Rate Of 15C Research Articles

Cobalt doped spinel LiMn2O4 cathode toward high-rate performance lithium-ion batteries

Great efforts have been devoted to improving the cycling stability and the high-rate performance of spinel LiMn2O4 cathode. Herein, we demonstrate that Co doping can improve the electrochemical performance of spinel LiMn2O4. We elucidate the atomic position of Co in spinel LiMn2O4 configuration and the stability improvement mechanism of the Co-doped LiMn2O4 cathode by using the state-of-art spherical aberration-corrected scanning transmission electron microscopy (Cs-STEM). The results show that the Co3+ ions occupy the Mn octahedral 16d sites to reconstruct a more robust LiCoxMn2−xO4 framework, which is beneficial for stabilizing the LiMn2O4 crystal structure by ameliorating Mn dissolution and inhibiting Jahn-Teller distortion. Concomitantly, the doped Co atoms can offer short path lengths for Li+ ions intercalation and deintercalation that leads to accelerated Li+ diffusion kinetics. The as-designed optimal LiCo0.05Mn1.95O4 presents a respectable capacity retention of 83.81 % after 1000 cycles at 10C (1C = 148 mAh g−1), with an initial discharge capacity of 86.31 mAh g−1. Especially, excellent capacity retention of 78.52 % is obtained after 1000 cycles even at a high current rate of 15C. Our research shed light on the microscopic mechanism of Co doping on the cycling stability enhancement of spinel LiMn2O4 toward high-rate performance LIBs.

Excellent High‐Rate Electrochemical Performances of Microspherical High‐Voltage Spinel Cathodes Synthesized by a Polyacrylamide‐Assisted Co‐Precipitation Method

A convenient strategy to construct microspherical LiNi0.5Mn1.5O4 (LNMO‐P) or Mg‐doped LiNi0.5Mn1.5O4 (LNMO‐P‐M) cathodes by polyacrylamide (PAAM)‐assisted coprecipitation is developed. Due to the coacervation effect of PAAM, the microspherical LNMO‐P and LNMO‐P‐M samples with small primary particle sizes and the uniform primary particles distribution are identified, resulting in a remarkable electrochemical performance with conventional electrolytes. The first coulomb efficiency of the LNMO‐P sample is enhanced to 84.7% and a high discharge capacity of 133.2 mAh g−1 is observed. Of significance, the LNMO‐P‐M sample prepared with PAAM shows excellent high‐rate electrochemical performance. Its capacity retention is 94.9% at the charge rate of 5C after 300 cycles and 95.3% at the discharge rate of 15C after 500 cycles. The improvement electrochemical performance of LNMO‐P‐M sample can be attributed to its strengthened crystal structure, moderate Mn3+ content by the action of Mg, and its improved uniform composition distribution caused by PAAM.

Enhanced electrochemical behavior of LiNi0.8Co0.1Mn0.1O2 cathode materials by nickel boride coating for LIB

A thin layer of nickel boride with high conductivity and stability was successfully coated on the surface of Ni-rich LiNi0.8Co0.1Mn0.1O2 cathode materials with the assistance of polyvinyl pyrrolidone (PVP). Various characterization methods including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), cyclic voltammetry (CV), etc., were used to characterize the as-prepared nickel boride coated LiNi0.8Co0.1Mn0.1O2 materials. An appropriate amount of nickel boride is helpful for reducing the diffusion resistance of lithium ions and the electrode polarization. Compared with the pristine [email protected] wt%Ni2B sample, the [email protected] wt%Ni2B sample coated with 0.75 wt% nickel boride possesses the best electrochemical properties. At the rate of 15C, the [email protected] wt%Ni2B sample has the discharge capacity of 159.5 mAh g−1, which is 20.1 mAh g−1 higher than that of the [email protected] wt%Ni2B sample. Moreover, the [email protected] wt%Ni2B sample has a better cycle performance than the [email protected] wt%Ni2B sample at 1C within different voltage range of both 2.8–4.3 V and 2.8–4.5 V for 100 charge/discharge cycles. The relatively better electrochemical properties of the [email protected] wt%Ni2B sample is ascribed to the lower electrochemical polarization and charge conduction impedance.

Mn2O3 Incorporated Carbonized Bacterial Cellulose As Sulfur Host for Lithium-Sulfur Batteries

Early development and commercialization of lithium-ion batteries (LIBs) have enabled the portable electronic devices and powered the world. However, the ever-increasing demand for higher energy batteries have led to the quest for further improvement. Lithium-sulfur batteries (LSBs), with lithium anode and sulfur-based composite as cathode, have high theoretical specific energy of 2600 W h kg-1 (around 10 folds higher than LIBs system). Moreover, sulfur is produced as a by-product from petroleum refineries making research in LSBs more lucrative. However, there are a few critical challenges which restrict the commercialization of LSBs. First, insulating nature of sulfur (5 × 10-30 S cm-1) and lithium sulfide (Li2S, 10-13 S cm-1) impedes the electronic conductivity which results in low utilization of active sulfur. Secondly, the dissolution and diffusion of long-chain lithium polysulfides in electrolyte to lithium anode under concentration gradient causes series of severe issues such as loss of active sulfur, pulverization of lithium anode. Thirdly, the volume change during lithiation (up to 80%) results in degradation of cathode.To tackle aforementioned issues, we have utilized Mn2O3 incorporated carbonized bacterial cellulose (Mn2O3@CBC) as sulfur host for LSB. A facile melt-diffusion approach was adopted to encapsulate sulfur into Mn2O3@CBC matrix. The material was characterized using various physicochemical techniques - X-ray diffraction spectroscopy, Raman spectroscopy, Thermal gravimetric analysis, and Surface area analyzer. The Mn2O3@CBC system developed in this work offers the following benefits: (a) interconnected carbon nanofiber assembly which helps in fast diffusion of Li-ion and electrons; (b) porous morphology to accommodate volume change and to act as a reservoir for long-chain lithium polysulfides accumulation; (c) Mn2O3 as long-chain lithium polysulfide binding site and catalyst for conversion of long-chain lithium polysulfides to short-chain lithium polysulfides.To investigate the electrochemical property of the material, the performance is compared to bare sulfur and sulfur incorporated carbonized bacterial cellulose (S-CBC). Various electrochemical characterization such as cyclic voltammograms, galvanostatic charge-discharge, rate capability, long-term cycling was performed to investigate the performance of the materials. The material (S-Mn2O3@CBC) exhibited initial reversible capacity of 1150 mA h g-1 at 0.1C and retained 254.4 mA h g-1 at the extremely high current rate of 15C which is far ahead than the bare sulfur and S-CBC. Furthermore, the cycle life of LSB with low and high-sulfur loading was performed to further establish the advantage of using Mn2O3 as electro catalyst. Moreover, first-principles calculation was carried out to understand the functional mechanism for interaction of Mn2O3@CBC and intermediate lithium polysulfides. The excellent electrochemical performance substantiates that the S-Mn2O3@CBC is a good choice for cathode for LSBs. Figure 1

Constructing a Low-Impedance Interface on a High-Voltage LiNi0.8Co0.1Mn0.1O2 Cathode with 2,4,6-Triphenyl Boroxine as a Film-Forming Electrolyte Additive for Li-Ion Batteries.

Compared with other commercial cathode materials, the LiNi0.8Co0.1Mn0.1O2 cathode (NCM811) has high specific capacity and a relatively low cost. Nevertheless, the higher nickel content in NCM811 leads to an extremely unstable interface between the electrode and the electrolyte, resulting in inferior cyclic stability of the corresponding cell. Use of film-forming additives is regarded as the most feasible and economic approach to construct a stable interface on the NCM811 cathode. However, less effective electrolyte additives have been reported to date. Herein, we propose a valid film-forming electrolyte additive, 2,4,6-triphenyl boroxine (TPBX), for application in a high-voltage NCM811 cathode. Experimental and computational results reveal that the TPBX additive can be preferentially oxidized to generate a highly stable and conductive cathode electrolyte interface (CEI) layer on the NCM811 cathode, which efficiently suppresses the detrimental side reaction and improves the electrochemical performance eventually. In detail, the cyclic stability of the Li/NCM811 half-cell is enhanced from 57% (without additive) to 78% (with 5% TPBX) after 200 cycles at 1C between 3.0 and 4.35 V. At a high current rate of 15C, the TPBX-containing electrode delivers a capacity of about 135 mAh g-1, which is much higher than that of the electrode without the additive (80 mAh g-1). Interestingly, the TPBX is also reduced earlier than the ethylene carbonate (EC) solvent to form an ionically conductive solid electrolyte interface (SEI) film on the graphite anode. Due to the CEI layer on the cathode and the SEI film on the anode simultaneously formed by the TPBX additive, the cyclic performance of the graphite/LiNi0.8Co0.1Mn0.1O2 full cell is enhanced. Therefore, the incorporation of the TPBX additive into the electrolyte provides a convenient method for the commercial application of the high-energy-density NCM811 cathode in high-voltage lithium-ion batteries.

Hierarchical Mesoporous Iron Fluoride and Reduced Graphene Oxide Nanocomposite as Cathode Materials for High-Performance Sodium-Ion Batteries.

Sodium-ion batteries have been considered as one of ideal power sources for energy storage system. However, the choice of cathode material with good cycling stability and high capacity is limited. Herein, a nanocomposite of hierarchical mesoporous iron fluoride and reduced graphene oxide is prepared by an in situ approach. The as-prepared nanocomposite exhibits remarkably high discharge specific capacity of 227.5 mAh/g at 0.1C. Specifically, the discharge specific capacity of the sample still remains 87.5 mAh/g at a high rate of 15C after the 100th cycle. The electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT) measurements show that the addition of reduced graphene oxide can effectively reduce the charge transfer resistance and enhance the Na+ diffusion rate in the FeF3·0.33H2O nanoparticles. The structural changes of FeF3·0.33H2O is further investigated by ex-situ XRD, XPS, and ex situ high-resolution transmission electron microscopy.

Enhancing the high rate performance of synergistic hybrid LiFePO4·LiVPO4F/C cathode for lithium ion battery

The (1-x)LiFePO4·xLiVPO4F/C (x = 0, 0.05, 0.10, 0.20, 0.40, 0.60, 0.80, 1) composites with high rate performance were successfully prepared by an improved solid-phase method. Their physicochemical properties were characterized by different test instruments. Through X-ray Diffractometer and structural refinement, it was found that modification with certain amount of LiVPO4F on the LiFePO4 material induced bi-phase co-existence with mutual doping. By Scanning Electron Microscope and Transmission Electron Microscopy detection assisted with Energy Dispersion Spectrum and Fast Fourier Transform analysis, it can be confirmed that the composite material was evenly distributed. Sample 0.9LiFePO4·0.1LiVPO4F/C had the highest specific capacity and specific energy in all samples, with its discharge capacity of 137.4, 129.0, 121.4, 109.6 and 94.0 mAh g−1 at the rate of 3C, 5C, 7C, 10C and 15C, respectively. Furthermore, at the rate of 15C, the specific energy of 0.9LiFePO4·0.1LiVPO4F/C was more than 2 times of that of sample LiFePO4/C. After 800 cycles at 10C, the capacity retention ratio still maintained at 91.42%. Compared with the untreated material, sample 0.9LiFePO4·0.1LiVPO4F/C possessed smaller impedance and larger lithium diffusion coefficient, which is conducive to improve the electrochemical properties of LiFePO4 materials. It indicated that the heterogeneous double active phase shows good synergistic effect.

Novel design and preparation of N-doped graphene decorated Na3V2(PO4)3/C composite for sodium-ion batteries

N-doped graphene (N-graphene) has been a very powerful tool to tailor the property of the pure graphene and it has been proved to be an excellent conducting matrix for preparing high-rate sodium-ion batteries. In this work, we design a facile and rapid route to fabricate the advanced cathode in which the carbon-coated Na3V2(PO4)3 nanocrystals are wrapped on the surface of N-graphene (Na3V2(PO4)3/C@N-graphene). The highly conducting N-graphene sheets significantly enhance the electrochemical performance of the composite, which presents excellent high-rate capability and long-cycle stability. The initial specific capacity of the composite can be up to 115.2mAhg−1 at 0.1C between 2.5 and 3.8V, which is approximately 97.6% of the theoretical capacity. Moreover, the composite shows a long-cycle performance exceeding 1000cycles at high rate of 15C and a high capacity retention ratio. These superior electrochemical properties could be ascribed to many reasons, including the superior electronic conductivity of N-graphene matrix and the nanosized Na3V2(PO4)3/C particles, which are helpful for the transport of e− and Na+. The results demonstrate that the Na3V2(PO4)3/C@N-graphene is a promising candidate to be used in sodium-ion batteries.

The low and high temperature electrochemical performance of Li3VO4/C anode material for Li-ion batteries

The carbon-coated Li3VO4 (Li3VO4/C) sample was synthesized by simple solid-state reaction method using glucose as carbon source. Rietveld refinement, XPS and element analysis results show that, though it is synthesized in the presence of carbon and reducing atmosphere, both the single-phase Li3VO4/C and the valence of vanadium of +5 can be retained. The SEM and TEM images reveal that Li3VO4/C composite has uniform particles with size less than 1μm. Electrochemical testing results show that Li3VO4/C at high operation temperatures holds both higher specific capacity and cyclic performance than that of low temperatures. The initial discharge capacities for the Li3VO4/C electrodes at temperatures of −20, 0, 25 and 50°C are 312, 600, 760 and 721mAhg−1 with the coulombic efficiency of 40.45%, 72.09%, 74.34% and 73.41%, respectively. Even at a high discharge/charge rate of 15C, the capacities of the Li3VO4/C electrodes at −20, 0, 25 and 50°C still can retain about 20, 120, 370 and 450mAhg−1, respectively. The CV results demonstrate that the higher operation temperature can decrease the voltage polarization of the electrode, thus benefit the electrochemical performance of the Li3VO4/C electrode. In addition, the EIS results indicate that larger charge-transfer resistance and smaller lithium diffusion coefficient can be obtained at low operation temperatures, which should be one of the major reasons for its poor low-temperature performance of the Li3VO4/C electrode.

Solid-state synthesis of graphite carbon-coated Li4Ti5O12 anode for lithium ion batteries

Graphites are widely used for their high electrical conductivity and good thermal and chemical stability. In this work, graphitic carbon-coated lithium titanium (Li4Ti5O12/GC) was successfully synthesized by a simple one-step solid-state reaction process with the assistance of sucrose without elevating sintering temperature. The lattice fringe of 0.208 nm clearly seen from the high-resolution transmission electron microscopy (HRTEM) images was assigned to graphite (010). The average grain size of the as-prepared Li4Ti5O12/GC was about 100–200 nm, 1 order smaller than that of pure Li4Ti5O12 prepared similarly. The rate performance and cycle ability were significantly improved by the hybrid conducting network formed by graphitic carbon on the grains and amorphous carbon between them. The specific capacity retention rate was 66.7 % when discharged at a rate of 12C compared with the capacity obtained at 0.5C. After 300 cycles, the capacity retention was more than 90 % at a high rate of 15C.

Growth of the vertically aligned graphene@ amorphous GeOx sandwich nanoflakes and excellent Li storage properties

Germanium oxide is a promising anode material for lithium ion batteries due to its theoretical capacity (1100mAh/g) is 3 times higher than the commercial graphite anode (only 372mAh/g). However, so far only a few studies have reported the application of germanium oxide in LIBs and the cycling performance is unsatisfactory. In this report, we have prepared a unique VAG@ amorphous GeOx sandwich nanostructure by a non-toxic, low temperature CVD method with vertically aligned graphene(VAG) as templates. The graphene sheets form a fast electron transport channel duo to its superior electron conductivity and the vertically aligned sandwich nanoflakes can offer a short pathway for lithium ion thanks to the unified orientation. Additionally, the GeOx sediments that evenly distribute on the surface of graphene flakes have an amorphous structure and their thickness is less than 10nm, which can mitigate the mechanical stress generating in the lithiation/delithiation process. Owing to these advantages, the as-prepared anode shows a stable capacity of 1008mAh/g for 100 cycles (with capacity retention of 96%). Rate performance reveals the anode can maintain a capacity of 545mAh/g even at the rate of 15C. Our results are demonstrated to be so far the most stable performance for germanium oxide anodes.

Electrochemical performance of Li3V2(PO4)3/C cathode materials using stearic acid as a carbon source

The Li3V2(PO4)3/C cathode materials are synthesized by a simple solid-state reaction process using stearic acid as both reduction agent and carbon source. Scanning electron microscopy and transmission electron microscopy observations show that the Li3V2(PO4)3/C composite synthesized at 700°C has uniform particle size distribution and fine carbon coating. The Li3V2(PO4)3/C shows a high initial discharge capacity of 130.6 and 124.4mAhg−1 between 3.0 and 4.3V, and 185.9 and 140.9mAhg−1 between 3.0 and 4.8V at 0.1 and 5C, respectively. Even at a charge–discharge rate of 15C, the Li3V2(PO4)3/C still can deliver a discharge capacity of 103.3 and 112.1mAhg−1 in the potential region of 3.0–4.3V and 3.0–4.8V, respectively. Based on the analysis of cyclic voltammograms and electrochemical impedance spectra, the apparent diffusion coefficients of Li ions in the composites are in the region of 1.09×10−9 and 4.95×10−8cm2s−1.