Carbon electrode with NiO and RuO
2
nanoparticles improves the
cycling life of non-aqueous lithium-oxygen batteries
P. Tan, W. Shyy, M.C. Wu, Y.Y. Huang, T.S. Zhao
*
Department of Mechanical and Aerospace Engineering, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China
highlights graphical abstract
We develop carbon electrodes with
NiO and RuO
2
nanoparticles for Li-O
2
batteries.
RuO
2
nanoparticles catalyze both the
oxygen reduction and evolution
reactions.
NiO nanoparticles promote the
decomposition of the side products.
This study offers a new strategy to
improve the cycling life of carbon
electrodes.
article info
Article history:
Received 5 May 2016
Received in revised form
20 June 2016
Accepted 4 July 2016
Keywords:
Lithium-oxygen battery
Lithium peroxide
Side products
Nanoparticle
Charge voltage
abstract
Carbon has been regarded as one of the most attractive cathode materials for non-aqueous lithium-
oxygen batteries due to its excellent conductivity, high specific area, large porosity, and low cost.
However, a key disadvantage of carbon electrodes lies in the fact that carbon may react with Li
2
O
2
and
electrolyte to form irreversible side products (e.g. Li
2
CO
3
) at the active surfaces, leading to a high charge
voltage and a short cycling life. In this work, we address this issue by decorating NiO and RuO
2
nano-
particles onto carbon surfaces. It is demonstrated that the NiO-RuO
2
nanoparticle-decorated carbon
electrode not only catalyzes both the oxygen reduction and evolution reactions, but also promotes the
decomposition of side products. As a result, the battery fitted with the novel carbon cathode delivers a
capacity of 3653 mAh g
1
at a current density of 400 mA g
1
, with a charge plateau of 4.01 V. This
performance is 440 mV lower than that of the battery fitted with a pristine carbon cathode. The present
cathode is also able to operate for 50 cycles without capacity decay at a fixed capacity of 1000 mAh g
1
,
which is more than twice the cycle number of that of the pristine carbon cathode.
© 2016 Elsevier B.V. All rights reserved.
1. Introduction
Non-aqueous lithium-oxygen batteries have been considered as
one of the most promising power sources for electric vehicles and
portable devices, due to the high theoretical capacity
(3.86 10
3
mAh g
1
) and energy density (1.14 10
4
Wh kg
1
) [1].
To make this technology commercially viable, however, a number
of barriers must be overcome, including low practical discharge
capacity, low energy efficiency, and short cycling life [2,3]. The
electrochemical reactions in the discharge and charge processes
involve the reversible formation and decomposition of lithium
peroxide (Li
2
O
2
) as 2Li
þ
þ 2e
þ O
2
% Li
2
O
2
. As Li
2
O
2
is insoluble in
the electrolyte [4], it grows in the pores of the porous cathode when
the capacity is increased, and can eventually block the transport
* Corresponding author.
E-mail address: metzhao@ust.hk (T.S. Zhao).
Contents lists available at ScienceDirect
Journal of Power Sources
journal homepage: www.elsevier.com/locate/jpowsour
http://dx.doi.org/10.1016/j.jpowsour.2016.07.012
0378-7753/© 2016 Elsevier B.V. All rights reserved.
Journal of Power Sources 326 (2016) 303e312