Patent Application
20140065457
1. Field
The disclosed embodiments relate to batteries for portable electronic devices. More specifically, the disclosed embodiments relate to techniques for creating multiple thicknesses in electrode substrates of batteries for portable electronic devices.
2. Related Art
Rechargeable batteries are presently used to provide power to a wide variety of portable electronic devices, including laptop computers, tablet computers, mobile phones, personal digital assistants (PDAs), digital music players and cordless power tools. The most commonly used type of rechargeable battery is a lithium battery, which can include a lithium-ion or a lithium-polymer battery.
Lithium-polymer batteries often include cells that are packaged in flexible pouches. Such pouches are typically lightweight and inexpensive to manufacture. Moreover, these pouches may be tailored to various cell dimensions, allowing lithium-polymer batteries to be used in space-constrained portable electronic devices such as mobile phones, laptop computers, and/or digital cameras. For example, a lithium-polymer battery cell may achieve a packaging efficiency of 90-95% by enclosing rolled electrodes and electrolyte in an aluminized laminated pouch. Multiple pouches may then be placed side-by-side within a portable electronic device and electrically coupled in series and/or in parallel to form a battery for the portable electronic device.
Furthermore, a reduction in one or more battery dimensions may enable the creation of portable electronic devices with small, thin, portable, and/or aesthetically pleasing form factors. For example, an increase in the energy density of a battery may facilitate a decrease in the battery's thickness while maintaining the battery's capacity. In turn, the decreased thickness may allow for a corresponding decrease in the thickness of the portable electronic device powered by the battery and/or the freeing up of space within the portable electronic device to accommodate other components (e.g., display, processor, memory, etc.).
Consequently, the use of portable electronic devices may be facilitated by improvements related to the packaging efficiency, capacity, form factor, design, and/or manufacturing of battery packs containing lithium-polymer battery cells.
The disclosed embodiments provide a battery cell. The battery cell includes an electrode containing an active material and a continuous substrate. The continuous substrate includes a first thickness to maintain a tensile strength of the continuous substrate and a second thickness that is less than the first thickness to accommodate the active material. The first and second thicknesses may thus improve the energy density and/or rate capability of the battery cell without producing manufacturing defects associated with the use of thinner electrode substrates in battery cells.
In some embodiments, the electrode is at least one of a cathode and an anode.
In some embodiments, the battery cell also includes a separator. During manufacture of the battery cell, the cathode, the anode, and the separator may be wound to create a jelly roll. Alternatively, the layers may be used to form other types of battery cell structures, such as bi-cell structures.
In some embodiments, the first and second thicknesses are created on one side or both sides of the continuous substrate.
In some embodiments, the first and second thicknesses are associated with at least one of a rectangular shape, a square shape, a triangular shape, a honeycomb shape, and a three-dimensional (3D) shape.
In some embodiments, the first and second thicknesses are created using at least one of an etching technique, a blasting technique, and a preferential-stretching technique.
In the figures, like reference numerals refer to the same figure elements.
The following description is presented to enable any person skilled in the art to make and use the embodiments, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present disclosure. Thus, the present invention is not limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.
The data structures and code described in this detailed description are typically stored on a computer-readable storage medium, which may be any device or medium that can store code and/or data for use by a computer system. The computer-readable storage medium includes, but is not limited to, volatile memory, non-volatile memory, magnetic and optical storage devices such as disk drives, magnetic tape, CDs (compact discs), DVDs (digital versatile discs or digital video discs), or other media capable of storing code and/or data now known or later developed.
The methods and processes described in the detailed description section can be embodied as code and/or data, which can be stored in a computer-readable storage medium as described above. When a computer system reads and executes the code and/or data stored on the computer-readable storage medium, the computer system performs the methods and processes embodied as data structures and code and stored within the computer-readable storage medium.
Furthermore, methods and processes described herein can be included in hardware modules or apparatus. These modules or apparatus may include, but are not limited to, an application-specific integrated circuit (ASIC) chip, a field-programmable gate array (FPGA), a dedicated or shared processor that executes a particular software module or a piece of code at a particular time, and/or other programmable-logic devices now known or later developed. When the hardware modules or apparatus are activated, they perform the methods and processes included within them.
In one or more embodiments, battery 100 is designed to accommodate the space constraints of computer system 102. For example, battery 100 may include battery cells of different sizes and thicknesses that are placed side-by-side, top-to-bottom, and/or stacked within computer system 102 to fill up the free space within computer system 102. The use of space within computer system 102 may additionally be optimized by omitting a separate enclosure for battery 100. For example, battery 100 may include non-removable pouches of lithium-polymer cells encased directly within the enclosure for computer system 102. As a result, the cells of battery 100 may be larger than the cells of a comparable removable battery, which in turn may provide increased battery capacity and weight savings over the removable battery.
To further facilitate use of computer system 102 with battery 100, battery 100 may include a continuous electrode substrate with two or more thicknesses. For example, the electrode substrate may include a first thickness to maintain a tensile strength of the substrate and a second thickness to accommodate active material for the electrode. In turn, battery 100 may have a higher energy density and/or better rate capability than those of conventional lithium-polymer batteries. Improving the energy density and/or rate capability of lithium-polymer batteries is discussed in further detail below with respect to
More specifically, jelly roll 202 may include one strip of cathode material (e.g., aluminum foil coated with a lithium compound) and one strip of anode material (e.g., copper foil coated with carbon) separated by one strip of separator material (e.g., conducting polymer electrolyte). The cathode, anode, and separator layers may then be wound on a mandrel to form a spirally wound structure. Alternatively, the layers may be used to form other types of battery cell structures, such as bi-cell structures. Jelly rolls are well known in the art and will not be described further.
During assembly of battery cell 200, jelly roll 202 is enclosed in a flexible pouch, which is formed by folding a flexible sheet along a fold line 212. For example, the flexible sheet may be made of aluminum with a polymer film, such as polypropylene and/or polyethylene. After the flexible sheet is folded, the flexible sheet can be sealed, for example, by applying heat along a side seal 210 and along a terrace seal 208.
Jelly roll 202 also includes a set of conductive tabs 206 coupled to the cathode and the anode. Conductive tabs 206 may extend through seals in the pouch (for example, formed using sealing tape 204) to provide terminals for battery cell 200. Conductive tabs 206 may then be used to electrically couple battery cell 200 with one or more other battery cells to form a battery pack. For example, the battery pack may be formed by coupling the battery cells in a series, parallel, or series-and-parallel configuration.
As shown in
First thickness 310 may maintain a tensile strength of continuous substrate 302 to mitigate manufacturing defects such as breaks, crinkles, convolutions, nicks, and/or dents during creation of the electrode and/or battery cell. On the other hand, the removed portion 308 may accommodate additional active material 304 in the battery cell, thus increasing the energy density of the battery cell over that of a conventional battery cell with a flat electrode substrate. For example, portion 308 may increase the thickness of active material 304 from 53 microns to 61 microns, thus providing a corresponding increase in the energy density of the battery cell. The removed portion 308 may also increase the surface area of continuous substrate 302, resulting in a corresponding increase in the rate capability and/or capacity rate (c-rate) of the battery cell over that of the conventional battery cell if both battery cells contain the same amount of active material 304-306.
Portion 308 may be removed in a way that forms various shapes in continuous substrate 302. For example, the periodic removal of portion 308 may create rectangular, square, triangular, honeycomb, and/or three-dimensional (3D) shapes in continuous substrate 302. Shapes associated with multiple thicknesses in continuous substrates for battery cells are discussed in further detail below with respect to
Moreover, portion 308 may be removed from first thickness 310 using a variety of techniques. For example, the second thickness may be formed by removing portion 308 using an etching (e.g., photo etching, chemical etching, laser etching) technique. Alternatively, a blasting (e.g., sand blasting, bead blasting) technique may be used to selectively remove portion 308 from various parts of continuous substrate 302. Finally, the first and second thicknesses may be formed in continuous substrate 302 using a preferential-stretching technique, in which portion 308 is removed from continuous substrate 302 to form a set of shapes and/or patterns and continuous substrate 302 is stretched in one or more dimensions to increase the width of the shapes and/or patterns.
In addition, multiple thicknesses may be created in the continuous substrate by removing portions 404-406 of the continuous substrate from both sides (e.g., top and bottom) of the continuous substrate. For example, portions 404-406 that are 6 microns deep and 20-2000 microns wide may be removed from the continuous substrate in an alternating pattern so that a center thickness 402 of 4 microns is maintained throughout the continuous substrate and an additional thickness of the continuous substrate above or below thickness 402 is the same (e.g., 6 microns) at any point in the continuous substrate. Such removal of portions 404-406 may accommodate active material disposed over the top and bottom of the continuous substrate and/or increase the surface area of the continuous substrate, thus increasing the energy density of the battery cell and/or facilitating faster discharge of the battery cell.
Shape 602 may taper at an angle from the top of a first thickness of the continuous substrate, and then drop vertically until a boundary of a second thickness in the continuous substrate is reached. On the other hand, shape 604 may drop vertically from the top of the first thickness, and then taper at an angle until the boundary of the second thickness is reached. Shapes 602-604 may also be included in the same continuous substrate. For example, shape 602 may be created along the top of the continuous substrate, while shape 604 may be created along the bottom of the continuous substrate. The varying thicknesses of shapes 602-604 may maintain a tensile strength that averts manufacturing defects in the electrode and/or battery cell while enabling improvements in the energy density and/or rate capability of the battery cell.
Initially, a continuous substrate for the battery cell is obtained (operation 702). The continuous substrate may be copper foil or aluminum foil for a lithium-polymer battery cell. Next, a first thickness and a second thickness that is less than the first thickness are formed in the continuous substrate (operation 704). The first and second thicknesses may be formed on one or both sides of the continuous substrate using an etching technique, a blasting technique, and/or a preferential-stretching technique. In addition, the first and second thicknesses may be associated with a rectangular, square, triangular, honeycomb, and/or 3D shape.
An electrode for the battery cell is then formed by depositing active material for the electrode onto the continuous substrate (operation 706). For example, cathode and/or anode active material may be coated, deposited, and/or sputtered onto the continuous substrate to form a cathode and/or anode for the battery cell. The first thickness may maintain the tensile strength of the continuous substrate, while the second thickness may accommodate the active material. Consequently, the first and second thicknesses may improve the energy density and/or rate capability of the battery cell without producing manufacturing defects associated with the use of thinner electrode substrates in battery cells.
A separator for the battery cell is also obtained (operation 708), and the cathode, anode, and separator are wound to create a jelly roll (operation 710). The winding step may be skipped and/or altered if the layers are used to create other battery cell structures, such as bi-cells. Finally, the jelly roll is sealed in a pouch to form the battery cell (operation 712). For example, the battery cell may be formed by placing the cathode, anode, and separator layers into the pouch, filling the pouch with electrolyte, and forming side and terrace seals along the edges of the pouch.
The above-described rechargeable battery cell can generally be used in any type of electronic device. For example,
The foregoing descriptions of various embodiments have been presented only for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the forms disclosed. Accordingly, many modifications and variations will be apparent to practitioners skilled in the art. Additionally, the above disclosure is not intended to limit the present invention.
