Electrodes with silicon oxide active materials for lithium ion cells achieving high capacity, high energy density and long cycle life performance
Improved negative electrodes can comprise a silicon based active material blended with graphite to provide more stable cycling at high energy densities. In some embodiments, the negative electrodes comprise a blend of polyimide binder mixed with a more elastic polymer binder with a nanoscale carbon conductive additive. The silicon-based blended graphite negative electrodes can be matched with positive electrodes comprising nickel rich lithium nickel manganese cobalt oxides to form high energy density cells with good cycling properties.
1. A negative electrode for a lithium ion cell comprising from about 78 wt % to about 92 wt % an active material, from about 1 wt % to about 7 wt % nanoscale conductive carbon and from about 6 wt % to about 20 wt % polymer binder, wherein the polymer binder comprises at least about 50 wt % polyimide and at least about 5 wt % of a distinct second polymer binder with an elastic modulus of no more than about 2.4 GPa.
2. The electrode of claim 1 wherein the active material comprises a silicon-based composition.
3. The electrode of claim 2 wherein the silicon based composition comprises a silicon oxide-silicon-carbon composite composition.
4. The electrode of claim 2 wherein the active material comprises from about 5 wt % to about 60 wt % graphite blended with the silicon-based composition.
5. The electrode of claim 1 wherein the distinct second polymer binder comprises poly vinylidene fluoride, carboxymethyl cellulose, styrene-butadiene rubber, lithiated polyacrylic acid, copolymers thereof and mixtures thereof and has an elongation of at least about 35%.
6. The electrode of claim 1 wherein the polyimide has a tensile strength of at least about 60 MPa.
7. The electrode of claim 1 wherein the nanoscale conductive carbon comprises carbon black, carbon nanofibers, carbon nanotubes, or a combination thereof.
8. The electrode of claim 1 comprising from about 78 wt % to about 88 wt % an active material, from about 2 wt % to about 6 wt % nanoscale conductive carbon and from about 8 wt % to about 18 wt % polymer binder.
9. The electrode of claim 1 wherein the polymer binder comprises from about 60 wt % to about 90 wt % polyimide, and at least about 10 wt % distinct polymer binder having an elastic modulus of no more than about 2 GPa.
10. The electrode of claim 1 wherein the active material comprises from about 50 wt % to about 90 wt % silicon-oxide based material and from about 10 wt % to about 50 wt % graphite, wherein the graphite has a BET surface area from about 2 m 2 /g to about 100 m 2 /g.
11. The electrode of claim 1 having a specific capacity at least about 1000 mAh/g cycled against lithium metal from 5 millivolts (mV) to 1.5V at a rate of C/3.