Improved Cycling Performance of a Si Nanoparticle Anode Utilizing Citric Acid as a Surface-Modifying Agent

Citric acid and its analogues have been investigated as surface modifying agents for Si nanoparticle anode using electrochemical cycling, attenuated total reflectance infrared (ATR IR) and X-ray photoelectron spectroscopy (XPS). Si nanoparticle anode prepared with citric acid (CA) has better capacity retention than the one containing 1,2,3,4-butanetetracarboxylic (BA) acid but both electrodes outperform Si-PVDF. Si-CA anode has an initial specific capacity of 3530 mAh/g and a first cycle efficiency of 82%. Surprisingly, the Si-CA electrode maintains a high specific capacity similar to 2200 mAh/g after 250 cycles, corresponding to 64% capacity retention which is similar to the Si prepared with the long chain poly(acrylic acid) (PAA). On the contrary, silicon electrode prepared with PVDF has a fast capacity fade and retains only 980 mAh/g after 50 cycles. The IR and XPS data show that the Si-CA electrode has an SEI composed primarily of lithium citrate, during the first 50 cycles, resulting from the electrochemical reduction of citric acid. Only low concentrations of electrolyte reduction products are observed. The lithium citrate layer derived from CA stabilizes silicon surface and suppresses electrolyte reduction which likely contributes to the enhanced cycling performance of Si nanoparticle anode.