WO2023245619A1 - 二次电池、用于制备二次电池的方法、电池模块、电池包及用电装置 - Google Patents

二次电池、用于制备二次电池的方法、电池模块、电池包及用电装置 Download PDF

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WO2023245619A1
WO2023245619A1 PCT/CN2022/101117 CN2022101117W WO2023245619A1 WO 2023245619 A1 WO2023245619 A1 WO 2023245619A1 CN 2022101117 W CN2022101117 W CN 2022101117W WO 2023245619 A1 WO2023245619 A1 WO 2023245619A1
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electrolyte
secondary battery
lithium
optionally
positive electrode
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PCT/CN2022/101117
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English (en)
French (fr)
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吴则利
韩昌隆
郭洁
陈慧玲
黄磊
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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 PCT/CN2022/101117 priority Critical patent/WO2023245619A1/zh
Priority to CN202280015633.2A priority patent/CN117015882A/zh
Publication of WO2023245619A1 publication Critical patent/WO2023245619A1/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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • 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

  • This application belongs to the field of battery technology, and specifically relates to a secondary battery, a method for preparing a secondary battery, a battery module, a battery pack and an electrical device.
  • Secondary batteries rely on lithium ions to reciprocate and deintercalate between the positive and negative electrodes for charging and discharging. They have outstanding characteristics such as high energy density, long cycle life, no pollution, and no memory effect. Therefore, as a clean energy source, secondary batteries have gradually spread from electronic products to energy storage power systems such as hydraulic, thermal, wind and solar power stations, as well as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. Multiple areas.
  • Cobalt is an important component of cathode active materials for secondary batteries. However, cobalt is less abundant in the earth's crust, difficult to mine, and expensive. Therefore, low-cobalt or cobalt-free cathode active materials have become an inevitable development trend. However, cobalt contributes greatly to the lithium ion diffusion rate of the cathode active material. Low cobalt or no cobalt will reduce the lithium ion diffusion rate of the cathode active material and affect the cycle life of the secondary battery.
  • the purpose of this application is to provide a secondary battery, a method for preparing a secondary battery, a battery module, a battery pack and an electrical device, aiming to stabilize the crystal structure of a low-cobalt or cobalt-free cathode active material and improve its internal Lithium ion diffusion rate.
  • the inventor of the present application accidentally discovered during the research process that by making the electrolyte contain lithium tetrafluoroborate and making the mass percentage content x% of lithium tetrafluoroborate and the cobalt element content c in the low-cobalt or cobalt-free cathode active material satisfy x >0 and 0.05 ⁇ c+x/10 ⁇ 0.15, it can stabilize the crystal structure of low-cobalt or cobalt-free cathode active materials and increase the lithium ion diffusion rate inside them, thus enabling the secondary battery to have significantly improved cycle performance.
  • the secondary battery of the present application can also have good storage performance and dynamic performance.
  • the compacted density of the positive electrode sheet is Pg/cm 3
  • the secondary battery satisfies: 25 ⁇ P/(c+x/10) ⁇ 65, optionally, 30 ⁇ P/(c+x/10) ⁇ 50.
  • the secondary battery can have improved power performance on the premise of improved cycle performance and high energy density.
  • the compacted density P g/cm 3 of the positive electrode piece satisfies P from 3.3 to 3.6. This contributes to the secondary battery having high energy density.
  • the electrolyte further includes one or more of fluoroethylene carbonate, fluorosulfonyl imide lithium salt, and fluorosulfonyl lithium salt.
  • the mass percentage content of the fluorinated ethylene carbonate is y1%
  • the mass percentage content of the fluorosulfonimide lithium salt in the electrolyte is y2%
  • the fluorine in the electrolyte solution The mass percentage of lithium sulfonate salt is y3%, which is based on the total mass of the electrolyte, and the electrolyte satisfies: y1 ⁇ 0, y2 ⁇ 0, y3 ⁇ 0 and 0 ⁇ y1+y2+ y3 ⁇ 15. This helps to form a more stable interface film on the positive electrode and/or the negative electrode, thereby further improving the electrochemical performance of the secondary battery.
  • the molecular formula of the fluorosulfonimide lithium salt is LiN(SO 2 R 1 )(SO 2 R 2 ), and R 1 and R 2 each independently represent F or C n F 2n+1 , n is an integer from 1 to 10.
  • the fluorosulfonimide lithium salt includes lithium bisfluorosulfonimide, lithium bistrifluoromethanesulfonimide, or a combination thereof.
  • the molecular formula of the lithium fluorosulfonate salt is LiSO 3 R 3 , R 3 represents F, a partially fluorinated or fully fluorinated C1-C10 alkyl group, optionally,
  • the lithium fluorosulfonate salt includes lithium fluorosulfonate, lithium trifluoromethanesulfonate or combinations thereof.
  • the mass percentage y1% of the fluoroethylene carbonate in the electrolyte satisfies 0 ⁇ y1 ⁇ 2.5, optionally, 0 ⁇ y1 ⁇ 2.0. This can stabilize the negative electrode interface film and effectively improve the cycle performance of the secondary battery.
  • the mass percentage y1% of the fluoroethylene carbonate in the electrolyte satisfies 0.5 ⁇ y1/x ⁇ 4.0, optionally, 0.5 ⁇ y1/x ⁇ 2.0. In this way, the synergistic effect of lithium tetrafluoroborate and fluoroethylene carbonate can be fully exerted.
  • the mass percentage y1% of the fluoroethylene carbonate in the electrolyte satisfies 0 ⁇ y1 ⁇ 2.5 and .5 ⁇ y1/x ⁇ 4.0.
  • the mass percentage y2% of the fluorosulfonimide lithium salt in the electrolyte satisfies 0 ⁇ y2 ⁇ 14. This can significantly improve the rate performance and low-temperature performance of the secondary battery.
  • the mass percentage y2% of the fluorosulfonimide lithium salt in the electrolyte satisfies 1 ⁇ y2/x ⁇ 28. This enables the synergistic effect of lithium tetrafluoroborate and lithium fluorosulfonyl imide salt to be fully exerted.
  • the mass percentage y2% of the fluorosulfonimide lithium salt in the electrolyte satisfies 0 ⁇ y2 ⁇ 14 and 1 ⁇ y2/x ⁇ 28.
  • the mass percentage y2% of the fluorosulfonimide lithium salt in the electrolyte satisfies 0 ⁇ y2 ⁇ 5 and/or 1 ⁇ y2/x ⁇ 10.
  • the mass percentage y2% of the fluorosulfonimide lithium salt in the electrolyte satisfies 5 ⁇ y2 ⁇ 14 and/or 10 ⁇ y2/x ⁇ 28.
  • the mass percentage y2% of the fluorosulfonimide lithium salt in the electrolyte satisfies 5 ⁇ y2 ⁇ 14 and/or 10 ⁇ y2/x ⁇ 28.
  • 16 ⁇ y2/x ⁇ 28 satisfies 5 ⁇ y2 ⁇ 14;
  • the mass percentage y2% of the fluorosulfonimide lithium salt in the electrolyte satisfies 5 ⁇ y2 ⁇ 14 and/or 10 ⁇ y2/x ⁇ 28.
  • 16 ⁇ y2/x ⁇ 28 satisfies 5 ⁇ y2 ⁇ 14 and/or 10 ⁇ y2/x ⁇ 28.
  • the mass percentage y3% of the lithium fluorosulfonate salt in the electrolyte satisfies 0 ⁇ y3 ⁇ 1.0, optionally, 0 ⁇ y3 ⁇ 0.5. This can greatly improve the high-temperature performance of the secondary battery.
  • the mass percentage y3% of the lithium fluorosulfonate salt in the electrolyte satisfies 0.001 ⁇ y3/x ⁇ 2.0, optionally, 0.001 ⁇ y3/x ⁇ 1.0 . In this way, the synergistic effect of lithium tetrafluoroborate and lithium fluorosulfonate salt can be fully exerted.
  • the mass percentage y3% of the lithium fluorosulfonate salt in the electrolyte satisfies 0 ⁇ y3 ⁇ 1.0 and 0.001 ⁇ y3/x ⁇ 2.0.
  • the electrolyte further includes fluoroethylene carbonate, lithium fluorosulfonimide and lithium fluorosulfonate, and the electrolyte satisfies: 0 ⁇ y1 ⁇ 2.5, 0 ⁇ y2 ⁇ 14, 0 ⁇ y3 ⁇ 1.0, 0.5 ⁇ y1/x ⁇ 4.0, 1 ⁇ y2/x ⁇ 28, 0.001 ⁇ y3/x ⁇ 2.0 and 0.5 ⁇ y2/y1 ⁇ 48. At this time, the overall performance of the secondary battery is further improved.
  • the electrolyte when 0 ⁇ b ⁇ 0.7, the electrolyte satisfies: 0 ⁇ y1 ⁇ 2.5, 0 ⁇ y2 ⁇ 5, 0 ⁇ y3 ⁇ 1.0, 0.5 ⁇ y1/x ⁇ 4.0, 1 ⁇ y2/x ⁇ 10, 0.001 ⁇ y3/x ⁇ 2.0 and 0.5 ⁇ y2/y1 ⁇ 10.
  • the electrolyte satisfies: 0 ⁇ y1 ⁇ 2.5, 5 ⁇ y2 ⁇ 14, 0 ⁇ y3 ⁇ 1.0, 0.5 ⁇ y1/x ⁇ 4.0, 10 ⁇ y2/x ⁇ 28, 0.001 ⁇ y3/x ⁇ 2.0 and 6 ⁇ y2/y1 ⁇ 48.
  • the electrolyte solution satisfies: the electrolyte solution further includes fluoroethylene carbonate, fluorosulfonimide lithium salt and fluorosulfonyl lithium salt, and the electrolyte solution satisfies: 0 ⁇ y1 ⁇ 2.5, 0 ⁇ y2 ⁇ 14, 0 ⁇ y3 ⁇ 1.0, 0.5 ⁇ y1/x ⁇ 4.0, 1 ⁇ y2/x ⁇ 28, 0.001 ⁇ y3/x ⁇ 2.0, 0.5 ⁇ y2/y1 ⁇ 48 and 0.036 ⁇ x/(y2+y3) ⁇ 1.0.
  • This helps to form an inorganic/organic composite interface film with excellent performance on the positive electrode and the negative electrode, thereby further improving the overall performance of the secondary battery.
  • the electrolyte when 0 ⁇ b ⁇ 0.7, the electrolyte satisfies: 0 ⁇ y1 ⁇ 2.5, 0 ⁇ y2 ⁇ 5, 0 ⁇ y3 ⁇ 1.0, 0.5 ⁇ y1/x ⁇ 4.0, 1 ⁇ y2/x ⁇ 10, 0.001 ⁇ y3/x ⁇ 2.0, 0.5 ⁇ y2/y1 ⁇ 10 and 0.1 ⁇ x/(y2+y3) ⁇ 1.0.
  • the electrolyte satisfies: 0 ⁇ y1 ⁇ 2.5, 5 ⁇ y2 ⁇ 14, 0 ⁇ y3 ⁇ 1.0, 0.5 ⁇ y1/x ⁇ 4.0, 10 ⁇ y2/x ⁇ 28, 0.001 ⁇ y3/x ⁇ 2.0, 6 ⁇ y2/y1 ⁇ 48 and 0.036 ⁇ x/(y2+y3) ⁇ 0.1.
  • the mass percentage of the layered material with the molecular formula Li a Ni b Co c M1 d M2 e Of A g is 80% to 99%, based on the positive electrode film layer Optionally 85% to 99% based on total mass.
  • the secondary battery further satisfies that: the mass of the electrolyte is 10% to 20% of the total mass of the secondary battery. This is beneficial to forming a dense and low-resistance interface film on the surface of the positive electrode active material.
  • a second aspect of the present application provides a method for preparing a secondary battery, which at least includes the following steps: Step 1: Assemble a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte into a secondary battery, and the positive electrode sheet It includes a positive electrode current collector and a positive electrode film layer located on the surface of the positive electrode current collector.
  • the secondary batteries obtained by the preparation method of the present application can have significantly improved cycle performance and good storage performance and kinetic performance.
  • the method further includes the step of screening out secondary batteries satisfying 0 ⁇ x ⁇ 1.0 and 0.05 ⁇ c+x/10 ⁇ 0.15 from the secondary batteries obtained in step 2. At this time, the prepared secondary battery has further improved cycle performance.
  • the method further includes the step of screening out secondary batteries satisfying 25 ⁇ P/(c+x/10) ⁇ 65 from the secondary batteries obtained in step 2, P g/ cm3 represents the compacted density of the positive electrode piece.
  • the prepared secondary battery can have significantly improved cycle performance and high energy density, as well as improved power performance.
  • the method further includes the step of: screening out the secondary batteries obtained in step 2 that satisfy 0 ⁇ y1+y2+y3 ⁇ 15, 0 ⁇ y1 ⁇ 2.5, 0 ⁇ y2 ⁇ 14 , 0 ⁇ y3 ⁇ 1.0, 0.5 ⁇ y1/x ⁇ 4.0, 1 ⁇ y2/x ⁇ 28, 0.001 ⁇ y3/x ⁇ 2.0 and 0.5 ⁇ y2/y1 ⁇ 48 secondary batteries. At this time, the overall performance of the prepared secondary battery is further improved.
  • the method further includes the step of: screening out secondary batteries obtained in step 2 that satisfy 0 ⁇ y1+y2+y3 ⁇ 15, 0 ⁇ y1 ⁇ 2.5, 0 ⁇ y2 ⁇ 5, 0 ⁇ y3 ⁇ 1.0, 0.5 ⁇ y1/x ⁇ 4.0, 1 ⁇ y2/x ⁇ 10, 0.001 ⁇ y3/x ⁇ 2.0 and 0.5 ⁇ y2/y1 ⁇ 10 secondary batteries.
  • the method further includes the step of: screening out secondary batteries obtained in step 2 that satisfy 0 ⁇ y1+y2+y3 ⁇ 15, 0 ⁇ y1 ⁇ 2.5, 5 ⁇ y2 ⁇ 14, 0 ⁇ y3 ⁇ 1.0, 0.5 ⁇ y1/x ⁇ 4.0, 10 ⁇ y2/x ⁇ 28, 0.001 ⁇ y3/x ⁇ 2.0 and 6 ⁇ y2/y1 ⁇ 48 secondary batteries.
  • the method further includes the step of: screening out the secondary batteries obtained in step 2 that satisfy 0 ⁇ y1+y2+y3 ⁇ 15, 0 ⁇ y1 ⁇ 2.5, 0 ⁇ y2 ⁇ 14 , 0 ⁇ y3 ⁇ 1.0, 0.5 ⁇ y1/x ⁇ 4.0, 1 ⁇ y2/x ⁇ 28, 0.001 ⁇ y3/x ⁇ 2.0, 0.5 ⁇ y2/y1 ⁇ 48 and 0.036 ⁇ x/(y2+y3) ⁇ 1.0 of secondary batteries.
  • the overall performance of the prepared secondary battery is further improved.
  • the method further includes the step of: screening out secondary batteries obtained in step 2 that satisfy 0 ⁇ y1+y2+y3 ⁇ 15, 0 ⁇ y1 ⁇ 2.5, 0 ⁇ y2 ⁇ 5, 0 ⁇ y3 ⁇ 1.0, 0.5 ⁇ y1/x ⁇ 4.0, 1 ⁇ y2/x ⁇ 10, 0.001 ⁇ y3/x ⁇ 2.0, 0.5 ⁇ y2/y1 ⁇ 10 and 0.1 ⁇ x/(y2+y3 ) ⁇ 1.0 for secondary batteries.
  • the method further includes the step of: screening out secondary batteries obtained in step 2 that satisfy 0 ⁇ y1+y2+y3 ⁇ 15, 0 ⁇ y1 ⁇ 2.5, 5 ⁇ y2 ⁇ 14, 0 ⁇ y3 ⁇ 1.0, 0.5 ⁇ y1/x ⁇ 4.0, 10 ⁇ y2/x ⁇ 28, 0.001 ⁇ y3/x ⁇ 2.0, 6 ⁇ y2/y1 ⁇ 48 and 0.036 ⁇ x/(y2+y3 ) ⁇ 0.1 secondary batteries.
  • a third aspect of the present application provides a battery module, including the secondary battery of the first aspect of the present application or a secondary battery prepared by the method of the second aspect of the present application.
  • a fourth aspect of this application provides a battery pack, including one of the secondary battery of the first aspect of this application, the secondary battery prepared by the method of the second aspect of this application, and the battery module of the third aspect of this application.
  • the fifth aspect of this application provides an electrical device, including the secondary battery of the first aspect of this application, the secondary battery prepared by the method of the second aspect of this application, the battery module of the third aspect of this application, and the fourth aspect of this application. At least one of the battery packs.
  • the secondary battery of the present application has significantly improved cycle performance and good storage performance and dynamic performance.
  • the battery module, battery pack and electrical device of the present application include the secondary battery provided by the present application, and therefore have at least the same characteristics as the two The same advantages of secondary batteries.
  • FIG. 1 is a schematic diagram of an embodiment of the secondary battery of the present application.
  • FIG. 2 is an exploded schematic view of the embodiment of the secondary battery of FIG. 1 .
  • FIG. 3 is a schematic diagram of an embodiment of the battery module of the present application.
  • FIG. 4 is a schematic diagram of an embodiment of the battery pack of the present application.
  • FIG. 5 is an exploded schematic view of the embodiment of the battery pack shown in FIG. 4 .
  • FIG. 6 is a schematic diagram of an embodiment of a power consumption device including the secondary battery of the present application as a power source.
  • Ranges disclosed herein are defined in terms of lower and upper limits. A given range is defined by selecting a lower limit and an upper limit that define the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive of the endpoints, and may be arbitrarily combined, that is, any lower limit may be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, understand that ranges of 60-110 and 80-120 are also expected. Furthermore, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2- 3, 2-4 and 2-5.
  • the numerical range “a-b” represents an abbreviated representation of any combination of real numbers between a and b, where a and b are both real numbers.
  • the numerical range “0-5" means that all real numbers between "0-5" have been listed in this article, and "0-5" is just an abbreviation of these numerical combinations.
  • a certain parameter is an integer ⁇ 2
  • the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially.
  • step (c) means that step (c) may be added to the method in any order.
  • the method may include steps (a), (b) and (c). , may also include steps (a), (c) and (b), may also include steps (c), (a) and (b), etc.
  • condition "A or B” is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists) ; Or both A and B are true (or exist).
  • Secondary batteries also known as rechargeable batteries or storage batteries, refer to batteries that can be recharged to activate active materials and continue to be used after the battery is discharged.
  • a secondary battery includes a positive electrode plate, a negative electrode plate, a separator and an electrolyte.
  • lithium ions are inserted and detached back and forth between the positive electrode piece and the negative electrode piece.
  • the isolation film is placed between the positive electrode piece and the negative electrode piece. It mainly prevents short circuit between the positive electrode and the negative electrode and allows lithium ions to pass through.
  • the electrolyte plays a role in conducting lithium ions between the positive electrode piece and the negative electrode piece.
  • the cobalt element in the cathode active material will affect the ion conduction characteristics of the cathode active material: (1) When the cobalt element content in the cathode active material is high, the lithium ions in the bulk phase can be replenished to the surface of the cathode active material in a timely manner; ( 2) When the content of cobalt in the cathode active material is low, the lithium ions in the bulk phase cannot be replenished to the surface of the cathode active material, and the lithium ions on the surface have been desorbed, which will lead to excessive lithium removal from the surface of the cathode active material, thus Affects the crystal structure of the cathode active material (for example, irreversible distortion of the cathode active material and an increase in the number of lattice defects), reducing the
  • cobalt can stabilize the crystal structure of the cathode active material.
  • the dissolution rate of metal ions, especially manganese ions, in the positive electrode active material is accelerated.
  • the eluted manganese ions are reduced to metallic manganese after migrating to the negative electrode.
  • the metal manganese formed is equivalent to a "catalyst", which can catalyze the decomposition of the SEI film (solid electrolyte interphase, solid electrolyte interface film) on the surface of the negative electrode.
  • Part of the by-products produced are gases, which can easily cause the battery to expand and affect the safety of the secondary battery.
  • the other part is deposited on the surface of the negative electrode, blocking the passage of lithium ions in and out of the negative electrode, causing the impedance of the secondary battery to increase and affecting the dynamic performance of the secondary battery.
  • the electrolyte and active lithium ions inside the battery are continuously consumed, which also has an irreversible impact on the capacity retention rate of the secondary battery.
  • the inventor of the present application surprisingly discovered after extensive research that by making the electrolyte contain an appropriate content of lithium tetrafluoroborate and making the content of lithium tetrafluoroborate and the cobalt element content in the cathode active material comply with a specific relationship, low cobalt or low cobalt or The crystal structure of the cobalt-free cathode active material increases the lithium ion diffusion rate within it.
  • a secondary battery which includes an electrolyte and a positive electrode piece.
  • the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer located on the surface of the positive electrode current collector.
  • the electrolyte is one of the key factors affecting the performance of secondary batteries.
  • the most widely used electrolyte system currently commercially is a mixed carbonate solution of lithium hexafluorophosphate.
  • the thermal stability of lithium hexafluorophosphate is poor in high temperature environments. It will decompose to form PF 5 at high temperature.
  • PF 5 has strong Lewis acidity and will interact with the lone pair of electrons on the oxygen atoms in the organic solvent molecules to decompose the organic solvent.
  • PF 5 is highly sensitive to trace amounts of moisture in the electrolyte and will not react with water.
  • lithium hexafluorophosphate not only does not increase the lithium ion diffusion rate of low-cobalt or cobalt-free cathode active materials, but also easily corrodes the cathode active material and destroys its crystal structure. Therefore, there is a need to improve the electrolyte.
  • the inventor of the present application accidentally discovered during the research process that by making the electrolyte contain lithium tetrafluoroborate and making the mass percentage content x% of lithium tetrafluoroborate and the cobalt element content c in the low-cobalt or cobalt-free cathode active material satisfy x >0 and 0.05 ⁇ c+x/10 ⁇ 0.15, it can stabilize the crystal structure of low-cobalt or cobalt-free cathode active materials and increase the lithium ion diffusion rate inside them, thus enabling the secondary battery to have significantly improved cycle performance.
  • the secondary battery of the present application can also have good storage performance and dynamic performance.
  • lithium tetrafluoroborate when the mass percentage x% of lithium tetrafluoroborate and the cobalt element content c in the low-cobalt or cobalt-free cathode active material satisfy x>0 and 0.05 ⁇ c+x/10 ⁇ 0.15, lithium tetrafluoroborate It can form a dense and low-resistance interface film on the surface of the cathode active material, and the B atoms in lithium tetrafluoroborate can fully combine with the O atoms in the cathode active material, thereby reducing the charge transfer resistance of the cathode active material and reducing the The diffusion resistance of lithium ions in the bulk phase of the cathode active material prevents excessive lithium removal from the surface of the cathode active material and stabilizes the crystal structure of the cathode active material.
  • the crystal structure of the cathode active material of the present application is more stable, thereby further reducing the probability of problems such as unstable structural properties, chemical properties or electrochemical properties of the cathode active material due to excessive delithiation on the surface. Therefore, the secondary battery of the present application can have improved electrochemical performance, and in particular, can have significantly improved cycle performance.
  • lithium tetrafluoroborate when the mass percentage x% of lithium tetrafluoroborate and the cobalt element content c in the low-cobalt or cobalt-free cathode active material satisfy x>0 and 0.05 ⁇ c+x/10 ⁇ 0.15, lithium tetrafluoroborate It can form a dense and low-resistance interface film on the surface of the cathode active material. On the one hand, it can effectively reduce the direct contact between the cathode active material and the electrolyte. On the other hand, it can reduce the surface oxygen activity of the cathode active material. This can reduce the presence of the electrolyte in the cathode active material.
  • the oxidative decomposition of the positive electrode and the reduction of the dissolution of transition metal ions can thereby improve the electrochemical performance of the secondary battery, such as reducing the irreversible consumption of active lithium ions, reducing the battery volume expansion rate, and reducing the positive electrode interface resistance, etc. Therefore, the secondary battery of the present application can also have good storage performance and dynamic performance.
  • lithium tetrafluoroborate has high thermal stability and is insensitive to moisture, which can improve the high-temperature stability of secondary batteries.
  • the content of lithium tetrafluoroborate in the electrolyte is not enough to form a dense and low-resistance interface film on the surface of the low-cobalt or cobalt-free cathode active material, and lithium tetrafluoroborate cannot effectively reduce the low-resistance of the cathode active material.
  • the charge transfer resistance of cobalt or cobalt-free cathode active materials cannot effectively reduce the diffusion resistance of lithium ions in the bulk phase of low-cobalt or cobalt-free cathode active materials and inhibit excessive delithiation on the surface of low-cobalt or cobalt-free cathode active materials.
  • c+x/10>0.15 the content of lithium tetrafluoroborate in the electrolyte is too high. Due to its low solubility in the electrolyte, there is incompletely dissociated molecular tetrafluoroborate in the electrolyte. Lithium borate is easy to precipitate in the electrolyte, especially in low-temperature environments, which increases safety risks such as puncture of the isolation film. Therefore, the safety performance and cycle performance of secondary batteries are poor; in addition, precipitation Lithium tetrafluoroborate will also damage the electrode interface, thereby increasing the self-discharge of the secondary battery.
  • the mass percentage x% of lithium tetrafluoroborate satisfies x>0.
  • the content of lithium tetrafluoroborate is high, due to its low solubility in the electrolyte, there is incompletely dissociated molecular lithium tetrafluoroborate in the electrolyte, which is easy to precipitate in the electrolyte, especially The degree of precipitation increases in low-temperature environments, which in turn increases safety risks such as puncture of the isolation film. Therefore, when the content of lithium tetrafluoroborate is high, the safety performance and cycle performance of the secondary battery may be deteriorated. In addition, the precipitated lithium tetrafluoroborate will also damage the electrode interface, thereby increasing the self-discharge of the secondary battery. In some embodiments, optionally, 0 ⁇ x ⁇ 1.0.
  • the cobalt element content in the cathode active material will also affect the electronic conduction characteristics of the cathode active material: (1) When the cobalt element content in the cathode active material is high, the cathode activity The material has good electron conduction properties; (2) When the cobalt element content in the cathode active material is low, the electron conduction properties of the cathode active material become worse, and thus the power performance of the secondary battery becomes worse. In addition, the greater the compaction density of the positive electrode sheet, the worse the power performance of the secondary battery. Therefore, in order to ensure that the secondary battery has good power performance, the strategy usually adopted by the existing technology is to reduce the compaction density of the positive electrode sheet. , but the energy density of the secondary battery will be sacrificed.
  • the inventor of this application surprisingly found that when the compacted density of the positive electrode sheet P g/cm 3 , the mass percentage content of lithium tetrafluoroborate x% and the cobalt element content c in the low-cobalt or cobalt-free positive electrode active material further satisfy When 25 ⁇ P/(c+x/10) ⁇ 65, the secondary battery can have improved cycle performance and high energy density, as well as improved power performance, such as the initial power and cycle performance of the secondary battery. The power growth can be significantly improved.
  • the secondary battery can have improved power performance on the premise of improved cycle performance and high energy density. And it can effectively avoid the following situation: when P/(c+x/10) ⁇ 25, the compaction density of the positive electrode piece may be small, so the electronic conductive network in the positive electrode piece is poor and cannot effectively improve the secondary
  • the power performance of the battery is sacrificed at the same time as the energy density of the secondary battery; or the content of lithium tetrafluoroborate may be higher, which may cause the stability of the negative electrode interface film to become worse, resulting in higher internal resistance of the battery and worse power performance.
  • the compacted density P g/cm 3 of the positive electrode piece satisfies P from 3.3 to 3.6, more optionally from 3.4 to 3.5. This contributes to the secondary battery having high energy density.
  • the electrolyte may also include one of fluoroethylene carbonate (FEC), fluorosulfonyl imide lithium salt, fluorosulfonyl lithium salt, or Various, the mass percentage of the fluorinated ethylene carbonate in the electrolyte is y1%, and the mass percentage of the fluorosulfonimide lithium salt in the electrolyte is y2%, The mass percentage content of the lithium fluorosulfonate in the electrolyte is y3%, based on the total mass of the electrolyte, and the electrolyte satisfies: y1 ⁇ 0, y2 ⁇ 0, y3 ⁇ 0 and 0 ⁇ y1+y2+y3 ⁇ 15.
  • FEC fluoroethylene carbonate
  • fluorosulfonyl imide lithium salt fluorosulfonyl lithium salt
  • fluorosulfonyl lithium salt fluorosulfonyl lithium salt
  • Lithium tetrafluoroborate can form a dense and low-resistance interface film on the surface of the positive electrode active material.
  • the long-term stability of the interface film formed by lithium tetrafluoroborate on the negative electrode is poor. Therefore, when the electrolyte also contains the above compounds, it helps A more stable interfacial film is formed on the positive electrode and/or negative electrode, thereby further improving the electrochemical performance of the secondary battery.
  • the electrolyte may further include fluoroethylene carbonate.
  • the mass percentage y1% of the fluoroethylene carbonate satisfies 0 ⁇ y1 ⁇ 2.5.
  • y1 can be a range of 0.10, 0.20, 0.50, 0.75, 1.0, 1.25, 1.50, 1.75, 2.0, 2.5 or any of the above values. More optionally, 0 ⁇ y1 ⁇ 2.0, 0 ⁇ y1 ⁇ 1.75, 0 ⁇ y1 ⁇ 1.5, 0 ⁇ y1 ⁇ 1.25, 0 ⁇ y1 ⁇ 1.0, 0 ⁇ y1 ⁇ 0.75 or 0 ⁇ y1 ⁇ 0.5.
  • fluorinated ethylene carbonate can undergo a reductive decomposition reaction at a higher potential and form a SEI film with certain flexibility on the surface of the negative active material. It can also inhibit the degradation of organic solvents with lower potentials. Reduce decomposition and inhibit the insertion of organic solvents into the negative active material. Therefore, when the electrolyte also contains fluorinated ethylene carbonate, the negative electrode interface film can be stabilized, thereby effectively improving the cycle performance of the secondary battery.
  • fluorinated ethylene carbonate is resistant to high-pressure oxidation and is conducive to matching high-voltage cathode active materials, thereby helping to increase the energy density of secondary batteries.
  • fluoroethylene carbonate will form HF when it decomposes at high temperatures.
  • HF will increase the acidity of the electrolyte, destroy the structural stability of the cathode active material, and increase the gas production of the secondary battery, thereby worsening the high-temperature storage of the secondary battery. performance. Therefore, the content of fluoroethylene carbonate should not be too high.
  • the mass percentage x% of lithium tetrafluoroborate and the mass percentage y1% of fluoroethylene carbonate can also satisfy 0.5 ⁇ y1/x ⁇ 4.0.
  • the inventor of this application surprisingly discovered that by reasonably controlling the relationship between the mass percentage content x% of lithium tetrafluoroborate and the mass percentage content y1% of fluoroethylene carbonate, and making it satisfy 0.5 ⁇ y1/x ⁇ 4.0 When used, the synergistic effect of lithium tetrafluoroborate and fluoroethylene carbonate can be fully exerted, thereby not only not significantly increasing the gas production of the secondary battery, but also further improving the cycle performance of the secondary battery.
  • lithium tetrafluoroborate serves as a stabilizer for the cathode active material, and the B atoms in its structure also have the function of interacting with the O atoms on the surface of the cathode active material, thereby inhibiting the impact of HF on the structure of the cathode active material. of destruction.
  • the electrolyte may further include fluorosulfonimide lithium salt.
  • the molecular formula of the fluorosulfonimide lithium salt can be LiN(SO 2 R 1 )(SO 2 R 2 ), R 1 and R 2 each independently represent F or C n F 2n+1 , and n is 1 to An integer of 10.
  • the lithium fluorosulfonimide salt includes lithium bisfluorosulfonimide (LiFSI), lithium bistrifluoromethanesulfonimide (LiTFSI) or a combination thereof.
  • the mass percentage y2% of the fluorosulfonimide lithium salt satisfies 0 ⁇ y2 ⁇ 14.
  • y2 can be a range of 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or any of the above values.
  • the fluorosulfonyl imide anion is a weakly coordinated anion centered on N. It contains a conjugated group and strongly electroattractive -F or -C n F 2n+1 .
  • the anion charge is highly delocalized, and the anion is closely related to the lithium ion. The interaction between them is weak. Therefore, the fluorosulfonimide lithium salt has a low lattice energy and is easy to dissociate, thereby improving the ionic conductivity of the electrolyte, reducing the viscosity of the electrolyte, and improving the rate performance and low-temperature performance of the secondary battery.
  • the fluorosulfonimide lithium salt also has the characteristics of high thermal stability and not easy to hydrolyze, which can form a thinner SEI film with lower impedance and higher thermal stability on the surface of the negative active material, thereby reducing the Side reaction between negative active material and electrolyte. Therefore, when the electrolyte further contains fluorosulfonimide lithium salt, the rate performance and low-temperature performance of the secondary battery can be significantly improved.
  • fluorosulfonyl imide lithium salt is not resistant to high voltages and will corrode the positive electrode current collector (for example, aluminum foil) at higher potentials, increase side reactions between the positive electrode active material and the electrolyte, and easily affect the cycle of the secondary battery. performance. Therefore, the content of fluorosulfonimide lithium salt should not be too high.
  • the mass percentage x% of lithium tetrafluoroborate and the mass percentage y2% of lithium fluorosulfonimide salt can also satisfy 1 ⁇ y2/x ⁇ 28.
  • the inventor of the present application surprisingly discovered that the relationship between the mass percentage x% of lithium tetrafluoroborate and the mass percentage y2% of the lithium fluorosulfonyl imide salt can be reasonably controlled and make it satisfy 1 ⁇ y2/x When ⁇ 28, the synergistic effect of lithium tetrafluoroborate and fluorosulfonyl imide lithium salt can be fully exerted. Not only will the cycle performance of the secondary battery not be significantly deteriorated, but the rate performance and low-temperature performance of the secondary battery can be further improved.
  • lithium tetrafluoroborate as a stabilizer for the cathode active material, can form a dense and low-resistance interface film on the surface of the cathode active material, inhibiting side reactions between the cathode active material and the electrolyte;
  • tetrafluoroborate Lithium has a passivating effect on the cathode current collector. It can be oxidized and decomposed preferentially on the surface of the cathode current collector and form a passivation film, thereby effectively improving the corrosion of the fluorosulfonimide lithium salt on the cathode current collector.
  • the inventor also found that the nickel element content b in the cathode active material will affect the improvement effect of the fluorosulfonimide lithium salt on the performance of the secondary battery.
  • the content of nickel element is high, the thermal stability of the cathode active material is poor, and the high-temperature capacity decay is accelerated. Therefore, when a higher content of fluorosulfonimide lithium salt is used, its improvement effect on the high-temperature performance of the secondary battery It is more obvious; when the content of nickel element is low, the thermal stability of the cathode active material is better, and as the content of fluorosulfonimide lithium salt in the electrolyte increases, its improvement effect on the high temperature performance of the secondary battery will not last Increase.
  • the mass percentage y2% of the fluorosulfonimide lithium salt in the electrolyte satisfies: 0 ⁇ y2 ⁇ 5 and/or 1 ⁇ y2 /x ⁇ 10.
  • the mass percentage y2% of the fluorosulfonimide lithium salt in the electrolyte satisfies: 5 ⁇ y2 ⁇ 14 and/or 10 ⁇ y2 /x ⁇ 28.
  • the electrolyte may further include lithium fluorosulfonate salt.
  • the molecular formula of the lithium fluorosulfonate salt may be LiSO 3 R 3 , and R 3 represents F, a partially fluorinated or fully fluorinated C1-C10 alkyl group.
  • the lithium fluorosulfonate salt includes Lithium fluoromethanesulfonate, lithium trifluoromethanesulfonate or combinations thereof.
  • the mass percentage y3% of the lithium fluorosulfonate salt satisfies 0 ⁇ y3 ⁇ 1.0.
  • y3 can be a range of 0.10, 0.20, 0.30, 0.40, 0.50, 0.60, 0.70, 0.80, 0.90, 1.0 or any above value. More optionally, 0 ⁇ y3 ⁇ 0.9, 0 ⁇ y3 ⁇ 0.8, 0 ⁇ y3 ⁇ 0.7, 0 ⁇ y3 ⁇ 0.6, 0 ⁇ y3 ⁇ 0.5, 0 ⁇ y3 ⁇ 0.4, 0 ⁇ y3 ⁇ 0.3 or 0 ⁇ y3 ⁇ 0.2.
  • Lithium fluorosulfonate can not only form an interface film on the surface of the negative active material, but also can form an interface film on the surface of the positive active material. At the same time, it has high thermal stability, which can greatly improve the charging performance of secondary batteries at high temperatures. Discharge characteristics, improve the high-temperature cycle capacity retention rate of secondary batteries and suppress gas generation. However, the ion conductivity of lithium fluorosulfonate salt is low, which easily affects the dynamic performance of secondary batteries. Therefore, the content of lithium fluorosulfonate should not be too high.
  • the mass percentage x% of lithium tetrafluoroborate and the mass percentage y3% of lithium fluorosulfonate salt can also satisfy 0.001 ⁇ y3/x ⁇ 2.0.
  • the inventor of this application surprisingly discovered that the relationship between the mass percentage content x% of lithium tetrafluoroborate and the mass percentage content y3% of lithium fluorosulfonate salt can be reasonably controlled to satisfy 0.001 ⁇ y3/x ⁇ 2.0 , can give full play to the synergistic effect of lithium tetrafluoroborate and lithium fluorosulfonate salt, thereby helping to form a dense, stable and low-resistance interface film on the positive and negative electrodes, which can further improve the high-temperature performance of secondary batteries.
  • the electrolyte may further include any two of fluoroethylene carbonate, fluorosulfonimide lithium salt, and fluorosulfonyl lithium salt.
  • the electrolyte may include a combination of fluoroethylene carbonate and fluorosulfonimide lithium salt.
  • the mass percentage y1% of the fluorinated ethylene carbonate satisfies 0 ⁇ y1 ⁇ 2.5
  • the mass percentage y2% of the fluorosulfonimide lithium salt satisfies 0 ⁇ y2 ⁇ 14
  • 0 ⁇ y1+y2 ⁇ 15 the mass percentage y1% of the fluorinated ethylene carbonate satisfies 0 ⁇ y1 ⁇ 2.5
  • the mass percentage y2% of the fluorosulfonimide lithium salt satisfies 0 ⁇ y2 ⁇ 14
  • 0 ⁇ y1+y2 ⁇ 15 0 ⁇ y1+y2 ⁇ 15.
  • the mass percentage x% of lithium tetrafluoroborate, the mass percentage y1% of fluoroethylene carbonate, and the mass percentage y2% of fluorosulfonimide lithium salt further satisfy 0.5 ⁇ y1/ x ⁇ 4.0 and/or 1 ⁇ y2/x ⁇ 28.
  • the secondary battery not only has significantly improved cycle performance, but also has improved rate performance and low-temperature performance.
  • the mass percentage of fluoroethylene carbonate y1% and the mass percentage of fluorosulfonimide lithium salt y2% can further satisfy 0.5 ⁇ y2/y1 ⁇ 48.
  • the mass percentage x% of lithium tetrafluoroborate, the mass percentage y1% of fluoroethylene carbonate, and the mass percentage y2% of lithium fluorosulfonimide salt also satisfy 0.5 ⁇ y1/x ⁇ 4.0, 1 ⁇ y2/x ⁇ 28 and 0.5 ⁇ y2/y1 ⁇ 48.
  • Fluorinated ethylene carbonate can effectively improve the cycle performance of secondary batteries.
  • Fluorinated sulfonimide lithium salt can improve the rate performance and low-temperature performance of secondary batteries.
  • Lithium tetrafluoroborate as a stabilizer for cathode active materials, can A dense and low-resistance interface film is formed on the surface of the cathode active material, which significantly improves the lithium ion diffusion rate of the low-cobalt or cobalt-free cathode active material, while inhibiting side reactions between the cathode active material and the electrolyte, and inhibiting the effects of HF on the cathode active material. Structural damage. Therefore, when the content relationship between the three components is further reasonably adjusted to satisfy 0.5 ⁇ y1/x ⁇ 4.0, 1 ⁇ y2/x ⁇ 28 and 0.5 ⁇ y2/y1 ⁇ 48 at the same time, it will be beneficial to give full play to the above three components. The synergistic effect between the components can fully suppress the defects when each component is used alone, and it can also form a dense, stable and low-resistance positive electrode interface film and negative electrode interface film.
  • the electrolyte when 0 ⁇ b ⁇ 0.7, can satisfy 0 ⁇ y1 ⁇ 2.5 and 0 ⁇ y2 ⁇ 5; optionally, the electrolyte can further satisfy 0.5 ⁇ y1/x ⁇ 4.0 and 1 ⁇ y2/x ⁇ 10; more optionally, the electrolyte can further satisfy 0.5 ⁇ y2/y1 ⁇ 10.
  • the electrolyte when 0.7 ⁇ b ⁇ 0.98, can satisfy 0 ⁇ y1 ⁇ 2.5 and 5 ⁇ y2 ⁇ 14; optionally, the electrolyte can further satisfy 0.5 ⁇ y1/x ⁇ 4.0 and 10 ⁇ y2/x ⁇ 28; more optionally, the electrolyte can further satisfy 6 ⁇ y2/y1 ⁇ 48.
  • the electrolyte may include a combination of fluoroethylene carbonate and lithium fluorosulfonate.
  • the mass percentage content y1% of the fluoroethylene carbonate satisfies 0 ⁇ y1 ⁇ 2.5
  • the mass percentage content y3% of the lithium fluorosulfonate salt satisfies 0 ⁇ y3 ⁇ 1.0.
  • the mass percentage x% of lithium tetrafluoroborate, the mass percentage y1% of fluoroethylene carbonate, and the mass percentage y3% of lithium fluorosulfonate salt further satisfy 0.5 ⁇ y1/x ⁇ 4.0 and/or 0.001 ⁇ y3/x ⁇ 2.0.
  • the secondary battery thus has significantly improved cycle performance while also having improved high-temperature performance.
  • the electrolyte may include a combination of lithium fluorosulfonimide salt and lithium fluorosulfonate salt.
  • the mass percentage y2% of the fluorosulfonimide lithium salt satisfies 0 ⁇ y2 ⁇ 14
  • the mass percentage y3% of the fluorosulfonyl lithium salt satisfies 0 ⁇ y3 ⁇ 1.0, And 0 ⁇ y2+y3 ⁇ 15.
  • the mass percentage x% of lithium tetrafluoroborate, the mass percentage y2% of the lithium fluorosulfonimide salt, and the mass percentage y3% of the lithium fluorosulfonate salt further satisfy 1 ⁇ y2 /x ⁇ 28 and/or 0.001 ⁇ y3/x ⁇ 2.0.
  • the secondary battery has significantly improved cycle performance, as well as improved rate performance, low-temperature performance, and high-temperature performance.
  • the mass percentage content of lithium tetrafluoroborate is x%
  • the mass percentage content of lithium fluorosulfonyl imide salt is y2%
  • the mass percentage content of lithium fluorosulfonate salt is y3%
  • the electrolyte when 0 ⁇ b ⁇ 0.7, can satisfy 0 ⁇ y2 ⁇ 5 and 0 ⁇ y3 ⁇ 1.0; optionally, the electrolyte can further satisfy 1 ⁇ y2/x ⁇ 10 and 0.001 ⁇ y3/x ⁇ 2.0; more optionally, the electrolyte can further satisfy 0.1 ⁇ x/(y2+y3) ⁇ 1.0.
  • the electrolyte when 0.7 ⁇ b ⁇ 0.98, can satisfy 5 ⁇ y2 ⁇ 14 and 0 ⁇ y3 ⁇ 1.0; optionally, the electrolyte can further satisfy 10 ⁇ y2/x ⁇ 28 and 0.001 ⁇ y3/x ⁇ 2.0; more optionally, the electrolyte can further satisfy 0.036 ⁇ x/(y2+y3) ⁇ 0.1.
  • the electrolyte may also include fluoroethylene carbonate, fluorosulfonimide lithium salt, and fluorosulfonyl lithium salt.
  • the mass percentage content y1% of the fluorinated ethylene carbonate satisfies 0 ⁇ y1 ⁇ 2.5
  • the mass percentage content y2% of the fluorinated sulfonylimide lithium salt satisfies 0 ⁇ y2 ⁇ 14
  • the mass percentage y3% of the lithium fluorosulfonate salt satisfies 0 ⁇ y3 ⁇ 1.0, and 0 ⁇ y1+y2+y3 ⁇ 15.
  • the electrolyte further satisfies 0.5 ⁇ y1/x ⁇ 4.0, 1 ⁇ y2/x ⁇ 28 and 0.001 ⁇ y3/x ⁇ 2.0.
  • the secondary battery has significantly improved cycle performance, as well as improved rate performance, low-temperature performance, and high-temperature performance.
  • the electrolyte also satisfies 0.5 ⁇ y1/x ⁇ 4.0, 1 ⁇ y2/x ⁇ 28, 0.001 ⁇ y3/x ⁇ 2.0 and 0.5 ⁇ y2/y1 ⁇ 48 at the same time. At this time, the overall performance of the secondary battery is further improved.
  • the electrolyte also satisfies 0.5 ⁇ y1/x ⁇ 4.0, 1 ⁇ y2/x ⁇ 28, 0.001 ⁇ y3/x ⁇ 2.0, 0.5 ⁇ y2/y1 ⁇ 48 and 0.036 ⁇ x/(y2 +y3) ⁇ 1.0. This helps to form an inorganic/organic composite interface film with excellent performance on the positive electrode and the negative electrode, thereby further improving the overall performance of the secondary battery.
  • the electrolyte when 0 ⁇ b ⁇ 0.7, can satisfy 0 ⁇ y1 ⁇ 2.5, 0 ⁇ y2 ⁇ 5 and 0 ⁇ y3 ⁇ 1.0; optionally, the electrolyte can further satisfy 0.5 ⁇ y1/ x ⁇ 4.0, 1 ⁇ y2/x ⁇ 10 and 0.001 ⁇ y3/x ⁇ 2.0; more optionally, the electrolyte can further satisfy 0.5 ⁇ y2/y1 ⁇ 10 and/or 0.1 ⁇ x/(y2+ y3) ⁇ 1.0.
  • the electrolyte when 0.7 ⁇ b ⁇ 0.98, can satisfy 0 ⁇ y1 ⁇ 2.5, 5 ⁇ y2 ⁇ 14 and 0 ⁇ y3 ⁇ 1.0; optionally, the electrolyte can further satisfy 0.5 ⁇ y1/ x ⁇ 4.0, 10 ⁇ y2/x ⁇ 28 and 0.001 ⁇ y3/x ⁇ 2.0; more optionally, the electrolyte can further satisfy: 6 ⁇ y2/y1 ⁇ 48 and/or 0.036 ⁇ x/(y2 +y3) ⁇ 0.1.
  • the electrolyte further includes a lithium salt and an organic solvent.
  • the types of the lithium salt and the organic solvent are not specifically limited and can be selected according to actual needs.
  • the lithium salt may include lithium hexafluorophosphate (LiPF 6 ), lithium perchlorate (LiClO 4 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium difluorooxaloborate (LiDFOB), lithium dioxalatoborate (LiBOB) , one or more of lithium difluorophosphate (LiPO 2 F 2 ), lithium difluorodioxalate phosphate (LiDFOP) and lithium tetrafluorooxalate phosphate (LiTFOP).
  • the lithium salt includes lithium hexafluorophosphate.
  • the organic solvent may include ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dicarbonate Propyl ester (DPC), methylpropyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), Propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4 - one or more of butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS) and diethyl sulfone (ESE).
  • EC ethylene carbonate
  • the electrolyte does not exclude other components except the above-mentioned components.
  • the electrolyte may optionally include other additives, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, additives that improve battery low-temperature power performance, etc.
  • the mass of the electrolyte may be 10% to 20% of the total mass of the secondary battery. This is beneficial to forming a dense and low-resistance interface film on the surface of the positive electrode active material. And it can effectively avoid the following situations: when the mass fraction of the electrolyte is less than 10%, the wettability of the positive and negative electrolytes is poor, the interface impedance is high, and the impedance increases rapidly after cycling, which may lead to poor capacity and poor cycle performance of the secondary battery.
  • the electrolyte solution can be prepared according to conventional methods in the art.
  • organic solvent, lithium salt, lithium tetrafluoroborate, optional fluoroethylene carbonate, optional fluorosulfonimide lithium salt, optional fluorosulfonyl lithium salt and other components can be mixed evenly , get the electrolyte.
  • the order of adding each material is not particularly limited.
  • lithium salt, lithium tetrafluoroborate, optional fluorinated ethylene carbonate, optional fluorinated sulfonyl imide lithium salt, optional fluorinated sulfonyl imide can be added.
  • each component and its content in the electrolyte can be determined according to methods known in the art. For example, it can be measured by gas chromatography-mass spectrometry (GC-MS), ion chromatography (IC), liquid chromatography (LC), nuclear magnetic resonance spectroscopy (NMR), or the like.
  • GC-MS gas chromatography-mass spectrometry
  • IC ion chromatography
  • LC liquid chromatography
  • NMR nuclear magnetic resonance spectroscopy
  • the electrolyte can be obtained from the secondary battery.
  • An exemplary method of obtaining electrolyte from a secondary battery includes the following steps: discharging the secondary battery to the discharge cut-off voltage (for safety reasons, the battery is generally in a fully discharged state), then centrifuging, and then centrifuging an appropriate amount to obtain The liquid is the electrolyte.
  • the electrolyte can also be obtained directly from the filling port of the secondary battery.
  • the positive electrode sheet of the present application includes a positive electrode current collector and a positive electrode film layer located on the surface of the positive electrode current collector.
  • the positive electrode current collector has two surfaces opposite in its thickness direction, and the positive electrode film layer is located on any one or both of the two opposite surfaces of the positive electrode current collector.
  • the positive electrode current collector may be a metal foil or a composite current collector.
  • a metal foil aluminum foil can be used.
  • the composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer.
  • the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy.
  • the polymer material base layer may include polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), One or more types of polyethylene (PE).
  • the positive electrode film layer typically contains a positive electrode active material and optionally a binder and an optional conductive agent.
  • the positive electrode film layer is usually formed by coating the positive electrode slurry on the positive electrode current collector, drying and cold pressing.
  • the cathode slurry is usually formed by dispersing the cathode active material, optional conductive agent, optional binder and any other components in a solvent and stirring evenly.
  • the solvent may be N-methylpyrrolidone (NMP), but is not limited thereto.
  • the binder used for the positive electrode membrane layer may include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoroethylene One or more of propylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.
  • PVDF polyvinylidene fluoride
  • PTFE polytetrafluoroethylene
  • PTFE polytetrafluoroethylene
  • vinylidene fluoride-tetrafluoroethylene-propylene terpolymer vinylidene fluoride-hexafluoroethylene
  • fluorine-containing acrylate resin fluorine-containing acrylate resin
  • the conductive agent used for the positive electrode film layer may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. .
  • the positive active material includes a layered material with the above molecular formula Li a Ni b Co c M1 d M2 e Of A g .
  • the layered material with the molecular formula Li a Ni b Co c M1 d M2 e Of A g is optionally doped and modified with M2 cations, doped with A anions, or is doped with M2 cations and A anions.
  • doping modification makes the crystal structure of the layered material obtained after doping more stable, which can further improve the electrochemical performance of secondary batteries, such as cycle performance, rate performance, etc.
  • A is selected from F.
  • F fluoride-based material
  • the structure of Li a Ni b Co c M1 d M2 e O f A g is more stable, which enables the secondary battery to have better cycle performance and rate performance.
  • M1 is selected from Mn.
  • M1 is selected from Al.
  • M1 is selected from a combination of Mn and Al.
  • the molar ratio of Mn and Al is not particularly limited and can be selected according to actual needs.
  • 0.50 ⁇ b ⁇ 0.98 0.50 ⁇ b ⁇ 0.98.
  • c 0.
  • 0 ⁇ c ⁇ 0.1 0 ⁇ c ⁇ 0.09, 0 ⁇ c ⁇ 0.08, 0 ⁇ c ⁇ 0.07, 0 ⁇ c ⁇ 0.06, 0 ⁇ c ⁇ 0.05, 0 ⁇ c ⁇ 0.04, 0 ⁇ c ⁇ 0.03, 0 ⁇ c ⁇ 0.02 or 0 ⁇ c ⁇ 0.01.
  • e 0.
  • 0 ⁇ e ⁇ 0.5 In some embodiments, 0 ⁇ e ⁇ 0.45, 0 ⁇ e ⁇ 0.40, 0 ⁇ e ⁇ 0.35, 0 ⁇ e ⁇ 0.30, 0 ⁇ e ⁇ 0.25, 0 ⁇ e ⁇ 0.20, 0 ⁇ e ⁇ 0.15, 0 ⁇ e ⁇ 0.10 or 0 ⁇ e ⁇ 0.05.
  • 0 ⁇ f ⁇ 2, 0 ⁇ g ⁇ 2, and f+g 2.
  • layered materials with the molecular formula Li a Ni b Co c M1 d M2 e Of A g include but are not limited to LiNi 0.7 Mn 0.3 O 2 , LiNi 0.69 Co 0.01 Mn 0.3 O 2 , LiNi 0.68 Co 0.02 Mn 0.3 O 2.
  • LiNi 0.65 Co 0.05 Mn 0.3 O 2 LiNi 0.63 Co 0.07 Mn 0.3 O 2 , LiNi 0.61 Co 0.09 Mn 0.3 O 2 .
  • Li a Ni b Co c M1 d M2 e Of A g can be prepared according to conventional methods in the art.
  • An exemplary preparation method is as follows: a lithium source, a nickel source, a cobalt source, an M1 element precursor, an optional M2 element precursor, and an optional A element precursor are mixed and then sintered.
  • the sintering atmosphere may be an oxygen-containing atmosphere, such as an air atmosphere or an oxygen atmosphere.
  • the O2 concentration of the sintering atmosphere is, for example, 70% to 100%.
  • the sintering temperature and sintering time can be adjusted according to actual conditions.
  • lithium sources include, but are not limited to, lithium oxide (Li 2 O), lithium phosphate (Li 3 PO 4 ), lithium dihydrogen phosphate (LiH 2 PO 4 ), lithium acetate (CH 3 COOLi), lithium hydroxide (LiOH ), one or more of lithium carbonate (Li 2 CO 3 ) and lithium nitrate (LiNO 3 ).
  • the nickel source includes, but is not limited to, one or more of nickel sulfate, nickel nitrate, nickel chloride, nickel oxalate, and nickel acetate.
  • the cobalt source includes, but is not limited to, one or more of cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt oxalate, and cobalt acetate.
  • the M1 element precursor includes, but is not limited to, one or more of the oxides of the M1 element, nitric acid compounds, carbonic acid compounds, hydroxide compounds, and acetic acid compounds.
  • the M2 element precursor includes, but is not limited to, one or more of an oxide of the M2 element, a nitric acid compound, a carbonic acid compound, a hydroxide compound, and an acetic acid compound.
  • precursors of element A include, but are not limited to, ammonium fluoride, lithium fluoride, hydrogen fluoride, ammonium chloride, lithium chloride, hydrogen chloride, ammonium nitrate, ammonium nitrite, ammonium carbonate, ammonium bicarbonate, ammonium phosphate, phosphoric acid , one or more of ammonium sulfate, ammonium bisulfate, ammonium bisulfite, ammonium sulfite, ammonium bisulfide, hydrogen sulfide, lithium sulfide, ammonium sulfide and elemental sulfur.
  • the surface of Li a Ni b Co c M1 d M2 e Of A g may also have a coating layer, such as a carbon coating layer.
  • the carbon coating layer is beneficial to stabilizing the surface of the cathode active material, further reducing the charge transfer resistance of the cathode active material, and reducing the diffusion resistance of lithium ions in the bulk phase of the cathode active material.
  • the carbon coating layer includes amorphous carbon, such as soft carbon, hard carbon, or a combination thereof.
  • the positive active material does not exclude other components besides Li a Ni b Co c M1 d M2 e Of A g .
  • the positive active material may also include lithium-containing phosphate.
  • the lithium-containing phosphate may include lithium iron phosphate, a composite material of lithium iron phosphate and carbon, a composite material of lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, a composite material of lithium manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon.
  • the materials and their respective modifying compounds are examples of the materials and their respective modifying compounds.
  • the mass percentage of the layered material with the molecular formula Li a Ni b Co c M1 d M2 e Of A g is 80% to 99%, based on the total mass of the cathode film layer.
  • the mass percentage of a layered material with the molecular formula Li a Ni b Co c M1 d M2 e Of A g is 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87 %, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or any range above.
  • the mass percentage of the layered material with the molecular formula Li a Ni b Co c M1 d M2 e Of A g is 85% to 99%, 90% to 99%, 95% to 99%, 80% to 98%, 85% to 98%, 90% to 98%, 95% to 98%, 80% to 97%, 85% to 97%, 90% to 97% or 95% to 97%.
  • the secondary battery according to the present application further includes a negative electrode plate.
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer located on the surface of the negative electrode current collector.
  • the negative electrode current collector has two surfaces opposite in its thickness direction, and the negative electrode film layer is located on any one or both of the two opposite surfaces of the negative electrode current collector.
  • the negative electrode current collector can be a metal foil or a composite current collector.
  • the metal foil copper foil can be used.
  • the composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer.
  • the metal material may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys.
  • the polymer material base layer may include polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and One or more types of polyethylene (PE).
  • the negative electrode film layer usually contains a negative electrode active material, an optional binder, an optional conductive agent, and other optional auxiliaries.
  • the negative electrode film layer is usually formed by coating the negative electrode slurry on the negative electrode current collector, drying, and cold pressing.
  • the negative electrode slurry coating is usually formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional auxiliaries in a solvent and stirring evenly.
  • the solvent may be N-methylpyrrolidone (NMP) or deionized water, but is not limited thereto.
  • the binder used for the negative electrode film layer may include styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (for example, polyacrylic acid PAA, polymethacrylic acid PMAA, polysodium acrylate PAAS ), one or more of polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA) and carboxymethyl chitosan (CMCS).
  • the conductive agent used for the negative electrode film layer may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.
  • Other optional auxiliaries may include thickeners (eg, sodium carboxymethylcellulose CMC-Na), PTC thermistor materials, etc.
  • the negative active material may be a negative active material known in the art for secondary batteries.
  • the negative active material may include one or more of natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate.
  • the silicon-based material may include one or more of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitride composite and silicon alloy material.
  • the tin-based material may include one or more of elemental tin, tin oxide and tin alloy materials.
  • the present application is not limited to these materials, and other conventionally known materials that can be used as negative electrode active materials for secondary batteries can also be used. Only one type of these negative electrode active materials may be used alone, or two or more types may be used in combination.
  • the secondary battery according to the present application may further include a separator film.
  • the isolation film is disposed between the positive electrode piece and the negative electrode piece to play an isolation role.
  • the material of the isolation membrane may include one or more of fiberglass, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.
  • the isolation film may be a single-layer film or a multi-layer composite film. When the isolation film is a multi-layer composite film, the materials of each layer may be the same or different.
  • the positive electrode piece, the isolation film and the negative electrode piece can be made into an electrode assembly through a winding process and/or a lamination process.
  • the secondary battery may include an outer packaging.
  • the outer packaging can be used to package the above-mentioned electrode assembly and electrolyte.
  • the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc.
  • the outer packaging of the secondary battery may also be a soft bag, such as a bag-type soft bag.
  • the material of the soft bag may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.
  • This application has no particular limitation on the shape of the secondary battery, which can be cylindrical, square or any other shape. As shown in FIG. 1 , a square-structured secondary battery 5 is shown as an example.
  • the outer package may include a housing 51 and a cover 53 .
  • the housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose to form a receiving cavity.
  • the housing 51 has an opening communicating with the accommodation cavity, and the cover plate 53 is used to cover the opening to close the accommodation cavity.
  • the positive electrode piece, the negative electrode piece and the isolation film can be formed into the electrode assembly 52 through a winding process or a lamination process.
  • the electrode assembly 52 is packaged in the containing cavity.
  • the electrolyte soaks into the electrode assembly 52 .
  • the number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and can be adjusted according to needs.
  • the secondary batteries according to the present application can be assembled into a battery module.
  • 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 schematic diagram of the battery module 4 as an example.
  • a plurality of secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4 .
  • the plurality of secondary batteries 5 can be fixed by fasteners.
  • the battery module 4 may further include a housing having a receiving space in which a plurality of secondary batteries 5 are received.
  • the above-mentioned 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 arranged in the battery box.
  • the battery box includes an upper box 2 and a lower box 3 .
  • the upper box 2 is used to cover the lower box 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 embodiment of the present application also provides a method for preparing a secondary battery, which method at least includes step 1 and step 2.
  • Step 1 Assemble a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte into a secondary battery.
  • the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer located on the surface of the positive electrode current collector.
  • Step 2 Screen out the secondary batteries satisfying 0.05 ⁇ c+x/10 ⁇ 0.15 from the secondary batteries obtained in step 1.
  • the secondary battery When the secondary battery satisfies x>0 and 0.05 ⁇ c+x/10 ⁇ 0.15, it can stabilize the crystal structure of the low-cobalt or cobalt-free cathode active material and increase the lithium ion diffusion rate inside it. Therefore, the secondary batteries obtained by the preparation method of the present application can have significantly improved cycle performance as well as good storage performance and kinetic performance.
  • the method further includes the step of screening out secondary batteries satisfying 0 ⁇ x ⁇ 1.0 and 0.05 ⁇ c+x/10 ⁇ 0.15 from the secondary batteries obtained in step 2. At this time, the prepared secondary battery has further improved cycle performance.
  • the secondary battery satisfies 0.05 ⁇ c+x/10 ⁇ 0.12.
  • the method further includes the step of: screening out secondary batteries that satisfy 25 ⁇ P/(c+x/10) ⁇ 65 from the secondary batteries obtained in step 2, and Pg/cm 3 represents the Describe the compacted density of the positive electrode piece.
  • the prepared secondary battery can have significantly improved cycle performance and high energy density, as well as improved power performance.
  • the secondary battery satisfies 30 ⁇ P/(c+x/10) ⁇ 50.
  • the method further includes the step of screening out secondary batteries that meet at least one of the following conditions (1) to (3) from the secondary batteries obtained in step 2:
  • the prepared secondary battery has further improved at least one of cycle performance, storage performance, rate performance, low temperature performance and high temperature performance.
  • the method further includes the step of: screening out secondary batteries obtained in step 2 that satisfy 0 ⁇ y1+y2+y3 ⁇ 15, 0 ⁇ y1 ⁇ 2.5, 0 ⁇ y2 ⁇ 14, 0 ⁇ y3 ⁇ 1.0, 0.5 ⁇ y1/x ⁇ 4.0, 1 ⁇ y2/x ⁇ 28, 0.001 ⁇ y3/x ⁇ 2.0 and 0.5 ⁇ y2/y1 ⁇ 48 secondary batteries. At this time, the overall performance of the prepared secondary battery is further improved.
  • the method further includes the step of: screening out secondary batteries obtained in step 2 that satisfy 0 ⁇ y1+y2+y3 ⁇ 15, 0 ⁇ y1 ⁇ 2.5, 0 ⁇ y2 ⁇ 5, 0 ⁇ y3 ⁇ 1.0, 0.5 ⁇ y1/x ⁇ 4.0, 1 ⁇ y2/x ⁇ 10, 0.001 ⁇ y3/x ⁇ 2.0 and 0.5 ⁇ y2/y1 ⁇ 10 secondary batteries.
  • the method further includes the step of: screening out secondary batteries obtained in step 2 that satisfy 0 ⁇ y1+y2+y3 ⁇ 15, 0 ⁇ y1 ⁇ 2.5, 5 ⁇ y2 ⁇ 14, 0 ⁇ y3 ⁇ 1.0, 0.5 ⁇ y1/x ⁇ 4.0, 10 ⁇ y2/x ⁇ 28, 0.001 ⁇ y3/x ⁇ 2.0 and 6 ⁇ y2/y1 ⁇ 48 secondary batteries.
  • the method further includes the step of: screening out secondary batteries obtained in step 2 that satisfy 0 ⁇ y1+y2+y3 ⁇ 15, 0 ⁇ y1 ⁇ 2.5, 0 ⁇ y2 ⁇ 14, 0 ⁇ y3 ⁇ 1.0, 0.5 ⁇ y1/x ⁇ 4.0, 1 ⁇ y2/x ⁇ 28, 0.001 ⁇ y3/x ⁇ 2.0, 0.5 ⁇ y2/y1 ⁇ 48 and 0.036 ⁇ x/(y2+y3) ⁇ 1.0 quadratic Battery. At this time, the overall performance of the prepared secondary battery is further improved.
  • the method further includes the step of: screening out secondary batteries obtained in step 2 that satisfy 0 ⁇ y1+y2+y3 ⁇ 15, 0 ⁇ y1 ⁇ 2.5, 0 ⁇ y2 ⁇ 5, 0 ⁇ y3 ⁇ 1.0, 0.5 ⁇ y1/x ⁇ 4.0, 1 ⁇ y2/x ⁇ 10, 0.001 ⁇ y3/x ⁇ 2.0, 0.5 ⁇ y2/y1 ⁇ 10 and 0.1 ⁇ x/(y2+y3 ) ⁇ 1.0 for secondary batteries.
  • the method further includes the step of: screening out secondary batteries obtained in step 2 that satisfy 0 ⁇ y1+y2+y3 ⁇ 15, 0 ⁇ y1 ⁇ 2.5, 5 ⁇ y2 ⁇ 14, 0 ⁇ y3 ⁇ 1.0, 0.5 ⁇ y1/x ⁇ 4.0, 10 ⁇ y2/x ⁇ 28, 0.001 ⁇ y3/x ⁇ 2.0, 6 ⁇ y2/y1 ⁇ 48 and 0.036 ⁇ x/(y2+y3 ) ⁇ 0.1 secondary batteries.
  • An embodiment of the present application also provides an electrical device, which includes at least one of a secondary battery, a battery module or a battery pack of the present application.
  • the secondary battery, battery module or battery pack may be used as a power source for the electrical device or as an energy storage unit for the electrical device.
  • the electrical device may be, but is not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric Golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.
  • the power-consuming device can select a secondary battery, a battery module or a battery pack according to its usage requirements.
  • FIG. 6 is a schematic diagram of an electrical device as an example.
  • the electric device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, etc.
  • battery packs or battery modules can be used.
  • the power-consuming device may be a mobile phone, a tablet computer, a laptop computer, etc.
  • the electrical device is usually required to be light and thin, and secondary batteries can be used as power sources.
  • the positive electrode active material LiNi 0.65 Co 0.05 Mn 0.3 O 2 , conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) are fully stirred and mixed in an appropriate amount of solvent NMP according to the mass ratio of 97.5:1.4:1.1 to form a uniform positive electrode. Slurry; the positive electrode slurry is evenly coated on the surface of the positive electrode current collector aluminum foil, and after drying and cold pressing, the positive electrode piece is obtained. The compacted density of the positive electrode piece is 3.5g/cm 3 .
  • a porous polyethylene (PE) film is used as the isolation membrane.
  • LiPF 6 and LiBF 4 were uniformly dissolved in the above-mentioned organic solvent to obtain an electrolyte. Based on the total mass of the electrolyte, the mass percentage of LiPF 6 was 12.5% and the mass percentage of LiBF 4 was 0.1%.
  • the mass of the electrolyte is 15% of the total mass of the secondary battery.
  • the preparation method of the secondary battery is similar to Example 1, except that the type of positive active material and the preparation parameters of the electrolyte are adjusted.
  • the specific parameters are shown in Table 1. "/" indicates that the corresponding component is not added to the electrolyte.
  • the secondary battery At 25°C, charge the secondary battery to 4.3V with a constant current of 1C, and continue charging with a constant voltage until the current is 0.05C. At this time, the secondary battery is fully charged; discharge the secondary battery with a constant current of 0.5C and adjust When the secondary battery reaches 50% SOC, the voltage of the secondary battery at this time is recorded as U 1 ; the secondary battery is discharged with a constant current of 4C I 1 for 30 seconds, using a 0.1 second sampling point, and the voltage at the end of the discharge is recorded as U 2 .
  • the initial DC internal resistance of the secondary battery is represented by the discharge DC internal resistance of the secondary battery at 50% SOC.
  • the initial DC internal resistance of the secondary battery (m ⁇ ) (U 1 -U 2 )/I 1 .
  • the open circuit voltage of the secondary battery at this time is recorded as OCV1.
  • the open circuit voltage of the secondary battery is recorded as OCV2.
  • the self-discharge rate of a secondary battery stored at 25°C for 3 months [(OCV1-OCV2)/OCV1] ⁇ 100%. The lower the self-discharge rate of the secondary battery, the better the capacity performance and safety performance.
  • Table 1 shows the performance test results of Examples 1-1 to 1-16 and Comparative Examples 1-1 to 1-7.
  • the inventor further studied the effects of components other than lithium tetrafluoroborate in the electrolyte on the performance of secondary batteries.
  • Example 2-1 to 2-20 The secondary battery preparation methods of Examples 2-1 to 2-20 are similar to Example 1-3, except that the preparation parameters of the electrolyte are adjusted. The specific parameters are shown in Table 2. "/" indicates that the corresponding component is not added to the electrolyte.
  • Example 2-9 Combining the test results of Example 2-9 and Examples 1-3, 2-1 to 2-6, it can be seen that when further adding fluoroethylene carbonate, bisfluoroethylene carbonate and bisfluoride to the electrolyte of Example 1-3, When using lithium sulfonyl imide and lithium fluorosulfonate, it helps to obtain a secondary battery with better overall performance.

Abstract

本申请提供一种二次电池、用于制备二次电池的方法、电池模块、电池包及用电装置。所述二次电池包括电解液和正极极片，其中，所述正极极片包括分子式为Li aNi bCo cM1 dM2 eO fA g的层状材料，0.8≤a≤1.2，0<b<0.98，0≤c<0.1，0<d<0.5，0≤e≤0.5，0≤f≤2，0≤g≤2，b+c+d+e＝1，f+g＝2；所述电解液包括四氟硼酸锂，所述电解液中的所述四氟硼酸锂的质量百分含量为x％，基于所述电解液的总质量计，并且所述二次电池满足：x>0和0.05≤c+x/10≤0.15。本申请能稳定低钴或无钴正极活性材料的晶体结构并提升其内部的锂离子扩散速率。

Description

二次电池、用于制备二次电池的方法、电池模块、电池包及用电装置 技术领域
本申请属于电池技术领域，具体涉及一种二次电池、用于制备二次电池的方法、电池模块、电池包及用电装置。
背景技术
二次电池依靠锂离子在正极和负极之间往复脱嵌来进行充电和放电，其具有能量密度高、循环寿命长，以及无污染、无记忆效应等突出特点。因此，二次电池作为清洁能源，已由电子产品逐渐普及到水力、火力、风力和太阳能电站等储能电源系统，以及电动工具、电动自行车、电动摩托车、电动汽车、军事装备、航空航天等多个领域。钴是二次电池正极活性材料重要组成元素，但是，钴在地壳中含量较少、开采困难且价格昂贵，因此，低钴或无钴成为正极活性材料必然的发展趋势。然而，钴对正极活性材料锂离子扩散速率贡献很大，低钴或无钴会降低正极活性材料的锂离子扩散速率，影响二次电池的循环寿命。
发明内容
本申请的目的在于提供一种二次电池、用于制备二次电池的方法、电池模块、电池包及用电装置，旨在稳定低钴或无钴正极活性材料的晶体结构并提升其内部的锂离子扩散速率。
本申请第一方面提供一种二次电池，包括电解液和正极极片，其中，所述正极极片包括正极集流体和位于所述正极集流体表面的正极膜层，所述正极膜层包括分子式为Li aNi bCo cM1 dM2 eO fA g的层状材料，M1选自Mn、Al或其组合，M2选自Si、Ti、Mo、V、Ge、Se、Zr、Nb、Ru、Pd、Sb、Ce、Te及W中的一种或多种，A选自F、N、P及S中的一种或多种，0.8≤a≤1.2，0<b<0.98，0≤c<0.1，0<d<0.5，0≤e≤0.5，0≤f≤2，0≤g≤2，b+c+d+e＝1，f+g＝2；所述电解液包括四氟硼酸锂，所述电解液中的所述四氟硼酸锂的质量百分含量为x％，基于所述电解液的总质量计，并且所述二次电池满足：x>0和0.05≤c+x/10≤0.15。
本申请发明人在研究过程中意外发现，通过使电解液含有四氟硼酸锂并使四氟硼酸锂的质量百分含量x％与低钴或无钴正极活性材料中的钴元素含量c满足x>0和0.05≤c+x/10≤0.15时，能够稳定低钴或无钴正极活性材料的晶体结构并提升其内部的锂离子扩散速率，进而能够使二次电池具有显著改善的循环性能。此外，本申请的二次电池还能够具有良好的存储性能和动力学性能。
在本申请的任意实施方式中，0.05≤c+x/10≤0.12。
在本申请的任意实施方式中，0<x≤1.0。
在本申请的任意实施方式中，所述正极极片的压实密度为Pg/cm 3，并且所述二次电池满足：25≤P/(c+x/10)≤65，可选地，30≤P/(c+x/10)≤50。由此二次电池能够在具有改善的循环性能和高能量密度的前提下，还具有改善的功率性能。
在本申请的任意实施方式中，所述正极极片的压实密度P g/cm 3满足P为3.3至3.6。由此有助于二次电池具有高能量密度。
在本申请的任意实施方式中，所述电解液还包括氟代碳酸乙烯酯、氟代磺酰亚胺锂盐、氟代磺酸锂盐中的一种或多种，所述电解液中的所述氟代碳酸乙烯酯的质量百分含量为y1％，所述电解液中的所述氟代磺酰亚胺锂盐的质量百分含量为y2％，所述电解液中的所述氟代磺酸锂盐的质量百分含量为y3％，均基于所述电解液的总质量计，并且所述电解液满足：y1≥0，y2≥0，y3≥0且0<y1+y2+y3≤15。由此有助于在正极和/或负极形成更稳定的界面膜，从而进一步改善二次电池的电化学性能。
在本申请的任意实施方式中，所述氟代磺酰亚胺锂盐的分子式为LiN(SO 2R 1)(SO 2R 2)，R 1、R 2各自独立地表示F或C nF 2n+1，n为1～10的整数，可选地，所述氟代磺酰亚胺锂盐包括双氟磺酰亚胺锂、双三氟甲磺酰亚胺锂或其组合。
在本申请的任意实施方式中，所述氟代磺酸锂盐的分子式为LiSO 3R 3，R 3表示F、部分氟化或全部氟化的C1-C10的烷基，可选地，所述氟代磺酸锂盐包括氟磺酸锂、三氟甲磺酸锂或其组合。
在本申请的任意实施方式中，所述电解液中的所述氟代碳酸乙烯酯的质量百分含量y1％满足0<y1≤2.5，可选地，0<y1≤2.0。由此能够稳定负极界面膜，有效提升二次电池的循环性能。
在本申请的任意实施方式中，所述电解液中的所述氟代碳酸乙烯酯的质量百分含量y1％满足0.5≤y1/x≤4.0，可选地，0.5≤y1/x≤2.0。由此能够充分发挥四氟硼酸锂和氟代碳酸乙烯酯的协同作用。
在本申请的任意实施方式中，所述电解液中的所述氟代碳酸乙烯酯的质量百分含量y1％满足0<y1≤2.5和.5≤y1/x≤4.0。
在本申请的任意实施方式中，所述电解液中的所述氟代磺酰亚胺锂盐的质量百分含量y2％满足0<y2≤14。由此能够显著改善二次电池的倍率性能和低温性能。
在本申请的任意实施方式中，所述电解液中的所述氟代磺酰亚胺锂盐的质量百分含量y2％满足1≤y2/x≤28。由此能够充分发挥四氟硼酸锂和氟代磺酰亚胺锂盐的协同作用。
在本申请的任意实施方式中，所述电解液中的所述氟代磺酰亚胺锂盐的质量百分含量y2％满足0<y2≤14和1≤y2/x≤28。
在本申请的任意实施方式中，当0<b≤0.7时，所述电解液中的所述氟代磺酰亚胺锂盐的质量百分含量y2％满足0<y2≤5和/或1≤y2/x≤10。可选地，0<y2≤2.5；可选地，1≤y2/x≤5。
在本申请的任意实施方式中，当0.7≤b<0.98时，所述电解液中的所述氟代磺酰亚胺锂盐的质量百分含量y2％满足5≤y2≤14和/或10≤y2/x≤28。可选地，8≤y2≤14；可选地，16≤y2/x≤28。
在本申请的任意实施方式中，所述电解液中的所述氟代磺酸锂盐的质量百分含量y3％满足0<y3≤1.0，可选地，0<y3≤0.5。由此能够较大地改善二次电池的高温性能。
在本申请的任意实施方式中，所述电解液中的所述氟代磺酸锂盐的质量百分含量y3％满足0.001≤y3/x≤2.0，可选地，0.001≤y3/x≤1.0。由此能够充分发挥四氟硼酸锂和氟代磺酸锂盐的协同作用。
在本申请的任意实施方式中，所述电解液中的所述氟代磺酸锂盐的质量百分含量y3％满足0<y3≤1.0和0.001≤y3/x≤2.0。
在本申请的任意实施方式中，所述电解液还包括氟代碳酸乙烯酯、氟代磺酰亚胺锂盐和氟代磺酸锂盐，并且所述电解液满足：0<y1≤2.5，0<y2≤14，0<y3≤1.0，0.5≤y1/x≤4.0，1≤y2/x≤28，0.001≤y3/x≤2.0和0.5≤y2/y1≤48。此时，二次电池的综合性能得到进一步改善。
可选地，当0<b≤0.7时，所述电解液满足：0<y1≤2.5，0<y2≤5，0<y3≤1.0，0.5≤y1/x≤4.0，1≤y2/x≤10，0.001≤y3/x≤2.0和0.5≤y2/y1≤10。
可选地，当0.7≤b<0.98时，所述电解液满足：0<y1≤2.5，5≤y2≤14，0<y3≤1.0，0.5≤y1/x≤4.0，10≤y2/x≤28，0.001≤y3/x≤2.0和6≤y2/y1≤48。
在本申请的任意实施方式中，所述电解液满足：所述电解液还包括氟代碳酸乙烯酯、氟代磺酰亚胺锂盐和氟代磺酸锂盐，并且所述电解液满足：0<y1≤2.5，0<y2≤14，0<y3≤1.0，0.5≤y1/x≤4.0，1≤y2/x≤28，0.001≤y3/x≤2.0，0.5≤y2/y1≤48和0.036≤x/(y2+y3)≤1.0。由此有助于在正极和负极形成性能优良的无机/有机复合界面膜，从而能够进一步改善二次电池的综合性能。
可选地，当0<b≤0.7时，所述电解液满足：0<y1≤2.5，0<y2≤5，0<y3≤1.0，0.5≤y1/x≤4.0，1≤y2/x≤10，0.001≤y3/x≤2.0，0.5≤y2/y1≤10和0.1≤x/(y2+y3)≤1.0。
可选地，当0.7≤b<0.98时，所述电解液满足：0<y1≤2.5，5≤y2≤14，0<y3≤1.0，0.5≤y1/x≤4.0，10≤y2/x≤28，0.001≤y3/x≤2.0，6≤y2/y1≤48和0.036≤x/(y2+y3)≤0.1。
在本申请的任意实施方式中，0<c<0.1。
在本申请的任意实施方式中，c＝0。
在本申请的任意实施方式中，所述分子式为Li aNi bCo cM1 dM2 eO fA g的层状材料的质量百分含量为80％至99％，基于所述正极膜层的总质量计，可选地为85％至99％。
在本申请的任意实施方式中，所述二次电池还满足：所述电解液的质量为所述二次电池总质量的10％至20％。由此有利于在正极活性材料表面形成致密且低阻抗的界面膜。
本申请第二方面提供一种用于制备二次电池的方法，至少包括如下步骤：步骤1，将正极极片、隔离膜、负极极片、电解液组装成二次电池，所述正极极片包括正极集流体和位于所述正极集流体表面的正极膜层，所述正极膜层包括分子式为Li aNi bCo cM1 dM2 eO fA g的层状材料，M1选自Mn、Al或其组合，M2选自Si、Ti、Mo、V、Ge、Se、Zr、Nb、Ru、Pd、Sb、Ce、Te及W中的一种或多种，A选自F、N、P及S中的一种或多种，0.8≤a≤1.2，0<b<0.98，0≤c<0.1，0<d<0.5，0≤e≤0.5，0≤f≤2，0≤g≤2，b+c+d+e＝1，f+g＝2，所述电解液包括四氟硼酸锂、可选的氟代碳酸乙烯酯、可选的氟代磺酰亚胺锂盐和可选的氟代磺酸锂盐，所述电解液中的所述四氟硼酸锂 的质量百分含量为x％，所述电解液中的所述氟代碳酸乙烯酯的质量百分含量为y1％，所述电解液中的所述氟代磺酰亚胺锂盐的质量百分含量为y2％，所述电解液中的所述氟代磺酸锂盐的质量百分含量为y3％，均基于所述电解液的总质量计，x>0，y1≥0，y2≥0，y3≥0；步骤2，从步骤1所得到的二次电池中筛选出满足0.05≤c+x/10≤0.15的二次电池。
通过本申请制备方法得到的二次电池均能具有显著改善的循环性能以及良好的存储性能和动力学性能。
在本申请的任意实施方式中，所述方法还包括步骤：从步骤2所得到的二次电池中筛选出满足0<x≤1.0和0.05≤c+x/10≤0.15的二次电池。此时，制备的二次电池具有进一步改善的循环性能。
在本申请的任意实施方式中，所述方法还包括步骤：从步骤2所得到的二次电池中筛选出满足25≤P/(c+x/10)≤65的二次电池，P g/cm 3表示所述正极极片的压实密度。此时，制备的二次电池能够在具有显著改善的循环性能和高能量密度的前提下，还具有改善的功率性能。
在本申请的任意实施方式中，所述方法还包括步骤：从步骤2所得到的二次电池中筛选出满足0<y1+y2+y3≤15，0<y1≤2.5，0<y2≤14，0<y3≤1.0，0.5≤y1/x≤4.0，1≤y2/x≤28，0.001≤y3/x≤2.0和0.5≤y2/y1≤48的二次电池。此时，制备的二次电池的综合性能得到进一步改善。
可选地，当0<b≤0.7时，所述方法还包括步骤：从步骤2所得到的二次电池中筛选出满足0<y1+y2+y3≤15，0<y1≤2.5，0<y2≤5，0<y3≤1.0，0.5≤y1/x≤4.0，1≤y2/x≤10，0.001≤y3/x≤2.0和0.5≤y2/y1≤10的二次电池。
可选地，当0.7≤b<0.98时，所述方法还包括步骤：从步骤2所得到的二次电池中筛选出满足0<y1+y2+y3≤15，0<y1≤2.5，5≤y2≤14，0<y3≤1.0，0.5≤y1/x≤4.0，10≤y2/x≤28，0.001≤y3/x≤2.0和6≤y2/y1≤48的二次电池。
在本申请的任意实施方式中，所述方法还包括步骤：从步骤2所得到的二次电池中筛选出满足0<y1+y2+y3≤15，0<y1≤2.5，0<y2≤14，0<y3≤1.0，0.5≤y1/x≤4.0，1≤y2/x≤28，0.001≤y3/x≤2.0，0.5≤y2/y1≤48和0.036≤x/(y2+y3)≤1.0的二次电池。此时，制备的二次电池的综合性能得到进一步改善。
可选地，当0<b≤0.7时，所述方法还包括步骤：从步骤2所得到的二次电池中筛选出满足0<y1+y2+y3≤15，0<y1≤2.5，0<y2≤5，0<y3≤1.0，0.5≤y1/x≤4.0，1≤y2/x≤10，0.001≤y3/x≤2.0，0.5≤y2/y1≤10和0.1≤x/(y2+y3)≤1.0的二次电池。
可选地，当0.7≤b<0.98时，所述方法还包括步骤：从步骤2所得到的二次电池中筛选出满足0<y1+y2+y3≤15，0<y1≤2.5，5≤y2≤14，0<y3≤1.0，0.5≤y1/x≤4.0，10≤y2/x≤28，0.001≤y3/x≤2.0，6≤y2/y1≤48和0.036≤x/(y2+y3)≤0.1的二次电池。
本申请第三方面提供一种电池模块，包括本申请第一方面的二次电池或通过本申请第二方面的方法制备的二次电池。
本申请第四方面提供一种电池包，包括本申请第一方面的二次电池、通过本申请第二方面的方法制备的二次电池、本申请第三方面的电池模块中的一种。
本申请第五方面提供一种用电装置，包括本申请第一方面的二次电池、通过本申请 第二方面的方法制备的二次电池、本申请第三方面的电池模块、本申请第四方面的电池包中的至少一种。
本申请的二次电池具有显著改善的循环性能以及良好的存储性能和动力学性能，本申请的电池模块、电池包和用电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
为了更清楚地说明本申请实施例的技术方案，下面将对本申请实施例中所需要使用的附图作简单地介绍。显而易见地，下面所描述的附图仅仅是本申请的一些实施方式，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是本申请的二次电池的一实施方式的示意图。
图2是图1的二次电池的实施方式的分解示意图。
图3是本申请的电池模块的一实施方式的示意图。
图4是本申请的电池包的一实施方式的示意图。
图5是图4所示的电池包的实施方式的分解示意图。
图6是包含本申请的二次电池作为电源的用电装置的一实施方式的示意图。
在附图中，附图未必按照实际的比例绘制。附图标记说明如下：1电池包，2上箱体，3下箱体，4电池模块，5二次电池，51壳体，52电极组件，53盖板。
具体实施方式
以下，适当地参照附图详细说明具体公开了本申请的二次电池、用于制备二次电池的方法、电池模块、电池包及用电装置的实施方式。但是会有省略不必要的详细说明的情况。例如，有省略对已众所周知的事项的详细说明、实际相同结构的重复说明的情况。这是为了避免以下的说明不必要地变得冗长，便于本领域技术人员的理解。此外，附图及以下说明是为了本领域技术人员充分理解本申请而提供的，并不旨在限定权利要求书所记载的主题。
本申请所公开的“范围”以下限和上限的形式来限定，给定范围是通过选定一个下限和一个上限进行限定的，选定的下限和上限限定了特别范围的边界。这种方式进行限定的范围可以是包括端值或不包括端值的，并且可以进行任意地组合，即任何下限可以与任何上限组合形成一个范围。例如，如果针对特定参数列出了60-120和80-110的范围，理解为60-110和80-120的范围也是预料到的。此外，如果列出的最小范围值1和2，和如果列出了最大范围值3，4和5，则下面的范围可全部预料到：1-3、1-4、1-5、2-3、2-4和2-5。在本申请中，除非有其他说明，数值范围“a-b”表示a到b之间的任意实数组合的缩略表示，其中a和b都是实数。例如数值范围“0-5”表示本文中已经全部列出了“0-5”之间的全部实数，“0-5”只是这些数值组合的缩略表示。另外，当表述某个参数为≥2的整数，则相当于公开了该参数为例如整数2、3、4、5、6、7、8、9、10、11、12等。
如果没有特别的说明，本申请的所有实施方式以及可选实施方式可以相互组合形成 新的技术方案，并且这样的技术方案应被认为包含在本申请的公开内容中。
如果没有特别的说明，本申请的所有技术特征以及可选技术特征可以相互组合形成新的技术方案，并且这样的技术方案应被认为包含在本申请的公开内容中。
如果没有特别的说明，本申请的所有步骤可以顺序进行，也可以随机进行，优选是顺序进行的。例如，所述方法包括步骤(a)和(b)，表示所述方法可包括顺序进行的步骤(a)和(b)，也可以包括顺序进行的步骤(b)和(a)。例如，所述提到所述方法还可包括步骤(c)，表示步骤(c)可以任意顺序加入到所述方法，例如，所述方法可以包括步骤(a)、(b)和(c)，也可包括步骤(a)、(c)和(b)，也可以包括步骤(c)、(a)和(b)等。
如果没有特别的说明，本申请所提到的“包括”和“包含”表示开放式，也可以是封闭式。例如，所述“包括”和“包含”可以表示还可以包括或包含没有列出的其他组分，也可以仅包括或包含列出的组分。
如果没有特别的说明，在本申请中，术语“或”是包括性的。举例来说，短语“A或B”表示“A，B，或A和B两者”。更具体地，以下任一条件均满足条件“A或B”：A为真(或存在)并且B为假(或不存在)；A为假(或不存在)而B为真(或存在)；或A和B都为真(或存在)。
在本申请中，术语“多个”、“多种”是指两个或两种以上。
二次电池又称为充电电池或蓄电池，是指在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，二次电池包括正极极片、负极极片、隔离膜以及电解液。二次电池充放电过程中，锂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，主要起到防止正极和负极短路的作用，同时可以使锂离子通过。电解液在正极极片和负极极片之间起到传导锂离子的作用。
二次电池充电时，锂离子优先从正极活性材料表面脱出，随后正极活性材料体相内的锂离子及时补充到表面。正极活性材料中的钴元素会影响正极活性材料的离子传导特性：(1)当正极活性材料中的钴元素含量较高时，体相内的锂离子能及时地补充到正极活性材料表面；(2)当正极活性材料中的钴元素含量较低时，体相内的锂离子来不及补充到正极活性材料表面，而表面的锂离子已经脱出，由此会导致正极活性材料表面过脱锂，从而影响正极活性材料的晶体结构(例如，正极活性材料不可逆畸变和晶格缺陷数量增加)，降低二次电池的循环性能。
此外，钴元素还能稳定正极活性材料的晶体结构。当正极活性材料中的钴元素含量降低或者不含钴元素时，正极活性材料中的金属离子，特别是锰离子溶出速度加快。溶出的锰离子在迁移到负极后，被还原成金属锰。这些形成的金属锰相当于“催化剂”，能够催化负极表面的SEI膜(solid electrolyte interphase，固态电解质界面膜)分解，产生的副产物一部分为气体，容易导致电池发生膨胀，影响二次电池的安全性能，另一部分沉积在负极表面，阻碍锂离子进出负极的通道，造成二次电池的阻抗增加，影响二次电池的动力学性能。此外，为补充损失的SEI膜，电解液和电池内部的活性锂离子还被不断消耗，由此还给二次电池的容量保持率带来不可逆的影响。
因此，稳定低钴或无钴正极活性材料的晶体结构并提升其内部的锂离子扩散速率具有重要的实际意义。研究者们一直致力于提升低钴或无钴正极活性材料的锂离子扩散速 率，但是目前尚没有很好的解决方案。
本申请的发明人经过大量研究惊喜发现，通过使电解液含有合适含量的四氟硼酸锂并且使四氟硼酸锂的含量与正极活性材料中的钴元素含量符合特定关系式，能够稳定低钴或无钴正极活性材料的晶体结构并提升其内部的锂离子扩散速率。
二次电池
具体地，本申请实施方式提供了一种二次电池，其包括电解液和正极极片。所述正极极片包括正极集流体和位于所述正极集流体表面的正极膜层，所述正极膜层包括分子式为Li aNi bCo cM1 dM2 eO fA g的层状材料，M1选自Mn、Al或其组合，M2选自Si、Ti、Mo、V、Ge、Se、Zr、Nb、Ru、Pd、Sb、Ce、Te及W中的一种或多种，A选自F、N、P及S中的一种或多种，0.8≤a≤1.2，0<b<0.98，0≤c<0.1，0<d<0.5，0≤e≤0.5，0≤f≤2，0≤g≤2，b+c+d+e＝1，f+g＝2；所述电解液包括四氟硼酸锂(LiBF 4)，所述电解液中的所述四氟硼酸锂的质量百分含量为x％，基于所述电解液的总质量计，并且所述二次电池满足：x>0和0.05≤c+x/10≤0.15。
电解液是影响二次电池性能的关键因素之一，目前商业化应用最广的电解液体系为六氟磷酸锂的混合碳酸酯溶液，但是，六氟磷酸锂在高温环境下的热稳定性较差，其在较高温度下会分解生成PF 5。PF 5具有较强的路易斯酸性，会与有机溶剂分子中氧原子上的孤对电子作用而使有机溶剂发生分解；此外，PF 5对于电解液中微量的水分具有较高的敏感性，遇水会产生HF，从而增加电解液的酸度，进而容易腐蚀正极活性材料和正极集流体、造成正极活性材料中过渡金属离子溶出。由此，六氟磷酸锂不仅不会提升低钴或无钴正极活性材料的锂离子扩散速率，而且还容易腐蚀正极活性材料、破坏其晶体结构。因此，需要对电解液进行改进。
本申请发明人在研究过程中意外发现，通过使电解液含有四氟硼酸锂并使四氟硼酸锂的质量百分含量x％与低钴或无钴正极活性材料中的钴元素含量c满足x>0和0.05≤c+x/10≤0.15时，能够稳定低钴或无钴正极活性材料的晶体结构并提升其内部的锂离子扩散速率，进而能够使二次电池具有显著改善的循环性能。此外，本申请的二次电池还能够具有良好的存储性能和动力学性能。
尽管机理尚不十分明确，发明人推测可能的原因包括如下几点。
第一，当四氟硼酸锂的质量百分含量x％与低钴或无钴正极活性材料中的钴元素含量c满足x>0和0.05≤c+x/10≤0.15时，四氟硼酸锂能在正极活性材料表面形成致密且低阻抗的界面膜，并且四氟硼酸锂中的B原子能够充分地与正极活性材料中的O原子结合，由此能够降低正极活性材料的电荷转移阻抗，降低锂离子在正极活性材料体相内的扩散阻力、避免正极活性材料表面过脱锂、并稳定正极活性材料的晶体结构。本申请的正极活性材料的晶体结构更稳定，从而由于表面出现过脱锂而导致的正极活性材料结构性质、化学性质或电化学性质变得不稳定等问题出现的概率还进一步降低。因此，本申请的二次电池能够具有改善的电化学性能，特别地，能够具有显著改善的循环性能。
第二，当四氟硼酸锂的质量百分含量x％与低钴或无钴正极活性材料中的钴元素含量c满足x>0和0.05≤c+x/10≤0.15时，四氟硼酸锂能在正极活性材料表面形成致密且低阻抗的界面膜，一方面能够有效减少正极活性材料和电解液直接接触，另一方面能够降低正极活性材料的表面氧活性，由此，能够减少电解液在正极的氧化分解和降低过渡金 属离子溶出量，进而能够改善二次电池的电化学性能，例如减少活性锂离子不可逆消耗、降低电池体积膨胀率、降低正极界面阻抗等。因此，本申请的二次电池还能够具有良好的存储性能和动力学性能。
第三，四氟硼酸锂具有较高的热稳定性且对水分不敏感，由此能够提高二次电池的高温稳定性。
当c+x/10<0.05时，电解液中四氟硼酸锂的含量不足以在低钴或无钴正极活性材料表面形成致密且低阻抗的界面膜，并且四氟硼酸锂也不能有效降低低钴或无钴正极活性材料的电荷转移阻抗，不能有效降低锂离子在低钴或无钴正极活性材料体相内的扩散阻力并抑制低钴或无钴正极活性材料表面过脱锂，因此，二次电池难以具有显著改善的循环性能。当c+x/10>0.15时，电解液中四氟硼酸锂的含量过高，由于其在电解液中的溶解度较低，由此使得电解液中存在未完全解离的分子状态的四氟硼酸锂，其在电解液中容易析出，特别是在低温环境下析出程度加剧，进而会增加隔离膜被刺穿等安全风险，因此二次电池的安全性能的循环性能均较差；此外，析出的四氟硼酸锂还会破坏电极界面，由此还会增加二次电池的自放电。在一些实施例中，可选地，0.05≤c+x/10≤0.14，0.05≤c+x/10≤0.13，0.05≤c+x/10≤0.12，0.05≤c+x/10≤0.11或0.05≤c+x/10≤0.10。
在本申请中，四氟硼酸锂的质量百分含量x％满足x>0。四氟硼酸锂的含量较高时，由于其在电解液中的溶解度较低，由此使得电解液中存在未完全解离的分子状态的四氟硼酸锂，其在电解液中容易析出，特别是在低温环境下析出程度加剧，进而会增加隔离膜被刺穿等安全风险。因此，四氟硼酸锂的含量较高时，二次电池的安全性能的循环性能可能变差。此外，析出的四氟硼酸锂还会破坏电极界面，由此还会增加二次电池的自放电。在一些实施例中，可选地，0<x≤1.0。
本申请的发明人在进一步研究过程中还发现，正极活性材料中的钴元素含量还会影响正极活性材料的电子传导特性：(1)当正极活性材料中的钴元素含量较高时，正极活性材料具有良好的电子传导特性；(2)当正极活性材料中的钴元素含量较低时，正极活性材料的电子传导特性变差，进而二次电池的功率性能变差。另外，正极极片的压实密度越大，二次电池的功率性能越差，由此为了保证二次电池具有良好的功率性能，现有技术通常采用的策略是降低正极极片的压实密度，但是由此会牺牲二次电池的能量密度。
本申请的发明人惊喜发现，当正极极片的压实密度P g/cm 3、四氟硼酸锂的质量百分含量x％和低钴或无钴正极活性材料中的钴元素含量c进一步满足25≤P/(c+x/10)≤65时，二次电池能够在具有改善的循环性能和高能量密度的前提下，还具有改善的功率性能，例如二次电池的初始功率以及循环中的功率增长都能得到明显改善。尽管机理尚不十分明确，发明人推测可能的原因在于：第一，四氟硼酸锂的含量在合适的范围内时，能够稳定低钴或无钴正极活性材料的晶体结构，由此使其具有良好的电子传导特性；第二，合适的压实密度有助于正极极片形成良好的电子导电网络。
因此，当25≤P/(c+x/10)≤65时，二次电池能够在具有改善的循环性能和高能量密度的前提下，还具有改善的功率性能。并且能够有效避免以下情况：当P/(c+x/10)<25时，正极极片的压实密度可能较小，由此正极极片中的电子导电网络较差，不能有效改善二次电池的功率性能，同时牺牲了二次电池的能量密度；或者四氟硼酸锂的含量可能较高，由此可能导致负极界面膜的稳定性变差，进而导致电池内阻较高、功率性能变差；当 P/(c+x/10)>65时，四氟硼酸锂的含量可能不足以弥补正极极片压实密度增加对二次电池功率性能的恶化，由此二次电池的功率性能也较差。可选地，25≤P/(c+x/10)≤60，25≤P/(c+x/10)≤55，25≤P/(c+x/10)≤50，25≤P/(c+x/10)≤45，25≤P/(c+x/10)≤40，30≤P/(c+x/10)≤65，30≤P/(c+x/10)≤60，30≤P/(c+x/10)≤55，30≤P/(c+x/10)≤50或30≤P/(c+x/10)≤45。
在一些实施例中，可选地，所述正极极片的压实密度P g/cm 3满足P为3.3至3.6，更可选地为3.4至3.5。由此有助于二次电池具有高能量密度。
[电解液]
在一些实施例中，所述电解液除了包含四氟硼酸锂外，还可以包括氟代碳酸乙烯酯(FEC)、氟代磺酰亚胺锂盐、氟代磺酸锂盐中的一种或多种，所述电解液中的所述氟代碳酸乙烯酯的质量百分含量为y1％，所述电解液中的所述氟代磺酰亚胺锂盐的质量百分含量为y2％，所述电解液中的所述氟代磺酸锂盐的质量百分含量为y3％，均基于所述电解液的总质量计，并且所述电解液满足：y1≥0，y2≥0，y3≥0且0<y1+y2+y3≤15。四氟硼酸锂能在正极活性材料表面形成致密且低阻抗的界面膜，但是四氟硼酸锂在负极形成的界面膜的长期稳定性较差，因此当电解液还含有上述化合物时，有助于在正极和/或负极形成更稳定的界面膜，从而进一步改善二次电池的电化学性能。
在一些实施例中，所述电解液还可以包括氟代碳酸乙烯酯。可选地，所述氟代碳酸乙烯酯的质量百分含量y1％满足0<y1≤2.5。例如，y1可以为0.10，0.20，0.50，0.75，1.0，1.25，1.50，1.75，2.0，2.5或以上任何数值所组成的范围。更可选地，0<y1≤2.0，0<y1≤1.75，0<y1≤1.5，0<y1≤1.25，0<y1≤1.0，0<y1≤0.75或0<y1≤0.5。
对二次电池而言，氟代碳酸乙烯酯能在较高的电位下发生还原分解反应，并在负极活性材料表面形成具有一定柔韧性的SEI膜，同时还能抑制较低电位的有机溶剂的还原分解以及抑制有机溶剂嵌入负极活性材料。因此，当电解液中还含有氟代碳酸乙烯酯时，能够稳定负极界面膜，从而有效提升二次电池的循环性能。此外，氟代碳酸乙烯酯耐高压氧化，有利于匹配高电压正极活性材料，从而有利于提升二次电池的能量密度。但是，氟代碳酸乙烯酯高温下分解时会形成HF，HF会增加电解液的酸度、破坏正极活性材料的结构稳定性、增加二次电池的产气量，由此会恶化二次电池的高温存储性能。因此，氟代碳酸乙烯酯的含量不宜太高。
在一些实施例中，四氟硼酸锂的质量百分含量x％和氟代碳酸乙烯酯的质量百分含量y1％还可以满足0.5≤y1/x≤4.0。本申请的发明人惊喜发现，通过合理控制四氟硼酸锂的质量百分含量x％和氟代碳酸乙烯酯的质量百分含量y1％之间的关系并使其满足0.5≤y1/x≤4.0时，能够充分发挥四氟硼酸锂和氟代碳酸乙烯酯的协同作用，由此不仅不会明显增加二次电池的产气量，还会进一步改善二次电池的循环性能。可能的原因在于，四氟硼酸锂作为一种正极活性材料的稳定剂，其结构中的B原子还具有与正极活性材料表面的O原子相互作用的功能，由此能够抑制HF对正极活性材料结构的破坏。可选地，0.5≤y1/x≤3.5，0.5≤y1/x≤3.0，0.5≤y1/x≤2.5，0.5≤y1/x≤2.0，0.5≤y1/x≤1.5或0.5≤y1/x≤1.0。
在一些实施例中，所述电解液还可以包括氟代磺酰亚胺锂盐。所述氟代磺酰亚胺锂盐的分子式可以为LiN(SO 2R 1)(SO 2R 2)，R 1、R 2各自独立地表示F或C nF 2n+1，n为1～10的 整数。可选地，所述氟代磺酰亚胺锂盐包括双氟磺酰亚胺锂(LiFSI)、双三氟甲磺酰亚胺锂(LiTFSI)或其组合。
可选地，所述氟代磺酰亚胺锂盐的质量百分含量y2％满足0<y2≤14。例如，y2可以为0.5，1，2，3，4，5，6，7，8，9，10，11，12，13，14或以上任何数值所组成的范围。
氟代磺酰亚胺阴离子是以N为中心的弱配位阴离子，含有共轭基团和强吸电性的-F或-C nF 2n+1，阴离子电荷高度离域，阴离子与锂离子之间的作用力较弱。因此，氟代磺酰亚胺锂盐具有较低的晶格能、容易解离，从而能够提高电解液的离子电导率、降低电解液的粘度，提升二次电池的倍率性能和低温性能。同时，氟代磺酰亚胺锂盐还具有热稳定性高且不易水解的特性，从而能在负极活性材料表面形成更薄、阻抗更低且热稳定性更高的SEI膜，由此能够减少负极活性材料与电解液之间的副反应。因此，当电解液中进一步含有氟代磺酰亚胺锂盐时，能够显著改善二次电池的倍率性能和低温性能。但是，氟代磺酰亚胺锂盐不耐高压，在较高电位下会腐蚀正极集流体(例如，铝箔)、增加正极活性材料与电解液之间的副反应，容易影响二次电池的循环性能。因此，氟代磺酰亚胺锂盐的含量不宜太高。
在一些实施例中，四氟硼酸锂的质量百分含量x％和氟代磺酰亚胺锂盐的质量百分含量y2％还可以满足1≤y2/x≤28。本申请的发明人惊喜发现，合理控制四氟硼酸锂的质量百分含量x％和氟代磺酰亚胺锂盐的质量百分含量y2％之间的关系并使其满足1≤y2/x≤28时，能够充分发挥四氟硼酸锂和氟代磺酰亚胺锂盐的协同作用，不仅不会明显恶化二次电池的循环性能，还能进一步改善二次电池的倍率性能和低温性能。可能的原因在于，四氟硼酸锂作为一种正极活性材料的稳定剂，能在正极活性材料表面形成致密且低阻抗的界面膜，抑制正极活性材料与电解液之间的副反应；四氟硼酸锂对正极集流体具有钝化作用，其可以优先在正极集流体表面被氧化分解并形成一层钝化膜，从而有效改善氟代磺酰亚胺锂盐对正极集流体的腐蚀。
发明人在进一步研究中还发现，正极活性材料中的镍元素含量b会影响氟代磺酰亚胺锂盐对二次电池性能的改善效果。当镍元素含量较高时，正极活性材料的热稳定较差，高温容量衰减加速，由此当采用更高含量的氟代磺酰亚胺锂盐时，其对二次电池高温性能的改善效果更明显；当镍元素含量较低时，正极活性材料的热稳定较好，并且随着电解液中氟代磺酰亚胺锂盐含量增加，其对二次电池高温性能的改善效果不会持续增加。
在一些实施例中，当0<b≤0.7时，所述电解液中的所述氟代磺酰亚胺锂盐的质量百分含量y2％满足：0<y2≤5和/或1≤y2/x≤10。
可选地，0<y2≤4.5，0<y2≤4，0<y2≤3.5，0<y2≤3，0<y2≤2.5，0<y2≤2，0<y2≤1.5或0<y2≤1。
可选地，1≤y2/x≤9，1≤y2/x≤8，1≤y2/x≤7，1≤y2/x≤6，1≤y2/x≤5，1≤y2/x≤4，1≤y2/x≤3或1≤y2/x≤2。
在一些实施例中，当0.7≤b<0.98时，所述电解液中的所述氟代磺酰亚胺锂盐的质量百分含量y2％满足：5≤y2≤14和/或10≤y2/x≤28。
可选地，5≤y2≤13，5≤y2≤12，5≤y2≤11，5≤y2≤10，6≤y2≤14，6≤y2≤13，6≤y2≤12，6≤y2≤11，6≤y2≤10，7≤y2≤14，7≤y2≤13，7≤y2≤12，7≤y2≤11，7≤y2≤10，8≤y2≤14，8≤y2≤13，8≤y2≤12，8≤y2≤11或8≤y2≤10。
可选地，12≤y2/x≤28，12≤y2/x≤26，12≤y2/x≤24，12≤y2/x≤22，12≤y2/x≤20，14≤y2/x≤28，14≤y2/x≤26，14≤y2/x≤24，14≤y2/x≤22，14≤y2/x≤20，16≤y2/x≤28，16≤y2/x≤26，16≤y2/x≤24，16≤y2/x≤22或16≤y2/x≤20。
在一些实施例中，所述电解液还可以包括氟代磺酸锂盐。所述氟代磺酸锂盐的分子式可以为LiSO 3R 3，R 3表示F、部分氟化或全部氟化的C1-C10的烷基，可选地，所述氟代磺酸锂盐包括氟磺酸锂、三氟甲磺酸锂或其组合。
可选地，所述氟代磺酸锂盐的质量百分含量y3％满足0<y3≤1.0。例如，y3可以为0.10，0.20，0.30，0.40，0.50，0.60，0.70，0.80，0.90，1.0或以上任何数值所组成的范围。更可选地，0<y3≤0.9，0<y3≤0.8，0<y3≤0.7，0<y3≤0.6，0<y3≤0.5，0<y3≤0.4，0<y3≤0.3或0<y3≤0.2。
氟代磺酸锂盐不仅可以在负极活性材料表面形成界面膜，还可以在正极活性材料材料表面形成界面膜，同时其热稳定性较高，由此能够较大地改善二次电池高温下的充放电特性，提高二次电池的高温循环容量保持率并抑制气体产生。但是，氟代磺酸锂盐的离子电导率较低，容易影响二次电池的动力学性能。因此，氟代磺酸锂盐的含量不宜太高。
在一些实施例中，四氟硼酸锂的质量百分含量x％和氟代磺酸锂盐的质量百分含量y3％还可以满足0.001≤y3/x≤2.0。本申请的发明人惊喜发现，合理控制四氟硼酸锂的质量百分含量x％和氟代磺酸锂盐的质量百分含量y3％之间的关系使其满足0.001≤y3/x≤2.0时，能够充分发挥四氟硼酸锂和氟代磺酸锂盐的协同作用，从而有助于在正极和负极形成致密、稳定且低阻抗的界面膜，由此能够进一步改善二次电池的高温性能，例如改善高温循环性能和高温存储性能，同时不明显恶化二次电池的动力学性能。可选地，0.001≤y3/x≤1.5，0.001≤y3/x≤1.25，0.001≤y3/x≤1.0，0.001≤y3/x≤0.75，0.001≤y3/x≤0.5或0.001≤y3/x≤0.25。
在一些实施例中，所述电解液还可以包括氟代碳酸乙烯酯、氟代磺酰亚胺锂盐、氟代磺酸锂盐中的任意两种。
例如，在一些实施例中，所述电解液可以包括氟代碳酸乙烯酯和氟代磺酰亚胺锂盐的组合。可选地，所述氟代碳酸乙烯酯的质量百分含量y1％满足0<y1≤2.5，所述氟代磺酰亚胺锂盐的质量百分含量y2％满足0<y2≤14，并且0<y1+y2≤15。
可选地，四氟硼酸锂的质量百分含量x％、氟代碳酸乙烯酯的质量百分含量y1％和氟代磺酰亚胺锂盐的质量百分含量y2％进一步满足0.5≤y1/x≤4.0和/或1≤y2/x≤28。由此二次电池在具有显著改善的循环性能的同时，还具有改善的倍率性能和低温性能。
可选地，氟代碳酸乙烯酯的质量百分含量y1％和氟代磺酰亚胺锂盐的质量百分含量y2％还可以进一步满足0.5≤y2/y1≤48。
更可选地，四氟硼酸锂的质量百分含量x％、氟代碳酸乙烯酯的质量百分含量y1％和氟代磺酰亚胺锂盐的质量百分含量y2％还同时满足0.5≤y1/x≤4.0，1≤y2/x≤28和0.5≤y2/y1≤48。氟代碳酸乙烯酯能有效提升二次电池的循环性能，氟代磺酰亚胺锂盐能够改 善二次电池的倍率性能和低温性能，四氟硼酸锂作为一种正极活性材料的稳定剂，能在正极活性材料表面形成致密且低阻抗的界面膜，显著改善低钴或无钴正极活性材料的锂离子扩散速率，同时抑制正极活性材料与电解液之间的副反应、抑制HF对正极活性材料结构的破坏。因此，当进一步合理调节三种组分之间的含量关系使其同时满足0.5≤y1/x≤4.0，1≤y2/x≤28和0.5≤y2/y1≤48时，有利于充分发挥上述三者之间的协同作用，并充分抑制各组分单独使用时的缺陷，同时还能够形成致密、稳定且低阻抗的正极界面膜和负极界面膜。
特别地，当0<b≤0.7时，所述电解液可以满足0<y1≤2.5和0<y2≤5；可选地，所述电解液可以进一步满足0.5≤y1/x≤4.0和1≤y2/x≤10；更可选地，所述电解液还可以进一步满足0.5≤y2/y1≤10。
特别地，当0.7≤b<0.98时，所述电解液可以满足0<y1≤2.5和5≤y2≤14；可选地，所述电解液可以进一步满足0.5≤y1/x≤4.0和10≤y2/x≤28；更可选地，所述电解液还可以进一步满足6≤y2/y1≤48。
例如，在一些实施例中，所述电解液可以包括氟代碳酸乙烯酯和氟代磺酸锂盐的组合。可选地，所述氟代碳酸乙烯酯的质量百分含量y1％满足0<y1≤2.5，所述氟代磺酸锂盐的质量百分含量y3％满足0<y3≤1.0。更可选地，四氟硼酸锂的质量百分含量x％、氟代碳酸乙烯酯的质量百分含量y1％和氟代磺酸锂盐的质量百分含量y3％进一步满足0.5≤y1/x≤4.0和/或0.001≤y3/x≤2.0。由此二次电池在具有显著改善的循环性能的同时，还具有改善的高温性能。
例如，在一些实施例中，所述电解液可以包括氟代磺酰亚胺锂盐和氟代磺酸锂盐的组合。可选地，所述氟代磺酰亚胺锂盐的质量百分含量y2％满足0<y2≤14，所述氟代磺酸锂盐的质量百分含量y3％满足0<y3≤1.0，并且0<y2+y3≤15。
可选地，四氟硼酸锂的质量百分含量x％、氟代磺酰亚胺锂盐的质量百分含量y2％和氟代磺酸锂盐的质量百分含量y3％进一步满足1≤y2/x≤28和/或0.001≤y3/x≤2.0。由此二次电池在具有显著改善的循环性能的同时，还具有改善的倍率性能、低温性能和高温性能。更可选地，四氟硼酸锂的质量百分含量x％、氟代磺酰亚胺锂盐的质量百分含量y2％和氟代磺酸锂盐的质量百分含量y3％还同时满足1≤y2/x≤28，0.001≤y3/x≤2.0和0.036≤x/(y2+y3)≤1.0。由此有助于在正极和负极形成性能优良的无机/有机复合界面膜，从而能够进一步改善二次电池的综合性能。
特别地，当0<b≤0.7时，所述电解液可以满足0<y2≤5和0<y3≤1.0；可选地，所述电解液可以进一步满足1≤y2/x≤10和0.001≤y3/x≤2.0；更可选地，所述电解液还可以进一步满足0.1≤x/(y2+y3)≤1.0。
特别地，当0.7≤b<0.98时，所述电解液可以满足5≤y2≤14和0<y3≤1.0；可选地，所述电解液可以进一步满足10≤y2/x≤28和0.001≤y3/x≤2.0；更可选地，所述电解液还可以进一步满足0.036≤x/(y2+y3)≤0.1。
在一些实施例中，所述电解液还可以同时包括氟代碳酸乙烯酯、氟代磺酰亚胺锂盐和氟代磺酸锂盐。可选地，所述氟代碳酸乙烯酯的质量百分含量y1％满足0<y1≤2.5，所述氟代磺酰亚胺锂盐的质量百分含量y2％满足0<y2≤14，所述氟代磺酸锂盐的质量百分含量y3％满足0<y3≤1.0，并且0<y1+y2+y3≤15。
可选地，所述电解液进一步满足0.5≤y1/x≤4.0，1≤y2/x≤28和0.001≤y3/x≤2.0。由此，二次电池在具有显著改善的循环性能的同时，还具有改善的倍率性能、低温性能和高温性能。更可选地，所述电解液还同时满足0.5≤y1/x≤4.0，1≤y2/x≤28，0.001≤y3/x≤2.0和0.5≤y2/y1≤48。此时，二次电池的综合性能得到进一步改善。进一步可选地，所述电解液还同时满足0.5≤y1/x≤4.0，1≤y2/x≤28，0.001≤y3/x≤2.0，0.5≤y2/y1≤48和0.036≤x/(y2+y3)≤1.0。由此有助于在正极和负极形成性能优良的无机/有机复合界面膜，从而能够进一步改善二次电池的综合性能。
特别地，当0<b≤0.7时，所述电解液可以满足0<y1≤2.5，0<y2≤5和0<y3≤1.0；可选地，所述电解液可以进一步满足0.5≤y1/x≤4.0，1≤y2/x≤10和0.001≤y3/x≤2.0；更可选地，所述电解液还可以进一步满足0.5≤y2/y1≤10和/或0.1≤x/(y2+y3)≤1.0。
特别地，当0.7≤b<0.98时，所述电解液可以满足0<y1≤2.5，5≤y2≤14和0<y3≤1.0；可选地，所述电解液可以进一步满足0.5≤y1/x≤4.0，10≤y2/x≤28和0.001≤y3/x≤2.0；更可选地，所述电解液还可以进一步满足：6≤y2/y1≤48和/或0.036≤x/(y2+y3)≤0.1。
在一些实施例中，所述电解液还包括锂盐和有机溶剂。在本申请中，所述锂盐和所述有机溶剂的种类不受具体的限制，可根据实际需求进行选择。
作为示例，所述锂盐可包括六氟磷酸锂(LiPF 6)、高氯酸锂(LiClO 4)、六氟砷酸锂(LiAsF 6)、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)和四氟草酸磷酸锂(LiTFOP)中的一种或多种。可选地，所述锂盐包括六氟磷酸锂。
作为示例，所述有机溶剂可包括碳酸乙烯酯(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)、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)和二乙砜(ESE)中的一种或多种。
在本申请的二次电池的实施方式中，所述电解液并不排除除了上述组分外的其他组分。在一些实施例中，所述电解液中还可选地包括其他添加剂，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、改善电池低温功率性能的添加剂等。
在一些实施例中，所述电解液的质量可以为所述二次电池总质量的10％至20％。由此有利于在正极活性材料表面形成致密且低阻抗的界面膜。并且能够有效避免以下情况：电解液的质量分数小于10％时，正极和负极电解液浸润性差、界面阻抗高且循环后阻抗增长快，由此可能导致二次电池的容量发挥差、循环性能差；电解液的质量分数大于20％时，电解液与正极以及电解液与负极的界面副反应增加，活性锂离子的不可逆消耗增加且电池体积膨胀严重，由此也可能会导致二次电池的循环性能变差。
所述电解液可以按照本领域常规的方法制备。例如，可以将有机溶剂、锂盐、四氟硼酸锂、可选的氟代碳酸乙烯酯、可选的氟代磺酰亚胺锂盐、可选的氟代磺酸锂盐等组分混合均匀，得到电解液。各物料的添加顺序并没有特别的限制，例如，可以将锂盐、四氟硼酸锂、可选的氟代碳酸乙烯酯、可选的氟代磺酰亚胺锂盐、可选的氟代磺酸锂盐等组分加入到有机溶剂中混合均匀，得到电解液；或者，先将锂盐加入有机溶剂中，然 后再将四氟硼酸锂、可选的氟代碳酸乙烯酯、可选的氟代磺酰亚胺锂盐、可选的氟代磺酸锂盐等组分加入有机溶剂中混合均匀，得到电解液。
在本申请中，电解液中各组分及其含量可以按照本领域已知的方法测定。例如，可以通过气相色谱-质谱联用法(GC-MS)、离子色谱法(IC)、液相色谱法(LC)、核磁共振波谱法(NMR)等进行测定。
需要说明的是，本申请的电解液测试时，可以从二次电池中获取电解液。从二次电池中获取电解液的一个示例性方法包括如下步骤：将二次电池放电至放电截止电压(为了安全起见，一般使电池处于满放状态)后进行离心处理，之后取适量离心处理得到的液体即为电解液。也可以从二次电池的注液口直接获取电解液。
[正极极片]
本申请的正极极片包括正极集流体和位于所述正极集流体表面的正极膜层。例如，所述正极集流体具有在自身厚度方向相对的两个表面，所述正极膜层位于所述正极集流体的两个相对表面中的任意一者或两者上。
所述正极集流体可采用金属箔片或复合集流体。作为金属箔片的示例，可采用铝箔。复合集流体可包括高分子材料基层以及形成于高分子材料基层至少一个表面上的金属材料层。作为示例，所述金属材料可包括铝、铝合金、镍、镍合金、钛、钛合金、银、银合金中的一种或多种。作为示例，所述高分子材料基层可包括聚丙烯(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)中的一种或多种。
所述正极膜层通常包含正极活性材料以及可选的粘结剂和可选的导电剂。正极膜层通常是将正极浆料涂布在正极集流体上，经干燥、冷压而成的。正极浆料通常是将正极活性材料、可选的导电剂、可选的粘结剂以及任意的其他组分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)，但不限于此。作为示例，用于正极膜层的粘结剂可包括聚偏氟乙烯(PVDF)、聚四氟乙烯(PTFE)、偏氟乙烯-四氟乙烯-丙烯三元共聚物、偏氟乙烯-六氟丙烯-四氟乙烯三元共聚物、四氟乙烯-六氟丙烯共聚物、含氟丙烯酸酯树脂中的一种或多种。作为示例，用于正极膜层的导电剂可包括超导碳、导电石墨、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯、碳纳米纤维中的一种或多种。
所述正极活性材料包括上述分子式为Li aNi bCo cM1 dM2 eO fA g的层状材料。
在一些实施例中，分子式为Li aNi bCo cM1 dM2 eO fA g的层状材料可选地被M2阳离子掺杂改性、A阴离子掺杂改性或被M2阳离子和A阴离子同时掺杂改性，掺杂后得到的层状材料晶体结构更加稳定，能进一步提升二次电池的电化学性能，例如循环性能、倍率性能等。
在一些实施例中，A选自F。经F掺杂改性后，Li aNi bCo cM1 dM2 eO fA g的结构更加稳定，能使二次电池具有更好的循环性能和倍率性能。
在一些实施例中，M1选自Mn。
在一些实施例中，M1选自Al。
在一些实施例中，M1选自Mn和Al的组合。Mn和Al的摩尔比没有特别的限制，可根据实际需求进行选择。
在一些实施例中，0.50≤b<0.98。可选地，0.55≤b<0.98，0.60≤b<0.98，0.65≤b<0.98，0.70≤b<0.98，0.75≤b<0.98或0.80≤b<0.98。
在一些实施例中，c＝0。
在一些实施例中，0<c<0.1。可选地，0<c≤0.09，0<c≤0.08，0<c≤0.07，0<c≤0.06，0<c≤0.05，0<c≤0.04，0<c≤0.03，0<c≤0.02或0<c≤0.01。
在一些实施例中，0<d≤0.45。可选地，0<d≤0.40，0<d≤0.35，0<d≤0.30，0<d≤0.25，0<d≤0.20，0<d≤0.15或0<d≤0.10。
在一些实施例中，e＝0。
在一些实施例中，0<e≤0.5。可选地，0<e≤0.45，0<e≤0.40，0<e≤0.35，0<e≤0.30，0<e≤0.25，0<e≤0.20，0<e≤0.15，0<e≤0.10或0<e≤0.05。
在一些实施例中，f＝2，g＝0。
在一些实施例中，f＝0，g＝2。
在一些实施例中，0<f<2，0<g<2，且f+g＝2。
作为示例，分子式为Li aNi bCo cM1 dM2 eO fA g的层状材料包括但不限于LiNi 0.7Mn 0.3O 2、LiNi 0.69Co 0.01Mn 0.3O 2、LiNi 0.68Co 0.02Mn 0.3O 2、LiNi 0.65Co 0.05Mn 0.3O 2、LiNi 0.63Co 0.07Mn 0.3O 2、LiNi 0.61Co 0.09Mn 0.3O 2中的一种或多种。
Li aNi bCo cM1 dM2 eO fA g可以按照本领域常规方法制备。示例性制备方法如下：将锂源、镍源、钴源、M1元素前驱体、可选的M2元素前驱体、可选的A元素前驱体混合后烧结得到。烧结气氛可为含氧气氛，例如，空气气氛或氧气气氛。烧结气氛的O 2浓度例如为70％至100％。烧结温度和烧结时间可根据实际情况进行调节。作为示例，锂源包括但不限于氧化锂(Li 2O)、磷酸锂(Li 3PO 4)、磷酸二氢锂(LiH 2PO 4)、醋酸锂(CH 3COOLi)、氢氧化锂(LiOH)、碳酸锂(Li 2CO 3)及硝酸锂(LiNO 3)中的一种或多种。作为示例，镍源包括但不限于硫酸镍、硝酸镍、氯化镍、草酸镍及醋酸镍中的一种或多种。作为示例，钴源包括但不限于硫酸钴、硝酸钴、氯化钴、草酸钴及醋酸钴中的一种或多种。作为示例，M1元素前驱体包括但不限于M1元素的氧化物、硝酸化合物、碳酸化合物、氢氧化合物及醋酸化合物中的一种或多种。作为示例，M2元素前驱体包括但不限于M2元素的氧化物、硝酸化合物、碳酸化合物、氢氧化合物及醋酸化合物中的一种或多种。作为示例，A元素的前驱体包括但不限于氟化铵、氟化锂、氟化氢、氯化铵、氯化锂、氯化氢、硝酸铵、亚硝酸铵、碳酸铵、碳酸氢铵、磷酸铵、磷酸、硫酸铵、硫酸氢铵、亚硫酸氢铵、亚硫酸铵、硫化氢铵、硫化氢、硫化锂、硫化铵及单质硫中的一种或多种。
在一些实施例中，Li aNi bCo cM1 dM2 eO fA g的表面还可以具有包覆层，例如碳包覆层。碳包覆层有利于稳定正极活性材料表面，并进一步降低正极活性材料的电荷转移阻抗，降低锂离子在正极活性材料体相内的扩散阻力。可选地，所述碳包覆层包括无定形碳，例如软碳、硬碳或其组合。
在一些实施例中，所述正极活性材料并不排除除了Li aNi bCo cM1 dM2 eO fA g之外的其他组分，例如，所述正极活性材料还可以包括含锂磷酸盐及其改性化合物中的一种或多种。作为示例，所述含锂磷酸盐可包括磷酸铁锂、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各自的改性化合物中的一种或多种。
在一些实施例中，所述分子式为Li aNi bCo cM1 dM2 eO fA g的层状材料的质量百分含量为80％至99％，基于所述正极膜层的总质量计。例如，分子式为Li aNi bCo cM1 dM2 eO fA g的层状材料的质量百分含量为80％，81％，82％，83％，84％，85％，86％，87％，88％，89％，90％，91％，92％，93％，94％，95％，96％，97％，98％，99％或以上任何数值所组成的范围。可选地，分子式为Li aNi bCo cM1 dM2 eO fA g的层状材料的质量百分含量为85％至99％，90％至99％，95％至99％，80％至98％，85％至98％，90％至98％，95％至98％，80％至97％，85％至97％，90％至97％或95％至97％。
[负极极片]
根据本申请的二次电池还包括负极极片。在一些实施例中，所述负极极片包括负极集流体和位于所述负极集流体表面的负极膜层。例如，所述负极集流体具有在自身厚度方向相对的两个表面，所述负极膜层位于所述负极集流体的两个相对表面中的任意一者或两者上。
所述负极集流体可采用金属箔片或复合集流体。作为金属箔片的示例，可采用铜箔。复合集流体可包括高分子材料基层以及形成于高分子材料基层至少一个表面上的金属材料层。作为示例，所述金属材料可包括铜、铜合金、镍、镍合金、钛、钛合金、银和银合金中的一种或多种。作为示例，所述高分子材料基层可包括聚丙烯(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)和聚乙烯(PE)中的一种或多种。
所述负极膜层通常包含负极活性材料、可选的粘结剂、可选的导电剂以及其他可选的助剂。所述负极膜层通常是将负极浆料涂布在负极集流体上，经干燥、冷压而成的。所述负极浆料涂通常是将负极活性材料、可选的导电剂、可选地粘结剂、其他可选的助剂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，但不限于此。作为示例，用于负极膜层的粘结剂可包括丁苯橡胶(SBR)、水溶性不饱和树脂SR-1B、水性丙烯酸树脂(例如，聚丙烯酸PAA、聚甲基丙烯酸PMAA、聚丙烯酸钠PAAS)、聚丙烯酰胺(PAM)、聚乙烯醇(PVA)、海藻酸钠(SA)和羧甲基壳聚糖(CMCS)中的一种或多种。作为示例，用于负极膜层的导电剂可包括超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯和碳纳米纤维中一种或多种。其他可选的助剂可包括增稠剂(例如，羧甲基纤维素钠CMC-Na)、PTC热敏电阻材料等。
所述负极活性材料可采用本领域公知的用于二次电池的负极活性材料。作为示例，所述负极活性材料可包括天然石墨、人造石墨、软炭、硬炭、硅基材料、锡基材料和钛酸锂中的一种或多种。所述硅基材料可包括单质硅、硅氧化物、硅碳复合物、硅氮复合物和硅合金材料中的一种或多种。所述锡基材料可包括单质锡、锡氧化物和锡合金材料中的一种或多种。本申请并不限定于这些材料，还可以使用其他可被用作二次电池负极活性材料的传统公知的材料。这些负极活性材料可以仅单独使用一种，也可以将两种以上组合使用。
[隔离膜]
根据本申请的二次电池还可以包括隔离膜。所述隔离膜设置在所述正极极片和所述 负极极片之间，起到隔离的作用。本申请对所述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膜。
在一些实施例中，所述隔离膜的材质可以包括玻璃纤维、无纺布、聚乙烯、聚丙烯和聚偏二氟乙烯中的一种或多种。所述隔离膜可以是单层薄膜，也可以是多层复合薄膜。所述隔离膜为多层复合薄膜时，各层的材料相同或不同。
在一些实施例中，所述正极极片、所述隔离膜和所述负极极片可通过卷绕工艺和/或叠片工艺制成电极组件。
在一些实施例中，所述二次电池可可以包括外包装。该外包装可用于封装上述电极组件及电解液。二次电池的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。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二次电池5。
在一些实施例中，如图2所示，外包装可包括壳体51和盖板53。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用于盖设所述开口，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。二次电池5所含电极组件52的数量可以为一个或多个，可根据需求来调节。
在本申请的一些实施方式中，根据本申请的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的示意图。如图3所示，在电池模块4中，多个二次电池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的示意图。如图4和图5所示，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用于盖设下箱体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。
制备方法
本申请实施方式还提供了一种用于制备二次电池的方法，所述方法至少包括步骤1和步骤2。
步骤1，将正极极片、隔离膜、负极极片、电解液组装成二次电池，所述正极极片包括正极集流体和位于所述正极集流体表面的正极膜层，所述正极膜层包括分子式为Li aNi bCo cM1 dM2 eO fA g的层状材料，M1选自Mn、Al或其组合，M2选自Si、Ti、Mo、V、Ge、Se、Zr、Nb、Ru、Pd、Sb、Ce、Te及W中的一种或多种，A选自F、N、P及S中的一种或多种，0.8≤a≤1.2，0<b<0.98，0≤c<0.1，0<d<0.5，0≤e≤0.5，0≤f≤2， 0≤g≤2，b+c+d+e＝1，f+g＝2，所述电解液包括四氟硼酸锂、可选的氟代碳酸乙烯酯、可选的氟代磺酰亚胺锂盐和可选的氟代磺酸锂盐，所述电解液中的所述四氟硼酸锂的质量百分含量为x％，所述电解液中的所述氟代碳酸乙烯酯的质量百分含量为y1％，所述电解液中的所述氟代磺酰亚胺锂盐的质量百分含量为y2％，所述电解液中的所述氟代磺酸锂盐的质量百分含量为y3％，均基于所述电解液的总质量计，x>0，y1≥0，y2≥0，y3≥0。
步骤2，从步骤1所得到的二次电池中筛选出满足0.05≤c+x/10≤0.15的二次电池。
二次电池满足x>0和0.05≤c+x/10≤0.15时，能够稳定低钴或无钴正极活性材料的晶体结构并提升其内部的锂离子扩散速率。因此，通过本申请制备方法得到的二次电池均能具有显著改善的循环性能以及良好的存储性能和动力学性能。
在一些实施例中，所述方法还包括步骤：从步骤2所得到的二次电池中筛选出满足0<x≤1.0和0.05≤c+x/10≤0.15的二次电池。此时，制备的二次电池具有进一步改善的循环性能。可选地，二次电池满足0.05≤c+x/10≤0.12。
在一些实施例中，所述方法还包括步骤：从步骤2所得到的二次电池中筛选出满足25≤P/(c+x/10)≤65的二次电池，Pg/cm 3表示所述正极极片的压实密度。此时，制备的二次电池能够在具有显著改善的循环性能和高能量密度的前提下，还具有改善的功率性能。可选地，二次电池满足30≤P/(c+x/10)≤50。
在一些实施例中，所述方法还包括步骤：从步骤2所得到的二次电池中筛选出满足如下条件(1)至(3)中至少一者的二次电池：
(1)0<y1≤2.5，0.5≤y1/x≤4.0，可选地，0.5≤y1/x≤2.0；
(2)0<y2≤14，1≤y2/x≤28；
(3)0<y3≤1.0，0.001≤y3/x≤2.0，可选地，0.001≤y3/x≤1.0。
此时，制备的二次电池具有进一步改善的循环性能、存储性能、倍率性能、低温性能和高温性能中的至少一者。
在一些实施例中，所述方法还包括步骤：从步骤2所得到的二次电池中筛选出满足0<y1+y2+y3≤15，0<y1≤2.5，0<y2≤14，0<y3≤1.0，0.5≤y1/x≤4.0，1≤y2/x≤28，0.001≤y3/x≤2.0和0.5≤y2/y1≤48的二次电池。此时，制备的二次电池的综合性能得到进一步改善。
可选地，当0<b≤0.7时，所述方法还包括步骤：从步骤2所得到的二次电池中筛选出满足0<y1+y2+y3≤15，0<y1≤2.5，0<y2≤5，0<y3≤1.0，0.5≤y1/x≤4.0，1≤y2/x≤10，0.001≤y3/x≤2.0和0.5≤y2/y1≤10的二次电池。
可选地，当0.7≤b<0.98时，所述方法还包括步骤：从步骤2所得到的二次电池中筛选出满足0<y1+y2+y3≤15，0<y1≤2.5，5≤y2≤14，0<y3≤1.0，0.5≤y1/x≤4.0，10≤y2/x≤28，0.001≤y3/x≤2.0和6≤y2/y1≤48的二次电池。
在一些实施例中，所述方法还包括步骤：从步骤2所得到的二次电池中筛选出满足0<y1+y2+y3≤15，0<y1≤2.5，0<y2≤14，0<y3≤1.0，0.5≤y1/x≤4.0，1≤y2/x≤28，0.001≤y3/x≤2.0，0.5≤y2/y1≤48和0.036≤x/(y2+y3)≤1.0的二次电池。此时，制备的二次电池的综合性能得到进一步改善。
可选地，当0<b≤0.7时，所述方法还包括步骤：从步骤2所得到的二次电池中筛选出满足0<y1+y2+y3≤15，0<y1≤2.5，0<y2≤5，0<y3≤1.0，0.5≤y1/x≤4.0，1≤y2/x≤10，0.001≤y3/x≤2.0，0.5≤y2/y1≤10和0.1≤x/(y2+y3)≤1.0的二次电池。
可选地，当0.7≤b<0.98时，所述方法还包括步骤：从步骤2所得到的二次电池中筛选出满足0<y1+y2+y3≤15，0<y1≤2.5，5≤y2≤14，0<y3≤1.0，0.5≤y1/x≤4.0，10≤y2/x≤28，0.001≤y3/x≤2.0，6≤y2/y1≤48和0.036≤x/(y2+y3)≤0.1的二次电池。
用电装置
本申请实施方式还提供一种用电装置，所述用电装置包括本申请的二次电池、电池模块或电池包中的至少一种。所述二次电池、电池模块或电池包可以用作所述用电装置的电源，也可以用作所述用电装置的能量存储单元。所述用电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。
所述用电装置可以根据其使用需求来选择二次电池、电池模块或电池包。
图6是作为一个示例的用电装置的示意图。该用电装置为纯电动车、混合动力电动车、或插电式混合动力电动车等。为了满足该用电装置对高功率和高能量密度的需求，可以采用电池包或电池模块。
作为另一个示例的用电装置可以是手机、平板电脑、笔记本电脑等。该用电装置通常要求轻薄化，可以采用二次电池作为电源。
实施例
下述实施例更具体地描述了本申请公开的内容，这些实施例仅仅用于阐述性说明，因为在本申请公开内容的范围内进行各种修改和变化对本领域技术人员来说是明显的。除非另有声明，以下实施例中所报道的所有份、百分比和比值都是基于重量计，而且实施例中使用的所有试剂都可商购获得或是按照常规方法进行合成获得，并且可直接使用而无需进一步处理，以及实施例中使用的仪器均可商购获得。
实施例1-1
正极极片的制备
将正极活性材料LiNi 0.65Co 0.05Mn 0.3O 2、导电剂炭黑、粘结剂聚偏氟乙烯(PVDF)按照质量比97.5:1.4:1.1在适量的溶剂NMP中充分搅拌混合，形成均匀的正极浆料；将正极浆料均匀涂覆于正极集流体铝箔的表面上，经干燥、冷压后，得到正极极片。正极极片的压实密度为3.5g/cm 3。
负极极片的制备
将负极活性材料石墨、粘结剂丁苯橡胶(SBR)、增稠剂羧甲基纤维素钠(CMC-Na)、导电剂炭黑(SuperP)按照质量比96.2:1.8:1.2:0.8在适量的溶剂去离子水中充分搅拌混合，形成均匀的负极浆料；将负极浆料均匀涂覆于负极集流体铜箔的表面上，经干燥、冷压后，得到负极极片。
隔离膜
采用多孔聚乙烯(PE)膜作为隔离膜。
电解液的制备
将碳酸乙烯酯(EC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)按照体积比1:1:1混合，得到有机溶剂。将LiPF 6和LiBF 4均匀溶解在上述有机溶剂中得到电解液，基于电解液的总质量计，LiPF 6的质量百分含量为12.5％，LiBF 4的质量百分含量为0.1％。
二次电池的制备
将正极极片、隔离膜、负极极片按顺序堆叠并卷绕，得到电极组件；将电极组件放入外包装中，加入上述电解液，经封装、静置、化成、老化等工序后，得到二次电池。电解液的质量为二次电池总质量的15％。
实施例1-2至L16和对比例1-1至1-7
二次电池的制备方法与实施例1类似，不同之处在于调整了正极活性材料种类以及电解液的制备参数，具体参数详见表1。“/”表示电解液中未加入对应的组分。
测试部分
(1)二次电池常温循环性能测试
在25℃下，将二次电池以1C恒流充电至4.3V，继续恒压充电至电流为0.05C，此时二次电池为满充状态，记录此时的充电容量，即为第1圈充电容量；将二次电池静置5min后，以1C恒流放电至2.8V，此为一个循环充放电过程，记录此时的放电容量，即为第1圈放电容量。将二次电池按照上述方法进行循环充放电测试，记录每圈循环后的放电容量。二次电池25℃循环600圈容量保持率(％)＝600圈循环后的放电容量/第1圈放电容量×100％。
(2)二次电池高温循环性能测试
在45℃下，将二次电池以1C恒流充电至4.3V，继续恒压充电至电流为0.05C，此时二次电池为满充状态，记录此时的充电容量，即为第1圈充电容量；将二次电池静置5min后，以1C恒流放电至2.8V，此为一个循环充放电过程，记录此时的放电容量，即为第1圈放电容量。将二次电池按照上述方法进行循环充放电测试，记录每圈循环后的放电容量。二次电池45℃循环600圈容量保持率(％)＝600圈循环后的放电容量/第1圈放电容量×100％。
(3)二次电池初始直流内阻测试
在25℃下，将二次电池以1C恒流充电到4.3V，继续恒压充电至电流为0.05C，此时二次电池为满充状态；将二次电池以0.5C恒流放电并调整二次电池至50％SOC，此时二次电池的电压记为U 1；将二次电池以4C的电流I 1恒流放电30秒，采用0.1秒采点，放电末期电压记为U 2。用二次电池50％SOC时的放电直流内阻表示二次电池的初始直流内阻，二次电池的初始直流内阻(mΩ)＝(U 1-U 2)/I 1。
(4)二次电池高温存储性能测试
在60℃下，将二次电池以1C恒流充电到4.3V，继续恒压充电至电流为0.05C，此时用排水法测试二次电池的体积并记为V 0；将二次电池放入60℃的恒温箱，存储30天后取出，此时用排水法测试二次电池的体积并记为V 1。二次电池60℃存储30天后的体积膨胀率(％)＝[(V 1-V 0)/V 0]×100％。
(5)二次电池自放电率测试
在25℃下，将二次电池充电至70％SOC，测试此时二次电池的开路电压记为OCV1；将二次电池放入25℃恒温箱中，存储3个月后取出，再次测试二次电池的开路电压记为 OCV2。二次电池25℃存储3个月的自放电率＝[(OCV1-OCV2)/OCV1]×100％。二次电池的自放电率越低，容量性能和安全性能越好。
(6)二次电池低温性能测试
在-10℃下，将二次电池以0.2C恒流充电至4.3V，继续恒压充电至电流为0.05C，此时二次电池为满充状态，记录此时的充电容量，即为第1圈充电容量；将二次电池静置30min后，以0.2C恒流放电至2.8V，此为一个循环充放电过程，记录此时的放电容量，即为第1圈放电容量。将二次电池按照上述方法进行循环充放电测试，记录每圈循环后的放电容量。二次电池-10℃循环200圈容量保持率(％)＝200圈循环后的放电容量/第1圈放电容量×100％。
表1给出实施例1-1至1-16和对比例1-1至1-7的性能测试结果。
从表1的测试结果可以看出，当电解液含有四氟硼酸锂并且使四氟硼酸锂的质量百分含量x％与低钴或无钴正极活性材料中的钴元素含量c满足x>0和0.05≤c+x/10≤0.15时，二次电池具有显著改善的循环性能以及良好的存储性能和动力学性能。当电解液不含有四氟硼酸锂、或者四氟硼酸锂含量过多或过少不能满足0.05≤c+x/10≤0.15时，均不能有效改善低钴或无钴二次电池的循环性能，同时二次电池的内阻也较高。
从表1的测试结果还可以看出，当正极极片的压实密度P g/cm 3、四氟硼酸锂的质量百分含量x％和低钴或无钴正极活性材料中的钴元素含量c进一步满足25≤P/(c+x/10)≤65时，二次电池还能具有更低的内阻。
发明人进一步研究了电解液中四氟硼酸锂以外的其他组分对二次电池性能的影响。
实施例2-1至2-20的二次电池制备方法与实施例1-3类似，不同之处在于调整了电解液的制备参数，具体参数详见表2。“/”表示电解液中未加入对应的组分。
从表2的测试结果可以看出，当实施例2-1至2-20的电解液进一步含有氟代碳酸乙烯酯(FEC)、双氟磺酰亚胺锂(LiFSI)和氟磺酸锂中的一者或多者时，有助于进一步改善二次电池的综合性能。
综合实施例2-9与实施例1-3、2-1至2-6的测试结果可以看出，当在实施例1-3的电解液基础上进一步同时加入氟代碳酸乙烯酯、双氟磺酰亚胺锂和氟磺酸锂时，有助于得到综合性能更好的二次电池。
综合实施例2-7至2-20的测试结果还可以看出，通过调节氟代碳酸乙烯酯的质量百分含量y1％、双氟磺酰亚胺锂的质量百分含量y2％和氟磺酸锂的质量百分含量y3％使其同时满足0.5≤y1/x≤4.0，1≤y2/x≤28，0.001≤y3/x≤2.0，0.5≤y2/y1≤48和0.036≤x/(y2+y3)≤1.0时，有助于得到综合性能更好的二次电池。可能的原因在于，此时能够在正极和负极均形成性能优良的无机/有机复合界面膜。
需要说明的是，本申请不限定于上述实施方式。上述实施方式仅为示例，在本申请的技术方案范围内具有与技术思想实质相同的构成、发挥相同作用效果的实施方式均包含在本申请的技术范围内。此外，在不脱离本申请主旨的范围内，对实施方式施加本领域技术人员能够想到的各种变形、将实施方式中的一部分构成要素加以组合而构筑的其它方式也包含在本申请的范围内。
Figure PCTCN2022101117-appb-000001
Figure PCTCN2022101117-appb-000002

Claims (23)

  1. 一种二次电池，包括电解液和正极极片，其中，
    所述正极极片包括正极集流体和位于所述正极集流体表面的正极膜层，所述正极膜层包括分子式为Li aNi bCo cM1 dM2 eO fA g的层状材料，M1选自Mn、Al或其组合，M2选自Si、Ti、Mo、V、Ge、Se、Zr、Nb、Ru、Pd、Sb、Ce、Te及W中的一种或多种，A选自F、N、P及S中的一种或多种，0.8≤a≤1.2，0<b<0.98，0≤c<0.1，0<d<0.5，0≤e≤0.5，0≤f≤2，0≤g≤2，b+c+d+e＝1，f+g＝2；
    所述电解液包括四氟硼酸锂，所述电解液中的所述四氟硼酸锂的质量百分含量为x％，基于所述电解液的总质量计，并且所述二次电池满足：x>0和0.05≤c+x/10≤0.15。
  2. 根据权利要求1所述的二次电池，其中，
    0.05≤c+x/10≤0.12；和/或，
    0<x≤1.0。
  3. 根据权利要求1或2所述的二次电池，其中，所述正极极片的压实密度为P g/cm 3，并且所述二次电池满足：25≤P/(c+x/10)≤65，可选地，30≤P/(c+x/10)≤50，
    可选地，P为3.3至3.6。
  4. 根据权利要求1-3中任一项所述的二次电池，其中，所述电解液还包括氟代碳酸乙烯酯、氟代磺酰亚胺锂盐、氟代磺酸锂盐中的一种或多种，所述电解液中的所述氟代碳酸乙烯酯的质量百分含量为y1％，所述电解液中的所述氟代磺酰亚胺锂盐的质量百分含量为y2％，所述电解液中的所述氟代磺酸锂盐的质量百分含量为y3％，均基于所述电解液的总质量计，并且所述电解液满足：y1≥0，y2≥0，y3≥0且0<y1+y2+y3≤15。
  5. 根据权利要求4所述的二次电池，其中，
    所述氟代磺酰亚胺锂盐的分子式为LiN(SO 2R 1)(SO 2R 2)，R 1、R 2各自独立地表示F或C nF 2n+1，n为1～10的整数，可选地，所述氟代磺酰亚胺锂盐包括双氟磺酰亚胺锂、双三氟甲磺酰亚胺锂或其组合；和/或，
    所述氟代磺酸锂盐的分子式为LiSO 3R 3，R 3表示F、部分氟化或全部氟化的C1-C10的烷基，可选地，所述氟代磺酸锂盐包括氟磺酸锂、三氟甲磺酸锂或其组合。
  6. 根据权利要求4或5所述的二次电池，其中，所述电解液中的所述氟代碳酸乙烯酯的质量百分含量y1％满足：
    0<y1≤2.5，可选地，0<y1≤2.0；和/或，
    0.5≤y1/x≤4.0，可选地，0.5≤y1/x≤2.0。
  7. 根据权利要求4-6中任一项所述的二次电池，其中，所述电解液中的所述氟代磺酰亚胺锂盐的质量百分含量y2％满足：
    0<y2≤14；和/或，
    1≤y2/x≤28。
  8. 根据权利要求7所述的二次电池，其中，
    当0<b≤0.7时，所述电解液中的所述氟代磺酰亚胺锂盐的质量百分含量y2％满足：0<y2≤5和/或1≤y2/x≤10，可选地，0<y2≤2.5，可选地，1≤y2/x≤5；
    当0.7≤b<0.98时，所述电解液中的所述氟代磺酰亚胺锂盐的质量百分含量y2％满足：5≤y2≤14和/或10≤y2/x≤28，可选地，8≤y2≤14，可选地，16≤y2/x≤28。
  9. 根据权利要求4-8中任一项所述的二次电池，其中，所述电解液中的所述氟代磺酸锂盐的质量百分含量y3％满足：
    0<y3≤1.0，可选地，0<y3≤0.5；和/或，
    0.001≤y3/x≤2.0，可选地，0.001≤y3/x≤1.0。
  10. 根据权利要求4或5所述的二次电池，其中，所述电解液还包括氟代碳酸乙烯酯、氟代磺酰亚胺锂盐和氟代磺酸锂盐，并且所述电解液满足：0<y1≤2.5，0<y2≤14，0<y3≤1.0，0.5≤y1/x≤4.0，1≤y2/x≤28，0.001≤y3/x≤2.0和0.5≤y2/y1≤48，
    可选地，当0<b≤0.7时，所述电解液满足：0<y1≤2.5，0<y2≤5，0<y3≤1.0，0.5≤y1/x≤4.0，1≤y2/x≤10，0.001≤y3/x≤2.0和0.5≤y2/y1≤10；
    可选地，当0.7≤b<0.98时，所述电解液满足：0<y1≤2.5，5≤y2≤14，0<y3≤1.0，0.5≤y1/x≤4.0，10≤y2/x≤28，0.001≤y3/x≤2.0和6≤y2/y1≤48。
  11. 根据权利要求4或5所述的二次电池，其中，所述电解液还包括氟代碳酸乙烯酯、氟代磺酰亚胺锂盐和氟代磺酸锂盐，并且所述电解液满足：0<y1≤2.5，0<y2≤14，0<y3≤1.0，0.5≤y1/x≤4.0，1≤y2/x≤28，0.001≤y3/x≤2.0，0.5≤y2/y1≤48和0.036≤x/(y2+y3)≤1.0，
    可选地，当0<b≤0.7时，所述电解液满足：0<y1≤2.5，0<y2≤5，0<y3≤1.0，0.5≤y1/x≤4.0，1≤y2/x≤10，0.001≤y3/x≤2.0，0.5≤y2/y1≤10和0.1≤x/(y2+y3)≤1.0；
    可选地，当0.7≤b<0.98时，所述电解液满足：0<y1≤2.5，5≤y2≤14，0<y3≤1.0，0.5≤y1/x≤4.0，10≤y2/x≤28，0.001≤y3/x≤2.0，6≤y2/y1≤48和0.036≤x/(y2+y3)≤0.1。
  12. 根据权利要求1-11中任一项所述的二次电池，其中，0<c<0.1。
  13. 根据权利要求1-11中任一项所述的二次电池，其中，c＝0。
  14. 根据权利要求1-13中任一项所述的二次电池，其中，所述分子式为Li aNi bCo cM1 dM2 eO fA g的层状材料的质量百分含量为80％至99％，基于所述正极膜层的总质量计，可选地为85％至99％。
  15. 根据权利要求1-14中任一项所述的二次电池，其中，所述二次电池还满足：所述电解液的质量为所述二次电池总质量的10％至20％。
  16. 一种用于制备二次电池的方法，至少包括如下步骤：
    步骤1，将正极极片、隔离膜、负极极片、电解液组装成二次电池，
    所述正极极片包括正极集流体和位于所述正极集流体表面的正极膜层，所述正极膜层包括分子式为Li aNi bCo cM1 dM2 eO fA g的层状材料，M1选自Mn、Al或其组合，M2选自Si、Ti、Mo、V、Ge、Se、Zr、Nb、Ru、Pd、Sb、Ce、Te及W中的一种或多种，A选自F、N、P及S中的一种或多种，0.8≤a≤1.2，0<b<0.98，0≤c<0.1，0<d<0.5，0≤e≤0.5，0≤f≤2，0≤g≤2，b+c+d+e＝1，f+g＝2，
    所述电解液包括四氟硼酸锂、可选的氟代碳酸乙烯酯、可选的氟代磺酰亚胺锂盐和可选的氟代磺酸锂盐，所述电解液中的所述四氟硼酸锂的质量百分含量为x％，所述电解液中的所述氟代碳酸乙烯酯的质量百分含量为y1％，所述电解液中的所述氟代磺酰亚胺锂 盐的质量百分含量为y2％，所述电解液中的所述氟代磺酸锂盐的质量百分含量为y3％，均基于所述电解液的总质量计，x>0，y1≥0，y2≥0，y3≥0；
    步骤2，从步骤1所得到的二次电池中筛选出满足0.05≤c+x/10≤0.15的二次电池。
  17. 根据权利要求16述的方法，还包括步骤：从步骤2所得到的二次电池中筛选出满足0<x≤1.0和0.05≤c+x/10≤0.15的二次电池。
  18. 根据权利要求16所述的方法，还包括步骤：从步骤2所得到的二次电池中筛选出满足25≤P/(c+x/10)≤65的二次电池，P g/cm 3表示所述正极极片的压实密度。
  19. 根据权利要求16所述的方法，还包括步骤：从步骤2所得到的二次电池中筛选出满足0<y1+y2+y3≤15，0<y1≤2.5，0<y2≤14，0<y3≤1.0，0.5≤y1/x≤4.0，1≤y2/x≤28，0.001≤y3/x≤2.0和0.5≤y2/y1≤48的二次电池，
    可选地，当0<b≤0.7时，还包括步骤：从步骤2所得到的二次电池中筛选出满足0<y1+y2+y3≤15，0<y1≤2.5，0<y2≤5，0<y3≤1.0，0.5≤y1/x≤4.0，1≤y2/x≤10，0.001≤y3/x≤2.0和0.5≤y2/y1≤10的二次电池；
    可选地，当0.7≤b<0.98时，还包括步骤：从步骤2所得到的二次电池中筛选出满足0<y1+y2+y3≤15，0<y1≤2.5，5≤y2≤14，0<y3≤1.0，0.5≤y1/x≤4.0，10≤y2/x≤28，0.001≤y3/x≤2.0和6≤y2/y1≤48的二次电池。
  20. 根据权利要求16所述的方法，还包括步骤：从步骤2所得到的二次电池中筛选出满足0<y1+y2+y3≤15，0<y1≤2.5，0<y2≤14，0<y3≤1.0，0.5≤y1/x≤4.0，1≤y2/x≤28，0.001≤y3/x≤2.0，0.5≤y2/y1≤48和0.036≤x/(y2+y3)≤1.0的二次电池，
    可选地，当0<b≤0.7时，还包括步骤：从步骤2所得到的二次电池中筛选出满足0<y1+y2+y3≤15，0<y1≤2.5，0<y2≤5，0<y3≤1.0，0.5≤y1/x≤4.0，1≤y2/x≤10，0.001≤y3/x≤2.0，0.5≤y2/y1≤10和0.1≤x/(y2+y3)≤1.0的二次电池；
    可选地，当0.7≤b<0.98时，还包括步骤：从步骤2所得到的二次电池中筛选出满足0<y1+y2+y3≤15，0<y1≤2.5，5≤y2≤14，0<y3≤1.0，0.5≤y1/x≤4.0，10≤y2/x≤28，0.001≤y3/x≤2.0，6≤y2/y1≤48和0.036≤x/(y2+y3)≤0.1的二次电池。
  21. 一种电池模块，包括权利要求1-15中任一项所述的二次电池或通过权利要求16-20中任一项所述的方法得到的二次电池。
  22. 一种电池包，包括权利要求1-15中任一项所述的二次电池、通过权利要求16-20中任一项所述的方法得到的二次电池、权利要求21所述的电池模块中的一种。
  23. 一种用电装置，包括权利要求1-15中任一项所述的二次电池、通过权利要求16-20中任一项所述的方法得到的二次电池、权利要求21所述的电池模块、权利要求22所述的电池包中的至少一种。
PCT/CN2022/101117 2022-06-24 2022-06-24 二次电池、用于制备二次电池的方法、电池模块、电池包及用电装置 WO2023245619A1 (zh)

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