UC San Diego

The current commercial lithium ion battery utilizes “host-guest” electrodes that allow for the intercalation of lithium between the crystal lattice of the anode and cathode materials. The lithium ions are transported through the electrolyte medium during the charge/discharge process, Given their success, lithium ion batteries have now penetrated the electric vehicle market and large scale grid storage, which require batteries with much higher energy densities. To meet this demand, alternative anode and cathode chemistries are required. Consequently, this will put high strain on the electrolyte which will decompose at both low and high potentials to form a passivation layer known as the solid electrolyte interphase (SEI).

Herein, the fundamental reduction mechanism of fluoroethylene carbonate (FEC) is investigated as an additive for conventional electrolytes to improve the SEI formation on various silicon anodes using a series of advanced spectroscopic and microscopic techniques. For the first time, the direct visualization of the SEI generated on the silicon nanoparticle is investigated by scanning electron microscopy and its chemical composition by electron energy loss spectroscopy. The SEI is further investigated on lithium metal anode. Highly concentrated bisalt ether electrolytes form a SEI that is dominated by salt decomposition rather than solvent decomposition, which enables high lithium metal cycling efficiencies.

At high potentials the electrolyte oxidizes on the cathode to form the cathode electrolyte interphase (CEI). With the discovery of 5V cathode materials, a new electrolyte is required. Therefore, sulfone based electrolytes are studied as potential high voltage electrolyte. Combined with lithium bis(fluorosulfonyl) imide, this solvent-salt synergy addresses the traditional performance issues that develop at the interface of high voltage cathodes.

The factors that affect the cycling performance of cathode materials for lithium ion batteries are also seen in sodium ion batteries. Atomic layer deposition (ALD) is widely used to improve the cycling performance, coulombic efficiency of batteries, and to maintain electrode integrity for LIBs. Therefore, this approach is used to understand the effect of Al2O3 ALD coating on P2-Na2/3Ni1/3Mn2/3O2 cathodes, which lowers the cathode impedance and improves particle morphology after cycling. Improving the electrode-electrolyte interface is critical to the development of next generation high density energy storage systems.