NEES Teleseminars

NEW DATE: EFRC NEES Teleseminar - LiPON Protective Layer for 3D conversion electrode/Li metal anode
Tuesday, March 8, 2016
4:00 p.m.
UMD location: 1146 AVW
For More Information:
Elizabeth Lathrop
301 405 7801
lathrop5@umd.edu

Solid Electrolyte Lithium Phosphous Oxynitride (LiPON) as a Protective Layer for 3D High-Capacity Conversion Electrodes and Li Metal Anode

Speakers: Dr. Chuan-Fu Lin; Dr. Malachi Noked. Rubloff research group, Materials Science and Engineering, UMD.

We utilize herein a recently published ALD process for conformal intephasial protection of two electrode/electrolyte interfaces, model system for conversion electrode (RuO2) and Li metal- both in conventional alkyl carbonate electrolyte solutions of Li ion.

Conversion electrode Materials which undergo conversion reactions to form different materials upon lithiation typically offer high specific capacity for energy storage applications such as Li ion batteries (LIBs).  However, since the reaction products often involve complex mixtures of electrically insulating and conducting particles and significant changes in volume and phase, the reversibility of conversion reactions is poor, preventing their use in rechargeable (secondary) batteries.  We fabricated 3D conversion electrodes by coating multi-walled carbon nanotubes (MWCNT) first with a model conversion material, RuO₂, and subsequently protecting it with conformal thin-film, lithium phosphous oxynitride (LiPON), a well-known solid-state electrolyte. Atomic layer deposition (ALD) is used to deposit the RuO₂ and the LiPON, thus forming core double-shell MWCNT@RuO₂@LiPON electrodes as a model system.  We find that the LiPON protection layer enhances cyclability of the conversion electrode, which we attribute to two factors. (1) The LiPON layer provides high Li ion conductivity at the interface between the electrolyte and the electrode. (2) By constraining the electrode materials mechanically, the LiPON protection layer ensures electronic connectivity and thus conductivity during lithiation/delithiation cycles.  These two mechanisms are striking in their ability to preserve capacity despite the profound changes in structure and composition intrinsic to conversion electrode materials. This LiPON-protected structure exhibits superior cycling stability and reversibility as well as decreased overpotentials compared to the unprotected core-shell structure. Furthermore, even at very low lithiation potential (0.05V), the LiPON-protected electrode largely reduces the formation of solid electrolyte interphase (SEI).  

Li Metal- The SEI on graphite is protecting the electrode, preventing continued decomposition of the electrolyte species on the anode at low potential while still enabling the diffusion of Li+ ions at reasonable rates. In contrast to graphite, the surface of a Li metal anode is fluctuating upon charge/discharge. Repeating deposition and stripping of li ion on the lithium interface cause microscopic cracks in the SEI, which form more favorable sites for lithium ion deposition due to local enhancement of the electrochemical field, hence facilitating dendritic growth of lithium upon cycles. Therefore, when utilizing alkyl carbonate based electrolytes with Li as anode, the Li anode continuously reacts with the electrolyte species (both solvent and salt), resulting in the consumption of organic solvent, formation of a thick layer on the surface of the anode that impede the battery cycle life. We demonstrate herein hybridization of elastomeric protection layer applied by electrochemical polymerization on the Li surface followed by synthesis of 22nm of LiPON directly on the Li metal surface by atomic layer deposition (ALD).  We further show that application of this ASEI on the Li surface can suppress dendrite formation up to current densities of 2 mAcm^-2.

This Event is For: Graduate • Undergraduate • Faculty • Post-Docs