Confining Nano-GeP in Nitrogenous Hollow Carbon Fibers toward Flexible and High-Performance Lithium-Ion Batteries

Abstract

Although graphite has been used as anodes of lithium-ion batteries (LiBs) for 30 years, its unsatisfactory energy density makes it insufficient toward some new electronic products such as unmanned aerial vehicles. Herein, in situ synthesis of nano-GeP confined in nitrogen-doped carbon (GeP@NC) fibers was designed and performed via coaxial electrospinning followed by a phosphating process. This way ensured the paper-like GeP@NC-x electrode with high conductivity, high flexibility, and lightweight properties, which simultaneously solved the key scientific problems of difficulty in structural design and severe volume expansion of GeP. The inner diameter and wall thickness of the nanofibers can be effectively controlled by adjusting the size of electrospinning needles. It was suggested that the fibers not only effectively inhibited the growth of GeP, resulting in the synthesis of nano-GeP with size less than 50 nm, but also alleviated the volume expansion/agglomeration and improved the diffusion kinetics of Li+ in nano-GeP during cycling. The Li+ diffusion coefficient can be improved by reducing the inner diameter and wall thickness of the fibers. As a model system, the paper-like electrode (GeP@NC-2) with a fiber diameter of 280 nm and a wall thickness of 110 nm exhibited the best electrochemical performance. When applied as anodes in LiBs, it displayed a reversible capacity of 612 mAh g–1 at the 600th cycle at 1 A g–1, while GeP@NC-0 with a solid structure only delivered 239 mAh g–1. Furthermore, the GeP@NC-2 also exhibited good long-term cycling stability at 5 A g–1, and the capacity displayed a slight difference of 221.2 and 209.0 mAh g–1 in a voltage range of 0∼3 V and 0∼1.5 V, respectively. The well-defined synthetic approach combined with unique nanostructural design provided a meaningful reference for the rational design and development of next-generation flexible and high-performance LiB anodes.

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

“…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.…”

Metal Phosphides as Promising Electrode Materials for Alkali Metal Ion Batteries and Supercapacitors: A Review

“…The material achieved stable cycling performance and good rate capability, and provided a new strategy for the preparation of GeP-based electrode materials. [135,136]…”

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

“…13 Among them, the emerging GeP phosphide has attracted increasing attention in recent years owing to its unique layered structure property, better reaction kinetics, and higher conductivity than oxides and sulfides. 14,15 On one hand, both the Ge and P components in GeP make Li-storage contribution for energy storage by multi-electron reactions (e.g., Li 4.4 Ge and Li 3 P), thus promoting a large theoretical capacity up to 1913 mA h/g, 5 times higher than that of graphite. 16 Besides, typical monoclinic GeP possesses a unique layered structure with superior flexibility, endowing itself with the ability of fast Li-ion diffusion along interlayer spacing and quick charge transfer along the intralayer.…”

“…Among the current electrochemical power sources, the Li-ion batteries (LIBs) are considered as the promising energy storage devices for electric vehicles (EVs) owing to the environmental-friendliness and non-memory effect. , However, triggered by the urgent demand of EVs’ driving mileage (>800 km), recent commercial graphite anode with a low capacity (372 mA h/g) , cannot further enhance the energy density demand (>500 W h/kg) for LIBs. , In comparison, the alloying-type Ge-based materials such as GeO, GeS, GeSe, GeTe, GeP x , , and so on are proposed to be served as the alternative anode materials for next-generation LIBs due to their much higher capacity (>1000 mA h/g) . Among them, the emerging GeP phosphide has attracted increasing attention in recent years owing to its unique layered structure property, better reaction kinetics, and higher conductivity than oxides and sulfides. , On one hand, both the Ge and P components in GeP make Li-storage contribution for energy storage by multi-electron reactions (e.g., Li 4.4 Ge and Li 3 P), thus promoting a large theoretical capacity up to 1913 mA h/g, 5 times higher than that of graphite . Besides, typical monoclinic GeP possesses a unique layered structure with superior flexibility, endowing itself with the ability of fast Li-ion diffusion along interlayer spacing and quick charge transfer along the intralayer. , Such impressive layered mechanical flexibility can be even expanded, exfoliated, and self-assembled into various nanoarchitectures to satisfy the requirement of flexible in-plane/sandwich device design. , With a smaller band gap of ∼0.51 eV, the electronic conductivity of GeP is much higher than that of other Ge-based oxides and sulfides (>1.5 eV) .…”