Elsevier

Electrochimica Acta

Volume 297, 20 February 2019, Pages 872-878
Electrochimica Acta

Lithium storage behavior of MoO3–P2O5 glass as cathode material for Li-ion batteries

https://doi.org/10.1016/j.electacta.2018.12.039Get rights and content

Abstract

MoO3-P2O5 glasses were prepared by a simple melt quenching method. XRD and DSC investigations confirmed the amorphous state of 60Mo-40P, 70Mo-30P and 75Mo-25P glass. Interestingly, HRTEM images revealed the inherent crystallization behavior in Mo enriched glass. The existing nanocrystals performed a synergetic effect with the glass matrix to relax the stress caused by Li ions insertion/extraction. As a result, 75Mo-25P glass with distinct nanocrystals showed excellent long cycling stability. The structural transition of MoO3-P2O5 glass and the valence change of Mo ions during cycling were discussed. Furthermore, CV and EIS measurements were performed to elucidate the difference of redox reaction, electrons transport and ions diffusion in 75Mo-25P glass and crystalline MoO3. This study provides an avenue to exploit new cathode materials with long cycling life for Li-ion batteries.

Introduction

Rechargeable lithium ion batteries (LIBs) have been widely investigated for effective energy storage since 1990s. The sustainable development of LIBs depends mainly on the availability of electrode materials with high-energy capacity and cycling stability [1,2]. Among the compositions of LIBs, cathode materials generally determine the whole achievable capacity due to their lower capacity compared with anode materials. Until now, a large variety of crystalline materials, which possess the tight, regular and intercalated host structure, have been deeply developed as cathode materials for LIBs [3]. However, these crystalline cathode materials suffer from low charge/discharge capacity and/or poor cycling performance [4]. Unlike the traditional crystalline materials, amorphous materials are composed of open networks and free of grain boundaries, which are expected to achieve high specific capacity beyond the crystalline cathode materials [5,6]. Recently, amorphous vanadium oxides have been explored as cathode materials, such as V2O5 [7], LiV3O8 [8], LixV2O5 [9]. Their unique open structure and multiple oxidation states (V5+ to V2+) help to realize additional Li+ ions insertion without significant structure rearrangement and thus achieve high charge/discharge capacity and stable cycling performance. Furthermore, vanadium based glasses by melt quenching (e.g., V2O5-P2O5 [10], TeO2-V2O5 [11] and Li2O-V2O5-P2O5 [12]) also exhibit excellent cycling stability when used as cathode materials. Unfortunately, vanadium oxides and vanadium based glasses are susceptible to moisture and vanadium pentoxide is highly toxic. In this regard, molybdenum seems to be the best substitute of vanadium due to its multiple oxidation states and nontoxicity.

To best of our knowledge, MoO3-P2O5 binary glass have not been investigated as electrode materials for LIBs. There are only investigations on electrical properties of MoO3-P2O5 glass [13], and the modified Mo-phosphate glass MoO3-Fe2O3-P2O5 [14], Na2O-MoO3-P2O5 [15] or LiF-MoO3-P2O5 [16], and so on. In Mo-based glass, there exists an electronic hopping conduction mechanism between Mo5+ and Mo6+. In this paper, the feasibility, limitations and the lithium storage behaviors of xMoO3-1/2 (1-x) P2O5 glasses as cathode materials for LIBs have been investigated.

Section snippets

Glass preparation and materials characterization

xMoO3-1/2 (1-x) P2O5 (x = 0.1–0.9) glass were synthesized by melting (NH4)2MoO4 (Aladdin, AR) and (NH4)2HPO4 (Aladdin, AR) at 800 °C for 1 h in air using an alumina crucible, then pouring the melts on a stainless steel plate. The structure of as-quenched glass was investigated through a Bruker X-ray diffractometer (XRD). The glass transition temperature (Tg) and crystallization temperature (Tc) were determined by differential scanning calorimeter (DSC) (NETZSCH STA 449F3 thermal analyzer).

Structure and morphology analysis

XRD results demonstrate that the glass formation region of Mo/P is from atomic ratio 50:50 to 75:25. Fig. 1a shows the XRD patterns of xMoO3-1/2 (1-x) P2O5 (x = 0.6, 0.7 and 0.75) glass samples, which are named as 60Mo-40P, 70Mo-30P and 75Mo-25P glass, respectively. All the patterns exhibit a typical broad hump without any crystalline plane diffraction peaks, indicating that the as-quenched powders are amorphous. Furthermore, the hump gradually shifts to the high angle with increasing Mo, which

Conclusions

xMoO3-1/2(1-x)P2O5 glass were prepared through a melt quenching method. The glass formation region was determined to be from 50:50 to 75:25 (mole ratio MoO3/P2O5). XRD and DSC results confirmed the amorphous state of obtained glass. HRTEM observations revealed the presence and the formation trend of nanocrystals with increasing Mo. 75Mo-25P glass with distinct nanocrystals exhibited a high initial discharge capacity (291 mAh·g−1) and long cycling stability. During discharge/charge process,

Acknowledgment

This work has been financially supported by Shenzhen Basic Research Project Funds (JCYJ20170817161127616).

References (32)

  • J.W. Fergus

    J. Power Sources

    (2010)
  • D.A. Semenenko et al.

    Electrochem. Commun.

    (2010)
  • M.A. Kebede et al.

    J. Alloy. Comp.

    (2018)
  • Y. Zhang et al.

    Nanomater. Energy

    (2018)
  • G. Delaizir et al.

    Solid State Ionics

    (2013)
  • A. Moguš-Milanković et al.

    J. Non-Cryst. Solids

    (2004)
  • L. Bih et al.

    Mater. Lett.

    (2001)
  • M. Nagarjuna et al.

    Physica B

    (2009)
  • J.E. Garbarczyk et al.

    Solid State Ionics

    (2015)
  • M.Y. Hassaan et al.

    J. Non-Cryst. Solids

    (2014)
  • T. Honma et al.

    Ceram. Int.

    (2010)
  • Q. Xia et al.

    J. Power Sources

    (2013)
  • T. Li et al.

    Nanomater. Energy

    (2016)
  • K.A. Gesheva et al.

    Surf. Coating. Technol.

    (2007)
  • D. Boudlich et al.

    J. Non-Cryst. Solids

    (1998)
  • T.K. Pietrzak et al.

    Solid State Ionics

    (2012)
  • Cited by (0)

    View full text