Flexible Lithium-Ion Batteries with High Areal Capacity Enabled by Smart Conductive Textiles.

Introduction Stretchable devices have been highly demanded because of wearable devices in the IoT society. Stretchable lithium ion batteries are crucial to growth of IoT society, since the current developed devices possesses only interface part. The batteries and devices require higher stretchability and robustness to deformation. Liquid metal (LM) is one of the prominent materials for stretchable sensors(1) and wiring circuit(2). In addition, LMs have self-healing characteristics(3) and high capacity (Ga:769 mAh/g, Sn:990 mAh/g) in lithium ion batteries. Here, we investigated the electrochemical characteristics and improvement of robustness using liquid metal nano particles (LMNP) anode in stretchable lithium ion batteries. In this study, stretchable 3D porous LMNP electrodes are fabricated and assembled into stretchable batteries. The stretchable batteries consist of stretchable LMNP and LiFePO4 (LFP) electrodes based on 3D porous polydimethylsiloxane (PDMS)/Ecoflex/Super P carbon composites, stretchable separator, [Li(G4)][TFSI] electrolyte and stretchable package. The batteries have high stretchability and robustness to deformation. Experiment 3D porous PDMS/Ecoflex/Super P carbon composites were used for stretchable electrode substrates. The porous structure was prepared by sacrifice-template method using sugar(4). 3D porous PDMS/Ecoflex/Super P carbon composites was composed of PDMS, Ecoflex with the weight ratio of 6:4 and coating Super P carbon on the surface. LMNP was prepared by ultra-sonication GaSn (Ga:Sn=88:12) alloy. The LMNP alloy was used as active materials of anode. The anode slurries were prepared by mixing the LMNP, Super P carbon, poly(vinylidene fluoride) (PVDF) in N-methyl-2-pyrrolidione (NMP) solvent. LFP was used as active materials of cathode. The cathode slurries consisted of LFP, Super P carbon, PVDF. Stretchable electrodes were fabricated by drop cast method with the electrode slurries on the 3D porous substrates. [Li(G4)][TFSI] was composed of LiTFTI and Tetraethylene glycol dimethyl ether (G4). Stretchable batteries were assembled using the PDMS/Ecoflex/Super P carbon/LMNP anode, PDMS/Ecoflex/Super P carbon/LFP cathode, stretchable separator and stretchable packaging. The nickel/aluminum tabs are attached to PDMS/Ecoflex/Super P carbon/LMNP and PDMS/Ecoflex/Super P carbon/LFP electrode by using small amount of epoxy resin adhesive(Fig. 1). Results and Discussion To investigate the electrochemical characteristics of the stretchable electrode on lithium ion batteries, we respectively conducted galvanostatic tests of the stretchable LMNP anode and the stretchable LFP cathode in half-cell configurations paired with lithium metal as counter and reference electrode. The results show the electrodes can charge/discharge on lithium ion batteries at 1 C. In addition, the electrochemical performance of the stretchable LMNP electrode was investigated. The charge/discharge curves were measured after 100% strain-release cycle 50 and 100 times. The results of the stretchable LMNP electrode showed the capacity retention was higher than the stretchable Si NP (silicone nano particle) electrode. The LMNP used as active materials improve robustness to stretching were confirmed. The full cells were tested using PDMS/Ecoflex/Super P carbon/LMNP and PDMS/Ecoflex/Super P carbon/LFP electrode with charge/discharge measurement. As a result, the full battery could work. Acknowledgement This work was supported by JST CREST Grant Number JPMJCR1905, Japan, by the Japan Science and Technology Agency, PRESTO Grant Number JPMJPR18J2, and by JSPS Grant-in-Aid for Challenging Exploratory Research. References (1) Yuji Gao et al, Advanced. Materials , 2017, 1701985(2) Guangyong Li et al, Sensors and Actuators B , 2015, 221, 1114-1119(3) Yingpeng Wui et al, Energy & Environmental Science , 2017, 10, 1854-1861(4) Hongsen Li et al, Advanced. Materials , 2017, 1700898 Image Figure 1 Self-healing behavior of LMNP (left). Schematic diagram of stretchable battery (right). Figure 1

Olivine-structured lithium iron phosphates are promising cathode materials in the development of high power lithium ion batteries for electric vehicles. However, the low electronic conductivity and ionic conductivity of lithium iron phosphates hinder their commercialization pace. This work aims to verify the approaches for improving the electrochemical properties of lithium iron phosphates. In this work, sol-gel method was used to synthesize carbon coated lithium iron phosphates and nickel doped lithium iron phosphates, and their particle sizes were controlled in the nanometer to sub-micrometer range. The crystalline structures of the synthesized lithium iron phosphates were characterized by X-ray diffraction, and their morphologies were analyzed by scanning electron microscopy. To study their electrochemical properties, prototype lithium ion batteries were assembled with the synthesized lithium iron phosphates as cathode active materials, and with lithium metal discs as the anodes, and the discharge / charge properties and cycling behaviors of the prototype batteries were tested at different rates. The synthesized lithium iron phosphate materials exhibited high capacity and high cycling stability. It was confirmed that particle size reduction, carbon coating and metal doping are three effective approaches for increasing the conductivity of lithium iron phosphates, and thus improving their electrochemical properties. Experimental results show that by combing the three approaches for improving the electrochemical properties, lithium iron phosphate composites with characteristics favorable for their applications in lithium ion batteries for electric vehicles can be developed, including high specific capacity, high rate capacity, flat discharge voltage plateau and high retention ratio.

Hierarchical nano-branched c-Si/SnO2 nanowires for high areal capacity and stable lithium-ion battery

<p indent=0mm>During the past two decades, wearable devices have been broadly used for a variety of fields such as biomedical system, communication and microelectronics. The power system such as lithium-ion batteries is essential to the operation of wearable devices, which should adapt to irregular substrates and sustain complex deformations. A promising strategy is to fabricate high-performance energy storage devices in a fiber shape, e.g., fiber lithium-ion batteries (LIBs). These fiber LIBs with diameters ranging from tens to hundreds of micrometers can be readily integrated with human body and work stably under constant body motions. They can also be woven into breathable fabrics to satisfy the needs of wearable electronics. The key challenges facing fiber LIBs include effective loading of active materials on fiber electrodes, efficient charge transfer along fiber electrodes and interface stability of fiber electrodes under operation and deformation. Fiber electrodes are thus designed with hierarchical and aligned channels to effectively load active materials, so an effective electric field can be established between the fiber cathode and anode. Aligned carbon nanotubes (CNTs) can be made with conductive additives and active materials into fiber electrodes by a continuous spinning process. Conventional metal current collectors, binders and conductive agents are not required, and active materials may reach 90% of the electrode by weight. The resulting hierarchically helical CNT fiber electrode shows high flexibility, high strength, and high electrical conductivity. The flexural rigidity is as low as <sc>10⁻⁷ nN/m²,</sc> which is several orders of magnitude lower than those of ordinary synthetic fibers. The specific strength reaches 10⁷ Nm/kg, which is higher than those of ordinary synthetic fibers. The conductivity reaches <sc>10⁴ S/cm,</sc> which can meet the needs of batteries. The aligned CNT composite fiber permits efficient electron transport, where the electrons hop among neighboring CNTs. Besides, due to the capillary force, the electrolyte can penetrate throughout the entire fiber via micrometer-sized and nanometer-sized channels, benefiting ion transport. The twisted CNT bundles firmly bind active materials and prevent their significant volume variations during charge and discharge processes. Therefore, the efficient conductive pathways can be maintained to deliver both high rate and cyclic stability. Fiber LIBs could be fabricated by assembling two fiber electrodes in parallel, twisting or coaxial structure. Gel electrolyte avoids the potential safety risks stemmed from liquid electrolytes. The continuously fiber LIBs show both high flexibility and energy storage capacity. After bending for 100000 cycles, the capacities have been well maintained, and the energy densities exceed 100 Wh/kg. Based on the similar strategy, a series of fiber energy storage devices such as supercapacitors, lithium-sulfur batteries, lithium-air batteries, zinc-ion batteries, zinc-air batteries and aluminum-air batteries, have been also produced. To summarize, fiber energy storage devices can be woven into flexible fabrics or integrated with energy harvesting devices to satisfy the next-generation electronics. Such a new strategy establishes an efficient avenue to particularly accelerate the development of wearable electronics in the future.

Lithium-ion batteries have been widely used in current numerous devices include laptops, smartphones, medical devices, and electric vehicles. The high specific energy with low maintenance and limited self-discharge characteristics of lithium-ion batteries changed the way of communications and transportations during the last few decades. The current commercial anode material for lithium-ion batteries is graphite because of its well-defined layered structure and good cycling stability with a specific capacity of 372 mAh g-1. But the energy density of graphite is limited and will not likely satisfy the increasing market demand on high capacity batteries. Therefore, it is essential to develop and investigate alternative anode materials.Currently, there is growing interest in using other group IV elements such as silicon (Si), germanium (Ge), tin (Sn) due to their high theoretical capacity. However, the intrinsic volume changes during (de)lithiation processes lead to mechanical pulverization and unstable solid electrolyte interface of the active materials, resulting in delamination and capacity fading issues. To address these problems, fundamental understandings related to the chemical and microstructural evolutions of high capacity anode materials are necessary and beneficial.This dissertation is mainly focused on the chemical and morphological evolutions of Ge, Sn, and gallium liquid metal-based anode materials by using synchrotron-based characterizations including transmission X-ray microscopy (TXM), X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), and computed nanotomography (NanoCT). The main objective is to investigate the morphological and chemical evolutions of the active materials. The impacts caused by particle size and shape variations and the interactions between different particles on the same electrode has been examined and interpreted by employing tin as the anode. Composites containing a high capacity anode and stress accommodating phase is a promising approach to withstand massive strain in the high capacity anode materials. The effect of selenium doping into germanium anode and the formation of the in-situ formed stress accommodation phase have been studied to explain the good cycling and rate capability of selenium-doped germanium comparing to the germanium anode itself. Pulverization and delamination are a major concern which limits the implementation of high capacity anode materials. Combining a liquid metal anode with a solid electrolyte provides a potential strategy to solve cracking problems due to its self-healing ability at room temperature. Cracks formed due to volume expansion can be recovered by the fluidity ofthe liquid metal and the performance of the gallium tin alloy typed anode has been presented. Although the battery system involves a complex structure including electrodes, membrane, electrolyte, etc. The complicated architecture limits the understanding of the material itself. Therefore, it is in need to investigate the active material stand along without interferences caused by other factors. A novel designed single particle schematic has been implemented and interpreted herein which provides insights into the dynamic compositional and morphological characteristics of the selenium-doped germanium anodes under the operational condition that helps understand the outstanding reversibility and cycling performance.

3D printed reticular manganese dioxide cathode with high areal capacity for aqueous zinc ion batteries

With the fast development of diverse electronics, the demand for safe energy storage systems with high energy density and high stability has increased rapidly. So far, lithium-ion batteries (LIBs) have dominated the market, from small smart electronics to electric vehicles. Nevertheless, LIBs have several limitations, such as high cost, limited raw material resources, high flammability, and harsh environmental impact. Therefore, novel rechargeable batteries which can mitigate these shortcomings must be explored. Aqueous zinc-ion batteries (ZIBs) have shown a promising future. Zinc with high theoretical volumetric capacity (5855 mAh cm-3) and high stability in aqueous electrolytes should enable high-performing, safe, and low-cost batteries. Additionally, the simple assembly of ZIBs in the ambient environment results in low capital costs. Despite these attractive merits, developing cathode materials with high capacity, rate performance, and stability in order to build commercial high-performing ZIBs, remains a great challenge.Cathode materials directly influence the electrochemical performance of ZIBs. Manganese oxide (MnO2) has been investigated as a promising cathode in ZIBs research due to its good specific capacity, low cost and high safety. However, the low ionic conductivity, slow diffusion kinetics, and low stability of MnO2 severely deteriorate the electrochemical performance and cycling stability of zinc-ion batteries. Recently, a series of studies have revealed the high effectiveness of coating on improving MnO2 cathode stability, including polymer coatings, carbon-based material coatings, artificial cathode-electrolyte interfaces, and metal oxide coatings.[1] Nevertheless, the improvement of other parameters, such as the rate performance, could be further improved for practical usage. In this research, we develop a novel modification method combining coating and doping strategies to induce MnO2 cathode with high capacity, high rate performance and low capacity decay after long-term operation. First, we utilize a facile one-step hydrothermal synthesis for Ag-doped α-MnO2. Different amounts of AgNO3 are added into reactors with KMnO4 and MnSO4 (n(Ag):n(Mn)=1:100-4:100) to investigate the influence of doping on capacity and rate performance. Subsequently, the doped tunnel-type MnO2 cathodes are mixed with precursor solutions of Al2O3 and then thoroughly stirred. Finally, an annealing process is conducted to achieve a nanoscale Al2O3 coating on the tunnel type MnO2. The coating configurations influence the electrochemical performance of cathodes;[2] thus, we test precursor solutions with different concentrations (1-3 wt% Al2O3) and annealing temperatures (500-700 °C) to investigate the influence of coating thickness and annealing treatment.With the assistance of scanning and transmission electron microscopes, the nanoscale Al2O3 layer coating on the doped active material is verified. The stable Al2O3 coating protects active materials from dissolution and structural collapse, improving cycling stability and resulting in high capacity retention after long-term operation. Moreover, a significant improvement in rate performance compared to unmodified MnO2 is verified through electrochemical tests. The X-ray photoelectron spectroscopy (XPS) and EPR spectra showed that the doped Ag+ ions lead to oxygen vacancies due to the formation of Ag-O-Mn.[3] The abundant vacancies act as active sites, significantly improving conductivity and ion insertion rates. The ex-situ X-ray diffractometer (XRD) and electrochemical tests are used to investigate the ion insertion mechanism during charging/discharging operations. The Ag-MnO2 @ Al2O3 cathode is synthesized through a facile methodology with environment-friendly materials. The modified cathode exhibits promising performance, especially regarding cycling stability and rate performance, which will be a crucial step for developing high-performing cathodes in aqueous zinc-ion batteries.Reference:[1] Shi, W., Lee, W. S. V., & Xue, J. (2021). Recent development of Mn‐based oxides as zinc‐ion battery cathode. ChemSusChem, 14(7), 1634-1658.[2] Zhou, A., Xu, J., Dai, X., Yang, B., Lu, Y., Wang, L., ... & Li, J. (2016). Improved high-voltage and high-temperature electrochemical performances of LiCoO2 cathode by electrode sputter-coating with Li3PO4. Journal of Power Sources, 322, 10-16.[3] Pu, X., Li, X., Wang, L., Maleki Kheimeh Sari, H., Li, J., Xi, Y., ... & Wu, Y. (2022). Enriching Oxygen Vacancy Defects via Ag–O–Mn Bonds for Enhanced Diffusion Kinetics of δ-MnO2 in Zinc-Ion Batteries. ACS Applied Materials & Interfaces, 14(18), 21159-21172. Figure 1

Mesh-like vertical structures enable both high areal capacity and excellent rate capability

Graphitic carbon is extensively used as anode material in most of the commercial lithium-ion batteries due to its low cost and high coulombic efficiency. However, capacity of carbon anode (372mAh/g and 830mAh/mL) is limited by the reversible electrochemical intercalation of lithium ions in its structure. So, alternative research directions and different anode materials are currently being investigated with an aim to achieve high capacity and cycling stability. Recently, nano-material research has shed light on many high performing materials. Among these, metal oxide based materials such as SnO2, MoO2, Co(OH)2 have been recognized as one of the potential candidates for anode material of lithium–ion batteries because of its higher specific lithium storage capacity [1, 2, 3]. But, their poor capacity retention over long-term charge-discharge cycling due to low electrical conductivity has prevented its use as commercial anode material in lithium-ion batteries. Furthermore, during the electrochemical cycling, metal oxides typically break into small metal clusters, resulting in a large volume expansion and a loss of capacity [4]. For improving the performance of metal oxide based materials, nanostructured materials have received much attention as battery electrodes due to the short transport lengths for both electrons and Li ions, higher electrode-electrode contact area, and better accommodation of the strain of Li insertion/extraction [5]. Although there have been reports in the electrochemical behavior and performance improvement on metal oxide based anode materials for lithium ion batteries, it is still difficult to prove the reaction mechanism and abnormal capacity clearly. For accurate explanation of reaction mechanism and abnormal capacity, it is important to analyze each region systematically. Herein, we successfully synthesized nano-structured metal oxide materials through simple synthetic strategy. This research also included its novel reaction mechanism during electrochemical cycling with lithium. Structure and electrochemical properties of synthesized material were studied by diverse electrochemical tests, combination of the synchrotron radiation XRD and XAS techniques. Especially, the changes in the local structures during cycling were investigated systematically on the basis of XAS analysis. Based on these results, novel reaction mechanism about the nano-structured metal oxide based anode material during electrochemical cycling was suggested specifically. This finding will not only be helpful in a more complete understanding of the reaction mechanism of metal oxide based anode materials but also will offer valuable guidance for developing new anode materials with abnormal high capacity for next generation rechargeable batteries. More detailed discussion will be presented at the time of meeting. [1]. Dong, Q et al., Materials Research Bulletin, 2011. 46(8): p. 1156-1162. [2]. I. A. Courtney and J. R. Dahn, J. Electrochem. Soc., 1997, 144, 2045 [3]. Wang, Z. Y et al., Chem. Commun. 2010, 46, 6906−6908 [4]. Poizot, P et al., Nature 2000, 407, 496−499 [5]. Maier, J et al., Nat. Mater. 2005, 4, 805−815.

All-solid-state batteries using sulfide-based solid electrolytes with high lithium-ion conductivity equivalent to that of organic electrolyte solution are attracting attention as a next-generation battery with excellent safety. The sulfide-based all-solid-state batteries are especially expected to be used as a power source for electric vehicles, and high-capacity batteries are needed to realize such applications. Increasing in the areal capacity of the electrode by increasing the thickness of the electrode is one of the effective approaches to increasing the capacity of the batteries. Coating metal foils with slurry containing binders used in the fabrication of electrodes for the conventional electrolyte-solution-based lithium-ion batteries is effective for mass production processes, but it causes cracking and delamination in the coating layer when the electrode is made too thick. In addition, the addition of binder to the slurry increases the internal resistance of the battery resulting in lower battery performance. In this study, we developed a fabrication technique for the binder-free and a high areal capacity electrode by vacuum filtration of a slurry containing carbon nanotubes (CNTs) in order to realize high-capacity sulfide-based all-solid-state batteries, and evaluated the charge-discharge performance of the cell. Lithium nickel cobalt manganese oxide (LiNi0.5Co0.2Mn0.3O2, NCM) and artificial graphite (Gr) were used as active materials for the cathode and anode, respectively, and a slurry was prepared by mixing them with an argyrodite-type sulfide solid electrolyte (SE, A-SOLiD®, Mitsui Mining & Smelting Co., Ltd.) and CNTs. The slurry was vacuum filtered and then vacuum dried to obtain cathode and anode. The NCM cathode with a high areal capacity of 4 mAh cm-2 without cracking was obtained by vacuum filtration of the CNT-containing slurry, although it contained no binder. As with the cathode, the Gr anode was also crack-free and had a high areal capacity of 5 mAh cm-2. The NCM cathode and Gr anode thus obtained and the solid electrolyte sheets prepared using the argyrodite-type sulfide solid electrolyte were punched to 13 mm and 14 mm diameters, respectively. A full cell of NCM cathode/SE sheet/Gr anode was fabricated by pressing these staked materials, and the cell performance was evaluated in a coin cell (CR2032 type). The full-cell consisting of NCM cathode and Gr anode prepared by vacuum filtration of CNT-containing slurry showed a stable cycling performance of over 50 cycles.

3D-printed hierarchical porous and multidimensional conductive network based on conducting polymer/graphene oxide

Significant efforts continue to be directed toward the construction of anode materials with high specific capacity and long cycling stability for lithium-ion batteries (LIBs). In this context, silicon is preferred due to its high capacity even though it has a problem of excessive volume expansion during electrochemical reactions as well as poor cyclability due to a reduction in conductivity. Hence, the hybridization of silicon with suitable materials could be a promising approach to overcome the abovementioned problems. Herein, we demonstrate the uniform decoration of nickel oxide (NiO) nanoparticles (15–20 nm) on silicon nanosheets using bis(cyclopentadienyl) nickel(ii) (C10H10Ni) at low temperatures, taking advantage of the presence of two unpaired electrons in an antibonding orbital in the cyclopentadienyl group. The formation and growth mechanism are discussed in detail. The electrochemical study of the nanocomposite revealed an initial delithiation capacity of 2507 mA h g−1 with a reversible capacity of 2162 mA h g−1, having 86% retention and better cycling stability for up to 500 cycles. At the optimum concentration, NiO nanoparticles facilitate Li+-ion adsorption, which in turn accelerates the transport of Li+-ions to active sites of silicon. The Warburg coefficient and Li+-ion diffusion at the electrodes confirm the enhancement in the charge transfer process at the electrode/electrolyte interface with NiO nanoparticles. Further, the NiO nanoparticles with uniform distribution suppress the agglomeration of Si nanosheets and provide sufficient space to accommodate a volume change in Si during cycling, which also reduces the diffusion path length of the Li-ions. It also helps to strengthen the mechanical stability, which might be helpful in preventing the cracking of silicon due to volume expansion and maintains the Li-ion transport pathway of the active material, resulting in enhanced cycling stability. Due to the synergic effect between NiO nanoparticles and Si sheets, the nanocomposite delivers high reversible capacity.

Lithium iron phosphate (LFP) is widely used as an active material in a cathode electrode for lithium-ion batteries (LIBs). LFP has many remarkable properties such as high working voltage and excellent thermal stability. However, it suffers with slow ion diffusion and low electrical conductivity. Graphene foam has many outstanding properties such as large surface area and great electrical conductivity. These properties are suitable for improving the cathode electrode. In this work, the graphene foam was synthesized by chemical vapor deposition. The cathode electrode was prepared by dropping the LFP on the graphene foam. We found that the specific capacity of battery which contained the LFP between the anode and the graphene foam (LFP/GF) was 23.1 mAh⸳g-1 at 3C, while the specific capacity of battery which contained the graphene foam between the anode and the LFP (GF/LFP) was 112.6 mAh⸳g-1 at 3C. The diffusion coefficients of Li+ of GF/LFP was 9.1 times higher than that of LFP/GF. The specific capacity of GF/LFP was higher than that of LFP/GF at high current density due to the high ion transfer rate which arises from the graphene foam.

Here, we report 3D hierarchical SnO2 nanowire (NW) core-amorphous silicon shell on free-standing carbon nanotube paper (SnO2@a-Si/CNT paper) as an effective anode for flexible lithium-ion battery (LIB) application. This binder-free electrode exhibits a high initial discharge capacity of 3020 mAh g−1 with a large reversible charge capacity of 1250 mAh g−1 at a current density of 250 mA g−1. Compared to other SnO2 NW or its core–shell nanostructured anodes, the fabricated SnO2@a-Si/CNT structure demonstrates an outstanding performance with high mass loading (∼5.9 mg cm−2), high areal capacity (∼5.2 mAh cm−2), and large volumetric capacity (∼1750 mAh cm−3) after 25 cycles. Due to the incorporation of CNT paper as the current collector, the weight and thickness of the total electrode is effectively reduced with respect to the conventional LIB anodes. The fabricated electrode has a total thickness of only 30 μm and considering the total weight of the electrode (active mass + current collector), an initial discharge/charge capacity of 2460/1018 mAh g−1 is obtained. Hence, this thin, lightweight and highly flexible structure is proposed as an excellent candidate for high-performance LIB anode materials, especially in flexible electronics.

Ultra-thick porous films of graphene-encapsulated silicon nanoparticles as flexible anodes for lithium ion batteries