according to one embodiment of the present invention , a lead - chromium secondary cell is provided . referring to fig1 the lead - chromium secondary cell comprises lead as the positive electrode 1 , a chromium complex as the negative electrode 2 , a lead foil or lead alloy foil as the positive plate 3 , a copper foil as the negative plate 4 , a diluted sulfuric acid as the electrolyte 5 , and a spacer ( not shown ) disposed between the positive and negative electrodes . by may of example , the positive electrode consists essentially of pbo 2 ( 0 . 1 to 0 . 5 mole ) and a chelating agent ( 0 . 05 - 0 . 3 mole ) and the negative electrode is chromium complex ( 0 . 05 to 0 . 3 mole ). the electrolyte consists essentially of h 2 so 4 having a concentration of 10 - 50 % and may include hcl . the reaction scheme of the charge / discharge thereof is as follows : ( charge ) 3pbso 4 + 6h 2 o + 2cr 3 + → 3pbo 2 + 12h + + 3so 4 2 − + 2cr ( positive electrode ) pbso 4 + 2h 2 o → pbo 2 + 4h + + so 4 2 − + 2 e − during the charge , water is being consumed and the acid increases in concentration until the reaction is complete . since the chromium for a chromium complex during the charge , it does not react and combine with the sulfate radical and thus the capacitance of the secondary cell can be significantly increased . ( discharge ) 3pbo 2 + 12h + + 3so 4 2 − + 2cr → 3pbso 4 + 6h 2 o + 2cr + 3 ( positive electrode ) pbo 2 + 4h + + so 4 2 − → pbso 4 + 2h 2 o during the discharge of the lead - chromium cell , the acid decreases in concentration until any one of the sulfate radical and chromium is exhausted or the chromium complex has a saturated concentration . according to another embodiment of the present invention , an aluminum - chromium secondary cell is provided . referring to fig2 the aluminum - chromium secondary cell comprises a chromium complex as the positive electrode 6 , an aluminum complex as the negative electrode 7 , an aluminum foil as the positive plate 8 , a copper foil as the negative plate 9 , a diluted potassium hydroxide as the electrolyte 10 , and a spacer ( not shown ) disposed between the positive and negative electrodes . by may of example , the positive electrode of this embodiment consists of cr 2 + ( 0 . 1 - 0 . 4 mole ) and the negative electrode consists essentially of aluminum complex ( 0 . 1 - 0 . 4 mole ); the koh electrolyte has a preferred concentration of 5 - 40 %. those skilled in the art will appreciate that a chelating agent in an amount such as 0 . 05 - 0 . 3 mole may be included . the reaction scheme of the charge / discharge thereof is as follows : ( charge ) 2cr 2 + + 7h 2 o + al 3 + complex → cr 2 o 7 2 − + 14h ++ 2al ( positive electrode ) 2cr 2 + + 7h 2 o → cr 2 o 7 2 − + 14h + + 6 e − during the charge of the aluminum - chromium cell , hydroxide ion is formed , so that the electrolyte increases in hydroxide ion concentration until it reaches the original concentration . ( discharge ) cr 2 o 7 2 − + 14h + + 2al → 2cr 2 + + 7h 2 o + al 3 + complex ( positive electrode ) cr 2 o 7 2 − + 14h + + 6 e − → cr 2 + + 7h 2 o during the discharge of the aluminum - chromium cell , the electrolyte decreases in hydroxide ion concentration until any one of the lead and chromate is completely reacted . when charged , overcharge should be avoided because it will result in the depletion of the water in the electrolyte and cause a short circuit . according to still another embodiment of the present invention , a manganese - zinc secondary cell is provided . referring to fig3 the manganese - zinc secondary cell comprises a manganese complex as the positive electrode 11 , a zinc complex as the negative electrode 12 , a lead foil as the positive plate 13 , a copper foil as the negative plate 14 , a diluted potassium hydroxide as the electrolyte 15 , and a spacer ( not shown ) disposed between the positive and negative electrodes . the positive electrode preferably consists essentially of mno 2 ( 0 . 05 - 0 . 2 mole ) and negative electrode preferably consists essentially of zinc complex ( 0 . 1 - 0 . 4 mole ). a chelating agent in an amount such as 0 . 05 to 0 . 3 mole is preferably included . the koh electrolyte may have a concentration of 5 to 30 %. the reaction scheme of the charge / discharge thereof is as follows : ( charge ) 2mn 2 + + 5zn 2 + complex + 8h 2 o → 2mno 4 − + 16h + + 5zn ( positive electrode ) mn 2 + + 4h 2 o → mno 4 − + 8h + + 5 e − during the charge , the hydrogen ion and hydroxide ion ionized from the water will combine with zinc to form a hydrated zinc ion . the hydroxide ion concentration in the electrolyte should be controlled in order to avoid the occurrence of overcharge . ( discharge ) 2mno 4 − + 16h + + 5zn → 2mn 2 + + zn 2 + complex + 8h 2 o ( positive electrode ) mno 4 − + 8h + + 5 e − → mn 2 + + 4h 2 o during the discharge of the manganese - zinc cell , the zinc will result in the occurrence of a hydrated ion or combine with hydrogen to form a zinc - hydrogen complex . a lead - chromium secondary cell comprising lead as the positive electrode , a chromium complex as the negative electrode , a lead foil as the positive plate , a copper foil as the negative plate , a spacer disposed between the positive and negative electrodes , and a diluted sulfuric acid as the electrolyte was prepared . the secondary cell was made into a standard battery for an ordinary mobile phone . the resulting standard battery was fully charged . thereafter , the capacitance and the discharge voltage thereof at room temperature were measured and had 800 mah and 2 . 4 volts , respectively . an aluminum - chromium secondary cell comprising a chromium complex as the positive electrode , an aluminum complex as the negative electrode , an aluminum foil as the positive plate , a copper foil as the negative plate , a spacer disposed between the positive and negative electrodes , and a diluted potassium hydroxide as the electrolyte was prepared . the secondary cell was made into a standard battery for an ordinary mobile phone . the resulting standard battery was fully charged . thereafter , the capacitance and the discharge voltage thereof at room temperature were measured and had 2000 mah and 3 . 0 volts , respectively . a manganese - zinc secondary cell comprising a manganese complex as the positive electrode , a zinc complex as the negative electrode , a lead foil as the positive plate , and a copper foil as the negative plate , a spacer disposed between the positive and negative electrodes , and a diluted potassium hydroxide as the electrolyte was prepared . the secondary cell was made into a standard battery for an ordinary mobile phone . the resulting standard battery was fully charged . thereafter , the capacitance and the discharge voltage thereof at room temperature were measured and had 2000 mah and 2 . 4 volts , respectively . it can be seen from the results of the above examples and descriptions that a secondary cell , according to the present invention has relatively high capacitance and can be manufactured at low cost . moreover , it is used safely and can be stably charged / discharged with large current .