Electrochemical Performance Of Graphite Anodes Research Articles

Unraveling the relationship between the mineralogical characteristics and lithium storage performance of natural graphite anode materials

Anode materials play critical role in cycling life of lithium-ion batteries in practical applications such as electric vehicles (EVs), portable electronic devices, and large-scale power grids. Natural graphite is one of the most successful anodes for commercial lithium-ion batteries due to its high theoretical capacity and low cost and low operating voltage. The mineralogical properties of graphite minerals have an important effect on the electrochemical performance of graphite anode, while their relationship remains ambiguous. In this work, natural graphite samples from four main graphite mining areas in China were selected as the research object, and their mineralogical characteristics were characterized by XRD, SEM, Raman, ICP, SEM, FIB, BET and other test methods. The properties of crystallinity, morphology, surface/phase defects, impurities, and specific surface area of graphite were studied. The results show that the cyclic stability of graphite is mainly affected by bulk defects and crystallinity, and the initial coulombic efficiency is mainly affected by surface defects and specific surface area. Graphite samples with appropriate surface defects, fewer volume defects, appropriate crystallinity, and small specific surface area have better electrochemical performance. It is hoped that this work should guide the manufacture and modification of the natural graphite anodes and promote its wider application in lithium-ion batteries.

Optimizing the performance of a graphite anode for innovative metal-ion batteries and hybrid capacitors

Herein, we present an optimum method for maximizing the electrochemical performance of graphite anodes using two heat treatment methods involving graphite intercalated compound (GIC) group within graphite, namely, thermal shock (TS; directly input target temperature) and gradual heating (GH; including ramping time). Different heating methods for preparing expanded graphite (EG) involve different reactions, relaxation times, and diffusion pathways for the diffusion of metal ions into EG. We find that rapidly shocking the layered structure can facilitate faster lithium and potassium ion diffusion from EG (TS) (heated for 30 min) via different intercalation/deintercalation processes compared to that from EG (GH). Consequently, EG (TS) exhibits the most significantly improved electrochemical performance among the lithium and potassium ion half-cells. For full lithium-ion hybrid capacitors (LIHCs), EG (TS)||activated carbon (AC) shows reasonable values of maximum power density (2.8 kW kg−1 with 59.12 Wh kg−1) and energy density (196.41 Wh kg−1), demonstrating its ultrahigh durability (capacity retention: 70.01%) over 12000 cycles at 2.0 A g−1. In addition, for potassium-ion hybrid capacitors (PIHCs), reasonable performance is achieved (average capacity of 82.02 mAh g−1 at 1.0 A g−1 over 2000 cycles with 94.35% capacity retention), demonstrating the high efficiency of PIHCs for substituting LIHCs without any systematic alterations.

Electrochemical Performance of Dry Processed Graphite Electrode with PTFE Binder for Lithium-Ion Batteries

Both cathode and anode in Lithium-ion batteries (LIBs) are being manufactured by slurry coating process; however, currently used wet coating process has some drawbacks, including the difficulty in further increasing the electrode thickness as well as high fabrication cost mainly due to the use of facility for drying process. To address these issues, dry electrode fabrication process has been proposed and actively investigated as an alternative electrode manufacturing process. Dry electrode fabrication process with PTFE binder offers several advantages over conventionally used slurry coating process such as high manufacturing efficiency due to the non-solvent process and the ease of increasing the electrode thickness resulting from fibrillization of the PTFE binder. However, the instability of PTFE binder in dry processed graphite anodes remains a challenge, as the irreversible reaction of PTFE binder leads to the deterioration of the electrode. Furthermore, the properties of graphite materials including specific surface area, the particle size and shape can also affect the microstructure of the electrode and the electrochemical performance of graphite anode. In this work, the relationship between the properties of graphite and the electrochemical performance of dry processed graphite anode was investigated using various analytical techniques and the electrochemical characterization techniques. More detailed analyses results will be discussed in the presentation.

Effect of mechanical properties on processing behavior and electrochemical performance of aqueous processed graphite anodes for lithium-ion batteries

A combination of styrene-butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC) is a well-established binder system in aqueous processed anodes for lithium-ion batteries. The main function of SBR is to increase the adhesive strength between the active anode layer and the current collector, providing a robust connection capable of withstanding mechanical stresses encountered during cell manufacturing and cell cycling. To determine the optimal adhesion level ensuring failure-free processing without compromising the electrochemical performance we variated SBR concentration and investigated the effect on the processability and electrochemical performance of graphite anodes with application relevant mass loadings (5.7 mg cm−2 and 10.1 mg cm−2).Our results indicate that the inclusion of SBR enhances cohesion of anodes, a vital factor in preserving the mechanical integrity during bending, winding and cutting, particularly at elevated mass loadings. However, our findings reveal that unnecessarily high adhesion does not yield benefits on the processability of anodes. Furthermore, SBR is virtually dispensable for adhesion during cell cycling, and it proves to be counterproductive, primarily due to the rise in internal resistance and, most likely, SBR degradation. For the system investigated here, optimal adhesion was found for 1.5 % SBR in the current collector-free anode.

Astonishing performance improvements of dry-film graphite anode for reliable lithium-ion batteries

The electric vehicle (EV) market now requires advanced graphite anodes that can enable both high loading and quick charging. However, meeting these requirements simultaneously is challenging because of uneven electrochemical reactions and Li-plating on the surface of graphite anodes during fast-charging. In this study, high current density graphite anodes (≈6 mA cm−2) were fabricated through a solvent-free dry-electrode process using homogeneously dispersed polytetrafluoroethylene fibrils (2.0 wt% in electrode). This approach significantly improved the mechanical properties and electrochemical performance of graphite anodes during charge/discharge cycles. Dry-processed graphite anodes outperformed conventional wet-processed electrodes in terms of rate performance and capacity retention. Furthermore, LiNi0.6Co0.2Mn0.2O2 (NCM)/graphite coin-type full cells are rapidly charged at a 3C-rate to induce Li-plating on the graphite surface. Thus, dry-processed graphite anodes exhibited less Li-plating than wet-processed anodes, implying that dry-processed electrodes are capable of fast-charging even under high-loading conditions. In addition, dry-processed graphite anodes retain 88.2 % capacity retention after 300 cycles, indicating a stable full-cell operation. Consequently, this research highlights the dry-electrode process as an innovative technique for electrode manufacturing, with the potential to reduce battery production costs while improving electrochemical performance during fast-charging.

Advancements and Prospects of Graphite Anode for Potassium-Ion Batteries.

Potassium-ion batteries (KIBs) have recently attracted considerable attention owing to their resource abundance, low cost and environmental friendliness. Graphite as a mature commercial anode material for lithium-ion batteries, has been proved as a promising anode candidate for KIBs by reversible forming potassium-graphite intercalation compounds. However, large volume expansion and sluggish K+ kinetics caused by the incompatibility between large radius of K+ and the small interlayer spacing of graphite, result in the poor cycle stability and rate performances, hindering its practical application. Extensive research efforts have focused on improving the potassium storage performance of graphite anodes. This review provides an overview of recent advances in addressing these challenges and optimizing the electrochemical performance of graphite anodes for KIBs. Various strategies to improve the electrochemical performance of graphite and graphitic carbon anodes, such as microcrystalline regulation, heteroatom doping, morphological adjustment, and coating modification, are discussed, while the critical issues and challenges associated with graphite anodes and the prospects for their advancement in KIBs are highlighted. The review offers valuable guidelines for rational structural design and promotes the commercial development of high-performance graphite anode materials for KIBs.

Enhanced capacity and thermal safety of lithium-ion battery graphite anodes with conductive binder

Thermal safety is critical for marketable batteries. Numerous safety incidents from graphite anode instability impede lithium-ion battery (LIB) use for large-scale energy storage. Herein, we compare thermal safety and electrochemical performance of graphite anodes with commercial conducting polymer poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and standard polyvinylidene fluoride (PVDF) binders. Thermal analyses with differential scanning calorimetry (DSC) elucidates thermal runaway mechanisms. Reduced wettability of the PEDOT:PSS binder and lower specific surface area of the graphite anode composite contributes to less heat generation from solid electrolyte interphase (SEI) decomposition as compared to PVDF between 100 and 150ۥ°C, particularly when carbon black (CB) additive is excluded, evolving 143, 37.5, and 102 J g−1 for PVDF/CB, PEDOT:PSS, and PEDOT:PSS/CB composite binders, respectively. Additionally, conducting binders provide enhanced stability against LiXC6, generating less than 16% of the 728 J g−1 from the PVDF/CB graphite anode. In full-cell thermal safety studies with LiCoO2 (LCO) cathode using multimode calorimetry (MMC), this reduces heat generation at temperatures (<140 °C) where thermal runaway may still be circumvented. Electrochemical performance is not sacrificed as PEDOT:PSS/CB provides improved capacity (400 vs. 360 mAh g−1 after 100 cycles at C/5) and kinetics (260 and 189 mAh g−1 at 1C) over PVDF/CB.

Diazotization Grafting Phenol for Improving the Electrochemical Performance of Graphite Anode

Capacity fading resulting from graphite exfoliation is a thorny problem for real application of the graphite anodes in lithium-ion batteries. In this paper, we report on diazotization grafting phenol for graphite flakes to settle this issue, using 4-aminophenol and tert-butyl nitrite as the diazonium reagents. Diazotization grafting phenol enables expansion of graphite interlayer spacing and formation of surface protective layer, yielding modified graphite anodes with improved electrode kinetics, and significantly improved cycling stability. Also, the phenol modifier contributes additional specific capacity to the anode through reversible redox reaction of phenol hydroxyls with Li+ ions. The modified graphite anode with mole percent of 4-aminophenol to graphite being 5% retains a discharge specific capacity of 361 mA h g‒1 after 300 cycles at 1C, presenting capacity retention of 90.5% relative to the initial cycle, much higher than that of 156 mA h g‒1 and 54.2% for pristine graphite.

On the connection between slurry rheology and electrochemical performance of graphite anodes in Lithium-ion batteries

Many current lithium-ion battery anodes are prepared from a slurry containing graphite, polyvinylidene fluoride (PVDF), n-methyl-2-pyrrolidone (NMP), and small amounts of conductive carbon black (CB). The rheology of this four-component slurry is an important indicator of its microstructure, that affects the structure of the dried electrode. This in turn has consequences on the electrochemical performance of the anode. We modulate the rheology of the slurry by choosing three different commercially available carbon blacks that are used in lithium-ion batteries and establish a connection between slurry rheology and electrochemical performance. We show that the storage modulus is the key factor that impacts the electrochemical performance.

Effect of Solid Content in Electrochemical Performance of Graphite Anode of Lithium-ion Batteries

Rechargeable batteries have been implemented in most portable electronic devices. Lithium-ion battery (LIB), as the main power source, dominates the mobile device market due to its high energy density, long shelf life, and environmentally friendly operation. In the rechargeable lithium-ion battery, there are four main components, one of which is the anode. The anode material used is commercial graphite. Thus, this study aims to determine the effect of solid content solvents on battery performance. The main discussion in this study is to analyze the effect of solvent variations of N, N Dimethyl Acetamide (DMAC) on the characteristics of the sheet and the difference in solid content of graphite anode sheets on battery performance. Identification of the formed phase was carried out by XRD, reduction and oxidation reactions by cyclic voltammetry test, battery capacity by charge/discharge test, and study of the electrochemical characteristics of the electrode material by electrochemical impedance spectroscopy test. The best anode sheet is produced by mixing 2.5 mL DMAC solvent at a thickness of 0.07 mm with a solid content of 25%. The results of the charge-discharge test showed a specific capacity of 309.33 mAh/g in the first cycle.

On the Connection between Slurry Rheology and Electrochemical Performance of Graphite Anodes in Lithium-Ion Batteries

On the Connection between Slurry Rheology and Electrochemical Performance of Graphite Anodes in Lithium-Ion Batteries

Graphite Anode for Potassium Ion Batteries: Current Status and Perspective

With the increased demand from the storage of renewable energy sources, some safe and inexpensive energy storage technologies instead of Li‐ion batteries become urgently needed. Therefore, K‐ion batteries (KIBs) have attracted much attention and evolved significant development because of the low price, safety, and similar property compared with Li‐ion batteries. Due to the high reversibility, stability, and low potential plateau, graphite becomes a current research focus and is regarded as one of the most promising KIB's anode materials. In this review, we mainly discuss the electrochemical reaction mechanism of graphite during potassiation‐depotassiation process and analyze the effects of electrode/electrolyte interface on graphite for K‐ion storage. Besides, we summarize several kinds of methods to improve the performance of graphite for KIBs, including the design of graphite structure, selection of appropriate binder, solvent chemistry, and salt chemistry. Meanwhile, a concept of “relative energy density” is raised, which can be more accurate to evaluate the genuine electrochemical performance of graphite anode involving the specific capacity and potential. In addition, we also summarize the considerable challenges to current graphite anode in KIBs and we believe our work will offer alterative solutions to further explore high‐performance graphite anode of K‐ion storage.

Boosted electrochemical performance of graphite anode enabled by polytetrafluoroethylene-derived F-doping

Pure graphite anode exhibits inferior rate performance and cyclability in lithium-ion batteries. Herein, graphite was mixed in polytetrafluoroethylene (PTFE) aqueous emulsion followed by heating the parched mixture at 400 °C for 5 h. The common lipophilic behavior of the two materials allows the melted PTFE to reveal good wettability to graphite, and the large concentration gradient of fluorine element between graphite and the melted PTFE drives fluorine diffusion into graphite to achieve F-doped graphite. The as-modified product with a PTFE/graphite mass ratio of 1.2% reveals a reversible capacity of 390.8 mAh g−1 after 60 cycles at 0.1C, and a capacity of 319.3 mAh g−1 after 100 cycles at 0.5C, markedly superior to the performance of the pristine graphite. The appreciable property of the PTFE-modified graphite is attributable to the uniform PTFE coating for avoiding the direct interaction of electrolyte with graphite and enhancing the coulombic efficiency of first lithiation/de-lithiation cycle, the F-doping for facilitating electron transfer, the augmented mesopore volume and specific surface area for Li-ion storage, and the enlarged lattice spacing of graphite for Li-ion diffusion.

Temperature dependent electrochemical performance of graphite anodes for K-ion and Li-ion batteries

The electrochemical behavior of graphite anode for potassium-ion batteries (KIBs) is investigated in detail over varying operating temperatures (0–40 °C) with comparisons made to lithium-ion batteries (LIBs). Three main categories of cell performance are analyzed and evaluated, namely, kinetics, aging, and polarization. At 10 °C and below, the KIBs exhibit poor rate capability, which can be attributed to the decreased solid-state diffusion coefficient, and the amplified charge-transfer and SEI resistances. In comparison to LIBs, KIBs exhibit rapid cell aging at elevated temperatures, owing to augmented SEI growth induced by the significant volumetric change of graphite during potassiation. 3-electrode cell studies reveal the dramatic polarization of K metal at 0 °C (161 mV), while the extreme reactivity of K metal causes a severe rise in impedance from cell storage at 50 °C. A full cell system comprising Prussian blue cathode and graphite anode is evaluated, which removes the issues associated with the K metal counter electrode and enhances rate performance at 0 °C. These findings provide a thorough basis for understanding the temperature dependent behavior of graphite anode for KIBs and its performance concerns at low and elevated temperatures.

Effects of functional binders on electrochemical performance of graphite anode in potassium-ion batteries

Electrochemical properties of the graphite electrode in potassium-ion batteries (KIBs) depend on the selection of the proper binder. The results in our experiment show that compared with the conventional binders of poly(vinylidene fluoride) (PVDF) and carboxymethylcellulose sodium (CMCNa), the polyacrylate sodium (PAANa) binder can greatly improve the electrochemical performance during the potassiation and depotassiation. Specifically, the initial discharge and charge capacity of the graphite-PAANa electrode are 415.4 and 238.5 mAh g−1, respectively. Even after 50 cycles, it still has a high charge capacity retention of 96.9%. Considering the good swelling property of the PAANa binder, the adhesive and mechanical strength of composite electrodes are obviously enhanced. In addition, the graphite-PAANa electrode can also decrease the electrolyte decomposition on the graphite particle surface and restrain the capacity fading resulted from the repeatedly volume expansion.

Unraveling the role of LiFSI electrolyte in the superior performance of graphite anodes for Li-ion batteries

While lithium bis(fluorosulfonyl) imide (LiFSI) is widely used in current Li-ion batteries (LIBs), the role of LiFSI in the LIB performance remains elusive. We herein elucidate the effects of LiFSI on the electrochemical performance of graphite anodes in comparison with those of lithium hexafluorophosphate (LiPF6). An in-depth electrochemical analysis using graphite/Li half cells and graphite/graphite symmetric cells confirms that LiFSI provides little improvement to the cyclability of the graphite anode at 25 °C, but enables far better performance in cycle and storage tests at 60 °C. The superior thermal stability of the graphite anode in LiFSI electrolyte is attributed to the formation of a thin, inorganic-rich solid electrolyte interphase (SEI) layer as indicated by differential scanning calorimetry (DSC) and X-ray photoelectron spectroscopy (XPS) measurements.

Effects of Boric Acid Tris-(2-oxo-[1,3]dioxolan-4-ylmethyl) Ester as an Additive on the Electrochemical Performance of Graphite Anode

To improve the cycle performance of lithium ion battery (LIB), boric acid tris-(2-oxo-[1,3]dioxolan- 4-ylmethyl) ester (BATE) as a novel electrolyte additive in 1mol•L-1 LiPF6-EC:DMC (1:1 vol., Lithium Battery-grade) electrolyte was investigated. BATE derived from glycerol carbonate, which had the same ring structure as ethylene carbonate (EC). Additionally, the carbonyl group (-C=O) and electron deficient boron atom contained in the BATE molecular structure had been proved to be effective in maintaining the stability of the lithium salt (LiPF6) and increasing the durability of the electrolyte for formation of a solid electrolyte interface (SEI) layer, which plays a critical role in the cycle life of lithium ion battery (LIB). The electrochemical measurements and investigations of the compound BATE as additive were carried out by charge-discharge test, electrochemical impedance spectroscope (EIS), cyclic voltammetry (CV) test and scanning electron microscope (SEM). Results confirmed that BATE decomposed on the graphite anode earlier than electrolyte solvents to form the solid electrolyte interface (SEI) film. BATE could improve cycle stability of the cell significantly, especially when addition of 1.0% BATE, the capacity retention was up to 98.1% after 20 cycles. And the internal resistance change of cell with cycles was decreased after 20 cycles.

Electrochemical performance of graphite anode with various electrode compressibilities for long-life Li-ion battery

The effect of electrode compressibility for discharge rate and cycle performance on the natural graphite (NG) anode in Li-ion batteries was studied. Roll-pressing the NG electrode increases electrical contact, which benefits the high discharge rate. However, high roll pressing of NG electrodes accumulates stress and limits the volume increase, thereby leading to poor cyclability. The mixture of NG and mesocarbon microbeads (MCMBs) provides more appropriate electrical contact and exhibits excellent cycle performance as compared to pure NG and MCMB. Therefore, NG–MCMB composite electrodes may emerge as practical and promising anode materials for secondary Li-ion batteries.

Effects of ethylene sulfite as a supplementary film-forming additive on the electrochemical performance of graphite anode in EC-based electrolyte

The effect of ethylene sulfite (ES) as a supplementary film-forming additive on the electrochemical performance of graphite anode in ethylene carbon (EC)-based electrolyte is studied in this research by constant current charge–discharge test, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). Results show that ES addition can change the composition of solid electrolyte interface (SEI) coating on the surface of graphite anode by inhibiting the formation of inorganic compounds in a specific stage. XPS and SEM results confirm that SEI formed in the ES-added electrolyte contains less inorganic compounds. EIS measurements further reveal that ES addition can significantly reduce the resistance of the SEI layer and interface of graphite anode–electrolyte.

Enhanced Electrochemical Performance of Graphite Anodes for Lithium-Ion Batteries by Dry Coating with Hydrophobic Fumed Silica

Coating of electrode materials for lithium-ion batteries is usually performed in order to improve performance, safety and the processability of the raw material. Here, we apply a dry coating method of graphite with hydrophobic fumed silica particles. This method excludes the use of any harmful solvents and the nano-scale particles cover and stick to the graphite substrate by only adhesive forces. Furthermore, this dry coating method is easily mass-scalable and a high throughput can be obtained in a short processing time. The nanoparticle coating reduces the van-der-Waals forces between the graphite particles and leads in this way to better flowability of the graphite powder which is important for further processing and the production of electrode tapes. Furthermore, these core-shell particles were processed to composite negative graphite electrodes in combination with the water soluble binder sodium carboxy-methylcellulose. Electrodes obtained with the coated material displayed a smooth surface, a high mechanical stability and outperformed the unmodified ones in the electrochemical investigations.