Synthesis and Fast Exfoliation of Layered GeP Nanosheets for Advanced Li-Ion Batteries

Abstract

The layered GeP shows great advantages for high-energy Li-ion batteries (LIBs) owing to its large capacity and suitable plateau. However, the morphology of GeP nanosheets is difficult to obtain since recent GeP is always synthesized by a high-energy ball-milled method, resulting in serious amorphous features and failure of smart morphology design for flexible devices. Herein, ultra-thin GeP nanosheets are successfully prepared in a large scale by first synthesizing single-crystal GeP via a typical flux method following a fast electrochemical exfoliation. Compared to traditional ultrasonic or mechanical stripping, such electrochemical exfoliation shows a much higher stripping efficiency and quality to meet the large-scale requirement for battery applications. When served as an anode for LIBs, these GeP nanosheets deliver a large capacity (1150 mA h/g) and superior cyclability (>500 cycles) and rate performance (346 mA h/g at 2000 mA/g) for energy storage. More importantly, benefitting from intrinsic layered structural flexibility, these GeP nanosheets enable self-assembling with reduced graphene oxide (RGO) and carbon nanotubes (CNTs) toward free-standing electrode fabrication without a binder and conductive agent. Consequently, a sandwich-like GeP@RGO@CNT hybrid electrode is well-designed, enabling a high capacity (870 mA h/g) and good performances for LIBs as well. This fast exfoliation of GeP nanosheets and free-standing electrode construction can be easily extended to other layered materials toward advanced energy storage.

Novel Ni–Ge–P anodes for lithium-ion batteries with enhanced reversibility and reduced redox potential

“…S18, † the rate performance of Ni-Ge-P 2 /C in this work is superior to those of previously reported Ni-, Ge-, and P-based anodes, and the capacity and cycling performance of Ni-Ge-P 2 /C are both better than those of reported NiP 2 @C, Ni 2 P@rGO and Cu 2 Ge 8 -based anodes. [47][48][49][50][51]…”

State‐of‐the‐Art Two‐Dimensional Metal Phosphides for High Performance Lithium‐ion Batteries: Progress and Prospects

“…In addition, Wei et al synthesized single crystal massive GeP by typical flux method and successfully prepared GeP nanosheets on a large scale by electrochemical exfoliation method. [100] When used as the anode of LIB, these exfoliated GeP nanosheets show high performance in energy storage with the reversible capacity as high as 1150 mAh g À 1 in the first cycle. After 500 cycles at 100 mA g À 1 , the reversible capacity of 330 mAh g À 1 could still be obtained (Figure 10f).…”

“…Li 3 P + Co. The main group MPs stores Li not only by conversion reaction of P but also by alloying with Li to form Li x M. For example, in GeP, Ge and Li are alloyed to generate Li 4.4 Ge and P and Li are combined to generate Li 3 P. [99,100] The above lithium storage behavior is expressed as : Ge + 4.4Li ! Li 4.4 Ge; LixGeP + (3À x)Li !…”

“…The lithium storage of 2D TMPs largely depends on the conversion reaction of P. For example, CoP achieves lithium storage by combining P with Li to generate Li 3 P, [23,51] and its expression is CoP+3Li + +3e − $${ \mathbin{{\stackrel{\textstyle\rightarrow} { {\smash{\leftarrow}\vphantom{_{\vbox to.5ex{\vss}}}} } }} }$$ Li 3 P+Co. The main group MPs stores Li not only by conversion reaction of P but also by alloying with Li to form Li x M. For example, in GeP, Ge and Li are alloyed to generate Li 4.4 Ge and P and Li are combined to generate Li 3 P [99,100] . The above lithium storage behavior is expressed as : Ge+ 4.4Li $${ \mathbin{{\stackrel{\textstyle\rightarrow} { {\smash{\leftarrow}\vphantom{_{\vbox to.5ex{\vss}}}} } }} }$$ Li 4.4 Ge; Li x GeP+(3− x )Li $${ \mathbin{{\stackrel{\textstyle\rightarrow} { {\smash{\leftarrow}\vphantom{_{\vbox to.5ex{\vss}}}} } }} }$$ Li 3 P+Ge.…”

“…Because of its large specific surface area, 2D structure increase the contact area between material and dielectric, thus shortening the diffusion path of Li and improving the ion diffusion rate, which generally makes the lithium storage capacity of 2D materials higher than that of bulk MPs. [100] In addition, compared with bulk MPs, 2D materials with unique advantages can reduce the structural damage caused by repeated cycles, thus achieving relatively stable capacity retention. For example, The first reversible capacity of Ni 2 P nanosheets is higher than that of Ni 2 P nanoparticles, and the capacity retention rate is better than that of nanoparticles.…”