Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
2002-06-07
2004-09-21
Chaney, Carol (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S231500, C429S231600
Reexamination Certificate
active
06794085
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to metal oxide compounds and to preparation methods thereof. More specifically, this invention relates to doped metal oxide insertion compounds for use in lithium and lithium-ion batteries.
BACKGROUND OF THE INVENTION
Metal oxides such as lithium metal oxides have found utility in various applications. For example, lithium metal oxides have been used as cathode materials in lithium secondary batteries. Lithium and lithium ion batteries can be used for large power applications such as for electric vehicles. In this specific application, lithium or lithium ion cells are put in series to form a module. In the event that one or more of the cells in the module fails, the rest of the cells become overcharged resulting possibly in explosion of the cells. Therefore, it is important that each cell is individually monitored and protected against overcharging.
The most attractive materials for use as cathode materials for lithium ion secondary batteries have been LiCoO
2
, LiNiO
2
, and LiMn
2
O
4
. However, although these cathode materials are attractive for use in lithium ion secondary batteries, there are definite drawbacks associated with these materials. One of the apparent benefits for using LiNiO
2
and LiCoO
2
as cathode materials is that those lithium metal oxides have a theoretical capacity of 275 mA·hr/g. Nevertheless, the full capacity of these materials cannot be achieved in practice. In fact, for pure LiNio
2
and LiCoO
2
, only about 140-150 mA·hr/g can be used. The further removal of lithium by further charging (overcharging) the LiNiO
2
and LiCoO
2
material degrades the cycleability of these materials by moving nickel or cobalt into the lithium layers. Furthermore, the further removal of lithium causes exothermic decomposition of the oxide in contact with the organic electrolyte under heated conditions which poses safety hazards. Therefore, lithium ion cells using LiCoO
2
or LiNiO
2
are typically overcharge protected.
LiCoO
2
and LiNiO
2
have additional disadvantages when used in lithium ion batteries. Specifically, LiNiO
2
raises safety concerns because it has a sharper exothermic reaction at a lower temperature than LiCoO
2
. As a result, the charged end product, NiO
2
, is unstable and can undergo an exothermic decomposition reaction releasing O
2
(Dahn et al, Solid State Ionics, Vol. 69, 265 (1994)). Accordingly, pure LiNiO
2
is generally not selected for use in commercial lithium-ion batteries. Additionally, cobalt is a relatively rare and expensive transition metal, which makes the positive electrode expensive.
Unlike LiCoO
2
and LiNiO
2
, LiMn
2
O
4
spinel is believed to be overcharge safe and is a desirable cathode material for that reason. Nevertheless, although cycling over the full capacity range for pure LiMn
2
O
4
can be done safely, the specific capacity of LiMn
2
O
4
is low. Specifically, the theoretical capacity of LiMn
2
O
4
is only 148 mA·hr/g and typically no more than about 115-120 mA·hr/g can be obtained with good cycleability. The orthorhombic LiMnO
2
and the tetragonally distorted spinel Li
2
Mn
2
O
4
have the potential for larger capacities than is obtained with the LiMn
2
O
4
spinel. However, cycling over the full capacity range for LiMnO
2
and Li
2
Mn
2
O
4
results in a rapid capacity fade.
Various attempts have been made to either improve the specific capacity or safety of the lithium metal oxides used in secondary lithium batteries. For example, in an attempt to improve the safety and/or specific capacity of these lithium metal oxides, these lithium metal oxides have been doped with other cations. For example, lithium and cobalt cations have been used in combination in lithium metal oxides. Nevertheless, although the resulting solid solution LiNi
1−X
Co
X
O
2
(0≦X≦1) may have somewhat improved safety characteristics over LiNiO
2
and larger useful capacity below 4.2 V versus Li than LiCoO
2
, this solid solution still has to be overcharge protected just as LiCoO
2
and LiNiO
2
.
One alternative has been to dope LiNiO
2
with ions that have no remaining valence electrons thereby forcing the material into an insulator state at a certain point of charge, and therefore protecting the material from overcharge. For example, Ohzuku et al (Journal of Electrochemical Soc., Vol. 142, 4033 (1995)) describe that the use of Al
3+
as a dopant for lithium nickelates (LiNi
0.75
Al
0.25
O
4
) can produce improved overcharge protection and thermal stability in the fully charged state as compared to LiNiO
2
. However, the cycle life performance of this material is unknown. Alternatively, U.S. Pat. No. 5,595,842 to Nakare et al. demonstrates the use of Ga
3+
instead of Al
3+
. In another example, Davidson et al (U.S. Pat. No. 5,370,949) demonstrates that introducing chromium cations into LiMnO
2
can produce a tetragonally distorted spinel type of structure which is air stable and has good reversibility on cycling in lithium cells.
Although doping lithium metal oxides with single dopants has been successful in improving these materials, the choice of single dopants which can be used to replace the metal in the lithium metal oxide is limited by many factors. For example, the dopant ion has to have the right electron configuration in addition to having the right valency. For example, Co
3+
, Al
3+
, and Ga
3+
all have the same valency but Co
3+
can be oxidized to Co
4+
while Al
3+
, and Ga
3+
cannot. Therefore doping LiNiO
2
with Al or Ga can produce overcharge protection while doping with cobalt does not have the same effect. The dopant ions also have to reside at the correct sites in the structure. Rossen et al (Solid State Ionics Vol. 57, 311 (1992)) shows that introducing Mn into LiNiO
2
promotes cation mixing and therefore has a detrimental effect on performance. Furthermore, one has to consider the ease at which the doping reaction can be carried out, the cost of the dopants, and the toxicity of the dopants. All of these factors further limit the choice of single dopants.
SUMMARY OF THE INVENTION
The present invention uses multiple dopants to replace the transition metal M in lithium metal oxides and metal oxides having the formula LiM
y
O
z
or M
y
O
z
to have a collective effect on these intercalation compounds. As a result, the choice of dopants is not limited to elements having the same valency or site preference in the structure as the transition metal M, to elements having only a desired electron configuration, and to elements having the ability to diffuse into LiM
y
O
z
or M
y
O
z
under practical conditions. The use of a carefully chosen combination of multiple dopants widens the choices of dopants which can be used in the intercalation compounds and also can bring about more beneficial effects than a single dopant. For example, the use of multiple dopants can result in better specific capacity, cycleability, stability, handling properties and/or cost than has been achieved in single dopant metal oxides. The doped intercalation compounds of the invention can be used as cathode materials in electrochemical cells for lithium and lithium-ion batteries.
The doped lithium metal oxides and doped metal oxides of the invention have the formula:
LiM
y−x
[A]
x
O
z
or M
y−x
[A]
x
O
z
,
wherein M is a transition metal, 0<x≦y, [A]=
∑
i
=
1
n
w
i
B
i
wherein B
i
is an element used to replace the transition metal M and w
i
is the fractional amount of element B
i
in the total dopant combination such that
∑
i
=
1
n
w
i
=
1
,
n is the total number of dopant elements used and is a positive integer of two or more, the fractional amount w
i
of dopant element B
i
is determined by the relationship
∑
i
=
1
n
w
i
E
i
=
the
oxidation
state
of
the
replaced
transition
metal
M
±
0.5
,
E
i
is the oxi
Ebner Walter B.
Gao Yuan
Yakovleva Marina
Chaney Carol
FMC Corporation
Myers Bigel & Sibley Sajovec, PA
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