Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Electrode
Reexamination Certificate
2000-10-18
2004-05-04
Kalafut, Stephen (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Electrode
C029S623100, C429S223000, C429S224000, C429S231100, C429S231950
Reexamination Certificate
active
06730435
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an active material for non-aqueous secondary battery, and a non-aqueous secondary battery using the same.
2. Description of the Related Art
With the rapid advance of portable and cordless electronic equipment, non-aqueous secondary batteries which can realize smaller size, lighter weight and larger capacity compared with conventional secondary batteries have been developed. Among them, a lithium secondary battery is already put to practical use as power sources; for a portable telephone and a notebook personal computer. Batteries of large size and high output have also been studied as power sources for electric vehicles. Since a non-aqueous electrolyte solution dissolving a supporting salt in a flammable organic solvent; and a flammable polymer electrolyte are used for a non-aqueous secondary battery, needs of safety securing means are increasing along with the tendency of batteries having higher energy density and larger size. Development of an active material having improved safety while maintaining high performance has been earnestly required.
As a method for improving the safety of an active material, studies have been performed actively, for example, a part of nickel of lithiated nickel dioxide used for a cathode is substituted by other element, such as aluminum, and although the safety is improved, there has been a problem of capacity falling.
Moreover, studies for improving the safety of a large-sized battery have been conducted, with using spinel type lithium manganese oxide which is a material having high safety as a cathode active material. However, in case of spinel type lithium manganese oxide, when the charging/discharging at a high temperature is repeated, the capacity falling occurs quickly, namely, there is a problem that a high-temperature cycle characteristic is inferior. In order to improve this point, lithium rich composition (Li/Mn>0.5) or substitution of a part of manganese by other element, such as chromium, is studied, but it results to reduce the already small capacity of 4V region further, thus, the coexistence of the safety and the battery performance is difficult.
The object of the present invention is to solve the above-mentioned problem, and to provide an active material for non-aqueous secondary battery having improved safety with maintaining the capacity and the cycle characteristic, and a non-aqueous secondary battery using the same.
SUMMARY OF THE INVENTION
As a result of extensive studies, the present inventors have found that an active material for non-aqueous secondary battery having improved safety with maintaining the capacity and the cycle characteristic can be obtained by that: the active material is an active material that can be doped/undoped with an alkali metal ion; the active material is a compound particle comprising three or more of constituting elements; and the active material has a region where concentration of one constituting element selected from a specific group is decreasing continuously in the direction of from the particle surface to the particle core; and the ratio of the mean width of this region towards the depth direction to the mean radius of the particle is in a specific range, and accomplished the present invention.
That is, the present invention relates to:
[1] an active material for non-aqueous secondary battery wherein the active material can be doped/undoped with an alkali metal ion; the active material is a compound particle comprising three or more of constituting elements, and contains an element A selected from Li, Na, K, Mg, Ca, Sr, Ba, B, Al, Ga, In, Si, Zr, Sn, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Ag and Zn as one of the constituting elements; the particle has a region where the concentration of element A is decreasing continuously in the direction of from the particle surface to the particle core; and the ratio (d/D) of the mean width (d) of this region towards the depth direction to the mean radius (D) of the particle is 0.001<d/D<0.5.
Further, the present invention relates to:
[2] a process for preparing the active material for non-aqueous secondary battery of the above [1] comprising the first process of obtaining an active material that can be doped/undoped with an alkali metal ion by heat-treatment of a raw material compound and the second process of conducting heat-treatment after coating-treatment of the active material with a compound containing the element A, and the heat-treatment time in the second process is shorter than that in the first process.
Furthermore, the present invention relates to:
[3] a non-aqueous secondary battery, wherein the active material for non-aqueous secondary battery of the above [1] is used as an active material of a cathode and/or an anode.
DETAILED DESCRIPTION OF THE INVENTION
The active material for non-aqueous secondary battery of the present invention is an active material that can be doped/undoped with an alkali metal ion. The active material is a compound particle which comprises three or more of constituting elements, and contains an element A selected from Li, Na, K, Mg, Ca, Sr, Ba, B, Al, Ga, In, Si, Zr, Sn, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Ag and Zn as one of the constituting elements. The particle has a region where the concentration of element A is decreasing continuously in the direction of from the particle surface to the particle core; and the ratio (d/D) of the mean width (d) of this region towards the depth direction to the mean radius (D) of the particle is 0.001<d/D<0.5.
When the element A is not distributed in a particle so that there is a region where the concentration of element A is decreasing continuously from the particle surface to the particle core, deterioration of the cycle characteristic of battery is remarkable. When the ratio d/D is 0.001 or less, where d is the mean width of the region towards the depth direction where the concentration of element A is decreasing continuously from the particle surface to the particle core, and D is the mean radius of the particle, the adding effect of element A is hardly exhibited. On the other hand, when d/D is 0.5 or more, the capacity falling becomes remarkable. In order to make capacity falling still small, and to exhibit the effect of the element A much more, it is suitably in 0.01<d/D<0.3.
The ratio d/D of the mean width d towards the depth direction of the region where the concentration of element A is decreasing continuously from the particle surface to the particle core, to the mean radius D of the particle can be determined as follows.
That is, the compound particle is dissolved in an acid etc. sequentially by a unit of about 0.5 to 1% of the whole compound particle. Each solution is analyzed by ICP emission spectroscopy method, and “the molar fraction of element A to the sum of element A and other constituting elements” of each solution is calculated.
Here, the above-mentioned other constituting elements can be selected arbitrarily, as long as the constituting element exists in a constant concentration at least whole of the one particle.
The region where the molar fraction of the above element A decreases continuously from the particle surface to the particle core until it becomes almost constant is “a region where the concentration of element A is decreasing continuously”.
And d/D is calculated, by selecting a constituting element which exists over the whole particle in a constant concentration, from the amount of the constituting element in “the region which is decreasing continuously”, and the amount of said constituting element in other regions, assuming that the particle is a spherical form, and the particle changes in the state reducing the radius by dissolution with maintaining the similarity of spherical form.
The region of decreasing continuously in the direction of from the particle surface to the particle core does not need to start from the particle surface. Moreover, 1 or 2 or more of the regions may exist.
When the above regi
Kawakami Yoshihiro
Nakane Kenji
Nishida Yasunori
Ogawa Hiroshi
Dove Tracy
Kalafut Stephen
Sughrue & Mion, PLLC
Sumitomo Chemical Company Limited
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