CN108695509B - Composite lithium battery positive electrode with high energy storage efficiency, preparation method thereof and lithium battery - Google Patents
Composite lithium battery positive electrode with high energy storage efficiency, preparation method thereof and lithium battery Download PDFInfo
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- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
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- 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
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
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- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
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- H—ELECTRICITY
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- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
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Abstract
The invention discloses a composite lithium battery anode with high energy storage efficiency, a preparation method and a lithium battery, wherein the lithium battery anode comprises an anode current collector and anode active slurry coated on the surface of the anode current collector; the positive active slurry consists of a modified silicate composite material, a conductive agent and a binder; the positive current collector is a modified carbon nano tube/carbon nano fiber composite membrane. Compared with the prior art, the anode current collector improves the energy density of the battery, resists electrolyte corrosion and improves the adhesion, the modified silicate composite material adopts a silicate precursor prepared by in-situ carbonization compounding and ball milling/spray drying, can prevent sintering and agglomeration among silicate particles, shortens the transmission path of lithium ions, coats a fast ion conductor layer on the outer surface of a silicate active material to form a mosaic structure, avoids direct contact between the material and the electrolyte, improves the diffusion capacity of the lithium ions, and reduces the interface resistance between the material and the electrolyte.
Description
Technical Field
The invention relates to the technical field of lithium batteries, in particular to a composite lithium battery positive electrode with high energy storage efficiency, a preparation method thereof and a lithium battery.
Background
Since the concept of rechargeable lithium batteries was proposed in the early seventies of the twentieth century and since lithium ion batteries were produced and commercialized, lithium ion batteries have rapidly become a research hotspot of multiple disciplines such as advanced energy, materials, electrochemistry and the like due to their superior performance, and have been widely used as driving power sources for small electronic devices and medical instruments such as notebook computers, mobile phones, digital cameras, mp3 players and the like.
The positive electrode material in the lithium ion battery is a key factor influencing the performance of the battery, the ideal positive electrode material of the lithium ion battery has the advantages of high capacity, high multiplying power, high cycle performance, environmental friendliness, low cost and the like, the polyanion material becomes a new generation positive electrode material of the lithium ion battery with great development potential due to the advantages of high theoretical capacity, outstanding safety and the like, silicate in various polyanions is particularly attractive due to the characteristics of rich natural resources and environmental friendliness, and the Li with an orthogonal structure synthesized by a solid phase method has the advantages of high capacity, high multiplying power and high cycle performance2FeSiO4The material is a lithium ion battery anode material, and charging and discharging at 60 ℃ can obtain about 140mAhg-1The specific capacity of the material is large, the distribution is uneven, and the phase is not pure(ii) a Synthesis of orthorhombic Li by modified sol-gel method2FeSiO4Reversible intercalation of 0.6 Li per chemical formula is realized in the first discharge process under the condition of C/30 low-rate charge and discharge, but impurities are easy to appear in the synthesis process; solid phase method synthesizes Li2VOSiO4The material is subjected to carbon coating treatment by a mechanical ball milling method to be used as a lithium ion battery anode material, and 100mAhg is obtained under the conditions of low current charge and discharge-1Reversible capacity, but poor rate capability of the material. To improve these problems, doping and cladding modification of materials are effective methods. The surface coating is a common modification means, and researches show that the coating can be used as a protective layer to relieve the corrosion of electrolyte to the anode material, inhibit the structural collapse and obviously improve the cycle stability and the thermal stability of the ternary material. The thermal stability, rate capability and cycle stability of the ternary cathode material are remarkably improved by selecting different coating materials.
The current collector adopted by the anode of the lithium ion battery generally consists of aluminum foil and an anode material coated on the aluminum foil. The traditional current collector generally adopts an aluminum foil with a smooth surface, 99.7% purity aluminum foil is directly coated with active substances, the aluminum foil does not contribute to the battery capacity as the current collector, but the mass of the aluminum foil accounts for 15% of the total positive electrode, and the energy density of the battery is restricted during the process of raising; the aluminum foil with a smooth surface is loosely combined with the active material, so that the requirements on the quality of raw materials and auxiliary materials and the process are high, the phenomenon that the active material falls off or powder falls off easily occurs in the processing and charging and discharging processes, the cyclic charging and discharging efficiency and the service life of the battery are reduced, the contact resistance between components is improved, and the conductivity of the positive plate is reduced, so that the comprehensive performance of the battery is influenced, and the comprehensive performance of lithium ions is seriously influenced.
Disclosure of Invention
In order to solve the technical problems, the invention provides a composite lithium battery anode with high energy storage efficiency and a preparation method thereof, which are used for solving the problems of effectively improving the migration rate of electrons and lithium ions at an electrode interface, improving the average discharge capacity and the recycling efficiency, improving the energy density of a battery and increasing the conductivity of the battery.
The technical scheme adopted by the invention is as follows: the utility model provides a compound high energy storage efficiency compound lithium cell positive pole of high energy storage efficiency, the key lies in: the positive electrode current collector comprises a positive electrode current collector and positive electrode active slurry coated on the surface of the positive electrode current collector; the positive active slurry comprises the following components in percentage by mass (94-98): (0.5-3): (1-3) the modified silicate composite material, a conductive agent and a binder; the positive current collector is a modified carbon nanotube/carbon nanofiber composite membrane.
Preferably, the modified silicate composite material is composed of a silicate active material and a fast ion conductor layer coated on the outer surface of the silicate active material, and the silicate active material is Li2FexMn1-x SiO4X is more than 0.4 and less than 0.8; the fast ion conductor layer comprises Li7La3Zr2O12The thickness of the fast ion conductor layer is 50-1000 nm, and the mass ratio of the silicate active material to the fast ion conductor layer is 1: (0.05-0.3).
Preferably, the modified carbon nanotube is prepared by the following method: respectively putting n-butyl chloride and methylimidazole into toluene, wherein the volume ratio of the n-butyl chloride to the toluene is 3: 2, the volume ratio of the methylimidazole to the toluene is 3: 2, stirring and reacting at 70-90 ℃ for 24-36h, cooling the system to-2-0 ℃, freezing for 2-4h, separating a lower-layer product, washing the lower-layer product with toluene and cyclohexane respectively, and then carrying out pressure distillation to obtain imidazole chloride ionic liquid; mixing a mixture of 1: 1 imidazolium chloride ionic liquid and FeCl3Stirring and reacting for 10-18h under the protection of nitrogen to obtain magnetic ionic liquid; and then adding the multi-walled carbon nanotube into the magnetic ionic liquid, wherein the mass-volume ratio of the multi-walled carbon nanotube to the magnetic ionic liquid is 2 mg: 1ml, grinding to obtain carbon nanotube gel, centrifuging the carbon nanotube gel to separate out precipitate, washing the precipitate, and vacuum drying at 60 ℃ for 10-15h to obtain the modified carbon nanotube.
Preferably, the modified silicate composite material is prepared according to the following steps:
a. mixing lithium source compound, manganese source compound, iron source compound salt, and silicic acidTetraethyl ester is synthesized by the molar ratio of Li: ca: fe: mn: SiO 24 2-2: x: (1-x): 1, putting the mixture into a reactor after accurate weighing, adding a catalyst, fully and uniformly stirring, and reacting for 18-36h at the temperature of 100 ℃ and 150 ℃ in a sealed state to obtain gel;
b. taking out the gel, drying, mixing with a carbon source compound, ball-milling the mixture in a ball mill, and pumping into a spray drying tower for spray drying to obtain a silicate precursor;
c. adding a silicate precursor into a metal ion mixed salt solution, dropwise adding a precipitator while stirring, stirring to react for 0.5-2h after dropwise adding is completed, separating out a precipitate, washing the precipitate, drying, adding LiOH, grinding, tabletting, sintering at high temperature by microwave under the protection of inert gas, and cooling to room temperature along with a furnace to obtain the modified silicate composite material.
Preferably, the lithium source compound is lithium acetate, the manganese source compound is manganese acetate, the iron source is iron acetate, and the catalyst is prepared by mixing acetic acid and ethanol in a mass ratio of 1: (20-30) acetic acid-ethanol mixture.
Preferably, the carbon source compound is one or a mixture of more than two of glucose, sucrose and polyethylene glycol; the mass ratio of the silicate precursor to the carbon source compound is 1: (0.01-0.2); the ball milling conditions are as follows: ball milling is carried out by adopting a planetary ball mill, deionized water is used as a ball milling medium, the deionized water and the deionized water are mixed for 3 hours at the rotating speed of 400r/min, and the mixture is prepared into homogenate with the mass concentration of 10-25% wt; the spray granulation conditions are as follows: pumping the homogenate into a spray drying tower for granulation, wherein the spray gas is air or nitrogen, the inlet temperature is 200-150 ℃, and the outlet temperature is 120-100 ℃.
Preferably, the metal ion mixed salt solution is Zr and La metal ion mixed salt solution, the precipitator is ammonia water with the mass fraction of (10-25)% wt, and the total molar ratio of the ammonia water to the two metal ions is NH3·H2O: (Zr + La) ═ 1-1.5: 1; the microwave high-temperature sintering conditions are as follows: vacuumizing the microwave high-temperature atmosphere experimental furnace, introducing inert gas which is argon or a mixed gas of argon and hydrogen, and heating at the speed of 100 ℃/minAnd keeping the temperature for 5-15min at 500-900 ℃.
Preferably, the conductive agent is one of acetylene black, flake graphite or carbon nanofibers; the binder is one of polyvinylidene fluoride, styrene butadiene rubber or sodium carboxymethylcellulose.
The preparation method of the composite lithium battery anode with high energy storage efficiency is characterized by comprising the following steps:
step one, preparing a modified carbon nano tube/carbon nano fiber composite membrane: dissolving polyacrylonitrile in dimethyl sulfoxide to form a polyacrylonitrile solution with the mass fraction of 8-12% by weight, and then mixing the polyacrylonitrile solution with the mass ratio of (0.5-2): (3-10) mixing the modified carbon nano tube with a polyacrylonitrile solution, ultrasonically dispersing the mixture into a spinning solution at room temperature, preparing the spinning solution into a nanofiber membrane under the conditions that the environmental temperature is 15-30 ℃, the environmental humidity is 5-70 percent, a high-voltage electrostatic spraying device is utilized, the voltage of an electrostatic generator is 10kV-20kV, the distance between a metal needle and a filament collector is 12-15cm, the flow rate is 0.5-3mL/h and the strand rotation speed is 500-3000rpm/min, transferring the nanofiber membrane into a tube furnace, heating to 150-200 ℃ at the heating rate of 0.2-4 ℃/min under the air atmosphere, preserving heat for 20-48h, heating to 280-380 ℃ at the heating rate of 0.2-4 ℃/min, preserving heat for 3-8h for pre-oxidation treatment, heating to 700-900 ℃ under the nitrogen atmosphere, preserving heat for 1-3h, then naturally cooling to room temperature under the protection of atmosphere to obtain the modified carbon nano tube/carbon nano fiber composite membrane;
step two, preparing positive active slurry: putting the modified silicate composite material, the conductive agent, the binder and a proper amount of N-methyl pyrrolidone into a stirring kettle according to the proportion, controlling the stirring speed to be 100-6000 rpm/min, stirring for 30min to obtain a mixture, and then dispersing the mixture by using a high-speed dispersion machine, wherein the dispersion speed is 3000-4000r/min, and the dispersion viscosity reaches 3500-6000mPa & s to obtain the anode active slurry;
step three, preparing the positive plate: the positive active slurry is processed according to the conditions of 152-2Coating the nano carbon fiber film with the surface density, drying and coating the nano carbon fiber film with the surface density of 3.3-3.9g/mm3And rolling the compacted density to obtain the positive plate.
A lithium battery is characterized in that: the composite lithium battery with high energy storage efficiency comprises the positive electrode, the negative electrode, the diaphragm and electrolyte.
Has the advantages that: compared with the prior art, the invention provides the composite lithium battery anode with high energy storage efficiency, the preparation method and the lithium battery, so that the rapid charge transmission in the charge and discharge process is realized, and the stability and the battery multiplying power performance in the cycle process are improved; the positive current collector adopts a modified carbon nanotube/carbon nanofiber composite membrane, has a unique microstructure and good conductivity, can improve the energy density of the battery, has strong binding force with active substances due to a porous structure on the surface, can increase the peeling strength of the active substances, reduces the using amount of a binder during preparation of the pole piece, reduces the contact internal resistance of the pole piece, can improve the phenomena of swelling and powder falling caused by a long-term circulation process of the battery pole piece in the prior art, can also prolong the cycle service life and the rate capability of the battery, and can effectively prevent the corrosion of decomposition products in organic electrolyte on the metal of the current collector; the modified silicate composite material can work under higher voltage, greatly improves the battery capacity, prevents sintering and agglomeration among silicate particles by adopting a silicate precursor prepared by in-situ carbonization compounding and ball milling/spray drying, is more concentrated in particle size distribution, is favorable for ensuring the uniformity of material performance, shortens the transmission path of lithium ions in the electrochemical process, is favorable for realizing good multiplying power performance, can improve the contact conductance among the particles and the integral electronic conductance of the material, and is also favorable for realizing good multiplying power performance; the outer surface of the silicate active material is coated with the fast ion conductor layer, the silicate active material in the silicate active material and the fast ion conductor layer coated on the surface are mutually diffused to be organically connected to form an embedded structure, the bonding strength is improved, the uniformly coated composite material is obtained, a stable-structure and corrosion-resistant firewall is established between the anode material and the electrolyte, the direct contact between the material and the electrolyte is avoided, and the coating layer can improve the lithium ion diffusion capacity of the material and reduce the interface resistance between the material and the electrolyte as an ion conductor; .
Detailed Description
The present invention will be described in detail with reference to specific embodiments in order to make those skilled in the art better understand the technical solutions of the present invention.
Example 1 preparation of high energy storage efficiency composite lithium battery cathode I
Step one, preparing a modified carbon nano tube/carbon nano fiber composite membrane: dissolving polyacrylonitrile in dimethyl sulfoxide to form a polyacrylonitrile solution with the mass fraction of 8% by weight, and then mixing polyacrylonitrile and water in a mass ratio of 0.5: 3, mixing the modified carbon nano tube with a polyacrylonitrile solution, ultrasonically dispersing the mixture at room temperature to form a spinning solution, preparing the spinning solution into a nano fiber membrane under the conditions that the ambient temperature is 15-30 ℃, the ambient humidity is 5-70%, a high-voltage electrostatic spraying device is utilized, the voltage of an electrostatic generator is 10-20 kV, the distance between a metal needle and a filament collector is 12cm, the flow rate is 0.5mL/h and the strand rotating speed is 500rpm/min, transferring the nano fiber membrane to a tube furnace, heating to 150 ℃ at the heating rate of 0.2 ℃/min under the air atmosphere and preserving heat for 20h, heating to 280 ℃ at the heating rate of 0.2 ℃/min and preserving heat for 3-5h for pre-oxidation treatment, heating to 700 ℃ under the nitrogen atmosphere and preserving heat for 1-3h, naturally cooling to room temperature under the atmosphere protection, obtaining a modified carbon nano tube/carbon nano fiber composite membrane;
step two, preparing positive active slurry: putting the modified silicate composite material, acetylene black, polyvinylidene fluoride and a proper amount of N-methyl pyrrolidone into a stirring kettle according to a ratio, controlling the stirring speed to be 100-6000 rpm/min, stirring for 30min to obtain a mixture, and then dispersing the mixture by using a high-speed dispersion machine, wherein the dispersion speed is 3000-4000r/min, and the dispersion viscosity reaches 3500-6000mPa & s to obtain the anode active slurry;
the modified silicate composite material is prepared by the following method: lithium acetate, manganese acetate, iron acetate and tetraethyl orthosilicate are mixed according to the mol ratio of Li: ca: fe: mn: SiO 24 2-2: 0.4: 0.6: 1, putting the mixture into a reactor after accurately weighing the mixture, and then adding a catalyst, wherein the catalyst is prepared by mixing acetic acid and ethanol in a mass ratio of 1: 20, stirring well, and reacting at 100 deg.C for 18-36 hr under sealed condition to obtain gel(ii) a Taking out the gel, drying and mixing with glucose, wherein the mass ratio of the fast ion precursor to the glucose is 1: 0.01, ball-milling the mixture in a planetary ball mill, wherein the ball-milling medium is deionized water, mixing at the rotating speed of 400r/min for 3h, preparing the mixture into homogenate with the mass concentration of 10 wt%, pumping the homogenate into a spray drying tower for granulation, wherein the spray gas is air, the inlet temperature is 200 ℃, and the outlet temperature is 120 ℃ to obtain a silicate precursor; then adding a silicate precursor into a mixed salt solution of Zr and La metal ions, dropwise adding ammonia water with the mass concentration of 10 wt. percent while stirring, wherein the total molar weight ratio of the ammonia water to the two metal ions is NH3·H2O: (Zr + La) ═ 1: 1, stirring and reacting for 0.5-2h after dropwise adding is finished, separating out a precipitate, washing the precipitate, drying, adding LiOH for grinding, tabletting, placing in a microwave high-temperature atmosphere experimental furnace, vacuumizing the microwave high-temperature atmosphere experimental furnace, introducing argon, heating to 500 ℃ at the speed of 100 ℃/min, keeping the temperature for 5min, and cooling to room temperature along with the furnace to obtain the modified silicate composite material I, wherein the modified silicate composite material I is composed of a silicate active material and a fast ion conductor layer coated on the outer surface of the silicate active material, and the silicate active material is Li2Fe0.4Mn0.6SiO4The fast ion conductor layer comprises Li7La3Zr2O12The thickness of the rapid ion conductor layer is 50nm, and the mass ratio of the silicate active material to the rapid ion conductor layer is 1: 0.05.
step three, preparing the positive plate: coating the positive active slurry on a modified carbon nanotube/carbon nanofiber composite membrane, drying at 120 ℃, and rolling under the pressure of 1.6MPa to obtain the modified carbon nanotube/carbon nanofiber composite membrane with the surface density of 152g/cm2Compacted density of 3.3g/mm3The positive electrode I of (1).
Example 2 preparation of high energy storage efficiency composite lithium battery cathode II
Step one, preparing a modified carbon nano tube/carbon nano fiber composite membrane: dissolving polyacrylonitrile in dimethyl sulfoxide to form a polyacrylonitrile solution with the mass fraction of 12% by weight, and then mixing polyacrylonitrile and water in a mass ratio of 2: 10, mixing the modified carbon nano tube with a polyacrylonitrile solution, performing ultrasonic dispersion at room temperature to obtain a spinning solution, preparing the spinning solution into a nano fiber membrane under the conditions that the ambient temperature is 15-30 ℃, the ambient humidity is 5-70%, a high-voltage electrostatic spraying device is utilized, the voltage of an electrostatic generator is 10-20 kV, the distance between a metal needle and a filament collector is 15cm, the flow rate is 3mL/h and the strand rotating speed is 3000rpm/min, transferring the nano fiber membrane into a tubular furnace, heating to 200 ℃ at the heating rate of 4 ℃/min under the air atmosphere and preserving heat for 48h, heating to 380 ℃ at the heating rate of 4 ℃/min and preserving heat for 5-8h for pre-oxidation treatment, heating to 900 ℃ under the nitrogen atmosphere and preserving heat for 1-3h, and naturally cooling to room temperature under the protection of the atmosphere, obtaining a modified carbon nano tube/carbon nano fiber composite membrane;
step two, preparing positive active slurry: putting the modified silicate composite material, the flaked graphite, the styrene butadiene rubber and a proper amount of N-methyl pyrrolidone into a stirring kettle according to the proportion, controlling the stirring speed to be 100-6000 rpm/min, stirring for 30min to obtain a mixture, and then dispersing the mixture by using a high-speed dispersion machine, wherein the dispersion speed is 3000-4000r/min, and the dispersion viscosity reaches 3500-6000mPa & s to obtain the anode active slurry;
the modified silicate composite material is prepared by the following method: lithium acetate, manganese acetate, iron acetate and tetraethyl orthosilicate are mixed according to the mol ratio of Li: ca: fe: mn: SiO 24 2-2: 0.8: 0.2: 1, putting the mixture into a reactor after accurately weighing the mixture, and then adding a catalyst, wherein the catalyst is prepared by mixing acetic acid and ethanol in a mass ratio of 1: 30, stirring the mixture fully and uniformly, and reacting for 18-36h at 150 ℃ in a sealed state to obtain gel; taking out the gel, drying and mixing with sucrose, wherein the mass ratio of the fast ion precursor to the sucrose is 1: 0.2, ball-milling the mixture in a planetary ball mill, wherein the ball-milling medium is deionized water, mixing at the rotating speed of 400r/min for 3h, preparing the mixture into homogenate with the mass concentration of 25 wt%, pumping the homogenate into a spray drying tower for granulation, wherein the spray gas is nitrogen, the inlet temperature is 150 ℃, and the outlet temperature is 100 ℃ to obtain a silicate precursor; then adding the silicate precursor into the mixed salt solution of Zr and La metal ions, and dripping the silicate precursor into the mixed salt solution while stirringAmmonia water with the amount concentration of 25% wt., wherein the total molar amount ratio of the ammonia water to the two metal ions is NH3·H2O: (Zr + La) ═ 1.5: 1, stirring and reacting for 0.5-2h after dropwise adding is finished, separating out a precipitate, washing the precipitate, drying, adding LiOH for grinding, tabletting, placing in a microwave high-temperature atmosphere experimental furnace, vacuumizing the microwave high-temperature atmosphere experimental furnace, introducing argon and nitrogen, heating to 900 ℃ at the speed of 100 ℃/min, keeping the temperature for 15min, and cooling to room temperature along with the furnace to obtain the modified silicate composite material II, wherein the modified silicate composite material II is composed of a silicate active material and a fast ion conductor layer coated on the outer surface of the silicate active material, and the silicate active material is Li2Fe0.8Mn0.2SiO4The fast ion conductor layer comprises Li7La3Zr2O12The thickness of the rapid ion conductor layer is 1000nm, and the mass ratio of the silicate active material to the rapid ion conductor layer is 1: 0.3.
step three, preparing the positive plate: coating the positive active slurry on a modified carbon nanotube/carbon nanofiber composite membrane, drying at 120 ℃, and rolling under the pressure of 1.6MPa to obtain the modified carbon nanotube/carbon nanofiber composite membrane with the surface density of 168g/cm2Compacted density of 3.9g/mm3Positive electrode II of (1).
Example 3 preparation of high energy storage efficiency composite lithium battery cathode III
Step one, preparing a modified carbon nano tube/carbon nano fiber composite membrane: dissolving polyacrylonitrile in dimethyl sulfoxide to form a polyacrylonitrile solution with the mass fraction of 10% by weight, and then mixing polyacrylonitrile and water in a mass ratio of 0.15: 8, mixing the modified carbon nano tube with a polyacrylonitrile solution, performing ultrasonic dispersion at room temperature to obtain a spinning solution, preparing the spinning solution into a nano fiber membrane under the conditions that the ambient temperature is 15-30 ℃, the ambient humidity is 5-70%, a high-voltage electrostatic spraying device is utilized, the voltage of an electrostatic generator is 10-20 kV, the distance between a metal needle and a filament collector is 14cm, the flow rate is 2mL/h, the strand rotating speed is 1500rpm/min, transferring the nano fiber membrane into a tubular furnace, heating to 180 ℃ at the heating rate of 1.5 ℃/min under the air atmosphere and preserving heat for 25h, heating to 350 ℃ at the heating rate of 3 ℃/min and preserving heat for 4-6h for pre-oxidation treatment, heating to 800 ℃ under the nitrogen atmosphere and preserving heat for 1-3h, then naturally cooling to room temperature under the atmosphere protection, obtaining a modified carbon nano tube/carbon nano fiber composite membrane;
step two, preparing positive active slurry: putting the modified silicate composite material, the carbon nanofibers, the sodium carboxymethylcellulose and a proper amount of N-methyl pyrrolidone into a stirring kettle according to a ratio, controlling the stirring speed to be 100-6000 rpm/min, stirring for 30min to obtain a mixture, and then dispersing the mixture by using a high-speed dispersion machine, wherein the dispersion speed is 3000-4000r/min, and the dispersion viscosity reaches 3500-6000mPa & s to obtain the anode active slurry;
the modified silicate composite material is prepared by the following method: lithium acetate, manganese acetate, iron acetate and tetraethyl orthosilicate are mixed according to the mol ratio of Li: ca: fe: mn: SiO 24 2-2: 0.5: 0.5: 1, putting the mixture into a reactor after accurately weighing the mixture, and then adding a catalyst, wherein the catalyst is prepared by mixing acetic acid and ethanol in a mass ratio of 1: 25, stirring the mixture fully and uniformly, and reacting for 18-36h at 120 ℃ in a sealed state to obtain gel; taking out the gel, drying and mixing with polyethylene glycol, wherein the mass ratio of the fast ion precursor to the polyethylene glycol is 1: 0.1, ball-milling the mixture in a planetary ball mill, wherein the ball-milling medium is deionized water, mixing at the rotating speed of 400r/min for 3h, preparing the mixture into homogenate with the mass concentration of 15 wt%, pumping the homogenate into a spray drying tower for granulation, wherein the spray gas is nitrogen, the inlet temperature is 180 ℃, and the outlet temperature is 100 ℃ to obtain a silicate precursor; then adding a silicate precursor into a mixed salt solution of Zr and La metal ions, dropwise adding ammonia water with the mass concentration of 22 wt% while stirring, wherein the total molar weight ratio of the ammonia water to the two metal ions is NH3·H2O: (Zr + La) ═ 1.2: 1, stirring and reacting for 0.5-2h after dropwise adding is finished, separating out a precipitate, washing the precipitate, drying, adding LiOH for grinding, tabletting, placing in a microwave high-temperature atmosphere experimental furnace, vacuumizing the microwave high-temperature atmosphere experimental furnace, introducing argon, heating to 800 ℃ at the speed of 100 ℃/min, preserving heat for 10min, and cooling to room temperature along with the furnace to obtain the modified silicate compositeThe material III is composed of a silicate active material and a fast ion conductor layer coated on the outer surface of the silicate active material, wherein the silicate active material is Li2Fe0.5Mn0.5SiO4The fast ion conductor layer comprises Li7La3Zr2O12The thickness of the rapid ion conductor layer is 200nm, and the mass ratio of the silicate active material to the rapid ion conductor layer is 1: 0.15.
step three, preparing the positive plate: coating the positive active slurry on a modified carbon nanotube/carbon nanofiber composite membrane, drying at 120 ℃, and rolling under the pressure of 1.6MPa to obtain the modified carbon nanotube/carbon nanofiber composite membrane with the surface density of 165g/cm2The compacted density is 3.8g/mm3The positive electrode III of (1).
Example 4 comparative example
The equipment and operation were the same as in example 3, except that the modified carbon nanotube/carbon nanofiber composite membrane was replaced with aluminum foil to obtain the positive electrode IV.
Example 5 comparative example
The apparatus and operation were the same as in example 3, except that Li was added2MnSO4Substituted Li2FexMn1-x SiO4To obtain the positive electrode V.
Electrochemical performance tests were performed on the positive electrode active materials prepared in each example:
and (3) assembling the anode I-V prepared in each embodiment into a button type half cell I-IV by taking a lithium sheet as a cell cathode, 1M LiPF6 electrolyte and a glass fiber diaphragm, and performing constant current charge-discharge performance test on a LAND cell test system, wherein the voltage interval is 1.5-4.8V.
The charge-discharge cycle performance test was performed on the button half cell I-V, and the test results are shown in table 1.
Testing the specific discharge capacity for the first time: the prepared battery was subjected to current density of 0.1C, and the first discharge capacity and the remaining capacity after 100 test cycles of the battery were recorded.
And (3) rate test of the simulated battery: and respectively testing the discharge specific capacities of 0.5C, 1C and 3C.
TABLE 1 comparison of the charge-discharge cycle performance test results of each button half cell I-IV
Finally, it should be noted that the above-mentioned description is only a preferred embodiment of the present invention, and those skilled in the art can make various similar representations without departing from the spirit and scope of the present invention.
Claims (8)
1. The utility model provides a compound lithium cell positive pole of high energy storage efficiency which characterized in that: the positive electrode active slurry comprises a positive electrode current collector and positive electrode active slurry coated on the surface of the positive electrode current collector; the positive active slurry comprises the following components in percentage by mass (94-98): (0.5 to 3): (1-3) the modified silicate composite material, a conductive agent and a binder; the positive current collector is a modified carbon nanotube/carbon nanofiber composite membrane; the modified carbon nano tube is prepared by the following method: respectively putting n-butyl chloride and methylimidazole into toluene, wherein the volume ratio of the n-butyl chloride to the toluene is 3: 2, the volume ratio of the methylimidazole to the toluene is 3: 2, stirring and reacting at 70-90 ℃ for 24-36h, cooling the system to-2-0 ℃, freezing for 2-4h, separating a lower-layer product, washing the lower-layer product with toluene and cyclohexane respectively, and then carrying out pressure distillation to obtain imidazole chloride ionic liquid; mixing a mixture of 1: 1 imidazolium chloride ionic liquid and FeCl 3Stirring and reacting for 10-18h under the protection of nitrogen to obtain magnetic ionic liquid; and then adding the purified carbon nano tube into the magnetic ionic liquid, wherein the mass-volume ratio of the multi-wall carbon nano tube to the magnetic ionic liquid is 2 mg: 1ml, grinding to obtain carbon nanotube gel, centrifuging the carbon nanotube gel to separate out precipitate, washing the precipitate, and vacuum-drying at 60 ℃ for 10-15h to obtain a modified carbon nanotube;
the modified silicate composite material is composed of a silicate active material and a fast ion conductor layer coated on the outer surface of the silicate active materialThe material is Li2Fe x Mn1-x SiO4X is more than 0.4 and less than 0.8; the fast ion conductor layer comprises Li7 La 3 Zr2 O12The thickness of the fast ion conductor layer is 50-1000 nm, and the mass ratio of the silicate active material to the fast ion conductor layer is 1: (0.05-0.3).
2. The positive electrode of the high-energy-storage-efficiency composite lithium battery as claimed in claim 1, wherein the modified silicate composite material is prepared by the following steps:
a. and mixing a lithium source compound, a manganese source compound, an iron source compound salt and tetraethyl orthosilicate according to the molar ratio of Li: fe: mn: SiO 24 2- 2: x: (1-x): 1, putting the mixture into a reactor after accurate weighing, adding a catalyst, fully and uniformly stirring, and reacting for 18-36h at the temperature of 100 ℃ and 150 ℃ in a sealed state to obtain gel;
b. taking out the gel, drying, mixing with a carbon source compound, ball-milling the mixture in a ball mill, and pumping into a spray drying tower for spray drying to obtain a silicate precursor;
c. adding a silicate precursor into a metal ion mixed salt solution, namely a Zr and La metal ion mixed salt solution, dropwise adding a precipitator while stirring, stirring for reacting for 0.5-2h after dropwise adding is finished, separating out a precipitate, washing the precipitate, drying, adding LiOH, grinding, tabletting, heating to 500-900 ℃ by microwave under the protection of inert gas, sintering, and cooling to room temperature along with a furnace to obtain the modified silicate composite material.
3. The positive electrode for a high energy storage efficiency composite lithium battery according to claim 2, wherein: the lithium source compound is lithium acetate, the manganese source compound is manganese acetate, the iron source is iron acetate, and the catalyst is prepared by mixing acetic acid and ethanol in a mass ratio of 1: (20-30) acetic acid-ethanol mixture.
4. The positive electrode for a high energy storage efficiency composite lithium battery according to claim 2 or 3, characterized in that: the carbon source compound is one or a mixture of more than two of glucose, sucrose and polyethylene glycol; the mass ratio of the silicate precursor to the carbon source compound is 1: (0.01-0.2); the ball milling conditions are as follows: ball milling is carried out by adopting a planetary ball mill, deionized water is used as a ball milling medium, the deionized water and the deionized water are mixed for 3 hours at the rotating speed of 400r/min, and the mixture is prepared into homogenate with the mass concentration of 10-25% wt; the spray granulation conditions are as follows: pumping the homogenate into a spray drying tower for granulation, wherein the spray gas is air or nitrogen, the inlet temperature is 200-150 ℃, and the outlet temperature is 120-100 ℃.
5. The positive electrode for a high-energy-storage-efficiency composite lithium battery according to claim 4, wherein: the precipitator is ammonia water with the mass fraction of (10-25)% wt, and the total molar weight ratio of the ammonia water and the two metal ions is NH3·H 2O: (Zr + La) = (1-1.5): 1; the microwave high-temperature sintering conditions are as follows: vacuumizing a microwave high-temperature atmosphere experimental furnace, introducing inert gas, heating to 500-900 ℃ at the speed of 100 ℃/min, and preserving heat for 5-15 min.
6. The positive electrode for a high-energy-storage-efficiency composite lithium battery according to claim 5, wherein: the conductive agent is one of acetylene black, phosphorus flake graphite or carbon nanofibers; the binder is one of polyvinylidene fluoride, styrene butadiene rubber or sodium carboxymethylcellulose.
7. A method for preparing a positive electrode of a high energy storage efficiency composite lithium battery as claimed in any one of claims 1 to 6, comprising the steps of:
step one, preparing a modified carbon nano tube/carbon nano fiber composite membrane: dissolving polyacrylonitrile in dimethyl sulfoxide to form a polyacrylonitrile solution with the mass fraction of 8-12% by weight, and then mixing the polyacrylonitrile solution with the mass ratio of (0.5-2): (3-10) mixing the modified carbon nano tube with a polyacrylonitrile solution, ultrasonically dispersing the mixture into a spinning solution at room temperature, preparing the spinning solution into a nanofiber membrane under the conditions that the environmental temperature is 15-30 ℃, the environmental humidity is 5-70%, a high-voltage electrostatic spraying device is utilized, the voltage of an electrostatic generator is 10kV-20kV, the distance between a metal needle and a filament collector is 12-15cm, the flow rate is 0.5-3mL/h and the strand rotation speed is 500-3000 r/min, transferring the nanofiber membrane into a tube furnace, heating to 150-200 ℃ at the heating rate of 0.2-4 ℃/min and preserving heat for 20-48h under the air atmosphere, heating to 280-380 ℃ at the heating rate of 0.2-4 ℃/min and preserving heat for 3-8h for pre-oxidation treatment, then heating to 700-900 ℃ in nitrogen atmosphere, preserving the heat for 1-3h, and naturally cooling to room temperature under the atmosphere protection to obtain a modified carbon nanotube/carbon nanofiber composite membrane;
step two, preparing positive active slurry: putting the modified silicate composite material, the conductive agent, the binder and a proper amount of N-methyl pyrrolidone into a stirring kettle according to the proportion, controlling the stirring speed to be 100-4000 r/min, stirring for 30min to obtain a mixture, and then dispersing the mixture by using a high-speed dispersion machine, wherein the dispersion speed is 3000-4000r/min, and the dispersion viscosity reaches 500-6000mPa & s to obtain the anode active slurry;
step three, preparing the positive plate: the positive active slurry is processed according to the conditions of 152-2Coating the surface density of the carbon nano tube/carbon nano fiber composite membrane on the modified carbon nano tube/carbon nano fiber composite membrane, drying the carbon nano tube/carbon nano fiber composite membrane according to the proportion of 3.3 to 3.9g/mm3 And rolling the compacted density to obtain the positive plate.
8. A lithium battery, characterized in that: the high energy storage efficiency composite lithium battery positive electrode, the negative electrode, the separator and the electrolyte according to any one of claims 1 to 7.
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