Cross-linked hyperbranched polyethylenimine as an efficient multidimensional binder for silicon anodes in lithium-ion batteries

We report the use of cross-linked hyperbranched polyethylenimine (PEI) as a commercially available, eco-friendly, water-soluble, efficient polymer binder for silicon anode of lithium ion battery for the first time. Compared with traditional one-dimensional linear binders, the PEI with 3-dimensional topological hyperbranched structure and high density of amino groups can facilitate stronger multidimensional hydrogen-bonding interactions with silicon nanoparticles which may more effectively buffer large volume change of silicon particles during lithiation/delithiation process. In addition, the cross-linked 3-dimensional network of PEI limits movement of silicon nanoparticles and maintains integrity of the anode. Through optimizing the amount of cross-linking agent, 1,4-butanediol diglycidyl ether, to balance bonding reversibility and mechanical strength of PEI, the cross-linked Si/PEI anode shows significantly improved cycling performance with a specific capacity of 2180 mAh g−1 at a current density of 500 mA g−1 after 100 cycles.