Conductive polymer and Si nanoparticles composite secondary particles and structured current collectors for high loading lithium ion negative electrode application

Abstract

Embodiments of the present invention disclose a composition of matter comprising a silicon (Si) nanoparticle coated with a conductive polymer. Another embodiment discloses a method for preparing a composition of matter comprising a plurality of silicon (Si) nanoparticles coated with a conductive polymer comprising providing Si nanoparticles, providing a conductive polymer, preparing a Si nanoparticle, conductive polymer, and solvent slurry, spraying the slurry into a liquid medium that is a non-solvent of the conductive polymer, and precipitating the silicon (Si) nanoparticles coated with the conductive polymer. Another embodiment discloses an anode comprising a current collector, and a composition of matter comprising a silicon (Si) nanoparticle coated with a conductive polymer.

Claims

1. A composition of matter comprising a silicon (Si) nanoparticle coated with a conductive polymer, wherein the conductive polymer is poly(9,9-dioctylfluorene-co-fluorenone) (PFFO), poly(9,9-dioctylfluorene-co-fluorenone-co-methylbenzoic acid) (PFFOMB), or poly(9,9-dioctylfluorene-co-fluorenone-co-benzoic acid) (PFFOBA).

2. The composition of matter of claim 1 wherein the conductive polymer is poly(9,9-dioctylfluorene-co-fluorenone-co-methylbenzoic acid) (PFFOMB).

3. The composition of matter of claim 1 wherein the conductive polymer is poly(9,9-dioctylfluorene-co-fluorenone) (PFFO).

4. The composition of matter of claim 1 wherein the conductive polymer is poly(9,9-dioctylfluorene-co-fluorenone-co-benzoic acid) (PFFOBA).

5. The composition of matter of claim 1 wherein the weight ratio of the conductive polymer to Si nanoparticle ranges from 0.01 to 100.

6. The composition of matter of claim 1 wherein the Si nanoparticle is n-doped or p-doped.

7. The composition of matter of claim 1 wherein a porosity of the composition of matter ranges from 1% to 70% void space.

8. The composition of matter of claim 1 wherein the silicon (Si) nanoparticle coated with a conductive polymer forms a secondary particle.

9. The composition of matter of claim 8 wherein the secondary particle can be spherical, two-dimensional plates, or fibers.

10. The composition of matter of claim 9 wherein the dimension of the secondary particle ranges from 1 nm to 1000 m in diameter.

11. The composition of matter of claim 9 wherein the dimension of the fiber secondary particle ranges from 1 nm to 1000 m in diameter and 2 nm to 10000 m in length.

12. The composition of matter of claim 9 wherein the dimension of the two-dimensional plate secondary particle ranges from 1 nm to 1000 m in thickness and 2 nm to 5000 m in length.

13. An anode comprising: a current collector; and a composition of matter comprising a silicon (Si) nanoparticle coated with a conductive polymer, wherein the conductive polymer is poly(9,9-dioctylfluorene-co-fluorenone) (PFFO), poly(9,9-dioctylfluorene-co-fluorenone-co-methylbenzoic acid) (PFFOMB), or poly(9,9-dioctylfluorene-co-fluorenone-co-benzoic acid) (PFFOBA).

14. The anode of claim 13 wherein the current collector comprises projections perpendicular to a base.

15. The anode of claim 13 wherein the current collector comprises copper (Cu).

16. A method for preparing a composition of matter comprising a plurality of silicon (Si) nanoparticles coated with a conductive polymer comprising: providing Si nanoparticles; providing a conductive polymer; preparing a Si nanoparticles, conductive polymer, and solvent slurry; sonication spraying the slurry into a liquid medium that is a non-solvent of the conductive polymer; and precipitating silicon (Si) nanoparticles that are coated with the conductive polymer.

17. The method of claim 16 wherein the conductive polymer is poly (9,9-dioctylfluorene-co-fluorenone-co-methylbenzoic acid) (PFFOMB).

18. The method of claim 16 wherein the conductive polymer is poly(9,9-dioctylfluorene-co-fluorenone) (PFFO).

19. The method of claim 16 wherein the conductive polymer is poly(9,9-dioctylfluorene-co-fluorenone-co-benzoic acid) (PFFOBA).

20. The method of claim 16 wherein the weight ratio of the conductive polymer to Si nanoparticle ranges from 0.01 to 100.

21. The method of claim 16 wherein the Si nanoparticles are n-doped or p-doped.

22. The method of claim 16 wherein a porosity of the composition of matter ranges from 1% to 70% void space.

23. The method of claim 16 wherein the silicon (Si) nanoparticles coated with a conductive polymer forms a secondary particle.

24. The method of claim 23 wherein the secondary particles can be spherical or fibers.

25. The method of claim 24 wherein the dimension of the secondary particles ranges from 1 nm to 1000 m in diameter.

26. The method of claim 24 wherein the dimension of the fiber secondary particle ranges from 1 nm to 1000 m in diameter and 2 nm to 10000 m in length.

27. The method of claim 16 wherein the solvent comprises chlorobenzene or toluene.

28. The method of claim 16 wherein the liquid medium is methanol or hexane.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention is described with respect to particular exemplary embodiments thereof and reference is accordingly made to the drawings in which:

(2) FIG. 1 illustrates a conceptual approach of Si nanoparticles to form hierarchy structures.

(3) FIG. 2 illustrates a secondary spherical structure for Si/polymer composite. The diameter of the spheres is controlled for lithium-ion diffusion during lithiation and delithiation. The blue color spheres includes Si and conductive polymer.

(4) FIG. 3 illustrates a fiber structure for the Si/polymer composite. The diameter of the fiber is controlled for Lithium-ion diffusion during lithiation and delithiation. The blue color fiber includes Si and conductive polymer.

(5) FIG. 4 illustrates a plate structure for the Si/polymer composite. The thickness is controlled for lithium-ion diffusion during lithiation and delithiation. The other dimensions of the plate are controlled for easy electrode slurry mixing and coatings. The plate includes Si and conductive polymer.

(6) FIG. 5 illustrates a cross-section image of structured Cu current collector, and when coated with polymer composite electrode materials.

(7) FIG. 6 (a) illustrates Si gravimetric specific capacity based on Nano Si particles with PFFOMB polymer and FIG. 6 (b) illustrates electrode cycling stability decay when electrode Si area loading increases.

(8) FIG. 7 illustrates a method for preparing Si/PFFOMB composite spheres.

(9) FIG. 8 illustrates SEM images of secondary Si composite particles made with the spray precipitation method.

(10) FIG. 9 illustrates SEM-EDX maps of Si composite particles. The maps show a uniform distribution of Si, Carbon and Oxygen of the composite particles.

(11) FIG. 10 illustrates a method to fabricate the Si anode electrode with a spray precipitated secondary composite particle electrode.

(12) FIG. 11 illustrates SEM images of the surface of electrode made with the method. FIG. 11 (a)-(e) depicts different magnifications of the electrode. FIG. 11 (d) is a SEM image of composite particles covered by acetylene black.

(13) FIG. 12 illustrates cycling stability of the Si electrode made with the Si/PFFOMB composite secondary particles.

(14) FIG. 13 illustrates a method to fabricate the Si anode electrode with the spray precipitated secondary composite particle electrode.

(15) FIG. 14 illustrates SEM images of the electrode made with the second method. FIG. 14 (a)-(d) are surface images of the electrode at different magnification. FIG. 14 (e)-(h) are cross section images of the electrode.

(16) FIG. 15 illustrates cycling stability of the Si electrode made with the Si/PFFOMB composite secondary particles.

(17) FIG. 16 illustrates SEM images of the electrode surface after cycling.

(18) FIG. 17 illustrates SEM images of the electrode cross-section after cycling.

DETAILED DESCRIPTION OF THE INVENTION

(19) Embodiments of the present invention address the low energy density and limited lifetime of the lithium-ion battery for EV/PHEV application, by applying new anode materials and engineering development. The two main issues that prevent Si from being used as negative electrodes in the lithium-ion chemistry are 1) limited cycling capacity (Limited energy density barrier); although Si promises high energy density, the achievable energy density is low due to the limited material loading (area specific capacity), and 2) high degree of side reactions (Limited lifetime); the reaction between electrolyte and Si surface causes significant high first cycle loss and subsequent fast fade of the lithium-ion cells. Embodiments of the present invention achieve higher energy density as well as prolonged cycling and storage lifetime.

(20) Approach

(21) Si nanoparticles are mixed with a conductive polymer (such as a conductive polymer as described in U.S. patent application Ser. No. 13/294,885 entitled: Electrically Conductive Polymer Binder for Lithium-Ion Battery Electrode, incorporated by reference herein as if fully set forth in its entirety) to form micron size secondary particles as shown in FIG. 1. The conductive matrix is elastic to accommodate volume change within the structure of the secondary particles. The conductive matrix is impermeable to electrolyte solvent penetration, but allows Li ion reversible doping. This will limit direct electrolyte exposure to Si surface, and therefore minimize side reactions.

(22) Si Particles (0.1 nm-10 Micron).

(23) Nano size Si particles can withstand repeated volume change during the Li ion insertion and removal process. These particles can be made by chemical vapor deposition (CVD), colloidal or processed from bulk Si ingot, or other processes. The Si can be n-dopted, p-doped or un-doped particles or a mixture of the above.

(24) Conductive Polymers.

(25) The conductive polymer can be the polymers as described in U.S. patent application Ser. No. 13/294,885, but may not be limited to such polymers. For example, PFFO (poly(9,9-dioctylfluorene-co-fluorenone)), PFFOMB (poly(9,9-dioclylfluorene-co-fluorenone-co-methylbenzoic acid)), PFFOBA (poly(9,9-dioctylfluorene-co-fluorenone-co-benzoic acid))

(26) Formation of Secondary Polymer/Si Composite Structures

(27) One aspect of an embodiment of the invention is to form conductive polymer/primary Si nanoparticles composite secondary particles. These secondary particles can be nano to micron size at different dimensions. The weight ratio of the conductive polymer to Si nanoparticle ranges from 0.01 to 100. Weight ratio of the secondary particles: Polymer:Si=0.01, Si component dominates. Polymer:Si=100, Polymer component dominates.

(28) The optimum size and shape depends on the Si nanoparticle size, the nature of the polymer and the performance of the Si nanoparticle/polymer electrode. The porosity of the secondary composite particles ranges from 0% to 70% void space or free volume. There are a variety of methods to generate these secondary composite particles. The Nanocomposite particles can be spherical particles, two-dimensional plates, or fibers. The discussion below describes the structural features and possible methods to achieve these features.

(29) Sprayed Spherical Secondary Composite Particles

(30) FIG. 2 illustrates a secondary spherical structure for Si/polymer composite. The diameter of the spheres is controlled for lithium-ion diffusion during lithiation and delithiation. The depicted sphere includes Si and conductive polymer.

(31) Slurry preparation: combine Si nanoparticles (0.09 g), a conductive polymer such as PFFOMB (poly(9,9-dioctylfluorene-co-fluorenone-co-methylbenzoic acid)) (0.18 g) in chlorobenzene (5 g) and sonicate for 2 minutes. A Branson 450 sonicator equipped with a solid horn may be used. The sonication power may be set at 70%. A continuous sequence of 2 s pulses followed by 58 s rests may be used. The 100 nm diameter (or smaller) Si nanoparticles sample may be purchased from Sigma-Aldrich.

(32) Spray: The slurry is sprayed to a liquid medium (Hexane or methanol), which is a non-solvent of the polymer. The chlorobenzene solvent will diffuse into the liquid medium (Hexane or methanol). Therefore the nanoparticles solidify into polymer composite particles in the liquid and precipitates out.

(33) Slurry was pumped to a wide spray ultrasonic atomizer nozzle and generator (Model 130K50ST, 130 kHz by Sonaer Inc, operating with 100% of power.) with syringe pump (Model 100 by KD Scientific). The sprayed fine particles were precipitated from 500 mL of methanol with magnetic stirring with a yield of 44%. The concentration of this slurry also effects the final composite particle size and porosity.

(34) In sum, the slurry is sprayed to form micron size Si/conductive polymer composite particles. The size of the secondary particle is controlled by the slurry concentration and spray speed. The micron size composite secondary particle is advantageous for the stability of the Si electrode. This secondary particle limits the amount of surface area that can be exposed to an electrolyte, and therefore increases the surface stability of the electrolyte. The hydrophobic and carbon based conductive polymer minimizes the electrolyte penetration into the secondary particles and facilitates the SIE formation on the secondary particles. The volume expansion is accommodated within the secondary composite particles so there is minimum volume change of the secondary particles.

(35) The polymer composite-Si secondary particle will be collected and used as negative electrode active materials to make electrodes with traditional approaches. The dimension of secondary composite particles range from 1 nm-1000 micron in diameter.

(36) Spanned Fibers

(37) FIG. 3 illustrates a fiber structure for the Si/polymer composite. The diameter of the fiber is controlled for lithium-ion diffusion during lithiation and delithiation. The fiber includes Si and conductive polymer.

(38) Since Li-ion transport is a main issue in the composite particles, spherical particles have a 3-d dimension within the same lithium ion diffusion distance. Another approach is to allow one dimension to expand and leave the other two dimensions within controlled, limited diffusion distance. A fiber geometry is described for this application. The cylindrical structure of the fiber allows two-dimension in the limited distance as the diameter of the fiber. The lithium-ion will diffuse through the fiber wall into the core at a limited distance, while the 3.sup.rd-dimension, along the fiber direction may provide good mechanical properties of the particle and electrode. The fiber diameter will be in the range of 1 nm-1000 micron, and the fiber length is in the range of 2 nm-10000 m. The composite fiber can be made by electro spinning or other methods.

(39) 2-Dimensional Plates

(40) FIG. 4 illustrates a plate structure for the Si/polymer composite. The thickness is controlled for lithium-ion diffusion during lithiation and delithiation. The other dimensions of the plate are controlled for easy electrode slurry mixing and coatings. The plate includes Si and conductive polymer. Another approach is to elongate the spherical particle approach in two dimensions to form a plate structure. Only one dimension is controlled for Li ion diffusion through the plate plain. The other two dimensions are adjusted for easy processing for electrode coating but not for lithium-ion diffusion into the particle. The thickness of the composite plate is in the range of 1 nm-1000 micron. The other 2-dimensions will be in the range of 2 nm-5000 micron.

(41) Electrode Laminate Made with these Composite Particles.

(42) These secondary particles will be used to form electrodes using regular Styrene-Butadiene Rubber (SBR) water soluble binder (or neutralized polyacrylic acid water soluble binder) or other available polymer binder materials and acetylene black additive. The secondary particles have stable dimensions during lithium insertion and removal. Therefore the electrode does not have stress build up during cycling. High loading of Si material of high area specific capacity (>=3 mAh/cm.sup.2) can be achieved in this invention.

(43) Structured Current Collectors as a Method to Improve Active Material Area Specific Loading and Performance

(44) FIG. 5 illustrates a cross-section image of 1) a structured Cu current collector, and 2) a structured Cu current collector when coated with polymer composite electrode materials. To further improve both the area specific loading of the electrode and to improve rate performance, a structured current collector is disclosed to integrate with the Si/polymer composite electrode. The current collector can be made of Cu or any metals that do not react with lithium-ion in the 0-2 V Li/Li.sup.+. The structure on the surface of the current collector (vertical projections) can be the same material as the substrate or other materials that provide electric conductivity.

(45) For example, the structure on a Cu substrate (vertical projections) may be cylinders of approximately 10 micron diameter and 100 micron long. The cylinders are 100 micron distance from each other. The Si/polymer is formulated into slurry and directly applied onto the structured current collector surface. Alternatively, the secondary particles described above are formulated into slurry and applied onto the structured current collector.

(46) Dry Hot Embalming or Solvent Based Embalming

(47) Another embodiment of the invention discloses definition of micron or nanosized structures in addition to the fabrication of a sphere, a plate or a fiber. Additional embodiments of the invention define generation of structure on the coated conductive polymer and Si composite directly. Both dry embalming and solvent embalming have demonstrated defining precise structure features in the nano and micro scale. Additional embodiments of the invention disclose fine tuning the structural features as the conditions require. A structural feature is first developed on a stamp, the stamp may then roll over the polymer/Si composite electrode to stamp out negative features on the electrode laminate.

(48) FIG. 6 illustrates (a) Si gravimetric specific capacity of 2500 mAh/g can be obtained based on Nano Si particles with PFFOMB polymer. However active loading is low 0.5 mg/cm.sup.2 and capacity is around 0.5 mAh/cm.sup.2 Porosity. FIG. 6 (b) Illustrates the electrode cycling stability decays when the electrode Si area loading increases.

(49) In order to improve area loading of Si, a Si/PFFOMB polymer composite is made into composite spheres with an average diameter of 10 micron. The spheres are formed in a methanol solution and collected by decanting the methanol. The process is referred to as a spray precipitation method. FIG. 7 illustrates a method for preparing Si/PFFOMB composite spheres. Step 702 comprises spraying Si/PFFPMB (0.18 g/0.09 g) in chlorobenzene (5 g) slurry. Step 704 precipitating into 500 mL methanol. Step 706 collecting by decanting methanol.

(50) FIG. 8 illustrates SEM images of secondary Si composite particles made with the spray precipitation method. FIG. 8 (a)-(f) are particles at different magnifications. FIG. 8 (g)-(h) are higher magnifications of the secondary composite particle surface.

(51) FIG. 9 illustrates SEM-EDX maps of Si composite particles. The maps show the uniform distribution of Si, Carbon and Oxygen of the composite particles. FIG. 9 (a) illustrates a SEM image of a secondary Si/PFFOMB composite particles. FIG. 9 (b) is the Si map. FIG. 9 (c) is the Carbon map. FIG. 9 (d) is the Oxygen map.

(52) FIG. 10 illustrates a method to fabricate the Si anode electrode with a spray precipitated secondary composite particle electrode. High speed is at above 1000 RPM. Step 1002 comprises decanting the methanol. Step 1004 adding CMC/AB glue. Step 1006 stirring at high speed. Step 1008 casting the electrode.

(53) FIG. 11 illustrates SEM images of the surface of an electrode made with the first method of FIG. 10. Most of the composite particles are broken. FIG. 11 (a)-(e) are different magnifications of the electrode. FIG. 11 (d) is a SEM image of composite particles covered by acetylene black.

(54) FIG. 12 illustrates cycling stability of the Si electrode improved significantly when made with the Si/PFFOMB composite secondary particles.

(55) FIG. 13 illustrates a method to fabricate the Si anode electrode with the spray precipitated secondary composite particle electrode. Low speed is around 100 RPM. Step 1302 comprises decanting the methanol. Step 1304 adding CMC/AB glue. Step 1306 magnetic stirring. Step 1308 casting the electrode.

(56) FIG. 14 illustrates SEM images of the electrode made with the second method of FIG. 13. The composite particle structures are preserved. FIG. 14 (a)-(d) are surface images of the electrode at different magnification. FIG. 14 (e)-(h) are cross section images of the electrode.

(57) FIG. 15 illustrates cycling stability of the Si electrode improved significantly made with the Si/PFFOMB composite secondary particles.

(58) FIG. 16 illustrates SEM images of the electrode surface after cycling at different magnifications. FIG. 16 (a)-(d) are images at different magnifications.

(59) FIG. 17 illustrates SEM images of the electrode cross-section after cycling. FIG. 17 (a)-(d) are images at different magnifications.