NH4F surface modification of Li-rich layered cathode materials

Li, Linhu; Chang, Yajie; Xia, Hui; Song, Bang‐Sup; Yang, Jer−Ren; Lee, K.S.; Li, Lü

doi:10.1016/j.ssi.2014.06.012

Cited by 36 publications

(33 citation statements)

References 47 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Preparation of Li ( 30 In a typical process, an aqueous solution containing metal sulphates in a molar ratio of Mn : Ni : Co ¼ 0.54 : 0.13 : 0.13 was rstly prepared. Then, this solution was slowly dripped into an as-prepared NH 4 HCO 3 /Na 2 CO 3 solution with continuous stirring at pH ¼ 8, T ¼ 60 C to obtain the (Mn 0.54 Ni 0.13 Co 0.13 )(CO 3 ) 0.8 precursor.…”

Section: Methodsmentioning

confidence: 99%

Nano-structural changes in Li-ion battery cathodes during cycling revealed by FIB-SEM serial sectioning tomography

et al. 2015

View full text Add to dashboard Cite

The growing demand for reliable, durable electrical energy systems to power electric and hybrid vehicles motivates worldwide efforts aimed at developing high-energy, high-power density batteries. One of the obstacles to widespread industry adoption is the lack of profound understanding and the ability to monitor and control the long-term degradation and capacity fading observed in these systems. Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM) serial sectioning is used to reconstruct the evolution of the three-dimensional structure of Li-ion battery electrodes during extended cycling. High resolution imaging reveals microstructural information at the level of the composite framework consisting of the spheroidal micro-particles of the active material held together by the polymer matrix. The evolution of damage within the micro-particles of the active material can be seen in the form of voiding, cracking and ultimate fragmentation. In particular, when spherical micro-particles of Li-rich layered oxides are used as the cathode, it is found that the extent of fragmentation varied in the direction of Li + diffusion current from the particle surface inwards. We use a simple model of the strain and strain gradient effects of Li + transient diffusion within the electrode to identify the driving force for particle fragmentation, and discuss the implication of these results. † Electronic supplementary information (ESI) available: 3D reconstructions of electrodes aer the 1st charge and the 1st cycle in addition to XRD and SEM observations of Li-rich particles. See

show abstract

Section: Methodsmentioning

confidence: 99%

Nano-structural changes in Li-ion battery cathodes during cycling revealed by FIB-SEM serial sectioning tomography

et al. 2015

View full text Add to dashboard Cite

show abstract

“…[61] Co-doping has shown to be an effective route towards improving the electrochemical properties of cathode material for LIBs. [57,62] Though fluorination has been performed when synthesizing precursor materials, generally fluoride is added during lithiation from solid F-sources like LiF, [56,58,63,64] NH 4 F, [59,65] and NH 4 HF 2 . [66] Polyvinylidendifluoride (PVDF) [60] and polytetrafluoroethylene (PTFE) [67] have also been used as a fluoride source as well as the treatments of CAMs with F-sources in gaseous F 2 [68] and NF 3 .…”

Section: Surface Modification and Dopingmentioning

confidence: 99%

Fluorination of Li‐Rich Lithium‐Ion‐Battery Cathode Materials by Fluorine Gas: Chemistry, Characterization, and Electrochemical Performance in Half Cells

et al. 2019

View full text Add to dashboard Cite

Mild fluorination of high‐energy nickel‐cobalt‐manganese (HE‐NCM) materials with low pressures of elementary fluorine gas (F2) at room temperature was systematically studied. The fluorinated HE‐NCM samples were analysed by ion chromatography, inductively coupled plasma mass spectrometry, FT‐IR spectroscopy, powder X‐ray diffraction, magic angle spinning NMR spectroscopy, scanning electron microscopy, thermo‐gravimetric analysis, differential thermal analysis, electrochemical testing, and X‐ray photoelectron spectroscopy. The treatment of the cathode materials with low pressures (a few hundred mbar) of elementary fluorine gas at room temperature led to the elimination of the basic surface film (LiOH, Li2CO3, Li2O, etc.), and the resulting thin amorphous LiF film led to increased capacity and long‐term stability of the battery. Impedance built‐up was greatly reduced for these systems throughout cycling. Fluorination with F2 only causes the formation of O−Me−F bonds (Me=Transition Metal), when treated with F2 at higher pressures. If O−Me−F bonds are formed, it may be detrimental to the electrode surface film resistance and cycle stability of the electrodes. However, it may be that the LiF surface content, which can expand as long as the LiMeO2 structure can be oxidized and Li+ can be extracted, has become too large and thus detrimental. Considering the evolution of differential capacity plots and taking into account the thermodynamic driving force of the F2 treatment, it is likely that the same activation processes that occur electrochemically in Li‐rich materials also occur chemically, when the material is exposed to F2. Differential capacity plots show enhanced Mn4+ reduction peaks upon lithiation, when the material was exposed to F2, only possible after activation of the Li2MnO3 phase. For this reason, we believe fluorination promotes to some extent an activation of this phase.

show abstract

“…To this end, much effort has been directed to optimize surface chemistry and stabilize surface structure using coating techniques and surface treatments. [31][32][33][34][35][36] Little attention was paid to the surface structure of pristine cathode materials until in recent years. [ 37,38 ] Several transmission electron microscopy (TEM) studies revealed that Ni tends to segregate on certain surface facets in Li-Mn-rich (LMR) oxides which results in structural and chemical modifi cations of the surface layer.…”

Section: Introductionmentioning

confidence: 99%

Ni and Co Segregations on Selective Surface Facets and Rational Design of Layered Lithium Transition‐Metal Oxide Cathodes

Yan

Zheng

et al. 2016

Advanced Energy Materials

103

View full text Add to dashboard Cite

The chemical processes occurring on the surface of cathode materials during battery cycling play a crucial role in determining battery's performance. However, the understanding of such surface chemistry is far from clear due to the complexity of redox chemistry during battery charge/discharge. Through intensive aberration corrected STEM investigation on ten layered oxide cathode materials, two important findings on the pristine oxides are reported. First, Ni and Co show strong plane selectivity when building up their respective surface segregation layers (SSLs). Specifically, Ni‐SSL is exclusively developed on (200)m facet in Li–Mn‐rich oxides (monoclinic C2/m symmetry) and on (012)h facet in Mn–Ni equally rich oxides (hexagonal R‐3m symmetry), while Co‐SSL has a strong preference to (20−2)m plane with minimal Co‐SSL also developed on some other planes in Li–Mn‐rich cathodes. Structurally, Ni‐SSLs tend to form spinel‐like lattice while Co‐SSLs are in a rock‐salt‐like structure. Second, by increasing Ni concentration in these layered oxides, Ni and Co SSLs can be suppressed and even eliminated. The findings indicate that Ni and Co SSLs are tunable through controlling particle morphology and oxide composition, which opens up a new way for future rational design and synthesis of cathode materials.

show abstract

NH4F surface modification of Li-rich layered cathode materials

Cited by 36 publications

References 47 publications

Nano-structural changes in Li-ion battery cathodes during cycling revealed by FIB-SEM serial sectioning tomography

Nano-structural changes in Li-ion battery cathodes during cycling revealed by FIB-SEM serial sectioning tomography

Fluorination of Li‐Rich Lithium‐Ion‐Battery Cathode Materials by Fluorine Gas: Chemistry, Characterization, and Electrochemical Performance in Half Cells

Ni and Co Segregations on Selective Surface Facets and Rational Design of Layered Lithium Transition‐Metal Oxide Cathodes

Contact Info

Product

Resources

About