Ilias Belharouak

Evolution of lattice structure and chemical composition of the surface reconstruction layer in Li1.2Ni0.2Mn0.6O2 cathode material for lithium ion batteries

Voltage and capacity fading of layer structured lithium and manganese rich (LMR) transition metal oxide is directly related to the structural and composition evolution of the material during the cycling of the battery. However, understanding such evolution at atomic level remains elusive. On the basis of atomic level structural imaging, elemental mapping of the pristine and cycled samples, and density functional theory calculations, it is found that accompanying the hoping of Li ions is the simultaneous migration of Ni ions toward the surface from the bulk lattice, leading to the gradual depletion of Ni in the bulk lattice and thickening of a Ni enriched surface reconstruction layer (SRL). Furthermore, Ni and Mn also exhibit concentration partitions within the thin layer of SRL in the cycled samples where Ni is almost depleted at the very surface of the SRL, indicating the preferential dissolution of Ni ions in the electrolyte. Accompanying the elemental composition evolution, significant structural evolution is also observed and identified as a sequential phase transition of C2/m → I41 → Spinel. For the first time, it is found that the surface facet terminated with pure cation/anion is more stable than that with a mixture of cation and anion. These findings firmly established how the elemental species in the lattice of LMR cathode transfer from the bulk lattice to surface layer and further into the electrolyte, clarifying the long-standing confusion and debate on the structure and chemistry of the surface layer and their correlation with the voltage fading and capacity decaying of LMR cathode. Therefore, this work provides critical insights for design of cathode materials with both high capacity and voltage stability during cycling.

Highly Cyclable Lithium-Sulfur Batteries with a Dual-Type Sulfur Cathode and a Lithiated Si/SiOx Nanosphere Anode.

Lithium-sulfur batteries could become an excellent alternative to replace the currently used lithium-ion batteries due to their higher energy density and lower production cost; however, commercialization of lithium-sulfur batteries has so far been limited due to the cyclability problems associated with both the sulfur cathode and the lithium-metal anode. Herein, we demonstrate a highly reliable lithium-sulfur battery showing cycle performance comparable to that of lithium-ion batteries; our design uses a highly reversible dual-type sulfur cathode (solid sulfur electrode and polysulfide catholyte) and a lithiated Si/SiOx nanosphere anode. Our lithium-sulfur cell shows superior battery performance in terms of high specific capacity, excellent charge-discharge efficiency, and remarkable cycle life, delivering a specific capacity of ∼750 mAh g(-1) over 500 cycles (85% of the initial capacity). These promising behaviors may arise from a synergistic effect of the enhanced electrochemical performance of the newly designed anode and the optimized layout of the cathode.

Nanostructured Lithium Nickel Manganese Oxides for Lithium-Ion Batteries

Nanostructured lithium nickel manganese oxides were investigated as advanced positive electrode materials for lithium-ion batteries designated to power plug-in hybrid electric vehicles and all-electric vehicles. The investigation included material characterization and electrochemical testing. In cell tests, the Li{sub 1.375}Ni{sub 0.25}Mn{sub 0.75}O{sub 2.4375} composition achieved high capacity (210 mAh g{sup -1}) at an elevated rate (230 mA g{sup -1}), which makes this material a promising candidate for high energy density Li-ion batteries, as does its being cobalt-free and uncoated. The material has spherical morphology with nanoprimary particles embedded in micrometer-sized secondary particles, possesses a multiphase character (spinel and layered), and exhibits a high packing density (over 2 g cm{sup -3}) that is essential for the design of high energy density positive electrodes. When combined with the Li{sub 4}Ti{sub 5}O{sub 12} stable anode, the cell showed a capacity of 225 mAh g{sup -1} at the C/3 rate (73 mA g{sup -1}) with no capacity fading for 200 cycles. Other chemical compositions, Li{sub (1+x)}Ni{sub 0.25}Mn{sub 0.75}O{sub (2.25+x/2)} (0.32 {le} x {le} 0.65), were also studied, and the relationships among their structural, morphological, and electrochemical properties are reported.

Radially aligned hierarchical columnar structure as a cathode material for high energy density sodium-ion batteries

Delivery of high capacity with good retention is a challenge in developing cathodes for rechargeable sodium-ion batteries. Here we present a radially aligned hierarchical columnar structure in spherical particles with varied chemical composition from the inner end (Na[Ni0.75Co0.02Mn0.23]O2) to the outer end (Na[Ni0.58Co0.06Mn0.36]O2) of the structure. With this cathode material, we show that an electrochemical reaction based on Ni(2+/3+/4+) is readily available to deliver a discharge capacity of 157 mAh (g-oxide)(-1) (15 mA g(-1)), a capacity retention of 80% (125 mAh g(-1)) during 300 cycles in combination with a hard carbon anode, and a rate capability of 132.6 mAh g(-1) (1,500 mA g(-1), 10 C-rate). The cathode also exhibits good temperature performance even at -20°C. These results originate from rather unique chemistry of the cathode material, which enables the Ni redox reaction and minimizes the surface area contacting corrosive electrolyte.

Insight into Sulfur Reactions in Li–S Batteries

Understanding and controlling the sulfur reduction species (Li2Sx, 1 ≤ x ≤ 8) under realistic battery conditions are essential for the development of advanced practical Li-S cells that can reach their full theoretical capacity. However, it has been a great challenge to probe the sulfur reduction intermediates and products because of the lack of methods. This work employed various ex situ and in situ methods to study the mechanism of the Li-S redox reactions and the properties of Li2Sx and Li2S. Synchrotron high-energy X-ray diffraction analysis used to characterize dry powder deposits from lithium polysulfide solution suggests that the new crystallite phase may be lithium polysulfides. The formation of Li2S crystallites with a polyhedral structure was observed in cells with both the conventional (LiTFSI) electrolyte and polysulfide-based electrolyte. In addition, an in situ transmission electron microscopy experiment observed that the lithium diffusion to sulfur during discharge preferentially occurred at the sulfur surface and formed a solid Li2S crust. This may be the reason for the capacity fade in Li-S cells (as also suggested by EIS experiment in Supporting Information ). The results can be a guide for future studies and control of the sulfur species and meanwhile a baseline for approaching the theoretical capacity of the Li-S battery.

Visualizing nanoscale 3D compositional fluctuation of lithium in advanced lithium-ion battery cathodes

The distribution of cations in Li-ion battery cathodes as a function of cycling is a pivotal characteristic of battery performance. The transition metal cation distribution has been shown to affect cathode performance; however, Li is notoriously challenging to characterize with typical imaging techniques. Here laser-assisted atom probe tomography (APT) is used to map the three-dimensional distribution of Li at a sub-nanometre spatial resolution and correlate it with the distribution of the transition metal cations (M) and the oxygen. As-fabricated layered Li1.2Ni0.2Mn0.6O2 is shown to have Li-rich Li2MO3 phase regions and Li-depleted Li(Ni0.5Mn0.5)O2 regions. Cycled material has an overall loss of Li in addition to Ni-, Mn- and Li-rich regions. Spinel LiNi0.5Mn1.5O4 is shown to have a uniform distribution of all cations. APT results were compared to energy dispersive spectroscopy mapping with a scanning transmission electron microscope to confirm the transition metal cation distribution.

A comprehensive study of the role of transition metals in O3-type layered Na[NixCoyMnz]O2 (x = 1/3, 0.5, 0.6, and 0.8) cathodes for sodium-ion batteries

A comprehensive study of Na[NixCoyMnz]O2 (x = 1/3, 0.5, 0.6, and 0.8) cathodes is carried out to determine the optimal composition as the electrochemical, structural, and thermal properties of O3-type layered cathodes are strongly dependent on the transition metal composition. Here, the role of each transition metal in [NixCoyMnz]O2 cathodes is identified via electrochemical property characterization, structural analysis, and thermal stability testing. Briefly, an increase of the Ni fraction resulted in an increasingly higher capacity but is accompanied by progressively poor capacity retention. On the other hand, the Co metal played an important role in stabilizing the structure, while the Mn content contributed to enhancing the capacity retention and thermal stability. The present study highlights the importance of appropriately balancing the transition metal composition in a layered Na[NixCoyMnz]O2 cathode. Furthermore, this work provides a design guideline for developing an ideal Na[NixCoyMnz]O2 cathode with both high capacity and optimal cycle retention in addition to thermal stability.

Crystal structure of the alluaudite Ag2Mn3(VO4)3

Abstract The new compound Ag2Mn3(VO4)3 was synthesized by hydrothermal and solid state reaction routes, and its crystal structure was determined from single-crystal X-ray diffraction data. Ag2Mn3(VO4)3 crystallizes with a monoclinic symmetry, space group C2/c, with a=11.8968(11) Å, b=13.2057(13) Å, c=6.8132(7) Å, β=111.3166(15) (°) and V=997.16(17) Å3 (Z=4). Its crystal refinement yielded the residual factors R(F)=0.0249 and wR(F2)=0.0704 for 95 parameters and 1029 independent reflections at a 3σ(I) level. Ag2Mn3(VO4)3 can be considered as a new member of the AA′MM′2(XO4)3 alluaudite family. The specific arrangement of M and M′ octahedral sites and of X tetrahedral sites gives rise to two different channels aligned along the crystallographic c-axis and containing the A and A′ sites. The A, A′, M, and X sites are fully occupied by Ag+, Mn2+, and V5+, respectively; whereas a Mn2+/Mn3+ mixture is observed in the M′ site.

An all-solid-state electrochemical double-layer capacitor based on a plastic crystal electrolyte

A plastic crystal, solid electrolyte was prepared by mixing tetrabutylammonium hexafluorophosphate salt, (C4H9)4NPF6, (10 molar %) with succinonitrile, SCN, (N C−CH2−CH2−C N), [SCN-10%TBA-PF6]. The resultant waxy material shows a plastic crystalline phase that extend from -36 °C up to its melting at 23 °C. It shows a high ionic conductivity reaching 4 × 10−5 S/cm in the plastic crystal phase (15 °C) and ~ 3 × 10−3 S/cm in the molten state (25 °C). These properties along with the high electrochemical stability rendered the use of this material as an electrolyte in an electrochemical double-layer capacitor (EDLC). The EDLC was assembled and its performance was tested by cyclic voltammetry, AC impedance spectroscopy and galvanostatic charge-discharge methods. Specific capacitance values in the range of 4-7 F/g. (of electrode active material) were obtained in the plastic crystal phase at 15 °C, that although compare well with those reported for some polymer electrolytes, can be still enhanced with further development of the device and its components, and only demonstrate their great potential use for capacitors as a new application.

Synthesis, structural characterization, and hydrogen bonds of Co9(OH)14[SO4]2

Abstract The new compound Co9(OH)14[SO4]2 was synthesized using a hydrothermal method from LiF, Na2SO3, and Co(CH3COO)2·4H2O in a molar ratio of 1:1:1 in the presence of atmospheric oxygen. Its crystal structure was determined from single crystal X-ray diffraction data. Co9(OH)14[SO4]2 crystallizes in the triclinic system, space group P1̅ with a=7.693(2) Å, b=8.318(2) Å, c=8.351(2) Å, α=82.375(5)°, β=77.832(4)°, γ=68.395(4)°, V=484.8(2) Å3, and Z=2. Its structure is composed of cobalt-containing sheets interconnected by SO4 tetrahedra. Bent and symmetrically trifurcated hydrogen bonds have been observed. Furthermore, structural similarities with hydrozincite and brucite minerals have been noticed.