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

Abstract

Provided are a nonaqueous electrolyte secondary battery having improved cycle characteristics and a method for manufacturing the same. The nonaqueous electrolyte secondary battery includes an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte, wherein the positive electrode contains a first positive electrode active material and a second positive electrode active material, wherein the second positive electrode active material contains a solid solution having an oxidation potential based on lithium of 4.4 V or more and is at least partially electrochemically inactivated by a charge reaction, the solid solution contains a solid solution of a lithium manganese oxide and a lithium transition metal oxide, and the negative electrode contains a Si-based negative electrode active material.

Description

Technical Field

[0001] The embodiments of the present invention relate to a non-aqueous electrolyte secondary battery and a method for manufacturing the same.

[0002] This application is based on and claims priority to Japanese Patent Application No. 2024-231225, filed with the Japan Patent Office on December 26, 2024, the entire contents of which are incorporated herein by reference. Background Technology

[0003] With the technological advancements in mobile devices, the demand for secondary batteries as an energy source is rapidly increasing. Among secondary batteries, lithium-ion batteries, characterized by high energy density and voltage, long cycle life, and low self-discharge rate, are already commercially available and used in a wide range of applications. Currently, many attempts are being made to improve the capacity of lithium-ion secondary batteries by using silicon materials with high theoretical capacity (Patent Document 1).

[0004] However, as the capacity of lithium-ion secondary batteries increases, the cycle characteristics (also known as lifespan characteristics) obtained during charge and discharge are insufficient, thus requiring improved cycle characteristics.

[0005] [Existing Technical Documents]

[0006] [Patent Literature]

[0007] Patent Document 1: Japanese Patent Application Publication No. 2018-152250 Summary of the Invention

[0008] Technical issues

[0009] The present invention aims to provide a non-aqueous electrolyte secondary battery with improved cycle characteristics and a method for manufacturing the same.

[0010] Technical solution

[0011] To improve cycle performance, the inventors focused on pre-doping lithium ions into the negative electrode active material to compensate for the decrease in charge / discharge efficiency with cycling. After careful study, the inventors discovered that adding a solid solution of lithium manganese oxide and lithium transition metal oxide to the positive electrode as a pre-doped positive electrode active material and charging it with a high voltage in the first cycle improves cycle performance.

[0012] The present invention may include the following embodiments.

[0013] [1] A non-aqueous electrolyte secondary battery, comprising: an electrode assembly including a positive electrode, a negative electrode and a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, wherein the positive electrode contains a first positive electrode active material and a second positive electrode active material, wherein the second positive electrode active material contains a lithium-based solid solution with an oxidation potential of 4.4 V or higher, and is at least partially electrochemically deactivated by a charging reaction, wherein the solid solution contains a solid solution of lithium manganese oxide and lithium transition metal oxide, and wherein the negative electrode contains a Si-based negative electrode active material.

[0014] [2] The non-aqueous electrolyte secondary battery as described in [1], wherein the lithium manganese oxide is Li2MnO3.

[0015] [3] The non-aqueous electrolyte secondary battery as described in [1] or [2], wherein the lithium transition metal oxide is represented by LiMeO2 (Me is at least one element selected from the group consisting of Co, Ni and Mn).

[0016] [4] A non-aqueous electrolyte secondary battery as described in any one of [1] to [3], wherein the second positive electrode active material comprises Li 1+a (Ni x Co y Mn z ) 1-a O2 represents lithium excess transition metal oxide, where 0 <a<0.3,0≤x<1,0≤y<1,0<z≤1,x+y+z=1。

[0017] [5] The non-aqueous electrolyte secondary battery as described in any one of [1] to [4], wherein the first positive electrode active material is a nickel-containing lithium transition metal oxide with a nickel content of more than 50 mol% of the total transition metal.

[0018] [6] The non-aqueous electrolyte secondary battery as described in any one of [1] to [5], wherein the ratio of the amount of Mn in the second positive electrode active material to the total amount of transition metals is higher than the ratio of the amount of Mn in the first positive electrode active material to the total amount of transition metals.

[0019] [7] The non-aqueous electrolyte secondary battery as described in any one of [1] to [6], wherein the content of the second positive electrode active material is from 0.1% to 50% by mass based on the total mass of the first positive electrode active material and the second positive electrode active material.

[0020] [8] The non-aqueous electrolyte secondary battery as described in any one of [1] to [7], wherein the Si-type negative electrode active material is pre-doped with lithium ions derived from the second positive electrode active material.

[0021] [9] The non-aqueous electrolyte secondary battery as described in any one of [1] to [8], wherein the second positive electrode active material does not have an oxidation potential in the range of less than 4.4V that would cause an irreversible oxidation reaction.

[0022]

[10] A non-aqueous electrolyte secondary battery as described in any one of [1] to [9], wherein, in the DSC curve of the positive electrode containing the positive electrode active material obtained by differential scanning calorimetry (DSC) involving heating from room temperature at a heating rate of 10 °C / min, the low-temperature slope of the exothermic peak on the lowest temperature side is less than 1.5 W / °C·g.

[0023]

[11] A non-aqueous electrolyte secondary battery as described in any one of [1] to

[10] , wherein, in the DSC curve of the positive electrode containing the positive electrode active material obtained by differential scanning calorimetry (DSC) involving heating from room temperature at a heating rate of 10 °C / min, the low-temperature slope of the exothermic peak on the lowest temperature side is less than 70% of the low-temperature slope of the maximum peak of the first positive electrode active material alone.

[0024]

[12] A hybrid electric vehicle (HEV) or a plug-in hybrid electric vehicle (PHEV) comprising any one of [1] to

[11] a non-aqueous electrolyte secondary battery.

[0025]

[13] A method for manufacturing a non-aqueous electrolyte secondary battery, the battery comprising: an electrode assembly including a positive electrode, a negative electrode and a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, wherein the positive electrode contains a first positive electrode active material and a second positive electrode active material, wherein the second positive electrode active material contains a lithium-based oxidation potential of 4.4 V or higher and is at least partially electrochemically deactivated by a charging reaction, the solid solution containing a solid solution of lithium manganese oxide and lithium transition metal oxide, wherein the negative electrode contains a Si-based negative electrode active material, the method comprising: performing an initial charging process at least once charging the non-aqueous electrolyte secondary battery with a voltage of 4.4 V or higher based on lithium, thereby pre-doping lithium ions from the second positive electrode active material into the Si-based negative electrode active material.

[0026]

[14] The method for manufacturing a non-aqueous electrolyte secondary battery as described in

[13] , wherein the charging voltage during the initial charging process is higher than the charging voltage during the second and subsequent cycles.

[0027] Beneficial effects

[0028] According to the present invention, a non-aqueous electrolyte secondary battery with improved cycle characteristics and a method thereof can be provided.

[0029] The above effects are provided for illustrative purposes only, and the present invention may provide many other advantages. Attached Figure Description

[0030] Figure 1 The X-ray diffraction (XRD) patterns of the positive electrodes of Example 3 and Comparative Examples 1 and 2 are shown.

[0031] Figure 2 An example of a peak measured by differential scanning calorimetry (DSC) is shown.

[0032] Figure 3 The slopes of the peaks obtained by DSC for the positive electrode active materials of Examples 1 to 3 and Comparative Examples 1 and 2 are shown.

[0033] Figure 4 The heat generation of the positive electrode active materials of Examples 1 to 3 and Comparative Examples 1 and 2 is shown by DSC. Detailed Implementation

[0034] The following description will illustrate the non-aqueous electrolyte secondary battery according to embodiments. These embodiments represent implementations of the present invention and are not intended to limit the invention; any modifications and changes can be made within the scope of the invention. Furthermore, any of the various elements and features in the embodiments can be combined together.

[0035] Non-aqueous electrolyte secondary battery

[0036] The non-aqueous electrolyte secondary battery of this embodiment includes: an electrode assembly comprising a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. The positive electrode contains a first positive electrode active material and a second positive electrode active material, the second positive electrode active material comprising a lithium-based solid solution with an oxidation potential of 4.4 V or higher, and at least partially electrochemically deactivated during the initial charging process through a charging reaction, the solid solution comprising a solid solution of lithium manganese oxide and lithium transition metal oxide, and the negative electrode contains a Si-based negative electrode active material.

[0037] Specific examples of secondary batteries may include lithium-ion secondary batteries, which have advantages in high energy density, discharge voltage, and output stability.

[0038] Although the following description uses lithium-ion secondary batteries as an example, the present invention is not limited to lithium-ion secondary batteries and can also be applied to many other types of non-aqueous electrolyte secondary batteries.

[0039] positive electrode

[0040] In the lithium-ion secondary battery of the embodiment, the positive electrode includes a positive current collector and a positive active material layer formed on one or both sides of the positive current collector. The positive active material layer may be formed on all or part of the surface of the positive current collector.

[0041] Positive current collector

[0042] The positive current collector used for the positive electrode is not limited to a specific current collector and can include any material that does not cause chemical changes and is conductive in the battery. For example, the positive current collector can include: stainless steel; aluminum; nickel; titanium; sintered carbon; or aluminum or stainless steel with a surface treated with carbon, nickel, titanium, or silver.

[0043] The thickness of the positive current collector can range from 3 μm to 500 μm. The positive current collector can have a finely textured surface to improve adhesion to the positive electrode active material. The positive current collector can be of various types, such as films, sheets, foils, meshes, porous materials, foams, or nonwoven fabrics.

[0044] Positive electrode active material layer

[0045] The positive electrode active material layer can be formed, for example, by coating a positive electrode active material slurry onto a positive electrode current collector, followed by drying and rolling. The positive electrode active material slurry comprises a mixture of positive electrode active material, conductive material, and binder dissolved and dispersed in a solvent. If necessary, the mixture may also contain dispersants, fillers, or any other additives. For example, based on the total mass of the positive electrode active material layer, the content of the positive electrode active material can be from 80% to 99% by mass.

[0046] Positive electrode active material

[0047] In the lithium-ion secondary battery of the embodiment, the positive electrode active material includes a first positive electrode active material and a second positive electrode active material. The positive electrode active material layer may also include positive electrode active materials other than the first and second positive electrode active materials.

[0048] First positive electrode active material

[0049] The first positive electrode active material may comprise a compound capable of reversibly inserting (intercalating) and extracting (deintercalating) lithium. Specific examples may include, for instance, lithium transition metal oxides containing at least one metal selected from cobalt, manganese, nickel, copper, vanadium, or aluminum, and lithium. More specifically, the lithium transition metal oxide may include: lithium manganese oxides (e.g., LiMnO2, ...). LiMnO3, LiMn2O3, LiMn₂O₄); lithium cobalt oxides (e.g., LiCoO₂); lithium nickel oxides (e.g., LiNiO₂). ； Lithium copper oxides (e.g., Li2CuO2); Lithium-vanadium oxides (e.g., LiV3O8); lithium-nickel-manganese oxides (e.g., LiNi 1-z Mn z O2(0 < z < 1), LiMn 2-z Ni z O4(0 < z < 2)); lithium-nickel-cobalt oxides (e.g., LiNi 1-y Co y O2(0 < y < 1)); lithium-manganese-cobalt oxides (e.g., LiCo 1-z Mn z O2(0 < z < 1), LiMn 2-y Co y O4(0 < y < 2)); lithium-nickel-manganese-cobalt oxides (e.g., Li(Ni x Co y Mn z )O2(0<x<1, 0<y<1, 0<z<1, x+y+z=1), Li(Ni x Co y Mn z )O4(0<x<2, 0<y<2, 0<z<2, x+y+z=2)); lithium-nickel-cobalt metal (M) oxides (e.g., Li(Ni x Co y Mn z M w )O2 (M is selected from the group consisting of Al, Fe, V, Cr, Ti, Ta, Mg and Mo, 0<x<1, 0<y<1, 0<z<1, 0<w<1, x+y+z+w=1); and compounds in which transition metal elements are partially substituted by one or more other metal elements. The first positive electrode active material layer may comprise at least one of these compounds, but is not limited thereto.

[0050] The oxidation potential of the first positive electrode active material may be 4.2 V or lower. The first positive electrode active material can achieve reversible intercalation and deintercalation of lithium at 4.2 V or lower. Therefore, the first positive electrode active material has high reversible capacity due to its contribution to charge and discharge reactions at 4.2 V or lower.

[0051] To improve the capacity characteristics of the battery, the first positive electrode active material preferably contains a nickel-containing lithium transition metal oxide, more preferably a nickel-rich lithium transition metal oxide. Here, "nickel-rich" refers to a nickel content of 50 mol% or more based on the total amount of transition metal. As mentioned above, a high-nickel lithium transition metal oxide containing 50 mol% or more of nickel can help achieve both high capacity and improved electrode resistance characteristics in lithium-ion secondary batteries. For example, the first positive electrode active material may contain a lithium transition metal oxide containing 60 mol% or more, 70 mol% or more, 80 mol% or more, or 90 mol% or more of nickel based on the total amount of transition metal. More specifically, a lithium-nickel-cobalt-manganese ternary positive electrode active material, such as Li(Ni) 0.5 Mn 0.3 Co 0.2 O2, Li(Ni) 0.6 Mn 0.2 Co 0.2 O2, Li(Ni) 0.7 Mn 0.15 Co 0.15 O2 or Li(Ni) 0.8 Mn 0.1 Co 0.1 )O2.

[0052] Based on the total amount of positive electrode active material, the amount of the first positive electrode active material contained in the positive electrode active material layer can be, for example, 30% by mass, 40% or more by mass, 50% or more by mass, 60% or more by mass, 70% or more by mass, less than 99.9% by mass, less than 90% by mass, or less than 80% by mass. When the amount of the first positive electrode active material is within the above range, high capacity characteristics can be achieved.

[0053] Second positive electrode active material

[0054] The second positive electrode active material comprises at least one lithium metal composite oxide with an oxidation potential of 4.4 V or higher and which is at least partially electrochemically deactivated by a charging reaction. Specifically, the second positive electrode active material contains a solid solution of lithium manganese oxide and lithium transition metal oxide. Here, "electrochemical deactivation" refers to a structural or property change caused by the charging reaction, where lithium ions do not migrate back during discharge and cannot directly participate in the charge-discharge reaction. This solid solution exhibits high thermal stability and low initial charge-discharge efficiency at high voltages. Examples of lithium manganese oxide include Li₂MnO₃, LiMnO₂, and LiMn₂O₄. The lithium transition metal oxide can be represented by LiMeO₂ (where Me is at least one element selected from Co, Ni, and Mn). Examples of lithium transition metal oxides include the lithium transition metal oxide of the first positive electrode active material described above. In particular, the lithium transition metal oxide preferably comprises a solid solution of Li₂MnO₃ composed of Li… 1+a (Nix Co y Mn z ) 1-a O2 (where 0 < a < 0.3, 0 ≤ x < 1, 0 ≤ y < 1, 0 < z ≤ 1, x + y + z = 1) represents a Li excess transition metal oxide. In the Li excess transition metal oxide, the ratio of Mn to the total amount of transition metal is preferably 30% or more, 40% or more, 50% or more, 60% or more, 70% or more, 80% or more, or 90% or more.

[0055] Li₂MnO₃ is a monoclinic crystal system. Overcharging triggers oxygen release rather than oxide ion oxidation, resulting in a heterogeneous composition where a lithium-ion-depleted, oxygen-lost MnO₂-like structure coexists with the original monoclinic structure. During discharge, lithium ions insert into the MnO₂-like structure, but because their lithium-ion acceptance ability is almost inert, most of the lithium ions pre-doped into the negative electrode active material do not migrate back to the second positive electrode active material. Therefore, the second positive electrode active material should preferably contain materials with high irreversible capacity and low charge-discharge efficiency in the first cycle.

[0056] Lithium manganese oxides contain a large amount of Mn and have high electrical resistance. Therefore, when lithium manganese oxides are used as active materials, it is necessary to reduce the resistance or particle size to fully utilize it. When using solid solutions, they can be effectively used as active materials due to their higher degree of electronic conductivity compared to using lithium manganese oxides such as Li₂MnO₃ alone. Compared to Mn alone, lithium ions are more likely to undergo electrochemical migration due to the presence of Co or Ni, which is presumably due to hybridization with the 2p orbitals of oxygen (interaction between O₂p and 3d electrons of transition metals), mixed valence state effects, and suppression of cation vacancies that are prone to occur in Mn alone.

[0057] Starting with the second positive electrode active material, during the initial charging process at high voltage, excess lithium ions can be pre-doped into the negative electrode active material. "Excess lithium ions" refers to lithium ions that, in addition to the capacity from the first positive electrode active material, are extracted from and inserted into the negative electrode active material during charging at a voltage higher than the oxidation potential of the second positive electrode active material. Therefore, the excess lithium ions pre-doped into the negative electrode active material can compensate for the decrease in charge-discharge efficiency during repeated charge-discharge cycles, thereby improving cycle characteristics.

[0058] Furthermore, preferably, the second positive electrode active material does not have an irreversible oxidation potential with high capacity in the range of less than 4.4V. When the second positive electrode active material does not have a high irreversible capacity in the range of less than 4.4V, there will be no decrease in charge-discharge efficiency caused by the second positive electrode active material. Therefore, the decrease in cycle characteristics due to the addition of the second positive electrode active material can be prevented within the operating voltage range.

[0059] Based on the total amount of the positive electrode active material, the total amount of the second positive electrode active material contained in the positive electrode active material layer is, for example, 0.1% to 70% by mass, 0.1% to 60% by mass, 0.1% to 50% by mass, 1% to 40% by mass, or 10% to 30% by mass. When the amount of the second positive electrode active material with sufficiently high irreversible capacity is above 0.1% by mass, improvements in battery cycle characteristics or electrode resistance characteristics can be expected. When the amount of the second positive electrode active material is below 50% by mass, sufficient energy density can be obtained.

[0060] The mass ratio of the first positive electrode active material to the second positive electrode active material is, for example, 99.9:0.1 to 30:70, 90:10 to 50:50, or 80:20 to 60:40. When the mass ratio of the first positive electrode active material to the second positive electrode active material is within the above range, high cycle performance and safety can be achieved.

[0061] The ratio of Mn to total transition metals in the second positive electrode active material is preferably higher than that in the first positive electrode active material. The ratio of Mn to total transition metals in the second positive electrode active material can be 0.2 or higher, 0.3 or higher, or 0.4. The above explanation demonstrates that the presence of a large amount of thermally stable manganese in the positive electrode active material improves its thermal stability. In particular, it is speculated that the solid solution containing Li₂MnO₃ transforms into a MnO₂-like structure containing oxygen and consumed lithium during the initial charging process. This structure can suppress the release of oxygen from the crystal lattice in the event of an internal short circuit or other abnormal event in the battery, thereby improving safety.

[0062] Thermal stability evaluation

[0063] The thermal stability of the positive electrode active material can be evaluated using differential scanning calorimetry (DSC). When the second positive electrode active material contains a large amount of thermally stable manganese, the thermal stability of the positive electrode active material can be improved. Thermal stability can be evaluated by DSC based on the heat of generation, specifically the heat of generation from 150°C to 300°C at the onset of the exothermic reaction. When the second positive electrode active material is appropriately selected, thermal stability can be improved by reducing the heat of generation in the 150°C to 300°C range compared to the first positive electrode active material. Therefore, when the first and second positive electrode active materials are mixed together, the heat of generation is reduced compared to the first positive electrode active material alone, thereby improving the safety of lithium-ion secondary batteries.

[0064] In the DSC curve depicting the heat flow per unit temperature obtained by DSC involving heating from room temperature at a heating rate of 10 °C / min, the low-temperature slope of the exothermic peak on the lowest temperature side of the mixture of the first and second positive electrode active materials is less than the low-temperature slope of the maximum exothermic peak of each of the first and second positive electrode active materials. Here, the slope of the exothermic peak refers to the slope of the straight line connecting 80% and 40% of the peak height in the rising portion of the peak (unit: W / (°C·g)). The slope of the exothermic peak is 1.7 W / °C·g or less, 1.6 W / °C·g or less, 1.5 W / °C·g or less, 1.4 W / °C·g or less, 1.3 W / °C·g or less, 1.2 W / °C·g or less.

[0065] In the DSC curve depicting the heat flow per unit temperature obtained by DSC involving heating from room temperature at a heating rate of 10 °C / min, the low-temperature slope of the exothermic peak on the lowest temperature side of the mixture of the first positive electrode active material and the second positive electrode active material is less than 80%, less than 75%, less than 70%, or less than 65% of the low-temperature slope of the maximum peak of the first positive electrode active material alone.

[0066] Compared to the first and second positive electrode active materials individually, when the first and second positive electrode active materials are mixed together, rapid heating within a short period of time can be suppressed, thereby improving thermal stability. Therefore, when a mixture of the first and second positive electrode active materials is used, stability against thermal runaway can be achieved in the event of battery failure or inactivation.

[0067] conductive materials

[0068] Conductive materials are not limited to a specific type and may include any conductive material that does not cause chemical changes. Examples of conductive materials may include, but are not limited to, one or a mixture of the following materials: carbonaceous materials, including artificial graphite, natural graphite, carbon black, acetylene black, Ketjen black, Denka black, thermally cracked carbon black, channel black, furnace black, lamp black, carbon nanotubes, and carbon fibers; metal powders or metal fibers, including aluminum, tin, bismuth, silicon, antimony, nickel, copper, titanium, vanadium, chromium, manganese, iron, cobalt, zinc, molybdenum, tungsten, silver, gold, lanthanum, ruthenium, platinum, and iridium; conductive whiskers, including zinc oxide and potassium titanate; conductive metal oxides, including titanium oxide; and conductive polymers, including polyaniline, polythiophene, polyacetylene, polypyrrole, and polyphenylene derivatives.

[0069] Based on the total mass of the positive electrode active material layer, the amount of conductive material can be from 0.1% by mass to 30% by mass. The amount of conductive material is preferably from 0.5% by mass to 15% by mass, more preferably from 0.5% by mass to 5% by mass. When the amount of conductive material is within the above range, due to sufficient conductivity, the amount of positive electrode active material will not decrease, thereby ensuring battery capacity.

[0070] adhesives

[0071] Adhesives are added to facilitate adhesion between active materials and conductive materials or to current collectors. The adhesive is not limited to a specific type and may include any type of adhesive commonly used in the relevant technical field. Examples of adhesives include, but are not limited to, polyvinylidene fluoride (PVdF), polyvinyl alcohol (PVA), polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), polyacrylic acid, acrylamide, polyimide, fluororubber, copolymers thereof, or mixtures thereof.

[0072] Based on the total mass of the positive electrode active material layer, the amount of binder can be from 0.1% to 30% by mass. The amount of binder is preferably from 0.5% to 20% by mass, more preferably from 1% to 10% by mass. When the amount of binder is within the above range, it can prevent battery capacity decay and provide sufficient adhesion in the electrode.

[0073] solvent

[0074] The solvents used in the positive electrode active material slurry are not limited to a specific type and may include any type of solvent commonly used in the manufacture of positive electrodes. Examples of solvents may include, but are not limited to: amine solvents (including N,N-dimethylaminopropylamine, diethylenetriamine, and N,N-dimethylformamide (DMF)), ether solvents (including tetrahydrofuran), ketone solvents (including methyl ethyl ketone), ester solvents (including methyl acetate), amide solvents (including dimethylacetamide and N-methyl-2-pyrrolidone (NMP)), dimethyl sulfoxide, or mixtures thereof.

[0075] Taking into account the coating thickness or manufacturing yield of the slurry, the amount of solvent used is sufficient for the viscosity required to dissolve or disperse the positive electrode active material, conductive material and binder and to coat the slurry with high thickness uniformity onto the positive electrode current collector.

[0076] Method for manufacturing positive electrode

[0077] Conductive materials and binders are added to the positive electrode active material. In this case, any additives, such as dispersants or thickeners, may be added if necessary. When they are dispersed in a solvent, a positive electrode active material slurry is obtained. That is, the positive electrode active material slurry comprises the positive electrode active material, conductive material, binder, and solvent obtained as described above.

[0078] The positive electrode active material slurry can be coated onto the positive electrode current collector, then dried and rolled to obtain a positive electrode with a positive electrode active material layer on the positive electrode current collector.

[0079] Alternatively, for example, the positive electrode active material slurry can be cast onto a support, and the film layer obtained by peeling off the support can be pressed onto the positive electrode current collector to manufacture the positive electrode. Any other method can be used to form the positive electrode active material layer on the positive electrode current collector.

[0080] negative electrode

[0081] In the lithium-ion secondary battery of the embodiment, the negative electrode includes a negative electrode current collector and a negative electrode active material layer formed on one or both sides of the negative electrode current collector. The negative electrode active material layer may be formed on all or part of the surface of the negative electrode current collector.

[0082] negative current collector

[0083] The negative electrode current collector used for the negative electrode is not limited to a specific current collector and can be any material in the battery that does not cause chemical changes and is conductive. For example, the negative electrode current collector can include: copper; stainless steel; aluminum; nickel; titanium; sintered carbon; copper or stainless steel with a surface treated with carbon, nickel, titanium or silver; or aluminum-cadmium alloy.

[0084] The thickness of the negative electrode current collector can range from 3 μm to 500 μm. The negative electrode current collector can have a finely textured surface to improve adhesion to the negative electrode active material. The negative electrode current collector can be of various types, such as films, sheets, foils, meshes, porous materials, foams, or nonwoven fabrics.

[0085] Negative electrode active material layer

[0086] The negative electrode active material layer may comprise a negative electrode active material, a binder, a conductive material, and additives. For example, the negative electrode active material layer can be formed by coating a negative electrode active material slurry onto a negative electrode current collector, followed by drying and rolling, or by casting a negative electrode active material slurry onto a support and pressing a film layer obtained by peeling it from the support onto the negative electrode current collector. Here, the negative electrode active material slurry is prepared by mixing the negative electrode active material, binder, and conductive material and dissolving or dispersing the mixture in a solvent. If necessary, the mixture may also contain a dispersant, filler, or any other additives.

[0087] Negative electrode active materials

[0088] Negative electrode active materials include Si-based materials. Si-based materials are materials containing silicon as a primary component. Examples of Si-based materials include, but are not limited to, one or a mixture of the following materials: silicon-based materials including silicon powder, amorphous silicon, silicon nanofibers, and silicon nanowires; silicon alloys, silicon oxide (SiO2). x (0 < x ≤ 2), silicon compounds including silicon oxides doped with alkali metals and alkaline earth metals (lithium or magnesium), and Si-C composites of silicon-based and carbon-based materials. The negative electrode active material layer may also contain negative electrode active materials other than silicon-based materials. In this specification, "negative electrode active material" refers to all materials that contribute to the charge-discharge reaction of the negative electrode.

[0089] Based on the total mass of the negative electrode active material layer, the content of the negative electrode active material is 70% to 99% by mass, more preferably 80% to 99% by mass. When the amount of negative electrode active material is within the above range, high energy density, electrode adhesion, and conductivity can be achieved.

[0090] Sufficient amount of negative electrode active material is included to accept excess lithium ions from the second positive electrode active material in addition to the equivalent amount of the first positive electrode active material.

[0091] Furthermore, the content of the negative electrode active material exceeds the number of moles required for the charge-discharge reaction with the total amount of the first and second positive electrode active materials. Preferably, the amount of the negative electrode active material is more than 100% and less than 120%, more than 100% and less than 110%, and more than 100% and less than 105% of the number of moles required for the charge-discharge reaction.

[0092] Adhesives and conductive materials

[0093] The types and amounts of binders and conductive materials used in the negative electrode active material slurry are the same as those used in the positive electrode.

[0094] Thickener

[0095] When applying the negative electrode active material to the negative electrode current collector, the negative electrode active material slurry may contain a thickener. Specifically, the thickener may contain cellulose compounds such as carboxymethyl cellulose (CMC). For example, based on the total mass of the negative electrode active material layer, the content of the thickener may be more than 0.5% by mass and less than 10% by mass.

[0096] solvent

[0097] The solvent used in the negative electrode active material slurry is not limited to a specific type and may include any type of solvent commonly used in the manufacture of negative electrodes. Examples of solvents may include, but are not limited to, one or a mixture of N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide (DMSO), isopropanol, acetone, and water.

[0098] Method for manufacturing the negative electrode

[0099] The negative electrode active material is dissolved or dispersed in a solvent together with a binder, a conductive material, and a thickener to obtain a negative electrode active material slurry. This negative electrode active material slurry can be coated onto a negative electrode current collector, and then dried and rolled to obtain a negative electrode with a negative electrode active material layer on the negative electrode current collector.

[0100] Alternatively, for example, a negative electrode active material slurry can be cast onto a support, and the film layer obtained by peeling off the support can be pressed onto the negative electrode current collector to manufacture the negative electrode. Any other method can be used to form the negative electrode active material layer on the negative electrode current collector.

[0101] diaphragm

[0102] In the lithium-ion secondary battery of the embodiments, the separator separates the negative electrode from the positive electrode and provides a channel for the movement of lithium ions. It is not limited to a specific type and can include any commonly used separator for lithium-ion secondary batteries. In particular, the separator preferably has low electrolyte ion migration resistance and high electrolyte wettability. For example, the separator can include a porous polymer membrane made of polyolefin polymers (including ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer), or a laminated structure of two or more layers thereof. Alternatively, the separator can include a porous nonwoven fabric, such as a nonwoven fabric made of high-melting-point glass fiber or polyethylene terephthalate fiber. Furthermore, to ensure heat resistance or mechanical strength, a ceramic or polymer-coated separator can be used.

[0103] Non-aqueous electrolytes

[0104] In the non-aqueous electrolyte secondary battery of the embodiment, the non-aqueous electrolyte may include, but is not limited to, organic liquid electrolyte, inorganic liquid electrolyte or solid electrolyte used to manufacture the secondary battery.

[0105] Non-aqueous electrolytes may contain organic solvents and lithium salts, and may also contain additives if necessary. In the following text, liquid electrolytes are also referred to as "electrolytes".

[0106] organic solvents

[0107] Organic solvents are not limited to a specific type and may include any type of organic solvent that serves as a medium for the movement of ions participating in the electrochemical reactions of the battery. Examples of organic solvents may include, but are not limited to, one or a mixture of the following solvents: ester solvents, including methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents, including dibutyl ether and tetrahydrofuran; ketone solvents, including cyclohexanone; aromatic solvents, including benzene and fluorobenzene; carbonate solvents, including dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents, including ethanol and isopropanol; nitrile solvents, including R-CN (where R is a hydrocarbon group having a linear, branched, or cyclic structure from C2 to C20 and may contain exocyclic double bonds or ether bonds); amide solvents, including dimethylformamide; dioxolane solvents, including 1,3-dioxolane; and sulfolane solvents. In particular, carbonate solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant, and low viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate) are more preferred, resulting in improved battery charge-discharge performance. In this case, using the mixture when the cyclic carbonate and linear carbonate are mixed in a volume ratio of 1:1 to 1:9 ensures high electrolyte performance.

[0108] lithium salts

[0109] Lithium salts are not limited to specific types and may include any compound that provides lithium ions for use in lithium-ion secondary batteries. Examples of lithium salts may include, but are not limited to, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, or mixtures thereof. For example, the concentration of lithium salts in the electrolyte may be from 0.1 mol / L to 2 mol / L. Below L. When the concentration of lithium salt is within the above range, the electrolyte has appropriate conductivity and viscosity, resulting in high electrolyte performance, thereby enabling efficient movement of lithium ions.

[0110] additive

[0111] Additives may be optionally used to improve battery life characteristics, suppress battery capacity decay, and improve battery discharge capacity. Examples of additives may include, but are not limited to, one or a mixture of the following: halogenated alkylene carbonates (including vinylene carbonate (VC), fluoroethylene carbonate (FEC), or difluoroethylene carbonate (DFEC)), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glycol ethers, hexamethylphosphoric triamine, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidinanes, ethylene glycol dialkyl ethers, ammonium salts, pyrroles, 2-methoxyethanol, and aluminum trichloride. For example, the content of the additive may be from more than 0.1% by mass to less than 15% by mass, based on the total mass of the electrolyte.

[0112] Manufacturing method and application method of non-aqueous electrolyte secondary battery

[0113] The method for manufacturing and using the lithium-ion secondary battery according to the embodiments includes the following steps: (1) Manufacturing lithium-ion secondary batteries; (2) The lithium-ion secondary battery is charged and discharged during the first cycle; and (3) Use lithium-ion secondary batteries after initial charge and discharge.

[0114] (1) Steps in manufacturing a battery

[0115] The lithium-ion secondary battery of the embodiment can be manufactured by placing a separator and an electrolyte between the negative and positive electrodes. More specifically, the battery can be manufactured by forming an electrode assembly by placing a separator between the negative and positive electrodes, placing the electrode assembly in a cylindrical or prismatic battery casing, and injecting an electrolyte. Alternatively, the battery can also be manufactured by stacking the electrode assemblies, filling them with an electrolyte, placing the resulting product in a battery casing, and sealing the battery casing. Any other methods known in the art can be used to manufacture the battery.

[0116] (2) Steps for charging and discharging the battery during the first cycle

[0117] The method for manufacturing a lithium-ion secondary battery according to the embodiment includes an initial charging process in which the lithium-ion secondary battery is charged at least once with a voltage of 4.4 V or higher based on lithium. The charging voltage of the initial charging process can be higher than the oxidation potential of the second positive electrode active material. When the initial charging is performed with a voltage higher than the oxidation potential of the second positive electrode active material, lithium ions in the second positive electrode active material can be pre-doped into the negative electrode active material. This voltage can be higher than the design voltage, preferably 4.4 V or higher, 4.5 V or higher, 4.6 V or higher, or 4.7 V or higher based on lithium, for example, 4.8 V. The charging rate during the initial charging process can be in the range of 0.05C to 1.0C, for example. Simultaneously, a process for removing the generated gas can be performed after the initial charging.

[0118] After the initial charge, the battery is fully discharged. The discharge rate may be, for example, in the range of 0.05C to 1.0C. The lithium-ion secondary battery may undergo an initial charge-discharge process at least once before leaving the factory. The initial charge-discharge process may include repeating the above charge-discharge process 1 to 3 times.

[0119] (3) Steps for using lithium-ion secondary batteries after initial charge and discharge.

[0120] When lithium-ion secondary batteries are actually used, the state of charge (SOC) is limited within the upper and lower voltage limits that achieve the nominal capacity. During use, charging is performed at a voltage above the main oxidation potential of the first positive electrode active material and below the oxidation potential of the second positive electrode active material. During use, charging and discharging can, for example, be performed within a range of upper charging limits of 4.3V, 4.25V, 4.2V, 4.1V, or 4.0V and lower discharging limits of 2.5V, 2.6V, 2.7V, 2.8V, 2.9V, or 3.0V. The charge / discharge rate can, for example, be in the range of 0.1C to 1.0C.

[0121] During use, within the aforementioned voltage range, the second positive electrode active material does not participate in charging and discharging. During the initial charging process, a redox reaction primarily occurs between the pre-doped lithium-ion negative electrode active material and the first positive electrode active material, thus achieving a highly reversible charge-discharge reaction. It can be expected that the stable charge-discharge reaction will suppress the increase in internal resistance with repeated cycling.

[0122] Effect

[0123] To compensate for the irreversible capacity of the negative electrode active material, lithium ions have been pre-doped into it. This method effectively compensates for the irreversible capacity of the negative electrode itself, thereby improving charge and discharge efficiency, but it requires pretreatment before cell assembly. Using metallic lithium in the pre-doped negative electrode before cell assembly makes electrode manipulation difficult. Furthermore, it increases the complexity of the manufacturing process.

[0124] In this embodiment, the lithium-ion secondary battery does not pre-dope lithium ions into the negative electrode active material before cell assembly. Instead, pre-doping is performed during the initial charging process after battery assembly using a high voltage. Therefore, the electrodes are easily manipulated before cell assembly, simplifying the manufacturing process.

[0125] Furthermore, the battery of the present invention can achieve stability against thermal runaway in the event of a fault or failure, while controlling excess charge to adjust the available SOC range, thereby improving capacity retention. Moreover, because the design and manufacturing processes are combinable, the upper and lower limits of voltage (ΔSOC) can be arbitrarily set according to the usage conditions of hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or electric vehicles (EVs), thereby effectively utilizing excess capacity during the initial charging process, thus suppressing capacity decay during durability cycling, and enabling the construction of a battery system with high durability.

[0126] Example

[0127] Embodiments and comparative examples will be described below. However, the present invention is not limited thereto. Furthermore, the following description is provided illustratively to aid in understanding the present invention and is not intended to limit the invention.

[0128] Example 1

[0129] Preparation of positive electrode

[0130] Weigh 100 parts by mass of the positive electrode active material (LiNi with an average particle size of approximately 11 μm, used as the first positive electrode active material). 0.8 Co 0.1 Mn 0.1 O2 (NCM) powder and Li2MnO3 and LiNi, which have an average particle size of about 5 μm, are used as the second positive electrode active material. 0.326 Co 0.116 Mn 0.558 A 9:1 (mass ratio) mixture of lithium-rich NCM (Li:Ni:Mn:Co = 1.14:0.28:0.48:0.10 molar ratio) powder in solid solution of O2, 2 parts by mass of PVdF as a binder, and 1.5 parts by mass of carbon black as a conductive material were mixed in N-methyl-2-pyrrolidone as a solvent to prepare a positive electrode active material slurry. The obtained positive electrode active material slurry was coated onto an aluminum foil serving as the positive electrode current collector, dried at 130°C for 1 hour in a dry environment, and then rolled to form the positive electrode.

[0131] Example 2

[0132] Except that the mass ratio of the first positive electrode active material to the second positive electrode active material is 7:3, the positive electrode active material slurry is prepared by the same method as in Example 1, and the positive electrode is manufactured by the same method.

[0133] Example 3

[0134] Except that the mass ratio of the first positive electrode active material to the second positive electrode active material is 5:5, the positive electrode active material slurry is prepared by the same method as in Example 1, and the positive electrode is manufactured by the same method.

[0135] Comparative Example 1

[0136] Except for not adding a second positive electrode active material, the positive electrode active material slurry was prepared by the same method as in Example 1, and the positive electrode was manufactured by the same method.

[0137] Comparative Example 2

[0138] Except for not adding the first positive electrode active material, the positive electrode active material slurry was prepared by the same method as in Example 1, and the positive electrode was manufactured by the same method.

[0139] Evaluation Example 1: X-ray Diffraction (XRD) Pattern Measurement

[0140] For each positive electrode obtained in Example 3 and Comparative Examples 1 and 2, lithium metal was used as the counter electrode to manufacture a coin cell. Each coin cell in Example 3 and Comparative Examples 1 and 2 was initially charged to 4.65V at a charging rate of 0.2C and then discharged to 2.5V. Subsequently, the coin cell was disassembled to remove the positive electrode, and cleaned with dimethyl carbonate (DMC). After cleaning, the positive electrode active material layer, excluding the current collector, was scraped off, and XRD measurements were performed using Cuα as an X-ray source.

[0141] After charging and discharging, the positive electrodes of Comparative Examples 1 and 2 exhibited peaks at different positions around 19°. Furthermore, the positive electrode of Example 3, after charging and discharging, showed two peaks originating from a mixture of the first and second positive electrode active materials.

[0142] Evaluation Example 2: Measurement of Excess Charge During Initial Charging

[0143] For each positive electrode obtained in Examples 1 to 3 and Comparative Examples 1 and 2, lithium metal was used as the counter electrode to manufacture a coin cell. Each coin cell of Examples 1 to 3 and Comparative Example 2 was initially charged to 4.65V at a charging rate of 0.2C and then discharged to 2.5V. In the second cycle, charging and discharging were performed at a charging termination voltage of 4.25V and a discharging termination voltage of 2.5V (0.2C rate). Since the coin cell of Comparative Example 1 did not contain a second positive electrode active material operating in the high potential range, charging and discharging were performed at a charging termination voltage of 4.25V and a discharging termination voltage of 2.5V (0.2C rate) in both the first and second charging cycles.

[0144] Here, the difference between the initial charging capacity and the initial discharging capacity is called the initial irreversible capacity, while the "second true charge" or the sum of the initial irreversible capacity and the second cycle charging capacity is defined as follows: The "second true charge" represents the capacity when a second cycle of charging is performed from a fully discharged state before charging and discharging.

[0145] Mathematical Formula 1

[0146] Second actual charge capacity (mAh / g) = Initial irreversible capacity (mAh / g) + Second cycle charge capacity (mAh / g)

[0147] Furthermore, the pre-doping ratio (β) is a value obtained by subtracting 1 from the value obtained by dividing the initial charge capacity by the second actual charge capacity, and it is defined as follows. β represents a measure of the amount of excess capacity that can be charged through the initial charge when the second cycle charge capacity is set to 1.

[0148] Mathematical formula 2

[0149] β = (Initial charging capacity) / (Second actual charging capacity) - 1

[0150] The table below summarizes the results of Evaluation Example 1 and the manufacturing conditions described above.

[0151] Table 1

[0152] Referring to Table 1, it was confirmed that when the second positive electrode active material was added and high-voltage charging (4.65V) was performed during the initial charging process, the excess charging capacity corresponding to β was found. This excess charging capacity can be controlled by adjusting the amount of the second positive electrode active material.

[0153] Evaluation Example 3: Battery Life Characteristics Evaluation

[0154] Preparation of negative electrode

[0155] A mixture of silica (SiO) powder with an average particle size of approximately 8 μm (as the negative electrode active material), an aqueous dispersion (0.4% solids) of carbon black (CB) and single-walled carbon nanotubes (SWCNTs) (as conductive materials), styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener, was prepared at a mass ratio of 88.8:3.3:0.25:3.65:4.0. First, the negative electrode active material, CB, and CMC were completely mixed. Then, the SWCNT dispersion and water were added and mixed. Finally, SBR was added and mixed to prepare a negative electrode active material slurry. The resulting negative electrode active material slurry was uniformly coated onto a copper foil and vacuum dried at 110°C for 10 hours to manufacture the negative electrode.

[0156] Preparation of lithium-ion secondary batteries

[0157] The negative electrode prepared as described above was stacked with the positive electrodes of Examples 1 to 3 and Comparative Example 1, separated by a polyethylene separator (thickness: approximately 20 μm), to fabricate an electrode assembly. The electrode assembly was then placed in a battery casing, and an electrolyte was injected into the casing to fabricate a lithium-ion secondary battery. The electrolyte was prepared by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a volume ratio of 3:7, dissolving 1M LiPF6 as a lithium salt, and... It is prepared by adding 1.0% by mass of vinylene carbonate (VC).

[0158] Charge and discharge test

[0159] Each battery using the positive electrode of the Examples and Comparative Examples was charged and discharged at 0.1C and 4.6V during the first cycle (discharge termination voltage 2.5V). In the second and subsequent cycles, charge-discharge was performed up to 300 cycles at a charge termination voltage of 4.2V and a discharge termination voltage of 2.5V. At the initial charge, the amounts of both the positive and negative electrodes were adjusted to approximately 90% of the design capacity for the negative electrode. Cycling tests were performed by two charge-discharge cycles at 25°C, followed by a charge-discharge cycle at 0.5C at 45°C up to 300 cycles. Capacity retention (%) was the ratio of the discharge capacity after 300 cycles at 45°C to the discharge capacity of the first cycle.

[0160] In addition, DCR measurements were performed at 50% SOC before and after cyclic testing. DCR was calculated by dividing the voltage drop by the current before and after a 2.5C current flows for 10 seconds.

[0161] Table 2 below summarizes the results of Evaluation Example 2. In Table 2, the DCR increase rate represents the increase (%) of DCR after 300 cycles at 45°C relative to the DCR after the first cycle.

[0162] Table 2

[0163] In the batteries of Examples 1 to 3, it was confirmed that, compared with Comparative Example 1 without a second positive electrode active material, the capacity retention was improved by adding a second positive electrode active material and adjusting the excess charge of the negative electrode. Furthermore, the increase in DCR after 300 cycles was suppressed. It is believed that by adding a second positive electrode active material and charging at a high voltage in the first cycle to pre-dope excess lithium into the negative electrode, and then charging at 4.2V under conditions of oxidation and reduction of the first positive electrode active material in the second and subsequent cycles, the SOC difference between the positive and negative electrodes was suppressed.

[0164] Evaluation Example 4: Thermal stability of positive electrode active materials

[0165] Subsequently, differential scanning calorimetry (DSC) was performed on each positive electrode active material in Examples 1 to 3 and Comparative Examples 1 and 2 as follows. Coin cells were manufactured using each positive electrode in the same manner as in Evaluation Example 2, and charge-discharge cycles were performed. After the second charge cycle, the coin cells were disassembled to remove the positive electrode, which was then cleaned with dimethyl carbonate (DMC). After cleaning, the positive electrode active material layer, excluding the current collector, was scraped off, dried, and 4 mg was weighed. The positive electrode active material layer, along with 6 μl of a solution containing 1 M LiPF6 dissolved in a 3:7 (volume ratio) solvent mixture of ethylene carbonate (EC) and methyl ethyl carbonate (EMC), was placed in a sealed DSC pan, and measurements were performed while heating from room temperature at a heating rate of 10 °C / min. As the measurement results, the following results were obtained for Examples 1 to 3 and Comparative Examples 1 and 2 respectively: Figure 2 The graph shown illustrates this. From the graph, the slope representing the heat generated per unit time, and the heat generation (area) from 150°C to 300°C were calculated. Figure 3 A graph comparing the slopes of Examples 1 to 3 with those of Comparative Examples 1 and 2. Figure 4 The graph shows a comparison of the calorific value of Examples 1 to 3 with Comparative Examples 1 and 2.

[0166] See Figure 4 The heat generation of the positive electrode active materials in Examples 1 to 3 was compared with that in Comparative Examples 1 and 2, confirming that the heat generation decreased as the amount of the second positive electrode active material increased. In other words, it was confirmed that the second positive electrode active material exhibits higher thermal stability because it generates less heat between 150°C and 300°C. Furthermore, Examples 1 to 3, which used a mixture of the first and second positive electrode active materials, showed even lower heat generation than Comparative Example 1, which used only the first positive electrode active material.

[0167] In addition, in the DSC peaks observed from heating from room temperature, the slope (W / (℃·g)) of the straight line connecting the points of 80% and 40% of the peak height was calculated for the left side of the peak on the lowest temperature side (i.e., the rising edge of the peak). Figure 3 The slopes of Examples 1 to 3 and Comparative Examples 1 and 2 are shown.

[0168] Comparative Examples 1 (first positive electrode active material only) and 2 (second positive electrode active material only) showed steeper DSC peak slopes, while Examples 1 to 3, using both the first and second positive electrode active materials, showed gentler peak slopes. This slope represents the heat flow per unit temperature, but since this test was conducted at a heating rate of 10°C / min, it also indicates the heat flow per unit time, representing how quickly heat is generated in a short time. Compared to Comparative Examples 1 and 2, which used only one type of positive electrode active material, Examples 1 to 3, using a mixture of the first and second positive electrode active materials, showed a reduced slope, confirming improved thermal stability.

Claims

1. A non-aqueous electrolyte secondary battery, comprising: An electrode assembly comprising a positive electrode, a negative electrode, and a diaphragm disposed between the positive and negative electrodes; and Non-aqueous electrolytes in, The positive electrode contains a first positive electrode active material and a second positive electrode active material. The second positive electrode active material comprises a lithium-based solid solution with an oxidation potential of 4.4 V or higher, and is at least partially electrochemically deactivated through a charging reaction. The solid solution contains a solid solution of lithium manganese oxide and lithium transition metal oxide. The negative electrode contains a Si-based negative electrode active material.

2. The non-aqueous electrolyte secondary battery as described in claim 1, in, The lithium manganese oxide is Li2MnO3.

3. The non-aqueous electrolyte secondary battery as described in claim 1, in, The lithium transition metal oxide is represented by LiMeO2, wherein Me is at least one element selected from the group consisting of Co, Ni and Mn.

4. The non-aqueous electrolyte secondary battery as described in claim 1, in, The second positive electrode active material comprises Li 1+a (Ni x Co y Mn z ) 1-a O2 represents lithium excess transition metal oxide, where 0 <a<0.3,0≤x<1,0≤y<1,0<z≤1,x+y+z=1。 5. The non-aqueous electrolyte secondary battery as described in claim 1, in, The first positive electrode active material is a nickel-containing lithium transition metal oxide with a nickel content of more than 50 mol% of the total transition metal content.

6. The non-aqueous electrolyte secondary battery as described in claim 1, in, The ratio of Mn content to total transition metal content in the second positive electrode active material is higher than that in the first positive electrode active material.

7. The non-aqueous electrolyte secondary battery as described in claim 1, in, Based on the total mass of the first positive electrode active material and the second positive electrode active material, the content of the second positive electrode active material is from 0.1% by mass to 50% by mass.

8. The non-aqueous electrolyte secondary battery as described in claim 1, in, The Si-type negative electrode active material is pre-doped with lithium ions derived from the second positive electrode active material.

9. The non-aqueous electrolyte secondary battery as described in claim 1, in, The second positive electrode active material does not have an oxidation potential in the range of less than 4.4V that would cause an irreversible oxidation reaction.

10. The non-aqueous electrolyte secondary battery as described in claim 1, in, In the DSC curve of the positive electrode active material contained in the positive electrode, obtained by differential scanning calorimetry (DSC) involving heating from room temperature at a heating rate of 10 °C / min, the low-temperature slope of the exothermic peak on the lowest temperature side is less than 1.5 W / °C·g.

11. The non-aqueous electrolyte secondary battery as described in claim 1, in, In the DSC curve of the positive electrode active material contained in the positive electrode, obtained by differential scanning calorimetry (DSC) involving heating from room temperature at a heating rate of 10 °C / min, the low-temperature slope of the exothermic peak on the lowest temperature side is less than 70% of the low-temperature slope of the maximum peak of the first positive electrode active material alone.

12. A hybrid electric vehicle (HEV) or a plug-in hybrid electric vehicle (PHEV) comprising a non-aqueous electrolyte secondary battery as described in any one of claims 1 to 11.

13. A method for manufacturing a non-aqueous electrolyte secondary battery, the battery comprising: an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, wherein, The positive electrode contains a first positive electrode active material and a second positive electrode active material, wherein the second positive electrode active material comprises a lithium-based solid solution with an oxidation potential of 4.4V or higher, and is at least partially electrochemically deactivated through a charging reaction, the solid solution comprising a solid solution of lithium manganese oxide and lithium transition metal oxide, wherein the negative electrode contains a Si-based negative electrode active material, and the method includes: An initial charging process is performed at least once to charge the non-aqueous electrolyte secondary battery with a voltage of 4.4 V or higher based on lithium, thereby pre-doping lithium ions from the second positive electrode active material into the Si-type negative electrode active material.

14. The method for manufacturing a non-aqueous electrolyte secondary battery as described in claim 13, in, The charging voltage during the initial charging process is higher than the charging voltage in the second and subsequent cycles.

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