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 is increasedThe long effect is more pronounced than in supercapacitors. 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 provides a lithium ion capacitor negative electrode plate with an Ag transition layer, and a preparation method and application thereof, so that a hybrid lithium ion capacitor has lower initial internal resistance, and can still keep lower internal resistance and better electrical property to continue working after being recycled.
In order to achieve the above object, in a first aspect, the present invention provides a lithium ion capacitor negative electrode plate with an Ag transition layer, including a negative electrode current collector, both sides of the negative electrode current collector are respectively covered with Ag transition layers formed by magnetron sputtering, and surfaces of the Ag transition layers facing away from the negative electrode current collector are respectively covered with a lithium titanate coating.
Preferably, the thicknesses of the Ag transition layers are respectively 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: and respectively carrying out magnetron sputtering on two sides of the negative current collector to form Ag transition layers, and then respectively coating lithium titanate coatings to obtain the negative pole piece of the lithium ion capacitor. Preferably, the process conditions of the magnetron sputtering are as follows: bombarding Ag target with Ar gas under the vacuum of 6.0-7.0X 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.
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.
Compared with the prior art, the invention has the beneficial effects that:
(1) the invention modifies the current collector of the negative pole piece, and forms a thin Ag transition layer on the two sides of the current collector respectively, so that the contact internal resistance of the lithium titanate coating and the current collector of the negative pole piece is greatly reduced, and the reduction of the whole internal resistance of the lithium ion capacitor is realized.
(2) In the working process of the hybrid lithium ion supercapacitor applying the negative pole piece, the Ag transition layer and the lithium titanate coating can generate electrochemical reaction, and Ag ions can guide Li ions in the electrolyte to be embedded into crystal lattices of the lithium titanate coating in an accelerated manner, so that the damage of the lithium titanate crystal lattices in the embedding process is reduced, and the effect of stabilizing a 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. Therefore, the existence of the Ag transition layer can ensure that 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 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.
(3) When the obtained lithium ion capacitor pole piece is used for preparing a lithium ion capacitor, full-automatic impregnation sealing and assembling of the positive pole piece and the negative pole piece in a drying room can be selected, and compared with the impregnation sealing and assembling in a traditional glove box, the efficiency is improved by more than 10 times.
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 larger initial internal resistance of a hybrid lithium ion capacitor, severe increase of internal resistance and reduction of electrical property after recycling, the invention provides a lithium ion capacitor negative electrode plate with an Ag transition layer. The current collector of the negative pole piece is modified, the Ag transition layers are formed on the two surfaces of the current collector respectively, so that the contact internal resistance of the lithium titanate coating and the current collector is greatly reduced, the reduction of the overall internal resistance of the hybrid lithium ion capacitor is realized, in the working process of the hybrid lithium ion capacitor, the Ag transition layers and the lithium titanate coating can generate electrochemical reaction, Ag ions can guide Li ions in electrolyte to be accelerated to be embedded into crystal lattices of the lithium titanate coating, the damage of the embedding process to the lithium titanate crystal lattices is reduced, and the effect of stabilizing a crystal lattice framework is achieved; in the process of lithium removal, the buffer effect is achieved, and the stability of a lithium titanate lattice frame is also protected, so that the existence of the Ag transition layer can ensure that the crystal structure of a lithium titanate coating is very stable, the volume is hardly changed, the increase of internal resistance and the capacity attenuation are effectively avoided, and therefore, the low contact internal resistance and the good electrical property can be kept to work continuously after the lithium titanate coating is recycled (such as being recycled for five thousand times), and the service life of a lithium ion capacitor product is greatly prolonged.
The thickness of the Ag transition layer is preferably 100-200 nm. In some embodiments, the Ag transition layer has a thickness of 100nm, 120nm, 150nm, 180nm, or 200 nm. The thicknesses of the two Ag transition layers can 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.
The preparation method of the negative pole piece of the lithium ion capacitor is preferable,the method comprises the following steps: and performing magnetron sputtering on two sides of the negative current collector to form Ag transition layers, and then respectively coating lithium titanate coatings to obtain the negative pole piece of the lithium ion capacitor. In some embodiments, rolling is performed after applying the lithium titanate coating layer. The magnetron sputtering can select Ar gas to bombard the Ag target. 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.
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. 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. The negative pole piece comprises a negative current collector, two surfaces of the negative current collector are covered with Ag transition layers, and the surfaces of the Ag transition layers, which are far away from the negative current collector, are respectively covered with lithium titanate coatings; 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 positive and negative pole pieces comprises the following steps:
negative pole piece: forming an Ag transition layer on the two sides of the aluminum foil current collector by magnetron sputtering respectively, wherein the process conditions of the magnetron sputtering are as follows: the diameter of the Ag target material is 60mm, the thickness is 3mm, and the purity is 5N; bombarding the Ag target material with Ar gas, the back vacuum is 6.0 multiplied by 10-4Pa, the cavity pressure is 0.4Pa, the Ar gas flow is 20sccm, heating is not carried out, the target base distance is 3cm, the sputtering power is 60W, and the sputtering time is 5min, so that an Ag transition layer with the thickness of 100nm is obtained; and coating the composite lithium titanate slurry on the surface of the aluminum foil current collector with the Ag transition layer, baking to prepare a negative electrode plate, and rolling until the thickness of the negative electrode plate is 140 microns.
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 499 and 503 mOmega, after 5000 times of circulation, the capacity retention rate is up to more than 65 percent, the internal resistance is only about 697 and 704 mOmega, and the rising rate is only 40 percent. 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 schematic structural diagram of the lithium ion capacitor pole piece is shown in fig. 3. The negative pole piece comprises a current collector, wherein both surfaces of the negative pole current collector are covered with Ag transition layers, and the surfaces of the Ag transition layers, which are far away from the negative pole current collector, are respectively covered with lithium titanate coatings; 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: forming an Ag transition layer on the two sides of the aluminum foil current collector by magnetron sputtering respectively, wherein the process conditions of the magnetron sputtering are as follows: the diameter of the Ag target material is 60mm, the thickness is 3mm, and the purity is 5N; bombarding the Ag target material with Ar gas, the back vacuum is 6.5 multiplied by 10-4Pa, the cavity pressure is 0.5Pa, the Ar gas flow is 30sccm, heating is not carried out, the target base distance is 5cm, the sputtering power is 65W, and the sputtering time is 5min, so that an Ag transition layer with the thickness of 150nm is obtained; and coating the composite lithium titanate slurry on the surface of the aluminum foil current collector with the Ag transition layer, baking to prepare a negative electrode plate, and rolling until the thickness of the negative electrode plate is 160 mu m.
Positive pole piece: coating the carbon slurry on an aluminum foil current collector without a transition layer, baking to prepare a positive pole piece, obtaining a positive pole piece and a negative pole piece, and then 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 118-. 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, Ag transition layers are arranged on two sides of the negative current collector, and the surfaces of the Ag 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: respectively carrying out magnetron sputtering on the Ag transition layer on the two sides of the aluminum foil current collector, wherein the magnetron sputtering process conditions are as follows: the diameter of the Ag target material is 60mm, the thickness is 3mm, and the purity is 5N; bombarding the Ag target material with Ar gas, the back vacuum is 7.0 multiplied by 10-4Pa, the cavity pressure is 0.6Pa, the Ar gas flow is 40sccm, heating is not carried out, the target base distance is 7cm, the sputtering power is 70W, and the sputtering time is 5min, so that an Ag transition layer with the thickness of 200nm is obtained; and coating the composite lithium titanate slurry on the surface of the aluminum foil current collector with the Ag transition layer, baking to prepare a negative electrode plate, and rolling until the thickness of the negative electrode plate 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 35-37m omega, after 5000 times of circulation, the capacity retention rate is up to more than 60%, the internal resistance is only about 52-55m omega, and the rising rate is only 50%. 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 positive and negative pole pieces of the lithium ion capacitor comprises the following steps:
(1) coating the composite lithium titanate slurry on the two sides of the aluminum foil current collector without the transition layer, baking to prepare a negative electrode plate, coating the carbon slurry on the two sides of 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 rolling the obtained positive and negative electrode plates by a roller press until the thickness of the positive electrode plate is 200 mu m and the thickness of the negative electrode plate is 140 mu m to obtain the positive and negative electrode plates of the lithium ion capacitor.
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 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 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.
Comparative example 2
The comparative example provides a lithium ion capacitor electrode sheet, wherein the negative electrode sheet is the same as that in example 1; the positive pole piece comprises a positive current collector, the two surfaces of the positive current collector are covered with Ag transition layers, and the surfaces of the Ag transition layers, which are far away from the positive current collector, are respectively covered with carbon coatings. The positive and negative current collectors are aluminum foil current collectors.
The preparation method of the positive and negative pole pieces of the lithium ion capacitor comprises the following steps:
(1) respectively carrying out magnetron sputtering on an Ag transition layer on two side surfaces of an aluminum foil current collector, wherein the magnetron sputtering process conditions are as follows: the diameter of the Ag target material is 60mm, the thickness is 3mm, and the purity is 5N; bombarding the Ag target material by using Ar gas, wherein the back bottom vacuum is 6.0Pa, the cavity pressure is 0.4Pa, the Ar gas flow is 20sccm, the heating is not carried out, the target base distance is 5cm, the sputtering power is 60W, and the sputtering time is 5min, so that Ag transition layers with the thicknesses of 100nm are obtained;
(2) coating the composite lithium titanate slurry on a current collector with two sides containing an Ag transition layer, and baking to prepare a negative pole piece; coating the carbon paste on a current collector with two surfaces containing an Ag transition layer, baking to prepare a positive pole piece, and obtaining a positive pole piece and a negative pole piece;
(3) 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 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 and comparison of the initial internal resistance and the internal resistance after the cycle on the obtained lithium ion capacitor, setting 5 groups of parallel tests, and obtaining a test result shown in figure 8.
From the test results, it was determined that the initial internal resistance was 480-. After 5000 times of circulation, the capacity retention rate is low and is only 0.8F, because the positive pole piece is provided with the Ag transition layer, the leakage current is large, the negative lithium titanate crystal structure is influenced, and the crystal collapse is caused. After 5000 cycles, the internal resistance of the lithium titanate reaches 2600m omega, which is also caused by the damage of leakage current to the structure of the negative lithium titanate. Therefore, unlike the super capacitor, the positive electrode of the hybrid lithium ion super capacitor should not have an Ag transition layer, so as to avoid the damage of the negative electrode structure.
The composite lithium titanate slurry, the carbon slurry and the aluminum foil current collector adopted in each of the above examples and comparative examples are the same.
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.