热电池正极材料的研究进展

热电池是一种热激活贮备式电池,由于其优良的贮存稳定性、放电可靠性等特点,广泛应用于多种军用武器的内部电源。为了满足当前不同军用武器装备的需求,热电池的发展趋于在提高电化学性能的同时实现小型化、微型化。热电池电化学性能的提高主要取决于正极材料的发展,目前对现有正极材料的优化改性和新型正极材料的开发是提高热电池性能的主要方法。本文从合成和改性方法的角度综述了近年来硫化物、氯化物、氟化物热电池正极材料的研究进展,并对其材料特性和放电性能进行了综合评估。最后,基于热电池特殊的应用场景,从热稳定性、放电电压、电导率等方面对热电池正极材料未来的发展方向进行了总结与展望。

氟氮共掺杂多孔碳纳米片的制备及其储钾性能研究

钾离子电容器是一种新型的电化学储能器件,碳基材料被认为是最有前途的储钾候选材料之一.然而,K+半径较大使得迁移速率缓慢,脱嵌过程中材料的结构易破坏,导致性能显著下降.因此,开发出低成本的碳材料来适应K+扩散的热力学与动力学需求,已成为当前发展的瓶颈.煤沥青是煤焦油经蒸馏提取液体馏分后得到的残余物,它的组成主要为稠环芳烃,具有高的含碳量、可塑性好、资源集中、价格低廉等显著优点,是一种优质的碳基材料前驱体.鉴于此,本工作采用煤沥青作为碳源、聚四氟乙烯为氟源,氯化钠为模板剂,通过直接高温碳化的策略制备了氟氮共掺杂的多孔碳纳米片(FNCPC).研究表明,纳米片层的结构设计有效缩短了离子的传输路径,F、N共掺杂拓宽了碳的层间距,缓解了体积膨胀问题,并且形成更多的表面缺陷,可为K+的存储提供更多的反应活性位点.此外,电化学动力学分析和密度泛函理论(DFT)表明,FNCPC具备显著的赝电容特性和强的对K吸附能.得益于结构和化学性质的协同优化,FNCPC负极展现出优异的储钾能力(2 A·g^(-1)电流密度下具有212.8 mAh·g^(-1)的比容量)和循环稳定性.进一步将商业化活性炭(AC)为正极,FNCPC为负极构筑了钾离子电容器(AC//FNCPC),该器件能实现最大的能量密度为87.5 Wh·kg^(-1),并且在循环3000次后具有86.1%的容量保持率,展现出广阔的应用前景.

Li10GeP2S12固态电解质电极界面特性研究

采用高温固相法合成了固态电解质Li10GeP2S12,其室温离子电导率为2.02×10-3 S/cm,并组装了LiNbO3@LiNi1/3Co1/3Mn1/3O2/Li10GeP2S12/Li全固态电池.恒流充放电测试表明全固态电池首次放电容量121.2 mAh/g,库伦效率40周后稳定在99.8%左右,循环100周后容量保持率达93.7%.电化学阻抗谱的测试结果表明,其典型的阻抗谱图由高频区半圆(HFS)、中频区半圆(MFS)和低频区斜线(LFL)组成,其中,HFS归属于电解质阻抗(Rel//Qel),MFS归属于电荷传递过程(Rct//Qdl),LFL归属于锂离子的固态扩散过程.通过选取适当的等效电路,对实验所得的电化学阻抗谱数据进行拟合,并分析了Rel和Rct随电极电位的变化规律.

Mechanism of intercalation and deintercalation of lithium ions in graphene nanosheets

Graphene nanosheets (GNSs) were synthesized by reducing exfoliated graphite oxides. Their structure, surface morphology and lithium storage mechanism were characterized and investigated systematically using X-ray diffraction, atomic force microscopy, scanning electron microscopy, charge-discharge tests, cyclic voltammetry and electrochemical impedance spectroscopy. It was found that the GNSs, which were obtained via chemical synthesis, were primarily less than 10 graphene layers. The GNS electrodes, which were fabricated from the reduced GNSs, exhibited an enhanced reversible lithium storage capacity and good cyclic stability when serving as anodes in lithium-ion batteries. Also, the first-cycle irreversible capacities of the system were relatively high, because of the formation of a solid electrolyte interphase film on the surface of the GNS electrode and the spontaneous stacking of GNSs during the first lithiation. The electrochemical impedance spectroscopy results suggest that the solid electrolyte interphase film on the GNS electrode during first lithiation were primarily formed at potentials between 0.95 and 0.7 V. Also, the symmetry factor of the charge transfer was measured to be 0.446.

An electrochemical impedance spectroscopic study of the electronic and ionic transport properties of LiCoO_2 cathode

The storage behavior and process of the first delithiation-lithiation of LiCoO2 cathode were investigated by electrochemical impedance spectroscopy(EIS). The electronic and ionic transport properties of LiCoO2 cathode along with variation of electrode potential were obtained in 1 mol·L?1 LiPF6-EC:DMC:DEC electrolyte solution. It was found that after 9 h storage of the LiCoO2 cathode in electrolyte solu-tions,a new arc appears in the medium frequency range in Nyquist plots of EIS,which increases with increasing the storage time. In the charge/discharge processes,the diameter of the new arc is reversi-bly changed with electrode potential. Such variation coincides well with the electrode potential de-pendence of electronic conductivity of the LiCoO2. Thus this new EIS feature is attributed to the change of electronic conductivity of LixCoO2 during storage of the LiCoO2 cathode in electrolyte solutions,as well as in processes of intercalation-deintercalationtion of lithium ions. It has been revealed that the reversible increase and decrease of the resistance of SEI film in charge-discharge processes can be also ascribed to the variation of electronic conductance of active materials of the LiCoO2 cathode.

Two-and three-electrode impedance spectroscopic studies of graphite electrode in the first lithiation

The first lithiation of graphite electrode was investigated by electrochemical impedance spectroscopy (EIS) and scanning electron microscope (SEM) in a two-electrode button cell and a three-electrode glass cell. The results demonstrate that the study of the variation of EIS feature of the graphite electrode in the two-electrode button cell with electrode polarization potential decreasing in the first lithiation cannot be used to investigate the formation mechanism of the solid electrolyte interphase (SEI) film. However, the formation and growth process of the SEI film can be acquired by investigating the variation of EIS features of the graphite electrode in the three-electrode glass cell with the decrease of electrode po-larization potential in the first lithiation. Moreover, the results also point out that the SEI film on graph-ite electrode is mainly formed between 1.0 and 0.6 V in the first lithiation.

Studies of the first lithiation of graphite materials by electrochemical impedance spectroscopy

First lithiation of graphite electrode in 1 mol/L LiPF6-EC:DEC:DMC electrolyte was investi- gated by electrochemical impedance spectroscopy (EIS). The results illustrated that the first arc in the high-frequency range observed in the Nyquist dia- gram appears near 0.9 V in the initial lithiation of graphite electrode, and its diameter increases with the decrease of polarization potential. These EIS features were attributed to the formation and growth of SEI film. Appropriate equivalent circuit was pro- posed to fit the experimental EIS data. The fitting results revealed the process of the formation and growth of SEI film, and evaluated quantitatively the resistance of charge transfer, as well as the capaci- tance of double layer along with the increase of po- larization potentials.

Preparation and characteriza-tion of a novel composite mi-croporous polymer electrolyte for Li-ion batteries

A novel composite microporous polymer elec- trolyte composed of poly(vinylidene fluoride-co-hexafluorop- ropylene) (PVdF-HFP) and mesoporous SBA-15 was pre- pared. The composite solid polymer electrolyte (CSPE) ex- hibits ionic conductivity as high as 0.30 mS·cm?1 with a composition of SBA-15︰PVdF-HFP=3︰8 at room tem- perature. Infrared transmission spectroscopic results sug- gested that the mechanism of micropore formation is similar to that of the phase inversion. X-ray diffraction (XRD) results demonstrated that the addition of SBA-15 inhibits the crys- tallization of PVdF-HFP, while the SBA-15 preserves well its ordered mesoporous structure during the course of prepara- tion. The Li/CSPE/MCF of half-cell was assembled, and it showed a good electrochemical and cyclability performance during charge-discharge cycles.