VARIABLE CAPACITY CELL ASSEMBLY
Electrochemical cells containing nanostructured negative active materials and composite positive active materials and methods of fabricating such electrochemical cells are provided. Positive active materials may have inactive components and active components. Inactive components may be activated and release additional lithium ions, which may offset some irreversible capacity losses in the electrochemical cells. In certain embodiments, the activation releases lithium ion having a columbic content of at least about 400 mAh/g based on the weight of the activated material.
1 . An electrochemical cell comprising:
a negative electrode containing a nanostructured high capacity active material; and
a positive electrode containing a composite active material having an inactive component and an active component, wherein the inactive component is convertible to the active component when activated.
2 . The electrochemical cell of claim 1 , wherein the activation comprises a release of lithium ions having a columbic content of at least about 100 mAh/g based on the weight of the converted inactivate component.
3 . The electrochemical cell of claim 1 , wherein the activation comprises a release of lithium ions having a columbic content of at least about 300 mAh/g based on the weight of the inactive component.
4 . The electrochemical cell of claim 1 , wherein the amount of the inactive component in the positive electrode prior to activation is sufficient to approximately match the irreversible lithium insertion capacity of the negative electrode.
5 . The electrochemical cell of claim 1 , wherein a stoichiometric ratio of the active component to the inactive component prior to the activation is between about 1/10 and 10.
6 . The electrochemical cell of claim 1 ,
wherein the active component comprises LiMO 2 , wherein M comprises one or more ions with an average oxidation state of three selected from the group consisting of vanadium (V), manganese (Mn), iron (Fe), cobalt (Co), and nickel (Ni); and
wherein the inactive component is in the form of Li 2 M′O 3 , wherein M′ comprises one or more ions with an average oxidation state of four selected from the group consisting of manganese (Mn), titanium (Ti), zirconium (Zr), ruthenium (Ru), rhenium (Re), and platinum (Pt).
7 . The electrochemical cell of claim 1 , wherein the nanostructured active material comprises silicon-containing nanowires substrate rooted to a conductive substrate.
8 . The electrochemical cell of claim 1 , wherein the nanostructured active material comprises a core and a shell and wherein the material of the core is different from the material of the shell.
9 . The electrochemical cell of claim 1 , wherein the nanostructured active material comprises structures having an average aspect ratio of at least about 100 in a fully discharged state.
10 . The electrochemical cell of claim 1 , wherein the nanostructured active material comprises structures having an average cross-section dimension of between about 1 nanometer and 300 nanometers in a fully discharged state.
11 . The electrochemical cell of claim 1 , wherein the nanostructured active material comprises structures having an average length of at least about 100 micrometer in a fully discharged state.
12 . The electrochemical cell of claim 1 , wherein the nanostructured active material forms a layer having a porosity of less than about 75 percent.
13 . The electrochemical cell of claim 1 , wherein the negative electrode has a capacity to sufficient to lithiate all lithium ions available for transfer between the two electrodes after the activation of the inactive component.
14 . A method of fabricating an electrochemical cell comprising a negative electrode with a nanostructured active material and a positive electrode with a composite active material comprising an inactive component and an active component, the method comprising:
activating at least a fraction of the inactive component by converting the fraction into an active form accompanied by release of lithium ions having a columbic content of at least about 100 mAh/g based on the weight of the fraction
wherein the negative electrode comprises an irreversibly inserted amount of lithium that is no less than the released lithium ions.
15 . The method of claim 14 , wherein at least a fraction of the irreversibly inserted amount of lithium ions is inserted into the negative electrode during the activation.
16 . The method of claim 14 , wherein the nanostructured active material having a reversible lithium insertion capacity of at least about 700 mAh/g and an irreversible lithium insertion capacity of at least about 200 mAh/g after at least 20 cycles.
17 . The method of claim 14 further comprising:
aligning the negative electrode relative to the positive electrode to form an assembly selected from the group consisting of a jellyroll and a stack; and
encapsulating the assembly into a case,
wherein the activation is performed after the encapsulation of the assembly.
18 . The method of claim 14 , wherein the activation comprises charging the electrochemical cell to at least about 4.4V.
19 . The method of claim 14 , wherein the activation is performed after at least one cycle of the electrochemical cell.
20 . A battery pack comprising an electrochemical cell that includes
a negative electrode containing a nanostructured high capacity active material; and
a positive electrode containing a composite active material having an inactive component and an active component, wherein the inactive component is convertible to the active component when activated.