Researchers at the U.S. Department of Energy’s (DOE) Argonne National Laboratory have developed an electrolyte mixture and additive they claim boosts the energy density of next generation lithium-ion batteries by up to 50%.
To develop its electrolyte additive the scientists added small amount of a second salt containing doubly or triply charged metal cations magnesium (Mg2+), calcium (Ca2+), zinc (Zn2+), or aluminium (Al3+).
During charging, the metal cations migrated into the silicon-based anode along with the lithium ions to form lithium-metal-silicon phases, which are more stable than lithium-silicon.
Of the four metal salts tested, the researchers found electrolyte salts with either Mg2+ or Ca2+ cations worked best over hundreds of charge–discharge cycles.
The energy densities obtained with these cells surpassed those for comparable cells using graphite chemistry by up to 50%, reported the team.
Silicon is seen as a suitable replacement for graphite on lithium-ion electrodes because it has almost ten times the theoretical energy storage capacity.
To date a stumbling block to commercialisation has been silicon-based anodes in a lithium-ion cell become reactive with the electrolyte while cycling.
This process degrades the cell over time, causing a shortened cycle life, said Jack Vaughey, a senior chemist in Argonne’s Chemical Sciences and Engineering (CSE) division.
Argonne’s new cell chemistry reduces the detrimental side reactions between the silicon anode and electrolyte, claim the researchers.
A paper based on the study, ’Using mixed salt electrolytes to stabilize silicon anodes for lithium-ion batteries via in situ formation of Li-M-Si Ternaries (M=Mg, Zn, Al, Ca)’ appeared in ACS Applied Materials & Interfaces.
Image by Argonne National Laboratory shows charging results in doubly or triply charged metal cations, such as Mg2+ (orange spheres), along with singly charged lithium ions (green spheres) being co-inserted from the electrolyte into the silicon (blue spheres) anode material. This process stabilises the anode, enabling long term cycling of lithium-ion batteries.
