Abstract:
A system and/or method for replenishing lithium-ion battery capacity that is lost due to side reactions over the lifetime of a battery in one embodiment includes a battery with a first electrode, a second electrode, a separator region configured to electronically isolate the first and second electrodes, a first portion of lithium metal encapsulated within a first ionically insulating barrier configured to prevent transport of lithium ions therethrough, a memory in which command instructions are stored, and a processor configured to execute the command instructions to (i) determine a first lithium content of the first electrode, (ii) compare the first lithium content of the first electrode to a first threshold, and (iii) activate the first portion of lithium metal based on the comparison of the first lithium content to the first threshold.

Description:
[0001]    This application claims the benefit of U.S. Provisional Application No. 61/555,357, filed Nov. 3, 2012. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present disclosure relates to batteries and more particularly to lithium-ion batteries. 
       BACKGROUND 
       [0003]    Rechargeable lithium-ion batteries are attractive energy storage systems for portable electronics and hybrid-electric vehicles because of their high energy density and rate capability. However, they generally suffer degradation mechanisms that limit their useful life. These degradation mechanisms can be classified as power fade (an increase in internal resistance of the battery) and capacity fade (a decrease in useable capacity). Capacity fade, in turn, can be divided into (i) degradation or loss of the active material that serves as a host to the lithium ions in the two working electrodes and (ii) loss of charge due to side reactions at one or both of the electrodes. Christensen, J. and J. Newman, “Effect of Anode Film Resistance on the Charge/Discharge Capacity of a Lithium-ion Battery”,  Journal of the Electrochemical Society,  150 (2003) A1416; Christensen, J. and J. Newman, “Cyclable Lithium and Capacity Loss in Li-Ion Cells”,  Journal of the Electrochemical Society,  152 (2005) A818. 
         [0004]    A typical Li-ion cell  10 , as shown in  FIG. 1 , contains a negative electrode  20 , a positive electrode  22 , and a separator region  24  between the negative and positive electrodes  20 / 22 . Both electrodes  20 / 22  contain active materials  26  and  28 , respectively, into which lithium can be inserted, inert materials  36 , and a current collector  38 / 40 , respectively. The active materials  26 / 28  are also referred to as lithium-insertion materials. The separator  24  contains an electrolyte with a lithium cation, and serves as a physical barrier between the electrodes  20 / 22  such that the electrodes  20 / 22  are not electronically connected within the cell  10 . 
         [0005]    Typically, during charging, there is generation of electrons at the positive electrode  22  and consumption of an equal amount of electrons at the negative electrode  20 , and these electrons are transferred via an external circuit  30 . In the ideal operation of the cell  10 , these electrons are generated at the positive electrode  22  because there is extraction of lithium ions from the active material  28  of the positive electrode  22 , and the electrons are consumed at the negative electrode  20  because there is insertion of lithium ions into the active material  26  of the negative electrode  20 . During discharging, the exact opposite reactions occur. 
         [0006]    The main charge-transfer reactions that occur at the two electrodes  20 / 22  during charge, which results in Li  +  moving in the direction of arrow  32 , are: 
         [0000]      LiP→Li++e−+P (at the positive electrode  22 ) and
 
         [0000]      Li++e−+N→LiN (at the negative electrode  20 )
 
         [0000]    wherein P represents the positive electrode material  28  and N the negative electrode material  26 . Accordingly, LiP and LiN are the positive electrode materials and negative electrode materials, respectively, intercalated with lithium. For discharging, these reactions proceed in the opposite direction with Li +  moving in the direction of arrow  34 . 
         [0007]    The charge/discharge cycle for an ideal cell is represented in  FIGS. 2A-2E . As shown in the figures, lithium (represented by shading) starts in the positive electrode in the discharged state of the cell ( FIG. 2A ). During charge ( FIG. 2B ), lithium is transferred to the negative electrode. At full charge, all of the lithium is transferred to the negative electrode ( FIG. 2C ). During the subsequent discharge ( FIG. 2D ), the opposite reactions occur, and all of the lithium is transferred back to the positive electrode at full discharge ( FIG. 2E ). In the ideal operation of the cell, there are no other charge-transfer reactions, besides the main reactions. 
         [0008]    Side reactions have been defined as those charge-transfer reactions that occur other than the insertion or extraction of lithium ions into or out of the active material, with common examples including decomposition of the solvent or formation of the solid electrolyte interphase (SEI) at the negative electrode as reported by Arora, P., R. E. White, and M Doyle,  “Capacity Fade Mechanisms and Side Reactions in Lithium-ion Batteries”, Journal of the Electrochemical Society,  145 (1998) 3647, and Aurbach, D., “The Role of Surface Films on Electrodes in Li-ion Batteries”, in  Advances in Lithium-Ion Batteries,  W. A. van Schalkwijk and B. Scrosati, Eds. Academic/Plenem Publishers: New York, 2002; p 7. For non-ideal cells, some charge can be consumed via a side reaction. This results in a permanent capacity loss if the side reaction is not fully reversible. In contrast, the main reactions as described above with respect to  FIGS. 2A-2E  are typically fully reversible. 
         [0009]      FIGS. 3A-3E  depict an example in which an irreversible side reaction occurs at the negative electrode  20  during charge, consuming electrons that ideally should be consumed by the main reaction.  FIG. 3A  represents the initial discharged state of the cell.  FIG. 3B  represents the cell during charge and  FIG. 3C  represents the cell after the cell is fully charged.  FIG. 3D  represents the cell during discharge and  FIG. 3E  represents the cell after the cell is fully discharged. In  FIG. 3B , “S” is a generic reactant that could represent the solvent, an anion, or a contaminant. The product  5   −  may be soluble in the electrolyte, or can form a solid precipitate with the lithium cation. Because this reaction is irreversible in this example, the reverse reaction does not occur during discharge ( FIG. 3D ), and the charge cannot be transferred back to the positive electrode  22 . 
         [0010]    The small box  40  below the negative-electrode box  20  thus represents charge that is consumed via the side reaction. It is shaded after the cell is charged to show that some of the charge has been consumed irreversibly ( FIG. 3C ). However, the total area of the shaded regions in all of the boxes remains constant because charge is conserved. While the example depicted in  FIGS. 3A-3E  present a completely irreversible reaction, some side reactions may be somewhat reversible, in which case a fraction of the charge consumed by the side reaction can be returned to the positive electrode. 
         [0011]    The capacity of the cell is proportional to the number of electrons that are reversibly transferred from one electrode to the other via the external circuit. Thus, as seen from the example in  FIGS. 3A-3E , the cell&#39;s capacity is reduced because of side reactions. 
         [0012]    Some effort has been made to ameliorate the reduced capacity which results from undesired side reactions. U.S. Pat. No. 6,025,093 issued to Herr in 1998, discloses a system wherein cells have been designed to compensate for first-cycle lithium loss during SEI formation. As noted above, SEI is a side reaction. 
         [0013]    U.S. Pat. No. 6,335,115, issued to Meissner in 2002 describes the use of an auxiliary lithium electrode that compensates for lithium loss throughout the life of the cell. In the &#39;115 patent, two means of isolating the auxiliary electrode from the working electrodes are disclosed. One such isolation means is ionic isolation and the second isolation means is an electronic isolation. Ionic isolation involves an orientation of the battery in which the lithium-ion containing electrolyte contacts the two working electrodes, but not the auxiliary electrode. The lithium auxiliary electrode is presumably always in electronic contact with one of the working electrodes, but replenishment of lithium to the depleted working electrode does not occur until the cell is reoriented such that the electrolyte is in contact with both the working electrode and the auxiliary electrode. 
         [0014]    The ionic isolation approach has some limitations. For example, in a lithium-ion battery the battery would have to be designed such that the electrolyte does not completely fill the pores of the separator and working electrodes. However, the porous separator would naturally act as a wick that transports the electrolyte to the region of the separator that contacts the auxiliary electrode. Even residual electrolyte on the pores of this region of the separator would allow transport of lithium from the auxiliary electrode to the working electrode. Lithium transfer would continue until the potentials of the working and auxiliary electrodes equilibrated. Excessive lithium transfer, beyond the point of capacity balance between the two working electrodes, would result in reduction of the cell&#39;s capacity as reported by Christensen, J. and J. Newman, “Effect of Anode Film Resistance on the Charge/Discharge Capacity of a Lithium-ion Battery”,  Journal of the Electrochemical Society,  150 (2003) A1416, and Christensen, J. and J. Newman, “Cyclable Lithium and Capacity Loss in Li-Ion Cells”,  Journal of the Electrochemical Society,  152 (2005) A818. 
         [0015]    Moreover, shorting of the auxiliary-electrode-working-electrode circuit via imperfect ionic isolation would lead to rapid transfer of lithium to the working electrode and possible deposition of lithium on the electrode surface. Such lithium deposition can pose a safety risk and/or degrade the cell because the lithium metal reacts rapidly and exothermically with the organic solvent used in the electrolyte as reported by Arora, P., M. Doyle, and R. E. White, “Mathematical Modeling of the Lithium Deposition Overcharge Reaction in Lithium-ion Batteries Using Carbon-based Negative Electrodes”,  Journal of the Electrochemical Society,  146 (1999) 3543. 
         [0016]    Even if it were possible to maintain ionic isolation of the auxiliary electrode until lithium transfer is required, the cell design disclosed in the &#39;115 patent would require additional electrode and separator material that is unutilized. Moreover, the orientation of the cell in FIG. 1 of the &#39;115 patent is such that the two working electrodes are not in ionic contact, and therefore, lithium transport between the two electrodes is impossible in this orientation. 
         [0017]    Even if the foregoing shortcomings are addressed, a system which relies upon reorientation of the battery significantly reduces the number of potential applications. For example, battery-powered devices such as power tools may be used in any orientation, meaning that the auxiliary-electrode-working-electrode circuit could be closed unintentionally during standard operation of the battery. Hence, the device disclosed in the &#39;115 patent appears to be limited to applications that have a fixed orientation. 
         [0018]    Another approach disclosed in U.S. Pat. No. 7,726,975, issued to Christensen et al. in June 2010, involves the use of an auxiliary lithium electrode that can be electronically connected to or isolated from one or more of the working electrodes. The system in the &#39;975 patent circumvents the issues raised above by relying upon electronic, rather than ionic, isolation of the lithium reservoir electrode (LRE) from the working electrodes. The &#39;115 patent also discloses such electronic isolation. However, the lithium auxiliary electrode proposed in the &#39;115 patent is placed “between the positive and negative electrodes.” Such placement would reduce the uniformity of current distribution, and therefore the rate capability of the cell, when transferring lithium from one working electrode to the other. The approach in the &#39;975 patent avoids this problem by placing the LRE outside the current path between the two working electrodes. 
         [0019]    Approaches that rely upon an auxiliary lithium electrode typically suffer from the problem of large length scales associated with the distance of the auxiliary electrode from the working electrodes. A typical length scale between two working electrodes, which are pressed together on either side of a porous separator, is on the order of 100 microns, while the distance from an auxiliary lithium electrode to the farthest region of each working electrode can be on the order of 1 cm or more, even when the auxiliary lithium electrode is sandwiched between the two working electrodes. This is because the auxiliary electrode may not span the entire separator, as this would block ionic transport from one working electrode to the other. Moreover, dendrites could easily form and short one or more working electrode with the auxiliary electrode in this case. 
       SUMMARY 
       [0020]    A battery management system in one embodiment includes a battery including a first electrode and a second electrode, a separator region configured to electronically isolate the first and second electrodes, and a first portion of lithium metal encapsulated within a first ionically insulating barrier configured to prevent transport of lithium ions therethrough. The battery management system further includes a memory in which command instructions are stored and a processor configured to execute the command instructions to (i) determine a first lithium content of the first electrode, (ii) compare the first lithium content of the first electrode to a first threshold, and (iii) activate the first portion of lithium metal based on the comparison of the first lithium content to the first threshold. 
         [0021]    The battery management system implements a method to restore the lost capacity in the battery. The method includes determining a first lithium content of a first electrode of the battery, comparing the first lithium content of the first electrode to a first threshold, and activating transfer of a first portion of lithium metal to the electrode based on the comparison of the first lithium content to the first threshold, the first portion of lithium metal encapsulated within a first ionically insulating barrier configured to prevent transport of lithium ions therethrough until the BMS activates the transfer (i.e., causes the barrier to become transparent to Li ions). 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  depicts a typical prior art Li-ion battery; 
           [0023]      FIGS. 2A-2E  depict an ideal charge/discharge cycle of the battery of  FIG. 1 ; 
           [0024]      FIGS. 3A-3E  depict a charge/discharge cycle of the battery of  FIG. 1  with a side reaction; 
           [0025]      FIG. 4  depicts a Li-ion battery incorporating a selectively activated additive in accordance with the disclosure; 
           [0026]      FIG. 5  depicts a cross sectional view of an additive of  FIG. 4 ; 
           [0027]      FIG. 6  depicts a battery management system that can be used to control selective activation of the additive of  FIG. 5 ; 
           [0028]      FIGS. 7A-7C  depict the effect of the additive of  FIG. 4  on the lithium content in the battery of  FIG. 4 ; and 
           [0029]      FIG. 8  depicts a procedure that can be executed under the control of the battery management system of  FIG. 6  to selectively activate a lithium additive. 
       
    
    
     DESCRIPTION 
       [0030]    For the purpose of promoting an understanding of the principles of the disclosure, reference will now be made to the embodiments illustrated in the drawings and described in the following written specification. It is understood that no limitation to the scope of the disclosure is thereby intended. It is further understood that the disclosure includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the disclosure as would normally occur to one skilled in the art to which this disclosure pertains. 
         [0031]      FIG. 4  shows a cell with Li replenishment additives contained in the positive electrode. The cell  100  contains a negative electrode  102  and a positive electrode  104 . The negative electrode  102  includes a lithium insertion material  106 , inert materials  108 , and a current collector  110 . The positive electrode  104  includes a lithium insertion material  116 , inert materials  108 , and a current collector  120 . The cell  100  also includes a separator region  122  that contains an electrolyte with a lithium cation, and serves as a physical barrier between the electrodes  102 / 104  such that the electrodes  102 / 104  are electronically isolated within the cell  100 . The electrolyte enables lithium-ion transfer between the negative and positive electrodes  102 / 104 , which are referred to herein as the working electrodes. 
         [0032]    With reference to  FIGS. 4 and 5 , the cell  100  additionally contains additive  130  which is provided in either or both of the electrodes  102 / 104  in different embodiments. The additive  130  consists of Li metal particles  132  that are coated with a material  134  that is ionically insulating and, in some embodiments, is electronically conductive. Ionic insulation or barrier  134  prevents transport of Li from the particles  132  to the surrounding composite electrode during normal cell operation. In the embodiment of  FIG. 4 , a second additive  140  is provided. The additive  140  consists of Li metal particles  142  that are coated with a material  144  that is ionically insulating and, in some embodiments, is electronically conductive. 
         [0033]    The two batches of additives  130 / 140  are independently activated by compromising the insulating material  134 / 144 , such as by breaking, dissolving, or decomposing the insulating material  134 / 144 , or by causing the insulating material  134 / 144  to be ionically conductive and therefore permeable to Li ions. The activation step in some embodiments involves increasing the temperature of the cell  100  outside the normal operating range, compressing the cell  100  such that enough stress is imparted to the barrier  134  that it fractures, injecting an additive into the electrolyte of the cell  100  that reacts with and decomposes the barrier  134 , or changing the potential of the electrode that contains the additive  130  beyond its normal operating range. The insulating material  144  can be independently compromised either by providing an insulating material  144  with a different compromising mechanism, or with a different set point. Thus, at a first temperature the insulating material  134  fractures, while the insulating material  144  does not fracture until a second, higher temperature or cell compression is achieved. 
         [0034]    The insulating material  134 / 144  is preferably at least partially electronically conductive to facilitate transport of electrons from the Li metal core  132 / 142  to the electronically conductive matrix of the positive electrode  104 . Hence, when activated, electrons spontaneously are transferred from the Li metal  132  to the electrode active material  116  through electronically conductive phases, while Li ions are spontaneously transferred to the active material  116  through ionically conductive phases. The transfer is spontaneous because the active insertion materials  116  have a potential higher than that of Li metal  132 . While only two insulating materials  134 / 144  are identified above, several different coatings may be applied to various additives in a particular embodiment. Alternatively, the thickness of the shells may be controlled to provide different compromise set points. 
         [0035]    Beneficially, the cell  100  in one embodiment is manufactured in any desired configuration (e.g., spirally wound, prismatically stacked, etc.), and has two terminals, one each for the positive electrode  104  and negative electrode  102 . 
         [0036]    In one embodiment, the cell  100  is incorporated into a battery management system  200  which is depicted in  FIG. 6 . The battery system  200  includes an I/O device  202 , a processing circuit  204  and a memory  206 . The I/O device  202  in one embodiment includes a user interface, graphical user interface, keyboards, pointing devices, remote and/or local communication links, displays, and other devices that allow externally generated information to be provided to the battery system  200 , and that allow internal information of the battery system  200  to be communicated externally. The battery management system  200  in one embodiment is configured to obtain measurements directly from the cell  100  or to obtain data from an intermediate source. 
         [0037]    The processing circuit  204  in some embodiments is suitably a general purpose computer processing circuit such as a microprocessor and its associated circuitry. The processing circuit  204  is operable to carry out the operations attributed to it herein. 
         [0038]    Within the memory  206  are various program instructions  208 . The program instructions  208 , some of which are described more fully below, are executable by the processing circuit  204  and/or any other components as appropriate. Insulating material databases  210  are also located within the memory  206 . The insulating material databases  210  stores data used to identify the conditions required for compromising the insulating material  134 / 144  such as a pressure, temperature, additive, etc. 
         [0039]    The battery management system  200  further includes compromise control equipment  212  and compromise condition detector suite  214 . The compromise control equipment  212  is configured to establish and maintain conditions which result in compromising the insulating material  134 / 144 . 
         [0040]    During normal operation, the positive and negative electrode terminals  104 / 102  are connected to either end of a load  150  during discharge, and to a power supply  150  during charge ( FIG. 4 ). The additives  130 / 140  remain inactive during normal operation. When the battery system  200  determines it is appropriate to replenish the capacity of the cell  100  lost due to side reactions, the additive, or a single batch of additives  130 / 140 , is activated by establishing conditions which compromise the insulating material  134 / 144  using the compromise control equipment  212 . In one embodiment, the compromise control equipment  212  is equipment used during normal operation of the battery such as a heating element. In another embodiment, the compromise control equipment  212  is used uniquely for establishing compromise conditions, such as a pressure applying device, a heating element, or syringe for adding chemicals to the electrolyte. 
         [0041]    Accordingly, a compromising condition is established which in various embodiments includes one or more of increasing the temperature of the cell  100  outside the normal operating range, compressing the cell  100  such that enough stress is imparted to the additives  130 / 140  that it fractures, injecting an additive into the electrolyte of the cell  100  that reacts with and decomposes the barrier(s)  134 / 144 , or changing the potential of the electrode that contains the additives  130 / 140  beyond its normal operating range. In one embodiment, the BMS  200  uses the compromise condition detector suite  214  to monitor the precise environment established by the compromise control equipment  212 . 
         [0042]    Once the additives  130 / 140  are activated, lithium ions are transferred ionically from the Li metal core(s)  132 / 142  of the additives  130 / 140  into the active insertion material  116  that is a constituent of the composite electrode that contains the additive. This transfer in one embodiment is facilitated by simultaneous transport of electrons through the electronically conductive additives  130 / 140 , or electronically conductive portion of the additives  130 / 140 , or by compression of the electrode to establish electronic contact directly between the active insertion material  116  and the Li metal core(s)  132 / 142  of the additives  130 / 140 . Hence, the cell capacity can be restored to its original value, or close to its original value. 
         [0043]      FIGS. 7A-7C  illustrate how charge from the additive batch(es), which is contained in the positive electrode, replaces the charge that was lost due to the side reaction illustrated in  FIGS. 3A-E . To replace the lost charge of a cell in the discharged state due to the side reaction  40  ( FIG. 7A ), the additive batch  130  or batches are activated in the positive electrode  104 , allowing electrons to flow from the additive  130  to the positive electrode active material in the direction of arrow  52  ( FIG. 7B ). Simultaneously, lithium dissolves from the additive  130  and is transferred through the electrolyte in the positive electrode  104  to the active material  116 , where it is inserted via the main insertion reaction ( FIG. 7B ). The correct amount of charge to be transferred is determined by the battery management system  200 , such that the cell returns to its original capacity, or close to its original capacity ( FIG. 7C ). This process in one embodiment is repeated several times throughout the life of the cell, depending upon the number of batches of additive available for independent activation. 
         [0044]    An inherent challenge in using such an additive is that it is difficult to determine the amount of Li to be transferred to each of the working electrodes. Insertion of too much lithium into the working electrodes can degrade the cell and create a significant safety risk. For example, excess lithiation of one or more working electrode could result in a capacity imbalance between the two electrodes, thereby reducing the capacity of the cell below the value of an optimally balanced cell. Therefore, it is important to know the appropriate time to activate the additive, or additive batch, such that the active insertion material is not overlithiated 
         [0045]    The present system accounts for this important need to determine the amount of lithium to be transferred by using a battery management system (BMS)  200  for determining the amount of capacity that has been lost from the system due to side reactions. The BMS  200  must therefore estimate the state of charge (SOC) of each working electrode. The SOC of each working electrode corresponds to the amount of lithium contained in it. When the lithium concentration is at its maximum value, the SOC of the electrode is 1, and when it is at its minimum, the SOC is 0. The additive is used to increase the SOC of one or both of the working electrodes through the selective transfer of lithium ions and electrons. 
         [0046]    With reference to  FIG. 8 , the processor  204  executes command instructions  208  stored within memory  206  in accordance with a procedure  300  to determine the lost cell capacity and selectively activate the additive  130 / 140  if certain conditions are met. Initially, criteria for operating the system  200  are stored in the memory  206 , at block  302 . The criteria may be stored in the form of a battery model and a diagnostic algorithm with different additive activation profiles provided for different factors. 
         [0047]    In some embodiments, multiple algorithms are associated with the cell depending on the desired complexity of the system. By way of example, the criteria in some of these embodiments include, among other criteria, a nominal charge voltage (“V c ”) and a nominal discharge voltage (“V d ”) for the cell. Additionally, in some of these embodiments, an initial open cell potential (“OCP”)/SOC relationship for the cell is stored in the memory. The stored criteria provide values for the algorithm that the processor uses to implement the different additive activation profiles. The criteria stored in the memory are obtained in any desired manner. 
         [0048]    The BMS  200  uses the battery model and the diagnostic algorithm to deconvolute the SOCs of the two working electrodes from measurements of the full-cell potential and current (block  304 ). An example of a system and method that can be modified to calculate the SOC of the working electrodes is found in U.S. application Ser. No. 12/396,918, filed on Mar. 3, 2009, the entire contents of which are incorporated by reference herein. The estimated SOC values are then transformed into a total lithium content in each electrode by the BMS  200  (block  306 ). 
         [0049]    The BMS  200  computes the difference between the present Li content in each electrode and the desired Li content in each electrode that indicates a balance of capacity between the two electrodes (block  308 ). The BMS  200  compares this difference to the amount of Li contained in one or more additive batches in the respective electrode(s) using data stored in the memory  206  (block  310 ). If the amount of Li contained in the batches is more than the difference between the present and desired Li content in the electrode(s) at block  312 , the process  300  returns to block  304  for continued monitoring of the SOCs of the electrode(s). If the amount of Li contained in one of the batches is close to, for example, within 2% or less of the difference between the present and desired Li content in the electrode(s) at block  312 , the process  300  continues to block  314 . At block  314 , the BMS activates the one or more batches of additive to bring the Li content of the electrodes to the desired level. 
         [0050]    In one embodiment, the BMS  200  is located in a single device. In another embodiment, portions of the BMS  200  are located apart from other portions of the BMS  200 . In yet other embodiments, functions of the processor are performed by multiple processors. By way of example, the electrodes and Li additives in one embodiment are located within a vehicle battery . A processor carried in the vehicle monitors the SOC of the battery and provides a warning signal to a user when the available Li content of one or more of the electrodes falls below a predetermined threshold. The user then proceeds to a service station where the compromise control equipment is located and used to activate additional Li under control of a processor associated with the compromise control equipment. In some embodiments, communications between the processor within the vehicle and the processor within the compromise control equipment are established using a CAN communication bus or other communication protocol/system. 
         [0051]    While the disclosure has been illustrated and described in detail in the drawings and foregoing description, the same should be considered as illustrative and not restrictive in character. It is understood that only the preferred embodiments have been presented and that all changes, modifications and further applications that come within the spirit of the disclosure are desired to be protected.