WO2017101233A1 - 一种正极材料及其制备方法和应用 - Google Patents

一种正极材料及其制备方法和应用 Download PDF

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WO2017101233A1
WO2017101233A1 PCT/CN2016/077116 CN2016077116W WO2017101233A1 WO 2017101233 A1 WO2017101233 A1 WO 2017101233A1 CN 2016077116 W CN2016077116 W CN 2016077116W WO 2017101233 A1 WO2017101233 A1 WO 2017101233A1
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spinel
lithium nickel
mol
type lithium
manganese oxide
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PCT/CN2016/077116
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French (fr)
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曹安民
朴俊宇
万立骏
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中国科学院化学研究所
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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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • 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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • 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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • 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
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • 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 lithium ion battery materials, and in particular to a cathode material and a preparation method and application thereof.
  • lithium-ion battery As a reliable and efficient energy storage device, lithium-ion battery has established its unshakable position since its inception. Among them, the positive electrode material as the core of lithium ion battery has always been the focus of researchers. At present, the commonly used cathode materials are not satisfactory for users due to their lower energy density and higher price. Therefore, the development of high energy density cathode materials has extremely important practical significance.
  • the spinel-type lithium nickel manganese oxide developed from lithium manganate has an operating voltage of up to 4.7V (vs. Li/Li + ) and can store more electric energy at the same capacity. Moreover, its energy density is higher than the commonly used lithium cobaltate, lithium manganate and lithium iron phosphate.
  • the three-dimensional lithium ion diffusion channel existing in the spinel structure effectively ensures the high power performance of the material, and considering that the preparation process is simple and the raw materials are cheap and easy to obtain, lithium nickel manganese oxide is considered to be a promising power. Battery cathode material.
  • Unmodified lithium nickel manganese oxide materials have some insurmountable drawbacks. For example, during the charging and discharging process, since the working voltage of lithium nickel manganese oxide is high, the surface of the electrode may be side-reacted with the electrolyte, and Li + is consumed, resulting in a decrease in effective lithium and a serious capacity decay. Further, the lithium nickel manganese oxide crystals often exist Mn 3+, Mn 3+ generated surface of the material easy to disproportionation Mn 2+ and dissolved in the electrolytic solution, it causes the material surface is damaged, eventually resulting in material capacity fading.
  • the invention aims to provide a positive electrode material and a preparation method and application thereof, wherein the deposition process is controllable, and a metal element doping and a certain thickness can be formed in situ on the surface of the core spinel type lithium nickel manganate.
  • Surface modification layer also called doped layer or shell layer
  • the presence of the shell layer can significantly improve the material during charge and discharge Thermal stability, cycle stability and stability of the material's own structure.
  • the present invention provides a positive electrode material which is a spinel type lithium nickel manganese oxide LiNi 0.5 Mn 1.5 O 4- ⁇ (0 ⁇ ⁇ ⁇ 0.1), the spinel type nickel manganese a lithium metal having a gradually decreasing concentration of in-plane doping from the surface, thereby forming a doped layer similar to the core structure and closely connected, also referred to as a shell layer, the shell layer having a thickness greater than 0, the metal
  • the doping amount of the element accounts for the percentage of the weight of the spinel-type nickel manganate, and is represented by x, which satisfies 0 ⁇ x ⁇ 10 wt%.
  • the doping amount of the metal element is 0 ⁇ x ⁇ 5 wt%; more preferably, 0 ⁇ x ⁇ 2 wt%; further preferably, 0.29 wt% ⁇ x ⁇ 0.89 wt%; still more preferably, 0.56 Wt% ⁇ x ⁇ 0.62 wt%.
  • the thickness of the shell layer is from 1 to 50 nm; preferably from 1 to 30 nm; more preferably from 10 to 25 nm, for example, 15 nm or 20 nm.
  • the metal element is one or more selected from the group consisting of Mg, Ca, Al, Ti, Fe, Co, Cu, Zn, and Zr.
  • the present invention also provides a method of preparing the above positive electrode material, the method comprising the steps of:
  • the reaction in the step (1) is a precipitation-heat osmosis reaction of a metal ion; the solvent is water or ethanol.
  • the precipitating agent in the step (1) is one or more of a carbonate, a hydrogencarbonate, a formate, an acetate, a hydrogen phosphate, a urotropine, and a phosphate.
  • the precipitating agent is selected from the group consisting of ammonium hydrogencarbonate, ammonium carbonate, sodium hydrogencarbonate, sodium carbonate, potassium hydrogencarbonate, potassium carbonate, ammonium formate, ammonium acetate, formamide, acetamide, urotropine, urea, hydrogen phosphate
  • ammonium, ammonium dihydrogen phosphate, triammonium phosphate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, sodium phosphate, potassium monohydrogen phosphate, potassium dihydrogen phosphate, and potassium phosphate further preferably hydrogen phosphate a mixture of ammonium and ammonium formate, ammonium formate, sodium bicarbonate, urotropine or urea.
  • the precursor in the step (1) is at least one selected from the group consisting of a chloride, a sulfate, a nitrate, a perchlorate, an acetate, and an alkoxide of a metal element; preferably, the metal element may be Is one or more of Mg, Ca, Al, Ti, Fe, Co, Cu, Zn, Zr; the precursor may be, for example, aluminum nitrate nonahydrate, ferric chloride hexahydrate, zinc acetate dihydrate or titanium One or more of tetrabutyl phthalate.
  • a regulator is added in the step (1) to adjust the pH of the reaction system to 2.0 to 5.5; more preferably 3.0 to 5.0; the regulator is selected from the group consisting of formic acid, acetic acid, hydrochloric acid, nitric acid, sulfuric acid, perchloric acid, One of ammonia water, sodium hydroxide and potassium hydroxide.
  • the stirring reaction temperature in the step (1) is 20 to 95 ° C, preferably 30 to 80 ° C; more preferably 45 to 90 ° C; and the reaction time is 2 to 4 hours.
  • it may be stirred at 45 ° C for 2 hours; or at 50 ° C for 2 hours; or at 90 ° C for 4 hours; or at 90 ° C for 4 hours.
  • the concentration of the raw material spinel-type lithium nickel manganese oxide is from 0.01 g/L to 1000 g/L, preferably from 0.1 g/L to 100 g/L, further preferably 1 g/ L to 80 g/L, more preferably 20 to 50 g/L.
  • the concentration of the precursor is from 1 ⁇ 10 -6 mol / L to 0.1 mol / L; preferably from 1 ⁇ 10 -5 mol / L to 0.01 mol / L; further preferably from 1 ⁇ 10 -4 mol / L to 1 ⁇ 10 -3 mol/L.
  • the concentration of the precipitating agent is from 1 ⁇ 10 -6 mol / L to 10 mol / L, preferably from 1 ⁇ 10 -5 mol / L to 1 mol / L.
  • the temperature is raised to 200 to 1200 ° C at a temperature increase rate of 1 to 50 ° C / minute for 1 to 10 hours; preferably, the temperature is raised to 450 to 800 ° C at a temperature increase rate of 3 to 15 ° C / minute. , calcined for 3 to 4 hours.
  • the present invention further provides an electrode comprising the above positive electrode material.
  • the invention further provides a battery comprising the electrode described above.
  • the invention adopts a controlled precipitation method to quantitatively deposit a metal element on the surface of a spinel-type lithium nickel manganate, and then uses a heat treatment method to infiltrate a metal element from the surface of the spinel-type nickel manganate to the inside, so that the core spines in the core
  • a surface of a stone-type lithium nickel manganese oxide is in situ formed with a metal element doped spinel type lithium nickel manganate surface modification layer (also referred to as a doped layer or a shell layer).
  • the invention obtains a spinel-type lithium nickel manganese oxide electrode material having a novel core-shell structure by modifying a special metal element on the surface of the spinel-type lithium nickel manganate cathode material particle, and the core thereof is Spinel-type lithium nickel manganese oxide, that is, LiNi 0.5 Mn 1.5 O 4- ⁇ (0 ⁇ ⁇ ⁇ 0.1), and the shell layer is a metal element doped spinel type lithium nickel manganese oxide doped layer.
  • the spinel-type lithium nickel manganese oxide electrode material prepared by the invention has a very high structural similarity and good compatibility due to the structural similarity between the shell layer and the inner core, thereby perfectly solving the problem of core shell peeling.
  • the presence of the shell layer can significantly improve the thermal stability, cycle stability and stability of the material itself during charging and discharging, and has a high practical application prospect in the field of energy storage.
  • the preparation method of the spinel-type lithium nickel manganate electrode material with the novel core-shell structure provided by the invention effectively combines the advantages of the two modification methods of coating and doping in the prior art, and is stable. Effective surface doping method. Specifically, the method can passivate the surface of the material without affecting the overall performance of the material, significantly reduce surface corrosion and surface side reactions, and can effectively solve the problem of peeling of the shell layer and the core during the cycle.
  • a novel core-shell structure of a spinel-type lithium nickel manganate material composed of a high-performance core and a stable shell layer is prepared. The large-scale mature application of lithium nickel manganese oxide materials has extremely practical significance.
  • Example 1 is a transmission electron micrograph of a spinel-type lithium nickel manganate having a surface-aluminum-doped core-shell structure of Example 1;
  • Example 2 is an EDS test result of a spinel-type lithium nickel manganese oxide having a surface-aluminum-doped core-shell structure of Example 1;
  • Example 3 is a spherical aberration-corrected electron micrograph of a spinel-type lithium nickel manganese oxide having a surface-aluminum-doped core-shell structure of Example 1;
  • Example 4 is a cycle performance of charge and discharge of a spinel-type lithium nickel manganese oxide having a surface-aluminum-doped core-shell structure of Example 1 at a 2 C rate.
  • the present invention provides a positive electrode material which is a spinel type lithium nickel manganese oxide LiNi 0.5 Mn 1.5 O 4- ⁇ (0 ⁇ ⁇ ⁇ 0.1), which is in the spinel type lithium nickel manganese oxide.
  • the percentage of the weight of the spinel-type lithium nickel manganate is recorded as x, satisfying 0 ⁇ x ⁇ 10% by weight; preferably, 0 ⁇ x ⁇ 5wt%; more preferably, 0 ⁇ x ⁇ 2wt% Further preferably, 0.29 wt% ⁇ x ⁇ 0.89 wt%; still more preferably, 0.56 wt% ⁇ x ⁇ 0.62 wt%.
  • the present invention obtains a doped layer having a passivated surface (ie, a shell layer) by doping a specific metal element on a surface of a spinel type lithium nickel manganate LiNi 0.5 Mn 1.5 O 4- ⁇ (0 ⁇ ⁇ ⁇ 0.1). ), the surface corrosion and surface side reactions are significantly reduced, and since the shell layer is formed in situ on the surface of the core, the structure of the shell layer is highly similar to the core structure, effectively solving the shell layer and the core during the battery cycle.
  • the problem of peeling has resulted in a new core-shell structure of spinel-type lithium nickel manganate material composed of a high-performance core and a stable shell layer.
  • the thickness of the shell layer is from 1 to 50 nm; preferably from 1 to 30 nm; more preferably from 10 to 25 nm. For example, it may be 15 nm or 20 nm.
  • the present invention can control the thickness of the shell layer during the preparation process by controlling parameters such as the deposition time of the doped metal precursor and the subsequent calcination temperature and time.
  • the invention also provides a preparation method of the above positive electrode material, comprising the following steps:
  • the intermediate product of the step (1) is uniformly ground, calcined, and cooled to room temperature to obtain a positive electrode material of the present invention.
  • the precursor form of the doped metal element is used for the purpose of facilitating the quantitative and uniform deposition of the solid phase compound containing the doped metal element on the surface of the core spinel type lithium nickel manganate.
  • the precursor is selected from at least one of a chloride, a sulfate, a nitrate, a perchlorate, an acetate, and an alkoxide of a metal element.
  • the metal element may be one or more of Mg, Ca, Al, Ti, Fe, Co, Cu, Zn, and Zr.
  • the precursor may be one or more of aluminum nitrate nonahydrate, ferric chloride hexahydrate, zinc acetate dihydrate or tetrabutyl titanate.
  • the pH of the reaction system is adjusted to 1.5 to 7.0, mainly considering that if the pH is too low, the material may be greatly damaged, so that the pH of the initial reaction system is adjusted to a suitable level.
  • the reaction system is heated and stirred to cause a reaction.
  • the stirring reaction temperature is 20 to 95 ° C; more preferably 30 to 80 ° C; further preferably 45 to 90 ° C.
  • the reaction time is 2 to 4 hours. For example, it may be stirred at 45 ° C for 2 hours; or at 50 ° C for 2 hours; or at 90 ° C for 4 hours.
  • the introduced precursor is converted into a solid phase compound containing the doped metal element by heating and stirring the reaction. Accumulated on the surface of spinel-type lithium nickel manganate. After the reaction is completed, separation, washing, and drying are carried out to obtain an intermediate product.
  • the concentration of the raw material spinel-type lithium nickel manganese oxide is from 0.01 g/L to 1000 g/L, preferably from 0.1 g/L to 100 g/L, further preferably 1 g/ L to 80 g/L, more preferably 20 to 50 g/L. If the concentration of the raw material is too high, it will cause the deposition to be too fast, which may cause the synthesis of the intermediate product to fail. If the concentration of the raw materials is too low, too little product will be synthesized in one reaction.
  • the concentration of the precursor is 1 ⁇ 10 -6 mol/L to 0.1 mol/L; preferably 1 ⁇ 10 ⁇ 5 mol/L to 0.01 mol/L; further preferably 1 ⁇ 10 ⁇ 4 mol/L ⁇ 1 ⁇ 10 -3 mol / L. If the concentration of the precursor is too high, the doping amount is too high, which affects the performance of the positive electrode material; if the concentration of the precursor is too low, the intermediate product is difficult to form, which affects the doping success rate.
  • the concentration of the precipitating agent is 1 ⁇ 10 -6 mol/L to 10 mol/L, preferably 1 ⁇ 10 -5 mol/L to 1 mol/L. If the concentration of the precipitant is too high, the deposition of metal elements will be too fast, resulting in uneven doping; on the contrary, if the concentration of the precipitant is too low, the deposition of metal elements will be too low, resulting in the doping of metal elements in the positive electrode material. Too low the amount of impurities will also affect the performance of the cathode material.
  • the intermediate product obtained in the step (1) is uniformly ground and then calcined at a temperature, preferably at a temperature increase rate of from 1 to 50 ° C /min to 200 to 1200 ° C for 1 to 10 hours. More preferably, the temperature is raised to 450 to 800 ° C at a temperature increase rate of 3 to 15 ° C /min, and calcination is carried out for 3 to 4 hours.
  • the present invention preferably controls the temperature increase rate, the calcination temperature and the time within the above range.
  • the present invention further provides an electrode comprising the above positive electrode material.
  • the invention further provides a battery comprising the above electrode.
  • spinel-type lithium nickel manganese oxide LiNi 0.5 Mn 1.5 O 4- ⁇ (0 ⁇ ⁇ ⁇ 0.1) powder 0.5 g, aluminum precursor 20 ml of aluminum nitrate nonahydrate, precipitation agent diammonium hydrogen phosphate 10 mg, precipitation 2 g of ammonium formate was dispersed in 30 ml of water to obtain a reaction system.
  • the concentration of the spinel-type lithium nickel manganese oxide is 16.7 g / L; the concentration of the aluminum nitrate nonahydrate is 1.8 ⁇ 10 -3 mol / L; the diammonium hydrogen phosphate The concentration was 2.5 ⁇ 10 -3 mol/L, and the concentration of the ammonium formate was 1.06 mol/L.
  • the regulator hydrochloric acid was added to the reaction system to adjust the pH of the reaction system to 3, and the reaction was stirred at 45 ° C for 2 hours, centrifuged, washed, and dried to obtain an intermediate product.
  • the intermediate product was heated to 800 ° C at a rate of 4 ° C / min, calcined at this temperature for 3 hours, and then cooled to room temperature to obtain a surface aluminum-doped core-shell structure of spinel-type lithium nickel manganese oxide powder.
  • the core is spinel-type lithium nickel manganate LiNi 0.5 Mn 1.5 O 4- ⁇ (0 ⁇ ⁇ ⁇ 0.1), and the doping amount of aluminum in the shell layer is 0.29 wt.% of the spinel-type lithium nickel manganese oxide. .
  • Example 1 is a transmission electron micrograph of a spinel-type lithium nickel manganate having a surface-aluminum-doped core-shell structure obtained in Example 1, and it can be seen that there is no abnormal change in the surface of lithium nickel manganese oxide. This indicates that the core-shell structure of the spinel-type lithium nickel manganate cathode material has good compatibility with the shell layer, and there is no excessive structural difference, that is, the structure is highly similar.
  • FIG. 2 is a result of EDS test of a spinel-type lithium nickel manganese oxide having a surface-aluminum-doped core-shell structure obtained in Example 1.
  • FIG. It can be seen that the concentration of the Al element from the surface inwardly is gradually decreased, and the thickness of the Al-doped shell layer is about 10 nm.
  • FIG. 3 is a spherical aberration-corrected electron micrograph of a spinel-type lithium nickel manganese oxide having a surface-aluminum-doped core-shell structure obtained in Example 1.
  • FIG. It can be seen that the surface doping layer (round frame) is different from the core (box) atomic arrangement, which indicates that a doped layer (also called a shell layer) is formed on the surface of the material.
  • spinel-type lithium nickel manganese oxide powder prepared by the above-mentioned surface aluminum-doped core-shell structure, and conductive additive super-p (supplied by Hefei Kejing Material Technology Co., Ltd.) 0.03 g, binder PVDF (Polyvinylidene fluoride) 0.03g mixed with a little solvent NMP (N-methylpyrrolidone), slurried, smeared (aluminum foil as a current collector), dried to obtain a surface-aluminum-doped core-shell structure of spinel Lithium nickel manganese oxide electrode.
  • binder PVDF Polyvinylidene fluoride
  • the battery was subjected to a constant current charge and discharge test using a battery charge and discharge tester, and the test voltage range was 3.0 to 5.0 V, and the test temperature was 25 °C. Both the battery capacity and the charge and discharge current were calculated based on the mass of the spinel-type lithium nickel manganate having a surface-aluminum-doped core-shell structure.
  • Figure 4 shows the cycle performance of the battery of this material at a 2C rate charge and discharge. After 100 cycles of the battery, the battery capacity is basically no attenuation, still maintained at around 115 mAh / g, coulombic efficiency is basically 100%, with good capacity retention, life and coulombic efficiency.
  • spinel-type lithium nickel manganese oxide LiNi 0.5 Mn 1.5 O 4- ⁇ (0 ⁇ ⁇ ⁇ 0.1) powder 0.5 g, iron precursor 15 mg ferric chloride hexahydrate, and precipitant amine formate 2 g dispersed in 30 ml In water, the reaction system is obtained.
  • the concentration of the spinel-type lithium nickel manganese oxide is 16.7 g/L; the concentration of the ferric chloride hexahydrate is 1.9 ⁇ 10 -3 mol/L; the concentration of the ammonium formate It is 1.06 mol/L.
  • the regulator nitric acid was added to the reaction system to adjust the pH of the reaction system to 2.0, stirred at 50 ° C for 2 hours, centrifuged, washed, and dried to obtain an intermediate product.
  • the intermediate product was heated to 800 ° C at a rate of 3 ° C / minute, and calcined at this temperature for 3 hours to obtain a spinel-type lithium nickel manganese oxide powder having a surface iron-doped core-shell structure.
  • the core is spinel lithium nickel manganese oxide LiNi 0.5 Mn 1.5 O 4- ⁇ (0 ⁇ ⁇ ⁇ 0.1), and the iron doping amount of the shell layer is 0.62 wt% of the spinel lithium nickel manganese oxide.
  • the thickness of the shell layer is approximately 25 nm.
  • the battery was subjected to a constant current charge and discharge test using a battery charge and discharge tester, and the test voltage range was 3.0 to 5.0 V, and the test temperature was 25 °C. Both the battery capacity and the charge and discharge current were calculated based on the mass of the surface-iron-doped core-shell structure of the spinel-type lithium nickel manganate.
  • the cycle performance of the battery in Example 2 under charge and discharge at 2C rate is as follows: after 100 cycles of the battery, the battery capacity is substantially no attenuation, still maintained at about 115 mAh/g, the coulombic efficiency is basically 100%, and has a good capacity retention rate. , life and coulombic efficiency.
  • the regulator acetic acid was added to the reaction system to adjust the pH to 5.5, stirred at 90 ° C for 4 hours, centrifuged, washed, and dried to obtain an intermediate product.
  • the intermediate product was further heated to 800 ° C at a rate of 10 ° C / minute, and calcined at this temperature for 4 hours to obtain a spinel-type lithium nickel manganese oxide powder having a surface zinc-doped core-shell structure.
  • the core is spinel lithium nickel manganese oxide LiNi 0.5 Mn 1.5 O 4- ⁇ (0 ⁇ ⁇ ⁇ 0.1), and the zinc doping amount of the shell layer is 0.89 wt% of the spinel lithium nickel manganese oxide.
  • the thickness of the shell layer is approximately 10 nm.
  • the battery was subjected to a constant current charge and discharge test using a battery charge and discharge tester, and the test voltage range was 3.0 to 5.0 V, and the test temperature was 25 °C. Both the battery capacity and the charge and discharge current were calculated based on the mass of the spinel-type lithium nickel manganate having a surface-zinc doped core-shell structure.
  • the cycle performance of the battery in Example 3 under charge and discharge at 2C rate is as follows: after 100 cycles of the battery, the battery capacity is substantially no attenuation, still maintained at about 114 mAh/g, the coulombic efficiency is basically 100%, and has a good capacity retention rate. , life and coulombic efficiency.
  • the intermediate product was further heated to 800 ° C at a rate of 15 ° C / minute and calcined at this temperature for 4 hours to obtain a surface-titanium-doped core-shell structure of spinel-type lithium nickel manganese oxide powder.
  • the core is spinel lithium nickel manganese oxide LiNi 0.5 Mn 1.5 O 4- ⁇ (0 ⁇ ⁇ ⁇ 0.1), and the iron doping amount of the outer shell is 0.56 wt% of the spinel lithium nickel manganese oxide.
  • the thickness of the shell layer is approximately 15 nm.
  • the battery was subjected to a constant current charge and discharge test using a battery charge and discharge tester, and the test voltage range was 3.0 to 5.0 V, and the test temperature was 25 °C. Both the battery capacity and the charge and discharge current were calculated based on the mass of the spinel-type lithium nickel manganate having a surface-titanium-doped core-shell structure.
  • the cycle performance of the battery in Example 4 under charge and discharge at 2C rate is as follows: after 100 cycles of the battery, the battery capacity is substantially no attenuation, still maintained at about 114 mAh/g, the coulombic efficiency is basically 100%, and has a good capacity retention rate. , life and coulombic efficiency.

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Abstract

一种正极材料及其制备方法和应用，其为尖晶石型镍锰酸锂LiNi 0.5Mn 1.5O 4- δ(0≤δ＜0.1)，其具有自表面向内掺杂浓度逐渐降低的金属元素，从而形成了与内核结构相近且紧密连接厚度大于0的壳层，金属元素的掺杂量占尖晶石型镍锰酸锂重量的百分含量记为x，满足0<x≤10wt％。采用可控沉淀的方法在镍锰酸锂表面定量沉积金属元素，再利用热处理使金属元素从镍锰酸锂表面向内部渗透，在内核镍锰酸锂表面原位形成壳层，壳层与内核的结构相似度非常高，相容性好，完美解决了核壳剥离的问题。壳层的存在显著提高了正极材料在充放电过程中的热稳定性、循环稳定性及材料自身结构的稳定性，在能源存储领域有着很高的实用性应用前景。

Description

一种正极材料及其制备方法和应用 技术领域
本发明属于锂离子电池材料技术领域，具体而言，涉及一种正极材料及其制备方法和应用。
背景技术
作为一种可靠、高效的储能器件，锂离子电池自问世以来，就确立了其无可动摇的地位。其中，正极材料作为锂离子电池的核心，历来是科研人员关注的重点。目前常用的正极材料，囿于其较低的能量密度以及较高的价格，其表现尚不能让用户满意。因而，高能量密度正极材料的研发，具有极其重要的现实意义。
由锰酸锂基础上发展而来的尖晶石型镍锰酸锂，工作电压高达4.7V(vs.Li/Li+)，在相同的容量下可以储存更多的电能。而且其能量密度高于常用的钴酸锂、锰酸锂和磷酸铁锂。尖晶石结构中存在的三维锂离子扩散通道，有效保证了材料的高功率性能，再考虑到其制备工艺简单，原料廉价易得，可以认为镍锰酸锂是一种相当有应用前景的动力电池正极材料。
未改性的镍锰酸锂材料存在一些难以克服的缺陷。如在充放电过程中，由于镍锰酸锂工作电压较高，电极表面会与电解液发生副反应，消耗Li+，导致有效锂减少，容量衰减严重。另外，镍锰酸锂晶体中往往存在着Mn3+，材料表面的Mn3+易歧化生成Mn2+并溶解在电解液中，导致材料表面被破坏，最终造成材料容量衰减。
研究表明，通过在镍锰酸锂表面引入一层稳定的外壳，可以有效抑制材料表面的副反应，提高材料的结构稳定性。目前，最常见的构筑稳定外壳的方式 就是包覆改性。其中，氧化锌、氧化铝、氟化铝等物质是最为常见的包覆剂。但是，这些物质的锂离子迁移率和电子电导率往往不好，材料的倍率性能往往会受到负面影响。而且，通过包覆的方法构筑的壳层，由于壳层与内核结构完全不同，在充放电的时候由于体积变化，容易出现剥离的现象。因而，需要寻找更为合理的手段来构筑核壳结构。
发明内容
本发明旨在提供一种正极材料及其制备方法和应用，该方法沉积过程可控，且可在内核尖晶石型镍锰酸锂的表面原位形成一层有金属元素掺杂及确定厚度的表面修饰层(也称掺杂层或壳层)，从而得到一种新型的核壳结构的尖晶石型镍锰酸锂正极材料，该壳层的存在能够显著提高材料在充放电过程中的热稳定性、循环稳定性及材料自身结构的稳定性。
为了实现上述目的，本发明提供了一种正极材料，该正极材料为尖晶石型镍锰酸锂LiNi0.5Mn1.5O4-δ(0≤δ＜0.1)，所述尖晶石型镍锰酸锂中具有自表面向内掺杂的浓度逐渐降低的金属元素，从而形成了与内核结构相近且紧密连接的掺杂层，也称壳层，所述壳层的厚度大于0，所述金属元素的掺杂量占尖晶石型镍锰酸锂重量的百分含量，记为x，满足0＜x≤10wt％。
优选地，所述金属元素的掺杂量为0＜x≤5wt％；更优选地，0＜x≤2wt％；进一步优选地，0.29wt％≤x≤0.89wt％；更进一步优选地，0.56wt％≤x≤0.62wt％。
进一步地，壳层的厚度为1～50nm；优选为1～30nm；更优选为10～25nm，例如可以为15nm或者20nm。
进一步地，所述金属元素选自Mg、Ca、Al、Ti、Fe、Co、Cu、Zn、Zr中的一种或多种。
本发明还提供了一种制备上述正极材料的方法，所述方法包括以下步骤：
(1)将原材料尖晶石型镍锰酸锂LiNi0.5Mn1.5O4-δ(0≤δ＜0.1)，掺杂金属的前驱体和沉淀剂分散在溶剂中，加入调节剂以调节反应体系的pH值至 1.5～7.0，加热搅拌反应，使得引入的所述前驱体转化为含有该掺杂金属元素的固相化合物，并均匀沉积在所述尖晶石型镍锰酸锂的表面，反应完成后分离，洗涤，干燥，得到中间产物；
(2)将所述中间产物研磨均匀，煅烧，冷却至室温，得到所述正极材料。
进一步地，步骤(1)中所述反应为金属离子的沉淀-热渗透反应；所述溶剂为水或乙醇。
进一步地，步骤(1)中所述沉淀剂为碳酸盐、碳酸氢盐、甲酸盐、乙酸盐、磷酸氢盐、乌洛托品和磷酸盐中的一种或多种。进一步地，沉淀剂选自碳酸氢铵、碳酸铵、碳酸氢钠、碳酸钠、碳酸氢钾、碳酸钾、甲酸铵、乙酸铵、甲酰胺、乙酰胺、乌洛托品、尿素、磷酸氢二铵、磷酸二氢铵、磷酸三铵、磷酸一氢钠、磷酸二氢钠、磷酸钠、磷酸一氢钾、磷酸二氢钾和磷酸钾中的一种或多种；进一步优选为磷酸氢二铵与甲酸铵的混合物、甲酸铵、碳酸氢钠、乌洛托品或尿素。
进一步地，步骤(1)中所述前驱体选自金属元素的氯化盐、硫酸盐、硝酸盐、高氯酸盐、醋酸盐和醇盐中的至少一种；优选所述金属元素可以为Mg、Ca、Al、Ti、Fe、Co、Cu、Zn、Zr中的一种或多种；所述前驱体例如可以为九水合硝酸铝，六水合氯化铁、二水合乙酸锌或钛酸四丁酯中的一种或多种。
进一步地，步骤(1)中加入调节剂以调节所述反应体系的pH值至2.0～5.5；更优选为3.0～5.0；调节剂选自甲酸、乙酸、盐酸、硝酸、硫酸、高氯酸、氨水、氢氧化钠和氢氧化钾中的一种。
进一步地，步骤(1)中的搅拌反应温度为20～95℃，优选30～80℃；进一步优选为45～90℃；反应时间为2～4小时。例如可以在45℃下搅拌2小时；或者在50℃下搅拌2小时；或者在90℃下搅拌4小时；或者在90℃下搅拌4小时。
进一步地，在步骤(1)的反应体系中，原材料尖晶石型镍锰酸锂的浓度为0.01g/L～1000g/L，优选为0.1g/L～100g/L，进一步优选为1g/L～80g/L，更优选 为20～50g/L。所述前驱体的浓度为1×10-6mol/L～0.1mol/L；优选1×10-5mol/L～0.01mol/L；进一步优选为1×10-4mol/L～1×10-3mol/L。所述沉淀剂的浓度为1×10-6mol/L～10mol/L，优选1×10-5mol/L～1mol/L。
进一步地，步骤(2)中，以1～50℃/分钟的升温速率升温至200～1200℃煅烧1～10小时；优选地，以3～15℃/分钟的升温速率升温至450～800℃，煅烧3～4小时。
本发明又提供了一种电极，其包括上述的正极材料。
本发明进一步提供了一种电池，其包括上述的电极。
本发明的有益效果：
本发明采用可控沉淀的方法使金属元素在尖晶石型镍锰酸锂表面定量沉积，再利用热处理手段使金属元素从尖晶石型镍锰酸锂表面向内部渗透，这样在内核尖晶石型镍锰酸锂的表面原位形成一层金属元素掺杂的尖晶石型镍锰酸锂表面修饰层(也称掺杂层或壳层)。本发明通过对尖晶石型镍锰酸锂正极材料颗粒的表面进行特殊的金属元素修饰，从而得到了具备一种新型的核壳结构的尖晶石型镍锰酸锂电极材料，其内核为尖晶石型镍锰酸锂，即LiNi0.5Mn1.5O4-δ(0≤δ＜0.1)，壳层为金属元素掺杂的尖晶石型镍锰酸锂掺杂层。本发明制备的核壳结构的尖晶石型镍锰酸锂电极材料，由于其壳层与内核的结构相似度非常高，相容性好，从而完美解决了核壳剥离的问题。该壳层的存在能够显著提高材料在充放电过程中的热稳定性、循环稳定性及材料自身结构的稳定性，在能源存储领域有着很高的实用性应用前景。
本发明提供的具备新型核壳结构的尖晶石型镍锰酸锂电极材料的制备方法，有效地结合了现有技术中包覆与掺杂这两种改性方式的优点，是一种稳定有效的表面掺杂方法。具体而言，该方法可以在不影响材料整体性能的前提下钝化材料表面，明显降低表面腐蚀以及表面副反应，并可以有效地解决壳层与内核在循环过程中剥离的问题。同时，本发明的表面掺杂方法，制备出了由高性能内核以及稳定壳层构成的新型的核壳结构的尖晶石型镍锰酸锂材料，这对 于镍锰酸锂材料的大规模成熟应用，具有极为现实的意义。
附图说明
图1为实施例1的表面铝掺杂的核壳结构的尖晶石型镍锰酸锂的透射电子显微镜照片；
图2为实施例1的表面铝掺杂的核壳结构的尖晶石型镍锰酸锂的EDS测试结果；
图3为实施例1的表面铝掺杂的核壳结构的尖晶石型镍锰酸锂的球差校正电子显微镜照片；以及
图4为实施例1的表面铝掺杂的核壳结构的尖晶石型镍锰酸锂在2C倍率下充放电的循环性能。
具体实施方式
如上所述，本发明提供了一种正极材料，其为尖晶石型镍锰酸锂LiNi0.5Mn1.5O4-δ(0≤δ＜0.1)，所述尖晶石型镍锰酸锂中具有自表面向内掺杂地浓度逐渐降低地金属元素，从而形成了与内核结构相近且紧密连接的掺杂层，也称壳层，所述壳层的厚度大于0，所述金属元素的掺杂量占所述尖晶石型镍锰酸锂重量的百分含量记为x，满足0＜x≤10wt％；优选地，0＜x≤5wt％；更优选地，0＜x≤2wt％；进一步优选地，0.29wt％≤x≤0.89wt％；更进一步优选地，0.56wt％≤x≤0.62wt％。
本发明通过在尖晶石型镍锰酸锂LiNi0.5Mn1.5O4-δ(0≤δ＜0.1)的表面掺杂特定的金属元素，得到了具有钝化表面的掺杂层(即壳层)，明显降低了表面腐蚀以及表面副反应的发生，并且由于是在内核的表面原位形成壳层，因而壳层的结构与内核结构高度相似，有效地解决壳层与内核在电池循环过程中剥离的问题，得到了由高性能内核以及稳定壳层构成的新型的核壳结构的尖晶石型镍锰酸锂材料。
根据本发明，壳层的厚度为1～50nm；优选为1～30nm；更优选为10～25nm。例如还可以为15nm或者20nm。本发明可以在制备过程中通过控制掺杂金属前驱体的沉积时间以及后续煅烧温度和时间等参数来控制壳层的厚度。
本发明还提供了一种上述正极材料的制备方法，包括以下步骤：
(1)将原材料尖晶石型镍锰酸锂LiNi0.5Mn1.5O4-δ(0≤δ＜0.1)，掺杂金属前驱体和沉淀剂分散在溶剂(所述溶剂可以为水或乙醇)中；之后加入调节剂以调节反应体系的pH值至1.5～7.0，加热搅拌反应，使得引入的所述前驱体转化为含有该掺杂金属元素的固相化合物，并均匀沉积在所述尖晶石型镍锰酸锂的表面，反应完成后分离，洗涤，干燥，得到中间产物。
(2)将步骤(1)的中间产物研磨均匀，煅烧，冷却至室温，得到本发明的正极材料。
采用所述掺杂金属元素的前驱体形式，是为了便于实现所述含有该掺杂金属元素的固相化合物在内核尖晶石型镍锰酸锂的表面进行定量、均匀沉积。所述前驱体选自金属元素的氯化盐、硫酸盐、硝酸盐、高氯酸盐、醋酸盐和醇盐中的至少一种。优选金属元素可以为Mg、Ca、Al、Ti、Fe、Co、Cu、Zn、Zr中的一种或多种。例如前驱体可以为九水合硝酸铝，六水合氯化铁、二水合乙酸锌或钛酸四丁酯等中的一种或多种。
根据本发明，步骤(1)中，调节反应体系的pH值至1.5～7.0，主要是考虑到若pH太低，有可能对材料造成较大的伤害，因此将初始反应体系的pH调至合适的范围。
根据本发明，在步骤(1)中，调节反应体系的pH值后，对反应体系加热并搅拌使其发生反应。优选的，搅拌反应温度为20～95℃；更优选为30～80℃；进一步优选为45～90℃。所述反应时间为2～4小时。例如可以在45℃下搅拌2小时；或者在50℃下搅拌2小时；或者在90℃下搅拌4小时。通过加热搅拌反应使得引入的所述前驱体转化为含有该掺杂金属元素的固相化合物并均匀沉 积在尖晶石型镍锰酸锂的表面。待反应完成后进行分离，洗涤，干燥，得到中间产物。
根据本发明，在步骤(1)的反应体系中，原材料尖晶石型镍锰酸锂的浓度为0.01g/L～1000g/L，优选0.1g/L～100g/L，进一步优选为1g/L～80g/L，更优选为20～50g/L。如果原材料的浓度太高，会导致沉积过快，可能造成中间产物合成失败。如果原材料的浓度太低，会导致一次反应合成的产品过少。
其中，所述前驱体的浓度为1×10-6mol/L～0.1mol/L；优选1×10-5mol/L～0.01mol/L；进一步优选为1×10-4mol/L～1×10-3mol/L。如果前驱体的浓度过高，会导致掺杂量过高，影响正极材料的性能；如果前驱体的浓度过低，会导致中间产物难以形成，影响掺杂成功率。
其中，所述沉淀剂的浓度为1×10-6mol/L～10mol/L，优选为1×10-5mol/L～1mol/L。如果沉淀剂的浓度过高，会导致金属元素沉积过快，造成掺杂不均；相反，如果沉淀剂的浓度过低，会导致金属元素沉积量过低，从而造成正极材料中金属元素的掺杂量过低，同样会影响正极材料的性能。
根据本发明，步骤(2)中，将步骤(1)中得到的中间产物研磨均匀之后升温煅烧，优选以1～50℃/分钟的升温速率升温至200～1200℃煅烧1～10小时。更优选以3～15℃/分钟的升温速率升温至450～800℃，煅烧3～4小时。考虑到煅烧温度的高低以及煅烧时间的长短会影响到掺杂的成功率及掺杂深度，因此，经综合考虑，本发明优选将升温速率、煅烧温度和时间控制在上述的范围内。
本发明进一步提供了一种电极，其包括上述正极材料。
本发明进一步提供了一种电池，其包括上述电极。
以下结合附图和实施例对本发明作进一步的详细说明。但本领域技术人员了解，本发明的保护范围不仅限于以下实施例。根据本发明公开的内容，本领域技术人员将认识到在不脱离本发明技术方案所给出的技术特征和范围的情况下，对以上所述实施例做出许多变化和修改都属于本发明的保护范围。
实施例1
1、制备表面铝掺杂的核壳结构型镍锰酸锂
在烧瓶中将尖晶石型镍锰酸锂LiNi0.5Mn1.5O4-δ(0≤δ＜0.1)粉末0.5g、铝的前驱体九水合硝酸铝20mg、沉淀剂磷酸氢二铵10mg、沉淀剂甲酸铵2g分散在30ml水中，得到反应体系。在所述反应体系中，所述尖晶石型镍锰酸锂的浓度为16.7g/L；所述九水合硝酸铝的浓度为1.8×10-3mol/L；所述磷酸氢二铵的浓度为2.5×10-3mol/L，所述甲酸铵的浓度为1.06mol/L。
向反应体系中加入调节剂盐酸以调节所述反应体系的pH至3，在45℃下搅拌反应2小时，经离心、洗涤、干燥得到中间产物。
将中间产物以4℃/分钟的速率升温至800℃，在此温度下煅烧3小时，之后冷却至室温，得到表面铝掺杂的核壳结构的尖晶石型镍锰酸锂粉末。其内核为尖晶石型镍锰酸锂LiNi0.5Mn1.5O4-δ(0≤δ＜0.1)，壳层中的铝的掺杂量为尖晶石型镍锰酸锂的0.29wt.％。
图1为实施例1中得到的表面铝掺杂的核壳结构的尖晶石型镍锰酸锂的透射电子显微镜照片，可以看出镍锰酸锂的表面无异常变化。这说明制备的核壳结构的尖晶石型镍锰酸锂正极材料的内核与壳层的相容性好，没有过大的结构差异，即结构高度相似。
图2为实施例1中得到的表面铝掺杂的核壳结构的尖晶石型镍锰酸锂的EDS测试结果。可以看出Al元素自表面向内掺杂的浓度逐渐降低，掺杂Al的壳层的厚度约为10nm。
图3为实施例1中得到的表面铝掺杂的核壳结构的尖晶石型镍锰酸锂的球差校正电子显微镜照片。可以看到表面掺杂层(圆框)与内核(方框)原子排布是不同的，这说明在材料表面形成了掺杂层(也称壳层)。
2、制备表面铝掺杂的核壳结构的尖晶石型镍锰酸锂的电极
取上述制备的表面铝掺杂的核壳结构的尖晶石型镍锰酸锂粉末0.24g，与导电添加剂super-p(由合肥科晶材料技术有限公司公司提供)0.03g、粘结剂PVDF (聚偏氟乙烯)0.03g和少许溶剂NMP(N-甲基吡咯烷酮)混合，经制浆、涂片(铝箔作为集流体)、干燥，得到表面铝掺杂的核壳结构的尖晶石型镍锰酸锂电极。
3、组装电池
以上述步骤2中得到的表面铝掺杂的核壳结构的尖晶石型镍锰酸锂电极作为正极，与锂负极组装成电池，电解液选择浓度为1M的碳酸酯电解液，其中，溶剂为：DMC(碳酸二甲酯):DEC(碳酸二乙酯):EC(碳酸乙烯酯)＝1:1:1(W/W)，溶质为1.0M LiPF6。
4、电池测试
使用蓄电池充放电测试仪对上述电池进行恒流充放电测试，测试电压区间为3.0～5.0V，测试温度为25℃。电池容量和充放电电流均以表面铝掺杂的核壳结构的尖晶石型镍锰酸锂的质量计算。
图4为此材料的电池在2C倍率下充放电的循环性能。电池经过100圈循环，电池容量基本无衰减，仍保持在115mAh/g左右，库仑效率基本在100％，具有良好的容量保持率、寿命和库仑效率。
实施例2
1、制备表面铁掺杂的核壳结构型镍锰酸锂
在烧瓶中将尖晶石型镍锰酸锂LiNi0.5Mn1.5O4-δ(0≤δ＜0.1)粉末0.5g、铁的前驱体六水合氯化铁15mg、沉淀剂甲酸胺2g分散在30ml水中，得到反应体系。在所述反应体系中，所述尖晶石型镍锰酸锂的浓度为16.7g/L；所述六水合氯化铁的浓度为1.9×10-3mol/L；所述甲酸铵的浓度为1.06mol/L。
向反应体系中加入调节剂硝酸以调节所述反应体系的pH至2.0，在50℃下搅拌2小时，经离心、洗涤、干燥得到中间产物。
将中间产物以3℃/分钟的速率升温至800℃，在此温度下煅烧3小时，得到表面铁掺杂的核壳结构的尖晶石型镍锰酸锂粉末。其内核为尖晶石镍锰酸锂 LiNi0.5Mn1.5O4-δ(0≤δ＜0.1)，壳层的铁掺杂量为尖晶石镍锰酸锂的0.62wt％。壳层的厚度约为25nm。
2、制备表面铁掺杂的核壳结构的尖晶石型镍锰酸锂的电极
将上述制备的表面铁掺杂的核壳结构的尖晶石型镍锰酸锂粉末0.24g与导电添加剂super-p 0.03g、粘结剂PVDF(聚偏氟乙烯)0.03g和少许溶剂NMP混合，经制浆、涂片(铝箔作为集流体)、干燥，得到表面铁掺杂的核壳结构的尖晶石型镍锰酸锂电极。
3、组装电池
以上述步骤2中得到的表面铁掺杂的核壳结构的尖晶石型镍锰酸锂电极作为正极，与锂负极组装成电池，电解液选择浓度为1M的碳酸酯电解液，其中，溶剂为：DMC:DEC:EC＝1:1:1(W/W)，溶质为1.0M LiPF6。
4、电池测试
使用蓄电池充放电测试仪对上述电池进行恒流充放电测试，测试电压区间为3.0～5.0V，测试温度为25℃。电池容量和充放电电流均以表面铁掺杂的核壳结构的尖晶石型镍锰酸锂的质量计算。
实施例2中的电池在2C倍率下充放电的循环性能如下：电池经过100圈循环，电池容量基本无衰减，仍保持在115mAh/g左右，库仑效率基本在100％，具有良好的容量保持率、寿命和库仑效率。
实施例3
1、制备表面锌掺杂的核壳结构型镍锰酸锂
在烧瓶中将尖晶石型镍锰酸锂LiNi0.5Mn1.5O4-δ(0≤δ＜0.1)粉末0.5g、锌的前驱体二水合乙酸锌15.0mg、沉淀剂碳酸氢钠2g分散在30ml水中，得到反应体系。在所述反应体系中，所述尖晶石型镍锰酸锂的浓度为16.7g/L；所述二水合乙酸锌的浓度为2.2×10-3mol/L；所述碳酸氢钠的浓度为0.79mol/L。
向反应体系中加入调节剂醋酸以调节pH至5.5，在90℃下搅拌4小时，经离心、洗涤、干燥得到中间产物。
将中间产物再以10℃/分钟的速率升温至800℃，在此温度下煅烧4小时，得到表面锌掺杂的核壳结构的尖晶石型镍锰酸锂粉末。其内核为尖晶石镍锰酸锂LiNi0.5Mn1.5O4-δ(0≤δ＜0.1)，壳层的锌掺杂量为尖晶石镍锰酸锂的0.89wt％。壳层的厚度约为10nm。
2、制备表面锌掺杂的核壳结构的尖晶石型镍锰酸锂的电极
将上述制备的表面锌掺杂的核壳结构的尖晶石型镍锰酸锂粉末0.24g与导电添加剂super-p 0.03g、粘结剂PVDF 0.03g和少许溶剂NMP混合，经制浆、涂片(铝箔作为集流体)、干燥，得到表面锌掺杂的核壳结构的尖晶石型镍锰酸锂电极。
3、组装电池
以上述步骤2中得到的表面锌掺杂的核壳结构的尖晶石型镍锰酸锂电极为正极，与锂负极组装成电池，电解液选择浓度为1M的碳酸酯电解液，其中，溶剂为：DMC:DEC:EC＝1:1:1(W/W)，溶质为1.0M LiPF6。
4、电池测试
使用蓄电池充放电测试仪对上述电池进行恒流充放电测试，测试电压区间为3.0～5.0V，测试温度为25℃。电池容量和充放电电流均以表面锌掺杂的核壳结构的尖晶石型镍锰酸锂的质量计算。
实施例3中的电池在2C倍率下充放电的循环性能如下：电池经过100圈循环，电池容量基本无衰减，仍保持在114mAh/g左右，库仑效率基本在100％，具有良好的容量保持率、寿命和库仑效率。
实施例4
1、制备表面钛掺杂的核壳结构型镍锰酸锂
在烧瓶中将尖晶石型镍锰酸锂LiNi0.5Mn1.5O4-δ(0≤δ＜0.1)粉末0.5g、钛的前驱体钛酸四丁酯20mg、沉淀剂尿素2g分散在30ml乙醇中，得到反应体系。在所述反应体系中，所述尖晶石型镍锰酸锂的浓度为16.7g/L；所述钛酸四丁酯的浓度为2.0×10-3mol/L；所述尿素的浓度为1.11mol/L。
向反应体系中加入1ml的调节剂盐酸(1mol/L)调节pH值至5，在90℃下搅拌4小时，经离心、洗涤、干燥得到中间产物。
将中间产物再以15℃/分钟的速率升温至800℃并在此温度下煅烧4小时，得到表面钛掺杂的核壳结构的尖晶石型镍锰酸锂粉末。其内核为尖晶石镍锰酸锂LiNi0.5Mn1.5O4-δ(0≤δ＜0.1)，外壳的铁掺杂量为尖晶石镍锰酸锂的0.56wt％。壳层的厚度约为15nm。
2、制备表面钛掺杂的核壳结构的尖晶石型镍锰酸锂的电极
将上述制备的表面钛掺杂的核壳结构的尖晶石型镍锰酸锂粉末0.24g与导电添加剂super-p 0.03g、粘结剂PVDF 0.03g和少许溶剂NMP混合，经制浆、涂片(铝箔作为集流体)、干燥，得到表面钛掺杂的核壳结构的尖晶石型镍锰酸锂电极。
3、组装电池
以上述表面钛掺杂的核壳结构的尖晶石型镍锰酸锂电极为正极，与锂负极组装成电池，电解液选择浓度为1M的碳酸酯电解液，其中，溶剂为：DMC:DEC:EC＝1:1:1(W/W)，溶质为1.0M LiPF6。
4、电池测试
使用蓄电池充放电测试仪对上述电池进行恒流充放电测试，测试电压区间为3.0～5.0V，测试温度为25℃。电池容量和充放电电流均以表面钛掺杂的核壳结构的尖晶石型镍锰酸锂的质量计算。
实施例4中的电池在2C倍率下充放电的循环性能如下：电池经过100圈循环，电池容量基本无衰减，仍保持在114mAh/g左右，库仑效率基本在100％，具有良好的容量保持率、寿命和库仑效率。

Claims (10)

  1. 一种正极材料，其特征在于，所述正极材料为尖晶石型镍锰酸锂LiNi0.5Mn1.5O4-δ(0≤δ＜0.1)，所述尖晶石型镍锰酸锂中具有自表面向内掺杂地浓度逐渐降低地金属元素，从而形成了与内核结构相近且紧密连接的掺杂层，也称壳层，所述壳层的厚度大于0，所述金属元素的掺杂量占所述尖晶石型镍锰酸锂重量的百分含量记为x，满足0＜x≤10wt％；
    优选地，0＜x≤5wt％；更优选地，0＜x≤2wt％；进一步优选地，0.29wt％≤x≤0.89wt％；更进一步优选地，0.56wt％≤x≤0.62wt％。
  2. 根据权利要求1所述的正极材料，其特征在于，所述壳层的厚度为1～50nm；优选为1～30nm；更优选为10～25nm，例如可以为15nm或者20nm。
    优选地，所述金属元素选自Mg、Ca、Al、Ti、Fe、Co、Cu、Zn、Zr中的一种或多种。
  3. 一种制备权利要求1或2中所述正极材料的方法，其特征在于，所述方法包括以下步骤：
    (1)将原材料尖晶石型镍锰酸锂LiNi0.5Mn1.5O4-δ(0≤δ＜0.1)，掺杂金属的前驱体和沉淀剂分散在溶剂中，加入调节剂以调节反应体系的pH值至1.5～7.0，加热搅拌反应，使得引入的所述前驱体转化为含有该掺杂金属元素的固相化合物，并均匀沉积在所述尖晶石型镍锰酸锂的表面，反应完成后分离，洗涤，干燥，得到中间产物；
    (2)将所述中间产物研磨均匀，煅烧，冷却至室温，得到所述正极材料。
    步骤(1)中，所述反应为金属离子的沉淀-热渗透反应。
    步骤(1)中，所述溶剂为水或乙醇。
    步骤(1)中，所述沉淀剂为碳酸盐、碳酸氢盐、甲酸盐、乙酸盐、磷酸氢盐、乌洛托品和磷酸盐中的一种或多种。
    步骤(1)中，所述前驱体选自金属元素的氯化盐、硫酸盐、硝酸盐、高氯酸盐、醋酸盐和醇盐中的至少一种；优选所述金属元素可以为Mg、Ca、Al、Ti、Fe、Co、Cu、Zn、Zr中的一种或多种；所述前驱体例如可以为九水合硝酸铝，六水合氯化铁、二水合乙酸锌或钛酸四丁酯中的一种或多种。
  4. 根据权利要求3所述的方法，其特征在于，所述步骤(2)中，以1～50℃/分钟的升温速率升温至200～1200℃煅烧1～10小时；
    优选地，以3～15℃/分钟的升温速率升温至450～800℃，煅烧3～4小时。
  5. 根据权利要求3或4所述的制备方法，其特征在于,
    所述沉淀剂选自碳酸氢铵、碳酸铵、碳酸氢钠、碳酸钠、碳酸氢钾、碳酸钾、甲酸铵、乙酸铵、甲酰胺、乙酰胺、乌洛托品、尿素、磷酸氢二铵、磷酸二氢铵、磷酸三铵、磷酸一氢钠、磷酸二氢钠、磷酸钠、磷酸一氢钾、磷酸二氢钾和磷酸钾中的一种或多种；进一步优选为磷酸氢二铵与甲酸铵的混合物、甲酸铵、碳酸氢钠、乌洛托品或尿素。
  6. 根据权利要求3-5任一项所述的制备方法，其特征在于，
    步骤(1)中，加入调节剂以调节所述反应体系的pH值至2.0～5.5；更优选为3.0～5.0；
    优选地，所述调节剂选自甲酸、乙酸、盐酸、硝酸、硫酸、高氯酸、氨水、氢氧化钠和氢氧化钾中的一种。
  7. 根据权利要求3-6中任一项所述的制备方法，其特征在于，
    所述步骤(1)中的搅拌反应温度为20～95℃，优选30～80℃；进一步优选为45～90℃；反应时间为2～4小时；
    例如可以在45℃下搅拌2小时；或者在50℃下搅拌2小时；或者在90℃下搅拌4小时；或者在90℃下搅拌4小时。
    可选地，所述步骤(2)中，以1～50℃的升温速率升温至200～1200℃煅烧1～10小时；优选升温至450～800℃，煅烧3～4小时。
  8. 根据权利要求3-7中任一项所述的制备方法，其特征在于，在步骤(1)的反应体系中，所述原材料尖晶石镍锰酸锂的浓度为0.01g/L～1000g/L，优选为0.1g/L～100g/L，进一步优选为1g/L～80g/L，更优选为20～50g/L；
    所述前驱体的浓度为1×10-6mol/L～0.1mol/L；优选1×10-5mol/L～0.01mol/L；进一步优选为1×10-4mol/L～1×10-3mol/L；
    所述沉淀剂的浓度为1×10-6mol/L～10mol/L，优选1×10-5mol/L～1mol/L。
  9. 一种电极，其包括权利要求1或2所述的正极材料。
  10. 一种电池，其包括权利要求9所述的电极。
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