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  
         [0001]    The present invention relates to a process for the preparation of LiBF 4 .  
         BACKGROUND OF THE INVENTION  
         [0002]    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.  
           [0003]    U.S. Pat. No. 5,079,109 discloses the use of LiBF 4  as a non-aqueous electrolyte for a lithium battery.  
           [0004]    While several methods are known for the preparation of LiBF 4  in the prior art such methods suffer from the following disadvantages:  
           [0005]    1. The purity of the product is low  
           [0006]    2. The yield of the product is low  
           [0007]    3. Ambient temperature reaction for the product yield  
           [0008]    4. Side reactions occur  
           [0009]    5. Multiplicity of steps are required.  
         OBJECTS OF THE INVENTION  
         [0010]    The main object of this invention is to prepare LiBF 4  by a simple chemical reaction.  
           [0011]    Another object of the invention is to obtain LiBF 4  with high yield.  
           [0012]    A further object of the invention is to obtain LiBF 4  by an efficient process.  
           [0013]    The process of the invention overcomes the disadvantages of the prior art enumerated above.  
         SUMMARY OF THE INVENTION  
         [0014]    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 .  
           [0015]    In one embodiment of the invention, LiBO 2  is suspended in aqueous media/nonaqueous media and reacted with HF.  
           [0016]    In a further embodiment of the invention, a paste of LiBO 2  is added in HF.  
           [0017]    In another embodiment of the invention, LiBO 2  is pasted with water and reacted with HF. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]    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.  
         [0019]    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                          
 
       EXAMPLE 1  
     Preparation of LiBO 2    
       [0020]    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    
       [0021]    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.  
         [0022]    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    
       [0023]    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    
       [0024]    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 .  
         [0025]    In the present invention the following advantages are claimed for the synthesis of LiBF 4 :  
         [0026]    1. No side reactions occur  
         [0027]    2. A one step procedure is sufficient to prepare this compound  
         [0028]    3. Required quantity of the product can be prepared by reacting the calculated quantity of reactants.  
         [0029]    4. The product obtained is of high purity  
         [0030]    5. The product yield becomes 100% if the temperature is kept at −4° C.  
         [0031]    6. Wetting of LiBO 2  prevents evaporation of BF 4  formed during the reaction.