This invention relates to secondary lithium batteries, and in particular to lithium ion prismatic cells.
Rechargeable batteries, also known as secondary batteries, contain active materials that are regenerated by charging. When the energy produced by these batteries drops below optimum efficiency, they may be recharged in any one of many manners, depending upon their construction. Rechargeable batteries are broken down into two main classifications based upon the chemical composition of the battery. Both of these classifications, alkaline secondary and lithium secondary, contain a wide assortment of battery styles.
In contrast to secondary cells, primary electrochemical cells are meant to be discharged, e.g., to exhaustion, only once, and then discarded. Primary cells are not intended to be recharged. Primary cells are described, for example, in David Linden, Handbook of Batteries (McGraw-Hill, 2d ed. 1995).
Secondary electrochemical cells can be recharged many times, e.g., more than fifty times, more than a hundred times, or more. In some cases, secondary cells can include relatively robust separators, such as those having many layers and/or that are relatively thick. Secondary cells can also be designed to accommodate changes, such as swelling, that can occur in the cells. Secondary cells are described, e.g., in Falk & Salkind, “Alkaline Storage Batteries”, John Wiley & Sons, Inc. 1969; U.S. Pat. No. 345,124; and French Patent No. 164,681, all hereby incorporated by reference.
Digital cameras and other electronic devices (for example, cell phones, MP3 players, and personal digital assistants (PDA's) such as BlackBerries®) operate on batteries, such as secondary nickel metal hydride batteries or secondary lithium ion batteries. One type of battery that has been used in digital cameras is a 3.7 V secondary, prismatic lithium ion. Such batteries are commercially available, for example from Panasonic under the tradename Pentax D-L12. Batteries referred to as “prismatic cells” generally have a thickness that is much less than their width and length. For example, the Pentax D-L12 battery has a length of about 53.0 mm, a width of about 35.2 mm, and a thickness of about 7.0 mm. Many prismatic cells have dimensions in the ranges of 40-60 mm long by 30-40 mm wide by 4-10 mm thick.
In general, the invention features lithium ion secondary batteries in the form of prismatic cells. The cells include a housing having a prismatic shape, and, disposed within the housing, an anode, a cathode including lithium as an active component, a separator and an electrolyte.
In one aspect, the invention features prismatic cell type Li-ion secondary batteries in which the cathode contains LiFePO4. Thus, in one aspect, the invention features a secondary battery comprising a prismatic-shaped housing that houses an anode, a cathode including LiFePO4, and a separator between the anode and the cathode. These batteries have desirable properties for use in digital cameras and other applications.
In some cases, the batteries described herein are fast-charge capable rechargeable cells that can provide more than 100 cycles, typically many hundreds or thousands of cycles, before they need to be replaced. Some preferred batteries have a capacity of greater than about 5 mAh.
The cells also have a charge capability of 15 minutes or less, preferably 5 minutes or less. In addition, preferred cells made using LiFePO4 cathodes generally exhibit good safety, fast charging (e.g., 5 minutes or less), good power density, consistent performance, and environmental acceptability. The fast charge capability of 5 minutes or less minimizes user inconvenience. Preferred batteries also provide excellent cycle life (e.g., greater than 1000 cycles and preferably greater than 1500 cycles to 80% of initial capacity at 0.5 A/0.5 A rates) and shelf life (3 years).
In another aspect, the invention features a lithium ion prismatic cell comprising cell components, including an anode, a cathode comprising lithium, and a separator between the anode and cathode, and a housing in which the cell components are disposed. The housing includes a plurality of vents, at least two of the vents being configured to burst when the internal pressure of the prismatic cell reaches different predetermined levels.
Some implementations include one or more of the following features. At least one of the vents may be in a side surface of the housing. At least one of the vents may be a coined feature. At least one of the vents may be an elongated groove having a triangular or trapezoidal cross-section. In one preferred implementation, one of the vents comprises an elongated groove. The elongated groove may have a length of about 0.05 to 0.70 inch, a depth of about 0.006 to 0.008 inch, and a width of about 0.004 to 0.006 inch. The elongated groove may have a length that is about 50 to 80% of the width of the cell, a depth such that the wall thickness in the groove is about 20 to 30% of the wall thickness of the housing, and a width that is about 50 to 60% of the wall thickness of the housing. The elongated groove may be close to an upper edge of the cell, e.g., the elongated groove may extend parallel to the top surface of the cell, on a side wall of the cell, at a distance of about 20 to 40% of the total height of the cell from the top edge of the housing.
The invention also features methods of making a prismatic cell that include deforming an area of the cell housing to form an elongated groove having a triangular or trapezoidal cross-section. Deformation of the housing may be accomplished by coining or electrochemical machining.
In a further aspect, the invention features a lithium ion prismatic cell comprising a housing having at least one substantially flat side running along the length of said housing the housing defining a negative contact and a positive contact, within the housing, an anode, and a cathode comprising lithium, wherein at least the cathode is in the form of a sheet having a predetermined length, and, a plurality of connection tabs disposed at spaced locations along the length of the cathode to connect the cathode to the positive contact.
Some implementations include one or more of the following features. The cathode may include a sheet form metal substrate, for example aluminum foil, and a coating of active material disposed on the substrate. The connection tabs may be disposed along an upper edge of the cathode. The connection tabs may be evenly spaced along the length of the cathode. The cell may comprise two, three or more connection tabs. The connection tabs may be formed of aluminum. The cathode may comprise a single sheet with multiple tabs, or multiple sheets, each sheet having at least one tab. The connection tabs may be integral with the substrate, or may be welded to the substrate.
For the purposes of this application, a “prismatic cell” has at least four generally flat sides, and has one dimension (e.g., thickness) that is substantially smaller than two other dimensions (e.g., length and width). As an example, a prismatic cell can have a thickness of between about 2 mm and about 15 mm (e.g., between about 4 mm and about 10 mm), a width of between about 10 mm and about 50 mm (e.g., between about 20 mm and about 40 mm), and a length of between about 20 mm and about 60 mm (e.g., between about 30 mm and about 40 mm). The length, width and thickness are measured as indicated by L, W and T, respectively, in
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features and advantages of the invention will be apparent from the description and drawings, and from the claims.
Referring to
As shown in
A cell header 121 is joined, e.g., by laser welding, to the top edge of the housing 102. The structure of cell header 121, shown in
Referring to
Referring to
Referring now to
The negative contact 108 and positive contact 106 may be of nickel or copper. The terms “nickel” and “copper” as used herein is intended to extend to alloys of these metals wherein nickel or copper comprises at least a substantial proportion thereof.
If the exposed contact surface of terminals 108 and 106 is of nickel, the electrical resistance between such terminal contacts and corresponding terminals of some digital cameras can be sufficiently high as to interfere with proper performance of the camera. For example, the elevated contact resistance may interfere with obtaining the required pulsed power necessary to operate the cameras in the most effective manner. Accordingly, in some implementations the exposed surfaces of the nickel contact 108 and 106 are plated with a layer of gold 108a and 106b respectively, as described in U.S. 2005/0158621, the full disclosure of which is incorporated by reference herein.
Although nickel is the preferred substrate for terminals 108 and 106 other substrates 108b and 106b, for example, copper or silver, may be used.
The cell header, shown in
The battery uses a wound electrode design with interspaced cathode and anodes to increase the surface area, as shown in
In some preferred batteries, the cathode 154 includes LiFePO4 as its active material. The cathode may also include a binder. The thickness of the cathode will depend upon the cell configuration and performance characteristics.
The anode is generally a carbon anode. Other suitable anode materials may include alloy-based anodes (e.g., Li metal alloyed with Al, Si or Sn), lithium titanate (Li4Ti5O12) with carbon, and various metal oxides.
The battery will also include an electrolyte 162, as is well known in the battery art. In the cells described herein, the electrolyte is generally not consumed during charge and discharge. Accordingly, the amount of electrolyte is determined by the porous volume available in the electrodes and separator.
Each electrode (cathode and anode) can be fabricated by providing a substrate and coating the substrate on both sides with the appropriate material, for example carbon for the anode and a mixture of binder, conductive carbon and active material for the cathode. Preferably, for the cathode the coating on each side is from about 30 to 45 microns thick, so that the total cathode thickness, prior to winding or folding, is about 70 to 90 microns. For the anode, it is preferred that the coating on each side be about 15 to 20 microns thick, so that the total anode thickness, prior to folding, is about 45 to 55 microns. The substrate for the cathode may be, for example, aluminum foil, and may have a thickness of from about 8 to about 35 microns. The substrate for the anode may be, for example, copper foil, and may have a thickness of from about 4 to about 35 microns.
The separator 158 may be sprayed onto either one or both of the electrodes for ease of assembly, or may be a separate component that is disposed between the cathode and anode.
Referring now to
Generally, it is preferable to evenly space the cathode tabs along the length of the cathode. However, other spacings may be used to facilitate manufacturing.
The cells described herein exhibit good performance characteristics, for example as illustrated in
A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention.
For example, the venting arrangement and/or the multiple connecting tabs described above may be utilized with other cell chemistries. Other lithium ion chemistries may be used, for example lithium cobalt oxide or lithium nickel oxide. If these chemistries are used it may be necessary to add a thermistor or other device or electronics for charge control, as is well known in the art.
Accordingly, other embodiments are within the scope of the following claims.