Understanding the stability of MnPO₄

Abstract

We have revealed the critical role of carbon coating in the stability and thermal behaviour of olivine MnPO 4 obtained by chemical delithiation of LiMnPO 4 . (Li)MnPO 4 samples with various particle sizes and carbon contents were studied. Carbon-free LiMnPO 4 obtained by solid state synthesis in O 2 becomes amorphous upon delithiation. Small amounts of carbon (0.3 wt%) help to stabilize the olivine structure, so that completely delithiated crystalline olivine MnPO 4 can be obtained. Larger amount of carbon (2 wt%) prevents full delithiation. Heating in air, O 2 , or N 2 results in structural disorder (<300 C), formation of an intermediate sarcopside Mn 3 (PO 4 ) 2 phase (350-450 C), and complete decomposition to Mn 2 P 2 O 7 on extended heating at 400 C. Carbon coating protects MnPO 4 from reacting with environmental water, which is detrimental to its structural stability.

Facile Synthesis of MnPO4·H2O Nanowire/Graphene Oxide Composite Material and Its Application as Electrode Material for High Performance Supercapacitors

“…In Figure 4b, the Mn 3p spectrum for MnPO 4 ·H 2 O nanowire/GO material is fitted to two components, which are centered at 641.29 eV and 653.82 eV belonging to Mn 2p 3/2 and Mn 2p 1/2 . These results conform to the reported Mn III compounds [33,34].…”

Energetics and cathode voltages of LiMPO4 olivines ( M=Fe , Mn) from extended Hubbard functionals

“…The de-lithiated member of the Mn olivine system has not been very much studied, probably due to its poor thermal stability (its tendency to decompose and to release oxygen), actually still under investigation (see, e.g., Ref. [178] and references therein). Its computational characterization has been also quite sporadic with studies predicting either halfmetallic [82] or semiconducting [179] behavior.…”

An Aqueous Symmetric Sodium‐Ion Battery with NASICON‐Structured Na3MnTi(PO4)3

“…Thecyclic voltammogram (CV) of the Na 3 MnTi(PO 4 ) 3 electrode features apair of redox peaks centered at about 0.6 Vv s. Ag/AgCl (Figure 3A), which can be attributed to the reversible reactions of the Mn 3+ /Mn 2+ redox couple in the NASICON lattice with extraction/insertion of sodium-ions from/into Na 3 MnTi-(PO 4 ) 3 .T he redox voltage of Mn 3+ /Mn 2+ in the NASICONstructured Na 3 MnTi(PO 4 ) 3 is well-below the oxygen evolution potential in the neutral aqueous electrolyte (1.1 Vv s. Ag/ AgCl), which therefore enables it to be used as ahigh-voltage cathode for aqueous sodium-ion batteries. [43][44][45] In accordance with the CV results,t he Na 3 MnTi(PO 4 ) 3 electrode exhibited charge and discharge profiles with well-defined voltage plateaus centered at about 0.6 Vv s. Ag/AgCl with little polarization ( Figure 3B), corresponding to the reversible reaction of Na 3 MnTi(PO 4 ) 3 ÀNa + Àe À QNa 2 MnTi(PO 4 ) 3 ,w ith the oxidation of Mn 2+ to Mn 3+ on charge and the reduction of Mn 3+ to Mn 2+ on discharge, [46,47] keeping the valence state of Ti 4+ unchanged ( Figure S2, Supporting Information). The Na 3 MnTi(PO 4 ) 3 electrode delivers ad ischarge capacity of 58.4 mAh g À1 at ar ate of 0.5 C( 1C= 58.7 mA g À1 ), corresponding to an early 100 %u tilization of its one sodium extraction/insertion capacity of the Na 3 MnTi(PO 4 ) 3 electrode through the Mn 3+ /Mn 2+ redox couple.T he structural change of Na 3 MnTi(PO 4 ) 3 is reversible during extraction and insertion of one sodium-ion per formula unit through the Mn 3+ / Mn 2+ redox couple.When charging the electrode to 1.0 Vvs.…”