Lithium metal deposition

The Li-Ion system was developed to eliminate problems of lithium metal deposition. On charge, lithium metal electrodes deposit moss-like or dendrite-like metallic lithium on the surface of the metal anode. Once such metallic lithium is deposited, the battery is vulnerable to internal shorting, which may cause dangerous thermal run away. The use of carbonaceous material as the anode active material can completely prevent such dangerous phenomenon. Carbon materials can intercalate lithium into their structure (up to LiCe). The intercalation reaction is very reversible and the intercalated carbons have a potential about 50mV from the lithium metal potential. As a result, no lithium metal is found in the Li-Ion cell. The electrochemical reactions at the surface insert the lithium atoms formed at the electrode surface directly into the carbon anode matrix (Li insertion). There is no lithium metal, only lithium ions in the cell (this is the reason why Li-Ion batteries are named). Therefore, carbonaceous material is the key material for Li-Ion batteries. Carbonaceous anode materials are the key to their ever-increasing capacity. No other proposed anode material has proven to perform as well. The carbon materials have demonstrated lower initial irreversible capacities, higher cycle-ability and faster mobility of Li in the solid phase. 

Irreversible Capacity. Because an SEI and surface film form on both the anode and cathode, a certain amount of electrolyte is permanently consumed. As has been shown in section 6, this irreversible process of SEI or surface layer formation is accompanied by the quantitative loss of lithium ions, which are immobilized in the form of insoluble salts such as Li20 or lithium alkyl carbonate. Since most lithium ion cells are built as cathode-limited in order to avoid the occurrence of lithium metal deposition on a carbonaceous anode at the end of charging, this consumption of the limited lithium ion source during the initial cycles results in permanent capacity loss of the cell. Eventually the cell energy density as well as the corresponding cost is compromised because of the irreversible capacities during the initial cycles. 

Sony dubbed the new cell, lithium-ion, as only lithium-ions and not lithium metal are involved in the electrode reactions. The lithiated carbon had a voltage of about 0.05 V vs. lithium metal and avoided the safety issues of mossy and dendritic lithium metal deposits. The lithium-ion rechargeable battery system has replaced the heavier, bulkier, Ni-Cd and Ni-MH cells in most applications,... 

This section deals only with solvents whose reduction products are insoluble in the presence of lithium ions. The list includes open chain ethers such as diethyl ether, dimethoxy ethane, and other polyethers of the glyme family cyclic ethers such as THF, 2Me-THF, and 1,4-dioxane cyclic ketals such as 1,3-dioxolane and 1,3-dioxane, esters such as y-butyrolactone and methyl formate and alkyl carbonates such as PC, EC, DMC, and ethylmethyl carbonate. This list excludes the esters, ethyl and methyl acetates, and diethyl carbonate, whose reduction products are soluble in them (in spite of the presence of Li ions). Solutions of solvents such as acetonitrile and dimethyl formamide are also not included in this section for the same reasons. Figure 6 presents typical steady state voltammo-grams obtained with gold, platinum, and silver electrodes in Li salt solutions in which solvent reduction products are formed and precipitate at potentials above that of lithium metal deposition. These voltammograms are typical of the above-mentioned solvent groups and are characterized by the following features ... 

Fig. 13. XPS spectra for lithium metal deposited on Ni metal in propylene carbonate containing 1.0 mol dm-3 LiPF6 (reproduced with permission from J. Electroanal. Chem., 394 (1995) 49 [24]).

Below 0. V (Li/Li+), pronounced bulk lithium metal deposition occurs. On the anodic side, when the metals are gold or platinum, solvent oxidation limits the electrochemical window. In general, the ethers are... 

The name lithium-ion now is accepted by the battery community worldwide, although there is no lithium metal in the cell. However, very often lithium-metal deposition occurs during charging with the graphite anode and it may cause the many troubles on the LIB. Both electrodes operate by intercalation of lithium ions into the structure of the active materials. AT Battery Co., a joint venture of Toshiba Battery Co. and Asahi Chemical Co., was the second to commercialize the technology using Asahi patent portfolio. Table 2 shows the prominent patents in the lithium-ion battery field. 

Figure 4 would represent a typical example of the LIB graphite anode in several tens of cycles. Some graphite would be damaged or exfoliated and would not accept Li intercalation, but it would facilitate lithium-metal deposition instead. Conditioning process aims to establish a stable and robust SEI film in order to avoid this scenario. 

As described in the relevant report, the tert-aUcylbenzene compound decomposes by oxidation at a potential of +4.6 to +5.0 V (relative value to that of lithium), and cobalt or nickel in the positive electrode rapidly dissolves and deposits on the negative electrode to inhibit a reaction of a carbonate in the non-aqueous electrolytic solution with a lithium metal deposited on the negative electrode. Further, in the invention, the internal short circuit may be formed in the battery by the deposition of cobalt and nickel, whereby the overcharge inhibitive effect can be attained and the safety of battery can be assured [133]. 

Arora et al. [71] use the equations presented above to simulate lithium metal deposition on carbon negative electrodes during overcharge. Lithium metal deposition will occur wherever the potential of the electrode is driven more negative than the potential of lithium metal, i.e., where < 0. 

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