Lithiated oxide materials and methods of manufacture

Details Lithiated oxide materials and methods of manufacture Lithiated oxide materials and methods of manufacture

2001-03-06

2003-12-09

Chaney, Carol (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

Current producing cell, elements, subcombinations and...

Electrode

C429S218100, C429S223000, C429S224000, C423S596000

Reexamination Certificate

active

06660432

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to lithiated oxides with a well-layered crystal structure for use as cathode materials, and methods of manufacturing such materials.
2. Background Art
Rechargeable lithium batteries are of commercial interest due to their high energy and power density, and their long cycle life. Lithium ion batteries (i.e. batteries which do not use metallic lithium as the anode) have replaced lithium batteries since extended cycling using lithium metal as the anode is problematic. The majority of rechargeable lithium ion batteries use anode materials, which do not contain lithium metal, for example carbon or tin containing materials. This has resulted in the requirement that cathodes must contain lithium which can be extracted during first charge, as well as cycle well over several hundreds of charge-discharge cycles. Prior to the introduction of lithium ion batteries, all materials which cycled well, including sulfides, were candidates for cathodes. Since the introduction of Li-ion batteries the choice of materials has in practice drastically reduced.
Most interesting as cathodes for rechargeable lithium ion batteries are lithium transition metal oxides such as spinel Li
1+x
Mn
2−x
O
4
(and its modifications) and LiCoO
2
. Spinel Li
1+x
Mn
2−x
O
4
is low cost and does not contain hazardous materials. However, its applications are limited since the capacity of materials which cycle well is only around 115 mAh/g. Additionally, the capacity retention during cycling at elevated temperatures (if cycled at 55° C. for example) is not sufficient. LiCoO
2
cycles well, and has a capacity of approximately 140 mAh/g, however Co is toxic and expensive. Promising alternatives to Li
1+x
Mn
2−x
O
4
and LiCoO
2
are LiNiO
2
-based materials. Nickel is less toxic and less costly than Co. Furthermore, in cells LiNiO
2
has a larger reversible capacity than LiCoO
2
.
LiNiO
2
and LiCoO
2
are layered materials having the alpha-NaFeO
2
type structure (space group R-3m). Layered materials are of interest for cathodes since a layered structure provides for the fast diffusion of lithium. In this structure, layers of transition metal octahedrally surrounded by oxygen (leading to MO
2
sheets) are separated by lithium cations in the lithium layers. The formula can be written as LiMO
2
. In this document the formula will often be written as Li[M]O
2
, or as {LiM}[M]O
2
, where [M] stands for all cations residing in the transition metal layers, and {M} stands for non-lithium cations in the lithium layers. In many prior art LiNiO
2
-based materials, the lithium layers are partially filled by transition metal ions. An example is nickel rich LiNiO
2
which can be written as {Li
0.9
Ni
0.1
}[Ni]O
2
. Especially promising for cathode applications are well-layered materials, i.e. materials which have little or no transition metal M located on lithium sites. Such well ordered structures provide for fast lithium intercalation and de-intercalation.
It is difficult to prepare LiNiO
2
with an acceptable capacity retention during extended cycling. LiNiO
2
materials also generally suffer from some irreversible capacity loss in the first cycle, i.e. less lithium can be reinserted during first discharge than was extracted during first charge. A large irreversible capacity is undesirable for practical applications. Good capacity retention and small irreversible capacity correlate with a well-layered crystal structure. An ideal well-layered crystal structure has a large c:a ratio and a small amount of transition metals mislocated on lithium sites. However, in practice, preparation of samples with only a small amount of Ni in the Li layer sites is difficult. The amount of Ni on lithium sites can be estimated from Rietveld refinements of X-ray diffraction data. Alternatively, Dahn et al. in Solid State Ionics 44 (1990) 87 defined an R-factor which sensitively correlates with the concentration of Ni on lithium sites. R is defined as the ratio of integrated intensities of the 101, 006 and 102 peaks of the diffraction pattern of the layered material having the R-3m structure. Many prior art disclosures suggest ways to prepare LiNiO
2
with a small amount of misplaced Ni on lithium sites, i.e. they try to prepare LiNiO
2
materials with a small value R, but these methods have not completely solved the problem, or are not economically feasible.
Another basic problem of LiNiO
2
-based materials is that they become very reactive if overcharged, i.e. charged to voltages where significantly more than around 60% of the nickel is oxidized from the 3+ to the 4+ state. In large cells the overcharged cathode decomposes slowly, generating more heat than the cell can release to the environment. This accelerates the decomposition reaction ultimately leading to thermal runaway with explosion, ignition or venting of the battery. In practice large batteries cannot use LiNiO
2
as cathodes because they tend to go into thermal runaway, and are therefore unsafe.
Dahn et al. in Solid State Ionics 69 (1994) 265 showed that charged LiNiO
2
is hazardous since Li
1−x
NiO
2
contains the very reactive tetravalent Ni ion. The cathode tends to react to form a rocksalt type Li
x
Ni
1−x
O as discussed in Arai et al. in Solid State Ionics 109 (1998) 295. In the rocksalt structure Ni has a more preferred lower average valence state. The reaction is accompanied by a release of oxygen which can react with the electrolyte.
Doping LiNiO
2
with less reactive or non-reactive materials can lead to materials where the reactive Ni
4+
is diluted. Substitution of Ni ions with other cations has also been shown to improve the electrochemical performance in some cases. For example, U.S. Pat. No. 5,750,288 (Rayovac) issued May 12, 1998, describes the modification of LiNiO
2
by substituting up to 30% of the Ni by a non-transition metal element from the group Al, Ga, Sn and Zn. Substitution has been shown to improve the safety of LiNiO
2
-type materials to some degree by doping with Al by Ohzuku et al in J. Electrochem. Soc. 142 (1995) 4033, and by doping with Mg
1/2
Ti
1/2
by Gao et al in Electrochemical and Solid State Letters 1 (1998) 117.
Substitution of nickel with a fraction of cobalt (e.g. Li[Ni
1−x
Co
x
]O
2
where x is about 0.2 to 0.3) can lead to a material with good electrochemical properties. Such materials are described for example by Delmas et al. in J. Power Sources 43/44 (1993) 595. However, the safety problems associated with LiNiO
2
are not completely solved, as shown by Paulsen and Dahn in Abstract 43, Proceedings of the 195
th
Meeting of the Electrochemical Society, Seattle, May 2-6, 1999. Furthermore the substitution of nickel by cobalt increases the cost of the material relative to LiNiO
2
.
The use of manganese as a dopant in LiNiO
2
-based compounds has been anticipated to provide certain advantages. Since manganese is cheap and non-hazardous, a large Mn content in an LiNiO
2
based cathode would be desired not only for safety considerations but also for price.
Substitution of Ni in LiNiO
2
by manganese was described by Dahn et al. in Solid State Tonics 57 (1992) 311. In that report it was shown that LiNiO
2
can be substituted with manganese leading to Li[Ni
1−x
Mn
x
]O
2
with a maximum substitution limit of x being approximately 0.5. Where x>0.5, the materials were not monophase but a phase mixture containing Li
2
MnO
3
, and Li
y
Ni
1−y
O with the rocksalt structure. However it was reported that LiNiO
2
with large amounts of manganese, especially Li[Ni
1/2
Mn
1/2
]O
2
, did not cycle well.
U.S. Pat. No. 5,264,201 (Dahn et al.) issued Nov. 23, 1993, described a method for making LiNi
1−y
M
y
O
2
where M may be Co, Fe, Cr, Ti, Mn or V and y is less than about 0.2 (with the exception that y is less than about 0.5 when M is Co). The method was intended to provide a material which was sub

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