ЛИТИРОВАНИЕ ЭЛЕКТРООСАЖДЕННЫХ ПЛЕНОК КРЕМНИЯ

Ti, F Codoped Sodium Manganate of Layered P2-Na _0.7 MnO _2.05 Cathode for High Capacity and Long-Life Sodium-Ion Battery

Lithium-Air Battery (LAB) is believed to be an ultimate secondary battery due to its much high potential capacity, predicted to have 5-10 times larger capacity than that of conventional lithium ion battery (LIB). As the practical properties of LAB cell are dominated largely by air electrode, developing efficient air electrode is a key challenge for realizing commercially viable LAB cell. At the surface of air electrode, cycle deposition/decomposition of discharge product occurs during discharge/charge cycle. As a result, air electrode in LAB cell experiences great volume expansion and contraction, especially at high capacity cycle beyond LIB. The air electrodes comprised of powdery carbons are often reported they are not tolerate to such large volume change. In contrast, CNT can be a promising material for air electrode toward high capacity LAB cell, maintaining conductive network within the material in the face of volume change at high capacity cycle. In order to bringing out the high energy density nature of LAB, it is important to study the behavior of CNT air electrode during the discharge/charge cycle. Here in this study, we investigated how large cell capacity can be attained in LAB coin cell using CNT sheet air electrode and observed the morphological change after the battery operation. Two types of CNT sheets, CNT-IPA and CNT-NMP, were prepared in several thicknesses by vacuum filtration of single-walled CNT (e-DIPS, 2 nm diameter) ultrasonically-dispersed in isopropanol (IPA) and N-methylpyrrolidone (NMP), respectively. SEM observation revealed the sheets are composed of CNT bundles of averaged diameter of 52 nm and 145 nm for CNT-IPA and CNT-NMP, respectively. The sheets were evaluated the performance as air electrode of LAB under flowing oxygen gas, using CR2032 coin cell that comprised the layers of lithium metal anode (j16 mm, 0.2 mm thick), GF/A glass-fiber separator, and the CNT sheet cut into j16 mm. The electrolyte was composed of 1 M LiTFSI in tetraethylene glycol dimethyl ether (TEGDME) with water content less than 10 ppm. The cells were disassembled after the discharge/charge test to analyze the morphological change of the CNT sheet and discharge product by electron microscopy (SEM, TEM) and x-ray diffraction (XRD). Both CNT sheets worked as air electrode, showing 2.65 V discharge voltage and 4.20 V charge voltage at 0.1 mA discharge current in a limited cycle capacity of 1.0 mAh. Figure 1 shows the discharge capacity each cell achieved (2.0 V cut) plotted against the weight of sheets. The graph shows the considerable variation of discharge capacities per cell, however, the highest discharge capacity with CNT-IPA air electrode at each weight increased along with the weight of the sheet (5000 mAh/gCNT), attaining a maximum capacity of 24 mAh per cell with a CNT-IPA sheet of 5 mg (54 μm thick). This achieved capacity corresponds to the capacity per unit area of 12 mAh/cm2, which is ~5 times higher than that of conventional LIB. It was also confirmed that even from such deeply discharged state the cells were able to be fully charged with charge voltage below 4.5 V. Corresponding to the discharge/charge cycle, SEM observation revealed a reversible swelling/contraction behavior of the sheets. Figure 2 shows the XRD patterns of CNT-IPA after discharge test. The sheet increased its intensity of the peaks attributed to the lithium peroxide Li2O2 diffraction along with the discharge capacity, suggesting a deposition of Li2O2 on CNT surface as a discharge product. The discharge product had toroid shape with a diameter of ~100 nm and the toroidal particle increased its number of pieces through the discharge process, as can be seen in Figure 3 that shows SEM images of the CNT-IPA before and after discharge ((a)~(e)). In addition to the toroid deposit, TEM observation of the CNT-IPA after discharge also revealed a presence of thin skin deposit (< 5 nm) around CNT bundles. After the full charge from those discharged states, however, those deposits were disappeared and the sheet almost recovered in terms of the SEM (Figure 3 (f)) and TEM appearances. Compared to the air electrode behavior of CNT-IPA, the discharge capacity of coin cells with CNT-NMP air electrodes did not increase, showing discharge capacity of 1.0 mAh for almost all of cells regardless of the sheet weight. We will reveal the capacity difference from their nanostructures and discuss the effective design of CNT sheet for developing high performance air electrode. Figure 1

Carbon has been used as stable anode material for lithium-ion secondary batteries. However, instead of graphite with a low capacity, a new material with a high capacity that can increase the energy density per volume or mass of a lithium ion secondary battery is required. Among the various candidates, silicon has a high capacity of about 4000 mAh/g, making it a major research subject. Graphite is a combination of 6 carbon atoms and 1 lithium ion, but silicon accepts 4.4 lithium ions per atom, resulting in high volume expansion. In this way, excessive volume expansion causes cracks in the electrode and electrochemical disconnection, which eventually leads to a decrease in battery capacity. The large volume change and low electrical conductivity of silicon limits its application to anodes. Potential silicon-based materials include silicon oxide-based (SiOx), carbon-silicon composite (SiC), and pure silicon (pure Si). Silicon-based oxides have the advantages of high capacity and stable battery life, but have the limitations of low initial efficiency and low electrical conductivity. Carbon-composite silicon has high initial efficiency, high ionic conductivity, high capacity, and can be applied in the same slurry system as existing graphite electrodes. Selection of a stable binder and conductive material is important for active use of silicon-based materials. Promising binders include polyvinyl alcohol (PVA), polyacrylic acid (PAA), and polyacrylamide (PAM), and conductive materials include single-walled carbon nano tube (SWCNT), multi-walled carbon nano tube (MWCNT), and carbon-based conductive materials. In this study, we applied poly(vinyl alcohol-co-acrylic acid) random copolymer polymer as a binder and analyzed the characteristics of silicon-based batteries with various conductive materials. Slurry analyzes such as slurry dispersibility, phase stability, and rheology were performed. The initial efficiencies and cycle performances of different types of silicon-based materials were compared. It was confirmed that the type of silicon-based negative electrode material and the type of conductive material affect battery performance.

Exploring Advanced Polymeric Binders and Solid Electrolytes for Energy Storage Devices

Li-O2 battery is one of the possible candidates for future energy devices and has attracted much attention in the beyond lithium ion battery research field.1-3 Despite its specific high energy capacity, many obstructions, including lower capacity, impede their use for practical applications. In typical Li-O2 batteries, Li metal and carbon were applied as the anode and the cathode materials, respectively, and the Li2O2 is formed as the discharge product and deposited on the cathode. As Li2O2 shows inherent low electron conductivity,4,5 once the positive electrode was fully covered with the deposition, it inhibits the continuous discharging and then the discharge potential is suddenly dropped. Several strategies such as control of the solubility of LiO2, which is an intermediate in the discharge reaction, have been studied with interest for sustainable discharge. It is known that Donor Number (DN), the indicator of Lewis basicity of solvents, highly influences on the solubility of LiO2.6 The electrolytes with higher DN solvents enhance the discharge capacity of Li-O2 batteries, because solubility of LiO2 is increased and Li2O2 is formed in the solution (solution pathway). In contrast, Li2O2 is formed on the cathode surface in solvents of lower DN (surface pathway). The effect of additives in solvents on enhancing the solubility of LiO2 was also reported,7-9 however, the understanding of the underlying principles that determine the discharge capacity is still limited. Herein we present an alternative indicator to DN that controls the discharge capacity in the Li-O2 batteries. We focused on the effect of the range of combinations of cathode substrates and electrolytes on the discharge capacity. When we used Au-mesh as cathode, higher discharge capacity was obtained in a higher DN of dimethyl sulfoxide (DMSO) electrolytes (LiTFSI in DMSO) than that obtained in a lower DN of acetonitrile (MeCN) electrolyte, as reported previously.6 However, interestingly, higher capacity was obtained in the MeCN electrolytes when a carbon material was applied as the cathode. Through these experiments, we also found that the negative differential resistance (NDR), which appears when the coverage of the inhibitor on the electrode depends on the potential of the electrode, is a critical indicator determining the discharge capacity of Li-O2 batteries. The NDR in the oxygen reduction reaction (ORR) potential region implies that LiO2 works as an inhibitor of ORR. The higher discharge capacity can be obtained when the ORR proceeds at higher potential than NDR region, because LiO2 is desorbed from the electrode and the solution pathway is promoted. Our results indicate that this correlation between the NDR and the discharge capacity is generally applied to Li-O2 battery system. 1) Abraham, K.M. et. al. J. Electrochem. Soc. 143, 1-5 (1996).2) Ogasawara, T. et. al. J. Am. Chem. Soc. 128, 1390-1393 (2006).3) Luntz, A.C. & McCloskey, B.D. Chem. Rev. 114, 11721-11750 (2014).4) Viswanathan, V. et al. J. Chem. Phys. 135, 214704 (2011).5) Luntz, A.C. et al. J. Phys. Chem. Lett. 4, 3494-3499 (2013).6) Johnson, L. et al. Nat. Chem. 6, 1091-1099 (2014).7) Aetukuri, N.B. et al. Nat. Chem. 7, 50-56 (2015).8) Burke, C.M. et. al. PNAS 112, 9293-9298 (2015).9) Matsuda, S., Uosaki, K. & Nakanishi, S. J. Power Sources 356, 12-17 (2017).

The Ge-based compounds show great potential as replacements for traditional graphite anode in lithium-ion batteries (LIBs). However, large volume changes and low conductivity of such materials result in a poor electrochemical cycling and rate performance. Herein, we fabricate a self-supported and three-dimensional (3D) sponge-like structure of interlinked Zn2GeO4 ultrathin nanosheets anchored vertically on a nickel foam (ZGO NSs@NF) via a simple hydrothermal process assisted by cetyltrimethyl ammonium bromide (CTAB). Such robust self-supported hybrid structures greatly improve the structural tolerance of the active materials and accommodate the volume variation that occurs during repeated electrochemical cycling. As expected, the self-supported ZGO NSs@NF composites demonstrate an excellent lithium storage with a high discharge capacity, a long cycling life, and a good rate capability when used as binder-free anodes for LIBs. A high reversible discharge capacity of 794 mA h g-1 is maintained after 500 cycles at 200 mA g-1, corresponding to 81% capacity retention of the second cycle. Further evaluation at a higher current density (2 A g-1) also delivers a reversible discharge capacity (537 mA h g-1) for this binder-free anode. This novel 3D structure of the self-supported ultrathin nanosheets on a conductive substrate, with its volume buffer effect and good interfacial contacts, can stimulate the progress of other energy-efficient technologies.

Development in high-rate electrode materials capable of storing vast amounts of charge in a short duration to decrease charging time and increase power in lithium-ion batteries is an important challenge to address. Here, we introduce a synthesis strategy with a series of composition-controlled NMC cathodes, including LiNi0.2Mn0.6Co0.2O2(NMC262), LiNi0.3Mn0.5Co0.2O2(NMC352), and LiNi0.4Mn0.4Co0.2O2(NMC442). A very high-rate performance was achieved for Mn-rich LiNi0.2Mn0.6Co0.2O2 (NMC262). It has a very high initial discharge capacity of 285 mAh g−1 when charged to 4.7 V at a current of 20 mA g−1 and retains the capacity of 201 mAh g−1 after 100 cycles. It also exhibits an excellent rate capability of 138, and 114 mAh g−1 even at rates of 10 and 15 C (1 C = 240 mA g−1). The high discharge capacities and excellent rate capabilities of Mn-rich LiNi0.2Mn0.6Co0.2O2 cathodes could be ascribed to their structural stability, controlled particle size, high surface area, and suppressed phase transformation from layered to spinel phases, due to low cation mixing and the higher oxidation state of manganese. The cathodic and anodic diffusion coefficient of the NMC262 electrode was determined to be around 4.76 × 10−10 cm2 s−1 and 2.1 × 10−10 cm2 s−1, respectively.

Lithium-oxygen (Li-O2) batteries are among the most prominent alternative battery chemistries to lithium-ion batteries with their high theoretical capacities. However, attaining their high theoretical capacity is difficult due to the poor cell design and insufficient cell materials. In this study, machine learning algorithms are used to determine the effective cell design factors and the most promising materials for reaching high discharge capacities and voltages. Association rule mining (ARM) and decision tree (DT) algorithms show that bulk cathode materials, especially N-doped carbons, graphene and porous carbons, are beneficial for achieving high performances. Moreover, ARM analysis indicates that cathode ingredients, namely LaFe oxides and Ni oxides, should be utilized for high discharge capacities. In addition, the choice of the electrolyte solvent seems to be highly influential on the discharge capacities. Dimethyl sulfoxide (DMSO) is shown to be one of the best options for high cell voltages and discharge capacities.

Development of advanced energy-storage systems needs to consider a balance among cost, cycle life, safety, energy, power, and environmental benignity. With these requirements, lithium-sulfur (Li-S) and sodium-sulfur (Na-S) batteries are promising candidates as next-generation energy-storage systems because of the high charge-storage capacity, natural abundance, and environmental friendliness of sulfur. However, the practical utility of Li-S and Na-S cells is hampered by the low electrochemical utilization of sulfur and severe polysulfide diffusion from the cathode to the anode. These drawbacks result in low discharge capacity and poor cycle life. The Li-S and Na-S battery chemistries have several scientific challenges in common. The degradation of both the anode and cathode active materials, as well as the decomposition of the liquid electrolyte, causes a fast capacity fade and low electrochemical utilization of the active material. Unfortunately, the efforts to overcome the persistent problems often result in the incorporation of excessive conductive carbon into the electrode and low sulfur loading per unit area. In fact, it is often easy in the literature to obtain greatly improved performance by using either low sulfur content, low sulfur loading, or low sulfur mass in a cathode. The use of low-sulfur-loading cathodes can defeat the energy-density advantage of sulfur cathodes and the purpose of Li-S and Na-S cells replacing the current lithium-ion technology. Moreover, the traditional cathode configuration borrowed from the commercial insertion-compound cathodes may not allow the pure sulfur cathode to put its unique materials chemistry to good use due to the very different battery chemistries between the solid insertion-compound oxide cathodes and the electrochemical conversion-reaction sulfur cathodes. Recognizing the importance of operating the Li-S and Na-S cells with high-sulfur-loading cathodes for being competitive with the existing lithium-ion technology, this presentation will focus on unique approaches in engineering the sulfur cathodes with high-sulfur loadings and employing solid electrolytes. The cathode engineering presented can lead the way towards employing high-loading cathodes with promising cell performance while the easily-prepared pure sulfur powders are utilized as the active material. The first high-capacity cathode engineering involves a layer-by-layer strategy. This method confines sulfur powders between porous carbon nanofiber (PCN) multi-layers. The layer-by-layer cathode facilitates fast ion and electron transport and traps the soluble polysulfide intermediates within the multilayered electrode configuration. A single-sulfur-layer cathode coupled with two-PCN layers offers a high discharge capacity of 1265 mAh g-1 at C/5 rate with good cyclability. The cathode engineering further facilitates high areal sulfur loading by increasing the number of sulfur layers. For example, a six-sulfur-layer cathode attains a high areal sulfur loading of 11.4 mg cm-2. The high-sulfur-loading cathode delivers a high initial discharge capacity of 995 mA h g-1 at C/10 rate with a corresponding areal capacity of 11.3 mA h cm-2. The second high-capacity cathode engineering involves an edge-encapsulation method. An omurice-type cathode consists of a light-weight multiwall carbon nanotube (MWCNT) thin-film as the omelette cover and the active-material filling as the fried rice. The active-material paste is first dropped onto an aluminum-foil current collector and then covered by the MWCNT thin-film, followed by pressing the edge of the electrode for the favorable edge-encapsulation of the sulfur core. As a result, the polysulfide migration is stabilized within the structural cathode due to the strong tortuosity of MWCNT layer and the edge-encapsulated cathode configuration, benefiting the capacity retention. The omurice-type cathodes exhibit a high discharge capacity (1190 mAh g-1), a long lifespan (500 cycles), and low capacity fade (0.08 % cycle-1). In addition, the structural cathodes with a good balance among high sulfur loading (4.2 – 10.0 mg cm-2), high sulfur content (50 – 60 wt. %), and high sulfur mass (4.2 – 10.0 mg cathode-1) are able to attain a high areal capacity (5.1 – 7.8 mAh cm-2). In addition, polysulfide-trapping interlayers, multi-functional separators, and solid electrolyte membranes developed in our group are integrated with the above advanced structural cathodes for suppressing polysulfide migration and alkali-metal dendrite growth. The integrated cells with high active-material loading exhibit good cyclability.

Anderson type polyoxomolybdate as cathode material of lithium battery and its reaction mechanism

Controlling Reversible Expansion of Li2O2 Formation and Decomposition by Modifying Electrolyte in Li-O2 Batteries

Lithium-ion batteries have become a new hot spot in battery research due to their high-energy density, environmental friendliness, and multiple charge/discharge times. Silicon-based materials have become the best choice of anode materials for lithium-ion batteries due to their advantages of low lithium insertion voltage, high specific theoretical capacity, and large reserves on the planet. However, the silicon-based material has a large volume expansion (about 300%) during cycling, which causes the active silicon to fall off from the surface of the conducting material. This expansion will also break the solid electrolyte interphase (SEI) on the surface of the silicon electrode, and will consume additional Li+, causing the battery’s capacity to drop rapidly as the times of circulation increases. In addition, the conductivity of silicon-based materials is lower than that of graphite anode, which have already been used commercially, led to the worse performance of the silicon anode. These drawbacks force silicon-based anode materials to encounter huge resistance in the commercialization process. Therefore, research on the improvement of performance of the silicon-based anode materials is of great significance.

All-solid-state fluoride ion batteries (ASSFIBs) show remarkable potential as energy storage devices due to their low cost, superior safety, and high energy density. However, the poor ionic conductivity of F- conductor, large volume expansion, and the lack of a suitable anode inhibit their development. In this work, PbSnF4 solid electrolytes in different phases (β- and γ-PbSnF4) are successfully synthesized and characterized. The ASSFIBs composed of β-PbSnF4 electrolytes, a BiF3 cathode, and micrometer/nanometer size (µ-/n-) Sn anodes, exhibit substantial capacities. Compared to the μ-Sn anode, the n-Sn anode with nanostructure exhibits superior battery performance in the BiF3/β-PbSnF4/Sn battery. The optimized battery delivers a high initial discharge capacity of 181.3 mAh g-1 at 8mA g-1 and can be reversibly cycled at 40mA g-1 with a high discharge capacity of over 100.0 mAh g-1 after 120 cycles at room temperature. Additionally, it displays high discharge capacities over 90.0 mAh g-1 with excellent cyclability over 100 cycles under -20°C. Detailed characterization has confirmed that reducing Sn particle size and boosting external pressure are crucial for achieving good defluorination/fluorination behaviors in the Sn anode. These findings pave the way to designing ASSFIBs with high capacities and superior cyclability under different operating temperatures.

Manganese oxides are of great interest as low cost and environmentally sound intercalation cathodes for rechargeable lithium ba tteries, but have suffered from limited capacity and instability upon cycling at the moderately high temperatures (50-70°C) encountered in many applications. Here, we show that Li xAl0.05Mn0.95O2 of both the monoclinic and orthorhombic ordered rock salt structures exhibit stable cycling and high discharge capacities at elevated temperatures, after an initial transient associated with a spinel like phase t ransformation. In cells utilizing Li anodes tested at 55°C, rechargeable capacities of 150 mAh/g for the orthorhombic and 200 mAh/g for t he monoclinic phase and energy densities ~500 Wh/kg were achieved over more than 100 cycles (2.0-4.4 V). At low current densities, cha rge capacities approached the theoretical limit. The temperature stability and excellent electrochemical performance, combined with nontoxicity and low raw materials cost, make these compounds attractive cathodes for advanced lithium batteries. © 1999 The Electrochemical Society. S1099-0062(98)07-062-1. All rights reserved. Manuscript submitted July 15, 1998; revised manuscript received October 12, 1998. Available electronically January 11, 1999. Lithium-ion batteries are presently the power source of choice for portable electronics due to their reliability, safety, and high energy density on a volume or weight basis. Commercial applications of batteries based on LiCoO 2 intercalation cathodes have undergone enormous growth since 1995, and provided that performance and cost can reach accepted goals, implementation in larger scale applications such as electric vehicles is anticipated. An intensive search for new electrode materials has been driven by the need for higher energy density at lower cost. Lithium manganese spinels have been the focus of many cathode studies,1-4 in large part due to their low cost and toxicity compared to LiCoO 2 and LiNiO 2 . However, LiMn 2 O 4 spinel exhibits lower rechargeable capacity than LiCoO 2 (115-120 vs. 120-135 mAh/g),5 and rapid capacity fade at elevated temperatures in the range of 5070°C.6-9 Several recent studies have focused on metastable or disordered manganese oxides. Monoclinic LiMnO 2 (m-LiMnO 2 ) with the layered rock salt structure ( α-NaFeO 2 type) has been synthesized by ion exchange of lithium salts with NaMnO 2 10 and by hydrothermal reaction,11 but capacity is low and significant fade has been reported in room-temperature tests to date. Orthorhombic LiMnO 2 (o-LiMnO 2 ) of the ordered rock salt structure described by Hoppe et al. 12 has also been studied by several groups, 13-15 and has been prepared with varying degrees of crystallographic disorder. Increased capacity (initial values at room temperature exceeding 200 mAh/g) is seen in the more disordered forms of this material, but is also accompanied by greater capacity fade.15 As we show, the cycling performance of o-LiMnO 2 at elevated temperatures is also poor. Amorphous manganese oxyiodide16 and manganese oxide17 cathodes have recently been synthesized, in which high rechargeable capacities (260-278 mAh/g) are achievable upon insertion to lower voltages (< 2 V). The elevated temperature properties of these materials have not been reported. An attractive cathode material would meet or exceed the electrochemical performance and elevated temperature stability of LiCoO 2 , while retaining the low cost of the manganese oxides. The aluminumdoped manganese oxides of this work appear to meet this goal. We originally focused on Li x Al y Mn 1-y O 2 solid solutions in order to investigate the effect of aluminum doping on intercalation voltage, extending a study in which aluminum doping was found to increase voltage in LiCoO 2 .18 m-LiMnO 2 (C2/m) has the same layered cation ordering as LiCoO 2 (R3 _ m space group, α-NaFeO 2 structure type). In a previous paper we showed that Li x Al y Mn 1-y O 2 solid solutions can be stabilized in this structure under reducing synthesis conditions. 19 As discussed later, the solid solubility of Al in LiMnO 2 is too low for a meaningful test of voltage effects in this system. However, the monoclinic phase of composition LiAl 0.25 Mn 0.75 O 2 showed discharge capacity as high as 180 mAh/g at room temperature in short term cycling. 19 Here we

The success of the rechargeable Li-S cell is limited in part by the dissolution of lithium-polysulfide in the electrolyte. Remarkably, it is found that removal of the conventional membrane separator in a Li-S cell improves sulfur utilization and cycling performance, whether the sulfur is initially contained in the cathode or electrolyte. An optimized cell design yields discharge capacities as high as 980 mA h g-1 after 100 cycles.