Cathode and Anode Materials for Na-Ion Battery - Low-cost Nanomaterials: Toward Greener and More Efficient Energy Applications - page 388

A major obstacle hindering the broad market penetration of these two types of Na
batteries is the long-term stability and endurance of the battery components at high
temperatures of C300C.
2 Na-Ion Batteries and Problems
If a room temperature Na-ion rocking chair battery (Na-ion battery) (Fig. 1 ) can be
achieved, it would bring about great improvement in safety and operational sim-
plicity with respect to the conventional high-temperature Na batteries and also a
remarkable decrease in cost with regard to Li-ion batteries, thus ensuring sus-
tainable applications for large-scale electric energy storage. Since Na-ion batteries
have the similar working principle as Li-ion batteries, the development of this
system would benefit greatly from the knowledge as well as configurations gained
within Li-ion batteries. However, it should be noted that: 1. the gravimetric
capacity of Na is lower (1,165 mAh g -1 ) than lithium (3,829 mAh g -1 ) due to its
larger molecular mass [ 1 ]. Thus, the Na-ion battery system will achieve lower
energy density than Li-ion batteries. 2. Na ions are about 40 % larger than Li ions
in radius, which make them more stable in rigid lattices [ 1 ]. Thus, it will be harder
to find proper materials that are able to realize reversible Na storage and release.
Due to its large dimensions, the insertion and extraction of Na ions can arouse
more serious stress changes of the host materials, causing rapid collapse of lattice
structure and therefore poor cycling stability. The diffusion of Na-ions in lattice is
also slow, resulting in poor electrochemical utilization and rate capability. 3. Na
metal is more chemically active than Li, which needs very strict restriction of the
moisture and oxygen content on the experimental environment. In this chapter,
recent research progress in electrode materials is reviewed for Na-ion batteries.
The practical specific capacity and operating voltage of some of the electrode
materials for Na-ion battery are summarized in Fig. 2 .
3 Cathode Materials for Na-Ion Batteries
The electrochemical performance of Na-ion batteries mainly depends on the
structures and properties of electrode materials and electrolytes. As one of the key
components of Na-ion batteries, suitable cathode materials should meet the fol-
lowing requirements:
1. High redox potential, which is less influenced by the concentration of Na ions
in the lattices, to maintain high and even charge/discharge voltage.
2. Small electrochemical equivalent, i.e., light molecular weight and more elec-
trons transferred per unit of the active material, to provide high specific
capacity.