WO2021042983A1 - 正极活性材料、其制备方法、正极极片、锂离子二次电池与包含锂离子二次电池的电池模块、电池包和装置 - Google Patents

正极活性材料、其制备方法、正极极片、锂离子二次电池与包含锂离子二次电池的电池模块、电池包和装置 Download PDF

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WO2021042983A1
WO2021042983A1 PCT/CN2020/109843 CN2020109843W WO2021042983A1 WO 2021042983 A1 WO2021042983 A1 WO 2021042983A1 CN 2020109843 W CN2020109843 W CN 2020109843W WO 2021042983 A1 WO2021042983 A1 WO 2021042983A1
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positive electrode
active material
electrode active
valence
doping element
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PCT/CN2020/109843
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English (en)
French (fr)
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钭舒适
胡春华
蒋耀
吴奇
何金华
邓斌
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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 EP20860638.4A priority Critical patent/EP3920283A4/en
Publication of WO2021042983A1 publication Critical patent/WO2021042983A1/zh
Priority to US17/565,450 priority patent/US11417883B2/en

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    • C01G53/44—Nickelates containing alkali metals, e.g. LiNiO2 containing manganese
    • C01G53/50—Nickelates containing alkali metals, e.g. LiNiO2 containing manganese of the type [MnO2]n-, e.g. Li(NixMn1-x)O2, Li(MyNixMn1-x-y)O2
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    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
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    • H01M4/64—Carriers or collectors
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Definitions

  • This application belongs to the technical field of secondary batteries, and specifically relates to a positive electrode active material, a preparation method thereof, a positive electrode pole piece, a lithium ion secondary battery and a battery module, a battery pack and a device containing the lithium ion secondary battery.
  • Lithium-ion secondary battery is a kind of rechargeable battery, which mainly relies on the movement of lithium ions between the positive electrode and the negative electrode to work, and is a clean energy that is currently widely used.
  • the positive electrode active material provides lithium ions that reciprocate between the positive and negative electrodes for the battery charging and discharging process. Therefore, the positive electrode active material is very important to the performance of the battery.
  • Lithium-nickel-based cathode active materials have a higher theoretical capacity.
  • the lithium-ion secondary battery using lithium-nickel-based anode active materials can be expected to achieve higher energy density, but research has found that the high-temperature cycle performance of the lithium-ion secondary battery is poor .
  • the positive electrode active material provided in this application includes a nickel-containing lithium composite oxide with a specific chemical composition and structure, so that the positive electrode active material has higher charge and discharge voltage and specific capacity characteristics, and a lithium ion secondary battery using the positive electrode active material Can show higher capacity performance and energy density.
  • the positive electrode active material also includes a doping element M. When the positive electrode active material is in a 78% delithiation state, at least part of the doping element M has a valence of +3 or more.
  • the surface oxygen valence Vo of the positive electrode active material in the 78% delithiation state and the ground state oxidation valence (-2 valence) are within a small range, which can significantly improve the structural stability of the positive electrode active material , And reduce surface side reactions, thereby significantly improving the high temperature cycle performance of the battery. Therefore, the use of the positive electrode active material of the present application enables the lithium ion secondary battery to have both higher energy density and high-temperature cycle performance.
  • the surface oxygen average valence V O of the positive electrode active material in the 78% delithiation state is -1.9 ⁇ V O ⁇ -1.6.
  • the battery using the positive electrode active material has higher energy density and high-temperature cycle performance.
  • the positive electrode active material may include secondary particles aggregated from primary particles, and the relative deviation of the local mass concentration of the doping element M in the secondary particles may be 32% or less, Optional less than 20%.
  • the distribution of doping elements in the secondary particles is more uniform, which can more effectively reduce the surface oxygen activity of the positive electrode active material and increase the oxygen defect formation energy of the bulk structure of the positive electrode active material, thereby better improving the overall performance of the battery .
  • the battery can have higher energy density and high temperature cycle performance.
  • the formation energy ⁇ E O-vac of the bulk structure oxygen defect of the positive electrode active material in the 78% delithiation state can satisfy: ⁇ E O-vac ⁇ 0.5 eV; optionally, ⁇ E O-vac ⁇ 0.7eV; optional, ⁇ E O-vac ⁇ 1.0eV.
  • the ⁇ E O-vac of the positive electrode active material within the above range can have high structural stability and ensure that it provides a good carrier for the deintercalation of lithium ions, thereby obtaining a high initial capacity and cycle capacity retention rate, thereby Improve the energy density and high temperature cycle performance of the battery.
  • the doping element M when the positive electrode active material is in the 78% delithiation state, the doping element M may have two or more different valence states, and the valence of the doping element M in the highest valence state It can be one or more of +4, +5, +6, +7, and +8. The optional ones are +5, +6, +7, and +8 One or more.
  • the doping element M can contribute more electrons to the positive electrode active material, further reduce the surface oxygen activity of the positive electrode active material, stabilize the material structure, and reduce surface side reactions, thereby further improving the high-temperature cycle performance of the battery.
  • the doping element M can bind oxygen atoms more effectively, and increase the oxygen defect formation energy ⁇ E O- vac and structural stability of the positive electrode active material.
  • the doping element M may include one or more of Ti, V, Se, Zr, Nb, Ru, Pd, Sb, Te, and W.
  • the doping element M may include one or more of Ti, Se, Zr, Nb, Ru, Sb, Te, and W. The given doping element M can better improve the energy density and high temperature cycle performance of the lithium ion secondary battery.
  • the actual doping concentration ⁇ of the positive electrode active material can satisfy 2300 ⁇ g/cm 3 ⁇ 49100 ⁇ g/cm 3 , optionally 3000 ⁇ g/cm 3 ⁇ 30000 ⁇ g/cm 3 , optional 14830 ⁇ g/cm 3 ⁇ 49080 ⁇ g/cm 3 , optional 24890 ⁇ g/cm 3 ⁇ 31210 ⁇ g/cm 3 .
  • the actual doping concentration of the positive electrode active material is within the above range, which can effectively reduce the surface oxygen activity of the positive electrode active material and increase the formation energy of oxygen defects in the bulk structure. It also ensures that the particles have a higher lithium ion transport and diffusion capacity, thereby improving the battery’s performance. Energy density and high temperature cycle performance.
  • the deviation ⁇ of the mass concentration of the doping element M in the positive electrode active material relative to the average mass concentration of the doping element M in the particles of the positive electrode active material may satisfy ⁇ 50 %; Optional, ⁇ 30%; Optional, ⁇ 20%. If the ⁇ of the positive electrode active material is within the above range, its macroscopic and microscopic consistency is better, and the overall stability of the particles is higher, which is conducive to obtaining higher capacity and high-temperature cycle performance, thereby improving the corresponding performance of the battery.
  • the positive electrode active material to meet the true density ⁇ true 4.6g / cm 3 ⁇ true ⁇ 4.9g / cm 3.
  • the positive electrode active material can have a higher specific capacity, which can increase the energy density of the battery.
  • the volume average particle size D v 50 of the positive electrode active material may be 5 ⁇ m to 20 ⁇ m, optionally 8 ⁇ m to 15 ⁇ m, and further optionally 9 ⁇ m to 11 ⁇ m. If the D v 50 of the positive electrode active material is within the above range, the cycle performance and rate performance of the lithium ion secondary battery can be improved, and the energy density of the battery can also be improved.
  • the specific surface area of the positive electrode active material may be 0.2m 2 /g ⁇ 1.5m 2 / g, alternatively it is 0.3m 2 / g ⁇ 1m 2 / g.
  • the specific surface area of the positive electrode active material within the above range can enable the battery to obtain higher energy density and cycle performance.
  • the tap density of the positive electrode active material may be 2.3 g/cm 3 to 2.8 g/cm 3 . If the tap density of the positive electrode active material is within the above range, the lithium ion secondary battery can have a higher energy density.
  • the compacted density of the positive electrode active material under a pressure of 5 tons can be selected from 3.1 g/cm 3 to 3.8 g/cm 3 .
  • the compaction density of the positive electrode active material is within the given range, which is beneficial for the lithium ion secondary battery to obtain a higher energy density.
  • the second aspect of the present application provides a method for preparing a positive electrode active material, which includes the following steps:
  • the positive electrode active material precursor, the lithium source and the doping element precursor are mixed to obtain a mixture, wherein the positive electrode active material precursor is selected from oxides and hydroxides containing Ni, optional Co and optional Mn And one or more of carbonates;
  • the positive electrode active material has a layered crystal structure and belongs to Space group
  • the positive electrode active material When the positive electrode active material is in the 78% delithiation state, at least part of the doping element M has a valence of +3 or more, and the surface oxygen average valence V O of the positive electrode active material is -2.0 ⁇ V O ⁇ -1.5.
  • the positive electrode active material obtained by the preparation method provided in this application includes a nickel-containing lithium composite oxide, the transition metal site of which is doped with M element, and when the positive electrode active material is in the 78% delithiation state, the valence of at least part of the doped element M is +3 valence or more, and the difference between the surface oxygen valence of the positive electrode active material and the ground state oxidation valence (-2 valence) is within a small range, which enables the lithium ion secondary battery to have both high energy density and high temperature Cycle performance.
  • the doping element precursor can be selected from titanium oxide, vanadium oxide, selenium oxide, zirconium oxide, niobium oxide, ruthenium oxide, palladium oxide, antimony oxide, tellurium oxide One or more of oxide and tungsten oxide.
  • the doping element precursor may be selected from TiO 2 , TiO, V 2 O 5 , V 2 O 4 , V 2 O 3 , SeO 2 , ZrO 2 , Nb 2 O 5 , NbO 2 , RuO 2 One or more of, PdO, Sb 2 O 5 , Sb 2 O 3 , TeO 2 , WO 2 , and WO 3.
  • the sintering treatment may satisfy at least one of the following:
  • the oxygen concentration of the oxygen-containing atmosphere is 80%-100%
  • the temperature of the sintering treatment is 600°C to 900°C, and 700°C to 900°C is optional;
  • the sintering treatment time is 5h-25h, optional 10h-20h.
  • the doping element precursor can be equally divided into L parts or arbitrarily divided into L parts, and divided into L batches for doping, where L is 1 to 5, and optionally 2 ⁇ 3, including: mixing the precursor of the positive electrode active material, the lithium source, and the first batch of doping element precursors, and performing the first sintering treatment; the product of the first sintering treatment is doped with the second batch
  • the element precursors are mixed, and the second sintering process is performed; and so on, until the product of the L-1 sintering process is mixed with the L batch of doped element precursors, and the L sintering process is performed,
  • the positive electrode active material is obtained.
  • the temperature of each sintering treatment is 600°C to 1000°C, optionally 600°C to 900°C, and optionally 700°C to 900°C;
  • the time of each sintering treatment is 1h to 20h, which can be The selection is 2h-18h; the total sintering time is 5h-25h, and the optional is 10h-20h.
  • a third aspect of the present application provides a positive pole piece, which includes a positive current collector and a positive active material layer disposed on the positive current collector, the positive active material layer includes the positive active material of the first aspect of the present application, or A positive electrode active material obtained according to the preparation method of the second aspect of the present application.
  • the lithium ion secondary battery using the same can have higher energy density and high-temperature cycle performance.
  • a fourth aspect of the present application provides a lithium ion secondary battery, which includes the positive pole piece of the third aspect of the present application.
  • the lithium ion secondary battery of the present application includes the positive pole piece, it can have higher energy density and high-temperature cycle performance.
  • a fifth aspect of the present application provides a battery module, which includes the lithium ion secondary battery of the fourth aspect of the present application.
  • a sixth aspect of the present application provides a battery pack, which includes the lithium ion secondary battery of the fourth aspect of the present application or the battery module of the fifth aspect of the present application.
  • a seventh aspect of the present application provides a device, which includes at least one of the lithium ion secondary battery of the fourth aspect of the present application, the battery module of the fifth aspect of the present application, or the battery pack of the sixth aspect of the present application.
  • the battery module, battery pack, and device of the present application include the lithium ion secondary battery of the present application, and thus have at least the same or similar effects as the lithium ion secondary battery.
  • Figure 1 is an image of the doping element distribution of the secondary particles of the positive electrode active material of Example 1.
  • the cross section is prepared by using the IB-09010CP cross section polisher (CP) of JEOL Company, using Oxford instruments X-Max Energy Dispersive Spectroscopy (EDS) test is obtained; the bright spots in the figure indicate the doped elements, and the doped elements are uniformly distributed in the particles.
  • CP IB-09010CP cross section polisher
  • EDS Oxford instruments X-Max Energy Dispersive Spectroscopy
  • FIG. 2 is a schematic diagram showing the location of the relative deviation test of the local mass concentration of doping elements in the secondary particles of the positive electrode active material of Examples 1-25 and Comparative Examples 1-4.
  • XPS X-ray photoelectron spectroscopy
  • Fig. 4 is an XPS spectrum of the 0 1s orbital in the 78% delithiation state of the positive electrode active material of Example 1.
  • FIG. 5 is a schematic diagram of an embodiment of a lithium ion secondary battery.
  • Fig. 6 is an exploded view of Fig. 5.
  • Fig. 7 is a schematic diagram of an embodiment of a battery module.
  • Fig. 8 is a schematic diagram of an embodiment of a battery pack.
  • Fig. 9 is an exploded view of Fig. 8.
  • FIG. 10 is a schematic diagram of an embodiment of a device in which a lithium ion secondary battery is used as a power source.
  • any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, and any upper limit can be combined with any other upper limit to form an unspecified range.
  • every point or single value between the end points of the range is included in the range. Therefore, each point or single numerical value can be used as its own lower limit or upper limit, combined with any other point or single numerical value, or combined with other lower or upper limits to form an unspecified range.
  • the term "or” is inclusive.
  • the phrase "A or (or) B” means “A, B, or both A and B.” More specifically, any of the following conditions satisfy the condition "A or B”: 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).
  • “78% delithiation state” refers to the state when the molar content of lithium extracted from the positive electrode active material accounts for 78% of the theoretical lithium content during the charging process of the battery.
  • a “full charge state” is generally set, and a corresponding “charging cut-off voltage” is set to ensure the safe use of the battery.
  • “Fully charged state” means that the state of charge (SOC) of the secondary battery is 100%.
  • SOC state of charge
  • the “full charge state” or “charging cut-off voltage” will have certain differences due to the difference in the positive electrode active material or the difference in safety requirements.
  • the delithiation state of the positive electrode active material is generally around the "78% delithiation state" to ensure normal use.
  • the corresponding relationship between the "delithiation state” and the charging voltage is combined to obtain the positive electrode active material in the "78% delithiation state" for research.
  • a series of batteries using the positive electrode active material will be charged to 2.8V, 2.9V, 3.0V, 3.1V, 3.2V, 3.3V,...4.0V, 4.1V, 4.2V, at a rate of 0.1C, respectively.
  • the positive pole piece of the battery is removed, the electrolyte is removed by washing, the positive electrode active material is digested, and the inductively coupled plasma-emission spectrometer (inductively coupled plasma-Optical Emission spectrometers, ICP-OES) test the mass concentration of Li, transition metals, and O elements of the positive electrode active material, calculate the stoichiometric ratio of each element of the positive electrode active material at the charging voltage, and convert to obtain the positive electrode active material at the charging voltage The chemical formula of, and then get the charging voltage corresponding to the "78% de-lithium state".
  • ICP-OES inductively coupled plasma-Optical Emission spectrometers
  • the battery containing the positive electrode active material to be tested is charged to the voltage corresponding to the "78% delithiation state", and then the positive electrode active material in the "78% delithiation state" can be obtained for further study.
  • the surface oxygen valence state V O and the valence of the doping element M of the "78% delithium state" positive electrode active material can be obtained by X-ray photoelectron spectroscopy (XPS) testing. More accurate, can be obtained through Synchrotron radiation photoelectron spectroscopy (SRPES) test.
  • the positive electrode active material of the embodiment of the present application includes nickel-containing lithium composite oxide with a specific chemical composition and structure, so that the positive electrode active material has higher charge and discharge voltage and specific capacity characteristics.
  • the battery can show higher capacity performance and energy density.
  • the surface oxidation valence of the positive electrode active material that has not been delithiated is low (such as -2 valence), and during the delithiation process of the positive electrode active material (during battery charging), as the lithium ions are extracted from the positive electrode active material, the positive electrode active material Electrons continue to escape to reach the negative electrode.
  • the positive electrode active material also includes the doping element M. When the positive electrode active material is in the 78% delithiation state, the valence of part or all of the doping element M is +3 or more. The doping element M with a larger valence can contribute more electrons in the positive electrode active material, and the corresponding oxygen atom of the positive electrode active material will lose the number of electrons.
  • the surface oxygen activity of the positive electrode active material is always kept at a low level, especially the average valence state V O of the surface oxygen of the positive electrode active material in the 78% delithiation state is -2.0 to -1.5.
  • the surface oxygen valence Vo of the positive electrode active material in the 78% delithiation state has a small difference from the ground state oxidation valence (-2 valence), which can significantly improve the structural stability of the positive electrode active material, so that The positive electrode active material is less prone to oxygen release during heating and high temperature cycles, inhibits oxygen defects, and effectively prevents irreversible phase transition of the positive electrode active material, thereby improving the capacity retention rate of the positive electrode active material during the high temperature cycle. Therefore, this application can significantly improve the high-temperature cycle performance of the battery by doping the M element at the transition metal site of the nickel-containing lithium composite oxide. In addition, the thermal stability and high temperature safety performance of the battery have also been improved.
  • the surface oxygen activity of the positive electrode active material is low, and it can also effectively inhibit the side reaction of the electrolyte on the surface of the material particles, inhibit gas production, reduce heat generation, and reduce the consumption of reversible lithium ions, inhibit the increase of positive electrode impedance, and reduce the positive electrode polarization , Is conducive to improving the high temperature cycle performance of the battery.
  • the use of the positive electrode active material provided in the embodiments of the present application enables the lithium ion secondary battery to simultaneously take into account higher capacity performance, energy density, and high-temperature cycle performance.
  • the mole percentage of nickel in the transition metal site element of the nickel-containing lithium composite oxide may be 50% to 90%, for example, 70% to 90%.
  • the high nickel positive electrode active material has higher specific capacity characteristics and can improve the capacity performance and energy density of the battery.
  • the battery using the positive electrode active material has higher energy density and high-temperature cycle performance.
  • the doping element M with a valence of +3 or higher has a strong binding ability to oxygen, that is, the bond energy with oxygen is large, which can effectively bind oxygen atoms, so that the positive electrode active material is not easy to release oxygen during heating and high temperature cycling.
  • Improve the oxygen defect formation energy ⁇ E O-vac of the positive electrode active material improves the oxygen defect formation energy ⁇ E O-vac of the positive electrode active material.
  • the bulk structure oxygen defect formation energy ⁇ E O-vac of the positive electrode active material in the 78% delithiation state satisfies ⁇ E O-vac ⁇ 0.5 eV.
  • the oxygen defect formation energy ⁇ E O-vac of the bulk structure of the positive electrode active material in the "78% delithiation state" satisfies the formula (1).
  • ⁇ E O-vac represents the oxygen defect formation energy of the positive electrode active material in the "78% delithiation state" in the ground state
  • Epristine represents the formation energy of the positive electrode active material with complete structure in the ground state in the "78% delithiation state”
  • E defect represents the bulk structure energy of the positive electrode active material with oxygen defects in the ground state in the "78% delithiation state”
  • E O represents the energy (chemical potential) of the oxygen atoms in the ground state.
  • E pristine , E defect, and E O can be calculated by the first-principles calculation software VASP based on density functional theory.
  • the exchange correlation functional can be obtained by using Generalized Gradient Approximation (GGA) to add a Hubbard parameter U corresponding Item, namely GGA+U exchange correlation functional.
  • GGA Generalized Gradient Approximation
  • step S20 to subtract different oxygen atoms to obtain the defect formation energies of different oxygen atoms, and select the smallest value as the bulk structure oxygen defect formation energy ⁇ E O-vac of the positive electrode active material in the "78% delithiation state".
  • the accuracy of the calculation parameters used ensures that the structural energy of the optimized calculation converges to less than 10 -6 eV, and the force converges to less than It can ensure that the calculation results are more reliable.
  • the oxygen defect formation energy of the positive electrode active material in the "78% delithium state" bulk structure ⁇ E O-vac is within the above range, so that the oxygen atoms in the positive electrode active material will not easily deviate from the original during the charging process and in the fully charged state.
  • Oxygen defects are formed in the lattice position of the positive electrode, so that the positive electrode active material has high structural stability and always remains in the layered phase state with strong electrochemical activity, thereby providing a good carrier for the deintercalation of lithium ions and making the positive electrode active
  • the material has a high initial capacity and cycle capacity retention rate, thereby improving the energy density and high temperature cycle performance of the battery.
  • the bulk structure oxygen defect formation energy ⁇ E O-vac of the positive electrode active material in the "78% delithium state" is within the above range, so that the positive electrode active material is not prone to oxygen release during heating and high temperature cycles, which is beneficial to improve The thermal stability and high temperature safety performance of the battery.
  • the doping element M in the positive electrode active material in the 78% delithiation state, has two or more different valence states, and the valence of the M element in the highest valence state is +4, + One or more of valence 5, valence +6, valence +7, and valence +8.
  • the highest valence state of the M element in the 78% delithiation state of the positive electrode active material, is one or more of +5 valence, +6 valence, +7 valence, and +8 valence.
  • the doping element M which has a higher valence state and a variable valence state, can contribute more electrons to the positive electrode active material.
  • the oxygen atom in the positive electrode active material loses fewer electrons, thereby further reducing the surface oxygen of the positive electrode active material. Active, stabilize the material structure, and reduce surface side reactions, thereby improving the high temperature cycle performance of the battery.
  • doping elements with higher valence have stronger binding ability with oxygen, can more effectively bind oxygen atoms, increase the oxygen defect formation energy ⁇ E O-vac and structural stability of the positive electrode active material, thereby improving the performance of the battery.
  • the doping element M has more than two different valence states, and the lower valence doping element can further contribute electrons to support the positive electrode to release more lithium ions. As a result, the energy density of the battery is further improved.
  • the doping element M includes one or more of Ti, V, Se, Zr, Nb, Ru, Pd, Sb, Te, and W.
  • the doping element M includes one or more of Ti, Se, Zr, Nb, Ru, Sb, Te, and W. The use of a suitable doping element M can better exert the above effects, and further improve the energy density and high temperature cycle performance of the lithium ion secondary battery.
  • the positive active material includes secondary particles aggregated from primary particles. Further, the relative deviation of the local mass concentration of the doping element in the secondary particles is 32% or less, optionally 30% or less, and further optionally 20% or less, 16% or less, 13% or less, 11% or less , Or less than 10%.
  • the local mass concentration of doping elements in secondary particles is the mass concentration of doping elements in the finite volume element of any selected positioning point in the secondary particles, which can be determined by EDX (Energy Dispersive X-Ray Spectroscopy , Energy dispersive X-ray spectrometer) or EDS element analysis combined with TEM (Transmission Electron Microscope) or SEM (Scanning Electron Microscope) single-point scanning test element concentration distribution or other similar methods.
  • EDX Electronicgy Dispersive X-Ray Spectroscopy , Energy dispersive X-ray spectrometer
  • EDS element analysis combined with TEM (Transmission Electron Microscope) or SEM (Scanning Electron Microscope) single-point scanning test element concentration distribution or other similar methods.
  • the mass concentration of doping elements in ⁇ g/g at different positions in the secondary particles is recorded as ⁇ 1 , ⁇ 2 , ⁇ 3 ,..., ⁇ n , where n is a positive integer greater than 15.
  • the average mass concentration of doping elements in secondary particles is the mass concentration of doping elements in the range of single or multiple secondary particles.
  • the element concentration distribution can be tested by EDX or EDS element analysis combined with TEM or SEM surface scanning or other Obtained in a similar way.
  • the test surface includes all the points in the single-point test.
  • the average mass concentration of doped elements in the secondary particles is denoted as The unit is ⁇ g/g.
  • the relative deviation ⁇ of the local mass concentration of doping elements in the secondary particles can be calculated according to formula (2):
  • the secondary particles satisfy ⁇ below 32%, optionally 30% or less, and further optionally 20% or less, which means that the distribution uniformity of the doping element in the secondary particles is relatively high. Uniform doping can more effectively reduce the surface oxygen activity of the positive electrode active material and increase the oxygen defect formation energy of the bulk structure of the positive electrode active material, thereby better improving the overall performance of the battery.
  • the uniformly doped positive electrode active material particles have the same properties everywhere in the particles, the migration and diffusion capacity of lithium ions in different areas of the particles are at the same level, the anti-deformation capabilities of the particles are close to each other, and the stress distribution in the particles is uniform.
  • the positive electrode active material is not prone to cracking, and it can prevent the side reaction and the deterioration of capacity and cycle performance caused by the fresh surface exposed by the crack, so that the positive electrode active material has a higher capacity development and high-temperature cycle capacity retention rate, so that the battery has Higher capacity performance, energy density and high temperature cycle performance.
  • the positive electrode active material, the true doping concentration ⁇ satisfies 1500 ⁇ g / cm 3 ⁇ 60000 ⁇ g / cm 3 . Further optional, 2300 ⁇ g/cm 3 ⁇ 49100 ⁇ g/cm 3 , 3000 ⁇ g/cm 3 ⁇ 30000 ⁇ g/cm 3 , 14830 ⁇ g/cm 3 ⁇ 49080 ⁇ g/cm 3 , 14830 ⁇ g/cm 3 ⁇ 36690 ⁇ g/ cm 3 , or 24890 ⁇ g/cm 3 ⁇ 31210 ⁇ g/cm 3 .
  • the true doping concentration ⁇ of the positive electrode active material can be calculated by formula (3):
  • ⁇ is the true doping concentration of the positive electrode active material, and the unit is ⁇ g/cm 3 .
  • ⁇ true positive electrode active material the true density in units of g / cm 3, which is equal to the ratio of the mass and the true volume of the positive electrode active material of the positive electrode active material, wherein the true volume is the actual volume of the solid material does not include pores inside of the particles.
  • ⁇ true can be measured by using instruments and methods known in the art, for example, the gas volume method can be performed by using a powder true density tester.
  • the mass concentration of the doping element in the positive electrode active material in ⁇ g/g that is, the mass of the doping element contained in each gram of the positive electrode active material.
  • the actual doping concentration of the positive electrode active material is within the above range, which can effectively reduce the surface oxygen activity of the positive electrode active material and increase the oxygen defect formation energy of the bulk structure; it also makes the positive electrode active material have a good layered crystal structure, ensuring the positive electrode activity
  • the material provides a good carrier for the deintercalation of lithium ions, facilitates the intercalation and deintercalation of lithium ions, prevents reversible lithium ions from being consumed on the electrode surface or in the electrolyte, so that the positive electrode active material has a higher initial capacity and cycle capacity retention rate, thereby Improve the energy density and high temperature cycle performance of the battery.
  • the actual doping concentration of the positive electrode active material is within the above range, which also ensures that the doping element is doped in the transition metal layer, prevents it from entering the lithium layer, and ensures that the particles have a higher lithium ion transport and diffusion ability, so that the battery has a better performance. High capacity and cycle performance.
  • the mass concentration of the doping element in the positive electrode active material is Relative to the average mass concentration of doped elements in the particles of the positive electrode active material
  • the deviation of ⁇ is ⁇ , and ⁇ satisfies ⁇ 50%. Optionally, ⁇ 45%. Optionally, ⁇ 30%. Further optionally, ⁇ 20%, or ⁇ 10%.
  • the particles of the positive electrode active material may include primary particles and/or secondary particles.
  • the average mass concentration of doping elements in primary particles and the average mass concentration of doping elements in primary particles and secondary particles can refer to the average mass concentration of doping elements in secondary particles mentioned above. carry out testing.
  • the mass concentration of doped elements in the positive electrode active material Relative to the average mass concentration of doped elements in the particles of the positive electrode active material
  • the deviation ⁇ of can be calculated by the following formula (4):
  • the positive electrode active material satisfies ⁇ within the above range, which means that the doping elements are smoothly incorporated into the particles of the positive electrode active material, and the content of doping elements distributed in other phases on the surface of the particles and the doping elements embedded in the gaps between the particles is higher. Less, the positive electrode active material has better macro and micro consistency, and the structure is uniform. During the charge-discharge cycle process, the expansion and contraction of each particle is consistent, and the particle stability is high, which is conducive to its higher capacity and high-temperature cycle performance.
  • the positive electrode active material the true density ⁇ satisfies true 4.6g / cm 3 ⁇ true ⁇ 4.9g / cm 3
  • a positive electrode active material can have a high specific capacity, thereby improving the performance of the battery capacity And energy density.
  • the volume average particle diameter D v 50 of the positive electrode active material particles may be 5 ⁇ m-20 ⁇ m, further may be 8 ⁇ m-15 ⁇ m, and may also be 9 ⁇ m-11 ⁇ m.
  • the D v 50 of the positive electrode active material is within the above range, and the migration path of lithium ions and electrons in the particles is relatively short, which can improve the transmission and diffusion performance of lithium ions and electrons in the positive electrode active material, reduce battery polarization, and thereby increase lithium ions.
  • the cycle performance and rate performance of the secondary battery in addition, it can also make the positive electrode active material have a higher compaction density and improve the energy density of the battery.
  • the D v 50 of the positive electrode active material within the above range is also beneficial to reduce the side reaction of the electrolyte on the surface of the positive electrode active material, and reduce the agglomeration between the positive electrode active material particles, thereby improving the normal temperature and high temperature cycle performance of the positive electrode active material. Safety performance.
  • the specific surface area of the positive electrode active material is selected to 0.2m 2 /g ⁇ 1.5m 2 / g, optionally further 0.3m 2 / g ⁇ 1m 2 / g.
  • the specific surface area of the positive electrode active material is within the above range, which ensures that the positive electrode active material has a higher active specific surface area, and at the same time helps to reduce the side reaction of the electrolyte on the surface of the positive electrode active material, thereby improving the capacity and cycle life of the positive electrode active material
  • it can also inhibit the agglomeration between particles of the positive electrode active material in the process of preparing the slurry and charging and discharging, and improve the energy density and cycle performance of the battery.
  • the tap density of the positive electrode active material may be 2.3 g/cm 3 to 2.8 g/cm 3 .
  • the tap density of the positive electrode active material is within the above range, which is beneficial for the lithium ion secondary battery to have higher capacity performance and energy density.
  • the compacted density of the positive electrode active material under a pressure of 5 tons can be selected from 3.1 g/cm 3 to 3.8 g/cm 3 .
  • the higher compaction density of the positive electrode active material is conducive to the higher capacity performance and energy density of the lithium ion secondary battery.
  • the morphology of the positive electrode active material particles provided in the embodiments of the present application is one or more of spheres and spheres.
  • the D v 50 of the positive electrode active material has a well-known meaning in the art, and is also called the median particle size, which represents the particle size corresponding to 50% of the volume distribution of the positive electrode active material particles.
  • the D v 50 of the positive electrode active material can be measured with a well-known instrument and method in the art, for example, it can be conveniently measured with a laser particle size analyzer (such as the Mastersizer 3000 of Malvern Instruments Co., Ltd., UK).
  • the specific surface area of the positive electrode active material is a well-known meaning in the art, and it can be measured by instruments and methods known in the art. For example, it can be measured by the nitrogen adsorption specific surface area analysis test method and calculated by the BET (Brunauer Emmett Teller) method, where The nitrogen adsorption specific surface area analysis test can be performed by the NOVA2000e specific surface area and pore size analyzer of Kanta Corporation of the United States.
  • the test method is as follows: take 8.000g ⁇ 15.000g of positive electrode active material in a weighed empty sample tube, stir and weigh the positive electrode active material, and put the sample tube into the NOVA 2000e degassing station for degassing , Weigh the total mass of the positive electrode active material and the sample tube after degassing, and calculate the mass G of the positive electrode active material after degassing by subtracting the mass of the empty sample tube from the total mass.
  • the tap density of the positive electrode active material is a well-known meaning in the art, and can be measured with a well-known instrument and method in the art, for example, a tap density meter (such as FZS4-4B type) can be conveniently measured.
  • a tap density meter such as FZS4-4B type
  • the compaction density of the positive electrode active material is a well-known meaning in the art, and can be measured with a well-known instrument and method in the art, such as an electronic pressure tester (such as UTM7305).
  • the preparation method includes:
  • the positive electrode active material precursor, the lithium source, and the doping element precursor are mixed and sintered to obtain the positive electrode active material.
  • the foregoing positive electrode active material precursor may be one or more of oxides, hydroxides, and carbonates containing Ni and optionally Co and/or Mn in a stoichiometric ratio, for example, containing Ni in a stoichiometric ratio. Hydroxides of Ni, Co and Mn.
  • the positive electrode active material precursor can be obtained by a method known in the art, for example, prepared by a co-precipitation method, a gel method, or a solid phase method.
  • the Ni source, Co source, and Mn source are dispersed in a solvent to obtain a mixed solution; the mixed solution, strong alkali solution and complexing agent solution are simultaneously pumped into a stirred reactor by means of continuous co-current reaction. , Control the pH of the reaction solution to be 10-13, the temperature in the reactor is 25°C to 90°C, and pass inert gas protection during the reaction; after the reaction is completed, it is aged, filtered, washed and vacuum dried to obtain Ni , Co and Mn hydroxides.
  • the Ni source may be a soluble nickel salt, such as one or more of nickel sulfate, nickel nitrate, nickel chloride, nickel oxalate, and nickel acetate, and another example, one or more of nickel sulfate and nickel nitrate, Another example is nickel sulfate;
  • the Co source can be a soluble cobalt salt, such as one or more of cobalt sulfate, cobalt nitrate, cobalt chloride, cobalt oxalate, and cobalt acetate, and another example is cobalt sulfate and cobalt nitrate.
  • the Mn source may be a soluble manganese salt, such as one or more of manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate and manganese acetate, and another example is sulfuric acid One or more of manganese and manganese nitrate, and another example is manganese sulfate.
  • the strong base may be one or more of LiOH, NaOH, and KOH, for example, NaOH.
  • the complexing agent may be one or more of ammonia, ammonium sulfate, ammonium nitrate, ammonium chloride, ammonium citrate, and disodium ethylenediaminetetraacetate (EDTA), for example, ammonia.
  • the solvents of the mixed solution, strong base solution and complexing agent solution are each independently deionized water, methanol, ethanol, acetone, and isopropyl.
  • the solvents of the mixed solution, strong base solution and complexing agent solution are each independently deionized water, methanol, ethanol, acetone, and isopropyl.
  • the inert gas introduced during the reaction is, for example, one or more of nitrogen, argon, and helium.
  • the above-mentioned lithium source may be 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), lithium carbonate One or more of (Li 2 CO 3 ) and lithium nitrate (LiNO 3 ). Further, the lithium source is one or more of lithium carbonate, lithium hydroxide, and lithium nitrate; further, the lithium source is lithium carbonate.
  • the aforementioned doping element precursor may be one or more of oxides of doping elements, nitric acid compounds, carbonic acid compounds, hydroxide compounds, and acetic acid compounds.
  • oxides of doping elements such as titanium oxide (such as TiO 2 , TiO, etc.), vanadium oxide (such as V 2 O 5 , V 2 O 4 , V 2 O 3, etc.), selenium oxide (such as SeO 2, etc.) ), zirconium oxide (such as ZrO 2 etc.), niobium oxide (such as Nb 2 O 5 , NbO 2 etc.), ruthenium oxide (such as RuO 2 etc.), palladium oxide (such as PdO, etc.), antimony oxide (such as Sb 2 O 5 , Sb 2 O 3, etc.), tellurium oxide (such as TeO 2 ), and tungsten oxide (such as WO 2 , WO 3, etc.).
  • the doping element precursor may contain a low-valence doping element, so that when the obtained positive electrode active material is in a 78% delithiation state, the doping element M has two or more different valence states.
  • low valence state means that the valence of the doping element is lower than its highest stable valence state.
  • the precursor of the positive electrode active material, the lithium source and the precursor of the doping element can be mixed by a ball mill mixer or a high-speed mixer.
  • the mixed materials are put into the atmosphere sintering furnace for sintering.
  • the sintering atmosphere is an oxygen-containing atmosphere, for example, an air atmosphere or an oxygen atmosphere.
  • the oxygen concentration of the oxygen-containing atmosphere is 80%-100%.
  • the sintering temperature is, for example, 600°C to 1000°C.
  • the sintering temperature is 600° C. to 900° C., further 700° C. to 900° C., which is beneficial to make the dopant elements have a higher uniformity of distribution.
  • the sintering time can be adjusted according to actual conditions, for example, 5h-25h, and for example 10h-20h.
  • the positive electrode active material there are a variety of theoretically feasible ways to control the structure and characteristics of the positive electrode active material, adjust the regularity of its layered structure and the position and uniformity of doping elements, and change it.
  • the surface oxygen activity and average valence during the cycle for example, by adjusting the type of doping element, the content of doping element, the morphology of the precursor particles of the positive electrode active material, the sintering time in the preparation of the positive electrode active material, the sintering temperature, and the sintering The number of times and the oxygen concentration during sintering, etc.
  • some measures of solid-phase sintering doping methods are listed.
  • the positive electrode active material obtained is 78% free of lithium
  • the average valence state of surface oxygen V O at the time of state is -2.0 ⁇ V O ⁇ -1.5. It should be understood that the method described in this specification is only for explaining the application, not for limiting the application.
  • the doping element precursor may be divided into L batches for doping of the doping element, where L may be 1-5, such as 2-3.
  • the preparation method of the positive electrode active material may include the following steps: mixing the positive electrode active material precursor, the lithium source, and the first batch of doping element precursors, and performing the first sintering treatment; The product of the second sintering treatment is mixed with the second batch of doping element precursors, and the second sintering treatment is carried out; and so on, until the products of the L-1 sintering treatment are combined with the L batch of doping element precursors The body is mixed and subjected to the L-th sintering treatment to obtain a positive electrode active material.
  • the doping element precursor can be equally divided into L parts or arbitrarily divided into L parts to perform L batches of doping.
  • the temperature of each sintering process is the same or different.
  • the time of each sintering treatment is the same or different. Those skilled in the art can adjust the sintering temperature and time according to the type and amount of doping elements.
  • the temperature of each sintering treatment can be 600°C ⁇ 1000°C, such as 600°C ⁇ 900°C, and then 700°C ⁇ 900°C;
  • the time of each sintering treatment can be 1h ⁇ 20h, such as 2h ⁇ 18h;
  • the sintering time can be 5h-25h, such as 10h-20h.
  • the sintering temperature and/or the sintering time can be increased within a certain range to improve the doping uniformity.
  • the sintered product can also be crushed and sieved to obtain a positive electrode active material with optimized particle size distribution and specific surface area.
  • a particle crusher There are no special restrictions on the crushing method, and it can be selected according to actual needs, such as using a particle crusher.
  • This application provides a positive electrode sheet, which uses any one or several positive electrode active materials of this application.
  • the lithium ion secondary battery can take into account both good room temperature and high temperature cycle performance and higher energy density at the same time.
  • the positive pole piece includes a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector.
  • the positive electrode current collector includes two opposite surfaces in its thickness direction, and the positive electrode active material layer is stacked on either or both of the two surfaces of the positive electrode current collector.
  • the positive active material layer includes the positive active material of the present application.
  • the positive electrode active material layer may further include a conductive agent and a binder.
  • a conductive agent and a binder This application does not specifically limit the types of conductive agents and binders in the positive active material layer, and can be selected according to actual needs.
  • the conductive agent may be one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers;
  • the binder may be styrene-butadiene Rubber (SBR), water-based acrylic resin, carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB) ), ethylene-vinyl acetate copolymer (EVA), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene
  • SBR styrene-butadiene Rubber
  • EVA ethylene-vinyl acetate copoly
  • the positive electrode current collector can be a metal foil or porous metal plate with good electrical conductivity and mechanical properties, and the material can be one or more of aluminum, copper, nickel, titanium, silver, and their respective alloys.
  • the positive electrode current collector is, for example, aluminum foil.
  • the positive pole piece can be prepared according to conventional methods in the art. For example, disperse the positive electrode active material, conductive agent, and binder in a solvent.
  • the solvent can be N-methylpyrrolidone (NMP) or deionized water to form a uniform positive electrode slurry.
  • NMP N-methylpyrrolidone
  • the positive electrode slurry is coated on the positive electrode current collector. Above, after drying, rolling and other processes, the positive pole piece is obtained.
  • the present application provides a lithium ion secondary battery, which includes a positive pole piece, a negative pole piece, a separator and an electrolyte, wherein the positive pole piece is any positive pole piece of the application.
  • the lithium ion secondary battery adopts the positive pole piece of the present application, it can take into account good room temperature and high temperature cycle performance and high energy density at the same time.
  • the negative pole piece may be a metal lithium piece.
  • the negative pole piece may also include a negative current collector and a negative active material layer provided on at least one surface of the negative current collector.
  • the negative electrode current collector includes two opposite surfaces in the thickness direction of the negative electrode current collector, and the negative electrode active material layer is stacked on either or both of the two surfaces of the negative electrode current collector.
  • the anode active material layer includes an anode active material.
  • the embodiments of the present application do not specifically limit the types of negative electrode active materials, and can be selected according to actual needs.
  • the negative active material layer may further include a conductive agent and a binder.
  • a conductive agent is one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers
  • the binder is styrene butadiene rubber One or more of (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), and water-based acrylic resin.
  • the negative active material layer may also optionally include a thickener, such as sodium carboxymethyl cellulose (CMC-Na).
  • a thickener such as sodium carboxymethyl cellulose (CMC-Na).
  • the negative electrode current collector can be a metal foil or porous metal plate with good electrical conductivity and mechanical properties, and its material can be one or more of copper, nickel, titanium, iron, and their respective alloys.
  • the negative electrode current collector is, for example, copper foil.
  • the negative pole piece can be prepared according to conventional methods in the art. For example, disperse the negative electrode active material, conductive agent, binder and thickener in a solvent.
  • the solvent can be N-methylpyrrolidone (NMP) or deionized water to form a uniform negative electrode slurry, and then coat the negative electrode slurry.
  • NMP N-methylpyrrolidone
  • the electrolyte may be a solid electrolyte, such as a polymer electrolyte, an inorganic solid electrolyte, etc., but it is not limited thereto. Electrolyte can also be used as the electrolyte.
  • a solvent and a lithium salt dissolved in the solvent are included.
  • the solvent may be a non-aqueous organic solvent, such as ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC) , Dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethylene propyl carbonate (EPC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate ( One or more of PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB) and ethyl butyrate (EB), For example, two or more.
  • EC ethylene carbonate
  • PC propylene carbonate
  • EMC diethyl carbonate
  • DMC dimethyl carbonate
  • DPC dipropyl carbonate
  • MPC methyl propyl carbonate
  • MPC methyl propy
  • the lithium salt can be LiPF 6 (lithium hexafluorophosphate), LiBF 4 (lithium tetrafluoroborate), LiClO 4 (lithium perchlorate), LiAsF 6 (lithium hexafluoroarsenate), LiFSI (lithium bisfluorosulfonimide), LiTFSI (Lithium bistrifluoromethanesulfonimide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalate borate), LiBOB (lithium bisoxalate borate), LiPO 2 F 2 (lithium difluorophosphate), One or more of LiDFOP (lithium difluorooxalate phosphate) and LiTFOP (lithium tetrafluorooxalate phosphate), such as LiPF 6 (lithium hexafluorophosphate), LiBF 4 (lithium tetrafluoroborate), LiBOB (lithium
  • the electrolyte may also optionally contain other additives, such as vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), three Fluoromethyl ethylene carbonate (TFPC), succinonitrile (SN), adiponitrile (ADN), glutaronitrile (GLN), hexanetrinitrile (HTN), 1,3-propane sultone (1 ,3-PS), ethylene sulfate (DTD), methylene disulfonate (MMDS), 1-propene-1,3-sultone (PST), 4-methyl ethylene sulfate (PCS), 4-ethyl ethylene sulfate (PES), 4-propyl ethylene sulfate (PEGLST), propylene sulfate (TS), 1,4-butane sultone (1,4- BS), ethylene sulfite (DTO), dimethyl sulfite (
  • the lithium ion secondary battery in the embodiments of the present application has no special restrictions on the separator.
  • Any well-known separator with a porous structure with electrochemical stability and mechanical stability can be selected, such as glass fiber, non-woven fabric, polyethylene (PE ), polypropylene (PP) and polyvinylidene fluoride (PVDF) one or more of single-layer or multi-layer films.
  • PE polyethylene
  • PP polypropylene
  • PVDF polyvinylidene fluoride
  • the positive pole piece and the negative pole piece are alternately stacked, and an isolation film is arranged between the positive pole piece and the negative pole piece for isolation to obtain a battery core, which can also be obtained after winding. Placing the electric core in the casing, injecting electrolyte, and sealing to obtain a lithium ion secondary battery.
  • FIG. 5 shows a lithium ion secondary battery 5 with a square structure as an example.
  • the secondary battery may include an outer package.
  • the outer packaging is used to encapsulate the positive pole piece, the negative pole piece and the electrolyte.
  • the outer package may include a housing 51 and a cover 53.
  • the housing 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose to form an accommodating cavity.
  • the housing 51 has an opening communicating with the containing cavity, and a cover plate 53 can cover the opening to close the containing cavity.
  • the positive pole piece, the negative pole piece, and the separator may be formed into the cell 52 through a winding process or a lamination process.
  • the battery core 52 is encapsulated in the containing cavity.
  • the electrolyte can be an electrolyte, and the electrolyte is infiltrated in the cell 52.
  • the number of battery cells 52 contained in the lithium ion secondary battery 5 can be one or several, which can be adjusted according to requirements.
  • the outer packaging of the lithium ion secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, or the like.
  • the outer packaging of the secondary battery may also be a soft bag, such as a pouch type soft bag.
  • the material of the soft bag can be plastic, for example, it can include one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), and the like.
  • the lithium ion secondary battery can be assembled into a battery module, and the number of lithium ion 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. 7 is the battery module 4 as an example.
  • a plurality of lithium ion secondary batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, it can also be arranged in any other manner. Furthermore, the plurality of lithium ion secondary batteries 5 can be fixed by fasteners.
  • the battery module 4 may further include a housing having an accommodating space, and a plurality of lithium ion secondary batteries 5 are accommodated in the accommodating space.
  • 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.
  • FIGS 8 and 9 show the battery pack 1 as an example.
  • the battery pack 1 may include a battery box and a plurality of battery modules 4 provided in the battery box.
  • the battery box includes an upper box body 2 and a lower box body 3.
  • the upper box body 2 can be covered on the lower box body 3 and forms a closed space for accommodating the battery module 4.
  • a plurality of battery modules 4 can be arranged in the battery box in any manner.
  • the present application also provides a device, which includes at least one of the lithium ion secondary battery, battery module, or battery pack described in the present application.
  • the lithium ion secondary battery, battery module or battery pack can be used as a power source of the device, and can also be used as an energy storage unit of the device.
  • the device can be, but is not limited to, mobile devices (such as mobile phones, laptop computers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf Vehicles, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.
  • the device can select a lithium ion secondary battery, battery module, or battery pack according to its usage requirements.
  • Fig. 10 is a device as an example.
  • the device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc.
  • a battery pack or a battery module can be used.
  • the device may be a mobile phone, a tablet computer, a notebook computer, and the like.
  • the device is generally required to be light and thin, and a lithium ion secondary battery can be used as a power source.
  • the doping element is Sb
  • the doping element precursor antimony oxide Sb 2 O 3 is roughly equally divided into two batches for Sb doping.
  • the preparation method includes:
  • the precursor of the positive electrode active material [Ni 0.8 Co 0.1 Mn 0.1 ](OH) 2 , lithium hydroxide LiOH and the first batch of antimony oxide were added to the high-speed mixer for mixing for 1 hour to obtain a mixed material, wherein the positive electrode active
  • the molar ratio of the material precursor to lithium hydroxide Li/Me is 1.05, and Me represents the total molar amount of Ni, Co, and Mn in the precursor of the positive electrode active material; the mixture is placed in an atmosphere sintering furnace for the first sintering and sintering
  • the temperature is 850°C
  • the sintering time is 8 hours
  • the sintering atmosphere is an oxygen-containing atmosphere with an O 2 concentration of 90%.
  • the product of the first sintering treatment and the second batch of antimony oxide were added to the high-speed mixer for 1h, and the second sintering was carried out.
  • the sintering temperature and sintering atmosphere were the same as those of the first sintering, and the sintering time was 12h.
  • the total sintering time is 20h.
  • the high nickel ternary positive electrode active material can be obtained.
  • the amount of antimony oxide added makes the actual doping concentration of Sb in the positive electrode active material 25090 ⁇ g/cm 3 . As shown in Figure 1, Sb is uniformly distributed in the positive electrode active material particles.
  • the positive pole piece, the isolation film and the metal lithium piece are stacked in sequence, and the above-mentioned electrolyte is injected to assemble the button battery.
  • the negative active material artificial graphite, hard carbon, conductive agent acetylene black, binder styrene butadiene rubber (SBR), thickener sodium carbon methyl cellulose (CMC) are dispersed in a weight ratio of 90:5:2:2:1 Mix evenly in deionized water to obtain a negative electrode slurry; uniformly coat the negative electrode slurry on the negative electrode current collector aluminum foil, dry and cold press to obtain a negative electrode pole piece.
  • PE Polyethylene
  • Example 1 The difference from Example 1 is that the relevant parameters in the preparation step of the positive electrode active material are changed, and the types of doping elements are mixed, the content of each batch, the sintering temperature is 650°C ⁇ 850°C, and the total sintering time is 10h ⁇ 20h to obtain Positive electrode active material with predetermined doping element type, doping amount and doping uniformity; Among them, Example 4 and Example 12 involving multi-element doping, the content of each doping element is basically the same; Comparative Example 1 is not doped Elements are added; other parameters are shown in Table 1.
  • Example 14 The difference from Example 1 is that the doping element in Example 14 is added in a single batch, and the sintering temperature is 715°C; the doping element in Example 15 is added in a single batch, and the sintering temperature is 670°C; other parameters are shown in Table 1.
  • Example 22 The difference from Example 1 is that in Example 22, the temperature of the first sintering is 810°C and the time is 12h, and the temperature of the second sintering is 660°C and the time is 2h. Among them, the second batch of doping elements accounts for the total doped elements. 65% of the content of miscellaneous elements;
  • Example 23 The difference from Example 1 is that in Example 23, the temperature of the first sintering is 790°C and the time is 7h, and the temperature of the second sintering is 630°C and the time is 2h. Among them, the second batch of doped elements accounts for the total doped elements. 75% of the content of miscellaneous elements.
  • Example 1 The difference from Example 1 is that the positive electrode active material precursors of Examples 24 and 25 and Comparative Example 4 are [Ni 0.5 Co 0.2 Mn 0.3 ](OH) 2 , and there are differences in the types of dopant elements mixed in; Comparative Example 3
  • the precursor of the positive electrode active material is [Ni 0.5 Co 0.2 Mn 0.3 ](OH) 2 , with no doping elements added; other parameters are shown in Table 1.
  • charge 18 button batteries with a constant current of 1C to the upper limit of the charge-discharge cut-off voltage, then charge at a constant voltage to a current of ⁇ 0.05mA, then leave it aside for 2 minutes, and then discharge at a constant current of 1C to the charge-discharge cut-off voltage Lower limit.
  • the 18 button batteries after the above charge and discharge were charged to 2.8V, 2.9V, 3.0V, 3.1V, 3.2V, 3.3V,...4.0V, 4.1V, 4.2V, at a rate of 0.1C, respectively.
  • 4.3V, 4.4V, 4.5V that is, the charging voltage interval is 0.1V).
  • the chemical formula under each voltage was obtained, and then each Delithiation state at two voltages.
  • the chemical formula of the positive electrode active material is Li 0.22 Ni 0.8 Co 0.1 Mn 0.1 O 2 converted by the ICP-OES test
  • the corresponding voltage is The voltage corresponding to the 78% delithiation state.
  • the unit cell parameters, element occupancy and other information of the "78% delithiation state" positive electrode active material were obtained, and the bulk structure model of the complete structure of the positive electrode active material in the 78% delithiation state was constructed based on this, and its structure satisfies
  • the space group uses the first-principles calculation software VASP based on density functional theory, and the exchange correlation functional uses GGA+U to optimize the structure of the model to energy convergence, and extract the optimized structure energy, which is recorded as Epristine .
  • step (2) to subtract different oxygen atoms to obtain the defect formation energy of different oxygen atoms, and select the minimum value as the bulk structure oxygen defect formation energy ⁇ E O- of the positive electrode active material in the "78% delithiation state" vac .
  • the mass concentration of the doping element at the point, the test method is as follows: the detection element selects Li, O, Ni, Co, Mn and the doping element, and the SEM parameter is set to 20kV acceleration voltage, 60 ⁇ m aperture, 8.5mm working distance, 2.335A current, When performing EDS-SEM test, stop the test when the spectrum area reaches more than 250,000 cts (controlled by acquisition time and acquisition rate), and collect data to obtain the mass concentration of doping elements ⁇ 1 , ⁇ 2 , ⁇ 3 at each point ,..., ⁇ 17 .
  • test area covers all the points scanned by the above secondary particle points and does not exceed the cross section of the secondary particle.
  • the true density ⁇ true of the positive electrode active material is measured by the TD2400 powder true density tester of Beijing Biood Electronic Technology Co., Ltd.
  • n is the molar mass of gas in the sample cup
  • R is the ideal gas constant, which is 8.314
  • T is the ambient temperature, which is 298.15K.
  • the 7000DV ICP-OES of Platinum Elmer (PE) was used to test the mass concentration of doped elements in the positive electrode active material
  • the test method is as follows: take the pole piece containing the positive electrode active material and punch it into a disc with a total mass greater than 0.5g or take at least 5g of the positive electrode active material powder sample, weigh the recorded sample mass and put it into the digestion tank, and slowly add 10mL of aqua regia as
  • the digestion reagents are assembled and put into the Mars5 microwave digestion instrument of CEM Company in the United States, and digested at a microwave emission frequency of 2450Hz; the digested sample solution is transferred to a volumetric flask and shaken well, and the sample is put into the PE7000DV ICP-OES inlet
  • the sample system was used to test the mass concentration of doped elements in the positive electrode active material with 0.6MPa argon pressure and 1300W radio frequency power.
  • the true doping concentration ⁇ of the positive electrode active material is calculated according to the aforementioned formula (3).
  • the battery can be disassembled in a dry room, the middle part of the positive electrode piece can be taken out and put into a beaker, pour an appropriate amount of high-purity anhydrous dimethyl carbonate DMC, and replace the DMC every 8 hours. Clean three times in a row, and then put it in the vacuum static box of the drying room, keep the vacuum state (-0.096MPa), dry for 12 hours, after drying, cut a sample of the pole piece of preset size for testing; or use a blade to dry Scrape a predetermined quality of positive electrode active material powder from the room as a test sample.
  • Example 1 to 23 and Comparative Examples 1 to 2 the charge-discharge cut-off voltage of the button cell is 2.8V-4.25V, and the charge-discharge cut-off voltage of the full battery is 2.8V-4.2V; in Example 24 ⁇ 25 and Comparative Examples 3 to 4, the charge-discharge cut-off voltage of the button cell is 2.8V-4.35V, and the charge-discharge cut-off voltage of the full battery is 2.8V-4.3V.
  • Examples 24 to 25 and Comparative Examples 3 to 4 that by making the transition metal sites of the positive electrode active material include the doping element M, the doping element M
  • the valence of the positive electrode active material is above +3, and the average valence of surface oxygen V O in the 78% delithiation state of the positive electrode active material is -2.0 ⁇ -1.5.
  • the lithium ion secondary battery not only has a higher initial gram capacity, but also Has high high temperature cycle performance.

Abstract

本申请公开了一种正极活性材料、其制备方法、正极极片、锂离子二次电池与包含锂离子二次电池的电池模块、电池包和装置。正极活性材料包括含镍的锂复合氧化物，含镍的锂复合氧化物满足化学式Li 1+a[Ni xCo yMn zM b]O 2，式中，M为过渡金属位掺杂元素，0.5≤x<1，0≤y<0.3，0≤z<0.3，-0.1≤a<0.2，0<b<0.3，x+y+z+b＝1；正极活性材料具有层状晶体结构，属于(I)空间群；正极活性材料在78％脱锂态时，至少部分掺杂元素M的化合价为+3价以上、且正极活性材料的表面氧平均价态V O满足-2.0≤V O≤-1.5。

Description

正极活性材料、其制备方法、正极极片、锂离子二次电池与包含锂离子二次电池的电池模块、电池包和装置
相关申请的交叉引用
本申请要求享有于2019年09月02日提交的名称为“正极活性材料、正极极片及锂离子二次电池”的中国专利申请201910845573.7的优先权，该申请的全部内容通过引用并入本文中。
技术领域
本申请属于二次电池技术领域，具体涉及一种正极活性材料、其制备方法、正极极片、锂离子二次电池与包含锂离子二次电池的电池模块、电池包和装置。
背景技术
锂离子二次电池是一种充电电池，它主要依靠锂离子在正极和负极之间移动来工作，是当前被广泛应用的清洁能源。正极活性材料作为锂离子二次电池的重要组成部分，为电池充放电过程提供在正负极往复移动的锂离子，因此正极活性材料对电池性能的发挥至关重要。
锂镍基正极活性材料具有较高的理论容量，采用锂镍基正极活性材料的锂离子二次电池可期望获得较高的能量密度，但是研究发现该锂离子二次电池的高温循环性能较差。
发明内容
本申请第一方面提供一种正极活性材料，其包括含镍的锂复合氧化物，含镍的锂复合氧化物满足化学式Li 1+a[Ni xCo yMn zM b]O 2，式中，M为过渡金属位掺杂元素，0.5≤x<1，0≤y<0.3，0≤z<0.3，-0.1≤a<0.2，0<b<0.3，x+y+z+b＝1，其中，正极活性材料具有层状晶体结构，属于R3m空间群；正极活性材料在78％脱锂态时，至少部分掺杂元素M的化合价为+3价以上、且正极活性材料的表面氧平均价态V O满足-2.0≤V O≤-1.5。
本申请提供的正极活性材料包括具有特定化学组成及结构的含镍的锂复合氧化物，使得正极活性材料具有较高的充放电电压和比容量特性，采用该正极活性材料的锂离子二次电池能够表现出较高的容量性能和能量密度。正极活性材料还包括掺杂元素M，正极活性材料在78％脱锂态时，至少部分掺杂元素M的化合价为+3价以上。通过M元素掺杂改性使得正极活性材料在78％脱锂态的表面氧价态Vo与基态氧化合价(-2价)相差在较小的范围内，能显著提高正极活性材料的结构稳定性、并减少表面副反应，从而显著提高电池的高温循环性能。因此，采用本申请的正极活性材料，使得锂离子二次电池同时兼顾较高的能量密度及高温循环性能。
在上述任意实施方式中，0.7≤x≤0.9，0<y<0.3，0<z<0.3；所述正极活性材料在78％脱锂态的表面氧平均价态V O为-1.9≤V O≤-1.6。采用该正极活性材料的电池具有更高的能量密度及高温循环性能。
在上述任意实施方式中，所述正极活性材料可包括由一次颗粒聚集而成的二次颗粒，所述二次颗粒中所述掺杂元素M的局部质量浓度的相对偏差可以为32％以下，可选为20％以下。掺杂元素在二次颗粒中的分布均匀性较高，能更有效地降低正极活性材料表面氧活性、以及提高正极活性材料的体相结构氧缺陷形成能，从而更好地提升电池的整体性能。其中，电池能具有更高的能量密度和高温循环性能。
在上述任意实施方式中，所述正极活性材料在78％脱锂态的体相结构氧缺陷形成能ΔE O-vac可满足：ΔE O-vac≥0.5eV；可选的，ΔE O-vac≥0.7eV；可选的，ΔE O-vac≥1.0eV。正极活性材料的ΔE O-vac在上述范围内，能具有较高的结构稳定性，并确保其为锂离子的脱嵌提供良好载体，由此获得较高的初始容量及循环容量保持率，从而提升电池的能量密度和高温循环性能。
在上述任意实施方式中，所述正极活性材料在78％脱锂态时，所述掺杂元素M可具有两个以上不同的价态，且处于最高价态的所述掺杂元素M的化合价可以为+4价、+5价、+6价、+7价及+8价中的一种或多种，可选的为+5价、+6价、+7价及+8价中的一种或多种。掺杂元素M能在正极活性材料中贡献更多的电子，进一步降低正极活性材料的表面氧活性，稳定材料结构，并减少表面副反应，从而进一步提高电池的高温循环性能。并且，掺杂元素M能更有效地束缚氧原子，提高正极活性材料的氧缺陷形成能ΔE O- vac及结构稳定性。
在上述任意实施方式中，所述掺杂元素M可包括Ti、V、Se、Zr、Nb、Ru、Pd、Sb、Te及W中的一种或多种。可选的，掺杂元素M可包括Ti、Se、Zr、Nb、Ru、Sb、Te及W中的一种或多种。所给掺杂元素M能更好地改善锂离子二次电池的能量密度和高 温循环性能。
在上述任意实施方式中，所述正极活性材料的真实掺杂浓度ω可满足2300μg/cm 3≤ω≤49100μg/cm 3，可选的3000μg/cm 3≤ω≤30000μg/cm 3，可选的14830μg/cm 3≤ω≤49080μg/cm 3，可选的24890μg/cm 3≤ω≤31210μg/cm 3。正极活性材料的真实掺杂浓度在上述范围内，能有效降低正极活性材料的表面氧活性和提高体相结构氧缺陷形成能，还保证颗粒具有较高锂离子传输扩散能力，从而能提升电池的能量密度及高温循环性能。
在上述任意实施方式中，所述正极活性材料中所述掺杂元素M的质量浓度相对于所述正极活性材料的颗粒中所述掺杂元素M的平均质量浓度的偏差ε可满足ε<50％；可选的，ε≤30％；可选的，ε≤20％。正极活性材料的ε在上述范围内，其宏观和微观一致性较好，颗粒整体稳定性较高，有利于获得更高的容量发挥和高温循环性能，从而能提升电池的相应性能。
在上述任意实施方式中，所述正极活性材料的真密度ρ 真可满足4.6g/cm 3≤ρ 真≤4.9g/cm 3。正极活性材料能具有较高的比容量，从而可提高电池的能量密度。
在上述任意实施方式中，所述正极活性材料的体积平均粒径D v50可以为5μm～20μm，可选的为8μm～15μm，进一步可选的为9μm～11μm。正极活性材料的D v50在上述范围内，能提高锂离子二次电池的循环性能和倍率性能，还可提升电池的能量密度。
在上述任意实施方式中，所述正极活性材料的比表面积可以为0.2m 2/g～1.5m 2/g，可选的为0.3m 2/g～1m 2/g。正极活性材料的比表面积在上述范围内，能使电池获得较高的能量密度和循环性能。
在上述任意实施方式中，所述正极活性材料的振实密度可选为2.3g/cm 3～2.8g/cm 3。正极活性材料的振实密度在上述范围内，能使锂离子二次电池具有较高的能量密度。
在上述任意实施方式中，所述正极活性材料在5吨(相当于49kN)压力下的压实密度可选为3.1g/cm 3～3.8g/cm 3。正极活性材料的压实密度在所给范围内，有利于使锂离子二次电池获得较高的能量密度。
本申请第二方面提供一种正极活性材料的制备方法，其包括以下步骤：
将正极活性材料前驱体、锂源和掺杂元素前驱体混合，得到混合料，其中所述正极活性材料前驱体选自含有Ni、可选的Co和可选的Mn的氧化物、氢氧化物及碳酸盐中的一种或多种；
在含氧气氛、600℃～1000℃温度下对所述混合料烧结处理，得到正极活性材料；
其中，所述正极活性材料包括含镍的锂复合氧化物，所述含镍的锂复合氧化物满足化学式Li 1+a[Ni xCo yMn zM b]O 2，式中，M为过渡金属位掺杂元素，0.5≤x<1，0≤y<0.3， 0≤z<0.3，-0.1≤a<0.2，0<b<0.3，x+y+z+b＝1；
所述正极活性材料具有层状晶体结构，属于
Figure PCTCN2020109843-appb-000001
空间群；
所述正极活性材料在78％脱锂态时，至少部分所述掺杂元素M的化合价为+3价以上、且所述正极活性材料的表面氧平均价态V O为-2.0≤V O≤-1.5。
本申请提供的制备方法所得正极活性材料包括含镍的锂复合氧化物，其过渡金属位掺杂有M元素，并且正极活性材料在78％脱锂态时，至少部分掺杂元素M的化合价为+3价以上，且正极活性材料的表面氧价态Vo与基态氧化合价(-2价)相差在较小的范围内，由此能使锂离子二次电池同时兼顾较高的能量密度及高温循环性能。
在上述任意实施方式中，所述掺杂元素前驱体可选自钛氧化物、钒氧化物、硒氧化物、锆氧化物、铌氧化物、钌氧化物、钯氧化物、锑氧化物、碲氧化物及钨氧化物中的一种或多种。可选的，所述掺杂元素前驱体可选自TiO 2、TiO、V 2O 5、V 2O 4、V 2O 3、SeO 2、ZrO 2、Nb 2O 5、NbO 2、RuO 2、PdO、Sb 2O 5、Sb 2O 3、TeO 2、WO 2、WO 3中的一种或多种。
在上述任意实施方式中，所述烧结处理可满足如下中的至少一项：
所述含氧气氛的氧气浓度为80％～100％；
烧结处理的温度为600℃～900℃，可选的为700℃～900℃；
烧结处理的时间为5h～25h，可选的为10h～20h。
在上述任意实施方式中，可以将所述掺杂元素前驱体等分为L份或任意分为L份，分为L个批次进行掺杂，其中L为1～5，可选的为2～3，其中包括：将正极活性材料前驱体、锂源及第1批次掺杂元素前驱体混合，并进行第1次烧结处理；将第1次烧结处理的产物与第2批次掺杂元素前驱体进行混合，并进行第2次烧结处理；以此类推，直至将第L-1次烧结处理的产物与第L批次掺杂元素前驱体进行混合，并进行第L次烧结处理，得到正极活性材料。
可选的，每次烧结处理的温度为600℃～1000℃，可选的为600℃～900℃，还可选的为700℃～900℃；每次烧结处理的时间为1h～20h，可选的为2h～18h；总的烧结处理时间为5h～25h，可选的为10h～20h。
本申请第三方面提供一种正极极片，其包括正极集流体以及设置于所述正极集流体上的正极活性物质层，所述正极活性物质层包括本申请第一方面的正极活性材料、或根据本申请第二方面的制备方法得到的正极活性材料。
本申请的正极极片由于包含所述的正极活性材料，因而能使采用其的锂离子二次电池具有较高的能量密度和高温循环性能。
本申请第四方面提供一种锂离子二次电池，其包括本申请第三方面的正极极片。
本申请的锂离子二次电池由于包含所述的正极极片，因而能具有较高的能量密度和高温循环性能。
本申请第五方面提供一种电池模块，其包括本申请第四方面的锂离子二次电池。
本申请第六方面提供一种电池包，其包括本申请第四方面的锂离子二次电池、或本申请第五方面的电池模块。
本申请第七方面提供一种装置，其包括本申请第四方面的锂离子二次电池、本申请第五方面的电池模块、或本申请第六方面的电池包中的至少一种。
本申请的电池模块、电池包和装置包括本申请的锂离子二次电池，因而至少具有与所述锂离子二次电池相同或相似的效果。
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例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据附图获得其他的附图。
图1为实施例1的正极活性材料二次颗粒的掺杂元素分布图像，其是采用日本电子(JEOL)公司的IB-09010CP型截面抛光仪(Cross Section Polisher，CP)制备截面，采用牛津仪器X-Max型能谱仪(Energy Dispersive Spectroscopy，EDS)测试获得；图中亮点表示掺杂元素，掺杂元素在颗粒中均匀分布。
图2为实施例1～25及对比例1～4的正极活性材料二次颗粒中掺杂元素的局部质量浓度的相对偏差测试的取点位置示意图。
图3为实施例1的正极活性材料在78％脱锂态的Sb 3d轨道的X射线光电子能谱分析(X-ray photoelectron spectroscopy，XPS)谱图。
图4为实施例1的正极活性材料在78％脱锂态的O 1s轨道的XPS谱图。
图5是锂离子二次电池的一实施方式的示意图。
图6是图5的分解图。
图7是电池模块的一实施方式的示意图。
图8是电池包的一实施方式的示意图。
图9是图8的分解图。
图10是锂离子二次电池用作电源的装置的一实施方式的示意图。
具体实施方式
为了使本申请的发明目的、技术方案和有益技术效果更加清晰，以下结合实施例对本申请进行进一步详细说明。应当理解的是，本说明书中描述的实施例仅仅是为了解释本申请，并非为了限定本申请。
为了简便，本文仅明确地公开了一些数值范围。然而，任意下限可以与任何上限组合形成未明确记载的范围；以及任意下限可以与其它下限组合形成未明确记载的范围，同样任意上限可以与任意其它上限组合形成未明确记载的范围。此外，尽管未明确记载，但是范围端点间的每个点或单个数值都包含在该范围内。因而，每个点或单个数值可以作为自身的下限或上限与任意其它点或单个数值组合或与其它下限或上限组合形成未明确记载的范围。
在本文的描述中，需要说明的是，除非另有说明，“以上”、“以下”为包含本数，“一种或多种”中的“多种”的含义是两种以上，“一个或多个”中的“多个”的含义是两个以上。
在本文的描述中，除非另有说明，术语“或(or)”是包括性的。举例来说，短语“A或(or)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)。
本申请的上述发明内容并不意欲描述本申请中的每个公开的实施方式或每种实现方式。如下描述更具体地举例说明示例性实施方式。在整篇申请中的多处，通过一系列实施例提供了指导，这些实施例可以以各种组合形式使用。在各个实例中，列举仅作为代表性组，不应解释为穷举。
正极活性材料
本申请第一方面的正极活性材料包括含镍的锂复合氧化物，含镍的锂复合氧化物满足化学式Li 1+a[Ni xCo yMn zM b]O 2，其中，M为过渡金属位掺杂元素，0.5≤x<1，0≤y<0.3，0≤z<0.3，-0.1≤a<0.2，0<b<0.3，x+y+z+b＝1；正极活性材料具有层状晶体结构，属于
Figure PCTCN2020109843-appb-000002
空间群；正极活性材料在78％脱锂态时，至少部分掺杂元素M的化合价为+3价以上、且正极活性材料的表面氧平均价态V O为-2.0≤V O≤-1.5。
在本文中，“78％脱锂态”是指电池在充电过程中，从正极活性材料中脱出的锂的摩尔含量占理论锂含量为78％时的状态。二次电池在实际使用过程中，一般会设定一个“满充状态”，并对应设置一个“充电截止电压”，以保证电池的安全使用。“满充状态” 是指二次电池的荷电状态(State of Charge，SOC)为100％，换句话说，包含上述正极活性材料的正极组成的二次电池在进行可逆充放电的范围内被充电至充电截止电压。该“满充状态”或“充电截止电压”因正极活性材料的不同或安全性要求的差异，会存在一定的差异。对于含镍的锂复合氧化物正极活性材料制备的二次电池在“满充状态”时，正极活性材料的脱锂状态一般在“78％脱锂态”左右，以保证正常使用。
在本文中，结合“脱锂态”和充电电压的对应关系，以获得处于“78％脱锂态”的正极活性材料进行研究。具体的，将使用该正极活性材料的一系列电池，分别以0.1C倍率充电至2.8V、2.9V、3.0V、3.1V、3.2V、3.3V、…、4.0V、4.1V、4.2V、4.3V、4.4V、4.5V(即充电电压间隔为0.1V)，随后拆出电池的正极极片，经洗涤除去电解液，消解正极活性材料，用电感耦合等离子体-发射光谱仪(inductively coupled plasma-Optical Emission spectrometers，ICP-OES)测试正极活性材料的Li、过渡金属、O元素的质量浓度，计算该充电电压下正极活性材料的各元素化学计量比，换算得到该充电电压下正极活性材料的化学式，进而得到“78％脱锂态”所对应的充电电压。
将包含待测正极活性材料的电池充电至“78％脱锂态”所对应的电压，即可拆解获得处于“78％脱锂态”的正极活性材料进行进一步研究。“78％脱锂态”正极活性材料的表面氧价态V O及掺杂元素M的化合价可通过X射线光电子能谱分析(XPS)测试得到。更精确的，可通过同步辐射光电子能谱分析(Synchrotron radiation photoelectron spectroscopy，SRPES)测试获得。
本申请实施例的正极活性材料包括具有特定化学组成及结构的含镍的锂复合氧化物，使得正极活性材料具有较高的充放电电压和比容量特性，采用该正极活性材料的锂离子二次电池能够表现出较高的容量性能和能量密度。
未脱锂的正极活性材料表面氧化合价较低(如-2价)，而在正极活性材料脱锂过程中(电池充电过程中)，随着锂离子从正极活性材料脱出，正极活性材料中的电子也不断脱出达到负极。正极活性材料还包括掺杂元素M，正极活性材料在78％脱锂态时，部分或全部掺杂元素M的化合价为+3价以上。具有较大化合价的掺杂元素M能在正极活性材料中贡献较多的电子，相应的正极活性材料的氧原子失去电子的数量就会降低，使得正极活性材料在脱锂过程中及脱锂后的表面氧活性始终保持在较低水平，尤其是正极活性材料在78％脱锂态的表面氧平均价态V O为-2.0～-1.5。
通过M元素的掺杂改性，使得正极活性材料在78％脱锂态的表面氧价态Vo与基态氧化合价(-2价)相差较小，能显著提高正极活性材料的结构稳定性，使得正极活性材料在加热升温和高温循环过程中不易发生释氧现象，抑制氧缺陷，并有效防止正极活性材料 发生不可逆相变，从而提高正极活性材料在高温循环过程中的容量保持率。因此，本申请通过在含镍的锂复合氧化物的过渡金属位掺杂M元素，能显著提高电池的高温循环性能。此外，电池的热稳定性和高温安全性能也得到改善。
正极活性材料的表面氧活性较低，还能有效抑制电解液在材料颗粒表面的副反应，抑制产气、减少产热量，并减少可逆锂离子的消耗，抑制正极阻抗增加，减小正极极化，有利于提升电池的高温循环性能。
采用本申请实施例提供的正极活性材料，能使锂离子二次电池同时兼顾较高的容量性能、能量密度及高温循环性能。
在一些可选的实施方式中，含镍的锂复合氧化物的过渡金属位元素中镍的摩尔百分含量可以为50％～90％，例如为70％～90％。该高镍正极活性材料具有较高的比容量特性，能提高电池的容量性能及能量密度。
可选地，含镍的锂复合氧化物的化学式中，0.7≤x≤0.9，0<y<0.3，0<z<0.3；且正极活性材料在“78％脱锂态”的表面氧平均价态V O为-1.9≤V O≤-1.6。采用该正极活性材料的电池具有更高的能量密度及高温循环性能。
化合价为+3价以上的掺杂元素M与氧的结合能力强，即与氧结合的键能大，能有效束缚氧原子，使正极活性材料在加热升温及高温循环过程中不易发生释氧，提高正极活性材料的氧缺陷形成能ΔE O-vac。在一些实施方式中，正极活性材料在78％脱锂态的体相结构氧缺陷形成能ΔE O-vac满足ΔE O-vac≥0.5eV。可选的，ΔE O-vac≥0.7eV。可选的，ΔE O-vac≥1.0eV。
正极活性材料在“78％脱锂态”的体相结构氧缺陷形成能ΔE O-vac满足式(1)。
ΔE O-vac＝E pristine-E defect-E O    式(1)
式(1)中，ΔE O-vac表示基态下正极活性材料在“78％脱锂态”的体相结构氧缺陷形成能；E pristine表示基态下结构完整的正极活性材料在“78％脱锂态”的体相结构能量；E defect表示基态下存在氧缺陷的正极活性材料在“78％脱锂态”的体相结构能量；E O表示基态下氧原子的能量(化学势)。
E pristine、E defect和E O均可通过基于密度泛函理论的第一性原理的计算软件VASP计算得到，交换关联泛函可以采用广义梯度近似(Generalized Gradient Approximation，GGA)加入一个Hubbard参数U对应项，即GGA+U交换关联泛函。作为示例，可以包括以下步骤：
S10，基于“78％脱锂态”正极活性材料的X射线衍射(X-ray diffraction，XRD)分 析结果，获得“78％脱锂态”正极活性材料的晶胞参数、元素占位等信息，据此构建结构完整的正极活性材料在“78％脱锂态”的体相结构模型，其结构满足
Figure PCTCN2020109843-appb-000003
空间群，使用基于密度泛函理论的第一性原理的计算软件VASP，交换关联泛函采用GGA+U，对模型进行结构优化至能量收敛，提取优化后的结构能量，记为E pristine。
S20，在上述优化后的“78％脱锂态”正极活性材料体相结构模型基础上，扣除一个氧原子，得到存在氧缺陷的正极活性材料在“78％脱锂态”的体相模型，使用基于密度泛函理论的第一性原理的计算软件VASP，交换关联泛函采用GGA+U，对含氧缺陷的体相模型进行结构优化至能量收敛，提取优化后的结构能量，记为E defect。
S30，使用基于密度泛函理论的第一性原理的计算软件VASP，交换关联泛函采用GGA+U，优化氧气分子至能量收敛，提取优化后的氧气能量除以2，记为E O。
S40，将得到的E pristine、E defect和E O的数值代入式(1)，计算得到一个氧原子的氧缺陷形成能。
参照步骤S20扣除不同的氧原子，以得到不同氧原子的缺陷形成能，并选择其中的最小值作为“78％脱锂态”的正极活性材料的体相结构氧缺陷形成能ΔE O-vac。
上述步骤S10、S20、S30的计算过程，使用的计算参数精度保证优化计算的结构能量收敛至小于10 -6eV、力收敛至小于
Figure PCTCN2020109843-appb-000004
可确保计算结果更加可靠。
正极活性材料在“78％脱锂态”的体相结构氧缺陷形成能ΔE O-vac在上述范围内，使得正极活性材料在充电过程中及满充状态下，其中的氧原子不易脱离原有的晶格位置而形成氧缺陷，使得正极活性材料具有较高的结构稳定性、并始终保持在具有强电化学活性的层状相状态，从而为锂离子的脱嵌提供良好载体，使正极活性材料具有较高的初始容量及循环容量保持率，进而提升电池的能量密度及高温循环性能。
正极活性材料在“78％脱锂态”时的体相结构氧缺陷形成能ΔE O-vac在上述范围内，使得正极活性材料在加热升温和高温循环过程中不易发生释氧现象，有利于提高电池的热稳定性和高温安全性能。
在一些可选的实施方式中，处于78％脱锂态的正极活性材料中，掺杂元素M具有两个以上不同的价态，且处于最高价态的M元素的化合价为+4价、+5价、+6价、+7价及+8价中的一种或多种。可选的，78％脱锂态的正极活性材料中，M元素的最高价态为+5价、+6价、+7价及+8价中的一种或多种。价态较高且存在变化价态的掺杂元素M能在正极活性材料中贡献更多的电子，相应地正极活性材料中氧原子失去电子的数量更少，从而进一步降低正极活性材料的表面氧活性，稳定材料结构，并减少表面副反应，进而提高电池的高温循环性能。并且，价态较高的掺杂元素与氧的结合能力更强，能更有效地 束缚氧原子，提高正极活性材料的氧缺陷形成能ΔE O-vac及结构稳定性，进而提高电池的性能。
此外，正极活性材料在78％脱锂态时，掺杂元素M具有两个以上不同的价态，其中较低价态的掺杂元素能进一步贡献电子以支持正极释放出更多的锂离子，从而使得电池的能量密度得到进一步提升。
可选的，掺杂元素M包括Ti、V、Se、Zr、Nb、Ru、Pd、Sb、Te及W中的一种或多种。可选的，掺杂元素M包括Ti、Se、Zr、Nb、Ru、Sb、Te及W中的一种或多种。采用合适的掺杂元素M能更好地发挥上述效果，进一步提高锂离子二次电池的能量密度及高温循环性能。
在一些可选的实施方式中，正极活性材料包括由一次颗粒聚集而成的二次颗粒。进一步地，二次颗粒中掺杂元素的局部质量浓度的相对偏差为32％以下，可选的为30％以下，进一步可选的为20％以下，16％以下，13％以下，11％以下，或10％以下。
在本文中，二次颗粒中掺杂元素的局部质量浓度为在二次颗粒中任意选定位点的有限体积元内，掺杂元素占所有元素的质量浓度，可由EDX(Energy Dispersive X-Ray Spectroscopy，能量色散X射线光谱仪)或EDS元素分析结合TEM(Transmission Electron Microscope，透射电子显微镜)或SEM(Scanning Electron Microscope，扫描电子显微镜)单点扫描测试元素浓度分布或其它类似方式得到。其中以EDX或EDS元素分析结合TEM或SEM单点扫描测试时，二次颗粒中不同位点处以μg/g计的掺杂元素的质量浓度分别记作η 1、η 2、η 3、…、η n，n为大于15的正整数。
二次颗粒中掺杂元素的平均质量浓度为在单个或多个二次颗粒范围内掺杂元素占所有元素的质量浓度，可由EDX或EDS元素分析结合TEM或SEM面扫描测试元素浓度分布或其它类似方式得到。其中以EDX或EDS元素分析结合TEM或SEM面扫描测试元素浓度分布的方式测试时，测试面包括上述单点测试中的所有点。二次颗粒中掺杂元素的平均质量浓度记作
Figure PCTCN2020109843-appb-000005
单位为μg/g。
二次颗粒中掺杂元素的局部质量浓度的相对偏差σ可根据式(2)计算得到：
Figure PCTCN2020109843-appb-000006
二次颗粒满足σ在32％以下，可选30％以下，进一步可选20％以下，意味着掺杂元素在二次颗粒中的分布均匀性较高。均匀掺杂能更有效地降低正极活性材料表面氧活性、以及提高正极活性材料的体相结构氧缺陷形成能，从而更好地提升电池的整体性能。
另外，均匀掺杂的正极活性材料颗粒内部各处的性质保持一致，锂离子在颗粒内部不同区域的迁移扩散能力处于同一水平，颗粒各处的抗变形能力接近，颗粒内的应力分布均匀，从而提高正极活性材料的结构稳定性。正极活性材料不易发生破裂，能防止因破裂暴露出的新鲜表面引起的副反应和容量及循环性能的恶化，从而使正极活性材料具有较高的容量发挥及高温循环容量保持率，因而使电池具有较高的容量性能、能量密度及高温循环性能。
二次颗粒中掺杂元素的局部质量浓度的相对偏差越小，则颗粒中掺杂元素的分布越均匀，越能提高正极活性材料的结构稳定性、以及提高正极活性材料的容量发挥及高温循环性能。
在一些可选的实施方式中，正极活性材料的真实掺杂浓度ω满足1500μg/cm 3≤ω≤60000μg/cm 3。进一步可选的，2300μg/cm 3≤ω≤49100μg/cm 3，3000μg/cm 3≤ω≤30000μg/cm 3，14830μg/cm 3≤ω≤49080μg/cm 3，14830μg/cm 3≤ω≤36690μg/cm 3，或24890μg/cm 3≤ω≤31210μg/cm 3。
在本文中，正极活性材料的真实掺杂浓度ω可由式(3)计算所得：
Figure PCTCN2020109843-appb-000007
式(3)中，ω为正极活性材料的真实掺杂浓度，单位为μg/cm 3。
ρ 真为正极活性材料真密度，单位为g/cm 3，其等于正极活性材料的质量与正极活性材料的真体积的比值，其中真体积是固体物质的实际体积，不包括粒子内部的孔隙。ρ真可以用本领域公知的仪器及方法进行测定，例如气体容积法，可以采用粉末真密度测试仪进行。
Figure PCTCN2020109843-appb-000008
为正极活性材料中以μg/g为单位的掺杂元素的质量浓度，即每克正极活性材料中所含有的掺杂元素的质量。其中，
Figure PCTCN2020109843-appb-000009
代表宏观正极活性材料整体中掺杂元素的含量，包括掺入正极活性材料的颗粒中的掺杂元素、在正极活性材料颗粒表面其他相中富集的掺杂元素、以及位于正极活性材料颗粒间的掺杂元素。
Figure PCTCN2020109843-appb-000010
可通过正极活性材料溶液吸收光谱，如ICP(Inductive Coupled Plasma Emission Spectrometer，电感耦合等离子光谱发生仪)、XAFS(X-ray absorption fine structure spectroscopy，X射线吸收精细结构谱)等测试得到。
正极活性材料的真实掺杂浓度在上述范围内，能有效降低正极活性材料的表面氧活性和提高体相结构氧缺陷形成能；还使正极活性材料具有良好的层状晶体结构，保证了正极活性材料为锂离子的脱嵌提供良好载体，有利于锂离子的嵌入、脱出，防止可逆锂离子消耗在电极表面或电解液中，使正极活性材料具有较高的初始容量及循环容量保持率，从而提升电池的能量密度及高温循环性能。
此外，正极活性材料的真实掺杂浓度在上述范围内，还保证了掺杂元素掺杂于过渡金属层，防止其进入锂层，保证颗粒具有较高的锂离子传输扩散能力，使得电池具有较高的容量发挥及循环性能。
在一些可选的实施方式中，正极活性材料中掺杂元素的质量浓度
Figure PCTCN2020109843-appb-000011
相对于正极活性材料的颗粒中掺杂元素的平均质量浓度
Figure PCTCN2020109843-appb-000012
的偏差为ε，ε满足ε<50％。可选的，ε≤45％。可选的，ε≤30％。进一步可选的，ε≤20％，或≤10％。
此处，正极活性材料的颗粒可以包括一次颗粒和/或二次颗粒。其中一次颗粒中掺杂元素的平均质量浓度、以及一次颗粒和二次颗粒中掺杂元素的平均质量浓度均可以参照前文所述二次颗粒中掺杂元素的平均质量浓度
Figure PCTCN2020109843-appb-000013
进行测试。
正极活性材料中掺杂元素的质量浓度
Figure PCTCN2020109843-appb-000014
相对于正极活性材料的颗粒中掺杂元素的平均质量浓度
Figure PCTCN2020109843-appb-000015
的偏差ε可由下式(4)计算得到：
Figure PCTCN2020109843-appb-000016
可以理解的是，当正极活性材料的颗粒为二次颗粒时，
Figure PCTCN2020109843-appb-000017
正极活性材料满足ε在上述范围内，意味着掺杂元素顺利掺入正极活性材料的颗粒中，在颗粒表面其他相中分布的掺杂元素以及包埋于颗粒缝隙间的掺杂元素的含量较少，正极活性材料宏观和微观一致性较好，结构均一。各颗粒在充放电循环过程中，膨胀收缩程度保持一致，颗粒稳定性高，有利于其具有较高的容量发挥及高温循环性能。
在一些可选的实施方式中，正极活性材料的真密度ρ 真满足4.6g/cm 3≤ρ 真≤4.9g/cm 3，正极活性材料能具有较高的比容量，从而提高电池的容量性能及能量密度。
本申请实施例中，正极活性材料颗粒的体积平均粒径D v50可选为5μm～20μm，进一步可选为8μm～15μm，还可选为9μm～11μm。正极活性材料的D v50在上述范围内，锂离子和电子在颗粒中的迁移路径较短，能提高正极活性材料中锂离子和电子的传输扩散性能，减小电池极化，从而提高锂离子二次电池的循环性能及倍率性能；此外还能使正极活性材料具有较高的压实密度，提升电池的能量密度。
正极活性材料的D v50在上述范围内，还有利于减少电解液在正极活性材料表面的副反应，以及减少正极活性材料颗粒之间的团聚，从而提高正极活性材料的常温及高温循环性能和安全性能。
本申请实施例中，正极活性材料的比表面积可选为0.2m 2/g～1.5m 2/g，进一步可选为0.3m 2/g～1m 2/g。正极活性材料的比表面积在上述范围内，保证了正极活性材料具有较高的活性比表面积，同时有利于减少电解液在正极活性材料表面的副反应，从而提高正极 活性材料的容量发挥及循环寿命；此外，还能抑制正极活性材料在制备浆料及充放电过程中发生颗粒与颗粒之间的团聚，提高电池的能量密度及循环性能。
本申请实施例中，正极活性材料的振实密度可选为2.3g/cm 3～2.8g/cm 3。正极活性材料的振实密度在上述范围内，有利于使锂离子二次电池具有较高的容量性能及能量密度。
本申请实施例中，正极活性材料在5吨(相当于49kN)压力下的压实密度可选为3.1g/cm 3～3.8g/cm 3。正极活性材料的压实密度较高，有利于使锂离子二次电池具有较高的容量性能及能量密度。
可选地，本申请实施例提供的正极活性材料颗粒的形貌为球体及类球体中的一种或多种。
在本文中，正极活性材料的D v50为本领域公知的含义，又称为中值粒径，表示正极活性材料颗粒的体积分布50％对应的粒径。正极活性材料的D v50可以用本领域公知的仪器及方法进行测定，例如可以用激光粒度分析仪(如英国马尔文仪器有限公司的Mastersizer 3000型)方便地测定。
正极活性材料的比表面积为本领域公知的含义，可以用本领域公知的仪器及方法进行测定，例如可以用氮气吸附比表面积分析测试方法测试，并用BET(Brunauer Emmett Teller)法计算得出，其中氮气吸附比表面积分析测试可以是通过美国康塔公司的NOVA2000e型比表面积与孔径分析仪进行。作为具体的示例，测试方法如下：用称重后的空样品管取8.000g～15.000g正极活性材料，将正极活性材料搅拌均匀并称重，把样品管放入NOVA 2000e脱气站中脱气，称量脱气后的正极活性材料和样品管总质量，用总质量减去空样品管的质量计算得到脱气后正极活性材料的质量G。将样品管放入NOVA 2000e，测定不同相对压力下的氮气在正极活性材料表面的吸附量，基于布朗诺尔-埃特-泰勒多层吸附理论及其公式求得单分子层吸附量，进而计算出正极活性材料总表面积A，通过A/G计算得到正极活性材料的比表面积。
正极活性材料的振实密度为本领域公知的含义，可以用本领域公知的仪器及方法进行测定，例如用振实密度测定仪(如FZS4-4B型)方便地测定。
正极活性材料的压实密度为本领域公知的含义，可以用本领域公知的仪器及方法进行测定，例如用电子压力试验机(如UTM7305型)方便地测定。
接下来示意性地说明一种正极活性材料的制备方法。根据该制备方法能够制备得到上述任意一种正极活性材料。制备方法包括：
将正极活性材料前驱体、锂源及掺杂元素前驱体混合，并进行烧结处理，得到正极 活性材料。
上述正极活性材料前驱体可以为按照化学计量比含有Ni及可选的含有Co和/或Mn的氧化物、氢氧化物及碳酸盐中的一种或多种，例如为按照化学计量比含有Ni、Co及Mn的氢氧化物。
正极活性材料前驱体可以通过本领域已知的方法获得，例如通过共沉淀法、凝胶法或固相法制备获得。
作为一个示例，将Ni源、Co源及Mn源分散在溶剂中得到混合溶液；采用连续并流反应的方式，将混合溶液、强碱溶液和络合剂溶液同时泵入带搅拌的反应釜中，控制反应溶液的pH值为10～13，反应釜内的温度为25℃～90℃，反应过程中通惰性气体保护；反应完成后，经陈化、过滤、洗涤和真空干燥，得到含有Ni、Co及Mn的氢氧化物。
Ni源可以为可溶性的镍盐，例如为硫酸镍、硝酸镍、氯化镍、草酸镍及醋酸镍中的一种或多种，再例如为硫酸镍及硝酸镍中的一种或多种，再例如为硫酸镍；Co源可以为可溶性的钴盐，例如为硫酸钴、硝酸钴、氯化钴、草酸钴及醋酸钴中的一种或多种，再例如为硫酸钴及硝酸钴中的一种或多种，再例如为硫酸钴；Mn源可以为可溶性的锰盐，例如为硫酸锰、硝酸锰、氯化锰、草酸锰及醋酸锰中的一种或多种，再例如为硫酸锰及硝酸锰中的一种或多种，再例如为硫酸锰。
强碱可以为LiOH、NaOH及KOH中的一种或多种，例如为NaOH。络合剂可以为氨水、硫酸铵、硝酸铵、氯化铵、柠檬酸铵及乙二胺四乙酸二钠(EDTA)中的一种或多种，例如为氨水。
对混合溶液、强碱溶液和络合剂溶液的溶剂均没有特别的限制，例如混合溶液、强碱溶液和络合剂溶液的溶剂各自独立地为去离子水、甲醇、乙醇、丙酮、异丙醇及正己醇中的一种或多种，如为去离子水。
反应过程中通入的惰性气体例如为氮气、氩气、氦气中的一种或多种。
上述锂源可以为氧化锂(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。进一步地，锂源为碳酸锂、氢氧化锂及硝酸锂中的一种或多种；更进一步地，锂源为碳酸锂。
上述掺杂元素前驱体可以为掺杂元素的氧化物、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。例如为掺杂元素的氧化物，例如为氧化钛(如TiO 2、TiO等)、氧化钒(如V 2O 5、V 2O 4、V 2O 3等)、氧化硒(如SeO 2等)、氧化锆(如ZrO 2等)、氧化铌(如Nb 2O 5、NbO 2等)、氧化钌(如RuO 2等)、氧化钯(如PdO 等)、氧化锑(如Sb 2O 5、Sb 2O 3等)、氧化碲(如TeO 2等)及氧化钨(如WO 2、WO 3等)中的一种或多种。
可以通过使掺杂元素前驱体中包含低价态的掺杂元素，以使所获得的正极活性材料在78％脱锂态时，掺杂元素M具有两个以上不同的价态。此处“低价态”指的是掺杂元素的化合价低于其最高稳定价态。
正极活性材料前驱体、锂源及掺杂元素前驱体可以采用球磨混合机或高速混合机来进行混合。将混合后的物料加入气氛烧结炉中进行烧结。烧结气氛为含氧气氛，例如为空气气氛或氧气气氛。可选的，含氧气氛的氧气浓度为80％～100％。烧结温度例如为600℃～1000℃。可选的，烧结温度为600℃～900℃，进一步地为700℃～900℃，这有利于使掺杂元素具有较高的分布均匀性。烧结时间可根据实际情况进行调节，例如为5h～25h，再例如为10h～20h。
需要说明的是，在正极活性材料制备时，具有多种理论可行的方式可以调控正极活性材料的结构及特性，调整其层状结构的规整程度及掺杂元素的位置和均匀程度，以及改变其在循环过程中的表面氧活性和平均价态，例如通过调控掺杂元素种类、掺杂元素含量、正极活性材料前驱体颗粒的形貌、正极活性材料制备中的烧结时间、烧结温度、烧结的次数及烧结时的氧气浓度等。在本申请中，列举了固相烧结掺杂方式的一些措施，通过调整烧结次数、分批掺入掺杂元素、控制整体烧结时间和烧结温度等方式，获得的正极活性材料在78％脱锂态时的表面氧平均价态V O为-2.0≤V O≤-1.5。应当理解的是，本说明书中所描述的方法，仅是为了解释本申请，并非为了限定本申请。
作为示例，可以将掺杂元素前驱体分为L个批次进行掺杂元素的掺杂，其中L可以是1～5，如2～3。在这些实施例中，正极活性材料的制备方法可以包括以下步骤：将正极活性材料前驱体、锂源及第1批次掺杂元素前驱体混合，并进行第1次烧结处理；之后将第1次烧结处理的产物与第2批次掺杂元素前驱体进行混合，并进行第2次烧结处理；以此类推，直至将第L-1次烧结处理的产物与第L批次掺杂元素前驱体进行混合，并进行第L次烧结处理，得到正极活性材料。
可以将掺杂元素前驱体等分为L份或任意分为L份，来进行L个批次的掺杂。
每次烧结处理的温度相同或不同。每次烧结处理的时间相同或不同。本领域技术人员可以根据掺杂元素的种类及掺杂量来进行烧结温度和时间的调整。例如，每次烧结处理的温度可以为600℃～1000℃，如600℃～900℃，再如700℃～900℃；每次烧结处理的时间可以为1h～20h，如2h～18h；总的烧结时间可以为5h～25h，如10h～20h。
在掺杂过程中，例如可以通过在一定范围内提高烧结温度和/或延长烧结时间来提高 掺杂均匀性。
在一些实施例中，还可以将烧结产物进行破碎处理并筛分，以获得具有优化的粒径分布及比表面积的正极活性材料。其中对破碎的方式并没有特别的限制，可根据实际需求进行选择，例如使用颗粒破碎机。
正极极片
本申请提供一种正极极片，其采用本申请任意一种或几种正极活性材料。
本申请实施例的正极极片由于采用了本申请的正极活性材料，因而能使锂离子二次电池同时兼顾良好的常温及高温循环性能和较高的能量密度。
具体地，正极极片包括正极集流体以及设置于正极集流体至少一个表面上的正极活性物质层。例如，正极集流体在自身厚度方向上包括相对的两个表面，正极活性物质层层叠设置于正极集流体的两个表面中的任意一者或两者上。
正极活性物质层包括本申请的正极活性材料。
另外，正极活性物质层中还可以包括导电剂和粘结剂。本申请对正极活性物质层中的导电剂及粘结剂的种类不做具体限制，可以根据实际需求进行选择。
作为示例，导电剂可以为石墨、超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中一种或多种；粘结剂可以为丁苯橡胶(SBR)、水性丙烯酸树脂(water-based acrylic resin)、羧甲基纤维素(CMC)、聚偏二氟乙烯(PVDF)、聚四氟乙烯(PTFE)、聚乙烯醇缩丁醛(PVB)、乙烯-醋酸乙烯酯共聚物(EVA)、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、含氟丙烯酸树脂及聚乙烯醇(PVA)中的一种或多种。
正极集流体可以采用导电性能及力学性能良好的金属箔材或多孔金属板，其材质可以为铝、铜、镍、钛、银及它们各自的合金中的一种或多种。正极集流体例如为铝箔。
正极极片可以按照本领域常规方法制备。例如将正极活性材料、导电剂及粘结剂分散于溶剂中，溶剂可以是N-甲基吡咯烷酮(NMP)或去离子水，形成均匀的正极浆料，将正极浆料涂覆在正极集流体上，经烘干、辊压等工序后，得到正极极片。
锂离子二次电池
本申请提供一种锂离子二次电池，其包括正极极片、负极极片、隔离膜和电解质，其中正极极片为本申请任意的正极极片。
锂离子二次电池由于采用了本申请的正极极片，因而能同时兼顾良好的常温及高温循环性能和较高的能量密度。
负极极片可以是金属锂片。
负极极片还可以是包括负极集流体以及设置于负极集流体至少一个表面上的负极活性物质层。例如，负极集流体在自身厚度方向上包括相对的两个表面，负极活性物质层层叠设置于负极集流体的两个表面中的任意一者或两者上。
负极活性物质层包括负极活性材料。本申请实施例对负极活性材料的种类不做具体地限制，可以根据实际需求进行选择。作为示例，负极活性材料可以是天然石墨、人造石墨、中间相微碳球(MCMB)、硬碳、软碳、硅、硅-碳复合物、SiO m(0<m<2，如m＝1)、Li-Sn合金、Li-Sn-O合金、Sn、SnO、SnO 2、尖晶石结构的钛酸锂Li 4Ti 5O 12、Li-Al合金及金属锂中的一种或多种。
负极活性物质层还可以包括导电剂和粘结剂。本申请实施例对负极活性物质层中的导电剂和粘结剂的种类不做具体限制，可以根据实际需求进行选择。作为示例，导电剂为石墨、超导碳、乙炔黑、炭黑、科琴黑、碳点、碳纳米管、石墨烯及碳纳米纤维中的一种或多种；粘结剂为丁苯橡胶(SBR)、聚偏二氟乙烯(PVDF)、聚四氟乙烯(PTFE)、聚乙烯醇缩丁醛(PVB)、水性丙烯酸树脂中的一种或多种。
负极活性物质层还可选地包括增稠剂，例如羧甲基纤维素钠(CMC-Na)。
负极集流体可以采用具有良好导电性能及力学性能的金属箔材或多孔金属板，其材质可以为铜、镍、钛、铁及它们各自的合金中的一种或多种。负极集流体例如为铜箔。
负极极片可以按照本领域常规方法制备。例如将负极活性物质、导电剂、粘结剂及增稠剂分散于溶剂中，溶剂可以是N-甲基吡咯烷酮(NMP)或去离子水，形成均匀的负极浆料，将负极浆料涂覆在负极集流体上，经烘干、辊压等工序后，得到负极极片。
本申请实施例的锂离子二次电池，电解质可以采用固体电解质，如聚合物电解质、无机固态电解质等，但并不限于此。电解质也可以采用电解液。作为上述电解液，包括溶剂和溶解于溶剂中的锂盐。
其中，溶剂可以为非水有机溶剂，例如碳酸亚乙酯(EC)、碳酸亚丙酯(PC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)、碳酸二甲酯(DMC)、碳酸二丙酯(DPC)、碳酸甲丙酯(MPC)、碳酸乙丙酯(EPC)、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)及丁酸乙酯(EB)中的一种或多种，例如两种以上。
锂盐可以为LiPF 6(六氟磷酸锂)、LiBF 4(四氟硼酸锂)、LiClO 4(高氯酸锂)、LiAsF 6(六氟砷酸锂)、LiFSI(双氟磺酰亚胺锂)、LiTFSI(双三氟甲磺酰亚胺锂)、LiTFS(三氟甲磺酸锂)、LiDFOB(二氟草酸硼酸锂)、LiBOB(双草酸硼酸锂)、LiPO 2F 2(二氟磷酸锂)、LiDFOP(二氟草酸磷酸锂)及LiTFOP(四氟草酸磷酸锂)中 的一种或多种，例如为LiPF 6(六氟磷酸锂)、LiBF 4(四氟硼酸锂)、LiBOB(双草酸硼酸锂)、LiDFOB(二氟草酸硼酸锂)、LiTFSI(双三氟甲磺酰亚胺锂)及LiFSI(双氟磺酰亚胺锂)中的一种或多种。
电解液中还可选地含有其它添加剂，例如碳酸亚乙烯酯(VC)、碳酸乙烯亚乙酯(VEC)、氟代碳酸亚乙酯(FEC)、二氟碳酸亚乙酯(DFEC)、三氟甲基碳酸亚乙酯(TFPC)、丁二腈(SN)、己二腈(ADN)、戊二腈(GLN)、己烷三腈(HTN)、1,3-丙烷磺内酯(1,3-PS)、硫酸亚乙酯(DTD)、甲基二磺酸亚甲酯(MMDS)、1-丙烯-1,3-磺酸内酯(PST)、4-甲基硫酸亚乙酯(PCS)、4-乙基硫酸亚乙酯(PES)、4-丙基硫酸亚乙酯(PEGLST)、硫酸亚丙酯(TS)、1,4-丁烷磺内酯(1,4-BS)、亚硫酸亚乙酯(DTO)、二甲基亚硫酸酯(DMS)、二乙基亚硫酸酯(DES)、磺酸酯环状季铵盐、三(三甲基硅烷)磷酸酯(TMSP)及三(三甲基硅烷)硼酸酯(TMSB)中的一种或多种，但并不限于此。
本申请实施例的锂离子二次电池对隔离膜没有特别的限制，可以选用任意公知的具有电化学稳定性和机械稳定性的多孔结构隔离膜，例如玻璃纤维、无纺布、聚乙烯(PE)、聚丙烯(PP)及聚偏二氟乙烯(PVDF)中的一种或多种的单层或多层薄膜。
将正极极片和负极极片交替层叠设置，并在正极极片与负极极片之间设置隔离膜以起到隔离的作用，得到电芯，也可以是经卷绕后得到电芯。将电芯置于外壳中，注入电解液，并封口，得到锂离子二次电池。
本申请对锂离子二次电池的形状没有特别的限制，其可以是圆柱形、方形或其他任意的形状。如图5是作为一个示例的方形结构的锂离子二次电池5。
在一些实施例中，二次电池可包括外包装。该外包装用于封装正极极片、负极极片和电解质。
在一些实施例中，参照图6，外包装可包括壳体51和盖板53。其中，壳体51可包括底板和连接于底板上的侧板，底板和侧板围合形成容纳腔。壳体51具有与容纳腔连通的开口，盖板53能够盖设于所述开口，以封闭所述容纳腔。
正极极片、负极极片和隔离膜可经卷绕工艺或叠片工艺形成电芯52。电芯52封装于所述容纳腔。电解质可采用电解液，电解液浸润于电芯52中。锂离子二次电池5所含电芯52的数量可以为一个或几个，可根据需求来调节。
在一些实施例中，锂离子二次电池的外包装可以是硬壳，例如硬塑料壳、铝壳、钢壳等。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，如可包括聚丙烯(PP)、聚对苯二甲酸丁二醇酯(PBT)、聚丁二酸丁二醇酯(PBS)等中的 一种或几种。
在一些实施例中，锂离子二次电池可以组装成电池模块，电池模块所含锂离子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7是作为一个示例的电池模块4。参照图7，在电池模块4中，多个锂离子二次电池5可以是沿电池模块4的长度方向依次排列设置。当然，也可以按照其他任意的方式进行排布。进一步可以通过紧固件将该多个锂离子二次电池5进行固定。
可选地，电池模块4还可以包括具有容纳空间的外壳，多个锂离子二次电池5容纳于该容纳空间。
在一些实施例中，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8和图9是作为一个示例的电池包1。参照图8和图9，在电池包1中可以包括电池箱和设置于电池箱中的多个电池模块4。电池箱包括上箱体2和下箱体3，上箱体2能够盖设于下箱体3，并形成用于容纳电池模块4的封闭空间。多个电池模块4可以按照任意的方式排布于电池箱中。
本申请还提供一种装置，所述装置包括本申请所述的锂离子二次电池、电池模块、或电池包中的至少一种。所述锂离子二次电池、电池模块或电池包可以用作所述装置的电源，也可以作为所述装置的能量存储单元。所述装置可以但不限于是移动设备(例如手机、笔记本电脑等)、电动车辆(例如纯电动车、混合动力电动车、插电式混合动力电动车、电动自行车、电动踏板车、电动高尔夫球车、电动卡车等)、电气列车、船舶及卫星、储能系统等。
所述装置可以根据其使用需求来选择锂离子二次电池、电池模块或电池包。
图10是作为一个示例的装置。该装置为纯电动车、混合动力电动车、或插电式混合动力电动车等。为了满足该装置对二次电池的高功率和高能量密度的需求，可以采用电池包或电池模块。
作为另一个示例的装置可以是手机、平板电脑、笔记本电脑等。该装置通常要求轻薄化，可以采用锂离子二次电池作为电源。
实施例
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
正极活性材料的制备
掺杂元素为Sb，将掺杂元素前驱体氧化锑Sb 2O 3大致等分为2个批次进行Sb的掺杂。制备方法包括：
将正极活性材料前驱体[Ni 0.8Co 0.1Mn 0.1](OH) 2、氢氧化锂LiOH及第1批次的氧化锑加入高速混料机中进行混料1h，得到混合物料，其中，正极活性材料前驱体与氢氧化锂的摩尔比Li/Me为1.05，Me表示正极活性材料前驱体中Ni、Co、Mn的总摩尔量；将混合物料放入气氛烧结炉中进行第1次烧结，烧结温度为850℃，烧结时间为8h，烧结气氛为O 2浓度为90％的含氧气氛。
将第1次烧结处理的产物与第2批次的氧化锑加入高速混料机中混料1h，并进行第2次烧结，烧结温度及烧结气氛与第1次烧结相同，烧结时间为12h。总烧结时间为20h。
第2次烧结处理的产物经破碎、过筛后，即可得到高镍三元正极活性材料。氧化锑的加入量使得正极活性材料中Sb的真实掺杂浓度为25090μg/cm 3。如图1所示，Sb在正极活性材料颗粒中均匀分布。
电解液的制备
将EC、DEC、DMC按照体积比1:1:1进行混合后，得到溶剂，再将锂盐LiPF 6溶解于上述溶剂中，获得电解液，其中LiPF 6的浓度为1mol/L。
扣式电池的制备
将上述制备的正极活性材料、导电炭黑及粘结剂PVDF按照重量比90:5:5分散至溶剂N-甲基吡咯烷酮(NMP)中进行混合均匀，得到正极浆料；将正极浆料均匀涂布于正极集流体铝箔上，经烘干、冷压后，得到正极极片。
在扣电箱中，将正极极片、隔离膜及金属锂片依次层叠设置，并注入上述电解液，组装得到扣式电池。
全电池的制备
将上述制备的正极活性材料、导电剂乙炔黑及粘结剂PVDF按照重量比94:3:3分散至溶剂NMP中进行混合均匀，得到正极浆料；将正极浆料均匀涂布于正极集流体铝箔上，经烘干、冷压后，得到正极极片。
将负极活性材料人造石墨、硬碳、导电剂乙炔黑、粘结剂丁苯橡胶(SBR)、增稠剂碳甲基纤维素钠(CMC)按照重量比90:5:2:2:1分散至去离子水中进行混合均匀，得到负极浆料；将负极浆料均匀涂布于负极集流体铝箔上，经烘干、冷压后，得到负极极片。
以聚乙烯(PE)多孔聚合薄膜作为隔离膜。将正极极片、隔离膜、负极极片按顺序叠好得到裸电芯，将裸电芯置于外包装中，注入上述电解液并封装，得到全电池。
实施例2～13、实施例16～21及对比例1～2
与实施例1不同的是，改变正极活性材料制备步骤中的相关参数，并调整掺杂元素混入时的种类、各批次含量、烧结温度650℃～850℃，总烧结时间10h～20h，获得具有预定掺杂元素种类、掺杂量及掺杂均匀性的正极活性材料；其中涉及多元素掺杂的实施例4和实施例12，各掺杂元素含量基本相同；对比例1未有掺杂元素加入；其余参数见表1。
实施例14、15
与实施例1不同的是，实施例14中掺杂元素单批次加入，烧结温度715℃；实施例15中的掺杂元素单批次加入，烧结温度670℃；其余参数见表1。
实施例22、23
与实施例1不同的是，实施例22中第1次烧结的温度为810℃、时间为12h，第2次烧结的温度为660℃、时间为2h，其中第2批掺杂元素占总掺杂元素含量的65％；
与实施例1不同的是，实施例23中第1次烧结的温度为790℃、时间为7h，第2次烧结的温度为630℃、时间为2h，其中第2批掺杂元素占总掺杂元素含量的75％。
实施例24、25与对比例3、4
与实施例1不同的是，实施例24、25与对比例4的正极活性材料前驱体是[Ni 0.5Co 0.2Mn 0.3](OH) 2，混入的掺杂元素种类存在差别；对比例3的正极活性材料前驱体是[Ni 0.5Co 0.2Mn 0.3](OH) 2，未有掺杂元素加入；其余参数见表1。
测试部分
1)“78％脱锂态”正极活性材料的表面氧平均价态V O及掺杂元素M的化合价测试
在25℃下，将18个扣式电池分别以1C恒流充电至充放电截止电压上限，再恒压充电至电流≤0.05mA，之后搁置2分钟，然后以1C恒流放电至充放电截止电压下限。
之后，将上述充放电后的18个扣式电池，分别以0.1C倍率充电到2.8V、2.9V、3.0V、3.1V、3.2V、3.3V、…、4.0V、4.1V、4.2V、4.3V、4.4V、4.5V(即充电电压间隔为0.1V)。取每个充电后的扣式电池，在干燥房中拆解出正极极片作为样品，称取记录样品质量后放入消解罐中，缓慢加入10mL王水作为消解试剂，之后放入CEM-Mars5微波消解仪中，以2450Hz微波发射频率进行消解；将消解后的样品溶液转移到容量瓶中摇匀，取样放入美国铂金埃尔默(PE)公司的7000DV型ICP-OES的进样系统，以0.6MPa氩气压力，1300W射频功率对正极活性材料进行Li、O、Ni、Co、Mn和掺杂元素质量浓度测试，基于各个元素的质量浓度换算得到每个电压下的化学式，进而得到每个电压下 的脱锂态。当用ICP-OES测试换算得到正极活性材料的化学式为Li 0.22Ni 0.8Co 0.1Mn 0.1O 2时，则对应的脱锂态为(1-0.22)×100％＝78％，对应的电压即为78％脱锂态对应的电压。
将包含待测正极活性材料的电池充电至“78％脱锂态”所对应的电压，之后在干燥房中用剪刀拆开电池，取出整个正极极片放入烧杯中，倒入适量高纯无水碳酸二甲酯(DMC)，每8h更换一次DMC，连续清洗3次，然后放入干燥房的真空静置箱中，保持抽真空状态为-0.096MPa，干燥12h；从将干燥后的正极极片作为XPS测试样品。
将极片样品通过3M绝缘胶带贴于Kratos公司的AXIS Supra型XPS的样品台上，自动进样后，抽真空至少1h。用单色Al靶(Al Kα，1486.6eV)作为激发源，以1eV步长、160eV通能进行全谱扫面，以0.1eV步长、40eV通能进行氧元素和掺杂元素的精细谱扫描，利用XPSpeak分峰软件，以C 1s的结合能为284.8eV进行荷电矫正；对p、d、f能级的光电子峰，设置分裂峰的峰强度比为：p 1/2:p 3/2＝1:2，d 3/2:d 5/2＝2:3，f 5/2:f 7/2＝3:4，通过分峰对标特定元素的标准XPS特征峰确定元素价态。
2)“78％脱锂态”正极活性材料的氧缺陷形成能ΔE O-vac的测试
(1)依据JIS K0131-1996 X射线衍射分析通则，采用BRUKER D8 DISCOVER型X射线衍射仪，以CuK α射线为辐射源，射线波长
Figure PCTCN2020109843-appb-000018
扫描2θ角范围为15°～70°，扫描速率为4°/min，对“78％脱锂态”正极活性材料进行XRD分析。基于XRD结果，获得“78％脱锂态”正极活性材料的晶胞参数、元素占位等信息，据此构建结构完整的正极活性材料在78％脱锂态的体相结构模型，其结构满足
Figure PCTCN2020109843-appb-000019
空间群，使用基于密度泛函理论的第一性原理的计算软件VASP，交换关联泛函采用GGA+U，对模型进行结构优化至能量收敛，提取优化后的结构能量，记为E pristine。
(2)在上述优化后的“78％脱锂态”的正极活性材料体相结构模型基础上，扣除一个氧原子，得到存在氧缺陷的正极活性材料在“78％脱锂态”的体相模型，使用基于密度泛函理论的第一性原理的计算软件VASP，交换关联泛函采用GGA+U，对含氧缺陷的体相模型进行结构优化至能量收敛，提取优化后的结构能量，记为E defect。
(3)使用基于密度泛函理论的第一性原理的计算软件VASP，交换关联泛函采用GGA+U，优化氧气分子至能量收敛，提取优化后的氧气能量除以2，记为E O。
(4)将E pristine、E defect和E O的数值代入前文所述的公式(1)，计算得到一个氧原子的氧缺陷形成能。
参照步骤(2)扣除不同的氧原子，以得到不同氧原子的缺陷形成能，并选择其中的最小值作为“78％脱锂态”的正极活性材料的体相结构氧缺陷形成能ΔE O-vac。
在步骤(1)、(2)、(3)，各个参数精度等于或高于如下参数：
Figure PCTCN2020109843-appb-000020
3)二次颗粒中掺杂元素的局部质量浓度的相对偏差σ测试
(1)二次颗粒中不同位点的掺杂元素的质量浓度测试
称取2g正极活性材料粉末样品，将样品均匀洒落在粘有导电胶的样品台上，再轻压使粉末固定，或者从电池正极极片中裁剪出1cm×1cm的极片，粘贴到样品台上作为待测样品。将样品台装入真空样品仓内并固定好，采用日本电子(JEOL)公司的IB-09010CP型氩离子截面抛光仪制备二次颗粒的截面，参照图2所示二次颗粒截面的17个位置取点，每个点的面积为20nm×20nm，采用英国牛津仪器集团的X-Max型能谱仪(EDS)结合德国ZEISS的Sigma-02-33型扫描电子显微镜(SEM)测试该17个位点的掺杂元素质量浓度，测试方法如下：检测元素选择Li、O、Ni、Co、Mn和掺杂元素，设置SEM参数为20kV加速电压，60μm光栏，8.5mm工作距离，2.335A电流，进行EDS-SEM测试时须待谱图面积达到250000cts以上(通过采集时间和采集速率来控制)时停止测试，并采集数据，得到各位点的掺杂元素的质量浓度η 1、η 2、η 3、…、η 17。
(2)二次颗粒中掺杂元素的平均质量浓度
Figure PCTCN2020109843-appb-000021
的测试
采取上述EDS-SEM测试方法，如图2虚线框所示，测试面积覆盖上述二次颗粒点扫描的所有点，且不超出该二次颗粒的截面。
(3)根据式(2)计算得到二次颗粒中掺杂元素的局部质量浓度的相对偏差σ。
4)正极活性材料的真实掺杂浓度ω测试：
采用北京彼奥德电子技术有限公司的TD2400型粉末真密度测试仪测定正极活性材料的真密度ρ 真，测试方法如下：25℃下取一定质量的正极活性材料置于样品杯中，记录正极活性材料的质量m；把装有正极活性材料的样品杯放入真密度仪测试腔中，密闭测试系统，通入氦气或氮气等小分子直径的惰性气体，通过检测样品室和膨胀室中的气体的压力，再根据玻尔定律PV＝nRT测量被测材料的真体积V，通过m/V计算得到二次颗粒的真密度ρ 真。其中n为样品杯中气体的摩尔量；R为理想气体常数，取8.314；T为环境温度，为298.15K。
采用美国铂金埃尔默(PE)公司的7000DV型ICP-OES测试正极活性材料中掺杂元素的质量浓度
Figure PCTCN2020109843-appb-000022
测试方法如下：取包含正极活性材料的极片冲成总质量大于0.5g的圆片 或取至少5g正极活性材料粉末样品，称取记录样品质量后放入消解罐中，缓慢加入10mL王水作为消解试剂，组装后放入美国CEM公司的Mars5型微波消解仪中，以2450Hz微波发射频率进行消解；将消解后的样品溶液转移到容量瓶中摇匀，取样放入PE7000DV型ICP-OES的进样系统，以0.6MPa氩气压力，1300W射频功率进行正极活性材料中掺杂元素的质量浓度测试。
之后根据前文所述的式(3)计算正极活性材料的真实掺杂浓度ω。
为了测试全电池中的正极活性材料，可以在干燥房中拆解电池，取出正极极片的中间部分放入烧杯中，倒入适量高纯无水碳酸二甲酯DMC，每8小时更换DMC，连续清洗3次，然后放入干燥房的真空静置箱中，保持抽真空状态(-0.096MPa)，干燥12小时，干燥后裁取预设大小的极片样品进行测试；或者用刀片在干燥房中刮取预定质量的正极活性材料粉末作为测试样品。
5)根据前文所述的式(4)计算正极活性材料中掺杂元素的质量浓度
Figure PCTCN2020109843-appb-000023
相对于二次颗粒中掺杂元素的平均质量浓度
Figure PCTCN2020109843-appb-000024
的偏差ε。
6)扣式电池的初始克容量测试
在25℃下，将电池以0.1C恒流充电至充放电截止电压上限，再恒压充电至电流小于等于0.05mA，之后搁置2分钟，然后以0.1C恒流放电至充放电截止电压下限，此次的放电容量即为扣式电池的初始克容量。
7)全电池的初始克容量测试
在25℃下，将电池以1/3C恒流充电至充放电截止电压上限，再恒压充电至电流小于等于0.05mA，之后搁置5分钟，然后以1/3C恒流放电至充放电截止电压下限，此次的放电容量即为全电池的初始克容量。
8)全电池的高温循环性能测试
在45℃下，将电池以1C恒流充电至充放电截止电压上限，再恒压充电至电流小于等于0.05mA，之后搁置5分钟，再以1C恒流放电至充放电截止电压下限，此为一个充放电循环，此次的放电容量记为第1次循环的放电比容量D 1。将电池按照上述方法进行400次循环充放电测试，记录第400次循环的放电比容量D 400。
全电池45℃、1C/1C循环400次容量保持率(％)＝D 400/D 1×100％
以上测试中：在实施例1～23及对比例1～2，扣式电池的充放电截止电压为2.8V～4.25V，全电池的充放电截止电压为2.8V～4.2V；在实施例24～25及对比例3～4，扣式电池的充放电截止电压为2.8V～4.35V，全电池的充放电截止电压为2.8V～4.3V。
实施例1～25和对比例1～4的测试结果示于表1和表2。
表1
Figure PCTCN2020109843-appb-000025
表1中，化合价为示出了掺杂元素的最低价态和最高价态；各批次质量比＝第1批次掺杂元素前驱体的质量∶第2批次掺杂元素前驱体的质量。
表2
Figure PCTCN2020109843-appb-000026
由实施例1～21与对比例1～2、实施例24至25与对比例3～4的比较结果可以看出，通过使正极活性材料的过渡金属位包括掺杂元素M，掺杂元素M的化合价为+3价以上，且正极活性材料在78％脱锂态的表面氧平均价态V O为-2.0～-1.5，锂离子二次电池不仅拥有较高的初始克容量，而且还兼具较高的高温循环性能。
由实施例1、5～12的结果可以看出，当掺杂量过小时，掺杂元素对正极材料结构稳定性提升不足，导致电池的容量较低，高温循环性能较差。当掺杂量超过49100μg/cm 3时， 过多的掺杂元素破坏了原有的正极结构，电池的容量和45℃循环性能同样不如真实掺杂浓度为2300μg/cm 3～49100μg/cm 3的正极活性材料。
由实施例13～15的结果可以看出，当二次颗粒中掺杂元素的局部质量浓度的相对偏差为20％以下时，掺杂元素在活性材料内部分布非常均匀，对材料的稳定性提升比较明显，相应电芯的容量和循环性能较优。反之，当二次颗粒中掺杂元素的局部质量浓度的相对偏差超过20％后，掺杂不均匀区域的晶格应力大，恶化了电池的容量和高温循环性能。
由实施例1、22、23的结果可以看出，当正极活性材料满足ε在30％以下时，说明较多的掺杂元素已掺入二次颗粒内部，充分发挥掺杂元素对正极材料结构稳定性的提升作用，提高了电池容量和高温循环性能。而当ε大于30％时，较多的掺杂元素分布在二次颗粒的缝隙或表面，掺杂元素对正极活性材料的改善效果不佳，但分布在表面的掺杂元素起到一定的包覆隔绝电解液副反应作用，因此此时电芯容量和高温循环性能略有下降。
以上所述，仅为本申请的具体实施方式，但本申请的保护范围并不局限于此，任何熟悉本技术领域的技术人员在本申请揭露的技术范围内，可轻易想到各种等效的修改或替换，这些修改或替换都应涵盖在本申请的保护范围之内。因此，本申请的保护范围应以权利要求的保护范围为准。

Claims (20)

  1. 一种正极活性材料，包括含镍的锂复合氧化物，所述含镍的锂复合氧化物满足化学式Li 1+a[Ni xCo yMn zM b]O 2，式中，M为过渡金属位掺杂元素，0.5≤x<1，0≤y<0.3，0≤z<0.3，-0.1≤a<0.2，0<b<0.3，x+y+z+b＝1，其中，
    所述正极活性材料具有层状晶体结构，属于
    Figure PCTCN2020109843-appb-100001
    空间群；
    所述正极活性材料在78％脱锂态时，至少部分所述掺杂元素M的化合价为+3价以上、且所述正极活性材料的表面氧平均价态V O满足-2.0≤V O≤-1.5。
  2. 根据权利要求1所述的正极活性材料，其中，所述正极活性材料包括由一次颗粒聚集而成的二次颗粒，所述二次颗粒中所述掺杂元素M的局部质量浓度的相对偏差为32％以下，可选为20％以下。
  3. 根据权利要求1或2所述的正极活性材料，其中，所述正极活性材料在78％脱锂态的体相结构氧缺陷形成能ΔE O-vac满足：ΔE O-vac≥0.5eV；可选的，ΔE O-vac≥0.7eV；可选的，ΔE O-vac≥1.0eV。
  4. 根据权利要求1至3任一项所述的正极活性材料，其中，所述正极活性材料在78％脱锂态时，所述掺杂元素M具有两个以上不同的价态，且处于最高价态的所述掺杂元素M的化合价为+4价、+5价、+6价、+7价及+8价中的一种或多种，可选的为+5价、+6价、+7价及+8价中的一种或多种。
  5. 根据权利要求1至4任一项所述的正极活性材料，其中，所述掺杂元素M包括Ti、V、Se、Zr、Nb、Ru、Pd、Sb、Te及W中的一种或多种；可选的，掺杂元素M包括Ti、Se、Zr、Nb、Ru、Sb、Te及W中的一种或多种。
  6. 根据权利要求1至5任一项所述的正极活性材料，其中，所述正极活性材料的真实掺杂浓度ω满足2300μg/cm 3≤ω≤49100μg/cm 3，可选的3000μg/cm 3≤ω≤30000μg/cm 3，可选的14830μg/cm 3≤ω≤49080μg/cm 3，可选的24890μg/cm 3≤ω≤31210μg/cm 3。
  7. 根据权利要求1至6任一项所述的正极活性材料，其中，所述正极活性材料中所述掺杂元素M的质量浓度相对于所述正极活性材料的颗粒中所述掺杂元素M的平均质量浓度的偏差ε满足ε<50％；可选的，ε≤30％；可选的，ε≤20％。
  8. 根据权利要求1至7任一项所述的正极活性材料，其中，所述正极活性材料的真密度ρ 真满足4.6g/cm 3≤ρ 真≤4.9g/cm 3。
  9. 根据权利要求1至8任一项所述的正极活性材料，其中，所述正极活性材料还满足如下(1)～(4)中的一个或多个：
    (1)所述正极活性材料的体积平均粒径D v50为5μm～20μm，可选的为8μm～15μm，进一步可选的为9μm～11μm；
    (2)所述正极活性材料的比表面积为0.2m 2/g～1.5m 2/g，可选的为0.3m 2/g～1m 2/g；
    (3)所述正极活性材料的振实密度为2.3g/cm 3～2.8g/cm 3；
    (4)所述正极活性材料在5吨(相当于49kN)压力下的压实密度为3.1g/cm 3～3.8g/cm 3。
  10. 根据权利要求1至9任一项所述的正极活性材料，其中，0.7≤x≤0.9，0<y<0.3，0<z<0.3；
    所述正极活性材料在78％脱锂态的表面氧平均价态V O为-1.9≤V O≤-1.6。
  11. 一种正极活性材料的制备方法，包括以下步骤：
    将正极活性材料前驱体、锂源和掺杂元素前驱体混合，得到混合料，其中所述正极活性材料前驱体选自含有Ni、可选的Co和可选的Mn的氧化物、氢氧化物及碳酸盐中的一种或多种；
    在含氧气氛、600℃～1000℃温度下对所述混合料烧结处理，得到正极活性材料；
    其中，所述正极活性材料包括含镍的锂复合氧化物，所述含镍的锂复合氧化物满足化学式Li 1+a[Ni xCo yMn zM b]O 2，式中，M为过渡金属位掺杂元素，0.5≤x<1，0≤y<0.3，0≤z<0.3，-0.1≤a<0.2，0<b<0.3，x+y+z+b＝1；
    所述正极活性材料具有层状晶体结构，属于
    Figure PCTCN2020109843-appb-100002
    空间群；
    所述正极活性材料在78％脱锂态时，至少部分所述掺杂元素M的化合价为+3价以上、且所述正极活性材料的表面氧平均价态V O为-2.0≤V O≤-1.5。
  12. 根据权利要求11所述的方法，其中，所述掺杂元素前驱体选自钛氧化物、钒氧化物、硒氧化物、锆氧化物、铌氧化物、钌氧化物、钯氧化物、锑氧化物、碲氧化物及钨氧化物中的一种或多种；可选的，所述掺杂元素前驱体选自TiO 2、TiO、V 2O 5、V 2O 4、V 2O 3、SeO 2、ZrO 2、Nb 2O 5、NbO 2、RuO 2、PdO、Sb 2O 5、Sb 2O 3、TeO 2、WO 2、WO 3中的一种或多种。
  13. 根据权利要求11或12所述的方法，其中，所述烧结处理满足如下中的至少一项：
    所述含氧气氛的氧气浓度为80％～100％；
    烧结处理的温度为600℃～900℃，可选的为700℃～900℃；
    烧结处理的时间为5h～25h，可选的为10h～20h。
  14. 根据权利要求11-13任一项所述的方法，其中，将所述掺杂元素前驱体等分为L份或任意分为L份，分为L个批次进行掺杂，其中L为1～5，可选的为2～3，其中包括：将正极活性材料前驱体、锂源及第1批次掺杂元素前驱体混合，并进行第1次烧结处理；将第1次烧结处理的产物与第2批次掺杂元素前驱体进行混合，并进行第2次烧结处理；以此类推，直至将第L-1次烧结处理的产物与第L批次掺杂元素前驱体进行混合，并进行第L次烧结处理，得到正极活性材料。
  15. 根据权利要求14所述的方法，其中，每次烧结处理的温度为600℃～1000℃，可选的为600℃～900℃，还可选的为700℃～900℃；每次烧结处理的时间为1h～20h，可选的为2h～18h；总的烧结处理时间为5h～25h，可选的为10h～20h。
  16. 一种正极极片，包括正极集流体以及设置于所述正极集流体上的正极活性物质层，所述正极活性物质层包括根据权利要求1至10任一项所述的正极活性材料、或根据权利要求11至15任一项所述的制备方法得到的正极活性材料。
  17. 一种锂离子二次电池，包括根据权利要求16所述的正极极片。
  18. 一种电池模块，包括根据权利要求17所述的锂离子二次电池。
  19. 一种电池包，包括根据权利要求17所述的锂离子二次电池、或根据权利要求18所述的电池模块。
  20. 一种装置，包括根据权利要求17所述的锂离子二次电池、根据权利要求18所述的电池模块、或根据权利要求19所述的电池包中的至少一种。
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