WO2023087214A1 - 一种电池包及其用电装置 - Google Patents

一种电池包及其用电装置 Download PDF

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WO2023087214A1
WO2023087214A1 PCT/CN2021/131491 CN2021131491W WO2023087214A1 WO 2023087214 A1 WO2023087214 A1 WO 2023087214A1 CN 2021131491 W CN2021131491 W CN 2021131491W WO 2023087214 A1 WO2023087214 A1 WO 2023087214A1
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battery
battery cell
battery pack
battery cells
positive electrode
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PCT/CN2021/131491
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English (en)
French (fr)
Inventor
欧阳少聪
付成华
董苗苗
叶永煌
别常峰
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宁德时代新能源科技股份有限公司
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Priority to EP21962756.9A priority Critical patent/EP4228079A4/en
Priority to PCT/CN2021/131491 priority patent/WO2023087214A1/zh
Priority to CN202180095372.5A priority patent/CN116964855A/zh
Priority to US18/117,400 priority patent/US20230207938A1/en
Publication of WO2023087214A1 publication Critical patent/WO2023087214A1/zh

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    • 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
    • H01M50/50—Current conducting connections for cells or batteries
    • H01M50/502—Interconnectors for connecting terminals of adjacent batteries; Interconnectors for connecting cells outside a battery casing
    • H01M50/509—Interconnectors for connecting terminals of adjacent batteries; Interconnectors for connecting cells outside a battery casing characterised by the type of connection, e.g. mixed connections
    • 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
    • H01M50/20—Mountings; Secondary casings or frames; Racks, modules or packs; Suspension devices; Shock absorbers; Transport or carrying devices; Holders
    • H01M50/204—Racks, modules or packs for multiple batteries or multiple cells
    • 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
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • 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
    • H01M10/44—Methods for charging or discharging
    • H01M10/441—Methods for charging or discharging for several batteries or cells simultaneously or sequentially
    • 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
    • H01M4/136—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
    • H01M4/48—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
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/20—Mountings; Secondary casings or frames; Racks, modules or packs; Suspension devices; Shock absorbers; Transport or carrying devices; Holders
    • H01M50/204—Racks, modules or packs for multiple batteries or multiple cells
    • H01M50/207—Racks, modules or packs for multiple batteries or multiple cells characterised by their shape
    • H01M50/211—Racks, modules or packs for multiple batteries or multiple cells characterised by their shape adapted for pouch cells
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M6/00—Primary cells; Manufacture thereof
    • H01M6/42—Grouping of primary cells into batteries
    • 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
    • H01M2004/028—Positive electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2220/00—Batteries for particular applications
    • H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
    • 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

Definitions

  • the present application relates to the field of secondary batteries, in particular to a battery pack and an electrical device thereof.
  • Secondary batteries have become the most popular energy storage systems due to their low cost, long life, and good safety. They have been widely used in pure electric vehicles, hybrid electric vehicles, and smart grids. A plurality of secondary batteries are arranged in a certain space to form a battery pack, which can be directly used as a power source for electric vehicles.
  • the present application was made in view of the above-mentioned problems, and an object thereof is to provide a battery pack that solves the technical problem that the discharge performance of the battery pack significantly decreases at low temperature or in winter.
  • the first aspect of the present application provides a battery pack, which includes a first type of battery cell and a second type of battery cell, the first type of battery cell includes n first battery cells, so The second type of battery cells includes m second battery cells, n and m are each independently selected from an integer greater than 1,
  • the internal resistance of the second battery cell is smaller than that of the first battery cell, and the difference between the internal resistance of the first battery cell and the second battery cell is ⁇ 0.15mohm;
  • the length and width diagonal of the battery pack is Lc, the area formed by connecting four points at the respective 1/4Lc bisection points of the two diagonal lines Lc is defined as A area, and the remaining area is defined as B area, wherein the number of the first battery cells in the battery cells contained in the A area accounts for 20% to 100%, and the number of the second battery cells in the battery cells included in the B area accounts for 20% to 100%.
  • the ratio is 5% to 100%.
  • the A region is located in the inner region of the battery pack, and relatively speaking, the B region is located in the outer region of the battery pack.
  • the proportion of the first battery cells among the battery cells contained in the region A may be further 60% to 100%, optionally 80%. -100%.
  • the proportion of the second battery cells in the battery cells included in the B region may be further 40% to 100%, optionally 60% to 100%.
  • the battery dynamics in different regions of the battery pack under low temperature conditions can be further regulated performance, which is conducive to further improving the low-temperature discharge performance of the battery pack.
  • the difference between the internal resistance of the first battery cell and the second battery cell is ⁇ 0.20mohm, optionally ⁇ 0.25mohm.
  • the difference between the internal resistance of the first battery cell and the second battery cell is within the above-mentioned range, it is possible to ensure that the dynamic performance of the battery cells in different regions in the battery pack is consistent at low temperature
  • the number of second battery cells in the B area of the battery pack is appropriately reduced to further improve the electrical performance consistency of the battery pack at room temperature or high temperature.
  • the ratio of the internal resistance of the first battery cell to the internal resistance of the second battery cell is ⁇ 1.1; optionally, it is 1.2 to 1.5.
  • the internal resistance of the first battery cell is 1.5mohm-1.8mohm
  • the internal resistance of the second battery cell is 1.2mohm-1.5mohm.
  • the first battery cell contains a first positive electrode active material represented by formula (I), and the second battery cell contains a second positive electrode active material represented by formula (II):
  • 0 ⁇ x1 ⁇ 0.1, 0 ⁇ x2 ⁇ 0.1, M1 and M2 are each independently selected from one or more of Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr and Ti , and M 2 includes at least Mn.
  • the mass proportion of the Mn element in the second positive electrode active material is greater than the mass proportion of the Mn element in the first positive electrode active material.
  • the volume average particle diameter of the second positive electrode active material is smaller than the volume average particle diameter of the first positive electrode active material.
  • the volume average particle diameter D50 of the second positive electrode active material is 0.3 ⁇ m-0.8 ⁇ m
  • the volume average particle diameter D50 of the first positive electrode active material is 0.8 ⁇ m-2.0 ⁇ m. The difference in the volume average particle size of the positive electrode active material and its value range also contribute to the realization of the difference in the resistance value of different battery cells.
  • the first battery cell contains the third positive electrode active material represented by formula (III), and the second battery cell contains the fourth positive electrode active material represented by formula (IV) :
  • M3 is selected from Mn, Fe, Cr , one or more of Ti, Zn, V, Al, Zr and Ce
  • A is selected from one or more of S, F, Cl and I
  • -0.1 ⁇ x4 ⁇ 0.2 , 0 ⁇ e ⁇ 2, 0 ⁇ d ⁇ 1, M4 is one or more of Ni, Fe, Cr, Ti, Zn, V, Al, Mg, Zr and Ce
  • B is S, N, F , Cl, Br and I in one or more.
  • both the first battery cell and the second battery cell contain electrolyte, and the conductivity of the electrolyte in the second battery cell is greater than that of the first battery cell The conductivity of the electrolyte in the .
  • the conductivity of the electrolyte in the second battery cell is 9mS/cm-14mS/cm, and the conductivity of the electrolyte in the first battery cell is 5mS/cm-8mS/cm .
  • the battery cells at at least four corner positions of the battery pack are all the second battery cells.
  • the battery cells at the four corners of the battery pack are the second battery cells.
  • the discharge capacity of the battery pack at -7°C is 82%-96% of the rated capacity of the battery pack. Therefore, the discharge capacity retention rate of the battery pack at low temperature or in winter can be maintained at a relatively good level.
  • the second aspect of the present application provides an electric device, which includes the battery pack selected from the first aspect of the present application.
  • FIG. 1 is a schematic diagram of a lithium ion secondary battery in one embodiment of the present application.
  • FIG. 2 is an exploded view of the lithium-ion secondary battery in one embodiment of the present application shown in FIG. 1 .
  • Fig. 3 is a schematic diagram of a battery pack in an embodiment of the present application.
  • FIG. 4 is an exploded view of the battery pack shown in FIG. 3 in an embodiment of the present application.
  • FIG. 5 is a schematic diagram of the area division of the battery pack and the arrangement of the battery cells shown in FIG. 3 in one embodiment of the present application.
  • Fig. 6 is a schematic diagram of a device in which a battery pack is used as a power source in an embodiment of the present application.
  • any lower limit can be combined with any upper limit to form an unexpressed range; and any lower limit can be combined with any other lower limit to form an unexpressed range, just as any upper limit can be combined with any other upper limit to form an unexpressed range.
  • each individually disclosed point or individual value may serve as a lower or upper limit by itself in combination with any other point or individual value or with other lower or upper limits to form an unexpressly recited range.
  • the overall discharge capacity of the battery pack is usually increased by enhancing the insulation measures of the battery pack; however, in winter, the heat dissipation rate of different areas of the battery pack is different, which leads to the inconsistent discharge capacity of the battery cells in different areas. There is no effective solution at the battery pack packaging level.
  • a technical solution for placing battery cells with different dynamic characteristics at different positions at the battery pack level is proposed to improve the discharge consistency of the battery pack at low temperatures or in different regions in winter , thereby improving the low-temperature discharge performance of the battery pack.
  • the first aspect of the present application provides a battery pack, which includes a first type of battery cell and a second type of battery cell, the first type of battery cell includes n first battery cells, and the first type of battery cell includes n first battery cells.
  • the second type of battery cell includes m second battery cells, n and m are each independently selected from an integer greater than 1,
  • the internal resistance of the second battery cell is smaller than that of the first battery cell, and the difference between the internal resistance of the first battery cell and the second battery cell is ⁇ 0.15mohm;
  • the length and width diagonal of the battery pack is Lc, the area formed by connecting four points at the respective 1/4Lc bisection points of the two diagonal lines Lc is defined as A area, and the remaining area is defined as B area, wherein the number of the first battery cells in the battery cells contained in the A area accounts for 20% to 100%, and the number of the second battery cells in the battery cells included in the B area accounts for 20% to 100%.
  • the ratio is 5% to 100%.
  • the battery pack of the present application is a square or similar square battery pack.
  • the length of the battery pack is La
  • the width is Lb
  • the length and width diagonals are Lc.
  • the area enclosed by connecting four points at the respective 1/4Lc bisection points of the two length-width diagonal lines Lc is defined as the A area
  • the remaining area is defined as the B area.
  • Area A is located relatively inside the battery pack, and the battery cells contained in this area have at most only one surface exposed to the external air, and even most of the battery cells do not have surfaces exposed to the external atmosphere.
  • the battery cells in the region A thus have a poor heat dissipation coefficient, which will cause the temperature of the battery cells to rise after a certain number of charge and discharge cycles of the battery pack.
  • the B area is located outside the battery pack, and the battery cells contained therein have a relatively large area in contact with the external atmosphere, and there may even be three surfaces in contact with the external atmosphere, thereby making the battery cells therein contact with the external atmosphere. Has a large heat dissipation coefficient. After a certain number of charge and discharge cycles, the temperature of the battery cells in the B region is relatively lower than that of the battery cells in the A region.
  • the temperature difference of the battery cells in the inner and outer regions of the battery pack can cause differences in the battery discharge capacity in different regions.
  • the battery cells located in the relatively inner A region have better dynamic performance due to higher temperature, so that the discharge capacity can be better maintained; relatively, the battery cells located in the outer B region are due to The lower the temperature, the worse the dynamic performance is.
  • the overall discharge capacity of the battery pack at low temperature decreases significantly with the increase of working time. This reduction in the discharge consistency of the inner and outer areas may significantly reduce the overall discharge capacity of the battery pack, and even in extreme cases, the overall power failure of the battery pack due to the low temperature of some battery cells in the outer area will cause the battery pack to fail to work .
  • the discharge consistency of the battery cells in the inner and outer areas (ie, area B) at low temperatures can be effectively improved. performance, which ultimately improves the discharge capacity retention rate of the battery pack as a whole at low temperatures or in winter.
  • the battery pack includes a first type of battery cell and a second type of battery cell, the first type of battery cell includes n first battery cells, and the second type of battery cell
  • the single cell includes m second battery single cells, and n and m are each independently selected from an integer greater than 1.
  • n and m are each independently selected from 4, 8, 12 or even 16 or more integers.
  • At least one of the first battery cells and at least one of the second battery cells are electrically connected in series.
  • the internal resistance of the second battery cell is smaller than that of the first battery cell, and that the difference between the internal resistances of the first battery cell and the second battery cell is ⁇ 0.15 mohm.
  • Battery dynamics of the second battery cell are superior to those of the first battery cell due to the internal resistance of the second battery cell being at least 0.15 mohm less than the internal resistance of the first battery cell Kinetics so that the second battery cell, even at a relatively low temperature, can discharge comparable to the first battery cell at a relatively high temperature, or discharge at low temperatures or in winter There was no significant difference in the degree of capacity retention.
  • the battery pack provided by the present application contains the first battery cells with a quantity ratio of 20% to 100% in the area A defined above, and contains 5 cells in the area B defined above. % to 100% of the second battery cells, successfully keeping the difference in discharge capacity, or reduction in discharge capacity, of the battery cells in the inner and outer regions relatively consistent at low temperatures or in winter level. Both the A region and the B region may contain the first battery cell and the second battery cell at the same time.
  • the number of the first battery cells in the A region is more than that of the second battery cells; on the contrary, the number of the second battery cells in the B region is more than that of the first battery cells.
  • the number of the first battery cells in the battery cells contained in the region A accounts for 60% to 100%, optionally 80% to 100%.
  • the quantity of the second battery cells in the battery cells included in the B region is 40% to 100%, optionally 60% to 100%.
  • the difference between the internal resistances of the first battery cell and the second battery cell is > 0.20 mohm, optionally > 0.25 mohm.
  • the difference between the internal resistance of the first battery cell and the second battery cell is within the above-mentioned range, it is possible to ensure that the dynamic performance of the battery cells in different regions in the battery pack is consistent at low temperature At the same time, the number of second battery cells in the B area of the battery pack is appropriately reduced to further improve the electrical performance consistency of the battery pack at room temperature or high temperature.
  • the ratio of the internal resistance of the first battery cell to the internal resistance of the second battery cell is ⁇ 1.1; optionally, 1.2 to 1.5.
  • the difference between the internal resistances of the first battery cell and the second battery cell is increased, which further compensates for the difference in discharge capacity between the two caused by the difference in temperature.
  • the internal resistance of the first battery cell is 1.5mohm-1.8mohm
  • the internal resistance of the second battery cell is 1.2mohm-1.5mohm.
  • the internal resistance of the battery cell can be measured by the method described in the examples below. By selecting appropriate internal resistance ranges for the two battery cells, accurate control of the overall discharge capacity of the battery pack can be achieved.
  • both the first battery cell and the second battery cell are lithium ion secondary batteries.
  • the lithium ion secondary battery has a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, the positive electrode sheet includes a positive electrode current collector and a positive electrode material layer arranged on at least one surface of the positive electrode current collector, the positive electrode material The layer contains a positive electrode active material and carbon.
  • the first battery cell contains a first positive active material represented by formula (I)
  • the second battery cell contains a second positive active material represented by formula (II):
  • 0 ⁇ x1 ⁇ 0.1, 0 ⁇ x2 ⁇ 0.1, M1 and M2 are each independently selected from one or more of Cu, Mn, Cr, Zn, Pb, Ca, Co, Ni, Sr and Ti , and M 2 includes at least Mn. Since x2 is greater than 0 and M2 includes at least Mn, the second positive electrode active material represented by formula (II) is lithium manganese iron phosphate positive electrode active material. When x1 is 0, the first positive electrode active material represented by formula (I) is manganese-free lithium iron phosphate.
  • the mass proportion of the Mn element in the second positive electrode active material is greater than the mass proportion of the Mn element in the first positive electrode active material.
  • the doping of a higher content of manganese can increase the unit cell parameters of the second positive active material shown in formula (II), improve the diffusion rate of Li + , and improve the comprehensive electrochemical performance of the positive active material, thereby
  • the internal resistance of the second battery cell containing the second positive electrode active material is smaller than that of the first battery cell containing the first positive electrode active material represented by formula (I). This reduction in internal resistance in turn enables the second battery cell to have better dynamic performance at low temperatures than the first battery cell, and through the spatial arrangement of the two battery cells in the battery pack.
  • the special design realizes the improvement of the overall discharge capacity retention rate and consistency of the battery pack.
  • the volume average particle diameter of the second positive electrode active material is smaller than the volume average particle diameter of the first positive electrode active material.
  • the volume average particle diameter D50 of the second positive electrode active material is 0.3 ⁇ m-0.8 ⁇ m
  • the volume average particle diameter D50 of the first positive electrode active material is 0.8 ⁇ m-2.0 ⁇ m.
  • the volume average particle diameter of the positive electrode active material can be measured according to GB/T19077-2016/ISO 13320:2009. Since the volume average particle diameter D50 value of the second positive electrode active material is smaller than the volume average particle diameter D50 value of the first positive electrode active material, the Li + ions in the second positive electrode active material are diffused in solid phase inside the positive electrode active material particles The distance is relatively small.
  • the lower volume average particle diameter D50 makes the second positive active material have a higher bulk density than the first positive active material. These factors make the second positive active material have better overall electrochemical performance, so that the internal resistance of the second battery cell containing the second positive active material is smaller than that of the first battery cell containing the first positive active material . As mentioned above, the reduction in the internal resistance value allows the second battery cell to have better kinetic performance at low temperature compared to the first battery cell.
  • the first battery cell contains the third positive electrode active material represented by formula (III), and the second battery cell contains the fourth positive electrode active material represented by formula (IV) :
  • M3 is selected from Mn, Fe, Cr , one or more of Ti, Zn, V, Al, Zr and Ce
  • A is selected from one or more of S, F, Cl and I
  • -0.1 ⁇ x4 ⁇ 0.2 , 0 ⁇ e ⁇ 2, 0 ⁇ d ⁇ 1, M4 is one or more of Ni, Fe, Cr, Ti, Zn, V, Al, Mg, Zr and Ce
  • B is S, N, F , Cl, Br and I in one or more.
  • both the first battery cell and the second battery cell contain electrolyte, and the conductivity of the electrolyte in the second battery cell is greater than that of the first battery cell The conductivity of the electrolyte in the . Due to the high conductivity of the electrolyte in the second battery cell, the comprehensive electrochemical performance of the second battery cell is better than that of the first battery cell; correspondingly, the internal resistance of the second battery cell is less than The first battery cell.
  • the conductivity of the electrolyte in the second battery cell is 9mS/cm-14mS/cm, and the conductivity of the electrolyte in the first battery cell is 5mS/cm-8mS/cm . The conductivity of the electrolyte in the battery cell can be measured by a conductivity tester.
  • the spatial arrangement of different battery cells in the battery pack can be further set, so as to achieve precise control over the discharge performance of the battery pack.
  • the battery cells at at least four corner positions are all the second battery cells; optionally, in the B area, only The battery cells at the four corners of the battery pack are the second battery cells. Since at least three surfaces of the battery cells at the four corners of the battery pack are in contact with the external atmosphere, their heat dissipation coefficients are the highest among all the battery cells in the battery pack. Arranging the second battery cells with smaller internal resistance and thus better discharge performance at these positions further balances the difference in discharge capacity between the inner and outer regions due to temperature differences.
  • the discharge capacity of a battery pack can be significantly lower than its rated capacity at low temperatures.
  • the discharge capacity of the provided battery pack at -7°C is 82%-96% of the rated capacity of the battery pack. Since the battery pack of the present application uses a larger number of second battery cells with better dynamic performance in its outer B area, the overall discharge consistency of the battery pack has been improved, and the discharge of the battery cells located outside The loss of capacity is small, so the overall discharge capacity of the battery pack at low temperature is also small compared to the rated capacity loss of the battery pack.
  • both the first battery cell and the second battery cell are lithium ion secondary batteries.
  • a lithium-ion secondary battery typically includes a positive pole piece, a negative pole piece, a separator, and an electrolyte.
  • active ions are intercalated and extracted back and forth between the positive electrode and the negative electrode.
  • the separator is arranged between the positive pole piece and the negative pole piece to play the role of isolation.
  • the electrolyte plays the role of conducting ions between the positive pole piece and the negative pole piece.
  • the electrolyte plays the role of conducting ions between the positive pole piece and the negative pole piece.
  • the electrolytic solution includes electrolyte salts and solvents.
  • the electrolyte salt can be a common electrolyte salt in lithium ion secondary batteries, such as lithium salt, including lithium salt that can be the above-mentioned lithium salt as a high thermal stability salt, lithium salt as a low impedance additive, or lithium salt that inhibits aluminum foil corrosion. Salt.
  • the electrolyte salt may be selected from LiPF 6 (lithium hexafluorophosphate), LiBF 4 (lithium tetrafluoroborate), LiAsF 6 (lithium hexafluoroarsenate), LiFSI (lithium bisfluorosulfonimide), LiTFSI (bistrifluoromethane Lithium sulfonyl imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalate borate), LiPO 2 F 2 (lithium difluorophosphate), LiDFOP (lithium difluorodifluorooxalate phosphate), LiSO 3 F (lithium fluorosulfonate), NDFOP (difluorodioxalate), Li 2 F(SO 2 N) 2 SO 2 F, KFSI, CsFSI, Ba(FSI) 2 and LiFSO 2 NSO 2 CH 2 CH 2 CF 3 more than one of them
  • the solvent is not particularly limited, and can be selected according to actual needs.
  • the solvent is a non-aqueous solvent.
  • the solvent may include one or more of chain carbonates, cyclic carbonates, and carboxylates.
  • the solvent may be selected from ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), Dipropyl Carbonate (DPC), Methyl Propyl Carbonate (MPC), Ethyl Propyl Carbonate (EPC), Butylene Carbonate (BC), Fluoroethylene Carbonate (FEC), Methyl Formate (MF), Methyl Acetate Ester (MA), Ethyl Acetate (EA), Propyl Acetate (PA), Methyl Propionate (MP), Ethyl Propionate (EP), Propyl Propionate (PP), Methyl Butyrate (MB) , e
  • the electrolyte may optionally include other additives.
  • additives can include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain performances of batteries, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and battery low-temperature performance. additives, etc.
  • the additive is selected from cyclic carbonate compounds containing unsaturated bonds, halogen-substituted cyclic carbonate compounds, sulfate ester compounds, sulfite compounds, sultone compounds, disulfonic acid compounds, nitrile compounds , aromatic compounds, isocyanate compounds, phosphazene compounds, cyclic acid anhydride compounds, phosphite compounds, phosphate compounds, borate compounds, and carboxylate compounds.
  • the positive electrode sheet includes a positive electrode current collector and a positive electrode material layer arranged on at least one surface of the positive electrode current collector, and the positive electrode material layer includes positive electrode active material and carbon.
  • the positive electrode current collector has two opposing surfaces in its own thickness direction, and the positive electrode material layer is disposed on any one or both of the two opposing surfaces of the positive electrode current collector.
  • the positive electrode current collector may be a metal foil or a composite current collector.
  • aluminum foil can be used as the metal foil.
  • the composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base.
  • the composite current collector can be formed by metal materials (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) Formed on substrates such as polyethylene formate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.
  • the positive electrode material layer provided on the surface of the positive electrode current collector includes a positive electrode active material.
  • the positive active material used in the present application may have the structure of formula (I), formula (II), formula (III) or formula (IV) as described above and various numerical definitions defined therein.
  • the positive electrode active material of the formula (I), formula (II), formula (III) or formula (IV) accounts for 60-100% of the total weight of the positive electrode active material of the battery cell in each case % by weight, optionally 80-100% by weight.
  • the positive electrode active material may also contain one or more selected from lithium transition metal oxides, lithium-containing phosphates with olivine structure, and their respective modified compounds. kind.
  • lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide One or more of lithium nickel cobalt aluminum oxide and its modified compounds.
  • olivine-structured lithium-containing phosphates may include, but are not limited to, lithium iron phosphate, a composite of lithium iron phosphate and carbon, lithium manganese phosphate, a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, lithium manganese iron phosphate One or more of the composite materials with carbon and their modified compounds. These materials are all commercially available. Carbon may be coated on the surface of the positive electrode active material.
  • the positive electrode material layer optionally includes a conductive agent.
  • a conductive agent there is no specific limitation on the type of conductive agent, which can be selected by those skilled in the art according to actual needs.
  • the conductive agent used for the positive electrode material may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the positive electrode material layer also optionally includes a binder.
  • the binder can be styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid ( One or more of PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA) and polyvinyl butyral (PVB).
  • SBR styrene-butadiene rubber
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • EVA ethylene-vinyl acetate copolymer
  • PAA polyacrylic acid
  • CMC carboxymethyl cellulose
  • PVA polyvinyl alcohol
  • PVB polyvinyl butyral
  • the positive electrode sheet can be prepared according to methods known in the art.
  • a positive electrode active material coated with carbon, a conductive agent, and a binder can be dispersed in a solvent (such as N-methylpyrrolidone (NMP)) to form a uniform positive electrode slurry; the positive electrode slurry is coated on the positive electrode On the current collector, after drying, cold pressing and other processes, the positive electrode sheet is obtained.
  • NMP N-methylpyrrolidone
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer arranged on at least one surface of the negative electrode current collector, and the negative electrode material layer includes a negative electrode active material.
  • the negative electrode current collector has two opposing surfaces in its own thickness direction, and the negative electrode material layer is disposed on any one or both of the two opposing surfaces of the negative electrode current collector.
  • the negative electrode current collector may be a metal foil or a composite current collector.
  • copper foil can be used as the metal foil.
  • the composite current collector may include a base layer of polymer material and a metal layer formed on at least one surface of the base material of polymer material.
  • Composite current collectors can be formed by metal materials (such as copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver and silver alloys, etc.) Formed on substrates such as polyethylene formate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.
  • the negative electrode material layer usually includes negative electrode active material and optional binder, optional conductive agent and other optional additives, usually formed by coating and drying negative electrode slurry into.
  • the negative electrode slurry coating is usually formed by dispersing the negative electrode active material and optional conductive agent and binder in a solvent and stirring them evenly.
  • the solvent can be N-methylpyrrolidone (NMP) or deionized water.
  • the negative electrode active material is not limited, and active materials known in the art that can be used for the negative electrode of lithium ion secondary batteries can be used, and those skilled in the art can select according to actual needs.
  • the negative electrode active material can be selected from one or more of graphite, soft carbon, hard carbon, mesocarbon microspheres, carbon fibers, carbon nanotubes, simple silicon, silicon oxide compounds, silicon-carbon composites, and lithium titanate. kind.
  • the conductive agent may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the binder may be selected from styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), One or more of polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).
  • SBR styrene-butadiene rubber
  • PAA polyacrylic acid
  • PAAS sodium polyacrylate
  • PAM polyacrylamide
  • PVA polyvinyl alcohol
  • SA sodium alginate
  • PMAA polymethacrylic acid
  • CMCS carboxymethyl chitosan
  • thickeners such as sodium carboxymethylcellulose (CMC-Na)
  • CMC-Na sodium carboxymethylcellulose
  • a separator is also included in a lithium ion secondary battery using an electrolytic solution.
  • the separator is arranged between the positive pole piece and the negative pole piece to play the role of isolation.
  • the present application has no particular limitation on the type of the isolation membrane, and any known porous structure isolation membrane with good chemical stability and mechanical stability can be selected.
  • the material of the isolation film can be selected from more than one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • the separator can be a single-layer film or a multi-layer composite film, without any particular limitation. When the separator is a multilayer composite film, the materials of each layer may be the same or different, and there is no particular limitation.
  • the positive pole piece, the negative pole piece and the separator can be made into an electrode assembly through a winding process or a lamination process.
  • a lithium ion secondary battery may include an outer package.
  • the outer package can be used to package the above-mentioned electrode assembly and electrolyte.
  • the outer package of the lithium-ion secondary battery may be a hard case, such as a hard plastic case, aluminum case, steel case, and the like.
  • the outer packaging of the lithium-ion secondary battery may also be a soft bag, such as a pouch-type soft bag.
  • the material of the soft bag may be plastic, and examples of plastic include polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).
  • FIG. 1 shows a square-shaped lithium-ion secondary battery 5 as an example.
  • the outer package may include a housing 51 and a cover 53 .
  • the housing 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plates enclose to form an accommodating cavity.
  • the housing 51 has an opening communicating with the accommodating cavity, and the cover plate 53 can cover the opening to close the accommodating cavity.
  • the positive pole piece, the negative pole piece and the separator can be formed into an electrode assembly 52 through a winding process or a lamination process.
  • the electrode assembly 52 is packaged in the accommodating cavity. Electrolyte is infiltrated in the electrode assembly 52 .
  • the number of electrode assemblies 52 contained in the lithium-ion secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.
  • the lithium-ion secondary battery can be assembled into a battery module 4, and the number of lithium-ion secondary batteries contained in the battery module 4 can be one or more, and the specific number can be determined by those skilled in the art according to the application of the battery module 4 and capacity selection.
  • a plurality of lithium-ion secondary batteries 5 may be arranged in sequence along the length direction of the battery module. Of course, they can also be arranged in other arbitrary ways. Furthermore, the plurality of lithium-ion secondary batteries 5 can be fixed by fasteners.
  • the battery module 4 may also include a housing with a containing space in which a plurality of lithium-ion secondary batteries 5 are housed.
  • the above-mentioned lithium-ion secondary batteries 5 or battery modules 4 can be assembled into a battery pack 1, and the number of lithium-ion secondary batteries 5 or battery modules 4 contained in the battery pack 1 can be determined by those skilled in the art according to the battery pack 1 Choose from your application and capacity.
  • the battery pack 1 may include a battery box and a plurality of battery cells disposed in the battery box.
  • the battery box includes an upper box body 2 and a lower box body 3 , the upper box body 2 can cover the lower box body 3 and form a closed space for accommodating battery cells.
  • FIG. 5 is a schematic diagram of the area division of the battery pack and the arrangement of the battery cells in one embodiment of the present application.
  • the area enclosed by connecting four points at the respective 1/4Lc bisect points of the two long-width diagonal lines Lc is defined as the A area, and the remaining area is defined as the B area.
  • the battery cells are placed in corresponding areas according to the type and quantity ratio described in this application, so as to realize the adjustment of discharge performance in different areas.
  • the present application also provides a device, which includes the battery pack provided in the present application.
  • the battery pack can be used as a power source for the device and also as an energy storage unit for the device.
  • the device can be, but not limited to, a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf vehicles, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.
  • a battery pack can be selected according to its usage requirements.
  • Figure 6 is an example device.
  • the device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle.
  • battery packs or battery modules can be employed.
  • Electrolyte conductivity measurement Use the equipment model Leici DDSJ-318 conductivity tester to test the conductivity of the electrolyte. First, place the electrode probe in the standard electrolyte for calibration, and then place it in the electrolyte to be tested. To measure, repeat the measurement three times, take the average value, and keep two decimal places.
  • Battery pack discharge capacity retention rate at -7°C The ratio of C2/C1 is the discharge capacity retention rate of the battery pack at -7°C.
  • LiPF lithium iron phosphate
  • conductive agent acetylene black conductive agent acetylene black
  • binder polyvinylidene fluoride PVDF
  • NMP solvent N-methylpyrrolidone
  • the lithium iron phosphate material with the Mn content shown in Table 1 is selected as the positive electrode active material (the lithium iron phosphate material may inherently contain a certain amount of Mn as an impurity; if the Mn impurity content is insufficient, Mn can be deliberately doped to achieve the indicated Mn levels).
  • lithium manganese iron phosphate materials with specific Mn contents as shown in Table 2 were obtained by doping the lithium iron phosphate material with Mn as positive electrode active materials.
  • the selected granular materials of lithium iron phosphate and lithium iron manganese phosphate are screened using a particle screening machine, and the various materials are further screened into fractions with different volume average particle diameters D50 values, and are respectively applied to different Preparation of battery cells.
  • the positive electrode slurry is evenly coated on the aluminum positive electrode current collector, and then dried, cold pressed, and cut to obtain the positive electrode sheet.
  • Negative active material artificial graphite, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), thickener carboxymethylcellulose sodium (CMC-Na) are dissolved in the solvent according to the weight ratio of 95:2:2:1 deionized water, mixed uniformly to prepare negative electrode slurry.
  • the negative electrode slurry is uniformly coated on the copper foil of the negative electrode current collector, and after drying, it is subjected to cold pressing and slitting to obtain negative electrode sheets.
  • ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) were prepared according to The weight ratios listed in Table 1 and Table 2 were uniformly mixed, lithium hexafluorophosphate (LiPF 6 ) was added and adjusted to a concentration of 1M/L, and stirred evenly to obtain the corresponding electrolyte solution.
  • LiPF 6 lithium hexafluorophosphate
  • the electrolyte with the conductivity as described in Table 1 and Table 2 was obtained for preparing corresponding battery cells.
  • the positive electrode sheet obtained in the above (1) and the negative electrode sheet obtained in the above (2) use the polypropylene film as the separator, and stack the positive electrode sheet, separator, and negative electrode sheet in order, so that The separator is placed between the positive and negative pole pieces to play the role of isolation, and then wound to obtain the electrode assembly.
  • the electrode assembly is placed in the battery casing, after being dried, the electrolyte solution is injected, and then the lithium-ion secondary battery is obtained as a battery cell through formation and standing.
  • first battery cell and the second battery cell Place the first battery cell and the second battery cell with different Mn contents, positive electrode active material volume average particle diameter D50 values, and electrolyte conductivity prepared as described above according to the number and area shown in Table 3 , to obtain battery packs with different arrangements of battery cells.
  • the battery pack assembled in the embodiment of the present application only the first battery cell and the second battery cell prepared as described above are contained; wherein, the total number of all battery cells in area A is 48, and B The total number of all battery cells in the area is 72.
  • the particle size D50 value of lithium manganese iron phosphate in the second battery cell is smaller than that of the first battery cell.
  • the resistance value of the second battery cell is obviously smaller than the resistance value of the first battery cell.
  • the number of the second battery cells in the area B in Comparative Example 1 is 0, which means that all the battery cells in the area B are the first battery cells at this time, that is, the battery cells in all areas of the battery pack in Comparative Example 1 All of the bodies are first battery cells.
  • the discharge capacity retention rate of the battery pack at this time is only 80.2%, which is the lowest discharge capacity retention rate among all the battery packs prepared in the examples of the present application.
  • Comparative Example 2 in which the battery cells in the B area are all the first battery cells, and the battery cells in the A area are all the second battery cells. Comparing Comparative Example 2 with Example 5, the arrangement of battery cells in the battery pack is completely opposite. The discharge capacity test results for the two show that the discharge capacity retention rate of the battery pack of Example 5 is significantly greater than that of Comparative Example 2. This shows that even with the same number of battery cells of the same type, the discharge capacity retention rate of the battery pack at low temperatures will change significantly under different spatial arrangements. Compared with the prior art, the low-temperature discharge capacity retention rate of the battery pack prepared in the present application has been significantly improved under the same conditions.

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Abstract

本申请涉及一种电池包，包括第一类电池单体和第二类电池单体，所述第一类电池单体包括n个第一电池单体，所述第二类电池单体包括m个第二电池单体，n和m各自独立地选自1以上的整数，其中，所述第二电池单体的内阻小于所述第一电池单体，并且所述第一电池单体与所述第二电池单体的内阻之差≥0.15mohm；所述电池包的长宽对角线为Lc，两条所述对角线Lc的各自1/4Lc等分点处的4个点相连所围成的区域定义为A区域，剩余区域定义为B区域，其中A区域所包含的电池单体中所述第一电池单体的数量占比为20％至100％，并且B区域所包含的电池单体中所述第二电池单体的数量占比为5％至100％。本申请的电池包具有改善的低温下内外区域放电容量一致性以及放电容量保持率。本申请还涉及包含所述电池包的用电装置。

Description

一种电池包及其用电装置 技术领域
本申请涉及二次电池领域，尤其涉及一种电池包及其用电装置。
背景技术
二次电池因其成本低、寿命长，安全性好等特点成为最受欢迎的能量存储系统，现已被广泛应用于纯电动汽车、混合电动汽车以及智能电网等领域。由多个二次电池通过一定的空间排布形成电池包，可直接作为电动汽车的动力来源。
然而，目前消费者在选择使用电动汽车时，普遍存在“里程焦虑”的问题，尤其是在冬季。如何改善二次电池在低温下或在冬季的放电性能，提升动力电池在低温下的续航里程已成为一项亟需解决的技术问题。
发明内容
本申请是鉴于上述课题而进行的，其目的在于提供一种电池包，以解决在低温下或在冬季电池包的放电性能明显下降的技术问题。
为了达到上述目的，本申请第一方面提供一种电池包，其包括第一类电池单体和第二类电池单体，所述第一类电池单体包括n个第一电池单体，所述第二类电池单体包括m个第二电池单体，n和m各自独立地选自1以上的整数，
其中，所述第二电池单体的内阻小于所述第一电池单体，并且所述第一电池单体与所述第二电池单体的内阻之差≥0.15mohm；
所述电池包的长宽对角线为Lc，两条所述对角线Lc的各自1/4Lc等 分点处的4个点相连所围成的区域定义为A区域，剩余区域定义为B区域，其中A区域所包含的电池单体中所述第一电池单体的数量占比为20％至100％，并且B区域所包含的电池单体中所述第二电池单体的数量占比为5％至100％。
本申请中，A区域处于所述电池包的内部区域，相对而言，B区域处于所述电池包的外部区域。通过在电池包的外部区域至少放置部分内阻更小的第二电池单体，在电池包的内部区域至少放置部分内阻略高的第一电池单体，利用电池单体的内阻差异，实现电池包不同区域的动力学性能的差异性调控。由此，能够在提高电池包的整体放电量的同时，实现在低温下电池包内部区域和外部区域电池单体的放电容量一致性，从而在相当程度上抵销了在低温条件下，当电池包中内部区域与外部区域温度不一致时，不同区域的电池单体放电容量的差异，解决了在低温下或在冬季电池包整体放电性能明显下降的问题。
在任意实施方式中，在所述电池包中，所述A区域所包含的电池单体中所述第一电池单体的数量占比可进一步为60％至100％，可选地为80％-100％。所述B区域所包含的电池单体中所述第二电池单体的数量占比可进一步为为40％至100％，可选地为60％-100％。本申请中，当电池包的A区域和B区域中，各自所包含的第一电池单体和第二电池单体在上述范围内时，可以进一步调控低温条件下电池包不同区域的电池动力学性能，有利于进一步提升电池包的低温放电性能。
在任意实施方式中，在所述电池包中，所述第一电池单体与所述第二电池单体的内阻之差≥0.20mohm，可选地≥0.25mohm。本申请中，当所述第一电池单体与所述第二电池单体的内阻之差在上述范围内时，可以在保证低温下电池包中不同区域的电池单体的动力学性能一致性较高的同时，适当减少电池包中B区域第二电池单体的数量，进一步提升电池包在常温 或高温下的电性能一致性。
在任意实施方式中，在所述电池包中，所述第一电池单体的内阻与所述第二电池单体的内阻之比≥1.1；可选地，为1.2至1.5。通过提高所述第一电池单体与所述第二电池单体的内阻之差，可以进一步改进电池包的内外区域的放电容量一致性。
在任意实施方式中，所述第一电池单体的内阻值为1.5mohm-1.8mohm，并且所述第二电池单体的内阻值为1.2mohm-1.5mohm。通过选择具有合适的内阻值范围的两种电池单体的组合，可以进一步改善电池单体特定布置带来的效果。
在一些实施方式中，所述第一电池单体中含有式(I)所示的第一正极活性物质，所述第二电池单体中含有式(II)所示的第二正极活性物质：
LiFe 1-x1M 1 x1PO 4      式(I)
LiFe 1-x2M 2 x2PO 4       式(II)
其中，0≤x1≤0.1，0<x2≤0.1，M 1和M 2各自独立地选自Cu、Mn、Cr、Zn、Pb、Ca、Co、Ni、Sr和Ti中的一种或多种，且M 2至少包括Mn。
在一些实施方式中，所述第二正极活性物质中Mn元素的质量占比大于所述第一正极活性物质中Mn元素的质量占比。通过选择各电池单体中正极活性物质的种类、结构以及Mn含量，有助于进一步实现不同电池单体的动力学性能差异。
在一些实施方式中，所述第二正极活性物质的体积平均粒径小于所述第一正极活性物质的体积平均粒径。可选地，所述第二正极活性物质的体积平均粒径D50值为0.3μm-0.8μm，并且所述第一正极活性物质的体积平均粒径D50值为0.8μm-2.0μm。正极活性物质的体积平均粒径的差异及其数值范围也有助于实现不同电池单体的电阻值差异。
在另一些实施方式中，所述第一电池单体中含有式(III)所示的第三正极活性物质，所述第二电池单体中含有式(IV)所示的第四正极活性物质：
Li 1+x3Ni aCo bM 3 1-a-bO 2-y3A y3    式(III)
Li 1+x4Mn eM 4 2-eO 4-dB d      式(IV)
其中，式(III)中，-0.1≤x3≤0.2，0.3≤a＜0.95，0＜b＜0.2，0＜a+b＜1，0≤y3＜0.2，M 3选自Mn、Fe、Cr、Ti、Zn、V、Al、Zr和Ce中的一种或几种，A选自S、F、Cl和I中的一种或几种；式(IV)中，-0.1≤x4≤0.2，0＜e≤2，0≤d＜1，M 4为Ni、Fe、Cr、Ti、Zn、V、Al、Mg、Zr及Ce中的一种或多种，B为S、N、F、Cl、Br及I中的一种或多种。
在任意实施方式中，所述第一电池单体和所述第二电池单体中均含有电解液，且所述第二电池单体中的电解液的电导率大于所述第一电池单体中的电解液的电导率。可选地，所述第二电池单体中的电解液的电导率为9mS/cm-14mS/cm，并且所述第一电池单体中的电解液的电导率为5mS/cm-8mS/cm。通过选择两种电池单体的电解液电导率大小和数值范围，可以实现电池单体的内阻以及放电容量差异。
在任意实施方式中，在所述B区域中，所述电池包的至少四个顶角位置处的电池单体均为所述第二电池单体。可选地，所述B区域中，仅有所述电池包的四个顶角位置处的电池单体为所述第二电池单体。通过选择特定位置布置不同的电池单体，可实现对电池包整体放电容量的精准控制。
在任意实施方式中，所述电池包在-7℃下的放电容量为所述电池包的额定容量的82％-96％。由此，所述电池包在低温或冬季的放电容量保持率可维持在相对较好的程度。
本申请的第二方面提供一种用电装置，其包括选自本申请的第一方面的电池包。
附图说明
为了更清楚地说明本申请的技术方案，下面将对本申请实施例中所需要使用的附图作简单的介绍。显而易见地，下面所描述的附图仅仅是本申请的一些实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据附图获得其他的附图。
图1是本申请一个实施方式中的锂离子二次电池的示意图。
图2是图1所示的本申请一个实施方式中的锂离子二次电池的分解图。
图3是本申请一个实施方式中的电池包的示意图。
图4是图3所示的本申请一个实施方式中的电池包的分解图。
图5是图3所示的本申请一个实施方式中的电池包的区域划分以及电池单体排布的示意图。
图6是本申请一个实施方式中的电池包用作电源的装置的示意图。
附图标记说明
1电池包
2上箱体
3下箱体
4电池模块
5锂离子二次电池
51壳体
52电极组件
53盖板
具体实施方式
为了简明，本申请具体地公开了一些数值范围。然而，任意下限可以与任意上限组合形成未明确记载的范围；以及任意下限可以与其它下限组合形成未明确记载的范围，同样任意上限可以与任意其它上限组合形成未明确记载的范围。此外，每个单独公开的点或单个数值自身可以作为下限或上限与任意其它点或单个数值组合或与其它下限或上限组合形成未明确记载的范围。
申请人经研究发现：电动汽车在冬季续航里程差，主要受两个关键因素影响：①冬季温度低，导致电池包整体动力学差，电池包整体放电量低；②冬季温度低，导致电池包不同区域温度分布差异大，从而导致不同区域电池单体放电量不一致。针对第一个问题，通常通过增强电池包保温措施，来提升电池包整体放电量；但针对在冬季电池包的不同区域的散热速度不同，从而导致不同区域电池单体放电量不一致的问题，目前在电池包封装层级暂无有效解决措施。
为了有效改善电动汽车在低温下或在冬季的续航里程、解决电池包在低温下或在冬季不同区域的放电容量不一致的问题。在本申请的一个实施方式中，提出了一种在电池包层级，不同位置放置不同动力学特性的电池单体的技术方案，以提高电池包在低温下或在冬季的不同区域的放电一致性，从而提升电池包的低温放电性能。
具体的，本申请第一方面提供一种电池包，其包括第一类电池单体和第二类电池单体，所述第一类电池单体包括n个第一电池单体，所述第二类电池单体包括m个第二电池单体，n和m各自独立地选自1以上的整数，
其中，所述第二电池单体的内阻小于所述第一电池单体，并且所述第一电池单体与所述第二电池单体的内阻之差≥0.15mohm；
所述电池包的长宽对角线为Lc，两条所述对角线Lc的各自1/4Lc等 分点处的4个点相连所围成的区域定义为A区域，剩余区域定义为B区域，其中A区域所包含的电池单体中所述第一电池单体的数量占比为20％至100％，并且B区域所包含的电池单体中所述第二电池单体的数量占比为5％至100％。
本申请的电池包为方形或类似方形的电池包。所述电池包的长度为La，宽度为Lb，长宽对角线为Lc。在所述电池包的由长度和宽度所定义的表面上，将两条所述长宽对角线Lc的各自1/4Lc等分点处的4个点相连所围成的区域定义为A区域，剩余区域定义为B区域。A区域位于电池包的相对内部，该区域中所包含的电池单体最多仅有一个面暴露于外部空气中，甚至大多数电池单体不含暴露于外部大气的表面。所述A区域中的电池单体由此具有较差的散热系数，在电池包经过一定圈数的充放电循环之后，会导致电池单体的温度升高。与之相比，所述B区域位于电池包的外部，其中所包含的电池单体与外部大气接触的面积较大，甚至可能有三个面均与外部大气接触，由此使得其中的电池单体具有较大的散热系数。在经历了一定圈数的充放电循环之后，B区域中的电池单体的温度相较于所述A区域中的电池单体而言相对较低。
在低温下或在冬季，这种电池包内外区域中电池单体的温度差异会导致不同区域中的电池放电量产生差异。例如，位于相对内部的A区域中的电池单体由于温度较高而具有更好的动力学性能，从而使得放电量得以较好地保持；相对地，位于外部的B区域中的电池单体由于温度较低而动力学性能恶化明显，由于短板效应，使得低温下电池包的整体放电量随着工作时间的增加而出现明显的降低。这种内外区域的放电一致性降低可能会使得电池包的整体放电量出现明显降低，甚至在极端情况下，由于外部区域中部分电池单体的温度过低而导致电池包整体断电而无法工作。因此，本申请中，通过在电池包的不同位置放置内阻不同的第一电池单体和第二 电池单体，可以有效提升低温下内、外部区域(即B区域)电池单体的放电一致性，最终提高了电池包整体在低温下或在冬季的放电容量保持率。
在本申请的实施方案中，所述电池包包括第一类电池单体和第二类电池单体，所述第一类电池单体包括n个第一电池单体，所述第二类电池单体包括m个第二电池单体，n和m各自独立地选自1以上的整数。可选地，可选地，n和m各自独立地选自4、8、12甚至16以上的整数。
在本申请的一个实施方案中，至少1个所述第一电池单体与至少1个所述第二电池单体以串联的形式电连接。对本申请而言，重要的是所述第二电池单体的内阻小于所述第一电池单体，并且所述第一电池单体与所述第二电池单体的内阻之差≥0.15mohm。由于所述第二电池单体的内阻比所述第一电池单体的内阻小至少0.15mohm，使得所述第二电池单体的电池动力学优于所述第一电池单体的电池动力学，从而使得第二电池单体，即使处于相对较低的温度下，其放电量也可与处于相对较高的温度下的第一电池单体相当，或者说在低温下或冬季的放电容量的保持程度没有显著的差异。
本申请所提供的电池包通过在如上所定义的A区域中包含数量占比为20％至100％的所述第一电池单体，并且在如上所定义的B区域中包含数量占比为5％至100％的所述第二电池单体，成功地使得内部和外部区域中的电池单体在低温下或冬季彼此之间的放电量的差异、或者说放电容量的降低保持在较为一致的水平。所述A区域和B区域中均可同时包含所述第一电池单体和第二电池单体。
可选地，所述A区域中第一电池单体的数量多于第二电池单体；与之相反的，所述B区域中第二电池单体的数量多于第一电池单体。
在一些实施方式中，所述A区域所包含的电池单体中所述第一电池单体的数量占比为60％至100％，可选地为80％-100％。所述B区域所包含 的电池单体中所述第二电池单体的数量占比为40％至100％，可选地为60％-100％。通过对电池包中不同区域的电池单体的内阻差值进行调整，本申请所提供的电池包实现了对于在低温下或冬季由于内外温差所导致的放电量差异的适当补偿，降低了不同区域的温度差对于电池包整体性能的影响，提高了电池包整体放电性能的一致性。
在一些实施方式中，所述第一电池单体与所述第二电池单体的内阻之差≥0.20mohm，可选地≥0.25mohm。本申请中，当所述第一电池单体与所述第二电池单体的内阻之差在上述范围内时，可以在保证低温下电池包中不同区域的电池单体的动力学性能一致性较高的同时，适当减少电池包中B区域第二电池单体的数量，进一步提升电池包在常温或高温下的电性能一致性。
在一些实施方式中，所述第一电池单体的内阻与所述第二电池单体的内阻之比≥1.1；可选地，为1.2至1.5。所述第一电池单体与所述第二电池单体的内阻之差增大，进一步补偿了二者由于温度的差异导致的放电容量之差。
在一些实施方式中，所述第一电池单体的内阻值为1.5mohm-1.8mohm，并且所述第二电池单体的内阻值为1.2mohm-1.5mohm。所述电池单体的内阻值可通过下文实施例中所述的方法进行测量。通过对两种电池单体分别选择合适的内阻值范围，可以实现对电池包整体放电容量的准确控制。
在一些实施方式中，所述第一电池单体和第二电池单体均为锂离子二次电池。所述锂离子二次电池具有正极极片、负极极片、隔离膜及电解液，所述正极极片包括正极集流体和设置于正极集流体至少一个表面上的正极材料层，所述正极材料层包含正极活性物质和碳。在一些实施方式中，所述第一电池单体中含有式(I)所示的第一正极活性物质，所述第二 电池单体中含有式(II)所示的第二正极活性物质：
LiFe 1-x1M 1 x1PO 4        式(I)
LiFe 1-x2M 2 x2PO 4       式(II)
其中，0≤x1≤0.1，0<x2≤0.1，M 1和M 2各自独立地选自Cu、Mn、Cr、Zn、Pb、Ca、Co、Ni、Sr和Ti中的一种或多种，且M 2至少包括Mn。由于x2大于0且M 2至少包括Mn，式(II)所示的第二正极活性物质为磷酸锰铁锂类正极活性物质。当x1为0时，式(I)所示的第一正极活性物质即为不含锰的磷酸铁锂。
在一些实施方式中，所述第二正极活性物质中Mn元素的质量占比大于所述第一正极活性物质中Mn元素的质量占比。更高含量的锰元素的掺杂可以使式(II)所示的第二正极活性物质的晶胞参数变大，改善Li +的扩散速率，提高所述正极活性物质的综合电化学性能，从而使得包含所述第二正极活性物质的第二电池单体的内阻值小于含有式(I)所示的第一正极活性物质的第一电池单体。这种内阻值的减小进而使得第二电池单体在低温下相比于第一电池单体具有更好的动力学性能，并通过这两种电池单体在电池包中空间排布上的特殊设计，实现了电池包整体放电容量保持率和一致性的改善。
在一些实施方式中，所述第二正极活性物质的体积平均粒径小于所述第一正极活性物质的体积平均粒径。可选地，所述第二正极活性物质的体积平均粒径D50值为0.3μm-0.8μm，并且所述第一正极活性物质的体积平均粒径D50值为0.8μm-2.0μm。所述正极活性物质的体积平均粒径可根据GB/T19077-2016/ISO 13320:2009进行测量。由于所述第二正极活性物质的体积平均粒径D50值小于所述第一正极活性物质的体积平均粒径D50值，第二正极活性物质中的Li +离子在正极活性物质颗粒内部固相扩散的距离相对就比较小。另外，更低的体积平均粒径D50值使得所述第二正极活性 物质具有比第一正极活性物质更高的堆积密度。这些因素使得第二正极活性物质具有更好的综合电化学性能，从而使得包含所述第二正极活性物质的第二电池单体的内阻值小于含有第一正极活性物质的第一电池单体。如上所述，内阻值的减小使得第二电池单体在低温下相比于第一电池单体具有更好的动力学性能。
在另一些实施方式中，所述第一电池单体中含有式(III)所示的第三正极活性物质，所述第二电池单体中含有式(IV)所示的第四正极活性物质：
Li 1+x3Ni aCo bM 3 1-a-bO 2-y3A y3    式(III)
Li 1+x4Mn eM 4 2-eO 4-dB d       式(IV)
其中，式(III)中，-0.1≤x3≤0.2，0.3≤a＜0.95，0＜b＜0.2，0＜a+b＜1，0≤y3＜0.2，M 3选自Mn、Fe、Cr、Ti、Zn、V、Al、Zr和Ce中的一种或几种，A选自S、F、Cl和I中的一种或几种；式(IV)中，-0.1≤x4≤0.2，0＜e≤2，0≤d＜1，M 4为Ni、Fe、Cr、Ti、Zn、V、Al、Mg、Zr及Ce中的一种或多种，B为S、N、F、Cl、Br及I中的一种或多种。
在一些实施方式中，所述第一电池单体和所述第二电池单体中均含有电解液，且所述第二电池单体中的电解液的电导率大于所述第一电池单体中的电解液的电导率。由于第二电池单体中的电解液的电导率较大，则第二电池单体的综合电化学性能优于第一电池单体；相应地，第二电池单体的内阻值也就小于第一电池单体。可选地，所述第二电池单体中的电解液的电导率为9mS/cm-14mS/cm，并且所述第一电池单体中的电解液的电导率为5mS/cm-8mS/cm。电池单体中电解液的电导率可以通过电导率测试仪进行测量。
在本申请中，可对电池包中不同电池单体的空间排布进一步的设定，从而实现对于电池包放电性能的精确控制。在一些实施方式中，在所述电 池包的所述B区域中，至少四个顶角位置处的电池单体均为所述第二电池单体；可选地，所述B区域中，仅有所述电池包的四个顶角位置处的电池单体为所述第二电池单体。电池包的四个顶角位置处的电池单体由于至少三个表面均与外部大气相接触，因此其散热系数是电池包的所有电池单体中散热系数最高的。在这些位置处布置内阻值较小因而放电性能较好的所述第二电池单体，进一步平衡了内外区域由于温度不同所导致的放电容量的差异。
如上所述，电池包的放电容量在低温下会明显低于其额定容量。通过本申请的技术方案，在一些实施方式中，所提供的电池包在-7℃下的放电容量为所述电池包的额定容量的82％-96％。由于本申请的电池包在其外部的B区域中使用了较大量的动力学性能较好的第二电池单体，使得电池包整体的放电一致性得到了提升，位于外部的电池单体的放电容量的损失较小，因此电池包在低温下的整体放电容量相较于电池包的额定容量损失也较小。
下面对电池包中所包含的电池单体进行详细阐述。在一些实施方式中，所述第一电池单体和第二电池单体均为锂离子二次电池。
通常情况下，锂离子二次电池包括正极极片、负极极片、隔离膜及电解质。在电池充放电过程中，活性离子在正极极片和负极极片之间往返嵌入和脱出。隔离膜设置在正极极片和负极极片之间，起到隔离的作用。电解质在正极极片和负极极片之间起到传导离子的作用。
[电解液]
电解液在正极极片和负极极片之间起到传导离子的作用。电解液包括电解质盐和溶剂。
在本申请中，电解质盐可为锂离子二次电池中的常用电解质盐，例如锂盐，包括可为上述作为高热稳定性盐的锂盐、作为低阻抗添加剂的锂盐 或抑制铝箔腐蚀的锂盐。作为实例，电解质盐可选自LiPF 6(六氟磷酸锂)、LiBF 4(四氟硼酸锂)、LiAsF 6(六氟砷酸锂)、LiFSI(双氟磺酰亚胺锂)、LiTFSI(双三氟甲磺酰亚胺锂)、LiTFS(三氟甲磺酸锂)、LiDFOB(二氟草酸硼酸锂)、LiPO 2F 2(二氟磷酸锂)、LiDFOP(二氟二草酸磷酸锂)、LiSO 3F(氟磺酸锂)、NDFOP(二氟二草酸盐)、Li 2F(SO 2N) 2SO 2F、KFSI、CsFSI、Ba(FSI) 2及LiFSO 2NSO 2CH 2CH 2CF 3中的一种以上。
所述溶剂的种类没有特别的限制，可根据实际需求进行选择。在一些实施方式中，所述溶剂为非水性溶剂。可选地，所述溶剂可包括链状碳酸酯、环状碳酸酯、羧酸酯中的一种或几种。在一些实施方式中，溶剂可选自碳酸亚乙酯(EC)、碳酸亚丙酯(PC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)、碳酸二甲酯(DMC)、碳酸二丙酯(DPC)、碳酸甲丙酯(MPC)、碳酸乙丙酯(EPC)、碳酸亚丁酯(BC)、氟代碳酸亚乙酯(FEC)、甲酸甲酯(MF)、乙酸甲酯(MA)、乙酸乙酯(EA)、乙酸丙酯(PA)、丙酸甲酯(MP)、丙酸乙酯(EP)、丙酸丙酯(PP)、丁酸甲酯(MB)、丁酸乙酯(EB)、1,4-丁内酯(GBL)、四氢呋喃、环丁砜(SF)、二甲砜(MSM)、甲乙砜(EMS)及二乙砜(ESE)中的一种以上。
在一些实施方式中，所述电解液中还可选地包括其他添加剂。例如添加剂可以包括负极成膜添加剂，也可以包括正极成膜添加剂，还可以包括能够改善电池某些性能的添加剂，例如改善电池过充性能的添加剂、改善电池高温性能的添加剂、以及改善电池低温性能的添加剂等。作为示例，所述添加剂选自含有不饱和键的环状碳酸酯化合物、卤素取代的环状碳酸酯化合物、硫酸酯化合物、亚硫酸酯化合物、磺酸内酯化合物、二磺酸化合物、腈化合物、芳香化合物、异氰酸酯化合物、磷腈化合物、环状酸酐 化合物、亚磷酸酯化合物、磷酸酯化合物、硼酸酯化合物、羧酸酯化合物中的至少一种。
[正极极片]
正极极片包括正极集流体以及设置在正极集流体至少一个表面的正极材料层，所述正极材料层包括正极活性物质和碳。
作为示例，正极集流体具有在其自身厚度方向相对的两个表面，正极材料层设置在正极集流体相对的两个表面的其中任意一者或两者上。
本申请的锂离子二次电池中，所述正极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可采用铝箔。复合集流体可包括高分子材料基层和形成于高分子材料基层至少一个表面上的金属层。复合集流体可通过将金属材料(例如铝、铝合金、镍、镍合金、钛、钛合金、银及银合金等)形成在高分子材料基材(如聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)、聚乙烯(PE)等的基材)上而形成。
设置于正极集流体的表面上的正极材料层包括正极活性物质。本申请中所用的正极活性物质可具有如上文所述的式(I)、式(II)、式(III)或式(IV)的结构以及其中限定的各种数值定义。可选地，所述式(I)、式(II)、式(III)或式(IV)的正极活性物质在每种情况下占该种电池单体的正极活性物质总重量的60-100重量％，可选地为80-100重量％。在一些实施方式中，所述正极活性物质除了上述物质之外，还可包含其他选自锂过渡金属氧化物、橄榄石结构的含锂磷酸盐及其各自的改性化合物中的一种或几种。锂过渡金属氧化物的示例可包括但不限于锂钴氧化物、锂镍氧化物、锂锰氧化物、锂镍钴氧化物、锂锰钴氧化物、锂镍锰氧化物、锂镍钴锰氧化物、锂镍钴铝氧化物及其改性化合物中的一种或几种。橄榄石结构的含锂磷酸盐的示例可包括但不限于磷酸铁锂、磷酸铁锂与碳的复合材料、磷酸锰锂、 磷酸锰锂与碳的复合材料、磷酸锰铁锂、磷酸锰铁锂与碳的复合材料及其改性化合物中的一种或几种。这些材料均可以通过商业途径获得。正极活性物质表面上可包覆有碳。
正极材料层可选地包括导电剂。但对导电剂的种类不做具体限制，本领域技术人员可以根据实际需求进行选择。作为示例，用于正极材料的导电剂可以选自超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的一种以上。
正极材料层还可选地包括粘结剂。作为示例，粘结剂可以为丁苯橡胶(SBR)、水性丙烯酸树脂、聚偏二氟乙烯(PVDF)、聚四氟乙烯(PTFE)、乙烯-醋酸乙烯酯共聚物(EVA)、聚丙烯酸(PAA)、羧甲基纤维素(CMC)、聚乙烯醇(PVA)及聚乙烯醇缩丁醛(PVB)中的一种或几种。
本申请中可按照本领域已知的方法制备正极极片。作为示例，可以将包覆碳的正极活性物质、导电剂和粘结剂分散于溶剂(例如N-甲基吡咯烷酮(NMP))中，形成均匀的正极浆料；将正极浆料涂覆在正极集流体上，经烘干、冷压等工序后，得到正极极片。
[负极极片]
负极极片包括负极集流体以及设置在负极集流体至少一个表面上的负极材料层，所述负极材料层包括负极活性物质。
作为示例，负极集流体具有在其自身厚度方向相对的两个表面，负极材料层设置在负极集流体相对的两个表面中的任意一者或两者上。
本申请的锂离子二次电池中，所述负极集流体可采用金属箔片或复合集流体。例如，作为金属箔片，可以采用铜箔。复合集流体可包括高分子材料基层和形成于高分子材料基材至少一个表面上的金属层。复合集流体可通过将金属材料(例如铜、铜合金、镍、镍合金、钛、钛合金、银及银 合金等)形成在高分子材料基材(如聚丙烯(PP)、聚对苯二甲酸乙二醇酯(PET)、聚对苯二甲酸丁二醇酯(PBT)、聚苯乙烯(PS)、聚乙烯(PE)等的基材)上而形成。
本申请的锂离子二次电池中，所述负极材料层通常包含负极活性物质以及可选的粘结剂、可选的导电剂和其他可选助剂，通常是由负极浆料涂布干燥而成的。负极浆料涂通常是将负极活性物质以及可选的导电剂和粘结剂等分散于溶剂中并搅拌均匀而形成的。溶剂可以是N-甲基吡咯烷酮(NMP)或去离子水。
所述负极活性物质的具体种类不做限制，可以采用本领域已知的能够用于锂离子二次电池负极的活性物质，本领域技术人员可以根据实际需求进行选择。作为示例，负极活性物质可选自石墨、软碳、硬碳、中间相碳微球、碳纤维、碳纳米管、单质硅、硅氧化合物、硅碳复合物、钛酸锂中的一种或几种。
作为示例，导电剂可选自超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的一种以上。
作为示例，粘结剂可选自丁苯橡胶(SBR)、聚丙烯酸(PAA)、聚丙烯酸钠(PAAS)、聚丙烯酰胺(PAM)、聚乙烯醇(PVA)、海藻酸钠(SA)、聚甲基丙烯酸(PMAA)及羧甲基壳聚糖(CMCS)中的一种以上。
其他可选助剂例如是增稠剂(如羧甲基纤维素钠(CMC-Na))等。
[隔离膜]
采用电解液的锂离子二次电池中还包括隔离膜。隔离膜设置在正极极片和负极极片之间，起到隔离的作用。本申请对隔离膜的种类没有特别的限制，可以选用任意公知的具有良好的化学稳定性和机械稳定性的多孔结构隔离膜。在一些实施方式中，隔离膜的材质可选自玻璃纤维、无纺布、 聚乙烯、聚丙烯及聚偏二氟乙烯中的一种以上。隔离膜可以是单层薄膜，也可以是多层复合薄膜，没有特别限制。在隔离膜为多层复合薄膜时，各层的材料可以相同或不同，没有特别限制。
在一些实施方式中，正极极片、负极极片和隔离膜可通过卷绕工艺或叠片工艺制成电极组件。
在一些实施方式中，锂离子二次电池可包括外包装。该外包装可用于封装上述电极组件及电解质。
在一些实施方式中，锂离子二次电池的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。锂离子二次电池的外包装也可以是软包，例如袋式软包。软包的材质可以是塑料，作为塑料，可列举出聚丙烯(PP)、聚对苯二甲酸丁二醇酯(PBT)以及聚丁二酸丁二醇酯(PBS)等。
本申请对锂离子二次电池的形状没有特别的限制，其可以是圆柱形、方形或其他任意的形状。例如，图1是作为一个示例的方形结构的锂离子二次电池5。
在一些实施方式中，参照图2，外包装可包括壳体51和盖板53。其中，壳体51可包括底板和连接于底板上的侧板，底板和侧板围合形成容纳腔。壳体51具有与容纳腔连通的开口，盖板53能够盖设于所述开口，以封闭所述容纳腔。正极极片、负极极片和隔离膜可经卷绕工艺或叠片工艺形成电极组件52。电极组件52封装于所述容纳腔内。电解液浸润于电极组件52中。锂离子二次电池5所含电极组件52的数量可以为一个或多个，本领域技术人员可根据具体实际需求进行选择。
在一些实施方式中，锂离子二次电池可以组装成电池模块4，电池模块4所含锂离子二次电池的数量可以为一个或多个，具体数量本领域技术人员可根据电池模块4的应用和容量进行选择。在电池模块4中，多个锂离子二次电池5可以是沿电池模块的长度方向依次排列设置。当然，也可 以按照其他任意的方式进行排布。进一步可以通过紧固件将该多个锂离子二次电池5进行固定。可选地，电池模块4还可以包括具有容纳空间的外壳，多个锂离子二次电池5容纳于该容纳空间。
在一些实施方式中，上述锂离子二次电池5或者电池模块4可以组装成电池包1，电池包1所含锂离子二次电池5或者电池模块4的数量可由本领域技术人员根据电池包1的应用和容量进行选择。
图3和图4是作为一个示例的电池包1。参照图3和图4，在电池包1中可以包括电池箱和设置于电池箱中的多个电池单体。电池箱包括上箱体2和下箱体3，上箱体2能够盖设于下箱体3，并形成用于容纳电池单体的封闭空间。
图5是本申请的一个实施方式中的电池包的区域划分以及电池单体排布的示意图。其中，将两条长宽对角线Lc的各自1/4Lc等分点处的4个点相连所围成的区域定义为A区域，剩余区域定义为B区域。电池单体按照本申请所描述的种类和数量占比放置于对应区域中，从而实现不同区域放电性能的调节。
另外，本申请还提供一种装置，所述装置包括本申请提供的电池包。所述电池包可以用作所述装置的电源，也可以用作所述装置的能量存储单元。所述装置可以但不限于是移动设备(例如手机、笔记本电脑等)、电动车辆(例如纯电动车、混合动力电动车、插电式混合动力电动车、电动自行车、电动踏板车、电动高尔夫球车、电动卡车等)、电气列车、船舶及卫星、储能系统等。
作为所述装置，可以根据其使用需求来选择电池包。
图6是作为一个示例的装置。该装置为纯电动车、混合动力电动车、或插电式混合动力电动车等。为了满足该装置对锂离子二次电池的高功率和高能量密度的需求，可以采用电池包或电池模块。
实施例
以下，说明本申请的实施例。下面描述的实施例是示例性的，仅用于解释本申请，而不能理解为对本申请的限制。实施例中未注明具体技术或条件的，按照本领域内的文献所描述的技术或条件或者按照产品说明书进行。所用试剂或仪器未注明生产厂商者，均为可以通过市购获得的常规产品。
1.电池单元各参数以及电池包放电容量测试方法如下：
1)Mn元素含量测定：用ZEISS sigma 300扫描电子显微镜进行测试，将取适量粉末置于导电胶上，之后将样品装入样品仓中，关闭样品仓，抽真空，之后打开EDS，EDS软件自动收集元素分布信息；
2)正极活性物质平均粒径D50值测定：用设备型号马尔文2000(MasterSizer 2000)激光粒度仪，参考标准流程：GB/T19077-2016/ISO13320:2009，具体测试流程：取待测样品适量(样品浓度保证8-12％遮光度即可)，加入20ml去离子水，同时外超5min(53KHz/120W)，确保样品完全分散，之后按照GB/T19077-2016/ISO 13320:2009标准对样品进行测定。
3)电解液电导率测定：用设备型号雷磁DDSJ-318电导率测试仪对电解液电导率进行测试，首先将电极探头置于标准电解液中进行标定，之后置于待测电解液中，进行测量，重复测量三次，取平均值，保留两位小数。
4)电池内阻测试：
调整电池单体容量至50％SOC：在25℃环境中，以固定倍率1/3C对锂离子电池进行充放电(1C＝电池单体额定容量)，充放电电压区间为2.8-3.65V，重复此步骤三次，所取第三次放电容量记为电池单体标称容量 C0，以1/3C0开始充电至标称容量一半，调整电池单体SOC状态为50％SOC；
电池内阻测试：在25℃环境中，将如上电池单体，采用4C0放电30s，记录放电前后电压值，分别为V0和V1，(V0-V1)/4C0记为电池内阻值。
5)电池包放电容量测试：
25℃放电容量测试：将电池包置于25℃环境中，以固定倍率1/3C对锂离子电池进行充放电(1C＝电池单体额定容量)，充放电电压区间为2.8-3.65V，重复此步骤三次，所取第三次放电容量记为电池包标称容量C1；
-7℃放电容量测试：将电池包置于25℃环境中，以固定倍率1/3C1对锂离子电池进行放电，放电至截至电压2.0V，记录此时放电容量为C2；
-7℃电池包放电容量保持率：C2/C1比值即为电池包在-7℃放电容量保持率。
2.电池单元的制备
(1)正极极片的制备
将作为正极活性物质的包覆碳的磷酸铁锂(LFP)、导电剂乙炔黑、粘结剂聚偏二氟乙烯(PVDF)按照重量比为96:2:2溶于溶剂N-甲基吡咯烷酮(NMP)中，充分搅拌混合均匀后得到正极浆料。其中对于第一电池单体，选择具有如表1所示的Mn含量的磷酸铁锂材料作为正极活性材料(磷酸铁锂材料中可固有地含有一定量的Mn作为杂质；如Mn杂质含量不足，可特意掺杂Mn以实现所示Mn含量)。对于第二电池单体，通过对磷酸铁锂材料进行Mn掺杂得到如表2所示的具有各自的特定Mn含量的磷酸锰铁锂材料作为正极活性材料。另外，使用颗粒筛分机对所选择的 磷酸铁锂颗粒材料以及磷酸锰铁锂颗粒材料进行筛分，将各种材料进一步筛分成具有不同体积平均粒径D50值的级分，并分别应用于不用电池单体的制备中。将正极浆料均匀涂覆于铝正极集流体上，之后经过烘干、冷压、分切，得到正极极片。
(2)负极片的制备
将负极活性物质人造石墨、导电剂乙炔黑、粘结剂丁苯橡胶(SBR)、增稠剂羧甲基纤维素钠(CMC-Na)按照重量比为95:2:2:1溶于溶剂去离子水中，均匀混合后制备成负极浆料。将负极浆料均匀涂覆在负极集流体铜箔上，烘干后经过冷压、分切得到负极极片。
(3)电解液的制备
在氩气气氛手套箱中(H 2O<0.1ppm，O 2<0.1ppm)，将有机溶剂碳酸亚乙酯(EC)、碳酸二甲酯(DMC)以及碳酸甲乙酯(EMC)分别按照表1和表2中列出的重量比均匀混合，加入六氟磷酸锂(LiPF 6)并调节至1M/L的浓度，搅拌均匀，得到相应的电解液。通过调节电解液中溶剂的组成、用量以及电解质盐的浓度，获得具有如表1和表2中所述电导率的电解液用于制备相应的电池单体。
(4)锂离子二次电池的制备
使用上述(1)中制得的正极极片和上述(2)中制得的负极极片，以聚丙烯膜作为隔离膜，将正极极片、隔离膜、负极极片按顺序叠好，使隔离膜处于正、负极极片之间起到隔离的作用，然后卷绕得到电极组件。将电极组件置于电池壳体中，干燥后注入电解液，再经过化成、静置，制得锂离子二次电池作为电池单体。
3.电池包的组装
将如上所述制备的具有不同的Mn含量、正极活性物质体积平均粒径D50值以及电解液电导率的第一电池单体和第二电池单体按照表3中所示 的数量和区域进行放置，得到具有不同电池单体排布的电池包。在本申请实施例所组装的电池包中，仅含有如上文所述制备的第一电池单体和第二电池单体；其中，A区域中所有电池单体的总数均为48个，并且B区域中所有电池单体的总数均为72个。
对各实施例中所制备的电池包进行放电容量测试，测试结果显示于表3中。
表1：第一电池单体A1-A7的相应参数以及测试的内阻值
Figure PCTCN2021131491-appb-000001
表2：第二电池单体B1-B9的相应参数以及测试的内阻值
Figure PCTCN2021131491-appb-000002
Figure PCTCN2021131491-appb-000003
表3：实施例1-7以及对比例1-2的电池包放电容量测试结果
Figure PCTCN2021131491-appb-000004
由表1可见，对于第一电池单体，在其正极活性物质磷酸铁锂粒径D50值和电解液电导率保持不变不的情况下，其电阻值随着正极活性物质中Mn含量的略微增加而稍有减小。同样，在其他两个条件不变的情况下，第一电池单体的电阻值随着磷酸铁锂粒径D50值增大而增大，并随着电解液电导率增大而减小。
类似的情况对于第二电池单体也适用，参见表2。如表2所示，对于第二电池单体，在其正极活性物质磷酸锰铁锂粒径D50值和电解液电导率保持不变不的情况下，其电阻值随着正极活性物质中Mn含量的增加而明显减小。同样，在其他两个条件不变的情况下，第二电池单体的电阻值随着磷酸锰铁锂粒径D50值增大而增大，并随着电解液电导率增大而减小。总体而言，由于第二电池单体的正极活性物质中的Mn含量以及电解液电导率高于第一电池单体，而第二电池单体中的磷酸锰铁锂粒径D50值小于第一电池单体中的磷酸铁锂粒径D50值，第二电池单体的电阻值明显小于第一电池单体的电阻值。
从表3所示的实验数据可以看出，在A区域中的电池单体全部为第一电池单体的情况下，随着B区域中第二电池单体数量(以及数量占比)的提高，电池包整体上的放电容量保持率随之升高。在电池包中各电池单体数量和排布方式比较一致的情况下，第二电池单体的电阻值越小，则电池包的放电容量保持率也就越高。
对比例1中B区域中第二电池单体的数量为0，意指此时B区域中的电池单体全部为第一电池单体，即对比例1的电池包的所有区域中的电池单体全部为第一电池单体。此时的电池包的放电容量保持率仅为80.2％，其为本申请实施例中制备的所有电池包中最低的放电容量保持率。
值得注意的是对比例2，其中B区域中的电池单体全部为第一电池单体，而A区域中的电池单体全部为第二电池单体。将对比例2与实施例5 进行对比，其中电池包的电池单体排布完全相反。针对二者的放电容量测试结果表明，实施例5的电池包的放电容量保持率明显大于对比例2的放电容量保持率。这说明即使是同样数量的同种类的电池单体，在不同的空间排布下，电池包在低温下的放电容量保持率也会产生显著的变化。本申请所制备的电池包在同等条件下的低温放电容量保持率相比于现有技术实现了明显改善。
虽然已经参考实施例对本申请进行了描述，但在不脱离本申请的范围的情况下，可以对其进行各种改进并且可以用等效物替换其中的部件。尤其是，只要不存在结构冲突，各个实施例中所提到的各项技术特征均可以任意方式组合起来。本申请并不局限于文中公开的特定实施例，而是包括落入权利要求的范围内的所有技术方案。

Claims (14)

  1. 一种电池包，包括第一类电池单体和第二类电池单体，所述第一类电池单体包括n个第一电池单体，所述第二类电池单体包括m个第二电池单体，n和m各自独立地选自1以上的整数，
    其中，所述第二电池单体的内阻小于所述第一电池单体，并且所述第一电池单体与所述第二电池单体的内阻之差≥0.15mohm；
    所述电池包的长宽对角线为Lc，两条所述对角线Lc的各自1/4 Lc等分点处的4个点相连所围成的区域定义为A区域，剩余区域定义为B区域，其中A区域所包含的电池单体中所述第一电池单体的数量占比为20％至100％，并且B区域所包含的电池单体中所述第二电池单体的数量占比为5％至100％。
  2. 根据权利要求1所述的电池包，其中，所述第一电池单体与所述第二电池单体的内阻之差≥0.20mohm，可选地≥0.25mohm。
  3. 根据权利要求1或2所述的电池包，其中，所述第一电池单体的内阻与所述第二电池单体的内阻之比≥1.1；可选地，为1.2至1.5。
  4. 根据权利要求1至3中任一项所述的电池包，其中，所述第一电池单体的内阻值为1.5mohm-1.8mohm，并且所述第二电池单体的内阻值为1.2mohm-1.5mohm。
  5. 根据权利要求1至4中任一项所述的电池包，其中，所述第一电池单体中含有式(I)所示的第一正极活性物质，所述第二电池单体中含有式(II)所示的第二正极活性物质：
    LiFe 1-x1M 1 x1PO 4  式(I)
    LiFe 1-x2M 2 x2PO 4  式(II)
    其中，0≤x1≤0.1，0<x2≤0.1，M 1和M 2各自独立地选自Cu、Mn、 Cr、Zn、Pb、Ca、Co、Ni、Sr和Ti中的一种或多种，且M 2至少包括Mn。
  6. 根据权利要求5所述的电池包，其中，所述第二正极活性物质中Mn元素的质量占比大于所述第一正极活性物质中Mn元素的质量占比。
  7. 根据权利要求5或6所述的电池包，其中，所述第二正极活性物质的体积平均粒径小于所述第一正极活性物质的体积平均粒径，
    可选地，所述第二正极活性物质的体积平均粒径D50值为0.3μm-0.8μm，并且所述第一正极活性物质的体积平均粒径D50值为0.8μm-2.0μm。
  8. 根据权利要求1至4中任一项所述的电池包，其中，所述第一电池单体中含有式(III)所示的第三正极活性物质，所述第二电池单体中含有式(IV)所示的第四正极活性物质：
    Li 1+x3Ni aCo bM 3 1-a-bO 2-y3A y3  式(III)
    Li 1+x4Mn eM 4 2-eO 4-dB d  式(IV)
    其中，式(III)中，-0.1≤x3≤0.2，0.3≤a＜0.95，0＜b＜0.2，0＜a+b＜1，0≤y3＜0.2，M 3选自Mn、Fe、Cr、Ti、Zn、V、Al、Zr和Ce中的一种或几种，A选自S、F、Cl和I中的一种或几种；式(IV)中，-0.1≤x4≤0.2，0＜e≤2，0≤d＜1，M 4为Ni、Fe、Cr、Ti、Zn、V、Al、Mg、Zr及Ce中的一种或多种，B为S、N、F、Cl、Br及I中的一种或多种。
  9. 根据权利要求1至8中任一项所述的电池包，其中，所述第一电池单体和所述第二电池单体中均含有电解液，且所述第二电池单体中的电解液的电导率大于所述第一电池单体中的电解液的电导率，
    可选地，所述第二电池单体中的电解液的电导率为9mS/cm-14mS/cm，并且所述第一电池单体中的电解液的电导率为5mS/cm-8mS/cm。
  10. 根据权利要求1至9中任一项所述的电池包，其中，所述B区域 中，所述电池包的至少四个顶角位置处的电池单体均为所述第二电池单体；可选地，所述B区域中，仅有所述电池包的四个顶角位置处的电池单体为所述第二电池单体。
  11. 根据权利要求1至10中任一项所述的电池包，其中，所述A区域所包含的电池单体中所述第一电池单体的数量占比为60％至100％，可选地为80％-100％。
  12. [根据细则91更正 22.12.2021]　
    根据权利要求1至11中任一项所述的电池包，其中，所述B区域所包含的电池单体中所述第二电池单体的数量占比为40％至100％，可选地为60％-100％。
  13. [根据细则91更正 22.12.2021]　
    根据权利要求1至112中任一项所述的电池包，其中，所述电池包在-7℃下的放电容量为所述电池包的额定容量的82％-96％。
  14. [根据细则91更正 22.12.2021]　
    一种用电装置，其包括选自权利要求1-13中任一项所述的电池包。
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