Electronically conductive polymer binder for lithium-ion battery electrode
A family of carboxylic acid groups containing fluorene/fluorenon copolymers is disclosed as binders of silicon particles in the fabrication of negative electrodes for use with lithium ion batteries. Triethyleneoxide side chains provide improved adhesion to materials such as, graphite, silicon, silicon alloy, tin, tin alloy. These binders enable the use of silicon as an electrode material as they significantly improve the cycle-ability of silicon by preventing electrode degradation over time. In particular, these polymers, which become conductive on first charge, bind to the silicon particles of the electrode, are flexible so as to better accommodate the expansion and contraction of the electrode during charge/discharge, and being conductive promote the flow battery current.
1. A polymeric composition with repeating units of the formula:
wherein: R 1 is selected from the group consisting of: naphthalene, anthracene, pyrene, fluorene, fluorenone and oligophenylene, R 2 is (OCH 2 CH 2 ) m CH 3 where m=0-1000, R 3 is selected from the group consisting of: H, OH, alkyloxide, alkanol, ethyleneoxide, carbonate and trialkylamine, a+b+c=1 wherein 0<a<1, 0<b<1, and 0<c<1, and n=1-10 million.
2. A method for making an electrode for use in a lithium ion battery comprising the steps of:
a) forming a solution of a solvent and a conductive polymer of the formula
wherein: R 1 is selected from the group consisting of: naphthalene, anthracene, pyrene, fluorene, fluorenone and oligophenylene, R 2 is (OCH 2 CH 2 ) m CH 3 where m=0-1000, R 3 is selected from the group consisting of: H, OH, alkyloxide, alkanol, ethyleneoxide, carbonate and trialkylamine, a+b+c=1 wherein 0<a<1, 0<b<1, and 0<c<1, and n=1-10 million;
b) to this solution adding micro or nanoparticles of at least 1 element selected from the group consisting of: silicon, Sn, and graphite to form a slurry;
c) mixing the slurry to form a homogenous mixture;
d) depositing a thin film of said thus obtained mixture over top of a substrate;
e) drying the resulting composite to form said silicon electrode.
3. A lithium ion battery having a silicon electrode incorporating a conductive polymer binder having repeating units of the formula:
wherein: R 1 is selected from the group consisting of: naphthalene, anthracene, pyrene, fluorene, fluorenone and oligophenylene, R 2 is (OCH 2 CH 2 ) m CH 3 where m=0-1000, R 3 is selected from the group consisting of: H, OH, alkyloxide, alkanol, ethyleneoxide, carbonate and trialkylamine, a+b+c=1 wherein 0<a<1, 0<b<1, and 0<c<1, and n=1-10 million.