WO2023130779A1 - 一种具有核壳结构的高电压三元正极材料及其制备方法 - Google Patents

一种具有核壳结构的高电压三元正极材料及其制备方法 Download PDF

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WO2023130779A1
WO2023130779A1 PCT/CN2022/122136 CN2022122136W WO2023130779A1 WO 2023130779 A1 WO2023130779 A1 WO 2023130779A1 CN 2022122136 W CN2022122136 W CN 2022122136W WO 2023130779 A1 WO2023130779 A1 WO 2023130779A1
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core
positive electrode
electrode material
voltage
manganese
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French (fr)
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胡进
董明霞
张新
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巴斯夫杉杉电池材料有限公司
中南大学
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the invention belongs to the technical field of positive electrode materials for lithium ion batteries, and in particular relates to a high-voltage ternary positive electrode material with a core-shell structure and a preparation method thereof.
  • Nickel-manganese-cobalt ternary materials inherently have a tendency to develop towards high voltage, and the discharge specific capacity increases with the increase of the charge cut-off voltage.
  • the upper limit cut-off voltage is increased from 4.2V to 4.5V
  • the lithium in the unit ternary material The number of ions released may increase from 0.45 mol to 0.60 mol, and the greater the gram capacity of the corresponding positive electrode material, the higher the capacity of the battery.
  • the high operating voltage poses a great challenge to the interface stability between the cathode material and the electrolyte.
  • Ion doping refers to doping a small amount of heterogeneous ions into the crystal lattice without affecting the crystal structure of the positive electrode material, improving the stability of the crystal structure of the material and increasing the unit cell parameter c, expanding the lithium ion transmission channel, thereby improving the ternary material. capacity, rate and cycle stability.
  • Surface coating forms a layer of compound on the surface of the ternary material to avoid direct contact between the electrolyte and the positive electrode material, delaying the phase transition, thereby playing a protective role and improving the cycle stability and thermal stability of the electrode material.
  • the Al(PO 3 ) 3 coated NCM811 positive electrode material mentioned in the CN202110525350.X patent dry-grind the commercial NCM811 and Al(PO 3 ) 3 powders until the particle size is moderate, and after the distribution is uniform, the Sintering at high temperature, keeping the temperature for a period of time and then cooling down naturally, after the powder is taken out, a high-nickel ternary cathode material doped and coated with Al(PO 3 ) 3 is obtained, which improves the rate performance and cycle stability of the material.
  • CN201810954002.2 patent proposes a high-nickel ternary cathode material modified by doping with alkali metal elements or non-metal elements.
  • the ternary precursor powder is mixed with lithium-containing compounds and doping element-containing compounds, and a co-doped modified high-nickel ternary material is obtained through two-step heating and sintering, which reduces the mixing degree of Ni 2+ and Li + , and expands The layer spacing is reduced to make the structure more stable and optimize the rate performance and cycle stability of the material.
  • the CN202110416541.2 patent proposes a Ni x Co y Mnz (OH) 2 spherical hydroxide precursor synthesized by coprecipitation, mixed with lithium source, boron source, and sodium source for low-temperature roasting, and then high-temperature sintering to obtain nickel-cobalt
  • the manganese single crystal material is then calcined with the aluminum source in the air environment to modify the single crystal material at high temperature, so as to achieve the first charge and discharge specific capacity of 184mAh/g under the 4.6V high voltage test system.
  • CN201810954002.2 patent proposes a high-nickel ternary cathode material modified by doping with alkali metal elements or non-metal elements. Although the structural stability of the material is improved, the improvement of material performance by this method cannot meet the current market demand , and the material obtained by this method cannot further increase the energy density of the material by increasing the working voltage.
  • the CN202110416541.2 patent realizes the first charge-discharge specific capacity of 184mAh/g under the 4.6V high-voltage test system through single crystallization, but the technologies and methods involved in this method cannot avoid problems such as poor rate and cycle performance of single crystal materials.
  • the technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the above background technology, and provide a high-voltage ternary positive electrode material with a core-shell structure and a preparation method thereof, which combines NMC ternary positive electrode material and nickel-manganese The materials are combined to obtain a high-voltage ternary cathode material with a core-shell structure and overall lithium-rich, which can work stably at an ultra-high voltage of 4.7V, and also has ultra-high discharge specific capacity and excellent rate performance .
  • the inner core includes nickel-manganese-cobaltate lithium ternary material, and the molar ratio of nickel, manganese and cobalt is: (0.65-0.80):(0.05-0.60):(0.02-0.15);
  • the shell layer includes lithium nickel manganese oxide binary material, and the molar ratio of nickel to manganese is: (0.10 ⁇ 0.60):(0.60 ⁇ 0.90);
  • M is a doping element derived from the core and/or shell.
  • the thickness of the shell layer is 0.25-1.25 ⁇ m, and the ratio of the particle diameter D50 of the ternary positive electrode material to the thickness of the shell layer is (10-35):1. Further preferably, the particle size of the ternary positive electrode material is The ratio of diameter D50 to shell thickness is (13-20):1.
  • the shell is too thick, the capacity of the material may decrease, and the high-manganese shell is too thin to effectively protect the material from cycling at a high voltage of 3.0-4.7V stability.
  • M is selected from one or more of Al, Zr, Mg, Ti, Ta, W, Nb, Sn, Co, Na.
  • the voltage DQ/DV differential capacity curve obtained from the first cycle charging curve is higher than the voltage V1
  • the voltage value corresponding to the apex of the oxidation peak is in the range of 4.5-4.58V.
  • the value range of x is 1.06 ⁇ x ⁇ 1.23; the molar ratio of nickel, manganese and cobalt in the core is (0.65 ⁇ 0.80):(0.10 ⁇ 0.25):(0.05 ⁇ 0.1); the shell The molar ratio of nickel and manganese is (0.20 ⁇ 0.30):(0.70 ⁇ 0.80).
  • the particle size D50 of the high-voltage ternary cathode material is 11.0-14.5 ⁇ m, and the BET is 0.2-0.6 m 2 /g.
  • the present invention provides a method for preparing a high-voltage ternary positive electrode material with a core-shell structure, comprising the following steps:
  • the lye is 8-11 mol/L NaOH solution; the concentration of the ammonia solution is 6-8 mol/L;
  • step (2) the ammonia value in the reactor is controlled between 7 ⁇ 8g/L by adjusting the feed rate of ammonia solution; Between 5 and 6g/L.
  • the total molar ratio of the lithium source to the Ni, Mn and Co elements in the core-shell structure precursor is (1.10-1.40):1.
  • the molar ratio of the total molar amounts of Ni, Mn, and Co elements in the precursor of the core-shell structure to the lithium source is determined to be in the range of 1.10 to 1.40, so that the corresponding DQ/
  • the first charge curve in the DV differential capacity curve has a significant oxidation peak around 4.5V.
  • the molar ratio of the lithium source to the total molar amount of Ni, Mn, and Co elements in the core-shell precursor is 1.10 ⁇ 1.28:1.
  • the sintering temperature is 700-950° C., and the time is 8-14 hours.
  • the sintering temperature is too high or the time is too long, the primary particle size of the secondary spherical particles of the positive electrode material will be too large, the Mn element in the shell layer will diffuse seriously to the core layer, and the lithium-rich manganese-based shell structure will become very thin or disappear.
  • the advantages of cycle performance cannot be exerted under high voltage; when the sintering temperature is too low or the sintering time is too short, the residual lithium of the material will increase, and at the same time, the primary particles of the sample are too small, the crystallinity of the material is poor, and the layered structure is relatively weak. Poor, the material cannot effectively exert high capacity and cycle stability under high voltage.
  • the temperature is raised to the sintering temperature at a rate of 2-3° C./min under an air atmosphere or an oxygen atmosphere.
  • the nickel source that adopts comprises one or more in nickel nitrate, nickel sulfate, nickel chloride, nickel acetate;
  • the cobalt source that adopts comprises a kind of in cobalt nitrate, cobalt sulfate, cobalt chloride, cobalt acetate or more;
  • the manganese source used includes one or more of manganese nitrate, manganese sulfate, manganese chloride, manganese acetate;
  • the lithium source used includes lithium carbonate, lithium nitrate, lithium oxalate, lithium acetate, monohydrate hydroxide One or more of lithium and lithium hydroxide.
  • the present invention there is a high-voltage ternary positive electrode material with a core-shell structure, and the shell layer includes a lithium nickel manganese oxide binary material, which contains a low content of nickel element, a high content of manganese element, Lithium and oxygen elements can improve the overall thermal stability and electrochemical stability of the ternary positive electrode material; based on the composition of the core-shell components, the present invention further strictly controls the ratio of the radius of the core to the thickness of the shell in the core-shell, etc.
  • the high-voltage ternary positive electrode material with a core-shell structure provided by the present invention has the characteristics of lithium-rich manganese-based materials operating at high voltage, which can broaden the battery test range of the ternary material system to 3.0-4.7V, which improves the high-voltage cycle performance of the material.
  • the more significant effect is that on the DQ/DV curve corresponding to the first charge-discharge curve of the material, the first-cycle charging curve appears in the voltage range of 4.40-4.60V.
  • the oxidation peak corresponds to the characteristic oxidation peak of lithium-rich manganese-based materials rather than conventional ternary materials, that is, the element design and core-shell ratio design of the core-shell structure in the present invention make the final finished material show rich Lithium-manganese-based properties have relatively excellent electrical performance data.
  • the assembled button battery can reach 221.0mAh/g for the first time in the voltage range of 3.0-4.7V, and the first-time Coulombic efficiency can reach 85.4%.
  • the discharge specific capacity can reach 182.1mAh/g, and the capacity can still reach 203.4mAh/g after 30 cycles at a rate of 0.1C.
  • the preparation method of the high-voltage ternary positive electrode material with a core-shell structure of the present invention does not need to be washed after sintering, and the washing process of conventional high-nickel materials is removed, The damage to the surface of the material by water washing is alleviated, and the synthesis process of the material does not require secondary sintering coating.
  • the preparation process of the present invention does not involve additional resources and energy consumption, reduces the production cost of the material, and can ensure that the total residual lithium content on the surface of the material is ⁇ 1000ppm while removing the washing process, which meets the standard value of the industry standard.
  • the preparation process of the present invention is simple and easy to scale up, and it is easy to realize the expansion of positive electrode materials from laboratory-level preparation to production line production.
  • Fig. 1 is the cross-sectional SEM image of the high-voltage ternary positive electrode material prepared in Example 1 of the present invention
  • Fig. 2 is the SEM image of the high-voltage ternary positive electrode material prepared in Example 1 of the present invention
  • Fig. 3 is the EDS surface scanning atlas of the high-voltage ternary positive electrode material prepared in Example 1 of the present invention
  • Fig. 4 is the XRD spectrum of the high-voltage ternary positive electrode material prepared in Example 1 of the present invention.
  • Fig. 5 is the first charge and discharge curve of the high-voltage ternary positive electrode material prepared in Example 1 of the present invention.
  • Fig. 6 is the DQ/DV curve of the high-voltage ternary positive electrode material prepared in Example 1 of the present invention.
  • Figure 7 is the rate performance of the high voltage ternary cathode material prepared in Example 1 of the present invention.
  • Figure 8 is the cycle performance of the high-voltage ternary cathode material prepared in Example 1 of the present invention at 0.1C;
  • Fig. 9 is the cycle performance of the high-voltage ternary cathode material prepared in Example 1 of the present invention at 1C;
  • Figure 10 is the first charge and discharge curve of the non-lithium-rich high manganese core-shell structure positive electrode material prepared in Comparative Example 1 of the present invention
  • Figure 11 is the cycle performance of the non-lithium-rich high manganese core-shell structure positive electrode material prepared in Comparative Example 1 of the present invention at 1C.
  • FIG. 1 is a cross-sectional SEM of the above-mentioned high-voltage ternary cathode material The image shows that after sintering, the ternary positive electrode material still has an obvious core-shell structure, including the core and the shell.
  • the core includes nickel-manganese-cobalt oxide lithium ternary material, and the molar ratio of nickel, manganese, and cobalt is 0.70:0.20: 0.10
  • the shell layer includes lithium nickel manganese oxide binary material, the molar ratio of nickel to manganese is 0.30:0.70; among them, the particle size D50 of the ternary positive electrode material is 11.5 ⁇ m, the thickness of the shell layer is about 0.75 ⁇ m, and the BET is 0.54m 2 /g, the ratio of the particle size D50 of the ternary cathode material to the shell thickness is about 15.4.
  • the above-mentioned particle size D50 can be obtained by testing with a Malvern particle size analyzer, and the thickness of the shell can be obtained through the cross-sectional SEM image of the high-voltage ternary positive electrode material. Since the thickness of the shell prepared by the process of the embodiment of the present invention is relatively uniform, one and The overall shell thickness of the high-voltage ternary cathode material can be known from the cross-sectional view of the secondary particle with a relatively close D50 particle size value. If the thickness of the shell layer is found to be different by observing the cross-sectional SEM image, those skilled in the art can According to the situation and requirements, the shell thickness of the cross-sectional images of multiple secondary particles is taken and averaged to obtain the shell thickness.
  • the shell thickness of the material is basically inherited from the precursor, but due to the influence of mixing, sintering, crushing and other processes, the D50 of the finished core-shell cathode material may not be completely consistent with the D50 of the precursor.
  • the preparation method comprises the following steps:
  • control mixed metal salt solution B feeding speed is 60ml/min, by regulating the pH value of NaOH solution feeding speed regulation and control reaction system to 9.2,
  • the ammonia value of the reactor is controlled to maintain between 5-6g/L, stirring, and the feed is stopped when the particle size D50 is 12.0 ⁇ m, and then filtered, washed, and dried to obtain the core-shell structure hydrogen Oxide precursor Ni 0.57 Mn 0.36 Co 0.07 (OH) 2 .
  • the molar ratio of the amount is 1.24:1; then, under an oxygen atmosphere, at a heating rate of 2°C/min, the temperature is raised to 800°C for 12 hours to complete the high-temperature solid-phase sintering reaction, and the sintered product after the reaction is crushed, sieved and separated to obtain A high-voltage ternary cathode material with a core-shell structure.
  • Fig. 2 is an SEM image of a high-voltage ternary positive electrode material with a core-shell structure after lithiation and sintering.
  • the prepared high-voltage ternary positive electrode material is a secondary sphere composed of a large number of primary spherical particles.
  • the element surface distribution analysis was carried out on the cross section of the material, and the results are shown in Figure 3. It can be seen that the element distribution of the secondary spherical section is that the core layer of Ni and Co elements is high and the shell layer is low, and the core layer of Mn element is low and the shell layer is high, indicating that the The prepared positive electrode material has a high manganese shell layer.
  • the preparation method of battery comprises the following steps:
  • the first charge-discharge curve of the prepared positive electrode material As shown in Figure 5, the first charge-discharge curve of the prepared positive electrode material, the first discharge specific capacity of the prepared Li 1.19 Ni 0.57 Mn 0.36 Co 0.07 O 2 positive electrode material is 221.0mAh/g, and the corresponding DQ/DV curve is shown in the figure
  • the charge-discharge curve of the core-shell structure ternary material with surface lithium-rich characteristics is different from that of conventional ternary materials, and the oxidation peak near 4.55V of the DQ/DV curve is consistent with that of lithium-rich manganese-based materials, showing The uniqueness of the lithium-rich high manganese shell.
  • the rate performance test is completed in the mode of charging at the same rate and discharging at different rates.
  • the charging is completed at a rate of 0.5C, and the discharge is completed at a rate of 0.1C, 0.5C, 1.0C, and 2.0C.
  • Figure 7 shows the rate performance test results of the material.
  • the discharge specific capacity of the prepared Li 1.19 Ni 0.57 Mn 0.36 Co 0.07 O 2 cathode material at each rate is 208.1mAh/g, 192.2mAh/g, and 182.1mAh/g. and 168.1mAh/g.
  • the cycle performance test of the electrode material was carried out at a current density of 0.1C, and the results obtained are shown in Figure 8.
  • the specific discharge capacity of the button battery for the first cycle is 214.4mAh/g, and the discharge specific capacity after 30 cycles is 203.4mAh /g, the cycle retention rate was 94.8%.
  • the specific discharge capacity of the first cycle of the sample at a high current density of 1.0C is 167.4mAh/g, and the discharge capacity after 50 cycles is 135.6mAh/g, indicating that the material has good performance under high voltage. surface stability and structural stability.
  • a high-voltage ternary cathode material with a core-shell structure Its overall chemical formula is Li 1.23 Ni 0.60 Mn 0.34 Co 0.06 O 2 , which can be determined by ICP element content testing.
  • the ternary cathode material includes a core and a shell, and the core Including lithium nickel manganese cobalt oxide ternary material, the molar ratio of nickel, manganese, and cobalt is 0.80:0.10:0.10, and the shell layer includes lithium nickel manganese oxide binary material, and the molar ratio of nickel and manganese is 0.30:0.70; among them, three
  • the particle size D50 of the primary cathode material is 11.8 ⁇ m
  • the shell thickness is about 0.90 ⁇ m
  • the BET is 0.46 m 2 /g.
  • the ratio of the particle size D50 of the ternary cathode material to the shell thickness is about 13.2:1.
  • the preparation method comprises the following steps:
  • control mixed metal salt solution B feeding speed is 60ml/min, by adjusting the pH value of NaOH solution feeding speed regulation and control reaction system to 8
  • the ammonia value of the reactor is maintained between 5-6g/L, stirred, and when the particle size D50 is 11.8 ⁇ m, the feed is stopped, and then the core-shell structure is obtained by filtering, washing and drying Hydroxide precursor Ni 0.60 Mn 0.34 Co 0.06 (OH) 2 .
  • the preparation method of battery comprises the following steps:
  • the Li 1.23 Ni 0.60 Mn 0.34 Co 0.06 O 2 positive electrode material obtained in step (2) was uniformly mixed with the conductive agent SP and the binder (PVDF) according to the ratio of 90:5:5.
  • PVDF binder
  • the steps of pole piece drying and button cell assembly are the same as in Example 1.
  • the electrochemical performance test of the above-mentioned button battery that has been left still was started on the LAND battery test system.
  • the test voltage range is 3.0-4.7V, and the deduction test system is the same as that in Embodiment 1.
  • the prepared Li 1.23 Ni 0.60 Mn 0.34 Co 0.06 O 2 positive electrode material has an obvious oxidation peak around 4.55V on the first cycle DQ/DV differential capacity curve, which corresponds to the characteristic peak of lithium-rich manganese-based materials.
  • the first discharge specific capacity is 218.1mAh/g
  • the discharge specific capacity at each rate (0.1C, 0.5C, 1.0C, 2.0C) is 202.3mAh/g, 185.2mAh/g, 174.6mAh/g and 160.8mAh /g.
  • the activated button battery has a discharge specific capacity of 208.1mAh/g in the first cycle at a current density of 0.1C. After 30 cycles, the discharge specific capacity is 196.4mAh/g, and the cycle retention rate is 94.3%.
  • the material still has good surface stability and structural stability.
  • a high-voltage ternary cathode material with a core-shell structure Its overall chemical formula can be determined as Li 1.06 Ni 0.57 Mn 0.40 Co 0.03 O 2 through the ICP element content test.
  • the ternary cathode material includes a core and a shell, and the core includes Lithium nickel manganese cobalt oxide ternary material, the molar ratio of nickel, manganese, and cobalt is 0.75:0:20:0.05; the shell layer includes lithium nickel manganese oxide binary material, and the molar ratio of nickel and manganese is 0.20:0.80; wherein,
  • the D50 of the ternary cathode material is 12.0 ⁇ m, the shell thickness is about 0.62 ⁇ m, and the BET is 0.38 m 2 /g.
  • the ratio of the particle size D50 of the ternary cathode material to the shell thickness is about 19.4:1.
  • a high-voltage ternary positive electrode material with a core-shell structure comprising the following steps:
  • control mixed metal salt solution B feeding speed is 60ml/min, by regulating the pH value of NaOH solution feeding speed regulation and control reaction system to 8, At the same time, by adjusting the feed rate of the ammonia solution, the ammonia value of the reactor is controlled to maintain between 5-6g/L, stirring, and when the particle size D50 is 11.8 ⁇ m, the feed is stopped, and then the core-shell structure hydrogen is obtained by filtering, washing and drying.
  • Oxide precursor Ni 0.57 Mn 0.40 Co 0.03 (OH) 2 is added in the above-mentioned reactor simultaneously.
  • the preparation method of battery comprises the following steps:
  • the voltage test range and test system of the above-mentioned button battery that has been left still on the LAND battery test system are the same as in Example 1.
  • the oxidation peak corresponding to the characteristic peak of the lithium-rich manganese-based material also appeared on the first cycle DQ/DV differential capacity curve of the sample material near 4.55V.
  • the first discharge specific capacity of Li 1.06 Ni 0.57 Mn 0.40 Co 0.03 O 2 positive electrode material is 215.6mAh/g
  • the discharge specific capacity at 0.1C, 0.5C, 1.0C and 2.0C are 199.7mAh/g and 183.7mAh respectively /g, 173.3mAh/g and 159.7mAh/g.
  • the discharge specific capacity of the first cycle of the material is 205.5mAh/g, after 30 cycles, the discharge specific capacity is 191.1mAh/g, and the cycle retention rate is 92.9%.
  • a high-voltage ternary cathode material with a core-shell structure whose overall chemical formula can be determined by ICP element content testing as Li 1.23 Ni 0.50 Mn 0.43 Co 0.07 Al 0.007 O 2
  • the ternary cathode material includes a core and a shell
  • the core includes lithium nickel manganese cobalt oxide ternary material, and the molar ratio of nickel, manganese, and cobalt is 0.65:0.25:0.10
  • the shell layer includes lithium nickel manganese oxide binary material, and the molar ratio of nickel and manganese is 0.20:0.80;
  • the particle size D50 of the ternary cathode material is 11.8 ⁇ m
  • the shell thickness is about 0.75 ⁇ m
  • the BET is 0.26m 2 /g
  • the ratio of the particle size D50 of the ternary cathode material to the shell thickness is about 15.8:1.
  • the preparation method comprises the following steps:
  • metal salt solution B prepare a NaOH solution with a concentration of 9 mol/L and an ammonia solution with a concentration of 7 mol/L at the same time.
  • control mixed metal salt solution B feeding speed is 60ml/min, by regulating the pH value of NaOH solution feeding speed regulation and control reaction system to 8,
  • the ammonia value of the reactor is controlled to maintain between 5-6g/L, stirring, and the feed is stopped when the particle size D50 is 12.0 ⁇ m, and then filtered, washed, and dried to obtain the core-shell structure hydrogen Oxide precursor Ni 0.50 Mn 0.43 Co 0.07 Al 0.007 (OH) 2 .
  • the preparation method of battery comprises the following steps:
  • the voltage test range and test system of the above-mentioned button battery that has been left still on the LAND battery test system are the same as in Example 1.
  • On the DQ/DV curve of the first cycle of the sample there is also an obvious oxidation peak corresponding to the characteristics of the shell material around 4.55V.
  • Li 1.23 Ni 0.50 Mn 0.43 Co 0.07 Al 0.007 O 2 The first discharge specific capacity of the positive electrode material is 214.0mAh/g, and the discharge specific capacity at 0.1C, 0.5C, 1.0C, 2.0C and other rates are 198.6mAh/g, 181.3mAh/g, 170.5mAh/g and 156.7mAh/g.
  • the discharge specific capacity of the first cycle of the material is 204.8mAh/g, after 30 cycles, the discharge specific capacity is 198.6mAh/g, and the cycle retention rate is 97.0%.
  • the heterogeneous core-shell materials still have good surface stability and structural stability.
  • a method for preparing a non-lithium-rich high manganese core-shell structure positive electrode material comprising the following steps:
  • control mixed metal salt solution B feeding speed is 70ml/min, by regulating the pH value of NaOH solution feeding speed regulation and control reaction system to 10.0,
  • the ammonia value of the reactor is controlled to maintain between 5-6g/L, stirring, and the feed is stopped when the particle size D50 is 12.0 ⁇ m, and then filtered, washed, and dried to obtain the core-shell structure hydrogen Oxide precursor Ni 0.84 Mn 0.06 Co 0.10 (OH) 2 .
  • the molar ratio is mixed evenly in the mixer; then the temperature is raised to 800°C for 12 hours at a heating rate of 2°C/min under an oxygen atmosphere to complete the high-temperature solid-phase sintering reaction, and the sintered products after the reaction are crushed and separated by sieving.
  • the core-shell structure cathode material Li 1.02 Ni 0.84 Mn 0.06 Co 0.10 O 2 was obtained.
  • the D50 of the cathode material was 11.6 ⁇ m, the shell thickness was about 0.25 ⁇ m, the BET was 0.18m 2 /g, and the particle size of the high-voltage ternary cathode material was D50 corresponds to a ratio of particle radius to shell thickness of about 46.4:1.
  • the preparation method of battery comprises the following steps:
  • Example 1 The voltage test range and test system of the button battery that has been statically infiltrated in the above steps on the LAND battery test system are the same as in Example 1.
  • the first charge and discharge curve of Li 1.02 Ni 0.84 Mn 0.06 Co 0.10 O 2 cathode material the first discharge specific capacity is 234.3mAh/g, the cathode material at 0.1C, 0.5C, 1.0C, 2.0C, etc.
  • the discharge specific capacities under the rate are 221.6mAh/g, 207.5mAh/g, 200.4mAh/g and 193.0mAh/g, respectively.
  • the discharge specific capacity of the material in the first cycle of the cycle is 196.7mAh/g
  • the discharge specific capacity is 109.6mAh/g
  • the cycle retention rate is 55.7%. Comparative Example 1 Due to the absence of the protection of the high manganese shell, the cycle stability of the material becomes significantly worse under high voltage, which is far from meeting the needs of practical applications.
  • a preparation method of a core-shell structure positive electrode material comprising the following steps:
  • control mixed metal salt solution B feeding speed is 60ml/min, by regulating the pH value of NaOH solution feeding speed regulation and control reaction system to 9.2,
  • the ammonia value of the reactor is controlled to maintain between 5-6g/L, stirring, and when the particle size D50 is 13.2 ⁇ m, the feed is stopped, and then filtered, washed, and dried to obtain the core-shell structure hydrogen Oxide precursor Ni 0.50 Mn 0.45 Co 0.05 (OH) 2 .
  • the molar ratio is mixed evenly in the mixer, that is, the total molar ratio of lithium hydroxide monohydrate to Ni, Mn, and Co elements in the core-shell structure precursor is 1.03:1; Raise the temperature to 800°C and keep it for 12 hours to complete the high-temperature solid-phase sintering reaction. After the reaction, the sintered product is crushed, sieved and separated to obtain a high-voltage ternary cathode material with a core-shell structure.
  • the shell thickness is about 1.35 ⁇ m
  • the particle size D50 of the ternary cathode material is 12.6 ⁇ m
  • the BET is 0.20m 2 /g.
  • the ratio of the particle size D50 of the primary cathode material to the thickness of the shell layer is about 9.3.
  • the preparation method of battery comprises the following steps:
  • Example 1 The voltage test range and test system of the button battery that has been statically infiltrated in the above steps on the LAND battery test system are the same as in Example 1.
  • the first discharge specific capacity of LiNi 0.50 Mn 0.45 Co 0.05 O 2 cathode material is 209.9mAh/g
  • the discharge specific capacity of the cathode material at 0.1C, 0.5C, 1.0C, 2.0C and other rates are 193.4mAh/g, 176.1 mAh/g, 165.1mAh/g and 142.6mAh/g.
  • the discharge specific capacity of the material in the first cycle of the cycle is 155.7mAh/g
  • the discharge specific capacity is 106.1mAh/g
  • the cycle retention rate is 68.1%.
  • Comparative Example 2 Due to the high manganese shell layer is too thick, the ratio of the positive electrode material D50 to the shell thickness is too small, the capacity of the sample under high pressure decreases, the rate performance deteriorates, and the cycle stability also deteriorates.

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Abstract

本发明提供了一种具有核壳结构的高电压三元正极材料及其制备方法，该高电压三元正极材料的化学式为Li xNi aMn bCo cM dO 2，其中1.03＜x≤1.3，0.50≤a≤0.65，0.30≤b≤0.45，0＜c≤0.10，a+b+c＝1，0≤d≤0.025，高电压三元正极材料包括内核和壳层；内核包括镍锰钴酸锂三元材料，镍、锰、钴的摩尔比为：(0.65～0.80):(0.05～0.60):(0.02～0.15)；壳层包括镍锰酸锂二元材料，镍、锰的摩尔比为：(0.10～0.60):(0.60～0.90)；其中，M为来源于内核和/或壳层的掺杂元素。本发明高电压三元正极材料能够在4.7V的超高电压下稳定工作，且具有超高的放电比容量和优异的倍率性能。

Description

一种具有核壳结构的高电压三元正极材料及其制备方法 技术领域
本发明属于锂离子电池正极材料技术领域，尤其涉及一种具有核壳结构的高电压三元正极材料及其制备方法。
背景技术
开发高镍层状和中低镍高电压层状氧化物是目前实现锂离子电池正极材料高能量密度的两条技术路线。但随着Ni含量的提高，高镍二次球颗粒的循环性能、热稳定性明显降低，由于锂镍混排程度的增大，导致材料表面的稳定性变差，同时材料在循环充放电过程中发生H2→H3相变并伴随着氧释放，导致晶格常数、晶胞体积反复收缩与膨胀，从而产生应力导致颗粒破碎，电解液浸入颗粒内部，加剧副反应恶化材料的电化学性能。镍锰钴三元材料天生就具有向高电压发展的趋势，放电比容量随着充电截止电压的升高而升高，当上限截止电压从4.2V提高至4.5V时，单位三元材料内锂离子的脱出数量可能会由0.45mol提高至0.60mol，相应的正极材料的克容量发挥越大，电池的容量越高。然而高的工作电压对正极材料与电解液之间的界面稳定性带来极大挑战。
为解决这些问题，目前产业界和学术界主要处理方式包括表面包覆、表面/体相掺杂等改性手段。离子掺杂指在不影响正极材料晶体结构的同时向晶格中掺入少量异质离子，提高材料晶体结构的稳定性并增大晶胞参数c，扩充锂离子传输通道，从而提升三元材料的容量、倍率和循环稳定性。表面包覆通过在三元材料的表面形成一层化合物，避免电解液与正极材料的直接接触，延缓相变，从而起到保护作用，提高电极材料的循环稳定性和热稳定性等。如CN202110525350.X专利提到的Al(PO 3) 3包覆NCM811正极材料，将商用NCM811和Al(PO 3) 3粉末干法研磨至颗粒细度适中，分布均匀后，在300℃-500℃温度下进行烧结，经保温一段时间再自然降温，待粉体取出，得到掺杂包覆了Al(PO 3) 3的高镍三元正极材料，改善了材料的倍率性能和循环稳定性。如CN201810954002.2专利中提出了一种碱金属元素或非金属元素掺杂改性的高镍三元正极材料。将三元前驱体粉末与含锂化合物、含掺杂元素的化合物混合，通过两步升温烧结获得共掺杂改性的高镍三元材料，降低了Ni 2+与Li +混排度，扩大了层间距从而使得结构更稳定，优化材料的倍率性能和循环稳定性。如CN202110416541.2专利提出了一种共沉淀法合成的Ni xCo yMn z(OH) 2球形氢氧化物前驱体与锂源、硼源、钠源混合低温焙烧，再高温烧结获得的镍钴锰单晶材料，再与铝源在空气环境下进行高温煅烧改性单晶材料，从而实现4.6V高电压测试体系下首次充放电比容量达184mAh/g。
上述技术方案虽然在有针对性的提升了材料的结构和/或表面稳定性，改善了材料的某一 方面的电化学性能，但其本质上，但并不能从材料的结构本身使得正极材料的性能得到优化，常常存在不同电化学性能指标或成本方面的制衡效果。CN202110525350.X专利提到的Al(PO 3) 3包覆NCM811正极材料，虽然改善了材料的表面稳定性，但存在包覆量过少时包覆不均匀，包覆量过多时材料的容量受到严重影响等问题，而且对于提升正极材料的工作电压没有有益效果。CN201810954002.2专利提出了一种碱金属元素或非金属元素掺杂改性的高镍三元正极材料，虽然改善了材料的结构稳定性，但该方法对材料性能的提升无法满足目前的市场需求，且该方法获得的材料无法通过提升工作电压进一步提升材料的能量密度。CN202110416541.2专利通过单晶化实现了4.6V高电压测试体系下首次充放电比容量达184mAh/g，但该方法中涉及的技术和方法无法避免单晶材料倍率和循环性能差等问题。
发明内容
本发明所要解决的技术问题是，克服以上背景技术中提到的不足和缺陷，提供一种具有核壳结构的高电压三元正极材料及其制备方法，其将NMC三元正极材料和镍锰材料结合起来，获得一种具有核壳结构且整体富锂的高电压三元正极材料，该材料能够在4.7V的超高电压下稳定工作，还具有超高的放电比容量和优异的倍率性能。
为解决上述技术问题，本发明提出的技术方案为：
一种具有核壳结构的高电压三元正极材料，所述高电压三元正极材料的化学式为Li xNi aMn bCo cM dO 2，其中1.03＜x≤1.3，0.50≤a≤0.65，0.30≤b≤0.45，0＜c≤0.10，a+b+c＝1，0≤d≤0.025，所述高电压三元正极材料包括内核和壳层；
所述内核包括镍锰钴酸锂三元材料，镍、锰、钴的摩尔比为：(0.65～0.80):(0.05～0.60):(0.02～0.15)；
所述壳层包括镍锰酸锂二元材料，镍、锰的摩尔比为：(0.10～0.60):(0.60～0.90)；
其中，M为来源于内核和/或壳层的掺杂元素。
优选的，壳层的厚度为0.25～1.25μm，所述三元正极材料的粒径D50与壳层厚度的比值为(10～35):1，进一步优选的，所述三元正极材料的粒径D50与壳层厚度的比值为(13～20):1。
对于本发明具有核壳结构的高电压三元正极材料，若壳层太厚，材料的容量可能会下降，而高锰壳层太薄，无法有效保护材料在3.0～4.7V高电压下的循环稳定性。
优选的，M选自Al、Zr、Mg、Ti、Ta、W、Nb、Sn、Co、Na中的一种或几种。
优选的，由所述高电压三元正极材料制作的扣式电池，在室温下以0.05C倍率充电至4.7V时，由首圈充电曲线得到的电压DQ/DV微分容量曲线上于电压V 1～V 2之间出现明显的氧化峰，且V 1＞4.4V，V 2＜4.6V。进一步优选的，所述氧化峰的峰顶点所对应的电压值在4.5～4.58V范围内。
优选的，x的取值范围为1.06＜x≤1.23；所述内核中镍、锰、钴的摩尔比为(0.65～0.80):(0.10～0.25):(0.05～0.1)；所述壳层中镍、锰的摩尔比为(0.20～0.30):(0.70～0.80)。
优选的，所述高电压三元正极材料的粒径D50为11.0～14.5μm，BET为0.2～0.6m 2/g。
作为一个总的发明构思，本发明提供了一种具有核壳结构的高电压三元正极材料的制备方法，包括以下步骤：
(1)按照内核的化学计量比，配制含有Ni 2+、Co 2+、Mn 2+和M元素的混合金属盐溶液，按照壳层的化学计量比，配制含有Ni 2+、Mn 2+和M元素的镍锰混合金属盐溶液；
(2)将混合金属盐溶液、碱液、氨水溶液同时加入反应釜，控制反应釜中的pH为10～12，反应形成设计粒径的氢氧化物前驱体核之后，停止进料，得到氢氧化物前驱体核；
(3)然后向所述反应釜中同时通入所述镍锰混合金属盐溶液以及碱液、氨水溶液，控制反应釜中的pH为8～10，在氢氧化物前驱体核表面反应得到设计厚度的前驱体壳层之后，过滤、洗涤、干燥得到核壳结构前驱体；
(4)将锂源、核壳结构前驱体混合均匀，烧结后破碎，得到具有核壳结构的高电压三元正极材料。
优选的，所述碱液为8～11mol/L的NaOH溶液；所述氨水溶液的浓度为6～8mol/L；
步骤(2)中，通过调节氨水溶液的进料速度控制反应釜中氨值在7～8g/L之间；步骤(3)中，通过调节氨水溶液的进料速度控制反应釜中氨值在5～6g/L之间。
优选的，步骤(4)中，所述锂源与核壳结构前驱体中Ni、Mn、Co元素的总摩尔比为(1.10～1.40):1。本发明通过结合壳层的厚度以及烧结温度等参数，确定了锂源与核壳结构前驱体中Ni、Mn、Co元素的总摩尔量的摩尔比为1.10～1.40的范围，使相应的DQ/DV微分容量曲线中的首圈充电曲线在4.5V附近出现的氧化峰较为显著。进一步优选的，所述锂源与核壳结构前驱体中Ni、Mn、Co元素的总摩尔量的摩尔比为1.10～1.28:1。
优选的，步骤(4)中，所述烧结的温度为700～950℃，时间为8～14h。当烧结温度过高或时间过长时，正极材料二次球颗粒的一次颗粒尺寸会偏大，壳层Mn元素向核层扩散严重，富锂锰基壳层结构将变很薄或者消失，材料无法在高电压下发挥循环性能的优势；烧结温度过低时或者烧结时间过短时，材料的残锂会升高，同时样品的一次颗粒过小，材料的结晶度较差，层状结构较差，材料在高电压下无法有效发挥高容量以及循环稳定性。
进一步优选的，烧结时在空气气氛或者氧气气氛下以2～3℃/min的升温速率升温至烧结的温度。
本发明中，采用的镍源包括硝酸镍、硫酸镍、氯化镍、乙酸镍中的一种或多种；采用的钴源包括硝酸钴、硫酸钴、氯化钴、乙酸钴中的一种或多种；采用的锰源包括硝酸锰、硫酸 锰、氯化锰、乙酸锰中的一种或多种；采用的锂源包括碳酸锂、硝酸锂、草酸锂、醋酸锂、单水氢氧化锂、氢氧化锂中的一种或多种。
与现有技术相比，本发明的有益效果：
(1)本发明中具有核壳结构的高电压三元正极材料，壳层包括镍锰酸锂二元材料，该镍锰酸锂二元材料含有低含量的镍元素、高含量的锰元素、锂元素以及氧元素，可提高三元正极材料整体的热稳定性和电化学稳定性；基于核壳组分的构成，本发明进一步通过严格控制核壳中内核的半径与壳层厚度的比值等，对最终得到核壳结构的三元正极材料的镍钴锰元素分布情况进行严格控制，同时还使材料整体中锂的摩尔含量大于过渡金属元素(包括镍钴锰以及选择性使用的掺杂或包覆元素)的摩尔含量，最终发现本发明提供的具有核壳结构的高电压三元正极材料具有富锂锰基材料在高电压下运行的特征，可将三元材料体系的电池测试范围拓宽至3.0～4.7V，提高了材料的高电压循环性能，更显著的效果发现是，在材料首次充放电曲线对应的DQ/DV曲线上，首圈充电曲线在4.40～4.60V电压范围内出现明显的氧化峰，该峰位与富锂锰基材料的特征氧化峰对应而非常规的三元材料，即本发明中核壳结构的元素设计、核壳比例设计，使得最终得到的成品材料显现出富锂锰基的性质并具有较为优异的电性能数据，其组装的扣式电池在3.0～4.7V的电压区间内首次放电比容量可达221.0mAh/g，首次库伦效率可达到85.4％，在1C下的放电比容量可达182.1mAh/g，在0.1C的倍率下经过30次循环后容量依然可达203.4mAh/g。
(2)本发明具有核壳结构的高电压三元正极材料的制备方法，具有核壳结构的三元氢氧化物前驱体经过烧结之后的材料无需水洗，去除了常规高镍材料的水洗工艺，缓解了水洗对材料表面的破坏，且材料的合成过程无需二次烧结包覆，一方面降低了传统包覆层的存在对材料容量的影响，另一方面节省了生产成本。本发明制备过程中不涉及附加的资源及能源消耗，降低了材料的生产成本，且在去除水洗工艺的同时能够保证材料的表面总残锂量≤1000ppm，符合行业规范的标准值。
(3)本发明制备工艺简单且易于放大，容易实现正极材料实验室级制备向产线生产扩大，过程简单且易于排查解决放大过程产生的差异，降低了放大复试材料、资源的成本消耗。
附图说明
为了更清楚地说明本发明实施例或现有技术中的技术方案，下面将对实施例或现有技术描述中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图是本发明的一些实施例，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，还可以根据这些附图获得其他的附图。
图1是本发明实施例1中制备的高电压三元正极材料的截面SEM图像；
图2是本发明实施例1中制备的高电压三元正极材料的SEM图像；
图3是本发明实施例1中制备的高电压三元正极材料的EDS面扫描图谱；
图4是本发明实施例1中制备的高电压三元正极材料的XRD图谱；
图5是本发明实施例1中制备的高电压三元正极材料的首次充放电曲线；
图6是本发明实施例1中制备的高电压三元正极材料的DQ/DV曲线；
图7是本发明实施例1中制备的高电压三元正极材料的倍率性能；
图8是本发明实施例1中制备的高电压三元正极材料在0.1C下的循环性能；
图9是本发明实施例1中制备的高电压三元正极材料在1C下的循环性能；
图10是本发明对比例1中制备的非富锂高锰核壳结构正极材料的首次充放电曲线；
图11是本发明对比例1中制备的非富锂高锰核壳结构正极材料在1C下的循环性能。
具体实施方式
为了便于理解本发明，下文将结合说明书附图和较佳的实施例对本发明做更全面、细致地描述，但本发明的保护范围并不限于以下具体实施例。
除非另有定义，下文中所使用的所有专业术语与本领域技术人员通常理解含义相同。本文中所使用的专业术语只是为了描述具体实施例的目的，并不是旨在限制本发明的保护范围。
除非另有特别说明，本发明中用到的各种原材料、试剂、仪器和设备等均可通过市场购买得到或者可通过现有方法制备得到。
实施例1：
一种具有核壳结构的高电压三元正极材料，经ICP元素含量测试可确定其整体的化学式为Li 1.19Ni 0.57Mn 0.36Co 0.07O 2，图1为上述高电压三元正极材料的截面SEM图像，表明经过烧结后，该三元正极材料依然具有明显的核壳结构，包括内核和壳层，内核包括镍锰钴酸锂三元材料，镍、锰、钴的摩尔比为0.70:0.20:0.10，壳层包括镍锰酸锂二元材料，镍、锰的摩尔比为0.30:0.70；其中，三元正极材料的粒径D50为11.5μm，壳层厚度为0.75μm左右，BET为0.54m 2/g，三元正极材料的粒径D50与壳层厚度的比值约为15.4。
上述粒径D50可由马尔文粒度仪测试得到，壳层厚度可通过高电压三元正极材料的截面SEM图像得到，由于采用本发明中的实施例工艺制备出来的壳层厚度较为均一，可取一与D50粒径数值较为接近的二次颗粒截面图，即可知道高电压三元正极材料的整体壳厚，若通过观察截面SEM图像发现壳层的厚度有所差异，本领域技术人员也可根据实际情况及需求，取多个二次颗粒的截面图像的壳厚并作平均值从而得到壳层厚度。在合适的烧结温度下，材料的壳厚基本继承自前驱体，但是由于混料、烧结、破碎等工序的影响，成品核-壳正极材料的D50可能会和前驱体的D50不完全一致。
制备方法包括以下步骤：
(1)前驱体的制备：以纯水作为溶剂，选取NiSO 4·6H 2O、CoSO 4·7H 2O、MnSO 4·H 2O作为原料，按照Ni 2+:Co 2+:Mn 2+(摩尔比)＝0.70:0.10:0.20配制2mol/L混合金属盐溶液A，按照Ni 2+:Mn 2+(摩尔比)＝0.30:0.70配制2mol/L混合金属盐溶液B，同时配制浓度为9mol/L的NaOH溶液和浓度为7mol/L的氨水溶液。
通过质量流量计将溶液混合金属盐溶液A、NaOH溶液、氨水溶液同时加入反应釜中，控制混合金属盐溶液A的进料速度为110ml/min，通过调节NaOH溶液进料速度调控反应体系的pH值至11，同时通过调节氨水溶液的进料速度控制反应釜氨值维持在7～8g/L之间，搅拌，当颗粒粒度D50为10.5μm时停止进料，得到的氢氧化物前驱体核Ni 0.7Mn 0.2Co 0.1(OH) 2。
然后将混合金属盐溶液B、NaOH溶液、氨水溶液同时加入上述反应釜中，控制混合金属盐溶液B进料速度为60ml/min，通过调节NaOH溶液进料速度调控反应体系的pH值至9.2，同时通过调节氨水溶液的进料速度控制反应釜氨值维持在5～6g/L之间，搅拌，当颗粒粒度D50为12.0μm时停止进料，然后经过滤、洗涤、干燥得到核壳结构氢氧化物前驱体Ni 0.57Mn 0.36Co 0.07(OH) 2。
(2)正极材料的制备：
将步骤(1)得到的核壳结构氢氧化物前驱体Ni 0.57Mn 0.36Co 0.07(OH) 2，与单水氢氧化锂按Li:Me(Me＝Ni+Mn+Co)＝1.24:1的摩尔比例在混料机中混合均匀，其中Li:Me(Me＝Ni+Mn+Co)＝1.24:1即表示单水氢氧化锂与核壳结构前驱体中Ni、Mn、Co元素的总摩尔量的摩尔比为1.24:1；然后在氧气气氛下以2℃/min的升温速率，升温至800℃保温12h，完成高温固相烧结反应，反应之后的烧结产物进行破碎、过筛分离，得到具有核壳结构的高电压三元正极材料。
图2为完成锂化烧结之后的核壳结构高电压三元正极材料的SEM图像，所制备的高电压三元正极材料为大量的一次球颗粒组成的二次球。对材料截面进行了元素面分布分析，结果如图3所示，可以看出二次球截面的元素分布为Ni、Co元素核层高壳层低，Mn元素核层低壳层高，表明所制备的正极材料具有高锰壳层。
如图4所示，为正极材料的XRD图谱，样品的所有衍射峰均与具有六方α-NaFeO 2层状结构的LiNiO 2(JCPDS CardNo.74-0919)相保持一致，但所有衍射峰的位置均向小角度方向发生了微小的偏移，这主要是由于离子半径较大的Co 2+和Mn 2+取代了部分的Ni 2+，导致材料的晶格扩张，晶面间距增大。
电池的制备方法包括以下步骤：
将步骤(2)得到的料Li 1.19Ni 0.57Mn 0.36Co 0.07O 2正极材料与导电剂SP、粘结剂(PVDF)按 照8:1:1的比例混合均匀。用移液枪量取2mLNMP溶液作为溶剂加入到上述混合粉体材料中，搅拌20min后涂布在铝箔上，放入鼓风干燥箱中在110℃的温度下烘干。按照负极壳→垫片→锂片→电解液→隔膜→电解液→正极片→垫片→弹片→正极壳的顺序依次放置各组件及电解液，在扣式电池封口机模具上完成封装后静置12h。
将上述完成静置浸润的扣式电池置于LAND电池测试系统上进行电化学性能的测试。首先在3.0～4.7V的电压区间、0.05C(1C＝215mAh/g)的倍率下通过恒流充电+恒压充电的模式完成电池的活化，然后在0.05C的倍率下进行首次充放电测试。
如图5所示，所制备的正极材料的首次充放电曲线，所制备的Li 1.19Ni 0.57Mn 0.36Co 0.07O 2正极材料首次放电比容量为221.0mAh/g，对应的DQ/DV曲线如图6所示，具有表面富锂特性的核壳结构的三元材料的充放电曲线与常规三元材料形状不同，DQ/DV曲线4.55V附近的氧化峰与富锂锰基材料保持一致，表现出富锂高锰壳层的独特性。倍率性能的测试以相同倍率充电-不同倍率放电的模式完成测试，充电在0.5C的倍率下完成，放电分别在0.1C、0.5C、1.0C、2.0C的倍率下完成。图7为材料的倍率性能测试结果，所制备的料Li 1.19Ni 0.57Mn 0.36Co 0.07O 2正极材料在各个倍率下的放电比容量依次为208.1mAh/g、192.2mAh/g、182.1mAh/g和168.1mAh/g。在0.1C的电流密度下进行电极材料的循环性能测试，得到的结果如图8所示，扣式电池的循环首次放电比容量为214.4mAh/g，经过30次循环之后放电比容量为203.4mAh/g，循环保持率为94.8％。此外，如图9所示，样品在1.0C大电流密度下的循环首圈放电比容量为167.4mAh/g，经过50圈循环后放电容量为135.6mAh/g，表明材料在高电压下具有良好的表面稳定性和结构稳定性。
实施例2：
一种具有核壳结构的高电压三元正极材料，经ICP元素含量测试可确定其整体的化学式为Li 1.23Ni 0.60Mn 0.34Co 0.06O 2，该三元正极材料依包括内核和壳层，内核包括镍锰钴酸锂三元材料，镍、锰、钴的摩尔比为0.80:0.10:0.10，壳层包括镍锰酸锂二元材料，镍、锰的摩尔比为0.30:0.70；其中，三元正极材料的粒径D50为11.8μm，壳层厚度为0.90μm左右，BET为0.46m 2/g。三元正极材料的粒径D50与壳层厚度的比值约为13.2:1。
制备方法包括以下步骤：
(1)前驱体的制备：以纯水作为溶剂，选取NiSO 4·6H 2O、CoSO 4·7H 2O、MnSO 4·H 2O作为原料，按照Ni 2+:Co 2+:Mn 2+(摩尔比)＝0.80:0.10:0.10配制3mol/L的混合金属盐溶液A，按照Ni 2+:Mn 2+(摩尔比)＝0.30:0.70配制3mol/L混合金属盐溶液B，同时配制浓度为10mol/L的NaOH溶液和浓度为7mol/L的氨水溶液。
通过质量流量计将溶液混合金属盐溶液A、NaOH溶液、氨水溶液同时加入反应釜中， 控制混合金属盐溶液A的进料速度为110ml/min，通过调节NaOH溶液进料速度调控反应体系的pH值至12，同时通过调节氨水溶液的进料速度控制反应釜氨值维持在7～8g/L之间，搅拌，当颗粒粒度D50为10.0μm时停止进料，得到的氢氧化物前驱体核Ni 0.8Mn 0.1Co 0.1(OH) 2。
然后，将混合金属盐溶液B、NaOH溶液、氨水溶液同时加入上述反应釜中，控制混合金属盐溶液B进料速度为60ml/min，通过调节NaOH溶液进料速度调控反应体系的pH值至8，同时通过调节氨水溶液的进料速度控制反应釜氨值维持在5～6g/L之间，搅拌，当颗粒粒度D50为11.8μm时停止进料，然后经过滤、洗涤、干燥得到核壳结构氢氧化物前驱体Ni 0.60Mn 0.34Co 0.06(OH) 2。
(2)正极材料的制备：
将步骤(1)得到的核壳结构氢氧化物前驱体Ni 0.60Mn 0.34Co 0.06(OH) 2，与碳酸锂按Li:Me(Me＝Ni+Mn+Co)＝1.28:1的摩尔比例在混料机中混合均匀；然后采用两步法烧结工艺，在氧气氛围中以2℃/min的升温速率升温至500℃，保温6h后再升温至850℃，保温10h，完成高温固相烧结反应，反应之后的烧结产物进行破碎、过筛分离，得到具有核壳结构的高电压三元正极材料。
电池的制备方法包括以下步骤：
将步骤(2)得到的Li 1.23Ni 0.60Mn 0.34Co 0.06O 2正极材料与导电剂SP、粘结剂(PVDF)按照90:5:5的比例混合均匀。用移液枪量取1mLNMP溶液作为溶剂加入到上述混合粉体材料中，搅拌30min后涂布在铝箔上。极片烘干、扣式电池组装等步骤同实施例1。
将上述完成静置的扣式电池于LAND电池测试系统上开始电化学性能的测试。测试电压区间为3.0～4.7V，扣电测试制度同实施例1。
所制备的Li 1.23Ni 0.60Mn 0.34Co 0.06O 2正极材料首圈DQ/DV微分容量曲线上在4.55V附近出现明显的氧化峰，和富锂锰基材料特征峰相对应。首次放电比容量为218.1mAh/g，在各个倍率下(0.1C、0.5C、1.0C、2.0C)的放电比容量分别为202.3mAh/g、185.2mAh/g、174.6mAh/g和160.8mAh/g。活化后的扣式电池在0.1C的电流密度下循环首圈放电比容量为208.1mAh/g，经过30次循环之后放电比容量为196.4mAh/g，循环保持率为94.3％，在高电压下该材料依然具有良好的表面稳定性和结构稳定性。
实施例3：
一种具有核壳结构的高电压三元正极材料，经ICP元素含量测试可确定其整体的化学式为Li 1.06Ni 0.57Mn 0.40Co 0.03O 2，该三元正极材料包括内核和壳层，内核包括镍锰钴酸锂三元材料，镍、锰、钴的摩尔比为0.75:0:20:0.05；壳层包括镍锰酸锂二元材料，镍、锰的摩尔比为0.20:0.80；其中，三元正极材料的D50为12.0μm，壳层厚度为0.62μm左右，BET为0.38m 2/g。三元正极材 料的粒径D50与壳层厚度的比值约为19.4:1。
一种具有核壳结构的高电压三元正极材料，制备方法包括以下步骤：
(1)前驱体的制备：以纯水作为溶剂，选取NiSO 4·6H 2O、CoSO 4·7H 2O、MnSO 4·H 2O作为原料，按照Ni 2+:Co 2+:Mn 2+(摩尔比)＝0.75:0.05:0:20配制2mol/L混合金属盐溶液A，按照Ni 2+:Mn 2+(摩尔比)＝0.20:0.80配制2mol/L混合金属盐溶液B，同时配制浓度为9mol/L的NaOH溶液和浓度为7mol/L的氨水溶液。
通过质量流量计将溶液混合金属盐溶液A、NaOH溶液、氨水溶液同时加入反应釜中，控制混合金属盐溶液A的进料速度为100ml/min，通过调节NaOH溶液进料速度调控反应体系的pH值至10，同时通过调节氨水溶液的进料速度控制反应釜氨值维持在7～8g/L之间，搅拌，当颗粒粒度D50为10.3μm时停止进料，得到的氢氧化物前驱体核Ni 0.75Mn 0.20Co 0.05(OH) 2。
然后将混合金属盐溶液B、NaOH溶液、氨水溶液同时加入上述反应釜中，控制混合金属盐溶液B进料速度为60ml/min，通过调节NaOH溶液进料速度调控反应体系的pH值至8，同时通过调节氨水溶液的进料速度控制反应釜氨值维持在5～6g/L之间，搅拌，当颗粒粒度D50为11.8μm时停止进料，然后经过滤、洗涤、干燥得到核壳结构氢氧化物前驱体Ni 0.57Mn 0.40Co 0.03(OH) 2。
(2)正极材料的制备：
将步骤(1)得到的核壳结构氢氧化物前驱体Ni 0.57Mn 0.40Co 0.03(OH) 2，与氢氧化锂按Li:Me(Me＝Ni+Mn+Co)＝1.12:1的摩尔比例在混料机中混合均匀；然后在空气气氛下以3℃/min的升温速率，升温至950℃保温10h，完成高温固相烧结反应，反应之后的烧结产物进行破碎、过筛分离，得到具有核壳结构的高电压三元正极材料。
电池的制备方法包括以下步骤：
由步骤(2)得到的Li 1.06Ni 0.57Mn 0.40Co 0.03O 2正极材料的扣式电池涂布配方、扣式电池组装工艺同实施例1。
将上述完成静置的扣式电池在LAND电池测试系统上的电压测试区间以及测试制度同实施例1。样品材料的首圈DQ/DV微分容量曲线上同样地在4.55V附近出现了和富锂锰基材料特征峰相对应的氧化峰。Li 1.06Ni 0.57Mn 0.40Co 0.03O 2正极材料首次放电比容量为215.6mAh/g，在0.1C、0.5C、1.0C、2.0C等倍率下的放电比容量分别为199.7mAh/g、183.7mAh/g、173.3mAh/g和159.7mAh/g。在0.1C的电流密度下材料的循环首圈放电比容量为205.5mAh/g，经过30次循环之后放电比容量为191.1mAh/g，循环保持率为92.9％，在高电压下该材料依然具有良好的表面稳定性和结构稳定性。
实施例4：
一种具有核壳结构的高电压三元正极材料，经ICP元素含量测试可确定其整体的化学式为Li 1.23Ni 0.50Mn 0.43Co 0.07Al 0.007O 2，该三元正极材料包括内核和壳层，内核包括镍锰钴酸锂三元材料，镍、锰、钴的摩尔比为0.65:0.25:0.10；壳层包括镍锰酸锂二元材料，镍、锰的摩尔比为0.20:0.80；其中，三元正极材料的粒径D50为11.8μm，壳层厚度为0.75μm左右，BET为0.26m 2/g，三元正极材料的粒径D50与壳层厚度的比值约为15.8:1。
制备方法包括以下步骤：
(1)前驱体的制备：以纯水作为溶剂，选取NiSO 4·6H 2O、CoSO 4·7H 2O、MnSO 4·H 2O、硝酸铝作为原料，按照Ni 2+:Co 2+:Mn 2+(摩尔比)＝0.65:0.10:0.25配制2mol/L混合金属盐溶液A，按照Ni 2+:Mn 2+:Al 3+(摩尔比)＝0.20:0.80:0.02配制2mol/L混合金属盐溶液B，同时配制浓度为9mol/L的NaOH溶液和浓度为7mol/L的氨水溶液。
通过质量流量计将溶液混合金属盐溶液A、NaOH溶液、氨水溶液同时加入反应釜中，控制混合金属盐溶液A的进料速度为110ml/min，通过调节NaOH溶液进料速度调控反应体系的pH值至11，同时通过调节氨水溶液的进料速度控制反应釜氨值维持在7～8g/L之间，搅拌，当颗粒粒度D50为10.5μm时停止进料，得到的氢氧化物前驱体核Ni 0.65Mn 0.25Co 0.1(OH) 2。
然后将混合金属盐溶液B、NaOH溶液、氨水溶液同时加入上述反应釜中，控制混合金属盐溶液B进料速度为60ml/min，通过调节NaOH溶液进料速度调控反应体系的pH值至8，同时通过调节氨水溶液的进料速度控制反应釜氨值维持在5～6g/L之间，搅拌，当颗粒粒度D50为12.0μm时停止进料，然后经过滤、洗涤、干燥得到核壳结构氢氧化物前驱体Ni 0.50Mn 0.43Co 0.07Al 0.007(OH) 2。
(2)正极材料的制备：
将步骤(1)得到的核壳结构氢氧化物前驱体Ni 0.50Mn 0.43Co 0.07Al 0.007(OH) 2，与单水氢氧化锂按Li:Me(Me＝Ni+Mn+Co)＝1.27:1的摩尔比例在混料机中混合均匀；然后在氧气气氛下以2℃/min的升温速率，升温至850℃保温12h，完成高温固相烧结反应，反应之后的烧结产物进行破碎、过筛分离，得到具有核壳结构的高电压三元正极材料。
电池的制备方法包括以下步骤：
由步骤(2)得到的Li 1.23Ni 0.50Mn 0.43Co 0.07Al 0.007O 2正极材料的扣式电池涂布配方、扣式电池组装工艺同实施例1。
将上述完成静置的扣式电池在LAND电池测试系统上的电压测试区间以及测试制度同实施例1。样品的首圈DQ/DV曲线上，在4.55V附近同样的出现了和壳层材料特征相对应的明显的氧化峰。Li 1.23Ni 0.50Mn 0.43Co 0.07Al 0.007O 2正极材料首次放电比容量为214.0mAh/g，在0.1C、0.5C、1.0C、2.0C等倍率下的放电比容量分别为198.6mAh/g、181.3mAh/g、170.5mAh/g和156.7mAh/g。 在0.1C的电流密度下材料的循环首圈放电比容量为204.8mAh/g，经过30次循环之后放电比容量为198.6mAh/g，循环保持率为97.0％，在高电压下该壳层掺杂的核壳材料依然具有良好的表面稳定性和结构稳定性。
对比例1：
一种非富锂高锰核壳结构正极材料的制备方法，包括以下步骤：
(1)前驱体的制备：以纯水作为溶剂，选取NiSO 4·6H 2O、CoSO 4·7H 2O、MnSO 4·H 2O作为原料，按照Ni 2+:Co 2+:Mn 2+(摩尔比)＝0.87:0.10:0.03配制2mol/L混合金属盐溶液A，按照Ni 2+:Co 2+:Mn 2+(摩尔比)＝0.60:0.10:0.30配制2mol/L混合金属盐溶液B，同时配制浓度为9mol/L的NaOH溶液和浓度为7mol/L的氨水溶液。
通过质量流量计将溶液混合金属盐溶液A、NaOH溶液、氨水溶液同时加入反应釜中，控制混合金属盐溶液A的进料速度为110ml/min，通过调节NaOH溶液进料速度调控反应体系的pH值至11，同时通过调节氨水溶液的进料速度控制反应釜氨值维持在7～8g/L之间，搅拌，当颗粒粒度D50为11.5μm时停止进料，得到的氢氧化物前驱体核Ni 0.87Mn 0.03Co 0.10(OH) 2。
然后将混合金属盐溶液B、NaOH溶液、氨水溶液同时加入上述反应釜中，控制混合金属盐溶液B进料速度为70ml/min，通过调节NaOH溶液进料速度调控反应体系的pH值至10.0，同时通过调节氨水溶液的进料速度控制反应釜氨值维持在5～6g/L之间，搅拌，当颗粒粒度D50为12.0μm时停止进料，然后经过滤、洗涤、干燥得到核壳结构氢氧化物前驱体Ni 0.84Mn 0.06Co 0.10(OH) 2。
(2)正极材料的制备：
将步骤(1)得到的核壳结构氢氧化物前驱体Ni 0.84Mn 0.06Co 0.10(OH) 2，与单水氢氧化锂按Li:Me(Me＝Ni+Mn+Co)＝1.06:1的摩尔比例在混料机中混合均匀；然后在氧气气氛下以2℃/min的升温速率，升温至800℃保温12h，完成高温固相烧结反应，反应之后的烧结产物进行破碎、过筛分离，得到核壳结构正极材料Li 1.02Ni 0.84Mn 0.06Co 0.10O 2，该正极材料的D50为11.6μm，壳层厚度为0.25μm左右，BET为0.18m 2/g，高电压三元正极材料粒径D50对应颗粒半径与壳层厚度的比值约为46.4:1。
电池的制备方法包括以下步骤：
由步骤(2)得到的Li 1.02Ni 0.84Mn 0.06Co 0.10O 2正极材料的扣式电池涂布配方、扣式电池组装工艺同实施例1。
将上述步骤中完成静置浸润的扣式电池在LAND电池测试系统上的电压测试区间以及测试制度同实施例1。
如图10所示为Li 1.02Ni 0.84Mn 0.06Co 0.10O 2正极材料的首次充放电曲线，首次放电比容量为234.3mAh/g，该正极材料在0.1C、0.5C、1.0C、2.0C等倍率下的放电比容量分别为221.6mAh/g、207.5mAh/g、200.4mAh/g和193.0mAh/g。如图11所示在1.0C的电流密度下材料的循环首圈放电比容量为196.7mAh/g，经过50次循环之后放电比容量为109.6mAh/g，循环保持率为55.7％，对比例1由于没有高锰壳层的保护，在高电压下材料的循环稳定性明显变差，远达不到实际应用的需求。
对比例2：
一种核壳结构正极材料的制备方法，包括以下步骤：
(1)前驱体的制备：以纯水作为溶剂，选取NiSO 4·6H 2O、CoSO 4·7H 2O、MnSO 4·H 2O作为原料，按照Ni 2+:Co 2+:Mn 2+(摩尔比)＝0.70:0.10:0.20配制2mol/L混合金属盐溶液A，按照Ni 2+:Mn 2+(摩尔比)＝0.30:0.70配制2mol/L混合金属盐溶液B，同时配制浓度为9mol/L的NaOH溶液和浓度为7mol/L的氨水溶液。
通过质量流量计将溶液混合金属盐溶液A、NaOH溶液、氨水溶液同时加入反应釜中，控制混合金属盐溶液A的进料速度为110ml/min，通过调节NaOH溶液进料速度调控反应体系的pH值至11，同时通过调节氨水溶液的进料速度控制反应釜氨值维持在7～8g/L之间，搅拌，当颗粒粒度D50为10.5μm时停止进料，得到的氢氧化物前驱体核Ni 0.7Mn 0.2Co 0.1(OH) 2。
然后将混合金属盐溶液B、NaOH溶液、氨水溶液同时加入上述反应釜中，控制混合金属盐溶液B进料速度为60ml/min，通过调节NaOH溶液进料速度调控反应体系的pH值至9.2，同时通过调节氨水溶液的进料速度控制反应釜氨值维持在5～6g/L之间，搅拌，当颗粒粒度D50为13.2μm时停止进料，然后经过滤、洗涤、干燥得到核壳结构氢氧化物前驱体Ni 0.50Mn 0.45Co 0.05(OH) 2。
(2)正极材料的制备：
将步骤(1)得到的核壳结构氢氧化物前驱体Ni 0.50Mn 0.45Co 0.05(OH) 2，与单水氢氧化锂按Li:Me(Me＝Ni+Mn+Co)＝1.03:1的摩尔比例在混料机中混合均匀，即单水氢氧化锂与核壳结构前驱体中Ni、Mn、Co元素的总摩尔比为1.03:1；然后在氧气气氛下以2℃/min的升温速率，升温至800℃保温12h，完成高温固相烧结反应，反应之后的烧结产物进行破碎、过筛分离，得到具有核壳结构的高电压三元正极材料。经ICP元素含量测试可确定其整体的化学式为LiNi 0.50Mn 0.45Co 0.05O 2，壳层厚度为1.35μm左右，三元正极材料的粒径D50为12.6μm，BET为0.20m 2/g，三元正极材料的粒径D50与壳层厚度的比值约为9.3。
电池的制备方法包括以下步骤：
由步骤(2)得到的LiNi 0.50Mn 0.45Co 0.05O 2正极材料的扣式电池涂布配方、扣式电池组装 工艺同实施例1。
将上述步骤中完成静置浸润的扣式电池在LAND电池测试系统上的电压测试区间以及测试制度同实施例1。
LiNi 0.50Mn 0.45Co 0.05O 2正极材料首次放电比容量为209.9mAh/g，该正极材料在0.1C、0.5C、1.0C、2.0C等倍率下的放电比容量分别为193.4mAh/g、176.1mAh/g、165.1mAh/g和142.6mAh/g。如图11所示在1.0C的电流密度下材料的循环首圈放电比容量为155.7mAh/g，经过50次循环之后放电比容量为106.1mAh/g，循环保持率为68.1％，对比例2由于高锰壳层过厚，正极材料D50与壳厚比值过小，样品在高压下的容量下降，倍率性能变差，循环稳定性也变差。

Claims (10)

  1. 一种具有核壳结构的高电压三元正极材料，其特征在于，所述高电压三元正极材料的化学式为Li xNi aMn bCo cM dO 2，其中1.03＜x≤1.3，0.50≤a≤0.65，0.30≤b≤0.45，0＜c≤0.10，a+b+c＝1，0≤d≤0.025，所述高电压三元正极材料包括内核和壳层；
    所述内核包括镍锰钴酸锂三元材料，镍、锰、钴的摩尔比为：(0.65～0.80):(0.05～0.60):(0.02～0.15)；
    所述壳层包括镍锰酸锂二元材料，镍、锰的摩尔比为：(0.10～0.60):(0.60～0.90)；
    其中，M为来源于内核和/或壳层的掺杂元素。
  2. 根据权利要求1所述的高电压三元正极材料，其特征在于，所述壳层的厚度为0.25～1.25μm，所述三元正极材料的粒径D50与壳层厚度的比值为(10～35):1。
  3. 根据权利要求1所述的高电压三元正极材料，其特征在于，M选自Al、Zr、Mg、Ti、Ta、W、Nb、Sn、Co、Na中的一种或几种。
  4. 根据权利要求1～3任一项所述的高电压三元正极材料，其特征在于，由所述高电压三元正极材料制作的扣式电池，在室温下以0.05C倍率充电至4.7V时，由首圈充电曲线得到的电压DQ/DV微分容量曲线上于电压V 1～V 2之间出现明显的氧化峰，且V 1＞4.4V，V 2＜4.6V。
  5. 根据权利要求1～3任一项所述的高电压三元正极材料，其特征在于，x的取值范围为1.06＜x≤1.23；所述内核中镍、锰、钴的摩尔比为(0.65～0.80):(0.10～0.25):(0.05～0.1)；所述壳层中镍、锰的摩尔比为(0.20～0.30):(0.70～0.80)。
  6. 根据权利要求1～3任一项所述的高电压三元正极材料，其特征在于，所述高电压三元正极材料的粒径D50为11.0～14.5μm，BET为0.2～0.6m 2/g。
  7. 一种如权利要求1～6中任一项所述的具有核壳结构的高电压三元正极材料的制备方法，其特征在于，包括以下步骤：
    (1)按照内核的化学计量比，配制含有Ni 2+、Co 2+、Mn 2+和M元素的混合金属盐溶液，按照壳层的化学计量比，配制含有Ni 2+、Mn 2+和M元素的镍锰混合金属盐溶液；
    (2)将混合金属盐溶液、碱液、氨水溶液同时加入反应釜，控制反应釜中的pH为10～12，反应形成设计粒径的氢氧化物前驱体核之后，停止进料，得到氢氧化物前驱体核；
    (3)然后向所述反应釜中同时通入所述镍锰混合金属盐溶液以及碱液、氨水溶液，控制反应釜中的pH为8～10，在氢氧化物前驱体核表面反应得到设计厚度的前驱体壳层之后，过滤、洗涤、干燥得到核壳结构前驱体；
    (4)将锂源、核壳结构前驱体混合均匀，烧结后破碎，得到具有核壳结构的高电压三元正极材料。
  8. 根据权利要求7所述的制备方法，其特征在于，所述碱液为8～11mol/L的NaOH溶液； 所述氨水溶液的浓度为5～8mol/L；
    步骤(2)中，通过调节氨水溶液的进料速度控制反应釜中氨值在7～8g/L之间；步骤(3)中，通过调节氨水溶液的进料速度控制反应釜中氨值在5～6g/L之间。
  9. 根据权利要求7或8所述的制备方法，其特征在于，步骤(4)中，所述锂源与核壳结构前驱体中Ni、Mn、Co元素的总摩尔量的摩尔比为(1.10～1.40):1。
  10. 根据权利要求7或8所述的制备方法，其特征在于，步骤(4)中，所述烧结的温度为700～950℃，时间为8～14h。
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