Electrochemical Performance For Lithium-ion Batteries Research Articles

Electrochemical performance of lithium-ion batteries with two-layer gradient electrode architectures

Thick electrodes whose active materials have high areal density may improve the energy densities of lithium-ion batteries. However, the weakened rate abilities and cycle lifetimes of such electrodes significantly limit their practical applications. In this study, a modified two-dimensional model was built to evaluate the influence of the electrode structure on the lithiation process. Gradient electrodes with different particle sizes along the thickness direction are designed and fabricated via a two-layer coating process. The gradient design in the thickness direction is confirmed by three-dimensional digital microscopy, energy-dispersive spectroscopy, X-ray diffraction, and scanning electron microscopy. Galvanostatic charge/discharge cycling tests and electrochemical impedance spectroscopy are performed to investigate the electrochemical properties of the fabricated gradient electrodes. The simulation results indicate that the gradient electrode structure can enhance the utilization of electrode particles on the current collector side and alleviate the nonuniformity of the solid-phase Li concentration along the thickness direction. High electrochemical performance and long-term cycling stability of the designed gradient electrodes are verified by electrochemical test. The gradient structure fabricated via multi-layer coating processes can be used to improve the electrochemical performance of thick electrodes.

A First-Principles Study of Anion Doping in LiFePO4 Cathode Materials for Li-Ion Batteries.

Doping anions into LiFePO4 can improve the electrochemical performance of lithium-ion batteries. In this study, structures, electronic properties and Li-ion migration of anion (F- , Cl- , and S2- ) doping into LiFePO4 were systematically investigated by means of density functional theory calculations. Anion substitution for oxygen atoms leads to an expansion of the LiFePO4 lattice, significantly facilitating Li-ion diffusion. For Cl- and F- anion doped into LiFePO4 , the energy barrier of Li-ion migration gets lowered to 0.209 eV and 0.283 eV from 0.572 eV. The introduction of anions narrows the forbidden band of LiFePO4 , enhancing its electronic conductivity. This work pays a way towards the rational design of high-performance lithium-ion batteries.

Synthesis of nanoscale LiCoPO4/C between few-layer graphene and its influence on electrochemical performance for lithium-ion batteries

In this study, the composite cathode material of LiCoPO4/C and graphene is synthesized using solvothermal method assisted by oleylamine. The effect of graphene addition on the material properties is fully investigated, and the synergistic effect of amorphous carbon and graphene is also studied. Graphene serves as a conductive skeleton and provides abundant diffusion paths for electrons. The nanoscale LiCoPO4 material synthesized by solvothermal method is evenly distributed around the few-layer graphene with the assistance of oleylamine, and the amorphous carbon formed after the pyrolysis of oleylamine at high temperature tightly connects LiCoPO4 to the graphene, which improves the conductivity and electrochemical performance of the sample. The results of characterization reveal that adding graphene can prepare LiCoPO4 materials with good crystallization and improve the specific surface area and pore size of the material. At the same time, the amorphous carbon and graphene inside the material also show a good degree of graphitization. Electrochemical test results show that doping graphene with a mass ratio of 6% can enhance the electrochemical performance and cycle stability of LCPC-6%G sample. The initial discharge capacity of LCPC-6%G sample reaches 157.2 mA h g−1 at 0.1 C. In this study, nanoscale LiCoPO4 samples are successfully synthesized on the surface of graphene, which provides a new idea for the preparation of nanoelectrode materials and conductive skeleton composite samples.

WS2 nanosheets vertically grown on Ti3C2 as superior anodes for lithium-ion batteries

Tungsten disulfide (WS2) is considered as a promising anode material for high-performance lithium-ion batteries (LIBs) result from its inherent characteristics such as high theoretical capacity, large interlayer spacing and weak interlayer Van der Waals force. Nevertheless, WS2 has the drawbacks of easy agglomeration, severe volume expansion and high Li+ migration barrier, which lead to rapid capacity degradation and imperfect rate ability. In this work, a novel two-dimensional (2D) hierarchical composite (Ti3C2/WS2) consisting of WS2 nanosheets vertically grown on titanium carbide (Ti3C2) nanosheets is prepared. Thanks to this distinctive hierarchical structure and synergy between WS2 and Ti3C2, the Ti3C2/WS2 composite demonstrates exceptional electrochemical performance in LIBs. In addition, we investigate the effect of the mass proportion of WS2 in Ti3C2/WS2 composite on the electrochemical performance, and find that the optimal mass ratio of WS2 is 60%. As expected, the optimal electrode exhibits a high specific capacity (650 mAh/g at 0.1 A/g after 100 cycles) and ultra-long cycle stability (400 mAh/g at 1.0 A/g after 5000 cycles).

Controllable synthesis of aluminium-doped LiMnPO4/C cathode materials with stable electrochemical performance for lithium-ion battery

The Al3+ ion doped Li1-3xAlxMnPO4/C cathode materials are prepared by a two-step synthetic method, the co-precipitation combined with hydrothermal routine, and the doping effects on phase structure, surface morphology and electrochemical properties are studied. XRD patterns confirm that some tiny AlPO4 impurity generates in the synthesized Al3+ ion doped Li3PO4 precursors, after the hydrothermal process a single olivine-type phase Li1-3xAlxMnPO4/C samples are prepared without impurity phase. SEM results show that the concentration of Al3+ ion has some impacts on particle diameter, the porosity and agglomeration degree of the primary particles of Al3+ ion doped Li3PO4 precursors and LiMnPO4/C samples. Among all the samples, Li0.7Al0.1MnPO4/C sample delivers the maximum discharge capacity of 147.8 mAh/g (0.05 C) and 135.7 mAh/g (1 C) for the first cycle. At 0.05 C, the capacity loss is kept at 9.9% after 200 cycles. The analysis indicate that the electrochemical performance of LiMnPO4/C cathodes have been improved by doping a certain amount of aluminium ions.

Picosecond laser structuring of graphite anodes—Ablation characteristics and process scaling

Laser structuring of graphite anodes substantially improves the electrochemical performance of lithium-ion batteries by facilitating lithium-ion diffusion through the electrode coatings. However, laser structuring is not yet established in industrial battery production due to limited knowledge of its ablation behavior and a low processing rate. This publication addresses these issues with a combination of experimental and theoretical approaches. In a comprehensive process study with picosecond pulsed laser radiation, the influence of various laser parameters on the obtained structure geometries, i.e., the hole diameters and depths, was examined. Wavelengths of 532 and 355 nm combined with pulse bursts and fluences of approximately 10 J cm−2 eventuated in favorable hole geometries with a high aspect ratio. Compared to singlebeam laser structuring, a nearly tenfold reduction in the processing time was achieved by beam splitting with a diffractive optical element without compromising structure geometries or mechanical electrode integrity. The experimental findings were used to model the scalability of electrode laser structuring, revealing the significant influence of the hole pattern and distance on the potential processing rate. Ultrashort pulsed laser powers in the kilowatt regime were found to be necessary to laser-structure electrodes at industrial processing rates resulting in estimated costs of roughly 1.96 $/kWh. The findings support the industrialization of laser electrode structuring for commercial lithium-ion battery production.

Si@C anode with excellent electrochemical performance for lithium-ion batteries: Microcapsules composed of N-doped carbon shell and diffusely distributed nano-silicon inside

As a promising candidate for the next generation of new anode materials, the modification and optimization of silica-based anode materials are significant. Using chitosan (CS) as the carbonaceous precursor, the N-containing Si@C microcapsules were prepared by emulsification cross-linking combined with high-temperature pyrolysis method. The microcapsule structure offers additional space for nano-Si and effectively enhances the electrochemical properties of the anode. Moreover, optimizing the CS:Si ratio is advantageous in achieving a synergistic effect between silicon and carbon. When CS:Si = 4:1, the first specific capacity was 762.78 mAh/g and the retention rate was 69.27 % after 100 cycles. To further enhance the material properties, urea was added to a ratio of CS:Si = 4:1 as an N supplement for elemental doping modification. The specific capacity of the anode had a positive correlation with N content within a certain range. As the N content increases, the pyridine-N content and density of C vacancies also increase, which improves the storage form and diffusion path of Li+. When 0.75 g urea was added, the first reversible specific capacity reached 1108.88 mAh/g and the retention rate was 92.41 % after 100 cycles. This work offers environmentally friendly and safe methods, as well as a new modification concept for N-doped microsphere-encapsulated silicon-carbon composites.

Optimized Ti Doping in CoMoO4 Nanorods as Anodes with Enhanced Electrochemical Performance for Lithium-Ion Batteries

Optimized Ti Doping in CoMoO₄ Nanorods as Anodes with Enhanced Electrochemical Performance for Lithium-Ion Batteries

Flower-like SnS2/honeycomb-like g-C3N4 composite as an anode material for high-rate, long-term lithium-ion batteries

The electrochemical performance of lithium-ion batteries (LIBs) can be improved by developing new structural composite materials. Therefore, this study uses a hydrothermal technique to produce flower-like SnS2 anchored on H-g-C3N4 (honeycomb-like g-C3N4) nanosheets. At higher current densities, the SnS2-H-g-C3N4-HC composite demonstrates superior cycle stability, high-rate capacity, and structural integrity for LIBs. The LIBs that employ SnS2-H-g-C3N4-HC as an anode exhibit high-rate performance, long-term stability, and a high discharge capacity of 370.7 mAh g−1 at 10C after 3000 cycles with a 100.3 % coulombic efficiency. The enormous surface area of the SnS2-H-g-C3N4-HC composite electrode provides highly active sites and increases the passage of lithium ions during charge and discharge cycles. It is also responsible for the outstanding electrochemical performance of the electrode. Further, the SnS2-H-g-C3N4-HC composite electrode has a synergistic effect that lowers the charge-transfer resistance, making it possible for Sn and lithium ions (Li+) to react during charge and discharge cycles. H-g-C3N4, which acts as a spacer, can buffer changes in volume effectively and reduce SnS2 electrode collapse or clumping after many cycles.

Experimental and Computational Study on SEI Composition and Electrochemical Performance of Lithium-Ion Battery with Silicon Oxide-Graphite Composite Electrode

Demand on batteries with high energy density is surging. Conventionally, carbon materials have been used as an anode active material, but recently silicon materials are likely to be incorporated to form a composite anode in lithium-ion batteries (LIBs) for higher energy density. However, LIBs which include silicon materials in anode tend to show a low cycle performance especially the ratio of silicon materials in the anode increases. Commercial LIBs still have difficulty in incorporating large amount of silicon materials especially under the requirements where multiple aspects like safety, charging rate and energy density should be totally met.One potential pathway to improve the cycle performance in LIBs with silicon materials is to tune the nature of solid electrolyte interphase (SEI), a thin film which forms at the interface between anode active material and electrolyte. The nature of SEI is particularly important for LIBs with silicon materials because such silicon active materials show large volume changes during battery operation and SEI is dynamically reconstructed. It has been qualitatively reported so far that LiF is an important component for better battery performance. Our work suggests that the ratio of LiF in initially formed SEI is a crucial factor to realize improved cycle performance in such LIBs.In our work, anode with silicon oxide (SiOx)-graphite composite is considered. We investigated the relationship between electrochemical performance of the cell with such composite electrode and the nature of the film estimated by characterization and molecular simulation. We systematically changed the composition of liquid electrolyte to form various types of SEI on anode surface. For characterization, both fresh and aged cells with different electrolytes were dismantled, and SEI components were extracted by designated solvents, then NMR (nuclear magnetic resonance) was applied to identify the SEI species and quantify the amounts of major SEI components. Comparison between the evolution of SEI amount and an impedance element in electrochemical impedance spectroscopy during aging indicates that degradation of the cells is closely related to the growth of SEI. To further deepen understanding the role of LiF, molecular dynamics simulation was carried out, where the mixture of LiF and typical organic SEI was modelled. Correlation between calculated mechanical property and measured electrochemical performance of the cells were revealed. In our presentation, the requirements that SEI should satisfy will be discussed from the insight of electrochemical measurements, NMR characterization and modeling approaches.

Hybrid Sub-1 nm Nanosheets of Co-assembled MnZnCuOx and Polyoxometalate Clusters as Anodes for Li-ion Batteries.

Transition metal oxide (TMO) anode materials in lithium-ion batteries (LIBs) usually suffer from serious volume expansion leading to the pulverization of structures, further giving rise to lower specific capacity and worse cycling stability. Herein, by introducing polyoxometalate (POM) clusters into TMOs and precisely controlling the amount of POMs, the MnZnCuOx -phosphomolybdic acid hybrid sub-1 nm nanosheets (MZC-PMA HSNSs) anode is successfully fabricated, where the special electron rich structure of POMs is conducive to accelerating the migration of lithium ions on the anode to obtain higher specific capacity, and the non-covalent interactions between POMs and TMOs make the HSNSs possess excellent structural and chemical stability, thus exhibiting outstanding electrochemical performance in LIBs, achieving a high reversible capacity (1157 mAh g-1 at 100 mA g-1 ) and an admirable long-term cycling stability at low and high current densities.

Hybrid Sub‐1 nm Nanosheets of Co‐assembled MnZnCuOx and Polyoxometalate Clusters as Anodes for Li‐ion Batteries

AbstractTransition metal oxide (TMO) anode materials in lithium‐ion batteries (LIBs) usually suffer from serious volume expansion leading to the pulverization of structures, further giving rise to lower specific capacity and worse cycling stability. Herein, by introducing polyoxometalate (POM) clusters into TMOs and precisely controlling the amount of POMs, the MnZnCuOx‐phosphomolybdic acid hybrid sub‐1 nm nanosheets (MZC‐PMA HSNSs) anode is successfully fabricated, where the special electron rich structure of POMs is conducive to accelerating the migration of lithium ions on the anode to obtain higher specific capacity, and the non‐covalent interactions between POMs and TMOs make the HSNSs possess excellent structural and chemical stability, thus exhibiting outstanding electrochemical performance in LIBs, achieving a high reversible capacity (1157 mAh g−1 at 100 mA g−1) and an admirable long‐term cycling stability at low and high current densities.

Spray fabrication of additive-free electrodes for advanced Lithium-Ion storage technologies

Polymer binders and carbon conductivity enhancers are inevitably required to make improvements in structural durability and electrochemical performance of lithium-ion battery (LIB) electrodes, although these additive constituents incur weight and volume penalties on the overall battery capacity. Here, additive-free electrode architectures were successfully fabricated over 20 × 20 cm2 electrode areas using a layer-by-layer spray coating approach, with the ultimate goal to boost gravimetric/volumetric electrode capacity and to reduce the total cost of LIB cells. Initially, the binder fraction of spray-coated Li4Ti5O12 (LTO) electrodes was reduced progressively, from 40 to 0 wt%. The electrochemical behavior of electrodes was then re-optimized as a proportion of conductivity enhancers within the binder-free electrode decreased to zero. Further, the otherwise identical spray coating process was applied to manufacture LiFePO4 (LFP) positive electrodes, leading to all-additive-free full-cell LIB configurations with attractive energy density of ∼310 Wh/kg and power performance of ∼1500 W/kg.

Encapsulation of SnO2 by carbon nanotubes and WS2 to form high-performance lithium-ion batteries materials

Optimizing the structure of materials has proven to be an efficient solution for improving the electrochemical performance of lithium-ion batteries. In this work, SnO2-WS2-CNTS (SWC) ternary composites were prepared by hydrothermal and ball milling methods to first obtain SnO2-WS2 mixture, which was then embedded on CNTS to form a special multi-level structure. Due to the special 2D structure of transition metal sulfide WS2 and CNTS, the de-intercalation speed of lithium ions is greatly increased and the inherent particle aggregation phenomenon of SnO2 is weakened. The three materials show their advantages while compensating for each other's disadvantages, forming an interesting synergistic effect which results in extremely stable anode materials. At 0.2Ag-1, the capacity of SWC reaches 930.71 mAhg-1 after 100 cycles, and reaches 1043 mAhg-1 after 1000 cycles at 1.0Ag-1. It is worth noting that after multiple cycles, SWC still exhibits an extremely stable state in the SEM image. The above results confirm that the special structure of SWC leads to excellent electrochemical performance, and its simple preparation method makes it a potential leading battery anode material in the future.

A Rapid Synthesis of Zeolitic Imidazolate Framework-14 Cobalt (ZIF-14 Co) for Surface Modification of LiFePO<sub>4</sub> as Lithium‑Ion Battery Cathode Material

The main limitation of LiFePO4 (LFP) as a cathode material for lithium-ion battery (LIB) is its poor rate performance due to its low electronic conductivity values. At present, there are three main efforts being intensively carried out to overcome this: cation doping, crystal morphology adjustment, and LFP surface modification. Surface modification of LFPs has become a major concern in efforts to improve battery performance. The use of zeolitic imidazolate frameworks 8 (ZIF-8) and 67 (ZIF 67) as N-doped C sources for surface modification of LIB cathodes carried out in several studies has shown an improvement in the electrochemical performance of LIB. However, the thermal, solvothermal and chemical stability of ZIF-8 and ZIF-67, which adopt the sodalite (SOD) topology, is still not enough for this purpose. Zeolitic imidazolate frameworks 14 (ZIF-14), which is homologous to ZIF-8 and ZIF-67 with its crystals adopting analcime (ANA) topology, has better thermal, solvothermal, and chemical stability than ZIF-8 and ZIF-67. Apart from its topology, ZIF-14 cobalt (ZIF-14 Co) can be synthesized rapidly in a water-based system at room temperature, so that its use becomes more effective and efficient. This paper will describe the synthesis and characterization procedure of ZIF-14 Co for use as a modification material for the cathode surface of LIB.

Prominent enhancement of stability under high current density of LiFePO4-based multidimensional nanocarbon composite as cathode for lithium-ion batteries

A facile method for synthesizing carbon-coated lithium iron phosphate (LiFePO4, LFP) and an LFP-based multidimensional nanocarbon composite to enhance the electrochemical performance of lithium-ion batteries is presented herein. Three types of cathode materials are prepared: carbon-coated LFP (LC), carbon-coated LFP with carbon nanotubes (LC@C), and carbon-coated LFP with carbon nanotubes/graphene quantum dots (LC@CG). The electrochemical performances of the LC-nanocarbon composites are compared, and both LC@C and LC@CG show improved electrochemical performance than LC. Compared with both the LC and LC@C electrodes, the LC@CG electrode exhibits the highest specific capacity of 107.1 mA h g−1 under 20C of current density, as well as higher capacities and greater stability over all measured current densities. Moreover, after 300 charge–discharge cycles, the LC@CG electrode exhibits the best stability than the LC and LC@C electrodes. This is attributable to the graphene quantum dots, which enhance the morphological stability of the LC@CG electrode during electrochemical measurements. Our findings suggest that LFP-nanocarbon composites are promising as cathode materials and highlight the potential of graphene quantum dots for improving the stability of cathodes.

Unraveling the improved lithium-storage mechanism by interfacial engineering based on metallic MoS2/MoN heterostructure

The boom in anode materials with the splendid electrochemical performance of lithium-ion batteries (LIBs) is key to meet energy storage. As a typical anode material with the good capacity property and sandwich structure, molybdenum disulfide (MoS2) exhibited the poor lithium storage performance owing to the inferior conductivity and rapid capacity decay. Introducing a highly conductive material into MoS2 to construct a rational heterostructure is an effective strategy to tackle this challenge. Herein, we prepared MoS2 by a simple hydrothermal method and then successfully synthesized MoS2/MoN heterostructure by calcination under NH3 atmosphere. Density functional theory (DFT) calculation results show that the MoS2/MoN heterostructure with strong chemical bonding at the interface of MoS2 and MoN can enhance lithium storage, which are well verified by our experimental results. The experiment and calculation results reveal that the MoS2/MoN heterostructure shows the improved electrical conductivity after introducing metallic MoN, thus promoting the diffusion of electrons and Li+ ions. Moreover, due to the synergistic effect and the action of strong built-in electric field, the MoS2/MoN heterostructure exhibits higher initial discharge capacity and theoretical maximum capacity, as well as the better rate performance. This study offers possible approaches for the development of high-performance heterostructure-based anode materials in LIBs and other electrochemical energy storage (EES) devices.

Flame-retardant oligomeric electrolyte additive for self-extinguishing and highly-stable lithium-ion batteries: Beyond small molecules

Preparing both safe and high-performance lithium-ion batteries (LIBs) based on commonly used commercial electrolytes is highly desirable, yet challenging. To overcome the poor compatibility of conventional small-molecular flame-retardants as electrolyte additives for safe LIBs with graphite anodes, in this study, we propose and design a novel low-cost flame-retardant oligomer that achieves an accurate and complete reconciliation of fire safety and electrochemical performance in LIBs. Owing to the integration of phosphonate units and polyethylene glycol (PEG) chains, this oligomer, which is a phosphonate-containing PEG-based oligomer (PPO), not only endows commercial electrolytes with excellent flame retardancy but also helps stabilize the electrodes and Li-ion migration. Specifically, adding 15 wt% of PPO can reduce 70% of the self-extinguishing time and 54% of total heat release for commercial electrolytes. Moreover, LiFePO4/lithium and graphite/lithium cells as well as LiFePO4/graphite pouch full cells exhibit good long-term cycling stability.

Composite Membrane Containing Titania Nanofibers for Battery Separators Used in Lithium-Ion Batteries

In order to improve the electrochemical performance of lithium-ion batteries, a new kind of composite membrane made using inorganic nanofibers has been developed via electrospinning and the solvent-nonsolvent exchange process. The resultant membranes present free-standing and flexible properties and have a continuous network structure of inorganic nanofibers within polymer coatings. Results show that polymer-coated inorganic nanofiber membranes have better wettability and thermal stability than those of a commercial membrane separator. The presence of inorganic nanofibers in the polymer matrix enhances the electrochemical properties of battery separators. This results in lower interfacial resistance and higher ionic conductivity, leading to the good discharge capacity and cycling performance of battery cells assembled using polymer-coated inorganic nanofiber membranes. This provides a promising solution via which to improve conventional battery separators for the high performance of lithium-ion batteries.

Synthesis of PMIA/MIL-101(Cr) composite separators with high Li+ transmission for boosting safety and electrochemical performance of lithium-ion batteries

Energy storage devices require separators with sufficient lithium-ion transfer and restrained lithium dendrite growth. Herein, PMIA separators tuned using MIL-101(Cr) (PMIA/MIL-101) were designed and fabricated by a one-step casting process. At 150 °C, the Cr3+ in the MIL-101(Cr) framework sheds two water molecules to form an active metal site that complexes with PF6- in the electrolyte on the solid/liquid interface, leading to improved Li+ transport. The Li+ transference number of the PMIA/MIL-101 composite separator was found to be 0.65, which is about 3 times higher than that of the pure PMIA separator (0.23). Additionally, MIL-101(Cr) can modulate the pore size and porosity of the PMIA separator, while its porous structure also functions as additional storage space for the electrolyte, enhancing the electrochemical performance of the PMIA separator. After 50 charge/discharge cycles, batteries assembled using the PMIA/MIL-101 composite separator and the PMIA separator presented a discharge specific capacity of 120.4 and 108.6 mAh/g, respectively. The battery assembled using PMIA/MIL-101 composite separator significantly outperformed both the batteries assembled from pure PMIA and commercial PP separators in terms of cycling performance at 2 C, displaying a discharge specific capacity of 1.5 times that of the battery assembled from PP separators. The chemical complexation of Cr3+ and PF6- plays a critical role to improve the electrochemical performance of the PMIA/MIL-101 composite separator. The tunability and enhanced properties of the PMIA/MIL-101 composite separator make it a promising candidate for use in energy storage devices.