Aqueous rechargeable battery

Details Aqueous rechargeable battery Aqueous rechargeable battery

1995-03-22

2002-06-11

Chaney, Carol (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

Fluid active material or two-fluid electrolyte combination...

C429S206000

Reexamination Certificate

active

06403253

ABSTRACT:

FIELD OF THE INVENTION
The invention pertains to the field of batteries. Specifically, the invention deals with novel aqueous rechargeable batteries that employ insertion compounds for the electrode materials.
BACKGROUND OF THE INVENTION
The demand for rechargeable batteries with higher gravimetric and volumetric energy densities has been increasing in recent years. Potential applications for these energy sources range from consumer electronics devices to motive power for electric vehicles. To meet these demands, a variety of novel or improved electrochemical systems are being developed. Several such systems have recently been introduced on a commercial basis, and include products based on nickel-metal hydride (Ni-MH) or on lithium ion (also known as “rocking chair”) systems. The former is an example of an aqueous rechargeable battery product, while the latter is an example of a non-aqueous product.
Aqueous rechargeable battery systems have been used commercially for decades. Common uses include smaller Ni-Cd products for household electronics devices and larger Pb acid products for SLI (starting-lighting-ignition) requirements for automobiles. Typically, aqueous battery products share several advantages over non-aqueous battery products. Being water based, the contents of the battery generally cannot ignite and burn. Thus, in abuse situations, aqueous batteries offer a relatively low risk of fire. (Of course, the risk of fire and/or explosion as a result of hydrogen generation in certain aqueous systems is well known). Additionally, aqueous electrolytes have ionic conductivities that are typically from 2 to 3 orders of magnitude greater than those of non-aqueous electrolytes at a given temperature. Thus, it is possible to design high rate (power) aqueous batteries with much thicker electrodes than those required for a corresponding high rate non-aqueous battery. The ability to fabricate high rate batteries, using relatively thick electrodes, translates into easier fabrication and easier prevention of defects with a corresponding reduction in cost. Finally, aqueous electrolytes are generally preferred over non-aqueous electrolytes from an environmental viewpoint.
Non-aqueous systems, on the other hand, have the advantage that they are not limited by the electrochemical stability of a water based electrolyte. Thus, such systems may operate at relatively high cell voltages (>3 volts), resulting in batteries with high energy densities. For example, battery systems employing lithium metal anodes often have theoretical energy densities of order of several hundreds of Wh/kg or Wh/l. In practice however, the safety characteristics of lithium batteries have limited both the practical energy densities obtained as well as the maximum battery size in commercial products to date.
Recently, lithium batteries based on lithium ion or “rocking chair” electrochemistries have entered the marketplace. These electrochemistries employ two suitable lithium insertion compounds as the active electrode materials and a non-aqueous electrolyte. Typically a carbonaceous material (partially graphitized) is employed as the anode, and a lithium transition metal oxide is employed as the cathode. During a discharge of the battery, lithium is removed from the host anode insertion compound and is inserted into the host cathode insertion compound. On recharge, the reverse process occurs. No plating process of a transported ionic species is fundamentally involved. The battery voltage is determined by the difference in the chemical potential of lithium in the two host electrodes, which is on average about 3½ electron volts. Lithium ion batteries thus offer high voltage with corresponding high energy densities, and these systems can cycle extremely well (over 1000 cycles).
Commercial lithium ion batteries can deliver energies of order of 200 Wh/l and 100 Wh/kg. This is achieved, in part, by using a minimal amount of non-aqueous electrolyte in the battery. Unlike some electrochemistries (eg. Pb acid, Ni—Cd), the Li ion electrolyte does not participate in the reactions on charge or discharge and merely serves as a conduit for Li ions between the electrodes. The low ionic conductivity of the Li ion electrolyte however requires that thin electrodes (of order of 100 &mgr;m thick) be used in the battery construction. With the use of very thin electrode substrates (eg. Al or Cu foil) and thin separators however, a relatively high loading of active electrode material can still be obtained in the fabricated battery. Approximately 45% of the overall weight of small cylindrical cells (eg. 4/3 A size) can be active electrode material.
The safety of lithium ion batteries is significantly better than that of similarly sized lithium metal batteries. There is still however a risk of fire or explosion under some types of mechanical or thermal abuse. This poses a problem for the commercialization of larger batteries or battery arrays. Also, those skilled in the art are aware that the risk of fire during abuse situations places limits on the deliverable capacity of such batteries. For instance, the amount of lithium that can be removed reversibly from commercial LiCoO
2
based cathodes is significantly greater than that actually used in practice for reasons of safety.
There are other disadvantages associated with conventional non-aqueous lithium ion type electrochemistries. The thin electrode requirement means that costly separator and foil current collectors must be used. The thin electrode assembly is correspondingly more complex. The active materials used in the electrodes must obviously be significantly smaller than the electrode itself. Thus, fine electrode powders (with a corresponding higher reactive surface area) may need to be used even though large particles may be sufficient for a given discharge rate.
Although the fine electrode powders are generally stable in air, a significant amount of water can be adsorbed onto the large surface area presented by such powders. Additionally, the electrolytes used in lithium ion electrochemistries are also generally hygroscopic. Since it is detrimental to include water in an assembled battery, many fabrication steps involve water removal or shielding from moisture in the air (typically in dry room environments).
Another less well known problem arises from the instability of many common materials to oxidation at the high operating potentials at the typical lithium ion cathode. Fortunately, aluminum is an inexpensive material that is acceptable for use as hardware at the cathode potential for most but not all lithium ion electrochemistries. However, a significant problem can arise due to the presence of certain impurities in the cathode materials themselves. The presence of even one small particle of an oxidizable metal contaminant (such as copper, stainless steel, iron) in the cathode can result in the development of an internal short in the battery. At the high operating voltages of such batteries, these contaminants can dissolve and plate over to the anode, creating an electrically conducting contaminant bridge between the electrodes. The thin separators (approx. 25 &mgr;m) employed in such batteries are not completely effective in preventing such internal shorts. Even with stringent quality control and cleanliness procedures, it is not uncommon in the applicant's experience to obtain from 5 to 10% internal shorts in developmental 4/3 A batteries. Those skilled in the art who are aware of this problem will appreciate the difficulties that this will pose in fabricating large defect free batteries.
The choice of appropriate insertion compounds is fundamental to the construction of a lithium ion battery. Currently, lithiated transition metal oxides including LiCoO
2
, LiNiO
2
, LiMn
2
O
4
(described in U.S. Pat. Nos. 4,302,518 and 4,312,930) and the like are among those favoured as cathode materials, while partially graphitized carbon or graphite (described in U.S. Pat. Nos. 4,702,977 or 5,028,500 and Japanese Patent Publication No. 57-208079) are favoured as anode materi

Affiliated with

Also associated with

Rating

Aqueous rechargeable battery does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Aqueous rechargeable battery, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Aqueous rechargeable battery will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2930006