Patent Application: US-29620406-A

Abstract:
novel process for the preparation of finely divided , nano - structured , olivine lithium metal phosphates materials have been developed . this so called polyol ” method consists of heating of suited precursor materials in a multivalent , high - boiling point multivalent alcohol like glycols with the general formula ho —. sub . n - h where n = 1 - 10 or ho —. sub . n .- h where n = 1 - 10 , or other polyols with the general formula hoch 2 —. sub . n - h where n = 1 - 10 , like for example the tridecane - 1 , 4 , 7 , 10 , 13 - pentaol . a novel method for implementing the resulting materials as cathode materials for li .- ion batteries is also developed .

Description:
hereinafter , a method for manufacturing lithium metal phosphate ( where metal is manganese , iron , cobalt , copper , nickel , vanadium , titanium and mix of them ) according to the invention and a method for manufacturing a positive electrode active material will be described . firstly , a method for manufacturing limpo . sub . 4 according to the invention will be described . the present invention discloses a type of synthesis that turned out to be well - suited for the preparation of spherical oxide particles of 20 - 150 nm in size is so - called “ polyol ” method . the basis of this method is the precipitation of a solid while heating sufficient precursors in a multivalent alcohol with a high - boiling point like glycols with the general formula ho —(— c 2 h 4 o —). sub . n - h where n = 1 - 10 or ho —(— c 3 h 6 o —). sub . n .- h where n = 1 - 10 , or other polyols with the general formula hoch 2 —(— c 3 h 5 oh —). sub . n - h where n = 1 - 10 , like for example the tridecane - 1 , 4 , 7 , 10 , 13 - pentaol , wherein metal m is iron , manganese , cobalt , nickel , vanadium , copper , titanium or a mixture of those compounds . the alcohol itself acts as a stabilizer , limiting particle growth and prohibiting agglomeration . the high boiling point of the alcohol means that temperature can be applied (& gt ; 150 ° c . ), that result in highly crystalline oxides . the method for manufacturing limpo . sub . 4 according to the invention is a method of obtaining limpo . sub . 4 by carrying out the steps of dissolution , hydrolysis , drying and eventually calcination . the present invention discloses a “ polyol ” method to prepare lithium metal phosphates . polyol - mediated preparation is carried out by dissolving a suited metal ( mn , fe , co , cu , ni , v . . . ) precursors ( e . g . acetates , alcoholates , oxides , alkoxides ) in a suited solvent ( e . g . ethylene glycol , propylene glycol , diethylene glycol , tetraethylene glycol etc .) according to this mechanism , the polyol acts first as a solvent for the starting inorganic precursors due to the rather dielectric constant of these organic media . in diethylene glycol for instance , salts such as manganese acetates , cobalt acetates , iron acetates hydrate are soluble to such an extent that a complete dissolution is observed as the first step of the reaction . the molar ratio metal salts / polyol can be varied from 0 . 01 to 0 . 15 . in some cases , a few cubic centimetres of an aqueous solution can be added to increase the solubility of the salts . the solution is heated from 100 to 150 ° c . ( depending of the solvent ) for 1 to 3 hours to complete the dissolution . the polyol also acts as solvent with a chelating effect which avoids agglomeration of particles during the preparation . stoichiometric amounts of suitable lithium salts ( e . g . lithium acetate hydrate ) and phosphate salts ( e . g . ammonium dihydrogeno phosphate ) were dissolved in a minimum volume of water . the solution was added to the polyol media . the water acts as a hydrolysis agent . the emerging suspension was heated for several hours up to 170 - 200 ° c . under stirring . a dehydration occurred at high temperature . in addition to water , an acid can also be used to hydrolyse the solution . the solid material was separated from the suspension by centrifugation and washed twice with ethanol . the “ as synthesized ” sample was dried at 80 ° c . for one day under air . the material shows the correct olivine structure after this treatment . the specific surface area is about 30 to 70 m . sub . 2 / g ( particles size is about 60 to 25 nm ) to obtain a complete crystalline phase , the material can be heated at different temperatures ( 300 - 500 ° c .) from 30 minutes to 1 hour in air . the resulting powder was ground in a mortar and characterised by x - ray diffraction study . the specific surface area is approximately / in the range 20 to 50 m . sub . 2 / g ( particle size is approximately / in the range 90 to 35 nm ). next , a method for manufacturing a positive electrode active material according to the invention will be described . the method for manufacturing the positive electrode active material according to the invention is characterized by blending a conductive agent with the limpo . sub . 4 obtained according to the above method for manufacturing the limpo . sub . 4 and limpo . sub . 4 used in the invention , being obtained according to a manufacturing method described in the “ a . method for manufacturing limpo . sub . 4 ”, is omitted from describing here . furthermore , the conductive agent used in the invention , as far as it can improve the electrical conductivity , is not particularly restricted . for instance , graphite or carbon black such as acetylene black can be cited . the conductive agent is added in the range of 5 to 25 parts by weight , preferably in the range of 10 to 20 parts by weight to 100 parts by weight of limpo . sub . 4 . when an amount of the conductive agent is less than necessary , the electrical conductivity may not be sufficiently improved , and , when it is more than necessary , since an amount of limpo . sub . 4 becomes relatively less , the performances as the positive electrode active material may be deteriorated . in the invention , a method of blending the limpo . sub . 4 and the conductive agent is not particularly restricted . however , for instance , the physical blending is preferable and the mechanical blending is particularly preferable . specifically , a ball mill pulverizing method or the like can be cited . furthermore , applications of the positive electrode active material obtained according to the invention are not particularly restricted . however , it can be used in , for instance , lithium secondary batteries . the present invention discloses improved electrochemical performances of limpo . sub . 4 / carbon composite . this composite was obtained by high energy milling of limpo . sub . 4 with acetylene black in a stainless steel container using a planetary ball mill for several hours . the present invention also discloses electrode preparation of limpo . sub . 4 / c composite to improve electrochemical performances . electrode of limpo . sub4 / c active material was prepared by mixing of the active material ( composite ) with a carbon black and a binder in n - methyl - 2 - pyrrolidinon . the slurry was then coated on an aluminium foil , serving as the current collector . the n - methyl - 2 - pyrrolidinon was subsequently evaporated in air on titanium hot plate . hereinafter , the invention will be more specifically described with reference to examples . preparation of nanosized lithium manganese phosphate : to 100 ml of diethylene glycol , 20 ml of a solution of 1 . 5 mol . l . sup .- 1 of manganese ( ii ) acetate tetrahydrate ( c . sub . 4 h . sub . 6 o . sub . 4 mn , ( h . sub . 2 o ). sub . 4 ) was added . the mixture was heated at 140 ° c . for about 1 hour . a dark brown solution was obtained . 2 ml of concentrated acetic acid was added to the solution . 20 ml of a solution of 1 . 5 mol . l . sup .- 1 of lithium acetate dihydrate ( c . sub . 2h . sub . 3 o . sub . 2 li , ( h . sub . 2 o ). sub . 2 ) and ammonium di - hydrogeno phosphate ( h . sub . 6 no . sub . 4 p ) was added to the glycol solution . a brownish precipitate was formed . under extreme agitation , the mixture was heated at 180 ° c . under reflux for 4 hours . to remove the diethylene glycol , the mixture was cooled down at room temperature , centrifuged and washed twice with ethanol . the precipitate was dried at 80 ° c . for 1 day . the material was then calcined at 350 ° c . for 1 hour under air . x - ray pattern of this material indicates a pure crystallized phase of lithium manganese phosphate ( limnpo . sub . 4 ). the particle sizes of the material were included in the range 90 - 20 nm . the powder of limnpo . sub . 4 was placed in a 250 ml stainless steel container and ball milled with a planetary ball mill using 9 stainless steel balls of 20 mm diameter for one hour . in addition , 20 % in weight of acetylene black was added to the milled limnpo . sub . 4 and ball milled again for 3 hours . a composite of limnpo . sub . 4 / c was then obtained . a positive electrode composition of limnpo . sub4 / c active material was prepared by mixing of the active material ( composite ) with a carbon black ( c55 from shawinigan ) and a binder ( polyvinylidene difluoride — pvdf ) with the mass ratio ( 90 : 5 : 5 ), in n - methyl - 2 - pyrrolidinon . the slurry was then coated on an aluminium foil , serving as the current collector . the n - methyl - 2 - pyrrolidinon was subsequently evaporated in air at 100 ° c . for 1 hour and 120 ° c . for 30 minutes on titanium hot plate . the electrode was then dry at 160 ° c . overnight under vacuum . the positive electrode of example 3 was tested in standard laboratory swagelok test cells versus li metal . microporous celgard membrane served as separator . the electrolyte was made of 1m of lipf . sub . 6 dissolved in a 1 : 1 : 3 by volume mixture of dried and purified propylene carbonate ( pc ), ethylene carbonate ( ec ) and dimethyl carbonate ( dmc ). the electrochemical properties of limnpo . sub4 / c electrodes were measured using an arbin bt 2000 electrochemical measurement system by galvanostatic charge / discharge and cyclic voltammetry . the battery prepared above was charged under a current density of 0 . 03 ma / cm . sup . 2 until a termination voltage of 4 . 7 volt was reached . then the charged battery was discharged at a current density of 0 . 03 ma / cm . sup . 2 until a termination voltage of 2 . 3 volt was reached . preparation of nanosized lithium cobalt phosphate : to 100 ml of diethylene glycol , 20 ml of a solution of 1 . 5 mol . l sup .- 1 of cobalt ( ii ) acetate tetrahydrate ( c . sub . 4h . sub . 6 o . sub . 4 co , ( h . sub . 2 o ). sub . 4 ) was added . the mixture was heated at 140 ° c . for about 1 hour . a dark solution was obtained . 20 ml of a solution of 1 . 5 mol . l . sup .- 1 of lithium acetate dihydrate ( c . sub . 2h . sub . 3 o . sub . 2 li , ( h . sub . 2 o ). sub . 2 ) and ammonium di - hydrogeno phosphate ( h . sub . 6 no . sub . 4 p ) was added to the glycol solution . a precipitate was formed . under extreme agitation the mixture was heated at 180 ° c . under reflux for 4 hours . the mixture was cooled down at room temperature . the mixture was then centrifuged and washed twice with ethanol to remove the diethylene glycol . the precipitate was dried at 80 ° c . for 1 day . the material was then calcined at 350 ° c . for 1 hour under air . x - ray pattern of this material indicates a pure phase of lithium cobalt phosphate ( licopo . sub . 4 ). the particle sizes of the material were included in the range 90 - 20 nm . preparation of nanosized lithium iron phosphate : to 100 ml of diethylene glycol , 20 ml of a solution of 1 . 5 mol . l sup .- 1 of iron ( ii ) acetate ( c . sub . 4h . sub . 6 o . sub . 4 fe ) was added . the mixture was heated at 140 ° c . for about 1 hour . a dark solution was obtained . 20 ml of a solution of 1 . 5 mol . l . sup .- 1 of lithium acetate dihydrate ( c . sub . 2h . sub . 3 o . sub . 2 li , ( h . sub . 2 o ). sub . 2 ) and ammonium di - hydrogeno phosphate ( h . sub . 6 no . sub . 4 p ) was added to the glycol solution . a brownish precipitate was formed . under agitation the mixture was heated at 180 ° c . under reflux for 4 hours and cooled down to room temperature . the mixture was then centrifuged and washed twice with ethanol to remove the diethylene glycol . the precipitate was dried at 80 ° c . for 1 day . the material was then calcined at 350 ° c . for 1 hour under air . x - ray pattern of this material indicates a pure phase of lithium iron phosphate ( lifepo . sub . 4 ). the particle sizes of the material were included in the range 90 - 20 nm . preparation of nanosized lithium manganese phosphate : to 100 ml of diethylene glycol , 20 ml of a solution of 1 . 5 mol . l . sup .- 1 of manganese ( ii ) acetate tetrahydrate ( c . sub . 4 h . sub . 6 o . sub . 4 mn , ( h . sub . 2 o ). sub . 4 ) was added and 2 ml of concentrated acetic acid . the mixture was heated at 120 ° c . for about 1 hour . a dark brown solution was obtained . 20 ml of a solution of 1 . 5 mol . l . sup .- 1 of lithium acetate dihydrate ( c . sub . 2h . sub . 3 o . sub . 2 li , ( h . sub . 2 o ). sub . 2 ) and ammonium di - hydrogeno phosphate ( h . sub . 6 no . sub . 4 p ) was added to the glycol solution . a brownish precipitate was formed . under extreme agitation the mixture was heated at 160 ° c . under reflux for 5 hours and cooled down to room temperature . the mixture was then filtered and washed twice with acetone to remove the diethylene glycol . the powder was dried at 80 ° c . for 1 day . the material was then calcined at 500 ° c . for 1 hour under air . x - ray pattern of this material indicates a pure crystallized phase of lithium manganese phosphate ( limnpo . sub . 4 ). the particle sizes of the material were included in the range 90 - 40 nm . the synthesis of nanoparticles of limnpo . sub . 4 was performed according to those in example 1 characterized in that the dried powder at 80 ° c . is already crystallised and no calcination step was applied . the particle sizes of the material were included in the range 50 - 20 nm . the synthesis of nanoparticles of limnpo . sub . 4 was performed according to those in example 1 characterized in that the solvent is a multivalent alcohol with a high - 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