This paper presents experimental and analytical studies on the characteristic resistance of NI (no-insulation) ReBCO pancake coils, which are used in an equivalent circuit model to characterize 'radial as well as spiral' current paths within the NI coils. We identified turn-to-turn contact resistance as a major source of the characteristic resistance of an NI coil. In order to verify this, three single pancake NI HTS coils-60, 40, 20 turns-were fabricated with their winding tension carefully maintained constant. A sudden discharge test was performed on each coil to obtain its characteristic resistance, and the relation between the turn-to-turn contact and the characteristic resistance was investigated. Based on the characteristic resistance and the n-value model, an equivalent circuit model was proposed to characterize the time-varying response of the NI coils. Charging tests were performed on the three test coils and the experimental results were compared with the simulated ones to validate the proposed approach with the equivalent circuit model.

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An artificial organic/inorganic composite protecting film for lithium metal anode with one-side surface pits structure was prepared by poly­(vinylidene fluoride-co-hexafluoropropylene) and Al2O3+LiNO3 inorganic additives. Due to the unique surface structure, the composite film can not only serve as an artificial protective film, but also act as an additional lithium plating host, which synergistically enabled the lithium metal anode to adapt to high current densities meanwhile maintain dendrite-free during long-term cycling. As a result, the protected lithium metal anode can operate stably for 1000 h at a high current density of 10.0 mA cm–2. When paired with a LiFePO4 or sulfur cathode, the full cells with unflooded electrolyte showed significantly improved cycling performance, demonstrating great potential of this artificial protecting film in lithium metal batteries.

YBCO tapes are expected to be used in future high temperature superconductor (HTS) applications as they have better c characteristics at high temperatures and in high magnetic fields. For power applications such as transmission cables, YBCO tapes and a copper former are connected in parallel and they might be subjected to a short-circuit fault current that is 10 to 30 times the normal operating current. Therefore, the over-current behavior, including the hot-spot and the distribution of transport current between the copper-laminated YBCO tapes and the copper former, is very important to examine the stability and feasibility of the cable. This paper describes the experimental results for over-current pulses of a 1-m single-layer cable fabricated with five copper-laminated YBCO tapes and a copper former. Further, we performed numerical simulations by using a newly developed computer program based on the 3D finite element method.

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