Process for preparation of a lithiated or overlithiated...

Details Process for preparation of a lithiated or overlithiated... Process for preparation of a lithiated or overlithiated...

1999-12-07

2003-11-25

Kalafut, Stephen (Department: 1745)

Metal working

Method of mechanical manufacture

Electrical device making

C429S231100, C429S224000, C429S231950, C423S592100, C423S599000

Reexamination Certificate

active

06652605

ABSTRACT:

This invention relates to a process for preparation of a lithiated or overlithiated transition metal oxide, this lithiated or overlithiated oxide beneficially being usable as an active electrode material and more particularly for a positive electrode.
The invention also relates to the electrode, and particularly the positive electrode containing this material.
Finally, the invention relates to lithium batteries with a metallic or composite negative electrode using the said positive electrode.
The technical domain of the invention may generally be considered as being rechargeable Secondary Lithium Cells or Secondary Lithium Batteries.
A historical overview of the development of rechargeable secondary lithium batteries is given in the document by K. BRANDT “Historical Development of Secondary Lithium Batteries”, Solid State Ionics 69 (1994), 173-183.
The operating principle of all lithium battery systems is the same: each time that the battery is charged or discharged, lithium in ionic form (Li
+
) is exchanged between the positive and negative electrodes. The quantity of energy exchanged during each charge or discharge (supplied by the battery during discharge or supplied to the battery during charge) is exactly proportional to the quantity of lithium that can be exchanged during the electrochemical reaction.
This “exchangeable” lithium must be supplied by a lithium “source”. This source is the negative electrode in the case of systems using a lithium metal negative electrode. For systems using a carbon based negative electrode which in principle does not contain any lithium by construction, the lithium source must be contained in the positive electrode. In this case, the active material in the positive electrode acts as the lithium source. Therefore, it can be seen that it becomes necessary to include the largest possible quantity of lithium in the active material of the positive electrode during its synthesis, in order to provide a sufficient reserve of lithium to obtain interesting electrochemical performances.
A cell is characterized by its operating voltage, which is determined by the potential difference between the negative electrode and the positive electrode. The absolute potential (non-measurable) of the negative electrode made of lithium metal is constant, since it is a pure metal.
Therefore, the voltage of a cell with a lithium metal negative electrode depends entirely on the potential of the positive electrode, which depends on the crystallographic structure of the active material in the positive electrode, and which changes as a function of the quantity of the lithium contained in it. As the cell discharges, the lithium enters the crystalline structure of this active material in which the potential drops regularly. The cell voltage drops. This is the reverse of what occurs during charging.
Active materials all have a different variation of their potential (with respect to Li/Li+) with time depending on the quantity of lithium contained in them; thus each active material has a characteristic “electrochemical signature”. In some, lithium is inserted at between 3.5 and 4.5 Volts, for example as in the case of cobalt oxides for which the potential (with respect to Li/Li+) varies between 3.5 V (for LiCoO
2
) and 4.5 Volts (for Li
1−x
CoO
2
, where x≈0.7 after the cell has been charged).
As another example, the potential (with respect to Li/Li+) of manganese oxides with a composition similar to Li
0.3
MnO
2
used by TADIRAN Batteries Ltd. for batteries made using the technology described in patent U.S. Pat. No. 5,506,068 at which lithium is inserted is between 3.4 Volts (the composition of the active material in the positive electrode is then close to Li
0.3
MnO
2
) and 2 Volts (the composition of the active material in the positive electrode is then close to LiMnO
2
). This is the “3 Volts Lithium-metal liquid electrolyte” system.
Other materials based on manganese oxides are more versatile; thus manganese oxides with a spinel structure usually have two operating potential “plateaus”. For example for the compound with a spinel structure and formula LiMn
2
O
4
, most of the lithium is extracted from this structure at between about 3.2 Volts and 4.4 Volts (with respect to Li/Li
+
) (the composition of the active material in the positive electrode after the charge to 4.4 Volts is then close to Mn
2
O
4
), whereas lithium can be inserted between about 3.2 Volts and 1.8 Volts in the LiMn
2
O
4
structure (the composition of the active material in the positive electrode at the end of the discharge of the cell to 1.8 Volts is then close to Li
2
Mn
2
O
4
).
Therefore, it can be seen that it is possible and even necessary to choose the active compound in the positive electrode to optimize the global performances of the system.
Lithium cells may be classified in different categories or systems, the first of these systems being the “3 Volts” lithium metal liquid electrolyte system.
Chronologically, the first lithium cells developed about 20 years ago used a lithium metal negative electrode.
Although these batteries provide high energy densities due to the large reserve of lithium contained in the negative electrode, this system was abandoned by most battery manufacturers due to the poor reconstitution of the metal surface at the negative electrode/electrolyte interface during charging and discharging cycles, resulting in inadequate lives (~200 cycles). Experience showed that dendritic growth phenomena (in the form of needles) appeared gradually during reconstitution of the lithium metal, during successive charging/discharging cycles. These needles eventually filled in the space between the negative electrode and the positive electrode after about 200 cycles, which caused internal short circuits.
However, some battery manufacturers have successfully limited this phenomenon. For example, the document by E. MENGERITSKY, P. DAN, I. WEISSMAN, A. ZABAN; D. AURBACH, “Safety and Performances of TADIRAN TLR-7103 Rechargeable Batteries”, J. Electrochem, Soc, Vol. 143, No. 7, July 1996 describes a battery operating at between 2 and 3.4 volts with a lithium metal negative electrode and with a liquid electrolyte with an interesting life due to a new electrolyte formulation, but the life is nevertheless limited to about 500 charging/discharging cycles.
An additional improvement may be achieved by the use of a positive electrode material containing a larger quantity of lithium.
A different system called the 4 Volt “Lithium-ion” system was suggested at the beginning of the 1980s in order to overcome the difficulty caused by dendritic growth.
This system consists of substituting a carbon based lithium insertion compound to replace the lithium metal negative electrode.
In this case, the lithium metal negative electrode is replaced by an electrode containing a carbon based lithium insertion compound in which lithium is reversibly inserted during successive cycles, in exactly the same way as it does in the positive electrode insertion compound. This is the “4 Volt lithium-ION” system.
However, due to this choice:
the negative electrode is no longer capable of acting as a reservoir for the lithium necessary for the electrochemical reaction, which makes it essential to use a positive electrode compound containing lithium by construction.
part of the lithium originating from the positive electrode is irreversibly consumed by the carbon negative electrode the first time that the cell is charged (corresponding to the first time that lithium is inserted in the carbonated negative electrode) which results in an equivalent loss of capacity of the cell.
These limitations confirm that it would be useful to be able to synthesize a positive electrode active material containing the largest possible amount of lithium.
For example, up to now, the compounds based on manganese oxide with the best electrochemical characteristics in the “4 Volt lithium-ION” system described above, are products with a spinel structure and a composition similar to LiMn
2
O
4
. They enable electrochemic

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