P-Redox Mechanism at the Origin of the High Lithium Storage in NiP₂-Based Batteries

Abstract

The Li reactivity of NiP2 is investigated by means of electrochemical tests, in situ XRD, and 31P NMR characterizations as well as first principles DFT calculations. A two-step insertion/conversion reaction is shown to transform the NiP2 starting electrode into an intermediate Li2NiP2 single phase and then to convert into the Li3P/Ni° nanocomposite. The ternary phase is fully characterized and is shown to be structurally very close to the starting NiP2 regarding the Ni ions environment. This demonstrates that its formation results from a P-redox insertion mechanism associated with a very good reversibility. However, its nucleation upon delithiation from the fully converted Li3P/Ni composite is shown to be kinetically limited (poor structural relationship) which strongly suggests that restricted lithiation is required for best cycleability of the NiP2/Li cell.

Beyond Intercalation‐Based Li‐Ion Batteries: The State of the Art and Challenges of Electrode Materials Reacting Through Conversion Reactions

“…Density function theory (DFT) calculations have revealed that the very covalent nature of the M-P bonds yields electronic structures around the Fermi level (i.e., the electronic states involved in the redox activity of the compounds) in which bands with a strong P(3 s ,3 p ) character lie at high energy. [232][233][234][235] As a matter of fact, the attractive redox activity of phosphorus has led to efforts to investigate the performance of a Li-P battery. [ 236 ] While no conversion has been observed for phosphides containing early transition metals such as Ti or V, [237][238][239] …”

“…Both the cubic and the monoclinic polymorphs convert to Li 3 P and Ni, with a intermediate step of insertion for the latter, [ 235 ] upon discharge to 0 V, producing a total of 1000-1300 mAh g − 1 . [ 234 ] Fair reversibility is observed upon the fi rst charge, and the capacity in powder electrodes decays noticeably within the fi rst 10 cycles, even at low rates.…”

Lithium transition metal pnictides – structural chemistry, electrochemistry, and function

“…FeP n with n = 0.33, 0.5, 1, 2, and 4 have been intensively investigated by Monconduit and coworkers (Boyanov et al 2006(Boyanov et al , 2009a. A closed and condensed polyhedral structure of FeP 6 octahedra is present in FeP, opening up some channels between the corner-shared polyhedra in FeP 2 , and finally leading to a layered structure of edgesharing octahedra in the case of FeP 4 .…”

“…NiP 2 prepared via a solid-state route from the elements (Boyanov et al 2009a) and by ball milling (Hayashi et al 2009) has been tested in a common battery setup using liquid electrolytes and by a solid electrolyte, respectively. A two-step intercalation/conversion mechanism has been identified during the lithiation/delithiation process via a solid solution Li 1.5 NiP 2 -Li 2 NiP 2 to Li 3 P and Ni.…”

A Functionalized Co2P Negative Electrode for Batteries Demanding High Li-Potential Reaction

“…Density Functional Theory (DFT) calculations have revealed that the high covalent nature of the M-P yields electronic structures around the Fermi level in which levels with a strong P(3s, 3p) character lie at high energy. 27 In the present work, electrodeposited Co 2 P films are prepared under a galvanostatic regime. The high potential reaction with lithium of theses phases as opposed to potential reaction found in other metal phosphides as CoP 3 and CoP is highlighted.…”