AU2015100980A4

AU2015100980A4 - A new lithium pre-insertion method for lithium ion capacitors

Info

Publication number: AU2015100980A4
Application number: AU2015100980A
Authority: AU
Inventors: Guansheng Fu; Dianbo Ruan; Fudi Zeng
Original assignee: Ningbo CSR New Energy Technology Co Ltd
Current assignee: Ningbo CRRC New Energy Technology Co Ltd
Priority date: 2014-12-12
Filing date: 2015-07-23
Publication date: 2015-09-17
Anticipated expiration: 2023-07-23
Also published as: WO2016090977A1; CN104681311B; NL2015824A; NL2015824B1; CN104681311A

Abstract

Abstract The present invention relates to a new lithium pre-insertion method for lithium ion capacitors, comprising: (1) assembling a battery cell and immersing the battery cell into an organic solution containing lithium salt; (2) connecting the anode and the cathode to a charge-discharge tester, performing 1 to 100 cycles, each of the cycles including a charge operation followed by a discharge operation as one cycle, so as to complete the lithium pre-insertion for the cathode; and (3) taking out the battery cell after the lithium pre-insertion and putting the same into a cast, injecting with electrolyte and assembling a lithium ion capacitor monomer. The present invention can effectively reduce the expensive manufacturing cost brought by the lithium metal, porous current collectors, etc., improve safety, and simplify process, and is preferable for industrial production.

Description

A new lithium pre-insertion method for lithium ion capacitors Technical Field The present invention relates to the field of lithium ion capacitors, particularly to a new lithium pre-insertion method for lithium ion capacitors. Background Art Lithium ion capacitor is a new representative hybrid energy storage device, which is a "deep-combination" of lithium-ion batteries and electric double layer super capacitors (EDLC), and has the advantages of lithium ion capacitors such as high capacity density and the advantages of super capacitors such as high power density and long life duration, etc. Lithium ion capacitors have a broad prospect of application in military aerospace, green energy and other areas. Conventionally methods of lithium ion capacitor manufacturing normally follow the method described in Chinese Patent CN101138058B, assigned to Fuji Heavy Industries Ltd, which includes the steps of: using lithium metal as a lithium source, using a metal foil with through-holes as a current collector, disposing the lithium metal in a position opposite to the cathode, shorting the lithium metal with the cathode, inserting lithium into the cathode by a potential difference discharging between the lithium metal and the cathode. This method is good at obtaining a large-capacity large-scale power storage device having high energy density and output density and a good charge and discharge characteristic, but still faces the following problems: (1) lithium foils have an extremely active chemical property, thereby imposing a strict environment requirement during the manufacturing of lithium ion capacitors; (2) the dosage amount of lithium needs a precise control, i.e. less dosage amount would be unable to improve the voltage as expected, excess dosage amount would bring the monomers into a highly risk status, causing the monomers with degraded consistency; (3) the manufacturing process for the lithium-ion capacitors is complicated, with a high 1 manufacturing cost for the use of key raw materials such as lithium metal, porous current collectors and the likes. Other prior art process also uses the above-mentioned lithium ion capacitor structure, but does not short the lithium metal with the cathode neither discharge to insert the lithium. Instead, the process connects a charge-discharge tester between the cathode and the lithium metal, injecting the lithium into the carbon cathode material by a discharge cycle or a charge-discharge cycle. This process improves the performance of the lithium-ion capacitor monomers, but still can not solve the technical issues such as safety, manufacturing costs and so on. Chinese Patent CN102385991A discloses a method of manufacturing a lithium ion capacitor and a lithium ion capacitor manufactured using the same. In this invention, the lithium pre-insertion method is depositing a lithium film on one surface of a membrane by vacuum vapor deposition, thereby making the lithium film opposite to the cathode, and then pre-inserting the Li+ in the lithium film into the cathode. Comparing to the method used by Fuji Heavy Industries, this method has the following advantages: (1) Since the lithium film is in direct contact with the cathode to facilitate lithium pre-insertion in the subsequent process, the use of through-holes current collectors is eliminated, which can reduce the internal resistance of the product; (2) This method may easily control the dosage amount of lithium, improving the safety; (3) each level of cathode is in direct contact with the lithium film for lithium insertion, which can greatly short the lithium pre-insertion time. This method is theoretically feasible, but its actual feasibility remains to be verified. A research team leaded by Mr. Jianping Zheng (W.J. Cao, J.P. Zheng, Li-ion capacitors with carbon cathode and hard carbon/stabilized lithium metal powder anode electrodes, Journal of Power Sources, 213( 2012) 180- 185) has attempted to use a nanometer-level lithium metal powder with passivation film on the surface as the lithium source, which is mixed with hard carbon and then proceed by a dry process to form the cathode, with the activated carbon used as the anode and thereby forming a lithium ion capacitor monomer. Compared with the Fuji Heavy Industries structure using lithium metal foils, the lithium ion capacitor of this structure can be manufactured in a dry room, without the need of glove box in a harsh environment, 2 thereby greatly increasing the operability. Summary of Invention In order to resolve the problems relating to the lithium pre-insertion of lithium ion capacitors, for example, expensive manufacturing cost, potential safety risk, and complicated process, we propose a new pre lithium-insertion method for lithium-ion capacitors. The present invention can effectively reduce the expensive manufacturing cost brought by the lithium metal, porous current collectors, etc., improve safety, and simplify process, and is preferable for industrial production. The present invention is implemented by the following technical scheme: To achieve the above object, the present invention provides a lithium pre-insertion method for lithium ion capacitors, including the following steps: (1) sequentially laminating or wounding a cathode, a membrane, an anode and a membrane, and then fastening with tapes to form a battery cell; immersing the battery cell into an organic solution containing lithium salt; (2) connecting the anode and the cathode to a charge-discharge tester, performing 1 to 100 cycles, each of the cycles including a charge operation followed by a discharge operation as one cycle, so as to complete the lithium pre-insertion for the cathode; (3) taking out the battery cell after the lithium pre-insertion and putting the same into a cast, injecting with electrolyte and assembling a lithium ion capacitor monomer. Preferably, the above-mentioned anode current collector may be a foil or mesh made by aluminum, stainless steel, iron, nickel and other metals, the foil may be porous or non-porous. Preferably, the above-mentioned cathode current collector may be a foil or mesh made by copper, stainless steel, iron, nickel and other metals, the foil may be porous or non-porous. Preferably, the above used lithium salt may be one or more of the lithium salt that is soluble dissolved in organic solutions, such as LiPF 6 , LiBF 4 , LiClO 4 , LiAlO 4 , LiOH, Li 2

CO

3 , CH 3 COOLi, LiNO 3 , LiB(C 2 0 4

)

2 , LiP(C 6

H

4 0 2

)

3 , LiPF 3

(C

2

F

5

)

3 , 3 LiN(S0 2

CF

3

)

2 and other lithium salt. Preferably, the organic solution is at least one of the followings: PC, EC, DEC, DMC, DMF, DME, THF, SL. Preferably, the anode and cathode are connected by connecting the anode and cathode through a charge-discharge device. Resistors can be added in series into the circuitry. Alternatively, it can be directly connected without any resistors. Preferably, the battery cell immersed in the lithium salt organic solution is operated in a cycle operation including charging-> discharging or charging -> self-discharging. The charging current and the discharge current are constant current. Specifically, the constant current can be a current value calculated based on the anode mass or cathode mass or cell mass with 0.01C-10C rate. Preferably, the number of the cycles of charge and discharge cycle operation is 1 to 100 times, the maximum charge-cutoff voltage is between 3.6V ~ 4.2V, and the charge-cutoff voltages among the cycles may be the same or not. Preferably, the charging currents among the cycles may be the same or not. The discharging currents among the cycles may be the same or not. After the end of each charging process there may be a constant voltage process. Alternatively, it may not include this constant voltage process. Preferably, the self-discharge time in each cycle is lmin-10h. Besides, the self-discharge time among different cycles may be the same or not. Compared with the prior art, the beneficial effects of the present invention is: (1) Replacing the lithium foil or nanometer-level lithium metal with an organic solution containing lithium salt, which reduces costs. The use of non-porous current collector also significantly reduces the cost; (2) Replacing the lithium foil with an organic solution containing lithium salt also eliminates the need of machining in harsh environment, improving the safety of processing; (3) Connecting the anode and cathode with a charge-discharge tester may short the time of the lithium pre-insertion and increase the effect of lithium pre-insertion; (4) Simplifying the process, this makes it applicable for large-scale industrial manufacturing. 4 DESCRIPTIONS OF DRAWINGS Figure 1 is a schematic diagram of a specific capacity test for a capacitor; In the Figure: the y-coordinate depicts different capacitor specific capacity measured under different discharging currents, and the x-coordinate depicts the discharging currents. DETAILED DESCRIPTION Hereinafter it describes, in connection with the embodiments, more specifically the content of the present invention. It should be understood that the embodiment of the present invention is not limited to the following examples, any modifications or changes to the form of the present invention is made to fall within the scope of the present invention; and examples of the method of the following embodiments, unless otherwise specified, are conventional methods in the art. Embodiment 1 A method of making a lithium ion capacitor comprises the following steps: (1) adhering a slurry having activated carbon as the active material onto the non-porous aluminum foil to form the anode, adhering a slurry having meso carbon microbeads as the active material onto the non-porous copper foil to form the cathode, using a PP/PE/PP triple-layer polymer film to be the membrane, laminating sequentially a membrane, the cathode, a membrane and the anode to form a battery cell and fastening the battery cell with a tape, and welding the anode current collector and the cathode current collector, respectively, with an anode tab and a cathode tab, or with leading-out terminals; (2) After drying, immersing the battery cell into a beaker containing LiPF6-EC/PC/DEC solution; (3) connecting the positive and negative poles of a charge-discharge tester with the anode and the cathode, respectively, constant charging with a current equivalent to 0.1C to 3.8V, and remaining in a constant voltage of 3.8V for lh (one hour), then disconnecting the circuitry for lh to allow the monomer to nature discharge, repeating 5 the above process for three charge/self-discharge pulse cycles; and (4) taking out the battery cell after step (3), and placing it in a aluminum plastic cast, injecting with an electrolyte, and then assembling to be a soft-packaging monomer. Embodiment 2 A method of making a lithium ion capacitor comprises the following steps: (1) adhering a slurry having activated carbon as the active material onto the non-porous aluminum foil to form the anode, adhering a slurry having artificial graphite as the active material onto the non-porous copper foil to form the cathode, using a PP/PE/PP triple-layer polymer film to be the membrane, laminating sequentially a membrane, the cathode, a membrane and the anode to form a battery cell and fastening the battery cell with a tape, and welding the anode current collector and the cathode current collector, respectively, with an anode tab and a cathode tab, or with leading-out terminals; (2) After drying, immersing the battery cell into a beaker containing LiBF4-PC/DMF solution; (3) connecting the positive and negative poles of a charge-discharge tester with the anode and the cathode, respectively, constant charging with a current equivalent to O.1C to 3.8V, then disconnecting the circuitry for 2h to allow the monomer to nature discharge, after two hours, re-connecting the circuitry to constant charge to 3.8V with a current equivalent to 0. 1C, then disconnecting the circuitry to allow the monomer to nature discharge for 2h, repeating the above steps for ten charge/self-discharge pulse cycles; and (4) taking out the battery cell after step (3), and placing it in a square-shaped aluminum cast, injecting with an electrolyte, and then assembling to be a square-shaped monomer. Embodiment 3 A method of making a lithium ion capacitor comprises the following steps: (1) adhering a slurry having activated carbon as the active material onto the 6 non-porous aluminum foil to form the anode, adhering a slurry having hard carbon as the active material onto the non-porous copper foil to form the cathode, using a single-layer PP polymer film to be the membrane, wounding sequentially a membrane, the cathode, a membrane and the anode to form a battery cell and fastening the battery cell with a tape, and welding the anode current collector and the cathode current collector, respectively, with an anode tab and a cathode tab, or with leading-out terminals; (2) After drying, immersing the battery cell into a beaker containing Li 2

CO

3 organic solution; (3) connecting the positive and negative poles of a charge-discharge tester with the anode and the cathode, respectively, constant charging with a current equivalent to 0.2C to 3.8V, then disconnecting the circuitry to allow the monomer to nature discharge for a certain time period, after two hours, re-connecting the circuitry to constant charge to 3.8V with a current equivalent to 0.2C, then disconnecting the circuitry to allow the monomer to nature discharge for a certain time period, repeating the above steps for fifty charge/self-discharge pulse cycles (wherein the self-discharge time for the 1st to 10th cycles is 0.5h, the self-discharge time for the list to 20th cycles is lh, the self-discharge time for the 21st to 30th cycles is 1.5h, the self-discharge time for the 31st to 40th cycles is 2h, the self-discharge time for the 41st to 50th cycles is 3h); and (4) taking out the battery cell after step (3), and placing it in a round-shaped aluminum cast, injecting with an electrolyte, and then assembling to be a round-shaped monomer. Reference Example 1 A method of making a lithium ion capacitor comprises the following steps: (1) adhering a slurry having activated carbon as the active material onto the non-porous aluminum foil to form the anode, adhering a slurry having hard carbon as the active material onto the non-porous copper foil to form the cathode, using a PP/PE/PP triple-layer polymer film to be the membrane, tightly pressing a lithium foil onto a copper foil to form a lithium pole, laminating sequentially a membrane, the 7 anode, a membrane, the cathode, a membrane, the lithium pole and a membrane to form a battery cell and fastening the battery cell with a tape, and welding the anode current collector, the cathode current collector and the lithium current collector, respectively, with an anode tab and a cathode tab, or with leading-out terminals; (2) placing the battery cell in a aluminum plastic cast, injecting with an LiPF6-EC/PC/DEC solution electrolyte, and then assembling to be a soft-packaging monomer; (3) shorting lithium insertion: shorting the cathode and the lithium pole with a conductive line to perform discharge lithium insertion. Reference Example 2 A method of making a lithium ion capacitor comprises the following steps: (1) adhering a slurry having activated carbon as the active material onto the non-porous aluminum foil to form the anode, adhering a slurry having artificial graphite as the active material onto the non-porous copper foil to form the cathode, using a PP/PE/PP triple-layer polymer film to be the membrane, tightly pressing a lithium foil onto a copper foil to form a lithium pole, laminating sequentially a membrane, the anode, a membrane, the cathode, a membrane, the lithium pole and a membrane to form a battery cell and fastening the battery cell with a tape, and welding the anode current collector, the cathode current collector and the lithium current collector, respectively, with an anode tab and a cathode tab, or with leading-out terminals; (2) placing the battery cell in a square-shaped aluminum cast, injecting with an LiBF4-PC/DMF solution electrolyte, and then assembling to be a square-shaped monomer; (3) shorting lithium insertion: shorting the cathode and the lithium pole with a conductive line to perform discharge lithium insertion. Reference Example 3 A method of making a lithium ion capacitor comprises the following steps: (1) adhering a slurry having activated carbon as the active material onto the 8 non-porous aluminum foil to form the anode, adhering a slurry having artificial graphite as the active material onto the non-porous copper foil to form the cathode, using a single-layer PP polymer film to be the membrane, tightly pressing a lithium foil onto a copper foil to form a lithium pole, wounding sequentially a membrane, the anode, a membrane, the cathode, a membrane, the lithium pole and a membrane to form a battery cell and fastening the battery cell with a tape, and welding the anode current collector, the cathode current collector and the lithium current collector, respectively, with an anode tab and a cathode tab, or with leading-out terminals; (2) placing the battery cell in a round-shaped aluminum cast, injecting with an Li 2

CO

3 solution electrolyte, and then assembling to be a round-shaped monomer; (3) shorting lithium insertion: shorting the cathode and the lithium pole with a conductive line to perform discharge lithium insertion. Reference Example 4 Super capacitor FB series, commercially available from NEC-tokin Testing method and results: 1, the Specific Capacity of the capacitor using the LRBT-02 battery performance comprehensive tester, performing a discharge specific capacity test between the Embodiments and Reference Examples respectively under 1C, 5C and 10C. Results are shown in Figure 1. 2, Capacity Retention Rate charging and discharging the Embodiments and Reference Examples by using 1C, 5C and 10C, respectively, and recording the capacity retention rate. Results are shown in Table 1. 3, Initial Lithium Insertion Amount monitoring in real-time the lithium insertion amount for the capacitors by connecting an external charge-discharge tester. Results are shown in Table 2. As shown in Figure 1, the lithium ion capacitor as manufactured by using the method of the present invention achieves a significantly higher specific capacity. Besides, in a high current discharge situation, the decline amount of the specific 9 capacity of the present lithium ion capacitor is smaller than that of the lithium ion capacitor made according to traditional manufacturing methods. Table 1: Charge-discharge Initial After 100 After 500 Current Discharge cycles cycles Capacity (mAh/g) Embodiment 1 1C 48 ±2 98.9±0.3% 97.8±0.4% 5C 47±3 98.3±0.6% 97.5±0.6% 10C 46±3 98.0±0.7% 97.2±0.5% Embodiment 2 1C 48 ±2 99.0±0.2% 97.9±0.5% 5C 48±2 98.5±0.4% 97.7±0.4% 10C 46±3 98.2±0.7% 97.3±0.7% Embodiment 3 1C 49±2 99.1±0.2% 98.0±0.3% 5C 48 ±3 98.6±0.4% 97.8±0.4% 10C 48 ±3 98.3 ±0.8% 97.3 ±0.8% Reference 1 1C 46±2 97.8 ±0.5% 93.7 ±0.9% 5C 45±3 97.3±0.8% 93.4±0.8% 10C 42±5 97.1±1.0% 93.0±0.9% Reference 2 1C 46±2 97.9±0.3% 93.8±1.0% 5C 44±4 97.5 ±0.7% 93.1±1.1% 10C 42±5 97.3 ±0.6% 93.4±0.9% Reference 3 1C 46 ± 3 97.9±0.2% 93.8±0.7% 5C 46±4 97.5 ±0.7% 93.3 ±0.5% 10C 41±8 97.0±0.9% 93.0±0.9% Reference 4 1C 48±2 98.3 ±0.5% 94.5±0.7% 5C 47±4 98.0±0.8% 94.1±0.8% 10C 47±4 97.6±1.2% 93.9±0.9% 10 As seen from Table 1, with respect to the lithium ion capacitor made by shorting the cathode and the lithium pole to perform lithium pre-insertion, the lithium ion capacitor made according to the method of the present invention may achieve a higher capacity retention rate in small number of cycles under each of the different charge and discharge currents. Besides, in large number of charge-discharge cycles, the lithium ion capacitor made according to the method of the present invention may obtain an even higher capacity retention rate, together with stable performance under different currents. The lithium insertion degree will affect the life duration and performance of the capacitors. The results in Table 1 illustrates a conclusion that the lithium pre-insertion method used in the present invention may impose a better effect on the capacitors, that may ensure the basic operations of the capacitors and meanwhile enhances the capacitors to have a more stable long-term performance, which increases the life duration of the capacitors. Table 2: Embodiment 1 Embodiment 2 Embodiment 3 Initial Lithium 112.3 ±5.7 114.2±6.1 114.5 ± 9.4 Insertion Amount (mAh/g) Table 2 shows that, different charge-discharge cycles with different time and current value have little effects on the amount of the initial lithium insertion for capacitors. A smaller current will require a longer charge-discharge time, which may then slightly increase the lithium insertion amount for capacitors, and may increase the life duration and charge-discharge efficiency for capacitors. It will be understood that the term "comprise" and any of its derivatives (eg comprises, comprising) as used in this specification is to be taken to be inclusive of features to which it refers, and is not meant to exclude the presence of any additional features unless otherwise stated or implied. 11 The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement of any form of suggestion that such prior art forms part of the common general knowledge. It will be appreciated by those skilled in the art that the invention is not restricted in its use to the particular application described. Neither is the present invention restricted in its preferred embodiment with regard to the particular elements and/or features described or depicted herein. It will be appreciated that various modifications can be made without departing from the principles of the invention. Therefore, the invention should be understood to include all such modifications in its scope. 12

Claims

1. A new lithium pre-insertion method for lithium ion capacitors, comprising: (1) sequentially laminating or wounding a cathode, a membrane, an anode and a membrane, and then fastening with tapes to form a battery cell; immersing the battery cell into an organic solution containing lithium salt; (2) connecting the anode and the cathode to a charge-discharge tester, performing 1 to 100 cycles, each of the cycles including a charge operation followed by a discharge operation as one cycle, so as to complete the lithium pre-insertion for the cathode; and (3) taking out the battery cell after the lithium pre-insertion and putting the same into a cast, injecting with electrolyte and assembling a lithium ion capacitor monomer.

2. The new lithium pre-insertion method for lithium ion capacitors of claim 1, wherein a current collector in the anode and a current collector in the cathode is a porous or non-porous current collector.

3. The new lithium pre-insertion method for lithium ion capacitors of claim 1, wherein the lithium salt is one or more of the lithium salt that is soluble dissolved in organic solutions, such as LiPF 6 , LiBF 4 , LiClO 4 , LiAlO 4 , LiOH, Li 2 CO 3 , CH 3 COOLi, LiNO 3 , LiB(C 2 0 4 ) 2 , LiP(C 6 H 4 0 2 ) 3 , LiPF 3 (C 2 F 5 ) 3 , LiN(S0 2 CF 3 ) 2 and other lithium salt, wherein the organic solutions is at least one of the followings: PC, EC, DEC, DMC, DMF, DME, THF, SL.

4. The new lithium pre-insertion method for lithium ion capacitors of claim 1, wherein the discharge in the cycle is tester discharge or battery cell self-discharge.

5. The new lithium pre-insertion method for lithium ion capacitors of claim 1, wherein the charge and discharge current are constant current, and wherein the current value is 0.01C-10C. 13

6. The new lithium pre-insertion method for lithium ion capacitors of claim 1, wherein the maximum charge-cutoff voltage is between 3.6V ~ 4.2V.

7. The new lithium pre-insertion method for lithium ion capacitors of anyone of claims 1, 4, 5 and 6, wherein the charging currents and discharging currents, the charging voltage and discharging voltage among the cycles may be the same or not.

8. The new lithium pre-insertion method for lithium ion capacitors of anyone of claims 1, 4, 5 and 7, wherein the discharge time in each cycle is lmin-10h. 14