Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/058—Construction or manufacture
  • H01M10/0585—Construction or manufacture of accumulators having only flat construction elements, i.e. flat positive electrodes, flat negative electrodes and flat separators
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/058—Construction or manufacture
  • H01M10/0587—Construction or manufacture of accumulators having only wound construction elements, i.e. wound positive electrodes, wound negative electrodes and wound separators
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/04—Construction or manufacture in general
  • H01M10/0431—Cells with wound or folded electrodes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/052—Li-accumulators
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
  • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
  • H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/362—Composites
  • H01M4/364—Composites as mixtures
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
  • H01M4/386—Silicon or alloys based on silicon
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
  • H01M4/483—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides for non-aqueous cells
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
  • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
  • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
  • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
  • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
  • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
  • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
  • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
  • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
  • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
  • H01M4/624—Electric conductive fillers
  • H01M4/625—Carbon or graphite
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
  • H01M50/10—Primary casings; Jackets or wrappings
  • H01M50/102—Primary casings; Jackets or wrappings characterised by their shape or physical structure
  • H01M50/105—Pouches or flexible bags
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M2004/021—Physical characteristics, e.g. porosity, surface area
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
  • H01M2004/027—Negative electrodes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
  • H01M2004/028—Positive electrodes
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
  • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

• This disclosure relates to secondary batteries, positive electrodes, and compositions for positive electrode mixture layers.
• Secondary batteries are small, lightweight, and have a high voltage, making them widely used in electronic devices such as notebook PCs, mobile phones, smartphones, and tablet PCs.
• EVs electric vehicles
• HEVs hybrid electric vehicles
• positive electrode active materials has a drawback in that it is difficult to achieve both cycle characteristics and rate characteristics, compared to conventional active materials such as Li a CoO 2 and Li a (Ni 1/3 Mn 1/3 Co 1/3 ) O 2 (0 ⁇ a ⁇ 1).
• a positive electrode for a lithium-ion secondary battery is characterized by containing olivine-type lithium iron phosphate and a carbon black composite in which fibrous carbon and carbon black are linked together and the ash content as specified in JIS K 1469 is 1.0 mass% or less (see, for example, Patent Document 1).
• Patent Document 1 does not consider methods for improving the rate characteristics and cycle characteristics of secondary batteries having a structure in which positive and negative electrodes are stacked in the thickness direction, such as laminate-type secondary batteries.
• the present disclosure has been made in consideration of the above-mentioned conventional circumstances, and aims to provide a secondary battery having a structure in which multiple positive electrodes and negative electrodes are stacked in the thickness direction and which has excellent rate characteristics and cycle characteristics, and a composition for a positive electrode and a positive electrode mixture layer that can be used to fabricate a secondary battery having a structure in which multiple positive electrodes and negative electrodes are stacked in the thickness direction and which has excellent rate characteristics and cycle characteristics.
• a secondary battery including a positive electrode including a positive electrode current collector and a positive electrode mixture layer containing a positive electrode active material disposed on the positive electrode current collector, a negative electrode including a negative electrode current collector and a negative electrode mixture layer containing a negative electrode active material disposed on the negative electrode current collector, and an exterior material that houses the positive electrode and the negative electrode, the secondary battery having a structure in which the positive electrode and the negative electrode are laminated in a thickness direction,
• the positive electrode mixture layer contains fibrous carbon, and when the secondary battery is discharged from a fully charged state to a discharge end voltage at a current of 5 C, ⁇ /A is 0.35 (° C./Ah) or less, where ⁇ (° C.) is a standard deviation of temperature rise at temperature measurement points on the exterior material, and A (Ah) is a rated capacity of the battery.
• ⁇ 2> The secondary battery according to ⁇ 1>, wherein when the secondary battery is discharged at a current of 5 C from a fully charged state to a discharge cut-off voltage, the ⁇ /A is 0.30 (° C./Ah) or less.
• ⁇ 3> The secondary battery according to ⁇ 1> or ⁇ 2>, wherein when the secondary battery is charged at a current of 5 C from a fully discharged state to a charge cut-off voltage, the ⁇ /A is 0.25 (° C./Ah) or less.
• ⁇ 4> The secondary battery according to any one of ⁇ 1> to ⁇ 3>, wherein the average electrode area per positive electrode is 20 cm 2 to 10,000 cm 2 .
• ⁇ 5> The secondary battery according to any one of ⁇ 1> to ⁇ 4>, wherein the secondary battery is a laminate type.
• ⁇ 6> The secondary battery according to ⁇ 5>, wherein the number of layers of the positive electrodes and the negative electrodes is 4 or more.
• ⁇ 7> The secondary battery according to any one of ⁇ 1> to ⁇ 4>, wherein the secondary battery is a wound type.
• ⁇ 8> The secondary battery according to ⁇ 7>, wherein the number of windings is 4 or more.
• ⁇ 9> The secondary battery according to any one of ⁇ 1> to ⁇ 8>, wherein the positive electrode mixture layer further contains carbon black.
• ⁇ 10> The secondary battery according to any one of ⁇ 1> to ⁇ 9>, wherein the positive electrode mixture layer and the negative electrode mixture layer each have a thickness of 30 ⁇ m or more.
• ⁇ 11> The secondary battery according to any one of ⁇ 1> to ⁇ 10>, wherein the positive electrode mixture layer has a density of 3.0 g/cm 3 or more, and the negative electrode mixture layer has a density of 1.3 g/cm 3 or more.
• ⁇ 12> The secondary battery according to any one of ⁇ 1> to ⁇ 11>, wherein the positive electrode mixture layer has a basis weight of 10.0 mg/ cm2 or more and the negative electrode mixture layer has a basis weight of 5.0 mg/ cm2 or more.
• the positive electrode active material contains LiMPO 4 (M is at least one selected from Fe, Co, Mn, and Ni).
• M is at least one selected from Fe, Co, Mn, and Ni.
• ⁇ 16> The secondary battery according to ⁇ 15>, wherein the positive electrode mixture layer has a density of 2.0 g/cm 3 or more, and the negative electrode mixture layer has a density of 1.3 g/cm 3 or more.
• the negative electrode active material contains at least one selected from the group consisting of Si, SiO x (0 ⁇ x ⁇ 2), soft carbon, hard carbon, graphite, a composite of silicon and carbon, Li 4 Ti 5 O 12 , and metallic Li.
• the negative electrode active material contains graphite.
• a positive electrode comprising a positive electrode current collector and a positive electrode mixture layer containing a positive electrode active material disposed on the positive electrode current collector,
• the positive electrode mixture layer contains fibrous carbon
• the secondary battery has a structure in which the positive electrode and the negative electrode are laminated in a thickness direction, and the secondary battery is discharged at a current of 5 C from a fully charged state to a discharge end voltage, the standard deviation of the temperature rise at temperature measurement points on the exterior material is ⁇ (° C.), and the rated capacity of the battery is A (Ah).
• This positive electrode has a structure in which the positive electrode and the negative electrode are laminated in a thickness direction, and the secondary battery is discharged at a current of 5 C from a fully charged state to a discharge end voltage.
• the secondary battery including: a positive electrode including a positive electrode current collector and a positive electrode mixture layer formed from the composition for a positive electrode mixture layer disposed on the positive electrode current collector; a negative electrode; and an exterior material that houses the positive electrode and the negative electrode, the secondary battery having a structure in which a plurality of positive electrodes and a plurality of negative electrodes are laminated in a thickness direction, the secondary battery being discharged at a current of 5 C from a fully charged
• a secondary battery having a structure in which multiple positive electrodes and negative electrodes are stacked in the thickness direction and which has excellent rate characteristics and cycle characteristics, and a composition for a positive electrode and a positive electrode mixture layer that can fabricate a secondary battery having a structure in which multiple positive electrodes and negative electrodes are stacked in the thickness direction and which has excellent rate characteristics and cycle characteristics.
• FIG. 2 is a cross-sectional view in the thickness direction of a laminated secondary battery.
• FIG. 1 is a perspective view of a laminated secondary battery.
• FIG. 2 is a perspective view of a positive electrode, a negative electrode, and a separator housed in an exterior material of a laminated secondary battery.
• 1 is a graph showing the measurement results of initial DCR in Example 1 and Comparative Example 1.
• 1 is a graph showing the DCR change rate when the positive electrode basis weight is 17.0 mg/cm 2 in Example 1 and Comparative Example 1.
• 1 is a graph showing the relationship between the current value and the charge capacity ratio when the positive electrode coating weight is 17.0 mg/cm 2 in Example 1 and Comparative Example 1.
• 1 is a graph showing the relationship between the current value and the charge capacity ratio when the positive electrode coating weight is 24.5 mg/cm 2 in Example 1 and Comparative Example 1.
• 1 is a graph showing the discharge capacity retention rate when a high-rate charge/discharge test was performed in Example 2 and Comparative Example 2.
• 1 is a graph showing the ratio of the discharge capacity at 5 C charge/discharge when the discharge capacity at 0.2 C charge/discharge is taken as 100% in Example 2 and Comparative Example 2.
• 13 is a graph showing changes in a voltage curve over cycles in Comparative Example 2.
• 11 is a graph showing changes in a voltage curve over cycles in Example 2.
• 1 is a graph showing voltage curves during charging and discharging after 400 cycles of a high-rate charge-discharge test in Example 2 and Comparative Example 2.
• the term "step” includes not only a step that is independent of other steps, but also a step that cannot be clearly distinguished from other steps as long as the purpose of the step is achieved.
• the numerical range indicated using “to” includes the numerical values before and after "to” as the minimum and maximum values, respectively.
• the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages.
• the upper or lower limit value of the numerical range may be replaced with a value shown in the examples.
• each component may contain multiple types of the corresponding substance.
• the content or amount of each component means the total content or amount of the multiple substances present in the composition, unless otherwise specified.
• the particles corresponding to each component may include multiple types.
• the particle size of each component means the value for a mixture of the multiple types of particles present in the composition, unless otherwise specified.
• the terms "layer” and “film” include cases where the layer or film is formed over the entire area when the area in which the layer or film is present is observed, as well as cases where the layer or film is formed over only a portion of the area.
• laminate refers to stacking layers, where two or more layers may be bonded together or two or more layers may be removable.
• the secondary battery of the present disclosure is a secondary battery including a positive electrode including a positive electrode current collector and a positive electrode mixture layer containing a positive electrode active material disposed on the positive electrode current collector, a negative electrode including a negative electrode current collector and a negative electrode mixture layer containing a negative electrode active material disposed on the negative electrode current collector, and an exterior material that houses the positive electrode and the negative electrode, wherein the positive electrode and the negative electrode have a structure in which a plurality of layers are laminated in a thickness direction, the positive electrode mixture layer contains fibrous carbon, and when the secondary battery is discharged from a fully charged state to a discharge end voltage with a current of 5 C, ⁇ /A is 0.35 (° C./Ah) or less, where ⁇ (° C.) is a standard deviation of temperature rise at temperature measurement points on the exterior material, and A (Ah) is a rated capacity of the battery.
• the positive electrode and the negative electrode have a structure in which multiple layers are stacked in the thickness direction, so that the temperature rise at the temperature measurement points on the exterior material can be measured, and the standard deviation of the temperature rise, which is the variation in the temperature rise at multiple temperature measurement points, can be evaluated. Furthermore, by adopting a positive electrode mixture layer containing fibrous carbon, it is easy to adjust ⁇ /A to 0.35 (°C/Ah) or less during high-rate discharge, and by setting ⁇ /A to 0.35 (°C/Ah) or less, it is assumed that the current flows more uniformly, the increase in DC resistance after cycling is reduced, and the cycle characteristics of the secondary battery are improved.
• the "fully charged state” refers to the state after the battery is charged at 0.2 C to an end voltage of 4.2 V or higher, in the case of a secondary battery.
• the "fully discharged state” refers to, in the case of a secondary battery, the state after the battery is discharged at 0.2 C until the end voltage is 2.8 V or less.
• the charge end voltage is set to 4.2V or higher, and the discharge end voltage is set to 2.8V or lower.
• the secondary battery may be in the form of a laminated secondary battery or a wound secondary battery, as long as it has a structure in which positive and negative electrodes housed in an exterior material are stacked in the thickness direction.
• a wound secondary battery may be, for example, a cylindrical secondary battery in which an electrode pair and an electrolyte obtained by rolling up a laminate in which positive and negative electrodes are stacked with a separator between them are enclosed in a cylindrical exterior body, or a cylindrical secondary battery in which a cell obtained by rolling up a laminate in which positive and negative electrodes are stacked with a solid electrolyte between them is enclosed in a cylindrical exterior body.
• the secondary battery may be a battery in which a laminate formed by stacking a positive electrode and a negative electrode with a separator between them and an electrolyte is housed in an exterior material, or a battery in which a laminate formed by stacking a positive electrode and a negative electrode with a solid electrolyte between them is housed in an exterior material.
• the number of stacked positive electrodes and negative electrodes may each be 2 or more, 3 or more, or 4 or more.
• stacking the positive electrodes and negative electrodes makes it possible to measure a temperature rise at a temperature measurement point on the exterior material, and by setting the standard deviation of the temperature rise within an appropriate range, a secondary battery excellent in rate characteristics and cycle characteristics can be obtained.
• the upper limit of the number of stacked positive electrodes and negative electrodes is not particularly limited, and may be, for example, 100 or less, or 50 or less.
• the number of layers means the number of windings.
• Figures 1 to 3 show examples of laminated secondary batteries.
• Figure 1 is a cross-sectional view of a laminated secondary battery in the thickness direction
• Figure 2 is a perspective view of a laminated secondary battery
• Figure 3 is a perspective view of the positive electrode, negative electrode, and separator housed in the exterior material of the laminated secondary battery.
• FIG. 1 in the secondary battery 10, a laminate formed by stacking a positive electrode 1 and a negative electrode 3 with a separator 5 interposed therebetween is housed in an exterior material 6.
• the positive electrode tab 2A and the negative electrode tab 2B extend to the outside of the exterior body 6.
• a secondary battery having six negative electrode layers and five positive electrode layers is illustrated, but in this disclosure, the number of negative electrode layers and positive electrode layers is not limited to these.
• the positive electrodes 1 and negative electrodes 3 are alternately arranged in the thickness direction. Furthermore, a separator 5 is arranged between the positive electrodes 1 and the negative electrodes 3.
• the positive electrodes 1 and negative electrodes 3 are arranged so that the positive electrode tabs 2A overlap each other and the negative electrode tabs 2B overlap each other when the various components are stacked.
• the positive electrodes 1, negative electrodes 3, and separators 5 arranged in this positional relationship are housed in an exterior material 6, and the electrolyte is then housed in the exterior material 6, after which the opening is sealed by heat fusion or the like, to obtain the laminate-type secondary battery 10 shown in FIG. 2.
• the standard deviation of the temperature rise at the temperature measurement points on the exterior material can be obtained, for example, as follows. First, the secondary battery is charged at a constant current of 0.2 C with a charge end voltage of 4.2 V, and then discharged at a constant current of 5 C with a discharge end voltage of 2.5 V. During this constant current discharge, the temperature is measured at seven points on the exterior material. For example, when measuring the temperature using the laminated secondary battery 10 shown in FIG. 2, the temperature may be measured in seven areas shown by dotted circles. In this case, from the viewpoint of grasping the temperature variation at each measurement point, it is desirable to set the distance between adjacent measurement points to 10 mm or more. The temperature measurement during charging is performed during constant current charging, when constant current discharge is performed at a current of 0.2 C with a discharge end voltage of 2.5 V, and then constant current charging is performed at a current of 5 C with a charge end voltage of 4.2 V.
• the temperature is measured in seven regions, and the temperature rise during charging (maximum temperature - minimum temperature) and the temperature rise during discharging (maximum temperature - minimum temperature) at each measurement point are determined. Then, the standard deviation ⁇ of the temperature rise during high-rate discharging can be determined from each measurement result of the temperature rise during discharging. Similarly, the standard deviation ⁇ of the temperature rise during high-rate charging can be determined from each measurement result of the temperature rise during charging.
• ⁇ /A is 0.35 (°C/Ah) or less, and from the viewpoint of rate characteristics and cycle characteristics, ⁇ /A is preferably 0.33 (°C/Ah) or less, more preferably 0.32 (°C/Ah) or less, and even more preferably 0.30 (°C/Ah) or less.
• the lower limit of the standard deviation of the temperature rise during discharge is not particularly limited, and may be, for example, 0.10 (° C./Ah) or more.
• ⁇ /A at the temperature measurement point on the exterior material is preferably less than 0.28 (° C./Ah), more preferably 0.25 (° C./Ah) or less, and even more preferably 0.20 (° C./Ah) or less.
• the lower limit of the standard deviation of the temperature rise during charging is not particularly limited, and may be, for example, 0.05 (° C./Ah) or more.
• the type of secondary battery is not particularly limited, and examples thereof include lithium-based secondary batteries, sodium-based secondary batteries, potassium-based secondary batteries, magnesium-based secondary batteries, aluminum-based secondary batteries, etc.
• lithium-based secondary batteries that can achieve high energy density at high voltage and sodium-based secondary batteries that can be reduced in cost are preferred.
• an example of a lithium-based secondary battery will be described, but the present invention is not limited thereto.
• the secondary battery includes a positive electrode including a positive electrode current collector and a positive electrode mixture layer containing a positive electrode active material disposed on the positive electrode current collector.
• the material of the positive electrode current collector is not particularly limited as long as it is a material that is not oxidized and dissolved at a high potential and has electron conductivity, and can be selected from aluminum, copper, nickel, titanium, stainless steel, etc.
• the state of the positive electrode current collector is not particularly limited, and can be selected from foil, perforated foil, mesh, etc. As an example, an aluminum foil is used as the positive electrode current collector.
• a positive electrode mixture layer composition containing a positive electrode active material and fibrous carbon, and optionally carbon black, a binder, a solvent, etc. is applied onto a positive electrode current collector, the applied slurry is dried, and then pressed to form a positive electrode mixture layer on the positive electrode current collector.
• the thickness of the positive electrode mixture layer may be 30 ⁇ m or more, 50 ⁇ m to 70 ⁇ m, or 70 ⁇ m to 100 ⁇ m, from the viewpoints of energy density and safety.
• the density of the positive electrode mixture layer may be 2.0 g/cm 3 or more, 3.0 g/cm 3 or more, or may be 3.0 g/cm 3 to 4.0 g/cm 3 .
• the basis weight of the positive electrode mixture layer may be 10.0 mg/cm 2 or more, or may be 10.0 mg/cm 2 to 30.0 mg/cm 2 from the viewpoints of energy density and safety.
• the average electrode area (average positive electrode area and average negative electrode area) per sheet may be 20 cm 2 to 10,000 cm 2 , or may be 300 cm 2 to 10,000 cm 2 .
• the positive electrode mixture layer includes a positive electrode active material.
• the positive electrode active material can be appropriately selected according to the type of secondary battery, and examples thereof include compounds containing at least one of lithium, sodium, potassium, magnesium, and aluminum. Examples of the positive electrode active material include oxides containing nickel, phosphates having an olivine structure, and the like.
• Examples of the positive electrode active material represented by LiMPO 4 include LiFePO 4 , LiFe 0.5 Mn 0.5 PO 4 , LiFe 0.3 Mn 0.7 PO 4 , LiCoPO 4 , and LiCo 0.5 Mn 0.5 PO 4 .
• At least a portion of the surface of the positive electrode active material may be coated with amorphous carbon.
• Methods for coating with amorphous carbon include known methods such as heating the positive electrode active material and flowing a hydrocarbon gas therethrough to perform CVD, or mixing a carbon precursor and the positive electrode active material and carbonizing the carbon precursor by performing a heat treatment in a state in which the carbon precursor is attached to at least a portion of the surface of the positive electrode active material.
• the 50% particle size (D n50 ) of the primary particle size of the positive electrode active material in the number-based cumulative particle size distribution is preferably 0.01 ⁇ m or more, more preferably 0.02 ⁇ m or more, and even more preferably 0.03 ⁇ m or more, from the viewpoint of obtaining a sufficient capacity ratio.
• the 50% particle size (D n50 ) of the primary particle size of the positive electrode active material in the number-based cumulative particle size distribution is preferably 2.0 ⁇ m or less, more preferably 1.7 ⁇ m or less, and even more preferably 1.5 ⁇ m or less, from the viewpoint of obtaining sufficient rate characteristics.
• the 50% particle diameter (D n50 ) of the primary particle diameter of the positive electrode active material in the number-based cumulative particle size distribution can be obtained by arbitrarily selecting 100 primary particles of the positive electrode active material from the SEM photograph and cross-sectional SEM photograph of the electrode, and arithmetically averaging the results of measuring the maximum particle lengths using image recognition software.
• the 50% particle size (D n50 ) in the number-product-based cumulative particle size distribution of the secondary particles of the positive electrode active material is preferably 0.5 ⁇ m or more, more preferably 1.0 ⁇ m or more, and even more preferably 2.0 ⁇ m or more, from the viewpoints of excellent powder handleability and easy increase in electrode density.
• the 50% particle size (D n50 ) in the number-product-based cumulative particle size distribution of the secondary particles of the positive electrode active material is preferably 30.0 ⁇ m or less, more preferably 25.0 ⁇ m or less, and even more preferably 20.0 ⁇ m or less, from the viewpoints of obtaining sufficient rate characteristics and preventing abnormal unevenness from occurring during electrode coating.
• the 50% particle diameter (D n50 ) of the secondary particle diameter of the positive electrode active material in the number-based cumulative particle size distribution can be obtained by arbitrarily selecting 100 secondary particles of the positive electrode active material from the SEM photograph and cross-sectional SEM photograph of the electrode, and arithmetically averaging the results of measuring the maximum particle lengths using image recognition software.
• the primary particle of the positive electrode active material refers to one that can be recognized as a single grain in an SEM photograph at 3,000 to 30,000 magnifications.
• the secondary particles of the positive electrode active material are agglomerates formed by the aggregation of the primary particles.
• the secondary particles of the positive electrode active material can be confirmed from a SEM photograph.
• the positive electrode active material is simply referred to as "particles", it refers to primary particles or secondary particles.
• the content of the positive electrode active material is preferably 90.0 mass% or more, more preferably 93.0 mass% or more, and even more preferably 95.0 mass% or more, from the viewpoint of positive electrode capacity.
• the content of the positive electrode active material is preferably 98.0% by mass or less, more preferably 97.0% by mass or less, and even more preferably 96.5% by mass or less, from the viewpoint of ensuring the amount of other components.
• the positive electrode mixture layer contains fibrous carbon.
• fibrous carbon include carbon fiber, vapor grown carbon fiber, carbon nanotubes such as single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT), and carbon nanofibers.
• Vapor grown carbon fiber is preferred because it has excellent dispersibility, can reduce the resistance of the electrode, and can suitably suppress the variation in temperature rise during high-rate discharge.
• the vapor grown carbon fiber may be combined with other fibrous carbon, for example, carbon nanotubes such as single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT).
• the positive electrode mixture layer may contain one type of fibrous carbon or may contain two or more types of fibrous carbon.
• the average fiber diameter of the fibrous carbon is preferably 1 nm to 200 nm, more preferably 100 nm to 200 nm, and even more preferably 120 nm to 180 nm.
• the average fiber diameter of the fibrous carbon can be calculated from the arithmetic mean of the diameters of 300 arbitrary fibers observed by SEM of the electrode.
• the diameter of one fiber can be calculated by measuring the width of a certain fiber at 10 arbitrary points in the SEM photograph and calculating the arithmetic mean.
• the width of the fiber refers to the dimension of the fiber in the direction perpendicular to the longitudinal direction.
• the average fiber length of the fibrous carbon is preferably 1 ⁇ m to 20 ⁇ m, more preferably 3 ⁇ m to 15 ⁇ m, and even more preferably 4 ⁇ m to 10 ⁇ m.
• the average fiber length of fibrous carbon can be measured as follows. First, the electrodes are washed with a solvent, and the binder and other materials are removed. The resulting powder is dispersed in a dispersion medium, spread on aluminum foil or the like, dried, and observed under a SEM. The length of 300 random fibers along the fiber axis is measured, and the average fiber length can be calculated by taking the arithmetic average.
• the fibrous carbon preferably contains fibrous carbon having an average fiber diameter of 100 nm to 200 nm and an average fiber length of 3 ⁇ m to 15 ⁇ m, and more preferably contains vapor-grown carbon fibers or carbon nanotubes having an average fiber diameter of 100 nm to 200 nm and an average fiber length of 3 ⁇ m to 15 ⁇ m.
• fibrous carbon examples include VGCF (registered trademark)-X (manufactured by Showa Denko K.K.) and VGCF (registered trademark)-H (manufactured by Showa Denko K.K.).
• the content of fibrous carbon in the positive electrode mixture layer is preferably 0.1 mass% or more, more preferably 0.3 mass% or more, and even more preferably 0.5 mass% or more.
• the content of fibrous carbon is preferably 3.0 mass% or less, more preferably 2.0 mass% or less, and even more preferably 1.0 mass% or less, from the viewpoint of ensuring the capacity of the positive electrode.
• the ratio of vapor-grown carbon fiber to carbon nanotubes is not particularly limited. From the viewpoint of cycle characteristics during high-rate charging and discharging, for example, the ratio of vapor-grown carbon fiber:carbon nanotubes may be 20:1 to 1:1, 10:1 to 1:1, or 5:1 to 2:1.
• the positive electrode mixture layer may further contain carbon black.
• Carbon black is used as a conductive assistant for secondary batteries.
• Examples of carbon black include DENKA BLACK (registered trademark, manufactured by Denka Co., Ltd.), C-NERGY (registered trademark) Super C45, C65 (manufactured by Imerys Graphite & Carbon), and KETJEN BLACK (manufactured by KETJEN BLACK INTERNATIONAL).
• the primary particle diameter of carbon black may be 10 nm to 100 nm.
• the primary particle here refers to the part that corresponds to one bead in a bead-like structure called an aggregate. If the primary particle diameter of carbon black is within this range, it tends to be uniformly dispersed on the active material surface. From the viewpoint of improving dispersibility, the primary particle diameter of carbon black is preferably 20 nm to 80 nm, and more preferably 30 nm to 70 nm.
• the primary particle diameter of carbon black can be determined by randomly selecting 100 primary carbon black particles from the SEM photographs and cross-sectional SEM photographs of the electrode, and calculating the arithmetic average of the maximum particle length measurements using image recognition software.
• the carbon black content is preferably 0.2 mass% or more, more preferably 0.6 mass% or more, and even more preferably 1.0 mass% or more, from the viewpoint of obtaining excellent cycle characteristics and rate characteristics.
• the carbon black content is preferably 6.0 mass% or less, more preferably 4.0 mass% or less, and even more preferably 2.0 mass% or less, from the viewpoint of ensuring the capacity of the positive electrode.
• the mass ratio of carbon black to fibrous carbon is preferably 1:5 to 5:1, more preferably 1:4 to 4:1, and even more preferably 1:1 to 3:1, from the viewpoint of further reducing the resistance of the positive electrode mixture layer by combining the two.
• the positive electrode mixture layer may contain a binder.
• a binder used in a positive electrode mixture layer for a normal lithium ion secondary battery can be suitably used.
• the binder include polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PTFE).
• the binder content is preferably 1.0 mass% or more, more preferably 1.5 mass% or more, and even more preferably 2.0 mass% or more, from the viewpoint of obtaining the binder function.
• the binder content is preferably 5.0 mass% or less, more preferably 4.5 mass% or less, and even more preferably 4.0 mass% or less, from the viewpoint of suppressing an increase in the resistance of the positive electrode.
• the positive electrode mixture layer may contain other components such as a dispersant, an additive, etc.
• a dispersant for dispersing the positive electrode active material, agents for surface modification of the positive electrode active material, etc.
• the secondary battery includes a negative electrode including a negative electrode current collector and a negative electrode mixture layer containing a negative electrode active material disposed on the negative electrode current collector.
• the material of the negative electrode current collector is not particularly limited as long as it is an electron conductive material, and can be selected from aluminum, copper, nickel, titanium, stainless steel, etc.
• the state of the negative electrode current collector is not particularly limited, and can be selected from foil, perforated foil, mesh, etc. As an example, a copper foil is used as the negative electrode current collector.
• a negative electrode mixture layer composition containing a negative electrode active material and, if necessary, a conductive additive, binder, solvent, etc. is applied onto a negative electrode current collector, the applied slurry is dried, and then pressed to form a negative electrode mixture layer on the negative electrode current collector.
• the thickness of the negative electrode mixture layer may be 30 ⁇ m or more, may be 50 ⁇ m to 100 ⁇ m, or may be 100 ⁇ m to 150 ⁇ m.
• the density of the negative electrode mixture layer may be 1.3 g/cm 3 or more, or may be 1.5 g/cm 3 to 2.0 g/cm 3 , from the viewpoints of energy density and safety.
• the weight per unit area of the negative electrode mixture layer may be 5.0 mg/cm 2 or more, or may be 10.0 mg/cm 2 to 20.0 mg/cm 2 , from the viewpoints of energy density and safety.
• the negative electrode mixture layer contains a negative electrode active material.
• the negative electrode active material include Si, SiO x (0 ⁇ x ⁇ 2), soft carbon, hard carbon, graphite, a composite of silicon and carbon, Li 4 Ti 5 O 12 , and metallic Li. Among them, it is preferable that the negative electrode active material contains graphite. At least a part of the surface of the negative electrode active material may be coated with amorphous carbon.
• the negative electrode mixture layer may contain a conductive additive, such as the above-mentioned carbon materials including fibrous carbon, carbon black, and graphene.
• the negative electrode mixture layer may contain a binder.
• the binder include PVdF, PTFE, and the like, as in the positive electrode mixture layer, as well as styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), and the like.
• the exterior material for housing the positive electrode and the negative electrode is not limited as long as it can house the positive electrode and the negative electrode, and if necessary, a separator and an electrolytic solution or a solid electrolyte, etc.
• Examples of the exterior material include battery packs that are usually available on the market, 18650 type cylindrical cells, and those packed in aluminum packaging material, and the exterior material can be freely designed and used.
• the secondary battery may have a separator between the positive electrode and the negative electrode.
• the separator can be freely selected from those that can be used in general secondary batteries, such as microporous films made of polyethylene or polypropylene. Separators containing particles such as SiO 2 and Al 2 O 3 as fillers, and separators having these particles attached to the surface can also be used.
• an electrolyte may be contained in the exterior material.
• an electrolyte that can be used in a normal secondary battery can be suitably used.
• an organic solvent in which 0.5 mol/L to 2.0 mol/L of lithium salt is dissolved can be used.
• lithium salt examples include LiPF 6 , LiBF 4 , LiClO 4 , LiAsF 6 , and LiFSI.
• organic solvents examples include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DEC), diethyl carbonate (DEC), and propylene carbonate (PC).
• EC ethylene carbonate
• EMC ethyl methyl carbonate
• DEC dimethyl carbonate
• DEC diethyl carbonate
• PC propylene carbonate
• additives for the electrolyte include vinylene carbonate (VC), propane sultone (PS), and fluoroethylene carbonate (FEC).
• the content of the additive is preferably 0.01% to 20% by mass, more preferably 0.1% to 10% by mass, and even more preferably 0.5% to 5% by mass, relative to 100% by mass of the organic solvent.
• An ionic liquid may be used as the electrolyte, or the ionic liquid may be used in combination with the organic solvent described above.
• the ionic liquid is not particularly limited, and examples thereof include a combination of a cation such as an imidazolium cation, a pyrrolidinium cation, a piperidinium cation, or an ammonium cation with an anion such as a bis(trifluoromethane)sulfonamide anion.
• Solid electrolyte A solid electrolyte may be used as the electrolyte.
• a separator is not required, and a battery (for example, an all-solid-state lithium ion secondary battery) can be formed in which a positive electrode and a negative electrode are sandwiched between the solid electrolyte.
• Examples of the solid electrolyte include polymer electrolytes and inorganic solid electrolytes.
• Examples of the polymer electrolyte include, but are not limited to, polymers such as polyethylene oxide impregnated with the lithium salts.
• Examples of the inorganic solid electrolyte include, but are not limited to, Li 13 Ti 1.7 Al 0.3 (PO 4 ) 3 , Li 2 S-P 2 S 5 , etc.
• the positive electrode of the secondary battery of the present disclosure is obtained by applying a positive electrode mixture layer composition containing a positive electrode active material and fibrous carbon on a positive electrode current collector, and further containing carbon black, a binder, a solvent, etc. as necessary, drying the applied slurry, and then pressing to form a positive electrode mixture layer on the positive electrode current collector.
• the positive electrode mixture layer composition of the present disclosure is a positive electrode mixture layer composition used to form a positive electrode mixture layer containing a positive electrode active material, and the positive electrode mixture layer composition contains fibrous carbon. Furthermore, when a secondary battery is formed having a structure in which a positive electrode mixture layer formed using the positive electrode mixture layer composition of the present disclosure, a negative electrode, and an exterior material that houses the positive electrode and the negative electrode, and the positive electrode and the negative electrode are laminated in a thickness direction, when the secondary battery is discharged at a current of 5C from a fully charged state to a discharge end voltage, ⁇ (°C) is the standard deviation of the temperature rise at the temperature measurement points on the exterior material, and A (Ah) is the rated capacity of the battery. ⁇ /A is 0.35 (°C/Ah) or less. As a result, by using the composition for positive electrode mixture layer of the present disclosure, it is possible to fabricate a secondary battery that has excellent rate characteristics and cycle characteristics.
• the preferred configurations of the positive electrode active material and fibrous carbon contained in the composition for the positive electrode mixture layer of the present disclosure, as well as the carbon black, binder, and other components contained as necessary, are the same as those described above in the section on the secondary battery of the present disclosure.
• composition for the positive electrode mixture layer of the present disclosure may contain a solvent.
• the solvent is not particularly limited, and an example of the solvent is N-methyl-2-pyrrolidone (NMP).
• the composition for a positive electrode mixture layer of the present disclosure can be prepared, for example, as follows. (1) The positive electrode active material and fibrous carbon are weighed, and further, if necessary, carbon black, a binder, etc. are weighed, and these are mixed while adding a solvent. (2) The mixture obtained in (1) above is kneaded while adding a solvent to obtain a composition for a positive electrode mixture layer having an appropriate viscosity.
• composition for the positive electrode mixture layer may be applied onto the positive electrode current collector using a doctor blade or a coating machine, and the positive electrode current collector on which the composition for the positive electrode mixture layer has been applied may be placed on a heating device such as a hot plate to dry the solvent. After that, vacuum drying is performed to remove the remaining solvent.
• the product obtained after removing the solvent is pressed and molded using a roll press, uniaxial press, or the like to obtain a positive electrode.
• the positive electrode of the present disclosure includes a positive electrode current collector and a positive electrode mixture layer including a positive electrode active material disposed on the positive electrode current collector, the positive electrode mixture layer including fibrous carbon. Furthermore, when a secondary battery is formed by discharging the secondary battery from a fully charged state to a discharge end voltage at a current of 5 C, the standard deviation of the temperature rise at the temperature measurement points on the exterior material is ⁇ (° C.), and the rated capacity of the battery is A (Ah). ⁇ /A is 0.35 (° C./Ah). As a result, by using the positive electrode of the present disclosure, it is possible to fabricate a secondary battery having excellent rate characteristics and cycle characteristics.
• the positive electrode of the present disclosure can be prepared, for example, using the positive electrode mixture layer composition of the present disclosure.
• the electrodes can be stacked and packed for use, or the single cells can be connected in series to be used as a battery, module, etc.
• the secondary battery disclosed herein can be used as a power source for electronic devices such as smartphones, tablet PCs, and personal digital assistants; as a power source for electric motors for power tools, vacuum cleaners, electric bicycles, drones, and electric vehicles; and for storing electricity obtained from fuel cells, solar power generation, wind power generation, and the like.
• Example 1 (Preparation of Positive Electrode)
• NMC811 Li( Ni0.8Mn0.1Co0.1 ) O2 , 1.0 part by mass of carbon black (primary particle Dn50 : 100 nm ), 0.5 parts by mass of fibrous carbon having an average fiber diameter of 150 nm and an average fiber length of 6 ⁇ m, and 2.0 parts by mass of PVdF was weighed and mixed in a kneader. Thereafter, the mixture was mixed in the kneader while appropriately adding NMP to prepare a positive electrode slurry with adjusted viscosity.
• the 50% particle size (D n50 ) of the primary particles in the number-based cumulative particle size distribution of the positive electrode active material NMC811 was 0.5 ⁇ m, and the 50% particle size (D n50 ) of the secondary particles in the number-based cumulative particle size distribution was 10.1 ⁇ m.
• the positive electrode slurry was applied to an aluminum foil having a thickness of 20 ⁇ m using a roll coater, dried, and then vacuum-dried to obtain a positive electrode sheet.
• the thickness of the positive electrode mixture layer was adjusted to 53 ⁇ m by roll pressing, and the density of the positive electrode mixture layer was adjusted to 3.2 g/ cm3 .
• the negative electrode slurry was applied to a copper foil having a thickness of 20 ⁇ m using a roll coater, dried, and then vacuum-dried to obtain a negative electrode sheet.
• the thickness of the negative electrode mixture layer was adjusted to 88 ⁇ m by roll pressing, and the density of the negative electrode mixture layer was adjusted to 1.4 g/ cm3 .
• a laminate type full cell for evaluation of Example 1 was prepared in a glove box maintained in a dry argon gas atmosphere with a dew point of ⁇ 80° C. or less as follows.
• the positive electrode sheet and the negative electrode sheet obtained by the above-mentioned positive electrode preparation and negative electrode preparation were punched out to obtain a positive electrode and a negative electrode having an area of 20 cm 2.
• An Al tab was attached to the Al foil of the positive electrode, and a Ni tab was attached to the Cu foil of the negative electrode.
• a polypropylene microporous membrane as a separator was sandwiched between the negative electrode and the positive electrode to obtain a stacked cell having a plurality of negative electrodes and a plurality of positive electrodes, and a separator was disposed between the negative electrode and the positive electrode.
• the stacked cell was entirely wrapped in an aluminum laminate packaging material except for the tab, and 2890 ⁇ L of electrolyte was injected into it. Thereafter, the opening was sealed by heat fusion to prepare a laminated full cell for evaluation, which is a secondary battery.
• the electrolyte solution was prepared by mixing ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a volume ratio of 3:5:2, mixing vinylene carbonate (VC) to a concentration of 1 mass%, and dissolving the electrolyte LiPF6 in the mixture to a concentration of 1.2 mol/L.
• the design capacity of the laminated full cell for evaluation was 1000 mAh.
• laminate-type full cells for evaluation having different capacity ratios (negative electrode/positive electrode) and basis weights of the positive electrode mixture layer were produced using stacked cells having different numbers of stacked negative electrodes and positive electrodes as shown in Table 1.
• a laminate-type full cell for evaluation was produced in the same manner as in Example 1 using the positive electrode sheet produced in Comparative Example 1 and the negative electrode sheet produced in Example 1.
• laminate-type full cells for evaluation having different capacity ratios (negative electrode/positive electrode) and different basis weights of the positive electrode mixture layer were produced using stacked cells having different numbers of stacked negative electrodes and positive electrodes as shown in Table 1.
• the laminated full cell thus fabricated was subjected to an aging treatment.
• the laminated full cell after aging (positive electrode mixture layer basis weight 17.0 mg/ cm2 , capacity ratio (negative electrode/positive electrode) 1.1, 8 negative electrode layers and 7 positive electrode layers) was subjected to constant current charging at a current of 0.2 C with an end voltage of 4.2 V.
• constant current discharging was performed at a current of 5 C with an end voltage of 2.5 V.
• the temperature was measured at 7 points on the exterior material.
• constant current discharging was performed at a current of 0.2 C with an end voltage of 2.5 V.
• constant current charging was performed at a current of 5 C with an end voltage of 4.2 V.
• the temperature was measured at 7 points on the exterior material.
• the temperature was measured at the following locations in a plan view of the laminate-type full cell: (1) center, (2) upper left center (lower left tab), (3) upper right center (lower right tab), (4) left center, (5) right center, (6) lower left center, and (7) lower right center of the exterior material.
• the temperatures were measured at seven points on the exterior material during constant current charging and constant current discharging, and the temperature rise during charging (maximum temperature - minimum temperature) and the temperature rise during discharging (maximum temperature - minimum temperature) at each measurement point were calculated, and the standard deviation ⁇ of the temperature rise at the temperature measurement points was calculated. Furthermore, ⁇ /A (°C/Ah) was calculated, with the rated capacity of the battery being A (Ah). The results are shown in Tables 2 and 3.
• the DCR was measured at the 100th, 200th, 300th, 400th, 500th and 600th cycles as described below, and the DCR change (%) at each cycle was calculated relative to the reference (initial DCR value of Comparative Example 1 in FIG. 5 ) being 100%.
• the battery was charged and discharged at a constant current of 1 C for a predetermined number of times in a thermostatic chamber at 25° C., then fully charged, and discharged at 0.1 C to half the discharge capacity of the first cycle. After a 30-minute break, the battery was discharged at 1000 mA for 5 seconds.
• the cycle was performed by charging the laminated full cell at a constant current of 1 C in a thermostatic chamber at 25° C. with a final voltage of 4.2 V, and then discharging at a constant current of 1 C with a final voltage of 2.8 V.
• the charging operation to fully charge the cell and the discharging operation to make the soc 50% immediately before the DCR measurement in each cycle were not counted in the number of cycles.
• the DCR change (%) shown in Table 3 means, for Example 1, the rate of increase relative to the initial DCR value of Example 1, and for Comparative Example 1, the rate of increase relative to the initial DCR value of Comparative Example 1.
• Example 2 (Preparation of Positive Electrode)
• NMC811 Li( Ni0.8Mn0.1Co0.1 ) O2 , 1.1 parts by mass of carbon black (primary particle Dn50 : 100 nm ), 0.3 parts by mass of fibrous carbon having an average fiber diameter of 150 nm and an average fiber length of 6 ⁇ m, 0.1 parts by mass of multi-walled carbon nanotubes (MWCNT), and 2.0 parts by mass of PVdF was weighed and mixed in a kneader. Thereafter, the mixture was mixed in a kneader while appropriately adding NMP to prepare a positive electrode slurry with adjusted viscosity.
• NMC811 Li( Ni0.8Mn0.1Co0.1 ) O2
• carbon black primary particle Dn50 : 100 nm
• fibrous carbon having an average fiber diameter of 150 nm and an average fiber length of 6 ⁇ m 0.1 parts by mass of multi-walled carbon nanotubes (MWCNT)
• MWCNT multi-walled carbon nano
• the 50% particle size (D n50 ) of the primary particles in the number-based cumulative particle size distribution of the positive electrode active material NMC811 was 0.5 ⁇ m, and the 50% particle size (D n50 ) of the secondary particles in the number-based cumulative particle size distribution was 10.1 ⁇ m.
• the positive electrode slurry was applied to an aluminum foil having a thickness of 20 ⁇ m using a roll coater, dried, and then vacuum-dried to obtain a positive electrode sheet.
• the positive electrode mixture layer was roll-pressed to a thickness of 53 ⁇ m, a basis weight of 11.3 mg/ cm2 , and a density of 3.2 g/ cm3 .
• a negative electrode slurry was obtained in the same manner as in Example 1.
• the negative electrode slurry was applied to a copper foil having a thickness of 20 ⁇ m using a roll coater, dried, and then vacuum-dried to obtain a negative electrode sheet.
• the negative electrode mixture layer was roll-pressed to a thickness of 88 ⁇ m, a basis weight of 8 mg/ cm2 , and a density of 1.4 g/ cm3 .
• a laminate type full cell for evaluation of Example 2 was prepared in a glove box maintained in a dry argon gas atmosphere with a dew point of ⁇ 80° C. or less as follows.
• the positive electrode sheet and the negative electrode sheet obtained by the above-mentioned positive electrode preparation and negative electrode preparation were punched out to obtain a positive electrode and a negative electrode having an area of 20 cm 2.
• An Al tab was attached to the Al foil of the positive electrode, and a Ni tab was attached to the Cu foil of the negative electrode.
• a polypropylene microporous membrane as a separator was sandwiched between the negative electrode and the positive electrode to obtain a stacked cell having five negative electrodes and four positive electrodes, and a separator disposed between the negative electrode and the positive electrode.
• the stacked cell was entirely wrapped in an aluminum laminate packaging material except for the tab, and 1800 ⁇ L of electrolyte was injected into it. Thereafter, the opening was sealed by heat fusion to prepare a laminated full cell for evaluation, which is a secondary battery.
• the electrolyte solution was prepared by mixing ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a volume ratio of 3:5:2, mixing vinylene carbonate (VC) to a concentration of 1 mass%, and dissolving the electrolyte LiPF6 in the mixture to a concentration of 1.2 mol/L.
• the design capacity of the laminated full cell for evaluation was 570 mAh, and the capacity ratio (negative electrode/positive electrode) was 1.1.
• Comparative Example 2 A positive electrode sheet and a negative electrode sheet were produced in the same manner as in Comparative Example 1, except that the basis weight of the positive electrode mixture layer was 11.3 mg/cm 2 and the basis weight of the negative electrode mixture layer was 8 mg/cm 2 .
• a laminate-type full cell for evaluation was produced in the same manner as in Example 2 using the positive electrode sheet produced in Comparative Example 2 and the negative electrode sheet produced in Comparative Example 2.
• the laminated type full cells produced in Example 2 and Comparative Example 2 were subjected to pre-charging and aging treatments.
• the pre-charging was performed by placing the laminated full cell in a thermostatic chamber set at 45° C. under the conditions of CC/CV 0.03 C, 3.4 V, 0.01 C, cut off. After the pre-charging, gas was released.
• the aging treatment was performed as follows. First, the first charge was performed at 45°C under the conditions of CC/CV 0.1C 4.2V 0.02C Cut off. After the first charge, the laminated full cell was held for 12 hours and degassed. Next, the first discharge was performed at 25°C under the conditions of CC 0.1C, 2.8V. Then, the second charge was performed at 25°C under the conditions of CC/CV 0.2C 4.2V 0.05C Cut off, and the second discharge was performed at 25°C under the conditions of CC 0.2C, 2.8V.
• Example 2 had excellent cycle characteristics at a high rate, despite having the same cell capacity as Comparative Example 2.
• the discharge capacity retention ratio dropped sharply from around 230 cycles, but in Example 2, the drop in the discharge capacity retention ratio was gradual even after 400 cycles of charge and discharge at a high rate.
• 9 shows the ratio of the discharge capacity at 5 C charge/discharge to the discharge capacity at 0.2 C charge/discharge, which is taken as 100%. The decrease in discharge capacity during high-rate charge/discharge was smaller in Example 2 than in Comparative Example 2, and Example 2 was superior in high-rate discharge capacity.
• Example 2 The voltage curves obtained when the charge/discharge process was performed at a high rate in Example 2 and Comparative Example 2 are shown in Figures 10 and 11. As shown in Figure 10, Comparative Example 2 showed a voltage curve with a large IR drop from the beginning of the cycle, and degradation as the cycle progressed was significant. On the other hand, as shown in Figure 11, Example 2 showed a small IR drop, and the change in the voltage curve as the cycle progressed was small.
• Example 2 and Comparative Example 2 after 400 cycles of charge and discharge at a high rate, charging was performed under the conditions of CC/CV 0.2C, 4.2V, and 0.05C Cut off at 25° C., and then discharging was performed under the conditions of CC 0.2C and 2.8V Cut off at 25° C.
• the results are shown in FIG. 12, even after 400 cycles, almost no capacity degradation was observed and the shape of the voltage curve was good in Example 2.
• Comparative Example 2 the capacity was small and the curve showed a high resistance, and degradation of the cell was confirmed.

Landscapes

• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• General Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Inorganic Chemistry (AREA)
• Manufacturing & Machinery (AREA)
• Materials Engineering (AREA)
• Composite Materials (AREA)
• Crystallography & Structural Chemistry (AREA)
• Battery Electrode And Active Subsutance (AREA)
• Secondary Cells (AREA)

Priority Applications (5)

Applications Claiming Priority (2)

Publications (1)

Family

ID=91032918

Family Applications (1)

Country Status (7)

Citations (4)

Family Cites Families (6)

• 2023
  • 2023-10-31 JP JP2024557356A patent/JPWO2024101231A1/ja active Pending
  • 2023-10-31 WO PCT/JP2023/039354 patent/WO2024101231A1/ja not_active Ceased
  • 2023-10-31 US US18/862,045 patent/US20260188677A1/en active Pending
  • 2023-10-31 EP EP23888579.2A patent/EP4618213A4/en active Pending
  • 2023-10-31 CN CN202380037127.8A patent/CN119111008A/zh active Pending
  • 2023-10-31 KR KR1020247036279A patent/KR102874890B1/ko active Active
  • 2023-11-06 TW TW112142653A patent/TW202420620A/zh unknown

Patent Citations (4)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events