Patent Application: US-27946908-A

Abstract:
a process for the production of nano - structured olivine lithium manganese phosphate electrode material comprising of the following steps : sol gel preparation in a chelating environment ; preparation of lithium manganese phosphate / carbon composite by ball - milling ; and electrode preparation .

Description:
hereinafter , a method for manufacturing lithium manganese phosphate ( limnpo . sub . 4 ) according to the invention and a method for manufacturing a positive electrode active material will be detailed . firstly , a method for manufacturing limnpo . sub . 4 according to the invention will be described . the present invention discloses sol gel methods to prepare lithium manganese phosphate ( limnpo . sub . 4 ). limnpo . sub . 4 . the success of the alkoxides as precursors of the sol - gel process is their facility to undergo hydrolysis because the hydrolysis is the main step in the transformation of alkoxides to oxides . all metals are capable of forming an alkoxide in which an alkyl group is bonded to the metal by means of oxygen atom . the choice of the alkyl group may be made according to availability , but one must be careful because the reaction rate varies throughout the process depending on the alkyl group used . the method for manufacturing limnpo . sub . 4 according to the invention is a method of obtaining limnpo . sub . 4 by carrying out the steps of mixing and gel formation , drying and calcination . the present invention discloses sol - gel methods to prepare lithium manganese phosphate ( limnpo . sub . 4 ). most sol - gel processes are preferably accomplished in a common solvent . water is the solvent chosen in this system . a mixing of different optimised precursors together is done in the solvent . the final solution should be stirred long enough to ensure homogeneity . hydrolysis and polycondensation reactions of metal alkoxides lead to the formation of metal oxides . the fundamental chemical process involved in this processing is influenced by several parameters , which allow the control of homogeneity and the nanostructure of the derived materials . a hydrolysis — condensation reaction must take place : precursors of metal alkoxides will be hydrolysed in presence of water . lithium acetate dihydrate ( c . sub . 2h . sub . 3o . sub . 2 li , ( h . sub . 2o ). sub . 2 ), manganese ( ii ) acetate tetrahydrate ( c . sub . 4h . sub . 6o . sub . 4mn , ( h . sub . 2o ). sub . 4 ) and ammonium dihydrogen phosphate ( h . sub . 6no . sub . 4p ) are used as precursors . the starting materials were dissolved in distilled water at room temperature . hydrolysis rates of highly reactive alkoxides can be control by using chelating organic ligands such as organic acids . the formation of the metal complex with a multidentated ligand will decrease the hydrolysis rate . as chelating agents glycolic acid ( c . sub . 2h . sub . 4o . sub . 3 ), oxalic acid ( c . sub2h . sub . 2o . sub . 4 ), citric acid ( c . sub6h . sub . 8o . sub . 7 ), etc were used . in addition to water , an acid can also be used to hydrolyse the solution . hnosub . 3 is used to acidify the solution from ph 4 . 5 to 1 . 5 . this solution was further heated to 60 - 90 ° c . to form the gel . once the solution has been condensed into a gel , solvent removal must be carried out . drying is the term used for the removal of solvent . after drying , a porous and homogeneous aerogel is obtained . once the gel has been dried , a sintering step is needed to collapse the pore structure and solidify the gel . this gel was dried 14 hours at 80 ° c . and 10 hours at 120 ° c . under air . in this step , the complex decompositions of organic precursor take place , and the organic substances added for the preparation of the gel are almost completely removed , leading to amorphous powders . dta - tga experiments are performed to study the decompositions of organic precursors , from which one can determine a minimal calcination temperature . in the case of limnpo . sub . 4 sol - gel synthesis the temperature is fixed at 350 ° c . during calcination , pore - formation occurs via a process of particle bonding by thermal energy . the driving force behind sintering is a reduction in the surface area . the calcination step is required to obtain the desired crystallinity . the powder was heated at different temperatures ( 400 - 900 ° c .) from 1 to 5 hours in air . the resulting powder was ground in a mortar and characterised by x - ray diffraction study . measuring the cell parameters of the orthorhombic structure indicates measurements as follow : a = 10 . 4539 ( 6 ) å , b = 6 . 1026 ( 4 ) å , c = 4 . 7469 ( 3 ) å . the specific surface area is about 7 to 20 m . sub . 2 / g ( particle size is about 260 to 90 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 limnpo . sub . 4 obtained according to the above method for manufacturing the limnpo . sub . 4 and . limnpo . sub . 4 used in the invention , being obtained according to a manufacturing method described in the “ a . method for manufacturing limnpo . 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 limnpo . 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 limnpo . sub . 4 becomes relatively less , the performances as the positive electrode active material may be deteriorated . in the invention , a method of blending the limnpo . 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 limnpo . sub . 4 / carbon composite . this composite was obtained by high energy milling of limnpo . 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 limnpo . sub . 4 / c composite to improve electrochemical performances . electrode of limnpo . 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 . 0 . 03 mol of manganese ( ii ) acetate tetrahydrate ( c . sub . 4h . sub . 6o . sub . 4mn , ( h . sub . 2o ). sub . 4 ) 0 . 03 mol of lithium acetate dihydrate ( c . sub . 2h . sub . 3o . sub . 2 li , ( h . sub . 2o ). sub . 2 ) 0 . 12 mol of glycolic acid ( hydroxyacetic acid — c . sub . 2h . sub . 4o . sub . 3 ) 0 . 03 mol of ammonium di - hydrogeno phosphate ( h . sub . 6no . sub . 4p ) were dissolved under magnetic stirring at room temperature . ph of the solution was adjusted to 2 by using concentrated nitric acid ( hno . sub . 3 ). the solution was stirred under magnetic stirring and heated to 80 ° c . in an oil bath until formation of a green - ish coloured gel was achieved . the gel was dried , under air , overnight at 80 ° c . and one day at 120 ° c . in an oven . the powder was then heated at 350 ° c . for 5 hours under air prior to being further heated at different temperatures ( 450 - 800 ° c .) for 3 hours in air . x - ray spectrum of this material indicates a pure phase of lithium manganese phosphate ( limnpo . sub . 4 ). 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 . 0 . 03 mol of manganese ( ii ) acetate tetrahydrate ( c . sub . 4h . sub . 6o . sub . 4mn , ( h . sub . 2o ). sub . 4 ) 0 . 03 mol of lithium acetate dihydrate ( c . sub . 2h . sub . 3o . sub . 2 li , ( h . sub . 2o ). sub . 2 ) 0 . 03 mol of glycolic acid ( hydroxyacetic acid — c . sub . 2h . sub . 4o . sub . 3 ) 0 . 03 mol of ammonium di - hydrogeno phosphate ( h . sub . 6no . sub . 4p ) were dissolved under magnetic stirring at room temperature . ph of the solution was 4 . 3 . the solution was stirred under magnetic stirring and heated to 80 ° c . in an oil bath until formation of a brownish gel is achieved . the gel was dried , under air , over night at 80 ° c . and one day at 120 ° c . in an oven . the powder was then heated at 350 ° c . for 5 hours under air prior to being further heated at different temperatures ( 400 - 900 ° c .) for 3 hours in air . x - ray spectrum of this material indicates a pure phase of lithium manganese phosphate ( limnpo . sub . 4 ). the composite limnpo . sub . 4 / c , cell preparation and test conditions were performed according example 2 , 3 and 4 . 0 . 03 mol of manganese ( ii ) acetate tetrahydrate ( c . sub . 4h . sub . 6o . sub . 4mn , ( h . sub . 2o ). sub . 4 ) 0 . 03 mol of lithium acetate dihydrate ( c . sub . 2h . sub . 3o . sub . 2 li , ( h . sub . 2o ). sub . 2 ) 0 . 12 mol of glycolic acid ( hydroxyacetic acid — c . sub . 2h . sub . 4o . sub . 3 ) 0 . 03 mol of ammonium di - hydrogeno phosphate ( 1h . sub . 6no . sub . 4p ) were dissolved under magnetic stirring at room temperature . ph of the solution was adjusted to 2 by using concentrated nitric acid ( hno . sub . 3 ). the solution was stirred under magnetic stirring and heated to 80 ° c . in an oil bath until the formation of a greenish gel was achieved . the gel was dried , under air , over night at 80 ° c . and one day at 120 ° c . in an oven . the powder was then heated at 350 ° c . for 5 hours under air prior to being further heated at different temperatures ( 450 - 800 ° c .) for 3 hours in air . x - ray spectrum of this material indicates a pure phase of lithium manganese phosphate ( limnpo . sub . 4 ). the composite limnpo . sub . 4 / c , cell preparation and test conditions were performed according to those in example 2 , 3 and 4 . 0 . 03 mol of manganese ( ii ) acetate tetrahydrate ( c . sub . 4h . sub . 6o . sub . 4mn , ( h . sub . 2o ). sub . 4 ) 0 . 03 mol of lithium acetate dihydrate ( c . sub . 2h . sub . 3o . sub . 2 li , ( h . sub . 2o ). sub . 2 ) 0 . 06 mol of citric acid ( c . sub6h . sub . 8o . sub . 7 ) 0 . 03 mol of ammonium di - hydrogeno phosphate ( h . sub . 6no . sub . 4p ) were dissolved under magnetic stirring at room temperature . ph of the solution was adjusted to 2 by using concentrated nitric acid ( hno . sub . 3 ). the solution was stirred under magnetic stirring and heated to 80 ° c . in an oil bath until the formation of a greenish gel was achieved . the gel was dried , under air , over night at 80 ° c . and one day at 120 ° c . in an oven . the powder was then heated at 350 ° c . for 5 hours under air prior to being further heated at different temperatures ( 450 - 800 ° c .) for 3 hours in air . x - ray spectrum of this material indicates a pure phase of lithium manganese phosphate ( limnpo . sub . 4 ). the composite limnpo . sub . 4 / c , cell preparation and test conditions were performed according to those in example 2 , 3 and 4 . 0 . 03 mol of manganese ( ii ) acetate tetrahydrate ( c . sub . 4h . sub . 6o . sub . 4mn , ( h . sub . 2o ). sub . 4 ) 0 . 03 mol of lithium acetate dihydrate ( c . sub . 2h . sub . 3o . sub . 2 li , ( h . sub . 2o ). sub . 2 ) 0 . 06 mol of oxalic acid ( c . sub2h . sub . 2o . sub . 4 ) 0 . 03 mol of ammonium di - hydrogeno phosphate ( h . sub . 6no . sub . 4p ) were dissolved under magnetic stirring at room temperature . ph of the solution was adjusted to 2 by using concentrated nitric acid ( hno . sub . 3 ). the solution was stirred under magnetic stirring and heated to 80 ° c . in an oil bath until the formation of a greenish gel was achieved . the gel was dried , under air , over night at 80 ° c . and one day at 120 ° c . in an oven . the powder was then heated at 350 ° c . for 5 hours under air prior to being further heated at different temperatures ( 450 - 800 ° c .) for 3 hours in air . x - ray spectrum of this material indicates a pure phase of lithium manganese phosphate ( limnpo . sub . 4 ). the composite limnpo . sub . 4 / c , cell preparation and test conditions were performed according to those in example 2 , 3 and 4 . 1 . k . mizushima , p . c . jones , p . j . wiseman , and j . b . goodenough , mat . res . bull ., 15 , 783 ( 1980 ). 2 . m . m . thackeray , progress in batteries and battery materials , vol . 14 , r . j . brodd , ed ., ite press , inc ., brunswick , ohio , p . 1 ( 1995 ), and references therein 5 . padhi , a . k ; nanjudaswamy , k . s . ; goodenough , j . b . jes 1997 , 144 ( 4 ) 1188 6 . c delacourt ; p . poizot ; m . morcrette ; j .- m . tarascon and c . masquelier chem . mater . 2004 , 16 , 93 - 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