CN108807920B - LASO-coated octahedral-structure lithium nickel manganese oxide composite material and preparation method thereof - Google Patents

LASO-coated octahedral-structure lithium nickel manganese oxide composite material and preparation method thereof Download PDF

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CN108807920B
CN108807920B CN201810633258.3A CN201810633258A CN108807920B CN 108807920 B CN108807920 B CN 108807920B CN 201810633258 A CN201810633258 A CN 201810633258A CN 108807920 B CN108807920 B CN 108807920B
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manganese oxide
nickel manganese
lithium nickel
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octahedral
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史灵琪
刘耀春
卢鹏
李明
刘清泉
魏奇
张远
尹延谋
沈浪
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Huai'an New Energy Materials Technology Research Institute
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Abstract

The invention discloses an LASO-coated octahedral-structure lithium nickel manganese oxide composite material and a preparation method thereof.

Description

LASO-coated octahedral-structure lithium nickel manganese oxide composite material and preparation method thereof
Technical Field
The invention belongs to the technical field of new energy materials, and particularly relates to a nano Li-Al-Si-O (LASO) inorganic solid electrolyte coated octahedral Lithium Nickel Manganese Oxide (LNMO) composite material and a preparation method thereof.
Background
At present, the traditional fossil energy is in shortage, the environmental pollution is serious, the economic development is not feasible only by the traditional energy, and electric vehicles and hybrid electric vehicles begin to enter the visual field of people. Lithium ion power batteries are currently recognized as the most promising vehicle-mounted batteries. Compared with the traditional secondary battery, the lithium ion power battery has the remarkable advantages of high energy density, long cycle life, high working voltage, no memory effect and the like, and is rapidly the subject of controversial research by researchers. The common lithium battery is composed of several key materials, namely a positive electrode material, a negative electrode material, a diaphragm, electrolyte and a battery shell, and the selection of the positive electrode material is particularly important.
The anode materials widely researched at present mainly comprise lithium manganate, lithium cobaltate, lithium iron phosphate and the like, and compared with the anode materials, spinel lithium nickel manganese oxide has 146.7 mAh.g due to the fact that the spinel lithium nickel manganese oxide has a voltage platform as high as 4.7V-1The material has high theoretical specific capacity, only contains two transition metal elements of Ni and Mn, has rich resources, and is a feasible material capable of being used on a large scale on a power lithium ion battery. However, due to its high voltage plateau, the electrolyte generally undergoes a severe side reaction at a high potential (> 4.5V) to undergo an oxidative decomposition reaction with the surface of the positive electrode to form a thick interfacial film (CEI) of the electrolyte, so that the cycle performance of the battery is reduced. Meanwhile, another index for evaluating the lithium nickel manganese oxide is the high temperature resistance of the lithium nickel manganese oxide, so that how to improve the electrochemical performance of the lithium nickel manganese oxide is the current main research direction.
Disclosure of Invention
The invention aims to provide a nano LASO-coated octahedral lithium nickel manganese oxide-based composite material and a preparation method thereof, aiming at overcoming the defects of the existing preparation method, the product has good appearance and excellent electrochemical performance, and particularly the high-temperature electrochemical performance of the lithium nickel manganese oxide anode material is improved.
The invention is realized by the following technical scheme:
the preparation method of the LASO-coated octahedral lithium nickel manganese oxide composite material comprises the following preparation steps:
(1) taking nickel sulfate and manganese sulfate according to the molar ratio of nickel to manganese elements of 1:3, adding the mixture into deionized water in proportion, and magnetically stirring the mixture until the mixture is dissolved to obtain a solution A; adding sodium hydroxide into deionized water, and dissolving by magnetic stirring to form a solution B with the concentration of 0.5-2 mol/L; slowly dripping the solution B into the solution A through a constant-pressure separating funnel under the condition that the solution A is in a water bath at the temperature of 80 ℃, and stirring while dripping to obtain a mixed solution C; continuing stirring the mixed solution C for 1h under the condition of 80 ℃ water bath, stopping stirring, standing at normal temperature, performing vacuum filtration, and drying to obtain a lithium nickel manganese oxide precursor; mixing a lithium nickel manganese oxide precursor with lithium carbonate, and performing dry ball milling to obtain powder, wherein the molar ratio of Mn + Ni in the lithium nickel manganese oxide precursor to Li in the lithium carbonate is 1: 1.08; the powder is calcined after being screened by a 100-mesh sieve, and the calcining process comprises the following steps: heating to 400-600 ℃ at the speed of 1-5 ℃/min, and preserving heat for 2-6 hours; then heating to 800-950 ℃ at the speed of 1-5 ℃/min, and preserving heat for 15-25 hours; then cooling to 650 ℃ at the speed of 1-5 ℃/min, and cooling along with the furnace to obtain octahedral structure lithium nickel manganese oxide powder;
(2) and (3) LASO coating: weighing aluminum nitrate nonahydrate and citric acid monohydrate in ethanol-water solution according to the coating amount and the stoichiometric ratio, and adding Al3+: the citric acid molar ratio is 1:1, the volume ratio of ethanol to water in the ethanol-water solution is 1:1, and the mixture is magnetically stirred until the mixture is dissolved; weighing the octahedral lithium nickel manganese oxide powder obtained in the step (1), adding the octahedral lithium nickel manganese oxide powder into the solution, and stirring to fully disperse the octahedral lithium nickel manganese oxide powder; mixing the components in a volume ratio of 1: 10 dispersing ethyl silicate in ethanol, slowly adding the ethyl silicate into the solution drop by drop according to the coating amount and the stoichiometric ratio, and continuously stirring for 2 hours; adjusting the pH of the solution to about 11 by using LiOH solution with the concentration of 1mol/L, and continuing stirring; carrying out suction filtration, washing, drying and grinding on the obtained solution, and mixing lithium carbonate with 5% of lithium excess according to the coating amount and the stoichiometric ratio for dry ball milling; the powder is sintered after being screened by a 100-mesh sieve, and the sintering process comprises the following steps: heating to 650 ℃ at a heating rate of 10 ℃/min for 2h, and cooling along with the furnace to obtain the LASO-coated octahedral-structure lithium nickel manganese oxide composite material, wherein the surface coating substance is Li-Al-Si-O inorganic solid electrolyte, and Li2O：Al2O3：SiO2The molecular ratio was 1:2: 8.3.
The invention is further preferable, in the ball milling process in the step (1) and the step (2), the ball milling tank is made of polytetrafluoroethylene, the ball milling beads are made of zirconium dioxide, the particle size of the ball milling beads is 5-10 mm, the rotating speed of the ball mill is 300-400 rad/min, and the mass ratio of the ball milling beads to the mixture is 1: 3-4.
The invention also provides the nano LASO-coated octahedral-structure lithium nickel manganese oxide-based composite material prepared by the preparation method, preferably, the coating amount of the inorganic solid electrolyte Li-Al-Si-O is 0.2-1% of the mass of the lithium nickel manganese oxide; more preferably, the coating amount of the inorganic solid electrolyte Li-Al-Si-O is 0.8 percent of the mass of the lithium nickel manganese oxide.
Compared with the prior art, the invention has the following obvious advantages:
(1) the lithium nickel manganese oxide anode material prepared by the method is in a regular octahedral structure, and the particle size is nano-scale, so that the migration path of lithium ions is shortened, and the diffusion of the lithium ions is facilitated. More importantly, the surface of the battery is coated with a layer of inorganic solid electrolyte Li-Al-Si-O (LASO), the coating is continuous and uniform, compared with other coating materials, the LASO has the common function of other coating layers, can avoid direct contact between electrolyte and the surface of a positive electrode material, and reduces or even prevents the electrolyte from generating oxidative decomposition reaction with the surface of the positive electrode under high potential (more than 4.5V), and the LASO has a wider working temperature range, has good lithium ion conductivity, chemical stability and electrochemical stability, does not generate chemical reaction with an electrode material, especially has higher electrochemical decomposition voltage, and can normally work under high temperature and high pressure, so that the cycle performance of the battery is obviously improved, and particularly the high temperature performance is obviously enhanced.
(2) The inorganic solid electrolyte Li-Al-Si-O is coated layer by layer, and an aluminum source, a silicon source and a lithium source are added firstly, so that each coating is ensured, the coating is more uniform and effective, and the effect is better; and the used raw materials of aluminum nitrate nonahydrate, ethyl silicate and lithium carbonate are more common and are easy to prepare.
Drawings
FIG. 1 is a scanning electron microscope photograph at 120000 times for comparative example 1.
FIG. 2 shows the results of example 4 and comparative example 1 at 0.2C under ambient test conditionsCycle performance map of (c). Wherein the abscissa is cycle number, and the ordinate is specific capacity/mA h g-1。
FIG. 3 is a graph of the cycle performance at 0.2C for example 4 and comparative example 1 at 55 deg.C test conditions. Wherein the abscissa is cycle number, and the ordinate is specific capacity/mA h g-1。
Detailed Description
The present invention will be described in further detail below, and the conditions used in the examples can be further adjusted according to the actual circumstances, but the present invention is not limited to the examples.
Comparative example 1
Preparation of lithium nickel manganese oxide positive electrode material
According to the stoichiometric mole ratio of nickel and manganese elements of 1:3, accurately weighing nickel sulfate tetrahydrate and manganese sulfate monohydrate in a beaker in proportion, adding deionized water, and magnetically stirring until the nickel sulfate tetrahydrate and the manganese sulfate monohydrate are dissolved to obtain a solution A; weighing sodium hydroxide in a beaker, adding deionized water, and magnetically stirring for 2 hours to obtain a solution B with the concentration of 0.5-2 mol/L; slowly dripping the solution B into the solution A (every drop is not connected into a string) through a constant-pressure separating funnel under the condition that the solution A is in a water bath at the temperature of 80 ℃, and stirring while dripping to obtain a mixed solution C; continuing stirring the mixed solution C for 1h in a water bath at 80 ℃, stopping stirring, standing for 30min at normal temperature, performing suction filtration, and drying to obtain a lithium nickel manganese oxide precursor; grinding the precursor, pouring the ground precursor into a ball milling tank, mixing lithium carbonate, and performing dry ball milling for 4 hours; wherein the ball milling tank is made of polytetrafluoroethylene, the ball milling beads are made of zirconium dioxide, the particle size of the ball milling beads is 5mm, and the rotating speed of the ball mill is 350 rad/min. The mass ratio of the ball milling beads to the mixture is 4: 1. The molar ratio of Mn + Ni in the nickel manganese precursor to Li in the lithium salt is 1: 1.08 (lithium must be in slight excess because it will sublime in part at high temperatures). Sieving the above powder with 100 mesh sieve, and keeping at room temperature for 5 min-1The temperature is raised to 450 ℃ at the temperature raising rate, the temperature is kept for 4 hours, and the temperature is raised for 2 min-1Heating to 850 deg.C, maintaining for 18h at-0.5 deg.C for min-1Cooling to 650 ℃, and cooling along with the furnace and sieving with a 300-mesh sieve to obtain the lithium nickel manganese oxide cathode material.
Comparative example 2
0.8%Al2O3Coated lithium nickel manganese oxide positive electrode materialPreparation of
Accurately weighing aluminum nitrate nonahydrate and citric acid monohydrate in an ethanol-water solution according to the coating amount and the stoichiometric ratio, and magnetically stirring until the aluminum nitrate nonahydrate and the citric acid monohydrate are dissolved, wherein the volume ratio of ethanol to water in the ethanol-water solution is 1:1, and Al is3+Citric acid in a ratio of 1:1 (molar ratio); weighing 5g of the lithium nickel manganese oxide cathode material in the comparative example 1, stirring for 4h to disperse the lithium nickel manganese oxide cathode material, adjusting the pH of the solution to about 11 by using 1mol/L LiOH solution, continuing stirring for 1h, carrying out suction filtration, washing, drying, grinding, heating to 650 ℃ at the heating rate of 10 ℃/min for heat treatment for 2h, and cooling along with a furnace. Sieving with 300 mesh sieve to obtain 0.8% Al2O3And coating the lithium nickel manganese oxide positive electrode material.
Example 1
Preparation of 0.2% LASO-coated lithium nickel manganese oxide positive electrode material
Accurately weighing aluminum nitrate nonahydrate and citric acid monohydrate in an ethanol-water solution according to the coating amount and the stoichiometric ratio, and magnetically stirring until the aluminum nitrate nonahydrate and the citric acid monohydrate are dissolved, wherein the volume ratio of ethanol to water in the ethanol-water solution is 1:1, and Al is3+Citric acid in a ratio of 1:1 (molar ratio); weighing 5g of the lithium nickel manganese oxide positive electrode material in the comparative example 1 in the solution, and stirring for 4 hours to disperse the lithium nickel manganese oxide positive electrode material; mixing the components in a volume ratio of 1: 10 dispersing ethyl silicate in ethanol, slowly adding the ethyl silicate into the solution drop by drop according to the coating amount and the stoichiometric ratio, and continuously stirring; dispersing ethyl silicate in ethanol according to the stoichiometric ratio of the coating amount, dropwise and slowly adding the ethyl silicate into the solution, and continuously stirring for 2 hours; adjusting the pH value of the solution to about 11 by using 1mol/L LiOH solution, continuously stirring for 1h, carrying out suction filtration, washing, drying and grinding on the solution, mixing 5% of lithium excess according to the coating amount and the stoichiometric ratio, pouring the lithium carbonate into a ball milling tank, and carrying out dry ball milling for 4h, wherein the ball milling tank is made of polytetrafluoroethylene, ball milling beads are made of zirconium dioxide, the particle size of the ball milling beads is 5mm, and the rotating speed of the ball mill is 350 rad/min. The mass ratio of the ball milling beads to the mixture is 4:1, and the lithium is excessive by 5%. After the powder is sieved by a 100-mesh sieve, the temperature is raised to 650 ℃ at the heating speed of 10 ℃/min for heat treatment for 2h, and the powder is cooled along with a furnace. And sieving the lithium manganate with a 300-mesh sieve to obtain the 0.2 percent LASO coated lithium nickel manganese oxide cathode material.
Example 2
Preparation of 0.4% LASO-coated lithium nickel manganese oxide positive electrode material
Accurately weighing aluminum nitrate nonahydrate and citric acid monohydrate in an ethanol-water solution according to the coating amount and the stoichiometric ratio, and magnetically stirring until the aluminum nitrate nonahydrate and the citric acid monohydrate are dissolved, wherein the volume ratio of ethanol to water in the ethanol-water solution is 1:1, and Al is3+Citric acid in a ratio of 1:1 (molar ratio); weighing 5g of the lithium nickel manganese oxide positive electrode material in the comparative example 1 in the solution, and stirring for 4 hours to disperse the lithium nickel manganese oxide positive electrode material; dispersing ethyl silicate in ethanol, gradually and slowly adding the ethyl silicate into the solution according to the coating amount and the stoichiometric ratio, continuously stirring for 2 hours, adjusting the pH of the solution to about 11 by using 1mol/L LiOH solution, continuously stirring for 1 hour, carrying out suction filtration, washing, drying and grinding on the solution, mixing 5% of lithium excess according to the coating amount and the stoichiometric ratio, pouring lithium carbonate into a ball milling tank, and carrying out dry ball milling for 4 hours, wherein the ball milling tank is made of polytetrafluoroethylene, ball milling beads are made of zirconium dioxide, the particle size of the ball milling beads is 5mm, and the rotating speed of the ball milling tank is 350 rad/min. The mass ratio of the ball milling beads to the mixture is 4:1, and the lithium is excessive by 5%. After the powder is sieved by a 100-mesh sieve, the temperature is raised to 650 ℃ at the heating speed of 10 ℃/min for heat treatment for 2h, and the powder is cooled along with a furnace. And sieving the lithium manganate with a 300-mesh sieve to obtain the 0.4 percent LASO coated lithium nickel manganese oxide cathode material.
Example 3
Preparation of 0.6% LASO-coated lithium nickel manganese oxide positive electrode material
Accurately weighing aluminum nitrate nonahydrate and citric acid monohydrate in an ethanol-water solution according to the coating amount and the stoichiometric ratio, and magnetically stirring until the aluminum nitrate nonahydrate and the citric acid monohydrate are dissolved, wherein the volume ratio of ethanol to water in the ethanol-water solution is 1:1, and Al is3+Citric acid in a ratio of 1:1 (molar ratio); weighing 5g of the lithium nickel manganese oxide positive electrode material in the comparative example 1 in the solution, and stirring for 4 hours to disperse the lithium nickel manganese oxide positive electrode material; dispersing ethyl silicate in ethanol, gradually and slowly adding the ethyl silicate into the solution according to the coating amount and the stoichiometric ratio, continuously stirring for 2 hours, adjusting the pH of the solution to about 11 by using 1mol/L LiOH solution, continuously stirring for 1 hour, carrying out suction filtration, washing, drying and grinding on the solution, mixing 5% of lithium excess according to the coating amount and the stoichiometric ratio, pouring lithium carbonate into a ball milling tank, and carrying out dry ball milling for 4 hours, wherein the ball milling tank is made of polytetrafluoroethylene, ball milling beads are made of zirconium dioxide, the particle size of the ball milling beads is 5mm, and the rotating speed of the ball milling tank is 350 rad/min. Quality of ball milling beads and mixtureThe ratio was 4:1 with 5% lithium excess. After the powder is sieved by a 100-mesh sieve, the temperature is raised to 650 ℃ at the heating speed of 10 ℃/min for heat treatment for 2h, and the powder is cooled along with a furnace. And sieving the lithium manganate with a 300-mesh sieve to obtain the 0.6 percent LASO coated lithium nickel manganese oxide cathode material.
Example 4
Preparation of 0.8% LASO-coated lithium nickel manganese oxide positive electrode material
Accurately weighing aluminum nitrate nonahydrate and citric acid monohydrate in an ethanol-water solution according to the coating amount and the stoichiometric ratio, and magnetically stirring until the aluminum nitrate nonahydrate and the citric acid monohydrate are dissolved, wherein the volume ratio of ethanol to water in the ethanol-water solution is 1:1, and Al is3+Citric acid in a ratio of 1:1 (molar ratio); weighing 5g of the lithium nickel manganese oxide positive electrode material in the comparative example 1 in the solution, and stirring for 4 hours to disperse the lithium nickel manganese oxide positive electrode material; dispersing ethyl silicate in ethanol, gradually and slowly adding the ethyl silicate into the solution according to the coating amount and the stoichiometric ratio, continuously stirring for 2 hours, adjusting the pH of the solution to about 11 by using 1mol/L LiOH solution, continuously stirring for 1 hour, carrying out suction filtration, washing, drying and grinding on the solution, mixing 5% of lithium excess according to the coating amount and the stoichiometric ratio, pouring lithium carbonate into a ball milling tank, and carrying out dry ball milling for 4 hours, wherein the ball milling tank is made of polytetrafluoroethylene, ball milling beads are made of zirconium dioxide, the particle size of the ball milling beads is 5mm, and the rotating speed of the ball milling tank is 350 rad/min. The mass ratio of the ball milling beads to the mixture is 4:1, and the lithium is excessive by 5%. After the powder is sieved by a 100-mesh sieve, the temperature is raised to 650 ℃ at the heating speed of 10 ℃/min for heat treatment for 2h, and the powder is cooled along with a furnace. And sieving the lithium manganate with a 300-mesh sieve to obtain the 0.8 percent LASO coated lithium nickel manganese oxide cathode material.
Example 5
Preparation of 1.0% LASO-coated lithium nickel manganese oxide positive electrode material
Accurately weighing aluminum nitrate nonahydrate and citric acid monohydrate in an ethanol-water solution according to the coating amount and the stoichiometric ratio, and magnetically stirring until the aluminum nitrate nonahydrate and the citric acid monohydrate are dissolved, wherein the volume ratio of ethanol to water in the ethanol-water solution is 1:1, and Al is3+Citric acid in a ratio of 1:1 (molar ratio); weighing 5g of the lithium nickel manganese oxide positive electrode material in the comparative example 1 in the solution, and stirring for 4 hours to disperse the lithium nickel manganese oxide positive electrode material; dispersing ethyl silicate in ethanol, slowly adding into the above solution dropwise according to coating amount and stoichiometric ratio, stirring for 2 hr, adjusting pH to about 11 with 1mol/L LiOH solution, stirring for 1 hr, vacuum filteringAnd washing, drying, grinding, mixing lithium carbonate with 5% of lithium excess according to the coating amount and the stoichiometric ratio, pouring the mixture into a ball-milling tank, and performing dry ball milling for 4 hours, wherein the ball-milling tank is made of polytetrafluoroethylene, ball-milling beads are made of zirconium dioxide, the particle size of the ball-milling beads is 5mm, and the rotating speed of the ball mill is 350 rad/min. The mass ratio of the ball milling beads to the mixture is 4:1, and the lithium is excessive by 5%. After the powder is sieved by a 100-mesh sieve, the temperature is raised to 650 ℃ at the heating speed of 10 ℃/min for heat treatment for 2h, and the powder is cooled along with a furnace. And sieving the lithium manganate with a 300-mesh sieve to obtain the 1.0 percent LASO coated lithium nickel manganese oxide anode material.
And (3) morphology characterization:
fig. 1 is an SEM image of the sample of comparative example 1. The particle size range is about 300-400nm, and the particles are uniform and fine. Such small particles shorten the lithium ion intercalation and deintercalation path, thereby improving the electrochemical properties of the material.
And (3) electrochemical performance testing:
the materials prepared in the comparative examples 1 and 2 and the examples 1 to 5 are used as active ingredients to prepare the working electrode by adopting a coating method, and the specific operation is that the active ingredients (lithium nickel manganese oxide positive electrode material), the conductive agent Super-Pcarbon and the binder NMP are mixed according to the mass ratio of 90:5:5, then the mixture is uniformly coated on an aluminum foil, and the electrode pole piece is obtained after vacuum drying at 120 ℃ and compaction under 6 Mpa. Metal lithium as reference electrode, Celgard2400 as separator, 1mol/LLIPF6The EC/DEC/DMC (volume ratio of 1:1:1) solution of (A) is used as the electrolyte. And assembling the cell into a CR2032 button cell, and respectively carrying out constant-current charge-discharge performance test on a cell test system at the normal temperature of 25 ℃ and the high temperature of 55 ℃. The charging voltage range is 3.5-5V.
FIG. 2 is a graph of the cycling performance at 0.2C for the uncoated lithium nickel manganese oxide positive electrode material of comparative example 1 and the 0.8% LASO coated lithium nickel manganese oxide positive electrode material of example 4 under 25 deg.C testing conditions. Comparative example 1 had a specific discharge capacity of 128.6mAh g in the first turn-1The capacity retention rate after 50 cycles is 93.7%, and the first-turn specific discharge capacity of example 4 is 136.5mAh g-1The capacity remains almost unchanged after 50 cycles, and the attenuation is almost zero. Therefore, the cycle performance of the lithium nickel manganese oxide anode material is improved to a certain extent by coating the LASO at normal temperature, because a layer similar to a protective layer is formed on the surface of the lithium nickel manganese oxide anodeThe interface of the protective layer can effectively avoid the direct contact of the electrolyte and the anode material, prevent the electrolyte from generating side reaction, enhance the cycle performance of the material and improve the electrochemical performance of the material.
FIG. 3 is a graph of the cycling performance at 0.2C for the uncoated lithium nickel manganese oxide positive electrode material of comparative example 1 and the 0.8% LASO coated lithium nickel manganese oxide positive electrode material of example 4 under 55 deg.C testing conditions. Comparative example 1 had a first-turn specific discharge capacity of 118.7mAh · g-1The capacity retention rate after 50 cycles is 73.2%, and the first-turn specific discharge capacity of example 4 is 126.4mAh g-1The capacity retention rate after 50 cycles is 88.0 percent, and the capacity retention rate is greatly improved. Therefore, the coating LASO has a great positive effect on the cycle performance of the lithium nickel manganese oxide cathode material at high temperature, and the LASO coating can inhibit the formation of a passivation layer, can be used as a high-efficiency lithium ion conductor, has good lithium ion conductivity at high temperature, and improves the transmission rate of lithium ions at high temperature, so that the high-temperature cycle performance of the battery is obviously improved.
Table 1 shows experimental data for examples 1-5 compared to comparative examples 1, 2 at 25 ℃ test conditions, as can be seen in Table one: when the coating amount of the LASO is 0.8%, the specific discharge capacity of the material is the highest, and the capacity retention rate of the material after 50 cycles is also the highest. Compared with the uncoated lithium nickel manganese oxide cathode material, the capacity retention rate of other materials with different LASO coating amounts after 50 circles is improved to a certain extent. It is worth noting that: when the LASO coating amount is 1%, the first discharge specific capacity of the anode material is reduced compared with that of the uncoated anode material. The reason is that an increased content of the coating material leads to a reduction of the active substance in the material. However, after long-time testing, the capacity retention rate of the material is not greatly reduced compared with the capacity retention rate of the material, and the reason is that the coating substance can effectively separate the electrolyte from the active substance, so that the occurrence of side reactions is reduced, and the cycle performance of the material is improved. When the coating amounts were all 0.8%, the LASO coating was compared with the conventional coating Al2O3The coated lithium nickel manganese oxide showed better cycling performance due to the material of the LASO itself. Different from other goldThe oxides are coated on the surface of the material in a granular state, and the LASO layer is in a glass state and can be continuously and uniformly coated on the surface of the material to separate the electrolyte from the active substance, so that the occurrence of side reactions is reduced, and the cycle performance of the material is better.
TABLE 1
Figure DEST_PATH_IMAGE002A
Table 2 shows experimental data for examples 1-4 compared to comparative examples 1, 2 at 55 ℃ test conditions, as can be seen in Table 2: when the coating amount of the LASO is 0.8%, the specific discharge capacity of the material is the highest, the capacity retention rate of the material after 50 times of circulation is also the highest, and compared with the capacity retention rate of the uncoated lithium nickel manganese oxide, the capacity retention rate of the material is greatly improved, and particularly the capacity retention rate of the material is as high as that of 0.8% Al2O3The coating comparison also shows good capacity retention. This is because at elevated temperatures (55 c), manganese ions dissolve in the electrolyte, forming a passivation layer on the electrode surface during cycling, making lithium ion diffusion more difficult. The continuous and uniform LASO coating inhibits the formation of a passivation layer and is used as a high-efficiency lithium ion conductor, so that the high-temperature cycle performance of the lithium nickel manganese oxide cathode material is improved. Compared with the conventional Al2O3The coating has more excellent cycle performance at high temperature.
TABLE 2
Figure DEST_PATH_IMAGE004
In light of the foregoing description of the preferred embodiments of the present invention, it is to be understood that various changes and modifications may be made by one skilled in the art without departing from the spirit and scope of the invention. The technical scope of the present invention is not limited to the content of the specification, and must be determined according to the scope of the claims.

Claims (5)

  1. The preparation method of the LASO-coated octahedral lithium nickel manganese oxide composite material is characterized by comprising the following preparation steps of:
    (1) taking nickel sulfate and manganese sulfate according to the molar ratio of nickel to manganese elements of 1:3, adding the mixture into deionized water in proportion, and magnetically stirring the mixture until the mixture is dissolved to obtain a solution A; adding sodium hydroxide into deionized water, and dissolving by magnetic stirring to form a solution B with the concentration of 0.5-2 mol/L; slowly dripping the solution B into the solution A through a constant-pressure separating funnel under the condition that the solution A is in a water bath at the temperature of 80 ℃, and stirring while dripping to obtain a mixed solution C; continuing stirring the mixed solution C for 1h under the condition of 80 ℃ water bath, stopping stirring, standing at normal temperature, performing vacuum filtration, and drying to obtain a lithium nickel manganese oxide precursor; mixing a lithium nickel manganese oxide precursor with lithium carbonate, and performing dry ball milling to obtain powder, wherein the molar ratio of Mn + Ni in the lithium nickel manganese oxide precursor to Li in the lithium carbonate is 1: 1.08; the powder is calcined after being screened by a 100-mesh sieve, and the calcining process comprises the following steps: heating to 400-600 ℃ at the speed of 1-5 ℃/min, and preserving heat for 2-6 hours; then heating to 800-950 ℃ at the speed of 1-5 ℃/min, and preserving heat for 15-25 hours; then cooling to 650 ℃ at the speed of 1-5 ℃/min, and cooling along with the furnace to obtain octahedral structure lithium nickel manganese oxide powder;
    (2) and (3) LASO coating: weighing aluminum nitrate nonahydrate and citric acid monohydrate in ethanol-water solution according to the coating amount and the stoichiometric ratio, and adding Al3+: the citric acid molar ratio is 1:1, the volume ratio of ethanol to water in the ethanol-water solution is 1:1, and the mixture is magnetically stirred until the mixture is dissolved; weighing the octahedral lithium nickel manganese oxide powder obtained in the step (1), adding the octahedral lithium nickel manganese oxide powder into the solution, and stirring to fully disperse the octahedral lithium nickel manganese oxide powder; mixing the components in a volume ratio of 1: 10 dispersing ethyl silicate in ethanol, slowly adding the ethyl silicate into the solution drop by drop according to the coating amount and the stoichiometric ratio, and continuously stirring for 2 hours; adjusting the pH of the solution to about 11 by using LiOH solution with the concentration of 1mol/L, and continuing stirring; carrying out suction filtration, washing, drying and grinding on the obtained solution, and mixing lithium carbonate with 5% of lithium excess according to the coating amount and the stoichiometric ratio for dry ball milling; the powder is sintered after being screened by a 100-mesh sieve, and the sintering process comprises the following steps: heating to 650 ℃ at a heating rate of 10 ℃/min for 2h, and cooling along with the furnace to obtain the LASO-coated octahedral-structure lithium nickel manganese oxide composite material, wherein the surface coating substance is Li-Al-Si-O inorganic solid electrolyte, and Li2O：Al2O3：SiO2The molecular ratio was 1:2: 8.3.
  2. 2. The preparation method of the LASO-coated octahedral lithium nickel manganese oxide composite material according to claim 1, characterized in that: in the ball milling process in the steps (1) and (2), the ball milling tank is made of polytetrafluoroethylene, the ball milling beads are made of zirconium dioxide, the particle size of the ball milling beads is 5-10 mm, the rotating speed of the ball mill is 300-400 rad/min, and the mass ratio of the ball milling beads to the mixture is 1: 3-4.
  3. 3. The LASO-coated octahedral-structure lithium nickel manganese oxide composite material prepared by the preparation method according to claim 1 or 2, is characterized in that: the nano Li-Al-Si-O inorganic solid electrolyte coats octahedral lithium nickel manganese oxide to form the composite material.
  4. 4. The LASO-coated octahedral lithium nickel manganese oxide composite material according to claim 3, characterized in that: the coating amount of the inorganic solid electrolyte Li-Al-Si-O is 0.2-1% of the mass of the lithium nickel manganese oxide.
  5. 5. The LASO-coated octahedral lithium nickel manganese oxide composite material according to claim 4, wherein: the coating amount of the inorganic solid electrolyte Li-Al-Si-O is 0.8 percent of the mass of the lithium nickel manganese oxide.
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