Increasing the Capacity Performance in Lithium Metal Secondary Battery By Using Nafion-Coated Cathodes

Lithium metal has a high theoretical energy density (3860 mAh g-1), which makes it a good anode material for use in secondary lithium batteries. Instead of a lithium-foil electrode, a lithium-powder electrode is used as anode material to prohibit dendrite growth and to improve on the electrochemical behavior[1], [2], When lithium-powder is used directly as a anode electrode, the non-lithiated cathode must have the ability of intercalation and deintercalation of lithium ions.

Lithium trivanadate (LiV3O8, LVO) is a promising non-lithiated cathode material in which lithium ions can inserted and removed from the LVO’s layered structure. LVO is relatively high theoretical capacity (280 mAh g-1) and good cycle stability. However, because of the low conductivities of LVO, the cell exhibits adverse effects in rate retention and degradation during cycle is progressed. Nafion is a well-known cation exchange polymer with high ionic conductivity and excellent stability, which can be coated onto the surface of cathode to solve the LVO’s drawback.

Lithium-powder particles and lithium trivanadate are synthesized by the droplet emulsion technique (DET) and solid-state method, respectively. And Nafion-coated cathode is easily synthesized by using a dip-coating technique. Dip-coating is a facile and fast process, and a simple way to generate a thin uniform film on the surface of LVO[3].

The structure, morphology, and electrochemical properties of lithium metal secondary battery’s electrode were investigated by the implementation of X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), and energy dispersive spectroscopy (EDS)[4]. All cells were cycled 50 times at a C-rate of 0.2 and various C-rate with the cut-off voltage ranging from 1.8 to 4.0V (versus Li/Li+). The result was analyzed by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV)[5].

As the dip-coating the nafion is performed, layered cathode electrode has higher ionic conductivity. Thanks to effect of coating, lithium-powder/LVO cell appears better electrochemical performance, rate retention in various c-rate and mitigated degradation.

[1] J. S. Kim, W. Y. Yoon, Electrochim. Acta 2004, 50, 531–534

[2] J. H. Chung, W. S. Kim, W. Y. Yoon, S. W. Min, B. W. Cho, J. Power Sources 2006, 163, 191-195

[3] S. J. Oh, J. K. Lee, W. Y. Yoon, ChemSusChem 2014, 7, 2562-2566

[4] D. Wang, L. Cao, J. Huang, J. Wu, Cera. Inte, 38, 2012, 2647-2652

[5] Y.Q. Qiao, J.P. Tu, X.L. Wang, J. Zhang, Y.X. Yu, and C.D. Gu, J. Phys. Chem, 115, 2011 25508-25518