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While the theoretical capacity of LiCoO2 is as high as 274 mA h g−1, its practical specific capacity is only about 140 mA h g−1 when it was first applied in lithium-ion batteries. Raising the charg...

Ni-rich cathode materials LiNixCoyMn1–x–yO2 (x ≥ 0.6) have attracted much attention due to their high capacity and low cost. However, they usually suffer from rapid capacity decay and short cycle l...

With the growing demand for high specific volume energy-density, surface modifications are devoted to increasing the electrochemical performances of LiCoO2 at high operating voltage. In this work, LiCoO2 materials with a phosphate-rich coating layer are developed using a facile spray-drying method. The stable phosphate-rich coating layer acts as protection and effectively suppresses the impedance growth in LiCoO2 cells. The phosphate-rich layer coated LiCoO2 samples show long cycle-life and good rate performance when cycled with a high cut-off voltage of 4.5 V at room temperature and 45 °C.

A hexagonal FeSe nanoparticle anode with a novel reaction mechanism and mechanical stability may fully facilitate the desirable rate capability and cycling performance in sodium-ion batteries. In situ TEM reveals that hexagonal FeSe nanoparticle transition to the Fe and Na2Se phase during sodiation, while the products transform to the tetragonal FeSe phase after desodiation.

Layered germanium phosphide (GeP), a recently developed two-dimensional material, promises highly attractive theoretical capacity for use as a lithium-ion battery anode. Here, we comprehensively investigate its electrochemical performance and the modification mechanism. GeP flakes demonstrate large initial discharge/charge capacity and high initial Coulombic efficiency. However, the cycling performance is disappointing in the potential window of 0.001-3 V in which capacity retention is only ∼18% after 100 cycles. In situ transmission electron microscopy reveals that the poor cycling behavior results in the unexpected large volume change induced by complex reaction processes in cycles. Serious cracking and fracture appear clearly on the electrode surface after cycling. Narrowing the working voltage window to 0.001-0.85 V, cycling stability will be greatly enhanced, with 75% capacity retaining after 100 cycles and ∼50% left after 350 cycles due to the absence of the dealloying of Li

Binders play a significant role in the electrochemical performance of electrodes in batteries, especially for high-capacity conversion/alloying-type electrodes. However, the effects of binders on the electrochemical performance of the conversion/alloying-type anodes in sodium ion batteries are not widely investigated. In this work, we use SnS 2 as a model anode and comparatively investigate the performance of six different types of binders in SnS 2 electrodes of sodium ion batteries by half-cell testing. The binders are sodium carboxymethyl cellulose (CMC-Na), sodium polyacrylate (PAA-Na), CMC-Na-PAA-Na (1:1, wt%, denoted as PAA-CMC), sodium alginate (ALG-Na), PVDF, PTFE. The PAA-CMC binder electrodes exhibit outstanding cycling and rate performance, delivering a reversible capacity of 400 mAh g −1 at the current density of 100 mA g −1 within 70 cycles. Our results indicate that the binder with a large fraction of carboxylate and hydroxyl groups, which lead to stronger hydrogen bonds and/or covalent chemical bonds with the carbon black and active materials, is advantageous for the electrochemical performances of SnS 2 electrodes. The synergistic interactions among the binder and the surface of both the active materials of SnS 2 and the conductive additive of ketjen black have been also schematically proposed in this study.

Although various cathode materials have been explored to improve the energy density of lithium-ion batteries, LiCoO2 is still the first choice for 3C consumer electronics due to the high tap density and high volumetric energy density. However, only 0.5 mol of lithium ions can be extracted from LiCoO2 to avoid side reactions and irreversible structure change, which typically occur at high voltage (>4.2 V). To improve the electrochemical performances of the LiCoO2 cathode material at high cut-off voltage and elevated temperature for higher energy density, an in situ formed spinel interfacial coating layer of LiCoxMn2–xO4 is achieved by the reaction of the surface region of the LiCoO2 host. The capacity retention of the modified LiCoO2 cycled at a high voltage of 4.5 V is significantly increased from 15.5 to 82.0% after 300 cycles at room temperature, due to the stable spinel interfacial inhibiting interfacial reactions between LiCoO2 and the electrolyte as confirmed by impedance spectroscopy. We further dem...

A series composited membranes of sulfonated poly(arylene ether sulfone) and graphene oxide (SPAES-GO-x) have been exploited as proton exchange membrane. The properties of SPAES-GO-x membranes were evaluated including proton conductivity, water uptake, swelling ratio, oxide and thermal stability. Incorporating GO into SPAES matrix restrained the composite membranes swelling and enhanced their proton conductivity. The SPAES-GO-3% membrane showed a conductivity value of 0.183 S cm−1 at 120 °C and relative humidity 100%. Compared with the pristine SPAES membrane, the swelling ratio of SPAES-GO-2% membrane was reduced by 55.7% at 90 °C. Small-Angle X-ray Scattering (SAXS) revealed GO promoted SPAES molecular chain movement to form bigger ionic clusters in favor of enhancing proton transport. X-Ray Diffraction and Field Emission Scanning Electron Microscope (XRD and FE-SEM) analysis further demonstrated GO was exfoliated and distributed throughout the SPAES matrix. These results indicated GO was an effective filler to trade off proton conductivity and swelling of composite membrane.

Li2MnO3-based Li-rich cathode materials can offer high capacities for lithium-ion batteries but suffer from poor rate capability, low initial coulombic efficiency, and voltage fade upon extended cycling. Significant attention has been focused on the replacement of Li2MnO3 with other materials featuring Li2MO3 (M = Ru, Mo, etc.) components; however, the cycle performance of these materials is inferior. Herein, coating with Al2O3 is proposed to improve the electrochemical performance of the Li2RuO3-based Li-rich cathode material Li1.2Ni0.2Mn0.2Ru0.4O2. Rietveld refinement data indicate Ru-Ru dimer formation in these samples. The Al2O3 coating can enhance the initial coulombic efficiency, cycling stability, rate performance, and mitigate the voltage decay. In situ X-ray diffraction (XRD) demonstrates that the compound remains a layered structure during the first cycle. The formation of Ru-Ru dimers is suggested to be responsible for the unusual lattice parameter changes during the initial charge.

Room-temperature sodium-ion batteries offer an alternative solution for large-scale energy storage system because of the huge abundant, and low cost of sodium resources. An O3-type sodium-excess layered material Na1.2Ni0.2Mn0.2Ru0.4O2 (0.4Na2RuO3·0.4NaNi0.5Mn0.5O2) is prepared as a cathode material for sodium-ion batteries, which reveals an enhanced cycling stability, high coulombic efficiency, and superior dynamics properties. In-situ X-ray diffraction analysis is conducted to get insight into the sodium storage mechanism. Keywords: Sodium-ion batteries, O3-type cathode materials, In-situ X-ray diffraction, Structure evolution

As a promising additive for film forming on anodes, fluoroethylene carbonate (FEC) has been applied widely in commercial lithium ion batteries (LIBs). However, the influence of FEC in high-voltage Li+ energy storage systems are still under disputing for the negative effects on cathodes. Considering a FEC molecule would be electro-oxidized to a radical onium ion, we investigate hexamethylene diisocyanate (HDI) as the additive which can react with the intermediate to form an amide-based polymer via thermodynamic processes. The polymer would be stable at high potential. In the FEC-containing electrolyte with HDI added, a surface layer is formed on the LiNi0.5Mn1.5O4 cathode, which would protect the compounds from decomposing and improve the performances of the batteries. The capacity retention of Li/LiNi0.5Mn1.5O4 cells cycled between 3.5–4.9 V (vs. Li+/Li) is significantly increased from 59.1% to 76.1% in 200 cycles, and the rate capability is also improved compared with the ones without HDI. The electrolyte system also shows a good compatibility with graphite, presenting a promising prospect for the practical application of high-voltage LIBs.

Li2Ru0.5Mn0.5O3, a high capacity lithium-rich layered cathode material for lithium-ion batteries, was subject to comprehensive diagnostic studies, including in situ/ex situ X-ray diffraction, X-ray absorption spectroscopy (XAS), pair distribution function, and high resolution scanning transmission electron microscopy analysis, to understand the correlations between transition-metal chemistry, structure, and lithium storage electrochemical behavior. Ru–Ru dimers were identified in the as-prepared sample and found to be preserved upon prolonged cycling. Presence of these dimers, which are likely caused by the delocalized nature of 4d electrons, is found to favor the stabilization of the structure in a layered phase. The in situ XAS results confirm the participation of oxygen redox into the charge compensation at high charge voltage, and the great flexibility of the covalent bond between Ru and O may provide great reversibility of the global structure despite the significant local distortion around Ru. In co...

The development of high-performance lithium ion batteries requires the discovery of new materials and the optimization of key components. By contrast with traditional one-by-one method, high-throughput method can synthesize and characterize a large number of compositionally varying samples, which is able to accelerate the pace of discovery, development and optimization process of materials. Because of rapid progress in thin film and automatic control technologies, thousands of compounds with different compositions could be synthesized rapidly right now, even in a single experiment. However, the lack of rapid or combinatorial characterization technologies to match with high-throughput synthesis methods, limit the application of high-throughput technology. Here, we review a series of representative high-throughput characterization methods used in lithium batteries, including high-throughput structural and electrochemical characterization methods and rapid measuring technologies based on synchrotron light sources.

The superior tap density (4.1 g cm−3) and high theoretical specific capacity (274 mA h·g−1) of LiCoO2 make it still the first choice of cathode for batteries in next-generation portable electronic devices. However, the structural instability in the deeply delithiated state severely restricts the reversible capacity of LiCoO2 for practical applications. Owing to the recently popular Ni and Mn elements in ternary cathodes, we explored the effects of Ni–Mn co-doping and each individual dopant on the electrochemical behavior and structural evolution of LiCoO2 at a high upper cut-off voltage of 4.6 V by the means of in-situ XRD and GITT measurements. LiMn0.05Co0.95O2 shows the best cycle stability at 4.6 V with a capacity retention of 55% after 100 cycles. The doping suppresses various two-phase transitions, especially, the O3/H1-3 phase transition at ∼4.55 V, leading to better cycling stability of LiCoO2 at 4.6 V. Due to the significant stabilizing effect on the structure, Mn seems to be an ideal choice for the modification of high-voltage LiCoO2 in the future.

The lithium-rich Li[Li0.2Ni0.13Mn0.54Co0.13]O2 nanoplates were synthesized using a molten-salt method. The nanoplates showed an initial reversible discharge capacity of 233 mA&middot, h&middot, g&minus, 1, with a fast capacity decay. The morphology and micro-structural change, after different cycles, were studied by a scanning electron microscope (SEM) and transmission electron microscopy (TEM) to understand the mechanism of the capacity decay. Our results showed that the cracks generated from both the particle surface and the inner, and increased with long-term cycling at 0.1 C rate (C = 250 mA&middot, 1), together with the layered to spinel and rock-salt phase transitions. These results show that the cracks and phase transitions could be responsible for the capacity decay. The results will help us to understand capacity decay mechanisms, and to guide our future work to improve the electrochemical performance of lithium-rich cathode materials.

Layered germanium phosphide, which combines the advantages of both germanium and phosphorus, is believed to be a potential anode for sodium ion battery. Here, the sodium storage mechanism and electrochemical performance of layered germanium phosphide have been deeply investigated by advanced in-situ transmission electron microscopy technique combining half-cell testing. Dynamic reaction process reveals that individual layered germanium phosphide nanoflake undergoes total area expansion of 248% without any detectable fracture or cracking in sodiation. In contrast, germanium phosphide experiences multi-step reactions, i.e. intercalation and alloying, accompanied by sequentially forming NaxGeP (0

Large-scale energy storage technologies are in great demands for the enhanced power grid efficiency and wide renewable energy source applications. Various electrochemical energy storage devices, including lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) et al. with long operating life and high energy conversion efficiency, have achieved rapid growth in the past 30 years, which make them the best choice for the large energy storage applications. Recently, SIBs have been proposed as the most promising solution for the large-scale energy storage systems because of the huge abundant and low cost of sodium resources. High energy-density cathode materials are now the main limits for high performance SIBs. Herein, the advances made in high energy-density cathodes for SIBs, together with the sodium storage mechanism; the remaining challenges and perspectives for high energy-density cathode materials, are discussed thoroughly based on recent researches and publications. Meanwhile, the achievement of material simulations in the design and development of cathode materials for SIBs, especially the high-throughput strategy and data science, is also introduced. This review is expected to accelerate the progress on SIB studies for high energy-density cathode materials, and more importantly, open up new opportunities for the high-energy cathode materials design in sodium storage.

Li- and Mn-rich (LMR) cathode materials have been considered as promising candidates for energy storage applications due to high energy density. However, these materials suffer from a serious problem of voltage fade. Oxygen loss and the layered-to-spinel phase transition are two major contributors of such voltage fade. In this paper, using a combination of X-ray diffraction (XRD), pair distribution function (PDF), X-ray absorption (XAS) techniques, and aberration-corrected scanning transmission electron microscopy (STEM), we studied the effects of micro structural defects, especially the grain boundaries, on the oxygen loss and layered-to-spinel phase transition through prelithiation of a model compound Li2Ru0.5Mn0.5O3. It is found that the nanosized micro structural defects, especially the large amount of grain boundaries created by the prelithiation can greatly accelerate the oxygen loss and voltage fade. Defects (such as nanosized grain boundaries) and oxygen release form a positive feedback loop, prom...

Lithium ion batteries are important electrochemical energy storage devices for consumer electronics and the most promising candidates for electrical/hybrid vehicles. The surface chemistry influences the performance of the batteries significantly. In this short review, the evolution of the surface structure of the cathode materials at different states of the pristine, storage and electrochemical reactions are summarized. The main methods for the surface modification are also introduced.

Li-rich layered materials are important cathode compounds used in commercial lithium ion batteries, which, however, suffers from some drawbacks including the so-called voltage fade upon electrochemical cycling. This study employs novel transmission X-ray microscopy to investigate the electrochemical reaction induced morphological and chemical changes in the Li-rich Li2Ru0.5Mn0.5O3 cathode particles at the meso to nano scale. Combined X-ray spectroscopy, diffraction and microscopy experiments are performed to systematically study this cathode material's evolution upon cycling as well as to establish a comprehensive understanding of the structural origin of capacity fade through 2D and 3D fine length scale morphology and heterogeneity change of this material. This work suggests that atomic manipulation (e.g. doping, substitution etc.) or nano engineering (e.g. nano-sizing, heterogeneous structure) are important strategies to mitigate the internal strain and defects induced by extensive lithium insertion/extraction. It also shows that maintaining the structural integrity is the key in designing and synthesizing lithium-rich layered materials with better cycle stability.