Electrode

Abstract

The present application relates to an electrode, a method for manufacturing the electrode, and a secondary battery comprising the electrode. The present application relates to an electrode comprising a current collector, an active material layer, and a thiophene polymer layer formed on the active material layer and can provide an electrode capable of ensuring a higher level of adhesion force between particles and adhesion force between the active material layer and the current collector relative to the binder content in the active material layer. In addition, the present application can provide a method for manufacturing the electrode, and a secondary battery comprising the same.

Claims

1. An electrode, comprising: a current collector; a lithium layer formed on the current collector; and a thiophene polymer layer formed on the lithium layer and comprising a thiophene polymer having a functional group selected from a first functional group, a second functional group, or a combination thereof, wherein the first functional group is selected from a carboxyl group, a hydroxy group, a nitro group, an amino group, an ether group, a carbonyl group or a combination thereof.

2. The electrode according to claim 1, wherein the lithium layer has a thickness in a range of 10 μm to 50 μm.

3. The electrode according to claim 1, wherein the second functional group is an alkyl group with 3 or more carbon atoms, an alkoxy group with 3 or more carbon atoms, an alkylcarbonyl group having an alkyl group with 3 or more carbon atoms, an alkylcarbonyloxy group having an alkyl group with 3 or more carbon atoms, or a group of the following formula 1: ##STR00009## wherein, L.sub.1 is a single bond or an alkylene group, L.sub.2 is an alkylene group, R.sub.1 is an alkyl group, and n is a number within a range of 1 to 10.

4. The electrode according to claim 1, wherein in the thiophene polymer layer, a ratio (M/S) of a mole number (M) of the functional group to a mole number (S) of sulfur atoms is in a range of 0.1 to 10.

5. The electrode according to claim 1, wherein the thiophene polymer simultaneously comprises a first functional group, and a second functional group.

6. The electrode according to claim 5, wherein a ratio (M1/M2) of a mole number (M1) of the first functional group to a mole number (M2) of the second functional group is in a range of 0.5 to 10.

7. The electrode according to claim 1, wherein the thiophene polymer comprises a polymerized unit of the following formula 2: ##STR00010## wherein, L.sub.3 and L.sub.4 are each independently a single bond or an alkylene group, R.sub.2 is a carboxyl group, a carboxylalkyl group, a hydroxy group, a hydroxyalkyl group, an amino group, an aminoalkyl group, a nitro group, an ether-containing group, a carbonyl-containing group or the second functional group, and R.sub.3 is hydrogen, a carboxyl group, a carboxylalkyl group, a hydroxy group, a hydroxyalkyl group, an amino group, an aminoalkyl group, a nitro group, an ether-containing group, a carbonyl-containing group or the second functional group.

8. The electrode according to claim 7, wherein at least one of L.sub.3 or L.sub.4 is an alkylene group, and the sum of carbon atoms present in L.sub.3 and L.sub.4 is in a range of 1 to 20.

9. The electrode according to claim 1, wherein the thiophene polymer simultaneously comprises a polymerized unit of the following formula 3 and a polymerized unit of the following formula 4: ##STR00011## wherein, L.sub.5 and L.sub.6 are each independently a single bond or an alkylene group, R.sub.4 is a carboxyl group, a carboxyalkyl group, a hydroxy group, a hydroxyalkyl group, an amino group, an aminoalkyl group, a nitro group, an ether-containing group or a carbonyl-containing group, and R.sub.5 is hydrogen, a carboxyl group, a carboxylalkyl group, a hydroxy group, a hydroxyalkyl group, an amino group, an aminoalkyl group, a nitro group, an ether-containing group or a carbonyl-containing group: ##STR00012## wherein, L.sub.7 and L.sub.8 are each independently a single bond or an alkylene group, R.sub.6 is the second functional group, and R.sub.7 is hydrogen or the second functional group.

10. The electrode according to claim 9, wherein a ratio (M4/M5) of a mole number (M4) of the polymerized unit of Formula 3 to a mole number (M5) of the polymerized unit of Formula 4 is in a range of 0.1 to 10.

11. The electrode according to claim 1, wherein the thiophene polymer has a weight average molecular weight in a range of 500 to 100,000 g/mol.

12. The electrode according to claim 1, wherein the thiophene polymer has an oxidation potential in a range of 1.5 to 5V.

13. The electrode according to claim 1, wherein the thiophene polymer layer has a thickness in a range of 100 nm to 10 μm.

14. A method for manufacturing an electrode, comprising: forming a thiophene polymer layer on a laminate comprising a current collector and a lithium layer, wherein the thiophene polymer layer comprises a thiophene polymer having a functional group selected from a first functional group, a second functional group, or a combination thereof, and wherein the first functional group is selected from a carboxyl group, a hydroxy group, a nitro group, an amino group, an ether group, a carbonyl group or a combination thereof.

15. The method for manufacturing an electrode according to claim 14, wherein the thiophene polymer layer is formed by coating a coating composition on the lithium layer, wherein the coating composition comprises the thiophene polymer.

16. The method for manufacturing an electrode according to claim 14, wherein the thiophene polymer layer is formed by polymerizing a thiophene monomer on the lithium layer.

17. The method for manufacturing an electrode according to claim 16, wherein the thiophene-based monomer is represented by the following formula 5: ##STR00013## wherein, L.sub.3 and L.sub.4 are each independently a single bond or an alkylene group, R.sub.2 is a carboxyl group, a carboxylalkyl group, a hydroxy group, a hydroxyalkyl group, an amino group, an aminoalkyl group, a nitro group, an ether-containing group, a carbonyl-containing group or the second functional group, R.sub.3 is hydrogen, a carboxyl group, a carboxylalkyl group, a hydroxy group, a hydroxyalkyl group, an amino group, an aminoalkyl group, a nitro group, an ether-containing group, a carbonyl-containing group or the second functional group, and R.sub.8 and R.sub.9 are each independently hydrogen or halogen.

18. A secondary battery comprising the electrode of claim 1.

19. The electrode according to claim 1, wherein the lithium layer comprises lithium or a lithium alloy.

Description

DESCRIPTION OF DRAWINGS

[0084] FIG. 1 is a cross-sectional diagram of an exemplary electrode of the present application.

[0085] FIG. 2 is an NMR result of the monomer (A) of Preparation Example 1.

[0086] FIG. 3 is an NMR result of the monomer (B) of Preparation Example 2.

MODE FOR INVENTION

[0087] Hereinafter, the laminate of the present application and the like will be specifically described through Examples and Comparative Examples, but the scope of the laminate of the present application and the like is not limited by the following examples.

[0088] 1. NMR Analysis Method

[0089] 1H-NMR analyses in Examples and Synthesis Examples were performed at room temperature using an NMR spectrometer including a Bruker UltraShield (300 MHz) spectrometer having a triple resonance 5 mm probe. An analyte material was diluted to a concentration of about 10 mg/ml or so in a solvent (CDCl.sub.3) for NMR measurement and used, where the chemical shift was expressed in ppm.

[0090] 2. GPC (Gel Permeation Chromatograph)

[0091] Number average molecular weights (Mn) and molecular weight distributions were measured using GPC (gel permeation chromatography). Polymers of Examples, etc. were each put in a 5 mL vial, and diluted in chloroform to a concentration of about 1 mg/mL or so. Thereafter, the standard sample for calibration and the sample to be analyzed were filtered through a syringe filter (pore size: 0.45 μm) and then measured. As the analysis program, Waters' Empower 3 was used, and the weight average molecular weight (Mw) and number average molecular weight (Mn) were each obtained by comparing the elution time of the sample with the calibration curve, and the molecular weight distribution (PDI) was calculated as the ratio (Mw/Mn). The measurement conditions of GPC are as follows.

[0092] <GPC Measurement Conditions> [0093] Instrument: 2414 from Waters [0094] Column: using 3 Styragel from Waters [0095] Solvent: THF [0096] Column temperature: 35° C. [0097] Sample concentration: 1 mg/mL, 1 mL injection [0098] Standard sample: Polystyrene (Mp: 3900000, 723000, 316500, 52200, 31400, 7200, 3940, 485)

[0099] 3. Thickness Measurement of Thiophene Polymer Layer

[0100] A thickness of a thiophene polymer layer was measured using an SEM (Scanning Electron Microscope) (Hitachi, S4800) after the electrode was cross-sectioned using an ion milling equipment (Hitachi, IM4000).

[0101] 4. Ionic Conductivity Measurement Method

[0102] A thiophene polymer was prepared in a disk-shaped sample with a diameter of 1.3 cm, where the thiophene polymer sample was placed between two disk-shaped stainless steels with the same diameter as above to prepare a sandwich structure and electrodes were connected to the stainless steels, and then it was evaluated using a potentiometer (Princeton Applied Research, Parstat 2273).

[0103] 5. Cycle Retention Measurement Method

[0104] Cycle retention was evaluated by manufacturing a coin cell. Upon manufacturing the coin cell, the electrodes of Examples or Comparative Examples were each applied as a negative electrode, a positive electrode containing lithium nickel-manganese-cobalt oxide as an active material was applied as a positive electrode, and an LiPF.sub.6 1M solution (solvent: EC/EMC/DMC=3:3:4 mass ratio) was used as an electrolyte.

[0105] An electrode prepared by applying a slurry comprising lithium nickel-manganese-cobalt oxide (LixMyO2, wherein M is Ni1-a-bMnaCob, a is 0.2, b is 0.2, and x is 1.05), a carbon-based conductive material (ECP (Ketjen Black) 0.5%, SFG (Trimrex graphite) 0.4%, DB (Denka Black) 0.4%), PVDF (polyvinylidene fluoride) and NMP (N-methyl-2-pyrrolidone) in a weight ratio of 75:1:1:23 on an aluminum current collector (thickness: 20 μm) with a doctor blade to a thickness of about 40 μm or so, and drying it at room temperature, following further drying and rolling under vacuum conditions at 120° C. was used as the positive electrode.

[0106] The capacity of a battery having a reference capacity of 170 mAh/g was measured after performing 30 charge/discharge cycles at 25° C., and a ratio to the initial capacity was calculated. The 30 charge/discharge cycles mean that a process of setting the charge cutoff voltage to 4.3V and the charge cutoff current to 0.2 mA to charge it in the CC (constant current)/CV (constant voltage) method at a rate of 0.33 C and setting the discharge cutoff voltage to 2.5V to discharge it in the CC (constant current) method at a rate of 0.33 C as one cycle is carried out 30 times repeatedly. Cycle retention was measured as the ratio of the discharge capacity after 30 repetitions to the discharge capacity after one charge/discharge.

Preparation Example 1. Synthesis of Monomer (A)

[0107] Compound 1 (3,4-[2,2′-bis(bromomethyl)propylenedioxy]thiophene) of Scheme 1 below was synthesized in the following manner.

##STR00006##

[0108] 5 g (34.68 mmol, 1 eq) of 3,4-dimethoxythiophene and 10.9 g (41.61 mmol, 1.2 eq) of 2,2-bisbromomethyl-1,3-propanediol were mixed by dissolving them in 200 ml of toluene together with 500 mg of p-toluenesulfonic acid (p-TsOH). The mixture was reacted under reflux at 120° C. to remove methanol generated by the reaction (transetherification) with a 4A type molecular sieve charged with a soxhlet extractor. The reactant was quenched with water after refluxing for 24 hours, extracted with ethyl acetate, and then washed with brine, and dried over magnesium sulfate (MgSO.sub.4). The solvent was removed by a rotary evaporator, and the residue was purified by column chromatography eluting with methylene chloride/hexane (1:4) to obtain Compound 1 above (3,4-(2,2′-bis(bromomethyl)propylenedioxy)thiophene).

[0109] Subsequently, Compound 1 above was used to synthesize Compound 2 (3,4-[2,2′-bis(carboxymethyl)propylenedioxy]thiophene) of Scheme 2 below.

##STR00007##

[0110] Step 1:

[0111] 1.20 g of Compound 1 above (3.51 mmol, 1 eq) and 2.07 g of sodium cyanide (42.26 mmol, 12 eq) were dissolved in 150 ml of dimethyl sulfoxide (hereinafter, DMSO), and stirred at room temperature for 10 days. The mixture was quenched with deionized water, dried over magnesium sulfate (MgSO.sub.4), and then evaporated under vacuum to remove the solvent, and the residue was purified by column chromatography eluting with methylene chloride/hexane (2:1) to obtain Compound 1a of Scheme 2.

[0112] 1 g of Compound 1a above (4.27 mmol, 1 eq) was dissolved in a mixed solution of 100 ml of 1M aqueous sodium hydroxide (NaOH) solution and 100 ml of ethylene glycol, and refluxed at 95° C. for 24 hours. The mixture was cooled to room temperature, and then quenched with 1N hydrochloric acid (HCl) and extracted with diethyl ether. The solution was dried over magnesium sulfate (MgSO.sub.4) and then evaporated under vacuum. The residue was precipitated with chloroform to prepare the target compound 2 (3,4-[2,2′-bis(carboxymethyl)propylenedioxy]thiophene) (monomer (A)).

[0113] The results of NMR analysis of the target compound are the same as FIG. 2.

Preparation Example 2. Synthesis of Monomer (B)

[0114] Compound 4 of Scheme 4 below (3,4-(2,2′-bis[2-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)methyl]propylenedioxy)thiophene) was synthesized in the following manner.

##STR00008##

[0115] 0.561 g of sodium hydride (NaH) (60% with oil, 14.03 mmol, 6 eq) and 62 mg of 18-crown-6-ether (0.234 mmol, 0.1 eq) were dispersed in 15 ml of tetrahydrofuran (hereinafter, THF) under an argon atmosphere. After the dispersion was cooled to 0° C., 0.8 g (2.34 mmol, 1 eq) of Compound 1 formed in Preparation Example 1 was injected thereto, and then stirred at room temperature for 1 hour. After the mixed solution was cooled to 0° C. again, 1.461 g (7.017 mmol, 3 eq) of tetraethylene glycol monomethyl ether was injected thereto and stirred at room temperature for 3 hours, and then heated to 80° C. and further stirred for 24 hours, and then cooled to room temperature and quenched with 1N hydrochloric acid (HCl). The quenched mixed solution was extracted using diethyl ether, and then washed with 1N hydrochloric acid (HCl), and the reactant was dried over magnesium sulfate (MgSO.sub.4). The solvent was evaporated with a rotary evaporator, and the residue was purified by column chromatography eluting with methylene chloride/hexanes (1:2) to prepare the target compound 4 (3,4-(2,2′-bis [2-(2)-(2-(2-methoxyethoxy)ethoxy)ethoxy)methyl]propylenedioxy)thiophene) (monomer (B)).

[0116] The results of NMR analysis of the target compound are the same as FIG. 3.

Preparation Example 3. Synthesis of Polythiophene (A)

[0117] 1.79 g (6.57 mmol, 1 eq) of the monomer (A) of Preparation Example 1 was introduced to a solution obtained by dissolving 3.20 g (19.71 mmol, 3 eq) of iron (III) chloride in 150 ml of methylene chloride, and polymerized at 25° C. for 24 hours to prepare polythiophene (A). The mixed solution was placed in an osmotic membrane having an MWCO (molecular weight of cut-off) of 5000, and then immersed in 200 ml of an acetonitrile solvent to remove the unreacted iron (III) chloride and monomer (A). The residue deposited inside the osmosis membrane was washed with methanol and dried at 60° C. for 12 hours to prepare polythiophene (A).

[0118] The prepared polythiophene (A) had a weight average molecular weight of about 7,500 g/mol, and an oxidation potential of about 2.6 V or so. The oxidation potential was identified with a potentiometer.

Preparation Example 4. Synthesis of Polythiophene (B)

[0119] To a solution obtained by dissolving 2.92 g (18 mmol, 6 eq) of iron (III) chloride in 150 ml of methylene chloride, 0.82 g (3.0 mmol, 1 eq) of the monomer (A) of Preparation Example 1 above and 1.79 g (3.0 mmol) of the monomer (B) of Preparation Example 2 were introduced and polymerized at 25° C. for 24 hours to prepare polythiophene (B). The mixed solution was placed in an osmotic membrane having an MWCO (molecular weight of cut-off) of 5000, and then immersed in 200 ml of an acetonitrile solvent to remove the unreacted iron (III) chloride and unreacted monomers. The residue deposited inside the osmosis membrane was washed with methanol and dried at 60° C. for 12 hours to prepare polythiophene (B).

[0120] The polythiophene (B) comprised the polymerized unit (A) derived from the monomer (A) and the polymerized unit (B) derived from the monomer (B) in a molar ratio (A:B) of about 1:1, and had a weight average molecular weight of about s 9400 g/mol, and an oxidation potential of about 2.8 V or so. The evaluation method of the oxidation potential is the same as in Preparation Example 3.

Preparation 5. Synthesis of Polythiophene (C)

[0121] Polythiophene (C) was synthesized in the same manner as in Preparation Example 4, except that as the monomers, 1.64 g (6.0 mmol, 2 eq) of the monomer (A) of Preparation Example 1 and 1.79 g (3.0 mmol, 1 eq) of the monomer (B) of Preparation Example 2 were used. The polythiophene (C) had a weight average molecular weight (Mw) of about 7,800 g/mol, and an oxidation potential of about 2.7V.

Preparation Example 6. Synthesis of Polythiophene (D)

[0122] Polythiophene (C) was synthesized in the same manner as in Preparation Example 4, except that as the monomers, 1.64 g (6.0 mmol, 2 eq) of the monomer (A) of Preparation Example 1 and 1.19 g (2.0 mmol, 1 eq) of the monomer (B) of Preparation Example 2 were used. The polythiophene (C) had a weight average molecular weight (Mw) of about 8,700 g/mol, and an oxidation potential of about 2.7V.

Example 1

[0123] The polythiophene (A) of Preparation Example 3 was dispersed at a concentration of about 5 weight % in chloroform to prepare a coating composition.

[0124] The coating composition was coated using a doctor blade on a lithium metal film having a thickness of about 40 μm or so formed on a current collector as a copper foil, and dried at 90° C. for 10 minutes to form a thiophene polymer layer having a thickness of about 500 nm or so, thereby preparing an electrode.

Example 2

[0125] An electrode was prepared in the same manner as in Example 1, except that the polythiophene (B) of Preparation Example 4 was used.

Example 3

[0126] An electrode was prepared in the same manner as in Example 1, except that the polythiophene (C) of Preparation Example 5 was used.

Example 4

[0127] An electrode was prepared in the same manner as in Example 1, except that the polythiophene (D) of Preparation Example 6 was used.

Comparative Example 1

[0128] A lithium metal film having a thickness of about ˜ or so formed on a current collector as a copper foil, was applied as an electrode as such without additional treatment.

[0129] The evaluation results of the Examples and Comparative Examples were summarized and described in Table 1 below.

TABLE-US-00001 TABLE 1 Lithium ionic conductivity Cycle retention Example 1 6.3 × 10.sup.−3 S/cm 80% Example 2 5.1 × 10.sup.−3 S/cm 85% Example 3 7.0 × 10.sup.−3 S/cm 75% Example 4 1.1 × 10.sup.−3 S/cm 65% Comparative Example 1 — 20%