Abstract:
A method for filling a battery cell with electrolyte, comprising:
       a) connecting the battery cell and a lower portion of a fill head chamber connected through respective first, second, third and fourth valves to a source of high pressure, the free atmosphere, a source of high vacuum and optionally a source of low vacuum, wherein only one of said valves can be open at any time, while said second valve is open;   b) opening said third valve for a predetermined first period to discharge air from the interior of said battery cell through said chamber;   c) separating the major upper portion of said chamber from the lower portion thereof by a sliding shut-off plunger and opening said second valve;   d) dispensing a prescribed amount of electrolyte into said upper portion of said chamber above said plunger, while keeping said second valve open;   e) raising said plunger to let a major portion of said dispensed liquid be sucked into said battery cell under the effect of the vacuum established therein in step b) and allowing any gas bubble in said battery cell to get removed through the electrolyte;   f) opening said first valve for a second predetermined period to push said electrolyte into said battery cell;   g) opening said second valve for a third predetermined period;   h) repeating steps f) and g) at least once for the more complete removal of gases from the battery cell and filling the prescribed volume of electrolyte; and,   i) disconnecting said battery cell from said fill head.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a method for filling electrolyte into a battery cell, to an apparatus for carrying out the method. More particularly, the electrolyte is non-aqueous in nature and used in battery cells such as lithium ion batteries. 
       BACKGROUND OF THE INVENTION 
       [0002]    Batteries have become increasingly popular over the last decade due to the advent of a myriad of portable electronic devices. Especially lithium ion secondary batteries have become the predominant power source for the devices such as cellular phones, notebook or laptop computers, camcorders, digital cameras and more. 
         [0003]    Lithium ion secondary batteries contain a spirally wound electrode assembly installed in a suitable battery case that has to be filled with non-aqueous electrolyte. In the battery case with the electrode assembly installed in it, a large number of small voids are formed. Typically, the air in the internal space of the battery is being drawn out by means of applying a vacuum and the electrolyte is filled under vacuum against atmospheric pressure. However, long time is required for completely exhausting the voids. Further, some time is required until the non-aqueous electrolyte has permeated into the electrode assembly, and it is very difficult to inject the electrolyte within a short time. 
         [0004]    JP-07099050(A) describes an apparatus, comprising a battery arranged in a chamber and with an electrolyte to be injected into it, and a predetermined amount of electrolyte is filled in an electrolyte reservoir mounted on the injection nozzle. Then, the pressure in the chamber is reduced, and gas such as the air in the electrolyte or the electrode assembly is removed. Then, the pressure is restored to atmospheric pressure, and the electrolyte is injected. In this apparatus, however, a funnel-like member with a reservoir corresponding to the amount of the electrolyte to be injected is mounted while the top portion of the battery base with the battery element is opened, and the space inside the battery case is exhausted. A part of the electrolyte is injected into the battery case before exhausting and is permeated into the battery element. As a result, the exhausting from the voids in the electrode assembly is insufficient because of the presence of the electrolyte. Exhausting is performed while the electrolyte is present in the reservoir, which comprises a funnel-like member on the top portion of the battery case, and the pressure is applied as the atmospheric pressure. As a result, air bubbles are generated when the air passes through the funnel-like unit from inside the battery case, and these air bubbles are sent into the battery. 
         [0005]    U.S. Pat. No. 5,738,690 teaches a method of filling a battery cell for electric vehicle applications. In this method, a special apparatus arrangement enables vacuum assisted filling of electrolyte against atmospheric pressure. The time required and the achieved electrolyte fill level are not mentioned, but will be limited by the driving force of atmospheric pressure. 
         [0006]    U.S. Pat. No. 6,497,976 describes a method for electrolyte filling of a small size rectangular battery with a small electrolyte injection hole in the battery case. In this method, the battery case is exhausted by vacuum followed by electrolyte injection under pressure of up to 2 kgf/cm 2  (196 kPa) to enable quick filling of electrolyte. Filling according to this method can be achieved in 60 seconds, but cannot achieve maximum electrolyte fill levels. A problem in this filling method lies in that the high pressure is maintained till the end of the filling process, wherein the small voids cannot be filled as the air cannot escape. 
         [0007]    One result of the presence of voids after filling is the wide deviation range of battery weight which is due to the fact that different individual battery cells can take different amount of electrolyte. The battery performance is negatively influenced by the presence of voids and by the incomplete filling of the available battery space with electrolyte. 
         [0008]    Since maximum electrolyte fill level is very important to battery performance, some companies have started to go through 2 or 3 electrolyte fill operations on their existing vacuum fillers, which involves considerable slow down in production speeds and increased parts handing. 
       OBJECT OF THE INVENTION 
       [0009]    The primary object of the invention is to provide an electrolyte filling method that can efficiently fill the available space and remove all gases, and which can provide such a filling within reasonable time and with high speed. 
         [0010]    A further objective is to provide an apparatus for carrying out the method, which can produce batteries with highly uniform electrolyte volume. 
         [0011]    A still further object is to carry out the method on a plurality of batteries at a time, whereby production rate can be increased. 
       SUMMARY OF THE INVENTION 
       [0012]    According to the present invention it has been recognized that a special order of individual steps is required for the optimum filling, wherein between the individual steps like vacuum discharge and pressurized filling, transitional periods should be provided, in which gas bubbles can discharge, and to provide for the required transient states a special design of the filling head should be provided, making use of the fact that the electrolyte as such is a perfect separation means between the interior of the battery and the pressure conditions prevailing in the filling chamber. 
         [0013]    By utilizing this recognition according to the first aspect of the invention a method has been provided for filling a battery cell with electrolyte, wherein the battery cell is provided with an electrolyte injection receptacle, comprising the steps of: 
         [0014]    a) establishing a sealed connection between said electrolyte injection receptacle and a connection nozzle of a fill head defining a chamber connected through respective valves to a source of high pressure, to the free atmosphere, to a source of high vacuum and optionally to a source of low vacuum, wherein only one of said four valves can be open at any time, while during the present step a) said valve leading to the free atmosphere being open; 
         [0015]    b) opening said valve leading to said high vacuum for a predetermined first period to discharge air from the interior of said battery cell through said chamber; 
         [0016]    c) separating the major upper portion of the interior of said chamber from the lower portion thereof communicating with said connection nozzle by means of a sliding shut-off plunger and opening said valve connecting to the free atmosphere; 
         [0017]    d) dispensing a prescribed amount of electrolyte in said upper part of said chamber through a temporarily opened electrolyte fill port so that the electrolyte fills a part of said interior above said shut-off plunger, while keeping said valve leading to the free atmosphere open; 
         [0018]    e) raising said shut-off plunger to let a major portion of said dispensed liquid be sucked into the interior of said battery cell under the effect of the vacuum established therein in step b) and allowing any gas bubble in said battery cell to get removed through the electrolyte; 
         [0019]    f) providing a mechanical support for said battery cell and opening said valve connected to said source of high pressure for a second predetermined period to push said electrolyte in said battery cell; 
         [0020]    g) opening said valve leading to the free atmosphere for a third predetermined period; and 
         [0021]    h) repeating steps f) and g) at least once for the more complete removal of gases from the battery cell and filling the prescribed volume of electrolyte; and 
         [0022]    i) disconnecting said battery cell from said fill head. 
         [0023]    A further recognition lies in that the pressure filling should be continued with a short atmospheric period and with a further vacuum that may drive out any existing gases. If these steps are correctly repeated, a perfect filling can be reached. 
         [0024]    According to a second aspect of the invention a specially designed and arranged filling apparatus, mainly a fill head has been provided which uses on the one hand four valves connected to different sources of different pressure levels (high pressure, atmospheric, low vacuum and high vacuum), wherein only one of the valves can be open at a time, and on the other hand, a vertically movable plunger valve that can close down the lower portion of the fill head, to enable separation of the volume underneath and above, which will have significance if electrolyte is dispensed on the closed plunger, which—when raised—will let the electrolyte flow down and separate itself the cell interior from the space in the filling chamber. A well synchronized operation of the plunger, of the filling and of the opening of the valves enables the smooth realization of an optimum filling method. 
         [0025]    According to a further aspect of the invention a filling head assembly has been provided, in which a number of filling heads are arranged mechanically side-by side, and the assembly enables simultaneous filling with each of its filling heads. The assembly uses only four valves for all chambers, however, each chamber is provided with an assigned plunger, and the filling (metering of the electrolyte) occurs also simultaneously through ports that open and close simultaneously by the sliding of a bar driven by a cam-follower. 
         [0026]    The filling speed can be further increased if these assemblies are placed on respective positions of an index table, moved discretely around a central axis, wherein in a first position the placement and pick up of the assemblies can take place in a smooth and synchronized way. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    The invention will now be described in connection with preferable embodiments thereof, wherein reference will be made to the accompanying drawings. In the drawing: 
           [0028]      FIGS. 1 to 8  show the eight distinctive stages of the electrolyte fill method; 
           [0029]      FIG. 9  shows a timing diagram of the electrolyte fill method; 
           [0030]      FIG. 10   a  shows a top section view of a fill head assembly for filling 8 stations simultaneously; 
           [0031]      FIG. 10   b  shows a front section view of a fill head assembly for filling 8 stations simultaneously; 
           [0032]      FIG. 11   a  shows a 3D view of an 8 fill head assembly with the slide valve in closed position; 
           [0033]      FIG. 11   b  shows a 3D view of an 8 fill head assembly with the slide valve in open position; 
           [0034]      FIG. 11   c  shows a side section view of an 8 fill head assembly with the slide valve in open position and the electrolyte fill nozzles engaged; 
           [0035]      FIG. 12  shows a schematic top view of a rotary index apparatus with 8×8 fill head assemblies; and 
           [0036]      FIG. 13  shows the electrolyte weight distribution of a test fill of 18650 Li-Ion battery cells. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0037]    In  FIGS. 1 to 8  eight discrete steps of the electrolyte filling method according to the invention has been schematically illustrated. Each of these schematic drawings show the same electrolyte fill head  1  as coupled to a battery cell  100  which is kept securely in a cell support  6 . The electrolyte fill head  1  comprises a pre-metering chamber  2 , a cell size specific adapter nozzle  3 , an elastomer seal  3   a  engaging with an appropriate connection element of the battery cell  100 , a shut-off plunger  4 , a slider plate valve  5 , an electrolyte fill port  8  with an O-ring seal around its top circumference (see  FIG. 4 ) and four commercial pressure valves  7   a - d  such as SS-8BK-1C from the Swagelok company. The pressure valves  7   a - d  have respective first sides communicating with the interior of the pre metering chamber well above the zone of movement of the shut-off plunger  4 . The other sides of the valves  7   a - d  are coupled to different pressure or vacuum means as illustrated by the corresponding blocks bearing the reference of the type of the particular means. Valve  7   a  is coupled to a source of high pressure, valve  7   b  leads to the free atmosphere, valve  7   c  is coupled to a source of low vacuum and finally, valve  7   d  is coupled to a source of high vacuum. 
         [0038]    The vertical operating rod of the shut-off plunger  4  is extending out through the top cover of the pre-metering chamber  2  by means of a sealed sliding connection and it can be moved up and down by means of an actuator not shown in the drawing. In the illustrated embodiment the pre-metering chamber  2  has a downwardly narrowing conical neck portion that communicates with the adapter nozzle  3 . The shut-off plunger  4  has also a conical design which fits in the lower section of the conical neck and in a fully downward position the plunger  4  provides a perfect sealing between the upper and lower parts of the chamber  2  separated thereby. It can be seen in the figures that all other connections of the pre-metering chamber  2  are arranged in the upper part of the interior. 
         [0039]    The battery cell  100  comprises a battery can  101 , a spirally wound electrode assembly  102  and a weld tabs  103  that is extending out of the battery can into adapter nozzle  3  and constitutes the connection means or filing adapter of the battery cell  100 . 
         [0040]    In the first stage of the operation shown in  FIG. 1  the shut-off plunger  4  and valve  7   b  are open, valves  7   a, c  and  d  are closed; therefore, the chamber  2  and battery cell  100  are at atmospheric pressure. 
         [0041]      FIG. 2  shows the second stage of the electrolyte fill method. In this stage, the shut-off plunger  4  is still open, but valve  7   b  is closed and valve  7   d  is open enabling high vacuum, both the valves  7   a  and  7   c  are closed; therefore, the chamber  2  and the interior of the battery cell  100  is now evacuated to a pressure of about 5.3 kPa. 
         [0042]    In the present specification the following pressure unit conversions have been used: 
         [0000]      1 atm=101325 Pa=1.10325 bar=760 torr=14.696 psi 
         [0000]    In this step, which is set for a predetermined amount of time, the air is removed from the battery cell  100 . 
         [0043]      FIG. 3  shows the third stage of the electrolyte fill method. In this stage, the shut-off plunger  4  is lowered and closed, and the battery cell  100  and the adapter nozzle  3  remain evacuated at 5.3 kPa. The valve  7   d  is closed and the valve  7   b  is opened enabling atmospheric pressure in the pre-metering chamber  2  above the plunger  4 . The valves  7   a  and  7   c  remain closed; therefore, the interior of the chamber  2  returns to the atmospheric pressure. 
         [0044]      FIG. 4  shows the fourth stage of the electrolyte fill method. In this stage, the shut-off plunger  4  remains closed and the battery cell  100  and the adapter nozzle  3  remain evacuated at 5.3 kPa. The positions of the valves  7   a - d  remain as in  FIG. 3 . In this stage the slide valve  5  opens, and electrolyte fill nozzles indicated by the block “electrolyte” engage with the electrolyte fill port  8 , and a predetermined amount of electrolyte  200  is being dispensed into chamber  2  under atmospheric pressure. The electrolyte is being dispensed with a standard electrolyte pump model 2BC12 from Hibar Systems Limited. The predetermined electrolyte volume is the amount required to fill the electrolyte cavities of the battery cell  100  or it is by a few percent higher. The so introduced electrolyte gets into the conical neck of the chamber  2  just above the plunger  4 . 
         [0045]      FIG. 5  shows the fifth stage of the electrolyte fill method. In this stage, the slide valve  5  is closed shut again and the settings for the valves  7   a - d  remain as in  FIG. 4 . After the slide valve  5  is closed, the shut-off plunger  4  is opened (raised), and the vacuum in the battery cell  100  and the adapter nozzle  3  will suck in the electrolyte as they have been previously evacuated to 5.3 kPa before and the pressure above the electrolyte is at atmospheric pressure. Not all of the pre-metered electrolyte  200  will flow into the battery cell  100  at this stage, and certain amount of electrolyte  200  will remain in the adapter nozzle  3  area at varying levels depending on each individual cell condition. The reason of the incomplete filling lies in that even after the application of the vacuum, certain air-bubbles can remain in the cavities of the battery cell  100  and cannot provide space for the inflowing electrolyte. 
         [0046]      FIG. 6  shows the sixth stage of the electrolyte fill method. In this stage, the slide valve  5  remains closed and the shut-off plunger  4  opened. The valve  7   b  is closed and the valve  7   a  is opened while the valves  7   c  and  7   d  are closed. Opening the high pressure valve  7   a  causes a high pressure of approx. 800 kPa to be applied over the electrolyte, which forces the electrolyte further into the battery cell  100 . Not all of the pre-metered electrolyte  200  will flow into battery cell  100  at this stage, and certain volume of the electrolyte  200  will remain in the adapter nozzle  3  area at varying levels depending on each individual cell condition. At this stage of high pressure soak, the battery cell  100  has to be supported by an at least equivalent counter-pressure that is provided by a pneumatic cylinder acting on the cell support  6 . 
         [0047]      FIG. 7  shows the seventh stage of the electrolyte fill method. In this stage, the slide valve  5  remains closed and the shut-off plunger  4  is opened. The valve  7   a  is closed and the valve  7   b  is opened, while the valves  7   c  and  7   d  are closed. Opening the atmospheric pressure valve  7   b  allows for the gases trapped in the battery cell  100  to be released. 
         [0048]      FIG. 8  shows the eighth stage of the electrolyte fill method. In this stage, the slide valve  5  remains closed and the shut-off plunger  4  opened. The valve  7   b  is closed and the valve  7   c  is opened while the valves  7   a  and  7   d  are closed. Opening the low vacuum valve  7   c  (that provides a vacuum pressure of about 41.3 kPa) causes further remaining gases to be drawn out from the battery cell  100 . 
         [0049]    In this electrolyte fill method, the steps of  FIGS. 6 to 8  can be repeated as often as necessary to achieve a complete fill of all the predetermined amount of electrolyte into the battery cell  100 . It has been found that a single repeated cycle through the steps shown in  FIGS. 6 to 8  is sufficient for achieving a complete fill. However, depending on the electrolyte composition and the cell configuration, more cycles may be needed. 
         [0050]    Several tests have been carried out in order to achieve an optimum time/performance timing for the different steps illustrated. As a result, an optimum timing has been devised which is illustrated in  FIG. 9  showing the duration of the steps shown in  FIGS. 1 through 8 . The battery load/unload section with a time allocation of 5 seconds represents the stage of  FIG. 1 . The high vacuum stage of  FIG. 2  is applied for 24 seconds followed by a short 1 second return to atmosphere stage of  FIG. 3 . The electrolyte dispense stage of  FIG. 4  has a time allotment of 3 seconds followed by a short 1 second return to the atmosphere stage of  FIG. 5 . Next, the first loop of  FIG. 6  with high pressure for 30 seconds follows, then a short 1 second return to atmosphere stage of  FIG. 7  and another 1 second of low vacuum stage of  FIG. 8 . Next, a second loop of  FIGS. 6-8  stages follows with 45 seconds high pressure, 1 second atmosphere and 1 second low vacuum. At this stage, all the electrolyte has been filled into the battery cell  100  and the battery cell  100  can be disengaged from the adapter nozzle  3 . The timing cycle has also a provision for flushing the pre-metering chamber  2  with an appropriate solvent to clean the chamber  2  from salt deposits, which cleaning step has not been illustrated in  FIGS. 1 to 8 . This cleaning period lasts for 5 seconds and a 2 seconds spare time remains for a total cycle time of 120 seconds per fill head. 
         [0051]    A preferable embodiment of an electrolyte filling apparatus that operates according to the aforementioned methods uses eight electrolyte fill heads  1  constituting a fill head assembly.  FIGS. 10   a  and  10   b  show in respective top and elevation sectional views such a fill head assembly for simultaneously filling eight battery cell stations. The reference numerals in  FIGS. 10   a  and  10   b  refer to the same parts as in the schematic drawings of  FIGS. 1-8 , but have the letters a-h added for each of the fill heads. 
         [0052]    Referring to the top view of  FIG. 10   a,  the fill head assembly has eight electrolyte fill heads  1   a  through  h,  one slider plate assembly  5  with eight access holes  9   a  through  9   h,  one pressure manifold  12  connecting to the chambers  2   a  through  2   h  of all the eight fill heads, and connectors  13   a - 13   d,  which connect to the pressure valves  7   a - 7   d.  The manifold  12  has an optional spare connector  13   e,  which can be used for flushing and cleaning the whole fill head assembly. Furthermore, the manifold  12  has an inlet adapter  14 , which connects to an industrial pressure transducer  15  such as model number K-68073-06 from Cole Parmer Instrument Company of Vernon Hills, Ill., USA. Note that in this view of  FIG. 10   a,  the slider plate assembly  5  is in closed position. The slider plate assembly  5  will move to the left as indicated by arrow  16  until the access holes  9   a - h  will align with the electrolyte fill ports  8   a - h,  guided by cams  10   a - b  and cam follower  11   a - b.  The lateral movement of the slider plate assembly  5  is facilitated by a pneumatic cylinder (not shown) that is connected to it. 
         [0053]    Referring to  FIG. 10   b,  the two cams  10   a - b  and the two cam followers  11   a - b  can be seen in a side view with the slider plate assembly  5  in the closed position. The battery cells  100  are engaged to the fill heads adapter nozzles  3  and sealed via elastomer seals  3   a.  In  FIGS. 11   a  and  11   b  respective three-dimensional (3D) top views are shown for the fill head assembly with the slider plate assembly  5  provided with eight filling heads, wherein  FIG. 11   a  shows the closed and  FIG. 11   b  the open positions. In  FIG. 11   a,  the slider plate assembly  5  is in the closed position, the electrolyte fill ports  8   a - h  are tightly sealed to the bottom surface of the slider plate assembly  5  by means of O-ring seals that are present around the circumference of the electrolyte fill ports  8   a - h  and squeezed together by the action of the profile of the cams  10   a - b,  and the cam followers  11   a - b  engage in this position. 
         [0054]    In  FIG. 11   b,  the slide plate assembly  5  is in the open position, the electrolyte fill ports  8   a - h  are in line with the access holes  9   a - h  of the slide plate assembly  5 . The O-ring seals that are present around the circumference of the electrolyte fill ports  8   a - h  are not squeezed in this position as a result of the profile of the cams  10   a - b.  In  FIG. 11   c  an elevation sectional view of one of the eight fill heads of the electrolyte fill head assembly is shown with the slide plate assembly  5  in the open position and the electrolyte fill nozzles engaged into the electrolyte fill ports  8   a - h.  The electrolyte fill ports  8   a - h  remain in line with the access holes  9   a - h  of the slide plate assembly  5  and the O-ring seals that are present around the circumference of the electrolyte fill ports  8   a - h  remain not squeezed. There is a clearance between the electrolyte fill ports  8  and the electrolyte fill nozzles  17  so that they are subject to ambient pressures. The electrolyte fill nozzles  17  engage deep down into the pre-metering chamber  2  to avoid splashing of the electrolyte and they are mounted to a nozzle adapter  18  that is mounted on motorized controls (not shown) for the insertion and retraction of the nozzles. The motorized nozzles move down and up as well as towards and away from the fill heads. The nozzle connector  19  connects to the electrolyte line of a standard electrolyte pump (not shown) model 2BC12 from Hibar Systems Limited. 
         [0055]      FIG. 12  shows a schematic top view of a rotary index apparatus with 8×8 fill head assemblies set at a speed of one revolution per 120 seconds for a production fill rate of 32 battery cells per minute. The rotary index table has 8 distinct index positions  1  to  8  and in each position a respective one of the fill head assemblies can be found. At a set speed of 120 seconds per revolution, a time allocation of 15 seconds per each index position is mandated. To index from one position to the next, 2 seconds are required leaving 13 seconds dwell period in this position. The dwell period can be increased or decreased as required, but will affect the production rate. An increase of the dwell period will reduce the production output rate and a decrease in dwell time will increase the production output. The optimum dwell period will depend on the electrolyte composition, desired electrolyte weight to be filled and the specifics of the battery cell  100 . The pressure valves  7   a - d  of each 8-up electrolyte fill head assembly are connected to a commercial rotary union manifold model # AP361 supplied by Scott Rotary Seals Inc. of Hindsdale, N.Y., USA, which enables the provision for continuous application of vacuum or pressure on the battery cells  100  engaged to nozzles  3   a - h  while they are on the rotary index apparatus. 
         [0056]    The battery cells  100  are transported in their corresponding cell supports  6  on a conveyor  25  towards a pick and place station  23 . The pick and place station  23  picks up the cell support  6  including the battery cells  100 , rotates by an angle of 180° and places the cell support  6  including the battery cells  100  onto the first of the eight index stations (position  1  in  FIG. 12 ). After all the eight index positions have been loaded one by one with cell supports  6  including the battery cells  100 , the pick and place station  23  will unload the cell support  6  including the battery cells  100  when returning again at the first index station, while simultaneously picking up the next cell support  6  including the battery cells  100  to be loaded at this first index station. After the 180° rotation, the filled battery cells  100  in the cell support  6  arrive on the conveyor  25 , a position gate  22  releases and the filled battery cells  100  in the cell support  6  will travel downstream on the conveyor  25  to the next station in the process. At the same time, pre-stage gate  21  opens and lets the next cell support  6  including the battery cells  100  advance to the pick and place position gate  22 . Pre-stage clamp  20  holds the upstream cell support  6  including the battery cells  100  in place so that only one cell support  6  including the battery cells  100  can advance to the pick and place position gate  23 . Return conveyor  19  returns empty cell supports  6  for loading with battery cells  100 . 
         [0057]    Referring to the timing diagram of  FIG. 9  which corresponds to a preferred operation of the rotary index table and reference is also made to the eight stages explained in connection with  FIGS. 1 to 8 . The load/unload section with a time allocation of 5 seconds is done in position  1  of the rotary index table and this position also represents the stage of  FIG. 1 . Still in this position  1 , the high vacuum stage of  FIG. 2  starts. Once the total index time of 15 seconds is used up, the 8-up fill head assembly with the battery cells  100  engaged and under vacuum is indexed counterclockwise to the position  2  and the applied vacuum stage continues for a total of 24 seconds followed by a short 1 second return to atmosphere stage of  FIG. 3 . At the 30 second mark, the rotary table indexes again to the next position  3 . In this position, the electrolyte dispense stage of  FIG. 4  has a time allotment of 3 seconds followed by a short 1 second return to atmosphere stage of  FIG. 5 . Still in position  3 , the first loop of  FIG. 6  with high pressure starts. Once the total index time of 15 seconds is used up in this position, the 8-up fill head assembly with the battery cells  100  engaged and under continued high pressure is indexed counterclockwise to the position  4  and thus the previously applied high pressure stage continues. Once the total index time of 15 seconds is used up in this position, the 8-up fill head assembly with the battery cells  100  engaged and still under high pressure is indexed counterclockwise to the position  5 , and the applied high pressure stage continues for a total of 30 seconds, then a short 1 second return to the atmosphere stage of  FIG. 7  takes place and another 1 second of low vacuum stage of  FIG. 8  follows. Still in the position  5 , a second loop corresponding to the stages of  FIGS. 6-8  starts. Once the total index time of 15 seconds is used up in this position, the 8-up fill head assembly with the battery cells  100  engaged and under high pressure is indexed counterclockwise to the position  6  and the applied high pressure stage continues. Once the total index time of 15 seconds is used up in this position, the 8-up fill head assembly with the battery cells  100  engaged and high pressure applied is indexed counterclockwise to the position  7  and the applied high pressure stage continues. Once the total index time of 15 seconds is used up in this position, the 8-up fill head assembly with the battery cells  100  engaged and the high pressure applied is indexed counterclockwise to the position  8  and the applied high pressure stage continues for a total of 45 seconds high pressure, 1 second atmosphere and 1 second low vacuum. At this stage all the electrolyte has been filled into the battery cells  100 , and the battery cells can disengage from the adapter nozzles  3   a - h.  In the position  8 , a provision for flushing the chambers  2   a - h  with a solvent to clean the chambers from salt deposits is provided and applied for 5 seconds. A 2 seconds spare time is allotted for a total cycle time of 120 seconds per fill head. 
         [0058]    It should be noted that during the stage of high pressure soak, the battery cells  100  in the cell support  6  have to be supported by at least an equally high counter-pressure. This is accomplished by means of a pneumatic cylinder acting on the cell support  6 . 
         [0059]    To test the efficacy of this electrolyte fill method a test run of filling semi-finished standard 18650 size Li-Ion battery cells  100  was carried out. The test electrolyte was propylene carbonate (PC) from Ferro Corporation of Cleveland, Ohio. With prior art electrolyte fill systems, 2 fillings with 2.5 g each were needed to achieve a 5 g electrolyte fill. With the method of the present invention it was possible to achieve an average electrolyte weight of 5.3 g during a single fill cycle.  FIG. 13  shows the distribution of the electrolyte weight for a test fill of 2404 battery cell samples. The distribution curve of  FIG. 13  is a very expressive illustration of the superior properties of the method according to the present invention. The battery cells have become filled with optimum volume of electrolyte, leaving practically no void spaces, and the weight-distribution (filling volume) was very uniform. The apparatus according to the present invention has been able to provide such a fast and uniform filling with a high productivity. The small standard deviation of the average weight demonstrates that there was no need for using a further fill cycle. 
         [0060]    In another embodiment, an electrolyte filling apparatus was provided with 16 electrolyte fill heads  1 . This rotary index apparatus with 8×16 fill head assemblies was also set to operate at a speed of one revolution per 120 seconds, thus the production fill rate was 64 battery cells per minute.