PATENT DOCUMENT

Publication Number: US-11489211-B2
Application Number: US-202016739457-A
Country: US
Kind Code: B2

Title: Asymmetric battery pack with varied electrode and current collector properties to achieve C-Rate balancing

Abstract:
Battery packs having jelly roll battery cells of different designs or capacities may have an imbalance in the charging and/or discharging current supplied to and provided by each jelly roll due to differences in capacity specific impedance between the battery cells of the battery pack. A C-rate (i.e., current relative to rated capacity) of a first and second battery cell connected in parallel may be balanced by altering properties of an active layer and/or a thickness of a current collector of the second battery cell to reduce an impedance of the second battery cell.

Claims:
What is claimed is: 
     
       1. A battery pack, comprising:
 a first battery cell, the first battery cell comprising a wound set of layers comprising a cathode layer, an anode layer, and a separator layer disposed between the cathode layer and the anode layer; 
 a second battery cell connected in parallel with the first battery cell, the second battery cell comprising a wound set of layers comprising a cathode layer, an anode layer, and a separator layer disposed between the cathode layer and the anode layer;
 wherein the cathode layer of the first battery cell comprises a first active layer coated on a first current collector, the first current collector having a first thickness; and 
 wherein the cathode layer of the second battery cell comprises a second active layer coated on a second current collector, the second current collector having a second thickness that is greater than the first thickness to reduce an impedance of the second battery cell and balance a C-rate of the second battery cell with a C-rate of the first battery cell. 
 
 
     
     
       2. The battery pack of  claim 1 , wherein an in-plane impedance of the second current collector of the cathode layer of the second battery cell is less than an in-plane impedance of the first current collector of the cathode layer of the first battery cell. 
     
     
       3. The battery pack of  claim 1 , wherein the second active layer of the cathode layer of the second battery cell has a thickness that is less than a thickness of the first active layer of the cathode layer of the first battery cell. 
     
     
       4. The battery pack of  claim 3 , wherein a thru-plane impedance of the second active layer of the cathode layer of the second battery cell is less than a thru-plane impedance of the first active layer of the cathode layer of the first battery cell. 
     
     
       5. The battery pack of  claim 1 , wherein the anode layer of the second battery cell comprises a current collector having a thickness that is greater than a thickness of a current collector of the anode layer of the first battery cell. 
     
     
       6. The battery pack of  claim 5 , wherein an in-plane impedance of the current collector of the anode layer of the second battery cell is less than an in-plane impedance of the current collector of the anode layer first battery cell. 
     
     
       7. The battery pack of  claim 1 , wherein the anode layer of the second battery cell comprises an active layer having a thickness that is less than a thickness of an active layer of the anode layer of the first battery cell. 
     
     
       8. The battery pack of  claim 7 , wherein a thru-plane impedance of the active layer of the anode layer of the second battery cell is less than a thru-plane impedance of the active layer of the anode layer first battery cell. 
     
     
       9. The battery pack of  claim 1 , wherein the first battery cell has a first capacity and the second battery cell has a second capacity that is greater than the first capacity. 
     
     
       10. The battery pack of  claim 1 , wherein the first battery cell further comprises a first battery design with a first capacity; and
 the second battery cell further comprises a second battery design with a second capacity, wherein the second battery design is different than the first battery design and the second capacity is the same as the first capacity.

Description:
PRIORITY 
     This application claims the benefit under 35 U.S.C. § 119(e) of U.S. Provisional Patent Application Ser. No. 62/864,085, entitled “ASYMMETRIC BATTERY PACK WITH VARIED ELECTRODE AND CURRENT COLLECTOR PROPERTIES TO ACHIEVE C-RATE BALANCING,” filed on Jun. 20, 2019, which is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to battery cells, and more particularly, to a battery pack having varied electrode and/or current collector properties to achieve C-Rate balancing. 
     BACKGROUND 
     A jelly roll battery cell includes wound layers of a cathode and an anode, with tabs extending from each to enable electrical connection to the cathode and anode layers. Jelly rolls having higher capacities typically require longer and/or wider cathode and anode layers compared to jelly rolls with lower capacities. Connecting two or more jelly rolls in parallel where the jelly rolls have differing capacities, may result in an imbalance in the charging and/or discharging current supplied to and provided by each jelly roll. In addition, jelly rolls connected in parallel that each have a differing battery cell design (e.g., differing electrode shape among two or more jelly rolls) but substantially equal capacities, may nonetheless have an imbalance in the charging and/or discharging current supplied to and provided by each jelly roll due to differences in their impedance. 
     In such instances, it may be desirable to balance a C-Rate (i.e., current relative to rated capacity) of connected battery cells by minimizing the difference in capacity specific impedance (“QSI”). In other words, the charging and discharging current is split in proportion to the respective capacity of each connected battery cell. Specifically, because jelly rolls connected in parallel share the same charge and discharge voltage, a voltage drop of each jelly roll should be made equal, i.e., ΔV=I i Z i =I j Z j  . . . =I n  Z n , where “I” is the load or current in amperes and “Z” is impedance. With C-Rate balancing, the QSI of each jelly roll should be made equal, i.e., QSI=Q i Z i =Q j Z j  . . . =Q n Z n , where “Q” is the capacity and “Z” is impedance. The QSI for a particular jelly roll is a function of electrode length and/or width because the longer and/or wider an electrode, the larger the QSI. Generally speaking, QSI can be considered to be the sum of in-plane (such as current collector resistance) and thru-plane QSI contributions such as charge transfer and electrolyte impedance. Thru-plane QSI is expected to be balanced (equal) between two jelly rolls with same electrode properties such as active layer thickness, but in-plane QSI will vary with current collector length and/or width (among the two, length often affects in-plane QSI much more than width). 
     SUMMARY 
     The disclosed embodiments provide for a battery pack that utilizes C-Rate balancing by reducing an impedance of a battery cell to balance a C-Rate of the battery pack. The battery pack includes a first battery cell having a wound set of layers comprising a cathode layer, an anode layer, and a separator layer disposed between the cathode layer and the anode layer. The battery pack also includes a second battery cell connected in parallel with the first battery cell. The second battery cell includes a wound set of layers comprising a cathode layer, an anode layer, and a separator layer disposed between the cathode layer and the anode layer. The cathode layer of the first battery cell has a first active layer coated on a first current collector. The first current collector having a first thickness. The cathode layer of the second battery cell has a second active layer coated on a second current collector. The second current collector having a second thickness that is greater than the first thickness to reduce an impedance of the second battery cell and balance a C-rate of the second battery cell with a C-rate of the first battery cell. 
     The disclosed embodiments provide for a battery pack that utilizes C-Rate balancing by reducing an impedance of a battery cell to balance a C-Rate of the battery pack. The battery pack includes a first battery cell having a wound set of layers comprising a cathode layer, an anode layer, and a separator layer disposed between the cathode layer and the anode layer. The battery pack also includes a second battery cell connected in parallel with the first battery cell. The second battery cell includes a wound set of layers comprising a cathode layer, an anode layer, and a separator layer disposed between the cathode layer and the anode layer. The anode layer of the first battery cell has a first active layer coated on a first current collector. The first current collector has a first thickness. The anode layer of the second battery cell has a second active layer coated on a second current collector. The second current collector has a second thickness that is greater than the first thickness to reduce an impedance of the second battery cell and balance a C-rate of the second battery cell with a C-rate of the first battery cell. 
     In some embodiments, a method for balancing a C-rate of an asymmetric battery pack is disclosed. The method includes packaging a first jelly roll battery cell and a second jelly roll battery cell into a battery pack. The method further includes balancing a C-rate of the second jelly roll battery cell with a C-rate of the first jelly roll battery cell by increasing a thickness of a current collector of a cathode layer of the second jelly roll battery cell to reduce an impedance of the second jelly roll battery cell. The method also includes connecting the first jelly roll battery cell and the second jelly roll battery cell in parallel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The embodiments herein may be better understood by referring to the following description in conjunction with the accompanying drawings in which like reference numerals indicate identical or functionally similar elements. Understanding that these drawings depict only exemplary embodiments of the disclosure and are not therefore to be considered to be limiting of its scope, the principles herein are described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
         FIG. 1A  illustrates a perspective view of a battery pack, in accordance with various aspects of the subject technology; 
         FIG. 1B  illustrates a perspective view of a battery pack, in accordance with various aspects of the subject technology; 
         FIG. 2A  illustrates a cross-section view of a battery cell, in accordance with various aspects of the subject technology; 
         FIG. 2B  illustrates a cross-section view of a battery cell, in accordance with various aspects of the subject technology; 
         FIG. 3A  illustrates a detailed view of an electrode, in accordance with various aspects of the subject technology; 
         FIG. 3B  illustrates a detailed view of an electrode, in accordance with various aspects of the subject technology; 
         FIG. 3C  illustrates a detailed view of an electrode, in accordance with various aspects of the subject technology; 
         FIG. 3D  illustrates a detailed view of an electrode, in accordance with various aspects of the subject technology; 
         FIG. 4  illustrates a portable electronic device, in accordance with various aspects of the subject technology; and 
         FIG. 5  illustrates an example method for balancing a C-rate of an asymmetric battery pack, in accordance with various aspects of the subject technology. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments of the disclosure are discussed in detail below. While specific implementations are discussed, it should be understood that this is done for illustration purposes only. A person skilled in the relevant art will recognize that other components and configurations may be used without parting from the spirit and scope of the disclosure. 
     A jelly roll battery cell includes wound layers of a cathode and an anode, with tabs extending from each to enable electrical connection to the cathode and anode layers. Jelly rolls having higher capacities typically require longer and/or wider cathode and anode layers compared to jelly rolls with lower capacities. Connecting two or more jelly rolls in parallel with each jelly roll having a different capacity, may result in the higher capacity jelly roll having an increased in-plane QSI compared to the lower capacity jelly roll due to the increased length and/or width of an active layer disposed on the current collectors of the higher capacity jelly roll. Further, jelly rolls connected in parallel that each have a differing battery cell design (e.g., differing electrode shape among two or more jelly rolls) but substantially equal capacities, may nonetheless have an imbalance in the charging and/or discharging current supplied to and provided by each jelly roll due to differences in their in-plane QSI. Generally, the longer the electrode length, or wider the electrode width, the higher the in-plane QSI. Jelly rolls having a significant difference in capacity and/or QSI that are connected in parallel, may result in an imbalance in the charging and/or discharging current supplied to and provided by each jelly roll. An imbalance may lead to a lower QSI jelly roll consuming a larger proportion of a charging C-Rate of the battery pack. C-Rate or QSI imbalance may lead to a lower QSI jelly roll battery cell to be charged at a higher C-Rate to cause reduced anode potential thereby triggering Li-plating. Moreover, the lower QSI jelly roll battery cell will charge faster and consequently spend more charge time at a high state of charge to cause higher cell impedance growth while waiting for the larger QSI battery cell to be fully charged. The end result is that the lower QSI battery cell will fail sooner. Accordingly, there is a need for certain embodiments of a battery pack having jelly rolls of different capacities, shapes, and/or designs that have the same C-Rate to enable the jelly rolls of the battery pack to split the charging and discharging current in proportion to their respective capacities or impedances to prevent premature failure. 
     The disclosed technology addresses the foregoing limitations of conventional asymmetric battery packs by balancing a C-Rate of a higher capacity jelly roll with a C-Rate of a lower capacity jelly roll by altering properties of an active layer and/or thickness of a current collector to adjust an impedance or QSI of the jelly rolls to thereby balance a C-Rate of the jelly rolls. The disclosed technology further addresses the foregoing limitations of conventional asymmetric battery packs that comprise battery cells connected in parallel that each have a differing battery cell design (e.g., differing electrode shape among two or more battery cells) but substantially equal capacities, by altering properties of an active layer and/or thickness of a current collector to adjust an impedance of the jelly rolls to thereby balance a C-Rate of the battery cells. C-Rate balancing allows battery cells connected in parallel to be charged and discharged at the same C-Rate. In other words, the charging and discharging current is split in proportion to the respective capacity of each connected battery cell. Specifically, because jelly rolls connected in parallel share the same charge and discharge voltage, a voltage drop of each jelly roll should be made equal. With C-Rate balancing, the QSI of each jelly roll is made equal. The in-plane QSI contribution for a particular jelly roll is a function of electrode length, width or current collector thickness because the longer, wider an electrode or the thinner the current collector, the higher the in-plane QSI. The thru-plane QSI contribution for a particular jelly roll is a function of electrode properties including active layer thickness and density because the thinner or more porous an active layer, the lower the thru-plane QSI due to reduced electrolyte impedance. 
       FIGS. 1A and 1B  illustrate perspective views of a battery pack  100 , in accordance with various aspects of the subject technology. The battery pack  100  includes a first jelly roll  120  and a second jelly roll  130  connected in parallel, enclosed in an enclosure  110 . The first jelly roll  120  may have a lower capacity compared to the second jelly roll  130 . As a result, the first jelly roll  120  may be formed of electrodes (e.g., a cathode and an anode layer) that have a length that is less than a length of electrodes of the second jelly roll  130 . The first jelly roll  120  may therefore have a smaller width and/or thickness “t” compared to a width and/or thickness “T” of the second jelly roll  130  based on the number of windings in each of the first and second jelly rolls,  120  and  130  respectively. Each of the first and second jelly rolls,  120  and  130  respectively, may have tabs extending from their respective electrodes disposed at an end of the electrodes of each of the first and second jelly rolls,  120  and  130  respectively. Because the first and second jelly rolls,  120  and  130  respectively, have different electrode length and/or width, the QSI of the second jelly roll  130  would have been higher than the QSI of the first jelly roll  120  if not otherwise modified, as discussed further below with reference to  FIGS. 3A-3D . 
     As shown in  FIG. 1A , the first and second jelly rolls,  120  and  130  respectively, may be arranged in a side-by-side configuration. Referring to  FIG. 1B , the first and second jelly rolls,  120  and  130  respectively, may be arranged in a stacked configuration. Other arrangements and battery pack  100  configurations are contemplated without departing from the scope of the subject technology. 
     It is also understood that the battery pack  100  may comprise a first battery cell  120  and a second battery cell  130  connected in parallel, each having the same capacity. The second battery cell  130 , however, may have a higher impedance than the first battery cell  120  based on a different battery cell design for the second battery cell  130 . For example, the second battery cell  130  may have a length that is 2× longer than a length of the first battery cell  120 , and the second battery cell  130  may have a width that is ½ narrower than a width of the first battery cell  120 . Each of the first and second battery cells,  120  and  130  respectively, may therefore, have a substantially equal surface area (A=L*W) and thus, have a substantially equal capacity, but with an impedance imbalance if not otherwise modified, as discussed further below with reference to  FIGS. 3A-3D . In this example, because the second battery cell  130  has a length that substantially greater than the length of the first battery cell  120 , the impedance of the second battery cell  130  would have been greater due to larger in-plane impedance than the impedance of the first battery cell  120 . It is also understood that the first battery cell  120  and the second battery cell  130  may each comprise a stacked cell connected in parallel and having an impedance imbalance, or one of a stacked cell and a jelly roll cell connected in parallel and having an impedance imbalance, without departing from the scope of the subject technology. 
       FIG. 2A  illustrates a cross-section view of the first battery cell  120 , in accordance with various aspects of the subject technology. The first battery cell  120  may comprise a wound set of layers comprising a cathode layer  210 A, an anode layer  220 A, a first separator layer  230 A disposed between the cathode layer  210 A and the anode layer  220 A, and a second separator layer  240 A disposed between the anode layer  220 A and the cathode layer  210 A. Proximate to or at a first end of the cathode layer  210 A and the anode layer  220 A of the first battery cell  120 , a first cathode tab  215 A may extend from the cathode layer  210 A, and a first anode tab  225 A may extend from the anode layer  220 A. 
       FIG. 2B  illustrates a cross-section view of the second battery cell  130 , in accordance with various aspects of the subject technology. The second battery cell  130  may comprise a wound set of layers comprising a cathode layer  210 B, an anode layer  220 B, a first separator layer  230 B disposed between the cathode layer  210 B and the anode layer  220 B, and a second separator layer  240 B disposed between the anode layer  220 B and the cathode layer  210 B. The second battery cell  130  further comprises a first cathode tab  215 B extending from the cathode layer  210 B, and a first anode tab  225 B extending from the anode layer  220 B. 
       FIGS. 3A-3D  illustrate detailed views of an electrode, in accordance with various aspects of the subject technology. The electrode may comprise the cathode layer  210 A,B or the anode layer  220 A,B. Each of the cathode layer  210 A,B and the anode layer  220 A,B may comprise an active layer  310  disposed or coated on a current collector  320 . For the cathode layer  210 A, B, the active layer  310  may comprise a lithium compound (e.g., LiCoO 2 , LiFePO 4 , Li(NiMnCo)O 2 , LiMnO 4 , Li 2 FeP 2 O 7 ). For the anode layer  220 A, B, the active layer  310  may comprise carbon or graphite, or other materials such as silicon, lithium titanium oxide, tin, phosphorus, or lithium metal. For the cathode layer  210 A, B, the current collector  320  may comprise an aluminum foil. For the anode layer  220 A, B, the current collector  320  may comprise a copper foil. 
     The separator  230 A,B and  240 A,B may include polyethylene (PE), polypropylene (PP), and/or a combination of PE and PP, such as PE/PP or PP/PE/PP. The wound set of layers are enclosed within the enclosure  110  and immersed in an electrolyte, which for example, can be a LiPF6-based electrolyte that can include Ethylene Carbonate (EC), Polypropylene Carbonate (PC), Ethyl Methyl Carbonate (EMC) or DiMethyl Carbonate (DMC). The electrolyte can also include additives such as Vinyl carbonate (VC) or Polyethylene Soltone (PS). The electrolyte can additionally be in the form of a solution or a gel. 
     In one aspect, properties of the active layer  310  may be altered to modify an impedance (e.g., thru-plane impedance) of the active layer  310 . The properties of the active layer  310  that may be modified include porosity, density, thickness, particle size and size distribution, process orientation, material properties and ratio between active material, conductive additives, and adhesion additives. For example, an impedance of an electrode may be reduced by reducing a thickness of the active layer  310 . Conversely, an impedance of an electrode may be increased by increasing a thickness of the active layer  310 . 
     In another aspect, properties of the current collector  320  may be altered to modify an impedance of the current collector  320 . The properties of the current collector  320  that may be modified include thickness, surface morphology, roughness, hydrophobicity (water contact angle), or whether there is an additional thin carbon coating layer or not. For example, an impedance of an electrode may be reduced by increasing a thickness of the current collector  320 . Conversely, an impedance of an electrode may be increased by reducing a thickness of the current collector  320 . 
     Referring to  FIG. 3A , an initial thickness D 0  of the active layer  310  of the second battery cell  130  may be reduced to a thickness D 1  in order to reduce the thru-plane impedance of the cathode layer  210 B and/or anode layer  220 B of the second battery cell  130  and to balance a C-rate of the second battery cell  130  with a C-rate of the first battery cell  120 . To maintain the rated capacity of the second battery cell  130 , however, electrode length or width may need to increase. This may cause an increase in in-plane impedance and may partially cancel out a reduction of thru-plane impedance. As one example, for a baseline thickness D 0  of the active layer  310  of 50 μm for the cathode layer  210 B and 60 μm for the anode layer  220 B, reducing the thickness to D 1  for both the cathode layer  210 B and the anode layer  220 B to about 25 μm will result in a reduction of thru-plane impedance of about 50%, but in-plane impedance may also increase—less so on a change of width and more on a change of length due to doubling of the total electrode area to maintain the same rated capacity. Other values and ranges for the reduced thickness D 1  are contemplated and are within the scope of the subject technology. 
     In one aspect, the thickness D 1  of the active layer  310  of the cathode layer  210 B and/or anode layer  220 B of the second battery cell  130  may be less than a thickness of the active layer  310  of the cathode layer  210 A and/or anode layer  220 A of the first battery cell  120 . In another aspect, because the second battery cell  130  has a higher capacity or a greater length or width when compared to the first battery cell  120 , reduction of the thickness of the active layer  310  (e.g., cathode layer  210 B and/or anode layer  220 B) of the second battery cell  130  reduces a thru-plane impedance of the second battery cell  130  in order to balance the C-rate of the second battery cell  130  with the C-rate of the first battery cell  120 . As such, despite the second battery cell  130  having a higher capacity or QSI compared to the first battery cell  120 , the QSI of the second battery cell  130  may be reduced compared to a conventional battery cell due to the reduced thickness of the active layer  310 , thereby enabling splitting of a charging or discharging current in proportion to the respective capacities of the first battery cell  120  and the second battery cell  130 . 
     For example, the first battery cell  120  may have a capacity of 1,000 mAh and an impedance of 200 milli-ohms, and the second battery cell  130  may have a capacity of 2,000 mAh and a reduced impedance of 100 milli-ohms due to the active layer  310  of the cathode layer  210 B and/or anode layer  220 B of the second battery cell  130  having a reduced thickness D 1 . 
     Referring to  FIG. 3B , an initial thickness d 0  of the current collector  320  of the second battery cell  130  may be increased to a thickness d 1  in order to reduce in-plane impedance of the cathode layer  210 B and/or anode layer  220 B of the second battery cell  130  and to balance a C-rate of the second battery cell  130  with a C-rate of the first battery cell  120 . As one example, for a baseline thickness d 0  of 10 μm for the current collector  320  of the cathode layer  210 B and/or anode layer  220 B of the second battery cell  130 , an increased thickness d 1  in a range of about 15 μm to 25 μm for the cathode layer  210 B and/or anode layer  220 B, results in reducing in-plane impedance by about 50%. In another example, the thickness d 1  may be about 20 μm. Other values and ranges for the increased thickness d 1  are contemplated and are within the scope of the subject technology. 
     In one aspect, the thickness d 1  of the current collector  320  of the cathode layer  210 B and/or anode layer  220 B of the second battery cell  130  may be greater than a thickness of the current collector  320  of the cathode layer  210 A and/or anode layer  220 A of the first battery cell  120 . In another aspect, because the second battery cell  130  has a higher capacity or a greater length or width when compared to the first battery cell  120 , increase of the thickness of the current collector  320  (e.g., cathode layer  210 B and/or anode layer  220 B) of the second battery cell  130  reduces an impedance of the second battery cell  130  in order to balance the C-rate of the second battery cell  130  with the C-rate of the first battery cell  120 . As such, despite the second battery cell  130  having a higher capacity compared to the first battery cell  120 , the QSI of the second battery cell  130  may be reduced compared to a conventional battery cell due to the increased thickness of the current collector  320 , thereby enabling splitting of a charging or discharging current in proportion to the respective capacities of the first battery cell  120  and the second battery cell  130 . 
     For example, the first battery cell  120  may have a capacity of 1,000 mAh and an impedance of 200 milli-ohms, and the second battery cell  130  may have a capacity of 2,000 mAh and a reduced impedance of 100 milli-ohms due to the current collector  320  of the cathode layer  210 B and/or anode layer  220 B of the second battery cell  130  having an increased thickness d 1 . 
     It is also understood that the second battery cell  130  may have both a decreased thickness D 1  of the active layer  310  and an increased thickness d 1  of the current collector  320  in order to reduce an impedance of the cathode layer  210 B and/or anode layer  220 B of the second battery cell  130  and to balance a C-rate of the second battery cell  130  with a C-rate of the first battery cell  120 . 
     Referring to  FIG. 3C , an initial thickness D 0  of the active layer  310  of the first battery cell  120  may be increased to a thickness D 2  in order to increase the thru-plane impedance of the cathode layer  210 A and/or anode layer  220 A of the first battery cell  120  and to balance a C-rate of the first battery cell  120  with a C-rate of the second battery cell  130 . To maintain the rated capacity of the first battery cell  120 , however, electrode length or width may need to be reduced. This may cause a moderate decrease in in-plane impedance and may partially cancel out an increase in thru-plane impedance. In one example, for a baseline thickness D 0  of the active layer  310  of 50 μm for the cathode layer  210 A and 60 μm for the anode layer  220 A, doubling the thickness to D 2  for both the cathode layer  210 A and the anode layer  220 A will increase thru-plane impedance by about 100%, and in-plane impedance will decrease slightly due to reduced electrode length and/or electrode width to maintain the same rated capacity. In another example, the thickness D 2  may be about 50 μm. Other values and ranges for the increased thickness D 2  are contemplated and are within the scope of the subject technology. 
     In one aspect, the thickness D 2  of the active layer  310  of the cathode layer  210 A and/or anode layer  220 A of the first battery cell  120  may be greater than a thickness of the active layer  310  of the cathode layer  210 B and/or anode layer  220 B of the second battery cell  130 . In another aspect, because the first battery cell  120  has a lower capacity or a shorter length or width when compared to the second battery cell  130 , increase of the thickness of the active layer  310  (e.g., cathode layer  210 A and/or anode layer  220 A) of the first battery cell  120  increases an impedance of the first battery cell  120  in order to balance the C-rate of the first battery cell  120  with the C-rate of the second battery cell  130 . As such, despite the first battery cell  120  having a lower capacity (and normally a lower impedance) compared to the second battery cell  130 , the impedance of the first battery cell  120  may be increased compared to a conventional battery cell due to the increased thickness of the active layer  310 , thereby enabling splitting of a charging or discharging current in proportion to the respective capacities of the first battery cell  120  and the second battery cell  130 . 
     For example, the first battery cell  120  may have a capacity of 1,000 mAh and an increased impedance of 400 milli-ohms due to the active layer  310  of the cathode layer  210 A and/or anode layer  220 A of the first battery cell  120  having an increased thickness D 2 , and the second battery cell  130  may have a capacity of 2,000 mAh and an impedance of 200 milli-ohms. 
     Referring to  FIG. 3D , an initial thickness d 0  of the current collector  320  of the first battery cell  120  may be reduced to a thickness d 2  in order to increase an in-plane impedance of the cathode layer  210 A and/or anode layer  220 A of the first battery cell  120  and to balance a C-rate of the first battery cell  120  with a C-rate of the second battery cell  130 . As one example, for a baseline thickness d 0  of 10 μm for the current collector  320  of the cathode layer  210 A and/or anode layer  220 A of the first battery cell  120 , a reduced thickness d 2  of about 5 μm for the cathode layer  210 A and/or anode layer  220 A, results in increasing in-plane impedance by about 100%. Other values and ranges for the reduced thickness d 2  are contemplated and are within the scope of the subject technology. 
     In one aspect, the thickness d 2  of the current collector  320  of the cathode layer  210 A and/or anode layer  220 A of the first battery cell  120  may be less than a thickness of the current collector  320  of the cathode layer  210 B and/or anode layer  220 B of the second battery cell  130 . In another aspect, because the first battery cell  120  has a lower capacity or a shorter length or width when compared to the second battery cell  130 , reduction of the thickness of the current collector  320  (e.g., cathode layer  210 A and/or anode layer  220 A) of the first battery cell  120  increases an impedance of the first battery cell  120  in order to balance the C-rate of the first battery cell  120  with the C-rate of the second battery cell  130 . As such, despite the first battery cell  120  having a lower capacity (and normally a lower impedance) compared to the second battery cell  130 , the QSI of the first battery cell  120  may be increased compared to a conventional battery cell due to the reduced thickness of the current collector  320 , thereby enabling splitting of a charging or discharging current in proportion to the respective capacities of the first battery cell  120  and the second battery cell  130 . 
     For example, the first battery cell  120  may have a capacity of 1,000 mAh and an increased impedance of 400 milli-ohms due to the current collector  320  of the cathode layer  210 A and/or anode layer  220 A of the first battery cell  120  having a reduced thickness d 2 , and the second battery cell  130  may have a capacity of 2,000 mAh and an impedance of 200 milli-ohms. 
     It is also understood that the first battery cell  120  may have both an increased thickness D 2  of the active layer  310  and a decreased thickness d 2  of the current collector  320  in order to increase an impedance of the cathode layer  210 A and/or anode layer  220 A of the first battery cell  120  and to balance a C-rate of the first battery cell  120  with a C-rate of the second battery cell  130 . 
       FIG. 4  illustrates a portable electronic device  400 , in accordance with various aspects of the subject technology. The above-described rechargeable battery pack  100  can generally be used in any type of electronic device. For example,  FIG. 4  illustrates a portable electronic device  400  which includes a processor  402 , a memory  404  and a display  406 , which are all powered by the battery pack  100 . Portable electronic device  400  may correspond to a laptop computer, tablet computer, mobile phone, personal digital assistant (PDA), digital music player, watch, and wearable device, and/or other type of battery-powered electronic device. Battery pack  100  may correspond to a battery pack that includes one or more battery cells  120 ,  130 . Each battery cell  120 ,  130  may include a set of layers, including a cathode  210 A,B with an active layer  310  disposed on a current collector  320 , a separator, an anode  220 A,B with an active layer  310  disposed on a current collector  320 , with the battery pack  100  utilizing C-Rate balancing as described above. 
       FIG. 5  illustrates an example method  500  for balancing a C-rate of an asymmetric battery pack, in accordance with various aspects of the subject technology. It should be understood that, for any process discussed herein, there can be additional, fewer, or alternative steps performed in similar or alternative orders, or in parallel, within the scope of the various embodiments unless otherwise stated. 
     At operation  510 , a first jelly roll having a first capacity and a second jelly roll having a second capacity that is greater than the first capacity are packaged into a battery pack. The first and second jelly rolls each comprise a cathode layer, an anode layer, and a separator layer disposed between the cathode layer and the anode layer. At operation  520 , a C-rate of the second jelly roll is balanced with a C-rate of the first jelly roll by increasing a thickness of a current collector of the cathode layer of the second jelly roll to reduce an impedance of the second jelly roll. At operation  530 , the first jelly roll and the second jelly roll are connected in parallel. In one aspect the method may further comprise increasing a thickness of a current collector of an anode layer of the second jelly roll to reduce an impedance of the second jelly roll. The method may also include reducing a thickness of an active layer of the cathode layer of the second jelly roll to reduce an impedance of the second jelly roll. The method may also include reducing a thickness of an active layer of an anode layer of the second jelly roll to reduce an impedance of the second jelly roll. 
     In another aspect, the method may include increasing a thickness of an active layer of the cathode layer of the first jelly roll to increase an impedance of the first jelly roll to balance a C-rate of the first jelly roll with a C-rate of the second jelly roll. The method may also include increasing a thickness of an active layer of the anode layer of the first jelly roll to increase an impedance of the first jelly roll to balance a C-rate of the first jelly roll with a C-rate of the second jelly roll. The method may further include decreasing a thickness of a current collector of the cathode layer of the first jelly roll to increase an impedance of the first jelly roll to balance a C-rate of the first jelly roll with a C-rate of the second jelly roll. The method may also include decreasing a thickness of a current collector of the anode layer of the first jelly roll to increase an impedance of the first jelly roll to balance a C-rate of the first jelly roll with a C-rate of the second jelly roll. 
     In another aspect, an example method for balancing a C-rate of jelly rolls of different impedances may include packaging a first jelly roll having a first impedance and a second jelly roll having a second impedance that is greater than the first impedance into a battery pack. The first and second jelly rolls each comprise a cathode layer, an anode layer, and a separator layer disposed between the cathode layer and the anode layer. A C-rate of the second jelly roll is balanced with a C-rate of the first jelly roll by increasing a thickness of a current collector of the cathode layer of the second jelly roll to reduce an impedance of the second jelly roll. The method may also include increasing a thickness of a current collector of an anode layer of the second jelly roll to reduce an impedance of the second jelly roll. The method may also include reducing a thickness of an active layer of the cathode layer of the second jelly roll to reduce an impedance of the second jelly roll. The method may also include reducing a thickness of an active layer of an anode layer of the second jelly roll to reduce an impedance of the second jelly roll. 
     Conversely, the method may also include increasing a thickness of an active layer of the cathode layer of the first jelly roll to increase an impedance of the first jelly roll to balance a C-rate of the first jelly roll with a C-rate of the second jelly roll. The method may also include increasing a thickness of an active layer of the anode layer of the first jelly roll to increase an impedance of the first jelly roll. The method may further include decreasing a thickness of a current collector of the cathode layer of the first jelly roll to increase an impedance of the first jelly roll. The method may also include decreasing a thickness of a current collector of the anode layer of the first jelly roll to increase an impedance of the first jelly roll. 
     Although a variety of examples and other information was used to explain aspects within the scope of the appended claims, no limitation of the claims should be implied based on particular features or arrangements in such examples, as one of ordinary skill would be able to use these examples to derive a wide variety of implementations. Further and although some subject matter may have been described in language specific to examples of structural features and/or method steps, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to these described features or acts. For example, such functionality can be distributed differently or performed in components other than those identified herein. Rather, the described features and steps are disclosed as examples of components of systems and methods within the scope of the appended claims.

Metadata:
Filing Date: 20200110
Publication Date: 20221101
Grant Date: 20221101
Priority Date: 20190620
Inventors: ROY, LOREN L.
GUO, QINGZHI
RAMADASS, PREMANAND
YOON, HYUNGOOK
SHI, JINJUN
Assignee: APPLE INC
CPC Classifications: [{"code": "H01M2010/4292", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01M10/4207", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M10/0587", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M50/534", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01M50/112", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M50/103", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M10/0587", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M50/538", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M10/0525", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M50/538", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M50/112", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M4/70", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M10/0431", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M50/112", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M4/13", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M4/36", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M2220/30", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01M4/0404", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01M50/103", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M50/414", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M4/661", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01M10/0431", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M10/441", "inventive": true, "first": true, "tree": "[]"}, {"code": "H01M10/0587", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M4/64", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M50/103", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M50/538", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M50/534", "inventive": false, "first": false, "tree": "[]"}, {"code": "Y02P70/50", "inventive": false, "first": false, "tree": "[]"}, {"code": "Y02E60/10", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01M4/13", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M50/534", "inventive": false, "first": false, "tree": "[]"}, {"code": "H01M50/538", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M10/0431", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M4/70", "inventive": true, "first": false, "tree": "[]"}, {"code": "H01M10/441", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 71409479