Charge-discharge Specific Capacity Research Articles

Application of porous carbon nanoelectrode materials for lithium-ion batteries

Abstract In order to achieve carbon neutrality and gradually improve the current global warming environmental situation, the world’s major research teams are committed to developing lithium-ion batteries with better performance, trying to use in various new energy facilities, such as electric vehicles, which can effectively reduce polluting gas emissions. Nowadays, many electrode materials that can improve the performance of lithium-ion batteries have been continuously emerging, such as carbon nanotubes and silicon-based nanomaterials. However, carbon nanotube electrode materials have the disadvantages of high irreversible capacity, voltage lag and high manufacturing cost, while silicon-based nanomaterials also have the drawbacks of volume expansion and poor electrical conductivity. Based on the mature research of carbon materials, extensive raw material sources and large reserves, completely non-toxic and low comprehensive cost, this research analyzes three new porous carbon nanoelectrode materials with high development potential, and shows their electrochemical performance advantages, such as high charge-discharge specific capacity, excellent rate performance, and low charge transfer impedance.

Synthesis and Properties of the LiMn2O4 Cathode Material for Lithium-ion Batteries

Spinel LiMn2O4 was synthesized by high-temperature solid-state method with lithium salt and manganese salt as raw materials, which were mixing with anhydrous ethanol as solvent under stirring, and calcining at high temperature in in the oxygen atmosphere. X-ray diffraction (XRD) and scanning electron microscope (SEM) showed that the size of lithium manganese particles with spinel structure was 80 to 200 nm, and the particle size distribution was uniform. The results showed that the prepared LiMn2O4 sample sintered at 700°C exhibited superior electrochemical performance when used as a cathode material for lithium-ion batteries with a voltage window of 2.5–4.8 V. The first charge-discharge specific capacity and first discharge capacity can reach 158.0 mAh‧g-1 and 138.4 mAh‧g-1, respectively, at 0.1 A‧g-1 current density, and the first Coulomb retention efficiency is 87.6%. The discharge specific capacity of the LiMn2O4 material can be maintained at 114 mAh‧g-1 when the test current density was returned to 0.1 A‧g-1 after 60 cycles.

Nano GeSe2/C anchored in carbon sponge skeleton for free-standing flexible lithium-ion battery electrodes

As a typical conversion alloyed anode material, Germanium selenide (GeSe2) exhibits isotropic lithiation behavior and high theoretical charge-discharge specific capacity. However, pure GeSe2 anode faces significant volume expansion (∼250 %−360 %) and further exploration is needed in the preparation of flexible electrode materials and structural design. Herein, a simple strategy is designed to load GeSe2/C-2 nanoparticles with porous carbon-coated structure on a flexible cross-networking substrate. The 3D network substrate is composed of highly conductive carbon nanotubes and adhesive cotton cellulose fibers. A two-step method involving coating and cross-linking is designed to achieve the fabrication of self-supporting flexible electrodes. As an anode for LIBs, the one layer GeSe2 discs with ∼0.65 mm thickness manifest capacities of 827.1, 744.4, 676.3, and 472.9 mAh g−1 at 0.1, 0.2, 0.5, and 1 A g−1, respectively. This superior Li+ storage performance can be attributed to the positive collective impact from the integration of nano-scale material, low crystalline properties, and carbon sponge skeleton. Furthermore, the GITT tests indicate that the diffusion coefficient of Li+ in the GeSe2-based electrodes ranged from 10−15 to 10−12 cm2/s, and the thickness of the flexible electrode (including two layers) has a negligible impact on its electrochemical performance.

Electrochemical in-situ generation of Ni-Mn MOF nanomaterials as anode materials for lithium-ion batteries

Due to their low cost and high theoretical lithium storage capacity, binary transition metal materials are very suitable as anode materials for lithium-ion batteries (LIBs). However, the low electrical conductivity and poor cycling stability caused by volume change during the charge-discharge process limit its application as an energy storage material. Herein, in this paper, the preparation of Ni/Mn binary compounds and the in-situ synthesis of metal-organic framework (MOF) nanosheets were realized by the one-step electroconversion method for the first time. In this method, NiMn-MOF nanomaterials were successfully prepared by using the characteristics that the cathode can generate OH- ions and the organic framework (p-phthalic acid, PTA) can be dissolved in alkali solution so that PTA was uniformly coated on the surface of Ni-Mn hydroxide. NiMn-MOF exhibits excellent performance as an anode for Li-ion batteries. Its charge-discharge specific capacity is 1024/1554 mAh·g−1, with a small charge transfer impedance, but it inherits the poor rate performance of transition metals. After 1000 cycles, the coulombic efficiency is 100%. Even after 600 cycles, the charge and discharge capacity rises steadily. MOF-derived porous structures can not only provide conductive pathways and increase the transport of electrons and lithium ions but also alleviate volume expansion. As the first successful in-situ electroconversion of PTA to synthesize NiMn-MOF, this method's low cost and good electrochemical performance provide hope for its large-scale application in Li-ion batteries.

Effective stripping and reutilization of LiFePO4 cathode waste from retired lithium ion batteries

The recycling of retired lithium ion batteries (LIBs) plays a vital role in alleviating the energy crisis and preventing secondary pollution. However, the unstable properties of waste materials greatly restricts the reuse of recycled materials in the industrial energy domain. Herein, we applied water as stripping solvent to effectively dispose of lithium iron phosphate (LiFePO4) cathode scrap. The results showed that the stripping rate of cathode scrap could reach more than 92%, and the recycling did not give rise to any impact on the structure of the cathode material under optimized condition. The molar ratios of elements were signed as n (Li): n (Fe): n (P) = 5 : 4.6: 4.95 by inductively coupled plasma emission spectroscopy (ICP-OES) and energy disperse spectroscopy (EDS). The Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) showed that the PVDF was completely invisible after sintering. The LiFePO4 materials calcined at different temperature for 10 h under argon atmosphere showed excellent constant current charge-discharge performance and good cycle life, which reflected the stability of the olivine structure. The LiFePO4 cathode material directly calcined at 650 °C for 10 h exhibited the best charge-discharge specific capacity with a high Coulombic efficiency of 99.2%. Cyclic voltammetry (CV) tests showed that the re-sintered LiFePO4 material had a less redox polarized potential compared with the retired LiFePO4 material. The non-structure-damaging recycling mode also provides a green and effective direction for the recovery and recyclability of retired LiFePO4.

Composite Nanoarchitectonics with CoS2 Nanoparticles Embedded in Graphene Sheets for an Anode for Lithium-Ion Batteries.

Cobalt sulfides are attractive as intriguing candidates for anodes in Lithium-ion batteries (LIBs) due to their unique chemical and physical properties. In this work, CoS2@rGO (CSG) was synthesized by a hydrothermal method. TEM showed that CoS2 nanoparticles have an average particle size of 40 nm and were uniformly embedded in the surface of rGO. The battery electrode was prepared with this nanocomposite material and the charge and discharge performance was tested. The specific capacity, rate, and cycle stability of the battery were systematically analyzed. In situ XRD was used to study the electrochemical transformation mechanism of the material. The test results shows that the first discharge specific capacity of this nanocomposite reaches 1176.1 mAhg−1, and the specific capacity retention rate is 61.5% after 100 cycles, which was 47.5% higher than that of the pure CoS2 nanomaterial. When the rate changes from 5.0 C to 0.2 C, the charge-discharge specific capacity of the nanocomposite material can almost be restored to the initial capacity. The above results show that the CSG nanocomposites as a lithium-ion battery anode electrode has a high reversible specific capacity, better rate performance, and excellent cycle performance.

Synthesis of C/MoS2-CoMo2S4 for application in Li-O2 batteries

High efficiency electrocatalyst is the key factor to achieve high charge-discharge specific capacity and long cycle life of Li-O2 batteries (LOBs). In this work, the C/MoS2CoMo2S4 was successfully prepared by calcining the hybrid of ZIF-67 and C/MoS2 at 800 °C. The composite materials have three advantages for oxygen reduction and evolution reaction (ORR/OER) of LOBs, including highly efficient catalysis of CoMo2S4, abundant porous network and a surface conducive to Li2O2 precipitation. The LOBs with acid-pickled C/MoS2CoMo2S4–800 showed a high discharge specific capacity (17,551 mAh g−1) and an excellent cycle stability of 336 cycles at a current density of 500 mA g−1 and capacity limit of 1000 mAh g−1. Interestingly, the catalytic activity of C/MoS2CoMo2S4 can be improved by acid pickling or the increasement of calcination temperature from 700 to 800 °C.

Preparation and Performance of Li4Ti5O12 by Solid Phase Method

In this paper, Li4Ti5O12 was prepared by high temperature solid-state method using titanium dioxide as titanium source and lithium carbonate as lithium source. The effects of lithium-titanium molar ratio, calcination temperature and sucrose as carbon source on the preparation of Li4Ti5O12 were studied. The experimental results show that when the molar ratio of lithium to titanium is 0.95 and the calcination temperature is 800 °C, pure phase Li4Ti5O12 can be prepared. The addition of sucrose carbon source effectively reduces the agglomeration of the product, making the particle size of the prepared lithium titanate sample about 1–2 microns. The first full specific capacity of pure lithium titanate is 160 mAh.g-1 at 0.1 C ratio and 123 mAh/g at 1 C ratio. After adding sucrose, the first charge-discharge specific capacity of lithium titanate was 168 mAh/g at 0.1 C ratio, 150 mAh/g at 1 C ratio, and the high specific capacity of lithium titanate with changed properties increased significantly after adding sucrose.

Preparation of Nano-spherical Iron Phosphate by Hydrothermal Method and Its Application as the Precursor of Lithium Iron Phosphate

Abstract First, nano-spherical iron phosphate was prepared using the hydrothermal method. Then, the carbothermal reduction method was applied to synthesize the LiFePO4/C composite material capable of good carbon coating effect with the prepared nano-spherical iron phosphate as a precursor. By means of scanning electron microscope, transmission electron microscope, Zeta potentiometer, inductively coupled plasma spectrometer, X-ray diffraction, X-ray photoelectron spectroscopy, electrochemical testing, and other methods, the material was characterized and tested for its morphology, particle size, composition, structure, and electrochemical performance. According to the test results, when the initial mass concentration of Fe3+ in the reaction solution is 2%, the amount of N and S impurity is merely 19 and 27 ppm, respectively. In the meantime, particle size is small, with a range of roughly 50–100 nm, and a spherical morphology is shown. The synthesized LiFePO4/C retains its nano-spherical morphology, which leads to a desirable carbon coating effect and an excellent electrochemical performance. The first charge–discharge specific capacity at 0.1 C rate reached 163.7 and 161.4 mAh/g, the charge–discharge efficiency was 98.6%, and the capacity retention rate at 50 charge–discharge cycles at 1 C rate reached 98.52%.

RETRACTED ARTICLE: Fabrication of flexible lithium-ion battery electrodes for wearable full battery with high electrochemical performance

A new method is provided for preparing self-supporting flexible lithium-ion battery electrodes of a textile structure by using extrusion 3D printing technology, using a high concentration of polyvinylidene fluoride as a viscosity modifier, carbon nanotube as a conductive agent, lithium iron phosphate or lithium titanate as an electrode active material. A printable ink prepared in the paper, with an apparent viscosity of approximately 105 Pa s, exhibits significant shear thinning behavior, and the storage modulus platform value reaches a high value of 105 Pa; its excellent rheological properties are beneficial for the printing and solidification process. Electrochemical test results show that the two printing electrodes have a stable and well-matched charge–discharge specific capacity, so the assembled soft-packed lithium-ion battery displays a discharge specific capacity of up to 108 mAh·g−1, and after bending the battery, the discharge specific capacity under the same current density (50 mA·g−1) is about 111 mAh·g−1. The outstanding electrochemical properties open up possibilities for flexible and wearable electronics applications.

The effects of multiple metals (K, Cu, Al) substitution on LiNi0.66Co0.20Mn0.14O2 for lithium-ion batteries

The high-nickel ternary cathode material LiNixCoyMn1-x-yO2 has high theoretical capacity and can be filled the power density requirement of a foot-powered car. It is placed on high expectations. However, Li/Ni mixing occurred during charging and discharging, resulting in poor cycle performance of the material. The related literatures have found that the K, Cu, and Al doping can improve the cycle performance of high-nickel materials. In this paper, we designed the orthogonal experiment and synthesized [Li(1-y)Ky](Ni0.66Co0.20Mn0.14)(1-x-z)[CuxAlz]O2 (x,y,z) = 0.00, 0.01, 0.02, 0.03, 0.04) cathode materials by the co-precipitation method. The initial charge–discharge specific capacity of [Li0.99K0.01](Ni0.66Co0.20Mn0.14)0.94[Cu0.03Al0.03]O2 can reach 214.7 mAh/g and 210.8 mAh/g, coulomb efficiency is 98.18%. After 30 cycles at 1C, capacity retention is 87%. According to the orthogonal test, results are as follows: about initial discharge specific capacity of the material, K presents the greatest effect, followed by Al, with minimal effect on Cu. However, Al has the greatest influence on the capacity retention rate of the material at high rate, followed by K element and Cu element. This will provide guidance for the future study of the modification of doping metal elements in high-nickel ternary lithium ion cathode materials.

Synergy of interlayer expansion and capacitive contribution promoting sodium ion storage in S, N-Doped mesoporous carbon nanofiber

Heteroatoms doping is proved to be an effective strategy to improve the electrochemical performance of carbon materials by adjusting its physical and chemical properties. In this work, sulfur, nitrogen co-doped carbon nanofiber (SNCNF) is prepared by electrospinning technique with the following heat and hydrothermal treatment route. Benefiting from the S, N co-doping, SNCNF demonstrates perfect pseudocapacitance characteristic improving rate performance (N-doping) and large interlayer distances promoting reversible insertion/extraction of Na+ (S-doping). SCNNF displays high charge-discharge specific capacity (290.3 mA h g−1 at 0.1 A g−1), superior cycling stability (247.4 mA h g−1 and 98.2% retention at 0.5 A g−1 over 600 cycles) and ultra-long circulation characteristics at high current rate (160.2 mA h g−1 at 10.0 A g−1 after 10,000 cycles), which can be served as a very promising material as anode for sodium ion batteries.

Surface-Coated LiNi0.8Co0.1Mn0.1O2 (NCM811) Cathode Materials by Al2O3, ZrO2, and Li2O-2B2O3 Thin-Layers for Improving the Performance of Lithium Ion Batteries

In this paper, the precursor Ni0.8Co0.1Mn0.1(OH)2 is prepared by a co-precipitation method. By mixing this material with LiOH in proportion and sintering twice under 500℃ and 800 ℃, respectively, the cathode material of LiNi0.8Co0.1Mn0.1O2 (NCM811) for lithium ion batteries (LIBs) is synthesized. To improve the performance of this NCM811 material, Al2O3, ZrO2 and LBO (Li2O-2B2O3) are respectively used to coat it by a wet chemical method. The effects of Al2O3, ZrO2 and LBO thin coating layers (~20～200 nm) on the morphology, structure and electrochemical property of NCM811 are studied using XRD, SEM, TEM, XPS, and electrochemical measurements. Coin LIBs are assembled with the uncoated, Al2O3-coated, ZrO2-coated and LBO-coated NCM811 cathode materials for performance validation. The experiment results confirm that the charge-discharge specific capacity, Coulomb efficiency, water absorption stability, cycle characteristics and resistance stability of the NCM811 cathode material can be significantly improved by coating it with LBO particularly. Therefore, the surface coating to the particles of cathode materials using LBO is expected to be an effective and practical modification method to improve the electrochemical performance of LIBs.

Electrochemical Impedance Spectroscopy on the Performance Degradation of LiFePO4/Graphite Lithium-Ion Battery Due to Charge-Discharge Cycling under Different C-Rates

Lithium-ion batteries (LIBs) using a LiFePO4 cathode and graphite anode were assembled in coin cell form and subjected to 1000 charge-discharge cycles at 1, 2, and 5 C at 25 °C. The performance degradation of the LIB cells under different C-rates was analyzed by electrochemical impedance spectroscopy (EIS) and scanning electron microscopy. The most severe degradation occurred at 2 C while degradation was mitigated at the highest C-rate of 5 C. EIS data of the equivalent circuit model provided information on the changes in the internal resistance. The charge-transfer resistance within all the cells increased after the cycle test, with the cell cycled at 2 C presenting the greatest increment in the charge-transfer resistance. Agglomerates were observed on the graphite anodes of the cells cycled at 2 and 5 C; these were more abundantly produced in the former cell. The lower degradation of the cell cycled at 5 C was attributed to the lowered capacity utilization of the anode. The larger cell voltage drop caused by the increased C-rate reduced the electrode potential variation allocated to the net electrochemical reactions, contributing to the charge-discharge specific capacity of the cells.

Preparation and Electrochemical Properties of Si@C/Graphite Composite as Anode for Lithium-Ion Batteries

In this study, Si@C/Graphite composite anodes were synthesized through spray drying and pyrolysis using silica, artificial graphite, and two kinds of organics (phenolic resin or pitch). The Si@PR-C/Graphite exhibits enhanced electrochemical performance for lithium-ion batteries. The first charge-discharge specific capacity is 512.8mAh/g and 621.8mAh/g, respectively, the initial coulombic efficiency is 82.5% at 100mA/g, and its capacity retention rate reached as high as 85.4% with the capacity fade rate of less than 0.18% per cycle after 85 cycles. The Si@PI-C/Graphite also presents excellent discharge specific capacity of 702.8mAh/g with the capacity retention rate of 76.9% after 30 cycles. Mechanisms for high electrochemical performances of the Si@C/Graphite composite anode are discussed. It found that the enhanced electrochemical performance due to the formation of core/shell microstructure. These encouraging experimental results suggest that proper organic carbon source has great potential for improvement of electrochemical properties of pure silicon as anode. Key words:lithium-ion batteries; anode; Si@C/Graphite composite; electrochemical performance

Synthesis and performance of Al3+-doped cathode materials 0.6Li[Li1/3Mn2/3]O2 · 0.4Li[Ni1/3Mn1/3Co(1/3-y)Al y ]O2 by high temperature solid-state method

Abstract 0.6Li[Li1/3Mn2/3]O2 · 0.4Li[Ni1/3Mn1/3Co(1/3-y)Al y ]O2 (y = 0, 0.03, 0.08, 0.13) was prepared by a high-temperature solid-state method as cathode material for lithium-ion batteries. X-ray diffraction and scanning electron microscopy were used to assess the structure and morphology of the samples. Electrochemical performance testing, AC impedance testing, and cyclic voltammetry testing were performed to study various aspects of the cathode materials. The results showed that the addition of Al3+ had little effect on the charge–discharge performance, but the cycling performance and stability of the material were significantly enhanced. When the doping fraction of Al3+ was 0.08, the cathode material 0.6Li[Li1/3Mn2/3]O2 · 0.4Li[Ni1/3Mn1/3Co(19/75) Al0.08]O2 had good electrochemical performance. The first discharge specific capacity reached 161.1 mAh · g−1 in the charge and discharge test at 0.1 C rate. After 20 cycles, the discharge capacity was still 159.7 mAh · g−1. The charge–discharge specific capacity had almost no attenuation.

Effect of Prelithiation Process for Hard Carbon Negative Electrode on the Rate and Cycling Behaviors of Lithium-Ion Batteries

Two prelithiation processes (shallow Li-ion insertion, and thrice-repeated deep Li-ion insertion and extraction) were applied to the hard carbon (HC) negative electrode (NE) used in lithium-ion batteries (LIBs). LIB full-cells were assembled using Li(Ni0.5Co0.2Mn0.3)O2 positive electrodes (PEs) and the prelithiated HC NEs. The assembled full-cells were charged and discharged under a low current density, increasing current densities in a stepwise manner, and then constant under a high current density. The prelithiation process of shallow Li-ion insertion resulted in the high Coulombic efficiency (CE) of the full-cell at the initial charge-discharge cycles as well as in a superior rate capability. The prelithiation process of thrice-repeated Li-ion insertion and extraction attained an even higher CE and a high charge-discharge specific capacity under a low current density. However, both prelithiation processes decreased the capacity retention during charge-discharge cycling under a high current density, ascertaining a trade-off relationship between the increased CE and the cycling performance. Further elimination of the irreversible capacity of the HC NE was responsible for the higher utilization of both the PE and NE, attaining higher initial performances, but allowing the larger capacity to fade throughout charge-discharge cycling.

Effect of Nanophase Li₃PO₄ and Li₄P₂O7 on the Electrochemical Performance of LiFePO₄ Cathode Materials.

The Li3PO4 modified LiFePO4/C and Li4P2O7 modified LiFePO4/C cathode materials were synthesized by in-situ synthesis method, respectively. Phase compositions and microstructures of the products were characterized by X-ray powder diffraction (XRD), scanning electronic microscope (SEM). Results indicate that Li3PO4 and Li4P2O7 can sufficiently coat on the LiFePO4 surface and does not alter LiFePO4 crystal structure. The electrochemical behavior of cathode materials was analyzed using galvanostatic measurement and cyclic voltammetry (CV). Compared with Li3PO4, the existence of Li4P2O7 can better improve the electrochemical performance of LiFePO4 cathode materials in specific capability and lithium ion diffusion of cathode materials. The charge-discharge specific capacity and apparent lithium ion diffusion coefficient increase with Li4P2O7 content and maximizes around the Li4P2O7 content is 5 wt%. The results indicated that the Li4P2O7 adding enhances the lithium ion diffusion rate of LiFePO4. However, because of the interface fracture between Li4P2O7 and LiFePO4 particles during charging and discharging process, the cycling performance of Li4P2O7 modified LiFePO4/C cathode materials is very poor.

Electrochemical performance and thermal stability of the electrospun PTFE nanofiber separator for lithium‐ion batteries

ABSTRACTSeparator is a very important set of lithium‐ion batteries. At present, low porosity and poor thermal stability are two major disadvantages of separator. In this work, we first apply electrospinning method to prepare the Polytetrafluoroethylene (PTFE) nanofiber separator, which has the advantages of electrospinning method and PTFE materials. The effect of the PTFE nanofiber separator is investigated by scanning electron microscope, Capillary Flow Porometer, thermogravimetric–differential scanning calorimeter, linear sweep voltammeter, AC impedance, and charge/discharge cycling tests. The results demonstrate that the PTFE nanofiber separator has a special fiber structure made from PTFE particles gathering one by one along the fibers. Moreover, the PTFE nanofiber separator exhibits several advantages, including suitable pore diameter, uniform pore size distribution, high porosity, and electrolyte uptake, which enhance the ionic conductivity. The thermal stability of the PTFE nanofiber separator is much better than that of the conventional polyolefin separator. The Li/LiCoO2 cell equipped with PTFE nanofiber separator exhibits excellent rate performance and first charge–discharge specific capacity of 142 and 131 mA h g−1, respectively, accompanied by relatively stable cycle performance at 0.2 C rate. It is supposed to be a candidate for application in lithium‐ion batteries. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46508.

Effect of symbiotic compound Fe2P2O7 on electrochemical performance of LiFePO4/C cathode materials

In order to study the effect of symbiotic compound Fe2P2O7 on electrochemical performance of LiFePO4/C cathode materials, the LiFePO4/Fe2P2O7/C cathode materials were synthesized by in-situ synthesis method. The phase compositions and microstructures of the products were characterized by X-ray powder diffraction (XRD) and field emission scanning electron microscope (FESEM). Results indicate that the existence of Fe2P2O7 does not alter LiFePO4 crystal structure and the existence of Fe2P2O7 decreases the particles size of LiFePO4. The electrochemical behavior of cathode materials was analyzed using galvanostatic measurement and cyclic voltammetry (CV). The results show that the existence of Fe2P2O7 improves electrochemical performance of LiFePO4 cathode materials in specific capability and lithium ion diffusion rate. The charge–discharge specific capacity and apparent lithium ion diffusion coefficient increase with Fe2P2O7 content and maximizes around the Fe2P2O7 content is 5 wt%. It has been had further proved that the Fe2P2O7 adding enhances the lithium ion transport to improve the electrochemical performance of LiFePO4 cathode materials. However, excessive Fe2P2O7 will block the electron transfer pathway and affect the electrochemical performances of LiFePO4 directly.