Lithium-ion secondary battery and manufacturing method of negative electrode for lithium-ion secondary battery

Abstract

The present application provides a lithium ion secondary battery having sufficient discharge capacity and low internal resistance in a low SOC range. The lithium ion secondary battery includes a positive electrode having a positive electrode mixture and a negative electrode having a negative electrode mixture, wherein the positive electrode mixture contains a positive electrode active material represented by the following formula (1), Li 1+X M A O2(1), wherein: X satisfies -0.15 ≤ X ≤ 0.15, M A represents an element group containing at least one selected from Mn and Al, Ni, and Co, the negative electrode mixture contains a negative electrode active material containing a carbon-based material, a negative electrode additive containing copper oxide, and a binder, and the negative electrode mixture contains the copper oxide at a concentration of 0.5 wt% or more and 15 wt% or less based on the total weight of the negative electrode active material and the negative electrode additive.

Description

TECHNICAL FIELD

[0001] The present application relates to a lithium-ion secondary battery and a manufacturing method of a negative electrode for a lithium-ion secondary battery. BACKGROUND

[0002] In the automobile industry, fuel consumption restrictions and environmental restrictions are being strengthened. In order to comply with these restrictions, the technology development of electric vehicles, which use a battery as a power source and do not emit carbon dioxide, and fuel cell vehicles, which use hydrogen as a fuel source, is attracting attention. However, electric vehicles and fuel cell vehicles have various problems such as insufficient infrastructure development. Therefore, PHEVs (Plug-in Hybrid Electric Vehicles) and HEVs (Hybrid Electric Vehicles), which use both an internal combustion engine and a battery as a power source and emit less carbon dioxide, are promising candidates for coping with fuel consumption restrictions and environmental restrictions.

[0003] A lithium-ion secondary battery is used in a PHEV or a HEV. In Patent Literature 1, a positive electrode active material containing lithium nickel manganese tungsten complex oxide particles having a hexagonal layered structure is described, which enables high capacity and high output of a lithium-ion secondary battery, and the like. In Patent Literature 2, a lithium-ion secondary battery having a negative electrode composed of a graphite composite to which copper oxide is attached and a binder material is described, in which the graphite composite to which copper oxide is attached is manufactured by generating copper oxide on the surface of graphite particles through a chemical reaction, and it is described that the lithium-ion secondary battery can have a high discharge capacity.

[0004] PRIOR ART DOCUMENTS

[0005] PATENT LITERATURE

[0006] Patent Literature 1: Japanese Patent Application Publication No. 2020-123494

[0007] Patent Literature 2: Japanese Patent Application Publication No. H8-45499 SUMMARY

[0008] PROBLEMS TO BE SOLVED BY THE INVENTION

[0009] In a PHEV or an HEV, a lithium ion secondary battery having sufficient discharge capacity and capable of supplying stable output in a low SOC (State of Charge) range is required. In order to obtain stable output in the low SOC range, it is required to reduce the internal resistance of the lithium ion secondary battery in the low SOC range. However, according to the present inventors' knowledge, a lithium ion secondary battery using the positive electrode active material described in Patent Literature 1 has a tendency to have a high internal resistance in the low SOC range. In addition, in Patent Literature 2, there is no description about the internal resistance in the low SOC range.

[0010] Thus, a lithium ion secondary battery having sufficient discharge capacity and having a low internal resistance in a low SOC range is provided.

[0011] Technical means for solving the technical problem

[0012] According to one embodiment of the present application, a lithium ion secondary battery is provided, which includes: a positive electrode having a positive electrode mixture, and a negative electrode having a negative electrode mixture, wherein the positive electrode mixture contains a positive electrode active material represented by the following formula (1),

[0013] Li 1+X M A O2(1)

[0014] In the formula, X satisfies -0.15 ≤ X ≤ 0.15,

[0015] M A represents a group containing at least one selected from Mn and Al, Ni, and Co,

[0016] The negative electrode mixture contains: a negative electrode active material containing a carbon-based material, a negative electrode additive containing copper oxide, and a binder,

[0017] The negative electrode mixture contains the copper oxide at a concentration of 0.5 wt% or more and 15 wt% or less based on the total weight of the negative electrode active material and the negative electrode additive (i.e., the negative electrode mixture contains the copper oxide at a concentration of 0.5 wt% or more and 15 wt% or less based on the total weight of the negative electrode active material and the negative electrode additive).

[0018] According to another embodiment of the present application, a method for manufacturing a negative electrode for a lithium ion secondary battery is provided, which includes: mixing a negative electrode active material containing a carbon-based material, a negative electrode additive containing copper oxide, and a binder; and applying the mixture to a negative electrode current collector, the mixture containing the copper oxide at a concentration of 0.5 wt% or more and 15 wt% or less based on the total weight of the negative electrode active material and the negative electrode additive.

[0019] This specification includes the content of Japanese Patent Application No. 2021-033765 on which this application is based for priority.

[0020] Effects of the Invention

[0021] The lithium-ion secondary battery of the present application has sufficient discharge capacity and has a low internal resistance in a low SOC range. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is an appearance perspective view of a lithium-ion secondary battery.

[0023] Figure 2 is an exploded perspective view of a lithium-ion secondary battery.

[0024] Figure 3 is a perspective view of a part of a wound assembly being unfolded. DETAILED DESCRIPTION

[0025] Hereinafter, embodiments will be described with appropriate reference to the accompanying drawings. The present application is not limited to the following embodiments, and various design changes can be made within the scope of the spirit of the present application recited in the claims. In addition, in the drawings referred to in the following description, the same reference numerals are sometimes assigned to the same parts or parts having the same function, and repeated description is omitted. In addition, in order to facilitate the description, the size ratio of the drawing may, at times, be different from the actual ratio, or a part of a part may be omitted from the drawing. In addition, in the present specification, the numerical range indicated using the notation “~” includes the numerical values recited before and after the notation “~” as lower limit values and upper limit values, respectively.

[0026] Figure 1 、 2 The lithium-ion secondary battery 100 of the embodiment shown includes a battery case 1 and a battery lid 6. The battery case 1 has a rectangular bottom surface 1d, side surfaces including a pair of relatively large opposing wide side surfaces 1b and a pair of relatively small opposing narrow side surfaces 1c that rise from the bottom surface 1d, and an opening portion 1a that is open upward at the upper ends of the wide side surfaces 1b and the narrow side surfaces 1c. Here, upward refers to the Z direction of the battery case 1. Figure 1 、 2

[0027] The opening portion 1a of the battery case 1 is sealed by the battery lid 6. The battery lid 6 is a substantially rectangular flat plate that is welded to seal the battery case 1 in a manner that closes the opening portion 1a of the battery case 1.

[0028] An exhaust valve 10 is integrally provided in the battery lid 6. When the pressure inside the battery case 1 rises, the exhaust valve 10 ruptures to discharge gas from the inside of the battery case 1, and the pressure inside the battery case 1 decreases. Thereby, the safety of the lithium-ion secondary battery 100 can be ensured.​

[0029] A liquid injection port 9 for injecting electrolyte into the battery casing 1 is provided through the battery cover 6. After the electrolyte is injected into the battery casing 1, the liquid injection port 9 is sealed by the liquid injection plug 11. The liquid injection plug 11 is joined to the battery cover 6 by laser welding to seal the liquid injection port 9, thereby sealing the lithium-ion secondary battery 100.

[0030] The battery cover 6 also has a through hole 46 on the positive side and a through hole 26 on the negative side.

[0031] Above the battery cover 6, there are positive external terminals 14 and negative external terminals 12. Inside the battery casing 1 below the battery cover 6, there are positive current collectors 44 and negative current collectors 24.

[0032] For example, aluminum alloy can be used as the forming material for the positive electrode external terminal 14 and the positive electrode current collector 44, and copper alloy can be used as the forming material for the negative electrode external terminal 12 and the negative electrode current collector 24.

[0033] The positive external terminal 14 and the negative external terminal 12 each have a welding joint for welding to a busbar or the like. The welding joint has a rectangular block shape protruding upward from the battery cover 6. The lower surface of the welding joint is opposite to the surface of the battery cover 6, and the upper surface of the welding joint is located at a predetermined height and is approximately parallel to the battery cover 6.

[0034] The positive current collector plate 44 has a rectangular plate-shaped positive current collector plate base 41 opposite to the lower surface of the battery cover 6, and a positive electrode side connection end 42 extending from the side end of the positive current collector plate base 41 along the wide side surface 1b of the battery case 1 towards the bottom surface 1d. Similarly, the negative current collector plate 24 has a rectangular plate-shaped negative current collector plate base 21 opposite to the lower surface of the battery cover 6, and a negative electrode side connection end 22 extending from the side end of the negative current collector plate base 21 along the wide side surface 1b of the battery case 1 towards the bottom surface 1d. A positive electrode side opening hole 43 and a negative electrode side opening hole 23 are formed in the positive current collector plate base 41 and the negative current collector plate base 21, respectively.

[0035] A positive electrode connection portion 14a and a negative electrode connection portion 12a are provided such that they protrude from the lower surfaces of the positive electrode external terminal 14 and the negative electrode external terminal 12, respectively. The positive electrode connection portion 14a and the negative electrode connection portion 12a are integrally formed with the positive electrode external terminal 14 and the negative electrode external terminal 12, respectively.

[0036] The positive electrode connection portion 14a has a cylindrical shape with a positive electrode side through hole 46 that can be inserted into the battery cover 6 and a positive electrode side opening hole 43 in the positive electrode current collector base 41. Similarly, the negative electrode connection portion 12a has a cylindrical shape with a negative electrode side through hole 26 that can be inserted into the battery cover 6 and a negative electrode side opening hole 23 in the negative electrode current collector base 21. The positive electrode connection portion 14a passes through the battery cover 6 and the positive electrode current collector base 41 through the positive electrode side through hole 46 and the positive electrode side opening hole 43 in the positive electrode current collector base 41. The positive electrode external terminal 14 is electrically connected to the positive electrode current collector 44 via the positive electrode connection portion 14a and is fixed to the battery cover 6. Similarly, the negative electrode connection portion 12a passes through the battery cover 6 and the negative electrode current collector base 21 through the negative electrode side through hole 26 and the negative electrode side opening hole 23 in the negative electrode current collector base 21. The negative external terminal 12 is electrically connected to the negative current collector 24 via the negative connection part 12a and is fixed to the battery cover 6.

[0037] The positive external terminal 14 is electrically connected to the winding assembly 3 (described later) via the positive connection portion 14a and the positive current collector 44. Similarly, the negative external terminal 12 is electrically connected to the winding assembly 3 via the negative connection portion 12a and the negative current collector 24. When the lithium-ion secondary battery 100 is charging, the winding assembly 3 is powered from an external power source via the positive external terminal 14, the positive connection portion 14a and the positive current collector 44, and the negative external terminal 12, the negative connection portion 12a and the negative current collector 24. When the lithium-ion secondary battery 100 is discharging, the winding assembly 3 is powered to an external load via the positive external terminal 14, the positive connection portion 14a and the positive current collector 44, and the negative external terminal 12, the negative connection portion 12a and the negative current collector 24.

[0038] To ensure electrical insulation between the positive current collector 44, the negative current collector 24, the positive external terminal 14, and the negative external terminal 12 and the battery cover 6, gaskets 5 are provided between each terminal of the positive external terminal 14 and the negative external terminal 12 and the battery cover 6, and insulating plates 7 are provided between each current collector of the positive current collector 44 and the negative current collector 24 and the battery cover 6. Materials used for the insulating plates 7 and the gaskets 5 include, for example, insulating resins such as polybutylene terephthalate, polyphenylene sulfide, and perfluoroalkoxy resins.

[0039] The electrolyte and winding assembly 3 are housed inside the battery casing 1.

[0040] The electrolyte is injected into the battery casing 1 through the injection port 9. For example, a non-aqueous electrolyte in which lithium salts such as lithium hexafluorophosphate (LiPF6) are dissolved in a carbonate-based organic solvent such as ethylene carbonate can be used.

[0041] like Figure 3As shown, the winding assembly 3 has a negative electrode 32, a positive electrode 34, and two separators 33 and 35. The separators 35, 32, 33, and 34 are overlapped in this order and wound into a flat shape. The separator 35 is located at the outermost periphery of the winding assembly 3, and the negative electrode 32 is located inside it. The two separators 33 and 35 electrically insulate the positive electrode 34 from the negative electrode 32.

[0042] The winding assembly 3 has a pair of opposing end faces 3a and 3b perpendicular to the winding shaft, and a side surface 3c between the pair of end faces 3a and 3b. The side surface 3c has a pair of opposing curved portions with a semi-circular cross-section, and a flat portion continuously formed between the pair of curved portions. The winding assembly 3 is disposed within the battery housing 1 such that the flat portion of the side surface 3c is substantially parallel to the wide side surface 1b of the battery housing 1.

[0043] The positive electrode 34 has a positive current collector 34a and a positive electrode flux layer 34b formed on both sides of the positive current collector 34a.

[0044] The positive current collector 34a is formed of any material with high conductivity that does not alloy with lithium ions. The positive current collector 34a can have a plate-like (sheet-like) shape. For example, aluminum foil can be used as the positive current collector 34a. At one end of the positive current collector 34a, a portion not covered by the positive electrode binder layer 34b (hereinafter referred to as the "positive current collector exposed portion") 34c is provided. The positive current collector exposed portion 34c is provided on and near the end face 3a of the winding assembly 3. The positive current collector exposed portion 34c is opposite to and electrically connected to the positive electrode side connection end 42 of the positive current collector plate 44.

[0045] The positive electrode mixture layer 34b contains a positive electrode active material represented by the following formula (1):

[0046] Li 1+X M A O2(1)

[0047] (In the formula:

[0048] X satisfies -0.15 ≤ X ≤ 0.15,

[0049] M A (This indicates a group of elements containing at least one of Mn and Al, Ni, and Co).

[0050] Because -0.15≤X≤0.15, the positive electrode active material has high true density and high reversibility.

[0051] M AIn addition to Ni and Co, it also contains at least one selected from Mn and Al, thus the positive electrode active material exhibits high thermal stability and high stability at high potential states. Consequently, the lithium-ion secondary battery 100 possesses high safety.

[0052] M A It may also contain at least one selected from Zr, Ti, Cr, Fe, Cu, Zn, Ge, Sn, Mg, Ag, Ta, Nb, B, P, Ca, Sr, and Ba. In M A In the presence of Zr, the internal resistance of the lithium-ion secondary battery 100 decreases at low temperatures. The Zr content relative to the total amount of Ni, Co, Mn, and Al can be 0.1–2.0 mol%, particularly 0.2–1.0 mol%. Furthermore, the composition of Mn... A The proportion of elements other than Ni, Co, Mn, and Al in the total elements can be less than 10 mol%, especially less than 3 mol%. Therefore, the lithium-ion secondary battery 100 can have sufficient discharge capacity.

[0053] The amount of each element in the positive electrode active material can be measured using the ICP (Inductively Coupled Plasma) method.

[0054] The positive electrode binder layer 34b may also contain an adhesive and a conductive agent.

[0055] As an adhesive, for example, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyethylene, polystyrene, polybutadiene, polyacrylonitrile, polyvinyl fluoride, polyfluoropropylene, polychloroprene, butyl rubber, nitrile rubber, styrene-butadiene rubber (SBR), polysulfide rubber, nitrocellulose, cyanoethyl cellulose, various latexes, acrylic resins, or mixtures thereof can be used.

[0056] Carbon-based materials can be used as conductive agents. These materials can be crystalline carbon, amorphous carbon, or mixtures thereof. Examples of crystalline carbon include synthetic graphite, natural graphite (e.g., flake graphite), or mixtures thereof. Examples of amorphous carbon include carbon black (e.g., acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking black, or mixtures thereof).

[0057] The positive electrode 34 can be formed, for example, as described below. A paste or slurry mixture is prepared by dispersing a positive electrode active material and an arbitrary conductive agent and binder in a solvent (e.g., N-methyl-2-pyrrolidone (NMP), water). This mixture is then applied to the surface of the positive electrode current collector 34a and dried. A calendering process is then performed as needed to form a positive electrode mixture layer 34b. The positive electrode 34 is thus obtained.

[0058] The negative electrode 32 has a negative current collector 32a and a negative electrode binder layer 32b formed on both sides of the negative current collector 32a.

[0059] The negative current collector 32a is formed of any material with high conductivity that does not alloy with lithium ions. At one end of the negative current collector 32a, a portion (hereinafter referred to as the "exposed negative current collector portion") 32c is provided that is not covered by the negative electrode binder layer 32b. The exposed negative current collector portion 32c is provided on and near the end face 3b of the winding assembly 3. The exposed negative current collector portion 32c is opposite to and electrically connected to the negative electrode side connection end 22 of the negative current collector plate 24.

[0060] The negative electrode compound layer 32b contains negative electrode active material, negative electrode additives and binder.

[0061] The negative electrode active material contains carbon-based materials capable of allowing lithium ions to insert and detach (de-intercalate), or is substantially formed from carbon-based materials. Examples of such carbon-based materials include natural graphite, artificial graphite, hard carbon (difficult to graphitize), soft carbon (easily graphitized), graphite coated with amorphous carbon, mixtures of carbon black (e.g., acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking black) as conductive additives with graphite, composites obtained by coating such mixtures with amorphous carbon, mixtures of graphite with hard or easily graphitized carbon, and mixtures thereof. The negative electrode active material can be particulate. The shape of the particulate negative electrode active material is not particularly limited; for example, it can be spherical, flake-like, fibrous, or obtained by crushing it.

[0062] The negative electrode additive contains copper oxide, or is substantially formed of copper oxide. The copper oxide can be copper(I) (Cu₂O), copper(II) (CuO), or a mixture thereof. The negative electrode additive can be granular. The shape of the granular negative electrode additive is not particularly limited; for example, it can be spherical, flake-like, fibrous, or pulverized. The granular negative electrode additive can be particles containing copper(I) (Cu₂O), copper(II) (CuO), or a mixture thereof, or it can be particles substantially formed of copper(I) (Cu₂O), copper(II) (CuO), or a mixture thereof. These various granular negative electrode additives can be used alone or in combination.

[0063] In the negative electrode additive layer 32b, the particulate negative electrode active material and the particulate negative electrode additive can exist as independent particles without mutual recombination. This allows the particulate negative electrode active materials to be well electrically connected without being hindered by the high-resistivity particulate negative electrode additive, thus suppressing the increase in the internal resistance of the lithium-ion secondary battery. Furthermore, the particulate negative electrode active material can have a median diameter (median particle size) of 4–20 μm. The particulate negative electrode additive can have a median diameter smaller than that of the particulate negative electrode active material, and can have a median diameter of 1–10 μm. This allows the particulate negative electrode active materials to be well electrically connected without being hindered by the high-resistivity particulate negative electrode additive, thus suppressing the increase in the internal resistance of the lithium-ion secondary battery. The median diameter d50 of the particulate negative electrode active material and the particulate negative electrode additive can be determined based on the volumetric reference particle size distribution measured using a laser diffraction particle size distribution measuring device.

[0064] The negative electrode compound layer 32b contains copper oxide at a concentration of 0.5 wt% or more and 15 wt% or less, based on the total weight of the negative electrode active material and negative electrode additives. Therefore, as shown in the embodiments described later, the lithium-ion secondary battery can have low internal resistance and high battery capacity. When the copper oxide is Cu2O, the negative electrode compound layer 32b can contain copper oxide at a concentration of 0.9 wt% or more and 15 wt% or less, based on the total weight of the negative electrode active material and negative electrode additives. Therefore, the lithium-ion secondary battery can have even lower internal resistance. Furthermore, when the copper oxide is Cu2O, the negative electrode compound layer 32b can contain copper oxide at a concentration of 1.4 wt% or more and 12 wt% or less, based on the total weight of the negative electrode active material and negative electrode additives. Therefore, the lithium-ion secondary battery can have particularly low internal resistance and particularly high battery capacity. When the copper oxide is CuO, the negative electrode additive layer 32b may contain copper oxide at a concentration of 0.5 wt% or more and 8.3 wt% or less, or 0.78 wt% or more and 6.7 wt% or less, based on the total weight of the negative electrode active material and negative electrode additives. As a result, the lithium-ion secondary battery can have exceptionally low internal resistance and exceptionally high battery capacity.

[0065] The reaction between Cu₂O and CuO is shown in the following formula:

[0066] Cu₂O + 2Li + +2e - →2Cu+Li2O

[0067] CuO + 2Li + +2e - →Cu+Li2O.

[0068] The theoretical capacities of Cu2O and CuO are 375 mAh / g-Cu2O and 674 mAh / g-CuO, respectively, with CuO having approximately 1.8 times the theoretical capacity of Cu2O. Therefore, for example, the effects obtained when the Cu2O concentration is 0.9 wt% and 15 wt% based on the total weight of the negative electrode active material and negative electrode additive are comparable to the effects obtained when the CuO concentration is 0.5 wt% and 8.3 wt% based on the total weight of the negative electrode active material and negative electrode additive, respectively.

[0069] As the adhesive for the negative electrode binder layer 32b, the same materials listed as those that can be used as adhesives for the positive electrode binder layer 34b can be used.

[0070] The negative electrode mixture layer 32b can further contain a dispersant. Carboxymethyl cellulose (CMC) can be used as the dispersant.

[0071] The negative electrode 32 can be formed, for example, as described below. First, a negative electrode active material containing a carbon-based material, a negative electrode additive containing copper oxide, a binder, and an optional dispersant are prepared. The negative electrode active material and the negative electrode additive can be in particulate form. The particulate negative electrode active material and the particulate negative electrode additive can be independent particles that do not recombine with each other. The negative electrode active material, the negative electrode additive, the binder, and the optional dispersant are dispersed in a solvent (e.g., N-methyl-2-pyrrolidone (NMP), water) to prepare a paste or slurry mixture. This mixture contains copper oxide at a concentration of 0.5 wt% or more and 15 wt% or less based on the total weight of the negative electrode active material and the aforementioned negative electrode additive. When the copper oxide is Cu2O, the mixture may contain copper oxide at a concentration of 0.9 wt% or more and 15 wt% or less, or 1.4 wt% or more and 12 wt% or less based on the total weight of the negative electrode active material and the negative electrode additive. When the copper oxide is CuO, the mixture may contain copper oxide at a concentration of 0.5 wt% to 8.3 wt% or more, or 0.78 wt% to 6.7 wt% or more, based on the total weight of the negative electrode active material and the negative electrode additive. The prepared mixture is coated onto the surface of the negative electrode current collector 32a and dried. A rolling process is then performed as needed to form a negative electrode additive layer 32b. Thus, the negative electrode 32 can be obtained.

[0072] The diaphragms 33 and 35 have the functions of preventing short circuits between the positive electrode 34 and the negative electrode 32, and of maintaining the non-aqueous electrolyte. As diaphragms 33 and 35, porous sheets made of resins such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide, or laminated sheets of them (e.g., a three-layer sheet of PP / PE / PP structure) can be used.

[0073] Alternatively, a layer containing inorganic materials (such as alumina particles) and an adhesive can be provided on one or both sides of the separators 33 and 35. This prevents the separators 33 and 35 from melting and maintains their insulating function, even when the lithium-ion secondary battery 100 is used under abnormal conditions (e.g., when the temperature of the lithium-ion secondary battery rises above 160°C due to overcharging or crushing). Therefore, the safety of the lithium-ion secondary battery 100 is improved.

[0074] Alternatively, a core can be configured at the innermost circumference of the winding assembly 3 as needed. As the core, a structure can be obtained by winding a resin sheet that has higher bending rigidity than any of the positive current collector, negative current collector, and separators 33 and 35.

[0075] Example

[0076] The present invention will be specifically described below with reference to specific embodiments, but the present invention is not limited to these embodiments.

[0077] Examples 1-5

[0078] Li has prepared 1.0 Ni 0.33 Co 0.33 Mn 0.33 O2 powder was used as the positive electrode active material. The elemental ratios in the positive electrode active material were determined by ICP analysis. Acetylene black was used as a conductive agent, and polyvinylidene fluoride (PVdF) was used as a binder.

[0079] The positive electrode active material, conductive agent, and binder are mixed in a weight ratio of 90:5:5. N-methyl-2-pyrrolidone (NMP) is added to the resulting mixture to adjust the viscosity, thus obtaining the positive electrode slurry.

[0080] A 15 μm thick aluminum foil was prepared as the positive current collector. A positive electrode slurry was coated on both sides of the positive current collector using a slot die coating method, forming a positive electrode slurry layer. Next, the positive electrode slurry layer was dried and pressurized. This yielded a positive electrode with positive electrode slurry layers formed on both sides of the positive current collector.

[0081] Natural graphite particles coated with amorphous carbon were prepared as the negative electrode active material, copper oxide (I) (Cu2O) particles as the negative electrode additive, styrene-butadiene rubber (SBR) as the binder, and carboxymethyl cellulose (CMC) as the dispersant. The volume-based particle size distribution of the natural graphite particles and Cu2O particles was measured using a laser diffraction particle size distribution measuring device, and the median diameter d50 of each particle size distribution was determined. The median diameter of the natural graphite particles was 10 μm, and the median diameter of the Cu2O particles was 3 μm. The negative electrode active material, negative electrode additive, binder, and dispersant were mixed at a weight ratio of 100-x:x:1:1. The values ​​of x in each embodiment are shown in Table 1, corresponding to the weight percentage concentration of the negative electrode additive (i.e., copper oxide) based on the total weight of the negative electrode active material and negative electrode additive. Ion-exchanged water was added to the resulting mixture to adjust the viscosity, obtaining the negative electrode slurry. A copper foil with a thickness of 10 μm was prepared as the negative electrode current collector. A negative electrode slurry was applied to both sides of the negative electrode current collector using a slit-type coating method, forming a negative electrode mixture layer. This negative electrode mixture layer was then dried and pressurized. Thus, the negative electrode was obtained.

[0082] The diaphragm, negative electrode, another diaphragm, and positive electrode are sequentially overlapped and wound together. This process manufactures a... Figure 3 The winding assembly is shown. Additionally, ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of 1:2, and LiPF6 was dissolved in the resulting mixture. This yielded a 1.0 mol / L LiPF6 solution as a non-aqueous electrolyte. Using the winding assembly and the non-aqueous electrolyte, a [product / process] was manufactured. Figure 1 , 2 The lithium-ion secondary battery shown.

[0083] Examples 6-8

[0084] Using copper(II) oxide (CuO) particles as the negative electrode additive, the negative electrode active material, negative electrode additive, binder, and dispersant were mixed in a weight ratio of 100-x:x:1:1 (the values ​​of x in each example are shown in Table 1), and a lithium-ion secondary battery was manufactured in the same manner as in Example 1. The median diameter of the CuO particles obtained in the same manner as in Example 1 was 3 μm.

[0085] Comparative Example 1

[0086] A lithium-ion secondary battery was manufactured in the same manner as in Example 1, except that negative electrode active material, binder and dispersant were mixed in a weight ratio of 100:1:1 without the use of negative electrode additives.

[0087] Comparative Examples 2 and 3

[0088] A lithium-ion secondary battery was manufactured in the same manner as in Example 1, except that the negative electrode active material, negative electrode additive, binder and dispersant were mixed in a weight ratio of 100-x:x:1:1 (the value of x in each example is as recorded in Table 1).

[0089] (1) Measuring battery capacity

[0090] The lithium-ion secondary batteries manufactured in the above embodiments and comparative examples were charged with a constant current of 1 CA until the battery voltage reached 4.2V, and then charged with a constant voltage of 4.2V. The total charging time was 2.5 hours. After a 30-minute pause, the lithium-ion secondary batteries were discharged with a constant current of 0.02 CA until the battery voltage reached 2.9V, and the discharge capacity was calculated. This discharge capacity was taken as the battery capacity. Table 1 shows the battery capacities of the lithium-ion secondary batteries of each embodiment and comparative example, obtained by standardizing (normalizing) the battery capacity of the lithium-ion secondary battery of Comparative Example 1 to 100.

[0091] (2) Measuring DC resistance (DCR)

[0092] The lithium-ion secondary battery was charged until the battery voltage reached 4.2V. Then, the battery capacity was discharged by 5%. After a 2-hour pause, the open-circuit voltage (OCV) of the lithium-ion secondary battery was measured. This process of discharging the battery by 5% and measuring OCV was repeated to determine the relationship between SOC and OCV.

[0093] Based on the relationship between SOC and OCV, a lithium-ion secondary battery was charged from 0% SOC to 20% SOC using a constant current-constant voltage (CC-CV) method. The charging current during constant current charging was set to 1CA. The lithium-ion secondary battery was then held in a -10°C thermostat for 5 hours. Afterward, the lithium-ion battery was discharged at a constant current of 5CA for 10 seconds, and the voltage drop caused by the discharge was measured. Furthermore, the same constant current discharge was performed at discharge currents of 10CA and 15CA. A graph was plotted with the discharge current on the horizontal axis and the voltage drop on the vertical axis, and the slope of the curve was determined as the DCR. The determined DCR is the DCR in the low SOC range below 20%. Table 1 shows the DCRs of the lithium-ion secondary batteries of each embodiment and comparative example, normalized to 100 using the DCR of Comparative Example 1's lithium-ion secondary battery. The smaller the DCR value, the lower the internal resistance of the lithium-ion secondary battery in the low SOC range.

[0094] [Table 1]

[0095] Negative electrode additive x Battery capacity (relative value) DCR (relative value) Example 1 [Cu2O] 0.5 99 93 Example 2 [Cu2O] 0.9 98 84 Example 3 [Cu2O] 1.4 98 75 Example 4 [Cu2O] 12 84 41 Example 5 [Cu2O] 15 80 40 Example 6 CuO 0.5 98 84 Example 7 CuO 0.78 98 75 Example 8 CuO 6.7 84 41 Comparative Example 1 － 0 100 100 Comparative Example 2 [Cu2O] 0.3 99 95 Comparative Example 3 [Cu2O] 20 73 39

[0096] The lithium-ion secondary batteries of Examples 1 to 8, in which x is in the range of 0.5 to 15, exhibited lower DCR compared to Comparative Examples 1 and 2, in which x is 0 and 0.3 respectively, and higher battery capacity compared to Comparative Example 3, in which x is 20.

[0097] In Examples 1-5, which use Cu2O particles as a negative electrode additive, the lithium-ion secondary batteries of Examples 2-5, with x in the range of 0.9-15, exhibited lower (specifically, below 85) DCR, while the lithium-ion secondary batteries of Examples 3 and 4, with x in the range of 1.4-12, exhibited particularly low (specifically, below 75) DCR and particularly high (specifically, above 80) battery capacity.

[0098] Examples 6-8, which use CuO particles as a negative electrode additive, have x in the range of 0.5 to 8.3. In particular, the lithium-ion secondary batteries of Examples 7 and 8, with x in the range of 0.78 to 6.7, exhibit particularly low (specifically, below 75) DCR and particularly high (specifically, above 80) battery capacity.

[0099] All publications, patents and patent applications cited in this specification are incorporated herein by reference.

[0100] Explanation of reference numerals in the attached figures

[0101] 32 Negative electrode

[0102] 32a Negative Current Collector

[0103] 32b Negative Electrode Mixture Layer

[0104] 34 Positive electrode

[0105] 34a Positive current collector

[0106] 34b Positive electrode mixture layer

[0107] 100 Lithium-ion secondary battery.

Claims

1. A lithium-ion secondary battery, characterized in that, include: A positive electrode containing a positive electrode compound and a negative electrode containing a negative electrode compound. The positive electrode mixture contains a positive electrode active substance represented by the following formula (1). Li 1+X M A O2(1) In the formula: X satisfies -0.15 ≤ X ≤ 0.15, M A This represents an element group that, in addition to containing at least one of Mn and Al, also contains Ni and Co. The negative electrode mixture comprises: a negative electrode active material containing carbon-based materials, a negative electrode additive containing copper oxide, and a binder. The negative electrode mixture comprises copper oxide at a concentration of 0.5 wt% to 15 wt% based on the total weight of the negative electrode active material and the negative electrode additive. The negative electrode active material has a median diameter of 4–20 μm, and the negative electrode additive has a median diameter smaller than that of the negative electrode active material, and within the range of 1–10 μm. Both the negative electrode active material and the negative electrode additive are in granular form. The negative electrode active material and the negative electrode additive are independent particles that do not combine with each other. The copper oxide is Cu₂O, CuO, or a mixture thereof. The particulate negative electrode active materials are electrically connected to each other without being hindered by the particulate negative electrode additives, thus suppressing the increase in the internal resistance of the lithium-ion secondary battery.

2. The lithium-ion secondary battery as described in claim 1, characterized in that: The copper oxide is Cu2O. The negative electrode mixture contains copper oxide at a concentration of 0.9 wt% or more and 15 wt% or less, based on the total weight of the negative electrode active material and the negative electrode additive.

3. The lithium-ion secondary battery as described in claim 2, characterized in that: The negative electrode mixture contains copper oxide at a concentration of 1.4 wt% or more and 12 wt% or less, based on the total weight of the negative electrode active material and the negative electrode additive.

4. The lithium-ion secondary battery as described in claim 1, characterized in that: The copper oxide is CuO. The negative electrode mixture comprises copper oxide at a concentration of 0.5 wt% or more and 8.3 wt% or less, based on the total weight of the negative electrode active material and the negative electrode additive.

5. The lithium-ion secondary battery as described in claim 4, characterized in that: The negative electrode mixture contains copper oxide at a concentration of 0.78 wt% or more and 6.7 wt% or less, based on the total weight of the negative electrode active material and the negative electrode additive.

6. A method for manufacturing a negative electrode for a lithium-ion secondary battery, characterized in that, include: A mixture of anode active material containing carbon-based materials, anode additive containing copper oxide, and binder is prepared. and The mixture is coated onto the negative electrode current collector. The mixture contains copper oxide at a concentration of 0.5 wt% to 15 wt% based on the total weight of the negative electrode active material and the negative electrode additive. The negative electrode active material has a median diameter of 4–20 μm, and the negative electrode additive has a median diameter smaller than that of the negative electrode active material, and within the range of 1–10 μm. Both the negative electrode active material and the negative electrode additive are in granular form. The negative electrode active material and the negative electrode additive are independent particles that do not combine with each other. The copper oxide is Cu₂O, CuO, or a mixture thereof. The particulate negative electrode active materials are electrically connected to each other without being hindered by the particulate negative electrode additives, thus suppressing the increase in the internal resistance of the lithium-ion secondary battery.

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