Even as electric vehicles (EVs) rapidly grow their share of the market, manufacturers continue to improve the technologies to better meet consumer demands. Amongst these developments, lithium-ion batteries (LIBs) with fast charging capabilities are expected to play an important part in promoting the adoption of EVs by eliminating consumers’ “range anxiety.”
The importance of fast charging to the rollout of EVs is well illustrated by the United States Department of Energy’s stated goals of achieving “Extreme Fast Charging” (XFC) – safely charging to 80 percent capacity in 15 minutes or less – by 2028. Optomized LIB electrolytes play an important role in achieving this goal.
StoreDot’s patent relates to innovative Li-ion battery electrolyte additives that stabilize the solid-electrolyte interface at the surfaces of the anode, and/or stabilize the cathode electrolyte interface at the surface of the cathode, as well as acting as oxygen scavengers to prevent cell degradation in fast charging EV batteries.
Li-ion batteries currently used in EVs are typically based on the chemistry of a graphite or graphite/silicon anode, a lithium transition metal oxide cathode (layered cathode), and a LiPF6-carbonate based electrolyte.
These electrolytes consist mainly of a LiPF6 salt dissolved in a carbonate-based solvent mixture. Such electrolytes cannot support fast charge without detrimental impacts on performance and lifespan. Fast charge aggravates parasitic reactions of the electrolyte solvents and structural degradation of the lithium layered transition metal oxide cathode materials.
This leads to not only the depletion of electrolyte solvents but also the loss of cyclable Li+ ions, accompanied by an increase in impedance and volumetric swelling of the electrodes.
Hence, StoreDot’s patent describes LIBs and electrolytes that include electrolyte additives containing dithioester functional group(s) that stabilize the SEI (solid-electrolyte interface) at the surface of the anode material particles, and/or stabilize the CEI (cathode electrolyte interface) at the surface of the cathode material particles. These additives also act as oxygen scavengers to prevent cell degradation.
The electrolyte additives act as polymerization controlling and/or chain transfer agents that regulate the level of polymerization of other electrolyte components, such as VC (vinyl carbonate) and improve the formation and operation of the batteries. The lithium ion batteries may have metalloid-based anodes - including mostly Si, Ge and/or Sn as anode active material particles.
These polymerization controlling agents may also be used to control the chain lengths/molecular weights and distribution of the poly-olefins, whilst preventing the continuous and related parasitic reaction that consumes electrolyte, reduces the ionic conductivity of the electrolyte and reduces the electronic conductivity of the anode material particles.
Alternatively or complementarily, " chain transfer agents ” - defined as compounds comprising a weak bond (i.e. a dithioester functional group) - which facilitate a chain transfer reaction can be used as polymerization controlling agents, to control chain length of the poly-olefins.
Through the use of electrolyte additives as described in StoreDot’s patent the lithium-ion battery’s performance can be optimized with respect to the cycle life, charging/discharging rates, safety and/or capacity.