Binder, preparation method therefor, secondary battery, battery module, battery pack and power consuming device
The present application provides a binder, a preparation method therefor, a secondary battery, a battery module, a battery pack, and a power consuming device. The binder is a polymer containing structural units as represented by formula I and formula II, wherein R 1 , R 2 , R 3 , R 5 , R 6 , and R 7 are each independently selected from hydrogen or C 1-3 alkyl unsubstituted or substituted by a substituent, R 4 is selected from hydrogen, cyano, an aldehyde group, or an ester group, and M is selected from H, Li, Na, K or NH 4 . The binder of the present application has excellent swelling resistance, and the corresponding secondary batteries have significantly improved cycling performance and power performance.
1 . A method for preparing a binder, wherein the binder is a polymer containing structural units as represented by formula I and formula II,
wherein R 1 , R 2 , R 3 , R 5 , R 6 , and R 7 are each independently selected from hydrogen or substituted or unsubstituted C 1-3 alkyl, R 4 is selected from hydrogen, cyano, an aldehyde group, or an ester group, and M is selected from H, Li, Na, K or NH 4 ;
the polymer comprises a first structural unit represented by formula I where R 4 is an aldehyde group or an ester group and a second structural unit represented by formula I where R 4 is hydrogen or cyano, wherein the first structural unit is different from the second structural unit;
a molar content of the structural unit represented by formula II is 0.1%-60%, based on a total number of moles of all structural units in the polymer;
wherein the method comprises:
preparing an intermediate polymer comprising polymerizing a monomer represented by formula III to form the intermediate polymer containing at least cyano, an aldehyde group, or an ester group,
wherein in the formula III, R 1 , R 2 , and R 3 are each independently selected from hydrogen and substituted or unsubstituted C 1-3 alkyl, and R 4 is selected from hydrogen, cyano, an aldehyde group, or an ester group;
wherein the monomer is selected from a first monomer represented by formula III where R 4 is an aldehyde group or an ester group and a second monomer represented by formula III where R 4 is hydrogen or cyano, the first monomer corresponds to the first structural unit, the second monomer corresponds to the second structural unit, and the second monomer is different from the first monomer in structure; and
performing a modification reaction comprising subjecting the intermediate polymer and an aqueous solution of an alkaline substance to a modification reaction, such that at least part of the cyano, aldehyde groups or ester groups in the intermediate polymer are converted into COOM groups, wherein M is selected from H, Li, Na, K or NH 4 .
2 . The method according to claim 1 , wherein a molar content of the second structural unit is 20%-90%, based on the total number of moles of all structural units in the polymer.
3 . The method according to claim 1 , wherein a molar ratio of the second monomer to the first monomer is 2:8-9:1.
4 . The method according to claim 1 , wherein the first monomer is selected from one or more of acrolein, acrylonitrile, methyl acrylate, ethyl acrylate, butyl acrylate, isooctyl acrylate, and methyl methacrylate.
5 . The method according to claim 1 , wherein the second monomer is selected from one or more of ethylene, propylene, butylene, and acrylonitrile.
6 . The method according to claim 1 , wherein the intermediate polymer has a weight average molecular weight of 5×10 4 -1.5×10 6 g/mol.
7 . The method according to claim 1 , wherein the alkaline substance is selected from one or more of lithium hydroxide, sodium hydroxide, potassium hydroxide, and ammonia water.
8 . The method according to claim 1 , wherein a molar ratio of a total amount of the cyano, aldehyde and ester functional groups in the first monomer to a total amount of the alkaline substance is 1:0.1-1:2.
9 . The method according to claim 1 , wherein a reaction temperature of the modification reaction is 35° C.-120° C.
10 . The method according to claim 1 , wherein a reaction time of the modification reaction is 1 h-24 h.
11 . The method according to claim 1 , further comprising:
after performing the modification reaction, adding an acidic solution to a reaction mixture of the modification reaction to adjust a pH value of the modification reaction mixture to 6-8.