CN114927693B - Positive electrode active material, method for preparing same, electrochemical device, and electronic apparatus - Google Patents

Positive electrode active material, method for preparing same, electrochemical device, and electronic apparatus Download PDF

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CN114927693B
CN114927693B CN202210605411.8A CN202210605411A CN114927693B CN 114927693 B CN114927693 B CN 114927693B CN 202210605411 A CN202210605411 A CN 202210605411A CN 114927693 B CN114927693 B CN 114927693B
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positive electrode
active material
electrode active
titanium
source
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CN114927693A (en
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莫方杰
朱呈岭
杨元婴
闫永思
李�昊
杨文龙
孙化雨
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Envision Power Technology Jiangsu Co Ltd
Envision Ruitai Power Technology Shanghai Co Ltd
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Envision Power Technology Jiangsu Co Ltd
Envision Ruitai Power Technology Shanghai Co Ltd
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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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • 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
    • H01M4/36—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
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
    • 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

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Inorganic Chemistry (AREA)
  • Composite Materials (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Manufacturing & Machinery (AREA)
  • Battery Electrode And Active Subsutance (AREA)

Abstract

The invention provides a positive electrode active material, a preparation method thereof, an electrochemical device and electronic equipment, wherein the positive electrode active material comprises a ternary material core and a titanium compound coated on the surface of the ternary material core, and the ternary material core comprises zirconium element and strontium element; the total content of zirconium element in the positive electrode active material is 1400ppm to 2200ppm, the total content of strontium element in the positive electrode active material is 200ppm to 800ppm, and the content of titanium element in the titanium compound is 500ppm to 1000ppm based on the total mass of metal element in the positive electrode active material. The positive electrode active material has good crystallinity and interface stability, and has higher gram capacity, coulombic efficiency and cycle stability.

Description

Positive electrode active material, method for preparing same, electrochemical device, and electronic apparatus
Technical Field
The invention belongs to the technical field of batteries, and relates to a positive electrode active material, a preparation method thereof, an electrochemical device and electronic equipment.
Background
The ternary layered material LiNi xCoyMn1-x-yO2 is widely applied to a power battery system with high energy density due to higher theoretical specific capacity (274 mAh/g), high reaction platform voltage (3.0V to 4.4V) and excellent reaction kinetics. In order to give consideration to the safety performance of the material, the Ni content, namely the x value, in the ternary material is often controlled below 0.7. Meanwhile, considering that Co is increasingly being supplied as a rare mineral resource in raw materials, the Co content in raw materials, i.e., y value, generally needs to be controlled to be 0.2 or less.
In the ternary material, the capacity is mainly determined by the content of Ni, and the decrease in Ni causes the capacity of the material to be reduced, thereby further reducing the energy density of the battery as a whole. The reduction of the Co content can influence the overall conductivity of the material, and improves the diffusion barrier of lithium ions in crystal lattices, so that serious reaction kinetics retardation problem is brought, and the capacity exertion of a battery is finally influenced. Therefore, the energy density, the dynamic performance and the cycle performance of the ternary material are simultaneously considered while the Ni content and the Co content in the ternary material are reduced, and the ternary material is a problem to be solved.
Disclosure of Invention
In view of the shortcomings of the prior art, the invention aims to provide a positive electrode active material, a preparation method thereof, an electrochemical device and electronic equipment. According to the preparation method, the ternary material is doped and coated and modified, the ternary material core is doped with zirconium element and strontium element with specific content, meanwhile, the core is coated with the positive electrode active material with the titanium compound with proper content, and the crystallinity and interface stability of the positive electrode active material are controlled within the optimal range, so that the product with excellent capacity and cycle performance is obtained.
To achieve the purpose, the invention adopts the following technical scheme:
In a first aspect, the invention provides a positive electrode active material, which comprises a ternary material core and a titanium compound coated on the surface of the ternary material core, wherein the ternary material core comprises zirconium element and strontium element;
The total content of zirconium element in the positive electrode active material is 1400ppm to 2200ppm, the total content of strontium element in the positive electrode active material is 200ppm to 800ppm, and the content of titanium element in the titanium compound is 500ppm to 1000ppm based on the total mass of metal element in the positive electrode active material.
In the present invention, the total content of zirconium element in the positive electrode active material is 1400ppm to 2200ppm, and for example, 1400ppm, 1500ppm, 1600ppm, 1700ppm, 1800ppm, 1900ppm, 2000ppm, 2100ppm, 2200ppm, or the like; the total content of strontium element in the positive electrode active material is 200ppm to 800ppm, and may be 200ppm, 300ppm, 400ppm, 500ppm, 600ppm, 700ppm, 800ppm, or the like, for example; the titanium element content in the titanium compound is 500ppm to 1000ppm, and for example, 500ppm, 600ppm, 700ppm, 800ppm, 900ppm, 1000ppm, or the like can be used.
The positive electrode active material comprises a ternary material inner core and a titanium compound coated on the surface of the ternary material inner core, wherein the ternary material inner core is doped with a specific content of strontium element and zirconium element, the inner core is coated with a specific content of titanium element, and the strontium element, the zirconium element and the titanium element are distributed in the positive electrode active material in a proper proportion, so that the crystallinity and the interface stability of the material can be improved, and the material has higher capacity and better cycle stability.
The principle of the invention is as follows: the first and the strontium have stronger oxygen binding force, the sintering temperature in the material preparation process can be reduced, 200ppm to 800ppm of strontium and 1400ppm to 2200ppm of zirconium are combined and doped into the ternary material core, and the crystallinity and interface stability of the material can be improved by mutually matching the strontium and the zirconium with specific content, and the capacity, the thermal performance and the long-term circulation stability of the material can be improved; secondly, titanium compounds with specific content are coated on the surface of the material, the titanium content is 500ppm to 1000ppm, the dynamics of the surface of the material can be further improved, the material is prevented from being corroded by electrolyte, and the material is protected; thirdly, the zirconium, the strontium and the titanium with specific contents in the invention are synergistic, so that the material with the optimal crystallinity and interface stability can be obtained, and the gram capacity, the coulombic efficiency and the cycle stability of the positive electrode active material are improved.
Preferably, the titanium element is distributed inward along the surface of the positive electrode active material to a depth of 140nm to 560nm, and may be 140nm, 180nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, 560nm, or the like, for example.
In the present invention, the titanium element is distributed inwards along the surface of the positive electrode active material, the depth thereof includes the thickness of the titanium compound, and when the titanium element permeates into the ternary material core, the thickness thereof also includes the permeation depth of the titanium element into the ternary material core.
Preferably, the D50 particle diameter of the positive electrode active material is 2 μm to 6 μm, and may be, for example, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm,5 μm, 5.5 μm, or 6 μm, etc.; the positive electrode active material prepared by the method has proper particle size, meanwhile, titanium element has proper penetration depth (140 nm to 560 nm) in the positive electrode active material, and the crystallinity and interface stability of the material can be improved by matching proper penetration depth of titanium element in the particle size range.
Preferably, the titanium compound comprises titanium oxide.
Preferably, the ternary material core further comprises titanium element.
Preferably, zirconium oxide and/or strontium oxide is also included between the ternary material core and the titanium compound.
The strontium element and the zirconium element of the positive electrode active material are doped in the ternary material core, and can also partially exist between the ternary material core and the titanium compound in the forms of strontium oxide and zirconium oxide; besides the titanium element is coated on the surface of the ternary material core in the form of titanium compound, the titanium element can also partially permeate into the crystal lattice of the ternary material core, so that the capacity and the cycling stability of the battery are further improved.
Preferably, the surface of the positive electrode active material includes free lithium, and the content of the free lithium is 350ppm to 1150ppm based on the total mass of metal elements in the positive electrode active material, and may be, for example, 350ppm, 400ppm, 500ppm, 600ppm, 700ppm, 800ppm, 900ppm, 1100ppm, 1150ppm, or the like.
In a second aspect, the present invention provides a method for preparing the positive electrode active material according to the first aspect, the method comprising the steps of:
(1) Mixing a ternary material precursor, a lithium source, a zirconium source and a strontium source, and performing primary sintering at 920-975 ℃ to obtain a first product;
(2) Mixing the first product with a titanium source, and performing secondary sintering at 150-400 ℃ to obtain the anode active material;
Wherein, based on the total mass of metal elements in the ternary material precursor, the lithium source, the zirconium source, the strontium source and the titanium source, the content of the zirconium element in the zirconium source is 2000ppm to 3000ppm, the content of the strontium element in the strontium source is 300ppm to 1000ppm, and the content of the titanium element in the titanium source is 800ppm to 1500ppm.
The primary sintering temperature in the present invention is 920℃to 975℃and may be, for example, 920℃to 925℃to 930℃to 935℃to 940℃to 945℃to 950℃to 955℃to 960℃to 965℃to 970℃or 975℃or the like; the secondary sintering temperature is 150 to 400 ℃, and may be 150, 180, 200, 220, 240, 260, 280, 300, 320, 340, 360, 380, 400, etc., for example.
In the present invention, the content of the zirconium element in the zirconium source is 2000ppm to 3000ppm, for example, 2000ppm, 2100ppm, 2200ppm, 2300ppm, 2400ppm, 2500ppm, 2600ppm, 2700ppm, 2800ppm, 2900ppm, 3000ppm, or the like, based on the total mass of the metal elements in the ternary material precursor, lithium source, zirconium source, strontium source, and titanium source; the strontium element content in the strontium source is 300ppm to 1000ppm, and for example, 300ppm, 400ppm, 500ppm, 600ppm, 700ppm, 800ppm, 900ppm, 1000ppm, or the like; the titanium element content in the titanium source is 800ppm to 1500ppm, and may be 800ppm, 900ppm, 1000ppm, 1100ppm, 1200ppm, 1300ppm, 1400ppm, 1500ppm, or the like, for example.
The method adopts a two-step sintering mode, firstly mixes and sinters a zirconium source and a strontium source, a ternary material precursor and a lithium source at a specific temperature, most of zirconium and strontium in the zirconium source and the strontium source can enter a crystal lattice of the ternary material precursor, and a small amount of zirconium and strontium remains on the surface of the precursor in the form of compounds (such as zirconium oxide and strontium oxide); then adding a titanium source to perform secondary sintering at a specific temperature, reacting more active titanium with residual lithium on the surface of the material, coating most of the titanium on the surface of the material in the form of titanium compounds (such as titanium oxide), and allowing a small part of titanium to permeate into the lattice of the material to obtain the anode active material.
In the invention, when sintering is carried out at 920-975 ℃, a zirconium source and a strontium source with specific contents are added into a ternary material precursor, the strontium has stronger oxygen binding force, the sintering temperature can be reduced, and the combination of zirconium and strontium can improve the capacity, the thermal performance and the long-term cycle stability of the material; meanwhile, a strontium source and a zirconium source are added at the temperature to sinter, so that zirconium element can permeate into the crystal lattice, and the crystal lattice crystallinity is improved by the synergistic effect of the strontium source and the zirconium source and the effect of reducing the sintering temperature, so that the disorder of the crystal lattice is prevented. And adding a titanium source during secondary sintering at 150-400 ℃ to enable a titanium compound to be coated on the surface of the material, so that the dynamics of the surface of the material can be further improved, the material is prevented from being corroded by electrolyte, and the material is protected. According to the invention, zirconium, strontium and titanium are synergistic in a certain proportion, sintering conditions are controlled, so that the material with the best crystallinity and interface stability can be obtained, and the gram capacity, coulombic efficiency and cycle stability of the positive electrode active material are improved.
As a preferred technical scheme of the preparation method, the temperature of the primary sintering is 930 ℃ to 975 ℃.
Preferably, the time of the primary sintering is 12h to 24h, for example, 12h, 14h, 16h, 18h, 20h, 22h or 24h, etc.
Preferably, the atmosphere for the primary sintering includes oxygen, and the volume content of the oxygen is 80% or more based on the total volume of the atmosphere, for example, 80%, 82%, 84%, 96%, 88%, 90%, 92%, 94%, 96%, 98% or 100% or the like.
Preferably, the temperature of the secondary sintering is 200 ℃ to 400 ℃.
Preferably, the time of the secondary sintering is 4h to 10h, for example, 4h, 5h, 6h, 7h, 8h, 9h or 10h, etc.
Preferably, the atmosphere of the secondary sintering includes oxygen, and the volume content of the oxygen is 80% or more based on the total volume of the atmosphere, for example, 80%, 82%, 84%, 96%, 88%, 90%, 92%, 94%, 96%, 98% or 100% or the like.
According to the invention, by further optimizing the temperatures of primary sintering and secondary sintering and matching with a certain content of zirconium source, strontium source and titanium source, the material with the best crystallinity and interface stability is obtained, and the gram capacity, coulombic efficiency and cycle stability of the positive electrode active material are further improved.
Preferably, the chemical formula of the ternary material precursor is Ni xCoyMn1-x-y(OH)2, wherein x is more than or equal to 0.56 and less than or equal to 0.60, such as 0.56, 0.57, 0.58, 0.59 or 0.6, y is more than or equal to 0.09 and less than or equal to 0.13, such as 0.09, 0.1, 0.11, 0.12 or 0.13, and the like.
Preferably, the lithium source comprises lithium carbonate and/or lithium hydroxide.
Preferably, the zirconium source comprises zirconium oxide.
Preferably, the strontium source comprises strontium oxide.
Preferably, the titanium source comprises titanic acid.
The zirconium oxide, strontium oxide and titanium acid in the present invention may also be replaced with other zirconium, strontium or titanium-containing compounds, such as zirconium hydroxide, lithium zirconate (Li 2ZrO3), zirconium carbonate, strontium hydroxide, strontium carbonate, lithium titanate (Li 4Ti5O12), titanium dioxide or titanium oxide, respectively.
The zirconia and the strontium oxide in the invention can adopt nano zirconia and nano strontium oxide, and the D50 particle size of the nano zirconia and the nano strontium oxide is in the range of 50nm to 500nm.
In a third aspect, the present invention provides an electrochemical device comprising the positive electrode active material according to the first aspect in a positive electrode of the electrochemical device.
The anode active material provided by the invention has good crystallinity and stable interface structure, and an electrochemical device prepared by adopting the anode active material has higher capacity and better cycle performance.
In an alternative embodiment, the instant invention provides a method for detecting whether an electrochemical device comprises the positive electrode active material of the instant invention, comprising:
And splitting the electrochemical device sample to obtain a positive electrode, washing the positive electrode by using a solvent, drying, scraping the positive electrode surface to obtain active material powder, performing ICP test on the active material powder, and observing that the content of Ti, sr and Zr elements is in a defined range (Ti: 500-1000 ppm, sr: 200-800 ppm and Zr: 1400-2200 ppm), thereby confirming that the positive electrode of the electrochemical device sample contains the positive electrode active material. And performing a time-of-flight secondary ion mass spectrometer to test the distribution depth of Ti element, observing to find that the penetration depth of Ti element is within a limited range (140 nm to 560 nm), and further confirming that the positive electrode of the electrochemical device sample contains the positive electrode active material.
In an alternative embodiment, the present invention provides a method for preparing the positive electrode, including:
And mixing the positive electrode active material, the conductive agent and the binder with a solvent to obtain positive electrode slurry, coating the positive electrode slurry on an aluminum foil, and rolling to obtain the positive electrode.
Preferably, the conductive agent includes conductive carbon black (SP) and/or Carbon Nanotubes (CNT).
Preferably, the binder comprises polyvinylidene fluoride (PVDF).
Preferably, the mass ratio of the positive electrode active material, SP, CNT, and PVDF is (90 to 99): 1:0.5:1, for example, may be 90:1:0.5:1, 92:1:0.5:1, 94:1:0.5:1, 96:1:0.5:1, 98:1:0.5:1, 99:1:0.5:1, or the like.
In an alternative embodiment, the electrochemical device is a lithium ion battery.
In an alternative embodiment, the negative electrode of the electrochemical device comprises graphite, SP, carboxymethylcellulose (CMC), and Styrene Butadiene Rubber (SBR), the mass ratio of graphite, SP, CMC, and SBR being (90 to 99): 1.5:2, for example, may be 90:1:1.5:2, 92:1:1.5:2, 94:1:1.5:2, 96:1:1.5:2, 98:1:1.5:2, or 99:1:1.5:2, etc.
In an alternative embodiment, the electrolyte of the electrochemical device includes a lithium salt and a solvent.
In an alternative embodiment, the lithium salt comprises LiPF 6.
In an alternative embodiment, the lithium salt is present in an amount of 4wt% to 24wt%, such as 4wt%, 8wt%, 10wt%, 15wt%, 20wt%, 24wt%, etc., based on 100wt% of the electrolyte.
In an alternative embodiment, the solvent includes at least one or a combination of any two of Ethylene Carbonate (EC), ethylmethyl carbonate (EMC), dimethyl carbonate (DMC) and Polycarbonate (PC), for example, a combination of EC and EMC, a combination of DMC and PC, a combination of EC, EMC and DMC, or a combination of EC, EMC, DMC and PC, etc.
In an alternative embodiment, the mass ratio of EC, EMC, DMC to PC in the solvent is (2 to 4): 3 to 5): 2 to 4): 0 to 1, the selection range of EC (2 to 4) may be, for example, 2, 2.5, 3, 3.5 or 4, etc., the selection range of EMC (3 to 5) may be, for example, 3, 3.5, 4, 4.5 or 5, etc., the selection range of DMC (2 to 4) may be, for example, 2, 2.5, 3, 3.5 or 4, etc., the selection range of PC (0 to 1) may be, for example, 0, 0.1, 0.2, 0.3, 0.5, 0.7 or 1, etc., and when PC is 0, it means that PC is not contained in the solvent.
In an alternative embodiment, the separator of the electrochemical device has a thickness of 9 μm to 18 μm, for example, 9 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, or the like.
In an alternative embodiment, the separator of the electrochemical device has an air permeability of 180s/100mL to 380s/100mL, and may be, for example, 180s/100mL, 200s/100mL, 240s/100mL, 250s/100mL, 280s/100mL, 300s/100mL, 250s/100mL, 380s/100mL, or the like.
In an alternative embodiment, the porosity of the separator of the electrochemical device is 30% to 50%, for example, 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48% or 50%, etc.
The application selects the diaphragm with proper parameters to be matched with the positive electrode and the negative electrode to prepare the electrochemical device, thereby improving the capacity and the circulation stability of the electrochemical device.
In a fourth aspect, the present invention provides an electronic device comprising the electrochemical apparatus according to the third aspect.
The electronic device according to the invention may be, for example, a mobile computer, a cellular phone, a memory card, a liquid crystal television, an automobile, a motorcycle, a motor, a timepiece, a camera, etc.
Compared with the prior art, the invention has the beneficial effects that:
The positive electrode active material comprises a ternary material core doped with strontium element and zirconium element and a titanium compound coated on the surface of the ternary material core, wherein the strontium has strong oxygen binding force, the sintering temperature in the material preparation process can be reduced, and the specific content of the strontium element and the zirconium element is combined and doped into the ternary material core, so that the crystallinity and the interface stability of the material can be improved, and the capacity, the thermal performance and the long-term circulation stability of the material can be improved. The ternary material is coated with titanium compound with specific content outside the core, so that the dynamics of the material surface can be further improved, the material is prevented from being corroded by electrolyte, and the material is protected. The strontium element, the zirconium element and the titanium element are distributed in the positive electrode active material in a proper proportion, and the materials with the optimal crystallinity and interface stability are obtained through synergistic effect, so that the gram capacity, the coulombic efficiency and the cycle stability of the positive electrode active material are improved.
Detailed Description
The technical scheme of the invention is further described by the following specific embodiments.
Example 1
The embodiment provides a positive electrode active material, which comprises a ternary material core LiNi 0.58Co0.11Mn0.31O2 and titanium oxide coated on the surface of the ternary material core, wherein the ternary material core is doped with zirconium element, strontium element and titanium element, and the surface of the positive electrode active material also comprises free lithium; based on the total mass of metal elements (Li, ni, co, mn, zr, sr and Ti) in the positive electrode active material, the total content of zirconium element in the positive electrode active material is 1892ppm, the total content of strontium element is 544ppm, the content of titanium element in titanium oxide is 665ppm, the depth of inward distribution of titanium element along the surface of the positive electrode active material is 243nm, and the content of free lithium on the surface of the positive electrode active material is 670ppm.
The embodiment also provides a preparation method of the positive electrode active material, which comprises the following steps:
(1) Mixing ternary material precursors Ni 0.58Co0.11Mn0.31(OH)2, lithium carbonate, nano zirconia and nano strontium oxide, and sintering for 17 hours in an oxygen atmosphere at 950 ℃ to obtain a first product;
(2) Mixing the first product with titanic acid, and performing secondary sintering for 6 hours in an oxygen atmosphere at the temperature of 300 ℃ to obtain the positive electrode active material;
Wherein, based on the total mass of the metal elements (Li, ni, co, mn, zr, sr and Ti) in Ni 0.58Co0.11Mn0.31(OH)2, lithium carbonate, nano zirconia, nano strontium oxide and titanic acid, the content of the zirconium element in the nano zirconia is 2000ppm, the content of the strontium element in the nano strontium oxide is 600ppm, the content of the titanium element in the titanic acid is 1000ppm, and the molar ratio of the lithium carbonate to the Ni 0.58Co0.11Mn0.31(OH)2 is 1.02:1.
1. Assembly of lithium ion batteries
(1) Preparation of positive electrode: mixing the positive electrode active materials, SP, CNT and PVDF prepared in the examples and the comparative examples according to the mass ratio of 97.5:1:0.5:1 with Nitrogen Methyl Pyrrolidone (NMP) to prepare positive electrode slurry, coating the positive electrode slurry on an aluminum foil, and rolling to obtain a positive electrode;
(2) Preparation of the negative electrode: mixing graphite, SP, CMC and SBR according to the mass ratio of 95.5:1:1.5:2 to prepare slurry, coating the slurry on copper foil, and rolling to obtain a negative electrode;
(3) Preparation of a lithium ion battery: and (3) adhering an aluminum positive electrode tab to the positive electrode, adhering a copper negative electrode tab to the negative electrode, selecting a diaphragm with the thickness of 10 mu m, the air permeability of 200s/100mL and the porosity of 40%, sequentially and tightly stacking the positive electrode, the diaphragm and the negative electrode together in sequence, injecting electrolyte of EC, EMC, DMC and PC with the solute of 5wt% LiPF 6 and the solvent of 3:4:3:0.5 into two sides of the diaphragm, and obtaining the battery cell after stacking the battery cell to the required layer number.
2. Performance testing
(1) Testing of positive electrode active material:
the content of Zr, sr and Ti elements was tested by using an Inductively Coupled Plasma (ICP) method.
The depth test method for the inward distribution of Ti element along the surface of the positive electrode active material comprises the following steps: the powder particles of the positive electrode active material were cut by a focused ion beam method, and then the distribution depth of Ti element was measured by a time-of-flight secondary ion mass spectrometer.
Testing the free lithium content on the surface of the positive electrode active material: and (3) placing 1g of positive electrode active material powder into deionized water, stirring for 5min by a glass rod, standing for 4h, taking supernatant, and testing the content of LiOH and Li 2CO3 by using a potentiometric titrator, wherein the content of lithium element is the content of free lithium coated on the surface.
(2) Testing of lithium ion batteries:
performing a first discharge gram capacity test and an 800-week cycle capacity retention test by adopting a Cheng Hong electric appliance stock electric company battery performance test system (equipment model: BTS05/10C 8D-HP);
The first discharge gram capacity test method comprises the following steps: charging and discharging for one week at 25 ℃ in a charging and discharging mode of 0.063A/g, wherein the voltage interval is 2.8V to 4.35V, and the obtained charge and discharge capacity is divided by the positive electrode usage amount, namely the first charge/discharge gram capacity. The first discharge capacity divided by the first charge capacity is the first coulombic efficiency.
800 Week cycle capacity retention test method: under the condition of 25, the cycle is carried out in a charge-discharge system of 0.19A/g (calculated by the mass of the positive electrode material), and the voltage interval is 2.8V to 4.35V. After cycling to 800 weeks, dividing the discharge capacity of the battery at the moment by the discharge capacity of the first cycle, namely the 800-cycle capacity retention rate of the battery.
Examples 2 to 5 and comparative examples 1 to 6 were subjected to parameter modification based on the procedure of example 1, and the specific modified parameters and test results are shown in tables 1 to 6.
TABLE 1
TABLE 2
Gram Capacity for first discharge (mAh/g) First coulombic efficiency (%) 800 Cycle capacity retention (%)
Example 1 187.2 87.3 95
Example 2 189.1 88.2 94
Example 3 186.4 87.7 96
TABLE 3 Table 3
TABLE 4 Table 4
As is clear from comparison of examples 1 with examples 4 to 5 and comparative examples 1 to 2 in tables 3 and 4, the temperatures of primary sintering and secondary sintering in the present invention affect the content and distribution of elements in the positive electrode active material, affect the crystallinity and interfacial stability of the material, and further affect the gram capacity, coulombic efficiency and capacity retention of the material.
In comparative examples 1 and 4, when the secondary sintering temperature is low, titanic acid cannot fully react with free lithium on the surface of the material and cannot further permeate the interior of the material, and most of the titanic acid is coated on the surface of the material in the form of titanium compound, so that the contents of Ti in the titanium compound and free lithium on the surface of the material in comparative example 1 are too high, and the gram capacity for the first discharge, the coulombic efficiency and the 800-cycle capacity retention rate of the material are lower than those in example 1; in comparative examples 1 and 1, when the secondary sintering temperature is too high, most of the titanium element enters the interior of the crystal lattice of the material, the Ti element penetrates deeper inward along the surface of the positive electrode active material, and the titanium element content on the surface of the material is small, which affects the contact of the material with the electrolyte, and thus, the gram capacity for the first discharge, the coulombic efficiency and the 800-cycle capacity retention rate of comparative example 1 are lower than those of example 1.
In comparative examples 1 and 5, when the primary sintering temperature is low, the free lithium on the surface is high, meanwhile, the primary sintering temperature influences the distribution of titanium element during secondary sintering, the penetration depth of titanium element in example 5 is shallow, and the gram capacity and the cycle stability of the material are poor; in comparative examples 1 and 2, when the primary sintering temperature is too high, the free lithium on the surface is too small, meanwhile, the penetration depth of titanium element in comparative example 2 is deeper, the content of coated titanium oxide is smaller, gram capacity exertion of the material is affected, and the cycle stability is also poor.
TABLE 5
As can be seen from the comparison of example 1 and comparative examples 3 to 5 in Table 5, the present invention has suitable contents of three elements, and when sintering is performed under the same conditions, the amounts of the three elements of zirconium, strontium and titanium are changed, so that the contents of the three elements in the positive electrode active material are changed, and the discharge capacity and the cycle stability of the finally prepared lithium ion battery are affected. When the addition amount of a certain element is singly changed out of the optimal range, the discharge gram capacity and the first efficiency are reduced, and the cycle stability is also deteriorated, so that the three elements of zirconium, strontium and titanium in the embodiment 1 are all in the optimal content range, and the discharge gram capacity and the cycle stability of the prepared lithium ion battery are optimal.
Comparative example 6
This comparative example was identical to example 1 except that no secondary sintering was performed and that titanic acid was directly added at 950 ℃ primary sintering.
TABLE 6
Gram Capacity for first discharge (mAh/g) First coulombic efficiency (%) 800 Cycle capacity retention (%)
Example 1 187.2 87.3 95
Comparative example 6 182.7 86.8 36
As can be seen from the comparison of the embodiment 1 and the comparative example 6, the method provided by the invention has the advantages that the sintering is carried out twice at a specific temperature, the zirconium source and the strontium source are firstly added for doping, and then the titanium source is added for coating, so that most of titanium element is combined with the ternary material core in the form of a coating layer, the crystallinity and the interface stability of the positive electrode active material can be improved, the synergistic effect among the three elements can be fully exerted, and the gram capacity, the coulomb efficiency and the cycle stability of the positive electrode active material are improved; in comparative example 6, the titanium element is doped into the core by directly adding the titanic acid during the primary sintering, and the titanium element content of the coating layer is too low, so that the doping and coating effects are poor, and the prepared material has poor cycle stability.
In summary, as can be seen from examples 1 to 5, the present invention performs doping and cladding modification on the ternary material to obtain the positive electrode active material in which the core is doped with zirconium element and strontium element in specific content, and is coated with titanium compound in proper content, so that the crystallinity and interfacial stability of the positive electrode active material can be controlled within the optimal range, and thus the product with excellent capacity and cycle performance can be obtained.
While the foregoing is directed to embodiments of the present invention, other and further details of the invention may be had by the present invention, it should be understood that the foregoing description is merely illustrative of the present invention and that no limitations are intended to the scope of the invention, except insofar as modifications, equivalents, improvements or modifications are within the spirit and principles of the invention.

Claims (9)

1. The positive electrode active material is characterized by comprising a ternary material core and a titanium compound coated on the surface of the ternary material core, wherein the ternary material core comprises zirconium element and strontium element; the precursor for preparing the ternary material core is a low-nickel low-cobalt material, and the chemical formula of the low-nickel low-cobalt material is Ni xCoyMn1-x-y(OH)2, wherein x is more than or equal to 0.56 and less than or equal to 0.60,0.09 and y is more than or equal to 0.13;
The total content of zirconium element in the positive electrode active material is 1400ppm to 2200ppm, the total content of strontium element in the positive electrode active material is 200ppm to 800ppm, and the content of titanium element in the titanium compound is 500ppm to 1000ppm based on the total mass of metal element in the positive electrode active material;
The titanium element is distributed inward along the surface of the positive electrode active material to a depth of 140nm to 560nm.
2. The positive electrode active material according to claim 1, wherein the positive electrode active material has a particle diameter D50 of 2 μm to 6 μm.
3. The positive electrode active material according to claim 1, wherein the positive electrode active material satisfies any one of the following conditions (a) to (d):
(a) The titanium compound comprises titanium oxide;
(b) The ternary material core also comprises titanium element;
(c) Zirconium oxide and/or strontium oxide are/is also included between the ternary material core and the titanium compound;
(d) The surface of the positive electrode active material includes free lithium, and the content of the free lithium is 350ppm to 1150ppm based on the total mass of metal elements in the positive electrode active material.
4. A method for producing the positive electrode active material according to any one of claims 1 to 3, characterized in that the method comprises the steps of:
(1) Mixing a ternary material precursor, a lithium source, a zirconium source and a strontium source, and performing primary sintering at 920-975 ℃ to obtain a first product;
(2) Mixing the first product with a titanium source, and performing secondary sintering at 150-400 ℃ to obtain the anode active material;
Wherein, based on the total mass of metal elements in the ternary material precursor, the lithium source, the zirconium source, the strontium source and the titanium source, the content of the zirconium element in the zirconium source is 2000ppm to 3000ppm, the content of the strontium element in the strontium source is 300ppm to 1000ppm, and the content of the titanium element in the titanium source is 800ppm to 1500ppm.
5. The method according to claim 4, wherein the primary sintering satisfies any one of the following conditions (e) to (g):
(e) The temperature of the primary sintering is 930 ℃ to 975 ℃;
(f) The time of the primary sintering is 12 to 24 hours;
(g) The primary sintering atmosphere comprises oxygen, and the volume content of the oxygen is more than or equal to 80 percent based on the total volume of the atmosphere.
6. The production method according to claim 4, wherein the secondary sintering satisfies any one of the following conditions (h) to (j):
(h) The temperature of the secondary sintering is 200-400 ℃;
(i) The secondary sintering time is 4 to 10 hours;
(j) The secondary sintering atmosphere comprises oxygen, and the volume content of the oxygen is more than or equal to 80 percent based on the total volume of the atmosphere.
7. The method of claim 4, wherein the ternary material precursor, zirconium source, strontium source, and titanium source satisfy any one of the following conditions (k) to (m):
(k) The zirconium source comprises zirconium oxide;
(l) The strontium source comprises strontium oxide;
(m) the titanium source comprises titanic acid.
8. An electrochemical device, characterized in that the positive electrode of the electrochemical device includes the positive electrode active material according to any one of claims 1 to 3 therein.
9. An electronic device, characterized in that the electrochemical device according to claim 8 is included in the electronic device.
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