US009203O84B2 (12) United States Patent (10) Patent No.: US 9.203,084 B2 Wang et al. (45) Date of Patent: Dec. 1, 2015 (54) CATHODE ACTIVE MATERIAL-COATED USPC ............ 429/217, 212, 231.8, 231.7, 219, 405 DISCRETE GRAPHENE SHEETS FOR See application file for complete search history. LITHIUM BATTERIES AND PROCESS FOR PRODUCING SAME (56) References Cited (71) Applicants:Yanbo Wang, Huber Heights, OH (US); U.S. PATENT DOCUMENTS Bor Z, Jang, Centerville, OH (US); Hui 7,824,651 B2 11/2010 Zhamu et al. He, Beavercreek, OH (US); Aruna 8,236,446 B2* 8/2012 Lu ................................. 429,209 Zhamu, Centerville, OH (US) 8,765,302 B2* 7/2014 Chen et al. ... ... 429,219 2011/O165466 A1* 7, 2011 Zhamu et al. .. 429,231.8 (72) Inventors: Yanbo Wang, Huber Heights, OH (US); 2013/0323,603 A1* 12/2013 Ryu et al. ... ... 429/320 Bor Z, Jang, Centerville, OH (US); Hui 2014/0013588 A1* 1/2014 Wang et al. ... 29.623.2 He, Beavercreek, OH (US); Aruna 2014/0141328 A1* 5, 2014 Dai et al. ...................... 429,217 Zhamu, Centerville, OH (US) OTHER PUBLICATIONS (73) Assignee: Nanotek Instrurments, Inc., Dayton, Y. Ding, et al. "Preparation of nano-structured LiFePO4, graphene OH (US) composites by co-precipitation method.” Electrochemistry Commu nications 12 (2010) 10-13. (*) Notice: Subject to any disclaimer, the term of this patent is extended or adjusted under 35 * cited by examiner U.S.C. 154(b) by 179 days. Primary Examiner — Nina Bhat (21) Appl. No.: 13/987,567 (57) ABSTRACT (22) Filed: Aug. 8, 2013 Provided is a cathode (positive electrode) of a lithium battery and a process for producing this cathode. The electrode com (65) Prior Publication Data prises a cathode active material-coated graphene sheet and the graphene sheet has two opposed parallel Surfaces, US 2015/OO44556A1 Feb. 12, 2015 wherein at least 50% area (preferably greater than 80%) of one of the two Surfaces is coated with a cathode active mate (51) Int. Cl. rial coating. The graphene material is in an amount of from HOLM 4/36 (2006.01) 0.1% to 99.5% by weight and the cathode active material is in HOLM 4/04 (2006.01) an amount of at least 0.5% by weight (preferably greater than HOIM 4/O2 (2006.01) 80% and more preferably greater than 90%), all based on the HOIM IO/O56 (2010.01) total weight of the graphene material and the cathode active (52) U.S. Cl. material combined. The cathode active material is preferably CPC ................ H01 M 4/366 (2013.01); H01 M 4/04 an inorganic material, an organic or polymeric material, a (2013.01); H0 IM 4/0421 (2013.01): HOIM metal oxide/phosphate/sulfide, or a combination thereof. 10/056 (2013.01); HOIM 2004/028 (2013.01) Also provided is a lithium battery, including a lithium-ion, (58) Field of Classification Search lithium-metal, or lithium-sulfur battery. CPC ....... H01M6/00; H01M 10/00; H01M 10/04; HO1 M 4/625 35 Claims, 10 Drawing Sheets 3:3::::::::38:88:8 38:::::::::::::::38x: U.S. Patent Dec. 1, 2015 Sheet 2 of 10 US 9.203,084 B2 : U.S. Patent Dec. 1, 2015 Sheet 3 of 10 US 9.203,084 B2 U.S. Patent Dec. 1, 2015 Sheet 4 of 10 US 9.203,084 B2 '.s: ''.; : axxxix: 8x8x8 8888: 8x88ig 8:888: 888 : {... k. U.S. Patent Dec. 1, 2015 Sheet 5 of 10 US 9.203,084 B2 Cathode current Anode current collector (e.g. collector (e.g. Al foil) Culfoil) Anode active Cathode active material layer .. material layer (e.g. (e.g. Si coating) LiCoO2 coating) Pofous separator Anode current F.G. 5(A)( ) pprior art collector (e.g. Cu foil) Cathode current collector (e.g. Al foil) : ::::: Cathode active -/ \t-1 material layer (e.g. Anode active LiCoO2 particles) material layer (e.g. SnO2 Porous particles) separator FIG. 5(B) prior art U.S. Patent Dec. 1, 2015 Sheet 6 of 10 US 9.203,084 B2 (. A prior art * O. : B U.S. Patent Dec. 1, 2015 Sheet 7 of 10 US 9.203,084 B2 s:-- U.S. Patent Dec. 1, 2015 Sheet 8 of 10 US 9.203,084 B2 U.S. Patent Dec. 1, 2015 Sheet 9 of 10 US 9.203,084 B2 .xes xxxting 8888 x 88 ga:8888 88: U.S. Patent Dec. 1, 2015 Sheet 10 of 10 US 9.203,084 B2 8:8: S v S S S S S S S S M S S S S S S S S S S S S 3. 883 & 83 8: 888 :88: 388: 88: 88: 8: 88. : ::: US 9,203,084 B2 1. 2 CATHODE ACTIVE MATERAL-COATED a conductive additive for the cathode of a lithium battery. DISCRETE GRAPHENE SHEETS FOR These include carbon nano-tubes (CNTs), vapor-grown car LITHIUM BATTERIES AND PROCESS FOR bon nano-fibers (VG-CNFs), and simple carbon coating on PRODUCING SAME the surface of cathode active material particles. The result has not been satisfactory and hence, as of today, carbon black and FIELD OF THE INVENTION artificial graphite particles are practically the only two types of cathode conductive additives widely used in lithium ion The present invention relates generally to the field of battery industry. Thereasons are beyondjust the obvious high lithium metal or lithium ion batteries and, in particular, to a costs of both CNTs and VG-CNFs. The difficulty in disentan graphene-enhanced cathode of a lithium metal battery, 10 gling CNTs and VG-CNFs and uniformly dispersing them in lithium-sulfur battery, or lithium-ion battery. a liquid or Solid medium has been an impediment to the more widespread utilization of these expensive materials as a con BACKGROUND ductive additive. Additionally, the production of both CNTs Due to extremely poor electrical conductivity of all cath- 15 and VG-CNFs normally require the use of a significant ode (positive electrode) active materials in a lithium-ion, amount of transition metal nano particles as a catalyst. It is lithium metal, or lithium-sulfur cell, a conductive additive difficult to remove and impossible to totally remove these (e.g. carbon black, fine graphite particles, expanded graphite transition metal particles, which can have adverse effect on particles, or their combinations), typically in the amount of the cycling stability of a lithium metal. 5%-20%, must be added into the electrode. In the case of a As for the less expensive carbon coating, being considered lithium-sulfur cell, a carbon amount as high as 50% by weight for use in lithium iron phosphate, the conductivity of the is used as a conductive Support for Sulfur in the cathode. carbon coating (typically obtained by converting a precursor However, the conductive additive is not an electrode active Such as Sugar or resin via pyrolyzation) is relatively low. It material (i.e. it is not capable of reversibly storing lithium would take a graphitization treatment to render the carbon ions). The use of a non-active material means that the relative 25 coating more conductive, but this treatment requires a tem proportion of an electrode active material, such as LiFePO, perature higher than 2,000° C., which would degrade the is reduced or diluted. For instance, the incorporation of 5% by underlying cathode active material (e.g., LiFePO). weight of PVDF as a binder and 5% of carbon black as a As an alternative approach, Ding, et al investigated the conductive additive in a cathode would mean that the maxi electrochemical behavior of LiFePO/graphene composites mum amount of the cathode active material (e.g., lithium 30 cobalt oxide) is only 90%, effectively reducing the total Y. Ding, et al. “Preparation of nano-structured LiFePO/ lithium ion storage capacity. Since the specific capacities of graphene composites by co-precipitation method.” Electro the more commonly used cathode active materials are already chemistry Communications 12 (2010) 10-13. The co-pre very low (140-170 mAh/g), this problem is further aggravated cipitation method leads to the formation of LiFePO nano ifa significant amount of non-active materials is used to dilute 35 particles coated on both primary Surfaces of graphene nano the concentration of the active material. sheets. The cathode is then prepared by stacking these State-of-the-art carbon black (CB) materials, as a conduc LiFePO-coated graphene sheets together. This approach has tive additive, have several drawbacks: several major drawbacks: (1) CBS are typically available in the form of aggregates of (1) With the two primary surfaces of a graphene sheet multiple primary particles that are typically spherical in 40 attached with LiFePO nano-particles, the resulting shape. Due to this geometric feature (largest dimension-to electrode entails many insulator-to-insulator contacts Smallest dimension ratio or aspect ratio ~1) and the notion between two adjoining coated sheets in a stack. that CBS are a minority phase dispersed as discrete par (2) Only less than 30% of the graphene surface area is ticles in an electrically insulating matrix (e.g. lithium covered by LiFePO particles on either side. This is a cobalt oxide and lithium iron phosphate), a large amount of 45 relatively low proportion of the cathode active material. CBs is required to reach a percolation threshold where the (3) The LiFePO particles are easily detached from CB particles are combined to form a 3-D network of elec graphene sheets during handling and electrode produc tron-conducting paths. tion. (2) CBs themselves have a relatively low electrical conduc (4) We have found that the nano particle-attached graphene tivity and, hence, the resulting electrode remains to be of 50 sheets as prepared by the co-precipitation method are relatively low conductivity even when the percolation not amenable to fabrication of cathodes with current threshold is reached.