CN107732137B - Preparation method of lithium titanate negative electrode - Google Patents
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Abstract
The invention relates to a preparation method of a lithium titanate cathode, and belongs to the technical field of new energy storage devices. The preparation method comprises the following steps: s1, drying lithium titanate, weighing the dried lithium titanate, a conductive agent and a binder according to mass fractions of 63-90%, 0-7% and 10-30%, and then colliding and mixing uniformly by high-speed air flow; s2, forming the negative electrode of the mixture on a vertical rolling machine at 100-150 ℃, and then rolling the mixture on a horizontal rolling machine at 100-150 ℃ to prepare a lithium titanate film; s3, pasting the lithium titanate film on a current collector coated with a conductive adhesive layer in advance, and then rolling on a horizontal rolling machine at the temperature of 100-150 ℃ to obtain the lithium titanate cathode. The invention adopts a dry method cathode preparation process technology and realizes the preparation of the anhydrous lithium titanate cathode by means of a binder high-temperature forming mode.
Description
Technical Field
The invention relates to a preparation method of a lithium titanate cathode, and belongs to the technical field of new energy storage devices.
Background
With the rapid development of the national energy storage and energy conservation and new energy public transportation industries, the new energy industry taking a novel energy storage element as a core becomes the post industry of various national policies such as national thirteen-five planning, industrial high-base engineering, one-road-taking and the like. Among many energy storage elements, a new energy storage device using lithium titanate as a negative energy storage material has been developed particularly rapidly because of the following reasons: lithium titanate (Li)4Ti5O12) The material has the outstanding advantages of high safety, high power (10-30C rapid charge and discharge), long cycle service life (the number of use times is more than 2 ten thousand), and the like. At present, the research and application of the energy storage device become important components of the high-efficiency and energy-saving energy storage devices.
But on the other hand Ti due to the lithium titanate itself4+During charging and discharging, the element is easy to catalyze organic solvents (such as propylene carbonate, ethyl carbonate and the like) in the electrolyte, and the influence of the moisture content in the element can directly influence the decomposition of the solvent in the electrolyte. The electrolyte in the electrolyte can generate a separation-melting-type reaction with water in lithium titanate to generate gas, the higher the moisture content is, the more gas is generated by the lithium titanate cathode, and finally, the rapid gas expansion phenomenon occurs in the lithium titanate battery or the lithium titanate hybrid capacitor. For the above reasons, in the preparation process of the conventional negative electrode of the lithium titanate battery or the lithium titanate hybrid capacitor, an organic solvent (nitrogen methyl pyrrolidone, NMP) is often used as a solvent, and polyvinylidene fluoride (PVDF) is used as a binder to prepare the negative electrode. For example, patent application with publication number CN 105470454 discloses a preparation method of a lithium titanate negative electrode plate, which comprises the following steps: mixing 87-94%, 3-8% and 2-7% of lithium titanate, a binder and a conductive agent, adding NMP (N-methyl pyrrolidone) which is 1-1.5 times of the total mass of the lithium titanate, the binder and the conductive agent to obtain slurry, uniformly coating the slurry on a current collector, drying and rolling to obtain the lithium titanate negative electrode piece. However, the preparation process needs a large amount of organic solvent (NMP), which not only easily causes environmental pollution, but also inevitably contacts moisture in the preparation process due to the high hygroscopicity of NMP, so that the lithium titanate negative electrode always has the influence of too high moisture content in the preparation process, and finally, the obtained battery or hybrid capacitor has the defects of swelling, too fast performance attenuation and the like in the high-temperature and long-time recycling process.
Disclosure of Invention
The invention aims to provide a preparation method of a lithium titanate negative electrode, aiming at the problems in the prior art. The preparation method avoids the defects of the use of a large amount of organic solvents and the introduction of trace moisture content in the traditional lithium titanate negative electrode preparation process.
In order to achieve the purpose, the invention adopts the following technical scheme: a preparation method of a lithium titanate negative electrode comprises the following steps:
s1, drying lithium titanate, weighing the dried lithium titanate, a conductive agent and a binder according to mass fractions of 63-90%, 0-7% and 10-30%, and then colliding and mixing uniformly by high-speed air flow;
s2, forming the negative electrode of the mixture on a vertical rolling machine at 100-150 ℃, and then rolling the mixture on a horizontal rolling machine at 100-150 ℃ to prepare a lithium titanate film;
s3, pasting the lithium titanate film on a current collector coated with a conductive adhesive layer in advance, and then rolling on a horizontal rolling machine at the temperature of 100-150 ℃ to obtain the lithium titanate cathode.
In the prior art, a wet method is mainly used for preparing the lithium titanate negative electrode, as mentioned above, a large amount of NMP solvent is used in the wet method preparation process, and water is inevitably brought to the lithium titanate negative electrode while the environment is polluted, so that the final service life of a battery or a capacitor is influenced. The preparation process of the cathode made of other materials can also use a dry method in addition to a wet method, as disclosed in the invention patent application with the publication number of CN 106848312: the modified porous graphene, the conductive agent and the adhesive are mixed according to the mass percentage (75-93): (2-10): (5-15) uniformly mixing, and rolling to form the graphene carbon film, wherein the rolling pressure is 100-300 MPa, the rolling comprises vertical rolling and horizontal rolling, then the graphene carbon film and a copper foil current collector are adhered together through a conductive adhesive, and the modified porous graphene negative electrode plate can be obtained after heating and curing. However, due to the particularity of the lithium titanate material, if a common dry process is used, the adhesion between the lithium titanate material and a current collector is poor, and the capacity and the cycle performance of a final product are affected. Therefore, the inventor researches a novel method suitable for dry preparation of lithium titanate negative electrodes, which is different from dry preparation of other negative electrodes, the lithium titanate, the conductive agent and the binder are mixed according to a proper mass fraction, the mixture is rolled by a vertical rolling machine and a horizontal rolling machine at a high temperature of 100-150 ℃, and after the mixture is stuck on a current collector, the current collector is continuously rolled by a vertical horizontal rolling machine at a high temperature of 100-150 ℃ to prepare the lithium titanate negative electrode. The high temperature of 100-150 ℃ used in the invention can prevent moisture infiltration in the preparation process and enhance the adhesion of the lithium titanate material and the current collector.
Preferably, the drying treatment in the step S1 is vacuum drying treatment of lithium titanate at 100-150 ℃ for 12-24 h. The lithium titanate is removed moisture to the maximum extent, and the adverse effect of the moisture on the battery or the capacitor is relieved.
Preferably, the high-speed air flow collision mixing is carried out in a high-speed air flow pulverizer with the rotating speed of 3000-6000 rpm for 1-4 h. The mixing speed and mixing time used in the invention are far greater than those of dry mixing in the prior art, and the mixture cannot be uniformly mixed at the ordinary dry mixing speed and time, so that the later lithium titanate film pasting effect is influenced.
Preferably, the lithium titanate is nano lithium titanate, micron spherical lithium titanate, carbon-coated lithium titanate or a graphene/lithium titanate composite material. The type of lithium titanate can be selected according to actual product requirements.
Preferably, the conductive agent is acetylene black, a graphene/carbon black composite or a graphene/carbon nanotube/carbon black composite conductive agent.
Preferably, the binder is one or more of Polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), Styrene Butadiene Rubber (SBR), polyvinylpyrrolidone (PVP), polyvinyl butyral (PVB). Preferably, the binder is a mixture of PTFE and SBR in a mass fraction of 75-86% and 14-25%. The invention adopts the adhesive PTFE and SBR to be matched for use, forms a point-line type bonding structure system, further improves the use effect of the adhesive and reduces the use amount of the adhesive.
Preferably, the thickness of the lithium titanate film in the step S2 is 30-80 μm. The thickness of the lithium titanate film layer determines the electrochemical performance of the battery or the capacitor, the thickness of the lithium titanate film is too large, the adhesion between the lithium titanate film and the current collector is poor, the phenomena of material falling, foil leakage, low surface density and the like are easy to occur, and the thickness of the lithium titanate film is too small, so that the components of the electrode material coated on the surface of the current collector are too few, and the capacity of the battery or the capacitor is influenced.
Preferably, in the step S3, the lithium titanate film is adhered to the current collector at a speed of 3-5 m/min. The pasting speed is too fast or too slow, air bubbles are easily generated between the lithium titanate film and the current collector, the adhesiveness of the lithium titanate film and the current collector is influenced,
preferably, the current collector in the S3 step is an aluminum foil, a copper foil, or a nickel foil.
The preparation of the lithium titanate cathode adopts a dry-method electrode preparation process technology, realizes the preparation of the anhydrous lithium titanate cathode by means of a binder high-temperature forming mode, and realizes the preparation of the lithium titanate cathode with long service life and low gas production. The implementation of the preparation method avoids the defects of the use of a large amount of organic solvents and the introduction of trace moisture content in the traditional lithium titanate negative electrode preparation process, thoroughly avoids the problem of environmental pollution in the preparation process of the lithium titanate energy storage device, and provides a brand-new solution for long-life and flatulence-free lithium titanate batteries or hybrid capacitors. In addition, the method has simple process, easy control and obvious large-scale application prospect.
Drawings
Fig. 1 shows a dry lithium titanate negative electrode film prepared in example 1 of the present invention.
Detailed Description
The following is a description of specific embodiments of the present invention with reference to the drawings, and the technical solutions of the present invention will be further described, but the present invention is not limited to these embodiments. The raw materials used in the examples of the present invention are those commonly used in the art, and the methods used in the examples are those conventional in the art, unless otherwise specified.
Example 1
Drying the nano lithium titanate for 12 hours at the temperature of 120 ℃ in vacuum. Then, mixing the dried nano lithium titanate and PTFE in a high-speed airflow pulverizer according to the mass fractions of 90% and 10%, wherein the rotating speed in the mixing process is controlled to be 4000rpm, and the mixing time is 2 hours; rolling the obtained mixture on a vertical rolling machine at 120 ℃, then rolling the obtained lithium titanate film on a horizontal rolling machine at 120 ℃ again, and controlling the roller spacing of two rolling processes to obtain the negative electrode film for the lithium titanate mixed capacitor with the negative electrode film thickness of 30 mu m; as shown in fig. 1, the lithium titanate film is double-faced adhered to a corrosive aluminum foil (the thickness of the aluminum foil is 20 micrometers) coated with a conductive adhesive layer in advance at a rate of 3m/min, and the dry lithium titanate negative electrode is rolled at a temperature of 120 ℃ to obtain the dry lithium titanate negative electrode for the hybrid capacitor.
And assembling the lithium titanate cathode, the activated carbon anode for the hybrid capacitor and the diaphragm into a 300F flexible package capacitor sample in a Z-shaped lamination mode, and testing the cycle life and the flatulence condition of the sample.
Example 2
Drying the nano lithium titanate for 12 hours at the temperature of 120 ℃ in vacuum. Then, mixing the dried nano lithium titanate and PTFE in a high-speed airflow pulverizer according to the mass fraction of 90:10, and controlling the rotating speed of the mixing process to be 4000rpm and the mixing time to be 2 hours; rolling the obtained mixture on a vertical rolling machine at 120 ℃, then rolling the obtained lithium titanate film on a horizontal rolling machine at 120 ℃ again, and controlling the roller spacing of two rolling processes to obtain the negative electrode film for the lithium titanate mixed capacitor with the negative electrode film thickness of 100 mu m; and (3) adhering the lithium titanate film on a corrosion aluminum foil (the thickness of the aluminum foil is 20 microns) coated with a conductive adhesive layer in advance on two sides at the speed of 3m/min, and rolling the dry lithium titanate cathode at the temperature of 120 ℃ to obtain the dry lithium titanate cathode for the hybrid capacitor.
And assembling the lithium titanate cathode, the activated carbon anode for the hybrid capacitor and the diaphragm into a 300F flexible package capacitor sample in a Z-shaped lamination mode, and testing the cycle life and the flatulence condition of the sample.
Example 3
And drying the carbon-coated lithium titanate for 12 hours at 140 ℃ in vacuum. Then, mixing lithium titanate, acetylene black and SBR according to the mass fractions of 70%, 5% and 25% in a high-speed jet mill, controlling the rotating speed of the mixing process to be 6000rpm, and controlling the mixing time to be 2 hours; rolling the obtained mixture on a vertical rolling machine at 140 ℃, then rolling the obtained lithium titanate film on a horizontal rolling machine at 110 ℃ again, and controlling the roller spacing of the two rolling processes to obtain the negative electrode film for the lithium titanate battery with the negative electrode film thickness of 80 mu m; and (3) adhering the lithium titanate membrane on a corrosion aluminum foil (the thickness of the aluminum foil is 20 microns) coated with a conductive adhesive layer in advance on two sides at the speed of 4m/min, and rolling the dry lithium titanate cathode at the temperature of 150 ℃ to obtain the dry lithium titanate cathode for the lithium ion battery.
The lithium titanate negative electrode, the ternary positive electrode for the lithium ion battery and the diaphragm are assembled into a 10Ah flexible package battery in a Z-shaped lamination mode, and the cycle life and the flatulence condition of the battery are tested.
Example 4
And drying the carbon-coated lithium titanate for 12 hours at 140 ℃ in vacuum. Then, mixing lithium titanate, acetylene black and a binder in a high-speed jet mill according to the mass fractions of 70%, 5% and 25%, wherein the binder is a mixture formed by PTFE and SBR in the mass fractions of 78% and 22%, the rotating speed in the mixing process is controlled to be 6000rpm, and the mixing time is 2 hours; rolling the obtained mixture on a vertical rolling machine at 140 ℃, then rolling the obtained lithium titanate film on a horizontal rolling machine at 110 ℃ again, and controlling the roller spacing of the two rolling processes to obtain the negative electrode film for the lithium titanate battery with the negative electrode film thickness of 80 mu m; and (3) adhering the lithium titanate membrane on a corrosion aluminum foil (the thickness of the aluminum foil is 20 microns) coated with a conductive adhesive layer in advance on two sides at the speed of 4m/min, and rolling the dry lithium titanate cathode at the temperature of 150 ℃ to obtain the dry lithium titanate cathode for the lithium ion battery.
The lithium titanate negative electrode, the ternary positive electrode for the lithium ion battery and the diaphragm are assembled into a 10Ah flexible package battery in a Z-shaped lamination mode, and the cycle life and the flatulence condition of the battery are tested.
Example 5
And drying the carbon-coated lithium titanate for 12 hours at 140 ℃ in vacuum. Then, mixing lithium titanate, acetylene black and SBR according to the mass fractions of 70%, 5% and 25% in a high-speed jet mill, controlling the rotating speed of the mixing process to be 6000rpm, and controlling the mixing time to be 2 hours; rolling the obtained mixture on a vertical rolling machine at 140 ℃, then rolling the obtained lithium titanate film on a horizontal rolling machine at 110 ℃ again, and controlling the roller spacing of the two rolling processes to obtain the negative electrode film for the lithium titanate battery with the negative electrode film thickness of 80 mu m; and (3) adhering the lithium titanate membrane on a corrosion aluminum foil (the thickness of the aluminum foil is 20 microns) coated with a conductive adhesive layer in advance on two sides at the speed of 7m/min, and rolling the dry lithium titanate cathode at the temperature of 150 ℃ to obtain the dry lithium titanate cathode for the lithium ion battery.
The lithium titanate negative electrode, the ternary positive electrode for the lithium ion battery and the diaphragm are assembled into a 10Ah flexible package battery in a Z-shaped lamination mode, and the cycle life and the flatulence condition of the battery are tested.
Example 6
Drying the micron spherical lithium titanate for 24 hours at the temperature of 120 ℃ in vacuum. Then mixing lithium titanate, a graphene/carbon black compound and PTFE in a high-speed jet mill according to the mass fractions of 80%, 7% and 13%, wherein the graphene/carbon black compound is a compound formed by graphene and carbon black in a mass ratio of 1:1, the rotating speed in the mixing process is controlled to be 4000rpm, and the mixing time is 1.5 h; rolling the obtained mixture on a vertical rolling machine at 100 ℃, then rolling the obtained lithium titanate film on a horizontal rolling machine at 150 ℃ again, and controlling the roller spacing of two rolling processes to obtain the cathode film for the lithium titanate battery with the cathode film thickness of 60 microns; and (3) adhering the lithium titanate membrane on a corrosion aluminum foil (the thickness of the aluminum foil is 20 microns) coated with a conductive adhesive layer in advance on two sides at the speed of 5m/min, and rolling the dry lithium titanate cathode at the temperature of 150 ℃ to obtain the dry lithium titanate cathode for the lithium ion battery.
And assembling the lithium titanate cathode, the lithium manganate anode for the lithium ion battery and the diaphragm into a 10Ah flexible package battery in a Z-shaped lamination mode, and testing the cycle life and the gas expansion condition of the battery.
The conductive adhesive in the above embodiments is a common conductive adhesive in the prior art.
Comparative example 1
And drying the carbon-coated lithium titanate for 12 hours at 140 ℃ in vacuum. Then, mixing lithium titanate, acetylene black and PTFE in a high-speed jet mill according to the mass fractions of 70%, 5% and 25%, wherein the rotating speed in the mixing process is controlled to be 1000rpm, and the mixing time is 0.5 h; forming a negative electrode film for a lithium titanate battery with the negative electrode film thickness of 80 mu m by vertically rolling and horizontally rolling the obtained mixture under 150 MPa; and (3) adhering the lithium titanate membrane on a corrosion aluminum foil (the thickness of the aluminum foil is 20 microns) coated with a conductive adhesive layer in advance on two sides at the speed of 4m/min, and heating and curing at 160 ℃ for 20 minutes to obtain the dry lithium titanate cathode for the lithium ion battery.
The lithium titanate negative electrode, the ternary positive electrode for the lithium ion battery and the diaphragm are assembled into a 10Ah flexible package battery in a Z-shaped lamination mode, and the cycle life and the flatulence condition of the battery are tested.
Comparative example 2
And drying the carbon-coated lithium titanate for 12 hours at 140 ℃ in vacuum. Then, mixing lithium titanate, acetylene black and SBR according to the mass fractions of 70%, 5% and 25% in a high-speed jet mill, controlling the rotating speed of the mixing process to be 6000rpm, and controlling the mixing time to be 2 hours; rolling the obtained mixture on a vertical rolling machine at 80 ℃, then rolling the obtained lithium titanate film on a horizontal rolling machine at 80 ℃ again, and controlling the roller spacing of the two rolling processes to obtain the negative electrode film for the lithium titanate battery with the negative electrode film thickness of 80 mu m; and (3) adhering the lithium titanate membrane on a corrosion aluminum foil (the thickness of the aluminum foil is 20 microns) coated with a conductive adhesive layer in advance on two sides at the speed of 4m/min, and rolling the dry lithium titanate cathode at the temperature of 80 ℃ to obtain the dry lithium titanate cathode for the lithium ion battery.
The lithium titanate negative electrode, the ternary positive electrode for the lithium ion battery and the diaphragm are assembled into a 10Ah flexible package battery in a Z-shaped lamination mode, and the cycle life and the flatulence condition of the battery are tested.
Comparative example 3
And drying the carbon-coated lithium titanate for 12 hours at 140 ℃ in vacuum. Then, mixing lithium titanate, acetylene black and SBR according to the mass fractions of 70%, 5% and 25% in a high-speed jet mill, controlling the rotating speed of the mixing process to be 6000rpm, and controlling the mixing time to be 2 hours; rolling the obtained mixture on a vertical rolling machine at 170 ℃, then rolling the obtained lithium titanate film on a horizontal rolling machine at 170 ℃ again, and controlling the roller spacing of the two rolling processes to obtain the negative electrode film for the lithium titanate battery with the negative electrode film thickness of 80 mu m; and (3) adhering the lithium titanate membrane on a corrosion aluminum foil (the thickness of the aluminum foil is 20 microns) coated with a conductive adhesive layer in advance on two sides at the speed of 4m/min, and rolling the dry lithium titanate cathode at the temperature of 170 ℃ to obtain the dry lithium titanate cathode for the lithium ion battery.
The lithium titanate negative electrode, the ternary positive electrode for the lithium ion battery and the diaphragm are assembled into a 10Ah flexible package battery in a Z-shaped lamination mode, and the cycle life and the flatulence condition of the battery are tested.
Comparative example 4
Comparative example 4 is different from example 3 in that the mass fractions of lithium titanate, acetylene black and SBR in comparative example 4 are 60%, 7% and 33%, and the rest is the same as example 3 and is not described herein.
Comparative example 5
Comparative example 5 is different from example 3 in that the mixing of lithium titanate, acetylene black and SBR is carried out for 0.5h at 1000rpm, and the rest is the same as example 3 and is not repeated.
TABLE 1 electrochemical performance of capacitors or batteries of examples 1-6 and comparative examples 1-5
Comparative example 1 is a negative electrode prepared by using the conventional dry method, and it can be seen from table 1 that the initial performance and the performance after 10000 cycles of the comparative example 1 are remarkably reduced compared to the examples of the present invention, and the performance of the comparative examples 2 to 5 is also reduced to a different degree compared to the examples.
In addition, the technical scope of the invention is not exhaustive, and new technical solutions formed by equivalent replacement of single or multiple technical features in the embodiment technical solutions are also within the scope of the invention; meanwhile, in all the embodiments of the invention, which are listed or not listed, each parameter in the same embodiment represents only one example (i.e., a feasible solution) of the technical scheme.
The specific embodiments described herein are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the invention as defined in the appended claims.
While the invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.
Claims (5)
1. A preparation method of a lithium titanate negative electrode is characterized by comprising the following steps:
s1, drying lithium titanate, weighing the dried lithium titanate, a conductive agent and a binder according to mass fractions of 63-90%, 0-7% and 10-30%, and then colliding and mixing uniformly by high-speed air flow;
s2, forming the negative electrode of the mixture on a vertical rolling machine at 100-150 ℃, and then rolling the mixture on a horizontal rolling machine at 100-150 ℃ to prepare a lithium titanate film;
s3, pasting a lithium titanate film on a current collector coated with a conductive adhesive layer in advance, and then rolling on a horizontal rolling machine at the temperature of 100-150 ℃ to obtain a lithium titanate cathode;
the binder is a mixture of 75-86% and 14-25% of polytetrafluoroethylene and styrene butadiene rubber in mass fraction;
the thickness of the lithium titanate film in the step S2 is 30-80 μm;
in the step S3, the lithium titanate film is pasted on a current collector at a speed of 3-5 m/min;
the high-speed air flow collision mixing is carried out for 1-4 hours in a high-speed air flow pulverizer with the rotating speed of 3000-6000 rpm.
2. The method for preparing a lithium titanate negative electrode according to claim 1, wherein the drying treatment in the step S1 is vacuum drying treatment of lithium titanate at 100-150 ℃ for 12-24 hours.
3. The method of claim 1 or 2, wherein the lithium titanate is a nano lithium titanate, a micro spherical lithium titanate, a carbon-coated lithium titanate, or a graphene/lithium titanate composite material.
4. The method for preparing a lithium titanate negative electrode according to claim 1, wherein the conductive agent is acetylene black, a graphene/carbon black composite or a graphene/carbon nanotube/carbon black composite conductive agent.
5. The method of claim 1, wherein the current collector in step S3 is an aluminum foil, a copper foil, or a nickel foil.
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| CN105355470A (en) * | 2015-12-15 | 2016-02-24 | 宁波南车新能源科技有限公司 | Preparation method for ultrathin lithium titanate electrode |
| CN106848312A (en) * | 2016-12-27 | 2017-06-13 | 宁波中车新能源科技有限公司 | A kind of modified porous Graphene, modified porous Graphene negative electricity pole piece and preparation method thereof |
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