Method of preparing anode of lithium ion batteries or electrode plate of supercapacitor

Abstract

A method of preparing an anode of lithium ion batteries or an electrode plate of a supercapacitor. The method includes admixing a terpene resin-based aqueous binder. The terpene resin-based aqueous binder includes a terpene resin emulsion including between 20 and 80 wt. % of a terpene resin, and the terpene resin emulsion has a viscosity of between 2000 and 10000 mPa.Math.s.

Claims

1. A method of preparing an anode of lithium ion batteries or an electrode plate of a supercapacitor, the anode or the electrode plate comprising a terpene resin-based aqueous binder, an active material, and a conductive agent; wherein: the terpene resin-based aqueous binder comprises an additive and a terpene resin emulsion comprising between 20 wt. % and 80 wt. % of a terpene resin, the terpene resin emulsion has a viscosity of between 2000 mPa.Math.s and 10000 mPa.Math.s; and a mass ratio of the active material to the conductive agent to a total mass of the terpene resin and the additive is 70-95: 1-20: 4-10; the method comprising: 1) uniformly mixing, stirring and dispersing the active material and the conductive agent to yield a first mixture; 2) adding the additive to deionized water to yield an aqueous solution, and adding the aqueous solution to the first mixture obtained in 1) and uniformly stirring, to yield a second mixture; 3) adding the terpene resin emulsion to the second mixture obtained in 2), and adding deionized water and uniformly stirring, to yield an electrode slurry; and 4) coating the electrode slurry obtained in 3) on a Cu foil or an Al foil, fully drying, to yield the anode of lithium ion batteries or the electrode plate of a supercapacitor.

2. The method of claim 1, wherein a solid content of the electrode slurry obtained in 3) is between 30% and 45%, and a viscosity thereof is between 2500 mPa.Math.s and 4000 mPa.Math.s.

3. The method of claim 1, wherein the coated Cu foil or Al foil is dried under vacuum for between 24 hours and 48 hours at a constant temperature of between 80 C. and 90 C.

4. The method of claim 1, wherein the active material is graphite, activated carbon, silicon, or lithium titanate, and the conductive agent is a carbonaceous conducting material selected from the group consisting of acetylene black, super P, vapor-grown carbon fiber (VGCF), and carbon nanotubes (CNTs).

5. The method of claim 1, wherein the additive is carboxylated cellulose or a salt thereof.

6. The method of claim 1, wherein the additive is carboxymethyl cellulose.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows cycle performance curves of a graphite electrode and a comparison electrode in Example 1 at the charge-discharge current density of 0.2 C;

(2) FIG. 2 shows cycle performance curves of a graphite electrode and a comparison electrode in Example 2 at different charge-discharge current densities;

(3) FIG. 3 shows impedance test results of a graphite electrode and a comparison electrode in Example 3 at the rate of 0.2 C;

(4) FIG. 4 shows impedance test results of a graphite electrode and a comparison electrode in Example 4 at the rate of 1 C;

(5) FIG. 5 shows an initial charge-discharge curve of a silicon electrode in Example 5 at the charge-discharge current density of 0.1 C;

(6) FIG. 6 shows a cycle performance curve of a lithium titanate electrode in Example 6 at the charge-discharge rate of 0.5 C;

(7) FIG. 7 shows a cycle stability curve of an activated carbon supercapacitor in Example 7 at the charge-discharge current density of 200 mA/g; and

(8) FIG. 8 shows the peeling strength of TX and PVDF films.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(9) For further illustrating the invention, experiments detailing a terpene resin-based aqueous binder and methods of preparing and using the same are described below. It should be noted that the following examples are intended to describe and not to limit the invention.

(10) A method of preparing an anode of lithium ion batteries or an electrode plate of a supercapacitor, comprises:

(11) 1) uniformly mixing, stirring and dispersing an active material and a conductive agent to yield a first mixture;

(12) 2) adding an additive to deionized water to yield an aqueous solution, and adding the aqueous solution to the first mixture obtained in 1) and uniformly stirring, to yield a second mixture;

(13) 3) adding terpene resin emulsion to the second mixture obtained in 2), followed by addition of appropriate deionized water and uniformly stirring, to yield an electrode slurry;

(14) 4) coating the electrode slurry obtained in 3) on a Cu foil or an Al foil, fully drying, to yield the anode of lithium ion batteries or the electrode plate of a supercapacitor; and

(15) 5) cutting and weighing the electrode plate, and employing the obtained electrode plate to prepare a battery.

(16) The terpene resin emulsion involved in the following examples is purchased from Guangzhou Songbao Chemical Co., LTD, and the specific type is water-based terpene resin tackifying emulsion No. 8218. In the examples, TX is an abbreviation of terpene resin.

(17) The peeling strength of TX and PVDF films is measured as follows.

(18) The terpene resin emulsion was coated on an Al foil and fully dried under vacuum at 120 C. for 24 h, to yield a homogeneous film. PVDF film was prepared in the similar way, except that it was dissolved in NMP. The polymer films were respectively attached to 3 M adhesive tape, and the peel strength of the sample was measured with a high-precision micromechanical test system (Delaminator Adhesion Test System; Shenzhen Kaiqiangli, KQL, China). The adhesive tape was removed by peeling at an angle of 180 at a constant displacement rate of 50 mm/min.

(19) Results and Analysis

(20) FIG. 8 shows the peel strength of TX and PVDF films. As shown in the figure, TX has twice peel strength as high as PVDF, indicating better adhesive properties than PVDF.

EXAMPLE 1

(21) 1. Preparation of a Test Electrode

(22) The mass ratio of graphite to a conductive agent to a total mass of the terpene resin and an additive of a terpene resin-based aqueous binder was 95:1:4. Graphite and the conductive agent were uniformly mixed, stirred and dispersed to yield a first mixture. The additive was added to deionized water to yield an aqueous solution, which was added to the first mixture and uniformly stirred to yield a second mixture. Thereafter, the terpene resin emulsion was mixed with the second mixture (TX/CMC=3/2), followed by the addition of appropriate deionized water and uniformly stirring, to yield an electrode slurry (with a solid content of 45%). The electrode slurry was coated on a Cu foil and fully dried under vacuum at 90 C., to yield an anode plate of lithium ion batteries. The anode plate was cut, weighed, and then installed in a No. 2025 battery case in a glove box, with a lithium plate as a counter electrode, polyethylene membrane as a separator, 1 M LiPF.sub.6 EC/DMC/DEC (v/v/v=1/1/1) as an electrolyte, a battery was assembled and performed with a galvanostatic charge-discharge test.

(23) 2. Preparation of a Comparison Electrode

(24) Employ SBR/CMC as a binder and follow the above method to prepare a comparison electrode.

(25) 3. Electrochemical Test

(26) The charge-discharge cycle stability of the test electrode and the comparison electrode are measured.

(27) 4. Results and Analysis

(28) FIG. 1 shows the cycle performance curves of the test electrode and the comparison electrode at the charge-discharge current density of 0.2 C, and Table. 2 shows the corresponding specific capacity and initial charge-discharge efficiency. As shown in the table, the initial efficiency of the graphite electrode with TX/CMC as binder is 92.2%, which is higher than the initial efficiency (91.5%) of the graphite electrode with SBR/CMC with binder. In addition, after 50 cycles, the specific capacity of the graphite electrode with TX/CMC as a binder has almost no decrease, while the specific capacity of the graphite electrode with SBR/CMC as binder decreases greatly.

(29) TABLE-US-00001 TABLE 2 Initial charge-discharge efficiency of graphite electrodes prepared with different binders Binder Initial charge-discharge efficiency of graphite electrode TX/CMC 92.2 SBR/CMC 91.5%

EXAMPLE 2

(30) 1. Preparation of a Test Electrode

(31) The example is basically the same as that in Example 1 except that the test electrode adopts TX/CMC as a binder, and TX/CMC=4:1.

(32) 2. Preparation of a Comparison Electrode

(33) The same as that in Example 1.

(34) 3. Electrochemical Test

(35) The charge-discharge cycle stability and rate performance of the test electrode and the comparison electrode are measured.

(36) 4. Results and Analysis

(37) FIG. 2 shows the cycle performance curves of the test electrode and the comparison electrode at different charge-discharge current densities. As shown in the figure, the graphite electrode with TX/CMC as binder exhibits good high rate performance. When the rate is higher than 0.5 C, the performance of the graphite electrode with TX/CMC as binder is far higher than that with SBR/CMC as a binder. When the rate is 1 C, the specific capacity of the graphite electrode with TX/CMC as a binder is 339 mAh/g, which is significantly higher than that of the graphite electrode with SBR/CMC as a binder (329 mAh/g).

EXAMPLE 3

(38) 1. Preparation of a Test Electrode

(39) The example is basically the same as that in Example 1 except that the test electrode adopts TX/CMC as a binder, and TX/CMC=100:1.

(40) 2. Preparation of a Comparison Electrode

(41) The same as that in Example 1.

(42) 3. Electrochemical Test

(43) After three charge-discharge cycles, the impedance of the test electrode and the comparison electrode was measured.

(44) 4. Results and Analysis

(45) FIG. 3 shows the impedance test results of the test electrode and the comparison electrode with TX/CMC and SBR/CMC as binders, respectively, at the rate of 0.2 C after three charge-discharge cycles. The results show that, the impedance of the graphite electrode with TX/CMC as a binder is relatively smaller than that of the graphite electrode with SBR/CMC as a binder.

EXAMPLE 4

(46) 1. Preparation of a Test Electrode

(47) The example is basically the same as that in Example 1 except that the test electrode adopts TX/CMC as a binder, and TX/CMC=1:100.

(48) 2. Preparation of a Comparison Electrode

(49) The same as that in Example 1.

(50) 3. Electrochemical Test

(51) After five charge-discharge cycles, the impedance of the test electrode and the comparison electrode was measured.

(52) 4. Results and Analysis

(53) FIG. 4 shows the impedance test results of the test electrode and the comparison electrode with TX/CMC and SBR/CMC as binders, respectively, at the rate of 1 C after five charge-discharge cycles. The results show that, the impedance of the graphite electrode with TX/CMC as a binder is relatively smaller than that of the graphite electrode with SBR/CMC as a binder.

EXAMPLE 5

(54) 1. Preparation of a Test Electrode

(55) The test electrode also adopted the terpene resin emulsion as a binder, and silicon (Si) as an active material. The mass ratio of silicon to a conductive agent to a total mass of the terpene resin and carboxymethyl cellulose of a terpene resin-based aqueous binder was 70:20:10. Silicon and the conductive agent were uniformly mixed, stirred and dispersed to yield a first mixture. Carboxymethyl cellulose was added to deionized water to yield an aqueous solution, which was added to the first mixture and uniformly stirred to yield a second mixture. Thereafter, the terpene resin emulsion was mixed with the second mixture (TX/CMC=3/2), followed by the addition of appropriate deionized water and uniformly stirring, to yield an electrode slurry (with a solid content of 30%). The electrode slurry was coated on a Cu foil and fully dried, to yield a silicon anode plate. The anode plate was cut, weighed, and then installed in a No. 2025 battery case in a glove box, with a lithium plate as a counter electrode, polyethylene membrane as a separator, 1 M LiPF.sub.6 EC/DMC/DEC (v/v/v=1/1/1) as an electrolyte, a battery was assembled and performed with a galvanostatic charge-discharge test.

(56) 3. Electrochemical Test

(57) The charge-discharge cycle stability of the test electrode was measured.

(58) 4. Results and Analysis

(59) FIG. 5 shows the initial charge-discharge curve of the silicon electrode at the charge-discharge current density of 0.1 C, the initial efficiency is 80%, and the initial specific capacity is 1800 mAh/g.

EXAMPLE 6

(60) 1. Preparation of a Test Electrode

(61) The test electrode also adopted the terpene resin emulsion as a binder, and lithium titanate (LTO) as an active material. The mass ratio of lithium titanate to a conductive agent to a total mass of the terpene resin and carboxymethyl cellulose of a terpene resin-based aqueous binder was 80:10:10. Lithium titanate and the conductive agent were uniformly mixed, stirred and dispersed to yield a first mixture. Carboxymethyl cellulose was added to deionized water to yield an aqueous solution, which was added to the first mixture and uniformly stirred to yield a second mixture. Thereafter, the terpene resin emulsion was mixed with the second mixture (TX/CMC=3/2), followed by the addition of appropriate deionized water and uniformly stirring, to yield an electrode slurry (with a solid content of 40%). The electrode slurry was coated on an Al foil and fully dried, to yield a lithium titanate anode plate. The anode plate was cut, weighed, and then installed in a No. 2025 battery case in a glove box, with a lithium plate as a counter electrode, polyethylene membrane as a separator, 1 M LiPF.sub.6 EC/DMC/DEC (v/v/v=1/1/1) as an electrolyte, a battery was assembled and performed with a galvanostatic charge-discharge test.

(62) 3. Electrochemical Test

(63) The charge-discharge cycle stability of the test electrode was measured.

(64) 4. Results and Analysis

(65) FIG. 6 shows the cycle stability of the lithium titanate electrode at the charge-discharge rate of 0.5 C. The initial efficiency is 84%, and after 60 cycles, the specific capacity retention percentage reaches 99%.

EXAMPLE 7

(66) 1. Preparation of a Test Electrode

(67) The test electrode also adopted the terpene resin emulsion as a binder, and activated carbon (C) as an active material. The mass ratio of activated carbon to a conductive agent to a total mass of the terpene resin and carboxymethyl cellulose of a terpene resin-based aqueous binder was 85:10:5. Activated carbon and the conductive agent were uniformly mixed, stirred and dispersed to yield a first mixture. Carboxymethyl cellulose was added to deionized water to yield an aqueous solution, which was added to the first mixture and uniformly stirred to yield a second mixture. Thereafter, the terpene resin emulsion was mixed with the second mixture (TX/CMC=3/2), followed by the addition of appropriate deionized water and uniformly stirring, to yield an electrode slurry (with a solid content of 40%). The electrode slurry was coated on an Al foil and fully dried, to yield an activated carbon anode plate. The anode plate was cut, weighed, and installed in a button cell case along with a separator, followed by dropwise addition of an electrolyte and sealing, whereby yielding a symmetrical activated carbon supercapacitor. The cycle stability of the supercapacitor was tested.

(68) 3. Electrochemical Test

(69) The charge-discharge cycle stability of the test electrode was measured at the current density of 200 mA/g.

(70) 4. Results and Analysis

(71) FIG. 7 shows the cycle stability curve of the activated carbon supercapacitor with TX/CMC as a binder at the charge-discharge current density of 200 mA/g and a voltage of 0-2.5 V. The initial specific capacitance is 110 F/g, and after 200 cycles, the specific capacity retention percentage reaches 96.9%, which means, the supercapacitor has good cycle stability.

(72) While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.