Lithium Storage Performance of Hard Carbons Anode Materials Prepared by Different Precursors

以聚丙烯腈、石油沥青和花生壳为前驱体,在1200℃下碳化制备三种不同的硬碳材料。通过扫描电子显微、X射线衍射、氮气吸附/脱附测试和拉曼光谱等方法探究不同前驱体所制备的硬碳材料的表面形貌和物相结构。通过恒流充放电测试考察了这三种硬碳负极材料的电化学性能。结果表明,花生壳基硬碳的初始放电比容量最高,但首圈库仑效率最低,石油沥青基硬碳的首圈库仑效率最高但是比容量最低,聚丙烯腈基硬碳具有较高的循环比容量和稳定性。Hard carbon is one of the most promising anode material for lithium ion batteries (LIBs) owing to its high stability, widespread availability, low-cost, and excellent performance. The electrochemical properties of hard carbon materials depend strongly on the type of precursors. It is, therefore, very important to choose an excellent hard carbon precursor. Polyacrylonitrile, petroleum pitch and peanut shells were used as raw materials to prepare different hard carbon anode materials for LIBs. These hard carbon anode materials were successfully synthesized in two steps. The selected precursor was firstly carbonized at 600℃ for 1 h in argon atmosphere using heating rate of 1℃·min-1, and then was further carbonized at 1200℃ for 1h in argon atmosphere using heating rate of 5℃·min-1. Under such a low heating rate, a relatively small specific surface area could be obtained as much as possible for the hard carbon anode material. The surface morphology and phase structure of as synthesized hard carbon materials were analyzed by scanning electron microscopy, X-ray diffractometer, nitrogen adsorption analyzer and Raman spectrometer. The ion carrier storage mechanism was further investigated using cyclic voltammetry by examining whether the ion insertion/extraction mechanism is surface-controlled pseudocapacitance or diffusion-limited intercalation. It was further verified that the lithium storage mechanism of hard carbon anode materials is in line with the “adsorption-intercalation” mechanism. The results indicated that polyacrylonitrile-derived hard carbon anode material had low impedance by EIS test. This may be the reason why the low voltage platform of polyacrylonitrile-derived hard carbon materials had a higher specific capacity. The electrochemical performance of different hard carbon materials were investigated through galvanostatic charge and discharge tests. The peanut shell-derived hard carbon material showed the highest initial specific capacity (579.1 mAh·g-1), but the lowest initial coulombic efficiency (49.35%). The petroleum pitch-derived one delivered the highest initial coulombic efficiency (85.97%), but the lowest initial specific capacity (301.7 mAh·g-1). Comparing the cycle performance of these three hard carbon materials, polyacrylonitrile-derived hard carbon materials exhibited the excellent cycling performance (87.17% of capacity over 500 cycles). This study would provide useful assistance to understand the precursor-derived electrochemical properties of hard carbon anode material in practical applications.国家自然科学基金面上项目(21673051);广东省科技厅国际合作项目资助(2019A050510043);广东省科技厅产学研重大专项(2017B010119003)通讯作者:施志聪E-mail:[email protected]:Zhi-CongShiE-mail:[email protected]广东工业大学材料与能源学院,新能源材料与器件系,广东 广州 510000Department of New Energy Materials and Devices, School of Materials and Energy, Guangdong University of Technology, Guangzhou 510000, Guangdong, Chin

Measurement of integrated luminosity of data collected at 3.773 GeV by BESIII from 2021 to 2024

We present a measurement of the integrated luminosity e+e- of collision data collected by the BESIII detector at the BEPCII collider at a center-of-mass energy of Ecm = 3.773 GeV. The integrated luminosities of the datasets taken from December 2021 to June 2022, from November 2022 to June 2023, and from October 2023 to February 2024 were determined to be 4.995±0.019 fb-1, 8.157±0.031 fb-1, and 4.191±0.016 fb-1, respectively, by analyzing large angle Bhabha scattering events. The uncertainties are dominated by systematic effects, and the statistical uncertainties are negligible. Our results provide essential input for future analyses and precision measurements

Determination of the number of ψ(3686) events taken at BESIII

The number of ψ(3686) events collected by the BESIII detector during the 2021 run period is determined to be (2259.3±11.1)×106 by counting inclusive ψ(3686) hadronic events. The uncertainty is systematic and the statistical uncertainty is negligible. Meanwhile, the numbers of ψ(3686) events collected during the 2009 and 2012 run periods are updated to be (107.7±0.6)×106 and (345.4±2.6)×106, respectively. Both numbers are consistent with the previous measurements within one standard deviation. The total number of ψ(3686) events in the three data samples is (2712.4±14.3)×10^