Activated carbon also called activated charcoal activated coal

有關碳名詞的說明 Activated carbon (活性碳), also called activated charcoal(木炭), activated coal , is a form of carbon that has been processed to make it extremely porous and thus to have a very large surface area available for adsorption or chemical reactions. Glassy carbon, also called vitreous carbon, is a non-graphitizing carbon. Glassy carbon is widely used as an electrode material in electrochemistry. The structure of glassy carbon has long been a subject of debate. Early structural models assumed that both sp 2 - and sp 3 -bonded atoms were present, but it is now known that glassy carbon is 100% sp 2. However, more recent research has suggested that glassy carbon has a fullerene-related structure. Note that glassy carbon should not be confused with amorphous carbon. This from IUPAC: "Glass-like carbon cannot be described as amorphous carbon because it consists of two-dimensional structural elements and does not exhibit ‘dangling’ bonds. “ Amorphous carbon has both sp 2 and sp 3 hybridized bonds present in the material. The properties of amorphous carbon films vary depending on the parameters used during deposition. One of the most common ways to characterize amorphous carbon is through the ratio sp 2 to sp 3 hybridized bonds present in the material. Graphite consists purely of sp 2 hybridized bonds, whereas diamond consists purely of sp 3 hybridized bonds. Carbon black is a material produced by the incomplete combustion of heavy petroleum products such as FCC tar(瀝青), coal tar, ethylene cracking tar, and a small amount from vegetable oil. Carbon black is a form of amorphous carbon that has a high surface-area-to-volume ratio, although its surface-areato-volume ratio is low compared to that of activated carbon. Coke (焦炭)is the solid carbonaceous material derived from destructive distillation of low-ash, lowsulfur bituminous coal (煙煤). Volatile constituents of the coal—including water, coal-gas, and coaltar—are driven off by baking in an airless furnace or oven at temperatures as high as 2, 000 o. C, usually around 1000 -1100 o. C.

二次鋰電池負極材料碳的不同型態 Graphite Hard carbons Soft carbons Carbon nanotubes Soft carbon Unit value Hard carbon Unit HCP Particle Size（D 50） μm 8. 0~14. 0 Particle Size（D 50） μm 6. 0～ 15. 0 Real Density g/cm 3 ≥ 1. 70 Real Density g/cm 3 1. 50～ 1. 70 Surface Area m 2/g 1. 6~3. 0 Surface Area m 2/g 3. 0～ 7. 0 Capacity m. Ah/g ≥ 240. 0 Capacity m. Ah/g ≥ 250. 0

Li. C 6 375 m. Ah/g XRD pattern of the coke sample heat treat at various temperature Relationships between reversible specific capacity and heat treatment temperature. Closed and open symbols are soft and hard carbons, respectively. BSU basic structural unit Structural evolution of a graphitic carbon as a function of temperature Charge and discharge characteristics of natural graphite powder

in plane structure of stage-1 Li-GIC Stage structure of GIC 每一層碳 每兩層碳 每三層碳 每四層碳 一層鋰 The stage structure changes successively from a higher to a lower stage during lithium intercalation. The dilute stage-1 (1’)denotes a phase where lithium ion is intercalated randomly within graphite and stage -2 L denotes a liquid-like stage-2 phase that has no inplane ordering. Phase diagram of Lix. C 6 obtained by an electrochemical method.

Charge and discharge characteristic of MCMB heat-treated at 1800 o. C at 1 st and 2 nd cycles in 1 MLi. Cl. O 4/EC+DEC (region B) Charge/discharge of petroleum. Charge/discharge of MCMB 700 (region C) pitch-based pseudo-isotropic carbon (region D) (region C) 量測值 計算值 Variation of the reversible capacity of soft carbon with heattreatment temperature.

An energy state model to explain voltage of region C soft carbon. Site A and B denote the intercalation and bonding sites. C H bonding site Li intercalation site

Improvement of natural graphite as a lithium-ion battery anode material, from raw flake to carbon-coated sphere Schematic views of the MCMB, shuttle-shaped and spherical natural graphite. Schematic views of the raw natural graphite flakes (upside) and shuttle-shaped natural graphite particles (downside) spread on the copper foil (current substrate).

1. Graphite is very sensitive towards electrolytes and can easily be exfoliated in PC (propylene carbonate)-based electrolytes, which in turn decompose PC into propylene Gas. The organic propylene gas is likely to cause explosion under some abuse conditions, which could be a potential hazard for battery users. On the other hand, EC (ethylene carbonate)-based electrolytes are compatible with graphite anode materials and appear as strong contenders with PC based ones. Unfortunately, EC has a much higher melting point than PC (mp. EC 39 u. C; mp. PC 249 u. C), which will limit its utilization at low temperatures. 2. Natural graphite is highly anisotropic. In other words, natural graphite flakes have wider dimensions in the parallel directions but thinner dimensions in the perpendicular direction to the basal planes. This kind of particle morphology has at least two shortcomings. Firstly, the natural graphite flakes are difficult to spread thinly and uniformly on the current collector substrate (copper foil). Secondly, natural graphite flakes coated on the copper foil generally demonstrate high orientation with the basal-plane surface exposed towards the current flow direction with edge-plane surface vertical to current flow. This type of alignment of graphite particles is not good for the rate capacity since Li + intercalates into graphene layers via edge-plane surfaces. 3. To solve the first problem, we have applied a thermal vapor decomposition (TVD) technique to coat carbon onto natural graphite surfaces and to protect the natural graphite ‘‘core’’ from direct contact with the electrolytes. The electrochemical performance of natural graphite was greatly improved in both the EC and PC-based electrolytes after TVD carbon coating. As for the second problem, we have tried to change the particle shape of the natural graphite ‘‘core’’. The shuttleshaped graphite particles demonstrate randomly stacked patterns when being spread with binder onto the copper foil to fabricate the electrode. However, Li+ intercalation will get sluggish at high current densities. This disadvantage mostly originates from the high orientation of graphene layers within each graphite ‘‘core’’ particle. If the natural graphite ‘‘core’’ could be rolled into a sphere, the problem of low rate capacity coming from high orientation might be solved.

Comparison of the initial charge-discharge curves for the spherical natural graphite coated with different amounts carbon. All these curves demonstrate the typical plateau characteristic of the stage transformations between Ligraphite intercalation compounds. The irreversible capacity means the capacity difference between the charge and discharge curves. It can be obviously seen that the irreversible capacity corresponding to the ‘‘bare’’ natural graphite sample is bigger than the irreversible capacities of other carbon-coated graphite samples. All the chargedischarge curves corresponding to carbon coated samples almost overlap and there is little difference in the irreversible capacity values. Although 3 wt% is a very tiny amount, its influence on covering the surface of the spherical natural graphite ‘‘core’’ and preventing PC decomposition is comparable to the carbon-coating amount of 10 and 13 wt%.

The superiority of spherical graphite coated with 3 wt% carbon over the highly-graphitized MCMB could be observed in the following respects. Firstly, the reversible capacity of the spherical graphite coated with 3 wt% carbon is higher than that of MCMB. Secondly, the irreversible capacity of the spherical graphite coated with 3 wt% carbon is smaller than that of MCMB, so the coulombic efficiency of the former sample is higher than that of the latter sample. Thirdly, the polarization between the charge and curves for the spherical graphite coated with 3 wt% carbon is lower than that corresponding to MCMB, Comparison of the initial charge-discharge curves of MCMB and spherical natural graphite coated with 3 which means that lithium-ion batteries using the former sample wt% have a higher working voltage than the latter sample under the same conditions in the lithium-ion batteries. Comparison of the rate capacities of MCMB and spherical natural graphite coated with 3 wt. % carbon (SNG). The discharge capacity decrease with the increase of thickness of the electrode at a certain rate. The slope of each curve correlating discharge capacity with electrode thickness becomes more tilted as the thickness increases. Moreover, the curves of discharge capacity vs. electrode thickness shift downside as the rate becomes higher (the current density increases) for each sample. The curves corresponding to the spherical natural graphite coated with 3 wt% carbon lie over those for MCMB given the same rate. This fact implies that the spherical natural graphite coated with 3 wt% carbon could deliver more capacities than MCMB under the same conditions like current densities and electrode thickness.

SEI (Solid Electrolyte interface) film It is well known that the physicochemical nature of the cathode and anode materials determines the current and voltage outputs of the battery. The separator prevents the direct contact of the cathode and anode, and thus deters the short circuit of the battery. The electrolyte serves as the medium for the transfer of lithium ions and separates the transport of electrons from that of the lithium ions. To ensure the long cycling life of the battery, the electrolyte must be inert toward both cathode and anode materials during the operation of the battery. However, thermodynamically, such an electrolyte should be impossible considering the strongly oxidizing and reducing potencies of the cathode and anode materials employed in the high energy density LIBs. However, practical LIB systems have demonstrated that some nonaqueous electrolytes are apparently stable, enduring hundreds of charge– discharge cycles. To explain this surprising stability, it was suggested that in practical LIB systems, the electrode, which is in contact with the electrolyte solution, might be covered by a passivation layer. This layer consists of some insoluble products from the reaction of the electrode with the electrolyte and can kinetically prevent any sustained consumption of the electrolyte [3– 5]. Because this passivation layer lies between the electrode and the electrolyte, and is conductive to ions but is nonconductive to electrons. It has generally become accepted that the SEI determines the battery’s electrochemical performance to a large extent.

First voltammetric cycle of artificial at low sweep rate 0. 01 m. V/s. Schematic illustration of the film forming mechanism via decomposition of Li(solv)y. C.

Series of consecutive voltammograms, each series taken with only one graphite electrode in EC-DME(50: 50)/I MLi. CIO 4 with scanning rate 0. 1 m. V/s. There is a strong irreversible reduction ('filming') in sweep no. 4, the onset of this reduction is indicated in sweep no. 3, it is almost finished in sweep no. 5. Due to film forming a peak at potentials around 0. 8 V versus Li/Li+ was observed during the first reduction. The reversibility of this peak was examined by cyclic voltammetry; in addition, the crystal expansion/contraction was checked by means of dilatometry. The results indicate that ternary solvated graphite-intercalation compounds (GICs) were formed at those potentials leading to drastic expansion of the graphite matrix (> 150%). These Li(EC)y 1(DME)y 2 C, -GICs decompose and build up a protective layer on the graphite that prevents further solvent co-intercalation. The beneficial effect of EC-containing electrolytes on the stability of lithium—carbon anodes seems to be related to inorganic films formed via secondary chemical decomposition of electrochemically formed EC-GICs. The key-role of inorganic films is also demonstrated by the fact that inorganic additives, such as carbon dioxide, suppress the formation of solvated GICs. Furthermore, it can be seen that lithium-carbon negatives can even be operated in inorganic electrolytes such as SO 2 and SOCl 2.

Reduction mechanism of EC on graphite proposed by Aurbach et. al.

Electrochemical impedance of Electrolyte/electrode interfaces of lithium-ion rechargeable batteries

(a) Scheme of three-dimensional complex plot of the impedance, (b) the three-dimensional impedance shell and the cross section perpendicular to the time axis, (c) the instantaneous impedance obtained from the cross section.

The real and imaginary parts of impedance in figure take the plus and minus values, respectively, indicating the capacitive behavior. The diameter of capacitive loop takes a large value at the early period of the first cycle charge and decreases abruptly with the charge time. The impedance after approximately 10000 s in (a) shows two capacitive loops, and does not show apparent time variation. The impedance spectrum at the initial period of the first cycle discharge in (b) shows the capacitive loops, and the diameters of loops decrease with the discharge time.

Potential–capacity curves of the graphite electrode in EC/EMC (3: 7 by volume) containing 1 M Li. PF 6 and 1 wt. % ethylene sulfite in the first cycle charge and the complex plane plots of the instantaneous impedance. The dc current density is 0. 2 m. Acm− 2.

Rsei: SEI film resistance Rct: charge transfer resistance From two resistances Rsei and Rct for graphite electrode, the change of negative electrode/electrolyte interface and the formation mechanism of SEI film were analyzed. The effect of the VC addition into the electrolyte solution was investigated, and it has been clarified that the VC helps to form the high quality SEI film at the early period of first cycle charge. On the other hand, the Rsei took a large value by the addition of ES, suggesting the formation of thick SEI film on the graphite electrode. And the irreversible capacity was 35% at the first cycle charge in EC/EMC+ 1 wt. % ES, which was larger value than that in the presence of VC.

Low voltage lithium-ion cells The comparison of the potential ranges of lithium intercalation electrodes.