DISPERSANT FOR LITHIUM ION BATTERY AND PREPARATION METHOD THEREOF, POSITIVE SLURRY, AND LITHIUM ION BATTERY

Abstract

A dispersant for a lithium ion battery and a preparation method thereof, a positive slurry, and a lithium ion battery are provided. The dispersant includes a structural unit A derived from N-vinylpyrrolidone, a structural unit B derived from a conjugated diene monomer, and a structural unit C derived from an organic acid monomer. The organic acid monomer includes one or more of an unsaturated sulfonic acid monomer, an unsaturated phosphoric acid monomer, and an unsaturated carboxylic acid monomer.

Claims

1. A dispersant for a lithium ion battery, the dispersant comprising a structural unit A derived from N-vinylpyrrolidone, a structural unit B derived from a conjugated diene monomer, and a structural unit C derived from an organic acid monomer, wherein the organic acid monomer comprises one or more of an unsaturated sulfonic acid monomer, an unsaturated phosphoric acid monomer, and an unsaturated carboxylic acid monomer.

2. The dispersant according to claim 1, wherein based on a total amount of the dispersant, a molar proportion of the structural unit A is in a range of 30%-90%, a molar proportion of the structural unit B is in a range of 5%-50%, and a molar proportion of the structural unit C is in a range of 1%-30%.

3. The dispersant according to claim 1, wherein the unsaturated sulfonic acid monomer comprises one or more of vinyl sulfonic acid, allyl sulfonic acid, methylallyl sulfonic acid, 2-acrylamide-2-methylpropane sulfonic acid, styrene sulfonic acid, 3-allyloxy-2-hydroxypropane sulfonic acid, 2-methyl-2-acrylate-2-sulfonic ethyl ester, 3-sulfopropyl acrylate, 3-sulfopropyl methacrylate, and salts thereof; the unsaturated phosphoric acid monomer comprises one or more of vinyl phosphonic acid, (1-phenylvinyl) phosphonic acid, allyl phosphonic acid, bis[2-(methacryloxy)ethyl] phosphoric acid, 2-(methacryloyloxy)ethyl 2-(trimethylammonio)ethyl phosphate, and 2-methyl-2-propenoic acid 2-(phosphonooxy)ethyl ester; and the unsaturated carboxylic acid monomer comprises one or more of acrylic acid, methacrylic acid, 2-ethylacrylic acid, α-acetoxyacrylic acid, butenoic acid, crotonic acid, maleic acid, itaconic acid, and fumaric acid.

4. The dispersant according to claim 2, wherein the unsaturated sulfonic acid monomer comprises one or more of vinyl sulfonic acid, allyl sulfonic acid, methylallyl sulfonic acid, 2-acrylamide-2-methylpropane sulfonic acid, styrene sulfonic acid, 3-allyloxy-2-hydroxypropane sulfonic acid, 2-methyl-2-acrylate-2-sulfonic ethyl ester, 3-sulfopropyl acrylate, 3-sulfopropyl methacrylate, and salts thereof; the unsaturated phosphoric acid monomer comprises one or more of vinyl phosphonic acid, (1-phenylvinyl) phosphonic acid, allyl phosphonic acid, bis[2-(methacryloxy)ethyl] phosphoric acid, 2-(methacryloyloxy)ethyl 2-(trimethylammonio)ethyl phosphate, and 2-methyl-2-propenoic acid 2-(phosphonooxy)ethyl ester; and the unsaturated carboxylic acid monomer comprises one or more of acrylic acid, methacrylic acid, 2-ethylacrylic acid, α-acetoxyacrylic acid, butenoic acid, crotonic acid, maleic acid, itaconic acid, and fumaric acid.

5. The dispersant according to claim 1, wherein the conjugated diene monomer comprises one or more of 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, 1,3-decadiene, and 2-methyl-1,5-heptadiene.

6. The dispersant according to claim 2, wherein the conjugated diene monomer comprises one or more of 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, 1,3-decadiene, and 2-methyl-1,5-heptadiene.

7. The dispersant according to claim 3, wherein the conjugated diene monomer comprises one or more of 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, 1,3-decadiene, and 2-methyl-1,5-heptadiene.

8. The dispersant according to claim 4, wherein the conjugated diene monomer comprises one or more of 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, 1,3-pentadiene, 1,3-hexadiene, 1,3-decadiene, and 2-methyl-1,5-heptadiene.

9. The dispersant according to claim 1, wherein a weight average molecular weight of the dispersant is in a range of 5000-100000.

10. The dispersant according to claim 2, wherein a weight average molecular weight of the dispersant is in a range of 5000-100000.

11. The dispersant according to claim 3, wherein a weight average molecular weight of the dispersant is in a range of 5000-100000.

12. The dispersant according to claim 4, wherein a weight average molecular weight of the dispersant is in a range of 5000-100000.

13. The dispersant according to claim 5, wherein a weight average molecular weight of the dispersant is in a range of 5000-100000.

14. The dispersant according to claim 6, wherein a weight average molecular weight of the dispersant is in a range of 5000-100000.

15. A method for preparing a dispersant for a lithium ion battery, comprising: performing a polymerization reaction on a monomer raw material comprising N-vinylpyrrolidone, a conjugated diene monomer, and an organic acid monomer to obtain the dispersant for a lithium ion battery, wherein the organic acid monomer comprises one or more of an unsaturated sulfonic acid monomer, an unsaturated phosphoric acid monomer, and an unsaturated carboxylic acid monomer.

16. The method according to claim 6, wherein the preparation method further comprises: performing a hydrogenation reaction on the polymer formed through the polymerization reaction of the monomer raw material.

17. The method according to claim 6, wherein based on a total mass of the monomer raw material, a proportion of the N-vinylpyrrolidone is in a range of 30%-90%, a proportion of the conjugated diene monomer is in a range of 5%-40%, and a proportion of the organic acid monomer is in a range of 1%-40%.

18. A positive slurry, comprising a positive active material, a conductive agent, a binder, a dispersant, and a solvent, wherein the dispersant is the dispersant according to claim 1.

19. The positive slurry according to claim 9, wherein a mass of the dispersant does not exceed 0.4% of a mass of the positive active material.

20. A lithium ion battery, comprising a positive plate, wherein the positive plate comprises a current collector and a positive material layer arranged on the current collector; the positive material layer comprises a positive active material, a conductive agent, a binder, and a dispersant; and the dispersant is the dispersant according to claim 1.

Description

DETAILED DESCRIPTION

[0033] The following provides exemplary implementations of the present disclosure. It should be noted that a person of ordinary skill in the art may make several improvements and refinements without departing from the principles of the present disclosure. These improvements and refinements are considered to fall within the protection scope of the present disclosure.

[0034] The present disclosure is further described below through the following embodiments.

Embodiment 1

[0035] A method for preparing a dispersant for a lithium ion battery includes:

[0036] dissolving N-vinylpyrrolidone, 1,3-butadiene, and vinyl phosphonic acid in N, N-dimethylformamide (DMF) at a mass ratio of 70:20:10, adding an initiator azobisisobutyronitrile and a chain transfer agent dodecyl mercaptan, performing polymerization at 60° C. for 4 hours at a pressure of 4 MPa, performing cooling to terminate the reaction, washing and drying a resulting reactant to obtain a dispersant 1′, and hydrogenating the dispersant 1′ to obtain a dispersant 1. A weight average molecular weight of the dispersant 1 is measured as about 50000.

[0037] A method for preparing a positive plate includes: dissolving 2 g of binder PVDF in 40 g of N-methylpyrrolidone (NMP), and adding 0.3 g of the above dispersant 1 after full dissolution, and performing stirring for 20 min; adding 20 g of carbon nanotube dispersion (solvent: NMP, solid content: 5 wt%) and performing stirring for 20 min; adding 97 g of lithium iron phosphate positive active material and performing stirring for 1.5 h to obtain a positive slurry; and coating the positive slurry on aluminum foil and performing drying at 130° C. for 30 min to form a positive material layer, thereby completing the production of a lithium iron phosphate positive plate.

Embodiment 2

[0038] A method for preparing a dispersant for a lithium ion battery includes:

[0039] dissolving N-vinylpyrrolidone, 1,3-pentadiene, and bis[2-(methacryloxy)ethyl] phosphoric acid in dioxane at a mass ratio of 50:20:30, adding an initiator azobisisobutyronitrile and a chain transfer agent dodecyl mercaptan, performing polymerization at 60° C. for 4 hours at a pressure of 4 MPa, performing cooling to terminate the reaction, and washing and drying a resulting reactant to obtain a dispersant 2. A weight average molecular weight of the dispersant 2 is measured as 10000.

[0040] In a method for preparing a positive plate, 0.3 g of dispersant 1 in Embodiment 1 is replaced with 0.3 g of dispersant 2, and other conditions are the same as those in Embodiment 1.

Embodiment 3

[0041] A method for preparing a dispersant for a lithium ion battery includes: dissolving N-vinylpyrrolidone, 1,3-hexadiene, and 2-ethylacrylic acid in dioxane at a mass ratio of 90:5:5, adding an initiator azobisisobutyronitrile and a chain transfer agent ethyl acetate, performing polymerization at 60° C. for 4 hours at a pressure of 4 MPa, performing cooling to terminate the reaction, and washing and drying a resulting reactant to obtain a dispersant 3. A weight average molecular weight of the dispersant 3 is measured as about 86000.

[0042] In a method for preparing a positive plate, 0.3 g of dispersant 1 in Embodiment 1 is replaced with 0.3 g of dispersant 3, and other conditions are the same as those in Embodiment 1.

Embodiment 4

[0043] A method for preparing a dispersant for a lithium ion battery includes:

[0044] dissolving N-vinylpyrrolidone, isoprene, and vinyl sulfonic acid in DMF at a mass ratio of 65:30:5, adding an initiator azobisisobutyronitrile and a chain transfer agent dodecyl mercaptan, performing polymerization at 60° C. for 4 hours at a pressure of 4 MPa, performing cooling to terminate the reaction, washing and drying a resulting reactant to obtain a dispersant 4′, and hydrogenating the dispersant 4′ to obtain a dispersant 4. A weight average molecular weight of the dispersant 4 is measured as about 22000.

[0045] A method for preparing a positive plate includes: dissolving 1 g of binder PVDF in 30 g of NMP, and adding 0.3 g of dispersant 4 after full dissolution, and performing stirring for 20 min; adding 10 g of carbon nanotube NMP dispersion (solid content: 5 wt%) and 1.5 g of carbon black as a conductive agent, and performing stirring for 20 min; adding 97 g of positive active material NCM622 (LiNi.sub.0.6Co.sub.0.2Mn.sub.0.2O.sub.2) and performing stirring for 1.5 h to obtain a positive slurry; and coating the positive slurry on aluminum foil and performing drying at 130° C. for 30 min to form a positive material layer, thereby completing the production of an NCM ternary positive plate.

Embodiment 5

[0046] A method for preparing a dispersant for a lithium ion battery includes:

[0047] dissolving N-vinylpyrrolidone, 1,3-butadiene, 2-acrylamide-2-methylpropane sulfonic acid in DMF at a mass ratio of 60:30:10, adding an initiator azobisisobutyronitrile and a chain transfer agent ethyl acetate, performing polymerization at 60° C. for 4 hours at a pressure of 4 MPa, performing cooling to terminate the reaction, washing and drying a resulting reactant to obtain a dispersant 5′, and hydrogenating the dispersant 5′ to obtain a dispersant 5. A weight average molecular weight of the dispersant 5 is measured as about 40000.

[0048] In a method for preparing a positive plate, 0.3 g of dispersant 4 in Embodiment 4 is replaced with 0.3 g of dispersant 5, and other conditions are the same as those in Embodiment 4.

Embodiment 6

[0049] A method for preparing a dispersant for a lithium ion battery includes:

[0050] dissolving N-vinylpyrrolidone, isoprene, and maleic acid in dioxane at a mass ratio of 50:35:15, adding an initiator azobisisobutyronitrile and a chain transfer agent dodecyl mercaptan, performing polymerization at 60° C. for 4 hours at a pressure of 4 MPa, performing cooling to terminate the reaction, washing and drying a resulting reactant to obtain a dispersant 6′, and hydrogenating the dispersant 6′ to obtain a dispersant 6. A weight average molecular weight of the dispersant 6 is measured as 55000.

[0051] In a method for preparing a positive plate, 0.3 g of dispersant 4 in Embodiment 4 is replaced with 0.3 g of dispersant 6, and other conditions are the same as those in Embodiment 4.

[0052] The following comparative examples 1-4 are set up below to highlight the beneficial effects of the present disclosure.

Comparative Example 1

[0053] A main difference between a lithium iron phosphate positive plate in Comparative example 1 and that in Embodiment 1 is that no dispersant is added but a larger amount of solvent is used during the preparation of the lithium iron phosphate positive plate.

[0054] A method for preparing a lithium iron phosphate positive plate in Comparative example 1 includes: fully dissolving 2 g of binder PVDF in 50 g of NMP; adding 20 g of carbon nanotube NMP dispersion (solid content: 5 wt%), and performing stirring for 20 min; adding 97 g of lithium iron phosphate positive active material and performing stirring for 3 h to obtain a positive slurry; and coating the positive slurry on aluminum foil and performing drying at 130° C. for 30 min to form a positive material layer, thereby completing the production of a lithium iron phosphate positive plate.

Comparative Example 2

[0055] A main difference between a lithium iron phosphate positive plate in Comparative example 2 and that in Embodiment 1 is that 1.0 g of the existing dispersant PVP is added during the preparation of the lithium iron phosphate positive plate.

[0056] A method for preparing a lithium iron phosphate positive plate in Comparative example 2 includes: dissolving 2 g of binder PVDF in 40 g of NMP, and adding 1.0 g of dispersant PVP after full dissolution, and performing stirring for 20 min; adding 20 g of carbon nanotube NMP dispersion (solid content: 5 wt%), and performing stirring for 20 min; adding 97 g of lithium iron phosphate positive active material and performing stirring for 1.5 h to obtain a positive slurry; and coating the positive slurry on aluminum foil and performing drying at 130° C. for 30 min to form a positive material layer, thereby completing the production of a lithium iron phosphate positive plate.

Comparative Example 3

[0057] A main difference between a ternary positive plate in Comparative example 3 and that in Embodiment 4 is that no dispersant is added but a larger amount of solvent is used during the preparation of the NCM ternary positive plate.

[0058] A method for preparing a ternary positive plate in Comparative example 2 includes: fully dissolving 1 g of binder PVDF in 40 g of NMP; adding 10 g of carbon nanotube dispersion (5 wt%) and 1.5 g of carbon black as a conductive agent, and performing stirring for 20 min; adding 97 g of positive active material NCM622 (LiNi.sub.0.6Co.sub.0.2Mn.sub.0.2O.sub.2) and performing stirring for 3 h to obtain a positive slurry; and coating the positive slurry on aluminum foil and performing drying at 130° C. for 30 min to form a positive material layer, thereby completing the production of an NCM ternary positive plate.

Comparative Example 4

[0059] A main difference between a ternary positive plate in Comparative example 4 and that in Embodiment 4 is that 1.0 g of dispersant PVP is added during the preparation of the NCM ternary positive plate.

[0060] A method for preparing an NCM positive plate in Comparative example 4 includes: dissolving 1 g of binder PVDF in 30 g of NMP, and adding 1.0 g of dispersant PVP after full dissolution, and performing stirring for 20 min; adding 10 g of carbon nanotube dispersion (5 wt%) and 1.5 g of carbon black as a conductive agent, and performing stirring for 20 min; adding 97 g of positive active material NCM622 and performing stirring for 1.5 h to obtain a positive slurry; and coating the positive slurry on aluminum foil and performing drying at 130° C. for 30 min to form a positive material layer, thereby completing the production of an NCM ternary positive plate.

[0061] In order to support the beneficial effects of the present disclosure, the observed viscosity and solid content of the positive slurry in each embodiment and comparative example, content of the positive active material in the positive material layer, and flexibility of the positive plate are summarized in the following Table 1.

TABLE-US-00001 Summary of results of embodiments and comparative examples Viscosity of positive slurry (mPa.Math.s) Solid content of positive slurry (%) Content of positive active material in positive material layer (%) Flexibility of positive plate Embodiment 1 3280 63.0 96.7 Aluminum foil exposed from the crease, opaque Embodiment 2 3250 63.0 96.7 Aluminum foil exposed from the crease, opaque Embodiment 3 3370 63.0 96.7 No aluminum foil exposed from the crease, opaque Comparative example 1 3300 59.2 97.0 Plate broken at the crease, transparent Comparative example 2 3210 63.0 96.0 Aluminum foil exposed from the crease, transparent Embodiment 4 2330 71.7 96.7 No aluminum foil exposed from the crease, opaque Embodiment 5 2110 71.7 96.7 Aluminum foil exposed from the crease, opaque Embodiment 6 2200 71.7 96.7 Aluminum foil exposed from the crease, opaque Comparative example 3 2120 66.8 97.0 Plate broken at the crease, transparent Comparative example 4 2070 71.7 96.0 Aluminum foil exposed from the crease, transparent

[0062] The viscosities of the positive slurries in the above Table 1 are measured by using a rheometer with a reference model of Anton Paar MCR 302. The flexibilities of the positive plates are obtained through visual observation after folding the positive plates in half in the same condition.

[0063] Through comparison between Embodiments 1-3 and Comparative example 1 and between Embodiments 4-6 and Comparative example 3, it may be learned from Table 1 that the viscosities of the positive slurries approximate each other, and the positive slurry including a small amount of dispersant provided in the embodiments of the present disclosure has a higher solid content and a shorter time is spent in producing a positive slurry with a desirable dispersion effect in a case that the content of the positive active material in the positive material layer is almost constant (or varies slightly). In addition, it may be learned through comparison between Embodiments 1-3 and Comparative example 2 and between Embodiments 4-6 and Comparative example 4 that when the positive slurries have the same solid content, an amount of PVP added is far greater than that of the dispersant provided in the embodiments of the present disclosure, which causes a proportion of active substances in the positive material layer in the corresponding comparative example to be less, thus subsequently reducing a specific capacity of a battery. The results indicate that the dispersant provided in the present disclosure has a high dispersion capability for the positive slurry. Moreover, compared with the positive plate in the corresponding comparative example, the positive plate including the dispersant in the embodiments of the present disclosure has a larger flexibility, and is unlikely to crack and transmit light after being folded in half, which indicates that the positive plate in the embodiments of the present disclosure has desirable processing performance.

[0064] The foregoing embodiments show only several implementations of the present disclosure and are described in detail, which, however, are not to be construed as a limitation to the patent scope of the present disclosure. It should be noted that a person of ordinary skill in the art may make several transformations and improvements can be made without departing from the idea of the present disclosure. The transformations and improvements belong to the protection scope of the present disclosure. Therefore, the protection scope of the patent of the present disclosure shall be subject to the appended claims.