Li-Si system

To understand the interest to move toward o, nanoparticles and nanostructure of silicon, it is important to look at the Li-Si system. 

From the phase diagram established in 1976 by Sharma and actualized by Okamoto and coulometric titration of stability areas of potential for each intermetallic crystalline Li-Si compound at 415°C established in 1981 by Huggins et it 

At 415°C, the electrochemical formation of each intermetallic crystalline silicon compound results on galvanostatic curves with a plateau. At room temperature, onty one plateau is observed in the insertion of Li, as shown in Fig. 11.13. The compound is metastable, Lii5Si4, observed by X-ray diffraction (XRD) , Raman spectroscopy, and electron microscopy at high-resolution (HREM) i at the end of discharge. At a temperature of 25°C, the 

Discharge/charge curve at the first cycle for a silicon-based electrode at 25°C and C/10 rate. 

The most electro chemically lithiated phase at room temperature is therefore not Li2iSi5 but 1145814. The maximum capacity reachable is not 4008 mAh g but 3579 mAh-g . 45814 formation is accompanied by a volume expansion of 281%. 

---

Figure 14. Charge-discharge curves for the upper plateau in the Li Si system iaside a matrix of the Lio jjSn phase at 415 °C. The upper panel shows the effect of current density, whereas the lower panel shows that the potential overshoot related to the nucleation of the second phase is mostly eliminated if the electrode is not cycled to the ends of the plateau 144].

The large irreversible capacity observed on the initial cycle may be attributed to a partial reduction of the native surface oxide and the formation of an SEI layer, as previously discussed for the silicon system. The peaks in the differential capacity [350 mV (insertion) and 500 mV (extraction)] in the first cycle disappear after the first few cycles and are indicative of the solid-electrol5de reaction to form the SEI layer. The first cycle capacity loss is approximately 70% of what was observed in the Li-Si system. The lower irreversible capacity on the first cycle is attributed to a reduced native oxide layer, which is only a few monolayers thick. 

Estimated data on a number of ternary lithium systems theoretically investigated as extensions of the Li-Si binary system are included in Table 2. Also included are comparable data for the binary Li-Si alloy... 

The lithium-silicon system has also been of interest for use in the negative electrodes of elevated-temperature molten salt electrolyte lithium batteries. A composition containing 44 wt.% Li, where Li/Si=3.18, has been used in commercial... 

The fibrous crystals of C take up lithium preferably. Pure samples of C can be obtained readily in good yield from Li,Na gels. E, an important phase in the Li,Na system, appears as needle-like crystals or aggregates with a constant Si/Al ratio of 1. The potassium-exchanged form is identical with K-F, which was thought to be a typical product in the potassium field (5). Unexchanged crystals of E contain appreciable amounts of both Li and Na. 

The major differences in the choice of a detection system for this application between Si(Li) and Silicon drift detector is the Peak-to-Background (PfS) ratio, wMch typically is better using a Si (Li) detection system. Future developments in the SDD technology show that P/B ratios are improving. 

C.R. 6dal, CoUisional depolarization and rotational energy tiansfer of the Li2(B /7 )-Li( Si/2) system from laser-induced fluorescence. Chem. Phys. 35, 215 (1978)... 

Li] Li, H., Morris, A., Evaluation of Unified Interaction Parameter Model Parameters for Calculating Activities of Ferromanganese Alloys Mn-Fe-C, Mn-Fe-Si, and Mn-Fe-C-Si Systems , Metall. Mater. Trans. B, 28, 553-562 (1997) (Thermodyn., Calculation, 41) [1998Jun] Jun, J.-H., Baik, S.-H., Lee, Y.-K., Choi, C.-S., The Influence of Aging on Damping Capacity of Fe-17%Mn-X%C Alloys , Scr. Mater, 39, 39-44 (1998) (Experimental, Phase Relations, Meehan. Prop.)... 

Commercial systems consist of an optical microscope for observation of the sample area and an ED-based XRF systan with a low-power, microfocused X-ray source using Kumakhov optics, a filter wheel, and a detector (Si[Li], Si-PIN, SDD). The X-ray source is generally air-cooled, and... 

The base unit for length in the SI system is the meter. The exact definition of meter has changed over the years, but it s now defined as the distance that li t travels in a vacuum in J499.792.4s8 of a second. Here are some SI units of lei th ... 

---