Investigating Low-Temperature Behavior of Alloy Anodes for Lithium-Ion Batteries

Lithium-ion batteries do not reversibly operate below 0 C, with complete failure below about -30 C. The poor low-temperature behavior is largely due to sluggish diffusion of lithium within the graphite anode, along with electrolyte transport limitations and freezing. Thus, even with improved electrolytes, new anode materials with high specific capacities and fast lithium diffusion must be developed and understood to enable high-energy, low-temperature batteries. Here, we investigate the performance and structural evolution of various alloy anodes (antimony, silicon, and tin) at temperatures as low as -40 C, using a tailored ether electrolyte. Galvanostatic cycling reveals that antimony can be used as an anode material at -40 C and still provide a specific capacity of over 400 mAh g^-1 on the first cycle. Tin and silicon can only be reversibly cycled at -30 C and 0 C, respectively, due to increased overpotential causing simultaneous lithium plating. While all materials tested provide high initial capacities at low temperatures, only antimony exhibits relatively stable capacity retention over tens of cycles. To gain insight into electrochemical mechanisms, the galvanostatic intermittent titration technique (GITT) is used to extract thermodynamic and kinetic contributions to the materials’ behavior as a function of temperature. GITT reveals that the kinetic overpotential makes up a larger portion of the overall voltage hysteresis for tin and antimony at low temperatures, while the opposite is true for silicon at all temperatures. Additionally, the thermodynamic voltage hysteresis for silicon and tin become larger at lower temperatures, while they stay relatively constant for antimony after the first cycle. Finally, ex-situ X-ray diffraction of antimony electrodes shows that, despite large kinetic overpotentials, antimony is still able to form crystalline Li₃Sb on lithiation and reform crystalline Sb on delithiation at low temperatures, but with smaller crystallite sizes. Overall, these results provide new fundamental insight into the electrochemical alloying and dealloying processes at low temperatures and are a vital first step in developing this promising class of anode materials for low temperature lithium-ion batteries.