CN107316992B - Lithium titanate negative electrode material and preparation method thereof - Google Patents
Lithium titanate negative electrode material and preparation method thereof Download PDFInfo
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- 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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Abstract
The invention belongs to the technical field of energy storage materials, and particularly relates to a lithium titanate negative electrode material which comprises a core structure and a shell structure, wherein the core structure is a secondary particle structure and comprises a main electric conduction network with a porous structure and nano lithium titanate primary particles filled in the porous main electric conduction network; an auxiliary electric conduction network is distributed between the main electric conduction network and the primary nano lithium titanate particles and tightly connects the main electric conduction network and the primary nano lithium titanate particles, so that the lithium titanate negative electrode material is ensured to have excellent electrochemical performance.
Description
Technical Field
The invention belongs to the technical field of energy storage materials, and particularly relates to a lithium titanate negative electrode material and a preparation method thereof.
Background
Since birth, lithium ion batteries have revolutionary changes in the field of energy storage due to their advantages of rapid charging and discharging, good low-temperature performance, large specific energy, small self-discharge rate, small volume, light weight, and the like, and are widely used in various portable electronic devices and electric vehicles. However, with the improvement of living standard of people, higher user experience puts higher requirements on the lithium ion battery: faster charging and discharging (such as 5C or even 10C), wider temperature range (such as minus thirty degrees centigrade), and the like; in order to solve the above problems, it is necessary to find a new electrode material having more excellent properties.
The current commercialized lithium ion battery cathode material is mainly graphite, but cannot meet the urgent needs of users due to low charge and discharge speed (generally, the charge and discharge speed is within 1C) and poor low-temperature performance (generally, the use temperature is above-10 ℃); therefore, development of an anode material having a higher charge/discharge rate and used in a wider temperature range is urgently needed. As a negative electrode material of a lithium ion battery, lithium titanate has been attracting attention: the charge and discharge speed can be more than 10 ℃, and the material still can exert more ideal capacity at the temperature of minus 30 ℃, so the material is one of the optimal choices of the new generation of fast-charging anode materials.
However, the lithium titanate material particles have poor conductivity, so that the internal resistance of the battery after the battery is assembled is high, and gas is easily generated in the charging and discharging process, so that the use of the battery is influenced, and the wider application of the battery is limited. In order to solve the problems, the prior art mainly comprises the steps of nano-crystallization of lithium titanate particles, addition of a conductive material with excellent conductive performance into lithium titanate material particles and the like so as to improve the conductive performance of the whole particles of the lithium titanate material; meanwhile, the coating technology is adopted, so that the problem of gas generation in the process of using the material after being prepared into a battery is solved.
However, the lithium titanate particles with the nano structure are easy to agglomerate and have high dispersion difficulty; the commonly used conductive agent materials are generally small in size (nanometer), large in specific surface area and difficult to disperse. However, in order to maximize the conductive effect of the conductive agent and to prepare a lithium titanate secondary particle material with better performance, it is necessary to ensure that the nano lithium titanate particles and the conductive agent are uniformly dispersed. Meanwhile, the contact area between the nano-structure lithium titanate material and the conductive agent is small, and the gap is large, so that the contact resistance is relatively large, the nano-structure lithium titanate material is easy to contact with an electrolyte to generate gas, the prepared battery has high internal resistance, and the gas production rate is larger in the using process, so that the electrochemical performance of the lithium titanate negative electrode material is influenced.
In view of the above, there is a need for a lithium titanate negative electrode material and a preparation method thereof, which can uniformly disperse two materials (nano lithium titanate particles and conductive agent) with high dispersion difficulty, and ensure that the two materials are tightly connected together, thereby preparing a lithium titanate negative electrode material with excellent performance.
Disclosure of Invention
The invention aims to: aiming at the defects of the prior art, the lithium titanate anode material comprises a core structure and a shell structure, wherein the core structure is a secondary particle structure and comprises a main electric conduction network with a porous structure and nano lithium titanate primary particles filled in the pore structure of the main electric conduction network; and an auxiliary electric conduction network is distributed between the main electric conduction network and the primary nano lithium titanate particles and tightly connects the main electric conduction network and the primary nano lithium titanate particles together. Thereby ensuring that the lithium titanate negative electrode material has excellent electrochemical performance.
In order to achieve the purpose, the invention adopts the following technical scheme:
a lithium titanate negative electrode material comprises a core structure and a shell structure, wherein the core structure is a secondary particle structure and comprises a main electric conducting network with a porous structure and nano lithium titanate primary particles filled in the pore structure of the main electric conducting network; an auxiliary electric conduction network is distributed between the main electric conduction network and the primary nano lithium titanate particles, and the auxiliary electric conduction network tightly connects the main electric conduction network and the primary nano lithium titanate particles together. The shell structure is a coating layer commonly used for cathode materials and is mainly obtained by coating and carbonizing materials such as asphalt and the like, so that the invention is not explained in detail.
As an improvement of the lithium titanate negative electrode material, the main power transmission network is at least one of a porous amorphous carbon network structure, a porous hard carbon network structure, an open graphene structure, an open expanded graphite structure and a worm-like graphene structure; the auxiliary electric conduction network is obtained by carbonizing a high polymer material, and the mass of the auxiliary electric conduction network is 0.5% -10% of that of the lithium titanate primary particles.
As an improvement of the lithium titanate negative electrode material, the high polymer material is obtained by in-situ polymerization of high polymer monomers.
As an improvement of the lithium titanate negative electrode material, the auxiliary conducting network further comprises at least one of conductive carbon black, super conductive carbon, ketjen black, carbon nanotubes, graphene and acetylene black; the primary particles further comprise non-nano lithium titanate negative electrode particles; the non-nano lithium titanate negative electrode particles are at least one of natural graphite, artificial graphite, mesocarbon microbeads, soft carbon, hard carbon, petroleum coke, carbon fibers, pyrolytic resin carbon, silicon-based negative electrode materials, tin-based negative electrode materials, transition metal nitrides, tin-based alloys, germanium-based alloys, aluminum-based alloys, antimony-based alloys and magnesium-based alloys.
The invention also discloses a preparation method of the lithium titanate negative electrode material, which is characterized by mainly comprising the following steps:
step 1, precursor preparation: mixing the primary particles and the polymer monomer, and kneading to obtain a precursor in which the polymer monomer is uniformly dispersed on the surface of the nano primary particles;
step 2, preparing a main power guide network structure: preparing a main electric conducting network structure with a porous structure for later use;
step 3, filling: filling the precursor prepared in the step 1 into a main power supply network structure;
step 4, polymerization reaction: placing the product obtained in the step (3) in an environment with an initiator to promote the polymerization of the high molecular monomers dispersed on the surface of the primary particles to obtain a high molecular polymer; the polymer generated at this time can tightly bond the primary particles and the main electric conducting network together;
and 5, coating and carbonizing the product obtained in the step 4 to obtain the finished lithium titanate negative electrode material.
As an improvement of the preparation method of the lithium titanate negative electrode material, in the step 1, the polymer monomer comprises acrylates, methacrylates, styrene, acrylonitrile, methacrylonitrile, polyethylene glycol dimethacrylate, polyethylene glycol diacrylate, divinylbenzene, trimethylolpropane trimethacrylate, methyl methacrylate, N-dimethylacrylamide, N-acryloylmorpholine, methyl acrylate, ethyl acrylate, butyl acrylate, hexyl N-acrylate, cyclohexyl 2-acrylate, dodecyl acrylate, ethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, neopentyl glycol diacrylate, 1, 6-hexanediol diacrylate, tetraethylene glycol diacrylate, tripropylene glycol diacrylate, ethylene glycol diacrylate, propylene glycol diacrylate, ethylene, At least one of ethoxylated pentaerythritol tetraacrylate, propoxylated pentaerythritol acrylate, bis-trihydroxypropane tetraacrylate, pentaerythritol triacrylate, trimethylolpropane trimethacrylate, propoxylated glycerol triacrylate, tris (2-hydroxyethyl) isocyanurate triacrylate trimethylolpropane triacrylate, propoxylated trimethylolpropane triacrylate, ethoxylated trimethylolpropane triacrylate, pentaerythritol tetraacrylate; and 4, at least one of initiator cumene hydroperoxide, tert-butyl hydroperoxide, dicumyl peroxide, di-tert-butyl peroxide, dibenzoyl peroxide, lauroyl peroxide, tert-butyl peroxybenzoate, tert-butyl peroxypivalate, diisopropyl peroxydicarbonate and dicyclohexyl peroxydicarbonate.
As an improvement of the preparation method of the lithium titanate negative electrode material, the nano primary particles in the step 1 contain nano lithium titanate particles; the nano primary particles can also comprise non-nano lithium titanate negative electrode particles, and the non-nano lithium titanate negative electrode particles are at least one of natural graphite, artificial graphite, mesocarbon microbeads, soft carbon, hard carbon, petroleum coke, carbon fibers, pyrolytic resin carbon, silicon-based negative electrode material particles, tin-based negative electrode materials, transition metal nitrides, tin-based alloys, germanium-based alloys, aluminum-based alloys, antimony-based alloys and magnesium-based alloys; during the kneading reaction, a high molecular polymer, a carbon source component, a conductive agent component or/and a solvent component can be added, wherein the high molecular polymer comprises at least one of polymethyl methacrylate (PMMA), polyvinylidene fluoride (PVDF), Styrene Butadiene Rubber (SBR), sodium carboxymethylcellulose (CMC) and polyacrylonitrile, the carbon source component comprises glucose, sucrose, soluble starch, cyclodextrin, furfural, sucrose, glucose, corn starch, tapioca starch, wheat starch, cellulose, polyvinyl alcohol, polyethylene glycol, polyethylene wax, phenolic resin, vinyl pyrrolidone, epoxy resin, polyvinyl chloride, polyalditol, furan resin, urea-formaldehyde resin, polymethyl methacrylate, polyvinylidene fluoride or polyacrylonitrile, petroleum coke, oil-based needle coke and coal-based needle coke, and the conductive agent component comprises at least one of conductive carbon black, conductive carbon, conductive agent component or/and solvent component, At least one of super conductive carbon, Ketjen black, carbon nanotubes, graphene and acetylene black, and at least one of water, alcohols, ketones, alkanes, esters, aromatics, N-methylpyrrolidone, dimethylformamide, diethylformamide, dimethyl sulfoxide and tetrahydrofuran.
As an improvement of the preparation method of the lithium titanate negative electrode material, the kneading process in the step 1 is as follows: kneading the nano primary particles, the surfactant 1, the polymer monomer and the solvent 1 to obtain a mixture 1; kneading the conductive agent component, the surfactant 2 and the solvent 2 to obtain a mixture 2; and blending the mixture 1 and the mixture 2 in a blending mode including at least one of kneading, ball milling, sand milling, high-pressure homogenization and high-speed shearing, and dispersing uniformly to obtain precursor slurry.
As an improvement of the preparation method of the lithium titanate negative electrode material, the preparation process of the main power conducting network structure in the step 2 comprises the following steps:
preparing a porous amorphous carbon network structure and a porous hard carbon network structure: carbonizing after the carbon source component reacts with the foaming agent, directly reacting with a template method and a polymer to obtain a porous structure, and then carbonizing;
preparing an open graphene structure, an open expanded graphite structure and a vermicular graphene structure: the method is characterized in that crystalline flake graphite or microcrystalline graphite (vermicular graphene can be prepared, graphene lamellae are tightly connected together, developed gap structures are distributed among the lamellae to facilitate filling of primary particles, the particle size of the microcrystalline graphene is small, the particle size of the prepared vermicular graphene is about 10 mu m and is matched with the diameter of a final finished product lithium titanate negative electrode particle) is used as a raw material, the degree of oxidation intercalation (mainly moderate degree of oxidation, too low degree of oxidation and incapability of forming a porous structure, and too high degree of oxidation, graphite lamellae are completely stripped in the reduction process and cannot form a connected porous structure) is controlled, and then reduction is carried out, so that the porous structure with openings among the same graphite lamellae connected together and between the lamellae can be obtained.
As an improvement of the preparation method of the lithium titanate negative electrode material, the filling process in the step 3 is as follows:
pretreating the porous main conducting network structure material, wherein the pretreatment comprises surface activation or/and surfactant addition;
before filling, placing the porous main conducting network structure material in a vacuum environment, vacuumizing, removing air in a pore structure, vacating a space for filling a precursor, and then placing the porous main conducting network structure material in precursor slurry to start filling;
in the filling process, pressure is applied to extrude the precursor into the hole; the temperature is increased, and the viscosity of the precursor is reduced; and (5) adding mechanical disturbance and opening the hole opening.
As an improvement of the preparation method of the lithium titanate negative electrode material, the surfactant 1 accounts for 0.01-10% of the mass of the nano lithium titanate, and the solid content of the slurry is not lower than 1%; the surfactant 2 accounts for 0.01-10% of the mass of the conductive agent, and the solid content of the slurry is not lower than 0.5%.
As an improvement of the preparation method of the lithium titanate negative electrode material, the surfactant 1 comprises at least one of a wetting agent, a dispersing agent, a penetrating agent, a solubilizer, a cosolvent and a cosolvent; the solvent 1 is at least one of water, alcohols, ketones, alkanes, esters, aromatics, N-methylpyrrolidone, dimethylformamide, diethylformamide, dimethyl sulfoxide and tetrahydrofuran. The surfactant 2 comprises at least one of a wetting agent, a dispersing agent, a penetrating agent, a solubilizer, a cosolvent and a latent solvent; the solvent 2 is at least one of water, alcohols, ketones, alkanes, esters, aromatics, N-methylpyrrolidone, dimethylformamide, diethylformamide, dimethyl sulfoxide and tetrahydrofuran.
As an improvement of the preparation method of the lithium titanate negative electrode material, an initiator can be added in the step 1, but the condition needs to be specially controlled, so that the initiator does not initiate the polymerization reaction of the monomers before the filling step in the step 3 is completed; after the filling process is completed, the reaction conditions are controlled to promote the polymerization of the monomers to form the polymer.
The invention has the advantages that:
1. the main power conducting network structure can play double roles of electronic conduction and primary particle structure fixation, and can stabilize the macrostructure of lithium titanate material particles while ensuring the excellent electrical conductivity inside the lithium titanate negative electrode material particles;
2. the auxiliary conducting network structure tightly connects the main conducting network structure and the primary particles, increases the contact area between the main conducting network structure and the primary particles, reduces the contact resistance, and ensures that all the primary particles can be effectively and tightly connected with the main conducting network structure to form an electronic channel; thereby ensuring that the electrochemical performance of each primary particle can be fully exerted in the circulating process, and simultaneously reducing the resistance in the material to the maximum extent;
3. in the preparation process, the high molecular monomer with low viscosity and the primary particles are kneaded and dispersed, so that the uniform dispersion of the primary nanoparticles can be ensured, and the high molecular monomer is uniformly distributed on the surfaces of the primary nanoparticles;
4. the precursor with lower viscosity (because the high molecular monomer has low viscosity) is easier to fill into the pore structure of the main conducting network, and the primary particles are all filled in the pores of the porous structure of the main conducting network.
Detailed Description
The present invention and its advantageous effects will be described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.
Comparative example, a lithium titanate secondary particulate material having a particle diameter of 10 μm was prepared;
step 1, mixing: lithium titanate with the particle size of 100nm, conductive carbon black, sodium dodecyl sulfate, polyvinylpyrrolidone and NMP (solid content is 0.5%) are mixed and stirred for 10 hours according to the mass ratio of the lithium titanate, the conductive carbon black, the sodium dodecyl sulfate and the polyvinylpyrrolidone, wherein the mass ratio of the lithium titanate, the conductive carbon black, the sodium dodecyl sulfate and the polyvinylpyrrolidone is 94:4.9:1:0.1, and the slurry is obtained.
Step 2, preparing secondary particles: adjusting spray drying conditions to prepare lithium titanate secondary particles with the particle diameter of 10 mu m; and then coating and carbonizing to obtain the lithium titanate negative electrode material.
Example 1 is different from the comparative example in that the present example includes the following steps:
step 1, precursor preparation: mixing lithium titanate with the particle size of 100nm, methyl methacrylate, sodium dodecyl sulfate (the mass ratio of lithium titanate to methyl methacrylate to sodium dodecyl sulfate is 100:2:1) and NMP, kneading the mixture (the solid content is 10%), revolving the mixture at 30 revolutions per minute and rotating the mixture at 300 revolutions per minute; kneading for 4h to obtain a uniformly dispersed precursor;
step 2, preparing a main electric conducting network structure of the vermicular graphene: selecting microcrystalline graphite as a raw material, adding concentrated sulfuric acid and potassium permanganate to perform oxidation intercalation to obtain graphite oxide with oxygen-containing functional groups accounting for 15% of the whole graphite oxide, and performing heat treatment to obtain vermicular graphene for later use;
step 3, filling: vacuumizing the vermicular graphene obtained in the step 2, then placing the vermicular graphene in the precursor obtained in the step 1, applying pressure to the precursor, simultaneously performing ultrasonic oscillation to enable the precursor to be filled into a vermicular graphene pore structure, and separating to obtain the vermicular graphene filled with the precursor;
step 4, polymerization reaction: and (3) dissolving tert-butyl peroxybenzoate in NMP to obtain a solution, spraying the solution onto the surface of the precursor-filled vermicular graphene obtained in the step (3), and heating to promote the polymerization of methyl methacrylate dispersed on the surface of the primary particles, so that the primary particles and the vermicular graphene sheet layer are tightly bonded together.
And 5, coating and carbonizing the product obtained in the step 4 (and carbonizing the coating layer and the polymer at the same time) to obtain the finished lithium titanate negative electrode material.
Embodiment 2 is different from embodiment 1 in that this embodiment includes the following steps:
step 2, preparing a main electric conducting network structure of the vermicular graphene: selecting microcrystalline graphite as a raw material, adding concentrated sulfuric acid and potassium permanganate to perform oxidation intercalation to obtain graphite oxide with oxygen-containing functional groups accounting for 5% of the whole graphite oxide, and performing heat treatment to obtain vermicular graphene for later use;
the rest is the same as the embodiment 1, and the description is omitted.
Embodiment 3 is different from embodiment 1 in that this embodiment includes the following steps:
step 2, preparing a main electric conducting network structure of the vermicular graphene: selecting microcrystalline graphite as a raw material, adding concentrated sulfuric acid and potassium permanganate to perform oxidation intercalation to obtain graphite oxide with oxygen-containing functional groups accounting for 20% of the whole graphite oxide, and performing heat treatment to obtain vermicular graphene for later use;
the rest is the same as the embodiment 1, and the description is omitted.
Embodiment 4 is different from embodiment 1 in that this embodiment includes the following steps:
step 2, preparing a main electric conducting network structure of the vermicular graphene: selecting microcrystalline graphite as a raw material, adding concentrated sulfuric acid and potassium permanganate to perform oxidation intercalation to obtain graphite oxide with oxygen-containing functional groups accounting for 25% of the whole graphite oxide, and performing heat treatment to obtain vermicular graphene for later use;
the rest is the same as the embodiment 1, and the description is omitted.
Embodiment 5 differs from embodiment 1 in that this embodiment includes the following steps:
step 2, preparing a main electric conducting network structure of the vermicular graphene: selecting microcrystalline graphite as a raw material, adding concentrated sulfuric acid and potassium permanganate to perform oxidation intercalation to obtain graphite oxide with oxygen-containing functional groups accounting for 40% of the whole graphite oxide, and performing heat treatment to obtain vermicular graphene for later use;
the rest is the same as the embodiment 1, and the description is omitted.
Example 6 is different from the comparative example in that the present example includes the following steps:
step 1, precursor preparation: mixing lithium titanate with the particle size of 100nm, N-dimethylacrylamide, isooctyl sodium sulfonate (the mass ratio of lithium titanate to N, N-dimethylacrylamide to isooctyl sodium sulfonate is 100:0.5:1) and ethanol, kneading the mixture (the solid content is 10%), revolving the mixture at 30 revolutions per minute and rotating the mixture at 300 revolutions per minute; kneading for 4h to obtain a uniformly dispersed precursor, adding tert-butyl peroxybenzoate, and uniformly stirring;
step 2, preparing a main conducting network structure of the open expanded graphite: flake graphite is selected as a raw material, concentrated sulfuric acid and potassium permanganate are added for oxidation intercalation to obtain graphite oxide with oxygen-containing functional groups accounting for 20% of the whole graphite oxide, and then the graphite oxide is subjected to heat treatment to obtain open expanded graphite for later use;
step 3, filling: vacuumizing the open expanded graphite obtained in the step (2), then placing the open expanded graphite in the precursor obtained in the step (1), applying pressure to the precursor, simultaneously performing ultrasonic oscillation to enable the precursor to be filled into the open expanded graphite pore structure, and separating to obtain the open expanded graphite filled with the precursor;
step 4, polymerization reaction: heating to promote the polymerization of the methyl methacrylate dispersed on the surface of the primary particles, thereby tightly bonding the primary particles and the open expanded graphite sheet together.
And 5, coating and carbonizing the product obtained in the step 4 (and carbonizing the coating layer and the polymer at the same time) to obtain the finished lithium titanate negative electrode material.
Embodiment 7 is different from embodiment 6 in that this embodiment includes the following steps:
step 1, precursor preparation: mixing lithium titanate with the particle size of 100nm, N-dimethylacrylamide, isooctyl sodium sulfonate (the mass ratio of lithium titanate to N, N-dimethylacrylamide to isooctyl sodium sulfonate is 100:1:1) and ethanol, kneading the mixture (the solid content is 10%), revolving the mixture at 30 revolutions per minute and rotating the mixture at 300 revolutions per minute; kneading for 4h to obtain a uniformly dispersed precursor, adding tert-butyl peroxybenzoate, and uniformly stirring;
the rest is the same as example 6, and the description is omitted.
Embodiment 8 differs from embodiment 6 in that this embodiment includes the following steps:
step 1, precursor preparation: mixing lithium titanate with the particle size of 100nm, N-dimethylacrylamide, isooctyl sodium sulfonate (the mass ratio of lithium titanate to N, N-dimethylacrylamide to isooctyl sodium sulfonate is 100:2:1) and ethanol, kneading the mixture (the solid content is 10%), revolving the mixture at 30 revolutions per minute and rotating the mixture at 300 revolutions per minute; kneading for 4h to obtain a uniformly dispersed precursor, adding tert-butyl peroxybenzoate, and uniformly stirring;
the rest is the same as example 6, and the description is omitted.
Embodiment 9 differs from embodiment 6 in that this embodiment includes the following steps:
step 1, precursor preparation: mixing lithium titanate with the particle size of 100nm, N-dimethylacrylamide, isooctyl sodium sulfonate (the mass ratio of lithium titanate to N, N-dimethylacrylamide to isooctyl sodium sulfonate is 100:5:1) and ethanol, kneading the mixture (the solid content is 10%), revolving the mixture at 30 revolutions per minute and rotating the mixture at 300 revolutions per minute; kneading for 4h to obtain a uniformly dispersed precursor, adding tert-butyl peroxybenzoate, and uniformly stirring;
the rest is the same as example 6, and the description is omitted.
Embodiment 10 differs from embodiment 6 in that this embodiment includes the following steps:
step 1, precursor preparation: mixing lithium titanate with the particle size of 100nm, N-dimethylacrylamide, isooctyl sodium sulfonate (the mass ratio of lithium titanate to N, N-dimethylacrylamide to isooctyl sodium sulfonate is 100:10:1) and ethanol, kneading the mixture (the solid content is 10%), revolving the mixture at 30 revolutions per minute and rotating the mixture at 300 revolutions per minute; kneading for 4h to obtain a uniformly dispersed precursor, adding tert-butyl peroxybenzoate, and uniformly stirring;
the rest is the same as example 6, and the description is omitted.
Embodiment 11 differs from embodiment 1 in that this embodiment includes the following steps:
step 1, precursor preparation: mixing lithium titanate with the particle size of 100nm, methyl methacrylate, sodium dodecyl sulfate (the mass ratio of lithium titanate to methyl methacrylate to sodium dodecyl sulfate is 100:2:1) and NMP, kneading the mixture (the solid content is 2%), revolving the mixture at 30 revolutions per minute and rotating the mixture at 300 revolutions per minute; kneading for 4h to obtain a uniformly dispersed precursor;
the rest is the same as the embodiment 1, and the description is omitted.
Embodiment 12 differs from embodiment 1 in that this embodiment includes the following steps:
step 1, precursor preparation: mixing lithium titanate with the particle size of 100nm, methyl methacrylate, sodium dodecyl sulfate (the mass ratio of lithium titanate to methyl methacrylate to sodium dodecyl sulfate is 100:2:1) and NMP, kneading the mixture (the solid content is 20 percent), revolving the mixture at 30 revolutions per minute and rotating the mixture at 300 revolutions per minute; kneading for 4h to obtain a uniformly dispersed precursor;
the rest is the same as the embodiment 1, and the description is omitted.
Embodiment 13 differs from embodiment 1 in that this embodiment includes the following steps:
step 1, kneading: mixing lithium titanate with the particle size of 100nm, artificial graphite (the mass ratio of lithium titanate to artificial graphite is 9:1), ethylene glycol dimethacrylate, hexadecyl dimethyl allyl ammonium chloride (the mass ratio of lithium titanate to artificial graphite is 100:2:1), and water, kneading the mixture (the solid content is 10%), revolving the mixture at 5 revolutions per minute and rotating the mixture at 10 revolutions per minute; kneading for 8h to obtain a mixture 1; mixing graphene, polyoxyethylene alkylphenol ether (graphene: polyoxyethylene alkylphenol ether ═ 4.9:0.1) and ethanol, kneading (solid content: 4%), revolving at 5 revolutions/min, and rotating at 10 revolutions/min; kneading for 8h to obtain a mixture 2; mixing the mixture 1 and the mixture 2 (the mass ratio of (lithium titanate + artificial graphite): graphene is 100:4.9), kneading continuously, revolving for 5 revolutions per minute, and rotating for 10 revolutions per minute; kneading for 6h to obtain a precursor in which the polymer monomer is uniformly coated on the surface of the primary particles, the polymer monomer and the graphene are uniformly dispersed, and the graphene and the primary particles are uniformly dispersed;
step 2, preparing the amorphous carbon main conducting network structure: and (3) selecting asphalt to mix with a foaming agent, then carrying out foaming reaction and carbonization to obtain the amorphous carbon main conducting network structure.
The rest is the same as the embodiment 1, and the description is omitted.
Assembling the battery: stirring the lithium titanate negative electrode material prepared in comparative example, example 1 to example 13 with a conductive agent, a binder and a solvent to obtain electrode slurry, and then coating the electrode slurry on a current collector to form a negative electrode; assembling the negative electrode, the positive electrode (lithium cobaltate is used as an active substance) and the isolating membrane to obtain a bare cell, and then bagging to perform top side sealing, drying, liquid injection, standing, formation, shaping and degassing to obtain a finished battery.
And (3) testing the material performance:
and (3) gram capacity test: the gram capacity test of the battery cores prepared from the lithium titanate materials in the examples and the comparative examples is carried out in an environment at 25 ℃ according to the following procedures: standing for 3 min; charging to 2.8V at a constant current of 1C and charging to 0.1C at a constant voltage of 2.8V; standing for 3 min; discharging the 1C at constant current to 1.5V to obtain discharge capacity D1; standing for 3 min; charging the 1C to 2.35V by constant current; and (3) standing for 3min, completing the capacity test, and dividing the weight of the lithium titanate material in the cathode electrode piece by D1 to obtain the gram capacity of the cathode, wherein the obtained result is shown in Table 1.
Testing internal resistance: the internal resistance of the battery cells prepared from the lithium titanate materials in the examples and the comparative examples is tested in an environment at 25 ℃ according to the following procedures: standing for 3 min; charging to 2.35V at a constant current of 1C and charging to 0.1C at a constant voltage of 2.35V; standing for 3 min; and testing the DCR value of the battery cell by adopting an electrochemical workstation, wherein the obtained result is shown in table 1.
And (3) rate performance test: the rate capability test of the battery cell prepared from the lithium titanate materials of the examples and the comparative examples is carried out in an environment of 25 ℃ according to the following procedures: standing for 3 min; charging to 2.8V at a constant current of 1C and charging to 0.1C at a constant voltage of 2.8V; standing for 3 min; discharging to 1.5V at constant current of 0.5C to obtain discharge capacity D1; standing for 3 min; charging to 2.8V at a constant current of 1C and charging to 0.1C at a constant voltage of 2.8V; standing for 3 min; discharging at constant current of 5C to 1.5V to obtain discharge capacity D2; standing for 3 min; rate performance testing was then completed and the cell rate performance was D2/D1 x 100% with the results shown in table 1.
And (3) carrying out cycle test on the battery cells prepared from the lithium titanate carbon materials of the examples and the comparative examples in an environment at 25 ℃ according to the following flow: standing for 3 min; charging to 2.8V at a constant current of 1C and charging to 0.1C at a constant voltage of 2.8V; standing for 3 min; discharging the 1C at constant current to 1.5V to obtain discharge capacity D1; standing for 3min, charging to 2.8V at constant current of 1C and charging to 0.1C at constant voltage of 2.8V; standing for 3 min; discharging to 1.5V at constant current at 1C to obtain discharge capacity Di; standing for 3min "and repeating 999 times to obtain D1000, then completing the cycle test, and calculating the capacity retention rate to be D1000/D1 × 100%, and obtaining the results shown in Table 1.
And (3) evaluating the gas production: and observing the appearance of the battery subjected to the cycle test, and judging the gas production amount of the battery. The results are shown in Table 1.
TABLE 1 electrochemical properties of assembled cells made of lithium titanate negative electrode materials prepared in different comparative examples and examples
From table 1, the lithium titanate negative electrode material with excellent performance can be prepared, and the battery core assembled by taking the lithium titanate negative electrode material as the negative electrode active substance has excellent electrochemical performance. Specifically, comparing the comparative example with examples 1 to 5, it can be seen that, with the increase of oxygen-containing functional groups, the performance of the battery assembled from the lithium titanate electrode material tends to be better and worse, because there are too few oxygen-containing functional groups, the prepared porous framework has fewer voids, and the amount of the filled primary particles is less; the prepared porous skeleton has too many gaps due to too many oxygen-containing functional groups, and the conductivity of the skeleton cannot be fully exerted. Comparative example 6 to example 10, it can be seen that as the quality of the subsidiary electric conduction network increases, the battery performance becomes better and then worse, because the content of the subsidiary electric conduction network is too low to sufficiently exert its electric conduction performance; the content is too high, the lithium titanate content in the prepared lithium titanate material secondary particles is low, the porosity is large, the material capacity is low, and gas generation is easier. Comparative examples 1, 11 and 12 show that solid content control is also required in primary particle kneading because of high solid content, uneven dispersion, low solid content, high production cost and influence on filling effect. The present invention has general applicability as can be seen from the various embodiments.
Variations and modifications to the above-described embodiments may also occur to those skilled in the art, which fall within the scope of the invention as disclosed and taught herein. Therefore, the present invention is not limited to the above-mentioned embodiments, and any obvious improvement, replacement or modification made by those skilled in the art based on the present invention is within the protection scope of the present invention. Furthermore, although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
Claims (8)
1. A lithium titanate negative electrode material comprises a core structure and a shell structure, wherein the core structure is a secondary particle structure and comprises a main electric conduction network with a porous structure and nano lithium titanate primary particles filled in the pore structure of the main electric conduction network; an auxiliary electric conduction network is distributed between the main electric conduction network and the primary nano lithium titanate particles and tightly connects the main electric conduction network and the primary nano lithium titanate particles together; the preparation method mainly comprises the following steps:
step 1, precursor preparation: mixing the primary particles and the polymer monomer, and kneading to obtain a precursor in which the polymer monomer is uniformly dispersed on the surface of the nano primary particles;
step 2, preparing a main power guide network structure: preparing a main electric conducting network structure with a porous structure for later use;
step 3, filling: filling the precursor prepared in the step 1 into a main power supply network structure;
step 4, polymerization reaction: placing the product obtained in the step (3) in an environment with an initiator to promote the polymerization of the high molecular monomers dispersed on the surface of the primary particles to obtain a high molecular polymer;
and 5, coating and carbonizing the product obtained in the step 4 to obtain the finished lithium titanate negative electrode material.
2. The lithium titanate negative electrode material of claim 1, wherein the main conductive network is at least one of a porous amorphous carbon network structure, a porous hard carbon network structure, an open graphene structure, an open expanded graphite structure, a vermicular graphene structure; the auxiliary electric conduction network is obtained by carbonizing a high polymer material, and the mass of the auxiliary electric conduction network is 0.5% -10% of that of the lithium titanate primary particles.
3. A lithium titanate negative electrode material according to claim 2, characterized in that the polymer material is obtained by in-situ polymerization of a polymer monomer.
4. The lithium titanate negative electrode material as claimed in claim 1, wherein the secondary conductive network further comprises at least one of conductive carbon black, super conductive carbon, carbon nanotubes, and graphene; the primary particles further comprise non-nano lithium titanate negative electrode particles; the non-nano lithium titanate negative electrode particles are at least one of natural graphite, artificial graphite, mesocarbon microbeads, soft carbon, hard carbon, petroleum coke, carbon fibers, silicon-based negative electrode materials, tin-based negative electrode materials, transition metal nitrides, germanium-based alloys, aluminum-based alloys, antimony-based alloys and magnesium-based alloys.
5. The lithium titanate negative electrode material of claim 1, wherein the polymer monomer of step 1 comprises methacrylate, styrene, acrylonitrile, methacrylonitrile, polyethylene glycol dimethacrylate, polyethylene glycol diacrylate, divinylbenzene, N-dimethylacrylamide, N-acryloylmorpholine, methyl acrylate, ethyl acrylate, butyl acrylate, hexyl N-acrylate, cyclohexyl 2-acrylate, dodecyl acrylate, ethylene glycol dimethacrylate, neopentyl glycol diacrylate, 1, 6-hexanediol diacrylate, tetraethylene glycol diacrylate, tripropylene glycol diacrylate, ethoxylated pentaerythritol tetraacrylate, propoxylated pentaerythritol acrylate, bis-trimethylolpropane tetraacrylate, pentaerythritol triacrylate, styrene, acrylonitrile, methacrylonitrile, polyethylene glycol diacrylate, divinylbenzene, N-dimethylacrylamide, N-acryloylmorpholine, methyl acrylate, ethyl acrylate, butyl acrylate, hexyl N-acrylate, cyclohexyl 2-acrylate, dodecyl acrylate, ethylene glycol dimethacrylate, neopentyl glycol diacrylate, tetraethylene glycol diacrylate, tetra-propylene glycol diacrylate, tripropylene glycol diacrylate, ethoxylated, At least one of trimethylolpropane trimethacrylate, propoxylated glycerol triacrylate, tris (2-hydroxyethyl) isocyanuric acid triacrylate, propoxylated trimethylolpropane triacrylate, ethoxylated trimethylolpropane triacrylate, pentaerythritol tetraacrylate; and 4, the initiator comprises at least one of cumene hydroperoxide, tert-butyl hydroperoxide, dicumyl peroxide, ditert-butyl peroxide, dibenzoyl peroxide, lauroyl peroxide, tert-butyl peroxybenzoate, tert-butyl peroxypivalate, diisopropyl peroxydicarbonate and dicyclohexyl peroxydicarbonate.
6. A lithium titanate negative electrode material as claimed in claim 1, wherein the nano primary particles of step 1 comprise nano lithium titanate particles; the nano primary particles also comprise non-nano lithium titanate negative electrode particles; during kneading reaction, high molecular polymer, carbon source component, conducting agent component and solvent component are also added.
7. A lithium titanate negative electrode material as claimed in claim 1, wherein the kneading process in step 1 is: kneading the nano primary particles, the surfactant 1, the polymer monomer and the solvent 1 to obtain a mixture 1; kneading the conductive agent component, the surfactant 2 and the solvent 2 to obtain a mixture 2; and then blending the mixture 1 and the mixture 2, and uniformly dispersing to obtain precursor slurry.
8. A lithium titanate negative electrode material as claimed in claim 1, wherein the filling process in step 3 is:
pretreating the main conducting network structure material, wherein the pretreatment comprises surface activation or/and surfactant addition;
before filling, the main power transmission network structure material is placed in a vacuum environment and vacuumized, air in the structure is discharged to vacate space for filling a precursor, and then the material is placed in precursor slurry to start filling;
in the filling process, pressure is applied to extrude the precursor into the hole; the temperature is increased, and the viscosity of the precursor is reduced; and (5) adding mechanical disturbance and opening the hole opening.
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| CN110400924B (en) * | 2019-07-29 | 2021-07-20 | 吉林中溢炭素科技有限公司 | Lithium ion power battery negative electrode material and preparation method thereof |
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| CN115000373A (en) * | 2022-06-08 | 2022-09-02 | 万向一二三股份公司 | Preparation method of lithium titanate/graphite composite negative electrode material |
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