POLYMER BINDER WITH HIGH PEEL STRENGTH AND APPLICATION THEREOF IN SECONDARY LITHIUM BATTERY

Abstract

A polymer binder with high peel strength is used in a secondary lithium battery. The polymer binder is obtained by a ring-opening reaction of polyvinylene carbonate by a nucleophile. The polyvinylene carbonate accounts for 10-90% of the total mass of the polymer binder while the nucleophile accounts for 10-90% of the total mass of the polymer binder. The polymer binder has high peel strength (0.02-0.6 N/mm) and high decomposition voltages (4.5-6.0 V), and can be used as an electrode material binder in a secondary lithium battery.

Claims

1. A polymer binder with high peel strength, characterized in that the polymer binder is obtained by a ring-opening reaction of polyvinylene carbonate by a nucleophile, wherein the polyvinylene carbonate accounts for 10-90% of the total mass of the polymer binder; and the nucleophile accounts for 10-90% of the total mass of the polymer binder.

2. The polymer binder with high peel strength according to claim 1, characterized in that the polyvinylene carbonate generates the ring-opening reaction by the nucleophile at −10 to 100° C.

3. The polymer binder with high peel strength according to claim 1, characterized in that the nucleophile is one or more of compounds containing amino, hydroxyl or sulfhydryl functional groups.

4. The polymer binder with high peel strength according to claim 3, characterized in that the nucleophiles is one or more of glucosamine, chitosan, amino acid, ##STR00009## compound, wherein in the above structural formulas of the compounds, the value of n is 1-2, and the value of m is 0-200; X is selected from O, S or NH; Y is selected from PF.sub.6.sup.−, BF.sub.4.sup.−, TFSI.sup.−, FSI.sup.− or CH.sub.3OSO.sub.3.sup.−; R.sub.1 is selected from H, Me or Et.

5. An application of the polymer binder with high peel strength of claim 1, characterized by an application of a polymer binder in preparation of an electrode of a secondary lithium battery.

6. A polymer binder based electrode with high peel strength, characterized in that the electrode comprises electrode active material, the polymer binder with high peel strength of claim 1, and a conductive agent, wherein the mass fraction of the electrode active material in the electrode is 50-95%; the mass fraction of the polymer binder with high peel strength in the electrode is 5-25%; and the mass fraction of the conductive agent in the electrode is 5-25%.

7. A preparation method of the polymer binder base electrode with high peel strength of claim 6, characterized in that the above electrode active material, the polyvinylene carbonate, the nucleophile and the conductive agent are added to an organic solvent, and uniformly mixed at −10 to 100° C. for 2 min to 2 h to obtain uniform slurry; the slurry is coated on a conductive current collector by a doctor blade; the coated current collector is dried in an oven at 60° C. for 20 min to 2 h; and then the coated current collector is dried in a vacuum oven at 60-120° C. for 24 h to obtain an electrode sheet.

8. A preparation method of the polymer binder based electrode with high peel strength of claim 6, characterized in that the polyvinylene carbonate and the nucleophile are dissolved in the organic solvent, and react at −10 to 100° C. for 2 min to 2 h; then, the conductive agent is added and uniformly mixed to obtain uniform slurry; the slurry is coated on the conductive current collector by the doctor blade; the coated current collector is dried in an oven at 60° C. for 20 min to 2 h; and then the coated current collector is dried in a vacuum oven at 60-120° C. for 24 h to obtain an electrode sheet.

9. The preparation method of the polymer binder based electrode with high peel strength according to claim 7, characterized in that the electrode material is cathode active material or anode active material, wherein the cathode active material is one or more of lithium cobalt oxide, lithium iron phosphate, lithium manganese phosphate, lithium manganate, lithium nickel manganese oxide, lithium-rich manganese, ternary material, sulfur, sulfur complex, lithium iron sulfate, lithium ion fluorophosphate, lithium vanadium fluorophosphate, lithium iron fluorophosphate, lithium manganese oxide and conductive polymer; the anode active material is one or more of lithium metal alloy, graphite, hard carbon, molybdenum disulfide, lithium titanate, carbon silicon composite material, carbon germanium composite material, carbon tin composite material, antimony oxide, antimony carbon composite material, tin antimony composite material, lithium titanium oxide and lithium metal nitride; and the conductive agent comprises one or more of graphite, Super P, KS6 graphite, Ketjen Black and acetylene black.

10. The preparation method of the polymer binder based electrode with high peel strength according to claim 7, characterized in that the organic solvent comprises one or more of dichloromethane, chloroform, 1,4-dioxane, dimethoxyethane, acetone, acetonitrile, dimethyl sulfoxide, sulfolane, dimethyl sulfite, diethyl sulfite, tetrahydrofuran, 1,2-dichloroethane, ethyl acetate, N-methylpyrrolidone, N,N-dimethylformamide and N,N-dimethylacetamide, wherein the organic solvent accounts for 10-80% of the total weight of the slurry; the conductive current collector comprises one of copper foil, aluminum foil, titanium foil, stainless steel, carbon paper, foamed nickel, copper mesh and aluminum mesh.

Description

DESCRIPTION OF DRAWINGS

[0031] FIG. 1 shows long cycling performance of a battery assembled with electrodes at room temperature and 0.5 C. in embodiment 1 provided by embodiments of the present invention.

[0032] FIG. 2 shows long cycling performance of a battery assembled with electrodes at room temperature and 0.2 C. in embodiment 2 provided by embodiments of the present invention.

[0033] FIG. 3 is a charging and discharging curve of the 100th cycle of a battery assembled with electrodes at room temperature and 0.1 C. in embodiment 3 provided by embodiments of the present invention.

[0034] FIG. 4 shows long cycling performance of a battery assembled with electrodes at room temperature and 0.1 C in embodiment 4 provided by embodiments of the present invention.

[0035] FIG. 5 shows long cycling performance of a battery assembled with electrodes at room temperature and 0.5 C in embodiment 5 provided by embodiments of the present invention.

[0036] FIG. 6 shows long cycling performance of a battery assembled with electrodes at room temperature and 0.5 C in embodiment 6 provided by embodiments of the present invention.

DETAILED DESCRIPTION

[0037] Detailed description of the present invention is further illustrated below in combination with examples. It shall be noted that the detailed description described herein is only used to illustrate and explain the present invention, not limited to the present invention.

Embodiment 1

[0038] Preparation of polymer binder A1:

[0039] The cathode active material lithium nickel manganese oxide, Super P and binder A1 precursor

##STR00004##

(m=44, which accounted for 60% of the total mass of the polymer) and polyvinylene carbonate (which accounted for 40% of the total mass of the polymer)] were added into a mortar according to a mass ratio of 8:1:1 as slurry; NMP was added (which had a mass ratio of 10% in the slurry); and the mixture was continuously ground and stirred at 30° C. for 20 min to obtain uniform slurry. The above slurry was evenly coated on an aluminum foil, dried in an oven at 60° C. for 2 h, punched into an electrode sheet with appropriate size through a punching machine, dried in the oven at 100° C. for 24 h, and placed in a glove box for later use.

[0040] The electrode obtained above was used as a cathode and graphite was used as an anode for assembling a lithium nickel manganese oxide//graphite full battery. The peel strength of the cathode and long cycling performance of the battery at room temperature and 0.5 C. were detected (see FIG. 1 and Table 1). It can be seen from FIG. 1 that after cycling for 250 cycles under charging and discharging at 0.5 C, the capacity retention was 75%.

TABLE-US-00001 TABLE 1 Cathode active material Polyvinylene Lithium nickel Conductive Anode Peeling carbonate Nucleophile manganese agent active strength Component P1 Nu1 oxide Super P Electrolyte material (N/mm) Mass 4% 6% 80% 10% 1M LiTFSI Graphite 0.20 fraction in DME

[0041] It can be seen from above results that the polymer binder has high peel strength and excellent electrochemical performance, which can be attributed to the abundant polar functional groups and rigid cross-linked skeleton structure of the binder.

Embodiment 2

[0042] Preparation of polymer binder A2:

##STR00005##

(which accounted for 10% of the total mass of the polymer) and polyvinylene carbonate (which accounted for 90% of the total mass of the polymer) were dissolved in acetonitrile (which had a mass ratio of 80% in the slurry), and stirred at 100° C. for 2 h to prepare a solution of polymer binder A2.
Polymer binder A2 based electrodes with high peel strength:

[0043] The cathode active material sulfur, graphite and the acetonitrile solution of the polymer binder A2 obtained above were ground and stirred in the mortar according to a mass ratio of 70:5:25 to obtain uniform slurry. The above slurry was evenly coated on an aluminum foil, and dried in an oven at 60° C. for 0.5 h. The coated aluminum foil was punched into an electrode sheet with appropriate size through a punching machine, and dried in the oven at 80° C. for 12 h.

[0044] The electrode obtained above was used as a cathode and lithium was used as an anode for assembling a sulfur//lithium full battery. The peel strength of sulfur electrodes and the long-term cycling performance of the battery at room temperature and 0.2 C. were detected (see FIG. 2 and Table 2). It can be seen from FIG. 2 that after cycling for 200 cycles under charging and discharging at 0.2 C, the specific discharge capacity still kept at 891 mAh/g and coulombic efficiency was 99%.

TABLE-US-00002 TABLE 2 Cathode Polyvinylene active Conductive Anode Peeling carbonate Nucleophile material agent active strength Component P1 Nu2 Sulfur Graphite Electrolyte material (N/nm) Mass 22.5% 2.5% 70% 5% 1M LiTFSI Lithium 0.02 fraction in DME

[0045] It can be seen from above results that the polymer binder has high peel strength and excellent electrochemical performance because the binder has abundant polar functional groups and three-dimensional rigid cross-linked skeleton structure providing better bonding performance and mechanical properties.

Embodiment 3

[0046] Preparation of polymer binder A3:

[0047] Nu3 with structure

##STR00006##

(which accounted for 33% of the total mass of the polymer) and polyvinylene carbonate (which accounted for 67% of the total mass of the polymer) were dissolved in tetrahydrofuran (which had a mass ratio of 80% in the slurry), and stirred at −10° C. for 2 min to prepare a solution of polymer binder A2.
Polymer binder A3 based electrodes with high peel strength:

[0048] Ternary cathode material, acetylene black and the tetrahydrofuran solution of the polymer binder A3 obtained above were ground and stirred in the mortar according to a mass ratio of 6.5:1.8:1.7 to obtain uniform slurry. The above slurry was evenly coated on an aluminum foil, and dried in an oven at 60° C. for 20 min. The coated aluminum foil was punched into an electrode sheet with appropriate size through a punching machine, dried in a vacuum oven at 60° C. for 12 h and placed in a glove box for later use.

[0049] The electrode obtained above was used as a cathode and lithium was used as an anode for assembling a ternary material (622 type)/lithium battery. The peel strength of ternary electrodes and the charging and discharging curve of the battery at room temperature were detected (see FIG. 3 and Table 3). It can be seen from FIG. 3 that after cycling for 100 cycles at room temperature and 1 C, the assembled electrode still maintained a specific discharge capacity of 134 mAh/g.

TABLE-US-00003 TABLE 3 Cathode active material Conductive Polyvinylene Ternary agent Anode Peeling carbonate Nucleophile material Acetylene active strength Component P1 Nu3 (622 type) black Electrolyte material (N/mm) Mass 12% 6% 65% 17% 1M LiDFOB Lithium 0.15 fraction in DMC

[0050] It can be seen from above results that the excellent electrochemical performance of the polymer binder in the ternary cathode-based lithium battery results from the introduction of ionic liquid structural units, thereby improving ionic conductivity and oxidation stability.

Embodiment 4

[0051] Polymer binder A4 based electrodes with high peel strength:

[0052] The cathode active material silicon carbon, KS6 graphite and binder A4 precursor [Nu4

##STR00007##

(m=10, which accounted for 90% of the total mass of the polymer) and polyvinylene carbonate (which accounted for 10% of the total mass of the polymer)] were added into the mortar according to a mass ratio of 50:25:25 as slurry; DMF (which had a mass ratio of 65% in the slurry) was added; and the mixture was continuously ground and stirred at 80° C. for 1 h to obtain uniform slurry. The above slurry was evenly coated on an aluminum foil, and dried in an oven at 60° C. for 2 h. The coated aluminum foil was punched into an electrode sheet with appropriate size through a punching machine, dried in a vacuum oven at 120° C. for 18 h and placed in a glove box for later use.

[0053] The electrode obtained above was used as a cathode and lithium was used as an anode for assembling a half battery. The peel strength of silicon/carbon electrodes and the long-term cycling performance of the assembled battery at room temperature and 0.1 C were detected (see FIG. 4 and Table 4). It can be seen from FIG. 4 that after cycling for 130 cycles under charging and discharging at 0.1 C, the assembled battery still maintained a specific discharge capacity of 500 mAh/g.

TABLE-US-00004 TABLE 4 Cathode active Conductive Polyvinylene material agent Anode Peeling carbonate Nucleophile Silicon KS6 active strength Component P1 Nu4 carbon graphite Electrolyte material (N/mm) Mass 2.5% 22.5% 50% 25% 1M LiBOB Lithium 0.45 fraction in EC

[0054] It can be seen from above results that high peeling property of the polymer binder that originates from abundant polar functional groups and cross-linked network skeleton structure of the polymer endows as-prepared batteries with superior electrochemical performance.

Embodiment 5

[0055] Polymer binder A5 based electrodes with high peel strength:

[0056] Nano sulfur, acetylene black and polymer binder A5 precursor [Nu5

##STR00008##

[0057] (m =10, which accounted for 50% of the total mass of the polymer) and polyvinylene carbonate (which accounted for 50% of the total mass of the polymer)] were mixed into the mortar according to a mass ratio of 90:5: 5 as slurry; dimethyl sulfoxide (which had a mass ratio of 50% in the slurry) was added; and the mixture was continuously ground and stirred at 40° C. for 10 min to obtain uniform slurry. The above slurry was evenly coated on an aluminum foil, and dried in an oven at 60° C. for 1 h. The coated aluminum foil was punched into an electrode sheet with appropriate size through a punching machine, dried in the oven at 100° C. for 10 h and placed in a glove box for later use.

[0058] The electrode obtained above was used as a cathode and lithium was used as an anode for assembling a lithium-sulfur battery. The peel strength of sulfur cathodes and the long-term cycling performance of the assembled battery at room temperature and 0.1 C were detected (see FIG. 5 and Table 5). It can be seen from FIG. 5 that after cycling for 100 cycles under charging and discharging at 0.1 C, the assembled battery still kept a specific discharge capacity of 600 mAh/g.

TABLE-US-00005 TABLE 5 Cathode active Conductive Polyvinylene material agent Anode Peeling carbonate Nucleophile Nano Acetylene active strength Component P1 Nu5 sulfur black Electrolyte material (N/mm) Mass 2.5% 2.5% 90% 5% 1M LiPF.sub.6 Lithium 0.5 fraction in DMC

[0059] It can be seen from above results that high peeling property of the polymer binder that results from the polymer skeleton of the 3D network structure and abundant polar functional groups renders high battery performance.

Embodiment 6

[0060] Polymer binder A6 based electrodes with high peel strength:

[0061] The cathode active material lithium cobalt oxide, Ketjen Black and polymer binder A6 precursor (Nu6 glucosamine accounted for 60% of the total mass of the polymer and polyvinylene carbonate accounted for 40% of the total mass of the polymer) were added into the mortar according to a mass ratio of 8:1:1 as slurry; NMP (which had a mass ratio of 45% in the slurry) was added; and the mixture was ground and stirred at 0° C. for 5 min to obtain uniform slurry. The above slurry was evenly coated on an aluminum foil, and dried in an oven at 60° C. for 2 h. The coated aluminum foil was punched into an electrode sheet with appropriate size through a punching machine, and then dried in the vacuum oven at 110° C. for 12 h.

[0062] The electrode obtained above was used as a cathode and lithium was used as an anode for assembling a lithium cobalt oxide/lithium battery. The peel strength of the cathodes and the charging and discharging curves of the battery at room temperature were detected (see FIG. 6 and Table 6). It can be seen from FIG. 6 that after cycling for 200 cycles under charging and discharging at 0.5 C, the capacity retention of the battery was 90% together with coulombic efficiency of 99%.

TABLE-US-00006 TABLE 6 Cathode active material Conductive Polyvinylene Lithium agent Anode Peeling carbonate Nucleophile cobalt Ketjen active strength Component P1 Nu6 oxide Black Electrolyte material (N/mm) Mass 4% 6% 80% 10% 1M LiDFOB Lithium 0.6 fraction in DMC/EC (v/v = 1:1)

[0063] It can be seen from above results that high electrochemical performance of the polymer binder indicates that the polyvinylene carbonate binder derived from saccharides possesses high application potential.

The test of the battery performance in above various embodiments comprises the following steps:
(1) Battery assembly

[0064] A corresponding half-cell or battery structure was put into a battery case and the battery case was sealed to obtain a battery.

(2) Test of battery performance

[0065] The long-term cycling performance and rate performance of the secondary lithium battery were tested with a LAND battery charging and discharging instrument. The electrochemical performance of the electrolyte was tested with an electrochemical workstation.