Overdischarge protection in high-temperature cells and batteries
First Claim
1. An electrochemical cell having overdischarge indication and reserve characterized by an output voltage plateau at the midportion of the cell cycle and a gradient in output voltage towards the discharged end of the cycle, said cell comprising:
- a negative electrode containing lithium alloy as active material in the charged state and a matrix containing aluminum in the uncharged state, said negative electrode characterized by a voltage plateau at the central portion of the cell cycle and a gradient in voltage towards the discharge end of the cycle, said gradient in negative electrode voltage is attributable to the presence of a low lithium activity phase that is leaner in lithium than a corresponding phase present in the central portion of the cell cycle;
a positive electrode containing transition metal chalcogenide as active material in the charged state and transition metal with lithium chalcogenide as active material in the uncharged state, said positive electrode including sufficient charged active material to be present concurrently with said low lithium activity phase in the negative electrode wherein said cell exhibits electrochemical capacity at a lower output voltage than that of the output voltage plateau of the cell cycle; and
an electrolyte disposed between said positive and negative electrodes and having high lithium solubility to allow for transfer of lithium between the electrodes.
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Accused Products
Abstract
Overdischarge indication and protection is provided in a lithium alloy - metal sulfide, secondary electrochemical cell and batteries of such cells through use of a low lithium activity phase that ordinarily is not matched with positive electrode material. Low lithium activity phases such as Li0.1 Al0.9 and LiAlSi in correspondence with positive electrode material cause a downward gradient in cell voltage as an indication of overdischarge prior to damage to the cell. Moreover, the low lithium activity phase contributes lithium into the electrolyte and provides a lithium shuttling current as overdischarge protection after all of the positive electrode material is discharged.
42 Citations
16 Claims
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1. An electrochemical cell having overdischarge indication and reserve characterized by an output voltage plateau at the midportion of the cell cycle and a gradient in output voltage towards the discharged end of the cycle, said cell comprising:
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a negative electrode containing lithium alloy as active material in the charged state and a matrix containing aluminum in the uncharged state, said negative electrode characterized by a voltage plateau at the central portion of the cell cycle and a gradient in voltage towards the discharge end of the cycle, said gradient in negative electrode voltage is attributable to the presence of a low lithium activity phase that is leaner in lithium than a corresponding phase present in the central portion of the cell cycle; a positive electrode containing transition metal chalcogenide as active material in the charged state and transition metal with lithium chalcogenide as active material in the uncharged state, said positive electrode including sufficient charged active material to be present concurrently with said low lithium activity phase in the negative electrode wherein said cell exhibits electrochemical capacity at a lower output voltage than that of the output voltage plateau of the cell cycle; and an electrolyte disposed between said positive and negative electrodes and having high lithium solubility to allow for transfer of lithium between the electrodes. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. An overdischarge protection method in a battery of secondary electrochemical cells having lithium alloy negative electrodes and transition metal chalcogenide positive electrodes, said method comprising;
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providing negative electrodes that exhibit a plateau in discharge voltage over a major portion of their discharge capacity and a gradient in discharge voltage at the discharged end of their capacity corresponding to a low lithium activity phase; providing positive electrodes that exhibit a plateau voltage over a major portion of their discharge capacity extending into correspondence with said negative electrode voltage plateau and with a major portion of the capacity at said low lithium activity phase; operating said battery while monitoring its output voltage and reducing its output current when voltage drop corresponding to the gradient in negative electrode voltage occurs to prevent irreversible damage in the most deeply discharged cells. - View Dependent Claims (10, 11, 12, 13, 14, 15)
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16. An electrochemical cell having overdischarge protection comprising a negative electrode having a lithium alloy capacity of NODC+NCYC+NOCC and a positive electrode having a capacity of at least PCYC+POCC and wherein the negative electrode capacity, NODC extends beyond the discharge of all matching positive electrode active material.
Specification