Aqueous Rechargeable Lithium Batteries Research Articles

Synthesis of LaW/Ag/GNRs nanocomposite: Application as transducer material for the simultaneous nano molar detection of synthetic dyes and as anode material for Li ion batteries

In this present research, we have synthesized the lanthanum tungstate/silver nanoparticle/graphene nanoribbons (LaW/Ag/GNRs) nanocomposite as a novel system for the simultaneous electrochemical determination of two synthetic food colorants sunset yellow (SY) and acid yellow (AY). The synthesised nanocomposite modified graphite electrode (Gr) provides the presence of more active sites for the transfer of electrons, allowing for a stronger voltametric response that is due to the faster rate of electron transfer from the analytes. The as-synthesized nanocomposite was characterized by different analytical methods. The enhanced anodic peak currents represented the excellent analytical performance for simultaneous detection of SY and AY in the range of 20 nm to 450 nM, with a low limit of detection (LOD) of 0.025 nm for SY and 0.050 nM for AY. This proposed sensor showed excellent recovery values real sample analysis. Further the nanocomposite was used as the anode material in Li ion batteries and was evaluated in an aqueous saturated Li2SO4 electrolyte. In terms of cycle performance, enhanced rate capability, and high discharge capacity, LaW/Ag/GNRs nanocomposite has made significant advancements. The lithiated LaW/Ag/GNRs nanocomposite half-cell vs. SCE offers a 227.86 mA h g−1 capacity up to 10 cycles at 0.08 mA. In the potential range of 1.0 to 0.0 V, the whole cell configuration LaW/AgNPs/GNRs|aq.saturated Li2SO4|LiMn2O4 produced a discharge capacity of 240.24 mA h g−1. With 96.95% columbic efficiency, the battery performance of the cell has greatly boosted. This excellent result clearly fits this material as an anode in future aqueous rechargeable lithium batteries for energy technology.

Enhanced charge transport properties of an LFP/C/graphite composite as a cathode material for aqueous rechargeable lithium batteries.

Electrodes that offer quick ion transport, a large surface area, and excellent electrical conductivity support high performance aqueous rechargeable lithium batteries. LiFePO4 (LFP) nanoparticles have been successfully coated with carbon by a chemical sol-gel route, and assembled on graphite by an ultrasonication method to acquire LFP/C/graphite. This LFP/C/graphite composite exhibits exceptional electrochemical performance at various current densities (1C to 20C). LFP/C/graphite delivers better capacity that is higher than that of LFP/C particles and high stability after 60 cycles at a current density of 1C for aqueous rechargeable lithium batteries as a cathode material. The graphite serves as a good volume buffer in improving the lithium performance of LFP/C/graphite during the charge/discharge process. The LFP/C/graphite composite shows high rate capability at 20C that returned to the initial capacity at 1C after 25 cycles with coulombic efficiency of 97%. Therefore, this effort presents a super low-cost route to fabricate high performance cathode materials in aqueous rechargeable lithium batteries and other energy storage appliances.

Improved cycling performance of polypyrrole coated potassium trivanadate as an anode for aqueous rechargeable lithium batteries

The energy storage properties of layered metal vanadate, especially alkali metal vanadates have been extensively studied. Metal vanadates have a more robust electrochemical output in contrast with pristine vanadium oxides. However, the detailed processes underlying the efficiency contrast of vanadates and vanadium oxides have rarely been studied. Herein a facile hydrothermal and low-temperature polymerization method was introduced to synthesize KV3O8 and KV3O8@PPy nanowire bundles as anode material for an aqueous rechargeable Lithium batteries. The nanowires are composed of KV3O8·0.59H2O calculated using thermal gravimetric analysis (TGA). Successfully synthesized layered vanadium based KV3O8 0.59H2O (KVO) and KV3O8 0.59H2O@PPy (KVO@PPy) nanowires and investigated the source of the improved electrochemical efficiency of PPy coated potassium vanadates compared to pristine KVO using crystal structure analysis and electrochemical tests. We demonstrated increase in electrochemical stability for KVO@PPy caused by synergistic effect of K+ in vanadate nanowires and PPy coating. In KVO the oxygen atoms have close contact with the K ions, and the stable K+ serve as “pillars” between interlayers to shield the layered structures from collapse during the charge/discharge phase, while the PPy reduces charge transfer resistance. This research adds helps us design better electrode materials to be used as an anode material for ARLB using alkali metal vanadate.

Electrochemical Characterization of Graphene–LiMn2O4 Composite Cathode Material for Aqueous Rechargeable Lithium Batteries

A series of graphene– LiMn2O4 composite electrodes were prepared by physical mixing of graphene powder and LiMn2O4 cathode material. LiMn2O4was synthesized by reactions under autogenic pressure at elevated temperature method. CV, galvanostatic charge-discharge experiments and EIS studies revealed that the addition of graphene significantly decreases the charge-transfer resistance of LiMn2O4 electrodes. 5 wt. % graphene–LiMn2O4 composite electrode exhibits better electrochemical performance by increasing the reaction reversibility and capacity compared to that of the pristine LiMn2O4 electrode. Improved electrochemical performances are thus achieved, owing to the synergic effect between graphene and the LiMn2O4 active nanoparticles. The ultrathin flexible graphene layers can provide a support for anchoring well-dispersed active cathode particles and work as a highly conductive matrix for enabling good contact between them. At the same time, the anchoring of active nanoparticles on graphene effectively reduces the degree of restacking of graphene sheets and consequently keeps a highly active surface area which increases the lithium storage capacity and cycling performance.

Evaluation of the Stability of Carbon Conductor in the Cathode of Aqueous Rechargeable Lithium Batteries against Overcharging

Three major components in a cathode of aqueous rechargeable lithium batteries are the active material, the polymer binder, and the carbon conductive additive. The stability of each component in the battery is the key to long service life. To evaluate the stability of the carbon component, we introduce here a quick and direct testing method. LiMn2O4 is chosen as a typical active material for the preparation of the cathode, with polyvinylidene fluoride (PVdF), and a commercial carbon, which is chosen among Acetylene black, superP, superP-Li, Ketjen black 1, Ketjen black 2, Graphite, KS-6, splintered glassy carbon, and splintered spherical carbon. This method reveals the correlation between the electrochemical stability of a carbon and its physical and structural properties. This helps researchers choose the right carbon component for a Li-ion cathode if they want the battery to be robust, especially at near full state of charge.

Effect of cation size on alkali acetate-based ‘water-in-bisalt’ electrolyte and its application in aqueous rechargeable lithium battery

In this study, the properties of aqueous electrolytes based on alkali metal (Li, Na, K and Cs) acetates have been systematically investigated in order to figure out the effects of cations on the stability windows of corresponding electrolytes. At the same concentration of 7 m (molar-salt in kg-solvent), it is discovered that the stability windows of KOAc and CsOAc-based aqueous electrolytes are wider than those of LiOAc and NaOAc-based ones. This is due to enhanced polymer-like chains and weakened hydrogen bonds for the aqueous electrolytes with cations of larger size and higher mass. It is found that saturated 45 m CsOAc ‘water-in-salt’ electrolyte (WiSE) has an electrochemical stability window of 3.4 V, which is further mixed with 7 m LiOAc to form a mixed cation ‘water-in-bisalt’ electrolyte (WiBSE), prepared from a hydrated second salt (LiOAc•2H2O), delivering a stability window of 2.95 V. CR2032 coin cells are assembled based on the 45 m CsOAc + 7 m LiOAc WiBSE, with a VO2 nanobelt anode and LiNi0.5Mn1.5O4 hollow microsphere cathode, which deliver an operating voltage of 2.5 V. It exhibits a maximum specific discharge capacity of 68.1 mAh•g − 1 and relevant energy density of 114.8 Wh•kg−1 (calculated on the total mass of cathode and anode) under 1 C rate. At 4 C rate, the coin cell has a coulombic efficiency (CE) of about 99% reaching near 100% at certain cycles, and a desired capacity retention of 86.5% during the 1200 cycles. The crystal structure of the VO2 prepared in this study has been refined by GSAS+EXPGUI and it was found the lattice parameters are smaller than the conventional VO2 (B) phase although they share the same symmetry.

Cl- Doping Strategy to Boost the Lithium Storage Performance of Lithium Titanium Phosphate.

Because of energy storage limitations and the high demand for energy, aqueous rechargeable lithium batteries (ARLBs) are receiving widespread attention due to their excellent performance and high safety. Lithium titanium phosphate (LiTi2(PO4)3) exhibits the potential to serve as anodes for ARLBs because it has a three-dimensional channel and a stable structure. We employed an anion (Cl−) doping strategy to boost the lithium storage performance of LiTi2(PO4)3. A series of LiTi2(PO4)3/C composites doped with Cl− on were successfully synthesized with a sol-gel technique as anodes for ARLBs. The effects of chlorine doping with different content on the properties of LiTi2(PO4)3−xCl3x/C (x = 0.05, 0.10, and 0.15) were investigated systematically. The doping of chlorine in appropriate amounts did not significantly impact the main structure and morphology of LiTi2(PO4)3/C. However, chlorine doping greatly increased the performance of LiTi2(PO4)3/C. LiTi2(PO4)2.9Cl0.3/C (LCl-10) showed the best electrochemical properties. It delivered a discharge capacity of 108.5 and 85.5 mAh g−1 at 0.5 and 15°C, respectively, with an increase of 13.2 and 43.3 mAh g−1 compared to blank LiTi2(PO4)3 (LCl). In addition, the discharge capacity of LCl-10 was maintained at 61.3% after 1,000 cycles at 5°C, implying an apparent improvement compared to LCl (35.3%). Our study showed that a chlorine-doped LiTi2(PO4)3/C composite is a potential anode for high-performance ARLBs.

The role of anions on the Helmholtz Plane for the solid-liquid interface in aqueous rechargeable lithium batteries

Abstract The Li-ion transport at the electrode/electrolyte interface in lithium ion batteries (LIBs) relies on the structure of the electrical double layer. Our previous work indicates that the constructing of Janus amphiphilic coordination interface on LiFePO4 in aqueous electrolyte relieves the energy barriers of the Li+ solvation/desolvation process. Here, aqueous electrolytes with different salts (LiNO3, LiCl, Li2SO4 and CH3COOLi) were tested in LiFePO4 single nanoparticle, and Ab initio calculations and simulation were carried out. H2O has a stronger binding energy with Fe and Li on the surface of LiFePO4 to form Janus interface, so the activation energies of Li-ion in Janus layer are the same in the four electrolytes. The simulation result confirms that the Li-ion transport at the interface have a close relationship with the anionic physical characteristics. Combing with the experimental and calculated results, it can be inferred that the activation energy (Ea) of Li-ion includes Janus interface, anion adsorption layer and cation adsorption layer. Owing to the same Janus interface and cation adsorption layer, the difference of Ea in the four kinds of electrolytes must come from the anion adsorption layer in inner Helmholtz plane (IHP). This work provides a guiding significance on development of aqueous electrolyte systems.

Surface-Modified Li4Ti5O12 in Highly Concentrated Aqueous Solutions for Use in Aqueous Rechargeable Lithium Batteries

The high voltage of aqueous rechargeable lithium batteries is a key challenge to improve battery performance in terms of safety and high energy density. In this study, we examined the charge and discharge characteristics of Li4Ti5O12, which cannot be stably used in conventional aqueous electrolytes, by combining the use of a highly concentrated aqueous solution and surface modification of the active material. With surface modification of 5 wt%, the hydrogen evolution reaction during charging was suppressed, but the discharge capacity decreased rapidly with cycling. On the other hand, the amount of surface coating at 1 wt% showed a stable discharge capacity even after 50 cycles. An analysis of the surface composition by X-ray photoelectron spectroscopy revealed that the surface coating was composed of AlF3 and Al2O3, implying that these components reacted with the aqueous solution and changed into a resistive layer for lithium ion conduction.

Carbon‐Supported Organic Electrode Materials for Aqueous Rechargeable Lithium‐Ion Batteries

AbstractElectro active organic compounds represent one of the most capable electrode materials for the next generation green and sustainable rechargeable lithium ion batteries. In this context, we highlight the synthesis of an organic electrode material of azo derivative; diazoaminobenzene (DAAB) by diazotization method followed by lithiation using conventional technique. The electrochemical performances of the electro‐active species are examined by Cyclic Voltammetry, Galvanostatic Cycling with Potential Limitation and Potentio‐electrochemical Impedance Spectroscopy in an aqueous saturated Li2SO4 electrolyte. DAAB has shown considerable progress in terms of cyclic performance, better rate capability and high reversible capacity. The electroactivity of active species are enhanced by the addition of carboxy‐functionalized carbon nanotubes (CNTs‐COOH) as an additive. The half‐cell of lithiated diazoaminobenzene/CNTs‐COOH (dLiDAAB) vs. SCE delivers a capacity of 173.7 mA h g−1 up to 10 cycles at 0.08 mA. The full cell configuration dLiDAAB | aq. Saturated Li2SO4 | 2‐[1H‐indol‐2‐yl (1H‐indol‐3‐yl) methyl] phenol (b‐IMP) delivered a discharge capacity of 81.99 mA h g−1 in the potential window of −0.2 V to 1.2 V. The battery performance of the cell has been increased significantly by the influence of CNTs‐COOH group with 96.95% columbic efficiency. This agreeable result markably suits this material as an anode in aqueous rechargeable lithium batteries for future needs of energy technology.

Development of LiFePO4/FePO4 Electrode for Electro-Osmotic Pump using Li+ Migration

Olivine structure of LiFePO4 (LFP) is one of the most commonly used materials in aqueous rechargeable lithium batteries (ARLBs), and can store and release charge through the insertion/de-insertion of Li+ between LFP and FP. We have fabricated LFP and LFP/FP electrodes on titanium paper and studied their electrochemical properties in 2 M Li2SO4. The LFP/FP electrode was determined to be a suitable electrode for electo-ostmotic pump (EOP) in terms of efficiency in water and 0.5 mM Li2SO4 solution. Experiments to determine the effect of cations and anions on the performance of EOP using LFP/FP electrode have shown that Li+ is the best cation and that the anion does not significantly affect the performance of the EOP. As the concentration of Li2SO4 solution was increased, the current increased. The flow rate peaked at 4.8 μL/30 s in 1.0 mM Li2SO4 solution and then decreased. When the EOP was tested continuously in 1.0 mM Li2SO4 solution, the EOP transported approximately 35 mL of fluid while maintaining a stable flow rate and current for 144 h. Keywords: Electro-osmotic pump (EOP), Aqueous rechargeable lithium-ion battery (ARLB), Lithium iron phosphate (LFP), Electrode, Lithium ion (Li+)

Origin of the Electrochemical Stability of Aqueous Concentrated Electrolyte Solutions

The electrochemical stability of an electrolyte solution, its so-called "potential window", is simply determined by the oxidative potential and reductive potential of the solvent, if solutes dissolved in the electrolyte solution are electrochemically stable within the potential window of the solvent. Water is the most conventional solvent in the field of electrochemistry, and its potential window is as narrow as 1.23 V, thermodynamically. Practically, however, the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) need certain overpotentials, which extends the potential windows of aqueous solutions. Besides the catalytic activities of the electrode materials, the properties of aqueous solutions such as hydration structures and salt concentrations also affect the potential window.Recently, aqueous rechargeable lithium batteries (ARLBs) have attracted much attention due to their low cost and safety. However, the working voltage of ARLBs is limited to below 1.5 V due to the narrow potential window of water. Recently, a few papers have discussed the potential window of concentrated aqueous solutions with neutral pH. However, there are still fundamental unanswered questions regarding the pH-dependence of the potential window of water. In this study, the potential window of concentrated electrolyte solutions with neutral pH and the expansion of the potential window were investigated from the viewpoint of the local pH change and water concentration. Here, we shed light on the dependence of the potential window of water on local pH changes and water concentrations. Next, we focused on the water concentration, since the potential windows are determined by the water electrolysis reactions (OER and HER). The potential windows are shown in Fig. 1 as a function of the water concentrations. In this study, the onset potential of the OER/HER was defined when the current density was ± 0.1 mA cm-2 in CVs at 1 mV s-1. There are two clear tendencies in Fig. 1. First, the windows in neutral pH electrolyte solutions (closed symbols in Fig. 1) were obviously wider than those in acidic/alkaline electrolyte solutions (open symbols in Fig. 1), even at a dilute salt concentration (ca. 55 M water concentration). Second, the windows in neutral pH electrolyte solution (closed symbols in Fig. 1) were not affected by the kind of the electrolyte salt, but depended linearly on the water concentration. The windows were expanded when the water concentration decreased, i.e., the electrolyte salt concentrations increased. Potential windows of aqueous solutions were investigated systematically using various salts at different concentrations. Cyclic voltammetry measurements of Pt electrodes revealed two important points. First, the potential window in unbuffered neutral pH solution was broader than that in acidic/alkaline solutions. This expansion of potential windows can be explained by the shift in the reaction potential with local pH changes in the vicinity of the electrode. Second, the potential windows were not affected by electrolyte salts, but rather depended linearly on the water concentration. The difference for OER overpotentials was much larger than that for HER overpotentials. While HER overpotentials were derived from a local pH change, OER overpotentials were derived from both a reduced water concentration and local pH change. This study highlights the importance of these two main factors (water concentration and local pH change) in determining the potential windows of concentrated electrolyte solutions. Figure 1

Aqueous Dual-Ion Battery Based on a Hematite Anode with Exposed {1 0 4} Facets.

The aqueous rechargeable lithium battery (ARLB) is one of the most promising devices for large-scale grid applications. Currently, a key issue for ARLBs is to develop promising anode materials with favorable electrochemical performances. Here, for the first time, we demonstrate an aqueous battery that utilizes the reversible redox reaction with hydroxide ions (OH- ) in the hematite (Fe2 O3 ) anode and a commercial Li ion intercalation compound in neutral solution as the cathode. The fabricated aqueous battery displays a reversible capacity of 92 mAh g-1 . The morphology of the used Fe2 O3 anode with exposed {1 0 4} facets for this aqueous battery is unique and attractive. Importantly, with the dual-pH neutral-alkaline hybrid electrolyte, many excellent anode materials that previously could only work in alkaline electrolytes can now be successfully combined with commercial cathodes in neutral solutions, which may significantly enrich the range of anode materials for ARLBs. In addition, the reported battery configuration can be extended to other aqueous batteries beyond Li-ion ones with lower cost.

Advanced LiTi2(PO4)3 anode with high performance for aqueous rechargeable lithium battery

In this work, a high-performance LiTi2(PO4)3 coated with N-doped carbon was prepared throught sol-gel method followed by high-temperature carbonization using polyacrylonitrile (PAN) as both carbon and nitrogen sources. The morphology, structure, and electrochemical properties of LiTi2(PO4)3 samples with various carbon content are investigated. LiTi2(PO4)3 composite with 5.9% carbon exhibits the best electrochemical properties due to good dispersion, proper thickness of carbon layer, nitrogen doping for carbon layer. When tested as anode for aqueous rechargeable lithium battery, LiTi2(PO4)3 with 5.9% carbon demonstrates outstanding rate and cycling performance. The composite delivers the discharge capacity of 120.0, 106.9, and 79.1 mAh g−1 at 1, 5, and 20 C, respectively, and the capacity retention can reach 86.4% after 1000 cycles at 5 C. The excellent properties of as-synthesized sample mainly come from the accelerated transfer of lithium ions and electrons due to formation of more nano-scale channel and nitrogen doping for carbon layer. Our study reveals that PAN shows a promising prospect as both carbon and nitrogen sources in synthesis of LiTi2(PO4)3-based electrode.

High‐Energy Aqueous Lithium Batteries

AbstractOwing to the high voltage of lithium‐ion batteries (LIBs), the dominating electrolyte is non‐aqueous. The idea of an aqueous rechargeable lithium battery (ARLB) dates back to 1994, but it had attracted little attention due to the narrow stable potential window of aqueous electrolytes, which results in low energy density. However, aqueous electrolytes were employed during the 2000s for the fundamental studies of electrode materials in the absence of side reactions such as the decomposition of organic species. The high solubility of lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) in water has introduced new opportunities for high‐voltage ARLBs. Nonetheless, these ideas are somehow overshadowed by the common perception about the essential limitation of the aqueous electrolyte. The electrochemical behaviour of conventional electrode materials can be substantially tuned in the water‐in‐salt electrolytes. The latest idea of utilising a graphite anode in the aqueous water‐in‐salt electrolytes has paved the way towards not only 4‐V ARLB but also a new generation of Li−S batteries with a higher operating voltage and energy efficiency. Furthermore, aqueous electrolytes can provide a cathodically stable environment for Li−O2 batteries. The present paper aims to highlight these emerging opportunities possibly leading to a new generation of LIBs, which can be substantially cheaper and safer.

Acrylonitrile copolymer/graphene skinned cathode for long cycle life rechargeable hybrid aqueous batteries at high-temperature

For aqueous rechargeable lithium battery (ARLB), excellent cycling stability at elevated temperature is highly desirable in its application of electric vehicles (EVs). However, most state-of-art ARLBs show poor durability under high-temperature operation. Herein, we demonstrate a facile coating approach that can construct a thin acrylonitrile copolymer (ANC)/graphene skin on the top-surface of the LiMn2O4 (LMO) cathode in a rechargeable hybrid aqueous lithium battery (ReHAB). Featuring the continuous coverage and the facile electron transport, the ANC/graphene skinned cathode shows a capacity retention of 61% after 300 cycles at 60 °C, two times larger than the battery without the skin. In the cathode, ANC helps to suppress unwanted interfacial side reactions, and graphene renders a robust ion diffusion framework. Quantitative analysis of Mn suggests that the ANC/graphene skin can greatly suppress dissolution of Mn from the LMO into the aqueous electrolyte, while maintaining the charge transfer kinetics. The polymer-based nanocomposite skin on small (1.15 mAh cell) and large (7 mAh cell) cathodes show similar electrochemical improvement, indicting good scale-up potentials.

Electrochemical Performance of Structure‐Dependent LiNi1/3Co1/3Mn1/3O2 in Aqueous Rechargeable Lithium‐Ion Batteries

AbstractThis work is focused on the relationship between electrochemical performance and morphology of LiNi1/3Co1/3Mn1/3O2 (NCM) in an aqueous rechargeable lithium battery, and provides a reference for the selection of novel battery materials. In this work, NCM microrods, microspheres, and nanoblocks were successfully synthesized by solvothermal, coprecipitation, and sol–gel methods, respectively. Of the three samples, NCM nanoblocks, which are formed by agglomeration of a large number of nanoparticles, show the best electrochemical performance. During cycling, the NCM nanoblock exhibits an initial discharge capacity of 137.4 mAh g−1 and an impressive capacity of 130.8 mAh g−1 after 20 cycles at a current density of 1C (=160 mA g−1). Even at a high current density of 50C, this NCM nanoblock provides a capacity of 50.1 mAh g−1, which shows the great potential of the nanoblock as a cathode in aqueous rechargeable lithium‐ion batteries.

Electrochemical performance of LiFePO4/C synthesized by sol-gel method as cathode for aqueous lithium ion batteries

Rechargeable lithium ion batteries with aqueous electrolyte are low-cost, safe, and environmental friendly compared with organic electrolyte. Lithium iron phosphate (LiFePO4) is a potential candidate as the cathode for aqueous rechargeable lithium batteries (ARLBs), due to its excellent electrochemical window, stable structure and high theoretical capacity. However, the poor electronic conductivity and low lithium ion diffusion rate in bulk considerably restrict the electrochemical performance of LiFePO4. Herein, LiFePO4/C composites were successfully prepared by a facile sol-gel approach. Physical and electrochemical properties of the LiFePO4/C composites as cathode material in aqueous electrolyte were investigated. The LiFePO4/C composites exhibit a high reversible capacity of 163.5 mAh g−1 at 0.1C. Moreover, LiFePO4/C shows excellent rate capability and cycling capability. The improved electrochemical performance could be attributed to the positive effects of homogenous conductive carbon, which ensures the nanoscale Li-ion diffusion path and continuous electrical contact in bulk electrode.

Enhancing the electrochemical properties of LiTi2(PO4)3/C anode for aqueous rechargeable lithium battery by Li vacancy

In this paper, Li1–xTi2(PO4)3/C composites (x=0, 0.03, 0.05, 0.07) were synthesized by sol-gel approach, and the influence of Li vacancy on electrochemical performance of LiTi2(PO4)3/C anode for aqueous rechargeable lithium battery was studied. Li vacancy hardly influences the crystal structure and morphology of the composite. Electrochemical measurement results demonstrated that Li1–xTi2(PO4)3/C exhibited better performance compared with pristine LiTi2(PO4)3/C, and Li0.95Ti2(PO4)3/C has the best properties. Li0.95Ti2(PO4)3/C delivered the discharge capacity of 104.3, 92.6, and 71.8mAhg−1 at 0.2, 5, and 20C (1C=150mAg−1), 4.1, 27.3, and 34.4mAhg−1 larger than that of Li0.95Ti2(PO4)3/C at corresponding rates, respectively. After 1000cycles at 5C, the discharge capacity retention for Li0.95Ti2(PO4)3/C can reach 75.3%, 15.4% larger than that for LiTi2(PO4)3/C. Our study reveals that Li vacancy is an efficient method to enhance the electrochemical properties of LiTi2(PO4)3-based materials.

Synthesis of LiCoO2 via sol-gel method for aqueous rechargeable lithium batteries

A crystalline structure of LiCoO2 sample was synthesized at different stirring times via sol-gel method. This was followed by the electrochemical characterization of LiCoO2 in 5 M LiNO3 aqueous electrolyte. The hexagonal LiCoO2 was stirred for 30 h produced the highest peak intensity and smallest particle size. A morphological analysis showed the particle size distribution within the range of 0.32–0.47 μm. At lower scan rates of cyclic voltammetry, three pairs of redox peaks at ESCE = 0.81/0.65, 0.89/0.83 and 1.01/0.95 V were observed. The peak separation was proportionally consistent with Li+ diffusion coefficients of 7.42 × 10−8 cm2 s−1 (anodic) and 3.59 × 10−8 cm2 s−1 (cathodic). For specific capacity, the LiCoO2 demonstrated a higher initial specific capacity (115.49 mA h g−1). A small difference (1.92 Ω) in the charge transfer resistance before and after a charge discharge analysis indicated that the Li+ ions had been well-diffused during the intercalation/de-intercalation process.