USOO8722004B2 (12) United States Patent (10) Patent No.: US 8,722,004 B2 Wu et al. (45) Date of Patent: May 13, 2014 (54) METHOD FOR THE PREPARATION OFA 6,730,281 B2 * 5/2004 Barker et al. ................. 423.306 LITHIUM PHOSPHATE COMPOUND WITH 2006/0147365 A1* 7, 2006 Okada et al. ... ... 423.306 2006/0257307 A1* 11/2006 Yang ........... ... 423.306 AN OLIVINE CRYSTAL STRUCTURE 2008, 0008938 A1* 1/2008 Wu et al. ... 429,221 2010.0059.706 A1 3/2010 Dai et al. ................... 252, 1821 (75) Inventors: Mark Y. Wu, Wujie Township, Yilan County (TW); Cheng-Yu Hsieh, Wujie FOREIGN PATENT DOCUMENTS Township, Yilan County (TW); Chih-Hao Chiu, Wujie Township, Yilan TW I254.031 5, 2006 County (TW) TW I29263.5 1, 2008 (73) Assignee: Phosage, Inc., Yilan County (TW) OTHER PUBLICATIONS (*) Notice: Subject to any disclaimer, the term of this Shiraishi et al., “Formation of impurities on phospho-olivine patent is extended or adjusted under 35 LiFePO4 during hydrothermal synthesis,” Journal of Power Sources, U.S.C. 154(b) by 710 days. 2005, pp. 555-558, vol. 146. (21) Appl. No.: 12/478,387 * cited by examiner (22) Filed: Jun. 4, 2009 Primary Examiner — Melvin C Mayes (65) Prior Publication Data Assistant Examiner — Colette Nguyen US 2010/O2O2951A1 Aug. 12, 2010 (74) Attorney, Agent, or Firm — Muncy, Geissler, Olds & Lowe, P.C. (30) Foreign Application Priority Data (57) ABSTRACT Feb. 12, 2009 (TW) ............................... 98104490 A The present invention relates to a method for the preparation (51) Int. Cl. of a lithium phosphate compound with an olivine crystal COB 25/26 (2006.01) structure, which has a chemical formula of Li, M.M'PO, (52) U.S. Cl. wherein 0.1sXs 1,0sys1. The nano-scale lithium phosphate USPC ............ 423/305:423/306: 423/299; 423/302 ceramic powder was synthesized by using a self-propagating (58) Field of Classification Search combustion with reactants of soluble salts and the proper USPC .................................................. 423/306, 305 oxidizing agents, followed by heat treatment of powder to See application file for complete search history. obtain nano-scale lithium phosphate compound with an oli vine crystal structure in a complete crystal phase. The method (56) References Cited of the present invention uses low cost materials and simple processes. The uniform crystal product materials are benefi U.S. PATENT DOCUMENTS cial to the industrial application. 5,910,382 A 6/1999 Goodenough et al. 6,528,033 B1 3/2003 Barker et al. 6,716,372 B2* 4/2004 Barker et al. .............. 252,518.1 24 Claims, 2 Drawing Sheets U.S. Patent May 13, 2014 Sheet 1 of 2 US 8,722,004 B2 500 400 300 200 100 Fig. 1 U.S. Patent May 13, 2014 Sheet 2 of 2 US 8,722,004 B2 1OOO 800 600 400 2OO Fig. 2 US 8,722,004 B2 1. 2 METHOD FOR THE PREPARATION OF A The main synthesis methods for LFP include solid-state LITHIUM PHOSPHATE COMPOUND WITH reaction, carbonthermal reduction method, hydrothermal AN OLIVINE CRYSTAL STRUCTURE synthesis and so on. These methods are briefly described below. BACKGROUND OF THE INVENTION 1. Solid State Reaction In general, lithium salts, ferrous compounds and phosphate 1. Field of the Invention compounds are mixed and heated to react and yield lithium The present invention relates to a method for the prepara iron phosphate after diffusion. As mentioned in U.S. Pat. No. tion of a lithium phosphate compound with an olivine crystal 5,910,382, Li(CO), Fe(CHCOO), and NHHPO were structure, which has a chemical formula of Li, M.M'PO, 10 mixed according to the Stoichiometric ratio and put into a high wherein 0.1sXs 1,0sys1, in particular to a method for the temperature oven, heated at 650-800° C. for 24 hours at the preparation of a nano-scale lithium phosphate ceramic pow presence of inert gas. The LFP products were grinded into der by a self-propagating solution combustion. proper particle sizes. However, the method needs an exces 2. The Prior Arts sively high temperature in long time, which is energy con 15 Suming and causes grouping of products. The distribution of The secondary lithium-ion battery has several advantages product sizes is uneven after grinding, and the instrument can Such as high energy density and Superior life cycle, which has be contaminated easily. Therefore the method is of less eco rapidly substituted the nickel-cadmium battery and nickel nomical value, and the poor quality of product is not suitable metal hydride battery after developed. The market of lithium for mass industrial application. ion battery has increased consistently after the commercial The Taiwan Patent No. I292635 discloses an alternative ized product was launched by Sony in 1991. The total pro method using a metallic crucible as the container of powder duction Volume in more than 10 years was more than the and carbonate salt as a reactant to generate a protective atmo Summary of the nickel-cadmium battery and nickel metal sphere in order to save the cost of inert gas. There are still hydride battery. The application area of lithium-ion battery drawbacks of energy consuming, uneven particles and con has been expanded with the improvement or presence of new 25 tamination due to high temperature in long time. materials and battery technology. The 3C (Computer, Com 2. Carbonthermal Reduction munication and Consumer) product has the properties of The abovementioned solid State reaction using compounds being light, thin, short and Small, which makes the lithium with Fe" as reactant, which is more expensive than com secondary battery the best choice. pounds with Fe". In order to solve the above problems, the 30 precursors of carbon are generally added to reactants of Lithium iron phosphate (LiFePO) battery (LFP) is the new lithium compound, Fe" compound and phosphate during the generation of lithium secondary battery, which has been preparation to reduce Fe" to Fe" as mentioned in U.S. Pat. attracting enormous research interest in vehicle, electric Nos. 6,528,033, 6,716,372, and 6,730,281. The amount of tools, and aviation industry. The commercialized product was carbon is difficult to control in these methods though the cost launched in 2004, way behind the launches of nickel metal 35 of reactants could be decreased. Too little carbon will affect hydride battery in 1990 and lithium cobalt (the battery used in the characteristics in materials since Fe" could not be 3C products at present) in 1992. Lithium iron phosphate reduced, while too much carbon could result in reducing the offers no safety problems of overheating or explosion, 4 to 5 iron compound to iron metal, followed by lowering the elec times of cycle life and 8 to 10 fold of high power discharge tronic capacity. (high power density, which can generate larger current Sud 40 Another method in Taiwan Patent No. I254031 discloses denly) in comparison to general lithium-ion battery. In addi heating a carbon Source to generate fine carbon particles, then tion, the total weight at the same energy density of a lithium carrying these particles to reacting area by inert gas to reduce iron phosphate battery is 30-50% lower than that of other Fe" to produce Fe" to overcome the drawback mentioned lithium-ion battery. Major corporations including Boeing, above. However, the processes are more complicated, and are General Motors, Ford, Segway, and Black & Decker all are 45 still time- and energy-consuming since the carbon Source highly interested in development of Lithium iron phosphate needs to be heated at 300° C. to decompose first, then reacted battery. at 700° C. Lithium iron phosphate batteries also have their draw 3. Hydrothermal Synthesis backs. The energy density of lithium iron phosphate batteries Hydrothermal methods have been applied to the synthesis is 25-40% lower than that of LiCoO, which is not applicable 50 of lithium iron phosphates by reacting Soluble lithium com in portable 3C products with high energy density. In addition, pound, ferrous compound and phosphate salt under high tem the high threshold in powder sintering technology and diffi perature and high pressure in aqueous solution. Nano-scale culties in mass production of lithium iron phosphate battery lithium iron phosphate particles at even size of 0.5 um were have made it expensive to be used broadly in related industry. synthesized by reacting lithium hydroxide (LiOH), ferrous The ceramic crystal of LFP has an olivine structure, a 55 sulfate (FeSO4) and phosphate at 150-200° C. in hydrother slightly twisted hexagonal close-packed structure which mal condition, followed by treatment at 400°C. with nitrogen commonly exists among natural minerals. The artificial Syn gas for several hours (Keisuke Shiraishi et al., Journal of thesized powder is used widely since LFP has very low purity Power Sources 146 (2005)555-558). However, this study was in natural mineral olivines. The crystal structures of MO limited to the academic field because of harsh synthetic con octahedra and PO tetrahedra limit the change in crystal lat 60 dition, expensive equipments, and drawbacks of high cost as tice volume, which affects the insertion and extraction of well as difficulties with mass production. lithium ions, further lowers the diffusion rate of lithium ions and causes the decrease of lithium ion electronic conductivity SUMMARY OF THE INVENTION and diffusion coefficient. Therefore, artificial synthesis through decreasing the particle size or doping has become a 65 The objective of the present invention is to provide a key point for the recent research and development as well as method for the preparation of a nano-scale lithium phosphate the objective for the present invention.