(644a) Influence of Cobalt and Sodium Doping on MnO/CNT Composite Anode Materials for Li-Ion Batteries

Influence of Cobalt and Sodium Doping on MnO/CNT Composite Anode
Materials for Li-Ion Batteries

A. Palmieri, R. Kashfi, S. Yazdani, M. Pettes, and W. E. Mustain
(University of Connecticut)

Abstract Text:

Li ion batteries (LIBs) have been the leading technology in the
portable electronics market since their discovery by Sony in the 1990s.
Commercially, their setup is constituted by a graphite anode, a lithium metal
oxide cathode and LiPF₆ dissolved in a mixture of carbonates as electrolyte,
characterized by a maximum energy specific density 150 Wh/Kg [1]. However, the
needs of newer and cleaner forms of energy is pushing lithium ion batteries
towards higher scale applications, such as the electric grid or automotive,
requiring the energy and power density to be at least doubled in the near
future. 

Materials advances at both sides of the cell have been actively investigated
for several years. The cathodic side of the cell presents very few choices of
materials that are suitable to be used in LIBs (LiCoO₂, LiMnO₂,
LiFeO₄), all with a theoretical capacity lower than 300 mAh/g, and
even lower practically achievable capacity. 

At the anode, there is a much wider choice of active materials. Silicon has
been one of the most widely investigated options in recent years because of its
very high theoretical capacity (>3000 mAh/g) and availability. However, pure
silicon materials show very rapid deep capacity fade due to the large
volumetric expansion occurring during the alloying/dealloying electrochemical
reaction (more than 250% of the initial volume).  To mitigate this, several
materials and operational adjustments have been made and modern silicon composites
are only able to achieve a capacity ca. 1000 mAh/g, only 1/3 of the theoretical
capacity [2]. Moreover, reference [3] showed that, due to the cathodic
limitation of the cell, there is a “capacity penalty” when the anode material
capacity is too much larger than the cathode material, and the anode capacity
should only be around 700 mAh/g (until new cathode materials are discovered) to
fully realize improvements to the overall cell performance.

This opens up the periodic table to a wide number of available chemistries including
metal oxides [4] which have been the focus of many electrochemical studies so
far because of their higher capacity relative to graphite and environmental
friendliness. Among the metal oxides, manganese oxides are attractive because
they are inexpensive and highly available [5].  Unfortunately, to date few studies
have been shown with acceptable capacity and retention have been reported,
particularly under realistic operating conditions. 

In this work, our team will discuss the synthesis of a novel bi-metallic Mn/Co
oxide active material imbedded into a low loading multiwalled carbon nanotubes matrix,
as shown in Figure 1. We will show the impact of cobalt doping on half-cell
performance. Different Cobalt dopant contents (0%,5%,10%,15% and 20%) were
prepared and their electrochemical performance was tested, including capacity
retention (Figure 2) and rate capability up to 1600 mA/g. Lastly, Na was used
as a doping as well, increasing the performance of the manganese active
material, which can be tied to enhancement in the electronic conductivity.

References. 

1. M.M. Thackeray, C. Wolverton and E.D. Isaacs, Energy and Environmental Science, 5, (2012), 7854.
2. T. Osaka, H. Nara, T. Momma and T. Yokoshima, J. Mater. Chem. A, 2, (2014) 883. 
3. M. Karulkar, J. Power Sources, 273 (2015) 1194-1201. 
4. N. Spinner, L. Zhang and W.E. Mustain, J. Mat. Chem. A, 2(6) (2014) 1627.
5. L. Li, A.R.O. Raji and J.M. Tour, Advanced Materials, 25, (2013), 6298.

Figure 1: Mn/Co oxide nanoparticles supported on
multiwalled carbon nanotubes

Figure 2: Mn/Co oxide different weight percentages
capacity retention