BINDER, NEGATIVE-ELECTRODE SLURRY, NEGATIVE ELECTRODE, AND LITHIUM-ION BATTERY

Abstract

The present application discloses a binder, a negative-electrode slurry, a negative electrode, and a lithium-ion battery. In the present application, the binder comprises a first block polymer and a second block polymer. The first block polymer is a lithiated tetrablock polymer having a structure shown as B-C-B-A, wherein A represents a polymer block A, B represents a polymer block B, and C represents a polymer block C; the polymer block A is polymerized from alkenyl formic acid monomers; the polymer block B is polymerized from aromatic vinyl monomers; and the polymer block C is polymerized from acrylate monomers. The second block polymer is a lithiated triblock polymer having a structure shown as E-F-E, wherein E represents a polymer block E, and F represents a polymer block F; the polymer block E is polymerized from alkenyl formic acid monomers; and the polymer block F is polymerized from acrylate monomers.

Claims

1. A binder, comprising a first block polymer and a second block polymer, wherein the first block polymer is a lithiated tetrablock polymer, and the tetrablock polymer has a structure shown as B-C-B-A, wherein A represents a polymer block A, B represents a polymer block B, and C represents a polymer block C; the polymer block A is polymerized from an alkenyl formic acid monomer; the polymer block B is polymerized from an aromatic vinyl monomer; the polymer block C is polymerized from an acrylate monomer; and the second block polymer is a lithiated triblock polymer, and the triblock polymer has a structure shown as E-F-E, wherein E represents a polymer block E, and F represents a polymer block F; the polymer block E is polymerized from an alkenyl formic acid monomer; the polymer block F is polymerized from an acrylate monomer.

2. The binder according to claim 1, wherein in the tetrablock polymer, a structure of the alkenyl formic acid monomer is ##STR00021## wherein R.sup.11 and R.sup.12 are independently hydrogen or a C.sub.1-4 alkyl group; and/or in the tetrablock polymer, a structure of the aromatic vinyl monomer is ##STR00022## wherein R.sup.21, R.sup.22, R.sup.23, R.sup.24, R.sup.25, and R.sup.26 are independently hydrogen or a C.sub.1-4 alkyl group; and/or in the tetrablock polymer, a structure of the acrylate monomer is ##STR00023## wherein R.sup.31 is a linear or branched C.sub.1-10 alkyl group; and/or in the triblock polymer, the alkenyl formic acid monomer is ##STR00024## wherein R.sup.51 and R.sup.52 are independently hydrogen or a C.sub.1-4 alkyl group; and/or in the triblock polymer, the acrylate monomer is ##STR00025## wherein R.sup.61 is a C.sub.1-4 alkyl group.

3. The binder according to claim 2, wherein in the tetrablock polymer, the alkenyl formic acid monomer is an acrylic acid; and/or in the tetrablock polymer, the aromatic vinyl monomer is styrene; and/or in the tetrablock polymer, a structure of the acrylate monomer is ##STR00026## wherein R.sup.31 is a linear or branched C.sub.4-8 alkyl group; and/or in the triblock polymer, the alkenyl formic acid monomer is an acrylic acid; and/or in the triblock polymer, the acrylate monomer is methyl acrylate.

4. The binder according to claim 1, wherein the first block polymer has a structure shown as Formula (I), wherein n is 10˜50; x is 200˜500; y is 400˜1000; z is 200˜500, R.sup.41 is a C.sub.4-8 alkyl group, and R.sup.42 and R.sup.43 are a phenyl group or a C.sub.1-4 alkyl group substituted phenyl group; ##STR00027## and/or the second block polymer has a structure shown as Formula (II), wherein k is 70˜700, 1 is 70˜700, and m is 70˜700; ##STR00028##

5. The binder according to claim 4, wherein the first block polymer is ##STR00029## wherein n is 10˜50; x is 200˜500; y is 400˜1000; z is 200˜500.

6. The binder according to claim 1, wherein a mass ratio of the first block polymer to the second block polymer is 99:1˜1:99.

7. The binder according to claim 1, wherein a mass ratio of the first block polymer to the second block polymer is 9:1.

8. The binder according to claim 1, wherein in the tetrablock polymer, a degree of polymerization of the polymer block A is 10˜50, a degree of polymerization of the polymer block B is 200˜500, and a degree of polymerization of the polymer block C is 400˜1000; and/or in the triblock polymer, a degree of polymerization of the polymer block E is 70˜700, and a degree of polymerization of the polymer block F is 70˜700.

9. A negative-electrode slurry for a lithium-ion battery, wherein the negative-electrode slurry comprises a negative-electrode active material, a conductive agent, and the binder according to claim 1.

10. The negative-electrode slurry according to claim 9, wherein a mass ratio of the negative-electrode active material to the conductive agent to the binder is a:b:c, wherein a is 93˜97, b is 3˜5, c is 3˜5, and a+b+c=100.

11. A negative electrode, comprising a current collector and a negative-electrode active material layer coated on the current collector, wherein the negative-electrode active material layer is formed by coating a negative-electrode slurry on the current collector.

12. The negative electrode according to claim 11, wherein the negative-electrode active material comprises graphite and/or a graphite-containing compound.

13. A lithium-ion battery, comprising a positive electrode, a separator, an electrolyte, and the negative electrode according to claim 11.

Description

DETAILED DESCRIPTION OF DISCLOSED EMBODIMENTS

[0049] In order for the objectives, technical solutions, and advantages of the embodiments of the disclosure to be clearer, each embodiment of the disclosure will be described in detail below with reference to specific examples. However, it should be understood that persons skilled in the art will appreciate that in each embodiment of the disclosure, numerous technical details are set forth in order to provide the reader with a better understanding of the present application. However, even without the technical details and various changes and modifications based on the following embodiments, the technical solutions claimed in the present application may still be implemented. In the following examples, experimental methods without specific conditions are usually in accordance with conventional conditions or in accordance with conditions suggested by the manufacturer. Percentages and parts are calculated by weight unless otherwise indicated.

Example 1 Preparation of Lithiated Polyacrylic Acid-Styrene-Isooctyl Acrylate-Styrene (PAALi-PSt-PEHA-PSt)

Step 1: Preparation of a Polyacrylic Acid (PAA)

[0050] ##STR00011##

[0051] 1.0 g of 2-mercapto-S-thiobenzoylacetic acid (molecular weight of 212.3 g/mol) was weighed, mixed with 3.0˜17.0 g of refined acrylic monomer, and poured into a 500 mL three-necked flask. Another 0.2˜0.5 g of potassium persulfate was weighed, dissolved in 5˜10 g of deionized water and stored at low temperature for later use. The flask was placed on a water bath cauldron, added with magnets, stirred and dissolved at room temperature, then passed nitrogen for 30 min to remove oxygen therein, heated to 60˜80° C., added with the potassium persulfate aqueous solution, reacted for 12˜20 hours, and the polyacrylic acid (PAA) was obtained.

Step 2: Preparation of Polyacrylic Acid-Styrene (PAA-PSt)

[0052] ##STR00012##

[0053] 98.0˜245.0 g of styrene monomer was weighed, slowly added into the flask after the reaction in Step 1 through a syringe, continued reacting at 60˜80° C. for 2˜8 hours, and the polyacrylic acid-styrene (PAA-PSt) was obtained.

Step 3: Preparation of Polyacrylic Acid-Styrene-Isooctyl Acrylate (PAA-PSt-PEHA)

[0054] ##STR00013##

[0055] 347.0˜866.0 g of isooctyl acrylate monomer was weighed, slowly added into the flask after the reaction in Step 2 through a syringe, continued reacting at 60˜80° C. for 2˜6 h, and the polyacrylic acid-styrene-isooctyl acrylate (PAA-PSt-PEHA) was obtained.

Step 4: Preparation of Polyacrylic Acid-Styrene-Isooctyl Acrylate-Styrene (PAA-PSt-PEHA-PSt)

[0056] ##STR00014##

[0057] 98.0˜245.0 g of styrene monomer was weighed, slowly add into the flask after the reaction in Step 3 through a syringe, continued reacting at 60˜80° C. for 2˜8 hours, the reacted product was washed with deionized water until the pH is 3˜6, and the polyacrylic acid-styrene-isooctyl acrylate-styrene (PAA-PSt-PEHA-PSt) was obtained.

Step 5: Preparation of Lithiated Polyacrylic Acid-Styrene-Isooctyl Acrylate-Styrene (PAA-PSt-PEHA-PSt)

[0058] ##STR00015##

[0059] 500 g of the polyacrylic acid-styrene-isooctyl acrylate-styrene (PAA-PSt-PEHA-PSt) obtained in Step 4 and 15˜25 g of lithium hydroxide solution with a mass fraction of 5%˜15% (containing 0.75˜3.75 g of lithium hydroxide) were taken, stirred at a rotational speed of 300 rpm/h for 60 minutes, and the lithiated polyacrylic acid-styrene-isooctyl acrylate-styrene (PAA-PSt-PEHA-PSt) was obtained.

Example 2 Preparation of Lithiated Polyacrylic Acid-Methyl Acrylate-Acrylic Acid (PAALi-PMA-PAALi)

Step 1: Preparation of a Polyacrylic Acid (PAA)

[0060] ##STR00016##

[0061] 0.6 parts of RAFT reagent, 0.2 parts of initiator, and 20 parts of acrylic monomer were in 150 parts of deionized water solvent, stirred at 70° C. for 18 hours, and a reaction mixture containing the compound of Formula (1′) was obtained; wherein the RAFT reagent was

##STR00017##

wherein R was an acetate group; Z was a benzyl group; the initiator was potassium persulfate.

Step 2: Preparation of Polyacrylic Acid-Methyl Acrylate (PAA-PMA)

[0062] ##STR00018##

[0063] 60 parts of methyl acrylate monomer was added into the reaction mixture obtained in Step 1, then continued stirring 70° C. for 6 hours, and a reaction mixture containing the compound of Formula (2′) was obtained.

Step 3: Preparation of Polyacrylic Acid-Methyl Acrylate-Acrylic Acid (PAA-PMA-PAA)

[0064] ##STR00019##

[0065] 20 parts of acrylic acid monomer was added into the reaction mixture obtained in Step 2, then continued stirring at 70° C. for 18 hours, and a reaction mixture containing the compound of Formula (3′) was obtained.

Step 4: Preparation of Lithiated Polyacrylic Acid-Methyl Acrylate-Acrylic Acid (PAALi-PMA-PAALi)

[0066] ##STR00020##

[0067] The pH of the reaction mixture obtained in Step 3 was adjusted to 5, a lithium hydroxide aqueous solution with a mass fraction of 10% was added, and lithiated at 25° C. for 4 hours.

[0068] After the lithiation reaction was completed, the reaction mixture was precipitated, washed, and dried, and the lithiated polyacrylic acid-methyl acrylate-acrylic acid (PAALi-PMA-PAALi) shown as Formula (I′) was obtained. The molecular weight of the finally obtained polymer was about 20,000.

Example 3 Preparation of a Binder

[0069] The lithiated polyacrylic acid-styrene-isooctyl acrylate-styrene (PAALi-PSt-PEHA-PSt) prepared in Example 1 and the lithiated polyacrylic acid-methyl acrylate-acrylic acid (PAALi-PMA-PAALi) prepared in Example 2 were stirred and mixed according to the mass ratio of 9:1, the stirring speed was 200 rpm, the temperature was 30° C., and the time was 2 hours.

TABLE-US-00001 TABLE 1 Group Mass ratio of PAALi-St-PEHA-St to PAALi-PMA-PAALi Example 4 8:2 Example 5 7:3 Example 6 6:4 Example 7 5:5 Example 8 4:6 Example 9 3:7 Example 10 2:8 Example 11 1:9

Example 12 Preparation of Lithium-Ion Battery

[0070] Preparation of a Positive Electrode Piece

[0071] A positive-electrode active material NCM523, conductive carbon black Super-P, and binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 96:2:2, then dispersed in N-methyl-2-pyrrolidone (NMP), and a positive-electrode slurry was obtained. The obtained positive-electrode slurry was evenly coated on two surfaces of an aluminum foil, dried, calendered, and vacuum-dried at 80°, an aluminum lead wire was welded using an ultrasonic welder, a positive electrode plate was obtained, and the thickness of the plate was 120˜150 μm.

[0072] Preparation of a Negative Electrode Piece

[0073] Composite negative-electrode active material graphite, conductive carbon black Super-P, and the binder prepared in Example 3 were mixed in a mass ratio of 95:2:3, then dispersed in deionized water, and a negative-electrode slurry was obtained. The slurry was coated on two surfaces of a copper foil, dried, calendered, and vacuum-dried, a nickel lead wire was welded using an ultrasonic welder, a negative electrode plate was obtained, and the thickness of the plate was 80˜100 μm.

[0074] Preparation of a Core

[0075] A separator with a thickness of 20 μm was placed between the positive electrode plate and the negative electrode plate, a sandwich structure composed of the positive electrode plate, the negative electrode plate, and the separator was then wound, the wound body was flattened and placed in an aluminum foil packaging bag, vacuum-baked at 85° C. for 48 h, and the core to be injected was obtained.

[0076] Core Injection

[0077] An electrolyte was injected into the core in a glove box, vacuum-sealed, and kept at rest for 24 h. Then, the routinization of the first charging was performed according to the following steps of: charging to 3.05 V with 0.02 C constant current, charging to 3.75 V with 0.05 C constant current, charging to 4.05 V with 0.2 C constant current, and vacuum-sealed. Then, further charged to 4.2 V with 0.33 C constant current, and after being left at room temperature for 24 hours, discharged to 3.0 V with 0.2 C constant current.

[0078] For Example 13 to Example 20, the lithium-ion battery was prepared according to the same method as Example 12, and the difference was that in the preparation of the negative electrode piece, the binder used was respectively the binder prepared in Example 3 to Example 11.

Comparative Example 1 Preparation of a Lithium-Ion Battery

[0079] Preparation of a Positive Electrode Piece

[0080] A positive-electrode active material NCM523, conductive carbon black Super-P, and binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 96:2:2, then dispersed in N-methyl-2-pyrrolidone (NMP), and a positive-electrode slurry was obtained. The obtained positive-electrode slurry was evenly coated on two surfaces of an aluminum foil, dried, calendered, and vacuum-dried at 80°, an aluminum lead wire was welded using an ultrasonic welder, a positive electrode plate was obtained, and the thickness of the plate was 120˜150 μm.

[0081] Preparation of a Negative Electrode Piece

[0082] Composite negative-electrode active material graphite, conductive carbon black Super-P, and PAA binder were mixed in a mass ratio of 95:2:3, then dispersed in deionized water, and a negative-electrode slurry was obtained. The slurry was coated on two surfaces of a copper foil, dried, calendered, and vacuum-dried, a nickel lead wire was welded using an ultrasonic welder, a negative electrode plate was obtained, and the thickness of the plate was 80˜100 μm.

[0083] Preparation of a Core

[0084] A separator with a thickness of 20 μm was placed between the positive electrode plate and the negative electrode plate, a sandwich structure composed of the positive electrode plate, the negative electrode plate, and the separator was then wound, the wound body was flattened and placed in an aluminum foil packaging bag, vacuum-baked at 85° C. for 48 h, and the core to be injected was obtained.

[0085] Core Injection

[0086] An electrolyte was injected into the core in a glove box, vacuum-sealed, and kept at rest for 24 h. Then, the routinization of the first charging was performed according to the following steps of: charging to 3.05 V with 0.02 C constant current, charging to 3.75 V with 0.05 C constant current, charging to 4.05 V with 0.2 C constant current, and vacuum-sealed. Then, further charged to 4.2 V with 0.33 C constant current, and after being left at room temperature for 24 hours, discharged to 3.0 V with 0.2 C constant current.

[0087] For Comparative Example 2, the lithium-ion battery was prepared according to the same method as Comparative Example 1, and the difference was that in the preparation of the negative electrode piece, the binder used was an SBR binder.

[0088] For Comparative Example 3, the lithium-ion battery was prepared according to the same method as Comparative Example 1, and the difference was that in the preparation of the negative electrode piece, the binder used was only lithiated polyacrylic acid-styrene-isooctyl acrylate-styrene (PAALi-PSt-PEHA-PSt).

[0089] For Comparative Example 4, the lithium-ion battery was prepared according to the same method as Comparative Example 1, and the difference was that in the preparation of the negative electrode piece, the binder used was only lithiated polyacrylic acid-methyl acrylate-acrylic acid (PAALi-PMA-PAALi).

Test Example 1

[0090] (1) Tensile Performance Test of the Binder

[0091] The binder prepared in Example 3 was made into a film, and the preparation process was as follows: 1.2 g of the binder was poured into a polytetrafluoroethylene watch glass with a diameter of 10 cm, covered with a layer of filter paper, the filter paper was held down, placed into a fume hood, dried in convection at room temperature for a week, then placed into a vacuum oven at 60° C., vacuum-dried for 12 h, and sample preparation was completed.

[0092] Dumbbell-shaped splines were cut on a cutting machine according to the dimensions indicated for Type 2 and Type 4 specimens in ISO 37-1994 and implemented in accordance with the GB 16421-1996 standard, and the number of splines for each polymer was 5. The tensile test was performed using a universal material testing machine. Test conditions: a force sensor with a range of 50 N was used, the tensile rate was 1 mm/min, each polymer sample was subjected to 5 parallel tests, and an average value was obtained. The results obtained are shown in Table 2.

[0093] The tensile performance test of the binder, the PAA binder, the SBR binder, the lithiated polyacrylic acid-styrene-isooctyl acrylate-styrene (PAALi-PSt-PEHA-PSt), and the lithiated polyacrylic acid-methyl acrylate-acrylic acid (PAALi-PMA-PAALi) prepared in Examples 4 to 11 were according to the same method. The results obtained are shown in Table 2.

TABLE-US-00002 TABLE 2 Group Modulus/MPa Example 3 20.4 Example 4 22.5 Example 5 25.1 Example 6 27.9 Example 7 30.2 Example 8 31.7 Example 9 33.5 Example 10 38.7 Example 11 40.0 PAA binder 85.3 SBR binder 19.3 Lithiated polyacrylic acid-styrene- isooctyl acrylate- 18.2 styrene (PAALi-PSt-PEHA-PSt) Lithiated polyacrylic acid-methyl acrylate-acrylic acid 48.5 (PAALi-PMA-PAALi)

[0094] (2) Fast Charging Capability Test

[0095] At 25° C., a constant current charging test was performed on the lithium-ion battery prepared in the examples and the comparative examples by adopting a rate of 2 C, a rate charging capacity retention rate was calculated (the charging retention rate of a battery at the rate of 2 C=the capacity released after the battery is charged at the rate of 2 C/the capacity released after the battery is charged at a rate of 1/3 C). The results obtained are shown in Table 3.

[0096] (3) Direct Current Internal Resistance (DCR) Test

[0097] At 25° C., the battery prepared in the examples and the comparative examples was respectively discharged at 4 C for 30 s at a state of charge (SOC) of 50%, and the direct current internal resistance R=−(V1−V2)/I, wherein V1 is the voltage before discharge, V2 is the voltage after discharge, and I is the discharge current, and the direct current internal resistance was calculated. The results obtained are shown in Table 3.

[0098] (4) Low Temperature Discharge Capability Test

[0099] The battery prepared in the examples and the comparative examples was taken, and a discharge capacity retention rate at −20° C. was measured: at 25° C., the fully charged battery was discharged to 3.0 V at 1 C, and an initial discharge capacity was recorded as DC (25° C.). Then, at 25° C., charged to 4.2 V with 1 C constant current and constant voltage, and the cut-off current was 0.05 C. Then, cooled to −20° C., kept at rest for 4 h, then discharged to 3.0 V at 1 C, and the discharge capacity DC (−20° C.) was recorded. At −20° C., the discharge capacity retention rate=100%*DC (−20° C.)/DC (25° C.). The results obtained are shown in Table 3.

TABLE-US-00003 TABLE 3 2 C charging Room temperature −20° C. capacity 50% 4 C 30 s discharge capacity Group retention rate discharge DCR retention rate Example 12 85.2% 39.2 mΩ 81.3% Example 13 84.6% 40.2 mΩ 79.2% Example 14 83.2% 43.2 mΩ 77.6% Example 15 83.4% 44.5 mΩ 74.2% Example 16 83.2% 43.9 mΩ 76.2% Example 17 82.1% 46.7 mΩ 72.1% Example 18 81.9% 46.6 mΩ 74.2% Example 19 80.7% 47.5 mΩ 71.2% Example 20 80.5% 48.4 mΩ 69.5% Comparative 65.2% 82 mΩ 56.1% Example 1 Comparative 61.4% 89 mΩ 54.3% Example 2 Comparative 80.2% 45.2 mΩ 75.8% Example 3 Comparative 80.3% 48.6 mΩ 68.7% Example 4

[0100] Persons skilled in the art can understand that the above examples are specific examples for implementing the disclosure. However, in practical applications, various changes in form and details may be made without departing from the spirit and the scope of the disclosure.