SILICON-BASED NEGATIVE ELECTRODE SLURRY, PREPARATION METHOD THEREFOR, AND NEGATIVE ELECTRODE PIECE

Abstract

The present application relates to a silicon-based negative electrode slurry, a preparation method therefor and a negative electrode piece. The preparation method comprises: (1) mixing CMC and a solvent to obtain a primary adhesive solution; (2) mixing PAA, a silicon-based negative electrode material, a conductive agent, a solvent, and the obtained adhesive solution, then performing double planetary mixing to obtain a secondary glue solution; (3) mixing a solvent and the obtained secondary adhesive solution to obtain a coarse slurry; and (4) mixing the SBR and the obtained coarse slurry to obtain a silicon-based negative electrode slurry. In the homogenization method of the present application, after the PAA and the SBR are incorporated in separate steps, a three-dimensional cross-linked network can be formed, good tensile behavior is exhibited, a bonding effect is improved, same can adapt well to volumetric expansion of silicon negative electrodes, and the cycling stability of silicon negative electrodes is improved.

Claims

1. A preparation method for a silicon-based negative electrode slurry, which comprises: (1) mixing CMC and a first solvent to obtain a primary binder liquid; (2) mixing PAA, a silicon-based negative electrode material, a conductive agent, a second solvent, and the obtained binder liquid, and performing double-planetary stirring to obtain a secondary binder liquid; (3) mixing a third solvent and the obtained secondary binder liquid to obtain a crude slurry; and (4) mixing SBR and the obtained crude slurry to obtain the silicon-based negative electrode slurry.

2. The preparation method according to claim 1, wherein the first solvent, the second solvent, and the third solvent are water.

3. The preparation method according to claim 1, wherein a solid content of the primary binder liquid in step (1) is 1-2%.

4. The preparation method according to claim 1, wherein the process of the double-planetary stirring in step (2) comprises low-speed stirring first, followed by medium-speed stirring.

5. The preparation method according to claim 1, wherein stirring is further comprised after the mixing in step (3); optionally, the stirring is performed at a revolution speed of 20-30 rpm and a rotation speed of 100-300 rpm; optionally, the stirring is performed for a period of 80-100 min; optionally, kneading is further comprised after the stirring; optionally, the crude slurry in step (3) has a solid content of 50-55%; optionally, the crude slurry in step (3) has a viscosity of 3500-4500 mPa.Math.s.

6. The preparation method according to claim 1, wherein the SBR in step (4) is an SBR dispersing solution; optionally, the SBR dispersing solution has a mass concentration of 35-45 wt %; optionally, vacuuming and double-planetary stirring are further comprised after the mixing in step (4); optionally, the double-planetary stirring is performed for a period of 20-40 min; optionally, the double-planetary stirring is performed at a revolution speed of 20-30 rpm and a rotation speed of 700-900 rpm; optionally, the silicon-based negative electrode slurry obtained in step (4) is stored under vacuum.

7. The preparation method according to claim 1, wherein the preparation method comprises: (1) dividing solvent water which is required for preparing the silicon-based negative electrode slurry into a first solvent, a second solvent, and a third solvent, wherein a mass of the first solvent is 35-40 wt % of the total mass of the solvent water, a mass of the second solvent is 55-65 wt % of the total mass of the solvent water, and a mass of the third solvent is 1-3 wt % of the total mass of the solvent water; mixing CMC and the first solvent to obtain a primary binder liquid with a solid content of 1-2%; a mass of the CMC is 0.1-0.5 wt % of the mass of non-solvent materials of the silicon-based negative electrode slurry; (2) mixing PAA, a silicon-based negative electrode material, a conductive agent, the second solvent, and the obtained binder liquid according to a formula amount, and performing double-planetary stirring, which comprises first performing low-speed stirring at a revolution speed of 20-30 rpm and a rotation speed of 100-300 rpm for 10-30 min, and then performing medium-speed stirring at a revolution speed of 15-25 rpm and a rotation speed of 1500-2000 rpm for 80-100 min, to obtain a secondary binder liquid; a mass of the PAA is 1-1.5 wt % of the mass of non-solvent materials of the silicon-based negative electrode slurry; a mass of the silicon-based negative electrode material is 96-97 wt % of the mass of non-solvent materials of the silicon-based negative electrode slurry; and a mass of the conductive agent is 0.5-1.5 wt % of the mass of non-solvent materials of the silicon-based negative electrode slurry; (3) mixing the third solvent and the obtained secondary binder liquid, stirring at a revolution speed of 20-30 rpm and a rotation speed of 100-300 rpm for 80-100 min, and then kneading to obtain a crude slurry with a solid content of 50-55% and a viscosity of 3500-4500 mPa.Math.s; and (4) mixing an SBR dispersing solution with a mass concentration of 35-45 wt % and the obtained crude slurry, vacuumizing, and performing double-planetary stirring at a revolution speed of 20-30 rpm and a rotation speed of 700-900 rpm for 20-40 min to obtain the silicon-based negative electrode slurry; a mass of the SBR is 1-2 wt % of the mass of non-solvent materials of the silicon-based negative electrode slurry.

8. A silicon-based negative electrode slurry, which is prepared by the preparation method according to claim 1.

9. The silicon-based negative electrode slurry according to claim 8, wherein the silicon-based negative electrode slurry has a solid content of 50-55%; optionally, the silicon-based negative electrode slurry has a viscosity of 2500-4500 cp.

10. A negative electrode sheet, which is prepared from the silicon-based negative electrode slurry according to claim 8.

11. The preparation method according to claim 2, wherein a mass of the first solvent in step (1) is 35-40 wt % of the total amount of the solvents in the silicon-based negative electrode slurry.

12. The preparation method according to claim 2, wherein a mass of the second solvent in step (2) is 55-65 wt % of the total amount of the solvents in the silicon-based negative electrode slurry.

13. The preparation method according to claim 2, wherein a mass of the third solvent in step (3) is 1-3 wt % of the total amount of the solvents in the silicon-based negative electrode slurry.

14. The preparation method according to claim 1, wherein a mass of the CMC in step (1) is 0.1-0.5 wt % of the mass of non-solvent materials of the silicon-based negative electrode slurry.

15. The preparation method according to claim 1, wherein a mass of the PAA in step (2) is 1-1.5 wt % of the mass of non-solvent materials of the silicon-based negative electrode slurry.

16. The preparation method according to claim 1, wherein a mass of the silicon-based negative electrode material in step (2) is 96-97 wt % of the mass of non-solvent materials of the silicon-based negative electrode slurry.

17. The preparation method according to claim 1, wherein a mass of the conductive agent in step (2) is 0.5-1.5 wt % of the mass of non-solvent materials of the silicon-based negative electrode slurry.

18. The preparation method according to claim 1, wherein a mass of the SBR in step (4) is 1-2 wt % of the mass of non-solvent materials of the silicon-based negative electrode slurry.

19. The preparation method according to claim 4, wherein the low-speed stirring is performed at a revolution speed of 20-30 rpm and a rotation speed of 100-300 rpm; optionally, the low-speed stirring is performed for a period of 10-30 min.

20. The preparation method according to claim 4, wherein the medium-speed stirring is performed at a revolution speed of 15-25 rpm and a rotation speed of 1500-2000 rpm; optionally, the medium-speed stirring is performed for a period of 80-100 min.

Description

DETAILED DESCRIPTION

Example 1

[0063] This example provides a preparation method for a silicon-based negative electrode slurry, and the preparation method comprises: [0064] (1) solvent water which was required for preparing the silicon-based negative electrode slurry was divided into a first solvent, a second solvent, and a third solvent, wherein a mass of the first solvent was 38 wt % of the total mass of the solvent water, a mass of the second solvent was 60 wt % of the total mass of the solvent water, and a mass of the third solvent was 2 wt % of the total mass of the solvent water; CMC and the first solvent were mixed to obtain a primary binder liquid with a solid content of 2%; a mass of the CMC was 0.3 wt % of the mass of the silicon-based negative electrode slurry; [0065] (2) PAA, a silicon-based negative electrode material, conductive carbon nano-tubes, the second solvent, and the obtained binder liquid were mixed according to a formula amount and subjected to double-planetary stirring, wherein low-speed stirring was first performed at a revolution speed of 25 rpm and a rotation speed of 200 rpm for 30 min, and then medium-speed stirring was performed at a revolution speed of 20 rpm and a rotation speed of 1800 rpm for 100 min, so as to obtain a secondary binder liquid; a mass of the PAA was 1.1 wt % of the mass of the silicon-based negative electrode slurry; a mass of the silicon-based negative electrode material was 96.1 wt % of the mass of the silicon-based negative electrode slurry; and a mass of the conductive agent was 1 wt % of the mass of the silicon-based negative electrode slurry; [0066] (3) the third solvent and the obtained secondary binder liquid were mixed, stirred at a revolution speed of 25 rpm and a rotation speed of 200 rpm for 100 min, and then kneaded to obtain a crude slurry with a solid content of 50% and a viscosity of 3500 mPa.Math.s; and [0067] (4) an SBR dispersing solution with a mass concentration of 40 wt % and the obtained crude slurry were mixed, vacuumized and then subjected to double-planetary stirring at a revolution speed of 25 rpm and a rotation speed of 800 rpm for 40 min to obtain the silicon-based negative electrode slurry; a mass of the SBR was 1.5 wt % of the mass of the silicon-based negative electrode slurry.

Example 2

[0068] This example provides a preparation method for a silicon-based negative electrode slurry, and the preparation method comprises: [0069] (1) solvent water which was required for preparing the silicon-based negative electrode slurry was divided into a first solvent, a second solvent, and a third solvent, wherein a mass of the first solvent was 35 wt % of the total mass of the solvent water, a mass of the second solvent was 64 wt % of the total mass of the solvent water, and a mass of the third solvent was 1 wt % of the total mass of the solvent water; CMC and the first solvent were mixed to obtain a primary binder liquid with a solid content of 1.5%; a mass of the CMC was 0.1 wt % of the mass of the silicon-based negative electrode slurry; [0070] (2) PAA, a silicon-based negative electrode material, carbon black, the second solvent, and the obtained binder liquid were mixed according to a formula amount and subjected to double-planetary stirring, wherein low-speed stirring was first performed at a revolution speed of 20 rpm and a rotation speed of 100 rpm for 20 min, and then medium-speed stirring was performed at a revolution speed of 25 rpm and a rotation speed of 2000 rpm for 90 min, so as to obtain a secondary binder liquid; a mass of the PAA was 1 wt % of the mass of the silicon-based negative electrode slurry; a mass of the silicon-based negative electrode material was 96 wt % of the mass of the silicon-based negative electrode slurry; and a mass of the conductive agent was 0.5 wt % of the mass of the silicon-based negative electrode slurry; [0071] (3) the third solvent and the obtained secondary binder liquid were mixed, stirred at a revolution speed of 20 rpm and a rotation speed of 100 rpm for 90 min, and then kneaded to obtain a crude slurry with a solid content of 52% and a viscosity of 4000 mPa.Math.s; and [0072] (4) an SBR dispersing solution with a mass concentration of 35 wt % and the obtained crude slurry were mixed, vacuumized and then subjected to double-planetary stirring at a revolution speed of 20 rpm and a rotation speed of 700 rpm for 30 min to obtain the silicon-based negative electrode slurry; a mass of the SBR was 1 wt % of the mass of the silicon-based negative electrode slurry.

Example 3

[0073] This example provides a preparation method for a silicon-based negative electrode slurry, and the preparation method comprises: [0074] (1) solvent water which was required for preparing the silicon-based negative electrode slurry was divided into a first solvent, a second solvent, and a third solvent, wherein a mass of the first solvent was 40 wt % of the total mass of the solvent water, a mass of the second solvent was 57 wt % of the total mass of the solvent water, and a mass of the third solvent was 3 wt % of the total mass of the solvent water; CMC and the first solvent were mixed to obtain a primary binder liquid with a solid content of 1%; a mass of the CMC was 0.5 wt % of the mass of the silicon-based negative electrode slurry; [0075] (2) PAA, a silicon-based negative electrode material, carbon nano-tubes, the second solvent, and the obtained binder liquid were mixed according to a formula amount and subjected to double-planetary stirring, wherein low-speed stirring was first performed at a revolution speed of 30 rpm and a rotation speed of 300 rpm for 10 min, and then medium-speed stirring was performed at a revolution speed of 25 rpm and a rotation speed of 2000 rpm for 80 min, so as to obtain a secondary binder liquid; a mass of the PAA was 1.5 wt % of the mass of the silicon-based negative electrode slurry; a mass of the silicon-based negative electrode material was 96 wt % of the mass of the silicon-based negative electrode slurry; and a mass of the conductive agent was 0.5 wt % of the mass of the silicon-based negative electrode slurry; [0076] (3) the solvent and the obtained secondary binder liquid were mixed, stirred at a revolution speed of 30 rpm and a rotation speed of 300 rpm for 80 min, and then kneaded to obtain a crude slurry with a solid content of 55% and a viscosity of 4500 mPa.Math.s; and [0077] (4) an SBR dispersing solution with a mass concentration of 45 wt % and the obtained crude slurry were mixed, vacuumized and then subjected to double-planetary stirring at a revolution speed of 30 rpm and a rotation speed of 900 rpm for 20 min to obtain the silicon-based negative electrode slurry; a mass of the SBR was 1 wt % of the mass of the silicon-based negative electrode slurry.

Example 4

[0078] This example provides a preparation method for a silicon-based negative electrode slurry, which differs from Example 1 in that a solid content of the primary binder liquid in step (1) was 3%.

Example 5

[0079] This example provides a preparation method for a silicon-based negative electrode slurry, which differs from Example 1 in that a solid content of the primary binder liquid in step (1) was 0.5%.

Example 6

[0080] This example provides a preparation method for a silicon-based negative electrode slurry, which differs from Example 1 in that the low-speed stirring of the double-planetary stirring in step (2) was not performed.

Example 7

[0081] This example provides a preparation method for a silicon-based negative electrode slurry, which differs from Example 1 in that the medium-speed stirring of the double-planetary stirring in step (2) was not performed.

Example 8

[0082] This example provides a preparation method for a silicon-based negative electrode slurry, which differs from Example 1 in that a solid content of the crude slurry in step (3) was 45%.

Example 9

[0083] This example provides a preparation method for a silicon-based negative electrode slurry, which differs from Example 1 in that a solid content of the crude slurry in step (3) was 60%.

Example 10

[0084] This example provides a preparation method for a silicon-based negative electrode slurry, which differs from Example 1 in that a viscosity of the crude slurry in step (3) was 3000 mPa.Math.s.

Example 11

[0085] This example provides a preparation method for a silicon-based negative electrode slurry, which differs from Example 1 in that a viscosity of the crude slurry in step (3) was 4000 mPa.Math.s.

Example 12

[0086] This example provides a preparation method for a silicon-based negative electrode slurry, which differs from Example 1 in that the SBR dispersing solution in step (4) was replaced by solid SBR.

Example 13

[0087] This example provides a preparation method for a silicon-based negative electrode slurry, which differs from Example 1 in that a mass of the solvent in step (1) was 50 wt % of the total amount of the solvents in the silicon-based negative electrode slurry, a mass of the solvent in step (2) was 40 wt % of the total amount of the solvents in the silicon-based negative electrode slurry, and a mass of the solvent in step (3) was 10 wt % of the total amount of the solvents in the silicon-based negative electrode slurry.

Comparative Example 1

[0088] This comparative example provides a preparation method for a silicon-based negative electrode slurry, which differs from Example 1 in that the CMC in step (1) was replaced by PAA with an equal mass, and the PAA in step (2) was replaced by CMC with an equal mass.

Comparative Example 2

[0089] This comparative example provides a preparation method for a silicon-based negative electrode slurry, which differs from Example 1 in that the CMC in step (1) was replaced by PAA with an equal mass, the PAA in step (2) was replaced by CMC with an equal mass, and the low-speed stirring of the double-planetary stirring in step (2) was not performed.

Comparative Example 3

[0090] This comparative example provides a preparation method for a silicon-based negative electrode slurry, which differs from Example 1 in that the CMC in step (1) was replaced by PAA with an equal mass, the PAA in step (2) was replaced by CMC with an equal mass, and the medium-speed stirring of the double-planetary stirring in step (2) was not performed.

Comparative Example 4

[0091] This comparative example provides a preparation method for a silicon-based negative electrode slurry, which differs from Example 1 in that the SBR dispersing solution in step (4) was replaced by a PAA dispersing solution with an equal mass.

Comparative Example 5

[0092] This comparative example provides a preparation method for a silicon-based negative electrode slurry, which differs from Example 1 in that the mixing with water in step (2) and step (3) was performed in step (1).

[0093] The above obtained silicon-based negative electrode slurries were coated on a current collector to prepare negative electrode sheets, and assembled into lithium-ion batteries with positive electrode sheets of ternary material (NCM111) as the positive electrode material. Testing the lithium-ion batteries and the test results are shown in Table 1.

TABLE-US-00001 TABLE 1 Volume Test No. expansion rate Cycle performance Rate capability Example 1 0.24% 6 A-70 A cycle 50 A: 75% C.sub.N 92%@400 cyc. Example 2 0.43% 6 A-70 A cycle 50 A: 70% C.sub.N 89%@400 cyc. Example 3 0.57% 6 A-70 A cycle 50 A: 70% C.sub.N 90%@400 cyc. Example 4 3.7% 6 A-70 A cycle 50 A: 65% C.sub.N 70%@400 cyc. Example 5 2.6% 6 A-70 A cycle 50 A: 70% C.sub.N 72%@400 cyc. Example 6 1.7% 6 A-70 A cycle 50 A: 60% C.sub.N 62%@300 cyc. Example 7 2.3% 6 A-70 A cycle 50 A: 58% C.sub.N 57%@300 cyc. Example 8 5.8% 6 A-70 A cycle 50 A: 45% C.sub.N 300 cyc. plunge Example 9 6.1% 6 A-70 A cycle 50 A: 41% C.sub.N 300 cyc. plunge Example 10 7.1% 6 A-70 A cycle 50 A: 40% C.sub.N 300 cyc. plunge Example 11 6.8% 6 A-70 A cycle 50 A: 42% C.sub.N 300 cyc. plunge Example 12 4.3% 6 A-70 A cycle 50 A: 65% C.sub.N 72%@400 cyc. Example 13 Failed to be kneaded together Comparative 0.7% 6 A-70 A cycle 50 A: 70% C.sub.N Example 1 83%@400 cyc. Comparative 2.7% 6 A-70 A cycle 50 A: 45% C.sub.N Example 2 55%@300 cyc. Comparative 3.3% 6 A-70 A cycle 50 A: 40% C.sub.N Example 3 50%@300 cyc. Comparative 3.7% 6 A-70 A cycle 50 A: 61% C.sub.N Example 4 70%@400 cyc. Comparative Unqualified slurry Example 5 Failed to meet standards for granularity and fineness

[0094] The following conclusions can be obtained from Table 1.

[0095] As can be seen from Examples 1-3, in the slurry-homogenizing method of the present application, by combining PAA and SBR in a step-by-step manner, a three-dimensional crosslinked network can be formed, which shows a good tensile property, and can improve the bonding effect, be well adapted to the volume expansion of the silicon negative electrode, and improve the cycle stability of the silicon negative electrode.

[0096] As can be seen from the comparison of Examples 4 and 5 to Example 1, in a case where the solid content of the primary binder liquid is out of the preferred range of the present application, the bonding effect of the homogenized slurry is poor, and the inhibition effect on the expansion of the silicon negative electrode material is poor.

[0097] As can be seen from the comparison of Examples 6 and 7 to Example 1, the stirring process of the double-planetary stirring is improved in the present application, so that the secondary binder liquid is mixed thoroughly and evenly, with a good bonding effect, which is conducive to the formation of crosslinked network structure. When the stirring process is changed, the effect of slurry-homogenizing is affected, resulting in poor cycle stability of the battery.

[0098] As can be seen from the comparison of Examples 8 and 9 to Example 1, in a case where the solid content of the crude slurry is not within the preferred range of the present application, the bonding effect of the homogenized slurry is poor, and the inhibition effect on the expansion of the silicon negative electrode material is poor.

[0099] As can be seen from the comparison of Examples 10 and 11 to Example 1, in a case where the viscosity of the crude slurry is not within the preferred range of the present application, the bonding effect of the homogenized slurry is poor, and the inhibition effect on the expansion of the silicon negative electrode material is poor.

[0100] As can be seen from the comparison of Example 12 and Comparative Example 4 to Example 1, the method of mixing the SBR dispersing solution and the PAA crude slurry adopted in the present application improves the bonding effect of the homogenized slurry, and is conducive to inhibiting the expansion of the silicon-based negative electrode in the slurry, and improves the cycle stability.

[0101] As can be seen from the comparison of Example 13 and Comparative Example 5 to Example 1, in the present application, the slurry-homogenizing method where the solvent is added sequentially by three steps, with the controlled additive amount of water, is conducive to improving the bonding effect.

[0102] As can be seen from the comparison of Comparative Example 1 and Example 1, because PAA is a water-soluble polymer with high strength, high toughness, and extremely strong adhesion, and

[0103] PAA can use its large number of carboxyl groups to crosslink with itself or with other auxiliary polymers, by controlling the feeding sequence of PAA and CMC, the carboxyl groups on PAA undergo crosslinking during the feeding process, which further improves the bonding effect of the homogenized slurry, and is conducive to inhibiting the expansion of the silicon-based negative electrode in the slurry, and improves the cycle stability.

[0104] As can be seen from the comparison of Examples 6 and 7 and Comparative Examples 2 and 3 to Example 1, in the present application, there is a synergistic effect between the controlling of the feeding sequence of PAA and CMC and the stirring process of the double-planetary stirring, which improves the bonding effect of the homogenized slurry, and is conducive to inhibiting the expansion of the silicon-based negative electrode slurry, and improves the cycle stability.