions of these composite oxides mainly proceed through a single solid-phase reaction, therefore their potential increases in stages as the battery is charged. Regarding Li... + The potential increase of the outermost positive electrode active material layer caused by the embedding of the negative electrode active material layer, and the potential of the active material containing the positive electrode active material layer that performs a single solid-phase reaction, also increases with Li. + The insertion process proceeds in stages. Therefore, in secondary batteries using lithium manganese nickel composite oxide and lithium nickel cobalt manganese composite oxide in the positive electrode active material, it is easy to control the formation of the film on the outermost positive electrode by adjusting the process.

[0035] When using room-temperature molten salt as the battery electrolyte, it is preferable to use electrolytes containing lithium iron phosphate or LiFePO4. x Positive electrode active materials include VPO4F (0≤x≤1), lithium manganese composite oxides, lithium nickel composite oxides, lithium nickel cobalt composite oxides, or mixtures thereof. These compounds exhibit low reactivity with room-temperature molten salts, thus improving cycle life. Details regarding room-temperature molten salts are described later.

[0036] The primary particle size of the positive electrode active material is preferably above 100 nm and below 1 μm. Positive electrode active materials with a primary particle size of above 100 nm are easy to process in industrial production. Positive electrode active materials with a primary particle size of below 1 μm can smoothly undergo solid-state internal diffusion of lithium ions.

[0037] The specific surface area of ​​the positive electrode active material is preferably 0.1 m². 2 / g or more and 10m 2 / g or less. Has 0.1m 2 Positive electrode active materials with a specific surface area of ​​over / g can adequately ensure the insertion and extraction sites of Li ions. (The last part, "10m," appears to be an unrelated fragment and is omitted from the translation.) 2 Positive electrode active materials with a specific surface area of ​​less than 1 g are easy to process in industrial production and can ensure good charge-discharge cycle performance.

[0038] Binders are used to fill the gaps between dispersed positive electrode active materials and to bond the positive electrode active materials and current collector. Examples of binders include: polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, polyacrylic acid compounds, imide compounds, carboxymethyl cellulose (CMC), and salts of CMC. One of these can be used as a binder, or two or more can be used in combination.

[0039] Conductive agents are used to improve current collection performance and suppress contact resistance between the positive electrode active material and the current collector. Examples of conductive agents include vapor-grown carbon fiber (VGCF), carbon black such as acetylene black, and carbonaceous materials such as graphite. One of these agents can be used as a conductive agent, or a combination of two or more can be used. Alternatively, the conductive agent can be omitted.

[0040] In the layers containing positive electrode active material, the positive electrode active material and the binder are preferably mixed in proportions of more than 80% by mass and less than 98% by mass and more than 2% by mass and less than 20% by mass, respectively.

[0041] Sufficient electrode strength can be obtained by making the amount of binder 2% by mass or more. Furthermore, the binder functions as an insulator. Therefore, if the amount of binder is 20% by mass or less, the amount of insulator contained in the electrode is reduced, thus reducing internal resistance.

[0042] When adding a conductive agent, it is preferable that the positive electrode active material, binder and conductive agent are mixed in proportions of 77% or more and 95% or less by mass, 2% or more and 20% or less by mass, and 3% or more and 15% or less by mass, respectively.

[0043] The aforementioned effects can be achieved by ensuring that the amount of the conductive agent is 3% by mass or more. Furthermore, by ensuring that the amount of the conductive agent is 15% by mass or less, the proportion of the conductive agent in contact with the electrolyte can be reduced. If this proportion is low, electrolyte decomposition can be reduced under high-temperature storage conditions.

[0044] The current collector uses a material that is electrochemically stable at the potential for lithium (Li) insertion and extraction in the active material. For example, the positive current collector is preferably aluminum foil or an aluminum alloy foil containing one or more elements selected from Mg, Ti, Zn, Ni, Cr, Mn, Fe, Cu and Si.

[0045] The thickness of the aluminum foil or aluminum alloy foil is preferably 5 μm or more and 20 μm or less, more preferably 15 μm or less. The purity of the aluminum foil is preferably 99% by mass or more. The content of transition metals such as iron, copper, nickel, and chromium contained in the aluminum foil or aluminum alloy foil is preferably 1% by mass or less.

[0046] Additionally, the positive current collector can be included in the portion of its surface where no layer of positive active material is formed. This portion can function as a positive current collector tab.

[0047] 2) Negative electrode The negative electrode may comprise a negative current collector and a layer containing a negative active material. The layer containing the negative active material may be formed on one or both sides of the current collector. The layer containing the negative active material may comprise the negative active material and any conductive agent and binder.

[0048] As a negative electrode active material, carbon materials and metal oxides can be used, for example. Examples of metal oxide active materials include lithium titanate (e.g., Li₂) with an orthorhombic manganese oxide structure. 2+y Ti3O7, 0≤y≤3), lithium titanate with spinel structure (e.g., Li), 4+x Ti5O 12 The following are types of titanium oxides: 0≤x≤3, titanium dioxide (TiO2), anatase titanium dioxide, rutile titanium dioxide, niobium pentoxide (Nb2O5), manganese barium ore titanium composite oxides, orthorhombic titanium composite oxides, and monoclinic niobium titanium oxides.

[0049] As an example of the orthorhombic titanium-containing composite oxides mentioned above, Li can be cited. 2+a M I 2-b Ti 6-c M II d O 14+σ The compound represented. Here, M I It is selected from at least one of Sr, Ba, Ca, Mg, Na, Cs, Rb, and K. M II It is selected from at least one of Zr, Sn, V, Nb, Ta, Mo, W, Y, Fe, Co, Cr, Mn, Ni, and Al. The subscripts in the composition formula are 0 ≤ a ≤ 6, 0 ≤ b < 2, 0 ≤ c < 6, 0 ≤ d < 6, and -0.5 ≤ σ ≤ 0.5. As a specific example of an orthorhombic titanium-containing composite oxide, Li can be cited. 2+a Na2Ti6O 14 (0≤a≤6).

[0050] As an example of the aforementioned monoclinic niobium titanium oxide, Li can be cited as an example. x Ti 1-y M1 y Nb 2-z M2 z O 7+δ The compound is represented by M1, which is selected from at least one of Zr, Si, and Sn. M2 is selected from at least one of V, Ta, and Bi. The subscripts in the composition formula are 0 ≤ x ≤ 5, 0 ≤ y < 1, 0 ≤ z < 2, and -0.3 ≤ δ ≤ 0.3. Li can be cited as a specific example of a monoclinic niobium titanium oxide. x Nb2TiO7 (0≤x≤5).

[0051] Other examples of monoclinic niobium titanium oxides include Li x Ti 1-y M3 y+z Nb 2-z O 7-δ The compound is represented by M3, which is selected from at least one of Mg, Fe, Ni, Co, W, Ta, and Mo. The subscripts in the composition formula are 0 ≤ x ≤ 5, 0 ≤ y < 1, 0 ≤ z < 2, and -0.3 ≤ δ ≤ 0.3.

[0052] It is possible to more preferably use Li in the layer containing the negative electrode active material. + A diffuse-activity negative electrode active material. Specifically, a negative electrode active material in which the lithium intercalation-deintercalation reaction (charge-discharge reaction) is mainly a single solid-phase reaction is preferred. When using such a negative electrode active material, during the adjustment of Li + It is easy to embed into the outermost layer containing the negative electrode active material. Examples of compounds that can be used as negative electrode active materials and undergo a single solid-phase reaction include the orthorhombic titanium composite oxide and the monoclinic niobium titanium oxide mentioned above.

[0053] Conductive agents are used to improve current collection performance and suppress contact resistance between the negative electrode active material and the current collector. Examples of conductive agents include vapor-grown carbon fiber (VGCF), carbon black such as acetylene black, carbonaceous materials such as graphite, carbon nanotubes, and carbon nanofibers. One of these agents can be used as a conductive agent, or a combination of two or more can be used. Alternatively, instead of using a conductive agent, the surface of the active material particles can be coated with carbon or an electronically conductive inorganic material.

[0054] The binder is used to fill the gaps between the dispersed negative electrode active material and to bond the negative electrode active material to the current collector. Examples of binders include: polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluororubber, styrene-butadiene rubber, polyacrylic acid compounds, imide compounds, carboxymethyl cellulose (CMC), and salts of CMC. One of these can be used as a binder, or two or more can be used in combination.

[0055] The negative electrode active material, conductive agent, and binder in the negative electrode active material layer are preferably formulated in proportions of 68% to 96% by mass, 2% to 30% by mass, and 2% to 30% by mass, respectively. Setting the amount of conductive agent to 2% by mass or more improves the current-collecting performance of the negative electrode active material layer. Furthermore, by setting the amount of binder to 2% by mass or more, sufficient adhesion between the negative electrode active material layer and the current collector is achieved, resulting in excellent cycle performance. On the other hand, setting the amount of conductive agent and binder to 30% by mass or less is preferred for achieving high capacity.

[0056] The density of the negative electrode active material layer (excluding the current collector) is preferably 1.8 g / cm³. 3 Above and 3.2g / cm 3 The following describes the negative electrode with excellent energy density and electrolyte retention within a given density range for the negative electrode active material layer. A more preferred density for the negative electrode active material layer is 2.1 g / cm³. 3 Above and 3.0 g / cm 3 the following.

[0057] The negative current collector is preferably made of copper, nickel, stainless steel, or aluminum, or an aluminum alloy containing one or more elements selected from Mg, Ti, Zn, Mn, Fe, Cu, and Si. The thickness of the current collector is preferably 5 μm or more and 20 μm or less. A current collector with this thickness achieves a balance between electrode strength and lightweight design.

[0058] Additionally, the negative current collector can be included in the portion of its surface where no layer of negative active material is formed. This portion can function as a negative current collector tab.

[0059] 3) Electrolytes As the electrolyte, for example, a liquid non-aqueous electrolyte or a gel-like non-aqueous electrolyte can be used. A liquid non-aqueous electrolyte is prepared by dissolving an electrolyte salt, which is the solute, in an organic solvent. The concentration of the electrolyte salt is preferably 0.5 mol / L or more and 2.5 mol / L or less.

[0060] Examples of electrolyte salts include lithium salts such as lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3), and lithium bis(trifluoromethanesulfonyl)imide (LiN(CF3SO2)2), as well as mixtures thereof. The electrolyte salt is preferably a salt that is difficult to oxidize even at high potentials, with LiPF6 being the most preferred.

[0061] In addition to the electrolyte salts mentioned above, the electrolyte may also contain at least one additive compound selected from the group consisting of sulfur-containing compounds, boron-containing compounds, phosphorus-containing compounds, and fluorine-containing compounds. Examples of sulfur-containing compounds include 1,3-propanesulfonyl lactone (PS), 1,3-propenesulfonyl lactone, ethylene sulfite, ethylene sulfate, 1,4-butanesulfonyl lactone, and 2,4-butanesulfonyl lactone. Examples of boron-containing compounds include lithium difluorooxalate borate (LiBF2C2O4:LiDFOB) and lithium bis(oxalate borate) (LiB(C2O4)2:LiBOB). Examples of phosphorus-containing compounds include tris(trimethylsilyl) phosphate (TMSP) and lithium difluorophosphate (LiPO2F2; LiDFP). Examples of fluorine-containing compounds include fluoroethylene carbonate (FEC), lithium bis(trifluoromethanesulfonyl)imide (LiN(SO₂CF₃)₂; LiTFSI), lithium bis(fluorosulfonyl)imide (LiN(SO₂F)₂; LiFSI), LiDFOB, and LiDFP. These added compounds can serve as sources of S, B, P, and F-containing compounds, i.e., coating components, formed at the positive electrode, particularly the outermost positive electrode layer, during the aforementioned adjustments. It should be noted that among the lithium salts mentioned above, fluorine-containing salts such as LiPF₆ and LiBF₄ can also serve as sources of F-containing compounds, i.e., F-based coatings, formed at the positive electrode.

[0062] Examples of organic solvents include: cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), and vinylene carbonate (VC); chain carbonates such as diethyl carbonate (DEC), dimethyl carbonate (DMC), and methyl ethyl carbonate (MEC); cyclic ethers such as tetrahydrofuran (THF), 2-methyl tetrahydrofuran (2MeTHF), and dioxolane (DOX); chain ethers such as dimethoxyethane (DME) and diethoxyethane (DEE); methyl formate (MF), ethyl formate (EF), propyl formate (AN), ethyl acetate (EA), propyl acetate (PA), and ethyl propionate (E). Chain carboxylic acid esters such as Propionate (EP), Propyl Propionate (PP), Methyl Butyrate (MB), Ethyl Butyrate (EB), and Propyl Butyrate (PB); γ-butyrolactone (GBL), acetonitrile (AN), and sulfolane (SL). These organic solvents can be used alone or as mixed solvents.

[0063] Gel-like nonaqueous electrolytes can be modulated by combining liquid nonaqueous electrolytes with polymeric materials. Examples of polymeric materials include polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO), or mixtures thereof.

[0064] Alternatively, as a non-aqueous electrolyte, in addition to liquid non-aqueous electrolytes and gel non-aqueous electrolytes, room-temperature molten salts (ionic melts) containing lithium ions, polymeric solid electrolytes, and inorganic solid electrolytes can also be used.

[0065] Room-temperature molten salts (ionic melts) refer to compounds of organic salts composed of a combination of organic cations and anions that exist as liquids at room temperature (above 15°C and below 25°C). Room-temperature molten salts include those that exist as liquids alone, those that become liquids by mixing with electrolyte salts, those that become liquids by dissolving in organic solvents, or mixtures thereof. Typically, room-temperature molten salts used in secondary batteries have melting points below 25°C. Furthermore, the organic cations usually possess a quaternary ammonium framework.

[0066] Polymer solid electrolytes are prepared by dissolving electrolyte salts in polymer materials and then solidifying them.

[0067] Inorganic solid electrolytes are solid substances that exhibit Li-ion conductivity. Here, Li-ion conductivity refers to a conductivity of 1×10⁻⁶ at 25°C. -6 Lithium-ion conductivity of S / cm or higher. Examples of inorganic solid electrolytes include oxide-based solid electrolytes and sulfide-based solid electrolytes. Specific examples of inorganic solid electrolytes are described below.

[0068] As an oxide-based solid electrolyte, it is preferable to use an electrolyte with a NASICON (Sodium (Na) Super Ionic Conductor) type structure and composed of the general formula Li 1+x Mα2(PO4)3 represents a lithium phosphate solid electrolyte. In the above general formula, Mα is, for example, selected from one or more of titanium (Ti), germanium (Ge), strontium (Sr), zirconium (Zr), tin (Sn), aluminum (Al), and calcium (Ca). The subscript x is in the range of 0 ≤ x ≤ 2.

[0069] As a specific example of a lithium phosphate solid electrolyte with a NASICON-type structure, one could cite Li... 1+x Al x Ti 2-x (PO4)3 represents LATP compounds with a value of 0.1 ≤ x ≤ 0.5; [The text abruptly ends here, likely due to an incomplete sentence or missing information.] 1+x Al y Mβ 2-y (PO4)3 represents a compound in which Mβ is selected from one or more of Ti, Ge, Sr, Zr, Sn, and Ca, and is 0≤x≤1 and 0≤y≤1; derived from Li 1+x Al x Ge 2-x (PO4)3 represents a compound that is 0 ≤ x ≤ 2; and compounds derived from Li 1+x Al x Zr 2-x (PO4)3 represents a compound that is 0 ≤ x ≤ 2; derived from Li 1+x+y Al x Mγ2- x Si y P 3-y O 12 This indicates that Mγ is a compound selected from Ti and Ge, and that 0 < x ≤ 2 and 0 ≤ y < 3; derived from Li 1+ 2x Zr 1-x Ca x (PO4)3 represents a compound that is 0 ≤ x < 1.

[0070] In addition to the aforementioned lithium phosphate solid electrolyte, other oxide-based solid electrolytes include those made from Li... x PO y N z This refers to amorphous LIPON compounds (e.g., Li) with the following properties: 2.6 ≤ x ≤ 3.5, 1.9 ≤ y ≤ 3.8, and 0.1 ≤ z ≤ 1.3. 2.9 PO 3.3 N 0.46 ); La with garnet-type structure 5+x A x La 3-x Mδ2O 12 This indicates a compound in which A is selected from one or more compounds in the group consisting of Ca, Sr, and Ba, Mδ is selected from one or more compounds in the group consisting of Nb and Ta, and 0 ≤ x ≤ 0.5; Li3Mδ 2- x L2O 12 This indicates that Mδ is a compound selected from the group consisting of Nb and Ta, L may contain Zr and 0≤x≤0.5; [The text abruptly ends here, likely due to an incomplete sentence or missing information.] 7-3x Al x La3Zr3O 12 Represents compounds in which 0 ≤ x ≤ 0.5; derived from Li 5+x La3Mδ 2-x Zr x O 12 Mδ represents an LLZ compound selected from the group consisting of Nb and Ta, where 0 ≤ x ≤ 2 (e.g., Li7La3Zr2O). 12 ); and those with a perovskite-type structure and composed of La 2 / 3-x Li x TiO3 represents compounds in which 0.3 ≤ x ≤ 0.7.

[0071] One or more of the above-mentioned compounds may be used as a solid electrolyte. Two or more of the above-mentioned solid electrolytes may also be used.

[0072] 4) Diaphragm The diaphragm can be formed, for example, from a porous membrane containing polyethylene (PE), polypropylene (PP), cellulose, or polyvinylidene fluoride (PVdF) or a nonwoven fabric made of synthetic resin. From a safety point of view, a porous membrane made of polyethylene or polypropylene is preferred. This is because these porous membranes melt at a certain temperature, which can interrupt the current.

[0073] 5) Outer packaging components As an outer packaging component, containers formed of laminated film or metal containers can be used, for example.

[0074] The thickness of the laminated film is, for example, 0.5 mm or less, preferably 0.2 mm or less.

[0075] As a laminated film, a multilayer film comprising multiple resin layers and a metal layer sandwiched between these resin layers can be used. The resin layers may contain polymers such as polypropylene (PP), polyethylene (PE), nylon, and polyethylene terephthalate (PET). For weight reduction, the metal layer is preferably formed of aluminum foil or aluminum alloy foil. The laminated film can be sealed by hot-melt bonding to form the shape of an outer packaging component.

[0076] The wall thickness of the metal container is preferably 1 mm or less, more preferably 0.5 mm or less, and even more preferably 0.2 mm or less.

[0077] Metal containers can be made of materials such as aluminum or aluminum alloys. Preferably, the aluminum alloy contains elements such as magnesium, zinc, and silicon. When the aluminum alloy contains transition metals such as iron, copper, nickel, and chromium, their content is preferably less than 100 ppm by mass.

[0078] The shape of the outer packaging component is not particularly limited. The outer packaging component can be, for example, flat (thin), square, cylindrical, coin-shaped, or button-shaped. The outer packaging component can be selected appropriately based on the battery size and intended use.

[0079] 6) Positive extreme The positive terminal can be in a potential range of 3V or higher and 4.5V or lower relative to the redox potential of lithium (vs. Li / Li). + The positive terminal is formed of a material that is electrically stable and conductive. Examples of materials for the positive terminal include aluminum or aluminum alloys containing at least one element selected from Mg, Ti, Zn, Mn, Fe, Cu, and Si. To reduce the contact resistance with the positive current collector, the positive terminal is preferably formed of the same material as the positive current collector.

[0080] 7) Negative extremes The negative terminal can be formed of a material that is electrochemically stable and conductive at the Li insertion / deintercalation potential of the aforementioned negative electrode active material. Specifically, examples of materials for the negative terminal include copper, nickel, stainless steel, or aluminum, or an aluminum alloy containing at least one element selected from Mg, Ti, Zn, Mn, Fe, Cu, and Si. Aluminum or an aluminum alloy is preferred as the material for the negative terminal. To reduce the contact resistance with the negative electrode current collector, the negative terminal is preferably formed of the same material as the negative electrode current collector.

[0081] Next, the secondary battery of the embodiment will be described in more detail with reference to the accompanying drawings.

[0082] Figure 1 This is a cross-sectional view that roughly represents an example of a secondary battery. Figure 2 It is Figure 1 An enlarged cross-sectional view of part A of the secondary battery shown.

[0083] Figure 1 and Figure 2 The secondary battery 100 shown has Figure 1 The bag-shaped outer packaging component 2 shown Figure 1 and Figure 2 The electrode assembly 1 and the electrolyte (not shown) are shown. The electrode assembly 1 and the electrolyte are housed within a bag-shaped outer packaging component 2. The electrolyte (not shown) is held within the electrode assembly 1.

[0084] The bag-shaped outer packaging component 2 is formed of a laminate containing two resin layers and a metal layer between them.

[0085] like Figure 1 As shown, electrode group 1 is a flat, wound electrode group. Figure 2 As shown, the flat and coiled electrode assembly 1 includes a negative electrode 3, a diaphragm 4, and a positive electrode 5. The diaphragm 4 is located between the negative electrode 3 and the positive electrode 5.

[0086] The negative electrode 3 includes a negative current collector 3a and negative active material layers 3b formed on both sides thereof. However, for convenience, the portion of the negative electrode 3 located at the outermost shell of the wound electrode assembly 1 is distinguished as the outermost negative electrode portion from the outermost negative electrode portion 30. Furthermore, among the active material layers formed on the surface of the negative current collector 3a in the outermost negative electrode portion 30, the active material layer located on the outside of the electrode assembly 1 is distinguished from the outermost negative active material layer 30a and other negative active material layers 3b.

[0087] The positive electrode 5 includes a positive current collector 5a and positive active material layers 5b formed on both sides thereof. However, for convenience, the portion of the positive electrode 5 located closest to the outer shell of the wound electrode assembly 1 is distinguished from the outermost positive electrode portion 50 as the outermost positive electrode portion. Furthermore, among the active material layers formed on the surface of the positive current collector 5a in the outermost positive electrode portion 50, the active material layer closest to the outer side of the electrode assembly 1 is distinguished from the outermost positive active material layer 50a and other positive active material layers 5b.

[0088] The outermost layer containing the negative electrode active material 30a is not opposed to the positive electrode active material layer 5b and the outermost layer containing the positive electrode active material 50a. The entire surface of the outermost layer containing the negative electrode active material 30a facing outwards from the electrode assembly 1 is a non-opposing surface that is not opposed to other active material layers. The negative electrode active material layer 3b located inside the electrode assembly 1 in the outermost negative electrode layer 30 is opposed to the outermost positive electrode active material layer 50a through a separator 4. In the portion other than the outermost negative electrode layer 30 and the outermost positive electrode layer 50, the negative electrode active material layer 3b is opposed to the positive electrode active material layer 5b through a separator 4.

[0089] like Figure 1 As shown, the negative terminal 6 and the positive terminal 7 are located near the outer periphery of the wound electrode assembly 1. The negative terminal 6 is connected to the negative current collector 3a at the outermost layer 30 of the negative electrode. Similarly, the positive terminal 7 is connected to the positive current collector 5a at the outermost layer 50 of the positive electrode. These negative terminals 6 and positive terminals 7 extend outward from the opening of the bag-shaped outer packaging component 2. A thermoplastic resin layer is provided on the inner surface of the bag-shaped outer packaging component 2, and the opening is sealed by thermally melting and bonding it.

[0090] The secondary batteries involved in the implementation methods are not limited to Figure 1 and Figure 2 The secondary battery shown can also be, for example, a... Figure 3 and Figure 4 The battery configuration shown.

[0091] Figure 3 This is a partial cutaway perspective view schematically representing other examples of secondary batteries. Figure 4 yes Figure 3 An enlarged cross-sectional view of part B of the secondary battery shown.

[0092] Figure 3 and Figure 4 The secondary battery 100 shown has Figure 3 and Figure 4 Electrode group 1 shown Figure 3 The outer packaging component 2 and the electrolyte (not shown) are shown. The electrode assembly 1 and the electrolyte are housed within the outer packaging component 2. The electrolyte is held within the electrode assembly 1.

[0093] The outer packaging component 2 is formed of a laminated film comprising two resin layers and a metal layer sandwiched between them.

[0094] Electrode group 1 as follows Figure 4 The electrode assembly shown is a stacked type. The stacked type electrode assembly 1 has a structure in which a separator 4 is sandwiched between the negative electrode 3 and the positive electrode 5 and the negative electrode 3 and the positive electrode 5 are stacked alternately. However, the negative electrode disposed on the outer side of the electrode assembly 1 among the multiple negative electrodes is referred to here as the outermost negative electrode part, which is the outermost negative electrode 13. Figure 4 Only the lower part of electrode group 1 is shown. The outermost negative electrode 13 is only shown as a piece located near the bottom layer of electrode group 1, but electrode group 1 also includes another outermost negative electrode 13 near the top layer. For multiple positive electrodes, the positive electrode adjacent to the outermost negative electrode 13, which serves as the outermost positive electrode portion, is referred to as the outermost positive electrode 15. Regarding the outermost positive electrode 15, it includes not only the piece shown on the lower layer side, but also another outermost positive electrode 15 on the upper layer side.

[0095] The electrode assembly 1 includes a plurality of negative electrodes 3. Each of the plurality of negative electrodes 3 has a negative current collector 3a and a layer 3b containing negative active material supported on both sides of the negative current collector 3a. In addition, as described above, the electrode assembly 1 includes two outermost negative electrodes 13. Each outermost negative electrode 13 has a negative current collector 3a and an outermost layer 13a and a layer 3b containing negative active material supported on one side and the other side of the negative current collector 3a, respectively. In detail, the outermost layer 13a containing negative active material is supported on the side of the negative current collector 3a facing outward from the electrode assembly 1, and the layer 3b containing negative active material is supported on the side facing inward from the electrode assembly 1 on its back side.

[0096] The electrode assembly 1 includes a plurality of positive electrodes 5. Each of the plurality of positive electrodes 5 has a positive current collector 5a and a layer 5b containing positive active material supported on both sides of the positive current collector 5a. In addition, as described above, the electrode assembly 1 includes two outermost positive electrodes 15. Each outermost positive electrode 15 has a positive current collector 5a, and an outermost layer 15a and a layer 5b containing positive active material supported on one side and the other side of the positive current collector 5a, respectively. In detail, the outermost layer 15a containing positive active material is supported on the side of the positive current collector 5a facing outwards from the electrode assembly 1, and the layer 5b containing positive active material is supported on the side facing inwards from the electrode assembly 1 on its back side.

[0097] Each negative electrode 3's negative current collector 3a includes a portion on one side where neither surface supports the negative active material layer 3b. Similarly, for the outermost negative electrode 13, one side of the negative current collector 3a includes a portion that does not support the outermost negative active material layer 13a and the negative active material layer 3b. This portion functions as the negative current collector tab 3c. Figure 4 As shown, the negative collector tab 3c does not overlap with the positive electrode 5. Furthermore, multiple negative collector tabs 3c are electrically connected to the strip-shaped negative terminal 6. The front end of the strip-shaped negative terminal 6 extends to the outside of the outer packaging component 2.

[0098] Furthermore, although not illustrated, each positive electrode 5's positive current collector 5a also includes a portion on one side where neither surface supports the positive active material layer 5b. Similarly, for the outermost positive electrode 15, one side of the positive current collector 5a includes a portion that does not support the outermost positive active material layer 15a and the positive active material layer 5b. This portion functions as a positive current collector tab. The positive current collector tab, like the negative current collector tab 3c, does not overlap with the negative electrode 3. Furthermore, the positive current collector tab is located on the opposite side of the electrode group 1 relative to the negative current collector tab 3c. The positive current collector tab is electrically connected to the strip-shaped positive terminal 7. The front end of the strip-shaped positive terminal 7 is located on the opposite side of the negative terminal 6 and extends to the outside of the outer packaging component 2.

[0099] For any of the above examples of secondary batteries 100, at least in the outermost positive electrode portion ( Figure 2 The outermost layer 50 of the positive electrode shown Figure 4 The outermost positive electrode 15 shown contains a compound containing at least one selected from the group consisting of sulfur, boron, phosphorus and fluorine, and the concentration of the compound in the outermost positive electrode is higher than the concentration in the inner positive electrode 5 of the electrode assembly 1.

[0100] <Manufacturing Method> The secondary battery involved in the implementation method can be manufactured as follows.

[0101] Prepare electrodes, electrolyte, and outer packaging components. Assemble the battery precursor by housing the electrodes and electrolyte within the outer packaging components. Perform conditioning treatment on the battery precursor, embedding Li into the non-opposite surface of the negative electrode active material layer, which is not opposite to the positive electrode active material layer. + .

[0102] Electrodes can be fabricated, for example, by the following method: First, an active material, a conductive agent, and a binder are suspended in a solvent to prepare a slurry. This slurry is then coated onto both sides of a current collector. Next, the coated slurry is dried to obtain a laminate containing the active material layer and the current collector. Then, pressure is applied to the laminate. This process fabricates the electrode.

[0103] Alternatively, the electrode can be fabricated using the following method: First, an active material, a conductive agent, and a binder are mixed to obtain a mixture. Next, this mixture is granulated. Then, these granules are disposed on a current collector, thereby obtaining the positive electrode.

[0104] Electrolytes can be prepared, for example, by the methods described above.

[0105] In a plurality of electrodes, at least one layer containing a positive electrode active material and at least one layer containing a negative electrode active material are prepared. The electrodes and electrolyte are housed together in a separately prepared outer packaging component, with at least one pair of positive electrode active material layers and portions of negative electrode active material layers having their main surfaces facing each other, and the other portion of the negative electrode active material layer not facing the positive electrode active material layer having its main surface facing outwards. The "partial" and "other" portions of the negative electrode active material layer mentioned here can also refer to either a single negative electrode active material layer among a plurality of negative electrode active material layers, or a specific portion within a single negative electrode active material layer and a portion different from it. As a specific example of the former, in Figure 4 Of the multiple layers containing negative electrode active material shown, the negative electrode 3 and the outermost negative electrode 13 containing negative electrode active material layer 3b are counted as a portion of the positive electrode active material layer 5b whose main surface faces the positive electrode 5 and the outermost positive electrode active material layer 15a of the outermost positive electrode 15. The outermost negative electrode active material layer 13a of the outermost negative electrode 13 is counted as another portion whose main surface does not face the positive electrode active material layer. As a specific example of the latter, in Figure 2 The diagram shows two layers containing negative electrode active material respectively disposed on the upper and lower surfaces of the negative electrode current collector 3a. The portion of the negative electrode active material layer on the upper surface is regarded as the negative electrode active material layer 3b whose main surface is opposite to the positive electrode active material layer, and the outermost negative electrode active material layer 30a whose main surface is not opposite to the positive electrode active material layer, depending on the position in the electrode assembly and whether it is opposite to the positive electrode active material layer.

[0106] As described above, when an electrode is arranged with a portion of the negative electrode active material layer facing the positive electrode active material layer, for example, an electrode assembly can be fabricated by placing a separator between the negative electrode active material layer and the positive electrode active material layer. As an electrode assembly, a stacked electrode assembly or a wound electrode assembly can be constructed. In a stacked electrode assembly, multiple separators can be sandwiched between the negative electrode active material layer and the positive electrode active material layer, or a strip-shaped separator can be bent, with each portion along its long side sandwiched between the negative electrode active material layer and the positive electrode active material layer.

[0107] The outer packaging containing the electrodes and electrolyte configured as described above is sealed to obtain a battery precursor. The battery precursor undergoes repeated charge-discharge cycles (also known as conditioning, adjustment, or activation), including constant-current constant-voltage charging (CCCV charging) and constant-current discharging under very low current convergence conditions at 45°C. Specifically, at 45°C, constant-current charging is performed at 1C to 100% SOC, and charging is terminated when the current reaches 1 / 1000C or less, followed by constant-current charging at the achieved voltage. Then, constant-current discharging is performed at 1C to 0% SOC. This charge-discharge cycle is repeated for a total of 10 to 50 cycles.

[0108] By performing the above-mentioned adjustment process, Li is embedded in the outermost negative electrode or the non-opposite portion of the negative electrode located in the outermost part of the negative electrode, that is, in the negative electrode active material layer or a part of the negative electrode active material layer that is not opposite to the positive electrode active material layer. + In addition, Li + The embedding of Li into the non-opposite portion of the negative electrode is not biased towards its outer periphery, but can be embedded uniformly and throughout the surface direction. + Li is embedded into the non-opposite portion of the negative electrode through pre-conditioning. + It can promote the formation of the film in the outermost layer containing positive electrode active material.

[0109] <Determination Method> The measurement methods for batteries are explained. Specifically, the methods for measuring the concentration of S, B, P, and F compounds in the positive electrode active material layer, the methods for measuring the Li content in the outermost negative electrode active material layer, and the methods for confirming the electrode active materials are explained.

[0110] Concentration of compounds containing at least one of S, B, P, and F The concentration of compounds containing at least one of S, B, P, and F in an electrode containing a positive electrode active material layer can be determined using inductively coupled plasma mass spectrometry (ICP) and hard X-ray photoelectron spectroscopy (HAXPES).

[0111] For any measurement, first, the battery's state of charge (SOC) is adjusted to 100% or 50%. The battery adjusted to 100% or 50% charge is disassembled, and the electrode containing the positive electrode active material layer is removed. For example, in the case of a battery with multiple positive electrodes, such as one using a stacked electrode assembly, the outermost positive electrode and the innermost positive electrode are removed separately. As the innermost positive electrode, it is preferable to select a positive electrode located as far away from the outermost layer as possible. For example, in the case of a stacked electrode assembly containing 7 positive electrode layers, the fourth positive electrode is selected as the innermost positive electrode. For example, in the case of a battery with a wound electrode assembly, where a single positive electrode is stacked by winding, the positive electrode is cut from the outermost and innermost portions of the wound body, respectively. For the portion from which the positive electrode is cut, it is preferable to select a position as far away from the outermost layer as possible. For example, the positive electrode is cut from the innermost circumference of the wound structure. The collected electrodes are washed with an organic solvent. As an organic solvent, a solvent with a relatively low dielectric constant, such as ethyl methyl carbonate, can be used. The cleaning process takes about 10 minutes.

[0112] For the electrode used as the sample for ICP-MS determination, after cleaning as described above, the electrode is immersed in a highly polar solvent and heated to 60°C on a hot plate for 1 hour to extract the coating components. Acetonitrile is an example of a highly polar solvent. The resulting extract is then analyzed by ICP-MS to determine the concentrations of S, B, P, and F. Based on the ICP-MS results, the amounts of S, B, P, and F compounds present on the surface of the electrode before immersion in the highly polar solvent can be determined. The concentration of S, B, P, and F compounds is obtained by dividing this amount of compound by the weight of the active material layer.

[0113] The electrode used as the sample for HAXPES determination is cleaned as described above and then vacuum dried at room temperature. The dried sample electrode is then attached to the HAXPES sample holder using carbon tape inside an argon-filled glove box. The sample holder is placed inside a transfer container and sealed. The transfer container is then completely removed from the glove box and installed at the sample inlet of the HAXPES apparatus. The sample electrode is introduced into the apparatus without exposure to the atmosphere by transferring the sample holder within the apparatus.

[0114] The analysis using HAXPES was performed as follows. Energy was measured using Au4f. 7 / 2 After calibration (5870 eV), measurements were performed. The excitation energy was 5956.01 eV. The beam size was 20 μm vertically × 30 μm horizontally. The electron analyzer (e.g., Scienta Omicron R4000L1) was set to 1012 keV. The photoelectron detection angle was set to an oblique incidence configuration of approximately 88.589°. Charge neutralization was set to unused.

[0115] Subtract the background from the results obtained through the above analysis.

[0116] Background subtraction and area calculation can be performed using the Shirley method. For example, in determining Ni2p origin... 3 / 2 When determining the peak area in the HAXPES analysis results for the binding energy range of 850 eV to 865 eV, the Shirley method is used to subtract the background. After background subtraction, a graph is plotted with normalized intensity (intensity (normalized)) on the vertical axis and binding energy (in eV) on the horizontal axis. This graph is used as the HAXPES spectrum. In the HAXPES spectrum, the range of binding energy above 850 eV to 865 eV is used as the integration range. The peak area is then determined.

[0117] Because of its deep detection depth, HAXPES can analyze both the components of the active material layer and the components of the coating material layer in the analytical results, even if a film forms on the surface containing the active material layer. Therefore, this study evaluates the peak area A of the peaks from compounds containing S, B, P, and F, which are components of the coating material. SBPF Peak P relative to active ingredient AM Peak area A AM The ratio.

[0118] Peak P, derived from active substances AM For example, examples can be derived from Ni2p. 3 / 2 The peaks appearing in the range above 850 eV and below 865 eV originate from Co2p. 3 / 2 Peaks appearing in the range of 775 eV above and 787 eV, and those originating from Mn2p 3 / 2 The peaks appear in the range of 635 eV and below 650 eV. For example, these peaks can be detected by HAXPES analysis of electrodes containing lithium nickel cobalt manganese composite oxides as active materials. The peaks P in each of these ranges vary depending on the ratio of nickel (Ni), cobalt (Co), and manganese (Mn) in the active material. AM Peak area A AM Increase or decrease them respectively. For example, when the proportion of Ni in the lithium nickel cobalt manganese composite oxide is the highest, the peak P in the above three ranges will be higher. AM From Ni2p 3 / 2 The peak with the largest area was selected. The peak corresponding to the element with the highest proportion among Ni, Co, and Mn in the active material was chosen as peak P. AM Analyze and calculate the peak area A. AM The methods for determining the elemental composition of active substances will be described later.

[0119] Regarding the peaks derived from compounds containing S, B, P and F, mentionable are: a peak derived from S1s of S-containing compounds that appears within a range of 2470 eV to 2484 eV inclusive, a peak derived from B1s of B-containing compounds that appears within a range of 180 eV to 200 eV inclusive, a peak derived from P1s of P-containing compounds that appears within a range of 2143 eV to 2157 eV inclusive, and a peak derived from F1s of F-containing compounds that appears within a range of 680 eV to 692 eV inclusive. The total sum of the peak areas of the peaks appearing in each of the above ranges is designated as the peak area A of the comprehensive peaks from S, B, P, F-containing compounds SBPF .

[0120] The peak area A of the peaks from S, B, P, F-containing compounds obtained from a sample collected from the outermost positive electrode part SBPF is divided by the peak area A of the peak P from the active material AM to obtain (P AM (P AM / A AM ), thereby calculating the peak area ratio AR1 of the outermost positive electrode part. Similarly, the peak area A of the peaks from S, B, P, F-containing compounds obtained from a sample collected from the internal positive electrode part SBPF is divided by the peak area A of the peak P from the active material AM to obtain (P AM (P AM / A AM ), thereby calculating the peak area ratio AR2 of the internal positive electrode part. In addition, the ratio AR1 / AR2 of the former AR1 to the latter AR2 is calculated. When the secondary battery according to the embodiment is subjected to HAXPES analysis as described above, the relationship of 1.1<AR1 / AR2<10 can be satisfied.

[0121] Even if one or more of S, B, P and F are contained in the active material composition, they can be distinguished from S, B, P, F-containing compounds as coating components as described below. The constituent elements of the active material composition are detected by HAXPES, but they are difficult to be detected in ICP-MS measurement of the above extraction solution. Therefore, by comparing the concentration in the extraction solution measured by ICP-MS and the concentration in the surface of the active material-containing layer based on HAXPES, it can be determined whether the S, B, P, F-containing compound belongs to the active material component or the coating component.

[0122] Li content in the outermost negative active material-containing layer The amount of Li intercalated into the outermost negative active material-containing layer through adjustment + can be confirmed as follows.

[0123] The battery is adjusted to 100% SOC. The battery, adjusted to 100% charge, is disassembled, and the electrode containing the outermost layer of negative electrode active material is removed. For example, in the case of a battery with multiple negative electrodes, such as one using a stacked electrode assembly, the outermost negative electrode is removed. In the case of a battery with a wound electrode assembly, where a single negative electrode is stacked by winding, the negative electrode is cut from the outermost layer of the wound electrode. The collected electrode is washed with an organic solvent. For example, a solvent with a relatively low dielectric constant, such as ethyl methyl carbonate, can be used as the organic solvent. The washing is performed for approximately 10 minutes. Next, vacuum drying is performed at room temperature. The active material layer located on the back side of the current collector relative to the outermost layer of negative electrode active material is peeled off from the dried sample electrode. Using the electrode with only the remaining outermost layer of negative electrode active material on the current collector as the working electrode, a single-electrode cell, such as a coin cell, using Li metal as the counter electrode is fabricated. The resulting single-electrode cell is measured at 25°C and discharged at 0.1C to 3.0V (vs. Li / Li). + The measured discharge capacity (mAh) is divided by the weight of the outermost negative electrode active material layer to obtain the amount of Li contained in the outermost negative electrode active material layer (mAh / g).

[0124] Electrode active material The crystal structure and elemental composition of the electrode active materials contained in each active material layer can be confirmed by powder X-ray diffraction (XRD) and inductively coupled plasma (ICP) luminescence spectrophotometry.

[0125] In the secondary battery according to the first embodiment, the concentration of a compound containing at least one selected from sulfur, boron, phosphorus, and fluorine in the outermost positive electrode portion located on the outermost side of the electrode assembly is higher than the concentration of the same compound in the inner positive electrode portion located on the inner side of the electrode assembly. This secondary battery exhibits a long lifespan.

[0126] (Second Implementation) According to a second embodiment, a battery pack is provided. This battery pack includes a plurality of secondary batteries according to a first embodiment.

[0127] In this battery pack, the individual cells can be configured to be connected in series or in parallel, or a combination of series and parallel connections can be configured.

[0128] Next, an example of a battery pack according to the embodiment will be described with reference to the accompanying drawings.

[0129] Figure 5 This is a three-dimensional diagram that roughly represents an example of a battery pack. Figure 5The battery pack 200 shown includes five individual cells 100a-100e, four busbars 21, a positive electrode lead 22, and a negative electrode lead 23. The five individual cells 100a-100e are secondary batteries according to the third embodiment.

[0130] Bus 21 connects, for example, the negative terminal 6 of a single cell 100a to the positive terminal 7 of the adjacent single cell 100b. Thus, five single cells 100 are connected in series via four buses 21. Figure 5 The battery pack 200 is a battery pack of 5 connected in series. Although no example is illustrated, in a battery pack containing multiple individual cells connected in parallel, for example, multiple negative terminals are connected to each other via a bus, and multiple positive terminals are connected to each other via a bus, so that multiple individual cells can be electrically connected.

[0131] The positive terminal 7 of at least one of the five individual cells 100a to 100e is electrically connected to the positive side lead 22 for external connection. In addition, the negative terminal 6 of at least one of the five individual cells 100a to 100e is electrically connected to the negative side lead 23 for external connection.

[0132] The battery pack according to the second embodiment includes the secondary battery according to the first embodiment. Therefore, it can exhibit a long lifespan.

[0133] (Third implementation method) According to a third embodiment, a battery pack is provided. This battery pack includes the battery pack according to the second embodiment. Alternatively, the battery pack may include a single secondary battery according to the first embodiment instead of the battery pack according to the second embodiment.

[0134] The battery pack can be further equipped with a protection circuit. This protection circuit controls the charging and discharging of the secondary battery. Alternatively, the protection circuitry within a device that uses the battery pack as a power source (such as electronic devices, automobiles, etc.) can be used as the battery pack's protection circuitry.

[0135] Furthermore, the battery pack may also include external terminals for power supply. These external terminals are used to supply current from the secondary battery to the external source and / or to the secondary battery from the external source. In other words, when the battery pack is used as a power source, current is supplied to the external source through the external terminals. Additionally, when charging the battery pack, charging current (including regenerative energy from the power source of a vehicle, etc.) is supplied to the battery pack through the external terminals.

[0136] Next, an example of the battery pack according to the embodiments will be described with reference to the accompanying drawings.

[0137] Figure 6 This is an exploded perspective view that roughly represents an example of a battery pack. Figure 7It means Figure 6 A block diagram of an example of the circuitry for the battery pack shown.

[0138] Figure 6 and Figure 7 The battery pack 300 shown includes a storage container 31, a cover 32, a protective sheet 33, a battery pack 200, a printed circuit board 34, wiring 35, and an insulating plate (not shown).

[0139] Figure 6 The storage container 31 shown is a square container with a rectangular base. The storage container 31 is configured to hold the protective sheet 33, the battery pack 200, the printed circuit board 34, and the wiring 35. The cover 32 has a rectangular shape. The cover 32 covers the storage container 31 to hold the aforementioned battery pack 200, etc. Although not shown, the storage container 31 and the cover 32 are provided with openings or connection terminals for connecting to external devices, etc.

[0140] The battery pack 200 includes multiple individual cells 100, a positive electrode lead 22, a negative electrode lead 23, and an adhesive tape 24.

[0141] At least one of the plurality of single cells 100 is a secondary battery according to the first embodiment. For example... Figure 7 As shown, multiple individual cells 100 are connected in series with ground. Multiple individual cells 100 can also be connected in parallel with ground, or a combination of series and parallel connections. When multiple individual cells 100 are connected in parallel, the battery capacity increases compared to a series connection.

[0142] Adhesive tape 24 is used to secure multiple individual cells 100 together. Alternatively, heat shrinkable tape can be used instead of adhesive tape 24 to secure multiple individual cells 100. In this case, protective sheets 33 are placed on both sides of the battery pack 200, and after the heat shrinkable tape is wrapped around it, the heat shrinkable tape is heat-shrinked to secure the multiple individual cells 100 together.

[0143] One end of the positive electrode lead 22 is connected to the battery pack 200. One end of the positive electrode lead 22 is electrically connected to the positive electrode of one or more individual cells 100. One end of the negative electrode lead 23 is connected to the battery pack 200. One end of the negative electrode lead 23 is electrically connected to the negative electrode of one or more individual cells 100.

[0144] The printed circuit board 34 is disposed along one of the width directions of the inner side surface of the receiving container 31. The printed circuit board 34 includes a positive-side connector 342, a negative-side connector 343, a thermistor 345, a protection circuit 346, wirings 342a and 343a, an external terminal 350 for power supply, positive-side wiring 348a, and negative-side wiring 348b. One main surface of the printed circuit board 34 faces one side of the battery pack 200. An insulating plate (not shown) is located between the printed circuit board 34 and the battery pack 200.

[0145] The other end 22a of the positive lead 22 is electrically connected to the positive connector 342. The other end 23a of the negative lead 23 is electrically connected to the negative connector 343.

[0146] A thermistor 345 is fixed to one main surface of the printed circuit board 34. The thermistor 345 detects the temperature of each individual cell 100 and sends its detection signal to the protection circuit 346.

[0147] An external terminal 350 for power supply is fixed to another main surface of the printed circuit board 34. The external terminal 350 for power supply is electrically connected to a device located outside the battery pack 300. The external terminal 350 for power supply includes a positive terminal 352 and a negative terminal 353.

[0148] The protection circuit 346 is fixed to another main surface of the printed circuit board 34. The protection circuit 346 is connected to the positive terminal 352 via a positive side wiring 348a. The protection circuit 346 is connected to the negative terminal 353 via a negative side wiring 348b. Additionally, the protection circuit 346 is electrically connected to the positive connector 342 via wiring 342a. The protection circuit 346 is electrically connected to the negative connector 343 via wiring 343a. Furthermore, the protection circuit 346 is electrically connected to each of the multiple individual cells 100 via wiring 35.

[0149] The protective sheet 33 is disposed on the two inner sides of the storage container 31 along its length and on the inner side of the container 31 along its width, which faces the printed circuit board 34 across the battery pack 200. The protective sheet 33 is formed, for example, from resin or rubber.

[0150] The protection circuit 346 controls the charging and discharging of multiple individual batteries 100. In addition, based on the detection signal sent from the thermistor 345, or the detection signal sent from each individual battery 100 or battery pack 200, the protection circuit 346 disconnects the electrical connection between the protection circuit 346 and the external terminals 350 (positive terminal 352, negative terminal 353) used to power external devices.

[0151] As a detection signal sent from the thermistor 345, an example could be a signal indicating that the temperature of a single cell 100 is above a predetermined temperature. As a detection signal sent from each single cell 100 or the battery pack 200, examples could be signals indicating overcharging, over-discharging, and overcurrent of a single cell 100. When detecting overcharging in each single cell 100, the battery voltage, or the positive or negative electrode potential, can be detected. In the latter case, a lithium electrode serving as a reference electrode is embedded in each single cell 100.

[0152] In addition, as a protection circuit 346, a circuit contained in a device that uses the battery pack 300 as a power source (such as an electronic device, a car, etc.) can also be used.

[0153] Furthermore, as described above, the battery pack 300 includes an external terminal 350 for power supply. Therefore, the battery pack 300 can output current from the battery pack 200 to an external device and input current from an external device to the battery pack 200 via the external terminal 350. In other words, when the battery pack 300 is used as a power source, current from the battery pack 200 is supplied to the external device through the external terminal 350. Additionally, when charging the battery pack 300, charging current from the external device is supplied to the battery pack 300 through the external terminal 350. When the battery pack 300 is used as a vehicle battery, the regenerative energy from the vehicle's power source can be used as the charging current from the external device.

[0154] Furthermore, the battery pack 300 may also include multiple battery groups 200. In this case, the multiple battery groups 200 may be connected in series, in parallel, or in a combination of series and parallel connections. Additionally, the printed circuit board 34 and wiring 35 may be omitted. In this case, the positive lead 22 and the negative lead 23 may be used as the positive terminal 352 and negative terminal 353 of the external terminal 350 for power supply, respectively.

[0155] Such battery packs are used in applications requiring excellent cycle performance when drawing high currents. Specifically, they are used as power sources for electronic devices, stationary batteries, and in-vehicle batteries for various vehicles. Examples of electronic devices include digital cameras. This battery pack is particularly suitable for use as an in-vehicle battery.

[0156] The battery pack according to the third embodiment includes either the secondary battery according to the first embodiment or the battery pack according to the second embodiment. Therefore, it can exhibit a long lifespan.

[0157] Example The following describes the embodiments, but the implementation is not limited to the embodiments described below.

[0158] <Production> (Example 1) The aforementioned Nb₂TiO₇(TNO) powder, used as the negative electrode active material, acetylene black (AB), used as the conductive agent, carboxymethyl cellulose (CMC), used as the binder, and styrene-butadiene rubber (SBR), used as the binder, were prepared separately. These materials were mixed in pure water at a mass ratio of TNO:AB:CMC:SBR = 100:10:2:2 to prepare a negative electrode slurry. The obtained negative electrode slurry was coated on both sides of a negative electrode current collector formed from an aluminum foil with a thickness of 12 μm. The negative electrode slurry was then dried and pressed to adjust the density, resulting in a negative electrode sheet. The negative electrode sheet was punched into a rectangular shape to obtain multiple negative electrodes.

[0159] Prepare LiNi as positive electrode active material respectively 0.8 Co 0.1 Mn 0.1 O2 (NCM), AB as a conductive agent, and polyvinylidene fluoride (PVdF) as a binder were mixed in N-methyl-2-pyrrolidone (NMP) at a mass ratio of NCM:AB:PVdF = 90:5:5 to prepare a positive electrode slurry. The resulting positive electrode slurry was coated onto both sides of a positive electrode current collector formed from a 12 μm thick aluminum foil. The positive electrode slurry was then dried and pressed to adjust the density, resulting in a positive electrode sheet. The positive electrode sheet was then punched into a rectangular shape to obtain multiple positive electrodes.

[0160] A cellulose membrane with a thickness of 15 μm is prepared as the separator. The prepared separator is bent, and the separator, the negative electrode, and the positive electrode are stacked in the order of negative electrode, separator, positive electrode, and separator to obtain a laminate. Specifically, the negative electrode and the positive electrode are alternately inserted into the space defined by the bent separator. However, the number of negative electrode sheets is one more than the number of positive electrode sheets, and the negative electrode is arranged as the outermost layer on both sides of the laminate. A laminated (stacked) electrode assembly is thus produced.

[0161] Propylene carbonate (PC) and diethyl carbonate (DEC) were mixed in a volume ratio of PC:DEC = 1:2 to obtain a mixed solvent. 1.0 M lithium hexafluorophosphate (LiPF6) was dissolved in the mixed solvent. 0.5% by mass of propane sulpholol (PS) was further added as an additive to prepare a liquid non-aqueous electrolyte.

[0162] The positive terminal is electrically connected to the positive electrode of the aforementioned electrode assembly, and the negative terminal is electrically connected to the negative electrode. The electrode assembly with positive and negative terminals is housed in a pouch-shaped outer packaging component formed of a laminated film, which consists of aluminum foil and polypropylene layers formed on both sides. Then, leaving the opening for electrolyte injection open, the remaining parts of the outer packaging component are sealed by thermal fusion bonding. Next, a liquid non-aqueous electrolyte is injected into the outer packaging component. The opening of the outer packaging component is sealed by thermal fusion bonding, thereby fabricating the battery precursor.

[0163] For the obtained battery precursor, after the initial charge and discharge at room temperature (25°C), the following adjustments were made: Until 100% State of Charge (SOC) at 45°C, a 1C CCCV charge was performed with a current convergence condition of 1 / 1000C cut, i.e., constant current charging at 1C until the charging termination voltage was reached, followed by constant voltage charging until the current converged to 1 / 1000C. Then, a 1C discharge was performed until the SOC reached 0%. This cycle of 1C CCCV charge and 1C discharge was repeated for a total of 30 charge-discharge cycles.

[0164] In this way, a secondary battery with a capacity of 1.5Ah was produced.

[0165] (Example 2) The amount of PS added to the liquid electrolyte was changed to 1.0% by mass, and otherwise a secondary battery was made in the same manner as in Example 1.

[0166] (Example 3) The amount of PS added to the liquid electrolyte was changed to 1.5% by mass, and otherwise a secondary battery was prepared in the same manner as in Example 1.

[0167] (Example 4) Instead of PS, 0.5% by mass of lithium bis(oxalatoborate) (LiBOB) was added to the liquid electrolyte, and the secondary battery was prepared in the same manner as in Example 1.

[0168] (Example 5) Instead of PS, 1.0% by mass of LiBOB was added to the liquid electrolyte, and the secondary battery was prepared in the same manner as in Example 1.

[0169] (Example 6) Instead of PS, 1.5% by mass of LiBOB was added to the liquid electrolyte, and the secondary battery was prepared in the same manner as in Example 1.

[0170] (Example 7) Instead of PS, 0.5% by mass of lithium difluorophosphate (LiDFP) was added to the liquid electrolyte, and the secondary battery was prepared in the same manner as in Example 1.

[0171] (Example 8) In addition to 0.5% by mass PS, 0.5% by mass LiBOB was added to the liquid electrolyte, and otherwise a secondary battery was prepared in the same manner as in Example 1.

[0172] (Example 9) The secondary battery was fabricated in the same manner as in Example 1, except that the addition of PS to the liquid electrolyte was omitted.

[0173] (Comparative Example 1) The addition of PS to the liquid electrolyte is omitted. The conditioning conditions of the battery precursor are changed as follows, and the secondary battery is fabricated in the same manner as in Example 1. Until the SOC reaches 100% at 25°C, a 1C CCCV charge is performed with a current convergence condition of 1 / 20C cut, i.e., constant current charging at 1C until the charging termination voltage is reached. Then, constant voltage charging is performed until the current converges to 1 / 20C. Next, a 1C discharge is performed until the SOC reaches 0%. This cycle of 1C CCCV charging and 1C discharging is repeated for a total of 30 charge-discharge cycles.

[0174] (Comparative Example 2) The addition of PS to the liquid electrolyte is omitted. The conditioning conditions of the battery precursor are changed as follows, and the secondary battery is fabricated in the same manner as in Example 1. Until the SOC reaches 100% at 25°C, a 1C CCCV charge is performed with a current convergence condition of 1 / 50C cut, i.e., constant current charging at 1C until the charging termination voltage is reached, followed by constant voltage charging until the current converges to 1 / 50C. Then, a 1C discharge is performed until the SOC reaches 0%. This cycle of 1C CCCV charging and 1C discharging is repeated for a total of 30 charge-discharge cycles.

[0175] (Comparative Example 3) The adjustment conditions of the battery precursor were modified as follows, but the secondary battery was fabricated in the same manner as in Example 1. Until the SOC reached 100% at 25°C, a 1C CCCV charge was performed with a current convergence condition of 1 / 20C cut, i.e., constant current charging at 1C until the charging termination voltage was reached, followed by constant voltage charging until the current converged to 1 / 20C. Then, a 1C discharge was performed until the SOC reached 0%. This cycle of 1C CCCV charging and 1C discharging was repeated for a total of 30 charge-discharge cycles.

[0176] (Comparative Example 4) The amount of PS added to the liquid electrolyte was changed to 1.0% by mass, and otherwise a secondary battery was made in the same manner as in Comparative Example 3.

[0177] (Comparative Example 5) Instead of PS, 0.5% by mass of (LiBOB) was added to the liquid electrolyte, and a secondary battery was prepared in the same manner as in Comparative Example 3.

[0178] (Comparative Example 6) Instead of PS, 1.0% by mass of LiBOB was added to the liquid electrolyte, and a secondary battery was prepared in the same manner as in Comparative Example 3.

[0179] (Comparative Example 7) Instead of PS, 0.5% by mass of LiDFP was added to the liquid electrolyte, and a secondary battery was prepared in the same manner as in Comparative Example 3.

[0180] (Comparative Example 8) Instead of PS, 1.0% by mass of LiDFP was added to the liquid electrolyte, and a secondary battery was prepared in the same manner as in Comparative Example 3.

[0181] The adjustment conditions for each example are summarized in Table 1 below. Specifically, the additives added to the electrolyte and the temperature and charging termination conditions, i.e., convergence current, during charge-discharge cycles are shown.

[0182] <Evaluation> (ICP-MS determination) Using the previously described ICP-MS method, the concentration of compounds containing at least one of S, B, P, and F in the active material layer was measured for the positive electrodes taken from the outermost and center of the electrode assembly in each example. The measurement results for the outermost positive electrode are shown in Table 2, and the measurement results for the inner positive electrode taken from the center are shown in Table 3.

[0183] (HAXPES assay) For the positive electrodes taken from the battery in each example, samples were taken from the outermost and center layers of the electrode assembly, respectively, and HAXPES measurements were performed using the previously described method. Based on the obtained energy spectra, the 2p0 of Ni was calculated. 3 / 2 The peak area A of the peak (850 eV-865 eV) AM Calculate the peak areas of S, B, F, and P, as well as the peak areas of their respective 1s peaks (2470 eV-2484 eV), B (180 eV-200 eV), F (680 eV-692 eV), and P (2143 eV-2157 eV). Calculate the total peak area A for S, B, F, and P. SBPF For the outermost positive electrode, calculate A. SBPFCompared to A AM Given AR1, calculate A for the internal positive electrode sampled from the center. SBPF Compared to A AM The calculation results for the outermost positive electrode are shown in Table 2, and the calculation results for the inner positive electrode are shown in Table 3.

[0184] (Li content in the non-opposite part of the negative electrode) Using the method described above, the Li content in the active material layer (outermost layer containing negative electrode active material) of the outermost negative electrode in each example, which is not opposite to the positive electrode, was determined. The measurement results are shown in Table 4.

[0185] (High-temperature storage performance) For the secondary batteries produced in each example, the high-temperature storage performance is evaluated as follows.

[0186] First, at 25°C and 50% SOC, a 1C CCCV charge with a current convergence condition of 1 / 20C cut is performed. This means constant current charging at 1C until the charging termination voltage is reached, followed by constant voltage charging until the current converges to 1 / 20C. For the battery adjusted to 50% SOC, the battery volume V is determined using the Archimedes method. Next, the charge rate is adjusted to 100% SOC using a 1C CCCV charge with a current convergence condition of 1 / 20C cut, and the battery in this state is placed in a 70°C thermostat. The battery is left in the thermostat for two weeks. After cooling to 25°C, the charge rate is adjusted to 0% SOC using a 1C constant current discharge. Then, a 1C CCCV charge with a current convergence condition of 1 / 20C cut is performed at 25°C to adjust the battery charge rate to 50% SOC. In this state, the battery volume V' is assumed using the Archimedes method. The amount of gas generated during high-temperature storage (V'-V) is calculated by subtracting the battery volume V before high-temperature storage from the battery volume V' after high-temperature storage. The calculation results are shown in Table 4.

[0187] Table 4 shows the relative concentrations between the outermost and inner cathodes of compounds containing at least one of S, B, P, and F in each example, the ratio of the peak intensity AR1 of the outermost cathode to the peak intensity AR2 of the inner cathode calculated by HAXPES energy dispersive spectroscopy (AR1 / AR2), the Li content in the non-opposite active material layer of the outermost negative electrode (the outermost active material layer containing the negative electrode), and the amount of gas generated during high-temperature storage.

[0188] As shown in Table 4, in the secondary batteries prepared in Examples 1 to 9, the concentration of S, B, P, and F compounds in the outermost positive electrode was more than 1.1 times higher than the same concentration in the inner positive electrode. In contrast, in the secondary batteries prepared in Comparative Examples 1 to 8, the concentration of S, B, P, and F compounds in the outermost positive electrode was less than 1.0 times that in the inner positive electrode. As shown in Table 4, in Comparative Examples 1 to 8, the amount of Li in the outermost layer containing the negative electrode active material was significantly lower than the amount of Li in Examples 1 to 9, indicating that a large amount of Li could not be intercalated during adjustment. + Therefore, it can be seen that the insufficient formation of the coating in the outermost positive electrode results in an increase in the amount of gas generated during high-temperature storage as the outermost positive electrode deteriorates.

[0189] According to one or more embodiments and examples described above, a secondary battery is provided. This secondary battery includes an electrode assembly having at least one electrode stacked or wound together and an electrolyte. Each electrode includes a current collector and active material layers respectively disposed on its two main surfaces. The active material layers include at least one positive electrode active material layer and at least one negative electrode active material layer. The concentration of a compound containing at least one selected from sulfur, boron, phosphorus, and fluorine in the outermost positive electrode portion of the electrode assembly, which is located on the outermost side of the electrode assembly, is higher than the concentration of the same compound in the inner positive electrode portion located further inside the electrode assembly than the outermost positive electrode portion. Based on this configuration, a long-life secondary battery and battery pack can be provided.

[0190] Several embodiments of the present invention have been described, but these embodiments are given by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other ways, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the invention as described in the claims and its equivalents.

[0191] Furthermore, the above-described implementation methods can be summarized into the following technical solutions.

[0192] (Technical Solution 1) A secondary battery comprising an electrode assembly and an electrolyte, wherein the electrode assembly includes at least one electrode and has a structure in which the electrode is stacked or wound, and the electrode includes a current collector and layers containing active material respectively disposed on two main surfaces of the current collector. The active material layer includes at least one layer containing a positive active material and at least one layer containing a negative active material. In a portion of said electrode comprising said positive electrode active material-containing layer, the concentration of the compound containing at least one selected from the group consisting of sulfur, boron, phosphorus and fluorine in the outermost positive electrode part located at the outermost side in the electrode assembly is higher than the concentration of said compound in the inner positive electrode part located closer to the inner side of said electrode assembly than said outermost positive electrode part in said portion.

[0193] (Technical Solution 2) According to the foregoing Technical Solution 1, the positive electrode active material-containing layer comprises a lithium nickel cobalt manganese composite oxide.

[0194] (Technical Solution 3) According to the foregoing Technical Solution 2, for the total peak area A of peaks appearing within the ranges of 180eV-200eV, 680eV-692eV, 2143 eV-2157 eV and 2470 eV-2484 eV respectively in an X-ray photoelectron spectroscopy spectrum of the outermost positive electrode active material-containing layer which is located at the outermost side of the electrode assembly in the positive electrode active material-containing layer comprised in the outermost positive electrode part SBPF with respect to the maximum peak P appearing in any range of 635 eV-650 eV, 775 eV-787 eV or 850 eV-865 eV AM , the peak area A AM , the peak area ratio AR1, and for the total peak area A in the X-ray photoelectron spectroscopy spectrum of the positive electrode active material-containing layer comprised in the inner positive electrode part SBPF with respect to the peak area A AM , the peak area ratio AR2 satisfies a relationship of 1.1 < AR1 / AR2 < 10.

[0195] (Technical Solution 4) According to any one of the foregoing Technical Solutions 1 to 3, a portion of the negative electrode active material-containing layer is located at the outermost layer of said electrode assembly.

[0196] (Technical Solution 5) According to the foregoing Technical Solution 4, a portion of said negative electrode active material-containing layer located at the outermost layer of said electrode assembly contains 10 mAh / g or more of lithium.

[0197] (Technical Solution 6) A battery pack, comprising the secondary battery according to any one of the foregoing Technical Solutions 1 to 5.

[0198] (Technical Solution 7) According to the foregoing Technical Solution 6, the battery pack further comprises an external terminal for energization and a protection circuit.

[0199] (Technical Solution 8) According to the foregoing Technical Solution 6 or 7, the battery pack comprises a plurality of said secondary batteries, said secondary batteries are electrically connected in series, in parallel, or in a combination of series and parallel.

Claims

1. A secondary battery comprising an electrode assembly and an electrolyte, the electrode assembly including at least one electrode and having a structure in which the electrode is stacked or wound, the electrode including a current collector and layers containing active material respectively disposed on two main surfaces of the current collector. in, The active material layer includes at least one layer containing a positive active material and at least one layer containing a negative active material. In the portion of the electrode containing the positive electrode active material layer, the concentration of a compound containing at least one selected from sulfur, boron, phosphorus, and fluorine in the outermost positive electrode portion of the electrode assembly is higher than the concentration of the compound in the inner positive electrode portion of the portion located further inside the electrode assembly than the outermost positive electrode portion.

2. The secondary battery according to claim 1, wherein, The positive electrode active material layer contains a lithium nickel cobalt manganese composite oxide.

3. The secondary battery according to claim 2, wherein, For the outermost positive electrode active material-containing layer located at the outermost side of the electrode group among the positive electrode active material-containing layers included in the outermost positive electrode portion, the total peak area A of peaks appearing in respective ranges of 180eV-200eV, 680eV-692eV, 2143eV-2157eV and 2470eV-2484eV in the X-ray photoelectron spectroscopy spectrum SBPF relative to the peak P with the largest area appearing in any range of 635eV-650eV, 775eV-787eV or 850eV-865eV AM , the peak area ratio AR1 of the total peak area A AM to the peak area P, and the peak area ratio AR2 of said total peak area A in the X-ray photoelectron spectroscopy spectrum of the positive electrode active material-containing layer included in the internal positive electrode portion SBPF relative to said peak area P AM satisfies the relationship of 1.1 < AR1 / AR2 < 10.

4. The secondary battery according to any one of claims 1 to 3, wherein, A portion of the layer containing the negative electrode active material is located on the outermost layer of the electrode assembly.

5. The secondary battery according to claim 4, wherein, A portion of the outermost layer containing the negative electrode active material of the electrode assembly contains more than 10 mAh / g of lithium.

6. A battery pack comprising the secondary battery according to any one of claims 1 to 5.

7. The battery pack according to claim 6, further comprising an external terminal for power supply and a protection circuit.

8. The battery pack according to claim 6, comprising a plurality of said secondary batteries, The secondary batteries are electrically connected in series, parallel, or a combination of series and parallel connections.

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