WO2021189997A1 - 正极材料及其制备方法，正极、锂离子电池和车辆 - Google Patents

正极材料及其制备方法，正极、锂离子电池和车辆 Download PDF

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WO2021189997A1
WO2021189997A1 PCT/CN2020/137771 CN2020137771W WO2021189997A1 WO 2021189997 A1 WO2021189997 A1 WO 2021189997A1 CN 2020137771 W CN2020137771 W CN 2020137771W WO 2021189997 A1 WO2021189997 A1 WO 2021189997A1
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positive electrode
salt solution
particles
electrode material
precursor
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PCT/CN2020/137771
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French (fr)
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朱金鑫
王鹏飞
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蜂巢能源科技有限公司
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Priority to EP20927634.4A priority Critical patent/EP4131485A4/en
Priority to US17/764,568 priority patent/US20230009617A1/en
Publication of WO2021189997A1 publication Critical patent/WO2021189997A1/zh

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    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
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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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Definitions

  • the present invention relates to the field of materials, in particular, to a positive electrode material and a preparation method thereof, a positive electrode, a lithium ion battery and a vehicle.
  • the cathode material is an important factor that determines the energy density and safety performance of the battery.
  • lithium nickel cobalt manganate LiNi a Co b Mn (1-ab) O 2 , LNCM is a relatively important ternary cathode material.
  • the positive electrode material can increase its specific capacity through high nickel, thereby meeting the requirement of high energy density of the battery.
  • continuously increasing the nickel content will cause problems such as a decrease in the stability of the material's crystal structure and serious lithium/nickel mixing problems in the crystal lattice, which will affect the cycle performance and safety performance of the lithium-ion battery.
  • cathode materials especially high nickel content lithium nickel cobalt manganese oxide cathode materials and preparation methods, cathodes, lithium ion batteries and vehicles still need to be improved.
  • the present invention is made based on the inventor's discovery and recognition of the following facts and problems:
  • the single crystal form of the cathode material can solve the cycle performance problem caused by the grain boundary stress inside the particles, the electrolyte of this type of cathode material still has serious corrosion of the cathode material, poor conductivity of the material, or the gap between the cathode material and the electrolyte. Problems such as poor interface quality and poor stability. Therefore, if at least one of the above problems can be improved while maintaining the single crystal structure of the cathode material, the performance of the lithium cobalt phosphate cathode material with high nickel content will be further improved to a large extent.
  • the present invention provides a cathode material.
  • the positive electrode material includes: base particles, the base particles are single crystal particles, the single crystal particles include lithium nickel manganese oxide and lithium nickel cobalt manganate, the base particles have a buffer layer near the surface layer, the buffer layer The content of at least one of Ni, Co, and Mn is lower than the content at other positions of the matrix particles.
  • the positive electrode material has at least one of the advantages of high specific capacity, the buffer layer can alleviate the corrosion of the electrolyte and inhibit the precipitation of active oxygen, and the cycle stability and safety performance are better.
  • the chemical formula of the cathode material matrix is Li 1+ ⁇ Ni ⁇ Mn ⁇ Co ⁇ M (1- ⁇ - ⁇ - ⁇ ) O 2 , where 0 ⁇ 0.1, 0.8 ⁇ 1, 0.01 ⁇ 0.1, 0 ⁇ 0.1, 0.01 ⁇ 1- ⁇ - ⁇ - ⁇ 0.05, M is selected from at least one of Al, Ti, Mg, Zr, Zn, Ce and Cr, N is selected It is selected from at least one of O, F, B, and P, and the molar content of the M element in the buffer layer is higher than the molar content of the non-buffer layer. As a result, the performance of the positive electrode material can be further improved.
  • the chemical formula of the cathode material matrix is Li 1+ ⁇ Ni ⁇ Mn ⁇ Co ⁇ M (1- ⁇ - ⁇ - ⁇ ) O 2 , where 0 ⁇ 0.1, 0.8 ⁇ 1, 0.01 ⁇ 0.1, 0 ⁇ 0.1, M is selected from at least one of Al, Ti, Mg, Zr, Zn, Ce, and Cr, and N is selected from at least one of O, F, B, and P
  • M is selected from at least one of Al
  • N is selected from at least one of O, F, B, and P
  • the molar content of the M element in the buffer layer is higher than the molar content of the non-buffer layer.
  • the positive electrode material further includes a coating layer covering the surface layer of the base particles, the coating layer does not contain Li, Ni, Co, and Mn, and the coating layer is M' ⁇ N ⁇ , the M'includes any one or a combination of at least two of Al, Ti, Mg, Zr, Zn, Ce, Cr, and B, and N is any of O, F, B, and P One or a combination of at least two, wherein 1 ⁇ 3, 1 ⁇ 6, and the type of M'in the coating layer is the same as the M in the matrix particles. As a result, the performance of the positive electrode material can be further improved.
  • M′ includes any one or a combination of at least two of Al, Ti, Zr, and Mg. As a result, the performance of the positive electrode material can be further improved.
  • the coating layer is at least one of AlF 3 , TiO 2 , Al 2 O 3 , and ZrO.
  • the thickness of the coating layer is 10-100 nm. As a result, the performance of the positive electrode material can be further improved.
  • the positive electrode material satisfies at least one of the following conditions: the particle size of the base particles is 0.2-10 ⁇ m; the distance between the buffer layer and the surface layer of the base particles is 0.05-0.5 ⁇ m .
  • the performance of the positive electrode material can be further improved.
  • the present invention provides a method for preparing the aforementioned positive electrode material.
  • the method includes: under the conditions suitable for the crystal growth of the precursor particles, the precursor raw materials including the metal salt solution and the alkaline solution are separately injected into a closed reactor for co-precipitation to obtain the precursor Particles; the precursor particles and the lithium salt are mixed and subjected to the first calcination treatment to obtain a positive electrode material.
  • the method is easy to operate, and the obtained positive electrode material has at least one of the advantages of higher specific capacity, better cycle stability, and better safety performance.
  • the buffer layer can alleviate the corrosion of the electrolyte and inhibit the precipitation of active oxygen.
  • the metal salt solution includes a nickel salt solution, a cobalt salt solution, and a manganese salt solution
  • the precursor raw material includes an M salt solution
  • the method includes: The injection rate of the M salt solution is reduced, and the injection rate of at least one of the nickel salt solution, cobalt salt solution, and manganese salt solution is reduced until the end of crystal growth of the precursor particles, and all of the The injection rate of the metal salt solution and the M salt solution is restored to the initial injection rate until the co-precipitation ends, and the M in the M salt includes at least of Al, Ti, Mg, Zr, Zn, Ce, and Cr
  • the first predetermined time is earlier than the end of crystal growth of the precursor particles.
  • the first predetermined time is the time required for the co-precipitation reaction to reach the particle size of the precursor particles from 90% to 99% of the predetermined particle size.
  • the precursor particles of the single crystal particles can be better formed.
  • the injection flow rates of the nickel salt solution, the cobalt salt solution and the manganese salt solution are respectively and independently reduced by 30%-50% of the initial value of the flow rate.
  • the precursor particles of the single crystal particles can be better formed.
  • the injection flow rate of the M salt solution is increased to 120%-140% of the initial value of the flow rate.
  • the precursor particles of the single crystal particles can be better formed.
  • the method further includes the steps of filtering, washing and drying the reaction product after the co-precipitation is completed;
  • the particle size of the precursor is 1 ⁇ m-8 ⁇ m.
  • the precursor particles of the single crystal particles can be better formed.
  • the specific surface area of the precursor is 5m 2 /g-25m 2 /g.
  • the precursor particles of the single crystal particles can be better formed.
  • the tap density of the precursor is 1.1 g/cc-1.9 g/cc.
  • the precursor particles of the single crystal particles can be better formed.
  • the method further includes: mixing the positive electrode material with a coating agent and performing a second calcination treatment to form a coating layer, and the coating agent satisfies at least one of the following conditions:
  • the coating agent includes aluminum isopropoxide, aluminum fluoride, aluminum oxide, cerium oxide, titanium isopropoxide, titanium oxide, boron oxide, boric acid, magnesium oxide, zirconium oxide, zirconium n-butoxide, ammonium fluoride, fluoride At least one of ammonium dihydrogen, ammonium monohydrogen fluoride, and magnesium metaborate; the particle size of the coating agent does not exceed 50 nm. As a result, the performance of the final cathode material can be further improved.
  • the present invention provides a positive electrode.
  • the positive electrode includes a positive electrode piece, and a positive electrode material distributed on the positive electrode piece.
  • the positive electrode material is the aforementioned positive electrode material or is prepared by the aforementioned method.
  • the positive electrode has all the features and advantages of the positive electrode material described above, and will not be repeated here.
  • the positive electrode has at least one of the advantages of strong stability of the positive electrode active material, and the lithium ion battery prepared by using the positive electrode has higher specific capacity, good cycle performance, and better stability.
  • the present invention provides a lithium ion battery.
  • the lithium ion battery includes the aforementioned positive electrode, negative electrode, and a separator separating the positive electrode and the negative electrode.
  • the lithium-ion battery has all the features and advantages of the aforementioned positive electrode, which will not be repeated here.
  • the lithium ion battery has at least one of the advantages of high specific capacity, good cycle performance, and good stability.
  • the present invention provides a vehicle.
  • the vehicle includes the aforementioned lithium-ion battery. Therefore, the vehicle has all the features and advantages of the aforementioned lithium-ion battery, which will not be repeated here. In general, the vehicle has at least one of the advantages of higher mileage, better safety performance and stability, and less mileage attenuation.
  • Fig. 1 shows a schematic structural diagram of a cathode material according to an embodiment of the present invention
  • Fig. 2 shows a schematic structural diagram of a cathode material according to another embodiment of the present invention
  • Fig. 3 shows a schematic structural diagram of a positive electrode according to an embodiment of the present invention
  • Figure 4 shows a schematic flow chart of a method for preparing a positive electrode material according to an embodiment of the present invention
  • Fig. 5 shows scanning electron microscope images of the positive electrode material according to the embodiment 1 to the embodiment 4 of the present invention
  • Fig. 6 shows a scanning electron microscope image of a positive electrode material according to Comparative Example 1 of the present invention
  • Fig. 7 shows a scanning electron microscope image of a positive electrode material according to Comparative Example 2 of the present invention
  • FIG. 8 shows the first charge and discharge curves of the positive electrode material according to the embodiment 1 to the embodiment 4 of the present invention
  • FIG. 9 shows the discharge specific capacity curves of the cathode materials according to the embodiment 1 to the embodiment 4 of the present invention under different current densities
  • Fig. 10 shows the cycle curves of the discharge specific capacity of the positive electrode materials according to Examples 1 to 4 of the present invention during 50 cycles.
  • the present invention provides a cathode material.
  • the cathode material 100 includes base particles 110 formed of single crystal particles.
  • the base particles 110 have a buffer layer 120 near the surface layer.
  • the content of at least one of Ni, Co, and Mn in the buffer layer is lower than that of the base particles. Content at other locations.
  • the positive electrode material has at least one of the following advantages: higher specific capacity, better cycle stability and safety performance, etc., and the buffer layer can alleviate the corrosion of the electrolyte and inhibit the precipitation of active oxygen.
  • M is selected from at least one of Al, Ti, Mg, Zr, Zn, Ce, and Cr
  • N is selected from at least one of O, F, B, and P
  • the molar content of the M element in the buffer layer is higher than Molar content at the non-buffer layer.
  • the chemical formula of the matrix particles may also satisfy 0 ⁇ 0.1, 0.8 ⁇ 1, 0.01 ⁇ 0.1, and 0 ⁇ 0.1.
  • the cathode material can be an LNCM material with a high nickel content and an M doping element.
  • M can be one or more of Al, Ti, Mg, Zr, Zn, Ce, and Cr, for example, it can contain two, Three or more M metals.
  • the positive electrode material also has one or more non-metallic N elements, and N is selected from at least one of O, F, B, and P, for example, it may contain one, two or more of the above-mentioned N elements. element.
  • the content of M doping elements in the positive electrode material proposed by the present invention can be higher. For example, when M is Al, the content of Al in the positive electrode material can exceed 1% (atomic ratio).
  • the specific structure of the positive electrode material and the principle of obtaining the above-mentioned beneficial effects will be described according to specific embodiments of the present invention.
  • the following embodiments are only for explaining and describing the present invention, and should not be construed as limiting the present invention.
  • the structure shown in FIG. 1 is only used to facilitate the description of the relative positional relationship between the base particles 110 and the buffer layer 120, and cannot be understood as a limitation on the shape of the positive electrode material particles.
  • the particles in the single crystal form may include lithium nickel manganese oxide and lithium nickel cobalt manganese oxide materials.
  • the buffer layer 120 is located near the surface layer of the base particles, and the chemical composition of the buffer layer 120 is different from other positions of the base particles, for example, the center position of the base particles and the chemical composition of the surface layer outside the buffer layer are different.
  • the content of at least one of Ni, Co, and Mn in the buffer layer 120 is relatively low, and the content of other elements contained in the matrix particles, such as the aforementioned M, is relatively high, such as Al, Ti, Mg, Zr, Zn, and Ce.
  • the content of, Cr, B and other elements is relatively high.
  • the cathode material may have a certain particle size.
  • at least 80% of the matrix particles have a particle size in the range of 1.5-10 microns
  • the thickness of the buffer layer can be no more than 200nm
  • the buffer layer can be located inside the matrix particles 0.05-0.5 microns from the outer surface.
  • the entire cathode material can be within a relatively suitable size range, and the thickness of the buffer layer outside the matrix particles is moderate, which will not fail to function due to being too thin, nor will the lithium ion mobility decrease due to being too thick. And other negative effects.
  • the buffer layer may seriously affect the migration and diffusion rate of lithium ions. When a large current is released, the buffer layer is too thick, which will cause the lithium ions to suffer too much "resistance".
  • the thickness of the buffer layer may specifically be 40-60 nm.
  • the positive electrode material is usually micron-sized particles, and the positive electrode material is composed of a plurality of particles having the aforementioned structure. Therefore, the particle size of the structure of the positive electrode material or the matrix particles is the average particle size of the positive electrode material, or the particle size range of most of the particles included in the structure of the positive electrode material, such as 50% or more or 80% or more. , 90% or more of the particle size range. Therefore, the particle size of some positive electrode materials can be larger or smaller than the above range. For example, the particle size of the positive electrode material can be in the range of 0.5-13 microns.
  • the cathode material may further include a coating layer 130.
  • the coating layer 130 may cover the surface layer of the base particles 110.
  • the base particles 110 of the positive electrode material may be composed of single crystal particles of lithium nickel manganate or lithium nickel cobalt manganate.
  • the chemical formula of the coating layer may be M' ⁇ N ⁇ , where M'includes any one or a combination of at least two of Al, Ti, Mg, Zr, Zn, Ce, Cr, and B , N is any one or a combination of at least two of O, F, B, and P, where 1 ⁇ 3 and 1 ⁇ 6.
  • the type of M'in the coating layer is the same as that of M in the base particles.
  • the coating layer may contain the aforementioned compound formed by the M element and the N element in the base particles.
  • it may contain at least one of halide, oxide, fluoride, and phosphide of the M element.
  • the coating layer 130 does not contain Li, Ni, Co, and Mn, and may contain substances composed of M and N elements in the matrix particles.
  • it may be in the form of at least one of fluoride and oxide.
  • the coating layer 130 may be AlF 3 , TiO 2 , Al 2 O 3 , ZrO, or the like.
  • the types of metal elements in the buffer layer and the coating layer can be the same, that is, the types of metal elements in the buffer layer can be the same as the types of metal elements contained in the coating layer, and the number is the same: when the buffer layer contains m types
  • the coating layer also contains m types of metals, and the elements of the m types of metals in the buffer layer and the m types of metals in the coating layer are completely the same, for example, they may be Al, Ti, or Zr at the same time. Therefore, on the one hand, it is beneficial to improve the conductivity of the positive electrode material and stabilize the interface of the positive electrode material/electrolyte.
  • the coating layer with the above-mentioned structure has the same M element with the buffer layer, so it is compatible The performance is better, which is beneficial to further improve the performance of the cathode material.
  • the chemical composition of the positive electrode material can satisfy:
  • M is selected from at least one of Al, Ti, Mg, Zr, Zn, Ce, and Cr, and N is selected from O, F, B and P At least one of.
  • the chemical composition of the cathode material can satisfy:
  • M is selected from at least one of Al, Ti, Mg, Zr, Zn, Ce, and Cr, and N is selected from at least one of O, F, B, and P.
  • the positive electrode material structure composed of the above-mentioned single crystal particles is also suitable for lithium nickel cobalt aluminate (LNCA) positive electrode materials.
  • LNCA lithium nickel cobalt aluminate
  • a buffer layer and a coating layer are formed outside the matrix particles (single crystal particles) of the positive electrode material, which further improves the conductivity of the positive electrode material, improves the interface between the positive electrode material and the electrolyte, and improves the stability. Therefore, when the cathode material is applied to a lithium ion battery, the lithium ion battery can also have better cycle performance.
  • the present invention provides a method for preparing the aforementioned positive electrode material.
  • the method is simple to operate, and the obtained positive electrode material has at least one of the advantages of specific capacity, higher cycle stability, and better safety performance.
  • the buffer layer can alleviate the corrosion of the electrolyte and inhibit the precipitation of active oxygen.
  • the precursor materials including the metal salt solution and the alkaline solution are separately injected into a closed reactor for co-precipitation to obtain the precursor particles . Since the injection of the metal salt solution and the alkaline solution is adjusted according to the crystal growth conditions suitable for the precursor particles, the precursor particles obtained in this step are subjected to subsequent calcination treatment to obtain matrix particles with a single crystal morphology.
  • the metal salt solution includes a plurality of metal salt solutions, for example, may include a nickel salt solution, a cobalt salt solution, and a manganese salt solution.
  • the precursor raw material also includes an M salt solution, and the M element may include at least one of Al, Ti, Mg, Zr, Zn, Ce, and Cr.
  • the salt solutions of multiple metals and M may be solutions of the same salt, for example, all solutions of sulfate or nitrate.
  • concentration of the metal salt solution and the M salt solution and the types of metal ions in the various metal salt solutions can be adjusted by those skilled in the art according to the chemical composition of the cathode material to be formed.
  • the concentrations of the various metal salt solutions can be independently 25-150g/L, for example 60-150g/L, specifically 50g/L, 70g/L, 80g/L, 90g/L, 100g/L, 120g/L, etc., or may be in the range of 25-150 Any point value within, or within the range formed by any two point values in 25-150.
  • the sulfate concentration of nickel can be 150-300g/L
  • the sulfate concentration of cobalt can be 10-20g/L
  • the sulfate concentration of manganese can be 10-20g/
  • the concentration of M salt solution can be 10-20g/L. L.
  • the concentration can be adjusted according to the chemical composition of the positive electrode particles to be prepared.
  • the molar content of nickel, cobalt, manganese and M in the positive electrode material can roughly meet: the molar content of nickel is 88%, the molar content of cobalt is 6%, and the molar content of manganese is 88%. It is 3% and the molar content of M is about 3%.
  • Those skilled in the art can adjust the concentration of the salt solution of nickel, cobalt, manganese and M elements according to the above-mentioned molar content.
  • the specific type of the alkaline solution is not particularly limited. Those skilled in the art can choose a familiar alkaline solution.
  • the alkaline solution may include ammonia water and sodium hydroxide solution, and the concentration of the alkaline solution may be 80- 240g/L.
  • the specific injection rate of the metal salt solution and the alkaline solution is not particularly limited, and those skilled in the art can use the volume of the reaction vessel, the concentration of the metal salt solution and the alkaline solution, and the specific chemical composition of the positive electrode material. Confirm and adjust.
  • the specific injection rate of the metal salt solution and the alkaline solution can be adjusted so that the pH of the solution in the reactor during the co-precipitation reaction is 10.5-11.9, for example, greater than 11 and less than 12.
  • the metal salt solution and the alkaline solution are separately injected into the closed reactor under the conditions suitable for the crystal growth of the precursor particles.
  • the closed reactor may be a reactor or the like.
  • the injection rate of the metal salt solution may be dynamically adjusted, and the dynamic adjustment is performed based on the crystal growth of the precursor particles.
  • the time at the end of particle growth can be estimated according to the crystal particle growth kinetic model, so as to adjust the flow rate (ie, the injection rate) of the metal salt solution injected into the reactor, for example, increase or decrease during a certain period of crystal growth.
  • the flow rate of the metal salt solution is adjusted to the initial flow rate value of each metal salt solution after the crystal growth stage is over, until the co-precipitation reaction ends.
  • the formed precursor particles can undergo the subsequent first calcination treatment to form single-crystal matrix particles, so as to finally obtain a positive electrode material without multiple grain boundaries inside.
  • the above-mentioned salt solution may include multiple salt solutions, and each salt solution may have an independent initial injection rate.
  • the injection rate is to adjust the injection rate of each salt solution independently, that is, to increase or decrease relative to the initial injection rate of the salt solution, and after the crystal growth phase is over, the salt The injection rate of the solution is restored to the initial injection rate of the salt solution of this element.
  • the initial injection rates of the above-mentioned multiple M elements may be equal or unequal, and the initial injection rates of the nickel salt solution, the cobalt salt solution, and the manganese salt solution may also be equal or unequal.
  • "adjust to its initial flow rate value" and "recover the initial injection rate" are relative to its own initial injection rate.
  • the injection rate of the nickel salt solution is restored to nickel
  • the injection rate of the cobalt salt solution is restored to the initial injection rate of the cobalt salt solution
  • the injection rate of the manganese salt solution is restored to the initial injection rate of the manganese salt solution.
  • the particle size distribution of the precursor particles can be monitored in real time during the co-precipitation process, and the injection rate of the metal salt solution can be adjusted based on the particle size distribution.
  • a part of the solution can be regularly extracted from a reaction vessel such as a reactor, and the particle size distribution can be analyzed by using instruments including but not limited to a laser particle size analyzer.
  • the injection rate of the M salt solution can be increased after the first predetermined time, and the injection rate of the nickel salt solution, cobalt salt solution, and manganese salt solution can be reduced until the end of the crystal growth of the precursor particles , And then restore the injection rate of all salt solutions to the initial injection rate until the end of co-precipitation.
  • the first predetermined time may be the time taken for the co-precipitation reaction to reach the particle size of the precursor particles from 90% to 99% of the preset particle size.
  • the injection flow rates of the nickel salt solution, cobalt salt solution and manganese salt solution can be independently reduced by 30%-50% of the initial value of the flow rate to increase the M salt solution
  • the injection flow rate is 120%-140% of the initial value of the flow rate.
  • M has a high concentration distribution area and a low concentration distribution area.
  • the molar ratio of M contained in the low concentration distribution area to the M contained in the high concentration distribution area is 0.01-0.5, and the low concentration distribution area is located.
  • the central area and the surface layer of the precursor particles, the high concentration distribution area is located within the range of 0.05-0.5 microns from the surface of the precursor particles, and a buffer layer can be formed in the subsequent steps.
  • the positive electrode material formed by the precursor particles with two concentration regions of M may have higher stability.
  • deionized water can be added to the reactor in advance and the temperature is increased to 40-90 degrees Celsius, and the temperature is 700-1100 rpm. Stir at a high speed, and then inject the metal salt solution, M salt solution and alkaline solution under stirring.
  • the product in the reactor can be filtered, washed, and vacuum dried to obtain precursor particles.
  • the product in the reactor can be filtered, and the filter residue is washed with deionized water and vacuum dried at 100-150 degrees Celsius for 6-12 hours.
  • the particle size of the precursor particles obtained in this step can range from 1 to 8 microns, the specific surface area can be 5-25 m 2 /g, and the tap density of the precursor particles is 1.1-1.9 g/cc.
  • the precursor particles thus obtained are ideal, which facilitates the subsequent first calcination treatment to obtain a positive electrode material with appropriate matrix particle size and better interface performance.
  • the chemical composition of the precursor particles obtained in this step can be:
  • the precursor particles and the lithium salt are mixed and subjected to a first calcination treatment to obtain a positive electrode material.
  • the specific type of lithium salt is not particularly limited, for example, it may be one or more of LiOH ⁇ H 2 O, LiF, Li 2 CO 3 and CH 3 COOLi.
  • the mixing ratio of the lithium salt and the precursor particles can be adjusted by those skilled in the art according to the chemical composition of the cathode material to be prepared.
  • the calcination temperature of the first calcination treatment may be 800-880 degrees Celsius, the rate of temperature increase during the first calcination treatment is 1.5-10 degrees Celsius/min, and the time of the first calcination treatment is 8-25 hours And the first calcination treatment is carried out in an oxygen atmosphere.
  • the precursor particles and the lithium salt may be respectively subjected to grinding treatment and vacuum drying treatment before mixing the precursor particles and the lithium salt.
  • the precursor particles and the lithium salt can be crushed in a manner including but not limited to grinding, etc., to obtain particles with a particle size of nanometer level, and then vacuum-dried.
  • the mixing of the lithium salt and the precursor particles can be carried out by mixing the powder with a mortar or the like, or by a high-speed mixer, as long as the two can be uniformly mixed before the first calcination treatment. Then, after the above-mentioned first-stage calcination treatment, the positive electrode material can be obtained.
  • the method may further include a step of forming a coating layer.
  • the positive electrode material and the coating agent are mixed, and the second calcination treatment is performed to form a coating layer on the surface of the matrix particles of the positive electrode material.
  • the structure and chemical composition of the positive electrode material the detailed description has been made above, and will not be repeated here.
  • the positive electrode material may be subjected to crushing treatment, cleaning treatment and vacuum drying treatment in sequence before mixing the positive electrode material and the coating agent.
  • the positive electrode material can be washed in a certain volume of deionized water for 3-10 minutes, and then the washed positive electrode material can be vacuum dried.
  • the vacuum drying can be carried out at 120-180 degrees Celsius, and the drying time can be 2-10 hours.
  • the coating agent may include aluminum isopropoxide, aluminum fluoride, aluminum oxide, cerium oxide, titanium isopropoxide, titanium oxide, boron oxide, boric acid, magnesium oxide, zirconium oxide, zirconium n-butoxide , At least one of ammonium fluoride, ammonium dihydrogen fluoride, ammonium monohydrogen fluoride and magnesium metaborate, and the particle size of the coating agent is not greater than 50nm.
  • the metal element in the coating agent can be selected from the same material as the M metal in the cathode material preform (for example, it may be metal elements other than Li, Co, Co, and Ni in the cathode material). , Which can better ensure the batch consistency of the product.
  • the temperature of the second calcination treatment may be 350-650 degrees Celsius
  • the temperature rise rate of the second calcination treatment may be 1-5 degrees Celsius/min
  • the time may be 3-15 hours. Carried out in an oxygen or nitrogen atmosphere.
  • the present invention provides a positive electrode.
  • the positive electrode includes: a positive pole piece 200, and a positive electrode material 100 distributed on the positive pole piece.
  • the positive electrode material 100 is the aforementioned one or is prepared by the aforementioned method. Therefore, the positive electrode has all the features and advantages of the positive electrode material described above, and will not be repeated here.
  • the positive electrode has at least one of the advantages of strong stability of the positive electrode active material, higher specific capacity, good cycle performance, and better stability of the lithium ion battery prepared by using the positive electrode.
  • the positive electrode may also have a structure including but not limited to tabs 210 to facilitate connection when forming a battery.
  • the structure shown in FIG. 3 is only for the convenience of showing the positional relationship between the positive pole piece 200 and the positive electrode material 100, and cannot be understood as a restriction on the specific position and distribution mode of the positive electrode material 100.
  • the positive electrode material 100 may be dispersed on a carrier including but not limited to an electrolyte, and distributed on the positive electrode sheet 200 by means of coating, rolling, or the like.
  • the present invention provides a lithium ion battery.
  • the lithium ion battery includes the aforementioned positive electrode, negative electrode, and a separator separating the positive electrode and the negative electrode.
  • the lithium-ion battery has all the features and advantages of the aforementioned positive electrode, which will not be repeated here.
  • the lithium ion battery has at least one of the advantages of high specific capacity, good cycle performance, and good stability.
  • the specific type of the lithium ion battery is not particularly limited.
  • a liquid electrolyte may be used, or an all-solid lithium ion battery may be used.
  • the lithium ion battery can also contain multiple independent sub-batteries, and has a structure such as a soft pack battery module.
  • the present invention provides a vehicle.
  • the vehicle includes the aforementioned lithium-ion battery. Therefore, the vehicle has all the features and advantages of the aforementioned lithium-ion battery, which will not be repeated here. In general, the vehicle has at least one of the advantages of higher mileage, better safety performance and stability, and less mileage attenuation.
  • the lithium ion battery may be used for driving a vehicle.
  • the specific location of the lithium ion battery in the vehicle is not particularly limited, and those skilled in the art can make a selection according to the actual situation. Since the battery has better safety and stability, it can have more flexible choices when selecting the specific location of the power battery.
  • nickel sulfate, cobalt sulfate, and manganese sulfate solutions with a concentration of about 130g/L, aluminum sulfate solution with a concentration of about 40g/L, and a ammonia solution with a concentration of about 150g/L and a sodium hydroxide solution with about 130g/L to the reactor.
  • 1.1L of deionized water was added to the reactor, the reaction kettle was heated to a constant temperature of 65°C, the pH of the reaction process was controlled to be about 11.4, the entire co-precipitation reaction time was 36h, and the stirring rate was 950rpm.
  • the feed flow rate of the nickel sulfate, cobalt sulfate, and manganese sulfate solutions was reduced to 30% of the initial value, and the aluminum sulfate solution feed flow rate was increased to 120% of the initial value.
  • the obtained material was filtered, washed with deionized water, and vacuum dried at 130 degrees Celsius for 10 hours to obtain precursor particles with a chemical composition of Ni 0.88 Co 0.06 Mn 0.03 Al 0.03 (OH) 2.
  • the dried cathode material preform powder material is thoroughly mixed with 4016ppm AlF 3 (particle size ⁇ 50nm), and then placed in a 500°C calciner, heating rate 1.5°C/min, and calcined in an oxygen atmosphere for 6h, and finally fully in a mortar After grinding or crushing in an ultracentrifugal grinding mill, a positive electrode material is obtained.
  • the chemical composition of the positive electrode material is 0.996LiNi 0.88 Co 0.06 Mn 0.03 Al 0.03 O 2 ⁇ 0.004AlF 3 .
  • the scanning electron microscope image is shown in Figure 5(a).
  • the feed flow rate of the nickel sulfate, cobalt sulfate, and manganese sulfate solutions was reduced to 30% of the initial value, and the titanium sulfate solution feed flow rate was increased to 130% of the initial value.
  • the obtained material was filtered, washed with deionized water, and vacuum dried at 130 degrees Celsius for 10 hours to obtain a precursor with a chemical formula of Ni 0.88 Co 0.06 Mn 0.03 Ti 0.03 (OH) 2.
  • the calcined powder sample was washed in deionized water for about 10 minutes and then dried in vacuum. Mix the dried powder material with 4016ppm TiO 2 (particle size ⁇ 50nm) thoroughly, then place it in a 550 degree Celsius calciner at a heating rate of 1.5 degrees Celsius/min, calcine in an oxygen atmosphere for 5.5 hours, and finally grind it in a mortar or ultra After being crushed in a centrifugal grinding mill, the molecular formula of the positive electrode material is 0.996LiNi 0.88 Co 0.06 Mn 0.03 Ti 0.03 O 2 ⁇ 0.004TiO 2 .
  • the scanning electron microscope image is shown in Figure 5(b).
  • nickel sulfate, cobalt sulfate, and manganese sulfate solutions with a concentration of about 130g/L, aluminum sulfate solution with a concentration of about 40g/L, and a ammonia solution with a concentration of about 150g/L and a sodium hydroxide solution with about 130g/L to the reactor.
  • 1.1L of deionized water was added to the reactor, the reaction kettle was heated to a constant temperature of 65°C, the pH of the reaction process was controlled to be about 11.4, the entire co-precipitation reaction time was 36h, and the stirring rate was 950rpm.
  • the feed flow rate of the nickel sulfate, cobalt sulfate, and manganese sulfate solutions was reduced to 30% of the initial value, and the aluminum sulfate solution feed flow rate was increased to 120% of the initial value.
  • the obtained material was filtered, washed with deionized water, and vacuum dried at 130°C for 10 hours to obtain a precursor with a chemical formula of Ni 0.88 Co 0.06 Mn 0.03 Al 0.03 (OH) 2.
  • the molecular formula of the positive electrode material is 0.996LiNi 0.88 Co 0.06 Mn 0.03 Al 0.03 O 2 ⁇ 0.004Al 2 O 3 .
  • the scanning electron microscope image is shown in Figure 5(c).
  • the feed flow rate of the nickel sulfate, cobalt sulfate, and manganese sulfate solutions was reduced to 30% of the initial value, and the zirconium sulfate solution feed flow rate was increased to 120% of the initial value.
  • the obtained material was filtered, washed with deionized water, and vacuum dried at 130 degrees Celsius for 10 hours to obtain a precursor with a chemical formula of Ni 0.88 Co 0.06 Mn 0.03 Zr 0.03 (OH) 2.
  • the dried cathode material preform powder material is thoroughly mixed with 4016ppm AlF 3 (particle size ⁇ 50nm), and then placed in a 500°C calciner, heating rate 1.5°C/min, and calcined in an oxygen atmosphere for 6h, and finally fully in a mortar After grinding or crushing in an ultracentrifugal grinding mill, a positive electrode material is obtained.
  • the chemical composition of the positive electrode material is 0.996LiNi 0.88 Co 0.06 Mn 0.03 Al 0.03 O 2 ⁇ 0.004AlF 3 .
  • Fig. 8 is the first charge and discharge curve corresponding to the positive electrode materials prepared in Examples 1-4.
  • the charge and discharge rates are 0.1C/0.1C, and the voltage range is 3-4.3V. It can be seen from Fig. 8 that the positive electrode materials prepared in Examples 1 to 4 all exhibited good initial charge and discharge performance.
  • the charge-discharge specific capacities are respectively 232.1mAh/g, 204.6mAh/g; 225.4mAh/g, 201.2mAh/g; 237.2mAh/g, 212.4mAh/g; 230mAh/g, 206.3mAh/g, both exceeding 200mAh /g.
  • Figure 9 shows the specific discharge capacity of the cathode materials prepared in Examples 1-4 under different current densities.
  • the charge and discharge rates are 0.1C/0.1C, 0.5C/0.5C, 0.5C/1C, 0.5C/2C, and the voltage range is 3-4.3V. It can be seen from FIG. 9 that when the discharge rate is 1C, the specific discharge capacity corresponding to each embodiment is 186 mAh/g, 179.6 mAh/g, 189.5 mAh/g and 187.5 mAh/g in order, and the rate performance is better.
  • the cycle capacity retention rate corresponding to each embodiment is 93.3%, 96.7%, 95.8%, and 94.7%, and the cycle capacity retention rate has reached a relatively high level. Therefore, the buffer layer and particle surface coating layer proposed by the present invention can maintain a high cycle stability of the sample and stabilize the crystal structure of the material.
  • the sample obtained by the evaluation comparative example 1 has a charge and discharge specific capacity of 234.8mAh/g and 202mAh/g at a rate of 0.1C, respectively; the first coulombic efficiency is 86%; the specific discharge capacity at a rate of 1C is 173mAh/g; and the charge rate is 0.5C.
  • the capacity retention rate was 91% after 50 charge-discharge cycles under 1C rate and discharge rate.
  • the specific capacity of the sample obtained in Comparative Example 2 was 233.1mAh/g and 203.9mAh/g at 0.1C rate, respectively; the first coulombic efficiency was 87.4%; the specific capacity at 1C rate was 180mAh/g; at the rate of 0.5C and 0.5C
  • the capacity retention rate was 89% after 50 charge-discharge cycles under 1C discharge rate. It can be seen that the samples according to the embodiments of the present invention have better cycle performance.

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Abstract

一种正极材料（100）及制备方法，正极、锂离子电池和车辆。该正极材料（100）包括：基体颗粒（110），所述基体颗粒（110）是单晶颗粒，所述单晶颗粒包括镍锰酸锂和镍钴锰酸锂，所述基体颗粒（110）中靠近表层处具有缓冲层（120），所述缓冲层（120）中Ni、Co、Mn元素的至少之一的含量低于所述基体颗粒（110）其他位置处的含量。该正极材料（100）具有比容量较高、循环稳定性与安全性能较好等优点的至少之一，缓冲层（120）可缓解电解液侵蚀以及抑制活性氧的析出。

Description

正极材料及其制备方法，正极、锂离子电池和车辆 技术领域
本发明涉及材料领域，具体地，涉及正极材料及其制备方法，正极、锂离子电池和车辆。
背景技术
随着绿色能源的推广以及能源安全和城市空气质量改善要求的不断提升，汽车电动化成为汽车行业的一个重要发展方向。近年来动力锂离子电池市场快速增长，但当前电动汽车的性能表现仍有待改善，其中续航里程和安全性问题尤为突出。而对于动力锂离子电池而言，正极材料是决定电池的能量密度和安全性能的重要因素。在目前已经实现商业化的正极材料中，镍钴锰酸锂(LiNi aCo bMn (1-a-b)O 2，LNCM)是较为重要的三元正极材料。该正极材料可通过高镍化增加其比容量，进而满足电池高能量密度的需求。然而不断提高镍含量会导致材料晶体结构稳定性下降以及晶格中锂/镍混排问题严重等问题，从而影响锂离子电池的循环性能以及安全性能。
因而，目前的正极材料，特别是高镍含量的镍钴锰酸锂正极材料及制备方法，正极、锂离子电池和车辆仍有待改进。
发明内容
本发明是基于发明人对于以下事实和问题的发现和认识作出的：
虽然单晶形式的正极材料可解决颗粒内部的晶界应力导致的循环性能问题，但该类型的正极材料仍存在电解液侵蚀正极材料较为严重，材料导电性欠佳或正极材料和电解液之间界面质量不佳、稳定性差等问题。因此，如能够在保持正极材料的单晶结构的同时改善上述问题中的至少之一，则将在很大程度上进一步提升高镍含量的磷酸钴锂正极材料的性能。
在本发明的一个方面，本发明提出了一种正极材料。该正极材料包括：基体颗粒，所述基体颗粒是单晶颗粒，所述单晶颗粒包括镍锰酸锂和镍钴锰酸锂，所述基体颗粒中靠近表层处具有缓冲层，所述缓冲层中Ni、Co、Mn元素的至少之一的含量低于所述基体颗粒其他位置处的含量。该正极材料具有比容量较高，缓冲层可缓解电解液侵蚀以及抑制活性氧的析出，循环稳定性与安全性能较好等优点的至少之一。
根据本发明的实施例，所述正极材料基体的化学式为Li 1+λNi αMn βCo γM (1-α-β-γ)O 2，其中，0≤λ<0.1，0.8≤α<1，0.01≤β<0.1，0≤γ<0.1，0.01≤1-α-β-γ≤0.05，M选自Al、Ti、Mg、Zr、Zn、Ce以及Cr中的至少一种，N选自O、F、B以及P中的至少一种，并且M元素在所述缓冲层中的摩尔含量高于在非缓冲层处的摩尔含量。由此，可进一步提高该正极材料的性能。
根据本发明的实施例，所述正极材料基体的化学式为Li 1+λNi αMn βCo γM (1-α-β-γ)O 2，其中，0≤λ<0.1，0.8≤α<1，0.01≤β<0.1，0≤γ<0.1，M选自Al、Ti、Mg、Zr、Zn、Ce以及Cr中的至少一种，N选自O、F、B以及P中的至少一种，并且M元素在所述缓冲层中的摩尔含量高于在非缓冲层处的摩尔含量。由此，可进一步提高该正极材料的性能。
根据本发明的实施例，该正极材料进一步包括包覆层，所述包覆层覆盖所述基体颗粒的表层，所述包覆层不含有Li、Ni、Co和Mn，所述包覆层为M' μN ν，所述M'包括Al、Ti、Mg、Zr、Zn、Ce、Cr和B中的任意一种或至少两种的组合，N为O、F、B、P中的任意一种或至少两种的组合，其中，1≤μ≤3，1≤ν≤6，所述包覆层中的M'的种类与所述基体颗粒中的M相同。由此，可进一步提高该正极材料的性能。
根据本发明的实施例，M'包括Al、Ti、Zr和Mg中的任意一种或至少两种的组合。由此，可进一步提高该正极材料的性能。
根据本发明的实施例，所述包覆层为AlF 3、TiO 2、Al 2O 3、ZrO中的至少一种。
根据本发明的实施例，所述包覆层的厚度为10-100nm。由此，可进一步提高该正极材料的性能。
根据本发明的实施例，所述正极材料的化学式为aLi 1+λNi αMn βCo γM (1-α-β-γ)O 2·bM μN ν，其中，a+b＝1，0<a<1，0<b<1。
根据本发明的实施例，所述正极材料满足以下条件的至少之一：所述基体颗粒的粒径为0.2-10微米；所述缓冲层距离所述基体颗粒的表层的距离为0.05-0.5μm。由此，可进一步提高该正极材料的性能。
在本发明的又一方面，本发明提出了一种制备前面所述的正极材料的方法。该方法包括：在适于所述前驱体颗粒的晶体生长的条件下，将包括金属盐溶液以及碱性溶液在内的前驱体原料分别独立地注入密闭的反应器中进行共沉淀以获得前驱体颗粒；将所述前驱体颗粒以及锂盐混合并进行第一煅烧处理，以获得正极材料。该方法操作简便，且获得的正极材料具有比容量较高、循环稳定性与安全性能较好等优点的至少之一，缓冲层可缓解电解液侵蚀以及抑制活性氧的析出。
根据本发明的实施例，所述金属盐溶液包括镍的盐溶液、钴的盐溶液、锰的盐溶液，所述前驱体原料包括M盐溶液，所述方法包括：在第一预定时间后提高所述M盐溶液注入速度，并降低所述镍的盐溶液、钴的盐溶液、锰的盐溶液中的至少之一的注入速度，直至所述前驱体颗粒的晶体生长末期，并将全部所述金属盐溶液和所述M盐溶液的注入速度恢复为初始注入速度，直至所述共沉淀结束，所述M盐中的M包括Al、Ti、Mg、Zr、Zn、Ce以及Cr中的至少一种，所述第一预定时间早于所述前驱体颗粒的晶体生长末期。由此，可简便地获得可形成单晶颗粒的前驱体颗粒。
根据本发明的实施例，所述第一预定时间为共沉淀反应至颗粒的粒度达到所述前驱体颗粒的预设粒度的90％-99％所用的时间。由此，可更好地形成单晶颗粒的前驱体颗粒。
根据本发明的实施例，分别独立地降低所述的镍的盐溶液、钴的盐溶液和锰的盐溶液的注入流速为其流速初始值的30％-50％。由此，可更好地形成单晶颗粒的前驱体颗粒。
根据本发明的实施例，提高M盐溶液的注入流速为流速的初始值的120％-140％。由此，可更好地形成单晶颗粒的前驱体颗粒。
根据本发明的实施例，所述方法还包括在共沉淀结束后，对反应产物进行过滤、洗涤和干燥的步骤；
根据本发明的实施例，所述前驱体粒度为1μm-8μm。由此，可更好地形成单晶颗粒的前驱体颗粒。
根据本发明的实施例，所述前驱体比表面积为5m 2/g-25m 2/g。由此，可更好地形成单晶颗粒的前驱体颗粒。
根据本发明的实施例，所述前驱体振实密度为1.1g/cc-1.9g/cc。由此，可更好地形成单晶颗粒的前驱体颗粒。
根据本发明的实施例，所述方法进一步包括：将所述正极材料与包覆剂进行混合并进行第二煅烧处理以形成包覆层，所述包覆剂满足以下条件的至少之一：所述包覆剂包括异丙醇铝、氟化铝、氧化铝、氧化铈、异丙醇钛、氧化钛、氧化硼、硼酸、氧化镁、氧化锆、正丁醇锆、氟化氨、氟化二氢铵、氟化一氢铵以及偏硼酸镁中的至少之一；所述包覆剂的颗粒尺寸不超过50nm。由此，可进一步提升最终获得的正极材料的性能。
在本发明的又一方面，本发明提出了一种正极。该正极包括：正极极片，以及分布于所述正极极片上的正极材料，所述正极材料为前面所述的正极材料，或是利用前面所述的方法制备的。该正极具有前面描述的正极材料所具有的全部特征以及优点，在此不再赘述。总的来说，该正极具有正极活性材料稳定性强，利用该正极制备的锂离子电池的比容量较高、循环性能好、稳定性较好等优点的至少之一。
在本发明的又一方面，本发明提出了一种锂离子电池。该锂离子电池包括前面描述的正极、负极，以及将正极以及负极之间绝缘间隔的隔膜。该锂离子电池具有前述的正极的全部特征以及优点，在此不再赘述。总的来说，该锂离子电池具有比容量较高、循环性能好、稳定性较好等优点的至少之一。
在本发明的又一方面，本发明提出了一种车辆。该车辆包括前面所述的锂离子电池。由此，该车辆具有前述的锂离子电池的全部特征以及优点，在此不再赘述。总的来说，该车辆具有里程数较高、安全性能以及稳定性较好，里程衰减较小等优点的至少之一。
附图说明
本发明的上述和/或附加的方面和优点从结合下面附图对实施例的描述中将变得明显和容易理解，其中：
图1显示了根据本发明一个实施例的正极材料的结构示意图；
图2显示了根据本发明另一个实施例的正极材料的结构示意图；
图3显示了根据本发明一个实施例的正极的结构示意图；
图4显示了根据本发明一个实施例的制备正极材料的方法的流程示意图；
图5显示了根据本发明实施例1-实施例4的正极材料的扫描电子显微镜图；
图6显示了根据本发明对比例1的正极材料的扫描电子显微镜图；
图7显示了根据本发明对比例2的正极材料的扫描电子显微镜图；
图8显示了根据本发明实施例1-实施例4的正极材料的首次充放电曲线；
图9显示了根据本发明实施例1-实施例4的正极材料在不同电流密度下的放电比容量曲线；
图10显示了根据本发明实施例1-实施例4的正极材料在50个循环过程中放电比容量的循环曲线。
具体实施方式
下面详细描述本发明的实施例，所述实施例的示例在附图中示出，其中，在不冲突的情况下，本发明中的实施例及实施例中的特征可以相互组合。下面通过参考附图描述的实施例是示例性的，仅用于解释本发明，而不能理解为对本发明的限制。
在本发明的一个方面，本发明提出了一种正极材料。参考图1，该正极材料100包括由单晶颗粒形成的基体颗粒110，基体颗粒110中靠近表层处具有缓冲层120，缓冲层中Ni、Co、Mn元素的至少之一的含量低于基体颗粒其他位置处的含量。该正极材料具有以下优点的至少之一：比容量较高、循环稳定性与安全性能较好等，缓冲层可缓解电解液侵蚀以及抑制活性氧的析出。根据本发明的实施例，基体颗粒的化学式可以为aLi 1+λNi αMn βCo γM (1-α-β-γ)O 2，其中，a+b＝1，0<a<1，0<b<1，0≤λ<0.1，0.5≤α<1，0.3≤β<1，0≤γ<0.2，0.01≤1-α-β-γ≤0.05。M选自Al、Ti、Mg、Zr、Zn、Ce以及Cr中的至少一种，N选自O、F、B以及P中的至少一种，并且M元素在缓冲层中的摩尔含量高于在非缓冲层处的摩尔含量。根据本发明一些具体的实施例，该基体颗粒的化学式还可满足0≤λ<0.1，0.8≤α<1，0.01≤β<0.1，0≤γ<0.1。
即该正极材料可以为具有高镍含量的LNCM材料，且具有M掺杂元素，M可为Al、Ti、Mg、Zr、Zn、Ce、Cr中一种或多种，例如可含有两种、三种或三种以上M金属。类似地，该正极材料中还具有一种或多种非金属N元素，N选自O、F、B以及P中的至少一种，例如可含有一种、两种或是两种以上上述N元素。需要特别说明的是，本发明提出的正极材料中M掺杂元素的含量可较高，例如当M为Al时，Al在该正极材料中的含量可超过1％(原子比)。
下面根据本发明的具体实施例，对该正极材料的具体结构及可获得上述有益效果的原理进行说明，下述的实施例仅为了解释和说明本发明，而不能够理解为对本发明的限制。例如图1中所示出的结构仅为了方便描述基体颗粒110、缓冲层120的相对位置关系，而不能够理解为对正极材料颗粒形状的限制。
该单晶形式的颗粒可包括镍锰酸锂和镍钴锰酸锂材料。缓冲层120位于基体颗粒中靠近表层的位置处，且缓冲层120的化学组成与基体颗粒其他位置不同，例如基体颗粒的中心位置以及位于缓冲层外侧的表层处的化学组成不同。具体地，缓冲层120处Ni、Co、Mn元素的至少之一的含量较低，基体颗粒含有的其他元素，如前述的M含量较高，具体例如Al、Ti、Mg、Zr、Zn、Ce、Cr、B等元素的含量较高。
根据本发明的实施例，该正极材料可具有一定的粒径。根据本发明的一些示例，至少80％的基体颗粒的颗粒粒径在1.5-10微米的范围内，缓冲层的厚度可以为不大于200nm，缓冲层可位于基体颗粒内部距离外表面0.05-0.5微米的近表层范围内。由此，该正极材料整体可处于一个较为适宜的尺寸范围内，且基体颗粒外部的缓冲层厚度适中，不会由于过薄而无法发挥作用，也不会由于过厚而导致锂离子迁移率降低等负面效果。例如，缓冲层过厚可能严重影响锂离子的迁移和扩散速率，在大电流放下时由于缓冲层过厚而导致锂离子受到“阻力”过大。缓冲层的厚度具体可以为40-60nm。本领域技术人员熟悉的是，正极材料通常为微米级别的颗粒，正极材料由多个具有前述结构的颗粒构成。因此正极材料或是基体颗粒等结构的粒径为正极材料的平均粒径，或是正极材料等结构中包括的多个颗粒中大多数颗粒的粒径范围，例如50％以上或是80％以上、90％以上的颗粒的粒径范围。因此，部分正极材料的颗粒粒径可大于或小于上述范围，例如正极材料的颗粒尺寸可以在0.5-13微米范围内，基体颗粒100中可存在粒径可大于10微米并小于12.5微米的颗粒。
根据本发明的实施例，参考图2，该正极材料还可以进一步包括包覆层130。包覆层130可覆盖基体颗粒110的表层。如前所述，该正极材料的基体颗粒110可由镍锰酸锂或是镍钴锰酸锂的单晶颗粒构成。根据本发明的实施例，包覆层的化学式可以为M' μN ν，其中M'包括Al、Ti、Mg、Zr、Zn、Ce、Cr和B中的任意一种或至少两种的组合，N为O、F、B、P中的任意一种或至少两种的组合，其中，1≤μ≤3，1≤ν≤6。包覆层中的M'的种类与基体颗粒中的M相同。也即是说，包覆层中可含有前述的基体颗粒中的M元素以及N元素形成的化合物。例如，可含有M元素的卤化物、氧化物、氟化物以及磷化物的至少之一。换句话说，包覆层130中不含有Li、Ni、Co和Mn，可含有基体颗粒中M和N元素构成的物质。例如可以具有氟化物和氧化物的至少之一的形式呈现，具体地包覆层130可为AlF 3、TiO 2、Al 2O 3、ZrO等等。例如具体地，缓冲层和包覆层中金属元素的类型可相同，即缓冲层中的金属元素的种类可以与包覆层中含有的金属元素的种类相同数量也相同：当缓冲层含有m种金属元素时，包覆层也含有m种金属，且缓冲层的m种金属和包覆层中的m种金属的元素是完全相同的，例如可同时为Al、同时为Ti或同时为Zr。由此，一方面有利于提升该正极材料的导电性，起到稳定正极材料/电解液界面的作用，另一方面，具有上述构成的包覆层由于和缓冲层具有共同的M元素，因此兼容性较好，有利于进一步提升该正极材料的性能。
根据本发明的实施例，当该正极材料具有包覆层时，该正极材料的化学组成可满足：
aLi 1+λNi αMn βCo γM (1-α-β-γ)O 2·bM μN ν，
其中a+b＝1，0<a≤1，0≤b<1，0≤λ<0.1，0.5≤α<1，0.3≤β<1，0≤γ<0.2，0.01≤1-α-β-γ≤0.05，1≤μ≤3，1≤ν≤6，M选自Al、Ti、Mg、Zr、Zn、Ce、Cr中的至少一种，N选自O、F、B以及P中的至少一种。
或者，该正极材料的化学组成可满足：
aLi 1+λNi αMn βCo γM (1-α-β-γ)O 2·bM μN ν，
其中a+b＝1，0<a<1，0<b<1，0≤λ<0.1，0.8≤α<1，0.01≤β<0.1,0≤γ<0.1，1≤μ≤3，1≤ν≤6，M选自Al、Ti、Mg、Zr、Zn、Ce、Cr中的至少一种，N选自O、F、B以及P中的至少一种。
发明人发现，上述单晶颗粒构成的正极材料结构同样适用于镍钴铝酸锂(LNCA)正极材料中。特别地，本申请在正极材料的基体颗粒(单晶颗粒)外部形成有缓冲层和包覆层，进一步提升了正极材料的导电性，改善了正极材料与电解液之间的界面并提高了稳定性，因此该正极材料应用于锂离子电池中时，可令该锂离子电池也具有较好的循环性能。
在本发明的另一方面，本发明提出了一种制备前面所述的正极材料的方法。该方法操作简便，且获得的正极材料具有比容量、较高循环稳定性与安全性能较好等优点的至少之一，缓冲层可缓解电解液侵蚀以及抑制活性氧的析出。参考图4，该方法包：
S100：获得前驱体颗粒
在该步骤中，在适于前驱体颗粒的晶体生长的条件下，将包括金属盐溶液以及碱性溶液在内的前驱体原料分别独立地注入密闭的反应器中进行共沉淀以获得前驱体颗粒。由于金属盐溶液和碱性溶液的注入是根据适于前驱体颗粒的晶体生长条件而调节的，因此该步骤中获得的前躯体颗粒经过后续的煅烧处理可获得具有单晶形态的基体颗粒。
根据本发明的实施例，金属盐溶液包括多种金属的盐溶液，例如可包括镍的盐溶液、钴的盐溶液、锰的盐溶液。前驱体原料还包括M盐溶液，M元素可包括Al、Ti、Mg、Zr、Zn、Ce、Cr中的至少一种。多种金属和M的盐溶液可为同一种盐的溶液，例如均为硫酸盐或硝酸盐的溶液。金属盐溶液以及M盐溶液的浓度和多种金属盐溶液中金属离子的类型本领域技术人员可根据需要形成的正极材料的化学组成进行调节，例如多种金属盐溶液的浓度可以分别独立地为25-150g/L，例如可以为60-150g/L，具体可为50g/L、70g/L、80g/L、90g/L、100g/L、120g/L等，或可为25-150范围内的任意点值，或在由25-150中的任意两个点值构成的范围内。具体地，镍的硫酸盐浓度可以为150-300g/L，钴的硫酸盐浓度可以为10-20g/L，锰的硫酸盐浓度可以为10-20g/，M的盐溶液浓度10-20g/L。该浓度可根据需要制备的正极颗粒的化学组成进行调整，例如正极材料中镍、钴、锰和M元素的摩尔含量可大致满足：镍摩尔含量88％、钴摩尔含量为6％、锰摩尔含量为3％、M摩尔含量约为3％。本领域技术人员可根据上述摩尔含量调整镍、钴、锰和M元素的盐溶液的浓度。碱溶液的具体类型也不受特别限制，本领域 技术人员可选择熟悉的碱溶液，例如根据本发明的一些实施例，碱溶液可以包括氨水和氢氧化钠溶液，碱溶液的浓度可以为80-240g/L。
根据本发明的实施例，金属盐溶液以及碱性溶液的具体注入速度不受特别限制，本领域技术人员可根据反应容器的容积、金属盐溶液和碱溶液的浓度，以及正极材料的具体化学组成确定并进行调节。例如，可调节金属盐溶液以及碱性溶液的具体注入速度，令共沉淀反应期间反应器中溶液的pH值为10.5-11.9，例如大于11小于12。
如前所述，该步骤中是在适于前驱体颗粒的晶体生长的条件下将金属盐溶液以及碱性溶液分别独立地注入密闭的反应器中的。密闭的反应器可以为反应釜等。根据本发明的具体实施例，金属盐溶液的注入速度可以是动态调节的，且该动态调节基于前驱体颗粒的晶体生长进行。具体而言，可按照晶体颗粒生长动力学模型推测颗粒生长末期的时间，以此调节上述金属盐溶液注入反应釜的流速(即注入速度)，例如在晶体生长中的某一时期升高或降低金属盐溶液的流速，在晶体生长阶段结束后，再将各金属盐溶液注入反应釜的流速调节到其初始的流速值，至共沉淀反应结束。由此，形成的前驱体颗粒可经过后续的第一煅烧处理形成单晶形式的基体颗粒，从而最终获得内部无多个晶界的正极材料。
此处需要特别说明的是，上述盐溶液可包括多种盐溶液，每一种盐溶液均可具有独立地初始注入速度。提高或降低注入速度是分别独立地对每一种盐溶液的注入速度进行调节，即相对于该种盐溶液的初始注入速度而增高或是降低，并在晶体生长阶段结束后，将该种盐溶液的注入速度恢复至这一元素的盐溶液的初始注入速度。例如，上述多种M元素的初始注入速度可以相等也可以不相等，镍的盐溶液、钴的盐溶液、锰的盐溶液的初始注入速度也可以相等或不相等。但“调节到其初始的流速值”、“恢复初始注入速度”均是相对于其自身的初始注入速度而言的，例如在晶体生长阶段结束后，将镍的盐溶液的注入速度恢复为镍的盐溶液的初始注入速度，将钴的盐溶液的注入速度恢复为钴的盐溶液的初始注入速度，将锰的盐溶液的注入速度恢复为锰的盐溶液的初始注入速度。
根据本发明的具体实施例，可以在共沉淀过程中实时监控前驱体颗粒的粒度分布，并基于粒度分布调节金属盐溶液的注入速度。例如可定期自反应釜等反应容器中抽取处部分溶液，利用包括但不限于激光粒度仪等仪器进行粒度分布的分析。
根据本发明的一些具体示例，可在第一预定时间后提高M盐溶液注入速度，并降低镍的盐溶液、钴的盐溶液、锰的盐溶液的注入速度，直至前驱体颗粒的晶体生长末期，随后恢复全部盐溶液的注入速度为初始注入速度，直至共沉淀结束。具体地，第一预定时间可以为共沉淀反应至颗粒的粒度达到前驱体颗粒的预设粒度的90％-99％所用的时间。例如，在第一预定时间之后可分别独立地降低所述的镍的盐溶液、钴的盐溶液和锰的盐溶液的注入流速为其流速初始值的30％–50％，提高M盐溶液的注入流速为流速的初始值的120％-140％。
由此获得的前驱体颗粒中，M具有高浓度分布区和低浓度分布区，低浓度分布区中含有的M和高浓度分布区中含有的M的摩尔比0.01-0.5，低浓度分布区位于前驱体颗粒的中心区 域以及表层，高浓度分布区位于距离前驱体颗粒表面0.05-0.5微米范围内，后续步骤中可形成缓冲层。M具有两个浓度分区的前驱体颗粒形成的正极材料可具有更高的稳定性。
根据本发明的实施例，在将金属盐溶液、M盐溶液以及碱性溶液注入反应器中之前，可预先在反应器中加入去离子水并升温至40-90摄氏度，并以700-1100rmp的速度进行搅拌，随后在搅拌下注入金属盐溶液、M盐溶液以及碱性溶液。
根据本发明的实施例，共沉淀反应结束后，可反应器中的产物进行过滤、洗涤以及真空干燥处理，以获得前驱体颗粒。具体可对反应器中的产物进行过滤，滤渣采用去离子水洗涤并在100-150摄氏度下进行真空干燥6-12小时。
该步骤中获得的前驱体颗粒的粒径范围可为1-8微米，比表面积可为5-25m 2/g，前驱体颗粒的振实密度为1.1-1.9g/cc。由此获得的前驱体颗粒较为理想，有利于后续通过第一煅烧处理获得基体颗粒尺寸适当、界面性能较好的正极材料。该步骤中获得的前驱体颗粒的化学组成可为：
Ni 0.88Co 0.06Mn 0.03Al 0.03(OH) 2、Ni 0.88Co 0.06Mn 0.03Zr 0.03(OH) 2、Ni 0.88Co 0.06Mn 0.03Ti 0.03(OH) 2、或者Ni 0.88Co 0.06Mn 0.03Mg 0.03(OH) 2等。
S200：将前驱体颗粒以及锂盐混合并进行第一煅烧处理
在该步骤中，将前驱体颗粒以及锂盐混合并进行第一煅烧处理，以获得正极材料。
根据本发明的具体实施例，锂盐的具体类型不受特别限制，例如可以为LiOH·H 2O、LiF、Li 2CO 3以及CH 3COOLi中的一种或者几种。锂盐和前驱体颗粒的混合比例本领域技术人员可根据需要制备的正极材料的化学组成进行调整。
根据本发明的一些具体示例，第一煅烧处理的煅烧温度可以为800-880摄氏度，第一煅烧处理过程中升温的速率为1.5-10摄氏度/min，第一煅烧处理的时间为8-25小时，且第一煅烧处理是在氧气气氛中进行的。
为了进一步提高第一煅烧处理的效果，前驱体颗粒和锂盐混合之前可以对前驱体颗粒和锂盐分别进行研磨处理以及真空干燥处理。例如可将前驱体颗粒和锂盐分别进行包括但不限于研磨等方式进行破碎处理，以获得颗粒尺寸在纳米级别的颗粒，随后进行真空干燥。将锂盐和前驱体颗粒进行混合可以是利用研钵等对粉末进行混合，或通过高速混料机进行的，只要能够将二者在第一煅烧处理前混合均匀即可。随后，经过上述的第一段煅烧处理，即可获得正极材料。
根据本发明的实施例，该方法还可以进一步包括形成包覆层的步骤。在该步骤中将正极材料与包覆剂进行混合，并进行第二煅烧处理，以在正极材料的基体颗粒表面形成包覆层。关于该正极材料的结构以及化学组成，前面已经进行了详细的描述，在此不再赘述。
为进一步提高第二煅烧处理的效果，正极材料与包覆剂进行混合之前可对正极材料预先依次经过破碎处理、清洗处理以及真空干燥处理。具体地，可将正极材料置于一定体积的去 离子水中进行水洗3-10min，随后对水洗后的正极材料进行真空干燥。该真空干燥可在120–180摄氏度下进行，干燥时间可以为2-10小时。
根据本发明的实施例，包覆剂可以包括异丙醇铝、氟化铝、氧化铝、氧化铈、异丙醇钛、氧化钛、氧化硼、硼酸、氧化镁、氧化锆、正丁醇锆、氟化氨、氟化二氢铵、氟化一氢铵以及偏硼酸镁中的至少之一，包覆剂的颗粒尺寸不大于50nm。根据本发明的一些具体示例，可选择包覆剂中的金属元素与正极材料预制体中的M金属(例如可以为正极材料中除了Li、Co、Co和Ni以外的金属元素)元素相同的材料，由此可更好地保证产品的批次一致性。
根据本发明的实施例，第二煅烧处理的温度可以为350–650摄氏度，第二煅烧处理的升温速率可以为1-5摄氏度/min，时间可以为3-15小时，第二煅烧处理是在氧气或氮气气氛中进行的。
在本发明的又一方面，本发明提出了一种正极。参考图3，该正极包括：正极极片200，以及分布于正极极片上的正极材料100。正极材料100为前面所述的，或是利用前面所述的方法制备的。由此，该正极具有前面描述的正极材料所具有的全部特征以及优点，在此不再赘述。例如，该正极具有正极活性材料稳定性强，利用该正极制备的锂离子电池的比容量较高、循环性能好、稳定性较好等优点的至少之一。
此处需要特别说明的是，该正极还可具有包括但不限于极耳210等结构，以方便在构成电池时用于连接。图3中所示出的结构仅为了方便示出正极极片200和正极材料100的位置关系，而不能够理解为对正极材料100具体位置和分布方式的限制。例如，正极材料100可被分散于包括但不限于电解液等载体上，通过涂布、辊压等方式分布于正极极片200上。
在本发明的又一方面，本发明提出了一种锂离子电池。该锂离子电池包括前面描述的正极、负极，以及将正极以及负极之间绝缘间隔的隔膜。该锂离子电池具有前述的正极的全部特征以及优点，在此不再赘述。总的来说，该锂离子电池具有比容量较高、循环性能好、稳定性较好等优点的至少之一。
根据本发明的实施例，该锂离子电池的具体类型不受特别限制，例如可采用液态电解质，也可为全固态锂离子电池。该锂离子电池还可含有多个独立的子电池，具有软包电池模组等结构。
在本发明的又一方面，本发明提出了一种车辆。该车辆包括前面所述的锂离子电池。由此，该车辆具有前述的锂离子电池的全部特征以及优点，在此不再赘述。总的来说，该车辆具有里程数较高、安全性能以及稳定性较好，里程衰减较小等优点的至少之一。
根据本发明的具体实施例，该锂离子电池可以是用于车辆的驱动的。锂离子电池位于车辆中的具体位置不受特别限制，本领域技术人员可根据实际情况进行选择。由于该电池具有较好的安全性和稳定性，因此在选择动力电池的具体位置时可具有更灵活的选择。
下面通过具体的实施例对本发明的方案进行说明，需要说明的是，下面的实施例仅用于说明本发明，而不应视为限定本发明的范围。实施例中未注明具体技术或条件的，按照本领域内的文献所描述的技术或条件或者按照产品说明书进行。
实施例1
配制浓度约为130g/L的硫酸镍、硫酸钴、硫酸锰溶液，浓度约为40g/L的硫酸铝溶液、以及配制约150g/L的氨水溶液和约130g/L氢氧化钠溶液，向反应釜中加入1.1L的去离子水，将反应釜升温至恒温65℃、控制反应过程的pH约为11.4、整个共沉淀反应时间为36h，搅拌速率为950rmp。当反应进行到第33h时，将所述硫酸镍、硫酸钴、硫酸锰溶液的进料流速调低至初始值的30％、同时将硫酸铝溶液进料流速调高至初始值的120％，约40–60min后将以上盐溶液的进料流速调回初始值，并直到共沉淀反应结束。对所得的物料进行过滤、去离子水洗涤以及130摄氏度真空干燥10h，获得化学组成为Ni 0.88Co 0.06Mn 0.03Al 0.03(OH) 2的前驱体颗粒。
将1mol的前驱体颗粒与1.03mol的锂源(LiOH·H 2O)分别置于纳米研磨机中按照设定程序研磨，随后真空干燥。将得到的两种纳米物料粉末置于研磨中充分混合，随后置于约850摄氏度煅烧炉、6摄氏度/min的升温速率、纯氧气气氛煅烧20h。将煅烧后的粉末样品置于去离子水中水洗约10min后经真空干燥，获得正极材料预制体。
将干燥后的正极材料预制体粉末物料与4016ppm AlF 3(颗粒尺寸≤50nm)充分混合，随后置于500摄氏度煅烧炉、升温速率1.5摄氏度/min，氧气气氛中煅烧6h，最后经研钵中充分研磨或者超离心研磨粉碎机中破碎后，得到正极材料，该正极材料的化学组成为0.996LiNi 0.88Co 0.06Mn 0.03Al 0.03O 2·0.004AlF 3。扫描电子显微镜图如图5中的(a)所示出的。
实施例2
配制浓度约为130g/L的硫酸镍、硫酸钴、硫酸锰溶液，浓度约为36g/L的硫酸钛溶液、以及配制约150g/L的氨水溶液和约130g/L氢氧化钠溶液，向反应釜中加入1.1L的去离子水，将反应釜升温至恒温65℃、控制反应过程的pH约为11.5、整个共沉淀反应时间为36h、搅拌速率为950rmp。当反应进行到第33h时，将所述硫酸镍、硫酸钴、硫酸锰溶液的进料流速调低至初始值的30％、同时将硫酸钛溶液进料流速调高至初始值的130％，约40–60min后将以上盐溶液的进料流速调回初始值，并直到共沉淀反应结束。对所得的物料进行过滤、去离子水洗涤以及130摄氏度真空干燥10h，获得化学式为Ni 0.88Co 0.06Mn 0.03Ti 0.03(OH) 2的前驱体。
将1mol的前驱体(Ni 0.88Co 0.06Mn 0.03Ti 0.03(OH) 2)与1.03mol的锂源(LiOH·H 2O)分别置于纳米研磨机中按照设定程序研磨，随后真空干燥。将得到的两种纳米物料粉末置于研磨中充分混合，随后置于约850摄氏度煅烧炉、6摄氏度/min的升温速率、纯氧气气氛煅烧20h。
将煅烧后的粉末样品置于去离子水中水洗约10min后经真空干燥。将干燥后的粉末物料与4016ppm TiO 2(颗粒尺寸≤50nm)充分混合，随后置于550摄氏度煅烧炉、升温速率1.5摄 氏度/min，氧气气氛中煅烧5.5h，最后经研钵中充分研磨或者超离心研磨粉碎机中破碎后，得到正极材料分子式为0.996LiNi 0.88Co 0.06Mn 0.03Ti 0.03O 2·0.004TiO 2。扫描电子显微镜图如图5中的(b)所示出的。
实施例3
配制浓度约为130g/L的硫酸镍、硫酸钴、硫酸锰溶液，浓度约为40g/L的硫酸铝溶液、以及配制约150g/L的氨水溶液和约130g/L氢氧化钠溶液，向反应釜中加入1.1L的去离子水，将反应釜升温至恒温65℃、控制反应过程的pH约为11.4、整个共沉淀反应时间为36h、搅拌速率为950rmp。当反应进行到第33h时，将所述硫酸镍、硫酸钴、硫酸锰溶液的进料流速调低至初始值的30％、同时将硫酸铝溶液进料流速调高至初始值的120％，约40–60min后将以上盐溶液的进料流速调回初始值，并直到共沉淀反应结束。对所得的物料进行过滤、去离子水洗涤以及130℃真空干燥10h，获得化学式为Ni 0.88Co 0.06Mn 0.03Al 0.03(OH) 2的前驱体。
将1mol的前驱体(Ni 0.88Co 0.06Mn 0.03Al 0.03(OH) 2)与1.03mol的锂源(LiOH·H 2O)分别置于纳米研磨机中按照设定程序研磨，随后真空干燥。将得到的两种纳米物料粉末置于研磨中充分混合，随后置于约850摄氏度煅烧炉、6摄氏度/min的升温速率、纯氧气气氛煅烧20h。将煅烧后的粉末样品置于去离子水中水洗约10min后经真空干燥。将干燥后的粉末物料与4016ppm Al 2O 3(颗粒尺寸≤50nm)充分混合，随后置于450℃煅烧炉、升温速率2℃/min，氧气气氛中煅烧5h，最后经研钵中充分研磨或者超离心研磨粉碎机中破碎后，得到正极材料分子式为0.996LiNi 0.88Co 0.06Mn 0.03Al 0.03O 2·0.004Al 2O 3。扫描电子显微镜图如图5中的(c)所示出的。
实施例4
配制浓度约为130g/L的硫酸镍、硫酸钴、硫酸锰溶液，浓度约为44g/L的硫酸锆溶液、以及配制约150g/L的氨水溶液和约130g/L氢氧化钠溶液，向反应釜中加入1.1L的去离子水，将反应釜升温至恒温65℃、控制反应过程的pH约为11.7、整个共沉淀反应时间为36h、搅拌速率为950rmp。当反应进行到第33h时，将所述硫酸镍、硫酸钴、硫酸锰溶液的进料流速调低至初始值的30％、同时将硫酸锆溶液进料流速调高至初始值的120％，约40–60min后将以上盐溶液的进料流速调回初始值，并直到共沉淀反应结束。对所得的物料进行过滤、去离子水洗涤以及130摄氏度真空干燥10h，获得化学式为Ni 0.88Co 0.06Mn 0.03Zr 0.03(OH) 2的前驱体。
将1mol的前驱体(Ni 0.88Co 0.06Mn 0.03Zr 0.03(OH) 2)与1.03mol的锂源(LiOH·H 2O)分别置于纳米研磨机中按照设定程序研磨，随后真空干燥。将得到的两种纳米物料粉末置于研磨中充分混合，随后置于约850摄氏度煅烧炉、6摄氏度/min的升温速率、纯氧气气氛煅烧20h。将煅烧后的粉末样品置于去离子水中水洗约10min后经真空干燥。
将干燥后的粉末物料与4016ppm ZrO(颗粒尺寸≤50nm)充分混合，随后置于500摄氏度煅烧炉、升温速率1.5摄氏度/min，氧气气氛中煅烧6h，最后经研钵中充分研磨或者超离心研磨粉碎机中破碎后，得到分子式为0.996LiNi 0.88Co 0.06Mn 0.03Zr 0.03O 2·0.004ZrO的正极材料。扫描电子显微镜图如图5中的(d)所示出的。
对比例1
配制浓度约为290g/L的硫酸镍、约20g/L硫酸钴、约10g/L硫酸锰溶液，浓度约为10g/L的硫酸铝溶液、以及配制约150g/L的氨水溶液和约130g/L氢氧化钠溶液，向反应釜中加入1.1L的去离子水，将反应釜升温至恒温70℃、控制反应过程的pH约为11.4、整个共沉淀反应时间为52h，搅拌速率为960rmp。对所得的物料进行过滤、去离子水洗涤以及130摄氏度真空干燥10h，获得化学组成为Ni 0.88Co 0.06Mn 0.03Al 0.03(OH) 2的前驱体颗粒。
将1mol的前驱体颗粒与1.03mol的锂源(LiOH·H 2O)分别置于纳米研磨机中按照设定程序研磨，随后真空干燥。将得到的两种纳米物料粉末置于研磨中充分混合，随后置于约750摄氏度煅烧炉、2摄氏度/min的升温速率、纯氧气气氛煅烧16h。将煅烧后的粉末样品置于去离子水中水洗约10min后经真空干燥，获得正极材料预制体。
将干燥后的正极材料预制体粉末物料与4016ppm AlF 3(颗粒尺寸≤50nm)充分混合，随后置于500摄氏度煅烧炉、升温速率1.5摄氏度/min，氧气气氛中煅烧6h，最后经研钵中充分研磨或者超离心研磨粉碎机中破碎后，得到正极材料，该正极材料的化学组成为0.996LiNi 0.88Co 0.06Mn 0.03Al 0.03O 2·0.004AlF 3。扫描电子显微镜图如图6所示。
对比例2
配制浓度约为290g/L的硫酸镍、约20g/L硫酸钴、约10g/L硫酸锰溶液，浓度约为10g/L的硫酸铝溶液、以及配制约150g/L的氨水溶液和约130g/L氢氧化钠溶液，向反应釜中加入1.1L的去离子水，将反应釜升温至恒温65℃、控制反应过程的pH约为11.4、整个共沉淀反应时间为36h，搅拌速率为950rmp。对所得的物料进行过滤、去离子水洗涤以及130摄氏度真空干燥10h，获得化学组成为Ni 0.88Co 0.06Mn 0.03Al 0.03(OH) 2的前驱体颗粒。
将1mol的前驱体颗粒与1.03mol的锂源(LiOH·H 2O)分别置于纳米研磨机中按照设定程序研磨，随后真空干燥。将得到的两种纳米物料粉末置于研磨中充分混合，随后置于约850摄氏度煅烧炉、6摄氏度/min的升温速率、纯氧气气氛煅烧20h。将煅烧后的粉末样品置于去离子水中水洗约10min后经真空干燥，获得正极材料预制体。
将干燥后的正极材料预制体粉末物料与4016ppm AlF 3(颗粒尺寸≤50nm)充分混合，随后置于500摄氏度煅烧炉、升温速率1.5摄氏度/min，氧气气氛中煅烧6h，最后经研钵中充分研磨或者超离心研磨粉碎机中破碎后，得到正极材料，该正极材料的化学组成为0.996LiNi 0.88Co 0.06Mn 0.03Al 0.03O 2·0.004AlF 3。
扫描电子显微镜图如图7所示。
性能测试：
参考图5，实施例1-4制备的正极材料的扫描电子显微镜均显示出单晶颗粒的特征。由此可确认实施例1-4制备的正极材料与常规的多晶颗粒存在本质上的区别，并不包括多个一次颗粒组成，进而也就不存在一次颗粒之间的晶界形。随着充放电循环次数的增加，由于晶界应力以及微裂纹等问题导致电解液进入到颗粒内部发生电解液副反应以及结构上的破坏等问题也可得到解决。由图5可确认单晶颗粒本身为一个独立的颗粒，内部没有晶界破坏的隐患，因此在长时间的充放电循环过程中具有相对稳定保持原有的状态。
图8为对实施例1-4制备的正极材料对应的首次充放电曲线。充放电倍率分别为0.1C/0.1C，电压范围为3-4.3V。由图8可见，实施例1-4制备的正极材料均表现出了较好的首次充放电性能。充放电比容量依次分别为232.1mAh/g、204.6mAh/g；225.4mAh/g、201.2mAh/g；237.2mAh/g、212.4mAh/g；230mAh/g、206.3mAh/g，均超过了200mAh/g。
图9为实施例1-4制备的正极材料在不同电流密度下的放电比容量。充放电倍率分别为0.1C/0.1C、0.5C/0.5C、0.5C/1C、0.5C/2C，电压范围为3-4.3V。由图9可知，当放电倍率为1C时，各实施例对应的放电比容量依次为186mAh/g、179.6mAh/g、189.5mAh/g和187.5mAh/g，倍率性能较好。
图10为实施例1-4制备的正极材料在50个循环过程中放电比容量的保持情况，循环充放电的充电倍率为0.5C、放电倍率为1C，电压范围为3-4.3V。由图10可知，各实施例对应的循环容量保持率依次为93.3％、96.7％、95.8％和94.7％，循环容量保持率达到了较高的水平。因此本发明提出的缓冲层和颗粒表面包覆层能够使样品维持一个较高的循环稳定性，稳定了材料的晶体结构。
经评测对比例1获得的样品在0.1C倍率充电和放电比容量分别为234.8mAh/g和202mAh/g；首次库伦效率为86％；1C倍率放电比容量为173mAh/g；在充电0.5C倍率和放电1C倍率下进行50个充放电循环后容量保持率为91％。对比例2获得的样品在0.1C倍率充电和放电比容量分别为233.1mAh/g和203.9mAh/g；首次库伦效率为87.4％；1C倍率放电比容量为180mAh/g；在充电0.5C倍率和放电1C倍率下进行50个充放电循环后容量保持率为89％。可见根据本发明实施例的样品具有更好的循环性能。
在本发明的描述中，术语“内”、“外”、“表面”等指示的方位或位置关系为基于附图所示的方位或位置关系，仅是为了便于描述本发明而不是要求本发明必须以特定的方位构造和操作，因此不能理解为对本发明的限制。
在本说明书的描述中，参考术语“一个实施例”、“另一个实施例”等的描述意指结合该实施例描述的具体特征、结构、材料或者特点包含于本发明的至少一个实施例中。在本说明书中， 对上述术语的示意性表述不必须针对的是相同的实施例或示例。而且，描述的具体特征、结构、材料或者特点可以在任一个或多个实施例或示例中以合适的方式结合。此外，在不相互矛盾的情况下，本领域的技术人员可以将本说明书中描述的不同实施例或示例以及不同实施例或示例的特征进行结合和组合。
尽管上面已经示出和描述了本发明的实施例，可以理解的是，上述实施例是示例性的，不能理解为对本发明的限制，本领域的普通技术人员在本发明的范围内可以对上述实施例进行变化、修改、替换和变型。

Claims (12)

  1. 一种正极材料，其特征在于，包括：
    基体颗粒，所述基体颗粒是单晶颗粒，所述单晶颗粒包括镍锰酸锂和镍钴锰酸锂，所述基体颗粒中靠近表层处具有缓冲层，所述缓冲层中Ni、Co、Mn元素的至少之一的含量低于所述基体颗粒其他位置处的含量。
  2. 根据权利要求1所述的正极材料，其特征在于，所述基体颗粒的化学式为Li 1+λNi αMn βCo γM (1-α-β-γ)O 2，
    其中，0≤λ<0.1，0.5≤α<1，0.3≤β<1,0≤γ<0.2，0.01≤1-α-β-γ≤0.05，M选自Al、Ti、Mg、Zr、Zn、Ce以及Cr中的至少一种，N选自O、F、B以及P中的至少一种，
    并且M元素在所述缓冲层中的摩尔含量高于在非缓冲层处的摩尔含量。
  3. 根据权利要求1所述的正极材料，其特征在于，所述基体颗粒的化学式为Li 1+λNi αMn βCo γM (1-α-β-γ)O 2，
    其中，0≤λ<0.1，0.8≤α<1，0.01≤β<0.1,0≤γ<0.1，M选自Al、Ti、Mg、Zr、Zn、Ce以及Cr中的至少一种，N选自O、F、B以及P中的至少一种，
    并且M元素在所述缓冲层中的摩尔含量高于在非缓冲层处的摩尔含量。
  4. 根据权利要求2或3所述的正极材料，其特征在于，进一步包括包覆层，所述包覆层覆盖所述基体颗粒的表层，所述包覆层不含有Li、Ni、Co和Mn，所述包覆层为M' μN ν，所述M'包括Al、Ti、Mg、Zr、Zn、Ce、Cr和B中的任意一种或至少两种的组合，N为O、F、B、P中的任意一种或至少两种的组合，其中，1≤μ≤3，1≤ν≤6，所述包覆层中的M'的种类与所述基体颗粒中的M相同；
    优选地，M'包括Al、Ti、Zr和Mg中的任意一种或至少两种的组合；
    优选地，所述包覆层为AlF 3、TiO 2、Al 2O 3、ZrO中的至少一种；
    任选地，所述包覆层的厚度为10-100nm。
  5. 根据权利要求4所述的正极材料，其特征在于，所述正极材料的化学式为aLi 1+λNi αMn βCo γM (1-α-β-γ)O 2·bM μN ν，其中，a+b＝1，0<a<1，0<b<1。
  6. 根据权利要求1所述的正极材料，其特征在于，所述正极材料满足以下条件的至少之一：
    所述基体颗粒的粒径为1.5-10微米；
    所述缓冲层位于所述基体颗粒内部距离外表面0.05μm–0.5μm的近表层范围内。
  7. 一种制备1-6任一项所述的正极材料的方法，其特征在于，包括：
    在适于前驱体颗粒的晶体生长的条件下，将包括金属盐溶液以及碱性溶液在内的前驱体原料分别独立地注入密闭的反应器中进行共沉淀以获得前驱体颗粒；
    将所述前驱体颗粒以及锂盐混合并进行第一煅烧处理，以获得所述正极材料。
  8. 根据权利要求7所述的方法，其特征在于，所述金属盐溶液包括镍的盐溶液、钴的盐溶液、锰的盐溶液，所述前驱体原料包括M盐溶液，所述方法包括：
    在第一预定时间后提高所述M盐溶液注入速度，并降低所述镍的盐溶液、钴的盐溶液、锰的盐溶液中的至少之一的注入速度，直至所述前驱体颗粒的晶体生长末期，并将全部所述金属盐溶液和所述M盐溶液的注入速度恢复为初始注入速度，直至所述共沉淀结束，
    所述M盐中的M包括Al、Ti、Mg、Zr、Zn、Ce以及Cr中的至少一种，所述第一预定时间早于所述前驱体颗粒的晶体生长末期；
    任选地，所述第一预定时间为共沉淀反应至颗粒的粒度达到所述前驱体颗粒的预设粒度的90％-99％所用的时间；
    优选地，分别独立地降低所述的镍的盐溶液、钴的盐溶液和锰的盐溶液的注入流速为其流速初始值的30％–50％；
    优选地，提高所述M盐溶液的注入流速为流速的初始值的120％–140％；
    优选地，所述方法还包括在共沉淀结束后，对反应产物进行过滤、洗涤和干燥的步骤；
    优选地，所述前驱体粒度为1μm-8μm；
    优选地，所述前驱体比表面积为5m 2/g-25m 2/g；
    优选地，所述前驱体振实密度为1.1g/cc-1.9g/cc。
  9. 根据权利要求7或8所述的方法，其特征在于，所述方法进一步包括：
    将所述正极材料与包覆剂进行混合并进行第二煅烧处理以形成包覆层，所述包覆剂满足以下条件的至少之一：
    所述包覆剂包括异丙醇铝、氟化铝、氧化铝、氧化铈、异丙醇钛、氧化钛、氧化硼、硼酸、氧化镁、氧化锆、正丁醇锆、氟化氨、氟化二氢铵、氟化一氢铵以及偏硼酸镁中的至少之一；
    所述包覆剂的颗粒尺寸不超过50nm。
  10. 一种正极，其特征在于，包括：
    正极极片，以及分布于所述正极极片上的正极材料，所述正极材料为权利要求1-6任一项所述的正极材料，或是利用权利要求7-9任一项所述的方法制备的。
  11. 一种锂离子电池，其特征在于，包括：
    权利要求10所述的正极；
    负极；以及
    隔膜，所述隔膜将所述正极以及所述负极之间绝缘间隔。
  12. 一种车辆，其特征在于，所述车辆包括权利要求11所述的锂离子电池。
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