The ever-increasing demand to develop battery technologies with higher energy density. Batteries using a Li metal anode could deliver a higher operating voltage (around 0.1 V) than the graphite anode, which increases the energy density. The problem is by using the Li metal anode, Li dendrites start to grow as we charge/discharge the device, causing limited Coulombic Efficiency (CE) and severe side-reactions with the components in the routine liquid electrolytes. This is mainly because the active Li metal can react with nearly all dipolar aprotic organic solvents.
Anode-free lithium metal batteries are a type of lithium metal batteries that have shown superior energy density in comparison to regular Li-ion batteries. The active Li+ ions are initially stored in the cathode material, making the cathode less sensitive to moisture/air. During the initial charging process, the Li+ ions are extracted from the cathode and migrate to the anode and form a Li anode layer on the bare current collector. Subsequently, the active Li-ions are stripped from the in-situ formed Li anode and migrate back into the cathode during the discharging process
So, the question is what is the bottleneck here?
Mr. Zhiao Yu and his co-workers at Stanford University have focused on a very important aspect of Li-metal batteries: chemically unstable and mechanically fragile solid-electrolyte interphase (SEI). The SEI layer is the Achilles heel as it easily cracks during cycling, leading to dendritic growth, “dead Li” formation, and irreversible Li loss. Their research focuses on tuning the SEI structure and quality, by molecular design of electrolyte.
In their work, Mr. Yu and co-workers target new solvent molecules that not only dissolve Li salt but also stay compatible when confronted with both Li metal anodes and high-voltage cathodes. fluorinated 1,4-dimethoxylbutane (FDMB), solely as the electrolyte solvent is paired with lithium bis(fluorosulfonyl)imide in a single-salt, single-solvent formulation (1 M LiFSI/FDMB) to enable stable and high-energy-density Li metal batteries.
Their Li|NMC fabricated full cells with limited-excess Li retain 90% capacity after 420 cycles with an average CE of 99.98%.
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