Li alloy electrodes

The good cycling stability of the tin in TCO is quite unusual, because the electrochemical cycling of Li ASn and also of other Li alloy electrodes is commonly associated with large volume changes in the... 

The subject of surface films on electrodes in non-aqueous solutions is mostly important for the field of batteries. The performance of both Li and Li-ion batteries depends strongly on passivation phenomena that relate to surface film formation on both the anodes and the cathodes. Lithium and lithiated carbon anodes reduce all the solvents and salt anions in electrolyte solutions relevant to Li batteries. The products of these surface reactions always contain insoluble Li salts that precipitate on the electrodes as surface films. All charge transfer processes of Li, Li-C, and Li alloy anodes in Li batteries involve the critical step of Li-ion migration through the surface films. Thereby, the composition, structure, morphology, and electrical properties of surface films on Li, Li-C, and Li alloy electrodes were smdied very intensively over the years. In contrast, reversible magnesium electrodes can function only in surface film-free conditions. ... 

In addition to carbon, the attention has been focused on alloys and lithiated metal oxides as new materials for anodes in Li-ion cells. The reversible insertion of Li in metal/alloys has been studied for maity years because of their application in high-temperature molten salts Li cells. The electrochemical reactions that occur during discharge of a Li alloy electrode is ... 

The good cyding stabihty of the tin in TCO is quite unusual, because the electrochemical cyding of li Sn and also of other Li alloy electrodes is commonly assodated with large volume changes in the order of 100-300% (Figure 15.19) [2, 7, 22, 24, 26, 349-351). Moreover, hthium alloys Li M have a highly ionic character ( Zintl-Phases, ). For this reason they are usually fairly brittle. Mechanical... 

Observations on metal hydride materials that undergo similar large volume changes have shown that the pulverization process does not continue indefinitely. Instead, there is a characteristic terminal particle size for each particular material, and particles below this size do not fracture further. Experiments on Li alloy electrodes have shown that electrochemical cycling is significantly improved if the initial particle size is very small, consistent with the terminal particle size phenomenon. With all of these problems in mind, a Si nanowire (SiNW)-based electrode was envisioned. While NW and nanorod materials have been used in Li-battery applications, the... 

An Li-Al Alloy was investigated for use as a negative electrode material for lithium secondary batteries. Figure 41 shows the cycle performance of a Li-Al electrode at 6% depth of discharge (DOD). The Li-Al alloy was prepared by an electrochemical method. The life of this electrode was only 250 cycles, and the Li-Al alloy was not adequate as a negative material for a practical lithium battery. 

Figure 41. Cycling performance of several Li-Al alloy electrodes (discharge end 6% of total Li in Li-Al alloy current density 1.1 mA cm 2 ).

Several metal additives were investigated to improve this nonuniform reaction. Figure 41 shows the cycle performance of several Li-Al alloy electrodes. It was found that Li-Al-Mn and Li-Al-Cr alloys had better rechargeability than Li-Al alloy in the Li-Al-Mn alloy, particularly no de-... 

From a thermodynamic point of view, apart from charge density and specific charge, the redox potential of lithium insertion into/removal from the electrode materials has to be considered also. For instance, the redox potential of many Li alloys is between -0.3 and -1.0 V vs. Li/Li+, whereas it is only -0.1 V vs. 

This is the first experimental demonstration of changes in the strength of CO adsorption at Pt-based alloy electrodes. Nprskov and co-workers theoretically predicted a similar linear relation between changes in ads(CO) and shifts in the (i-band center [Hammer et al., 1996 Hammer and Nprskov, 2000 Ruban et al., 1997]. Because the Pt4/7/2 CL shift due to alloying can be more easily measured by XPS than the li-band center can, this should be one of the most important parameters to aid in discovering CO-tolerant anode catalysts among Pt-based alloys or composites. 

Among diverse alloys, amorphous Sn composite oxide (ATCO) reported by Fuji photo film has caused a great deal of renewed interests in Li alloys as an alternative for use in the negative electrode of Li-ion batteries [176,177]. The ATCO provides a gravimetric capacity of >600mAh/g for reversible Li adsorption and release, which corresponds to more than 2200mAh/cm3 in terms of reversible capacity per unit volume, that is, about twice that of the carbon materials. 

A major part of the work with nonaqueous electrolyte solutions in modern electrochemistry relates to the field of batteries. Many important kinds of novel, high energy density batteries are based on highly reactive anodes, especially lithium, Li alloys, and lithiated carbons, in polar aprotic electrolyte systems. In fact, a great part of the literature related to nonaqueous electrolyte solutions which has appeared during the past two decades is connected to lithium batteries. These facts justify the dedication of a separate chapter in this book to the electrochemical behavior of active metal electrodes. 

Li alloys may form a rigid host matrix to which Li is inserted upon charging. Hence, the surface area of the anode remains stable upon cycling, as do the surface films that cover the electrode, so exposure of fresh, reactive Li to the solution is avoided. 

There are reports that the surface chemistry of Li alloys is indeed largely modified, compared with Li metal electrodes [303], It appears that they are less reactive with solution species, as is expected. The morphology of Li deposition on Li alloys may also be largely modified and smooth, compared with Li deposition on Li substrates [302,304], A critical point in the use of Li alloys as battery anodes is the lithium diffusion rates into the alloys. Typical values of Li diffusion coefficient into alloys are 3-LiAl —> 7 16 9 cm2/s [305], Li44Sn —> 2 10 9 cm2/s [306], LiCd and LiZn —> 1010 cm2/s [307], It should be emphasized that it is very difficult to obtain reliable values of Li diffusion coefficient into Li alloys, and thus the above values provide only a rough approximation for diffusion rates of Li into alloys. However, it is clear that Li diffusion into Li alloys is a slow process, and thus is the rate-limiting process of these electrodes. Li deposition of rates above that of Li diffusion leads to the formation of a bulk metallic lithium layer on the alloy s surface which may be accompanied by mas-... 

Historically, a Ca metal negative electrode was used with a fusible salt electrolyte (LiCl/KCl eutectic) and a metal oxide cathode, e.g., K2Cr207 (2.8— 3.3 V). Since the 1980s, Li alloy negatives have gained popularity and supplanted... 

Lithium insertion negative electrodes — (i) Some transition-metal oxides or chalcogenides insert Li ion reversibly at low redox potentials, for example, TiC>2, LL I iOy, M0S2, M0O2. (ii) Lithium alloys - in this case lithium ions, react with other elements polarized to low potentials to reversibly form Li alloys. The reaction usually proceeds reversibly according to the... 

Polyaniline is frequently used in r.b.s with lithium negative electrodes. However, in the course of the development of a commercialized system (Seiko/Bridgestone), there have only been a few examples with true lithium-metal negative electrodes, but many for the more practical LiAl alloy electrodes. The redox processes of RANI are basically the same in aqueous electrolytes and in Li -containing organic solutions. 

During charging and discharging, the overall composition of the Li-Al alloy electrode changes into a two-phase region limited on one side by a saturated solid solution of Li in A1 (a phase) and on the other side by the p phase of Li-Al alloy. These processes are accompanied by a first order phase transition, clearly indicated by the discontinuity of the AE relation (Fig. 3.56) and typical 3D nucleation and... 

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