Lithium ion chemistry

In retrospect, the significance of Dahn s seminal work lies in two aspects (1) the fundamental understanding of how carbonaceous materials operate in nonaqueous electrolytes and (2) the more practical side of how the above dilemma concerning energy density and reversibility can be overcome. This knowledge dictates the development of electrolytes for state-of-the-art lithium ion chemistry. 

According to Peled s model, the existence of an SEI constitutes the foundation on which lithium ion chemistry could operate reversibly. Therefore, an ideal SEI should meet the following requirements (1) electron transference number 4 = 0 (otherwise, electron tunneling would occur and enable continuous electrolyte decomposition), (2) high ion conductivity so that lithium ions can readily migrate to intercalate into or deintercalate from graphene layers, (3) uniform morphology and chemical composition for ho-... 

The anodic limit for the electrochemical stability of these carbonate mixtures has been determined to be around 5.5 V in numerous studies.Thus, new electrolyte formulations are needed for any applications requiring >5.0 V potentials. For most of the state-of-the-art cathode materials based on the oxides of Ni, Mn, and Co, however, these carbonate mixtures can provide a sufficiently wide electrochemical stability window such that the reversible lithium ion chemistry with an upper potential limit of 4.30 V is practical. 

Beyond any doubt, the electrode/electrolyte interfaces constitute the foundations for the state-of-the-art lithium ion chemistry and naturally have become the most active research topic during the past decade. However, the characterization of the key attributes of the corresponding surface chemistries proved rather difficult, and significant controversy has been generated. The elusive nature of these interfaces is believed to arise from the sensitivity of the major chemical compounds that originated from the decomposition of electrolyte components. 

The latter authors used anode and cathode symmetrical cells in EIS analysis in order to simplify the complication that often arises from asymmetrical half-cells so that the contributions from anode/ electrolyte and cathode/electrolyte interfaces could be isolated, and consequently, the temperature-dependences of these components could be established. This is an extension of their earlier work, in which the overall impedances of full lithium ion cells were studied and Ret was identified as the controlling factor. As Figure 68 shows, for each of the two interfaces, Ra dominates the overall impedance in the symmetrical cells as in a full lithium ion cell, indicating that, even at room temperature, the electrodic reaction kinetics at both the cathode and anode surfaces dictate the overall lithium ion chemistry. At lower temperature, this determining role of Ra becomes more pronounced, as Figure 69c shows, in which relative resistance , defined as the ratio of a certain resistance at a specific temperature to that at 20 °C, is used to compare the temperature-dependences of bulk resistance (i b), surface layer resistance Rsi), and i ct- For the convenience of comparison, the temperature-dependence of the ion conductivity measured for the bulk electrolyte is also included in Figure 69 as a benchmark. Apparently, both and Rsi vary with temperature at a similar pace to what ion conductivity adopts, as expected, but a significant deviation was observed in the temperature dependence of R below —10 °C. Thus, one... 

Table 3.4 Test Data for Fast Charging of Lithium-ion Chemistries ...

The overcharge-x dX A behavior of the lithium-ion chemistry is best explained starting from the overall cell equation, shown in a generalized form in Eq. 5.1. 

Other organic redox shuttles based on aromatic compoimds with heteroatom substitutions include phenothiazine [18], triphenylamine [89], diarylamines with different substitutions [38], and 2-(pentafluorophenyl)-tetrafluoro-l,3,2-benzodi-oxaborole [29, 137]. Nitroxide radicals such as (2,2,6,6-Tetramethylpiperidin-l-yl) oxy (TEMPO) have been studied as a redox shuttle as well but showed inferior rate of charge transfer compared with DDB [90]. In addition, lithium borate cluster salts (Li2Bi2Fi2) have also been reported to be suitable redox shuttle additives for 4-V lithium ion chemistry (Chen et al. [26]). 

One String of Batteries. Lithium-ion chemistry is recognized as one of the best solutions for today s and future EV s and BEV s because of high energy and power... 

Figure 27.1 Cell self-healing rate during forced thermal ramp test of Li-ion Gen 2 lithium-ion chemistry anode = MCMB electrolyte =1.2 M LiPFe In EC PC DMC I cathode = LiNio.gCoo.os AI0.05O2 I separator = Celgard 2325 trilayer (from Ref [15]).

Since then, there has been an extraordinary amount of work on aU aspects of the lithium-ion chemistry, battery design, manufacture and application. Indeed, the mention of a hthium-ion battery can imply dozens of different chemistries, both commercial and developmental as illustrated in Figure 1. 

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