US 2015 0000118A1 (19) United States (12) Patent Application Publication (10) Pub. No.: US 2015/0000118A1 ZHAO et al. (43) Pub. Date: Jan. 1, 2015

(54) METHOD FOR MANUFACTURING (52) U.S. Cl. GRAPHENE-INCORPORATED CPC ...... H0IM 10/04 (2013.01) RECHARGEABLE L-ION BATTERY USPC ...... 29/623.3; 29/623.1; 29/623.5 (71) Applicants:XIN ZHAO, New York, NY (US); (57) ABSTRACT Minjie Li, New York, NY (US) A method for manufacturing a graphene-incorporated rechargeable Li-ion battery discloses a graphene-incorpo (72) Inventors: XIN ZHAO, New York, NY (US); rated rechargeable Li-ion battery with enhanced energy and Minjie Li, New York, NY (US) power delivery abilities. The method comprises the steps (a) fabricating a high-performance anode film based on graphene or graphene hybrid; (b) introducing a desired amount of (21) Appl. No.: 13/927,125 lithium into the anode material to produce a prelithiated graphene-based anode; (c) constructing a full cell utilizing a (22) Filed: Jun. 26, 2013 cathode film and the prelithiated anode film. The graphene based anodes incorporating exfoliated graphene layers over Publication Classification come the large irreversible capacity and initial lithium ion consumption upon pre-lithiation, and demonstrate remark (51) Int. Cl. ably enhanced specific capacity and rate capability over con HIM I/04 (2006.01) ventional anodes.

Patent Application Publication Jan. 1, 2015 Sheet 1 of 4 US 2015/0000118A1

Figure 1A Figure 1B

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Figure 2. Patent Application Publication Jan. 1, 2015 Sheet 2 of 4 US 2015/0000118A1

Graphene nanoplatelet

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Figure 3. Patent Application Publication Jan. 1, 2015 Sheet 3 of 4 US 2015/0000118A1

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Figure 5 Patent Application Publication Jan. 1, 2015 Sheet 4 of 4 US 2015/0000118A1

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Figure 7. US 2015/0000118A1 Jan. 1, 2015

METHOD FOR MANUFACTURING to electrolyte. Nevertheless, these processes kill the intrinsic GRAPHENE-INCORPORATED advantageous features of graphene anode such as high spe RECHARGEABLE L-ION BATTERY cific surface area and Li ion diffusivity, which sacrifices the reversible capacity and rate capability of graphene anode. FIELD OF THE INVENTION 0005. Another common practice to address this issue is to load excess cathode material when assembling Li-ion batter 0001. The present invention relates to Li-ion batteries, and ies, so that the loss of Li ions during the initial cycles can be in particular to a method for manufacturing a graphene-in compensated by the excess Li ions introduced by cathode. corporated rechargeable Li-ion battery However, such method results in a battery cell having cathode and anode which are stoichiometrically unbalanced. The BACKGROUND OF THE INVENTION excess cathode material adds the weight and cost of the cell, 0002 Safety concerns over utilization of pure metallic and may lead to internal shorts, combustible gas generation lithium foils as negative electrodes for rechargeable lithium and thus catastrophic failure if the excess lithium is deposited ion batteries have led to the development of carbonaceous non-uniformly on the anode or isolated from both electrodes materials as alternative anode. Conventional Li-ion batteries (Referring to G. -A. Nazri and B. J. Howie, Method for comprise a primary graphite as a carbonaceous anode in Manufacturing Lithium-Deactivated Carbon Anodes, Euro conjunction with a lithium-containing metal oxide, for pean Patent EP 96201589.7.). example, lithium cobalt oxide (LiCoO2) and lithium manga nese oxide (LiMn2O4) as a cathode. Upon ideal charge/dis SUMMARY OF THE INVENTION charge reactions, lithium ions are intercalated and de-inter 0006. Accordingly, the object of the present invention is to calated between the stacked graphene layers reversibly, provide a method for manufacturing a graphene-incorporated yielding 100% charge/discharge efficiency. The resulting gra rechargeable Li-ion battery, wherein the battery has enhanced phitic compound intercalated with lithium ions may be power Supply ability and quick delivery of the charges. There expressed as LixC6, where x is typically less than 1 for fore the invention describes a design of graphene-incorpo well-ordered graphite without significant turbostratic disor rated rechargeable Li-ion batteries and overcomes the afore dering. This corresponds to a theoretical specific capacity of mentioned problems by prelithiating the graphene-based 372 mAh/g (x=1, e.g. LiC6). In order to minimize capacity electrodes. reduction due to this replacement, X in LixC6 must be maxi 0007. The battery cell contains a graphene-incorporated mized, and the irreversible capacity loss due to side reactions anode preloaded with appropriate amount of lithium, which is in the initial cycles must be minimized. positioned opposite a cathode. The anode and cathode is 0003 Graphene is considered a promising electrode mate physically separated by a non-aqueous ionic conductor in rial toward Li-ion batteries with high power and energy deliv liquid, Solid or gel format. ery, attributed to its high conductivity and high Surface area 0008. The approach of the present invention comprises (a) without pore tortuosity. The large specific Surface area, abun fabricating a high-performance anode film based on graphene dant edge planes and defects of graphene, as well as micro or graphene hybrid; (b) introducing a desired amount of cavities and pores present between rearranged graphene crys lithium into the anode film to produce a prelithiated tallites provide excess Li ion binding and storage sites graphene-based anode film; (c) constructing a full cell utiliz compared with conventional graphitic anodes (see FIGS. 1A ing a cathode film and the prelithiated graphene-based anode and 1B). FIGS. 1A and 1B show a structural model of an film. The graphene-based anodes incorporating pristine or ordered graphitic carbon (1A) and a disordered graphene functionalized graphene layers demonstrate remarkably stacks (1B). Pronounced improvement of reversible capacity enhanced specific capacity and rate capability over conven has therefore been demonstrated in graphene anode, and very tional graphitic anode (referring to FIG. 3), offering possi large reversible capacity up to 740 mAh/g (composition of bilities to achieve unprecedented combinations of energy and LiC3) can be envisioned. Besides, lithium intercalation into power output for high-performance Li-ion batteries. Lithiat graphene is not limited by the kinetics of lithium staging ing the graphene-based anodes prior to battery cell assembly reactions within conventional graphitic anodes. The high Li eliminates the Li ion consumption associated with the irre ion diffusivity and electrical conductivity greatly accelerates versible reactions of graphene efficiently, and the cells attain the kinetics of charge-transfer and diffusion reactions of improved electrode utilization, capacity retention and cycling graphene anode, which can therefore operate at very high efficiency with minimized safety hazards during operation. charge/discharge rates while retaining a high capacity. 0009 Lithiation of anode materials in a prior art Li-ion 0004. However, irreversible reactions usually occur inten battery usually induces a large Volumetric expansion to the sively in graphene anode when contacting with electrolyte. active particles and electrode films, for example 300-400% of This is caused by the large Surface area of irregular plates and its original dimension of silicon particle or thin film (see Ref. direct exposure of highly active edge planes of graphene 2). Such highly lithiated particles or films are extremely layers. The irreversible consumption of Li ions in the initial brittle and prone to pulverization or fragmentation during cycles leads to deficiency of Li ions in the battery cell and Successive charge/discharge cycling. These two issues can be destruction of original anode structures, and Subsequent significantly mitigated by the incorporation of graphene in capacity fading is evitable. To Suppress the irreversible reac the anode formation. First, the Small size and mechanical tions of Li ions with carbonaceous materials, the carbon flexibility of graphene sheets can readily accommodate any aceous particles are usually subjected to grinding and reas Li ion insertion/extraction stress and Volume variation, rep sembly to obtain a smooth Surface, or high-temperature resenting a highly stable lithium-retentive anode system that graphitization processes to eliminate structural disordering. can be coupled with lithium-free cathode materials to con Further irreversible reactions associated with edge planes can struct full battery cells (Ref.3). Such graphene-based anodes be reduced by coating the particles to prevent direct exposure with superb tolerance to structural deformation also provide a US 2015/0000118A1 Jan. 1, 2015 robust matrix to Support or incorporate other high-capacity ing a cathode film and the prelithiated graphene-based anode active species Such as metal and intermetallic alloys, which film. The graphene-based anodes incorporating pristine or could lead to a variety of high-performance composite functionalized graphene layers demonstrate remarkably anodes. The mechanical integrity of Such anodes is conse enhanced specific capacity and rate capability over conven quently preserved after lithiation. tional graphitic anode (referring to FIG. 3). FIG. 3 shows a preparation procedure of prelithiated graphene nanoplatelet BRIEF DESCRIPTION OF THE DRAWINGS: based anode.), offering possibilities to achieve unprecedented combinations of energy and power output for high-perfor 0010 FIG. 1A shows a structural model of an ordered mance Li-ion batteries. Lithiating the graphene-based anodes graphitic carbon (left). prior to battery cell assembly eliminates the Liion consump 0.011 FIG. 1B shows a structural model of a disordered tion associated with the irreversible reactions of graphene graphene stacks (right). efficiently, and the cells attain improved electrode utilization, 0012 FIG. 2 shows a Li-ion battery with a cathode and a capacity retention and cycling efficiency with minimized prelithiated graphene-based anode immersed in an electrolyte safety hazards during operation (as illustrated in FIG. 4). FIG. and isolated by a polymer separator. 4 shows a specific capacity and coulombic efficiency of 0013 FIG.3 shows a preparation procedure of prelithiated graphene nanoplatelet-based anodes at various current den graphene nanoplatelet-based anode. sities in comparison with conventional graphitic anode. 0014 FIG. 4 shows a specific capacity and coulombic 0021 Lithiation of anode materials in a prior art Li-ion efficiency of graphene nanoplatelet-based anodes at various battery usually induces a large Volumetric expansion to the current densities in comparison with conventional graphitic active particles and electrode films, for example 300-400% of anode. its original dimension of silicon particle or thin film (see A. 0015 FIG. 5 shows the charge/discharge curves of Zhamu and B. Z. Jang, Method of Producing Prelithiated graphene nanoplatelet-based anodes in comparison with con Anodes for Secondary Lithium Ion Batteries, U.S. patent ventional graphitic anode. application Ser. No. 12/291,689.) Such highly lithiated par 0016 FIG. 6 shows the discharge capacity and coulombic ticles or films are extremely brittle and prone to pulverization efficiency of Li-ion batteries with NMC cathode and or fragmentation during Successive charge/discharge cycling. graphene nanoplatelet-based anodes. The 1st cycle coulom 0022. The small size and mechanical flexibility of bic efficiency of cells with prelithiated graphene anode is graphene sheets can readily accommodate any Li ion inser 91% compared to 32% for non-lithiated anode. tion/extraction stress and Volume variation, representing a 0017 FIG. 7 shows the Charge/discharge curves of Li-ion highly stable lithium-retentive anode system that can be batteries with NMC cathode and graphene nanoplatelet coupled with lithium-free cathode materials to construct full based anodes. battery cells (Referring to N. Liu, L. Hu, M. T. McDowell, A. Jackson and Y. Cui, Prelithiated Silicon Nanowires as an DETAILED DESCRIPTION OF THE PREFERRED Anode for Lithium Ion Batteries, ACS Nano, 5 (2011), 6487 EMBODIMENTS 6493.). Such graphene-based anodes with superb tolerance to 0.018. In order that those skilled in the art can further structural deformation also provide a robust matrix to Support understand the present invention, a description will be or incorporate other high-capacity active species such as described in the following in details. However, these descrip metal and intermetallic alloys, which could lead to a variety of tions and the appended drawings are only used to cause those high-performance composite anodes. skilled in the art to understand the objects, features, and 0023 To fabricate a graphene-based anode, graphene characteristics of the present invention, but not to be used to nanoplatelets (GnP), functionalized graphene, reduced confine the scope and spirit of the present invention defined in graphene oxide etc. is mixed with a polymer binder and a the appended claims. conductive additive such as carbon black, carbon nanotubes 0019. The present invention describes a design of (CNTs) or carbon nanofibers (CNFs). The mixture is depos graphene-incorporated rechargeable Li-ion batteries and ited onto current collectors by tape casting, spin coating, dip overcomes the aforementioned problems by prelithiating the coating or lamination etc. The binders include at least one of graphene-based electrodes. The battery cell contains a polyvinylidene fluoride (PVDF), copolymers of PVDF e.g. graphene-incorporated anode 10 preloaded with appropriate poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF amount of lithium, which is positioned opposite a cathode 20 HFP), polyvinylchloride (PVC), polyethylene (PE), polypro (see FIG. 2). The anode and cathode is physically separated pylene (PP), ethylene vinyl acetate, polyvinyl alcohol (PVA), by a non-aqueous ionic conductor 30 in liquid, Solid or gel and celluloses e.g. methyl cellulose, carboxymethyl cellu format. FIG.2 shows a Li-ion battery with a cathode 20 and a lose, ethyl cellulose, butyl cellulose cellulose acetate and prelithiated graphene-based anode 10 immersed in an elec cellulose nitrate. Other electrochemically active species can trolyte 30 and isolated by a polymer separator 40. A layer of be introduced to graphene to form a hybrid active material. anode current collector 50 is arranged at an outer side of the These materials can be metals e.g. silicon, germanium and anode 10 for collecting current generating from the electrode tin, redox-based transition metal oxides e.g. tin oxide (SnO 10, and a layer of cathode current collector 60 is arranged at and SnO2), iron oxide (FexOy) and cobalt oxide (CoO and an outer side of the cathode 20 for collecting current gener Co3O4), and electrically conducting polymers. ating from the electrode 20. 0024. The cathode film is a blend of a conductive additive 0020. The approach of the present invention comprises (a) e.g. graphite flakes, CNTs, CNFS or graphene, a polymer fabricating a high-performance anode film based on graphene binder and an active material Such as intercalation materials or graphene hybrid; (b) introducing a desired amount of e.g. LiCoO2, LiMn2O4, lithium nickel oxide (LiNiO2), lithium into the anode film to produce a prelithiated lithium iron phosphate (LiFePO4), manganese oxide graphene-based anode film; (c) constructing a full cell utiliz (MnO2), vanadium oxide (V2O5) and molybdenum oxide US 2015/0000118A1 Jan. 1, 2015

(MoC)3), or Sulfur, or active organics e.g. electrically con CR2032-type coin cell. Metallic lithium is used as the counter ducting polymers and oxocarbon salts. electrode. The working electrode is fabricated by first pasting 0025. The electrolyte is a non-aqueous solution contain a mixture of graphite or GnP flakes, carbon black and PVDF ing one or a few types of carbonates e.g. ethylene carbonate with a weight ratio of 82:8:10 onto supper foil. The typical (EC), propylene carbonate (PC), dimethyl carbonate (DMC) mass loading level is about 1 mg percm2 area of the electrode. and diethyl carbonate (DEC) etc., and a lithium salt e.g. The electrode was dried at 90° C. for 12 hour under vacuum LiPF6, LiClO4, LiTFSI, LiBOB, LiAlO2 and LiBF4. before being assembled into a coin cell in an. Ar-filled glove 0026. Alternatively, the electrolyte can be a gel or solid box. The electrolyte solution is 1 M LiPF6/ethylene carbon film, which also acts as a separator. It consists of a polymer ate (EC)/dimethyl carbonate (DMC) (1:1 by volume). A host e.g. PVDF, PVDF-HFP. poly(ethylene oxide) (PEO), microporous glass-fiber membrane (Whatman) is used as the poly(acrylonitrile) (PAN), and poly(methyl methacrylate) separator. Lithium insertion into the electrode is referred to as (PMMA) or an ionic liquid e.g. PYR14FSI, BMIMICl and the discharge test, and extraction is referred to as the charge EMIMIC1, a lithium salt, and an optional plasticizer e.g. teSt. inorganic nanoparticles (SiO2, Al2O3 and MgO etc.), EC and 0031) To prelithiate the GnP electrode, the electrode film PC to strengthen the ionic conductivity. is directly attached to a lithium foil (0.38 mm thick, Sigma 0027. To prelithiate the anode film, one method is to dis Aldrich) with 1 M LiPF6/EC/DMC electrolyte between perse stabilized lithium metal powders in a non-polar solvent inside an Ar-filled glovebox. After 12 hours the electrode is which is then deposited onto the top surface of the anode film peeled off from the Li foil and washed with acetonitrile to uniformly via spray coating, drop casting or spin coating etc. remove the residual electrolyte and lithium salt if necessary. Alternatively, the stabilized lithium metal powders can be 0032 To assemble a full cell, the separator 40 is placed on mixed with the anode slurry during casting of anode films. the anode 10, and a lithium nickel manganese cobalt oxide These stabilized lithium metal powders are usually pre (NMC) cathode 20 is stacked on top. The full cell is sealed coated with a stable protection layer and therefore safe to be inside an aluminum laminated pouch with metal current col handled in an environment without moisture. A powderprod lectors 50, 60 extending out The electrolyte solution contain uct with metallic lithium content above 98% is commercially ing 1 M LiPF6/ethylene carbonate (EC)/dimethyl carbonate available from FMC Corporation. The amount of lithium is (DMC) (1:1 by volume) is injected into the pouch before determined by the irreversible capacity of the anode film, Sealing. which is sufficient to compensate the lost Li ions during the 0033. The present invention is thus described, it will be initial cycles. obvious that the same may be varied in many ways. Such 0028. Another method is to physically attach metallic variations are not to be regarded as a departure from the spirit lithium foils or ribbons to the top surface of the anode film in and Scope of the present invention, and all such modifications an inert atmosphere. An organic solvent e.g. DMC, PC or as would be obvious to one skilled in the art are intended to be above liquid electrolyte is injected to the lithium/anode inter included within the scope of the following claims. face if necessary, which functions as a media to accelerate Li What is claimed is: ion diffusion. The Li ions diffuse from the metallic lithium 1. A method for manufacturing a graphene-incorporated into the anode film spontaneously, and the residual lithium is rechargeable Li-ion battery comprising the steps of removed by detaching from the anode surface. The lithiation (a) fabricating a high-performance anode film based on depth of anode can be varied upon changing the lithiation graphene or graphene hybrid; time and monitored through the open circuit Voltage of the (b) introducing a predetermined amount of lithium into the cell. Typically 12-20 hour lithiation ensures a saturation of anode film to produce a prelithiated graphene-based lithium percentage in the anode film. anode film; 0029 Prelithiation can also be achieved galvanostatically (c) constructing a full cell utilizing a cathode film and the by assembling the anode film into a half cell e.g. a coin cell, prelithiated graphene-based anode film; the cathode and pouch cell or standard electrochemical cell containing a anode is immersed in a liquid electrolyte and a separator lithium counter electrode and electrolyte solution. The anode is placed in the electrolyte for separating the anode and film undergoes a first cycle followed by lithiation to a the cathode, alternatively, the electrolyte is one of a gel cathodic voltage limit vs. Li, which determines the lithiation or solid films; and depth. The half cell is then taken apart and the lithiated anode wherein the graphene-based anodes incorporating exfoli film can be reassembled into a full cell. ated graphene layers overcome the large irreversible capacity and initial lithium ion consumption upon pre EXAMPLE lithiation, and demonstrate remarkably enhanced spe 0030. To prepare partially oxidized GnP (ox-GnP), refer cific capacity and rate capability over conventional ring to FIG. 3, commercial GnP nanoplatelets are immersed anodes. in an acid, e.g. concentrated nitric acid or nitric acid and 2. The method of claim 1, wherein the step of introducing Sulfuric acid mixture. An oxidant e.g. potassium chlorate or a predetermined amount of lithium comprising the steps of potassium bichromate are added into mixture under vigorous depositing stabilized lithium metal powders onto a top Sur stirring. The reacted GnP is washed thoroughly and partially face of the anode film uniformly via spray coating, drop oxidized GnP intercalated with acid was obtained upon dry casting or spin coating; wherein an amount of lithium is ing. The ox-GnP is then re-intercalated with tetrabutylammo determined by an irreversible capacity of the anode film, nium hydroxide (TBA) or oleylamine solution in dimethyl which is sufficient to compensate lost Li ions during initial formamide (DMF) via stirring or solvothermal reaction at cycles; elevated temperature. After cooling down, the exfoliated ox 3. The method of claim 1, wherein the step of introducing GnP is washed and re-dispersed in DMF or N-methyl-2- a predetermined amount of lithium comprising the steps of pyrrolidone (NMP). charge/discharge tests were done using a attaching metallic lithium foils or ribbons physically to a top US 2015/0000118A1 Jan. 1, 2015

Surface of the anode film, and an organic solvent being (PVDF-HFP), polyvinyl chloride (PVC), polyethylene (PE), injected to the lithium/anode interface; then the Li ions dif polypropylene (PP), ethylene vinyl acetate, polyvinyl alcohol fusing from the metallic lithium into the anode film sponta (PVA), and celluloses. neously, and the residual lithium being removed by detaching 11. The method of claim 10, wherein the cellulose is one of from the anode Surface; methyl cellulose, carboxymethyl cellulose, ethyl cellulose, 4. The method of claim 1, wherein the step of introducing butyl cellulose cellulose acetate and cellulose nitrate. predetermined amount of lithium comprising the steps of 12. The method of claim 1, wherein the cathode film is a assembling the anode film into a half cell with Li counter blend of a conductive additive and at least one of active electrode and electrolyte, by galvanostatic cycling to a materials including lithium metal phosphate (LiFePO4, LiM cathodic voltage limit vs. Li, which determines the lithiation nPO4 etc.), manganese oxide (MnO2), vanadium oxide depth; the half cell is then taken apart and the lithiated anode (V2O5) and molybdenum oxide (MoC3), sulfur, or active film can be reassembled into a full cell. organic compounds. 5. The method of claim 1, wherein for forming a graphene 13. The method of claim 1, wherein the electrolyte between based anode, graphene nanoplatelets (GnP), functionalized the anode and cathode is a non-aqueous solution containing at graphene, reduced graphene oxide and other predetermined least one of carbonates and a lithium salt. materials are mixed with a polymer binder and a conductive 14. The method of claim 13, wherein the carbonate additive; the mixture is deposited onto anode current collector includes ethylene carbonate (EC), propylene carbonate (PC), and cathode current collector by tape casting, spin coating, dimethyl carbonate (DMC) and diethyl carbonate (DEC). dip coating or lamination. 15. The method of claim 13, wherein the lithium salt is one 6. The method of claim 1, wherein electrochemically active of LiPF6, LiClO4, LiTFSI, LiBOB, LiAlO2 and LiBF4. species are introduced to graphene to form a hybrid active 16. The method of claim 1, wherein a separator is placed in material, which are selected from metals or metal oxides or the electrolyte for separating the anode and the cathode. electrically conducting polymers. 17. The method of claim 16, wherein the separator is one of 7. The method of claim 6, wherein the metal is one of a microporous polymer film such as PVDF, PVDF-HFP. poly silicon, germanium and tin. (ethylene oxide) (PEO), poly(acrylonitrile) (PAN), and poly 8. The method of claim 6, wherein the metal oxide is at least (methyl methacrylate) (PMMA). one of redox-based transition metal oxides including tin oxide (SnO and SnO2), iron oxide (FexOy) and cobalt oxide 18. The method of claim 1, wherein the electrolyte is one of (CoO and Co3O4). an ionic liquid, a lithium salt, and an optional plasticizer Such 9. The method of claim 5, wherein the conductive additive as EC and PC for strengthening the ionic conductivity. includes carbon black, carbon nanotubes (CNTs) and carbon 19. The method of claim 18, wherein the ionic liquid is nanofibers (CNFs) selected from PYR14FSI, BMIMICl and EMIMIC1, and the 10. The method of claim 5, wherein the polymer binder optional plasticizer is selected from inorganic nanoparticles includes polyvinylidene fluoride (PVDF), copolymers of of SiO2, Al2O3 and MgO. PVDF; poly(vinylidene fluoride-co-hexafluoropropylene) k k k k k