Ying Shirley Meng

Layered SnS2‐Reduced Graphene Oxide Composite – A High‐Capacity, High‐Rate, and Long‐Cycle Life Sodium‐Ion Battery Anode Material

Author(s): Qu, Baihua; Ma, Chuze; Ji, Ge; Xu, Chaohe; Xu, Jing; Meng, Ying Shirley; Wang, Taihong; Lee, Jim Yang | Abstract: A layered SnS2-reduced graphene oxide (SnS2-RGO) composite is prepared by a facile hydrothermal route and evaluated as an anode material for sodium-ion batteries (NIBs). The measured electrochemical properties are a high charge specific capacity (630 mAh g-1 at 0.2 A g-1) coupled to a good rate performance (544 mAh g-1 at 2 A g-1) and long cycle-life (500 mAh g-1 at 1 A g -1 for 400 cycles).

Identifying surface structural changes in layered Li-excess nickel manganese oxides in high voltage lithium ion batteries: A joint experimental and theoretical study

High voltage cathode materials Li-excess layered oxide compounds Li[NixLi1/3−2x/3Mn2/3−x/3]O2 (0 < x < 1/2) are investigated in a joint study combining both computational and experimental methods. The bulk and surface structures of pristine and cycled samples of Li[Ni1/5Li1/5Mn3/5]O2 are characterized by synchrotron X-Ray diffraction together with aberration corrected Scanning Transmission Electron Microscopy (a-S/TEM). Electron Energy Loss Spectroscopy (EELS) is carried out to investigate the surface changes of the samples before/after electrochemical cycling. Combining first principles computational investigation with our experimental observations, a detailed lithium de-intercalation mechanism is proposed for this family of Li-excess layered oxides. The most striking characteristics in these high voltage high energy density cathode materials are 1) formation of tetrahedral lithium ions at voltage less than 4.45 V and 2) the transition metal (TM) ions migration leading to phase transformation on the surface of the materials. We show clear evidence of a new spinel-like solid phase formed on the surface of the electrode materials after high-voltage cycling. It is proposed that such surface phase transformation is one of the factors contributing to the first cycle irreversible capacity and the main reason for the intrinsic poor rate capability of these materials.

First principles computational materials design for energy storage materials in lithium ion batteries

First principles computation methods play an important role in developing and optimizing new energy storage and conversion materials. In this review, we present an overview of the computation approach aimed at designing better electrode materials for lithium ion batteries. Specifically, we show how each relevant property can be related to the structural component in the material and can be computed from first principles. By direct comparison with experimental observations, we hope to illustrate that first principles computation can help to accelerate the design and development of new energy storage materials.

Phase Stability of Nickel Hydroxides and Oxyhydroxides

In this paper, we investigate the phase stability of nickel hydroxides from first-principles. We predict that the previously uncharacterized crystal structure of III‐NiOOH is actually derived from the P3 host. Furthermore, we identify a plausible crystal structure for the -NiO2H2O0.67K0.33Hx phase that is consistent with available experimental observations. The proposed crystal structure has a P3 host and the K ions reside exactly between adjacent trigonal prismatic sites of the intercalation layer. We have also calculated the topotactic voltage curves for the and phases, and predict the existence of a large step in voltage at -NiOOH, which effectively limits the capacity of the Ni-hydroxide compound to one electron per Ni ion. Methodology We combine first-principles electronic structure calculations with a cluster expansion approach for the disorder of protons in the materials to calculate phase stability and thermodynamic properties of the nickel hydroxide system. The electronic structure calculations

Topological defect dynamics in operando battery nanoparticles

Watching defects during battery cycling Dislocations affect the mechanical properties of a material. Ulvestad et al. studied the influence of dislocations on a nanoparticle undergoing charge and discharge cycles in a lithium ion battery. The defects influenced the way the material expanded and contracted during cycling. In the future, it may be possible to tune the properties of a material through controlled defect engineering. Science, this issue p. 1344 Coherent x-rays image structural transformations in battery nanoparticles during electrochemical operation. Topological defects can markedly alter nanomaterial properties. This presents opportunities for “defect engineering,” where desired functionalities are generated through defect manipulation. However, imaging defects in working devices with nanoscale resolution remains elusive. We report three-dimensional imaging of dislocation dynamics in individual battery cathode nanoparticles under operando conditions using Bragg coherent diffractive imaging. Dislocations are static at room temperature and mobile during charge transport. During the structural phase transformation, the lithium-rich phase nucleates near the dislocation and spreads inhomogeneously. The dislocation field is a local probe of elastic properties, and we find that a region of the material exhibits a negative Poisson’s ratio at high voltage. Operando dislocation imaging thus opens a powerful avenue for facilitating improvement and rational design of nanostructured materials.

Performance and design considerations for lithium excess layered oxide positive electrode materials for lithium ion batteries

The Li-excess oxide compound is one of the most promising positive electrode materials for next generation batteries exhibiting high capacities of >300 mA h g−1 due to the unconventional participation of the oxygen anion redox in the charge compensation mechanism. However, its synthesis has been proven to be highly sensitive to varying conditions and parameters where nanoscale phase separation may occur that affects the overall battery performance and life. In addition, several thermodynamic and kinetic drawbacks including large first cycle irreversible capacity, poor rate capability, voltage fading, and surface structural transformation need to be addressed in order to reach commercialization. This review will focus on the recent progress and performance trends over the years and provide several guidelines and design considerations based on the library of work done on this particular class of materials.

Phase Transitions and High-Voltage Electrochemical Behavior of LiCoO2 Thin Films Grown by Pulsed Laser Deposition

The phase transitions and electrochemical behavior of LiCoO 2 thin-film cathodes prepared by pulsed laser deposition are studied for charging voltages ranging from 4.2 to 4.9 V. Two voltage plateaus at about 4.55 and 4.62 V are observed in the charge-discharge curves. Ex situ X-ray diffraction measurements confirm structural changes and a phase transition from the 03 to the H1-3 phase when LiCoO 2 is charged above 4.5 V. Thin-film LiCoO 2 electrodes show stable capacity retention up to 4.5 V but significant capacity fade above 4.5 V, which we attribute to damage from strain due to phase transitions and Li gradients. Li diffusion in the Li x CoO 2 thin film up to 4.5V is investigated by the potentiostatic intermittent titration technique. The chemical diffusion coefficient of Li reaches the maximum near x = 0.4 and starts to decrease when the Li content is further decreased.

Gas-solid interfacial modification of oxygen activity in layered oxide cathodes for lithium-ion batteries

Lattice oxygen can play an intriguing role in electrochemical processes, not only maintaining structural stability, but also influencing electron and ion transport properties in high-capacity oxide cathode materials for Li-ion batteries. Here, we report the design of a gas–solid interface reaction to achieve delicate control of oxygen activity through uniformly creating oxygen vacancies without affecting structural integrity of Li-rich layered oxides. Theoretical calculations and experimental characterizations demonstrate that oxygen vacancies provide a favourable ionic diffusion environment in the bulk and significantly suppress gas release from the surface. The target material is achievable in delivering a discharge capacity as high as 301 mAh g−1 with initial Coulombic efficiency of 93.2%. After 100 cycles, a reversible capacity of 300 mAh g−1 still remains without any obvious decay in voltage. This study sheds light on the comprehensive design and control of oxygen activity in transition-metal-oxide systems for next-generation Li-ion batteries.

Interface Limited Lithium Transport in Solid-State Batteries

Understanding the role of interfaces is important for improving the performance of all-solid-state lithium ion batteries. To study these interfaces, we present a novel approach for fabrication of electrochemically active nanobatteries using focused ion beams and their characterization by analytical electron microscopy. Morphological changes by scanning transmission electron microscopy imaging and correlated elemental concentration changes by electron energy loss spectroscopy mapping are presented. We provide first evidence of lithium accumulation at the anode/current collector (Si/Cu) and cathode/electrolyte (LixCoO2/LiPON) interfaces, which can be accounted for the irreversible capacity losses. Interdiffusion of elements at the Si/LiPON interface was also witnessed with a distinct contrast layer. These results highlight that the interfaces may limit the lithium transport significantly in solid-state batteries. Fabrication of electrochemically active nanobatteries also enables in situ electron microscopy observation of electrochemical phenomena in a variety of solid-state battery chemistries.

Probing the electrode/electrolyte interface in the lithium excess layered oxide Li1.2Ni0.2Mn0.6O2

A detailed surface investigation of the lithium-excess nickel manganese layered oxide Li1.2Ni0.2Mn0.6O2 structure was carried out using X-ray photoelectron spectroscopy (XPS), total electron yield and transmission X-ray absorption spectroscopy (XAS), and electron energy loss spectroscopy (EELS) during the first two electrochemical cycles. All spectroscopy techniques consistently showed the presence of Mn(4+) in the pristine material and a surprising reduction of Mn at the voltage plateau during the first charge. The Mn reduction is accompanied by the oxygen loss revealed using EELS. Upon the first discharge, the Mn at the surface never fully recovers back to Mn(4+). The electrode/electrolyte interface of this compound consists of the reduced Mn at the crystalline defect-spinel inner layer and an oxidized Mn species simultaneously with the presence of a superoxide species in the amorphous outer layer. This proposed model signifies that oxygen vacancy formation and lithium removal result in electrolyte decomposition and superoxide formation, leading to Mn activation/dissolution and surface layer-spinel phase transformation. The results also indicate that the role of oxygen is complex and significant in contributing to the extra capacity of this class of high energy density cathode materials.