Multiple diffusion pathways in Li_xNi_0.77Co_0.14Al_0.09O₂ (NCA) Li-ion battery cathodes

Abstract

Experimental evidence for the presence of two diffusion pathways, namely the oxygen dumbbell hop (ODH) and tetrahedral site hop (TSH), has been given for the first time by muon spin relaxation (µSR) in layered oxide lithium ion battery cathodes.

Stoichiometrically driven disorder and local diffusion in NMC cathodes

“…It is observed that as temperature increases there is a corresponding decrease in the eld distribution width due to Li + diffusion becoming more rapid and leading to a motional narrowing effect similar to that seen in previous investigations. 26,42 As [Ni] increases (and thus, [Mn] and [Co] decreases) there is a consistent decrease in D due to the signicantly smaller nuclear moment present in Ni, when compared to Mn or Co.…”

“…40 Previous investigations on isostructural materials have found the TSH mechanism to occur on a similar timescale (z10 À10 cm 2 s À1 ), but provides a lower activation energy (E a ) diffusion pathway (E TSH a z E ODH a /4). 26 However, the TSH mechanism is only available where [Li] < 1 (due to the requirement for a Li divacancy). In comparison, the C2/m structure has previously been reported to exhibit additional interplanar diffusion pathways between the Li and MO 6 slabs, which may be expected to provide enhanced Li ion conductivity.…”

“…To prepare the nanoparticulate NMC precursors a continuous hydrothermal ow synthesis (CHFS) process was used, which has been described elsewhere. 26,44 To summarise the process, three diaphragm pumps (Primeroyal K, Milton Roy, Pont-Saint-Pierre, France) were used to supply feeds of deionized water (P sw ), an aqueous solution of the metal salts ( S1. † The DI water feed from pump P sw was heated in ow to 450 C using a 7 kW custom-built in-line electrical heater.…”

“…mSR has previously been employed on isostructural materials such as the parent LiCoO 2 and sister Li n Ni x Co y Al z O 2 materials, and have been in good agreement with computational predictions of D Li and E a values. [23][24][25][26] Although many studies have been performed to characterise electrochemical performance, there is still a lack of understanding of the effect of increasing nickel concentration on the structure and its relationship with local lithium diffusion in NMC cathodes. Herein, we present the need for improved structural scrutiny and an evaluation of increasing Ni content on local structure by NPD and local diffusion by mSR.…”

Phase Evolution and Li Diffusion in LATP Solid‐State Electrolyte Synthesized via a Direct Heat‐Cycling Method

“…A slow decrease was observed from 200 to 500 K due to the motional narrowing of the magnetic environment the muon experienced, commensurate with preceding studies. [ 33,35,36 ] D Li was estimated by employing Equation ().where N i is the number of accessible Li + sites in the i th path, Z ν,i is the vacancy fraction of the destination sites, s i is the jump distance between Li + sites, and ν is the fluctuation rate at a given temperature. [ 37 ] Figure shows the electron density map for the hkl (0 1–4) plane along which diffusion occurs in LATP through three steps: 1) fully occupied M1 ( 6b ) to partially occupied M3 ( 36f ), M1→M3; 2) partially occupied M3 ( 36f ) to partially occupied M3 (3 6f ), M3→M3; and 3) partially occupied M3 ( 36f ) to fully occupied M1 ( 6b ) M3→M1.…”