Project description:The wettability of customized Li-O2 battery electrodes is altered by mixing acetylene black carbon particles with various binders. The wettability of the electrode can be characterized by the static contact angles between the electrode surface and nonaqueous electrolyte, which is 1 M bis(trifluoromethane)sulfonimide lithium salt (LiTFSI) dissolved in tetraethylene glycol dimethyl ether, and the double-layer capacitance measured by the cyclic voltammetry. Results show that electrodes containing poly(vinylidene difluoride) (PVDF) binder are lyophilic and increasing the fraction of poly(tetrafluoroethylene) (PTFE) increases the lyophobicity of electrodes. Li-O2 batteries are discharged at 0.1 mA/cm2 with the cut-off voltage of 2.0 V. The discharge capacity of the electrode with 15% PVDF (36.5°) carbon coatings is 1665.8 mAh/g, whereas the customized electrode with 15% PTFE (128.4°) carbon coatings obtains the discharge capacity of 4160.8 mAh/g. However, the discharge capacity decreases to 3109.5 and 2822.9 mAh/g as the PTFE content further increases to 25% (135.5°) and 35% (138.5°), respectively. The electrode composed of two lyophobic carbon coatings on top and bottom and one lyophilic carbon coating in the middle has the static contact angle of 118.8° and acquires the highest specific discharge capacity of 5149.5 mAh/g.
Project description:All-solid-state lithium-sulfur batteries offer a compelling opportunity for next-generation energy storage, due to their high theoretical energy density, low cost, and improved safety. However, their widespread adoption is hindered by an inadequate understanding of their discharge products. Using X-ray absorption spectroscopy and time-of-flight secondary ion mass spectrometry, we reveal that the discharge product of all-solid-state lithium-sulfur batteries is not solely composed of Li2S, but rather consists of a mixture of Li2S and Li2S2. Employing this insight, we propose an integrated strategy that: (1) manipulates the lower cutoff potential to promote a Li2S2-dominant discharge product and (2) incorporates a trace amount of solid-state catalyst (LiI) into the S composite electrode. This approach leads to all-solid-state cells with a Li-In alloy negative electrode that deliver a reversible capacity of 979.6 mAh g-1 for 1500 cycles at 2.0 A g-1 at 25 °C. Our findings provide crucial insights into the discharge products of all-solid-state lithium-sulfur batteries and may offer a feasible approach to enhance their overall performance.
Project description:Electrodepositing insulating lithium peroxide (Li2O2) is the key process during discharge of aprotic Li-O2 batteries and determines rate, capacity, and reversibility. Current understanding states that the partition between surface adsorbed and dissolved lithium superoxide governs whether Li2O2 grows as a conformal surface film or larger particles, leading to low or high capacities, respectively. However, better understanding governing factors for Li2O2 packing density and capacity requires structural sensitive in situ metrologies. Here, we establish in situ small- and wide-angle X-ray scattering (SAXS/WAXS) as a suitable method to record the Li2O2 phase evolution with atomic to submicrometer resolution during cycling a custom-built in situ Li-O2 cell. Combined with sophisticated data analysis, SAXS allows retrieving rich quantitative structural information from complex multiphase systems. Surprisingly, we find that features are absent that would point at a Li2O2 surface film formed via two consecutive electron transfers, even in poorly solvating electrolytes thought to be prototypical for surface growth. All scattering data can be modeled by stacks of thin Li2O2 platelets potentially forming large toroidal particles. Li2O2 solution growth is further justified by rotating ring-disk electrode measurements and electron microscopy. Higher discharge overpotentials lead to smaller Li2O2 particles, but there is no transition to an electronically passivating, conformal Li2O2 coating. Hence, mass transport of reactive species rather than electronic transport through a Li2O2 film limits the discharge capacity. Provided that species mobilities and carbon surface areas are high, this allows for high discharge capacities even in weakly solvating electrolytes. The currently accepted Li-O2 reaction mechanism ought to be reconsidered.
Project description:Thermal batteries with molten salt electrolytes are used for many military applications, primarily as power sources for guided missiles. The Li-B/CoS2 couple is designed for high-power, high-voltage thermal batteries. However, their capacity and safe properties are influenced by acute self-discharge that results from the dissolved lithium anode in molten salt electrolytes. To solve those problems, in this paper, carbon coated CoS2 was prepared by pyrolysis reaction of sucrose at 400 °C. The carbon coating as a physical barrier can protect CoS2 particles from damage by dissolved lithium and reduce the self-discharge reaction. Therefore, both the discharge efficiency and safety of Li-B/CoS2 thermal batteries are increased remarkably. Discharge results show that the specific capacity of the first discharge plateau of carbon-coated CoS2 is 243 mA h g-1 which is 50 mA h g-1 higher than that of pristine CoS2 at a current density of 100 mA cm-2. The specific capacity of the first discharge plateau at 500 mA cm-2 for carbon-coated CoS2 and pristine CoS2 are 283 mA h g-1 and 258 mA h g-1 respectively. The characterizations by XRD and DSC indicate that the carbonization process has no noticeable influence on the intrinsic crystal structure and thermal stability of pristine CoS2.
Project description:A novel solution combustion synthesis of nanoscale spinel-structured Co3O4 powder was proposed in this work. The obtained material was composed of loosely arranged nanoparticles whose average diameter was about 36 nm. The as-prepared cobalt oxide powder was also tested as the anode material for Li-ion batteries and revealed specific capacities of 1060 and 533 mAh·g-1 after 100 cycles at charge-discharge current densities of 100 and 500 mA·g-1, respectively. Moreover, electrochemical measurements indicate that even though the synthesized nanomaterial possesses a low active surface area, it exhibits a relatively high specific capacity measured at 100 mA·g-1 after 100 cycles and a quite good rate capability at current densities between 50 and 5000 mA·g-1.
Project description:In the past, sodium alanate, NaAlH4, has been widely investigated for its capability to store hydrogen, and its potential for improving storage properties through nanoconfinement in carbon scaffolds has been extensively studied. NaAlH4 has recently been considered for Li-ion storage as a conversion-type anode in Li-ion batteries. Here, NaAlH4 nanoconfined in carbon scaffolds as an anode material for Li-ion batteries is reported for the first time. Nanoconfined NaAlH4 was prepared by melt infiltration into mesoporous carbon scaffolds. In the first cycle, the electrochemical reversibility of nanoconfined NaAlH4 was improved from around 30 to 70% compared to that of nonconfined NaAlH4. Cyclic voltammetry revealed that nanoconfinement alters the conversion pathway, and operando powder X-ray diffraction showed that the conversion from NaAlH4 into Na3AlH6 is favored over the formation of LiNa2AlH6. The electrochemical reactivity of the carbon scaffolds has also been investigated to study their contribution to the overall capacity of the electrodes.
Project description:Non-crystalline Li-ion solid electrolytes (SEs), such as lithium phosphorus oxynitride, can uniquely enable high-rate solid-state battery operation over thousands of cycles in thin film form. However, they are typically produced by expensive and low throughput vacuum deposition, limiting their wide application and study. Here, we report non-crystalline SEs of composition Li-Al-P-O (LAPO) with ionic conductivities > 10-7 S cm-1 at room temperature made by spin coating from aqueous solutions and subsequent annealing in air. Homogenous, dense, flat layers can be synthesized with submicrometer thickness at temperatures as low as 230 °C. Control of the composition is shown to significantly affect the ionic conductivity, with increased Li and decreased P content being optimal, while higher annealing temperatures result in decreased ionic conductivity. Activation energy analysis reveals a Li-ion hopping barrier of ≈0.4 eV. Additionally, these SEs exhibit low room temperature electronic conductivity (< 10-11 S cm-1) and a moderate Young's modulus of ≈54 GPa, which may be beneficial in preventing Li dendrite formation. In contact with Li metal, LAPO is found to form a stable but high impedance passivation layer comprised of Al metal, Li-P, and Li-O species. These findings should be of value when engineering non-crystalline SEs for Li-metal batteries with high energy and power densities.
Project description:The development of new anode materials having high electrochemical performances and interesting reaction mechanisms is highly required to satisfy the need for long-lasting mobile electronic devices and electric vehicles. Here, we report a layer crystalline structured SnP3 and its unique electrochemical behaviors with Li. The SnP3 was simply synthesized through modification of Sn crystallography by combination with P and its potential as an anode material for LIBs was investigated. During Li insertion reaction, the SnP3 anode showed an interesting two-step electrochemical reaction mechanism comprised of a topotactic transition (0.7-2.0 V) and a conversion (0.0-2.0 V) reaction. When the SnP3-based composite electrode was tested within the topotactic reaction region (0.7-2.0 V) between SnP3 and LixSnP3 (x ≤ 4), it showed excellent electrochemical properties, such as a high volumetric capacity (1st discharge/charge capacity was 840/663 mA h cm-3) with a high initial coulombic efficiency, stable cycle behavior (636 mA h cm-3 over 100 cycles), and fast rate capability (550 mA h cm-3 at 3C). This layered SnP3 anode will be applicable to a new anode material for rechargeable LIBs.
Project description:Antiperovskite Li3OCl superionic conductor films are prepared via pulsed laser deposition using a composite target. A significantly enhanced ionic conductivity of 2.0 × 10-4 S cm-1 at room temperature is achieved, and this value is more than two orders of magnitude higher than that of its bulk counterpart. The applicability of Li3OCl as a solid electrolyte for Li-ion batteries is demonstrated.
Project description:Anode material Li2TiO3-coke was prepared and tested for lithium-ion batteries. The as-prepared material exhibits excellent cycling stability and outstanding rate performance. Charge/discharge capacities of 266 mA h g-1 at 0.100 A g-1 and 200 mA h g-1 at 1.000 A g-1 are reached for Li2TiO3-coke. A cycling life-time test shows that Li2TiO3-coke gives a specific capacity of 264 mA h g-1 at 0.300 A g-1 and a capacity retention of 92% after 1000 cycles of charge/discharge.