Characterization of a scroll compressor under extended operating conditions

Refrigeration and air-conditioning compressors are designed to work under well-defined conditions. In some applications it is interesting to observe their performances beyond these conditions, for example in the case of a high temperature two-stage heat pump or of a cooling system working at high temperature.In this study a compressor is characterized experimentally with refrigerant R134a and through 118 tests at condensing pressures varying from 8.6 up to 40.4 bar (t_sat = 33.9 °C to t_sat = 100.8 °C) and evaporating pressures varying from 1.6 up to 17.8 bar (t_sat = ?15.6 °C to t_sat = 62.4 °C). Under these conditions the compressor motor was pushed at its maximal current in several tests.This compressor’s performance is mainly characterized by its isentropic and volumetric efficiencies. It presents a maximal isentropic efficiency of 72%, corresponding to a pressure ratio of around 2.5–2.6. The volumetric efficiency decreases linearly from almost 1.0 (for a pressure ratio of 1.3) to 0.83 (for a pressure ratio of 9.7). A slight degradation of the isentropic and volumetric efficiencies is observed when the compressor supply and exhaust pressures are increased for a given pressure ratio; this could be due to an internal leakage.The compressor tests are used to identify the six parameters of a semi-empirical simulation model. After parameter identification, experimental and simulated results are in very good agreement, except for some points at high compressor power where the compressor is pushed at its maximal current.     

Operation of PEM fuel cells at 120–150 °C to improve CO tolerance

Sulfonic acid modified perfluorocarbon polymer proton exchange membrane (PEM) fuel cells operated at elevated temperatures (120–150 °C) can greatly alleviate CO poisoning on anode catalysts. However, fuel cells with these PEMs operated at elevated temperature and atmospheric pressure typically experience low relative humidity (RH) and thus have increased membrane and electrode resistance. To operate PEM fuel cells at elevated temperature and high RH, work is needed to pressurize the anode and cathode reactant gases, thereby decreasing the efficiency of the PEM fuel cell system. A liquid-fed hydrocarbon-fuel processor can produce reformed gas at high pressure and high relative humidity without gas compression. If the anode is fed with this high-pressure, high-relative humidity stream, the water in the anode compartment will transport through the membrane and into the ambient pressure cathode structure, decreasing the cell resistance. This work studied the effect of anode pressurization on the cell resistance and performance using an ambient pressure cathode. The results show that high RH from anode pressurization at both 120 and 150 °C can decrease the membrane resistance and therefore increase the cell voltage. A cell running at 150 °C obtains a cell voltage of 0.43 V at 400 mA cm⁻² even with 1% CO in H₂. The results presented here provide a concept for the application of a coupled steam reformer and PEM fuel cell system that can operate at 150 °C with reformate and an atmospheric air cathode.     

CO2 adsorption on porous NiO as a cathode material for molten carbonate fuel cells

Molten carbonate fuel cells (MCFC) are the systems suitable for large-scale energy production. The cathode material used in these cells is NiO. In this study the NiO cathode was synthesized by tape-casting method and the adsorption of CO₂, one of the cathode feeding gases, was investigated on it. The adsorption studies were carried out by the use of packed column and the adsorption analysis were performed using pulse response technique. There were two 1/4 in. diameter and 5 and 10 cm length columns prepared for the experiments and they were packed with 3 mm average particle sized NiO. The experiments were carried out with gas chromatography using He as a carrier gas. The response curves were taken after pulsing the columns with CO₂. The equilibrium constants and heat of adsorption of CO₂ on NiO were determined by the use of the first absolute moment equations corresponding to retention times. It was observed that the adsorption was physical in nature. From the adsorption constants determined at different temperatures and the heat of adsorption, ΔH⁰, was found as −1299 cal mol⁻¹.     

MCFC performance diagnosis by using the current-pulse method

Several problems prevent molten carbonate fuel cells (MCFC) operation for an extended period. However, if the degradation factors can be identified and resolved in a timely manner, MCFC could become a valuable technology. Therefore, a performance diagnosis should be developed which enables the simple and instantaneous determination of MCFC degradation factors. A suitable six parameter equation obtained by a current-pulse method, obtainable from MCFC's transient response in 100 ms, is expressible in an equivalent circuit composed of three sub-circuits. The relationship between these parameters and each degradation factor is evaluated by a single MCFC cell, the electrode area of which is 16 cm². Degradation factors include cross-leakage, electrolytic loss, cell temperature distribution and gas composition/flow rate. As a result, each of six parameters in the MCFC transient response corresponds to an ohmic potential drop, anode/cathode gas diffusion resistance, reactive resistance, three-phase interfacial resistance and electrolyte properties, respectively. The proposed performance diagnosis specifies the degradation factors by combining the six parameters. Performance diagnosis was applied to a single MCFC cell of an electrode area of 81 cm in extended operations, and the degradation factor diagnosed. As a result, the diagnosis was able to specify the cell degradation factors from the degradation factor ratio, corresponding to cell voltage, cell resistance and the N₂ concentration of MCFC single cell performance. Therefore, the proposed performance diagnosis is able to easily specify the driven MCFC degradation factors in a timely manner.     

Integration of solid oxide fuel cell and palladium membrane reactor: Technical and economic analysis

This paper presents a technical and economic analysis of a solid oxide fuel cell system equipped with a palladium membrane reactor (PMR–SOFC) with the aim of determining the benefits of such an integrated unit over the conventional reformer module (CON-SOFC). The performance of both SOFC systems under the conditions for energetically self-sustaining operation (Q_NET = 0) was achieved by varying the fuel utilization for each operating voltage. Two types of fuels, i.e., methane and desulphurized biogas, are considered. The simulation results show that the maximum power density of the CON-SOFC fuelled by methane (0.423 W/cm²) is higher than that of the CON-SOFC fuelled by biogas (0.399 W/cm²) due to the presence of CO₂ in biogas. For the PMR–SOFC, it is found that the operation at a higher permeation pressure offers higher power density because lower fuel utilization is required when operating the SOFC at the energy self-sustained condition. When the membrane reactor is operated at the permeation pressure of 1 bar, the methane-fuelled and biogas-fuelled PMR–SOFCs can achieve the maximum power density of 0.4398 and 0.4213 W/cm², respectively. Although the PMR–SOFC can offer higher power density, compared with the CON-SOFC, the capital costs of supporting units, i.e., palladium membrane reactor, high-pressure compressor, and vacuum pump, for PMR–SOFC need to be taken into account. The economic analysis shows that the PMR–SOFC is not a good choice from an economic viewpoint because of the requirement of a large high-pressure compressor for feeding gas to the membrane reactor.     

Mathematical modeling and simulation of a cogeneration plant

This work aims to develop mathematical models to simulate a single shaft gas turbine based cogeneration plant with variable geometry compressor. At off-design the variable vanes are re-staggered to improve the cogeneration performance. Two modes of operation are identified with the first mode being for part load of less than 50% running to meet the part load demand. This is achieved by controlling the fuel flow and air bleeding at the downstream of the compressor to avoid surge formation. The second mode of operation is for part load greater than 50%. It is running to meet both the part load demand and the exhaust gas temperature set value by simultaneously regulating the fuel flow and the variable vanes opening. To accommodate change of compressor parameters during variable vanes re-stagger correction coefficients are introduced. A behavior of a 4.2 MW power generating cogeneration plant is simulated. The effect of variation of power and ambient temperature on cogeneration parameters like fuel consumption, temperature, pressure, variable vanes opening, efficiency and steam generated is studied. Comparison between the field data and the simulation results is in good agreement. To support the calculations required for off-design analysis, a computer program is developed in MatLAB environment.     

Construction of fuel reformer using proton conducting oxides electrolyte and hydrogen-permeable metal membrane cathode

We constructed a reformer of methane based on an electrochemical principle. This apparatus consists of the proton conducting ceramics electrolyte and the hydrogen-permeable metal membrane cathode. For methane reforming, a mixture of methane and oxygen gas is supplied to the porous Ag cathode. The hydrogen ions, which formed by the anode reaction: CH₄ + O₂ → CO₂ + 4H⁺ + 4e⁻, are transported through the proton conducting ceramics to the cathode. Then, the hydrogen is formed at the cathode by the reaction: 4H⁺ + 4e⁻ → 2H₂. The hydrogen, which permeates through the metal membrane cathode, is 100% purity.The hydrogen separation ability of the reformer was investigated at 400–650 °C by measuring the electric current through the proton conducting oxide electrolyte. Since the ionic transport number of the proton conducting oxide is nearly unity, the current through the electrolyte corresponds to the proton flux through the electrolyte.The current measurements showed that the extracted proton flux through the electrolyte increased with increasing the applied voltage as well as temperature as we expected. However, the current measurements under the low voltage revealed that the extracted current was lesser than the expected value from Ohm's law. The decrease of the current is possibly caused for the reduction of the effective voltage by the anode polarization. In order to separate the hydrogen with higher efficiency, the applied voltage must be as low as possible using the thinner electrolyte and the improved anode.     

Using aluminum and Li2CO3 particles to reinforce the α-LiAlO2 matrix for molten carbonate fuel cells

The electrolyte substrate (matrix) of a molten carbonate fuel cell (MCFC) provides both ionic conduction and gas sealing. During the starting-up and operating of MCFC stacks at 923 K, the matrix can experience mechanical stresses that can cause cracking. In particular, the pure α-LiAlO₂ that is generally used for the MCFC possesses poor mechanical strength. In this study, we employed Al and Li₂CO₃ particles as reinforcement materials to increase the mechanical strength of the α-LiAlO₂ matrix for its stable long-term operation. The mechanical strength of the matrix increased dramatically after adding Al particles into the pure matrix. Moreover, we operated a single cell for 2000 h after adding Li₂CO₃ particles into the Al-reinforced matrix to prevent a Li-ion shortage caused by a lithiated Al reaction in the matrix.     

Electrochemical behavior of polyamides with cyclic disulfide structure and their application to positive active material for lithium secondary battery

Polyamides (DTA-I, DTA-II, and DTA-III) containing cyclic disulfide structure were prepared by condensation between 1,2-dithiane-3,6-dicarboxylic acid (DTA) and alkyl diamine, NH₂–(CH₂)_n–NH₂ (DTA-I; n=4, DTA-II; n=6, DTA-III; n=8) and their application to positive active material for lithium secondary batteries was investigated. Cyclic voltammetry (CV) measurements under slow sweep rate (0.5 mV s⁻¹) with a carbon paste electrode containing the polyamide (DTA-I, DTA-II, or DTA-III) were performed. The results indicated that the polyamides were electroactive in the organic electrolyte solution (propylene carbonate (PC)-1,2-dimethoxyethane (DME), 1:1 by volume containing lithium salt, such as LiClO₄). The responses based on the redox of the disulfide bonds in the polyamide were observed.Test cells, Li/PC-DME (1:1. by volume) with 1 mol dm⁻³ LiClO₄/the polyamide cathode, were constructed and their performance was tested under constant current charge/discharge condition. The average capacity of the test cells with the DTA-III cathode was 64.3 Ah kg⁻¹ of cathode (135 Wh kg⁻¹ of cathode, capacity (Ah kg⁻¹) of the cathode×average cell voltage (2.10 V)). Performance of the cell with linear polyamide containing disulfide bond (–CO–(CH₂)₂–S–S–(CH₂)₂–CONH–(CH₂)₈–NH–, GTA-III) was also investigated and the average capacity was 56.8 Ah kg⁻¹ of cathode (100 Wh kg⁻¹ of cathode, capacity (Ah kg⁻¹) of the cathode×average cell voltage (1.76 V)). Cycle efficiency of the test cell with the DTA-III cathode was higher than that with the GTA-III cathode.     

An experimental analysis of the effect of refrigerant charge level on an automotive refrigeration system

The performance of an automotive refrigeration system is dependent on the refrigerant charge level. Due to inevitable leaks in the system, the amount of refrigerant will decrease over time and thus ultimately reduce the system's performance. A reduction in the amount of refrigerant charge results in excessive compressor cycling, a lower condenser pressure, a higher refrigeration temperature, and an increase in the amount of superheat. This paper identifies and quantifies the individual component losses in an automotive refrigeration system as a function of the refrigerant charge level. A second law analysis, based on nondimensional entropy generation, is carried out to quantify the thermodynamic losses. A passenger vehicle with a cycling-clutch, orifice tube refrigeration system was instrumented to measure various temperatures and pressures, and relative humidity. The data were collected at idle conditions. Thermodynamic equations, which are used to determine the system's thermal performance, are presented. The system's second law efficiency increases 26 % as the amount of refrigerant charge decreases by 44 %. Also the individual component losses are quantified as a function of the refrigerant charge level. The compressor and the condenser losses account for the largest percentage of the total losses, and are of similar magnitude. The evaporator–accumulator and the orifice tube losses account for a smaller percentage of the total losses, and are also of similar magnitude. With a reduction in the refrigerant charge level of 44 %, the losses in the compressor, the condenser, the evaporator–accumulator, and the orifice tube decrease 13 %, 8 %, 10 %, and 33 %, respectively.     

A novel polygeneration system integrating the acetylene production process and fuel cell

This paper presents a novel polygeneration system that integrates the acetylene process and the use of fuel cells. The system produces acetylene and power by a process of the partial oxidation/combustion (POC) of natural gas process, a water–gas shift reactor, a fuel cell and a waste heat boiler auxiliary system to recover the exhaust heat and gas from the fuel cell. Based on 584.3 kg/h of natural gas feedstock, a POC reactor temperature of 1773 K, an absorber pressure of 1.013 MPa and a degasser pressure of 0.103 MPa, the simulation results show that the new system achieved acetylene production of 1.9 MW, net electricity production of 1.7 MW, power generation efficiency of 26.8% and exergy efficiency of 43.4%, which was 20.2% higher than the traditional acetylene production process. The new system's exergy analysis and the flow rate of the products were investigated, and the results revealed that the energy conversion and systematic integration mechanism demonstrated the improvement of natural gas energy conversion efficiency.     

Decarbonized hydrogen and electricity from natural gas

This paper discusses configuration, attainable performances and thermodynamic features of stand-alone plants for the co-production of de-carbonized hydrogen and electricity from natural gas (NG) based on commercially available technology.We focus on the two basic technologies currently used in large industrial applications: fired tubular reformer (FTR) and auto-thermal reformer (ATR). In both cases we assume that NG is pre-heated and humidified in a saturator providing water for the reforming reaction; this reduces the amount of steam to be bled from the power cycle and increases electricity production. Outputs flows are made available at conditions suitable for transport via pipeline: 60 bar for pure hydrogen, 150 bar for pure CO₂. To reduce hydrogen compression power requirements reforming is carried out at relatively high pressures: 25 bar for FTR, 70 bar for ATR. Reformed gas is cooled and then passed through two water–gas shift reactors to optimize heat recovery and maximize the conversion to hydrogen. In plants with CO₂ capture, shifted gas goes through an amine-based chemical absorption system that removes most of the CO₂. Pure hydrogen is obtained by pressure swing absorption (PSA), leaving a purge gas utilized to fire the reformer (in FTR) and to boost electricity production.For the power cycle we consider conventional steam cycles (SC) and combined cycles (CC). The scale of plants based on a CC is determined by the gas turbine. To maintain NG input within the same range (around 1200 MW), we considered a General Electric 7FA for ATR, a 6FA for FTR. The scale of plants with SC is set by assuming the same NG input of the corresponding CC plant.Heat and mass balances are evaluated by a model accounting for the constraints posed by commercial technology, as well as the effects of scale. Results show that, from a performance standpoint, the technologies of choice for the production of de-carbonized hydrogen from NG are FTR with SC or ATR with CC. When operated at high steam-to-carbon ratios, the latter reach CO₂ emissions chargeable to hydrogen of 10–11 kg of CO₂ per GJ_LHV—less than 20% of NG—with an equivalent efficiency of hydrogen production in excess of 77%.     

Effects of coal syngas and H2S on the performance of solid oxide fuel cells: Single-cell tests

The performance of single-cell planar solid oxide fuel cells using coal syngas, with and without hydrogen sulfide (H₂S), was studied. A state-of-the-art gas delivery system, data acquisition system, and test stand were designed and assembled for experimentation. All cells were tested at 850 °C with a constant current load of 14.3 A (current density of 0.20 A cm⁻²). The results from using syngas with no H₂S indicated no degradation after 290 h of operation. After immediately injecting CO (and water) in the H₂–N₂ mixture, there was a slight tendency of improving performance (power) and then the behavior remained steady. On the other hand, results for the test with syngas in the presence of H₂S (200–240 ppm) indicated good performance over 570 h (650 h total operation time) with 10–12.5% degradation. The results suggest these cells can be used for extended periods of time for syngas applications, and in the presence of H₂S the cells show no major degradation.     

Studies on the initial behaviours of the molten carbonate fuel cell

Mathematical modelling of the unsteady-state of a unit molten carbonate fuel cell (MCFC) has been made. The behaviour of the fuel cell at the beginning of the operation is observed. The effects of the molar flow rates of gases and the utilization of fuel gas are studied. The current density decreases with time and reaches a steady-state value of 0.14 A cm⁻² at 0.58 s for the chosen reference conditions. As the inlet gas-flow rates or the hydrogen utilization are increased, the time required to reach a steady-state decreases. With increased flow rates of the anode and cathode gases, the average current density is high and the total concentration is low. The current density increases with increasing utilization of hydrogen.     

Metal membrane-type 25-kW methanol fuel processor for fuel-cell hybrid vehicle

A 25-kW on-board methanol fuel processor has been developed. It consists of a methanol steam reformer, which converts methanol to hydrogen-rich gas mixture, and two metal membrane modules, which clean-up the gas mixture to high-purity hydrogen. It produces hydrogen at rates up to 25 N m³/h and the purity of the product hydrogen is over 99.9995% with a CO content of less than 1 ppm. In this fuel processor, the operating condition of the reformer and the metal membrane modules is nearly the same, so that operation is simple and the overall system construction is compact by eliminating the extensive temperature control of the intermediate gas streams. The recovery of hydrogen in the metal membrane units is maintained at 70–75% by the control of the pressure in the system, and the remaining 25–30% hydrogen is recycled to a catalytic combustion zone to supply heat for the methanol steam-reforming reaction. The thermal efficiency of the fuel processor is about 75% and the inlet air pressure is as low as 4 psi. The fuel processor is currently being integrated with 25-kW polymer electrolyte membrane fuel-cell (PEMFC) stack developed by the Hyundai Motor Company. The stack exhibits the same performance as those with pure hydrogen, which proves that the maximum power output as well as the minimum stack degradation is possible with this fuel processor. This fuel-cell ‘engine’ is to be installed in a hybrid passenger vehicle for road testing.     

High power BaFe(VI)O4/MnO2 composite cathode alkaline super-iron batteries

This short communication demonstrates that not only pure Fe(VI) cathodes, but also MnO₂/Fe(VI) composite cathodes can substantially enhance the high power discharge of alkaline batteries. The 2.8 Ω and 0.7 W high power discharge of alkaline cells are investigated for 3:1 and 1:1 composite MnO₂/BaFeO₄ cathode cells, provide discharge energies intermediate to that found in the (non-composite) BaFeO₄ cathode cell. At a constant 2.8 Ω load, the 1:1 composite MnO₂/BaFeO₄ cell delivers up to 40% higher energy capacity than the MnO₂ pure cathode alkaline cell, and up to three-fold the capacity of the constant 0.7 W power MnO₂ discharge.     

Oil distribution in a transcritical CO2 air-conditioning system

To properly determine the oil charge to the compressor of a closed-loop vapor compression system, it is important to be able to accurately estimate how much oil is held-up in refrigeration cycle components other than the compressor. To provide such information, this paper reports the results of an experimental investigation of the oil distribution behavior in a specific transcritical CO₂ air-conditioning system. To experimentally measure the oil retention at each individual cycle component, a novel oil injection–extraction method was applied and a new test facility was developed. Experimental results show that as the oil concentration of the working fluids discharged from the compressor increases the oil retention volume in the heat exchangers and suction line also increases. Thirty-two percent and 24% of the total oil amount charged initially is retained in heat exchangers and suction line at 5 wt.% of oil circulating with the refrigerant at a mass flow rate of 14 and 27 g/s, respectively. Experimental results also show that the effect of the oil on the evaporator pressure drop increases as the oil concentration increases at constant refrigerant mass flow rate. For the refrigerant mass flow rate of 14 g/s and 27 g/s, the evaporator pressure drop increases up to 280% and 40%, respectively, when the oil concentration increases from 0 to 5 wt.% The effect of oil on pressure drop was found to be most profound at high vapor qualities where the local oil concentration is the highest. For a CO₂ air-conditioning system, the oil retention in gas cooler, evaporator, and suction line is expected to be less than 20% of the initial oil charge if the oil concentration is maintained less than 1 wt.%.     

Optimisation of processing and microstructural parameters of LSM cathodes to improve the electrochemical performance of anode-supported SOFCs

To improve the electrochemical performance of LSM-based anode-supported single cells, a systematic approach was taken for optimising processing and materials parameters. Four parameters were investigated in more detail: (1) the LSM/YSZ mass ratio of the cathode functional layer, (2) the grain size of LSM powder for the cathode current collector layer, (3) the thickness of the cathode functional layer and the cathode current collector layer, and (4) the influence of calcination of YSZ powder used for the cathode functional layer.Results from electrochemical measurements performed between 700 and 900 °C with H₂ (3 vol.% H₂O) as fuel gas and air as the oxidant showed that the performance was the highest using an LSM/YSZ mass ratio of 50/50. A further increase of the electrochemical performance was obtained by increasing the grain size of the outer cathode current collector layer: the highest performance was achieved with non-ground LSM powder. In addition, it was found that the thickness of the cathode functional layer and cathode current collector layer also affects the electrochemical performance, whereas no obvious detrimental effects occurred with the different qualities of YSZ powder for the cathode functional layer. The highest performance, i.e. 1.50 ± 0.05 A cm⁻² at 800 °C and 700 mV, was obtained with a cathode functional layer, characterised by an LSM/YSZ mass ratio of 50/50, a d₉₀ of the LSM powder of 1.0 μm, non-calcined YSZ powder, and a thickness of about 30 μm, and a cathode current collector layer, characterised by d₉₀ of the LSM powder of 26.0 μm (non-ground), and a thickness of 50–60 μm. Also interesting to note is that the use of non-ground LSM for the cathode current collector layer and non-calcined YSZ powder for the cathode functional layer obviously simplifies the production route of this type of fuel cell.     

Testing and modelling of a variable speed scroll compressor

Variable speed compressors offer continuous control, low noise level, reduced vibration, low-start current, rapid temperature control, by operating the compressor at higher speeds initially, and better COPs than the conventional on/off control. However, there exist some drawbacks concerning the inverter efficiency, the effect of the inverter on the induction motor and the effect of variable speed on the compressor isentropic and volumetric efficiencies. This study gives some experimental results as to inverter and compressor performances: it can be observed that the inverter efficiency varies between 95% and 98% for compressor electrical power varying between 1.5 and 6.5 kW ; and that compressor efficiencies are not enormously influenced by compressor supply frequency, but depend mainly on compressor pressure ratio, except the tests developed at 35 Hz and one test at 40 Hz, for which the difference is attributed to the compressor internal leakages due to a lack of lubrication at low speeds. At 75 Hz there was also observed a slight degradation that can be attributed to the electromechanical losses that increase with compressor speed. A maximal isentropic efficiency of 0.65 for a pressure ratio of the order of 2.2 is obtained. The volumetric efficiency decreases linearly from 0.98 for a pressure ratio of 1.5 to 0.83 for a pressure ratio of 5.6. In spite of the test conditions (condensing and evaporating pressures up to 40 and 20 bar, respectively), the compressor performance stays unchanged. The experimental results obtained at 50 Hz are used to identify six parameters of a semi-empirical model which is then used to simulate the different tests developed at different compressor speeds. The simulated results are in very good agreement with those measured with averages errors of ?0.5 K; +3 g s^?1 and ?24 W for the exhaust temperature, the refrigerant flow rate and the compressor electrical power, respectively. The results show that motor losses induced by the inverter are negligible.     

The preparation of NaV1−xCrxPO4F cathode materials for sodium-ion battery

The key to development of sodium-ion battery is the preparation of cathode/anode materials. Cr doped NaV_1−xCr_xPO₄F (x = 0, 0.04, 0.08) were prepared by the high temperature solid-state reaction for the application of cathode material of sodium-ion batteries. The structures and morphologies of the cathode materials were characterized by Flourier-infrared spectra (FT-IR), X-ray diffraction (XRD) and scanning electron microscope (SEM). The effects of Cr doping on performances of the cathode materials were analyzed in terms of the crystal structure, charge–discharge curves and cycle performances. The results showed that the as-prepared Cr-doped materials have a better cycle stability than the un-doped one, an initial reversible capacity of 83.3 mAh g⁻¹ can be obtained, and the first charge–discharge efficiency is about 90.3%. In addition, it was also observed that the reversible capacity retention of the material is still 91.4% in the 20th cycles.