Uniformly Confined Germanium Quantum Dots in 3D Ordered Porous Carbon Framework for High‐Performance Li‐ion Battery

Abstract

(1 of 11)Although abundant germanium (Ge)-based anode materials have been explored to obtain high specific capacity, high rate performance, and long charge/discharge lifespans for lithium-ion batteries (LIBs), their performances are still far from satisfactory due to the intrinsic defects of Ge and the relatively intricate anode structure. To work out these issues, a 3D ordered porous N-doped carbon framework with Ge quantum dots uniformly embedded (3DOP Ge@NC) as a binder-free anode for LIBs via a facile polystyrene colloidal nanospheres template-confined strategy is proposed. This unique structure not only facilitates Li-ion diffusion and electron transport that can guarantee rapid de/alloying reaction, but also alleviates the huge volume changes during reactions and improves cycling stability. Notably, the resulting anode delivers a high specific reversible capacity (≈1160 mA h g −1 at 1 A g −1 ), superior rate properties (exceeding 500 mA h g −1 at 40 A g −1 ), and excellent cycling stability (over 90% capacity retention after 1200 cycles even at 5 A g −1 ). Furthermore, both the 3DOP Ge@NC anode with high areal mass loading (up to 8 mg cm −2 ) and the full cell coupled with LiFePO 4 cathode display high capacity and cycling stability, further indicative of the favorable real-life application prospects for high-energy LIBs.

Ge nanocrystals tightly and uniformly distributed in a carbon matrix through nitrogen and oxygen bridging bonds for fast-charging high-energy-density lithium-ion batteries

“…2b) correspond to Ge crystals, and D and G peaks of carbon materials, respectively, to further confirm the existence of Ge and carbon. 13,17 High Intensity ratio (1.13) of D and G peaks suggests that the carbon contains plentiful defects beneficial for Li + storage. 8,10,13 Four elements of Ge (11.6 at%), C (73.2at%), N (9.1 at%), and O (6.1 at%) ( Ge-O, respectively, to imply the presence of elemental Ge, Ge-N-C, and Ge-O-C. 17,25 The C 1s spectrum ( Fig.…”

“…13,17 High Intensity ratio (1.13) of D and G peaks suggests that the carbon contains plentiful defects beneficial for Li + storage. 8,10,13 Four elements of Ge (11.6 at%), C (73.2at%), N (9.1 at%), and O (6.1 at%) ( Ge-O, respectively, to imply the presence of elemental Ge, Ge-N-C, and Ge-O-C. 17,25 The C 1s spectrum ( Fig. 2e) reveals three peaks at 284.8, 286.1, and 287.2 eV attributed to C-C, C-N/C-O, and C=O, respectively, 13,17 to confirm the formation of N,O co-doped carbon.…”

“…3,4 Consequently, enormous anodes with higher capacity and better rate capability are fabricated in recent years, such as Si, 5 Ge, 6 Sn, 7 and their corresponding oxide, [8][9][10][11][12] and transition metal sulfide 13,14 etc. Among them, Ge has come to public concern due to high specific/volumetric capacity of 1624 mAh g -1 /8600 mAh cm -3 , 15,16 and high Li + diffusivity 6,17 to lead to an amazing rate capability up to 1000 C. 18 However, Ge experiences large volume change of ~230% on cycling to bring about electrode pulverization, and thus cause poor cyclablity. 6,[15][16][17] In order to deal with the intractable problem, a lot of works have been made, such as designing Ge nanostructures including nanoparticles, 6 nanofibers, 16 nanotubes, 19 and nanowires, 20 and making Ge/C 3 nanocomposites.…”

“…Among them, Ge has come to public concern due to high specific/volumetric capacity of 1624 mAh g -1 /8600 mAh cm -3 , 15,16 and high Li + diffusivity 6,17 to lead to an amazing rate capability up to 1000 C. 18 However, Ge experiences large volume change of ~230% on cycling to bring about electrode pulverization, and thus cause poor cyclablity. 6,[15][16][17] In order to deal with the intractable problem, a lot of works have been made, such as designing Ge nanostructures including nanoparticles, 6 nanofibers, 16 nanotubes, 19 and nanowires, 20 and making Ge/C 3 nanocomposites. [20][21][22][23][24] The latter is regarded to be the most effective way because the added carbon not only can improve the electrical conductivity (EC) of Ge, but also can act as buffer layer/matrix to ease volume expansion.…”

“…17,23 For example, by confining Ge quantum dots in a porous N-doped carbon framework using a template-confined route, in which Ge-O-C and Ge-C bonds were formed, a high capacity of 1160 mAh g -1 after 200 cycles at 1 A g -1 was obtained. 17 By encapsulating Ge nanoparticles into N-doped carbon nanotube with a size of 80-200 nm, a high capacity of 1080 mAh g -1 after 1200 cycles with a capacity retention of ~90% at 0.8 A g -1 was obtained. 23 The last type is that Ge nanoparticles are uniformly dispersed into carbon matrix.…”