Origin of Enhanced Cyclability in Covalently Modified LiMnNiO Cathodes.

ACS Appl Mater Interfaces

Department of Chemistry , University of Illinois at Urbana-Champaign, 600 South Mathews Avenue , Urbana , Illinois 61801 , United States.

Published: October 2019

AI Article Synopsis

  • High-voltage lithium-ion batteries have great energy density but struggle with rapid capacity loss during use; surface modification of cathode materials with self-assembled monolayers (SAMs) can help enhance their lifespan.* -
  • This study explores how different silane-based SAM structures affect the electrochemical performance and surface chemistry of LiMnNiO (LMNO) electrodes, showing that both hydrophobic and hydrophilic monolayers improve capacity retention.* -
  • Specifically, fluorinated alkyl-silanes led to over 96% capacity retention after 100 cycles, with the increased deposition of lithium fluoride (LiF) improving the electrode’s stability and overall performance during cycling.*

Article Abstract

High-voltage lithium-ion cathode materials exhibit exceptional energy densities; however, rapid capacity fade during cell cycling prohibits their widespread utilization. Surface modification of cathode-active materials by organic self-assembled monolayers (SAMs) has emerged as an approach to improve the longevity of high-voltage electrodes; however, the surface chemistry at the electrode/electrolyte interphase and its dependence on monolayer structure remains unclear. Herein, we investigate the interplay between monolayer structure, electrochemical performance, and surface chemistry of high-voltage LiMnNiO (LMNO) electrodes by the application of silane-based SAMs of variable length and chemical composition. We demonstrate that the application of both hydrophobic and hydrophilic monolayers results in improved galvanostatic capacity retention relative to unmodified LMNO. The extent of this improvement is tied to the structure of the monolayer with fluorinated alkyl-silanes exhibiting the greatest overall capacity retention, above 96% after 100 charge/discharge cycles. Postmortem surface analysis reveals that the presence of the monolayer enhances the deposition of LiF at the electrode surface during cell cycling and that the total surface concentration correlates with the overall improvements in capacity retention. We propose that the enhanced deposition of highly insulating LiF increases the anodic stability of the interphase, contributing to the improved galvanostatic performance of modified electrodes. Moreover, this work demonstrates that the modification of the electrode surface by the selection of an appropriate monolayer is an effective approach to tune the properties and behavior of the electrode/electrolyte interphase formed during battery operation.

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http://dx.doi.org/10.1021/acsami.9b12912DOI Listing

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