Method for preparing amorphous lithium borosilicate

A method of making a surface-modified electrode by a vapour deposition process, the electrode comprising an electrode active material, wherein a surface of said electrode is modified by an amorphous lithium borosilicate or doped lithium borosilicate compound, wherein the method comprises:

• (a) providing a vapour source of each component element of the amorphous compound, wherein the vapour sources comprise at least a source of lithium, a source of oxygen, a source of boron and a source of silicon, and, optionally, a source of at least one dopant element;
• (b) providing an electrode;
• (c) delivering a flow of said lithium, said oxygen, said boron and said silicon, and, optionally, said dopant element;
• and
• (d) co-depositing the component elements from the vapour sources onto the electrode, wherein the component elements react on the electrode to form the amorphous compound;
• wherein the amorphous lithium borosilicate or doped lithium borosilicate compound has a lithium content in the range 45-65 atomic %, a boron content in the range 15-35 atomic %, and a silicon content in the range 10-25 atomic %, based on the combined atomic percentages of lithium, boron and silicon.