Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
2000-11-28
2003-04-22
Ryan, Patrick (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C429S218100
Reexamination Certificate
active
06551744
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a positive electrode active material for a non-aqueous electrolyte battery. The invention also relates to a high-capacity and low-cost non-aqueous electrolyte secondary battery having a positive electrode containing a specific positive electrode active material.
In recent years, with the widespread use of cordless and portable AV appliances and personal computers, the need has been increasing for compact, light weight, and high energy density battery batteries as their power sources. In particular, lithium secondary batteries, because of their high energy density, are expected to be a dominant battery in the next generation battery, and their potential market is very large.
In most of the lithium secondary batteries currently available on the market, LiCoO
2
having a high voltage of 4 V is used as the positive electrode active material, but LiCoO
2
is costly because Co is expensive. Under these circumstances, research has been progressing to investigate various positive electrode active materials as substitutes for LiCoO
2
. Among them, lithium-containing transition metal oxides has been wholeheartedly researched, and LiNi
a
Co
b
O
2
(a+b≈1) is promising, and at present, it seems that LiMn
2
O
4
having a spinel structure has already been commercialized.
In addition, nickel and manganese as substitutes for expensive cobalt are also being researched vigorously.
LiNiO
2
having a layered structure, for example, is expected to have a large discharge capacity, but its crystal structure changes during charging and discharging and, therefore, it deteriorates rapidly. In view of this, it is proposed to add to LiNiO
2
an element that can stabilize the crystal structure during charging and discharging and thus prevent the deterioration. As the element to be added, there are exemplified, cobalt, manganese, titanium and aluminum, for example.
Prior art examples that use composite oxides of Ni and Mn as the positive electrode active material for lithium secondary batteries will be described below.
U.S. Pat. No. 5,393,622, for example, proposes a method in which a hydroxide of Ni, a hydroxide of Mn and a hydroxide of Li are dry-mixed together and baked and, after cooling them down to room temperature, the mixture is again heated and baked to obtain an active material having a composition represented by the formula Li
y
Ni
1−x
Mn
x
O
2
wherein 0≦x≦0.3, 0≦y≦1.3.
Further, U.S. Pat. No. 5,370,948 proposes a method in which a Li salt, a Ni salt and a Mn salt are mixed together into an aqueous solution, followed by drying and baking, to obtain an active material represented by the formula LiNi
1−x
Mn
x
O
2
wherein 0.005≦x≦0.45.
Further, U.S. Pat. No. 5,264,201 proposes a dry synthesis method in which hydroxides or oxides of nickel and manganese and an excess amount of lithium hydroxide are mixed together and baked, and a synthesis method in which an oxide of nickel and manganese is added to a saturated aqueous solution of lithium hydroxide to form a slurry and the slurry is then dried and baked under a reduced pressure, to obtain an active material represented by the formula Li
x
Ni
2−x−y
Mn
y
O
2
wherein 0.8≦x≦1.0, y≦0.2.
Furthermore, U.S. Pat. No. 5,629,110 proposes a dry mixing synthesis method which uses &bgr;-Ni(OH)
2
to obtain an active material represented by the formula LiNi
1−x
Mn
x
O
2
wherein 0<x≦0.2, y≦0.2.
Japanese Unexamined Patent Publication No. Hei 8-171910 proposes a method in which manganese and nickel are coprecipitated by adding an alkaline solution into an aqueous solution mixture of manganese and nickel, then lithium hydroxide is added and the resulting mixture is baked, to obtain an active material represented by the formula LiNi
x
Mn
x−1
O
2
wherein 0.7≦x≦0.95.
Further, Japanese Unexamined Patent Publication No. Hei 9-129230 discloses a preferred particulate active material having the composition represented by the formula LiNi
x
M
x−1
O
2
wherein M is at least one of Co, Mn, Cr, Fe, V and Al, 1>x≦0.5, and shows a material with x=0.15 as the active material containing Ni and Mn.
Further, Japanese Unexamined Patent Publication No. Hei 10-69910 proposes an active material synthesized by a coprecipitation synthesis method, represented by the formula Li
y−x1
Ni
1−x2
M
x
O
2
wherein M is Co, Al, Mg, Fe, Mg or Mn, 0<x
2
≦0.5, 0≦x
1
<0.2, x=x
1
+x
2
, and 0.9≦y≦1.3. This patent publication describes that the discharge capacity is inherently small if M is Mn, and the original function of the positive electrode active material intended to achieve a high-capacity lithium secondary battery is dismissed if x
2
is more than 0.5. LiNi
0.6
Mn
0.4
O
2
is exemplified as a material having the highest proportion of Mn.
U.S. Pat. No. 5,985,237 discloses a production method for LiMnO
2
having a layered structure, but this is essentially a 3 V level active material.
All the prior art examples disclosed in the above U.S. Patents and Japanese Unexamined Patent Publications are intended to improve the electrochemical properties such as the cycle characteristics of LiNiO
2
by adding a trace amount of an element into LiNiO
2
, while retaining the characteristic properties of LiNiO
2
itself. Accordingly, in the active material obtained after the addition, the amount of Ni is always larger than that of Mn, and the proportion of Ni:Mn=0.8:0.2 is proposed in many cases. As an example of a material having a proportion with a highest amount of Mn, Ni:Mn=0.55:0.45 is disclosed.
However, in any of these prior art examples, it is difficult to obtain a composite oxide having a single-phase crystal structure since LiNiO
2
is separated from LiMnO
2
. This is because Mn
2+
tends to be oxidized to Mn
3+
during coprecipitation and Mn
3+
is difficult to form a homogenous composite oxide with Ni
2+
.
As described above, as a substitute material for the currently commercialized high voltage 4V LiCoO
2
.LiNiO
2
and LiMnO
2
as high-capacity and low-cost positive electrode active materials having a layered structure like LiCoO
2
has been researched and developed.
However, the discharge curve of LiNiO
2
is not flat, and the cycle life is short. In addition, the heat resistance is low, and using this material as a substitute material for LiCoO
2
would involve a severe problem. In view of this, improvements have been attempted by adding various elements to LiNiO
2
, but satisfactory results have not been obtained yet. Further, it is only possible to obtain a voltage of 3 V with LiMnO
2
therefore, low-capacity LiMn
2
O
4
which does not have a layered structure but has a spinel structure is beginning to be researched.
Accordingly, an object of the present invention is to provide a positive electrode active material capable of solving the above-mentioned problems. Also, another object of the invention is to obtain a positive electrode active material that has a voltage of 4 V equivalent to that of LiCoO
2
, exhibits a flat discharge curve, and is higher in capacity and lower in cost than LiCoO
2
. Further, still another object of the present invention is to provide a non-aqueous electrolyte secondary battery using such a positive electrode active material and achieving a high capacity and excellent charge/discharge efficiency.
BRIEF SUMMARY OF THE INVENTION
The present invention relates to a positive electrode active material for a non-aqueous electrolyte battery comprising a crystalline particle of an oxide, said oxide containing nickel element and manganese element in substantially the same atomic ratios and having a crystal structure of a rhombohedral structure, which belongs to rhombohedral crystal system.
In other words, in the crystalline particle, nickel atoms and manganese atoms are uniformly or homogeneously dispersed.
It is effective that the crystal structure of the crystalline particle belongs to the hexagonal crystal system, and the length of c-
Nagayama Masatoshi
Ohzuku Tsutomu
Yoshizawa Hiroshi
Akin Gump Strauss Hauer & Feld L.L.P.
Matsushita Electric - Industrial Co., Ltd.
Ryan Patrick
Wills M.
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