Active material having extended cycle life

Abstract

In one embodiment, the invention provides a novel composition which is stabilized against decomposition when used as an active material for an electrochemical cell. The active material of the present invention comprises particles of spinel lithium manganese oxide (LMO) enriched with lithium by a decomposition product of lithium hydroxide forming a part of each of the LMO particles. The spinel LMO product formed by the decomposition of lithium hydroxide in the presence of the LMO is characterized by a reduced surface area and increased capacity retention (reduced capacity fading) as compared to the initial, non-treated, non-enriched spinel. In another aspect, the treated spinel LMO product is combined with lithium carbonate in a cathode mixture.

1 . A method of treating spinel lithium manganese oxide particles which comprises the steps of (a) forming a mixture comprising said lithium manganese oxide particles and lithium hydroxide; and (b) heating said mixture for a time and at a temperature sufficient to decompose said lithium hydroxide, and to provide treated spinel lithium manganese oxide characterized by reduced surface area and increased lithium content as compared to untreated spinel lithium manganese oxide.  
     
     
         2 . The method of  claim 1  wherein the untreated spinel lithium manganese oxide of step (a) is represented by the formula Li 1+x Mn 2−x O 4 ; and wherein said treated spinel having increased lithium content is represented by the formula Li 1+y Mn 2−y O 4 , where O<x<y≦0.20.  
     
     
         3 . The method of  claim 1  wherein the lithium hydroxide is in particle form in step (a).  
     
     
         4 . The method of  claim 1  wherein said heating step (b) is conducted in an air atmosphere.  
     
     
         5 . The method of  claim 1  wherein said heating is conducted at a temperature in a range of about 300 to about 450° C.  
     
     
         6 . The method of  claim 1  wherein said heating is conducted for a time of about 10 minutes to about 5 hours.  
     
     
         7 . The method of  claim 1  wherein the lithium hydroxide contained in the mixture of step (a) is present in an amount of up to about 10 percent by weight of the total mixture.  
     
     
         8 . The method of  claim 1  wherein the lithium hydroxide contained in the mixture of step (a) is present in an amount of up to about 5 percent by weight of the total mixture.  
     
     
         9 . The method of  claim 1  wherein the amount of lithium hydroxide is one to two percent by weight of the total mixture.  
     
     
         10 . A method of treating spinel lithium manganese oxide particles which comprises the steps of (a) forming a mixture comprising said lithium manganese oxide particles and a lithium containing compound which decomposes at a temperature less than about 450° C.; and (b) heating said mixture for a time and at a temperature sufficient to decompose said lithium containing compound, and to provide treated spinel lithium manganese oxide characterized by reduced surface area and increased lithium content as compared to untreated spinel lithium manganese oxide.  
     
     
         11 . A single phase composition comprising particles of spinel lithium manganese oxide (LMO) enriched with lithium by a decomposition product of lithium hydroxide forming a part of each said particle and further characterized by a reduced surface area and less capacity fading as compared to non-enriched spinel, said lithium-rich spinel having the formula Li 1+y Mn 2−y O 4 , O<y≦0.2.  
     
     
         12 . The composition of  claim 11  wherein said lithium rich spinel is represented by the formula Li 1+y Mn 2−y O 4  where 0.08≦y≦0.20.  
     
     
         13 . A mixture comprising particles of lithium-rich spinel lithium manganese oxide having the formula Li 1+y Mn 2−y O 4  where 0≦y≦0.20 and particles of lithium carbonate.  
     
     
         14 . The mixture of  claim 13  which further includes a binder and particles of conductive carbon, where the binder is intermingled with the spinel particles, the carbonate particles, and the carbon particles.  
     
     
         15 . An electrode having an active material and a binder, said active material comprising particles of lithium-rich spinel lithium manganese oxide having within said particles more lithium and less manganese at interstitial sites as compared to a stoichiometric spinel LiMn 2 O 4 ; said lithium-rich spinel having a formula Li 1+y Mn 2−y O 4  where y is greater than zero and less than or equal to 0.20, and a surface area less than 0.8 m 2 /g (square meter per gram).  
     
     
         16 . The electrode of  claim 15  wherein said active material has a discharge capacity per unit weight of over 90 milliamp hours per gram after 200 cycles.  
     
     
         17 . The electrode of  claim 15  which cycles over 200 cycles in a lithium ion cell at room temperature between about 3 and 4.2 volts.  
     
     
         18 . A lithium ion battery comprising a first electrode, a second electrode which is a counter to said first electrode, and an electrolyte between said electrodes; said first electrode having an active material and a binder, said active material comprising particles of lithium-rich spinel lithium manganese oxide having within said particles more lithium and less manganese at interstitial sites as compared to a stoichiometric spinel LiMn 2 O 4 ; said lithium-rich spinel having a formula Li 1+y Mn 2−y O 4  where y is greater than zero and less than or equal to 0.20, and a surface area less than 0.8 m 2 /g (square meter per gram).  
     
     
         19 . A lithium-rich spinel in particle form having the formula Li 1+y Mn 2−y O 4 , O<y≦0.2 and a surface area less than 0.8 m 2 /g hours per gram as compared to non-enriched spinel having the nominal formula LiMn 2 O 4 .  
     
     
         20 . The lithium-rich spinel of  claim 19  having a surface area of about 0.7 m 2 /g.  
     
     
         21 . The lithium-rich spinel of  claim 19  having a lattice constant, a, of 8.209 Å.