Lithium deintercalation

More recently, lithium vanadium phosphates (LisV2-(P04)s and Li3FeV(P04)3, with open NASICON framework structures, have also been studied. Reversible electrochemical lithium deintercalation/re-intercalation at a higher potential (in comparison to the couples seen for the oxides) of between 3... 

Delmas C, Maccario M, Croguennec L, Le Cras F, Weill F. Lithium deintercalation in LiFePC>4 nanoparticles via a domino-cascade model. Nature Mater. 2008 7 665-71. 

Reversible electrochemical lithium deintercalation from 2D and 3D materials is important for applications in lithium-ion batteries. New developments have been realized in two classes of materials that show exceptionally promising properties as cathode materials. The first includes mixed layered oxides exemplified by LijMn Nij, Co ]02, where the Mn remains inert to oxidation/reduction and acts as a framework stabilizer while the other elements carry the redox load. Another class that shows much potential is metal phosphates, which includes olivine-type LiFeP04, and the NASICON-related frameworks Li3M2(P04)3. 

Figure 5.15 (a) Logarithmic anodic current transients of the graphite electrode, theoretically determined by means of numerical analysis based upon the cell-impedance-controlled lithium deintercalation (b) /(t) versus In t plots reproduced from panel (a). (Reproduced with permission from (a) Ref. [18] (b) Ref. [96].)... 

Pyun etal. [18,82-84] have suggested that this abnormal behavior in CTs involving the inflexion point could be reasonably explained in terms of the difference in the kinetics of lithium deintercalation from two different lithium deintercalation sites having different activation energies for lithium deintercalation. The McNabb-Foster equation [101, 102] was modified to satisfy spherical symmetry and to represent the coexistence of two different types of trap site, and was also used as a governing... 

Figure S.17 The galvanostatic intermittent discharge (electrode potential) curve measured on the PVDF-bonded MCMB800 (0), MCMBIOOO ( ) and MCMB1200 (A) composite electrodes in 1 M LiPFfi-EC/DEC solution. Regions I, II, lll-l, and II1-2 represent the potential ranges necessary for lithium deintercalation from the sites for Type I, II, lll-l, and III-2, respectively. (Reproduced with permission from Ref. [82].)...

From the numerical solution to the modified McNabb-Foster equation, the anodic CTs determined at the potential jumps of 0.3, 0.2, and 0.05 V (versus Li/Li+) to various lithium extraction potentials Fext are illustrated in Figure 5.19a-c. The anodic CTs theoretically calculated based upon the modified McNabb-Foster equation, along with the cell-impedance-controlled constraint in Figure 5.19a-c, almost coincide with experimental CTs (see Figure 5.18a-c). This strongly indicates that the appearance of an inflexion point in the CT is due to the lithium deintercalation from two different kinds of sites with clearly distinguishable activation energies. 

The contribution of electric field to lithium transport has been considered by a few authors. Pyun et argued on the basis of the Armand s model for the intercalation electrode that lithium deintercalation from the LiCo02 composite electrode was retarded by the electric field due to the formation of an electron-depleted space charge layer beneath the electrode/electrolyte interface. Nichina et al. estimated the chemical diffusivity of lithium in the LiCo02 film electrode from the current-time relation derived from the Nernst-Planck equation for combined lithium migration and diffusion within the electrode. 

All the anodic CTs hold the non-Cottrell character during the entire lithium deintercalation. Moreover, it should be pointed out that, in spite of the linear increase in the magnitude of the potential jump, the initial current level increases very slowly and eventually decreases at the large potential jump (> 0.25 V). In other words, the relationship between initial current level and potential jump takes the form of a parabola (Figure 8b), rather than a monotonically increasing curve. 

Considering that the larger potential jump means the lower initial electrode potential, the parabolic relation in Figure 8(b) indicates that the deintercalation of lithium from the Li Ni02 is seriously retarded as the initial electrode potential is lowered below ca. 3.75 V v. Li/Li. This implies that some other factor along with the potential step considerably influences lithium deintercalation below 3.75 V vs. Li/Li. ... 

The new equilibrium is so strongly disturbed tliat the final electrode potentials are never really attained in the ranges below 3.65 V vs. LULi even if one holds the final electrode potentials throughout for 2 X 10 s, prior to lithium deintercalation. For the theoretical calculation of the anodic CTs, we actually inserted in the numerical value a nominal potential jump ( - ) sUghtly higher than what the real value was and at the same time a nominal internal cell resistance R tn much higher than what the real value was. Since such a rise in Rc outweighs the rise in ( app- )> the instantaneous currents are practically calculated to be lower than those currents determined experimentally. 

Moreover, the calculated current increases rather than deaeases with time to ca. 200, 600, and 800 s at the potential jumps of 3.65 to 4.00, 3.60 to 4.00, and 3.55 to 4.00 V vs. Li/Lr, respectively. This current increase in the cell-impedance controlled anodic CTs of Lii. gNi02 is due to the fact that the reduction in the potential difference (Eapp-E) is much exceeded by the fall in internal cell resistance Rcdt during lithium deintercalation, to enhance the driving force for lithium transport. This is readily predieted in the Rcdi vs. E plot of Figure 12. 

Figure 21(b) presents the theoretical anodic CTs of LiusNiOj at the potential jump from 3.55 to 4.00 V v. Li/Li, assmning that the internal cell resistance / remains constant (solid line) at the valne at 3.55 V vs. Li/Li over the lithium deintercalation time and that is varied with E (dotted line). The anodic CT nnder constant Rcen valne deviates strongly from the CT under the condition of Real - withont any increase in current with time in the short time range. 

Fig. 10.8 Typical charge/discharge characteristics of lithium cobalt oxide (LiCo02> positive electrode material. Charging corresponds to lithium deintercalation, and discharging refers to lithium intercalation...

DBMS) [ARM 06] nevertheless, the quantity of gas detected was not sufficient to compensate for the total quantity of lithium deintercalated on the plateau . It has been shown that this unusual mechanism arose due to the reversible participation of the oxygen anion in the redox processes. This original mechanism, demonstrated for the first time for layered oxides, is possible due to the particular composition of these Li- and Mn-rich materials the hybridization of transition metals nd levels and anions 2p levels leads to a mixed redox process involving both the cations and the anions [KOG 13a, SAT 13a, SAT 13b]. This mechanism, responsible for the exceptional reversible capacity these materials deliver, is enhanced for transition metals that are highly oxidized and electronegative (Figure 2.13). 

Panel (a) in Figure 8 shows a cyclic voltammogram at a slow scan rate of 0.5 mV s of HOPG basal plane in 1 M LiClO/EC + DEC." In the first cycle, three major cathodic peaks appeared at about 1.0, 0.8 and 0.5 V. These cathodic peaks disappeared in the second cycle, and hence are attributed to irreversible decomposition reactions of the electrolyte solution that are closely related to SEI formation as mentioned in the previous section. A large cathodic current rise observed at potentials close to 0.0 V could be assigned to lithium intercalation because of the presence of an anodic lithium deintercalation peak at about 1.0 V. However, the charge consumed for the current rise at around 0 V was much greater than that for the anodic peak, and hence a substantial fraction of the cathodic current at around 0 V was consumed by irreversible processes such as solvent decomposition. 

Menetrier M, Saadoune I, Levasseur S, Delmas C (1999) The insulator-metal transition upon lithium deintercalation from LiCo02 electronic properties and 7Li NMR study. J Mater Chem 9 1135-1140... 

Boesenberg U, Meirer F, Liu Y et al (2013) Mesoscale phase distribution in single particles of LiFeP04 following lithium deintercalation. Chem Mater 25 1664—1672. doi 10.1021/ cm400106k... 

After doping with Fe +, the potential for lithium deintercalation increases, resulting in more difficult oxidation of NP+. In addition, numerous Ni + or... 

From the above discussion, it is clear that the spinel structure is kept when lithium deintercalates from cubic sites in Li[Mn2]04, with a voltage in the 4 V region. In organic solvents, it is difficult for lithium to deintercalate completely without decomposition of the highly delithiated Li4.[Mn2]04 electrode. During the deintercalation process of lithium, several types of... 

---