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CN112151779B - Binary anode composite material and preparation method and application thereof - Google Patents

Binary anode composite material and preparation method and application thereof Download PDF

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Publication number
CN112151779B
CN112151779B CN202010986820.8A CN202010986820A CN112151779B CN 112151779 B CN112151779 B CN 112151779B CN 202010986820 A CN202010986820 A CN 202010986820A CN 112151779 B CN112151779 B CN 112151779B
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lithium
cobalt
composite material
positive electrode
precursor
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CN112151779A (en
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李旭
罗亮
杨顺毅
黄友元
杨才德
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BTR Nano Tech Co Ltd
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    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
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Abstract

The invention discloses a binary anode composite material and a preparation method and application thereof. The positive electrode composite material comprises a lithium nickelate inner core and a coating layer formed on the surface of the lithium nickelate inner core, wherein the coating layer comprises lithium cobaltate and a composite carbon material; wherein the composite carbon material comprises lithium sulfide and carbon. The positive electrode composite material disclosed by the invention has the advantages of low surface residual alkali, high capacity, good cycle performance and good safety, the capacity is more than 220mAh/g, and the capacity retention rate is more than 95% after the positive electrode composite material is circulated for 50 weeks at 0.5C/1C.

Description

Binary anode composite material and preparation method and application thereof
Technical Field
The invention relates to the field of lithium ion battery anode materials, in particular to a binary anode composite material and a preparation method and application thereof.
Background
High nickel ternary positive electrode material (LiNi) x M 1-x O 2 X is more than or equal to 0.8 and less than 1.0, and M is one or more of Co, Mn and Al) is more and more concerned due to higher energy density, but lithium nickelate has poor cycle and high safety risk, so that the development and application of the high-nickel ternary cathode material are limited, researchers at the present stage need to take the cycle performance and the safety of the cathode material into consideration while improving the nickel content, and lithium cobaltate is used as the cathode material with high safety performance and good cycle performanceThe material is always favored by the majority of battery manufacturers.
The prior art discloses a high-nickel anode material, a preparation method thereof and a lithium ion battery. The technical key points are as follows: the nickel hydroxide, the cobalt hydroxide and the manganese hydroxide are completely converted into the nickel oxyhydroxide, the cobalt oxyhydroxide and the manganese oxyhydroxide by using hydrogen peroxide, when the nickel oxyhydroxide and the lithium hydroxide are subjected to heat treatment together, hydrogen in the nickel oxyhydroxide can neutralize hydroxide ions in the lithium hydroxide, the pH value of the high-nickel ternary material is reduced, and the coating qualified rate of the prepared slurry is obviously high; meanwhile, the gram capacity and the service life of the prepared battery are also obviously improved. The structure of the high-nickel anode material prepared by the method is a secondary large particle shape formed by agglomerating primary small particles, the pole piece compaction of the high-nickel anode material with the structure is low, the structure is easy to damage, and a large amount of Ni still exists on the surface layer of the material 2+ /Ni 3+ Has a great influence on the safety of the battery.
In the preparation method of modified lithium nickelate in the prior art, a coprecipitation method is adopted to uniformly dope a metal element M into a precursor Ni (OH) 2 In the bulk phase of (2), Co is sintered 3 O 4 Coating the surface of the doped lithium nickelate to obtain lithium nickelate serving as a lithium ion battery anode material; according to the invention, the stability of the internal structure of the lithium nickelate crystal is improved through the uniform phase doping, and the Li of the nickel layer in the lithium nickelate crystal is reduced + /Ni 2+ The degree of mixing and arranging improves the rate capability and the cycle performance of the lithium ion battery anode material, and meanwhile, the cobaltosic oxide part coated on the surface reacts with residual lithium on the surface of the doped lithium nickelate to generate lithium cobaltate, so that the capacity of the lithium nickelate is increased while the residual lithium is consumed. However, lithium cobaltate has poor conductivity, which affects electron and ion transport.
How to improve the uniformity of a coated sample on the surface of lithium nickelate, reduce residual alkali and reduce a large amount of Ni 2+ /Ni 3+ The influence on the safety of the battery, the improvement of the discharge capacity of the sample, the consideration of the cycle stability and the safety, and the effective application to the large-scale production still have a plurality of difficulties to be overcome.
Disclosure of Invention
Based on the above, the application provides a binary positive electrode composite material, and a preparation method and application thereof. The positive electrode composite material has the advantages of low surface residual alkali, high capacity, good cycle performance and good safety.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a binary positive electrode composite material, comprising a lithium nickelate core and a coating layer formed on a surface of the lithium nickelate core, the coating layer comprising lithium cobaltate and a composite carbon material; wherein the composite carbon material comprises lithium sulfide and carbon.
Specifically, in the first aspect of the present invention, the lithium cobaltate coats the lithium nickelate core, and better cycle performance and safety performance are exhibited. Lithium sulfide and carbon in the composite carbon layer are tightly combined with lithium cobaltate, the composite carbon layer is coated, the reaction of trace water and materials is reduced, the decomposition of electrolyte is inhibited, the gas production behavior is reduced, the conductivity of the high-nickel ternary cathode material is improved, and the capacity of the material is improved by the lithium sulfide.
In the first aspect of the invention, the positive electrode composite material has the advantages of high capacity, good cycle performance and good safety, the capacity is more than 220mAh/g, and the capacity retention rate is more than 95% at 0.5C/1C cycle for 50 weeks.
In the first aspect of the present invention, the cobalt element in the lithium cobaltate is derived from cobalt sulfate.
The following is a preferred technical solution of the present invention, but not a limitation to the technical solution provided by the present invention, and the technical objects and advantageous effects of the present invention can be better achieved and achieved by the following preferred technical solution.
The coating layer is of a double-layer structure and comprises a lithium cobaltate layer and a composite carbon layer, wherein the lithium cobaltate layer is formed on the surface of the lithium nickelate inner core, and the composite carbon layer is the outermost layer; the composite carbon layer includes lithium sulfide and carbon.
Preferably, the thickness of the lithium cobaltate coating layer is 0.1 nm-1 μm.
Preferably, the thickness of the lithium sulfide/carbon coating layer is 0.1 nm-500 nm.
Preferably, the lithium nickelate inner core has a median particle diameter of 2 to 50 μm.
Preferably, in the coating layer, the molar ratio of the cobalt element to the nickel element is 0-1.0 and does not contain 0.
Preferably, the median particle diameter of the primary large particles of the positive electrode composite material is 2 to 50 μm.
Preferably, the chemical composition of the binary cathode composite material is LiNi x Co 1-x O 2 Wherein x is more than 0 and less than 1.0.
In a second aspect, the present invention provides a method for preparing a binary positive electrode composite material according to the first aspect, the method comprising the steps of:
adding lithium nickelate into a cobalt sulfate solution, taking lithium hydroxide as a precipitator, and precipitating the cobalt hydroxide on the surface of the lithium nickelate in situ to obtain a first precursor;
oxidizing the first precursor to convert cobalt hydroxide into cobalt oxyhydroxide and obtain a second precursor;
mixing the second precursor with a lithium source, and sintering for the first time to obtain a third precursor;
and mixing the third precursor, an organic carbon source and an organic solvent, and performing secondary sintering in an inert atmosphere to obtain the binary anode composite material.
In the second aspect of the invention, the lithium cobaltate coating layer is formed by in-situ generating cobalt hydroxide on the surface of the primary large particles of lithium nickelate, oxidizing the cobalt hydroxide by a strong oxidant to generate cobalt oxyhydroxide, and sintering the cobalt oxyhydroxide and lithium hydroxide at a high temperature; the lithium sulfide and carbon form a lithium sulfide/carbon coating layer, and the lithium sulfide/carbon coating layer is formed by high-temperature reaction of lithium sulfate remaining on the surface of the material and carbon obtained after high polymer carbonization.
Specifically, the first precursor is a primary large lithium nickelate particle coated with cobalt hydroxide, the second precursor is a primary large lithium nickelate particle coated with cobalt oxide, the third precursor is a primary large lithium nickelate particle coated with lithium cobaltate, the binary positive electrode composite material is a primary large lithium nickelate particle coated with a lithium sulfide/carbon coating layer and a lithium cobaltate coating layer, namely the primary large lithium nickelate particle coated with double layers is formed, the lithium nickelate core is coated with the lithium cobaltate coating layer in situ, and the lithium sulfide/carbon coating layer is coated with the lithium cobaltate coating layer on the outermost layer.
In a preferred embodiment of the method of the present invention, the molar ratio of the cobalt element to the nickel element in the first precursor is 0 to 1.0 and does not contain 0.
Preferably, the oxidation treatment comprises: and adding a strong oxidant, namely ferrate, into the first precursor solution to carry out oxidation.
Preferably, the lithium source is lithium hydroxide.
Preferably, the molar ratio of the lithium element in the lithium source to the cobalt element in the second precursor is 0.80-1.15.
Preferably, the temperature of the primary sintering is 300-1000 ℃.
Preferably, the time of the primary sintering is 2-24 h.
Preferably, the organic carbon source is a polymer, and preferably includes any one of or a combination of at least two of polyvinylpyrrolidone, alcohol-soluble polyacrylate, polyvinyl butyral, phenolic resin, polybutadiene, alcohol-soluble polyurethane, and melamine resin.
Preferably, the mass ratio of the organic carbon source to the third precursor is 0.001-0.5.
Preferably, the organic solvent includes at least one of methanol, ethanol, acetone, styrene, and trichloroethylene, preferably at least one of methanol, ethanol, and acetone.
Preferably, the temperature of the secondary sintering is 300-1200 ℃.
Preferably, the time of the secondary sintering is 2-24 h.
As a further preferred technical solution of the method of the present invention, the method comprises the steps of:
adding the lithium nickelate primary large particles into a cobalt sulfate solution, and taking lithium hydroxide as a precipitator to enable the cobalt hydroxide to grow on the surface of the lithium nickelate in situ to obtain lithium nickelate primary large particles coated by the cobalt hydroxide, wherein lithium sulfate is remained on the surface of the lithium nickelate primary large particles coated by the cobalt hydroxide, and the molar ratio of cobalt elements to nickel elements in the lithium nickelate primary large particles coated by the cobalt hydroxide is 0.005-0.3.
Adding ferrate into the lithium nickelate primary large particles coated by the cobalt hydroxide to obtain lithium nickelate primary large particles coated by the cobalt oxyhydroxide;
mixing the primary lithium nickelate large particles coated by the cobalt oxyhydroxide with a lithium hydroxide source, and sintering for 3-10 h at the temperature of 300-700 ℃; obtaining lithium cobaltate-coated lithium nickelate primary large particles; wherein the molar ratio of the lithium element in the lithium source to the cobalt element in the lithium nickelate primary large particles coated by the cobalt oxyhydroxide is 0.97-1.10;
mixing and heating the obtained lithium cobaltate-coated lithium nickelate primary large particles and a high polymer material in an organic solvent according to the mass ratio of 0.01-0.2, and sintering for 3-10 h under the conditions of inert gas and 400-800 ℃ after the solvent is evaporated; obtaining the binary anode composite material.
Wherein the mass ratio of the polymer to the lithium cobaltate-coated lithium nickelate primary large particles is 0.01-0.2; the secondary sintering temperature is 400-800 ℃, and the sintering time is 3-10 h, so that the nickel-cobalt primary large-particle binary anode composite material with the double-layer coated core-shell structure is obtained.
In the method provided by the second method of the present invention, both the primary sintering and the secondary sintering are high-temperature sintering.
Compared with the prior art, the method provided by the second aspect of the invention treats the primary large-particle lithium nickelate matrix by using cobalt sulfate and lithium hydroxide as raw materials, so that on one hand, the cobalt sulfate and the lithium hydroxide can be subjected to in-situ co-precipitation to prepare a lithium cobaltate coating layer, the residual alkali on the surface of the lithium nickelate material is reduced, and the capacity and the safety performance are improved; on the other hand, the cobalt sulfate and the lithium hydroxide generate lithium sulfate, the lithium sulfate and carbon can generate lithium sulfide at high temperature in the subsequent carbonization process, the lithium sulfide and the carbon are coated on the surface of the lithium nickelate together, the carbon coating reduces the reaction of trace water and materials, inhibits the decomposition of electrolyte, reduces the gas generation behavior, improves the conductivity of the high-nickel ternary cathode material, and the lithium sulfide improves the capacity of the material.
In a third aspect, the present invention provides a lithium ion battery comprising the secondary positive electrode composite material of the first aspect.
Advantages of embodiments of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of embodiments of the invention.
Drawings
Fig. 1 is a graph of the cycle performance of the binary positive electrode composite material prepared in example 1 of the present invention.
Detailed Description
The technical scheme of the invention is further explained by the specific implementation mode in combination with the attached drawings.
At present, lithium nickelate has higher energy density and is concerned in lithium ion batteries, but the lithium nickelate has poor cycle performance and high safety risk, and the development and the application of the lithium nickelate are limited. Although lithium cobaltate has the advantages of high safety and good cycle performance, the prior art can not achieve the effect of considering high discharge capacity, high cycle stability and safety in the process of actually combining the lithium cobaltate and the lithium cobaltate.
A binary positive electrode composite of an embodiment, the positive electrode composite including a lithium nickelate core and a coating layer formed on a surface of the lithium nickelate core, the coating layer including lithium cobaltate and a composite carbon material; wherein the composite carbon material comprises lithium sulfide and carbon.
The lithium cobaltate is coated on the lithium nickelate core, and the better cycle performance and safety performance are shown. Lithium sulfide and carbon in the composite carbon layer are tightly combined with lithium cobaltate, the composite carbon layer is coated, the reaction of trace water and materials is reduced, the decomposition of electrolyte is inhibited, the gas production behavior is reduced, the conductivity of the high-nickel ternary cathode material is improved, and the capacity of the material is improved by the lithium sulfide.
Specifically, the coating layer is of a double-layer structure and comprises a lithium cobaltate layer and a composite carbon layer, wherein the lithium cobaltate layer is formed on the surface of the lithium nickelate core, and the composite carbon layer is the outermost layer; the composite carbon layer includes lithium sulfide and carbon.
In some embodiments, the thickness of the lithium cobaltate coating layer is 0.1nm to 1 μm, specifically, 0.1nm, 5nm, 10nm, 30nm, 50nm, 100nm, 150nm, 200nm, 300nm, 500nm, 800nm, or 1 μm, but not limited to the recited values, and other values not recited in the range of values are also applicable, and a thickness too large may affect lithium ion transport, reduce material capacity, and increase cost; too small a thickness may result in uneven coating, resulting in reduced safety performance. Preferably 1nm to 500nm, and more preferably 1nm to 100 nm;
in some embodiments, the thickness of the composite carbon layer is 0.1nm to 500nm, specifically, 0.1nm, 0.5nm, 1nm, 2nm, 3nm, 5nm, 8nm, 10nm, 12nm, 15nm, 17nm, 20nm, 25nm, 28nm, 33nm, 36nm, 40nm, 45nm, 50nm, 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 950nm, or 1 μm, etc., but not limited to the recited values, and other non-recited values in the range of values also apply, and the lithium sulfide/carbon coating layer functions as a conductive and insulating water trace, and the coating layer too thick results in reduced material tap density, lower pole piece compaction, and affects material energy density; when the coating layer is too thin, uneven coating occurs, and a part of the material is exposed, so that the conductivity is reduced and the expected effect cannot be achieved. Preferably 0.1nm to 100nm, and more preferably 1nm to 50 nm.
In some embodiments, the lithium nickelate core has a median particle diameter of 2 μm to 50 μm, specifically, 2 μm, 5 μm, 10 μm, 12.5 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 38 μm, 40 μm, 45 μm, or 50 μm, etc., preferably 2 μm to 15 μm, and more preferably 2 μm to 10 μm.
In some embodiments, the molar ratio of the cobalt element to the nickel element in the coating layer is 0 to 1.0 and does not contain 0, specifically, 0.001, 0.05, 0.08, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 1.0, or the like, preferably 0.001 to 0.8, and more preferably 0.005 to 0.3.
In some embodiments, the median particle diameter of the primary large particles of the positive electrode composite material is 2 μm to 50 μm, and specifically, may be 3 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, or 50 μm, but is not limited to the recited values, and other values not recited in the numerical range may be applied.
In some embodiments, the chemical composition of the binary positive electrode composite is LiNi x Co 1-x O 2 Where 0 < x < 1.0, specifically, x may be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.85, 0.9 or 0.95, but is not limited to the recited values, and other values not recited within the numerical range may be applied.
Compared with the prior art, the positive electrode composite material provided by the embodiment of the invention has the advantages that the lithium cobaltate in-situ coats the lithium nickelate core, and the cycle performance and the safety performance are better. The lithium sulfide/carbon coating layer is tightly combined with the lithium cobaltate layer, the carbon coating reduces the reaction of trace water and materials, inhibits the decomposition of electrolyte, reduces the gas production behavior, improves the conductivity of the high-nickel ternary cathode composite material, and the lithium sulfide improves the capacity of the material.
Correspondingly, the embodiment of the invention provides a preparation method of the cathode composite material, which comprises the following steps:
adding lithium nickelate into a cobalt sulfate solution, taking lithium hydroxide as a precipitator, and precipitating the cobalt hydroxide on the surface of the lithium nickelate in situ to obtain a first precursor;
oxidizing the first precursor to convert cobalt hydroxide into cobalt oxyhydroxide and obtain a second precursor;
mixing the second precursor with a lithium source, and sintering for the first time to obtain a third precursor;
and mixing the third precursor, an organic carbon source and an organic solvent, and performing secondary sintering in an inert atmosphere to obtain the binary anode composite material.
In some embodiments, the surface of the residue is effectively reduced in Ni by coating the surface with lithium cobaltate and the composite carbon layer 2+ /Ni 3+ . And the obtained positive electrode composite material has better conductivity and ion transmission performance.
In some embodiments, the molar ratio of the cobalt element to the nickel element in the first precursor is 0 to 1.0 and does not include 0, specifically, 0.01, 0.15, 0.30, 0.65, 0.80, 1.0, etc., but is not limited to the recited values, and other values not recited in the numerical range are also applicable, and the cobalt content is small and does not perform a coating function; too high a cobalt content can result in a significant cost increase. Preferably 0.001 to 0.8, and more preferably 0.005 to 0.3.
In some embodiments, the oxidation treatment comprises: and adding a strong oxidant, namely ferrate, into the first precursor solution to carry out oxidation.
In some embodiments, the lithium source is lithium hydroxide.
In some embodiments, the molar ratio of the lithium element in the lithium source to the cobalt element in the second precursor is 0.80 to 1.15, specifically, 1.0, 1.05, 1.1, or 1.15, but not limited to the recited values, and other unrecited values in this range are also applicable, and too little lithium content may cause part of the cobalt in the material not to generate lithium cobaltate; too much lithium content results in higher residual alkali of the material, which affects the processability and safety of the material. Preferably 0.95 to 1.13, and more preferably 0.97 to 1.10.
In some embodiments, the temperature of the primary sintering is 300 to 1000 ℃, specifically, 300 ℃, 400 ℃, 450 ℃, 500 ℃, 550 ℃, 600 ℃, 650 ℃, 700 ℃, 750 ℃, 850 ℃, 900 ℃ or 1000 ℃, but not limited to the recited values, and other values not recited in the range of the values are also applicable, preferably 300 to 800 ℃, and more preferably 300 to 700 ℃.
In some embodiments, the time for the primary sintering is 2h to 24h, specifically, 3h, 5h, 10h, 12h, 15h, 18h, 20h, or 24h, but is not limited to the recited values, and other values not recited in the numerical range are also applicable, preferably 2h to 5h, and more preferably 3h to 10 h.
In some embodiments, the organic carbon source is a polymer, preferably includes any one or a combination of at least two of polyvinylpyrrolidone, alcohol-soluble polyacrylate, polyvinyl butyral, phenolic resin, polybutadiene, alcohol-soluble polyurethane, or melamine resin, more preferably polyvinylpyrrolidone, alcohol-soluble polyacrylate, and phenolic resin, and particularly preferably polyvinylpyrrolidone and phenolic resin;
in some embodiments, the mass ratio of the organic carbon source to the third precursor is 0.001 to 0.5, specifically, 0.01, 0.05, 0.10, 0.15, 0.20, 0.5, etc., but is not limited to the above-mentioned values, and other values not shown in the above-mentioned range are also applicable, preferably 0.01 to 0.3, and more preferably 0.01 to 0.2.
In some embodiments, the organic solvent comprises at least one of methanol, ethanol, acetone, styrene, and trichloroethylene, preferably at least one of methanol, ethanol, and acetone, and more preferably ethanol.
In some embodiments, the temperature of the secondary sintering is 200 ℃ to 1200 ℃, specifically, 200 ℃, 300 ℃, 400 ℃, 450 ℃, 500 ℃, 550 ℃, 600 ℃, 650 ℃, 700 ℃, 750 ℃, 850 ℃, 900 ℃, 1000 ℃, or 1200 ℃, etc., but not limited to the recited values, and other values not recited in the range of the values are also applicable, preferably 300 ℃ to 800 ℃, and more preferably 400 ℃ to 800 ℃.
In some embodiments, the time for the secondary sintering is 2h to 24h, specifically, 3h, 5h, 10h, 12h, 15h, 18h, 20h, or 24h, but is not limited to the recited values, and other values not recited in the numerical range are also applicable, preferably 2h to 5h, and more preferably 3h to 10 h.
According to the preparation method of the positive electrode composite material provided by the embodiment, the cobalt hydroxide grows on the surface of the lithium nickelate primary large particles in situ, the cobalt oxyhydroxide-coated lithium nickelate primary large particles are prepared by oxidation of a strong oxidant, and then the lithium mixture is sintered for the second time to obtain the lithium cobaltate-coated lithium nickelate primary large particles 2+ /Ni 3+ The safety and the cycle performance of the material are improved. Finally, the lithium sulfide/carbon and lithium cobaltate double-layer coated lithium nickelate primary large particles are prepared by high-temperature carbonization of the polymer coating, the residual alkali of the material is reduced, and the sample capacity is improved, so that the method successfully prepares the lithium nickelate with ultrahigh capacity, low residual alkali, high cycle performance and high cycle performanceThe nickel-cobalt primary large-particle binary anode composite material with the safety performance.
The embodiment of the invention also provides a lithium ion battery which adopts the binary anode composite material provided by the embodiment of the invention.
The following examples are intended to illustrate the invention in more detail. The embodiments of the present invention are not limited to the following specific embodiments. The present invention can be modified and implemented as appropriate within the scope of the main claim.
Example 1
The embodiment provides a binary anode composite material and a preparation method thereof, wherein the preparation method comprises the following steps:
(1) preparing 1.0mol/L solution from cobalt sulfate, adding lithium nickelate primary large particles with the median particle size of 5 mu m into the solution, and taking lithium hydroxide as a precipitator to enable the surface of the lithium nickelate to grow cobalt hydroxide in situ to obtain lithium nickelate primary large particles coated by the cobalt hydroxide, wherein the molar ratio of cobalt elements to nickel elements in the lithium nickelate primary large particles coated by the cobalt hydroxide is 0.05, and lithium sulfate remains on the surface;
(2) adding a strong oxidant, namely ferrate, into the solution obtained in the step (1) to obtain primary lithium nickelate large particles coated by the cobalt oxyhydroxide, wherein the molar ratio of the adding amount of the ferrate to the cobalt element is 1: 3.
(3) Mixing the large primary particles of lithium nickelate coated by the cobalt oxyhydroxide obtained in the step (2) with a lithium source, and performing secondary sintering;
wherein the lithium source is lithium hydroxide, the molar ratio of lithium element to cobalt element is 1:1, the primary sintering temperature is 700 ℃, and the sintering time is 10 hours, so as to obtain lithium cobaltate-coated lithium nickelate primary large particles;
(4) and (3) mixing, heating and stirring the lithium cobaltate-coated primary lithium nickelate large particles and a high-molecular material polyvinylpyrrolidone in ethanol, wherein the mass ratio of the lithium cobaltate-coated lithium nickelate to the polyvinylpyrrolidone is 100:0.2, carbonizing the mixture under argon gas after the ethanol is evaporated, reacting lithium sulfate with part of carbon to generate lithium sulfide, and finally obtaining the double-layer coated core-shell structure nickel-cobalt primary large particle binary anode composite material.
Wherein the secondary sintering temperature is 800 ℃, and the sintering time is 10h, so as to obtain the nickel-cobalt primary large-particle binary anode composite material with the double-layer coated core-shell structure, namely the binary anode composite material.
The binary positive electrode composite material obtained in the embodiment comprises a lithium nickelate core and a coating layer formed on the surface of the lithium nickelate core, wherein the coating layer is of a double-layer structure and comprises a lithium cobaltate layer and a composite carbon layer, the lithium cobaltate layer is formed on the surface of the lithium nickelate core, and the composite carbon layer is the outermost layer; the composite carbon layer comprises lithium sulfide and a carbon coating layer; the particle size of the finished product is 5 mu m, the thickness of the lithium cobaltate layer is 100nm, and the composite carbon layer is 20 nm.
Example 2
The embodiment provides a binary anode composite material and a preparation method thereof, wherein the preparation method comprises the following steps:
(1) preparing 0.5mol/L solution from cobalt sulfate, adding lithium nickelate primary large particles with the median particle size of 10 mu m into the solution, and taking lithium hydroxide as a precipitator to enable the surface of the lithium nickelate to grow cobalt hydroxide in situ to obtain lithium nickelate primary large particles coated by the cobalt hydroxide, wherein the molar ratio of cobalt elements to nickel elements in the lithium nickelate primary large particles coated by the cobalt hydroxide is 0.1, and lithium sulfate is remained on the surface;
(2) adding a strong oxidant, namely ferrate, into the solution obtained in the step (1) to obtain primary lithium nickelate large particles coated by the cobalt oxyhydroxide, wherein the molar ratio of the adding amount of the ferrate to the cobalt element is 1: 1.
(3) Mixing the large primary particles of lithium nickelate coated by the cobalt oxyhydroxide obtained in the step (2) with a lithium source, and performing secondary sintering;
wherein the lithium source is lithium hydroxide, the molar ratio of lithium element to cobalt element is 0.97:1, the primary sintering temperature is 800 ℃, and the sintering time is 8 hours, so as to obtain lithium cobaltate-coated lithium nickelate primary large particles;
(4) mixing, heating and stirring the lithium cobaltate-coated primary lithium nickelate large particles obtained in the step (3) and a high-molecular material alcohol-soluble polyacrylate in methanol, wherein the mass ratio of the lithium cobaltate-coated lithium nickelate to the alcohol-soluble polyacrylate is 100:0.1, carbonizing the mixture under argon gas after the methanol is evaporated, reacting lithium sulfate with part of carbon to generate lithium sulfide, and finally obtaining the double-layer coated core-shell structure nickel-cobalt primary large particle binary positive electrode composite material.
Wherein the secondary sintering temperature is 700 ℃, and the sintering time is 5 hours, so that the nickel-cobalt primary large-particle binary anode composite material with the double-layer coated core-shell structure is obtained.
The binary positive electrode composite material obtained in the embodiment comprises a lithium nickelate core, a lithium cobaltate coating layer growing on the surface of the core in situ, and a lithium sulfide/carbon coating layer wrapping the lithium cobaltate coating layer, wherein the particle size of a finished product is 10 mu m, the thickness of the lithium cobaltate coating layer is 50nm, and the thickness of the lithium sulfide/carbon coating layer is 10 nm.
Example 3
The embodiment provides a binary anode composite material and a preparation method thereof, wherein the preparation method comprises the following steps:
(1) preparing 0.1mol/L solution from cobalt sulfate, adding lithium nickelate primary large particles with the median particle size of 15 mu m into the solution, and taking lithium hydroxide as a precipitator to enable the surface of the lithium nickelate to grow cobalt hydroxide in situ to obtain lithium nickelate primary large particles coated by the cobalt hydroxide, wherein the molar ratio of cobalt elements to nickel elements in the lithium nickelate primary large particles coated by the cobalt hydroxide is 0.05, and lithium sulfate is remained on the surface;
(2) adding a strong oxidant, namely ferrate, into the solution obtained in the step (1) to obtain primary lithium nickelate large particles coated by the cobalt oxyhydroxide, wherein the molar ratio of the adding amount of the ferrate to the cobalt element is 1: 6.
(3) Mixing the large primary particles of lithium nickelate coated by the cobalt oxyhydroxide obtained in the step (2) with a lithium source, and performing secondary sintering;
wherein the lithium source is lithium hydroxide, the molar ratio of lithium element to cobalt element is 1.10:1, the primary sintering temperature is 600 ℃, and the sintering time is 10 hours, so as to obtain lithium cobaltate-coated lithium nickelate primary large particles;
(4) mixing the lithium cobaltate-coated lithium nickelate primary large particles obtained in the step (3) with a high-molecular material melamine resin in ethanol, heating and stirring, wherein the mass ratio of the lithium cobaltate-coated lithium nickelate to the melamine resin is 100:0.5, carbonizing the mixture under argon gas after the methanol is evaporated, reacting lithium sulfate with part of carbon to generate lithium sulfide, and finally obtaining the double-layer coated core-shell structure nickel-cobalt primary large particle binary positive electrode composite material.
Wherein the secondary sintering temperature is 600 ℃, and the sintering time is 10 hours, so as to obtain the nickel-cobalt primary large-particle binary anode composite material with the double-layer coated core-shell structure.
The binary anode composite material obtained in the embodiment comprises a lithium nickelate core, a lithium cobaltate coating layer growing on the surface of the core in situ, and a lithium sulfide/carbon coating layer wrapping the lithium cobaltate coating layer, wherein the particle size of a finished product is 15 micrometers, the thickness of the lithium cobaltate coating layer is 10nm, and the thickness of the lithium sulfide/carbon coating layer is 10 nm.
Example 4
The procedure and conditions were the same as in example 1 except that the molar ratio of cobalt element to nickel element in the primary large particles of cobalt hydroxide-coated lithium nickelate in step (1) was adjusted to 0.005.
Example 5
The procedure and conditions were the same as in example 1 except that the molar ratio of cobalt element to nickel element in the primary large particles of cobalt hydroxide-coated lithium nickelate in step (1) was adjusted to 0.3.
The procedure and conditions were the same as in example 1 except that the molar ratio of cobalt element to nickel element in the primary large particles of cobalt hydroxide-coated lithium nickelate in step (1) was adjusted to 0.8.
Example 6
The procedure and conditions were the same as in example 1 except that the molar ratio of lithium element to cobalt element in step (3) was adjusted to 0.8: 1.
Example 7
The procedure and conditions were the same as in example 1 except that the molar ratio of lithium element to cobalt element in step (3) was adjusted to 1.15: 1.
Example 8
The procedure and conditions were the same as in example 1 except that the temperature of the primary sintering was adjusted to 300 ℃.
Comparative example 1
Lithium nickelate which was not coated at all was used as the positive electrode material of 1.
Comparative example 2
The procedure and conditions were the same as in example 1 except that cobalt sulfate was replaced with cobalt chloride.
And (3) performance testing:
the invention adopts a Malvern laser particle size tester MS 2000 to test the particle size range of the material and the average particle size of the raw material particles.
The surface appearance, particle size and the like of the sample were observed by a scanning electron microscope of Hitachi S4800.
The residual alkali of the sample was measured using an automatic potentiometric titrator from Mettler corporation.
Electrochemical cycling performance was tested using the following method: mixing a positive electrode material, a conductive agent and an adhesive in a solvent according to the mass percentage of 94:1:5, controlling the solid content to be 50%, coating the mixture on an aluminum foil current collector, and drying in vacuum to obtain a positive electrode plate; then the negative electrode uses a lithium plate and 1mol/L LiPF 6 Conventional 2016 button cells were used for the electrolyte,/EC + DMC + EMC (v/v ═ 1:1:1), Celgard2400 separator, and housing. The charge and discharge test of the button cell is carried out on a LAND cell test system of Wuhanjinnuo electronic Limited company, the first discharge and the first effect are measured under the condition of normal temperature and 0.1C constant current charge and discharge, the cycle is measured under the condition of 0.5C/1C charge and discharge, the charge and discharge voltage is limited to 3.0-4.3V, and the cycle conservation rate is obtained.
The capacity of the positive electrode material was tested using a blue test system.
The results of the electrochemical properties and residual alkali tests are shown in Table 1.
TABLE 1
Figure BDA0002689536300000151
Figure BDA0002689536300000161
By comparing example 1 with examples 4-5, example 4 has lower cobalt content, uneven coating and poorer cycle performance, while example 5 has high cobalt content and thicker coating layer, which influences the exertion of material capacity.
Compared with the examples 6 to 7, the example 1 has the advantages that the lithium content is low, the cobalt reaction is incomplete, the material capacity exertion is influenced, and the lithium content is high in the example 7, so that the material residual alkali is higher, the subsequent processing performance is influenced, the gas generation condition of the battery is influenced, and the safety is further influenced.
Compared with the embodiment 8, the embodiment 1 has the advantages that the sintering temperature is lower, the cobalt reaction is incomplete, the material capacity exertion is influenced, the residual alkali is higher, the subsequent processing performance and the gas generation condition of the battery are influenced, and further the safety is influenced.
Compared with the comparative example 1, the comparative example 1 has the advantages of low material capacity, poor cycle, no coating layer, poor safety performance, high residual alkali and high residual alkali, and influences subsequent processing performance and battery gas generation condition, and further influences safety.
Compared with the comparative example 2, the comparative example 2 adopts cobalt chloride, has no sulfate radical, and can not generate lithium sulfide in the later period, so that the capacity of the material is lower.
The applicant states that the present invention is illustrated in detail by the above examples, but the present invention is not limited to the above detailed methods, i.e. it is not meant that the present invention must rely on the above detailed methods for its implementation. It should be understood by those skilled in the art that any modification of the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.

Claims (40)

1. A method for preparing a binary positive electrode composite material, the method comprising the steps of:
adding lithium nickelate into a cobalt sulfate solution, taking lithium hydroxide as a precipitator, and precipitating the cobalt hydroxide on the surface of the lithium nickelate in situ to obtain a first precursor;
oxidizing the first precursor to convert cobalt hydroxide into cobalt oxyhydroxide and obtain a second precursor;
mixing the second precursor with a lithium source, and sintering for the first time to obtain a third precursor;
mixing the third precursor, an organic carbon source and an organic solvent, and performing secondary sintering in an inert atmosphere to obtain a binary anode composite material;
the positive electrode composite material comprises a lithium nickelate inner core and a coating layer formed on the surface of the lithium nickelate inner core, wherein the coating layer comprises a lithium cobaltate layer and a composite carbon layer; wherein the composite carbon layer comprises lithium sulfide and carbon;
the coating layer is of a double-layer structure, the lithium cobaltate layer is formed on the surface of the lithium nickelate inner core, and the composite carbon layer is the outermost layer;
in the coating layer, the molar ratio of the cobalt element to the nickel element is 0-1.0 and does not contain 0.
2. The method for preparing the binary positive electrode composite material according to claim 1, wherein the thickness of the lithium cobalt oxide layer is 0.1nm to 1 μm.
3. The method for preparing the binary positive electrode composite material according to claim 2, wherein the thickness of the lithium cobalt oxide layer is 1nm to 500 nm.
4. The method for producing the binary positive electrode composite material according to claim 3, wherein the thickness of the lithium cobaltate layer is 1nm to 100 nm.
5. The method for producing the binary positive electrode composite material according to claim 1, wherein the thickness of the composite carbon layer is 0.1nm to 500 nm.
6. The method for producing the binary positive electrode composite material according to claim 5, wherein the thickness of the composite carbon layer is 0.1nm to 100 nm.
7. The method for producing the binary positive electrode composite material according to claim 6, wherein the thickness of the composite carbon layer is 1nm to 50 nm.
8. The method for preparing the binary positive electrode composite material according to claim 1, wherein the lithium nickelate core has a median particle diameter of 2 μm to 50 μm.
9. The method for preparing the binary positive electrode composite material according to claim 8, wherein the lithium nickelate core has a median particle diameter of 2 μm to 15 μm.
10. The method for preparing the binary positive electrode composite material according to claim 9, wherein the lithium nickelate core has a median particle diameter of 2 μm to 10 μm.
11. The method for producing a binary positive electrode composite material according to claim 1, wherein the molar ratio of cobalt element to nickel element in the coating layer is 0.001 to 0.8.
12. The method for producing a binary positive electrode composite material according to claim 1, wherein the molar ratio of cobalt element to nickel element in the coating layer is 0.005 to 0.3.
13. The method for producing a binary positive electrode composite material according to claim 1, wherein the positive electrode composite material has a primary large particle median diameter of 2 to 50 μm.
14. The method of claim 1, wherein the chemical composition of the binary positive electrode composite material is LiNi x Co 1-x O 2 Wherein x is more than 0 and less than 1.0.
15. The method according to claim 1, wherein the molar ratio of the cobalt element to the nickel element in the first precursor is 0 to 1.0 and 0 is not included.
16. The method according to claim 15, wherein the molar ratio of the cobalt element to the nickel element in the first precursor is 0.001 to 0.8.
17. The method according to claim 16, wherein a molar ratio of the cobalt element to the nickel element in the first precursor is 0.005 to 0.3.
18. The production method according to claim 1, wherein the oxidation treatment includes: and adding a strong oxidant, namely ferrate, into the first precursor solution to carry out oxidation.
19. The method of claim 1, wherein the lithium source is lithium hydroxide.
20. The method according to claim 1, wherein a molar ratio of the lithium element in the lithium source to the cobalt element in the second precursor is 0.80 to 1.15.
21. The method of claim 20, wherein the molar ratio of the lithium element in the lithium source to the cobalt element in the second precursor is 0.95 to 1.13.
22. The method of claim 21, wherein the molar ratio of the lithium element in the lithium source to the cobalt element in the second precursor is 0.97 to 1.10.
23. The method of claim 1, wherein the temperature of the primary sintering is 300 ℃ to 1000 ℃.
24. The method of claim 23, wherein the temperature of the primary sintering is 300 ℃ to 800 ℃.
25. The method of claim 24, wherein the temperature of the primary sintering is 300 ℃ to 700 ℃.
26. The preparation method of claim 25, wherein the time for the primary sintering is 2-24 h.
27. The method according to claim 1, wherein the organic carbon source is a polymer.
28. The method according to claim 27, wherein the organic carbon source comprises any one of polyvinylpyrrolidone, alcohol-soluble polyacrylate, polyvinyl butyral, phenol resin, polybutadiene, alcohol-soluble polyurethane, or melamine resin, or a combination of at least two thereof.
29. The method of claim 28, wherein the organic carbon source is polyvinylpyrrolidone, alcohol-soluble polyacrylate, and phenol resin.
30. The method of claim 28, wherein the organic carbon source is polyvinylpyrrolidone and phenol resin.
31. The method according to claim 1, wherein the mass ratio of the organic carbon source to the third precursor is 0.001 to 0.5.
32. The method according to claim 31, wherein the mass ratio of the organic carbon source to the third precursor is 0.01 to 0.3.
33. The method according to claim 32, wherein the mass ratio of the organic carbon source to the third precursor is 0.01 to 0.2.
34. The method of claim 1, wherein the organic solvent comprises methanol, ethanol, acetone styrene, and trichloroethylene.
35. The method of claim 1, wherein the temperature of the secondary sintering is 300 ℃ to 1200 ℃.
36. The method of claim 35, wherein the secondary sintering temperature is 300 ℃ to 800 ℃.
37. The method of claim 36, wherein the secondary sintering temperature is 400 ℃ to 800 ℃.
38. The preparation method according to claim 1, wherein the time for the secondary sintering is 2 to 24 hours.
39. The method for preparing according to claim 1, characterized in that it comprises the following steps:
adding the lithium nickelate primary large particles into a cobalt sulfate solution, and taking lithium hydroxide as a precipitator to enable the cobalt hydroxide to grow on the surface of the lithium nickelate in situ to obtain lithium nickelate primary large particles coated by the cobalt hydroxide, wherein lithium sulfate remains on the surface of the lithium nickelate primary large particles, and the molar ratio of a cobalt element to a nickel element in the lithium nickelate primary large particles coated by the cobalt hydroxide is 0.005-0.3;
adding ferrate into the lithium nickelate primary large particles coated by the cobalt hydroxide to obtain the lithium nickelate primary large particles coated by the cobalt oxyhydroxide;
mixing the primary lithium nickelate large particles coated by the cobalt oxyhydroxide with lithium hydroxide, and sintering for 3-10 h at the temperature of 300-700 ℃; obtaining lithium cobaltate-coated lithium nickelate primary large particles; wherein the molar ratio of the lithium element in the lithium source to the cobalt element in the lithium nickelate primary large particles coated by the cobalt oxyhydroxide is 0.97-1.10;
mixing and heating the obtained lithium cobaltate-coated lithium nickelate primary large particles and a high polymer material in an organic solvent according to the mass ratio of 0.01-0.2, and sintering for 3-10 h at the temperature of 400-800 ℃ in an inert gas after the solvent is evaporated; obtaining the binary anode composite material.
40. A lithium ion battery, which is characterized by comprising the binary positive electrode composite material prepared by the method of any one of items 1 to 39.
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