High-rate Discharge Performance Research Articles

Phase structure and electrochemical properties of A5B19 La0.8-xPrxMg0.2Ni3.8 (x = 0–0.3) hydrogen storage alloy anode material

The La0.8-xPrxMg0.2Ni3.8 (x = 0, 0.05, 0.1, 0.2, 0.3) alloy were synthesized useing the induction melting method. X-ray diffraction, scanning electron microscope, electron probe micro analyzer, and electrochemical tests were used to analyze the structure and electrochemical performance of the La0.8-xPrxMg0.2Ni3.8 (x = 0–0.3) alloy. It was studied how the Pr element affected the electrochemical characteristics and microstructure of the A5B19 La-Mg-Ni based hydrogen storage alloy. The results show that the alloy consists of the CaCu5-LaNi5 phase, 2 H-Pr5Co19 phase, and 3R-Ce5Co19 phase. The abundance of the A5B19 phase increase with the increase of Pr content, while the abundance of the LaNi5 phase decrease, and the addition of Pr promotes the formation of the 2 H-Pr5Co19 phase. According to the results of the electrochemical test, every sample has good activation qualities, and the activation can be completed in 3–4 times. The activation properties are not significantly altered by the addition of Pr. The maximum discharge capacity increases at first, then decreases, reaching the highest 371.15 mAh g−1 at x = 0.2. The cyclic stability gradually improves with increasing content of Pr, and the maximum capacity retention rate reaches 85.80 % after 100 cycles. The primary factor influencing the alloy's high rate discharge ability is the exchange current density. With the increase of the exchange current density, the high rate discharge performance is gradually enhanced.

An ultrafast rechargeable and high durability lithium metal battery using composite electrolyte with the three-dimensional inorganic framework by Li6.4La3Zr1.4Ta0.6O12 surface functionalization

The liquid electrolyte used in traditional lithium-ion batteries has risks of leakage, combustion and explosion. Solid electrolyte is one of the effective strategies to solve the safety problems of lithium-ion batteries. And the use of solid electrolytes makes it possible to use lithium metal as an anode to achieve higher energy densities. At present, the main factors restricting the performance improvement of all-solid-state lithium batteries are the low electrochemical performance of electrolytes and poor solid-solid interface contact. The composite electrolyte has the advantages of both inorganic materials and polymers, but its electrochemical performance is still not up to the requirements of use. In situ synthesis of LaRuO3 with perovskite structure on the surface of Li6.4La3Zr1.4Ta0.6O12(LLZTO) induces the formation of Li2Zr2O7 while introducing defects. The Li2Zr2O7 phase "welds" inorganic particles into three-dimensional(3D) inorganic framework, increasing the reaction sites between inorganic fillers and polymers. Compared with the primitive sample, the ionic conductivity of the modified electrolyte is increased by an order of magnitude at room temperature, wherein the lithium-ion conductivity of the composite electrolyte with 3% LaRuO3 is as high as 6.06 × 10−4 S cm−1. At 5C, the discharge specific capacity of LiFePO4 | [email protected] 3% LRO | Li can reach 114.6 mAh g−1; After 400 cycles, the discharge specific capacity remains at 129.6 mAh g−1. Under the same conditions, the discharge specific capacities of the unmodified samples are only 92.4 mAh g−1 and 35 mAh g−1. The high rate discharge performance of solid-state lithium metal battery supports the high torque output of motor, which improves the acceleration performance of electric vehicles or ships. The high capacity and excellent cycle performance of solid-state lithium metal battery can significantly extend the driving range and service life of electric vehicles.

Characteristics of electrochemical hydrogen storage of TiFe based alloys with Ni composite by mechanical milling

In this paper, Ti1.04Zr0.1La0.06Fe0.6Ni0.3Mn0.2 + x wt% Ni (x = 0, 2, 5, 7, 10) composite were prepared by ball milling for 1 h, and the effects of Ni powder addition on the structure, morphology and electrochemical properties of the alloy were investigated. As the results show that after ball milling for 1 h with Ni powder, the composite consists of TiFe, ZrMn2, and Ni triple phases. With increasing of Ni powder addition, the uniformity of Ni powder coating on the alloy surface is improved, and the discharge capacity, cycling stability and high-rate discharge (HRD) performance of the composite are significantly improved. The first discharge capacity of the x = 10% alloy was as high as 286.9 mAh/g, and the retention rate reaches 77.8% after 50 cycles, which is nearly 90% higher than that of the alloy with x = 0% alloy (38.7%). At a current density of 80 mA/g, the HRD value of the x = 10% alloy (59.4%) was improved by 97.8% compared to that of the non-Ni powder ball milling alloy (30.03%), and the kinetic parameters (D, IL and Rct) showed a trend consistent with the pattern of variation of high-rate discharge performance. The uniform coating of Ni powder with high electrical conductivity and excellent electrocatalytic activity on the alloy surface is a primary factor for the enhanced electrochemical properties of Ni composite.

(Digital Presentation) Synthesis and Properties of Llithium Iron Phosphate Cathode Materials without Carbon Coating with High-Rate Property

Lithium iron (ferrium) phosphate (LFP) use iron as a transition metal, so there is lower resource risk. And because of tolerant to overcharging, they have excellent safety and durability. Lithium-ion secondary batteries using LFP have become widely used as main power sources for EVs and ESSs in recent years. Originally, LFP has higher bulk resistance than other layered rock salt-based positive materials, so that carbon-coating was applied to surface of LFP particles. This idea was extremely effective in putting LFP into practical use. However, the use of the carbon coat has led disadvantage of high cost despite the use of cheaper iron because the manufacturing process increases. We report that we have developed LFP that has extremely high-rate charge and discharge performance even though it does not have carbon coating. Figure 1

Study on the evolution of phase and properties for ternary La-Y-Ni-based hydrogen storage alloys with different stoichiometric ratios

In recent years, some progress has been made in the development and application of the highly anticipated La-Y-Ni hydrogen storage alloy system. However, the relationship between the structure and properties of materials has not been studied systematically and thoroughly. In this paper, the evolution law of AB3-, A2B7- and A5B19-type phases for La-Y-Ni-based hydrogen storage alloys was proposed. The single-phase LaY2Ni9 (AB3), La2Y4Ni21 (A2B7) and La5Y10Ni57 (A5B19) alloys were synthesized by powder sintering method at 1173, 1353 and 1423 K, respectively. The XRD and SEM results of the alloys show that LaY2Ni9 alloy has a single PuNi3 phase (3 R), La2Y4Ni21 alloy is composed of Ce2Ni7 phase (2 H) and Gd2CO7 phase (3 R), and La5Y10Ni57 alloy contains Pr5Co19 phase (2 H) and Ce5Co19 phase (3 R). Among the three alloys, the La2Y4Ni21 alloy has the largest hydrogen storage capacity (1.59 wt%) in solid /H2 reaction at 313 K. The target alloys all exhibit excellent electrochemical activation ability. The maximum discharge capacity of LaY2Ni9, La2Y4Ni21 and La5Y10Ni57 alloys decreases gradually, but their cycle stability increases in turn. The high-rate discharge performance of La2Y4Ni21 alloy is the best, because its exchange current density (I0 = 75.55 mA/g) and hydrogen diffusion coefficient (D0 = 2.51 ×10−10 cm2/s) cooperate well. It is hoped that these findings can offer theoretical guidance and technical assistance for the development of La-Y-Ni-based hydrogen storage alloys.

Study on the possibility of diagonal line rule in elemental doping effects in Li4Ti5O12 by mechanochemical method

Li4Ti5O12 (LTO) were doped with the same group element (Zr4+), diagonal elements (Nb5+ and W6+), and same period element (V5+) of titanium, respectively, to quantitative doping effect and explore the possibility of diagonal line rule in doping. It is conducive to synthesis doping Li4Ti5O12 with excellent properties by the ammonia-assisted mechanical ball-milling method (AAMBM). Through systematic experimental comparison, Li4Ti4.95Nb0.05O12 (LTNO) exhibits finer particle, higher specific surface area, narrower band gap, and more excellent electrochemical performance compared to others, since Nb and Ti have similar ion polarization ability, standard electrode potential, and the conjugable outer electron arrangement (Nb 4d45s1 whose 5 s electrons can be delocalized to d orbits to form half full orbit state). Particularly, LTNO shows the highest initial first discharged capability up to 151 mAh g−1 and the capacity retention of 90% at 5 C rate after 300 cycles, indicating both outstanding high-rate discharge performance and cycling stability. The doping factor was proposed to roughly quantify their doping effect of Zr4+, Nb5+, V5+, and W6+, by using the ratio of specific capacity values of doped LTO and pure LTO after 500 cycles at 5 C, which are 1.2, 1.86, 1.05, and 1.08, respectively.

Electrochemical Properties of Layered LiMoO<sub>2 </sub>as Cathode for Li-Ion Batteries

With the development of new energy vehicles, it is necessary to develope new fast charging cathode materials for lithium ion batteries. This paper reports a simple carbon thermal reduction routine to synthesize layered LiMoO2 cathode for Li-ion batteries. Impurity-free micro-crystalline powders were synthesized by one-step method with a thermal treatment at 800°C for 5 hrs under N2 atmosphere. The structural, morphological and electrochemical properties of LiMoO2 were characterized by using X-ray diffraction pattern (XRD), scanning electronic microscopy (SEM), charge/discharge cycling and electrochemical impedance spectroscopy (EIS). The diffraction results indicate that the prepared sample has a layered hexagonal structure related to α-NaFeO2. The secondary particles are in order of 2.0 μm length on average with homogeneous distribution. The initial discharge capacity of LiMoO2 is 110.9 mAh·g-1 at 0.1 C, and the capacity can still remain 92.8 mAh·g-1 after 100 cycles. The good cycling performance and high rate discharge performance are attributed to the smaller charge-transfer resistance revealed by EIS results.

Properties of Carbon-coated SiO-C Negative Electrodes for Sulfide-type All-solid-state Batteries

Carbon-coated SiO (SiO-C) sheet-type electrodes without sulfide-based solid electrolytes on a current collector worked as negative electrode materials for all-solid-state batteries. The SiO-C sheet-type electrodes exhibited the high capacity (ca. 1500 mAh g−1), good cycle and high-rate discharge performance for all-solid-state batteries using sulfide solid electrolytes at room temperature. It is notice that SiO-C film electrodes are expected to promote new ionic-electronic conducting interface for sulfide-based solid electrolytes in all-solid-state batteries.

Effect of varying Ni content on hydrogen absorption–desorption and electrochemical properties of Zr-Ti-Ni-Cr-Mn high-entropy alloys

The crystal structure, pressure composition isotherms, and electrochemical properties of Zr0.2Ti0.2Ni0.2+xCr0.2Mn0.2 (x = 0, 0.025, 0.05, 0.075, and 0.1) high-entropy alloys (HEAs) were investigated. The crystal structures of all the HEAs consisted of two phases: a primary phase with a C14-type (Zr0.5Ti0.5)Mn2 hexagonal structure and a secondary phase with a B2-type Ti0.6Zr0.4Ni cubic structure. Rietveld analysis revealed that the secondary phase increased with an increase in the x value. The hydrogen storage capacity of the HEAs was lower than that of the alloy with x = 0 because of an increase in the B2-type Ti0.6Zr0.4Ni phase, whereas the change in enthalpy of hydride formation (|ΔH|) decreased with increasing x, leading to the instability of hydrides. The alkaline treatment was performed by immersing HEA powders or electrode in a 6 M KOH aqueous solution at 378 K for 2 h. The Zr0.2Ti0.2Ni0.2Cr0.2Mn0.2 alloy surface changed to a porous and rough structure, and a ZrO2 passive thin layer on their surface, which is replaced by NiO or Ni(OH)2 after the alkaline treatment. The charge–discharge tests conducted using the HEA negative electrodes for Ni-MH batteries depict that the discharge capacity increased with an increase in x, and the highest discharge capacity was 368 mAh g‐1 at x = 0.075 after the alkaline treatment. On increasing the x value, the high-rate dischargeability and cycle performance were also enhanced.

Study on the in situ sulfidation and electrochemical performance of spherical nickel hydroxide

In this paper, atmospheric reflux in water is used to directly form a nickel sulfide layer in-situ with excellent conductivity sulfide on the surface of spherical nickel hydroxide particles, significantly improving the conductivity of nickel hydroxide particles. The experimental results show that the spherical Ni(OH)2@NiS material synthesized by the in situ sulfurization method. As the cathode active material of nickel-iron batteries exhibits excellent electrochemical performance, especially high-rate discharge and cycle performance, which are better than nickel hydroxide electrodes with cobalt oxide. The atmospheric reflux method in water has a simple process and equipment and has no pollution to the environment. Spherical Ni(OH)2@NiS materials synthesized by in situ vulcanization can completely replace nickel hydroxide material with cobalt, and they have great commercial application value and market competitiveness as cathode active materials for alkaline nickel-based batteries.

Influence of Sm doping on thermodynamics and electrochemical performance of AB5+z alloys in low-temperature and high-power Ni-metal hydride batteries

AB5-type negative electrode materials have been extensively used for Ni-metal hydride batteries. However, their rate capabilities have hindered them from being more extensively applied, especially in hybrid electric vehicles at low temperatures. Here, a hyper-stoichiometric AB5.09 alloy is designed and Sm is doped to achieve high-power performance. The influence of the microstructural characteristics, thermodynamic stabilities and comprehensive electrochemical performance resulting from the substitution of Sm for La and Ce is investigated. This work demonstrates that the addition of Sm results in a decrease in the maximum capacity and hydride stability. Furthermore, with the stress concentration relieving effect from the increase of anisotropy of the c/a ratio, the cycling stability increases significantly. Due to the formation of the Ni2MnAl catalytic phase, all alloys possess a high density of phase boundaries and exhibit good high-rate discharge performance. The high-rate dischargeability and specific power are further improved after Sm doping, with the high-rate discharge capacity retention rate reaching 81.4% at 3000 mA g−1. Although Sm adversely affects the surface catalytic properties of the electrodes, the high Sm content alloy exhibits higher specific power and discharge capacity at −40 °C due to the decrease in hydride stability.

Preparation of neodymium‐doped LiMnPO 4 /C cathode by sol‐gel method with excellent electrochemical performance for lithium‐ion batteries

The porous spherical structure neodymium-doped LiMn1−xNdxPO4/C nanoparticles have been prepared through glycolic acid-assisted sol-gel method. The neodymium-ion doping effect on the crystalline microstructure, crystal appearance, and electrochemical parameters of LiMnPO4/C cathodes have been detected by X-ray diffractometer (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), charge and discharge test, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) method. XRD patterns show that a proper amount of neodymium-ion doping could not change the host crystal structure; combined with EDS spectra, we could conclude that Nd3+ has successful embedding into the lattice structure of LiMnPO4/C. SEM analysis shows that the LiMn0.94Nd0.06PO4/C sample has the uniform and fine particles diameter distribution in comparison with other doped samples. The electrochemical measurement results indicate that the LiMn0.94Nd0.06PO4/C has the initial discharge specific capacity of 155.2 mAh/g at 0.05 C discharge rate; after 200 cycles, the capacity value reduces slightly to 138.7 mAh/g, the capacity retention rate is maintained at 89.4%. The LiMn0.94Nd0.06PO4/C has high-rate discharge performance with the specific capacity value of 128.0 mAh/g (10 C). The results conclude that a proper amount of neodymium-ion doping ratio could effectively enhance the lithium-ion diffusivity and improve high-rate performance of LiMnPO4 cathode materials.

Operando Structural Analysis of Phase Transition of Graphite Electrode during Li De-Intercalation Process Using Synchrotron Radiation X-Ray Diffraction

Introduction : In order to promote development of electric vehicle, it is required to improve the capacity density, the low-temperature performance, and the high-rate property of the batteries. Understanding the lithium intercalation and de-intercalation mechanism at graphite electrode of the storage battery (LIB) is very important for this purpose. Crystal structure changes of lithium-intercalated graphite during charge and discharge processes were investigated by operando X-ray diffraction (XRD) measurements using a synchrotron radiation facility. Low-temperature operando XRD measurements were now available by the development of a new temperature-controlled cell jacket.1-2 This study confirmed in-plane structure change along a- and b-axis as well as stage structure change along c-axis.3 As a result, it was elucidated that crystallinity of graphitic carbon caused differences in phase transition during discharge and this phenomenon affected low-temperature and high-rate discharge performances. Experimental : Coin cells composed of carbon and NMC electrodes were firstly prepared and subjected to the evaluation of the battery performances from the low-temperature (0℃) to the room temperature. Coin cells of several graphitic carbon were evaluated.Crystal structures of lithium-intercalated graphite during discharge process were investigated by operando analysis using synchrotron radiation X-ray diffraction (SR-XRD) at BL28XU beam line of SPring-8. Al-laminated half-cells composed of graphitic carbon and Li electrodes were prepared and subjected to the analysis of operando measurement. The graphitic carbons of different crystallite sizes were analysed. Al-laminated half-cells conditioned by several cycles were used for the measurement. Operando XRD measurements were carried out during charge and discharge processes. X-ray of 25keV (its wavelength of 0.0496 nm) with a beam size of 0.2 mm ×0.5 mm was used to obtain diffraction patterns. The exposure time was set to 10 s. The diffraction patterns were obtained by two-dimensional detector, PILATUS 100K (DECTRIS). Two-dimensional image data were converted to one-dimensional 2q profiles, and the diffraction peaks were separated using the Lorentz functions.The test cell underwent an aging treatment was charged (Li insertion) at room temperature. Thereafter, structural transition were analyzed during the discharging process (Li de-intercalation) in 0.2C at room temperature and in 0.1C at 0℃. Results and Discussion : Figure 1 shows the SR-XRD patterns of lithium-intercalated graphite at the discharge process with current density of 0.2C at room temperature. The result showed the in-plane structure change along a- and b-axis as well as stage structure change along c-axis.The detailed analysis of in-plane structure change and stage structure change for each graphitic carbon was performed using the operando measurements. It was identified that the crystallinity of graphitic carbon caused differences in phase transition during discharge. These results showed that crystallite sizes influence the phase transition and give major effect on LIB performances of graphite negative electrode at low-temperature or high-rate discharge. The Li diffusivity in the graphitic carbon is likely dependent on the crystallite size. The battery reaction mechanism influenced by crystallite size was elucidated by operando XRD measurements. The present results confirm that the crystallinity of the graphitic carbon affects the low-temperature and high-rate discharge characteristics. The detail results will be shown in the conference. Acknowledgment: This work was supported by the Research and Development Initiative for Scientific Innovation of New Generation Battery 2 (RISING2) project administrated by the New Energy and Industrial Technology Development Organization (NEDO).

Effect of Mg content in the La3-xMgxNi9 battery anode alloys on the structural, hydrogen storage and electrochemical properties

The present work is focused on the studies of structure, hydrogen storage and electrochemical properties of the La3-xMgxNi9 (x = 1.0, 1.1 and 1.2) alloys as active materials of negative electrodes in the Nickel-Metal Hydride (Ni/MH) batteries. A change of Mg content affects properties of the studied alloys such as the phase homogeneity, hydrogen storage and electrochemical capacities, cycle stability, and high-rate discharge performance. X-ray diffraction study shows that Mg substitution for La and annealing of the La3-xMgxNi9 alloys promotes the formation of more homogeneous materials, with a predominant formation of the target AB3 PuNi3 structure type intermetallics. The electrodes prepared from the annealed alloys show the maximum discharge capacities of ∼400 mAh g−1 at discharge current density of ∼60 mA/g. The high rate discharge-abilities (HRD) at the discharge current density of 350 mA g−1 keep high values of the remaining reversible discharge capacities, ∼86, 85 and 80%, for the La2MgNi9, La1·9Mg1·1Ni9 and La1·8Mg1·2Ni9 alloy electrodes, respectively. After 200 cycles with 100% depth of discharge (DOD), the La1·9Mg1·1Ni9 alloy electrode exhibits a very good cycling stability with its discharge capacity remaining at a level of ∼64% of its initial capacity.

Electrochemical Studies of the Nickel‐based Hydroxide Electrode for the Oxygen Evolution Reaction and Coulombic Efficiency of the Electrode

AbstractNickel hydroxide, Ni(OH)2 electrode material has been used as a positive electrode in commercial alkaline secondary batteries for more than 100 years. This is because Ni(OH)2 has a good high rate discharge ability performance, wide operation and storage temperature range and relatively low. However, the Ni(OH)2 positive electrode exhibits poor performance which results from (i) competitive reactions of the oxidation of the active material and evolution of oxygen. (ii) The reduced charge acceptance of Ni(OH)2 positive electrode is suspected to be related to a relatively long distance between Ni(OH)2 particles and the nearest portion of the substrate. In this study, electrodes are prepared using β‐Ni(OH)2 powder as the active electrode material, hot‐pressed onto a nickel mesh current collector. The Ni2+ in the compound β‐Ni(OH)2 material is partially substituted with Co2+ and Al3+ metals and the performance of as‐prepared materials are optimized and examined. XRD, FTIR, TG‐DTA, SEM/EDS, and ICP confirms the formation of the expected compositions. The samples with 5 wt.% Co2+, and 10 wt.% Al3+ metals are found to be the optimal compositions with promising electrochemical activities. The modification of Ni(OH)2 by the partial substitution of Co2+ and Al3+ metals for Ni2+ shows some effect on the redox peaks of Ni(OH)2 and the oxygen evolution reaction (OER). E.g. the onset for oxidation of the active material is significantly improved with partial substitution of Ni2+ by Co2+. On the other hand partial substitution of Ni2+ with Al3+ moves the onset of electrode oxidation to higher potential. In addition, the partial substitution of 10 wt.% Al3+ metal improves both discharge capacity (from 128 mAh/g to 170 mAh/g), and the coulombic efficiency (from 87 % to 93 %) of the β‐Ni(OH)2 electrode.

Effect of Y substitution on the high rate dischargeability of AB4.6 alloys as an electrode material for nickel metal hydride batteries

AB4.6 alloys exhibit excellent high rate dischargeability (HRD) performance but the quick capacity degradation and low discharge capacity restrict application of nickel metal hydride batteries. This study investigated the effect of substituting La with Y on the multiphase structures and overall electrochemical characteristics of the La0.90-xCe0.08YxZr0.02Ni3.91Co0.14Mn0.25Al0.30 (x = 0, 0.3, 0.5, and 0.7) alloys. The results showed that Y tended to form stable [A2B4] subunit rather than [AB5] subunit, thus the Ce2Ni7-type phase abundance increased from 16.00 wt% to 26.30 wt%, and improved the maximum discharge capacity and hydrogen diffusion. The decrease of icorr and particle size demonstrated that the addition of Y enhanced anti-corrosion capability but degraded anti-pulverization capability, where small particles obtained via pulverization were very sensitive to corrosion, thus leading to degradation in discharge capacity. The La0.6Ce0.08Y0.3Zr0.02Ni3.91Co0.14Mn0.25Al0.30 alloy exhibited excellent electrochemical properties, with maximum discharge capacity of 350.4 mAh g−1, cycle stability of 80.15% after 100 cycles and HRD of 73.56% (3000 mA g−1).

Investigation of facial B2O3 surface modification effect on the cycling stability and high-rate capacity of LiNi1/3Co1/3Mn1/3O2 cathode

Abstract A LiNi1/3Co1/3Mn1/3O2 (NCM111) cathode with B2O3 surface modification was prepared in a facial synthesis method using H3BO3 as a modifier precursor. Both TEM and XPS measurements demonstrate that a thin layer of amorphous B2O3 is successfully coated on the surface of 1B2O3@NCM111 particles. XRD, SEM and TEM testing results show that the morphology and lattice structure present little change after coating. The B2O3 surface modified 1B2O3@NCM111 shows 43% improved high-rate (at 5C rate) discharge performance and enhanced cycling stability (with about 92% and 86% capacity retention at 1C and 2C rates after 50 and 100 cycles measurements) compared to the pristine NCM111. EIS and GITT results also present that the 1B2O3@NCM111 electrode with B2O3 surface modification retains higher Li+ chemical diffusion coefficient than the pristine NCM111 even after 50 charge/discharge cycles at 1C rate.

Clusters of flower-shaped CuO nanosheets: microstructure and enhanced high-rate dischargeability properties of LaNi3.81Mn0.30Co0.78Al0.11 alloy electrodes

Nickel metal hydride (Ni-MH) batteries play an important role in new-energy vehicles; however, the poor high rate dischargeability (HRD) of the negative electrode materials (hydrogen storage alloy) limits its further application in high-power fields. In this work, a facile strategy was applied to improve the HRD performance of AB5-type alloy (LaNi3.81Mn0.30Co0.78Al0.11) by introducing flower-shaped CuO nanosheets to the electrode. Compared with the bare alloy, the modificatory electrode (3 wt.% CuO) shows enhanced HRD performance of increasing from 8.4 to 31.4% at a discharge current density of 1800 mA g−1. Besides, the corresponding capacity retention rate at the 100th cycle (S100) increases from 83.3 to 93.6%. For kinetic property, the exchange current density increases from 144.6 to 267.9 mA g−1 and the hydrogen diffusion coefficient increases from 1.96 × 10−15 to 6.52 × 10−15 cm2 s−1 (3 wt.% CuO), which mean the faster hydrogen diffusion rate. These are contributed to the 3-dimensional clusters of flower-shaped CuO nanosheets seamlessly integrated with hydrogen storage alloy and the formation of Cu particles deposited at the surface of alloy particles during charge/discharge process, decreasing the internal resistance and polarization of the hybrid electrode.

Crystal Structures and Electrochemical Properties of R1.5Ca1.5MgNi14(R=Nd, Gd and Er) Hydrogen Storage Alloys

Ca3MgNi14, Nd1.5Ca1.5MgNi14, Gd1.5Ca1.5MgNi14 and Er1.5Ca1.5MgNi14 alloys were prepared by high frequency induction melting and sintering. Characterization and analysis were performed by X-ray diffraction/Rietveld full-spectrum fitting, gaseous P-C-T hydrogen storage test and electrochemical properties tests. It can be found that all alloys consist of Gd2Co7-type 3R phase and Ce2Ni7-type 2H phase. Although the hydrogen storage capacities of Nd1.5Ca1.5MgNi14, Gd1.5Ca1.5MgNi14 and Er1.5Ca1.5MgNi14 decrease to some extent compared to that of Ca3MgNi14, their equilibrium pressures for absorption and desorption increase markedly. Moreover, R1.5Ca1.5MgNi14 alloys have better cycling stabilities and high-rate discharge(HRD) properties as compared to Ca3MgNi14. The hydrogen diffusion in alloy electrodes is the main factor to influence the HRD performance.

Spherical Shaped Particle of Randomly Packed LiFePO4 Nanoplates for High-Rate of Li-Ion Batteries

Energy storage is the key factor for saving and using renewable energy. Among the various energy storage devices, Li-ion battery is the most promising storage device owing to its high energy density, efficiency and cycle life. Not only for the small application like mobile phone and laptop computer but also electric vehicles (EVs) and massive energy storage system (ESS), numerous applications have been used Li-ion battery. However its high energy density is like a double-edged sword, the safety issues have been a problem for the practical market. The safety problems from the Li-ion battery usually come from thermal runaway, which is mainly come from oxygen release from the cathode material. Lithium iron phosphate (LFP) has PO4 polyanion that oxygen atom is strongly bonded with phosphorus and prevents oxygen release, therefore, it is well known as the safe cathode material for the Li-ion battery. Also for the high power battery applications, LFP is a promising material owing to the ability of high-rate charge and discharge performance. For the high rate availability on LFP material, two important key factors should be satisfied; one is fast ion diffusion inside the material and the other is high electric conductivity. The Li-ion diffusivity coefficient and electron conductivity are intrinsic properties of the material, however, particle size or morphology and conducting agent coating can raise the speed of diffusion and conduction. Here, we demonstrated those factors by solvo-thermally synthesized plate shape nanoparticle and spherical secondary particle with carbon coating using spray-drying. The nanoparticle has a flat shape in b-axis, therefore, diffusion speed increase because the diffusion distance of lithium is greatly reduced. The nanoparticle without spray-drying showed low capacity and also poor C-rate performance even with the carbon coating. Besides, after forming the spherical particles, it showed 162mAh/g of initial capacity at the 0.1C rate and maintains more than 80% of initial capacity (~130.91mAh/g) at the 50C rate. Moreover, electrode density which is the intrinsic weakness of nanoscale electrode material has been improved and the spheres carried out excellent cycling ability which shows 98% capacity retention over 500cycles at 1C after the high C-rate test. In order to analyze the causes of such good characteristics, morphology and crystallographic directions were confirmed by SEM and TEM image, and electrical conductivity and diffusion coefficient were calculated by using Cyclic Voltammetry (CV), Galvanostatic Intermittent Titration Technique (GITT) and Electrochemical Impedance Spectroscopy (EIS). More details will be discussed at the meeting.