CN113690446A - Ternary positive electrode material, preparation method thereof and lithium secondary battery - Google Patents

Ternary positive electrode material, preparation method thereof and lithium secondary battery Download PDF

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CN113690446A
CN113690446A CN202111237831.7A CN202111237831A CN113690446A CN 113690446 A CN113690446 A CN 113690446A CN 202111237831 A CN202111237831 A CN 202111237831A CN 113690446 A CN113690446 A CN 113690446A
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positive electrode
tungsten oxide
ternary
electrode material
sintering
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CN113690446B (en
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李宇东
范江
曹勇富
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Yingde Keheng New Energy Technology Co ltd
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    • H—ELECTRICITY
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    • 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
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    • H01M4/02—Electrodes composed of, or comprising, active material
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    • 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
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    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
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Abstract

The invention belongs to the field of batteries, and discloses a ternary cathode material which comprises a base material, an inner cladding layer and an outer cladding layer, wherein the inner cladding layer and the outer cladding layer are used for cladding the base material; the inner coating layer is made of solid electrolyte, tungsten oxide and Li2WO4Sintering to obtain; the solid electrolyte, tungsten oxide and Li2WO4The mass ratio of (1): 5-10: 5-10. The ternary cathode material is formed by coating LLZTO, tungsten oxide and Li by a method of coating LLZTO and tungsten oxide2WO4The combined inner protective layer reduces the impedance of the anode material; and then, by a method of coating aluminum sulfate, the residual lithium carbonate on the surface of the high-nickel ternary positive electrode material reacts with the outer coating layer to form a lithium sulfate or lithium metaaluminate outer coating layer with high structural stability, so that the material is mechanically separated from the electrolyte, the surface side reaction of the high-nickel ternary positive electrode material is reduced, and the cycle performance is improved. Meanwhile, the invention also provides a preparation method of the cathode material and a lithium secondary battery using the cathode material.

Description

Ternary positive electrode material, preparation method thereof and lithium secondary battery
Technical Field
The invention relates to the field of batteries, in particular to a ternary cathode material, a preparation method thereof and a lithium secondary battery.
Background
With the rapid development of new energy automobile market in China, the power market prospect is wide, the requirement of a power lithium ion battery is greatly increased, and with the continuous improvement of the requirement on the energy density of the lithium ion battery, the market demand of ternary materials always keeps an increasing trend. At present, no matter policy guidance, market demand (endurance mileage demand) or technology evolution direction, in a long term, the nickel enrichment of ternary materials has become a necessary trend for the development of power lithium ion battery materials.
With the increase of the nickel content, the cycle performance and the safety performance of the cathode material are obviously reduced while the capacity of the cathode material is improved and the material cost is reduced. The development of high-capacity battery cell products is seriously restricted by the problems of high-nickel materials, a brand-new direction is opened for the development of high-capacity cathode materials by the surface coating technology of the super-nickel ternary materials, the surface coating technology of the super-nickel ternary materials is compared with the traditional coating technology of the ternary materials, the traditional coating technology of the ternary materials is mainly the surface coating technology of coating one or two metal oxides on the surface of the ternary materials, the surface coating technology of the super-nickel ternary materials is the coating technology of forming a coating layer on the surface of the ternary materials by a plurality of metal oxides or lithiates, and the super-nickel ternary materials have the characteristics of multi-layer structure, more stable chemical properties, material impedance reduction and other multifunctional combinations; the ultra-nickel ternary material treated by the ultra-high nickel surface coating technology is superior to the high-nickel ternary material treated by the traditional ternary coating technology in the indexes of energy density, cycle performance, thermal stability, gas production and the like. Kisuk Kang injects SO at the proper position during synthesis2Gas in the form of surfaceInsulating layer Li2SO4The surface specificity modification can be realized, the residual lithium is reduced under the condition of not degrading the layered crystal structure of the body, and the cycle stability of the lithium ion battery is improved. (Seong D W M, Cho D K, Park J. Controlling reactive Lithium in High-Nickel: (>90 %) Lithium Layered Oxides for Cathodes in Lithium-Ion Batteries[J]Angew. chem. int. Ed., 2020, 59,42: 18662-. But the insulating layer Li2SO4The charge and discharge polarization exists when the button cell is manufactured, the energy density is reduced, and in addition, the preparation method can generate corrosive gas, has great influence on the environment and is not beneficial to production and sustainable development.
In order to solve the problems, CN201310404279.5 discloses a preparation method of a lithium nickel cobalt manganese oxide composite positive electrode material, which comprises the following steps: 1) the method comprises the following steps of taking nickel cobalt lithium manganate or nickel cobalt lithium manganate doped with metal ions as a base material, taking lithium manganate fine powder as a coating substance, and uniformly mixing the nickel cobalt lithium manganate or the nickel cobalt lithium manganate doped with metal ions, the lithium manganate fine powder and a binding agent according to weight percentage, wherein the addition amount of the lithium manganate fine powder accounts for 0.1-40% of the weight percentage of a composite positive electrode material, and the addition amount of the binding agent accounts for 0.1-5% of the weight percentage of the composite positive electrode material; 2) and (2) putting the mixture obtained in the step 1) into a reaction furnace, carrying out sectional sintering in the air or oxygen atmosphere, heating to 300-700 ℃ for constant temperature treatment for 1-20 h, heating to 800-1000 ℃ for constant temperature treatment for 1-20 h, naturally cooling, and carrying out powder treatment to finally obtain the nickel cobalt lithium manganate composite cathode material.
In this embodiment, one of tungsten oxide, molybdenum oxide, and the like is used as a binder between the clad layer and the base material.
CN202110729926.4 discloses a preparation method of a lithium metaaluminate coated nickel-cobalt-manganese ternary cathode material, wherein the preparation method comprises the steps of mixing a nickel-cobalt-manganese ternary precursor with a lithium source, sintering at a high temperature to prepare the nickel-cobalt-manganese ternary cathode material, preparing the nickel-cobalt-manganese ternary cathode material by using aluminum isopropoxide through a hydro-thermal hydrolysis method, filtering and drying after the hydro-thermal reaction is finished, and grinding the nickel-cobalt-manganese ternary cathode material into powder; and placing the dried powder in a box-type calcining furnace, and calcining at high temperature to obtain the lithium metaaluminate coated nickel-cobalt-manganese ternary materialAnd (3) a positive electrode material. According to the preparation method, a lithium source is not required to be additionally added, but the lithium residues on the surface of the positive electrode material are used as raw materials, so that the lithium residues on the surface of the positive electrode material can be removed, and a layer of LiAlO is coated on the surface of the positive electrode material2The material is protected, so that the rate capability and the cycling stability of the anode material are improved.
The scheme adopts LiAlO2As coating agent, LiAlO is prepared by hydrolysis hydrothermal method by using aluminum isopropoxide2The coated positive electrode material utilizes residual lithium as a lithium source, so that the electrochemical performance of the positive electrode material is improved.
CN2013106721. X discloses a preparation method of a lithium ion battery surface-coated positive electrode material, which comprises the following steps: (1) mixing lithium iron phosphate, lithium nickel cobalt oxide, magnesium nitrate and cobalt oxide to form a positive material mixture, heating the positive material mixture to be above the melting point of the magnesium nitrate, reacting for 2-6 hours, and cooling; (2) grinding the cooled positive electrode material mixture, sieving the ground positive electrode material mixture with a 200-mesh sieve, placing the mixture in a mixing and drying kettle, and spraying a lithium hydroxide saturated solution into the mixing and drying kettle; (3) starting the mixer, and spraying aluminum sulfate into the mixing and drying kettle to obtain a hydrolysis reaction mixture; (4) and drying, carrying out heat treatment, cooling and crushing on the mixture obtained by the hydrolysis reaction, and then sieving the mixture with a 200-mesh sieve to obtain the surface-coated lithium ion battery anode material.
The scheme adopts aluminum sulfate and needs a lithium source for supplementing lithium hydroxide.
CN201410110568.9 discloses an aluminum coating method for a lithium ion cathode material, which comprises the following steps: a) preparing an uncoated positive electrode material by a conventional method; b) preparing an aluminum salt solution as a coating solution by using an inorganic aluminum salt and a solvent, wherein the aluminum salt is selected from aluminum nitrate, aluminum chloride, aluminum sulfate and aluminum acetate, and the solvent is selected from ethanol, methanol and isopropanol; c) adding an uncoated positive electrode material into the aluminum salt solution, stirring and heating to reflux; d) refluxing for 30min, filtering to remove solvent, and vacuum drying at 70-100 deg.C to obtain semi-finished product; e) and (4) roasting the semi-finished product in a muffle furnace, and naturally cooling to room temperature to obtain the aluminum-coated anode material.
In the research process, the performance of the coating material is closely related to the performance of the binding material between the base material and the coating material, and the method is crucial to achieving excellent cycle performance while solving the problem of high residual lithium of the high-nickel ternary material.
The technical problem to be solved by the scheme is as follows: how to solve the technical problems of high residual lithium, poor cycle performance and low safety of the existing high-nickel ternary material.
Disclosure of Invention
The invention aims to provide a ternary cathode material which is formed by coating LLZTO and tungsten oxide2WO4The combined inner protective layer reduces the impedance of the anode material; and then, by a method of coating aluminum sulfate, the residual lithium carbonate on the surface of the high-nickel ternary positive electrode material reacts with the outer coating layer to form a lithium sulfate or lithium metaaluminate outer coating layer with high structural stability, so that the material is mechanically separated from the electrolyte, the surface side reaction of the high-nickel ternary positive electrode material is reduced, and the cycle performance is improved.
Meanwhile, the invention also provides a preparation method of the cathode material and a lithium secondary battery using the cathode material.
In order to achieve the purpose, the invention provides the following technical scheme: a ternary cathode material comprises a substrate, an inner cladding layer and an outer cladding layer, wherein the inner cladding layer and the outer cladding layer are used for cladding the substrate;
the inner coating layer is made of solid electrolyte, tungsten oxide and Li2WO4Sintering to obtain; the solid electrolyte, tungsten oxide and Li2WO4The mass ratio of (1): 5-10: 5-10;
the outer cladding layer is Li2SO4、Al2O3、LiAlO2One or a mixture of at least two;
the base material is nickel cobalt lithium manganate;
the solid electrolyte is Li6.75La3Zr1.75Ta0.25O12。
In the ternary cathode material, D50 of the cathode material is 2-13 um.
In the ternary cathode material, the thickness of the inner cladding layer and the outer cladding layer is 8-30 nm.
In the above ternary positive electrode material, the base material is LiNi1-x-yCoxMnyO2， 0<x≤0.09，0<y≤0.06。
In the above ternary positive electrode material, the tungsten oxide is W18O49Or WO3。
Meanwhile, the invention also discloses a preparation method of the ternary cathode material, which comprises the following steps:
(1) a substrate, a solid electrolyte, tungsten oxide, and Li2WO4Adding into organic solvent, stirring, oven drying, and sintering at certain temperature to obtain semi-finished product with inner coating layer.
(2) Adding the semi-finished product and aluminum sulfate into an organic solvent, uniformly stirring, drying, and sintering at a certain temperature to obtain the ternary cathode material with an outer coating layer and an inner coating layer.
In step 1 and step 2, the amount of the substrate and the intermediate product added to the organic solvent is generally controlled to be 80 to 120g/100g of the solvent, but is not limited to be higher or lower, so as to achieve better dispersion.
In the preparation method of the ternary cathode material, in the step (1), the solid electrolyte, the tungsten oxide and the Li2WO4The amount in the organic solvent in the step (1) is 300-2000 ppm; the sintering temperature is 300-500 ℃, and the sintering time is 3-10 h.
In the above preparation method of the ternary cathode material, the addition amount of the aluminum sulfate in the step (2) is 800-3000 ppm; the sintering temperature is 400-550 ℃, and the sintering time is 5-10 h.
In the above preparation method of the ternary cathode material, the organic solvent in steps (1) and (2) is one of ethanol, ethylene glycol and methanol.
Finally, the invention also discloses a lithium secondary battery, and the anode material of the lithium secondary battery is the ternary anode material.
Compared with the prior art, the invention has the beneficial effects that:
formed by coating LLZTO, tungsten oxide3、Li2WO4The combined inner protective layer reduces the interface charge transfer resistance of the anode material; and then, by a method of coating aluminum sulfate, the residual lithium carbonate and aluminum sulfate on the surface of the high-nickel ternary positive electrode material are reacted to form a lithium sulfate and lithium metaaluminate outer coating layer with high structural stability, so that the material is mechanically separated from the electrolyte, the surface side reaction of the high-nickel ternary positive electrode material is reduced, and the cycle performance is improved.
Compared with the existing single-layer coating LLZTO and tungsten oxide technology, the mutual synergistic mechanism between the inner coating layer and the outer coating layer is as follows: after the high-nickel ternary cathode material only coats LLZTO and tungsten oxide and is sintered at high temperature, residual lithium carbonate still exists on the surface, because the tungsten oxide can only react with lithium hydroxide on the surface to form Li at the temperature of 500 ℃ at 300-2WO4But can not react with residual lithium carbonate with high surface interface charge transfer resistance, thereby blocking the diffusion of lithium ions; by means of coating aluminum sulfate, the lithium carbonate and aluminum sulfate remaining on the surface can react to form an outer coating layer of lithium sulfate and lithium metaaluminate with low interface charge transfer resistance, and the interface charge transfer resistance of the positive electrode material is further reduced.
Drawings
FIG. 1 is an AC impedance diagram of example 1;
FIG. 2 is an AC impedance diagram of comparative example 1;
FIG. 3 is a graph of the AC impedance of comparative example 2;
FIG. 4 is a graph showing cycle life of example 1 of the present invention and comparative examples 1 to 2.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
A preparation method of a ternary cathode material comprises the following steps:
(1) a substrate, a solid electrolyte, tungsten oxide, and Li2WO4Adding into organic solvent, stirring, oven drying, and sintering at certain temperature to obtain semi-finished product with inner coating layer.
Substrate LiNi1-x-yCoxMnyO2，x=0.08，y=0.04；
The solid electrolyte being Li6.75La3Zr1.75Ta0.25O12；
The tungsten oxide is tungsten trioxide;
solid electrolyte, tungsten oxide, Li2WO4The mass ratio of (1: 7: 7);
the organic solvent is methanol;
solid electrolyte, tungsten oxide, Li2WO4The total amount of the three components in the methanol is 1500 ppm.
The addition amount of the base material in each 100ml of methanol is 100 g;
the sintering temperature is 400 +/-20 ℃, and the sintering time is 8h
(2) Adding the semi-finished product and aluminum sulfate into methanol, uniformly stirring, drying, and sintering at a certain temperature to obtain a ternary cathode material with an outer coating layer and an inner coating layer;
the addition amount of aluminum sulfate in the methanol in the step is 1000 ppm; the sintering temperature is 500 +/-20 ℃, and the sintering time is 8 h;
the addition amount of the semi-finished product in each 100ml of methanol is 100 g.
The positive electrode material of this example had D50 of 3 um.
Example 2
A preparation method of a ternary cathode material comprises the following steps:
(1) a substrate, a solid electrolyte, tungsten oxide, and Li2WO4Adding into organic solvent and stirringAnd (4) homogenizing, drying and sintering at a certain temperature to obtain a semi-finished product with an inner cladding layer.
Substrate LiNi1-x-yCoxMnyO2，x=0.09，y=0.03；
The solid electrolyte being Li6.75La3Zr1.75Ta0.25O12；
The tungsten oxide is tungsten trioxide;
solid electrolyte, tungsten oxide, Li2WO4The mass ratio of (1: 5: 5);
the organic solvent is methanol;
solid electrolyte, tungsten oxide, Li2WO4The total amount of the three components in the methanol is 2000 ppm.
The addition amount of the base material in each 100ml of methanol is 80 g;
the sintering temperature is 450 +/-20 ℃, and the sintering time is 6h
(2) Adding the semi-finished product and aluminum sulfate into methanol, uniformly stirring, drying, and sintering at a certain temperature to obtain a ternary cathode material with an outer coating layer and an inner coating layer;
the addition amount of aluminum sulfate in the methanol in the step is 1500 ppm; the sintering temperature is 500 +/-20 ℃, and the sintering time is 8 h;
the addition amount of the semi-finished product in each 100ml of methanol is 80 g.
The positive electrode material of this example had D50 of 4.5 um.
Example 3
A preparation method of a ternary cathode material comprises the following steps:
(1) a substrate, a solid electrolyte, tungsten oxide, and Li2WO4Adding into organic solvent, stirring, oven drying, and sintering at certain temperature to obtain semi-finished product with inner coating layer.
Substrate LiNi1-x-yCoxMnyO2，x=0.09，y=0.03；
The solid electrolyte being Li6.75La3Zr1.75Ta0.25O12；
The tungsten oxide is tungsten trioxide;
solid electrolyte, tungsten oxide, Li2WO4The mass ratio of (1: 10: 10);
the organic solvent is methanol;
solid electrolyte, tungsten oxide, Li2WO4The total amount of the three components in the methanol is 700 ppm.
The addition amount of the base material in each 100ml of methanol is 120 g;
the sintering temperature is 300 +/-20 ℃, and the sintering time is 10h
(2) Adding the semi-finished product and aluminum sulfate into methanol, uniformly stirring, drying, and sintering at a certain temperature to obtain a ternary cathode material with an outer coating layer and an inner coating layer;
the addition amount of aluminum sulfate in the methanol in the step is 3000 ppm; the sintering temperature is 480 +/-20 ℃, and the sintering time is 6 h;
the addition amount of the semi-finished product in each 100ml of methanol is 120 g.
The positive electrode material of this example had D50 of 10 um.
Example 4
A preparation method of a ternary cathode material comprises the following steps:
(1) a substrate, a solid electrolyte, tungsten oxide, and Li2WO4Adding into organic solvent, stirring, oven drying, and sintering at certain temperature to obtain semi-finished product with inner coating layer.
Substrate LiNi1-x-yCoxMnyO2，x=0.06，y=0.06；
The solid electrolyte being Li6.75La3Zr1.75Ta0.25O12；
The tungsten oxide is tungsten trioxide;
solid electrolyte, tungsten oxide, Li2WO4The mass ratio of (1: 5: 10);
the organic solvent is methanol;
solid electrolyte, tungsten oxide, Li2WO4The total amount of the three components in the methanol is 300 ppm.
The addition amount of the base material in each 100ml of methanol is 90 g;
the sintering temperature is 450 +/-20 ℃, and the sintering time is 10h
(2) Adding the semi-finished product and aluminum sulfate into methanol, uniformly stirring, drying, and sintering at a certain temperature to obtain a ternary cathode material with an outer coating layer and an inner coating layer;
the addition amount of aluminum sulfate in the methanol in the step is 1000 ppm; the sintering temperature is 500 +/-20 ℃, and the sintering time is 8 h;
the addition amount of the semi-finished product in each 100ml of methanol is 90 g.
The positive electrode material of this example had D50 of 3.5 um.
Example 5
A preparation method of a ternary cathode material comprises the following steps:
(1) a substrate, a solid electrolyte, tungsten oxide, and Li2WO4Adding into organic solvent, stirring, oven drying, and sintering at certain temperature to obtain semi-finished product with inner coating layer.
Substrate LiNi1-x-yCoxMnyO2，x=0.03，y=0.06；
The solid electrolyte being Li6.75La3Zr1.75Ta0.25O12；
Tungsten oxide of W18O49；
Solid electrolyte, tungsten oxide, Li2WO4The mass ratio of (1: 10: 5);
the organic solvent is methanol;
solid electrolyte, tungsten oxide, Li2WO4The total amount of the three components in the methanol is 1000 ppm.
The addition amount of the base material in each 100ml of methanol is 80 g;
the sintering temperature is 450 +/-20 ℃, and the sintering time is 10h
(2) Adding the semi-finished product and aluminum sulfate into methanol, uniformly stirring, drying, and sintering at a certain temperature to obtain a ternary cathode material with an outer coating layer and an inner coating layer;
the addition amount of aluminum sulfate in the methanol in the step is 2000 ppm; the sintering temperature is 430 +/-20 ℃, and the sintering time is 7 h;
the addition amount of the semi-finished product in each 100ml of methanol is 80 g.
The positive electrode material of this example had D50 of 6 um.
Comparative example 1 (absence of solid electrolyte)
A preparation method of a ternary cathode material comprises the following steps:
(1) mixing base material, tungsten oxide and Li2WO4Adding into organic solvent, stirring, oven drying, and sintering at certain temperature to obtain semi-finished product with inner coating layer.
Substrate LiNi1-x-yCoxMnyO2，x=0.08，y=0.04；
The tungsten oxide is tungsten trioxide;
tungsten oxide, Li2WO4The mass ratio of (A) to (B) is 1: 1;
the organic solvent is methanol;
tungsten oxide, Li2WO4The total amount used in methanol was 1500 ppm.
The addition amount of the base material in each 100ml of methanol is 100 g;
the sintering temperature is 400 +/-20 ℃, and the sintering time is 8h
(2) Adding the semi-finished product and aluminum sulfate into methanol, uniformly stirring, drying, and sintering at a certain temperature to obtain a ternary cathode material with an outer coating layer and an inner coating layer;
the addition amount of aluminum sulfate in the methanol in the step is 1000 ppm; the sintering temperature is 500 +/-20 ℃, and the sintering time is 8 h;
the addition amount of the semi-finished product in each 100ml of methanol is 100 g.
The positive electrode material of this comparative example had D50 of 3 um.
Comparative example 2 (absence of Li)2WO4）
A preparation method of a ternary cathode material comprises the following steps:
(1) adding the base material, the solid electrolyte and the tungsten oxide into an organic solvent, uniformly stirring and drying, and sintering at a certain temperature to obtain a semi-finished product with an inner cladding layer.
Substrate LiNi1-x-yCoxMnyO2，x=0.08，y=0.04；
The solid electrolyte being Li6.75La3Zr1.75Ta0.25O12；
The tungsten oxide is tungsten trioxide;
the mass ratio of the solid electrolyte to the tungsten oxide is 1: 7;
the organic solvent is methanol;
the total amount of solid electrolyte, tungsten oxide in methanol was 1500 ppm.
The addition amount of the base material in each 100ml of methanol is 100 g;
the sintering temperature is 400 +/-20 ℃, and the sintering time is 8h
(2) Adding the semi-finished product and aluminum sulfate into methanol, uniformly stirring, drying, and sintering at a certain temperature to obtain a ternary cathode material with an outer coating layer and an inner coating layer;
the addition amount of aluminum sulfate in the methanol in the step is 1000 ppm; the sintering temperature is 500 +/-20 ℃, and the sintering time is 8 h;
the addition amount of the semi-finished product in each 100ml of methanol is 100 g.
The positive electrode material of this comparative example had D50 of 3 um.
Button cell manufacturing method
According to the mass ratio of 92: 5: 3, weighing the ternary material, the conductive agent acetylene black and the binder PVDF, uniformly mixing with a dispersant N-methyl pyrrolidone (NMP) to form slurry, coating the slurry on a current collector aluminum foil, drying at 120 ℃, and cutting into a circular positive pole piece of 1.56cm 2. And a metal lithium sheet is taken as a negative electrode, and a diaphragm, the positive electrode sheet and LiPF6 (EC: DEC = 1: 1) electrolyte are combined to assemble the 2016 type button cell in a glove box.
Performance testing
AC impedance testing
The test method of the alternating current impedance test comprises the following steps:
and (3) performing constant-current and constant-voltage charging at 0.1C on a Xinwei CT-4008-5V 10mA-164 charging and discharging test system, performing constant-current discharging at 0.1C for 3 times, performing constant-current charging and discharging at 1C once, performing constant-current charging to 4.4V, and taking down the rechargeable battery after constant-voltage charging for 1 h.
An alternating current impedance test is carried out on a Versa Studio PM1000 workstation of Princeton, the test potential is controlled to be 4.4V, the scanning frequency range is 100 kHz-0.01 Hz, and the amplitude of a current sine wave is 5 mV. And (3) taking down the battery, continuously performing 1C circulation 1st, 25th and 50th circulation in the new charging and discharging test system, performing constant-current charging to 4.4V, and performing alternating current impedance test after 1st, 25th and 50th circulation after constant-voltage charging for 1h, wherein the parameters are the same as the above.
Fitting the Nyquist curve from high frequency to low frequency by Z-view software, and analyzing to obtain the electrode-electrolyte interface charge transfer resistance Rct。
Referring to fig. 1-3, fig. 1 is an ac impedance plot for example 1, fig. 2 is an ac impedance plot for comparative example 1, and fig. 3 is an ac impedance plot for comparative example 2;
table 1 represents the following results:
in comparison with comparative example 1 (absence of solid electrolyte) and comparative example 2 (absence of Li)2WO4) R after 1st, 25th and 50th cycles of example 1ctAll are minimum, so that after the improvement of the technology, the interface charge transfer resistance R in the circulation process can be inhibitedctAn increase in the number of cells.
The results are shown in Table 1:
TABLE 1
Figure DEST_PATH_IMAGE001
Cycle life test
The testing method of the cycle life comprises the following steps: constant current charge and discharge tests were performed on the novei cell test system. And (3) testing conditions are as follows: current is 1.0C multiplying power, circulation is 100 weeks, and voltage range is 3.0-4.3V;
the results are shown in FIG. 4.
Comparative example 1 (absence of solid electrolyte), comparative example 2 (absence of Li)2WO4) The 100th cycle retention of example 1 was 91.11% (2 in fig. 4), 92.25% (3 in fig. 4), and 93.33% (1 in fig. 4), respectively, and thus the cycle retention was improved by the technical improvement of the present invention.
In conclusion, the invention coats LLZTO and oxidizesMethod for producing tungsten from LLZTO, WO3、Li2WO4The combined inner protective layer reduces the impedance of the anode material; and then, by a method of coating aluminum sulfate, the residual lithium carbonate and aluminum sulfate on the surface of the high-nickel ternary positive electrode material are reacted to form a lithium sulfate and lithium metaaluminate outer coating layer with high structural stability, so that the material is mechanically separated from the electrolyte, the surface side reaction of the high-nickel ternary positive electrode material is reduced, and the cycle performance is improved.
It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.

Claims (10)

1. The ternary cathode material is characterized by comprising a base material, an inner cladding layer and an outer cladding layer, wherein the inner cladding layer and the outer cladding layer are used for cladding the base material;
the inner coating layer is made of solid electrolyte, tungsten oxide and Li2WO4Sintering to obtain; the solid electrolyte, tungsten oxide and Li2WO4The mass ratio of (1): 5-10: 5-10;
the outer cladding layer is Li2SO4、Al2O3、LiAlO2One or a mixture of at least two;
the base material is nickel cobalt lithium manganate;
the solid electrolyte is Li6.75La3Zr1.75Ta0.25O12。
2. The ternary positive electrode material according to claim 1, wherein D50 of the ternary positive electrode material is 2-13 um.
3. The ternary positive electrode material according to claim 1, wherein the thickness of the inner and outer cladding layers is 8-30 nm.
4. The ternary positive electrode material according to claim 1, wherein the substrate is LiNi1-x-yCoxMnyO2， 0<x≤0.09，0<y≤0.06。
5. The ternary positive electrode material according to claim 1, wherein the tungsten oxide is W18O49Or WO3。
6. A method for preparing a ternary positive electrode material according to any one of claims 1 to 5, comprising the steps of:
step (1): a substrate, a solid electrolyte, tungsten oxide, and Li2WO4Adding the mixture into an organic solvent, uniformly stirring and drying the mixture, and sintering the mixture at a certain temperature to obtain a semi-finished product with an inner cladding layer;
step (2): adding the semi-finished product and aluminum sulfate into an organic solvent, uniformly stirring, drying, and sintering at a certain temperature to obtain the ternary cathode material with an outer coating layer and an inner coating layer.
7. The method for producing a ternary positive electrode material according to claim 6, wherein in the step (1), the solid electrolyte, tungsten oxide and Li are used2WO4The amount in the organic solvent in the step (1) is 300-2000 ppm; the sintering temperature is 300-500 ℃, and the sintering time is 3-10 h.
8. The method for preparing a ternary cathode material as claimed in claim 6, wherein the amount of aluminum sulfate added in step (2) to the organic solvent in step (2) is 800-3000 ppm; the sintering temperature is 400-550 ℃, and the sintering time is 5-10 h.
9. The method for preparing a ternary cathode material according to claim 7, wherein the organic solvent in steps (1) and (2) is one of ethanol, ethylene glycol and methanol.
10. A lithium secondary battery characterized in that a positive electrode material of the lithium secondary battery is the ternary positive electrode material according to any one of claims 1 to 5.
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