Non-aqueous electrolyte secondary battery and method for manufacturing the same

Abstract

The present application provides a nonaqueous electrolyte secondary battery in which capacity deterioration during repeated charge and discharge is suppressed, despite the fact that lithium manganate particles having a spinel crystal structure generate cracks. The nonaqueous electrolyte secondary battery disclosed herein has a positive electrode, a negative electrode, and a nonaqueous electrolyte. The positive electrode has a positive electrode active material layer. The positive electrode active material layer contains lithium manganate particles having a spinel crystal structure as a positive electrode active material. At least a portion of the lithium manganate particles has a cracked portion. The lithium manganate particles have a coating on the particle surface, including the surface of the cracked portion. The coating contains a P component including a LiMnPO4 component and an F component.

Description

Technical Field

[0001] This invention relates to a non-aqueous electrolyte secondary battery. This invention also relates to a method for manufacturing this non-aqueous electrolyte secondary battery. Background Technology

[0002] In recent years, non-aqueous electrolyte secondary batteries such as lithium-ion batteries have been well-suited for use as portable power sources for personal computers, mobile terminals, electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs).

[0003] In non-aqueous electrolyte secondary batteries, active materials capable of absorbing and releasing ions as charge carriers are generally used. Lithium manganese oxide (LiMn₂O₄), having a spinel-type crystal structure, is known as an active material used in the positive electrode. However, this crystal structure of lithium manganese oxide has the following drawback: during repeated charge-discharge cycles in non-aqueous electrolyte secondary batteries, the capacity is easily degraded due to the dissolution of manganese (Mn) into the electrolyte. A technique is known to involve forming a phosphorus-containing coating on the lithium manganese oxide particles to suppress the capacity degradation caused by the dissolution of Mn (see, for example, Patent Document 1).

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. Hei 9-259863 Summary of the Invention

[0007] With the increasing prevalence of non-aqueous electrolyte secondary batteries, there is a growing demand for higher performance. One known method for improving the performance of non-aqueous electrolyte secondary batteries is to increase the density of the positive electrode active material layer by pressurizing it, thereby increasing the energy density. However, the inventors have conducted in-depth research and discovered the following problem: when further increasing the density of the positive electrode active material layer through pressurization to further improve energy density, cracks form in the lithium manganese oxide particles, leading to the dissolution of Mn from these cracks and resulting in capacity degradation.

[0008] Therefore, the object of the present invention is to provide a non-aqueous electrolyte secondary battery in which the generation of cracks in lithium manganese oxide particles with spinel-type crystal structure and capacity degradation during repeated charge and discharge are suppressed.

[0009] The inventors conducted in-depth research and discovered that in the manufacture of non-aqueous electrolyte secondary batteries, when the positive electrode active material layer contains lithium phosphate and a coating is formed on it at a voltage much higher than the operating voltage of the non-aqueous electrolyte secondary battery, a coating that inhibits the dissolution of Mn is formed on the entire particle, including the crack portion, of the lithium manganese oxide particles with a spinel-type crystal structure. Furthermore, analysis of this coating revealed that it contains a specific component (i.e., LiMnPO4), thus completing this invention.

[0010] That is, the non-aqueous electrolyte secondary battery disclosed herein includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode includes a positive electrode active material layer. The positive electrode active material layer contains lithium manganese oxide particles having a spinel-type crystal structure as the positive electrode active material. At least a portion of the lithium manganese oxide particles has cracked portions. The lithium manganese oxide particles have a coating on the particle surface containing the cracked portions. The coating contains a P component and an F component comprising LiMnPO4. With this configuration, a non-aqueous electrolyte secondary battery can be provided in which capacity degradation during repeated charge and discharge is suppressed even when cracks occur in the lithium manganese oxide particles having a spinel-type crystal structure.

[0011] In a preferred embodiment of the non-aqueous electrolyte secondary battery disclosed herein, the ratio of the P concentration (expressed in atomic percent) to the F concentration (expressed in atomic percent) in the aforementioned coating, P / F, is 0.030 or higher. In this case, the capacity degradation suppression effect becomes even more pronounced.

[0012] In a preferred embodiment of the non-aqueous electrolyte secondary battery disclosed herein, the density of the aforementioned positive electrode active material layer is 2.6 g / cm³. 3 That's all. At this point, the capacity degradation suppression effect becomes particularly high.

[0013] In a preferred embodiment of the non-aqueous electrolyte secondary battery disclosed herein, the aforementioned positive electrode active material layer contains lithium phosphate. In this case, it is advantageous to form a film containing a P component comprising LiMnPO4 and an F component.

[0014] In a preferred embodiment of the non-aqueous electrolyte secondary battery disclosed herein, the non-aqueous electrolyte contains LiPF6 as the electrolyte salt. This is advantageous for forming a film containing a P component comprising LiMnPO4 and an F component.

[0015] From another perspective, the method for manufacturing a non-aqueous electrolyte secondary battery disclosed herein includes the following steps: a step of fabricating a positive electrode sheet having a positive electrode active material layer containing lithium manganese oxide particles and lithium phosphate particles as positive electrode active materials; a step of pressurizing the fabricated positive electrode sheet; a step of using the pressurized positive electrode sheet to fabricate a battery assembly having a positive electrode sheet, a negative electrode sheet, and a non-aqueous electrolyte; and a step of performing an initial charging treatment on the battery assembly to form a coating. In the pressurization step, the lithium manganese oxide particles develop cracks. In the coating formation step, a coating containing a P component and an F component, including LiMnPO4, is formed on the particle surface of the lithium manganese oxide particles containing cracks. Based on this configuration, a non-aqueous electrolyte secondary battery can be manufactured where capacity degradation during repeated charge-discharge cycles is suppressed despite the occurrence of cracks in lithium manganese oxide particles with a spinel-type crystal structure.

[0016] In a preferred embodiment of the method for manufacturing the non-aqueous electrolyte secondary battery disclosed herein, the aforementioned initial charging treatment is performed until a voltage of 4.7V or higher is reached. At this point, it is advantageous to form a film containing LiMnPO4 and F components.

[0017] In a preferred embodiment of the method for manufacturing a non-aqueous electrolyte secondary battery disclosed herein, the aforementioned pressurization treatment is performed to achieve a density of 2.6 g / cm³ for the positive electrode active material layer. 3 That's all. At this point, a particularly high capacity degradation suppression effect is achieved. Attached Figure Description

[0018] Figure 1 This is a schematic cross-sectional view illustrating the internal structure of a lithium-ion secondary battery according to one embodiment of the present invention.

[0019] Figure 2 This is an exploded schematic diagram showing the configuration of the wound electrode body of a lithium-ion secondary battery according to one embodiment of the present invention.

[0020] Figure 3 The graphs show the relationship between the density of the positive electrode active material layer and the capacity retention rate for Examples B1-B6, Comparative Examples B1-B6, Comparative Examples B7-12, and Comparative Examples B13-18.

[0021] Symbol Explanation

[0022] 20. Winded electrode body

[0023] 30 Battery casing

[0024] 36 Safety valve

[0025] 42 Positive extremes

[0026] 42a Positive Current Collector

[0027] 44 Negative extremes

[0028] 44a Negative Current Collector

[0029] 50 Positive Electrode Sheets (Positive Electrode)

[0030] 52 Positive current collector

[0031] 52a Non-forming portion of the positive electrode active material layer

[0032] 54 Positive electrode active material layer

[0033] 60 Negative electrode plate (negative electrode)

[0034] 62 Negative current collector

[0035] 62a Non-forming portion of the negative electrode active material layer

[0036] 64 Negative Electrode Active Material Layer

[0037] 70. Insulation plate (isolation component)

[0038] 80 Non-aqueous electrolyte

[0039] 100 Lithium-ion Secondary Battery Detailed Implementation

[0040] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that matters not mentioned in this specification but necessary for the implementation of the present invention can be grasped by those skilled in the art based on prior art in the field. The present invention can be implemented based on the disclosures in this specification and common technical knowledge in the field. Furthermore, in the following drawings, components and parts that serve the same function are labeled with the same symbols. Additionally, the dimensional relationships (length, width, thickness, etc.) in the drawings do not necessarily reflect actual dimensional relationships.

[0041] It should be noted that in this manual, "secondary battery" refers to a rechargeable and rechargeable energy storage device, encompassing energy storage components such as batteries and double-layer capacitors. Furthermore, in this manual, "lithium-ion secondary battery" refers to a secondary battery that uses lithium ions as charge carriers and achieves charging and discharging through the movement of lithium ions' charge between the positive and negative electrodes.

[0042] The present invention will now be described in detail using a flat, square lithium-ion secondary battery having a flat, wound electrode body and a flat, battery casing as an example, but it is not intended to limit the present invention to the solutions described in the above embodiments.

[0043] Figure 1The lithium-ion secondary battery 100 shown is a sealed battery constructed by housing a flat, wound electrode body 20 and a non-aqueous electrolyte 80 within a flat, square battery casing (i.e., outer container) 30. The battery casing 30 is provided with a positive terminal 42 and a negative terminal 44 for external connection, and a thin-walled safety valve 36 configured to release internal pressure when the internal pressure of the battery casing 30 rises above a predetermined level. Additionally, the battery casing 30 is provided with an injection port (not shown) for injecting the non-aqueous electrolyte 80. The positive terminal 42 is electrically connected to a positive current collector 42a. The negative terminal 44 is electrically connected to a negative current collector 44a. As the material for the battery casing 30, lightweight and thermally conductive metal materials such as aluminum can be used, for example. It should be noted that... Figure 1 The amount of non-aqueous electrolyte 80 was not accurately indicated.

[0044] like Figure 1 and Figure 2 As shown, the wound electrode body 20 is formed by winding a positive electrode sheet 50 and a negative electrode sheet 60 together along their long sides, with two elongated insulating sheets 70 in between. The positive electrode sheet 50 has a positive active material layer 54 formed on one or both sides (here, both sides) of the elongated positive current collector 52 along its long side. The negative electrode sheet 60 has a negative active material layer 64 formed on one or both sides (here, both sides) of the elongated negative current collector 62 along its long side. The non-formed portions 52a of the positive active material layer (i.e., the portions of the positive current collector 52 that do not form the positive active material layer 54 and expose the positive active material layer 54) and the non-formed portions 62a of the negative active material layer (i.e., the portions of the negative current collector 62 that do not form the negative active material layer 64 and expose the negative active material layer 64) are formed in a manner that protrudes outward from both ends of the winding axis of the wound electrode body 20 (i.e., the sheet width direction orthogonal to the aforementioned long side direction). The non-forming portion 52a of the positive electrode active material layer and the non-forming portion 62a of the negative electrode active material layer are respectively bonded with a positive electrode current collector 42a and a negative electrode current collector 44a.

[0045] As the positive current collector 52, any known positive current collector used in lithium-ion secondary batteries can be used. Examples of such current collectors include sheets or foils made of metals with good conductivity (e.g., aluminum, nickel, titanium, stainless steel, etc.). Aluminum foil is preferred as the positive current collector 52.

[0046] The size of the positive current collector 52 is not particularly limited, and can be appropriately determined according to the battery design. When aluminum foil is used as the positive current collector 52, its thickness is not particularly limited, for example, it is 5μm to 35μm, preferably 7μm to 20μm.

[0047] The positive electrode active material layer 54 contains a positive electrode active material. In this embodiment, the positive electrode active material uses lithium manganese oxide particles with a spinel-type crystal structure. Using this type of lithium manganese oxide provides high thermal stability to the lithium-ion secondary battery 100 and reduces its cost. In this embodiment, the lithium manganese oxide used can be in an excess of lithium. Furthermore, other metal elements can be added to the lithium manganese oxide within a range that does not significantly hinder the effects of the present invention.

[0048] The lithium manganese oxide used in this embodiment specifically has, for example, the general formula (I): Li 1+x Mn 2－x－y Me y O 4-δ The composition is represented by the formula (I). In the formula (I), Me is at least one metallic element selected from Ni, Co, Mg, Fe, Al, Cr, Ga, and Ti, preferably at least one metallic element selected from Mg and Al. x satisfies 0 ≤ x ≤ 0.20, preferably 0 ≤ x ≤ 0.15, more preferably 0 ≤ x ≤ 0.10. y satisfies 0 ≤ y ≤ 0.20, preferably 0 ≤ y ≤ 0.10, more preferably 0 ≤ y ≤ 0.05, and most preferably y = 0. δ is the oxygen deficiency value used to obtain electroneutrality, δ for example satisfies 0 ≤ δ ≤ 0.20, preferably 0 ≤ δ ≤ 0.05, and more preferably 0.

[0049] As lithium manganese oxide, one type of lithium manganese oxide within the range of formula (I) above can be used alone, or two or more types of lithium manganese oxide within the range of formula (I) above can be used in combination. Lithium manganese oxide having the general formula (II) is particularly preferred: Li 1+x Mn 2－x O4 represents the composition (where x satisfies 0 ≤ x ≤ 0.15).

[0050] In this embodiment, at least a portion of the lithium manganese oxide particles have cracks. These cracks are typically caused by pressure treatment during the high-density enrichment of the positive electrode active material layer 54, but the cause of the cracks is not particularly limited.

[0051] In this embodiment, the lithium manganese oxide particles have a coating on the surface of the crack portion. In other words, the lithium manganese oxide particles have a coating on the outer surface (or outer peripheral surface) and the surface of the crack portion. This coating contains a P component (containing P component) and an F component (containing F component). The P component contains LiMnPO4.

[0052] In conventional technologies, a phosphorus-containing coating is pre-formed to suppress the dissolution of manganese oxide (Mn) from lithium manganese oxide particles. However, when pressure treatment is applied to the positive electrode active material layer containing lithium manganese oxide particles with the phosphorus-containing coating, cracks can form in the lithium manganese oxide particles. Since the surface where the cracks form lacks a coating, Mn dissolves from the surface of these cracks, resulting in capacity degradation in the lithium-ion secondary battery.

[0053] In contrast, the lithium-ion secondary battery of this embodiment is typically obtained by the manufacturing method described later. Specifically, lithium phosphate is contained as a film-forming component in the positive electrode active material layer 54, and initial charging is performed at a specific voltage (i.e., 4.7V or higher). This specific voltage is much higher than the operating voltage of the lithium-ion secondary battery 100 (i.e., around 4.2V). Using such an extremely high voltage for initial charging results in the formation of a film containing P (including LiMnPO4) and F components on the surface of lithium manganese oxide particles, including cracked portions. The formation mechanism of this film is presumably as follows: At this voltage, the oxidative decomposition of the electrolyte salt is promoted, and the amount of HF increases. The generated HF causes lithium phosphate to dissolve in the non-aqueous electrolyte 80. In addition, a portion of the dissolved lithium phosphate undergoes electrochemical decomposition due to high voltage, and the surface of lithium manganese oxide particles reacts with a portion of the dissolved or decomposed lithium phosphate to form a coating containing LiMnPO4. Furthermore, decomposition products of non-aqueous electrolytes (mainly F components) are also introduced into the coating.

[0054] Therefore, in this embodiment, the lithium manganese oxide particles have a coating on their surface, including the cracked portion, and this coating contains a P component comprising LiMnPO4 and an F component. This coating can suppress the leaching of Mn from the cracked portion of the lithium manganese oxide particles, thereby suppressing capacity degradation of the lithium-ion secondary battery 100 during repeated charge-discharge cycles.

[0055] The F component typically consists of components derived from the decomposition products of non-aqueous electrolytes (especially electrolyte salts). Additionally, lithium phosphate and its decomposition products can be introduced into the membrane. Therefore, the P component can further contain P components other than LiMnPO4 (especially components derived from lithium phosphate and its decomposition products).

[0056] As the lithium phosphate-based coating is formed, the ratio of P concentration (in atomic percent) to F concentration (in atomic percent) in the coating, P / F, increases. Therefore, this P / F ratio is preferably 0.030 or higher. At this point, the lithium phosphate-based coating formation proceeds effectively, and the capacity degradation suppression effect becomes particularly high.

[0057] The presence of P and F components in the coating can be confirmed, for example, by analysis using energy-dispersive X-ray spectroscopy (TEM-EDX) with a transmission electron microscope (TEM).

[0058] The presence of LiMnPO4 in the coating can be confirmed, for example, by the following method: LiMnPO4 has an olivine-type crystal structure. Therefore, a high-angle annular dark-field image (HAAD image) is obtained using TEM, and the crystal structure is analyzed, thus confirming an olivine-type crystal structure. Furthermore, the coating is analyzed using TEM-EELS to confirm the presence of Li, divalent Mn, and P.

[0059] It should be noted that the ratio of P concentration (atomic%) to F concentration (atomic%), P / F, can be calculated, for example, as follows: The coating is analyzed using TEM-EDX. At this time, the P / F ratio is calculated at at least 10 locations on the outer surface of the lithium manganese oxide particles and at at least 10 locations on the surface of the cracked portion of the lithium manganese oxide particles, and the average value is taken as the P / F ratio of the lithium manganese oxide particle coating.

[0060] The average particle size (median particle size D50) of lithium manganese oxide particles is not particularly limited, for example, it is 0.05 μm to 25 μm, preferably 0.5 μm to 23 μm, and more preferably 3 μm to 22 μm. It should be noted that, unless otherwise specified, the average particle size (median particle size D50) in this specification refers to the particle size that has a cumulative frequency of 50% by volume percentage in the particle size distribution determined by laser diffraction scattering.

[0061] The positive electrode active material layer 54 may contain positive electrode active materials other than lithium manganese oxide particles within a range that does not significantly hinder the effects of the present invention. The content of the positive electrode active material is not particularly limited, but it is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 85% by mass or more in the positive electrode active material layer 54 (i.e., relative to the total mass of the positive electrode active material layer).

[0062] The positive electrode active material layer 54 may contain components other than the positive electrode active material. Examples include lithium phosphate, conductive materials, and binders.

[0063] Lithium phosphate (Li3PO4) is a component used in the formation of the film described above, as explained later, and is consumed during initial charging. In some cases, it is completely consumed (therefore, the lithium phosphate content is 0% by mass), while in others, residual lithium phosphate exists. When the positive electrode active material layer 54 contains lithium phosphate, the lithium phosphate content relative to the positive electrode active material is preferably less than 10% by mass, more preferably less than 5% by mass, and even more preferably less than 3% by mass.

[0064] As a conductive material, carbon black such as acetylene black (AB) and other carbon materials (e.g., graphite) are preferably used. The content of the conductive material in the positive electrode active material layer 54 is not particularly limited, for example, it is 0.1% to 20% by mass, preferably 1% to 15% by mass, and more preferably 2% to 10% by mass.

[0065] As a binder, polyvinylidene fluoride (PVdF) can be used, for example. The content of the binder in the positive electrode active material layer 54 is not particularly limited, but is, for example, 0.5% to 15% by mass, preferably 1% to 10% by mass, and more preferably 1.5% to 8% by mass.

[0066] The density of the positive electrode active material layer 54 is not particularly limited. The density of the positive electrode active material layer 54 can be 2.0 g / cm³. 3 The above can also be 2.3 g / cm³. 3 The above results in a positive electrode active material layer 54 with a density of 2.6 g / cm³. 3 During the above process, the lithium manganese oxide particles are prone to developing numerous cracks due to the pressure treatment. Therefore, capacity degradation is likely to be significant. Consequently, the capacity degradation suppression effect provided by the coating becomes particularly strong, and the density of the positive electrode active material layer 54 is preferably 2.6 g / cm³. 3 That's all. On the other hand, the density of the positive electrode active material layer 54 can be 3.3 g / cm³. 3 The following can also be 3.0 g / cm³ 3 It should be noted that, in this specification, the density of the positive electrode active material layer 54 refers to the apparent density of the positive electrode active material layer 54.

[0067] The thickness of the positive electrode active material layer 54 is not particularly limited, for example, it is 10μm to 300μm, preferably 20μm to 200μm.

[0068] As the negative electrode current collector 62, any known negative electrode current collector used in lithium-ion secondary batteries can be used. Examples of such current collectors include sheets or foils made of metals with good conductivity (such as copper, nickel, titanium, stainless steel, etc.). Copper foil is preferred as the negative electrode current collector 62.

[0069] The size of the negative electrode current collector 62 is not particularly limited and can be appropriately determined according to the battery design. When copper foil is used as the negative electrode current collector 62, its thickness is not particularly limited, for example, it is 5μm to 35μm, preferably 7μm to 20μm.

[0070] The negative electrode active material layer 64 contains a negative electrode active material. For example, carbon materials such as graphite, hard carbon, and soft carbon can be used as the negative electrode active material. Graphite can be natural graphite or artificial graphite, and can also be amorphous carbon-coated graphite in the form of amorphous carbon material coating.

[0071] The average particle size (median particle size D50) of the negative electrode active material is not particularly limited, for example, it is 0.1 μm to 50 μm, preferably 1 μm to 25 μm, and more preferably 5 μm to 20 μm.

[0072] The content of negative electrode active material in the negative electrode active material layer 64 is not particularly limited, but is preferably 90% by mass or more, and more preferably 95% by mass or more.

[0073] The negative electrode active material layer 64 may contain components other than the negative electrode active material, such as binders, thickeners, etc.

[0074] As a binder, for example, styrene-butadiene (SBR) and its modifiers, acrylonitrile-butadiene rubber and its modifiers, acrylic rubber and its modifiers, fluororubber, etc., can be used. Among them, SBR is preferred. The content of the binder in the negative electrode active material layer 64 is not particularly limited, but is preferably 0.1% to 8% by mass, more preferably 0.2% to 3% by mass.

[0075] As a thickener, for example, cellulose-based polymers such as carboxymethyl cellulose (CMC), methyl cellulose (MC), cellulose acetate phthalate (CAP), and hydroxypropyl methyl cellulose (HPMC) can be used; polyvinyl alcohol (PVA), etc. are also suitable. Among these, CMC is preferred. The content of the thickener in the negative electrode active material layer 64 is not particularly limited, but is preferably 0.3% to 3% by mass, more preferably 0.4% to 2% by mass.

[0076] The thickness of the negative electrode active material layer 64 is not particularly limited, for example, it is 10μm to 300μm, preferably 20μm to 200μm.

[0077] Examples of spacers 70 include porous sheets (films) made of resins such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide. These porous sheets can be single-layered or multi-layered (e.g., a three-layered structure with PP layers laminated on both sides of a PE layer). A heat-resistant layer (HRL) can be provided on the surface of the spacer 70.

[0078] The thickness of the spacer 70 is not particularly limited, for example, it is 5μm to 50μm, preferably 10μm to 30μm.

[0079] The non-aqueous electrolyte 80 typically contains a non-aqueous solvent and an electrolyte salt (i.e., an auxiliary salt). As the non-aqueous solvent, various organic solvents used in general lithium-ion secondary battery electrolytes, such as carbonates, ethers, esters, nitriles, sulfones, and lactones, can be used without particular limitation. Among these, carbonates are preferred, and specific examples include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), ethylene monofluorocarbonate (MFEC), ethylene difluorocarbonate (DFEC), difluoromethyl difluoromethyl carbonate (F-DMC), and dimethyl trifluorocarbonate (TFDMC). Such non-aqueous solvents can be used alone or in appropriate combinations of two or more.

[0080] As the electrolyte salt, fluorinated lithium salts such as LiPF6, LiBF4, and lithium bis(fluorosulfonyl)imide (LiFSI) can be used, just like in conventional lithium-ion secondary batteries. The fluorinated lithium salt generates HF hydrofluoric acid, necessary for film formation, and also serves as the F source for the film. Since it readily forms a film containing an appropriate amount of F, LiPF6 is preferred as the electrolyte salt. The concentration of the electrolyte salt is not particularly limited, but since it readily generates a sufficient amount of HF necessary for film formation, it is preferably 0.8 mol / L or more, more preferably 1.0 mol / L or more. On the other hand, from the viewpoint of suppressing the increase in battery resistance caused by the increased viscosity of the non-aqueous electrolyte 80, the concentration of the electrolyte salt is preferably 1.8 mol / L or less, more preferably 1.5 mol / L or less.

[0081] It should be noted that, as long as the effect of the present invention is not significantly impaired, the above-mentioned non-aqueous electrolyte 80 may also contain components other than those mentioned above, such as film-forming agents such as oxalate complexes; gas generators such as biphenyl (BP) and cyclohexylbenzene (CHB); and various additives such as thickeners.

[0082] Next, the manufacturing method of the non-aqueous electrolyte secondary battery of this embodiment will be described. The manufacturing method of the non-aqueous electrolyte secondary battery of this embodiment includes: a step of fabricating a positive electrode sheet (hereinafter referred to as the "positive electrode fabrication step"), wherein the positive electrode sheet has a positive electrode active material layer containing lithium manganese oxide particles and lithium phosphate particles as positive electrode active materials; a step of pressurizing the positive electrode sheet (hereinafter referred to as the "pressurization treatment step"); a step of using the pressurized positive electrode sheet to fabricate a battery assembly having a positive electrode sheet, a negative electrode sheet, and a non-aqueous electrolyte (hereinafter referred to as the "battery assembly fabrication step"); and a step of performing an initial charging treatment on the battery assembly to form a coating (hereinafter referred to as the "coating formation step"). In the pressurization treatment step, cracks are generated in the lithium manganese oxide particles. In the coating formation step, a coating containing a P component and an F component comprising LiMnPO4 is formed on the surface of the cracked portion of the lithium manganese oxide particles.

[0083] The following describes in detail the manufacturing method of the non-aqueous electrolyte secondary battery of this embodiment by taking the manufacture of the lithium-ion secondary battery 100 described above as an example.

[0084] In the positive electrode fabrication process, a positive electrode sheet 50 is fabricated having a positive electrode active material layer 54 containing lithium manganese oxide particles and lithium phosphate particles as positive electrode active materials. Specifically, for example, firstly, a paste for forming the positive electrode active material layer is fabricated, containing lithium manganese oxide particles and lithium phosphate particles as positive electrode active materials, a solvent (dispersion medium), and any components (e.g., conductive materials, binders, etc.). It should be noted that in this specification, "paste" refers to a mixture obtained by dispersing part or all of the solid components in a solvent, including so-called "slurry," "ink," etc.

[0085] The amount of lithium phosphate particles mixed is not particularly limited. From the viewpoint of forming a sufficient amount of film, the amount of lithium phosphate particles mixed relative to lithium manganese oxide particles is preferably 0.2% by mass or more, more preferably 0.3% by mass or more. On the other hand, if the amount of lithium phosphate particles is too large, it will lead to an increase in the resistance of the positive electrode active material layer 54 and a decrease in the energy density. Therefore, the amount of lithium phosphate particles mixed relative to lithium manganese oxide particles is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less.

[0086] The particle size of lithium phosphate is not particularly limited. When the particle size of lithium phosphate is small, its specific surface area increases, making it more readily consumed during film formation. In other words, a small particle size of lithium phosphate is advantageous for film formation. Therefore, the average particle size (median particle size D50) of lithium phosphate is preferably 10 μm or less, more preferably 5 μm or less, and even more preferably 3 μm or less. On the other hand, the average particle size of lithium phosphate can be 0.05 μm or more, or 0.1 μm or more.

[0087] The mixing amount of lithium manganese oxide particles and any other components can be the same as the above-mentioned content in the positive electrode active material layer 54.

[0088] As a solvent, N-methylpyrrolidone (NMP) can be used, for example. From the viewpoint of drying efficiency, the solid content concentration of the paste for forming the positive electrode active material layer is, for example, 45% by mass or more, preferably 50% to 80% by mass. Therefore, the solvent is used in an amount that brings the paste for forming the positive electrode active material layer to such a solid content concentration.

[0089] A paste for forming a positive electrode active material layer can be prepared by mixing lithium manganese oxide particles, lithium phosphate particles, solvents, and any other components using known mixing devices such as planetary mixers, homogenizers, CLEAMIX, FILMIX, bead mills, ball mills, and extrusion mixers.

[0090] Next, the paste for forming the positive electrode active material layer is coated onto the positive electrode current collector 52. This coating can be performed using known methods. For example, a slit coater, a die coater, a comma coater, a gravure coater, a dip coater, or other coating equipment can be used to coat the positive electrode active material layer paste onto the positive electrode current collector.

[0091] The coated positive electrode active material layer is dried using a paste to form a positive electrode active material layer 54. That is, a positive electrode sheet 50 having a positive electrode active material layer 54 can be obtained through this drying process.

[0092] The drying can be performed using known methods. For example, the solvent can be removed from the positive electrode current collector coated with the paste for forming the positive electrode active material layer using a known drying apparatus (e.g., a hot air drying oven, an infrared drying oven, etc.). The drying temperature and drying time can be appropriately determined based on the amount of solvent contained in the paste for forming the positive electrode active material layer, and are not particularly limited. The drying temperature is, for example, 70°C to 200°C (preferably 110°C to 180°C). The drying time is, for example, 5 minutes to 120 minutes.

[0093] Next, the pressurization process will be described. In this pressurization process, the positive electrode sheet 50 is pressurized. In this pressurization process, the positive electrode active material layer 54 of the positive electrode sheet 50 is compressed to increase its density. A known pressurization device can be used in the pressurization process, and since the pressurization process is performed continuously, a rolling device can be appropriately used.

[0094] In this embodiment, the lithium manganese oxide particles are cracked by the pressure treatment. The conditions for the pressure treatment are not particularly limited as long as they cause cracks in the lithium manganese oxide particles. The preferred pressure conditions are that the density of the positive electrode active material layer 54 is 2.0 g / cm³.3 The above, and more preferably 2.3 g / cm 3 The above, and more preferably 2.6 g / cm³ 3 The above method is used. The density of the positive electrode active material layer 54 is 2.6 g / cm³. 3 Under these conditions, numerous cracks form in the lithium manganese oxide particles, resulting in a particularly high capacity degradation suppression effect due to film formation. The density of the positive electrode active material layer 54 after pressure treatment can reach 3.3 g / cm³. 3 Below, or 3.0g / cm 3 the following.

[0095] Next, the battery assembly manufacturing process will be described. In this battery assembly manufacturing process, a battery assembly comprising a positive electrode 50, a negative electrode 60, and a non-aqueous electrolyte 80 is manufactured using the pressurized positive electrode 50. This battery assembly manufacturing process can be carried out according to known methods.

[0096] Specifically, for example, the negative electrode 60 can be manufactured according to known methods. For example, it can be manufactured by preparing a paste for forming a negative electrode active material layer containing a negative electrode active material, a solvent, and any components (such as thickeners, binders, etc.), coating the paste onto the negative electrode current collector 62, drying it, and then subjecting it to pressure treatment as needed.

[0097] The mixing amount of the negative electrode active material and any other component can be the same as the above-mentioned content in the negative electrode active material layer 64.

[0098] The solvent for the paste used to form the negative electrode active material layer can be water; a mixture of water and a water-soluble solvent (e.g., an alcohol having 1 to 4 carbon atoms), preferably water. From the viewpoint of drying efficiency, the solid content concentration of the paste used to form the negative electrode active material layer is, for example, 45% by mass or more, preferably 50% to 80% by mass. Therefore, the solvent is used in an amount that allows the paste used to form the negative electrode active material layer to achieve such a solid content concentration.

[0099] The specific details of the preparation, coating, drying, and pressurization processes of the paste for forming the negative electrode active material layer are the same as those of known methods, and specifically, the same as those for the production of the aforementioned positive electrode sheet 50.

[0100] The battery assembly can be manufactured, for example, by using a positive electrode 50, a negative electrode 60 and a separator 70 to make an electrode body 20, and then housing the electrode body 20 together with a non-aqueous electrolyte 80 in a battery casing 30 and sealing it.

[0101] Specifically, for example, if the electrode body 20 is a wound electrode body as shown in the example, such as... Figure 2As shown, a laminate is formed by overlapping positive electrode 50 and negative electrode 60 with two separators 70. After winding the laminate in the longitudinal direction, the wound body is flattened by pressure treatment or the like, thereby forming electrode body 20. When electrode body 20 is a laminated electrode body, multiple positive electrode 50 and multiple negative electrode 60 are alternately stacked with separators 70 sandwiched between them, thereby forming electrode body 20.

[0102] As the battery casing 30, for example, a battery casing is prepared having a casing body with an opening and a cover that closes the opening. The cover is provided with an injection port (not shown) for injecting a non-aqueous electrolyte 80.

[0103] A positive terminal 42 and a positive current collector 42a, as well as a negative terminal 44 and a negative current collector 44a, are mounted on the cover of the battery casing 30. The positive current collector 42a and the negative current collector 44a are respectively welded to the positive current collector 52 and the negative current collector 62 exposed at the ends of the electrode body 20 (i.e., the non-formed portion 52a of the positive active material layer and the non-formed portion 62a of the negative active material layer). Then, the electrode body 20 is retracted into the accommodating opening of the main body of the battery casing 30, and the main body of the battery casing 30 is welded to the cover.

[0104] Next, a non-aqueous electrolyte 80 is injected through the injection port, and then the injection port is sealed. This yields the battery assembly.

[0105] Next, the coating formation process will be described. In the coating formation process, the battery assembly is subjected to an initial charging treatment, and a coating containing P and F components, including LiMnPO4, is formed on the surface of the crack portion of the lithium manganese oxide particles (i.e., the outer surface (or outer peripheral surface) and the surface of the crack portion).

[0106] The initial charging process can be performed using a known charger or the like. There are no particular limitations on the charging conditions, as long as the surface of the cracked portion of the lithium manganese oxide particle forms the aforementioned coating on the particle surface.

[0107] As the most effective initial charging method for forming a film containing P and F components including LiMnPO4, an initial charging treatment is performed until a voltage of 4.7V or higher is reached. At such a high voltage, LiMnPO4 components can be readily generated on the surface of the lithium manganese oxide particles, thus facilitating the formation of a film containing P and F components including LiMnPO4. Since the capacity degradation suppression effect is further enhanced, it is preferable to perform the initial charging treatment until a voltage of 4.8V or higher is reached.

[0108] As an example of the initial charging process, the device is first charged using a constant current, for example, 0.05C to 2C (preferably 0.05C to 1C), until a voltage of 4.7V or higher is reached. There is no particular upper limit to this voltage. An upper limit is, for example, 5.1V, preferably 5.0V.

[0109] A coating can be formed by charging until a voltage of 4.7V or higher is reached. However, to increase the coating thickness, constant voltage charging can be performed after constant current charging. The duration of constant voltage charging is not particularly limited, but can be from 1 hour to 10 hours, preferably from 3 hours to 7 hours.

[0110] By implementing the above procedures, a lithium-ion secondary battery 100 can be obtained.

[0111] Despite the formation of cracks in the spinel-type crystal structure of lithium manganese oxide particles, the capacity degradation during repeated charge-discharge cycles in the lithium-ion secondary battery 100 described above is suppressed. Therefore, the lithium-ion secondary battery 100 exhibits excellent cycle characteristics. Furthermore, since a high-density positive electrode active material layer can be achieved through a pressure treatment that induces cracks in the lithium manganese oxide particles, a very high energy density can be achieved in the lithium-ion secondary battery 100. Therefore, the lithium-ion secondary battery 100 can achieve both long lifespan and high energy density.

[0112] The lithium-ion secondary battery 100 can be used for various applications. Suitable applications include power supplies for driving vehicles such as battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs). Additionally, the lithium-ion secondary battery 100 can be used as a battery for small energy storage devices. Typically, the lithium-ion secondary battery 100 can also be used in the form of a battery pack consisting of multiple batteries connected in series and / or in parallel.

[0113] It should be noted that, as an example, a square lithium-ion secondary battery 100 having a flat, wound electrode body 20 will be described. However, the non-aqueous electrolyte secondary battery disclosed herein can also be configured as a lithium-ion secondary battery having a stacked electrode body (i.e., an electrode body formed by alternating stacking of multiple positive electrodes and multiple negative electrodes). Furthermore, the non-aqueous electrolyte secondary battery disclosed herein can also be configured as a cylindrical lithium-ion secondary battery, a laminated shell type lithium-ion secondary battery, a coin-shaped lithium-ion secondary battery, etc. Additionally, the non-aqueous electrolyte secondary battery disclosed herein can also be configured as a non-aqueous electrolyte secondary battery other than a lithium-ion secondary battery according to known methods.

[0114] The following describes embodiments related to the present invention, but it is not intended to limit the present invention to the solutions shown in these embodiments.

[0115] <Preparation of Positive Electrode Active Material>

[0116] Li₂CO₃ as the Li source and Mn₃O₄ as the Mn source were dry-mixed for 1 hour. The mixing was carried out at a Li:Mn molar ratio of 1.1:1.9. The mixture was then placed in an alumina crucible and calcined in an electric furnace at 1000°C for 12 hours, followed by calcination at 600°C for 18 hours. This yielded lithium manganese oxide particles A with a spinel-type crystal structure. It should be noted that the average particle size (D50) of lithium manganese oxide particles A was 13.4 μm.

[0117] <Preparation of Coated Positive Electrode Active Material>

[0118] Using Li3PO4 as the sputtering target, the surface of the lithium manganese oxide particles A obtained above was sputtered with Li3PO4 using a drum sputtering method. At this time, the mass ratio of Li3PO4 to lithium manganese oxide particles A was 0.5% by mass. This resulted in coated lithium manganese oxide particles B with a Li3PO4 film.

[0119] <Evaluation of Each Embodiment and Comparative Example: Fabrication of Lithium-ion Secondary Batteries>

[0120] Examples A1 to A3

[0121] Lithium manganese oxide particles A (LMO-A), carbon black (CB) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were mixed in N-methyl-2-pyrrolidone (NMP) at a mass ratio of LMO-A:CB:PVdF = 94:4:2. Then, 0.5% by mass of Li3PO4 relative to the lithium manganese oxide particles was further mixed in to prepare a paste for forming the positive electrode active material layer. It should be noted that the average particle size (median particle size D50) of the Li3PO4 used was 2.1 μm.

[0122] The positive electrode active material layer is formed by coating a paste onto aluminum foil and drying it, followed by roll forming (i.e., high-density processing) to produce the positive electrode sheet. The roll forming process is performed to achieve a positive electrode active material layer density of 2.6 g / cm³. 3 The process is carried out in this manner. Cracks are generated in the lithium manganese oxide particles A through this pressure treatment. The positive electrode sheet is then cut to a size of 120mm × 100mm.

[0123] In addition, spherical graphite (C) as the negative electrode active material, styrene-butadiene rubber (SBR) as the binder, and carboxymethyl cellulose (CMC) as the thickener were mixed in ion-exchanged water at a mass ratio of C:SBR:CMC = 98:1:1 to prepare a paste for forming the negative electrode active material layer. This paste was coated onto copper foil and dried, then subjected to high-density treatment by roll pressing to fabricate the negative electrode sheet. The negative electrode sheet was cut to a size of 122 mm × 102 mm.

[0124] A porous polyolefin sheet is prepared as a separator. A laminated electrode body is fabricated by sandwiching the separator between the aforementioned positive and negative electrode sheets, and electrode terminals are installed onto this laminated electrode body. It is then housed together with a non-aqueous electrolyte in a laminated casing. The non-aqueous electrolyte is a solution obtained by dissolving LiPF6 at a concentration of 1.1 mol / L in a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 3:3:4. Finally, the laminated casing is sealed to fabricate a battery assembly.

[0125] As an initial charging process, the battery assembly was charged with a constant current of 0.1C until it reached 4.7V (A1), 4.8V (A2), or 4.9V (A3), respectively, followed by a 3-hour constant voltage charge, thus performing the initial charging. Subsequently, it was discharged with a constant current of 0.1C until it reached 3.0V, yielding the lithium-ion secondary batteries for evaluation in Examples A1 to A3.

[0126] Comparative Examples A1 to A8

[0127] Lithium manganese oxide particles A (LMO-A), carbon black (CB) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were mixed in N-methyl-2-pyrrolidone (NMP) at a mass ratio of LMO-A:CB:PVdF = 94:4:2 to prepare a paste for forming the positive electrode active material layer. Using this paste, a positive electrode sheet was fabricated using the same method as in Example A1, and a battery assembly was further fabricated.

[0128] The battery assembly was charged at a constant current of 0.1C until it reached 4.2V (A1), 4.3V (A2), 4.4V (A3), 4.5V (A4), 4.6V (A5), 4.7V (A6), 4.8V (A7), or 4.9V (A8), respectively, followed by a 3-hour constant voltage charge, thus performing the initial charge. It was then discharged at a constant current of 0.1C until it reached 3.0V, yielding the lithium-ion secondary batteries for evaluation, Comparative Examples A1 to A8.

[0129] Comparative Examples A9 to A16

[0130] Lithium manganese oxide particles B (LMO-B), carbon black (CB) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were mixed in N-methyl-2-pyrrolidone (NMP) at a mass ratio of LMO-B:CB:PVdF = 94:4:2 to prepare a paste for forming the positive electrode active material layer. Using this paste, a positive electrode sheet was fabricated using the same method as in Example A1, and a battery assembly was further fabricated.

[0131] The battery assembly was charged at a constant current of 0.1C until it reached 4.2V (A9), 4.3V (A10), 4.4V (A11), 4.5V (A12), 4.6V (A13), 4.7V (A14), 4.8V (A15), or 4.9V (A16), respectively, followed by a 3-hour constant voltage charge, thus performing the initial charge. It was then discharged at a constant current of 0.1C until it reached 3.0V, yielding the comparative examples A9 to A16, which are lithium-ion secondary batteries for evaluation.

[0132] Comparative Examples A17~A21

[0133] The battery assembly was fabricated using the same method as in Example A1. The battery assembly was then charged at a constant current of 0.1C until it reached 4.2V (A17), 4.3V (A18), 4.4V (A19), 4.5V (A20), or 4.6V (A21), respectively, followed by a 3-hour constant voltage charge to perform the initial charge. It was then discharged at a constant current of 0.1C until it reached 3.0V, yielding the evaluation lithium-ion secondary batteries of Comparative Examples A17 to A21.

[0134] <Cyclic Characteristic Evaluation>

[0135] The prepared lithium-ion secondary batteries were placed at 25°C. Each battery was then charged at a constant current of 0.1C until it reached 4.2V, followed by constant voltage charging until the current reached 1 / 50C, achieving full charge. Subsequently, each battery was discharged at a constant current of 0.1C until it reached 3.0V. The initial capacity was then determined by measuring the discharge capacity at this point.

[0136] Next, each evaluation lithium-ion secondary battery was placed in an environment of 60°C, and one cycle was defined as charging to 4.2V with a constant current of 0.5C and discharging to 3.0V with a constant current of 0.5C. This charge-discharge cycle was repeated 100 times. The discharge capacity after 100 cycles was calculated using the same method as the initial capacity. The capacity retention rate (%) was calculated as an indicator of cycle characteristics (capacity degradation tolerance) by multiplying (discharge capacity after 100 charge-discharge cycles / initial capacity) by 100. The results are shown in Table 1.

[0137] <Analysis of the membrane>

[0138] The lithium-ion secondary batteries evaluated in the examples and a portion of the comparative examples were disassembled, and the positive electrode active material layer was removed. The positive electrode active material layer was cut using a focused ion beam (FIB) analysis apparatus (Hitachi High-Tech Co., Ltd.) FB2100. The cross-section was observed using a transmission electron microscope (JFM-ARM300F) at an accelerating voltage of 200 kV. Ten locations were selected on the outer surface of lithium manganese oxide particles and the cracked areas of the particles within the cross-section, and analyzed using a TEM-EDX method (JED-2300T) instrument (JEOL Ltd.). This analysis was performed at magnifications of 200–1000 kV, thereby confirming the presence of P and F components. The average ratio of P concentration (atomic %) to F concentration (atomic %) was then calculated. The results are shown in Table 2.

[0139] Furthermore, the lattice images of the particle surface were examined at magnifications of 2M to 10M to confirm the presence of lattice images other than LiMn2O4. In the example, lattice images other than LiMn2O4 were observed, and further analysis based on HAADTEM images and electron energy loss spectroscopy (EELS) was performed. The results confirmed the presence of LiMnPO4 with an olivine-type crystal structure. The results are shown in Table 2.

[0140] [Table 1]

[0141]

[0142] [Table 2]

[0143]

[0144] In Comparative Examples A1 to A8, lithium manganese oxide particles A1 without a coating were used, and Li3PO4 was not added to the positive electrode active material layer. In Comparative Examples A1 to A8, a trend was observed where the initial charging voltage was higher and the capacity retention rate was lower.

[0145] In Comparative Examples A9 to A16, lithium manganese oxide particles B1 with a pre-formed Li3PO4 coating were used, and no Li3PO4 was added to the positive electrode active material layer. Comparison with Comparative Examples A1 to A8 shows that the Li3PO4 coating improves capacity degradation. However, when the initial charging voltage is above 4.7V, a sharp increase in capacity degradation is observed.

[0146] In Comparative Examples A17 to A21, lithium manganese oxide particles A1 without a coating were used, and Li3PO4 was added to the positive electrode active material layer. In the initial charging voltage range of 4.2V to 4.6V, the capacity degradation resistance was comparable to that of lithium manganese oxide particles B1 with a pre-formed Li3PO4 coating.

[0147] In Examples A1 to A3, lithium manganese oxide particles A1 without a coating were used, and Li3PO4 was added to the positive electrode active material layer. Although the initial charging voltage was in the range of 4.7V to 4.9V, the capacity retention was very high.

[0148] The results of Comparative Examples A1-A8 and A9-A16 show that, generally, when the voltage of the first charge is high, a greater capacity degradation occurs. However, according to the results of Comparative Examples A17-A21 and Examples A1-A3, when using lithium manganese oxide particles A1 without a coating and adding Li3PO4 to the positive electrode active material layer, an unusual phenomenon occurs.

[0149] Regarding this phenomenon, the analysis results of the coating shown in Table 2 indicate that when the initial charging voltage is above 4.7V, LiMnPO4 is newly formed in the coating. Therefore, it can be concluded that the novel coating containing P and F components including LiMnPO4 exhibits significantly higher capacity degradation resistance.

[0150] Based on the above results, it can be seen that, according to the non-aqueous electrolyte secondary battery disclosed herein, although cracks occur in lithium manganese oxide particles with spinel-type crystal structure, capacity degradation during repeated charge and discharge is suppressed.

[0151] Examples B1 to B6

[0152] The positive electrode sheet was fabricated using the same method as in Example A1. The density of the positive electrode active material layer in this positive electrode sheet reached 2.0 g / cm³. 3 (B1), 2.2 g / cm 3 (B2), 2.4 g / cm 3 (B3), 2.6 g / cm 3 (B4), 2.8 g / cm 3 (B5) or 3.0 g / cm³ 3The positive electrode sheet is rolled using method (B6). The positive electrode sheet is then cut to a size of 120mm × 100mm.

[0153] Using the cut positive electrode sheet, a battery assembly was fabricated using the same method as in Example A1. As an initial charging process, the battery assembly was charged with a constant current of 0.1C until 4.7V, followed by a constant voltage charge for 3 hours, thus performing the initial charging. Subsequently, it was discharged with a constant current of 0.1C until 3.0V, yielding the evaluation lithium-ion secondary batteries of Examples B1 to B6.

[0154] Comparative Examples B1 to B6

[0155] The positive electrode sheet was fabricated using the same method as Comparative Example A1. The density of the positive electrode active material layer in this positive electrode sheet reached 2.0 g / cm³. 3 (B1), 2.2 g / cm 3 (B2), 2.4 g / cm 3 (B3), 2.6 g / cm 3 (B4), 2.8 g / cm 3 (B5) or 3.0 g / cm³ 3 The positive electrode sheet is rolled using method (B6). The positive electrode sheet is then cut to a size of 120mm × 100mm.

[0156] Using the cut positive electrode sheet, a battery assembly was fabricated using the same method as in Example A1. As an initial charging process, the battery assembly was charged with a constant current of 0.1C until 4.7V, followed by a constant voltage charge for 3 hours, thus performing the initial charging. Subsequently, it was discharged with a constant current of 0.1C until 3.0V, yielding the lithium-ion secondary batteries for evaluation purposes of Comparative Examples B1 to B6.

[0157] Comparative Examples B7-B12

[0158] The positive electrode sheet was fabricated using the same method as Comparative Example A9. The density of the positive electrode active material layer in this positive electrode sheet was 2.0 g / cm³. 3 (B7), 2.2g / cm 3 (B8), 2.4 g / cm 3 (B9), 2.6 g / cm 3 (B10), 2.8 g / cm³ 3 (B11) or 3.0 g / cm³ 3 The positive electrode sheet is rolled using the (B12) method. The positive electrode sheet is then cut to a size of 120mm × 100mm.

[0159] Using the cut positive electrode sheet, a battery assembly was fabricated using the same method as in Example A1. As an initial charging process, the battery assembly was charged with a constant current of 0.1C until 4.7V, followed by a constant voltage charge for 3 hours, thus performing the initial charging. Subsequently, it was discharged with a constant current of 0.1C until 3.0V, yielding the evaluation lithium-ion secondary batteries of Comparative Examples B7 to B12.

[0160] Comparative Examples B13-B18

[0161] The positive electrode sheet was fabricated using the same method as in Example A1. The density of the positive electrode active material layer in this positive electrode sheet was 2.0 g / cm³. 3 (B13), 2.2 g / cm³ 3 (B14), 2.4 g / cm³ 3 (B15), 2.6 g / cm³ 3 (B16), 2.8 g / cm³ 3 (B17) or 3.0 g / cm³ 3 The positive electrode sheet is rolled using the method described in (B18). The positive electrode sheet is then cut to a size of 120mm × 100mm.

[0162] Using the cut positive electrode sheet, a battery assembly was fabricated using the same method as in Example A1. As an initial charging process, the battery assembly was charged with a constant current of 0.1C until 4.2V, followed by a constant voltage charge for 3 hours, thus performing the initial charging. Subsequently, it was discharged with a constant current of 0.1C until 3.0V, yielding the evaluation lithium-ion secondary batteries of Comparative Examples B13 to B18.

[0163] <Cyclic Characteristic Evaluation>

[0164] The capacity retention (%) of each of the evaluated lithium-ion secondary batteries fabricated above was determined using the same method described above. The results are shown in Table 3 and... Figure 3 .

[0165] [Table 3]

[0166]

[0167] According to Table 3 and Figure 3 The results show that in the comparative example, the density of the positive electrode active material layer is 2.6 g / cm³. 3 At these levels, the degree of capacity degradation increases. However, in the embodiment, even when the density of the positive electrode active material layer is 2.6 g / cm³, the degradation is still significant. 3 The capacity degradation is also relatively small. Therefore, it can be concluded that in the non-aqueous electrolyte secondary battery disclosed herein, the density of the positive electrode active material layer is 2.6 g / cm³. 3At the above levels, the inhibition effect on capacity degradation is particularly high.

[0168] The specific examples of the present invention have been described in detail above, but these are merely illustrative and do not limit the scope of protection claimed. The technology described in the scope of protection includes technical solutions with various modifications and alterations to the specific examples described above.

Claims

1. A method for manufacturing a non-aqueous electrolyte secondary battery, comprising the following steps: The process of manufacturing a positive electrode sheet includes a positive electrode active material layer containing lithium manganese oxide particles and lithium phosphate particles as positive electrode active materials. The process of applying pressure to the fabricated positive electrode sheet. The process of using the pressurized positive electrode to manufacture a battery assembly having a positive electrode, a negative electrode, and a non-aqueous electrolyte, and The process of performing an initial charging treatment on the battery assembly to form a coating film; The lithium manganese oxide particles have Li 1+x Mn 2－x O4 represents the composition, where x satisfies 0 ≤ x ≤ 0.

15. During the pressurization process, cracks are formed in the lithium manganese oxide particles. In the process of forming the film, the initial charging treatment is performed until a voltage of 4.7V or higher is reached, and a film containing P and F components is formed on the surface of the lithium manganese oxide particles, including the surface of the cracked portion. The P component includes LiMnPO4.

2. The manufacturing method according to claim 1, wherein, The ratio of the P concentration (in atomic percent) to the F concentration (in atomic percent) in the membrane, P / F, is 0.030 or higher.

3. The manufacturing method according to claim 1 or 2, wherein, The pressurization process is performed to reduce the density of the positive electrode active material layer to 2.6 g / cm³. 3 above.

4. The manufacturing method according to claim 1 or 2, wherein, The non-aqueous electrolyte contains LiPF6 as an electrolyte salt.

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