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 this 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 . a schematic of vehicle 100 is shown in fig6 . the vehicle 100 includes a vehicular battery system stack 102 and an oxygen reservoir 104 . a pressure regulator 106 governs provision of oxygen to the vehicular battery system stack 102 during discharge while a multi - stage oxygen compressor 108 is used to return oxygen to the oxygen reservoir 104 during charging operations . the vehicular battery system stack 102 includes one or more negative electrodes ( not shown ) separated from one or more positive electrodes ( not shown ) by one or more porous separators ( not shown ). the negative electrode ( not shown ) may be formed from lithium metal or a lithium - insertion compound ( e . g ., graphite , silicon , tin , lial , limg , li 4 ti 5 o 12 ), although li metal affords the highest specific energy on a cell level compared to other candidate negative electrodes . other metals may also be used to form the negative electrode , such as zn , mg , na , fe , al , ca , si , and other materials that can react reversibly and electrochemically . the positive electrode ( not shown ) in one embodiment includes a current collector ( not shown ) and electrode particles ( not shown ), optionally covered in a catalyst material , suspended in a porous matrix ( not shown ). the porous matrix ( not shown ) is an electrically conductive matrix formed from a conductive material such as conductive carbon or a nickel foam , although various alternative matrix structures and materials may be used . the separator ( not shown ) prevents the negative electrode ( not shown ) from electrically connecting with the positive electrode ( not shown ). the vehicular battery system stack 102 includes an electrolyte solution ( not shown ) present in the positive electrode ( not shown ) and in some embodiments in the separator ( not shown ). in some embodiments , the electrolyte solution includes a salt , lipf 6 ( lithium hexafluorophosphate ), dissolved in an organic solvent mixture . the organic solvent mixture may be any desired solvent . in certain embodiments , the solvent may be dimethyl ether ( dme ), acetonitrile ( mecn ), ethylene carbonate , or diethyl carbonate . in the case in which the metal is li , the vehicular battery system stack 102 discharges with lithium metal in the negative electrode ionizing into a li + ion with a free electron e − . li + ions travel through the separator toward the positive electrode . oxygen is supplied from the oxygen storage tank 104 through the pressure regulator . free electrons e − flow into the positive electrode ( not shown ). the oxygen atoms and li + ions within the positive electrode form a discharge product inside the positive electrode , aided by the optional catalyst material on the electrode particles . as seen in the following equations , during the discharge process metallic lithium is ionized , combining with oxygen and free electrons to form li 2 o 2 or li 2 o discharge product that may coat the surfaces of the carbon particles . the vehicular battery system stack 102 does not use air as an external source for oxygen . external sources , such as the atmosphere , include undesired gases and contaminants . thus , while the oxygen that reacts electrochemically with the metal in a metal / oxygen battery may come from the air , the presence of co 2 and h 2 o in air make it an unsuitable source for some of the media in which the metal / oxygen reactions are carried out and for some of the products that form . for example , in the reaction of li with oxygen in which li 2 o 2 is formed , h 2 o and co 2 can react with the li 2 o 2 to form lioh and / or li 2 co 3 , which can deleteriously affect the performance and rechargeability of the battery . as another example , in a basic medium co 2 can react and form carbonates that precipitate out of solution and cause electrode clogging . in fig6 , all of the components are stored on board the vehicle 100 . in the embodiment of fig6 , the oxygen storage reservoir 104 is separated from the vehicular battery system stack 102 where the reactions take place , but in other embodiments the oxygen storage is more closely integrated with the stack ( for example , incorporated within the cells ). in the embodiment of fig6 , the oxygen storage is done in a tank or other enclosure that is spatially separated from the stack or cells where the reactions are carried out such that a minimal amount of high - pressure housing is required for the vehicle 100 . during discharge ( in which oxygen is consumed ), the pressure of the oxygen gas is reduced by passing it through the pressure regulator 106 such that the pressure of the oxygen that reaches the stack is close to ambient ( i . e ., less than about 5 bar ). during discharge the compressor 108 does not operate . during charge the compressor 108 is operated to compress the oxygen that is being generated within the stack or cells where the reactions are taking place . the compressor 108 in various embodiments is of a different type . in one embodiment which is suitable and mature for a vehicle application in which it is desired to pressurize a gas to more than 100 bar in a unit with a compact size is a multi - stage rotary compressor . when embodied as a multi - stage rotary compressor , each compression step is nearly adiabatic because it involves the rapid action of a piston to compress the gas . commercial units of the appropriate size are widely available at a reasonable cost ; they are used for a variety of applications that require air compression . because each stage of the compressor is nearly adiabatic , in addition to an increase in the pressure there is also an increase in the temperature , as explained with reference to fig7 . fig7 shows the temperature at the end of a single adiabatic compression step starting at a pressure of 1 bar and a temperature of 298 . 15 k assuming constant gas properties . the figure shows that it is impractical to use a single compression step to achieve a pressure of , for example , 350 bar , because the output temperature would be far too high to inject into a tank of standard materials , which in turn is integrated in a vehicle that may have heat - sensitive components . in addition , the final pressure shown in fig7 is for the temperature at the end of the compression step ; thus , after cooling , the pressure will fall . it is important for the temperature of the compressed gas released into the tank to be within a certain range so that it is compatible with the tank material , which in different embodiments is a metal such as aluminum or a polymer , depending on the type of tank . in order to prevent the temperature from rising too high it is necessary to cool the gas at the end of each adiabatic compression step . this is accomplished using the radiator 110 shown in fig6 . the radiator 110 in some embodiments is the same radiator that is used to cool the vehicular battery system stack ; in such embodiments the heat exchange loop also extends into the other components of the battery system such as the vehicular battery system stack 102 and battery system oxygen storage 104 . typically , fluid is passed through the oxygen compressor 108 , removing heat from the oxygen gas after each compression step and bringing the temperature towards that of the radiator fluid . the fluid is passed through the radiator 110 where heat is exchanged with the atmosphere . the compressor is also insulated to prevent the exposure of other parts of the battery system or the vehicle 100 to high temperatures . the cooling of the oxygen after each compression step allows the system to operate closer to the isothermal compression work line shown in fig8 . in particular , fig8 shows the difference in the work required for a single - stage adiabatic compression ( assuming a diatomic gas and constant properties ) compared to the compression work required for isothermal compression . as the figure shows , significantly more work is required for adiabatic compression than isothermal compression . for a multi - stage adiabatic compression process with cooling between stages the amount of work required is between the pure isothermal and single - stage adiabatic lines . thus , the amount of work required for the compression can be lowered compared to adiabatic compression by using multiple compression stages with cooling of the gas at the end of each compression . the magnitude of the compression energy compared to the reaction energy also depends on the negative electrode material with which oxygen is reacting . for example , if the oxygen is reacting with li to form li 2 o 2 on discharge , the reaction energy is 159 wh / mole o 2 . thus , if the charging process takes place with 85 % efficiency , about 24 wh / mole o 2 would be required for cooling for the reaction , suggesting that the amount of cooling required for the compression should be smaller than that required for cooling the stack or cells . in the embodiment of fig6 , all processes associated with the operation of the battery system are controlled by a battery control system 112 . the battery control system 112 controls the flow rate of the fluid that is passed through the radiator 110 and the oxygen compressor 108 and possibly other components on the vehicle 100 . the battery control system 112 includes a memory ( not shown ) in which program instructions are stored and a processor ( not shown ) which executes the program instructions to control the temperature of the oxygen which is compressed into the storage system 104 . the processor is operatively connected to temperature sensors ( not shown ) in the vehicular battery system stack 102 , the oxygen storage 104 , the radiator 110 , and at various stages in the compressor 108 in order to more precisely control the system . in some embodiments , more or fewer temperature sensors are included . a schematic that shows how the temperatures are used by the battery control system 112 is shown in fig9 . in fig9 , the processor obtains a signal indicative of the temperature at the output of the compressor 108 and controls the flow rate of fluid based upon the obtained temperature . in some embodiments , the temperature of one or more intermediate stages of the compressor 108 is obtained , and cooling flow throw the particular stages is modified based upon the temperature . in some embodiments , the temperature of the cooling fluid is obtained , and used to determine or control the flow rate of the cooling fluid . the vehicular battery system stack 102 thus makes use of oxygen ( which may be pure or contain additional components ) stored within a battery cell or external to a cell in a tank or other volume . the oxygen reacts electrochemically with the metal ( which may include li , zn , mg , na , fe , al , ca , si , and others ) to produce energy on discharge , and on charge the metal is regenerated and oxygen gas ( and perhaps other species , such as h 2 o ) are evolved . beneficially , the battery system in the vehicle 100 is thus a completely closed system and species present in ambient air ( e . g ., h 2 o , co 2 , and others ) that may be detrimental to the cell operation are excluded . the battery system provides electrochemical compression of oxygen on charge , and the use of compressed oxygen on discharge , to reduce energy losses associated with mechanical oxygen compression ( which is typically carried out adiabatically , including in a multi - stage adiabatic process ) and to reduce the cost and complexity of a mechanical compressor . the components of the battery system are configured to handle the pressure of the compressed oxygen , including flow fields , bipolar plates , electrodes , separators , and high - pressure oxygen lines . the battery system in some embodiments includes high - pressure seals , an electrode , gas - diffusion layer , and flow field design that provide sufficient mechanical support to prevent pressure - induced fracture or bending ( including with pressure cycling ) that would be deleterious to cell performance and life , and a separator that is impervious to oxygen ( even at high pressures , including up to 350 bar or above ). the minimum pressure in some embodiments is chosen to eliminate delamination of cell components from one another . the minimum pressure in some embodiments is chosen to reduce mass transfer limitations and thereby increase the limiting current . the above described system provides a number of advantages . for example , the use of a multi - stage compressor results in a vehicle with a battery system that is smaller and more economical , and with a higher efficiency , than other compression strategies . additionally , a higher oxygen pressure in the tank can be achieved if the compressor is properly cooled than if there is not a good cooling solution . in addition the compression can be carried out more efficiently if the oxygen can be adequately cooled between each stage . moreover , the vehicle can be charged using only a wall outlet if a compressor is integrated into the vehicle system itself rather than stored externally from the vehicle . integration of the compressor on the vehicle allows for a completely closed gas handling system . if a compressor is stored separately from the vehicle a connection between the external compressor and the gas handling system on the vehicle may introduce contamination . 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 . only the preferred embodiments have been presented and all changes , modifications and further applications that come within the spirit of the disclosure are desired to be protected .