Effect of Transitional Metals (Mn and Ni) Substitution in LiCoPO4 Olivines.

Oriele Palumbo,Mariangela Curcio,Annalisa Paolone,Francesco M Vitucci,Jessica Manzi,Daniele Meggiolaro,Francesco Trequattrini,Sergio Brutti

doi:10.3390/molecules25030601

Oriele Palumbo, Mariangela Curcio + Show 6 more

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https://doi.org/10.3390/molecules25030601

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Abstract

Transition metal substitution is a key strategy to optimize the functional properties of advanced crystalline materials used as positive electrodes in secondary lithium batteries (LIBs). Here we investigate the structural alterations in the olivine lattice of Mn and Ni substituted LiCoPO4 phase and the impact on performance in LIBs. X-ray diffraction (XRD) and extended X-ray absorption experiments have been carried out in order to highlight the structural alterations induced by partial substitution of cobalt by manganese and nickel. XRD analysis suggests that substitution induces an expansion of the lattices and an increase of the antisite disorder between lithium and transition metal ions in the structure. XAS data highlight negligible electronic disorder but a relevant modulation in the local coordination around the different metal ions. Moreover, galvanostatic tests showed poor reversibility of the redox reaction compared to the pure LCP sample, and this failure is discussed in detail in view of the observed remarkable structural changes.

Highlights

The improvement of lithium-ion batteries technology requires the development of alternative electrodes and electrolytes materials, able to provide better performances in terms of energy densities, cycle life, safety, and sustainability
X-ray diffraction (XRD) analysis suggests that substitution induces an expansion of the lattices and an increase of the antisite disorder between lithium and transition metal ions in the structure
Among various positive electrode materials, olivine compounds such as LiCoPO4 (LCP) or LiFePO4 (LFP) have been exploited, with the aim to improve safety with respect to the use of the LiMn1.5 Ni0.5 O4 spinel or of carbonaceous cathodes

Summary

Introduction

The improvement of lithium-ion batteries technology requires the development of alternative electrodes and electrolytes materials, able to provide better performances in terms of energy densities, cycle life, safety, and sustainability. Among various positive electrode materials, olivine compounds such as LiCoPO4 (LCP) or LiFePO4 (LFP) have been exploited, with the aim to improve safety with respect to the use of the LiMn1.5 Ni0.5 O4 spinel or of carbonaceous cathodes. LCP is considered a promising cathode material for high energy Li-ion cells due to its very high working potential (>4.7 V vs Li) [1], but, compared to the isostructural and commercially exploited. LFP, LCP cathodes suffer poor reversibility in the first electrochemical de-insertion/insertion [2], a remarkable capacity fading on cycling [3,4], and a spontaneous self-discharge once fully charged [5,6]. In order to mitigate these drawbacks, a partial substitution of the Co2+ has been suggested [1]

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