Skip to content Skip to navigation

Precision Coatings Stabilize Metal Oxide Composites for Lithium Ion Battery Electrodes

Written by: 
Jeff Morse, Ph.D
Increasing the surface-to-volume ratio of the Lithium ion Battery electrode materials both increases the electrode contact area and reduces the Lithium ion (Li+) insertion distance, therefore modifying bulk or microscale metal oxide composites to nanometer-sized particles improves both the power and the capacity of the electrode material. The disadvantage of increased surface area for high voltage cathode materials includes undesirable side reactions such as the dissolution of the electrode material in the liquid electrolyte, resulting in degradation of capacity over charging cycles. Recently, Scott et. al. have investigated the use of atomic layer deposition (ALD) to coat metal oxide composite nanoparticles with an ultrathin layer to stabilize nanoparticles during charge/discharge cycling.


Reviewed by Jeff Morse, Ph.D, National Nanomanufacturing Network

  • Scott ID, Jung YS, Cavanagh AS, Yan Y, Dillon AC, George SM, and Lee SH. 2010.Ultrathin Coatings on Nano-LiCoO2 for Li-Ion Vehicular Applications. Nano Letters Article ASAP 17 December 2010. DOI: 10.1021/nl1030198.

As consumer demand continues to drive nanotechnology research, lithium ion battery (LIB) R&D is targeting high storage capacity, faster recharging time, greater cycling stability, and higher power output for applications such as electric vehicles. While historically these research goals have been divergent, the use of nanostructured materials and composites and emerging nanofabrication techniques over the past decade has merged critical performance parameters in order to expand their applications. For example, increasing the surface-to-volume ratio of the electrode material both increases the electrode contact area and reduces the Lithium ion (Li+) insertion distance, therefore modifying bulk or microscale metal oxide composites to nanometer-sized particles improves both the power and the capacity of the electrode material. The disadvantage of increased surface area for high voltage cathode materials includes undesirable side reactions such as the dissolution of the electrode material in the liquid electrolyte, resulting in degradation of capacity over charging cycles. Approaches to stabilize the metal oxide nanoparticles using sol-gel methods have resulted in poor control of the protective coating, which could act as a barrier to Li+ diffusion if too thick.

Scott Figure A
 Recently, Scott et. al. have investigated the use of atomic layer deposition (ALD) to coat metal oxide composite nanoparticles with an ultrathin layer to stabilize nanoparticles during charge/discharge cycling. ALD provides a method to grow conformal coatings having atomic precision facilitated by sequential, self-limiting surface reactions. In this investigation, the authors used ALD aluminum oxide (Al2O3) grown on LiCoO2 nanoparticles (nLCO) to demonstrate the effectiveness on standard, widely studied LIB cathode materials. nLCO powders were prepared using the molten salt method, providing high purity composite nanoparticles with an average diameter of ~400 nm, compared to bulk LCO with an average particle size of ~5 µm. Al2O3 films were then coated on the nLCO composite electrodes with each ALD cycle depositing a uniform, conformal layer ~1.1-2.2 Å thick. Transmission electron micrsoscopy (TEM) of the as-deposited films having 6 ALD cycles on nLCO show uniform coatings with smooth curvature, in contrast to wet-chemical coating methods that typically result in nonuniform, porous coatings with agglomerations ranging up to tens of nanometers.

LiCoO2 composite electrodes were prepared for testing by spreading the nLCO powder, acetylene black, and polyvinylidene fluoride (PVDF) binder onto aluminum foil.  The authors then tested the nLCO electrode coated with 2 ALD cycles of Al2O3 and compared these to similar electrodes prepared from bare nLCO and bare bulk LCO. When cycling the electrode between 3.3 and 4.5 V at a current rate of 16 mA/g (0.1C) for the first three charge-discharge cycles, then 500 mA/g (2.8C) for the subsequent cycles, the ALD coated nLCO exhibited no loss in capacity after 200 charge-discharge cycles, whereas the bare nLCO and bulk LCO exhibited almost complete loss of capacity after 50 charge cycles.  Furthermore, the 2 cycle ALD coated nLCO exhibited remarkable retention of capacity even after cycling at rates up to 1400 mA/g  (7.8C). The 133 mAh/g capacity by the ALD coated nLCO represents a 250% increase over bare bulk LCO composite elecytrodes under the same cycling conditions. Interestingly, nLCO coated with six cycles of ALD Al2O3 exhibited a decrease in capacity after cycling, likely as a result of the increased barrier to Li+ diffusion resulting from the thicker ALD layer on the nLCO.

Thus a scalable nanomanufacturing approach has been reported demonstrating the feasibility of creating durable LIB electrodes having high power and high energy density utilizing an ultrathin layer of Al2O3coated on metal oxide nanoparticles. The coating acts as a protective layer for theelecytrode composite and further enables stable high rate operation capability for the battery.

Image reproduced with permission from Scott ID, Jung YS, Cavanagh AS, Yan Y, Dillon AC, George SM, and Lee SH. 2010.Ultrathin Coatings on Nano-LiCoO2 for Li-Ion Vehicular Applications. Nano Letters Article ASAP 17 December 2010. DOI: 10.1021/nl1030198.Copyright 2010 American Chemical Society.

InterNano Taxonomy: