Negative Electrode For Rechargeable Batteries Research Articles

Macroscopically uniform and flat lithium thin film formed by electrodeposition using multicomponent additives

It is well-known that the electrodeposition of lithium usually results in the formation of dendrites on the electrode surface. This limits the utilization of metallic lithium as a material for, for example, the negative electrodes of rechargeable batteries. In aqueous solutions, similar dendritic growth of metals is often observed during electrodeposition; however, utilization of multicomponent additives has overcome this shortcoming. Here, we report that the simultaneous utilization of four different additives greatly suppresses the formation of lithium dendrites during electrodeposition in a tetraglyme-based solution. The roles of the additives are discussed, based on the results of electrochemical quartz crystal microbalance measurements and X-ray photoelectron spectroscopy.

Synthesize Fe2O3 Polyhedral Applying for Rechargeable Batteries

Polyhedral Fe2O3 materials were synthesized by hydrothermal method. Their structure, size, and morphology were investigated by X-ray diffraction and scanning electron microscopy. The electrochemical characteristics of Fe2O3 electrodes were studied via cyclic voltammetry measurement. The effects of the additives on the electrochemical properties of the electrode were also studied. The results show that the synthesized polyhedral Fe2O3 presented the clear redox peaks. Combined with electrode additive nanocarbon and electrolyte additive K2S, the Fe2O3/C composite electrodes gave higher redox current, larger redox peaks. This demonstrates the important role of additives such as nanocarbon increased the electrical conductivity and the active surface area of ​​the electrode, while K2S enhanced the redox reaction rate of iron, improved the cycleability of iron oxide, and thus increased the discharge capacity of Fe2O3/C electrodes. Polyhedral Fe2O3 synthesized via hydrothermal route has a potential applying as negative electrode in rechargeable batteries.

Promoting Lithium Electrodeposition Towards the Bottom of 3-D Copper Meshes in Lithium-Based Batteries

Lithium (Li) has been considered as the promising negative electrode in rechargeable batteries, owing to the negative redox potential (-3.04 V vs. SHE), low density (0.534 g/cm3), and high theoretical specific capacity (3,860 mAh/g). However, the non-uniform stripping/plating process of the metallic Li is still challenging.[1] As one of the solutions, three-dimensional (3-D) metallic scaffolds were introduced to the negative electrode. The uniform electric field applied in the porous scaffolds could suppress the dendritic growth of the Li during the plating process. In addition, a decrease in the effective current density prolonged Sand’s time.[2] However, such a Li deposition mainly proceeded on the top surface and led to rapid surface clogging due to the strong surface electric field. In this presentation, we show the preferred Li deposition inside the 3-D copper (Cu) scaffold using gold nanoparticles (Au NPs). The lower Li nucleation energy barrier on the Au surface than that on the typical Cu current collector was investigated intensively.[3] However, the role of Au for spatially promoting Li deposition was not studied in depth. We added the Au NPs with an average particle size of ~7.5 nm to the bottom of 3-D Cu. The Au NPs with a total ~28 nmol reduced the charge-transfer resistance, which suggested the fast Li nucleation on the Au. In addition, we coated aluminum oxide (Al2O3) layer with ~ 26 nm of thickness on the top surface of 3-D Cu scaffold through the atomic layer deposition (ALD) process. This insulating layer further suppressed the Li deposition on the surface. As a result, apparent Li deposition towards the bottom of 3-D Cu was clearly demonstrated. During Li plating/stripping cycles, the surface clogging of the 3-D Cu/Au by an accumulation of solid electrolyte interphase (SEI) was also dramatically alleviated even in the absence of Al2O3 layer. It demonstrated the continuous Li deposition towards the bottom of the 3-D Cu/Au scaffold. Besides, symmetric 3-D Cu/Au cells exhibited over 95 % of Coulombic efficiency (CE) for ~120 cycles. The full cells comprised of the 3-D Cu/Au and LiFePO4 (LFP) electrodes delivered stable 300 cycles with a capacity of ~140 mAh/g at 1 C-rate. I will discuss the detailed role of the Au NPs and the Al2O3 layer, and comparative cell performances in the presentation.

Reversible Sodium Metal Electrodes: Is Fluorine an Essential Interphasial Component?

AbstractAlkaline metals are an ideal negative electrode for rechargeable batteries. Forming a fluorine‐rich interphase by a fluorinated electrolyte is recognized as key to utilizing lithium metal electrodes, and the same strategy is being applied to sodium metal electrodes. However, their reversible plating/stripping reactions have yet to be achieved. Herein, we report a contrary concept of fluorine‐free electrolytes for sodium metal batteries. A sodium tetraphenylborate/monoglyme electrolyte enables reversible sodium plating/stripping at an average Coulombic efficiency of 99.85 % over 300 cycles. Importantly, the interphase is composed mainly of carbon, oxygen, and sodium elements with a negligible presence of fluorine, but it has both high stability and extremely low resistance. This work suggests a new direction for stabilizing sodium metal electrodes via fluorine‐free interphases.

Reversible Sodium Metal Electrodes: Is Fluorine an Essential Interphasial Component?

Alkaline metals are an ideal negative electrode for rechargeable batteries. Forming a fluorine‐rich interphase by a fluorinated electrolyte is recognized as key to utilizing lithium metal electrodes, and the same strategy is being applied to sodium metal electrodes. However, their reversible plating/stripping reactions have yet to be achieved. Herein, we report a contrary concept of fluorine‐free electrolytes for sodium metal batteries. A sodium tetraphenylborate/monoglyme electrolyte enables reversible sodium plating/stripping at an average Coulombic efficiency of 99.85 % over 300 cycles. Importantly, the interphase is composed mainly of carbon, oxygen, and sodium elements with a negligible presence of fluorine, but it has both high stability and extremely low resistance. This work suggests a new direction for stabilizing sodium metal electrodes via fluorine‐free interphases.

A Functionalized Co2P Negative Electrode for Batteries Demanding High Li-Potential Reaction

Co-P alloy films were electrodeposited on a titanium electrode. The controlled addition of phosphorous acid or sodium hypophosphite to a Co2+-containing solution leads to the formation of amorphous or crystalline CoP phases. Particularly, the orthorhombic Co2P phase is obtained at 80°C with a current density of 37.5 mA cm−2 during 10 and 20 min as determined by XRD and XPS analysis. The morphology of Co2P can be controlled from leopard-like spots to hexagonal symmetric particles as confirmed by SEM. This phase is for first time used as a negative electrode in rechargeable batteries. The electrochemical results in a lithium test cell of this unique product differ significantly from other metal phosphides reported in the literature. A high potential reaction at 1.3 V is observed in the first discharge. Successive charge/discharge branches are quite different to those reported so far. The preliminary results suggest that the Co to P ratio may affect the redox properties of the materials. In view of the limited amount of reports dealing with performances of cobalt phosphides in Li-cells, the properties presented here justify further effort to be done to evaluate their real potential application in Li-ion batteries with a predefined voltage operation.

Synthesis and electrochemical characterizations of the nanocrystalline Ti[Co xMg 1−x] ( x = 0.65) material as a hydrogen storage alloy

The millennium application of new hydrogen absorbing alloys as negative electrodes in rechargeable batteries has allowed the consideration of nickel/metal hydride (Ni–MH) batteries to replace the conventional nickel cadmium alkaline or lead acid batteries. In this study the mechanical alloying process was used for synthesizing nanocrystalline TiCo–Mg-type hydrogen storage materials. The pressing negative and positive electrode, polyethylene as a separator and 6 mol/l KOH as an electrolyte solution constructed the cells. The nanocrystalline alloys electrode was subjected to charge/discharge cycle for more than 200 cycles. The discharge capacities of the nanocrystalline alloys withstand at 240 mAh/g with a nominal fading in capacity on prolonged cycling. The results show that when using sealed batteries nanocrystalline Ti[Co 0.65Mg 0.35] alloy electrode shows two times more capacity than TiNi counterparts.

Electrochemical investigations and characterization of a metal hydride alloy (MmNi3.6Al0.4Co0.7Mn0.3) for nickel metal hydride batteries

The use of new hydrogen absorbing alloys as negative electrodes in rechargeable batteries has allowed the consideration of nickel/metal hydride (Ni/MH) batteries to replace the conventional nickel cadmium alkaline or lead acid batteries . In this study the performance of trisubstituted hydrogen storage alloy (MmNi 3.6 Al 0.4 Co 0.7 Mn 0.3 ) electrodes used as anodes in Ni/MH secondary batteries were evaluated. MH electrodes were prepared and the electrochemical utilization of the active material was investigated. Cyclic voltammetric technique was used to analyze the beneficial effect of the alloy by various substitutions. The electrochemical impedance spectroscopic measurements of the Ni/MH battery were made at various states of depth of discharge. The effect of temperature on specific capacity is studied and specific capacity as a function of discharge current density was also studied and the results were analyzed. The alloy metal hydride electrode was subjected to charge/discharge cycle for more than 200 cycles. The discharge capacities of the alloy remains at 250 mAh/g with a nominal fading in capacity (to the extent of ∼20 mAh/g) on prolonged cycling.

Reversibility of electrochemical magnesium deposition from Grignard solutions

The reversibility of electrochemical magnesium deposition from Grignard reagents was investigated with regard to potential application of magnesium as a negative electrode in rechargeable batteries. The reoxidation rate depends on the morphology of the magnesium deposit which is controlled by the substrate material. Good results were obtained using silver or gold substrates. Magnesium deposits on these materials was found to be of smooth and compact morphology. A nearly complete electrochemical reoxidation and a low self-discharge were observed.

Effects of pretreatment on the activation behavior of Zr(V 0.25Ni 0.75) 2 metal hydride electrodes in alkaline solution

Metal hydrides used as negative electrodes in rechargeable batteries are covered with surface oxides during preparation of the electrode. They inhibit or slow down the absorption rate of hydrogen and have to be dissolved or made conductive in an activation process. In order to minimize the activation cycles we have investigated the influence of the pretreatments of the metal hydride powder Zr(V 0.25Ni 0.75) 2 with KOH and fluoride-containing solutions on the surface composition of the alloy grains by means of X-ray photoelectron spectroscopy. The study establishes the relationship between the surface composition of the hydrogen-storing material and the electrode performance, e.g. discharge capacity and high-rate dischargeability. The speed of activation increased with increasing nickel content in the top surface layers (30 Å) of the metal hydride.

Characterization of electrochemically reduced dicadmium stannate

The two stable species of dicadmium stannate, namely oxidized (yellow) and reduced (green), have been studied using X-ray diffraction (XRD), Auger, and electron spectroscopy for chemical analysis (ESCA) techniques. Semiquantitative ESCA showed a chemical formula of Cd2SnO4 for yellow and Cd2SnO2 for the green compound. It appeared that both tin and cadmium can undergo a change in valency state during the electrochemical reduction. This explains the high energy density of the compound when used as active material for the negative electrode in rechargeable batteries. The variation of electrical conductivity of dicadmium stannate prepared under different conditions can be explained in terms of the reduction of tin, cadmium or both in the original compound.