(12) Patent Application Publication (10) Pub. No.: US 2013/0115491 A1 Bhardwaj Et Al

Home , Lithium polymer battery

US 2013 0115491A1 (19) United States (12) Patent Application Publication (10) Pub. No.: US 2013/0115491 A1 Bhardwaj et al. (43) Pub. Date: May 9, 2013

(54) PRESSURE-RELEF MECHANISM TO Publication Classification IMPROVE SAFETY IN LITHIUM-POLYMER BATTERY CELLS (51) Int. Cl. HOLM 2/2 (2006.01) (71) Applicant: Apple Inc., Cupertino, CA (US) HIM I/O58 (2006.01) (52) U.S. Cl. (72) Inventors: Ramesh C. Bhardwaj, Fremont, CA CPC ...... H0IM 2/1241 (2013.01); H0IM 10/058 (US); Taisup Hwang, Santa Clara, CA (2013.01) (US); Richard M. Mank, Cupertino, CA USPC ...... 429/82; 29/623.2 (US) (57) ABSTRACT The disclosed embodiments relate to a battery cell which (73) Assignee: APPLE INC., Cupertino, CA (US) includes a weakness for relieving pressure. This battery cell includes a jelly roll comprising layers which are wound together, including a cathode with an active coating, a sepa (21) Appl. No.: 13/722,734 rator and an anode with an active coating. The jelly roll also includes a first conductive tab coupled to the cathode and a second conductive tab coupled to the anode. The jelly roll is (22) Filed: Dec. 20, 2012 enclosed in a flexible pouch, wherein the first and second conductive tabs extend through seals in the pouch to provide Related U.S. Application Data terminals for the battery cell. This pouch includes a weakness (62) Division of application No. 12/622,788, filed on Nov. which yields when internal pressure in the pouch exceeds a 20, 2009. threshold to create a hole which releases the internal pressure.

TABS 103 TERRACE BATTERY SEAL CELL 104 100

SEALNG TAPE 104

SIDE SEAL 102

FOLD 108 Patent Application Publication May 9, 2013 Sheet 1 of 7 US 2013/0115491 A1

TABS 103 TERRACE BATTERY CELL 100

SEALING TAPE 104

SIDE SEAL 102

FOLD FIG. 1 108 Patent Application Publication May 9, 2013 Sheet 2 of 7 US 2013/0115491 A1

V-SHAPED

FIG. 2 Patent Application Publication May 9, 2013 Sheet 3 of 7 US 2013/0115491 A1

HALF CIRCLE 302 N

FIG. 3 Patent Application Publication May 9, 2013 Sheet 4 of 7 US 2013/0115491 A1

PATTERN OF TINY HOLES 402

FIG. 4 Patent Application Publication May 9, 2013 Sheet 5 of 7 US 2013/0115491 A1

CORNER

CUT 502

FIG. 5 Patent Application Publication May 9, 2013 Sheet 6 of 7 US 2013/0115491 A1

REGIONS ON POUCH a 602le.

FIG. 6 Patent Application Publication May 9, 2013 Sheet 7 of 7 US 2013/0115491 A1

DISPLAY 708

PROCESSOR BATTERY 702 706

MEMORY 704

PORTABLE COMPUTING DEVICE 700 FIG. 7 US 2013/01 15491 A1 May 9, 2013

PRESSURE-RELEF MECHANISMTO into a seal for the pouch; a pattern of tiny holes formed in a IMPROVE SAFETY IN LITHIUM-POLYMER seal for the pouch; and a thinned region of the pouch material. BATTERY CELLS 0011. In some embodiments, the weakness can be located on: a side seal for the pouch; a terrace seal for the pouch; a RELATED CASES corner of the pouch; a fold in the pouch material; and a 0001. The instant application is a divisional of, and hereby location on a Surface of the pouch which is not part of a seal. claims priority under 35 U.S.C. S 120 to, pending U.S. patent 0012. In some embodiments, the pouch is comprised of a application Ser. No. 12/622,788, which is titled “Pressure layer of aluminum and a layer of polypropylene. Relief Mechanism to Improve Safety in Lithium-Polymer 0013. In some embodiments, the battery cell is a lithium Battery Cells.” by Ramesh C. Bhardwaj, Taisup Hwang and polymer battery cell, or a silver-zinc battery cell. Richard M. Mank, which was filed on 20 Nov. 2009, and which is herein incorporated by reference. BRIEF DESCRIPTION OF THE FIGURES 0014 FIG. 1 illustrates a battery cell in accordance with BACKGROUND the disclosed embodiments. 0002 1. Field (0015 FIG. 2 illustrates a battery cell with V-shaped 0003. The disclosed embodiments relate to techniques for notches cut into seals for a pouch in accordance with the improving safety in rechargeable lithium-polymer battery disclosed embodiments. cells. More specifically, the disclosed embodiments relate to (0016 FIG. 3 illustrates a battery cell with half-circles cut the design of a pressure-relief mechanism which improves the into seals for a pouch in accordance with the disclosed safety in lithium-polymer battery cells. embodiments. 0004 2. Related Art 0017 FIG. 4 illustrates a battery cell with patterns of tiny 0005 Rechargeable batteries are presently used to provide holes formed in a seal for a pouch in accordance with the power to a wide variety of portable electronic devices, includ disclosed embodiments. ing laptop computers, cellphones, PDAs, digital music play 0018 FIG. 5 illustrates a battery cell including a pouch ers and cordless power tools. The most commonly used type with corner cuts in accordance with the disclosed embodi of rechargeable battery is a lithium battery, which can include mentS. a lithium-ion or a lithium-polymer battery. 0019 FIG. 6 illustrates a battery cell with weak regions 0006 A potential safety issue can arise if there is a gas formed in the pouch material inaccordance with the disclosed buildup within a rechargeable lithium battery cell. This can embodiments. occur, for example, if the cell is overcharged, if there is a short 0020 FIG. 7 illustrates a portable computing device in within the cell, or if the cell is left uncharged for a significant accordance with the disclosed embodiments. period of time. This type of gas buildup can potentially cause the battery cell to swell or even to explode, which can seri DETAILED DESCRIPTION ously damage the portable electronic device, and may even 0021. The following description is presented to enable any start a fire. person skilled in the art to make and use the disclosed 0007 To alleviate this problem, cylindrical lithium-ion embodiments, and is provided in the context of a particular battery cells are often equipped with a vent valve to release application and its requirements. Various modifications to the the internal pressure in the battery cell when a gas buildup disclosed embodiments will be readily apparent to those occurs. However, there exist no comparable pressure-relief skilled in the art, and the general principles defined herein mechanisms for lithium-polymer batteries, which are becom may be applied to other embodiments and applications with ing increasingly popular in portable electronic devices. A out departing from the spirit and scope of the disclosed lithium-polymer battery is typically enclosed in a flexible embodiments. Thus, the disclosed embodiments are not lim pouch, which is lightweight and inexpensive to manufacture. ited to the embodiments shown, but are to be accorded the However, no pressure-relief mechanism has been developed widest scope consistent with the principles and features dis for these pouches so far. closed herein. 0022. The data structures and code described in this SUMMARY detailed description are typically stored on a computer-read 0008. The disclosed embodiments relate to a battery cell able storage medium, which may be any device or medium which includes a weakness for relieving pressure. This bat that can store code and/or data for use by a computer system. tery cell includes a jelly roll comprising layers which are The computer-readable storage medium includes, but is not wound together, including a cathode with an active coating, a limited to, Volatile memory, non-volatile memory, magnetic separator, and an anode with an active coating. The jelly roll and optical storage devices Such as disk drives, magnetic tape, also includes a first conductive tab coupled to the cathode and CDs (compact discs), DVDs (digital versatile discs or digital a second conductive tab coupled to the anode. The jelly roll is Video discs), or other media capable of storing code and/or enclosed in a flexible pouch, wherein the first and second data now known or later developed. conductive tabs extend through seals in the pouch to provide 0023 The methods and processes described in the detailed terminals for the battery cell. This pouch includes a weakness description section can be embodied as code and/or data, which yields when internal pressure in the pouch exceeds a which can be stored in a computer-readable storage medium threshold to create a hole which releases the internal pressure. as described above. When a computer system reads and 0009. In some embodiments, the pouch includes multiple executes the code and/or data stored on the computer-read weaknesses at different locations on the pouch. able storage medium, the computer system performs the 0010. In some embodiments, the weakness can include: a methods and processes embodied as data structures and code V-shaped notch cut into a seal for the pouch; a half-circle cut and stored within the computer-readable storage medium. US 2013/01 15491 A1 May 9, 2013

Furthermore, the methods and processes described below can pouch; a terrace seal for the pouch; a corner of the pouch; a be included in hardware modules. For example, the hardware fold in the pouch material; and any location on a Surface of the modules can include, but are not limited to, application-spe pouch which is not part of a seal. Moreover, although a cific integrated circuit (ASIC) chips, field-programmable number of different types of weaknesses are illustrated in gate arrays (FPGAs), and other programmable-logic devices FIGS. 2-6, in general any type of weakness which yields to now known or later developed. When the hardware modules internal pressure in the battery cell can be used by the dis are activated, the hardware modules perform the methods and closed embodiments. processes included within the hardware modules. Computing Device Battery Cell 0031. The above-described rechargeable battery cell can 0024 FIG. 1 illustrates a battery cell 100 in accordance generally be used in any type of electronic device. For with the disclosed embodiments. Battery cell 100 includes a example, FIG. 7 illustrates a portable computing device 700 jelly roll 101 comprising a number of layers which are wound which includes a processor 702, a memory 704 and a display together, including a cathode with an active coating, a sepa 708, which are all powered by a battery 706. Battery 706 rator, and an anode with an active coating. Jelly rolls are well comprises a battery pack, which includes multiple battery known in the art and will not be described further. During cells that are coupled together in series and/or in parallel. assembly of battery cell 100, jelly roll 101 is enclosed in a 0032. The foregoing descriptions of embodiments have flexible pouch, which is formed by folding a flexible sheet been presented for purposes of illustration and description along a fold line 108. For example, the flexible sheet can be only. They are not intended to be exhaustive or to limit the comprised of aluminum with a polymer film, Such as polypro present description to the forms disclosed. Accordingly, pylene. After the flexible sheet is folded, the flexible sheet can many modifications and variations will be apparent to prac be sealed, for example by applying heat along side seals 102 titioners skilled in the art. Additionally, the above disclosure and along a terrace seal 104. is not intended to limit the present description. The scope of 0025. Note that jelly roll 101 includes conductive tabs 103 the present description is defined by the appended claims. coupled to the cathode and the anode. These conductive tabs What is claimed is: 103 extend through seals in the pouch (for example, formed 1. A battery cell with a weakness for relieving pressure, using sealing tape 104) to provide terminals for battery cell comprising: 1OO. a jelly roll comprising layers which are wound together, 0026. Also note that a battery pack can be formed by including a cathode with an active coating, a separator, coupling together a number of such battery cells: in series, in and an anode with an active coating: parallel, or both in series and in parallel. The coupled cells can a pouch, which encloses the jelly roll, wherein the pouch is then be enclosed in a hard case. flexible; a first conductive tab coupled to the cathode; and Battery Cell Including a Weakness a second conductive tab coupled to the anode, wherein the first and second conductive tabs extend 0027. As mentioned above, a gas buildup can potentially through seals in the pouch to provide terminals for the occur within battery cell 100 if: battery cell 100 is over battery cell; and charged; there is a short within battery cell 100; or battery cell wherein the pouch includes a weakness which yields when 100 is left uncharged for a significant period of time. This gas internal pressure in the pouch exceeds a threshold to buildup can potentially cause the battery cell to swell or even create a hole which releases the internal pressure. explode. To deal with this problem, the pouch includes one or 2. The battery cell of claim 1, wherein the pouch includes more preformed weaknesses which yield when internal pres multiple weaknesses at different locations on the pouch. sure in the pouch exceeds a threshold value to create a hole 3. The battery cell of claim 1, wherein the weakness which releases the internal pressure. includes one of 0028. There are a number of different ways to create such a weakness. For example, a number of V-shaped notches, a corner of the pouch which is cut; including V-shaped notch 202, can be cut into the seals for the a pattern of tiny holes formed in a seal for the pouch; and pouch as is illustrated in FIG. 2. These V-shaped notches can a thinned region of the pouch material. be cut using some type of cutting tool after the pouch is 4. The battery cell of claim 1, wherein the weakness is formed. Alternatively, a number half-circles, including half located on one of: circle 302, can be cut into the seals for the pouch as is illus a side seal for the pouch; trated in FIG. 3. In yet another embodiment which is illus a terrace seal for the pouch; trated in FIG. 4, instead of cutting notches in the seals, a corner of the pouch; weaknesses can be created by forming a pattern of tiny holes a fold in the pouch material; and 402 in the seals. a location on a Surface of the pouch which is not part of a 0029 Weaknesses can also be formed at other locations on seal. the battery cell pouch. For example, FIG. 5 illustrates a bat 5. The battery cell of claim 1, wherein the pouch is com tery cell having a pouch with weaknesses which are formed as prised of: corner cuts 502. Alternatively, FIG. 6 illustrates a battery cell a layer of aluminum; and with weak regions 602 which are formed at various locations a layer of polypropylene. on the pouch material. These weak regions 602 can be 6. The battery cell of claim 1, wherein the battery cell is one formed, for example, by thinning the pouch material. of: 0030. In general, such weaknesses can be formed at any a lithium-polymer battery cell; and location on the battery pouch, including at: a side seal for the a silver-zinc battery cell. US 2013/01 15491 A1 May 9, 2013

7. A battery pack comprising one or more battery cells wherein the first and second conductive tabs extend coupled together and enclosed in a hard case, wherein each of through seals in the pouch to provide terminals for the the one or more battery cells includes: battery cell; and a jelly roll comprising layers which are wound together, wherein the pouch includes a weakness which yields including a cathode with an active coating, a separator, when internal pressure in the pouch exceeds a thresh and an anode with an active coating: old to create a hole which releases the internal pres a pouch, which encloses the jelly roll, wherein the pouch is S. flexible; 15. The portable computing device of claim 14, wherein a first conductive tab coupled to the cathode; and the portable device includes one of: a second conductive tab coupled to the anode: a laptop or notebook computer system; wherein the first and second conductive tabs extend a personal digital assistant; and through seals in the pouch to provide terminals for the a cellular telephone. battery cell; and 16. A method for assembling a battery cell, comprising: wherein the pouch includes a weakness which yields when obtaining a jelly roll comprising layers which are wound internal pressure in the pouch exceeds a threshold to together, including a cathode with an active coating, a create a hole which releases the internal pressure. separator, and an anode with an active coating, wherein 8. The battery pack of claim 7, wherein the one or more the jelly roll includes a first conductive tab coupled to the battery cells are coupled together: cathode and a second conductive tab coupled to the in series; anode; in parallel; or obtaining a pouch to accommodate the jelly roll, wherein in series and parallel. the pouch is flexible; and 9. The battery pack of claim 7, wherein each pouch sealing the jelly roll in the pouch, wherein the pouch is includes multiple weaknesses at different locations on the sealed so that the first and second conductive tabs extend pouch. through seals in the pouch to provide terminals for the 10. The battery pack of claim 7, wherein the weakness battery cell; includes one of wherein the pouch includes or is configured to include one a corner of the pouch which is cut; or more weaknesses, which yield when internal pressure a pattern of tiny holes formed in a seal for the pouch; and in the pouch exceeds a threshold to create a hole which a thinned region of the pouch material. releases the internal pressure. 11. The battery pack of claim 7, wherein the weakness is 17. The method of claim 16, wherein the weakness in the located on one of: pouch is created: a side seal for the pouch; prior to sealing the jelly roll in the pouch; or a terrace seal for the pouch; after sealing the jelly roll in the pouch. a corner of the pouch; 18. The method of claim 16, wherein creating the weakness a fold in the pouch material; and in the pouch involves creating multiple weaknesses at differ a location on a Surface of the pouch which is not part of a ent locations on the pouch. seal. 19. The method of claim 16, wherein the weakness 12. The battery pack of claim 7, wherein the pouch is includes one of comprised of: a corner of the pouch which is cut; a layer of aluminum; and a pattern of tiny holes formed in a seal for the pouch; and a layer of polypropylene, a thinned region of the pouch material. 13. The battery pack of claim 7, wherein each battery cell 20. The method of claim 16, wherein the weakness is is one of located on one of: a lithium-polymer battery cell; and a side seal for the pouch; a silver-zinc battery cell. a terrace seal for the pouch; 14. A portable computing device, comprising: a corner of the pouch; a processor; a fold in the pouch material; and a memory; and a location on a Surface of the pouch which is not part of a a battery pack, which includes one or more battery cells seal. coupled together, 21. The method of claim 16, wherein the pouch is com wherein each of the one or more battery cells includes: prised of: a jelly roll comprising layers which are wound together, a layer of aluminum; and including a cathode with an active coating, a separa a layer of polypropylene, tor, and an anode with an active coating: 22. The method of claim 16, wherein the battery cell is one a pouch, which encloses the jelly roll, wherein the pouch of: is flexible: a lithium-polymer battery cell; and a first conductive tab coupled to the cathode; and a silver-zinc battery cell. a second conductive tab coupled to the anode: k k k k k