MELBOURNE, Aug 25 (Reuters) - Australian lithium producer Orocobre Ltd on Wednesday posted a 10% jump in annual revenue, boosted by higher demand from electric vehicle makers, and said it had completed a $1.4 billion merger with Galaxy Resources.

Prices of lithium, a key ingredient used in electric vehicle batteries, have surged over the past year amid a global push to cut carbon emissions and move to cleaner modes of transportation.

The company's acquisition of Galaxy Resources, announced in April, will create the world's fifth most valuable producer of lithium. The combined entity will be renamed Allkem Ltd.

"The merger consolidates the combined group's position in Argentina and provides an opportunty to build on a strong platform there and in our other key jurisdictions globally, including Australia, Japan and North America," Orocobre chief executive Martín Pérez de Solay said.

Galaxy was expected to be delisted from Aug. 26.

Orocobre, which operates the Olaroz Lithium Facility in northern Argentina, said its annual revenue was $84.8 million for the year ended June, compared with $77.1 million a year earlier.

However, its after-tax loss widened to $89.5 million from $67.2 million, hurt by a $74.9 million charge due to a change in the Argentine tax rate.

Orocobre also said that the second-stage expansion of the Olaroz Lithium Facility is expected to be completed in fiscal year 2022. (Reporting by Melanie Burton in Melbourne and Harish Sridharan in Bengaluru; editing by Uttaresh.V and Richard Pullin)