Method for producing low-acid lithium borate salts and mixtures of low-acid lithium borate salts and lithium hydride

1. A solvent-free mixture of a crude lithium borate salt and lithium hydride, wherein the lithium hydride is at least 0.001 wt. % and at most 10 wt. %, relative to the weight of crude lithium borate salt, wherein the mixture has a water content of at most 100 μmol/g and an acid content of at most 10 μmol H + /g of crude lithium borate salt.

2. A solvent-free mixture according to claim 1 , wherein the lithium hydride is present in powder form with an average particle size of at most 100 μm.

3. A solvent-free mixture according to claim 1 , wherein crude lithium borate salts according to formula I or formula II

are used, wherein L is a chelating agent having two terminal oxygen atoms of formula

and wherein

Y 1 and Y 2 together denote 0, where m=0 or 1, n=0 or 1, o=0 and R 1 and R 2 independently of one another denote H, F, Cl, Br, OR (R=alkyl) or R′ (alkyl), or

Y 1 , Y 2 , Y 3 , Y 4 independently of one another each denote OR (R=alkyl), H, F, Cl, Br, R′ (alkyl), where m=0 or 1, n=0, o=1, or

Y 1 , C 1 , Y 3 and C 2 are members of a 5- or 6-membered aromatic or heteroaromatic ring with at least one of N, O or S as a heteroelement, which can optionally be substituted with alkyl, alkoxy, carboxy or nitrile, wherein Y 2 and Y 4 are omitted, with n=0 and m=0 or 1, o=1.

4. A solvent-free mixture according to claim 1 , wherein the crude lithium borate salt is selected from the group comprising lithium bis(oxalato)borate, lithium malonato-oxalatoborate, lithium glycolato-oxalatoborate, lithium salicylate-oxalatoborate, lithium lactato-oxalatoborate, lithium catecholato-oxalatoborate, lithium difluorooxalatoborate, lithium difluoro-malonatoborate, lithium difluoroglycolatoborate, lithium difluoro salicylatoborate, lithium difluorolactatoborate, lithium difluorocatecholatoborate.

5. A process for producing a solvent-free mixture of lithium borate salts and lithium hydride wherein the lithium hydride is at least 0.001 wt. % and at most 10 wt. %, wherein the mixture has a water content of at most 100 μmol/g and an acid content of at most 10 μmol H + /g of lithium borate salt as in claim 1 , the process comprising

contacting a crude lithium borate salt in solid form or in suspension with an aprotic solvent or solvent blend which does not dissolve the crude lithium borate salt and the lithium hydride, and

removing the aprotic solvent or solvent blend to form a mixture of lithium borate salt and lithium hydride, either by distillation or by mechanical solid/liquid separation.

6. A process according to claim 5 , wherein the removing of the aprotic solvent or solvent blend is by distillation under reduced pressure.

7. A process for producing a solution of a lithium borate salt, which process comprises contacting

a solvent-free mixture of a crude lithium borate salt and lithium hydride, wherein the lithium hydride is at least 0.001 wt. % and at most 10 wt. %, relative to the weight of the crude lithium borate salt, wherein the mixture has a water content of at most 100 μmol/g and an acid content of at most 10 μmol H + /g of crude lithium borate salt, with

an aprotic solvent or solvent blend containing at least one aprotic solvent which dissolves the crude lithium borate salt, the crude lithium borate salt being dissolved therein,

wherein the solution comprises a lithium borate salt in the aprotic solvent or solvent blend, wherein the lithium borate salt has a concentration of at least 1 wt. % and at most 50 wt. %, water is at most 100 μmol/g and acids are at most 10 μmol H + per g of dissolved lithium borate salt.

8. A process according to claim 7 , wherein undissolved residues are removed by a solid/liquid separation operation.

9. A process for producing a solution of lithium borate salt in an aprotic solvent or solvent blend according to claim 7 , further comprising removing undissolved residues by either filtration or centrifugation.

10. A process according to claim 9 , wherein the removing is by membrane filtration, through a filter medium having a pore size of less than 0.5 μm.

11. A process for producing a lithium borate salt from solutions according to claim 7 , wherein the lithium borate salt is obtained from the solution by an operation selected from total evaporation, displacement crystallisation, and evaporative crystallisation and wherein the lithium borate salt is isolated in solid form.

12. A process according to claim 7 , wherein as crude lithium borate salts according to formula I or formula II

are used, wherein L is a chelating agent having two terminal oxygen atoms of formula

and wherein

Y 1 and Y 2 together denote 0, where m=0 or 1, n=0 or 1, o=0 and R 1 and R 2 independently of one another denote H, F, Cl, Br, OR (R=alkyl) or R′ (alkyl), or

Y 1 , Y 2 , Y 3 , Y 4 independently of one another each denote OR (R=alkyl), H, F, Cl, Br, R′ (alkyl), where m=0 or 1, n=0, o=1, or

Y 1 , C 1 , Y 3 and C 2 are members of a 5- or 6-membered aromatic or heteroaromatic ring with at least one of N, O or S as a heteroelement, which can optionally be substituted with alkyl, alkoxy, carboxy or nitrile, wherein Y 2 and Y 4 are omitted, with n=0 and m=0 or 1, o=1.

13. A process according to claim 7 , wherein the aprotic solvent or solvent blend which dissolves the crude lithium borate salt contains ethers, ketones, carbonic acid esters, carboxylic acid esters, γ-lactones and/or nitriles or consists thereof.

14. A process according to claim 7 , wherein the aprotic solvent or solvent blend which dissolves the crude lithium borate salt contains a hydrocarbon.

15. A process according to claim 7 , wherein the aprotic solvent or solvent blend which dissolves the crude lithium borate salt is selected from the group comprising ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone or γ-valerolactone.