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Lithium-ion battery (LIB) is regarded as a promising energy for its high energy density. LIB safety has been attracted much attention due to their frequent occurrence of accidents. The properties of battery material are the key parameters to influence the battery safety 1 . In this paper, the thermal and structural properties of cathode and anode with different states of charge (SOCs) were studied by high magnification microscope, SEM (Scanning electron microscopy), XRD (X-ray diffraction) and DSC (Differential Scanning Calorimetry). LIBs with Li(Ni 1/3 Co 1/3 Mn 1/3 )O 2 (NCM) as cathode, graphite as anode, and electrolyte of LiPF 6 in ethylene carbonate(EC)/diethyl carbonate(DC)/dimethyl carbonate (DMC) (1:1:1) were charged with different SOCs (0%, 20%, 40%, 60%, 80%, 100% and 120%). LIBs were disassembled in an argon-filled glove box, and cathode and anode materials were obtained, separately. The results of the high magnification microscope showed that the color of cathode changed from black to golden gradually with SOC increasing shown in Figure 1. This phenomenon probably resulted from the formation of LiC 6 and lithium metal produced by insertion of lithium ion into cathode carbon layer 2 . From the SEM images, it can be seen that the cathode were getting powdery with an increase in SOC. When SOC was 0%, the XRD result of cathode showed four diffraction peaks, which were at 2θ=25.23 with d=3.52, 2θ=26.40 with d=3.38, 2θ=42.36 with d=2.13 and 2θ=44.50 with d=2.03 respectively. Compared with the XRD standard spectra, they can be ascribed to plane (101), (102), (100) and (101) of LiC 6 and LiC 12 . The diffraction peak intensity of LiC 12 which is produced at the beginning of charge reduced 2 , while the diffraction peak intensity of LiC 6 increased along with the lithium ions intercalating into the graphite. From the DSC results, it can be seen that there were two exothermic peaks for cathode. The first exothermic peak which occurred at ~112 ℃ had no change with SOC increasing for the decomposition of electrolyte and SEI (solid electrolyte interface). The other one occurred at ~280 ℃, and its output heat increased with an increase in SOCs. From the SEM results of anode, it can be seen that an identical shape appeared below SOC=100%, whereas an obvious aggregation could be found in the SOC=120% sample for the lithium ion exchange reaction 2 . From the XRD results, it could be seen that all diffraction peak angles of anode are getting broader and shifting to lower diffraction angle with SOC increasing. This phenomenon suggests that an internal stress is induced by lithium extraction 3 . When SOC was 0%, the DSC results of anode showed that there was one endothermic peak at ~169 ℃ and two exothermic peaks. The two exothermic peaks were at ~289 ℃ and ~347 ℃.The endothermic peak could be ascribed to the melting of LiPF 6 4 . The onset temperature of the two exothermic peaks which are caused by the reactions between oxygen with electrolyte shifted to lower position with an increase in SOC. These reactions become more intense due to the increasing amount of releasing oxygen of anode. Reference: [1]. Inoue T, Mukai K. Roles of positive or negative electrodes in the thermal runaway of lithium-ion batteries: Accelerating rate calorimetry analyses with an all-inclusive microcell [J]. Electrochemistry Communications, 2017, 77: 28-31.. [2]. Hsieh C T, Mo C Y, Chen Y F, et al. Chemical-wet synthesis and electrochemistry of LiNi 1/3 Co 1/3 Mn 1/3 O 2 cathode materials for Li-ion batteries[J]. Electrochimica Acta, 2013, 106: 525-533. [3]. Makimura Y, Sasaki T, Oka H, et al. Studying the Charging Process of a Lithium-Ion Battery toward 10 V by In Situ X-ray Absorption and Diffraction: Lithium Insertion/Extraction with Side Reactions at Positive and Negative Electrodes[J]. Journal of The Electrochemical Society, 2016, 163(7): A1450-A1456. [4]. Yabuuchi N, Makimura Y, Ohzuku T. Solid-State Chemistry and Electrochemistry of LiCo 1/3 Ni 1/3 Mn 1/3 O 2 for Advanced Lithium-Ion Batteries III. Rechargeable Capacity and Cycleability [J]. Journal of the Electrochemical Society, 2007, 154(4): A314-A321. Figure 1
Polydopamine (PDA), inspired by the adhesive mussel foot proteins, is widely applied in chemical, biological, medical, and material science due to its unique surface coating capability and abundant active sites. Energetic materials (EMs) play an essential role in both military and civilian fields as a chemical energy source. Recently, PDA was introduced into EMs for the modification of crystal phase stability and the interfacial bonding effect, and, as a result, to enhance the mechanical, thermal, and safety performances. This mini-review summarizes the representative works in PDA modified EMs from three perspectives. Before that, the self-polymerization mechanisms of dopamine and the methods accelerating this process are briefly presented for consideration of researchers in this field. The future directions and remaining issues of PDA in this field are also discussed at last in this mini-review.
Based on the fact that the double-deck rail demonstrates excellent performance in preventing rails melting and gouging during electromagnetic launch tests, theory and simulation research studies were carried out on the lateral vibration of the double-deck rail and contact properties between the armature and the rail in this paper. We deduced the lateral vibration contact equations of the double-deck rail by simplifying the electromagnetic rail launcher as Bernoulli-Euler model based on the elastic foundation. A finite-element code was used to help us model the launch progress. The influence of the double-deck rail scheme has been analyzed. Both the characteristics of the contact surface between the rail and the armature and the displacement of the rail were considered. The results show that the double-deck rail can inhibit the propagation of bending waves and efficiently reduce rail gouging. Besides, the connection method of the two decks has much influence on this effect.
Porous nano‐aluminum@polymer microspheres with a narrow size range are fabricated to exploit the energy advantages of nano‐aluminum (nAl). Nitrocellulose (NC) and glycidyl azide polymer (GAP) act as functional binders and adhere tightly to the surface of nAl particles and aggregate them into spheres. The formed holes on the microsphere surface are considered gas diffusion channels to the microsphere interior. Confined combustion results show that nAl@GAP microspheres generate the highest peak pressure, and maximum pressurization rate of nAl@NC microspheres is comparatively higher than that of others. Given the microsphere structure, thermal behavior in air shows that the oxidation‐reaction mechanism of the microspheres is close to that of nAl particles. Interfacial reactions between nAl particles and gases produced by polymer decomposition enhance microsphere reactivity. The heat released by polymer decomposition maintains the structure, activates nAl particles, and accelerates combustion propagation, which are positively correlated with the energy content of the polymer. The unconfined test results showed that nAl@GAP microsphere combustion propagates faster than that of nAl@NC microspheres.
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