Graphite cycling behavior

The material was developed by the Research Institute of Electrocarbon Products (RIECP, Russian Federation) on the basis of natural graphite specially for application in Lithium-Ion cells. The samples were given with symbolic numbers, without certificates. The anodes, made of RIECP powder, had the capacity about 300 mA-h/g. The typical dicharge characteristic is submitted on Fig. 6. Irreversible capacity is about 16%. Concerning the cycle behavior, this material is not as stable as other ones tested (Fig. 10). 

Figure 1 presents results on the beneficial effect of a new electrolyte solvent on the cycling behavior of the lithium storage alloy Sn2Co. The influence of the adapted electrolyte may become even more clearly by taking a look at the cumulated charge losses (Fig. 22). It should be noted that this new electrolyte component is not able to suppress solvent co-intercalation into graphite [37], emphasizing the above-mentioned different requirements on the electrolyte.

As explained above, alloy-based active materials offer greater capacity than graphite, but their volumetric expansion is prohibitive for their cycling behavior in the long term (or forces us to considerably restrict the DODs by oversizing the electrode in relation to the positive counterpart material). 

It is well known that graphite is unstable in some aprotic electrolytes. For instance, when propylene carbonate (PC) is used as a solvent, the cointercalation of solvent molecules and the Li ions will lead to the exfoliation of graphite layers Only in some selected electrolyte systems such as LiPF in EC/DEC (EC for ethylene carbonate and DEC for diethyl carbonate), can graphite show better cycling behavior. Solvent decomposition on the surface of conductive carbon or lithium electrodes will lead to the formation of a passivating layer. Peled named this layer as solid electrolyte interphase (SEI). ° It is an ionic conductor but electron insulator, mainly composed of LijCOj and various lithium alkylcarbonates (ROCO Li) as well as small amounts of LiE, LijO, and nonconductive polymers. These compounds have been detected on carbon and Li electrodes in various electrolyte systems. Therefore, it would be an interesting question whether semiconductive nano-SnO anode is also sensitive to electrolyte and electrolyte decomposition takes place on it. This section will characterize the structures and compositions of the... 

Shu Z. X., McMillan R. S. and Murray J. J., Electrochemical intercalation of lithium into graphite. J. Electrochem. Soc. 140 (1993), 922-927. Besenhard J. O., Wagner M. W., Winter M., Jannakoudakis A. D., Jannakoudakis P. D. and Theodoridou E., Inorganic film-forming electrolyte additives improving the cycling behavior of metallic lithium electrodes and the self-discharge of carbon-lithium electrodes. /. Power Sources 44 (1993), 413-20. 

In less highly graphitized natural graphite, there are some impurities and defects, and as a result, the electrochemical performance is poorer. The reversible capacity drops below 300 mAh/g, the initial coulombic efficiency is less than 80%, and cycling behavior needs improvement. 

When a layer of C -N is coated on the surface of graphite, the capacity and cycling behavior of the composite improve, which also shows the favorable effects of the doped nitrogen. 

Cycling behavior of natural graphite (A) before and after mild oxidation by different oxidant solutions at 60°C. (Adapted from Wu, Y.P. et al., J. Power Sources 111 329-334, 2002.)... 

To summarize, coating polymers on graphite surfaces can effectively improve electrochemical performance of the composites in terms of the coulombic efficiency in the first cycle, the reversible capacity, the cycling behavior, and the rate capability. It is worthwhile to point out that some of the above favorable effects are slight only in some cases, and other kinds of polymers can also be used to coat graphite surfaces if they present the same or other favorable actions. 

Discharge and charge performance of lithium-ion batteries based on graphite and LiCo02 electrodes discharge curves at (a) different rates, (b) and (c) different temperatures, and (d) cycling behavior. (Permission from Ningbo Veken Battery Co. Ltd.)... 

Cycling behavior of 30650-type lithium-ion batteries with nominal capacities of 3 Ah and 10 Wh based on a LiNio7Coo.302 positive electrode material and a mixture of graphite and coke (weight ratio, 4 1) as the negative electrode material The charge and discharge current is 1190 mA. (Adapted from Kida, Y. et al., Electmchim. Acta, 47,2002.)... 

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