Active Material For Rechargeable Batteries Research Articles

Effects of a Solid Solution Outer Layer of TiO2 on the Surface and Electrochemical Properties of LiNi0.6Co0.2Mn0.2O2 Cathodes for Lithium-Ion Batteries through the Use of Thin-Film Electrodes

Thin-film electrodes are considered to be desirable for understanding the detailed surface characteristics of active materials for rechargeable batteries. This study attempts to elucidate the effects of a solid solution outer layer (SSOL) of TiO2 on the surface and electrochemical properties of LiNi0.6Co0.2Mn0.2O2 (NCM622) cathodes by using thin-film electrodes synthesized by a spin-coating technique. The SSOL phase is induced on the NCM622 thin-film surface by a post-annealing process after the TiO2 coating using atomic layer deposition. Structural and morphological analyses revealed that the bare NCM622 thin-film electrode without a thin SSOL has a spinel-like derivative phase induced by an oxygen vacancy at the surface, which is considered to be the crucial factor for the poor electrochemical properties of Ni-rich NCM. In particular, additional measurements including in situ Raman spectroscopy revealed that the spinel-like derivative phase rapidly makes the surface structure become corrupt and change to the amorphous state during electrochemical reactions. In contrast, the oxygen vacancy can be eliminated by forming a SSOL phase at the surface of the NCM622 thin-film through the rapid migration of Ni, Ti, and O atoms during the post-annealing process, significantly enhancing the structural stability, which ultimately improves the electrochemical performance, including cyclability and Coulombic efficiency.

Xanthogen Polysulfides As Active Materials for Rechargeable Batteries

Significant research strides taken in the past decade have shown that lithium-sulfur (Li-S) batteries are a promising technology to compete with current Li-ion batteries owing to their significantly higher specific energy. However, some fundamental and technical challenges, such as the polysulfide shuttle effect and the need for abundant electrolyte for battery operation, have beleaguered Li-S batteries from being the next practical high-energy-density solution.[1] Recent resurgence of Li-organosulfur batteries as alternative sulfur-based cathode chemistry has shown great potential to alleviate some of these challenges.[2] These materials offer control over the order of the lithium polysulfides formed during cycling through the presence of organic terminal groups, thus minimizing the polysulfide shuttle effect. Additionally, they possess the ability to operate under lean-electrolyte conditions, a critical parameter for maximizing cell-level specific energy. This work introduces a new member into the family of organosulfur cathode materials – xanthogen polysulfides. Diisopropyl xanthogen polysulfide (DIXPS) was used as a model compound to understand the electrochemical characteristics of this new material class. Its chemical transformations within a battery will be discussed. DIXPS shows excellent long-term performance with stability up to 1,000 cycles at a high rate of 4C. DIXPS also demonstrates the ability to deliver a high specific energy of 1,313 W h kg-1 and 1,694 W h L-1 while operating under high-loading and lean-electrolyte conditions. This illustrates the practical applicability of this material. Additionally, the feasibility of using alternate anodes such as sodium-metal will also be explored. The ability to synthesize such battery materials using natural feedstocks, such as sugars and alcohols will also be examined.

Charge Storage Mechanism and Structural Evolution of Viologen Crystals as the Cathode of Lithium Batteries.

Although organic ionic crystals represent an attractive class of active materials for rechargeable batteries owing to their high capacity and low solubility in electrolytes, they generally suffer from limited electronic conductivity and moderate voltage. Furthermore, the charge storage mechanism and structural evolution during the redox processes are still not clearly understood. Here we describe ethyl viologen iodide (EVI2 ) and ethyl viologen diperchlorate (EV(ClO4 )2 ) as cathode materials of lithium batteries which crystallize in a monoclinic system with alternating organic EV2+ layers and inorganic I- /ClO4 - layers. The EVI2 electrode exhibits a high initial discharge plateau of 3.7 V (vs. Li+ /Li) because of its anion storage ability. When I- is replaced by ClO4 - , the obtained EV(ClO4 )2 electrode displays excellent rate performance with a theoretical capacity of 78 % even at 5 C owing to the good electron conductivity of ClO4 - layers. EVI2 and EV(ClO4 )2 also show excellent cycling stability (capacity retention >96 % after 200 cycles).

Charge Storage Mechanism and Structural Evolution of Viologen Crystals as the Cathode of Lithium Batteries

AbstractAlthough organic ionic crystals represent an attractive class of active materials for rechargeable batteries owing to their high capacity and low solubility in electrolytes, they generally suffer from limited electronic conductivity and moderate voltage. Furthermore, the charge storage mechanism and structural evolution during the redox processes are still not clearly understood. Here we describe ethyl viologen iodide (EVI2) and ethyl viologen diperchlorate (EV(ClO4)2) as cathode materials of lithium batteries which crystallize in a monoclinic system with alternating organic EV2+ layers and inorganic I−/ClO4− layers. The EVI2 electrode exhibits a high initial discharge plateau of 3.7 V (vs. Li+/Li) because of its anion storage ability. When I− is replaced by ClO4−, the obtained EV(ClO4)2 electrode displays excellent rate performance with a theoretical capacity of 78 % even at 5 C owing to the good electron conductivity of ClO4− layers. EVI2 and EV(ClO4)2 also show excellent cycling stability (capacity retention >96 % after 200 cycles).

Electrodeposited Cu/MWCNT composite-film: a potential current collector of silicon-based negative-electrodes for Li-Ion batteries.

With the aim of developing the potential high theoretical capacity of Si as a negative electrode material for Li-ion batteries, a new type of composite current collector in which multi-walled carbon nanotubes (MWCNTs) are immobilized on a Cu surface was developed using an electroplating technique. For the Si electrode with a flat-Cu substrate, voltage plateaus related to the stepwise electrochemical lithiation were observed below 0.27 V (vs. Li/Li+), whereas the Cu/MWCNT substrate distinctly decreased the overvoltage to enhance charge/discharge capacities to approximately 1.6 times that obtained in the flat-Cu system. Field-emission scanning microscopy revealed that MWCNTs immobilized on the Cu surface extended inside the active material layer. Adhesion strength between the substrate and electrode mixture layer was reinforced by MWCNTs to increase the reversibility of change in electrode thickness before and after cycling: the expansion ratio was 200% and 134% for flat-Cu and Cu/MWCNT systems, respectively. Electrochemical impedance analysis demonstrated that MWCNTs served as an electron conduction pathway inside the electrode. By controlling the upper cutoff voltage from 2.0 V to 0.5 V, synergetic effects including improved adhesion strength and a more developed conduction pathway became noticeable: a reversible capacity of 1100 mA h g−1 with 64% capacity retention was achieved even after the 100th cycle. The results indicate that the Cu/MWCNT is a promising current collector for expansion/contraction-type active materials for rechargeable batteries.

Ferrocene-functionalized polyheteroacenes for the use as cathode active material in rechargeable batteries.

Herein we report the synthesis and characterization of new conjugated polymers bearing redox-active pendant groups for applications as cathode active materials in secondary batteries. The polymers comprise a ferrocene moiety immobilized at a poly(cyclopenta[2,1-b:3,4-b′]dithiophene) (pCPDT, P1) or a poly(dithieno[3,2-b:2′,3′-d]pyrrole) (pDTP, P2) backbone via an ester or an amide linker. Electrochemical and oxidative chemical polymerizations were performed in order to investigate the redox behaviour of the obtained polymers P1 and P2 and to synthesize materials on gram-scale for battery tests, respectively. During galvanostatic cycling in a typical battery environment, both polymers showed high reversible capacities of 90% and 87% of their theoretical capacity and excellent capacity retentions of 84% and 97% over 50 cycles.

Steric Effects on the Cyclability of Benzoquinone-type Organic Cathode Active Materials for Rechargeable Batteries

Abstract Benzoquinone derivatives, which undergo reversible two-electron redox reactions, should afford high capacity as positive electrode materials for rechargeable batteries. Although some benzoquinones have been reported as cathode active materials, their low cycle-life performance is a drawback. We prepared benzoquinones bearing alkyl groups with various degrees of bulkiness to investigate the relationship between the steric effects of the substituents on the benzoquinone skeleton and the battery performance. The introduction of bulky substituents, especially a tert-butyl group, on the skeleton significantly improved the cyclability.

Redox Behavior of Prussian Blue in Mg Salt Electrolytes

Prussian Blue (PB) and Prussian Blue analogues (PBAs) have been extensively studied as electrochromic materials, electrocatalytic materials, and positive electrode active materials for rechargeable batteries since Neff first reported the electrochemical redox behavior of a PB-modified electrode with a rapid color change.1 Fig. 1a shows the structure of a PBA AxMy[M’(CN)6]·nH2O. In this structure, transition metal cations M and M’ are coordinated with CN bonds to form a three-dimensional framework structure in which ions and water are accommodated. Ions are inserted/extracted with the redox reactions of the transition metal cations M and/or M’ for charge compensation. The framework structures of PB and PBAs are favorable specifically for the fast insertion and extraction of polyvalent cations, which have higher electrostatic interaction than monovalent cations.In the present work, we investigated the redox behavior of a PB thin film in electrolytes containing an Mg salt to investigate the possibility of using PB as a positive electrode for Mg batteries. Scanning electron microscopy (SEM) and optical images of the electrodeposited PB film are shown in Fig. 1b. The PB film had a bright blue color and cracks on its surface, and did not contain Na, K, or Cl elements, as confirmed by energy dispersive X-ray spectroscopy. Crack-less film was obtained by using KCl instead of NaCl as the supporting electrolyte. Fig. 2 shows the cyclic voltammogram (below) and corresponding weight change (above) measured by EQCM (electrochemical quartz crystal microbalance) in an aqueous solution containing 1.00 M MgSO4•7H2O. Large cathodic current was observed below 0.4 V vs. SHE during the cathodic sweep, and two small anodic peaks were observed at about 0.3 and 0.5 V. The weight of the PB film increased during the cathodic reaction and decreased during the anodic reaction, suggesting insertion and extraction of Mg2+ ions for the charge compensation of the PB film. However, there was a large deviation between the measured weight change and the weight change calculated from the current density assuming the insertion and extraction of completely desolvated Mg2+ ions. The measured weight change was significantly larger than the calculated weight change, indicating that Mg2+ ions were solvated (hydrated) with water molecules. The measured and calculated weight changes were comparable by assuming that the hydration number was 12 during the insertion of Mg2+ ions and 17 during the extraction of Mg2+ ions (at the 2nd cycle). It should be noted that the hydrated radius and hydration number of the Mg2+ ion is reported to be 0.300–0.428 nm and 7–36, respectively;2 the hydrated diameter of the Mg2+ ion is larger than the distance of the closest approach between Fe ions in the PB framework (0.507 nm). Therefore, it is possible that Mg2+ ions drag water molecules into/from the framework of PB, although hydrated Mg2+ ions should be transiently or partly dehydrated for the insertion and extraction. There is also a possibility that H+ ions are inserted and extracted. However, because no redox peaks of the PB film electrodeposited under the same conditions were observed in 1.00 M LiCl aqueous solution,3 this possibility can be discarded. This result also indicates that the insertion and extraction of hydrated Li+ ions did not occur even though hydrated Mg2+ ions were inserted and extracted as shown in Fig. 2. Generally, the hydration energies of polyvalent cations like Mg2+ ion are larger than those of monovalent cations, and the hydrated radius of the Li+ ion is smaller than that of the Mg2+ ion; the hydrated Li+ ions seem to be more easily inserted/extracted than hydrated Mg2+ ions. This apparent antinomy leads to the hypothesis that the primary (the innermost) hydration shell is not detached from either ion, and the size of the primary hydration shell of Mg2+ is smaller than that of Li+ because of the higher hydration energy of Mg2+. This point is now under intensive investigation.In the presentation, the electrochemical insertion/extraction behavior of other combinations of framework structures and electrolytes will also be presented.

Electrochemical Properties of Biphase Ni ( OH ) 2 Electrodes for Secondary Rechargeable Ni ∕ MH Batteries

The nanosized was synthesized by chemical coprecipitation in alcohol–water systems. Different contents of nanosized were added into microscale to form biphase electrode materials for secondary rechargeable nickel–metal hydride batteries. The electrochemical properties of the biphase electrodes were investigated with cyclic voltammetry and galvanostatic charge–discharge tests. The biphase electrode with 10 wt % nanosized exhibited better charge–discharge cycling stability and activity than other materials, and the discharge capacity was higher than that of the electrode. It may be a promising positive active material for rechargeable batteries.

Anode Performance of Pyrolyzed Bacterial Cellulose in Secondary Lithium-Ion Batteries and the Effect of Added Metal Phthalocyanines

Electrochemical properties of pyrolyzed bacterial cellulose and the effect of the addition of metal phthalocyanines have been investigated for application of the cellulose to electrodes of lithium-ion batteries. The electrodes made of pyrolyzed bacterial cellulose exhibit good stability and relatively high Coulombic efficiency in charge–discharge cycles. Furthermore, the addition of metal phthalocyanines before pyrolysis remarkably increases the charge–discharge capacities of the pyrolyzed bacterial cellulose. We propose the new application of bacterial cellulose as an electrode active material in rechargeable batteries.

Electrical and electrochemical properties of fly ash and effect of pyrolysis

The electrical and electrochemical characteristics of pyrolized fly ash which has a porous structure have been investigated for use as an electrode active material in rechargeable batteries. The electrodes of pyrolized fly ash show good stability and high Coulombic efficiency in charge–discharge cycles in LiClO4/PC. The charge–discharge capacity of pyrolized fly ash with a heat treatment temperature of 1100 °C is as high as 205 mA h/g. From the viewpoint of recycling of industrial waste, we propose to use fly ash as a negative electrode in a lithium ion secondary battery.

Poly- o-methylaniline used as a cathode material in rechargeable batteries

A new conducting polymer, poly- o-methylaniline, used as a cathode-active active material in rechargeable batteries, is very stable in aqueous solution. The cell, consisting of poly- o-methylaniline, Zn and 1.5 M ZnCl 2 (pH 2.68), had an open-circuit voltage of 1.3 V. The experimental capacity and energy density based on the weight of polymer employed in constructing the cell are 106.6 Ah kg −1 and 110.3 Wh kg −1 at a constant discharge current of 0.25 mA/cm 2 (average discharge voltage 1.04 V). The coulombic efficiency of poly- o-methylaniline is 100% at a constant current of 0.25 mA/cm 2.

Polyaniline: characterization as a cathode active material in rechargeable batteries in aqueous electrolytes

An analytically pure form of chemically synthesized polyaniline having the emeraldine oxidation state has been used as a cathode active material together with a Zn anode in the fabrication of rechargeable cells in 1.0 M aqueous ZnCl2 electrolyte (pH∼4). The experimental capacity and energy density based only on the weight of polymer employed in constructing the cell are 151.5 Ah kg−1 and 159.1 Wh kg−1 respectively at a constant discharge current of 0.75 mA cm−2 (average discharge voltage 1.05V). The cell reactions in the charge and discharge processes have been determined. The modified capacity and energy density, when taking into account the calculated weights of Zn and HCl involved in the discharge reactions, are 109.3 Ah kg−1 and 114.8 Wh kg−1 respectively. The cell shows excellent recyclability and coulombic efficiency.