Binder and positive active material composition for rechargeable lithium battery, and rechargeable lithium battery including same

1. A binder for a rechargeable lithium battery, the binder comprising a homogeneous mixture of:

a nitrile-based polymer nanoparticle having an average particle size ranging from about 100 nm to about 200 nm; and

a fluorine-containing polymer nanoparticle having an average particle size ranging from about 5 nm to about 300 nm, wherein the nitrile-based polymer nanoparticle and the fluorine-containing polymer nanoparticle are mixed at a weight ratio of about 30:70 to about 80:20.

2. The binder of claim 1 , wherein the fluorine-containing polymer nanoparticle has an average particle size ranging from about 100 nm to about 200 nm.

3. The binder of claim 1 , wherein an average particle size of the fluorine-containing polymer nanoparticle is between one to about two times an average particle size of the nitrile-based polymer nanoparticle.

4. The binder of claim 1 , wherein the nitrile-based polymer nanoparticle comprises poly(acrylonitrile-co-methylmethacrylate), poly(acrylonitrile-co-methacrylic acid), poly(acrylonitrile-co-methylacrylonitrile), poly(acrylonitrile-co-lithium methacrylic acid) (MALi), or a combination thereof.

5. The binder of claim 1 , wherein the fluorine-containing polymer nanoparticle comprises a polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), a polyvinylidenefluoride-tetrafluoroethylene copolymer (PVdF-TFE), or a combination thereof.

6. The binder of claim 1 , wherein the binder comprises a cellulose-based thickener.

7. The binder of claim 6 , wherein the cellulose-based thickener is included in an amount of about 10 parts by weight to about 30 parts by weight based on 100 parts by weight of the binder.

8. The binder of claim 6 , wherein the cellulose-based thickener comprises carboxylmethyl cellulose, methyl cellulose, ethyl cellulose, hydroxy propyl methyl cellulose, hydroxy propyl ethyl cellulose, or a combination thereof.

9. A positive active material composition for a rechargeable lithium battery, the positive active material composition comprising

a binder, the binder comprising a homogeneous mixture of a nitrile-based polymer nanoparticle having an average particle size ranging from about 100 mn to about 200 nm and a fluorine-containing polymer nanoparticle having an average particle size ranging from about 5 nm to about 300 nm, wherein the nitrile-based polymer nanoparticle and the fluorine-containing polymer nanoparticle are mixed at a weight ratio of about 30:70 to about 80:20;

a positive active material;

a conductive material; and

a solvent.

10. The positive active material composition of claim 9 , wherein the solvent comprises water.

11. The positive active material composition of claim 9 , wherein the solvent comprises a mixed solvent of water and an organic solvent.

12. The positive active material composition of claim 9 , wherein the positive active material is selected from the group consisting of Li a Mn 1−b X b D 2 (0.90≦a≦1.8, 0≦b≦0.5); Li a Mn 1−b X b O 2−c D c (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05); LiMn 2−b X b O 4 (0≦b≦0.5); LiMn 2−b X b O 4−c D c (0≦b≦0.5, 0≦c≦0.05); Li a Mn 1−b−c E b X c D α (0.90≦a≦1.8, 0 ≦b≦0.5, 0≦c≦0.05, 0<α≦2); Li a Mn 1−b−c E b X c O 2−α T α (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, 0<α<2); Li a Mn b E c G d O 2 (0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0.001≦d≦0.1); Li a Mn b Co c Ni d G e O 2 (0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5, 0.001≦e≦0.1); LiaMnG b O 2 (0.90≦a≦1.8, 0.001≦b≦0.1) Li a Mn 2 G b O 4 (0.90≦a≦1.8, 0.001≦b≦0.1); MnO 2 ; MnS 2 ; LiMnS 2 ; Li (3−f) Mn 2 (PO 4 ) 3 (0≦f≦2), in which X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; E is Co, Ni, or a combination thereof; T is F, S, P, or a combination thereof; and G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof.

13. A rechargeable lithium battery comprising:

a positive electrode including a positive active material, a conductive material and a binder, the binder comprising a homogeneous mixture of a nitrile-based polymer nanoparticle having an average particle size ranging from about 100 nm to about 200 nm and a fluorine-containing polymer nanoparticle having an average particle size ranging from about 5 nm to about 300 nm, wherein the nitrile-based polymer nanoparticle and the fluorine-containing polymer nanoparticle are mixed at a weight ratio of about 30:70 to about 80:20;

a negative electrode comprising a negative active material; and

a non-aqueous electrolyte.

14. The rechargeable lithium battery of claim 13 , wherein the positive active material is selected from the group consisting of Li a Mn 1−b X b D 2 (0.90≦a≦1.8, 0≦b ≦0.5); Li a Mn 1−b X b O 2−c D c (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05); LiMn 2−b X b O 4 (0≦b≦0.5); LiMn 2−b X b O 4−c D c (0≦b≦0.5, 0≦c≦0.05); Li a Mn 1−b−c E b X c D α (0.90≦a≦1.8, 0≦b ≦0.5, 0≦c≦0.05, 0<α≦2); Li a Mn 1−b−c E b X c O 2−α T α (0.90≦a≦1.8, 0≦b≦0.5, 0≦c≦0.05, 0<α<2); Li a Mn b E c G d O 2 (0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0.001≦d≦0.1); Li a Mn b Co c Ni d G e O 2 (0.90≦a≦1.8, 0≦b≦0.9, 0≦c≦0.5, 0≦d≦0.5, 0.001≦e≦0.1); LiaMnG b O 2 (0.90≦a≦1.8, 0.001≦b≦0.1); Li a Mn 2 G b O 4 (0.90≦a≦1.8, 0.001≦b≦0.1); MnO 2 ; MnS 2 ; LiMnS 2 ; Li (3-f) Mn 2 (PO 4 ) 3 (0≦f≦2), in which X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; E is Co, Ni, or a combination thereof; T is F, S, P, or a combination thereof; and G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof.