Dopamine-grafted heparin as an additive to the commercialized carboxymethyl cellulose/styrene-butadiene rubber binder for practical use of SiOx/graphite composite anode.

Graphite is used commercially as the active material in lithium ion batteries, frequently as part of a graphite/SiOx composite. Graphite is used in conjunction with SiOx to overcome the limited energy density of graphite, and to lessen the adverse effects of volume expansion of Si. However, electrodes based on graphite/SiOx composites can be made with only 3-5 wt % SiOx because of the increased failure of electrodes with higher SiOx contents. Here, we developed a new polymer binder, by combining dopamine-grafted heparin with the commercial binder carboxymethyl cellulose (CMC)/styrene butadiene rubber (SBR), in order to more effectively hold the SiOx particles together and prevent disintegration of the electrode during charging and discharging. The crosslinking using acid-base interactions between heparin and CMC and the ion-conducting sulfonate group in heparin, together with the strong adhesion properties of dopamine, yielded better physical properties for the dopamine-heparin-containing CMC/SBR-based electrodes than for the commercial CMC/SBR-based electrodes, and hence yielded excellent cell performance with a retention of 73.5% of the original capacity, a Coulombic efficiency of 99.7% at 150 cycles, and a high capacity of 200 mAh g-1 even at 20 C. Furthermore, a full cell test using the proposed electrode material showed stable cell performance with 89% retention at the 150th cycle.