In today's fast‐paced environment, the downsizing of electronic devices has become imperative. A high driving frequency is effective for the downsizing of electronic equipment. However, one problem with high driving frequency is that it increases the ac resistance and heat generation on passive devices. Using a magnetic coating on the copper wire can effectively reduce the ac resistance. In this study, we propose a method for wrapping a magnetic tape around a copper wire to easily provide a uniform magnetic coating for reducing the ac resistance. In the magnetic field simulation, we reduced the proximity effect in the coil by using a magnetic tape. The temperature rise at the thermal saturation was reduced by 26% for the experiment with a high‐frequency current of 4 A. Applying the magnetic tape to a single‐wire coil effectively reduced the ac resistance and heat generation. © 2020 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Introduction Lead Acid Batteries (LAB) are used in various fields, due to its low cost and excellent recyclability. Conventionally, LAB cannot be recharged after over-discharged and its performance is greatly declined. We have found that the above deterioration is causedby the formation of α-PbO2 on the surface of cathode active material β-PbO2 due to the reduction by local cell reaction between β-PbO2 and lead current collector. We also have revealed that the formation of α-PbO2 can be prevented by using gold instead of lead as current collector. In this case, the LAB can be recharged even after either discharging to 0 V or discharging to 0 V followed by 48 h open circuit [1,2]. In the case of carbon, electrode potential does not come out, so we thought that carbon has a role of stopping local cell reaction. We revealed that the LAB using graphite sheet with 5wt% polypropylene as current collector has high resistance to over-discharge [3,4,5]. This LAB can charge-discharge without performance degradation even after full discharge followed by 48 h rest period. In this study, we fabricated composite cathode composed of β-PbO2 as active material and expanded graphite as current collector, in order to get higher performance and ease of fabrication. We investigated performance of the LAB using the composite cathode. Experiment We made various kind of the composite cathode composed of β-PbO2 of 0.18-3.6 g, expanded graphite of 1.8 g and polypropylene of 0.09 g by a pressure molding. We conducted charge-discharge experiments by using the composite cathode. We used two-electrode glass cell for charge-discharge experiments. We used 35 % H2SO4 as electrolyte and lead plate as anode. Composite cathode was processed to 40 mm × 14 mm and the area immersed in sulfuric acid was 10 mm × 14 mm. As the stabilization cycle, we repeated discharge at 0.25 mA for 30 min and charge at 2 mA for 20 min for 20 times, then we conducted charge discharge experiment. Results and discussion After the stabilization cycle, we discharged LAB deep to 0 V and opened the circuit for 48 h, then we resumed charge-discharge cycle. Figure 1(a) shows the charge-discharge characteristics of conventional type LAB using lead plate cathode current collector. Conventional type LAB could not resume charge-discharge cycle after full discharge followed by48 h open circuit. Figure 1(b) shows the case of the LAB using composite cathode. It is indicated that the LAB can resume charge-discharge cycle even after full discharge followed by 48 h open circuit. It is confirmed that the composite cathode made the LAB so durable to over-discharge. Figure 2 shows detailed discharge curve of the LAB using the composite cathode composed of β-PbO2 of 3.6 g, expanded graphite of 1.8 g and polypropylene of 0.09 g. Weight composition of β-PbO2 in this composite cathode is about 65%. The charge rate was 2 mA, and the discharge rate was 0.1 mA, respectively. The flat discharge potential around at 1.6 V was observed. This means that the LAB using the composite cathode has excellent practical performance. It was indicated that the composite cathode made the LAB not only very durable in over discharge but also highly practical for use. Reference [1] T.Iwai, D.Kitajima, S.Takai, T.Yabutsuka and T.Yao, J. Electrochem. Soc. Vol 163, Issue 14, A3087-A3090 (2016) [2] T.Iwai, M.Murakami, S.Takai, T.Yabutsuka and T.Yao, Journal of Alloys and Compounds, Vol 780, 85-89 (2019) [3] T.Yao, H.Okano, T.Iwai, S.Takai, T.Yabutsuka, T.Hosokawa, N.Misaki, K.Kurihara “Positive Electrode for Lead Storage Battery and Lead Storage Battery Using Same” PCT/JP2018/005947 [4] Y.Nakamura, T.Ohkubo, H.Okano, T.Inoue, T.Hosokawa, A.Takeda, T.Iwai, T.Yabutsuka, S.takai and T.Yao, 235th ECS Meeting. Soc. Z01-2143 (2019) [5] Y.Hano, H.Okano, T.Inoue, T. Hosokawa, A.Takeda, T.Iwai, T.Yabutsuka, S.Takai, and T. Yao, PRIME 2020. Soc. Z01-3448 (2020) Figure 1

Introduction Lead Acid Batteries (LAB) are used in various fields, due to its low cost, high safety and excellent recyclability. Conventionally, LAB cannot be recharged after over-discharged and its performance is greatly declined. We have found that the above deterioration is caused by the formation of α-PbO2 on the surface of cathode active material β-PbO2 due to the reduction by local cell reaction between β-PbO2 and lead current collector. We also have revealed that the formation of α-PbO2 can be prevented by using gold instead of lead as current collector. In this case, the LAB can be recharged even after either discharging to 0 V or discharging to 0 V followed by 48 h open circuit [1,2]. In the case of carbon, electrode potential does not come out, so we thought that carbon has a role of stopping local cell reaction. We revealed that the LAB using graphite sheet with 5wt% polypropylene as current collector has high resistance to over-discharge [3,4]. This LAB can charge-discharge without performance degradation even after full discharge followed by 48 h rest period.We fabricated composite cathode composed of β-PbO2 as active material and expanded graphite adding 5wt% polypropylene as current collector, in order to have higher performance and ease of fabrication. It was found that the LAB using composite cathode can also be recharged even after full discharge followed by 48 h rest period. High resistance to over-discharge was indicated. Also the discharge characteristics of the LAB using the composite cathode improved, when the content of β-PbO2 was increased. The composite cathode made the LAB not only very durable in over discharge but also highly practical for use [5]. In this study, we fabricated the composite cathode of various thickness and investigated the effect of thickness on the LAB performance. Experiment We made the composite cathode with various thickness composed of expanded graphite, polypropylene 0.05 times the weight to expanded graphite and β-PbO2 1.0 times the weight to expanded graphite by a pressure molding. We used 35 % H2SO4 as electrolyte and lead plate as anode. The composite cathode was processed to 40 mm × 14 mm and the area immersed in sulfuric acid was 10 mm × 14 mm. We conducted charge-discharge experiments by using the LAB constructed as above mentioned. As the stabilization cycle, we repeated discharge at 0.25 mA for 30 min and charge at 2 mA for 20 min for 20 times, then we conducted charge discharge experiment. Results and discussion After the stabilization cycle, we discharged the LAB deep to 0 V and opened the circuit for 48 h, then we resumed charge-discharge cycle. Figure1(a) shows the charge-discharge characteristics of conventional type LAB using lead plate cathode current collector. Conventional type LAB could not resume charge-discharge cycle after full discharge followed by48 h open circuit. Figure1(b) shows the case of the LAB using composite cathode with 1.0 mm thickness. It was indicated that the LAB could resume charge-discharge cycle even after full discharge ...

Lead acid battery has been one of the most important battery for industry use. However, conventional lead acid battery cannot be recharged after over discharge and the performance is greatly declined. It has been revealed that the cause of not being able to be recharged is the formation of α‐PbO2 on the surface of β‐PbO2 cathode active material due to local cell reaction between lead current collector and β‐PbO2. Formation of α‐PbO2 is prevented by using gold as the current collector. In this study, we developed the lead acid battery with high resistance to over discharge using graphite materials as current collector. The formation of α‐PbO2 was prevented by using expanded natural graphite sheet as cathode current collector. The lead acid battery with current collector of expanded natural graphite sheet containing 5% polypropylene (PP) can repeat deep charge and discharge between 0 and 2 V for more than about 6 months and showed flat potential area between 1.9 and 1.3 V for every cycle. Furthermore, this battery can be charged again after over discharge for more than 4 month at the open circuit. We have succeeded to develop high performance lead acid battery.

Introduction Conventionally, Lead Acid Battery (LAB) cannot be recharged after over-discharge and its performance is greatly degraded. We have revealed that the above deterioration is caused by the formation of α-PbO2 on the surface of cathode active material β-PbO2 due to the reduction by local cell reaction between β-PbO2 and lead current collector. We revealed that the formation of α-PbO2 can be prevented by using gold instead of lead as cathode current collector and that this operation made the LAB rechargeable even after over-discharge [1,2]. We have also revealed that the LAB using graphite sheet as a current collector can charge-discharge even the circuit is opened for 48 h after over-discharge to 0V [3]. Especially in the improvement of tensile strength and discharge potential, it is concluded that 5wt% polypropylene addition to raw graphite sheet is most suitable for use as a cathode current collector in our previous study [4]. In this study, for practical use of this type of LAB, we investigated its characteristics, in particular the relationship between discharge energy and charge voltage. Experiment We used two-electrode glass cell for charge-discharge experiments. The cathode slurry was prepared by mixing β-PbO2 powder as active material, acetylene black as conductive additive and polyvinylidene fluoride as binder at the ratio of 8:1:1 in weight with solvent of N-methyl-pyrrolidone. We used graphite composite sheet with 5wt% polypropylene mixed for cathode current collector. We constructed the cathode by applying the cathode slurry to the current collector. We used 35% H2SO4 as electrolyte and lead plate as anode. As the stabilization cycle, we repeated discharge at 45μA cm2 -1 for 30 min and charge at 0.9 mA cm2 -1 for 20 min for 20 times, then we conducted charge discharge experiment. We determined charge-discharge rate using the coating area of cathode active material. Results and discussion Figure 1 shows the typical charge/discharge curve between 0 V and 2 V of the LAB using graphite sheet with 5wt% polypropylene as cathode current collector at about 1C discharge. It was confirmed that this LAB could be discharged to 0V and that showed flat discharge potential around between 2V and 0.7V. We charged this LAB to various potential and discharged to 0V. We calculated the discharge energy by the integral of the obtained discharge curve from each charge potential to 0.7V. Figure 2 shows discharge energy ratio at 2.0V, 1.8V, 1.6V and 1.4V charge voltage to discharge energy at 2.0V charge voltage. Discharge energy increased with charge voltage. It was found that this LAB using graphite composite sheet with 5wt% polypropylene mixed for cathode current collector could recover more than 50% of discharge energy obtained at 2.0V charge by charging to 1.8V. References [1] T. Iwai, D. Kitajima, S. Takai, T. Yabutsuka and T. Yao, J. Electrochem. Soc. Vol 163, Issue 14, A3087-A3090 (2016) [2] T. Iwai, M. Murakami, S. Takai, T. Yabutsuka and T. Yao, Journal of Alloys and Compounds, Vol 780, 85-89 (2019) [3] T. Yao, H. Okano, T. Iwai, S. Takai, T. Yabutsuka, T. Hosokawa, N. Misaki, K. Kurihara “Positive Electrode for Lead Storage Battery and Lead Storage Battery Using Same” PCT/JP2018/005947 [4] Y. Hano, H. Okano, T. Inoue, T. Hosokawa, A. Takeda, T. Iwai, T. Yabutsuka, S. Takai and T. Yao, 238th Electrothem. Soc. Z01-3448 (2020) Figure 1