Has Li4Ti5O12Lithium ion capacitor negative pole piece of transition layer and preparation method and application thereof
阅读说明：本技术 一种具有Li4Ti5O12过渡层的锂离子电容器负极极片及其制备方法与应用 (Has Li4Ti5O12Lithium ion capacitor negative pole piece of transition layer and preparation method and application thereof ) 是由 农剑 胡永清 朱归胜 沓世我 蓝海玲 于 2020-12-23 设计创作，主要内容包括：本发明提供了一种具有Li-4Ti-5O-(12)过渡层的锂离子电容器负极极片及其制备方法与应用,属于电容器领域。本发明对负极极片的集流体进行改性,在其双面上分别形成Li-4Ti-5O-(12)过渡层,因该过渡层与钛酸锂涂层属于同种材料,使得集流体与钛酸锂涂层之间的附着力更好,并使钛酸锂涂层与集流体的接触内阻更小,所得锂离子电容器循环使用后依然能保持较低的接触内阻及较好的电性能继续工作。(The invention provides a lithium battery with Li 4 Ti 5 O 12 A lithium ion capacitor negative pole piece of a transition layer and a preparation method and application thereof belong to the field of capacitors. The invention modifies the current collector of the negative pole piece, and Li is respectively formed on the two surfaces of the current collector 4 Ti 5 O 12 The transition layer and the lithium titanate coating belong to the same material, so that the adhesion between the current collector and the lithium titanate coating is better, the contact internal resistance between the lithium titanate coating and the current collector is smaller, and the obtained lithium ion capacitor can still keep lower contact internal resistance and better electrical property to continue working after being recycled.)
1. Has Li4Ti5O12The lithium ion capacitor negative pole piece with the transition layer is characterized by comprising a negative current collector, wherein two surfaces of the negative current collector are respectively covered with Li formed by magnetron sputtering4Ti5O12Transition layer of said Li4Ti5O12The surfaces of the transition layers facing away from the negative current collector are respectively covered with lithium titanate coatings.
2. The lithium ion capacitor negative electrode sheet of claim 1, wherein the Li is selected from the group consisting of Li, and wherein Li is selected from the group consisting of Li, and wherein Li is selected from the group4Ti5O12The thickness of the transition layer is 100-200 nm.
3. The lithium ion capacitor negative electrode tab of claim 1, wherein the thickness of the negative electrode tab is 140-180 μm.
4. The preparation method of the negative electrode plate of the lithium ion capacitor as claimed in any one of claims 1 to 3, wherein the preparation method comprises the following steps: respectively carrying out magnetron sputtering on two sides of a negative current collector to form Li4Ti5O12And (4) respectively coating a lithium titanate coating on the transition layer to obtain the lithium ion capacitor negative electrode plate.
5. The preparation method according to claim 4, wherein the magnetron sputtering process conditions are as follows: bombardment of Li with Ar gas4Ti5O12The vacuum of the target material at the back is 6.0-7.0 multiplied by 10-4Pa, the cavity pressure is 0.4-0.6Pa, the Ar gas flow is 20-40sccm, the target base distance is 3-7cm, the sputtering power is 60-70W, and the sputtering time is 5 min.
6. The production method according to claim 5, wherein the Li4Ti5O12The target material is prepared by mechanically pressing Li4Ti5O12Prepared by powder mode.
7. A lithium ion capacitor, characterized by comprising the lithium ion capacitor negative electrode sheet according to any one of claims 1 to 3.
8. The lithium ion capacitor according to claim 7, wherein the positive electrode sheet adopted by the lithium ion capacitor comprises a positive electrode current collector, and the two surfaces of the positive electrode current collector are respectively covered with carbon coatings.
9. The lithium ion capacitor of claim 8, wherein the thickness of the positive electrode tab is 200-240 μm.
10. The method for preparing a lithium ion capacitor according to any one of claims 7 to 9, comprising the steps of: after winding the positive and negative pole pieces of the lithium ion capacitor, respectively leading needles on the inner electrode and the outer electrode to form a battery cell, baking, and then carrying out full-automatic impregnation sealing and assembling under the drying condition that the dew point temperature is-55 ℃ to-80 ℃ to obtain the lithium ion capacitor.
Technical Field
The invention belongs to the field of capacitors, and particularly relates to a lithium ion battery with Li4Ti5O12A lithium ion capacitor negative pole piece of a transition layer, a preparation method and application thereof.
Background
The hybrid lithium ion super capacitor is a new and expensive capacitor family, compared with the super capacitor, the monomer voltage of the hybrid lithium ion super capacitor can reach 3.8V, the super capacitor can only reach 2.7-3.0V, the unique performance of the hybrid lithium ion super capacitor is favored by the industry, the hybrid lithium ion super capacitor is a compact energy source with power density and energy density between the super capacitor and a lithium ion battery, and the hybrid lithium ion super capacitor is expected to become a next generation energy storage device with high performance, safety and superiority such as large capacity, rapid large-current charge and discharge, long cycle life and the like by virtue of an electric double layer structure. In terms of the magnitude of capacitance, the capacitance provided by the hybrid lithium ion super capacitor can reach over farad level, the capacitance leap from the micro farad level of the traditional capacitor to the primary quality of the farad level is realized, and the capacitor is a revolutionary significant innovation with milestone significance in the energy technology history.
With the development of the hybrid lithium ion super capacitor, it can provide good performance indexes such as high voltage, high power and high reliability required by various applications, and thus has wide applications in many fields such as power systems, electric vehicles, portable devices, even military affairs and the like. Nowadays, hybrid lithium ion super capacitors have been widely used in the fields of automotive electronics, intelligent industrial control, smart home, 5G base stations, and even in the field of military electromagnetic guns. Aiming at the application in the field, the hybrid lithium ion super capacitor is in the role of a standby power supply or a starting power supply, and the hybrid lithium ion super capacitor is required to have longer service life, larger discharge current and performance under an extreme temperature environment. Aiming at the requirements, a key index technology, namely lower internal resistance, is provided for the hybrid lithium ion super capacitor. The internal resistance directly affects the service life of the hybrid lithium ion super capacitor, the maximum current carried by the hybrid lithium ion super capacitor and the like. The key core technology of the existing domestic preparation technology of the hybrid lithium ion super capacitor is the preparation of a pole piece, which is mainly realized by wet coating, and the technical level of the preparation of the pole piece directly determines whether the internal resistance of the hybrid lithium ion super capacitor is low enough.
The hybrid lithium ion super capacitor is essentially different from the super capacitor in that one half of the electrode is a lithium battery pole piece material, and the other half of the electrode is a carbon-based super-capacity material, so that the internal resistance increasing effect is more obvious than that of the super capacitor. The positive electrode of the hybrid super capacitor is made of active carbon material, the negative electrode is lithium titanate, belonging to a cubic spinel structure (Fd3m), and the hybrid super capacitor is a composite oxide consisting of transition metal titanium and low-potential metal lithium, belonging to AB2X4Series, structure and spinel LiMn2O4Similarly, Fd3m is the space lattice group, and the unit cell parameter a is 0.836nm as shown in FIG. 1. During the operation of the hybrid lithium ion supercapacitor, only 1mol of Li can be inserted into each mole of lithium titanate, oxygen in the lithium titanate occupies a 32e position, titanium occupies a 16c position of 5/6, and the rest part of the lithium ion supercapacitor is occupied by lithium ions. When discharged, the lithium originally located at the 8a position of the tetrahedron and the intercalated lithium migrate to the adjacent 16c position. Therefore, unlike a super capacitor, a hybrid lithium ion super capacitor is composed of a capacitor and a lithium battery, and has high power density and energy density by taking the advantages of both lithium battery and super capacitor.
As described above, since the negative electrode material is lithium titanate, during charging and discharging, electrochemical reaction occurs to insert and remove lithium, while the positive electrode only undergoes physical reaction, i.e. simple physical electrostatic adsorption, as shown in fig. 2. Therefore, during the use process of the hybrid lithium ion supercapacitor, the negative electrode undergoes electrochemical reaction for a long time, so that the crystal lattice changes, the internal resistance is increased, and the capacity is attenuated. At present, the initial internal resistance level and the internal resistance level after recycling of the hybrid lithium ion super capacitor are multiplied (the rising rate reaches 250%) due to the collapse of the lithium titanate crystal lattice of the negative electrode, and the service life and the electrical property of the hybrid lithium ion super capacitor are greatly influenced.
The traditional method for improving the internal resistance generally adopts formula adjustment and rolling shrinkage adjustment. If the formula is adjusted, the capacity performance is influenced, so that the stored energy is less; if the rolling shrinkage is adjusted, the production efficiency is affected because rolling is performed a plurality of times (3 times or more) to reduce the internal resistance. Moreover, the above method does not improve the problem of a drastic increase in internal resistance after recycling.
Therefore, how to make the hybrid lithium ion supercapacitor have lower initial internal resistance and still maintain lower internal resistance and better electrical property after being recycled becomes a difficult problem to be solved urgently.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a lithium battery with Li4Ti5O12The lithium ion capacitor negative pole piece of the transition layer and the preparation method and application thereof enable the hybrid lithium ion capacitor to have lower initial internal resistance and still keep lower internal resistance and better electrical property to continue working after being recycled.
To achieve the above object, in a first aspect, the present invention provides a lithium secondary battery having Li4Ti5O12The lithium ion capacitor negative pole piece of the transition layer comprises a negative current collector, wherein two surfaces of the negative current collector are respectively covered with Li formed by magnetron sputtering4Ti5O12Transition layer of said Li4Ti5O12The surfaces of the transition layers facing away from the negative current collector are respectively covered with lithium titanate coatings.
Preferably, the Li4Ti5O12The thickness of the transition layer is 100-200 nm.
Preferably, the thickness of the negative pole piece is 140-180 μm.
In a second aspect, the invention provides a preparation method of the lithium ion capacitor negative electrode plate, which comprises the following steps: respectively carrying out magnetron sputtering on two sides of a negative current collector to form Li4Ti5O12And (4) respectively coating a lithium titanate coating on the transition layer to obtain the lithium ion capacitor negative electrode plate.
Preferably, theThe process conditions of the magnetron sputtering are as follows: bombardment of Li with Ar gas4Ti5O12The vacuum of the target material at the back is 6.0-7.0 multiplied by 10-4Pa, the cavity pressure is 0.4-0.6Pa, the Ar gas flow is 20-40sccm, the target base distance is 3-7cm, the sputtering power is 60-70W, and the sputtering time is 5 min.
Preferably, the Li4Ti5O12The target material is prepared by mechanically pressing Li4Ti5O12Prepared by powder mode. Li4Ti5O12The target material is a powder target, has low preparation cost, can be repeatedly used, is the same as the lithium titanate coating raw material, and has high goodness of fit.
In a third aspect, the invention provides a lithium ion capacitor comprising the lithium ion capacitor negative electrode plate.
Preferably, the positive electrode plate used in the lithium ion capacitor comprises a positive electrode current collector, and both surfaces of the positive electrode current collector are respectively covered with carbon coatings.
Preferably, the thickness of the positive pole piece is 200-240 μm.
Preferably, the negative electrode current collector and the positive electrode current collector are respectively an aluminum foil current collector or a copper foil current collector.
In a fourth aspect, the invention provides a preparation method of the above lithium ion capacitor, which includes the following steps: after winding the positive and negative pole pieces of the lithium ion capacitor, respectively leading needles on the inner electrode and the outer electrode to form a battery cell, baking, and then carrying out full-automatic impregnation sealing and assembling under the drying condition that the dew point temperature is-55 ℃ to-80 ℃ to obtain the lithium ion capacitor.
To achieve full automation of the impregnation sealing and assembly, it is necessary to perform the impregnation sealing in a drying room (such as a drying workshop) instead of a glove box. Compare and soak in traditional glove box and seal and assemble, soak in the automated production who soaks and assemble in the drying chamber, enable efficiency and obtain the promotion more than 10 times.
Compared with the prior art, the invention has the beneficial effects that:
(1) the invention modifies the current collector to respectively form L on two surfaces of the current collectori4Ti5O12The transition layer and the lithium titanate coating belong to the same material, so that the adhesion between the current collector and the lithium titanate coating is better, the contact internal resistance of the lithium titanate coating and the current collector of the negative pole piece is smaller, and the reduction of the overall internal resistance of the lithium ion capacitor is realized;
(2) in the working process of the hybrid lithium ion super capacitor applying the negative pole piece, Li4Ti5O12The transition layer and the lithium titanate coating can generate electrochemical reaction, Li4Ti5O12The Li ions in the electrolyte can be guided to be embedded into the crystal lattice of the lithium titanate coating in an accelerating manner, so that the damage to the crystal lattice of the lithium titanate in the embedding process is reduced, and the effect of stabilizing the crystal lattice framework is achieved; in the process of lithium removal, the buffer effect is achieved, and the stability of the lithium titanate lattice framework is also protected. Thus, Li4Ti5O12Due to the transition layer, the crystal structure of the lithium titanate coating is very stable, the volume is hardly changed, and the increase of internal resistance and the capacity attenuation are effectively avoided, so that the obtained lithium ion capacitor can still keep low contact internal resistance and good electrical property to continuously work after being recycled (such as being recycled for five thousand times).
(3) Preparation of Li in accordance with the invention4Ti5O12The transition layer can be selected from Li4Ti5O12The powder is used as the raw material, and the preparation cost is lower.
(4) When the obtained lithium ion capacitor pole piece is used for preparing a lithium ion capacitor, full-automatic impregnation sealing and assembling can be performed in a drying room, and compared with the conventional glove box, the efficiency is improved by more than 10 times.
Description of the figures
FIG. 1 is a schematic diagram of a lithium titanate crystal structure;
FIG. 2 is a schematic diagram of the structure and operation of the positive and negative electrodes of the hybrid lithium-ion supercapacitor;
FIG. 3 is a schematic structural diagram of the lithium ion capacitor electrode sheet obtained in examples 1 to 3;
FIG. 4 is a performance effect diagram of the lithium ion capacitor obtained in example 1, (a) a charge-discharge curve, (b) a cycle performance curve, (c) a comparison diagram of the initial internal resistance and the internal resistance after the cycle, (d) a comparison diagram of the efficiency of the full-automatic impregnation assembly in the drying room and the impregnation assembly in the conventional glove box;
FIG. 5 is a performance effect diagram of the lithium ion capacitor obtained in example 2, (a) a charge-discharge curve diagram, (b) a cycle performance curve diagram, (c) a comparison diagram of initial internal resistance and internal resistance after cycle, (d) an efficiency comparison diagram of full-automatic impregnation assembly in a drying room and impregnation assembly in a conventional glove box;
FIG. 6 is a performance effect diagram of the lithium ion capacitor obtained in example 3, (a) a charge-discharge curve, (b) a cycle performance curve, (c) a comparison graph of the initial internal resistance and the internal resistance after the cycle, (d) a comparison graph of the efficiency of the full-automatic impregnation assembly in the drying room and the impregnation assembly in the conventional glove box;
FIG. 7 is a performance effect graph of the lithium ion capacitor obtained in comparative example 1, wherein (a) a cycle performance graph and (b) an initial internal resistance and a comparison graph of internal resistances after cycle are shown.
Detailed Description
To better illustrate the objects, aspects and advantages of the present invention, the present invention will be further described with reference to specific examples.
In order to solve the problems of large initial internal resistance, severe internal resistance increase after recycling and electrical property reduction of a mixed lithium ion capacitor, the invention provides a lithium ion capacitor with Li4Ti5O12The lithium ion capacitor pole piece of the transition layer comprises a pole current collector, wherein the two surfaces of the negative pole current collector are covered with Li formed by magnetron sputtering4Ti5O12Transition layer of Li4Ti5O12The surfaces of the transition layers, which face away from the negative current collector, are covered with lithium titanate coatings. The invention only modifies the current collector of the negative pole piece, and Li which is made of the same material as the lithium titanate coating is respectively formed on the two surfaces of the current collector4Ti5O12The transition layer enables the adhesion between the current collector and the lithium titanate coating to be better, and enables the contact internal resistance between the lithium titanate coating and the current collector to be smaller,realizes the reduction of the integral internal resistance of the hybrid lithium ion capacitor, and in the working process of the hybrid lithium ion capacitor, Li4Ti5O12The transition layer and the lithium titanate coating can generate electrochemical reaction, Li4Ti5O12The Li ions in the electrolyte can be guided to be embedded into the crystal lattice of the lithium titanate coating in an accelerating manner, so that the damage to the crystal lattice of the lithium titanate in the embedding process is reduced, and the effect of stabilizing the crystal lattice framework is achieved; during the process of lithium removal, the buffer effect is achieved, and the stability of the lithium titanate lattice framework is also protected, so that Li4Ti5O12Due to the transition layer, the crystal structure of the lithium titanate coating is very stable, the volume is hardly changed, and the increase of internal resistance and the capacity attenuation are effectively avoided, so that the obtained lithium ion capacitor can still keep lower contact internal resistance and better electrical property to continue working after being recycled (such as being recycled for five thousand times), and the service life of the lithium ion capacitor product is greatly prolonged.
Preferably Li4Ti5O12The thickness of the transition layer is 100-200 nm. In some embodiments, Li4Ti5O12The transition layer has a thickness of 100nm, 120nm, 150nm, 180nm, or 200 nm. Two layers of Li4Ti5O12The thickness of the transition layer may be the same or different.
The thickness of the negative pole piece is preferably 140-180 mu m. In some embodiments, the negative electrode tab has a thickness of 140nm, 150nm, 160nm, 170nm, or 180 nm. The thicknesses of the two lithium titanate coatings on the negative electrode plate can be the same or different, and are usually selected to be the same.
Preferably, the negative electrode current collector is an aluminum foil current collector or a copper foil current collector. Wherein, the aluminum foil current collector can be selected from a corrosion aluminum foil current collector, a porous aluminum foil current collector and the like; the copper foil current collector may be selected from a corrosion copper foil current collector, a porous copper foil current collector, and the like.
Preferably, the preparation method of the negative electrode plate of the lithium ion capacitor comprises the following steps: performing magnetron sputtering on two sides of a negative current collector to form Li4Ti5O12A transition layer is coated with a lithium titanate coating respectively to obtain lithium ionAnd (4) a container negative pole piece. Optionally adopting Ar gas to bombard Li in magnetron sputtering4Ti5O12A target material. In some embodiments, the backing vacuum is 6.0 to 7.0X 10-4Pa, the cavity pressure is 0.4-0.6Pa, the Ar gas flow is 20-40sccm, the target base distance is 3-7cm, the sputtering power is 60-70W, and the sputtering time is 5 min.
Preferably Li4Ti5O12The target material is prepared by mechanically pressing Li4Ti5O12Prepared by powder mode. Thus, Li4Ti5O12The target material is a powder target, has low preparation cost and can be repeatedly used.
Any lithium titanate slurry capable of preparing the cathode of the lithium ion capacitor can be selected to prepare the lithium titanate coating.
The lithium ion capacitor negative pole piece can be used for preparing a lithium ion capacitor. When used to make a hybrid lithium ion capacitor, the positive electrode sheet is typically a carbon-based material. Preferably, the positive electrode plate comprises a positive electrode current collector, and the two surfaces of the positive electrode current collector are respectively coated with carbon coatings. In some embodiments, the carbon coating is applied followed by rolling.
Preferably, the thickness of the positive pole piece is 200-240 μm. In some embodiments, the positive pole piece has a thickness of 200nm, 210nm, 220nm, 230nm, or 240 nm. The thicknesses of the two carbon coatings on the positive pole piece can be the same or different, and are usually selected to be the same.
Any carbon slurry capable of preparing the positive electrode of the lithium ion capacitor can be selected to prepare the carbon coating.
Preferably, the positive electrode current collector is an aluminum foil current collector or a copper foil current collector. Wherein, the aluminum foil current collector can be selected from a corrosion aluminum foil current collector, a porous aluminum foil current collector and the like; the copper foil current collector may be selected from a corrosion copper foil current collector, a porous copper foil current collector, and the like.
The method of making a lithium ion capacitor generally comprises the steps of: and winding the positive and negative pole pieces of the lithium ion capacitor to increase the opposite area, leading pins on the inner electrode and the outer electrode respectively to form a battery cell, baking, and then carrying out impregnation sealing and assembly to obtain the lithium ion capacitor. In some embodiments, the impregnation sealing and the assembly are performed under dry conditions with a dew point temperature of 55 ℃ to-80 ℃. In order to improve the production efficiency, it is preferable to automate the impregnation sealing and the assembly; in order to realize the large-scale automation of the impregnation sealing and the assembly, the impregnation sealing and the assembly treatment are preferably carried out in a drying room, such as a drying workshop, compared with the traditional glove box, the drying room is more beneficial to realizing the large-scale automation operation, and the efficiency can be improved by more than 10 times.
In some embodiments, the positive and negative electrode plates of the lithium ion capacitor are cut to desired specifications before being wound.
Example 1
The embodiment provides a lithium ion capacitor pole piece, and a schematic structural diagram of the lithium ion capacitor pole piece is shown in fig. 3. Wherein, the negative pole piece comprises a current collector, and the two sides of the negative current collector are covered with Li4Ti5O12The surfaces of the transition layers, which are far away from the negative current collector, are respectively covered with a lithium titanate coating; the positive pole piece comprises a positive current collector, and both sides of the positive current collector are covered with carbon coatings. The positive and negative current collectors are all corrosion aluminum foil current collectors.
The preparation method of the lithium ion capacitor pole piece comprises the following steps:
negative pole piece: mixing Li4Ti5O12Putting the powder material into a die with the diameter of 60mm and the thickness of 3mm for mechanical pressing to obtain Li4Ti5O12A target material (the target material is simple to prepare and can be repeatedly used); respectively carrying out magnetron sputtering on Li on two sides of an aluminum foil current collector4Ti5O12The transition layer has the following technological conditions of magnetron sputtering: bombarding the Li with Ar gas4Ti5O12Target material with back vacuum of 6.0X 10-4Pa, cavity pressure of 0.4Pa, Ar gas flow of 20sccm, no heating, target base distance of 3cm, sputtering power of 60W, and sputtering time of 5min to obtain Li with thickness of 100nm4Ti5O12A transition layer; coating composite lithium titanate slurry on Li4Ti5O12Baking the surface of the aluminum foil current collector of the transition layer to prepare a negative pole piece,then rolling to the thickness of the negative pole piece of 140 μm.
Positive pole piece: coating the carbon slurry on an aluminum foil current collector without a transition layer, baking to prepare a positive pole piece, and then rolling until the thickness of the positive pole piece is 200 mu m.
The lithium ion capacitor pole piece of the embodiment is used for preparing a lithium ion capacitor, and specifically comprises the following steps: cutting the positive and negative electrode plates of the lithium ion capacitor into thin strip electrode plates with the width of 7mm by using a cutting machine, calculating, taking the effective length of 53mm as the negative electrode and the effective length of 62mm as the positive electrode, increasing the opposite area of the positive electrode in a winding mode, leading pins on the inner electrode and the outer electrode to form a battery cell, baking, and then carrying out full-automatic impregnation sealing and assembling under the drying condition that the dew point temperature is-55 ℃ to obtain the lithium ion capacitor with the voltage capacity of 3.8V 2F. And performing subsequent charge and discharge tests, cycle performance tests, comparison of initial internal resistance and internal resistance after circulation and comparison of impregnation sealing and assembly efficiency in the traditional glove box on the obtained lithium ion capacitor, and setting 5 groups of parallel tests, wherein the test results are shown in figure 4.
As can be seen from the data in fig. 4, the obtained lithium ion capacitor has good charge and discharge performance, and the curve symmetry between the charge process and the discharge process is good; since the discharge plateau of lithium titanate is 1.5V, the charge-discharge curve starts from 1.5V up to 3.8V; the initial internal resistance is 553-558 mOmega, after 5000 cycles, the capacity retention rate is up to more than 65%, the internal resistance is only about 796-803 mOmega, and the rising rate is only 44%. And, be worth noting that, adopt the full-automatic mode of soaking equipment in dry house to soak and carry out monomer production, soak the equipment contrast in traditional glove box, efficiency obtains promotion more than 10 times, is favorable to mass production very much, can promote efficiency greatly.
Example 2
The embodiment provides a lithium ion capacitor pole piece, and a structural schematic diagram of the lithium ion capacitor pole piece is shown in fig. 1. Wherein, the negative pole piece comprises a negative current collector, and two surfaces of the negative current collector are covered with Li4Ti5O12The surfaces of the transition layers, which are far away from the negative current collector, are respectively covered with a lithium titanate coating; the positive pole piece comprises a positive pole current collector,both sides of the positive current collector are covered with carbon coatings. The positive and negative current collectors are all corrosion aluminum foil current collectors.
The preparation method of the lithium ion capacitor pole piece comprises the following steps:
negative pole piece: mixing Li4Ti5O12Putting the powder material into a die with the diameter of 60mm and the thickness of 3mm for mechanical pressing to obtain Li4Ti5O12A target material (the target material is simple to prepare and can be repeatedly used); respectively forming Li on two sides of aluminum foil current collector by magnetron sputtering4Ti5O12The transition layer has the following technological conditions of magnetron sputtering: bombarding the Li with Ar gas4Ti5O12Target material with back vacuum of 6.5X 10-4Pa, cavity pressure of 0.5Pa, Ar gas flow of 30sccm, no heating, target base distance of 5cm, sputtering power of 65W, and sputtering time of 5min to obtain Li with thickness of 150nm4Ti5O12A transition layer; coating composite lithium titanate slurry on Li4Ti5O12Baking the surface of the aluminum foil current collector of the transition layer to prepare a negative pole piece, and then rolling the negative pole piece until the thickness of the negative pole piece is 160 mu m.
Positive pole piece: and coating the carbon slurry on an aluminum foil current collector without a transition layer, baking to prepare a positive pole piece, and rolling until the thickness of the positive pole piece is 220 mu m.
The lithium ion capacitor pole piece of the embodiment is used for preparing a lithium ion capacitor, and specifically comprises the following steps: cutting the positive and negative electrode plates of the lithium ion capacitor into thin electrode plates with the width of 18mm by using a cutting machine, calculating to obtain a negative electrode with the effective length of 35mm and a positive electrode with the effective length of 39mm, increasing the opposite area of the positive electrode in a winding manner, leading pins on the inner electrode and the outer electrode to form a battery cell, baking, and then carrying out full-automatic impregnation sealing and assembly under the drying condition that the dew point temperature is-67.5 ℃ to obtain the lithium ion capacitor with the voltage capacity of 3.8V 50F. And performing subsequent charge and discharge tests, cycle performance tests, comparison of initial internal resistance and internal resistance after circulation and comparison of impregnation sealing and assembly efficiency in the traditional glove box on the obtained lithium ion capacitor, and setting 5 groups of parallel tests, wherein the test results are shown in figure 5.
As can be seen from the data in fig. 5, the obtained lithium ion capacitor has good charge and discharge performance, and the curve symmetry between the charge process and the discharge process is good; since the discharge plateau of lithium titanate is 1.5V, the charge-discharge curve starts from 1.5V up to 3.8V; the initial internal resistance is 145-148m omega, after 5000 cycles, the capacity retention rate is up to more than 65%, the internal resistance is only about 214-219m omega, and the rising rate is only 48%. And, be worth noting that, adopt the full-automatic mode of soaking equipment in dry house to soak and carry out monomer production, soak the equipment contrast in traditional glove box, efficiency obtains promotion more than 10 times, is favorable to mass production very much, can promote efficiency greatly.
Example 3
The embodiment provides a lithium ion capacitor pole piece, and a schematic structural diagram of the lithium ion capacitor pole piece is shown in fig. 3. The negative pole piece comprises a current collector, and the two sides of the negative current collector are covered with Li4Ti5O12The surfaces of the transition layers, which are far away from the negative current collector, are respectively covered with a lithium titanate coating; the positive pole piece comprises a positive current collector, and both sides of the positive current collector are covered with carbon coatings. The positive and negative current collectors are all corrosion aluminum foil current collectors.
The preparation method of the lithium ion capacitor pole piece comprises the following steps:
negative pole piece: mixing Li4Ti5O12Putting the powder material into a die with the diameter of 60mm and the thickness of 3mm for mechanical pressing to obtain Li4Ti5O12A target material (the target material is simple to prepare and can be repeatedly used); respectively forming Li on two sides of aluminum foil current collector by magnetron sputtering4Ti5O12The transition layer has the following technological conditions of magnetron sputtering: bombarding the Li with Ar gas4Ti5O12Target material with back vacuum of 7.0 × 10-4Pa, cavity pressure of 0.6Pa, Ar gas flow of 40sccm, no heating, target base distance of 7cm, sputtering power of 70W, and sputtering time of 5min to obtain Li with thickness of 200nm4Ti5O12A transition layer; coating composite lithium titanate slurry on Li4Ti5O12Baking the surface of the aluminum foil current collector of the transition layer to prepare a negative pole piece, and then rolling the negative pole piece until the thickness of the negative pole piece is 180 mu m.
Positive pole piece: and coating the carbon slurry on an aluminum foil current collector without a transition layer, baking to prepare a positive pole piece, and rolling until the thickness of the positive pole piece is 240 microns.
The lithium ion capacitor pole piece of the embodiment is used for preparing a lithium ion capacitor, and specifically comprises the following steps: cutting the positive and negative pole pieces of the lithium ion capacitor into thin pole pieces with the width of 30mm by using a cutting machine, calculating to obtain a negative pole with the effective length of 30mm and a positive pole with the effective length of 34mm, increasing the opposite area of the positive pole in a winding mode, leading pins on an inner electrode and an outer electrode to form a battery cell, baking, and then carrying out full-automatic impregnation sealing and assembling under the drying condition that the dew point temperature is-80 ℃ to obtain the lithium ion capacitor with the voltage capacity of 3.8V 100F. And performing subsequent charge and discharge tests, cycle performance tests, comparison of initial internal resistance and internal resistance after circulation and comparison of impregnation sealing and assembly efficiency in a traditional glove box on the obtained lithium ion capacitor, and setting 5 groups of parallel tests, wherein the test results are shown in figure 6.
As can be seen from the data in fig. 6, the obtained lithium ion capacitor has good charge and discharge performance, and the curve symmetry between the charge process and the discharge process is good; since the discharge plateau of lithium titanate is 1.5V, the charge-discharge curve starts from 1.5V up to 3.8V; the initial internal resistance is 53-57m omega, after 5000 times of circulation, the capacity retention rate is up to more than 60%, the internal resistance is only about 81-87m omega, and the rising rate is only 53%. And, be worth noting that, adopt the full-automatic mode of soaking equipment in dry house to soak and carry out monomer production, soak the equipment contrast in traditional glove box, efficiency obtains promotion more than 10 times, is favorable to mass production very much, can promote efficiency greatly.
Comparative example 1
This comparative example provides a lithium ion capacitor electrode sheet, which is the same as example 1 except that the negative electrode sheet does not contain a transition layer. The positive and negative current collectors are all corrosion aluminum foil current collectors.
The preparation method of the lithium ion capacitor pole piece comprises the following steps:
(1) coating the composite lithium titanate slurry on the surface of an aluminum foil current collector without a transition layer, baking to prepare a negative electrode plate, coating the carbon slurry on the aluminum foil current collector without the transition layer, baking to prepare a positive electrode plate, and obtaining a positive electrode plate and a negative electrode plate;
(2) and (3) rolling the obtained positive and negative pole pieces by a roller press until the thickness of the positive pole piece is 200 mu m and the thickness of the negative pole piece is 140 mu m to obtain the lithium ion capacitor pole piece.
The lithium ion capacitor pole piece of the comparative example is used for preparing a lithium ion capacitor, and specifically comprises the following steps: cutting the lithium ion capacitor pole piece into thin pole pieces with the width of 7mm by using a splitting machine, calculating to obtain a negative pole with the effective length of 53mm and a positive pole with the effective length of 62mm, increasing the opposite area of the positive pole in a winding mode, leading pins on an inner electrode and an outer electrode to form a battery cell, baking, and then carrying out full-automatic impregnation sealing and assembling under the drying condition that the dew point temperature is-55 ℃ to obtain the lithium ion capacitor with the voltage capacity of 3.8V 2F. And performing subsequent charge and discharge tests, cycle performance tests and comparison of the initial internal resistance and the internal resistance after the cycle on the obtained lithium ion capacitor, and setting 5 groups of parallel tests, wherein the test results are shown in figure 7.
From the test results, it can be determined that, if a lithium titanate negative electrode without a transition layer and a carbon positive electrode plate are used to form the lithium ion supercapacitor, the initial internal resistance is higher and is as high as 800m Ω, and the internal resistance after circulation is changed more and is as high as 2450m Ω, which is more than 3 times of the initial internal resistance. The capacity retention rate is also low, mainly because of the influence on the internal structure after the internal resistance is increased. After 5000 cycles, the capacity was only 0.6F.
Finally, it should be noted that the above embodiments are only used for illustrating the technical solutions of the present invention and not for limiting the protection scope of the present invention, and although the present invention is described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions can be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.