Complex Lithiation Mechanism of Siloxene and Germanane: Two Promising Battery Electrode Materials

L C Loaiza,C Davoisne,L Madec,L Monconduit,N Dupré,V Seznec

doi:10.1149/1945-7111/abd44a

Abstract

The layered siloxene and germanane, derived from CaSi2 and CaGe2, respectively, have shown very promising results as anodes for Lithium-ion batteries. Their delivered capacities, capacity retention and high rate cycling are superior compared to bulk Si and Ge. These positive features are most probably related to the layered morphology that buffers the volume changes and improves the kinetics. Despite numerous recently published studies regarding their electrochemical properties, very little is known about their electrochemical mechanism. In this work, we have used a combination of different characterization techniques to study the processes taking place during the lithiation of siloxene and germanane and compared with Si and Ge. Our results suggest a slightly different pathway for the lithiation of siloxene and germanane: their initial layered morphology is preserved after cycling, the crystalline Li15Si4 and Li15Ge4 characteristic of an alloying mechanism are absent and possibly different lithiated intermediates are formed. We provide then, an initial assessment of the involved LixSi and LixGe phases and propose the hypothesis of a reversible Li intercalation in the siloxene and germanane layers.

Highlights

Many attempts to increase the energy density and reduce the production cost of the Li-ion battery (LIB) have been performed in both business and academic fields since LIB is commercialized
We found out that the low Coulombic efficiency (CE) in the 1st cycle in LiNiO2 is ascribed to the low discharge capacity that is caused by a sluggish additional discharge reaction at ∼3.5 V rather than detrimental phase transitions such as H2−H3 at ∼4.2 V, which leads to a severe volume change
This indicates that the low 1st Coulombic efficiency behavior can be caused by a limited discharge capacity that can be caused by a limited discharge reaction rather than the multiple phase transitions such as H2−H3 occurs at 4.3 V

Summary

Introduction

Many attempts to increase the energy density and reduce the production cost of the Li-ion battery (LIB) have been performed in both business and academic fields since LIB is commercialized. As the demand for high energy density LIB increases, the conventional LCO material, with a lower practical capacity, has been replaced due to its structure instability after >50% delithiation and the substantial increase of the price of Co.. Ni-based layered materials such as LiNi1 −x−yMnxCoyO2 (NMC) and Li- Ni0.8Co0.15Al0.05O2 (NCA) have been of great interest because they can achieve high reversible capacity by only substituting Co with Ni. To further increase the energy density in Ni-based layered materials, the amount of Ni in the materials gets increased by reducing other transition metals such as Co and Mn because the Ni redox reaction determines the achievable capacity of the electrode materials.. As the Ni content increases in NMC and NCA materials, their electrochemical properties and structural changes via phase transformation behaviors during charge/discharge are increasingly similar to LiNiO2, an end member of Ni-rich electrode materials.. The understanding of the electrochemical activity of LiNiO2 can greatly help solving these problems of Ni-rich layered materials

Results

Discussion

Conclusion