Ge Nanoparticles Encapsulated in Interconnected Hollow Carbon Boxes as Anodes for Sodium Ion and Lithium Ion Batteries with Enhanced Electrochemical Performance

Abstract

A carbothermal reaction route to Ge nanoparticle homogeneously encapsulated hollow carbon boxes from NH4H3Ge2O6/resorcinol formaldehyde precursors is designed, using NH4H3Ge2O6 as a Ge precursor from commercial GeO2 and NH4OH. The Ge/C hybrid anode for sodium ion battery displays a higher Na+ storage capacity of 346 mA h g−1 after 500 cycles at a current density of 100 mA h g−1, almost approaching the theoretical capacity of Ge. Furthermore, Ge/C anode shows significantly improved electrochemical performance for Li+ storage, showing a higher initial Coulombic efficiency of 85.1% and a superior reversible capacity of 1336 mA h g−1 at a high current density of 200 mA g−1 after 150 cycles. An excellent rate capability with a capacity of 825 mA h g−1 at a current density of 4.0 A g−1 can be obtained based on Ge/C anodes. The enhanced electrochemical performance can be attributed to the unique microstructures of Ge/C hybrid anode. The internal void space of hollow carbon boxes can accommodate the volume expansion of Ge during lithiation or sodiation process, thus preserving the structural integrity of electrode material. The interconnected carbon shell can increase the electronic conductivity of the electrode, resulting in the high rate capability and cycling stability.

Recent Progress on the Alloy‐Based Anode for Sodium‐Ion Batteries and Potassium‐Ion Batteries

“…Nevertheless, in situ TEM [ 143 ] results confirmed that crystalline Ge do not sodiate, while amorphization can make the Ge an effective sodiation electrode, in which the observed volume expansion is more than 300% than expected based on final sodiated phase close to Na 1.6 Ge. Ge nanoparticles homogeneously encapsulated in hollow carbon boxes [ 144 ] is designed to show a high Na + storage capacity of 346 mAh g −1 after 500 cycles at 0.1 A g −1 ( Figure a). The internal void space of hollow carbon boxes can buffer the volume change of Ge during sodiation process, preserving structural stability of anode materials.…”

“…Ether-based electrolyte [179] can provide more stable interface, Figure 15. The relationship between reversible capacity and cycle number for typical reported alloy-based anode for SIBs [8,18,29,39,40,[87][88][89]106,122,128,144,152,154,156,158,166,168] and PIBs. [64,100,101,130,161] The inset image: main research process changes for alloy-based anode.…”

Peering into Alloy Anodes for Sodium‐Ion Batteries: Current Trends, Challenges, and Opportunities

“…Among the group 14 elements (Si, Ge, and Sn), Ge comes into the sights of the researchers could be due to multiple reasons: 1) Ge shows strong thermodynamic tendency to alloy with Na + (comparable to Sn and stronger than Si), 2) moderate volume expansion and bulk modulus (lower than Sn), and 3) faster Na + conductivity (comparable to Sn). Li et al have successfully synthesized Ge nanoparticles that are encapsulated in interconnected hollow carbon boxes via a carbothermal reducing route ( Figure a–c) . A specific capacity that is approaching the theoretical value of Ge (346 mAh g −1 ) is maintained at 100 mA g −1 after 500 cycles.…”

“…a) SEM and b,c) TEM images of the Ge nanoparticle encapsulated in hollow carbon box. Reproduced with permission . Copyright 2017, Wiley‐VCH.…”

Promoting Ge Alloying Reaction via Heterostructure Engineering for High Efficient and Ultra‐Stable Sodium‐Ion Storage

“…[ 16–19 ] Among various alloy‐type materials, Ge has been found to electrochemically react with Na to form Na x Ge (369 mAh g −1 ) with an atomic ratio of about 1:1. [ 20,21 ] However, bulk Ge is undesirable for sodium storage because of the sluggish kinetics. [ 22 ] Besides, the alloying reactions are usually accompanied by huge volume expansion of the host materials, which leads to anode degradation and poor capacity retention.…”