Spherical Natural Graphite Research Articles

Chitosan-covered spherical natural graphite: A perfect carbon source for efficient non-PGM catalysts for electrocatalysis

Developing non-precious metal catalysts to replace Pt-based catalysts for oxygen reduction reaction (ORR) is a hotspot presently, and transition metal-nitrogen co-doped carbon (TMNC) materials have been deemed as the most promising candidates. In this work, chitosan-derived-curved-carbon covered natural spherical graphite (SG) with a well-defined core-shell structure were prepared via hydrothermal carbonization (HTC) process followed by activation under NH3 atmosphere. A series of active transition metals (M=Fe, Co, Mn) and nitrogen atom were embedded into the curved carbon to form various MNC moieties on SG surface as active sites for ORR. Among the atomic precise MNC@NSG hybrid catalysts, the FeNC@NSG shows the best ORR performance and the half-wave potential is 0.95 V (vs. RHE), which are 108 % as high as that obtained by commercial Pt/C in alkaline environment. Besides, the electrochemical stability and methanol tolerance of the catalyst is also superior to commercial Pt/C. DFT calculations reveals that the high-performance stems from the curved FeNC units in the shell and high electrical conductivity of natural SG in the core for the typical core-shell structures. Moreover, the sluggish ORR kinetics can be efficiently accelerated by the increased FeN bond length, more positive-shifted d-band center and more positive surface charge of active Fe atoms in the curved FeNC units on spherical SG. This provides an enlightenment for developing efficient non-platinum group metal (PGM) catalysts using cheap and volume natural spherical graphite as building brick for energy storage and conversion devices.

Facile Synthesis of a SiOx-Graphite Composite toward Practically Accessible High-Energy-Density Lithium-Ion Battery Anodes.

SiOx-based material is a promising candidate for lithium-ion batteries (LIBs) owing to its high theoretical capacity. The inherent disadvantages of poor electronic conductivity and large volume variation can be solved by constructing the outermost carbon layer and reserving internal voids. However, the practical application of SiOx/C composites remains a great challenge due to the unsatisfactory energy density. Herein, we propose a facile synthetic approach for fabricating SNG/H-SiOx@C composites, which are constructed by amorphous carbon, hollow SiOx (H-SiOx), and spherical natural graphite (SNG). H-SiOx alleviates volume expansion, while amorphous carbon promotes Li+ migration and stable solid electrolyte interphase (SEI) formation. The as-prepared SNG/H-SiOx@C demonstrates a high reversible capacity (465 mAh g-1), excellent durability (93% capacity retention at 0.5C after 500 cycles), lower average delithiation potential than SNG (0.143 V after 500 cycles), and a 14% gravimetric energy density improvement at a loading level of 4.5 mg cm-2. Even at a compacted density of 1.5 g cm-3, the SNG/H-SiOx@C anode presents a modest volume deformation of 14.3% after 100 cycles at 0.1C.

Spherical Silicon/CNT/Carbon Composite Wrapped with Graphene as an Anode Material for Lithium-Ion Batteries

The assembly of the micron-sized Si/CNT/carbon composite wrapped with graphene (SCG composite) is designed and synthesized via a spray drying process. The spherical SCG composite exhibits a high discharge capacity of 1789 mAh g−1 with an initial coulombic efficiency of 84 %. Moreover, the porous architecture of SCG composite is beneficial for enhancing cycling stability and rate capability. In practice, a blended electrode consisting of spherical SCG composite and natural graphite with a reversible capacity of ~500 mAh g−1, shows a stable cycle performance with high cycling efficiencies (> 99.5%) during 100 cycles. These superior electrochemical performance are mainly attributed to the robust design and structural stability of the SCG composite during charge and discharge process. It appears that despite the fracture of micro-sized Si particles during repeated cycling, the electrical contact of Si particles can be maintained within the SCG composite by suppressing the direct contact of Si particles with electrolytes.

Achieving High-Performance Spherical Natural Graphite Anode through a Modified Carbon Coating for Lithium-Ion Batteries

The electrochemical performance of modified natural graphite (MNG) and artificial graphite (AG) was investigated as a function of electrode density ranging from 1.55 to 1.7 g∙cm−3. The best performance was obtained at 1.55 g∙cm−3 and 1.60 g∙cm−3 for the AG and MNG electrodes, respectively. Both AG, at a density of 1.55 g∙cm−3, and MNG, at a density of 1.60 g∙cm−3, showed quite similar performance with regard to cycling stability and coulombic efficiency during cycling at 30 and 45 °C, while the MNG electrodes at a density of 1.60 g∙cm−3 and 1.7 g∙cm−3 showed better rate performance than the AG electrodes at a density of 1.55 g∙cm−3. The superior rate capability of MNG electrodes can be explained by the following effects: first, their spherical morphology and higher electrode density led to enhanced electrical conductivity. Second, for the MNG sample, favorable electrode tortuosity was retained and thus Li+ transport in the electrode pore was not significantly affected, even at high electrode densities of 1.60 g∙cm−3 and 1.7 g∙cm−3. MNG electrodes also exhibited a similar electrochemical swelling behavior to the AG electrodes.

Preparation and Characteristics of Core-Shell Structure with Nano Si/Graphite Nanosheets Hybrid Layers Coated on Spherical Natural Graphite as Anode Material for Lithium-ion Batteries

Preparation and Characteristics of Core-Shell Structure with Nano Si/Graphite Nanosheets Hybrid Layers Coated on Spherical Natural Graphite as Anode Material for Lithium-ion Batteries

In-Situ EIS to Investigate Effect of C-Rate on Impedance Spectra of Positive Electrodes with Different Ratio of Conductive Additives in Lithium Ion Batteries

Active materials, conductive additives and binders are widely used for the fabrication of positive electrodes of lithium ion batteries (LIBs). The electrochemical performance of positive electrodes is affected by the addition rate of conductive additives on the electrode 1). It is important to investigate the effect of the addition rate of conductive additives on the electrode performance of the positive electrode during charge-discharge cycle in order to develop LIBs that can charge and discharge at high C-rate. In the present study, the in-situ EIS 2) was employed to investigate the effect of C-rate on impedance spectra of positive electrode with different additive rates of conductive additives.The positive electrode with different additive rates of acetylene black (AB) was fabricated by screen printing. The mixture of the slurry containing LiCoO2 powder, AB, polyvinylidene fluoride and N-methylpyrrolidone were screen-printed on the aluminum foil. In the present study, the positive electrode with different additive rates of AB was used for the impedance measurement. The spherical natural graphite fabricated on cupper foil was used as the negative electrode and a lithium wire was used as the reference electrode (RE). All measurements were carried out by the three-electrode cell (Toyo system co. ltd.) at room temperature in an argon atmosphere.The 3D impedance of positive electrode, negative electrode and full cell was measured by in-situ EIS during charge and discharge. In the 3D impedance of positive electrode, three loops were observed on the Nyquist plane during charge and discharge. As the diameter of loop in the low frequency range was decreased with the increase of the state of charge (SOC), this loop may be related to the time constant composed of the charge transfer resistance R ct and the electric double layer capacitance 2). In order to examine the effect of C-rate on impedance of positive electrode, the changes of R ct values during charge and discharge were estimated from the instantaneous impedance at arbitrary SOC on 3D impedance of positive electrode. The relationship between C-rate and additive rates of AB on the impedance of positive electrode was discussed.

The effect of mild activation on the electrochemical performance of pitch-coated graphite for the lithium-ion battery anode material

In order to improve the rate performance of a graphite anode for lithium-ion batteries (LIBs), mild activation was applied after a coating process to deposit unique coating layer with additional sites where lithium ions are able to be inserted on the graphite anode. In this study, we coated the pitch onto spherical natural graphite (SG) by using toluene and drying, before mild activation to control the coating layer structure, which contributes to preserving the intact structural integrity of graphite anodes during the repeated charging and discharging process. The crystal structure and surface of pitch-coated graphite with mild activation was observed using XRD, Raman spectra, TEM, SEM analyses to verify the formation of the coating layer. The pitch-coated graphite with mild activation can provide improved cycle stability (86.3% after 30 cycles at 0.5 C-rate) and high rate capability (91.0% at 1 C-rate/0.1 C-rate). Notably, complicated voltage profiles of as-prepared samples demonstrate that mild activation can be utilized to establish the lithium-ion insertion sites, such as partially charge transferring surface sites (Type 1), edges of carbon hexagon clusters (Type 3), and micro-void structures by hexagonal planes (Type 4).

In-situ EIS to Investigate Influence of Conductive Additive Addition Rate on Charge Transfer Resistance of Lithium Ion Batteries

In order to develop the lithium ion batteries (LIBs) with higher capacity, it is important to select the suitable compositions of conductive additives for the reduction of the internal resistance of the positive and negative electrodes of LIBs1). In the present study, the influence of the conductive additive addition rate on the internal resistance of the positive electrode was investigated by in-situ EIS 2). This method enables us to measure impedance spectra of the positive electrode, negative electrode and cell of LIBs simultaneously without stopping the measurement of charge/discharge curve. The positive electrode was fabricated by screen printing. The mixture of the slurry containing LiCoO2 powder, carbon nanowire (CNW), polyvinylidene fluoride and N-methylpyrrolidone were screen-printed on the aluminum foil. In this case, the compositions of CNW were 8 to 30 wt % as the conductive additive. In order to investigate the effect of CNW on electrochemical properties of LIB, an acetylene black (AB) was used as the conductive additives instead of the CNW. The spherical natural graphite on cupper foil was used as the negative electrode and a lithium wire was used as the reference electrode (RE). All measurements were carried out by the three-electrode cell (Toyo system co. ltd.) at room temperature (25℃) in an argon atmosphere. In the impedance spectrum of the positive electrode measured by the in-situ EIS, three loops were observed on the Nyquist plane. Since the diameter of the loop in the low frequency range was decreased with the increase of the states of charge (SOC), it is considered that this loop is related to the time constant of charge transfer resistance R ct and electric double layer capacitance 2). The values of R ct of the positive electrode estimated from the diameter of the loop in the low frequency range were decreased with increasing with the addition rate of the conductive additive. The effect of the addition rate of the conductive additive of the positive electrode on the values of R ct at each SOC were discussed.

Mechanofusion-Derived Si Alloy-Graphite Composite Electrode Material for Li-Ion Battery

Silicon-graphite composites are extremely promising negative electrode materials for Li-ion batteries. However, simple and effective methods to synthesize silicon-graphite composites with engineered structures are needed to realize this technology in practical applications. Here, we show that the environmentally friendly and low-cost dry mechanofusion (MF) process can effectively synthesize silicon alloy-graphite composites, in which silicon alloy particles can be well dispersed and embedded between flake graphite layers, as shown in Figure 1(a)-(b). This results in increased tap density and reduced surface area. The special structure provides a way to buffer volume expansion and contraction of the silicon alloy during lithiation and delithiation. As a result of this hierarchical arrangement, superior cyclability and rate capability are achieved compared to simple mixtures, with capacities of 950 mAh/g (i.e. 1473 Ah/L) and 900 mAh/g (i.e. 1432 Ah/L) at 2C and 4C, respectively (Figure 1(c)). Moreover, using this process, micron-sized silicon alloy particles can be well embedded within spherical natural graphite particles, as shown in Figure 1(d)-(e). The specially engineered structure created by the MF dry process leaves room for expansion and contraction of the silicon alloy during lithiation and delithiation process. In addition, the silicon alloy particles are protected within the graphite particle, which could be helpful to avoid excessive electrolyte exposure and improve cycle life. Figure 1

Preparation of Composites of Nano-Silicon and Spherical Natural Graphite for Li-Ion Batteries By a Drop-in Technology

We will describe a methodology to prepare nano-Si / natural graphite composite using an established transformation manufacturing process without significant changes to the initial process flow, thus minimizing the cost of implementation. First, a baseline was established by investigating half-cells made with anode using a mixture of coated spherical natural graphite, nano-Si and LiPAA binder. Then, a composite of graphite / nano-Si was prepared by carbonizing a dry mixture of spherical graphite, nano-Si and petroleum pitch. The silicon content was below 20 wt.% toward graphite and the pitch-to-nano-Si was optimized. Following these guidelines, a series of Si/graphite composites were prepared by first performing a spheronization process to a dry mixture of natural graphite flakes, nano-Si and carbon precursors to disperse the silicon in the core and on the surface of the graphite matrix. Followed by a carbonization step to form the amorphous carbon coating simultaneously on the graphite and nano-Si surface. The morphology and chemical composition of the composites' surface was investigated using XPS, SEM and HRTEM and the possible formation of silicon oxides or carbides was evaluated by XRD. Tap density, surface area and PSD were performed to assess if the prepared powders reached the battery grade specifications. The composites show very high reversible capacity when evaluated in coin-type, Li-ion half cells.

Graphite for Energy Applications

INTRODUCTION Graphite is widely used as active material for anodes in lithium ion batteries (LIB), and by selection and processing, graphitic materials can be optimized for energy and power applications, respectively. We have looked at contributions of particle size and materials processing to capacity and discharge rate capabilities of natural and artificial graphite. This work continues research reported earlier4. METHODOLOGY First, we compared coated spherical natural graphite of regular and fine size at discharge rates from C/20 to 30C. Our interest was to assess diffusion as limiting factor1,2, We then looked at two kinds of artificial graphite of similar size which were derived from different processes. The investigation was done on half cells (G/EC-DMC-LiPF6/Li). The electrode composition was the same throughout: 91 % graphite, 7% binder PVDF 9305 from Kureha and 2 % carbon black Super P. Thin electrodes (≈30mm, 1 g/cc) were prepared for high and thick electrodes (≈60mm, 1.5 g/cc) for lower rates. Due to its mechanical properties, the desired electrode density of 1.5 g/cc proved impossible for artificial graphite #2. The two first cycles with the thick electrodes were done at constant current (CC) at C/20, and then the intercalation was done at C/5 followed by a step at constant voltage (CV) to reach full intercalation. For thin electrodes the intercalation was at done at C/5 with CV step throughout. RESULTS AND DISCUSSION Physical and chemical characterization: Table (1) presents physical and chemical characteristics of the materials. Figure (1) exhibits differences in texture with artificial graphite #2 having higher rugosity. Test Analysis Natural #1 Natural #2 Artificial #1 Artificial #2 Type of Graphite Coated NG Coated NG Synthetic Synthetic Ash (%) 0.02 0.024 < 0.01 < 0.01 True Density (g/cc) 2.18 2.2 2.25 2.13 Tap Density (g/cc) 1.05 1.14 1.21 0.34 Surface Area (m2/g) 2.06 1.09 1.15 6.45 Particle size (Microtrac, mm) D10 5.51 10.62 5.38 4.22 D50 8.34 16.9 13.22 10.46 D90 13.47 27.09 28.59 20.71 Table (1): Characteristics of two kinds each of coated natural and of artificial graphite Figure (1): SEM of artificial graphite #1 (left) and #2 (right). Electrochemical Characterization: Artificial Graphite Artificial graphite #1 and #2 have comparable discharge capacity of 330 mAh/g at C rate, but differ significantly at higher discharge rates (table 2). Although at same level of graphitization3 (86-87%), the differences in processing show in surface area, tap density (table 1) and surface rugosity (figure 1). The evolution of the discharge capacities as a function of discharge rate are presented in figure (2). Figure (2): Charge and discharge of artificial graphite #1 and #2 in half-cell with thin electrode. Artificial #1 Artificial #2 Rates (C) 1/2 discharge voltage (V) Capacity (mAh/g at 2 V) Capacity (% of capacity at C) 1/2 discharge voltage (V) Capacity (mAh/g at 2 Volts) Capacity (% of capacity at C) 1 0.184 332 100 0.170 331 100 5 0.362 330 99 0.305 331 100 10 0.579 323 97 0.467 329 99 20 0.946 282 85 0.796 318 96 30 1.135 228 69 0.960 289 87 Table (2): Gravimetric capacity and voltage vs. Li/Li+ at half discharge for artificial graphite #1 and #2 Spherical coated natural graphite Electrochemical results from spherical graphite #1 and #2 at high rate discharge are presented in figure (3) showing similar behaviors up to 10C discharge. At 20C and 30C we see a higher impedance for the finer spherical graphite #1. Figure 3: High rate discharges of coarse (right) and fine (left) spherical graphite CONCLUSION We have seen that differences in processing are reflected both in physical characteristics and in electrochemical behavior. The nature of graphite affects both the intrinsic capacity and the ability to sustain high discharge rates. The discharge capacity at 30C of artificial graphite reached 280 mAh/g, 85% of the capacity at C rate. The lower packing density could be an issue for energy applications, but may not be acceptable for power applications. REFERENCES 1) Persson, K. et al. The journal of physical chemistry letters 1(8) (2010) 1176-1180. 2) Yu, P. et al. Journal of The Electrochemical Society, 146(1) (1999)8-14. 3) J. Maire, J. Mering. Chemistry and physics of carbon 6 (1970): 125-190. 4) Henry FX. et al. (2006) “New developments in the advanced graphite for lithium-ion batteries”. In: NATO Science Series II: Mathematics, Physics and Chemistry, vol 229. Springer, Dordrecht Figure 1

Carbon-coated isotropic natural graphite spheres as anode material for lithium-ion batteries

Abstract Carbon coated isotropic natural graphite spheres (INGS/C) has been prepared by spray granulation using the by-product of spherical natural graphite (i.e., superfine graphite powders) as starting materials. In INGS/C, small graphite flakes are packed in disordered orientation and form an isotropic structure, which may effectively reduce local stress concentration appearing in the process of Li + insertion/extraction. The pyrolytic carbon decomposed from polyvinyl alcohol (PVA) and citric acid is connecting the small graphite flakes and coating on the surface of INGS, respectively, thus forms a continuous conductive network to improve the electron transmission and maintain the micro-structural integrity of isotropic natural graphite spheres as well. With the help of synergetic effect between the isotropic structure of INGS and the continuous conductive network, the INGS/C electrode exhibits superior rate capability of 346 mA h g −1 at 3 C at low potential below 0.25 V.

Structure and Performance of Spherical Natural Graphite Modified by Ag-C Double Coating

Structure and Performance of Spherical Natural Graphite Modified by Ag-C Double Coating

Effect of Impurities on Electrochemical Performance of Low-Purity Natural Graphite As Anode Active Material for Lithium Ion Batteries

Natural graphite (NG) has been attracted as a promising anode material for lithium ion batteries due to its appropriate charge/discharge profile, high reversible capacity and low cost. However, high irreversible capacity and low capacity retention at first cycle have influenced on its practical use. Although low cost is the main advantage of natural graphite, the material cost of natural graphite should be reduced further in order to be used for electric vehicles (EVs) and energy saving systems (ESS). Generally, pristine natural graphite contains various impurities such as Al, Fe, and Si. For commercial use, pristine natural graphite should be refined since the impurities would have a negative effect on both electrolyte and electrode of lithium ion batteries. The purity grade of natural graphite can be classified based on the purification process. As the requirement for high purity increases, more purification steps are needed, resulting in high manufacturing cost. Therefore, the main issue for the application of natural graphite as an anode active material is to use low-purity natural graphite with purification process as less as possible. In this regard, effect of Fe as impurity on the electrochemical performance of the low-purity natural graphite as anode active material for lithium ion batteries was investigated in this study. Natural graphite powders with 5 wt% Fe (05Fe) and 10 wt% (10Fe) were synthesized by combustion method from the raw materials of Fe(III)(NO3)3 9H2O (Alfa Aesar) and high-purity spherical natural graphite (POSCO CHEMTECH) by calcination at 500 °C in air atmosphere. The morphology of the natural graphite powders was observed by scanning electron microscopy (SEM, JSM-5900, JEOL, Japan). The particle size of each powder was measured by a dynamic light scattering method (ELS 6000 zeta potential and particle size analyzer, Otsuka Electronics, Japan). Powder X-ray diffraction (XRD, MAX-2500, RIGAKU, Japan) analysis was conducted using Cu Kα radiation with a wavelength λ = 1.5406 Å. The crystallite sizes (La and Lc) were calculated on the basis of the d002XRD lines by application of the Scherrer’s equation. The crystallinity of the natural graphite powders was investigated by Raman spectroscopy (LabRAM, Horiba Jobin-Yvon, Japan). The concentrations of impurities in the natural graphite were determined by an inductively coupled plasma atomic emission spectrophotometer (ICP-AES). A working electrode paste was fabricated from a mixture of natural graphite with a binder consisting of carboxymethylcellulose (CMC)/styrene-butadiene rubber (SBR) and carbon black (Super-p) as a conductive agent dissolved in D.I. water. The weight ratio of graphite to binder (CMC:SBR:Super-p=2:2:1) was 95:2:2:1. The prepared paste was coated onto 10㎛ Cu foil by using a doctor blade and then dried under vacuum at 120 °C for 12 h. Electrochemical performance was evaluated using CR2032 coin-type cells with a 20 μm thick Cellgard 2300 porous membrane separator and 1 M LiPF6-EC/DMC (1:1 in volume ratio) electrolyte. Lithium metal foil was used as a counter electrode. All of the samples studied in this work were treated by sphericalization and the sphericalized natural graphite maintained a spherical shape after the calcination process at 500 °C for 4 h. All the samples have both hexagonal and rhombohedral phases which are the typical structure of natural graphite. Fe2O3 peaks (JCPDS card #33-0664) were indexed at 2θ = 33.1°, 35.6°, 62.4°, and 63.9°, respectively. The most of Fe2O3particles were located on a surface of natural graphite, based on the EDX mapping and back-scattered electron (BSE) images. The irreversible capacity during the charge-discharge reactions increased with increasing the Fe content. However, the cycle retention of the 05Fe, 10Fe, and NG are comparable. Therefore, it may be possible to use unrefined natural graphite as an anode active material for lithium-ion rechargeable batteries.

Preparation and Structure Regulation of Silicon Carbide-Derived Carbon/ Spherical Natural Graphite Composites

To meet the requirements of the energy storage materials for high energy density and high power density, porous silicon carbide/derived carbon-spherical natural graphite (SiC-CDCs@NG) composites were prepared. The composites were composed of tailored porous carbide-derived carbon and graphitized carbon with excellent conductivity and a high energy storage capacity. The composition, structure, morphology, pore structure, and specific surface area of the composites were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and N2 adsorption/ desorption analysis. The composites exhibited a high and adjustable specific surface area and micro-pore volume, with a micro-pore size of between 0.5 and 0.7 nm. Varying the molar ratio of NG and Si allowed optimization of the micro-pore volume, pore size distribution, specific surface area, and composition and content of the CDCs shell and NG core.

Effect of Carbon-Coating Morphologies on the Electrochemical Performance of Natural Graphite Spheres

Similar amount of carbon with three different types of morphologies, i.e. smooth pyrolytic carbon (SPC), granular pyrolytic carbon (GPC) and carbon nanofiber (CNF) was coated on the natural graphite (NG) spheres in a fluidized bed by chemical vapor deposition (CVD) from acetylene. The effect of carbon-coating morphologies on the electrochemical performance of NG spheres were studied, the results show that: PC is more effective in improving the first coulombic efficiency (CE); both GPC and CNF can improve the cyclability, however, GPC improves the first CE whereas CNF decreases the first CE.

Effect of polymeric binder type on the thermal stability and tolerance to roll-pressing of spherical natural graphite anodes for Li-ion batteries

The polymeric binder is seen to affect the thermal stability and deformation of spherical graphite used in lithium ion battery anodes. Spherical natural graphite anodes are prepared using three different binders: two aqueous-based binders, polyacrylic acid (PAA) and a mixture of carboxy-methyl cellulose and styrene butadiene rubber (abbreviated CMC/SBR), and an organic-based binder, polyvinylidene fluoride (PVDF). The thermal stability of fully lithiated electrodes is measured by differential scanning calorimetry (DSC). The PAA binder effectively suppresses heat evolution (43% (PVDF) and 23% (CMC/SBR) less heat) at low temperatures up to 200 °C during DSC scans of the lithiated electrodes, compared to the PVDF and CMC/SBR binders. In addition, the PAA binder allows the graphite electrode to maintain an appropriate porous structure (13% greater porosity than the PVDF and CMC/SBR electrodes) even at high electrode density after 6 kgf cm−2 compression, thus leading to enhanced effective cycles (11% (PVDF) and 60% (CMC/SBR) greater capacity after 50 cycles).

Enhanced performance of spherical natural graphite coated by Li4Ti5O12 as anode for lithium-ion batteries

The natural graphite (NG) is coated with Li4Ti5O12 (LTO) and the composite shows a markedly enhanced rate performance due to the decrease of charge transfer resistance after LTO coating. The specific capacity of the NG charge-discharged at 2 C is increased by 60.3% (128.7 vs. 80.3 mAh g−1) by coating it with 1 wt.% of Li4Ti5O12 (LTO). The comparison of the NG and that coated with 1 wt.% LTO at 0.1 C shows that the initial reversible capacity is increased from 318.1 mAh g−1 to 357.5 mAh g−1 after coating, while the total irreversible capacity loss after 50 cycles is decreased from 122.8 mAh g−1 to 103.9 mAh g−1. The composite improves the energy and power densities, safety, cycle life and lowers the price of the lithium-ion battery while avoiding the gas-swelling of full battery caused by Ti4+ because the final coating material is the lithiated LTO (Li7Ti5O12 or Li9Ti5O12).

Additives of Graphene Nanosheets on the Anode Performance of Spherical Natural Graphite for Lithium-Ion Batteries

Additives of Graphene Nanosheets on the Anode Performance of Spherical Natural Graphite for Lithium-Ion Batteries

A comparative study of polyacrylic acid and poly(vinylidene difluoride) binders for spherical natural graphite/LiFePO 4 electrodes and cells

Anodes containing spherical natural graphite (SNG12) and cathodes containing LiFePO 4, both from HydroQuebec, were prepared with aqueous-based polyacrylic acid (PAAH), its neutralized derivatives polyacrylic acid (PAAX) (X = Li, Na, and K), and with conventional poly(vinylidene difluoride) (PVDF) binders. A comparison of electrode performance was made between these three binder systems. The electrodes were optimized by adding elastic styrene butadiene rubber (SBR) and conductive vapor grown carbon fiber (VGCF) in the place of some of the PAAX. Initially, SNG12 and LiFePO 4 electrodes were characterized in half cells with Li as the counter electrode. The electrochemistry results show that the use of PAAX binders can significantly improve the initial coulombic efficiency, reversible capacity, and cyclability of SNG12 anodes and LiFePO 4 cathodes as compared to that of electrodes based on a PVDF binder. By using an optimized composition for the anode and cathode, SNG12/LiFePO 4 full cells with PAALi binder cycled 847 times with 70% capacity retention, which was a significant improvement over the electrodes with PVDF (223 cycles). This study demonstrates the possibility of manufacturing Li-ion batteries that cycle longer and use water in the processing, instead of hazardous organic solvents like NMP, thereby improving performance, reducing cost, and protecting the environment.