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High-nickel layered oxide cathodes are becoming appealing for lithium-ion batteries employed in portable electronics and electric vehicles because of their higher energy density, low or no cobalt c...

Interest in sodium-ion battery cathode materials, particularly for grid-scale energy-storage applications, has considerably increased in the last few years, sparking a push toward industrially prac...

High-nickel layered oxides, such as LiNi0.8Co0.1Mn0.1O2 (NCM-811), offer higher energy density than their low-nickel counterparts at a given voltage and are gaining major traction in automotive lit...

Increased interest in alternatives to lithium-ion batteries has led to promising work on sodium-ion batteries, particularly with layered oxide cathode materials. For practical applications, however...

With an increased energy density and cost advantage, ultrahigh-nickel layered oxides (LiNixM1 – xO2, x = 0.9–1.0) are becoming a front-runner as cathodes for next-generation lithium-based batteries...

The electrochemistry of lithium-sulfur (Li-S) batteries is heavily reliant on the structure and dynamics of lithium polysulfides, which dissolve into the liquid electrolyte and mediate the electrochemical conversion process during operation. This behavior is considerably distinct from the widely used lithium-ion batteries, necessitating new mechanistic insights to fully understand the electrochemical phenomena. Testing at low-temperature conditions presents a unique opportunity to glean new insights into the chemistry in kinetically constrained environments. Under such conditions, despite the low freezing point and favorable ionic conductivity of the glyme-based electrolyte, Li-S batteries exhibit counterintuitively poor performance. Here, we show that beyond just existing in single-molecule conformations, lithium polysulfides tend to cluster and aggregate in solution, particularly at low-temperature conditions, which subsequently constrains the kinetics of electrochemical conversion. Energetics and coordination implications of this behavior are extended towards a new framework for understanding the solution-coordination dynamics of dissolved lithium species. Based off this framework, a favorable strongly-bound lithium salt is introduced in the Li-S electrolyte to disrupt polysulfide clustered networks, enabling substantially enhanced low-temperature electrochemical performance. More broadly, this mechanistic insight heightens our understanding of polysulfide chemistry irrespective of temperature, confirming the link between the solution conformation of active material and electrochemical behavior.

Boosting the Ni content in LiMO2 (M = Ni, Co, Mn, etc.) layered oxides is a promising way to establish high-energy-density, low-cost cathodes, but the poor cathode surface stability is a daunting c...

While it is accepted that paired NiLi and LiNi antisite defects are present in the important family of NMC cathode materials with the general formula Li(NixMnyCoz)O2, their formation mechanism and ...

Ultrahigh-Ni layered oxide cathodes (Ni content >90%) are at the forefront for potentially enabling higher-energy-density lithium-ion batteries. Unfortunately, they suffer from rapid capacity fade,...

Pure and isovalent cation-substituted potassium hexagonal tungsten bronze (KHTB) have been synthesized and used as a model oxide host to study the electrochemically driven bulk diffusion of divalen...

High-nickel layered oxide cathodes with a Ni content of >90% show substantial potential for next-generation lithium-ion batteries (LIBs) due to their high capacity and lower cost. However, they are plagued by rapid capacity decay and poor thermal stability, which hamper their practical viability. We present here Li0.98Mg0.02Ni0.94Co0.06O2 (NC-Mg) with 2% Mg doping, aiming to provide a strategic guideline for solving the issues. The Mg2+ ions occupy the lithium layer and are proposed to act as pillar ions, which substantially enhance the structural reversibility and reduce the anisotropic lattice distortion upon cycling, thereby greatly improving the electrochemical and thermal stability of NC-Mg compared to the undoped LiNi0.94Co0.06O2 (NC). Specifically, NC-Mg delivers 214 mA h g–1 with a capacity retention of 80.1% after 500 cycles in pouch-type full cells, much higher than the retention of NC (56.3%). A discharge capacity of 158 mA h g–1 at 10C rate demonstrates its remarkable rate capability. Addition...

Layered oxide cathodes with a high Ni content of >0.6 are promising for high-energy-density lithium-ion batteries. However, parasitic electrolyte oxidation of the charged cathode and mechanical degradation arising from phase transitions significantly deteriorate the cell performance and cycle life as the Ni content increases. We demonstrate here a significantly prolonged cycle life with superior cell performance by substituting a small-dose of Al (2 mol %) for Ni in LiNi0.92Co0.06Al0.02O2; the capacity retention after operating a full cell fabricated with graphite anode for 1000 cycles increases from 47% to 83% on going from the Al-free LiNi0.94Co0.06O2 to the Al-doped LiNi0.92Co0.06Al0.02O2 cathode. Through in situ X-ray diffraction, we provide the operando evidence that the Al-doping tunes the H2–H3 phase transition process from a two-phase reaction to a quasi-monophase reaction, minimizing the mechanical degradation. Furthermore, secondary-ion mass spectrometry reveals considerably suppressed transitio...

Metal nanoparticles exsolved from perovskite oxides have created great interest as anode materials in solid oxide fuel cells (SOFC) due to their high catalytic activity and regenerative capability. However, the self-regeneration process generally occurs at relatively high temperatures (>800 °C), which might limit their practical application. Here, we present a perovskite anode material, La0.3Sr0.7Cr0.3Fe0.6Co0.1O3−δ, which allows Co–Fe nanoparticles exsolved on the oxide surface at intermediate operation temperatures (700 °C). The phase stability of the perovskite oxide and the reversibility of the exsolved alloy were carefully examined by the phase characterization and the nanoparticle morphology observation during the redox process. The electrochemical performance was evaluated by an electrolyte-supported single cell with hydrogen and propane fuels. The Co–Fe nanocatalysts enhance the maximum power density of the La0.3Sr0.7Cr0.3Fe0.6Co0.1O3−δ–Gd0.2Ce0.8O1.9 (GDC) composite anode more than 75% in compari...

To evaluate the self-regeneration feasibility of exsolved Co–Fe nanoparticles on the La0.3Sr0.7Cr0.3Fe0.6Co0.1O3−δ perovskite at intermediate operation temperature (700 °C), the evolution of surface morphology and particle phases during a redox process has been determined by scanning and transmission electron microscopy. Unlike the complete reincorporation of the exsolved metals back to the perovskite lattice at 800 °C during the reoxidation process, the transition-metal oxide remains on the surface as an intermediate phase because of a sluggish reincorporation rate at 700 °C. Although the transition-metal oxide particles grow and coarsen quickly in an oxidizing atmosphere, the nanoparticles could still be formed by a disintegration of the reduced spinel oxide in a reducing atmosphere. The hemispherical-like shape of the nanoparticles can be achieved by minimizing metallic surface energy and maintaining the strong metal–oxide interaction. The redispersion of Co–Fe nanoparticles completes the self-regenera...

To address the growing demand for energy density, the Ni-rich layered [Ni0.90Co0.05Mn0.05]O2 cathode has been synthesized and its electrochemical performance in lithium-ion cells has been benchmarked against a lower-Ni content Li[Ni0.6Co0.2Mn0.2]O2 cathode. Li[Ni0.90Co0.05Mn0.05]O2 delivers a high discharge capacity of 227 mA h g–1 compared to a capacity of 189 mA h g–1 for Li[Ni0.6Co0.2Mn0.2]O2 when cycled up to a lower cutoff voltage of 4.3 V, making it an appealing candidate for electric vehicles. With an increase in the charge cutoff voltage to 4.5 V, Li[Ni0.90Co0.05Mn0.05]O2 displays a capacity of 238 mA h g–1 compared to a capacity of 208 mA h g–1 for Li[Ni0.6Co0.2Mn0.2]O2. Although Li[Ni0.90Co0.05Mn0.05]O2 suffers during cycling from the usual rapid capacity fade in a manner similar to that of LiNiO2, 87 and 81% of the initial capacity could still be retained after 100 cycles even after cycling to higher cutoff voltages of 4.3 and 4.5 V, respectively. A comparison of Li[Ni0.90Co0.05Mn0.05]O2 and Li...

The performance characteristics of lithium-ion battery cathode materials are governed by the surface structure and chemistry. Synthesis is known to affect the structure of these materials; however, a full understanding of the effects of the surface structure is not well understood. Here, we explore the atomic scale structure of lithium-layered oxides prepared with two different thermal treatments. We show that, under certain thermal treatments, the surface perpendicular to the transition-metal layers is enriched in nickel, which results in Ni occupying the lithium layer of the layered oxide structure. Under both thermal treatments, this surface also shows a reduction of Mn, with some of the reduced Mn occupying sites in the lithium layer. The surface parallel to the transition-metal layers under both treatments shows significant Mn reduction, oxygen loss, and reduced Mn in the lithium layer. The Mn reduction and surface reconstruction are the result of unstable surface terminations and are intrinsic to la...

Low ionic conductivity limits the development of NASICON-type LiZr2(PO4)3 (LZP) for solid-state batteries. Here, we present the possible factors that may affect the conductivity and further establish the relationships among conductivity, crystal structure, relative density, grain size, chemical composition, and elemental distribution. The conditions for the existence of the four phases of LZP (α, α′, β, and β′) and the phase transition processes among them are systematically clarified. With secondary ion mass spectrometry, the spatial distribution of elements within the grains and grain boundaries is clearly presented. On the basis of our results, proper elemental doping, high sintering temperature, and especially fast cool down rate are all indispensable to stabilize the high-conductivity (α) phase at room temperature. Finally, we demonstrate the feasibility of lithium-based batteries with this LZP solid electrolyte and commercial cathodes. This work provides insights for preparing LZP with high conducti...

With an aim of enhancing their high-temperature phase stability, oxygen-storage capability, and electrocatalytic activity in intermediate-temperature solid oxide fuel cells (IT-SOFCs), RBaCo4O7+δ-based samples have been investigated with a co-substitution at the R site with Y, In, and Ca and Ga substitution at the Co site. YBaCo4–yGayO7+δ, Y1–xInxBaCo3.3Ga0.7O7+δ, Y1–xCaxBaCo3.3Ga0.7O7+δ, In1–xCaxBaCo3.3Ga0.7O7+δ, and Y0.5In0.5BaCo4–yGayO7+δ series of materials have been synthesized by a solid-state reaction, and the phase stabilities have been assessed by long-term testing at 600–800 °C for 120 h. The substitution of In for Y mitigates the phase decomposition but decreases the oxygen-storage capacity and electrochemical performance in IT-SOFCs. With In and Y co-dopants, Y0.5In0.5BaCo3.5Ga0.5O7+δ remains stable even with a smaller amount of Ga. In contrast, Ca doping reduces the phase stability regardless of its content. Via optimization of the compositions, Y0.9In0.1BaCo3.3Ga0.7O7+δ is found to exhibit t...

An amorphous red phosphorus-based composite has been synthesized via a facile and simple one-step high-energy mechanical milling process and investigated as an anode material for lithium-ion and sodium-ion batteries. The resultant P–TiP2–C nanocomposite exhibits a high reversible capacity of 1116 mA h g–1, excellent cyclability, and a remarkable initial Coulombic efficiency of 86% in lithium half cells. Furthermore, it delivers an initial desodiation capacity of 755 mA h g–1 with a high initial Coulombic efficiency of 80% and a good capacity retention of 80% after 100 cycles in sodium half cells. The greatly improved electrochemical performance is due to the unique nanoarchitecture composed of well-blended red phosphorus and crystalline TiP2 homogeneously embedded in a conductive carbon network. The presence of the conductive TiP2 inclusions plays a crucial role in offering structural stability as well as high conductivity to the phosphorus-based composite particles during cycling, thereby leading to supe...

Electrical and ionic conductivity has proven to be a major limiting factor in the adoption of high-voltage polyanion cathode materials, specifically LiMPO4 (M = Mn, Co, Ni). While the aliovalent substitution of V3+ for Fe2+ in LiFePO4 has been shown recently, no conclusive evidence is available for aliovalent substitutions in the analogous LiCoPO4. This study presents a low-temperature microwave-assisted solvothermal synthesis and characterization of aliovalently substituted LiCo1–3x/2Vx□x/2PO4 for x ≤ 0.07. The as synthesized LiCo1–3x/2Vx□x/2PO4 samples belonging to the Pn21a space group are transformed to the Pnma polymorph via calcination in an inert atmosphere at 525 °C. The LiCo1–3x/2Vx□x/2PO4 samples are characterized with scanning electron microscopy, X-ray diffraction, Rietveld refinement, inductively coupled plasma optical emissions spectroscopy, Raman and infrared spectroscopy, galvanostatic charge/discharge, electrochemical impedance spectroscopy, and cyclic voltammetry. Unlike the prior report...

In an attempt to enlarge the normal spinel phase diagram for the quaternary Li–Ni–Mn–Co–O system, the transformation at moderate temperatures (150–210 °C) of layered Li0.5(Ni1–y–zMnyCoz)O2 (R3m), which were obtained by an ambient-temperature extraction of lithium from Li0.5(Ni1–y–zMnyCoz)O2, into normal spinel-like (Fd3m) Li(Ni1–y–zMnyCoz)2O4 has been investigated. The phase-conversion mechanism has been studied by joint time-of-flight (TOF) neutron and X-ray diffractions, thermogravimetric analysis, and bond valence sum map. The ionic diffusion of lithium (3a, 6c) and nickel (3a, 3b) ions has been quantified as a function of temperature. The investigated spinel phases are metastable, and they are subject to change into rock-salt phases at higher temperatures. The phases have been characterized as cathodes in lithium-ion cells. The study may serve as a strategic model to access other metastable phases by low-temperature synthesis approaches.

Vanadyl phosphates (VOPO4) represent a class of attractive cathodes in lithium-ion batteries. However, the exploration of this type of materials in sodium-ion batteries is rare. Here, we report for the first time the synthesis of orthorhombic β-NaVOPO4 by first chemically extracting lithium from β-LiVOPO4 and then inserting sodium into the obtained β-VOPO4 by a microwave-assisted solvothermal process with NaI, which serves both as a reducing agent and sodium source. Intermediate NaxVOPO4 compositions with x = 0.3, 0.5, and 0.8 have also been obtained by controlling the amount of NaI in the reaction mixture. Joint Rietveld refinement of synchrotron X-ray diffraction (XRD) and neutron diffraction confirms that the fully sodiated β-NaVOPO4 is isostructural with the lithium counterpart β-LiVOPO4. Bond valence sum maps suggest that sodium ions possibly diffuse along the [010] direction in the lattice, similar to the ionic conduction pathway in β-LiVOPO4. Although the initial discharge capacity is low due to th...

Operation of sodium–sulfur batteries at room temperature has been proposed and studied for about a decade, but polysulfide-shuttle through the traditional battery separator and low-utilization of the sulfur cathode commonly have been the major challenges. Also, because of the highly active nature of the sodium metal, the conventional room temperature sodium–sulfur (RT Na–S) battery concept with the sodium–metal anode and elemental sulfur cathode imposes serious safety concerns. To overcome the above difficulties, we present here a RT Na–S system with an advanced membrane-electrode-assembly (MEA) comprising a carbon-coated, presodiated Nafion membrane (Na-Nafion) and a sodium sulfide (Na2S) cathode. The Na-Nafion membrane provides a facile Na+-ion conductive path and serves as a cation-selective shield to prevent the migration of the polysulfides to the anode. The carbon coating on the Na-Nafion plays an upper-current-collector role and thereby improves the electrochemical utilization of the active Na2S. E...

Vanadyl phostate (VOPO4) with a layered structure was successfully prepared by chemical delithiation of the tetragonal αI-LiVOPO4 at room temperature. X-ray diffraction (XRD) studies show the resulting VOPO4 has a crystal structure similar to αI-LiVOPO4. The V4+/V5+ redox couple exhibits a discharge plateau around 3.5 V vs Na/Na+ in sodium cells. The sample offers a capacity of ∼110 mAh g–1 (0.67 Na+) without any conductive coating and ∼150 mAh g–1 (0.90 Na+) with a preliminary optimization with reduced graphene oxide (rGO) nanosheets. The electrochemically sodiated VOPO4 electrodes show XRD patterns similar to the chemically sodiated VOPO4, indicating the formation of the same product by the two sodiation processes. Bond valence sum (BVS) map calculations suggest that sodium ions likely take the sites between two adjacent VOPO4 sheets. Rietveld refinement of the chemically sodiated Na0.8VOPO4 indicate that the sodium ions could take the 8j sites similar to the lithium ions in αI-LiVOPO4. This new layered...

The thermal conversion of chemically delithiated layered Li0.5Ni1–yMnyO2 (0.2 ≤ y ≤ 0.5) into spinel-like LiNi2–yMnyO4 (0.4 ≤ y ≤ 1) has been systematically investigated. The formed spinel-like phases are metastable and cannot be accessed by a conventional high-temperature solid-state method. The layered-to-spinel transformation mechanism has been studied by the Rietveld refinement of in situ neutron diffraction as a function of temperature (25–300 °C). In particular, the ionic diffusion of Li and M ions is quantified at different temperatures. Electrochemistry of the metastable spinel-like phases obtained has been studied in lithium-ion cells. A bond valence sum map has been performed to understand the ionic diffusion of lithium ions in the Ni-rich layered, spinel, and rock-salt structures. The study can aid the understanding of the possible phases that could be formed during the cycling of Ni-rich layered oxide cathodes.

The electronic and electrochemical properties of the high-voltage spinel LiMn1.5Ni0.5O4 as a function of cation ordering and lithium content have been investigated. Conductivity and activation energy measurements confirm that charge transfer occurs by small polaron hopping, and the charge carrier conduction is easier in the Ni:3d band than in the in Mn:3d band. Seebeck coefficient data reveal that the Ni2+/3+ and Ni3+/4+ redox couples are combined in a single 3d band, and that maximum charge carrier concentration occurs where the average Ni oxidation state is close to 3+, corresponding to x = 0.5 in Li Li1–xMn1.5Ni0.5O4. Accordingly, maximum electronic conductivity is found at x = 0.5, regardless of cation ordering. The thermodynamically stable phases formed during cycling were investigated by recording the X-ray diffraction (XRD) of chemically delithiated powders. The more ordered spinels maintained two separate two-phase regions upon lithium extraction, while the more disordered samples exhibited a soli...

LiVOPO4 is an attractive cathode for lithium-ion batteries with a high operating voltage and the potential to achieve the reversible insertion of two lithium ions between VOPO4 and Li2VOPO4. Among the three known forms of LiVOPO4 (α, β, and αI), the αI-LiVOPO4 has a layered structure that could promote better ionic mobility and reversibility than others. However, a comprehensive study of its lithiated product is not available as αI-LiVOPO4 is metastable and difficult to prepare by conventional approaches. We present here a facile synthesis of highly crystalline αI-LiVOPO4 and αI-LiVOPO4/rGO nanocomposite by a microwave-assisted solvothermal method and its electrochemical/chemical lithiation. The LiVOPO4/rGO cathodes exhibit a high reversible capacity of 225 mAh g–1, indicating the insertion of more than one lithium into VOPO4. Both electrochemical and chemical lithiation imply a solid-solution reaction mechanism on inserting the second lithium into αI-LiVOPO4, but a two-phase reaction feature could also o...