Wangda Li

Dynamic behaviour of interphases and its implication on high-energy-density cathode materials in lithium-ion batteries

Undesired electrode–electrolyte interactions prevent the use of many high-energy-density cathode materials in practical lithium-ion batteries. Efforts to address their limited service life have predominantly focused on the active electrode materials and electrolytes. Here an advanced three-dimensional chemical and imaging analysis on a model material, the nickel-rich layered lithium transition-metal oxide, reveals the dynamic behaviour of cathode interphases driven by conductive carbon additives (carbon black) in a common nonaqueous electrolyte. Region-of-interest sensitive secondary-ion mass spectrometry shows that a cathode-electrolyte interphase, initially formed on carbon black with no electrochemical bias applied, readily passivates the cathode particles through mutual exchange of surface species. By tuning the interphase thickness, we demonstrate its robustness in suppressing the deterioration of the electrode/electrolyte interface during high-voltage cell operation. Our results provide insights on the formation and evolution of cathode interphases, facilitating development of in situ surface protection on high-energy-density cathode materials in lithium-based batteries.

Overcoming the chemical instability on exposure to air of Ni-rich layered oxide cathodes by coating with spinel LiMn1.9Al0.1O4

Ni-rich layered oxide cathodes are facing a fundamental challenge of loss in performance as a result of air storage, hampering their practical application in lithium-ion batteries. We present here an investigation of extended air storage and a solution to overcome the chemical instability by coating the Ni-rich layered oxide with a Mn-based spinel oxide.

Long-Life Nickel-Rich Layered Oxide Cathodes with a Uniform Li2ZrO3 Surface Coating for Lithium-Ion Batteries

As nickel-rich layered oxide cathodes start to attract worldwide interest for the next-generation lithium-ion batteries, their long-term cyclability in full cells remains a challenge for electric vehicles. Here we report a long-life Ni-rich layered oxide cathode (LiNi0.7Co0.15Mn0.15O2) with a uniform surface coating of the cathode particles with Li2ZrO3. A pouch-type full cell fabricated with the Li2ZrO3-coated cathode and a graphite anode displays 73.3% capacity retention after 1500 cycles at a C/3 rate. The Li2ZrO3 coating has been optimized by a systematic study with different synthesis approaches, annealing temperatures, and coating amounts. The complex relationship among the coating conditions, uniformity, and morphology of the coating layer and their impacts on the electrochemical properties are discussed in detail.

High‐Performance Heterostructured Cathodes for Lithium‐Ion Batteries with a Ni‐Rich Layered Oxide Core and a Li‐Rich Layered Oxide Shell

The Ni‐rich layered oxides with a Ni content of >0.5 are drawing much attention recently to increase the energy density of lithium‐ion batteries. However, the Ni‐rich layered oxides suffer from aggressive reaction of the cathode surface with the organic electrolyte at the higher operating voltages, resulting in consequent impedance rise and capacity fade. To overcome this difficulty, we present here a heterostructure composed of a Ni‐rich LiNi0.7Co0.15Mn0.15O2 core and a Li‐rich Li1.2− xNi0.2Mn0.6O2 shell, incorporating the advantageous features of the structural stability of the core and chemical stability of the shell. With a unique chemical treatment for the activation of the Li2MnO3 phase of the shell, a high capacity is realized with the Li‐rich shell material. Aberration‐corrected scanning transmission electron microscopy (STEM) provides direct evidence for the formation of surface Li‐rich shell layer. As a result, the heterostructure exhibits a high capacity retention of 98% and a discharge‐voltage retention of 97% during 100 cycles with a discharge capacity of 190 mA h g−1 (at 2.0–4.5 V under C/3 rate, 1C = 200 mA g−1).

Blend Membranes Consisting of Sulfonated Poly(ether ether ketone) and Polysulfone Bearing 4-Nitrobenzimidazole for Direct Methanol Fuel Cells

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Blend Membranes Consisting of Sulfonated Poly(ether ether ketone) and 1H-Perimidine Tethered Polysulfone for Direct Methanol Fuel Cells

Blend membranes consisting of sulfonated poly(ether ether ketone) (SPEEK, an acidic polymer) and various amounts of 1H-perimidine tethered polysulfone (a basic polymer) have been prepared and characterized. The blend membranes show increased proton conductivity and decreased ion-exchange capacity and liquid uptake in water and methanol/water solutions com- pared to plain SPEEK. The blend membranes also exhibit better electrochemical performance and lower methanol crossover in direct methanol fuel cells compared to plain SPEEK and Nafion 115 membranes due to an enhancement in proton conductivity through acid―base interactions and an insertion of the 1H-perimidine groups into the ionic clusters of SPEEK.

Formation and Inhibition of Metallic Lithium Microstructures in Lithium Batteries Driven by Chemical Crossover

The formation of metallic lithium microstructures in the form of dendrites or mosses at the surface of anode electrodes (e.g., lithium metal, graphite, and silicon) leads to rapid capacity fade and poses grave safety risks in rechargeable lithium batteries. We present here a direct, relative quantitative analysis of lithium deposition on graphite anodes in pouch cells under normal operating conditions, paired with a model cathode material, the layered nickel-rich oxide LiNi0.61Co0.12Mn0.27O2, over the course of 3000 charge-discharge cycles. Secondary-ion mass spectrometry chemically dissects the solid-electrolyte interphase (SEI) on extensively cycled graphite with virtually atomic depth resolution and reveals substantial growth of Li-metal deposits. With the absence of apparent kinetic (e.g., fast charging) or stoichiometric restraints (e.g., overcharge) during cycling, we show lithium deposition on graphite is triggered by certain transition-metal ions (manganese in particular) dissolved from the cathode in a disrupted SEI. This insidious effect is found to initiate at a very early stage of cell operation (<200 cycles) and can be effectively inhibited by substituting a small amount of aluminum (∼1 mol %) in the cathode, resulting in much reduced transition-metal dissolution and drastically improved cyclability. Our results may also be applicable to studying the unstable electrodeposition of lithium on other substrates, including Li metal.

Interfacial Chemistry in Solid-State Batteries: Formation of Interphase and Its Consequences

Benefiting from extremely high shear modulus and high ionic transference number, solid electrolytes are promising candidates to address both the dendrite-growth and electrolyte-consumption problems inherent to the widely adopted liquid-phase electrolyte batteries. However, solid electrolyte/electrode interfaces present high resistance and complicated morphology, hampering the development of solid-state battery systems, while requiring advanced analysis for rational improvement. Here, we employ an ultrasensitive three-dimensional (3D) chemical analysis to uncover the dynamic formation of interphases at the solid electrolyte/electrode interface. While the formation of interphases widens the electrochemical window, their electronic and ionic conductivities determine the electrochemical performance and have a large influence on dendrite growth. Our results suggest that, contrary to the general understanding, highly stable solid electrolytes with metal anodes in fact promote fast dendritic formation, as a result of less Li consumption and much larger curvature of dendrite tips that leads to an enhanced electric driving force. Detailed thermodynamic analysis shows an interphase with low electronic conductivity, high ionic conductivity, and chemical stability, yet having a dynamic thickness and uniform coverage is needed to prevent dendrite growth. This work provides a paradigm for interphase design to address the dendrite challenge, paving the way for the development of robust, fully operational solid-state batteries.

The TEXT upgrade vertical interferometer

A far‐infrared interferometer has been installed on TEXT upgrade to obtain electron density profiles. The primary system views the plasma vertically through a set of large (60‐cm radial×7.62‐cm toroidal) diagnostic ports. A 1‐cm channel spacing (59 channels total) and fast electronic time response is used, to provide high resolution for radial profiles and perturbation experiments. Initial operation of the vertical system was obtained late in 1991, with six operating channels.