Initial Cycle Efficiency Research Articles

In-situ photodeposition of CoSx on Pa0.5Ba0.5Mn0.25Fe0.75O3-δ perovskite to boost bifunctional oxygen electrocatalysis for rechargeable Zn-air batteries

The single catalytic property with limited active sites severely restricts the development of perovskite materials as efficient oxygen electrocatalysts in rechargeable Zn-air batteries (ZABs). Although some researches on structural optimization and surface decoration of perovskite materials have improved their electrocatalytic performance, the complicated preparation process, and harsh treatment conditions urge the apparent of a creative attempt towards perovskite. Herein, we develop a highly-dispersed amorphous CoSx modified Pa0.5Ba0.5Mn0.25Fe0.75O3-δ composites (CoSx/PBMF) by a rapid and mild photochemistry-deposition method. The structural merit and the synergistic effect of integrating amorphous CoSx and PBMF result in a perovskite material with outstanding electrocatalytic activity and superior durability. Moreover, the liquid rechargeable ZAB assembled with integrated CoSx/PBMF electrocatalyst as air electrode demonstrates a maximal power density of 114 mW cm−2 and a long charge-discharge cycling life over 220 h with initial cycle efficiency of 60.5% and 0.03 V incensement of voltage gap. Meanwhile, the all-solid-state CoSx/PBMF-based ZABs maintain an open-circuit voltage of 3.92 V in series of three ZABs and powered LED panels stably, demonstrating its practical utility as the battery for portable electron devices.

3D spiral-like polyhedron nanocarbon confining uniformly dispersed Co nanoparticles for bifunctional electrocatalyst in metal-air battery

Reasonable design and feasible synthesis of catalysts with high efficiency for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are urgent demand, but remain a challenge in achieving extensive application of metal-air battery. In this work, we utilized the gas-foaming way to synthesize uniformly dispersed Co nanoparticles (Co NPs) anchored on 3D spiral-like polyhedron N-doped porous carbon structure. The optimized catalyst (CoSP-850-10) delivers prominent ORR activity with half-wave potential of 0.85 V and kinetic current density of 27 mA cm−2. Importantly, it also demonstrates satisfactory bifunctional performance with low overpotential. Furthermore, the Al-air battery with CoSP-850-10 offers remarkable specific capacity of 1670 mAh g−1 at 200 mA cm−2. The Zn-air battery delivers a stable working voltage of 1.25 V at 10 mA cm-2 and remarkable rechargeable performance with high initial cycle efficiency of 60.5% and long-term stability under 20 mA cm−2.

Sub-micron silicon/pyrolyzed carbon@natural graphite self-assembly composite anode material for lithium-ion batteries

Si/C@NGs composite containing flake-shaped sub-micron sized silicon (Si) enwrapped by pyrolyzed carbon and natural graphite (NG) was successfully prepared by spray-drying-assisted self-assembly method and was systematically studied as an anode material for lithium-ion batteries. The as-prepared Si/C@NGs composite material has a loading amount of sub-micron sized silicon as low as 6.7wt%. The Si/C@NGs composite has a hierarchical structure with Si/C embedded into natural graphite which further assembles into larger secondary particles of ∼20–50μm. Compared with pure silicon, the as-synthesized Si/C@NGs composite has multi-layer carbon coating as well as voids to alleviate the structural changes of Si during charging/discharging, exhibits an initial efficiency of 82.8% and a capacity retention of 428.1mAhg−1 (1524.0mAhg−1vs. Si) after 100 cycles at 0.1Ag−1. The remarkable cycling performances, high initial cycle efficiency together with low-cost manufacturing process make Si/C@NGs composite appealing for commercial applications.

Synthesis and electrochemical characterization of Ni- and Ti-substituted Li2MnO3 positive electrode material using coprecipitation–hydrothermal–calcination method

Homogeneous solid solutions of Ni- and Ti-substituted Li2MnO3 (Li1+x(Ni0.3Mn0.7-yTiy)1-xO2, 0<x<1/3, y=0, 0.1, 0.2) have been prepared using coprecipitation–hydrothermal–calcination method. With increasing Ti contents, the randomly-distributed transition metal structure became stable. The average valence state of Ni and Mn ions was reduced and additional transition metal ion was introduced in Li-layer by calcining in N2 atmosphere at the same Ti content. The electrochemical performance depended on the Ti content and calcination atmosphere. By incorporating Ti ion, although the initial capacity and initial cycle efficiency worsened, cyclability was drastically improved. By changing from air to N2 atmosphere, the initial capacity, initial cycle efficiency, voltage decay with cycle and cyclability improved. A combination of Ti substitution and calcination in N2 atmosphere, optimized composition, Li1+x(Ni0.3Mn0.5Ti0.2)1-xO2 is proposed because the sample exhibited high cyclability up to 30 cycles (95%) under a full-cell configuration.

Synthesis of Li-excess layered cathode material with enhanced reversible capacity for Lithium ion batteries through the optimization of precursor synthesis method

LixNi1/3Mn2/3O2 cathode materials have been synthesized through a facile reduction-ion exchange of P3-Na2/3Ni1/3Mn2/3O2 precursors prepared by solid state (SS), spray dry (SD) and co-precipitation (CP) methods. The influence of precursor synthesis method on the structure, morphology and electrochemical performances of LixNi1/3Mn2/3O2 has been investigated. X-ray diffraction (XRD) results of LixNi1/3Mn2/3O2 demonstrate that all the samples exhibit similar XRD patterns as those of Lithium-excess layered cathode materials. Scanning Electron Microscope (SEM) images and Brunauer-Emment-Teller (BET) results present that the particle size, particle aggregation and surface area changed greatly with the precursor synthesis method. Galvanostatic charge-discharge results show that Li1.41Ni0.32Mn0.66O2+δ cathode prepared from co-precipitation precursor exhibited high first discharge capacity of ca. 270 mAhg−1 with an initial cycle efficiency as high as 98%. The discharge capacity of Li1.41Ni0.32Mn0.66O2+δ cathode after 30 cycles is over 250 mAhg−1 and it can deliver a discharge capacity roughly 210 mAhg−1 at a current density of 500 mAg−1 (2C rate). Also, it was found that Li1.41Ni0.32Mn0.66O2+δ cathode shows enhanced electrochemical performance over the Li2/3Ni1/3Mn2/3O2 cathode with respect to reversible capacity and rate capability.

Roles of Fluorine-doping in Enhancing Initial Cycle Efficiency and SEI Formation of Li-, Al-cosubstituted Spinel Battery Cathodes

/EC:EMC. SEM imaging reveals that the facetting on higher surface energy plane of (101) is additionallydeveloped at the edges of an octahedron that is predominantly grown with the most thermodynamically stable(111) plane, which enhances interfacial reactivity. Fluorine-doping also increases the amount of interfaciallyreactive Mn

A Study of High-Voltage LiNi0.5Mn1.5O4 and High-Capacity Li1.5Ni0.25Mn0.75O2.5 Blends

Spinel-layered (S-L) cathode blends of LiNi0.5Mn1.5O4-δ and Li1.5Ni0.25Mn0.75O2.5 were prepared by physical mixing during electrode fabrication. The incorporation of the spinel component in the blends (S:L ratio = 1:1) has led to the following advantages: 1) the initial-cycle efficiency, which is usually lower than 80% for the layered component, increased to 90% as the extra capacity of the spinel below 3.0 V could be utilized in the blends; 2) the rate capability of the cells was improved and reached a maximum for the blend; 3) the cycling behavior of the cells was comparable to that of the pure layered component, but superior to that of the pure spinel component cycled between 2.0 and 4.8 V. The study revealed that the introduction of the spinel component in the blends could mitigate some of the weaknesses of the layered component, and vice versa.

Synthesis of high-capacity Ti- and/or Fe-substituted Li2MnO3 positive electrode materials with high initial cycle efficiency by application of the carbothermal reduction method

Carbothermal reduction using sucrose was applied to Fe- and/or Ti-substituted Li2MnO3 positive electrode materials to improve their poor initial cycle efficiency (<60%) of 2.0–4.8 V. The initial cycle efficiency was improved from 53% to 68% for Li1+x(Ti0.5Mn0.5)1−xO2, 63%–72% for Li1+x(Fe0.3Mn0.7)1−xO2, or 62%–78% for Li1+x(Fe0.2Ti0.2Mn0.6)1−xO2 by application of the carbothermal reduction process. All samples belong to 3.2 V class positive electrode material with high initial discharge capacity higher than 220 mAh g−1. The shape change of discharge curve with cycle progression was suppressed for all reduced samples. The compositional, transition metal valence state, and structural and powder property changes occurring before and after carbothermal reduction processing were examined to construct the material design concept of attractive Li2MnO3-based positive electrode candidates using only naturally abundant and cheap elements (Ti and Fe) as constituent metals.

Synthesis and electrochemical characterization of Fe and Ni substituted Li 2MnO 3—An effective means to use Fe for constructing “Co-free” Li 2MnO 3 based positive electrode material

Equal amounts of Fe- and Ni-substituted Li 2MnO 3 (chemical formula: Li 1+ x [(Fe 1/2Ni 1/2) y Mn 1− y ] 1− x O 2, 0 < x < 1/3, 0.2 ≤ y ≤ 0.8) were synthesized using coprecipitation–hydrothermal–calcination. Although the samples with y less than 0.5 are only monoclinic Li 2MnO 3-type structure ( C2/ m), samples with y larger than 0.6 show a two-phase nature consisting of the monoclinic phase and cubic LiFeO 2 phase ( F m 3 ¯ m ). Electrochemical characterization as a positive electrode shows that the Li 2O extraction region disappears above y = 0.6 on initial charging and that the energy density is decreased drastically above the composition on initial discharging. The optimized transition metal ratios are y = 0.4 and 0.5 because the initial average discharge voltage increases with y and the maximum initial cycle efficiency is attained. In the optimized composition, the Fe- and Ni-substituted Li 2MnO 3 is a 3.5 V class positive electrode, with similar charge and discharge profiles to those of the most attractive active material, NMC positive electrode (chemical formula: Li 1+ x [(Co 1/2Ni 1/2) y Mn 1− y ] 1− x O 2, 0 < x < 1/3, 0.2 ≤ y ≤ 0.8). Consequently, Fe can be used as an activator in combination with Ni for constructing “Co-free” Li 2MnO 3-based positive electrodes. The calcination-condition-dependence of electrochemical properties at the optimized composition is also examined. The effects of the Fe valence state on initial charge–discharge curves are discussed.

Decreasing the initial irreversible capacity loss of graphite negative electrode by alkali-addition

The effect of alkali function group contained in electrode binder was investigated. Carboxy methyl cellulose (CMC) improved the initial irreversible capacity loss in graphite negative electrode. Lithium acetate also improved the initial cycle efficiency. On the other hand, ethyl cellulose (EC) and hydroxyl propyl methyl cellulose (HPMC), which do not have a carboxylic group, did not decrease the reductive electrolyte decomposition. After charge and discharge cycle, the surface film composition on the electrode with CMC was less than on the electrode without CMC. This suggests that a carboxylic group in the binder acted as a catalyst and promoted the solid electrolyte interphase (SEI) formation which prevents the excess electrolyte decomposition on the graphite electrode.

Preparation and application of bamboo-like carbon nanotubes in lithium ion batteries

CNTs with bamboo-like structure (B-CNTs) has been prepared via a CVD process with novel carbon precursor. The potential application of B-CNTs as electric conductive additive and anode materials for lithium ion batteries was explored. The EIS spectra prove that it is better electric conductive additive than multiwalled CNTs and traditional carbon black (CB). The electric resistance of the electrode is decreased around 20 Ω when B-CNTs is used instead of CB. The cycle stability is also enhanced. However, the test cell with B-CNTs as anode material shows low reversible capacity of 135 mAh g −1 and very low initial cycle efficiency of 17.3%, which indicates that so-prepared B-CNTs is not suitable for anode material.

Investigations on the modified natural graphite as anode materials in lithium ion battery

Two kinds of natural graphite samples, flake graphite (FG) and microcrystalline graphite (MG) have been used as anode materials in lithium ion battery after various modifications based on the structural difference between FG and MG. FG should be focused on improving the cycle stability while MG on the initial cycle efficiency. Spherical treatment, particle grading and surface coating are effective to improve their electrochemical performance. Especially, mild-expansion modification was used to introduce defects into FG's structure, which greatly improved its cycle stability and capacity. Both FG and MG are promising commercial anode materials after a series of modifications.