Abstract:
The present invention describes a process for the preparation of LiBF 4  by reacting LiBO 2  with 10 to 48% HF solution in aqueous solution at ambient temperature, concentrating the product and recrystallizing to obtain high purity LiBF 4 .

Description:
FIELD OF THE INVENTION 
     The present invention relates to a process for the preparation of LiBF 4 . 
     BACKGROUND OF THE INVENTION 
     LiBF 4  has very useful applications in high voltage lithium primary/secondary cells. LiBF 4  is well known as a battery electrolyte. This compound was earlier prepared by procedures, which were cumbersome and the yield was poor. The purity of the sample prepared was poor and needed recrystallization. 
     U.S. Pat. No. 5,079,109 discloses the use of LiBF 4  as a non-aqueous electrolyte for a lithium battery. 
     While several methods are known for the preparation of LiBF 4  in the prior art such methods suffer from the following disadvantages: 
     1. The purity of the product is low 
     2. The yield of the product is low 
     3. Ambient temperature reaction for the product yield 
     4. Side reactions occur 
     5. Multiplicity of steps are required. 
     OBJECTS OF THE INVENTION 
     The main object of this invention is to prepare LiBF 4  by a simple chemical reaction. 
     Another object of the invention is to obtain LiBF 4  with high yield. 
     A further object of the invention is to obtain LiBF 4  by an efficient process. 
     The process of the invention overcomes the disadvantages of the prior art enumerated above. 
     SUMMARY OF THE INVENTION 
     Accordingly the present invention relates to a process for the preparation of LiBF 4  reacting LiBO 2  compound with 10 to 48% HF solution in aqueous solution at ambient temperature, concentrating the product and recrystallising to obtain high purity LiBF 4 . 
     In one embodiment of the invention, LiBO 2  is suspended in aqueous media/nonaqueous media and reacted with HF. 
     In a further embodiment of the invention, a paste of LiBO 2  is added in HF. 
     In another embodiment of the invention, LiBO 2  is pasted with water and reacted with HF. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the present invention LiBF 4  is prepared by treating suspended particles of LiBO 2 /Li 2 N 2 O 4  in aqueous solution or a paste of LiBO 2  in water with HF. The quantity of LiBO 2  and HF are calculated for the reaction separately. After the cessation of the reaction the product was concentrated and crystallized. The product formed was examined and confirmed by x-ray and the purity of the sample was examined. 
     A calculated quantity of HF was carefully added to a known weighed quantity of LiBO2 in aqueous solution. The reaction was allowed to proceed. When the reaction ceased, the product was concentrated and recrystallized to get very high purity of the sample. The product was examined for its purity and identified by x-ray. FIG. 1 indicates the x-ray analysis which matches with available literature (Table 1). 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
             
             
               
                   
                   
               
               
                   
                 LIBF 4   
                   
                 In- 
                   
               
             
          
           
               
                 350985 
                 2θ 
                 d value 
                 intensity 
                 OBS 
                 tensity 
                 Error 
               
               
                   
               
             
          
           
               
                 1 
                 18.618 
                 4.762 
                 70 
                 18.797 
                 4.717 
                 36 
                 2 
               
               
                 2 
                 26.722 
                 3.333 
                 100 
                 26.903 
                 3.311 
                 87 
                 2 
               
               
                 3 
                 27.903 
                 3.195 
                 100 
                 28.176 
                 3.165 
                 100 
                 3 
               
               
                 4 
                 34.872 
                 2.571 
                 30 
               
               
                 5 
                 37.565 
                 2.392 
                 100 
                 37.845 
                 2.375 
                 55 
                 3 
               
               
                 6 
                 37.938 
                 2.370 
                 30 
                 37.845 
                 2.375 
                 55 
                 −1 
               
               
                 7 
                 39.623 
                 2.273 
                 30 
               
               
                 8 
                 44.541 
                 2.033 
                 100 
                 44.732 
                 2.024 
                 75 
                 2 
               
               
                 9 
                 48.093 
                 1.890 
                 10 
               
               
                 10 
                 50.326 
                 1.812 
                 30 
                 50.521 
                 1.805 
                 17 
                 2 
               
               
                 11 
                 52.875 
                 1.730 
                 30 
                 52.875 
                 1.730 
                 12 
                 0 
               
               
                 12 
                 54.557 
                 1.681 
                 30 
               
               
                 13 
                 57.960 
                 1.590 
                 30 
                 57.960 
                 1.590 
                 13 
                 0 
               
               
                 14 
                 63.693 
                 1.460 
                 10 
                 64.005 
                 1.453 
                 7 
                 3 
               
               
                 15 
                 65.153 
                 1.431 
                 20 
               
               
                 16 
                 68.965 
                 1.361 
                 10 
               
               
                 17 
                 71.991 
                 1.311 
                 10 
               
               
                 18 
                 73.968 
                 1.280 
                 20 
                 74.078 
                 1.279 
                 8 
                 1 
               
               
                 19 
                 78.227 
                 1.221 
                 20 
                 78.227 
                 1.221 
                 10 
                 0 
               
               
                   
               
               
                 The synthesis of LiBO 2  is disclosed in our copending application.  
               
             
          
         
       
     
     EXAMPLE 1 
     Preparation of LiBO 2    
     Li 2 CO 3  (2.96 gm) and B 2 O 3  (2.8 gm) are mixed with heating up to 600° C. to obtain LiBO 2  with yield of more than 98%. The colour of the product was white and it was obtained in single phase. The single electrode potential of LiBO 2  with respect to Li in 1M LiClO 4  in propylene carbonate was 2.99 V. 
     EXAMPLE 2 
     Preparation of LiBO 2    
     Li 2 OH (1.68 gm) and B 2 O 3  (2.8 gm) are mixed with heating up to 600° C. to obtain LiBO 2  with yield of more than 98%. The colour of the product was white and it was obtained in single phase. The single electrode potential of LiBO 2  with respect to Li in 1M LiClO 4  in propylene carbonate was 2.99 V. 
     The LiBO 2  obtained by the processes of both examples 1 and 2 was high and no side reactions occur. 
     EXAMPLE 3 
     Preparation of LiBF 4    
     LiBO 2  and HF were mixed in a mole ratio of 1:4 by taking HF in water in a Teflon container, keeping the temperature at −4° C., slowly adding LiBO 2 . When the reaction ceases, the mixture is slowly heated upto dryness at about 100° C. to obtain dry LiBF 4  with a yield of about 95%. The colour of the product was white and the product was obtained in single phase. The single electrode potential of LiBO 4  with respect to Li in 1M LiClO 4  in propylene carbonate was 2.99 v. 
     EXAMPLE 4 
     Preparation of LiBF 4    
     LiBO 2  and HF were mixed in a mole ratio of 1:4 by taking HF in alcoholic solvent in a Teflon container, keeping the temperature at −4° C., slowly adding LiBO 2 . When the reaction ceases, the mixture is slowly heated upto dryness at about 100° C. to obtain dry LiBF 4  with a yield of about 95%. The colour of the product was white and the product was obtained in single phase. The equivalent conductance of LiBF 4  in 1 molar PC at 30° C. was 34.0 ohm −1  cm 2  mole −1 . 
     In the present invention the following advantages are claimed for the synthesis of LiBF 4 : 
     1. No side reactions occur 
     2. A one step procedure is sufficient to prepare this compound 
     3. Required quantity of the product can be prepared by reacting the calculated quantity of reactants. 
     4. The product obtained is of high purity 
     5. The product yield becomes 100% if the temperature is kept at −4° C. 
     6. Wetting of LiBO 2  prevents evaporation of BF 4  formed during the reaction.