Discharge Capacity Loss Research Articles

High Cycling Performance Cathode Material: Interconnected LiFePO4/Carbon Nanoparticles Fabricated by Sol‐Gel Method

Interconnected LiFePO4/carbon nanoparticles for Li‐ion battery cathode have been fabricated by sol‐gel method followed by a carbon coating process involving redox reactions. The carbon layers coated on the LiFePO4 nanoparticles not only served as a protection layer but also supplied fast electrons by building a 3D conductive network. As a cooperation, LiFePO4 nanoparticles encapsulated in interconnected conductive carbon layers provided the electrode reactions with fast lithium ions by offering the lithium ions shortening and unobstructed pathways. Field emission scanning electron microscopy (FESEM) and X‐ray diffraction (XRD) tests showed optimized morphology. Electrochemical characterizations including galvanostatic charge/discharge, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) tests, together with impedance parameters calculated, all indicated better electrochemical performance and excellent cycling performance at high rate (with less than 9.5% discharge capacity loss over 2000 cycles, the coulombic efficiency maintained about 100%).

Electrochemical Behavior of Polyaniline Microparticle Suspension as Flowing Anode for Rechargeable Lead Dioxide Flow Battery

A type of redox flow battery, based on lead (II) dissolved in the electrolyte, has emerged as possible system for energy storage. However, the formation of lead dendrite and the evolution of hydrogen in the last stage of charge have limited the application of soluble lead flow batteries. A comparison study on electrochemical behavior of polyaniline (PANI) suspension indicates that the electrochemical response of PANI suspension in flowing mode significantly differs from that in static state, exhibiting good charge transfer property due to continuous renewal of PANI microparticles by the flow of suspension. Therefore, PANI microparticle suspension is used as anode material to fabricate the lead dioxide flow battery. The cycle performance of the lead dioxide flow battery has been improved by replacing the lead electrode with the flowable PANI, and the average of discharge capacity loss is only 0.05% per cycle during 60 cycles. The coulombic efficiency shows no significant change with the number of cycles over the experiment. Furthermore, the working current density of 20 mA cm−2 in the proposed battery system has been achieved, which is greatly enhanced compared with the conventional PANI film batteries.

A single flow zinc//polyaniline suspension rechargeable battery

Both the electrochemical activity and the energy density of polyaniline (PANI) microparticles suspensions are enhanced by using the compact PANI powder, which is synthesized galvanostatically with 4,4′-diaminobiphenyl as additive. A Zn//PANI suspension rechargeable flow battery system is proposed, in which the flowable PANI suspension is used as cathode electroactive material, zinc plate as anode. A microporous membrane is used as separator to prevent PANI particles from getting into the anode compartment. Results obtained from the small laboratory battery show that the discharge capacity density gradually decreases with number of cycles and the average of discharge capacity loss during 32 cycles is about 0.07% per cycle. However, an average coulombic efficiency of 97% has been achieved at the current density of 20 mA cm−2 and the value of coulombic efficiency shows no significant change during 32 charge/discharge cycles. The flow-through mode for PANI cathode material enables the PANI-based battery to operate at a higher current density in comparison with the conventional Zn–PANI film batteries, and the present findings can mark a new route to improve the performance of conductive polymer-based energy storage devices.

Degradation mechanism of room temperature Na/Ni3S2 cells using Ni3S2 electrodes prepared by mechanical alloying

Ni3S2 powder has been fabricated by mechanical alloying Ni and S powders and the electrochemical properties of Na/Ni3S2 cells fabricated from Na anodes and Ni3S2 cathodes and 1 M sodium trifluoromethanesulfonate in tetraethyleneglycol dimethylether liquid electrolyte have been investigated. Upon discharging, the Ni3S2 cathode transformed to amorphous Na2S, Ni and residual unconverted Ni3S2. On charging, the pristine structure of Ni3S2 is fully recovered. The reversibility of this anode/cathode pair has been demonstrated and the discharge capacity loss of Na/Ni3S2 cells has been investigated over 100 cycles. From TEM, EDS, XRD, and EIS results, the degradation mechanism appears to be the formation of nano-particles of Ni3S2 and Na2S which become detached from the bulk cathode material causing the continuous increase in the interfacial resistance. Furthermore, many small cracks in Ni3S2 cathode material are caused during repeated cycling and this is an additional phenomenon that leads to further degradation of the discharge capacity during cycling.

Effect of Amino Acid Additives on the Positive Electrolyte of Vanadium Redox Flow Batteries

Two amino acids (L-glutamate and L-arginine) have been used respectively as an additive in a positive electrolyte containing 2.0 M VOSO4 and 3.0 M H2SO4 for all-vanadium redox flow batteries. The effects of each additive on the thermal stability and electrochemical properties of the positive electrolyte are investigated. The thermal stability tests show that the addition of L-glutamate to the positive electrolyte could delay the initiation of precipitation in the electrolyte for 12 hours at 40°C and 5 hours at 50°C. Cyclic voltammetry results suggest that the electrochemical reversibility of V(IV)/V(V) redox couple in the electrolyte has been improved by the addition of either L-glutamate or L-arginine. The diffusion coefficient of V(IV) has been increased from 0.47∼1.30 × 10−6 cm2/s in the pristine electrolyte to 0.54 ∼1.50 × 10−6 cm2/s in the electrolyte with L-glutamate and 0.70 ∼1.93 × 10−6 cm2/s in the electrolyte with L-arginine. The discharge capacity loss (312.4 mAh) of the cell with L-glutamate in the positive electrolyte is smaller compared to that (503.8 mAh) of the cell with the pristine positive electrolyte. The columbic efficiency and energy efficiency of the cell are also increased by 1.7% and 2.0%, respectively, by the addition of L-glutamate in the positive electrolyte of the cell.

Surface-coating Modification of Li-rich Cathode Materials Li[Li 0.2 Mn 0.4 Fe 0.4 ]O 2

Li-rich cathode material of Li[Li0.2Mn0.4Fe0.4]O2 was prepared by co-precipitation,and was modified by surface coating with Al2O3.The modified samples were characterized by X-ray diffraction,scanning electron microscopy,and electrochemical tests.It was found that the 4.0% Al2O3 coated Li[Li0.2Mn0.4Fe0.4]O2 exhibited a good cycling performance compared with the bare Li[Li0.2Mn0.4Fe0.4]O2.The discharge capacity loss of the surface coated Li[Li0.2Mn0.4Fe0.4]O2 after 50 cycling was about 9%.

Electrochemical Properties and Discharge Mechanism of Na/TiS2 Cells with Liquid Electrolyte at Room Temperature

The electrochemical properties of Na/TiS2 cells fabricated from Na anodes and TiS2 cathodes and 1M sodium trifluoromethanesulfonate in tetraethyleneglycol dimethylether liquid electrolyte have been investigated. The discharge curve has two plateau regions of 2.1 V and 1.6 V. The loss of discharge capacity appeared mainly in the upper plateau (UP) region (2.0–2.6 V) and the discharge capacity in the low plateau (LP) region (0.8–2.0 V) does not decrease and is consistent during 40 cycles. The discharge process between Na and TiS2 has a complex reaction mechanism, the intercalation at the upper plateau region and the conversion at the low plateau region. Because, a distorted TiS2 phase appeared in the upper plateau, a new phase of NaxTiS2 was observed in the lower plateau, and the NaxTiS2 phase was disappeared after full discharge from the XRD and TEM results. The decrease of discharge capacity during cycling is occurred from the formation of NaxTiS2 phase in the cathode after full charging and is accumulated over cycling

Electrochemical study of LaNi3.55Mn0.4Al0.3Fe0.75 as negative electrode in alkaline secondary batteries

Cobalt-free AB5-type hydrogen storage alloys have been examined for the purpose of lowering metal hydride raw material costs. For this purpose, the electrochemical behaviour of cobalt-free LaNi3.55Mn0.4Al0.3Fe0.75 alloy was investigated using chronopotentiometry and electrochemical impedance spectroscopy. It was shown that the discharge capacity decreases by 50% after fifty cycles. To investigate the capacity decrease, the impedance measurements were conducted during charging at different stages of life cycle. The experimental impedance spectroscopy reveals that the metal hydride electrode exhibits a porous behaviour. The results were then analyzed on the basis of equivalent circuit model involving the porous electrode behaviour according to de Levie's model, i.e. equivalent cylindrical pores connected in parallel. The pore texture of electrode material was then estimated namely by the pore number, mean values of cylinder radius and effective length. The loss of discharge capacity is due to that of the reactivity of the electrode material and not the collapsing of pore texture.

Ion exchange membranes as electrolyte for high performance Li-ion batteries

High ionic conductivity exceeding 10−3 S cm−1 at room temperature is achieved with lithiated perfluorinated sulfonic acid (PFSA-Li) ion exchange membranes by swelling in nonaqueous organic solvents. The dependence of ionic conductivity on the membrane equivalent weight, solvent uptake, solvent properties including viscosity and dielectric constant and temperature is investigated for PFSA-Li membranes. The high performance of Li-ion battery using the PFSA-Li membranes as both electrolyte and separator is demonstrated. This new battery shows very good thermal stability and cyclic performance as compared to conventional Li-ion battery using organic liquid electrolytes. At 55 °C, this battery shows less than 3% discharge capacity loss over 120 cycles, however battery with liquid electrolyte decreased to 76% of the initial capacity after 80 cycles.

Silicon nanowire core aluminum shell coaxial nanocomposites for lithium ion battery anodes grown with and without a TiN interlayer

We investigated the effect of aluminum coating layers and of the support growth substrates on the electrochemical performance of silicon nanowires (SiNWs) used as negative electrodes in lithium ion battery half-cells. Extensive TEM and SEM analysis was utilized to detail the cycling induced morphology changes in both the Al-SiNW nanocomposites and in the baseline SiNWs. We observed an improved cycling performance in the Si nanowires that were coated with 3 and 8 wt.% aluminum. After 50 cycles, both the bare and the 3 wt.% Al coated nanowires retained 2600 mAh/g capacity. However beyond 50 cycles, the coated nanowires showed higher capacity as well as better capacity retention with respect to the first cycle. Our hypothesis is that the nanoscale yet continuous electrochemically active aluminum shell places the Si nanowires in compression, reducing the magnitude of their cracking/disintegration and the subsequent loss of electrical contact with the electrode. We combined impedance spectroscopy with microscopy analysis to demonstrate how the Al coating affects the solid electrolyte interface (SEI). A similar thickness alumina (Al2O3) coating, grown via atomic layer deposition (ALD), was shown not to be as effective in reducing the long-term capacity loss. We demonstrate that an electrically conducting TiN barrier layer present between the nanowires and the underlying stainless steel current collector leads to a higher specific capacity during cycling and a significantly improved coulombic efficiency. Using TiN the irreversible capacity loss was only 6.9% from the initial 3581 mAh/g, while the first discharge (lithiation) capacity loss was only 4%. This is one of the best combinations reported in literature.

Charge–discharge performance of Cr-substituted V-based hydrogen storage alloy negative electrodes for use in nickel-metal hydride batteries

To improve the charge–discharge cycle durability of a TiV 2.1Ni 0.3 alloy negative electrode with a discharge capacity of ∼470 mAh g −1, the vanadium constituent was partially substituted with chromium. The TiV 2.1− x Cr x Ni 0.3 ( x = 0.1–0.4) alloys, which were prepared by arc-melting, were composed of two phases, similar to the TiV 2.1Ni 0.3 alloy. Each constituent was distributed in both phases, and the V and Cr content in the primary phase was higher than that in the secondary phase, although the Ti and Ni content was higher in the secondary phase. The maximum discharge capacity for the TiV 2.1− x Cr x Ni 0.3 ( x = 0.1–0.4) negative electrodes showed a slight decrease as the x value increased, and their cycle durability was significantly improved due to the effective suppression of the dissolution of V. In particular, the loss of discharge capacity per cycle for the TiV 1.7Cr 0.4Ni 0.3 negative electrode was about one-tenth that for the TiV 2.1Ni 0.3 negative electrode. The high-rate dischargeability (HRD) was also greatly improved by increasing the Cr content. At 200 mA g −1 the variations of the HRD and the charge transfer resistance ( R ct) with the Cr content were similar, while at 400 mA g −1 the change in the HRD at a lower Cr content was markedly different from the change in R ct. Moreover, at a lower Cr content the potential at a 50% degree of discharge stagnated at specific discharge currents over 200 mA g −1. These results strongly suggest that hydrogen diffusion in the primary phase served as the main hydrogen reservoir.

Nanosized Li4Ti5O12/graphene hybrid materials with low polarization for high rate lithium ion batteries

We report a simple strategy to prepare a hybrid of lithium titanate (Li4Ti5O12, LTO) nanoparticles well-dispersed on electrical conductive graphene nanosheets as an anode material for high rate lithium ion batteries. Lithium ion transport is facilitated by making pure phase Li4Ti5O12 particles in a nanosize to shorten the ion transport path. Electron transport is improved by forming a conductive graphene network throughout the insulating Li4Ti5O12 nanoparticles. The charge transfer resistance at the particle/electrolyte interface is reduced from 53.9Ω to 36.2Ω and the peak currents measured by a cyclic voltammogram are increased at each scan rate. The difference between charge and discharge plateau potentials becomes much smaller at all discharge rates because of lowered polarization. With 5wt.% graphene, the hybrid materials deliver a specific capacity of 122mAhg−1 even at a very high charge/discharge rate of 30C and exhibit an excellent cycling performance, with the first discharge capacity of 132.2mAhg−1 and less than 6% discharge capacity loss over 300 cycles at 20C. The outstanding electrochemical performance and acceptable initial columbic efficiency of the nano-Li4Ti5O12/graphene hybrid with 5wt.% graphene make it a promising anode material for high rate lithium ion batteries.

Li/LiFePO4 batteries with gel polymer electrolytes incorporating a guanidinium-based ionic liquid cycled at room temperature and 50 °C

Gel polymer electrolytes composed of PVdF-HFP microporous membrane incorporating a guanidinium-based ionic liquid with 0.8molkg−1 lithium bis(trifluoromethanesulfonylimide) are characterized as the electrolytes in Li/LiFePO4 batteries. The ionic conductivity of these gel polymer electrolytes is 3.16×10−4 and 8.32×10−4Scm−1 at 25 and 50°C, respectively. The electrolytes show good interfacial stability towards lithium metal and high oxidation stability, and the decomposition potential reaches 5.3 and 4.6V (vs. Li/Li+) at 25 and 50°C, respectively. Li/LiFePO4 cells using the PVdF-HFP/1g13TFSI-LiTFSI electrolytes show good discharge capacity and cycle stability, and no significant loss in discharge capacity of the battery is observed over 100 cycles. The cells deliver the capacity of 142 and 150mAhg−1 at the 100th cycling at 25 and 50°C, respectively.

Li4Ti5O12Heattreated under Nitrogen Ambient with Outstanding Rate Capabilities

The powders of spinel Li4Ti5O12were prepared by heat treating the mixture of rutile TiO2and Li acetate at800∘Cfor 3 h under a nitrogen atmosphere and, for comparison, under air as well. The powders heated underN2show a remarkably higher-rate capability and better cycle stability. The discharge capacity of Li4Ti5O12heated underN2at 19°C (corresponding to a 3.2-minute total discharge) reached 107 mA hg−1, 22 mA hg−1higher than that of Li4Ti5O12heated under air, which was 85 mA hg−1. The former material also shows a much better cycle stability, with no discharge capacity loss after 300 cycles at 6°C or 16.3°C. The results indicate that heat treatment under low-oxygen partial pressure atmosphere such asN2could significantly improve the high-rate performance of spinel Li4Ti5O12.

Effect of rhodium substitution on the electrochemical performance of LiFePO 4/C

The effect of rhodium (Rh) substitution on the electrochemical properties of LiFePO 4/C cathode materials was studied. The results of electrochemical measurement show that Rh substitution can improve the rate capability of LiFePO 4/C. However, heavy Rh substitution causes a discharge capacity loss. The LiFe 0.975Rh 0.025PO 4/C sample shows an excellent high rate performance and its discharge capacity at a 10 C rate is 117.0 mAh g −1 with a discharge voltage plateau of 3.31–3.0 V versus Li/Li +. LiFe 0.975Rh 0.025PO 4/C also shows a noticeably better cycling life at high temperature than LiFePO 4/C. It still remains a capacity of 135.4 mAh g −1 at the 300th cycle at 55 °C under a 1 C rate, which is 82.0% of its initial capacity.

A new solid-state process for synthesis of LiMn 1.5Ni 0.5O 4− δ spinel

A new two-step solid-state process was developed for synthesis of a pure phase 4.7 V LiMn 1.5Ni 0.5O 4− δ (LMNO) spinel of good electrochemical properties. This process which was based on formation of stable Ni 1− x Mn 2O 4− δ ( x ≤ 0.33) spinel followed by subsequent lithiation, demonstrated the emerging of LiMn 1.5Ni 0.5O 4− δ frame work at temperatures of as low as 350 °C. During this lithiation process, migration of metal ions (Ni/Mn) from partially occupied tetrahedral 8a sites (in Ni 0.67Mn 2O 4− δ ) toward octahedral 16d site occurred. The resultant spinel material displayed low irreversible loss, a 97% columbic efficiency and 6% loss in discharge capacity after 100 cycles at 60 °C.

Preparation and electrochemical properties of TiO 2 hollow spheres as an anode material for lithium-ion batteries

TiO 2 hollow spheres are fabricated by a sol–gel process using carbon spheres as template. The diameter and the shell thickness of the TiO 2 hollow spheres are about 400–600 nm and 60–80 nm, respectively. The electrochemical properties of the hollow spheres are investigated by galvanostatic cycling and cyclic voltammetry (CV) measurements. The initial discharge capacity reaches 291.2 mAh g −1 at a current density of 60 mA g −1. The average discharge capacity loss is about 1.72 mAh g −1 per cycle from the 2nd to the 40th cycles and the coulombic efficiency is approximately 98% after 40 cycles, indicating excellent cycling stability and reversibility.

Preparation and electrochemical properties of polymer Li-ion battery reinforced by non-woven fabric

A polymer electrolyte based on poly(vinylidene) fluoride-hexafluoropropylene was prepared by evaporating the solvent of dimethyl formamide, and non-woven fabric was used to reinforce the mechanical strength of polymer electrolyte and maintain a good interfacial property between the polymer electrolyte and electrodes. Polymer lithium batteries were assembled by using LiCoO2 as cathode material and lithium foil as anode material. Scanning electron microscopy, alternating current impedance, linear sweep voltammetry and charge-discharge tests were used to study the properties of polymer membrane and polymer Li-ion batteries. The results show that the technics of preparing polymer electrolyte by directly evaporating solvent is simple. The polymer membrane has rich micro-porous structure on both sides and exhibits 280% uptake of electrolyte solution. The electrochemical stability window of this polymer electrolyte is about 5.5 V, and its ionic conductivity at room temperature reaches 0.151 S/m. The polymer lithium battery displays an initial discharge capacity of 138 mA·h/g and discharge plateau of about 3.9 V at 0.2 current rate. After 30 cycles, its loss of discharge capacity is only 2%. When the battery discharges at 0.5 current rate, the voltage plateau is still 3.7 V. The discharge capacities of 0.5 and 1.0 current rates are 96% and 93% of that of 0.1 current rate, respectively.

Sr doped Co substituted Li nickelate cathode materials for Li cells with improved cycling and thermal stability

Samples of cathode material were synthesized from a highly dispersed precursor containing 0.002 at.% Sr. The synthesis was performed from a mixture of the precursor with some overstoichiometric excess of LiOH at 720 °C in oxygen atmosphere. Part of the samples were coated with a thin film of Li-borate glass. The cathode active material (CAM) was mixed with 15 wt.% of Teflonized acethylene black and pressed on thin Al discs. The cathodes were cycled between 4.20 V and 3.20 V at 1 mA cm−2 first at 25 °C and then at 50 °C, whereafter the cycling continued up to 50–60 cycles. A pulse interruption method was applied to measure the DC area-specific resistivity of the cathodes Rc as a function of the state of discharge x. The evolution of the parameters of the Rc/x plots during cycling lent valuable information on the processes responsible for the degradation of the intercalation compound. The stability of the CAM during overdischarge was evaluated after 10 cycles at 25 °C and 24 cycles at 50 °C at 1 mA cm−2. The cathode was shorted externally for 2 min to 0.00 V. In spite of the large current during the overdischarge the discharge capacity loss in the next cycle was only 3%.

Effects of synthetic parameters on structure and electrochemical performance of spinel lithium manganese oxide by citric acid-assisted sol–gel method

The spinel lithium manganese oxide cathode materials were prepared by citric acid-assisted sol–gel method at 623–1073 K in air. The effects of pH value, raw material, synthesis temperature and time on structure and electrochemical performance of spinel lithium manganese oxide are investigated by X-ray diffraction (XRD), scanning electronic microscope (SEM) and cyclic voltammetry (CV). XRD data results strongly suggest that the synthesis temperature is the dominating factors of the formation of spinel phase, and spinel lithium manganese oxide powder with various crystallites size can be obtained by controlling the sintering time. CV shows that spinel lithium manganese oxide powder formed about 973 K presents the best electrochemical performance with well separated two peaks and the highest peak current. Charge–discharge test indicates that spinel lithium manganese oxide powders calcined at higher temperatures have high discharge capacity and capacity loss, and sintered at lower temperatures has low discharge capacity and high capacity retention.