Synthesis, Crystal Structure, and Properties of the Alluaudite-Type Vanadates Ag_2–<i>x</i>Na_<i>x</i>Mn₂Fe(VO₄)₃

The new members of the Ag_2–<i>x</i>Na_<i>x</i>Mn₂Fe­(VO₄)₃ (0 ≤ <i>x</i> ≤ 2) solid solution were synthesized by a solid-state reaction route, and their crystal structures were determined from single-crystal X-ray diffraction data. The physical properties were characterized by Mössbauer and electrochemical impedance spectroscopies, galvanostatic cycling, and cyclic voltammetry. These materials crystallize with a monoclinic symmetry (space group <i>C</i>2/<i>c</i>), and the structure is considered to be a new member of the <i>AA</i>′<i>MM</i>′₂(<i>X</i>O₄)₃ alluaudite family. The <i>A</i>, <i>A</i>′, <i>M</i>, and <i>X</i> sites are fully occupied by Ag⁺/Na⁺, Ag⁺/Na⁺, Mn²⁺, and V⁵⁺, respectively, whereas a Mn²⁺/Fe³⁺ mixture is observed in the <i>M</i>′ site. The Mössbauer spectra confirm that iron is trivalent. The impedance measurements indicate that the silver phase is a better conductor than the sodium phase. Furthermore, these phases exhibit ionic conductivities 2 orders of magnitude higher than those of the homologous phosphates. The electrochemical tests prove that Na₂Mn₂Fe­(VO₄)₃ is active as positive and negative electrodes in sodium-ion batteries

Na Storage Capability Investigation of a Carbon Nanotube-Encapsulated Fe_1–<i>x</i>S Composite

A promising anode material consisting of Fe_1–<i>x</i>S nanoparticles and bamboo-like carbon nanotubes (CNTs) has been designed and prepared by an effective in situ chemical transformation. The resultant Fe_1–<i>x</i>S@CNTs with a three-dimensional network not only provide high conductivity paths and channels for electrons and ions but also offer the combined merits of iron sulfide and CNTs in electrochemical energy storage applications, leading to outstanding performance as an anode material for sodium-ion batteries. When tested in a half-cell, a high capacity of 449.2 mAh g^–1 can be retained after 200 cycles at 500 mA g^–1, corresponding to a high retention of 97.4%. Even at 8000 mA g^–1, a satisfactory capacity of 326.3 mAh g^–1 can be delivered. When tested in the full cell, a capacity of 438.5 mAh g^–1 with capacity retention of 85.0% is manifested after 80 cycles based on the mass of the anode. The appealing structure and electrochemical performance of this material demonstrate its great promise for applications in practical rechargeable batteries

An Alternative Approach to Enhance the Performance of High Sulfur-Loading Electrodes for Li–S Batteries

Due to lithium–sulfur battery’s high theoretical capacity and energy density, Li–S has been considered as a promising candidate for next-generation Li batteries. Despite this, Li–S batteries suffer from poor electrical conductivity and the shuttle effect, which result in loss of active material and active material loading limitation, thus hindering the practical application of Li–S. This Letter introduces the modified high sulfur-loading electrode (MHSE) with a loading of 10 mg cm^–2 which directly addresses these two drawbacks and employs a simple production process suitable for mass production through the use of elemental sulfur. The MHSE consists of three distinct components which provide additional conductivity, mechanical support, and polysulfide adsorption ability on each level to enhance electrochemical performance. The electrode manifested an initial discharge capacity of 1332 mAh g^–1 with a 91% cycle retention at the end of 50 cycles and cycled with stability from 0.1C to 2C during rate capability testing

Microstructure- and Interface-Modified Ni-Rich Cathode for High-Energy-Density All-Solid-State Lithium Batteries

Electric vehicles powered by Li-ion batteries pose a potential safety risk because the flammable liquid electrolytes can, under certain conditions, cause explosions. All-solid-state batteries (ASSBs) are safe alternative battery technologies. However, realizing high-energy-density ASSBs by employing Ni-rich layered cathodes is difficult because of the detrimental volume contraction near charge end. This study shows that the simultaneous B doping and coating of a Ni-rich Li[Ni0.9Co0.05Mn0.05]O2 cathode, which modifies the cathode microstructure and cathode–solid electrolyte interface, respectively, afford an ASSB that cycles stably for 300 cycles with minimal capacity fading. An ASSB featuring the B-doped, B-coated Li[Ni0.9Co0.05Mn0.05]O2 cathode demonstrates a discharge capacity of 214 mAh g–1, which represents one of the highest discharge capacities achieved by an ASSB; moreover, the ASSB retains 91% of its initial capacity after 300 cycles and easily outperforms previously reported ASSBs in terms of energy density without compromising cycling stability

Differences in the Interfacial Mechanical Properties of Thiophosphate and Argyrodite Solid Electrolytes and Their Composites

Interfacial mechanics are a significant contributor to the performance and degradation of solid-state batteries. Spatially resolved measurements of interfacial properties are extremely important to effectively model and understand the electrochemical behavior. Herein, we report the interfacial properties of thiophosphate (Li3PS4)- and argyrodite (Li6PS5Cl)-type solid electrolytes. Using atomic force microscopy, we showcase the differences in the surface morphology as well as adhesion of these materials. We also investigate solvent-less processing of hybrid electrolytes using UV-assisted curing. Physical, chemical, and structural characterizations of the materials highlight the differences in the surface morphology, chemical makeup, and distribution of the inorganic phases between the argyrodite and thiophosphate solid electrolytes

Highly Cyclable Lithium–Sulfur Batteries with a Dual-Type Sulfur Cathode and a Lithiated Si/SiO_<i>x</i> 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/SiO_<i>x</i> 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

Nanoscale Phase Separation, Cation Ordering, and Surface Chemistry in Pristine Li_1.2Ni_0.2Mn_0.6O₂ for Li-Ion Batteries

Li-rich layered material Li_1.2Ni_0.2Mn_0.6O₂ possesses high voltage and high specific capacity, which makes it an attractive candidate for the transportation industry and sustainable energy storage systems. The rechargeable capacity of the Li-ion battery is linked largely to the structural stability of the cathode materials during the charge–discharge cycles. However, the structure and cation distribution in pristine Li_1.2Ni_0.2Mn_0.6O₂ have not yet been fully characterized. Using a combination of aberration-corrected scanning transmission electron microscopy, X-ray energy-dispersive spectroscopy (XEDS), electron energy loss spectroscopy (EELS), and complementary multislice image simulation, we have probed the crystal structure, cation/anion distribution, and electronic structure of the Li_1.2Ni_0.2Mn_0.6O₂ nanoparticle. The electronic structure and valence state of transition-metal ions show significant variations, which have been identified to be attributed to the oxygen deficiency near certain particle surfaces. Characterization of the nanoscale phase separation and cation ordering in the pristine material are critical for understanding the capacity and voltage fading of this material for battery application

Conflicting Roles of Nickel in Controlling Cathode Performance in Lithium Ion Batteries

A variety of approaches are being made to enhance the performance of lithium ion batteries. Incorporating multivalence transition-metal ions into metal oxide cathodes has been identified as an essential approach to achieve the necessary high voltage and high capacity. However, the fundamental mechanism that limits their power rate and cycling stability remains unclear. The power rate strongly depends on the lithium ion drift speed in the cathode. Crystallographically, these transition-metal-based cathodes frequently have a layered structure. In the classic wisdom, it is accepted that lithium ion travels swiftly within the layers moving out/in of the cathode during the charge/discharge. Here, we report the unexpected discovery of a thermodynamically driven, yet kinetically controlled, surface modification in the widely explored lithium nickel manganese oxide cathode material, which may inhibit the battery charge/discharge rate. We found that during cathode synthesis and processing before electrochemical cycling in the cell nickel can preferentially move along the fast diffusion channels and selectively segregate at the surface facets terminated with a mix of anions and cations. This segregation essentially can lead to a higher lithium diffusion barrier near the surface region of the particle. Therefore, it appears that the transition-metal dopant may help to provide high capacity and/or high voltage but can be located in a “wrong” location that may slow down lithium diffusion, limiting battery performance. In this circumstance, limitations in the properties of lithium ion batteries using these cathode materials can be determined more by the materials synthesis issues than by the operation within the battery itself

Conflicting Roles of Nickel in Controlling Cathode Performance in Lithium Ion Batteries

A variety of approaches are being made to enhance the performance of lithium ion batteries. Incorporating multivalence transition-metal ions into metal oxide cathodes has been identified as an essential approach to achieve the necessary high voltage and high capacity. However, the fundamental mechanism that limits their power rate and cycling stability remains unclear. The power rate strongly depends on the lithium ion drift speed in the cathode. Crystallographically, these transition-metal-based cathodes frequently have a layered structure. In the classic wisdom, it is accepted that lithium ion travels swiftly within the layers moving out/in of the cathode during the charge/discharge. Here, we report the unexpected discovery of a thermodynamically driven, yet kinetically controlled, surface modification in the widely explored lithium nickel manganese oxide cathode material, which may inhibit the battery charge/discharge rate. We found that during cathode synthesis and processing before electrochemical cycling in the cell nickel can preferentially move along the fast diffusion channels and selectively segregate at the surface facets terminated with a mix of anions and cations. This segregation essentially can lead to a higher lithium diffusion barrier near the surface region of the particle. Therefore, it appears that the transition-metal dopant may help to provide high capacity and/or high voltage but can be located in a “wrong” location that may slow down lithium diffusion, limiting battery performance. In this circumstance, limitations in the properties of lithium ion batteries using these cathode materials can be determined more by the materials synthesis issues than by the operation within the battery itself

Evolution of Lattice Structure and Chemical Composition of the Surface Reconstruction Layer in Li_1.2Ni_0.2Mn_0.6O₂ 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 <i>C</i>2/<i>m</i> →<i>I</i>41 → 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