WO2023070768A1 - 锂离子二次电池、电池模块、电池包和用电装置 - Google Patents

锂离子二次电池、电池模块、电池包和用电装置 Download PDF

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WO2023070768A1
WO2023070768A1 PCT/CN2021/131275 CN2021131275W WO2023070768A1 WO 2023070768 A1 WO2023070768 A1 WO 2023070768A1 CN 2021131275 W CN2021131275 W CN 2021131275W WO 2023070768 A1 WO2023070768 A1 WO 2023070768A1
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positive electrode
electrode material
ion secondary
lithium
secondary battery
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PCT/CN2021/131275
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French (fr)
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周墨林
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宁德新能源科技有限公司
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Priority to CN202180045723.1A priority Critical patent/CN115956308A/zh
Priority to EP21962112.5A priority patent/EP4421916A1/en
Publication of WO2023070768A1 publication Critical patent/WO2023070768A1/zh
Priority to US18/644,696 priority patent/US20240282920A1/en

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    • 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
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    • 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
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    • 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
    • H01M4/1315—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx containing halogen atoms, e.g. LiCoOxFy
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    • 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
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    • H01M4/362—Composites
    • H01M4/364—Composites as mixtures
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    • 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
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    • 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
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    • 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
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    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
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    • 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

Definitions

  • the application relates to a lithium-ion secondary battery, a battery module, a battery pack and an electrical device.
  • a solid electrolyte interface (SEI) will be formed on the surface of the negative electrode, causing irreversible capacity loss and reducing the energy density of lithium-ion energy storage devices.
  • SEI solid electrolyte interface
  • the active lithium source is consumed on the first cycle.
  • anode materials with high specific capacity such as alloys (silicon, tin, etc.), oxides (silicon oxide, tin oxide, etc.) and amorphous carbon anodes
  • the consumption of active lithium sources will be further aggravated. Therefore, finding a suitable lithium supplementation method is of great significance for further improving the energy density of lithium-ion secondary batteries.
  • the industry has proposed a method of using lithium powder, such as stabilized lithium metal powder (SLMP, stabilized lithium metal powder), to supplement lithium at the negative electrode.
  • SLMP stabilized lithium metal powder
  • this method can increase the energy density of the battery, the lithium metal powder does not The reactivity is extremely high, it is easy to react with moisture in the air, and there are great safety hazards.
  • the control of moisture is also extremely strict, which increases the difficulty of the process. .
  • Patent Document 1 discloses a lithium-supplementing positive electrode material based on a lithium oxy compound, a lithium source and an alkyllithium.
  • the decomposition potential of the lithium-containing compound is high, and oxygen and other by-products are generated during the decomposition process, which will affect the life of the battery.
  • Li 2 NiO 2 -based lithium supplement materials are known as lithium supplement materials.
  • the content of free lithium on the surface of this kind of material is extremely high, and it is easy to cause the gel of the slurry during the slurry mixing process, which seriously affects the processing performance.
  • a large amount of active lithium is inserted into the negative electrode, resulting in a further decrease in the real potential of the negative electrode, and the solvent in the electrolyte continues to undergo a reduction reaction at the negative electrode, resulting in a continuous increase in impedance and affecting the cycle performance of the battery.
  • Patent Document 1 CN104037418A
  • the present application is developed in view of the above-mentioned circumstances, and its purpose is to provide a lithium-ion secondary battery capable of taking energy density, cycle life and rate performance into consideration.
  • the application provides a lithium ion secondary battery, which includes a positive pole piece, a negative pole piece, a separator and an electrolyte, characterized in that,
  • the positive electrode sheet includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector,
  • the positive electrode material layer comprises a first positive electrode material represented by the following general formula (1) and a second positive electrode material represented by the following general formula (2),
  • the electrolyte contains vinylene carbonate,
  • the content of the vinylene carbonate is not less than 0.1% by weight and not more than 5% by weight relative to the total weight of the electrolytic solution.
  • M includes one or more of Ti, Zr, V, Cr, A includes one or more of S, N, F, Cl, Br, x, y, z and t respectively satisfy: -0.1 ⁇ x ⁇ 0.1, 0 ⁇ y ⁇ 1, 0 ⁇ z ⁇ 1, 0 ⁇ y+z ⁇ 1, 0 ⁇ t ⁇ 0.2.
  • N includes one or more of Mn, Fe, Co, Al, V, Cr, Nb
  • B includes one or more of S, N, F, Cl, Br, r, p, q, v and s respectively satisfy: -0.2 ⁇ r ⁇ 0.2, -0.5 ⁇ p ⁇ 0.5, -0.5 ⁇ q ⁇ 0.5, 0 ⁇ v ⁇ 0.01, 0 ⁇ p+q-v ⁇ 0.2, 0 ⁇ s ⁇ 0.2.
  • the second positive electrode material forms a phase barrier compared with the existing Li2NiO2 type lithium supplementary material
  • the solid solution with lower purity and higher specific capacity which can effectively improve the energy density, cycle life and rate performance of the lithium-ion secondary battery in synergy with the first positive electrode material having an olivine structure.
  • vinylene carbonate additive in the electrolyte, it produces a synergistic effect with the first positive electrode material and the second positive electrode material of the present invention, and after the first cycle of charging, the negative electrode forms a more uniform and dense SEI film. The continuous loss of active lithium is suppressed, and the cycle life of the lithium-ion secondary battery is further improved.
  • p, q, v respectively satisfy: -0.1 ⁇ p ⁇ 0.1, -0.1 ⁇ q ⁇ 0.1, 0.002 ⁇ v ⁇ 0.008.
  • the positive electrode sheet satisfies the following formula (3).
  • R represents the resistance of the positive pole piece, and its unit is ⁇
  • P represents the compacted density of the positive pole piece, and its unit is g/cm 3
  • Q represents the resistance of the positive pole piece Single surface density, its unit is g/1540.25mm 2 .
  • the positive electrode sheet satisfy the above formula (3), the energy density, rate performance and cycle life of the lithium-ion secondary battery can be further improved.
  • the positive pole piece further satisfies the following formula (4)
  • the positive electrode sheet further satisfy the above formula (4), the energy density, rate performance and cycle life of the lithium-ion secondary battery can be further improved.
  • the resistance of the positive pole piece satisfies R ⁇ 3 ⁇ , optionally satisfies R ⁇ 1 ⁇ . By making the resistance of the positive pole piece within the specific range, it is beneficial to improve the cycle performance and rate performance of the lithium-ion secondary battery.
  • the compacted density P (unit: g/cm 3 ) of the positive electrode sheet satisfies 1.6 ⁇ P ⁇ 2.6.
  • the migration of electrons and ions in the positive electrode sheet is beneficial, thereby improving the cycle performance of the lithium-ion secondary battery.
  • the single surface density Q (unit: g/1540.25 mm 2 ) of the positive electrode sheet satisfies 0.16 ⁇ Q ⁇ 0.45.
  • the weight ratio of the first positive electrode material to the second positive electrode material is 5:1 to 99:1, optionally 9:1 to 99:1.
  • the first positive electrode material accounts for the majority in the combination of the first positive electrode material and the second positive electrode material, so that the positive electrode sheet has a higher
  • the structural stability can reduce the capacity loss and impedance increase caused by the structural damage of the positive electrode material, and maintain cycle stability and dynamic performance.
  • the content of the first positive electrode material is 80% to 98% by weight, optionally 85% to 98%.
  • the crystal structure of the second cathode material belongs to the Immm space group in the orthorhombic crystal system.
  • the characteristic diffraction peak A appears at 36° to 38° in the X-ray diffraction spectrum of the second positive electrode material after the first round of charging, and the characteristic diffraction peak B appears at 42° to 44°, and at 62°
  • the characteristic diffraction peak C appears at 64°.
  • a second aspect of the present application provides a battery module including the secondary battery according to the first aspect of the present application.
  • the third aspect of the present application provides a battery pack, which includes the battery module according to the second aspect of the present application.
  • the fourth aspect of the present application provides a device, which includes at least one of the secondary battery according to the first aspect of the present application, the battery module according to the second aspect of the present application, or the battery pack according to the third aspect of the present application.
  • the battery module, battery pack, and device of the present application include the secondary battery provided by the present application, and thus have at least the same advantages as the secondary battery.
  • FIG. 1 is a schematic diagram of a secondary battery according to one embodiment of the present application.
  • FIG. 2 is an exploded view of the secondary battery according to one embodiment of the present application shown in FIG. 1 .
  • FIG. 3 is a schematic diagram of a battery module according to an embodiment of the present application.
  • FIG. 4 is a schematic diagram of a battery pack according to an embodiment of the present application.
  • FIG. 5 is an exploded view of the battery pack according to one embodiment of the present application shown in FIG. 4 .
  • Example 6 is an X-ray diffraction spectrum of the positive pole piece of the lithium ion secondary battery obtained in Example 1 after the first round of charging.
  • any lower limit may be combined with any upper limit to form an unexpressed range; and any lower limit may be combined with any other lower limit to form an unexpressed range, just as any upper limit may be combined with any other upper limit to form an unexpressed range.
  • every point or individual value between the endpoints of a range is included within that range, although not expressly stated herein.
  • 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 inventors of the present application have conducted intensive research, and found that: by adding Cu element, Ti element and other optional elements to the existing Li 2 NiO 2 lithium supplementary materials Composite metal elements, the second positive electrode material forms a solid solution with a lower phase barrier and higher purity and specific capacity than Li 2 NiO 2 -type lithium-supplementing materials, synergistic with the first positive electrode material having an olivine structure
  • the second positive electrode material has the characteristics of high first-time charging specific capacity and low first-efficiency, which effectively compensates for the loss of active lithium caused by the formation of SEI, and there are enough lithium ions during the first discharge.
  • the first positive electrode material with an olivine structure of the present invention has a stable structure, a small volume change during charging and discharging, and excellent cycle stability. Further, the inventors of the present application have found that by adding a specific amount of vinylene carbonate to the electrolyte, there is a synergistic effect with the positive electrode sheet comprising the first positive electrode material and the second positive electrode material, and the negative electrode is formed after the first round of charging. A more uniform and dense SEI film inhibits the continuous loss of active lithium and further improves the cycle life of lithium-ion secondary batteries. Therefore, according to the lithium ion secondary battery of this embodiment, the lithium ion secondary battery can realize high energy density, good rate performance and long cycle life.
  • the present application relates to a lithium ion secondary battery, which includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, wherein the positive electrode sheet includes a positive electrode collector and is arranged on the positive electrode collector. a positive electrode material layer on at least one surface of the
  • the positive electrode material layer comprises a first positive electrode material represented by the following general formula (1) and a second positive electrode material represented by the following general formula (2),
  • the electrolyte contains vinylene carbonate,
  • the content of the vinylene carbonate is not less than 0.1% by weight and not more than 5% by weight relative to the total weight of the electrolytic solution.
  • M includes one or more of Ti, Zr, V, Cr, A includes one or more of S, N, F, Cl, Br, x, y, z and t respectively satisfy: -0.1 ⁇ x ⁇ 0.1, 0 ⁇ y ⁇ 1, 0 ⁇ z ⁇ 1, 0 ⁇ y+z ⁇ 1, 0 ⁇ t ⁇ 0.2.
  • N includes one or more of Mn, Fe, Co, Al, V, Cr, Nb
  • B includes one or more of S, N, F, Cl, Br, r, p, q, v and s respectively satisfy: -0.2 ⁇ r ⁇ 0.2, -0.5 ⁇ p ⁇ 0.5, -0.5 ⁇ q ⁇ 0.5, 0 ⁇ v ⁇ 0.01, 0 ⁇ p+q-v ⁇ 0.2, 0 ⁇ s ⁇ 0.2.
  • Lithium-ion secondary battery refers to a battery that can activate the active material by charging after the lithium-ion battery is discharged and continue to use.
  • a lithium-ion secondary battery 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 set between the positive pole piece and the negative pole piece, which can insulate electrons, prevent internal short circuit, and allow active ions to pass through and move between the positive and negative poles. Play the role of isolation.
  • the electrolyte plays the role of conducting ions between the positive pole piece and the negative pole piece.
  • the positive pole piece includes a positive current collector and a positive material layer disposed on at least one surface of the positive current collector.
  • the positive electrode current collector has two opposing surfaces in its own thickness direction, and the positive electrode material layer is disposed on either or both of the opposing two surfaces of the positive electrode current collector.
  • the positive electrode material layer includes a first positive electrode material represented by the following general formula (1) and a second positive electrode material represented by the following general formula (2).
  • M includes one or more of Ti, Zr, V, Cr, A includes one or more of S, N, F, Cl, Br, x, y, z and t respectively satisfy: -0.1 ⁇ x ⁇ 0.1, 0 ⁇ y ⁇ 1, 0 ⁇ z ⁇ 1, 0 ⁇ y+z ⁇ 1, 0 ⁇ t ⁇ 0.2.
  • N includes one or more of Mn, Fe, Co, Al, V, Cr, Nb
  • B includes one or more of S, N, F, Cl, Br, r, p, q, v and s respectively satisfy: -0.2 ⁇ r ⁇ 0.2, -0.5 ⁇ p ⁇ 0.5, -0.5 ⁇ q ⁇ 0.5, 0 ⁇ v ⁇ 0.01, 0 ⁇ p+q-v ⁇ 0.2, 0 ⁇ s ⁇ 0.2.
  • the lithium ion secondary battery can achieve high energy density, good rate performance and long cycle life.
  • x satisfies -0.1 ⁇ x ⁇ 0.1, from the perspective of further reducing the volume change in the charging and discharging process and further improving the cycle stability of the battery, x is preferably -0.1 ⁇ x ⁇ 0.05, more preferably Preferably -0.05 ⁇ x ⁇ 0.
  • y satisfies 0 ⁇ y ⁇ 1, and from the viewpoint of further improving the cycle stability of the battery, y is preferably 0.5 ⁇ y ⁇ 1, more preferably 0.5 ⁇ y ⁇ 0.95.
  • z satisfies 0 ⁇ z ⁇ 1, and from the viewpoint of improving the cycle stability of the battery, z is preferably 0 ⁇ z ⁇ 0.5, more preferably 0.025 ⁇ z ⁇ 0.45.
  • M is one or more selected from Ti, Zr, V, Cr, from producing a synergistic effect with the second positive electrode material, improving the energy density and cycle life of the lithium-ion secondary battery
  • M is preferably one or more selected from Ti, Zr, and V, more preferably one or more selected from Ti, Zr.
  • A includes one or more of S, N, F, Cl, and Br. From the viewpoint of maintaining excellent overall performance, A is preferably one or more of F, Cl, and Br, and more F is preferred.
  • t satisfies 0 ⁇ t ⁇ 0.2, and from the viewpoint of maintaining excellent overall performance, t is preferably 0 ⁇ t ⁇ 0.05.
  • y+z satisfies 0 ⁇ y+z ⁇ 1, from the viewpoint of producing a synergistic effect with the second positive electrode material and improving the energy density and cycle life of the lithium-ion secondary battery, y+z is preferably 0.95 ⁇ y+z ⁇ 1.
  • r satisfies -0.2 ⁇ r ⁇ 0.2, from the viewpoint of effectively making up for the loss of active lithium caused by the formation of SEI and further improving the energy density of the battery, r is preferably -0.05 ⁇ r ⁇ 0.2, More preferably, it is 0 ⁇ r ⁇ 0.2.
  • p satisfies -0.5 ⁇ p ⁇ 0.5.
  • p is preferably -0.1 ⁇ p ⁇ 0.1, more preferably -0.046 ⁇ p ⁇ 0.058, and even more preferably 0.002 ⁇ p ⁇ 0.054 .
  • q satisfies -0.5 ⁇ q ⁇ 0.5.
  • q is preferably -0.1 ⁇ q ⁇ 0.1, more preferably -0.046 ⁇ q ⁇ 0.058, and even more preferably 0.002 ⁇ q ⁇ 0.054.
  • v satisfies 0 ⁇ v ⁇ 0.01, from the perspective of better reducing the content of free lithium on the surface of the material, better improving the problem of positive electrode slurry gel, and effectively improving the energy density of the battery, v is preferably 0.002 ⁇ v ⁇ 0.008, more preferably 0.004 ⁇ v ⁇ 0.008.
  • s satisfies 0 ⁇ s ⁇ 0.2, and from the viewpoint of improving the cycle performance and energy density of the battery, s is preferably 0 ⁇ s ⁇ 0.1, more preferably 0 ⁇ s ⁇ 0.05.
  • N includes one or more of Mn, Fe, Co, Al, V, Cr, and Nb. From the viewpoint of improving the rate performance and cycle performance of the battery, N is preferably selected from Mn , Fe, Co, Cr one or more, more preferably one or more selected from Mn, Co.
  • B includes one or more of S, N, F, Cl, Br. From the viewpoint of maintaining excellent overall performance, B is preferably one or more selected from F, Cl, Br, and more F is preferred.
  • p+q-v satisfies 0 ⁇ p+q-v ⁇ 0.2
  • p+q-v preferably satisfies 0 ⁇ p+q-v ⁇ 0.1 from the viewpoint of improving the rate performance and cycle performance of the battery.
  • the positive electrode sheet satisfies the following formula (3).
  • R represents the resistance of the positive pole piece, and its unit is ⁇
  • P represents the compacted density of the positive pole piece, and its unit is g/cm 3
  • Q represents the resistance of the positive pole piece Single surface density, its unit is g/1540.25mm 2 .
  • the positive electrode sheet satisfy the above formula (3), the energy density, rate performance and cycle life of the lithium-ion secondary battery can be further improved.
  • the positive electrode sheet preferably further satisfies the following formula (4).
  • the calculation of R ⁇ P/Q only involves the calculation of numerical values.
  • the resistance R of the positive electrode is 0.5 ⁇
  • the compacted density P is 2.2g/cm 3
  • the resistance of the positive pole piece satisfies R ⁇ 3 ⁇ , preferably R ⁇ 1 ⁇ .
  • the resistance R of the positive pole piece is the value measured by the DC two-probe method, where the contact area between the probe and the positive pole piece is 49 ⁇ mm 2 , as an example, the upper and lower sides of the positive pole piece are clamped Hold between the two conductive terminals (14mm in diameter) of a pole piece resistance tester (Hioki EECORPORATION's BT23562 internal resistance tester), and apply a pressure of 15MPa to 27MPa to fix it, and use the pole piece resistance tester to measure The resistance of the positive pole piece.
  • a pole piece resistance tester Hioki EECORPORATION's BT23562 internal resistance tester
  • the compacted density P (unit: g/cm 3 ) of the positive electrode sheet satisfies 1.6 ⁇ P ⁇ 2.6.
  • the compaction density P of the positive electrode sheet in the specific range, the cycle performance and rate performance of the battery are avoided from deteriorating, thereby facilitating the migration of electrons and ions in the positive electrode sheet, and improving the cycle performance of the lithium-ion secondary battery .
  • the volume v of the positive electrode material layer may be the product of the area Ar of the positive electrode material layer and the thickness of the positive electrode material layer.
  • the single surface density Q (unit: g/1540.25 mm 2 ) of the positive electrode sheet satisfies 0.16 ⁇ Q ⁇ 0.45.
  • the weight ratio of the first positive electrode material to the second positive electrode material is 5:1 to 99:1, preferably 9:1 to 99:1, more preferably 10:1 to 48:1.
  • the first positive electrode material accounts for the majority in the combination of the first positive electrode material and the second positive electrode material, so that the positive electrode sheet has a higher
  • the structural stability can reduce the capacity loss and impedance increase caused by the structural damage of the positive electrode material, and maintain cycle stability and dynamic performance.
  • the content of the first positive electrode material is 80% to 98% by weight, preferably 85% to 98%.
  • the crystal structure of the second cathode material belongs to the Immm space group in the orthorhombic system.
  • the characteristic diffraction peak A appears at 36° to 38° in the X-ray diffraction spectrum of the second positive electrode material after the first round of charging, and the characteristic diffraction peak B appears at 42° to 44°, and at 62°
  • the characteristic diffraction peak C appears at 64°.
  • the positive electrode material layer of the present application may also contain other positive electrode materials, such as lithium transition metal oxides, within the range that does not impair the effect of the present application.
  • the positive electrode material layer of the present application includes optional binder and conductive agent.
  • the present invention does not specifically limit the types of the conductive agent and the binder, which can be selected according to actual needs.
  • the binder may comprise styrene butadiene rubber (SBR), water based acrylic resin (water based acrylic resin), carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene ( One or more of PTFE), polyvinyl butyral (PVB), ethylene-vinyl acetate copolymer (EVA) and polyvinyl alcohol (PVA).
  • SBR styrene butadiene rubber
  • water based acrylic resin water based acrylic resin
  • CMC carboxymethyl cellulose
  • PVDF polyvinylidene fluoride
  • PVDF polytetrafluoroethylene
  • PTFE polytetrafluoroethylene
  • PVB polyvinyl butyral
  • EVA ethylene-vinyl acetate copolymer
  • PVA polyvinyl alcohol
  • the conductive agent may include one or more of graphite, superconducting carbon, acetylene black, carbon black, Ke
  • the percentage by weight of the conductive agent in the positive electrode material layer is more than 0.5% by weight.
  • the weight percent of the binder in the positive electrode material layer is 2.5% by weight or less.
  • the positive electrode current collector can be metal foil, porous metal plate or composite current collector.
  • the metal foil and the porous metal plate for example, a foil or a porous plate of a metal such as aluminum, copper, nickel, titanium, or silver, or an alloy thereof can be used, and aluminum foil is preferable.
  • 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 thickness of the positive electrode current collector is 5 ⁇ m to 20 ⁇ m, preferably 6 ⁇ m to 18 ⁇ m, more preferably 8 ⁇ m to 16 ⁇ m.
  • the positive electrode sheet of the present application can be prepared according to common methods in the art. Specifically, the above-mentioned components for preparing the positive electrode sheet, such as the first positive electrode material, the second positive electrode material, an optional conductive agent, an optional binder, and any other components can be dispersed in a solvent (such as N -methylpyrrolidone) to form a positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained.
  • a positive electrode sheet can be manufactured by casting a positive electrode slurry for forming a positive electrode material layer on a separate carrier, and then laminating a film obtained by peeling off from the carrier on a positive electrode current collector .
  • the positive electrode slurry is prepared by directly mixing the first positive electrode material and the second positive electrode material, but it is not limited to this, and the second positive electrode material can also be separately prepared and coated on the first positive electrode material. upper or lower layer.
  • the negative electrode sheet generally includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector.
  • 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.
  • materials such as metal foil, porous metal plate or composite current collector can be used for the negative electrode current collector.
  • a metal foil or a porous metal plate a foil or a porous plate of a metal such as copper, nickel, titanium, or iron, or an alloy thereof can be used, and copper foil is preferable.
  • 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.
  • substrates such as polyethylene formate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.
  • the negative electrode material layer generally includes the negative electrode material and optional conductive agent, binder and thickener.
  • the negative electrode material can use the negative electrode material commonly used in the art to prepare the lithium ion secondary battery negative pole, such as natural graphite, artificial graphite, mesophase micro carbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon Composite, SiO, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO 2 , lithium titanate Li 4 Ti 5 O 12 with spinel structure, Li-Al alloy and metal lithium or more.
  • the negative electrode material commonly used in the art to prepare the lithium ion secondary battery negative pole, such as natural graphite, artificial graphite, mesophase micro carbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon Composite, SiO, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO 2 , lithium titanate Li 4 Ti 5 O 12 with spinel structure, Li-Al alloy and metal lithium or more.
  • the conductive agent may include one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.
  • the binder may include styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), water-based acrylic resin) and carboxymethyl cellulose (CMC) in one or more.
  • SBR styrene-butadiene rubber
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • PVB polyvinyl butyral
  • water-based acrylic resin and carboxymethyl cellulose
  • the thickener may be carboxymethylcellulose (CMC) or the like.
  • the present application is not limited to these materials, and the present application can also use other materials that can be used as lithium ion secondary batteries other than negative electrode materials, conductive agents, binders, and thickeners.
  • the negative electrode sheet of the present application can be prepared according to common methods in the art. Specifically, the negative electrode material and optional conductive agent, binder and thickener are dispersed in a solvent to form a uniform negative electrode slurry, and the negative electrode slurry is coated on the negative electrode current collector, dried, cooled Pressing and other processes to obtain the negative electrode.
  • the solvent may be N-methylpyrrolidone (NMP) or deionized water or the like.
  • the electrolytic solution of the present application includes an organic solvent, an electrolyte lithium salt and additives.
  • the present application does not specifically limit the types of organic solvents and electrolyte lithium salts, which can be selected according to actual needs.
  • the solvent may be selected from ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), carbonic acid Dipropyl ester (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate ( MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), butyl One or more of ethyl acetate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl
  • the electrolyte lithium salt may be selected from lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), lithium hexafluoroarsenate (LiAsF 6 ), bisfluorosulfonimide Lithium (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium difluorooxalate borate (LiBOB), lithium difluorophosphate ( One or more of LiPO 2 F 2 ), lithium difluorooxalate phosphate (LiDFOP) and lithium tetrafluorooxalate phosphate (LiTFOP).
  • LiPF 6 lithium hexafluorophosphate
  • LiBF 4 lithium perchlor
  • the electrolytic solution of the present application contains vinylene carbonate (VC) as an additive.
  • the content of the vinylene carbonate is not less than 0.1% by weight and not more than 5% by weight relative to the total weight of the electrolytic solution.
  • the electrolyte may also optionally include other additives.
  • the other additives may be any additives that can be used in lithium-ion secondary batteries, which are not specifically limited and can be selected according to actual needs.
  • additives may include ethylene carbonate (VEC), succinonitrile (SN), adiponitrile (AND), 1,3-propene sultone (PST), cyclic quaternary ammonium sulfonates , one or more of tris(trimethylsilane) phosphate (TMSP) and tris(trimethylsilane) borate (TMSB).
  • the electrolyte solution can be prepared according to common methods in the art. Specifically, an organic solvent, an electrolyte lithium salt, vinylene carbonate and other optional additives can be mixed uniformly to obtain an electrolyte.
  • the order of addition of the substances is not particularly limited.
  • electrolyte lithium salt, vinylene carbonate and other optional additives are added into an organic solvent and mixed uniformly to obtain an electrolyte solution.
  • the electrolyte lithium salt may be added into the organic solvent first, and then the vinylene carbonate and other optional additives may be added into the organic solvent separately or simultaneously.
  • the isolation film can be selected from glass fiber films, non-woven films, polyethylene films, polypropylene films, polyvinylidene fluoride films, and multilayer composite films containing one or more of them. one or several.
  • the positive pole piece, the separator and the negative pole piece are stacked in order, so that the separator is placed between the positive pole piece and the negative pole piece to play the role of isolation, and the electrode assembly is obtained, and the electrode assembly is placed outside In the packaging, the electrolyte solution is injected and sealed to obtain a lithium ion secondary battery.
  • the positive pole piece, the separator and the negative pole piece can also be wound to obtain the electrode assembly.
  • 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 can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS) and the like.
  • FIG. 1 is an example of a lithium-ion secondary battery 5 with a square structure.
  • the outer package may include a casing 51 and a cover plate 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 chamber. 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 several, and can be adjusted according to requirements.
  • lithium-ion secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.
  • FIG. 3 is a battery module 4 as an example.
  • a plurality of lithium-ion secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4 .
  • the plurality of secondary batteries 5 may be fixed by fasteners.
  • the battery module 4 may also include a case having a housing space in which a plurality of secondary batteries 5 are accommodated.
  • the above battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.
  • the battery pack 1 may include a battery box and a plurality of battery modules 4 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 the battery module 4 .
  • Multiple battery modules 4 can be arranged in the battery box in any manner.
  • the lithium ion secondary battery can be used as a power source of the device, and can also be used as an energy storage unit of 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.
  • the device can select lithium-ion secondary batteries, battery modules or battery packs according to its use requirements.
  • As an example device may be a cell phone, tablet, laptop, etc.
  • the device is usually required to be light and thin, and a lithium-ion secondary battery can be used as a power source.
  • the first positive electrode material LiFePO 4 , the second positive electrode material Li 2 Ni 0.498 Cu 0.498 Ti 0.002 O 2 , the binder polyvinylidene fluoride (PVDF), and the conductive agent carbon black are in a mass ratio of 92.4:4.0:2.1:1.5 Dissolved in the solvent N-methylpyrrolidone (NMP), fully stirred and mixed under vacuum to a uniform transparent system to obtain the positive electrode slurry; then evenly coated the positive electrode slurry on the aluminum foil of the positive electrode current collector, and then transferred to the oven Dry at 120° C., cold press and cut to obtain the positive electrode.
  • NMP solvent N-methylpyrrolidone
  • the weight percent content of the first positive electrode material LiFePO 4 is 92.4%
  • the weight percent content of the second positive electrode material Li 2 Ni 0.498 Cu 0.498 Ti 0.002 O 2 is 4.0%.
  • Negative electrode material artificial graphite, thickener sodium carboxymethyl cellulose (CMC-Na), binder styrene-butadiene rubber (SBR), conductive agent carbon black are dissolved in the solvent according to the mass ratio of 95.7:1.0:1.8:1.5. Ionized water was uniformly mixed under the action of a vacuum mixer to prepare negative electrode slurry; then the negative electrode slurry was evenly coated on the negative electrode current collector copper foil, and then transferred to an oven for drying at 120 ° C. After cold pressing, separation Cut to obtain the negative electrode sheet.
  • Ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were uniformly mixed in a volume ratio of 1:1:1 to obtain an organic solvent.
  • Dissolve 1 mol/L LiPF 6 in the organic solvent add 3% vinylene carbonate (VC) relative to the total mass of the electrolyte, and mix evenly to obtain the electrolyte.
  • VC vinylene carbonate
  • the positive pole piece, the separator, and the negative pole piece are stacked in order, so that the separator is between the positive pole piece and the negative pole piece to play the role of isolation, and then wound into an electrode assembly, welded to the tab, and the electrode assembly is assembled.
  • Into the casing inject the above-mentioned electrolyte and seal, and then go through the processes of standing, forming, shaping, etc. to produce a lithium-ion secondary battery.
  • a lithium ion secondary battery was prepared in the same manner as in Example 1, except that the type of the first positive electrode material, the type of the second positive electrode material, and the content of vinylene carbonate in the electrolyte were changed as shown in Table 1.
  • This is a charge-discharge cycle.
  • the lithium ion secondary battery is charged and discharged according to the above method, and the discharge capacity of each cycle is recorded until the discharge capacity of the lithium ion secondary battery decays to 80% of the discharge capacity of the first cycle, and the number of charge and discharge cycles is recorded.
  • the lithium-ion secondary battery was charged to 4.2V at a constant current rate of 0.5C, and then charged at a constant voltage until the current was less than or equal to 0.05C, and then discharged to 2.5V at a rate of 0.5C, and the 0.5C rate was recorded. discharge capacity.
  • the 2C rate discharge capacity retention (%) of the lithium ion secondary battery was obtained from the following formula, and this was defined as the rate performance (%).
  • Lithium-ion secondary battery 2C rate discharge capacity retention rate (%) 2C rate discharge capacity/0.5C rate discharge capacity ⁇ 100%
  • the lithium-ion secondary battery At 25°C, charge the lithium-ion secondary battery with a constant current of 0.2C rate to 4.2V, then charge it with a constant voltage until the current is less than or equal to 0.05C, then let it stand for 30 minutes, and then discharge it to 2.5V with a constant current rate of 0.2C , record the discharge capacity D 0 (Ah) and discharge platform V 0 (V) of the lithium-ion secondary battery at a rate of 0.2C. Weigh the weight of the lithium-ion battery and record it as m 0 (kg). Then, the energy density (unit: Wh/Kg) of the lithium ion secondary battery was calculated by the following formula.
  • the lithium-ion secondary battery prepared in Example 1 was charged to 4.2V at a constant current rate of 1C, and then charged at a constant voltage until the current was less than or equal to 0.05C. Disassemble to obtain the positive pole piece, and use an X-ray diffractometer to measure the positive pole piece, and the XRD spectrum of the obtained positive pole piece after the first cycle of charging is shown in FIG. 6 .
  • the sheet resistance of the positive electrode sheet was measured by the method shown below.
  • the compacted density and single surface density of the positive electrode sheet were calculated by the method shown below.
  • the resistance of the positive electrode sheet was measured with Hiji BT3562 resistance tester. Specifically, the positive pole piece is clamped between the two conductive terminals (14mm in diameter) of the internal resistance tester, and a pressure of 15MPa to 27MPa is applied to fix it, and the resistance R of the positive pole piece is tested.
  • the range is 5s ⁇ 17s.
  • the volume v of the positive electrode material layer is obtained by calculating the product of the area Ar of the positive electrode material layer and the thickness of the positive electrode material layer.
  • the energy density, rate performance and cycle life of the lithium-ion secondary battery can be further improved by making the positive pole piece satisfy the formula 0.5 ⁇ R ⁇ P/Q ⁇ 16.
  • the positive pole piece further satisfy the formula 1.5 ⁇ R ⁇ P/Q ⁇ 10, the energy density, rate performance and cycle life of the lithium-ion secondary battery can be further improved.

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Abstract

本申请公开了一种锂离子二次电池、电池模块、电池包和用电装置。所述锂离子二次电池包括正极极片、负极极片、隔离膜和电解液，所述正极极片包含正极集流体以及设置于该正极集流体的至少一个表面上的正极材料层，所述正极材料层包含下式(1)所示的第一正极材料和下式(2)所示的第二正极材料，所述电解液中包含碳酸亚乙烯酯，所述碳酸亚乙烯酯的含量相对于所述电解液的总重量为0.1重量％以上且5重量％以下。 Li 1+xFe yMn zM 1-y-zPO 4-tA t (1) (通式(1)中，M包括Ti、Zr、V、Cr中的一种或多种，A包括S、N、F、Cl、Br中的一种或多种，x、y、z和t分别满足：-0.1≤x＜0.1，0＜y≤1，0≤z＜1，0＜y+z≤1，0≤t＜0.2。) Li 2+rNi 0.5-pCu 0.5-qTi vN p+q-vO 2-sB s (2) (通式(2)中，N包括Mn、Fe、Co、Al、V、Cr、Nb中的一种或多种，B包括S、N、F、Cl、Br中的一种或多种，r、p、q、v和s分别满足：-0.2≤r≤0.2，-0.5＜p＜0.5，-0.5＜q＜0.5，0＜v＜0.01，0≤p+q-v＜0.2，0≤s＜0.2。)

Description

锂离子二次电池、电池模块、电池包和用电装置 技术领域
本申请涉及一种锂离子二次电池、电池模块、电池包和用电装置。
背景技术
锂离子二次电池在首次充放电过程中，负极表面会形成固态电解质界面(SEI)，造成不可逆容量损失，降低锂离子储能器件的能量密度。在使用了石墨负极的器件中，首次循环会消耗大约10％的活性锂源。进而，当采用高比容量的负极材料，例如合金类(硅、锡等)、氧化物类(氧化硅、氧化锡等)和无定形碳负极时，活性锂源的消耗将进一步加剧。因此，找到一种合适的补锂方法对进一步提升锂离子二次电池的能量密度具有重要的意义。
对此，业界提出有利用锂粉，例如稳定化金属锂粉(SLMP，stabilzed lithium metal powder)来进行负极补锂的方法，然而，这种方法虽然能够提高电池的能量密度，但金属锂粉的反应活性极高，容易与空气中的水分反应，安全隐患很大，在生产过程中除了要求采用不与锂反应的非水有机溶剂以外，对水分的控制也极为严苛，增大了工艺难度。
鉴于负极补锂策略面临着巨大的挑战，相对更加安全和便于操作的正极补锂方法得到了业界越来越多的关注。例如，专利文献1公开了一种基于锂氧化合物、锂源和烷基锂的正极补锂材料。但是，其中含锂化合物的分解电位较高，且分解过程中产生氧气和其它副产物，会影响电池的寿命。
另外，作为补锂材料，已知有Li 2NiO 2类补锂材料。但这类材料的表面游离锂含量极高，在调浆过程中极易造成浆料的凝胶，严重影响加工性能。此外，在首次充电时，大量的活性锂嵌入负极，导致负极的真实电位进一步降低，电解液中的溶剂持续在负极发生还原反应，造成阻抗的持续增长，影响电池的循环性能。
现有技术文献
专利文献
专利文献1：CN104037418A
发明内容
本申请是鉴于上述情况而研发的，其目的在于提供一种能够兼顾能量密度、循环寿命和倍率性能等的锂离子二次电池。
为了实现上述目的，本申请提供一种锂离子二次电池，其包括正极极片、负极极片、隔离膜和电解液，其特征在于，
所述正极极片包含正极集流体以及设置于所述正极集流体的至少一个表面上的正极材料层，
所述正极材料层包含下述通式(1)所示的第一正极材料和下述通式(2)所示的第二正极材料，
所述电解液中包含碳酸亚乙烯酯，
所述碳酸亚乙烯酯的含量相对于所述电解液的总重量为0.1重量％以上且5重量％以下。
Li 1+xFe yMn zM 1-y-zPO 4-tA t     (1)
(通式(1)中，M包括Ti、Zr、V、Cr中的一种或多种，A包括S、N、F、Cl、Br中的一种或多种，x、y、z和t分别满足：-0.1≤x＜0.1，0＜y≤1，0≤z＜1，0＜y+z≤1，0≤t＜0.2。)
Li 2+rNi 0.5-pCu 0.5-qTi vN p+q-vO 2-sB s    (2)
(通式(2)中，N包括Mn、Fe、Co、Al、V、Cr、Nb中的一种或多种，B包括S、N、F、Cl、Br中的一种或多种，r、p、q、v和s分别满足：-0.2≤r≤0.2，-0.5＜p＜0.5，-0.5＜q＜0.5，0＜v＜0.01，0≤p+q-v＜0.2，0≤s＜0.2。)
通过将同时包含所述第一正极材料和所述第二正极材料的正极材料层用于正极极片，第二正极材料形成与现有的Li 2NiO 2型补锂材料相比成相势垒更低且纯度和比容量更高的固溶体，其与具有橄榄石型结构的第一正极材料协同地，可以有效地提升锂离子二次电池的能量密度、循环寿命以及倍率性能。另外，通过在电解液中添加了特定量的碳酸亚乙烯酯添加剂，与本发明的第一正极材料和第二正极材料产生协同效应，首圈充电后使得负极形成了更加均匀致密的SEI膜，抑制 了活性锂的持续损失，进一步提升了锂离子二次电池的循环寿命。
在一些实施方式中，在通式(2)中，p、q、v分别满足：-0.1＜p＜0.1，-0.1＜q＜0.1，0.002≤v≤0.008。通过使p、q、v分别满足所述特定的范围，可以进一步降低材料的表面游离锂的含量，极大的改善正极浆料凝胶的问题，从而可以更好地兼顾能量密度、循环寿命和倍率性能。
在一些实施方式中，正极极片满足以下的式(3)。
0.5≤R·P/Q≤16     (3)
(式(3)中，R表示所述正极极片的电阻，其单位是Ω，P表示所述正极极片的压实密度，其单位是g/cm 3，Q表示所述正极极片的单面面密度，其单位是g/1540.25mm 2。)
通过使正极极片满足上述式(3)，能够进一步提升锂离子二次电池的能量密度，倍率性能和循环寿命。
在一些实施方式中，正极极片进一步满足以下的式(4)
1.5≤R·P/Q≤10     (4)
通过使正极极片进一步满足上述式(4)，能够更进一步提升锂离子二次电池的能量密度，倍率性能和循环寿命。
在一些实施方式中，正极极片的所述电阻满足R≤3Ω，可选地满足R≤1Ω。通过使正极极片的电阻在所述特定的范围，有利于提升锂离子二次电池的循环性能和倍率性能。
在一些实施方式中，正极极片的压实密度P(单位：g/cm 3)满足1.6＜P＜2.6。通过使正极极片的压实密度P在所述特定的范围，有利于正极极片中电子和离子的迁移，从而提高锂离子二次电池的循环性能。
在一些实施方式中，正极极片的单面面密度Q(单位：g/1540.25mm 2)满足0.16＜Q＜0.45。通过使正极极片的单面面密度Q在所述特定的范围，能够在保证充放电容量的同时，提高锂离子二次电池的循环性能和倍率性能。
在一些实施方式中，第一正极材料与第二正极材料的重量比为5:1至99:1，可选地为9:1至99:1。通过使第一正极材料与第二正极材料的重量比在所述特定的范围，从而在第一正极材料与第二正极材料的组 合中第一正极材料占大部分，使正极极片具有更高的结构稳定性，可以减少正极材料结构破坏所造成的容量损失和阻抗增加，保持循环稳定性和动力学性能。
在一些实施方式中，在正极材料层中，第一正极材料的含量以重量百分比计为80％至98％，可选地为85％至98％。通过使第一正极材料在正极材料层中的含量在所述特定的范围，从而进一步有利于正极极片的结构稳定，可以进一步减少正极材料结构破坏所造成的容量损失和阻抗增加，提高循环稳定性和动力学性能。
第二正极材料的晶体结构属于正交晶系中的Immm空间群。
在一些实施方式中，第二正极材料在首圈充电后的X射线衍射谱中在36°至38°处出现特征衍射峰A，在42°至44°处出现特征衍射峰B，在62°至64°处出现特征衍射峰C。
本申请第二方面提供一种电池模块，其包括根据本申请第一方面的二次电池。
本申请第三方面提供一种电池包，其包括根据本申请第二方面的电池模块。
本申请第四方面提供一种装置，其包括根据本申请第一方面的二次电池、根据本申请第二方面的电池模块、或根据本申请第三方面的电池包中的至少一种。
本申请的电池模块、电池包和装置包括本申请提供的二次电池，因而至少具有与所述二次电池相同的优势。
附图说明
图1是本申请的一个实施方式的二次电池的示意图。
图2是图1所示的本申请的一个实施方式的二次电池的分解图。
图3是本申请的一个实施方式的电池模块的示意图。
图4是本申请的一个实施方式的电池包的示意图。
图5是图4所示的本申请的一个实施方式的电池包的分解图。
图6是实施例1中得到的锂离子二次电池的正极极片在首圈充电后的X射线衍射谱图。
具体实施方式
为使本申请的目的、技术方案和优点更加清楚，下面将结合实施例对申请的实施方式进行详细地说明。然而，本领域的普通技术人员应当理解，这些实施例仅用于阐述本申请的技术方案而非限制。凡在本发明的精神和原则之内所作的任何修改，等同替换和改进等，均应包含在本发明的保护范围之内。
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，尽管未明确记载，但是范围端点间的每个点或单个数值都包含在该范围内。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。
在本文的描述中，需要说明的是，除非另有说明，“以上”、“以下”为包含本数，“一种或几种”中“几种”的含义是两种及两种以上。
本申请的上述发明内容并不意欲描述本申请中的每个公开的实施方式或每种实现方式。如下描述更具体地举例说明示例性实施方式。在整篇申请中的多处，通过一系列实施例提供了指导，这些实施例可以以各种组合形式使用。在各个实例中，列举仅作为代表性组，不应解释为穷举。
为了解决现有技术中所具有的上述问题，本申请的发明人进行了潜心研究，其结果发现：通过对现有的Li 2NiO 2型补锂材料进行了Cu元素、Ti元素以及其它可选的金属元素复合，第二正极材料形成与作为Li 2NiO 2型补锂材料相比成相势垒更低且纯度和比容量更高的固溶体，与具有橄榄石型结构的第一正极材料协同地，一方面，在电池首圈充电时，利用第二正极材料的首次充电比容量高、首效低的特点，有效地弥补了生成SEI造成的活性锂损失，首次放电时有足够的锂离子回嵌至第一正极材料中，有效地提升了电池的能量密度。另一方面，本发明的具有橄榄石型结构的第一正极材料的结构稳定，充放电过程体积变化小，循环稳定性优异。进一步，本申请的发明人发现：通过 在电解液中添加特定量的碳酸亚乙烯酯，与包含第一正极材料和第二正极材料的正极极片产生协同效应，首圈充电后使得负极形成了更加均匀致密的SEI膜，抑制了活性锂的持续损失，进一步提升了锂离子二次电池的循环寿命。因此，根据本实施方式的锂离子二次电池，能够使锂离子二次电池实现高能量密度，良好的倍率性能和长循环寿命。
即，本申请涉及一种锂离子二次电池，其包括正极极片、负极极片、隔离膜和电解液，其特征在于，所述正极极片包含正极集流体以及设置于所述正极集流体的至少一个表面上的正极材料层，
所述正极材料层包含下述通式(1)所示的第一正极材料和下述通式(2)所示的第二正极材料，
所述电解液中包含碳酸亚乙烯酯，
所述碳酸亚乙烯酯的含量相对于所述电解液的总重量为0.1重量％以上且5重量％以下。
Li 1+xFe yMn zM 1-y-zPO 4-tA t     (1)
(通式(1)中，M包括Ti、Zr、V、Cr中的一种或多种，A包括S、N、F、Cl、Br中的一种或多种，x、y、z和t分别满足：-0.1≤x＜0.1，0＜y≤1，0≤z＜1，0＜y+z≤1，0≤t＜0.2。)
Li 2+rNi 0.5-pCu 0.5-qTi vN p+q-vO 2-sB s       (2)
(通式(2)中，N包括Mn、Fe、Co、Al、V、Cr、Nb中的一种或多种，B包括S、N、F、Cl、Br中的一种或多种，r、p、q、v和s分别满足：-0.2≤r≤0.2，-0.5＜p＜0.5，-0.5＜q＜0.5，0＜v＜0.01，0≤p+q-v＜0.2，0≤s＜0.2。)
以下适当地参照附图对本申请的锂离子电池、电池模块、电池包和用电装置进行详细说明。
锂离子二次电池
锂离子二次电池，是指在锂离子电池放电后可通过充电的方式使活性材料激活而继续使用的电池。通常情况下，锂离子二次电池包括正极极片、负极极片、隔离膜及电解液。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，其可以对电子绝缘，防止内部发生短路，同时 使得活性离子能够透过并在正负极之间移动。起到隔离的作用。电解液在正极极片和负极极片之间起到传导离子的作用。
[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的至少一个表面上的正极材料层。作为示例，正极集流体具有在其自身厚度方向上相对的两个表面，正极材料层设置在正极集流体的相对的两个表面中的任一者或两者上。
正极材料层包含下述通式(1)所示的第一正极材料和下述通式(2)所示的第二正极材料。
Li 1+xFe yMn zM 1-y-zPO 4-tA t    (1)
(通式(1)中，M包括Ti、Zr、V、Cr中的一种或多种，A包括S、N、F、Cl、Br中的一种或多种，x、y、z和t分别满足：-0.1≤x＜0.1，0＜y≤1，0≤z＜1，0＜y+z≤1，0≤t＜0.2。)
Li 2+rNi 0.5-pCu 0.5-qTi vN p+q-vO 2-sB s    (2)
(通式(2)中，N包括Mn、Fe、Co、Al、V、Cr、Nb中的一种或多种，B包括S、N、F、Cl、Br中的一种或多种，r、p、q、v和s分别满足：-0.2≤r≤0.2，-0.5＜p＜0.5，-0.5＜q＜0.5，0＜v＜0.01，0≤p+q-v＜0.2，0≤s＜0.2。)
通过在正极材料层中同时包含上述第一正极材料和第二正极材料，能够使锂离子二次电池实现高能量密度，良好的倍率性能和长循环寿命。
在通式(1)中，x满足-0.1≤x＜0.1，从进一步使充放电过程中的体积变化小，进一步提高电池的循环稳定的观点考虑，x优选为-0.1≤x≤0.05，更优选为-0.05≤x≤0。另外，y满足0＜y≤1，从进一步提高电池的循环稳定的观点考虑，y优选为0.5≤y≤1，更优选为0.5≤y≤0.95。另外，z满足0≤z＜1，从改善电池的循环稳定的观点考虑，z优选为0≤z≤0.5，更优选为0.025≤z≤0.45。
在通式(1)中，M为选自Ti、Zr、V、Cr中的一种或多种，从与第二正极材料产生协同效应，提升锂离子二次电池的能量密度和循环寿命的观点考虑，M优选为选自Ti、Zr、V中的一种或多种，更优选为选自Ti、Zr中的一种或多种。另外，A包括S、N、F、Cl、Br中的 一种或多种，从保持优异的综合性能的观点考虑，A优选为选自F、Cl、Br中的一种或多种，更优选为F。另外，t满足0≤t＜0.2，从保持优异的综合性能的观点考虑，t优选为0≤t≤0.05。
在通式(1)中，y+z满足0＜y+z≤1，从与第二正极材料产生协同效应，提升锂离子二次电池的能量密度和循环寿命的观点考虑，y+z优选为0.95≤y+z≤1。
在通式(2)中，r满足-0.2≤r≤0.2，从有效地弥补生成SEI造成的活性锂的损失，进一步提升电池的能量密度的观点考虑，r优选为-0.05≤r≤0.2，更优选为0≤r≤0.2。另外，p满足-0.5＜p＜0.5，从进一步提升电池的能量密度的观点考虑，p优选为-0.1＜p＜0.1，更优选为-0.046≤p≤0.058，进一步优选为0.002≤p≤0.054。另外，q满足-0.5＜q＜0.5，从有效地提升电池的能量密度和循环寿命的观点考虑，q优选为-0.1＜q＜0.1，更优选为-0.046≤q≤0.058，进一步优选为0.002≤q≤0.054。进一步，v满足0＜v＜0.01，从更好地降低材料的表面游离锂的含量，更好地改善了正极浆料凝胶的问题，有效地提升电池的能量密度的观点考虑，v优选为0.002≤v≤0.008，更优选为0.004≤v≤0.008。进一步，s满足0≤s＜0.2，从提高电池的循环性能和能量密度的观点考虑，s优选为0≤s≤0.1，更优选为0≤s≤0.05。
在通式(2)中，N包括Mn、Fe、Co、Al、V、Cr、Nb中的一种或多种，从提高电池的倍率性能和循环性能的观点考虑，N优选为选自Mn、Fe、Co、Cr中的一种或多种，更优选为选自Mn、Co中的一种或多种。另外，B包括S、N、F、Cl、Br中的一种或多种，从保持优异的综合性能的观点考虑，B优选为选自F、Cl、Br中的一种或多种，更优选为F。
在通式(2)中，p+q-v满足0≤p+q-v＜0.2，从提高电池的倍率性能和循环性能的观点考虑，p+q-v优选满足0≤p+q-v≤0.1。
在一些实施方式中，正极极片满足以下的式(3)。
0.5≤R·P/Q≤16     (3)
(式(3)中，R表示所述正极极片的电阻，其单位是Ω，P表示所述正极极片的压实密度，其单位是g/cm 3，Q表示所述正极极片的单面面密度，其单位是g/1540.25mm 2。)
通过使正极极片满足上述式(3)，能够进一步提升锂离子二次电池的能量密度，倍率性能和循环寿命。
在一些实施方式中，正极极片优选进一步满足以下的式(4)。
1.5≤R·P/Q≤10      (4)
需要说明书的是，在本申请中，R·P/Q的计算仅涉及数值的计算，举例来说，正极的电阻R为0.5Ω，压实密度P为2.2g/cm 3，正极的单面面密度Q为0.3g/1540.25mm 2，则R·P/Q＝3.7。
在一些实施方式中，正极极片的电阻满足R≤3Ω，优选满足R≤1Ω。通过使正极极片的电阻在所述特定的范围，能够避免正极极片电阻过大而导致的锂离子二次电池的循环性能和倍率性能恶化，从而有利于提升锂离子二次电池的循环性能和倍率性能。在本申请中，正极极片的电阻R是采用直流两探针法所测得的值，其中探针与正极极片的接触面积为49πmm 2，作为一个示例，将正极极片的上下侧夹持于极片电阻测试仪(HIOKI E.E.CORPORATION制造的日置BT23562型内阻测试仪)的两个导电端子(直径为14mm)之间，并施加15MPa至27MPa的压力以固定，利用极片电阻测试仪测量正极极片的电阻。
在一些实施方式中，正极极片的压实密度P(单位：g/cm 3)满足1.6＜P＜2.6。通过使正极极片的压实密度P在所述特定的范围，避免电池的循环性能和倍率性能变差，从而有利于正极极片中电子和离子的迁移，提高锂离子二次电池的循环性能。在本申请中，正极的压实密度P可以通过公式P＝m/v计算得到，式中，m为正极材料层的重量，单位是g；v是正极材料层的体积，单位为cm 3。其中，正极材料层的体积v可以是正极材料层的面积A r与正极材料层的厚度之积。
在一些实施方式中，正极极片的单面面密度Q(单位：g/1540.25mm 2)满足0.16＜Q＜0.45。通过使正极极片的单面面密度Q在所述特定的范围，能够避免正极极片的单面面密度过大而导致的电池的循环寿命降低、对电池的倍率性能的影响和电池在高倍率下的放电容量降低，并且避免正极极片的单面面密度过小而导致的在相同电池容量下集流体和隔膜的长度的增加以及电池的内阻的增大，从而能够在保证充放电容量的同时，提高锂离子二次电池的循环性能和倍率 性能。在本申请中，正极极片的单面面密度Q可以通过公式Q＝1540.25m/A r计算得到，式中m是正极材料层的重量，单位为g；A r是正极活性材料层的面积，单位为mm 2。
在一些实施方式中，第一正极材料与第二正极材料的重量比为5:1至99:1，优选为9:1至99:1，更优选为10:1至48:1。通过使第一正极材料与第二正极材料的重量比在所述特定的范围，从而在第一正极材料与第二正极材料的组合中第一正极材料占大部分，使正极极片具有更高的结构稳定性，可以减少正极材料结构破坏所造成的容量损失和阻抗增加，保持循环稳定性和动力学性能。
在一些实施方式中，在正极材料层中，第一正极材料的含量以重量百分比计为80％至98％，优选为85％至98％。通过使第一正极材料在正极材料层中的含量在所述特定的范围，从而进一步有利于正极极片的结构稳定，可以进一步减少正极材料结构破坏所造成的容量损失和阻抗增加，提高循环稳定性和动力学性能。
在一些实施方式中，第二正极材料的晶体结构属于正交晶系中的Immm空间群。在一些实施方式中，第二正极材料在首圈充电后的X射线衍射谱中在36°至38°处出现特征衍射峰A，在42°至44°处出现特征衍射峰B，在62°至64°处出现特征衍射峰C。
本申请的正极材料层除了包含上述第一正极材料和上述第二正极材料以外，还可以在不损害本申请的效果的范围内包含其它正极材料，例如锂过渡金属氧化物等。
本申请的正极材料层包含可选的粘结剂和导电剂。本发明对导电剂及粘结剂的种类不做具体限制，可以根据实际需求进行选择。
作为示例，粘结剂可以包括选自丁苯橡胶(SBR)、水性丙烯酸树脂(water based acrylic resin)、羧甲基纤维素(CMC)、聚偏二氟乙烯(PVDF)、聚四氟乙烯(PTFE)、聚乙烯醇缩丁醛(PVB)、乙烯-醋酸乙烯酯共聚物(EVA)及聚乙烯醇(PVA)中的一种或多种。导电剂可以包括石墨、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一种或多种。
在一些实施方式中，导电剂在正极材料层中的重量百分比为0.5重量％以上。通过使导电剂的含量设定为上述范围，有利于获得较低的正极极片的电阻。
在一些实施方式中，粘结剂在正极材料层中的重量百分比为2.5重量％以下。通过使粘结剂的含量设定为上述范围，有利于获得较低的正极极片的电阻。
本申请的锂离子二次电池中，正极集流体可采用金属箔片、多孔金属板或复合集流体。作为金属箔片和多孔金属板，例如可以使用铝、铜、镍、钛或银等金属或它们的合金的箔材或多孔板，优选为铝箔。复合集流体可以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(例如聚丙烯(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。正极集流体的厚度为5μm至20μm，优选为6μm至18μm，更优选为8μm至16μm。
本申请的正极极片可以按照本领域通常的方法进行制备。具体来说，可以将上述用于制备正极极片的成分，例如第一正极材料、第二正极材料、可选的导电剂、可选的粘结剂和任意其他的成分分散于溶剂(例如N-甲基吡咯烷酮)中，形成正极浆料；将正极浆料涂覆在正极集流体上，经烘干、冷压等工序后，即可以得到正极极片。可替代地，可以通过如下方式来制造正极极片：将用于形成正极材料层的正极浆料流延在单独的载体上，然后将通过从载体剥离而获得的膜层压在正极集流体上。另外，在上述实施方式中，将第一正极材料和第二正极材料直接混合制备正极浆料，但并不限定于此，也可以将第二正极材料单独调浆，涂覆在第一正极材料的上层或下层。
[负极极片]
在锂离子二次电池中，负极极片通常包括负极集流体以及设置在负极集流体的至少一个表面上的负极材料层。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，负极集流体可以采用金属箔片、多孔金属板或复合集流体等材料。例如，作为金属箔片或多孔金属板，可以使用铜、镍、钛或铁等金属或它们的合金的箔材或多孔板，优选为铜箔。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(例如聚丙烯(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。
在本申请的锂离子二次电池中，负极材料层通常包括负极材料以及可选的导电剂、粘结剂和增稠剂。
负极材料可以使用本领域常用的用于制备锂离子二次电池负极的负极材料，例如可以是天然石墨、人造石墨、中间相微碳球(MCMB)、硬碳、软碳、硅、硅-碳复合物、SiO、Li-Sn合金、Li-Sn-O合金、Sn、SnO、SnO 2、尖晶石结构的钛酸锂Li 4Ti 5O 12、Li-Al合金及金属锂中的一种或多种。
作为示例，导电剂可以包括石墨、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或多种。
作为示例，粘结剂可以包括丁苯橡胶(SBR)、聚偏二氟乙烯(PVDF)、聚四氟乙烯(PTFE)、聚乙烯醇缩丁醛(PVB)、水性丙烯酸树脂(water-based acrylic resin)及羧甲基纤维素(CMC)中的一种或多种。
作为示例，增稠剂可以是羧甲基纤维素(CMC)等。
本申请并不限定于这些材料，本申请还可以使用可被用作锂离子二次电池的除了负极材料、导电剂、粘结剂和增稠剂以外的其它材料。
本申请的负极极片可以按照本领域通常的方法进行制备。具体来说，将负极材料及可选的导电剂、粘结剂和增稠剂分散于溶剂中，形成均匀的负极浆料，将负极浆料涂覆在负极集流体上，经烘干、冷压等工序得到负极。其中，溶剂可以是N-甲基吡咯烷酮(NMP)或去离子水等。
[电解液]
本申请的电解液包括有机溶剂、电解质锂盐和添加剂。本申请对有机溶剂和电解质锂盐的种类不进行具体地限制，可以根据实际需要进行选择。
作为示例，溶剂可以为选自碳酸亚乙酯(EC)、碳酸亚丙基酯(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)、氟代碳酸乙烯酯(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)、环丁砜(SF)、二甲砜(MSM)、甲乙砜(EMS)及二乙砜(ESE)中的一种或多种，优选使用两种以上。
作为示例，电解质锂盐可以为选自六氟磷酸锂(LiPF 6)、四氟硼酸锂(LiBF 4)、高氯酸锂(LiClO 4)、六氟砷酸锂(LiAsF 6)、双氟磺酰亚胺锂(LiFSI)、双三氟甲磺酰亚胺锂(LiTFSI)、三氟甲磺酸锂(LiTFS)、二氟草酸硼酸锂(LiDFOB)、二草酸硼酸锂(LiBOB)、二氟磷酸锂(LiPO 2F 2)、二氟二草酸磷酸锂(LiDFOP)及四氟草酸磷酸锂(LiTFOP)中的一种或多种。
本申请的电解液包含碳酸亚乙烯酯(VC)作为添加剂。所述碳酸亚乙烯酯的含量相对于所述电解液的总重量为0.1重量％以上且5重量％以下。通过在电解液中包含特定量的碳酸亚乙烯酯作为添加剂，可以与包含第一正极材料和第二正极材料的正极极片产生协同效应，首圈充电后使得负极形成了更加均匀致密的SEI膜，抑制了活性锂的持续损失，进一步提升了锂离子二次电池的循环寿命。
所述电解液还可选地包括其它添加剂。所述其它添加剂可以是任意地可被用于锂离子二次电池的添加剂，对此不进行具体地限制，可以根据实际需求进行选择。作为示例，添加剂可以包括碳酸乙烯亚乙酯(VEC)、丁二腈(SN)、己二腈(AND)、1,3-丙烯磺酸内酯(PST)、磺酸酯环状季铵盐、三(三甲基硅烷)磷酸酯(TMSP)及三(三甲基硅烷)硼酸酯(TMSB)中的一种或多种。
所述电解液可以按照本领域通常的方法进行制备。具体来说，可以将有机溶剂、电解质锂盐、碳酸亚乙烯酯及其它可选的添加剂混合 均匀，得到电解液。对各物质的添加顺序并没有特别的限制。例如，将电解质锂盐、碳酸亚乙烯酯及其它可选的添加剂加入到有机溶剂中混合均匀，得到电解液。其中，可以是先将电解质锂盐加入有机溶剂中，然后再将碳酸亚乙烯酯和其它可选的添加剂分别或同时加入有机溶剂中。
[隔离膜]
本申请实施例对隔离膜的种类没有特别的限制，可以选用任意公知的用于锂离子二次电池的具有电化学稳定性和化学稳定性的多孔结构隔离膜。例如，隔离膜可以为选自玻璃纤维薄膜、无纺布薄膜、聚乙烯薄膜、聚丙烯薄膜、聚偏二氟乙烯薄膜、以及包含它们中的一种或两种以上的多层复合薄膜中的一种或几种。
在一些实施方式中，将正极极片、隔离膜及负极极片按顺序堆叠，使隔离膜处于正极极片与负极极片之间起到隔离的作用，得到电极组件，将电极组件置于外包装中，注入电解液并封口，得到锂离子二次电池。除了上述叠片工艺以外，正极极片、隔离膜和负极极片也可以通过卷绕工艺得到电极组件。
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，如聚丙烯(PP)、聚对苯二甲酸丁二醇酯(PBT)、聚丁二酸丁二醇酯(PBS)等中的一种或多种。
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。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，外包装可以包括壳体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。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几个，可根据需求来调节。
在一些实施方式中，锂离子二次电池可以组装成电池模块，电池模块所含二次电池的数量可以为多个，具体数量可根据电池模块的应用和容量来调节。
图3是作为一个示例的电池模块4。参照图3，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4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，多个二次电池5容纳于该容纳空间。
在一些实施例中，上述电池模块还可以组装成电池包，电池包所含电池模块的数量可以根据电池包的应用和容量进行调节。
图4和图5是作为一个示例的电池包1。参照图4和图5，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模块4。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模块4的封闭空间。多个电池模块4可以按照任意的方式排布于电池箱中。
装置
本申请的另一方面提供一种装置，所述装置包括本申请提供的锂离子二次电池、电池模块、或电池包中的至少一种。所述锂离子二次电池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。
所述装置可以根据其使用需求来选择锂离子二次电池、电池模块或电池包。
作为一个示例的装置可以是手机、平板电脑、笔记本电脑等。该装置通常要求轻薄化，可以采用锂离子二次电池作为电源。
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。
实施例1
(1)正极极片的制备
将第一正极材料LiFePO 4、第二正极材料Li 2Ni 0.498Cu 0.498Ti 0.002O 2、粘结剂聚偏二氟乙烯(PVDF)、导电剂炭黑按照质量比为92.4:4.0:2.1:1.5溶于溶剂N-甲基吡咯烷酮(NMP)中，在真空下充分搅拌混合均匀至均一透明状体系，得到正极浆料；之后将正极浆料均匀涂覆于正极集流体铝箔上，之后转移至烘箱在120℃下进行干燥，经过冷压、分切，得到正极。在正极材料层中，第一正极材料LiFePO 4的重量百分含量为92.4％，第二正极材料Li 2Ni 0.498Cu 0.498Ti 0.002O 2的重量百分含量为4.0％。
(2)负极极片的制备
将负极材料人造石墨、增稠剂羧甲基纤维素钠(CMC-Na)、粘结剂丁苯橡胶(SBR)、导电剂炭黑按照质量比为95.7:1.0:1.8:1.5溶于溶剂去离子水中，在真空搅拌机的作用下均匀混合，制备成负极浆料；然后将负极浆料均匀涂覆在负极集流体铜箔上，之后转移至烘箱在120℃下进行干燥，经过冷压、分切，得到负极极片。
(3)电解液的制备
将碳酸乙烯酯(EC)、碳酸甲乙酯(EMC)及碳酸二乙酯(DEC)按照体积比为1:1:1混合均匀，得到有机溶剂。将1mol/L的LiPF 6溶解于该有机溶剂中，相对于电解液的总质量，再加入3％的碳酸亚乙烯酯(VC)，混合均匀，得到电解液。
(4)隔离膜的准备：以厚度为14μm的聚丙烯膜(Celgard公司制造)作为隔离膜。
(5)锂离子电池的制备
将正极极片、隔离膜、负极极片按顺序层叠设置，使隔离膜处于 正极极片、负极极片之间起到隔离的作用，然后卷绕成电极组件，焊接极耳，将电极组件装入外壳中，注入上述电解液并封口，再经过静置、化成、整形等工序制得锂离子二次电池。
实施例2～21以及对比例1～7
除了如表1所示改变第一正极材料的种类、第二正极材料的种类、电解液中的碳酸亚乙烯酯的含量以外，与实施例1同样地制备锂离子二次电池。
对于上述各实施例以及对比例中制得的锂离子二次电池，通过下述方法进行电池性能测试，将得到的结果示于表1中。
(1)锂离子二次电池的高温循环性能测试：
在60℃下，将锂离子二次电池以1C倍率恒流充电至4.2V，再恒压充电至电流小于等于0.05C，再以1C倍率恒流放电至2.5V，此为一个充放电循环，记录锂离子二次电池第一次循环的放电容量。将锂离子二次电池按照上述方法进行充放电循环，记录每一次循环的放电容量，直至锂离子二次电池的放电容量衰减至第一次循环的放电容量的80％，记录充放电循环次数。
(2)锂离子二次电池的倍率性能测试：
在25℃下，将锂离子二次电池以0.5C倍率恒流充电至4.2V，再恒压充电至电流小于等于0.05C，再以0.5C倍率恒流放电至2.5V，记录0.5C倍率的放电容量。
在25℃下，将锂离子二次电池以0.5C倍率恒流充电至4.2V，再恒压充电至电流小于等于0.05C，再以2C倍率恒流放电至2.5V，记录2C倍率的放电容量。
然后，通过以下的式子得到锂离子二次电池2C倍率放电容量保持率(％)，将其作为倍率性能(％)。
锂离子二次电池2C倍率放电容量保持率(％)＝2C倍率放电容量/0.5C倍率放电容量×100％
(3)锂离子二次电池的能量密度测试：
在25℃下，将锂离子二次电池以0.2C倍率恒流充电至4.2V，再恒压充电至电流小于等于0.05C，之后静置30分钟，再以0.2C倍率恒流放电至2.5V，记录锂离子二次电池0.2C倍率的放电容量D 0(Ah) 和放电平台V 0(V)。称量锂离子电池的重量，记为m 0(kg)。然后，通过下式算出锂离子二次电池的能量密度(单位：Wh/Kg)。
能量密度＝D 0*V 0/m 0。
(4)锂离子二次电池的正极极片的XRD谱图：
在25℃下，将实施例1中制得的锂离子二次电池以1C倍率恒流充电至4.2V，再恒压充电至电流小于等于0.05C，将首圈充电后的锂离子二次电池拆开，得到正极极片，使用X射线衍射仪对正极极片进行测定，将得到的正极极片的首圈充电后的XRD谱图示于图6中。
根据图6可知，在首圈充电后的X射线衍射谱中在36°至38°处出现特征衍射峰，在42°至44°处出现特征衍射峰，在62°至64°处出现特征衍射峰，上述特征衍射峰是岩盐相材料的特征峰，因此，可以确认第二正极材料在首圈充电后的X射线衍射谱中在36°至38°处出现特征衍射峰，在42°至44°处出现特征衍射峰，在62°至64°处出现特征衍射峰。
[表1]
Figure PCTCN2021131275-appb-000001
根据上述表1的结果可知，在同时具备本申请的第一正极材料和第二正极材料的实施例1～21中，可以使锂离子二次电池兼顾高能量密度、良好的倍率性能和长循环寿命。另一方面，在不具备本申请的第一正极材料或第二正极材料的对比例1～5中，锂离子二次电池的能量密度降低，高温循环次数减少。进一步，通过在电解液中加入特定含量的碳酸亚乙烯酯添加剂，可以诱导生成更加致密和轻薄的SEI层，阻止了电解液的持续消耗，从而进一步提升了锂离子二次电池的循环寿命。
(实施例22～27)
与实施例1的制备方法相似，不同点详见以下的表2。
另外，通过上述电池性能测试的方法对制得的锂离子二次电池的性能进行测试。将得到的结果示于表2中。
进一步，通过以下所示的方法对正极极片的膜片电阻进行测定。另外，通过以下所示的方法对正极极片的压实密度以及单面面密度进行计算。
(1)正极极片的膜片电阻R：
采用日置BT3562型电阻测试仪对正极极片的电阻进行测定。具体来说，将正极极片夹持于内阻测试仪的两个导电端子(直径为14mm)之间，并施加15MPa～27MPa的压力进行固定，测试正极极片的电阻R，采点时间的范围为5s～17s。
(2)正极极片的压实密度P：
正极的压实密度P通过公式P＝m/v计算而得到，式中，m为正极材料层的重量，单位是g；v是正极材料层的体积，单位为cm 3。其中，正极材料层的体积v通过计算正极材料层的面积A r与正极材料层的厚度的乘积而得到。
(3)正极极片的单面面密度Q：
正极极片的单面面密度Q通过公式Q＝1540.25m/A r计算而得到，式中m是正极材料层的重量，单位为g；A r是正极活性材料层的面积，单位为mm 2。
[表2]
Figure PCTCN2021131275-appb-000002
根据以上表2的结果可知，通过使正极极片满足式0.5≤R·P/Q≤16，能够进一步提升锂离子二次电池的能量密度、倍率性能和循环寿命。另外，通过使正极极片进一步满足式1.5≤R·P/Q≤10，能够更进 一步提升锂离子二次电池的能量密度，倍率性能和循环寿命。
本领域普通技术人员应当理解，上述各实施例仅是实现本申请的部分具体实施例，而在实际应用中，可以在形式上和细节上对其作各种改变和修改，均落入本申请的保护范围内。

Claims (10)

  1. 一种锂离子二次电池，其包括正极极片、负极极片、隔离膜和电解液，其特征在于，所述正极极片包含正极集流体以及设置于所述正极集流体的至少一个表面上的正极材料层，
    所述正极材料层包含下述通式(1)所示的第一正极材料和下述通式(2)所示的第二正极材料，
    Li 1+xFe yMn zM 1-y-zPO 4-tA t  (1)
    通式(1)中，M包括Ti、Zr、V或Cr中的一种或多种，A包括S、N、F、Cl或Br中的一种或多种，x、y、z和t分别满足：-0.1≤x＜0.1，0＜y≤1，0≤z＜1，0＜y+z≤1，0≤t＜0.2，
    Li 2+rNi 0.5-pCu 0.5-qTi vN p+q-vO 2-sB s  (2)
    通式(2)中，N包括Mn、Fe、Co、Al、V、Cr或Nb中的一种或多种，B包括S、N、F、Cl或Br中的一种或多种，r、p、q、v和s分别满足：-0.2≤r≤0.2，-0.5＜p＜0.5，-0.5＜q＜0.5，0＜v＜0.01，0≤p+q-v＜0.2，0≤s＜0.2，
    所述电解液中包含碳酸亚乙烯酯，
    所述碳酸亚乙烯酯的含量相对于所述电解液的总重量为0.1重量％以上且5重量％以下。
  2. 如权利要求1所述的锂离子二次电池，其特征在于，
    在所述通式(2)中，-0.1＜p＜0.1，-0.1＜q＜0.1，0.002≤v≤0.008。
  3. 如权利要求1或2所述的锂离子二次电池，其特征在于，
    所述正极极片满足以下的式(3)，
    0.5≤R·P/Q≤16  (3)
    式(3)中，R表示所述正极极片的电阻，其单位是Ω，P表示所述正极极片的压实密度，其单位是g/cm 3，Q表示所述正极极片的单面面密度，其单位是g/1540.25mm 2。
  4. 如权利要求3所述的锂离子二次电池，其特征在于，
    所述正极极片满足以下的条件中的至少一者，
    (1)所述正极极片满足以下的式(4)，
    1.5≤R·P/Q≤10  (4)；
    (2)所述正极极片的所述电阻满足R≤3Ω，可选地满足R≤1Ω；
    (3)所述正极极片的压实密度P满足1.6g/cm 3＜P＜2.6g/cm 3；
    (4)所述正极极片的单面面密度Q满足0.16g/1540.25mm 2＜Q＜0.45g/1540.25mm 2。
  5. 如权利要求1～4中任一项所述的锂离子二次电池，其特征在于，
    所述第一正极材料和所述第二正极材料满足以下的条件中的至少一者，
    (I)所述第一正极材料与所述第二正极材料的重量比为5:1至99:1，可选地为9:1至99:1；
    (II)在所述正极材料层中，所述第一正极材料的含量以重量百分比计为80％至98％，可选地为85％至98％。
  6. 如权利要求1～5中任一项所述的锂离子二次电池，其特征在于，所述第二正极材料的晶体结构属于Immm空间群。
  7. 如权利要求1～6中任一项所述的锂离子二次电池，其特征在于，
    所述第二正极材料在首圈充电后的X射线衍射谱中在36°至38°处出现特征衍射峰A，在42°至44°处出现特征衍射峰B，在62°至64°处出现特征衍射峰C。
  8. 一种电池模块，其包括权利要求1～7中任一项所述的锂离子二次电池。
  9. 一种电池包，其包括权利要求8所述的电池模块。
  10. 一种用电装置，其包括权利要求1～7中任一项所述的锂离子二次电池、权利要求8所述的电池模块或权利要求9所述的电池包中的 至少一种。
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